TY  - GEN
A1  - Schulze, Patricia S. C.
A1  - Bett, Alexander J.
A1  - Bivour, Martin
A1  - Caprioglio, Pietro
A1  - Gerspacher, Fabian M.
A1  - Kabaklı, Özde Ş.
A1  - Richter, Armin
A1  - Stolterfoht, Martin
A1  - Zhang, Qinxin
A1  - Neher, Dieter
A1  - Hermle, Martin
A1  - Hillebrecht, Harald
A1  - Glunz, Stefan W.
A1  - Goldschmidt, Jan Christoph
T1  - 25.1% high-efficiency monolithic perovskite silicon tandem solar cell with a high bandgap perovskite absorber
T2  - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe
N2  - Monolithic perovskite silicon tandem solar cells can overcome the theoretical efficiency limit of silicon solar cells. This requires an optimum bandgap, high quantum efficiency, and high stability of the perovskite. Herein, a silicon heterojunction bottom cell is combined with a perovskite top cell, with an optimum bandgap of 1.68 eV in planar p-i-n tandem configuration. A methylammonium-free FA(0.75)Cs(0.25)Pb(I0.8Br0.2)(3) perovskite with high Cs content is investigated for improved stability. A 10% molarity increase to 1.1 m of the perovskite precursor solution results in approximate to 75 nm thicker absorber layers and 0.7 mA cm(-2) higher short-circuit current density. With the optimized absorber, tandem devices reach a high fill factor of 80% and up to 25.1% certified efficiency. The unencapsulated tandem device shows an efficiency improvement of 2.3% (absolute) over 5 months, showing the robustness of the absorber against degradation. Moreover, a photoluminescence quantum yield analysis reveals that with adapted charge transport materials and surface passivation, along with improved antireflection measures, the high bandgap perovskite absorber has the potential for 30% tandem efficiency in the near future.
T3  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1197 
KW  - heterojunction silicon solar cells
KW  - interfaces
KW  - perovskite solar cells
KW  - tandem solar cells
KW  - thin films
Y1  - 2020
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-525668
SN  - 1866-8372
IS  - 7
ER  - 
TY  - JOUR
A1  - Schulze, Patricia S. C.
A1  - Bett, Alexander J.
A1  - Bivour, Martin
A1  - Caprioglio, Pietro
A1  - Gerspacher, Fabian M.
A1  - Kabaklı, Özde Ş.
A1  - Richter, Armin
A1  - Stolterfoht, Martin
A1  - Zhang, Qinxin
A1  - Neher, Dieter
A1  - Hermle, Martin
A1  - Hillebrecht, Harald
A1  - Glunz, Stefan W.
A1  - Goldschmidt, Jan Christoph
T1  - 25.1% high-efficiency monolithic perovskite silicon tandem solar cell with a high bandgap perovskite absorber
JF  - Solar RRL
N2  - Monolithic perovskite silicon tandem solar cells can overcome the theoretical efficiency limit of silicon solar cells. This requires an optimum bandgap, high quantum efficiency, and high stability of the perovskite. Herein, a silicon heterojunction bottom cell is combined with a perovskite top cell, with an optimum bandgap of 1.68 eV in planar p-i-n tandem configuration. A methylammonium-free FA(0.75)Cs(0.25)Pb(I0.8Br0.2)(3) perovskite with high Cs content is investigated for improved stability. A 10% molarity increase to 1.1 m of the perovskite precursor solution results in approximate to 75 nm thicker absorber layers and 0.7 mA cm(-2) higher short-circuit current density. With the optimized absorber, tandem devices reach a high fill factor of 80% and up to 25.1% certified efficiency. The unencapsulated tandem device shows an efficiency improvement of 2.3% (absolute) over 5 months, showing the robustness of the absorber against degradation. Moreover, a photoluminescence quantum yield analysis reveals that with adapted charge transport materials and surface passivation, along with improved antireflection measures, the high bandgap perovskite absorber has the potential for 30% tandem efficiency in the near future.
KW  - heterojunction silicon solar cells
KW  - interfaces
KW  - perovskite solar cells
KW  - tandem solar cells
KW  - thin films
Y1  - 2020
VL  - 4
IS  - 7
PB  - John Wiley & Sons, Inc.
CY  - New Jersey
ER  - 
TY  - JOUR
A1  - Assagra, Yuri A.O.
A1  - Altafim, Ruy Alberto Pisani
A1  - do Carmo, Joao P.
A1  - Altafim, Ruy A.C.
A1  - Rychkov, Dmitry
A1  - Wirges, Werner
A1  - Gerhard, Reimund
T1  - A new route to piezo-polymer transducers: 3D printing of polypropylene ferroelectrets
JF  - IEEE transactions on dielectrics and electrical insulation
N2  - Here, a promising approach for producing piezo-polymer transducers in a one-step process is presented. Using 3D-printing technology and polypropylene (PP) filaments, we are able to print a two-layered film structure with regular cavities of precisely controlled size and shape. It is found that the 3D-printed samples exhibit piezoelectric coefficients up to 200 pC/N, similar to those of other PP ferroelectrets, and their temporal and thermal behavior is in good agreement with those known of PP ferroelectrets. The piezoelectric response strongly decreases for applied pressures above 20 kPa, as the pressure in the air-filled cavities strongly influences the overall elastic modulus of ferroelectrets.
KW  - 3D printing
KW  - polymer ferroelectrets
KW  - sensors and actuators
KW  - piezoelectrets
KW  - electret polymers
KW  - soft electro-active materials
KW  - functional materials
KW  - soft matter
Y1  - 2020
U6  - https://doi.org/10.1109/TDEI.2020.008461
SN  - 1070-9878
SN  - 1558-4135
VL  - 27
IS  - 5
SP  - 1668
EP  - 1674
PB  - Inst. of Electr. and Electronics Engineers
CY  - Piscataway
ER  - 
TY  - JOUR
A1  - Gómez-Nava, Luis
A1  - Grossmann, Robert
A1  - Hintsche, Marius
A1  - Beta, Carsten
A1  - Peruani, Fernando
T1  - A novel approach to chemotaxis
BT  - active particles guided by internal clocks
JF  - epl : a letters journal exploring the frontiers of physics
N2  - Motivated by the observation of non-exponential run-time distributions of bacterial swimmers, we propose a minimal phenomenological model for taxis of active particles whose motion is controlled by an internal clock. The ticking of the clock depends on an external concentration field, e.g., a chemical substance. We demonstrate that these particles can detect concentration gradients and respond to them by moving up- or down-gradient depending on the clock design, albeit measurements of these fields are purely local in space and instantaneous in time. Altogether, our results open a new route in the study of directional navigation: we show that the use of a clock to control motility actions represents a generic and versatile toolbox to engineer behavioral responses to external cues, such as light, chemical, or temperature gradients.
Y1  - 2020
U6  - https://doi.org/10.1209/0295-5075/130/68002
SN  - 0295-5075
SN  - 1286-4854
VL  - 130
IS  - 6
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Gostkowska-Lekner, Natalia Katarzyna
A1  - Wallacher, Dirk
A1  - Grimm, Nico
A1  - Habicht, Klaus
A1  - Hofmann, Tommy
T1  - A novel electrochemical anodization cell for the synthesis of mesoporous silicon
JF  - Review of scientific instruments : a monthly journal devoted to scientific instruments, apparatus, and techniques
N2  - A novel design of an electrochemical anodization cell dedicated to the synthesis of mesoporous, single-crystalline silicon is presented. First and foremost, the design principle follows user safety since electrochemical etching of silicon requires highly hazardous electrolytes based on hydrofluoric (HF) acid. The novel cell design allows for safe electrolyte handling prior, during, and post-etching. A peristaltic pump with HF-resistant fluoroelastomer tubing transfers electrolytes between dedicated reservoirs and the anodization cell. Due to the flexibility of the cell operation, different processing conditions can be realized providing a large parameter range for the attainable sample thickness, its porosity, and the mean pore size. Rapid etching on the order of several minutes to synthesize micrometer-thick porous silicon epilayers on bulk silicon is possible as well as long-time etching with continuous, controlled electrolyte flow for several days to prepare up to 1000 mu m thick self-supporting porous silicon membranes. A highly adaptable, LabVIEW((TM))-based control software allows for user-defined etching profiles.
Y1  - 2020
U6  - https://doi.org/10.1063/5.0008536
SN  - 0034-6748
SN  - 1089-7623
VL  - 91
IS  - 10
PB  - American Institute of Physics
CY  - Melville, NY
ER  - 
TY  - JOUR
A1  - Großmann, Robert
A1  - Aranson, Igor S.
A1  - Peruani, Fernando
T1  - A particle-field approach bridges phase separation and collective motion in active matter
JF  - Nature Communications
N2  - Whereas self-propelled hard discs undergo motility-induced phase separation, self-propelled rods exhibit a variety of nonequilibrium phenomena, including clustering, collective motion, and spatio-temporal chaos. In this work, we present a theoretical framework representing active particles by continuum fields. This concept combines the simplicity of alignment-based models, enabling analytical studies, and realistic models that incorporate the shape of self-propelled objects explicitly. By varying particle shape from circular to ellipsoidal, we show how nonequilibrium stresses acting among self-propelled rods destabilize motility-induced phase separation and facilitate orientational ordering, thereby connecting the realms of scalar and vectorial active matter. Though the interaction potential is strictly apolar, both, polar and nematic order may emerge and even coexist. Accordingly, the symmetry of ordered states is a dynamical property in active matter. The presented framework may represent various systems including bacterial colonies, cytoskeletal extracts, or shaken granular media. Interacting self-propelled particles exhibit phase separation or collective motion depending on particle shape. A unified theory connecting these paradigms represents a major challenge in active matter, which the authors address here by modeling active particles as continuum fields.
Y1  - 2020
U6  - https://doi.org/10.1038/s41467-020-18978-5
SN  - 2041-1723
VL  - 11
IS  - 1
PB  - Nature Publishing Group
CY  - London
ER  - 
TY  - JOUR
A1  - Schaffenroth, Veronika
A1  - Casewell, Sarah L.
A1  - Schneider, D.
A1  - Kilkenny, David
A1  - Geier, Stephan
A1  - Heber, Ulrich
A1  - Irrgang, Andreas
A1  - Przybilla, Norbert
A1  - Marsh, Thomas R.
A1  - Littlefair, Stuart P.
A1  - Dhillon, Vik S.
T1  - A quantitative in-depth analysis of the prototype sdB plus BD system SDSS J08205+0008 revisited in the Gaia era
JF  - Monthly notices of the Royal Astronomical Society
N2  - Subdwarf B stars are core-helium-burning stars located on the extreme horizontal branch (EHB). Extensive mass loss on the red giant branch is necessary to form them. It has been proposed that substellar companions could lead to the required mass loss when they are engulfed in the envelope of the red giant star. J08205+0008 was the first example of a hot subdwarf star with a close, substellar companion candidate to be found. Here, we perform an in-depth re-analysis of this important system with much higher quality data allowing additional analysis methods. From the higher resolution spectra obtained with ESO-VLT/XSHOOTER, we derive the chemical abundances of the hot subdwarf as well as its rotational velocity. Using the Gaia parallax and a fit to the spectral energy distribution in the secondary eclipse, tight constraints to the radius of the hot subdwarf are derived. From a long-term photometric campaign, we detected a significant period decrease of -3.2(8) x 10(-12) dd(-1). This can be explained by the non-synchronized hot subdwarf star being spun up by tidal interactions forcing it to become synchronized. From the rate of period decrease we could derive the synchronization time-scale to be 4 Myr, much smaller than the lifetime on EHB. By combining all different methods, we could constrain the hot subdwarf to a mass of 0.39-0.50 M-circle dot and a radius of R-sdB = 0.194 +/- 0.008 R-circle dot, and the companion to 0.061-0.071 M-circle dot with a radius of R-comp = 0.092 +/- 0.005 R-circle dot, below the hydrogen-burning limit. We therefore confirm that the companion is most likely a massive brown dwarf.
KW  - stars: abundances
KW  - stars: atmospheres
KW  - stars: fundamental parameters
KW  - stars: horizontal branch
KW  - stars: low-mass
KW  - subdwarfs
Y1  - 2020
U6  - https://doi.org/10.1093/mnras/staa3661
SN  - 0035-8711
SN  - 1365-2966
VL  - 501
IS  - 3
SP  - 3847
EP  - 3870
PB  - Oxford Univ. Press
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Sajedi, Maryam
A1  - Krivenkov, Maxim
A1  - Marchenko, Dmitry
A1  - Varykhalov, Andrei
A1  - Sanchez-Barriga, Jaime
A1  - Rienks, Emile D. L.
A1  - Rader, Oliver
T1  - Absence of a giant Rashba effect in the valence band of lead halide perovskites
JF  - Physical review : B, Condensed matter and materials physics
N2  - For hybrid organic-inorganic as well as all-inorganic lead halide perovskites a Rashba effect has been invoked to explain the high efficiency in energy conversion by prohibiting direct recombination. Both a bulk and surface Rashba effect have been predicted. In the valence band of methylammonium (MA) lead bromide a Rashba effect has been reported by angle-resolved photoemission and circular dichroism with giant values of 7-11 eV angstrom. We present band dispersion measurements of MAPbBr(3) and spin-resolved photoemission of CsPbBr3 to show that a large Rashba effect detectable by photoemission or circular dichroism does not exist and cannot be the origin of the high effciency.
Y1  - 2020
U6  - https://doi.org/10.1103/PhysRevB.102.081116
SN  - 2469-9950
SN  - 2469-9969
VL  - 102
IS  - 8
PB  - American Institute of Physics; American Physical Society (APS)
CY  - Woodbury, NY
ER  - 
TY  - JOUR
A1  - Umlandt, Maren
A1  - Feldmann, David
A1  - Schneck, Emanuel
A1  - Santer, Svetlana
A1  - Bekir, Marek
T1  - Adsorption of photoresponsive surfactants at solid-liquid interfaces
JF  - Langmuir
N2  - We report on the adsorption kinetics of azoben-zene-containing surfactants on solid surfaces of different hydrophobicity. The understanding of this processes is of great importance for many interfacial phenomena that can be actuated and triggered by light, since the surfactant molecules contain a photoresponsive azobenzene group in their hydrophobic tail. Three surfactant types are studied, differing in the spacer connecting the headgroup and the azobenzene unit by between 6 and 10 CH2 groups. Under irradiation with light of a suitable wavelength, the azobenzene undergoes reversible photoisomerization between two states, a nonpolar trans-state and a highly polar cis-state. Consequently, the surfactant molecule changes its hydrophobicity and thus affinity to a surface depending on the photoisomerization state of the azobenzene. The adsorption behavior on hydrophilic (glass) and hydrophobic (TeflonAF) surfaces is analyzed using quartz crystal microbalance with dissipation (QCM-D) and zeta-potential measurements. At equilibrium, the adsorbed surfactant amount is almost twice as large on glass compared to TeflonAF for both isomers. The adsorption rate for the trans-isomers on both surfaces is similar, but the desorption rate of the trans-isomers is faster at the glass-water interface than at the Teflon-water interface. This result demonstrates that the trans-isomers have higher affinity for the glass surface, so the trans-to-cis ratios on glass and TeflonAF are 80/1 and 2/1, respectively, with similar trends for all three surfactant types.
Y1  - 2020
U6  - https://doi.org/10.1021/acs.langmuir.0c02545
SN  - 0743-7463
SN  - 1520-5827
VL  - 36
IS  - 46
SP  - 14009
EP  - 14018
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Evsevleev, Sergei
A1  - Paciornik, Sidnei
A1  - Bruno, Giovanni
T1  - Advanced deep learning-based 3D microstructural characterization of multiphase metal matrix composites
JF  - Advanced engineering materials
N2  - The quantitative analysis of microstructural features is a key to understanding the micromechanical behavior of metal matrix composites (MMCs), which is a premise for their use in practice. Herein, a 3D microstructural characterization of a five-phase MMC is performed by synchrotron X-ray computed tomography (SXCT). A workflow for advanced deep learning-based segmentation of all individual phases in SXCT data is shown using a fully convolutional neural network with U-net architecture. High segmentation accuracy is achieved with a small amount of training data. This enables extracting unprecedently precise microstructural parameters (e.g., volume fractions and particle shapes) to be input, e.g., in micromechanical models.
KW  - computed tomography
KW  - convolutional neural networks
KW  - deep learning
KW  - metal
KW  - matrix composites
KW  - segmentations
Y1  - 2020
U6  - https://doi.org/10.1002/adem.201901197
SN  - 1438-1656
SN  - 1527-2648
VL  - 22
IS  - 4
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Pelisoli, Ingrid
A1  - Vos, Joris
A1  - Geier, Stephan
A1  - Schaffenroth, Veronika
A1  - Baran, Andrzej S.
T1  - Alone but not lonely
BT  - observational evidence that binary interaction is always required to form hot subdwarf stars
JF  - Astronomy and astrophysics : an international weekly journal
N2  - Context. Hot subdwarfs are core-helium burning stars that show lower masses and higher temperatures than canonical horizontal branch stars. They are believed to be formed when a red giant suffers an extreme mass-loss episode. Binary interaction is suggested to be the main formation channel, but the high fraction of apparently single hot subdwarfs (up to 30%) has prompted single star formation scenarios to be proposed.Aims. We investigate the possibility that hot subdwarfs could form without interaction by studying wide binary systems. If single formation scenarios were possible, there should be hot subdwarfs in wide binaries that have undergone no interaction.Methods. Angular momentum accretion during interaction is predicted to cause the hot subdwarf companion to spin up to the critical velocity. The effect of this should still be observable given the timescales of the hot subdwarf phase. To study the rotation rates of companions, we have analysed light curves from the Transiting Exoplanet Survey Satellite for all known hot subdwarfs showing composite spectral energy distributions indicating the presence of a main sequence wide binary companion. If formation without interaction were possible, that would also imply the existence of hot subdwarfs in very wide binaries that are not predicted to interact. To identify such systems, we have searched for common proper motion companions with projected orbital distances of up to 0.1 pc to all known spectroscopically confirmed hot subdwarfs using Gaia DR2 astrometry.Results. We find that the companions in composite hot subdwarfs show short rotation periods when compared to field main sequence stars. They display a triangular-shaped distribution with a peak around 2.5 days, similar to what is observed for young open clusters. We also report a shortage of hot subdwarfs with candidate common proper motion companions. We identify only 16 candidates after probing 2938 hot subdwarfs with good astrometry. Out of those, at least six seem to be hierarchical triple systems, in which the hot subdwarf is part of an inner binary.Conclusions. The observed distribution of rotation rates for the companions in known wide hot subdwarf binaries provides evidence of previous interaction causing spin-up. Additionally, there is a shortage of hot subdwarfs in common proper motion pairs, considering the frequency of such systems among progenitors. These results suggest that binary interaction is always required for the formation of hot subdwarfs.
KW  - subdwarfs
KW  - binaries: general
KW  - stars: variables: general
Y1  - 2020
U6  - https://doi.org/10.1051/0004-6361/202038473
SN  - 0004-6361
SN  - 1432-0746
VL  - 642
PB  - EDP Sciences
CY  - Les Ulis
ER  - 
TY  - GEN
A1  - Ciemer, Catrin
A1  - Rehm, Lars
A1  - Kurths, Jürgen
A1  - Donner, Reik Volker
A1  - Winkelmann, Ricarda
A1  - Boers, Niklas
T1  - An early-warning indicator for Amazon droughts exclusively based on tropical Atlantic sea surface temperatures
T2  - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe
N2  - Droughts in tropical South America have an imminent and severe impact on the Amazon rainforest and affect the livelihoods of millions of people. Extremely dry conditions in Amazonia have been previously linked to sea surface temperature (SST) anomalies in the adjacent tropical oceans. Although the sources and impacts of such droughts have been widely studied, establishing reliable multi-year lead statistical forecasts of their occurrence is still an ongoing challenge. Here, we further investigate the relationship between SST and rainfall anomalies using a complex network approach. We identify four ocean regions which exhibit the strongest overall SST correlations with central Amazon rainfall, including two particularly prominent regions in the northern and southern tropical Atlantic. Based on the time-dependent correlation between SST anomalies in these two regions alone, we establish a new early-warning method for droughts in the central Amazon basin and demonstrate its robustness in hindcasting past major drought events with lead-times up to 18 months.
T3  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1207 
KW  - complex networks
KW  - droughts
KW  - prediction
KW  - Amazon rainforest
Y1  - 2019
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-525863
SN  - 1866-8372
IS  - 9
ER  - 
TY  - JOUR
A1  - Ciemer, Catrin
A1  - Rehm, Lars
A1  - Kurths, Jürgen
A1  - Donner, Reik Volker
A1  - Winkelmann, Ricarda
A1  - Boers, Niklas
T1  - An early-warning indicator for Amazon droughts exclusively based on tropical Atlantic sea surface temperatures
JF  - Environmental Research Letters
N2  - Droughts in tropical South America have an imminent and severe impact on the Amazon rainforest and affect the livelihoods of millions of people. Extremely dry conditions in Amazonia have been previously linked to sea surface temperature (SST) anomalies in the adjacent tropical oceans. Although the sources and impacts of such droughts have been widely studied, establishing reliable multi-year lead statistical forecasts of their occurrence is still an ongoing challenge. Here, we further investigate the relationship between SST and rainfall anomalies using a complex network approach. We identify four ocean regions which exhibit the strongest overall SST correlations with central Amazon rainfall, including two particularly prominent regions in the northern and southern tropical Atlantic. Based on the time-dependent correlation between SST anomalies in these two regions alone, we establish a new early-warning method for droughts in the central Amazon basin and demonstrate its robustness in hindcasting past major drought events with lead-times up to 18 months.
KW  - complex networks
KW  - droughts
KW  - prediction
KW  - Amazon rainforest
Y1  - 2019
VL  - 15
IS  - 9
PB  - IOP - Institute of Physics Publishing
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Abdalla, H.
A1  - Adam, R.
A1  - Aharonian, Felix A.
A1  - Benkhali, F. Ait
A1  - Angüner, Ekrem Oǧuzhan
A1  - Arcaro, C.
A1  - Armand, C.
A1  - Armstrong, T.
A1  - Ashkar, H.
A1  - Backes, M.
A1  - Baghmanyan, V.
A1  - Martins, V. Barbosa
A1  - Barnacka, A.
A1  - Barnard, M.
A1  - Becherini, Y.
A1  - Berge, D.
A1  - Bernlohr, K.
A1  - Bi, B.
A1  - Bottcher, M.
A1  - Boisson, C.
A1  - Bolmont, J.
A1  - de Lavergne, M. de Bony
A1  - Bordas, Pol
A1  - Breuhaus, M.
A1  - Brun, F.
A1  - Brun, P.
A1  - Bryan, M.
A1  - Buchele, M.
A1  - Bulik, T.
A1  - Bylund, T.
A1  - Caroff, S.
A1  - Carosi, A.
A1  - Casanova, Sabrina
A1  - Chand, T.
A1  - Chandra, S.
A1  - Chen, A.
A1  - Cotter, G.
A1  - Curylo, M.
A1  - Mbarubucyeye, J. Damascene
A1  - Davids, I. D.
A1  - Davies, J.
A1  - Deil, C.
A1  - Devin, J.
A1  - deWilt, P.
A1  - Dirson, L.
A1  - Djannati-Atai, A.
A1  - Dmytriiev, A.
A1  - Donath, A.
A1  - Doroshenko, V.
A1  - Duffy, C.
A1  - Dyks, J.
A1  - Egberts, Kathrin
A1  - Eichhorn, F.
A1  - Einecke, S.
A1  - Emery, G.
A1  - Ernenwein, J. -P.
A1  - Feijen, K.
A1  - Fegan, S.
A1  - Fiasson, A.
A1  - de Clairfontaine, G. Fichet
A1  - Fontaine, G.
A1  - Funk, S.
A1  - Fussling, Matthias
A1  - Gabici, S.
A1  - Gallant, Y. A.
A1  - Giavitto, G.
A1  - Giunti, L.
A1  - Glawion, D.
A1  - Glicenstein, J. F.
A1  - Gottschall, D.
A1  - Grondin, M. -H.
A1  - Hahn, J.
A1  - Haupt, M.
A1  - Hermann, G.
A1  - Hinton, J. A.
A1  - Hofmann, W.
A1  - Hoischen, Clemens
A1  - Holch, T. L.
A1  - Holler, M.
A1  - Horbe, M.
A1  - Horns, D.
A1  - Huber, D.
A1  - Jamrozy, M.
A1  - Jankowsky, D.
A1  - Jankowsky, F.
A1  - Jardin-Blicq, A.
A1  - Joshi, V.
A1  - Jung-Richardt, I.
A1  - Kasai, E.
A1  - Kastendieck, M. A.
A1  - Katarzynski, K.
A1  - Katz, U.
A1  - Khangulyan, D.
A1  - Khelifi, B.
A1  - Klepser, S.
A1  - Kluzniak, W.
A1  - Komin, Nu.
A1  - Konno, R.
A1  - Kosack, K.
A1  - Kostunin, D.
A1  - Kreter, M.
A1  - Lamanna, G.
A1  - Lemiere, A.
A1  - Lemoine-Goumard, M.
A1  - Lenain, J. -P.
A1  - Levy, C.
A1  - Lohse, T.
A1  - Lypova, I.
A1  - Mackey, J.
A1  - Majumdar, J.
A1  - Malyshev, D.
A1  - Malyshev, D.
A1  - Marandon, V.
A1  - Marchegiani, P.
A1  - Marcowith, Alexandre
A1  - Mares, A.
A1  - Marti-Devesa, G.
A1  - Marx, R.
A1  - Maurin, G.
A1  - Meintjes, P. J.
A1  - Meyer, M.
A1  - Mitchell, A.
A1  - Moderski, R.
A1  - Mohamed, M.
A1  - Mohrmann, L.
A1  - Montanari, A.
A1  - Moore, C.
A1  - Morris, P.
A1  - Moulin, Emmanuel
A1  - Muller, J.
A1  - Murach, T.
A1  - Nakashima, K.
A1  - Nayerhoda, A.
A1  - de Naurois, M.
A1  - Ndiyavala, H.
A1  - Niederwanger, F.
A1  - Niemiec, J.
A1  - Oakes, L.
A1  - O'Brien, Patrick
A1  - Odaka, H.
A1  - Ohm, S.
A1  - Olivera-Nieto, L.
A1  - Wilhelmi, E. de Ona
A1  - Ostrowski, M.
A1  - Oya, I.
A1  - Panter, M.
A1  - Panny, S.
A1  - Parsons, R. D.
A1  - Peron, G.
A1  - Peyaud, B.
A1  - Piel, Q.
A1  - Pita, S.
A1  - Poireau, V.
A1  - Noel, A. Priyana
A1  - Prokhorov, D. A.
A1  - Prokoph, H.
A1  - Puhlhofer, G.
A1  - Punch, M.
A1  - Quirrenbach, A.
A1  - Raab, S.
A1  - Rauth, R.
A1  - Reichherzer, P.
A1  - Reimer, A.
A1  - Reimer, O.
A1  - Remy, Q.
A1  - Renaud, M.
A1  - Rieger, F.
A1  - Rinchiuso, L.
A1  - Romoli, C.
A1  - Rowell, G.
A1  - Rudak, B.
A1  - Ruiz-Velasco, E.
A1  - Sahakian, V.
A1  - Sailer, S.
A1  - Sanchez, D. A.
A1  - Santangelo, Andrea
A1  - Sasaki, M.
A1  - Scalici, M.
A1  - Schussler, F.
A1  - Schutte, H. M.
A1  - Schwanke, U.
A1  - Schwemmer, S.
A1  - Seglar-Arroyo, M.
A1  - Senniappan, M.
A1  - Seyffert, A. S.
A1  - Shafi, N.
A1  - Shiningayamwe, K.
A1  - Simoni, R.
A1  - Sinha, A.
A1  - Sol, H.
A1  - Specovius, A.
A1  - Spencer, S.
A1  - Spir-Jacob, M.
A1  - Stawarz, L.
A1  - Sun, L.
A1  - Steenkamp, R.
A1  - Stegmann, C.
A1  - Steinmassl, S.
A1  - Steppa, C.
A1  - Takahashi, T.
A1  - Tavernier, T.
A1  - Taylor, A. M.
A1  - Terrier, R.
A1  - Tiziani, D.
A1  - Tluczykont, M.
A1  - Tomankova, L.
A1  - Trichard, C.
A1  - Tsirou, M.
A1  - Tuffs, R.
A1  - Uchiyama, Y.
A1  - van der Walt, D. J.
A1  - van Eldik, C.
A1  - van Rensburg, C.
A1  - van Soelen, B.
A1  - Vasileiadis, G.
A1  - Veh, J.
A1  - Venter, C.
A1  - Vincent, P.
A1  - Vink, J.
A1  - Volk, H. J.
A1  - Vuillaume, T.
A1  - Wadiasingh, Z.
A1  - Wagner, S. J.
A1  - Watson, J.
A1  - Werner, F.
A1  - White, R.
A1  - Wierzcholska, A.
A1  - Wong, Yu Wun
A1  - Yusafzai, A.
A1  - Zacharias, M.
A1  - Zanin, R.
A1  - Zargaryan, D.
A1  - Zdziarski, A. A.
A1  - Zech, Alraune
A1  - Zhu, S. J.
A1  - Ziegler, A.
A1  - Zorn, J.
A1  - Zouari, S.
A1  - Zywucka, N.
T1  - An extreme particle accelerator in the Galactic plane
BT  - HESS J1826-130
JF  - Astronomy and astrophysics : an international weekly journal
N2  - The unidentified very-high-energy (VHE; E > 0.1 TeV) gamma -ray source, HESS J1826-130, was discovered with the High Energy Stereoscopic System (HESS) in the Galactic plane. The analysis of 215 h of HESS data has revealed a steady gamma -ray flux from HESS J1826-130, which appears extended with a half-width of 0.21 degrees +/- 0.02 <br /> (stat)degrees <br /> stat degrees +/- 0.05 <br /> (sys)degrees sys degrees . The source spectrum is best fit with either a power-law function with a spectral index Gamma = 1.78 +/- 0.10(stat) +/- 0.20(sys) and an exponential cut-off at 15.2 <br /> (+5.5)(-3.2) -3.2+5.5 TeV, or a broken power-law with Gamma (1) = 1.96 +/- 0.06(stat) +/- 0.20(sys), Gamma (2) = 3.59 +/- 0.69(stat) +/- 0.20(sys) for energies below and above E-br = 11.2 +/- 2.7 TeV, respectively. The VHE flux from HESS J1826-130 is contaminated by the extended emission of the bright, nearby pulsar wind nebula, HESS J1825-137, particularly at the low end of the energy spectrum. Leptonic scenarios for the origin of HESS J1826-130 VHE emission related to PSR J1826-1256 are confronted by our spectral and morphological analysis. In a hadronic framework, taking into account the properties of dense gas regions surrounding HESS J1826-130, the source spectrum would imply an astrophysical object capable of accelerating the parent particle population up to greater than or similar to 200 TeV. Our results are also discussed in a multiwavelength context, accounting for both the presence of nearby supernova remnants, molecular clouds, and counterparts detected in radio, X-rays, and TeV energies.
KW  - ISM: supernova remnants
KW  - ISM: clouds
KW  - gamma rays: general
KW  - gamma rays:
KW  - ISM
Y1  - 2020
U6  - https://doi.org/10.1051/0004-6361/202038851
SN  - 0004-6361
SN  - 1432-0746
VL  - 644
PB  - EDP Sciences
CY  - Les Ulis
ER  - 
TY  - GEN
A1  - Munyaev, Vyacheslav
A1  - Smirnov, Lev A.
A1  - Kostin, Vasily
A1  - Osipov, Grigory V.
A1  - Pikovskij, Arkadij
T1  - Analytical approach to synchronous states of globally coupled noisy rotators
T2  - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe
N2  - We study populations of globally coupled noisy rotators (oscillators with inertia) allowing a nonequilibrium transition from a desynchronized state to a synchronous one (with the nonvanishing order parameter). The newly developed analytical approaches resulted in solutions describing the synchronous state with constant order parameter for weakly inertial rotators, including the case of zero inertia, when the model is reduced to the Kuramoto model of coupled noise oscillators. These approaches provide also analytical criteria distinguishing supercritical and subcritical transitions to the desynchronized state and indicate the universality of such transitions in rotator ensembles. All the obtained analytical results are confirmed by the numerical ones, both by direct simulations of the large ensembles and by solution of the associated Fokker-Planck equation. We also propose generalizations of the developed approaches for setups where different rotators parameters (natural frequencies, masses, noise intensities, strengths and phase shifts in coupling) are dispersed.
T3  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1188 
KW  - coupled rotators
KW  - synchronization transition
KW  - hysteresis
KW  - Kuramoto model
KW  - noisy systems
Y1  - 2019
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-524261
SN  - 1866-8372
IS  - 2
ER  - 
TY  - JOUR
A1  - Munyaev, Vyacheslav O.
A1  - Smirnov, Lev A.
A1  - Kostin, Vasily A.
A1  - Osipov, Grigory V.
A1  - Pikovskij, Arkadij
T1  - Analytical approach to synchronous states of globally coupled noisy rotators
JF  - New journal of physics : the open-access journal for physics
N2  - We study populations of globally coupled noisy rotators (oscillators with inertia) allowing a nonequilibrium transition from a desynchronized state to a synchronous one (with the nonvanishing order parameter). The newly developed analytical approaches resulted in solutions describing the synchronous state with constant order parameter for weakly inertial rotators, including the case of zero inertia, when the model is reduced to the Kuramoto model of coupled noise oscillators. These approaches provide also analytical criteria distinguishing supercritical and subcritical transitions to the desynchronized state and indicate the universality of such transitions in rotator ensembles. All the obtained analytical results are confirmed by the numerical ones, both by direct simulations of the large ensembles and by solution of the associated Fokker-Planck equation. We also propose generalizations of the developed approaches for setups where different rotators parameters (natural frequencies, masses, noise intensities, strengths and phase shifts in coupling) are dispersed.
KW  - coupled rotators
KW  - synchronization transition
KW  - hysteresis
KW  - Kuramoto
KW  - model
KW  - noisy systems
Y1  - 2020
U6  - https://doi.org/10.1088/1367-2630/ab6f93
SN  - 1367-2630
VL  - 22
IS  - 2
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Munyaev, Vyacheslav
A1  - Smirnov, Lev A.
A1  - Kostin, Vasily
A1  - Osipov, Grigory V.
A1  - Pikovskij, Arkadij
T1  - Analytical approach to synchronous states of globally coupled noisy rotators
JF  - New Journal of Physics
N2  - We study populations of globally coupled noisy rotators (oscillators with inertia) allowing a nonequilibrium transition from a desynchronized state to a synchronous one (with the nonvanishing order parameter). The newly developed analytical approaches resulted in solutions describing the synchronous state with constant order parameter for weakly inertial rotators, including the case of zero inertia, when the model is reduced to the Kuramoto model of coupled noise oscillators. These approaches provide also analytical criteria distinguishing supercritical and subcritical transitions to the desynchronized state and indicate the universality of such transitions in rotator ensembles. All the obtained analytical results are confirmed by the numerical ones, both by direct simulations of the large ensembles and by solution of the associated Fokker-Planck equation. We also propose generalizations of the developed approaches for setups where different rotators parameters (natural frequencies, masses, noise intensities, strengths and phase shifts in coupling) are dispersed.
KW  - coupled rotators
KW  - synchronization transition
KW  - hysteresis
KW  - Kuramoto model
KW  - noisy systems
Y1  - 2019
VL  - 22
IS  - 2
PB  - Springer Science
CY  - New York
ER  - 
TY  - JOUR
A1  - Perdigón-Toro, Lorena
A1  - Zhang, Huotian
A1  - Markina, Anastaa si
A1  - Yuan, Jun
A1  - Hosseini, Seyed Mehrdad
A1  - Wolff, Christian Michael
A1  - Zuo, Guangzheng
A1  - Stolterfoht, Martin
A1  - Zou, Yingping
A1  - Gao, Feng
A1  - Andrienko, Denis
A1  - Shoaee, Safa
A1  - Neher, Dieter
T1  - Barrierless free charge generation in the high-performance PM6:Y6 bulk heterojunction non-fullerene solar cell
JF  - Advanced materials
N2  - Organic solar cells are currently experiencing a second golden age thanks to the development of novel non-fullerene acceptors (NFAs). Surprisingly, some of these blends exhibit high efficiencies despite a low energy offset at the heterojunction. Herein, free charge generation in the high-performance blend of the donor polymer PM6 with the NFA Y6 is thoroughly investigated as a function of internal field, temperature and excitation energy. Results show that photocurrent generation is essentially barrierless with near-unity efficiency, regardless of excitation energy. Efficient charge separation is maintained over a wide temperature range, down to 100 K, despite the small driving force for charge generation. Studies on a blend with a low concentration of the NFA, measurements of the energetic disorder, and theoretical modeling suggest that CT state dissociation is assisted by the electrostatic interfacial field which for Y6 is large enough to compensate the Coulomb dissociation barrier.
KW  - driving force
KW  - non-fullerene acceptors
KW  - organic solar cells
KW  - photocurrent generation
Y1  - 2020
U6  - https://doi.org/10.1002/adma.201906763
SN  - 0935-9648
SN  - 1521-4095
VL  - 32
IS  - 9
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Emanuel, Marc D.
A1  - Cherstvy, Andrey G.
A1  - Metzler, Ralf
A1  - Gompper, Gerhard
T1  - Buckling transitions and soft-phase invasion of two-component icosahedral shells
JF  - Physical review / publ. by The American Physical Society. E, Statistical, nonlinear, and soft matter physics
N2  - What is the optimal distribution of two types of crystalline phases on the surface of icosahedral shells, such as of many viral capsids? We here investigate the distribution of a thin layer of soft material on a crystalline convex icosahedral shell. We demonstrate how the shapes of spherical viruses can be understood from the perspective of elasticity theory of thin two-component shells. We develop a theory of shape transformations of an icosahedral shell upon addition of a softer, but still crystalline, material onto its surface. We show how the soft component "invades" the regions with the highest elastic energy and stress imposed by the 12 topological defects on the surface. We explore the phase diagram as a function of the surface fraction of the soft material, the shell size, and the incommensurability of the elastic moduli of the rigid and soft phases. We find that, as expected, progressive filling of the rigid shell by the soft phase starts from the most deformed regions of the icosahedron. With a progressively increasing soft-phase coverage, the spherical segments of domes are filled first (12 vertices of the shell), then the cylindrical segments connecting the domes (30 edges) are invaded, and, ultimately, the 20 flat faces of the icosahedral shell tend to be occupied by the soft material. We present a detailed theoretical investigation of the first two stages of this invasion process and develop a model of morphological changes of the cone structure that permits noncircular cross sections. In conclusion, we discuss the biological relevance of some structures predicted from our calculations, in particular for the shape of viral capsids.
Y1  - 2020
U6  - https://doi.org/10.1103/PhysRevE.102.062104
SN  - 2470-0045
SN  - 2470-0053
SN  - 2470-0061
SN  - 1538-4519
VL  - 102
IS  - 6
PB  - Woodbury
CY  - New York
ER  - 
TY  - JOUR
A1  - Schulz, Christian
A1  - Lieutenant, Klaus
A1  - Xiao, Jie
A1  - Hofmann, Tommy
A1  - Wong, Deniz
A1  - Habicht, Klaus
T1  - Characterization of the soft X-ray spectrometer PEAXIS at BESSY II
JF  - Journal of synchrotron radiation
N2  - The performance of the recently commissioned spectrometer PEAXIS for resonant inelastic soft X-ray scattering (RIXS) and X-ray photoelectron spectroscopy and its hosting beamline U41-PEAXIS at the BESSY II synchrotron are characterized. The beamline provides linearly polarized light from 180 eV to 1600 eV allowing for RIXS measurements in the range 200-1200 eV. The monochromator optics can be operated in different configurations to provide either high flux with up to 10(12) photons s(-1) within the focal spot at the sample or high energy resolution with a full width at half maximum of <40 meV at an incident photon energy of similar to 400 eV. The measured total energy resolution of the RIXS spectrometer is in very good agreement with theoretically predicted values obtained by ray-tracing simulations. PEAXIS features a 5 m-long RIXS spectrometer arm that can be continuously rotated about the sample position by 106 degrees within the horizontal photon scattering plane, thus enabling the study of momentum-transfer-dependent excitations. Selected scientific examples are presented to demonstrate the instrument capabilities, including measurements of excitations in single-crystalline NiO and in liquid acetone employing a fluid cell sample manipulator. Planned upgrades of the beamline and the RIXS spectrometer to further increase the energy resolution to similar to 100 meV at 1000 eV incident photon energy are discussed.
KW  - resonant inelastic X-ray scattering
KW  - X-ray photoelectron spectroscopy
KW  - soft X-ray spectroscopy
KW  - soft X-ray beamline
KW  - X-ray emission
KW  - X-ray
KW  - absorption
KW  - BESSY II
Y1  - 2020
U6  - https://doi.org/10.1107/S1600577519014887
SN  - 1600-5775
VL  - 27
SP  - 238
EP  - 249
PB  - International Union of Crystallography
CY  - Chester
ER  - 
TY  - GEN
A1  - Schulz, Christian
A1  - Lieutenant, Klaus
A1  - Xiao, Jie
A1  - Hofmann, Tommy
A1  - Wong, Deniz
A1  - Habicht, Klaus
T1  - Characterization of the soft X-ray spectrometer PEAXIS at BESSY II
T2  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe
N2  - The performance of the recently commissioned spectrometer PEAXIS for resonant inelastic soft X-ray scattering (RIXS) and X-ray photoelectron spectroscopy and its hosting beamline U41-PEAXIS at the BESSY II synchrotron are characterized. The beamline provides linearly polarized light from 180 eV to 1600 eV allowing for RIXS measurements in the range 200-1200 eV. The monochromator optics can be operated in different configurations to provide either high flux with up to 10(12) photons s(-1) within the focal spot at the sample or high energy resolution with a full width at half maximum of <40 meV at an incident photon energy of similar to 400 eV. The measured total energy resolution of the RIXS spectrometer is in very good agreement with theoretically predicted values obtained by ray-tracing simulations. PEAXIS features a 5 m-long RIXS spectrometer arm that can be continuously rotated about the sample position by 106 degrees within the horizontal photon scattering plane, thus enabling the study of momentum-transfer-dependent excitations. Selected scientific examples are presented to demonstrate the instrument capabilities, including measurements of excitations in single-crystalline NiO and in liquid acetone employing a fluid cell sample manipulator. Planned upgrades of the beamline and the RIXS spectrometer to further increase the energy resolution to similar to 100 meV at 1000 eV incident photon energy are discussed.
T3  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1355 
KW  - resonant inelastic X-ray scattering;
KW  - X-ray photoelectron spectroscopy
KW  - soft X-ray spectroscopy
KW  - soft X-ray beamline
KW  - X-ray emission
KW  - X-ray absorption
KW  - BESSY II.
Y1  - 2020
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-549928
SN  - 1866-8372
ER  - 
TY  - JOUR
A1  - Erler, Alexander
A1  - Riebe, Daniel
A1  - Beitz, Toralf
A1  - Löhmannsröben, Hans-Gerd
A1  - Grothusheitkamp, Daniela
A1  - Kunz, Thomas
A1  - Methner, Frank-Jürgen
T1  - Characterization of volatile metabolites formed by molds on barley by mass and ion mobility spectrometry
JF  - Journal of mass spectrometr
N2  - The contamination of barley by molds on the field or in storage leads to the spoilage of grain and the production of mycotoxins, which causes major economic losses in malting facilities and breweries. Therefore, on-site detection of hidden fungus contaminations in grain storages based on the detection of volatile marker compounds is of high interest. In this work, the volatile metabolites of 10 different fungus species are identified by gas chromatography (GC) combined with two complementary mass spectrometric methods, namely, electron impact (EI) and chemical ionization at atmospheric pressure (APCI)-mass spectrometry (MS). The APCI source utilizes soft X-radiation, which enables the selective protonation of the volatile metabolites largely without side reactions. Nearly 80 volatile or semivolatile compounds from different substance classes, namely, alcohols, aldehydes, ketones, carboxylic acids, esters, substituted aromatic compounds, alkenes, terpenes, oxidized terpenes, sesquiterpenes, and oxidized sesquiterpenes, could be identified. The profiles of volatile and semivolatile metabolites of the different fungus species are characteristic of them and allow their safe differentiation. The application of the same GC parameters and APCI source allows a simple method transfer from MS to ion mobility spectrometry (IMS), which permits on-site analyses of grain stores. Characterization of IMS yields limits of detection very similar to those of APCI-MS. Accordingly, more than 90% of the volatile metabolites found by APCI-MS were also detected in IMS. In addition to different fungus genera, different species of one fungus genus could also be differentiated by GC-IMS.
KW  - APCI
KW  - fungus
KW  - gas chromatography
KW  - ion mobility spectrometry
KW  - mass
KW  - spectrometry
KW  - mold
KW  - soft X-ray
Y1  - 2020
U6  - https://doi.org/10.1002/jms.4501
SN  - 1076-5174
SN  - 1096-9888
VL  - 55
IS  - 5
SP  - 1
EP  - 10
PB  - Wiley
CY  - Hoboken
ER  - 
TY  - GEN
A1  - Alirezaeizanjani, Zahra
A1  - Großmann, Robert
A1  - Pfeifer, Veronika
A1  - Hintsche, Marius
A1  - Beta, Carsten
T1  - Chemotaxis strategies of bacteria with multiple run modes
T2  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe
N2  - Bacterial chemotaxis-a fundamental example of directional navigation in the living world-is key to many biological processes, including the spreading of bacterial infections. Many bacterial species were recently reported to exhibit several distinct swimming modes-the flagella may, for example, push the cell body or wrap around it. How do the different run modes shape the chemotaxis strategy of a multimode swimmer? Here, we investigate chemotactic motion of the soil bacterium Pseudomonas putida as a model organism. By simultaneously tracking the position of the cell body and the configuration of its flagella, we demonstrate that individual run modes show different chemotactic responses in nutrition gradients and, thus, constitute distinct behavioral states. On the basis of an active particle model, we demonstrate that switching between multiple run states that differ in their speed and responsiveness provides the basis for robust and efficient chemotaxis in complex natural habitats.
T3  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1418 
KW  - instability
KW  - flagellum
KW  - exploit
KW  - time
Y1  - 2020
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-519098
SN  - 1866-8372
IS  - 22
ER  - 
TY  - JOUR
A1  - Alirezaeizanjani, Zahra
A1  - Großmann, Robert
A1  - Pfeifer, Veronika
A1  - Hintsche, Marius
A1  - Beta, Carsten
T1  - Chemotaxis strategies of bacteria with multiple run modes
JF  - Science advances
N2  - Bacterial chemotaxis-a fundamental example of directional navigation in the living world-is key to many biological processes, including the spreading of bacterial infections. Many bacterial species were recently reported to exhibit several distinct swimming modes-the flagella may, for example, push the cell body or wrap around it. How do the different run modes shape the chemotaxis strategy of a multimode swimmer? Here, we investigate chemotactic motion of the soil bacterium Pseudomonas putida as a model organism. By simultaneously tracking the position of the cell body and the configuration of its flagella, we demonstrate that individual run modes show different chemotactic responses in nutrition gradients and, thus, constitute distinct behavioral states. On the basis of an active particle model, we demonstrate that switching between multiple run states that differ in their speed and responsiveness provides the basis for robust and efficient chemotaxis in complex natural habitats.
KW  - exploit
KW  - flagellum
KW  - instability
KW  - time
Y1  - 2020
U6  - https://doi.org/10.1126/sciadv.aaz6153
SN  - 2375-2548
VL  - 6
IS  - 22
PB  - American Association for the Advancement of Science
CY  - Washington
ER  - 
TY  - JOUR
A1  - Marschall, Raphael
A1  - Skorov, Yuri
A1  - Zakharov, Vladimir
A1  - Rezac, Ladislav
A1  - Gerig, Selina-Barbara
A1  - Christou, Chariton
A1  - Dadzie, S. Kokou
A1  - Migliorini, Alessandra
A1  - Rinaldi, Giovanna
A1  - Agarwal, Jessica
A1  - Vincent, Jean-Baptiste
A1  - Kappel, David
T1  - Cometary comae-surface links the physics of gas and dust from the surface to a spacecraft
JF  - Space science reviews
N2  - A comet is a highly dynamic object, undergoing a permanent state of change. These changes have to be carefully classified and considered according to their intrinsic temporal and spatial scales. The Rosetta mission has, through its contiguous in-situ and remote sensing coverage of comet 67P/Churyumov-Gerasimenko (hereafter 67P) over the time span of August 2014 to September 2016, monitored the emergence, culmination, and winding down of the gas and dust comae. This provided an unprecedented data set and has spurred a large effort to connect in-situ and remote sensing measurements to the surface. In this review, we address our current understanding of cometary activity and the challenges involved when linking comae data to the surface. We give the current state of research by describing what we know about the physical processes involved from the surface to a few tens of kilometres above it with respect to the gas and dust emission from cometary nuclei. Further, we describe how complex multidimensional cometary gas and dust models have developed from the Halley encounter of 1986 to today. This includes the study of inhomogeneous outgassing and determination of the gas and dust production rates. Additionally, the different approaches used and results obtained to link coma data to the surface will be discussed. We discuss forward and inversion models and we describe the limitations of the respective approaches. The current literature suggests that there does not seem to be a single uniform process behind cometary activity. Rather, activity seems to be the consequence of a variety of erosion processes, including the sublimation of both water ice and more volatile material, but possibly also more exotic processes such as fracture and cliff erosion under thermal and mechanical stress, sub-surface heat storage, and a complex interplay of these processes. Seasons and the nucleus shape are key factors for the distribution and temporal evolution of activity and imply that the heliocentric evolution of activity can be highly individual for every comet, and generalisations can be misleading.
KW  - comets
KW  - coma
KW  - gas
KW  - dust
KW  - dynamics
KW  - modelling
KW  - inversion
Y1  - 2020
U6  - https://doi.org/10.1007/s11214-020-00744-0
SN  - 0038-6308
SN  - 1572-9672
VL  - 216
IS  - 8
PB  - Springer
CY  - Dordrecht
ER  - 
TY  - JOUR
A1  - Kurilovich, Aleksandr A.
A1  - Mantsevich, Vladimir
A1  - Stevenson, Keith J.
A1  - Chechkin, Aleksei V.
A1  - Palyulin, V. V.
T1  - Complex diffusion-based kinetics of photoluminescence in semiconductor nanoplatelets
JF  - Physical chemistry, chemical physics : a journal of European Chemical Societies
N2  - We present a diffusion-based simulation and theoretical models for explanation of the photoluminescence (PL) emission intensity in semiconductor nanoplatelets. It is shown that the shape of the PL intensity curves can be reproduced by the interplay of recombination, diffusion and trapping of excitons. The emission intensity at short times is purely exponential and is defined by recombination. At long times, it is governed by the release of excitons from surface traps and is characterized by a power-law tail. We show that the crossover from one limit to another is controlled by diffusion properties. This intermediate region exhibits a rich behaviour depending on the value of diffusivity. The proposed approach reproduces all the features of experimental curves measured for different nanoplatelet systems.
Y1  - 2020
U6  - https://doi.org/10.1039/d0cp03744c
SN  - 1463-9076
SN  - 1463-9084
VL  - 22
IS  - 42
SP  - 24686
EP  - 24696
PB  - Royal Society of Chemistry
CY  - Cambridge
ER  - 
TY  - JOUR
A1  - Samajdar, Anuradha
A1  - Dietrich, Tim
T1  - Constructing Love-Q relations with gravitational wave detections
JF  - Physical review : D, Particles, fields, gravitation, and cosmology
N2  - Quasiuniversal relations between the tidal deformability and the quadrupole moment of neutron stars are predicted by theoretical computations, but have not been measured experimentally. We simulate 120 binary neutron star sources and find that Advanced LIGO and Advanced Virgo at design sensitivity could find possible deviations from predicted relations if the neutron stars are highly spinning. A network of envisaged third generation detectors will even allow extracting such relations, providing new tests of general relativity and nuclear physics predictions.
Y1  - 2020
U6  - https://doi.org/10.1103/PhysRevD.101.124014
SN  - 1550-7998
SN  - 1550-2368
VL  - 101
IS  - 12
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - GEN
A1  - Granado, Felipe Le Vot
A1  - Abad, Enrique
A1  - Metzler, Ralf
A1  - Yuste, Santos B.
T1  - Continuous time random walk in a velocity field
BT  - role of domain growth, Galilei-invariant advection-diffusion, and kinetics of particle mixing
T2  - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe
N2  - We consider the emerging dynamics of a separable continuous time random walk (CTRW) in the case when the random walker is biased by a velocity field in a uniformly growing domain. Concrete examples for such domains include growing biological cells or lipid vesicles, biofilms and tissues, but also macroscopic systems such as expanding aquifers during rainy periods, or the expanding Universe. The CTRW in this study can be subdiffusive, normal diffusive or superdiffusive, including the particular case of a Lévy flight. We first consider the case when the velocity field is absent. In the subdiffusive case, we reveal an interesting time dependence of the kurtosis of the particle probability density function. In particular, for a suitable parameter choice, we find that the propagator, which is fat tailed at short times, may cross over to a Gaussian-like propagator. We subsequently incorporate the effect of the velocity field and derive a bi-fractional diffusion-advection equation encoding the time evolution of the particle distribution. We apply this equation to study the mixing kinetics of two diffusing pulses, whose peaks move towards each other under the action of velocity fields acting in opposite directions. This deterministic motion of the peaks, together with the diffusive spreading of each pulse, tends to increase particle mixing, thereby counteracting the peak separation induced by the domain growth. As a result of this competition, different regimes of mixing arise. In the case of Lévy flights, apart from the non-mixing regime, one has two different mixing regimes in the long-time limit, depending on the exact parameter choice: in one of these regimes, mixing is mainly driven by diffusive spreading, while in the other mixing is controlled by the velocity fields acting on each pulse. Possible implications for encounter–controlled reactions in real systems are discussed.
T3  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1005 
KW  - diffusion
KW  - expanding medium
KW  - continuous time random walk
Y1  - 2020
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-479997
SN  - 1866-8372
IS  - 1005
SP  - 28
ER  - 
TY  - JOUR
A1  - Granado, Felipe Le Vot
A1  - Abad, Enrique
A1  - Metzler, Ralf
A1  - Yuste, Santos B.
T1  - Continuous time random walk in a velocity field
BT  - role of domain growth, Galilei-invariant advection-diffusion, and kinetics of particle mixing
JF  - New Journal of Physics
N2  - We consider the emerging dynamics of a separable continuous time random walk (CTRW) in the case when the random walker is biased by a velocity field in a uniformly growing domain. Concrete examples for such domains include growing biological cells or lipid vesicles, biofilms and tissues, but also macroscopic systems such as expanding aquifers during rainy periods, or the expanding Universe. The CTRW in this study can be subdiffusive, normal diffusive or superdiffusive, including the particular case of a Lévy flight. We first consider the case when the velocity field is absent. In the subdiffusive case, we reveal an interesting time dependence of the kurtosis of the particle probability density function. In particular, for a suitable parameter choice, we find that the propagator, which is fat tailed at short times, may cross over to a Gaussian-like propagator. We subsequently incorporate the effect of the velocity field and derive a bi-fractional diffusion-advection equation encoding the time evolution of the particle distribution. We apply this equation to study the mixing kinetics of two diffusing pulses, whose peaks move towards each other under the action of velocity fields acting in opposite directions. This deterministic motion of the peaks, together with the diffusive spreading of each pulse, tends to increase particle mixing, thereby counteracting the peak separation induced by the domain growth. As a result of this competition, different regimes of mixing arise. In the case of Lévy flights, apart from the non-mixing regime, one has two different mixing regimes in the long-time limit, depending on the exact parameter choice: in one of these regimes, mixing is mainly driven by diffusive spreading, while in the other mixing is controlled by the velocity fields acting on each pulse. Possible implications for encounter–controlled reactions in real systems are discussed.
KW  - diffusion
KW  - expanding medium
KW  - continuous time random walk
Y1  - 2020
U6  - https://doi.org/10.1088/1367-2630/ab9ae2
SN  - 1367-2630
VL  - 22
PB  - Dt. Physikalische Ges.
CY  - Bad Honnef
ER  - 
TY  - JOUR
A1  - Rosenblum, Michael
T1  - Controlling collective synchrony in oscillatory ensembles by precisely timed pulses
JF  - Chaos : an interdisciplinary journal of nonlinear science
N2  - We present an efficient technique for control of synchrony in a globally coupled ensemble by pulsatile action. We assume that we can observe the collective oscillation and can stimulate all elements of the ensemble simultaneously. We pay special attention to the minimization of intervention into the system. The key idea is to stimulate only at the most sensitive phase. To find this phase, we implement an adaptive feedback control. Estimating the instantaneous phase of the collective mode on the fly, we achieve efficient suppression using a few pulses per oscillatory cycle. We discuss the possible relevance of the results for neuroscience, namely, for the development of advanced algorithms for deep brain stimulation, a medical technique used to treat Parkinson's disease.
Y1  - 2020
U6  - https://doi.org/10.1063/5.0019823
SN  - 1054-1500
SN  - 1089-7682
VL  - 30
IS  - 9
PB  - American Institute of Physics
CY  - Melville
ER  - 
TY  - THES
A1  - Mandal, Partha Sarathi
T1  - Controlling the surface band gap in topological states of matter
N2  - In the present study, we employ the angle-resolved photoemission spectroscopy (ARPES) technique to study the electronic structure of topological states of matter. In particular, the so-called topological crystalline insulators (TCIs) Pb1-xSnxSe and Pb1-xSnxTe, and the Mn-doped Z2 topological insulators (TIs) Bi2Te3 and Bi2Se3. The Z2 class of strong topological insulators is protected by time-reversal symmetry and is characterized by an odd number of metallic Dirac type surface states in the surface Brillouin zone. The topological crystalline insulators on the other hand are protected by the individual crystal symmetries and exhibit an even number of Dirac cones. 

The topological properties of the lead tin chalcogenides topological crystalline insulators can be tuned by temperature and composition. Here, we demonstrate that Bi-doping of the Pb1-xSnxSe(111) epilayers induces a quantum phase transition from a topological crystalline insulator to a Z2 topological insulator. This occurs because Bi-doping lifts the fourfold valley degeneracy in the bulk. As a consequence a gap appears at ⌈¯, while the three Dirac cones at the M̅ points of the surface Brillouin zone remain intact. We interpret this new phase transition is caused by lattice distortion. Our findings extend the topological phase diagram enormously and make strong topological insulators switchable by distortions or electric field. In contrast, the bulk Bi doping of epitaxial Pb1-xSnxTe(111) films induces a giant Rashba splitting at the surface that can be tuned by the doping level. Tight binding calculations identify their origin as Fermi level pinning by trap states at the surface.

Magnetically doped topological insulators enable the quantum anomalous Hall effect (QAHE) which provide quantized edge states for lossless charge transport applications. The edge states are hosted by a magnetic energy gap at the Dirac point which has not been experimentally observed to date. Our low temperature ARPES studies unambiguously reveal the magnetic gap of Mn-doped Bi2Te3. Our analysis shows a five times larger gap size below the Tc than theoretically predicted. We assign this enhancement to a remarkable structure modification induced by Mn doping. Instead of a disordered impurity system, a self-organized alternating sequence of MnBi2Te4 septuple and Bi2Te3quintuple layers is formed. This enhances the wave-function overlap and gives rise to a large magnetic gap. Mn-doped Bi2Se3 forms similar heterostructure, but only a nonmagnetic gap is observed in this system. This correlates with the difference in magnetic anisotropy due to the much larger spin-orbit interaction in Bi2Te3 compared to Bi2Se3. These findings provide crucial insights for pushing lossless transport in topological insulators towards room-temperature applications.
N2  - In der vorliegenden Studie verwenden wir die Methode der winkelaufgelösten Photoemissionsspektroskopie (ARPES) zur Untersuchung der elektronischen Struktur von topologischen Zuständen der Materie. 
Insbesondere die sogenannten topologischen kristallinen Isolatoren (TCI) Pb1-xSnxSe und Pb1-xSnxTe sowie die Mn-dotierten Z2 topologischen Isolatoren (TI)  Bi2Te3 und Bi2Se3. Die Z2-Klasse der starken topologischen Isolatoren ist durch Zeitumkehrsymmetrie geschützt und durch eine ungerade Anzahl metallischer Dirac-Oberflächenzustände in der Oberflächenbrillouinzone gekennzeichnet. 
Die topologischen kristallinen Isolatoren hingegen sind durch einzelne Kristallsymmetrien geschützt und weisen eine gerade Anzahl von Dirac-Kegeln auf. Die topologischen Eigenschaften von Blei-Zinn-Chalkogenid-TCI lassen sich durch Temperatur sowie chemische Zusammensetzung einstellen. Hier wird gezeigt, dass Bi-Dotierung von eptiaktischen Pb1-xSnxSe(111)-Schichten einen Quantenphasenübergang von einem topologischen kristallinen Isolator zu einem Z2-topologischen Isolator hervorruft. Dies geschieht, weil die Dotierung mit Bi die vierfache Valley-Entartung im Volumen aufhebt. 
Als Konsequenz entsteht eine Lücke bei ⌈¯, während die drei Dirac-Kegel an den M̅-Punkten der Oberflächenbrillouinzone intakt bleiben. Wir interpretieren diesen neuen Phasenübergang als durch eine Gitterverzerrung verursacht. Unsere Ergebnisse erweitern das topologische Phasendiagramm enorm und machen starke topologische Isolatoren durch Verzerrungen oder elektrische Felder schaltbar. Im Gegensatz dazu induziert eine Bi-Dotierung im Volumen von epitaktischen Pb1-xSnxTe(111)-Schichten eine riesige Rashba-Aufspaltung an der Oberfläche, die durch das Ausmaß der Dotierung eingestellt werden kann. Tight-Binding-Berechnungen identifizieren ihren Ursprung in einem Fermi-Niveau-Pinning durch Trap-Zustände an der Oberfläche.
Magnetisch dotierte topologische Isolatoren ermöglichen den quantisierten anomalen Hall-Effekt (QAHE), der quantisierte Kantenzustände liefert, die für verlustfreien Ladungstransport eingesetzt werden können. Die Kantenzustände treten in einer magnetischen Energielücke am Dirac-Punkt auf, die bisher noch nicht experimentell beobachtet wurde. 
Unsere Tieftemperatur-ARPES-Untersuchungen weisen die magnetische Energielücke in Mn dotiertem Bi2Te3 eindeutig nach. Unsere Analyse zeigt unterhalb von Tc eine viermal größere Energielücke als theoretisch vorhergesagt. Wir führen diese Erhöhung auf eine bemerkenswerte Strukturmodifikation durch die Mn-Dotierung zurück. Statt eines Systems mit ungeordneten Mn Verunreinigungen entsteht eine selbstorganisierte alternierende Sequenz von MnBi2Te4-Septupel- und Bi2Te3-Quintupel-Schichten. 
Das erhöht den Überlapp der Wellenfunktionen und führt zu der großen magnetischen Energielücke. Mn-dotiertes Bi2Se3 bildet ähnliche Heterostrukturen aus, jedoch wird in diesem System nur eine nichtmagnetische Energielücke beobachtet. Dies korreliert mit der unterschiedlichen magnetischen Anisotropie aufgrund der viel größeren Spin-Bahn-Wechselwirkung im Bi2Te3 im Vergleich zu Bi2Se3. Diese Resultate liefern entscheidende Erkenntnisse, um verlustfreien Transport in topologischen Isolatoren für Anwendungen bei Raumtemperatur weiterzuentwickeln.
KW  - ARPES
KW  - Topological Insulator
KW  - Topological Crystalline Insulator
KW  - Rashba effect
KW  - Rashba-Effekt
KW  - Topologischer kristalliner Isolator
KW  - Topologischer Isolator
Y1  - 2020
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-480459
ER  - 
TY  - JOUR
A1  - Vinke, Kira
A1  - Gabrysch, Sabine
A1  - Paoletti, Emanuela
A1  - Rockström, Johan
A1  - Schellnhuber, Hans Joachim
T1  - Corona and the climate
BT  - a comparison of two emergencies
JF  - Global sustainability
N2  - Lessons from the corona crisis can help manage the even more daunting challenge of anthropogenic global warming.
KW  - adaptation and mitigation
KW  - ecology and biodiversity
KW  - human behaviour
KW  - natural resources (biological and non-biological)
KW  - policies
KW  - politics
KW  - and governance
Y1  - 2020
U6  - https://doi.org/10.1017/sus.2020.20
SN  - 2059-4798
VL  - 3
PB  - Cambridge Univ. Press
CY  - Cambridge
ER  - 
TY  - GEN
A1  - Wolff, Christian Michael
A1  - Canil, Laura
A1  - Rehermann, Carolin
A1  - Nguyen, Ngoc Linh
A1  - Zu, Fengshuo
A1  - Ralaiarisoa, Maryline
A1  - Caprioglio, Pietro
A1  - Fiedler, Lukas
A1  - Stolterfoht, Martin
A1  - Kogikoski, Junior, Sergio
A1  - Bald, Ilko
A1  - Koch, Norbert
A1  - Unger, Eva L.
A1  - Dittrich, Thomas
A1  - Abate, Antonio
A1  - Neher, Dieter
T1  - Correction to 'Perfluorinated self-assembled monolayers enhance the stability and efficiency of inverted perovskite solar cells' (2020, 14 (2), 1445−1456)
T2  - ACS nano
Y1  - 2020
U6  - https://doi.org/10.1021/acsnano.0c08081
SN  - 1936-0851
SN  - 1936-086X
VL  - 14
IS  - 11
SP  - 16156
EP  - 16156
PB  - American Chemical Society
CY  - Washington, DC
ER  - 
TY  - JOUR
A1  - Gong, Chen Chris
A1  - Tönjes, Ralf
A1  - Pikovsky, Arkady
T1  - Coupled Möbius maps as a tool to model Kuramoto phase synchronization
JF  - Physical review : E, Statistical, nonlinear and soft matter physics
N2  - We propose Mobius maps as a tool to model synchronization phenomena in coupled phase oscillators. Not only does the map provide fast computation of phase synchronization, it also reflects the underlying group structure of the sinusoidally coupled continuous phase dynamics. We study map versions of various known continuous-time collective dynamics, such as the synchronization transition in the Kuramoto-Sakaguchi model of nonidentical oscillators, chimeras in two coupled populations of identical phase oscillators, and Kuramoto-Battogtokh chimeras on a ring, and demonstrate similarities and differences between the iterated map models and their known continuous-time counterparts.
Y1  - 2020
U6  - https://doi.org/10.1103/PhysRevE.102.022206
SN  - 2470-0045
SN  - 2470-0053
SN  - 1063-651X
SN  - 2470-0061
SN  - 1550-2376
VL  - 102
IS  - 2
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Caetano, Daniel L. Z.
A1  - Carvalho, Sidney Jurado de
A1  - Metzler, Ralf
A1  - Cherstvy, Andrey G.
T1  - Critical adsorption of multiple polyelectrolytes onto a nanosphere
BT  - splitting the adsorption-desorption transition boundary
JF  - Interface : journal of the Royal Society
N2  - Employing extensive Monte Carlo computer simulations, we investigate in detail the properties of multichain adsorption of charged flexible polyelectrolytes (PEs) onto oppositely charged spherical nanoparticles (SNPs). We quantify the conditions of critical adsorption-the phase-separation curve between the adsorbed and desorbed states of the PEs-as a function of the SNP surface-charge density and the concentration of added salt. We study the degree of fluctuations of the PE-SNP electrostatic binding energy, which we use to quantify the emergence of the phase subtransitions, including a series of partially adsorbed PE configurations. We demonstrate how the phase-separation adsorption-desorption boundary shifts and splits into multiple subtransitions at low-salt conditions, thereby generalizing and extending the results for critical adsorption of a single PE onto the SNP. The current findings are relevant for finite concentrations of PEs around the attracting SNP, such as the conditions for PE adsorption onto globular proteins carrying opposite electric charges.
KW  - nanoparticles
KW  - polyelectrolytes
KW  - electrostatics
KW  - critical adsorption
KW  - phase-transition boundary
Y1  - 2020
U6  - https://doi.org/10.1098/rsif.2020.0199
SN  - 1742-5689
SN  - 1742-5662
VL  - 17
IS  - 167
PB  - Royal Society
CY  - London
ER  - 
TY  - JOUR
A1  - Awad, Emad
A1  - Metzler, Ralf
T1  - Crossover dynamics from superdiffusion to subdiffusion
BT  - models and solutions
JF  - Fractional calculus and applied analysis : an international journal for theory and applications
N2  - The Cattaneo or telegrapher's equation describes the crossover from initial ballistic to normal diffusion. Here we study and survey time-fractional generalisations of this equation that are shown to produce the crossover of the mean squared displacement from superdiffusion to subdiffusion. Conditional solutions are derived in terms of Fox H-functions and the dth-order moments as well as the diffusive flux of the different models are derived. Moreover, the concept of the distribution-like is proposed as an alternative to the probability density function.
KW  - Cattaneo equation
KW  - telegrapher's equation
KW  - crossover dynamics
KW  - fractional dynamic equations
KW  - anomalous diffusion
KW  - superdiffusion and
KW  - subdiffusion
KW  - Fox H-functions
Y1  - 2020
U6  - https://doi.org/10.1515/fca-2020-0003
SN  - 1311-0454
SN  - 1314-2224
VL  - 23
IS  - 1
SP  - 55
EP  - 102
PB  - De Gruyter
CY  - Berlin ; Boston
ER  - 
TY  - JOUR
A1  - Mishurova, Tatiana
A1  - Bruno, Giovanni
A1  - Evsevleev, Sergei
A1  - Sevostianov, Igor
T1  - Determination of macroscopic stress from diffraction experiments
BT  - a critical discussion
JF  - Journal of applied physics
N2  - The paper is motivated by some inconsistencies and contradictions present in the literature on the calculation of the so-called diffraction elastic constants. In an attempt at unifying the views that the two communities of Materials Science and Mechanics of Materials have on the subject, we revisit and define the terminology used in the field. We also clarify the limitations of the commonly used approaches and show that a unified methodology is also applicable to textured materials with a nearly arbitrary grain shape. We finally compare the predictions based on this methodology with experimental data obtained by in situ synchrotron radiation diffraction on additively manufactured Ti-6Al-4V alloy. We show that (a) the transverse isotropy of the material yields good agreement between the best-fit isotropy approximation (equivalent to the classic Kroner's model) and the experimental data and (b) the use of a general framework allows the calculation of all components of the tensor of diffraction elastic constants, which are not easily measurable by diffraction methods. This allows us to extend the current state-of-the-art with a predictive tool.
Y1  - 2020
U6  - https://doi.org/10.1063/5.0009101
SN  - 0021-8979
SN  - 1089-7550
VL  - 128
IS  - 2
PB  - American Institute of Physics
CY  - Melville
ER  - 
TY  - JOUR
A1  - Qiu, Xunlin
A1  - Benjamin, Aravindan Joseph
A1  - Raman Venkatesan, Thulasinath
A1  - Schmidt, Georg C.
A1  - Soler, Ricardo Alonso Quintana
A1  - Panicker, Pramul Muraleedhara
A1  - Gerhard, Reimund
A1  - Hübler, Arved Carl
T1  - Dielectric and electroacoustic assessment of screen-printed piezoelectric polymer layers as flexible transducers
BT  - influence of the electrode material
JF  - IEEE transactions on dielectrics and electrical insulation
N2  - Here, piezoelectric transducers consisting of a P(VDF-TrFE) layer with either silver or PEDOT:PSS screen-printed electrodes are studied. The influence of electrodes on the dielectric and electroacoustic properties are studied in dielectric-spectroscopy and ferroelectric-hysteresis measurements. Only when both the bottom and the top electrodes are made of silver, the typical dielectric relaxation of the P(VDF-TrFE) layer is clearly observed. When one or two of the electrodes are of PEDOT:PSS, a Debye-like relaxation is present. Compared with silver electrodes, PEDOT:PSS electrodes allow for moderate self-healing. Consequently, samples with bottom and top PEDOT:PSS electrodes can be poled to saturation, while samples with silver electrodes can hardly be poled to saturation due to destructive electric breakdown. Acoustic transducer measurements show that silver electrodes facilitate higher and broader frequency operation, while PEDOT:PSS electrodes bring slightly lower total harmonic distortion. Overall, the acoustic performance shows no significant deviations between differently electroded samples so that silver electrodes do not offer any advantages for the transducers studied here due to their much higher tendency for destructive electric breakdown.
KW  - poly(vinylidenefluoride-trifluoroethylene) P(VDF-TrFE)
KW  - dielectric
KW  - spectroscopy
KW  - ferroelectricity and piezoelectricity in polymers
KW  - screen
KW  - printing
KW  - printed electroacoustic thin-film transducers
Y1  - 2020
U6  - https://doi.org/10.1109/TDEI.2020.008864
SN  - 1070-9878
SN  - 1558-4135
SN  - 0018-9367
VL  - 27
IS  - 5
SP  - 1683
EP  - 1690
PB  - Institute of Electrical and Electronics Engineers
CY  - New York, NY
ER  - 
TY  - JOUR
A1  - Kosztolowicz, Tadeusz
A1  - Metzler, Ralf
T1  - Diffusion of antibiotics through a biofilm in the presence of diffusion and absorption barriers
JF  - Physical review : E, Statistical, nonlinear and soft matter physics
N2  - We propose a model of antibiotic diffusion through a bacterial biofilm when diffusion and/or absorption barriers develop in the biofilm. The idea of this model is: We deduce details of the diffusion process in a medium in which direct experimental study is difficult, based on probing diffusion in external regions. Since a biofilm has a gel-like consistency, we suppose that subdiffusion of particles in the biofilm may occur. To describe this process we use a fractional subdiffusion-absorption equation with an adjustable anomalous diffusion exponent. The boundary conditions at the boundaries of the biofilm are derived by means of a particle random walk model on a discrete lattice leading to an expression involving a fractional time derivative. We show that the temporal evolution of the total amount of substance that has diffused through the biofilm explicitly depends on whether there is antibiotic absorption in the biofilm. This fact is used to experimentally check for antibiotic absorption in the biofilm and if subdiffusion and absorption parameters of the biofilm change over time. We propose a four-stage model of antibiotic diffusion in biofilm based on the following physical characteristics: whether there is absorption of the antibiotic in the biofilm and whether all biofilm parameters remain unchanged over time. The biological interpretation of the stages, in particular their relation with the bacterial defense mechanisms, is discussed. Theoretical results are compared with empirical results of ciprofloxacin diffusion through Pseudomonas aeruginosa biofilm, and ciprofloxacin and gentamicin diffusion through Proteus mirabilis biofilm.
Y1  - 2020
U6  - https://doi.org/10.1103/PhysRevE.102.032408
SN  - 2470-0045
SN  - 2470-0053
VL  - 102
IS  - 3
PB  - American Physical Society
CY  - Melville, NY
ER  - 
TY  - JOUR
A1  - Magkos, Sotirios
A1  - Kupsch, Andreas
A1  - Bruno, Giovanni
T1  - Direct iterative reconstruction of computed tomography trajectories reconstruction from limited number of projections with DIRECTT
JF  - Review of scientific instruments : a monthly journal devoted to scientific instruments, apparatus, and techniques
N2  - X-ray computed tomography has many applications in materials science and non-destructive testing. While the standard filtered back-projection reconstruction of the radiographic datasets is fast and simple, it typically fails in returning accurate results from missing or inconsistent projections. Among the alternative techniques that have been proposed to handle such data is the Direct Iterative REconstruction of Computed Tomography Trajectories (DIRECTT) algorithm. We describe a new approach to the algorithm, which significantly decreases the computational time while achieving a better reconstruction quality than that of other established algorithms.
Y1  - 2020
U6  - https://doi.org/10.1063/5.0013111
SN  - 0034-6748
SN  - 1089-7623
SN  - 1527-2400
VL  - 91
IS  - 10
PB  - American Institute of Physics
CY  - Melville
ER  - 
TY  - JOUR
A1  - Bouakline, Foudhil
T1  - Does nuclear permutation symmetry allow dynamical localization in symmetric double-well achiral molecules?
JF  - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr
N2  - We discuss the effect of molecular symmetry on coherent tunneling in symmetric double-well potentials whose two molecular equilibrium configurations are interconverted by nuclear permutations. This is illustrated with vibrational tunneling in ammonia molecules, electronic tunneling in the dihydrogen cation, and laser-induced rotational tunneling of homonuclear diatomics. In this contribution, we reexamine the textbook picture of coherent tunneling in such potentials, which is depicted with a wavepacket shuttling back and forth between the two potential-wells. We show that the common application of this picture to the aforementioned molecules contravenes the principle of the indistinguishability of identical particles. This conflict originates from the sole consideration of the dynamics of the tunneling-mode, connecting the double-well energy minima, and complete omission of all the remaining molecular degrees of freedom. This gives rise to double-well wavepackets that are nonsymmetric under nuclear permutations. To obey quantum statistics, we show that the double-well eigenstates composing these wavepackets must be entangled with the wavefunctions that describe all the omitted molecular modes. These wavefunctions have compensating and opposite nuclear permutation symmetry. This in turn leads to complete quenching of interference effects behind localization in one potential-well or another. Indeed, we demonstrate that the reduced density of probability of the symmetrized molecular wavefunction, where all the molecular coordinates but the tunneling-mode are integrated out, is symmetrically distributed over the two potential-wells, at all times. This applies to any multilevel wavepacket of isotropic or fully aligned symmetric double-well achiral molecules. However, in the case of coherent electronic or vibrational tunneling, fully aligned molecules may exhibit dynamical localization in the space-fixed frame, where the tunneling-mode density shuttles between the opposite directions of the alignment axis. This dynamical spatial-localization results from linear combinations of molecular states that have opposite parity. In summary, this study shows that dynamical localization of the tunneling-mode density on either of the two indistinguishable molecular equilibrium configurations of symmetric double-well achiral molecules is forbidden by quantum statistics, whereas its dynamical localization in the space-fixed frame is allowed by parity. The subtle distinction between these two types of localization has far-reaching implications in the interpretation of many ultrafast molecular dynamics experiments.
Y1  - 2020
U6  - https://doi.org/10.1063/1.5141746
SN  - 0021-9606
SN  - 1089-7690
VL  - 152
IS  - 24
PB  - American Institute of Physics
CY  - Melville
ER  - 
TY  - JOUR
A1  - Mejia-Monasterio, Carlos
A1  - Metzler, Ralf
A1  - Vollmer, Jürgen
T1  - Editorial: anomalous transport
BT  - applications, mathematical perspectives, and big data
JF  - Frontiers in Physics
KW  - anomalous (or non-Fickian) diffusion
KW  - anomalous heat conduction
KW  - stochastic dynamics
KW  - molecular overcrowding
KW  - dynamical systems
Y1  - 2020
U6  - https://doi.org/10.3389/fphy.2020.622417
SN  - 2296-424X
VL  - 8
PB  - Frontiers Media
CY  - Lausanne
ER  - 
TY  - GEN
A1  - Varykhalov, Andrei
A1  - Freyse, Friedrich
A1  - Aguilera, Irene
A1  - Battiato, Marco
A1  - Krivenkov, Maxim
A1  - Marchenko, Dmitry
A1  - Bihlmayer, Gustav
A1  - Blugel, Stefan
A1  - Rader, Oliver
A1  - Sanchez-Barriga, Jaime
T1  - Effective mass enhancement and ultrafast electron dynamics of Au(111) surface state coupled to a quantum well
T2  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe
N2  - We show that, although the equilibrium band dispersion of the Shockley-type surface state of two-dimensional Au(111) quantum films grown on W(110) does not deviate from the expected free-electron-like behavior, its nonequilibrium energy-momentum dispersion probed by time- and angle-resolved photoemission exhibits a remarkable kink above the Fermi level due to a significant enhancement of the effective mass. The kink is pronounced for certain thicknesses of the Au quantum well and vanishes in the very thin limit. We identify the kink as induced by the coupling between the Au(111) surface state and emergent quantum-well states which probe directly the buried gold-tungsten interface. The signatures of the coupling are further revealed by our time-resolved measurements which show that surface state and quantum-well states thermalize together behaving as dynamically locked electron populations. In particular, relaxation of hot carriers following laser excitation is similar for both surface state and quantum-well states and much slower than expected for a bulk metallic system. The influence of quantum confinement on the interplay between elementary scattering processes of the electrons at the surface and ultrafast carrier transport in the direction perpendicular to the surface is shown to be the reason for the slow electron dynamics.
T3  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1354 
KW  - AG
KW  - films
Y1  - 2020
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-549892
SN  - 1866-8372
IS  - 1
ER  - 
TY  - JOUR
A1  - Varykhalov, Andrei
A1  - Freyse, Friedrich
A1  - Aguilera, Irene
A1  - Battiato, Marco
A1  - Krivenkov, Maxim
A1  - Marchenko, Dmitry
A1  - Bihlmayer, Gustav
A1  - Blugel, Stefan
A1  - Rader, Oliver
A1  - Sanchez-Barriga, Jaime
T1  - Effective mass enhancement and ultrafast electron dynamics of Au(111) surface state coupled to a quantum well
JF  - Physical Review Research
N2  - We show that, although the equilibrium band dispersion of the Shockley-type surface state of two-dimensional Au(111) quantum films grown on W(110) does not deviate from the expected free-electron-like behavior, its nonequilibrium energy-momentum dispersion probed by time- and angle-resolved photoemission exhibits a remarkable kink above the Fermi level due to a significant enhancement of the effective mass. The kink is pronounced for certain thicknesses of the Au quantum well and vanishes in the very thin limit. We identify the kink as induced by the coupling between the Au(111) surface state and emergent quantum-well states which probe directly the buried gold-tungsten interface. The signatures of the coupling are further revealed by our time-resolved measurements which show that surface state and quantum-well states thermalize together behaving as dynamically locked electron populations. In particular, relaxation of hot carriers following laser excitation is similar for both surface state and quantum-well states and much slower than expected for a bulk metallic system. The influence of quantum confinement on the interplay between elementary scattering processes of the electrons at the surface and ultrafast carrier transport in the direction perpendicular to the surface is shown to be the reason for the slow electron dynamics.
KW  - AG
KW  - Flims
Y1  - 2020
U6  - https://doi.org/10.1103/PhysRevResearch.2.013343
SN  - 0031-9007
VL  - 2
IS  - 1
SP  - 1
EP  - 9
PB  - American Physical Society
CY  - Ridge, NY
ER  - 
TY  - THES
A1  - Knigge, Xenia
T1  - Einzelmolekül-Manipulation mittels Nano-Elektroden und Dielektrophorese
T1  - Single molecule manipulation using nano-electrodes and dielectrophoresis
N2  - In dieser Arbeit wurden Nano-Elektroden-Arrays zur Einzel-Objekt-Immobilisierung mittels Dielektrophorese verwendet. Hierbei wurden fluoreszenzmarkierte Nano-Sphären als Modellsystem untersucht und die gewonnenen Ergebnisse auf biologische Proben übertragen. Die Untersuchungen in Kombination mit verschiedenen Elektrodenlayouts führten zu einer deterministischen Vereinzelung der Nano-Sphären ab einem festen Größenverhältnis zwischen Nano-Sphäre und Durchmesser der Elektrodenspitzen. An den Proteinen BSA und R-PE konnte eine dielektrophoretische Immobilisierung ebenfalls demonstriert und R-PE Moleküle zur Vereinzelung gebracht werden. Hierfür war neben einem optimierten Elektrodenlayout, das durch Feldsimulationen den Feldgradienten betreffend gesucht wurde, eine Optimierung der Feldparameter, insbesondere von Spannung und Frequenz, erforderlich.
Neben der Dielektrophorese erfolgten auch Beobachtungen anderer Effekte des elektrischen Feldes, wie z.B. Elektrolyse an Nano-Elektroden und Strömungen über dem Elektroden-Array, hervorgerufen durch Joulesche Wärme und AC-elektroosmotischen Fluss. Zudem konnte Dielektrophorese an Silberpartikeln beobachtet werden und mittels Fluoreszenz-, Atom-Kraft-, Raster-Elektronen-Mikroskopie und energiedispersiver Röntgenspektroskopie untersucht werden. Schließlich wurden die verwendeten Objektive und Kameras auf ihre Lichtempfindlichkeit hin analysiert, so dass die Vereinzelung von Biomolekülen an Nano-Elektroden nachweisbar war.
Festzuhalten bleibt also, dass die Vereinzelung von Nano-Objekten und Biomolekülen an Nano-Elektroden-Arrays gelungen ist. Durch den parallelen Ansatz erlaubt dies, Aussagen über das Verhalten von Einzelmolekülen mit guter Statistik zu treffen.
N2  - In this work, nanoelectrode arrays were used for single object immobilization by dielectrophoresis. Fluorescently labeled nanospheres were used as a model system and the results were transferred to biological samples. The experiments in combination with different electrode layouts led to a deterministic singling of the nanospheres for a fixed size ratio between nanosphere and tipdiameter. Dielectrophoretic immobilization could also be demonstrated for the proteins BSA and R-PE, while R-PE molecules were even immobilized as single objects. For this purpose, in addition to an optimized electrode layout, which was searched by numerical field calculations, an optimization of the field parameters was required, in particular of voltage and frequency.
Besides dielectrophoresis, observations of other effects were made, e.g. electrolysis at nanoelectrodes and fluid flows caused by Joule heating and AC-electroosmotic flow. In addition, dielectrophoresis was observed on silver nanoparticles, which was examined by fluorescence-, atomic force-, scanning electron microscopy and energy dispersive X-ray spectroscopy. Finally, the objectives and cameras were analyzed for their photosensitivity so that the singling of biomolecules on nanoelectrodes became detectable.
The successful singling of nanoobjects and biomolecules on nanoelectrodes has been shown in a parallel approach so that it is possible to make statements about the behavior of single molecules with good statistics.
KW  - Dielektrophorese
KW  - Einzelmolekül-Biosensor
KW  - parallele Immobilisierung von Biomolekülen
KW  - R-PE
KW  - Polystyrol Nano-Sphären
KW  - Nano-Elektroden
KW  - 3D-Feldsimulationen
KW  - Einzel-Objekt-Nachweis
KW  - Fluoreszenz-Mikroskopie
KW  - REM
KW  - dielectrophoresis
KW  - single-molecule biosensor
KW  - parallel immobilization of biomolecules
KW  - R-PE
KW  - polystyrene nano-spheres
KW  - nano-electrodes
KW  - 3D field calculations
KW  - single-object detection
KW  - fluorescence microscopy
KW  - SEM
Y1  - 2020
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-443137
ER  - 
TY  - THES
A1  - Wang, Jingwen
T1  - Electret properties of polypropylene with surface chemical modification and crystalline reconstruction
N2  - As one of the most-produced commodity polymers, polypropylene draws considerable scientific and commercial interest as an electret material. In the present thesis, the influence of the surface chemical modification and crystalline reconstruction on the electret properties of the polypropylene thin films will be discussed. The chemical treatment with orthophosphoric acid can significantly improve the surface charge stability of the polypropylene electrets by introducing phosphorus- and oxygen-containing structures onto the modified surface. The thermally stimulated discharge measurement and charge profiling by means of piezoelectrically generated pressure steps are used to investigate the electret behaviour. It is concluded that deep traps of limited number density are created during the treatment with inorganic chemicals. Hence, the improvement dramatically decreases when the surface-charge density is substantially higher than ±1.2×10^(-3) C·m^(-2). The newly formed traps also show a higher trapping energy for negative charges. The energetic distributions of the traps in the non-treated and chemically treated samples offer an insight regarding the surface and foreign-chemical dominance on the charge storage and transport in the polypropylene electrets. 

Additionally, different electret properties are observed on the polypropylene films with the spherulitic and transcrystalline structures. It indicates the dependence of the charge storage and transport on the crystallite and molecular orientations in the crystalline phase. In general, a more diverse crystalline growth in the spherulitic samples can result in a more complex energetic trap distribution, in comparison to that in a transcrystalline polypropylene. The double-layer transcrystalline polypropylene film with a crystalline interface in the middle can be obtained by crystallising the film in contact with rough moulding surfaces on both sides. A layer of heterocharges appears on each side of the interface in the double-layer transcrystalline polypropylene electrets after the thermal poling. However, there is no charge captured within the transcrystalline layers. The phenomenon reveals the importance of the crystalline interface in terms of creating traps with the higher activation energy in polypropylene. The present studies highlight the fact that even slight variations in the polypropylene film may lead to dramatic differences in its electret properties.
N2  - Als eines der meistproduzierten Polymere stößt Polypropylen (PP) auch als Elektretmaterial auf großes wissenschaftliches und kommerzielles Interesse. In der vorliegenden Arbeit wird der Einfluss chemischer Oberflächen-Modifikationen und kristalliner Rekonstruktionen auf die Elektreteigenschaften von dünnen Polypropylen-Schichten untersucht und diskutiert. Die nasschemische Behandlung mit Orthophosphorsäure kann die Oberflächenladungsstabilität der PP-Elektrete deutlich verbessern, indem phosphor- und sauerstoffhaltige Strukturen auf der modifizierten Oberfläche erzeugt und verankert werden. Aus thermisch stimulierten Entladungsexperimenten und Ladungsmessungen mit piezoelektrisch erzeugten Druckstufen ergibt sich, dass die Oberflächenbehandlung eine begrenzte Anzahl tiefer Haftstellen vor allem für negative Ladungen erzeugt. Daher nimmt die Verbesserung drastisch ab, wenn die Oberflächenladungsdichte einen wesentlich höheren Wert als ±1.2×10-3 C·m-2 hat. Die energetischen Verteilungen der Ladungsfallen in unbehandelten und in chemisch behandelten Proben ermöglichen Rückschlüsse auf die Oberfläche und auf die wesentliche Rolle der aufgebrachten chemischen Spezies für Ladungsspeicherung und -transport in PP-Elektreten.

Darüber hinaus werden an dünnen Polypropylenfolien mit entweder sphärolithischen oder transkristallinen Strukturen deutlich unterschiedliche Elektreteigenschaften beobachtet, was den starken Einfluss von Kristallstruktur und Molekülorientierung auf Ladungsspeicherung und -transport in der kristallinen Phase anzeigt. Generell führt das vielfältigere kristalline Wachstum in sphärolithischen Proben oft zu komplexeren energetischen Verteilungen der Ladungsfallen als in transkristallinen PP-Schichten. Zweischichtige transkristalline PP-Folien mit einer kristallinen Grenzfläche in der Mitte können durch beidseitige Kristallisation auf rauen Formgussoberflächen erzeugt werden. Auf jeder Seite der Grenzfläche in der Mitte der zweischichtigen transkristallinen PP-Elektrete findet sich nach thermischer Polung eine Schicht von Heteroladungen, während innerhalb der transkristallinen Schichten keine Ladungen beobachtet werden. Daraus wird die Bedeutung der kristallinen Grenzfläche für das Auftreten von Ladungsfallen mit hohen Aktivierungsenergien in Polypropylen deutlich. Die vorliegenden Studien zeigen, dass bereits geringe Variationen in der Nanostruktur der Polypropylenfolien zu dramatisch unterschiedlichen Elektreteigenschaften führen können.
KW  - electret
KW  - polypropylene
KW  - charge storage and transport
KW  - surface chemical treatment
KW  - transcrystalline polypropylene
KW  - Elektret
KW  - Polypropylen
KW  - Ladungsspeicherung und -transport
KW  - chemische Oberflächen-Modifikationen
KW  - transkristallines Polypropylen
Y1  - 2020
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-470271
ER  - 
TY  - JOUR
A1  - Rüdiger, Günther
A1  - Küker, Manfred
A1  - Käpylä, Petri J.
T1  - Electrodynamics of turbulent fluids with fluctuating electric conductivity
JF  - Journal of plasma physics
N2  - Consequences of fluctuating microscopic conductivity in mean-field electrodynamics of turbulent fluids are formulated and discussed. If the conductivity fluctuations are assumed to be uncorrelated with the velocity fluctuations then only the turbulence-originated magnetic diffusivity of the fluid is reduced and the decay time of a large-scale magnetic field or the cycle times of oscillating turbulent dynamo models are increased. If, however, the fluctuations of conductivity and flow in a certain well-defined direction are correlated, an additional diamagnetic pumping effect results, transporting the magnetic field in the opposite direction to the diffusivity flux vector <eta'u'>. In the presence of global rotation, even for homogeneous turbulence fields, an alpha effect appears. If the characteristic values of the outer core of the Earth or the solar convection zone are applied, the dynamo number of the new alpha effect does not reach supercritical values to operate as an alpha(2)-dynamo but oscillating alpha Omega-dynamos with differential rotation are not excluded.
KW  - astrophysical plasmas
KW  - plasma flows
Y1  - 2020
U6  - https://doi.org/10.1017/S0022377820000665
SN  - 0022-3778
SN  - 1469-7807
VL  - 86
IS  - 3
PB  - Cambridge Univ. Press
CY  - London
ER  - 
TY  - JOUR
A1  - Schneider, Sebastian
A1  - Hoffmann-Vogel, Regina
T1  - Electrostatic forces above graphene nanoribbons and edges interpreted as partly hydrogen-free
JF  - Nanoscale
N2  - Graphene nanoribbons' electronic transport properties strongly depend on the type of edge, armchair, zigzag or other, and on edge functionalization that can be used for band-gap engineering. For only partly hydrogenated edges interesting magnetic properties are predicted. Electric charge accumulates at edges and corners. Scanning force microscopy has so far shown the centre of graphene nanoribbons with atomic resolution using a quartz crystal tuning fork sensor of high stiffness. Weak long-range electrostatic forces related to the charge accumulation on the edges of graphene nanoribbons could not be imaged so far. Here, we show the electrostatic forces at the corners and edges of graphene nanoribbons are amenable to measurement. We use soft cantilevers and a bimodal imaging technique to combine enhanced sensitivity to weak long-range electrostatic forces with the high resolution of the second-frequency shift. Additionally, in our work the edges of the nanoribbons are mainly hydrogen-free, opening to the route to investigations of partly hydrogenated magnetic nanoribbons.
Y1  - 2020
U6  - https://doi.org/10.1039/d0nr03348k
SN  - 2040-3364
SN  - 2040-3372
VL  - 12
IS  - 34
SP  - 17895
EP  - 17901
PB  - Royal Society of Chemistry
CY  - Cambridge
ER  - 
TY  - JOUR
A1  - Mohammady, M. Hamed
A1  - Auffèves, Alexia
A1  - Anders, Janet
T1  - Energetic footprints of irreversibility in the quantum regime
JF  - Communications Physics
N2  - In classical thermodynamic processes the unavoidable presence of irreversibility, quantified by the entropy production, carries two energetic footprints: the reduction of extractable work from the optimal, reversible case, and the generation of a surplus of heat that is irreversibly dissipated to the environment. Recently it has been shown that in the quantum regime an additional quantum irreversibility occurs that is linked to decoherence into the energy basis. Here we employ quantum trajectories to construct distributions for classical heat and quantum heat exchanges, and show that the heat footprint of quantum irreversibility differs markedly from the classical case. We also quantify how quantum irreversibility reduces the amount of work that can be extracted from a state with coherences. Our results show that decoherence leads to both entropic and energetic footprints which both play an important role in the optimization of controlled quantum operations at low temperature.

In classical thermodynamics irreversibility occurs whenever a non-thermal system is brought into contact with a thermal environment. Using quantum trajectories the authors here establish two energetic footprints of quantum irreversible processes, and find that while quantum irreversibility leads to the occurrence of a quantum heat and a reduction of work production, the two are not linked in the same manner as the classical laws of thermodynamics would dictate.
KW  - entropy production
KW  - quantum mechanics
KW  - thermodynamics
Y1  - 2020
U6  - https://doi.org/10.1038/s42005-020-0356-9
SN  - 2399-3650
VL  - 3
IS  - 1
SP  - 1
EP  - 14
PB  - Springer Nature
CY  - London
ER  - 
TY  - GEN
A1  - Mohammady, M. Hamed
A1  - Auffèves, Alexia
A1  - Anders, Janet
T1  - Energetic footprints of irreversibility in the quantum regime
T2  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe
N2  - In classical thermodynamic processes the unavoidable presence of irreversibility, quantified by the entropy production, carries two energetic footprints: the reduction of extractable work from the optimal, reversible case, and the generation of a surplus of heat that is irreversibly dissipated to the environment. Recently it has been shown that in the quantum regime an additional quantum irreversibility occurs that is linked to decoherence into the energy basis. Here we employ quantum trajectories to construct distributions for classical heat and quantum heat exchanges, and show that the heat footprint of quantum irreversibility differs markedly from the classical case. We also quantify how quantum irreversibility reduces the amount of work that can be extracted from a state with coherences. Our results show that decoherence leads to both entropic and energetic footprints which both play an important role in the optimization of controlled quantum operations at low temperature.

In classical thermodynamics irreversibility occurs whenever a non-thermal system is brought into contact with a thermal environment. Using quantum trajectories the authors here establish two energetic footprints of quantum irreversible processes, and find that while quantum irreversibility leads to the occurrence of a quantum heat and a reduction of work production, the two are not linked in the same manner as the classical laws of thermodynamics would dictate.
T3  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1435 
KW  - entropy production
KW  - quantum mechanics
KW  - thermodynamics
Y1  - 2020
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-516766
SN  - 1866-8372
IS  - 1
ER  - 
TY  - JOUR
A1  - Holmes, Zoe
A1  - Anders, Janet
A1  - Mintert, Florian
T1  - Enhanced energy transfer to an optomechanical piston from indistinguishable photons
JF  - Physical review letters
N2  - Thought experiments involving gases and pistons, such as Maxwell's demon and Gibbs' mixing, are central to our understanding of thermodynamics. Here, we present a quantum thermodynamic thought experiment in which the energy transfer from two photonic gases to a piston membrane grows quadratically with the number of photons for indistinguishable gases, while it grows linearly for distinguishable gases. This signature of bosonic bunching may be observed in optomechanical experiments, highlighting the potential of these systems for the realization of thermodynamic thought experiments in the quantum realm.
Y1  - 2020
U6  - https://doi.org/10.1103/PhysRevLett.124.210601
SN  - 0031-9007
SN  - 1079-7114
VL  - 124
IS  - 21
PB  - American Physical Society
CY  - College Park, Md.
ER  - 
TY  - JOUR
A1  - Horton, Benjamin P.
A1  - Khan, Nicole S.
A1  - Cahill, Niamh
A1  - Lee, Janice S. H.
A1  - Shaw, Timothy A.
A1  - Garner, Andra J.
A1  - Kemp, Andrew C.
A1  - Engelhart, Simon E.
A1  - Rahmstorf, Stefan
T1  - Estimating global mean sea-level rise and its uncertainties by 2100 and 2300 from an expert survey
JF  - npj Climate and Atmospheric Science
N2  - Sea-level rise projections and knowledge of their uncertainties are vital to make informed mitigation and adaptation decisions. To elicit projections from members of the scientific community regarding future global mean sea-level (GMSL) rise, we repeated a survey originally conducted five years ago. Under Representative Concentration Pathway (RCP) 2.6, 106 experts projected a likely (central 66% probability) GMSL rise of 0.30-0.65 m by 2100, and 0.54-2.15 m by 2300, relative to 1986-2005. Under RCP 8.5, the same experts projected a likely GMSL rise of 0.63-1.32 m by 2100, and 1.67-5.61 m by 2300. Expert projections for 2100 are similar to those from the original survey, although the projection for 2300 has extended tails and is higher than the original survey. Experts give a likelihood of 42% (original survey) and 45% (current survey) that under the high-emissions scenario GMSL rise will exceed the upper bound (0.98 m) of the likely range estimated by the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, which is considered to have an exceedance likelihood of 17%. Responses to open-ended questions suggest that the increases in upper-end estimates and uncertainties arose from recent influential studies about the impact of marine ice cliff instability on the meltwater contribution to GMSL rise from the Antarctic Ice Sheet.
KW  - projections
KW  - Greenland
KW  - consequences
KW  - climate
Y1  - 2020
U6  - https://doi.org/10.1038/s41612-020-0121-5
SN  - 2397-3722
VL  - 3
IS  - 1
SP  - 1
EP  - 8
PB  - Springer Nature
CY  - London
ER  - 
TY  - GEN
A1  - Horton, Benjamin P.
A1  - Khan, Nicole S.
A1  - Cahill, Niamh
A1  - Lee, Janice S. H.
A1  - Shaw, Timothy A.
A1  - Garner, Andra J.
A1  - Kemp, Andrew C.
A1  - Engelhart, Simon E.
A1  - Rahmstorf, Stefan
T1  - Estimating global mean sea-level rise and its uncertainties by 2100 and 2300 from an expert survey
T2  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe
N2  - Sea-level rise projections and knowledge of their uncertainties are vital to make informed mitigation and adaptation decisions. To elicit projections from members of the scientific community regarding future global mean sea-level (GMSL) rise, we repeated a survey originally conducted five years ago. Under Representative Concentration Pathway (RCP) 2.6, 106 experts projected a likely (central 66% probability) GMSL rise of 0.30-0.65 m by 2100, and 0.54-2.15 m by 2300, relative to 1986-2005. Under RCP 8.5, the same experts projected a likely GMSL rise of 0.63-1.32 m by 2100, and 1.67-5.61 m by 2300. Expert projections for 2100 are similar to those from the original survey, although the projection for 2300 has extended tails and is higher than the original survey. Experts give a likelihood of 42% (original survey) and 45% (current survey) that under the high-emissions scenario GMSL rise will exceed the upper bound (0.98 m) of the likely range estimated by the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, which is considered to have an exceedance likelihood of 17%. Responses to open-ended questions suggest that the increases in upper-end estimates and uncertainties arose from recent influential studies about the impact of marine ice cliff instability on the meltwater contribution to GMSL rise from the Antarctic Ice Sheet.
T3  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1437 
KW  - projections
KW  - Greenland
KW  - consequences
KW  - climate
Y1  - 2020
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-516788
SN  - 1866-8372
IS  - 1
ER  - 
TY  - JOUR
A1  - Grebenkov, Denis S.
A1  - Sposini, Vittoria
A1  - Metzler, Ralf
A1  - Oshanin, Gleb
A1  - Seno, Flavio
T1  - Exact distributions of the maximum and range of random diffusivity processes
JF  - New Journal of Physics
N2  - We study the extremal properties of a stochastic process xt defined by the Langevin equation ẋₜ =√2Dₜ ξₜ, in which ξt is a Gaussian white noise with zero mean and Dₜ is a stochastic‘diffusivity’, defined as a functional of independent Brownian motion Bₜ.We focus on threechoices for the random diffusivity Dₜ: cut-off Brownian motion, Dₜt ∼ Θ(Bₜ), where Θ(x) is the Heaviside step function; geometric Brownian motion, Dₜ ∼ exp(−Bₜ); and a superdiffusive process based on squared Brownian motion, Dₜ ∼ B²ₜ. For these cases we derive exact expressions for the probability density functions of the maximal positive displacement and of the range of the process xₜ on the time interval ₜ ∈ (0, T).We discuss the asymptotic behaviours of the associated probability density functions, compare these against the behaviour of the corresponding properties of standard Brownian motion with constant diffusivity (Dₜ = D0) and also analyse the typical behaviour of the probability density functions which is observed for a majority of realisations of the stochastic diffusivity process.
KW  - random diffusivity
KW  - extremal values
KW  - maximum and range
KW  - diffusion
KW  - Brownian motion
Y1  - 2021
U6  - https://doi.org/10.1088/1367-2630/abd313
SN  - 1367-2630
VL  - 23
PB  - Dt. Physikalische Ges.
CY  - Bad Honnef
ER  - 
TY  - GEN
A1  - Grebenkov, Denis S.
A1  - Sposini, Vittoria
A1  - Metzler, Ralf
A1  - Oshanin, Gleb
A1  - Seno, Flavio
T1  - Exact distributions of the maximum and range of random diffusivity processes
T2  - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe
N2  - We study the extremal properties of a stochastic process xt defined by the Langevin equation ẋₜ =√2Dₜ ξₜ, in which ξt is a Gaussian white noise with zero mean and Dₜ is a stochastic‘diffusivity’, defined as a functional of independent Brownian motion Bₜ.We focus on threechoices for the random diffusivity Dₜ: cut-off Brownian motion, Dₜt ∼ Θ(Bₜ), where Θ(x) is the Heaviside step function; geometric Brownian motion, Dₜ ∼ exp(−Bₜ); and a superdiffusive process based on squared Brownian motion, Dₜ ∼ B²ₜ. For these cases we derive exact expressions for the probability density functions of the maximal positive displacement and of the range of the process xₜ on the time interval ₜ ∈ (0, T).We discuss the asymptotic behaviours of the associated probability density functions, compare these against the behaviour of the corresponding properties of standard Brownian motion with constant diffusivity (Dₜ = D0) and also analyse the typical behaviour of the probability density functions which is observed for a majority of realisations of the stochastic diffusivity process.
T3  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1142 
KW  - random diffusivity
KW  - extremal values
KW  - maximum and range
KW  - diffusion
KW  - Brownian motion
Y1  - 2021
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-503976
SN  - 1866-8372
IS  - 1142
ER  - 
TY  - JOUR
A1  - Yochelis, Arik
A1  - Beta, Carsten
A1  - Gov, Nir S.
T1  - Excitable solitons
BT  - annihilation, crossover, and nucleation of pulses in mass-conserving activator-inhibitor media
JF  - Physical review : E, Statistical, nonlinear and soft matter physics
N2  - Excitable pulses are among the most widespread dynamical patterns that occur in many different systems, ranging from biological cells to chemical reactions and ecological populations. Traditionally, the mutual annihilation of two colliding pulses is regarded as their prototypical signature. Here we show that colliding excitable pulses may exhibit solitonlike crossover and pulse nucleation if the system obeys a mass conservation constraint. In contrast to previous observations in systems without mass conservation, these alternative collision scenarios are robustly observed over a wide range of parameters. We demonstrate our findings using a model of intracellular actin waves since, on time scales of wave propagations over the cell scale, cells obey conservation of actin monomers. The results provide a key concept to understand the ubiquitous occurrence of actin waves in cells, suggesting why they are so common, and why their dynamics is robust and long-lived.
Y1  - 2020
U6  - https://doi.org/10.1103/PhysRevE.101.022213
SN  - 2470-0045
SN  - 2470-0053
VL  - 101
IS  - 2
PB  - American Physical Society
CY  - Melville, NY
ER  - 
TY  - JOUR
A1  - Tokmoldin, Nurlan
A1  - Hosseini, Seyed Mehrdad
A1  - Raoufi, Meysam
A1  - Phuong, Le Quang
A1  - Sandberg, Oskar J.
A1  - Guan, Huilan
A1  - Zou, Yingping
A1  - Neher, Dieter
A1  - Shoaee, Safa
T1  - Extraordinarily long diffusion length in PM6:Y6 organic solar cells
JF  - Journal of materials chemistry : A, materials for energy and sustainability
N2  - The PM6:Y6 bulk-heterojunction (BHJ) blend system achieves high short-circuit current (J(SC)) values in thick photovoltaic junctions. Here we analyse these solar cells to understand the observed independence of the short-circuit current upon photoactive layer thickness. We employ a range of optoelectronic measurements and analyses, including Mott-Schottky analysis, CELIV, photoinduced absorption spectroscopy, mobility measurements and simulations, to conclude that, the invariant photocurrent for the devices with different active layer thicknesses is associated with the Y6's diffusion length exceeding 300 nm in case of a 300 nm thick cell. This is despite unintentional doping that occurs in PM6 and the associated space-charge effect, which is expected to be even more profound upon photogeneration. This extraordinarily long diffusion length - which is an order of magnitude larger than typical values for organics - dominates transport in the flat-band region of thick junctions. Our work suggests that the performance of the doped PM6:Y6 organic solar cells resembles that of inorganic devices with diffusion transport playing a pivotal role. Ultimately, this is expected to be a key requirement for the fabrication of efficient, high-photocurrent, thick organic solar cells.
Y1  - 2020
U6  - https://doi.org/10.1039/d0ta03016c
SN  - 2050-7488
SN  - 2050-7496
VL  - 8
IS  - 16
SP  - 7854
EP  - 7860
PB  - Royal Society of Chemistry
CY  - Cambridge
ER  - 
TY  - JOUR
A1  - García-Benito, Inés
A1  - Quarti, Claudio
A1  - Queloz, Valentin I. E.
A1  - Hofstetter, Yvonne J.
A1  - Becker-Koch, David
A1  - Caprioglio, Pietro
A1  - Neher, Dieter
A1  - Orlandi, Simonetta
A1  - Cavazzini, Marco
A1  - Pozzi, Gianluca
A1  - Even, Jacky
A1  - Nazeeruddin, Mohammad Khaja
A1  - Vaynzof, Yana
A1  - Grancini, Giulia
T1  - Fluorination of organic spacer impacts on the structural and optical response of 2D perovskites
JF  - Frontiers in Chemistry
N2  - Low-dimensional hybrid perovskites have triggered significant research interest due to their intrinsically tunable optoelectronic properties and technologically relevant material stability. In particular, the role of the organic spacer on the inherent structural and optical features in two-dimensional (2D) perovskites is paramount for material optimization. To obtain a deeper understanding of the relationship between spacers and the corresponding 2D perovskite film properties, we explore the influence of the partial substitution of hydrogen atoms by fluorine in an alkylammonium organic cation, resulting in (Lc)(2)PbI4 and (Lf)(2)PbI4 2D perovskites, respectively. Consequently, optical analysis reveals a clear 0.2 eV blue-shift in the excitonic position at room temperature. This result can be mainly attributed to a band gap opening, with negligible effects on the exciton binding energy. According to Density Functional Theory (DFT) calculations, the band gap increases due to a larger distortion of the structure that decreases the atomic overlap of the wavefunctions and correspondingly bandwidth of the valence and conduction bands. In addition, fluorination impacts the structural rigidity of the 2D perovskite, resulting in a stable structure at room temperature and the absence of phase transitions at a low temperature, in contrast to the widely reported polymorphism in some non-fluorinated materials that exhibit such a phase transition. This indicates that a small perturbation in the material structure can strongly influence the overall structural stability and related phase transition of 2D perovskites, making them more robust to any phase change. This work provides key information on how the fluorine content in organic spacer influence the structural distortion of 2D perovskites and their optical properties which possess remarkable importance for future optoelectronic applications, for instance in the field of light-emitting devices or sensors.
KW  - fluorinated organic spacer
KW  - 2D perovskites
KW  - phase transition
KW  - temperature dependence
KW  - excitonic materials
Y1  - 2020
U6  - https://doi.org/10.3389/fchem.2019.00946
SN  - 2296-2646
VL  - 7
SP  - 1
EP  - 11
PB  - Frontiers Media
CY  - Lausanne
ER  - 
TY  - GEN
A1  - García-Benito, Inés
A1  - Quarti, Claudio
A1  - Queloz, Valentin I. E.
A1  - Hofstetter, Yvonne J.
A1  - Becker-Koch, David
A1  - Caprioglio, Pietro
A1  - Neher, Dieter
A1  - Orlandi, Simonetta
A1  - Cavazzini, Marco
A1  - Pozzi, Gianluca
A1  - Even, Jacky
A1  - Nazeeruddin, Mohammad Khaja
A1  - Vaynzof, Yana
A1  - Grancini, Giulia
T1  - Fluorination of organic spacer impacts on the structural and optical response of 2D perovskites
T2  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe
N2  - Low-dimensional hybrid perovskites have triggered significant research interest due to their intrinsically tunable optoelectronic properties and technologically relevant material stability. In particular, the role of the organic spacer on the inherent structural and optical features in two-dimensional (2D) perovskites is paramount for material optimization. To obtain a deeper understanding of the relationship between spacers and the corresponding 2D perovskite film properties, we explore the influence of the partial substitution of hydrogen atoms by fluorine in an alkylammonium organic cation, resulting in (Lc)(2)PbI4 and (Lf)(2)PbI4 2D perovskites, respectively. Consequently, optical analysis reveals a clear 0.2 eV blue-shift in the excitonic position at room temperature. This result can be mainly attributed to a band gap opening, with negligible effects on the exciton binding energy. According to Density Functional Theory (DFT) calculations, the band gap increases due to a larger distortion of the structure that decreases the atomic overlap of the wavefunctions and correspondingly bandwidth of the valence and conduction bands. In addition, fluorination impacts the structural rigidity of the 2D perovskite, resulting in a stable structure at room temperature and the absence of phase transitions at a low temperature, in contrast to the widely reported polymorphism in some non-fluorinated materials that exhibit such a phase transition. This indicates that a small perturbation in the material structure can strongly influence the overall structural stability and related phase transition of 2D perovskites, making them more robust to any phase change. This work provides key information on how the fluorine content in organic spacer influence the structural distortion of 2D perovskites and their optical properties which possess remarkable importance for future optoelectronic applications, for instance in the field of light-emitting devices or sensors.
T3  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1421 
KW  - fluorinated organic spacer
KW  - 2D perovskites
KW  - phase transition
KW  - temperature dependence
KW  - excitonic materials
Y1  - 2020
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-512420
SN  - 1866-8372
ER  - 
TY  - JOUR
A1  - Jelken, Joachim
A1  - Henkel, Carsten
A1  - Santer, Svetlana
T1  - Formation of half-period surface relief gratings in azobenzene containing polymer films
JF  - Applied physics : B, Lasers and optics
N2  - We study the peculiar response of photo-sensitive polymer films irradiated with a certain type of interference pattern where one interfering beam is S-polarized, while the second one is P-polarized. The polymer film, although in a glassy state, deforms following the local polarization distribution of the incident light, and a surface relief grating (SRG) appears whose period is half the optical one. All other types of interference patterns result in the matching of both periods. The topographical response is triggered by the alignment of photo-responsive azobenzene containing polymer side chains orthogonal to the local electrical field, resulting in a bulk birefringence grating (BBG). We investigate the process of dual grating formation (SRG and BBG) in a polymer film utilizing a dedicated set-up that combines probe beam diffraction and atomic force microscopy (AFM) measurements, and permits acquiring in situ and in real-time information about changes in local topography and birefringence. We find that the SRG maxima appear at the positions of linearly polarized light (tilted by 45 degrees relative to the grating vector), causing the formation of the half-period topography. This permits to inscribe symmetric and asymmetric topography gratings with sub-wavelength period, while changing only slightly the polarization of one of the interfering beams. We demonstrate an easy generation of sawtooth profiles (blazed gratings) with adjustable shape. With these results, we have taken a significant step in understanding the photo-induced deformation of azo-polymer films.
Y1  - 2020
U6  - https://doi.org/10.1007/s00340-020-07500-w
SN  - 0946-2171
SN  - 1432-0649
VL  - 126
IS  - 9
PB  - Springer
CY  - Heidelberg
ER  - 
TY  - JOUR
A1  - Fernandez, Ricardo
A1  - Bruno, Giovanni
A1  - Garces, Gerardo
A1  - Nieto-Luis, H.
A1  - Gonzalez-Doncel, Gaspar
T1  - Fractional brownian motion of dislocations during creep deformation of metals
JF  - Materials science & engineering. A, Structural materials
N2  - The present work offers an explanation on how the long-range interaction of dislocations influences their movement, and therefore the strain, during creep of metals. It is proposed that collective motion of dislocations can be described as a fractional Brownian motion. This explains the noisy appearance of the creep strain signal as a function of time. Such signal is split into a deterministic and a stochastic part. These terms can be related to two kinds of dislocation motions: individual and collective, respectively. The description is consistent with the fractal nature of strain-induced dislocation structures predicated in previous works. Moreover, it encompasses the evolution of the strain rate during all stages of creep, including the tertiary one. Creep data from Al99.8% and Al3.85%Mg tested at different temperatures and stresses are used to validate the proposed ideas: it is found that different creep stages present different diffusion characters, and therefore different dislocation motion character.
KW  - Creep
KW  - Aluminum alloys
KW  - Dislocation motion
KW  - Diffusion
KW  - Fractal
KW  - structures
Y1  - 2020
U6  - https://doi.org/10.1016/j.msea.2020.140013
SN  - 0921-5093
SN  - 1873-4936
VL  - 796
PB  - Elsevier
CY  - Lausanne
ER  - 
TY  - JOUR
A1  - Wang, Wei
A1  - Cherstvy, Andrey G.
A1  - Chechkin, Aleksei V.
A1  - Thapa, Samudrajit
A1  - Seno, Flavio
A1  - Liu, Xianbin
A1  - Metzler, Ralf
T1  - Fractional Brownian motion with random diffusivity
BT  - emerging residual nonergodicity below the correlation time
JF  - Journal of physics : A, Mathematical and theoretical
N2  - Numerous examples for a priori unexpected non-Gaussian behaviour for normal and anomalous diffusion have recently been reported in single-particle tracking experiments. Here, we address the case of non-Gaussian anomalous diffusion in terms of a random-diffusivity mechanism in the presence of power-law correlated fractional Gaussian noise. We study the ergodic properties of this model via examining the ensemble- and time-averaged mean-squared displacements as well as the ergodicity breaking parameter EB quantifying the trajectory-to-trajectory fluctuations of the latter. For long measurement times, interesting crossover behaviour is found as function of the correlation time tau characterising the diffusivity dynamics. We unveil that at short lag times the EB parameter reaches a universal plateau. The corresponding residual value of EB is shown to depend only on tau and the trajectory length. The EB parameter at long lag times, however, follows the same power-law scaling as for fractional Brownian motion. We also determine a corresponding plateau at short lag times for the discrete representation of fractional Brownian motion, absent in the continuous-time formulation. These analytical predictions are in excellent agreement with results of computer simulations of the underlying stochastic processes. Our findings can help distinguishing and categorising certain nonergodic and non-Gaussian features of particle displacements, as observed in recent single-particle tracking experiments.
KW  - stochastic processes
KW  - anomalous diffusion
KW  - fractional Brownian motion
KW  - diffusing diffusivity
KW  - weak ergodicity breaking
Y1  - 2020
U6  - https://doi.org/10.1088/1751-8121/aba467
SN  - 1751-8113
SN  - 1751-8121
VL  - 53
IS  - 47
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - THES
A1  - Brose, Robert
T1  - From dawn till dusk
BT  - modelling particle acceleration in supernova remnants
N2  - Supernova remnants are believed to be the source of cosmic rays with energies up to 10^15 eV that are produced within our Galaxy. The acceleration mechanism associated with the collision-less shocks in supernova remnants - diffusive shock acceleration - predicts a spectral index of the accelerated non-thermal particles of s = 2. However, measurements of non-thermal emission in radio, X-rays and gamma-rays reveal significant deviations of the particles spectral index from the canonical value of s = 2.

The youngest Galactic supernova remnant G1.9+0.3 is an interesting target for next-generation gamma-ray observatories. So far, the remnant is only detected in the radio and the X-ray bands, but its young age of ≈100 yrs and inferred shock speed of ≈ 14, 000 km/s could make it an efficient particle accelerator.
I performed spherical symmetric 1D simulations with the RATPaC code, in which I simultaneously solved the transport equation for cosmic rays, the transport equation for magnetic turbulence, and the hydro-dynamical equations for the gas flow. Separately computed distributions of the particles accelerated at the forward and the reverse shock were then used to calculate the spectra of synchrotron, inverse Compton, and Pion-decay radiation from the source.
The emission from G1.9+0.3 can be self-consistently explained within the test-particle limit. I find that the X-ray flux is dominated by emission from the forward shock while most of the radio emission originates near the reverse shock, which makes G1.9+0.3 the first remnant with non-thermal radiation detected from the reverse shock. The flux of very-high-energy gamma-ray emission from G1.9+0.3 is expected to be close to the sensitivity threshold of the Cherenkov Telescope Array. The limited time available to grow large-scale turbulence limits the maximum energy of particles to values below 100 TeV, hence G1.9+0.3 is not a PeVatron.

Although there are many models for the acceleration of cosmic rays in Supernova remnants, the escape of cosmic rays from these sources is yet understudied.
I use our time-dependent acceleration code RATPaC to study the acceleration of cosmic rays and their escape in post-adiabatic Supernova remnants and calculate the subsequent gamma-ray emission from inverse-Compton scattering and Pion decay. My simulations span 100,000 years, thus covering the free-expansion, the Sedov-Taylor, and the beginning of the post-adiabatic phase of the remnant’s evolution.
At later stages of the evolution cosmic rays over a wide range of energy can reside outside of the remnant, creating spectra that are softer than predicted by standard diffusive shock acceleration and feature breaks in the 10 - 100 GeV-range. The total spectrum of cosmic rays released into the interstellar medium has a spectral index of s ≈ 2.4 above roughly 10 GeV which is close to that required by Galactic propagation models. I further find the gamma-ray luminosity to peak around an age of 4,000 years for inverse-Compton-dominated high-energy emission. Remnants expanding in low-density media emit generally more inverse-Compton radiation matching the fact that the brightest known supernova remnants - RCW86, Vela Jr, HESSJ1721-347 and RXJ1713.7-3946 - are all expanding in low density environments.

The importance of feedback from the cosmic-rays on the hydrodynamical evolution of the remnants is debated as a possibility to obtain soft cosmic-ray spectra at low energies.
I performed spherically symmetric 1-D simulations with a modified version of the RATPaC code, in which I simultaneously solve the transport equation for cosmic rays and the hydrodynamical equations, including the back-reaction of the cosmic-ray pressure on the flow profiles.
Besides the known modification of the flow profiles and the consequently curved cosmic-ray spectra, steady-state models for non-linear diffusive shock acceleration overpredict the total compression ratio that can be reached with cosmic-ray feedback, as there is limited time for building these modifications. Further, I find modifications to the downstream flow structure that change the evolutionary behavior of the remnant and trigger a cosmic-ray-induced instability close to the contact discontinuity, if and when the cosmic-ray pressure becomes dominant there.
N2  - Es wird vermutet das Supernovaüberreste die Quelle der galaktischen kosmischen Strahlung mit Energien bis zu 10^15eV sein können. Der Beschleunigungsprozess der mit den kollisionsfreien Schocks in Supernovaüberresten in Verbindung gebracht wird - diffuse Schockwellenbeschleunigung - sagt nicht-thermische Teilchenspektren mit einem Spektralindex von s=2 voraus. Messungen nicht-thermischer Strahlung im Radio-, Röntgen- und Gammastrahlenbereich zeigen teils deutliche Abweichungen von dieser Vorhersage.

Der jüngste galaktische Supernovaüberrest G1.9+0.3 ist ein interessantes Ziel für zukünftige Gammastrahlenteleskope. Bis jetzt wurde der Überrest nur im Radio- und Röntgenband entdeckt aber sein geringes Alter von ~100 Jahren und die gemessenen hohen Schockgeschwindigkeiten von ~14,000km/s sollten Teilchenbeschleunigung auch bis zu sehr hohen Energien ermöglichen.
In dieser Arbeit wurden 1D-Simulationen der Teilchenbeschleunigung in G1.9+0.3 mit Hilfe der RATPaC-Programmbibliothek durchgeführt, wobei das System der gekoppelten Differentialgleichungen für den Teilchentransport, den Transport der magnetischen Turbulenz und der Standardgasgleichungen gelöst wurde. Die separat berechneten Verteilungen der Teilchen an Vorwärts- und Rückwärtsschock wurden benutzt um die Emission des Überrests im Radio-, Röntgen und Gammastrahlungsbereich zu bestimmen.
Die Emissionen von G1.9+0.3 können selbst konsistent in der Testteilchennäherung bestimmt werden. Die Röntgenemission wird vom Vorwärtsschock dominiert, während die Radioemissionen hauptsächlich vom Rückwätsschock stammen. Dies macht G1.9+0.3 zum ersten Überrest mit detektierter nich-thermischer Strahlung aus dem Bereich des Rückwärtsschocks. Die erwartet Gammastrahlungsemission ist nahe dem Detektionslimit des zukünftigen Cherenkov Telescope Arrays. Die geringe Alter von G1.9+0.3 begrenzt die Maximalenergie, die im Beschleunigungsprozess erreicht werden kann auf Werte unterhalb von 100TeV. Demnach ist G1.9+0.3 kein PeVatron.

Auch wenn es zahlreiche Modelle zur Teilchenbeschleunigung in Supernovaüberresten gibt, ist das Entkommen der Teilchen aus den Überresten zur Zeit wenig erforscht.
Mit Hilfe von RATPaC haben wir die Evolution und Teilchenbeschleunigung in Supernovaüberresten über 100,000 Jahre simuliert. Dieser Zeitraum deckt einen Großteil der Lebensspanne eines Supernovaüberrests ab und endet mit der letzten Teil der postadiabatischen Phase der Entwicklung des Überrests.
In den späten Phasen der Entwicklung des Überrests können Teilchen in einem großen Energiebereich aus dem Überrest entweichen. Dies erzeugt Emissionspektren, die weicher sind als durch Fermibeschleunigung vorhergesagt, und die spektrale Brüche im Bereich von 10-100GeV aufweisen. Das Produktionsspektren der Überreste hat einen spektralen Index von s~2.4 oberhalb von 10GeV, was ungefähr mit den Spektren übereinstimmt, die Quellen in galaktischen Propagationsmodellen aufweisen müssen. Weiterhin erreichen die Überreste ihre größte Helligkeit im Gammabereich nach etwa 4000 Jahren wenn diese durch inverse Comptonstreuung erzeugt werden. Dabei erreichen Überreste in Medien mit geringer Umgebungsdichte größere Helligkeiten, was sich mit den Beobachtungen der hellsten Supernovaüberreste - RCW86, Vela Jr., HESSJ1721-347 und RXJ1713.7-3946 - deckt, die alle in Bereichen sehr geringer Umgebungsdichte expandieren.

In der Literatur wird die Möglichkeit diskutiert, dass die Rückkopplung der Beschleunigten Teilchen auf die Struktur der Überreste für die beobachteten weichen Strahlungsspektren verantwortlich ist.
Im Rahmen dieser Arbeit wurde eine modifizierte Version von RATPaC entwickelt, die diesen Prozess abbilden kann.
Neben den bekannten Rückkopplungen zeigt sich, dass bisherige Modelle unter der Annahme eines Gleichgewichtszustandes für die beschleunigten Teilchen die erreicht maximal Kompression des Plasmas durch den Schock und damit die Härte der Teilchenspektren überschätzen. In unseren zeit aufgelösten Berechnungen ist die maximale Kompression durch die limitierte verfügbare Zeit begrenzt. Zusätzlich zeigt sich das Auftreten einer Instabilität die durch die Rückkopplung der kosmischen Strahlung nahe der Kontaktdiskontinuität hervorgerufen wird.
KW  - supernova remnant
KW  - particle acceleration
KW  - gamma rays
KW  - Supernovaüberrest
KW  - Teilchenbeschleunigung
KW  - Gammastrahlung
Y1  - 2020
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-470865
ER  - 
TY  - GEN
A1  - Grebenkov, Denis S.
A1  - Metzler, Ralf
A1  - Oshanin, Gleb
T1  - From single-particle stochastic kinetics to macroscopic reaction rates
BT  - fastest first-passage time of N random walkers
T2  - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe
N2  - We consider the first-passage problem for N identical independent particles that are initially released uniformly in a finite domain Ω and then diffuse toward a reactive area Γ, which can be part of the outer boundary of Ω or a reaction centre in the interior of Ω. For both cases of perfect and partial reactions, we obtain the explicit formulas for the first two moments of the fastest first-passage time (fFPT), i.e., the time when the first out of the N particles reacts with Γ. Moreover, we investigate the full probability density of the fFPT. We discuss a significant role of the initial condition in the scaling of the average fFPT with the particle number N, namely, a much stronger dependence (1/N and 1/N² for partially and perfectly reactive targets, respectively), in contrast to the well known inverse-logarithmic behaviour found when all particles are released from the same fixed point. We combine analytic solutions with scaling arguments and stochastic simulations to rationalise our results, which open new perspectives for studying the relevance of multiple searchers in various situations of molecular reactions, in particular, in living cells.
T3  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1018 
KW  - diffusion
KW  - first-passage
KW  - fastest first-passage time of N walkers
Y1  - 2020
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-484059
SN  - 1866-8372
IS  - 1018
ER  - 
TY  - JOUR
A1  - Grebenkov, Denis S.
A1  - Metzler, Ralf
A1  - Oshanin, Gleb
T1  - From single-particle stochastic kinetics to macroscopic reaction rates
BT  - fastest first-passage time of N random walkers
JF  - New Journal of Physics
N2  - We consider the first-passage problem for N identical independent particles that are initially released uniformly in a finite domain Ω and then diffuse toward a reactive area Γ, which can be part of the outer boundary of Ω or a reaction centre in the interior of Ω. For both cases of perfect and partial reactions, we obtain the explicit formulas for the first two moments of the fastest first-passage time (fFPT), i.e., the time when the first out of the N particles reacts with Γ. Moreover, we investigate the full probability density of the fFPT. We discuss a significant role of the initial condition in the scaling of the average fFPT with the particle number N, namely, a much stronger dependence (1/N and 1/N² for partially and perfectly reactive targets, respectively), in contrast to the well known inverse-logarithmic behaviour found when all particles are released from the same fixed point. We combine analytic solutions with scaling arguments and stochastic simulations to rationalise our results, which open new perspectives for studying the relevance of multiple searchers in various situations of molecular reactions, in particular, in living cells.
KW  - diffusion
KW  - first-passage
KW  - fastest first-passage time of N walkers
Y1  - 2020
U6  - https://doi.org/10.1088/1367-2630/abb1de
SN  - 1367-2630
VL  - 22
PB  - Dt. Physikalische Ges.
CY  - Bad Honnef
ER  - 
TY  - JOUR
A1  - Stojkoski, Viktor
A1  - Sandev, Trifce
A1  - Basnarkov, Lasko
A1  - Kocarev, Ljupco
A1  - Metzler, Ralf
T1  - Generalised geometric Brownian motion
BT  - theory and applications to option pricing
JF  - Entropy
N2  - Classical option pricing schemes assume that the value of a financial asset follows a geometric Brownian motion (GBM). However, a growing body of studies suggest that a simple GBM trajectory is not an adequate representation for asset dynamics, due to irregularities found when comparing its properties with empirical distributions. As a solution, we investigate a generalisation of GBM where the introduction of a memory kernel critically determines the behaviour of the stochastic process. We find the general expressions for the moments, log-moments, and the expectation of the periodic log returns, and then obtain the corresponding probability density functions using the subordination approach. Particularly, we consider subdiffusive GBM (sGBM), tempered sGBM, a mix of GBM and sGBM, and a mix of sGBMs. We utilise the resulting generalised GBM (gGBM) in order to examine the empirical performance of a selected group of kernels in the pricing of European call options. Our results indicate that the performance of a kernel ultimately depends on the maturity of the option and its moneyness.
KW  - geometric Brownian motion
KW  - Fokker– Planck equation
KW  - Black– Scholes model
KW  - option pricing
Y1  - 2020
U6  - https://doi.org/10.3390/e22121432
SN  - 1099-4300
VL  - 22
IS  - 12
PB  - MDPI
CY  - Basel
ER  - 
TY  - JOUR
A1  - Albrecht, Torsten
A1  - Winkelmann, Ricarda
A1  - Levermann, Anders
T1  - Glacial-cycle simulations of the Antarctic Ice Sheet with the Parallel Ice Sheet Model (PISM)
BT  - part 2: parameter ensemble analysis
JF  - The Cryosphere : TC ; an interactive open access journal of the European Geosciences Union
N2  - The Parallel Ice Sheet Model (PISM) is applied to the Antarctic Ice Sheet over the last two glacial cycles (approximate to 210 000 years) with a resolution of 16 km. An ensemble of 256 model runs is analyzed in which four relevant model parameters have been systematically varied using full-factorial parameter sampling. Parameters and plausible parameter ranges have been identified in a companion paper (Albrecht et al., 2020) and are associated with ice dynamics, climatic forcing, basal sliding and bed deformation and represent distinct classes of model uncertainties. The model is scored against both modern and geologic data, including reconstructed grounding-line locations, elevation-age data, ice thickness, surface velocities and uplift rates. An aggregated score is computed for each ensemble member that measures the overall model-data misfit, including measurement uncertainty in terms of a Gaussian error model (Briggs and Tarasov, 2013). The statistical method used to analyze the ensemble simulation results follows closely the simple averaging method described in Pollard et al. (2016). 
This analysis reveals clusters of best-fit parameter combinations, and hence a likely range of relevant model and boundary parameters, rather than individual best-fit parameters. The ensemble of reconstructed histories of Antarctic Ice Sheet volumes provides a score-weighted likely range of sea-level contributions since the Last Glacial Maximum (LGM) of 9.4 +/- 4.1m (or 6.5 +/- 2.0 x 10(6) km(3)), which is at the upper range of most previous studies. The last deglaciation occurs in all ensemble simulations after around 12 000 years before present and hence after the meltwater pulse 1A (MWP1a). Our ensemble analysis also provides an estimate of parametric uncertainty bounds for the present-day state that can be used for PISM projections of future sea-level contributions from the Antarctic Ice Sheet.
Y1  - 2020
U6  - https://doi.org/10.5194/tc-14-633-2020
SN  - 1994-0416
SN  - 1994-0424
VL  - 14
IS  - 2
SP  - 633
EP  - 656
PB  - Copernicus Publ.
CY  - Göttingen
ER  - 
TY  - JOUR
A1  - Wunderling, Nico
A1  - Willeit, Matteo
A1  - Donges, Jonathan
A1  - Winkelmann, Ricarda
T1  - Global warming due to loss of large ice masses and Arctic summer sea ice
JF  - Nature Communications
N2  - Several large-scale cryosphere elements such as the Arctic summer sea ice, the mountain glaciers, the Greenland and West Antarctic Ice Sheet have changed substantially during the last century due to anthropogenic global warming. However, the impacts of their possible future disintegration on global mean temperature (GMT) and climate feedbacks have not yet been comprehensively evaluated. Here, we quantify this response using an Earth system model of intermediate complexity. Overall, we find a median additional global warming of 0.43 degrees C (interquartile range: 0.39-0.46 degrees C) at a CO2 concentration of 400 ppm. Most of this response (55%) is caused by albedo changes, but lapse rate together with water vapour (30%) and cloud feedbacks (15%) also contribute significantly. While a decay of the ice sheets would occur on centennial to millennial time scales, the Arctic might become ice-free during summer within the 21st century. Our findings imply an additional increase of the GMT on intermediate to long time scales. The disintegration of cryosphere elements such as the Arctic summer sea ice, mountain glaciers, Greenland and West Antarctica is associated with temperature and radiative feedbacks. In this work, the authors quantify these feedbacks and find an additional global warming of 0.43 degrees C.
Y1  - 2020
U6  - https://doi.org/10.1038/s41467-020-18934-3
SN  - 2041-1723
VL  - 11
IS  - 1
PB  - Nature Publishing Group
CY  - Berlin
ER  - 
TY  - JOUR
A1  - Mkrtchian, Vanik E.
A1  - Henkel, Carsten
T1  - Green function solution of generalised boundary value problems
JF  - Physics Letters A
N2  - We construct an expression for the Green function of a differential operator satisfying nonlocal, homogeneous boundary conditions starting from the fundamental solution of the differential operator. This also provides the solution to the boundary value problem of an inhomogeneous partial differential equation with inhomogeneous, nonlocal boundary conditions. The construction applies for a broad class of linear partial differential equations and linear boundary conditions.
KW  - Boundary value problem
KW  - Green function
Y1  - 2020
U6  - https://doi.org/10.1016/j.physleta.2020.126573
SN  - 0375-9601
SN  - 1873-2429
SN  - 0031-9163
VL  - 384
IS  - 23
PB  - Elsevier
CY  - Amsterdam
ER  - 
TY  - JOUR
A1  - Xu, Yong
A1  - Liu, Xuemei
A1  - Li, Yongge
A1  - Metzler, Ralf
T1  - Heterogeneous diffusion processes and nonergodicity with Gaussian colored noise in layered diffusivity landscapes
JF  - Physical review : E, Statistical, nonlinear and soft matter physics
N2  - Heterogeneous diffusion processes (HDPs) with space-dependent diffusion coefficients D(x) are found in a number of real-world systems, such as for diffusion of macromolecules or submicron tracers in biological cells. Here, we examine HDPs in quenched-disorder systems with Gaussian colored noise (GCN) characterized by a diffusion coefficient with a power-law dependence on the particle position and with a spatially random scaling exponent. Typically, D(x) is considered to be centerd at the origin and the entire x axis is characterized by a single scaling exponent a. In this work we consider a spatially random scenario: in periodic intervals ("layers") in space D(x) is centerd to the midpoint of each interval. In each interval the scaling exponent alpha is randomly chosen from a Gaussian distribution. The effects of the variation of the scaling exponents, the periodicity of the domains ("layer thickness") of the diffusion coefficient in this stratified system, and the correlation time of the GCN are analyzed numerically in detail. We discuss the regimes of superdiffusion, subdiffusion, and normal diffusion realisable in this system. We observe and quantify the domains where nonergodic and non-Gaussian behaviors emerge in this system. Our results provide new insights into the understanding of weak ergodicity breaking for HDPs driven by colored noise, with potential applications in quenched layered systems, typical model systems for diffusion in biological cells and tissues, as well as for diffusion in geophysical systems.
Y1  - 2020
U6  - https://doi.org/10.1103/PhysRevE.102.062106
SN  - 2470-0045
SN  - 2470-0053
VL  - 102
IS  - 6
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Sandev, Trifce
A1  - Iomin, Alexander
A1  - Kocarev, Ljupco
T1  - Hitting times in turbulent diffusion due to multiplicative noise
JF  - Physical review : E, Statistical, nonlinear and soft matter physics
N2  - We study a distribution of times of the first arrivals to absorbing targets in turbulent diffusion, which is due to a multiplicative noise. Two examples of dynamical systems with a multiplicative noise are studied. The first one is a random process according to inhomogeneous diffusion, which is also known as a geometric Brownian motion in the Black-Scholes model. The second model is due to a random processes on a two-dimensional comb, where inhomogeneous advection is possible only along the backbone, while Brownian diffusion takes place inside the branches. It is shown that in both cases turbulent diffusion takes place as the one-dimensional random process with the log-normal distribution in the presence of absorbing targets, which are characterized by the Levy-Smirnov distribution for the first hitting times.
Y1  - 2020
U6  - https://doi.org/10.1103/PhysRevE.102.042109
SN  - 2470-0045
SN  - 2470-0053
VL  - 102
IS  - 4
PB  - American Institute of Physics
CY  - Woodbury, NY
ER  - 
TY  - JOUR
A1  - Jiang, Wei
A1  - Tao, Chen
A1  - Stolterfoht, Martin
A1  - Jin, Hui
A1  - Stephen, Meera
A1  - Lin, Qianqian
A1  - Nagiri, Ravi C. R.
A1  - Burn, Paul L.
A1  - Gentle, Ian R.
T1  - Hole-transporting materials for low donor content organic solar cells
BT  - charge transport and device performance
JF  - Organic electronics : physics, materials and applications
N2  - Low donor content solar cells are an intriguing class of photovoltaic device about which there is still considerable discussion with respect to their mode of operation. We have synthesized a series of triphenylamine-based materials for use in low donor content devices with the electron accepting [6,6]-phenyl-C71-butyric acid methyl ester (PC(7)0BM). The triphenylamine-based materials absorb light in the near UV enabling the PC(7)0BM to be be the main light absorbing organic semiconducting material in the solar cell. It was found that the devices did not operate as classical Schottky junctions but rather photocurrent was generated by hole transfer from the photo-excited PC(7)0BM to the triphenylamine-based donors. We found that replacing the methoxy surface groups with methyl groups on the donor material led to a decrease in hole mobility for the neat films, which was due to the methyl substituted materials having the propensity to aggregate. The thermodynamic drive to aggregate was advantageous for the performance of the low donor content (6 wt%) films. It was found that the 6 wt% donor devices generally gave higher performance than devices containing 50 wt% of the donor.
KW  - photoexcited hole transfer
KW  - photocurrent generation
KW  - synthesis
KW  - hole
KW  - mobility
KW  - low donor content
KW  - Schottky junction
Y1  - 2020
U6  - https://doi.org/10.1016/j.orgel.2019.105480
SN  - 1566-1199
SN  - 1878-5530
VL  - 76
PB  - Elsevier
CY  - Amsterdam
ER  - 
TY  - THES
A1  - Wolff, Christian Michael
T1  - Identification and reduction of losses in perovskite solar cells
N2  - Perovskite solar cells have become one of the most studied systems in the quest for new, cheap and efficient solar cell materials. Within a decade device efficiencies have risen to >25% in single-junction and >29% in tandem devices on top of silicon. This rapid improvement was in many ways fortunate, as e. g. the energy levels of commonly used halide perovskites are compatible with already existing materials from other photovoltaic technologies such as dye-sensitized or organic solar cells. Despite this rapid success, fundamental working principles must be understood to allow concerted further improvements. This thesis focuses on a comprehensive understanding of recombination processes in functioning devices.
First the impact the energy level alignment between the perovskite and the electron transport layer based on fullerenes is investigated. This controversial topic is comprehensively addressed and recombination is mitigated through reducing the energy difference between the perovskite conduction band minimum and the LUMO of the fullerene. Additionally, an insulating blocking layer is introduced, which is even more effective in reducing this recombination, without compromising carrier collection and thus efficiency. With the rapid efficiency development (certified efficiencies have broken through the 20% ceiling) and thousands of researchers working on perovskite-based optoelectronic devices, reliable protocols on how to reach these efficiencies are lacking. Having established robust methods for >20% devices, while keeping track of possible pitfalls, a detailed description of the fabrication of perovskite solar cells at the highest efficiency level (>20%) is provided. The fabrication of low-temperature p-i-n structured devices is described, commenting on important factors such as practical experience, processing atmosphere & temperature, material purity and solution age. Analogous to reliable fabrication methods, a method to identify recombination losses is needed to further improve efficiencies. Thus, absolute photoluminescence is identified as a direct way to quantify the Quasi-Fermi level splitting of the perovskite absorber (1.21eV) and interfacial recombination losses the transport layers impose, reducing the latter to ~1.1eV. Implementing very thin interlayers at both the p- and n-interface (PFN-P2 and LiF, respectively), these losses are suppressed, enabling a VOC of up to 1.17eV. Optimizing the device dimensions and the bandgap, 20% devices with 1cm2 active area are demonstrated. Another important consideration is the solar cells’ stability if subjected to field-relevant stressors during operation. In particular these are heat, light, bias or a combination thereof. Perovskite layers – especially those incorporating organic cations – have been shown to degrade if subjected to these stressors. Keeping in mind that several interlayers have been successfully used to mitigate recombination losses, a family of perfluorinated self-assembled monolayers (X-PFCn, where X denotes I/Br and n = 7-12) are introduced as interlayers at the n-interface. Indeed, they reduce interfacial recombination losses enabling device efficiencies up to 21.3%. Even more importantly they improve the stability of the devices. The solar cells with IPFC10 are stable over 3000h stored in the ambient and withstand a harsh 250h of MPP at 85◦C without appreciable efficiency losses. To advance further and improve device efficiencies, a sound understanding of the photophysics of a device is imperative. Many experimental observations in recent years have however drawn an inconclusive picture, often suffering from technical of physical impediments, disguising e. g. capacitive discharge as recombination dynamics. To circumvent these obstacles, fully operational, highly efficient perovskites solar cells are investigated by a combination of multiple optical and optoelectronic probes, allowing to draw a conclusive picture of the recombination dynamics in operation. Supported by drift-diffusion simulations, the device recombination dynamics can be fully described by a combination of first-, second- and third-order recombination and JV curves as well as luminescence efficiencies over multiple illumination intensities are well described within the model. On this basis steady state carrier densities, effective recombination constants, densities-of-states and effective masses are calculated, putting the devices at the brink of the radiative regime. Moreover, a comprehensive review of recombination in state-of-the-art devices is given, highlighting the importance of interfaces in nonradiative recombination. Different strategies to assess these are discussed, before emphasizing successful strategies to reduce interfacial recombination and pointing towards the necessary steps to further improve device efficiency and stability. Overall, the main findings represent an advancement in understanding loss mechanisms in highly efficient solar cells. Different reliable optoelectronic techniques are used and interfacial losses are found to be of grave importance for both efficiency and stability. Addressing the interfaces, several interlayers are introduced, which mitigate recombination losses and degradation.
N2  - Auf der Suche nach neuen, kostengünstigen und effizienten Systemen zur photovoltaischen Energiegewinnung, sind Perowskit Solarzellen zu einem der am meistuntersuchtesten Systeme avanciert. Innerhalb einer Dekade konnten unabhängig zertifizierte Umwandlungseffizienzen von >25% in Einzelschicht- und >29% in Mehrschichtzellen basierend auf Siliziumzellen realisiert werden. Die schnelle Entwicklung war in vielerlei Hinsicht glücklich, da beispielsweise die Energielevel typischer Perowskitschichten mit bereits existierenden Kontaktschichtsystemen anderer Photovoltaiksysteme, wie etwa Farbstoffsolarzellen oder Organische Solarzellen, kompatibel sind. Trotz dieses schnellen Erfolges, müssen zur weiteren Effizienzsteigerung grundlegende Wirkprinzipien der Solarzellen verstanden werden. Diese Arbeit beschäftigt sich mit dem umfassenden Verständnis von Rekombinationsprozessen in voll funktionstüchtigen Bauteilen. Zunächst wird der Einfluss unterschiedlicher Energielevel einer Transportschicht, basierend auf Fullerenen untersucht. Dieses kontrovers diskutierte Thema wurde umfassend untersucht und Rekombinationsverluste aufgrund ungünstiger Energielevel reduziert indem - durch die Wahl unterschiedlicher Fulleren-Derivate - der energetische Abstand zwischen Leitungsband des Perowskit und dem niedrigsten unbesetzten Zustand des Fullerenes reduziert wird. Zusätzlich wurde eine ultradünne elektrisch isolierende Zwischenschicht eingebracht, die noch effektiver Rekombinationsverluste unterdrückt, ohne die Fähigkeit zur Ladungsextraktion - und damit Effizienz einzuschränken. Das breite Interesse tausender Forschenden weltweit hat zur schnellen Entwicklung besagter hoher Effizienzen geführt, obgleich verlässliche, leicht nachzuvollziehende Herstellungsprotokolle nicht existierten. Auf Basis der hier entwickelten Protokolle, werden Methoden dargestellt, mit denen verlässlich >20% effiziente Solarzellen produziert werden können. Hierbei wird insbesondere auf sogenannte invertierte (p-i-n) Zellen eingegangen, wobei ein Fokus auf der Beschreibung essentieller Faktoren wie Atmosphärenkontrolle, Temperaturkontrolle, Materialreinheit oder praktischer Erfahrung liegt. Analog zu verlässlichen Herstellungsmethoden bedarf es robuster Techniken um Rekombinationsverluste zu identifizieren und zu lokalisieren. Zu diesem Zweck wird die Messung der absoluten Photolumineszenzeffizienz eingeführt, die erlaubt die Aufspaltung der Quasi-Fermi Level des Perowskiten zu quantifizieren (1.22eV). Ebenso ist es mit dieser Methode möglich Rekombinationsverluste an Grenzflächen zu lokalisieren, die die Leerlaufspannung auf 1.1V limitieren. Zur Vermeidung dieser Verluste werden erneut ultradünne Zwischenschichten an sowohl der p- als auch n- Grenzschicht eingebracht (PFN-P2 und LiF), die Leerlaufspannungen von bis zu 1.17V ermöglichen. Mithilfe eines optimierten Designs und einer Reduzierung der Bandlücke können Bauteile mit 20% Effizienz bei einer Größe von 1cm2 realisiert werden. Nebst hoher Effizienz ist die Stabilität der Bauteile unter einsatzrelevanten Umweltbedingungen ein wichtiger Faktor auf dem Weg zu einer Kommerzialisierung. Dies gilt insbesondere für Hitze, Beleuchtung, elektrische Ladung oder eine Kombination letzterer. Perowskitschichten -- insbesondere diejenigen, die organische Kationen beinhalten -- sind wohlbekannt dafür unter genannten Bedingungen zu degradieren. Das Konzept der ultradünnen Zwischenschichten wird daher um eine Familie fluornierter selbstorganisierender molekularer Monoschichten erweitert X-PFC_n, wobei X ein Halogen I/Br darstellt und n = 7-12 die Länge der fluorinerten Alkylkette angibt), die an der n-Grenzfläche zum Einsatz kommen. Diese Zwischenschicht reduziert Rekombinationsverluste resultierend in 21.3% effizienten Bauteilen und ermöglicht zusätzlich eine drastische erhöhte Stabilität. Bauteile mit dem Molekül IPFC10 sind über 3000h stabil unter Lagerungsbedingungen im Dunkeln und überstehen 250h unter voller Last bei 85°C ohne nennenswerte Verluste. Weitere Fortschritte in der Steigerung der Effizienz sind nur zu erwarten, wenn eine vollständige Beschreibung der Wirkprinzipien und Schwachstellen vorliegt. Eine Vielzahl experimenteller Studien haben bisher jedoch ein lückenhaftes Bild gemalt. Häufig sind physikalische Beschränkungen, etwa die hohe Kapazität aufgrund der sehr dünnen Schichten dafür verantwortlich, dass Rekombinationsdynamiken durch kapazitive Entladungsprozesse verdeckt werden. Um diese Probleme zu umgehen, werden hocheffiziente Solarzellen mit einer Kombination mehrerer optischer und optoelektronischer Messmethoden untersucht. Dies ermöglicht die Rekombinationsdynamik mit einer Superposition aus Rekombination erster, zweiter und dritter Ordnung der Ladungsträgerdichte vollumfänglich zu beschreiben. Drift-Diffusions Simulationen unterstützen die experimentellen Ergebnisse, selbst unter Einbeziehung mobiler Ionen. Weiterhin wird in einem Übersichtsartikel ein Ausblick auf den gegenwärtigen Stand des Wissens im Bezug auf Rekombinationsverluste in besagten Solarzellen gegeben. Unterschiedliche Messmethoden werden vorgestellt und erfolgreiche Methoden zur Minderung genannter Verluste diskutiert. Insgesamt stellt diese Arbeit einen Fortschritt im Verständnis und der Verminderung unterschiedlicher Verlustprozesse dar. Mithilfe unterschiedlicher verlässlicher optoelektronischer Messmethoden, wird gezeigt, dass der Ursprung von Rekombinations- und Stabilitätsverlusten häufig an den Grenzflächen liegt. Mithilfe gezielt eingesetzter ultradünner Zwischenschichten werden diese Verluste reduziert und die Stabilität erhöht.
T2  - Identifizierung und Reduzierung von Verlusten in Perowskit Solarzellen
KW  - perovskite solar cells
KW  - interfacial recombination
KW  - nonradiative losses
KW  - Perowskit Solarzellen
KW  - Grenzflächenrekombination
KW  - nichtstrahlende Verluste
Y1  - 2020
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-479301
ER  - 
TY  - JOUR
A1  - Sangian, Danial
T1  - Improving the performance of dielectric-elastomer actuators at elevated operating temperatures by means of thermal softening
JF  - Smart materials and structures
N2  - Dielectric elastomer devices operate on the principle of Maxwell stress and their operating performance significantly rely on the elastomer and compliant electrode's electrical and mechanical properties. This paper reports that performing actuation tests at elevated temperatures resulted in an enhanced performance due to the reduction of Young's modulus and the increase of dielectric permittivity. As a result, considerably higher isometric forces and isotonic strains were achieved above the ambient operating temperature. For actuators made of silicone, polyurethane and acrylic elastomers, 166%, 70% and 266% higher isometric forces and 450%, 250% and 54% higher isotonic strains were observed, respectively, when tested at the temperature of 100 degrees C in comparison to ambient temperature values using the same operating voltages. Values of up to 0.4 J kg(-1) and 3.1 W kg(-1) were achieved for the work and power outputs per mass, respectively, on a silicone elastomer driven with a voltage of 1.5 kV at a temperature of 100 degrees C.
KW  - elevated-temperature effects on the operation of dielectric-elastomer
KW  - actuators
KW  - thermally enhanced actuators
KW  - thermal stimulation of
KW  - electro-electrets
Y1  - 2020
U6  - https://doi.org/10.1088/1361-665X/ab6079
SN  - 0964-1726
SN  - 1361-665X
VL  - 29
IS  - 2
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Poudel, Amit
A1  - Tichy, Wolfgang
A1  - Brügmann, Bernd
A1  - Dietrich, Tim
T1  - Increasing the accuracy of binary neutron star simulations with an improved vacuum treatment
JF  - Physical review : D, Particles, fields, gravitation, and cosmology
N2  - Numerical-relativity simulations are essential for studying the last stages of the binary neutron star coalescence. Unfortunately, for stable simulations there is the need to add an artificial low-density atmosphere. Here we discuss a new framework in which we can effectively set the density surrounding the neutron stars to zero to ensure a more accurate simulation. We test our method with a number of single star test cases and for an equal-mass binary neutron star simulation. While the bulk motion of the system is not influenced, and hence there is no improvement with respect to the emitted gravitational-wave signal, we find that the new approach is superior with respect to mass conservation and it allows a much better tracking of outward moving material. This will allow a more accurate simulation of the ejected material and supports the interpretation of present and future multimessenger observations with more accurate numerical-relativity simulations.
Y1  - 2020
U6  - https://doi.org/10.1103/PhysRevD.102.104014
SN  - 2470-0010
SN  - 2470-0029
VL  - 102
IS  - 10
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - GEN
A1  - Cheng, Xin
A1  - Zhang, Jie
A1  - Kliem, Bernhard
A1  - Török, Tibor
A1  - Xing, Chen
A1  - Zhou, Zhenjun
A1  - Inhester, Bernd
A1  - Ding, Mingde
T1  - Initiation and early kinematic evolution of solar eruptions
T2  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe
N2  - We investigate the initiation and early evolution of 12 solar eruptions, including six active-region hot channel and six quiescent filament eruptions, which were well observed by the Solar Dynamics Observatory, as well as by the Solar Terrestrial Relations Observatory for the latter. The sample includes one failed eruption and 11 coronal mass ejections, with velocities ranging from 493 to 2140 km s(-1). A detailed analysis of the eruption kinematics yields the following main results. (1) The early evolution of all events consists of a slow-rise phase followed by a main-acceleration phase, the height-time profiles of which differ markedly and can be best fit, respectively, by a linear and an exponential function. This indicates that different physical processes dominate in these phases, which is at variance with models that involve a single process. (2) The kinematic evolution of the eruptions tends to be synchronized with the flare light curve in both phases. The synchronization is often but not always close. A delayed onset of the impulsive flare phase is found in the majority of the filament eruptions (five out of six). This delay and its trend to be larger for slower eruptions favor ideal MHD instability models. (3) The average decay index at the onset heights of the main acceleration is close to the threshold of the torus instability for both groups of events (although, it is based on a tentative coronal field model for the hot channels), suggesting that this instability initiates and possibly drives the main acceleration.
T3  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1420 
KW  - solar coronal mass ejections
KW  - stellar coronal mass ejections
KW  - solar storm
Y1  - 2020
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-519720
SN  - 1866-8372
IS  - 2
ER  - 
TY  - JOUR
A1  - Cheng, Xin
A1  - Zhang, Jie
A1  - Kliem, Bernhard
A1  - Török, Tibor
A1  - Xing, Chen
A1  - Zhou, Zhenjun
A1  - Inhester, Bernd
A1  - Ding, Mingde
T1  - Initiation and early kinematic evolution of solar eruptions
JF  - The Astrophysical Journal
N2  - We investigate the initiation and early evolution of 12 solar eruptions, including six active-region hot channel and six quiescent filament eruptions, which were well observed by the Solar Dynamics Observatory, as well as by the Solar Terrestrial Relations Observatory for the latter. The sample includes one failed eruption and 11 coronal mass ejections, with velocities ranging from 493 to 2140 km s(-1). A detailed analysis of the eruption kinematics yields the following main results. (1) The early evolution of all events consists of a slow-rise phase followed by a main-acceleration phase, the height-time profiles of which differ markedly and can be best fit, respectively, by a linear and an exponential function. This indicates that different physical processes dominate in these phases, which is at variance with models that involve a single process. (2) The kinematic evolution of the eruptions tends to be synchronized with the flare light curve in both phases. The synchronization is often but not always close. A delayed onset of the impulsive flare phase is found in the majority of the filament eruptions (five out of six). This delay and its trend to be larger for slower eruptions favor ideal MHD instability models. (3) The average decay index at the onset heights of the main acceleration is close to the threshold of the torus instability for both groups of events (although, it is based on a tentative coronal field model for the hot channels), suggesting that this instability initiates and possibly drives the main acceleration.
KW  - solar coronal mass ejections
KW  - stellar coronal mass ejections
KW  - solar storm
Y1  - 2020
U6  - https://doi.org/10.3847/1538-4357/ab886a
SN  - 1055-6796
SN  - 1476-3540
VL  - 894
IS  - 2
SP  - 1
EP  - 20
PB  - Cambridge Scientific Publishers
CY  - Cambridge
ER  - 
TY  - JOUR
A1  - Seroussi, Helene
A1  - Nowicki, Sophie
A1  - Payne, Antony J.
A1  - Goelzer, Heiko
A1  - Lipscomb, William H.
A1  - Abe-Ouchi, Ayako
A1  - Agosta, Cecile
A1  - Albrecht, Torsten
A1  - Asay-Davis, Xylar
A1  - Barthel, Alice
A1  - Calov, Reinhard
A1  - Cullather, Richard
A1  - Dumas, Christophe
A1  - Galton-Fenzi, Benjamin K.
A1  - Gladstone, Rupert
A1  - Golledge, Nicholas R.
A1  - Gregory, Jonathan M.
A1  - Greve, Ralf
A1  - Hattermann, Tore
A1  - Hoffman, Matthew J.
A1  - Humbert, Angelika
A1  - Huybrechts, Philippe
A1  - Jourdain, Nicolas C.
A1  - Kleiner, Thomas
A1  - Larour, Eric
A1  - Leguy, Gunter R.
A1  - Lowry, Daniel P.
A1  - Little, Chistopher M.
A1  - Morlighem, Mathieu
A1  - Pattyn, Frank
A1  - Pelle, Tyler
A1  - Price, Stephen F.
A1  - Quiquet, Aurelien
A1  - Reese, Ronja
A1  - Schlegel, Nicole-Jeanne
A1  - Shepherd, Andrew
A1  - Simon, Erika
A1  - Smith, Robin S.
A1  - Straneo, Fiammetta
A1  - Sun, Sainan
A1  - Trusel, Luke D.
A1  - Van Breedam, Jonas
A1  - van de Wal, Roderik S. W.
A1  - Winkelmann, Ricarda
A1  - Zhao, Chen
A1  - Zhang, Tong
A1  - Zwinger, Thomas
T1  - ISMIP6 Antarctica
BT  - a multi-model ensemble of the Antarctic ice sheet evolution over the 21st century
JF  - The Cryosphere : TC ; an interactive open access journal of the European Geosciences Union
N2  - Ice flow models of the Antarctic ice sheet are commonly used to simulate its future evolution in response to different climate scenarios and assess the mass loss that would contribute to future sea level rise. However, there is currently no consensus on estimates of the future mass balance of the ice sheet, primarily because of differences in the representation of physical processes, forcings employed and initial states of ice sheet models. This study presents results from ice flow model simulations from 13 international groups focusing on the evolution of the Antarctic ice sheet during the period 2015-2100 as part of the Ice Sheet Model Intercomparison for CMIP6 (ISMIP6). They are forced with outputs from a subset of models from the Coupled Model Intercomparison Project Phase 5 (CMIP5), representative of the spread in climate model results. Simulations of the Antarctic ice sheet contribution to sea level rise in response to increased warming during this period varies between 7:8 and 30.0 cm of sea level equivalent (SLE) under Representative Concentration Pathway (RCP) 8.5 scenario forcing. These numbers are relative to a control experiment with constant climate conditions and should therefore be added to the mass loss contribution under climate conditions similar to present-day conditions over the same period. The simulated evolution of the West Antarctic ice sheet varies widely among models, with an overall mass loss, up to 18.0 cm SLE, in response to changes in oceanic conditions. East Antarctica mass change varies between 6 :1 and 8.3 cm SLE in the simulations, with a significant increase in surface mass balance outweighing the increased ice discharge under most RCP 8.5 scenario forcings. The inclusion of ice shelf collapse, here assumed to be caused by large amounts of liquid water ponding at the surface of ice shelves, yields an additional simulated mass loss of 28mm compared to simulations without ice shelf collapse. The largest sources of uncertainty come from the climate forcing, the ocean-induced melt rates, the calibration of these melt rates based on oceanic conditions taken outside of ice shelf cavities and the ice sheet dynamic response to these oceanic changes. Results under RCP 2.6 scenario based on two CMIP5 climate models show an additional mass loss of 0 and 3 cm of SLE on average compared to simulations done under present-day conditions for the two CMIP5 forcings used and display limited mass gain in East Antarctica.
Y1  - 2020
U6  - https://doi.org/10.5194/tc-14-3033-2020
SN  - 1994-0416
SN  - 1994-0424
VL  - 14
IS  - 9
SP  - 3033
EP  - 3070
PB  - Copernicus
CY  - Göttingen
ER  - 
TY  - JOUR
A1  - Chigarev, Vladimir
A1  - Kazakov, Alexey
A1  - Pikovsky, Arkady
T1  - Kantorovich-Rubinstein-Wasserstein distance between overlapping attractor and repeller
JF  - Chaos : an interdisciplinary journal of nonlinear science
N2  - We consider several examples of dynamical systems demonstrating overlapping attractor and repeller. These systems are constructed via introducing controllable dissipation to prototypic models with chaotic dynamics (Anosov cat map, Chirikov standard map, and incompressible three-dimensional flow of the ABC-type on a three-torus) and ergodic non-chaotic behavior (skew-shift map). We employ the Kantorovich-Rubinstein-Wasserstein distance to characterize the difference between the attractor and the repeller, in dependence on the dissipation level.
Y1  - 2020
U6  - https://doi.org/10.1063/5.0007230
SN  - 1054-1500
SN  - 1089-7682
VL  - 30
IS  - 7
PB  - American Institute of Physics
CY  - Melville
ER  - 
TY  - JOUR
A1  - Arya, Pooja
A1  - Jelken, Joachim
A1  - Lomadze, Nino
A1  - Santer, Svetlana
A1  - Bekir, Marek
T1  - Kinetics of photo-isomerization of azobenzene containing surfactants
JF  - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistry
N2  - We report on photoisomerization kinetics of azobenzene containing surfactants in aqueous solution. The surfactant molecule consists of a positively charged trimethylammonium bromide head group, a hydrophobic spacer connecting via 6 to 10 CH2 groups to the azobenzene unit, and the hydrophobic tail of 1 and 3CH(2) groups. Under exposure to light, the azobenzene photoisomerizes from more stable trans- to metastable cis-state, which can be switched back either thermally in dark or by illumination with light of a longer wavelength. The surfactant isomerization is described by a kinetic model of a pseudo first order reaction approaching equilibrium, where the intensity controls the rate of isomerization until the equilibrated state. The rate constants of the trans-cis and cis-trans photoisomerization are calculated as a function of several parameters such as wavelength and intensity of light, the surfactant concentration, and the length of the hydrophobic tail. The thermal relaxation rate from cis- to trans-state is studied as well. The surfactant isomerization shows a different kinetic below and above the critical micellar concentration of the trans isomer due to steric hindrance within the densely packed micelle but does not depend on the spacer length.
KW  - genomic DNA conformation
KW  - water-interface
KW  - light photocontrol
KW  - driven
KW  - manipulation
KW  - photoisomerization
KW  - molecules
Y1  - 2020
U6  - https://doi.org/10.1063/1.5135913
SN  - 0021-9606
SN  - 1089-7690
VL  - 152
IS  - 2
PB  - American Institute of Physics
CY  - Melville
ER  - 
TY  - JOUR
A1  - Rüdiger, Günther
A1  - Schultz, Manfred
T1  - Large-scale dynamo action of magnetized Taylor-Couette flows
JF  - Monthly notices of the Royal Astronomical Society
N2  - A conducting Taylor-Couette flow with quasi-Keplerian rotation law containing a toroidal magnetic field serves as a mean-field dynamo model of the Tayler-Spruit type. The flows are unstable against non-axisymmetric perturbations which form electromotive forces defining a effect and eddy diffusivity. If both degenerated modes with m = +/- 1 are excited with the same power then the global a effect vanishes and a dynamo cannot work. It is shown, however, that the Tayler instability produces finite alpha effects if only an isolated mode is considered but this intrinsic helicity of the single-mode is too low for an alpha(2) dynamo. Moreover, an alpha Omega dynamo model with quasi-Keplerian rotation requires a minimum magnetic Reynolds number of rotation of Rm similar or equal to 2000 to work. Whether it really works depends on assumptions about the turbulence energy. For a steeper-than-quadratic dependence of the turbulence intensity on the magnetic field, however, dynamos are only excited if the resulting magnetic eddy diffusivity approximates its microscopic value, eta(T) similar or equal to eta. By basically lower or larger eddy diffusivities the dynamo instability is suppressed.
KW  - dynamo
KW  - instabilities
KW  - MHD
KW  - magnetic fields
Y1  - 2020
U6  - https://doi.org/10.1093/mnras/staa293
SN  - 0035-8711
SN  - 1365-2966
VL  - 493
IS  - 1
SP  - 1249
EP  - 1260
PB  - Oxford Univ. Press
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Capała, Karol
A1  - Padash, Amin
A1  - Chechkin, Aleksei V.
A1  - Shokri, Babak
A1  - Metzler, Ralf
A1  - Dybiec, Bartłomiej
T1  - Levy noise-driven escape from arctangent potential wells
JF  - Chaos : an interdisciplinary journal of nonlinear science
N2  - The escape from a potential well is an archetypal problem in the study of stochastic dynamical systems, representing real-world situations from chemical reactions to leaving an established home range in movement ecology. Concurrently, Levy noise is a well-established approach to model systems characterized by statistical outliers and diverging higher order moments, ranging from gene expression control to the movement patterns of animals and humans. Here, we study the problem of Levy noise-driven escape from an almost rectangular, arctangent potential well restricted by two absorbing boundaries, mostly under the action of the Cauchy noise. We unveil analogies of the observed transient dynamics to the general properties of stationary states of Levy processes in single-well potentials. The first-escape dynamics is shown to exhibit exponential tails. We examine the dependence of the escape on the shape parameters, steepness, and height of the arctangent potential. Finally, we explore in detail the behavior of the probability densities of the first-escape time and the last-hitting point.
Y1  - 2020
U6  - https://doi.org/10.1063/5.0021795
SN  - 1054-1500
SN  - 1089-7682
VL  - 30
IS  - 12
PB  - American Institute of Physics
CY  - Woodbury, NY
ER  - 
TY  - JOUR
A1  - Xu, Pengbo
A1  - Deng, Weihua
A1  - Sandev, Trifce
T1  - Levy walk with parameter dependent velocity
BT  - hermite polynomial approach and numerical simulation
JF  - Journal of physics : A, Mathematical and theoretical
N2  - To analyze stochastic processes, one often uses integral transform (Fourier and Laplace) methods. However, for the time-space coupled cases, e.g. the Levy walk, sometimes the integral transform method may fail. Here we provide a Hermite polynomial expansion approach, being complementary to the integral transform method, to the Levy walk. Two approaches are compared for some already known results. We also consider the generalized Levy walk with parameter dependent velocity. Namely, we consider the Levy walk with velocity which depends on the walking length or on the duration of each step. Some interesting features of the generalized Levy walk are observed, including the special shapes of the probability density function, the first passage time distributions, and various diffusive behaviors of the mean squared displacement.
KW  - Hermite polynomial expansion
KW  - Levy walk
KW  - anomalous diffusion
KW  - parameter
KW  - dependent velocity
Y1  - 2020
U6  - https://doi.org/10.1088/1751-8121/ab7420
SN  - 1751-8113
SN  - 1751-8121
VL  - 53
IS  - 11
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Arya, Pooja
A1  - Jelken, Joachim
A1  - Feldmann, David
A1  - Lomadze, Nino
A1  - Santer, Svetlana
T1  - Light driven diffusioosmotic repulsion and attraction of colloidal particles
JF  - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr
N2  - In this paper, we introduce the phenomenon of light driven diffusioosmotic long-range attraction and repulsion of porous particles under irradiation with UV light. The change in the inter-particle interaction potential is governed by flow patterns generated around single colloids and results in reversible aggregation or separation of the mesoporous silica particles that are trapped at a solid surface. The range of the interaction potential extends to several times the diameter of the particle and can be adjusted by varying the light intensity. The "fuel" of the process is a photosensitive surfactant undergoing photo-isomerization from a more hydrophobic trans-state to a rather hydrophilic cis-state. The surfactant has different adsorption affinities to the particles depending on the isomerization state. The trans-isomer, for example, tends to accumulate in the negatively charged pores of the particles, while the cis-isomer prefers to remain in the solution. This implies that when under UV irradiation cis-isomers are being formed within the pores, they tend to diffuse out readily and generate an excess concentration near the colloid's outer surface, ultimately resulting in the initiation of diffusioosmotic flow. The direction of the flow depends strongly on the dynamic redistribution of the fraction of trans- and cis-isomers near the colloids due to different kinetics of photo-isomerization within the pores as compared to the bulk. The unique feature of the mechanism discussed in the paper is that the long-range mutual repulsion but also the attraction can be tuned by convenient external optical stimuli such as intensity so that a broad variety of experimental situations for manipulation of a particle ensemble can be realized.
Y1  - 2020
U6  - https://doi.org/10.1063/5.0007556
SN  - 0021-9606
SN  - 1089-7690
VL  - 152
IS  - 19
PB  - American Institute of Physics
CY  - Melville, NY
ER  - 
TY  - JOUR
A1  - Tönjes, Ralf
A1  - Pikovsky, Arkady
T1  - Low-dimensional description for ensembles of identical phase oscillators subject to Cauchy noise
JF  - Physical review : E, Statistical, nonlinear and soft matter physics
N2  - We study ensembles of globally coupled or forced identical phase oscillators subject to independent white Cauchy noise. We demonstrate that if the oscillators are forced in several harmonics, stationary synchronous regimes can be exactly described with a finite number of complex order parameters. The corresponding distribution of phases is a product of wrapped Cauchy distributions. For sinusoidal forcing, the Ott-Antonsen low-dimensional reduction is recovered.
Y1  - 2020
U6  - https://doi.org/10.1103/PhysRevE.102.052315
SN  - 2470-0045
SN  - 2470-0053
VL  - 102
IS  - 5
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Xu, Pengbo
A1  - Zhou, Tian
A1  - Metzler, Ralf
A1  - Deng, Weihua
T1  - Lévy walk dynamics in an external harmonic potential
JF  - Physical review : E, Statistical, nonlinear, and soft matter physics
N2  - Levy walks (LWs) are spatiotemporally coupled random-walk processes describing superdiffusive heat conduction in solids, propagation of light in disordered optical materials, motion of molecular motors in living cells, or motion of animals, humans, robots, and viruses. We here investigate a key feature of LWs-their response to an external harmonic potential. In this generic setting for confined motion we demonstrate that LWs equilibrate exponentially and may assume a bimodal stationary distribution. We also show that the stationary distribution has a horizontal slope next to a reflecting boundary placed at the origin, in contrast to correlated superdiffusive processes. Our results generalize LWs to confining forces and settle some longstanding puzzles around LWs.
Y1  - 2020
U6  - https://doi.org/10.1103/PhysRevE.101.062127
SN  - 2470-0045
SN  - 2470-0053
SN  - 1550-2376
SN  - 1063-651X
SN  - 1539-3755
VL  - 101
IS  - 6
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Quade, Markus
A1  - Isele, Thomas
A1  - Abel, Markus
T1  - Machine learning control
BT  - explainable and analyzable methods
JF  - Physica : D, Nonlinear phenomena
N2  - Recently, the term explainable AI came into discussion as an approach to produce models from artificial intelligence which allow interpretation. For a long time, symbolic regression has been used to produce explainable and mathematically tractable models. In this contribution, we extend previous work on symbolic regression methods to infer the optimal control of a dynamical system given one or several optimization criteria, or cost functions. In earlier publications, network control was achieved by automated machine learning control using genetic programming. Here, we focus on the subsequent path continuation analysis of the mathematical expressions which result from the machine learning model. In particular, we use AUTO to analyze the solution properties of the controlled oscillator system which served as our model. As a result, we show that there is a considerable advantage of explainable symbolic regression models over less accessible neural networks. In particular, the roadmap of future works may be to integrate such analyses into the optimization loop itself to filter out robust solutions by construction.
KW  - Explainable AI
KW  - Machine learning control
KW  - Dynamical systems
KW  - Synchronization control
KW  - Genetic programming
Y1  - 2020
U6  - https://doi.org/10.1016/j.physd.2020.132582
SN  - 0167-2789
SN  - 1872-8022
VL  - 412
PB  - Elsevier
CY  - Amsterdam
ER  - 
TY  - JOUR
A1  - Wang, Qiong
A1  - Smith, Joel A.
A1  - Skroblin, Dieter
A1  - Steele, Julian A.
A1  - Wolff, Christian Michael
A1  - Caprioglio, Pietro
A1  - Stolterfoht, Martin
A1  - Köbler, Hans
A1  - Turren-Cruz, Silver-Hamill
A1  - Li, Meng
A1  - Gollwitzer, Christian
A1  - Neher, Dieter
A1  - Abate, Antonio
T1  - Managing phase purities and crystal orientation for high-performance and photostable cesium lead halide perovskite solar cells
JF  - Solar RRL
N2  - Inorganic perovskites with cesium (Cs+) as the cation have great potential as photovoltaic materials if their phase purity and stability can be addressed. Herein, a series of inorganic perovskites is studied, and it is found that the power conversion efficiency of solar cells with compositions CsPbI1.8Br1.2, CsPbI2.0Br1.0, and CsPbI2.2Br0.8 exhibits a high dependence on the initial annealing step that is found to significantly affect the crystallization and texture behavior of the final perovskite film. At its optimized annealing temperature, CsPbI1.8Br1.2 exhibits a pure orthorhombic phase and only one crystal orientation of the (110) plane. Consequently, this allows for the best efficiency of up to 14.6% and the longest operational lifetime, T-S80, of approximate to 300 h, averaged of over six solar cells, during the maximum power point tracking measurement under continuous light illumination and nitrogen atmosphere. This work provides essential progress on the enhancement of photovoltaic performance and stability of CsPbI3 - xBrx perovskite solar cells.
KW  - cesium lead halides
KW  - crystal orientation
KW  - inorganic perovskites
KW  - ISOS-L-1I protocol
KW  - phase purity
KW  - photostability
Y1  - 2020
VL  - 4
IS  - 9
PB  - WILEY-VCH
CY  - Weinheim
ER  - 
TY  - GEN
A1  - Wang, Qiong
A1  - Smith, Joel A.
A1  - Skroblin, Dieter
A1  - Steele, Julian A.
A1  - Wolff, Christian Michael
A1  - Caprioglio, Pietro
A1  - Stolterfoht, Martin
A1  - Köbler, Hans
A1  - Turren-Cruz, Silver-Hamill
A1  - Li, Meng
A1  - Gollwitzer, Christian
A1  - Neher, Dieter
A1  - Abate, Antonio
T1  - Managing phase purities and crystal orientation for high-performance and photostable cesium lead halide perovskite solar cells
T2  - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe
N2  - Inorganic perovskites with cesium (Cs+) as the cation have great potential as photovoltaic materials if their phase purity and stability can be addressed. Herein, a series of inorganic perovskites is studied, and it is found that the power conversion efficiency of solar cells with compositions CsPbI1.8Br1.2, CsPbI2.0Br1.0, and CsPbI2.2Br0.8 exhibits a high dependence on the initial annealing step that is found to significantly affect the crystallization and texture behavior of the final perovskite film. At its optimized annealing temperature, CsPbI1.8Br1.2 exhibits a pure orthorhombic phase and only one crystal orientation of the (110) plane. Consequently, this allows for the best efficiency of up to 14.6% and the longest operational lifetime, T-S80, of approximate to 300 h, averaged of over six solar cells, during the maximum power point tracking measurement under continuous light illumination and nitrogen atmosphere. This work provides essential progress on the enhancement of photovoltaic performance and stability of CsPbI3 - xBrx perovskite solar cells.
T3  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1210 
KW  - cesium lead halides
KW  - crystal orientation
KW  - inorganic perovskites
KW  - ISOS-L-1I protocol
KW  - phase purity
KW  - photostability
Y1  - 2020
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-525374
SN  - 1866-8372
IS  - 9
ER  - 
TY  - THES
A1  - Landau, Livnat
T1  - Mechanical stimulation of in-vitro tissue growth using magnetic beads
N2  - Cells and tissues are sensitive to mechanical forces applied to them. In particular, bone forming cells and connective tissues, composed of cells embedded in fibrous extracellular matrix (ECM), are continuously remodeled in response to the loads they bear. The mechanoresponses of cells embedded in tissue include proliferation, differentiation, apoptosis, internal signaling between cells, and formation and resorption of tissue.
Experimental in-vitro systems of various designs have demonstrated that forces affect tissue growth, maturation and mineralization. However, the results depended on different parameters such as the type and magnitude of the force applied in each study. Some experiments demonstrated that applied forces increase cell proliferation and inhibit cell maturation rate, while other studies found the opposite effect. When the effect of different magnitudes of forces was compared, some studies showed that higher forces resulted in a cell proliferation increase or differentiation decrease, while other studies observed the opposite trend or no trend at all.
In this study, MC3T3-E1 cells, a cell line of pre-osteoblasts (bone forming cells), was used. In this cell line, cell differentiation is known to accelerate after cells stop proliferating, typically at confluency. This makes this cell line an interesting subject for studying the influence of forces on the switch between the proliferation stage of the precursor cell and the differentiation to the mature osteoblasts.
A new experimental system was designed to perform systematic investigations of the influence of the type and magnitude of forces on tissue growth. A single well plate contained an array of 80 rectangular pores. Each pore was seeded with MC3T3-E1 cells. The culture medium contained magnetic beads (MBs) of 4.5 μm in diameter that were incorporated into the pre-osteoblast cells. Using an N52 neodymium magnet, forces ranging over three orders of magnitude were applied to MBs incorporated in cells at 10 different distances from the magnet. The amount of formed tissue was assessed after 24 days of culture. The experimental design allowed to obtain data concerning (i) the influence of the type of the force (static, oscillating, no force) on tissue growth; (ii) the influence of the magnitude of force (pN-nN range); (iii) the effect of functionalizing the magnetic beads with the tripeptide Arg-Gly-Asp (RGD). To learn about cell differentiation state, in the final state of the tissue growth experiments, an analysis for the expression of alkaline phosphatase (ALP), a well - known marker of osteoblast differentiation, was performed.
The experiments showed that the application of static magnetic forces increased tissue growth compared to control, while oscillating forces resulted in tissue growth reduction. A statistically significant positive correlation was found between the amount of tissue grown and the magnitude of the oscillating magnetic force. A positive but non-significant correlation of the amount of tissue with the magnitude of forces was obtained when static forces were applied. Functionalizing the MBs with RGD peptides and applying oscillating forces resulted in an increase of tissue growth relative to tissues incubated with “plain” epoxy MBs. ALP expression decreased as a function of the magnitude of force both when static and oscillating forces were applied. ALP stain intensity was reduced relative to control when oscillating forces were applied and was not significantly different than control for static forces.
The suggested interpretation of the experimental findings is that larger mechanical forces delay cell maturation and keep the pre-osteoblasts in a more proliferative stage characterized by more tissue formed and lower expression of ALP. While the influence of the force magnitude can be well explained by an effect of the force on the switch between proliferation and differentiation, the influence of force type (static or oscillating) is less clear. In particular, it is challenging to reconcile the reduction of tissue formed under oscillating forces as compared to controls with the simultaneous reduction of ALP expression. To better understand this, it may be necessary to refine the staining protocol of the scaffolds and to include the amount and structure of ECM as well as other factors that were not monitored in the experiment and which may influence tissue growth and maturation.
The developed experimental system proved well suited for a systematic and efficient study of the mechanoresponsiveness of tissue growth, it allowed a study of the dependence of tissue growth on force magnitude ranging over three orders of magnitude, and a comparison between the effect of static and oscillating forces. Future experiments can explore the multiple parameters that affect tissue growth as a function of the magnitude of the force: by applying different time-dependent forces; by extending the force range studied; or by using different cell lines and manipulating the mechanotransduction in the cells biochemically.
KW  - mechanobiology
KW  - magnetism
KW  - biophysics
KW  - tissue growth
KW  - magnetic beads
Y1  - 2020
ER  - 
TY  - JOUR
A1  - Smirnov, Artem
A1  - Berrendorf, Max
A1  - Shprits, Yuri
A1  - Kronberg, Elena A.
A1  - Allison, Hayley J.
A1  - Aseev, Nikita
A1  - Zhelavskaya, Irina
A1  - Morley, Steven K.
A1  - Reeves, Geoffrey D.
A1  - Carver, Matthew R.
A1  - Effenberger, Frederic
T1  - Medium energy electron flux in earth's outer radiation
belt (MERLIN)
BT  - a Machine learning model
JF  - Space weather : the international journal of research and applications
N2  - The radiation belts of the Earth, filled with energetic electrons, comprise complex and dynamic systems that pose a significant threat to satellite operation. While various models of electron flux both for low and relativistic energies have been developed, the behavior of medium energy (120-600 keV) electrons, especially in the MEO region, remains poorly quantified. At these energies, electrons are driven by both convective and diffusive transport, and their prediction usually requires sophisticated 4D modeling codes. In this paper, we present an alternative approach using the Light Gradient Boosting (LightGBM) machine learning algorithm. The Medium Energy electRon fLux In Earth's outer radiatioN belt (MERLIN) model takes as input the satellite position, a combination of geomagnetic indices and solar wind parameters including the time history of velocity, and does not use persistence. MERLIN is trained on >15 years of the GPS electron flux data and tested on more than 1.5 years of measurements. Tenfold cross validation yields that the model predicts the MEO radiation environment well, both in terms of dynamics and amplitudes o f flux. Evaluation on the test set shows high correlation between the predicted and observed electron flux (0.8) and low values of absolute error. The MERLIN model can have wide space weather applications, providing information for the scientific community in the form of radiation belts reconstructions, as well as industry for satellite mission design, nowcast of the MEO environment, and surface charging analysis.
KW  - machine learning
KW  - radiation belts
KW  - electron flux
KW  - empirical modeling
KW  - magnetosphere
KW  - electrons
Y1  - 2020
U6  - https://doi.org/10.1029/2020SW002532
SN  - 1542-7390
VL  - 18
IS  - 11
PB  - American geophysical union, AGU
CY  - Washington
ER  - 
TY  - THES
A1  - Aseev, Nikita
T1  - Modeling and understanding dynamics of charged particles in the Earth's inner magnetosphere
T1  - Modellierung und Untersuchung der Dynamik geladener Teilchen in der inneren Magnetosphäre der Erde
N2  - The Earth's inner magnetosphere is a very dynamic system, mostly driven by the external solar wind forcing exerted upon the magnetic field of our planet. Disturbances in the solar wind, such as coronal mass ejections and co-rotating interaction regions, cause geomagnetic storms, which lead to prominent changes in charged particle populations of the inner magnetosphere - the plasmasphere, ring current, and radiation belts. Satellites operating in the regions of elevated energetic and relativistic electron fluxes can be damaged by deep dielectric or surface charging during severe space weather events. Predicting the dynamics of the charged particles and mitigating their effects on the infrastructure is of particular importance, due to our increasing reliance on space technologies.

The dynamics of particles in the plasmasphere, ring current, and radiation belts are strongly coupled by means of collisions and collisionless interactions with electromagnetic fields induced by the motion of charged particles. Multidimensional numerical models simplify the treatment of transport, acceleration, and loss processes of these particles, and allow us to predict how the near-Earth space environment responds to solar storms. The models inevitably rely on a number of simplifications and assumptions that affect model accuracy and complicate the interpretation of the results. In this dissertation, we quantify the processes that control electron dynamics in the inner magnetosphere, paying particular attention to the uncertainties of the employed numerical codes and tools.

We use a set of convenient analytical solutions for advection and diffusion equations to test the accuracy and stability of the four-dimensional Versatile Electron Radiation Belt (VERB-4D) code. We show that numerical schemes implemented in the code converge to the analytical solutions and that the VERB-4D code demonstrates stable behavior independent of the assumed time step. The order of the numerical scheme for the convection equation is demonstrated to affect results of ring current and radiation belt simulations, and it is crucially important to use high-order numerical schemes to decrease numerical errors in the model.

Using the thoroughly tested VERB-4D code, we model the dynamics of the ring current electrons during the 17 March 2013 storm. The discrepancies between the model and observations above 4.5 Earth's radii can be explained by uncertainties in the outer boundary conditions. Simulation results indicate that the electrons were transported from the geostationary orbit towards the Earth by the global-scale electric and magnetic fields.
We investigate how simulation results depend on the input models and parameters. The model is shown to be particularly sensitive to the global electric field and electron lifetimes below 4.5 Earth's radii. The effects of radial diffusion and subauroral polarization streams are also quantified.

We developed a data-assimilative code that blends together a convection model of energetic electron transport and loss and Van Allen Probes satellite data by means of the Kalman filter. We show that the Kalman filter can correct model uncertainties in the convection electric field, electron lifetimes, and boundary conditions. It is also demonstrated how the innovation vector - the difference between observations and model prediction - can be used to identify physical processes missing in the model of energetic electron dynamics.

We computed radial profiles of phase space density of ultrarelativistic electrons, using Van Allen Probes measurements. We analyze the shape of the profiles during geomagnetically quiet and disturbed times and show that the formation of new local minimums in the radial profiles coincides with the ground observations of electromagnetic ion-cyclotron (EMIC) waves. This correlation indicates that EMIC waves are responsible for the loss of ultrarelativistic electrons from the heart of the outer radiation belt into the Earth's atmosphere.
N2  - Die innere Magnetosphäre der Erde ist ein sehr dynamisches System, das hauptsächlich vom äußeren Sonnenwind beeinflusst wird, der auf das Magnetfeld unseres Planeten einwirkt. Störungen im Sonnenwind, wie z.B. koronale Massenauswürfe und sogenannte Korotierende Wechselwirkungsbereiche, verursachen geomagnetische Stürme, die zu deutlichen Veränderungen der Populationen geladener Teilchen in der inneren Magnetosphäre führen - Plasmasphäre, Ringstrom und Strahlungsgürtel. Satelliten, die in Regionen mit erhöhten energetischen und relativistischen Elektronenflüssen betrieben werden, können durch tiefe dielektrische Ladung oder Oberflächenladungen bei schweren Weltraumwetterereignissen beschädigt werden. Die Vorhersage der Dynamik der geladenen Teilchen und die Abschwächung ihrer Auswirkungen auf die Infrastruktur sind heutzutage von besonderer Bedeutung, insbesondere aufgrund unserer zunehmenden Abhängigkeit von Weltraumtechnologien.

Die Dynamik von Teilchen in der Plasmasphäre, des Ringstrom und in den Strahlungsgürteln sind durch Kollisionen und kollisionsfreie Wechselwirkungen mit elektromagnetischen Feldern, die durch die Bewegung geladener Teilchen induziert werden, stark gekoppelt. Mehrdimensionale numerische Modelle vereinfachen die Betrachtung von Transport-, Beschleunigungs- und Verlustprozessen dieser Partikel und ermöglichen es uns, vorherzusagen, wie die erdnahe Weltraumumgebung auf Sonnenstürme reagiert. Die Modelle beruhen zwangsläufig auf einer Reihe von Vereinfachungen und Voraussetzungen, die sich auf die Modellgenauigkeit auswirken und die Interpretation der Ergebnisse erschweren. In dieser Dissertation quantifizieren wir die Prozesse, die die Dynamik der Elektronen in der inneren Magnetosphäre steuern. Dabei richten wir den Fokus insbesondere auch auf die Unsicherheiten der verwendeten numerischen Codes.

Wir verwenden eine Reihe praktischer analytischer Lösungen für Advektions- und Diffusionsgleichungen, um die Genauigkeit und Stabilität des 4-dimensionalen ''Versatile Electron Radiation Belt'' Codes (VERB-4D Code) zu testen. Wir zeigen, dass die im Code implementierten numerischen Schemata zu den analytischen Lösungen konvergieren und der Code sich unabhängig vom angenommenen Zeitschritt stabil verhält. Wir demonstrieren, wie die Genauigkeit des numerischen Schemas für die Konvektionsgleichung die Ergebnisse von Ringstrom- und Strahlungsgürtelsimulationen beeinflussen kann, und dass es von entscheidender Beteutung ist, numerische Schemata höherer Ordnung zu verwenden, um numerische Fehler im Modell zu reduzieren.

Mit dem ausführlich getesteten VERB-4D Code modellieren wir die Dynamik der Ringstromelektronen während des Sturms vom 17. März 2013. Wir zeigen, dass die Diskrepanzen zwischen dem Modell und Beobachtungen oberhalb von 4.5 Erdradien durch Unsicherheiten in den äußeren Randbedingungen erklärt werden können und dass die Elektronen durch die globalen elektrischen und magnetischen Felder von der geostationäre Umlaufbahn zur Erde transportiert wurden.
Wir untersuchen weiterhin, wie die Simulationsergebnisse von den Eingabemodellen und Parametern abhängen. Wir zeigen, dass das Modell besonders empfindlich für das globale elektrische Feld und die Lebensdauer der Elektronen unterhalb von 4.5 Erdradien ist. Außerdem quantifizieren wir auch die Auswirkungen von radialer Diffusion und subauroralen Polarisationsströmen.

Wir haben einen datenassimilativen Code entwickelt, der mithilfe des Kalman-Filters ein Konvektionsmodell für den Transport und den Verlust energetischer Elektronen mit den Satellitendaten der Van Allen Probes kombiniert. Wir zeigen, dass die Verwendung eines Kalman-Filters Modellunsicherheiten im elektrischen Konvektionsfeld, in der Lebensdauer der Elektronen und in den Randbedingungen korrigieren kann. Weiterhin zeigen wir, wie der Innovationsvektor - die Differenz zwischen Beobachtungen und Modellvorhersagen - verwendet werden kann, um physikalische Prozesse zu identifizieren, die im Modell der Dynamik der energetischen Elektronen fehlen.

Außerdem berechnen wir radiale Profile der Phasenraumdichte ultrarelativistischer Elektronen mithilfe von Van Allen Probes-Messungen. Wir analysieren die Form der Profile und zeigen, dass die Entstehung neuer lokaler Minima in den radialen Profilen mit den Bodenbeobachtungen von EMIC-Wellen übereinstimmt. Diese Korrelation legt nahe, dass EMIC-Wellen für den Verlust ultrarelativistischer Elektronen vom Herzen des äußeren Strahlungsgürtels in die Erdatmosphäre verantwortlich sind.
KW  - ring current electrons
KW  - radiation belts
KW  - mathematical modeling
KW  - wave-particle interactions
KW  - data assimilation
KW  - Ringstromelektronen
KW  - Strahlungsgürtel
KW  - mathematische Modellierung
KW  - Wellen-Teilchen Wechselwirkungen
KW  - Datenassimilation
Y1  - 2020
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-479211
ER  - 
TY  - JOUR
A1  - Steppa, Constantin
A1  - Egberts, Kathrin
T1  - Modelling the Galactic very-high-energy gamma-ray source population
JF  - Astronomy and astrophysics : an international weekly journal
N2  - Context. The High Energy Stereoscopic System Galactic plane survey (HGPS) is to date the most comprehensive census of Galactic gamma -ray sources at very high energies (VHE; 100 GeV <= E <= 100 TeV). As a consequence of the limited sensitivity of this survey, the 78 detected gamma -ray sources comprise only a small and biased subsample of the overall population. The larger part consists of currently unresolved sources, which contribute to large-scale diffuse emission to a still uncertain amount.Aims. We study the VHE gamma -ray source population in the Milky Way. For this purpose population-synthesis models are derived based on the distributions of source positions, extents, and luminosities.Methods. Several azimuth-symmetric and spiral-arm models are compared for spatial source distribution. The luminosity and radius function of the population are derived from the source properties of the HGPS data set and are corrected for the sensitivity bias of the HGPS. Based on these models, VHE source populations are simulated and the subsets of sources detectable according to the HGPS are compared with HGPS sources.Results. The power-law indices of luminosity and radius functions are determined to range between -1.6 and -1.9 for luminosity and -1.1 and -1.6 for radius. A two-arm spiral structure with central bar is discarded as spatial distribution of VHE sources, while azimuth-symmetric distributions and a distribution following a four-arm spiral structure without bar describe the HGPS data reasonably well. The total number of Galactic VHE sources is predicted to be in the range from 800 to 7000 with a total luminosity and flux of (1.6-6.3) x 10(36) ph s(-1) and (3-15) x 10(-10) ph cm(-2) s(-1), respectively.Conclusions. Depending on the model, the HGPS sample accounts for (68-87)% of the emission of the population in the scanned region. This suggests that unresolved sources represent a critical component of the diffuse emission measurable in the HGPS. With the foreseen jump in sensitivity of the Cherenkov Telescope Array, the number of detectable sources is predicted to increase by a factor between 5 and 9.
KW  - astroparticle physics
KW  - gamma rays: general
KW  - gamma rays: diffuse
KW  - background
KW  - methods: observational
KW  - methods: numerical
Y1  - 2020
U6  - https://doi.org/10.1051/0004-6361/202038172
SN  - 0004-6361
SN  - 1432-0746
VL  - 643
PB  - EDP Sciences
CY  - Les Ulis
ER  - 
TY  - JOUR
A1  - Cabalar, Pedro
A1  - Fandiño, Jorge
A1  - Lierler, Yuliya
T1  - Modular Answer Set Programming as a formal specification language
JF  - Theory and practice of logic programming
N2  - In this paper, we study the problem of formal verification for Answer Set Programming (ASP), namely, obtaining aformal proofshowing that the answer sets of a given (non-ground) logic programPcorrectly correspond to the solutions to the problem encoded byP, regardless of the problem instance. To this aim, we use a formal specification language based on ASP modules, so that each module can be proved to capture some informal aspect of the problem in an isolated way. This specification language relies on a novel definition of (possibly nested, first order)program modulesthat may incorporate local hidden atoms at different levels. Then,verifyingthe logic programPamounts to prove some kind of equivalence betweenPand its modular specification.
KW  - Answer Set Programming
KW  - formal specification
KW  - formal verification
KW  - modular logic programs
Y1  - 2020
U6  - https://doi.org/10.1017/S1471068420000265
SN  - 1471-0684
SN  - 1475-3081
VL  - 20
IS  - 5
SP  - 767
EP  - 782
PB  - Cambridge University Press
CY  - New York
ER  - 
TY  - GEN
A1  - Schué, Emmanuelle
A1  - Kopyshev, Alexey
A1  - Lutz, Jean-François
A1  - Börner, Hans G.
T1  - Molecular bottle brushes with positioned selenols
BT  - Extending the toolbox of oxidative single polymer chain folding with conformation analysis by atomic force microscopy
T2  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe
N2  - A synthesis route to controlled and dynamic single polymer chain folding is reported. Sequence-controlled macromolecules containing precisely located selenol moieties within a polymer chain are synthesized. Oxidation of selenol functionalities lead to diselenide bridges and induces controlled intramolecular crosslinking to generate single chain collapse. The cyclization process is successfully characterized by SEC as well as by H-1 NMR and 2D HSQC NMR spectroscopies. In order to gain insight on the molecular level to reveal the degree of structural control, the folded polymers are transformed into folded molecular brushes that are known to be visualizable as single molecule structures by AFM. The "grafting onto" approach is performed by using triazolinedione-diene reaction to graft the side chain polymers. A series of folded molecular brushes as well as the corresponding linear controls are synthesized. AFM visualization is proving the cyclization of the folded backbone by showing globular objects, where non-folded brushes show typical worm-like structures. (C) 2019 The Authors. Journal of Polymer Science published by Wiley Periodicals, Inc.
T3  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1397 
KW  - atomic force microscopy (AFM)
KW  - diselenide
KW  - grafted polymers
KW  - molecular bottle brushes
KW  - sequence-controlled polymers
KW  - single chain folding
Y1  - 2020
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-516184
SN  - 1866-8372
IS  - 1
SP  - 154
EP  - 162
ER  - 
TY  - JOUR
A1  - Schué, Emmanuelle
A1  - Kopyshev, Alexey
A1  - Lutz, Jean-François
A1  - Börner, Hans G.
T1  - Molecular bottle brushes with positioned selenols
BT  - Extending the toolbox of oxidative single polymer chain folding with conformation analysis by atomic force microscopy
JF  - Journal of Polymer Science
N2  - A synthesis route to controlled and dynamic single polymer chain folding is reported. Sequence-controlled macromolecules containing precisely located selenol moieties within a polymer chain are synthesized. Oxidation of selenol functionalities lead to diselenide bridges and induces controlled intramolecular crosslinking to generate single chain collapse. The cyclization process is successfully characterized by SEC as well as by H-1 NMR and 2D HSQC NMR spectroscopies. In order to gain insight on the molecular level to reveal the degree of structural control, the folded polymers are transformed into folded molecular brushes that are known to be visualizable as single molecule structures by AFM. The "grafting onto" approach is performed by using triazolinedione-diene reaction to graft the side chain polymers. A series of folded molecular brushes as well as the corresponding linear controls are synthesized. AFM visualization is proving the cyclization of the folded backbone by showing globular objects, where non-folded brushes show typical worm-like structures. (C) 2019 The Authors. Journal of Polymer Science published by Wiley Periodicals, Inc.
KW  - atomic force microscopy (AFM)
KW  - diselenide
KW  - grafted polymers
KW  - molecular bottle brushes
KW  - sequence-controlled polymers
KW  - single chain folding
Y1  - 2020
U6  - https://doi.org/10.1002/pola.29496
SN  - 2642-4169
VL  - 58
IS  - 1
SP  - 154
EP  - 162
PB  - Wiley
CY  - Hoboken
ER  - 
TY  - THES
A1  - Christ, Simon
T1  - Morphological transitions of vesicles exposed to nonuniform spatio-temporal conditions
N2  - Giant unilamellar vesicles are an important tool in todays experimental efforts to understand the structure and behaviour of biological cells. Their simple structure allows the isolation of the physical elastic properties of the lipid membrane. A central physical
property is the bending energy of the membrane, since the many different shapes of giant vesicles can be obtained by finding the minimum of the bending energy. In the spontaneous curvature model the bending energy is a function of the bending rigidity as well as the mean curvature and an additional parameter called the spontaneous curvature, which describes an internal preference of the lipid-bilayer to bend towards one side or the other. The spontaneous and mean curvature are local properties of the membrane.
Additional constraints arise from the conservation of the membrane surface area and the enclosed volume, which are global properties.
In this thesis the spontaneous curvature model is used to explain the experimental observation of a periodic shape oscillation of a giant unilamellar vesicle that was filled with a protein complex that periodically binds to and unbinds from the membrane.
By assuming that the binding of the proteins to the membrane induces a change in the spontaneous curvature the experimentally observed shapes could successfully be explained. This involves the numerical solution of the differential equations as obtained from the minimization of the bending energy respecting the area and volume constraints, the so called shape equations. Vice versa this approach can be used to estimate the spontaneous curvature from experimentally measurable quantities.
The second topic of this thesis is the analysis of concentration gradients in rigid conic membrane compartments. Gradients of an ideal gas due to gravity and gradients generated by the directed stochastic movement of molecular motors along a microtubulus were considered. It was possible to calculate the free energy and the bending energy analytically for the ideal gas. In the case of the non-equilibrium system with molecular motors, the characteristic length of the density profile, the jam-length, and its dependency on the opening angle of the conic compartment have been calculated in the mean-field limit.
The mean field results agree qualitatively with stochastic particle simulations.
N2  - Die Morphologie beschreibt die Struktur und Form von Organismen. Im Rahmen dieser Arbeit werden insbesondere die verschiedenen Formen von einfachen Lipidmembranen untersucht, die geschlossene Formen in Lösung bilden, die Vesikel. Der Fokus liegt dabei auf Begebenheiten, in denen die es inhomogene Zustände innerhalb oder außerhalb des Vesikels gibt.
Das betrifft zum einen die Erklärung der beobachteten Formen in einem Experiment, bei dem im Inneren des Vesikels Proteine plaziert wurden, die sich wiederkehrend an die innere Vesikelmembran heften und wieder ablösen. Dabei Verändert sich die Form des Vesikels von einer symmetrischen erdnussähnlichen Form zu einer asymmetrischen Form mit einem sehr dünnen Hals. Mittels eines theoretischem Modells, dass dem Anheften der Proteine eine Änderung in ihrer bevorzugten Krümmung zuweist, werden Formen berechnet, die den beobachteten Formen gleichen und nur durch das Variieren der bevorzugten Krümmung kann derselbe Formübergang erzielt werden.
Außerdem wird die Biegeenergie von Vesikeln, die durch die äußere Umgebung in eine kegelförmige Form gezwungen werden, in Abhängigkeit des Öffnungswinkels des Kegels analytisch berechnet. Es wird weiterhin die freie Energie eines idealen Gases, das durch die Kräfte der Gravitation inhomogen verteilt ist, innerhalb solcher starren kegelförmigen Vesikeln analytisch berechnet. Ein weiteres System, das betrachtet wird, sind molekulare Motoren, die die Fähigkeit besitzen, sich entlang bestimmter Stränge, der Mikrotubuli, gerichtet fortzubewegen und wenn sie sich nicht an einem Mikrotubulus
befinden, bewegen sie sich aufgrund der üblichen ungerichteten Kräfte, der Diffusion. Wenn nur ein Mikrotubulus und nur eine Art von Motoren vorhanden ist, entsteht dadurch eine Anhäufung von Teilchen auf der Seite in die die Motoren sich bewegen, ein Konzentrationsgradient. Es wird analytisch berechnet, wie sich dieser Konzentrationsgradient
verschiebt, wenn sich der Öffnungswinkel des Kegels ändert und mit Ergebnissen aus Computersimulationen verglichen.
T2  - Morphologische Übergänge von Vesikeln unter räumlich oder zeitlich inhomogenen Bedingunge
KW  - Formgleichungen von Vesikeln
KW  - Shape equations of vesicles
KW  - Molekulare Motoren
KW  - Molecular motors
KW  - Conic compartments
KW  - Kegelförmige Geometrien
KW  - Bending energy
KW  - Biegeenergie
KW  - Min-Proteine
KW  - Min-proteins
Y1  - 2020
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-480788
ER  - 
TY  - JOUR
A1  - Laing, Carlo R.
A1  - Omel'chenko, Oleh
T1  - Moving bumps in theta neuron networks
JF  - Chaos : an interdisciplinary journal of nonlinear science
N2  - We consider large networks of theta neurons on a ring, synaptically coupled with an asymmetric kernel. Such networks support stable "bumps" of activity, which move along the ring if the coupling kernel is asymmetric. We investigate the effects of the kernel asymmetry on the existence, stability, and speed of these moving bumps using continuum equations formally describing infinite networks. Depending on the level of heterogeneity within the network, we find complex sequences of bifurcations as the amount of asymmetry is varied, in strong contrast to the behavior of a classical neural field model.
Y1  - 2020
U6  - https://doi.org/10.1063/1.5143261
SN  - 1054-1500
SN  - 1089-7682
VL  - 30
IS  - 4
PB  - American Institute of Physics
CY  - Melville
ER  - 
TY  - THES
A1  - Grätz, Fabio M.
T1  - Nonlinear diffusion in granular gases and dense planetary rings
N2  - Small moonlets or moons embedded in dense planetary rings create S-shaped density modulations called propellers if their masses are smaller than a certain threshold, alternatively they create a circumferential gap in the disk if the embedded body’s mass exceeds this threshold (Spahn and Sremčević, 2000). The gravitational perturber scatters the ring particles, depletes the disk’s density, and, thus, clears a gap, whereas counteracting viscous diffusion of the ring material has the tendency to close the created gap, thereby forming a propeller. Propeller objects were predicted by Spahn and Sremčević (2000) and Sremčević et al. (2002) and were later discovered by the Cassini space probe (Tiscareno et al., 2006, Sremčević et al., 2007, Tiscareno et al., 2008, and Tiscareno et al., 2010). The ring moons Pan and Daphnis are massive enough to maintain the circumferential Encke and Keeler gaps in Saturn’s A ring and were detected by Showalter (1991) and Porco (2005) in Voyager and Cassini images, respectively. In this thesis, a nonlinear axisymmetric diffusion model is developed to describe radial density profiles of circumferential gaps in planetary rings created by embedded moons (Grätz et al., 2018). The model accounts for the gravitational scattering of the ring particles by the embedded moon and for the counteracting viscous diffusion of the ring matter back into the gap. With test particle simulations it is shown that the scattering of the ring particles passing the moon is larger for small impact parameters than estimated by Goldreich and Tremaine (1980). This is especially significant for the modeling of the Keeler gap. The model is applied to the Encke and Keeler gaps with the aim to estimate the shear viscosity of the ring in their vicinities. In addition, the model is used to analyze whether tiny icy moons whose dimensions lie below Cassini’s resolution capabilities would be able to cause the poorly understood gap structure of the C ring and the Cassini Division. One of the most intriguing facets of Saturn’s rings are the extremely sharp edges of the Encke and Keeler gaps: UVIS-scans of their gap edges show that the optical depth drops from order unity to zero over a range of far less than 100 m, a spatial scale comparable to the ring’s vertical extent. This occurs despite the fact that the range over which a moon transfers angular momentum onto the ring material is much larger. Borderies et al. (1982, 1989) have shown that this striking feature is likely related to the local reversal of the usually outward-directed viscous transport of angular momentum in strongly perturbed regions. We have revised the Borderies et al. (1989) model using a granular flow model to define the shear and bulk viscosities, ν and ζ, in order to incorporate the angular momentum flux reversal effect into the axisymmetric diffusion model for circumferential gaps presented in this thesis (Grätz et al., 2019). The sharp Encke and Keeler gap edges are modeled and conclusions regarding the shear and bulk viscosities of the ring are discussed. Finally, we explore the question of whether the radial density profile of the central and outer A ring, recently measured by Tiscareno and Harris (2018) in the highest resolution to date, and in particular, the sharp outer A ring edge can be modeled consistently from the balance of gravitational scattering by several outer moons and the mass and momentum transport. To this aim, the developed model is extended to account for the inward drifts caused by multiple discrete and overlapping resonances with multiple outer satellites and is then used to hydrodynamically simulate the normalized surface mass density profile of the A ring. This section of the thesis is based on studies by Tajeddine et al. (2017a) who recently discussed the common misconception that the 7:6 resonance with Janus alone maintains the outer A ring edge, showing that the combined effort of several resonances with several outer moons is required to confine the A ring as observed by the Cassini spacecraft.
KW  - celestial mechanics
KW  - diffusion
KW  - hydrodynamics
KW  - planets and satellites: rings
KW  - scattering
Y1  - 2020
ER  - 
TY  - JOUR
A1  - Omelʹchenko, Oleh E.
T1  - Nonstationary coherence-incoherence patterns in nonlocally coupled heterogeneous phase oscillators
JF  - Chaos : an interdisciplinary journal of nonlinear science
N2  - We consider a large ring of nonlocally coupled phase oscillators and show that apart from stationary chimera states, this system also supports nonstationary coherence-incoherence patterns (CIPs). For identical oscillators, these CIPs behave as breathing chimera states and are found in a relatively small parameter region only. It turns out that the stability region of these states enlarges dramatically if a certain amount of spatially uniform heterogeneity (e.g., Lorentzian distribution of natural frequencies) is introduced in the system. In this case, nonstationary CIPs can be studied as stable quasiperiodic solutions of a corresponding mean-field equation, formally describing the infinite system limit. Carrying out direct numerical simulations of the mean-field equation, we find different types of nonstationary CIPs with pulsing and/or alternating chimera-like behavior. Moreover, we reveal a complex bifurcation scenario underlying the transformation of these CIPs into each other. These theoretical predictions are confirmed by numerical simulations of the original coupled oscillator system.
KW  - chimera states
KW  - synchronization
KW  - networks
KW  - Kuramoto
KW  - populations
KW  - dynamics
KW  - bumps
KW  - model
Y1  - 2020
U6  - https://doi.org/10.1063/1.5145259
SN  - 1054-1500
SN  - 1089-7682
VL  - 30
IS  - 4
PB  - American Institute of Physics
CY  - Melville
ER  -