TY - JOUR
A1 - Smirnov, Artem
A1 - Berrendorf, Max
A1 - Shprits, Yuri Y.
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 - 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 - JOUR
A1 - Chen, Junchao
A1 - Lange, Thomas
A1 - Andjelkovic, Milos
A1 - Simevski, Aleksandar
A1 - Krstić, Miloš
T1 - Prediction of solar particle events with SRAM-based soft error rate monitor and supervised machine learning
JF - Microelectronics reliability
N2 - This work introduces an embedded approach for the prediction of Solar Particle Events (SPEs) in space applications by combining the real-time Soft Error Rate (SER) measurement with SRAM-based detector and the offline trained machine learning model. The proposed approach is intended for the self-adaptive fault-tolerant multiprocessing systems employed in space applications. With respect to the state-of-the-art, our solution allows for predicting the SER 1 h in advance and fine-grained hourly tracking of SER variations during SPEs as well as under normal conditions. Therefore, the target system can activate the appropriate mechanisms for radiation hardening before the onset of high radiation levels. Based on the comparison of five different machine learning algorithms trained with the public space flux database, the preliminary results indicate that the best prediction accuracy is achieved with the recurrent neural network (RNN) with long short-term memory (LSTM).
Y1 - 2020
U6 - https://doi.org/10.1016/j.microrel.2020.113799
SN - 0026-2714
VL - 114
PB - Elsevier
CY - Oxford
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 - 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 - Sandberg, Oskar J.
A1 - Kurpiers, Jona
A1 - Stolterfoht, Martin
A1 - Neher, Dieter
A1 - Meredith, Paul
A1 - Shoaee, Safa
A1 - Armin, Ardalan
T1 - On the question of the need for a built-in potential in Perovskite solar cells
JF - Advanced materials interfaces
N2 - Perovskite semiconductors as the active materials in efficient solar cells exhibit free carrier diffusion lengths on the order of microns at low illumination fluxes and many hundreds of nanometers under 1 sun conditions. These lengthscales are significantly larger than typical junction thicknesses, and thus the carrier transport and charge collection should be expected to be diffusion controlled. A consensus along these lines is emerging in the field. However, the question as to whether the built-in potential plays any role is still of matter of some conjecture. This important question using phase-sensitive photocurrent measurements and theoretical device simulations based upon the drift-diffusion framework is addressed. In particular, the role of the built-in electric field and charge-selective transport layers in state-of-the-art p-i-n perovskite solar cells comparing experimental findings and simulation predictions is probed. It is found that while charge collection in the junction does not require a drift field per se, a built-in potential is still needed to avoid the formation of reverse electric fields inside the active layer, and to ensure efficient extraction through the charge transport layers.
KW - built-in potential
KW - charge collection
KW - charge transport layers
KW - perovskite solar cells
Y1 - 2020
U6 - https://doi.org/10.1002/admi.202000041
SN - 2196-7350
VL - 7
IS - 10
PB - Wiley
CY - Hoboken
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 - 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 - Kirchartz, Thomas
A1 - Márquez, José A.
A1 - Stolterfoht, Martin
A1 - Unold, Thomas
T1 - Photoluminescence-based characterization of halide perovskites for photovoltaics
JF - Advanced Energy Materials
N2 - Photoluminescence spectroscopy is a widely applied characterization technique for semiconductor materials in general and halide perovskite solar cell materials in particular. It can give direct information on the recombination kinetics and processes as well as the internal electrochemical potential of free charge carriers in single semiconductor layers, layer stacks with transport layers, and complete solar cells. The correct evaluation and interpretation of photoluminescence requires the consideration of proper excitation conditions, calibration and application of the appropriate approximations to the rather complex theory, which includes radiative recombination, non-radiative recombination, interface recombination, charge transfer, and photon recycling. In this article, an overview is given of the theory and application to specific halide perovskite compositions, illustrating the variables that should be considered when applying photoluminescence analysis in these materials.
KW - metal halide perovskites
KW - numerical simulations
KW - photoluminescence
KW - photon recycling
Y1 - 2020
U6 - https://doi.org/10.1002/aenm.201904134
SN - 1614-6832
SN - 1614-6840
VL - 10
IS - 26
SP - 1
EP - 21
PB - Wiley
CY - Weinheim
ER -
TY - GEN
A1 - Kirchartz, Thomas
A1 - Márquez, José A.
A1 - Stolterfoht, Martin
A1 - Unold, Thomas
T1 - Photoluminescence-based characterization of halide perovskites for photovoltaics
T2 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe
N2 - Photoluminescence spectroscopy is a widely applied characterization technique for semiconductor materials in general and halide perovskite solar cell materials in particular. It can give direct information on the recombination kinetics and processes as well as the internal electrochemical potential of free charge carriers in single semiconductor layers, layer stacks with transport layers, and complete solar cells. The correct evaluation and interpretation of photoluminescence requires the consideration of proper excitation conditions, calibration and application of the appropriate approximations to the rather complex theory, which includes radiative recombination, non-radiative recombination, interface recombination, charge transfer, and photon recycling. In this article, an overview is given of the theory and application to specific halide perovskite compositions, illustrating the variables that should be considered when applying photoluminescence analysis in these materials.
T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1419
KW - metal halide perovskites
KW - numerical simulations
KW - photoluminescence
KW - photon recycling
Y1 - 2020
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-519702
SN - 1866-8372
IS - 26
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 - JOUR
A1 - Samson, Stephanie
A1 - Rech, Jeromy
A1 - Perdigón-Toro, Lorena
A1 - Peng, Zhengxing
A1 - Shoaee, Safa
A1 - Ade, Harald
A1 - Neher, Dieter
A1 - Stolterfoht, Martin
A1 - You, Wei
T1 - Organic solar cells with large insensitivity to donor polymer molar mass across all acceptor classes
JF - ACS applied polymer materials
N2 - Donor polymer number-average molar mass (M-n) has long been known to influence organic photovoltaic (OPV) performance via changes in both the polymer properties and the resulting bulk heterojunction morphology. The exact nature of these M-n effects varies from system to system, although there is generally some intermediate M-n that results in optimal performance. Interestingly, our earlier work with the difluorobenzotriazole (FTAZ)-based donor polymer, paired with either N2200 (polymer acceptor) or PC61BM (fullerene acceptor), PcBm demonstrated <10% variation in power conversion efficiency and a consistent morphology over a large span of M-n (30 kg/mol to over 100 kg/mol). Would such insensitivity to polymer M-n still hold true when prevailing small molecular acceptors were used with FTAZ? To answer this question, we explored the impact of FTAZ on OPVs with ITIC, a high-performance small-molecule fused-ring electron acceptor (FREA). By probing the photovoltaic characteristics of the resulting OPVs, we show that a similar FTAZ mn insensitivity is also found in the FTAZ:ITIC system. This study highlights a single-donor polymer which, when paired with an archetypal fullerene, polymer, and FREA, results in systems that are largely insensitive to donor M. Our results may have implications in polymer batch-to-batch reproducibility, in particular, relaxing the need for tight M-n control during synthesis.
KW - polymer solar cells
KW - conjugated polymers
KW - fullerenes
KW - fluorination
KW - molecular weight
KW - non-fullerene acceptors
KW - power conversion efficiency
Y1 - 2020
U6 - https://doi.org/10.1021/acsapm.0c01041
SN - 2637-6105
VL - 2
IS - 11
SP - 5300
EP - 5308
PB - American Chemical Society
CY - Washington
ER -
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 - Raoufi, Meysam
A1 - Hörmann, Ulrich
A1 - Ligorio, Giovanni
A1 - Hildebrandt, Jana
A1 - Pätzel, Michael
A1 - Schultz, Thorsten
A1 - Perdigón-Toro, Lorena
A1 - Koch, Norbert
A1 - List-Kratochvil, Emil
A1 - Hecht, Stefan
A1 - Neher, Dieter
T1 - Simultaneous effect of ultraviolet radiation and surface modification on the work function and hole injection properties of ZnO thin films
JF - Physica Status Solidi. A , Applications and materials science
N2 - The combined effect of ultraviolet (UV) light soaking and self-assembled monolayer deposition on the work function (WF) of thin ZnO layers and on the efficiency of hole injection into the prototypical conjugated polymer poly(3-hexylthiophen-2,5-diyl) (P3HT) is systematically investigated. It is shown that the WF and injection efficiency depend strongly on the history of UV light exposure. Proper treatment of the ZnO layer enables ohmic hole injection into P3HT, demonstrating ZnO as a potential anode material for organic optoelectronic devices. The results also suggest that valid conclusions on the energy-level alignment at the ZnO/organic interfaces may only be drawn if the illumination history is precisely known and controlled. This is inherently problematic when comparing electronic data from ultraviolet photoelectron spectroscopy (UPS) measurements carried out under different or ill-defined illumination conditions.
KW - charge injection across hybrid interfaces
KW - energy-level alignments
KW - hybrid metal oxides
KW - organic interfaces
Y1 - 2020
U6 - https://doi.org/10.1002/pssa.201900876
SN - 1862-6300
SN - 1862-6319
VL - 217
IS - 5
SP - 1
EP - 6
PB - Wiley-VCH
CY - Weinheim
ER -
TY - THES
A1 - Jay, Raphael Martin
T1 - Principles of charge distribution and separation
BT - the case of iron complexes probed by X-ray spectroscopy
N2 - The electronic charge distributions of transition metal complexes fundamentally determine their chemical reactivity. Experimental access to the local valence electronic structure is therefore crucial in order to determine how frontier orbitals are delocalized between different atomic sites and electronic charge is spread throughout the transition metal complex. To that end, X-ray spectroscopies are employed in this thesis to study a series of solution-phase iron complexes with respect to the response of their local electronic charge distributions to different external influences. Using resonant inelastic X-ray scattering (RIXS) and X-ray absorption spectroscopy (XAS) at the iron L-edge, changes in local charge densities are investigated at the iron center depending on different ligand cages as well as solvent environments. A varying degree of charge delocalization from the metal center onto the ligands is observed, which is governed by the capabilities of the ligands to accept charge density into their unoccupied orbitals. Specific solvents are furthermore shown to amplify this process. Solvent molecules of strong Lewis-acids withdraw charge from the ligand allowing in turn for more metal charge to be delocalized onto the ligand. The resulting local charge deficiencies at the metal center are, however, counteracted by competing electron-donation channels from the ligand towards the iron, which are additionally revealed. This is interpreted as a compensating effect which strives to maintain local charge densities at the iron center. This mechanism of charge density preservation is found to be of general nature. Using time-resolved RIXS and XAS at the iron L-edge, an analogous interplay of electron donation and back-donation channels is also revealed for the case of charge-transfer excited states. In such transient configurations, the electronic occupation of iron-centered frontier orbitals has been altered by an optical excitation. Changes in local charge densities that are expected to follow an increased or decreased population of iron-centered orbitals are, however, again counteracted. By scaling the degree of electron donation from the ligand onto the metal, local charge densities at the iron center can be efficiently maintained. Since charge-transfer excitations, however, often constitute the initial step in many electron transfer processes, these findings challenge common notions of charge-separation in transition metal dyes.
KW - L-edge spectroscopy
KW - charge-transfer excitations
KW - transition metal complexes
KW - electronic structure
KW - photo-chemical pathways
Y1 - 2020
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 - 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
(stat)degrees
stat degrees +/- 0.05
(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
(+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 - 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 - Cervantes Villa, Juan Sebastian
A1 - Shprits, Yuri Y.
A1 - Aseev, Nikita
A1 - Allison, Hayley J.
T1 - Quantifying the effects of EMIC wave scattering and magnetopause shadowing in the outer electron radiation belt by means of data assimilation
JF - Journal of geophysical research : Space physics
N2 - In this study we investigate two distinct loss mechanisms responsible for the rapid dropouts of radiation belt electrons by assimilating data from Van Allen Probes A and B and Geostationary Operational Environmental Satellites (GOES) 13 and 15 into a 3-D diffusion model. In particular, we examine the respective contribution of electromagnetic ion cyclotron (EMIC) wave scattering and magnetopause shadowing for values of the first adiabatic invariant mu ranging from 300 to 3,000 MeV G(-1). We inspect the innovation vector and perform a statistical analysis to quantitatively assess the effect of both processes as a function of various geomagnetic indices, solar wind parameters, and radial distance from the Earth. Our results are in agreement with previous studies that demonstrated the energy dependence of these two mechanisms. We show that EMIC wave scattering tends to dominate loss at lower L shells, and it may amount to between 10%/hr and 30%/hr of the maximum value of phase space density (PSD) over all L shells for fixed first and second adiabatic invariants. On the other hand, magnetopause shadowing is found to deplete electrons across all energies, mostly at higher L shells, resulting in loss from 50%/hr to 70%/hr of the maximum PSD. Nevertheless, during times of enhanced geomagnetic activity, both processes can operate beyond such location and encompass the entire outer radiation belt.
Y1 - 2020
U6 - https://doi.org/10.1029/2020JA028208
SN - 2169-9380
SN - 2169-9402
VL - 125
IS - 8
PB - American Geophysical Union
CY - Washington
ER -
TY - THES
A1 - Köhler, Raphael
T1 - Towards seasonal prediction: stratosphere-troposphere coupling in the atmospheric model ICON-NWP
N2 - Stratospheric variability is one of the main potential sources for sub-seasonal to seasonal predictability in mid-latitudes in winter. Stratospheric pathways play an important role for long-range teleconnections between tropical phenomena, such as the quasi-biennial oscillation (QBO) and El Niño-Southern Oscillation (ENSO), and the mid-latitudes on the one hand, and linkages between Arctic climate change and the mid-latitudes on the other hand. In order to move forward in the field of extratropical seasonal predictions, it is essential that an atmospheric model is able to realistically simulate the stratospheric circulation and variability. The numerical weather prediction (NWP) configuration of the ICOsahedral Non-hydrostatic atmosphere model ICON is currently being used by the German Meteorological Service for the regular weather forecast, and is intended to produce seasonal predictions in future. This thesis represents the first extensive evaluation of Northern Hemisphere stratospheric winter circulation in ICON-NWP by analysing a large set of seasonal ensemble experiments.
An ICON control climatology simulated with a default setup is able to reproduce the basic behaviour of the stratospheric polar vortex. However, stratospheric westerlies are significantly too weak and major stratospheric warmings too frequent, especially in January. The weak stratospheric polar vortex in ICON is furthermore connected to a mean sea level pressure (MSLP) bias pattern resembling the negative phase of the Arctic Oscillation (AO). Since a good representation of the drag exerted by gravity waves is crucial for a realistic simulation of the stratosphere, three sensitivity experiments with reduced gravity wave drag are performed. Both a reduction of the non-orographic and orographic gravity wave drag respectively, lead to a strengthening of the stratospheric vortex and thus a bias reduction in winter, in particular in January. However, the effect of the non-orographic gravity wave drag on the stratosphere is stronger. A third experiment, combining a reduced orographic and non-orographic drag, exhibits the largest stratospheric bias reductions. The analysis of stratosphere-troposphere coupling based on an index of the Northern Annular Mode demonstrates that ICON realistically represents downward coupling. This coupling is intensified and more realistic in experiments with a reduced gravity wave drag, in particular with reduced non-orographic drag. Tropospheric circulation is also affected by the reduced gravity wave drag, especially in January, when the strongly improved stratospheric circulation reduces biases in the MSLP patterns. Moreover, a retuning of the subgrid-scale orography parameterisations leads to a significant error reduction in the MSLP in all months. In conclusion, the combination of these adjusted parameterisations is recommended as a current optimal setup for seasonal simulations with ICON.
Additionally, this thesis discusses further possible influences on the stratospheric polar vortex, including the influence of tropical phenomena, such as QBO and ENSO, as well as the influence of a rapidly warming Arctic. ICON does not simulate the quasi-oscillatory behaviour of the QBO and favours weak easterlies in the tropical stratosphere. A comparison with a reanalysis composite of the easterly QBO phase reveals, that the shift towards the easterly QBO in ICON further weakens the stratospheric polar vortex. On the other hand, the stratospheric reaction to ENSO events in ICON is realistic. ICON and the reanalysis exhibit a weakened stratospheric vortex in warm ENSO years. Furthermore, in particular in winter, warm ENSO events favour the negative phase of the Arctic Oscillation, whereas cold events favour the positive phase. The ICON simulations also suggest a significant effect of ENSO on the Atlantic-European sector in late winter. To investigate the influence of Arctic climate change on mid-latitude circulation changes, two differing approaches with transient and fixed sea ice conditions are chosen. Neither ICON approach exhibits the mid-latitude tropospheric negative Arctic Oscillation circulation response to amplified Arctic warming, as it is discussed on the basis of observational evidence. Nevertheless, adding a new model to the current and active discussion on Arctic-midlatitude linkages, further contributes to the understanding of divergent conclusions between model and observational studies.
N2 - Die stratosphärische Variabilität ist eine der wichtigsten potentiellen Quellen für die Vorhersagbarkeit der atmosphärischen Zirkulation in den mittleren Breiten im Winter auf der Zeitskala von Wochen bis zu Jahreszeiten. Stratosphärische Prozesse spielen eine grundlegende Rolle für die Fernverbindungen (Telekonnektionen) zwischen tropischen Klimaphänomenen, wie der quasi-zweijährigen Schwingung (QBO) oder „El Niño-Südliche Oszillation“ (ENSO), und den mittleren Breiten, sowie den Telekonnektionen zwischen arktischen Klimaänderungen und der atmosphärischen Zirkulation in den mittleren Breiten. Die Fähigkeit eines atmosphärischen Modells, die stratosphärische Zirkulation und deren Variabilität realistisch zu simulieren, ist deshalb von grundlegender Bedeutung, um die Jahreszeitenvorhersage in den mittleren Breiten deutlich zu verbessern. Das nichthydrostatische Atmosphärenmodell ICON (ICOsahedral Non-hydrostatic atmosphere model) wird gegenwärtig beim Deutschen Wetterdienst (DWD) in der numerischen Wettervorhersagekonfiguration (ICON-NWP) für die Wettervorhersage genutzt, und soll zukünftig auch für Jahreszeitenvorhersagen benutzt werden. Darauf basierend, präsentiert die vorliegende Arbeit eine Vielzahl von saisonalen Ensembleexperimenten mit ICON-NWP und liefert damit die erste umfassende Bewertung der stratosphärischen Winterzirkulation der nördlichen Hemisphäre in ICON-NWP.
Die Klimatologie eines ICON-Modelllaufs im Standardsetup reproduziert die grundlegenden Eigenschaften des stratosphärischen Polarwirbels. Allerdings sind die stratosphärischen Westwinde deutlich schwächer als in den Beobachtungen, und starke Stratosphärenerwärmungen treten insbesondere im Januar zu häufig auf. Zudem ist der schwache stratosphärische Polarwirbel in ICON mit einem typischen Fehler-Muster des Bodenluftdrucks verknüpft, welches der negativen Phase der Arktischen Oszillation (AO) ähnelt. Da eine gute Darstellung des von Schwerewellen ausgeübten Widerstands für eine realistische Simulation der Stratosphäre entscheidend ist, werden drei Sensitivitätsexperimente mit reduziertem Schwerewellenwiderstand durchgeführt. Sowohl eine Verringerung des nicht-orographischen, als auch eine Verringerung des orographischen Schwerewellenwiderstands führen jeweils zu einer Verstärkung des stratosphärischen Wirbels und damit zu einer Verringerung des Fehlers im Winter, insbesondere im Januar. Die Wirkung des nicht-orographischen Schwerewellenwiderstands auf die Stratosphäre ist hierbei jedoch stärker. Ein drittes Experiment, welches den reduzierten orographischen und nicht-orographischen Widerstand kombiniert, zeigt die größten Verbesserungen in der Stratosphäre. Die auf dem Index des „Northern Annular Mode“ basierende Analyse der Stratosphären-Troposphären-Kopplung zeigt, dass ICON die nach unten gerichtete Kopplung zwischen der Stratosphäre und Troposphäre realistisch darstellt. Diese Kopplung wird in Experimenten mit einem reduzierten Schwerewellenwiderstand verstärkt und realistischer dargestellt, dies gilt insbesondere für den reduzierten nicht-orographischen Widerstand. Auch die troposphärische Zirkulation wird durch den reduzierten Schwerewellenwiderstand beeinflusst, vor allem im Januar, wenn die stark verbesserte stratosphärische Zirkulation den Fehler in den Bodenluftdruckfeldern reduziert. Darüber hinaus führt ein Tuning der Parameterisierung der subgrid-skaligen orographischen Schwerewellen zu einer signifikanten Fehlerreduktion des Bodenluftdrucks in allen Monaten. Die Kombination all dieser angepassten Parametrisierungen wird als derzeit optimales Setup für Jahreszeiten-Simulationen mit ICON vorgeschlagen.
Darüber hinaus werden in dieser Arbeit weitere mögliche Einflussfaktoren auf den stratosphärischen Polarwirbel diskutiert, darunter der Einfluss tropischer Phänomene, wie QBO und ENSO, sowie der Einfluss einer sich rasch erwärmenden Arktis. Das quasi-oszillierende Verhalten der QBO wird durch ICON nicht simuliert, sodass schwache Ostwinde in der tropischen Stratosphäre dominieren. Ein Vergleich mit einem Reanalyse-Komposit der östlichen QBO-Phase zeigt, dass die Verschiebung in Richtung der östlichen QBO in ICON den stratosphärischen Polarwirbel weiter abschwächt. Die stratosphärische Reaktion auf ENSO-Ereignisse in ICON ist jedoch realistisch. ICON und Reanalysedaten zeigen einen abgeschwächten Stratosphärenwirbel in warmen ENSO-Jahren. Darüber hinaus begünstigen insbesondere im Winter warme ENSO-Ereignisse die negative Phase der Arktischen Oszillation, während kalte Ereignisse die positive Phase begünstigen. Die ICON-Simulationen deuten auch auf einen signifikanten Effekt von ENSO auf den atlantisch-europäischen Sektor im Spätwinter hin. Um den Einfluss des arktischen Klimawandels auf Änderungen der Zirkulation in mittleren Breiten zu untersuchen, werden zwei unterschiedliche Ansätze mit transienten und festen Meereisgrenzen gewählt. Keiner der beiden ICON-Ansätze zeigt eine Tendenz zur negativen Phase der Arktische Oszillation als Reaktion auf die verstärkte Erwärmung der Arktis, wie sie in der Literatur anhand von Beobachtungsdaten häufig diskutiert wird. Jedoch wird somit der aktuellen und aktiven Diskussion zu den Auswirkungen des arktischen Klimawandels auf die Zirkulation der mittleren Breiten ein neues Modell hinzugefügt.
T2 - Im Hinblick auf die Jahreszeitenvorhersage: Stratosphären-Troposphären-Kopplung in dem Atmosphärenmodell ICON-NWP
KW - Seasonal prediction
KW - Stratosphere-troposphere coupling
KW - ICON
KW - Stratospheric polar vortex
KW - Jahreszeitenvorhersage
KW - Stratosphären-Troposphären-Kopplung
KW - ICON
KW - Stratosphärischer Polarwirbel
KW - El Niño-Southern Oscillation (ENSO)
KW - El Niño-Südliche Oszillation
KW - Arctic-midlatitude linkages
KW - Verbindungspfade zwischen der Arktis und den mittleren Breiten
Y1 - 2020
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-487231
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 - 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 -