TY  - JOUR
A1  - Freitas, Celso
A1  - Macau, Elbert
A1  - Pikovskij, Arkadij
T1  - Partial synchronization in networks of non-linearly coupled oscillators: The Deserter Hubs Model
JF  - Chaos : an interdisciplinary journal of nonlinear science
N2  - We study the Deserter Hubs Model: a Kuramoto-like model of coupled identical phase oscillators on a network, where attractive and repulsive couplings are balanced dynamically due to nonlinearity of interactions. Under weak force, an oscillator tends to follow the phase of its neighbors, but if an oscillator is compelled to follow its peers by a sufficient large number of cohesive neighbors, then it actually starts to act in the opposite manner, i.e., in anti-phase with the majority. Analytic results yield that if the repulsion parameter is small enough in comparison with the degree of the maximum hub, then the full synchronization state is locally stable. Numerical experiments are performed to explore the model beyond this threshold, where the overall cohesion is lost. We report in detail partially synchronous dynamical regimes, like stationary phase-locking, multistability, periodic and chaotic states. Via statistical analysis of different network organizations like tree, scale-free, and random ones, we found a measure allowing one to predict relative abundance of partially synchronous stationary states in comparison to time-dependent ones. (C) 2015 AIP Publishing LLC.
Y1  - 2015
U6  - https://doi.org/10.1063/1.4919246
SN  - 1054-1500
SN  - 1089-7682
VL  - 25
IS  - 4
PB  - American Institute of Physics
CY  - Melville
ER  - 
TY  - JOUR
A1  - Frieler, Katja
A1  - Clark, Peter U.
A1  - He, Feng
A1  - Buizert, Christo
A1  - Reese, Ronja
A1  - Ligtenberg, Stefan R. M.
A1  - van den Broeke, Michiel R.
A1  - Winkelmann, Ricarda
A1  - Levermann, Anders
T1  - Consistent evidence of increasing Antarctic accumulation with warming
JF  - Nature climate change
N2  - Projections of changes in Antarctic Ice Sheet (AIS) surface mass balance indicate a negative contribution to sea level because of the expected increase in precipitation due to the higher moisture holding capacity of warmer air(1). Observations over the past decades, however, are unable to constrain the relation between temperature and accumulation changes because both are dominated by strong natural variability(2-5). Here we derive a consistent continental-scale increase in accumulation of approximately 5 +/- 1% K-1, through the assessment of ice-core data (spanning the large temperature change during the last deglaciation, 21,000 to 10,000 years ago), in combination with palaeo-simulations, future projections by 35 general circulation models (GCMs), and one high-resolution future simulation. The ice-core data and modelling results for the last deglaciation agree, showing uniform local sensitivities of similar to 6% K-1. The palaeo-simulation allows for a continental-scale aggregation of accumulation changes reaching 4.3% K-1. Despite the different timescales, these sensitivities agree with the multi-model mean of 6.1 +/- 2.6% K-1 (GCMprojections) and the continental-scale sensitivity of 4.9% K-1 (high-resolution future simulation). Because some of the mass gain of the AIS is offset by dynamical losses induced by accumulation(6,7), we provide a response function allowing projections of sea-level fall in terms of continental-scale accumulation changes that compete with surface melting and dynamical losses induced by other mechanisms(6,8,9).
Y1  - 2015
U6  - https://doi.org/10.1038/nclimate2574
SN  - 1758-678X
SN  - 1758-6798
VL  - 5
IS  - 4
SP  - 348
EP  - 352
PB  - Nature Publ. Group
CY  - London
ER  - 
TY  - JOUR
A1  - Furniss, A.
A1  - Noda, K.
A1  - Boggs, S.
A1  - Chiang, J.
A1  - Christensen, F.
A1  - Craig, W.
A1  - Giommi, P.
A1  - Hailey, C.
A1  - Harisson, F.
A1  - Madejski, G.
A1  - Nalewajko, K.
A1  - Perri, M.
A1  - Stern, D.
A1  - Urry, M.
A1  - Verrecchia, F.
A1  - Zhang, W.
A1  - Ahnen, M. L.
A1  - Ansoldi, S.
A1  - Antonelli, L. A.
A1  - Antoranz, P.
A1  - Babic, A.
A1  - Banerjee, B.
A1  - Bangale, P.
A1  - de Almeida, U. Barres
A1  - Barrio, J. A.
A1  - Becerra Gonzalez, J.
A1  - Bednarek, W.
A1  - Bernardini, E.
A1  - Biasuzzi, B.
A1  - Biland, A.
A1  - Blanch Bigas, O.
A1  - Bonnefoy, S.
A1  - Bonnoli, G.
A1  - Borracci, F.
A1  - Bretz, T.
A1  - Carmona, E.
A1  - Carosi, A.
A1  - Chatterjee, A.
A1  - Clavero, R.
A1  - Colin, P.
A1  - Colombo, E.
A1  - Contreras, J. L.
A1  - Cortina, J.
A1  - Covino, S.
A1  - Da Vela, P.
A1  - Dazzi, F.
A1  - De Angelis, A.
A1  - De Caneva, G.
A1  - De Lotto, B.
A1  - de Ona Wilhelmi, E.
A1  - Delgado Mendez, C.
A1  - Di Pierro, F.
A1  - Prester, Dijana Dominis
A1  - Dorner, D.
A1  - Doro, M.
A1  - Einecke, S.
A1  - Eisenacher Glawion, D.
A1  - Elsaesser, D.
A1  - Fernandez-Barral, A.
A1  - Fidalgo, D.
A1  - Fonseca, M. V.
A1  - Font, L.
A1  - Frantzen, K.
A1  - Fruck, C.
A1  - Galindo, D.
A1  - Garcia Lopez, R. J.
A1  - Garczarczyk, M.
A1  - Garrido Terrats, D.
A1  - Gaug, M.
A1  - Giammaria, P.
A1  - Godinovic, N.
A1  - Gonzalez Munoz, A.
A1  - Guberman, D.
A1  - Hanabata, Y.
A1  - Hayashida, M.
A1  - Herrera, J.
A1  - Hose, J.
A1  - Hrupec, D.
A1  - Hughes, G.
A1  - Idec, W.
A1  - Kellermann, H.
A1  - Kodani, K.
A1  - Konno, Y.
A1  - Kubo, H.
A1  - Kushida, J.
A1  - La Barbera, A.
A1  - Lelas, D.
A1  - Lewandowska, N.
A1  - Lindfors, E.
A1  - Lombardi, S.
A1  - Longo, F.
A1  - Lopez, M.
A1  - Lopez-Coto, R.
A1  - Lopez-Oramas, A.
A1  - Lorenz, E.
A1  - Majumdar, P.
A1  - Makariev, M.
A1  - Mallot, K.
A1  - Maneva, G.
A1  - Manganaro, M.
A1  - Mannheim, K.
A1  - Maraschi, L.
A1  - Marcote, B.
A1  - Mariotti, M.
A1  - Martinez, M.
A1  - Mazin, D.
A1  - Menzel, U.
A1  - Miranda, J. M.
A1  - Mirzoyan, R.
A1  - Moralejo, A.
A1  - Nakajima, D.
A1  - Neustroev, V.
A1  - Niedzwiecki, A.
A1  - Nievas Rosillo, M.
A1  - Nilsson, K.
A1  - Nishijima, K.
A1  - Orito, R.
A1  - Overkemping, A.
A1  - Paiano, S.
A1  - Palacio, J.
A1  - Palatiello, M.
A1  - Paneque, D.
A1  - Paoletti, R.
A1  - Paredes, J. M.
A1  - Paredes-Fortuny, X.
A1  - Persic, M.
A1  - Poutanen, J.
A1  - Moroni, P. G. Prada
A1  - Prandini, E.
A1  - Puljak, I.
A1  - Reinthal, R.
A1  - Rhode, W.
A1  - Ribo, M.
A1  - Rico, J.
A1  - Garcia, J. Rodriguez
A1  - Saito, T.
A1  - Saito, K.
A1  - Satalecka, K.
A1  - Scapin, V.
A1  - Schultz, C.
A1  - Schweizer, T.
A1  - Shore, S. N.
A1  - Sillanpaa, A.
A1  - Sitarek, J.
A1  - Snidaric, I.
A1  - Sobczynska, D.
A1  - Stamerra, A.
A1  - Steinbring, T.
A1  - Strzys, M.
A1  - Takalo, L.
A1  - Takami, H.
A1  - Tavecchio, F.
A1  - Temnikov, P.
A1  - Terzic, T.
A1  - Tescaro, D.
A1  - Teshima, M.
A1  - Thaele, J.
A1  - Torres, D. F.
A1  - Toyama, T.
A1  - Treves, A.
A1  - Verguilov, V.
A1  - Vovk, I.
A1  - Will, M.
A1  - Zanin, R.
A1  - Archer, A.
A1  - Benbow, W.
A1  - Bird, R.
A1  - Biteau, Jonathan
A1  - Bugaev, V.
A1  - Cardenzana, J. V.
A1  - Cerruti, M.
A1  - Chen, Xuhui
A1  - Ciupik, L.
A1  - Connolly, M. P.
A1  - Cui, W.
A1  - Dickinson, H. J.
A1  - Dumm, J.
A1  - Eisch, J. D.
A1  - Falcone, A.
A1  - Feng, Q.
A1  - Finley, J. P.
A1  - Fleischhack, H.
A1  - Fortin, P.
A1  - Fortson, L.
A1  - Gerard, L.
A1  - Gillanders, G. H.
A1  - Griffin, S.
A1  - Griffiths, S. T.
A1  - Grube, J.
A1  - Gyuk, G.
A1  - Hakansson, Nils
A1  - Holder, J.
A1  - Humensky, T. B.
A1  - Johnson, C. A.
A1  - Kaaret, P.
A1  - Kertzman, M.
A1  - Kieda, D.
A1  - Krause, M.
A1  - Krennrich, F.
A1  - Lang, M. J.
A1  - Lin, T. T. Y.
A1  - Maier, G.
A1  - McArthur, S.
A1  - McCann, A.
A1  - Meagher, K.
A1  - Moriarty, P.
A1  - Mukherjee, R.
A1  - Nieto, D.
A1  - Ong, R. A.
A1  - Park, N.
A1  - Petry, D.
A1  - Pohl, Martin
A1  - Popkow, A.
A1  - Ragan, K.
A1  - Ratliff, G.
A1  - Reyes, L. C.
A1  - Reynolds, P. T.
A1  - Richards, G. T.
A1  - Roache, E.
A1  - Santander, M.
A1  - Sembroski, G. H.
A1  - Shahinyan, K.
A1  - Staszak, D.
A1  - Telezhinsky, Igor O.
A1  - Tucci, J. V.
A1  - Tyler, J.
A1  - Vassiliev, V. V.
A1  - Wakely, S. P.
A1  - Weiner, O. M.
A1  - Weinstein, A.
A1  - Wilhelm, Alina
A1  - Williams, D. A.
A1  - Zitzer, B.
A1  - Vince, O.
A1  - Fuhrmann, L.
A1  - Angelakis, E.
A1  - Karamanavis, V.
A1  - Myserlis, I.
A1  - Krichbaum, T. P.
A1  - Zensus, J. A.
A1  - Ungerechts, H.
A1  - Sievers, A.
A1  - Bachev, R.
A1  - Boettcher, Markus
A1  - Chen, W. P.
A1  - Damljanovic, G.
A1  - Eswaraiah, C.
A1  - Guver, T.
A1  - Hovatta, T.
A1  - Hughes, Z.
A1  - Ibryamov, S. I.
A1  - Joner, M. D.
A1  - Jordan, B.
A1  - Jorstad, S. G.
A1  - Joshi, M.
A1  - Kataoka, J.
A1  - Kurtanidze, O. M.
A1  - Kurtanidze, S. O.
A1  - Lahteenmaki, A.
A1  - Latev, G.
A1  - Lin, H. C.
A1  - Larionov, V. M.
A1  - Mokrushina, A. A.
A1  - Morozova, D. A.
A1  - Nikolashvili, M. G.
A1  - Raiteri, C. M.
A1  - Ramakrishnan, V.
A1  - Readhead, A. C. R.
A1  - Sadun, A. C.
A1  - Sigua, L. A.
A1  - Semkov, E. H.
A1  - Strigachev, A.
A1  - Tammi, J.
A1  - Tornikoski, M.
A1  - Troitskaya, Y. V.
A1  - Troitsky, I. S.
A1  - Villata, M.
T1  - First NuSTAR observations of MRK 501 within a radio to TeV multi-instrument campaign
JF  - The astrophysical journal : an international review of spectroscopy and astronomical physics
N2  - We report on simultaneous broadband observations of the TeV-emitting blazar Markarian 501 between 2013 April 1 and August 10, including the first detailed characterization of the synchrotron peak with Swift and NuSTAR. During the campaign, the nearby BL Lac object was observed in both a quiescent and an elevated state. The broadband campaign includes observations with NuSTAR, MAGIC, VERITAS, the Fermi Large Area Telescope, Swift X-ray Telescope and UV Optical Telescope, various ground-based optical instruments, including the GASP-WEBT program, as well as radio observations by OVRO, Metsahovi, and the F-Gamma consortium. Some of the MAGIC observations were affected by a sand layer from the Saharan desert, and had to be corrected using event-by-event corrections derived with a Light Detection and Ranging (LIDAR) facility. This is the first time that LIDAR information is used to produce a physics result with Cherenkov Telescope data taken during adverse atmospheric conditions, and hence sets a precedent for the current and future ground-based gamma-ray instruments. The NuSTAR instrument provides unprecedented sensitivity in hard X-rays, showing the source to display a spectral energy distribution (SED) between 3 and 79 keV consistent with a log-parabolic spectrum and hard X-ray variability on hour timescales. None (of the four extended NuSTAR observations) show evidence of the onset of inverse-Compton emission at hard X-ray energies. We apply a single-zone equilibrium synchrotron self-Compton (SSC) model to five simultaneous broadband SEDs. We find that the SSC model can reproduce the observed broadband states through a decrease in the magnetic field strength coinciding with an increase in the luminosity and hardness of the relativistic leptons responsible for the high-energy emission.
KW  - BL Lacertae objects: general
KW  - galaxies: individual (Markarian 501)
KW  - X-rays: galaxies
Y1  - 2015
U6  - https://doi.org/10.1088/0004-637X/812/1/65
SN  - 0004-637X
SN  - 1538-4357
VL  - 812
IS  - 1
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Förster, Daniel F.
A1  - Lindenau, Bernd
A1  - Leyendecker, Marko
A1  - Janssen, Franz
A1  - Winkler, Carsten
A1  - Schumann, Frank O.
A1  - Kirschner, Juergen
A1  - Holldack, Karsten
A1  - Föhlisch, Alexander
T1  - Phase-locked MHz pulse selector for x-ray sources
JF  - Optics letters : a publication of the Optical Society of America
N2  - Picosecond x-ray pulses are extracted with a phase-locked x-ray pulse selector at 1.25 MHz repetition rate from the pulse trains of the accelerator-driven multiuser x-ray source BESSY II preserving the peak brilliance at high pulse purity. The system consists of a specially designed in-vacuum chopper wheel rotating with approximate to 1 kHz angular frequency. The wheel is driven in an ultrahigh vacuum and is levitated on magnetic bearings being capable of withstanding high centrifugal forces. Pulses are picked by 1252 high-precision slits of 70 mu m width on the outer rim of the wheel corresponding to a temporal opening window of the chopper of 70 ns. We demonstrate how the electronic phase stabilization of +/- 2 ns together with an arrival time jitter of the individual slits of the same order of magnitude allows us to pick short single bunch x-ray pulses out of a 200 ns ion clearing gap in a multibunch pulse train as emitted from a synchrotron facility at 1.25 MHz repetition rate with a pulse purity below the shot noise detection limit. The approach is applicable to any high-repetition pulsed radiation source, in particular in the x-ray spectral range up to 10 keV. The opening window in a real x-ray beamline, its stability, as well as the limits of mechanical pulse picking techniques in the MHz range are discussed. (C) 2015 Optical Society of America
Y1  - 2015
U6  - https://doi.org/10.1364/OL.40.002265
SN  - 0146-9592
SN  - 1539-4794
VL  - 40
IS  - 10
SP  - 2265
EP  - 2268
PB  - Optical Society of America
CY  - Washington
ER  - 
TY  - JOUR
A1  - Ghani, Fatemeh
A1  - Opitz, Andreas
A1  - Pingel, Patrick
A1  - Heimel, Georg
A1  - Salzmann, Ingo
A1  - Frisch, Johannes
A1  - Neher, Dieter
A1  - Tsami, Argiri
A1  - Scherf, Ullrich
A1  - Koch, Norbert
T1  - Charge Transfer in and Conductivity of Molecularly Doped Thiophene-Based Copolymers
JF  - Journal of polymer science : B, Polymer physics
N2  - The electrical conductivity of organic semiconductors can be enhanced by orders of magnitude via doping with strong molecular electron acceptors or donors. Ground-state integer charge transfer and charge-transfer complex formation between organic semiconductors and molecular dopants have been suggested as the microscopic mechanisms causing these profound changes in electrical materials properties. Here, we study charge-transfer interactions between the common molecular p-dopant 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane and a systematic series of thiophene-based copolymers by a combination of spectroscopic techniques and electrical measurements. Subtle variations in chemical structure are seen to significantly impact the nature of the charge-transfer species and the efficiency of the doping process, underlining the need for a more detailed understanding of the microscopic doping mechanism in organic semiconductors to reliably guide targeted chemical design.
KW  - charge transfer
KW  - conducting polymers
KW  - doping
KW  - thiophene
Y1  - 2015
U6  - https://doi.org/10.1002/polb.23631
SN  - 0887-6266
SN  - 1099-0488
VL  - 53
IS  - 1
SP  - 58
EP  - 63
PB  - Wiley-Blackwell
CY  - Hoboken
ER  - 
TY  - JOUR
A1  - Ghosh, Surya K.
A1  - Cherstvy, Andrey G.
A1  - Metzler, Ralf
T1  - Non-universal tracer diffusion in crowded media of non-inert obstacles
JF  - Physical chemistry, chemical physics : a journal of European Chemical Societies
N2  - We study the diffusion of a tracer particle, which moves in continuum space between a lattice of excluded volume, immobile non-inert obstacles. In particular, we analyse how the strength of the tracer-obstacle interactions and the volume occupancy of the crowders alter the diffusive motion of the tracer. From the details of partitioning of the tracer diffusion modes between trapping states when bound to obstacles and bulk diffusion, we examine the degree of localisation of the tracer in the lattice of crowders. We study the properties of the tracer diffusion in terms of the ensemble and time averaged mean squared displacements, the trapping time distributions, the amplitude variation of the time averaged mean squared displacements, and the non-Gaussianity parameter of the diffusing tracer. We conclude that tracer-obstacle adsorption and binding triggers a transient anomalous diffusion. From a very narrow spread of recorded individual time averaged trajectories we exclude continuous type random walk processes as the underlying physical model of the tracer diffusion in our system. For moderate tracer-crowder attraction the motion is found to be fully ergodic, while at stronger attraction strength a transient disparity between ensemble and time averaged mean squared displacements occurs. We also put our results into perspective with findings from experimental single-particle tracking and simulations of the diffusion of tagged tracers in dense crowded suspensions. Our results have implications for the diffusion, transport, and spreading of chemical components in highly crowded environments inside living cells and other structured liquids.
Y1  - 2015
U6  - https://doi.org/10.1039/c4cp03599b
SN  - 1463-9076
SN  - 1463-9084
VL  - 17
IS  - 3
SP  - 1847
EP  - 1858
PB  - Royal Society of Chemistry
CY  - Cambridge
ER  - 
TY  - JOUR
A1  - Gimenez-Garcia, Angel
A1  - Torrejon, Jose Miguel
A1  - Eikmann, Wiebke
A1  - Martinez-Nunez, Silvia
A1  - Oskinova, Lida
A1  - Rodes-Roca, Jose Joaquin
A1  - Bernabeu, Guillermo
T1  - An XMM-Newton view of FeK alpha in high-mass X-ray binaries
JF  - Astronomy and astrophysics : an international weekly journal
N2  - We present a comprehensive analysis of the whole sample of available XMM-Newton observations of high-mass X-ray binaries (HMXBs) until August 2013, focusing on the FeK alpha emission line. This line is key to better understanding the physical properties of the material surrounding the X-ray source within a few stellar radii (the circumstellar medium). We collected observations from 46 HMXBs and detected FeK alpha in 21 of them. We used the standard classification of HMXBs to divide the sample into different groups. We find that (1) different classes of HMXBs display different qualitative behaviours in the FeK alpha spectral region. This is visible especially in SGXBs (showing ubiquitous Fe fluorescence but not recombination Fe lines) and in gamma Cass analogues (showing both fluorescent and recombination Fe lines). (2) FeK alpha is centred at a mean value of 6.42 keV. Considering the instrumental and fits uncertainties, this value is compatible with ionization states that are lower than Fe xviii. (3) The flux of the continuum is well correlated with the flux of the line, as expected. Eclipse observations show that the Fe fluorescence emission comes from an extended region surrounding the X-ray source. (4) We observe an inverse correlation between the X-ray luminosity and the equivalent width of FeK alpha (EW). This phenomenon is known as the X-ray Baldwin effect. (5) FeK alpha is narrow (sigma(line) < 0.15 keV), reflecting that the reprocessing material does not move at high speeds. We attempt to explain the broadness of the line in terms of three possible broadening phenomena: line blending, Compton scattering, and Doppler shifts (with velocities of the reprocessing material V similar to 1000 km s(-1)). (6) The equivalent hydrogen column (N-H) directly correlates to the EW of FeK alpha, displaying clear similarities to numerical simulations. It highlights the strong link between the absorbing and the fluorescent matter. (7) The observed NH in supergiant X-ray binaries (SGXBs) is in general higher than in supergiant fast X-ray transients (SFXTs). We suggest two possible explanations: different orbital configurations or a different interaction compact object - wind. (8) Finally, we analysed the sources IGR J16320-4751 and 4U 1700-37 in more detail, covering several orbital phases. The observed variation in NH between phases is compatible with the absorption produced by the wind of their optical companions. The results clearly point to a very important contribution of the donor's wind in the FeK alpha emission and the absorption when the donor is a supergiant massive star.
KW  - surveys
KW  - X-rays: binaries
KW  - binaries: general
KW  - circumstellar matter
KW  - stars: winds, outflows
KW  - stars: early-type
Y1  - 2015
U6  - https://doi.org/10.1051/0004-6361/201425004
SN  - 0004-6361
SN  - 1432-0746
VL  - 576
PB  - EDP Sciences
CY  - Les Ulis
ER  - 
TY  - JOUR
A1  - Godec, Aljaz
A1  - Metzler, Ralf
T1  - Optimization and universality of Brownian search in a basic model of quenched heterogeneous media
JF  - Physical review : E, Statistical, nonlinear and soft matter physics
N2  - The kinetics of a variety of transport-controlled processes can be reduced to the problem of determining the mean time needed to arrive at a given location for the first time, the so-called mean first-passage time ( MFPT) problem. The occurrence of occasional large jumps or intermittent patterns combining various types of motion are known to outperform the standard random walk with respect to the MFPT, by reducing oversampling of space. Here we show that a regular but spatially heterogeneous random walk can significantly and universally enhance the search in any spatial dimension. In a generic minimal model we consider a spherically symmetric system comprising two concentric regions with piecewise constant diffusivity. The MFPT is analyzed under the constraint of conserved average dynamics, that is, the spatially averaged diffusivity is kept constant. Our analytical calculations and extensive numerical simulations demonstrate the existence of an optimal heterogeneity minimizing the MFPT to the target. We prove that the MFPT for a random walk is completely dominated by what we term direct trajectories towards the target and reveal a remarkable universality of the spatially heterogeneous search with respect to target size and system dimensionality. In contrast to intermittent strategies, which are most profitable in low spatial dimensions, the spatially inhomogeneous search performs best in higher dimensions. Discussing our results alongside recent experiments on single-particle tracking in living cells, we argue that the observed spatial heterogeneity may be beneficial for cellular signaling processes.
Y1  - 2015
U6  - https://doi.org/10.1103/PhysRevE.91.052134
SN  - 1539-3755
SN  - 1550-2376
VL  - 91
IS  - 5
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Goychuk, Igor
T1  - Modeling magnetosensitive ion channels in the viscoelastic environment of living cells
JF  - Physical review : E, Statistical, nonlinear and soft matter physics
N2  - We propose and study a model of hypothetical magnetosensitive ionic channels which are long thought to be a possible candidate to explain the influence of weak magnetic fields on living organisms ranging from magnetotactic bacteria to fishes, birds, rats, bats, and other mammals including humans. The core of the model is provided by a short chain of magnetosomes serving as a sensor, which is coupled by elastic linkers to the gating elements of ion channels forming a small cluster in the cell membrane. The magnetic sensor is fixed by one end on cytoskeleton elements attached to the membrane and is exposed to viscoelastic cytosol. Its free end can reorient stochastically and subdiffusively in viscoelastic cytosol responding to external magnetic field changes and can open the gates of coupled ion channels. The sensor dynamics is generally bistable due to bistability of the gates which can be in two states with probabilities which depend on the sensor orientation. For realistic parameters, it is shown that this model channel can operate in the magnetic field of Earth for a small number (five to seven) of single-domain magnetosomes constituting the sensor rod, each of which has a typical size found in magnetotactic bacteria and other organisms or even just one sufficiently large nanoparticle of a characteristic size also found in nature. It is shown that, due to the viscoelasticity of the medium, the bistable gating dynamics generally exhibits power law and stretched exponential distributions of the residence times of the channels in their open and closed states. This provides a generic physical mechanism for the explanation of the origin of such anomalous kinetics for other ionic channels whose sensors move in a viscoelastic environment provided by either cytosol or biological membrane, in a quite general context, beyond the fascinating hypothesis of magnetosensitive ionic channels we explore.
Y1  - 2015
U6  - https://doi.org/10.1103/PhysRevE.92.042711
SN  - 1539-3755
SN  - 1550-2376
VL  - 92
IS  - 4
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Goychuk, Igor
T1  - Anomalous transport of subdiffusing cargos by single kinesin motors: the role of mechano-chemical coupling and anharmonicity of tether
JF  - Physical biology : a journal for the fundamental understanding of biological systems
N2  - Here we generalize our previous model of molecular motors trafficking subdiffusing cargos in viscoelastic cytosol by (i) including mechano-chemical coupling between cyclic conformational fluctuations of the motor protein driven by the reaction of ATP hydrolysis and its translational motion within the simplest two-state model of hand-over-hand motion of kinesin, and also (ii) by taking into account the anharmonicity of the tether between the motor and the cargo (its maximally possible extension length). It is shown that the major earlier results such as occurrence of normal versus anomalous transport depending on the amplitude of binding potential, cargo size and the motor turnover frequency not only survive in this more realistic model, but the results also look very similar for the correspondingly adjusted parameters. However, this more realistic model displays a substantially larger thermodynamic efficiency due to a bidirectional mechano-chemical coupling. For realistic parameters, the maximal thermodynamic efficiency can transiently be about 50% as observed for kinesins, and even larger, surprisingly also in a novel strongly anomalous (sub) transport regime, where the motor enzymatic turnovers become also anomalously slow and cannot be characterized by a turnover rate. Here anomalously slow dynamics of the cargo enforces anomalously slow cyclic kinetics of the motor protein.
KW  - anomalous diffusion and transport
KW  - molecular and Brownian motors
KW  - viscoelasticity and memory effects
KW  - mechano-chemical coupling and thermodynamic efficiency
Y1  - 2015
U6  - https://doi.org/10.1088/1478-3975/12/1/016013
SN  - 1478-3967
SN  - 1478-3975
VL  - 12
IS  - 1
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Goychuk, Igor
A1  - Goychuk, Andriy
T1  - Stochastic Wilson-Cowan models of neuronal network dynamics with memory and delay
JF  - New journal of physics : the open-access journal for physics
N2  - We consider a simple Markovian class of the stochastic Wilson-Cowan type models of neuronal network dynamics, which incorporates stochastic delay caused by the existence of a refractory period of neurons. From the point of view of the dynamics of the individual elements, we are dealing with a network of non-Markovian stochastic two-state oscillators with memory, which are coupled globally in a mean-field fashion. This interrelation of a higher-dimensional Markovian and lower-dimensional non-Markovian dynamics is discussed in its relevance to the general problem of the network dynamics of complex elements possessing memory. The simplest model of this class is provided by a three-state Markovian neuron with one refractory state, which causes firing delay with an exponentially decaying memory within the two-state reduced model. This basic model is used to study critical avalanche dynamics (the noise sustained criticality) in a balanced feedforward network consisting of the excitatory and inhibitory neurons. Such avalanches emerge due to the network size dependent noise (mesoscopic noise). Numerical simulations reveal an intermediate power law in the distribution of avalanche sizes with the critical exponent around -1.16. We show that this power law is robust upon a variation of the refractory time over several orders of magnitude. However, the avalanche time distribution is biexponential. It does not reflect any genuine power law dependence.
KW  - neuronal networks
KW  - stochastic models
KW  - memory and delay
KW  - critical avalanche dynamics
Y1  - 2015
U6  - https://doi.org/10.1088/1367-2630/17/4/045029
SN  - 1367-2630
VL  - 17
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Goychuk, Igor
A1  - Goychuk, Andriy
T1  - Stochastic Wilson
BT  - Cowan models of neuronal network dynamics with memory and delay
JF  - New journal of physics
N2  - We consider a simple Markovian class of the stochastic Wilson–Cowan type models of neuronal network dynamics, which incorporates stochastic delay caused by the existence of a refractory period of neurons. From the point of view of the dynamics of the individual elements, we are dealing with a network of non-Markovian stochastic two-state oscillators with memory, which are coupled globally in a mean-field fashion. This interrelation of a higher-dimensional Markovian and lower-dimensional non-Markovian dynamics is discussed in its relevance to the general problem of the network dynamics of complex elements possessing memory. The simplest model of this class is provided by a three-state Markovian neuron with one refractory state, which causes firing delay with an exponentially decaying memory within the two-state reduced model. This basic model is used to study critical avalanche dynamics (the noise sustained criticality) in a balanced feedforward network consisting of the excitatory and inhibitory neurons. Such avalanches emerge due to the network size dependent noise (mesoscopic noise). Numerical simulations reveal an intermediate power law in the distribution of avalanche sizes with the critical exponent around −1.16. We show that this power law is robust upon a variation of the refractory time over several orders of magnitude. However, the avalanche time distribution is biexponential. It does not reflect any genuine power law dependence.
KW  - neuronal networks
KW  - stochastic models
KW  - memory and delay
KW  - critical avalanche dynamics
Y1  - 2015
U6  - https://doi.org/10.1088/1367-2630/17/4/045029
SN  - 1367-2630
VL  - 17
IS  - 4
PB  - Deutsche Physikalische Gesellschaft, Institute of Physics
CY  - Bad Honnef, London
ER  - 
TY  - JOUR
A1  - Haeffner, Stephanie
A1  - Stegmann, Christian
A1  - Jung-Richardt, Ira
T1  - Systematic search for molecular clouds near supernova remnants as sources of very-high-energy gamma-ray emission
JF  - Astroparticle physics
N2  - Supernova remnants accelerate particles up to energies of at least 100 TeV as established by observations in very-high-energy gamma-ray astronomy. Molecular clouds in their vicinity provide an increased amount of target material for proton-proton interaction and subsequent neutral pion decay into gamma-rays of accelerated hadrons escaping the remnant. Therefore, these molecular clouds are potential gamma-ray sources. The gamma-ray emission from these clouds provides a unique environment to derive information on the propagation of very-high-nergy particles through the interstellar medium as well as on the acceleration of hadrons in supernova remnants. Current Imaging Atmospheric Cherenkov Telescope systems are suitable to explore a large parameter space of the propagation properties depending on the age of the supernova remnant and the distance between the remnant and the nearby molecular cloud.
 In this paper we present our strategy and results of a systematic search for gamma-ray emitting molecular clouds near supernova remnants which are potentially detectable with current experiments in the TeV energy range and explore the prospects of future experiments.
KW  - VHE gamma-ray astronomy
KW  - Supernova remnants
KW  - Molecular clouds
KW  - Cosmic rays
KW  - Galactic Ring Survey
KW  - HESS Galactic Plane Survey
Y1  - 2015
U6  - https://doi.org/10.1016/j.astropartphys.2015.05.004
SN  - 0927-6505
SN  - 1873-2852
VL  - 71
SP  - 36
EP  - 44
PB  - Elsevier
CY  - Amsterdam
ER  - 
TY  - JOUR
A1  - Hainich, Rainer
A1  - Pasemann, Diana
A1  - Todt, Helge Tobias
A1  - Shenar, Tomer
A1  - Sander, Andreas Alexander Christoph
A1  - Hamann, Wolf-Rainer
T1  - Wolf-Rayet stars in the Small Magellanic Cloud I. Analysis of the single WN stars
JF  - Astronomy and astrophysics : an international weekly journal
N2  - Context. Wolf-Rayet (WR) stars have a severe impact on their environments owing to their strong ionizing radiation fields and powerful stellar winds. Since these winds are considered to be driven by radiation pressure, it is theoretically expected that the degree of the wind mass-loss depends on the initial metallicity of WR stars.
 Aims. Following our comprehensive studies of WR stars in the Milky Way, M31, and the LMC, we derive stellar parameters and mass-loss rates for all seven putatively single WN stars known in the SMC. Based on these data, we discuss the impact of a low-metallicity environment on the mass loss and evolution of WR stars.
 Methods. The quantitative analysis of the WN stars is performed with the Potsdam Wolf-Rayet (PoWR) model atmosphere code. The physical properties of our program stars are obtained from fitting synthetic spectra to multi-band observations.
 Results. In all SMC WN stars, a considerable surface hydrogen abundance is detectable. The majority of these objects have stellar temperatures exceeding 75 kK, while their luminosities range from 10(5.5) to 10(6.1) L-circle dot. The WN stars in the SMC exhibit on average lower mass-loss rates and weaker winds than their counterparts in the Milky Way, M31, and the LMC.
 Conclusions. By comparing the mass-loss rates derived for WN stars in different Local Group galaxies, we conclude that a clear dependence of the wind mass-loss on the initial metallicity is evident, supporting the current paradigm that WR winds are driven by radiation. A metallicity effect on the evolution of massive stars is obvious from the HRD positions of the SMC WN stars at high temperatures and high luminosities. Standard evolution tracks are not able to reproduce these parameters and the observed surface hydrogen abundances. Homogeneous evolution might provide a better explanation for their evolutionary past.
KW  - stars: Wolf-Rayet
KW  - Magellanic Clouds
KW  - stars: early-type
KW  - stars: atmospheres
KW  - stars: winds, outflows
KW  - stars: mass-loss
Y1  - 2015
U6  - https://doi.org/10.1051/0004-6361/201526241
SN  - 1432-0746
VL  - 581
PB  - EDP Sciences
CY  - Les Ulis
ER  - 
TY  - JOUR
A1  - Hainich, Rainer
A1  - Rühling, U.
A1  - Pasemann, D.
A1  - Hamann, Wolf-Rainer
T1  - The WN population in the Magellanic Clouds
JF  - Wolf-Rayet Stars : Proceedings of an International Workshop held in Potsdam, Germany, 1.–5. June 2015
N2  - A detailed and comprehensive study of the Wolf-Rayet stars of the nitrogen sequence (WN
stars) in the Small Magellanic Cloud (SMC) and the Large Magellanic Cloud (LMC) is presented.
We derived the fundamental stellar and wind parameters for more than 100 massive stars, encompassing almost the whole WN population in the Magellanic Clouds (MCs). The observations are fitted with synthetic spectra, using the PotsdamWolf-Rayet model atmosphere
code (PoWR). For this purpose, large grids of line-blanket models for different metallicities have been calculated, covering a wide range of stellar temperatures, mass-loss rates, and hydrogen abundances. Our comprehensive sample facilitates statistical studies of the WN properties in the MCs without selection bias. To investigate the impact of the low LMC metallicity and the even lower SMC metallicity, we compare our new results to previous analyses of the Galactic WN population and the late type WN stars from M31. Based on these studies we derived an empirical relation between the WN mass-loss rates and the metallicity. Current stellar evolution tracks, even when accounting for rotationally induced mixing, partly fail to reproduce the observed ranges of luminosities and initial masses.
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-87806
SP  - 117
EP  - 120
ER  - 
TY  - JOUR
A1  - Hamann, Wolf-Rainer
T1  - Wind models and spectral analyses
JF  - Wolf-Rayet Stars : Proceedings of an International Workshop held in Potsdam, Germany, 1.–5. June 2015
N2  - The emission-line dominated spectra of Wolf-Rayet stars are formed in expanding layers of their atmosphere, i.e. in their strong stellar wind. Adequate modeling of such spectra has to face a couple of difficulties. Because of the supersonic motion, the radiative transfer is preferably formulated in the co-moving frame. The strong deviations from local thermodynamical equilibrium (LTE) require to solve the equations of statistical equilibrium for the population numbers, accounting for many hundred atomic energy levels and thousands of line transitions. Moreover, millions of lines from iron-group elements must be taken into account for their blanketing effect. Model atmospheres of the described kind can reproduce the observed WR spectra satisfyingly, and have been widely applied for corresponding spectral analyses.
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-87748
SP  - 91
EP  - 96
ER  - 
TY  - JOUR
A1  - Heuer, A.
A1  - Menzel, R.
A1  - Milonni, P. W.
T1  - Induced Coherence, Vacuum Fields, and Complementarity in Biphoton Generation
JF  - Physical review letters
N2  - It is well established that spontaneous parametric down-conversion with induced coherence across two coupled interferometers results in high-visibility single-photon interference. We describe experiments in which additional photon channels are introduced such that "which-path" information is made possible and the fringe visibility in single-photon interference is reduced in accordance with basic notions of complementarity. However, these additional pathways result in nearly perfect visibility when photons are counted in coincidence. A simplified theoretical model accounts for these observations and attributes them directly to the vacuum fields at the different crystals.
Y1  - 2015
U6  - https://doi.org/10.1103/PhysRevLett.114.053601
SN  - 0031-9007
SN  - 1079-7114
VL  - 114
IS  - 5
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Heuer, Axel
A1  - Menzel, Ralf
A1  - Milonni, P. W.
T1  - Complementarity in biphoton generation with stimulated or induced coherence
JF  - Physical review : A, Atomic, molecular, and optical physics
N2  - Coherence can be induced or stimulated in parametric down-conversion using two or three crystals when, for example, the idler modes of the crystals are aligned. Previous experiments with induced coherence [Phys. Rev. Lett. 114, 053601 (2015)] focused on which-path information and the role of vacuum fields in realizing complementarity via reduced visibility in single-photon interference. Here we describe experiments comparing induced and stimulated coherence. Different single-photon interference experiments were performed by blocking one of the pump beams in a three-crystal setup. Each counted photon is emitted from one of two crystals and which-way information may or not be available, depending on the setup. Distinctly different results are obtained in the induced and stimulated cases, especially when a variable transmission filter is inserted between the crystals. A simplified theoretical model accounts for all the experimental results and is also used to address the question of whether the phases of the signal and idler fields in parametric down-conversion are correlated.
Y1  - 2015
U6  - https://doi.org/10.1103/PhysRevA.92.033834
SN  - 1050-2947
SN  - 1094-1622
VL  - 92
IS  - 3
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Hoffmann, Holger
A1  - Seiss, Martin
A1  - Salo, Heikki
A1  - Spahn, Frank
T1  - Vertical structures induced by embedded moonlets in Saturn's rings
JF  - Icarus : international journal of solar system studies
N2  - We study the vertical extent of propeller structures in Saturn's rings (i) by extending the model of Spahn and Sremcevic (Spahn, F., Sremcevic, M. [2000]. Astron. Astrophys., 358, 368-372) to include the vertical direction and (ii) by performing N-body box simulations of a perturbing moonlet embedded into the rings. We find that the gravitational interaction of ring particles with a non-inclined moonlet does not induce considerable vertical excursions of ring particles, but causes a considerable thermal motion in the ring plane. We expect ring particle collisions to partly convert the lateral induced thermal motion into vertical excursions of ring particles in the course of a quasi-thermalization. The N-body box simulations lead to maximal propeller heights of about 0.6-0.8 Hill radii of the embedded perturbing moonlet. Moonlet sizes estimated by this relation are in good agreement with size estimates from radial propeller scalings for the propellers Bleriot and Earhart. For large propellers, the extended hydrodynamical propeller model predicts an exponential propeller height relaxation, confirmed by N-body box simulations of non-self gravitating ring particles. Exponential cooling constants, calculated from the hydrodynamical propeller model agree fairly well with values from fits to the tail of the azimuthal height decay of the N-body box simulations. From exponential cooling constants, determined from shadows cast by the propeller Earhart and imaged by the Cassini spacecraft, we estimate collision frequencies of about 6 collisions per particle per orbit in the propeller gap region and about 11 collisions per particle per orbit in the propeller wake region. (C) 2015 Elsevier Inc. All rights reserved.
KW  - Planetary rings
KW  - Saturn, rings
KW  - Saturn, satellites
KW  - Disks
Y1  - 2015
U6  - https://doi.org/10.1016/j.icarus.2015.02.003
SN  - 0019-1035
SN  - 1090-2643
VL  - 252
SP  - 400
EP  - 414
PB  - Elsevier
CY  - San Diego
ER  - 
TY  - JOUR
A1  - Hubrig, Swetlana
A1  - Schoeller, Markus
A1  - Fossati, Luca
A1  - Morel, Thierry
A1  - Castro, Neves
A1  - Oskinova, Lida
A1  - Przybilla, Norbert
A1  - Eikenberry, Stephen S.
A1  - Nieva, Maria Fernanda
A1  - Langer, Norbert
T1  - B fields in OB stars (BOB): FORS2 spectropolarimetric follow-up of the two rare rigidly rotating magnetosphere stars HD 23478 and HD 345439
JF  - Astronomy and astrophysics : an international weekly journal
N2  - Aims. Massive B-type stars with strong magnetic fields and fast rotation are very rare and pose a mystery for theories of star formation and magnetic field evolution. Only two such stars, called sigma Ori E analogues, were known until recently. A team involved in APOGEE, one of the Sloan Digital Sky Survey III programs, announced the discovery of two additional rigidly rotating magnetosphere stars, HD 23478 and HD 345439. The magnetic fields in these newly discovered sOri E analogues have not been investigated so far.
 Methods. In the framework of our ESO Large Programme and one normal ESO programme, we carried out low-resolution FORS 2 spectropolarimetric observations of HD 23478 and HD 345439.
 Results. In the measurements of hydrogen lines, we discover a rather strong longitudinal magnetic field of up to 1.5 kG in HD 23478 and up to 1.3 kG using the entire spectrum. The analysis of HD 345439 using four subsequent spectropolarimetric subexposures does not reveal a magnetic field at a significance level of 3 sigma. On the other hand, individual subexposures indicate that HD 345439 may host a strong magnetic field that rapidly varies over 88 min. The fast rotation of HD 345439 is also indicated by the behaviour of several metallic and He I lines in the low-resolution FORS 2 spectra that show profile variations already on this short time-scale.
KW  - stars: early-type
KW  - stars: fundamental parameters
KW  - stars: variables: general
KW  - stars: magnetic field
KW  - stars: individual: HD 23478
KW  - stars: individual: HD 345439
Y1  - 2015
U6  - https://doi.org/10.1051/0004-6361/201526262
SN  - 0004-6361
SN  - 1432-0746
VL  - 578
PB  - EDP Sciences
CY  - Les Ulis
ER  - 
TY  - JOUR
A1  - Hubrig, Swetlana
A1  - Schöller, Markus
A1  - Kholtygin, Alexander F.
A1  - Tsumura, Hiroki
A1  - Hoshino, Akio
A1  - Kitamoto, Shunji
A1  - Oskinova, Lida
A1  - Ignace, Richard
A1  - Todt, Helge Tobias
A1  - Ilyin, Ilya
T1  - New multiwavelength observations of the Of?p star CPD-28 degrees 2561
JF  - Monthly notices of the Royal Astronomical Society
N2  - A rather strong mean longitudinal magnetic field of the order of a few hundred gauss was detected a few years ago in the Of?p star CPD -28 degrees 2561 using FORS2 (FOcal Reducer low dispersion Spectrograph 2) low-resolution spectropolarimetric observations. In this work, we present additional low-resolution spectropolarimetric observations obtained during several weeks in 2013 December using FORS 2 mounted at the 8-m Antu telescope of the Very Large Telescope (VLT). These observations cover a little less than half of the stellar rotation period of 73.41 d mentioned in the literature. The behaviour of the mean longitudinal magnetic field is consistent with the assumption of a single-wave variation during the stellar rotation cycle, indicating a dominant dipolar contribution to the magnetic field topology. The estimated polar strength of the surface dipole B-d is larger than 1.15 kG. Further, we compared the behaviour of the line profiles of various elements at different rotation phases associated with different magnetic field strengths. The strongest contribution of the emission component is observed at the phases when the magnetic field shows a negative or positive extremum. The comparison of the spectral behaviour of CPD -28 degrees 2561 with that of another Of?p star, HD 148937 of similar spectral type, reveals remarkable differences in the degree of variability between both stars. Finally, we present new X-ray observations obtained with the Suzaku X-ray Observatory. We report that the star is X-ray bright with log L-X/L-bol approximate to -5.7. The low-resolution X-ray spectra reveal the presence of a plasma heated up to 24 MK. We associate the 24 MK plasma in CPD -28 degrees 2561 with the presence of a kG strong magnetic field capable to confine stellar wind.
KW  - stars: atmospheres
KW  - stars: individual: CPD-28 degrees 2561
KW  - stars: magnetic field
KW  - stars: mass-loss
KW  - stars: variables: general
KW  - X-rays: stars
Y1  - 2015
U6  - https://doi.org/10.1093/mnras/stu2516
SN  - 0035-8711
SN  - 1365-2966
VL  - 447
IS  - 2
SP  - 1885
EP  - 1894
PB  - Oxford Univ. Press
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Huenemoerder, D.
A1  - Gayley, K.
A1  - Hamann, Wolf-Rainer
A1  - Ignace, R.
A1  - Nichols, J.
A1  - Oskinova, Lida
A1  - Pollock, A. M. T.
A1  - Schulz, N.
T1  - High Resolution X-Ray Spectra of WR 6
JF  - Wolf-Rayet Stars : Proceedings of an International Workshop held in Potsdam, Germany, 1.–5. June 2015
N2  - As WR 6 is a putatively single WN4 star, and is relatively bright (V = 6.9), it is an ideal case for studying the wind mechanisms in these extremely luminous stars. To obtain higher resolution spectra at higher energy (above 1 keV) than previously obtained with the XMM/Newton RGS, we have observed WR 6 with the Chandra High Energy Transmission Grating Spectrometer for 450 ks. We have resolved emission lines of S, Si, Mg, Ne, and Fe, which all show a “fin"-shaped prole, characteristic of a self-absorbed uniformly expanding shell. Steep blue edges gives robust maximal expansion velocities of about 2000 km/s, somewhat larger than the 1700km/s derived from UV lines. The He-like lines all indicate that X-ray emitting plasmas are far from the photosphere – even at the higher energies where opacity is lowest { as was also the case for the longer wavelength lines observed with XMM-Newton/RGS. Abundances determined from X-ray spectral modeling indicate enhancements consistent with nucleosynthesis. The star was also variable in X-rays and in simultaneous optical photometry obtained with Chandra aspect camera, but not coherently with the optically known period of 3.765 days.
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-88236
SP  - 301
EP  - 304
ER  - 
TY  - JOUR
A1  - Huenemoerder, David P.
A1  - Gayley, K. G.
A1  - Hamann, Wolf-Rainer
A1  - Ignace, R.
A1  - Nichols, J. S.
A1  - Oskinova, Lida
A1  - Pollock, A. M. T.
A1  - Schulz, Norbert S.
A1  - Shenar, Tomer
T1  - Probing Wolf-Rayet winds: Chandra/HETG X-ray spectra of WR 6
JF  - The astrophysical journal : an international review of spectroscopy and astronomical physics
N2  - With a deep Chandra/HETGS exposure of WR 6, we have resolved emission lines whose profiles show that the X-rays originate from a uniformly expanding spherical wind of high X-ray-continuum optical depth. The presence of strong helium-like forbidden lines places the source of X-ray emission at tens to hundreds of stellar radii from the photosphere. Variability was present in X-rays and simultaneous optical photometry, but neither were correlated with the known period of the system or with each other. An enhanced abundance of sodium revealed nuclear-processed material, a quantity related to the evolutionary state of the star. The characterization of the extent and nature of the hot plasma in WR 6 will help to pave the way to a more fundamental theoretical understanding of the winds and evolution of massive stars.
KW  - stars: individual (WR 6)
KW  - stars: massive
KW  - stars: Wolf-Rayet
Y1  - 2015
U6  - https://doi.org/10.1088/0004-637X/815/1/29
SN  - 0004-637X
SN  - 1538-4357
VL  - 815
IS  - 1
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Ignace, R.
A1  - Toalá, Jesús Alberto
A1  - Oskinova, Lida
T1  - Inversion of Intensity Profiles for Bubble Emissivity
JF  - Wolf-Rayet Stars : Proceedings of an International Workshop held in Potsdam, Germany, 1.–5. June 2015
N2  - Under the assumption of spherical symmetry, the run of intensity with impact parameter for a spatially resolved and optically thin bubble can be inverted for an "effective emissivity" as a function of radius. The effective emissivity takes into account instrumental sensitivity and even interstellar absorption. This work was supported by a grant from NASA (G03-14008X).
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-88432
SP  - 358
ER  - 
TY  - JOUR
A1  - Intravaia, Francesco
A1  - Mkrtchian, Vanik E.
A1  - Buhmann, Stefan Yoshi
A1  - Scheel, Stefan
A1  - Dalvit, Diego A. R.
A1  - Henkel, Carsten
T1  - Friction forces on atoms after acceleration
JF  - Journal of physics : Condensed matter
N2  - The aim of this paper is to revisit the calculation of atom-surface quantum friction in the quantum field theory formulation put forward by Barton (2010 New J. Phys. 12 113045). We show that the power dissipated into field excitations and the associated friction force depend on how the atom is boosted from being initially at rest to a configuration in which it is moving at constant velocity (nu) parallel to the planar interface. In addition, we point out that there is a subtle cancellation between the one-photon and part of the two-photon dissipating power, resulting in a leading order contribution to the frictional power which goes as nu(4). These results are also confirmed by an alternative calculation of the average radiation force, which scales as nu(3).
KW  - quantum friction
KW  - non-equilibrium
KW  - atom-surface interaction
Y1  - 2015
U6  - https://doi.org/10.1088/0953-8984/27/21/214020
SN  - 0953-8984
SN  - 1361-648X
VL  - 27
IS  - 21
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Jordan, Thomas
A1  - Fechler, Nina
A1  - Xu, Jingsan
A1  - Brenner, Thomas J. K.
A1  - Antonietti, Markus
A1  - Shalom, Menny
T1  - "Caffeine Doping" of Carbon/Nitrogen-Based Organic Catalysts: Caffeine as a Supramolecular Edge Modifier for the Synthesis of Photoactive Carbon Nitride Tubes
JF  - ChemCatChem : heterogeneous & homogeneous & bio- & nano-catalysis ; a journal of ChemPubSoc Europe
N2  - An alternative method for the structure tuning of carbon nitride materials by using a supramolecular approach in combination with caffeine as lining-agent is described. The self-assembly of the precursor complex consisting of melamine and cyanuric acid can be controlled by this doping molecule in terms of morphology, electronic, and photophysical properties. Caffeine is proposed to insert as an edge-molecule eventually leading to hollow tube-like carbon nitride structures with improved efficiency of charge formation. Compared to the bulk carbon nitride, the caffeine-doped analogue possesses a higher photocatalytic activity for the degradation of rhodamineB dye. Furthermore, this approach is also shown to be suitable for the modification of carbon nitride electrodes.
KW  - caffeine
KW  - carbon nitride
KW  - films
KW  - photocatalysis
KW  - supramolecular chemistry
Y1  - 2015
U6  - https://doi.org/10.1002/cctc.201500343
SN  - 1867-3880
SN  - 1867-3899
VL  - 7
IS  - 18
SP  - 2826
EP  - 2830
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Kasyanenko, Nina
A1  - Lysyakova, Liudmila
A1  - Ramazanov, Ruslan
A1  - Nesterenko, Alexey
A1  - Yaroshevich, Igor
A1  - Titov, Evgenii
A1  - Alexeev, G.
A1  - Lezov, Andrey
A1  - Unksov, I.
T1  - Conformational and Phase Transitions in DNA-Photosensitive Surfactant Solutions: Experiment and Modeling
JF  - Biopolymers
N2  - DNA binding to trans- and cis-isomers of azobenzene containing cationic surfactant in 5 mM NaCl solution was investigated by the methods of dynamic light scattering (DLS), low-gradient viscometry (LGV), atomic force microscopy (AFM), circular dichroism (CD), gel electrophoresis (GE), flow birefringence (FB), UV-Vis spectrophotometry. Light-responsive conformational transitions of DNA in complex with photosensitive surfactant, changes in DNA optical anisotropy and persistent length, phase transition of DNA into nanoparticles induced by high surfactant concentration, as well as transformation of surfactant conformation under its binding to macromolecule were studied. Computer simulations of micelles formation for cis- and trans-isomers of azobenzene containing surfactant, as well as DNA-surfactant interaction, were carried out. Phase diagram for DNA-surfactant solutions was designed. The possibility to reverse the DNA packaging induced by surfactant binding with the dilution and light irradiation was shown. (c) 2014 Wiley Periodicals, Inc. Biopolymers 103: 109-122, 2015.
KW  - DNA-surfactant complexes
KW  - light-induced DNA de-compaction
KW  - phase diagram
KW  - DNA volume and persistent length
Y1  - 2015
U6  - https://doi.org/10.1002/bip.22575
SN  - 0006-3525
SN  - 1097-0282
VL  - 103
IS  - 2
SP  - 109
EP  - 122
PB  - Wiley-Blackwell
CY  - Hoboken
ER  - 
TY  - JOUR
A1  - Kniepert, Juliane
A1  - Lange, Ilja
A1  - Heidbrink, Jan
A1  - Kurpiers, Jona
A1  - Brenner, Thomas J. K.
A1  - Koster, L. Jan Anton
A1  - Neher, Dieter
T1  - Effect of Solvent Additive on Generation, Recombination, and Extraction in PTB7:PCBM Solar Cells: A Conclusive Experimental and Numerical Simulation Study
JF  - The journal of physical chemistry : C, Nanomaterials and interfaces
N2  - Time-delayed collection field (TDCF), bias-assisted charge extraction (BACE), and space charge-limited current (SCLC) measurements are combined with complete numerical device simulations to unveil the effect of the solvent additive 1,8-diiodooctane (DIO) on the performance of PTB7:PCBM bulk heterojunction solar cells. DIO is shown to increase the charge generation rate, reduce geminate and bimolecular recombination, and increase the electron mobility. In total, the reduction of loss currents by processing with the additive raises the power conversion efficiency of the PTB7:PCBM blend by a factor of almost three. The lower generation rates and higher geminate recombination losses in devices without DIO are consistent with a blend morphology comprising large fullerene clusters embedded within a PTB7-rich matrix, while the low electron mobility suggests that these fullerene clusters are themselves composed of smaller pure fullerene aggregates separated by disordered areas. Our device simulations show unambiguously that the effect of the additive on the shape of the currentvoltage curve (J-V) cannot be ascribed to the variation of only the mobility, the recombination, or the field dependence of generation. It is only when the changes of all three parameters are taken into account that the simulation matches the experimental J-V characteristics under all illumination conditions and for a wide range of voltages.
Y1  - 2015
U6  - https://doi.org/10.1021/jp512721e
SN  - 1932-7447
VL  - 119
IS  - 15
SP  - 8310
EP  - 8320
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Kollosche, Matthias
A1  - Kofod, Guggi
A1  - Suo, Zhigang
A1  - Zhu, Jian
T1  - Temporal evolution and instability in a viscoelastic dielectric elastomer
JF  - Journal of the mechanics and physics of solids
N2  - Dielectric elastomer transducers are being developed for applications in stretchable electronics, tunable optics, biomedical devices, and soft machines. These transducers exhibit highly nonlinear electromechanical behavior: a dielectric membrane under voltage can form wrinkles, undergo snap-through instability, and suffer electrical breakdown. We investigate temporal evolution and instability by conducting a large set of experiments under various prestretches and loading rates, and by developing a model that allows viscoelastic instability. We use the model to classify types of instability, and map the experimental observations according to prestretches and loading rates. The model describes the entire set of experimental observations. A new type of instability is discovered, which we call wrinkle-to-wrinkle transition. A flat membrane at a critical voltage forms wrinkles and then, at a second critical voltage, snaps into another state of winkles of a shorter wavelength. This study demonstrates that viscoelasticity is essential to the understanding of temporal evolution and instability of dielectric elastomers. (C) 2014 Elsevier Ltd. All rights reserved.
KW  - Dielectric elastomer
KW  - Viscoelasticity
KW  - Snap-through instability
KW  - Phase transition
KW  - Wrinkling
Y1  - 2015
U6  - https://doi.org/10.1016/j.jmps.2014.11.013
SN  - 0022-5096
SN  - 1873-4782
VL  - 76
SP  - 47
EP  - 64
PB  - Elsevier
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Komarov, Maxim
A1  - Pikovskij, Arkadij
T1  - Finite-size-induced transitions to synchrony in oscillator ensembles with nonlinear global coupling
JF  - Physical review : E, Statistical, nonlinear and soft matter physics
N2  - We report on finite-sized-induced transitions to synchrony in a population of phase oscillators coupled via a nonlinear mean field, which microscopically is equivalent to a hypernetwork organization of interactions. Using a self-consistent approach and direct numerical simulations, we argue that a transition to synchrony occurs only for finite-size ensembles and disappears in the thermodynamic limit. For all considered setups, which include purely deterministic oscillators with or without heterogeneity in natural oscillatory frequencies, and an ensemble of noise-driven identical oscillators, we establish scaling relations describing the order parameter as a function of the coupling constant and the system size.
Y1  - 2015
U6  - https://doi.org/10.1103/PhysRevE.92.020901
SN  - 1539-3755
SN  - 1550-2376
VL  - 92
IS  - 2
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Komarov, Maxim
A1  - Pikovskij, Arkadij
T1  - Intercommunity resonances in multifrequency ensembles of coupled oscillators
JF  - Physical review : E, Statistical, nonlinear and soft matter physics
N2  - We generalize the Kuramoto model of globally coupled oscillators to multifrequency communities. A situation when mean frequencies of two subpopulations are close to the resonance 2 : 1 is considered in detail. We construct uniformly rotating solutions describing synchronization inside communities and between them. Remarkably, cross coupling across the frequencies can promote synchrony even when ensembles are separately asynchronous. We also show that the transition to synchrony due to the cross coupling is accompanied by a huge multiplicity of distinct synchronous solutions, which is directly related to a multibranch entrainment. On the other hand, for synchronous populations, the cross-frequency coupling can destroy phase locking and lead to chaos of mean fields.
Y1  - 2015
U6  - https://doi.org/10.1103/PhysRevE.92.012906
SN  - 1539-3755
SN  - 1550-2376
VL  - 92
IS  - 1
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Kopyshev, Alexey
A1  - Lomadze, Nino
A1  - Feldman, David
A1  - Genzer, Jan
A1  - Santer, Svetlana
T1  - Making polymer brush photosensitive with azobenzene containing surfactants
JF  - Polymer : the international journal for the science and technology of polymers
N2  - We report on rendering polyelectrolyte brushes photosensitive by loading them with azobenzene-containing cationic surfactants. Planar poly(methacrylic acid) (PMAA) brushes are synthesized using the “grafting from” free-radical polymerization scheme followed by exposure to a solution of photosensitive surfactants consisting of positively-charged head groups and hydrophobic tails into which azobenzene moieties are inserted. In this study the length of the hydrophobic methylene spacer connecting the azobenzene and the charged head group ranges from 4 to 10 CH2 groups. Under irradiation with UV light, the photo-isomerization of azobenzene integrated into a surfactant results in a change in size, geometry, dipole moment and free volume of the whole molecule. When the brush loaded with photosensitive surfactants is exposed to irradiation with UV interference patterns, the topography of the brush deforms following the distribution of the light intensity, exhibiting surface relief gratings (SRG). Since SRG formation is accompanied by a local rupturing of polymer chains in areas from which the polymer material is receding, most of the polymer material is removed from the surface during treatment with good solvent, leaving behind characteristic patterns of lines or dots. The azobenzene molecules still integrated within the polymer film can be removed by washing the brush with water. The remaining nano-structured brush can then be re-used for further functionalization. Although the opto-mechanically induced rupturing occurs for all surfactants, larger species do not penetrate deep enough into the brush such that after rupturing a leftover layer of polymer material remains on the substrate. This indicates that rupturing occurs predominantly in regions of high surfactant density.
KW  - Azobenzene containing cationic surfactants
KW  - Photosensitive polymer brushes
KW  - Opto-mechanically induced scission of polymer chains
Y1  - 2015
U6  - https://doi.org/10.1016/j.polymer.2015.09.023
SN  - 0032-3861
VL  - 79
SP  - 65
EP  - 72
PB  - Elsevier Science
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Krüsemann, Henning
A1  - Godec, Aljaz
A1  - Metzler, Ralf
T1  - Ageing first passage time density in continuous time random walks and quenched energy landscapes
JF  - Journal of physics : A, Mathematical and theoretical
N2  - We study the first passage dynamics of an ageing stochastic process in the continuous time random walk (CTRW) framework. In such CTRW processes the test particle performs a random walk, in which successive steps are separated by random waiting times distributed in terms of the waiting time probability density function Psi (t) similar or equal to t(-1-alpha) (0 <= alpha <= 2). An ageing stochastic process is defined by the explicit dependence of its dynamic quantities on the ageing time t(a), the time elapsed between its preparation and the start of the observation. Subdiffusive ageing CTRWs with 0 < alpha < 1 describe systems such as charge carriers in amorphous semiconducters, tracer dispersion in geological and biological systems, or the dynamics of blinking quantum dots. We derive the exact forms of the first passage time density for an ageing subdiffusive CTRW in the semi-infinite, confined, and biased case, finding different scaling regimes for weakly, intermediately, and strongly aged systems: these regimes, with different scaling laws, are also found when the scaling exponent is in the range 1 < alpha < 2, for sufficiently long ta. We compare our results with the ageing motion of a test particle in a quenched energy landscape. We test our theoretical results in the quenched landscape against simulations: only when the bias is strong enough, the correlations from returning to previously visited sites become insignificant and the results approach the ageing CTRW results. With small bias or without bias, the ageing effects disappear and a change in the exponent compared to the case of a completely annealed landscape can be found, reflecting the build-up of correlations in the quenched landscape.
KW  - first passage
KW  - random walks
KW  - anomalous diffusion
Y1  - 2015
U6  - https://doi.org/10.1088/1751-8113/48/28/285001
SN  - 1751-8113
SN  - 1751-8121
VL  - 48
IS  - 28
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Kubátová, Brankica
A1  - Hamann, Wolf-Rainer
A1  - Todt, Helge Tobias
A1  - Sander, A.
A1  - Steinke, M.
A1  - Hainich, Rainer
A1  - Shenar, Tomer
T1  - Macroclumping in WR 136
JF  - Wolf-Rayet Stars : Proceedings of an International Workshop held in Potsdam, Germany, 1.–5. June 2015
N2  - Macroclumping proved to resolve the discordance between different mass-loss rate diagnostics for O-type stars, in particular between Hα and the P v resonance lines. In this paper, we report first results from a corresponding investigation for WR stars. We apply our detailed 3-D Monte Carlo (MC) line formation code to the P v resonance doublet and show, for the Galactic WNL star WR136, that macroclumping is require to bring this line in accordance with the mass-loss rate derived from the emission-line spectrum.
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-87823
SP  - 125
EP  - 128
ER  - 
TY  - JOUR
A1  - Kunnus, Kristjan
A1  - Schreck, Simon
A1  - Föhlisch, Alexander
T1  - Free-electron laser based resonant inelastic X-ray scattering on molecules and liquids
JF  - Journal of electron spectroscopy and related phenomena : the international journal on theoretical and experimental aspects of electron spectroscopy
N2  - The unprecedented beam properties of free-electron laser based X-ray sources enable novel resonant inelastic X-ray scattering (RIXS) experiments. Femtosecond time-resolved RIXS can be used to follow charge, spin and structural dynamics of dilute solute molecules in solution. Ultrashort X-ray pulses allow probing of highly radiation sensitive states of matter such as the metastable phase of supercooled liquid water. Nonlinear X-ray probes like amplified spontaneous emission and stimulated resonant X-ray scattering provide an enhanced selectivity and sensitivity as well as a path to control radiation damage and increase the photon yields in RIXS experiments. (C) 2015 Elsevier B.V. All rights reserved.
KW  - Free-electron laser
KW  - RIXS
KW  - Pump-probe
KW  - Nonlinear X-ray spectroscopy
KW  - Molecules
KW  - Liquids
Y1  - 2015
U6  - https://doi.org/10.1016/j.elspec.2015.08.012
SN  - 0368-2048
SN  - 1873-2526
VL  - 204
SP  - 345
EP  - 355
PB  - Elsevier
CY  - Amsterdam
ER  - 
TY  - JOUR
A1  - Lange, Ilja
A1  - Reiter, Sina
A1  - Kniepert, Juliane
A1  - Piersimoni, Fortunato
A1  - Paetzel, Michael
A1  - Hildebrandt, Jana
A1  - Brenner, Thomas J. K.
A1  - Hecht, Stefan
A1  - Neher, Dieter
T1  - Zinc oxide modified with benzylphosphonic acids as transparent electrodes in regular and inverted organic solar cell structures
JF  - Applied physics letters
N2  - An approach is presented to modify the work function of solution-processed sol-gel derived zinc oxide (ZnO) over an exceptionally wide range of more than 2.3 eV. This approach relies on the formation of dense and homogeneous self-assembled monolayers based on phosphonic acids with different dipole moments. This allows us to apply ZnO as charge selective bottom electrodes in either regular or inverted solar cell structures, using poly(3-hexylthiophene): phenyl-C71-butyric acid methyl ester as the active layer. These devices compete with or even surpass the performance of the reference on indium tin oxide/poly(3,4-ethylenedioxythiophene) polystyrene sulfonate. Our findings highlight the potential of properly modified ZnO as electron or hole extracting electrodes in hybrid optoelectronic devices. (C) 2015 AIP Publishing LLC.
Y1  - 2015
U6  - https://doi.org/10.1063/1.4916182
SN  - 0003-6951
SN  - 1077-3118
VL  - 106
IS  - 11
PB  - American Institute of Physics
CY  - Melville
ER  - 
TY  - JOUR
A1  - Louis, Rohan E.
A1  - Kliem, Bernhard
A1  - Ravindra, B.
A1  - Chintzoglou, Georgios
T1  - Triggering an Eruptive Flare by Emerging Flux in a Solar Active-Region Complex
JF  - Solar physics : a journal for solar and solar-stellar research and the study of solar terrestrial physics
N2  - A flare and fast coronal mass ejection originated between solar active regions NOAA 11514 and 11515 on 2012 July 1 (SOL2012-07-01) in response to flux emergence in front of the leading sunspot of the trailing region 11515. Analyzing the evolution of the photospheric magnetic flux and the coronal structure, we find that the flux emergence triggered the eruption by interaction with overlying flux in a non-standard way. The new flux neither had the opposite orientation nor a location near the polarity inversion line, which are favorable for strong reconnection with the arcade flux under which it emerged. Moreover, its flux content remained significantly smaller than that of the arcade (). However, a loop system rooted in the trailing active region ran in part under the arcade between the active regions, passing over the site of flux emergence. The reconnection with the emerging flux, leading to a series of jet emissions into the loop system, caused a strong but confined rise of the loop system. This lifted the arcade between the two active regions, weakening its downward tension force and thus destabilizing the considerably sheared flux under the arcade. The complex event was also associated with supporting precursor activity in an enhanced network near the active regions, acting on the large-scale overlying flux, and with two simultaneous confined flares within the active regions.
KW  - Flares, dynamics
KW  - Sunspots, magnetic fields
KW  - Chromosphere, active
KW  - Corona
KW  - Prominences, active
Y1  - 2015
U6  - https://doi.org/10.1007/s11207-015-0726-8
SN  - 0038-0938
SN  - 1573-093X
VL  - 290
IS  - 12
SP  - 3641
EP  - 3662
PB  - Springer
CY  - Dordrecht
ER  - 
TY  - JOUR
A1  - Lu, Guanghao
A1  - Koch, Norbert
A1  - Neher, Dieter
T1  - In-situ tuning threshold voltage of field-effect transistors based on blends of poly(3-hexylthiophene) with an insulator electret
JF  - Applied physics letters
N2  - Blending the conjugated polymer poly(3-hexylthiophene) (P3HT) with the insulating electret polystyrene (PS), we show that the threshold voltage V-t of organic field-effect transistors (OFETs) can be easily and reversely tuned by applying a gate bias stress at 130 degrees C. It is proposed that this phenomenon is caused by thermally activated charge injection from P3HT into PS matrix, and that this charge is immobilized within the PS matrix after cooling down to room temperature. Therefore, room-temperature hysteresis-free FETs with desired V-t can be easily achieved. The approach is applied to reversely tune the OFET mode of operation from accumulation to depletion, and to build inverters. (C) 2015 AIP Publishing LLC.
Y1  - 2015
U6  - https://doi.org/10.1063/1.4928554
SN  - 0003-6951
SN  - 1077-3118
VL  - 107
IS  - 6
PB  - American Institute of Physics
CY  - Melville
ER  - 
TY  - JOUR
A1  - Lysyakova, Liudmila
A1  - Lomadze, Nino
A1  - Neher, Dieter
A1  - Maximova, Ksenia
A1  - Kabashin, Andrei V.
A1  - Santer, Svetlana
T1  - Light-Tunable Plasmonic Nanoarchitectures Using Gold Nanoparticle-Azobenzene-Containing Cationic Surfactant Complexes
JF  - The journal of physical chemistry : C, Nanomaterials and interfaces
N2  - When arranged in a proper nanoaggregate architecture, gold nanoparticles can offer controllable plasmon-related absorption/scattering, yielding distinct color effects that depend critically on the relative orientation and distance between nanoparticle constituents. Herein, we report on the implementation of novel plasmonic nanoarchitectures based on complexes between gold nanoparticles and an azobenzene-modified cationic surfactant that can exhibit a light-tunable plasmonic response. The formation of such complexes becomes possible through the use of strongly negatively charged bare gold nanoparticles (similar to 10-nm diameter) prepared by the method of laser ablation in deionized water. Driven by electrostatic interactions, the cationic surfactant molecules attach and form a shell around the negatively charged nanoparticles, resulting in neutralization of the particle charge or even overcompensation beyond which the nanoparticles become positively charged. At low and high surfactant concentrations, Au nanoparticles are negatively and positively charged, respectively, and are represented by single species due to electric repulsion effects having absorption peaks around 523-527 nm, whereas at intermediate concentrations, the Au nanoparticles become neutral, forming nanoscale 100-nm clusterlike aggregates and exhibiting an additional absorption peak at gimel > 600 nm and a visible change in the color of the solution from red to blue. Because of the presence of the photosensitive azobenzene unit in the surfactant tail that undergoes trans-to-cis isomerization under irradiation with UV light, we then demonstrate a light-controlled nanoclustering of nanoparticles, yielding a switch in the plasmonic absorption band and a related change in the solution color. The formed hybrid architectures with a light-controlled plasmonic response could be important for a variety of tasks, including biomedical, surface-enhanced Raman spectroscopy (SERS), data transmission, and storage applications.
Y1  - 2015
U6  - https://doi.org/10.1021/jp511232g
SN  - 1932-7447
VL  - 119
IS  - 7
SP  - 3762
EP  - 3770
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Maerten, Lena
A1  - Bojahr, Andre
A1  - Gohlke, Mathias
A1  - Rössle, Matthias
A1  - Bargheer, Matias
T1  - Coupling of GHz Phonons to Ferroelastic Domain Walls in SrTiO3
JF  - Physical review letters
N2  - We study the linear and nonlinear acoustic response of SrTiO3 across its ferroelastic transition at T-a = 105 K by time domain Brillouin scattering. Above T-a we observe that for a strain amplitude of similar to 0.18% the sound velocity for compressive strain exceeds the tensile strain velocity by 3%. Below T-a we find a giant slowing down of the sound velocity by 12% and attribute this to the coupling of GHz phonons to ferroelastic twin domain walls. We propose a new mechanism for this coupling on the ultrafast time scale, providing an important new test ground for theories used to simulate atomic motion in domain forming crystals.
Y1  - 2015
U6  - https://doi.org/10.1103/PhysRevLett.114.047401
SN  - 0031-9007
SN  - 1079-7114
VL  - 114
IS  - 4
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Mardoukhi, Yousof
A1  - Jeon, Jae-Hyung
A1  - Metzler, Ralf
T1  - Geometry controlled anomalous diffusion in random fractal geometries: looking beyond the infinite cluster
JF  - Physical chemistry, chemical physics : a journal of European Chemical Societies
N2  - We investigate the ergodic properties of a random walker performing (anomalous) diffusion on a random fractal geometry. Extensive Monte Carlo simulations of the motion of tracer particles on an ensemble of realisations of percolation clusters are performed for a wide range of percolation densities. Single trajectories of the tracer motion are analysed to quantify the time averaged mean squared displacement (MSD) and to compare this with the ensemble averaged MSD of the particle motion. Other complementary physical observables associated with ergodicity are studied, as well. It turns out that the time averaged MSD of individual realisations exhibits non-vanishing fluctuations even in the limit of very long observation times as the percolation density approaches the critical value. This apparent non-ergodic behaviour concurs with the ergodic behaviour on the ensemble averaged level. We demonstrate how the non-vanishing fluctuations in single particle trajectories are analytically expressed in terms of the fractal dimension and the cluster size distribution of the random geometry, thus being of purely geometrical origin. Moreover, we reveal that the convergence scaling law to ergodicity, which is known to be inversely proportional to the observation time T for ergodic diffusion processes, follows a power-law similar to T-h with h < 1 due to the fractal structure of the accessible space. These results provide useful measures for differentiating the subdiffusion on random fractals from an otherwise closely related process, namely, fractional Brownian motion. Implications of our results on the analysis of single particle tracking experiments are provided.
Y1  - 2015
U6  - https://doi.org/10.1039/c5cp03548a
SN  - 1463-9076
SN  - 1463-9084
VL  - 17
IS  - 44
SP  - 30134
EP  - 30147
PB  - Royal Society of Chemistry
CY  - Cambridge
ER  - 
TY  - JOUR
A1  - Martin, Nicolas F.
A1  - Nidever, David L.
A1  - Besla, Gurtina
A1  - Olsen, Knut
A1  - Walker, Alistair R.
A1  - Vivas, A. Katherina
A1  - Gruendl, Robert A.
A1  - Kaleida, Catherine C.
A1  - Munoz, Ricardo R.
A1  - Blum, Robert D.
A1  - Saha, Abhijit
A1  - Conn, Blair C.
A1  - Bell, Eric F.
A1  - Chu, You-Hua
A1  - Cioni, Maria-Rosa L.
A1  - de Boer, Thomas J. L.
A1  - Gallart, Carme
A1  - Jin, Shoko
A1  - Kunder, Andrea
A1  - Majewski, Steven R.
A1  - Martinez-Delgado, David
A1  - Monachesi, Antonela
A1  - Monelli, Matteo
A1  - Monteagudo, Lara
A1  - Noel, Noelia E. D.
A1  - Olszewski, Edward W.
A1  - Stringfellow, Guy S.
A1  - van der Marel, Roeland P.
A1  - Zaritsky, Dennis
T1  - Hydra II: A faint and compact milky way dwarf galaxy found in the survey of the magellanic stellar history
JF  - The astrophysical journal : an international review of spectroscopy and astronomical physics ; Part 2, Letters
N2  - We present the discovery of a new dwarf galaxy, Hydra II, found serendipitously within the data from the ongoing Survey of the Magellanic Stellar History conducted with the Dark Energy Camera on the Blanco 4 m Telescope. The new satellite is compact (r(h) = 68 +/- 11 pc) and faint (MV = -4.8 +/- 0.3), but well within the realm of dwarf galaxies. The stellar distribution of Hydra II in the color-magnitude diagram is well-described by a metal-poor ([Fe/H] = -2.2) and old (13 Gyr) isochrone and shows a distinct blue horizontal branch, some possible red clump stars, and faint stars that are suggestive of blue stragglers. At a heliocentric distance of 134 +/- 10 kpc, Hydra II is located in a region of the Galactic halo that models have suggested may host material from the leading arm of the Magellanic Stream. A comparison with N-body simulations hints that the new dwarf galaxy could be or could have been a satellite of the Magellanic Clouds.
KW  - galaxies: individual (Hydra II)
KW  - Local Group
KW  - Magellanic Clouds
Y1  - 2015
U6  - https://doi.org/10.1088/2041-8205/804/1/L5
SN  - 2041-8205
SN  - 2041-8213
VL  - 804
IS  - 1
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Martinez-Nunez, Silvia
A1  - Sander, Angelika
A1  - Gimenez-Garcia, Angel
A1  - Gonzalez-Galan, Ana
A1  - Torrejon, Jose Miguel
A1  - Gonzalez-Fernandez, Carlos
A1  - Hamann, Wolf-Rainer
T1  - The donor star of the X-ray pulsar X1908+075
JF  - Astronomy and astrophysics : an international weekly journal
N2  - High-mass X-ray binaries consist of a massive donor star and a compact object. While several of those systems have been well studied in X-rays, little is known for most of the donor stars as they are often heavily obscured in the optical and ultraviolet regime. There is an opportunity to observe them at infrared wavelengths, however. The goal of this study is to obtain the stellar and wind parameters of the donor star in the X1908+075 high-mass X-ray binary system with a stellar atmosphere model to check whether previous studies from X-ray observations and spectral morphology lead to a sufficient description of the donor star. We obtained H-and K-band spectra of X1908+075 and analysed them with the Potsdam Wolf-Rayet (PoWR) model atmosphere code. For the first time, we calculated a stellar atmosphere model for the donor star, whose main parameters are: M-spec = 15 +/- 6 M-circle dot, T-* = 23(-3)(+6) kK, log g(eff) = 3.0 +/- 0.2 and log L/L-circle dot = 4.81 +/- 0.25. The obtained parameters point towards an early B-type (B0-B3) star, probably in a supergiant phase. Moreover we determined a more accurate distance to the system of 4.85 +/- 0.50 kpc than the previously reported value.
KW  - binaries: close
KW  - stars: individual: X1908+075
KW  - stars: massive
KW  - stars: winds
KW  - outflows
KW  - X-rays: binaries
Y1  - 2015
U6  - https://doi.org/10.1051/0004-6361/201424823
SN  - 0004-6361
SN  - 1432-0746
VL  - 578
PB  - EDP Sciences
CY  - Les Ulis
ER  - 
TY  - JOUR
A1  - Meier, Patrick
A1  - Motschmann, Uwe
A1  - Schmidt, Jurgen
A1  - Spahn, Frank
A1  - Hill, Thomas W.
A1  - Dong, Yaxue
A1  - Jones, Geraint H.
A1  - Kriegel, Hendrik
T1  - Modeling the total dust production of Enceladus from stochastic charge equilibrium and simulations
JF  - Planetary and space science
KW  - Enceladus
KW  - Plume
KW  - Nanograin charge
KW  - CAPS
Y1  - 2015
U6  - https://doi.org/10.1016/j.pss.2015.10.002
SN  - 0032-0633
VL  - 119
SP  - 208
EP  - 221
PB  - Elsevier
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Metzler, Ralf
A1  - Bauer, Maximilian
A1  - Rasmussen, Emil S.
A1  - Lomholt, Michael A.
T1  - Real sequence effects on the search dynamics of transcription factors on DNA
JF  - Scientific Reports
N2  - Recent experiments show that transcription factors (TFs) indeed use the facilitated diffusion mechanism to locate their target sequences on DNA in living bacteria cells: TFs alternate between sliding motion along DNA and relocation events through the cytoplasm. From simulations and theoretical analysis we study the TF-sliding motion for a large section of the DNA-sequence of a common E. coli strain, based on the two-state TF-model with a fast-sliding search state and a recognition state enabling target detection. For the probability to detect the target before dissociating from DNA the TF-search times self-consistently depend heavily on whether or not an auxiliary operator (an accessible sequence similar to the main operator) is present in the genome section. Importantly, within our model the extent to which the interconversion rates between search and recognition states depend on the underlying nucleotide sequence is varied. A moderate dependence maximises the capability to distinguish between the main operator and similar sequences. Moreover, these auxiliary operators serve as starting points for DNA looping with the main operator, yielding a spectrum of target detection times spanning several orders of magnitude. Auxiliary operators are shown to act as funnels facilitating target detection by TFs.
KW  - gene regulatory networks
KW  - biological physics
Y1  - 2015
U6  - https://doi.org/10.1038/srep10072
SN  - 2045-2322
VL  - 5
IS  - 10072
PB  - Nature Publishing Group
CY  - London
ER  - 
TY  - JOUR
A1  - Metzler, Ralf
A1  - Cherstvy, Andrey G.
A1  - Chechkin, Aleksei V.
A1  - Bodrova, Anna S.
T1  - Ultraslow scaled Brownian motion
JF  - New journal of physics : the open-access journal for physics
N2  - We define and study in detail utraslow scaled Brownian motion (USBM) characterized by a time dependent diffusion coefficient of the form . For unconfined motion the mean squared displacement (MSD) of USBM exhibits an ultraslow, logarithmic growth as function of time, in contrast to the conventional scaled Brownian motion. In a harmonic potential the MSD of USBM does not saturate but asymptotically decays inverse-proportionally to time, reflecting the highly non-stationary character of the process. We show that the process is weakly non-ergodic in the sense that the time averaged MSD does not converge to the regular MSD even at long times, and for unconfined motion combines a linear lag time dependence with a logarithmic term. The weakly non-ergodic behaviour is quantified in terms of the ergodicity breaking parameter. The USBM process is also shown to be ageing: observables of the system depend on the time gap between initiation of the test particle and start of the measurement of its motion. Our analytical results are shown to agree excellently with extensive computer simulations.
KW  - anomalous diffusion
KW  - stochastic processes
KW  - ageing
Y1  - 2015
U6  - https://doi.org/10.1088/1367-2630/17/6/063038
SN  - 1367-2630
VL  - 17
IS  - 063038
PB  - Dt. Physikalische Ges., IOP
CY  - Bad Honnef, London
ER  - 
TY  - JOUR
A1  - Mitzscherling, Steffen
A1  - Cui, Q.
A1  - Koopman, Wouter-Willem Adriaan
A1  - Bargheer, Matias
T1  - Dielectric function of two-phase colloid-polymer nanocomposite
JF  - Physical chemistry, chemical physics : a journal of European Chemical Societies
N2  - The plasmon resonance of metal nanoparticles determines their optical response in the visible spectral range. Many details such as the electronic properties of gold near the particle surface and the local environment of the particles influence the spectra. We show how the cheap but highly precise fabrication of composite nanolayers by spin-assisted layer-by-layer deposition of polyelectrolytes can be used to investigate the spectral response of gold nanospheres (GNS) and gold nanorods (GNR) in a self-consistent way, using the established Maxwell-Garnett effective medium (MGEM) theory beyond the limit of homogeneous media. We show that the dielectric function of gold nanoparticles differs from the bulk value and experimentally characterize the shape and the surrounding of the particles thoroughly by SEM, AFM and ellipsometry. Averaging the dielectric functions of the layered surrounding by an appropriate weighting with the electric field intensity yields excellent agreement for the spectra of several nanoparticles and nanorods with various cover-layer thicknesses.
Y1  - 2015
U6  - https://doi.org/10.1039/c5cp04326c
SN  - 1463-9076
SN  - 1463-9084
VL  - 17
IS  - 44
SP  - 29465
EP  - 29474
PB  - Royal Society of Chemistry
CY  - Cambridge
ER  - 
TY  - JOUR
A1  - Monreal-Ibero, Ana
A1  - Weilbacher, Peter Michael
A1  - Wendt, Martin
A1  - Selman, Fernando
A1  - Lallement, Rosine
A1  - Brinchmann, Jarle
A1  - Kamann, Sebastian
A1  - Sandin, Christer
T1  - Towards DIB mapping in galaxies beyond 100 Mpc A radial profile of the lambda 5780.5 diffuse interstellar band in AM1353-272 B
JF  - Astronomy and astrophysics : an international weekly journal
N2  - Context. Diffuse interstellar bands (DIBs) are non-stellar weak absorption features of unknown origin found in the spectra of stars viewed through one or several clouds of the interstellar medium (ISM). Research of DIBs outside the Milky Way is currently very limited. In particular, spatially resolved investigations of DIBs outside of the Local Group are, to our knowledge, inexistent.
 Aims. In this contribution, we explore the capability of the high-sensitivity integral field spectrograph, MUSE, as a tool for mapping diffuse interstellar bands at distances larger than 100 Mpc.
 Methods. We used MUSE commissioning data for AM1353-272 B, the member with the highest extinction of the Dentist's Chair, an interacting system of two spiral galaxies. High signal-to-noise spectra were created by co-adding the signal of many spatial elements distributed in a geometry of concentric elliptical half-rings.
 Results. We derived decreasing radial profiles for the equivalent width of the lambda 5780.5 DIB both in the receding and approaching side of the companion galaxy up to distances of similar to 4.6 kpc from the centre of the galaxy. The interstellar extinction as derived from the Ha/H beta line ratio displays a similar trend, with decreasing values towards the external parts. This translates into an intrinsic correlation between the strength of the DIB and the extinction within AM1353-272 B, consistent with the currently existing global trend between these quantities when using measurements for Galactic and extragalactic sightlines.
 Conclusions. It seems feasible to map the DIB strength in the Local Universe, which has up to now only been performed for the Milky Way. This offers a new approach to studying the relationship between DIBs and other characteristics and species of the ISM in addition to using galaxies in the Local Group or sightlines towards very bright targets outside the Local Group.
KW  - dust, extinction
KW  - ISM: lines and bands
KW  - galaxies: ISM
KW  - galaxies: individual: AM1353-272 B
Y1  - 2015
U6  - https://doi.org/10.1051/0004-6361/201525854
SN  - 0004-6361
SN  - 1432-0746
VL  - 576
PB  - EDP Sciences
CY  - Les Ulis
ER  - 
TY  - JOUR
A1  - Muraveva, Tatiana
A1  - Palmer, Max
A1  - Clementini, Gisella
A1  - Luri, Xavier
A1  - Cioni, Maria-Rosa L.
A1  - Moretti, Maria Ida
A1  - Marconi, Marcella
A1  - Ripepi, Vincenzo
A1  - Rubele, Stefano
T1  - New near-infrared period-luminosity-metallicity relations for RR lyrae stars and the outlock for GAIA
JF  - The astrophysical journal : an international review of spectroscopy and astronomical physics
N2  - We present results of the analysis of 70 RR Lyrae stars located in the bar of the Large Magellanic Cloud (LMC). Combining the spectroscopically determined metallicity of these stars from the literature with precise periods from the OGLE III catalog and multi-epoch K-s photometry from the VISTA survey of the Magellanic Clouds system, we derive a new near-infrared period-luminosity-metallicity (PLKsZ) relation for RR Lyrae variables. In order to fit the relation we use a fitting method developed specifically for this study. The zero-point of the relation is estimated two different ways: by assuming the value of the distance to the LMC and by using Hubble Space Telescope parallaxes of five RR Lyrae stars in the Milky Way (MW). The difference in distance moduli derived by applying these two approaches is similar to 0.2 mag. To investigate this point further we derive the PL(Ks)Z relation based on 23 MW RR Lyrae stars that had been analyzed in Baade-Wesselink studies. We compared the derived PL(Ks)Z relations for RR Lyrae stars in the MW and LMC. Slopes and zero-points are different, but still consistent within the errors. The shallow slope of the metallicity term is confirmed by both LMC and MW variables. The astrometric space mission Gaia is expected to provide a huge contribution to the determination of the RR Lyrae PL(Ks)Z relation; however, calculating an absolute magnitude from the trigonometric parallax of each star and fitting a PL(Ks)Z relation directly to period and absolute magnitude leads to biased results. We present a tool to achieve an unbiased solution by modeling the data and inferring the slope and zero-point of the relation via statistical methods.
KW  - astrometry
KW  - distance scale
KW  - Magellanic Clouds
KW  - methods: data analysis
KW  - stars: statistics
KW  - stars: variables: RR Lyrae
Y1  - 2015
U6  - https://doi.org/10.1088/0004-637X/807/2/127
SN  - 0004-637X
SN  - 1538-4357
VL  - 807
IS  - 2
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Murray, Claire E.
A1  - Stanimirovic, Snezana
A1  - McClure-Griffiths, Naomi M.
A1  - Putman, Mary E.
A1  - Liszt, Harvey S.
A1  - Wong, Tony
A1  - Richter, Philipp
A1  - Dawson, Joanne R.
A1  - Dickey, John M.
A1  - Lindner, Robert R.
A1  - Babler, Brian L.
A1  - Allison, James R.
T1  - First detection of HCO+ absorption in the magellanic system
JF  - The astrophysical journal : an international review of spectroscopy and astronomical physics
N2  - We present the first detection of HCO+ absorption in the Magellanic System. Using the ATCA, we observed nine extragalactic radio continuum sources behind the Magellanic System and detected HCO+ absorption toward one source located behind the leading edge of the Magellanic Bridge. The detection is located at an LSR velocity of v = 214.0 +/- 0.4 km s(-1), with an FWHM of Delta v = 4.5 +/- 1.0 km s(-1), and an optical depth of tau (HCO+) = 0.10 +/- 0.02. Although there is abundant neutral hydrogen (H I) surrounding the sight line in position-velocity space, at the exact location of the absorber the H I column density is low, <10(20) cm(-2), and there is little evidence for dust or CO emission from Planck observations. While the origin and survival of molecules in such a diffuse environment remain unclear, dynamical events such as H I flows and cloud collisions in this interacting system likely play an important role.
KW  - ISM: molecules
KW  - ISM: structure
KW  - Magellanic Clouds
Y1  - 2015
U6  - https://doi.org/10.1088/0004-637X/808/1/41
SN  - 0004-637X
SN  - 1538-4357
VL  - 808
IS  - 1
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Ni, Lei
A1  - Kliem, Bernhard
A1  - Lin, Jun
A1  - Wu, Ning
T1  - Fast magnetic reconnection in the solar chromosphere mediated by theplasmoid instability
JF  - The astrophysical journal : an international review of spectroscopy and astronomical physics
N2  - Magnetic reconnection in the partially ionized solar chromosphere is studied in 2.5 dimensional magnetohydrodynamic simulations including radiative cooling and ambipolar diffusion. A Harris current sheet with and without a guide field is considered. Characteristic values of the parameters in the middle chromosphere imply a high magnetic Reynolds number of similar to 10(6)-10(7) in the present simulations. Fast magnetic reconnection then develops as a consequence of the plasmoid instability without the need to invoke anomalous resistivity enhancements. Multiple levels of the instability are followed as it cascades to smaller scales, which approach the ion inertial length. The reconnection rate, normalized to the asymptotic values of magnetic field and Alfven velocity in the inflow region, reaches values in the range similar to 0.01-0.03 throughout the cascading plasmoid formation and for zero as well as for strong guide field. The outflow velocity reaches approximate to 40 km s(-1). Slow-mode shocks extend from the X-points, heating the plasmoids up to similar to 8 x 10(4) K. In the case of zero guide field, the inclusion of both ambipolar diffusion and radiative cooling causes a rapid thinning of the current sheet (down to similar to 30 m) and early formation of secondary islands. Both of these processes have very little effect on the plasmoid instability for a strong guide field. The reconnection rates, temperature enhancements, and upward outflow velocities from the vertical current sheet correspond well to their characteristic values in chromospheric jets.
KW  - magnetic reconnection
KW  - magnetohydrodynamics (MHD)
KW  - radiation: dynamics
KW  - Sun: activity
KW  - Sun: chromosphere
Y1  - 2015
U6  - https://doi.org/10.1088/0004-637X/799/1/79
SN  - 0004-637X
SN  - 1538-4357
VL  - 799
IS  - 1
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Nichols, Joy
A1  - Huenemoerder, David P.
A1  - Corcoran, Michael F.
A1  - Waldron, Wayne
A1  - Naze, Yael
A1  - Pollock, Andy M. T.
A1  - Moffat, Anthony F. J.
A1  - Lauer, Jennifer
A1  - Shenar, Tomer
A1  - Russell, Christopher M. P.
A1  - Richardson, Noel D.
A1  - Pablo, Herbert
A1  - Evans, Nancy Remage
A1  - Hamaguchi, Kenji
A1  - Gull, Theodore
A1  - Hamann, Wolf-Rainer
A1  - Oskinova, Lida
A1  - Ignace, Rosina
A1  - Hoffman, Jennifer L.
A1  - Hole, Karen Tabetha
A1  - Lomax, Jamie R.
T1  - A COORDINATED X-RAY AND OPTICAL CAMPAIGN OF THE NEAREST MASSIVE ECLIPSING BINARY, delta ORIONIS Aa. II. X-RAY VARIABILITY
JF  - The astrophysical journal : an international review of spectroscopy and astronomical physics
N2  - We present time-resolved and phase-resolved variability studies of an extensive X-ray high-resolution spectral data set of the delta Ori Aa binary system. The four observations, obtained with Chandra ACIS HETGS, have a total exposure time of approximate to 479 ks and provide nearly complete binary phase coverage. Variability of the total X-ray flux in the range of 5-25 is is confirmed, with a maximum amplitude of about +/- 15% within a single approximate to 125 ks observation. Periods of 4.76 and 2.04 days are found in the total X-ray flux, as well as an apparent overall increase in the flux level throughout the nine-day observational campaign. Using 40 ks contiguous spectra derived from the original observations, we investigate the variability of emission line parameters and ratios. Several emission lines are shown to be variable, including S XV, Si XIII, and Ne IX. For the first time, variations of the X-ray emission line widths as a function of the binary phase are found in a binary system, with the smallest widths at phi = 0.0 when the secondary delta Ori Aa2 is at the inferior conjunction. Using 3D hydrodynamic modeling of the interacting winds, we relate the emission line width variability to the presence of a wind cavity created by a wind-wind collision, which is effectively void of embedded wind shocks and is carved out of the X-ray-producing primary wind, thus producing phase-locked X-ray variability.
KW  - binaries: close
KW  - binaries: eclipsing
KW  - stars: individual ([HD 36486]delta Ori A)
Y1  - 2015
U6  - https://doi.org/10.1088/0004-637X/809/2/133
SN  - 0004-637X
SN  - 1538-4357
VL  - 809
IS  - 2
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Niebuhr, Mario
A1  - Zink, Christof
A1  - Jechow, Andreas
A1  - Heuer, Axel
A1  - Glebov, Leonid B.
A1  - Menzel, Ralf
T1  - Mode stabilization of a laterally structured broad area diode laser using an external volume Bragg grating
JF  - Optics express : the international electronic journal of optics
N2  - An external volume Bragg grating (VBG) is used for transverse and longitudinal mode stabilization of a broad area diode laser (BAL) with an on-chip transverse Bragg resonance (TBR) grating. The internal TBR grating defines a transverse low-loss mode at a specific propagation angle inside the BAL. Selection of the TBR mode was realized via the angular geometry of an external resonator assembly consisting of the TBR BAL and a feedback element. A feedback mirror provides near diffraction limited and spectral narrow output in the TBR mode albeit requiring an intricate alignment procedure. If feedback is provided via a VBG, adjustment proves to be far less critical and higher output powers were achieved. Moreover, additional modulation in the far field distribution became discernible allowing for a better study of the TBR concept. (C) 2015 Optical Society of America
Y1  - 2015
U6  - https://doi.org/10.1364/OE.23.012394
SN  - 1094-4087
VL  - 23
IS  - 9
SP  - 12394
EP  - 12400
PB  - Optical Society of America
CY  - Washington
ER  - 
TY  - JOUR
A1  - Niedl, Robert Raimund
A1  - Beta, Carsten
T1  - Hydrogel-driven paper-based microfluidics
JF  - LAB on a chip : miniaturisation for chemistry and biology
N2  - Paper-based microfluidics provide an inexpensive, easy to use technology for point-of-care diagnostics in developing countries. Here, we combine paper-based microfluidic devices with responsive hydrogels to add an entire new class of functions to these versatile low-cost fluidic systems. The hydrogels serve as fluid reservoirs. In response to an external stimulus, e.g. an increase in temperature, the hydrogels collapse and release fluid into the structured paper substrate. In this way, chemicals that are either stored on the paper substrate or inside the hydrogel pads can be dissolved, premixed, and brought to reaction to fulfill specific analytic tasks. We demonstrate that multi-step sequences of chemical reactions can be implemented in a paper-based system and operated without the need for external precision pumps. We exemplify this technology by integrating an antibody-based E. coli test on a small and easy to use paper device.
Y1  - 2015
U6  - https://doi.org/10.1039/c5lc00276a
SN  - 1473-0197
SN  - 1473-0189
VL  - 15
IS  - 11
SP  - 2452
EP  - 2459
PB  - Royal Society of Chemistry
CY  - Cambridge
ER  - 
TY  - JOUR
A1  - Oberg, H.
A1  - Gladh, Jörgen
A1  - Anniyev, Toyli
A1  - Beye, Martin
A1  - Coffee, Ryan
A1  - Föhlisch, Alexander
A1  - Katayama, T.
A1  - Kaya, Sarp
A1  - LaRue, Jerry
A1  - Mogelhoj, Andreas
A1  - Nordlund, Dennis
A1  - Ogasawara, Hirohito
A1  - Schlotter, William F.
A1  - Sellberg, Jonas A.
A1  - Sorgenfrei, Nomi
A1  - Turner, Joshua J.
A1  - Wolf, Martin
A1  - Wurth, W.
A1  - Ostrom, Henrik
A1  - Nilsson, Anders
A1  - Norskov, Jens K.
A1  - Pettersson, Lars G. M.
T1  - Optical laser-induced CO desorption from Ru(0001) monitored with a free-electron X-ray laser: DFT prediction and X-ray confirmation of a precursor state
JF  - Surface science
N2  - We present density functional theory modeling of time-resolved optical pump/X-ray spectroscopic probe data of CO desorption from Ru(0001). The BEEF van der Waals functional predicts a weakly bound state as a precursor to desorption. The optical pump leads to a near-instantaneous (<100 fs) increase of the electronic temperature to nearly 7000 K. The temperature evolution and energy transfer between electrons, substrate phonons and adsorbate is described by the two-temperature model and found to equilibrate on a timescale of a few picoseconds to an elevated local temperature of similar to 2000K. Estimating the free energy based on the computed potential of mean force along the desorption path, we find an entropic barrier to desorption (and by time-reversal also to adsorption). This entropic barrier separates the chemisorbed and precursor states, and becomes significant at the elevated temperature of the experiment (similar to 1.4 eV at 2000 K). Experimental pump-probe X-ray absorption/X-ray emission spectroscopy indicates population of a precursor state to desorption upon laser-excitation of the system (Dell'Angela et al., 2013). Computing spectra along the desorption path confirms the picture of a weakly bound transient state arising from ultrafast heating of the metal substrate. (C) 2015 Elsevier B.V. All rights reserved.
KW  - CO desorption
KW  - Potential of mean force
KW  - Two-temperature model
KW  - Pump-probe
KW  - X-ray spectroscopy
KW  - Density functional theory
Y1  - 2015
U6  - https://doi.org/10.1016/j.susc.2015.03.011
SN  - 0039-6028
SN  - 1879-2758
VL  - 640
SP  - 80
EP  - 88
PB  - Elsevier
CY  - Amsterdam
ER  - 
TY  - JOUR
A1  - Orienti, M.
A1  - Finke, J.
A1  - Raiteri, C. M.
A1  - Hovatta, T.
A1  - Larsson, J.
A1  - Max-Moerbeck, W.
A1  - Perkins, J.
A1  - Readhead, A. C. S.
A1  - Richards, J. L.
A1  - Beilicke, M.
A1  - Benbow, W.
A1  - Berger, K.
A1  - Bird, R.
A1  - Bugaev, V.
A1  - Cardenzana, J. V.
A1  - Cerruti, M.
A1  - Chen, Xuhui
A1  - Ciupik, L.
A1  - Dickinson, H. J.
A1  - Eisch, J. D.
A1  - Errando, M.
A1  - Falcone, A.
A1  - Finley, J. P.
A1  - Fleischhack, H.
A1  - Fortin, P.
A1  - Fortson, L.
A1  - Furniss, A.
A1  - Gerard, L.
A1  - Gillanders, G. H.
A1  - Griffiths, S. T.
A1  - Grube, J.
A1  - Gyuk, G.
A1  - Hakansson, Nils
A1  - Holder, J.
A1  - Humensky, T. B.
A1  - Kar, P.
A1  - Kertzman, M.
A1  - Khassen, Y.
A1  - Kieda, D.
A1  - Krennrich, F.
A1  - Kumar, S.
A1  - Lang, M. J.
A1  - Maier, G.
A1  - McCann, A.
A1  - Meagher, K.
A1  - Moriarty, P.
A1  - Mukherjee, R.
A1  - Nieto, D.
A1  - Ong, R. A.
A1  - Otte, A. N.
A1  - Pohl, Manuela
A1  - Popkow, A.
A1  - Prokoph, H.
A1  - Pueschel, Elisa
A1  - Quinn, J.
A1  - Ragan, K.
A1  - Reynolds, P. T.
A1  - Richards, G. T.
A1  - Roache, E.
A1  - Rousselle, J.
A1  - Santander, M.
A1  - Sembroski, G. H.
A1  - Smith, A. W.
A1  - Staszak, D.
A1  - Telezhinsky, Igor O.
A1  - Tucci, J. V.
A1  - Tyler, J.
A1  - Varlotta, A.
A1  - Vassiliev, V. V.
A1  - Wakely, S. P.
A1  - Weinstein, A.
A1  - Welsing, R.
A1  - Williams, D. A.
A1  - Zitzer, B.
T1  - The most powerful flaring activity from the NLSyl PMN J0948+0022
JF  - Monthly notices of the Royal Astronomical Society
N2  - We report on multifrequency observations performed during 2012 December-2013 August of the first narrow-line Seyfert 1 galaxy detected in gamma-rays, PMN J0948+0022 (z = 0.5846). A y -ray flare was observed by the Large Area Telescope on board Fermi during 2012 December-2013 January, reaching a daily peak flux in the 0.1-100 GeV energy range of (155 31) x 10 8 ph cm(-2) S-1 on 2013 January 1, corresponding to an apparent isotropic luminosity of similar to 1.5 x 1048 erg s(-1). The y -ray flaring period triggered Swift and Very Energetic Radiation Imaging Telescope Array System (VERITAS) observations in addition to radio and optical monitoring by Owens Valley Radio Observatory, Monitoring Of Jets in Active galactic nuclei with VLBA Experiments, and Catalina Real-time Transient Survey. A strong flare was observed in optical, UV, and X-rays on 2012 December 30, quasi-simultaneously to the y -ray flare, reaching a record flux for this source from optical to y gamma-rays. VERITAS observations at very high energy (E > 100 GeV) during 2013 January 6-17 resulted in an upper limit of F>0.2 Trev < 4.0 x 10(-12) ph cm(-2) s(-1). We compared the spectral energy distribution (SED) of the flaring state in 2013 January with that of an intermediate state observed in 2011. The two SEDs, modelled as synchrotron emission and an external Compton scattering of seed photons from a dust torus, can be modelled by changing both the electron distribution parameters and the magnetic field.
KW  - galaxies: active-galaxies: individual: PMN J0948+0022
KW  - galaxies: nuclei
KW  - galaxies: Seyfert
KW  - gamma-rays: general
Y1  - 2015
U6  - https://doi.org/10.1093/mnras/stu2251
SN  - 0035-8711
SN  - 1365-2966
VL  - 446
IS  - 3
SP  - 2456
EP  - 2467
PB  - Oxford Univ. Press
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Oskinova, Lida
T1  - X-ray emission from single WR stars
JF  - Wolf-Rayet Stars : Proceedings of an International Workshop held in Potsdam, Germany, 1.–5. June 2015
N2  - In this review I briefly summarize our knowledge of the X-ray emission from single WN, WC, and WO stars. These stars have relatively modest X-ray luminosities, typically not exceeding 1L⊙. The analysis of X-ray spectra usually reveals thermal plasma with temperatures reaching a few x10 MK. X-ray variability is detected in some WN stars. At present we don't fully understand how X-ray radiation in produced in WR stars, albeit there are some promising research avenues, such as the presence of CIRs in the winds of some stars. To fully understand WR stars we need to unravel mechanisms of X-ray production in their winds.
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-88228
SP  - 295
EP  - 300
ER  - 
TY  - JOUR
A1  - Oskinova, Lida
A1  - Todt, Helge Tobias
A1  - Huenemoerder, David P.
A1  - Hubrig, Swetlana
A1  - Ignace, Richard
A1  - Hamann, Wolf-Rainer
A1  - Balona, Luis
T1  - On X-ray pulsations in beta Cephei-type variables
JF  - Astronomy and astrophysics : an international weekly journal
N2  - Context. beta Cep-type variables are early B-type stars that are characterized by oscillations observable in their optical light curves. At least one beta Cep-variable also shows periodic variability in X-rays.
 Aims. Here we study the X-ray light curves in a sample of beta Cep-variables to investigate how common X-ray pulsations are for this type of stars.
 Methods. We searched the Chandra and XMM-Newton X-ray archives and selected stars that were observed by these telescopes for at least three optical pulsational periods. We retrieved and analyzed the X-ray data for kappa Sco, beta Cru, and alpha Vir. The X-ray light curves of these objects were studied to test for their variability and periodicity.
 Results. While there is a weak indication for X-ray variability in beta Cru, we find no statistically significant evidence of X-ray pulsations in any of our sample stars. This might be due either to the insufficient data quality or to the physical lack of modulations. New, more sensitive observations should settle this question.
KW  - stars: massive
KW  - stars: variables: general
KW  - X-rays: stars
Y1  - 2015
U6  - https://doi.org/10.1051/0004-6361/201525908
SN  - 0004-6361
SN  - 1432-0746
VL  - 577
PB  - EDP Sciences
CY  - Les Ulis
ER  - 
TY  - JOUR
A1  - Ostrom, H.
A1  - Oberg, H.
A1  - Xin, H.
A1  - Larue, J.
A1  - Beye, Martin
A1  - Gladh, J.
A1  - Ng, M. L.
A1  - Sellberg, J. A.
A1  - Kaya, S.
A1  - Mercurio, G.
A1  - Nordlund, D.
A1  - Hantschmann, Markus
A1  - Hieke, F.
A1  - Kuehn, D.
A1  - Schlotter, W. F.
A1  - Dakovski, G. L.
A1  - Turner, J. J.
A1  - Minitti, M. P.
A1  - Mitra, A.
A1  - Moeller, S. P.
A1  - Föhlisch, Alexander
A1  - Wolf, M.
A1  - Wurth, W.
A1  - Persson, Mats
A1  - Norskov, J. K.
A1  - Abild-Pedersen, Frank
A1  - Ogasawara, Hirohito
A1  - Pettersson, Lars G. M.
A1  - Nilsson, A.
T1  - Probing the transition state region in catalytic CO oxidation on Ru
JF  - Science
N2  - Femtosecond x-ray laser pulses are used to probe the carbon monoxide (CO) oxidation reaction on ruthenium (Ru) initiated by an optical laser pulse. On a time scale of a few hundred femtoseconds, the optical laser pulse excites motions of CO and oxygen (O) on the surface, allowing the reactants to collide, and, with a transient close to a picosecond (ps), new electronic states appear in the OK-edge x-ray absorption spectrum. Density functional theory calculations indicate that these result from changes in the adsorption site and bond formation between CO and O with a distribution of OC-O bond lengths close to the transition state (TS). After 1 ps, 10% of the CO populate the TS region, which is consistent with predictions based on a quantum oscillator model.
Y1  - 2015
U6  - https://doi.org/10.1126/science.1261747
SN  - 0036-8075
SN  - 1095-9203
VL  - 347
IS  - 6225
SP  - 978
EP  - 982
PB  - American Assoc. for the Advancement of Science
CY  - Washington
ER  - 
TY  - JOUR
A1  - Pablo, Herbert
A1  - Richardson, Noel D.
A1  - Moffat, Anthony F. J.
A1  - Corcoran, Michael
A1  - Shenar, Tomer
A1  - Benvenuto, Omar
A1  - Fuller, Jim
A1  - Naze, Yael
A1  - Hoffman, Jennifer L.
A1  - Miroshnichenko, Anatoly
A1  - Apellaniz, Jesus Maiz
A1  - Evans, Nancy
A1  - Eversberg, Thomas
A1  - Gayley, Ken
A1  - Gull, Ted
A1  - Hamaguchi, Kenji
A1  - Hamann, Wolf-Rainer
A1  - Henrichs, Huib
A1  - Hole, Tabetha
A1  - Ignace, Richard
A1  - Iping, Rosina
A1  - Lauer, Jennifer
A1  - Leutenegger, Maurice
A1  - Lomax, Jamie
A1  - Nichols, Joy
A1  - Oskinova, Lida
A1  - Owocki, Stan
A1  - Pollock, Andy
A1  - Russell, Christopher M. P.
A1  - Waldron, Wayne
A1  - Buil, Christian
A1  - Garrel, Thierry
A1  - Graham, Keith
A1  - Heathcote, Bernard
A1  - Lemoult, Thierry
A1  - Li, Dong
A1  - Mauclaire, Benjamin
A1  - Potter, Mike
A1  - Ribeiro, Jose
A1  - Matthews, Jaymie
A1  - Cameron, Chris
A1  - Guenther, David
A1  - Kuschnig, Rainer
A1  - Rowe, Jason
A1  - Rucinski, Slavek
A1  - Sasselov, Dimitar
A1  - Weiss, Werner
T1  - A coordinated X-Ray and optical campaign of the nearest massive eclipsing binary, delta ORIONIS Aa. III. Analysis of optical photometric (most) and spectroscopic (ground based) variations
JF  - The astrophysical journal : an international review of spectroscopy and astronomical physics
N2  - We report on both high-precision photometry from the Microvariability and Oscillations of Stars (MOST) space telescope and ground-based spectroscopy of the triple system delta Ori A, consisting of a binary O9.5II+early-B (Aa1 and Aa2) with P = 5.7 days, and a more distant tertiary (O9 IV P > 400 years). This data was collected in concert with X-ray spectroscopy from the Chandra X-ray Observatory. Thanks to continuous coverage for three weeks, the MOST light curve reveals clear eclipses between Aa1 and Aa2 for the first time in non-phased data. From the spectroscopy, we have a well-constrained radial velocity (RV) curve of Aa1. While we are unable to recover RV variations of the secondary star, we are able to constrain several fundamental parameters of this system and determine an approximate mass of the primary using apsidal motion. We also detected second order modulations at 12 separate frequencies with spacings indicative of tidally influenced oscillations. These spacings have never been seen in a massive binary, making this system one of only a handful of such binaries that show evidence for tidally induced pulsations.
KW  - binaries: close
KW  - binaries: eclipsing
KW  - stars: early-type
KW  - stars: individual (delta Ori A)
KW  - stars: mass-loss
KW  - stars: variables: general
Y1  - 2015
U6  - https://doi.org/10.1088/0004-637X/809/2/134
SN  - 0004-637X
SN  - 1538-4357
VL  - 809
IS  - 2
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Parezanovic, Vladimir
A1  - Laurentie, Jean-Charles
A1  - Fourment, Carine
A1  - Delville, Joel
A1  - Bonnet, Jean-Paul
A1  - Spohn, Andreas
A1  - Duriez, Thomas
A1  - Cordier, Laurent
A1  - Noack, Bernd R.
A1  - Abel, Markus
A1  - Segond, Marc
A1  - Shaqarin, Tamir
A1  - Brunton, Steven L.
T1  - Mixing layer manipulation experiment from open-loop forcing to closed-loop machine learning control
JF  - Flow, turbulence and combustion : an international journal published in association with ERCOFTAC
KW  - Shear flow
KW  - Turbulence
KW  - Active flow control
KW  - Extremum seeking
KW  - POD
KW  - Machine learning
KW  - Genetic programming
Y1  - 2015
U6  - https://doi.org/10.1007/s10494-014-9581-1
SN  - 1386-6184
SN  - 1573-1987
VL  - 94
IS  - 1
SP  - 155
EP  - 173
PB  - Springer
CY  - Dordrecht
ER  - 
TY  - JOUR
A1  - Pavlyukevich, Ilya
A1  - Li, Yongge
A1  - Xu, Yong
A1  - Chechkin, Aleksei V.
T1  - Directed transport induced by spatially modulated Levy flights
JF  - Journal of physics : A, Mathematical and theoretical
N2  - In this paper we study the dynamics of a particle in a ratchet potential subject to multiplicative alpha-stable Levy noise, alpha is an element of(0, 2), in the limit of a noise amplitude epsilon -> 0. We compare the dynamics for Ito and Marcus multiplicative noises and obtain the explicit asymptotics of the escape time in the wells and transition probabilities between the wells. A detailed analysis of the noise-induced current is performed for the Seebeck ratchet with a weak multiplicative noise for alpha is an element of(0, 2].
KW  - Levy flights
KW  - multiplicative noise
KW  - Seebeck ratchet
KW  - directed transport
Y1  - 2015
U6  - https://doi.org/10.1088/1751-8113/48/49/495004
SN  - 1751-8113
SN  - 1751-8121
VL  - 48
IS  - 49
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Perez-Velazquez, Jose Luis
A1  - Erra, Ramon Guevara
A1  - Rosenblum, Michael
T1  - The Epileptic Thalamocortical Network is a Macroscopic Self-Sustained Oscillator: Evidence from Frequency-Locking Experiments in Rat Brains
JF  - Scientific reports
N2  - The rhythmic activity observed in nervous systems, in particular in epilepsies and Parkinson's disease, has often been hypothesized to originate from a macroscopic self-sustained neural oscillator. However, this assumption has not been tested experimentally. Here we support this viewpoint with in vivo experiments in a rodent model of absence seizures, by demonstrating frequency locking to external periodic stimuli and finding the characteristic Arnold tongue. This result has important consequences for developing methods for the control of brain activity, such as seizure cancellation.
Y1  - 2015
U6  - https://doi.org/10.1038/srep08423
SN  - 2045-2322
VL  - 5
PB  - Nature Publ. Group
CY  - London
ER  - 
TY  - JOUR
A1  - Piatti, Andres E.
A1  - de Grijs, Richard
A1  - Ripepi, Vincenzo
A1  - Ivanov, Valentin D.
A1  - Cioni, Maria-Rosa L.
A1  - Marconi, Marcella
A1  - Rubele, Stefano
A1  - Bekki, Kenji
A1  - For, Bi-Qing
T1  - The VMC survey - XVI. Spatial variation of the cluster formation activity in the innermost regions of the Large Magellanic Cloud
JF  - Monthly notices of the Royal Astronomical Society
KW  - techniques: photometric
KW  - galaxies: individual: LMC
KW  - Magellanic Clouds
Y1  - 2015
U6  - https://doi.org/10.1093/mnras/stv2054
SN  - 0035-8711
SN  - 1365-2966
VL  - 454
IS  - 1
SP  - 839
EP  - 848
PB  - Oxford Univ. Press
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Piatti, Andres E.
A1  - de Grijs, Richard
A1  - Rubele, Stefano
A1  - Cioni, Maria-Rosa L.
A1  - Ripepi, Vincenzo
A1  - Kerber, Leandro
T1  - The VMC survey - XV. The Small Magellanic Cloud-Bridge connection history as traced by their star cluster populations
JF  - Monthly notices of the Royal Astronomical Society
N2  - We present results based on YJK(s) photometry of star clusters located in the outermost, eastern region of the Small Magellanic Cloud (SMC). We analysed a total of 51 catalogued clusters whose colour-magnitude diagrams (CMDs), having been cleaned from field-star contamination, were used to assess the clusters' reality and estimate ages of the genuine systems. Based on CMD analysis, 15 catalogued clusters were found to be possible non-genuine aggregates. We investigated the properties of 80 per cent of the catalogued clusters in this part of the SMC by enlarging our sample with previously obtained cluster ages, adopting a homogeneous scale for all. Their spatial distribution suggests that the oldest clusters, log(t yr(-1)) >= 9.6, are in general located at greater distances to the galaxy's centre than their younger counterparts - 9.0 <= log(t yr(-1)) <= 9.4 - while two excesses of clusters are seen at log(t yr(-1)) similar to 9.2 and log(t yr(-1)) similar to 9.7. We found a trail of younger clusters which follow the wing/bridge components. This long spatial sequence does not only harbour very young clusters, log(t yr(-1)) similar to 7.3, but it also hosts some of intermediate ages, log(t yr(-1)) similar to 9.1. The derived cluster and field-star formation frequencies as a function of age are different. The most surprising feature is an observed excess of clusters with ages of log(t yr(-1)) <9.0, which could have been induced by interactions with the LMC.
KW  - techniques: photometric
KW  - galaxies: individual: SMC
KW  - Magellanic Clouds
Y1  - 2015
U6  - https://doi.org/10.1093/mnras/stv635
SN  - 0035-8711
SN  - 1365-2966
VL  - 450
IS  - 1
SP  - 552
EP  - 563
PB  - Oxford Univ. Press
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Pieplow, Gregor
A1  - Henkel, Carsten
T1  - Cherenkov friction on a neutral particle moving parallel to a dielectric
JF  - Journal of physics : Condensed matter
N2  - We describe a simple mechanism of quantum friction for a particle moving parallel to a dielectric, based on a fully relativistic framework and the assumption of local equilibrium. The Cherenkov effect explains how the bare ground state becomes globally unstable and how fluctuations of the electromagnetic field and the particle's dipole are converted into pairs of excitations. Modeling the particle as a silver nano-sphere, we investigate the spectrum of the force and its velocity dependence. We find that the damping of the plasmon resonance in the silver particle has a relatively strong impact near the Cherenkov threshold velocity. We also present an expansion of the friction force near the threshold velocity for both damped and undamped particles.
KW  - quantum friction
KW  - quantum electrodynamics
KW  - Cherenkov radiation
KW  - transition radiation
KW  - fluctuation forces
Y1  - 2015
U6  - https://doi.org/10.1088/0953-8984/27/21/214001
SN  - 0953-8984
SN  - 1361-648X
VL  - 27
IS  - 21
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Piersimoni, Fortunato
A1  - Schlesinger, Raphael
A1  - Benduhn, Johannes
A1  - Spoltore, Donato
A1  - Reiter, Sina
A1  - Lange, Ilja
A1  - Koch, Norbert
A1  - Vandewal, Koen
A1  - Neher, Dieter
T1  - Charge Transfer Absorption and Emission at ZnO/Organic Interfaces
JF  - The journal of physical chemistry letters
N2  - We investigate hybrid charge transfer states (HCTS) at the planar interface between a-NPD and ZnO by spectrally resolved electroluminescence (EL) and external quantum efficiency (EQE) measurements. Radiative decay of HCTSs is proven by distinct emission peaks in the EL spectra of such bilayer devices in the NIR at energies well below the bulk a-NPD or ZnO emission. The EQE spectra display low energy contributions clearly red-shifted with respect to the a-NPD photocurrent and partially overlapping with the EL emission. Tuning of the energy gap between the ZnO conduction band and a-NPD HOMO level (E-int) was achieved by modifying the ZnO surface with self-assembled monolayers based on phosphonic acids. We find a linear dependence of the peak position of the NIR EL on E-int, which unambiguously attributes the origin of this emission to radiative recombination between an electron on the ZnO and a hole on a-NPD. In accordance with this interpretation, we find a strictly linear relation between the open-circuit voltage and the energy of the charge state for such hybrid organicinorganic interfaces.
Y1  - 2015
U6  - https://doi.org/10.1021/jz502657z
SN  - 1948-7185
VL  - 6
IS  - 3
SP  - 500
EP  - 504
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Pietzsch, Annette
A1  - Hennies, Franz
A1  - Miedema, Piter S.
A1  - Kennedy, Brian
A1  - Schlappa, Justine
A1  - Schmitt, Thorsten
A1  - Strocov, Vladimir N.
A1  - Föhlisch, Alexander
T1  - Snapshots of the Fluctuating Hydrogen Bond Network in Liquid Water on the Sub-Femtosecond Timescale with Vibrational Resonant Inelastic x-ray Scattering
JF  - Physical review letters
N2  - Liquid water molecules interact strongly with each other, forming a fluctuating hydrogen bond network and thereby giving rise to the anomalous phase diagram of liquid water. Consequently, symmetric and asymmetric water molecules have been found in the picosecond time average with IR and optical Raman spectroscopy. With subnatural linewidth resonant inelastic x-ray scattering (RIXS) at vibrational resolution, we take sub-femtosecond snapshots of the electronic and structural properties of water molecules in the hydrogen bond network. We derive a strong dominance of nonsymmetric molecules in liquid water in contrast to the gas phase on the sub-femtosecond timescale of RIXS and determine the fraction of highly asymmetrically distorted molecules.
Y1  - 2015
U6  - https://doi.org/10.1103/PhysRevLett.114.088302
SN  - 0031-9007
SN  - 1079-7114
VL  - 114
IS  - 8
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Pikovskij, Arkadij
T1  - First and second sound in disordered strongly nonlinear lattices: numerical study
JF  - Journal of statistical mechanics: theory and experiment
N2  - We study numerically secondary modes on top of a chaotic state in disordered nonlinear lattices. Two basic models are considered, with or without a local on-site potential. By performing periodic spatial modulation of displacement and kinetic energy, and following the temporal evolution of the corresponding spatial profiles, we reveal different modes which can be interpreted as first and second sound.
KW  - disordered systems (theory)
KW  - connections between chaos and statistical physics
Y1  - 2015
U6  - https://doi.org/10.1088/1742-5468/2015/08/P08007
SN  - 1742-5468
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Pikovskij, Arkadij
T1  - Maximizing Coherence of Oscillations by External Locking
JF  - Physical review letters
N2  - We study how coherence of noisy oscillations can be optimally enhanced by external locking. Based on the condition of minimizing the phase diffusion constant, we find the optimal forcing explicitly in the limits of small and large noise, in dependence of the phase sensitivity of the oscillator. We show analytically that the form of the optimal force bifurcates with the noise intensity; this is confirmed by the analysis of an optimal locking forcing for an experimentally obtained phase sensitivity of a neural cell. In the limit of small noise, the results are compared with purely deterministic conditions of optimal locking.
Y1  - 2015
U6  - https://doi.org/10.1103/PhysRevLett.115.070602
SN  - 0031-9007
SN  - 1079-7114
VL  - 115
IS  - 7
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Pikovskij, Arkadij
A1  - Rosenblum, Michael
T1  - Dynamics of globally coupled oscillators: Progress and perspectives
JF  - Chaos : an interdisciplinary journal of nonlinear science
N2  - In this paper, we discuss recent progress in research of ensembles of mean field coupled oscillators. Without an ambition to present a comprehensive review, we outline most interesting from our viewpoint results and surprises, as well as interrelations between different approaches. (c) 2015 AIP Publishing LLC.
Y1  - 2015
U6  - https://doi.org/10.1063/1.4922971
SN  - 1054-1500
SN  - 1089-7682
VL  - 25
IS  - 9
PB  - American Institute of Physics
CY  - Melville
ER  - 
TY  - JOUR
A1  - Pohl, Manuela
A1  - Wilhelm, Alina
A1  - Telezhinsky, Igor O.
T1  - Reacceleration of electrons in supernova remnants
JF  - Astronomy and astrophysics : an international weekly journal
N2  - Context. radio spectra of many shell-type supernova remnants show deviations from those expected on theoretical grounds.
 Aims. In this paper we determine the effect of stochastic reacceleration on the spectra of electrons in the GeV band and at lower energies, and we investigate whether reacceleration can explain the observed variation in radio spectral indices.
 Methods. We explicitely calculated the momentum diffusion coefficient for 3 types of turbulence expected downstream of the forward shock: fast-mode waves, small-scale non-resonant modes, and large-scale modes arising from turbulent dynamo activity. After noting that low-energy particles are efficiently coupled to the quasi-thermal plasma, a simplified cosmic-ray transport equation can be formulated and is numerically solved.
 Results. Only fast-mode waves can provide momentum diffusion fast enough to significantly modify the spectra of particles. Using a synchrotron emissivity that accurately reflects a highly turbulent magnetic field, we calculated the radio spectral index and find that soft spectra with index a alpha less than or similar to -0.6 can be maintained over more than 2 decades in radio frequency, even if the electrons experience reacceleration for only one acceleration time. A spectral hardening is possible but considerably more frequency-dependent. The spectral modification imposed by stochastic reacceleration downstream of the forward shock depends only weakly on the initial spectrum provided by, e.g., diffusive shock acceleration at the shock itself.
KW  - acceleration of particles
KW  - turbulence
KW  - cosmic rays
KW  - ISM: supernova remnants
Y1  - 2015
U6  - https://doi.org/10.1051/0004-6361/201425027
SN  - 0004-6361
SN  - 1432-0746
VL  - 574
PB  - EDP Sciences
CY  - Les Ulis
ER  - 
TY  - JOUR
A1  - Politi, Antonio
A1  - Rosenblum, Michael
T1  - Equivalence of phase-oscillator and integrate-and-fire models
JF  - Physical review : E, Statistical, nonlinear and soft matter physics
N2  - A quantitative comparison of various classes of oscillators (integrate-and-fire, Winfree, and Kuramoto-Daido type) is performed in the weak-coupling limit for a fully connected network of identical units. An almost perfect agreement is found, with only tiny differences among the models. We also show that the regime of self-consistent partial synchronization is rather general and can be observed for arbitrarily small coupling strength in any model class. As a byproduct of our study, we are able to show that an integrate-and-fire model with a generic pulse shape can be always transformed into a similar model with delta pulses and a suitable phase response curve.
Y1  - 2015
U6  - https://doi.org/10.1103/PhysRevE.91.042916
SN  - 1539-3755
SN  - 1550-2376
VL  - 91
IS  - 4
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Premont-Schwarz, Mirabelle
A1  - Schreck, Simon
A1  - Iannuzzi, Marcella
A1  - Nibbering, Erik T. J.
A1  - Odelius, Michael
A1  - Wernet, Philippe
T1  - Correlating Infrared and X-ray Absorption Energies for Molecular-Level Insight into Hydrogen Bond Making and Breaking in Solution
JF  - The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces & biophysical chemistry
N2  - While ubiquitous, the making and breaking of hydrogen bonds in solution is notoriously difficult to study due to the associated complex changes of nuclear and electronic structures. With the aim to reduce the according uncertainty in correlating experimental observables and hydrogen-bond configurations, we combine the information from proximate methods to study the N-H center dot center dot center dot O hydrogen bond in solution. We investigate hydrogen-bonding of the N-H group of N-methylaniline with oxygen from liquid DMSO and acetone with infrared spectra in the N-H stretching region and X-ray absorption spectra at the N K-edge. We experimentally observe blue shifts of the infrared stretching band and an X-ray absorption pre-edge peak when going from DMSO to acetone. With ab initio molecular dynamics simulations and calculated spectra, we qualitatively reproduce the experimental observables but we do not reach quantitative agreement with experiment. The infrared spectra support the notion of weakening the N-H center dot center dot center dot O hydrogen bond from DMSO to acetone. However, we fail to theoretically reproduce the measured shift of the X-ray absorption pre-edge peak. We discuss possible shortcomings of the simulation models and spectrum calculations. Common features and distinct differences with the O-H center dot center dot center dot O hydrogen bond are highlighted, and the implications for monitoring hydrogen-bond breaking in solution are discussed.
Y1  - 2015
U6  - https://doi.org/10.1021/acs.jpcb.5b02954
SN  - 1520-6106
VL  - 119
IS  - 25
SP  - 8115
EP  - 8124
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Pulkkinen, Otto
A1  - Metzler, Ralf
T1  - Variance-corrected Michaelis-Menten equation predicts transient rates of single-enzyme reactions and response times in bacterial gene-regulation
JF  - Scientific reports
N2  - Many chemical reactions in biological cells occur at very low concentrations of constituent molecules. Thus, transcriptional gene-regulation is often controlled by poorly expressed transcription-factors, such as E. coli lac repressor with few tens of copies. Here we study the effects of inherent concentration fluctuations of substrate-molecules on the seminal Michaelis-Menten scheme of biochemical reactions. We present a universal correction to the Michaelis-Menten equation for the reaction-rates. The relevance and validity of this correction for enzymatic reactions and intracellular gene-regulation is demonstrated. Our analytical theory and simulation results confirm that the proposed variance-corrected Michaelis-Menten equation predicts the rate of reactions with remarkable accuracy even in the presence of large non-equilibrium concentration fluctuations. The major advantage of our approach is that it involves only the mean and variance of the substrate-molecule concentration. Our theory is therefore accessible to experiments and not specific to the exact source of the concentration fluctuations.
Y1  - 2015
U6  - https://doi.org/10.1038/srep17820
SN  - 2045-2322
VL  - 5
PB  - Nature Publ. Group
CY  - London
ER  - 
TY  - JOUR
A1  - Pulkkinen, Otto
A1  - Metzler, Ralf
T1  - Variance-corrected Michaelis-Menten equation predicts transient rates of single-enzyme reactions and response times in bacterial gene-regulation
JF  - Scientific reports
N2  - Many chemical reactions in biological cells occur at very low concentrations of constituent molecules. Thus, transcriptional gene-regulation is often controlled by poorly expressed transcription-factors, such as E.coli lac repressor with few tens of copies. Here we study the effects of inherent concentration fluctuations of substrate-molecules on the seminal Michaelis-Menten scheme of biochemical reactions. We present a universal correction to the Michaelis-Menten equation for the reaction-rates. The relevance and validity of this correction for enzymatic reactions and intracellular gene-regulation is demonstrated. Our analytical theory and simulation results confirm that the proposed variance-corrected Michaelis-Menten equation predicts the rate of reactions with remarkable accuracy even in the presence of large non-equilibrium concentration fluctuations. The major advantage of our approach is that it involves only the mean and variance of the substrate-molecule concentration. Our theory is therefore accessible to experiments and not specific to the exact source of the concentration fluctuations.
Y1  - 2015
U6  - https://doi.org/10.1038/srep17820
SN  - 2045-2322
IS  - 5
PB  - Nature Publishing Group
CY  - London
ER  - 
TY  - JOUR
A1  - Raatz, Michael
A1  - Hintsche, Marius
A1  - Bahrs, Marco
A1  - Theves, Matthias
A1  - Beta, Carsten
T1  - Swimming patterns of a polarly flagellated bacterium in environments of increasing complexity
JF  - European physical journal special topics
N2  - The natural habitat of many bacterial swimmers is dominated by interfaces and narrow interstitial spacings where they frequently interact with the fluid boundaries in their vicinity. To quantify these interactions, we investigated the swimming behavior of the soil bacterium Pseudomonas putida in a variety of confined environments. Using microfluidic techniques, we fabricated structured microchannels with different configurations of cylindrical obstacles. In these environments, we analyzed the swimming trajectories for different obstacle densities and arrangements. Although the overall swimming pattern remained similar to movement in the bulk fluid, we observed a change in the turning angle distribution that could be attributed to collisions with the cylindrical obstacles. Furthermore, a comparison of the mean run length of the bacteria to the mean free path of a billiard particle in the same geometry indicated that, inside a densely packed environment, the trajectories of the bacterial swimmers are efficiently guided along the open spacings.
Y1  - 2015
U6  - https://doi.org/10.1140/epjst/e2015-02454-3
SN  - 1951-6355
SN  - 1951-6401
VL  - 224
IS  - 7
SP  - 1185
EP  - 1198
PB  - Springer
CY  - Heidelberg
ER  - 
TY  - JOUR
A1  - Reverey, Julia F.
A1  - Jeon, Jae-Hyung
A1  - Bao, Han
A1  - Leippe, Matthias
A1  - Metzler, Ralf
A1  - Selhuber-Unkel, Christine
T1  - Superdiffusion dominates intracellular particle motion in the supercrowded cytoplasm of pathogenic Acanthamoeba castellanii
JF  - Scientific reports
N2  - Acanthamoebae are free-living protists and human pathogens, whose cellular functions and pathogenicity strongly depend on the transport of intracellular vesicles and granules through the cytosol. Using high-speed live cell imaging in combination with single-particle tracking analysis, we show here that the motion of endogenous intracellular particles in the size range from a few hundred nanometers to several micrometers in Acanthamoeba castellanii is strongly superdiffusive and influenced by cell locomotion, cytoskeletal elements, and myosin II. We demonstrate that cell locomotion significantly contributes to intracellular particle motion, but is clearly not the only origin of superdiffusivity. By analyzing the contribution of microtubules, actin, and myosin II motors we show that myosin II is a major driving force of intracellular motion in A. castellanii. The cytoplasm of A. castellanii is supercrowded with intracellular vesicles and granules, such that significant intracellular motion can only be achieved by actively driven motion, while purely thermally driven diffusion is negligible.
Y1  - 2015
U6  - https://doi.org/10.1038/srep11690
SN  - 2045-2322
VL  - 5
PB  - Nature Publ. Group
CY  - London
ER  - 
TY  - JOUR
A1  - Richter, Philipp
A1  - de Boer, Klaas S.
A1  - Werner, Klaus
A1  - Rauch, Thomas
T1  - High-velocity gas toward the LMC resides in the Milky Way halo
JF  - Astronomy and astrophysics : an international weekly journal
N2  - Aims. To explore the origin of high-velocity gas in the direction of the Large Magellanic Cloud, (LMC) we analyze absorption lines in the ultraviolet spectrum of a Galactic halo star that is located in front of the LMC at d = 9.2(-7.2)(+4.1) kpc distance.
 Methods. We study the velocity-component structure of low and intermediate metal ions (CII, SiII, SiIII) in the spectrum of RXJ0439.8-6809, as obtained with the Cosmic Origins Spectrograph (COS) onboard the Hubble Space Telescope (HST), and measure equivalent widths and column densities for these ions. We supplement our COS data with a Far-Ultraviolet Spectroscopic Explorer (FUSE) spectrum of the nearby LMC star Sk-69 59 and with Hi 21 cm data from the Leiden-Argentina-Bonn (LAB) survey.
 Results. Metal absorption toward RXJ0439.8-6809 is unambiguously detected in three different velocity components near v(LSR) = 0, + 60, and + 150 km s(-1). The presence of absorption proves that all three gas components are situated in front of the star, thus located in the disk and inner halo of the Milky Way. For the high-velocity cloud (HVC) at v(LSR) = + 150 km s(-1), we derive an oxygen abundance of [O/H] = -0.63 (similar to 0.2 solar) from the neighboring Sk-69 59 sight line, in accordance with previous abundance measurements for this HVC. From the observed kinematics we infer that the HVC hardly participates in the Galactic rotation.
 Conclusions. Our study shows that the HVC toward the LMC represents a Milky Way halo cloud that traces low column density gas with relatively low metallicity. We rule out scenarios in which the HVC represents material close to the LMC that stems from a LMC outflow.
KW  - Galaxy: halo
KW  - Galaxy: evolution
KW  - ISM: abundances
KW  - ISM: structure
Y1  - 2015
U6  - https://doi.org/10.1051/0004-6361/201527451
SN  - 1432-0746
VL  - 584
PB  - EDP Sciences
CY  - Les Ulis
ER  - 
TY  - JOUR
A1  - Roland, Steffen
A1  - Neubert, Sebastian
A1  - Albrecht, Steve
A1  - Stannowski, Bernd
A1  - Seger, Mark
A1  - Facchetti, Antonio
A1  - Schlatmann, Rutger
A1  - Rech, Bernd
A1  - Neher, Dieter
T1  - Hybrid Organic/Inorganic Thin-Film Multijunction Solar Cells Exceeding 11% Power Conversion Efficiency
JF  - Advanced materials
N2  - Hybrid multijunction solar cells comprising hydrogenated amorphous silicon and an organic bulk heterojunction are presented, reaching 11.7% power conversion efficiency. The benefits of merging inorganic and organic subcells are pointed out, the optimization of the cells, including optical modeling predictions and tuning of the recombination contact are described, and an outlook of this technique is given.
Y1  - 2015
U6  - https://doi.org/10.1002/adma.201404698
SN  - 0935-9648
SN  - 1521-4095
VL  - 27
IS  - 7
SP  - 1262
EP  - 1267
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Rosenblum, Michael
A1  - Pikovskij, Arkadij
T1  - Two types of quasiperiodic partial synchrony in oscillator ensembles
JF  - Physical review : E, Statistical, nonlinear and soft matter physics
N2  - We analyze quasiperiodic partially synchronous states in an ensemble of Stuart-Landau oscillators with global nonlinear coupling. We reveal two types of such dynamics: in the first case the time-averaged frequencies of oscillators and of the mean field differ, while in the second case they are equal, but the motion of oscillators is additionally modulated. We describe transitions from the synchronous state to both types of quasiperiodic dynamics, and a transition between two different quasiperiodic states. We present an example of a bifurcation diagram, where we show the borderlines for all these transitions, as well as domain of bistability.
Y1  - 2015
U6  - https://doi.org/10.1103/PhysRevE.92.012919
SN  - 1539-3755
SN  - 1550-2376
VL  - 92
IS  - 1
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Rubensson, Jan-Erik
A1  - Soderstrom, Johan
A1  - Binggeli, Christian
A1  - Grasjo, Joakim
A1  - Andersson, Johan
A1  - Sathe, Conny
A1  - Hennies, Franz
A1  - Bisogni, Valentina
A1  - Huang, Yaobo
A1  - Olalde, Paul
A1  - Schmitt, Thorsten
A1  - Strocov, Vladimir N.
A1  - Föhlisch, Alexander
A1  - Kennedy, Brian
A1  - Pietzsch, Annette
T1  - Rydberg-Resolved Resonant Inelastic Soft X-Ray Scattering: Dynamics at Core Ionization Thresholds
JF  - Physical review letters
N2  - Resonant inelastic x-ray scattering spectra excited in the immediate vicinity of the core-level ionization thresholds of N-2 have been recorded. Final states of well-resolved symmetry-selected Rydberg series converging to valence-level ionization thresholds with vibrational excitations are observed. The results are well described by a quasi-two-step model which assumes that the excited electron is unaffected by the radiative decay. This threshold dynamics simplifies the interpretation of resonant inelastic x-ray scattering spectra considerably and facilitates characterization of low-energy excited final states in molecular systems.
Y1  - 2015
U6  - https://doi.org/10.1103/PhysRevLett.114.133001
SN  - 0031-9007
SN  - 1079-7114
VL  - 114
IS  - 13
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Safdari, Hadiseh
A1  - Chechkin, Aleksei V.
A1  - Jafari, Gholamreza R.
A1  - Metzler, Ralf
T1  - Aging scaled Brownian motion
JF  - Physical review : E, Statistical, nonlinear and soft matter physics
N2  - Scaled Brownian motion (SBM) is widely used to model anomalous diffusion of passive tracers in complex and biological systems. It is a highly nonstationary process governed by the Langevin equation for Brownian motion, however, with a power-law time dependence of the noise strength. Here we study the aging properties of SBM for both unconfined and confined motion. Specifically, we derive the ensemble and time averaged mean squared displacements and analyze their behavior in the regimes of weak, intermediate, and strong aging. A very rich behavior is revealed for confined aging SBM depending on different aging times and whether the process is sub- or superdiffusive. We demonstrate that the information on the aging factorizes with respect to the lag time and exhibits a functional form that is identical to the aging behavior of scale-free continuous time random walk processes. While SBM exhibits a disparity between ensemble and time averaged observables and is thus weakly nonergodic, strong aging is shown to effect a convergence of the ensemble and time averaged mean squared displacement. Finally, we derive the density of first passage times in the semi-infinite domain that features a crossover defined by the aging time.
Y1  - 2015
U6  - https://doi.org/10.1103/PhysRevE.91.042107
SN  - 1539-3755
SN  - 1550-2376
VL  - 91
IS  - 4
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Safdari, Hadiseh
A1  - Cherstvy, Andrey G.
A1  - Chechkin, Aleksei V.
A1  - Thiel, Felix
A1  - Sokolov, Igor M.
A1  - Metzler, Ralf
T1  - Quantifying the non-ergodicity of scaled Brownian motion
JF  - Journal of physics : A, Mathematical and theoretical
N2  - We examine the non-ergodic properties of scaled Brownian motion (SBM), a non-stationary stochastic process with a time dependent diffusivity of the form D(t) similar or equal to t(alpha-1). We compute the ergodicity breaking parameter EB in the entire range of scaling exponents a, both analytically and via extensive computer simulations of the stochastic Langevin equation. We demonstrate that in the limit of long trajectory lengths T and short lag times Delta the EB parameter as function of the scaling exponent a has no divergence at alpha - 1/2 and present the asymptotes for EB in different limits. We generalize the analytical and simulations results for the time averaged and ergodic properties of SBM in the presence of ageing, that is, when the observation of the system starts only a finite time span after its initiation. The approach developed here for the calculation of the higher time averaged moments of the particle displacement can be applied to derive the ergodic properties of other stochastic processes such as fractional Brownian motion.
KW  - scaled Brownian motion
KW  - anomalous diffusion
KW  - ageing
Y1  - 2015
U6  - https://doi.org/10.1088/1751-8113/48/37/375002
SN  - 1751-8113
SN  - 1751-8121
VL  - 48
IS  - 37
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Saleem, Hussam
A1  - Downey, Austin
A1  - Laflamme, Simon
A1  - Kollosche, Matthias
A1  - Ubertini, Filippo
T1  - Investigation of Dynamic Properties of a Novel Capacitive-based Sensing Skin for Nondestructive Testing
JF  - Materials evaluation
N2  - A capacitive-based soft elastomeric strain sensor was recently developed by the authors for structural health monitoring applications. Arranged in a network configuration, the sensor becomes a sensing skin, where local deformations can be monitored over a global area. The sensor transduces a change in geometry into a measurable change in capacitance, which can be converted into strain using a previously developed electromechanical model. Prior studies have demonstrated limitations of this electromechanical model for dynamic excitations beyond 15 Hz, because of a loss in linearity in the sensor's response. In this paper, the dynamic behavior beyond 15 Hz is further studied, and a new version of the electromechanical model is proposed to accommodate dynamic strain measurements up to 40 Hz. This behavior is characterized by subjecting the sensor to a frequency sweep and identifying possible sources of nonlinearities beyond 15 Hz. Results show possible frequency dependence of the materials' Poisson's ratios, which are successfully modeled and integrated into the electromechanical model. This demonstrates that the proposed sensor can be used for monitoring and evaluation of structural responses up to 40 Hz, a range covering the vast majority of the dominating frequency responses of civil infrastructures.
KW  - nondestructive testing
KW  - structural health monitoring
KW  - soft elastomeric capacitor
KW  - capacitive sensor
KW  - vibration monitoring
KW  - sensing skin
Y1  - 2015
SN  - 0025-5327
VL  - 73
IS  - 10
SP  - 1390
EP  - 1397
PB  - American Society for Nondestructive Testing
CY  - Columbus
ER  - 
TY  - JOUR
A1  - Sander, A.
A1  - Hamann, Wolf-Rainer
A1  - Hainich, Rainer
A1  - Shenar, Tomer
A1  - Todt, Helge Tobias
T1  - Hydrodynamic modeling of massive star atmospheres
JF  - Wolf-Rayet Stars : Proceedings of an International Workshop held in Potsdam, Germany, 1.–5. June 2015
N2  - In the last decades, stellar atmosphere codes have become a key tool in understanding massive stars, including precise calculations of stellar and wind parameters, such as temperature, massloss rate, and terminal wind velocity. Nevertheless, for these models the hydrodynamic equation is not solved in the wind. Motivated by the results of the CAK theory, the models typically use a beta velocity law, which however turns out not to be adequate for stars with very strong winds, and treat the mass-loss rate as a free parameter. In a new branch of the Potsdam Wolf-Rayet model atmosphere (PoWR) code, we solve the hydrodynamic equation consistently throughout the stellar atmosphere. The PoWR code performs the calculation of the radiative force without approximations (e.g. Sobolev). We show the impact of hydrodynamically consistent modelling on OB and WR stars in comparison to conventional models and discuss the obtained velocity fields and their impact on the observed spectral lines.
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-87857
SP  - 139
EP  - 142
ER  - 
TY  - JOUR
A1  - Sander, Andreas Alexander Christoph
A1  - Shenar, Tomer
A1  - Hainich, Rainer
A1  - Gimenez-Garcia, Ana
A1  - Todt, Helge Tobias
A1  - Hamann, Wolf-Rainer
T1  - On the consistent treatment of the quasi-hydrostatic layers in hot star atmospheres
JF  - Astronomy and astrophysics : an international weekly journal
N2  - Context. Spectroscopic analysis remains the most common method to derive masses of massive stars, the most fundamental stellar parameter. While binary orbits and stellar pulsations can provide much sharper constraints on the stellar mass, these methods are only rarely applicable to massive stars. Unfortunately, spectroscopic masses of massive stars heavily depend on the detailed physics of model atmospheres.
 Aims. We demonstrate the impact of a consistent treatment of the radiative pressure on inferred gravities and spectroscopic masses of massive stars. Specifically, we investigate the contribution of line and continuum transitions to the photospheric radiative pressure. We further explore the effect of model parameters, e.g., abundances, on the deduced spectroscopic mass. Lastly, we compare our results with the plane-parallel TLUSTY code, commonly used for the analysis of massive stars with photospheric spectra.
 Methods. We calculate a small set of O-star models with the Potsdam Wolf-Rayet (PoWR) code using different approaches for the quasi-hydrostatic part. These models allow us to quantify the effect of accounting for the radiative pressure consistently. We further use PoWR models to show how the Doppler widths of line profiles and abundances of elements such as iron affect the radiative pressure, and, as a consequence, the derived spectroscopic masses.
 Results. Our study implies that errors on the order of a factor of two in the inferred spectroscopic mass are to be expected when neglecting the contribution of line and continuum transitions to the radiative acceleration in the photosphere. Usage of implausible microturbulent velocities, or the neglect of important opacity sources such as Fe, may result in errors of approximately 50% in the spectroscopic mass. A comparison with TLUSTY model atmospheres reveals a very good agreement with PoWR at the limit of low mass-loss rates.
KW  - stars: early-type
KW  - stars: mass-loss
KW  - stars: winds, outflows
KW  - stars: atmospheres
KW  - stars: fundamental parameters
KW  - stars: massive
Y1  - 2015
U6  - https://doi.org/10.1051/0004-6361/201425356
SN  - 0004-6361
SN  - 1432-0746
VL  - 577
PB  - EDP Sciences
CY  - Les Ulis
ER  - 
TY  - JOUR
A1  - Sandev, Trifce
A1  - Chechkin, Aleksei V.
A1  - Kantz, Holger
A1  - Metzler, Ralf
T1  - Diffusion and fokker-planck-smoluchowski equations with generalized memory kernel
JF  - Fractional calculus and applied analysis : an international journal for theory and applications
N2  - We consider anomalous stochastic processes based on the renewal continuous time random walk model with different forms for the probability density of waiting times between individual jumps. In the corresponding continuum limit we derive the generalized diffusion and Fokker-Planck-Smoluchowski equations with the corresponding memory kernels. We calculate the qth order moments in the unbiased and biased cases, and demonstrate that the generalized Einstein relation for the considered dynamics remains valid. The relaxation of modes in the case of an external harmonic potential and the convergence of the mean squared displacement to the thermal plateau are analyzed.
KW  - continuous time random walk (CTRW)
KW  - Fokker-Planck-Smoluchowski equation
KW  - Mittag-Leffler functions
KW  - anomalous diffusion
KW  - multi-scaling
Y1  - 2015
U6  - https://doi.org/10.1515/fca-2015-0059
SN  - 1311-0454
SN  - 1314-2224
VL  - 18
IS  - 4
SP  - 1006
EP  - 1038
PB  - De Gruyter
CY  - Berlin
ER  - 
TY  - JOUR
A1  - Sandev, Trifce
A1  - Chechkin, Aleksei V.
A1  - Korabel, Nickolay
A1  - Kantz, Holger
A1  - Sokolov, Igor M.
A1  - Metzler, Ralf
T1  - Distributed-order diffusion equations and multifractality: Models and solutions
JF  - Physical review : E, Statistical, nonlinear and soft matter physics
N2  - We study distributed-order time fractional diffusion equations characterized by multifractal memory kernels, in contrast to the simple power-law kernel of common time fractional diffusion equations. Based on the physical approach to anomalous diffusion provided by the seminal Scher-Montroll-Weiss continuous time random walk, we analyze both natural and modified-form distributed-order time fractional diffusion equations and compare the two approaches. The mean squared displacement is obtained and its limiting behavior analyzed. We derive the connection between the Wiener process, described by the conventional Langevin equation and the dynamics encoded by the distributed-order time fractional diffusion equation in terms of a generalized subordination of time. A detailed analysis of the multifractal properties of distributed-order diffusion equations is provided.
Y1  - 2015
U6  - https://doi.org/10.1103/PhysRevE.92.042117
SN  - 1539-3755
SN  - 1550-2376
VL  - 92
IS  - 4
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Sellberg, Jonas A.
A1  - McQueen, Trevor A.
A1  - Laksmono, Hartawan
A1  - Schreck, Simon
A1  - Beye, Martin
A1  - DePonte, Daniel P.
A1  - Kennedy, Brian
A1  - Nordlund, Dennis
A1  - Sierra, Raymond G.
A1  - Schlesinger, Daniel
A1  - Tokushima, Takashi
A1  - Zhovtobriukh, Iurii
A1  - Eckert, Sebastian
A1  - Segtnan, Vegard H.
A1  - Ogasawara, Hirohito
A1  - Kubicek, Katharina
A1  - Techert, Simone
A1  - Bergmann, Uwe
A1  - Dakovski, Georgi L.
A1  - Schlotter, William F.
A1  - Harada, Yoshihisa
A1  - Bogan, Michael J.
A1  - Wernet, Philippe
A1  - Föhlisch, Alexander
A1  - Pettersson, Lars G. M.
A1  - Nilsson, Anders
T1  - X-ray emission spectroscopy of bulk liquid water in "no-man's land"
JF  - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr
N2  - The structure of bulk liquid water was recently probed by x-ray scattering below the temperature limit of homogeneous nucleation (T-H) of similar to 232 K [J. A. Sellberg et al., Nature 510, 381-384 (2014)]. Here, we utilize a similar approach to study the structure of bulk liquid water below T-H using oxygen K-edge x-ray emission spectroscopy (XES). Based on previous XES experiments [T. Tokushima et al., Chem. Phys. Lett. 460, 387-400 (2008)] at higher temperatures, we expected the ratio of the 1b(1)' and 1b(1)" peaks associated with the lone-pair orbital in water to change strongly upon deep supercooling as the coordination of the hydrogen (H-) bonds becomes tetrahedral. In contrast, we observed only minor changes in the lone-pair spectral region, challenging an interpretation in terms of two interconverting species. A number of alternative hypotheses to explain the results are put forward and discussed. Although the spectra can be explained by various contributions from these hypotheses, we here emphasize the interpretation that the line shape of each component changes dramatically when approaching lower temperatures, where, in particular, the peak assigned to the proposed disordered component would become more symmetrical as vibrational interference becomes more important. (C) 2015 AIP Publishing LLC.
Y1  - 2015
U6  - https://doi.org/10.1063/1.4905603
SN  - 0021-9606
SN  - 1089-7690
VL  - 142
IS  - 4
PB  - American Institute of Physics
CY  - Melville
ER  - 
TY  - JOUR
A1  - Shenar, Tomer
A1  - Hamann, Wolf-Rainer
A1  - Todt, Helge Tobias
T1  - The impact of rotation on the line profiles of Wolf-Rayet stars
JF  - Wolf-Rayet Stars : Proceedings of an International Workshop held in Potsdam, Germany, 1.–5. June 2015
N2  - The distribution of angular momentum in massive stars is a critical component of their evolution, yet not much is known on the rotation velocities of Wolf-Rayet stars. There are various indications that rapidly rotating Wolf-Rayet stars should exist. Unfortunately, due to their expanding atmospheres, rotational velocities of Wolf-Rayet stars are very difficult to measure. In this work, we model the effects of rotation on the atmospheres of Wolf-Rayet stars by implementing a 3D integration scheme in the PoWR code. We further investigate whether the peculiar spectra of five Wolf-Rayet stars may imply rapid rotation, infer the corresponding rotation parameters, and discuss the implications of our results. We find that rotation helps to reproduce the unique spectra analyzed here. However, if rotation is indeed involved, the inferred rotational velocities at the stellar surface are large (∼ 200 km/s), and the implied co-rotation radii (∼ 10R∗) suggest the existence of very strong photospheric magnetic fields (∼ 20 kG).
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-88008
SP  - 193
EP  - 196
ER  - 
TY  - JOUR
A1  - Shenar, Tomer
A1  - Oskinova, Lida
A1  - Hamann, Wolf-Rainer
A1  - Corcoran, Michael F.
A1  - Moffat, Anthony F. J.
A1  - Pablo, Herbert
A1  - Richardson, Noel D.
A1  - Waldron, Wayne L.
A1  - Huenemoerder, David P.
A1  - Maiz Apellaniz, Jesus
A1  - Nichols, Joy S.
A1  - Todt, Helge Tobias
A1  - Naze, Yael
A1  - Hoffman, Jennifer L.
A1  - Pollock, Andy M. T.
A1  - Negueruela, Ignacio
T1  - A coordinated X-Ray and optical campaign of the nearest massive eclipsing binary, delta ORIONIS Aa. IV. A multiwavelength, non-lte spectroscopic analysis
JF  - The astrophysical journal : an international review of spectroscopy and astronomical physics
N2  - Eclipsing systems of massive stars allow one to explore the properties of their components in great detail. We perform a multi-wavelength, non-LTE analysis of the three components of the massive multiple system delta Ori A, focusing on the fundamental stellar properties, stellar winds, and X-ray characteristics of the system. The primary's distance-independent parameters turn out to be characteristic for its spectral type (O9.5 II), but usage of the Hipparcos parallax yields surprisingly low values for the mass, radius, and luminosity. Consistent values follow only if delta Ori lies at about twice the Hipparcos distance, in the vicinity of the sigma-Orionis cluster. The primary and tertiary dominate the spectrum and leave the secondary only marginally detectable. We estimate the V-band magnitude difference between primary and secondary to be Delta V approximate to 2.(m)8. The inferred parameters suggest that the secondary is an early B-type dwarf (approximate to B1 V), while the tertiary is an early B-type subgiant (approximate to B0 IV). We find evidence for rapid turbulent velocities (similar to 200 km s(-1)) and wind inhomogeneities, partially optically thick, in the primary's wind. The bulk of the X-ray emission likely emerges from the primary's stellar wind (logL(X)/L-Bol approximate to -6.85), initiating close to the stellar surface at R-0 similar to 1.1 R-*. Accounting for clumping, the mass-loss rate of the primary is found to be log (M) over dot approximate to -6.4 (M-circle dot yr(-1))., which agrees with hydrodynamic predictions, and provides a consistent picture along the X-ray, UV, optical, and radio spectral domains.
KW  - binaries: close
KW  - binaries: eclipsing
KW  - stars: early-type
KW  - stars: individual ([HD 36486]delta Ori A)
KW  - X-rays: stars
Y1  - 2015
U6  - https://doi.org/10.1088/0004-637X/809/2/135
SN  - 0004-637X
SN  - 1538-4357
VL  - 809
IS  - 2
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Shin, Jaeoh
A1  - Cherstvy, Andrey G.
A1  - Kim, Won Kyu
A1  - Metzler, Ralf
T1  - Facilitation of polymer looping and giant polymer diffusivity in crowded solutions of active particles
JF  - New journal of physics : the open-access journal for physics
N2  - We study the dynamics of polymer chains in a bath of self-propelled particles (SPP) by extensive Langevin dynamics simulations in a two-dimensional model system. Specifically, we analyse the polymer looping properties versus the SPP activity and investigate how the presence of the active particles alters the chain conformational statistics. We find that SPPs tend to extend flexible polymer chains, while they rather compactify stiffer semiflexible polymers, in agreement with previous results. Here we show that higher activities of SPPs yield a higher effective temperature of the bath and thus facilitate the looping kinetics of a passive polymer chain. We explicitly compute the looping probability and looping time in a wide range of the model parameters. We also analyse the motion of a monomeric tracer particle and the polymer's centre of mass in the presence of the active particles in terms of the time averaged mean squared displacement, revealing a giant diffusivity enhancement for the polymer chain via SPP pooling. Our results are applicable to rationalising the dimensions and looping kinetics of biopolymers at constantly fluctuating and often actively driven conditions inside biological cells or in suspensions of active colloidal particles or bacteria cells.
KW  - diffusion
KW  - active transport
KW  - polymers
Y1  - 2015
U6  - https://doi.org/10.1088/1367-2630/17/11/113008
SN  - 1367-2630
VL  - 17
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Shin, Jaeoh
A1  - Cherstvy, Andrey G.
A1  - Metzler, Ralf
T1  - Self-subdiffusion in solutions of star-shaped crowders: non-monotonic effects of inter-particle interactions
JF  - New journal of physics : the open-access journal for physics
N2  - We examine by extensive computer simulations the self-diffusion of anisotropic star-like particles in crowded two-dimensional solutions. We investigate the implications of the area coverage fraction phi of the crowders and the crowder-crowder adhesion properties on the regime of transient anomalous diffusion. We systematically compute the mean squared displacement (MSD) of the particles, their time averaged MSD, and the effective diffusion coefficient. The diffusion is ergodic in the limit of long traces, such that the mean time averaged MSD converges towards the ensemble averaged MSD, and features a small residual amplitude spread of the time averaged MSD from individual trajectories. At intermediate time scales, we quantify the anomalous diffusion in the system. Also, we show that the translational-but not rotational-diffusivity of the particles Dis a nonmonotonic function of the attraction strength between them. Both diffusion coefficients decrease as the power law D(phi) similar to (1 - phi/phi*)(2 ... 2.4) with the area fraction phi occupied by the crowders and the critical value phi*. Our results might be applicable to rationalising the experimental observations of non-Brownian diffusion for a number of standard macromolecular crowders used in vitro to mimic the cytoplasmic conditions of living cells.
KW  - anomalous diffusion
KW  - crowded fluids
KW  - stochastic processes
Y1  - 2015
U6  - https://doi.org/10.1088/1367-2630/17/11/113028
SN  - 1367-2630
VL  - 17
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Shin, Jaeoh
A1  - Cherstvy, Andrey G.
A1  - Metzler, Ralf
T1  - Kinetics of polymer looping with macromolecular crowding: effects of volume fraction and crowder size
JF  - Soft matter
N2  - The looping of polymers such as DNA is a fundamental process in the molecular biology of living cells, whose interior is characterised by a high degree of molecular crowding. We here investigate in detail the looping dynamics of flexible polymer chains in the presence of different degrees of crowding. From the analysis of the looping-unlooping rates and the looping probabilities of the chain ends we show that the presence of small crowders typically slows down the chain dynamics but larger crowders may in fact facilitate the looping. We rationalise these non-trivial and often counterintuitive effects of the crowder size on the looping kinetics in terms of an effective solution viscosity and standard excluded volume. It is shown that for small crowders the effect of an increased viscosity dominates, while for big crowders we argue that confinement effects (caging) prevail. The tradeoff between both trends can thus result in the impediment or facilitation of polymer looping, depending on the crowder size. We also examine how the crowding volume fraction, chain length, and the attraction strength of the contact groups of the polymer chain affect the looping kinetics and hairpin formation dynamics. Our results are relevant for DNA looping in the absence and presence of protein mediation, DNA hairpin formation, RNA folding, and the folding of polypeptide chains under biologically relevant high-crowding conditions.
Y1  - 2015
U6  - https://doi.org/10.1039/c4sm02007c
SN  - 1744-683X
SN  - 1744-6848
VL  - 11
IS  - 3
SP  - 472
EP  - 488
PB  - Royal Society of Chemistry
CY  - Cambridge
ER  - 
TY  - JOUR
A1  - Shin, Jaeoh
A1  - Cherstvy, Andrey G.
A1  - Metzler, Ralf
T1  - Polymer looping is controlled by macromolecular crowding, spatial confinement, and chain stiffness
JF  - ACS Macro Letters
N2  - We study by extensive computer simulations the looping characteristics of linear polymers with varying persistence length inside a spherical cavity in the presence of macromolecular crowding. For stiff chains, the looping probability and looping time reveal wildly oscillating patterns as functions of the chain length. The effects of crowding differ dramatically for flexible versus stiff polymers. While for flexible chains the looping kinetics is slowed down by the crowders, for stiffer chains the kinetics turns out to be either decreased or facilitated, depending on the polymer length. For severe confinement, the looping kinetics may become strongly facilitated by crowding. Our findings are of broad impact for DNA looping in the crowded and compartmentalized interior of living biological cells.
Y1  - 2015
U6  - https://doi.org/10.1021/mz500709w
SN  - 2161-1653
VL  - 4
IS  - 2
SP  - 202
EP  - 206
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Shrader, C. R.
A1  - Hamaguchi, K.
A1  - Sturner, Steven J.
A1  - Oskinova, Lida
A1  - Almeyda, T.
A1  - Petre, R.
T1  - Hifg-energy properties of the enigmatic be STAR gamma Cassiopeiae
JF  - The astrophysical journal : an international review of spectroscopy and astronomical physics
N2  - We present the results of a broadband X-ray study of the enigmatic Be star Gamma Cassiopeiae (herein gamma Cas) based on observations made with both the Suzaku and INTEGRAL observatories.. Cas has long been recognized as the prototypical example of a small subclass of Be stars with moderately strong X-ray emission dominated by a hot thermal component in the 0.5-12 keV energy range (L-x approximate to 10(32)-10(33) erg s(-1)). This places them at the high end of the known luminosity distribution for stellar emission, but several orders of magnitude below typical accretion-powered Be X-ray binaries. The INTEGRAL observations spanned an eight-year baseline and represent the deepest measurement to date at energies above similar to 50 keV. We find that the INTEGRAL data are consistent within statistics to a constant intensity source above 20 keV, with emission extending up to similar to 100 keV, and that searches for all of the previously reported periodicities of the system at lower energies led to null results. We further find that our combined Suzaku and INTEGRAL spectrum, which we suggest is the most accurate broadband X-ray measurement of gamma Cas to date, is fitted extremely well with a thermal plasma emission model with a single absorption component. We found no compelling need for an additional non-thermal high-energy component. We discuss these results in the context of a currently favored models for gamma Cas and its analogs.
KW  - gamma rays: stars
KW  - stars: emission-line, Be
KW  - stars: individual (gamma Cassiopeiae)
KW  - white dwarfs
KW  - X-rays: binaries
KW  - X-rays: stars
Y1  - 2015
U6  - https://doi.org/10.1088/0004-637X/799/1/84
SN  - 0004-637X
SN  - 1538-4357
VL  - 799
IS  - 1
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Sillmann, Jana
A1  - Lenton, Timothy M.
A1  - Levermann, Anders
A1  - Ott, Konrad
A1  - Hulme, Mike
A1  - Benduhn, Francois
A1  - Horton, Joshua B.
T1  - COMMENTARY: No emergency argument for climate engineering
JF  - Nature climate change
Y1  - 2015
SN  - 1758-678X
SN  - 1758-6798
VL  - 5
IS  - 4
SP  - 290
EP  - 292
PB  - Nature Publ. Group
CY  - London
ER  - 
TY  - JOUR
A1  - Singh, Rajeev
A1  - Mellinger, Axel
T1  - Measurement of through-thickness thermal diffusivity of thermoplastics using thermal wave method
JF  - Indian journal of physics
N2  - Thermo-physical properties, such as thermal conductivity, thermal diffusivity and specific heat are important quantities that are needed to interpret and characterize thermoplastic materials. Such characterization is necessary for many applications, ranging from aerospace engineering to food packaging, electrical and electronic industry and medical science. In this work, the thermal diffusivity of commercially available polymeric films is measured in the thickness direction at room temperature using thermal wave method. The results obtained with this method are in good agreement with theoretical and experimental values.
KW  - Thermoplastics
KW  - Thermal diffusivity
KW  - Thermal wave method
KW  - Polymer
Y1  - 2015
U6  - https://doi.org/10.1007/s12648-014-0579-2
SN  - 0973-1458
SN  - 0974-9845
VL  - 89
IS  - 4
SP  - 361
EP  - 368
PB  - Indian Association for the Cultivation of Science
CY  - Kolkata
ER  - 
TY  - JOUR
A1  - Steinke, M.
A1  - Oskinova, Lida
A1  - Hamann, Wolf-Rainer
A1  - Sander, A.
T1  - The Wolf-Rayet stars WR102c and 102ka and their isolation
JF  - Wolf-Rayet Stars : Proceedings of an International Workshop held in Potsdam, Germany, 1.–5. June 2015
N2  - While the majority of very massive stars is clearly found in clusters, there are also very massive objects not associated with any cluster, suggesting they may have been born in isolation. In order to gain more insights, we studied the regions around two WR stars in the Galactic Center region. To understand the nature of the potential cluster around massive stars, photometry alone is not sufficient. We therefore used the ESO VLT/SINFONI integral field spectrograph to obtain photometry and spectra for the whole region around our two candidate stars. In total, more than 60 stars have been found and assigned a spectral type.
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-88503
SP  - 365
ER  -