@misc{NeherKniepertElimelechetal.2016,
  author    = {Neher, Dieter and Kniepert, Juliane and Elimelech, Arik and Koster, L. Jan Anton},
  title     = {A New Figure of Merit for Organic Solar Cells with Transport-limited Photocurrents},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-91414},
  pages     = {9},
  year      = {2016},
  abstract  = {Compared to their inorganic counterparts, organic semiconductors suffer from relatively low charge carrier mobilities. Therefore, expressions derived for inorganic solar cells to correlate characteristic performance parameters to material properties are prone to fail when applied to organic devices. This is especially true for the classical Shockley-equation commonly used to describe current-voltage (JV)-curves, as it assumes a high electrical conductivity of the charge transporting material. Here, an analytical expression for the JV-curves of organic solar cells is derived based on a previously published analytical model. This expression, bearing a similar functional dependence as the Shockley-equation, delivers a new figure of merit α to express the balance between free charge recombination and extraction in low mobility photoactive materials. This figure of merit is shown to determine critical device parameters such as the apparent series resistance and the fill factor.},
  language  = {en}
}
@misc{CherstvyMetzler2016,
  author    = {Cherstvy, Andrey G. and Metzler, Ralf},
  title     = {Anomalous diffusion in time-fluctuating non-stationary diffusivity landscapes},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-95901},
  pages     = {23840 -- 23852},
  year      = {2016},
  abstract  = {We investigate the ensemble and time averaged mean squared displacements for particle diffusion in a simple model for disordered media by assuming that the local diffusivity is both fluctuating in time and has a deterministic average growth or decay in time. In this study we compare computer simulations of the stochastic Langevin equation for this random diffusion process with analytical results. We explore the regimes of normal Brownian motion as well as anomalous diffusion in the sub- and superdiffusive regimes. We also consider effects of the inertial term on the particle motion. The investigation of the resulting diffusion is performed for unconfined and confined motion.},
  language  = {en}
}
@misc{PavlenkoSanderMitzscherlingetal.2016,
  author    = {Pavlenko, Elena S. and Sander, Mathias and Mitzscherling, Steffen and Pudell, Jan-Etienne and Zamponi, Flavio and R{\"o}ssle, Matthias and Bojahr, Andre and Bargheer, Matias},
  title     = {Azobenzene - functionalized polyelectrolyte nanolayers as ultrafast optoacoustic transducers},
  volume    = {8},
  doi       = {10.1039/C6NR01448H},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-101996},
  pages     = {13297 -- 13302},
  year      = {2016},
  abstract  = {We introduce azobenzene-functionalized polyelectrolyte multilayers as efficient, inexpensive optoacoustic transducers for hyper-sound strain waves in the GHz range. By picosecond transient reflectivity measurements we study the creation of nanoscale strain waves, their reflection from interfaces, damping by scattering from nanoparticles and propagation in soft and hard adjacent materials like polymer layers, quartz and mica. The amplitude of the generated strain ε ∼ 5 × 10-4 is calibrated by ultrafast X-ray diffraction.},
  language  = {en}
}
@misc{deCarvalhoMetzlerCherstvy2016,
  author    = {de Carvalho, Sidney J. and Metzler, Ralf and Cherstvy, Andrey G.},
  title     = {Critical adsorption of polyelectrolytes onto planar and convex highly charged surfaces},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-100295},
  pages     = {17},
  year      = {2016},
  abstract  = {We study the adsorption-desorption transition of polyelectrolyte chains onto planar, cylindrical and spherical surfaces with arbitrarily high surface charge densities by massive Monte Carlo computer simulations. We examine in detail how the well known scaling relations for the threshold transition—demarcating the adsorbed and desorbed domains of a polyelectrolyte near weakly charged surfaces—are altered for highly charged interfaces. In virtue of high surface potentials and large surface charge densities, the Debye-H{\"u}ckel approximation is often not feasible and the nonlinear Poisson-Boltzmann approach should be implemented. At low salt conditions, for instance, the electrostatic potential from the nonlinear Poisson-Boltzmann equation is smaller than the Debye-H{\"u}ckel result, such that the required critical surface charge density for polyelectrolyte adsorption σc increases. The nonlinear relation between the surface charge density and electrostatic potential leads to a sharply increasing critical surface charge density with growing ionic strength, imposing an additional limit to the critical salt concentration above which no polyelectrolyte adsorption occurs at all. We contrast our simulations findings with the known scaling results for weak critical polyelectrolyte adsorption onto oppositely charged surfaces for the three standard geometries. Finally, we discuss some applications of our results for some physical-chemical and biophysical systems.},
  language  = {en}
}
@misc{NiskanenKooserKoskeloetal.2016,
  author    = {Niskanen, Johannes and Kooser, Kuno and Koskelo, Jaakko and K{\"a}{\"a}mbre, Tanel and Kunnus, Kristjan and Pietzsch, Annette and Quevedo, Wilson and Hakala, Mikko and F{\"o}hlisch, Alexander and Huotari, Simo and Kukk, Edwin},
  title     = {Density functional simulation of resonant inelastic X-ray scattering experiments in liquids: acetonitrile},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-395133},
  pages     = {7},
  year      = {2016},
  abstract  = {In this paper we report an experimental and computational study of liquid acetonitrile (H3C-C[triple bond, length as m-dash]N) by resonant inelastic X-ray scattering (RIXS) at the N K-edge. The experimental spectra exhibit clear signatures of the electronic structure of the valence states at the N site and incident-beam-polarization dependence is observed as well. Moreover, we find fine structure in the quasielastic line that is assigned to finite scattering duration and nuclear relaxation. We present a simple and light-to-evaluate model for the RIXS maps and analyze the experimental data using this model combined with ab initio molecular dynamics simulations. In addition to polarization-dependence and scattering-duration effects, we pinpoint the effects of different types of chemical bonding to the RIXS spectrum and conclude that the H2C-C[double bond, length as m-dash]NH isomer, suggested in the literature, does not exist in detectable quantities. We study solution effects on the scattering spectra with simulations in liquid and in vacuum. The presented model for RIXS proved to be light enough to allow phase-space-sampling and still accurate enough for identification of transition lines in physical chemistry research by RIXS.},
  language  = {en}
}
@misc{KurpiersNeher2016,
  author    = {Kurpiers, Jona and Neher, Dieter},
  title     = {Dispersive Non-Geminate Recombination in an Amorphous Polymer:Fullerene Blend},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-91541},
  pages     = {10},
  year      = {2016},
  abstract  = {Recombination of free charge is a key process limiting the performance of solar cells. For low mobility materials, such as organic semiconductors, the kinetics of non-geminate recombination (NGR) is strongly linked to the motion of charges. As these materials possess significant disorder, thermalization of photogenerated carriers in the inhomogeneously broadened density of state distribution is an unavoidable process. Despite its general importance, knowledge about the kinetics of NGR in complete organic solar cells is rather limited. We employ time delayed collection field (TDCF) experiments to study the recombination of photogenerated charge in the high-performance polymer:fullerene blend PCDTBT:PCBM. NGR in the bulk of this amorphous blend is shown to be highly dispersive, with a continuous reduction of the recombination coefficient throughout the entire time scale, until all charge carriers have either been extracted or recombined. Rapid, contact-mediated recombination is identified as an additional loss channel, which, if not properly taken into account, would erroneously suggest a pronounced field dependence of charge generation. These findings are in stark contrast to the results of TDCF experiments on photovoltaic devices made from ordered blends, such as P3HT:PCBM, where non-dispersive recombination was proven to dominate the charge carrier dynamics under application relevant conditions.},
  language  = {en}
}
@misc{YangGuehrVecchioneetal.2016,
  author    = {Yang, Jie and Guehr, Markus and Vecchione, Theodore and Robinson, Matthew Scott and Li, Renkai and Hartmann, Nick and Shen, Xiaozhe and Coffee, Ryan and Corbett, Jeff and Fry, Alan and Gaffney, Kelly and Gorkhover, Tais and Hast, Carsten and Jobe, Keith and Makasyuk, Igor and Reid, Alexander and Robinson, Joseph and Vetter, Sharon and Wang, Fenglin and Weathersby, Stephen and Yoneda, Charles and Wang, Xijie and Centurion, Martin},
  title     = {Femtosecond gas phase electron diffraction with MeV electrons},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-394989},
  pages     = {19},
  year      = {2016},
  abstract  = {We present results on ultrafast gas electron diffraction (UGED) experiments with femtosecond resolution using the MeV electron gun at SLAC National Accelerator Laboratory. UGED is a promising method to investigate molecular dynamics in the gas phase because electron pulses can probe the structure with a high spatial resolution. Until recently, however, it was not possible for UGED to reach the relevant timescale for the motion of the nuclei during a molecular reaction. Using MeV electron pulses has allowed us to overcome the main challenges in reaching femtosecond resolution, namely delivering short electron pulses on a gas target, overcoming the effect of velocity mismatch between pump laser pulses and the probe electron pulses, and maintaining a low timing jitter. At electron kinetic energies above 3 MeV, the velocity mismatch between laser and electron pulses becomes negligible. The relativistic electrons are also less susceptible to temporal broadening due to the Coulomb force. One of the challenges of diffraction with relativistic electrons is that the small de Broglie wavelength results in very small diffraction angles. In this paper we describe the new setup and its characterization, including capturing static diffraction patterns of molecules in the gas phase, finding time-zero with sub-picosecond accuracy and first time-resolved diffraction experiments. The new device can achieve a temporal resolution of 100 fs root-mean-square, and sub-angstrom spatial resolution. The collimation of the beam is sufficient to measure the diffraction pattern, and the transverse coherence is on the order of 2 nm. Currently, the temporal resolution is limited both by the pulse duration of the electron pulse on target and by the timing jitter, while the spatial resolution is limited by the average electron beam current and the signal-to-noise ratio of the detection system. We also discuss plans for improving both the temporal resolution and the spatial resolution.},
  language  = {en}
}
@misc{RaetzelWilkensMenzel2016,
  author    = {R{\"a}tzel, Dennis and Wilkens, Martin and Menzel, Ralf},
  title     = {Gravitational properties of light},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-90553},
  year      = {2016},
  abstract  = {The gravitational field of a laser pulse of finite lifetime, is investigated in the framework of linearized gravity. Although the effects are very small, they may be of fundamental physical interest. It is shown that the gravitational field of a linearly polarized light pulse is modulated as the norm of the corresponding electric field strength, while no modulations arise for circular polarization. In general, the gravitational field is independent of the polarization direction. It is shown that all physical effects are confined to spherical shells expanding with the speed of light, and that these shells are imprints of the spacetime events representing emission and absorption of the pulse. Nearby test particles at rest are attracted towards the pulse trajectory by the gravitational field due to the emission of the pulse, and they are repelled from the pulse trajectory by the gravitational field due to its absorption. Examples are given for the size of the attractive effect. It is recovered that massless test particles do not experience any physical effect if they are co-propagating with the pulse, and that the acceleration of massless test particles counter-propagating with respect to the pulse is four times stronger than for massive particles at rest. The similarities between the gravitational effect of a laser pulse and Newtonian gravity in two dimensions are pointed out. The spacetime curvature close to the pulse is compared to that induced by gravitational waves from astronomical sources.},
  language  = {en}
}
@misc{GhoshCherstvyPetrovetal.2016,
  author    = {Ghosh, Surya K. and Cherstvy, Andrey G. and Petrov, Eugene P. and Metzler, Ralf},
  title     = {Interactions of rod-like particles on responsive elastic sheets},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-95882},
  year      = {2016},
  abstract  = {What are the physical laws of the mutual interactions of objects bound to cell membranes, such as various membrane proteins or elongated virus particles? To rationalise this, we here investigate by extensive computer simulations mutual interactions of rod-like particles adsorbed on the surface of responsive elastic two-dimensional sheets. Specifically, we quantify sheet deformations as a response to adhesion of such filamentous particles. We demonstrate that tip-to-tip contacts of rods are favoured for relatively soft sheets, while side-by-side contacts are preferred for stiffer elastic substrates. These attractive orientation-dependent substrate-mediated interactions between the rod-like particles on responsive sheets can drive their aggregation and self-assembly. The optimal orientation of the membrane-bound rods is established via responding to the elastic energy profiles created around the particles. We unveil the phase diagramme of attractive-repulsive rod-rod interactions in the plane of their separation and mutual orientation. Applications of our results to other systems featuring membrane-associated particles are also discussed.},
  language  = {en}
}
@misc{PimenovaGoldobinRosenblumetal.2016,
  author    = {Pimenova, Anastasiya V. and Goldobin, Denis S. and Rosenblum, Michael and Pikovskij, Arkadij},
  title     = {Interplay of coupling and common noise at the transition to synchrony in oscillator populations},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-103471},
  pages     = {7},
  year      = {2016},
  abstract  = {There are two ways to synchronize oscillators: by coupling and by common forcing, which can be pure noise. By virtue of the Ott-Antonsen ansatz for sine-coupled phase oscillators, we obtain analytically tractable equations for the case where both coupling and common noise are present. While noise always tends to synchronize the phase oscillators, the repulsive coupling can act against synchrony, and we focus on this nontrivial situation. For identical oscillators, the fully synchronous state remains stable for small repulsive coupling; moreover it is an absorbing state which always wins over the asynchronous regime. For oscillators with a distribution of natural frequencies, we report on a counter-intuitive effect of dispersion (instead of usual convergence) of the oscillators frequencies at synchrony; the latter effect disappears if noise vanishes.},
  language  = {en}
}