@article{MengelLevermannSchleussneretal.2012, author = {Mengel, Matthias and Levermann, Anders and Schleussner, Carl-Friedrich and Born, Andreas}, title = {Enhanced Atlantic subpolar gyre variability through baroclinic threshold in a coarse resolution model}, series = {Earth system dynamics}, volume = {3}, journal = {Earth system dynamics}, number = {2}, publisher = {Copernicus}, address = {G{\"o}ttingen}, issn = {2190-4979}, doi = {10.5194/esd-3-189-2012}, pages = {189 -- 197}, year = {2012}, abstract = {Direct observations, satellite measurements and paleo records reveal strong variability in the Atlantic subpolar gyre on various time scales. Here we show that variations of comparable amplitude can only be simulated in a coupled climate model in the proximity of a dynamical threshold. The threshold and the associated dynamic response is due to a positive feedback involving increased salt transport in the subpolar gyre and enhanced deep convection in its centre. A series of sensitivity experiments is performed with a coarse resolution ocean general circulation model coupled to a statistical-dynamical atmosphere model which in itself does not produce atmospheric variability. To simulate the impact of atmospheric variability, the model system is perturbed with freshwater forcing of varying, but small amplitude and multi-decadal to centennial periodicities and observational variations in wind stress. While both freshwater and wind-stress-forcing have a small direct effect on the strength of the subpolar gyre, the magnitude of the gyre's response is strongly increased in the vicinity of the threshold. Our results indicate that baroclinic self-amplification in the North Atlantic ocean can play an important role in presently observed SPG variability and thereby North Atlantic climate variability on multi-decadal scales.}, language = {en} } @article{HeuerSagahtiJechowetal.2012, author = {Heuer, Axel and Sagahti, A. and Jechow, Andreas and Skoczowsky, D. and Menzel, Ralf}, title = {Multi-wavelength, high spatial brightness operation of a phase-locked stripe-array diode laser}, series = {Laser physics}, volume = {22}, journal = {Laser physics}, number = {1}, publisher = {Pleiades Publ.}, address = {New York}, issn = {1054-660X}, doi = {10.1134/S1054660X12010057}, pages = {160 -- 164}, year = {2012}, abstract = {Stable continuous wave multi-wavelength operation of a stripe-array diode laser with an externalcavity spectral beam combining geometry is presented. In this setup each emitter of the stripe-array is forced to operate at a different wavelength, which leads to a decoupling between the usually phase-locked emitters. With a reflective diffraction grating with a period of 300 lines per mm, 33 equidistant laser lines around a center wavelength of 978 nm were realized, spanning a spectral range of 26 nm. With this novel approach near-diffraction limited emission with a beam quality of M (2) < 1.2 and an output power of 450 mW was achieved. This laser light source can be used for applications requiring low temporal but high spatial coherence.}, language = {en} } @article{FuerstLevermann2012, author = {F{\"u}rst, Johannes J. and Levermann, Anders}, title = {A minimal model for wind- and mixing-driven overturning threshold behavior for both driving mechanisms}, series = {Climate dynamics : observational, theoretical and computational research on the climate system}, volume = {38}, journal = {Climate dynamics : observational, theoretical and computational research on the climate system}, number = {1-2}, publisher = {Springer}, address = {New York}, issn = {0930-7575}, doi = {10.1007/s00382-011-1003-7}, pages = {239 -- 260}, year = {2012}, abstract = {We present a minimal conceptual model for the Atlantic meridional overturning circulation which incorporates the advection of salinity and the basic dynamics of the oceanic pycnocline. Four tracer transport processes following Gnanadesikan in Science 283(5410):2077-2079, (1999) allow for a dynamical adjustment of the oceanic pycnocline which defines the vertical extent of a mid-latitudinal box. At the same time the model captures the salt-advection feedback (Stommel in Tellus 13(2):224-230, (1961)). Due to its simplicity the model can be solved analytically in the purely wind- and purely mixing-driven cases. We find the possibility of abrupt transition in response to surface freshwater forcing in both cases even though the circulations are very different in physics and geometry. This analytical approach also provides expressions for the critical freshwater input marking the change in the dynamics of the system. Our analysis shows that including the pycnocline dynamics in a salt-advection model causes a decrease in the freshwater sensitivity of its northern sinking up to a threshold at which the circulation breaks down. Compared to previous studies the model is restricted to the essential ingredients. Still, it exhibits a rich behavior which reaches beyond the scope of this study and might be used as a paradigm for the qualitative behaviour of the Atlantic overturning in the discussion of driving mechanisms.}, language = {en} } @article{SereshkiLomholtMetzler2012, author = {Sereshki, L. E. and Lomholt, M. A. and Metzler, Ralf}, title = {A solution to the subdiffusion-efficiency paradox inactive states enhance reaction efficiency at subdiffusion conditions in living cells}, series = {epl : a letters journal exploring the frontiers of physics}, volume = {97}, journal = {epl : a letters journal exploring the frontiers of physics}, number = {2}, publisher = {EDP Sciences}, address = {Mulhouse}, issn = {0295-5075}, doi = {10.1209/0295-5075/97/20008}, pages = {6}, year = {2012}, abstract = {Macromolecular crowding in living biological cells effects subdiffusion of larger biomolecules such as proteins and enzymes. Mimicking this subdiffusion in terms of random walks on a critical percolation cluster, we here present a case study of EcoRV restriction enzymes involved in vital cellular defence. We show that due to its so far elusive propensity to an inactive state the enzyme avoids non-specific binding and remains well-distributed in the bulk cytoplasm of the cell. Despite the reduced volume exploration capability of subdiffusion processes, this mechanism guarantees a high efficiency of the enzyme. By variation of the non-specific binding constant and the bond occupation probability on the percolation network, we demonstrate that reduced nonspecific binding are beneficial for efficient subdiffusive enzyme activity even in relatively small bacteria cells. Our results corroborate a more local picture of cellular regulation.}, language = {en} } @article{RusconiVallerianiDunlopetal.2012, author = {Rusconi, Marco and Valleriani, Angelo and Dunlop, John William Chapman and Kurths, J{\"u}rgen and Weinkamer, Richard}, title = {Quantitative approach to the stochastics of bone remodeling}, series = {epl : a letters journal exploring the frontiers of physics}, volume = {97}, journal = {epl : a letters journal exploring the frontiers of physics}, number = {2}, publisher = {EDP Sciences}, address = {Mulhouse}, issn = {0295-5075}, doi = {10.1209/0295-5075/97/28009}, pages = {6}, year = {2012}, abstract = {During life bones constantly adapt their structure to their mechanical environment via a mechanically controlled process called bone remodeling. For trabecular bone, this process modifies the thickness of each trabecula leading occasionally to full resorption. We describe the irreversible dynamics of the trabecular thickness distribution (TTD) by means of a Markov chain discrete in space and time. By using thickness data from adult patients, we derive the transition probabilities in the chain. This allows a quantification, in terms of geometrical quantities, of the control of bone remodeling and thus to determine the evolution of the TTD with age.}, language = {en} } @article{AlbrechtLevermann2012, author = {Albrecht, Torsten and Levermann, Anders}, title = {Fracture field for large-scale ice dynamics}, series = {Journal of glaciology}, volume = {58}, journal = {Journal of glaciology}, number = {207}, publisher = {International Glaciological Society}, address = {Cambridge}, issn = {0022-1430}, doi = {10.3189/2012JoG11J191}, pages = {165 -- 176}, year = {2012}, abstract = {Recent observations and modeling studies emphasize the crucial role of fracture mechanics for the stability of ice shelves and thereby the evolution of ice sheets. Here we introduce a macroscopic fracture-density field into a prognostic continuum ice-flow model and compute its evolution incorporating the initiation and growth of fractures as well as their advection with two-dimensional ice flow. To a first approximation, fracture growth is assumed to depend on the spreading rate only, while fracture initiation is defined in terms of principal stresses. The inferred fracture-density fields compare well with observed elongate surface structures. Since crevasses and other deep-reaching fracture structures have been shown to influence the overall ice-shelf dynamics, we propose the fracture-density field introduced here be used as a measure for ice softening and decoupling of the ice flow in fracture-weakened zones. This may yield more accurate and realistic velocity patterns in prognostic simulations. Additionally, the memory of past fracture events links the calving front to the upstream dynamics. Thus the fracture-density field proposed here may be employed in fracture-based calving parameterizations. The aim of this study is to introduce the field and investigate which of the observed surface structures can be reproduced by the simplest physically motivated fracture source terms.}, language = {en} } @article{SeemuellerMuellerRoesler2012, author = {Seem{\"u}ller, Anna and M{\"u}ller, E. M. and R{\"o}sler, Frank}, title = {EEG-power and -coherence changes in a unimodal and a crossmodal working memory task with visual and kinesthetic stimuli}, series = {International journal of psychophysiology}, volume = {83}, journal = {International journal of psychophysiology}, number = {1}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0167-8760}, doi = {10.1016/j.ijpsycho.2011.10.009}, pages = {87 -- 95}, year = {2012}, abstract = {We investigated EEG-power and EEG-coherence changes in a unimodal and a crossmodal matching-to-sample working memory task with either visual or kinesthetic stimuli. Angle-shaped trajectories were used as stimuli presented either as a moving dot on a screen or as a passive movement of a haptic device. Effects were evaluated during the different phases of encoding, maintenance, and recognition. Alpha power was modulated during encoding by the stimulus modality, and in crossmodal conditions during encoding and maintenance by the expected modality of the upcoming test stimulus. These power modulations were observed over modality-specific cortex regions. Systematic changes of coherence for crossmodal compared to unimodal tasks were not observed during encoding and maintenance but only during recognition. There, coherence in the theta-band increased between electrode sites over left central and occipital cortex areas in the crossmodal compared to the unimodal conditions. The results underline the importance of modality-specific representations and processes in unimodal and crossmodal working memory tasks. Crossmodal recognition of visually and kinesthetically presented object features seems to be related to a direct interaction of somatosensory/motor and visual cortex regions by means of long-range synchronization in the theta-band and such interactions seem to take place at the beginning of the recognition phase, i.e. when crossmodal transfer is actually necessary.}, language = {en} } @article{SchneidervonDeimlingMeinshausenLevermannetal.2012, author = {Schneider von Deimling, Thomas and Meinshausen, Malte and Levermann, Anders and Huber, Veronika and Frieler, Katja and Lawrence, D. M. and Brovkin, Victor}, title = {Estimating the near-surface permafrost-carbon feedback on global warming}, series = {Biogeosciences}, volume = {9}, journal = {Biogeosciences}, number = {2}, publisher = {Copernicus}, address = {G{\"o}ttingen}, issn = {1726-4170}, doi = {10.5194/bg-9-649-2012}, pages = {649 -- 665}, year = {2012}, abstract = {Thawing of permafrost and the associated release of carbon constitutes a positive feedback in the climate system, elevating the effect of anthropogenic GHG emissions on global-mean temperatures. Multiple factors have hindered the quantification of this feedback, which was not included in climate carbon-cycle models which participated in recent model intercomparisons (such as the Coupled Carbon Cycle Climate Model Intercomparison Project - (CMIP)-M-4). There are considerable uncertainties in the rate and extent of permafrost thaw, the hydrological and vegetation response to permafrost thaw, the decomposition timescales of freshly thawed organic material, the proportion of soil carbon that might be emitted as carbon dioxide via aerobic decomposition or as methane via anaerobic decomposition, and in the magnitude of the high latitude amplification of global warming that will drive permafrost degradation. Additionally, there are extensive and poorly characterized regional heterogeneities in soil properties, carbon content, and hydrology. Here, we couple a new permafrost module to a reduced complexity carbon-cycle climate model, which allows us to perform a large ensemble of simulations. The ensemble is designed to span the uncertainties listed above and thereby the results provide an estimate of the potential strength of the feedback from newly thawed permafrost carbon. For the high CO2 concentration scenario (RCP8.5), 33-114 GtC (giga tons of Carbon) are released by 2100 (68\% uncertainty range). This leads to an additional warming of 0.04-0.23 degrees C. Though projected 21st century permafrost carbon emissions are relatively modest, ongoing permafrost thaw and slow but steady soil carbon decomposition means that, by 2300, about half of the potentially vulnerable permafrost carbon stock in the upper 3 m of soil layer (600-1000 GtC) could be released as CO2, with an extra 1-4\% being released as methane. Our results also suggest that mitigation action in line with the lower scenario RCP3-PD could contain Arctic temperature increase sufficiently that thawing of the permafrost area is limited to 9-23\% and the permafrost-carbon induced temperature increase does not exceed 0.04-0.16 degrees C by 2300.}, language = {en} } @article{TelezhinskyDwarkadasPohl2012, author = {Telezhinsky, Igor O. and Dwarkadas, Vikram V. and Pohl, Martin}, title = {Particle spectra from acceleration at forward and reverse shocks of young Type Ia Supernova Remnants}, series = {Astroparticle physics}, volume = {35}, journal = {Astroparticle physics}, number = {6}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0927-6505}, doi = {10.1016/j.astropartphys.2011.10.001}, pages = {300 -- 311}, year = {2012}, abstract = {We study cosmic-ray acceleration in young Type Ia Supernova Remnants (SNRs) by means of test-particle diffusive shock acceleration theory and 1-D hydrodynamical simulations of their evolution. In addition to acceleration at the forward shock, we explore the particle acceleration at the reverse shock in the presence of a possible substantial magnetic field, and consequently the impact of this acceleration on the particle spectra in the remnant. We investigate the time evolution of the spectra for various time-dependent profiles of the magnetic field in the shocked region of the remnant. We test a possible influence on particle spectra of the Alfvenic drift of scattering centers in the precursor regions of the shocks. In addition, we study the radiation spectra and morphology in a broad band from radio to gamma-rays. It is demonstrated that the reverse shock contribution to the cosmic-ray particle population of young Type la SNRs may be significant, modifying the spatial distribution of particles and noticeably affecting the volume-integrated particle spectra in young SNRs. In particular spectral structures may arise in test-particle calculations that are often discussed as signatures of non-linear cosmic-ray modification of shocks. Therefore, the spectrum and morphology of emission, and their time evolution, differ from pure forward-shock solutions.}, language = {en} } @article{KoenigSekharSanter2012, author = {K{\"o}nig, Tobias and Sekhar, Y. Nataraja and Santer, Svetlana}, title = {Surface plasmon nanolithography impact of dynamically varying near-field boundary conditions at the air-polymer interface}, series = {Journal of materials chemistry}, volume = {22}, journal = {Journal of materials chemistry}, number = {13}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {0959-9428}, doi = {10.1039/c2jm15864g}, pages = {5945 -- 5950}, year = {2012}, abstract = {It is well-known that surface plasmon generated near fields of suitably irradiated metal nano-structures can induce a patterning in an azobenzene-modified photosensitive polymer film placed on top. The change in the topography usually follows closely and permanently the underlying near field intensity pattern. With this approach, one can achieve a multitude of morphologies by additionally changing light intensity, polarization and the kind of metal used for nano-structuring. In this paper, we demonstrate that below a critical value of the polymer film thickness, the receding polymer material induces a change in refractive index of the glass-metal-polymer system, modifying the near field intensity distribution and causing a back-reaction on the flow of polymer material. This has a profound influence on the smallest size of topographical features that can be imprinted into the polymer.}, language = {en} } @article{HaakhHenkel2012, author = {Haakh, Harald Richard and Henkel, Carsten}, title = {Magnetic near fields as a probe of charge transport in spatially dispersive conductors}, series = {The European physical journal : B, Condensed matter and complex systems}, volume = {85}, journal = {The European physical journal : B, Condensed matter and complex systems}, number = {1}, publisher = {Springer}, address = {New York}, issn = {1434-6028}, doi = {10.1140/epjb/e2011-20567-1}, pages = {12}, year = {2012}, abstract = {We calculate magnetic field fluctuations above a conductor with a nonlocal response (spatial dispersion) and consider a large range of distances. The cross-over from ballistic to diffusive charge transport leads to a reduced noise spectrum at distances below the electronic mean free path, as compared to a local description. We also find that the mean free path provides a lower limit to the correlation (coherence) length of the near field fluctuations. The short-distance behaviour is common to a wide range of materials, including semiconductors and superconductors. Our discussion is aimed at atom chip experiments where spin-flip transitions give access to material properties with mesoscopic spatial resolution. The results also hint at fundamental limits to the coherent operation of miniaturised atom traps and matter-wave interferometers.}, language = {en} } @article{FrischSchubertPreisetal.2012, author = {Frisch, Johannes and Schubert, Marcel and Preis, Eduard and Rabe, J{\"u}rgen P. and Neher, Dieter and Scherf, Ullrich and Koch, Norbert}, title = {Full electronic structure across a polymer heterojunction solar cell}, series = {Journal of materials chemistry}, volume = {22}, journal = {Journal of materials chemistry}, number = {10}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {0959-9428}, doi = {10.1039/c1jm14968g}, pages = {4418 -- 4424}, year = {2012}, abstract = {We correlate the morphology and energy level alignment of bilayer structures comprising the donor poly(3-hexylthiophene) (P3HT) and the acceptor polyfluorene copolymer poly(9,90dialklylfluorene-alt-4,7-bis(2,5-thiendiyl)-2,1,3-benzothiadiazole) (PFTBTT) with the performance of these bilayers in organic photovoltaic cells (OPVCs). The conducting polymer poly(ethylenedioxythiophene): poly (styrenesulfonate) (PEDT:PSS) was used as the bottom electrode and Ca as the top electrode. Ultraviolet photoelectron spectroscopy (UPS) revealed that notable interface dipoles occur at all interfaces across the OPVC structure, highlighting that vacuum level alignment cannot reliably be used to estimate the electronic properties for device design. Particularly the effective electrode work function values (after contact formation with the conjugated polymers) differ significantly from those of the pristine electrode materials. Chemical reactions between PEDT: PSS and P3HT on the one hand and Ca and PFTBTT on the other hand are identified as cause for the measured interface dipoles. The vacuum level shift between P3HT and PFTBTT is related to mutual energy level pinning at gap states. Annealing induced morphological changes at the P3HT/PFTBTT interface increased the efficiency of OPVCs, while the electronic structure was not affected by thermal treatment.}, language = {en} } @article{GuetschowNesmeWerner2012, author = {Guetschow, Johannes and Nesme, Vincent and Werner, Reinhard F.}, title = {Self-similarity of cellular automata on abelian groups}, series = {Journal of cellular automata}, volume = {7}, journal = {Journal of cellular automata}, number = {2}, publisher = {Old City Publishing Science}, address = {Philadelphia}, issn = {1557-5969}, pages = {83 -- 113}, year = {2012}, abstract = {It is well known that the spacetime diagrams of some cellular automata have a self-similar fractal structure: for instance Wolfram's rule 90 generates a Sierpinski triangle. Explaining the self-similarity of the spacetime diagrams of cellular automata is a well-explored topic, but virtually all of the results revolve around a special class of automata, whose typical features include irreversibility, an alphabet with a ring structure, a global evolution that is a ring homomorphism, and a property known as (weakly) p-Fermat. The class of automata that we study in this article has none of these properties. Their cell structure is weaker, as it does not come with a multiplication, and they are far from being p-Fermat, even weakly. However, they do produce self-similar spacetime diagrams, and we explain why and how.}, language = {en} } @article{AdamcikJeonKarczewskietal.2012, author = {Adamcik, Jozef and Jeon, Jae-Hyung and Karczewski, Konrad J. and Metzler, Ralf and Dietler, Giovanni}, title = {Quantifying supercoiling-induced denaturation bubbles in DNA}, series = {Soft matter}, volume = {8}, journal = {Soft matter}, number = {33}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1744-683X}, doi = {10.1039/c2sm26089a}, pages = {8651 -- 8658}, year = {2012}, abstract = {In both eukaryotic and prokaryotic DNA sequences of 30-100 base-pairs rich in AT base-pairs have been identified at which the double helix preferentially unwinds. Such DNA unwinding elements are commonly associated with origins for DNA replication and transcription, and with chromosomal matrix attachment regions. Here we present a quantitative study of local DNA unwinding based on extensive single DNA plasmid imaging. We demonstrate that long-lived single-stranded denaturation bubbles exist in negatively supercoiled DNA, at the expense of partial twist release. Remarkably, we observe a linear relation between the degree of supercoiling and the bubble size, in excellent agreement with statistical modelling. Furthermore, we obtain the full distribution of bubble sizes and the opening probabilities at varying salt and temperature conditions. The results presented herein underline the important role of denaturation bubbles in negatively supercoiled DNA for biological processes such as transcription and replication initiation in vivo.}, language = {en} } @article{ZhuKolloscheLuetal.2012, author = {Zhu, Jian and Kollosche, Matthias and Lu, Tongqing and Kofod, Guggi and Suo, Zhigang}, title = {Two types of transitions to wrinkles in dielectric elastomers}, series = {Soft matter}, volume = {8}, journal = {Soft matter}, number = {34}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1744-683X}, doi = {10.1039/c2sm26034d}, pages = {8840 -- 8846}, year = {2012}, abstract = {A membrane of a dielectric elastomer coated with compliant electrodes may form wrinkles as the applied voltage is ramped up. We present a combination of experiment and theory to investigate the transition to wrinkles using a clamped membrane subject to a constant force and a voltage ramp. Two types of transitions are identified. In type-I transition, the voltage-stretch curve is N-shaped, and flat and wrinkled regions coexist in separate areas of the membrane. The type-I transition progresses by nucleation of small wrinkled regions, followed by the growth of the wrinkled regions at the expense of the flat regions, until the entire membrane is wrinkled. By contrast, in type-II transition, the voltage-stretch curve is monotonic, and the entire flat membrane becomes wrinkled with no nucleation barrier. The two types of transitions are analogous to the first and the second order phase transitions. While the type-I transition is accompanied by a jump in the vertical displacement, type-II transition is accompanied by a continuous change in the vertical displacement. Such transitions may enable applications in muscle-like actuation and energy harvesting, where large deformation and large energy of conversion are desired.}, language = {en} } @article{RisseKussmaulKruegeretal.2012, author = {Risse, Sebastian and Kussmaul, Bj{\"o}rn and Kr{\"u}ger, Hartmut and Kofod, Guggi}, title = {A versatile method for enhancement of electromechanical sensitivity of silicone elastomers}, series = {RSC Advances}, volume = {2}, journal = {RSC Advances}, number = {24}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {2046-2069}, doi = {10.1039/c2ra21541a}, pages = {9029 -- 9035}, year = {2012}, abstract = {Dielectric elastomer actuators (DEAs) draw their function from their dielectric and mechanical properties. The paper describes the fabrication and various properties of molecularly grafted silicone elastomer films. This was achieved by addition of high-dipole molecular co-substituents to off-the-shelf silicone elastomer kits, Elastosil RT 625 and Sylgard 184 by Wacker and Dow Corning, respectively. Strong push-pull dipoles were chemically grafted to both polymer networks during a one step film formation process. All manufactured films were characterized using (13) C-NMR and FT-IR spectroscopy, confirming a successful attachment of the dipoles to the silicone network. Differential scanning calorimetry (DSC) results showed that grafted dipoles were distributed homogeneously throughout the material avoiding the formation of nano-scale aggregates. The permittivity increased with the amount of dipole at all frequencies, while the Young's modulus and electrical breakdown strength were reduced. Actuation strain measurements in the pure shear configuration independently confirmed the increase in electromechanical sensitivity. The ability to enhance electromechanical properties of off-the-shelf materials could strongly expand the range of actuator properties available to researchers and end-users.}, language = {en} } @article{IlnytskyiSaphiannikovaNeheretal.2012, author = {Ilnytskyi, Jaroslav M. and Saphiannikova, Marina and Neher, Dieter and Allen, Michael P.}, title = {Modelling elasticity and memory effects in liquid crystalline elastomers by molecular dynamics simulations}, series = {Soft matter}, volume = {8}, journal = {Soft matter}, number = {43}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1744-683X}, doi = {10.1039/c2sm26499d}, pages = {11123 -- 11134}, year = {2012}, abstract = {We performed molecular dynamics simulations of a liquid crystal elastomer of side-chain architecture. The network is formed from a melt of 28 molecules each having a backbone of 100 hydrocarbon monomers, to which 50 side chains are attached in a syndiotactic way. Crosslinking is performed in the smectic A phase. We observe an increase of the smectic-isotropic phase transition temperature of about 5 degrees as compared to the uncrosslinked melt. Memory effects in liquid crystalline order and in sample shape are well reproduced when the elastomer is driven through the smectic-isotropic transition. Above this transition, in the isotropic phase, the polydomain smectic phase is induced by a uniaxial load. Below the transition, in a monodomain smectic A phase, both experimentally observed effects of homogeneous director reorientation and stripe formation are reproduced when the sample is stretched along the director. When the load is applied perpendicularly to the director, the sample demonstrates reversible deformation with no change of liquid crystalline order, indicating elasticity of the two-dimensional network of polymer layers.}, language = {en} } @article{HerzogSchickLeitenbergeretal.2012, author = {Herzog, Marc and Schick, Daniel and Leitenberger, Wolfram and Shayduk, Roman and van der Veen, Renske M. and Milne, Christopher J. and Johnson, Steven Lee and Vrejoiu, Ionela and Bargheer, Matias}, title = {Tailoring interference and nonlinear manipulation of femtosecond x-rays}, series = {New journal of physics : the open-access journal for physics}, volume = {14}, journal = {New journal of physics : the open-access journal for physics}, number = {1}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {1367-2630}, doi = {10.1088/1367-2630/14/1/013004}, pages = {9}, year = {2012}, abstract = {We present ultrafast x-ray diffraction (UXRD) experiments on different photoexcited oxide superlattices. All data are successfully simulated by dynamical x-ray diffraction calculations based on a microscopic model, that accounts for the linear response of phonons to the excitation laser pulse. Some Bragg reflections display a highly nonlinear strain dependence. The origin of linear and two distinct nonlinear response phenomena is discussed in a conceptually simpler model using the interference of envelope functions that describe the diffraction efficiency of the average constituent nanolayers. The combination of both models facilitates rapid and accurate simulations of UXRD experiments.}, language = {en} } @article{Tonita2012, author = {Tonita, Aaryn}, title = {Distributional sources for black hole initial data}, series = {Classical and quantum gravit}, volume = {29}, journal = {Classical and quantum gravit}, number = {1}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {0264-9381}, doi = {10.1088/0264-9381/29/1/015001}, pages = {16}, year = {2012}, abstract = {Black hole initial data are usually produced using Bowen-York-type puncture initial data or by applying an excision boundary condition. The benefits of the Bowen-York initial data are the ability to specify the spin and momentum of the system as parameters of the initial data. In an attempt to extend these benefits to other formulations of the Einstein constraints, the puncture method is reformulated using distributions as source terms. It is shown how the Bowen-York puncture black hole initial data and the trumpet variation are generated by distributional sources. A heuristic argument is presented to argue that these sources are the general sources of spin and momentum. In order to clarify the meaning of other distributional sources, an exact family of initial data with generalized sources to the Hamiltonian constraint are studied; spinning trumpet black hole initial data and black hole initial data with higher order momentum sources are also studied.}, language = {en} } @article{CampbellEisert2012, author = {Campbell, Earl T. and Eisert, Jens}, title = {Gaussification and entanglement distillation of continuous-variable systems a unifying picture}, series = {Physical review letters}, volume = {108}, journal = {Physical review letters}, number = {2}, publisher = {American Physical Society}, address = {College Park}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.108.020501}, pages = {5}, year = {2012}, abstract = {Distillation of entanglement using only Gaussian operations is an important primitive in quantum communication, quantum repeater architectures, and distributed quantum computing. Existing distillation protocols for continuous degrees of freedom are only known to converge to a Gaussian state when measurements yield precisely the vacuum outcome. In sharp contrast, non-Gaussian states can be deterministically converted into Gaussian states while preserving their second moments, albeit by usually reducing their degree of entanglement. In this work-based on a novel instance of a noncommutative central limit theorem-we introduce a picture general enough to encompass the known protocols leading to Gaussian states, and new classes of protocols including multipartite distillation. This gives the experimental option of balancing the merits of success probability against entanglement produced.}, language = {en} } @article{SalzmannHeimelDuhmetal.2012, author = {Salzmann, Ingo and Heimel, Georg and Duhm, Steffen and Oehzelt, Martin and Pingel, Patrick and George, Benjamin M. and Schnegg, Alexander and Lips, Klaus and Blum, Ralf-Peter and Vollmer, Antje and Koch, Norbert}, title = {Intermolecular hybridization governs molecular electrical doping}, series = {Physical review letters}, volume = {108}, journal = {Physical review letters}, number = {3}, publisher = {American Physical Society}, address = {College Park}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.108.035502}, pages = {5}, year = {2012}, abstract = {Current models for molecular electrical doping of organic semiconductors are found to be at odds with other well-established concepts in that field, like polaron formation. Addressing these inconsistencies for prototypical systems, we present experimental and theoretical evidence for intermolecular hybridization of organic semiconductor and dopant frontier molecular orbitals. Common doping-related observations are attributed to this phenomenon, and controlling the degree of hybridization emerges as a strategy for overcoming the present limitations in the yield of doping-induced charge carriers.}, language = {en} } @article{BerensteinBeta2012, author = {Berenstein, Igal and Beta, Carsten}, title = {Spatiotemporal chaos arising from standing waves in a reaction-diffusion system with cross-diffusion}, series = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr}, volume = {136}, journal = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr}, number = {3}, publisher = {American Institute of Physics}, address = {Melville}, issn = {0021-9606}, doi = {10.1063/1.3676577}, pages = {4}, year = {2012}, abstract = {We show that quasi-standing wave patterns appear in the two-variable Oregonator model of the Belousov-Zhabotinsky reaction when a cross-diffusion term is added, no wave instability is required in this case. These standing waves have a frequency that is half the frequency of bulk oscillations displayed in the absence of diffusive coupling. The standing wave patterns show a dependence on the systems size. Regular standing waves can be observed for small systems, when the system size is an integer multiple of half the wavelength. For intermediate sizes, irregular patterns are observed. For large sizes, the system shows an irregular state of spatiotemporal chaos, where standing waves drift, merge, and split, and also phase slips may occur.}, language = {en} } @article{TemirbayevZhanabaevTarasovetal.2012, author = {Temirbayev, Amirkhan A. and Zhanabaev, Zeinulla Zh. and Tarasov, Stanislav B. and Ponomarenko, Vladimir I. and Rosenblum, Michael}, title = {Experiments on oscillator ensembles with global nonlinear coupling}, series = {Physical review : E, Statistical, nonlinear and soft matter physics}, volume = {85}, journal = {Physical review : E, Statistical, nonlinear and soft matter physics}, number = {1}, publisher = {American Physical Society}, address = {College Park}, issn = {1539-3755}, doi = {10.1103/PhysRevE.85.015204}, pages = {4}, year = {2012}, abstract = {We experimentally analyze collective dynamics of a population of 20 electronic Wien-bridge limit-cycle oscillators with a nonlinear phase-shifting unit in the global feedback loop. With an increase in the coupling strength we first observe formation and then destruction of a synchronous cluster, so that the dependence of the order parameter on the coupling strength is not monotonic. After destruction of the cluster the ensemble remains nevertheless coherent, i.e., it exhibits an oscillatory collective mode (mean field). We show that the system is now in a self-organized quasiperiodic state, predicted in Rosenblum and Pikovsky [Phys. Rev. Lett. 98, 064101 (2007)]. In this state, frequencies of all oscillators are smaller than the frequency of the mean field, so that the oscillators are not locked to the mean field they create and their dynamics is quasiperiodic. Without a nonlinear phase-shifting unit, the system exhibits a standard Kuramoto-like transition to a fully synchronous state. We demonstrate a good correspondence between the experiment and previously developed theory. We also propose a simple measure which characterizes the macroscopic incoherence-coherence transition in a finite-size ensemble.}, language = {en} } @article{LaflammeKolloscheConnoretal.2012, author = {Laflamme, S. and Kollosche, Matthias and Connor, Jerome J. and Kofod, Guggi}, title = {Soft capacitive sensor for structural health monitoring of large-scale systems}, series = {Structural control \& health monitorin}, volume = {19}, journal = {Structural control \& health monitorin}, number = {1}, publisher = {Wiley-Blackwell}, address = {Hoboken}, issn = {1545-2263}, doi = {10.1002/stc.426}, pages = {70 -- 81}, year = {2012}, abstract = {Structural integrity of infrastructures can be preserved if damage is diagnosed, localized, and repaired in time. During the past decade, there has been a considerable effort to automate the process of structural health monitoring, which is complicated by the inherent large size of civil structures. Hence, a need has arisen to develop new approaches that enable more effective health monitoring. In this paper, a new sensing technique for damage localization on large civil structures is proposed. Specifically, changes in strain are detected using a capacitance sensor built with a soft, stretchable dielectric polymer with attached stretchable metal film electrodes. A change in strain causes a measurable change in the capacitance of the sensor, which can be directly monitored when the sensor is fixed to a structure. The proposed method is shown here to permit an accurate detection of cracks. The proposed system deploys a layer of dielectric polymer on the surface of a structural element, and regularly monitors any change in capacitance, giving in turn information about the structural state. The smart material is composed of inexpensive silicone elastomers, which make the monitoring system a promising application for large surfaces. Results from tests conducted on small- scale specimens showed that the technology is capable of detecting cracks, and tests conducted on large- size specimens demonstrated that several sensor patches organized on a sensor sheet are capable of localizing a crack. The sensor strain also exhibits a high correlation with the loss of stiffness.}, language = {en} } @article{ThompsonKliemToeroek2012, author = {Thompson, W. T. and Kliem, Bernhard and Toeroek, Tibor}, title = {3D reconstruction of a rotating erupting prominence}, series = {Solar physics : a journal for solar and solar-stellar research and the study of solar terrestrial physics}, volume = {276}, journal = {Solar physics : a journal for solar and solar-stellar research and the study of solar terrestrial physics}, number = {1-2}, publisher = {Springer}, address = {Dordrecht}, issn = {0038-0938}, doi = {10.1007/s11207-011-9868-5}, pages = {241 -- 259}, year = {2012}, abstract = {A bright prominence associated with a coronal mass ejection (CME) was seen erupting from the Sun on 9 April 2008. This prominence was tracked by both the Solar Terrestrial Relations Observatory (STEREO) EUVI and COR1 telescopes, and was seen to rotate about the line of sight as it erupted; therefore, the event has been nicknamed the "Cartwheel CME." The threads of the prominence in the core of the CME quite clearly indicate the structure of a weakly to moderately twisted flux rope throughout the field of view, up to heliocentric heights of 4 solar radii. Although the STEREO separation was 48A degrees, it was possible to match some sharp features in the later part of the eruption as seen in the 304 line in EUVI and in the H alpha-sensitive bandpass of COR1 by both STEREO Ahead and Behind. These features could then be traced out in three-dimensional space, and reprojected into a view in which the eruption is directed toward the observer. The reconstructed view shows that the alignment of the prominence to the vertical axis rotates as it rises up to a leading-edge height of a parts per thousand aEuro parts per thousand 2.5 solar radii, and then remains approximately constant. The alignment at 2.5 solar radii differs by about 115A degrees from the original filament orientation inferred from H alpha and EUV data, and the height profile of the rotation, obtained here for the first time, shows that two thirds of the total rotation are reached within a parts per thousand aEuro parts per thousand 0.5 solar radii above the photosphere. These features are well reproduced by numerical simulations of an unstable moderately twisted flux rope embedded in external flux with a relatively strong shear field component.}, language = {en} } @article{GuptaGuptaLeitenbergeretal.2012, author = {Gupta, Ranjeeta and Gupta, Ajay and Leitenberger, Wolfram and R{\"u}ffer, R.}, title = {Mechanism of stress relaxation in nanocrystalline Fe-N thin films}, series = {Physical review : B, Condensed matter and materials physics}, volume = {85}, journal = {Physical review : B, Condensed matter and materials physics}, number = {7}, publisher = {American Physical Society}, address = {College Park}, issn = {1098-0121}, doi = {10.1103/PhysRevB.85.075401}, pages = {7}, year = {2012}, abstract = {The mechanism of stress relaxation in nanocrystalline Fe-N thin film has been studied. The as-deposited film possesses a strong in-plane compressive stress which relaxes with thermal annealing. Precise diffusion measurements using nuclear resonance reflectivity show that stress relaxation does not involve any long-range diffusion of Fe atoms. Rather, a redistribution of nitrogen atoms at various interstitial sites, as evidenced by conversion electron Mossbauer spectroscopy, is responsible for the relaxation of internal stresses. On the other hand, formation of the. gamma'-Fe4N phase at temperatures above 523 K involves long-range rearrangement of Fe atoms. The activation energy for Fe self-diffusion is found to be 0.38 +/- 0.04 eV.}, language = {en} } @article{ZuritaSanchezHenkel2012, author = {Zurita-Sanchez, Jorge R. and Henkel, Carsten}, title = {Acoustic waves from mechanical impulses due to fluorescence resonant energy (Forster) transfer Blowing a whistle with light}, series = {epl : a letters journal exploring the frontiers of physics}, volume = {97}, journal = {epl : a letters journal exploring the frontiers of physics}, number = {4}, publisher = {EDP Sciences}, address = {Mulhouse}, issn = {0295-5075}, doi = {10.1209/0295-5075/97/43002}, pages = {6}, year = {2012}, abstract = {We present a momentum transfer mechanism mediated by electromagnetic fields that originates in a system of two nearby molecules: one excited (donor D*) and the other in ground state (acceptor A). An intermolecular force related to fluorescence resonant energy or Forster transfer (FRET) arises in the unstable D* A molecular system, which differs from the equilibrium van der Waals interaction. Due to the its finite lifetime, a mechanical impulse is imparted to the relative motion in the system. We analyze the FRET impulse when the molecules are embedded in free space and find that its magnitude can be much greater than the single recoil photon momentum, getting comparable with the thermal momentum (Maxwell-Boltzmann distribution) at room temperature. In addition, we propose that this FRET impulse can be exploited in the generation of acoustic waves inside a film containing layers of donor and acceptor molecules, when a picosecond laser pulse excites the donors. This acoustic transient is distinguishable from that produced by thermal stress due to laser absorption, and may therefore play a role in photoacoustic spectroscopy. The effect can be seen as exciting a vibrating system like a string or organ pipe with light; it may be used as an opto-mechanical transducer.}, language = {en} } @article{MalikZouMarwanetal.2012, author = {Malik, Nishant and Zou, Y. and Marwan, Norbert and Kurths, J{\"u}rgen}, title = {Dynamical regimes and transitions in plio-pleistocene Asian monsoon}, series = {epl : a letters journal exploring the frontiers of physics}, volume = {97}, journal = {epl : a letters journal exploring the frontiers of physics}, number = {4}, publisher = {EDP Sciences}, address = {Mulhouse}, issn = {0295-5075}, doi = {10.1209/0295-5075/97/40009}, pages = {6}, year = {2012}, abstract = {We propose a novel approach based on the fluctuation of similarity to identify regimes of distinct dynamical complexity in short time series. A statistical test is developed to estimate the significance of the identified transitions. Our method is verified by uncovering bifurcation structures in several paradigmatic models, providing more complex transitions compared with traditional Lyapunov exponents. In a real-world situation, we apply this method to identify millennial-scale dynamical transitions in Plio-Pleistocene proxy records of the South Asian summer monsoon system. We infer that many of these transitions are induced by the external forcing of the solar insolation and are also affected by internal forcing on Monsoonal dynamics, i.e., the glaciation cycles of the Northern Hemisphere and the onset of the Walker circulation.}, language = {en} } @article{DraganovaRichterFechner2012, author = {Draganova, Nadya and Richter, Philipp and Fechner, Cora}, title = {High-resolution observations of two O VI absorbers at z approximate to 2 toward PKS 1448-232}, series = {Astronomy and astrophysics : an international weekly journal}, volume = {538}, journal = {Astronomy and astrophysics : an international weekly journal}, number = {1}, publisher = {EDP Sciences}, address = {Les Ulis}, issn = {0004-6361}, doi = {10.1051/0004-6361/201116730}, pages = {8}, year = {2012}, abstract = {To explore the ionization conditions in highly-ionized absorbers at high redshift, we study in detail two intervening O vi absorbers at z approximate to 2 toward the quasar PKS 1448-232, based on high (R approximate to 75 000) and intermediate (R approximate to 45 000) resolution optical VLT/UVES spectra. We find that both absorption systems are composed of several narrow subcomponents with typical Civ/O VI Doppler-parameters of b < 10 km s(-1). This implies that the gas temperatures are T < 10(5) K and that the absorbers are photoionized by the UV background. The system at z = 2.1098 represents a simple, isolated O VI absorber that has only two absorption components and is relatively metal-rich (Z similar to 0.6 solar). Ioinization modeling implies that the system is photoionized with O VI, C IV, and H I coexisting in the same gas phase. The second system at z = 2.1660 represents a complicated, multi-component absorption system with eight O VI components spanning almost 300 km s(-1) in radial velocity. The photoionization modeling implies that the metallicity is non-uniform and relatively low (<= 0.1 solar) and that the O VI absorption must arise in a gas phase that differs from that traced by C IV, C III, and H I. Our detailed study of the two O VI systems towards PKS 1448-232 shows that multi-phase, multi-component high-ion absorbers similar to the one at z = 2.1660 can be described by applying a detailed ionization modeling of the various subcomponents to obtain reliable measurements of the physical conditions and the metal abundances in the gas.}, language = {en} } @article{HenaultBrunetOskinovaGuerreroetal.2012, author = {Henault-Brunet, V. and Oskinova, Lida and Guerrero, Mart{\´i}n A. and Sun, W. and Chu, Y.-H. and Evans, C. J. and Gallagher, J. S. and Gruendl, R. A. and Reyes-Iturbide, J.}, title = {Discovery of a Be/X-ray pulsar binary and associated supernova remnant in the wing of the small magellanic cloud}, series = {Monthly notices of the Royal Astronomical Society}, volume = {420}, journal = {Monthly notices of the Royal Astronomical Society}, number = {1}, publisher = {Wiley-Blackwell}, address = {Malden}, issn = {0035-8711}, doi = {10.1111/j.1745-3933.2011.01183.x}, pages = {L13 -- L17}, year = {2012}, abstract = {We report on a new Be/X-ray pulsar binary located in the Wing of the Small Magellanic Cloud (SMC). The strong pulsed X-ray source was discovered with the Chandra and XMM-Newton X-ray observatories. The X-ray pulse period of 1062 s is consistently determined from both Chandra and XMM-Newton observations, revealing one of the slowest rotating X-ray pulsars known in the SMC. The optical counterpart of the X-ray source is the emission-line star 2dFS 3831. Its B0-0.5(III)e+ spectral type is determined from VLT-FLAMES and 2dF optical spectroscopy, establishing the system as a Be/X-ray binary (Be-XRB). The hard X-ray spectrum is well fitted by a power law with additional thermal and blackbody components, the latter reminiscent of persistent Be-XRBs. This system is the first evidence of a recent supernova in the low-density surroundings of NGC602. We detect a shell nebula around 2dFS 3831 in H alpha and [OIII] images and conclude that it is most likely a supernova remnant. If it is linked to the supernova explosion that created this new X-ray pulsar, its kinematic age of (2-4) x 10(4) yr provides a constraint on the age of the pulsar.}, language = {en} } @article{Baushev2012, author = {Baushev, Anton N.}, title = {Interaction of clumpy dark matter with interstellar medium in astrophysical systems}, series = {Monthly notices of the Royal Astronomical Society}, volume = {420}, journal = {Monthly notices of the Royal Astronomical Society}, number = {1}, publisher = {Wiley-Blackwell}, address = {Malden}, issn = {0035-8711}, doi = {10.1111/j.1365-2966.2011.20067.x}, pages = {590 -- 595}, year = {2012}, abstract = {Contemporary cosmological conceptions suggest that the dark matter in haloes of galaxies and galaxy clusters has most likely a clumpy structure. If a stream of gas penetrates through it, a small-scale gravitational field created by the clumps disturbs the flow resulting in momentum exchange between the stream and the dark matter. In this article, we perform an analysis of this effect, based on the hierarchical halo model of the dark matter structure and Navarro-Frenk-White density profiles. We consider the clumps of various masses, from the smallest up to the highest ones M = 10(9) M circle dot. It has been found that in any event the effect grows with the mass of the clump: not only the drag force F acting on the clump but also its acceleration w = F/M increases. We discuss various astrophysical systems. The mechanism proved to be ineffective in the case of galaxy or galaxy cluster collisions. On the other hand, it played an important role during the process of galaxy formation. As a result, the dark matter should have formed a more compact, oblate and faster rotating substructure in the halo of our Galaxy. We have shown that this thick disc should be more clumpy than the halo. This fact is very important for the indirect detection experiments since it is the clumps that give the main contribution to the annihilation signal. Our calculations show that the mechanism of momentum exchange between the dark and baryon matter is ineffective on the outskirts of the galactic halo. It means that the clumps from there were not transported to the thick disc, and this region should be more clumpy than the halo on the average.}, language = {en} } @article{SchickBojahrHerzogetal.2012, author = {Schick, Daniel and Bojahr, Andre and Herzog, Marc and von Korff Schmising, Clemens and Shayduk, Roman and Leitenberger, Wolfram and Gaa, P. and Bargheer, Matias}, title = {Normalization schemes for ultrafast x-ray diffraction using a table-top laser-driven plasma source}, series = {Review of scientific instruments : a monthly journal devoted to scientific instruments, apparatus, and techniques}, volume = {83}, journal = {Review of scientific instruments : a monthly journal devoted to scientific instruments, apparatus, and techniques}, number = {2}, publisher = {American Institute of Physics}, address = {Melville}, issn = {0034-6748}, doi = {10.1063/1.3681254}, pages = {7}, year = {2012}, abstract = {We present an experimental setup of a laser-driven x-ray plasma source for femtosecond x-ray diffraction. Different normalization schemes accounting for x-ray source intensity fluctuations are discussed in detail. We apply these schemes to measure the temporal evolution of Bragg peak intensities of perovskite superlattices after ultrafast laser excitation.}, language = {en} } @article{LangeTilmannBarrientosetal.2012, author = {Lange, Dietrich and Tilmann, Frederik and Barrientos, Sergio E. and Contreras-Reyes, Eduardo and Methe, Pascal and Moreno, Marcos and Heit, Ben and Agurto, Hans and Bernard, Pascal and Vilotte, Jean-Pierre and Beck, Susan}, title = {Aftershock seismicity of the 27 February 2010 Mw 8.8 Maule earthquake rupture zone}, series = {Earth \& planetary science letters}, volume = {317}, journal = {Earth \& planetary science letters}, number = {2}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0012-821X}, doi = {10.1016/j.epsl.2011.11.034}, pages = {413 -- 425}, year = {2012}, abstract = {On 27 February 2010 the M-w 8.8 Maule earthquake in Central Chile ruptured a seismic gap where significant strain had accumulated since 1835. Shortly after the mainshock a dense network of temporary seismic stations was installed along the whole rupture zone in order to capture the aftershock activity. Here, we present the aftershock distribution and first motion polarity focal mechanisms based on automatic detection algorithms and picking engines. By processing the seismic data between 15 March and 30 September 2010 from stations from IRIS, IPGP, GFZ and University of Liverpool we determined 20,205 hypocentres with magnitudes M-w between 1 and 5.5. Seismic activity occurs in six groups: 1.) Normal faulting outer rise events 2.) A shallow group of plate interface seismicity apparent at 25-35 km depth and 50-120 km distance to the trench with some variations between profiles. Along strike, the aftershocks occur largely within the zone of coseismic slip but extend similar to 50 km further north, and with predominantly shallowly dipping thrust mechanisms. Along dip, the events are either within the zone of coseismic slip, or downdip from it, depending on the coseismic slip model used. 3.) A third band of seismicity is observed further downdip at 40-50 km depth and further inland at 150-160 km trench perpendicular distance, with mostly shallow dipping (similar to 28 degrees) thrust focal mechanisms indicating rupture of the plate interface significantly downdip of the coseismic rupture, and presumably above the intersection of the continental Moho with the plate interface. 4.) A deep group of intermediate depth events between 80 and 120 km depth is present north of 36 degrees S. Within the Maule segment, a large portion of events during the inter-seismic phase originated from this depth range. 5.) The magmatic arc exhibits a small amount of crustal seismicity but does not appear to show significantly enhanced activity after the M-w 8.8 Maule 2010 earthquake. 6.) Pronounced crustal aftershock activity with mainly normal faulting mechanisms is found in the region of Pichilemu (similar to 34.5 degrees S). These crustal events occur in a similar to 30 km wide region with sharp inclined boundaries and oriented oblique to the trench. The best-located events describe a plane dipping to the southwest, consistent with one of the focal planes of the large normal-faulting aftershock (M-w = 6.9) on 11 March 2010.}, language = {en} } @article{MarwanBellerFelsenbergetal.2012, author = {Marwan, Norbert and Beller, Gise and Felsenberg, Dieter and Saparin, Peter and Kurths, J{\"u}rgen}, title = {quantifying changes in the spatial structure of trabecular bone}, series = {International journal of bifurcation and chaos : in applied sciences and engineering}, volume = {22}, journal = {International journal of bifurcation and chaos : in applied sciences and engineering}, number = {2}, publisher = {World Scientific}, address = {Singapore}, issn = {0218-1274}, doi = {10.1142/S0218127412500277}, pages = {12}, year = {2012}, abstract = {We apply recently introduced measures of complexity for the structural quantification of distal tibial bone. For the first time, we are able to investigate the temporal structural alteration of trabecular bone. Based on four patients, we show how the bone may alter due to temporal immobilization.}, language = {en} } @unpublished{ScherfTian2012, author = {Scherf, Ullrich and Tian, He}, title = {Organic electronics/optics for an energetic life}, series = {Advanced materials}, volume = {24}, journal = {Advanced materials}, number = {5}, publisher = {Wiley-Blackwell}, address = {Malden}, issn = {0935-9648}, doi = {10.1002/adma.201104917}, pages = {576 -- 579}, year = {2012}, language = {en} } @article{WangLackXieetal.2012, author = {Wang, Feipeng and Lack, Alexander and Xie, Zailai and Fr{\"u}bing, Peter and Taubert, Andreas and Gerhard, Reimund}, title = {Ionic-liquid-induced ferroelectric polarization in poly(vinylidene fluoride) thin films}, series = {Applied physics letters}, volume = {100}, journal = {Applied physics letters}, number = {6}, publisher = {American Institute of Physics}, address = {Melville}, issn = {0003-6951}, doi = {10.1063/1.3683526}, pages = {4}, year = {2012}, abstract = {Thin films of ferroelectric beta-phase poly(vinylidene fluoride) (PVDF) were spin-coated from a solution that contained small amounts of the ionic liquid (IL) 1-ethyl-3-methylimidazolium nitrate. A remanent polarization of 60 mC/m(2) and a quasi-static pyroelectric coefficient of 19 mu C/m(2)K at 30 degrees C were observed in the films. It is suggested that the IL promotes the formation of the beta phase through dipolar interactions between PVDF chain-molecules and the IL. The dipolar interactions are identified as Coulomb attraction between hydrogen atoms in PVDF chains and anions in IL. The strong crystallinity increase is probably caused by the same dipolar interaction as well.}, language = {en} } @article{StromanPohlNiemiecetal.2012, author = {Stroman, Thomas and Pohl, Martin and Niemiec, Jacek and Bret, Antoine}, title = {Could cosmic rays affect instabilities in the Transition layer of nonrealativistic collisionless shocks?}, series = {The astrophysical journal : an international review of spectroscopy and astronomical physics}, volume = {746}, journal = {The astrophysical journal : an international review of spectroscopy and astronomical physics}, number = {1}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {0004-637X}, doi = {10.1088/0004-637X/746/1/24}, pages = {10}, year = {2012}, abstract = {There is an observational correlation between astrophysical shocks and nonthermal particle distributions extending to high energies. As a first step toward investigating the possible feedback of these particles on the shock at the microscopic level, we perform particle-in-cell (PIC) simulations of a simplified environment consisting of uniform, interpenetrating plasmas, both with and without an additional population of cosmic rays. We vary the relative density of the counterstreaming plasmas, the strength of a homogeneous parallel magnetic field, and the energy density in cosmic rays. We compare the early development of the unstable spectrum for selected configurations without cosmic rays to the growth rates predicted from linear theory, for assurance that the system is well represented by the PIC technique. Within the parameter space explored, we do not detect an unambiguous signature of any cosmic-ray-induced effects on the microscopic instabilities that govern the formation of a shock. We demonstrate that an overly coarse distribution of energetic particles can artificially alter the statistical noise that produces the perturbative seeds of instabilities, and that such effects can be mitigated by increasing the density of computational particles.}, language = {en} } @article{BergnerFrascaSciutoetal.2012, author = {Bergner, Andre and Frasca, M. and Sciuto, G. and Buscarino, A. and Ngamga, Eulalie Joelle and Fortuna, L. and Kurths, J{\"u}rgen}, title = {Remote synchronization in star networks}, series = {Physical review : E, Statistical, nonlinear and soft matter physics}, volume = {85}, journal = {Physical review : E, Statistical, nonlinear and soft matter physics}, number = {2}, publisher = {American Physical Society}, address = {College Park}, issn = {1539-3755}, doi = {10.1103/PhysRevE.85.026208}, pages = {7}, year = {2012}, abstract = {We study phase synchronization in a network motif with a starlike structure in which the central node's (the hub's) frequency is strongly detuned against the other peripheral nodes. We find numerically and experimentally a regime of remote synchronization (RS), where the peripheral nodes form a phase synchronized cluster, while the hub remains free with its own dynamics and serves just as a transmitter for the other nodes. We explain the mechanism for this RS by the existence of a free amplitude and also show that systems with a fixed or constant amplitude, such as the classic Kuramoto phase oscillator, are not able to generate this phenomenon. Further, we derive an analytic expression which supports our explanation of the mechanism.}, language = {en} } @article{AliuArlenAuneetal.2012, author = {Aliu, E. and Arlen, T. and Aune, T. and Beilicke, M. and Benbow, W. and Bouvier, A. and Bradbury, S. M. and Buckley, J. H. and Bugaev, V. and Byrum, K. and Cannon, A. and Cesarini, A. and Ciupik, L. and Collins-Hughes, E. and Connolly, M. P. and Cui, W. and Dickherber, R. and Duke, C. and Errando, M. and Falcone, A. and Finley, J. P. and Finnegan, G. and Fortson, L. and Furniss, A. and Galante, N. and Gall, D. and Godambe, S. and Griffin, S. and Grube, J. and Guenette, R. and Gyuk, G. and Hanna, D. and Holder, J. and Huan, H. and Hughes, G. and Hui, C. M. and Humensky, T. B. and Imran, A. and Kaaret, P. and Karlsson, N. and Kertzman, M. and Kieda, D. and Krawczynski, H. and Krennrich, F. and Lang, M. J. and LeBohec, S. and Madhavan, A. S. and Maier, G. and Majumdar, P. and McArthur, S. and McCann, A. and Moriarty, P. and Mukherjee, R. and Nunez, P. D. and Ong, R. A. and Orr, M. and Otte, A. N. and Park, N. and Perkins, J. S. and Pichel, A. and Pohl, Martin and Prokoph, H. and Quinn, J. and Ragan, K. and Reyes, L. C. and Reynolds, P. T. and Roache, E. and Rose, H. J. and Ruppel, J. and Saxon, D. B. and Schroedter, M. and Sembroski, G. H. and Sentuerk, G. D. and Skole, C. and Staszak, D. and Tesic, G. and Theiling, M. and Thibadeau, S. and Tsurusaki, K. and Tyler, J. and Varlotta, A. and Vassiliev, V. V. and Vincent, S. and Vivier, M. and Wakely, S. P. and Ward, J. E. and Weekes, T. C. and Weinstein, A. and Weisgarber, T. and Williams, D. A. and Zitzer, B.}, title = {Veritas observations of day-scale flaring of M 87 in 2010 April}, series = {The astrophysical journal : an international review of spectroscopy and astronomical physics}, volume = {746}, journal = {The astrophysical journal : an international review of spectroscopy and astronomical physics}, number = {2}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {0004-637X}, doi = {10.1088/0004-637X/746/2/141}, pages = {7}, year = {2012}, abstract = {VERITAS has been monitoring the very-high-energy (VHE; > 100 GeV) gamma-ray activity of the radio galaxy M87 since 2007. During 2008, flaring activity on a timescale of a few days was observed with a peak flux of (0.70 +/- 0.16) x 10(-11) cm(-2) s(-1) at energies above 350 GeV. In 2010 April, VERITAS detected a flare from M 87 with peak flux of (2.71 +/- 0.68) x 10(-11) cm(-2) s(-1) for E > 350 GeV. The source was observed for six consecutive nights during the flare, resulting in a total of 21 hr of good-quality data. The most rapid flux variation occurred on the trailing edge of the flare with an exponential flux decay time of 0.90(-0.15)(+0.22) days. The shortest detected exponential rise time is three times as long, at 2.87(+1.65)(-0.99) days. The quality of the data sample is such that spectral analysis can be performed for three periods: rising flux, peak flux, and falling flux. The spectra obtained are consistent with power-law forms. The spectral index at the peak of the flare is equal to 2.19 +/- 0.07. There is some indication that the spectrum is softer in the falling phase of the flare than the peak phase, with a confidence level corresponding to 3.6 standard deviations. We discuss the implications of these results for the acceleration and cooling rates of VHE electrons in M 87 and the constraints they provide on the physical size of the emitting region.}, language = {en} } @article{AbramowskiAceroAharonianetal.2012, author = {Abramowski, Attila and Acero, F. and Aharonian, Felix A. and Akhperjanian, A. G. and Anton, Gisela and Balzer, Arnim and Barnacka, Anna and de Almeida, U. Barres and Becherini, Yvonne and Becker, J. and Behera, B. and Bernl{\"o}hr, K. and Birsin, E. and Biteau, Jonathan and Bochow, A. and Boisson, Catherine and Bolmont, J. and Bordas, Pol and Brucker, J. and Brun, Francois and Brun, Pierre and Bulik, Tomasz and Buesching, I. and Carrigan, Svenja and Casanova, Sabrina and Cerruti, M. and Chadwick, Paula M. and Charbonnier, A. and Chaves, Ryan C. G. and Cheesebrough, A. and Clapson, A. C. and Coignet, G. and Cologna, Gabriele and Conrad, Jan and Dalton, M. and Daniel, M. K. and Davids, I. D. and Degrange, B. and Deil, C. and Dickinson, H. J. and Djannati-Ata{\"i}, A. and Domainko, W. and Drury, L. O'C. and Dubus, G. and Dutson, K. and Dyks, J. and Dyrda, M. and Egberts, Kathrin and Eger, P. and Espigat, P. and Fallon, L. and Farnier, C. and Fegan, S. and Feinstein, F. and Fernandes, M. V. and Fiasson, A. and Fontaine, G. and Foerster, A. and Fuessling, M. and Gallant, Y. A. and Gast, H. and Gerard, L. and Gerbig, D. and Giebels, B. and Glicenstein, J. F. and Glueck, B. and Goret, P. and Goering, D. and Haeffner, S. and Hague, J. D. and Hampf, D. and Hauser, M. and Heinz, S. and Heinzelmann, G. and Henri, G. and Hermann, G. and Hinton, James Anthony and Hoffmann, A. and Hofmann, W. and Hofverberg, P. and Holler, M. and Horns, D. and Jacholkowska, A. and de Jager, O. C. and Jahn, C. and Jamrozy, M. and Jung, I. and Kastendieck, M. A. and Katarzynski, K. and Katz, U. and Kaufmann, S. and Keogh, D. and Khangulyan, D. and Khelifi, B. and Klochkov, D. and Kluzniak, W. and Kneiske, T. and Komin, Nu. and Kosack, K. and Kossakowski, R. and Laffon, H. and Lamanna, G. and Lennarz, D. and Lohse, T. and Lopatin, A. and Lu, C. -C. and Marandon, V. and Marcowith, Alexandre and Masbou, J. and Maurin, D. and Maxted, N. and Mayer, M. and McComb, T. J. L. and Medina, M. C. and Mehault, J. and Moderski, R. and Moulin, Emmanuel and Naumann, C. L. and Naumann-Godo, M. and de Naurois, M. and Nedbal, D. and Nekrassov, D. and Nguyen, N. and Nicholas, B. and Niemiec, J. and Nolan, S. J. and Ohm, S. and Wilhelmi, E. de Ona and Opitz, B. and Ostrowski, M. and Oya, I. and Panter, M. and Arribas, M. Paz and Pedaletti, G. and Pelletier, G. and Petrucci, P. -O. and Pita, S. and Puehlhofer, G. and Punch, M. and Quirrenbach, A. and Raue, M. and Rayner, S. M. and Reimer, A. and Reimer, O. and Renaud, M. and de los Reyes, R. and Rieger, F. and Ripken, J. and Rob, L. and Rosier-Lees, S. and Rowell, G. and Rudak, B. and Rulten, C. B. and Ruppel, J. and Sahakian, V. and Sanchez, David M. and Santangelo, A. and Schlickeiser, R. and Schoeck, F. M. and Schulz, A. and Schwanke, U. and Schwarzburg, S. and Schwemmer, S. and Sheidaei, F. and Skilton, J. L. and Sol, H. and Spengler, G. and Stawarz, L. and Steenkamp, R. and Stegmann, Christian and Stinzing, F. and Stycz, K. and Sushch, Iurii and Szostek, A. and Tavernet, J. -P. and Terrier, R. and Tluczykont, M. and Valerius, K. and van Eldik, C. and Vasileiadis, G. and Venter, C. and Vialle, J. P. and Viana, A. and Vincent, P. and Voelk, H. J. and Volpe, F. and Vorobiov, S. and Vorster, M. and Wagner, S. J. and Ward, M. and White, R. and Wierzcholska, A. and Zacharias, M. and Zajczyk, A. and Zdziarski, A. A. and Zech, Alraune and Zechlin, H. -S. and Aleksic, J. and Antonelli, L. A. and Antoranz, P. and Backes, Michael and Barrio, J. A. and Bastieri, D. and Becerra Gonzalez, J. and Bednarek, W. and Berdyugin, A. and Berger, K. and Bernardini, E. and Biland, A. and Blanch Bigas, O. and Bock, R. K. and Boller, A. and Bonnoli, G. and Tridon, D. Borla and Braun, I. and Bretz, T. and Canellas, A. and Carmona, E. and Carosi, A. and Colin, P. and Colombo, E. and Contreras, J. L. and Cortina, J. and Cossio, L. and Covino, S. and Dazzi, F. and De Angelis, A. and De Cea del Pozo, E. and De Lotto, B. and Delgado Mendez, C. and Diago Ortega, A. and Doert, M. and Dominguez, A. and Prester, Dijana Dominis and Dorner, D. and Doro, M. and Elsaesser, D. and Ferenc, D. and Fonseca, M. V. and Font, L. and Fruck, C. and Garcia Lopez, R. J. and Garczarczyk, M. and Garrido, D. and Giavitto, G. and Godinovic, N. and Hadasch, D. and Haefner, D. and Herrero, A. and Hildebrand, D. and Hoehne-Moench, D. and Hose, J. and Hrupec, D. and Huber, B. and Jogler, T. and Klepser, S. and Kraehenbuehl, T. and Krause, J. and La Barbera, A. and Lelas, D. and Leonardo, E. and Lindfors, E. and Lombardi, S. and Lopez, M. and Lorenz, E. and Makariev, M. and Maneva, G. and Mankuzhiyil, N. and Mannheim, K. and Maraschi, L. and Mariotti, M. and Martinez, M. and Mazin, D. and Meucci, M. and Miranda, J. M. and Mirzoyan, R. and Miyamoto, H. and Moldon, J. and Moralejo, A. and Munar, P. and Nieto, D. and Nilsson, K. and Orito, R. and Oya, I. and Paneque, D. and Paoletti, R. and Pardo, S. and Paredes, J. M. and Partini, S. and Pasanen, M. and Pauss, F. and Perez-Torres, M. A. and Persic, M. and Peruzzo, L. and Pilia, M. and Pochon, J. and Prada, F. and Moroni, P. G. Prada and Prandini, E. and Puljak, I. and Reichardt, I. and Reinthal, R. and Rhode, W. and Ribo, M. and Rico, J. and Ruegamer, S. and Saggion, A. and Saito, K. and Saito, T. Y. and Salvati, M. and Satalecka, K. and Scalzotto, V. and Scapin, V. and Schultz, C. and Schweizer, T. and Shayduk, M. and Shore, S. N. and Sillanpaa, A. and Sitarek, J. and Sobczynska, D. and Spanier, F. and Spiro, S. and Stamerra, A. and Steinke, B. and Storz, J. and Strah, N. and Suric, T. and Takalo, L. and Takami, H. and Tavecchio, F. and Temnikov, P. and Terzic, T. and Tescaro, D. and Teshima, M. and Thom, M. and Tibolla, O. and Torres, D. F. and Treves, A. and Vankov, H. and Vogler, P. and Wagner, R. M. and Weitzel, Q. and Zabalza, V. and Zandanel, F. and Zanin, R. and Arlen, T. and Aune, T. and Beilicke, M. and Benbow, W. and Bouvier, A. and Bradbury, S. M. and Buckley, J. H. and Bugaev, V. and Byrum, K. and Cannon, A. and Cesarini, A. and Ciupik, L. and Connolly, M. P. and Cui, W. and Dickherber, R. and Duke, C. and Errando, M. and Falcone, A. and Finley, J. P. and Finnegan, G. and Fortson, L. and Furniss, A. and Galante, N. and Gall, D. and Godambe, S. and Griffin, S. and Grube, J. and Gyuk, G. and Hanna, D. and Holder, J. and Huan, H. and Hui, C. M. and Kaaret, P. and Karlsson, N. and Kertzman, M. and Khassen, Y. and Kieda, D. and Krawczynski, H. and Krennrich, F. and Lang, M. J. and LeBohec, S. and Maier, G. and McArthur, S. and McCann, A. and Moriarty, P. and Mukherjee, R. and Nunez, P. D. and Ong, R. A. and Orr, M. and Otte, A. N. and Park, N. and Perkins, J. S. and Pichel, A. and Pohl, Martin and Prokoph, H. and Ragan, K. and Reyes, L. C. and Reynolds, P. T. and Roache, E. and Rose, H. J. and Ruppel, J. and Schroedter, M. and Sembroski, G. H. and Sentuerk, G. D. and Telezhinsky, Igor O. and Tesic, G. and Theiling, M. and Thibadeau, S. and Varlotta, A. and Vassiliev, V. V. and Vivier, M. and Wakely, S. P. and Weekes, T. C. and Williams, D. A. and Zitzer, B. and de Almeida, U. Barres and Cara, M. and Casadio, C. and Cheung, C. C. and McConville, W. and Davies, F. and Doi, A. and Giovannini, G. and Giroletti, M. and Hada, K. and Hardee, P. and Harris, D. E. and Junor, W. and Kino, M. and Lee, N. P. and Ly, C. and Madrid, J. and Massaro, F. and Mundell, C. G. and Nagai, H. and Perlman, E. S. and Steele, I. A. and Walker, R. C. and Wood, D. L.}, title = {The 2010 very high energy gamma-ray flare and 10 years ofmulti-wavelength oservations of M 87}, series = {The astrophysical journal : an international review of spectroscopy and astronomical physics}, volume = {746}, journal = {The astrophysical journal : an international review of spectroscopy and astronomical physics}, number = {2}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, organization = {HESS Collaboration, MAGIC Collaboration, VERITAS Collaboration}, issn = {0004-637X}, doi = {10.1088/0004-637X/746/2/151}, pages = {18}, year = {2012}, abstract = {The giant radio galaxy M 87 with its proximity (16 Mpc), famous jet, and very massive black hole ((3-6) x 10(9) M-circle dot) provides a unique opportunity to investigate the origin of very high energy (VHE; E > 100 GeV) gamma-ray emission generated in relativistic outflows and the surroundings of supermassive black holes. M 87 has been established as a VHE gamma-ray emitter since 2006. The VHE gamma-ray emission displays strong variability on timescales as short as a day. In this paper, results from a joint VHE monitoring campaign on M 87 by the MAGIC and VERITAS instruments in 2010 are reported. During the campaign, a flare at VHE was detected triggering further observations at VHE (H.E.S.S.), X-rays (Chandra), and radio (43 GHz Very Long Baseline Array, VLBA). The excellent sampling of the VHE gamma-ray light curve enables one to derive a precise temporal characterization of the flare: the single, isolated flare is well described by a two-sided exponential function with significantly different flux rise and decay times of tau(rise)(d) = (1.69 +/- 0.30) days and tau(decay)(d) = (0.611 +/- 0.080) days, respectively. While the overall variability pattern of the 2010 flare appears somewhat different from that of previous VHE flares in 2005 and 2008, they share very similar timescales (similar to day), peak fluxes (Phi(>0.35 TeV) similar or equal to (1-3) x 10(-11) photons cm(-2) s(-1)), and VHE spectra. VLBA radio observations of 43 GHz of the inner jet regions indicate no enhanced flux in 2010 in contrast to observations in 2008, where an increase of the radio flux of the innermost core regions coincided with a VHE flare. On the other hand, Chandra X-ray observations taken similar to 3 days after the peak of the VHE gamma-ray emission reveal an enhanced flux from the core (flux increased by factor similar to 2; variability timescale <2 days). The long-term (2001-2010) multi-wavelength (MWL) light curve of M 87, spanning from radio to VHE and including data from Hubble Space Telescope, Liverpool Telescope, Very Large Array, and European VLBI Network, is used to further investigate the origin of the VHE gamma-ray emission. No unique, common MWL signature of the three VHE flares has been identified. In the outer kiloparsec jet region, in particular in HST-1, no enhanced MWL activity was detected in 2008 and 2010, disfavoring it as the origin of the VHE flares during these years. Shortly after two of the three flares (2008 and 2010), the X-ray core was observed to be at a higher flux level than its characteristic range (determined from more than 60 monitoring observations: 2002-2009). In 2005, the strong flux dominance of HST-1 could have suppressed the detection of such a feature. Published models for VHE gamma-ray emission from M 87 are reviewed in the light of the new data.}, language = {en} } @article{CaravelliHammaMarkopoulouetal.2012, author = {Caravelli, Francesco and Hamma, Alioscia and Markopoulou, Fotini and Riera, Arnau}, title = {Trapped surfaces and emergent curved space in the Bose-Hubbard model}, series = {Physical review : D, Particles, fields, gravitation, and cosmology}, volume = {85}, journal = {Physical review : D, Particles, fields, gravitation, and cosmology}, number = {4}, publisher = {American Physical Society}, address = {College Park}, issn = {1550-7998}, doi = {10.1103/PhysRevD.85.044046}, pages = {15}, year = {2012}, abstract = {A Bose-Hubbard model on a dynamical lattice was introduced in previous work as a spin system analogue of emergent geometry and gravity. Graphs with regions of high connectivity in the lattice were identified as candidate analogues of spacetime geometries that contain trapped surfaces. We carry out a detailed study of these systems and show explicitly that the highly connected subgraphs trap matter. We do this by solving the model in the limit of no back-reaction of the matter on the lattice, and for states with certain symmetries that are natural for our problem. We find that in this case the problem reduces to a one-dimensional Hubbard model on a lattice with variable vertex degree and multiple edges between the same two vertices. In addition, we obtain a (discrete) differential equation for the evolution of the probability density of particles which is closed in the classical regime. This is a wave equation in which the vertex degree is related to the local speed of propagation of probability. This allows an interpretation of the probability density of particles similar to that in analogue gravity systems: matter inside this analogue system sees a curved spacetime. We verify our analytic results by numerical simulations. Finally, we analyze the dependence of localization on a gradual, rather than abrupt, falloff of the vertex degree on the boundary of the highly connected region and find that matter is localized in and around that region.}, language = {en} } @article{RieraGogolinEisert2012, author = {Riera, Arnau and Gogolin, Christian and Eisert, Jens}, title = {Thermalization in nature and on a quantum computer}, series = {Physical review letters}, volume = {108}, journal = {Physical review letters}, number = {8}, publisher = {American Physical Society}, address = {College Park}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.108.080402}, pages = {5}, year = {2012}, abstract = {In this work, we show how Gibbs or thermal states appear dynamically in closed quantum many-body systems, building on the program of dynamical typicality. We introduce a novel perturbation theorem for physically relevant weak system-bath couplings that is applicable even in the thermodynamic limit. We identify conditions under which thermalization happens and discuss the underlying physics. Based on these results, we also present a fully general quantum algorithm for preparing Gibbs states on a quantum computer with a certified runtime and error bound. This complements quantum Metropolis algorithms, which are expected to be efficient but have no known runtime estimates and only work for local Hamiltonians.}, language = {en} } @article{SchwabedalPikovskijKralemannetal.2012, author = {Schwabedal, Justus T. C. and Pikovskij, Arkadij and Kralemann, Bj{\"o}rn and Rosenblum, Michael}, title = {Optimal phase description of chaotic oscillators}, series = {Physical review : E, Statistical, nonlinear and soft matter physics}, volume = {85}, journal = {Physical review : E, Statistical, nonlinear and soft matter physics}, number = {2}, publisher = {American Physical Society}, address = {College Park}, issn = {1539-3755}, doi = {10.1103/PhysRevE.85.026216}, pages = {9}, year = {2012}, abstract = {We introduce an optimal phase description of chaotic oscillations by generalizing the concept of isochrones. On chaotic attractors possessing a general phase description, we define the optimal isophases as Poincare surfaces showing return times as constant as possible. The dynamics of the resultant optimal phase is maximally decoupled from the amplitude dynamics and provides a proper description of the phase response of chaotic oscillations. The method is illustrated with the Rossler and Lorenz systems.}, language = {en} } @article{JeonMetzler2012, author = {Jeon, Jae-Hyung and Metzler, Ralf}, title = {Inequivalence of time and ensemble averages in ergodic systems: exponential versus power-law relaxation in confinement}, series = {Physical review : E, Statistical, nonlinear and soft matter physics}, volume = {85}, journal = {Physical review : E, Statistical, nonlinear and soft matter physics}, number = {2}, publisher = {American Physical Society}, address = {College Park}, issn = {1539-3755}, doi = {10.1103/PhysRevE.85.021147}, pages = {8}, year = {2012}, abstract = {Single-particle tracking has become a standard tool for the investigation of diffusive properties, especially in small systems such as biological cells. Usually the resulting time series are analyzed in terms of time averages over individual trajectories. Here we study confined normal as well as anomalous diffusion, modeled by fractional Brownian motion and the fractional Langevin equation, and show that even for such ergodic systems time-averaged quantities behave differently from their ensemble-averaged counterparts, irrespective of how long the measurement time becomes. Knowledge of the exact behavior of time averages is therefore fundamental for the proper physical interpretation of measured time series, in particular, for extraction of the relaxation time scale from data.}, language = {en} } @article{HerzogBojahrGoldshteynetal.2012, author = {Herzog, Marc and Bojahr, Andre and Goldshteyn, J. and Leitenberger, Wolfram and Vrejoiu, I. and Khakhulin, D. and Wulff, M. and Shayduk, Roman and Gaal, P. and Bargheer, Matias}, title = {Detecting optically synthesized quasi-monochromatic sub-terahertz phonon wavepackets by ultrafast x-ray diffraction}, series = {Applied physics letters}, volume = {100}, journal = {Applied physics letters}, number = {9}, publisher = {American Institute of Physics}, address = {Melville}, issn = {0003-6951}, doi = {10.1063/1.3688492}, pages = {4}, year = {2012}, abstract = {We excite an epitaxial SrRuO3 thin film transducer by a pulse train of ultrashort laser pulses, launching coherent sound waves into the underlying SrTiO3 substrate. Synchrotron-based x-ray diffraction (XRD) data exhibiting separated sidebands to the substrate peak evidence the excitation of a quasi-monochromatic phonon wavepacket with sub-THz central frequency. The frequency and bandwidth of this sound pulse can be controlled by the optical pulse train. We compare the experimental data to combined lattice dynamics and dynamical XRD simulations to verify the coherent phonon dynamics. In addition, we observe a lifetime of 130 ps of such sub-THz phonons in accordance with the theory.}, language = {en} } @article{HerzogSchickGaaletal.2012, author = {Herzog, Marc and Schick, Daniel and Gaal, P. and Shayduk, Roman and von Korff Schmising, Clemens and Bargheer, Matias}, title = {Analysis of ultrafast X-ray diffraction data in a linear-chain model of the lattice dynamics}, series = {Applied physics : A, Materials science \& processing}, volume = {106}, journal = {Applied physics : A, Materials science \& processing}, number = {3}, publisher = {Springer}, address = {New York}, issn = {0947-8396}, doi = {10.1007/s00339-011-6719-z}, pages = {489 -- 499}, year = {2012}, abstract = {We present ultrafast X-ray diffraction (UXRD) experiments which sensitively probe impulsively excited acoustic phonons propagating in a SrRuO3/SrTiO3 superlattice and further into the substrate. These findings are discussed together with previous UXRD results (Herzog et al. in Appl. Phys. Lett. 96, 161906, 2010; Woerner et al. in Appl. Phys. A 96, 83, 2009; v. Korff Schmising in Phys. Rev. B 78, 060404(R), 2008 and in Appl. Phys. B 88, 1, 2007) using a normal-mode analysis of a linear-chain model of masses and springs, thus identifying them as linear-response phenomena. We point out the direct correspondence of calculated observables with X-ray signals. In this framework the complex lattice motion turns out to result from an interference of vibrational eigenmodes of the coupled system of nanolayers and substrate. UXRD in principle selectively measures the lattice motion occurring with a specific wavevector, however, each Bragg reflection only measures the amplitude of a delocalized phonon mode in a spatially localized region, determined by the nanocomposition of the sample or the extinction depth of X-rays. This leads to a decay of experimental signals although the excited modes survive.}, language = {en} } @article{FangHollaenderWirgesetal.2012, author = {Fang, Peng and Hollaender, Lars and Wirges, Werner and Gerhard, Reimund}, title = {Piezoelectric d(33) coefficients in foamed and layered polymer piezoelectrets from dynamic mechano-electrical experiments, electro-mechanical resonance spectroscopy and acoustic-transducer measurements}, series = {Measurement science and technology}, volume = {23}, journal = {Measurement science and technology}, number = {3}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {0957-0233}, doi = {10.1088/0957-0233/23/3/035604}, pages = {9}, year = {2012}, abstract = {Piezoelectrets are novel transducer materials which can be widely applied in sensors and actuators. Here, three techniques for determining piezoelectric d(33) coefficients of piezoelectrets are reviewed and compared. Two types of piezoelectrets, polyethylene-naphthalate (PEN) polymer-foam piezoelectrets and fluorinated ethylene-propylene (FEP) copolymer-layer piezoelectrets, have been prepared and measured by means of dynamic, resonance, and acoustical methods. The dynamic measurements show that the d(33) coefficient of PEN-foam samples clearly decreases with increasing stress, but 80\% of the initial d(33) can be retained after 1800 cycles of a continuous dynamic measurement in a mechanical fatigue test. The resonance measurements demonstrate that both PEN-foam and FEP-layer samples exhibit clear electro-mechanical resonances. PEN-foam samples show elastic moduli in the range from 1 to 12 MPa and d(33) values up to 500 pC N-1, while FEP-layer samples show homogeneous elastic moduli of about 0.3 MPa and d(33) values of about 280 pC N-1. The acoustical measurements reveal that both PEN-foam and FEP-layer samples exhibit stable frequency responses in the range from 5.7 to 20 kHz. In addition, d(33) coefficients obtained with different experimental methods are in good agreement with each other, which confirms the reliability of all three techniques.}, language = {en} } @article{AlbrechtSchindlerKurpiersetal.2012, author = {Albrecht, Steve and Schindler, Wolfram and Kurpiers, Jona and Kniepert, Juliane and Blakesley, James C. and Dumsch, Ines and Allard, Sybille and Fostiropoulos, Konstantinos and Scherf, Ullrich and Neher, Dieter}, title = {On the field dependence of free charge carrier generation and recombination in blends of PCPDTBT/PC70BM influence of solvent additives}, series = {The journal of physical chemistry letters}, volume = {3}, journal = {The journal of physical chemistry letters}, number = {5}, publisher = {American Chemical Society}, address = {Washington}, issn = {1948-7185}, doi = {10.1021/jz3000849}, pages = {640 -- 645}, year = {2012}, abstract = {We have applied time-delayed collection field (TDCF) and charge extraction by linearly increasing voltage (CELIV) to investigate the photogeneration, transport, and recombination of charge carriers in blends composed of PCPDTBT/PC70BM processed with and without the solvent additive diiodooctane. The results suggest that the solvent additive has severe impacts on the elementary processes involved in the photon to collected electron conversion in these blends. First, a pronounced field dependence of the free carrier generation is found for both blends, where the field dependence is stronger without the additive. Second, the fate of charge carriers in both blends can be described with a rather high bimolecular recombination coefficients, which increase with decreasing internal field. Third, the mobility is three to four times higher with the additive. Both blends show a negative field dependence of mobility, which we suggest to cause bias-dependent recombination coefficients.}, language = {en} } @article{GrossNesmeVogtsetal.2012, author = {Gross, David and Nesme, V. and Vogts, H. and Werner, Reinhard F.}, title = {Index theory of one dimensional quantum walks and cellular automata}, series = {Communications in mathematical physics}, volume = {310}, journal = {Communications in mathematical physics}, number = {2}, publisher = {Springer}, address = {New York}, issn = {0010-3616}, doi = {10.1007/s00220-012-1423-1}, pages = {419 -- 454}, year = {2012}, abstract = {If a one-dimensional quantum lattice system is subject to one step of a reversible discrete-time dynamics, it is intuitive that as much "quantum information" as moves into any given block of cells from the left, has to exit that block to the right. For two types of such systems - namely quantum walks and cellular automata - we make this intuition precise by defining an index, a quantity that measures the "net flow of quantum information" through the system. The index supplies a complete characterization of two properties of the discrete dynamics. First, two systems S-1, S-2 can be "pieced together", in the sense that there is a system S which acts like S-1 in one region and like S-2 in some other region, if and only if S-1 and S-2 have the same index. Second, the index labels connected components of such systems: equality of the index is necessary and sufficient for the existence of a continuous deformation of S-1 into S-2. In the case of quantum walks, the index is integer-valued, whereas for cellular automata, it takes values in the group of positive rationals. In both cases, the map S bar right arrow. ind S is a group homomorphism if composition of the discrete dynamics is taken as the group law of the quantum systems. Systems with trivial index are precisely those which can be realized by partitioned unitaries, and the prototypes of systems with non-trivial index are shifts.}, language = {en} } @article{CubittEisertWolf2012, author = {Cubitt, Toby S. and Eisert, Jens and Wolf, Michael M.}, title = {The complexity of relating quantum channels to master equations}, series = {Communications in mathematical physics}, volume = {310}, journal = {Communications in mathematical physics}, number = {2}, publisher = {Springer}, address = {New York}, issn = {0010-3616}, doi = {10.1007/s00220-011-1402-y}, pages = {383 -- 418}, year = {2012}, abstract = {Completely positive, trace preserving (CPT) maps and Lindblad master equations are both widely used to describe the dynamics of open quantum systems. The connection between these two descriptions is a classic topic in mathematical physics. One direction was solved by the now famous result due to Lindblad, Kossakowski, Gorini and Sudarshan, who gave a complete characterisation of the master equations that generate completely positive semi-groups. However, the other direction has remained open: given a CPT map, is there a Lindblad master equation that generates it (and if so, can we find its form)? This is sometimes known as the Markovianity problem. Physically, it is asking how one can deduce underlying physical processes from experimental observations. We give a complexity theoretic answer to this problem: it is NP-hard. We also give an explicit algorithm that reduces the problem to integer semi-definite programming, a well-known NP problem. Together, these results imply that resolving the question of which CPT maps can be generated by master equations is tantamount to solving P = NP: any efficiently computable criterion for Markovianity would imply P = NP; whereas a proof that P = NP would imply that our algorithm already gives an efficiently computable criterion. Thus, unless P does equal NP, there cannot exist any simple criterion for determining when a CPT map has a master equation description. However, we also show that if the system dimension is fixed (relevant for current quantum process tomography experiments), then our algorithm scales efficiently in the required precision, allowing an underlying Lindblad master equation to be determined efficiently from even a single snapshot in this case. Our work also leads to similar complexity-theoretic answers to a related long-standing open problem in probability theory.}, language = {en} } @article{BodrovaSchmidtSpahnetal.2012, author = {Bodrova, Anna and Schmidt, J{\"u}rgen and Spahn, Frank and Brilliantov, Nikolai V.}, title = {Adhesion and collisional release of particles in dense planetary rings}, series = {Icarus : international journal of solar system studies}, volume = {218}, journal = {Icarus : international journal of solar system studies}, number = {1}, publisher = {Elsevier}, address = {San Diego}, issn = {0019-1035}, doi = {10.1016/j.icarus.2011.11.011}, pages = {60 -- 68}, year = {2012}, abstract = {We propose a simple theoretical model for aggregative and fragmentative collisions in Saturn's dense rings. In this model the ring matter consists of a bimodal size distribution: large (meter sized) boulders and a population of smaller particles (tens of centimeters down to dust). The small particles can adhesively stick to the boulders and can be released as debris in binary collisions of their carriers. To quantify the adhesion force we use the JKR theory (Johnson, K., Kendall, K., Roberts, A. [1971]. Proc. R. Soc. Lond. A 324, 301-313). The rates of release and adsorption of particles are calculated, depending on material parameters, sizes, and plausible velocity dispersions of carriers and debris particles. In steady state we obtain an expression for the amount of free debris relative to the fraction still attached to the carriers. In terms of this conceptually simple model a paucity of subcentimeter particles in Saturn's rings (French, R.G., Nicholson, P.D. [2000]. Icarus 145, 502-523; Marouf, E. et al. [2008]. Abstracts for "Saturn after Cassini-Huygens" Symposium, Imperial College London, UK, July 28 to August 1, p. 113) can be understood as a consequence of the increasing strength of adhesion (relative to inertial forces) for decreasing particle size. In this case particles smaller than a certain critical radius remain tightly attached to the surfaces of larger boulders, even when the boulders collide at their typical speed. Furthermore, we find that already a mildly increased velocity dispersion of the carrier-particles may significantly enhance the fraction of free debris particles, in this way increasing the optical depth of the system.}, language = {en} } @article{HorovitzHenkel2012, author = {Horovitz, Baruch and Henkel, Carsten}, title = {Surface plasmons at composite surfaces with diffusive charges}, series = {epl : a letters journal exploring the frontiers of physics}, volume = {97}, journal = {epl : a letters journal exploring the frontiers of physics}, number = {5}, publisher = {EDP Sciences}, address = {Mulhouse}, issn = {0295-5075}, doi = {10.1209/0295-5075/97/57010}, pages = {6}, year = {2012}, abstract = {Metal surfaces with disorder or with nanostructure modifications are studied, allowing for a localized charge layer (CL) in addition to continuous charges (CC) in the bulk, both charges having a compressional or diffusive nonlocal response. The notorious problem of "additional boundary conditions" is resolved with the help of a Boltzmann equation that involves the scattering between the two charge types. Depending on the strength of this scattering, the oscillating charges can be dominantly CC or CL; the surface plasmon (SP) resonance acquires then a relatively small linewidth, in agreement with a large set of data. With a few parameters our model describes a large variety of SP dispersions corresponding to observed data.}, language = {en} } @article{PalyulinMetzler2012, author = {Palyulin, Vladimir V. and Metzler, Ralf}, title = {How a finite potential barrier decreases the mean first-passage time}, series = {Journal of statistical mechanics: theory and experiment}, journal = {Journal of statistical mechanics: theory and experiment}, number = {1}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {1742-5468}, doi = {10.1088/1742-5468/2012/03/L03001}, pages = {10}, year = {2012}, abstract = {We consider the mean first-passage time of a random walker moving in a potential landscape on a finite interval, the starting and end points being at different potentials. From analytical calculations and Monte Carlo simulations we demonstrate that the mean first-passage time for a piecewise linear curve between these two points is minimized by the introduction of a potential barrier. Due to thermal fluctuations, this barrier may be crossed. It turns out that the corresponding expense for this activation is less severe than the gain from an increased slope towards the end point. In particular, the resulting mean first-passage time is shorter than for a linear potential drop between the two points.}, language = {en} } @article{SchubertDolfenFrischetal.2012, author = {Schubert, Marcel and Dolfen, Daniel and Frisch, Johannes and Roland, Steffen and Steyrleuthner, Robert and Stiller, Burkhard and Chen, Zhihua and Scherf, Ullrich and Koch, Norbert and Facchetti, Antonio and Neher, Dieter}, title = {Influence of aggregation on the performance of All-Polymer Solar Cells containing Low-Bandgap Naphthalenediimide Copolymers}, series = {dvanced energy materials}, volume = {2}, journal = {dvanced energy materials}, number = {3}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1614-6832}, doi = {10.1002/aenm.201100601}, pages = {369 -- 380}, year = {2012}, abstract = {The authors present efficient all-polymer solar cells comprising two different low-bandgap naphthalenediimide (NDI)-based copolymers as acceptors and regioregular P3HT as the donor. It is shown that these naphthalene copolymers have a strong tendency to preaggregate in specific organic solvents, and that preaggregation can be completely suppressed when using suitable solvents with large and highly polarizable aromatic cores. Organic solar cells prepared from such nonaggregated polymer solutions show dramatically increased power conversion efficiencies of up to 1.4\%, which is mainly due to a large increase of the short circuit current. In addition, optimized solar cells show remarkable high fill factors of up to 70\%. The analysis of the blend absorbance spectra reveals a surprising anticorrelation between the degree of polymer aggregation in the solid P3HT:NDI copolymer blends and their photovoltaic performance. Scanning near-field optical microscopy (SNOM) and atomic force microscopy (AFM) measurements reveal important information on the blend morphology. It is shown that films with high degree of aggregation and low photocurrents exhibit large-scale phase-separation into rather pure donor and acceptor domains. It is proposed that, by suppressing the aggregation of NDI copolymers at the early stage of film formation, the intermixing of the donor and acceptor component is improved, thereby allowing efficient harvesting of photogenerated excitons at the donoracceptor heterojunction.}, language = {en} } @article{MulanskyPicovsky2012, author = {Mulansky, Mario and Picovsky, Arkady S.}, title = {Re-localization due to finite response times in a nonlinear Anderson chain}, series = {The European physical journal : B, Condensed matter and complex systems}, volume = {85}, journal = {The European physical journal : B, Condensed matter and complex systems}, number = {3}, publisher = {Springer}, address = {New York}, issn = {1434-6028}, doi = {10.1140/epjb/e2012-21040-5}, pages = {3}, year = {2012}, abstract = {We study a disordered nonlinear Schrodinger equation with an additional relaxation process having a finite response time tau. Without the relaxation term, tau = 0, this model has been widely studied in the past and numerical simulations showed subdiffusive spreading of initially localized excitations. However, recently Caetano et al. [Eur. Phys. J. B 80, 321 (2011)] found that by introducing a response time tau > 0, spreading is suppressed and any initially localized excitation will remain localized. Here, we explain the lack of subdiffusive spreading for tau > 0 by numerically analyzing the energy evolution. We find that in the presence of a relaxation process the energy drifts towards the band edge, which enforces the population of fewer and fewer localized modes and hence leads to re-localization. The explanation presented here relies on former findings by Mulansky et al. [Phys. Rev. E 80, 056212 (2009)] on the energy dependence of thermalized states.}, language = {en} } @article{AliuArchambaultArlenetal.2012, author = {Aliu, E. and Archambault, S. and Arlen, T. and Aune, T. and Beilicke, M. and Benbow, W. and Bouvier, A. and Bradbury, S. M. and Buckley, J. H. and Bugaev, V. and Byrum, K. and Cannon, A. and Cesarini, A. and Christiansen, J. L. and Ciupik, L. and Collins-Hughes, E. and Connolly, M. P. and Cui, W. and Decerprit, G. and Dickherber, R. and Dumm, J. and Errando, M. and Falcone, A. and Feng, Q. and Ferrer, F. and Finley, J. P. and Finnegan, G. and Fortson, L. and Furniss, A. and Galante, N. and Gall, D. and Godambe, S. and Griffin, S. and Grube, J. and Gyuk, G. and Hanna, D. and Holder, J. and Huan, H. and Hughes, G. and Humensky, T. B. and Kaaret, P. and Karlsson, N. and Kertzman, M. and Khassen, Y. and Kieda, D. and Krawczynski, H. and Krennrich, F. and Lee, K. and Madhavan, A. S. and Maier, G. and Majumdar, P. and McArthur, S. and McCann, A. and Moriarty, P. and Mukherjee, R. and Ong, R. A. and Orr, M. and Otte, A. N. and Park, N. and Perkins, J. S. and Pohl, Martin and Prokoph, H. and Quinn, J. and Ragan, K. and Reyes, L. C. and Reynolds, P. T. and Roache, E. and Rose, H. J. and Ruppel, J. and Saxon, D. B. and Schroedter, M. and Sembroski, G. H. and Sentuerk, G. D. and Skole, C. and Smith, A. W. and Staszak, D. and Telezhinsky, Igor O. and Tesic, G. and Theiling, M. and Thibadeau, S. and Tsurusaki, K. and Varlotta, A. and Vassiliev, V. V. and Vincent, S. and Vivier, M. and Wagner, R. G. and Wakely, S. P. and Ward, J. E. and Weekes, T. C. and Weinstein, A. and Weisgarber, T. and Williams, D. A. and Zitzer, B.}, title = {VERITAS deep observations of the dwarf spheroidal galaxy Segue 1}, series = {Physical review : D, Particles, fields, gravitation, and cosmology}, volume = {85}, journal = {Physical review : D, Particles, fields, gravitation, and cosmology}, number = {6}, publisher = {American Physical Society}, address = {College Park}, issn = {1550-7998}, doi = {10.1103/PhysRevD.85.062001}, pages = {12}, year = {2012}, abstract = {The VERITAS array of Cherenkov telescopes has carried out a deep observational program on the nearby dwarf spheroidal galaxy Segue 1. We report on the results of nearly 48 hours of good quality selected data, taken between January 2010 and May 2011. No significant gamma-ray emission is detected at the nominal position of Segue 1, and upper limits on the integrated flux are derived. According to recent studies, Segue 1 is the most dark matter-dominated dwarf spheroidal galaxy currently known. We derive stringent bounds on various annihilating and decaying dark matter particle models. The upper limits on the velocity-weighted annihilation cross-section are (95\%) (CL) less than or similar to 10(-23) cm(3) s(-1), improving our limits from previous observations of dwarf spheroidal galaxies by at least a factor of 2 for dark matter particle masses m(chi) greater than or similar to 300 GeV. The lower limits on the decay lifetime are at the level of tau(95\%) (CL) greater than or similar to 10(24) s. Finally, we address the interpretation of the cosmic ray lepton anomalies measured by ATIC and PAMELA in terms of dark matter annihilation, and show that the VERITAS observations of Segue 1 disfavor such a scenario.}, language = {en} } @article{KielKloetzerMitzscherlingetal.2012, author = {Kiel, Mareike and Kloetzer, Madlen and Mitzscherling, Steffen and Bargheer, Matias}, title = {Measuring the Range of Plasmonic Interaction}, series = {Langmuir}, volume = {28}, journal = {Langmuir}, number = {10}, publisher = {American Chemical Society}, address = {Washington}, issn = {0743-7463}, doi = {10.1021/la204577m}, pages = {4800 -- 4804}, year = {2012}, abstract = {When gold nanoparticles are covered with nanometric layers of transparent polyelectrolytes, the plasmon absorption spectrum A(lambda) increases by a factor of approximately three and shifts to the red. These modifications of dissipative experimental observables stop when the cover layer thickness approaches the particle diameter. Spectral modifications of dispersive parameters like the reflection R, however, keep changing with increasing cover layer thickness. The shift of the plasmon resonance caused by two interacting particle layers is studied as a function of the separating distance between the two layers. We discuss these observations in the context of an effective medium theory and conclude that it can only be applied for a layer thickness on the order of the particle diameter.}, language = {en} } @article{ScharsichLohwasserSommeretal.2012, author = {Scharsich, Christina and Lohwasser, Ruth H. and Sommer, Michael and Asawapirom, Udom and Scherf, Ullrich and Thelakkat, Mukundan and Neher, Dieter and Koehler, Anna}, title = {Control of aggregate formation in poly(3-hexylthiophene) by solvent, molecular weight, and synthetic method}, series = {Journal of polymer science : B, Polymer physics}, volume = {50}, journal = {Journal of polymer science : B, Polymer physics}, number = {6}, publisher = {Wiley-Blackwell}, address = {Hoboken}, issn = {0887-6266}, doi = {10.1002/polb.23022}, pages = {442 -- 453}, year = {2012}, abstract = {Aggregate formation in poly(3-hexylthiophene) depends on molecular weight, solvent, and synthetic method. The interplay of these parameters thus largely controls device performance. In order to obtain a quantitative understanding on how these factors control the resulting electronic properties of P3HT, we measured absorption in solution and in thin films as well as the resulting field effect mobility in transistors. By a detailed analysis of the absorption spectra, we deduce the fraction of aggregates formed, the excitonic coupling within the aggregates, and the conjugation length within the aggregates, all as a function of solvent quality for molecular weights from 5 to 19 kDa. From this, we infer in which structure the aggregated chains pack. Although the 5 kDa samples form straight chains, the 11 and 19 kDa chains are kinked or folded, with conjugation lengths that increase as the solvent quality reduces. There is a maximum fraction of aggregated chains (about 55 +/- 5\%) that can be obtained, even for poor solvent quality. We show that inducing aggregation in solution leads to control of aggregate properties in thin films. As expected, the field-effect mobility correlates with the propensity to aggregation. Correspondingly, we find that a well-defined synthetic approach, tailored to give a narrow molecular weight distribution, is needed to obtain high field effect mobilities of up to 0.01 cm2/Vs for low molecular weight samples (=11 kDa), while the influence of synthetic method is negligible for samples of higher molecular weight, if low molecular weight fractions are removed by extraction.}, language = {en} } @inproceedings{SchuhPruckerLomadzeetal.2012, author = {Schuh, Christian and Prucker, Oswald and Lomadze, Nino and Kopyshev, Alexey and Santer, Svetlana and Ruehe, Juergen}, title = {Nanogradient polymer brushes}, series = {Abstracts of papers : joint conference / The Chemical Institute of Cananda, CIC, American Chemical Society, ACS}, volume = {243}, booktitle = {Abstracts of papers : joint conference / The Chemical Institute of Cananda, CIC, American Chemical Society, ACS}, publisher = {American Chemical Society}, address = {Washington}, issn = {0065-7727}, pages = {1}, year = {2012}, language = {en} } @article{McCarthyStoyanovRychkovetal.2012, author = {McCarthy, Denis N. and Stoyanov, Hristiyan and Rychkov, Dmitry and Ragusch, Huelya and Melzer, Michael and Kofod, Guggi}, title = {Increased permittivity nanocomposite dielectrics by controlled interfacial interactions}, series = {Composites science and technology}, volume = {72}, journal = {Composites science and technology}, number = {6}, publisher = {Elsevier}, address = {Oxford}, issn = {0266-3538}, doi = {10.1016/j.compscitech.2012.01.026}, pages = {731 -- 736}, year = {2012}, abstract = {The use of nanoparticles in polymer composite dielectrics has promised great improvements, but useful results have been elusive. Here, the importance of the interfacial interactions between the nanoparticles and the polymer matrix are investigated in TiO2 nanocomposites for dielectric materials using surface functionalisation. The interface is observed to dominate the nanocomposite properties and leads to a threefold increase in permittivity at volume fractions as low as 10\%. Surface functionalisation of the filler nanoparticles with silanes allows control of this interface, avoiding significant degradation of the other important material properties, particularly electrical breakdown strength, and resulting in a material that is demonstrated successfully as an active material in a dielectric elastomer actuator application with increased work output compared to the pure polymer. Although further permittivity increases are observed when the interface regions have formed a percolation network, the other material properties deteriorate. The observation of percolation behaviour allows the interface thickness to be estimated.}, language = {en} } @article{AlbrechtSchaeferLangeetal.2012, author = {Albrecht, Steve and Schaefer, Sebastian and Lange, Ilja and Yilmaz, Seyfullah and Dumsch, Ines and Allard, Sybille and Scherf, Ullrich and Hertwig, Andreas and Neher, Dieter}, title = {Light management in PCPDTBT:PC70BM solar cells: A comparison of standard and inverted device structures}, series = {Organic electronics : physics, materials and applications}, volume = {13}, journal = {Organic electronics : physics, materials and applications}, number = {4}, publisher = {Elsevier}, address = {Amsterdam}, issn = {1566-1199}, doi = {10.1016/j.orgel.2011.12.019}, pages = {615 -- 622}, year = {2012}, abstract = {We compare standard and inverted bulk heterojunction solar cells composed of PCPDTBT:PC70BM blends. Inverted devices comprising 100 nm thick active layers exhibited short circuit currents of 15 mA/cm(2), 10\% larger than in corresponding standard devices. Modeling of the optical field distribution in the different device stacks proved that this enhancement originates from an increased absorption of incident light in the active layer. Internal quantum efficiencies (IQEs) were obtained from the direct comparison of experimentally derived and modeled currents for different layer thicknesses, yielding IQEs of similar to 70\% for a layer thickness of 100 nm. Simulations predict a significant increase of the light harvesting efficiency upon increasing the layer thickness to 270 nm. However, a continuous deterioration of the photovoltaic properties with layer thickness was measured for both device architectures, attributed to incomplete charge extraction. On the other hand, our optical modeling suggests that inverted devices based on PCPDTBT should be able to deliver high power conversion efficiencies (PCEs) of more than 7\% provided that recombination losses can be reduced.}, language = {en} } @article{TrotzkyChenFleschetal.2012, author = {Trotzky, S. and Chen, Y-A. and Flesch, A. and McCulloch, I. P. and Schollw{\"o}ck, U. and Eisert, J. and Bloch, I.}, title = {Probing the relaxation towards equilibrium in an isolated strongly correlated one-dimensional Bose gas}, series = {Nature physics}, volume = {8}, journal = {Nature physics}, number = {4}, publisher = {Nature Publ. Group}, address = {London}, issn = {1745-2473}, doi = {10.1038/NPHYS2232}, pages = {325 -- 330}, year = {2012}, abstract = {The problem of how complex quantum systems eventually come to rest lies at the heart of statistical mechanics. The maximum-entropy principle describes which quantum states can be expected in equilibrium, but not how closed quantum many-body systems dynamically equilibrate. Here, we report the experimental observation of the non-equilibrium dynamics of a density wave of ultracold bosonic atoms in an optical lattice in the regime of strong correlations. Using an optical superlattice, we follow its dynamics in terms of quasi-local densities, currents and coherences-all showing a fast relaxation towards equilibrium values. Numerical calculations based on matrix-product states are in an excellent quantitative agreement with the experimental data. The system fulfills the promise of being a dynamical quantum simulator, in that the controlled dynamics runs for longer times than present classical algorithms can keep track of.}, language = {en} } @article{TurhanSaracGencturketal.2012, author = {Turhan, Metehan C. and Sarac, A. Sezai and Gencturk, Asli and Gilsing, Hans-Detlev and Faltz, Heike and Schulz, Burkhard}, title = {Electrochemical impedance characterization and potential dependence of poly[3,4-(2,2-dibutylpropylenedioxy)thiophene] nanostructures on single carbon fiber microelectrode}, series = {Synthetic metals : the journal of electronic polymers and electronic molecular materials}, volume = {162}, journal = {Synthetic metals : the journal of electronic polymers and electronic molecular materials}, number = {5-6}, publisher = {Elsevier}, address = {Lausanne}, issn = {0379-6779}, doi = {10.1016/j.synthmet.2012.01.012}, pages = {511 -- 515}, year = {2012}, abstract = {The electropolymerization of 3,4-(2,2-dibutylpropylenedioxy)thiophene (ProDOT-Bu-2) onto single carbon fiber microelectrode (SCFME) was conducted in acetonitrile (ACN) containing sodium perchlorate (NaClO4) as electrolyte and investigated by cyclic voltammetry (CV). The nanostructured films of poly[3,4-(2,2-dibutyl-propyleneclioxy)thiophene] (PProDOT-Bu-2) which were depositing showed complete reversible redox behavior in monomer-free electrolyte solution. The capacitive behavior of the films was investigated by electrochemical impedance spectroscopy (EIS) at applied potentials from 0.1 V to 1.3 V. The analysis by equivalent circuit modeling revealed an applied potential around 0.4V to be most suitable for the system PProDOT-Bu-2/SCFME as a double layer supercapacitor component inducing a double layer capacitance C-d, value of 62 mFcm(-2).}, language = {en} } @misc{GvaramadzeKniazevMiroshnichenkoetal.2012, author = {Gvaramadze, V. V. and Kniazev, A. Y. and Miroshnichenko, A. S. and Berdnikov, Leonid N. and Langer, N. and Stringfellow, G. S. and Todt, Helge Tobias and Hamann, Wolf-Rainer and Grebel, E. K. and Buckley, D. and Crause, L. and Crawford, S. and Gulbis, A. and Hettlage, C. and Hooper, E. and Husser, T. -O. and Kotze, P. and Loaring, N. and Nordsieck, K. H. and O'Donoghue, D. and Pickering, T. and Potter, S. and Colmenero, E. Romero and Vaisanen, P. and Williams, T. and Wolf, M. and Reichart, D. E. and Ivarsen, K. M. and Haislip, J. B. and Nysewander, M. C. and LaCluyze, A. P.}, title = {Discovery of two new Galactic candidate luminous blue variables with Wide-field Infrared Survey Explorer}, series = {Monthly notices of the Royal Astronomical Society}, volume = {421}, journal = {Monthly notices of the Royal Astronomical Society}, number = {4}, publisher = {Oxford Univ. Press}, address = {Oxford}, issn = {0035-8711}, doi = {10.1111/j.1365-2966.2012.20556.x}, pages = {3325 -- 3337}, year = {2012}, abstract = {We report the discovery of two new Galactic candidate luminous blue variable (LBV) stars via detection of circular shells (typical of confirmed and candidate LBVs) and follow-up spectroscopy of their central stars. The shells were detected at 22 mu m in the archival data of the Mid-Infrared All Sky Survey carried out with the Wide-field Infrared Survey Explorer (WISE). Follow-up optical spectroscopy of the central stars of the shells conducted with the renewed Southern African Large Telescope (SALT) showed that their spectra are very similar to those of the well-known LBVs P Cygni and AG Car, and the recently discovered candidate LBV MN112, which implies the LBV classification for these stars as well. The LBV classification of both stars is supported by detection of their significant photometric variability: one of them brightened in the R and I bands by 0.68 +/- 0.10 and 0.61 +/- 0.04 mag, respectively, during the last 1318 years, while the second one (known as Hen 3-1383) varies its B, V, R, I and Ks brightnesses by similar or equal to 0.50.9 mag on time-scales from 10 d to decades. We also found significant changes in the spectrum of Hen 3-1383 on a time-scale of similar or equal to 3 months, which provides additional support for the LBV classification of this star. Further spectrophotometric monitoring of both stars is required to firmly prove their LBV status. We discuss a connection between the location of massive stars in the field and their fast rotation, and suggest that the LBV activity of the newly discovered candidate LBVs might be directly related to their possible runaway status.}, language = {en} } @article{OskinovaFeldmeierKretschmar2012, author = {Oskinova, Lida and Feldmeier, Achim and Kretschmar, Peter}, title = {Clumped stellar winds in supergiant high-mass X-ray binaries: X-ray variability and photoionization}, series = {Monthly notices of the Royal Astronomical Society}, volume = {421}, journal = {Monthly notices of the Royal Astronomical Society}, number = {4}, publisher = {Wiley-Blackwell}, address = {Malden}, issn = {0035-8711}, doi = {10.1111/j.1365-2966.2012.20507.x}, pages = {2820 -- 2831}, year = {2012}, abstract = {The clumping of massive star winds is an established paradigm, which is confirmed by multiple lines of evidence and is supported by stellar wind theory. The purpose of this paper is to bridge the gap between detailed models of inhomogeneous stellar winds in single stars and the phenomenological description of donor winds in supergiant high-mass X-ray binaries (HMXBs). We use the results from time-dependent hydrodynamical models of the instability in the line-driven wind of a massive supergiant star to derive the time-dependent accretion rate on to a compact object in the BondiHoyleLyttleton approximation. The strong density and velocity fluctuations in the wind result in strong variability of the synthetic X-ray light curves. The model predicts a large-scale X-ray variability, up to eight orders of magnitude, on relatively short time-scales. The apparent lack of evidence for such strong variability in the observed HMXBs indicates that the details of the accretion process act to reduce the variability resulting from the stellar wind velocity and density jumps.}, language = {en} } @article{LeijnseJeonLoftetal.2012, author = {Leijnse, N. and Jeon, J. -H. and Loft, S. and Metzler, Ralf and Oddershede, L. B.}, title = {Diffusion inside living human cells}, series = {European physical journal special topics}, volume = {204}, journal = {European physical journal special topics}, number = {1}, publisher = {Springer}, address = {Heidelberg}, issn = {1951-6355}, doi = {10.1140/epjst/e2012-01553-y}, pages = {75 -- 84}, year = {2012}, abstract = {Naturally occurring lipid granules diffuse in the cytoplasm and can be used as tracers to map out the viscoelastic landscape inside living cells. Using optical trapping and single particle tracking we found that lipid granules exhibit anomalous diffusion inside human umbilical vein endothelial cells. For these cells the exact diffusional pattern of a particular granule depends on the physiological state of the cell and on the localization of the granule within the cytoplasm. Granules located close to the actin rich periphery of the cell move less than those located towards to the center of the cell or within the nucleus. Also, granules in cells which are stressed by intense laser illumination or which have attached to a surface for a long period of time move in a more restricted fashion than those within healthy cells. For granules diffusing in healthy cells, in regions away from the cell periphery, occurrences of weak ergodicity breaking are observed, similar to the recent observations inside living fission yeast cells [1].}, language = {en} } @article{MagdziarzMetzlerSzczotkaetal.2012, author = {Magdziarz, Marcin and Metzler, Ralf and Szczotka, Wladyslaw and Zebrowski, Piotr}, title = {Correlated continuous-time random walks-scaling limits and Langevin picture}, series = {Journal of statistical mechanics: theory and experiment}, journal = {Journal of statistical mechanics: theory and experiment}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {1742-5468}, doi = {10.1088/1742-5468/2012/04/P04010}, pages = {18}, year = {2012}, abstract = {In this paper we analyze correlated continuous-time random walks introduced recently by Tejedor and Metzler (2010 J. Phys. A: Math. Theor. 43 082002). We obtain the Langevin equations associated with this process and the corresponding scaling limits of their solutions. We prove that the limit processes are self-similar and display anomalous dynamics. Moreover, we extend the model to include external forces. Our results are confirmed by Monte Carlo simulations.}, language = {en} } @article{SanderHamannTodt2012, author = {Sander, A. and Hamann, Wolf-Rainer and Todt, Helge Tobias}, title = {The Galactic WC stars Stellar parameters from spectral analyses indicate a new evolutionary sequence}, series = {Astronomy and astrophysics : an international weekly journal}, volume = {540}, journal = {Astronomy and astrophysics : an international weekly journal}, publisher = {EDP Sciences}, address = {Les Ulis}, issn = {0004-6361}, doi = {10.1051/0004-6361/201117830}, pages = {79}, year = {2012}, abstract = {Context. The life cycles of massive stars from the main sequence to their explosion as supernovae or gamma ray bursts are not yet fully clear, and the empirical results from spectral analyses are partly in conflict with current evolutionary models. The spectral analysis of Wolf-Rayet stars requires the detailed modeling of expanding stellar atmospheres in non-LTE. The Galactic WN stars have been comprehensively analyzed with such models of the latest stage of sophistication, while a similarly comprehensive study of the Galactic WC sample remains undone. Aims. We aim to establish the stellar parameters and mass-loss rates of the Galactic WC stars. These data provide the empirical basis of studies of (i) the role of WC stars in the evolution of massive stars, (ii) the wind-driving mechanisms, and (iii) the feedback of WC stars as input to models of the chemical and dynamical evolution of galaxies. Methods. We analyze the nearly complete sample of un-obscured Galactic WC stars, using optical spectra as well as ultraviolet spectra when available. The observations are fitted with theoretical spectra, using the Potsdam Wolf-Rayet (PoWR) model atmosphere code. A large grid of line-blanked models has been established for the range of WC subtypes WC4 - WC8, and smaller grids for the WC9 parameter domain. Both WO stars and WN/WC transit types are also analyzed using special models. Results. Stellar and atmospheric parameters are derived for more than 50 Galactic WC and two WO stars, covering almost the whole Galactic WC population as far as the stars are single, and un-obscured in the visual. In the Hertzsprung-Russell diagram, the WC stars reside between the hydrogen and the helium zero-age main sequences, having luminosities L from 10(4.9) to 10(5.6) L-circle dot. The mass-loss rates scale very tightly with L-0.8. The two WO stars in our sample turn out to be outstandingly hot (approximate to 200 kK) and do not fit into the WC scheme. Conclusions. By comparing the empirical WC positions in the Hertzsprung-Russell diagram with evolutionary models, and from recent supernova statistics, we conclude that WC stars have evolved from initial masses between 20 solar masses and 45 M-circle dot. In contrast to previous assumptions, it seems that WC stars in general do not descend from the most massive stars. Only the WO stars might stem from progenitors that have been initially more massive than 45 M-circle dot.}, language = {en} } @article{LiermannHamannOskinova2012, author = {Liermann, A. and Hamann, Wolf-Rainer and Oskinova, Lida}, title = {The Quintuplet cluster III. Hertzsprung-Russell diagram and cluster age}, series = {Astronomy and astrophysics : an international weekly journal}, volume = {540}, journal = {Astronomy and astrophysics : an international weekly journal}, publisher = {EDP Sciences}, address = {Les Ulis}, issn = {0004-6361}, doi = {10.1051/0004-6361/201117534}, pages = {9}, year = {2012}, abstract = {The Quintuplet, one of three massive stellar clusters in the Galactic center (GC), is located about 30 pc in projection from Sagittarius A*. We aim at the construction of the Hertzsprung-Russell diagram (HRD) of the cluster to study its evolution and to constrain its star-formation history. For this purpose we use the most complete spectral catalog of the Quintuplet stars. Based on the K-band spectra we determine stellar temperatures and luminosities for all stars in the catalog under the assumption of a uniform reddening towards the cluster. We find two groups in the resulting HRD: early-type OB stars and late-type KM stars, well separated from each other. By comparison with Geneva stellar evolution models we derive initial masses exceeding 8 M-circle dot for the OB stars. In the HRD these stars are located along an isochrone corresponding to an age of about 4 Myr. This confirms previous considerations, where a similar age estimate was based on the presence of evolved Wolf-Rayet stars in the cluster. We derive number ratios for the various spectral subtype groups (e.g. N-WR/N-O, N-WC/N-WN) and compare them with predictions of population synthesis models. We find that an instantaneous burst of star formation at about 3.3 to 3.6 Myr ago is the most likely scenario to form the Quintuplet cluster. Furthermore, we apply a mass-luminosity relation to construct the initial mass function (IMF) of the cluster. We find indications for a slightly top-heavy IMF. The late-type stars in the LHO catalog are red giant branch (RGB) stars or red supergiants (RSGs) according to their spectral signatures. Under the assumption that they are located at about the distance of the Galactic center we can derive their luminosities. The comparison with stellar evolution models reveals that the initial masses of these stars are lower than 15 M-circle dot implying that they needed about 15 Myr (RSG) or even more than 30 Myr (RGB) to evolve into their present stage. It might be suspected that these late-type stars do not physically belong to the Quintuplet cluster. Indeed, most of them disqualify as cluster members because their radial velocities differ too much from the cluster average. Nevertheless, five of the brightest RGB/RSG stars from the LHO catalog share the mean radial velocity of the Quintuplet, and thus remain highly suspect for being gravitationally bound members. If so, this would challenge the cluster formation and evolution scenario.}, language = {en} } @article{BaibolatovSpahn2012, author = {Baibolatov, Yernur and Spahn, Frank}, title = {The role of adhesion for ensembles of mesoscopic particles}, series = {Granular matter}, volume = {14}, journal = {Granular matter}, number = {2}, publisher = {Springer}, address = {New York}, issn = {1434-5021}, doi = {10.1007/s10035-012-0325-4}, pages = {197 -- 202}, year = {2012}, abstract = {We present a toy-model for an ensemble of adhering mesoscopic constituents in order to estimate the effect of the granular temperature on the sizes of embedded aggregates. The major goal is to illustrate the relation between the mean aggregate size and the granular temperature in dense planetary rings. For sake of simplicity we describe the collective behavior of the ensemble by means of equilibrium statistical mechanics, motivated by the stationary temperature established by the balance between a Kepler-shear driven viscous heating and inelastic cooling in these cosmic granular disks. The ensemble consists of N' equal constituents which can form cluster(s) or move like a gas-or both phases may coexist-depending on the (granular) temperature of the system. We assume the binding energy levels of a cluster E-c = -N-c gamma a to be determined by a certain contact number N-c, given by the configuration of N constituents of the aggregate (energy per contact: -gamma a). By applying canonical and grand-canonical ensembles, we show that the granular temperature T of a gas of constituents (their mean kinetic energy) controls the size distribution of the aggregates. They are the smaller the higher the granular temperature T is. A mere gas of single constituents is sustained for T >> gamma a. In the case of large clusters (low temperatures T << gamma a) the size distribution becomes a Poissonian.}, language = {en} } @article{PingelSchwarzlNeher2012, author = {Pingel, P. and Schwarzl, R. and Neher, Dieter}, title = {Effect of molecular p-doping on hole density and mobility in poly(3-hexylthiophene)}, series = {Applied physics letters}, volume = {100}, journal = {Applied physics letters}, number = {14}, publisher = {American Institute of Physics}, address = {Melville}, issn = {0003-6951}, doi = {10.1063/1.3701729}, pages = {3}, year = {2012}, abstract = {Employing impedance spectroscopy, we have studied the hole density, conductivity, and mobility of poly(3-hexylthiophene), P3HT, doped with the strong molecular acceptor tetrafluorotetracyanoquinodimethane, F(4)TCNQ. We find that the hole density increases linearly with the F(4)TCNQ concentration. Furthermore, the hole mobility is decreased upon doping at low-to-medium doping level, which is rationalized by an analytic model of carrier mobility in doped organic semiconductors [V. I. Arkhipov, E. V. Emelianova, P. Heremans, and H. Bassler, Phys. Rev. B 72, 235202 (2005)]. We infer that the presence of ionized F(4)TCNQ molecules in the P3HT layer increases energetic disorder, which diminishes the carrier mobility.}, language = {en} } @article{TomovskiSandevMetzleretal.2012, author = {Tomovski, Zivorad and Sandev, Trifce and Metzler, Ralf and Dubbeldam, Johan}, title = {Generalized space-time fractional diffusion equation with composite fractional time derivative}, series = {Physica : europhysics journal ; A, Statistical mechanics and its applications}, volume = {391}, journal = {Physica : europhysics journal ; A, Statistical mechanics and its applications}, number = {8}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0378-4371}, doi = {10.1016/j.physa.2011.12.035}, pages = {2527 -- 2542}, year = {2012}, abstract = {We investigate the solution of space-time fractional diffusion equations with a generalized Riemann-Liouville time fractional derivative and Riesz-Feller space fractional derivative. The Laplace and Fourier transform methods are applied to solve the proposed fractional diffusion equation. The results are represented by using the Mittag-Leffler functions and the Fox H-function. Special cases of the initial and boundary conditions are considered. Numerical scheme and Grunwald-Letnikov approximation are also used to solve the space-time fractional diffusion equation. The fractional moments of the fundamental solution of the considered space-time fractional diffusion equation are obtained. Many known results are special cases of those obtained in this paper. We investigate also the solution of a space-time fractional diffusion equations with a singular term of the form delta(x). t-beta/Gamma(1-beta) (beta > 0).}, language = {en} } @article{KoenigSanter2012, author = {K{\"o}nig, Tobias and Santer, Svetlana}, title = {Stretching and distortion of a photosensitive polymer film by surface plasmon generated near fields in the vicinity of a nanometer sized metal pin hole}, series = {Nanotechnology}, volume = {23}, journal = {Nanotechnology}, number = {15}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {0957-4484}, doi = {10.1088/0957-4484/23/15/155301}, pages = {8}, year = {2012}, abstract = {Here we demonstrate how a surface plasmon (SP) generated near field pattern in the vicinity of a nano-scale pin hole can be used to generate reversible topography changes in a photosensitive polymer film above the opening. This can be achieved by simply changing the polarization state of the plasmon generating incoming light. In the case of linear polarization, the near field intensity pattern causes the film to laterally expand/contract according to the direction of the polarization. For circular polarization, two pronounced rims corresponding to maxima in the topography are observed. In all cases, the topographical variation is in close agreement with the SP intensity distribution computed from finite difference time domain simulation. Our results demonstrate the versatility of using SP near fields to imprint a variety of structures into photosensitive polymer films using only a single metallic mask.}, language = {en} } @article{Cherstvy2012, author = {Cherstvy, Andrey G.}, title = {Critical polyelectrolyte adsorption under confinement Planar slit, cylindrical pore, and spherical cavity}, series = {Biopolymers}, volume = {97}, journal = {Biopolymers}, number = {5}, publisher = {Wiley-Blackwell}, address = {Hoboken}, issn = {0006-3525}, doi = {10.1002/bip.22023}, pages = {311 -- 317}, year = {2012}, abstract = {We explore the properties of adsorption of flexible polyelectrolyte chains in confined spaces between the oppositely charged surfaces in three basic geometries. A method of approximate uniformly valid solutions for the Green function equation for the eigenfunctions of polymer density distributions is developed to rationalize the critical adsorption conditions. The same approach was implemented in our recent study for the inverse problem of polyelectrolyte adsorption onto a planar surface, and on the outer surface of rod-like and spherical obstacles. For the three adsorption geometries investigated, the theory yields simple scaling relations for the minimal surface charge density that triggers the chain adsorption, as a function of the Debye screening length and surface curvature. The encapsulation of polyelectrolytes is governed by interplay of the electrostatic attraction energy toward the adsorbing surface and entropic repulsion of the chain squeezed into a thin slit or small cavities. Under the conditions of surface-mediated confinement, substantially larger polymer linear charge densities are required to adsorb a polyelectrolyte inside a charged spherical cavity, relative to a cylindrical pore and to a planar slit (at the same interfacial surface charge density). Possible biological implications are discussed briefly in the end.}, language = {en} } @article{KalbitzGerhardTaylor2012, author = {Kalbitz, Rene and Gerhard, Reimund and Taylor, D. M.}, title = {Fixed negative interface charges compromise organic ferroelectric field-effect transistors}, series = {Organic electronics : physics, materials and applications}, volume = {13}, journal = {Organic electronics : physics, materials and applications}, number = {5}, publisher = {Elsevier}, address = {Amsterdam}, issn = {1566-1199}, doi = {10.1016/j.orgel.2012.01.034}, pages = {875 -- 884}, year = {2012}, abstract = {Capacitance-voltage (C-V) and current-voltage measurements have been undertaken on metal-ferroelectric-semiconductor capacitors and ferroelectric field-effect transistors (FeFETs) using the ferroelectric polymer poly(vinylidenefluoride-trifluoroethylene) as the gate insulator and poly(3-hexylthiophene) as the active semiconductor. C-V measurements, voltage-dependence of gate currents and FeFET transfer characteristics all confirm that ferroelectric polarization is stable and only reverses when positive/negative coercive fields are exceeded for the first time. The apparent instability observed following the application of depletion voltages arises from the development of a negative interfacial charge which more than compensates the ferroelectric-induced shift, resulting in a permanent shift in threshold voltage to positive values. Application of successive bipolar voltage sweeps to a diode-connected FeFET show that significant remanent polarization is only induced in an unpoled device when the coercive field is exceeded during the first application of accumulation voltages. This initial polarization and its growth during subsequent bipolar voltage sweeps is accompanied by the accumulation of the fixed interfacial negative charges which cause the positive turn on voltages seen in C-V and transfer characteristics. The origin of the negative charge is ascribed either to layers of irreversible ferroelectric domains at the insulator surface or to the drift to the insulator-semiconductor interface of F-ions produced electrolytically during the application of accumulation voltages.}, language = {en} } @article{KempfSramaGruenetal.2012, author = {Kempf, Sascha and Srama, Ralf and Gr{\"u}n, Eberhard and Mocker, Anna and Postberg, Frank and Hillier, Jon K. and Horanyi, Mihaly and Sternovsky, Zoltan and Abel, Bernd and Beinsen, Alexander and Thissen, Roland and Schmidt, J{\"u}rgen and Spahn, Frank and Altobelli, Nicolas}, title = {Linear high resolution dust mass spectrometer for a mission to the Galilean satellites}, series = {Planetary and space science}, volume = {65}, journal = {Planetary and space science}, number = {1}, publisher = {Elsevier}, address = {Oxford}, issn = {0032-0633}, doi = {10.1016/j.pss.2011.12.019}, pages = {10 -- 20}, year = {2012}, abstract = {The discovery of volcanic activity on Enceladus stands out amongst the long list of findings by the Cassini mission to Saturn. In particular the compositional analysis of Enceladus ice particles by Cassini's Cosmic Dust Analyser (CDA) (Srama et al., 2004) has proven to be a powerful technique for obtaining information about processes below the moon's ice crust. Small amounts of sodium salts embedded in the particles' ice matrices provide direct evidence for a subsurface liquid water reservoir, which is, or has been, in contact with the moon's rocky core (Postberg et al., 2009, 2011b). Jupiter's Galilean satellites Ganymede, Europa, and Callisto are also believed to have subsurface oceans and are therefore prime targets for future NASA and ESA outer Solar System missions. The Galilean moons are engulfed in tenuous dust clouds consisting of tiny pieces of the moons' surfaces (Kruger et al., 1999), released by hypervelocity impacts of micrometeoroids, which steadily bombard the surfaces of the moons. In situ chemical analysis of these grains by a high resolution dust spectrometer will provide spatially resolved mapping of the surface composition of Europa. Ganymede, and Callisto, meeting key scientific objectives of the planned missions. However, novel high-resolution reflectron-type dust mass spectrometers (Sternovsky et al., 2007; Srama et al., 2007) developed for dust astronomy missions (Gran et al., 2009) are probably not robust enough to be operated in the energetic radiation environment of the inner Jovian system. In contrast, CDA's linear spectrometer is much less affected by harsh radiation conditions because its ion detector is not directly facing out into space. The instrument has been continuously operated on Cassini for 11 years. In this paper we investigate the possibility of operating a CDA-like instrument as a high resolution impact mass spectrometer. We show that such an instrument is capable of reliably identifying traces of organic and inorganic materials in the ice matrix of ejecta expected to be generated from the surfaces of the Galilean moons. These measurements are complementary, and in some cases superior, compared to other traditional techniques such as infrared remote sensing or in situ ion or neutral mass spectrometers.}, language = {en} } @article{ValoriGreenDemoulinetal.2012, author = {Valori, Gherardo and Green, Lucie M. and Demoulin, Pascal and Vargas Dominguez, S. and van Driel-Gesztelyi, L. and Wallace, A. and Baker, Daniel N. and Fuhrmann, Marcel}, title = {Nonlinear force-free extrapolation of emerging flux with a global twist and serpentine fine structures}, series = {Solar physics : a journal for solar and solar-stellar research and the study of solar terrestrial physics}, volume = {278}, journal = {Solar physics : a journal for solar and solar-stellar research and the study of solar terrestrial physics}, number = {1}, publisher = {Springer}, address = {Dordrecht}, issn = {0038-0938}, doi = {10.1007/s11207-011-9865-8}, pages = {73 -- 97}, year = {2012}, abstract = {We study the flux emergence process in NOAA active region 11024, between 29 June and 7 July 2009, by means of multi-wavelength observations and nonlinear force-free extrapolation. The main aim is to extend previous investigations by combining, as much as possible, high spatial resolution observations to test our present understanding of small-scale (undulatory) flux emergence, whilst putting these small-scale events in the context of the global evolution of the active region. The combination of these techniques allows us to follow the whole process, from the first appearance of the bipolar axial field on the east limb, until the buoyancy instability could set in and raise the main body of the twisted flux tube through the photosphere, forming magnetic tongues and signatures of serpentine field, until the simplification of the magnetic structure into a main bipole by the time the active region reaches the west limb. At the crucial time of the main emergence phase high spatial resolution spectropolarimetric measurements of the photospheric field are employed to reconstruct the three-dimensional structure of the nonlinear force-free coronal field, which is then used to test the current understanding of flux emergence processes. In particular, knowledge of the coronal connectivity confirms the identity of the magnetic tongues as seen in their photospheric signatures, and it exemplifies how the twisted flux, which is emerging on small scales in the form of a sea-serpent, is subsequently rearranged by reconnection into the large-scale field of the active region. In this way, the multi-wavelength observations combined with a nonlinear force-free extrapolation provide a coherent picture of the emergence process of small-scale magnetic bipoles, which subsequently reconnect to form a large-scale structure in the corona.}, language = {en} } @article{AbouzarPoghossianCherstvyetal.2012, author = {Abouzar, Maryam H. and Poghossian, Arshak and Cherstvy, Andrey G. and Pedraza, Angela M. and Ingebrandt, Sven and Sch{\"o}ning, Michael J.}, title = {Label-free electrical detection of DNA by means of field-effect nanoplate capacitors experiments and modeling}, series = {Physica status solidi : A, Applications and materials science}, volume = {209}, journal = {Physica status solidi : A, Applications and materials science}, number = {5}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1862-6300}, doi = {10.1002/pssa.201100710}, pages = {925 -- 934}, year = {2012}, abstract = {Label-free electrical detection of consecutive deoxyribonucleic acid (DNA) hybridization/denaturation by means of an array of individually addressable field-effect-based nanoplate silicon-on-insulator (SOI) capacitors modified with gold nanoparticles (Au-NP) is investigated. The proposed device detects charge changes on Au-NP/DNA hybrids induced by the hybridization or denaturation event. DNA hybridization was performed in a high ionic-strength solution to provide a high hybridization efficiency. On the other hand, to reduce the screening of the DNA charge by counter ions and to achieve a high sensitivity, the sensor signal induced by the hybridization and denaturation events was measured in a low ionic-strength solution. High sensor signals of about 120, 90, and 80 mV were registered after the DNA hybridization, denaturation, and re-hybridization events, respectively. Fluorescence microscopy has been applied as reference method to verify the DNA immobilization, hybridization, and denaturation processes. An electrostatic charge-plane model for potential changes at the gate surface of a nanoplate field-effect sensor induced by the DNA hybridization has been developed taking into account both the Debye length and the distance of the DNA charge from the gate surface.}, language = {en} } @article{WendtMolaro2012, author = {Wendt, Martin and Molaro, P.}, title = {QSO 0347-383 and the invariance of m(p)/m(e) in the course of cosmic time}, series = {Astronomy and astrophysics : an international weekly journal}, volume = {541}, journal = {Astronomy and astrophysics : an international weekly journal}, number = {3}, publisher = {EDP Sciences}, address = {Les Ulis}, issn = {0004-6361}, doi = {10.1051/0004-6361/201218862}, pages = {8}, year = {2012}, abstract = {Context. The variation of the dimensionless fundamental physical constant mu = m(p)/m(e) - the proton to electron mass ratio - can be constrained via observation of Lyman and Werner lines of molecular hydrogen in the spectra of damped Lyman alpha systems (DLAs) in the line of sight to distant QSOs. Aims. Our intention is to maximize the possible precision of quasar absorption spectroscopy with regard to the investigation of the variation of the proton-to-electron mass-ratio mu. The demand for precision requires an understanding of the errors involved and effective techniques to handle present systematic errors. Methods. An analysis based on UVES high resolution data sets of QSO 0347-383 and its DLA is put forward and new approaches to some of the steps involved in the data analysis are introduced. We apply corrections for the observed offsets between discrete spectra and for the first time we find indications for inter-order distortions. Results. Drawing on VLT-UVES observations of QSO 0347-383 in 2009 our analysis yields Delta mu/mu = (4.3 +/- 7.2) x 10(-6) at z(abs) = 3.025. Conclusions. Current analyzes tend to underestimate the impact of systematic errors. Based on the scatter of the measured redshifts and the corresponding low significance of the redshift-sensitivity correlation we estimate the limit of accuracy of line position measurements to similar to 220 m s (1), consisting of roughly 150 m s (1) due to the uncertainty of the absorption line fit and about 150 m s (1) allocated to systematics related to instrumentation and calibration.}, language = {en} } @article{TelezhinskyDwarkadasPohl2012, author = {Telezhinsky, Igor O. and Dwarkadas, Vikram V. and Pohl, Martin}, title = {Time-dependent escape of cosmic rays from supernova remnants, and their interaction with dense media}, series = {Astronomy and astrophysics : an international weekly journal}, volume = {541}, journal = {Astronomy and astrophysics : an international weekly journal}, publisher = {EDP Sciences}, address = {Les Ulis}, issn = {0004-6361}, doi = {10.1051/0004-6361/201118639}, pages = {11}, year = {2012}, abstract = {Context. Supernova remnants (SNRs) are thought to be the main source of Galactic cosmic rays (CRs) up to the "knee" in CR spectrum. During the evolution of a SNR, the bulk of the CRs are confined inside the SNR shell. The highest-energy particles leave the system continuously, while the remaining adiabatically cooled particles are released when the SNR has expanded sufficiently and decelerated so that the magnetic field at the shock is no longer able to confine them. Particles escaping from the parent system may interact with nearby molecular clouds, producing.-rays in the process via pion decay. The soft gamma-ray spectra observed for a number of SNRs interacting with molecular clouds, however, challenge current theories of non-linear particle acceleration that predict harder spectra. Aims. We study how the spectrum of escaped particles depends on the time-dependent acceleration history in both Type Ia and core-collapse SNRs, as well as on different assumptions about the diffusion coefficient in the vicinity of the SNR. Methods. We solve the CR transport equation in a test-particle approach combined with numerical simulations of SNR evolution. Results. We extend our method for calculating the CR acceleration in SNRs to trace the escaped particles in a large volume around SNRs. We calculate the evolution of the spectra of CRs that have escaped from a SNR into a molecular cloud or dense shell for two diffusion models. We find a strong confinement of CRs in a close region around the SNR, and a strong dilution effect for CRs that were able to propagate out as far as a few SNR radii.}, language = {en} } @article{SurlanHamannKubatetal.2012, author = {Surlan, B. and Hamann, Wolf-Rainer and Kubat, Jirij and Oskinova, Lida and Feldmeier, Achim}, title = {Three-dimensional radiative transfer in clumped hot star winds I influence of clumping on the resonance line formation}, series = {Astronomy and astrophysics : an international weekly journal}, volume = {541}, journal = {Astronomy and astrophysics : an international weekly journal}, publisher = {EDP Sciences}, address = {Les Ulis}, issn = {0004-6361}, doi = {10.1051/0004-6361/201118590}, pages = {11}, year = {2012}, abstract = {Context. The true mass-loss rates from massive stars are important for many branches of astrophysics. For the correct modeling of the resonance lines, which are among the key diagnostics of stellar mass-loss, the stellar wind clumping has been found to be very important. To incorporate clumping into a radiative transfer calculation, three-dimensional (3D) models are required. Various properties of the clumps may have a strong impact on the resonance line formation and, therefore, on the determination of empirical mass-loss rates. Aims. We incorporate the 3D nature of the stellar wind clumping into radiative transfer calculations and investigate how different model parameters influence the resonance line formation. Methods. We develop a full 3D Monte Carlo radiative transfer code for inhomogeneous expanding stellar winds. The number density of clumps follows the mass conservation. For the first time, we use realistic 3D models that describe the dense as well as the tenuous wind components to model the formation of resonance lines in a clumped stellar wind. At the same time, we account for non-monotonic velocity fields. Results. The 3D density and velocity wind inhomogeneities show that there is a very strong impact on the resonance line formation. The different parameters describing the clumping and the velocity field results in different line strengths and profiles. We present a set of representative models for various sets of model parameters and investigate how the resonance lines are affected. Our 3D models show that the line opacity is lower for a larger clump separation and shallower velocity gradients within the clumps. Conclusions. Our model demonstrates that to obtain empirically correct mass-loss rates from the UV resonance lines, the wind clumping and its 3D nature must be taken into account.}, language = {en} } @article{MagdziarzMetzlerSzczotkaetal.2012, author = {Magdziarz, Marcin and Metzler, Ralf and Szczotka, Wladyslaw and Zebrowski, Piotr}, title = {Correlated continuous-time random walks in external force fields}, series = {Physical review : E, Statistical, nonlinear and soft matter physics}, volume = {85}, journal = {Physical review : E, Statistical, nonlinear and soft matter physics}, number = {5}, publisher = {American Physical Society}, address = {College Park}, issn = {1539-3755}, doi = {10.1103/PhysRevE.85.051103}, pages = {5}, year = {2012}, abstract = {We study the anomalous diffusion of a particle in an external force field whose motion is governed by nonrenewal continuous time random walks with correlated waiting times. In this model the current waiting time T-i is equal to the previous waiting time Ti-1 plus a small increment. Based on the associated coupled Langevin equations the force field is systematically introduced. We show that in a confining potential the relaxation dynamics follows power-law or stretched exponential pattern, depending on the model parameters. The process obeys a generalized Einstein-Stokes-Smoluchowski relation and observes the second Einstein relation. The stationary solution is of Boltzmann-Gibbs form. The case of an harmonic potential is discussed in some detail. We also show that the process exhibits aging and ergodicity breaking.}, language = {en} } @article{KuptsovKuznetsovPikovskij2012, author = {Kuptsov, Pavel V. and Kuznetsov, Sergey P. and Pikovskij, Arkadij}, title = {Hyperbolic chaos of turing patterns}, series = {Physical review letters}, volume = {108}, journal = {Physical review letters}, number = {19}, publisher = {American Physical Society}, address = {College Park}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.108.194101}, pages = {4}, year = {2012}, abstract = {We consider time evolution of Turing patterns in an extended system governed by an equation of the Swift-Hohenberg type, where due to an external periodic parameter modulation longwave and shortwave patterns with length scales related as 1:3 emerge in succession. We show theoretically and demonstrate numerically that the spatial phases of the patterns, being observed stroboscopically, are governed by an expanding circle map, so that the corresponding chaos of Turing patterns is hyperbolic, associated with a strange attractor of the Smale-Williams solenoid type. This chaos is shown to be robust with respect to variations of parameters and boundary conditions.}, language = {en} } @article{KolloscheZhuSuoetal.2012, author = {Kollosche, Matthias and Zhu, Jian and Suo, Zhigang and Kofod, Guggi}, title = {Complex interplay of nonlinear processes in dielectric elastomers}, series = {Physical review : E, Statistical, nonlinear and soft matter physics}, volume = {85}, journal = {Physical review : E, Statistical, nonlinear and soft matter physics}, number = {5}, publisher = {American Physical Society}, address = {College Park}, issn = {1539-3755}, doi = {10.1103/PhysRevE.85.051801}, pages = {4}, year = {2012}, abstract = {A combination of experiment and theory shows that dielectric elastomers exhibit complex interplay of nonlinear processes. Membranes of a dielectric elastomer are prepared in various states of prestretches by using rigid clamps and mechanical forces. Upon actuation by voltage, some membranes form wrinkles followed by snap-through instability, others form wrinkles without the snap-through instability, and still others fail by local instability without forming wrinkles. Membranes surviving these nonlinear processes are found to attain a constant dielectric strength, independent of the state of prestretches. Giant voltage-induced stretch of 3.6 is attained.}, language = {en} } @article{Richter2012, author = {Richter, Philipp}, title = {Cold gas accretion by high-velocity clouds and their connection to QSO Absorption-line systems}, series = {The astrophysical journal : an international review of spectroscopy and astronomical physics}, volume = {750}, journal = {The astrophysical journal : an international review of spectroscopy and astronomical physics}, number = {2}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {0004-637X}, doi = {10.1088/0004-637X/750/2/165}, pages = {11}, year = {2012}, abstract = {We combine H I 21 cm observations of the Milky Way, M31, and the local galaxy population with QSO absorption-line measurements to geometrically model the three-dimensional distribution of infalling neutral-gas clouds ("high-velocity clouds" (HVCs)) in the extended halos of low-redshift galaxies. We demonstrate that the observed distribution of HVCs around the Milky Way and M31 can be modeled by a radial exponential decline of the mean H I volume-filling factor in their halos. Our model suggests a characteristic radial extent of HVCs of R-halo similar to 50 kpc, a total H I mass in HVCs of similar to 10(8) M-circle dot, and a neutral-gas accretion rate of similar to 0.7 M-circle dot yr(-1) for M31/Milky-Way-type galaxies. Using a Holmberg-like luminosity scaling of the halo size of galaxies we estimate R-halo similar to 110 kpc for the most massive galaxies. The total absorption cross-section of HVCs at z approximate to 0 most likely is dominated by galaxies with total H I masses between 10(8.5) and 10(10) M-circle dot. Our model indicates that the H I disks of galaxies and their surrounding HVC population can account for 30\%-100\% of intervening QSO absorption-line systems with log N(H I) >= 17.5 at z approximate to 0. We estimate that the neutral-gas accretion rate density of galaxies at low redshift from infalling HVCs is dM(H) (I)/dt/dV approximate to 0.022 M-circle dot yr(-1) Mpc(-3), which is close to the measured star formation rate density in the local universe. HVCs thus may play an important role in the ongoing formation and evolution of galaxies.}, language = {en} } @article{AliuArchambaultArlenetal.2012, author = {Aliu, E. and Archambault, S. and Arlen, T. and Aune, T. and Beilicke, M. and Benbow, W. and Boettcher, Markus and Bouvier, A. and Bradbury, S. M. and Buckley, J. H. and Bugaev, V. and Byrum, K. and Cannon, A. and Cesarini, A. and Ciupik, L. and Collins-Hughes, E. and Connolly, M. P. and Coppi, P. and Cui, W. and Decerprit, G. and Dickherber, R. and Dumm, J. and Errando, Manel and Falcone, A. and Feng, Q. and Finley, J. P. and Finnegan, G. and Fortson, L. and Furniss, A. and Galante, N. and Gall, D. and Godambe, S. and Griffin, S. and Grube, J. and Gyuk, G. and Hanna, D. and Hawkins, K. and Holder, J. and Huan, H. and Hughes, G. and Humensky, T. B. and Kaaret, P. and Karlsson, N. and Kertzman, M. and Khassen, Y. and Kieda, D. and Krawczynski, H. and Krennrich, F. and Lang, M. J. and Lee, K. and Madhavan, A. S. and Maier, G. and Majumdar, P. and McArthur, S. and McCann, A. and Moriarty, P. and Mukherjee, Reshmi and Ong, R. A. and Orr, M. and Otte, A. N. and Palma, N. and Park, N. and Perkins, J. S. and Pichel, A. and Pohl, Martin and Prokoph, H. and Quinn, J. and Ragan, K. and Reyes, L. C. and Reynolds, P. T. and Roache, E. and Rose, H. J. and Ruppel, J. and Saxon, D. B. and Schroedter, M. and Sembroski, G. H. and Sentuerk, G. D. and Smith, A. W. and Staszak, D. and Telezhinsky, Igor O. and Tesic, G. and Theiling, M. and Thibadeau, S. and Tsurusaki, K. and Varlotta, A. and Vivier, M. and Wakely, S. P. and Ward, J. E. and Weekes, T. C. and Weinstein, A. and Weisgarber, T. and Williams, D. A. and Zitzer, B. and Fortin, P. and Horan, D.}, title = {Disovery of high-energy and very high energy gamma-ray emission from the blazar RBS 0413}, series = {The astrophysical journal : an international review of spectroscopy and astronomical physics}, volume = {750}, journal = {The astrophysical journal : an international review of spectroscopy and astronomical physics}, number = {2}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {0004-637X}, doi = {10.1088/0004-637X/750/2/94}, pages = {6}, year = {2012}, abstract = {We report on the discovery of high-energy (HE; E > 0.1 GeV) and very high energy (VHE; E > 100 GeV) gamma-ray emission from the high-frequency-peaked BL Lac object RBS 0413. VERITAS, a ground-based gamma-ray observatory, detected VHE. rays from RBS 0413 with a statistical significance of 5.5 standard deviations (sigma) and a gamma-ray flux of (1.5 +/- 0.6(stat) +/- 0.7(syst)) x 10(-8) photons m(-2) s(-1) (similar to 1\% of the Crab Nebula flux) above 250 GeV. The observed spectrum can be described by a power law with a photon index of 3.18 +/- 0.68(stat) +/- 0.30(syst). Contemporaneous observations with the Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope detected HE gamma rays from RBS 0413 with a (stat)istical significance of more than 9 sigma, a power-law photon index of 1.57 +/- 0.12(stat-0.12sys')(+0.11) and a gamma-ray flux between 300 MeV and 300 GeV of (1.64 +/- 0.43(stat-0.22sys)(+ 0.31)) x 10(-5) photons m(-2) s(-1). We present the results from Fermi-LAT and VERITAS, including a spectral energy distribution modeling of the gamma-ray, quasi-simultaneous X-ray (Swift-XRT), ultraviolet (Swift-UVOT), and R-band optical (MDM) data. We find that, if conditions close to equipartition are required, both the combined synchrotron self-Compton/external-Compton and the lepto-hadronic models are preferred over a pure synchrotron self-Compton model.}, language = {en} } @article{MelnickGarcinQuinterosetal.2012, author = {Melnick, Daniel and Garcin, Yannick and Quinteros, Javier and Strecker, Manfred and Olago, Daniel and Tiercelin, Jean-Jacques}, title = {Steady rifting in northern Kenya inferred from deformed Holocene lake shorelines of the Suguta and Turkana basins}, series = {Earth \& planetary science letters}, volume = {331}, journal = {Earth \& planetary science letters}, number = {10}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0012-821X}, doi = {10.1016/j.epsl.2012.03.007}, pages = {335 -- 346}, year = {2012}, abstract = {A comparison of deformation rates in active rifts over different temporal scales may help to decipher variations in their structural evolution, controlling mechanisms, and evolution of sedimentary environments through time. Here we use deformed lake shorelines in the Suguta and Turkana basins in northern Kenya as strain markers to estimate deformation rates at the 10(3)-10(4) yr time scale and compare them with rates spanning 10(1)-10(7) yr. Both basins are internally drained today, but until 7 to 5 kyr lake levels were 300 and 100 m higher, respectively, maintained by the elevation of overflow sills connecting them with the Nile drainage. Protracted high lake levels resulted in formation of a maximum highstand shoreline - a distinct geomorphic feature virtually continuous for several tens of kilometers. We surveyed the elevation of this geomorphic marker at 45 sites along >100 km of the rift, and use the overflow sills as vertical datum. Thin-shell elastic and thermomechanical models for this region predict up to similar to 10 m of rapid isostatic rebound associated with lake-level falls lasting until similar to 2 kyr ago. Holocene cumulative throw rates along four rift-normal profiles are 6.8-8.5 mm/yr, or 7.5-9.6 mm/yr if isostatic rebound is considered. Assuming fault dips of 55-65, inferred from seismic reflection profiles, we obtained extension rates of 3.2-6 mm/yr (including uncertainties in field measurements, fault dips, and ages), or 3.5-6.7 mm/yr considering rebound. Our estimates are consistent, within uncertainties, with extension rates of 4-5.1 mm/yr predicted by a modern plate-kinematic model and plate reconstructions since 3.2 Myr. The Holocene strain rate of 10(-15) s(-1) is similar to estimates on the similar to 10(6) yr scale, but over an order of magnitude higher than on the similar to 10(7) yr scale. This is coherent with continuous localization and narrowing of the plate boundary, implying that the lithospheric blocks limiting the Kenya Rift are relatively rigid. Increasing strain rate under steady extension rate suggests that, as the magnitude of extension and crustal thinning increases, the role of regional processes such as weakening by volcanism becomes dominant over far-field plate tectonics controlling the breakup process and the transition from continental rifting to oceanic spreading.}, language = {en} } @article{BauerMetzler2012, author = {Bauer, Maximilian and Metzler, Ralf}, title = {Generalized facilitated diffusion model for DNA-binding proteins with search and recognition states}, series = {Biophysical journal}, volume = {102}, journal = {Biophysical journal}, number = {10}, publisher = {Cell Press}, address = {Cambridge}, issn = {0006-3495}, doi = {10.1016/j.bpj.2012.04.008}, pages = {2321 -- 2330}, year = {2012}, abstract = {Transcription factors (TFs) such as the lac repressor find their target sequence on DNA at remarkably high rates. In the established Berg-von Hippel model for this search process, the TF alternates between three-dimensional diffusion in the bulk solution and one-dimensional sliding along the DNA chain. To overcome the so-called speed-stability paradox, in similar models the TF was considered as being present in two conformations (search state and recognition state) between which it switches stochastically. Combining both the facilitated diffusion model and alternating states, we obtain a generalized model. We explicitly treat bulk excursions for rodlike chains arranged in parallel and consider a simplified model for coiled DNA. Compared to previously considered facilitated diffusion models, corresponding to limiting cases of our generalized model, we surprisingly find a reduced target search rate. Moreover, at optimal conditions there is no longer an equipartition between the time spent by the protein on and off the DNA chain.}, language = {en} } @article{AmselemThevesBaeetal.2012, author = {Amselem, Gabriel and Theves, Matthias and Bae, Albert J. and Bodenschatz, Eberhard and Beta, Carsten}, title = {A stochastic description of dictyostelium chemotaxis}, series = {PLoS one}, volume = {7}, journal = {PLoS one}, number = {5}, publisher = {PLoS}, address = {San Fransisco}, issn = {1932-6203}, doi = {10.1371/journal.pone.0037213}, pages = {11}, year = {2012}, abstract = {Chemotaxis, the directed motion of a cell toward a chemical source, plays a key role in many essential biological processes. Here, we derive a statistical model that quantitatively describes the chemotactic motion of eukaryotic cells in a chemical gradient. Our model is based on observations of the chemotactic motion of the social ameba Dictyostelium discoideum, a model organism for eukaryotic chemotaxis. A large number of cell trajectories in stationary, linear chemoattractant gradients is measured, using microfluidic tools in combination with automated cell tracking. We describe the directional motion as the interplay between deterministic and stochastic contributions based on a Langevin equation. The functional form of this equation is directly extracted from experimental data by angle-resolved conditional averages. It contains quadratic deterministic damping and multiplicative noise. In the presence of an external gradient, the deterministic part shows a clear angular dependence that takes the form of a force pointing in gradient direction. With increasing gradient steepness, this force passes through a maximum that coincides with maxima in both speed and directionality of the cells. The stochastic part, on the other hand, does not depend on the orientation of the directional cue and remains independent of the gradient magnitude. Numerical simulations of our probabilistic model yield quantitative agreement with the experimental distribution functions. Thus our model captures well the dynamics of chemotactic cells and can serve to quantify differences and similarities of different chemotactic eukaryotes. Finally, on the basis of our model, we can characterize the heterogeneity within a population of chemotactic cells.}, language = {en} } @article{WeberFrankBommeletal.2012, author = {Weber, Cornelia and Frank, C. and Bommel, Sebastian and Rukat, Tammo and Leitenberger, Wolfram and Sch{\"a}fer, Peter and Schreiber, Frank and Kowarik, Stefan}, title = {Chain-length dependent growth dynamics of n-alkanes on silica investigated by energy-dispersive x-ray reflectivity in situ and in real-time}, series = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr}, volume = {136}, journal = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr}, number = {20}, publisher = {American Institute of Physics}, address = {Melville}, issn = {0021-9606}, doi = {10.1063/1.4719530}, pages = {7}, year = {2012}, abstract = {We compare the growth dynamics of the three n-alkanes C36H74, C40H82, and C44H90 on SiO2 using real-time and in situ energy-dispersive x-ray reflectivity. All molecules investigated align in an upright-standing orientation on the substrate and exhibit a transition from layer-by-layer growth to island growth after about 4 monolayers under the conditions employed. Simultaneous fits of the reflected intensity at five distinct points in reciprocal space show that films formed by longer n-alkanes roughen faster during growth. This behavior can be explained by a chain-length dependent height of the Ehrlich-Schwoebel barrier. Further x-ray diffraction measurements after growth indicate that films consisting of longer n-alkanes also incorporate more lying-down molecules in the top region. While the results reveal behavior typical for chain-like molecules, the findings can also be useful for the optimization of organic field effect transistors where smooth interlayers of n-alkanes without coexistence of two or more molecular orientations are required.}, language = {en} } @article{BurneckiWylomanskaBeletskiietal.2012, author = {Burnecki, Krzysztof and Wylomanska, Agnieszka and Beletskii, Aleksei and Gonchar, Vsevolod and Chechkin, Aleksei V.}, title = {Recognition of stable distribution with levy index alpha close to 2}, series = {Physical review : E, Statistical, nonlinear and soft matter physics}, volume = {85}, journal = {Physical review : E, Statistical, nonlinear and soft matter physics}, number = {5}, publisher = {American Physical Society}, address = {College Park}, issn = {1539-3755}, doi = {10.1103/PhysRevE.85.056711}, pages = {8}, year = {2012}, abstract = {We address the problem of recognizing alpha-stable Levy distribution with Levy index close to 2 from experimental data. We are interested in the case when the sample size of available data is not large, thus the power law asymptotics of the distribution is not clearly detectable, and the shape of the empirical probability density function is close to a Gaussian. We propose a testing procedure combining a simple visual test based on empirical fourth moment with the Anderson-Darling and Jarque-Bera statistical tests and we check the efficiency of the method on simulated data. Furthermore, we apply our method to the analysis of turbulent plasma density and potential fluctuations measured in the stellarator-type fusion device and demonstrate that the phenomenon of the L-H transition from low confinement, L mode, to a high confinement, H mode, which occurs in this device is accompanied by the transition from Levy to Gaussian fluctuation statistics.}, language = {en} } @article{ValoriDemoulinPariat2012, author = {Valori, Gherardo and Demoulin, Pascal and Pariat, E.}, title = {Comparing values of the relative magnetic helicity in finite volumes}, series = {Solar physics : a journal for solar and solar-stellar research and the study of solar terrestrial physics}, volume = {278}, journal = {Solar physics : a journal for solar and solar-stellar research and the study of solar terrestrial physics}, number = {2}, publisher = {Springer}, address = {Dordrecht}, issn = {0038-0938}, doi = {10.1007/s11207-012-9951-6}, pages = {347 -- 366}, year = {2012}, abstract = {Relative magnetic helicity, as a conserved quantity of ideal magnetohydrodynamics, has been highlighted as an important quantity to study in plasma physics. Due to its nonlocal nature, its estimation is not straightforward in both observational and numerical data. In this study we derive expressions for the practical computation of the gauge-independent relative magnetic helicity in three-dimensional finite domains. The derived expressions are easy to implement and rapid to compute. They are derived in Cartesian coordinates, but can be easily written in other coordinate systems. We apply our method to a numerical model of a force-free equilibrium containing a flux rope, and compare the results with those obtained employing known half-space equations. We find that our method requires a much smaller volume than half-space expressions to derive the full helicity content. We also prove that values of relative magnetic helicity of different magnetic fields can be compared with each other in the same sense as free-energy values can. Therefore, relative magnetic helicity can be meaningfully and directly compared between different datasets, such as those from different active regions, but also within the same dataset at different times. Typical applications of our formulae include the helicity computation in three-dimensional models of the solar atmosphere, e.g., coronal-field reconstructions by force-free extrapolation and discretized magnetic fields of numerical simulations.}, language = {en} } @article{FruebingWangWagener2012, author = {Fr{\"u}bing, Peter and Wang, Feipeng and Wagener, Michael}, title = {Relaxation processes and structural transitions in stretched films of polyvinylidene fluoride and its copolymer with hexafluoropropylene}, series = {Applied physics : A, Materials science \& processing}, volume = {107}, journal = {Applied physics : A, Materials science \& processing}, number = {3}, publisher = {Springer}, address = {New York}, issn = {0947-8396}, doi = {10.1007/s00339-012-6838-1}, pages = {603 -- 611}, year = {2012}, abstract = {Relaxation processes and structural transitions in nonstretched and uniaxially stretched films of poly(vinylidene fluoride-hexafluoropropylene) (P(VDF-HFP)) and its homopolymer polyvinylidene fluoride (PVDF) for comparison were investigated with the aim of understanding the electromechanical properties of this lower-modulus ferroelectric copolymer. The mechanical and the dielectric response at the glass transition ( relaxation) exhibit similar temperature dependence of the relaxation time, whereas mechanical and dielectric processes above the glass transition are not related. They represent a continuous softening process within the amorphous phase and the dielectric relaxation, respectively. The latter is attributed to conformational changes of VDF segments in lamellae of spherulites constituting the nonpolar crystalline phase. Furthermore, there is a contribution from melting of secondary crystallites formed in the amorphous phase during annealing or storage. Mechanically, this transition appears in nonstretched and stretched films as an accelerated decrease of the elastic modulus that terminates the rubber plateau. Dielectrically, this transition becomes visible as a frequency-independent loss peak only in stretched films, because stretching removes the relaxation, which superimposes the transition in nonstretched films. Melting of secondary crystallites is shown to appear in the homopolymer, too, though less pronounced because of more complete primary crystallisation. Stretching increases the modulus above the glass transition only slightly, and it does not significantly influence the softening process. On the other hand, stretching causes a spontaneous polarisation and introduces order within the amorphous phase, rendering it more polar. Melting of secondary crystallites provides an additional contribution to the polarisation. These findings may explain the relatively high electromechanical activity of P(VDF-HFP) but also its relatively low thermal stability. Moreover, they may be important for correct procedure and analysis of temperature-dependent dielectric measurements on partially crystalline polymers, in particular on those with less favourable sterical conditions for primary crystallisation.}, language = {en} } @article{RychkovYablokovRychkov2012, author = {Rychkov, Dmitry and Yablokov, M. and Rychkov, A.}, title = {Chemical and physical surface modification of PTFE films-an approach to produce stable electrets}, series = {Applied physics : A, Materials science \& processing}, volume = {107}, journal = {Applied physics : A, Materials science \& processing}, number = {3}, publisher = {Springer}, address = {New York}, issn = {0947-8396}, doi = {10.1007/s00339-012-6834-5}, pages = {589 -- 596}, year = {2012}, abstract = {The thermal stability of positive charge has been investigated in chemically and physically treated polytetrafluoroethylene (PTFE) films. It has been found that virgin films, oriented by the manufacturer, display an increase in thermal stability of positive charge with an increase of the initial value of surface potential. Such an anomalous behavior is explained by the influence of a negative tribocharge, trapped some small distance below the surface. In PTFE samples treated with orthophosphoric acid and with tetraethoxysilane, a considerable improvement of positive charge stability has been achieved, but no influence of the initial value of surface potential has been observed. However, this influence should be kept in mind when comparing charge stability in virgin and modified samples. In nonoriented PTFE films, no influence of the initial value of surface potential on charge stability has been observed. This could be due to the fact that these films did not possess a noticeable negative tribocharge. After the treatment in glow-discharge defluorination, oxidation and appearance of polar groups have been detected on the surface. These changes in chemical composition of a PTFE surface resulted in a noticeable improvement in thermal stability of positively charged electrets. This improvement is attributed to the formation of deeper traps on the modified surface.}, language = {en} } @article{WirgesRaabeQiu2012, author = {Wirges, Werner and Raabe, Sebastian and Qiu, Xunlin}, title = {Dielectric elastomer and ferroelectret films combined in a single device how do they reinforce each other?}, series = {Applied physics : A, Materials science \& processing}, volume = {107}, journal = {Applied physics : A, Materials science \& processing}, number = {3}, publisher = {Springer}, address = {New York}, issn = {0947-8396}, doi = {10.1007/s00339-012-6833-6}, pages = {583 -- 588}, year = {2012}, abstract = {Dielectric elastomers (DE) are soft polymer materials exhibiting large deformations under electrostatic stress. When a prestretched elastomer is stuck to a flat plastic frame, a complex structure that can be used as an actuator (DEA) is formed due to self-organization and energy minimization. Here, such a DEA was equipped with a ferroelectret film. Ferroelectrets are internally charged polymer foams or void-containing polymer-film systems combining large piezoelectricity with mechanical flexibility and elastic compliance. In their dielectric spectra, ferroelectrets show piezoelectric resonances that can be used to analyze their electromechanical properties. The antiresonance frequencies ( ) of ferroelectret films not only are directly related to their geometric parameters, but also are sensitive to the boundary conditions during measurement. In this paper, a fluoroethylenepropylene (FEP) ferroelectret film with tubular void channels was glued to a plastic frame prior to the formation of self-organized minimum-energy DEA structure. The dielectric resonance spectrum (DRS) of the ferroelectret film was measured in-situ during the actuation of the DEA under applied voltage. It is found that the antiresonance frequency is a monotropic function of the bending angle of the actuator. Therefore, the actuation of DEAs can be used to modulate the of ferroelectrets, while the can also be taken for in-situ diagnosis and for precise control of the actuation of the DEA. Combination of DEAs and ferroelectrets brings a number of possibilities for application.}, language = {en} } @misc{OverholtMelottPohl2012, author = {Overholt, Andrew C. and Melott, Adrian L. and Pohl, Martin}, title = {Testing the link between terrestrial climate change and galactic spiral-arm transit (vol 705, pg L101, 2009)}, series = {The astrophysical journal : an international review of spectroscopy and astronomical physics ; Part 2, Letters}, volume = {751}, journal = {The astrophysical journal : an international review of spectroscopy and astronomical physics ; Part 2, Letters}, number = {2}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {2041-8205}, doi = {10.1088/2041-8205/751/2/L45}, pages = {2}, year = {2012}, language = {en} } @article{SendAbboudLeitenbergeretal.2012, author = {Send, Sebastian and Abboud, Ali and Leitenberger, Wolfram and Weiss, Manfred S. and Hartmann, Robert and Str{\"u}der, Lothar and Pietsch, Ullrich}, title = {Analysis of polycrystallinity in hen egg-white lysozyme using a pnCCD}, series = {Journal of applied crystallography}, volume = {45}, journal = {Journal of applied crystallography}, number = {6}, publisher = {Wiley-Blackwell}, address = {Hoboken}, issn = {0021-8898}, doi = {10.1107/S0021889812015038}, pages = {517 -- 522}, year = {2012}, abstract = {A crystal of hen egg-white lysozyme was analyzed by means of energy-dispersive X-ray Laue diffraction with white synchrotron radiation at 2.7 angstrom resolution using a pnCCD detector. From Laue spots measured in a single exposure of the arbitrarily oriented crystal, the lattice constants of the tetragonal unit cell could be extracted with an accuracy of about 2.5\%. Scanning across the sample surface, Laue images with split reflections were recorded at various positions. The corresponding diffraction patterns were generated by two crystalline domains with a tilt of about 1 degrees relative to each other. The obtained results demonstrate the potential of the pnCCD for fast X-ray screening of crystals of macromolecules or proteins prior to conventional X-ray structure analysis. The described experiment can be automatized to quantitatively characterize imperfect single crystals or polycrystals.}, language = {en} } @article{AltafimAltafimQiuetal.2012, author = {Altafim, Ruy Alberto Pisani and Altafim, Ruy Alberto Pisani and Qiu, Xunlin and Raabe, Sebastian and Wirges, Werner and Basso, Heitor Cury and Gerhard, Reimund}, title = {Fluoropolymer piezoelectrets with tubular channels resonance behavior controlled by channel geometry}, series = {Applied physics : A, Materials science \& processing}, volume = {107}, journal = {Applied physics : A, Materials science \& processing}, number = {4}, publisher = {Springer}, address = {New York}, issn = {0947-8396}, doi = {10.1007/s00339-012-6848-z}, pages = {965 -- 970}, year = {2012}, abstract = {Ferro- or piezoelectrets are dielectric materials with two elastically very different macroscopic phases and electrically charged interfaces between them. One of the newer piezoelectret variants is a system of two fluoroethylenepropylene (FEP) films that are first laminated around a polytetrafluoroethylene (PTFE) template. Then, by removing the PTFE template, a two-layer FEP structure with open tubular channels is obtained. After electrical charging, the channels form easily deformable macroscopic electric dipoles whose changes under mechanical or electrical stress lead to significant direct or inverse piezoelectricity, respectively. Here, different PTFE templates are employed to generate channel geometries that vary in height or width. It is shown that the control of the channel geometry allows a direct adjustment of the resonance frequencies in the tubular-channel piezoelectrets. By combining several different channel widths in a single ferroelectret, it is possible to obtain multiple resonance peaks that may lead to a rather flat frequency-response region of the transducer material. A phenomenological relation between the resonance frequency and the geometrical parameters of a tubular channel is also presented. This relation may help to design piezoelectrets with a specific frequency response.}, language = {en} } @article{KussmaulRisseWegeneretal.2012, author = {Kussmaul, Bj{\"o}rn and Risse, Sebastian and Wegener, Michael and Kofod, Guggi and Kr{\"u}ger, Hartmut}, title = {Matrix stiffness dependent electro-mechanical response of dipole grafted silicones}, series = {Smart materials and structures}, volume = {21}, journal = {Smart materials and structures}, number = {6}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {0964-1726}, doi = {10.1088/0964-1726/21/6/064005}, pages = {6}, year = {2012}, abstract = {The properties of dielectric elastomer actuators can be optimized by modifying the dielectric or mechanical properties of the dielectric elastomer. This paper presents the simultaneous control of both dielectric and mechanical properties, in a silicone elastomer network comprising cross-linker, chains and grafted molecular dipoles. Chains with two different molecular weights were each combined with varying amounts of grafted dipole. Chemical and physical characterization showed that networks with stoichiometric control of cross-linking density and permittivity were obtained, and that longer chain lengths resulted in higher electrical field response due to the reduction in cross-linking density and correspondingly in mechanical stiffness. Both actuation sensitivities were enhanced by 6.3 and 4.6 times for the short and long chain matrix material, respectively.}, language = {en} } @article{RoyPikovskij2012, author = {Roy, S. and Pikovskij, Arkadij}, title = {Spreading of energy in the Ding-Dong model}, series = {Chaos : an interdisciplinary journal of nonlinear science}, volume = {22}, journal = {Chaos : an interdisciplinary journal of nonlinear science}, number = {2}, publisher = {American Institute of Physics}, address = {Melville}, issn = {1054-1500}, doi = {10.1063/1.3695369}, pages = {7}, year = {2012}, abstract = {We study the properties of energy spreading in a lattice of elastically colliding harmonic oscillators (Ding-Dong model). We demonstrate that in the regular lattice the spreading from a localized initial state is mediated by compactons and chaotic breathers. In a disordered lattice, the compactons do not exist, and the spreading eventually stops, resulting in a finite configuration with a few chaotic spots.}, language = {en} }