TY - JOUR A1 - Mengel, Matthias A1 - Levermann, Anders A1 - Schleussner, Carl-Friedrich A1 - Born, Andreas T1 - Enhanced Atlantic subpolar gyre variability through baroclinic threshold in a coarse resolution model JF - Earth system dynamics N2 - 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. Y1 - 2012 U6 - https://doi.org/10.5194/esd-3-189-2012 SN - 2190-4979 SN - 2190-4987 VL - 3 IS - 2 SP - 189 EP - 197 PB - Copernicus CY - Göttingen ER - TY - JOUR A1 - Heuer, Axel A1 - Sagahti, A. A1 - Jechow, Andreas A1 - Skoczowsky, D. A1 - Menzel, Ralf T1 - Multi-wavelength, high spatial brightness operation of a phase-locked stripe-array diode laser JF - Laser physics N2 - 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. Y1 - 2012 U6 - https://doi.org/10.1134/S1054660X12010057 SN - 1054-660X VL - 22 IS - 1 SP - 160 EP - 164 PB - Pleiades Publ. CY - New York ER - TY - JOUR A1 - Fürst, Johannes J. A1 - Levermann, Anders T1 - A minimal model for wind- and mixing-driven overturning threshold behavior for both driving mechanisms JF - Climate dynamics : observational, theoretical and computational research on the climate system N2 - 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. KW - Meridional overturning circulation KW - Northern sinking KW - Critical freshwater threshold KW - Overturning sensitivity KW - Conceptual model KW - Stability KW - Atlantic meridional overturning circulation KW - Pycnocline depth KW - Driving mechanism Y1 - 2012 U6 - https://doi.org/10.1007/s00382-011-1003-7 SN - 0930-7575 VL - 38 IS - 1-2 SP - 239 EP - 260 PB - Springer CY - New York ER - TY - JOUR A1 - Sereshki, L. E. A1 - Lomholt, M. A. A1 - Metzler, Ralf T1 - A solution to the subdiffusion-efficiency paradox inactive states enhance reaction efficiency at subdiffusion conditions in living cells JF - epl : a letters journal exploring the frontiers of physics N2 - 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. Y1 - 2012 U6 - https://doi.org/10.1209/0295-5075/97/20008 SN - 0295-5075 VL - 97 IS - 2 PB - EDP Sciences CY - Mulhouse ER - TY - JOUR A1 - Rusconi, Marco A1 - Valleriani, Angelo A1 - Dunlop, John William Chapman A1 - Kurths, Jürgen A1 - Weinkamer, Richard T1 - Quantitative approach to the stochastics of bone remodeling JF - epl : a letters journal exploring the frontiers of physics N2 - 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. Y1 - 2012 U6 - https://doi.org/10.1209/0295-5075/97/28009 SN - 0295-5075 VL - 97 IS - 2 PB - EDP Sciences CY - Mulhouse ER - TY - JOUR A1 - Albrecht, Torsten A1 - Levermann, Anders T1 - Fracture field for large-scale ice dynamics JF - Journal of glaciology N2 - 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. Y1 - 2012 U6 - https://doi.org/10.3189/2012JoG11J191 SN - 0022-1430 SN - 1727-5652 VL - 58 IS - 207 SP - 165 EP - 176 PB - International Glaciological Society CY - Cambridge ER - TY - JOUR A1 - Seemüller, Anna A1 - Müller, E. M. A1 - Rösler, Frank T1 - EEG-power and -coherence changes in a unimodal and a crossmodal working memory task with visual and kinesthetic stimuli JF - International journal of psychophysiology N2 - 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. KW - Visual representations KW - Kinesthetic representations KW - Synchronization KW - Crossmodal matching KW - Haptics Y1 - 2012 U6 - https://doi.org/10.1016/j.ijpsycho.2011.10.009 SN - 0167-8760 VL - 83 IS - 1 SP - 87 EP - 95 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Schneider von Deimling, Thomas A1 - Meinshausen, Malte A1 - Levermann, Anders A1 - Huber, Veronika A1 - Frieler, Katja A1 - Lawrence, D. M. A1 - Brovkin, Victor T1 - Estimating the near-surface permafrost-carbon feedback on global warming JF - Biogeosciences N2 - 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. Y1 - 2012 U6 - https://doi.org/10.5194/bg-9-649-2012 SN - 1726-4170 SN - 1726-4189 VL - 9 IS - 2 SP - 649 EP - 665 PB - Copernicus CY - Göttingen ER - TY - JOUR A1 - Telezhinsky, Igor O. A1 - Dwarkadas, Vikram V. A1 - Pohl, Martin T1 - Particle spectra from acceleration at forward and reverse shocks of young Type Ia Supernova Remnants JF - Astroparticle physics N2 - 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. KW - Supernova Remnants KW - Cosmic rays KW - Cosmic-ray acceleration KW - Hydrodynamics KW - Forward and reverse shocks Y1 - 2012 U6 - https://doi.org/10.1016/j.astropartphys.2011.10.001 SN - 0927-6505 VL - 35 IS - 6 SP - 300 EP - 311 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - König, Tobias A1 - Sekhar, Y. Nataraja A1 - Santer, Svetlana T1 - Surface plasmon nanolithography impact of dynamically varying near-field boundary conditions at the air-polymer interface JF - Journal of materials chemistry N2 - 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. Y1 - 2012 U6 - https://doi.org/10.1039/c2jm15864g SN - 0959-9428 VL - 22 IS - 13 SP - 5945 EP - 5950 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Haakh, Harald Richard A1 - Henkel, Carsten T1 - Magnetic near fields as a probe of charge transport in spatially dispersive conductors JF - The European physical journal : B, Condensed matter and complex systems N2 - 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. Y1 - 2012 U6 - https://doi.org/10.1140/epjb/e2011-20567-1 SN - 1434-6028 VL - 85 IS - 1 PB - Springer CY - New York ER - TY - JOUR A1 - Frisch, Johannes A1 - Schubert, Marcel A1 - Preis, Eduard A1 - Rabe, Jürgen P. A1 - Neher, Dieter A1 - Scherf, Ullrich A1 - Koch, Norbert T1 - Full electronic structure across a polymer heterojunction solar cell JF - Journal of materials chemistry N2 - 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. Y1 - 2012 U6 - https://doi.org/10.1039/c1jm14968g SN - 0959-9428 VL - 22 IS - 10 SP - 4418 EP - 4424 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Guetschow, Johannes A1 - Nesme, Vincent A1 - Werner, Reinhard F. T1 - Self-similarity of cellular automata on abelian groups JF - Journal of cellular automata N2 - 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. KW - fractal KW - abelian group KW - linear cellular automaton KW - substitution system KW - self-similarity Y1 - 2012 SN - 1557-5969 VL - 7 IS - 2 SP - 83 EP - 113 PB - Old City Publishing Science CY - Philadelphia ER - TY - JOUR A1 - Adamcik, Jozef A1 - Jeon, Jae-Hyung A1 - Karczewski, Konrad J. A1 - Metzler, Ralf A1 - Dietler, Giovanni T1 - Quantifying supercoiling-induced denaturation bubbles in DNA JF - Soft matter N2 - 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. Y1 - 2012 U6 - https://doi.org/10.1039/c2sm26089a SN - 1744-683X VL - 8 IS - 33 SP - 8651 EP - 8658 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Zhu, Jian A1 - Kollosche, Matthias A1 - Lu, Tongqing A1 - Kofod, Guggi A1 - Suo, Zhigang T1 - Two types of transitions to wrinkles in dielectric elastomers JF - Soft matter N2 - 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. Y1 - 2012 U6 - https://doi.org/10.1039/c2sm26034d SN - 1744-683X VL - 8 IS - 34 SP - 8840 EP - 8846 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Risse, Sebastian A1 - Kussmaul, Björn A1 - Krüger, Hartmut A1 - Kofod, Guggi T1 - A versatile method for enhancement of electromechanical sensitivity of silicone elastomers JF - RSC Advances N2 - 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. Y1 - 2012 U6 - https://doi.org/10.1039/c2ra21541a SN - 2046-2069 VL - 2 IS - 24 SP - 9029 EP - 9035 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Ilnytskyi, Jaroslav M. A1 - Saphiannikova, Marina A1 - Neher, Dieter A1 - Allen, Michael P. T1 - Modelling elasticity and memory effects in liquid crystalline elastomers by molecular dynamics simulations JF - Soft matter N2 - 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. Y1 - 2012 U6 - https://doi.org/10.1039/c2sm26499d SN - 1744-683X VL - 8 IS - 43 SP - 11123 EP - 11134 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Herzog, Marc A1 - Schick, Daniel A1 - Leitenberger, Wolfram A1 - Shayduk, Roman A1 - van der Veen, Renske M. A1 - Milne, Christopher J. A1 - Johnson, Steven Lee A1 - Vrejoiu, Ionela A1 - Bargheer, Matias T1 - Tailoring interference and nonlinear manipulation of femtosecond x-rays JF - New journal of physics : the open-access journal for physics N2 - 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. Y1 - 2012 U6 - https://doi.org/10.1088/1367-2630/14/1/013004 SN - 1367-2630 VL - 14 IS - 1 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Tonita, Aaryn T1 - Distributional sources for black hole initial data JF - Classical and quantum gravit N2 - 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. Y1 - 2012 U6 - https://doi.org/10.1088/0264-9381/29/1/015001 SN - 0264-9381 VL - 29 IS - 1 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Campbell, Earl T. A1 - Eisert, Jens T1 - Gaussification and entanglement distillation of continuous-variable systems a unifying picture JF - Physical review letters N2 - 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. Y1 - 2012 U6 - https://doi.org/10.1103/PhysRevLett.108.020501 SN - 0031-9007 VL - 108 IS - 2 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Salzmann, Ingo A1 - Heimel, Georg A1 - Duhm, Steffen A1 - Oehzelt, Martin A1 - Pingel, Patrick A1 - George, Benjamin M. A1 - Schnegg, Alexander A1 - Lips, Klaus A1 - Blum, Ralf-Peter A1 - Vollmer, Antje A1 - Koch, Norbert T1 - Intermolecular hybridization governs molecular electrical doping JF - Physical review letters N2 - 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. Y1 - 2012 U6 - https://doi.org/10.1103/PhysRevLett.108.035502 SN - 0031-9007 VL - 108 IS - 3 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Berenstein, Igal A1 - Beta, Carsten T1 - Spatiotemporal chaos arising from standing waves in a reaction-diffusion system with cross-diffusion JF - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr N2 - 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. Y1 - 2012 U6 - https://doi.org/10.1063/1.3676577 SN - 0021-9606 VL - 136 IS - 3 PB - American Institute of Physics CY - Melville ER - TY - JOUR A1 - Temirbayev, Amirkhan A. A1 - Zhanabaev, Zeinulla Zh. A1 - Tarasov, Stanislav B. A1 - Ponomarenko, Vladimir I. A1 - Rosenblum, Michael T1 - Experiments on oscillator ensembles with global nonlinear coupling JF - Physical review : E, Statistical, nonlinear and soft matter physics N2 - 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. Y1 - 2012 U6 - https://doi.org/10.1103/PhysRevE.85.015204 SN - 1539-3755 VL - 85 IS - 1 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Laflamme, S. A1 - Kollosche, Matthias A1 - Connor, Jerome J. A1 - Kofod, Guggi T1 - Soft capacitive sensor for structural health monitoring of large-scale systems JF - Structural control & health monitorin N2 - 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. KW - large-scale system KW - structural health monitoring KW - strain monitoring KW - capacitive sensor KW - dielectric polymer KW - stretchable sensor Y1 - 2012 U6 - https://doi.org/10.1002/stc.426 SN - 1545-2263 VL - 19 IS - 1 SP - 70 EP - 81 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Thompson, W. T. A1 - Kliem, Bernhard A1 - Toeroek, Tibor T1 - 3D reconstruction of a rotating erupting prominence JF - Solar physics : a journal for solar and solar-stellar research and the study of solar terrestrial physics N2 - 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. KW - Corona, active KW - Prominences, active KW - Coronal mass ejections KW - Initiation and propagation KW - Magnetic fields, corona Y1 - 2012 U6 - https://doi.org/10.1007/s11207-011-9868-5 SN - 0038-0938 VL - 276 IS - 1-2 SP - 241 EP - 259 PB - Springer CY - Dordrecht ER - TY - JOUR A1 - Gupta, Ranjeeta A1 - Gupta, Ajay A1 - Leitenberger, Wolfram A1 - Rüffer, R. T1 - Mechanism of stress relaxation in nanocrystalline Fe-N thin films JF - Physical review : B, Condensed matter and materials physics N2 - 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. Y1 - 2012 U6 - https://doi.org/10.1103/PhysRevB.85.075401 SN - 1098-0121 VL - 85 IS - 7 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Zurita-Sanchez, Jorge R. A1 - Henkel, Carsten T1 - Acoustic waves from mechanical impulses due to fluorescence resonant energy (Forster) transfer Blowing a whistle with light JF - epl : a letters journal exploring the frontiers of physics N2 - 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. Y1 - 2012 U6 - https://doi.org/10.1209/0295-5075/97/43002 SN - 0295-5075 VL - 97 IS - 4 PB - EDP Sciences CY - Mulhouse ER - TY - JOUR A1 - Malik, Nishant A1 - Zou, Y. A1 - Marwan, Norbert A1 - Kurths, Jürgen T1 - Dynamical regimes and transitions in plio-pleistocene Asian monsoon JF - epl : a letters journal exploring the frontiers of physics N2 - 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. Y1 - 2012 U6 - https://doi.org/10.1209/0295-5075/97/40009 SN - 0295-5075 VL - 97 IS - 4 PB - EDP Sciences CY - Mulhouse ER - TY - JOUR A1 - Draganova, Nadya A1 - Richter, Philipp A1 - Fechner, Cora T1 - High-resolution observations of two O VI absorbers at z approximate to 2 toward PKS 1448-232 JF - Astronomy and astrophysics : an international weekly journal N2 - 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. KW - intergalactic medium KW - quasars: absorption lines KW - cosmology: observations Y1 - 2012 U6 - https://doi.org/10.1051/0004-6361/201116730 SN - 0004-6361 VL - 538 IS - 1 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Henault-Brunet, V. A1 - Oskinova, Lida A1 - Guerrero, Martín A. A1 - Sun, W. A1 - Chu, Y.-H. A1 - Evans, C. J. A1 - Gallagher, J. S. A1 - Gruendl, R. A. A1 - Reyes-Iturbide, J. T1 - Discovery of a Be/X-ray pulsar binary and associated supernova remnant in the wing of the small magellanic cloud JF - Monthly notices of the Royal Astronomical Society N2 - 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. KW - stars: emission-line, Be KW - ISM: supernova remnants KW - Magellanic Clouds KW - X-rays: binaries Y1 - 2012 U6 - https://doi.org/10.1111/j.1745-3933.2011.01183.x SN - 0035-8711 VL - 420 IS - 1 SP - L13 EP - L17 PB - Wiley-Blackwell CY - Malden ER - TY - JOUR A1 - Baushev, Anton N. T1 - Interaction of clumpy dark matter with interstellar medium in astrophysical systems JF - Monthly notices of the Royal Astronomical Society N2 - 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. KW - elementary particles KW - cosmology: theory KW - dark matter Y1 - 2012 U6 - https://doi.org/10.1111/j.1365-2966.2011.20067.x SN - 0035-8711 VL - 420 IS - 1 SP - 590 EP - 595 PB - Wiley-Blackwell CY - Malden ER - TY - JOUR A1 - Schick, Daniel A1 - Bojahr, Andre A1 - Herzog, Marc A1 - von Korff Schmising, Clemens A1 - Shayduk, Roman A1 - Leitenberger, Wolfram A1 - Gaa, P. A1 - Bargheer, Matias T1 - Normalization schemes for ultrafast x-ray diffraction using a table-top laser-driven plasma source JF - Review of scientific instruments : a monthly journal devoted to scientific instruments, apparatus, and techniques N2 - 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. Y1 - 2012 U6 - https://doi.org/10.1063/1.3681254 SN - 0034-6748 VL - 83 IS - 2 PB - American Institute of Physics CY - Melville ER - TY - JOUR A1 - Lange, Dietrich A1 - Tilmann, Frederik A1 - Barrientos, Sergio E. A1 - Contreras-Reyes, Eduardo A1 - Methe, Pascal A1 - Moreno, Marcos A1 - Heit, Ben A1 - Agurto, Hans A1 - Bernard, Pascal A1 - Vilotte, Jean-Pierre A1 - Beck, Susan T1 - Aftershock seismicity of the 27 February 2010 Mw 8.8 Maule earthquake rupture zone JF - Earth & planetary science letters N2 - 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. KW - Maule 2010 earthquake KW - local seismicity KW - aftershock distribution KW - subduction zone KW - Central Chile KW - seismogenic zone Y1 - 2012 U6 - https://doi.org/10.1016/j.epsl.2011.11.034 SN - 0012-821X VL - 317 IS - 2 SP - 413 EP - 425 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Marwan, Norbert A1 - Beller, Gise A1 - Felsenberg, Dieter A1 - Saparin, Peter A1 - Kurths, Jürgen T1 - quantifying changes in the spatial structure of trabecular bone JF - International journal of bifurcation and chaos : in applied sciences and engineering N2 - 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. KW - 3D medical image analysis KW - pQCT KW - trabecular bone KW - patient immobilization Y1 - 2012 U6 - https://doi.org/10.1142/S0218127412500277 SN - 0218-1274 VL - 22 IS - 2 PB - World Scientific CY - Singapore ER - TY - INPR A1 - Scherf, Ullrich A1 - Tian, He T1 - Organic electronics/optics for an energetic life T2 - Advanced materials Y1 - 2012 U6 - https://doi.org/10.1002/adma.201104917 SN - 0935-9648 VL - 24 IS - 5 SP - 576 EP - 579 PB - Wiley-Blackwell CY - Malden ER - TY - JOUR A1 - Wang, Feipeng A1 - Lack, Alexander A1 - Xie, Zailai A1 - Frübing, Peter A1 - Taubert, Andreas A1 - Gerhard, Reimund T1 - Ionic-liquid-induced ferroelectric polarization in poly(vinylidene fluoride) thin films JF - Applied physics letters N2 - 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. KW - dielectric polarisation KW - ferroelectric thin films KW - polymer films KW - pyroelectricity KW - spin coating Y1 - 2012 U6 - https://doi.org/10.1063/1.3683526 SN - 0003-6951 VL - 100 IS - 6 PB - American Institute of Physics CY - Melville ER - TY - JOUR A1 - Stroman, Thomas A1 - Pohl, Martin A1 - Niemiec, Jacek A1 - Bret, Antoine T1 - Could cosmic rays affect instabilities in the Transition layer of nonrealativistic collisionless shocks? JF - The astrophysical journal : an international review of spectroscopy and astronomical physics N2 - 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. KW - cosmic rays KW - instabilities KW - plasmas KW - shock waves Y1 - 2012 U6 - https://doi.org/10.1088/0004-637X/746/1/24 SN - 0004-637X VL - 746 IS - 1 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Bergner, Andre A1 - Frasca, M. A1 - Sciuto, G. A1 - Buscarino, A. A1 - Ngamga, Eulalie Joelle A1 - Fortuna, L. A1 - Kurths, Jürgen T1 - Remote synchronization in star networks JF - Physical review : E, Statistical, nonlinear and soft matter physics N2 - 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. Y1 - 2012 U6 - https://doi.org/10.1103/PhysRevE.85.026208 SN - 1539-3755 VL - 85 IS - 2 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Aliu, E. A1 - Arlen, T. A1 - Aune, T. A1 - Beilicke, M. A1 - Benbow, W. A1 - Bouvier, A. A1 - Bradbury, S. M. A1 - Buckley, J. H. A1 - Bugaev, V. A1 - Byrum, K. A1 - Cannon, A. A1 - Cesarini, A. A1 - Ciupik, L. A1 - Collins-Hughes, E. A1 - Connolly, M. P. A1 - Cui, W. A1 - Dickherber, R. A1 - Duke, C. A1 - Errando, M. A1 - Falcone, A. A1 - Finley, J. P. A1 - Finnegan, G. A1 - Fortson, L. A1 - Furniss, A. A1 - Galante, N. A1 - Gall, D. A1 - Godambe, S. A1 - Griffin, S. A1 - Grube, J. A1 - Guenette, R. A1 - Gyuk, G. A1 - Hanna, D. A1 - Holder, J. A1 - Huan, H. A1 - Hughes, G. A1 - Hui, C. M. A1 - Humensky, T. B. A1 - Imran, A. A1 - Kaaret, P. A1 - Karlsson, N. A1 - Kertzman, M. A1 - Kieda, D. A1 - Krawczynski, H. A1 - Krennrich, F. A1 - Lang, M. J. A1 - LeBohec, S. A1 - Madhavan, A. S. A1 - Maier, G. A1 - Majumdar, P. A1 - McArthur, S. A1 - McCann, A. A1 - Moriarty, P. A1 - Mukherjee, R. A1 - Nunez, P. D. A1 - Ong, R. A. A1 - Orr, M. A1 - Otte, A. N. A1 - Park, N. A1 - Perkins, J. S. A1 - Pichel, A. A1 - Pohl, Martin A1 - Prokoph, H. A1 - Quinn, J. A1 - Ragan, K. A1 - Reyes, L. C. A1 - Reynolds, P. T. A1 - Roache, E. A1 - Rose, H. J. A1 - Ruppel, J. A1 - Saxon, D. B. A1 - Schroedter, M. A1 - Sembroski, G. H. A1 - Sentuerk, G. D. A1 - Skole, C. A1 - Staszak, D. A1 - Tesic, G. A1 - Theiling, M. A1 - Thibadeau, S. A1 - Tsurusaki, K. A1 - Tyler, J. A1 - Varlotta, A. A1 - Vassiliev, V. V. A1 - Vincent, S. A1 - Vivier, M. A1 - Wakely, S. P. A1 - Ward, J. E. A1 - Weekes, T. C. A1 - Weinstein, A. A1 - Weisgarber, T. A1 - Williams, D. A. A1 - Zitzer, B. T1 - Veritas observations of day-scale flaring of M 87 in 2010 April JF - The astrophysical journal : an international review of spectroscopy and astronomical physics N2 - 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. KW - galaxies: individual (M 87, VER J1230+123) KW - gamma rays: galaxies Y1 - 2012 U6 - https://doi.org/10.1088/0004-637X/746/2/141 SN - 0004-637X VL - 746 IS - 2 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Abramowski, Attila A1 - Acero, F. A1 - Aharonian, Felix A. A1 - Akhperjanian, A. G. A1 - Anton, Gisela A1 - Balzer, Arnim A1 - Barnacka, Anna A1 - de Almeida, U. Barres A1 - Becherini, Yvonne A1 - Becker, J. A1 - Behera, B. A1 - Bernlöhr, K. A1 - Birsin, E. A1 - Biteau, Jonathan A1 - Bochow, A. A1 - Boisson, Catherine A1 - Bolmont, J. A1 - Bordas, Pol A1 - Brucker, J. A1 - Brun, Francois A1 - Brun, Pierre A1 - Bulik, Tomasz A1 - Buesching, I. A1 - Carrigan, Svenja A1 - Casanova, Sabrina A1 - Cerruti, M. A1 - Chadwick, Paula M. A1 - Charbonnier, A. A1 - Chaves, Ryan C. G. A1 - Cheesebrough, A. A1 - Clapson, A. C. A1 - Coignet, G. A1 - Cologna, Gabriele A1 - Conrad, Jan A1 - Dalton, M. A1 - Daniel, M. K. A1 - Davids, I. D. A1 - Degrange, B. A1 - Deil, C. A1 - Dickinson, H. J. A1 - Djannati-Ataï, A. A1 - Domainko, W. A1 - Drury, L. O'C. A1 - Dubus, G. A1 - Dutson, K. A1 - Dyks, J. A1 - Dyrda, M. A1 - Egberts, Kathrin A1 - Eger, P. A1 - Espigat, P. A1 - Fallon, L. A1 - Farnier, C. A1 - Fegan, S. A1 - Feinstein, F. A1 - Fernandes, M. V. A1 - Fiasson, A. A1 - Fontaine, G. A1 - Foerster, A. A1 - Fuessling, M. A1 - Gallant, Y. A. A1 - Gast, H. A1 - Gerard, L. A1 - Gerbig, D. A1 - Giebels, B. A1 - Glicenstein, J. F. A1 - Glueck, B. A1 - Goret, P. A1 - Goering, D. A1 - Haeffner, S. A1 - Hague, J. D. A1 - Hampf, D. A1 - Hauser, M. A1 - Heinz, S. A1 - Heinzelmann, G. A1 - Henri, G. A1 - Hermann, G. A1 - Hinton, James Anthony A1 - Hoffmann, A. A1 - Hofmann, W. A1 - Hofverberg, P. A1 - Holler, M. A1 - Horns, D. A1 - Jacholkowska, A. A1 - de Jager, O. C. A1 - Jahn, C. A1 - Jamrozy, M. A1 - Jung, I. A1 - Kastendieck, M. A. A1 - Katarzynski, K. A1 - Katz, U. A1 - Kaufmann, S. A1 - Keogh, D. A1 - Khangulyan, D. A1 - Khelifi, B. A1 - Klochkov, D. A1 - Kluzniak, W. A1 - Kneiske, T. A1 - Komin, Nu. A1 - Kosack, K. A1 - Kossakowski, R. A1 - Laffon, H. A1 - Lamanna, G. A1 - Lennarz, D. A1 - Lohse, T. A1 - Lopatin, A. A1 - Lu, C. -C. A1 - Marandon, V. A1 - Marcowith, Alexandre A1 - Masbou, J. A1 - Maurin, D. A1 - Maxted, N. A1 - Mayer, M. A1 - McComb, T. J. L. A1 - Medina, M. C. A1 - Mehault, J. A1 - Moderski, R. A1 - Moulin, Emmanuel A1 - Naumann, C. L. A1 - Naumann-Godo, M. A1 - de Naurois, M. A1 - Nedbal, D. A1 - Nekrassov, D. A1 - Nguyen, N. A1 - Nicholas, B. A1 - Niemiec, J. A1 - Nolan, S. J. A1 - Ohm, S. A1 - Wilhelmi, E. de Ona A1 - Opitz, B. A1 - Ostrowski, M. A1 - Oya, I. A1 - Panter, M. A1 - Arribas, M. Paz A1 - Pedaletti, G. A1 - Pelletier, G. A1 - Petrucci, P. -O. A1 - Pita, S. A1 - Puehlhofer, G. A1 - Punch, M. A1 - Quirrenbach, A. A1 - Raue, M. A1 - Rayner, S. M. A1 - Reimer, A. A1 - Reimer, O. A1 - Renaud, M. A1 - de los Reyes, R. A1 - Rieger, F. A1 - Ripken, J. A1 - Rob, L. A1 - Rosier-Lees, S. A1 - Rowell, G. A1 - Rudak, B. A1 - Rulten, C. B. A1 - Ruppel, J. A1 - Sahakian, V. A1 - Sanchez, David M. A1 - Santangelo, A. A1 - Schlickeiser, R. A1 - Schoeck, F. M. A1 - Schulz, A. A1 - Schwanke, U. A1 - Schwarzburg, S. A1 - Schwemmer, S. A1 - Sheidaei, F. A1 - Skilton, J. L. A1 - Sol, H. A1 - Spengler, G. A1 - Stawarz, L. A1 - Steenkamp, R. A1 - Stegmann, Christian A1 - Stinzing, F. A1 - Stycz, K. A1 - Sushch, Iurii A1 - Szostek, A. A1 - Tavernet, J. -P. A1 - Terrier, R. A1 - Tluczykont, M. A1 - Valerius, K. A1 - van Eldik, C. A1 - Vasileiadis, G. A1 - Venter, C. A1 - Vialle, J. P. A1 - Viana, A. A1 - Vincent, P. A1 - Voelk, H. J. A1 - Volpe, F. A1 - Vorobiov, S. A1 - Vorster, M. A1 - Wagner, S. J. A1 - Ward, M. A1 - White, R. A1 - Wierzcholska, A. A1 - Zacharias, M. A1 - Zajczyk, A. A1 - Zdziarski, A. A. A1 - Zech, Alraune A1 - Zechlin, H. -S. A1 - Aleksic, J. A1 - Antonelli, L. A. A1 - Antoranz, P. A1 - Backes, Michael A1 - Barrio, J. A. A1 - Bastieri, D. A1 - Becerra Gonzalez, J. A1 - Bednarek, W. A1 - Berdyugin, A. A1 - Berger, K. A1 - Bernardini, E. A1 - Biland, A. A1 - Blanch Bigas, O. A1 - Bock, R. K. A1 - Boller, A. A1 - Bonnoli, G. A1 - Tridon, D. Borla A1 - Braun, I. A1 - Bretz, T. A1 - Canellas, A. A1 - Carmona, E. A1 - Carosi, A. A1 - Colin, P. A1 - Colombo, E. A1 - Contreras, J. L. A1 - Cortina, J. A1 - Cossio, L. A1 - Covino, S. A1 - Dazzi, F. A1 - De Angelis, A. A1 - De Cea del Pozo, E. A1 - De Lotto, B. A1 - Delgado Mendez, C. A1 - Diago Ortega, A. A1 - Doert, M. A1 - Dominguez, A. A1 - Prester, Dijana Dominis A1 - Dorner, D. A1 - Doro, M. A1 - Elsaesser, D. A1 - Ferenc, D. A1 - Fonseca, M. V. A1 - Font, L. A1 - Fruck, C. A1 - Garcia Lopez, R. J. A1 - Garczarczyk, M. A1 - Garrido, D. A1 - Giavitto, G. A1 - Godinovic, N. A1 - Hadasch, D. A1 - Haefner, D. A1 - Herrero, A. A1 - Hildebrand, D. A1 - Hoehne-Moench, D. A1 - Hose, J. A1 - Hrupec, D. A1 - Huber, B. A1 - Jogler, T. A1 - Klepser, S. A1 - Kraehenbuehl, T. A1 - Krause, J. A1 - La Barbera, A. A1 - Lelas, D. A1 - Leonardo, E. A1 - Lindfors, E. A1 - Lombardi, S. A1 - Lopez, M. A1 - Lorenz, E. A1 - Makariev, M. A1 - Maneva, G. A1 - Mankuzhiyil, N. A1 - Mannheim, K. A1 - Maraschi, L. A1 - Mariotti, M. A1 - Martinez, M. A1 - Mazin, D. A1 - Meucci, M. A1 - Miranda, J. M. A1 - Mirzoyan, R. A1 - Miyamoto, H. A1 - Moldon, J. A1 - Moralejo, A. A1 - Munar, P. A1 - Nieto, D. A1 - Nilsson, K. A1 - Orito, R. A1 - Oya, I. A1 - Paneque, D. A1 - Paoletti, R. A1 - Pardo, S. A1 - Paredes, J. M. A1 - Partini, S. A1 - Pasanen, M. A1 - Pauss, F. A1 - Perez-Torres, M. A. A1 - Persic, M. A1 - Peruzzo, L. A1 - Pilia, M. A1 - Pochon, J. A1 - Prada, F. A1 - Moroni, P. G. Prada A1 - Prandini, E. A1 - Puljak, I. A1 - Reichardt, I. A1 - Reinthal, R. A1 - Rhode, W. A1 - Ribo, M. A1 - Rico, J. A1 - Ruegamer, S. A1 - Saggion, A. A1 - Saito, K. A1 - Saito, T. Y. A1 - Salvati, M. A1 - Satalecka, K. A1 - Scalzotto, V. A1 - Scapin, V. A1 - Schultz, C. A1 - Schweizer, T. A1 - Shayduk, M. A1 - Shore, S. N. A1 - Sillanpaa, A. A1 - Sitarek, J. A1 - Sobczynska, D. A1 - Spanier, F. A1 - Spiro, S. A1 - Stamerra, A. A1 - Steinke, B. A1 - Storz, J. A1 - Strah, N. A1 - Suric, T. A1 - Takalo, L. A1 - Takami, H. A1 - Tavecchio, F. A1 - Temnikov, P. A1 - Terzic, T. A1 - Tescaro, D. A1 - Teshima, M. A1 - Thom, M. A1 - Tibolla, O. A1 - Torres, D. F. A1 - Treves, A. A1 - Vankov, H. A1 - Vogler, P. A1 - Wagner, R. M. A1 - Weitzel, Q. A1 - Zabalza, V. A1 - Zandanel, F. A1 - Zanin, R. A1 - Arlen, T. A1 - Aune, T. A1 - Beilicke, M. A1 - Benbow, W. A1 - Bouvier, A. A1 - Bradbury, S. M. A1 - Buckley, J. H. A1 - Bugaev, V. A1 - Byrum, K. A1 - Cannon, A. A1 - Cesarini, A. A1 - Ciupik, L. A1 - Connolly, M. P. A1 - Cui, W. A1 - Dickherber, R. A1 - Duke, C. A1 - Errando, M. A1 - Falcone, A. A1 - Finley, J. P. A1 - Finnegan, G. A1 - Fortson, L. A1 - Furniss, A. A1 - Galante, N. A1 - Gall, D. A1 - Godambe, S. A1 - Griffin, S. A1 - Grube, J. A1 - Gyuk, G. A1 - Hanna, D. A1 - Holder, J. A1 - Huan, H. A1 - Hui, C. M. A1 - Kaaret, P. A1 - Karlsson, N. A1 - Kertzman, M. A1 - Khassen, Y. A1 - Kieda, D. A1 - Krawczynski, H. A1 - Krennrich, F. A1 - Lang, M. J. A1 - LeBohec, S. A1 - Maier, G. A1 - McArthur, S. A1 - McCann, A. A1 - Moriarty, P. A1 - Mukherjee, R. A1 - Nunez, P. D. A1 - Ong, R. A. A1 - Orr, M. A1 - Otte, A. N. A1 - Park, N. A1 - Perkins, J. S. A1 - Pichel, A. A1 - Pohl, Martin A1 - Prokoph, H. A1 - Ragan, K. A1 - Reyes, L. C. A1 - Reynolds, P. T. A1 - Roache, E. A1 - Rose, H. J. A1 - Ruppel, J. A1 - Schroedter, M. A1 - Sembroski, G. H. A1 - Sentuerk, G. D. A1 - Telezhinsky, Igor O. A1 - Tesic, G. A1 - Theiling, M. A1 - Thibadeau, S. A1 - Varlotta, A. A1 - Vassiliev, V. V. A1 - Vivier, M. A1 - Wakely, S. P. A1 - Weekes, T. C. A1 - Williams, D. A. A1 - Zitzer, B. A1 - de Almeida, U. Barres A1 - Cara, M. A1 - Casadio, C. A1 - Cheung, C. C. A1 - McConville, W. A1 - Davies, F. A1 - Doi, A. A1 - Giovannini, G. A1 - Giroletti, M. A1 - Hada, K. A1 - Hardee, P. A1 - Harris, D. E. A1 - Junor, W. A1 - Kino, M. A1 - Lee, N. P. A1 - Ly, C. A1 - Madrid, J. A1 - Massaro, F. A1 - Mundell, C. G. A1 - Nagai, H. A1 - Perlman, E. S. A1 - Steele, I. A. A1 - Walker, R. C. A1 - Wood, D. L. T1 - The 2010 very high energy gamma-ray flare and 10 years ofmulti-wavelength oservations of M 87 JF - The astrophysical journal : an international review of spectroscopy and astronomical physics N2 - 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. KW - galaxies: active KW - galaxies: individual (M 87) KW - galaxies: jets KW - galaxies: nuclei KW - gamma rays: galaxies KW - radiation mechanisms: non-thermal Y1 - 2012 U6 - https://doi.org/10.1088/0004-637X/746/2/151 SN - 0004-637X VL - 746 IS - 2 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Caravelli, Francesco A1 - Hamma, Alioscia A1 - Markopoulou, Fotini A1 - Riera, Arnau T1 - Trapped surfaces and emergent curved space in the Bose-Hubbard model JF - Physical review : D, Particles, fields, gravitation, and cosmology N2 - 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. Y1 - 2012 U6 - https://doi.org/10.1103/PhysRevD.85.044046 SN - 1550-7998 VL - 85 IS - 4 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Riera, Arnau A1 - Gogolin, Christian A1 - Eisert, Jens T1 - Thermalization in nature and on a quantum computer JF - Physical review letters N2 - 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. Y1 - 2012 U6 - https://doi.org/10.1103/PhysRevLett.108.080402 SN - 0031-9007 VL - 108 IS - 8 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Schwabedal, Justus T. C. A1 - Pikovskij, Arkadij A1 - Kralemann, Björn A1 - Rosenblum, Michael T1 - Optimal phase description of chaotic oscillators JF - Physical review : E, Statistical, nonlinear and soft matter physics N2 - 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. Y1 - 2012 U6 - https://doi.org/10.1103/PhysRevE.85.026216 SN - 1539-3755 VL - 85 IS - 2 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Jeon, Jae-Hyung A1 - Metzler, Ralf T1 - Inequivalence of time and ensemble averages in ergodic systems: exponential versus power-law relaxation in confinement JF - Physical review : E, Statistical, nonlinear and soft matter physics N2 - 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. Y1 - 2012 U6 - https://doi.org/10.1103/PhysRevE.85.021147 SN - 1539-3755 VL - 85 IS - 2 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Herzog, Marc A1 - Bojahr, Andre A1 - Goldshteyn, J. A1 - Leitenberger, Wolfram A1 - Vrejoiu, I. A1 - Khakhulin, D. A1 - Wulff, M. A1 - Shayduk, Roman A1 - Gaal, P. A1 - Bargheer, Matias T1 - Detecting optically synthesized quasi-monochromatic sub-terahertz phonon wavepackets by ultrafast x-ray diffraction JF - Applied physics letters N2 - 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. KW - acoustic waves KW - epitaxial layers KW - phonon dispersion relations KW - terahertz waves KW - thin film devices KW - X-ray diffraction Y1 - 2012 U6 - https://doi.org/10.1063/1.3688492 SN - 0003-6951 VL - 100 IS - 9 PB - American Institute of Physics CY - Melville ER - TY - JOUR A1 - Herzog, Marc A1 - Schick, Daniel A1 - Gaal, P. A1 - Shayduk, Roman A1 - von Korff Schmising, Clemens A1 - Bargheer, Matias T1 - Analysis of ultrafast X-ray diffraction data in a linear-chain model of the lattice dynamics JF - Applied physics : A, Materials science & processing N2 - 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. Y1 - 2012 U6 - https://doi.org/10.1007/s00339-011-6719-z SN - 0947-8396 VL - 106 IS - 3 SP - 489 EP - 499 PB - Springer CY - New York ER - TY - JOUR A1 - Fang, Peng A1 - Hollaender, Lars A1 - Wirges, Werner A1 - Gerhard, Reimund T1 - Piezoelectric d(33) coefficients in foamed and layered polymer piezoelectrets from dynamic mechano-electrical experiments, electro-mechanical resonance spectroscopy and acoustic-transducer measurements JF - Measurement science and technology N2 - 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. KW - piezoelectret KW - ferroelectret KW - dielectric resonance spectroscopy KW - piezoelectric measurements KW - acoustic-transducer materials KW - polyethylene naphthalate (PEN) KW - fluorinated ethylene-propylene copolymer (FEP) Y1 - 2012 U6 - https://doi.org/10.1088/0957-0233/23/3/035604 SN - 0957-0233 VL - 23 IS - 3 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Albrecht, Steve A1 - Schindler, Wolfram A1 - Kurpiers, Jona A1 - Kniepert, Juliane A1 - Blakesley, James C. A1 - Dumsch, Ines A1 - Allard, Sybille A1 - Fostiropoulos, Konstantinos A1 - Scherf, Ullrich A1 - Neher, Dieter T1 - On the field dependence of free charge carrier generation and recombination in blends of PCPDTBT/PC70BM influence of solvent additives JF - The journal of physical chemistry letters N2 - 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. Y1 - 2012 U6 - https://doi.org/10.1021/jz3000849 SN - 1948-7185 VL - 3 IS - 5 SP - 640 EP - 645 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Gross, David A1 - Nesme, V. A1 - Vogts, H. A1 - Werner, Reinhard F. T1 - Index theory of one dimensional quantum walks and cellular automata JF - Communications in mathematical physics N2 - 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. Y1 - 2012 U6 - https://doi.org/10.1007/s00220-012-1423-1 SN - 0010-3616 VL - 310 IS - 2 SP - 419 EP - 454 PB - Springer CY - New York ER - TY - JOUR A1 - Cubitt, Toby S. A1 - Eisert, Jens A1 - Wolf, Michael M. T1 - The complexity of relating quantum channels to master equations JF - Communications in mathematical physics N2 - 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. Y1 - 2012 U6 - https://doi.org/10.1007/s00220-011-1402-y SN - 0010-3616 VL - 310 IS - 2 SP - 383 EP - 418 PB - Springer CY - New York ER -