@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 Buckley, J. H. and Bugaev, V. and Byrum, K. and Cesarini, A. and Ciupik, L. and Collins-Hughes, E. and Connolly, M. P. and Cui, W. and Dickherber, R. and Duke, C. and Dumm, J. and Falcone, A. and Federici, S. and Feng, Q. and Finley, J. P. and Finnegan, G. and Fortson, L. and Furniss, A. and Galante, N. and Gall, D. and Gillanders, G. H. 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 Khassen, Y. and Kieda, D. and Krawczynski, H. and Krennrich, F. and Lang, M. J. and LeBohec, S. and Lee, K. and Lyutikov, M. and Madhavan, A. S. and Maier, G. and Majumdar, P. and McArthur, S. and McCann, A. and Moriarty, P. and Mukherjee, R. and Nelson, T. and de Bhroithe, A. O'Faolain and Ong, R. A. and Orr, M. and Otte, A. N. and Park, N. and Perkins, J. S. and Pohl, M. and Prokoph, H. and Quinn, J. and Ragan, K. and Reyes, L. C. and Reynolds, P. T. and Roache, E. and Saxon, D. B. and Schr{\"o}dter, 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 Vincent, S. and Vivier, M. and Wagner, R. G. and Wakely, S. P. and Weekes, T. C. and Weinstein, A. and Welsing, R. and Williams, D. A. and Zitzer, B. and Kondratiev, V.}, title = {SEARCH FOR A CORRELATION BETWEEN VERY-HIGH-ENERGY GAMMA RAYS AND GIANT RADIO PULSES IN THE CRAB PULSAR}, series = {The astrophysical journal : an international review of spectroscopy and astronomical physics}, volume = {760}, 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/760/2/136}, pages = {13}, year = {2012}, abstract = {We present the results of a joint observational campaign between the Green Bank radio telescope and the VERITAS gamma-ray telescope, which searched for a correlation between the emission of very-high-energy (VHE) gamma rays (E-gamma > 150 GeV) and giant radio pulses (GRPs) from the Crab pulsar at 8.9 GHz. A total of 15,366 GRPs were recorded during 11.6 hr of simultaneous observations, which were made across four nights in 2008 December and in 2009 November and December. We searched for an enhancement of the pulsed gamma-ray emission within time windows placed around the arrival time of the GRP events. In total, eight different time windows with durations ranging from 0.033 ms to 72 s were positioned at three different locations relative to the GRP to search for enhanced gamma-ray emission which lagged, led, or was concurrent with, the GRP event. Furthermore, we performed separate searches on main pulse GRPs and interpulse GRPs and on the most energetic GRPs in our data sample. No significant enhancement of pulsed VHE emission was found in any of the preformed searches. We set upper limits of 5-10 times the average VHE flux of the Crab pulsar on the flux simultaneous with interpulse GRPs on single-rotation-period timescales. On similar to 8 s timescales around interpulse GRPs, we set an upper limit of 2-3 times the average VHE flux. Within the framework of recent models for pulsed VHE emission from the Crab pulsar, the expected VHE-GRP emission correlations are below the derived limits.}, 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{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{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{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{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} } @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{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{TeriacaAndrettaAuchereetal.2012, author = {Teriaca, Luca and Andretta, Vincenzo and Auchere, Frederic and Brown, Charles M. and Buchlin, Eric and Cauzzi, Gianna and Culhane, J. Len and Curdt, Werner and Davila, Joseph M. and Del Zanna, Giulio and Doschek, George A. and Fineschi, Silvano and Fludra, Andrzej and Gallagher, Peter T. and Green, Lucie and Harra, Louise K. and Imada, Shinsuke and Innes, Davina and Kliem, Bernhard and Korendyke, Clarence and Mariska, John T. and Martinez-Pillet, Valentin and Parenti, Susanna and Patsourakos, Spiros and Peter, Hardi and Poletto, Luca and Rutten, Robert J. and Schuehle, Udo and Siemer, Martin and Shimizu, Toshifumi and Socas-Navarro, Hector and Solanki, Sami K. and Spadaro, Daniele and Trujillo-Bueno, Javier and Tsuneta, Saku and Dominguez, Santiago Vargas and Vial, Jean-Claude and Walsh, Robert and Warren, Harry P. and Wiegelmann, Thomas and Winter, Berend and Young, Peter}, title = {LEMUR large european module for solar ultraviolet research}, series = {Experimental astronomy : an international journal on astronomical instrumentation and data analysis}, volume = {34}, journal = {Experimental astronomy : an international journal on astronomical instrumentation and data analysis}, number = {2}, publisher = {Springer}, address = {Dordrecht}, issn = {0922-6435}, doi = {10.1007/s10686-011-9274-x}, pages = {273 -- 309}, year = {2012}, abstract = {The solar outer atmosphere is an extremely dynamic environment characterized by the continuous interplay between the plasma and the magnetic field that generates and permeates it. Such interactions play a fundamental role in hugely diverse astrophysical systems, but occur at scales that cannot be studied outside the solar system. Understanding this complex system requires concerted, simultaneous solar observations from the visible to the vacuum ultraviolet (VUV) and soft X-rays, at high spatial resolution (between 0.1'' and 0.3''), at high temporal resolution (on the order of 10 s, i.e., the time scale of chromospheric dynamics), with a wide temperature coverage (0.01 MK to 20 MK, from the chromosphere to the flaring corona), and the capability of measuring magnetic fields through spectropolarimetry at visible and near-infrared wavelengths. Simultaneous spectroscopic measurements sampling the entire temperature range are particularly important. These requirements are fulfilled by the Japanese Solar-C mission (Plan B), composed of a spacecraft in a geosynchronous orbit with a payload providing a significant improvement of imaging and spectropolarimetric capabilities in the UV, visible, and near-infrared with respect to what is available today and foreseen in the near future. The Large European Module for solar Ultraviolet Research (LEMUR), described in this paper, is a large VUV telescope feeding a scientific payload of high-resolution imaging spectrographs and cameras. LEMUR consists of two major components: a VUV solar telescope with a 30 cm diameter mirror and a focal length of 3.6 m, and a focal-plane package composed of VUV spectrometers covering six carefully chosen wavelength ranges between 170 and 1270 . The LEMUR slit covers 280'' on the Sun with 0.14'' per pixel sampling. In addition, LEMUR is capable of measuring mass flows velocities (line shifts) down to 2 km s (-aEuro parts per thousand 1) or better. LEMUR has been proposed to ESA as the European contribution to the Solar C mission.}, 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{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{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{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{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{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{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{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{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{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{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{MariEisert2012, author = {Mari, A. and Eisert, J.}, title = {Opto- and electro-mechanical entanglement improved by modulation}, series = {New journal of physics : the open-access journal for physics}, volume = {14}, journal = {New journal of physics : the open-access journal for physics}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {1367-2630}, doi = {10.1088/1367-2630/14/7/075014}, pages = {12}, year = {2012}, abstract = {One of the main milestones in the study of opto- and electromechanical systems is to certify entanglement between a mechanical resonator and an optical or microwave mode of a cavity field. In this work, we show how a suitable time-periodic modulation can help to achieve large degrees of entanglement, building upon the framework introduced in Mari and Eisert (2009 Phys. Rev. Lett. 103 213603). It is demonstrated that with suitable driving, the maximum degree of entanglement can be significantly enhanced, in a way exhibiting a nontrivial dependence on the specifics of the modulation. Such time-dependent driving might help to experimentally achieve entangled mechanical systems also in situations when quantum correlations are otherwise suppressed by thermal noise.}, language = {en} } @article{CherstvyWinkler2012, author = {Cherstvy, Andrey G. and Winkler, R. G.}, title = {Polyelectrolyte adsorption onto oppositely charged interfaces image-charge repulsion and surface curvature}, series = {The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces \& biophysical chemistry}, volume = {116}, journal = {The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces \& biophysical chemistry}, number = {32}, publisher = {American Chemical Society}, address = {Washington}, issn = {1520-6106}, doi = {10.1021/jp304980e}, pages = {9838 -- 9845}, year = {2012}, abstract = {We analyze theoretically the influence of low-dielectric boundaries on the adsorption of flexible polyelectrolytes onto planar and spherical oppositely charged surfaces in electrolyte solutions. We rationalize to what extent polymer chains are depleted from adsorbing interfaces by repulsive image forces. We employ the WKB (Wentzel-Kramers-Brillouin) quantum mechanical method for the Green function of the Edwards equation to determine the adsorption equilibrium. Scaling relations are determined for the critical adsorption strength required to initiate polymer adsorption onto these low-dielectric supports. Image-force repulsion shifts the equilibrium toward the desorbed state, demanding larger surface charge densities and polyelectrolyte linear charge densities for the adsorption to take place. The effect is particularly pronounced for a planar interface in a low-salt regime, where a dramatic change in the scaling behavior for the adsorption-desorption transition is predicted. For the adsorbed state, polymers with higher charge densities are displaced further from the interface by image-charge repulsions. We discuss relevant experimental evidence and argue about possible biological applications of the results.}, language = {en} } @article{FrascaBergnerKurthsetal.2012, author = {Frasca, Mattia and Bergner, Andre and Kurths, J{\"u}rgen and Fortuna, Luigi}, title = {Bifurcations in a star-like network of Stuart-Landau oscillators}, 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 = {7}, publisher = {World Scientific}, address = {Singapore}, issn = {0218-1274}, doi = {10.1142/S0218127412501738}, pages = {13}, year = {2012}, abstract = {In this paper, we analytically study a star motif of Stuart-Landau oscillators, derive the bifurcation diagram and discuss the different forms of synchronization arising in such a system. Despite the parameter mismatch between the central node and the peripheral ones, an analytical approach independent of the number of units in the system has been proposed. The approach allows to calculate the separatrices between the regions with distinct dynamical behavior and to determine the nature of the different transitions to synchronization appearing in the system. The theoretical analysis is supported by numerical results.}, language = {en} } @article{GuimaraesAlbersSpahnetal.2012, author = {Guimaraes, Ana H. F. and Albers, Nicole and Spahn, Frank and Seiss, Martin and Vieira-Neto, Ernesto and Brilliantov, Nikolai V.}, title = {Aggregates in the strength and gravity regime Particles sizes in Saturn's rings}, series = {Icarus : international journal of solar system studies}, volume = {220}, journal = {Icarus : international journal of solar system studies}, number = {2}, publisher = {Elsevier}, address = {San Diego}, issn = {0019-1035}, doi = {10.1016/j.icarus.2012.06.005}, pages = {660 -- 678}, year = {2012}, abstract = {Particles in Saturn's main rings range in size from dust to kilometer-sized objects. Their size distribution is thought to be a result of competing accretion and fragmentation processes. While growth is naturally limited in tidal environments, frequent collisions among these objects may contribute to both accretion and fragmentation. As ring particles are primarily made of water ice attractive surface forces like adhesion could significantly influence these processes, finally determining the resulting size distribution. Here, we derive analytic expressions for the specific self-energy Q and related specific break-up energy Q(star) of aggregates. These expressions can be used for any aggregate type composed of monomeric constituents. We compare these expressions to numerical experiments where we create aggregates of various types including: regular packings like the face-centered cubic (fcc), Ballistic Particle Cluster Aggregates (BPCA), and modified BPCAs including e.g. different constituent size distributions. We show that accounting for attractive surface forces such as adhesion a simple approach is able to: (a) generally account for the size dependence of the specific break-up energy for fragmentation to occur reported in the literature, namely the division into "strength" and "gravity" regimes and (b) estimate the maximum aggregate size in a collisional ensemble to be on the order of a few tens of meters, consistent with the maximum particle size observed in Saturn's rings of about 10 m.}, language = {en} } @article{GaoWangBlakesleyetal.2012, author = {Gao, Feng and Wang, Jianpu and Blakesley, James C. and Hwang, Inchan and Li, Zhe and Greenham, Neil C.}, title = {Quantifying loss mechanisms in polymer Fullerene photovoltaic devices}, series = {dvanced energy materials}, volume = {2}, journal = {dvanced energy materials}, number = {8}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1614-6832}, doi = {10.1002/aenm.201200073}, pages = {956 -- 961}, year = {2012}, language = {en} } @article{BarkaiGariniMetzler2012, author = {Barkai, Eli and Garini, Yuval and Metzler, Ralf}, title = {Strange Kinetics of single molecules in living cells}, series = {Physics today}, volume = {65}, journal = {Physics today}, number = {8}, publisher = {American Institute of Physics}, address = {Melville}, issn = {0031-9228}, pages = {29 -- 35}, year = {2012}, 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{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{ModakSingleton2012, author = {Modak, Sujoy Kumar and Singleton, Douglas}, title = {Inflation with a graceful exit and entrance driven by Hawking radiation}, series = {Physical review : D, Particles, fields, gravitation, and cosmology}, volume = {86}, journal = {Physical review : D, Particles, fields, gravitation, and cosmology}, number = {12}, publisher = {American Physical Society}, address = {College Park}, issn = {1550-7998}, doi = {10.1103/PhysRevD.86.123515}, pages = {9}, year = {2012}, abstract = {We present a model for cosmological inflation which has a natural "turn on'' and a natural "turn off'' mechanism. In our model inflation is driven by the Hawking-like radiation that occurs in Friedmann-Robertson-Walker (FRW) space-time. This Hawking-like radiation results in an effective negative pressure "fluid'' which leads to a rapid period of expansion in the very early Universe. As the Universe expands the FRW Hawking temperature decreases and the inflationary expansion turns off and makes a natural transition to the power-law expansion of a radiation dominated universe. The turn on mechanism is more speculative, but is based on the common hypothesis that in a quantum theory of gravity at very high temperatures/high densities Hawking radiation will stop. Applying this speculation to the very early Universe implies that the Hawking-like radiation of the FRW space-time will be turned off and therefore the inflation driven by this radiation will turn off.}, language = {en} } @article{JeonMonneJavanainenetal.2012, author = {Jeon, Jae-Hyung and Monne, Hector Martinez-Seara and Javanainen, Matti and Metzler, Ralf}, title = {Anomalous diffusion of phospholipids and cholesterols in a lipid bilayer and its origins}, series = {Physical review letters}, volume = {109}, journal = {Physical review letters}, number = {18}, publisher = {American Physical Society}, address = {College Park}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.109.188103}, pages = {5}, year = {2012}, abstract = {Combining extensive molecular dynamics simulations of lipid bilayer systems of varying chemical compositions with single-trajectory analyses, we systematically elucidate the stochastic nature of the lipid motion. We observe subdiffusion over more than 4 orders of magnitude in time, clearly stretching into the submicrosecond domain. The lipid motion depends on the lipid chemistry, the lipid phase, and especially the presence of cholesterol. We demonstrate that fractional Langevin equation motion universally describes the lipid motion in all phases, including the gel phase, and in the presence of cholesterol. The results underline the relevance of anomalous diffusion in lipid bilayers and the strong effects of the membrane composition.}, language = {en} } @article{KoerzdoerferParrishMarometal.2012, author = {K{\"o}rzd{\"o}rfer, Thomas and Parrish, Robert M. and Marom, Noa and Sears, John S. and Sherrill, C. David and Bredas, Jean-Luc}, title = {Assessment of the performance of tuned range-separated hybrid density functionals in predicting accurate quasiparticle spectra}, series = {Physical review : B, Condensed matter and materials physics}, volume = {86}, journal = {Physical review : B, Condensed matter and materials physics}, number = {20}, publisher = {American Physical Society}, address = {College Park}, issn = {1098-0121}, doi = {10.1103/PhysRevB.86.205110}, pages = {9}, year = {2012}, abstract = {Long-range corrected hybrid functionals that employ a nonempirically tuned range-separation parameter have been demonstrated to yield accurate ionization potentials and fundamental gaps for a wide range of finite systems. Here, we address the question of whether this high level of accuracy is limited to the highest occupied/lowest unoccupied energy levels to which the range-separation parameter is tuned or whether it is retained for the entire valence spectrum. We examine several pi-conjugated molecules and find that orbitals of a different character and symmetry require significantly different range-separation parameters and fractions of exact exchange. This imbalanced treatment of orbitals of a different nature biases the resulting eigenvalue spectra. Thus, the existing schemes for the tuning of range-separated hybrid functionals, while providing for good agreement between the highest occupied energy level and the first ionization potential, do not achieve accuracy comparable to reliable G(0)W(0) computations for the entire quasiparticle spectrum.}, language = {en} } @article{BerensteinBeta2012, author = {Berenstein, Igal and Beta, Carsten}, title = {Flow-induced transitions in bistable systems}, series = {Physical review : E, Statistical, nonlinear and soft matter physics}, volume = {86}, 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.86.056205}, pages = {6}, year = {2012}, abstract = {We studied transitions between spatiotemporal patterns that can be induced in a spatially extended nonlinear chemical system by a unidirectional flow in combination with constant inflow concentrations. Three different scenarios were investigated. (i) Under conditions where the system exhibited two stable fixed points, the propagation direction of trigger fronts could be reversed, so that domains of the less stable fixed point invaded the system. (ii) For bistability between a stable fixed point and a limit cycle we observed that above a critical flow velocity, the unstable focus at the center of the limit cycle could be stabilized. Increasing the flow speed further, a regime of damped flow-distributed oscillations was found and, depending on the boundary values at the inflow, finally the stable fixed point dominated. Similarly, also in the case of spatiotemporal chaos (iii), the unstable steady state could be stabilized and was replaced by the stable fixed point with increasing flow velocity. We finally outline a linear stability analysis that can explain part of our findings.}, language = {en} } @article{ChechkinLenzKlages2012, author = {Chechkin, Aleksei V. and Lenz, F. and Klages, Rainer}, title = {Normal and anomalous fluctuation relations for gaussian stochastic dynamics}, series = {Journal of statistical mechanics: theory and experiment}, journal = {Journal of statistical mechanics: theory and experiment}, number = {4}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {1742-5468}, doi = {10.1088/1742-5468/2012/11/L11001}, pages = {12}, year = {2012}, abstract = {We study transient work fluctuation relations (FRs) for Gaussian stochastic systems generating anomalous diffusion. For this purpose we use a Langevin approach by employing two different types of additive noise: (i) internal noise where the fluctuation dissipation relation of the second kind (FDR II) holds, and (ii) external noise without FDR II. For internal noise we demonstrate that the existence of FDR II implies the existence of the fluctuation dissipation relation of the first kind (FDR I), which in turn leads to conventional (normal) forms of transient work FRs. For systems driven by external noise we obtain violations of normal FRs, which we call anomalous FRs. We derive them in the long-time limit and demonstrate the existence of logarithmic factors in FRs for intermediate times. We also outline possible experimental verifications.}, language = {en} } @article{GuendelmanSingletonYongram2012, author = {G{\"u}ndelman, Eduardo and Singleton, Douglas and Yongram, N.}, title = {A two measure model of dark energy and dark matter}, series = {Journal of cosmology and astroparticle physics}, journal = {Journal of cosmology and astroparticle physics}, number = {11}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {1475-7516}, doi = {10.1088/1475-7516/2012/11/044}, pages = {12}, year = {2012}, abstract = {In this work we construct a unified model of dark energy and dark matter. This is done with the following three elements: a gravitating scalar field, phi with a non-conventional kinetic term, as in the string theory tachyon; an arbitrary potential, V (phi); two measures - a metric measure (root-g) and a non-metric measure (Phi). The model has two interesting features: (i) For potentials which are unstable and would give rise to tachyonic scalar field, this model can stabilize the scalar field. (ii) The form of the dark energy and dark matter that results from this model is fairly insensitive to the exact form of the scalar field potential.}, language = {en} } @article{MihocSchickLuetgensetal.2012, author = {Mihoc, Carmen and Schick, Daniel and L{\"u}tgens, Matthias and Lathe, Christian and Burkel, Eberhard}, title = {Formation of Al67Cu23Fe10 quasicrystals by microwave heating}, series = {International journal of materials research : Zeitschrift f{\"u}r Metallkunde}, volume = {103}, journal = {International journal of materials research : Zeitschrift f{\"u}r Metallkunde}, number = {11}, publisher = {Hanser}, address = {M{\"u}nchen}, issn = {1862-5282}, doi = {10.3139/146.110786}, pages = {1340 -- 1344}, year = {2012}, abstract = {The present work was carried out to compare the formation of single icosahedral phase during conventional heating and microwave processing. Al67Cu23Fe10 alloy powder was synthesized from high purity (99.9\%) powder elements by mechanical alloying. Differential scanning calorimetry combined with in-situ synchrotron energy dispersive X-ray diffraction was used to identify the main solid state reactions and the phase evolution of the powders. Inductive microwave processing in the magnetic field anti-node was performed to obtain the quasicrystalline phase in only a few seconds. Due to the rapid cooling of the sample it was possible to stabilize the icosahedral phase against its competing quasicrystalline approximants. Laboratory X-ray diffraction analysis was used to characterise the atomic structure of the specimen and scanning electron microscopy was used to characterise the microstructure after the microwave processing.}, language = {en} } @article{MetzlerJeon2012, author = {Metzler, Ralf and Jeon, Jae-Hyung}, title = {The role of ergodicity in anomalous stochastic processes - analysis of single-particle trajectories}, series = {Physica scripta : an international journal for experimental and theoretical physics}, volume = {86}, journal = {Physica scripta : an international journal for experimental and theoretical physics}, number = {5}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {0031-8949}, doi = {10.1088/0031-8949/86/05/058510}, pages = {5}, year = {2012}, abstract = {Single-particle experiments produce time series x(t) of individual particle trajectories, frequently revealing anomalous diffusion behaviour. Typically, individual x(t) are evaluated in terms of time-averaged quantities instead of ensemble averages. Here we discuss the behaviour of the time-averaged mean squared displacement of different stochastic processes giving rise to anomalous diffusion. In particular, we pay attention to the ergodic properties of these processes, i.e. the (non)equivalence of time and ensemble averages.}, language = {en} } @article{KaeonikhomSingletonSushkovetal.2012, author = {Kaeonikhom, Chakkrit and Singleton, Douglas and Sushkov, Sergey V. and Yongram, N.}, title = {Dynamics of Dirac-Born-Infeld dark energy interacting with dark matter}, series = {Physical review : D, Particles, fields, gravitation, and cosmology}, volume = {86}, journal = {Physical review : D, Particles, fields, gravitation, and cosmology}, number = {12}, publisher = {American Physical Society}, address = {College Park}, issn = {1550-7998}, doi = {10.1103/PhysRevD.86.124049}, pages = {10}, year = {2012}, abstract = {We study the dynamics of Dirac-Born-Infeld (DBI) dark energy interacting with dark matter. The DBI dark energy model considered here has a scalar field with a nonstandard kinetic energy term, and has potential and brane tension that are power-law functions. The new feature considered here is an interaction between the DBI dark energy and dark matter through a phenomenological interaction between the DBI scalar field and the dark matter fluid. We analyze two different types of interactions between the DBI scalar field and the dark matter fluid. In particular we study the phase-space diagrams of and look for critical points of the phase space that are both stable and lead to accelerated, late-time expansion. In general we find that the interaction between the two dark components does not appear to give rise to late-time accelerated expansion. However, the interaction can make the critical points in the phase space of the system stable. Whether such stabilization occurs or not depends on the form of the interaction between the two dark components.}, language = {en} } @article{EmmerlingOrgzallDietzeletal.2012, author = {Emmerling, Franziska and Orgzall, Ingo and Dietzel, Birgit and Schulz, Burkhard and Larrucea, Julen}, title = {Ordering the amorphous - Structures in PBD LED materials}, series = {Journal of molecular structure}, volume = {1030}, journal = {Journal of molecular structure}, number = {23}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0022-2860}, doi = {10.1016/j.molstruc.2012.04.040}, pages = {209 -- 215}, year = {2012}, abstract = {The class of 2,5 disubstituted-1,3,4-oxadiazoles containing a biphenyl unit on one side is intensively used as electron transport materials to enhance the performance of organic light emitting diodes (OLEDs). In contrast to the ongoing research on these materials insights in their structure-property relationships are still incomplete. To overcome the structural tentativeness and ambiguities the crystal structures of 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole, that of the related compound 2-(4-biphenylyl)-5-phenyl-1,3,4-oxadiazole and of 2-(4-biphenylyl)-5-(2,6-dimethylphenyl)-1,3,4-oxadiazole are determined. A comparison with the results of GAUSSIAN03 calculations and similar compounds in the Cambridge Structural Database leads to a profound characterization.}, language = {en} } @article{KimberWrightO'Kaneetal.2012, author = {Kimber, Robin G. E. and Wright, Edward N. and O'Kane, Simon E. J. and Walker, Alison B. and Blakesley, James C.}, title = {Mesoscopic kinetic Monte Carlo modeling of organic photovoltaic device characteristics}, series = {Physical review : B, Condensed matter and materials physics}, volume = {86}, journal = {Physical review : B, Condensed matter and materials physics}, number = {23}, publisher = {American Physical Society}, address = {College Park}, issn = {1098-0121}, doi = {10.1103/PhysRevB.86.235206}, pages = {9}, year = {2012}, abstract = {Measured mobility and current-voltage characteristics of single layer and photovoltaic (PV) devices composed of poly{9,9-dioctylfluorene-co-bis[N,N'-(4-butylphenyl)]bis(N,N'-phenyl-1,4-phenylene)diamine} (PFB) and poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT) have been reproduced by a mesoscopic model employing the kinetic Monte Carlo (KMC) approach. Our aim is to show how to avoid the uncertainties common in electrical transport models arising from the need to fit a large number of parameters when little information is available, for example, a single current-voltage curve. Here, simulation parameters are derived from a series of measurements using a self-consistent "building-blocks" approach, starting from data on the simplest systems. We found that site energies show disorder and that correlations in the site energies and a distribution of deep traps must be included in order to reproduce measured charge mobility-field curves at low charge densities in bulk PFB and F8BT. The parameter set from the mobility-field curves reproduces the unipolar current in single layers of PFB and F8BT and allows us to deduce charge injection barriers. Finally, by combining these disorder descriptions and injection barriers with an optical model, the external quantum efficiency and current densities of blend and bilayer organic PV devices can be successfully reproduced across a voltage range encompassing reverse and forward bias, with the recombination rate the only parameter to be fitted, found to be 1 x 10(7) s(-1). These findings demonstrate an approach that removes some of the arbitrariness present in transport models of organic devices, which validates the KMC as an accurate description of organic optoelectronic systems, and provides information on the microscopic origins of the device behavior.}, language = {en} } @article{MaromCarusoRenetal.2012, author = {Marom, Noa and Caruso, Fabio and Ren, Xinguo and Hofmann, Oliver T. and K{\"o}rzd{\"o}rfer, Thomas and Chelikowsky, James R. and Rubio, Angel and Scheffler, Matthias and Rinke, Patrick}, title = {Benchmark of GW methods for azabenzenes}, series = {Physical review : B, Condensed matter and materials physics}, volume = {86}, journal = {Physical review : B, Condensed matter and materials physics}, number = {24}, publisher = {American Physical Society}, address = {College Park}, issn = {1098-0121}, doi = {10.1103/PhysRevB.86.245127}, pages = {16}, year = {2012}, abstract = {Many-body perturbation theory in the GW approximation is a useful method for describing electronic properties associated with charged excitations. A hierarchy of GW methods exists, starting from non-self-consistent G(0)W(0), through partial self-consistency in the eigenvalues and in the Green's function (scGW(0)), to fully self-consistent GW (scGW). Here, we assess the performance of these methods for benzene, pyridine, and the diazines. The quasiparticle spectra are compared to photoemission spectroscopy (PES) experiments with respect to all measured particle removal energies and the ordering of the frontier orbitals. We find that the accuracy of the calculated spectra does not match the expectations based on their level of self-consistency. In particular, for certain starting points G(0)W(0) and scGW(0) provide spectra in better agreement with the PES than scGW.}, language = {en} } @article{EliazarMetzler2012, author = {Eliazar, Iddo and Metzler, Ralf}, title = {The RARE model a generalized approach to random relaxation processes in disordered systems}, series = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr}, volume = {137}, journal = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr}, number = {23}, publisher = {American Institute of Physics}, address = {Melville}, issn = {0021-9606}, doi = {10.1063/1.4770266}, pages = {9}, year = {2012}, abstract = {This paper introduces and analyses a general statistical model, termed the RAndom RElaxations (RARE) model, of random relaxation processes in disordered systems. The model considers excitations that are randomly scattered around a reaction center in a general embedding space. The model's input quantities are the spatial scattering statistics of the excitations around the reaction center, and the chemical reaction rates between the excitations and the reaction center as a function of their mutual distance. The framework of the RARE model is versatile and a detailed stochastic analysis of the random relaxation processes is established. Analytic results regarding the duration and the range of the random relaxation processes, as well as the model's thermodynamic limit, are obtained in closed form. In particular, the case of power-law inputs, which turn out to yield stretched exponential relaxation patterns and asymptotically Paretian relaxation ranges, is addressed in detail.}, language = {en} } @article{Berenstein2012, author = {Berenstein, Igal}, title = {Distinguishing similar patterns with different underlying instabilities Effect of advection on systems with Hopf, Turing-Hopf, and wave instabilities}, series = {Chaos : an interdisciplinary journal of nonlinear science}, volume = {22}, journal = {Chaos : an interdisciplinary journal of nonlinear science}, number = {4}, publisher = {American Institute of Physics}, address = {Melville}, issn = {1054-1500}, doi = {10.1063/1.4766591}, pages = {4}, year = {2012}, abstract = {Systems with the same local dynamics but different types of diffusive instabilities may show the same type of patterns. In this paper, we show that under the influence of advective flow the scenario of patterns that is formed at different velocities change; therefore, we propose the use of advective flow as a tool to uncover the underlying instabilities of a reaction-diffusion system.}, language = {en} } @article{IsaevaKuznetsovSataev2012, author = {Isaeva, Olga B. and Kuznetsov, Sergey P. and Sataev, Igor R.}, title = {A "saddle-node" bifurcation scenario for birth or destruction of a Smale-Williams solenoid}, series = {Chaos : an interdisciplinary journal of nonlinear science}, volume = {22}, journal = {Chaos : an interdisciplinary journal of nonlinear science}, number = {4}, publisher = {American Institute of Physics}, address = {Melville}, issn = {1054-1500}, doi = {10.1063/1.4766590}, pages = {7}, year = {2012}, abstract = {Formation or destruction of hyperbolic chaotic attractor under parameter variation is considered with an example represented by Smale-Williams solenoid in stroboscopic Poincare map of two alternately excited non-autonomous van der Pol oscillators. The transition occupies a narrow but finite parameter interval and progresses in such way that periodic orbits constituting a "skeleton" of the attractor undergo saddle-node bifurcation events involving partner orbits from the attractor and from a non-attracting invariant set, which forms together with its stable manifold a basin boundary of the attractor.}, language = {en} } @article{KalimuthuLeimkuehlerBernhardt2012, author = {Kalimuthu, Palraj and Leimk{\"u}hler, Silke and Bernhardt, Paul V.}, title = {Low-potential amperometric enzyme biosensor for xanthine and hypoxanthine}, series = {Analytical chemistry}, volume = {84}, journal = {Analytical chemistry}, number = {23}, publisher = {American Chemical Society}, address = {Washington}, issn = {0003-2700}, doi = {10.1021/ac3025027}, pages = {10359 -- 10365}, year = {2012}, abstract = {The bacterial xanthine dehydrogenase (XDH) from Rhodobacter capsulatus was immobilized on an edge-plane pyrolytic graphite (EPG) electrode to construct a hypoxanthine/xanthine biosensor that functions at physiological pH. Phenazine methosulfate (PMS) was used as a mediator which acts as an artificial electron-transfer partner for XDH. The enzyme catalyzes the oxidation of hypoxanthine to xanthine and also xanthine to uric acid by an oxidative hydroxylation mechanism. The present electrochemical biosensor was optimized in terms of applied potential and pH. The electrocatalytic oxidation response showed a linear dependence on the xanthine concentration ranging from 1.0 X 10(-5) to 1.8 X 10(-3) M with a correlation coefficient of 0.994. The modified electrode shows a very low detection limit for xanthine of 0.25 nM (signal-to-noise ratio = 3) using controlled potential amperometry.}, language = {en} } @article{MariEisert2012, author = {Mari, Andrea and Eisert, Jens}, title = {Positive wigner functions render classical simulation of quantum computation efficient}, series = {Physical review letters}, volume = {109}, journal = {Physical review letters}, number = {23}, publisher = {American Physical Society}, address = {College Park}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.109.230503}, pages = {5}, year = {2012}, abstract = {We show that quantum circuits where the initial state and all the following quantum operations can be represented by positive Wigner functions can be classically efficiently simulated. This is true both for continuous-variable as well as discrete variable systems in odd prime dimensions, two cases which will be treated on entirely the same footing. Noting the fact that Clifford and Gaussian operations preserve the positivity of the Wigner function, our result generalizes the Gottesman-Knill theorem. Our algorithm provides a way of sampling from the output distribution of a computation or a simulation, including the efficient sampling from an approximate output distribution in the case of sampling imperfections for initial states, gates, or measurements. In this sense, this work highlights the role of the positive Wigner function as separating classically efficiently simulable systems from those that are potentially universal for quantum computing and simulation, and it emphasizes the role of negativity of the Wigner function as a computational resource.}, 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{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{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{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{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{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{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{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{RisseKussmaulKruegeretal.2012, author = {Risse, Sebastian and Kussmaul, Bjoern and Kr{\"u}ger, Hartmut and Kofod, Guggi}, title = {Synergistic improvement of actuation properties with compatibilized high permittivity filler}, series = {Advanced functional materials}, volume = {22}, journal = {Advanced functional materials}, number = {18}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1616-301X}, doi = {10.1002/adfm.201200320}, pages = {3958 -- 3962}, year = {2012}, abstract = {Electroactive polymers can be used for actuators with many desirable features, including high electromechanical energy density, low weight, compactness, direct voltage control, and complete silence during actuation. These features may enable personalized robotics with much higher ability to delicately manipulate their surroundings than can be achieved with currently available actuators; however, much work is still necessary to enhance the electroactive materials. Electric field-driven actuator materials are improved by an increase in permittivity and by a reduction in stiffness. Here, a synergistic enhancement method based on a macromolecular plasticizing filler molecule with a combination of both high dipole moment and compatibilizer moieties, synthesized to simultaneously ensure improvement of electromechanical properties and compatibility with the host matrix is presented. Measurements show an 85\% increase in permittivity combined with 290\% reduction in mechanical stiffness. NMR measurements confirm the structure of the filler while DSC measurements confirm that it is compatible with the host matrix at all the mixture ratios investigated. Actuation strain measurements in the pure shear configuration display an increase in sensitivity to the electrical field of more than 450\%, confirming that the filler molecule does not only improve dielectric and mechanical properties, it also leads to a synergistic enhancement of actuation properties by simple means.}, language = {en} } @article{BaushevFedericiPohl2012, author = {Baushev, Anton N. and Federici, S. and Pohl, M.}, title = {Spectral analysis of the gamma-ray background near the dwarf MilkyWay satellite Segue 1: Improved limits on the cross section of neutralino dark matter annihilation}, series = {Physical review : D, Particles, fields, gravitation, and cosmology}, volume = {86}, 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.86.063521}, pages = {7}, year = {2012}, abstract = {The indirect detection of dark matter requires that dark matter annihilation products be discriminated from conventional astrophysical backgrounds. Here, we re-analyze GeV-band gamma-ray observations of the prominent Milky Way dwarf satellite galaxy Segue 1, for which the expected astrophysical background is minimal. We explicitly account for the angular extent of the conservatively expected gamma-ray signal and keep the uncertainty in the dark-matter profile external to the likelihood analysis of the gamma-ray data.}, language = {en} } @article{ThielemannKuehnHoffmannFoehlisch2012, author = {Thielemann-K{\"u}hn, Nele and Hoffmann, P. and F{\"o}hlisch, Alexander}, title = {A versatile detector for total fluorescence and electron yield experiments}, 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 = {9}, publisher = {American Institute of Physics}, address = {Melville}, issn = {0034-6748}, doi = {10.1063/1.4754126}, pages = {3}, year = {2012}, abstract = {The combination of a non-coated silicon photodiode with electron repelling meshes makes a versatile detector for total fluorescence yield and electron yield techniques highly suitable for x-ray absorption spectroscopy. In particular, a copper mesh with a bias voltage allows to suppress or transmit the electron yield signal. The performance of this detection scheme has been characterized by near edge x-ray absorption fine structure studies of thermal oxidized silicon and sapphire. The results show that the new detector probes both electron yield and for a bias voltage exceeding the maximum photon energy the total fluorescence yield.}, language = {en} } @article{LiuKliemToeroeketal.2012, author = {Liu, Rui and Kliem, Bernhard and Toeroek, Tibor and Liu, Chang and Titov, Viacheslav S. and Lionello, Roberto and Linker, Jon A. and Wang, Haimin}, title = {Slow rise and partial eruption of a double-decker filament. I. observations and interpretation}, series = {The astrophysical journal : an international review of spectroscopy and astronomical physics}, volume = {756}, 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/756/1/59}, pages = {14}, year = {2012}, abstract = {We study an active-region dextral filament that was composed of two branches separated in height by about 13 Mm, as inferred from three-dimensional reconstruction by combining SDO and STEREO-B observations. This "double-decker" configuration sustained for days before the upper branch erupted with a GOES-class M1.0 flare on 2010 August 7. Analyzing this evolution, we obtain the following main results. (1) During the hours before the eruption, filament threads within the lower branch were observed to intermittently brighten up, lift upward, and then merge with the upper branch. The merging process contributed magnetic flux and current to the upper branch, resulting in its quasi-static ascent. (2) This transfer might serve as the key mechanism for the upper branch to lose equilibrium by reaching the limiting flux that can be stably held down by the overlying field or by reaching the threshold of the torus instability. (3) The erupting branch first straightened from a reverse S shape that followed the polarity inversion line and then writhed into a forward S shape. This shows a transfer of left-handed helicity in a sequence of writhe-twist-writhe. The fact that the initial writhe is converted into the twist of the flux rope excludes the helical kink instability as the trigger process of the eruption, but supports the occurrence of the instability in the main phase, which is indeed indicated by the very strong writhing motion. (4) A hard X-ray sigmoid, likely of coronal origin, formed in the gap between the two original filament branches in the impulsive phase of the associated flare. This supports a model of transient sigmoids forming in the vertical flare current sheet. (5) Left-handed magnetic helicity is inferred for both branches of the dextral filament. (6) Two types of force-free magnetic configurations are compatible with the data, a double flux rope equilibrium and a single flux rope situated above a loop arcade.}, language = {en} } @article{TepperGarciaRichterSchayeetal.2012, author = {Tepper-Garcia, Thorsten and Richter, Philipp and Schaye, Joop and Booth, C. M. and Dalla Vecchia, Claudio and Theuns, Tom}, title = {Absorption signatures of warm-hot gas at low redshift: broad H?i Lya absorbers}, series = {Monthly notices of the Royal Astronomical Society}, volume = {425}, journal = {Monthly notices of the Royal Astronomical Society}, number = {3}, publisher = {Wiley-Blackwell}, address = {Hoboken}, issn = {0035-8711}, doi = {10.1111/j.1365-2966.2012.21545.x}, pages = {1640 -- 1663}, year = {2012}, abstract = {We investigate the physical state of H?i absorbing gas at low redshift (z = 0.25) using a subset of cosmological, hydrodynamic simulations from the OverWhelmingly Large Simulations project, focusing in particular on broad (bHI=40 km s-1) H?i Lya absorbers (BLAs), which are believed to originate in shock-heated gas in the warm-hot intergalactic medium (WHIM). Our fiducial model, which includes radiative cooling by heavy elements and feedback by supernovae and active galactic nuclei, predicts that by z = 0.25 nearly 60?per cent of the gas mass ends up at densities and temperatures characteristic of the WHIM and we find that half of this fraction is due to outflows. The standard H?i observables (distribution of H?i column densities NH?I, distribution of Doppler parameters bHI, bHINH?I correlation) and the BLA line number density predicted by our simulations are in remarkably good agreement with observations. BLAs arise in gas that is hotter, more highly ionized and more enriched than the gas giving rise to typical Lya forest absorbers. The majority of the BLAs arise in warm-hot [log?(T/?K) similar to 5] gas at low (log?? < 1.5) overdensities. On average, thermal broadening accounts for at least 60?per cent of the BLA linewidth, which in turn can be used as a rough indicator of the thermal state of the gas. Detectable BLAs account for only a small fraction of the true baryon content of the WHIM at low redshift. In order to detect the bulk of the mass in this gas phase, a sensitivity at least one order of magnitude better than achieved by current ultraviolet spectrographs is required. We argue that BLAs mostly trace gas that has been shock heated and enriched by outflows and that they therefore provide an important window on a poorly understood feedback process.}, language = {en} } @article{AmselemThevesBaeetal.2012, author = {Amselem, Gabriel and Theves, Matthias and Bae, Albert J. and Beta, Carsten and Bodenschatz, Eberhard}, title = {Control parameter description of eukaryotic chemotaxis}, series = {Physical review letters}, volume = {109}, journal = {Physical review letters}, number = {10}, publisher = {American Physical Society}, address = {College Park}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.109.108103}, pages = {5}, year = {2012}, abstract = {The chemotaxis of eukaryotic cells depends both on the average concentration of the chemoattractant and on the steepness of its gradient. For the social amoeba Dictyostelium discoideum, we test quantitatively the prediction by Ueda and Shibata [Biophys. J. 93, 11 (2007)] that the efficacy of chemotaxis depends on a single control parameter only, namely, the signal-to-noise ratio (SNR), determined by the stochastic fluctuations of (i) the binding of the chemoattractant molecule to the transmembrane receptor and (ii) the intracellular activation of the effector of the signaling cascade. For SNR less than or similar to 1, the theory captures the experimental findings well, while for larger SNR noise sources further downstream in the signaling pathway need to be taken into account.}, language = {en} } @article{RettigPohl2012, author = {Rettig, R. and Pohl, M.}, title = {The properties of non-thermal X-ray filaments in young supernova remnants}, series = {Astronomy and astrophysics : an international weekly journal}, volume = {545}, journal = {Astronomy and astrophysics : an international weekly journal}, number = {5}, publisher = {EDP Sciences}, address = {Les Ulis}, issn = {0004-6361}, doi = {10.1051/0004-6361/201219409}, pages = {9}, year = {2012}, abstract = {Context. Young supernova remnants (SNRs) exhibit narrow filaments of non-thermal X-ray emission whose widths can be limited either by electron energy losses or damping of the magnetic field. Aims. We want to investigate whether or not different models of these filaments can be observationally tested. Methods. Using observational parameters of four historical remnants, we calculated the filament profiles and compared the spectra of the filaments with those of the total non-thermal emission. For that purpose, we solved a one-dimensional stationary transport equation for the isotropic differential number density of the electrons. Results. We find that the difference between the spectra of filament and total non-thermal emission above 1 keV is more pronounced in the damping model than in the energy-loss model. Conclusions. A considerable damping of the magnetic field can result in an observable difference between the spectra of filament and total non-thermal emission, thus potentially permitting an observational discrimination between the energy-loss model and the damping model of the X-ray filaments.}, language = {en} } @article{ThomasMatuschekGrima2012, author = {Thomas, Philipp and Matuschek, Hannes and Grima, Ramon}, title = {Intrinsic noise analyzer A software package for the exploration of stochastic biochemical kinetics using the system size expansion}, series = {PLoS one}, volume = {7}, journal = {PLoS one}, number = {6}, publisher = {PLoS}, address = {San Fransisco}, issn = {1932-6203}, doi = {10.1371/journal.pone.0038518}, pages = {20}, year = {2012}, abstract = {The accepted stochastic descriptions of biochemical dynamics under well-mixed conditions are given by the Chemical Master Equation and the Stochastic Simulation Algorithm, which are equivalent. The latter is a Monte-Carlo method, which, despite enjoying broad availability in a large number of existing software packages, is computationally expensive due to the huge amounts of ensemble averaging required for obtaining accurate statistical information. The former is a set of coupled differential-difference equations for the probability of the system being in any one of the possible mesoscopic states; these equations are typically computationally intractable because of the inherently large state space. Here we introduce the software package intrinsic Noise Analyzer (iNA), which allows for systematic analysis of stochastic biochemical kinetics by means of van Kampen's system size expansion of the Chemical Master Equation. iNA is platform independent and supports the popular SBML format natively. The present implementation is the first to adopt a complementary approach that combines state-of-the-art analysis tools using the computer algebra system Ginac with traditional methods of stochastic simulation. iNA integrates two approximation methods based on the system size expansion, the Linear Noise Approximation and effective mesoscopic rate equations, which to-date have not been available to non-expert users, into an easy-to-use graphical user interface. In particular, the present methods allow for quick approximate analysis of time-dependent mean concentrations, variances, covariances and correlations coefficients, which typically outperforms stochastic simulations. These analytical tools are complemented by automated multi-core stochastic simulations with direct statistical evaluation and visualization. We showcase iNA's performance by using it to explore the stochastic properties of cooperative and non-cooperative enzyme kinetics and a gene network associated with circadian rhythms. The software iNA is freely available as executable binaries for Linux, MacOSX and Microsoft Windows, as well as the full source code under an open source license.}, language = {en} } @article{MenzelPuhlmannHeueretal.2012, author = {Menzel, Ralf and Puhlmann, Dirk and Heuer, Axel and Schleich, Wolfgang P.}, title = {Wave-particle dualism and complementarity unraveled by a different mode}, series = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {109}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, number = {24}, publisher = {National Acad. of Sciences}, address = {Washington}, issn = {0027-8424}, doi = {10.1073/pnas.1201271109}, pages = {9314 -- 9319}, year = {2012}, abstract = {The precise knowledge of one of two complementary experimental outcomes prevents us from obtaining complete information about the other one. This formulation of Niels Bohr's principle of complementarity when applied to the paradigm of wave-particle dualism-that is, to Young's double-slit experiment-implies that the information about the slit through which a quantum particle has passed erases interference. In the present paper we report a double-slit experiment using two photons created by spontaneous parametric down-conversion where we observe interference in the signal photon despite the fact that we have located it in one of the slits due to its entanglement with the idler photon. This surprising aspect of complementarity comes to light by our special choice of the TEM01 pump mode. According to quantum field theory the signal photon is then in a coherent superposition of two distinct wave vectors giving rise to interference fringes analogous to two mechanical slits.}, language = {en} } @article{OhligerEisert2012, author = {Ohliger, M. and Eisert, J.}, title = {Efficient measurement-based quantum computing with continuous-variable systems}, series = {Physical review : A, Atomic, molecular, and optical physics}, volume = {85}, journal = {Physical review : A, Atomic, molecular, and optical physics}, number = {6}, publisher = {American Physical Society}, address = {College Park}, issn = {1050-2947}, doi = {10.1103/PhysRevA.85.062318}, pages = {12}, year = {2012}, abstract = {We present strictly efficient schemes for scalable measurement-based quantum computing using continuous-variable systems: These schemes are based on suitable non-Gaussian resource states, ones that can be prepared using interactions of light with matter systems or even purely optically. Merely Gaussian measurements such as optical homodyning as well as photon counting measurements are required, on individual sites. These schemes overcome limitations posed by Gaussian cluster states, which are known not to be universal for quantum computations of unbounded length, unless one is willing to scale the degree of squeezing with the total system size. We establish a framework derived from tensor networks and matrix product states with infinite physical dimension and finite auxiliary dimension general enough to provide a framework for such schemes. Since in the discussed schemes the logical encoding is finite dimensional, tools of error correction are applicable. We also identify some further limitations for any continuous-variable computing scheme from which one can argue that no substantially easier ways of continuous-variable measurement-based computing than the presented one can exist.}, 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{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{BarthelKliesch2012, author = {Barthel, Thomas and Kliesch, Martin}, title = {Quasilocality and efficient simulation of Markovian Quantum Dynamics}, series = {Physical review letters}, volume = {108}, journal = {Physical review letters}, number = {23}, publisher = {American Physical Society}, address = {College Park}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.108.230504}, pages = {5}, year = {2012}, abstract = {We consider open many-body systems governed by a time-dependent quantum master equation with short-range interactions. With a generalized Lieb-Robinson bound, we show that the evolution in this very generic framework is quasilocal; i.e., the evolution of observables can be approximated by implementing the dynamics only in a vicinity of the observables' support. The precision increases exponentially with the diameter of the considered subsystem. Hence, time evolution can be simulated on classical computers with a cost that is independent of the system size. Providing error bounds for Trotter decompositions, we conclude that the simulation on a quantum computer is additionally efficient in time. For experiments and simulations in the Schrodinger picture, our result can be used to rigorously bound finite-size effects.}, language = {en} } @article{BenBekhtiWinkelRichteretal.2012, author = {Ben Bekhti, Nadya and Winkel, B. and Richter, P. and Kerp, J. and Klein, U. and Murphy, M. T.}, title = {An absorption-selected survey of neutral gas in the Milky Way halo New results based on a large sample of Ca II, Na I, and H I spectra towards QSOs}, series = {Astronomy and astrophysics : an international weekly journal}, volume = {542}, journal = {Astronomy and astrophysics : an international weekly journal}, number = {2}, publisher = {EDP Sciences}, address = {Les Ulis}, issn = {0004-6361}, doi = {10.1051/0004-6361/201118673}, pages = {17}, year = {2012}, abstract = {Aims. We aim at analysing systematically the distribution and physical properties of neutral and mildly ionised gas in the Milky Way halo, based on a large absorption-selected data set. Methods. Multi-wavelength studies were performed combining optical absorption line data of Ca II and Na I with follow-up H I 21-cm emission line observations along 408 sight lines towards low-and high-redshift QSOs. We made use of archival optical spectra obtained with UVES/VLT. H I data were extracted from the Effelsberg-Bonn H I survey and the Galactic All-Sky survey. For selected sight lines we obtained deeper follow-up observations using the Effelsberg 100-m telescope. Results. Ca II (Na I) halo absorbers at intermediate and high radial velocities are present in 40-55\% (20-35\%) of the sightlines, depending on the column density threshold chosen. Many halo absorbers show multi-component absorption lines, indicating the presence of sub-structure. In 65\% of the cases, absorption is associated with H I 21-cm emission. The Ca II (Na I) column density distribution function follows a power-law with a slope of beta approximate to -2.2 (-1.4). Conclusions. Our absorption-selected survey confirms our previous results that the Milky Way halo is filled with a large number of neutral gas structures whose high column density tail represents the population of common H I high-and intermediate-velocity clouds seen in 21-cm observations. We find that Na I/Ca II column density ratios in the halo absorbers are typically smaller than those in the Milky Way disc, in the gas in the Magellanic Clouds, and in damped Lyman a systems. The small ratios (prominent in particular in high-velocity components) indicate a lower level of Ca depletion onto dust grains in Milky Way halo absorbers compared to gas in discs and inner regions of galaxies.}, language = {en} } @article{Berenstein2012, author = {Berenstein, Igal}, title = {Pattern formation in a reaction-diffusion-advection system with wave instability}, 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 = {10.1063/1.4704809}, pages = {4}, year = {2012}, abstract = {In this paper, we show by means of numerical simulations how new patterns can emerge in a system with wave instability when a unidirectional advective flow (plug flow) is added to the system. First, we introduce a three variable model with one activator and two inhibitors with similar kinetics to those of the Oregonator model of the Belousov-Zhabotinsky reaction. For this model, we explore the type of patterns that can be obtained without advection, and then explore the effect of different velocities of the advective flow for different patterns. We observe standing waves, and with flow there is a transition from out of phase oscillations between neighboring units to in-phase oscillations with a doubling in frequency. Also mixed and clustered states are generated at higher velocities of the advective flow. There is also a regime of "waving Turing patterns" (quasi-stationary structures that come close and separate periodically), where low advective flow is able to stabilize the stationary Turing pattern. At higher velocities, superposition and interaction of patterns are observed. For both types of patterns, at high velocities of the advective field, the known flow distributed oscillations are observed.}, 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{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{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{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{EiznerHorovitzHenkel2012, author = {Eizner, E. and Horovitz, Baruch and Henkel, Carsten}, title = {Van der waals-casimir-polder interaction of an atom with a composite surface}, series = {The European physical journal : D, Atomic, molecular, optical and plasma physics}, volume = {66}, journal = {The European physical journal : D, Atomic, molecular, optical and plasma physics}, number = {12}, publisher = {Springer}, address = {New York}, issn = {1434-6060}, doi = {10.1140/epjd/e2012-30294-x}, pages = {11}, year = {2012}, abstract = {We study the dispersion interaction of the van der Waals and Casimir-Polder (vdW-CP) type between a neutral atom and the surface of a conductor by allowing for nonlocal electrodynamics, i.e. electron diffusion. We consider two models: (i) bulk diffusion, and (ii) diffusion in a surface charge layer. In both cases, we find that the transition to a semiconductor as a function of the conductivity is continuous, unlike the case of a local model. The relevant parameter is the electric screening length and depends on the carrier diffusion constant. We find that for distances comparable to the screening length, vdW-CP data can distinguish between bulk and surface diffusion, hence it can be a sensitive probe for surface states.}, 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{BraunPikovskijMatiasetal.2012, author = {Braun, W. and Pikovskij, Arkadij and Matias, M. A. and Colet, P.}, title = {Global dynamics of oscillator populations under common noise}, series = {epl : a letters journal exploring the frontiers of physics}, volume = {99}, journal = {epl : a letters journal exploring the frontiers of physics}, number = {2}, publisher = {EDP Sciences}, address = {Mulhouse}, issn = {0295-5075}, doi = {10.1209/0295-5075/99/20006}, pages = {6}, year = {2012}, abstract = {Common noise acting on a population of identical oscillators can synchronize them. We develop a description of this process which is not limited to the states close to synchrony, but provides a global picture of the evolution of the ensembles. The theory is based on the Watanabe-Strogatz transformation, allowing us to obtain closed stochastic equations for the global variables. We show that at the initial stage, the order parameter grows linearly in time, while at the later stages the convergence to synchrony is exponentially fast. Furthermore, we extend the theory to nonidentical ensembles with the Lorentzian distribution of natural frequencies and determine the stationary values of the order parameter in dependence on driving noise and mismatch.}, language = {en} } @article{MulanskyPikovskij2012, author = {Mulansky, Mario and Pikovskij, Arkadij}, title = {Scaling properties of energy spreading in nonlinear Hamiltonian two-dimensional lattices}, series = {Physical review : E, Statistical, nonlinear and soft matter physics}, volume = {86}, 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.86.056214}, pages = {7}, year = {2012}, abstract = {In nonlinear disordered Hamiltonian lattices, where there are no propagating phonons, the spreading of energy is of subdiffusive nature. Recently, the universality class of the subdiffusive spreading according to the nonlinear diffusion equation (NDE) has been suggested and checked for one-dimensional lattices. Here, we apply this approach to two-dimensional strongly nonlinear lattices and find a nice agreement of the scaling predicted from the NDE with the spreading results from extensive numerical studies. Moreover, we show that the scaling works also for regular lattices with strongly nonlinear coupling, for which the scaling exponent is estimated analytically. This shows that the process of chaotic diffusion in such lattices does not require disorder.}, 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} } @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{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{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{ChechkinZaidLomholtetal.2012, author = {Chechkin, Aleksei V. and Zaid, Irwin M. and Lomholt, Michael A. and Sokolov, Igor M. and Metzler, Ralf}, title = {Bulk-mediated diffusion on a planar surface full solution}, series = {Physical review : E, Statistical, nonlinear and soft matter physics}, volume = {86}, journal = {Physical review : E, Statistical, nonlinear and soft matter physics}, number = {4}, publisher = {American Physical Society}, address = {College Park}, issn = {1539-3755}, doi = {10.1103/PhysRevE.86.041101}, pages = {11}, year = {2012}, abstract = {We consider the effective surface motion of a particle that intermittently unbinds from a planar surface and performs bulk excursions. Based on a random-walk approach, we derive the diffusion equations for surface and bulk diffusion including the surface-bulk coupling. From these exact dynamic equations, we analytically obtain the propagator of the effective surface motion. This approach allows us to deduce a superdiffusive, Cauchy-type behavior on the surface, together with exact cutoffs limiting the Cauchy form. Moreover, we study the long-time dynamics for the surface motion.}, language = {en} } @article{HuenemoerderOskinovaIgnaceetal.2012, author = {H{\"u}nem{\"o}rder, David P. and Oskinova, Lida and Ignace, Richard and Waldron, Wayne L. and Todt, Helge Tobias and Hamaguchi, Kenji and Kitamoto, Shunji}, title = {On the weak-wind problem in massive stars X-ray spectra reveal a massive hot wind in mu columbaea}, series = {The astrophysical journal : an international review of spectroscopy and astronomical physics ; Part 2, Letters}, volume = {756}, 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 = {10.1088/2041-8205/756/2/L34}, pages = {5}, year = {2012}, abstract = {mu Columbae is a prototypical weak-wind O star for which we have obtained a high-resolution X-ray spectrum with the Chandra LETG/ACIS instrument and a low-resolution spectrum with Suzaku. This allows us, for the first time, to investigate the role of X-rays on the wind structure in a bona fide weak-wind system and to determine whether there actually is a massive hot wind. The X-ray emission measure indicates that the outflow is an order of magnitude greater than that derived from UV lines and is commensurate with the nominal wind-luminosity relationship for O stars. Therefore, the "weak-wind problem"-identified from cool wind UV/optical spectra-is largely resolved by accounting for the hot wind seen in X-rays. From X-ray line profiles, Doppler shifts, and relative strengths, we find that this weak-wind star is typical of other late O dwarfs. The X-ray spectra do not suggest a magnetically confined plasma-the spectrum is soft and lines are broadened; Suzaku spectra confirm the lack of emission above 2 keV. Nor do the relative line shifts and widths suggest any wind decoupling by ions. The He-like triplets indicate that the bulk of the X-ray emission is formed rather close to the star, within five stellar radii. Our results challenge the idea that some OB stars are "weak-wind" stars that deviate from the standard wind-luminosity relationship. The wind is not weak, but it is hot and its bulk is only detectable in X-rays.}, language = {en} } @article{EvansHainichOskinovaetal.2012, author = {Evans, C. J. and Hainich, Rainer and Oskinova, Lida and Gallagher, J. S. and Chu, Y.-H. and Gruendl, R. A. and Hamann, Wolf-Rainer and Henault-Brunet, V. and Todt, Helge Tobias}, title = {A rare early-type star revealed in the wing of the small megellanic cloud}, series = {The astrophysical journal : an international review of spectroscopy and astronomical physics}, volume = {753}, 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/753/2/173}, pages = {10}, year = {2012}, abstract = {Sk 183 is the visually brightest star in the N90 nebula, a young star-forming region in the Wing of the Small Magellanic Cloud (SMC). We present new optical spectroscopy from the Very Large Telescope which reveals Sk 183 to be one of the most massive O-type stars in the SMC. Classified as an O3-type dwarf on the basis of its nitrogen spectrum, the star also displays broadened He I absorption, which suggests a later type. We propose that Sk 183 has a composite spectrum and that it is similar to another star in the SMC, MPG 324. This brings the number of rare O2- and O3-type stars known in the whole of the SMC to a mere four. We estimate physical parameters for Sk 183 from analysis of its spectrum. For a single-star model, we estimate an effective temperature of 46 +/- 2 kK, a low mass-loss rate of similar to 10(-7) M-circle dot yr(-1), and a spectroscopic mass of 46(-8)(+ 9) M-circle dot (for an adopted distance modulus of 18.7 mag to the young population in the SMC Wing). An illustrative binary model requires a slightly hotter temperature (similar to 47.5 kK) for the primary component. In either scenario, Sk 183 is the earliest-type star known in N90 and will therefore be the dominant source of hydrogen-ionizing photons. This suggests Sk 183 is the primary influence on the star formation along the inner edge of the nebula.}, 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{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{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{MalyarGorinStetsyuraetal.2012, author = {Malyar, I. V. and Gorin, D. A. and Stetsyura, S. V. and Santer, Svetlana}, title = {Effect of a nanodimensional polyethylenimine layer on current-voltage characteristics of hybrid structures based on single-crystal silicon}, series = {Journal of electronic materials}, volume = {41}, journal = {Journal of electronic materials}, number = {12}, publisher = {Springer}, address = {New York}, issn = {0361-5235}, doi = {10.1007/s11664-012-2266-4}, pages = {3427 -- 3435}, year = {2012}, abstract = {In this paper the study of the tunneling current-voltage (I-V) characteristics of silicon surfaces with n- and p-type conductivity as a function of roughness in the presence of an adsorbed insulating layer of polyethylenimine (PEI) is presented. A new approach is proposed for analysis of the tunnel current-voltage characteristics of a metal-insulator-semiconductor structure based on the combination of two models (Simmons and Schottky). Such joint analysis demonstrates the effect of surface states and evaluates changes in the band bending and electron affinity after the deposition of the polyelectrolyte layer on the semiconductor surface. As a result, we are able to differentiate between the equilibrium tunnel barrier (q phi (0)) and the barrier height (q phi (B)). It is shown that the deposition of the polymer leads to an increase of the equilibrium tunnel barrier by more than 250 meV, irrespective of the roughness and the conductivity type of the silicon substrate. The PEI deposition also leads to changes in the barrier height (less than 25 meV) that are smaller than the equilibrium tunnel barrier changes, indicating pinning of the Fermi level by the electron surface states that are energetically close to it. These surface states can trap charge carriers, a process leading to the formation of a depletion region and band bending on the semiconductor surface. Moreover, the change in the barrier height q Delta phi (B) depends on the conductivity type of the semiconductor, being positive for n-type and negative for p-type, in contrast to q Delta phi (0), which is positive for all substrates. The change is explained by capture of electrons preferably from the semiconductor space-charge region in the presence of a cationic polyelectrolyte, e.g., PEI.}, language = {en} } @article{ZakrevskyyRichterZakrevskaetal.2012, author = {Zakrevskyy, Yuriy and Richter, Marcel and Zakrevska, Svitlana and Lomadze, Nino and von Klitzing, Regine and Santer, Svetlana}, title = {Light-controlled reversible manipulation of microgel particle size using azobenzene-containing surfactant}, series = {Advanced functional materials}, volume = {22}, journal = {Advanced functional materials}, number = {23}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1616-301X}, doi = {10.1002/adfm.201200617}, pages = {5000 -- 5009}, year = {2012}, abstract = {The light-induced reversible switching of the swelling of microgel particles triggered by photo-isomerization and binding/unbinding of a photosensitive azobenzene-containing surfactant is reported. The interactions between the microgel (N-isopropylacrylamide, co-monomer: allyl acetic acid, crosslinker: N,N'-methylenebisacrylamide) and the surfactant are studied by UV-Vis spectroscopy, dynamic and electrophoretic light scattering measurements. Addition of the surfactant above a critical concentration leads to contraction/collapse of the microgel. UV light irradiation results in trans-cis isomerization of the azobenzene unit incorporated into the surfactant tail and causes an unbinding of the more hydrophilic cis isomer from the microgel and its reversible swelling. The reversible contraction can be realized by blue light irradiation that transfers the surfactant back to the more hydrophobic trans conformation, in which it binds to the microgel. The phase diagram of the surfactant-microgel interaction and transitions (aggregation, contraction, and precipitation) is constructed and allows prediction of changes in the system when the concentration of one or both components is varied. Remote and reversible switching between different states can be realized by either UV or visible light irradiation.}, language = {en} } @article{KoenigSanter2012, author = {K{\"o}nig, Tobias and Santer, Svetlana}, title = {Visualization of surface plasmon interference by imprinting intensity patterns on a photosensitive polymer}, series = {Nanotechnology}, volume = {23}, journal = {Nanotechnology}, number = {48}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {0957-4484}, doi = {10.1088/0957-4484/23/48/485304}, pages = {7}, year = {2012}, abstract = {We report on sub-wavelength structuring of photosensitive azo-containing polymer films induced by a surface plasmon interference intensity pattern. The two surface plasmon waves generated at neighboring nano-slits in the metal layer during irradiation interfere constructively, resulting in an intensity pattern with a periodicity three times smaller than the wavelength of the incoming light. The near field pattern interacts with the photosensitive polymer film placed above it, leading to a topography change which follows the intensity pattern exactly, resulting in the formation of surface relief gratings of a size below the diffraction limit. We analyze numerically and experimentally how the depth of the nano-slit alters the interference pattern of surface plasmons and find that the sub-wavelength patterning of the polymer surface could be optimized by modifying the geometry and the size of the nano-slit.}, language = {en} } @article{KoenigYadavalliSanter2012, author = {K{\"o}nig, Tobias and Yadavalli, Nataraja Sekhar and Santer, Svetlana}, title = {Near-Field induced reversible structuring of photosensitive polymer films Gold versus silver nano-antennas}, series = {Plasmonics}, volume = {7}, journal = {Plasmonics}, number = {3}, publisher = {Springer}, address = {New York}, issn = {1557-1955}, doi = {10.1007/s11468-012-9339-3}, pages = {535 -- 542}, year = {2012}, abstract = {We report on reversible structuring of photosensitive azo-containing polymer films induced by near-field intensity patterns emanating from illuminated nano-scale metal structures fabricated by colloidal lithography. Two different sets of these nano-antennas, consisting of either gold or silver, were investigated with respect to their ability to induce topography changes in a photosensitive polymer film placed above. Using in situ recorded atomic force microscopy micrographs of polymer topography changes during UV irradiation, we find that the response of the polymer film differs for the two metals at similar geometries of the metal nanostructures. The maximum topography change is stronger for Ag antennas as compared to the Au pattern, whereas the latter material revealed a pronounced splitting of topography maxima into two, a phenomenon less visible in the case of Ag. Finite difference time domain simulations of the electromagnetic field distribution in the vicinity of the metal structures confirm this remarkable observation. The local intensity is twice as large for the Ag as compared to the Au structures, and in each case, a splitting of the intensity pattern results, with a stronger modulation for Au. For both metals, the topography change was found to be reversible between a patterned and a flat by repeated change of irradiation conditions.}, 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{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{BanerjeeKroenerSaalfrank2012, author = {Banerjee, Shiladitya and Kr{\"o}ner, Dominik and Saalfrank, Peter}, title = {Resonance Raman and vibronic absorption spectra with Duschinsky rotation from a time-dependent perspective application to beta-carotene}, series = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr}, volume = {137}, journal = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr}, number = {22}, publisher = {American Institute of Physics}, address = {Melville}, issn = {0021-9606}, doi = {10.1063/1.4748147}, pages = {9}, year = {2012}, abstract = {The time-dependent approach to electronic spectroscopy, as popularized by Heller and co-workers in the 1980s, is applied here in conjunction with linear-response, time-dependent density functional theory to study vibronic absorption and resonance Raman spectra of beta-carotene, with and without a solvent. Two-state models, the harmonic and the Condon approximations are used in order to do so. A new code has been developed which includes excited state displacements, vibrational frequency shifts, and Duschinsky rotation, i.e., mode mixing, for both non-adiabatic spectroscopies. It is shown that Duschinsky rotation has a pronounced effect on the resonance Raman spectra of beta-carotene. In particular, it can explain a recently found anomalous behaviour of the so-called nu(1) peak in resonance Raman spectra [N. Tschirner, M. Schenderlein, K. Brose, E. Schlodder, M. A. Mroginski, C. Thomsen, and P. Hildebrandt, Phys. Chem. Chem. Phys. 11, 11471 (2009)], which shifts with the change in excitation wavelength.}, language = {en} } @article{FuechselTremblayKlamrothetal.2012, author = {F{\"u}chsel, Gernot and Tremblay, Jean Christophe and Klamroth, Tillmann and Saalfrank, Peter and Frischkorn, C.}, title = {Concept of a single temperature for highly nonequilibrium laser-induced hydrogen desorption from a ruthenium surface}, series = {Physical review letters}, volume = {109}, journal = {Physical review letters}, number = {9}, publisher = {American Physical Society}, address = {College Park}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.109.098303}, pages = {5}, year = {2012}, abstract = {Laser-induced condensed phase reactions are often interpreted as nonequilibrium phenomena that go beyond conventional thermodynamics. Here, we show by Langevin dynamics and for the example of femtosecond-laser desorption of hydrogen from a ruthenium surface that light adsorbates thermalize rapidly due to ultrafast energy redistribution after laser excitation. Despite the complex reaction mechanism involving hot electrons in the surface region, all desorption product properties are characterized by equilibrium distributions associated with a single, unique temperature. This represents an example of ultrahot chemistry on the subpicosecond time scale.}, 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{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{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} }