@article{AliuArchambaultArlenetal.2012, author = {Aliu, E. and Archambault, S. and Arlen, T. and Aune, T. and Beilicke, M. and Benbow, W. and Boettcher, Markus and Bouvier, A. and Bugaev, V. and Cannon, A. and Cesarini, A. and Ciupik, L. and Collins-Hughes, E. and Connolly, M. P. and Cui, W. and Dickherber, R. and Dumm, J. and Errando, M. and Falcone, A. and Federici, Stefania and Feng, Q. and Finley, J. P. and Finnegan, G. and Fortson, L. and Furniss, A. and Galante, N. and Gall, D. and Godambe, S. and Griffin, S. and Grube, J. and Gyuk, G. and Hanna, D. and Holder, J. and Huan, H. and Hughes, G. and Hui, C. M. and Imran, A. and Jameil, O. and Kaaret, P. and Karlsson, N. and Kertzman, M. and Kerr, J. and Khassen, Y. and Kieda, D. and Krawczynski, H. and Krennrich, F. and Lang, M. J. and Lee, K. and Madhavan, A. S. 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 Pichel, A. and Pohl, Martin and Quinn, J. and Ragan, K. and Reynolds, P. T. and Roache, E. and Ruppel, J. and Saxon, D. B. and Schroedter, M. and Sembroski, G. H. and Sentuerk, G. D. and Smith, A. W. and Staszak, D. and Stroh, M. and Telezhinsky, Igor O. and Tesic, G. and Theiling, M. and Thibadeau, S. and Tsurusaki, K. and Varlotta, A. and Vassiliev, V. V. and Vivier, M. and Wakely, S. P. and Ward, J. E. and Weinstein, A. and Welsing, R. and Williams, D. A. and Zitzer, B.}, title = {Multiwavelength observations of the AGN 1ES 0414+009 with veritas, FERMI-LAT, SWIFT-XRT, AND MDM}, series = {The astrophysical journal : an international review of spectroscopy and astronomical physics}, volume = {755}, 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/755/2/118}, pages = {7}, year = {2012}, abstract = {We present observations of the BL Lac object 1ES 0414+009 in the >200 GeV gamma-ray band by the VERITAS array of Cherenkov telescopes. 1ES 0414+009 was observed by VERITAS between 2008 January and 2011 February, resulting in 56.2 hr of good quality pointed observations. These observations resulted in a detection of 822 events from the source corresponding to a statistical significance of 6.4 standard deviations (6.4 sigma) above the background. The source flux, showing no evidence for variability, is measured as (5.2 +/- 1.1(stat) +/- 2.6(sys)) x 10(-12) photons cm(-2) s(-1) above 200 GeV, equivalent to approximately 2\% of the Crab Nebula flux above this energy. The differential photon spectrum from 230 GeV to 850 GeV is well fit by a power law with a photon index of Gamma = 3.4 +/- 0.5(stat) +/- 0.3(sys) and a flux normalization of (1.6 +/- 0.3(stat) +/- 0.8(sys)) x 10(-11) photons cm(-2) s(-1) at 300 GeV. We also present multiwavelength results taken in the optical (MDM), x-ray (Swift-XRT), and GeV (Fermi-LAT) bands and use these results to construct a broadband spectral energy distribution (SED). Modeling of this SED indicates that homogenous one-zone leptonic scenarios are not adequate to describe emission from the system, with a lepto-hadronic model providing a better fit to the data.}, language = {en} } @article{AliuArchambaultArlenetal.2012, author = {Aliu, E. and Archambault, S. and Arlen, T. and Aune, T. and Beilicke, M. and Benbow, W. and Bouvier, A. and Bradbury, S. M. and Buckley, J. H. and Bugaev, V. and Byrum, K. and Cannon, A. and Cesarini, A. and Christiansen, J. L. and Ciupik, L. and Collins-Hughes, E. and Connolly, M. P. and Cui, W. and Decerprit, G. and Dickherber, R. and Dumm, J. and Errando, M. and Falcone, A. and Feng, Q. and Ferrer, F. and Finley, J. P. and Finnegan, G. and Fortson, L. and Furniss, A. and Galante, N. and Gall, D. and Godambe, S. and Griffin, S. and Grube, J. and Gyuk, G. and Hanna, D. and Holder, J. and Huan, H. and Hughes, G. and Humensky, T. B. and Kaaret, P. and Karlsson, N. and Kertzman, M. and Khassen, Y. and Kieda, D. and Krawczynski, H. and Krennrich, F. and Lee, K. and Madhavan, A. S. and Maier, G. and Majumdar, P. and McArthur, S. and McCann, A. and Moriarty, P. and Mukherjee, R. and Ong, R. A. and Orr, M. and Otte, A. N. and Park, N. and Perkins, J. S. and Pohl, Martin and Prokoph, H. and Quinn, J. and Ragan, K. and Reyes, L. C. and Reynolds, P. T. and Roache, E. and Rose, H. J. and Ruppel, J. and Saxon, D. B. and Schroedter, M. and Sembroski, G. H. and Sentuerk, G. D. and Skole, C. and Smith, A. W. and Staszak, D. and Telezhinsky, Igor O. and Tesic, G. and Theiling, M. and Thibadeau, S. and Tsurusaki, K. and Varlotta, A. and Vassiliev, V. V. and Vincent, S. and Vivier, M. and Wagner, R. G. and Wakely, S. P. and Ward, J. E. and Weekes, T. C. and Weinstein, A. and Weisgarber, T. and Williams, D. A. and Zitzer, B.}, title = {VERITAS deep observations of the dwarf spheroidal galaxy Segue 1}, series = {Physical review : D, Particles, fields, gravitation, and cosmology}, volume = {85}, journal = {Physical review : D, Particles, fields, gravitation, and cosmology}, number = {6}, publisher = {American Physical Society}, address = {College Park}, issn = {1550-7998}, doi = {10.1103/PhysRevD.85.062001}, pages = {12}, year = {2012}, abstract = {The VERITAS array of Cherenkov telescopes has carried out a deep observational program on the nearby dwarf spheroidal galaxy Segue 1. We report on the results of nearly 48 hours of good quality selected data, taken between January 2010 and May 2011. No significant gamma-ray emission is detected at the nominal position of Segue 1, and upper limits on the integrated flux are derived. According to recent studies, Segue 1 is the most dark matter-dominated dwarf spheroidal galaxy currently known. We derive stringent bounds on various annihilating and decaying dark matter particle models. The upper limits on the velocity-weighted annihilation cross-section are (95\%) (CL) less than or similar to 10(-23) cm(3) s(-1), improving our limits from previous observations of dwarf spheroidal galaxies by at least a factor of 2 for dark matter particle masses m(chi) greater than or similar to 300 GeV. The lower limits on the decay lifetime are at the level of tau(95\%) (CL) greater than or similar to 10(24) s. Finally, we address the interpretation of the cosmic ray lepton anomalies measured by ATIC and PAMELA in terms of dark matter annihilation, and show that the VERITAS observations of Segue 1 disfavor such a scenario.}, language = {en} } @article{AliuArchambaultArlenetal.2012, author = {Aliu, E. and Archambault, S. and Arlen, T. and Aune, T. and Beilicke, M. and Benbow, W. and Bouvier, A. and Bradbury, S. M. and Buckley, J. H. and Bugaev, V. and Byrum, K. and Cannon, A. and Cesarini, A. and Ciupik, L. and Collins-Hughes, E. and Connolly, M. P. and Cui, W. and Decerprit, G. and Dickherber, R. and Duke, C. and Dumm, J. and Dwarkadas, Vikram V. and Errando, M. and Falcone, A. and Feng, Q. and Finley, J. P. and Finnegan, G. and Fortson, L. and Furniss, A. and Galante, N. and Gall, D. and Godambe, S. and Griffin, S. and Grube, J. and Gyuk, G. and Hanna, D. and Holder, J. and Huan, H. and Hughes, G. and Humensky, T. B. and Kaaret, P. and Karlsson, N. and Kertzman, M. and Khassen, Y. and Kieda, D. and Krawczynski, H. and Krennrich, F. and Lang, M. J. and Lee, K. and Maier, G. and Majumdar, P. and McArthur, S. and McCann, A. and Millis, J. and Moriarty, P. and Mukherjee, R. and Nunez, P. D. and Ong, R. A. and Orr, M. and Otte, A. N. and Pandel, D. 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 Rose, H. J. and Ruppel, J. and Saxon, D. B. and Schroedter, M. and Sembroski, G. H. and Skole, C. and Smith, A. W. and Staszak, D. and Telezhinsky, Igor O. and Tesic, G. and Theiling, M. and Thibadeau, S. and Tsurusaki, K. and Tyler, J. and Varlotta, A. and Vincent, S. and Vivier, M. and Wakely, S. P. and Ward, J. E. and Weekes, T. C. and Weinstein, A. and Weisgarber, T. and Welsing, R. and Williams, D. A. and Zitzer, B.}, title = {Veritas observations of the nova in V407 CYGNI}, series = {The astrophysical journal : an international review of spectroscopy and astronomical physics}, volume = {754}, 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/754/1/77}, pages = {7}, year = {2012}, abstract = {We report on very high energy (E > 100 GeV) gamma-ray observations of V407 Cygni, a symbiotic binary that underwent a nova outburst producing 0.1-10 GeV gamma rays during 2010 March 10-26. Observations were made with the Very Energetic Radiation Imaging Telescope Array System during 2010 March 19-26 at relatively large zenith angles due to the position of V407 Cyg. An improved reconstruction technique for large zenith angle observations is presented and used to analyze the data. We do not detect V407 Cygni and place a differential upper limit on the flux at 1.6 TeV of 2.3 x 10(-12) erg cm(-2) s(-1) (at the 95\% confidence level). When considered jointly with data from Fermi-LAT, this result places limits on the acceleration of very high energy particles in the nova.}, language = {en} } @article{AliuArchambaultArlenetal.2012, author = {Aliu, E. and Archambault, S. and Arlen, T. and Aune, T. and Beilicke, M. and Benbow, W. and Bouvier, A. and 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{AliuArlenAuneetal.2012, author = {Aliu, E. and Arlen, T. and Aune, T. and Beilicke, M. and Benbow, W. and Bouvier, A. and Bradbury, S. M. and Buckley, J. H. and Bugaev, V. and Byrum, K. and Cannon, A. and Cesarini, A. and Ciupik, L. and Collins-Hughes, E. and Connolly, M. P. and Cui, W. and Dickherber, R. and Duke, C. and Errando, M. and Falcone, A. and Finley, J. P. and Finnegan, G. and Fortson, L. and Furniss, A. and Galante, N. and Gall, D. and Godambe, S. and Griffin, S. and Grube, J. and Guenette, R. and Gyuk, G. and Hanna, D. and Holder, J. and Huan, H. and Hughes, G. and Hui, C. M. and Humensky, T. B. and Imran, A. and Kaaret, P. and Karlsson, N. and Kertzman, M. and Kieda, D. and Krawczynski, H. and Krennrich, F. and Lang, M. J. and LeBohec, S. and Madhavan, A. S. and Maier, G. and Majumdar, P. and McArthur, S. and McCann, A. and Moriarty, P. and Mukherjee, R. and Nunez, P. D. and Ong, R. A. and Orr, M. and Otte, A. N. and Park, N. and Perkins, J. S. and Pichel, A. and Pohl, Martin and Prokoph, H. and Quinn, J. and Ragan, K. and Reyes, L. C. and Reynolds, P. T. and Roache, E. and Rose, H. J. and Ruppel, J. and Saxon, D. B. and Schroedter, M. and Sembroski, G. H. and Sentuerk, G. D. and Skole, C. and Staszak, D. and Tesic, G. and Theiling, M. and Thibadeau, S. and Tsurusaki, K. and Tyler, J. and Varlotta, A. and Vassiliev, V. V. and Vincent, S. and Vivier, M. and Wakely, S. P. and Ward, J. E. and Weekes, T. C. and Weinstein, A. and Weisgarber, T. and Williams, D. A. and Zitzer, B.}, title = {Veritas observations of day-scale flaring of M 87 in 2010 April}, series = {The astrophysical journal : an international review of spectroscopy and astronomical physics}, volume = {746}, journal = {The astrophysical journal : an international review of spectroscopy and astronomical physics}, number = {2}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {0004-637X}, doi = {10.1088/0004-637X/746/2/141}, pages = {7}, year = {2012}, abstract = {VERITAS has been monitoring the very-high-energy (VHE; > 100 GeV) gamma-ray activity of the radio galaxy M87 since 2007. During 2008, flaring activity on a timescale of a few days was observed with a peak flux of (0.70 +/- 0.16) x 10(-11) cm(-2) s(-1) at energies above 350 GeV. In 2010 April, VERITAS detected a flare from M 87 with peak flux of (2.71 +/- 0.68) x 10(-11) cm(-2) s(-1) for E > 350 GeV. The source was observed for six consecutive nights during the flare, resulting in a total of 21 hr of good-quality data. The most rapid flux variation occurred on the trailing edge of the flare with an exponential flux decay time of 0.90(-0.15)(+0.22) days. The shortest detected exponential rise time is three times as long, at 2.87(+1.65)(-0.99) days. The quality of the data sample is such that spectral analysis can be performed for three periods: rising flux, peak flux, and falling flux. The spectra obtained are consistent with power-law forms. The spectral index at the peak of the flare is equal to 2.19 +/- 0.07. There is some indication that the spectrum is softer in the falling phase of the flare than the peak phase, with a confidence level corresponding to 3.6 standard deviations. We discuss the implications of these results for the acceleration and cooling rates of VHE electrons in M 87 and the constraints they provide on the physical size of the emitting region.}, language = {en} } @article{AltafimAltafimQiuetal.2012, author = {Altafim, Ruy Alberto Pisani and Altafim, Ruy Alberto Pisani and Qiu, Xunlin and Raabe, Sebastian and Wirges, Werner and Basso, Heitor Cury and Gerhard, Reimund}, title = {Fluoropolymer piezoelectrets with tubular channels resonance behavior controlled by channel geometry}, series = {Applied physics : A, Materials science \& processing}, volume = {107}, journal = {Applied physics : A, Materials science \& processing}, number = {4}, publisher = {Springer}, address = {New York}, issn = {0947-8396}, doi = {10.1007/s00339-012-6848-z}, pages = {965 -- 970}, year = {2012}, abstract = {Ferro- or piezoelectrets are dielectric materials with two elastically very different macroscopic phases and electrically charged interfaces between them. One of the newer piezoelectret variants is a system of two fluoroethylenepropylene (FEP) films that are first laminated around a polytetrafluoroethylene (PTFE) template. Then, by removing the PTFE template, a two-layer FEP structure with open tubular channels is obtained. After electrical charging, the channels form easily deformable macroscopic electric dipoles whose changes under mechanical or electrical stress lead to significant direct or inverse piezoelectricity, respectively. Here, different PTFE templates are employed to generate channel geometries that vary in height or width. It is shown that the control of the channel geometry allows a direct adjustment of the resonance frequencies in the tubular-channel piezoelectrets. By combining several different channel widths in a single ferroelectret, it is possible to obtain multiple resonance peaks that may lead to a rather flat frequency-response region of the transducer material. A phenomenological relation between the resonance frequency and the geometrical parameters of a tubular channel is also presented. This relation may help to design piezoelectrets with a specific frequency response.}, language = {en} } @article{AltafimRychkovWirgesetal.2012, author = {Altafim, Ruy Alberto Pisani and Rychkov, Dmitry and Wirges, Werner and Gerhard, Reimund and Basso, Heitor Cury and Altafim, Ruy Alberto Pisani and Melzer, Martin}, title = {Laminated tubular-channel ferroelectret systems from low-density Polyethylene Films and from Fluoroethylene-propylene Copolymer Films - A comparison}, series = {IEEE transactions on dielectrics and electrical insulation}, volume = {19}, journal = {IEEE transactions on dielectrics and electrical insulation}, number = {4}, publisher = {Inst. of Electr. and Electronics Engineers}, address = {Piscataway}, issn = {1070-9878}, pages = {1116 -- 1123}, year = {2012}, abstract = {A template-based lamination technique for the manufacture of ferroelectrets from uniform electret films was recently reported. In the present work, this technique is used to prepare similar ferroelectret structures from low-density polyethylene (LDPE) films and from fluoro-ethylene-propylene (FEP) copolymer films. A comparative analysis of the pressure-, temperature-, and frequency-dependent piezoelectric properties has been performed on the two ferroelectret systems. It is observed that the FEP ferroelectrets exhibit better piezoelectric responses and are thermally more stable. The difference between the piezoelectric d(33) coefficients of the two ferroelectret systems is partially explained here by their different elastic moduli. The anti-resonance peaks of both structures have been investigated by means of dielectric resonance spectroscopy and electroacoustic sound-pressure measurements. A difference of more than 10 kHz is observed between the anti-resonance frequencies of the two ferroelectret systems.}, 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{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} } @phdthesis{Anguiano2012, author = {Anguiano, Borja}, title = {The age-metallicity-velocity relation in the nearby disk}, address = {Potsdam}, pages = {164 S.}, year = {2012}, language = {en} } @article{ArlenAuneBeilickeetal.2012, author = {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 Cannon, A. and Cesarini, A. and Ciupik, L. and Collins-Hughes, E. and Connolly, M. P. and Cui, W. and Dickherber, R. 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 Godambe, S. and Griffin, S. and Grube, J. and Gyuk, G. and Holder, J. and Huan, H. and Hughes, G. and Humensky, T. B. and Imran, A. and Kaaret, P. and Karlsson, N. and Kertzman, M. and Khassen, Y. and Kieda, D. and Krawczynski, H. and Krennrich, F. and Lee, K. and Madhavan, A. S. and Maier, G. and Majumdar, P. and McArthur, S. and McCann, A. and Moriarty, P. and Mukherjee, R. and 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, Martin and Prokoph, H. and Quinn, J. and Ragan, K. and Reyes, L. C. and Reynolds, P. T. and Roache, E. and Ruppel, J. and Saxon, D. B. and Schroedter, M. and Sembroski, G. H. and Skole, C. and Smith, A. W. and Telezhinsky, Igor O. and Tesic, G. and Theiling, M. and Thibadeau, S. and Tsurusaki, K. and Varlotta, A. and Vivier, M. and Wakely, S. P. and Ward, J. E. and Weinstein, A. and Welsing, R. and Williams, D. A. and Zitzer, B. and Pfrommer, C. and Pinzke, A.}, title = {Constraints on cosmic rays, magnetic fields, and dark matter fromgamma-ray observations of the coma cluster of galaxies with veritas and fermi}, series = {The astrophysical journal : an international review of spectroscopy and astronomical physics}, volume = {757}, 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/757/2/123}, pages = {14}, year = {2012}, abstract = {Observations of radio halos and relics in galaxy clusters indicate efficient electron acceleration. Protons should likewise be accelerated and, on account of weak energy losses, can accumulate, suggesting that clusters may also be sources of very high energy (VHE; E > 100 GeV) gamma-ray emission. We report here on VHE gamma-ray observations of the Coma galaxy cluster with the VERITAS array of imaging Cerenkov telescopes, with complementing Fermi Large Area Telescope observations at GeV energies. No significant gamma-ray emission from the Coma Cluster was detected. Integral flux upper limits at the 99\% confidence level were measured to be on the order of (2-5) x 10(-8) photonsm(-2) s(-1) (VERITAS, >220 GeV) and similar to 2 x 10(-6) photonsm(-2) s(-1) (Fermi, 1-3GeV), respectively. We use the gamma-ray upper limits to constrain cosmic rays (CRs) and magnetic fields in Coma. Using an analytical approach, the CR-to-thermal pressure ratio is constrained to be < 16\% from VERITAS data and <1.7\% from Fermi data (averaged within the virial radius). These upper limits are starting to constrain the CR physics in self-consistent cosmological cluster simulations and cap the maximum CR acceleration efficiency at structure formation shocks to be <50\%. Alternatively, this may argue for non-negligible CR transport processes such as CR streaming and diffusion into the outer cluster regions. Assuming that the radio-emitting electrons of the Coma halo result from hadronic CR interactions, the observations imply a lower limit on the central magnetic field in Coma of similar to(2-5.5) mu G, depending on the radial magnetic field profile and on the gamma-ray spectral index. Since these values are below those inferred by Faraday rotation measurements in Coma (for most of the parameter space), this renders the hadronic model a very plausible explanation of the Coma radio halo. Finally, since galaxy clusters are dark matter (DM) dominated, the VERITAS upper limits have been used to place constraints on the thermally averaged product of the total self-annihilation cross section and the relative velocity of the DM particles, .}, 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{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{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{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{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{Baushev2012, author = {Baushev, Anton N.}, title = {Interaction of clumpy dark matter with interstellar medium in astrophysical systems}, series = {Monthly notices of the Royal Astronomical Society}, volume = {420}, journal = {Monthly notices of the Royal Astronomical Society}, number = {1}, publisher = {Wiley-Blackwell}, address = {Malden}, issn = {0035-8711}, doi = {10.1111/j.1365-2966.2011.20067.x}, pages = {590 -- 595}, year = {2012}, abstract = {Contemporary cosmological conceptions suggest that the dark matter in haloes of galaxies and galaxy clusters has most likely a clumpy structure. If a stream of gas penetrates through it, a small-scale gravitational field created by the clumps disturbs the flow resulting in momentum exchange between the stream and the dark matter. In this article, we perform an analysis of this effect, based on the hierarchical halo model of the dark matter structure and Navarro-Frenk-White density profiles. We consider the clumps of various masses, from the smallest up to the highest ones M = 10(9) M circle dot. It has been found that in any event the effect grows with the mass of the clump: not only the drag force F acting on the clump but also its acceleration w = F/M increases. We discuss various astrophysical systems. The mechanism proved to be ineffective in the case of galaxy or galaxy cluster collisions. On the other hand, it played an important role during the process of galaxy formation. As a result, the dark matter should have formed a more compact, oblate and faster rotating substructure in the halo of our Galaxy. We have shown that this thick disc should be more clumpy than the halo. This fact is very important for the indirect detection experiments since it is the clumps that give the main contribution to the annihilation signal. Our calculations show that the mechanism of momentum exchange between the dark and baryon matter is ineffective on the outskirts of the galactic halo. It means that the clumps from there were not transported to the thick disc, and this region should be more clumpy than the halo on the average.}, language = {en} } @article{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{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 = {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{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{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{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} } @phdthesis{Berger2012, author = {Berger, Florian}, title = {Different modes of cooperative transport by molecular motors}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-60319}, school = {Universit{\"a}t Potsdam}, year = {2012}, abstract = {Cargo transport by molecular motors is ubiquitous in all eukaryotic cells and is typically driven cooperatively by several molecular motors, which may belong to one or several motor species like kinesin, dynein or myosin. These motor proteins transport cargos such as RNAs, protein complexes or organelles along filaments, from which they unbind after a finite run length. Understanding how these motors interact and how their movements are coordinated and regulated is a central and challenging problem in studies of intracellular transport. In this thesis, we describe a general theoretical framework for the analysis of such transport processes, which enables us to explain the behavior of intracellular cargos based on the transport properties of individual motors and their interactions. Motivated by recent in vitro experiments, we address two different modes of transport: unidirectional transport by two identical motors and cooperative transport by actively walking and passively diffusing motors. The case of cargo transport by two identical motors involves an elastic coupling between the motors that can reduce the motors' velocity and/or the binding time to the filament. We show that this elastic coupling leads, in general, to four distinct transport regimes. In addition to a weak coupling regime, kinesin and dynein motors are found to exhibit a strong coupling and an enhanced unbinding regime, whereas myosin motors are predicted to attain a reduced velocity regime. All of these regimes, which we derive both by analytical calculations and by general time scale arguments, can be explored experimentally by varying the elastic coupling strength. In addition, using the time scale arguments, we explain why previous studies came to different conclusions about the effect and relevance of motor-motor interference. In this way, our theory provides a general and unifying framework for understanding the dynamical behavior of two elastically coupled molecular motors. The second mode of transport studied in this thesis is cargo transport by actively pulling and passively diffusing motors. Although these passive motors do not participate in active transport, they strongly enhance the overall cargo run length. When an active motor unbinds, the cargo is still tethered to the filament by the passive motors, giving the unbound motor the chance to rebind and continue its active walk. We develop a stochastic description for such cooperative behavior and explicitly derive the enhanced run length for a cargo transported by one actively pulling and one passively diffusing motor. We generalize our description to the case of several pulling and diffusing motors and find an exponential increase of the run length with the number of involved motors.}, language = {en} } @article{BergnerFrascaSciutoetal.2012, author = {Bergner, Andre and Frasca, M. and Sciuto, G. and Buscarino, A. and Ngamga, Eulalie Joelle and Fortuna, L. and Kurths, J{\"u}rgen}, title = {Remote synchronization in star networks}, series = {Physical review : E, Statistical, nonlinear and soft matter physics}, volume = {85}, journal = {Physical review : E, Statistical, nonlinear and soft matter physics}, number = {2}, publisher = {American Physical Society}, address = {College Park}, issn = {1539-3755}, doi = {10.1103/PhysRevE.85.026208}, pages = {7}, year = {2012}, abstract = {We study phase synchronization in a network motif with a starlike structure in which the central node's (the hub's) frequency is strongly detuned against the other peripheral nodes. We find numerically and experimentally a regime of remote synchronization (RS), where the peripheral nodes form a phase synchronized cluster, while the hub remains free with its own dynamics and serves just as a transmitter for the other nodes. We explain the mechanism for this RS by the existence of a free amplitude and also show that systems with a fixed or constant amplitude, such as the classic Kuramoto phase oscillator, are not able to generate this phenomenon. Further, we derive an analytic expression which supports our explanation of the mechanism.}, language = {en} } @phdthesis{Bidan2012, author = {Bidan, Cecile}, title = {Geometric control of tissue growth and organisation}, address = {Potsdam}, pages = {185 S.}, year = {2012}, language = {en} } @article{BodrovaSchmidtSpahnetal.2012, author = {Bodrova, Anna and Schmidt, J{\"u}rgen and Spahn, Frank and Brilliantov, Nikolai V.}, title = {Adhesion and collisional release of particles in dense planetary rings}, series = {Icarus : international journal of solar system studies}, volume = {218}, journal = {Icarus : international journal of solar system studies}, number = {1}, publisher = {Elsevier}, address = {San Diego}, issn = {0019-1035}, doi = {10.1016/j.icarus.2011.11.011}, pages = {60 -- 68}, year = {2012}, abstract = {We propose a simple theoretical model for aggregative and fragmentative collisions in Saturn's dense rings. In this model the ring matter consists of a bimodal size distribution: large (meter sized) boulders and a population of smaller particles (tens of centimeters down to dust). The small particles can adhesively stick to the boulders and can be released as debris in binary collisions of their carriers. To quantify the adhesion force we use the JKR theory (Johnson, K., Kendall, K., Roberts, A. [1971]. Proc. R. Soc. Lond. A 324, 301-313). The rates of release and adsorption of particles are calculated, depending on material parameters, sizes, and plausible velocity dispersions of carriers and debris particles. In steady state we obtain an expression for the amount of free debris relative to the fraction still attached to the carriers. In terms of this conceptually simple model a paucity of subcentimeter particles in Saturn's rings (French, R.G., Nicholson, P.D. [2000]. Icarus 145, 502-523; Marouf, E. et al. [2008]. Abstracts for "Saturn after Cassini-Huygens" Symposium, Imperial College London, UK, July 28 to August 1, p. 113) can be understood as a consequence of the increasing strength of adhesion (relative to inertial forces) for decreasing particle size. In this case particles smaller than a certain critical radius remain tightly attached to the surfaces of larger boulders, even when the boulders collide at their typical speed. Furthermore, we find that already a mildly increased velocity dispersion of the carrier-particles may significantly enhance the fraction of free debris particles, in this way increasing the optical depth of the system.}, language = {en} } @article{BojahrHerzogSchicketal.2012, author = {Bojahr, Andre and Herzog, Marc and Schick, Daniel and Vrejoiu, Ionela and Bargheer, Matias}, title = {Calibrated real-time detection of nonlinearly propagating strain waves}, series = {Physical review : B, Condensed matter and materials physics}, volume = {86}, journal = {Physical review : B, Condensed matter and materials physics}, number = {14}, publisher = {American Physical Society}, address = {College Park}, issn = {1098-0121}, doi = {10.1103/PhysRevB.86.144306}, pages = {5}, year = {2012}, abstract = {Epitaxially grown metallic oxide transducers support the generation of ultrashort strain pulses in SrTiO3 (STO) with high amplitudes up to 0.5\%. The strain amplitudes are calibrated by real-time measurements of the lattice deformation using ultrafast x-ray diffraction. We determine the speed at which the strain fronts propagate by broadband picosecond ultrasonics and conclude that, above a strain level of approx. 0.2\%, the compressive and tensile strain components travel at considerably different sound velocities, indicating nonlinear wave behavior. Simulations based on an anharmonic linear-chain model are in excellent accord with the experimental findings and show how the spectrum of coherent phonon modes changes with time.}, language = {en} } @article{BojahrSchickMaertenetal.2012, author = {Bojahr, Andre and Schick, Daniel and M{\"a}rten, Lena and Herzog, Marc and Vrejoiu, Ionela and von Korff Schmising, Clemens and Milne, Chris and Johnson, Steven Lee and Bargheer, Matias}, title = {Comparing the oscillation phase in optical pump-probe spectra to ultrafast x-ray diffraction in the metal-dielectric SrRuO3/SrTiO3 superlattice}, series = {Physical review : B, Condensed matter and materials physics}, volume = {85}, journal = {Physical review : B, Condensed matter and materials physics}, number = {22}, publisher = {American Physical Society}, address = {College Park}, issn = {1098-0121}, doi = {10.1103/PhysRevB.85.224302}, pages = {6}, year = {2012}, abstract = {We measured the ultrafast optical response of metal-dielectric superlattices by broadband all-optical pump-probe spectroscopy. The observed phase of the superlattice mode depends on the probe wavelength, making assignments of the excitation mechanism difficult. Ultrafast x-ray diffraction data reveal the true oscillation phase of the lattice which changes as a function of the excitation fluence. This result is confirmed by the fluence dependence of optical transients. We set up a linear chain model of the lattice dynamics and successfully simulated the broadband optical reflection by unit-cell resolved calculation of the strain-dependent dielectric functions of the constituting materials.}, 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{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} } @misc{BykovGehrelsKrawczynskietal.2012, author = {Bykov, Andrei and Gehrels, Neil and Krawczynski, Henric and Lemoine, Martin and Pelletier, Guy and Pohl, Martin}, title = {Particle acceleration in relativistic outflows}, series = {Space science reviews}, volume = {173}, journal = {Space science reviews}, number = {1-4}, publisher = {Springer}, address = {Dordrecht}, issn = {0038-6308}, doi = {10.1007/s11214-012-9896-y}, pages = {309 -- 339}, year = {2012}, abstract = {In this review we confront the current theoretical understanding of particle acceleration at relativistic outflows with recent observational results on various source classes thought to involve such outflows, e.g. gamma-ray bursts, active galactic nuclei, and pulsar wind nebulae. We highlight the possible contributions of these sources to ultra-high-energy cosmic rays.}, language = {en} } @article{BoedeckerHenkel2012, author = {B{\"o}decker, Geesche and Henkel, Carsten}, title = {Validity of the quantum regression theorem for resonance fluorescence in a photonic crystal}, series = {Annalen der Physik}, volume = {524}, journal = {Annalen der Physik}, number = {12}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {0003-3804}, doi = {10.1002/andp.201200135}, pages = {805 -- 813}, year = {2012}, abstract = {Correlation functions of a driven two-level system embedded in a photonic crystal are analyzed. The spectral density of the photonic bands near a gap makes this system non-Markovian. The equations of motion for two-time correlations are derived by two different methods, the quantum regression theorem and the fluctuation dissipation theorem, and found to be the same.}, 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{CaravelliHammaMarkopoulouetal.2012, author = {Caravelli, Francesco and Hamma, Alioscia and Markopoulou, Fotini and Riera, Arnau}, title = {Trapped surfaces and emergent curved space in the Bose-Hubbard model}, series = {Physical review : D, Particles, fields, gravitation, and cosmology}, volume = {85}, journal = {Physical review : D, Particles, fields, gravitation, and cosmology}, number = {4}, publisher = {American Physical Society}, address = {College Park}, issn = {1550-7998}, doi = {10.1103/PhysRevD.85.044046}, pages = {15}, year = {2012}, abstract = {A Bose-Hubbard model on a dynamical lattice was introduced in previous work as a spin system analogue of emergent geometry and gravity. Graphs with regions of high connectivity in the lattice were identified as candidate analogues of spacetime geometries that contain trapped surfaces. We carry out a detailed study of these systems and show explicitly that the highly connected subgraphs trap matter. We do this by solving the model in the limit of no back-reaction of the matter on the lattice, and for states with certain symmetries that are natural for our problem. We find that in this case the problem reduces to a one-dimensional Hubbard model on a lattice with variable vertex degree and multiple edges between the same two vertices. In addition, we obtain a (discrete) differential equation for the evolution of the probability density of particles which is closed in the classical regime. This is a wave equation in which the vertex degree is related to the local speed of propagation of probability. This allows an interpretation of the probability density of particles similar to that in analogue gravity systems: matter inside this analogue system sees a curved spacetime. We verify our analytic results by numerical simulations. Finally, we analyze the dependence of localization on a gradual, rather than abrupt, falloff of the vertex degree on the boundary of the highly connected region and find that matter is localized in and around that region.}, language = {en} } @article{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{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{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{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{CubittEisertWolf2012, author = {Cubitt, Toby S. and Eisert, Jens and Wolf, Michael M.}, title = {The complexity of relating quantum channels to master equations}, series = {Communications in mathematical physics}, volume = {310}, journal = {Communications in mathematical physics}, number = {2}, publisher = {Springer}, address = {New York}, issn = {0010-3616}, doi = {10.1007/s00220-011-1402-y}, pages = {383 -- 418}, year = {2012}, abstract = {Completely positive, trace preserving (CPT) maps and Lindblad master equations are both widely used to describe the dynamics of open quantum systems. The connection between these two descriptions is a classic topic in mathematical physics. One direction was solved by the now famous result due to Lindblad, Kossakowski, Gorini and Sudarshan, who gave a complete characterisation of the master equations that generate completely positive semi-groups. However, the other direction has remained open: given a CPT map, is there a Lindblad master equation that generates it (and if so, can we find its form)? This is sometimes known as the Markovianity problem. Physically, it is asking how one can deduce underlying physical processes from experimental observations. We give a complexity theoretic answer to this problem: it is NP-hard. We also give an explicit algorithm that reduces the problem to integer semi-definite programming, a well-known NP problem. Together, these results imply that resolving the question of which CPT maps can be generated by master equations is tantamount to solving P = NP: any efficiently computable criterion for Markovianity would imply P = NP; whereas a proof that P = NP would imply that our algorithm already gives an efficiently computable criterion. Thus, unless P does equal NP, there cannot exist any simple criterion for determining when a CPT map has a master equation description. However, we also show that if the system dimension is fixed (relevant for current quantum process tomography experiments), then our algorithm scales efficiently in the required precision, allowing an underlying Lindblad master equation to be determined efficiently from even a single snapshot in this case. Our work also leads to similar complexity-theoretic answers to a related long-standing open problem in probability theory.}, language = {en} } @article{deVeraBoettgerdelaTorreNoetzeletal.2012, author = {de Vera, Jean-Pierre Paul and B{\"o}ttger, Ute and de la Torre N{\"o}tzel, Rosa and Sanchez, Francisco J. and Grunow, Dana and Schmitz, Nicole and Lange, Caroline and H{\"u}bers, Heinz-Wilhelm and Billi, Daniela and Baque, Mickael and Rettberg, Petra and Rabbow, Elke and Reitz, G{\"u}nther and Berger, Thomas and M{\"o}ller, Ralf and Bohmeier, Maria and Horneck, Gerda and Westall, Frances and J{\"a}nchen, Jochen and Fritz, J{\"o}rg and Meyer, Cornelia and Onofri, Silvano and Selbmann, Laura and Zucconi, Laura and Kozyrovska, Natalia and Leya, Thomas and Foing, Bernard and Demets, Rene and Cockell, Charles S. and Bryce, Casey and Wagner, Dirk and Serrano, Paloma and Edwards, Howell G. M. and Joshi, Jasmin Radha and Huwe, Bj{\"o}rn and Ehrenfreund, Pascale and Elsaesser, Andreas and Ott, Sieglinde and Meessen, Joachim and Feyh, Nina and Szewzyk, Ulrich and Jaumann, Ralf and Spohn, Tilman}, title = {Supporting Mars exploration BIOMEX in Low Earth Orbit and further astrobiological studies on the Moon using Raman and PanCam technology}, series = {Planetary and space science}, volume = {74}, journal = {Planetary and space science}, number = {1}, publisher = {Elsevier}, address = {Oxford}, issn = {0032-0633}, doi = {10.1016/j.pss.2012.06.010}, pages = {103 -- 110}, year = {2012}, abstract = {The Low Earth Orbit (LEO) experiment Biology and Mars Experiment (BIOMEX) is an interdisciplinary and international space research project selected by ESA. The experiment will be accommodated on the space exposure facility EXPOSE-R2 on the International Space Station (ISS) and is foreseen to be launched in 2013. The prime objective of BIOMEX is to measure to what extent biomolecules, such as pigments and cellular components, are resistant to and able to maintain their stability under space and Mars-like conditions. The results of BIOMEX will be relevant for space proven biosignature definition and for building a biosignature data base (e.g. the proposed creation of an international Raman library). The library will be highly relevant for future space missions such as the search for life on Mars. The secondary scientific objective is to analyze to what extent terrestrial extremophiles are able to survive in space and to determine which interactions between biological samples and selected minerals (including terrestrial, Moon- and Mars analogs) can be observed under space and Mars-like conditions. In this context, the Moon will be an additional platform for performing similar experiments with negligible magnetic shielding and higher solar and galactic irradiation compared to LEO. Using the Moon as an additional astrobiological exposure platform to complement ongoing astrobiological LEO investigations could thus enhance the chances of detecting organic traces of life on Mars. We present a lunar lander mission with two related objectives: a lunar lander equipped with Raman and PanCam instruments which can analyze the lunar surface and survey an astrobiological exposure platform. This dual use of testing mission technology together with geo- and astrobiological analyses will significantly increase the science return, and support the human preparation objectives. It will provide knowledge about the Moon's surface itself and, in addition, monitor the stability of life-markers, such as cells, cell components and pigments, in an extraterrestrial environment with much closer radiation properties to the surface of Mars. The combination of a Raman data base of these data together with data from LEO and space simulation experiments, will lead to further progress on the analysis and interpretation of data that we will obtain from future Moon and Mars exploration missions.}, language = {en} } @phdthesis{Deneke2012, author = {Deneke, Carlus}, title = {Theory of mRNA degradation}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-61998}, school = {Universit{\"a}t Potsdam}, year = {2012}, abstract = {One of the central themes of biology is to understand how individual cells achieve a high fidelity in gene expression. Each cell needs to ensure accurate protein levels for its proper functioning and its capability to proliferate. Therefore, complex regulatory mechanisms have evolved in order to render the expression of each gene dependent on the expression level of (all) other genes. Regulation can occur at different stages within the framework of the central dogma of molecular biology. One very effective and relatively direct mechanism concerns the regulation of the stability of mRNAs. All organisms have evolved diverse and powerful mechanisms to achieve this. In order to better comprehend the regulation in living cells, biochemists have studied specific degradation mechanisms in detail. In addition to that, modern high-throughput techniques allow to obtain quantitative data on a global scale by parallel analysis of the decay patterns of many different mRNAs from different genes. In previous studies, the interpretation of these mRNA decay experiments relied on a simple theoretical description based on an exponential decay. However, this does not account for the complexity of the responsible mechanisms and, as a consequence, the exponential decay is often not in agreement with the experimental decay patterns. We have developed an improved and more general theory of mRNA degradation which provides a general framework of mRNA expression and allows describing specific degradation mechanisms. We have made an attempt to provide detailed models for the regulation in different organisms. In the yeast S. cerevisiae, different degradation pathways are known to compete and furthermore most of them rely on the biochemical modification of mRNA molecules. In bacteria such as E. coli, degradation proceeds primarily endonucleolytically, i.e. it is governed by the initial cleavage within the coding region. In addition, it is often coupled to the level of maturity and the size of the polysome of an mRNA. Both for S. cerevisiae and E. coli, our descriptions lead to a considerable improvement of the interpretation of experimental data. The general outcome is that the degradation of mRNA must be described by an age-dependent degradation rate, which can be interpreted as a consequence of molecular aging of mRNAs. Within our theory, we find adequate ways to address this much debated topic from a theoretical perspective. The improvements of the understanding of mRNA degradation can be readily applied to further comprehend the mRNA expression under different internal or environmental conditions such as after the induction of transcription or stress application. Also, the role of mRNA decay can be assessed in the context of translation and protein synthesis. The ultimate goal in understanding gene regulation mediated by mRNA stability will be to identify the relevance and biological function of different mechanisms. Once more quantitative data will become available, our description allows to elaborate the role of each mechanism by devising a suitable model.}, language = {en} } @phdthesis{Doumler2012, author = {Doumler, Timur}, title = {Constrained local universe simulations from galaxy peculliar velocities}, address = {Potsdam}, pages = {VI, 221 S.}, year = {2012}, language = {en} } @article{DraganovaRichterFechner2012, author = {Draganova, Nadya and Richter, Philipp and Fechner, Cora}, title = {High-resolution observations of two O VI absorbers at z approximate to 2 toward PKS 1448-232}, series = {Astronomy and astrophysics : an international weekly journal}, volume = {538}, journal = {Astronomy and astrophysics : an international weekly journal}, number = {1}, publisher = {EDP Sciences}, address = {Les Ulis}, issn = {0004-6361}, doi = {10.1051/0004-6361/201116730}, pages = {8}, year = {2012}, abstract = {To explore the ionization conditions in highly-ionized absorbers at high redshift, we study in detail two intervening O vi absorbers at z approximate to 2 toward the quasar PKS 1448-232, based on high (R approximate to 75 000) and intermediate (R approximate to 45 000) resolution optical VLT/UVES spectra. We find that both absorption systems are composed of several narrow subcomponents with typical Civ/O VI Doppler-parameters of b < 10 km s(-1). This implies that the gas temperatures are T < 10(5) K and that the absorbers are photoionized by the UV background. The system at z = 2.1098 represents a simple, isolated O VI absorber that has only two absorption components and is relatively metal-rich (Z similar to 0.6 solar). Ioinization modeling implies that the system is photoionized with O VI, C IV, and H I coexisting in the same gas phase. The second system at z = 2.1660 represents a complicated, multi-component absorption system with eight O VI components spanning almost 300 km s(-1) in radial velocity. The photoionization modeling implies that the metallicity is non-uniform and relatively low (<= 0.1 solar) and that the O VI absorption must arise in a gas phase that differs from that traced by C IV, C III, and H I. Our detailed study of the two O VI systems towards PKS 1448-232 shows that multi-phase, multi-component high-ion absorbers similar to the one at z = 2.1660 can be described by applying a detailed ionization modeling of the various subcomponents to obtain reliable measurements of the physical conditions and the metal abundances in the gas.}, language = {en} } @article{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{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{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} } @phdthesis{Eschenlohr2012, author = {Eschenlohr, Andrea}, title = {Element-resolved ultrafast magnetization dynamics in ferromagnetic alloys and multilayers}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-62846}, school = {Universit{\"a}t Potsdam}, year = {2012}, abstract = {The microscopic origin of ultrafast demagnetization, i.e. the quenching of the magnetization of a ferromagnetic metal on a sub-picosecond timescale after laser excitation, is still only incompletely understood, despite a large body of experimental and theoretical work performed since the discovery of the effect more than 15 years ago. Time- and element-resolved x-ray magnetic circular dichroism measurements can provide insight into the microscopic processes behind ultrafast demagnetization as well as its dependence on materials properties. Using the BESSY II Femtoslicing facility, a storage ring based source of 100 fs short soft x-ray pulses, ultrafast magnetization dynamics of ferromagnetic NiFe and GdTb alloys as well as a Au/Ni layered structure were investigated in laser pump - x-ray probe experiments. After laser excitation, the constituents of Ni50Fe50 and Ni80Fe20 exhibit distinctly different time constants of demagnetization, leading to decoupled dynamics, despite the strong exchange interaction that couples the Ni and Fe sublattices under equilibrium conditions. Furthermore, the time constants of demagnetization for Ni and Fe are different in Ni50Fe50 and Ni80Fe20, and also different from the values for the respective pure elements. These variations are explained by taking the magnetic moments of the Ni and Fe sublattices, which are changed from the pure element values due to alloying, as well as the strength of the intersublattice exchange interaction into account. GdTb exhibits demagnetization in two steps, typical for rare earths. The time constant of the second, slower magnetization decay was previously linked to the strength of spin-lattice coupling in pure Gd and Tb, with the stronger, direct spin-lattice coupling in Tb leading to a faster demagnetization. In GdTb, the demagnetization of Gd follows Tb on all timescales. This is due to the opening of an additional channel for the dissipation of spin angular momentum to the lattice, since Gd magnetic moments in the alloy are coupled via indirect exchange interaction to neighboring Tb magnetic moments, which are in turn strongly coupled to the lattice. Time-resolved measurements of the ultrafast demagnetization of a Ni layer buried under a Au cap layer, thick enough to absorb nearly all of the incident pump laser light, showed a somewhat slower but still sub-picosecond demagnetization of the buried Ni layer in Au/Ni compared to a Ni reference sample. Supported by simulations, I conclude that demagnetization can thus be induced by transport of hot electrons excited in the Au layer into the Ni layer, without the need for direct interaction between photons and spins.}, language = {en} } @article{EvansHainichOskinovaetal.2012, author = {Evans, C. J. and Hainich, Rainer and Oskinova, Lidia M. 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{FangHollaenderWirgesetal.2012, author = {Fang, Peng and Hollaender, Lars and Wirges, Werner and Gerhard, Reimund}, title = {Piezoelectric d(33) coefficients in foamed and layered polymer piezoelectrets from dynamic mechano-electrical experiments, electro-mechanical resonance spectroscopy and acoustic-transducer measurements}, series = {Measurement science and technology}, volume = {23}, journal = {Measurement science and technology}, number = {3}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {0957-0233}, doi = {10.1088/0957-0233/23/3/035604}, pages = {9}, year = {2012}, abstract = {Piezoelectrets are novel transducer materials which can be widely applied in sensors and actuators. Here, three techniques for determining piezoelectric d(33) coefficients of piezoelectrets are reviewed and compared. Two types of piezoelectrets, polyethylene-naphthalate (PEN) polymer-foam piezoelectrets and fluorinated ethylene-propylene (FEP) copolymer-layer piezoelectrets, have been prepared and measured by means of dynamic, resonance, and acoustical methods. The dynamic measurements show that the d(33) coefficient of PEN-foam samples clearly decreases with increasing stress, but 80\% of the initial d(33) can be retained after 1800 cycles of a continuous dynamic measurement in a mechanical fatigue test. The resonance measurements demonstrate that both PEN-foam and FEP-layer samples exhibit clear electro-mechanical resonances. PEN-foam samples show elastic moduli in the range from 1 to 12 MPa and d(33) values up to 500 pC N-1, while FEP-layer samples show homogeneous elastic moduli of about 0.3 MPa and d(33) values of about 280 pC N-1. The acoustical measurements reveal that both PEN-foam and FEP-layer samples exhibit stable frequency responses in the range from 5.7 to 20 kHz. In addition, d(33) coefficients obtained with different experimental methods are in good agreement with each other, which confirms the reliability of all three techniques.}, language = {en} } @phdthesis{FernandesGuimaraes2012, author = {Fernandes Guimar{\~a}es, Ana Helena}, title = {How does adhesion influence the small aggregates in Saturn's rings}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-61846}, school = {Universit{\"a}t Potsdam}, year = {2012}, abstract = {Particles in Saturn's main rings range in size from dust to even 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⋆ 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 meters, consistent with the maximum aggregate size observed in Saturn's rings of about 10m.}, language = {en} } @phdthesis{Florian2012, author = {Florian, Alexandra}, title = {Dynamic analysis of metabolism under circumstances of altererd photorespiratory flux}, address = {Potsdam}, pages = {138 S.}, year = {2012}, 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{FrischSchubertPreisetal.2012, author = {Frisch, Johannes and Schubert, Marcel and Preis, Eduard and Rabe, J{\"u}rgen P. and Neher, Dieter and Scherf, Ullrich and Koch, Norbert}, title = {Full electronic structure across a polymer heterojunction solar cell}, series = {Journal of materials chemistry}, volume = {22}, journal = {Journal of materials chemistry}, number = {10}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {0959-9428}, doi = {10.1039/c1jm14968g}, pages = {4418 -- 4424}, year = {2012}, abstract = {We correlate the morphology and energy level alignment of bilayer structures comprising the donor poly(3-hexylthiophene) (P3HT) and the acceptor polyfluorene copolymer poly(9,90dialklylfluorene-alt-4,7-bis(2,5-thiendiyl)-2,1,3-benzothiadiazole) (PFTBTT) with the performance of these bilayers in organic photovoltaic cells (OPVCs). The conducting polymer poly(ethylenedioxythiophene): poly (styrenesulfonate) (PEDT:PSS) was used as the bottom electrode and Ca as the top electrode. Ultraviolet photoelectron spectroscopy (UPS) revealed that notable interface dipoles occur at all interfaces across the OPVC structure, highlighting that vacuum level alignment cannot reliably be used to estimate the electronic properties for device design. Particularly the effective electrode work function values (after contact formation with the conjugated polymers) differ significantly from those of the pristine electrode materials. Chemical reactions between PEDT: PSS and P3HT on the one hand and Ca and PFTBTT on the other hand are identified as cause for the measured interface dipoles. The vacuum level shift between P3HT and PFTBTT is related to mutual energy level pinning at gap states. Annealing induced morphological changes at the P3HT/PFTBTT interface increased the efficiency of OPVCs, while the electronic structure was not affected by thermal treatment.}, language = {en} } @article{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{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{FuerstLevermann2012, author = {F{\"u}rst, Johannes J. and Levermann, Anders}, title = {A minimal model for wind- and mixing-driven overturning threshold behavior for both driving mechanisms}, series = {Climate dynamics : observational, theoretical and computational research on the climate system}, volume = {38}, journal = {Climate dynamics : observational, theoretical and computational research on the climate system}, number = {1-2}, publisher = {Springer}, address = {New York}, issn = {0930-7575}, doi = {10.1007/s00382-011-1003-7}, pages = {239 -- 260}, year = {2012}, abstract = {We present a minimal conceptual model for the Atlantic meridional overturning circulation which incorporates the advection of salinity and the basic dynamics of the oceanic pycnocline. Four tracer transport processes following Gnanadesikan in Science 283(5410):2077-2079, (1999) allow for a dynamical adjustment of the oceanic pycnocline which defines the vertical extent of a mid-latitudinal box. At the same time the model captures the salt-advection feedback (Stommel in Tellus 13(2):224-230, (1961)). Due to its simplicity the model can be solved analytically in the purely wind- and purely mixing-driven cases. We find the possibility of abrupt transition in response to surface freshwater forcing in both cases even though the circulations are very different in physics and geometry. This analytical approach also provides expressions for the critical freshwater input marking the change in the dynamics of the system. Our analysis shows that including the pycnocline dynamics in a salt-advection model causes a decrease in the freshwater sensitivity of its northern sinking up to a threshold at which the circulation breaks down. Compared to previous studies the model is restricted to the essential ingredients. Still, it exhibits a rich behavior which reaches beyond the scope of this study and might be used as a paradigm for the qualitative behaviour of the Atlantic overturning in the discussion of driving mechanisms.}, language = {en} } @article{GaalSchickHerzogetal.2012, author = {Gaal, P. and Schick, Daniel and Herzog, Marc and Bojahr, Andre and Shayduk, Roman and Goldshteyn, J. and Navirian, Hengameh A. and Leitenberger, Wolfram and Vrejoiu, Ionela and Khakhulin, D. and Wulff, M. and Bargheer, Matias}, title = {Time-domain sampling of x-ray pulses using an ultrafast sample response}, series = {Applied physics letters}, volume = {101}, journal = {Applied physics letters}, number = {24}, publisher = {American Institute of Physics}, address = {Melville}, issn = {0003-6951}, doi = {10.1063/1.4769828}, pages = {4}, year = {2012}, abstract = {We employ the ultrafast response of a 15.4 nm thin SrRuO3 layer grown epitaxially on a SrTiO3 substrate to perform time-domain sampling of an x-ray pulse emitted from a synchrotron storage ring. Excitation of the sample with an ultrashort laser pulse triggers coherent expansion and compression waves in the thin layer, which turn the diffraction efficiency on and off at a fixed Bragg angle during 5 ps. This is significantly shorter than the duration of the synchrotron x-ray pulse of 100 ps. Cross-correlation measurements of the ultrafast sample response and the synchrotron x-ray pulse allow to reconstruct the x-ray pulse shape.}, 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{GarzSandmannRadingetal.2012, author = {Garz, Andreas and Sandmann, Michael and Rading, Michael and Ramm, Sascha and Menzel, Ralf and Steup, Martin}, title = {Cell-to-cell diversity in a synchronized chlamydomonas culture as revealed by single-cell analyses}, series = {Biophysical journal}, volume = {103}, journal = {Biophysical journal}, number = {5}, publisher = {Cell Press}, address = {Cambridge}, issn = {0006-3495}, doi = {10.1016/j.bpj.2012.07.026}, pages = {1078 -- 1086}, year = {2012}, abstract = {In a synchronized photoautotrophic culture of Chlamydomonas reinhardtii, cell size, cell number, and the averaged starch content were determined throughout the light-dark cycle. For single-cell analyses, the relative cellular starch was quantified by measuring the second harmonic generation (SHG). In destained cells, amylopectin essentially represents the only biophotonic structure. As revealed by various validation procedures, SHG signal intensities are a reliable relative measure of the cellular starch content. During photosynthesis-driven starch biosynthesis, synchronized Chlamydomonas cells possess an unexpected cell-to-cell diversity both in size and starch content, but the starch-related heterogeneity largely exceeds that of size. The cellular volume, starch content, and amount of starch/cell volume obey lognormal distributions. Starch degradation was initiated by inhibiting the photosynthetic electron transport in illuminated cells or by darkening. Under both conditions, the averaged rate of starch degradation is almost constant, but it is higher in illuminated than in darkened cells. At the single-cell level, rates of starch degradation largely differ but are unrelated to the initial cellular starch content. A rate equation describing the cellular starch degradation}, language = {en} } @phdthesis{Ghani2012, author = {Ghani, Fatemeh}, title = {Nucleation and growth of unsubstituted metal phthalocyanine films from solution on planar substrates}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-64699}, school = {Universit{\"a}t Potsdam}, year = {2012}, abstract = {Organic solar cells (OSC) are interesting as low cost alternative to conventional solar cells. Unsubstituted Metal-phthalocyanines (Pc) are excellent electron donating molecules for heterojunction OSC. Usually organic solar cells with Pcs are produced by vapor deposition, although solution based deposition (like spin casting) is cheaper and offers more possibilities to control the structure of the film. With solution based deposition several parameters (like temperature, solvent and etc.) affect the self-organized structure formation via nucleation and growth. The reason why vapor deposition is typically used is the poor solubility of the metal-phthalocyanines in most common solvents. Furthermore the process of nucleation and growth of Pc aggregates from solution is not well understood. For preparation of Pc films from solution, it is necessary to find the appropriate solvents, assess the solution deposition techniques, such as dip coating, and spin casting. It is necessary to understand the nucleation and growth process for aggregation/precipitation and to use this knowledge to produce nanostructures appropriate for OSC. This is important because the nanostructure of the films determines their performance. In this thesis, optical absorption and the stability of 8 different unsubstituted metal Pc's were studied quantitatively in 28 different solvents. Among the several solution based deposited thin films produced based on this study, copper phthalocyanine (CuPc) dissolved in trifluoroacetic acid (TFA) is chosen as a model system for an in-depth study. CuPc has sufficient solubility and stability in TFA and upon solution processing forms appropriate structures for OSCs. CuPc molecules aggregate into layers of nanoribbons with a thickness of ~ 1 nm and an adjustable width and length. The morphology and the number of deposited layers in the thin films are controlled by different parameters, like temperature and solution concentration. Material properties of CuPc deposited from TFA are studied in detail via x-ray diffraction, UV-Vis and FT-IR spectroscopy. Atomic force microscopy was used to study the morphology of the dried film. The mechanism of the formation of CuPc nanoribbons from spin casted CuPc/TFA solution in ambient temperature is investigated and explained. The parameters (e.g. solution concentration profile) governing nucleation and growth are calculated based on the spin casting theory of a binary mixture of a nonvolatile solute and evaporative solvent. Based on this and intermolecular interactions between CuPc and substrate a nucleation and growth model is developed explaining the aggregation of CuPc in a supersaturated TFA solution. Finally, a solution processed thin film of CuPc is applied as a donor layer in a functioning bilayer heterojunction OSC and the influence of the structure on OSC performance is studied.}, language = {en} } @article{GrossNesmeVogtsetal.2012, author = {Gross, David and Nesme, V. and Vogts, H. and Werner, Reinhard F.}, title = {Index theory of one dimensional quantum walks and cellular automata}, series = {Communications in mathematical physics}, volume = {310}, journal = {Communications in mathematical physics}, number = {2}, publisher = {Springer}, address = {New York}, issn = {0010-3616}, doi = {10.1007/s00220-012-1423-1}, pages = {419 -- 454}, year = {2012}, abstract = {If a one-dimensional quantum lattice system is subject to one step of a reversible discrete-time dynamics, it is intuitive that as much "quantum information" as moves into any given block of cells from the left, has to exit that block to the right. For two types of such systems - namely quantum walks and cellular automata - we make this intuition precise by defining an index, a quantity that measures the "net flow of quantum information" through the system. The index supplies a complete characterization of two properties of the discrete dynamics. First, two systems S-1, S-2 can be "pieced together", in the sense that there is a system S which acts like S-1 in one region and like S-2 in some other region, if and only if S-1 and S-2 have the same index. Second, the index labels connected components of such systems: equality of the index is necessary and sufficient for the existence of a continuous deformation of S-1 into S-2. In the case of quantum walks, the index is integer-valued, whereas for cellular automata, it takes values in the group of positive rationals. In both cases, the map S bar right arrow. ind S is a group homomorphism if composition of the discrete dynamics is taken as the group law of the quantum systems. Systems with trivial index are precisely those which can be realized by partitioned unitaries, and the prototypes of systems with non-trivial index are shifts.}, language = {en} } @article{GuerreroRuizHamannetal.2012, author = {Guerrero, Mart{\´i}n A. and Ruiz, N. and Hamann, Wolf-Rainer and Chu, Y.-H. and Todt, Helge Tobias and Sch{\"o}nberner, Detlef and Oskinova, Lidia M. and Gr{\"u}ndl, R. A. and Steffen, M. and Blair, William P. and Toala, Jes{\´u}s Alberto}, title = {Rebirth of X-Ray emission from the born-again planetary Nebula A30}, series = {The astrophysical journal : an international review of spectroscopy and astronomical physics}, volume = {755}, 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/755/2/129}, pages = {15}, year = {2012}, abstract = {The planetary nebula A30 is believed to have undergone a very late thermal pulse resulting in the ejection of knots of hydrogen-poor material. Using multi-epoch Hubble Space Telescope images, we have detected the angular expansion of these knots and derived an age of 850(-150)(+280) yr. To investigate the spectral and spatial properties of the soft X-ray emission detected by ROSAT, we have obtained Chandra and XMM-Newton deep observations of A30. The X-ray emission from A30 can be separated into two components: a point source at the central star and diffuse emission associated with the hydrogen-poor knots and the cloverleaf structure inside the nebular shell. To help us assess the role of the current stellar wind in powering this X-ray emission, we have determined the stellar parameters and wind properties of the central star of A30 using a non-LTE model fit to its optical and UV spectra. The spatial distribution and spectral properties of the diffuse X-ray emission are highly suggestive that it is generated by the post-born-again and present fast stellar winds interacting with the hydrogen-poor ejecta of the born-again event. This emission can be attributed to shock-heated plasma, as the hydrogen-poor knots are ablated by the stellar winds, under which circumstances the efficient mass loading of the present fast stellar wind raises its density and damps its velocity to produce the observed diffuse soft X-rays. Charge transfer reactions between the ions of the stellar winds and material of the born-again ejecta have also been considered as a possible mechanism for the production of diffuse X-ray emission, and upper limits on the expected X-ray production by this mechanism have been derived. The origin of the X-ray emission from the central star of A30 is puzzling: shocks in the present fast stellar wind and photospheric emission can be ruled out, while the development of a new, compact hot bubble confining the fast stellar wind seems implausible.}, 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{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{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} } @misc{GvaramadzeKniazevMiroshnichenkoetal.2012, author = {Gvaramadze, V. V. and Kniazev, A. Y. and Miroshnichenko, A. S. and Berdnikov, Leonid N. and Langer, N. and Stringfellow, G. S. and Todt, Helge Tobias and Hamann, Wolf-Rainer and Grebel, E. K. and Buckley, D. and Crause, L. and Crawford, S. and Gulbis, A. and Hettlage, C. and Hooper, E. and Husser, T. -O. and Kotze, P. and Loaring, N. and Nordsieck, K. H. and O'Donoghue, D. and Pickering, T. and Potter, S. and Colmenero, E. Romero and Vaisanen, P. and Williams, T. and Wolf, M. and Reichart, D. E. and Ivarsen, K. M. and Haislip, J. B. and Nysewander, M. C. and LaCluyze, A. P.}, title = {Discovery of two new Galactic candidate luminous blue variables with Wide-field Infrared Survey Explorer}, series = {Monthly notices of the Royal Astronomical Society}, volume = {421}, journal = {Monthly notices of the Royal Astronomical Society}, number = {4}, publisher = {Oxford Univ. Press}, address = {Oxford}, issn = {0035-8711}, doi = {10.1111/j.1365-2966.2012.20556.x}, pages = {3325 -- 3337}, year = {2012}, abstract = {We report the discovery of two new Galactic candidate luminous blue variable (LBV) stars via detection of circular shells (typical of confirmed and candidate LBVs) and follow-up spectroscopy of their central stars. The shells were detected at 22 mu m in the archival data of the Mid-Infrared All Sky Survey carried out with the Wide-field Infrared Survey Explorer (WISE). Follow-up optical spectroscopy of the central stars of the shells conducted with the renewed Southern African Large Telescope (SALT) showed that their spectra are very similar to those of the well-known LBVs P Cygni and AG Car, and the recently discovered candidate LBV MN112, which implies the LBV classification for these stars as well. The LBV classification of both stars is supported by detection of their significant photometric variability: one of them brightened in the R and I bands by 0.68 +/- 0.10 and 0.61 +/- 0.04 mag, respectively, during the last 1318 years, while the second one (known as Hen 3-1383) varies its B, V, R, I and Ks brightnesses by similar or equal to 0.50.9 mag on time-scales from 10 d to decades. We also found significant changes in the spectrum of Hen 3-1383 on a time-scale of similar or equal to 3 months, which provides additional support for the LBV classification of this star. Further spectrophotometric monitoring of both stars is required to firmly prove their LBV status. We discuss a connection between the location of massive stars in the field and their fast rotation, and suggest that the LBV activity of the newly discovered candidate LBVs might be directly related to their possible runaway status.}, language = {en} } @article{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} } @phdthesis{Haakh2012, author = {Haakh, Harald Richard}, title = {Fluctuation-mediated interactions of atoms and surfaces on a mesoscopic scale}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-61819}, school = {Universit{\"a}t Potsdam}, year = {2012}, abstract = {Thermal and quantum fluctuations of the electromagnetic near field of atoms and macroscopic bodies play a key role in quantum electrodynamics (QED), as in the Lamb shift. They lead, e.g., to atomic level shifts, dispersion interactions (Van der Waals-Casimir-Polder interactions), and state broadening (Purcell effect) because the field is subject to boundary conditions. Such effects can be observed with high precision on the mesoscopic scale which can be accessed in micro-electro-mechanical systems (MEMS) and solid-state-based magnetic microtraps for cold atoms ('atom chips'). A quantum field theory of atoms (molecules) and photons is adapted to nonequilibrium situations. Atoms and photons are described as fully quantized while macroscopic bodies can be included in terms of classical reflection amplitudes, similar to the scattering approach of cavity QED. The formalism is applied to the study of nonequilibrium two-body potentials. We then investigate the impact of the material properties of metals on the electromagnetic surface noise, with applications to atomic trapping in atom-chip setups and quantum computing, and on the magnetic dipole contribution to the Van der Waals-Casimir-Polder potential in and out of thermal equilibrium. In both cases, the particular properties of superconductors are of high interest. Surface-mode contributions, which dominate the near-field fluctuations, are discussed in the context of the (partial) dynamic atomic dressing after a rapid change of a system parameter and in the Casimir interaction between two conducting plates, where nonequilibrium configurations can give rise to repulsion.}, language = {en} } @article{HaakhHenkel2012, author = {Haakh, Harald Richard and Henkel, Carsten}, title = {Magnetic near fields as a probe of charge transport in spatially dispersive conductors}, series = {The European physical journal : B, Condensed matter and complex systems}, volume = {85}, journal = {The European physical journal : B, Condensed matter and complex systems}, number = {1}, publisher = {Springer}, address = {New York}, issn = {1434-6028}, doi = {10.1140/epjb/e2011-20567-1}, pages = {12}, year = {2012}, abstract = {We calculate magnetic field fluctuations above a conductor with a nonlocal response (spatial dispersion) and consider a large range of distances. The cross-over from ballistic to diffusive charge transport leads to a reduced noise spectrum at distances below the electronic mean free path, as compared to a local description. We also find that the mean free path provides a lower limit to the correlation (coherence) length of the near field fluctuations. The short-distance behaviour is common to a wide range of materials, including semiconductors and superconductors. Our discussion is aimed at atom chip experiments where spin-flip transitions give access to material properties with mesoscopic spatial resolution. The results also hint at fundamental limits to the coherent operation of miniaturised atom traps and matter-wave interferometers.}, language = {en} } @article{HenaultBrunetOskinovaGuerreroetal.2012, author = {Henault-Brunet, V. and Oskinova, Lidia M. and Guerrero, Mart{\´i}n A. and Sun, W. and Chu, Y.-H. and Evans, C. J. and Gallagher, J. S. and Gruendl, R. A. and Reyes-Iturbide, J.}, title = {Discovery of a Be/X-ray pulsar binary and associated supernova remnant in the wing of the small magellanic cloud}, series = {Monthly notices of the Royal Astronomical Society}, volume = {420}, journal = {Monthly notices of the Royal Astronomical Society}, number = {1}, publisher = {Wiley-Blackwell}, address = {Malden}, issn = {0035-8711}, doi = {10.1111/j.1745-3933.2011.01183.x}, pages = {L13 -- L17}, year = {2012}, abstract = {We report on a new Be/X-ray pulsar binary located in the Wing of the Small Magellanic Cloud (SMC). The strong pulsed X-ray source was discovered with the Chandra and XMM-Newton X-ray observatories. The X-ray pulse period of 1062 s is consistently determined from both Chandra and XMM-Newton observations, revealing one of the slowest rotating X-ray pulsars known in the SMC. The optical counterpart of the X-ray source is the emission-line star 2dFS 3831. Its B0-0.5(III)e+ spectral type is determined from VLT-FLAMES and 2dF optical spectroscopy, establishing the system as a Be/X-ray binary (Be-XRB). The hard X-ray spectrum is well fitted by a power law with additional thermal and blackbody components, the latter reminiscent of persistent Be-XRBs. This system is the first evidence of a recent supernova in the low-density surroundings of NGC602. We detect a shell nebula around 2dFS 3831 in H alpha and [OIII] images and conclude that it is most likely a supernova remnant. If it is linked to the supernova explosion that created this new X-ray pulsar, its kinematic age of (2-4) x 10(4) yr provides a constraint on the age of the pulsar.}, language = {en} } @phdthesis{Herzog2012, author = {Herzog, Marc}, title = {Structural dynamics of photoexcited nanolayered perovskites studied by ultrafast x-ray diffraction}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-62632}, school = {Universit{\"a}t Potsdam}, year = {2012}, abstract = {This publication-based thesis represents a contribution to the active research field of ultrafast structural dynamics in laser-excited nanostructures. The investigation of such dynamics is mandatory for the understanding of the various physical processes on microscopic scales in complex materials which have great potentials for advances in many technological applications. I theoretically and experimentally examine the coherent, incoherent and anharmonic lattice dynamics of epitaxial metal-insulator heterostructures on timescales ranging from femtoseconds up to nanoseconds. To infer information on the transient dynamics in the photoexcited crystal lattices experimental techniques using ultrashort optical and x-ray pulses are employed. The experimental setups include table-top sources as well as large-scale facilities such as synchrotron sources. At the core of my work lies the development of a linear-chain model to simulate and analyze the photoexcited atomic-scale dynamics. The calculated strain fields are then used to simulate the optical and x-ray response of the considered thin films and multilayers in order to relate the experimental signatures to particular structural processes. This way one obtains insight into the rich lattice dynamics exhibiting coherent transport of vibrational energy from local excitations via delocalized phonon modes of the samples. The complex deformations in tailored multilayers are identified to give rise to highly nonlinear x-ray diffraction responses due to transient interference effects. The understanding of such effects and the ability to precisely calculate those are exploited for the design of novel ultrafast x-ray optics. In particular, I present several Phonon Bragg Switch concepts to efficiently generate ultrashort x-ray pulses for time-resolved structural investigations. By extension of the numerical models to include incoherent phonon propagation and anharmonic lattice potentials I present a new view on the fundamental research topics of nanoscale thermal transport and anharmonic phonon-phonon interactions such as nonlinear sound propagation and phonon damping. The former issue is exemplified by the time-resolved heat conduction from thin SrRuO3 films into a SrTiO3 substrate which exhibits an unexpectedly slow heat conductivity. Furthermore, I discuss various experiments which can be well reproduced by the versatile numerical models and thus evidence strong lattice anharmonicities in the perovskite oxide SrTiO3. The thesis also presents several advances of experimental techniques such as time-resolved phonon spectroscopy with optical and x-ray photons as well as concepts for the implementation of x-ray diffraction setups at standard synchrotron beamlines with largely improved time-resolution for investigations of ultrafast structural processes. This work forms the basis for ongoing research topics in complex oxide materials including electronic correlations and phase transitions related to the elastic, magnetic and polarization degrees of freedom.}, language = {en} } @article{HerzogBojahrGoldshteynetal.2012, author = {Herzog, Marc and Bojahr, Andre and Goldshteyn, J. and Leitenberger, Wolfram and Vrejoiu, I. and Khakhulin, D. and Wulff, M. and Shayduk, Roman and Gaal, P. and Bargheer, Matias}, title = {Detecting optically synthesized quasi-monochromatic sub-terahertz phonon wavepackets by ultrafast x-ray diffraction}, series = {Applied physics letters}, volume = {100}, journal = {Applied physics letters}, number = {9}, publisher = {American Institute of Physics}, address = {Melville}, issn = {0003-6951}, doi = {10.1063/1.3688492}, pages = {4}, year = {2012}, abstract = {We excite an epitaxial SrRuO3 thin film transducer by a pulse train of ultrashort laser pulses, launching coherent sound waves into the underlying SrTiO3 substrate. Synchrotron-based x-ray diffraction (XRD) data exhibiting separated sidebands to the substrate peak evidence the excitation of a quasi-monochromatic phonon wavepacket with sub-THz central frequency. The frequency and bandwidth of this sound pulse can be controlled by the optical pulse train. We compare the experimental data to combined lattice dynamics and dynamical XRD simulations to verify the coherent phonon dynamics. In addition, we observe a lifetime of 130 ps of such sub-THz phonons in accordance with the theory.}, language = {en} } @article{HerzogSchickGaaletal.2012, author = {Herzog, Marc and Schick, Daniel and Gaal, P. and Shayduk, Roman and von Korff Schmising, Clemens and Bargheer, Matias}, title = {Analysis of ultrafast X-ray diffraction data in a linear-chain model of the lattice dynamics}, series = {Applied physics : A, Materials science \& processing}, volume = {106}, journal = {Applied physics : A, Materials science \& processing}, number = {3}, publisher = {Springer}, address = {New York}, issn = {0947-8396}, doi = {10.1007/s00339-011-6719-z}, pages = {489 -- 499}, year = {2012}, abstract = {We present ultrafast X-ray diffraction (UXRD) experiments which sensitively probe impulsively excited acoustic phonons propagating in a SrRuO3/SrTiO3 superlattice and further into the substrate. These findings are discussed together with previous UXRD results (Herzog et al. in Appl. Phys. Lett. 96, 161906, 2010; Woerner et al. in Appl. Phys. A 96, 83, 2009; v. Korff Schmising in Phys. Rev. B 78, 060404(R), 2008 and in Appl. Phys. B 88, 1, 2007) using a normal-mode analysis of a linear-chain model of masses and springs, thus identifying them as linear-response phenomena. We point out the direct correspondence of calculated observables with X-ray signals. In this framework the complex lattice motion turns out to result from an interference of vibrational eigenmodes of the coupled system of nanolayers and substrate. UXRD in principle selectively measures the lattice motion occurring with a specific wavevector, however, each Bragg reflection only measures the amplitude of a delocalized phonon mode in a spatially localized region, determined by the nanocomposition of the sample or the extinction depth of X-rays. This leads to a decay of experimental signals although the excited modes survive.}, language = {en} } @article{HerzogSchickLeitenbergeretal.2012, author = {Herzog, Marc and Schick, Daniel and Leitenberger, Wolfram and Shayduk, Roman and van der Veen, Renske M. and Milne, Christopher J. and Johnson, Steven Lee and Vrejoiu, Ionela and Bargheer, Matias}, title = {Tailoring interference and nonlinear manipulation of femtosecond x-rays}, series = {New journal of physics : the open-access journal for physics}, volume = {14}, journal = {New journal of physics : the open-access journal for physics}, number = {1}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {1367-2630}, doi = {10.1088/1367-2630/14/1/013004}, pages = {9}, year = {2012}, abstract = {We present ultrafast x-ray diffraction (UXRD) experiments on different photoexcited oxide superlattices. All data are successfully simulated by dynamical x-ray diffraction calculations based on a microscopic model, that accounts for the linear response of phonons to the excitation laser pulse. Some Bragg reflections display a highly nonlinear strain dependence. The origin of linear and two distinct nonlinear response phenomena is discussed in a conceptually simpler model using the interference of envelope functions that describe the diffraction efficiency of the average constituent nanolayers. The combination of both models facilitates rapid and accurate simulations of UXRD experiments.}, language = {en} } @article{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{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{HuenemoerderOskinovaIgnaceetal.2012, author = {H{\"u}nem{\"o}rder, David P. and Oskinova, Lidia M. 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{IlnytskyiSaphiannikovaNeheretal.2012, author = {Ilnytskyi, Jaroslav M. and Saphiannikova, Marina and Neher, Dieter and Allen, Michael P.}, title = {Modelling elasticity and memory effects in liquid crystalline elastomers by molecular dynamics simulations}, series = {Soft matter}, volume = {8}, journal = {Soft matter}, number = {43}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1744-683X}, doi = {10.1039/c2sm26499d}, pages = {11123 -- 11134}, year = {2012}, abstract = {We performed molecular dynamics simulations of a liquid crystal elastomer of side-chain architecture. The network is formed from a melt of 28 molecules each having a backbone of 100 hydrocarbon monomers, to which 50 side chains are attached in a syndiotactic way. Crosslinking is performed in the smectic A phase. We observe an increase of the smectic-isotropic phase transition temperature of about 5 degrees as compared to the uncrosslinked melt. Memory effects in liquid crystalline order and in sample shape are well reproduced when the elastomer is driven through the smectic-isotropic transition. Above this transition, in the isotropic phase, the polydomain smectic phase is induced by a uniaxial load. Below the transition, in a monodomain smectic A phase, both experimentally observed effects of homogeneous director reorientation and stripe formation are reproduced when the sample is stretched along the director. When the load is applied perpendicularly to the director, the sample demonstrates reversible deformation with no change of liquid crystalline order, indicating elasticity of the two-dimensional network of polymer layers.}, language = {en} } @article{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} } @phdthesis{Jasiulek2012, author = {Jasiulek, Michael}, title = {Novel geometric methods in numerical relativity for isometric embeddings, quasi-local spin and the wave equation}, address = {Potsdam}, year = {2012}, language = {en} } @article{JeonMetzler2012, author = {Jeon, Jae-Hyung and Metzler, Ralf}, title = {Inequivalence of time and ensemble averages in ergodic systems: exponential versus power-law relaxation in confinement}, series = {Physical review : E, Statistical, nonlinear and soft matter physics}, volume = {85}, journal = {Physical review : E, Statistical, nonlinear and soft matter physics}, number = {2}, publisher = {American Physical Society}, address = {College Park}, issn = {1539-3755}, doi = {10.1103/PhysRevE.85.021147}, pages = {8}, year = {2012}, abstract = {Single-particle tracking has become a standard tool for the investigation of diffusive properties, especially in small systems such as biological cells. Usually the resulting time series are analyzed in terms of time averages over individual trajectories. Here we study confined normal as well as anomalous diffusion, modeled by fractional Brownian motion and the fractional Langevin equation, and show that even for such ergodic systems time-averaged quantities behave differently from their ensemble-averaged counterparts, irrespective of how long the measurement time becomes. Knowledge of the exact behavior of time averages is therefore fundamental for the proper physical interpretation of measured time series, in particular, for extraction of the relaxation time scale from data.}, language = {en} } @article{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{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{KalbitzGerhardTaylor2012, author = {Kalbitz, Rene and Gerhard, Reimund and Taylor, D. M.}, title = {Fixed negative interface charges compromise organic ferroelectric field-effect transistors}, series = {Organic electronics : physics, materials and applications}, volume = {13}, journal = {Organic electronics : physics, materials and applications}, number = {5}, publisher = {Elsevier}, address = {Amsterdam}, issn = {1566-1199}, doi = {10.1016/j.orgel.2012.01.034}, pages = {875 -- 884}, year = {2012}, abstract = {Capacitance-voltage (C-V) and current-voltage measurements have been undertaken on metal-ferroelectric-semiconductor capacitors and ferroelectric field-effect transistors (FeFETs) using the ferroelectric polymer poly(vinylidenefluoride-trifluoroethylene) as the gate insulator and poly(3-hexylthiophene) as the active semiconductor. C-V measurements, voltage-dependence of gate currents and FeFET transfer characteristics all confirm that ferroelectric polarization is stable and only reverses when positive/negative coercive fields are exceeded for the first time. The apparent instability observed following the application of depletion voltages arises from the development of a negative interfacial charge which more than compensates the ferroelectric-induced shift, resulting in a permanent shift in threshold voltage to positive values. Application of successive bipolar voltage sweeps to a diode-connected FeFET show that significant remanent polarization is only induced in an unpoled device when the coercive field is exceeded during the first application of accumulation voltages. This initial polarization and its growth during subsequent bipolar voltage sweeps is accompanied by the accumulation of the fixed interfacial negative charges which cause the positive turn on voltages seen in C-V and transfer characteristics. The origin of the negative charge is ascribed either to layers of irreversible ferroelectric domains at the insulator surface or to the drift to the insulator-semiconductor interface of F-ions produced electrolytically during the application of accumulation voltages.}, language = {en} } @article{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} } @phdthesis{Kappel2012, author = {Kappel, Marcel}, title = {Scattering effects in the sound wave propagation of instrument soundboards}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-62676}, school = {Universit{\"a}t Potsdam}, year = {2012}, abstract = {In the western hemisphere, the piano is one of the most important instruments. While its evolution lasted for more than three centuries, and the most important physical aspects have already been investigated, some parts in the characterization of the piano remain not well understood. Considering the pivotal piano soundboard, the effect of ribs mounted on the board exerted on the sound radiation and propagation in particular, is mostly neglected in the literature. The present investigation deals exactly with the sound wave propagation effects that emerge in the presence of an array of equally-distant mounted ribs at a soundboard. Solid-state theory proposes particular eigenmodes and -frequencies for such arrangements, which are comparable to single units in a crystal. Following this 'linear chain model' (LCM), differences in the frequency spectrum are observable as a distinct band structure. Also, the amplitudes of the modes are changed, due to differences of the damping factor. These scattering effects were not only investigated for a well-understood conceptional rectangular soundboard (multichord), but also for a genuine piano resonance board manufactured by the piano maker company 'C. Bechstein Pianofortefabrik'. To obtain the possibility to distinguish between the characterizing spectra both with and without mounted ribs, the typical assembly plan for the Bechstein instrument was specially customized. Spectral similarities and differences between both boards are found in terms of damping and tone. Furthermore, specially prepared minimal-invasive piezoelectric polymer sensors made from polyvinylidene fluoride (PVDF) were used to record solid-state vibrations of the investigated system. The essential calibration and characterization of these polymer sensors was performed by determining the electromechanical conversion, which is represented by the piezoelectric coefficient. Therefore, the robust 'sinusoidally varying external force' method was applied, where a dynamic force perpendicular to the sensor's surface, generates movable charge carriers. Crucial parameters were monitored, with the frequency response function as the most important one for acousticians. Along with conventional condenser microphones, the sound was measured as solid-state vibration as well as airborne wave. On this basis, statements can be made about emergence, propagation, and also the overall radiation of the generated modes of the vibrating system. Ultimately, these results acoustically characterize the entire system.}, language = {en} } @phdthesis{Karpitschka2012, author = {Karpitschka, Stefan}, title = {Dynamics of liquid interfaces with compositional gradients : sessile drop (non) coalescene and other effects}, address = {Potsdam}, pages = {135 S.}, year = {2012}, language = {en} } @phdthesis{Keller2012, author = {Keller, Corina}, title = {Coupled molecular motors : network representation \& dynamics of kinesin motor pairs}, address = {Potsdam}, pages = {109, XXX S.}, year = {2012}, 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} } @phdthesis{Kiel2012, author = {Kiel, Mareike}, title = {Static and ultrafast optical properties of nanolayered composites : gold nanoparticles embedded in polyelectrolytes}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-61823}, school = {Universit{\"a}t Potsdam}, year = {2012}, abstract = {In the course of this thesis gold nanoparticle/polyelectrolyte multilayer structures were prepared, characterized, and investigated according to their static and ultrafast optical properties. Using the dip-coating or spin-coating layer-by-layer deposition method, gold-nanoparticle layers were embedded in a polyelectrolyte environment with high structural perfection. Typical structures exhibit four repetition units, each consisting of one gold-particle layer and ten double layers of polyelectrolyte (cationic+anionic polyelectrolyte). The structures were characterized by X-ray reflectivity measurements, which reveal Bragg peaks up to the seventh order, evidencing the high stratication of the particle layers. In the same measurements pronounced Kiessig fringes were observed, which indicate a low global roughness of the samples. Atomic force microscopy (AFM) images veried this low roughness, which results from the high smoothing capabilities of polyelectrolyte layers. This smoothing effect facilitates the fabrication of stratified nanoparticle/polyelectrolyte multilayer structures, which were nicely illustrated in a transmission electron microscopy image. The samples' optical properties were investigated by static spectroscopic measurements in the visible and UV range. The measurements revealed a frequency shift of the reflectance and of the plasmon absorption band, depending on the thickness of the polyelectrolyte layers that cover a nanoparticle layer. When the covering layer becomes thicker than the particle interaction range, the absorption spectrum becomes independent of the polymer thickness. However, the reflectance spectrum continues shifting to lower frequencies (even for large thicknesses). The range of plasmon interaction was determined to be in the order of the particle diameter for 10 nm, 20 nm, and 150 nm particles. The transient broadband complex dielectric function of a multilayer structure was determined experimentally by ultrafast pump-probe spectroscopy. This was achieved by simultaneous measurements of the changes in the reflectance and transmittance of the excited sample over a broad spectral range. The changes in the real and imaginary parts of the dielectric function were directly deduced from the measured data by using a recursive formalism based on the Fresnel equations. This method can be applied to a broad range of nanoparticle systems where experimental data on the transient dielectric response are rare. This complete experimental approach serves as a test ground for modeling the dielectric function of a nanoparticle compound structure upon laser excitation.}, language = {en} } @article{KielKloetzerMitzscherlingetal.2012, author = {Kiel, Mareike and Kloetzer, Madlen and Mitzscherling, Steffen and Bargheer, Matias}, title = {Measuring the Range of Plasmonic Interaction}, series = {Langmuir}, volume = {28}, journal = {Langmuir}, number = {10}, publisher = {American Chemical Society}, address = {Washington}, issn = {0743-7463}, doi = {10.1021/la204577m}, pages = {4800 -- 4804}, year = {2012}, abstract = {When gold nanoparticles are covered with nanometric layers of transparent polyelectrolytes, the plasmon absorption spectrum A(lambda) increases by a factor of approximately three and shifts to the red. These modifications of dissipative experimental observables stop when the cover layer thickness approaches the particle diameter. Spectral modifications of dispersive parameters like the reflection R, however, keep changing with increasing cover layer thickness. The shift of the plasmon resonance caused by two interacting particle layers is studied as a function of the separating distance between the two layers. We discuss these observations in the context of an effective medium theory and conclude that it can only be applied for a layer thickness on the order of the particle diameter.}, language = {en} } @article{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} } @phdthesis{Klar2012, author = {Klar, Jochen}, title = {A detailed view of filaments and sheets of the warm-hot intergalactic medium}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-58038}, school = {Universit{\"a}t Potsdam}, year = {2012}, abstract = {In the context of cosmological structure formation sheets, filaments and eventually halos form due to gravitational instabilities. It is noteworthy, that at all times, the majority of the baryons in the universe does not reside in the dense halos but in the filaments and the sheets of the intergalactic medium. While at higher redshifts of z > 2, these baryons can be detected via the absorption of light (originating from more distant sources) by neutral hydrogen at temperatures of T ~ 10^4 K (the Lyman-alpha forest), at lower redshifts only about 20 \% can be found in this state. The remain (about 50 to 70 \% of the total baryons mass) is unaccounted for by observational means. Numerical simulations predict that these missing baryons could reside in the filaments and sheets of the cosmic web at high temperatures of T = 10^4.5 - 10^7 K, but only at low to intermediate densities, and constitutes the warm-hot intergalactic medium (WHIM). The high temperatures of the WHIM are caused by the formation of shocks and the subsequent shock-heating of the gas. This results in a high degree of ionization and renders the reliable detection of the WHIM a challenging task. Recent high-resolution hydrodynamical simulations indicate that, at redshifts of z ~ 2, filaments are able to provide very massive galaxies with a significant amount of cool gas at temperatures of T ~ 10^4 K. This could have an important impact on the star-formation in those galaxies. It is therefore of principle importance to investigate the particular hydro- and thermodynamical conditions of these large filament structures. Density and temperature profiles, and velocity fields, are expected to leave their special imprint on spectroscopic observations. A potential multiphase structure may act as tracer in observational studies of the WHIM. In the context of cold streams, it is important to explore the processes, which regulate the amount of gas transported by the streams. This includes the time evolution of filaments, as well as possible quenching mechanisms. In this context, the halo mass range in which cold stream accretion occurs is of particular interest. In order to address these questions, we perform particular hydrodynamical simulations of very high resolution, and investigate the formation and evolution of prototype structures representing the typical filaments and sheets of the WHIM. We start with a comprehensive study of the one-dimensional collapse of a sinusoidal density perturbation (pancake formation) and examine the influence of radiative cooling, heating due to an UV background, thermal conduction, and the effect of small-scale perturbations given by the cosmological power spectrum. We use a set of simulations, parametrized by the wave length of the initial perturbation L. For L ~ 2 Mpc/h the collapse leads to shock-confined structures. As a result of radiative cooling and of heating due to an UV background, a relatively cold and dense core forms. With increasing L the core becomes denser and more concentrated. Thermal conduction enhances this trend and may lead to an evaporation of the core at very large L ~ 30 Mpc/h. When extending our simulations into three dimensions, instead of a pancake structure, we obtain a configuration consisting of well-defined sheets, filaments, and a gaseous halo. For L > 4 Mpc/h filaments form, which are fully confined by an accretion shock. As with the one-dimensional pancakes, they exhibit an isothermal core. Thus, our results confirm a multiphase structure, which may generate particular spectral tracers. We find that, after its formation, the core becomes shielded against further infall of gas onto the filament, and its mass content decreases with time. In the vicinity of the halo, the filament's core can be attributed to the cold streams found in other studies. We show, that the basic structure of these cold streams exists from the very beginning of the collapse process. Further on, the cross section of the streams is constricted by the outwards moving accretion shock of the halo. Thermal conduction leads to a complete evaporation of the cold stream for L > 6 Mpc/h. This corresponds to halos with a total mass higher than M_halo = 10^13 M_sun, and predicts that in more massive halos star-formation can not be sustained by cold streams. Far away from the gaseous halo, the temperature gradients in the filament are not sufficiently strong for thermal conduction to be effective.}, language = {en} } @article{KliemToeroekThompson2012, author = {Kliem, Bernhard and T{\"o}r{\"o}k, Tibor and Thompson, William T.}, title = {A parametric study of erupting flux rope rotation modeling the "Cartwheel CME" on 9 April 2008}, series = {Solar physics : a journal for solar and solar-stellar research and the study of solar terrestrial physics}, volume = {281}, journal = {Solar physics : a journal for solar and solar-stellar research and the study of solar terrestrial physics}, number = {1}, publisher = {Springer}, address = {Dordrecht}, issn = {0038-0938}, doi = {10.1007/s11207-012-9990-z}, pages = {137 -- 166}, year = {2012}, abstract = {The rotation of erupting filaments in the solar corona is addressed through a parametric simulation study of unstable, rotating flux ropes in bipolar force-free initial equilibrium. The Lorentz force due to the external shear-field component and the relaxation of tension in the twisted field are the major contributors to the rotation in this model, while reconnection with the ambient field is of minor importance, due to the field's simple structure. In the low-beta corona, the rotation is not guided by the changing orientation of the vertical field component's polarity inversion line with height. The model yields strong initial rotations which saturate in the corona and differ qualitatively from the profile of rotation vs. height obtained in a recent simulation of an eruption without preexisting flux rope. Both major mechanisms writhe the flux rope axis, converting part of the initial twist helicity, and produce rotation profiles which, to a large part, are very similar within a range of shear-twist combinations. A difference lies in the tendency of twist-driven rotation to saturate at lower heights than shear-driven rotation. For parameters characteristic of the source regions of erupting filaments and coronal mass ejections, the shear field is found to be the dominant origin of rotations in the corona and to be required if the rotation reaches angles of order 90 degrees and higher; it dominates even if the twist exceeds the threshold of the helical kink instability. The contributions by shear and twist to the total rotation can be disentangled in the analysis of observations if the rotation and rise profiles are simultaneously compared with model calculations. The resulting twist estimate allows one to judge whether the helical kink instability occurred. This is demonstrated for the erupting prominence in the "Cartwheel CME" on 9 April 2008, which has shown a rotation of a parts per thousand aEuro parts per thousand 115(a similar to) up to a height of 1.5 R (aS (TM)) above the photosphere. Out of a range of initial equilibria which include strongly kink-unstable (twist I broken vertical bar=5 pi), weakly kink-unstable (I broken vertical bar=3.5 pi), and kink-stable (I broken vertical bar=2.5 pi) configurations, only the evolution of the weakly kink-unstable flux rope matches the observations in their entirety.}, 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{KunnusRajkovicSchrecketal.2012, author = {Kunnus, Kristjan and Rajkovic, Ivan and Schreck, Simon and Quevedo, Wilson and Eckert, Sebastian and Beye, Martin and Suljoti, Edlira and Weniger, Christian and Kalus, Christian and Gruebel, Sebastian and Scholz, Mirko and Nordlund, Dennis and Zhang, Wenkai and Hartsock, Robert W. and Gaffney, Kelly J. and Schlotter, William F. and Turner, Joshua J. and Kennedy, Brian and Hennies, Franz and Techert, Simone and Wernet, Philippe and F{\"o}hlisch, Alexander}, title = {A setup for resonant inelastic soft x-ray scattering on liquids at free electron laser light sources}, 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 = {12}, publisher = {American Institute of Physics}, address = {Melville}, issn = {0034-6748}, doi = {10.1063/1.4772685}, pages = {8}, year = {2012}, abstract = {We present a flexible and compact experimental setup that combines an in vacuum liquid jet with an x-ray emission spectrometer to enable static and femtosecond time-resolved resonant inelastic soft x-ray scattering (RIXS) measurements from liquids at free electron laser (FEL) light sources. We demonstrate the feasibility of this type of experiments with the measurements performed at the Linac Coherent Light Source FEL facility. At the FEL we observed changes in the RIXS spectra at high peak fluences which currently sets a limit to maximum attainable count rate at FELs. The setup presented here opens up new possibilities to study the structure and dynamics in liquids.}, 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{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{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} }