@article{TurnerPingelSteyrleuthneretal.2011, author = {Turner, Sarah T. and Pingel, Patrick and Steyrleuthner, Robert and Crossland, Edward J. W. and Ludwigs, Sabine and Neher, Dieter}, title = {Quantitative analysis of bulk heterojunction films using linear absorption spectroscopy and solar cell performance}, series = {Advanced functional materials}, volume = {21}, journal = {Advanced functional materials}, number = {24}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1616-301X}, doi = {10.1002/adfm.201101583}, pages = {4640 -- 4652}, year = {2011}, abstract = {A fundamental understanding of the relationship between the bulk morphology and device performance is required for the further development of bulk heterojunction organic solar cells. Here, non-optimized (chloroform cast) and nearly optimized (solvent-annealed o-dichlorobenzene cast) P3HT:PCBM blend films treated over a range of annealing temperatures are studied via optical and photovoltaic device measurements. Parameters related to the P3HT aggregate morphology in the blend are obtained through a recently established analytical model developed by F. C. Spano for the absorption of weakly interacting H-aggregates. Thermally induced changes are related to the glass transition range of the blend. In the chloroform prepared devices, the improvement in device efficiency upon annealing within the glass transition range can be attributed to the growth of P3HT aggregates, an overall increase in the percentage of chain crystallinity, and a concurrent increase in the hole mobilities. Films treated above the glass transition range show an increase in efficiency and fill factor not only associated with the change in chain crystallinity, but also with a decrease in the energetic disorder. On the other hand, the properties of the P3HT phase in the solvent-annealed o-dichlorobenzene cast blends are almost indistinguishable from those of the corresponding pristine P3HT layer and are only weakly affected by thermal annealing. Apparently, slow drying of the blend allows the P3HT chains to crystallize into large domains with low degrees of intra- and interchain disorder. This morphology appears to be most favorable for the efficient generation and extraction of charges.}, language = {en} } @article{TremblayMonturetSaalfrank2011, author = {Tremblay, Jean Christophe and Monturet, Serge and Saalfrank, Peter}, title = {The Effects of electron-hole pair coupling on the infrared laser-controlled vibrational excitation of NO on Au(111)}, series = {The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment \& general theory}, volume = {115}, journal = {The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment \& general theory}, number = {39}, publisher = {American Chemical Society}, address = {Washington}, issn = {1089-5639}, doi = {10.1021/jp205902k}, pages = {10698 -- 10707}, year = {2011}, abstract = {In this work, we present theoretical simulations of laser-driven vibrational control of NO adsorbed on a gold surface. Our goal is to tailor laser pulses to selectively excite specific modes and vibrational eigenstates, as well as to favor photodesorption of the adsorbed molecule. To this end, various control schemes and algorithms are applied. For adsorbates at metallic surfaces, the creation of electron hole pairs in the substrate is known to play a dominant role in the transfer of energy from the system to the surroundings. These nonadiabatic couplings are included perturbatively in our reduced density matrix simulations using a generalization of the state-resolved position-dependent anharmonic rate model we recently introduced. An extension of the reduced density matrix is also proposed to provide a sound model for photodesorption in dissipative systems.}, language = {en} } @article{TownsleyBroosCorcoranetal.2011, author = {Townsley, Leisa K. and Broos, Patrick S. and Corcoran, Michael F. and Feigelson, Eric D. and Gagne, Marc and Montmerle, Thierry and Oey, M. S. and Smith, Nathan and Garmire, Gordon P. and Getman, Konstantin V. and Povich, Matthew S. and Evans, Nancy Remage and Naze, Yael and Parkin, E. R. and Preibisch, Thomas and Wang, Junfeng and Wou, Scott J. and Chu, You-Hua and Cohen, David H. and Gruendl, Robert A. and Hamaguchi, Kenji and King, Robert R. and Mac Low, Mordecai-Mark and McCaughrean, Mark J. and Moffat, Anthony F. J. and Oskinova, Lida and Pittard, Julian M. and Stassun, Keivan G. and Ud-Doula, Asif and Walborn, Nolan R. and Waldron, Wayne L. and Churchwell, Ed and Nictiols, J. S. and Owocki, Stanley P. and Schulz, Norbert S.}, title = {An introduction to the chandra carina complex project}, series = {The astrophysical journal : an international review of spectroscopy and astronomical physics ; Supplement series}, volume = {194}, journal = {The astrophysical journal : an international review of spectroscopy and astronomical physics ; Supplement series}, number = {1}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {0067-0049}, doi = {10.1088/0067-0049/194/1/1}, pages = {28}, year = {2011}, abstract = {The Great Nebula in Carina provides an exceptional view into the violent massive star formation and feedback that typifies giant H II regions and starburst galaxies. We have mapped the Carina star-forming complex in X-rays, using archival Chandra data and a mosaic of 20 new 60 ks pointings using the Chandra X-ray Observatory's Advanced CCD Imaging Spectrometer, as a testbed for understanding recent and ongoing star formation and to probe Carina's regions of bright diffuse X-ray emission. This study has yielded a catalog of properties of > 14,000 X-ray point sources;> 9800 of them have multiwavelength counterparts. Using Chandra's unsurpassed X-ray spatial resolution, we have separated these point sources from the extensive, spatially-complex diffuse emission that pervades the region; X-ray properties of this diffuse emission suggest that it traces feedback from Carina's massive stars. In this introductory paper, we motivate the survey design, describe the Chandra observations, and present some simple results, providing a foundation for the 15 papers that follow in this special issue and that present detailed catalogs, methods, and science results.}, language = {en} } @misc{TodtPenaZuehlkeetal.2011, author = {Todt, Helge Tobias and Pe{\~n}a, Miriam and Z{\"u}hlke, Julia and Oskinova, Lida and Hamann, Wolf-Rainer and Gr{\"a}fener, G{\"o}tz}, title = {Weak emission line central stars of planetary nebulae}, series = {Planetary Nebulae: an Eye to the Future}, journal = {Planetary Nebulae: an Eye to the Future}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-413775}, pages = {2}, year = {2011}, abstract = {To understand the evolution and morphology of planetary nebulae, a detailed knowledge of their central stars is required. Central stars that exhibit emission lines in their spectra, indicating stellar mass-loss allow to study the evolution of planetary nebulae in action. Emission line central stars constitute about 10 \% of all central stars. Half of them are practically hydrogen-free Wolf-Rayet type central stars of the carbon sequence, [WC], that show strong emission lines of carbon and oxygen in their spectra. In this contribution we address the weak emission-lines central stars (wels). These stars are poorly analyzed and their hydrogen content is mostly unknown. We obtained optical spectra, that include the important Balmer lines of hydrogen, for four weak emission line central stars. We present the results of our analysis, provide spectral classification and discuss possible explanations for their formation and evolution.}, language = {en} } @phdthesis{Theilmann2011, author = {Theilmann, Florian}, title = {Die Kunst der Untersuchung : Essays zu einem erscheinungsorientierten Physikunterricht}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-56145}, school = {Universit{\"a}t Potsdam}, year = {2011}, abstract = {Die vorliegende Arbeit versammelt zwei einleitende Kapitel und zehn Essays, die sich als kritisch-konstruktive Beitr{\"a}ge zu einem "erlebenden Verstehen" (Buck) von Physik lesen lassen. Die traditionelle Anlage von Schulphysik zielt auf eine systematische Darstellung naturwissenschaftlichen Wissens, das dann an ausgew{\"a}hlten Beispielen angewendet wird: Schulexperimente beweisen die Aussagen der Systematik (oder machen sie wenigstens plausibel), ausgew{\"a}hlte Ph{\"a}nomene werden erkl{\"a}rt. In einem solchen Rahmen besteht jedoch leicht die Gefahr, den Bezug zur Lebenswirklichkeit oder den Interessen der Sch{\"u}ler zu verlieren. Diese Problematik ist seit mindestens 90 Jahren bekannt, didaktische Antworten - untersuchendes Lernen, Kontextualisierung, Sch{\"u}lerexperimente etc. - adressieren allerdings eher Symptome als Ursachen. Naturwissenschaft wird dadurch spannend, dass sie ein spezifisch investigatives Weltverh{\"a}ltnis stiftet: man m{\"u}sste gleichsam nicht Wissen, sondern "Fragen lernen" (und nat{\"u}rlich auch, wie Antworten gefunden werden...). Doch wie kann dergleichen auf dem Niveau von Schulphysik aussehen, was f{\"u}r einen theoretischen Rahmen kann es hier geben? In den gesammelten Arbeiten wird einigen dieser Spuren nachgegangen: Der Absage an das zu modellhafte Denken in der ph{\"a}nomenologischen Optik, der Abgrenzung formal-mathematischen Denkens gegen wirklichkeitsn{\"a}here Formen naturwissenschaftlicher Denkbewegungen und Evidenz, dem Potential alternativer Interpretationen von "Physikunterricht", der Frage nach dem "Verstehen" u.a. Dabei werden nicht nur Bez{\"u}ge zum modernen bildungstheoretischen Paradigma der Kompetenz sichtbar, sondern es wird auch versucht, eine ganze Reihe konkrete (schul-)physikalische Beispiele daf{\"u}r zu geben, was passiert, wenn nicht schon gewusste Antworten Thema werden, sondern Expeditionen, die sich der physischen Welt widmen: Die Schl{\"u}sselbegriffe des Fachs, die Methoden der Datenerhebung und Interpretation, die Such- und Denkbewegungen kommen dabei auf eine Weise zur Sprache, die sich nicht auf die Fachsystematik abst{\"u}tzen m{\"o}chte, sondern diese motivieren, konturieren und verst{\"a}ndlich machen will.}, language = {de} } @article{TepperGarciaRichterSchayeetal.2011, author = {Tepper-Garcia, Thorsten and Richter, Philipp and Schaye, Joop and Booth, C. M. and Vecchia, Claudio Dalla and Theuns, Tom and Wiersma, Robert P. C.}, title = {Absorption signatures of warm-hot gas at low redshift o vi}, series = {Monthly notices of the Royal Astronomical Society}, volume = {413}, journal = {Monthly notices of the Royal Astronomical Society}, number = {1}, publisher = {Wiley-Blackwell}, address = {Hoboken}, issn = {0035-8711}, doi = {10.1111/j.1365-2966.2010.18123.x}, pages = {190 -- 212}, year = {2011}, abstract = {We investigate the origin and physical properties of O vi absorbers at low redshift (z = 0.25) using a subset of cosmological, hydrodynamical simulations from the OverWhelmingly Large Simulations (OWLS) project. Intervening O vi absorbers are believed to trace shock-heated gas in the warm-hot intergalactic medium (WHIM) and may thus play a key role in the search for the missing baryons in the present-day Universe. When compared to observations, the predicted distributions of the different O vi line parameters (column density, Doppler parameter, rest equivalent width W-r) from our simulations exhibit a lack of strong O vi absorbers, a discrepancy that has also been found by Oppenheimer \& Dave. This suggests that physical processes on subgrid scales (e.g. turbulence) may strongly influence the observed properties of O vi systems. We find that the intervening O vi absorption arises mainly in highly metal enriched (10-1 < Z/Z(circle dot) less than or similar to 1) gas at typical overdensities of 1 < /<<>> less than or similar to 102. One-third of the O vi absorbers in our simulation are found to trace gas at temperatures T < 105 K, while the rest arises in gas at higher temperatures, most of them around T = 105.3 +/- 0.5 K. These temperatures are much higher than inferred by Oppenheimer \& Dave, probably because that work did not take the suppression of metal-line cooling by the photoionizing background radiation into account. While the O vi resides in a similar region of (, T)-space as much of the shock-heated baryonic matter, the vast majority of this gas has a lower metal content and does not give rise to detectable O vi absorption. As a consequence of the patchy metal distribution, O vi absorbers in our simulations trace only a very small fraction of the cosmic baryons (< 2 per cent) and the cosmic metals. Instead, these systems presumably trace previously shock-heated, metal-rich material from galactic winds that is now mixing with the ambient gas and cooling. The common approach of comparing O vi and H i column densities to estimate the physical conditions in intervening absorbers from QSO observations may be misleading, as most of the H i (and most of the gas mass) is not physically connected with the high-metallicity patches that give rise to the O vi absorption.}, language = {en} } @article{SunZhangXiaetal.2011, author = {Sun, Zhuanlan and Zhang, Xiaoqing and Xia, Zhongfu and Qiu, Xunlin and Wirges, Werner and Gerhard, Reimund and Zeng, Changchun and Zhang, Chuck and Wang, Ben}, title = {Polarization and piezoelectricity in polymer films with artificial void structure}, series = {Applied physics : A, Materials science \& processing}, volume = {105}, journal = {Applied physics : A, Materials science \& processing}, number = {1}, publisher = {Springer}, address = {New York}, issn = {0947-8396}, doi = {10.1007/s00339-011-6481-2}, pages = {197 -- 205}, year = {2011}, abstract = {Laminated polymer-film systems with well-defined void structures were prepared from fluoroethylenepropylene (FEP) and polytetrafluoroethylene (PTFE) layers. First the PTFE films were patterned and then fusion-bonded with the FEP films. The laminates were subjected to either corona or contact charging in order to obtain the desired piezoelectricity. The build-up of the "macro-dipoles" in the laminated films was studied by recording the electric hysteresis loops. The resulting electro-mechanical properties were investigated by means of dielectric resonance spectroscopy (DRS) and direct measurements of the stress-strain relationship. Moreover, the thermal stability of the piezoelectric d (33) coefficient was investigated at elevated temperatures and via thermally stimulated discharge (TSD) current measurements in short circuit. For 150 mu m thick laminated films, consisting of one 25 mu m thick PTFE layer, two 12.5 mu m thick FEP layers, and a void of 100 mu m height, the critical voltage necessary for the build-up of the "macro-dipoles" in the inner voids was approximately 1400 V, which agrees with the value calculated from the Paschen Law. A quasi-static piezoelectric d (33) coefficient up to 300 pC/N was observed after corona charging. The mechanical properties of the film systems are highly anisotropic. At room temperature, the Young's moduli of the laminated film system are around 0.37 MPa in the thickness direction and 274 MPa in the lateral direction, respectively. Using these values, the theoretical shape anisotropy ratio of the void was calculated, which agrees well with experimental observation. Compared with films that do not exhibit structural regularity, the laminates showed improved thermal stability of the d (33) coefficients. The thermal stability of d (33) can be further improved by pre-aging. E.g., the reduction of the d (33) value in the sample pre-aged at 150A degrees C for 5 h was less than 5\% after annealing for 30 h at a temperature of 90A degrees C.}, language = {en} } @article{SunYang2011, author = {Sun, Zhongkui and Yang, Xiaoli}, title = {Generating and enhancing lag synchronization of chaotic systems by white noise}, series = {Chaos : an interdisciplinary journal of nonlinear science}, volume = {21}, journal = {Chaos : an interdisciplinary journal of nonlinear science}, number = {3}, publisher = {American Institute of Physics}, address = {Melville}, issn = {1054-1500}, doi = {10.1063/1.3623440}, pages = {10}, year = {2011}, abstract = {In this paper, we study the crucial impact of white noise on lag synchronous regime in a pair of time-delay unidirectionally coupled systems. Our result demonstrates that merely via white-noise-based coupling lag synchronization could be achieved between the coupled systems (chaotic or not). And it is also demonstrated that a conventional lag synchronous regime can be enhanced by white noise. Sufficient conditions are further proved mathematically for noise-inducing and noise-enhancing lag synchronization, respectively. Additionally, the influence of parameter mismatch on the proposed lag synchronous regime is studied, by which we announce the robustness and validity of the new strategy. Two numerical examples are provided to illustrate the validity and some possible applications of the theoretical result.}, language = {en} } @article{SunHenniesPietzschetal.2011, author = {Sun, Y. -P. and Hennies, Franz and Pietzsch, Annette and Kennedy, B. and Schmitt, Thorsten and Strocov, Vladimir N. and Andersson, Joakim and Berglund, Martin and Rubensson, Jan-Erik and Aidas, K. and Gel'mukhanov, F. and Odelius, Michael and F{\"o}hlisch, Alexander}, title = {Intramolecular soft modes and intermolecular interactions in liquid acetone}, series = {Physical review : B, Condensed matter and materials physics}, volume = {84}, journal = {Physical review : B, Condensed matter and materials physics}, number = {13}, publisher = {American Physical Society}, address = {College Park}, issn = {1098-0121}, doi = {10.1103/PhysRevB.84.132202}, pages = {4}, year = {2011}, abstract = {Resonant inelastic x-ray scattering spectra excited at the O1s(-1)pi* resonance of liquid acetone are presented. Scattering to the electronic ground state shows a resolved vibrational progression where the dominant contribution is due to the C-O stretching mode, thus demonstrating a unique sensitivity of the method to the local potential energy surface in complex molecular systems. For scattering to electronically excited states, soft vibrational modes and, to a smaller extent, intermolecular interactions give a broadening, which blurs the vibrational fine structure. It is predicted that environmental broadening is dominant in aqueous acetone.}, language = {en} } @article{SunPietzschHenniesetal.2011, author = {Sun, Y-P and Pietzsch, Annette and Hennies, Franz and Rinkevicius, Z. and Karlsson, Hans O. and Schmitt, Thorsten and Strocov, Vladimir N. and Andersson, Joakim and Kennedy, B. and Schlappa, J. and F{\"o}hlisch, Alexander and Gel'mukhanov, F. and Rubensson, Jan-Erik}, title = {Internal symmetry and selection rules in resonant inelastic soft x-ray scattering}, series = {Journal of physics : B, Atomic, molecular and optical physics}, volume = {44}, journal = {Journal of physics : B, Atomic, molecular and optical physics}, number = {16}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {0953-4075}, doi = {10.1088/0953-4075/44/16/161002}, pages = {5}, year = {2011}, abstract = {Resonant inelastic soft x-ray scattering spectra excited at the dissociative 1 sigma(g) -> 3 sigma(u) resonance in gas-phase O(2) are presented and discussed in terms of state-of-the-art molecular theory. A new selection rule due to internal spin coupling is established, facilitating a deep analysis of the valence excited final states. Furthermore, it is found that a commonly accepted symmetry selection rule due to orbital parity breaks down, as the core hole and excited electron swap parity, thereby opening the symmetry forbidden 3 sigma(g) decay channel.}, language = {en} } @article{StraubePikovskij2011, author = {Straube, Arthur V. and Pikovskij, Arkadij}, title = {Pattern formation induced by time-dependent advection}, series = {Mathematical modelling of natural phenomena}, volume = {6}, journal = {Mathematical modelling of natural phenomena}, number = {1}, publisher = {EDP Sciences}, address = {Les Ulis}, issn = {0973-5348}, doi = {10.1051/mmnp/20116107}, pages = {138 -- 148}, year = {2011}, abstract = {We study pattern-forming instabilities in reaction-advection-diffusion systems. We develop an approach based on Lyapunov-Bloch exponents to figure out the impact of a spatially periodic mixing flow on the stability of a spatially homogeneous state. We deal with the flows periodic in space that may have arbitrary time dependence. We propose a discrete in time model, where reaction, advection, and diffusion act as successive operators, and show that a mixing advection can lead to a pattern-forming instability in a two-component system where only one of the species is advected. Physically, this can be explained as crossing a threshold of Turing instability due to effective increase of one of the diffusion constants.}, language = {en} } @article{StoyanovKolloscheRisseetal.2011, author = {Stoyanov, Hristiyan and Kollosche, Matthias and Risse, Sebastian and McCarthy, Denis N. and Kofod, Guggi}, title = {Elastic block copolymer nanocomposites with controlled interfacial interactions for artificial muscles with direct voltage control}, series = {Soft matter}, volume = {7}, journal = {Soft matter}, number = {1}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1744-683X}, doi = {10.1039/c0sm00715c}, pages = {194 -- 202}, year = {2011}, abstract = {Soft, physically crosslinking, block copolymer elastomers were filled with surface-treated nanoparticles, in order to evaluate the possibility for improvement of their properties when used as soft dielectric actuators. The nanoparticles led to improvements in dielectric properties, however they also reinforced the elastomer matrix. Comparing dielectric spectra of composites with untreated and surface-treated particles showed a measurable influence of the surface on the dielectric loss behaviour for high filler amounts, strongly indicating an improved host-guest interaction for the surface-treated particles. Breakdown strength was measured using a test bench and was found to be in good agreement with the results from the actuation measurements. Actuation responses predicted by a model for prestrained actuators agreed well with measurements up to a filler amount of 20\%(vol). Strong improvements in actuation behaviour were observed, with an optimum near 15\%(vol) nanoparticles, corresponding to a reduction in electrical field of 27\% for identical actuation strains. The use of physically crosslinking elastomer ensured the mechanical properties of the matrix elastomer were unchanged by nanoparticles effecting the crosslinking reaction, contrary to similar experiments performed with chemically crosslinking elastomers. This allows for a firm conclusion about the positive effects of surface-treated nanoparticles on actuation behavior.}, language = {en} } @phdthesis{Stoyanov2011, author = {Stoyanov, Hristiyan}, title = {Soft nanocomposites with enhanced electromechanical response for dielectric elastomer actuators}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-51194}, school = {Universit{\"a}t Potsdam}, year = {2011}, abstract = {Electromechanical transducers based on elastomer capacitors are presently considered for many soft actuation applications, due to their large reversible deformation in response to electric field induced electrostatic pressure. The high operating voltage of such devices is currently a large drawback, hindering their use in applications such as biomedical devices and biomimetic robots, however, they could be improved with a careful design of their material properties. The main targets for improving their properties are increasing the relative permittivity of the active material, while maintaining high electric breakdown strength and low stiffness, which would lead to enhanced electrostatic storage ability and hence, reduced operating voltage. Improvement of the functional properties is possible through the use of nanocomposites. These exploit the high surface-to-volume ratio of the nanoscale filler, resulting in large effects on macroscale properties. This thesis explores several strategies for nanomaterials design. The resulting nanocomposites are fully characterized with respect to their electrical and mechanical properties, by use of dielectric spectroscopy, tensile mechanical analysis, and electric breakdown tests. First, nanocomposites consisting of high permittivity rutile TiO2 nanoparticles dispersed in thermoplastic block copolymer SEBS (poly-styrene-coethylene-co-butylene-co-styrene) are shown to exhibit permittivity increases of up to 3.7 times, leading to 5.6 times improvement in electrostatic energy density, but with a trade-off in mechanical properties (an 8-fold increase in stiffness). The variation in both electrical and mechanical properties still allows for electromechanical improvement, such that a 27 \% reduction of the electric field is found compared to the pure elastomer. Second, it is shown that the use of nanofiller conductive particles (carbon black (CB)) can lead to a strong increase of relative permittivity through percolation, however, with detrimental side effects. These are due to localized enhancement of the electric field within the composite, which leads to sharp reductions in electric field strength. Hence, the increase in permittivity does not make up for the reduction in breakdown strength in relation to stored electrical energy, which may prohibit their practical use. Third, a completely new approach for increasing the relative permittivity and electrostatic energy density of a polymer based on 'molecular composites' is presented, relying on chemically grafting soft π-conjugated macromolecules to a flexible elastomer backbone. Polarization caused by charge displacement along the conjugated backbone is found to induce a large and controlled permittivity enhancement (470 \% over the elastomer matrix), while chemical bonding, encapsulates the PANI chains manifesting in hardly any reduction in electric breakdown strength, and hence resulting in a large increase in stored electrostatic energy. This is shown to lead to an improvement in the sensitivity of the measured electromechanical response (83 \% reduction of the driving electric field) as well as in the maximum actuation strain (250 \%). These results represent a large step forward in the understanding of the strategies which can be employed to obtain high permittivity polymer materials with practical use for electro-elastomer actuation.}, language = {en} } @article{StichBeta2011, author = {Stich, Michael and Beta, Carsten}, title = {Standing waves in a complex Ginzburg-Landau equation with time-delay feedback}, series = {Discrete and continuous dynamical systems : a journal bridging mathematics and sciences}, journal = {Discrete and continuous dynamical systems : a journal bridging mathematics and sciences}, number = {1}, publisher = {American Institute of Mathematical Sciences}, address = {Springfield}, issn = {1078-0947}, pages = {1329 -- 1334}, year = {2011}, abstract = {Standing waves are studied as solutions of a complex Ginsburg-Landau equation subjected to local and global time-delay feedback terms. The onset of standing waves is studied at the instability of the homogeneous periodic solution with respect to spatially periodic perturbations. The solution of this spatiotemporal wave pattern is given and is compared to the homogeneous periodic solution.}, language = {en} } @article{ShaydukNavirianLeitenbergeretal.2011, author = {Shayduk, Roman and Navirian, Hengameh and Leitenberger, Wolfram and Goldshteyn, Jevgenij and Vrejoiu, Ionela and Weinelt, Martin and Gaal, Peter and Herzog, Marc and von Korff Schmising, Clemens and Bargheer, Matias}, title = {Nanoscale heat transport studied by high-resolution time-resolved x-ray diffraction}, series = {New journal of physics : the open-access journal for physics}, volume = {13}, journal = {New journal of physics : the open-access journal for physics}, number = {11}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {1367-2630}, doi = {10.1088/1367-2630/13/9/093032}, pages = {11}, year = {2011}, abstract = {We report on synchrotron-based high-repetition rate ultrafast x-ray diffraction (UXRD) experiments monitoring the transport of heat from an epitaxial La(0.7)Sr(0.3)MnO(3)/SrTiO(3) superlattice (SL) into the substrate on timescales from 100 ps to 4 mu s. Transient thermal lattice expansion was determined with an accuracy of 10(-7), corresponding to a sensitivity to temperature changes down to 0.01 K. We follow the heat flow within the SL and into the substrate after the impulsive laser heating leads to a small temperature rise of Delta T = 6 K. The transient lattice temperature can be simulated very well using the bulk heat conductivities. This contradicts the interpretation of previous UXRD measurements, which predicted a long-lasting expansion of SrRuO(3) for more than 200 ps. The disagreement could be resolved by assuming that the heat conductivity changes in the first hundred picoseconds.}, language = {en} } @article{SeppTempelGramannetal.2011, author = {Sepp, T. and Tempel, E. and Gramann, M. and Nurmi, P. and Haupt, Michael}, title = {Studying the patterns of the universe}, series = {Baltic astronomy}, volume = {20}, journal = {Baltic astronomy}, number = {2}, publisher = {Institute of Theoretical Physics and Astronomy}, address = {Moletai}, issn = {1392-0049}, pages = {309 -- 312}, year = {2011}, abstract = {The SDSS galaxy catalog is one of the best databases for galaxy distribution studies. The SDSS DR8 data is used to construct the galaxy cluster catalog. We construct the clusters from the calculated luminosity density field and identify denser regions. Around these peak regions we construct galaxy clusters. Another interesting question in cosmology is how observable galaxy structures are connected to underlying dark matter distribution. To study this we compare the SDSS DR7 galaxy group catalog with galaxy groups obtained from the semi-analytical Millennium N-Body simulation. Specifically, we compare the group richness, virial radius, maximum separation and velocity dispersion distributions and find a relatively good agreement between the mock catalog and observations. This strongly supports the idea, that the dark matter distribution and galaxies in the semi-analytical models and observations are very closely linked.}, language = {en} } @article{SeissSpahn2011, author = {Seiss, Martin and Spahn, Frank}, title = {Hydrodynamics of saturn's dense rings}, series = {Mathematical modelling of natural phenomena}, volume = {6}, journal = {Mathematical modelling of natural phenomena}, number = {4}, publisher = {EDP Sciences}, address = {Les Ulis}, issn = {0973-5348}, doi = {10.1051/mmnp/20116409}, pages = {191 -- 218}, year = {2011}, abstract = {The space missions Voyager and Cassini together with earthbound observations revealed a wealth of structures in Saturn's rings. There are, for example, waves being excited at ring positions which are in orbital resonance with Saturn's moons. Other structures can be assigned to embedded moons like empty gaps, moon induced wakes or S-shaped propeller features. Furthermore, irregular radial structures are observed in the range from 10 meters until kilometers. Here some of these structures will be discussed in the frame of hydrodynamical modeling of Saturn's dense rings. For this purpose we will characterize the physical properties of the ring particle ensemble by mean field quantities and point to the special behavior of the transport coefficients. We show that unperturbed rings can become unstable and how diffusion acts in the rings. Additionally, the alternative streamline formalism is introduced to describe perturbed regions of dense rings with applications to the wake damping and the dispersion relation of the density waves.}, language = {en} } @phdthesis{Seewald2011, author = {Seewald, Gunter}, title = {Lineare und nichtlineare optische Untersuchungen am synthetischen Eumelanin und Entwicklung eines Kaskadenmodells}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-59967}, school = {Universit{\"a}t Potsdam}, year = {2011}, abstract = {Eumelanin ist ein Fluorophor mit teilweise recht ungew{\"o}hnlichen spektralen Eigenschaften. Unter anderem konnten in fr{\"u}heren Ver{\"o}ffentlichungen Unterschiede zwischen dem 1- und 2-photonen-angeregtem Fluoreszenzspektrum beobachtet werden, weshalb im nichtlinearen Anregungsfall ein schrittweiser Anregungsprozess vermutet wurde. Um diese und weitere optische Eigenschaften des Eumelanins besser zu verstehen, wurden in der vorliegenden Arbeit vielf{\"a}ltige messmethodische Ans{\"a}tze der linearen und nichtlinearen Optik an synthetischem Eumelanin in 0,1M NaOH verfolgt. Aus den Ergebnissen wurde ein Modell abgeleitet, welches die beobachteten photonischen Eigenschaften konsistent beschreibt. In diesem kaskadierten Zustandsmodell (Kaskaden-Modell) wird die aufgenommene Photonenenergie schrittweise von Anregungszust{\"a}nden hoher {\"U}bergangsenergien zu Anregungszust{\"a}nden niedrigerer {\"U}bergangsenergien transferiert. Messungen der transienten Absorption ergaben dominante Anteile mit kurzen Lebensdauern im ps-Bereich und ließen damit auf eine hohe Relaxationsgeschwindigkeit entlang der Kaskade schließen. Durch Untersuchung der nichtlinear angeregten Fluoreszenz von verschieden großen Eumelanin-Aggregaten konnte gezeigt werden, dass Unterschiede zwischen dem linear und nichtlinear angeregten Fluoreszenzspektrum nicht nur durch einen schrittweisen Anregungsprozess bei nichtlinearer Anregung sondern auch durch Unterschiede in den Verh{\"a}ltnissen der Quantenausbeuten zwischen kleinen und großen Aggregaten beim Wechsel von linearer zu nichtlinearer Anregung begr{\"u}ndet sein k{\"o}nnen. Durch Bestimmung des Anregungswirkungsquerschnitts und der Anregungspulsdauer-Abh{\"a}ngigkeit der nichtlinear angeregten Fluoreszenz von Eumelanin konnte jedoch ein schrittweiser 2-Photonen-Anregungsprozess {\"u}ber einen Zwischenzustand mit Lebendsdauern im ps-Bereich nachgewiesen werden.}, language = {de} } @article{SchuetzHolschneider2011, author = {Sch{\"u}tz, Nadine and Holschneider, Matthias}, title = {Detection of trend changes in time series using Bayesian inference}, series = {Physical review : E, Statistical, nonlinear and soft matter physics}, volume = {84}, 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.84.021120}, pages = {10}, year = {2011}, abstract = {Change points in time series are perceived as isolated singularities where two regular trends of a given signal do not match. The detection of such transitions is of fundamental interest for the understanding of the system's internal dynamics or external forcings. In practice observational noise makes it difficult to detect such change points in time series. In this work we elaborate on a Bayesian algorithm to estimate the location of the singularities and to quantify their credibility. We validate the performance and sensitivity of our inference method by estimating change points of synthetic data sets. As an application we use our algorithm to analyze the annual flow volume of the Nile River at Aswan from 1871 to 1970, where we confirm a well-established significant transition point within the time series.}, language = {en} } @phdthesis{Schulze2011, author = {Schulze, Andreas}, title = {Demographics of supermassive black holes}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-54464}, school = {Universit{\"a}t Potsdam}, year = {2011}, abstract = {Supermassive black holes are a fundamental component of the universe in general and of galaxies in particular. Almost every massive galaxy harbours a supermassive black hole (SMBH) in its center. Furthermore, there is a close connection between the growth of the SMBH and the evolution of its host galaxy, manifested in the relationship between the mass of the black hole and various properties of the galaxy's spheroid component, like its stellar velocity dispersion, luminosity or mass. Understanding this relationship and the growth of SMBHs is essential for our picture of galaxy formation and evolution. In this thesis, I make several contributions to improve our knowledge on the census of SMBHs and on the coevolution of black holes and galaxies. The first route I follow on this road is to obtain a complete census of the black hole population and its properties. Here, I focus particularly on active black holes, observable as Active Galactic Nuclei (AGN) or quasars. These are found in large surveys of the sky. In this thesis, I use one of these surveys, the Hamburg/ESO survey (HES), to study the AGN population in the local volume (z~0). The demographics of AGN are traditionally represented by the AGN luminosity function, the distribution function of AGN at a given luminosity. I determined the local (z<0.3) optical luminosity function of so-called type 1 AGN, based on the broad band B_J magnitudes and AGN broad Halpha emission line luminosities, free of contamination from the host galaxy. I combined this result with fainter data from the Sloan Digital Sky Survey (SDSS) and constructed the best current optical AGN luminosity function at z~0. The comparison of the luminosity function with higher redshifts supports the current notion of 'AGN downsizing', i.e. the space density of the most luminous AGN peaks at higher redshifts and the space density of less luminous AGN peaks at lower redshifts. However, the AGN luminosity function does not reveal the full picture of active black hole demographics. This requires knowledge of the physical quantities, foremost the black hole mass and the accretion rate of the black hole, and the respective distribution functions, the active black hole mass function and the Eddington ratio distribution function. I developed a method for an unbiased estimate of these two distribution functions, employing a maximum likelihood technique and fully account for the selection function. I used this method to determine the active black hole mass function and the Eddington ratio distribution function for the local universe from the HES. I found a wide intrinsic distribution of black hole accretion rates and black hole masses. The comparison of the local active black hole mass function with the local total black hole mass function reveals evidence for 'AGN downsizing', in the sense that in the local universe the most massive black holes are in a less active stage then lower mass black holes. The second route I follow is a study of redshift evolution in the black hole-galaxy relations. While theoretical models can in general explain the existence of these relations, their redshift evolution puts strong constraints on these models. Observational studies on the black hole-galaxy relations naturally suffer from selection effects. These can potentially bias the conclusions inferred from the observations, if they are not taken into account. I investigated the issue of selection effects on type 1 AGN samples in detail and discuss various sources of bias, e.g. an AGN luminosity bias, an active fraction bias and an AGN evolution bias. If the selection function of the observational sample and the underlying distribution functions are known, it is possible to correct for this bias. I present a fitting method to obtain an unbiased estimate of the intrinsic black hole-galaxy relations from samples that are affected by selection effects. Third, I try to improve our census of dormant black holes and the determination of their masses. One of the most important techniques to determine the black hole mass in quiescent galaxies is via stellar dynamical modeling. This method employs photometric and kinematic observations of the galaxy and infers the gravitational potential from the stellar orbits. This method can reveal the presence of the black hole and give its mass, if the sphere of the black hole's gravitational influence is spatially resolved. However, usually the presence of a dark matter halo is ignored in the dynamical modeling, potentially causing a bias on the determined black hole mass. I ran dynamical models for a sample of 12 galaxies, including a dark matter halo. For galaxies for which the black hole's sphere of influence is not well resolved, I found that the black hole mass is systematically underestimated when the dark matter halo is ignored, while there is almost no effect for galaxies with well resolved sphere of influence.}, language = {en} } @article{SchuhLomadzeRueheetal.2011, author = {Schuh, Christian and Lomadze, Nino and R{\"u}he, J{\"u}rgen and Kopyshev, Alexey and Santer, Svetlana}, title = {Photomechanical degrafting of Azo-functionalized Poly(methacrylic acid) (PMAA) brushes}, series = {The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces \& biophysical chemistry}, volume = {115}, journal = {The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces \& biophysical chemistry}, number = {35}, publisher = {American Chemical Society}, address = {Washington}, issn = {1520-6106}, doi = {10.1021/jp2041229}, pages = {10431 -- 10438}, year = {2011}, abstract = {We report on the preparation and characterization of photosensitive polymer brushes. The brushes are synthesized through polymer analogous attachment of azobenzene groups to surface-attached poly(methacrylic acid) (PMAA) chains. The topography of the photosensitive brushes shows a strong reaction upon irradiation with UV light. While homogeneous illumination leaves the polymer topography unchanged, irradiation of the samples with interference patterns with periodically varying light intensity leads to the formation of surface relief gratings (SRG). The height of the stripes of the grating can be controlled by adjusting the irradiation time. The SRG pattern can be erased through solvent treatment when the periodicity of the stripe pattern is less than the length of the fully stretched polymer chains. In the opposite case, photomechanical scission of receding polymer chains is observed during SRG formation, and the inscribed patterns are permanent.}, language = {en} } @article{SchuchHarrisonOsborneetal.2011, author = {Schuch, Norbert and Harrison, Sarah K. and Osborne, Tobias J. and Eisert, Jens}, title = {Information propagation for interacting-particle systems}, series = {Physical review : A, Atomic, molecular, and optical physics}, volume = {84}, journal = {Physical review : A, Atomic, molecular, and optical physics}, number = {3}, publisher = {American Physical Society}, address = {College Park}, issn = {1050-2947}, doi = {10.1103/PhysRevA.84.032309}, pages = {5}, year = {2011}, abstract = {We study the speed at which information propagates through systems of interacting quantum particles moving on a regular lattice and show that for a certain class of initial conditions there exists a maximum speed of sound at which information can propagate. Our argument applies equally to quantum spins, bosons such as in the Bose-Hubbard model, fermions, anyons, and general mixtures thereof, on arbitrary lattices of any dimension. It also pertains to dissipative dynamics on the lattice, and generalizes to the continuum for quantum fields. Our result can be seen as an analog of the Lieb-Robinson bound for strongly correlated models.}, language = {en} } @article{SchoellerHubrigIlyinetal.2011, author = {Schoeller, M. and Hubrig, Swetlana and Ilyin, Ilya and Kharchenko, N. V. and Briquet, Maryline and Gonzalez, J. F. and Langer, Norbert and Oskinova, Lida}, title = {Magnetic field studies of massive main sequence stars}, series = {Astronomische Nachrichten = Astronomical notes}, volume = {332}, journal = {Astronomische Nachrichten = Astronomical notes}, number = {9-10}, publisher = {Wiley-Blackwell}, address = {Malden}, organization = {MAGORI Collaboration}, issn = {0004-6337}, doi = {10.1002/asna.201111606}, pages = {994 -- 997}, year = {2011}, abstract = {We report on the status of our spectropolarimetric observations of massive stars. During the last years, we have discovered magnetic fields in many objects of the upper main sequence, including Be stars, beta Cephei and Slowly Pulsating B stars, and a dozen O stars. Since the effects of those magnetic fields have been found to be substantial by recent models, we are looking into their impact on stellar rotation, pulsation, stellar winds, and chemical abundances. Accurate studies of the age, environment, and kinematic characteristics of the magnetic stars are also promising to give us new insight into the origin of the magnetic fields. Furthermore, longer time series of magnetic field measurements allow us to observe the temporal variability of the magnetic field and to deduce the stellar rotation period and the magnetic field geometry. Studies of the magnetic field in massive stars are indispensable to understand the conditions controlling the presence of those fields and their implications on the stellar physical parameters and evolution.}, language = {en} } @article{Schmidt2011, author = {Schmidt, Hans-J{\"u}rgen}, title = {Perihelion advance for orbits with large eccentricities in the Schwarzschild black hole}, series = {Physical review : D, Particles, fields, gravitation, and cosmology}, volume = {83}, 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.83.124010}, pages = {9}, year = {2011}, abstract = {We deduce a new formula for the perihelion advance Theta of a test particle in the Schwarzschild black hole by applying a newly developed nonlinear transformation within the Schwarzschild space-time. By this transformation we are able to apply the well-known formula valid in the weak-field approximation near infinity also to trajectories in the strong-field regime near the horizon of the black hole. The resulting formula has the structure Theta = c(1) - c(2) ln(c(3)(2) - e(2)) with positive constants c(1,2,3) depending on the angular momentum of the test particle. It is especially useful for orbits with large eccentricities e < c(3) < 1 showing that Theta -> infinity as e -> c(3).}, language = {en} } @article{Schmidt2011, author = {Schmidt, Hans-J{\"u}rgen}, title = {Gauss-Bonnet lagrangian G lnG and cosmological exact solutions}, series = {Physical review : D, Particles, fields, gravitation, and cosmology}, volume = {83}, journal = {Physical review : D, Particles, fields, gravitation, and cosmology}, number = {8}, publisher = {American Physical Society}, address = {College Park}, issn = {1550-7998}, doi = {10.1103/PhysRevD.83.083513}, pages = {7}, year = {2011}, abstract = {For the Lagrangian L = G lnG where G is the Gauss-Bonnet curvature scalar we deduce the field equation and solve it in closed form for 3-flat Friedmann models using a state-finder parametrization. Further we show that among all Lagrangians F(G) this L is the only one not having the form G(r) with a real constant r but possessing a scale-invariant field equation. This turns out to be one of its analogies to f(R) theories in two-dimensional space-time. In the appendix, we systematically list several formulas for the decomposition of the Riemann tensor in arbitrary dimensions n, which are applied in the main deduction for n = 4.}, language = {en} } @article{SchmahMarwanThomsenetal.2011, author = {Schmah, Tanya and Marwan, Norbert and Thomsen, Jesper Skovhus and Saparin, Peter}, title = {Long range node-strut analysis of trabecular bone microarchitecture}, series = {Medical physics : the international journal of medical physics research and practice}, volume = {38}, journal = {Medical physics : the international journal of medical physics research and practice}, number = {9}, publisher = {American Association of Physicists in Medicine}, address = {Melville}, issn = {0094-2405}, doi = {10.1118/1.3622600}, pages = {5003 -- 5011}, year = {2011}, abstract = {Purpose: We present a new morphometric measure of trabecular bone microarchitecture, called mean node strength (NdStr), which is part of a newly developed approach called long range nodestrut analysis. Our general aim is to describe and quantify the apparent "latticelike" microarchitecture of the trabecular bone network. Methods: Similar in some ways to the topological node-strut analysis introduced by Garrahan et al. [J. Microsc. 142, 341-349 (1986)], our method is distinguished by an emphasis on long-range trabecular connectivity. Thus, while the topological classification of a pixel (after skeletonization) as a node, strut, or terminus, can be determined from the 3 x 3 neighborhood of that pixel, our method, which does not involve skeletonization, takes into account a much larger neighborhood. In addition, rather than giving a discrete classification of each pixel as a node, strut, or terminus, our method produces a continuous variable, node strength. The node strength is averaged over a region of interest to produce the mean node strength of the region. Results: We have applied our long range node-strut analysis to a set of 26 high-resolution peripheral quantitative computed tomography (pQCT) axial images of human proximal tibiae acquired 17 mm below the tibial plateau. We found that NdStr has a strong positive correlation with trabecular volumetric bone mineral density (BMD). After an exponential transformation, we obtain a Pearson's correlation coefficient of r - 0.97. Qualitative comparison of images with similar BMD but with very different NdStr values suggests that the latter measure has successfully quantified the prevalence of the "latticelike" microarchitecture apparent in the image. Moreover, we found a strong correlation (r - 0.62) between NdStr and the conventional node-terminus ratio (Nd/Tm) of Garrahan et al. The Nd/Tm ratios were computed using traditional histomorphometry performed on bone biopsies obtained at the same location as the pQCT scans. Conclusions: The newly introduced morphometric measure allows a quantitative assessment of the long-range connectivity of trabecular bone. One advantage of this method is that it is based on pQCT images that can be obtained noninvasively from patients, i.e., without having to obtain a bone biopsy from the patient.}, language = {en} } @phdthesis{Schiefele2011, author = {Schiefele, J{\"u}rgen}, title = {Casimir-Polder interaction in second quantization}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-54171}, school = {Universit{\"a}t Potsdam}, year = {2011}, abstract = {The Casimir-Polder interaction between a single neutral atom and a nearby surface, arising from the (quantum and thermal) fluctuations of the electromagnetic field, is a cornerstone of cavity quantum electrodynamics (cQED), and theoretically well established. Recently, Bose-Einstein condensates (BECs) of ultracold atoms have been used to test the predictions of cQED. The purpose of the present thesis is to upgrade single-atom cQED with the many-body theory needed to describe trapped atomic BECs. Tools and methods are developed in a second-quantized picture that treats atom and photon fields on the same footing. We formulate a diagrammatic expansion using correlation functions for both the electromagnetic field and the atomic system. The formalism is applied to investigate, for BECs trapped near surfaces, dispersion interactions of the van der Waals-Casimir-Polder type, and the Bosonic stimulation in spontaneous decay of excited atomic states. We also discuss a phononic Casimir effect, which arises from the quantum fluctuations in an interacting BEC.}, language = {en} } @article{SchiefeleHenkel2011, author = {Schiefele, Juergen and Henkel, Carsten}, title = {Bosonic enhancement of spontaneous emission near an interface}, series = {Modern physics letters : A, Particles and fields, gravitation, cosmology, nuclear physics}, volume = {375}, journal = {Modern physics letters : A, Particles and fields, gravitation, cosmology, nuclear physics}, number = {3}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0375-9601}, doi = {10.1016/j.physleta.2010.11.058}, pages = {680 -- 684}, year = {2011}, abstract = {We show how the spontaneous emission rate of an excited two-level atom placed in a trapped Bose-Einstein condensate of ground-state atoms is enhanced by bosonic stimulation. This stimulation depends on the overlap of the excited matter-wave packet with the macroscopically occupied condensate wave function, and provides a probe of the spatial coherence of the Bose gas. The effect can be used to amplify the distance-dependent decay rate of an excited atom near an interface.}, language = {en} } @article{ScheweLevermannMeinshausen2011, author = {Schewe, Jacob and Levermann, Anders and Meinshausen, Malte}, title = {Climate change under a scenario near 1.5 degrees C of global warming: monsoon intensification, ocean warming and steric sea level rise}, series = {Earth system dynamics}, volume = {2}, journal = {Earth system dynamics}, number = {1}, publisher = {Copernicus}, address = {G{\"o}ttingen}, issn = {2190-4979}, doi = {10.5194/esd-2-25-2011}, pages = {25 -- 35}, year = {2011}, abstract = {We present climatic consequences of the Representative Concentration Pathways (RCPs) using the coupled climate model CLIMBER-3 alpha, which contains a statistical-dynamical atmosphere and a three-dimensional ocean model. We compare those with emulations of 19 state-of-the-art atmosphere-ocean general circulation models (AOGCM) using MAGICC6. The RCPs are designed as standard scenarios for the forthcoming IPCC Fifth Assessment Report to span the full range of future greenhouse gas (GHG) concentrations pathways currently discussed. The lowest of the RCP scenarios, RCP3-PD, is projected in CLIMBER-3 alpha to imply a maximal warming by the middle of the 21st century slightly above 1.5 degrees C and a slow decline of temperatures thereafter, approaching today's level by 2500. We identify two mechanisms that slow down global cooling after GHG concentrations peak: The known inertia induced by mixing-related oceanic heat uptake; and a change in oceanic convection that enhances ocean heat loss in high latitudes, reducing the surface cooling rate by almost 50\%. Steric sea level rise under the RCP3-PD scenario continues for 200 years after the peak in surface air temperatures, stabilizing around 2250 at 30 cm. This contrasts with around 1.3 m of steric sea level rise by 2250, and 2 m by 2500, under the highest scenario, RCP8.5. Maximum oceanic warming at intermediate depth (300-800 m) is found to exceed that of the sea surface by the second half of the 21st century under RCP3-PD. This intermediate-depth warming persists for centuries even after surface temperatures have returned to present-day values, with potential consequences for marine ecosystems, oceanic methane hydrates, and ice-shelf stability. Due to an enhanced land-ocean temperature contrast, all scenarios yield an intensification of monsoon rainfall under global warming.}, language = {en} } @phdthesis{Schewe2011, author = {Schewe, Jacob}, title = {Basic physical mechanisms for monsoon failure in past and future climate}, address = {Potsdam}, pages = {135 S.}, year = {2011}, language = {en} } @article{SchenkHamiltonJohnsonetal.2011, author = {Schenk, Paul and Hamilton, Douglas P. and Johnson, Robert E. and McKinnon, William B. and Paranicas, Chris and Schmidt, J{\"u}rgen and Showalter, Mark R.}, title = {Plasma, plumes and rings saturn system dynamics as recorded in global color patterns on its midsize icy satellites}, series = {Icarus : international journal of solar system studies}, volume = {211}, journal = {Icarus : international journal of solar system studies}, number = {1}, publisher = {Elsevier}, address = {San Diego}, issn = {0019-1035}, doi = {10.1016/j.icarus.2010.08.016}, pages = {740 -- 757}, year = {2011}, abstract = {New global maps of the five inner midsize icy saturnian satellites, Mimas, Enceladus, Tethys, Dione, and Rhea, have been constructed in three colors (UV, Green and near-IR) at resolutions of 1 km/pixel. The maps reveal prominent global patterns common to several of these satellites but also three major color features unique to specific satellites or satellite subgroups. The most common features among the group are first-order global asymmetries in color properties. This pattern, expressed on Tethys, Dione and Rhea, takes the form of a similar to 1.4-1.8 times enhancement in redness (expressed as IR/UV ratio) of the surface at the center of the trailing hemisphere of motion, and a similar though significantly weaker IR/UV enhancement at the center of the leading hemisphere. The peak in redness on the trailing hemisphere also corresponds to a known decrease in albedo. These double hemispheric asymmetries are attributable to plasma and E-ring grain bombardment on the trailing and leading hemispheres, respectively, for the outer three satellites Tethys, Dione and Rhea, whereas as E-ring bombardment may be focused on the trailing hemisphere of Mimas due to its orbital location interior to Enceladus. The maps also reveal three major deviations from these basic global patterns. We observe the previously known dark bluish leading hemisphere equatorial band on Tethys but have also discovered a similar band on Mimas. Similar in shape, both features match the surface patterns expected for irradiation of the surface by incident MeV electrons that drift in a direction opposite to the plasma flow. The global asymmetry on Enceladus is offset similar to 40 degrees to the west compared to the other satellites. We do not consider Enceladus in detail here, but the global distribution of bluish material can be shown to match the deposition pattern predicted for plume fallback onto the surface (Kempf, S., Beckmann, U., Schmidt, S. [2010]. Icarus 206, 446-457. doi:10.1016/j.icarus.2009.09.016). E-ring deposition on Enceladus thus appears to mask or prevent the formation of the lenses and hemispheric asymmetries we see on the other satellites. Finally, we observe a chain of discrete bluish splotches along the equator of Rhea. Unlike the equatorial bands of Tethys and Mimas, these splotches form a very narrow great circle <= 10-km wide (north-to-south) and appear to be related to surface disruption, exposing fresh, bluish ice on older crater rims. This feature is unique to Rhea and may have formed by impact onto its surface of orbiting material.}, language = {en} } @article{SchaeferWestendorfBodenschatzetal.2011, author = {Schaefer, Edith and Westendorf, Christian and Bodenschatz, Eberhard and Beta, Carsten and Geil, Burkhard and Janshoff, Andreas}, title = {Shape oscillations of dictyostelium discoideum cells on ultramicroelectrodes monitored by impedance analysis}, series = {Small}, volume = {7}, journal = {Small}, number = {6}, publisher = {Wiley-Blackwell}, address = {Malden}, issn = {1613-6810}, doi = {10.1002/smll.201001955}, pages = {723 -- 726}, year = {2011}, language = {en} } @article{SanhuezaPinoKorupHetzeletal.2011, author = {Sanhueza-Pino, Katia and Korup, Oliver and Hetzel, Ralf and Munack, Henry and Weidinger, Johannes T. and Dunning, Stuart A. and Ormukov, Cholponbek and Kubik, Peter W.}, title = {Glacial advances constrained by Be-10 exposure dating of bedrock landslides, Kyrgyz Tien Shan}, series = {Quaternary research : an interdisciplinary journal}, volume = {76}, journal = {Quaternary research : an interdisciplinary journal}, number = {3}, publisher = {Elsevier}, address = {San Diego}, issn = {0033-5894}, doi = {10.1016/j.yqres.2011.06.013}, pages = {295 -- 304}, year = {2011}, abstract = {Numerous large landslide deposits occur in the Tien Shan, a tectonically active intraplate orogen in Central Asia. Yet their significance in Quaternary landscape evolution and natural hazard assessment remains unresolved due to the lack of "absolute" age constraints. Here we present the first Be-10 exposure ages for three prominent (>10(7) m(3)) bedrock landslides that blocked major rivers and formed lakes, two of which subsequently breached, in the northern Kyrgyz Tien Shan. Three Be-10 ages reveal that one landslide in the Alamyedin River occurred at 11-15 ka, which is consistent with two C-14 ages of gastropod shells from reworked loess capping the landslide. One large landslide in Aksu River is among the oldest documented in semi-arid continental interiors, with a Be-10 age of 63-67 ka. The Ukok River landslide deposit(s) yielded variable Be-10 ages, which may result from multiple landslides, and inheritance of Be-10. Two Be-10 ages of 8.2 and 5.9 ka suggest that one major landslide occurred in the early to mid-Holocene, followed by at least one other event between 1.5 and 0.4 ka. Judging from the regional glacial chronology, all three landslides have occurred between major regional glacial advances. Whereas Alamyedin and Ukok can be considered as postglacial in this context, Aksu is of interglacial age. None of the landslide deposits show traces of glacial erosion, hence their locations and I Be ages mark maximum extents and minimum ages of glacial advances, respectively. Using toe-to-headwall altitude ratios of 0.4-0.5, we reconstruct minimum equilibrium-line altitudes that exceed previous estimates by as much as 400 m along the moister northern fringe of the Tien Shan. Our data show that deposits from large landslides can provide valuable spatio-temporal constraints for glacial advances in landscapes where moraines and glacial deposits have low preservation potential. (C) 2011 University of Washington. Published by Elsevier Inc. All rights reserved.}, language = {en} } @article{RychkovKuznetsovRychkov2011, author = {Rychkov, Dmitry and Kuznetsov, Alexey and Rychkov, Andrey}, title = {Electret properties of polyethylene and polytetrafluoroethylene films with chemically modified surface}, series = {IEEE transactions on dielectrics and electrical insulation}, volume = {18}, journal = {IEEE transactions on dielectrics and electrical insulation}, number = {1}, publisher = {Inst. of Electr. and Electronics Engineers}, address = {Piscataway}, issn = {1070-9878}, doi = {10.1109/TDEI.2011.5704487}, pages = {8 -- 14}, year = {2011}, abstract = {This paper investigates the effect of chemical surface modification of polytetrafluoroethylene (PTFE) and low density polyethylene (LDPE) films on their electret properties. PTFE films were subjected to wet treatment with three different chemicals: orthophosphoric acid, tetrabutyl titanate and tetraethoxysilane. The technique based on the principles of molecular layer deposition (MLD) method was used to modify the surface of LDPE films with phosphorus trichloride vapors. The surfaces of the films were then corona charged, and the electret charge stability was studied by means of isothermal and thermally stimulated surface potential decay. Both PTFE and LDPE films, after the surface treatment, displayed a considerable enhancement in the charge stability compared to the virgin samples. It is important to note that the enhancement of the charge stability was achieved in the positively charged PTFE films, a result important to practical applications. We attribute this effect of charge stabilization to the formation of new energetically deep traps on the modified surface. Decrease in molecular mobility, due to attachment of new chemical structures to the surface macromolecules, may also contribute to the overall growth of the charge stability.}, language = {en} } @article{RychkovGerhard2011, author = {Rychkov, Dmitry and Gerhard, Reimund}, title = {Stabilization of positive charge on polytetrafluoroethylene electret films treated with titanium-tetrachloride vapor}, series = {Applied physics letters}, volume = {98}, journal = {Applied physics letters}, number = {12}, publisher = {American Institute of Physics}, address = {Melville}, issn = {0003-6951}, doi = {10.1063/1.3565166}, pages = {3}, year = {2011}, abstract = {The surface of polytetrafluoroethylene films was treated with titanium-tetrachloride vapor. The treatment was carried out in a flow reactor by means of molecular-layer deposition, a method from the arsenal of chemical nanotechnology. X-ray photoelectron spectroscopy reveals that such a treatment results in considerable changes in the chemical composition at and near the surface of the fluoropolymer film. Both, defluorination and oxidation of the surface were observed. At the same time, samples treated with titanium tetrachloride show a significant enhancement in the thermal stability of the positive homocharge. The thermally stimulated surface-potential-decay curves were observed to shift to higher temperatures by more than 100 degrees C.}, language = {en} } @article{RobinsonCalovGanopolski2011, author = {Robinson, Alexander and Calov, Reinhard and Ganopolski, Andrey}, title = {Greenland ice sheet model parameters constrained using simulations of the Eemian Interglacial}, series = {Climate of the past : an interactive open access journal of the European Geosciences Union}, volume = {7}, journal = {Climate of the past : an interactive open access journal of the European Geosciences Union}, number = {2}, publisher = {Copernicus}, address = {G{\"o}ttingen}, issn = {1814-9324}, doi = {10.5194/cp-7-381-2011}, pages = {381 -- 396}, year = {2011}, abstract = {Using a new approach to force an ice sheet model, we performed an ensemble of simulations of the Greenland Ice Sheet evolution during the last two glacial cycles, with emphasis on the Eemian Interglacial. This ensemble was generated by perturbing four key parameters in the coupled regional climate-ice sheet model and by introducing additional uncertainty in the prescribed "background" climate change. The sensitivity of the surface melt model to climate change was determined to be the dominant driver of ice sheet instability, as reflected by simulated ice sheet loss during the Eemian Interglacial period. To eliminate unrealistic parameter combinations, constraints from present-day and paleo information were applied. The constraints include (i) the diagnosed present-day surface mass balance partition between surface melting and ice discharge at the margin, (ii) the modeled present-day elevation at GRIP; and (iii) the modeled elevation reduction at GRIP during the Eemian. Using these three constraints, a total of 360 simulations with 90 different model realizations were filtered down to 46 simulations and 20 model realizations considered valid. The paleo constraint eliminated more sensitive melt parameter values, in agreement with the surface mass balance partition assumption. The constrained simulations resulted in a range of Eemian ice loss of 0.4-4.4m sea level equivalent, with a more likely range of about 3.7-4.4m sea level if the GRIP delta O-18 isotope record can be considered an accurate proxy for the precipitation-weighted annual mean temperatures.}, language = {en} } @phdthesis{Robinson2011, author = {Robinson, Alexander}, title = {Modeling the Greenland Ice Sheet response to climate change in the past and future}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-50430}, school = {Universit{\"a}t Potsdam}, year = {2011}, abstract = {The Greenland Ice Sheet (GIS) contains enough water volume to raise global sea level by over 7 meters. It is a relic of past glacial climates that could be strongly affected by a warming world. Several studies have been performed to investigate the sensitivity of the ice sheet to changes in climate, but large uncertainties in its long-term response still exist. In this thesis, a new approach has been developed and applied to modeling the GIS response to climate change. The advantages compared to previous approaches are (i) that it can be applied over a wide range of climatic scenarios (both in the deep past and the future), (ii) that it includes the relevant feedback processes between the climate and the ice sheet and (iii) that it is highly computationally efficient, allowing simulations over very long timescales. The new regional energy-moisture balance model (REMBO) has been developed to model the climate and surface mass balance over Greenland and it represents an improvement compared to conventional approaches in modeling present-day conditions. Furthermore, the evolution of the GIS has been simulated over the last glacial cycle using an ensemble of model versions. The model performance has been validated against field observations of the present-day climate and surface mass balance, as well as paleo information from ice cores. The GIS contribution to sea level rise during the last interglacial is estimated to be between 0.5-4.1 m, consistent with previous estimates. The ensemble of model versions has been constrained to those that are consistent with the data, and a range of valid parameter values has been defined, allowing quantification of the uncertainty and sensitivity of the modeling approach. Using the constrained model ensemble, the sensitivity of the GIS to long-term climate change was investigated. It was found that the GIS exhibits hysteresis behavior (i.e., it is multi-stable under certain conditions), and that a temperature threshold exists above which the ice sheet transitions to an essentially ice-free state. The threshold in the global temperature is estimated to be in the range of 1.3-2.3°C above preindustrial conditions, significantly lower than previously believed. The timescale of total melt scales non-linearly with the overshoot above the temperature threshold, such that a 2°C anomaly causes the ice sheet to melt in ca. 50,000 years, but an anomaly of 6°C will melt the ice sheet in less than 4,000 years. The meltback of the ice sheet was found to become irreversible after a fraction of the ice sheet is already lost - but this level of irreversibility also depends on the temperature anomaly.}, language = {en} } @article{RivnaySteyrleuthnerJimisonetal.2011, author = {Rivnay, Jonathan and Steyrleuthner, Robert and Jimison, Leslie H. and Casadei, Alberto and Chen, Zhihua and Toney, Michael F. and Facchetti, Antonio and Neher, Dieter and Salleo, Alberto}, title = {Drastic control of texture in a high performance n-Type polymeric semiconductor and implications for charge transport}, series = {Macromolecules : a publication of the American Chemical Society}, volume = {44}, journal = {Macromolecules : a publication of the American Chemical Society}, number = {13}, publisher = {American Chemical Society}, address = {Washington}, issn = {0024-9297}, doi = {10.1021/ma200864s}, pages = {5246 -- 5255}, year = {2011}, abstract = {Control of crystallographic texture from mostly face-on to edge-on is observed for the film morphology of the n-type semicrystalline polymer [N,N-9-bis(2-octyldodecyl)naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diy1]alt-5,59-(2,29-bithiophene)}, P(NDI2OD-T2), when annealing the film to the polymer melting point followed by slow cooling to ambient temperature. A variety of X-ray diffraction analyses, including pole figure construction and Fourier transform peak shape deconvolution, are employed to quantify the texture change, relative degree of crystallinity and lattice order. We find that annealing the polymer film to the melt leads to a shift from 77.5\% face-on to 94.6\% edge-on lamellar texture as well as to a 2-fold increase in crystallinity and a 40\% decrease in intracrystallite cumulative disorder. The texture change results in a significant drop in the electron-only diode current density through the film thickness upon melt annealing while little change is observed in the in-plane transport of bottom gated thin film transistors. This suggests that the texture change is prevalent in the film interior and that either the (bottom) surface structure is different from the interior structure or the intracrystalline order and texture play a secondary role in transistor transport for this material.}, language = {en} } @article{RichterKrauseFechneretal.2011, author = {Richter, Philipp and Krause, F. and Fechner, Cora and Charlton, Jane C. and Murphy, M. T.}, title = {The neutral gas extent of galaxies as derived from weak intervening Ca II absorbers}, series = {Astronomy and astrophysics : an international weekly journal}, volume = {528}, journal = {Astronomy and astrophysics : an international weekly journal}, number = {4}, publisher = {EDP Sciences}, address = {Les Ulis}, issn = {0004-6361}, doi = {10.1051/0004-6361/201015566}, pages = {22}, year = {2011}, abstract = {We present a systematic study of weak intervening CaII absorbers at low redshift (z < 0.5), based on the analysis of archival high-resolution (R >= 45 000) optical spectra of 304 quasars and active galactic nuclei observed with VLT/UVES. Along a total redshift path of Delta z approximate to 100 we detected 23 intervening CaII absorbers in both the CaII H \& K lines, with rest frame equivalent widths W-r,W-3934 = 15-799 m angstrom and column densities log N(CaII) = 11.25-13.04 (obtained by fitting Voigt-profile components). We obtain a bias-corrected number density of weak intervening CaII absorbers of dN/dz = 0.117 +/- 0.044 at < z(abs)> = 0.35 for absorbers with log N(CaII) >= 11.65 (W-r,W-3934 >= 32 m angstrom). This is similar to 2.6 times the value obtained for damped Lyman alpha absorbers (DLAs) at low redshift. All CaII absorbers in our sample show associated absorption by other low ions such as MgII and FeII; 45 percent of them have associated NaI absorption. From ionization modelling we conclude that intervening CaII absorption with log N(CaII) >= 11.5 arises in DLAs, sub-DLAs and Lyman-limit systems (LLS) at HI column densities of log N(HI) >= 17.4. Using supplementary HI information for nine of the absorbers we find that the CaII/HI ratio decreases strongly with increasing HI column density, indicating a column-density-dependent dust depletion of Ca. The observed column density distribution function of CaII absorption components follows a relatively steep power law, f(N) proportional to N-beta, with a slope of -beta = -1.68, which again points towards an enhanced dust depletion in high column density systems. The relatively large cross section of these absorbers together with the frequent detection of CaII absorption in high-velocity clouds (HVCs) in the halo of the Milky Way suggests that a considerable fraction of the intervening CaII systems trace (partly) neutral gas structures in the halos and circumgalactic environment of galaxies (i.e., they are HVC analogs). Based on the recently measured detection rate of CaII absorption in the Milky Way HVCs we estimate that the mean (projected) CaII covering fraction of galaxies and their gaseous halos is < f(c,CaII)> = 0.33. Using this value and considering all galaxies with luminosities L >= 0.05 L-star we calculate that the characteristic radial extent of (partly) neutral gas clouds with log N(HI) >= 17.4 around low-redshift galaxies is R-HVC approximate to 55 kpc.}, language = {en} } @misc{ReicheKratzHofmannetal.2011, author = {Reiche, J{\"u}rgen and Kratz, Karl and Hofmann, Dieter and Lendlein, Andreas}, title = {Current status of Langmuir monolayer degradation of polymeric biomaterials}, series = {The international journal of artificial organs}, volume = {34}, journal = {The international journal of artificial organs}, number = {2}, publisher = {Wichtig}, address = {Milano}, issn = {0391-3988}, doi = {10.5301/IJAO.2011.6401}, pages = {123 -- 128}, year = {2011}, abstract = {Langmuir monolayer degradation (LMD) experiments with polymers possessing outstanding biomedical application potential yield information regarding the kinetics of their hydrolytic or enzymatic chain scission under well-defined and adjustable degradation conditions. A brief review is given of LMD investigations, including the author's own work on 2-dimensional (2D) polymer systems, providing chain scission data, which are not disturbed by simultaneously occurring transport phenomena, such as water penetration into the sample or transport of scission fragments out of the sample. A knowledge-based approach for the description and simulation of polymer hydrolytic and enzymatic degradation based on a combination of fast LMD experiments and computer simulation of the water penetration is briefly introduced. Finally, the advantages and disadvantages of this approach are discussed.}, language = {en} } @book{Rabe2011, author = {Rabe, Thorid}, title = {Physikdidaktische Lehrerprofessionalisierung zwischen Anspruch und Wirklichkeit : Antrittsvorlesung 2011-06-08}, publisher = {Univ.-Bibl.}, address = {Potsdam}, year = {2011}, abstract = {Physiklehrer bestimmen durch die Gestaltung des Unterrichts und damit durch ihr professionelles Handeln maßgeblich mit, wie die individuellen Lernprozesse der Sch{\"u}ler zu Inhalten der Physik ablaufen. F{\"u}r die Entwicklung ihrer professionellen Handlungskompetenz m{\"u}ssen zuk{\"u}nftige Physiklehrer einerseits physikalisches, physikdidaktisches und p{\"a}dagogisches Wissen erwerben und andererseits motiviert sein, dieses Wissen auch anzuwenden. In ihrer Vorlesung geht Thorid Rabe der Frage nach, welche physikdidaktischen Kompetenzen Studierende im Rahmen der universit{\"a}ren Ausbildung erwerben sollten. Am Beispiel der Lehrveranstaltung "Physikalische Schulexperimente" zeigt sie, wie physikdidaktische Theorie und praktisches Lehrerhandeln aufeinander bezogen werden k{\"o}nnen. Zudem wird sie ein Forschungsprojekt vorstellen, das einem bisher vernachl{\"a}ssigten Aspekt professioneller Handlungskompetenz nachgeht, n{\"a}mlich den dom{\"a}nenspezifischen Selbstwirksamkeitserwartungen - dem Zutrauen in sich selbst, als Physiklehrer angemessen und erfolgreich handeln zu k{\"o}nnen.}, language = {de} } @article{QiuWirgesGerhard2011, author = {Qiu, Xunlin and Wirges, Werner and Gerhard, Reimund}, title = {Beneficial and detrimental fatigue effects of dielectric barrier discharges on the piezoelectricity of polypropylene ferroelectrets}, series = {Journal of applied physics}, volume = {110}, journal = {Journal of applied physics}, number = {2}, publisher = {American Institute of Physics}, address = {Melville}, issn = {0021-8979}, doi = {10.1063/1.3610507}, pages = {8}, year = {2011}, abstract = {Cellular polypropylene (PP) ferroelectrets combine a large piezoelectricity with mechanical flexibility and elastic compliance. Their charging process represents a series of dielectric barrier discharges (DBDs) that generate a cold plasma with numerous active species and thus modify the inner polymer surfaces of the foam cells. Both the threshold for the onset of DBDs and the piezoelectricity of ferroelectrets are sensitive to repeated DBDs in the voids. It is found that the threshold voltage is approximately halved and the charging efficiency is clearly improved after only 10(3) DBD cycles. However, plasma modification of the inner surfaces from repeated DBDs deteriorates the chargeability of the voids, leading to a significant reduction of the piezoelectricity in ferroelectrets. After a significant waiting period, the chargeability of previously fatigued voids shows a partial recovery. The plasma modification is, however, detrimental to the stability of the deposited charges and thus also of the macroscopic dipoles and of the piezoelectricity. Fatigue from only 10(3) DBD cycles already results in significantly less stable piezoelectricity in cellular PP ferroelectrets. The fatigue rate as a function of the number of voltage cycles follows a stretched exponential. Fatigue from repeated DBDs can be avoided if most of the gas molecules inside the voids are removed via a suitable evacuation process.}, language = {en} } @article{QiuGerhardMellinger2011, author = {Qiu, Xunlin and Gerhard, Reimund and Mellinger, Axel}, title = {Turning polymer foams or polymer-film systems into ferroelectrets dielectric barrier discharges in voids}, series = {IEEE transactions on dielectrics and electrical insulation}, volume = {18}, journal = {IEEE transactions on dielectrics and electrical insulation}, number = {1}, publisher = {Inst. of Electr. and Electronics Engineers}, address = {Piscataway}, issn = {1070-9878}, doi = {10.1109/TDEI.2011.5704490}, pages = {34 -- 42}, year = {2011}, abstract = {Polymer foams and void-containing polymer-film systems with internally charged voids combine large piezoelectricity with mechanical flexibility and elastic compliance. This new class of soft materials (often called ferro-or piezoelectrets) has attracted considerable attention from science and industry. It has been found that the voids can be internally charged by means of dielectric barrier discharges (DBDs) under high electric fields. The charged voids can be considered as man-made macroscopic dipoles. Depending on the ferroelectret structure and the pressure of the internal gas, the voids may be highly compressible. Consequently, very large dipole-moment changes can be induced by mechanical or electrical stresses, leading to large piezoelectricity. DBD charging of the voids is a critical process for rendering polymer foams piezoelectric. Thus a comprehensive exploration of DBD charging is essential for the understanding and the optimization of piezoelectricity in ferroelectrets. Recent studies show that DBDs in the voids are triggered when the internal electric field reaches a threshold value according to Townsend's model of Paschen breakdown. During the DBDs, charges of opposite polarity are generated and trapped at the top and bottom internal surfaces of the gas-filled voids, respectively. The deposited charges induce an electric field opposite to the externally applied one and thus extinguish the DBDs. Back discharges may eventually be triggered when the external voltage is reduced or turned off. In order to optimize the efficiency of DBD charging, the geometry (in particular the height) of the voids, the type of gas and its pressure inside the voids are essential factors to be considered and to be optimized. In addition, the influence of the plasma treatment on the internal void surfaces during the DBDs should be taken into consideration.}, language = {en} } @misc{Qiu2011, author = {Qiu, Xunlin}, title = {Patterned piezo-, pyro-, and ferroelectricity of poled polymer electrets}, series = {Journal of applied physics}, volume = {110}, journal = {Journal of applied physics}, number = {5}, publisher = {American Institute of Physics}, address = {Melville}, issn = {0021-8979}, doi = {10.1063/1.3638069}, pages = {1}, year = {2011}, language = {en} } @article{ProsenIlievski2011, author = {Prosen, Tomaz and Ilievski, Enej}, title = {Nonequilibrium phase transition in a periodically driven XY spin chain}, series = {Physical review letters}, volume = {107}, journal = {Physical review letters}, number = {6}, publisher = {American Physical Society}, address = {College Park}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.107.060403}, pages = {4}, year = {2011}, abstract = {We present a general formulation of Floquet states of periodically time-dependent open Markovian quasifree fermionic many-body systems in terms of a discrete Lyapunov equation. Illustrating the technique, we analyze periodically kicked XY spin-1/2 chain which is coupled to a pair of Lindblad reservoirs at its ends. A complex phase diagram is reported with reentrant phases of long range and exponentially decaying spin-spin correlations as some of the system's parameters are varied. The structure of phase diagram is reproduced in terms of counting nontrivial stationary points of Floquet quasiparticle dispersion relation.}, language = {en} } @article{Prosen2011, author = {Prosen, Tomaz}, title = {Complexity and nonseparability of classical Liouvillian dynamics}, series = {Physical review : E, Statistical, nonlinear and soft matter physics}, volume = {83}, journal = {Physical review : E, Statistical, nonlinear and soft matter physics}, number = {3}, publisher = {American Physical Society}, address = {College Park}, issn = {1539-3755}, doi = {10.1103/PhysRevE.83.031124}, pages = {5}, year = {2011}, abstract = {We propose a simple complexity indicator of classical Liouvillian dynamics, namely the separability entropy, which determines the logarithm of an effective number of terms in a Schmidt decomposition of phase space density with respect to an arbitrary fixed product basis. We show that linear growth of separability entropy provides a stricter criterion of complexity than Kolmogorov-Sinai entropy, namely it requires that the dynamics be exponentially unstable, nonlinear, and non-Markovian.}, language = {en} } @article{PostbergSchmidtHillieretal.2011, author = {Postberg, Frank and Schmidt, J. and Hillier, J. and Kempf, Sascha and Srama, Ralf}, title = {A salt-water reservoir as the source of a compositionally stratified plume on Enceladus}, series = {Nature : the international weekly journal of science}, volume = {474}, journal = {Nature : the international weekly journal of science}, number = {7353}, publisher = {Nature Publ. Group}, address = {London}, issn = {0028-0836}, doi = {10.1038/nature10175}, pages = {620 -- 622}, year = {2011}, abstract = {The discovery of a plume of water vapour and ice particles emerging from warm fractures ('tiger stripes') in Saturn's small, icy moon Enceladus(1-6) raised the question of whether the plume emerges from a subsurface liquid source(6-8) or from the decomposition of ice(9-12). Previous compositional analyses of particles injected by the plume into Saturn's diffuse E ring have already indicated the presence of liquid water(8), but the mechanisms driving the plume emission are still debated(13). Here we report an analysis of the composition of freshly ejected particles close to the sources. Salt-rich ice particles are found to dominate the total mass flux of ejected solids (more than 99 per cent) but they are depleted in the population escaping into Saturn's E ring. Ice grains containing organic compounds are found to be more abundant in dense parts of the plume. Whereas previous Cassini observations were compatible with a variety of plume formation mechanisms, these data eliminate or severely constrain non-liquid models and strongly imply that a salt-water reservoir with a large evaporating surface(7,8) provides nearly all of the matter in the plume.}, language = {en} } @article{PontiusKachelSchuesslerLangeheineetal.2011, author = {Pontius, N. and Kachel, T. and Sch{\"u}ssler-Langeheine, C. and Schlotter, W. F. and Beye, Martin and Sorgenfrei, Nomi and Chang, C. F. and F{\"o}hlisch, Alexander and Wurth, W. and Metcalf, P. and Leonov, I. and Yaresko, A. and Stojanovic, N. and Berglund, Martin and Guerassimova, N. and Duesterer, S. and Redlin, H. and Duerr, H. A.}, title = {Time-resolved resonant soft x-ray diffraction with free-electron lasers femtosecond dynamics across the Verwey transition in magnetite}, series = {Applied physics letters}, volume = {98}, journal = {Applied physics letters}, number = {18}, publisher = {American Institute of Physics}, address = {Melville}, issn = {0003-6951}, doi = {10.1063/1.3584855}, pages = {3}, year = {2011}, abstract = {Resonant soft x-ray diffraction (RSXD) with femtosecond (fs) time resolution is a powerful tool for disentangling the interplay between different degrees of freedom in strongly correlated electron materials. It allows addressing the coupling of particular degrees of freedom upon an external selective perturbation, e. g., by an optical or infrared laser pulse. Here, we report a time-resolved RSXD experiment from the prototypical correlated electron material magnetite using soft x-ray pulses from the free-electron laser FLASH in Hamburg. We observe ultrafast melting of the charge-orbital order leading to the formation of a transient phase, which has not been observed in equilibrium.}, language = {en} } @article{PohlEichler2011, author = {Pohl, Martin and Eichler, David}, title = {Origin of ultra-high-energy galactic cosmic rays the isotropy problem}, series = {The astrophysical journal : an international review of spectroscopy and astronomical physics}, volume = {742}, 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/742/2/114}, pages = {11}, year = {2011}, abstract = {We study the propagation of ultra-high-energy cosmic rays (UHECRs) in the Galaxy, concentrating on the energy range below the ankle in the spectrum at 4 EeV. A Monte Carlo method, based on analytical solutions to the time-dependent diffusion problem, is used to account for intermittency by placing sources at random locations. Assuming a source population that scales with baryon mass density or star formation (e.g., long GRB), we derive constraints arising from intermittency and the observational limits on the composition and anisotropy. It is shown that the composition and anisotropy at 10(18) eV are difficult to reproduce and require that either (1) the particle mean free path is much smaller than a gyroradius, implying the escape time is very long, (2) the composition is heavier than suggested by recent Auger data, (3) the ultra-high-energy sub-ankle component is mostly extragalactic, or (4) we are living in a rare lull in the UHECR production, and the current UHECR intensity is far below the Galactic time average. We therefore recommend a strong observational focus on determining the UHECR composition around 10(18) eV.}, language = {en} } @article{PikovskijRosenblum2011, author = {Pikovskij, Arkadij and Rosenblum, Michael}, title = {Dynamics of heterogeneous oscillator ensembles in terms of collective variables}, series = {Physica :D, Nonlinear phenomena}, volume = {240}, journal = {Physica :D, Nonlinear phenomena}, number = {9-10}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0167-2789}, doi = {10.1016/j.physd.2011.01.002}, pages = {872 -- 881}, year = {2011}, abstract = {We consider general heterogeneous ensembles of phase oscillators, sine coupled to arbitrary external fields. Starting with the infinitely large ensembles, we extend the Watanabe-Strogatz theory, valid for identical oscillators, to cover the case of an arbitrary parameter distribution. The obtained equations yield the description of the ensemble dynamics in terms of collective variables and constants of motion. As a particular case of the general setup we consider hierarchically organized ensembles, consisting of a finite number of subpopulations, whereas the number of elements in a subpopulation can be both finite or infinite. Next, we link the Watanabe-Strogatz and Ott-Antonsen theories and demonstrate that the latter one corresponds to a particular choice of constants of motion. The approach is applied to the standard Kuramoto-Sakaguchi model, to its extension for the case of nonlinear coupling, and to the description of two interacting subpopulations, exhibiting a chimera state. With these examples we illustrate that, although the asymptotic dynamics can be found within the framework of the Ott-Antonsen theory, the transients depend on the constants of motion. The most dramatic effect is the dependence of the basins of attraction of different synchronous regimes on the initial configuration of phases.}, language = {en} } @article{PikovskijFishman2011, author = {Pikovskij, Arkadij and Fishman, Shmuel}, title = {Scaling properties of weak chaos in nonlinear disordered lattices}, series = {Physical review : E, Statistical, nonlinear and soft matter physics}, volume = {83}, 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.83.025201}, pages = {4}, year = {2011}, abstract = {We study the discrete nonlinear Schrodinger equation with a random potential in one dimension. It is characterized by the length, the strength of the random potential, and the field density that determines the effect of nonlinearity. Following the time evolution of the field and calculating the largest Lyapunov exponent, the probability of the system to be regular is established numerically and found to be a scaling function of the parameters. This property is used to calculate the asymptotic properties of the system in regimes beyond our computational power.}, language = {en} } @article{PietzschSunHenniesetal.2011, author = {Pietzsch, Annette and Sun, Y. -P. and Hennies, Franz and Rinkevicius, Z. and Karlsson, Hans O. and Schmitt, Thorsten and Strocov, Vladimir N. and Andersson, Joakim and Kennedy, B. and Schlappa, J. and F{\"o}hlisch, Alexander and Rubensson, Jan-Erik and Gel'mukhanov, F.}, title = {Spatial quantum beats in vibrational resonant inelastic soft X-ray scattering at dissociating states in oxygen}, series = {Physical review letters}, volume = {106}, journal = {Physical review letters}, number = {15}, publisher = {American Physical Society}, address = {College Park}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.106.153004}, pages = {4}, year = {2011}, abstract = {Resonant inelastic soft x-ray scattering (RIXS) spectra excited at the 1 sigma(g) -> 3 sigma(u) resonance in gas-phase O-2 show excitations due to the nuclear degrees of freedom with up to 35 well-resolved discrete vibronic states and a continuum due to the kinetic energy distribution of the separated atoms. The RIXS profile demonstrates spatial quantum beats caused by two interfering wave packets with different momenta as the atoms separate. Thomson scattering strongly affects both the spectral profile and the scattering anisotropy.}, language = {en} } @phdthesis{Partl2011, author = {Partl, Adrian M.}, title = {Cosmological radiative transfer and the lonisation of the integalactic medium}, address = {Potsdam}, pages = {205 S.}, year = {2011}, language = {en} } @phdthesis{Osterloh2011, author = {Osterloh, Lukas}, title = {Retrieving aerosol microphysical properties from multiwavelength Lidar Data}, address = {Potsdam}, pages = {125 S.}, year = {2011}, language = {en} } @article{OskinovaTodtIgnaceetal.2011, author = {Oskinova, Lida and Todt, Helge Tobias and Ignace, Richard and Brown, John C. and Cassinelli, Joseph P. and Hamann, Wolf-Rainer}, title = {Early magnetic B-type stars X-ray emission and wind properties}, series = {Monthly notices of the Royal Astronomical Society}, volume = {416}, journal = {Monthly notices of the Royal Astronomical Society}, number = {2}, publisher = {Wiley-Blackwell}, address = {Hoboken}, issn = {0035-8711}, doi = {10.1111/j.1365-2966.2011.19143.x}, pages = {1456 -- 1474}, year = {2011}, abstract = {We present a comprehensive study of X-ray emission by, and wind properties of, massive magnetic early B-type stars. Dedicated XMM-Newton observations were obtained for three early-type B-type stars, xi(1) CMa, V2052 Oph and zeta Cas, with recently discovered magnetic fields. We report the first detection of X-ray emission from V2052 Oph and zeta Cas. The latter is one the softest X-ray sources among the early-type stars, while the former is one of the X-ray faintest. The observations show that the X-ray spectra of our programme stars are quite soft with the bulk of X-ray emitting material having a temperature of about 1 MK. We compile the complete sample of early B-type stars with detected magnetic fields to date and existing X-ray measurements, in order to study whether the X-ray emission can be used as a general proxy for stellar magnetism. We find that the X-ray properties of early massive B-type magnetic stars are diverse, and that hard and strong X-ray emission does not necessarily correlate with the presence of a magnetic field, corroborating similar conclusions reached earlier for the classical chemically peculiar magnetic Bp-Ap stars. We analyse the ultraviolet (UV) spectra of five non-supergiant B stars with magnetic fields (tau Sco, beta Cep, xi(1) CMa, V2052 Oph and zeta Cas) by means of non-local thermodynamic equilibrium (non-LTE) iron-blanketed model atmospheres. The latter are calculated with the Potsdam Wolf-Rayet (PoWR) code, which treats the photosphere as well as the wind, and also accounts for X-rays. With the exception of t Sco, this is the first analysis of these stars by means of stellar wind models. Our models accurately fit the stellar photospheric spectra in the optical and the UV. The parameters of X-ray emission, temperature and flux are included in the model in accordance with observations. We confirm the earlier findings that the filling factors of X-ray emitting material are very high. Our analysis reveals that the magnetic early-type B stars studied here have weak winds with velocities not significantly exceeding upsilon(esc). The mass-loss rates inferred from the analysis of UV lines are significantly lower than predicted by hydrodynamically consistent models. We find that, although the X-rays strongly affect the ionization structure of the wind, this effect is not sufficient in reducing the total radiative acceleration. When the X-rays are accounted for at the intensity and temperatures observed, there is still sufficient radiative acceleration to drive a stronger mass-loss than we empirically infer from the UV spectral lines.}, language = {en} } @article{OskinovaHamannCassinellietal.2011, author = {Oskinova, Lida and Hamann, Wolf-Rainer and Cassinelli, Joseph P. and Brown, John C. and Todt, Helge Tobias}, title = {X-ray emission from massive stars with magnetic fields}, series = {Astronomische Nachrichten = Astronomical notes}, volume = {332}, journal = {Astronomische Nachrichten = Astronomical notes}, number = {9-10}, publisher = {Wiley-Blackwell}, address = {Malden}, issn = {0004-6337}, doi = {10.1002/asna.201111602}, pages = {988 -- 993}, year = {2011}, abstract = {We investigate the connections between the magnetic fields and the X-ray emission from massive stars. Our study shows that the X-ray properties of known strongly magnetic stars are diverse: while some comply to the predictions of the magnetically confined wind model, others do not. We conclude that strong, hard, and variable X-ray emission may be a sufficient attribute of magnetic massive stars, but it is not a necessary one. We address the general properties of X-ray emission from "normal" massive stars, especially the long standing mystery about the correlations between the parameters of X-ray emission and fundamental stellar properties. The recent development in stellar structure modeling shows that small-scale surface magnetic fields may be common. We suggest a "hybrid" scenario which could explain the X-ray emission from massive stars by a combination of magnetic mechanisms on the surface and shocks in the stellar wind. The magnetic mechanisms and the wind shocks are triggered by convective motions in sub-photospheric layers. This scenario opens the door for a natural explanation of the well established correlation between bolometric and X-ray luminosities.}, language = {en} } @article{NavirianHerzogGoldshteynetal.2011, author = {Navirian, Hengameh A. and Herzog, Marc and Goldshteyn, J. and Leitenberger, Wolfram and Vrejoiu, Ionella and Khakhulin, D. and Wulff, M. and Shayduk, Roman and Gaal, P. and Bargheer, Matias}, title = {Shortening x-ray pulses for pump-probe experiments at synchrotrons}, series = {Journal of applied physics}, volume = {109}, journal = {Journal of applied physics}, number = {12}, publisher = {American Institute of Physics}, address = {Melville}, issn = {0021-8979}, doi = {10.1063/1.3601057}, pages = {3}, year = {2011}, abstract = {We implemented an experimental scheme for ultrafast x-ray diffraction at storage rings based on a laser-driven Bragg-switch that shortens the x-ray pulses emitted from an undulator. The increased time-resolution is demonstrated by observing changes of intensity, position and width of the diffraction peaks of a La(0.7)Sr(0.3)MnO(3)/SrTiO(3) superlattice sample after optical excitation, i.e., by quantitatively measuring the propagation of an expansion wave through the sample. These experimental transients with timescales of 35 to 60 ps evidence a reduction of the x-ray pulse duration by a factor of two.}, language = {en} } @article{MuellerHaakhCalarcoetal.2011, author = {M{\"u}ller, Matthias M. and Haakh, Harald R. and Calarco, Tommaso and Koch, Christiane P. and Henkel, Carsten}, title = {Prospects for fast Rydberg gates on an atom chip}, series = {Quantum information processing}, volume = {10}, journal = {Quantum information processing}, number = {6}, publisher = {Springer}, address = {New York}, issn = {1570-0755}, doi = {10.1007/s11128-011-0296-0}, pages = {771 -- 792}, year = {2011}, abstract = {Atom chips are a promising candidate for a scalable architecture for quantum information processing provided a universal set of gates can be implemented with high fidelity. The difficult part in achieving universality is the entangling two-qubit gate. We consider a Rydberg phase gate for two atoms trapped on a chip and employ optimal control theory to find the shortest gate that still yields a reasonable gate error. Our parameters correspond to a situation where the Rydberg blockade regime is not yet reached. We discuss the role of spontaneous emission and the effect of noise from the chip surface on the atoms in the Rydberg state.}, language = {en} } @article{MuellerGrossEisert2011, author = {M{\"u}ller, Markus P. and Gross, David and Eisert, Jens}, title = {Concentration of Measure for Quantum States with a Fixed Expectation Value}, series = {Communications in mathematical physics}, volume = {303}, journal = {Communications in mathematical physics}, number = {3}, publisher = {Springer}, address = {New York}, issn = {0010-3616}, doi = {10.1007/s00220-011-1205-1}, pages = {785 -- 824}, year = {2011}, abstract = {Given some observable H on a finite-dimensional quantum system, we investigate the typical properties of random state vectors vertical bar psi >> that have a fixed expectation value < psi vertical bar H vertical bar psi > = E with respect to H. Under some conditions on the spectrum, we prove that this manifold of quantum states shows a concentration of measure phenomenon: any continuous function on this set is almost everywhere close to its mean. We also give a method to estimate the corresponding expectation values analytically, and we prove a formula for the typical reduced density matrix in the case that H is a sum of local observables. We discuss the implications of our results as new proof tools in quantum information theory and to study phenomena in quantum statistical mechanics. As a by-product, we derive a method to sample the resulting distribution numerically, which generalizes the well-known Gaussian method to draw random states from the sphere.}, language = {en} } @phdthesis{Moesta2011, author = {M{\"o}sta, Philipp}, title = {Novel aspects of the dynamics of binary black-hole mergers}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-59820}, school = {Universit{\"a}t Potsdam}, year = {2011}, abstract = {The inspiral and merger of two black holes is among the most exciting and extreme events in our universe. Being one of the loudest sources of gravitational waves, they provide a unique dynamical probe of strong-field general relativity and a fertile ground for the observation of fundamental physics. While the detection of gravitational waves alone will allow us to observe our universe through an entirely new window, combining the information obtained from both gravitational wave and electro-magnetic observations will allow us to gain even greater insight in some of the most exciting astrophysical phenomena. In addition, binary black-hole mergers serve as an intriguing tool to study the geometry of space-time itself. In this dissertation we study the merger process of binary black-holes in a variety of conditions. Our results show that asymmetries in the curvature distribution on the common apparent horizon are correlated to the linear momentum acquired by the merger remnant. We propose useful tools for the analysis of black holes in the dynamical and isolated horizon frameworks and shed light on how the final merger of apparent horizons proceeds after a common horizon has already formed. We connect mathematical theorems with data obtained from numerical simulations and provide a first glimpse on the behavior of these surfaces in situations not accessible to analytical tools. We study electro-magnetic counterparts of super-massive binary black-hole mergers with fully 3D general relativistic simulations of binary black-holes immersed both in a uniform magnetic field in vacuum and in a tenuous plasma. We find that while a direct detection of merger signatures with current electro-magnetic telescopes is unlikely, secondary emission, either by altering the accretion rate of the circumbinary disk or by synchrotron radiation from accelerated charges, may be detectable. We propose a novel approach to measure the electro-magnetic radiation in these simulations and find a non-collimated emission that dominates over the collimated one appearing in the form of dual jets associated with each of the black holes. Finally, we provide an optimized gravitational wave detection pipeline using phenomenological waveforms for signals from compact binary coalescence and show that by including spin effects in the waveform templates, the detection efficiency is drastically improved as well as the bias on recovered source parameters reduced. On the whole, this disseration provides evidence that a multi-messenger approach to binary black-hole merger observations provides an exciting prospect to understand these sources and, ultimately, our universe.}, language = {en} } @article{MulanskyAhnertPikovskijetal.2011, author = {Mulansky, Mario and Ahnert, Karsten and Pikovskij, Arkadij and Shepelyansky, Dima L.}, title = {Strong and weak chaos in weakly nonintegrable many-body hamiltonian systems}, series = {Journal of statistical physics}, volume = {145}, journal = {Journal of statistical physics}, number = {5}, publisher = {Springer}, address = {New York}, issn = {0022-4715}, doi = {10.1007/s10955-011-0335-3}, pages = {1256 -- 1274}, year = {2011}, abstract = {We study properties of chaos in generic one-dimensional nonlinear Hamiltonian lattices comprised of weakly coupled nonlinear oscillators by numerical simulations of continuous-time systems and symplectic maps. For small coupling, the measure of chaos is found to be proportional to the coupling strength and lattice length, with the typical maximal Lyapunov exponent being proportional to the square root of coupling. This strong chaos appears as a result of triplet resonances between nearby modes. In addition to strong chaos we observe a weakly chaotic component having much smaller Lyapunov exponent, the measure of which drops approximately as a square of the coupling strength down to smallest couplings we were able to reach. We argue that this weak chaos is linked to the regime of fast Arnold diffusion discussed by Chirikov and Vecheslavov. In disordered lattices of large size we find a subdiffusive spreading of initially localized wave packets over larger and larger number of modes. The relations between the exponent of this spreading and the exponent in the dependence of the fast Arnold diffusion on coupling strength are analyzed. We also trace parallels between the slow spreading of chaos and deterministic rheology.}, language = {en} } @article{MulanskyAhnertPikovskij2011, author = {Mulansky, Mario and Ahnert, Karsten and Pikovskij, Arkadij}, title = {Scaling of energy spreading in strongly nonlinear disordered lattices}, series = {Physical review : E, Statistical, nonlinear and soft matter physics}, volume = {83}, 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.83.026205}, pages = {4}, year = {2011}, abstract = {To characterize a destruction of Anderson localization by nonlinearity, we study the spreading behavior of initially localized states in disordered, strongly nonlinear lattices. Due to chaotic nonlinear interaction of localized linear or nonlinear modes, energy spreads nearly subdiffusively. Based on a phenomenological description by virtue of a nonlinear diffusion equation, we establish a one-parameter scaling relation between the velocity of spreading and the density, which is confirmed numerically. From this scaling it follows that for very low densities the spreading slows down compared to the pure power law.}, language = {en} } @article{MontoyaBornLevermann2011, author = {Montoya, Marisa and Born, Andreas and Levermann, Anders}, title = {Reversed North Atlantic gyre dynamics in present and glacial climates}, series = {Climate dynamics : observational, theoretical and computational research on the climate system}, volume = {36}, journal = {Climate dynamics : observational, theoretical and computational research on the climate system}, number = {5-6}, publisher = {Springer}, address = {New York}, issn = {0930-7575}, doi = {10.1007/s00382-009-0729-y}, pages = {1107 -- 1118}, year = {2011}, abstract = {The dynamics of the North Atlantic subpolar gyre (SPG) are assessed under present and glacial boundary conditions by investigating the SPG sensitivity to surface wind-stress changes in a coupled climate model. To this end, the gyre transport is decomposed in Ekman, thermohaline, and bottom transports. Surface wind-stress variations are found to play an important indirect role in SPG dynamics through their effect on water-mass densities. Our results suggest the existence of two dynamically distinct regimes of the SPG, depending on the absence or presence of deep water formation (DWF) in the Nordic Seas and a vigorous Greenland-Scotland ridge (GSR) overflow. In the first regime, the GSR overflow is weak and the SPG strength increases with wind-stress as a result of enhanced outcropping of isopycnals in the centre of the SPG. As soon as a vigorous GSR overflow is established, its associated positive density anomalies on the southern GSR slope reduce the SPG strength. This has implications for past glacial abrupt climate changes, insofar as these can be explained through latitudinal shifts in North Atlantic DWF sites and strengthening of the North Atlantic current. Regardless of the ultimate trigger, an abrupt shift of DWF into the Nordic Seas could result both in a drastic reduction of the SPG strength and a sudden reversal in its sensitivity to wind-stress variations. Our results could provide insight into changes in the horizontal ocean circulation during abrupt glacial climate changes, which have been largely neglected up to now in model studies.}, language = {en} } @article{MizunoPohlNiemiecetal.2011, author = {Mizuno, Yosuke and Pohl, Martin and Niemiec, Jacek and Zhang, Bing and Nishikawa, Ken-Ichi and Hardee, Philip E.}, title = {Magnetic-field amplification by turbulence in a relativistic shockpropagating through an inhomogeneous medium}, series = {The astrophysical journal : an international review of spectroscopy and astronomical physics}, volume = {726}, 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/726/2/62}, pages = {11}, year = {2011}, abstract = {We perform two-dimensional relativistic magnetohydrodynamic simulations of a mildly relativistic shock propagating through an inhomogeneous medium. We show that the postshock region becomes turbulent owing to preshock density inhomogeneity, and the magnetic field is strongly amplified due to the stretching and folding of field lines in the turbulent velocity field. The amplified magnetic field evolves into a filamentary structure in two-dimensional simulations. The magnetic energy spectrum is flatter than the Kolmogorov spectrum and indicates that a so-called small-scale dynamo is occurring in the postshock region. We also find that the amount of magnetic-field amplification depends on the direction of the mean preshock magnetic field, and the timescale of magnetic-field growth depends on the shock strength.}, language = {en} } @phdthesis{Mielke2011, author = {Mielke, Moritz}, title = {Atmosph{\"a}rische Prozesstudien auf der Basis von Beobachtungen und regionalen Klimamodellsimulationen in der Arktis}, address = {Potsdam}, pages = {130 S.}, year = {2011}, language = {de} } @article{MellingerMellinger2011, author = {Mellinger, Axel and Mellinger, Olena}, title = {Breakdown threshold of dielectric barrier discharges in ferroelectrets where Paschen's law fails}, series = {IEEE transactions on dielectrics and electrical insulation}, volume = {18}, journal = {IEEE transactions on dielectrics and electrical insulation}, number = {1}, publisher = {Inst. of Electr. and Electronics Engineers}, address = {Piscataway}, issn = {1070-9878}, doi = {10.1109/TDEI.2011.5704491}, pages = {43 -- 48}, year = {2011}, abstract = {The piezoelectric activity of charged cellular foams (so-called ferroelectrets) is compared against simulations based on a multi-layer electromechanical model and Townsend's model of Paschen breakdown, with the distribution of void heights determined from scanning electron micrographs. While the calculated space charge hysteresis curves are in good agreement with experimental data, the onset of piezoelectric activity is observed at significantly higher electric fields than predicted by Paschen's law. One likely explanation is that the commonly accepted Paschen curve for electric breakdown in air poorly describes the critical electric field for dielectric barrier discharges in micrometer-size cavities.}, language = {en} } @phdthesis{Matthes2011, author = {Matthes, Heidrun}, title = {Interaction of land surface processes and the atmophere in the Arctic - senitivities and extremes}, address = {Potsdam}, pages = {123 S.}, year = {2011}, language = {en} } @article{MasanesMueller2011, author = {Masanes, Lluis and M{\"u}ller, Markus P.}, title = {A derivation of quantum theory from physical requirements}, series = {New journal of physics : the open-access journal for physics}, volume = {13}, journal = {New journal of physics : the open-access journal for physics}, number = {1}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {1367-2630}, doi = {10.1088/1367-2630/13/6/063001}, pages = {29}, year = {2011}, abstract = {Quantum theory (QT) is usually formulated in terms of abstract mathematical postulates involving Hilbert spaces, state vectors and unitary operators. In this paper, we show that the full formalism of QT can instead be derived from five simple physical requirements, based on elementary assumptions regarding preparations, transformations and measurements. This is very similar to the usual formulation of special relativity, where two simple physical requirements-the principles of relativity and light speed invariance-are used to derive the mathematical structure of Minkowski space-time. Our derivation provides insights into the physical origin of the structure of quantum state spaces (including a group-theoretic explanation of the Bloch ball and its three dimensionality) and suggests several natural possibilities to construct consistent modifications of QT.}, language = {en} } @article{MartinWinkelmannHaseloffetal.2011, author = {Martin, Maria A. and Winkelmann, Ricarda and Haseloff, M. and Albrecht, Tanja and Bueler, Ed and Khroulev, C. and Levermann, Anders}, title = {The Potsdam parallel ice sheet model (PISM-PIK) - Part 2: Dynamic equilibrium simulation of the Antarctic ice sheet}, series = {The Cryosphere : TC ; an interactive open access journal of the European Geosciences Union}, volume = {5}, journal = {The Cryosphere : TC ; an interactive open access journal of the European Geosciences Union}, number = {3}, publisher = {Copernicus}, address = {G{\"o}ttingen}, issn = {1994-0416}, doi = {10.5194/tc-5-727-2011}, pages = {727 -- 740}, year = {2011}, abstract = {We present a dynamic equilibrium simulation of the ice sheet-shelf system on Antarctica with the Potsdam Parallel Ice Sheet Model (PISM-PIK). The simulation is initialized with present-day conditions for bed topography and ice thickness and then run to steady state with constant present-day surface mass balance. Surface temperature and sub-shelf basal melt distribution are parameterized. Grounding lines and calving fronts are free to evolve, and their modeled equilibrium state is compared to observational data. A physically-motivated calving law based on horizontal spreading rates allows for realistic calving fronts for various types of shelves. Steady-state dynamics including surface velocity and ice flux are analyzed for whole Antarctica and the Ronne-Filchner and Ross ice shelf areas in particular. The results show that the different flow regimes in sheet and shelves, and the transition zone between them, are captured reasonably well, supporting the approach of superposition of SIA and SSA for the representation of fast motion of grounded ice. This approach also leads to a natural emergence of sliding-dominated flow in stream-like features in this new 3-D marine ice sheet model.}, language = {en} } @article{MariKielingNielsenetal.2011, author = {Mari, Andrea and Kieling, Konrad and Nielsen, B. Melholt and Polzik, E. S. and Eisert, Jens}, title = {Directly estimating nonclassicality}, series = {Physical review letters}, volume = {106}, journal = {Physical review letters}, number = {1}, publisher = {American Physical Society}, address = {College Park}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.106.010403}, pages = {4}, year = {2011}, abstract = {We establish a method of directly measuring and estimating nonclassicality-operationally defined in terms of the distinguishability of a given state from one with a positive Wigner function. It allows us to certify nonclassicality, based on possibly much fewer measurement settings than necessary for obtaining complete tomographic knowledge, and is at the same time equipped with a full certificate. We find that even from measuring two conjugate variables alone, one may infer the nonclassicality of quantum mechanical modes. This method also provides a practical tool to eventually certify such features in mechanical degrees of freedom in opto-mechanics. The proof of the result is based on Bochner's theorem characterizing classical and quantum characteristic functions and on semidefinite programming. In this joint theoretical-experimental work we present data from experimental optical Fock state preparation.}, language = {en} } @article{MannYoungFuuentesSchuller2011, author = {Mann, R. B. and Young, M. B. and Fu{\"u}ntes-Schuller, I.}, title = {A perturbative approach to inelastic collisions in a Bose-Einstein condensate}, series = {Journal of physics : B, Atomic, molecular and optical physics}, volume = {44}, journal = {Journal of physics : B, Atomic, molecular and optical physics}, number = {8}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {0953-4075}, doi = {10.1088/0953-4075/44/8/085301}, pages = {17}, year = {2011}, abstract = {It has recently been discovered that for certain rates of mode-exchange collisions analytic solutions can be found for a Hamiltonian describing the two-mode Bose-Einstein condensate. We proceed to study the behaviour of the system using perturbation theory if the coupling constants only approximately match these parameter constraints. We find that the model is robust to such perturbations. We study the effects of degeneracy on the perturbations and find that the induced changes differ greatly from the non-degenerate case. We also model inelastic collisions that result in particle loss or condensate decay as external perturbations and use this formalism to examine the effects of three-body recombination and background collisions.}, language = {en} } @phdthesis{Malik2011, author = {Malik, Nishant}, title = {Extremes in events and dynamics : a nonlinear data analysis perspective on the past and present dynamics of the Indian summer monsoon}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-58016}, school = {Universit{\"a}t Potsdam}, year = {2011}, abstract = {To identify extreme changes in the dynamics of the Indian Summer Monsoon (ISM) in the past, I propose a new approach based on the quantification of fluctuations of a nonlinear similarity measure, to identify regimes of distinct dynamical complexity in short time series. I provide an analytical derivation for the relationship of the new measure with the dynamical invariants such as dimension and Lyapunov exponents of the underlying system. A statistical test is also developed to estimate the significance of the identified transitions. Our method is justified by uncovering bifurcation structures in several paradigmatic models, providing more complex transitions compared with traditional Lyapunov exponents. In a real world situation, we apply the method to identify millennial-scale dynamical transitions in Pleistocene proxy records of the south Asian summer monsoon system. We infer that many of these transitions are induced by the external forcing of solar insolation and are also affected by internal forcing on Monsoonal dynamics, i.e., the glaciation cycles of the Northern Hemisphere and the onset of the tropical Walker circulation. Although this new method has general applicability, it is particularly useful in analysing short palaeo-climate records. Rainfall during the ISM over the Indian subcontinent occurs in form of enormously complex spatiotemporal patterns due to the underlying dynamics of atmospheric circulation and varying topography. I present a detailed analysis of summer monsoon rainfall over the Indian peninsular using Event Synchronization (ES), a measure of nonlinear correlation for point processes such as rainfall. First, using hierarchical clustering I identify principle regions where the dynamics of monsoonal rainfall is more coherent or homogenous. I also provide a method to reconstruct the time delay patterns of rain events. Moreover, further analysis is carried out employing the tools of complex network theory. This study provides valuable insights into the spatial organization, scales, and structure of the 90th and 94th percentile rainfall events during the ISM (June to September). I furthermore analyse the influence of different critical synoptic atmospheric systems and the impact of the steep Himalayan topography on rainfall patterns. The presented method not only helps in visualising the structure of the extremeevent rainfall fields, but also identifies the water vapor pathways and decadal-scale moisture sinks over the region. Furthermore a simple scheme based on complex networks is presented to decipher the spatial intricacies and temporal evolution of monsoonal rainfall patterns over the last six decades. Some supplementary results on the evolution of monsoonal rainfall extremes over the last sixty years are also presented.}, language = {de} } @article{MalicWeberRichteretal.2011, author = {Malic, E. and Weber, C. and Richter, M. and Atalla, V. and Klamroth, Tillmann and Saalfrank, Peter and Reich, Sebastian and Knorr, A.}, title = {Microscopic model of the optical absorption of carbon nanotubes functionalized with molecular spiropyran photoswitches}, series = {Physical review letters}, volume = {106}, journal = {Physical review letters}, number = {9}, publisher = {American Physical Society}, address = {College Park}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.106.097401}, pages = {4}, year = {2011}, abstract = {The adsorption of molecules to the surface of carbon nanostructures opens a new field of hybrid systems with distinct and controllable properties. We present a microscopic study of the optical absorption in carbon nanotubes functionalized with molecular spiropyran photoswitches. The switching process induces a change in the dipole moment leading to a significant coupling to the charge carriers in the nanotube. As a result, the absorption spectra of functionalized tubes reveal a considerable redshift of transition energies depending on the switching state of the spiropyran molecule. Our results suggest that carbon nanotubes are excellent substrates for the optical readout of spiropyran-based molecular switches. The gained insights can be applied to other noncovalently functionalized one-dimensional nanostructures in an externally induced dipole field.}, language = {en} } @article{MakhmudoMakhmudovTarkhanov2011, author = {Makhmudo, K. O. and Makhmudov, O. I. and Tarkhanov, Nikolai Nikolaevich}, title = {Equations of Maxwell type}, series = {Journal of mathematical analysis and applications}, volume = {378}, journal = {Journal of mathematical analysis and applications}, number = {1}, publisher = {Elsevier}, address = {San Diego}, issn = {0022-247X}, doi = {10.1016/j.jmaa.2011.01.012}, pages = {64 -- 75}, year = {2011}, abstract = {For an elliptic complex of first order differential operators on a smooth manifold X, we define a system of two equations which can be thought of as abstract Maxwell equations. The formal theory of this system proves to be very similar to that of classical Maxwell's equations. The paper focuses on boundary value problems for the abstract Maxwell equations, especially on the Cauchy problem.}, language = {en} } @article{LueckPikovskij2011, author = {Lueck, S. and Pikovskij, Arkadij}, title = {Dynamics of multi-frequency oscillator ensembles with resonant coupling}, series = {Modern physics letters : A, Particles and fields, gravitation, cosmology, nuclear physics}, volume = {375}, journal = {Modern physics letters : A, Particles and fields, gravitation, cosmology, nuclear physics}, number = {28-29}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0375-9601}, doi = {10.1016/j.physleta.2011.06.016}, pages = {2714 -- 2719}, year = {2011}, abstract = {We study dynamics of populations of resonantly coupled oscillators having different frequencies. Starting from the coupled van der Pol equations we derive the Kuramoto-type phase model for the situation, where the natural frequencies of two interacting subpopulations are in relation 2 : 1. Depending on the parameter of coupling, ensembles can demonstrate fully synchronous clusters, partial synchrony (only one subpopulation synchronizes), or asynchrony in both subpopulations. Theoretical description of the dynamics based on the Watanabe-Strogatz approach is developed.}, language = {en} } @article{LomadzeKopyshevRueheetal.2011, author = {Lomadze, Nino and Kopyshev, Alexey and R{\"u}he, J{\"u}rgen and Santer, Svetlana}, title = {Light-Induced chain scission in photosensitive polymer brushes}, series = {Macromolecules : a publication of the American Chemical Society}, volume = {44}, journal = {Macromolecules : a publication of the American Chemical Society}, number = {18}, publisher = {American Chemical Society}, address = {Washington}, issn = {0024-9297}, doi = {10.1021/ma201016q}, pages = {7372 -- 7377}, year = {2011}, abstract = {We report on a process inducing photomechanical fracture of chemical bonds in photosensitive PMAA polymer brushes. The photosensitive PMAA polymer brushes were prepared by covalent attachment of azobenzene groups to poly(methylacrylic acid) (PMAA) chains generated by surface-initiated polymerization. While homogeneous irradiation leaves the polymer topography unchanged, the azo-PMAA brushes show a strong response upon irradiation with UV interference patterns. The photoisomerization process in the surface-attached polymer films results in the irreversible formation of surface relief gratings (SRG), which are strongly enhanced upon washing with a good solvent for the polymer. The photomechanical forces during mass transport induced by the irradiation lead to the scission of covalent bounds and accordingly to a degrafting of the polymer chains in areas where the polymer is receding from. It is observed that the number of ruptured chains depends strongly on the amount of azo side chains in the polymer.}, language = {en} } @misc{LoksteinKrikunovaTeuchneretal.2011, author = {Lokstein, Heiko and Krikunova, Maria and Teuchner, Klaus and Voigt, Bernd}, title = {Elucidation of structure-function relationships in photosynthetic light-harvesting antenna complexes by non-linear polarization spectroscopy in the frequency domain (NLPF)}, series = {Journal of plant physiology : biochemistry, physiology, molecular biology and biotechnology of plants}, volume = {168}, journal = {Journal of plant physiology : biochemistry, physiology, molecular biology and biotechnology of plants}, number = {12}, publisher = {Elsevier}, address = {Jena}, issn = {0176-1617}, doi = {10.1016/j.jplph.2010.12.012}, pages = {1488 -- 1496}, year = {2011}, abstract = {Photosynthetically active pigments are usually organized into pigment-protein complexes. These include light-harvesting antenna complexes (LHCs) and reaction centers. Site energies of the bound pigments are determined by interactions with their environment, i.e., by pigment-protein as well as pigment-pigment interactions. Thus, resolution of spectral substructures of the pigment-protein complexes may provide valuable insight into structure-function relationships. By means of conventional (linear) and time-resolved spectroscopic techniques, however, it is often difficult to resolve the spectral substructures of complex pigment-protein assemblies. Nonlinear polarization spectroscopy in the frequency domain (NLPF) is shown to be a valuable technique in this regard. Based on initial experimental work with purple bacterial antenna complexes as well as model systems NLPF has been extended to analyse the substructure(s) of very complex spectra, including analyses of interactions between chlorophylls and "optically dark" states of carotenoids in LHCs. The paper reviews previous work and outlines perspectives regarding the application of NLPF spectroscopy to disentangle structure-function relationships in pigment-protein complexes.}, language = {en} } @article{LissoSchroederFisahnetal.2011, author = {Lisso, Janina and Schr{\"o}der, Florian and Fisahn, Joachim and Muessig, Carsten}, title = {NFX1-LIKE2 (NFXL2) Suppresses Abscisic Acid Accumulation and Stomatal Closure in Arabidopsis thaliana}, series = {PLoS one}, volume = {6}, journal = {PLoS one}, number = {11}, publisher = {PLoS}, address = {San Fransisco}, issn = {1932-6203}, doi = {10.1371/journal.pone.0026982}, pages = {12}, year = {2011}, abstract = {The NFX1-LIKE1 (NFXL1) and NFXL2 genes were identified as regulators of salt stress responses. The NFXL1 protein is a nuclear factor that positively affects adaptation to salt stress. The nfxl1-1 loss-of-function mutant displayed reduced survival rates under salt and high light stress. In contrast, the nfxl2-1 mutant, defective in the NFXL2 gene, and NFXL2-antisense plants exhibited enhanced survival under these conditions. We show here that the loss of NFXL2 function results in abscisic acid (ABA) overaccumulation, reduced stomatal conductance, and enhanced survival under drought stress. The nfxl2-1 mutant displayed reduced stomatal aperture under all conditions tested. Fusicoccin treatment, exposition to increasing light intensities, and supply of decreasing CO2 concentrations demonstrated full opening capacity of nfxl2-1 stomata. Reduced stomatal opening presumably is a consequence of elevated ABA levels. Furthermore, seedling growth, root growth, and stomatal closure were hypersensitive to exogenous ABA. The enhanced ABA responses may contribute to the improved drought stress resistance of the mutant. Three NFXL2 splice variants were cloned and named NFXL2-78, NFXL2-97, and NFXL2-100 according to the molecular weight of the putative proteins. Translational fusions to the green fluorescent protein suggest nuclear localisation of the NFXL2 proteins. Stable expression of the NFXL2-78 splice variant in nfxl2-1 plants largely complemented the mutant phenotype. Our data show that NFXL2 controls ABA levels and suppresses ABA responses. NFXL2 may prevent unnecessary and costly stress adaptation under favourable conditions.}, language = {en} } @article{LevnajicPikovskij2011, author = {Levnajic, Zoran and Pikovskij, Arkadij}, title = {Network reconstruction from random phase resetting}, series = {Physical review letters}, volume = {107}, journal = {Physical review letters}, number = {3}, publisher = {American Physical Society}, address = {College Park}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.107.034101}, pages = {4}, year = {2011}, abstract = {We propose a novel method of reconstructing the topology and interaction functions for a general oscillator network. An ensemble of initial phases and the corresponding instantaneous frequencies is constructed by repeating random phase resets of the system dynamics. The desired details of network structure are then revealed by appropriately averaging over the ensemble. The method is applicable for a wide class of networks with arbitrary emergent dynamics, including full synchrony.}, language = {en} } @article{Levnajic2011, author = {Levnajic, Zoran}, title = {Emergent multistability and frustration in phase-repulsive networks of oscillators}, series = {Physical review : E, Statistical, nonlinear and soft matter physics}, volume = {84}, journal = {Physical review : E, Statistical, nonlinear and soft matter physics}, number = {1}, publisher = {American Physical Society}, address = {College Park}, issn = {1539-3755}, doi = {10.1103/PhysRevE.84.016231}, pages = {10}, year = {2011}, abstract = {The collective dynamics of oscillator networks with phase-repulsive coupling is studied, considering various network sizes and topologies. The notion of link frustration is introduced to characterize and quantify the network dynamical states. In opposition to widely studied phase-attractive case, the properties of final dynamical states in our model critically depend on the network topology. In particular, each network's total frustration value is intimately related to its topology. Moreover, phase-repulsive networks in general display multiple final frustration states, whose statistical and stability properties are uniquely identifying them.}, language = {en} } @article{LemrCernochSoubustaetal.2011, author = {Lemr, Karel and Cernoch, A. and Soubusta, Jan and Kieling, Konrad and Eisert, Jens and Dusek, M.}, title = {Experimental implementation of the optimal linear-optical controlled phase gate}, series = {Physical review letters}, volume = {106}, journal = {Physical review letters}, number = {1}, publisher = {American Physical Society}, address = {College Park}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.106.013602}, pages = {4}, year = {2011}, abstract = {We report on the first experimental realization of optimal linear-optical controlled phase gates for arbitrary phases. The realized scheme is entirely flexible in that the phase shift can be tuned to any given value. All such controlled phase gates are optimal in the sense that they operate at the maximum possible success probabilities that are achievable within the framework of postselected linear-optical implementations with vacuum ancillas. The quantum gate is implemented by using bulk optical elements and polarization encoding of qubit states. We have experimentally explored the remarkable observation that the optimum success probability is not monotone in the phase.}, language = {en} } @article{LangeBlakesleyFrischetal.2011, author = {Lange, Ilja and Blakesley, James C. and Frisch, Johannes and Vollmer, Antje and Koch, Norbert and Neher, Dieter}, title = {Band bending in conjugated polymer layers}, series = {Physical review letters}, volume = {106}, journal = {Physical review letters}, number = {21}, publisher = {American Physical Society}, address = {College Park}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.106.216402}, pages = {4}, year = {2011}, abstract = {We use the Kelvin probe method to study the energy-level alignment of four conjugated polymers deposited on various electrodes. Band bending is observed in all polymers when the substrate work function exceeds critical values. Through modeling, we show that the band bending is explained by charge transfer from the electrodes into a small density of states that extends several hundred meV into the band gap. The energetic spread of these states is correlated with charge-carrier mobilities, suggesting that the same states also govern charge transport in the bulk of these polymers.}, language = {en} } @article{LachmuthDurkaSchurr2011, author = {Lachmuth, Susanne and Durka, Walter and Schurr, Frank Martin}, title = {Differentiation of reproductive and competitive ability in the invaded range of Senecio inaequidens the role of genetic Allee effects, adaptive and nonadaptive evolution}, series = {New phytologist : international journal of plant science}, volume = {192}, journal = {New phytologist : international journal of plant science}, number = {2}, publisher = {Wiley-Blackwell}, address = {Malden}, issn = {0028-646X}, doi = {10.1111/j.1469-8137.2011.03808.x}, pages = {529 -- 541}, year = {2011}, abstract = {Genetic differentiation in the competitive and reproductive ability of invading populations can result from genetic Allee effects or r/K selection at the local or range-wide scale. However, the neutral relatedness of populations may either mask or falsely suggest adaptation and genetic Allee effects. In a common-garden experiment, we investigated the competitive and reproductive ability of invasive Senecio inaequidens populations that vary in neutral genetic diversity, population age and field vegetation cover. To account for population relatedness, we analysed the experimental results with 'animal models' adopted from quantitative genetics. Consistent with adaptive r/K differentiation at local scales, we found that genotypes from low-competition environments invest more in reproduction and are more sensitive to competition. By contrast, apparent effects of large-scale r/K differentiation and apparent genetic Allee effects can largely be explained by neutral population relatedness. Invading populations should not be treated as homogeneous groups, as they may adapt quickly to small-scale environmental variation in the invaded range. Furthermore, neutral population differentiation may strongly influence invasion dynamics and should be accounted for in analyses of common-garden experiments.}, language = {en} } @article{Kuznetsov2011, author = {Kuznetsov, Sergey P.}, title = {Plykin type attractor in electronic device simulated in MULTISIM}, series = {Chaos : an interdisciplinary journal of nonlinear science}, volume = {21}, journal = {Chaos : an interdisciplinary journal of nonlinear science}, number = {4}, publisher = {American Institute of Physics}, address = {Melville}, issn = {1054-1500}, doi = {10.1063/1.3646903}, pages = {8}, year = {2011}, abstract = {An electronic device is suggested representing a non-autonomous dynamical system with hyperbolic chaotic attractor of Plykin type in the stroboscopic map, and the results of its simulation with software package NI MULTISIM are considered in comparison with numerical integration of the underlying differential equations. A main practical advantage of electronic devices of this kind is their structural stability that means insensitivity of the chaotic dynamics in respect to variations of functions and parameters of elements constituting the system as well as to interferences and noises.}, language = {en} } @article{KussmaulRisseKofodetal.2011, author = {Kussmaul, Bjoern and Risse, Sebastian and Kofod, Guggi and Wache, Remi and Wegener, Michael and McCarthy, Denis N. and Kr{\"u}ger, Hartmut and Gerhard, Reimund}, title = {Enhancement of dielectric permittivity and electromechanical response in silicone elastomers molecular grafting of organic dipoles to the macromolecular Network}, series = {Advanced functional materials}, volume = {21}, journal = {Advanced functional materials}, number = {23}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1616-301X}, doi = {10.1002/adfm.201100884}, pages = {4589 -- 4594}, year = {2011}, abstract = {A novel method is established for permittivity enhancement of a silicone matrix for dielectric elastomer actuators (DEAs) by molecular level modifications of the elastomer matrix. A push-pull dipole is synthesized to be compatible with the silicone crosslinking chemistry, allowing for direct grafting to the crosslinker molecules in a one-step film formation process. This method prevents agglomeration and yields elastomer films that are homogeneous down to the molecular level. The dipole-to-silicone network grafting reaction is studied by FTIR. The chemical, thermal, mechanical and electrical properties of films with dipole contents ranging from 0 wt\% to 13.4 wt\% were thoroughly characterized. The grafting of dipoles modifies the relative permittivity and the stiffness, resulting in the actuation strain at a given electrical field being improved by a factor of six.}, language = {en} } @article{KuehnPingelBreusingetal.2011, author = {Kuehn, Sergei and Pingel, Patrick and Breusing, Markus and Fischer, Thomas and Stumpe, Joachim and Neher, Dieter and Elsaesser, Thomas}, title = {High-Resolution Near-Field Optical Investigation of Crystalline Domains in Oligomeric PQT-12 Thin Films}, series = {Advanced functional materials}, volume = {21}, journal = {Advanced functional materials}, number = {5}, publisher = {Wiley-Blackwell}, address = {Malden}, issn = {1616-301X}, doi = {10.1002/adfm.201001978}, pages = {860 -- 868}, year = {2011}, abstract = {The structure and morphology on different length scales dictate both the electrical and optical properties of organic semiconductor thin films. Using a combination of spectroscopic methods, including scanning near-field optical microscopy, we study the domain structure and packing quality of highly crystalline thin films of oligomeric PQT-12 with 100 nanometer spatial resolution. The pronounced optical anisotropy of these layers measured by polarized light microscopy facilitates the identification of regions with uniform molecular orientation. We find that a hierarchical order on three different length scales exists in these layers, made up of distinct well-ordered dichroic areas at the ten-micrometer-scale, which are sub-divided into domains with different molecular in-plane orientation. These serve as a template for the formation of smaller needle-like crystallites at the layer surface. A high degree of crystalline order is believed to be the cause of the rather high field-effect mobility of these layers of 10(-3) cm 2 V(-1) s(-1), whereas it is limited by the presence of domain boundaries at macroscopic distances.}, language = {en} } @phdthesis{Krey2011, author = {Krey, Olaf}, title = {Zur Rolle der Mathematik in der Physik : Wissenschaftstheoretische Aspekte und Vorstellungen Physiklernender}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-59412}, school = {Universit{\"a}t Potsdam}, year = {2011}, abstract = {Mathematik spielt im Physikunterricht eine nicht unerhebliche Rolle - wenn auch eine zwiesp{\"a}ltige. Oft wird sie sogar zum Hindernis beim Lernen von Physik und kann ihr emanzipatorisches Potenzial nicht entfalten. Die vorliegende Arbeit stellt zwei Bausteine f{\"u}r eine begr{\"u}ndete Konzeption zum Umgang mit Mathematik beim Lernen von Physik zur Verf{\"u}gung. Im Theorieteil der Arbeit werden zum Einen wissenschaftstheoretische Aspekte der Rolle der Mathematik in der Physik aufgearbeitet und der physikdidaktischen Forschungsgemeinschaft im Zusammenhang zug{\"a}nglich gemacht. Zum anderen werden Forschungsergebnisse zu Vorstellungen Lernender {\"u}ber Physik und Mathematik sowie im Bereich der Epistemologie zusammengestellt. Im empirischen Teil der Arbeit werden Vorstellungen zur Rolle der Mathematik in der Physik von Sch{\"u}lerinnen und Sch{\"u}lern der Klassenstufen 10 und 12 sowie Physik-Lehramtstudierenden im Grundstudium mit Hilfe eines Fragebogens erhoben und unter Verwendung inhaltsanalytischer bzw. statistischer Methoden ausgewertet. Die Ergebnisse zeigen unter Anderem, dass Mathematik im Physikunterricht entgegen g{\"a}ngiger Meinungen bei den Lernenden nicht negativ, aber zumindest bei j{\"u}ngeren Lernenden formal und algorithmisch konnotiert ist.}, language = {de} } @article{KralemannPikovskijRosenblum2011, author = {Kralemann, Bj{\"o}rn and Pikovskij, Arkadij and Rosenblum, Michael}, title = {Reconstructing phase dynamics of oscillator networks}, series = {Chaos : an interdisciplinary journal of nonlinear science}, volume = {21}, journal = {Chaos : an interdisciplinary journal of nonlinear science}, number = {2}, publisher = {American Institute of Physics}, address = {Melville}, issn = {1054-1500}, doi = {10.1063/1.3597647}, pages = {10}, year = {2011}, abstract = {We generalize our recent approach to the reconstruction of phase dynamics of coupled oscillators from data [B. Kralemann et al., Phys. Rev. E 77, 066205 (2008)] to cover the case of small networks of coupled periodic units. Starting from a multivariate time series, we first reconstruct genuine phases and then obtain the coupling functions in terms of these phases. Partial norms of these coupling functions quantify directed coupling between oscillators. We illustrate the method by different network motifs for three coupled oscillators and for random networks of five and nine units. We also discuss nonlinear effects in coupling.}, language = {en} } @article{KoseskaVolkovKurths2011, author = {Koseska, Aneta and Volkov, Evgenii and Kurths, J{\"u}rgen}, title = {Synthetic multicellular oscillatory systems controlling protein dynamics with genetic circuits}, series = {Physica scripta : an international journal for experimental and theoretical physics}, volume = {84}, journal = {Physica scripta : an international journal for experimental and theoretical physics}, number = {4}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {0031-8949}, doi = {10.1088/0031-8949/84/04/045007}, pages = {10}, year = {2011}, abstract = {Synthetic biology is a relatively new research discipline that combines standard biology approaches with the constructive nature of engineering. Thus, recent efforts in the field of synthetic biology have given a perspective to consider cells as 'programmable matter'. Here, we address the possibility of using synthetic circuits to control protein dynamics. In particular, we show how intercellular communication and stochasticity can be used to manipulate the dynamical behavior of a population of coupled synthetic units and, in this manner, finely tune the expression of specific proteins of interest, e.g. in large bioreactors.}, language = {en} } @phdthesis{Koseska2011, author = {Koseska, Aneta}, title = {Dynamics of biological networks : data analysis, modeling and bifurcations}, address = {Potsdam}, year = {2011}, language = {en} } @article{KomarovPikovskij2011, author = {Komarov, Maxim and Pikovskij, Arkadij}, title = {Effects of nonresonant interaction in ensembles of phase oscillators}, series = {Physical review : E, Statistical, nonlinear and soft matter physics}, volume = {84}, journal = {Physical review : E, Statistical, nonlinear and soft matter physics}, number = {1}, publisher = {American Physical Society}, address = {College Park}, issn = {1539-3755}, doi = {10.1103/PhysRevE.84.016210}, pages = {12}, year = {2011}, abstract = {We consider general properties of groups of interacting oscillators, for which the natural frequencies are not in resonance. Such groups interact via nonoscillating collective variables like the amplitudes of the order parameters defined for each group. We treat the phase dynamics of the groups using the Ott-Antonsen ansatz and reduce it to a system of coupled equations for the order parameters. We describe different regimes of cosynchrony in the groups. For a large number of groups, heteroclinic cycles, corresponding to a sequential synchronous activity of groups and chaotic states where the order parameters oscillate irregularly, are possible.}, language = {en} } @article{KolloscheStoyanovLaflammeetal.2011, author = {Kollosche, Matthias and Stoyanov, Hristiyan and Laflamme, Simon and Kofod, Guggi}, title = {Strongly enhanced sensitivity in elastic capacitive strain sensors}, series = {Journal of materials chemistry}, volume = {21}, journal = {Journal of materials chemistry}, number = {23}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {0959-9428}, doi = {10.1039/c0jm03786a}, pages = {8292 -- 8294}, year = {2011}, abstract = {Strain sensors based on dielectric elastomer capacitors function by the direct coupling of mechanical deformations with the capacitance. The coupling can be improved by enhancing the relative permittivity of the dielectric elastomer. Here, this is carried out through the grafting of conducting polymer (poly-aniline) to the elastomer backbone, leading to molecular composites. An enhancement in capacitance response of 46 times is observed. This could help to extend the possible range of miniaturization towards even smaller device features.}, language = {en} } @article{KofodStoyanovGerhard2011, author = {Kofod, Guggi and Stoyanov, Hristiyan and Gerhard, Reimund}, title = {Multilayer coaxial fiber dielectric elastomers for actuation and sensing}, series = {Applied physics : A, Materials science \& processing}, volume = {102}, journal = {Applied physics : A, Materials science \& processing}, number = {3}, publisher = {Springer}, address = {New York}, issn = {0947-8396}, doi = {10.1007/s00339-010-6066-5}, pages = {577 -- 581}, year = {2011}, abstract = {A simple dip-coating technique was employed to manufacture coaxial actuators with multiple layers of alternating dielectric and conducting layers. A thin rubber string was coated with an electrode-insulator-electrode structure, giving rise to a thin, fiber-like actuator with coaxial geometry. The process was repeated to achieve a compact multilayer actuator with up to three coaxial dielectric layers. Mechanical and electromechanical characterization of the actuators is presented, showing actuation strains up to 8\% and proper voltage-thickness scaling behavior. Also presented is a capacitance vs. extension plot, demonstrating that these structures can be used for compact and accurate capacitive strain sensing.}, language = {en} } @article{KofodRisseStoyanovetal.2011, author = {Kofod, Guggi and Risse, Sebastian and Stoyanov, Hristiyan and McCarthy, Denis N. and Sokolov, Sergey and Kr{\"a}hnert, Ralph}, title = {Broad-spectrum enhancement of polymer composite dielectric constant at ultra low volume fractions of silica-supported copper nanoparticles}, series = {ACS nano}, volume = {5}, journal = {ACS nano}, number = {3}, publisher = {American Chemical Society}, address = {Washington}, issn = {1936-0851}, doi = {10.1021/nn103097q}, pages = {1623 -- 1629}, year = {2011}, abstract = {A new strategy for the synthesis of high permittivity polymer composites is demonstrated based on well-defined spatial distribution of ultralow amounts of conductive nanoparticles. The spatial distribution Was realized by immobilizing Cu nanoparticles within the pore system of Alia microspheres, preventing direct contact between individual Cu particles. Both Cu-loaded and unloaded silica microspheres were-then used as fillers in polymer composites prepared with thermoplastic SEBS rubber is the matrix. With a metallic Cu content of about 0.26 vol \% In the compoilte, a relative increase of 94\% In real permittivity was obtained. No Cu-induced relaxations were observed in the dielectric spectrum within the studied frequency range of 0.1 Hz to 1 MHz. When related to the amount of conductive nanoparticles, the obtained composites achieve the highest broad spectrum enhancement of permittivity ever reported for a polymer based composite.}, language = {en} } @article{KoenigGoldenbergKulikovskaetal.2011, author = {Koenig, Tobias and Goldenberg, Leonid M. and Kulikovska, Olga and Kulikovsky, Lazar and Stumpe, Joachim and Santer, Svetlana}, title = {Reversible structuring of photosensitive polymer films by surface plasmon near field radiation}, series = {Soft matter}, volume = {7}, journal = {Soft matter}, number = {9}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1744-683X}, doi = {10.1039/c0sm01164a}, pages = {4174 -- 4178}, year = {2011}, abstract = {We report on the fabrication and characterisation of a novel type of hybrid azo-modified photosensitive polymer film with a nanoscale metallic structuring integrated into the substrate. The metal structures permit to generate surface plasmon near fields when irradiated by UV-light from the rear without directly illuminating the polymer. This allows establishment of a localized, complex-shape intensity distribution at sub-wavelength resolution with a corresponding impact on the photosensitive polymer. The possibilities of exploiting this setup are manifold. We find that just by using the change of polarization of the incident light as means of control, the topography can be driven to change between various patterns reversibly. These results are confirmed by numerical simulations and compared with in situ recorded topography changes.}, language = {en} } @article{KniepertSchubertBlakesleyetal.2011, author = {Kniepert, Juliane and Schubert, Marcel and Blakesley, James C. and Neher, Dieter}, title = {Photogeneration and recombination in P3HT/PCBM solar cells probed by time-delayed collection field experiments}, series = {The journal of physical chemistry letters}, volume = {2}, journal = {The journal of physical chemistry letters}, number = {7}, publisher = {American Chemical Society}, address = {Washington}, issn = {1948-7185}, doi = {10.1021/jz200155b}, pages = {700 -- 705}, year = {2011}, abstract = {Time-delayed collection field (TDCF) experiments are performed on bulk heterojunction solar cells comprised of a blend of poly(3-hexylthiophene) and [6,6]-phenyl C-71 butyric acid methyl ester. TDCF is analogous to a pump-probe experiment using optical excitation and an electrical probe with a resolution of < 100 ns. The number of free charge carriers extracted after a short delay is found to be independent of the electric field during illumination. Also, experiments performed with a variable delay between the optical excitation and the electrical probe do not reveal any evidence for the generation of charge via field-assisted dissociation of bound long-lived polaron pairs. Photocurrent transients are well fitted by computational drift diffusion simulations with only direct generation of free charge carriers. With increasing delay times between pump and probe, two loss mechanisms are identified; first, charge-carriers are swept out of the device by the internal electric field, and second, bimolecular recombination of the remaining carriers takes place with a reduced recombination coefficient.}, language = {en} } @article{KlieschBarthelGogolinetal.2011, author = {Kliesch, Martin and Barthel, Thomas and Gogolin, C. and Kastoryano, M. and Eisert, J.}, title = {Dissipative quantum church-turing theorem}, series = {Physical review letters}, volume = {107}, journal = {Physical review letters}, number = {12}, publisher = {American Physical Society}, address = {College Park}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.107.120501}, pages = {5}, year = {2011}, abstract = {We show that the time evolution of an open quantum system, described by a possibly time dependent Liouvillian, can be simulated by a unitary quantum circuit of a size scaling polynomially in the simulation time and the size of the system. An immediate consequence is that dissipative quantum computing is no more powerful than the unitary circuit model. Our result can be seen as a dissipative Church-Turing theorem, since it implies that under natural assumptions, such as weak coupling to an environment, the dynamics of an open quantum system can be simulated efficiently on a quantum computer. Formally, we introduce a Trotter decomposition for Liouvillian dynamics and give explicit error bounds. This constitutes a practical tool for numerical simulations, e.g., using matrix-product operators. We also demonstrate that most quantum states cannot be prepared efficiently.}, language = {en} } @article{KielMoehwaldBargheer2011, author = {Kiel, Mareike and M{\"o}hwald, Helmuth and Bargheer, Matias}, title = {Broadband measurements of the transient optical complex dielectric function of a nanoparticle/polymer composite upon ultrafast excitation}, series = {Physical review : B, Condensed matter and materials physics}, volume = {84}, journal = {Physical review : B, Condensed matter and materials physics}, number = {16}, publisher = {American Physical Society}, address = {College Park}, issn = {1098-0121}, doi = {10.1103/PhysRevB.84.165121}, pages = {6}, year = {2011}, abstract = {We determined experimentally the complex transient optical dielectric function of a well-characterized polyelectrolyte/gold-nanoparticle composite system over a broad spectral range upon short pulse laser excitation by simultaneously measuring the time-dependent reflectance and transmittance of white light pulses with femtosecond pump-probe spectroscopy. We extracted directly the ultrafast changes in the real and imaginary parts of the effective dielectric function, epsilon(eff)(r) (omega,t)and epsilon(eff)(i) (omega,t), from the experiment. This complete experimental set of information on the time-dependent complex dielectric function challenges theories modeling the transient dielectric function of gold particles and the effective medium.}, language = {en} } @article{KhaderPachurMeieretal.2011, author = {Khader, Patrick H. and Pachur, Thorsten and Meier, Stefanie and Bien, Siegfried and Jost, Kerstin and Roesler, Frank}, title = {Memory-based decision-making with heuristics evidence for a controlled activation of memory representations}, series = {Journal of cognitive neuroscience}, volume = {23}, journal = {Journal of cognitive neuroscience}, number = {11}, publisher = {MIT Press}, address = {Cambridge}, issn = {0898-929X}, pages = {3540 -- 3554}, year = {2011}, abstract = {Many of our daily decisions are memory based, that is, the attribute information about the decision alternatives has to be recalled. Behavioral studies suggest that for such decisions we often use simple strategies (heuristics) that rely on controlled and limited information search. It is assumed that these heuristics simplify decision-making by activating long-term memory representations of only those attributes that are necessary for the decision. However, from behavioral studies alone, it is unclear whether using heuristics is indeed associated with limited memory search. The present study tested this assumption by monitoring the activation of specific long-term-memory representations with fMRI while participants made memory-based decisions using the "take-the-best" heuristic. For different decision trials, different numbers and types of information had to be retrieved and processed. The attributes consisted of visual information known to be represented in different parts of the posterior cortex. We found that the amount of information required for a decision was mirrored by a parametric activation of the dorsolateral PFC. Such a parametric pattern was also observed in all posterior areas, suggesting that activation was not limited to those attributes required for a decision. However, the posterior increases were systematically modulated by the relative importance of the information for making a decision. These findings suggest that memory-based decision-making is mediated by the dorsolateral PFC, which selectively controls posterior storage areas. In addition, the systematic modulations of the posterior activations indicate a selective boosting of activation of decision-relevant attributes.}, language = {en} } @phdthesis{Kellermann2011, author = {Kellermann, Thorsten}, title = {Accurate numerical relativity simulations of non-vacuumspace-times in two dimensions and applications to critical collapse}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-59578}, school = {Universit{\"a}t Potsdam}, year = {2011}, abstract = {This Thesis puts its focus on the physics of neutron stars and its description with methods of numerical relativity. In the first step, a new numerical framework the Whisky2D code will be developed, which solves the relativistic equations of hydrodynamics in axisymmetry. Therefore we consider an improved formulation of the conserved form of these equations. The second part will use the new code to investigate the critical behaviour of two colliding neutron stars. Considering the analogy to phase transitions in statistical physics, we will investigate the evolution of the entropy of the neutron stars during the whole process. A better understanding of the evolution of thermodynamical quantities, like the entropy in critical process, should provide deeper understanding of thermodynamics in relativity. More specifically, we have written the Whisky2D code, which solves the general-relativistic hydrodynamics equations in a flux-conservative form and in cylindrical coordinates. This of course brings in 1/r singular terms, where r is the radial cylindrical coordinate, which must be dealt with appropriately. In the above-referenced works, the flux operator is expanded and the 1/r terms, not containing derivatives, are moved to the right-hand-side of the equation (the source term), so that the left hand side assumes a form identical to the one of the three-dimensional (3D) Cartesian formulation. We call this the standard formulation. Another possibility is not to split the flux operator and to redefine the conserved variables, via a multiplication by r. We call this the new formulation. The new equations are solved with the same methods as in the Cartesian case. From a mathematical point of view, one would not expect differences between the two ways of writing the differential operator, but, of course, a difference is present at the numerical level. Our tests show that the new formulation yields results with a global truncation error which is one or more orders of magnitude smaller than those of alternative and commonly used formulations. The second part of the Thesis uses the new code for investigations of critical phenomena in general relativity. In particular, we consider the head-on-collision of two neutron stars in a region of the parameter space where two final states a new stable neutron star or a black hole, lay close to each other. In 1993, Choptuik considered one-parameter families of solutions, S[P], of the Einstein-Klein-Gordon equations for a massless scalar field in spherical symmetry, such that for every P > P⋆, S[P] contains a black hole and for every P < P⋆, S[P] is a solution not containing singularities. He studied numerically the behavior of S[P] as P → P⋆ and found that the critical solution, S[P⋆], is universal, in the sense that it is approached by all nearly-critical solutions regardless of the particular family of initial data considered. All these phenomena have the common property that, as P approaches P⋆, S[P] approaches a universal solution S[P⋆] and that all the physical quantities of S[P] depend only on |P - P⋆|. The first study of critical phenomena concerning the head-on collision of NSs was carried out by Jin and Suen in 2007. In particular, they considered a series of families of equal-mass NSs, modeled with an ideal-gas EOS, boosted towards each other and varied the mass of the stars, their separation, velocity and the polytropic index in the EOS. In this way they could observe a critical phenomenon of type I near the threshold of black-hole formation, with the putative solution being a nonlinearly oscillating star. In a successive work, they performed similar simulations but considering the head-on collision of Gaussian distributions of matter. Also in this case they found the appearance of type-I critical behaviour, but also performed a perturbative analysis of the initial distributions of matter and of the merged object. Because of the considerable difference found in the eigenfrequencies in the two cases, they concluded that the critical solution does not represent a system near equilibrium and in particular not a perturbed Tolmann-Oppenheimer-Volkoff (TOV) solution. In this Thesis we study the dynamics of the head-on collision of two equal-mass NSs using a setup which is as similar as possible to the one considered above. While we confirm that the merged object exhibits a type-I critical behaviour, we also argue against the conclusion that the critical solution cannot be described in terms of equilibrium solution. Indeed, we show that, in analogy with what is found in, the critical solution is effectively a perturbed unstable solution of the TOV equations. Our analysis also considers fine-structure of the scaling relation of type-I critical phenomena and we show that it exhibits oscillations in a similar way to the one studied in the context of scalar-field critical collapse.}, language = {en} }