@article{WangFruebingWirgesetal.2010, author = {Wang, Feipeng and Fr{\"u}bing, Peter and Wirges, Werner and Gerhard, Reimund and Wegener, Michael}, title = {Enhanced Polarization in Melt-quenched and Stretched Poly(vinylidene Fluoride-Hexafluoropropylene) Films}, issn = {1070-9878}, doi = {10.1109/TDEI.2010.5539679}, year = {2010}, abstract = {beta-phase poly(vinylidene fluoride-hexafluoropropylene) (P(VDF-HFP)) copolymer films were prepared by uniaxially stretching solution-cast or melt-quenched samples. Different preparation routes lead to different amounts of the crystalline alpha and beta phases in the films, as detected by means of Fourier-transform infrared spectroscopy and X-ray diffractometry. The beta phase is significantly enhanced in melt-quenched and stretched films in comparison to solution-cast and stretched films. This is particularly true for copolymer samples with higher HFP content. The beta- phase enhancement is also observed in ferroelectric-hysteresis experiments where a rather high polarization of 58 mC/ m(2) was found on melt-quenched and stretched samples after poling at electric fields of 140 MV/m. After poling at 160 MV/m, one of these samples exhibited a piezoelectric d(33) coefficient as high as 21 pC/N. An electric-field-induced partial transition from the alpha to the beta phase was also observed on the melt-quenched and stretched samples. This effect leads to a further increase in the applications-relevant dipole polarization. Uniaxially stretched ferroelectric- polymer films are highly anisotropic. Dielectric resonance spectroscopy reveals a strong increase of the transverse piezoelectric d(32) coefficient and a strong decrease of the transverse elastic modulus c(32) upon heating from 20 to 50 degrees C.}, language = {en} } @article{VotrubaFeldmeierKrtickaetal.2010, author = {Votruba, Viktor and Feldmeier, Achim and Krticka, Jiri and Kub{\´a}t, Jiř{\´i}}, title = {Multicomponent stellar wind from hot subdwarfs stars}, issn = {0004-640X}, doi = {10.1007/s10509-010-0402-2}, year = {2010}, abstract = {Stellar wind from hot subdwarf stars is mainly accelerated by the interaction of ultraviolet photospheric radiation with metals, mainly oxygen. Absorbing ions share momentum through Coulombic collisions with the remaining passive part of the plasma (namely protons). We found that in the case of the winds from hot subdwarfs, interactions could be so small that they stop the momentum transfer between the passive bulk of plasma and absorbing ions. As a result wind decouples at a certain point.}, language = {en} } @article{VladkovaKoynovaTeuchneretal.2010, author = {Vladkova, Radka and Koynova, Rumiana and Teuchner, Klaus and Tenchov, Boris}, title = {Bilayer structural destabilization by low amounts of chlorophyll a}, issn = {0005-2736}, doi = {10.1016/j.bbamem.2010.05.008}, year = {2010}, abstract = {The present study shows that small admixtures of one chlorophyll a (Chla) molecule per several hundred lipid molecules have strong destabilizing effect on lipid bilayers. This effect is clearly displayed in the properties of the L-alpha-H-II transformations and results from a Chla preference for the H-II relative to the L-alpha phase. Chla disfavors the lamellar liquid crystalline phase L-alpha and induces its replacement with inverted hexagonal phase H-II, as is consistently demonstrated by DSC and X-ray diffraction measurements on phosphatidylethanolamine (PE) dispersions. Chla lowers the L-alpha-H-II transition temperature (42 degrees C) of the fully hydrated dipalmitoleoyl PE (DPoPE) by similar to 8 degrees C and similar to 17 degrees C at Chla/DPoPE molar ratios of 1:500 and 1:100, respectively. Similar Chla effect was recorded also for dielaidoyl PE dispersions. The lowering of the transition temperature and the accompanying significant loss of transition cooperativity reflect the Chla repartitioning and preference for the H-II phase. The reduction of the H-II phase lattice constant in the presence of Chla is an indication that Chla favors v phase formation by decreasing the radius of spontaneous monolayer curvature, and not by filling up the interstitial spaces between the H-II phase cylinders. The observed Chla preference for H-II phase and the substantial bilayer destabilization in the vicinity of a bilayer-to-nonbilayer phase transformation caused by low Chla concentrations can be of interest as a potential regulatory or membrane-damaging factor.}, language = {en} } @article{VitaglianoRieraLatorre2010, author = {Vitagliano, Giuseppe and Riera, Arnau and Latorre, Jos{\´e} Ignacio}, title = {Volume-law scaling for the entanglement entropy in spin-1/2 chains}, issn = {1367-2630}, doi = {10.1088/1367-2630/12/11/113049}, year = {2010}, abstract = {Entanglement entropy obeys area law scaling for typical physical quantum systems. This may naively be argued to follow from the locality of interactions. We show that this is not the case by constructing an explicit simple spin chain Hamiltonian with nearest-neighbor interactions that presents an entanglement volume scaling law. This non- translational model is contrived to have couplings that force the accumulation of singlet bonds across the half-chain. This configuration of the couplings is suggested by real-space renormalization group arguments. Computation of the entanglement entropy is performed by mapping the system to free fermions and diagonalizing numerically its correlation matrix. An analytical relationship between the entanglement entropy and the Frobenius norm of the correlation matrix is also established. Our result is complementary to the known relationship between non-translational invariant, nearest- neighbor interacting Hamiltonians and quantum Merlin-Arthur (QMA)complete problems.}, language = {en} } @article{ValoriKliemToeroeketal.2010, author = {Valori, Gherardo and Kliem, Bernhard and T{\"o}r{\"o}k, Tibor and Titov, Viacheslav S.}, title = {Testing magnetofrictional extrapolation with the Titov-Demoulin model of solar active regions}, issn = {0004-6361}, doi = {10.1051/0004-6361/201014416}, year = {2010}, abstract = {We examine the nonlinear magnetofrictional extrapolation scheme using the solar active region model by Titov and Demoulin as test field. This model consists of an arched, line-tied current channel held in force-free equilibrium by the potential field of a bipolar flux distribution in the bottom boundary. A modified version with a parabolic current density profile is employed here. We find that the equilibrium is reconstructed with very high accuracy in a representative range of parameter space, using only the vector field in the bottom boundary as input. Structural features formed in the interface between the flux rope and the surrounding arcade - "hyperbolic flux tube" and "bald patch separatrix surface" - are reliably reproduced, as are the flux rope twist and the energy and helicity of the configuration. This demonstrates that force-free fields containing these basic structural elements of solar active regions can be obtained by extrapolation. The influence of the chosen initial condition on the accuracy of reconstruction is also addressed, confirming that the initial field that best matches the external potential field of the model quite naturally leads to the best reconstruction. Extrapolating the magnetogram of a Titov-Demoulin equilibrium in the unstable range of parameter space yields a sequence of two opposing evolutionary phases, which clearly indicate the unstable nature of the configuration: a partial buildup of the flux rope with rising free energy is followed by destruction of the rope, losing most of the free energy.}, language = {en} } @article{ToeroekBergerKliem2010, author = {T{\"o}r{\"o}k, Tibor and Berger, Mitch A. and Kliem, Bernhard}, title = {The writhe of helical structures in the solar corona}, issn = {0004-6361}, doi = {10.1051/0004-6361/200913578}, year = {2010}, abstract = {Context. Helicity is a fundamental property of magnetic fields, conserved in ideal MHD. In flux rope geometry, it consists of twist and writhe helicity. Despite the common occurrence of helical structures in the solar atmosphere, little is known about how their shape relates to the writhe, which fraction of helicity is contained in writhe, and how much helicity is exchanged between twist and writhe when they erupt. Aims. Here we perform a quantitative investigation of these questions relevant for coronal flux ropes. Methods. The decomposition of the writhe of a curve into local and nonlocal components greatly facilitates its computation. We use it to study the relation between writhe and projected S shape of helical curves and to measure writhe and twist in numerical simulations of flux rope instabilities. The results are discussed with regard to filament eruptions and coronal mass ejections (CMEs). Results. (1) We demonstrate that the relation between writhe and projected S shape is not unique in principle, but that the ambiguity does not affect low- lying structures, thus supporting the established empirical rule which associates stable forward (reverse) S shaped structures low in the corona with positive (negative) helicity. (2) Kink-unstable erupting flux ropes are found to transform a far smaller fraction of their twist helicity into writhe helicity than often assumed. (3) Confined flux rope eruptions tend to show stronger writhe at low heights than ejective eruptions (CMEs). This argues against suggestions that the writhing facilitates the rise of the rope through the overlying field. (4) Erupting filaments which are S shaped already before the eruption and keep the sign of their axis writhe (which is expected if field of one chirality dominates the source volume of the eruption), must reverse their S shape in the course of the rise. Implications for the occurrence of the helical kink instability in such events are discussed. (5) The writhe of rising loops can easily be estimated from the angle of rotation about the direction of ascent, once the apex height exceeds the footpoint separation significantly. Conclusions. Writhe can straightforwardly be computed for numerical data and can often be estimated from observations. It is useful in interpreting S shaped coronal structures and in constraining models of eruptions.}, language = {en} } @article{TodtPenaHamannetal.2010, author = {Todt, Helge Tobias and Pena, Maria A. and Hamann, Wolf-Rainer and Gr{\"a}fener, G{\"o}tz}, title = {The central star of the planetary nebula PB8 : a Wolf-Rayet-type wind of an unusual WN/WC chemical composition}, issn = {0004-6361}, doi = {10.1051/0004-6361/200912183}, year = {2010}, abstract = {A considerable fraction of the central stars of planetary nebulae (CSPNe) are hydrogen-deficient. As a rule, these CSPNe exhibit a chemical composition of helium, carbon, and oxygen with the majority showing Wolf-Rayet-like emission line spectra. These stars are classified as CSPNe of a spectral type [WC]. We perform a spectral analysis of CSPN PB 8 with the Potsdam Wolf-Rayet (PoWR) models for expanding atmospheres. The source PB8 displays wind-broadened emission lines from strong mass loss. Most strikingly, we find that its surface composition is hydrogen-deficient, but not carbon-rich. With mass fractions of 55\% helium, 40\% hydrogen, 1.3\% carbon, 2\% nitrogen, and 1.3\% oxygen, it differs greatly from the 30-50\% of carbon which are typically seen in [WC]-type central stars. The atmospheric mixture in PB8 has an analogy in the WN/WC transition type among the massive Wolf-Rayet stars. Therefore we suggest to introduce a new spectral type [WN/WC] for CSPNe, with PB8 as its first member. The central star of PB8 has a relatively low temperature of T-* = 52 kK, as expected for central stars in their early evolutionary stages. Its surrounding nebula is less than 3000 years old, i.e. relatively young. Existing calculations for the post-AGB evolution can produce hydrogen-deficient stars of the [WC] type, but do not predict the composition found in PB8. We discuss various scenarios that might explain the origin of this unique object.}, language = {en} } @article{TobieGieseHurfordetal.2010, author = {Tobie, Gabriel and Giese, Bernd and Hurford, Terry Anthony and Lopes, Rosaly M. and Nimmo, Francis and Postberg, Frank and Retherford, Kurt D. and Schmidt, J{\"u}rgen and Spencer, John R. and Tokano, Tetsuya and Turtle, Elizabeth P.}, title = {Surface, subsurface and atmosphere exchanges on the satellites of the outer solar system}, issn = {0038-6308}, doi = {10.1007/s11214-010-9641-3}, year = {2010}, abstract = {The surface morphology of icy moons is affected by several processes implicating exchanges between their subsurfaces and atmospheres (if any). The possible exchange of material between the subsurface and the surface is mainly determined by the mechanical properties of the lithosphere, which isolates the deep, warm and ductile ice material from the cold surface conditions. Exchanges through this layer occur only if it is sufficiently thin and/or if it is fractured owing to tectonic stresses, melt intrusion or impact cratering. If such conditions are met, cryomagma can be released, erupting fresh volatile-rich materials onto the surface. For a very few icy moons (Titan, Triton, Enceladus), the emission of gas associated with cryovolcanic activity is sufficiently large to generate an atmosphere, either long- lived or transient. For those moons, atmosphere-driven processes such as cryovolcanic plume deposition, phase transitions of condensable materials and wind interactions continuously re-shape their surfaces, and are able to transport cryovolcanically generated materials on a global scale. In this chapter, we discuss the physics of these different exchange processes and how they affect the evolution of the satellites' surfaces.}, language = {en} } @phdthesis{Tambornino2010, author = {Tambornino, Johannes}, title = {An analysis of the low energy regime of loop quantum gravity}, address = {Potsdam}, pages = {ix, 169 S.}, year = {2010}, language = {en} } @phdthesis{SanchezBarriga2010, author = {S{\´a}nchez-Barriga, Jaime}, title = {A photoemission study of quasiparticle excitations, electron-correlation effects and magnetization dynamics in thin magnetic systems}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-48499}, school = {Universit{\"a}t Potsdam}, year = {2010}, abstract = {This thesis is focused on the electronic, spin-dependent and dynamical properties of thin magnetic systems. Photoemission-related techniques are combined with synchrotron radiation to study the spin-dependent properties of these systems in the energy and time domains. In the first part of this thesis, the strength of electron correlation effects in the spin-dependent electronic structure of ferromagnetic bcc Fe(110) and hcp Co(0001) is investigated by means of spin- and angle-resolved photoemission spectroscopy. The experimental results are compared to theoretical calculations within the three-body scattering approximation and within the dynamical mean-field theory, together with one-step model calculations of the photoemission process. From this comparison it is demonstrated that the present state of the art many-body calculations, although improving the description of correlation effects in Fe and Co, give too small mass renormalizations and scattering rates thus demanding more refined many-body theories including nonlocal fluctuations. In the second part, it is shown in detail monitoring by photoelectron spectroscopy how graphene can be grown by chemical vapour deposition on the transition-metal surfaces Ni(111) and Co(0001) and intercalated by a monoatomic layer of Au. For both systems, a linear E(k) dispersion of massless Dirac fermions is observed in the graphene pi-band in the vicinity of the Fermi energy. Spin-resolved photoemission from the graphene pi-band shows that the ferromagnetic polarization of graphene/Ni(111) and graphene/Co(0001) is negligible and that graphene on Ni(111) is after intercalation of Au spin-orbit split by the Rashba effect. In the last part, a time-resolved x-ray magnetic circular dichroic-photoelectron emission microscopy study of a permalloy platelet comprising three cross-tie domain walls is presented. It is shown how a fast picosecond magnetic response in the precessional motion of the magnetization can be induced by means of a laser-excited photoswitch. From a comparision to micromagnetic calculations it is demonstrated that the relatively high precessional frequency observed in the experiments is directly linked to the nature of the vortex/antivortex dynamics and its response to the magnetic perturbation. This includes the time-dependent reversal of the vortex core polarization, a process which is beyond the limit of detection in the present experiments.}, language = {en} } @article{SureshSenthilkumarLakshmananetal.2010, author = {Suresh, R. and Senthilkumar, Dharmapuri Vijayan and Lakshmanan, Muthusamy and Kurths, J{\"u}rgen}, title = {Global phase synchronization in an array of time-delay systems}, issn = {1539-3755}, doi = {10.1103/Physreve.82.016215}, year = {2010}, abstract = {We report the identification of global phase synchronization (GPS) in a linear array of unidirectionally coupled Mackey-Glass time-delay systems exhibiting highly non-phase-coherent chaotic attractors with complex topological structure. In particular, we show that the dynamical organization of all the coupled time-delay systems in the array to form GPS is achieved by sequential synchronization as a function of the coupling strength. Further, the asynchronous ones in the array with respect to the main sequentially synchronized cluster organize themselves to form clusters before they achieve synchronization with the main cluster. We have confirmed these results by estimating instantaneous phases including phase difference, average phase, average frequency, frequency ratio, and their differences from suitably transformed phase coherent attractors after using a nonlinear transformation of the original non-phase-coherent attractors. The results are further corroborated using two other independent approaches based on recurrence analysis and the concept of localized sets from the original non-phase-coherent attractors directly without explicitly introducing the measure of phase.}, language = {en} } @article{SunYang2010, author = {Sun, Zong Kui and Yang, Xiao Li}, title = {Parameters identification and synchronization of chaotic delayed systems containing uncertainties and time- varying delay}, issn = {1024-123X}, doi = {10.1155/2010/105309}, year = {2010}, abstract = {Time delays are ubiquitous in real world and are often sources of complex behaviors of dynamical systems. This paper addresses the problem of parameters identification and synchronization of uncertain chaotic delayed systems subject to time-varying delay. Firstly, a novel and systematic adaptive scheme of synchronization is proposed for delayed dynamical systems containing uncertainties based on Razumikhin condition and extended invariance principle for functional differential equations. Then, the proposed adaptive scheme is used to estimate the unknown parameters of nonlinear delayed systems from time series, and a sufficient condition is given by virtue of this scheme. The delayed system under consideration is a very generic one that includes almost all well-known delayed systems (neural network, complex networks, etc.). Two classical examples are used to demonstrate the effectiveness of the proposed adaptive scheme.}, language = {en} } @article{StoyanovKolloscheMcCarthyetal.2010, author = {Stoyanov, Hristiyan and Kollosche, Matthias and McCarthy, Denis N. and Kofod, Guggi}, title = {Molecular composites with enhanced energy density for electroactive polymers}, issn = {0959-9428}, doi = {10.1039/C0jm00519c}, year = {2010}, abstract = {Actuators based on soft dielectric elastomers deform due to electric field induced Maxwell's stress, interacting with the mechanical properties of the material. The relatively high operating voltages of such actuators can be reduced by increasing the permittivity of the active material, while maintaining the mechanical properties and high electrical breakdown strength. Approaches relying on the use of highly polarizable molecules or conjugated polymers have so far provided the best results, however it has been difficult to maintain high breakdown strengths. In this work, a new approach for increasing the electrostatic energy density of a soft polymer based on molecular composites is presented, relying on chemically grafting soft gel-state pi-conjugated conducting macromolecules (polyaniline (PANI)) to a flexible elastomer backbone SEBS-g-MA (poly-styrene-co-ethylene-co-butylene-co-styrene-g-maleic anhydride). The approach was found to result in composites of increased permittivity (470\% over the elastomer matrix) with hardly any reduction in breakdown strength (from 140 to 120 V mu m(-1)), resulting in a large increase in stored electrostatic energy. This led to an improvement in the measured electromechanical response as well as in the maximum actuation strain. A transition was observed when amounts of PANI exceeded 2 vol\%, which was ascribed to the exhaustion of the MA- functionality of the SEBS-g-MA. The transition led to drastic increases in permittivity and conductivity, and a sharp drop in electrical breakdown strength. Although the transition caused further improvement of the electromechanical response, the reduction in electrical breakdown strength caused a limitation of the maximum achievable actuation strain.}, language = {en} } @phdthesis{Stock2010, author = {Stock, Maria}, title = {Charakterisierung der troposph{\"a}rischen Aerosolvariabilit{\"a}t in der europ{\"a}ischen Arktis}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-49203}, school = {Universit{\"a}t Potsdam}, year = {2010}, abstract = {Auf der Grundlage von Sonnenphotometermessungen an drei Messstationen (AWIPEV/ Koldewey in Ny-{\AA}lesund (78.923 °N, 11.923 °O) 1995-2008, 35. Nordpol Driftstation - NP-35 (84.3-85.5 °N, 41.7-56.6 °O) M{\"a}rz/April 2008, Sodankyl{\"a} (67.37 °N, 26.65 °O) 2004-2007) wird die Aerosolvariabilit{\"a}t in der europ{\"a}ischen Arktis und deren Ursachen untersucht. Der Schwerpunkt liegt dabei auf der Frage des Zusammenhanges zwischen den an den Stationen gemessenen Aerosolparametern (Aerosol optische Dicke, Angstr{\"o}m Koeffizient, usw.) und dem Transport des Aerosols sowohl auf kurzen Zeitskalen (Tagen) als auch auf langen Zeitskalen (Monate, Jahre). Um diesen Zusammenhang herzustellen, werden f{\"u}r die kurzen Zeitskalen mit dem Trajektorienmodell PEP-Tracer 5-Tage R{\"u}ckw{\"a}rtstrajektorien in drei Starth{\"o}hen (850 hPa, 700 hPa, 500 hPa) f{\"u}r die Uhrzeiten 00, 06, 12 und 18 Uhr berechnet. Mit Hilfe der nicht-hierarchischen Clustermethode k-means werden die berechneten R{\"u}ckw{\"a}rtstrajektorien dann zu Gruppen zusammengefasst und bestimmten Quellgebieten und den gemessenen Aerosol optischen Dicken zugeordnet. Die Zuordnung von Aerosol optischer Dicke und Quellregion ergibt keinen eindeutigen Zusammenhang zwischen dem Transport verschmutzter Luftmassen aus Europa oder Russland bzw. Asien und erh{\"o}hter Aerosol optischer Dicke. Dennoch ist f{\"u}r einen konkreten Einzelfall (M{\"a}rz 2008) ein direkter Zusammenhang von Aerosoltransport und hohen Aerosol optischen Dicken nachweisbar. In diesem Fall gelangte Waldbrandaerosol aus S{\"u}dwestrussland in die Arktis und konnte sowohl auf der NP-35 als auch in Ny-{\AA}lesund beobachtet werden. In einem weiteren Schritt wird mit Hilfe der EOF-Analyse untersucht, inwieweit großskalige atmosph{\"a}rische Zirkulationsmuster f{\"u}r die Aerosolvariabilit{\"a}t in der europ{\"a}ischen Arktis verantwortlich sind. {\"A}hnlich wie bei der Trajektorienanalyse ist auch die Verbindung der atmosph{\"a}rischen Zirkulation zu den Photometermessungen an den Stationen in der Regel nur schwach ausgepr{\"a}gt. Eine Ausnahme findet sich bei der Betrachtung des Jahresganges des Bodendruckes und der Aerosol optischen Dicke. Hohe Aerosol optische Dicken treten im Fr{\"u}hjahr zum einen dann auf, wenn durch das Islandtief und das sibirische Hochdruckgebiet Luftmassen aus Europa oder Russland/Asien in die Arktis gelangen, und zum anderen, wenn sich ein kr{\"a}ftiges Hochdruckgebiet {\"u}ber Gr{\"o}nland und weiten Teilen der Arktis befindet. Ebenso zeigt sich, dass der {\"U}bergang zwischen Fr{\"u}hjahr und Sommer zumindest teilweise bedingt ist durch denWechsel vom stabilen Polarhoch im Winter und Fr{\"u}hjahr zu einer st{\"a}rker von Tiefdruckgebieten bestimmten arktischen Atmosph{\"a}re im Sommer. Die geringere Aerosolkonzentration im Sommer kann zum Teil mit einer Zunahme der nassen Deposition als Aerosolsenke begr{\"u}ndet werden. F{\"u}r Ny-{\AA}lesund wird neben den Transportmustern auch die chemische Zusammensetzung des Aerosols mit Hilfe von Impaktormessungen an der Zeppelinstation auf dem Zeppelinberg (474m {\"u}.NN) nahe Ny-{\AA}lesund abgeleitet. Dabei ist die positive Korrelation der Aerosoloptischen Dicke mit der Konzentration von Sulfationen und Ruß sehr deutlich. Beide Stoffe gelangen zu einem Großteil durch anthropogene Emissionen in die Atmosph{\"a}re. Die damit nachweisbar anthropogen gepr{\"a}gte Zusammensetzung des arktischen Aerosols steht im Widerspruch zum nicht eindeutig herstellbaren Zusammenhang mit dem Transport des Aerosols aus Industrieregionen. Dies kann nur durch einen oder mehrere gleichzeitig stattfindende Transformationsprozesse (z. B. Nukleation von Schwefels{\"a}urepartikeln) w{\"a}hrend des Transportes aus den Quellregionen (Europa, Russland) erkl{\"a}rt werden.}, language = {de} } @article{StichBeta2010, author = {Stich, Michael and Beta, Carsten}, title = {Control of pattern formation by time-delay feedback with global and local contributions}, issn = {0167-2789}, doi = {10.1016/j.physd.2010.05.001}, year = {2010}, abstract = {We consider the suppression of spatiotemporal chaos in the complex Ginzburg-Landau equation by a combined global and local time-delay feedback. Feedback terms are implemented as a control scheme, i.e., they are proportional to the difference between the time-delayed state of the system and its current state. We perform a linear stability analysis of uniform oscillations with respect to space-dependent perturbations and compare with numerical simulations. Similarly, for the fixed-point solution that corresponds to amplitude death in the spatially extended system, a linear stability analysis with respect to space-dependent perturbations is performed and complemented by numerical simulations.}, language = {en} } @article{SteyrleuthnerSchubertJaiseretal.2010, author = {Steyrleuthner, Robert and Schubert, Marcel and Jaiser, Frank and Blakesley, James C. and Chen, Zhihua and Facchetti, Antonio and Neher, Dieter}, title = {Bulk electron transport and charge injection in a high mobility n-type semiconducting polymer}, issn = {0935-9648}, doi = {10.1002/adma.201000232}, year = {2010}, abstract = {Bulk electron transport in a high mobility n-type polymer is studied by time-of-flight photocurrent measurements and electron-only devices. Bulk electron mobilities of similar to 5 x 10(-3) cm(2)/Vs are obtained. The analysis of the electron currents suggests the presence of an injection barrier for all conventionally used low workfunction cathodes.}, language = {en} } @article{SkoczowskyJechowStuermeretal.2010, author = {Skoczowsky, Danilo and Jechow, Andreas and St{\"u}rmer, Herbert and Poßner, Torsten and Sacher, Joachim and Menzel, Ralf}, title = {Quasi-monolithic ring resonator for efficient frequency doubling of an external cavity diode laser}, issn = {0946-2171}, doi = {10.1007/s00340-009-3802-7}, year = {2010}, abstract = {A quasi-monolithic second-harmonic-generation ring resonator assembled with miniaturized components is presented. The ring contains a 10-mm-long bulk periodically poled lithium niobate crystal for second-harmonic generation, four plane mirrors and two gradient-index lenses. All parts are mounted on a glass substrate with an overall size of 19.5 mmx8.5 mmx4 mm. As pump source a broad-area laser diode operated in an external resonator with Littrow arrangement is utilized. This external cavity diode laser provides near diffraction limited, narrow-bandwidth emission with an optical output power of 450 mW at a wavelength of 976 nm. Locking of the diode laser emission to the resonance frequency of the ring cavity was achieved by an optical self-injection locking technique. With this setup more than 126 mW of diffraction-limited blue light at 488 nm could be generated. The opto-optical conversion efficiency was 28\% and a wall plug efficiency better than 5.5\% could be achieved.}, language = {en} } @article{SkoczowskyJechowMenzeletal.2010, author = {Skoczowsky, Danilo and Jechow, Andreas and Menzel, Ralf and Paschke, Katrin and Erbert, G{\"o}tz}, title = {Efficient second-harmonic generation using a semiconductor tapered amplifier in a coupled ring-resonator geometry}, issn = {0146-9592}, doi = {10.1364/OL.35.000232}, year = {2010}, abstract = {A new approach for efficient second-harmonic generation using diode lasers is presented. The experimental setup is based on a tapered amplifier operated in a ring resonator that is coupled to a miniaturized enhancement ring resonator containing a periodically poled lithium niobate crystal. Frequency locking of the diode laser emission to the resonance frequency of the enhancement cavity is realized purely optically, resulting in stable, single-frequency operation. Blue light at 488 nm with an output power of 310 mW is generated with an optical-to-optical conversion efficiency of 18\%.}, language = {en} } @article{ShklyaevStraube2010, author = {Shklyaev, Sergey and Straube, Arthur V.}, title = {Superexponential droplet fractalization as a hierarchical formation of dissipative compactons}, issn = {1539-3755}, doi = {10.1103/Physreve.82.020601}, year = {2010}, abstract = {We study the dynamics of a thin film over a substrate heated from below in a framework of a strongly nonlinear one-dimensional Cahn-Hilliard equation. The evolution leads to a fractalization into smaller and smaller scales. We demonstrate that a primitive element in the appearing hierarchical structure is a dissipative compacton. Both direct simulations and the analysis of a self-similar solution show that the compactons appear at superexponentially decreasing scales, which means vanishing dimension of the fractal.}, language = {en} } @article{ShklyaevStraube2010, author = {Shklyaev, Sergey and Straube, Arthur V.}, title = {Formation and evolution of bubbly screens in confined oscillating bubbly liquids}, issn = {1539-3755}, doi = {10.1103/Physreve.81.016321}, year = {2010}, abstract = {We consider the dynamics of dilute monodisperse bubbly liquid confined by two plane solid walls and subject to small-amplitude high-frequency oscillations normal to the walls. The initial state corresponds to the uniform distribution of bubbles and motionless liquid. The period of external driving is assumed much smaller than typical relaxation times for a single bubble but larger than the period of volume eigenoscillations. The time-averaged description accounting for the two-way coupling between the liquid and the bubbles is applied. We show that the model predicts accumulation of bubbles in thin sheets parallel to the walls. These singular structures, which are formally characterized by infinitely thin width and infinitely high concentration, are referred to as bubbly screens. The formation of a bubbly screen is described analytically in terms of a self-similar solution, which is in agreement with numerical simulations. We study the evolution of bubbly screens and detect a one-dimensional stationary state, which is shown to be unconditionally unstable.}, language = {en} } @article{SenthilkumarMuruganandamLakshmanan2010, author = {Senthilkumar, Dharmapuri Vijayan and Muruganandam, Paulsamy and Lakshmanan, Muthusamy}, title = {Scaling and synchronization in a ring of diffusively coupled nonlinear oscillators}, issn = {1539-3755}, doi = {10.1103/Physreve.81.066219}, year = {2010}, abstract = {Chaos synchronization in a ring of diffusively coupled nonlinear oscillators driven by an external identical oscillator is studied. Based on numerical simulations we show that by introducing additional couplings at (mN(c) + 1)-th oscillators in the ring, where m is an integer and N-c is the maximum number of synchronized oscillators in the ring with a single coupling, the maximum number of oscillators that can be synchronized can be increased considerably beyond the limit restricted by size instability. We also demonstrate that there exists an exponential relation between the number of oscillators that can support stable synchronization in the ring with the external drive and the critical coupling strength epsilon(c) with a scaling exponent gamma. The critical coupling strength is calculated by numerically estimating the synchronization error and is also confirmed from the conditional Lyapunov exponents of the coupled systems. We find that the same scaling relation exists for m couplings between the drive and the ring. Further, we have examined the robustness of the synchronous states against Gaussian white noise and found that the synchronization error exhibits a power-law decay as a function of the noise intensity indicating the existence of both noise-enhanced and noise-induced synchronizations depending on the value of the coupling strength epsilon. In addition, we have found that epsilon(c) shows an exponential decay as a function of the number of additional couplings. These results are demonstrated using the paradigmatic models of Rossler and Lorenz oscillators.}, language = {en} } @article{SenthilkumarKurths2010, author = {Senthilkumar, Dharmapuri Vijayan and Kurths, J{\"u}rgen}, title = {Characteristics and synchronization of time-delay systems driven by a common noise}, issn = {1951-6355}, doi = {10.1140/epjst/e2010-01273-4}, year = {2010}, abstract = {We investigate the characteristics of time-delay systems in the presence of Gaussian noise. We show that the delay time embedded in the time series of time-delay system with constant delay cannot be estimated in the presence noise for appropriate values of noise intensity thereby forbidding any possibility of phase space reconstruction. We also demonstrate the existence of complete synchronization between two independent identical time-delay systems driven by a common noise without explicitly establishing any external coupling between them.}, language = {en} } @article{SeissSpahnSchmidt2010, author = {Seiß, Martin and Spahn, Frank and Schmidt, J{\"u}rgen}, title = {Moonlet induced wakes in planetary rings : analytical model including eccentric orbits of moon and ring particles}, issn = {0019-1035}, doi = {10.1016/j.icarus.2010.06.013}, year = {2010}, abstract = {Saturn's rings host two known moons, Pan and Daphnis, which are massive enough to clear circumferential gaps in the ring around their orbits. Both moons create wake patterns at the gap edges by gravitational deflection of the ring material (Cuzzi, J.N., Scargle, J.D. [1985]. Astrophys. J. 292, 276-290; Showalter, MR., Cuzzi, J.N., Marouf, E.A., Esposito, LW. [1986]. Icarus 66, 297-323). New Cassini observations revealed that these wavy edges deviate from the sinusoidal waveform, which one would expect from a theory that assumes a circular orbit of the perturbing moon and neglects particle interactions. Resonant perturbations of the edges by moons outside the ring system, as well as an eccentric orbit of the embedded moon, may partly explain this behavior (Porco, CC., and 34 colleagues [2005]. Science 307, 1226-1236; Tiscareno, M.S., Burns, J.A., Hedman, MM., Spitale, J.N., Porco, CC., Murray, C.D., and the Cassini Imaging team [2005]. Bull. Am. Astron. Soc. 37, 767; Weiss, J.W., Porco, CC., Tiscareno, M.S., Burns, J.A., Dones, L [2005]. Bull. Am. Astron. Soc. 37, 767; Weiss, J.W., Porco, CC., Tiscareno, M.S. [2009]. Astron. J. 138, 272-286). Here we present an extended non-collisional streamline model which accounts for both effects. We describe the resulting variations of the density structure and the modification of the nonlinearity parameter q. Furthermore, an estimate is given for the applicability of the model. We use the streamwire model introduced by Stewart (Stewart, G.R. [1991]. Icarus 94, 436-450) to plot the perturbed ring density at the gap edges. We apply our model to the Keeler gap edges undulated by Daphnis and to a faint ringlet in the Encke gap close to the orbit of Pan. The modulations of the latter ringlet, induced by the perturbations of Pan (Burns, J.A., Hedman, M.M., Tiscareno, M.S., Nicholson, P.D., Streetman, B.J., Colwell, J.E., Showalter, M.R., Murray, C.D., Cuzzi, J.N., Porco, CC., and the Cassini ISS team [2005]. Bull. Am. Astron. Soc. 37, 766), can be well described by our analytical model. Our analysis yields a Hill radius of Pan of 17.5 km, which is 9\% smaller than the value presented by Porco (Porco, CC., and 34 colleagues [2005]. Science 307, 1226- 1236), but fits well to the radial semi-axis of Pan of 17.4 km. This supports the idea that Pan has filled its Hill sphere with accreted material (Porco, C.C., Thomas, P.C., Weiss, J.W., Richardson, D.C. [2007]. Science 318, 1602-1607). A numerical solution of a streamline is used to estimate the parameters of the Daphnis-Keeler gap system, since the close proximity of the gap edge to the moon induces strong perturbations, not allowing an application of the analytic streamline model. We obtain a Hill radius of 5.1 km for Daphnis, an inner edge variation of 8 km, and an eccentricity for Daphnis of 1.5 x 10(-5). The latter two quantities deviate by a factor of two from values gained by direct observations (Jacobson, R.A., Spitale, J., Porco, C.C., Beurle, K., Cooper, N.J., Evans, M.W., Murray, C.D. [2008]. Astron. J. 135, 261-263; Tiscareno, M.S., Burns, J.A., Hedman, M.M., Spitale, J.N., Porco, C.C., Murray, C.D., and the Cassini Imaging team [2005]. Bull. Am. Astron. Soc. 37, 767), which might be attributed to the neglect of particle interactions and vertical motion in our model.}, language = {en} } @phdthesis{Schwabedal2010, author = {Schwabedal, Justus Tilmann Caspar}, title = {Phase dynamics of irregular oscillations}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-50115}, school = {Universit{\"a}t Potsdam}, year = {2010}, abstract = {In der vorliegenden Dissertation wird eine Beschreibung der Phasendynamik irregul{\"a}rer Oszillationen und deren Wechselwirkungen vorgestellt. Hierbei werden chaotische und stochastische Oszillationen autonomer dissipativer Systeme betrachtet. F{\"u}r eine Phasenbeschreibung stochastischer Oszillationen m{\"u}ssen zum einen unterschiedliche Werte der Phase zueinander in Beziehung gesetzt werden, um ihre Dynamik unabh{\"a}ngig von der gew{\"a}hlten Parametrisierung der Oszillation beschreiben zu k{\"o}nnen. Zum anderen m{\"u}ssen f{\"u}r stochastische und chaotische Oszillationen diejenigen Systemzust{\"a}nde identifiziert werden, die sich in der gleichen Phase befinden. Im Rahmen dieser Dissertation werden die Werte der Phase {\"u}ber eine gemittelte Phasengeschwindigkeitsfunktion miteinander in Beziehung gesetzt. F{\"u}r stochastische Oszillationen sind jedoch verschiedene Definitionen der mittleren Geschwindigkeit m{\"o}glich. Um die Unterschiede der Geschwindigkeitsdefinitionen besser zu verstehen, werden auf ihrer Basis effektive deterministische Modelle der Oszillationen konstruiert. Hierbei zeigt sich, dass die Modelle unterschiedliche Oszillationseigenschaften, wie z. B. die mittlere Frequenz oder die invariante Wahrscheinlichkeitsverteilung, nachahmen. Je nach Anwendung stellt die effektive Phasengeschwindigkeitsfunktion eines speziellen Modells eine zweckm{\"a}ßige Phasenbeziehung her. Wie anhand einfacher Beispiele erkl{\"a}rt wird, kann so die Theorie der effektiven Phasendynamik auch kontinuierlich und pulsartig wechselwirkende stochastische Oszillationen beschreiben. Weiterhin wird ein Kriterium f{\"u}r die invariante Identifikation von Zust{\"a}nden gleicher Phase irregul{\"a}rer Oszillationen zu sogenannten generalisierten Isophasen beschrieben: Die Zust{\"a}nde einer solchen Isophase sollen in ihrer dynamischen Entwicklung ununterscheidbar werden. F{\"u}r stochastische Oszillationen wird dieses Kriterium in einem mittleren Sinne interpretiert. Wie anhand von Beispielen demonstriert wird, lassen sich so verschiedene Typen stochastischer Oszillationen in einheitlicher Weise auf eine stochastische Phasendynamik reduzieren. Mit Hilfe eines numerischen Algorithmus zur Sch{\"a}tzung der Isophasen aus Daten wird die Anwendbarkeit der Theorie anhand eines Signals regelm{\"a}ßiger Atmung gezeigt. Weiterhin zeigt sich, dass das Kriterium der Phasenidentifikation f{\"u}r chaotische Oszillationen nur approximativ erf{\"u}llt werden kann. Anhand des R{\"o}ssleroszillators wird der tiefgreifende Zusammenhang zwischen approximativen Isophasen, chaotischer Phasendiffusion und instabilen periodischen Orbits dargelegt. Gemeinsam erm{\"o}glichen die Theorien der effektiven Phasendynamik und der generalisierten Isophasen eine umfassende und einheitliche Phasenbeschreibung irregul{\"a}rer Oszillationen.}, language = {de} } @article{SchwabedalPikovskij2010, author = {Schwabedal, Justus T. C. and Pikovskij, Arkadij}, title = {Effective phase description of noise-perturbed and noise-induced oscillations}, issn = {1951-6355}, doi = {10.1140/epjst/e2010-01271-6}, year = {2010}, abstract = {An effective dynamical description of a general class of stochastic phase oscillators is presented. For this, the effective phase velocity is defined either by the stochastic phase oscillators invariant probability density or its first passage times. Using the first approach the effective phase exhibits the correct frequency and invariant distribution density, whereas the second approach models the proper phase resetting curve. The discrepancy of the effective models is most pronounced for noise-induced oscillations and is related to non-monotonicity of the stochastic phase variable due to fluctuations.}, language = {en} } @article{SchwabedalPikovskij2010, author = {Schwabedal, Justus T. C. and Pikovskij, Arkadij}, title = {Effective phase dynamics of noise-induced oscillations in excitable systems}, issn = {1539-3755}, doi = {10.1103/Physreve.81.046218}, year = {2010}, abstract = {We develop an effective description of noise-induced oscillations based on deterministic phase dynamics. The phase equation is constructed to exhibit correct frequency and distribution density of noise-induced oscillations. In the simplest one-dimensional case the effective phase equation is obtained analytically, whereas for more complex situations a simple method of data processing is suggested. As an application an effective coupling function is constructed that quantitatively describes periodically forced noise-induced oscillations.}, language = {en} } @article{SchulzOrgzallDiezetal.2010, author = {Schulz, Burkhard and Orgzall, Ingo and Diez, Isabel and Dietzel, Birgit and Tauer, Klaus}, title = {Template mediated formation of shaped polypyrrole particles}, issn = {0927-7757}, doi = {10.1016/j.colsurfa.2009.11.034}, year = {2010}, abstract = {The formation of different micro- and nanostructures during the chemical synthesis of polypyrrole is reviewed shortly based on the conceptions of hard- and soft-templating models. Contrary to other models that emphasize the role of micelles it is found here that during the oxidative polymerization of pyrole using sulfonic acid dopants a crystalline hard template is found in the first steps of the reaction before the addition of the oxidant. This template is formed by a complex consisting of 2,5-bis(pyrrole-2-yl)pyrrolidine and the sulfonic acid anion. The acid catalyzed formation of this specific tripyrrole is discussed. (C) 2009 Elsevier B.V. All rights reserved.}, language = {en} } @article{SchmidtZamoraLopezKurths2010, author = {Schmidt, G. and Zamora-Lopez, Gorka and Kurths, J{\"u}rgen}, title = {Simulation of large scale cortical networks by individual neuron dynamics}, issn = {0218-1274}, doi = {10.1142/S0218127410026149}, year = {2010}, abstract = {Understanding the functional dynamics of the mammalian brain is one of the central aims of modern neuroscience. Mathematical modeling and computational simulations of neural networks can help in this quest. In recent publications, a multilevel model has been presented to simulate the resting-state dynamics of the cortico-cortical connectivity of the mammalian brain. In the present work we investigate how much of the dynamical behavior of the multilevel model can be reproduced by a strongly simplified model. We find that replacing each cortical area by a single Rulkov map recreates the patterns of dynamical correlation of the multilevel model, while the outcome of other models and setups mainly depends on the local network properties, e. g. the input degree of each vertex. In general, we find that a simple simulation whose dynamics depends on the global topology of the whole network is far from trivial. A systematic analysis of different dynamical models and coupling setups is required.}, language = {en} } @phdthesis{Schattauer2010, author = {Schattauer, Sylvia}, title = {Hybride D{\"u}nnschicht-Solarzellen aus mesopor{\"o}sem Titandioxid und konjugierten Polymeren}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-52619}, school = {Universit{\"a}t Potsdam}, year = {2010}, abstract = {Das Ziel dieser Arbeit ist die Untersuchung der aktiven Komponenten und ihrer Wechselwirkungen in teilorganischen Hybrid-Solarzellen. Diese bestehen aus einer d{\"u}nnen Titandioxidschicht, kombiniert mit einer d{\"u}nnen Polymerschicht. Die Effizienz der Hybrid-Solarzellen wird durch die Lichtabsorption im Polymer, die Dissoziation der gebildeten Exzitonen an der aktiven Grenzfl{\"a}che zwischen TiO2 und Polymer, sowie durch Generation und Extraktion freier Ladungstr{\"a}ger bestimmt. Zur Optimierung der Solarzellen wurden grundlegende physikalische Wechselwirkungen zwischen den verwendeten Materialen sowie der Einfluss verschiedener Herstellungsparameter untersucht. Unter anderem wurden Fragen zum optimalen Materialeinsatz und Pr{\"a}parationsbedingungen beantwortet sowie grundlegende Einfl{\"u}sse wie Schichtmorphologie und Polymerinfiltration n{\"a}her betrachtet. Zun{\"a}chst wurde aus unterschiedlich hergestelltem Titandioxid (Akzeptor-Schicht) eine Auswahl f{\"u}r den Einsatz in Hybrid-Solarzellen getroffen. Kriterium war hierbei die unterschiedliche Morphologie aufgrund der Oberfl{\"a}chenbeschaffenheit, der Film-Struktur, der Kristallinit{\"a}t und die daraus resultierenden Solarzelleneigenschaften. F{\"u}r die anschließenden Untersuchungen wurden mesopor{\"o}se TiO2-Filme aus einer neuen Nanopartikel-Synthese, welche es erlaubt, kristalline Partikel schon w{\"a}hrend der Synthese herzustellen, als Elektronenakzeptor und konjugierte Polymere auf Poly(p-Phenylen-Vinylen) (PPV)- bzw. Thiophenbasis als Donatormaterial verwendet. Bei der thermischen Behandlung der TiO2-Schichten erfolgt eine temperaturabh{\"a}ngige {\"A}nderung der Morphologie, jedoch nicht der Kristallstruktur. Die Auswirkungen auf die Solarzelleneigenschaften wurden dokumentiert und diskutiert. Um die Vorteile der Nanopartikel-Synthese, die Bildung kristalliner TiO2-Partikel bei tiefen Temperaturen, nutzen zu k{\"o}nnen, wurden erste Versuche zur UV-Vernetzung durchgef{\"u}hrt. Neben der Beschaffenheit der Oxidschicht wurde auch der Einfluss der Polymermorphologie, bedingt durch L{\"o}sungsmittelvariation und Tempertemperatur, untersucht. Hierbei konnte gezeigt werden, dass u.a. die Viskosit{\"a}t der Polymerl{\"o}sung die Infiltration in die TiO2-Schicht und dadurch die Effizienz der Solarzelle beeinflusst. Ein weiterer Ansatz zur Erh{\"o}hung der Effizienz ist die Entwicklung neuer lochleitender Polymere, welche m{\"o}glichst {\"u}ber einen weiten spektralen Bereich Licht absorbieren und an die Bandl{\"u}cke des TiO2 angepasst sind. Hierzu wurden einige neuartige Konzepte, z.B. die Kombination von Thiophen- und Phenyl-Einheiten n{\"a}her untersucht. Auch wurde die Sensibilisierung der Titandioxidschicht in Anlehnung an die h{\"o}heren Effizienzen der Farbstoffzellen in Betracht gezogen. Zusammenfassend konnten im Rahmen dieser Arbeit wichtige Einflussparameter auf die Funktion hybrider Solarzellen identifiziert und z.T. n{\"a}her diskutiert werden. F{\"u}r einige limitierende Faktoren wurden Konzepte zur Verbesserung bzw. Vermeidung vorgestellt.}, language = {de} } @phdthesis{Neumeyer2010, author = {Neumeyer, Steffen}, title = {Entwicklung und Evaluation eines Lernortes Praktikum f{\"u}r die Schule}, address = {Potsdam}, pages = {253 Bl. : Ill., graph. Darst.}, year = {2010}, language = {de} } @article{Mikelskis2010, author = {Mikelskis, Helmut F.}, title = {Physics schoolbooks - their history and future}, isbn = {978-3-8309-2018-2}, year = {2010}, language = {en} } @phdthesis{Lara2010, author = {Lara, Luc{\´i}a Santamar{\´i}a}, title = {Coalescence of black-hole binaries : from theoretical source models to applications in gravitational-wave astronomy}, address = {Potsdam}, pages = {xxii, 172 S. : graph. Darst.}, year = {2010}, language = {en} } @phdthesis{Ksianzou2010, author = {Ksianzou, Viachaslau}, title = {Second-order nonlinear optical interactions and cascading effects in thinorganic films}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-49186}, school = {Universit{\"a}t Potsdam}, year = {2010}, abstract = {The presented work describes new concepts of fast switching elements based on principles of photonics. The waveguides working in visible and infra-red ranges are put in a basis of these elements. And as materials for manufacturing of waveguides the transparent polymers, dopped by molecules of the dyes possessing second order nonlinear-optical properties are proposed. The work shows how nonlinear-optical processes in such structures can be implemented by electro-optical and opto-optical control circuit signals. In this paper we consider the complete cycle of fabrication of several types of integral photonic elements. The theoretical analysis of high-intensity beam propagation in media with second-order optical nonlinearity is performed. Quantitative estimations of necessary conditions of occurrence of the nonlinear-optical phenomena of the second order taking into account properties of used materials are made. The paper describes the various stages of manufacture of the basic structure of the integrated photonics: a planar waveguide. Using the finite element method the structure of the electromagnetic field inside the waveguide in different modes was analysed. A separate part of the work deals with the creation of composite organic materials with high optical nonlinearity. Using the methods of quantum chemistry, the dependence of nonlinear properties of dye molecules from its structure were investigated in details. In addition, the paper discusses various methods of inducing of an optical nonlinearity in dye-doping of polymer films. In the work, for the first time is proposed the use of spatial modulation of nonlinear properties of waveguide according Fibonacci law. This allows involving several different nonlinear optical processes simultaneously. The final part of the work describes various designs of integrated optical modulators and switches constructed of organic nonlinear optical waveguides. A practical design of the optical modulator based on Mach-Zehnder interferometer made by a photolithography on polymer film is presented.}, language = {en} } @phdthesis{Krobath2010, author = {Krobath, Heinrich}, title = {Binding cooperativity and domain energies of membrane adhesion receptors}, address = {Potsdam}, pages = {106 S. : graph. Darst.}, year = {2010}, language = {en} } @phdthesis{Kralemann2010, author = {Kralemann, Bj{\"o}rn Christian}, title = {Die Rekonstruktion invarianter Phasenmodelle aus Daten}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-45057}, school = {Universit{\"a}t Potsdam}, year = {2010}, abstract = {Ziel dieser Arbeit ist die {\"U}berwindung einer Differenz, die zwischen der Theorie der Phase bzw. der Phasendynamik und ihrer Anwendung in der Zeitreihenanalyse besteht: W{\"a}hrend die theoretische Phase eindeutig bestimmt und invariant unter Koordinatentransformationen bzw. gegen{\"u}ber der jeweils gew{\"a}hlten Observable ist, f{\"u}hren die Standardmethoden zur Absch{\"a}tzung der Phase aus gegebenen Zeitreihen zu Resultaten, die einerseits von den gew{\"a}hlten Observablen abh{\"a}ngen und so andererseits das jeweilige System keineswegs in eindeutiger und invarianter Weise beschreiben. Um diese Differenz deutlich zu machen, wird die terminologische Unterscheidung von Phase und Protophase eingef{\"u}hrt: Der Terminus Phase wird nur f{\"u}r Variablen verwendet, die dem theoretischen Konzept der Phase entsprechen und daher das jeweilige System in invarianter Weise charakterisieren, w{\"a}hrend die observablen-abh{\"a}ngigen Absch{\"a}tzungen der Phase aus Zeitreihen als Protophasen bezeichnet werden. Der zentrale Gegenstand dieser Arbeit ist die Entwicklung einer deterministischen Transformation, die von jeder Protophase eines selbsterhaltenden Oszillators zur eindeutig bestimmten Phase f{\"u}hrt. Dies erm{\"o}glicht dann die invariante Beschreibung gekoppelter Oszillatoren und ihrer Wechselwirkung. Die Anwendung der Transformation bzw. ihr Effekt wird sowohl an numerischen Beispielen demonstriert - insbesondere wird die Phasentransformation in einem Beispiel auf den Fall von drei gekoppelten Oszillatoren erweitert - als auch an multivariaten Messungen des EKGs, des Pulses und der Atmung, aus denen Phasenmodelle der kardiorespiratorischen Wechselwirkung rekonstruiert werden. Abschließend wird die Phasentransformation f{\"u}r autonome Oszillatoren auf den Fall einer nicht vernachl{\"a}ssigbaren Amplitudenabh{\"a}ngigkeit der Protophase erweitert, was beispielsweise die numerischen Bestimmung der Isochronen des chaotischen R{\"o}ssler Systems erm{\"o}glicht.}, language = {de} } @article{KliemRustSeehafer2010, author = {Kliem, Bernhard and Rust, S. and Seehafer, Norbert}, title = {Helicity transport in a simulated coronal mass ejection}, series = {Proceedings of the International Astronomical Union}, journal = {Proceedings of the International Astronomical Union}, publisher = {International Astronomical Union}, address = {Cambridge}, issn = {1743-9213}, doi = {10.1017/S1743921311006715}, pages = {125 -- 128}, year = {2010}, language = {en} } @phdthesis{Klasczyk2010, author = {Klasczyk, Benjamin}, title = {Interactions of ions with membranes}, address = {Potsdam}, pages = {116 S.}, year = {2010}, language = {en} } @article{HerzogLeitenbergerShayduketal.2010, author = {Herzog, Marc and Leitenberger, Wolfram and Shayduk, Roman and van der Veen, Renske Marjan and Milne, Chris J. and Johnson, Steven Lee and Vrejoiu, Ionela and Alexe, Marin and Hesse, Dietrich and Bargheer, Matias}, title = {Ultrafast manipulation of hard x-rays by efficient Bragg switches}, issn = {0003-6951}, doi = {10.1063/1.3402773}, year = {2010}, abstract = {We experimentally demonstrate efficient switching of the hard x-ray Bragg reflectivity of a SrRuO3 /SrTiO3 superlattice by optical excitation of large-amplitude coherent acoustic superlattice phonons. The rocking curve changes drastically on a 1 ps timescale. The (0 0 116) reflection is almost extinguished (Delta R/R-0=-0.91), while the (0 0 118) reflection increases by more than an order of magnitude (Delta R/R-0=24.1). The change of the x-ray structure factor depends nonlinearly on the phonon amplitude, allowing manipulation of the x-ray response on a timescale considerably shorter than the phonon period. Numerical simulations for a superlattice with slightly changed geometry and realistic parameters predict a switching-contrast ratio Delta R/R-0 of 700 with high reflectivity.}, language = {en} } @article{HenniesPietzschBerglundetal.2010, author = {Hennies, Franz and Pietzsch, Annette and Berglund, Martin and F{\"o}hlisch, Alexander and Schmitt, Thorsten and Strocov, Vladimir and Karlsson, Hans O. and Andersson, Joakim and Rubensson, Jan-Erik}, title = {Resonant inelastic scattering spectra of free molecules with vibrational resolution}, issn = {0031-9007}, doi = {10.1103/Physrevlett.104.193002}, year = {2010}, abstract = {Inelastic x-ray scattering spectra excited at the 1s(-1) pi* resonance of gas phase O-2 have been recorded with an overall energy resolution that allows for well-resolved vibrational progressions. The nuclear wave packet dynamics in the intermediate state is reflected in vibrational excitations of the electronic ground state, and by fine-tuning the excitation energy the dissociation dynamics in the predissociative B' (3) Pi(g) final state is controlled.}, language = {en} } @article{HenkelIntravaia2010, author = {Henkel, Carsten and Intravaia, Francesco}, title = {On the Casimir entropy between "perfect crystals"}, issn = {0217-751X}, doi = {10.1142/S0217751x10049608}, year = {2010}, abstract = {We give a re-interpretation of an 'entropy defect' in the electromagnetic Casimir effect. The electron gas in a perfect crystal is an electromagnetically disordered system whose entropy contains a finite Casimir- like contribution. The Nernst theorem (third law of thermodynamics) is not applicable.}, language = {en} } @article{Hamann2010, author = {Hamann, Wolf-Rainer}, title = {Stellar winds from hot low-mass stars}, issn = {0004-640X}, doi = {10.1007/s10509-010-0344-8}, year = {2010}, abstract = {Stellar winds appear as a persistent feature of hot stars, irrespective of their wide range of different luminosities, masses, and chemical composition. Among the massive stars, the Wolf-Rayet types show considerably stronger mass loss than the O stars. Among hot low-mass stars, stellar winds are seen at central stars of planetary nebulae, where again the hydrogen-deficient stars show much stronger winds than those central stars with "normal" composition. We also studied mass-loss from a few extreme helium stars and sdOs. Their mass-loss rate roughly follows the same proportionality with luminosity to the power 1.5 as the massive O stars. This relation roughly marks a lower limit for the mass loss from hot stars of all kinds, and provides evidence that radiation pressure on spectral lines is the basic mechanism at work. For certain classes of stars the mass-loss rates lie significantly above this relation, for reasons that are not yet fully understood. Mass loss from low-mass stars may affect their evolution, by reducing the envelope mass, and can easily prevent diffusion from establishing atmospheric abundance patterns. In close binary systems, their winds can feed the accretion onto a companion.}, language = {en} } @article{HaakhIntravaiaHenkel2010, author = {Haakh, Harald Richard and Intravaia, Francesco and Henkel, Carsten}, title = {Temperature dependence of the plasmonic Casimir interaction}, issn = {1050-2947}, doi = {10.1103/Physreva.82.012507}, year = {2010}, abstract = {We investigate the role of surface plasmons in the electromagnetic Casimir effect at finite temperature, including situations out of global thermal equilibrium. The free energy is calculated analytically and expanded for different regimes of distances and temperatures. Similar to the zero-temperature case, the interaction changes from attraction to repulsion with distance. Thermal effects are shown to be negligible for small plate separations and at room temperature but become dominant and repulsive at large values of these parameters. In configurations out of global thermal equilibrium, we show that the selective excitation of surface plasmons can create a repulsive Casimir force between metal plates.}, language = {en} } @article{GvaramadzeKniazevHamannetal.2010, author = {Gvaramadze, Vasily V. and Kniazev, Alexei Y. and Hamann, Wolf-Rainer and Berdnikov, Leonid N. and Fabrika, Sergei Nikolaevich and Valeev, Azamat F.}, title = {A new Wolf-Rayet star and its circumstellar nebula in Aquila}, issn = {0035-8711}, doi = {10.1111/j.1365-2966.2009.16126.x}, year = {2010}, abstract = {We report the discovery of a new Wolf-Rayet star in Aquila via detection of its circumstellar nebula (reminiscent of ring nebulae associated with late WN stars) using the Spitzer Space Telescope archival data. Our spectroscopic follow-up of the central point source associated with the nebula showed that it is a WN7h star (we named it WR121b). We analysed the spectrum of WR 121b by using the Potsdam Wolf-Rayet model atmospheres, obtaining a stellar temperature of similar or equal to 50 kK. The stellar wind composition is dominated by helium with similar to 20 per cent of hydrogen. The stellar spectrum is highly reddened [E(B - V) = 2.85 mag]. Adopting an absolute magnitude of M-v = 5.7, the star has a luminosity of log L/L-circle dot = 5.75 and a mass-loss rate of 10(-4.7)M(circle dot)yr(-1), and resides at a distance of 6.3 kpc. We searched for a possible parent cluster of WR 121b and found that this star is located at similar or equal to 1 degrees from the young star cluster embedded in the giant HII region W43 (containing a WN7+a/OB? star - WR121a). We also discovered a bow shock around the O9.5III star ALS 9956, located at similar or equal to 0 degrees.5 from the cluster. We discuss the possibility that WR121b and ALS 9956 are runaway stars ejected from the cluster in W43.}, language = {en} } @article{GrossMuellerColbecketal.2010, author = {Gross, David and Mueller, Markus and Colbeck, Roger and Dahlsten, Oscar C. O.}, title = {All reversible dynamics in maximally nonlocal theories are trivial}, issn = {0031-9007}, doi = {10.1103/Physrevlett.104.080402}, year = {2010}, abstract = {A remarkable feature of quantum theory is nonlocality ( Bell inequality violations). However, quantum correlations are not maximally nonlocal, and it is natural to ask whether there are compelling reasons for rejecting theories in which stronger violations are possible. To shed light on this question, we consider post-quantum theories in which maximally nonlocal states ( nonlocal boxes) occur. We show that reversible transformations in such theories are trivial: they consist solely of local operations and permutations of systems. In particular, no correlations can be created; nonlocal boxes cannot be prepared from product states and classical computers can efficiently simulate all such processes.}, language = {en} } @article{GrossLiuFlammiaetal.2010, author = {Gross, David and Liu, Yi-Kai and Flammia, Steven T. and Becker, Stephen and Eisert, Jens}, title = {Quantum state tomography via compressed sensing}, issn = {0031-9007}, doi = {10.1103/Physrevlett.105.150401}, year = {2010}, abstract = {We establish methods for quantum state tomography based on compressed sensing. These methods are specialized for quantum states that are fairly pure, and they offer a significant performance improvement on large quantum systems. In particular, they are able to reconstruct an unknown density matrix of dimension d and rank r using O(rdlog(2)d) measurement settings, compared to standard methods that require d(2) settings. Our methods have several features that make them amenable to experimental implementation: they require only simple Pauli measurements, use fast convex optimization, are stable against noise, and can be applied to states that are only approximately low rank. The acquired data can be used to certify that the state is indeed close to pure, so no a priori assumptions are needed.}, language = {en} } @article{GrossEisert2010, author = {Gross, David and Eisert, Jens}, title = {Quantum computational webs}, issn = {1050-2947}, doi = {10.1103/Physreva.82.040303}, year = {2010}, abstract = {We discuss the notion of quantum computational webs: These are quantum states universal for measurement-based computation, which can be built up from a collection of simple primitives. The primitive elements-reminiscent of building blocks in a construction kit-are (i) one-dimensional states (computational quantum wires) with the power to process one logical qubit and (ii) suitable couplings, which connect the wires to a computationally universal web. All elements are preparable by nearest-neighbor interactions in a single pass, of the kind accessible in a number of physical architectures. We provide a complete classification of qubit wires, a physically well-motivated class of universal resources that can be fully understood. Finally, we sketch possible realizations in superlattices and explore the power of coupling mechanisms based on Ising or exchange interactions.}, language = {en} } @article{GrecoWangWegener2010, author = {Greco, Tonino and Wang, Feipeng and Wegener, Michael}, title = {Multifunctional silver poly(vinylidene fluoride) nanocomposites : nanoparticle synthesis, film processing, and structural characterization}, issn = {0015-0193}, doi = {10.1080/00150193.2010.482896}, year = {2010}, abstract = {Scope of this work was the synthesis of homogeneously dispersed silver nanoparticles in the ferroelectric polymer poly(vinylidene fluoride) (PVDF) and the study of the resulting properties affecting both the electro-active matrix and the optically-active nanofiller. In the nanocomposites surface plasmon resonances can be tuned across the UV- vis to the NIR spectral range. From IR spectra and DSC measurements it is concluded that the - to -phase transformation is observed and no degradation of the polymer matrix occurs. Finally, electrical poling was performed in order to investigate the influence of the embedded silver particles on the polarization behavior of the ferroelectric polymer.}, language = {en} } @phdthesis{Ganesan2010, author = {Ganesan, Lakshmi Meena}, title = {Coupling of the electrical, mechanical and optical response in polymer/liquid-crystal composites}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-41572}, school = {Universit{\"a}t Potsdam}, year = {2010}, abstract = {Micrometer-sized liquid-crystal (LC) droplets embedded in a polymer matrix may enable optical switching in the composite film through the alignment of the LC director along an external electric field. When a ferroelectric material is used as host polymer, the electric field generated by the piezoelectric effect can orient the director of the LC under an applied mechanical stress, making these materials interesting candidates for piezo-optical devices. In this work, polymer-dispersed liquid crystals (PDLCs) are prepared from poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) and a nematic liquid crystal (LC). The anchoring effect is studied by means of dielectric relaxation spectroscopy. Two dispersion regions are observed in the dielectric spectra of the pure P(VDF-TrFE) film. They are related to the glass transition and to a charge-carrier relaxation, respectively. In PDLC films containing 10 and 60 wt\% LC, an additional, bias-field-dependent relaxation peak is found that can be attributed to the motion of LC molecules. Due to the anchoring effect of the LC molecules, this relaxation process is slowed down considerably, when compared with the related process in the pure LC. The electro-optical and piezo-optical behavior of PDLC films containing 10 and 60 wt\% LCs is investigated. In addition to the refractive-index mismatch between the polymer matrix and the LC molecules, the interaction between the polymer dipoles and the LC molecules at the droplet interface influences the light-scattering behavior of the PDLC films. For the first time, it was shown that the electric field generated by the application of a mechanical stress may lead to changes in the transmittance of a PDLC film. Such a piezo-optical PDLC material may be useful e.g. in sensing and visualization applications. Compared to a non-polar matrix polymer, the polar matrix polymer exhibits a strong interaction with the LC molecules at the polymer/LC interface which affects the electro-optical effect of the PDLC films and prevents a larger increase in optical transmission.}, language = {en} } @book{Foehlisch2010, author = {F{\"o}hlisch, Alexander}, title = {Phasen{\"u}berg{\"a}nge und Ultrakurzzeitdynamik : Antrittsvorlesung 2010-05-12}, publisher = {Univ.-Bibl.}, address = {Potsdam}, year = {2010}, abstract = {F{\"o}hlisch wird in seinem Vortrag die großen Zukunftsthemen der Mensch streifen: Energie, Umwelt und Struktur der Materie. Die Komplexit{\"a}t ihrer elementaren Prozesse erfordert die komplement{\"a}re Betrachtung der damit verbundene Dimensionen von Energie, Zeit und Raum. Dies l{\"a}sst sich inzwischen mit Synchrotronstrahlungsquellen in gr{\"o}ßter Pr{\"a}ision darstellen.}, language = {de} } @article{FoxWakkerSmokeretal.2010, author = {Fox, Andrew J. and Wakker, Bart P. and Smoker, Jonathan V. and Richter, Philipp and Savage, Blair D. and Sembach, Kenneth R.}, title = {Exploring the origin and fate of the Magellanic stream with ultraviolet and optical absorption}, issn = {0004-637X}, doi = {10.1088/0004-637x/718/2/1046}, year = {2010}, abstract = {We present an analysis of ionization and metal enrichment in the Magellanic Stream (MS), the nearest gaseous tidal stream, using Hubble Space Telescope/STIS and FUSE ultraviolet spectroscopy of two background active galactic nuclei. The targets are NGC 7469, lying directly behind the MS with log N(H I)(MS) = 18.63 +/- 0.03(stat) +/- 0.08(syst), and Mrk 335, lying 24 degrees.7 away with log N(H I)(MS) = 16.67 +/- 0.05. For NGC 7469, we include optical spectroscopy from VLT/UVES. In both sight lines, the MS is detected in low-ion (O I, C II, C III, Si II, Si III, Al II, Ca II) and high-ion (O VI, C IV, Si IV) absorption. Toward NGC 7469, we measure an MS oxygen abundance [O/H](MS) = [O I/ H I]= -1.00 +/- 0.05(stat) +/- 0.08(syst), supporting the view that the Stream originates in the Small Magellanic Cloud rather than the Large Magellanic Cloud. We use CLOUDY to model the low-ion phase of the Stream as a photoionized plasma using the observed Si III/Si II and C III/C II ratios. Toward Mrk 335, this yields an ionization parameter between log U= -3.45 and -3.15, a gas density log (n(H)/cm(-3)) between-2.51 and -2.21, and a hydrogen ionization fraction of 98.9\%- 99.5\%. Toward NGC 7469, we derive sub-solar abundance ratios for [Si/O], [Fe/O], and [Al/O], indicating the presence of dust in the MS. The high-ion column densities are too large to be explained by photoionization, but also cannot be explained by a single-temperature collisional ionization model (equilibrium or non-equilibrium). This suggests that the high-ion plasma is multi-phase, with an Si IV region, a hotter O VI region, and C IV potentially contributing to each. Summing over the low-ion and high-ion phases, we derive conservative lower limits on the ratio N(total H II)/N(H I) of greater than or similar to 19 toward NGC 7469 and greater than or similar to 330 toward Mrk 335, showing that along these two directions the vast majority of the Stream has been ionized. The presence of warm-hot plasma together with the small-scale structure observed at 21 cm provides evidence for an evaporative interaction with the hot Galactic corona. This scenario, predicted by hydrodynamical simulations, suggests that the fate of the MS will be to replenish the Galactic corona with new plasma, rather than to bring neutral fuel to the disk.}, language = {en} }