TY - THES A1 - Bierbaum, Veronika T1 - Chemomechanical coupling and motor cycles of the molecular motor myosin V T1 - Chemomechanische Kopplung und Motorzyklen für den molekularen Motor Myosin V N2 - In the living cell, the organization of the complex internal structure relies to a large extent on molecular motors. Molecular motors are proteins that are able to convert chemical energy from the hydrolysis of adenosine triphosphate (ATP) into mechanical work. Being about 10 to 100 nanometers in size, the molecules act on a length scale, for which thermal collisions have a considerable impact onto their motion. In this way, they constitute paradigmatic examples of thermodynamic machines out of equilibrium. This study develops a theoretical description for the energy conversion by the molecular motor myosin V, using many different aspects of theoretical physics. Myosin V has been studied extensively in both bulk and single molecule experiments. Its stepping velocity has been characterized as a function of external control parameters such as nucleotide concentration and applied forces. In addition, numerous kinetic rates involved in the enzymatic reaction of the molecule have been determined. For forces that exceed the stall force of the motor, myosin V exhibits a 'ratcheting' behaviour: For loads in the direction of forward stepping, the velocity depends on the concentration of ATP, while for backward loads there is no such influence. Based on the chemical states of the motor, we construct a general network theory that incorporates experimental observations about the stepping behaviour of myosin V. The motor's motion is captured through the network description supplemented by a Markov process to describe the motor dynamics. This approach has the advantage of directly addressing the chemical kinetics of the molecule, and treating the mechanical and chemical processes on equal grounds. We utilize constraints arising from nonequilibrium thermodynamics to determine motor parameters and demonstrate that the motor behaviour is governed by several chemomechanical motor cycles. In addition, we investigate the functional dependence of stepping rates on force by deducing the motor's response to external loads via an appropriate Fokker-Planck equation. For substall forces, the dominant pathway of the motor network is profoundly different from the one for superstall forces, which leads to a stepping behaviour that is in agreement with the experimental observations. The extension of our analysis to Markov processes with absorbing boundaries allows for the calculation of the motor's dwell time distributions. These reveal aspects of the coordination of the motor's heads and contain direct information about the backsteps of the motor. Our theory provides a unified description for the myosin V motor as studied in single motor experiments. N2 - Die hier vorgelegte Arbeit entwickelt unter Verwendung vieler verschiedener Aspekte der statistischen Physik eine Theorie der chemomechanischen Kopplung für den Energieumsatz des molekularen Motors Myosin V. Das Myosin V ist sowohl in chemokinetischen wie in Einzelmolekülexperimenten grundlegend untersucht worden. Seine Schrittgeschwindigkeit ist in Abhängigkeit verschiedener externer Parameter, wie der Nukleotidkonzentration und einer äußeren Kraft, experimentell bestimmt. Darüber hinaus ist eine große Anzahl verschiedener chemokinetischer Raten, die an der enzymatischen Reaktion des Moleküls beteiligt sind, quantitativ erfasst. Unter der Wirkung externer Kräfte, die seine Anhaltekraft überschreiten, verhält sich der Motor wie eine Ratsche: Für Kräfte, die entlang der Schrittbewegung des Motors wirken, hängt seine Geschwindigkeit von der ATP-Konzentration ab, für rückwärts angreifende Kräfte jedoch ist die Bewegung des Motors unabhängig von ATP. Auf der Grundlage der chemischen Zustände des Motors wird eine Netzwerktheorie aufgebaut, die die experimentellen Beobachtungen des Schrittverhaltens für Myosin V einschließt. Diese Netzwerkbeschreibung dient als Grundlage für einen Markovprozess, der die Dynamik des Motors beschreibt. Die Verwendung diskreter Zustände bietet den Vorteil der direkten Erfassung der chemischen Kinetik des Moleküls. Darüber hinaus werden chemische und mechanische Eigenschaften des Motors in gleichem Maße im Modell berücksichtigt. Durch die Erfassung der Enzymkinetik mittels eines stochastischen Prozesses lässt sich die Motordynamik mit Hilfe des stationären Zustands der Netzwerkdarstellung beschreiben. Um diesen zu bestimmen, verwenden wir eine graphentheoretische Methode, die auf Kirchhoff zurückgreift. Wir zeigen in Einklang mit den Gesetzen der Thermodynamik für Nichtgleichgewichtssysteme, dass das Schrittverhalten des Motors von mehreren chemomechanischen Zyklen beeinflusst wird. Weiterhin untersuchen wir das funktionale Verhalten mechanischer Schrittraten in Abhängigkeit der äußeren Kraft unter Verwendung einer geeigneten Fokker-Planck-Gleichung. Hierfür wird auf die Theorie einer kontinuierlichen Beschreibung von molekularen Methoden zurückgegriffen. Wir berechnen Größen wie die mittlere Schrittgeschwindigkeit, das Verhältnis von Vorwärts- und Rückwärtsschritten, und die Lauflänge des Motors in Abhängigkeit einer äußeren angreifenden Kraft sowie der Nukleotidkonzentration, und vergleichen diese mit experimentellen Daten. Für Kräfte, die kleiner als die Anhaltekraft des Motors sind, unterscheidet sich der chemomechanische Zyklus grundlegend von demjenigen, der für große Kräfte dominiert. Diese Eigenschaft resultiert in einem Schrittverhalten, das mit den experimentellen Beobachtungen übereinstimmt. Es ermöglicht weiterhin die Zerlegung des Netzwerks in einzelne Zyklen, die die Bewegung des Motors für verschiedene Bereiche externer Kräfte erfassen. Durch die Erweiterung unseres Modells auf Markovprozesse mit absorbierenden Zuständen können so die Wartezeitenverteilungen für einzelne Zyklen des Motors analytisch berechnet werden. Sie erteilen Aufschluss über die Koordination des Motors und enthalten zudem direkte Informationen über seine Rückwärtsschritte, die experimentell nicht erfasst sind. Für das gesamte Netzwerk werden die Wartezeitenverteilungen mit Hilfe eines Gillespie-Algorithmus bestimmt. Unsere Theorie liefert eine einheitliche Beschreibung der Eigenschaften von Myosin V, die in Einzelmolekülexperimenten erfasst werden können. KW - statistische Physik KW - Markov-Prozesse KW - molekulare Motoren KW - statistical physics KW - markov processes KW - molecular motors Y1 - 2011 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-53614 ER - TY - THES A1 - Boeche, Corrado T1 - Chemical gradients in the Milky Way from unsupervised chemical abundances measurements of the RAVE spectroscopic data set T1 - Chemische Gradienten in der Milchstraße aus unüberwachten chemischen Häufigkeitsmessungen aus dem RAVE spektroskopischen Datenset N2 - The present thesis was born and evolved within the RAdial Velocity Experiment (RAVE) with the goal of measuring chemical abundances from the RAVE spectra and exploit them to investigate the chemical gradients along the plane of the Galaxy to provide constraints on possible Galactic formation scenarios. RAVE is a large spectroscopic survey which aims to observe spectroscopically ~10^6 stars by the end of 2012 and measures their radial velocities, atmospheric parameters and chemical abundances. The project makes use of the UK Schmidt telescope at Australian Astronomical Observatory (AAO) in Siding Spring, Australia, equipped with the multiobject spectrograph 6dF. To date, RAVE collected and measured more than 450,000 spectra. The precision of the chemical abundance estimations depends on the reliability of the atomic and atmosphere parameters adopted (in particular the oscillator strengths of the absorption lines and the effective temperature, gravity, and metallicity of the stars measured). Therefore we first identified 604 absorption lines in the RAVE wavelength range and refined their oscillator strengths with an inverse spectral analysis. Then, we improved the RAVE stellar parameters by modifying the RAVE pipeline and the spectral library the pipeline rely on. The modifications removed some systematic errors in stellar parameters discovered during this work. To obtain chemical abundances, we developed two different processing pipelines. Both of them perform chemical abundances measurements by assuming stellar atmospheres in Local Thermodynamic Equilibrium (LTE). The first one determines elements abundances from equivalent widths of absorption lines. Since this pipeline showed poor sensibility on abundances relative to iron, it has been superseded. The second one exploits the chi^2 minimization technique between observed and model spectra. Thanks to its precision, it has been adopted for the creation of the RAVE chemical catalogue. This pipeline provides abundances with uncertains of about ~0.2dex for spectra with signal-to-noise ratio S/N>40 and ~0.3dex for spectra with 20>S/N>40. For this work, the pipeline measured chemical abundances up to 7 elements for 217,358 RAVE stars. With these data we investigated the chemical gradients along the Galactic radius of the Milky Way. We found that stars with low vertical velocities |W| (which stay close to the Galactic plane) show an iron abundance gradient in agreement with previous works (~-0.07$ dex kpc^-1) whereas stars with larger |W| which are able to reach larger heights above the Galactic plane, show progressively flatter gradients. The gradients of the other elements follow the same trend. This suggests that an efficient radial mixing acts in the Galaxy or that the thick disk formed from homogeneous interstellar matter. In particular, we found hundreds of stars which can be kinetically classified as thick disk stars exhibiting a chemical composition typical of the thin disk. A few stars of this kind have already been detected by other authors, and their origin is still not clear. One possibility is that they are thin disk stars kinematically heated, and then underwent an efficient radial mixing process which blurred (and so flattened) the gradient. Alternatively they may be a transition population" which represents an evolutionary bridge between thin and thick disk. Our analysis shows that the two explanations are not mutually exclusive. Future follow-up high resolution spectroscopic observations will clarify their role in the Galactic disk evolution. N2 - Die vorliegende Doktorarbeit wurde im Rahmen des RAdial Velocity Experiment (RAVE) angefertigt. Ihr Ziel ist es, chemische Elementhäufigkeiten an RAVE-Spektren zu messen und zur Untersuchung chemischer Gradienten in der Milchstrassenebene zu benutzen, um verschieden Szenarien der Galaxienentstehung einzugrenzen. RAVE ist eine große spektrokopische Durchmusterung, deren Ziel es ist, bis zum Ende des Jahres 2012 insgesamt 10^6 Sterne zu spektroskopieren, um deren Radialgeschwindigkeiten, sternatmosphärische Parameter und chemische Häufigkeiten zu messen. Das Projekt benutzt das UK Schmidt Teleskop am Australian Astronomical Observatory (AAO) in Siding Spring, Australien, welches mit dem Multiobjekt-Spektrographen 6dF bestückt ist. Bis heute hat RAVE die Spektren von mehr als 450,000 Sternen gesammelt und untersucht. Die Genauigkeit, mit der die Elementhäufigkeiten abgeschätzt werden können, hängt von der Zuverlässigkeit der verwendeten Parameter, (insbesondere der Oszillatorstärken der Absorptionslinien sowie von der effektiven Temperatur, Schwerebeschleunigung und der Metallizität des gemessenen Sterns) ab. Daher identifizierten wir zunächst 604 Absorptionslinien im Wellenlängenbereich von RAVE und verbesserten deren Oszillatorstärken durch eine inverse Spektralanalyse. Dann wurden die stellaren Parameter von RAVE verbessert, indem die RAVE Pipeline und die stellaren Parameter, auf denen sie beruht, modifiziert wurden. Die Änderungen eliminierten einen Teil der systematischen Fehler von stellaren Parametern, die im Laufe dieser Arbeit gefunden wurden. Um Elementhäufigkeiten zu bestimmen, haben wir zwei verschiedene Prozessierungs-Pipelines entwickelt. Beide berechnen die Elementhäufigkeiten unter der Annahme von Sternatmosphären im lokalen thermischen Gleichgewicht (local thermal equilibrium, LTE). Die erste Pipeline berechnete Elemenhäufigkeiten anhand der Äquivalentbreiten von Absorptionslinien. Da diese Methode eine geringe Empfindlichkeit für die Elementhäufigeiten relativ zu Eisen erreichte, wurde sie ersetzt. Die neue Pipeline benutzt chi^2-Fits von Modellspektren an die beobachteten Spektren. Dank Ihrer Präzision wurde diese für die Erstellung des RAVE-Katalogs von Elementhäufigkeiten verwendet. Diese Pipeline liefert Elementhäufigkeiten mit einer Genauigkeit von ~0.2dex, während für Spektren mit 20>S/N>40 immerhin noch ~0.3dex Genauigkeit erreicht werden. Für die vorliegende Arbeit wurden für 217.358 Sterne die Häufigkeiten von sieben chemischen Elementen bestimmt. Mit diesen Daten wurde der radiale chemische Gradient unserer Milchstraße untersucht. Wir finden, dass Sterne mit kleinen vertikalen Geschwindigkeiten |W|, die also nahe der galaktischen Ebene bleiben, einen radialen Gradienten der Eisenhäufigkeit zeigen, der mit früheren Studien übereinstimmt (~-0.07 dex Kpc^-1), während Sterne mit großen |W|, also solche, die größere galaktische Höhen erreichen, einen progressiv flachere Gradienten zeigen. Die Gradienten der anderen Element folgen dem gleichen Trend. Das lässt darauf schließen, dass entweder die Durchmischung der galaktischen dicken Scheibe effizient arbeitet oder aber dass die dicke Scheibe aus interstellarer Materie gebildet wurde, die chemisch recht homogen war. Speziell fanden wir hunderte von Sternen, die zwar kinematisch als zur dicken Scheibe zugehörig klassifiziert werden können, die aber die typische chemische Zusammensetzung der dünnen Scheibe aufweisen. Einige wenige dieser Sterne wurden bereits von anderen Autoren entdeckt, aber ihre Herkunft bleibt immer noch unklar. Eine Möglichkeit ist, dass die Sterne der dünnen Scheibe kinematische geheizt werden, sodass sie effizienter radial gemischt werden, was die chemischen Gradienten verwischt und auch flacher macht. Alternativ dazu könnten diese Sterne einer "Übergangspopulation" angehören, welche hinsichtlich der Scheibenevolution die Verbindung zwischen der dünnen und der dicken Scheibe darstellt. Unsere Untersuchung zeigt, dass sich diese beiden Erklärungen gegenseitig nicht ausschließen. Künftige Nachspektroskopierung mit hoher Auflösung wird die Rolle dieser Sterne in der Entwicklungsgeschichte der galaktischen Scheibe aufklären. KW - Galaxie KW - Milchstraße KW - Spektroskopie KW - chemische Häufigkeiten KW - Galaxy KW - Milky Way KW - Spectroscopy KW - Chemical Abundances Y1 - 2011 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-52478 ER - TY - JOUR A1 - Sanhueza-Pino, Katia A1 - Korup, Oliver A1 - Hetzel, Ralf A1 - Munack, Henry A1 - Weidinger, Johannes T. A1 - Dunning, Stuart A. A1 - Ormukov, Cholponbek A1 - Kubik, Peter W. T1 - Glacial advances constrained by Be-10 exposure dating of bedrock landslides, Kyrgyz Tien Shan JF - Quaternary research : an interdisciplinary journal N2 - 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. KW - Landslide KW - Rock avalanche KW - Be-10 exposure dating KW - Quaternary glaciations KW - Tien Shan Y1 - 2011 U6 - https://doi.org/10.1016/j.yqres.2011.06.013 SN - 0033-5894 VL - 76 IS - 3 SP - 295 EP - 304 PB - Elsevier CY - San Diego ER - TY - JOUR A1 - Fuhrmann, Marcel A1 - Seehafer, Norbert A1 - Valori, Gherardo A1 - Wiegelmann, Thomas T1 - A comparison of preprocessing methods for solar force-free magnetic field extrapolation Y1 - 2011 UR - http://www.aanda.org/index.php?option=com_article&access=standard&Itemid=129&url=/articles/aa/full_html/ 2011/02/aa15453-10/aa15453-10.html SN - 0004-6361 ER - TY - JOUR A1 - Fuhrmann, Marcel A1 - Seehafer, Norbert A1 - Valori, Gherardo A1 - Wiegelmann, T. T1 - A comparison of preprocessing methods for solar force-free magnetic field extrapolation JF - Astronomy and astrophysics : an international weekly journal N2 - Context. Extrapolations of solar photospheric vector magnetograms into three-dimensional magnetic fields in the chromosphere and corona are usually done under the assumption that the fields are force-free. This condition is violated in the photosphere itself and a thin layer in the lower atmosphere above. The field calculations can be improved by preprocessing the photospheric magnetograms. The intention here is to remove a non-force-free component from the data. Aims. We compare two preprocessing methods presently in use, namely the methods of Wiegelmann et al. (2006, Sol. Phys., 233, 215) and Fuhrmann et al. (2007, A&A, 476, 349). Methods. The two preprocessing methods were applied to a vector magnetogram of the recently observed active region NOAA AR 10 953. We examine the changes in the magnetogram effected by the two preprocessing algorithms. Furthermore, the original magnetogram and the two preprocessed magnetograms were each used as input data for nonlinear force-free field extrapolations by means of two different methods, and we analyze the resulting fields. Results. Both preprocessing methods managed to significantly decrease the magnetic forces and magnetic torques that act through the magnetogram area and that can cause incompatibilities with the assumption of force-freeness in the solution domain. The force and torque decrease is stronger for the Fuhrmann et al. method. Both methods also reduced the amount of small-scale irregularities in the observed photospheric field, which can sharply worsen the quality of the solutions. For the chosen parameter set, the Wiegelmann et al. method led to greater changes in strong-field areas, leaving weak-field areas mostly unchanged, and thus providing an approximation of the magnetic field vector in the chromosphere, while the Fuhrmann et al. method weakly changed the whole magnetogram, thereby better preserving patterns present in the original magnetogram. Both preprocessing methods raised the magnetic energy content of the extrapolated fields to values above the minimum energy, corresponding to the potential field. Also, the fields calculated from the preprocessed magnetograms fulfill the solenoidal condition better than those calculated without preprocessing. KW - Sun: magnetic topology KW - Sun: atmosphere KW - magnetohydrodynamics (MHD) Y1 - 2011 U6 - https://doi.org/10.1051/0004-6361/201015453 SN - 0004-6361 VL - 526 PB - EDP Sciences CY - Les Ulis ER - TY - THES A1 - Schiefele, Jürgen T1 - Casimir-Polder interaction in second quantization T1 - Casimir-Polder Wechselwirkung in zweiter Quantisierung N2 - 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. N2 - Die durch (quantenmechanische und thermische) Fluktuationen des elektromagnetischen Feldes hervorgerufene Casimir-Polder-Wechselwirkung zwischen einem elektrisch neutralen Atom und einer benachbarten Oberfläche stellt einen theoretisch gut untersuchten Aspekt der Resonator-Quantenelektrodynamik (cavity quantum electrodynamics, cQED) dar. Seit kurzem werden atomare Bose-Einstein-Kondensate (BECs) verwendet, um die theoretischen Vorhersagen der cQED zu überprüfen. Das Ziel der vorliegenden Arbeit ist es, die bestehende cQED Theorie für einzelne Atome mit den Techniken der Vielteilchenphysik zur Beschreibung von BECs zu verbinden. Es werden Werkzeuge und Methoden entwickelt, um sowohl Photon- als auch Atom-Felder gleichwertig in zweiter Quantisierung zu beschreiben. Wir formulieren eine diagrammatische Störungstheorie, die Korrelationsfunktionen des elektromagnetischen Feldes und des Atomsystems benutzt. Der Formalismus wird anschließend verwendet, um für in Fallen nahe einer Oberfläche gehaltene BECs Atom-Oberflächen-Wechselwirkungen vom Casimir-Polder-Typ und die bosonische Stimulation des spontanen Zerfalls angeregter Atome zu untersuchen. Außerdem untersuchen wir einen phononischen Casimir-Effekt, der durch die quantenmechanischen Fluktuationen in einem wechselwirkenden BEC entsteht. KW - Hohlraum-Quantenelektrodynamik KW - Bose-Einstein-Kondensation KW - Casimir-Polder-Interaktion KW - Vakuumschwankungen KW - van der Waals-Kräfte KW - cavity quantum electrodynamics KW - Bose-Einstein condensation KW - Casimir-Polder interaction KW - vacuum fluctuations KW - van der Waals forces Y1 - 2011 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-54171 ER - TY - JOUR A1 - Cockburn, S. P. A1 - Negretti, Antonio A1 - Proukakis, N. P. A1 - Henkel, Carsten T1 - Comparison between microscopic methods for finite-temperature Bose gases JF - Physical review : A, Atomic, molecular, and optical physics N2 - We analyze the equilibrium properties of a weakly interacting, trapped quasi-one-dimensional Bose gas at finite temperatures and compare different theoretical approaches. We focus in particular on two stochastic theories: a number-conserving Bogoliubov (NCB) approach and a stochastic Gross-Pitaevskii equation (SGPE) that have been extensively used in numerical simulations. Equilibrium properties like density profiles, correlation functions, and the condensate statistics are compared to predictions based upon a number of alternative theories. We find that due to thermal phase fluctuations, and the corresponding condensate depletion, the NCB approach loses its validity at relatively low temperatures. This can be attributed to the change in the Bogoliubov spectrum, as the condensate gets thermally depleted, and to large fluctuations beyond perturbation theory. Although the two stochastic theories are built on different thermodynamic ensembles (NCB, canonical; SGPE, grand-canonical), they yield the correct condensate statistics in a large Bose-Einstein condensate (BEC) (strong enough particle interactions). For smaller systems, the SGPE results are prone to anomalously large number fluctuations, well known for the grand-canonical, ideal Bose gas. Based on the comparison of the above theories to the modified Popov approach, we propose a simple procedure for approximately extracting the Penrose-Onsager condensate from first-and second-order correlation functions that is both computationally convenient and of potential use to experimentalists. This also clarifies the link between condensate and quasicondensate in the Popov theory of low-dimensional systems. Y1 - 2011 U6 - https://doi.org/10.1103/PhysRevA.83.043619 SN - 1050-2947 SN - 1094-1622 VL - 83 IS - 4 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Müller, Matthias M. A1 - Haakh, Harald R. A1 - Calarco, Tommaso A1 - Koch, Christiane P. A1 - Henkel, Carsten T1 - Prospects for fast Rydberg gates on an atom chip JF - Quantum information processing N2 - 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. KW - Optimal control KW - Phase gate KW - Rydberg atoms KW - Cavity quantum electrodynamics Y1 - 2011 U6 - https://doi.org/10.1007/s11128-011-0296-0 SN - 1570-0755 VL - 10 IS - 6 SP - 771 EP - 792 PB - Springer CY - New York ER - TY - JOUR A1 - Schiefele, Juergen A1 - Henkel, Carsten T1 - Bosonic enhancement of spontaneous emission near an interface JF - Modern physics letters : A, Particles and fields, gravitation, cosmology, nuclear physics N2 - 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. KW - Bose-Einstein condensation KW - Correlation function KW - Bosonic stimulation KW - Superradiance KW - Spontaneous decay KW - Cavity-quantum electrodynamics Y1 - 2011 U6 - https://doi.org/10.1016/j.physleta.2010.11.058 SN - 0375-9601 VL - 375 IS - 3 SP - 680 EP - 684 PB - Elsevier CY - Amsterdam ER - TY - BOOK A1 - Rabe, Thorid T1 - Physikdidaktische Lehrerprofessionalisierung zwischen Anspruch und Wirklichkeit : Antrittsvorlesung 2011-06-08 N2 - Physiklehrer bestimmen durch die Gestaltung des Unterrichts und damit durch ihr professionelles Handeln maßgeblich mit, wie die individuellen Lernprozesse der Schüler zu Inhalten der Physik ablaufen. Für die Entwicklung ihrer professionellen Handlungskompetenz müssen zukünftige Physiklehrer einerseits physikalisches, physikdidaktisches und pädagogisches 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 universitären Ausbildung erwerben sollten. Am Beispiel der Lehrveranstaltung "Physikalische Schulexperimente" zeigt sie, wie physikdidaktische Theorie und praktisches Lehrerhandeln aufeinander bezogen werden können. Zudem wird sie ein Forschungsprojekt vorstellen, das einem bisher vernachlässigten Aspekt professioneller Handlungskompetenz nachgeht, nämlich den domänenspezifischen Selbstwirksamkeitserwartungen - dem Zutrauen in sich selbst, als Physiklehrer angemessen und erfolgreich handeln zu können. Y1 - 2011 UR - http://info.ub.uni-potsdam.de/multimedia/show_multimediafile.php?mediafile_id=548 PB - Univ.-Bibl. CY - Potsdam ER - TY - THES A1 - Partl, Adrian M. T1 - Cosmological radiative transfer and the lonisation of the integalactic medium Y1 - 2011 CY - Potsdam ER - TY - THES A1 - Osterloh, Lukas T1 - Retrieving aerosol microphysical properties from multiwavelength Lidar Data Y1 - 2011 CY - Potsdam ER - TY - THES A1 - Matthes, Heidrun T1 - Interaction of land surface processes and the atmophere in the Arctic - senitivities and extremes Y1 - 2011 CY - Potsdam ER - TY - THES A1 - Dosche, Carsten T1 - Funktionale Farbstoffe und ihre Photophysik und Anwendung in komplexen Matrizes Y1 - 2011 CY - Potsdam ER - TY - BOOK A1 - Brehmer, Ludwig T1 - Die Brandeburgische Landeshochschule zu Potsdam im Jahre eins : die Hochschule in Potsdamer Schulen ; Daten und Fakten ; Kommentare und Dokumente Y1 - 2011 SN - 978-3-00-034135-9 VL - 4 PB - Eigenverl. des Verf CY - Potsdam ER - TY - THES A1 - Schewe, Jacob T1 - Basic physical mechanisms for monsoon failure in past and future climate Y1 - 2011 CY - Potsdam ER - TY - THES A1 - Mielke, Moritz T1 - Atmosphärische Prozesstudien auf der Basis von Beobachtungen und regionalen Klimamodellsimulationen in der Arktis Y1 - 2011 CY - Potsdam ER - TY - THES A1 - Koseska, Aneta T1 - Dynamics of biological networks : data analysis, modeling and bifurcations Y1 - 2011 CY - Potsdam ER - TY - JOUR A1 - Janotta, Peter A1 - Gogolin, Christian A1 - Barrett, Jonathan A1 - Brunner, Nicolas T1 - Limits on nonlocal correlations from the structure of the local state space JF - New journal of physics : the open-access journal for physics N2 - The outcomes of measurements on entangled quantum systems can be nonlocally correlated. However, while it is easy to write down toy theories allowing arbitrary nonlocal correlations, those allowed in quantum mechanics are limited. Quantum correlations cannot, for example, violate a principle known as macroscopic locality, which implies that they cannot violate Tsirelson's bound. This paper shows that there is a connection between the strength of nonlocal correlations in a physical theory and the structure of the state spaces of individual systems. This is illustrated by a family of models in which local state spaces are regular polygons, where a natural analogue of a maximally entangled state of two systems exists. We characterize the nonlocal correlations obtainable from such states. The family allows us to study the transition between classical, quantum and super-quantum correlations by varying only the local state space. We show that the strength of nonlocal correlations-in particular whether the maximally entangled state violates Tsirelson's bound or not-depends crucially on a simple geometric property of the local state space, known as strong self-duality. This result is seen to be a special case of a general theorem, which states that a broad class of entangled states in probabilistic theories-including, by extension, all bipartite classical and quantum states-cannot violate macroscopic locality. Finally, our results show that models exist that are locally almost indistinguishable from quantum mechanics, but can nevertheless generate maximally nonlocal correlations. Y1 - 2011 U6 - https://doi.org/10.1088/1367-2630/13/6/063024 SN - 1367-2630 VL - 13 IS - 23 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Brandao, F. G. S. L. A1 - Eisert, Jens A1 - Horodecki, M. A1 - Yang, Dong T1 - Entangled inputs cannot make imperfect quantum channels perfect JF - Physical review letters N2 - Entangled inputs can enhance the capacity of quantum channels, this being one of the consequences of the celebrated result showing the nonadditivity of several quantities relevant for quantum information science. In this work, we answer the converse question (whether entangled inputs can ever render noisy quantum channels to have maximum capacity) to the negative: No sophisticated entangled input of any quantum channel can ever enhance the capacity to the maximum possible value, a result that holds true for all channels both for the classical as well as the quantum capacity. This result can hence be seen as a bound as to how "nonadditive quantum information can be.'' As a main result, we find first practical and remarkably simple computable single-shot bounds to capacities, related to entanglement measures. As examples, we discuss the qubit amplitude damping and identify the first meaningful bound for its classical capacity. Y1 - 2011 U6 - https://doi.org/10.1103/PhysRevLett.106.230502 SN - 0031-9007 VL - 106 IS - 23 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Schmidt, Hans-Jürgen T1 - Perihelion advance for orbits with large eccentricities in the Schwarzschild black hole JF - Physical review : D, Particles, fields, gravitation, and cosmology N2 - 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). Y1 - 2011 U6 - https://doi.org/10.1103/PhysRevD.83.124010 SN - 1550-7998 VL - 83 IS - 12 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Worseck, Gabor A1 - Prochaska, J. Xavier A1 - McQuinn, Matthew A1 - Dall'Aglio, Aldo A1 - Fechner, Cora A1 - Hennawi, Joseph F. A1 - Reimers, Dieter A1 - Richter, Philipp A1 - Wisotzki, Lutz T1 - The end of Helium Reionization at z similar or equal to 2.7 Inferred from cosmic variance in HST/COS He II Ly alpha Absorption spectra JF - The astrophysical journal : an international review of spectroscopy and astronomical physics ; Part 2, Letters N2 - We report on the detection of strongly varying intergalactic He II absorption in HST/COS spectra of two z(em) similar or equal to 3 quasars. From our homogeneous analysis of the He II absorption in these and three archival sightlines, we find a marked increase in the mean He II effective optical depth from similar or equal to 1 at z similar or equal to 2.3 to greater than or similar to 5 at z similar or equal to 3.2, but with a large scatter of 2 less than or similar to tau(eff, He II) less than or similar to 5 at 2.7 < z < 3 on scales of similar to 10 proper Mpc. This scatter is primarily due to fluctuations in the He II fraction and the He II-ionizing background, rather than density variations that are probed by the coeval Hi forest. Semianalytic models of He II absorption require a strong decrease in the He II-ionizing background to explain the strong increase of the absorption at z greater than or similar to 2.7, probably indicating He II reionization was incomplete at z(reion) greater than or similar to 2.7. Likewise, recent three-dimensional numerical simulations of He II reionization qualitatively agree with the observed trend only if He II reionization completes at z(reion) similar or equal to 2.7 or even below, as suggested by a large tau(eff, He II) greater than or similar to 3 in two of our five sightlines at z < 2.8. By doubling the sample size at 2.7 less than or similar to z less than or similar to 3, our newly discovered He II sightlines for the first time probe the diversity of the second epoch of reionization when helium became fully ionized. KW - dark ages, reionization, first stars KW - diffuse radiation KW - intergalactic medium KW - quasars: absorption lines KW - quasars: individual (SDSS J092447.36+485242.8, SDSS J110155.74+105302.3) Y1 - 2011 U6 - https://doi.org/10.1088/2041-8205/733/2/L24 SN - 2041-8205 VL - 733 IS - 2 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Zakharova, Anna A1 - Kurths, Jürgen A1 - Vadivasova, Tatyana A1 - Koseska, Aneta T1 - Analysing dynamical behavior of cellular networks via stochastic bifurcations JF - PLoS one N2 - The dynamical structure of genetic networks determines the occurrence of various biological mechanisms, such as cellular differentiation. However, the question of how cellular diversity evolves in relation to the inherent stochasticity and intercellular communication remains still to be understood. Here, we define a concept of stochastic bifurcations suitable to investigate the dynamical structure of genetic networks, and show that under stochastic influence, the expression of given proteins of interest is defined via the probability distribution of the phase variable, representing one of the genes constituting the system. Moreover, we show that under changing stochastic conditions, the probabilities of expressing certain concentration values are different, leading to different functionality of the cells, and thus to differentiation of the cells in the various types. Y1 - 2011 U6 - https://doi.org/10.1371/journal.pone.0019696 SN - 1932-6203 VL - 6 IS - 5 PB - PLoS CY - San Fransisco ER - TY - JOUR A1 - Jewitt, David A1 - Weaver, Harold A1 - Mutchler, Max A1 - Larson, Stephen A1 - Agarwal, Jessica T1 - Hubble space telescope observations of main-belt comet (596) scheila JF - The astrophysical journal : an international review of spectroscopy and astronomical physics ; Part 2, Letters N2 - We present Hubble Space Telescope Observations of (596) Scheila during its recent dust outburst. The nucleus remained point-like with absolute magnitude H(V) = 8.85 +/- 0.02 in our data, equal to the pre-outburst value, with no secondary fragments of diameter >= 100m (for assumed albedos 0.04). We find a coma having a peak scattering cross section similar to 2.2x10(4) km(2), corresponding to a mass in micron-sized particles of similar to 4x10(7) kg. The particles are deflected by solar radiation pressure on projected spatial scales similar to 2x10(4) km, in the sunward direction, and swept from the vicinity of the nucleus on timescales of weeks. The coma fades by similar to 30% between observations on UT 2010 December 27 and 2011 January 4. The observed mass loss is inconsistent with an origin either by rotational instability of the nucleus or by electrostatic ejection of regolith charged by sunlight. Dust ejection could be caused by the sudden but unexplained exposure of buried ice. However, the data are most simply explained by the impact, at similar to 5 km s(-1), of a previously unknown asteroid similar to 35m in diameter. KW - comets: general KW - comets: individual ((596) Scheila) KW - minor planets, asteroids: general Y1 - 2011 U6 - https://doi.org/10.1088/2041-8205/733/1/L4 SN - 2041-8205 VL - 733 IS - 1 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Postberg, Frank A1 - Schmidt, J. A1 - Hillier, J. A1 - Kempf, Sascha A1 - Srama, Ralf T1 - A salt-water reservoir as the source of a compositionally stratified plume on Enceladus JF - Nature : the international weekly journal of science N2 - 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. Y1 - 2011 U6 - https://doi.org/10.1038/nature10175 SN - 0028-0836 VL - 474 IS - 7353 SP - 620 EP - 622 PB - Nature Publ. Group CY - London ER - TY - JOUR A1 - Kar, Parimal A1 - Lipowsky, Reinhard A1 - Knecht, Volker T1 - Importance of polar solvation for cross-reactivity of antibody and its variants with steroids JF - The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces & biophysical chemistry N2 - Understanding the factors determining the binding of ligands to receptors in detail is essential for rational drug design. Here, the free energies of binding of the steroids progesterone (PRG) and 5 beta-androstane-3,17-dione (SAD) to the Diels-Alderase antibody 1E9, as well as the Leu(H47)Trp/Arg(H100)Trp 1E9 double mutant (1E9dm) and the corresponding single mutants, have been estimated and decomposed using the molecular mechanics-Poisson-Boltzmann surface area (MM-PBSA) method. Also the difference in binding free energies between the PRG-1E9dm complex and the complex of PRG with the antiprogesterone antibody DB3 have been evaluated and decomposed. The steroids bind less strongly to 1E9 than to DB3, but the mutations tend to improve the steroid affinity, in quantitative agreement with experimental data. Although the complexes formed by PRG or SAD with 1E9dm and by PRG with DB3 have similar affinity, the binding mechanisms are different. Reduced Waals for SAD-1E9dm versus PRG-1E9dm or for PRG-1E9dm versus PRG-DB3 are energetically compensated by an increased solvation of polar groups, partly contrasting previous conclusions based on structural inspection. Our study illustrates that deducing binding mechanisms from structural models alone can be misleading. Therefore, taking into account solvation effects as in MM-PBSA calculations is essential to elucidate molecular recognition. Y1 - 2011 U6 - https://doi.org/10.1021/jp201538t SN - 1520-6106 VL - 115 IS - 23 SP - 7661 EP - 7669 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Masanes, Lluis A1 - Müller, Markus P. T1 - A derivation of quantum theory from physical requirements JF - New journal of physics : the open-access journal for physics N2 - 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. Y1 - 2011 U6 - https://doi.org/10.1088/1367-2630/13/6/063001 SN - 1367-2630 VL - 13 IS - 1 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Makhmudo, K. O. A1 - Makhmudov, O. I. A1 - Tarkhanov, Nikolai Nikolaevich T1 - Equations of Maxwell type JF - Journal of mathematical analysis and applications N2 - 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. KW - Electromagnetic waves KW - Scattering KW - Elliptic complex KW - Green formulas KW - Stratton-Chu formulas KW - Cauchy problem Y1 - 2011 U6 - https://doi.org/10.1016/j.jmaa.2011.01.012 SN - 0022-247X VL - 378 IS - 1 SP - 64 EP - 75 PB - Elsevier CY - San Diego ER - TY - JOUR A1 - Baumgärtel, Hellmut T1 - A Characteristic decay semigroup for the resonances of trace class perturbations with analyticity conditions of semibounded hamiltonians JF - International journal of theoretical physic N2 - To asymptotic complete scattering systems {M(+) + V, M(+)} on H(+) := L(2)(R(+), K, d lambda), where M(+) is the multiplication operator on H(+) and V is a trace class operator with analyticity conditions, a decay semigroup is associated such that the spectrum of the generator of this semigroup coincides with the set of all resonances (poles of the analytic continuation of the scattering matrix into the lower half plane across the positive half line), i.e. the decay semigroup yields a "time-dependent" characterization of the resonances. As a counterpart a "spectral characterization" is mentioned which is due to the "eigenvalue-like" properties of resonances. KW - Resonances KW - Scattering theory KW - Lax-Phillips theory KW - Decay semigroups Y1 - 2011 U6 - https://doi.org/10.1007/s10773-010-0533-9 SN - 0020-7748 VL - 50 IS - 7 SP - 2002 EP - 2008 PB - Springer CY - New York ER - TY - JOUR A1 - Grass, T. D. A1 - dos Santos, Francisca E. A. A1 - Pelster, Axel T1 - Real-time Ginzburg-Landau theory for bosons in optical lattices JF - Laser physics N2 - Within the Schwinger-Keldysh formalism we derive a Ginzburg-Landau theory for the Bose-Hubbard model which describes the real-time dynamics of the complex order parameter field. Analyzing the excitations in the vicinity of the quantum phase transitions it turns out that particle/hole dispersions in the Mott phase map continuously onto corresponding amplitude/phase excitations in the superfluid phase. Furthermore, in the superfluid phase we find a sound mode, which is in accordance with recent Bragg spectroscopy measurements in the Bogoliubov regime, as well as an additional gapped mode, which seems to have been detected via lattice modulation. Y1 - 2011 U6 - https://doi.org/10.1134/S1054660X11150096 SN - 1054-660X SN - 1555-6611 VL - 21 IS - 8 SP - 1459 EP - 1463 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Levnajic, Zoran T1 - Emergent multistability and frustration in phase-repulsive networks of oscillators JF - Physical review : E, Statistical, nonlinear and soft matter physics N2 - 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. Y1 - 2011 U6 - https://doi.org/10.1103/PhysRevE.84.016231 SN - 1539-3755 VL - 84 IS - 1 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Fechner, Cora T1 - Reconstructing the intergalactic UV background with QSO absorption lines JF - Astronomy and astrophysics : an international weekly journal N2 - We present a new approach to observationally constraining the spectral energy distribution of the intergalactic UV background by studying metal absorption systems. We study single-component metal line systems that exhibit various well-measured species. Among the observed transitions, at least two ratios of ionization stages from the same element are required, e. g. C III/C IV and Si III/Si IV. For each system photoionization models are constructed by varying the spectrum of the ionizing radiation. The spectral energy distribution can then be constrained by comparing the models with the observed column density ratios. Extensive tests with artificial absorbers show that the spectrum of the ionizing radiation cannot be reconstructed unambiguously, but it is possible to constrain the main characteristics of the spectrum. Furthermore, the resulting physical parameters of the absorber, such as ionization parameter, metallicity, and relative abundances, may depend strongly on the adopted ionizing spectrum. Even in case of well-fitting models, the uncertainties can be as high as similar to 0.5 dex for the ionization parameter and up to similar to 1.5 dex for the metallicity. Therefore, it is essential to know the hardness of the UV background when estimating the metallicity of the intergalactic medium. Applying the procedure to a small sample of 3 observed single-component metal line systems yields a soft ionizing radiation at z > 2 and a slightly harder spectrum at z < 2. The resulting energy distributions exhibit strong He II Lya re-emission features, suggesting that reprocessing by intergalactic He II is important. Comparing the observed systems to UV background spectra from the literature indicates that a recent model that includes sawtooth modulation due to reprocessing by intergalactic He II with delayed helium reionization fits the investigated systems very well. KW - intergalactic medium KW - quasars: absorption lines KW - diffuse radiation Y1 - 2011 U6 - https://doi.org/10.1051/0004-6361/201117080 SN - 0004-6361 VL - 532 IS - 2 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Gerhardt, Matthias A1 - Groeger, Gillian A1 - MacCarthy, Niall T1 - Monopolar vs. bipolar subretinal stimulation-An in vitro study JF - Journal of neuroscience methods N2 - This study uses an in vitro rd10 mouse model to quantify and compare the ability of the monopolar and the (concentric) bipolar electrode configurations for subretinal stimulation. To allow for results which can be directly compared an identical region of the retina was stimulated due to the circumstance that the bipolar electrode configuration allows also for monopolar stimulation, if the concentric counter-electrode is set potential-free (floating). A ganglion cell, located centrally over the bipolar electrode configuration was selected to extracellularly record action potentials during stimulation. To analyse the recorded action potentials, we introduce a new method which combines the advantages of (a) singular value decomposition (SVD) for weighting similar modulation patterns with which the recorded action potentials are characterized and (b) multi curve fitting to identify a common threshold level, required to finally assemble a strength-duration relationship (SDR). By directly comparing the obtained SDR curves, we found that the efficiency of stimulation with the monopolar electrode configuration is significantly higher than with the bipolar electrode configuration. All obtained SDR curves were fitted using the Lapicque model to estimate the chronaxie times and the rheobase currents. Liquid inclusions, eventually separating the retina from the electrodes are discussed to be a major cause for low ganglion cell responses during stimulation with the bipolar electrode configuration. KW - SVD KW - Subretinal KW - Electrodes KW - Monopolar KW - Bipolar KW - Retina KW - Ganglion KW - Cells Y1 - 2011 U6 - https://doi.org/10.1016/j.jneumeth.2011.04.017 SN - 0165-0270 VL - 199 IS - 1 SP - 26 EP - 34 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Prosen, Tomaz A1 - Ilievski, Enej T1 - Nonequilibrium phase transition in a periodically driven XY spin chain JF - Physical review letters N2 - 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. Y1 - 2011 U6 - https://doi.org/10.1103/PhysRevLett.107.060403 SN - 0031-9007 VL - 107 IS - 6 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - DiGuglielmo, J. A1 - Samblowski, A. A1 - Hage, B. A1 - Pineda, Carlos A1 - Eisert, Jens A1 - Schnabel, R. T1 - Experimental Unconditional Preparation and Detection of a Continuous Bound Entangled State of Light JF - Physical review letters N2 - Among the possibly most intriguing aspects of quantum entanglement is that it comes in free and bound instances. The existence of bound entangled states certifies an intrinsic irreversibility of entanglement in nature and suggests a connection with thermodynamics. In this Letter, we present a first unconditional, continuous-variable preparation and detection of a bound entangled state of light. We use convex optimization to identify regimes rendering its bound character well certifiable, and continuously produce a distributed bound entangled state with an extraordinary and unprecedented significance of more than 10 standard deviations away from both separability and distillability. Our results show that the approach chosen allows for the efficient and precise preparation of multimode entangled states of light with various applications in quantum information, quantum state engineering, and high precision metrology. Y1 - 2011 U6 - https://doi.org/10.1103/PhysRevLett.107.240503 SN - 0031-9007 VL - 107 IS - 24 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Lisso, Janina A1 - Schröder, Florian A1 - Fisahn, Joachim A1 - Muessig, Carsten T1 - NFX1-LIKE2 (NFXL2) Suppresses Abscisic Acid Accumulation and Stomatal Closure in Arabidopsis thaliana JF - PLoS one N2 - 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. Y1 - 2011 U6 - https://doi.org/10.1371/journal.pone.0026982 SN - 1932-6203 VL - 6 IS - 11 PB - PLoS CY - San Fransisco ER - TY - JOUR A1 - Abel, M. W. A1 - Shepelyansky, Dima L. T1 - Google matrix of business process management JF - The European physical journal : B, Condensed matter and complex systems N2 - Development of efficient business process models and determination of their characteristic properties are subject of intense interdisciplinary research. Here, we consider a business process model as a directed graph. Its nodes correspond to the units identified by the modeler and the link direction indicates the causal dependencies between units. It is of primary interest to obtain the stationary flow on such a directed graph, which corresponds to the steady-state of a firm during the business process. Following the ideas developed recently for the World Wide Web, we construct the Google matrix for our business process model and analyze its spectral properties. The importance of nodes is characterized by PageRank and recently proposed CheiRank and 2DRank, respectively. The results show that this two-dimensional ranking gives a significant information about the influence and communication properties of business model units. We argue that the Google matrix method, described here, provides a new efficient tool helping companies to make their decisions on how to evolve in the exceedingly dynamic global market. Y1 - 2011 U6 - https://doi.org/10.1140/epjb/e2010-10710-y SN - 1434-6028 VL - 84 IS - 4 SP - 493 EP - 500 PB - Springer CY - New York ER - TY - JOUR A1 - Abdolvahab, Rouhollah Haji A1 - Metzler, Ralf A1 - Ejtehadi, Mohammad Reza T1 - First passage time distribution of chaperone driven polymer translocation through a nanopore homopolymer and heteropolymer cases JF - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr N2 - Combining the advection-diffusion equation approach with Monte Carlo simulations we study chaperone driven polymer translocation of a stiff polymer through a nanopore. We demonstrate that the probability density function of first passage times across the pore depends solely on the Peclet number, a dimensionless parameter comparing drift strength and diffusivity. Moreover it is shown that the characteristic exponent in the power-law dependence of the translocation time on the chain length, a function of the chaperone-polymer binding energy, the chaperone concentration, and the chain length, is also effectively determined by the Peclet number. We investigate the effect of the chaperone size on the translocation process. In particular, for large chaperone size, the translocation progress and the mean waiting time as function of the reaction coordinate exhibit pronounced sawtooth-shapes. The effects of a heterogeneous polymer sequence on the translocation dynamics is studied in terms of the translocation velocity, the probability distribution for the translocation progress, and the monomer waiting times. (C) 2011 American Institute of Physics. Y1 - 2011 U6 - https://doi.org/10.1063/1.3669427 SN - 0021-9606 VL - 135 IS - 24 PB - American Institute of Physics CY - Melville ER - TY - JOUR A1 - Gruber, W. A1 - Chakravarty, S. A1 - Baehtz, C. A1 - Leitenberger, Wolfram A1 - Bruns, M. A1 - Kobler, A. A1 - Kübel, Christian A1 - Schmidt, H. T1 - Strain relaxation and vacancy creation in thin platinum films JF - Physical review letters N2 - Synchrotron based combined in situ x-ray diffractometry and reflectometry is used to investigate the role of vacancies for the relaxation of residual stress in thin metallic Pt films. From the experimentally determined relative changes of the lattice parameter a and of the film thickness L the modification of vacancy concentration and residual strain was derived as a function of annealing time at 130 degrees C. The results indicate that relaxation of strain resulting from compressive stress is accompanied by the creation of vacancies at the free film surface. This proves experimentally the postulated dominant role of vacancies for stress relaxation in thin metal films close to room temperature. Y1 - 2011 U6 - https://doi.org/10.1103/PhysRevLett.107.265501 SN - 0031-9007 VL - 107 IS - 26 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Kuznetsov, Sergey P. T1 - Plykin type attractor in electronic device simulated in MULTISIM JF - Chaos : an interdisciplinary journal of nonlinear science N2 - 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. Y1 - 2011 U6 - https://doi.org/10.1063/1.3646903 SN - 1054-1500 VL - 21 IS - 4 PB - American Institute of Physics CY - Melville ER - TY - JOUR A1 - Feudel, Fred A1 - Bergemann, Kay A1 - Tuckerman, Laurette S. A1 - Egbers, C. A1 - Futterer, B. A1 - Gellert, Marcus A1 - Hollerbach, Rainer T1 - Convection patterns in a spherical fluid shell JF - Physical review : E, Statistical, nonlinear and soft matter physics N2 - Symmetry-breaking bifurcations have been studied for convection in a nonrotating spherical shell whose outer radius is twice the inner radius, under the influence of an externally applied central force field with a radial dependence proportional to 1/r(5). This work is motivated by the GeoFlow experiment, which is performed under microgravity condition at the International Space Station where this particular central force can be generated. In order to predict the observable patterns, simulations together with path-following techniques and stability computations have been applied. Branches of axisymmetric, octahedral, and seven-cell solutions have been traced. The bifurcations producing them have been identified and their stability ranges determined. At higher Rayleigh numbers, time-periodic states with a complex spatiotemporal symmetry are found, which we call breathing patterns. Y1 - 2011 U6 - https://doi.org/10.1103/PhysRevE.83.046304 SN - 1539-3755 VL - 83 IS - 4 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Richter, Philipp A1 - Krause, F. A1 - Fechner, Cora A1 - Charlton, Jane C. A1 - Murphy, M. T. T1 - The neutral gas extent of galaxies as derived from weak intervening Ca II absorbers JF - Astronomy and astrophysics : an international weekly journal N2 - 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. KW - galaxies: halos KW - galaxies: formation KW - galaxies: ISM KW - intergalactic medium KW - quasars: absorption lines Y1 - 2011 U6 - https://doi.org/10.1051/0004-6361/201015566 SN - 0004-6361 VL - 528 IS - 4 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Müller, Markus P. A1 - Gross, David A1 - Eisert, Jens T1 - Concentration of Measure for Quantum States with a Fixed Expectation Value JF - Communications in mathematical physics N2 - 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. Y1 - 2011 U6 - https://doi.org/10.1007/s00220-011-1205-1 SN - 0010-3616 VL - 303 IS - 3 SP - 785 EP - 824 PB - Springer CY - New York ER - TY - JOUR A1 - Mann, R. B. A1 - Young, M. B. A1 - Fuüntes-Schuller, I. T1 - A perturbative approach to inelastic collisions in a Bose-Einstein condensate JF - Journal of physics : B, Atomic, molecular and optical physics N2 - 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. Y1 - 2011 U6 - https://doi.org/10.1088/0953-4075/44/8/085301 SN - 0953-4075 VL - 44 IS - 8 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Valleriani, Angelo A1 - Zhang, Gong A1 - Nagar, Apoorva A1 - Ignatova, Zoya A1 - Lipowsky, Reinhard T1 - Length-dependent translation of messenger RNA by ribosomes JF - Physical review : E, Statistical, nonlinear and soft matter physics N2 - A simple measure for the efficiency of protein synthesis by ribosomes is provided by the steady state amount of protein per messenger RNA (mRNA), the so-called translational ratio, which is proportional to the translation rate. Taking the degradation of mRNA into account, we show theoretically that both the translation rate and the translational ratio decrease with increasing mRNA length, in agreement with available experimental data for the prokaryote Escherichia coli. We also show that, compared to prokaryotes, mRNA degradation in eukaryotes leads to a less rapid decrease of the translational ratio. This finding is consistent with the fact that, compared to prokaryotes, eukaryotes tend to have longer proteins. Y1 - 2011 U6 - https://doi.org/10.1103/PhysRevE.83.042903 SN - 1539-3755 VL - 83 IS - 4 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Tepper-Garcia, Thorsten A1 - Richter, Philipp A1 - Schaye, Joop A1 - Booth, C. M. A1 - Vecchia, Claudio Dalla A1 - Theuns, Tom A1 - Wiersma, Robert P. C. T1 - Absorption signatures of warm-hot gas at low redshift o vi JF - Monthly notices of the Royal Astronomical Society N2 - 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. KW - methods: numerical KW - galaxies: formation KW - intergalactic medium KW - quasars: absorption lines KW - cosmology: theory Y1 - 2011 U6 - https://doi.org/10.1111/j.1365-2966.2010.18123.x SN - 0035-8711 VL - 413 IS - 1 SP - 190 EP - 212 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Schmidt, Hans-Jürgen T1 - Gauss-Bonnet lagrangian G lnG and cosmological exact solutions JF - Physical review : D, Particles, fields, gravitation, and cosmology N2 - 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. Y1 - 2011 U6 - https://doi.org/10.1103/PhysRevD.83.083513 SN - 1550-7998 VL - 83 IS - 8 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Beye, Martin A1 - Föhlisch, Alexander T1 - A soft X-ray approach to electron-phonon interactions beyond the Born-Oppenheimer approximation JF - Journal of electron spectroscopy and related phenomena : the international journal on theoretical and experimental aspects of electron spectroscopy N2 - With modern soft X-ray methods, the whole field of electron-phonon interactions becomes accessible directly in the ultrafast time domain with ultrashort pulsed X-ray sources, as well as in the energy domain through modern highly resolving spectrometers. The well-known core-hole clock approach plays an intermediate role, resolving energetic and temporal features at the same time. In this perspective paper, we review several experiments to illustrate the modern advances in the selective study of electron-phonon interactions as fundamentally determining ingredients for materials properties. We present the different complementary approaches that can be taken with soft X-ray methods to conquer this field beyond the Born-Oppenheimer approximation. KW - Electron-phonon coupling KW - Resonant inelastic X-ray scattering KW - X-ray emission spectroscopy KW - Near edge X-ray absorption fine structure Y1 - 2011 U6 - https://doi.org/10.1016/j.elspec.2010.12.032 SN - 0368-2048 VL - 184 IS - 3-6 SP - 313 EP - 317 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Campbell, Earl T. T1 - Catalysis and activation of magic states in fault-tolerant architectures JF - Physical review : A, Atomic, molecular, and optical physics N2 - In many architectures for fault-tolerant quantum computing universality is achieved by a combination of Clifford group unitary operators and preparation of suitable nonstabilizer states, the so-called magic states. Universality is possible even for some fairly noisy nonstabilizer states, as distillation can convert many noisy copies into fewer purer magic states. Here we propose protocols that exploit multiple species of magic states in surprising ways. These protocols provide examples of previously unobserved phenomena that are analogous to catalysis and activation well known in entanglement theory. Y1 - 2011 U6 - https://doi.org/10.1103/PhysRevA.83.032317 SN - 1050-2947 VL - 83 IS - 3 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Schaefer, Edith A1 - Westendorf, Christian A1 - Bodenschatz, Eberhard A1 - Beta, Carsten A1 - Geil, Burkhard A1 - Janshoff, Andreas T1 - Shape oscillations of dictyostelium discoideum cells on ultramicroelectrodes monitored by impedance analysis JF - Small Y1 - 2011 U6 - https://doi.org/10.1002/smll.201001955 SN - 1613-6810 VL - 7 IS - 6 SP - 723 EP - 726 PB - Wiley-Blackwell CY - Malden ER -