TY - JOUR A1 - Pattyn, Frank A1 - Perichon, Laura A1 - Durand, Gael A1 - Favier, Lionel A1 - Gagliardini, Olivier A1 - Hindmarsh, Richard C. A. A1 - Zwinger, Thomas A1 - Albrecht, Torsten A1 - Cornford, Stephen A1 - Docquier, David A1 - Furst, Johannes J. A1 - Goldberg, Daniel A1 - Gudmundsson, Gudmundur Hilmar A1 - Humbert, Angelika A1 - Huetten, Moritz A1 - Huybrechts, Philippe A1 - Jouvet, Guillaume A1 - Kleiner, Thomas A1 - Larour, Eric A1 - Martin, Daniel A1 - Morlighem, Mathieu A1 - Payne, Anthony J. A1 - Pollard, David A1 - Rueckamp, Martin A1 - Rybak, Oleg A1 - Seroussi, Helene A1 - Thoma, Malte A1 - Wilkens, Nina T1 - Grounding-line migration in plan-view marine ice-sheet models: results of the ice2sea MISMIP3d intercomparison JF - Journal of glaciology N2 - Predictions of marine ice-sheet behaviour require models able to simulate grounding-line migration. We present results of an intercomparison experiment for plan-view marine ice-sheet models. Verification is effected by comparison with approximate analytical solutions for flux across the grounding line using simplified geometrical configurations (no lateral variations, no buttressing effects from lateral drag). Perturbation experiments specifying spatial variation in basal sliding parameters permitted the evolution of curved grounding lines, generating buttressing effects. The experiments showed regions of compression and extensional flow across the grounding line, thereby invalidating the boundary layer theory. Steady-state grounding-line positions were found to be dependent on the level of physical model approximation. Resolving grounding lines requires inclusion of membrane stresses, a sufficiently small grid size (<500 m), or subgrid interpolation of the grounding line. The latter still requires nominal grid sizes of <5 km. For larger grid spacings, appropriate parameterizations for ice flux may be imposed at the grounding line, but the short-time transient behaviour is then incorrect and different from models that do not incorporate grounding-line parameterizations. The numerical error associated with predicting grounding-line motion can be reduced significantly below the errors associated with parameter ignorance and uncertainties in future scenarios. Y1 - 2013 U6 - https://doi.org/10.3189/2013JoG12J129 SN - 0022-1430 VL - 59 IS - 215 SP - 410 EP - 422 PB - International Glaciological Society CY - Cambridge ER - TY - JOUR A1 - Neumann, Bernhard A1 - Horstkemper, Marianne A1 - Krüger, Wolfgang A1 - Wilkens, Martin A1 - Bohlen, Andreas A1 - Frübing, Peter A1 - Wegener, Michael A1 - Scheff, Ullrich A1 - Neher, Dieter A1 - Brehmer, Ludwig A1 - Kleinpeter, Erich A1 - Wolf, Gunter A1 - Koetz, Joachim A1 - Peter, Martin G. A1 - Senkbeil, Sigrid A1 - Meyer, Till T1 - Portal = Im Trend: Physiker und Chemiker erforschen "Soft Matter" BT - Die Potsdamer Universitätszeitung N2 - Aus dem Inhalt: Im Trend: Physiker und Chemiker erforschen „Soft Matter“ -Brandenburger Netzwerk für Existenzgründer erhält Förderung -Universität leistet Beitrag zum Romantik-Jahr -Musiksender MTV und Bryan Adams auf dem Campus T3 - Portal: Das Potsdamer Universitätsmagazin - 06/2002 Y1 - 2002 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-501441 SN - 1618-6893 VL - 2002 ER - TY - JOUR A1 - Räder, Andy A1 - Eisert, Jens A1 - Wilkens, Martin A1 - Schmidt, Robert A1 - Micka, Bettina A1 - Ostermeyer, Martin A1 - Zill, Rüdiger A1 - Baur, Jürgen A1 - Schmidt, Renate A1 - Leppin, Karin A1 - Slotowski, Agnes A1 - Resch-Esser, Ursula T1 - Portal = Albert Einsteins Erbe: Uni-Physiker forschen weiter BT - Die Potsdamer Universitätszeitung N2 - Aus dem Inhalt: - Albert Einsteins Erbe: Uni-Physiker forschen weiter - Uni-Studiengang im europäischen Exzellenzprogramm - Sternenstaubsammler - Mit Einfallsreichtum gegen den Trend T3 - Portal: Das Potsdamer Universitätsmagazin - 01-03/2005 Y1 - 2005 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-439846 SN - 1618-6893 IS - 01-03/2005 ER - TY - JOUR A1 - Volk, Benno A1 - Markert, Doreen A1 - Riejok, Henriette A1 - Dittberner, Jürgen A1 - Wanka, Johanna A1 - Wilkens, Martin A1 - Görtemaker, Manfred A1 - Regierer, Babette A1 - Steup, Martin A1 - Müller-Röber, Bernd A1 - Wernicke, Matthias A1 - Altenberger, Uwe A1 - Stölting, Erhard A1 - Ferý, Carolin A1 - Egenter, Peter A1 - Lenz, Claudia A1 - Jakubowski, Zuzanna A1 - Klötzer, Sylvia A1 - Krause, Michael A1 - Dietsch, Ulrich T1 - Portal = Vor der Präsidenten-Wahl: Erwartungen, Wünsche, Vorschläge BT - Die Potsdamer Universitätszeitung N2 - Aus dem Inhalt: - Vor der Präsidenten-Wahl: Erwartungen, Wünsche, Vorschläge - Der AStA in der Krise? - Über Satire und Macht in der DDR - Vom Fünf-Sterne-Koch zum Mensaleiter T3 - Portal: Das Potsdamer Universitätsmagazin - 04-05/2006 Y1 - 2006 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-440005 SN - 1618-6893 IS - 04-05/2006 ER - TY - JOUR A1 - Rätzel, Dennis A1 - Wilkens, Martin A1 - Menzel, Ralf T1 - Effect of polarization entanglement in photon-photon scattering JF - Physical review : A, Atomic, molecular, and optical physics N2 - It is found that the differential cross section of photon-photon scattering is a function of the degree of polarization entanglement of the two-photon state. A reduced general expression for the differential cross section of photon-photon scattering is derived by applying simple symmetry arguments. An explicit expression is obtained for the example of photon-photon scattering due to virtual electron-positron pairs in quantum electrodynamics. It is shown how the effect in this explicit example can be explained as an effect of quantum interference and that it fits with the idea of distance-dependent forces. Y1 - 2017 U6 - https://doi.org/10.1103/PhysRevA.95.012101 SN - 2469-9926 SN - 2469-9934 VL - 95 IS - 1 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Lewenstein, Maciej A1 - Cirauqui, David A1 - Angel Garcia-March, Miguel A1 - Corominas, Guillem Guigo A1 - Grzybowski, Przemyslaw A1 - Saavedra, Jose R. M. A1 - Wilkens, Martin A1 - Wehr, Jan T1 - Haake-Lewenstein-Wilkens approach to spin-glasses revisited JF - Journal of physics : A, Mathematical and theoretical N2 - We revisit the Haake-Lewenstein-Wilkens approach to Edwards-Anderson (EA) model of Ising spin glass (SG) (Haake et al 1985 Phys. Rev. Lett. 55 2606). This approach consists in evaluation and analysis of the probability distribution of configurations of two replicas of the system, averaged over quenched disorder. This probability distribution generates squares of thermal copies of spin variables from the two copies of the systems, averaged over disorder, that is the terms that enter the standard definition of the original EA order parameter, qEA 0 0 KW - Edwards-Anderson order parameter KW - Haake-Lewenstein-Wilkens approach KW - spin glass KW - Saddle Point KW - Steppest Descend method Y1 - 2022 U6 - https://doi.org/10.1088/1751-8121/ac9d10 SN - 1751-8113 SN - 1751-8121 VL - 55 IS - 45 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Enderlein, Hinrich A1 - Zimmermann, Matthias A1 - Peter, Andreas A1 - Micka, Bettina A1 - Wilkens, Martin A1 - Lohnwasser, Roswitha A1 - Horn-Conrad, Antje T1 - Portal = Gesichter und Geschichten einer jungen Universität BT - Das Potsdamer Universitätsmagazin N2 - Aus dem Inhalt: - 20 Jahre Universität Potsdam - Gesichter und Geschichten einer jungen Universität T3 - Portal: Das Potsdamer Universitätsmagazin - 02/2011 Y1 - 2011 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-440456 SN - 1618-6893 IS - 02/2011 ER - TY - JOUR A1 - Wilkens, Martin A1 - Sütterlin, Sabine A1 - Weller, Nina A1 - Horn-Conrad, Antje A1 - Kampe, Heike A1 - Eckardt, Barbara A1 - Görlich, Petra A1 - Jäger, Sophie A1 - Zimmermann, Matthias A1 - Mitsch, Wolfgang T1 - Portal Wissen = Zeit BT - Das Forschungsmagazin der Universität Potsdam N2 - „Was ist also 'Zeit'?“ seufzt Augustinus von Hippo im 11. Buch seiner „Confessiones“ melancholisch, und fährt fort „Wenn mich niemand danach fragt, weiß ich es; will ich einem Fragenden es erklären, weiß ich es nicht.“ Auch heute, 1584 Jahre nach Augustinus, erscheint 'Zeit' immer noch rätselhaft. Abhandlungen über das Wesen der Zeit füllen Bibliotheken. Oder eben dieses Heft. Wesensfragen sind den modernen Wissenschaften allerdings fremd. Zeit ist – zumindest in der Physik – unproblematisch. „Time is defined so that Motion looks simple“ erkärt man kurz und trocken, und verabschiedet sich damit vom Augustinischen Rätsel oder der Newtonschen Vorstellung einer absoluten Zeit, deren mathematischen Fluss man durch irdische Instrumente eh immer nur näherungsweise erfassen kann. In der Alltagssprache, selbst in den Wissenschaften, reden wir zwar weiterhin vom Fluss der Zeit, aber Zeit ist schon lange keine natürliche Gegebenheit mehr. Zeit ist vielmehr ein konventioneller Ordnungsparameter für Änderung und Bewegung. Geordnet werden Prozesse, indem eine Klasse von Prozessen als Zählsystem dient, um andere Prozesse mit ihnen zu vergleichen und anhand der temporären Kategorien „vorher“, „während“ und „nachher“ anzuordnen. Zu Galileis Zeiten galt der eigene Pulsschlag als Zeitstandard für den Flug von Kanonenkugeln. Mit zunehmender Verfeinerung der Untersuchungsmethoden erschien das zu unpraktisch: Die Weg-Zeit-Diagramme frei fliegender Kanonenkugeln erweisen sich in diesem Standard ziemlich verwackelt, schlecht reproduzierbar, und keineswegs „simpel“. Heutzutage greift man zu Cäsium-Atomen. Demnach dauert ein Prozess eine Sekunde, wenn ein 133Cs-Atom genau 9 192 631 770 Schwingungen zwischen zwei sogenannten Hyperfeinzuständen des Grundzustands vollführt hat. Und ein Meter ist die Entfernung, die Licht im Vakuum in exakt 1/299 792 458 Sekunden zurücklegt. Glücklicherweise sind diese Daten im General Positioning System GPS hart kodiert, so dass der Nutzer sie nicht jedes Mal aufs Neue eingeben muss, wenn er wissen will, wo er ist. Aber schon morgen muss er sich vielleicht ein Applet runterladen, weil der Zeitstandard durch raffinierte Übergänge in Ytterbium ersetzt wurde. Der konventionelle Charakter des Zeitbegriffs sollte nicht dazu verführen zu glauben, alles sei irgendwie relativ und daher willkürlich. Die Beziehung eines Pulsschlags zu einer Atomuhr ist absolut, und genauso real, wie die Beziehung einer Sanduhr zum Lauf der Sonne. Die exakten Wissenschaften sind Beziehungswissenschaften. Sie handeln nicht vom Ding an sich, was Newton und Kant noch geträumt haben, sondern von Beziehungen – worauf schon Leibniz und später Mach hingewiesen haben. Kein Wunder, dass sich für andere Wissenschaften der physikalische Zeit-Standard als ziemlich unpraktisch erweist. Der Psychologie der Zeitwahrnehmung entnehmen wir – und jeder wird das bestätigen können – dass das gefühlte Alter durchaus verschieden ist vom physikalischen Alter. Je älter man ist, desto kürzer erscheinen einem die Jahre. Unter der einfachen Annahme, dass die gefühlte Dauer umgekehrt proportional zum physikalischen Alter ist, und man als Zwanzigjähriger ein physikalisches Jahr auch psychologisch als ein Jahr empfindet, ergibt sich der erstaunliche Befund, dass man mit 90 Jahren 90 Jahre ist. Und – bei einer angenommenen Lebenserwartung von 90 Jahren – mit 20 (bzw. 40) physikalischen Jahren bereits 67 (bzw. 82) Prozent seiner gefühlten Lebenszeit hinter sich hat. Bevor man angesichts der „Relativität von Zeit“ selbst in Melancholie versinkt, vielleicht die Fortsetzung des Eingangszitats von Augustinus: „Aber zuversichtlich behaupte ich zu wissen, dass es vergangene Zeit nicht gäbe, wenn nichts verginge, und nicht künftige Zeit, wenn nichts herankäme, und nicht gegenwärtige Zeit wenn nichts seiend wäre.“ Tja – oder mit Bob Dylan „The times they're a changing“. Ich wünsche Ihnen eine spannende Zeit bei der Lektüre dieser Ausgabe. Prof. Dr. Martin Wilkens Professor für Quantenoptik T3 - Portal Wissen: Das Forschungsmagazin der Universität Potsdam [Deutsche Ausgabe] - 02/2014 Y1 - 2014 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-440842 SN - 2194-4237 IS - 02/2014 ER - TY - JOUR A1 - Wilkens, Martin A1 - Sütterlin, Sabine A1 - Kampe, Heike A1 - Eckardt, Barbara A1 - Jäger, Sophie A1 - Zimmermann, Matthias T1 - Portal Wissen = Time BT - The Research Magazine of the University of Potsdam N2 - “What then is time?”, Augustine of Hippo sighs melancholically in Book XI of “Confessions” and continues, “If no one asks me, I know; if I want to explain it to a questioner, I don’t know.” Even today, 1584 years after Augustine, time still appears mysterious. Treatises about the essence of time fill whole libraries – and this magazine. However, questions of essence are alien to modern sciences. Time is – at least in physics – unproblematic: “Time is defined so that motion looks simple”, briefly and prosaically phrased, waves goodbye to Augustine’s riddle and to the Newtonian concept of absolute time, whose mathematical flow can only be approximately recorded with earthly instruments anyway. In our everyday language and even in science we still speak of the flow of time but time has not been a natural condition for quite a while now. It is rather a conventional order parameter for change and movement. Processes are arranged by using a class of processes as a counting system in order to compare other processes and to organize them with the help of the temporary categories “before”, “during”, and “after”. During Galileo’s time one’s own pulse was seen as the time standard for the flight of cannon balls. More sophisticated examination methods later made this seem too impractical. The distance-time diagrams of free-flying cannon balls turned out to be rather imprecise, difficult to replicate, and in no way “simple”. Nowadays, we use cesium atoms. A process is said to take one second when a caesium-133 atom completes 9,192,631,770 periods of the radiation corresponding to the transition between two hyperfine levels of the ground state. A meter is the length of the path travelled by light in a vacuum in exactly 1/299,792,458 of a second. Fortunately, these data are hard-coded in the Global Positioning System GPS so users do not have to reenter them each time they want to know where they are. In the future, however, they might have to download an app because the time standard has been replaced by sophisticated transitions to ytterbium. The conventional character of the time concept should not tempt us to believe that everything is somehow relative and, as a result, arbitrary. The relation of one’s own pulse to an atomic clock is absolute and as real as the relation of an hourglass to the path of the sun. The exact sciences are relational sciences. They are not about the thing-initself as Newton and Kant dreamt, but rather about relations as Leibniz and, later, Mach pointed out. It is not surprising that the physical time standard turned out to be rather impractical for other scientists. The psychology of time perception tells us – and you will all agree – that the perceived age is quite different from the physical age. The older we get the shorter the years seem. If we simply assume that perceived duration is inversely related to physical age and that a 20-year old also perceives a physical year as a psychological one, we come to the surprising discovery that at 90 years we are 90 years old. With an assumed life expectancy of 90 years, 67% (or 82%) of your felt lifetime is behind you at the age of 20 (or 40) physical years. Before we start to wallow in melancholy in the face of the “relativity of time”, let me again quote Augustine. “But at any rate this much I dare affirm I know: that if nothing passed there would be no past time; if nothing were approaching, there would be no future time; if nothing were, there would be no present time.” Well, – or as Bob Dylan sings “The times they are a-changin”. I wish you an exciting time reading this issue. Prof. Martin Wilkens Professor of Quantum Optics T3 - Portal Wissen: The research magazine of the University of Potsdam [Englische Ausgabe] - 02/2014 Y1 - 2014 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-441497 SN - 2198-9974 IS - 02/2014 ER - TY - JOUR A1 - Albus, Alexander P. A1 - Gardiner, Simon A. A1 - Illuminati, Fabrizio A1 - Wilkens, Martin T1 - Quantum field theory of dilute homogeneous Bose-Fermi-mixtures at zero temperature : general formalismand beyond mean-field corrections N2 - We consider a dilute homogeneous mixture of bosons and spin-polarized fermions at zero temperature. We first construct the formal scheme for carrying out systematic perturbation theory in terms of single particle Green's functions. We introduce a new relevant object, the renormalized boson-fermion T-matrix which we determine to second order in the boson-fermion s-wave scattering length. We also discuss how to incorporate the usual boson-boson T-matrix in mean-field approximation to obtain the total ground state properties of the system. The next order term beyond mean- field stems from the boson-fermion interaction and is proportional to $a_{scriptsize BF}k_{scriptsize F}$. The total ground-state energy-density reads $E/V =epsilon_{scriptsize F} + epsilon_{scriptsize B} + (2pihbar^{2}a_{ m BF}n_{scriptsize B}n_{scriptsize F}/m) [1 + a_{scriptsize BF}k_{scriptsize F}f(delta)/pi]$. The first term is the kinetic energy of the free fermions, the second term is the boson-boson mean-field interaction, the pre-factor to the additional term is the usual mean-field contribution to the boson-fermion interaction energy, and the second term in the square brackets is the second-order correction, where $f(delta)$ is a known function of $delta= (m_{scriptsize B} - m_{scriptsize F})/(m_{scriptsize B} + m_{scriptsize F})$. We discuss the relevance of this new term, how it can be incorporated into existing theories of boson-fermion mixtures, and its importance in various parameter regimes, in particular considering mixtures of $^{6}$Li and $^{7}$Li and of $^{3}$He and $^{4}$He. Y1 - 2002 UR - http://xxx.lanl.gov/abs/cond-mat/0201102 ER - TY - JOUR A1 - Wilkens, Martin A1 - Illuminati, Fabrizio A1 - Krämer, Meret T1 - Transition temperature of the weakly interacting Bose gas: perturbative solution of the crossover equations in the canonical ensemble N2 - We compute the shift of the critical temperature Tc with respect to the ideal case for a weakly interacting uniform Bose gas. We work in the framework of the canonical ensemble, extending the criterion of condensation provided by the canonical particle counting statistics for the zero-momentum state of the uniform ideal gas. The perturbative solution of the crossover equation to lowest order in power of the scattering length yields (Tc - Tc0)/Tc0=-0,93ap 1/3, where Tc0 is the transition temperature of the corresponding ideal Bose gas , a is the scattering length, and p is the particle number density. This is at vaiance with the standard grand canonical prediction of a null shift of the critical temperature in the lowest perturbative order. The non-equevalence of statistical ensemble for the ideal Bose gas is thus confirm (at the lowestperturbative level) also in the presence of interactions. Y1 - 2000 ER - TY - JOUR A1 - Pu, Han A1 - Zhang, Weiping A1 - Wilkens, Martin A1 - Meystre, Pierre T1 - Phonon Spectrum and Dynamical Stability of a Dilute Quantum Degenerate Bose-Fermi Mixture N2 - We calculate the phonon excistation spectrum in a zero-temperature dilute boson-fermion gaseous mixture. We show how the sound velocity changes due to the boson-fermion interaction, and we determine the dynamical stability regime of a homogeneous mixture. We identify a resonant phonon-exchange interaction between the fermions as the physical mechanism leading to the instability. Y1 - 2002 ER - TY - JOUR A1 - Rzazewski, Kazimierz A1 - Goral, K. A1 - Cirone, M. A. A1 - Wilkens, Martin T1 - Bose-Einstein Condensation of two interacting particles N2 - We investigate the notion of Bose-Einstein condensation of interacting particles. The definition of the condensate is based on the existence of the dominant eigenvalue of the single-particle density matrix. The statistical properies and the characteristics temperature are computed exactly in the soluble models of two interacting atoms. Y1 - 2001 ER - TY - JOUR A1 - Albus, Alexander P. A1 - Illuminati, Fabrizio A1 - Wilkens, Martin T1 - Ground-state properties of trapped Bose-Fermi mixtures: Role of exchange correlation Y1 - 2003 ER - TY - JOUR A1 - Weiss, Christoph A1 - Wilkens, Martin T1 - Particle number counting statistics in ideal Bose gases N2 - We discuss the exact particle number counting statistics of degenerate ideal Bose gases in the microcanonical, canonical, and grand-canonical ensemble, respectively, for various trapping potentials. We then invoke the Maxwell's Demon ensemble [P. Navez et al., Phys. Rev. Lett.(1997)] and show that for large total number of particles the root-mean-square fluctuation of the condensate occupation scales delta n0 proportional to [T/Tc]r Ns with scaling exponents r=3/2, s=1/2 for the 3D harmonic oscillator trapping potential, and r=1, s=2/3 for the 3D box. We derive an explicit expression for r and s in terms of spatial dimension D and spectral index sigma of the single- particle energy spectrum. Our predictions also apply to systems where Bose-Einstein condensation does not occur. We point out that the condensate fluctuations in the microcanonical and canonical ensemble respect the principle of thermodynamic equivalence. Y1 - 1997 UR - http://epubs.osa.org/oearchive/source/2372.htm ER - TY - JOUR A1 - Wilkens, Martin A1 - Weiss, Christoph T1 - Particle number fluctuations in an ideal Bose gas N2 - We analyse occupation number fluctuations of an ideal Bose gas in a trap which is isolated from theenvironment with respect to particle exchange (canonical ensemble). We show that in contrast to the predictions of thegrand- canonical ensemble, the counting statistics of particles in the trap ground state changes from monotonously decreasing above the condensation temperature to single-peaked below that temperature. For the exactly solvable case of a harmonic oscillator trapping potential in one spatial dimension we extract a Landau-Ginzburg functional which - despite the non- interacting nature of the system - displays the characteristic behaviour of a weakly interacting Bose gas. We also compare our findings with the usual treatment which is base on the grand-canonical ensemble. We show that for an ideal Bose gas neither are the grand-canonical and canonical ensemble thermodynamically equivalent, nor the grand-canonical ensemble can be viewed as a small system in diffusive contact with a particle reservoir. Y1 - 1997 ER - TY - JOUR A1 - Power, W. L. A1 - Pfau, T. A1 - Wilkens, Martin T1 - Loading atoms into a surface trap: simulations of an experimental scheme N2 - We present simulations of a scheme for the continuous loading of pre-cooled atoms into the lowest energy states of an optical surface trap. The atoms fall under gravity towards the surface of a prism where evanescent waves are used to decelerate the falling atoms and to pump them into a trapped state in an optical standing wave. The simulations are performed using the Monte-Carlo wavefunction technique and are designed to represent the proposed experimental scheme as closely as is practically possible. The probabilities of atoms being pumped into the different trapped states have been calculated as a function of the properties of the braking and pumping fields. The effective temperature of the final distribution of the atoms is calculated in order to find the change in phase-space density. Y1 - 1997 ER - TY - JOUR A1 - Öhberg, P. A1 - Surkov, E. L. A1 - Tittonen, I. A1 - Stenholm, Stig A1 - Wilkens, Martin A1 - Shlyapnikov, G. V. T1 - Low-energy elementary excitations of a trapped Bose-condensed gas N2 - We develop a method of finding analytical sotutions of the Bogolyubov-de Gennes equations for the excitations of a Bose condensate in the Thomas-Fermi regime in harmonic traps of any asymmetry and introduce a classification of eigenstates. In the case of cylindrical symmetry we emphasize the presence of an accidental degeneracy in the excitation spectrum at certain values of the projection of orbital angular momentum on the symmetry axis and discuss possible consequences of the degeneracy in the context of new signatures of Bose- Einstein condensation Y1 - 1997 ER - TY - JOUR A1 - Javanainen, Juha A1 - Wilkens, Martin T1 - Phase and Phase Diffusion of a Split Bose-Einstein Condensate N2 - We analyze theoretically an experiment in which a trapped Bose-Einstein condensate is cut in half, and the parts are subsequently allowed to interfere. If the delay cutting and atom detection is small, the interference pattern of the two halves of the condensate is the same in every experiment. However, for longer delays the spatial phase of the interference shows random fluctuations from one experiment to the other. This phase diffusion is characterized quantitatively. Y1 - 1997 ER - TY - JOUR A1 - Stenholm, Stig A1 - Wilkens, Martin T1 - Jumps in quantum theory N2 - In this paper we review the discussion about quantum jumps. We sketch the historical background before we present the recent revival of this problem originating in the field of atomic investigations. We present both the theoretical methods and their motivations, the relevance to experiments and an attempt at a preliminary discussion of the role of these developments in our fundamental understanding of quantum physics. Y1 - 1997 ER - TY - JOUR A1 - Hassler, Gerda A1 - Wilkens, Martin A1 - Scheerer-Neumann, Gerheid A1 - Kretschmann, Martina A1 - Resch-Esser, Ursula A1 - Wagner, Karen A1 - Pabst, Markus T1 - Portal = Nach PISA: Reformbedarf auch für die Lehrerbildung BT - Die Potsdamer Universitätszeitung N2 - Aus dem Inhalt: - Nach PISA: Reformbedarf auch für die Lehrerbildung - Neue Regelungen im Hochschulrahmengesetz - Bunsen-Gesellschaft für Pysikalische Chemie tagt in Potsdam - Abschied: Neue Aufgaben für Barbara Schneider-Kempf T3 - Portal: Das Potsdamer Universitätsmagazin - 03-04/2002 Y1 - 2002 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-439583 SN - 1618-6893 EP - 03-04/2002 ER - TY - GEN A1 - Rätzel, Dennis A1 - Wilkens, Martin A1 - Menzel, Ralf T1 - Gravitational properties of light BT - the gravitational field of a laser pulse N2 - The gravitational field of a laser pulse of finite lifetime, is investigated in the framework of linearized gravity. Although the effects are very small, they may be of fundamental physical interest. It is shown that the gravitational field of a linearly polarized light pulse is modulated as the norm of the corresponding electric field strength, while no modulations arise for circular polarization. In general, the gravitational field is independent of the polarization direction. It is shown that all physical effects are confined to spherical shells expanding with the speed of light, and that these shells are imprints of the spacetime events representing emission and absorption of the pulse. Nearby test particles at rest are attracted towards the pulse trajectory by the gravitational field due to the emission of the pulse, and they are repelled from the pulse trajectory by the gravitational field due to its absorption. Examples are given for the size of the attractive effect. It is recovered that massless test particles do not experience any physical effect if they are co-propagating with the pulse, and that the acceleration of massless test particles counter-propagating with respect to the pulse is four times stronger than for massive particles at rest. The similarities between the gravitational effect of a laser pulse and Newtonian gravity in two dimensions are pointed out. The spacetime curvature close to the pulse is compared to that induced by gravitational waves from astronomical sources. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 222 KW - electromagnetic radiation KW - general relativity KW - gravity KW - laser pulses KW - linearized gravity KW - pp-wave solutions Y1 - 2016 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-90553 ER - TY - JOUR A1 - Rätzel, Dennis A1 - Wilkens, Martin A1 - Menzel, Ralf T1 - Gravitational properties of light BT - the gravitational field of a laser pulse JF - New journal of physics : the open-access journal for physics N2 - The gravitational field of a laser pulse of finite lifetime, is investigated in the framework of linearized gravity. Although the effects are very small, they may be of fundamental physical interest. It is shown that the gravitational field of a linearly polarized light pulse is modulated as the norm of the corresponding electric field strength, while no modulations arise for circular polarization. In general, the gravitational field is independent of the polarization direction. It is shown that all physical effects are confined to spherical shells expanding with the speed of light, and that these shells are imprints of the spacetime events representing emission and absorption of the pulse. Nearby test particles at rest are attracted towards the pulse trajectory by the gravitational field due to the emission of the pulse, and they are repelled from the pulse trajectory by the gravitational field due to its absorption. Examples are given for the size of the attractive effect. It is recovered that massless test particles do not experience any physical effect if they are co-propagating with the pulse, and that the acceleration of massless test particles counter-propagating with respect to the pulse is four times stronger than for massive particles at rest. The similarities between the gravitational effect of a laser pulse and Newtonian gravity in two dimensions are pointed out. The spacetime curvature close to the pulse is compared to that induced by gravitational waves from astronomical sources. KW - gravity KW - general relativity KW - laser pulses KW - electromagnetic radiation KW - linearized gravity KW - pp-wave solutions Y1 - 2016 U6 - https://doi.org/10.1088/1367-2630/18/2/023009 SN - 1367-2630 VL - 18 SP - 1 EP - 16 PB - IOP Science CY - London ER - TY - JOUR A1 - Tino, G. M. A1 - Cacciapuoti, L. A1 - Bongs, K. A1 - Bordé, Ch. J. A1 - Bouyer, P. A1 - Dittus, H. A1 - Ertmer, W. A1 - Görlitz, A. A1 - Inguscio, M. A1 - Landragin, A. A1 - Lemonde, P. A1 - Lämmerzahl, C. A1 - Peters, A. A1 - Rasel, E. A1 - Reichel, J. A1 - Salomon, C. A1 - Schiller, S. A1 - Schleich, W. A1 - Sengstock, K. A1 - Sterr, U. A1 - Wilkens, Martin T1 - Atom interferometers and optical atomic clocks : new quantum sensors for fundamental physics experiments in space N2 - We present projects for future space missions using new quantum devices based on ultracold atoms. They will enable fundamental physics experiments testing quantum physics, physics beyond the standard model of fundamental particles and interactions, special relativity, gravitation and general relativity. Y1 - 2007 ER - TY - JOUR A1 - Janicke, U. A1 - Wilkens, Martin T1 - Atomic matter wave amplification by optical pumping N2 - The atom laser (or `Boser') is a device that delivers a beam of atomic de Broglie waves with high coherence and monochromaticity. In this review, we concentrate on an all-optical scheme of an atom laser that is based on optical pumping. The model is first presented in terms of kinetic equations, and its relation to the ordinary laser and the Bose-Einstein condensation is discussed. We then derive a master equation for the quantum statistics dynamics of the atom laser. Neglecting photon reabsorption processes, the master equation is solved and the counting statistics is computed. Finally, the effects of the inelastic reabsorption processes are investigated for the particular case of two atoms. It is shown that the onset of atom-lasing is suppressed in large resonators, but may be achieved in small and/or low-dimensional resonators. Y1 - 1998 ER - TY - JOUR A1 - Navez, Patrick A1 - Wilkens, Martin T1 - Single molecule in a Bose-Einstein condensate N2 - We study a model describing a rotating linear rigid molicule interacting with a Bose-Einstein condensate. A generalization of the Landau criterion is established and gives the limit for which the molecule moves translationally and rotationally into the condensate without any friction. In particular, we show that the rotational energy released by the molecule is large enough to eject one atom out of the condensate. The detection of such an atom provides a direct measurement of the low-energy cross section of the scattering with the rotating molecule. Finally, increases of inertia and of centrifugal distortion of the molecule due to the surrounding condensate are estimated and compared with the experimental data obtained for a He4 droplet. Y1 - 1999 ER - TY - JOUR A1 - Idziaszek, Zbigniew A1 - Gajda, M. A1 - Navez, Patrick A1 - Wilkens, Martin A1 - Rzazewski, Kazimierz T1 - Fluctuation of the Weakly Interacting Bose-Einstein Condensate N2 - We consider the role of weak interaction on the fluctuations of the number of condensed atoms within canonical and microanonical ensembles. Unlike the correspinding case of the ideal gas this is not a clean, well-defined problem of mathematical physics. Two related reasons are the following: there is no unique way of defining the condensate fraction of the interacting system and no exact energy levels of the interacting system are known. Y1 - 1999 ER - TY - JOUR A1 - Power, W. L. A1 - Tan, S. M. A1 - Wilkens, Martin T1 - A scheme for the simultaneous measurement of atomic position and momentum N2 - We propose an optical scheme for the simultaneous measurement of the position and momentum of a single atom. The scheme involves the coupling of the atom of two light fields with different spatical and polarization characteristics. The proposed technique is closely related to the Arthurs-Kelly measurement scheme; the principal difference is that in the present case the electromagnetic fields rather than from shifts in the position of a pointer. Y1 - 1997 ER - TY - JOUR A1 - Idziaszek, Zbigniew A1 - Wilkens, Martin T1 - Scattering of atoms on the Bose-Einstein condensate N2 - We investigate the scattering of slowly moving atoms on the Bose-Einstein condensate. The condensate excitations are described by Bogolyubov-de Gennes equatins. We derive the analytic expressions for the differential cross section for both elastic and ineladtic channels. For the elastic channel we obtain analytic results for total cross sections, and discuss their scaling with the number of condensed atoms. For inelastic channels we present numerical results for the total cross section. Y1 - 1999 ER - TY - JOUR A1 - Busch, Thomas A1 - Englert, Bertold-Georg A1 - Rzazewski, Kazimierz A1 - Wilkens, Martin T1 - Two cold atoms in a harmonic trap N2 - Two ultracold atoms moving in a trap interact weakly at a very short distance. This interaction can be modeled by a properly regularized contact potential. We solve the corresponding time-independent Schrödinger equation under the assumption of a parabolic, spherically symmetric trapping potential. Y1 - 1998 ER - TY - JOUR A1 - Leonhardt, Ulf A1 - Wilkens, Martin T1 - Aharonov-Bohm scattering of neutral atoms N2 - We study the scattering of quantum particles in the presence of an Aharonov-Bohm vortex and in an arbitrary cylindrically symmetric potential. In particular we address the scattering of atoms carrying dipole moments induced by an electrically charged wire and a homogeneous magnetic field. We argue that, despite the strong attraction of the wire, an Aharoniv-Bohm effect will be visible. Y1 - 1998 ER - TY - JOUR A1 - Wilkens, Martin T1 - Quantum Phase of a Moving Dipole N2 - It is shown that a neutral particle with an electric dipole moment which moves in a magnetic field acquires a topological phase. This phase may be observed in atom or molecular interferometry. Y1 - 1998 ER - TY - JOUR A1 - Javanainen, Juha A1 - Wilkens, Martin T1 - Phase and phase diffusion of a split Bose-Einstein condensate Y1 - 1998 ER - TY - JOUR A1 - Illuminati, Fabrizio A1 - Navez, Patrick A1 - Wilkens, Martin T1 - Thermodynamic identities and paricle number fluctuations in weakly interacting Bose-Einstein condensates N2 - We derive exact thermodynamic identities relating the average number of condensed atoms and the root-mean- square fluctuations determined in different statistical ensembles for the weakly interacting Bose gas confined in a box. This is achieved by introducing the concept of auxiliary partition functions for model Hamiltonians that do conserve the total number of particles. Exploiting such thermodynamic identities, we provide the first, completely analytical prediction of the microcanonical particle number fluctuations in the weakly interacting Bose gas. Such fluctuations, as a function of the volume V of the box are found to behave normally, in contrast wiht the anomalous scaling behaviour V3/ 4 of the fluctuations in the ideal Bose gas. Y1 - 1999 ER - TY - JOUR A1 - Eisert, Jens A1 - Wilkens, Martin T1 - Catlysis of Entanglement Manipulation for Mixed States N2 - We consider entanglement-assisted remote quantum state manipulation of bipartite mixed states. Several aspects are addressed: we present a class of mixed states of rank two that can be transformed into another class of mixed states under entanglement-assisted local operations with classical communication, but for which such a transformation is impossible without assistance. Furthermore, we demonstrate enhancement of the efficiency of purification protocols with the help of entanglement-assisted operations. Finally, transformations from one mixed state to mixed target states which are sufficiently close to the source state are contrasted with similar transformations in the pure-state case. Y1 - 2000 ER - TY - JOUR A1 - Felbinger, Timo A1 - Santos, L. A1 - Wilkens, Martin A1 - Lewenstein, Maciej T1 - Time Correlations of a laser-induced Bose-Einstein condensate N2 - We analyze the multi-time correlations of a laser-induced Bose Einstein condensate. We use quantum stochastic methods to obtain under certain circumstances a Fokker-Planck equation which describes the phase-difussion process, and obtain an analytical expression of the two-time correlations. We perform also quantum Monte Carlo numerical simulations of the correlations, which are in good agreement with the predicted analytical results. Y1 - 2000 ER - TY - JOUR A1 - Eisert, Jens A1 - Wilkens, Martin T1 - Quantum games N2 - In these lecture notes we investigate the implications of the identification of strategies with quantum operations in game theory beyond the results presented in [J. Eisert, M. Wilkens, and M. Lewenstein, Phys. Rev. Lett. 83, 3077 (1999)]. After introducing a general framework, we study quantum games with a classical analogue in order to flesh out the peculiarities of game theoretical settings in the quantum domain. Special emphasis is given to a detailed investigation of different sets of quantum strategies. Y1 - 2000 UR - http://xxx.lanl.gov/abs/quant-ph/0004076 ER - TY - JOUR A1 - Eisert, Jens A1 - Felbinger, Timo A1 - Papadopolous, P. A1 - Plenio, M. B. A1 - Wilkens, Martin T1 - Classical information and distillable entanglement N2 - We establish a quantitative connection between the amount of lost classical information about a quantum state and the concomitant loss of entanglement. Using menthods that have been developed for the optimal purification of miced states, we find a class of miced states with known distillable entanglement. These results can be used to determine the quantum capacity of a quantum channel which randomizes the order of transmitted signals. Y1 - 2000 ER - TY - JOUR A1 - Eisert, Jens A1 - Wilkens, Martin A1 - Lewenstein, Maciej T1 - Quantum Games and Quantum Strategies N2 - We investigate the quantization of nonzero sum games. For the particular case of the Prisoners' Dilemma we show that this game ceases to pose a dilemma if quantum strategies are allowed for. We also construct a particular quantum strategy which always gives reward if played against any classical strategy. Y1 - 1999 ER - TY - JOUR A1 - Felbinger, Timo A1 - Wilkens, Martin T1 - Stochastic Wave-function Simulation of Two-time Correlation Functions N2 - We propose an algorithm for the numerical simulation of two-time correlation functions by means of stochastic wave function. As a first application, we investigate the two-time correlation function of a nonlinear optical parametric oscillator. Y1 - 1999 ER - TY - JOUR A1 - Raetzel, Dennis A1 - Wilkens, Martin A1 - Menzel, Ralf T1 - Gravitational properties of light: The emission of counter-propagating laser pulses from an atom JF - Physical review : D, Particles, fields, gravitation, and cosmology Y1 - 2017 U6 - https://doi.org/10.1103/PhysRevD.95.084008 SN - 2470-0010 SN - 2470-0029 VL - 95 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Wilkens, Martin T1 - AS TIME GOES BY. Rythmizität Zyklizität - Kategorien zeitlicher Stukturierung JF - Zyklizität & Rhythmik: eine multidisziplinäre Vorlesungsreihe Y1 - 2020 SN - 978-3-86464-169-5 SP - 71 EP - 84 PB - trafo CY - Berlin ER - TY - JOUR A1 - Behrmann, Günter C. A1 - Kohlmann, Birgit A1 - Rupprecht, Holger A1 - Voigt, Sylvia A1 - Paulisch, Antje A1 - Piegler, Sandra A1 - Falk, André A1 - Kozakowski, Melanie A1 - Heike, Sylvester A1 - Eisner, Beate A1 - John, Peter A1 - Wilkens, Martin A1 - Lohwaßer, Roswitha A1 - Schründer-Lenzen, Agi A1 - Lauterbach, Wolfgang A1 - Schubarth, Wilfried T1 - Portal alumni T2 - Das Ehemaligen-Magazin der Universität Potsdam N2 - Das gerade begonnene Jahr wird für die Universität Potsdam ein besonderes werden, ist es doch das 20. Jahr ihres Bestehens. Auf das Erreichte ist die Hochschule mit Recht stolz. Die Universität Potsdam ist für Studieninteressierte ungebrochen attraktiv, was die steigenden Bewerberzahlen zeigen. Allein im vergangenen Jahr haben Uni-Wissenschaftler knapp 42 Millionen Euro Drittmittel eingeworben und die Liste gemeinsamer Verbundprojekte mit außeruniversitären Forschungseinrichtungen der Region wächst weiter. Zu den Erfolgen zählt weiterhin auch die steigende Anzahl von Absolventinnen und Absolventen der Hochschule. In die Gründung der Universität Potsdam am 15. Juli 1991 flossen zwei Vorgängereinrichtungen ein. Die wichtigste war die Brandenburgische Landeshochschule, vorher Pädagogische Hochschule, die über vier Jahrzehnte hinweg Lehrerinnen und Lehrer ausgebildet hat. Die Lehrerbildung hat auch für die Universität Potsdam profilbildenden Charakter, denn allein vier der fünf Fakultäten sind an der Lehrerbildung beteiligt und haben Generationen von jungen Leuten für den Lehrerberuf qualifiziert. Heute ist das Ziel aller an der Lehrerbildung Beteiligten, eine professionsorientierte, qualitativ hochwertige Lehrerbildung zu sichern, die sich an den Kompetenzen Erziehen, Unterrichten, Beraten, Betreuen, Innovieren und Organisieren orientiert. Eine besondere Herausforderung sieht die Universität Potsdam dabei in der Vernetzung von wissenschaftlicher Forschung und Lehrerbildung. Portal alumni stellt in der hier vorliegenden Ausgabe im Jubiläumsjahr zwölf Absolventen der Lehrerbildung vor. Sie berichten aus jeweils individueller Perspektive, wie sie ihr Studium an der Universität Potsdam erlebt haben und wie es sie geprägt hat. Und natürlich stellt das Magazin zugleich aktuelle Entwicklungstrends in der Lehrerbildung vor. Wie in allen Heften zuvor berichten wir von der Alumni-Arbeit des Jahres 2010 und stellen Höhepunkte des Unialltags vor. Wir wünschen Ihnen eine unterhaltsame Lektüre und sind gespannt auf Ihr Feedback zu diesem Heft. T3 - Portal alumni : das Ehemaligen-Magazin der Universität Potsdam - 8/2011 Y1 - 2010 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-444587 SN - 1613-2343 IS - 8 ER - TY - JOUR A1 - Rätzel, Dennis A1 - Wilkens, Martin A1 - Menzel, Ralf T1 - Gravitational properties of light-the gravitational field of a laser pulse JF - NEW JOURNAL OF PHYSICS N2 - The gravitational field of a laser pulse of finite lifetime, is investigated in the framework of linearized gravity. Although the effects are very small, they may be of fundamental physical interest. It is shown that the gravitational field of a linearly polarized light pulse is modulated as the norm of the corresponding electric field strength, while no modulations arise for circular polarization. In general, the gravitational field is independent of the polarization direction. It is shown that all physical effects are confined to spherical shells expanding with the speed of light, and that these shells are imprints of the spacetime events representing emission and absorption of the pulse. Nearby test particles at rest are attracted towards the pulse trajectory by the gravitational field due to the emission of the pulse, and they are repelled from the pulse trajectory by the gravitational field due to its absorption. Examples are given for the size of the attractive effect. It is recovered that massless test particles do not experience any physical effect if they are co-propagating with the pulse, and that the acceleration of massless test particles counter-propagating with respect to the pulse is four times stronger than for massive particles at rest. The similarities between the gravitational effect of a laser pulse and Newtonian gravity in two dimensions are pointed out. The spacetime curvature close to the pulse is compared to that induced by gravitational waves from astronomical sources. KW - gravity KW - general relativity KW - laser pulses KW - electromagnetic radiation KW - linearized gravity KW - pp-wave solutions Y1 - 2016 U6 - https://doi.org/10.1088/1367-2630/18/2/023009 SN - 1367-2630 VL - 18 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Rätzel, Dennis A1 - Wilkens, Martin A1 - Menzel, Ralf T1 - The effect of entanglement in gravitational photon-photon scattering JF - epl : a letters journal exploring the frontiers of physics N2 - The differential cross-section for gravitational photon-photon scattering calculated in perturbative quantum gravity is shown to depend on the degree of polarization entanglement of the two photons. The interaction between photons in the symmetric Bell state is stronger than between not entangled photons. In contrast, the interaction between photons in the anti-symmetric Bell state is weaker than between not entangled photons. The results are interpreted in terms of quantum interference, and it is shown how they fit into the idea of distance-dependent forces. Copyright (C) EPLA, 2016 Y1 - 2016 U6 - https://doi.org/10.1209/0295-5075/115/51002 SN - 0295-5075 SN - 1286-4854 VL - 115 SP - S12 EP - S13 PB - EDP Sciences CY - Mulhouse ER - TY - JOUR A1 - Henkel, Carsten A1 - Wilkens, Martin T1 - Heating of trapped atoms near thermal surfaces N2 - We study the electromagnetic coupling and concomitant heating of a particle in a miniaturized trap close to a solid surface. Two dominant heating mechanisms are identified: proximity fields generated by thermally exicted currents in the absorbing solid and timedependent image potentials due to elastic surfaces distortions (Rayleigh phonons. Estimates for the lifetime of the trap ground state are given. Ions are paricularly sinsitive to electric proximity fields: for a silver substrate, we find a lifetime below one second at distrances closer than some ten 10^-6m to the surfaces. Neutral atoms may approach the surface more closely: if they have a magnetic moment, a minimum distance of one 10^-6m is estimatied in tight traps, the heat being transferred via magnetic proximity fields. For spinless atoms, heat is transferred by inelastic scattering of virtual photons off sorface phonons. The corresponding lifetime, however, is estimated to be extremely long compared to the timescale of typical experiments. Y1 - 1999 ER - TY - JOUR A1 - Henkel, Carsten A1 - Wilkens, Martin T1 - Heating of trapped particles close to surfaces-blackbody and beyond N2 - We discuss heating and decoherencw in traps fpr ions and neutral paricles close to metallic surfaces. We focus on simple trap geometries and compute noise spectra of thermally excited electromagnetic fields. If the trap is located in the near field of the substrate, the field fluctuations are largely increased compared to the level of the blackbody field, leading to much shorter coherence and life times of the trapped atoms. The correspinding time constants are computed for ion traps and magnetic traps. Analytical estimates for the size dependence of the noise spectrum are given. We finally discuss prospects for the coherent transport of matter waves in integrated surface waveguides. Y1 - 2000 ER - TY - JOUR A1 - Henkel, Carsten A1 - Poetting, Sierk A1 - Wilkens, Martin T1 - Loss and heating of particles in small and noisy traps N2 - We derive the time and loss rate for a trapped atom that is coupled to fluctuating fields in the vicinity of a room-temperature metallic and/or dielectric surface. Our results indicate a clear predominance of near-field effects over ordinary blackbody radiation. We develop a theoretical framework for both charged ions and neutral atoms with and without spin. Loss processes that are due to a transition to an untrapped internal state are included. Y1 - 1999 ER - TY - JOUR A1 - Szameitat, Ulrike A1 - Wilkens, Martin A1 - Görlich, Petra A1 - Horn-Conrad, Antje A1 - Zimmermann, Matthias A1 - Reinhardt, Kristin A1 - Kampe, Heike A1 - Jäger, Heidi A1 - Wenzel, Anna Theresa A1 - Scholz, Jana T1 - Portal = Unter einem Dach: Lehrerbildung und Bildungsforschung BT - Das Potsdamer Universitätsmagazin N2 - Aus dem Inhalt: - Unter einem Dach: Lehrerbildung und Bildungsforschung - Waldweit - Nicht ohne Eisen und Schwefel T3 - Portal: Das Potsdamer Universitätsmagazin - 02/2015 Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-440634 SN - 1618-6893 IS - 02/2015 ER -