@article{MizunoPohlNiemiecetal.2011, author = {Mizuno, Yosuke and Pohl, Martin and Niemiec, Jacek and Zhang, Bing and Nishikawa, Ken-Ichi and Hardee, Philip E.}, title = {Magnetic-field amplification by turbulence in a relativistic shockpropagating through an inhomogeneous medium}, series = {The astrophysical journal : an international review of spectroscopy and astronomical physics}, volume = {726}, journal = {The astrophysical journal : an international review of spectroscopy and astronomical physics}, number = {2}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {0004-637X}, doi = {10.1088/0004-637X/726/2/62}, pages = {11}, year = {2011}, abstract = {We perform two-dimensional relativistic magnetohydrodynamic simulations of a mildly relativistic shock propagating through an inhomogeneous medium. We show that the postshock region becomes turbulent owing to preshock density inhomogeneity, and the magnetic field is strongly amplified due to the stretching and folding of field lines in the turbulent velocity field. The amplified magnetic field evolves into a filamentary structure in two-dimensional simulations. The magnetic energy spectrum is flatter than the Kolmogorov spectrum and indicates that a so-called small-scale dynamo is occurring in the postshock region. We also find that the amount of magnetic-field amplification depends on the direction of the mean preshock magnetic field, and the timescale of magnetic-field growth depends on the shock strength.}, language = {en} } @article{MellingerMellinger2011, author = {Mellinger, Axel and Mellinger, Olena}, title = {Breakdown threshold of dielectric barrier discharges in ferroelectrets where Paschen's law fails}, series = {IEEE transactions on dielectrics and electrical insulation}, volume = {18}, journal = {IEEE transactions on dielectrics and electrical insulation}, number = {1}, publisher = {Inst. of Electr. and Electronics Engineers}, address = {Piscataway}, issn = {1070-9878}, doi = {10.1109/TDEI.2011.5704491}, pages = {43 -- 48}, year = {2011}, abstract = {The piezoelectric activity of charged cellular foams (so-called ferroelectrets) is compared against simulations based on a multi-layer electromechanical model and Townsend's model of Paschen breakdown, with the distribution of void heights determined from scanning electron micrographs. While the calculated space charge hysteresis curves are in good agreement with experimental data, the onset of piezoelectric activity is observed at significantly higher electric fields than predicted by Paschen's law. One likely explanation is that the commonly accepted Paschen curve for electric breakdown in air poorly describes the critical electric field for dielectric barrier discharges in micrometer-size cavities.}, language = {en} } @phdthesis{Matthes2011, author = {Matthes, Heidrun}, title = {Interaction of land surface processes and the atmophere in the Arctic - senitivities and extremes}, address = {Potsdam}, pages = {123 S.}, year = {2011}, language = {en} } @article{MasanesMueller2011, author = {Masanes, Lluis and M{\"u}ller, Markus P.}, title = {A derivation of quantum theory from physical requirements}, series = {New journal of physics : the open-access journal for physics}, volume = {13}, journal = {New journal of physics : the open-access journal for physics}, number = {1}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {1367-2630}, doi = {10.1088/1367-2630/13/6/063001}, pages = {29}, year = {2011}, abstract = {Quantum theory (QT) is usually formulated in terms of abstract mathematical postulates involving Hilbert spaces, state vectors and unitary operators. In this paper, we show that the full formalism of QT can instead be derived from five simple physical requirements, based on elementary assumptions regarding preparations, transformations and measurements. This is very similar to the usual formulation of special relativity, where two simple physical requirements-the principles of relativity and light speed invariance-are used to derive the mathematical structure of Minkowski space-time. Our derivation provides insights into the physical origin of the structure of quantum state spaces (including a group-theoretic explanation of the Bloch ball and its three dimensionality) and suggests several natural possibilities to construct consistent modifications of QT.}, language = {en} } @article{MartinWinkelmannHaseloffetal.2011, author = {Martin, Maria A. and Winkelmann, Ricarda and Haseloff, M. and Albrecht, Tanja and Bueler, Ed and Khroulev, C. and Levermann, Anders}, title = {The Potsdam parallel ice sheet model (PISM-PIK) - Part 2: Dynamic equilibrium simulation of the Antarctic ice sheet}, series = {The Cryosphere : TC ; an interactive open access journal of the European Geosciences Union}, volume = {5}, journal = {The Cryosphere : TC ; an interactive open access journal of the European Geosciences Union}, number = {3}, publisher = {Copernicus}, address = {G{\"o}ttingen}, issn = {1994-0416}, doi = {10.5194/tc-5-727-2011}, pages = {727 -- 740}, year = {2011}, abstract = {We present a dynamic equilibrium simulation of the ice sheet-shelf system on Antarctica with the Potsdam Parallel Ice Sheet Model (PISM-PIK). The simulation is initialized with present-day conditions for bed topography and ice thickness and then run to steady state with constant present-day surface mass balance. Surface temperature and sub-shelf basal melt distribution are parameterized. Grounding lines and calving fronts are free to evolve, and their modeled equilibrium state is compared to observational data. A physically-motivated calving law based on horizontal spreading rates allows for realistic calving fronts for various types of shelves. Steady-state dynamics including surface velocity and ice flux are analyzed for whole Antarctica and the Ronne-Filchner and Ross ice shelf areas in particular. The results show that the different flow regimes in sheet and shelves, and the transition zone between them, are captured reasonably well, supporting the approach of superposition of SIA and SSA for the representation of fast motion of grounded ice. This approach also leads to a natural emergence of sliding-dominated flow in stream-like features in this new 3-D marine ice sheet model.}, language = {en} } @article{MariKielingNielsenetal.2011, author = {Mari, Andrea and Kieling, Konrad and Nielsen, B. Melholt and Polzik, E. S. and Eisert, Jens}, title = {Directly estimating nonclassicality}, series = {Physical review letters}, volume = {106}, journal = {Physical review letters}, number = {1}, publisher = {American Physical Society}, address = {College Park}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.106.010403}, pages = {4}, year = {2011}, abstract = {We establish a method of directly measuring and estimating nonclassicality-operationally defined in terms of the distinguishability of a given state from one with a positive Wigner function. It allows us to certify nonclassicality, based on possibly much fewer measurement settings than necessary for obtaining complete tomographic knowledge, and is at the same time equipped with a full certificate. We find that even from measuring two conjugate variables alone, one may infer the nonclassicality of quantum mechanical modes. This method also provides a practical tool to eventually certify such features in mechanical degrees of freedom in opto-mechanics. The proof of the result is based on Bochner's theorem characterizing classical and quantum characteristic functions and on semidefinite programming. In this joint theoretical-experimental work we present data from experimental optical Fock state preparation.}, language = {en} } @article{MannYoungFuuentesSchuller2011, author = {Mann, R. B. and Young, M. B. and Fu{\"u}ntes-Schuller, I.}, title = {A perturbative approach to inelastic collisions in a Bose-Einstein condensate}, series = {Journal of physics : B, Atomic, molecular and optical physics}, volume = {44}, journal = {Journal of physics : B, Atomic, molecular and optical physics}, number = {8}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {0953-4075}, doi = {10.1088/0953-4075/44/8/085301}, pages = {17}, year = {2011}, abstract = {It has recently been discovered that for certain rates of mode-exchange collisions analytic solutions can be found for a Hamiltonian describing the two-mode Bose-Einstein condensate. We proceed to study the behaviour of the system using perturbation theory if the coupling constants only approximately match these parameter constraints. We find that the model is robust to such perturbations. We study the effects of degeneracy on the perturbations and find that the induced changes differ greatly from the non-degenerate case. We also model inelastic collisions that result in particle loss or condensate decay as external perturbations and use this formalism to examine the effects of three-body recombination and background collisions.}, language = {en} } @article{MalicWeberRichteretal.2011, author = {Malic, E. and Weber, C. and Richter, M. and Atalla, V. and Klamroth, Tillmann and Saalfrank, Peter and Reich, Sebastian and Knorr, A.}, title = {Microscopic model of the optical absorption of carbon nanotubes functionalized with molecular spiropyran photoswitches}, series = {Physical review letters}, volume = {106}, journal = {Physical review letters}, number = {9}, publisher = {American Physical Society}, address = {College Park}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.106.097401}, pages = {4}, year = {2011}, abstract = {The adsorption of molecules to the surface of carbon nanostructures opens a new field of hybrid systems with distinct and controllable properties. We present a microscopic study of the optical absorption in carbon nanotubes functionalized with molecular spiropyran photoswitches. The switching process induces a change in the dipole moment leading to a significant coupling to the charge carriers in the nanotube. As a result, the absorption spectra of functionalized tubes reveal a considerable redshift of transition energies depending on the switching state of the spiropyran molecule. Our results suggest that carbon nanotubes are excellent substrates for the optical readout of spiropyran-based molecular switches. The gained insights can be applied to other noncovalently functionalized one-dimensional nanostructures in an externally induced dipole field.}, language = {en} } @article{MakhmudoMakhmudovTarkhanov2011, author = {Makhmudo, K. O. and Makhmudov, O. I. and Tarkhanov, Nikolai Nikolaevich}, title = {Equations of Maxwell type}, series = {Journal of mathematical analysis and applications}, volume = {378}, journal = {Journal of mathematical analysis and applications}, number = {1}, publisher = {Elsevier}, address = {San Diego}, issn = {0022-247X}, doi = {10.1016/j.jmaa.2011.01.012}, pages = {64 -- 75}, year = {2011}, abstract = {For an elliptic complex of first order differential operators on a smooth manifold X, we define a system of two equations which can be thought of as abstract Maxwell equations. The formal theory of this system proves to be very similar to that of classical Maxwell's equations. The paper focuses on boundary value problems for the abstract Maxwell equations, especially on the Cauchy problem.}, language = {en} } @article{LueckPikovskij2011, author = {Lueck, S. and Pikovskij, Arkadij}, title = {Dynamics of multi-frequency oscillator ensembles with resonant coupling}, series = {Modern physics letters : A, Particles and fields, gravitation, cosmology, nuclear physics}, volume = {375}, journal = {Modern physics letters : A, Particles and fields, gravitation, cosmology, nuclear physics}, number = {28-29}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0375-9601}, doi = {10.1016/j.physleta.2011.06.016}, pages = {2714 -- 2719}, year = {2011}, abstract = {We study dynamics of populations of resonantly coupled oscillators having different frequencies. Starting from the coupled van der Pol equations we derive the Kuramoto-type phase model for the situation, where the natural frequencies of two interacting subpopulations are in relation 2 : 1. Depending on the parameter of coupling, ensembles can demonstrate fully synchronous clusters, partial synchrony (only one subpopulation synchronizes), or asynchrony in both subpopulations. Theoretical description of the dynamics based on the Watanabe-Strogatz approach is developed.}, language = {en} }