11,056 research outputs found

    Nonequilibrium dynamical mean-field theory for bosonic lattice models

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    We develop the nonequilibrium extension of bosonic dynamical mean field theory (BDMFT) and a Nambu real-time strong-coupling perturbative impurity solver. In contrast to Gutzwiller mean-field theory and strong coupling perturbative approaches, nonequilibrium BDMFT captures not only dynamical transitions, but also damping and thermalization effects at finite temperature. We apply the formalism to quenches in the Bose-Hubbard model, starting both from the normal and Bose-condensed phases. Depending on the parameter regime, one observes qualitatively different dynamical properties, such as rapid thermalization, trapping in metastable superfluid or normal states, as well as long-lived or strongly damped amplitude oscillations. We summarize our results in non-equilibrium "phase diagrams" which map out the different dynamical regimes.Comment: 18 pages, 8 figure

    Influence of electromagnetic Field Damping on the Vibration Stability of soft mounted Induction Motors with Sleeve Bearings, based on a Multibody Model

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    The paper shows an analytical vibration model for stability analysis of soft mounted induction motors with sleeve bearings, especially focusing on the influence of electromagnetic field damping on the limit of  vibration stability. The model is a multibody model, considering the electromagnetic influence – including the electromagnetic field damping effect –, stiffness and internal material damping of the rotor structure, stiffness and damping of the bearing housings and end shields, stiffness and damping of the foundation elements and stiffness and damping of the oil film of the sleeve bearings. The aim of the paper is to unite all these influences in a model and to derive a procedure for calculating the limit of vibration stability, with considering the electromagnetic field damping effect. Additionally, a numerical example is presented, where the influence of electromagnetic field damping on the limit of vibration stability is shown, as well as the influence of the foundation elements and of the internal damping of the rotor. The procedure and  conclusions can also be adopted into finite-element analysis

    Glacier motion estimation using SAR offset-tracking procedures

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    Two image-to-image patch offset techniques for estimating feature motion between satellite synthetic aperture radar (SAR) images are discussed. Intensity tracking, based on patch intensity cross-correlation optimization, and coherence tracking, based on patch coherence optimization, are used to estimate the movement of glacier surfaces between two SAR images in both slant-range and azimuth direction. The accuracy and application range of the two methods are examined in the case of the surge of Monacobreen in Northern Svalbard between 1992 and 1996. Offset-tracking procedures of SAR images are an alternative to differential SAR interferometry for the estimation of glacier motion when differential SAR interferometry is limited by loss of coherence, i.e., in the case of rapid and incoherent flow and of large acquisition time intervals between the two SAR images. In addition, an offset-tracking procedure in the azimuth direction may be combined with differential SAR interferometry in the slant-range direction in order to retrieve a two-dimensional displacement map when SAR data of only one orbit configuration are available

    Electro-Disintegration of Tensor Polarized Deuterium

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    A tensor polarized target in Hall A at Jefferson Lab would offer the possibility to measure the D(e, e\u27p)n cross section for the Ms = 0 and the Ms = ±1 states separately (the quantization axis is along the momentum transfer). These data would serve as a new, stringent test of our current understanding of the deuteron structure for missing momenta up to 450 MeV/c, a region where the deuteron wave function is dominated by the D-state. No data exist to date for missing momenta above 150 MeV/c. The technique to separate these cross sections, possible kinematic settings, and a rough estimate of the achievable precision is presented

    X-SAR: The X-band synthetic aperture radar on board the Space Shuttle

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    The X-band synthetic aperture radar (X-SAR) is the German/Italian contribution to the NASA/JPL Shuttle Radar Lab missions as part of the preparation for the Earth Observation System (EOS) program. The Shuttle Radar Lab is a combination of several radars: an L-band (1.2 GHz) and a C-band (5.3 GHz) multipolarization SAR known as SIR-C (Shuttle Imaging Radar); and an X-band (9.6 GHz) vertically polarized SAR which will be operated synchronously over the same target areas to deliver calibrated multifrequency and multipolarization SAR data at multiple incidence angles from space. A joint German/Italian project office at DARA (German Space Agency) is responsible for the management of the X-SAR project. The space hardware has been developed and manufactured under industrial contract by Dornier and Alenia Spazio. Besides supporting all the technical and scientific tasks, DLR, in cooperation with ASI (Agencia Spaziale Italiano) is responsible for mission operation, calibration, and high precision SAR processing. In addition, DLR developed an airborne X-band SAR to support the experimenters with campaigns to prepare for the missions. The main advantage of adding a shorter wavelength (3 cm) radar to the SIR-C radars is the X-band radar's weaker penetration into vegetation and soil and its high sensitivity to surface roughness and associated phenomena. The performance of each of the three radars is comparable with respect to radiometric and geometric resolution
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