3,777 research outputs found

    Vortex state and dynamics of a d-wave superconductor: Finite-element analysis

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    The finite-element method is extended to simulate the d-wave time-dependent Ginzburg-Landau equations. By utilizing this method and in the context of the (s+d)-wave pairing, we discuss the nature of a single vortex, the structure of equilibrium vortex lattices in bulk samples, the nature of vortices in finite-size samples, and most importantly the transport of the vortices. In particular, the low-field free-flux-flow resistivity turns out to obey the law of corresponding states discovered in conventional superconductors, while the high-field resistivity reveals a noticeable effect of the s-wave coupling on lifting the effective upper critical field. The flux flow near and above the depinning current in the presence of a twin boundary or random impurities also assumes a conventional behavior: The current dependence of the flux-flow resistivity can be well described by an overdamped model for a particle subject to driving and pinning forces. However, our results show a noticeable difference between the flux-flow resistivities at large currents in the presence and absence of pinning.published_or_final_versio

    Vortex flow in a two-component unconventional superconductor

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    Using a time-dependent two-component Ginzburg-Landau theory, we have studied the flow resistivity of vortices in the time-reversal-symmetry-breaking (T-breaking) phases of unconventional superconductors. The free vortex flow resistivity is found to be generally nonlinear against the magnetic field. The relevance of these results in explaining a recent experiment by Wu et al. is addressed.published_or_final_versio

    Resistive behavior of high-Tc superconductors with a logarithmiclike pinning potential

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    The flux motion in a superconductor with a periodic logarithmiclike bare pinning potential is investigated. The effective barrier UJ(J) is derived and is shown to bear close resemblance with the related experimental results. The details of the pinning potential profile turn out to have significant influences on the functional form of the effective barrier. The linear response of the superconductor under a small current is analyzed and a slightly new formula is derived for resistivity in the thermally activated flux flow regimes. The distinct regimes for flux creep and flux flow and the crossover in between are treated simultaneously, and the familiar power-law behavior is demonstrated and is further confirmed by examining the dln E/dJ versus H relation. Satisfactory agreement is found between our results and related experimental observations. The experimentally observed field-dependent resistance broadening effect is also reproduced in this model. © 1994 The American Physical Society.published_or_final_versio

    Finite-temperature Gutzwiller projection for strongly correlated electron systems

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    We generalized the Gutzwiller projectional variational method for the ground state of strongly correlated electron systems to the case of finite temperature. Under the Gutzwiller approximation, we show that this maps to a finite temperature renormalized mean-field theory. As one of the key ingredients in the theory, we obtained an explicit expression of the projection entropy or the entropy change due to the projection. We illustrate the application of the theory to the Anderson impurity problem and the half-filled Hubbard model and compare the theory to more elaborate techniques. We find qualitative agreement. The theory can be applied to a wide variety of Hubbard, t-J, and Anderson impurity models. © 2010 The American Physical Society.published_or_final_versio

    Hole dispersions in the G- and C-type orbital ordering backgrounds: Doped manganese oxides

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    In the framework of the linear spin-wave theory and orbital-charge separation, we calculate quasiparticle (QP) dispersions for two different antiferromagnetic orbital structures in the fully saturated spin phase of manganese oxides. Although with the same orbital wave excitations, the QP bands of C- and G-type orbital structures exhibit completely different shapes. The pseudogap observed in the density of states and spectral functions around ω=0 is related with the large antiferromagnetic orbital fluctuation. The minimal band energy for G-type is lower than that for C-type orbital order, while these band curves almost coincide in some momentum points. Larger energy splitting occurs between the two branches of k z=0 and k z=π when increasing the superexchange coupling J, suggesting that the orbital scattering plays an essential role in the QP dispersions. ©2000 The American Physical Society.published_or_final_versio

    Orbital ordering and two ferromagnetic phases in low-doped La 1-xSr xMnO 3

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    We present a theory for the transition between two ferromagnetic phases observed experimentally in lightly doped La 1-xSr xMnO 3. Starting from an electronic model, the instabilities to various types of orbital orderings are studied within the random-phase approximation. In most cases, the instabilities occur in the region of strong correlations. A phase diagram is calculated in the case of strong correlation by means of the projected perturbation technique and the Schwinger boson technique. A phase transition between two types of orbital ordering occurs at a low doping, which may be closely relevant to recent experimental observations.published_or_final_versio

    A new adaptive interpolation algorithm for 3D ultrasound imaging with speckle reduction and edge preservation

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    Author name used in this publication: Qinghua HuangAuthor name used in this publication: Yongping ZhengAuthor name used in this publication: Minhua Lu2008-2009 > Academic research: refereed > Publication in refereed journalAccepted ManuscriptPublishe

    An optical coherence tomography (OCT)-based air jet indentation system for measuring the mechanical properties of soft tissues

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    2008-2009 > Academic research: refereed > Publication in refereed journalAccepted ManuscriptPublishe

    Superpixel-based Two-view Deterministic Fitting for Multiple-structure Data

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    This paper proposes a two-view deterministic geometric model fitting method, termed Superpixel-based Deterministic Fitting (SDF), for multiple-structure data. SDF starts from superpixel segmentation, which effectively captures prior information of feature appearances. The feature appearances are beneficial to reduce the computational complexity for deterministic fitting methods. SDF also includes two original elements, i.e., a deterministic sampling algorithm and a novel model selection algorithm. The two algorithms are tightly coupled to boost the performance of SDF in both speed and accuracy. Specifically, the proposed sampling algorithm leverages the grouping cues of superpixels to generate reliable and consistent hypotheses. The proposed model selection algorithm further makes use of desirable properties of the generated hypotheses, to improve the conventional fit-and-remove framework for more efficient and effective performance. The key characteristic of SDF is that it can efficiently and deterministically estimate the parameters of model instances in multi-structure data. Experimental results demonstrate that the proposed SDF shows superiority over several state-of-the-art fitting methods for real images with single-structure and multiple-structure data.Comment: Accepted by European Conference on Computer Vision (ECCV