The vortex dynamics of a Ginzburg-Landau system under pinning effect

It is proved that the vortices are attracted by impurities or inhomogeities in the superconducting materials. The strong H^1-convergence for the corresponding Ginzburg-Landau system is also proved.Comment: 23page

Signal enhancement of the in-plane and out-of-plane Rayleigh wave components

Several groups have reported an enhancement of the ultrasonic Rayleigh wave when scanning close to a surface-breaking defect in a metal sample. This enhancement may be explained as an interference effect where the waves passing directly between source and receiver interfere with those waves reflected back from the defect. We present finite element models of the predicted enhancement when approaching a defect, along with experiments performed using electromagnetic acoustic transducers sensitive to either in-plane or out-of-plane motion. A larger enhancement of the in-plane motion than the out-of-plane motion is observed and can be explained by considering ultrasonic reflections and mode conversion at the defect

Nonequilibrium Green's function approach to mesoscopic thermal transport

We present a formulation of a nonequilibrium Green's function method for thermal current in nanojunction atomic systems with nonlinear interactions. This first-principle approach is applied to the calculation of the thermal conductance in carbon nanotube junctions. It is shown that nonlinearity already becomes important at low temperatures. Nonlinear interactions greatly suppress phonon transmission at room temperature. The peak of thermal conductance is found to be around 400K, in good agreement with experiments. High-order phonon scattering processes are important for diffusive heat transport.Comment: 4 pages, 4 figure

Oscillatory Magneto-Thermopower and Resonant Phonon Drag in a High-Mobility 2D Electron Gas

Experimental and theoretical evidence is presented for new low-magnetic-field ($B<5$ kG) 1/B-oscillations in the thermoelectric power of a high-mobility GaAs/AlGaAs two-dimensional (2D) electron gas. The oscillations result from inter-Landau-Level resonances of acoustic phonons carrying a momentum equal to twice the Fermi wavenumber at $B = 0$. Numerical calculations show that both 3D and 2D phonons can contribute to this effect.Comment: 4 pages, 5 figure

Shear wave generation using a spiral electromagnetic acoustic transducer

A spiral electromagnetic acoustic transducer (EMAT) is efficient in eddy current generation and has been used for surface defect inspection using Rayleigh waves or thickness gauging based on plane waves in echo mode. Measured and calculated particle velocities and directivities are presented. It is found that the shear wave is not predominantly a plane wave. It has zero amplitude on the axis of the generation EMAT and has maximum amplitude at the critical angle. The shear wave could be used in the steel industry for both internal and surface defect inspections together with Rayleigh wave

Weakly nonlinear quantum transport: an exactly solvable model

We have studied the weakly non-linear quantum transport properties of a two-dimensional quantum wire which can be solved exactly. The non-linear transport coefficients have been calculated and interesting physical properties revealed. In particular we found that as the incoming electron energy approaches a resonant point given by energy $E=E_r$, where the transport is characterized by a complete reflection, the second order non-linear conductance changes its sign. This has interesting implications to the current-voltage characteristics. We have also investigated the establishment of the gauge invariance condition. We found that for systems with a finite scattering region, correction terms to the theoretical formalism are needed to preserve the gauge invariance. These corrections were derived analytically for this model.Comment: 15 pages, LaTeX, submitted to Phys. Rev.

Spins of the supermassive black hole in M87: new constraints from TeV observations

The rapid TeV $\gamma-$ray variability detected in the well-known nearby radio galaxy M87 implies an extremely compact emission region (5-10 Schwarzschild radii) near the horizon of the supermassive black hole in the galactic center. TeV photons are affected by dilution due to interaction with the radiation field of the advection-dominated accretion flow (ADAF) around the black hole, and can thus be used to probe the innermost regions around the black hole. We calculate the optical depth of the ADAF radiation field to the TeV photons and find it strongly depends on the spin of the black hole. We find that transparent radii of 10 TeV photons are of $5R_{\rm S}$ and $13R_{\rm S}$ for the maximally rotating and non-rotating black holes, respectively. With the observations, the calculated transparent radii strongly suggest the black hole is spinning fast in the galaxy. TeV photons could be used as a powerful diagnostic for estimating black hole spins in galaxies in the future.Comment: 4 pages, 4 figures. to appear in ApJ

Quantum Electronic Transport through a Precessing Spin

The conductance through a local nuclear spin precessing in a magnetic field is studied by using the equations-of-motion approach. The characteristics of the conductance is determined by the tunneling matrix and the position of equilibrium chemical potential. We find that the spin flip coupling between the electrons on the spin site and the leads produces the conductance oscillation. When the spin is precessing in the magnetic field at Larmor frequency ($\omega_{L}$), the conductance develops the oscillation with the frequency of both $\omega_{L}$ and 2$\omega_{L}$ components, the relative spectrum weight of which can be tuned by the chemical potential and the spin flip coupling.Comment: 5 pages, 3 figure

Isospin dependence of pseudospin symmetry in nuclear resonant states

The relativistic mean field theory in combination with the analytic continuation in the coupling constant method is used to determine the energies and widths of single-particle resonant states in Sn isotopes. It is shown that there exists clear shell structure in the resonant levels as appearing in the bound levels. In particular, the isospin dependence of pseudospin symmetry is clearly shown in the resonant states, is consistent with that in the bound states, where the splittings of energies and widths between pseudospin doublets are found in correlation with the quantum numbers of single-particle states, as well as the nuclear mass number. The similar phenomenon also emerges in the spin partners.Comment: 7 pages, 6 figure