What are the left-handed media and what is interesting about them?

We review the intensively discussed ideas about wave propagation and refraction in media where both electric permittivity and magnetic permeability are negative. The criticism against negative refraction as violating the causality principle is considered. Starting from the initial wave equations, refraction of beams at the boundary of a left-handed medium is analyzed. The physics of a perfect lens formed by a flat layer of a left-handed material is considered.Comment: 21 pages, 8 figure

Dielectric behavior of oblate spheroidal particles: Application to erythrocytes suspensions

We have investigated the effect of particle shape on the eletrorotation (ER) spectrum of living cells suspensions. In particular, we consider coated oblate spheroidal particles and present a theoretical study of ER based on the spectral representation theory. Analytic expressions for the characteristic frequency as well as the dispersion strength can be obtained, thus simplifying the fitting of experimental data on oblate spheroidal cells that abound in the literature. From the theoretical analysis, we find that the cell shape, coating as well as material parameters can change the ER spectrum. We demonstrate good agreement between our theoretical predictions and experimental data on human erthrocytes suspensions.Comment: RevTex; 5 eps figure

Many-body dipole-induced dipole model for electrorheological fluids

Theoretical investigations on electrorheological (ER) fluids usually rely on computer simulations. An initial approach for these studies would be the point-dipole (PD) approximation, which is known to err considerably when the particles approach and finally touch due to many-body and multipolar interactions. Thus various work attempted to go beyond the PD model. Being beyond the PD model, previous attempts have been restricted to either local-field effects only or multipolar effects only, but not both. For instance, we recently proposed a dipole-induced-dipole (DID) model which is shown to be both more accurate than the PD model and easy to use. This work is necessary because the many-body (local-field) effect is included to put forth the many-body DID model. The results show that the multipolar interactions can indeed be dominant over the dipole interaction, while the local-field effect may yield an important correction.Comment: RevTeX, 3 eps figure

Nonlinear ac responses of electro-magnetorheological fluids

We apply a Langevin model to investigate the nonlinear ac responses of electro-magnetorheological (ERMR) fluids under the application of two crossed dc magnetic (z axis) and electric (x axis) fields and a probing ac sinusoidal magnetic field. We focus on the influence of the magnetic fields which can yield nonlinear behaviors inside the system due to the particles with a permanent magnetic dipole moment. Based on a perturbation approach, we extract the harmonics of the magnetic field and orientational magnetization analytically. To this end, we find that the harmonics are sensitive to the degree of anisotropy of the structure as well as the field frequency. Thus, it is possible to real-time monitor the structure transformation of ERMR fluids by detecting the nonlinear ac responses.Comment: 21 pages, 4 figure

Depairing currents in superconducting films of Nb and amorphous MoGe

We report on measuring the depairing current J_{dp} in thin superconducting films as a function of temperature. The main difficulties in such measurements are that heating has to be avoided, either due to contacts, or to vortex flow. The latter is almost unavoidable since the sample cross-section is usually larger than the superconducting coherence length \xi_s and the magnetic field penetration depth \lambda_s. On the other hand, vortex flow is helpful since it homogenizes the distribution of the current across the sample. We used a pulsed current method, which allows to overcome the difficulties caused by dissipation and measured the depairing current in films of thin polycrystalline Nb (low \lambda_s, low specific resistance \rho) and amorphous Mo_{0.7}Ge_{0.3} (high \lambda_s, high \rho), structured in the shape of bridges of various width. The experimental values of J_{dp} for different bridge dimensions are compared with theoretical predictions by Kupriyanov and Lukichev for dirty limit superconductors. For the smallest samples we find a very good agreement with theory, over essentially the whole temperature interval below the superconducting critical temperature.Comment: 5 pages, 6 figure

Supercurrent fluctuations in short filaments

We evaluate the average and the standard deviation of the supercurrent in superconducting nanobridges, as functions of the temperature and the phase difference, in an equilibrium situation. We also evaluate the autocorrelation of the supercurrent as a function of the elapsed time. The behavior of supercurrent fluctuations is qualitatively different from from that of the normal current: they depend on the phase difference, have a different temperature dependence, and for appropriate range their standard deviation is independent of the probing time. We considered two radically different filaments and obtained very similar results for both. Fluctuations of the supercurrent can in principle be measured

The Deuteron Spin Structure Functions in the Bethe-Salpeter Approach and the Extraction of the Neutron Structure Function g1n(x)g_1^n(x)

The nuclear effects in the spin-dependent structure functions $g_1^D$ and $b_2^D$ are calculated in the relativistic approach based on the Bethe-Salpeter equation with a realistic meson-exchange potential. The results of calculations are compared with the non-relativistic calculations. The problem of extraction of the neutron spin structure function, $g_1^n$, from the deuteron data is discussed.Comment: (Talk given at the SPIN'94 International Symposium, September 15-22, 1994, Bloomington, Indiana), 6 pages, 5 figures, Preprint Alberta Thy 29-9