131,527 research outputs found
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
The nuclear effects in the spin-dependent structure functions and
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,
, 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
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