2,082 research outputs found
Onset of Delocalization in Quasi-1D Waveguides with Correlated Surface Disorder
We present first analytical results on transport properties of many-mode
waveguides with rough surfaces having long-range correlations. We show that
propagation of waves through such waveguides reveals a quite unexpected
phenomena of a complete transparency for a subset of propagating modes. These
modes do not interact with each other and effectively can be described by the
theory of 1D transport with correlated disorder. We also found that with a
proper choice of model parameters one can arrange a perfect transparency of
waveguides inside a given window of energy of incoming waves. The results may
be important in view of experimental realizations of a selective transport in
application to both waveguides and electron/optic nanodevices.Comment: RevTex, 4 pages, no figures, few references are adde
Manifestation of the Roughness-Square-Gradient Scattering in Surface-Corrugated Waveguides
We study a new mechanism of wave/electron scattering in multi-mode
surface-corrugated waveguides/wires. This mechanism is due to specific
square-gradient terms in an effective Hamiltonian describing the surface
scattering, that were neglected in all previous studies. With a careful
analysis of the role of roughness slopes in a surface profile, we show that
these terms strongly contribute to the expression for the inverse attenuation
length (mean free path), provided the correlation length of corrugations is
relatively small. The analytical results are illustrated by numerical data.Comment: 13 pages, 3 figure
Gradient and Amplitude Scattering in Surface-Corrugated Waveguides
We investigate the interplay between amplitude and square-gradient scattering
from the rough surfaces in multi-mode waveguides (conducting quantum wires).
The main result is that for any (even small in height) roughness the
square-gradient terms in the expression for the wave scattering length
(electron mean free path) are dominant, provided the correlation length of the
surface disorder is small enough. This important effect is missed in existing
studies of the surface scattering.Comment: 4 pages, one figur
Eigenvalue Problem for the Second Order Differential Equation with Nonlocal
The paper deals with numerical methods for eigenvalue problem for the second order ordinary differential operator with variable coefficient subject to nonlocal integral condition. FD-method (functional-discrete method) is derived and analyzed for calculating of eigenvalues, particulary complex eigenvalues. The convergence of FD-method is proved. Finally numerical procedures are suggested and computational results are schown
Astrometric Effects of a Stochastic Gravitational Wave Background
A stochastic gravitational wave background causes the apparent positions of
distant sources to fluctuate, with angular deflections of order the
characteristic strain amplitude of the gravitational waves. These fluctuations
may be detectable with high precision astrometry, as first suggested by
Braginsky et al. in 1990. Several researchers have made order of magnitude
estimates of the upper limits obtainable on the gravitational wave spectrum
\Omega_gw(f), at frequencies of order f ~ 1 yr^-1, both for the future
space-based optical interferometry missions GAIA and SIM, and for VLBI
interferometry in radio wavelengths with the SKA. For GAIA, tracking N ~ 10^6
quasars over a time of T ~ 1 yr with an angular accuracy of \Delta \theta ~ 10
\mu as would yield a sensitivity level of \Omega_gw ~ (\Delta \theta)^2/(N T^2
H_0^2) ~ 10^-6, which would be comparable with pulsar timing. In this paper we
take a first step toward firming up these estimates by computing in detail the
statistical properties of the angular deflections caused by a stochastic
background. We compute analytically the two point correlation function of the
deflections on the sphere, and the spectrum as a function of frequency and
angular scale. The fluctuations are concentrated at low frequencies (for a
scale invariant stochastic background), and at large angular scales, starting
with the quadrupole. The magnetic-type and electric-type pieces of the
fluctuations have equal amounts of power.Comment: 23 pages, 2 figures, references added and minor text correction
Transition from Knudsen to molecular diffusion in activity of absorbing irregular interfaces
We investigate through molecular dynamics the transition from Knudsen to
molecular diffusion transport towards 2d absorbing interfaces with irregular
geometry. Our results indicate that the length of the active zone decreases
continuously with density from the Knudsen to the molecular diffusion regime.
In the limit where molecular diffusion dominates, we find that this length
approaches a constant value of the order of the system size, in agreement with
theoretical predictions for Laplacian transport in irregular geometries.
Finally, we show that all these features can be qualitatively described in
terms of a simple random-walk model of the diffusion process.Comment: 4 pages, 4 figure
Calculating loops without loop calculations: NLO computation of pentaquark correlators
We compute next-to-leading order (NLO) perturbative QCD corrections to the
correlators of interpolating pentaquark currents. We employ modular techniques
in configuration space which saves us from the onus of having to do loop
calculations. The modular technique is explained in some detail. We present
explicit NLO results for several interpolating pentaquark currents that have
been written down in the literature. Our modular approach is easily adapted to
the case of NLO corrections to multiquark correlators with an arbitrary number
of quarks/antiquarks.Comment: 23 pages, 1 figure, published version. arXiv admin note: text overlap
with arXiv:hep-lat/031001
Wind regime peculiarities in the lower thermosphere in the winter of 1983/84
Temporal variations of prevailing winds at 90 to 100 km obtained from measurements carried out in winter 1983 to 1984 at three sites in the USSR and two sites in East Germany are reported. These variations are compared with those of the thermal stratospheric regime. Measurements were carried out using the drifts D2 method (meteor wind radar) and the D1 method (ionospheric drifts). Temporal variations of zonal and meridional prevailing wind components for all the sites are given. Also presented are zonal wind data obtained using the partial reflection wind radar. Wind velocity values were obtained by averaging data recorded at between 105 and 91 km altitude. Wind velocity data averaged in such a way can be related to about the same height interval to which the data obtained by the meteor radar and ionospheric methods at other sites, i.e., the mean height of the meteor zone (about 95 km). The results presented show that there are significant fluctuations about the seasonal course of both zonal and meridional prevailing winds
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