5,497 research outputs found
Disorder Effects in Fluctuating One-Dimensional Interacting Systems
The zero temperature localization of interacting electrons coupled to a
two-dimensional quenched random potential, and constrained to move on a
fluctuating one-dimensional string embedded in the disordered plane, is studied
using a perturbative renormalization group approach. In the reference frame of
the electrons the impurities are dynamical and their localizing effect is
expected to decrease. We consider several models for the string dynamics and
find that while the extent of the delocalized regime indeed grows with the
degree of string fluctuations, the critical interaction strength, which
determines the localization-delocalization transition for infinitesimal
disorder,does not change unless the fluctuations are softer than those of a
simple elastic string.Comment: 15 page
Mission Capabilities of Ion Engines. Phase II
Payloads and mission times were calculated for space vehicles propelled by ion rockets using nuclear power supplies having specific weights from 10 t o 50 lb/kw. Included in the study were five missions: low-altitude lunar satellite, low-altitude Venus satellite, solar probe, Saturn probe, and a Jupiter satellite with a circular orbit at the altitude of Jupiter's fourth moon. The variation of payload with the ration of power supply weight to gross weight was studied and the optimum power levels thereby determined. The ion rocket payload capabilities were compared with those of high-thrust vehicles using hydrogen-oxygen rockets and tungsten-core nuclear rockets; in addition the performance of high- and low-thrust systems staged in combination has been investigated. Launch vehicles considered in this study were the Atlas-Centaur, the Saturn C-1, and the Saturn C-5
Mission Capabilities of Ion Engines Using SNAP-8 Power Supplies
Mission performance capabilities of ion engines powered by the 30 kw and 60 kw SNAP-8 power supplies are compared for the following missions: a 24-hr equatorial satellite, a 100 n mi lunar satellite, a 500 n mi Mars satellite, a Mercury probe, and an out-of-the-ecliptic probe. The capabilities of arc- jet engines and chemical engines for the same missions are compared with those of the ion engines. The majority of the comparisons are for 8500-lb spacecraft which are boosted into a 300 n mi orbit by the Atlas-Centaur. Variations in initial orbit altitude, the use of actual launch dates rather than dates based on simplifying assumptions, and the combined use of chemical and electrical propulsion systems were also evaluated in terms of their effect on mission performance
The two-fluid model with superfluid entropy
The two-fluid model of liquid helium is generalized to the case that the
superfluid fraction has a small entropy content. We present theoretical
arguments in favour of such a small superfluid entropy. In the generalized
two-fluid model various sound modes of HeII are investigated. In a
superleak carrying a persistent current the superfluid entropy leads to a new
sound mode which we call sixth sound. The relation between the sixth sound and
the superfluid entropy is discussed in detail.Comment: 22 pages, latex, published in Nuovo Cimento 16 D (1994) 37
Spin flip lifetimes in superconducting atom chips: BCS versus Eliashberg theory
We investigate theoretically the magnetic spin-flip transitions of neutral
atoms trapped near a superconducting slab. Our calculations are based on a
quantum-theoretical treatment of electromagnetic radiation near dielectric and
metallic bodies. Specific results are given for rubidium atoms near a niobium
superconductor. At the low frequencies typical of the atomic transitions, we
find that BCS theory greatly overestimates coherence effects, which are much
less pronounced when quasiparticle lifetime effects are included through
Eliashberg theory. At 4.2 K, the typical atomic spin lifetime is found to be
larger than a thousand seconds, even for atom-superconductor distances of one
micrometer. This constitutes a large enhancement in comparison with normal
metals.Comment: 10 pages, 4 figure
Electroweak Radiative Corrections To Polarized M{\o}ller Scattering Asymmetries
One loop electroweak radiative corrections to left-right parity violating
M{\o}ller scattering () asymmetries are presented. They
reduce the standard model (tree level) prediction by 40 \% where the
main shift and uncertainty stem from hadronic vacuum polarization loops. A
similar reduction also occurs for the electron-electron atomic parity violating
interaction. That effect can be attributed to an increase of
by in running from to 0. The
sensitivity of the asymmetry to ``new physics'' is also discussed.Comment: 14 pages, Revtex, postscript file including figures is available at
ftp://ttpux2.physik.uni-karlsruhe.de/ttp95-14/ttp95-14.ps or via WWW at
http://ttpux2.physik.uni-karlsruhe.de/cgi-bin/preprints/ (129.13.102.139
On the origin of the decrease in the torsional oscillator period of solid He4
A decrease in the rotational period observed in torsional oscillator
measurements was recently taken as a possible indication of a supersolid state
of helium. We reexamine this interpretation and note that the decrease in the
rotation period is also consistent with a solidification of a small liquid-like
component into a low-temperature glass. Such a solidification may occur by a
low-temperature quench of topological defects (e.g., grain boundaries or
dislocations) which we examined in an earlier work. The low-temperature glass
can account for not only a monotonic decrease in the rotation period as the
temperature is lowered but also explains the peak in the dissipation occurring
near the transition point. Unlike the non-classical rotational inertia
scenario, which depends on the supersolid fraction, the dependence of the
rotational period on external parameters, e.g., the oscillator velocity,
provides an alternate interpretation of the oscillator experiments. Future
experiments might explore this effect.Comment: 10 pages, 3 figures; to appear in Phys. Rev.
Body-assisted van der Waals interaction between two atoms
Using fourth-order perturbation theory, a general formula for the van der
Waals potential of two neutral, unpolarized, ground-state atoms in the presence
of an arbitrary arrangement of dispersing and absorbing magnetodielectric
bodies is derived. The theory is applied to two atoms in bulk material and in
front of a planar multilayer system, with special emphasis on the cases of a
perfectly reflecting plate and a semi-infinite half space. It is demonstrated
that the enhancement and reduction of the two-atom interaction due to the
presence of a perfectly reflecting plate can be understood, at least in the
nonretarded limit, by using the method of image charges. For the semi-infinite
half space, both analytical and numerical results are presented.Comment: 17 pages, 9 figure
London relation and fluxoid quantization for monopole currents in U(1) lattice gauge theory
We explore the analogy between quark confinement and the Meissner effect in
superconductors. We measure the response of color-magnetic "supercurrents" from
Dirac magnetic monopoles to the presence of a static quark-antiquark pair in
four dimensional U(1) lattice gauge theory. Our results indicate that in the
confined phase these currents screen the color-electric flux due to the quarks
in an electric analogy of the Meisner effect. We show that U(1) lattice guage
theory obeys both a dual London equation and an electric fluxoid quantization
condition.Comment: LSUHEP-1-92 May 1992, 13 page
Nonequilibrium orbital magnetization of strongly localized electrons
The magnetic response of strongly localized electrons to a time-dependent
vector potential is considered. The orbital magnetic moment of the system, away
from steady-state conditions, is obtained. The expression involves the
tunneling and phonon-assisted hopping currents between localized states. The
frequency and temperature dependence of the orbital magnetization is analyzed
as function of the admittances connecting localized levels. It is shown that
quantum interference of the localized wave functions contributes to the moment
a term which follows adiabatically the time-dependent perturbation.Comment: RevTeX 3.
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