8,654 research outputs found
Predicted electric field near small superconducting ellipsoids
We predict the existence of large electric fields near the surface of
superconducting bodies of ellipsoidal shape of dimensions comparable to the
penetration depth. The electric field is quadrupolar in nature with significant
corrections from higher order multipoles. Prolate (oblate) superconducting
ellipsoids are predicted to exhibit fields consistent with negative (positive)
quadrupole moments, reflecting the fundamental charge asymmetry of matter.Comment: To be published in Phys.Rev.Let
Electrodynamics of superconductors
An alternate set of equations to describe the electrodynamics of
superconductors at a macroscopic level is proposed. These equations resemble
equations originally proposed by the London brothers but later discarded by
them. Unlike the conventional London equations the alternate equations are
relativistically covariant, and they can be understood as arising from the
'rigidity' of the superfluid wave function in a relativistically covariant
microscopic theory. They predict that an internal 'spontaneous' electric field
exists in superconductors, and that externally applied electric fields, both
longitudinal and transverse, are screened over a London penetration length, as
magnetic fields are. The associated longitudinal dielectric function predicts a
much steeper plasmon dispersion relation than the conventional theory, and a
blue shift of the minimum plasmon frequency for small samples. It is argued
that the conventional London equations lead to difficulties that are removed in
the present theory, and that the proposed equations do not contradict any known
experimental facts. Experimental tests are discussed.Comment: Small changes following referee's and editor's comments; to be
published in Phys.Rev.
New Physics Signals through CP Violation in B -> rho,pi
We describe here a method for detecting physics beyond the standard model via
CP violation in B->rho,pi decays. Using a Dalitz-plot analysis to obtain alpha,
along with an analytical extraction of the various tree (T) and penguin (P)
amplitudes, we obtain a criterion for the absence of new physics (NP). This
criterion involves the comparison of the measured |P/T| ratio with its value as
predicted by QCD factorization. We show that the detection of NP via this
method has a good efficiency when compared with the corresponding technique
using B->pi,pi decays.Comment: 8 pages, 4 figures, talk given at MRST 2004: From Quarks to
Cosmology, Concordia University, Montreal, May 200
Voltage from mechanical stress in type-II superconductors: Depinning of the magnetic flux by moving dislocations
Mechanical stress causes motion of defects in solids. We show that in a
type-II superconductor a moving dislocation generates a pattern of current that
exerts the depinning force on the surrounding vortex lattice. Concentration of
dislocations and the mechanical stress needed to produce critical depinning
currents are shown to be within practical range. When external magnetic field
and transport current are present this effect generates voltage across the
superconductor. Thus a superconductor can serve as an electrical sensor of the
mechanical stress.Comment: 3 pages, 1 figure
Spin currents in superconductors
It is argued that experiments on rotating superconductors provide evidence
for the existence of macroscopic spin currents in superconductors in the
absence of applied external fields. Furthermore it is shown that the model of
hole superconductivity predicts the existence of such currents in all
superconductors. In addition it is pointed out that spin currents are required
within a related macroscopic (London-like) electrodynamic description of
superconductors recently proposed. The spin current arises through an intrinsic
spin Hall effect when negative charge is expelled from the interior of the
metal upon the transition to the superconducting state
Geothermal reservoir engineering research
The Stanford University research program on the study of stimulation and reservoir engineering of geothermal resources commenced as an interdisciplinary program in September, 1972. The broad objectives of this program have been: (1) the development of experimental and computational data to evaluate the optimum performance of fracture-stimulated geothermal reservoirs; (2) the development of a geothermal reservoir model to evaluate important thermophysical, hydrodynamic, and chemical parameters based on fluid-energy-volume balances as part of standard reservoir engineering practice; and (3) the construction of a laboratory model of an explosion-produced chimney to obtain experimental data on the processes of in-place boiling, moving flash fronts, and two-phase flow in porous and fractured hydrothermal reservoirs
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
Symmetry of paraspinal muscle denervation in clinical lumbar spinal stenosis: Support for a hypothesis of posterior primary ramus stretching?
Introduction Denervation of the paraspinal muscles in spinal disorders is frequently attributed to radiculopathy. Therefore, patients with lumbar spinal stenosis causing asymmetrical symptoms should have asymmetrical paraspinal denervation. Methods Seventy‐three patients with clinical lumbar spinal stenosis, aged 55–85 years, completed a pain drawing and underwent masked electrodiagnostic testing, including bilateral paraspinal mapping and testing of 6 muscles on the most symptomatic (or randomly chosen) limb. Results With the exception of 10 subjects with unilateral thigh pain ( P = 0.043), there was no relationship between side of pain and paraspinal mapping score for any subgroups (symmetrical pain, pain into 1 calf only). Among those with positive limb EMG (tested on 1 side), no relationship between side of pain and paraspinal EMG score was found. Conclusion Evidence suggests that paraspinal denervation in spinal stenosis may not be due to radiculopathy, but rather due to stretch or damage to the posterior primary ramus. Muscle Nerve , 48: 198–203, 2013Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/99085/1/mus23750.pd
Exploring CP Violation with B_d -> D K_s Decays
We (re)examine CP violation in the decays B_d -> D K_s, where D represents
D^0, D(bar), or one of their excited states. The quantity can be extracted from the time-dependent rates for and , where the decays to
. If one considers a non-CP-eigenstate hadronic final state to
which both D(bar) and D^0 can decay (e.g. ), then one can obtain two
of the angles of the unitarity triangle from measurements of the time-dependent
rates for and .
There are no penguin contributions to these decays, so all measurements are
theoretically clean.Comment: 15 pages, LaTeX, no figure
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