7,386 research outputs found
Generation Efficiencies for Propagating Modes in a Supersolid
Using Andreev and Lifshitz's supersolid hydrodynamics, we obtain the
propagating longitudinal modes at non-zero applied pressure (necessary
for solid 4He), and their generation efficiencies by heaters and transducers.
For small , a solid develops an internal pressure . This
theory has stress contributions both from the lattice and an internal pressure
. Because both types of stress are included, the normal mode analysis
differs from previous works. Not surprisingly, transducers are significantly
more efficient at producing elastic waves and heaters are significantly more
efficient at producing fourth sound waves. We take the system to be isotropic,
which should apply to systems that are glassy or consist of many crystallites;
the results should also apply, at least qualitatively, to single-crystal hcp
4He.Comment: 10 pages. Accepted by Physical Review
Thermal Equilibration and Thermally-Induced Spin Currents in a Thin-Film Ferromagnet on a Substrate
Recent spin-Seebeck experiments on thin ferromagnetic films apply a
temperature difference along the length and measure a
(transverse) voltage difference along the width . The
connection between these effects is complex, involving: (1) thermal
equilibration between sample and substrate; (2) spin currents along the height
(or thickness) ; and (3) the measured voltage difference. The present work
studies in detail the first of these steps, and outlines the other two steps.
Thermal equilibration processes between the magnons and phonons in the sample,
as well as between the sample and the substrate leads to two surface modes,
with surface lengths , to provide for thermal equilibration.
Increasing the coupling between the two modes increases the longer mode length
and decreases the shorter mode length. The applied thermal gradient along
leads to a thermal gradient along that varies as ,
which can in turn produce fluxes of the carriers of up- and down- spins along
, and gradients of their associated \textit{magnetoelectrochemical
potentials} , which vary as
. By the inverse spin Hall effect, this spin current along
can produce a transverse (along ) voltage difference , which
also varies as .Comment: 14 pages, 7 figures, 1 tabl
Andreev-Lifshitz Hydrodynamics Applied to an Ordinary Solid under Pressure
We have applied the Andreev-Lifshitz hydrodynamic theory of supersolids to an
ordinary solid. This theory includes an internal pressure , distinct from
the applied pressure and the stress tensor . Under uniform
static , we have . For , Maxwell relations imply that . The theory also permits
vacancy diffusion but treats vacancies as conserved. It gives three sets of
propagating elastic modes; it also gives two diffusive modes, one largely of
entropy density and one largely of vacancy density (or, more generally, defect
density). For the vacancy diffusion mode (or, equivalently, the lattice
diffusion mode) the vacancies behave like a fluid within the solid, with the
deviations of internal pressure associated with density changes nearly
canceling the deviations of stress associated with strain. We briefly consider
pressurization experiments in solid He at low temperatures in light of this
lattice diffusion mode, which for small has diffusion constant . The general principles of the theory -- that both volume and
strain should be included as thermodynamic variables, with the result that both
and appear -- should apply to all solids under pressure,
especially near the solid-liquid transition. The lattice diffusion mode
provides an additional degree of freedom that may permit surfaces with
different surface treatments to generate different responses in the bulk.Comment: 10 pages. Accepted by Physical Review
Effect of substrate surface topography on forensic development of latent fingerprints with iron oxide powder suspension
This is a pre-print version of the article. The official published version can be accessed from the link below - Copyright @ 2010 Wiley-BlackwellLatent fingerprint deposition and effectiveness of detection are strongly affected by the surface on which prints are deposited. Material properties, surface roughness, morphology, chemistry and hydrophobicity can affect the usefulness or efficacy of forensic print development techniques. Established protocols outline appropriate techniques and sequences of processes for broad categories of operational surfaces. This study uses atomic force microscopy and scanning electron microscopy to investigate a series of surfaces classified as smooth, non-porous plastic. Latent prints developed with iron oxide powder suspension are analysed on a range of scales from macro to nano to help elucidate the interaction mechanisms between the latent fingerprint, development agent and underlying surface. Differences between surfaces have a strong effect, even within this single category. We show that both average roughness and topographical feature shape, characterised by skew, kurtosis and lay, are important factors to consider for the processing of latent fingerprints. Copyright (C) 2010 John Wiley & Sons, Ltd.This work is part-funded by the UK Home Office project 7088762
Andreev-Lifshitz Supersolid Hydrodynamics Including the Diffusive Mode
We have re-examined the Andreev-Lifshitz theory of supersolids. This theory
implicitly neglects uniform bulk processes that change the vacancy number, and
assumes an internal pressure in addition to lattice stress .
Each of and takes up a part of an external, or applied,
pressure (necessary for solid 4He). The theory gives four pairs of
propagating elastic modes, of which one pair corresponds to a fourth-sound
mode, and a single diffusive mode, which has not been analyzed previously. The
diffusive mode has three distinct velocities, with the superfluid velocity much
larger than the normal fluid velocity, which in turn is much larger than the
lattice velocity. The mode structure depends on the relative values of certain
kinetic coefficients and thermodynamic derivatives. We consider pressurization
experiments in solid 4He at low temperatures in light of this diffusion mode
and a previous analysis of modes in a normal solid with no superfluid
component.Comment: 8 pages. Accepted by Physical Review
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