5,469 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
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
National Transonic Facility: A review of the operational plan
The proposed National Transonic Facility (NTF) operational plan is reviewed. The NTF will provide an aerodynamic test capability significantly exceeding that of other transonic regime wind tunnels now available. A limited number of academic research program that might use the NTF are suggested. It is concluded that the NTF operational plan is useful for management, technical, instrumentation, and model building techniques available in the specialized field of aerodynamic analysis and simulation. It is also suggested that NASA hold an annual conference to discuss wind tunnel research results and to report on developments that will further improve the utilization and cost effectiveness of the NTF and other wind tunnels
The masked cognate translation priming effect for different-script bilinguals is modulated by the phonological similarity of cognate words: Further support for the phonological account
The effect of phonological similarity on L1-L2 cognate translation priming was examined with Japanese-English bilinguals. According to the phonological account, the cognate priming effect for different-script bilinguals consists of additive effects of phonological and conceptual facilitation. If true, then the size of the cognate priming effect would be directly influenced by the phonological similarity of cognate translation equivalents. The present experiment tested and confirmed this prediction: the cognate priming effect was significantly larger for cognate prime-target pairs with high-phonological similarity than pairs with low-phonological similarity. Implications for the nature of lexical processing in same-versus different-script bilinguals are discussed
Formalism for obtaining nuclear momentum distributions by the Deep Inelastic Neutron Scattering technique
We present a new formalism to obtain momentum distributions in condensed
matter from Neutron Compton Profiles measured by the Deep Inelastic Neutron
Scattering technique. The formalism describes exactly the Neutron Compton
Profiles as an integral in the momentum variable . As a result we obtain a
Volterra equation of the first kind that relates the experimentally measured
magnitude with the momentum distributions of the nuclei in the sample. The
integration kernel is related with the incident neutron spectrum, the total
cross section of the filter analyzer and the detectors efficiency function. A
comparison of the present formalism with the customarily employed approximation
based on a convolution of the momentum distribution with a resolution function
is presented. We describe the inaccuracies that the use of this approximation
produces, and propose a new data treatment procedure based on the present
formalism.Comment: 11 pages, 8 figure
Auroral Energy Input from Energetic Electrons and Joule Heating at Chatanika
With the incoherent scatter radar at Chatanika, Alaska, a wide variety of measurements can be made related to the ionosphere, magnetosphere, and neutral atmosphere. A significant parameter is the amount of energy transferred from the magnetosphere into the ionosphere and neutral atmosphere during periods of auroral activity. In this report we examine a procedure whereby the incident energy flux of auroral electrons is ascertained from radar measurements. As part of the process we compare radar-determined fluxes with those ascertained from simultaneous photometric observations at 4278 Å. The fluxes obtained by both techniques had similar magnitudes and time variations. If we assume that the largest uncertainty in the radar/photometer comparison is the effective recombination coefficient, then that coefficient can also be deduced. We find a value 3 × 10−7 cm³/s at about 105 km, which is in good agreement with other recent determinations during active auroral conditions. We then combine this technique with one to ascertain the Joule heating to determine the energy input from the magnetosphere to the ionosphere in a region localized above the radar on March 22, 1973, in the midnight sector. The energy input is continuous at a significant level, i.e., greater than the 3 ergs/cm² s that could be delivered by the sun, were it overhead. Moreover, at times, each of these inputs became as great as 30 ergs/cm² s
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