77 research outputs found
Theoretical Aspects of Blunt Body Magnetoaerodynamics
Supersonic magnetoaerodynamic flow about blunt body with self contained magnetic field sourc
Type II superconductivity in SrPd2Ge2
Previous investigations have shown that SrPd2Ge2, a compound isostructural
with "122" iron pnictides but iron- and pnictogen-free, is a conventional
superconductor with a single s-wave energy gap and a strongly three-dimensional
electronic structure. In this work we reveal the Abrikosov vortex lattice
formed in SrPd2Ge2 when exposed to magnetic field by means of scanning
tunneling microscopy and spectroscopy. Moreover, by examining the differential
conductance spectra across a vortex and estimating the upper and lower critical
magnetic fields by tunneling spectroscopy and local magnetization measurements,
we show that SrPd2Ge2 is a strong type II superconductor with \kappa >>
sqrt(2). Also, we compare the differential conductance spectra in various
magnetic fields to the pair breaking model of Maki - de Gennes for dirty limit
type II superconductor in the gapless region. This way we demonstrate that the
type II superconductivity is induced by the sample being in the dirty limit,
while in the clean limit it would be a type I superconductor with \kappa\ <<
sqrt(2), in concordance with our previous study (T. Kim et al., Phys. Rev. B
85, (2012)).Comment: 9 pages, 4 figure
Josephson Coupling through a Quantum Dot
We derive, via fourth order perturbation theory, an expression for the
Josephson current through a gated interacting quantum dot. We analyze our
expression for two different models of the superconductor-dot-superconductor
(SDS) system. When the matrix elements connecting dot and leads are featureless
constants, we compute the Josephson coupling J_c as a function of the gate
voltage and Coulomb interaction. In the diffusive dot limit, we compute the
probability distribution P(J_c) of Josephson couplings. In both cases, pi
junction behavior (J_c < 0) is possible, and is not simply dependent on the
parity of the dot occupancy.Comment: 9 pages; 3 encapsulated PostScript figure
Frictional drag between quantum wells mediated by fluctuating electromagnetic field
We use the theory of the fluctuating electromagnetic field to calculate the
frictional drag between nearby two-and three dimensional electron systems. The
frictional drag results from coupling via a fluctuating electromagnetic field,
and can be considered as the dissipative part of the van der Waals interaction.
In comparison with other similar calculations for semiconductor two-dimensional
system we include retardation effects. We consider the dependence of the
frictional drag force on the temperature , electron density and separation
. We find, that retardation effects become dominating factor for high
electron densities, corresponding thing metallic film, and suggest a new
experiment to test the theory. The relation between friction and heat transfer
is also briefly commented on.Comment: 14 pages, 4 figure
Frictional drag between quantum wells mediated by phonon exchange
We use the Kubo formalism to evaluate the contribution of acoustic phonon
exchange to the frictional drag between nearby two-dimensional electron
systems. In the case of free phonons, we find a divergent drag rate
(). However, becomes finite when phonon
scattering from either lattice imperfections or electronic excitations is
accounted for. In the case of GaAs quantum wells, we find that for a phonon
mean free path smaller than a critical value, imperfection
scattering dominates and the drag rate varies as over many
orders of magnitude of the layer separation . When exceeds the
critical value, the drag rate is dominated by coupling through an
electron-phonon collective mode localized in the vicinity of the electron
layers. We argue that the coupled electron-phonon mode may be observable for
realistic parameters. Our theory is in good agreement with experimental results
for the temperature, density, and -dependence of the drag rate.Comment: 45 pages, LaTeX, 8 postscript file figure
Numerical Study of Magnetoaerodynamic Flow Around a Hemisphere
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/83560/1/AIAA-49278-455.pd
Utility rate structures and distributed thermal energy storage: a cost/benefit analysis. Basic research report, October 1978-February 1979
This paper examines three alternative methods by which electric utilities might take advantage of distributed thermal energy storage to smooth out their load profiles. These three methods are: time-specific rates, time-invariant rates with subsidized storage, and direct load controls. The optimal form of each of these policies is determined, and formulas indicating the relative desirability of each policy are developed
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