1,181 research outputs found
An Aerothermoelastic Analysis Framework Enhanced by Model Order Reduction With Applications
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/143034/1/6.2017-1601.pd
Spin Injection and Relaxation in Ferromagnet-Semiconductor Heterostructures
We present a complete description of spin injection and detection in
Fe/Al_xGa_{1-x}As/GaAs heterostructures for temperatures from 2 to 295 K.
Measurements of the steady-state spin polarization in the semiconductor
indicate three temperature regimes for spin transport and relaxation. At
temperatures below 70 K, spin-polarized electrons injected into quantum well
structures form excitons, and the spin polarization in the quantum well depends
strongly on the electrical bias conditions. At intermediate temperatures, the
spin polarization is determined primarily by the spin relaxation rate for free
electrons in the quantum well. This process is slow relative to the excitonic
spin relaxation rate at lower temperatures and is responsible for a broad
maximum in the spin polarization between 100 and 200 K. The spin injection
efficiency of the Fe/Al_xGa_{1-x}As Schottky barrier decreases at higher
temperatures, although a steady-state spin polarization of at least 6 % is
observed at 295 K.Comment: 3 Figures Submitted to Phys. Rev. Let
Quantum Films Adsorbed on Graphite: Third and Fourth Helium Layers
Using a path-integral Monte Carlo method for simulating superfluid quantum
films, we investigate helium layers adsorbed on a substrate consisting of
graphite plus two solid helium layers. Our results for the promotion densities
and the dependence of the superfluid density on coverage are in agreement with
experiment. We can also explain certain features of the measured heat capacity
as a function of temperature and coverage.Comment: 13 pages in the Phys. Rev. two-column format, 16 Figure
Relative spins and excitation energies of superdeformed bands in 190Hg: Further evidence for octupole vibration
An experiment using the Eurogam Phase II gamma-ray spectrometer confirms the
existence of an excited superdeformed (SD) band in 190Hg and its very unusual
decay into the lowest SD band over 3-4 transitions. The energies and dipole
character of the transitions linking the two SD bands have been firmly
established. Comparisons with RPA calculations indicate that the excited SD
band can be interpreted as an octupole-vibrational structure.Comment: 12 pages, latex, 4 figures available via WWW at
http://www.phy.anl.gov/bgo/bc/hg190_nucl_ex.htm
Lattice Instability in the Spin-Ladder System under Magnetic Field
We study theoretically the lattice instability in the spin gap systems under
magnetic field. With the magnetic field larger than a critical value h_{c1},
the spin gap is collapsed and the magnetization arises. We found that the
lattice distortion occurs in the spin-ladder at an incommensurate wavevector
corresponding to the magnetization, while it does not occur in the Haldane
system. At low temperatures the magnetization curve shows a first order phase
transition with this lattice distortion.Comment: 10 pages, REVTEX, 2 figures(ps file), minor change
On the existence of supersolid helium-4 monolayer films
Extensive Monte Carlo simulations of helium-4 monolayer films adsorbed on
weak substrates have been carried out, aimed at ascertaining the possible
occurrence of a quasi-two-dimensional supersolid phase. Only crystalline films
not registered with underlying substrates are considered. Numerical results
yield strong evidence that helium-4 will not form a supersolid film on {any}
substrate strong enough to stabilize a crystalline layer. On weaker substrates,
continuous growth of a liquid film takes place
Tilted Rotation and Wobbling Motion in Nuclei
The self-consistent harmonic oscillator model including the three-dimensional
cranking term is extended to describe collective excitations in the random
phase approximation. It is found that quadrupole collective excitations
associated with wobbling motion in rotating nuclei lead to the appearance of
two- or three-dimensional rotation.Comment: 9 pages, 2 Postscript figures, corrected typo
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