9,577 research outputs found
Spin-dependent resonant tunneling through semimetallic ErAs quantum wells
Resonant tunneling through semimetallic ErAs quantum wells embedded in GaAs
structures with AlAs barriers was recently found to exhibit an intriguing
behavior in magnetic fields which is explained in terms of tunneling selection
rules and the spin-polarized band structure including spin-orbit coupling.Comment: 4 pages, figures supplied as self-unpacking figures.uu, uses
epsfig.sty to incorporate figures in preprin
A second anniversary operational review of the OmniTRACS(R): The first two-way mobile Ku-band satellite communications system
A novel two-way mobile satellite communications and vehicle position reporting system that is currently operational in the United States and Europe is described. The system characteristics and service operations are described in detail. Technical descriptions of the equipment and signal processing techniques are provided
Phononic Self energy effects and superconductivity in CaC
We study the graphite intercalated compound CaC by means of Eliashberg
theory, focusing on the anisotropy properties. An analysis of the
electron-phonon coupling is performed, and we define a minimal 6-band
anisotropy structure. Comparing with Superconducting Density Functional Theory
(SCDFT) the condition under which Eliashberg theory is able to reproduce the
SCDFT gap structure is determined, and we discuss the role of Coulomb
interactions. The Engelsberg-Schrieffer polaron structure is computed by
solving the Eliashberg equation on the Matsubara axis and analytically
continuing it to the full complex plane. This reveals the polaronic
quasiparticle bands anisotropic features as well as the interplay with
superconductivity
On minimal coupling of the ABC-superparticle to supergravity background
By rigorous application of the Hamiltonian methods we show that the
ABC-formulation of the Siegel superparticle admits consistent minimal coupling
to external supergravity. The consistency check proves to involve all the
supergravity constraints.Comment: 8 pages RevTex file, to appear in Phys. Rev.
Plasmons in coupled bilayer structures
We calculate the collective charge density excitation dispersion and spectral
weight in bilayer semiconductor structures {\it including effects of interlayer
tunneling}. The out-of-phase plasmon mode (the ``acoustic'' plasmon) develops a
long wavelength gap in the presence of tunneling with the gap being
proportional to the square root (linear power) of the tunneling amplitude in
the weak (strong) tunneling limit. The in-phase plasmon mode is qualitatively
unaffected by tunneling. The predicted plasmon gap should be a useful tool for
studying many-body effects.Comment: 10 pages, 6 figures. to appear in Phys. Rev. Let
One-loop Renormalization of Black Hole Entropy Due to Non-minimally Coupled Matter
The quantum entanglement entropy of an eternal black hole is studied. We
argue that the relevant Euclidean path integral is taken over fields defined on
-fold covering of the black hole instanton. The statement that
divergences of the entropy are renormalized by renormalization of gravitational
couplings in the effective action is proved for non-minimally coupled scalar
matter. The relationship of entanglement and thermodynamical entropies is
discussed.Comment: 17 pages, latex, no figure
The angular size - redshift relation in power-law cosmologies
A linear evolution of the cosmological scale factor is a feature in several
models designed to solve the cosmological constant problem via a coupling
between scalar or tensor classical fields to the space-time curvature as well
as in some alternative gravity theories. In this paper, by assuming a general
time dependence of the scale factor, , we investigate
observational constraints on the dimensionless parameter from
measurements of the angular size for a large sample of milliarcsecond compact
radio sources. In particular, we find that a strictly linear evolution, i.e.,
is favoured by these data, which is also in agreement with
limits obtained from other independent cosmological tests. The dependence of
the critical redshift (at which a given angular size takes its minimal
value) with the index is briefly discussed.Comment: 5 pages, 4 figures, LaTe
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Small, Low-energy, Dispersive Solar Energetic Particle Events Observed by Parker Solar Probe
The Energetic Particle Instrument–Low Energy (EPI-Lo) experiment has detected several weak, low-energy (~30–300 keV nucleon⁻¹) solar energetic particle (SEP) events during its first two closest approaches to the Sun, providing a unique opportunity to explore the sources of low-energy particle acceleration. As part of the Parker Solar Probe (PSP) Integrated Science Investigation of the Sun (IS⊙IS) suite, EPI-Lo was designed to investigate the physics of energetic particles; however, in the special lowest-energy "time-of-flight only" product used in this study, it also responds to solar photons in a subset of approximately sunward-looking apertures lacking special light-attenuating foils. During the first three perihelia, in a frame rotating with the Sun, PSP undergoes retrograde motion, covering a 17° heliographic longitudinal range three times during the course of the ~11-day perihelion passes, permitting a unique spatial and temporal study into the location, correlation, and persistence of previously unmeasurable SEPs. We examine the signatures of these SEPs (during the first PSP perihelion pass only) and the connection to possible solar sources using remote observations from the Solar Dynamics Observatory (SDO), the Solar TErrestrial RElations Observatory (STEREO), and the ground-based Global Oscillation Network Group (GONG). The orientation of the Sun relative to STEREO, SDO, and GONG makes such identifications challenging, but we do have several candidates, including an equatorial coronal hole at a Carrington longitude of ~335°. To analyze observations from EPI-Lo, which is a new type of particle instrument, we examine instrumental effects and provide a preliminary separation of the ion signal from the photon background
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