4,897 research outputs found
Diffusion and Transport Coefficients in Synthetic Opals
Opals are structures composed of the closed packing of spheres in the size
range of nano-to-micro meter. They are sintered to create small necks at the
points of contact. We have solved the diffusion problem in such structures. The
relation between the diffusion coefficient and the termal and electrical
conductivity makes possible to estimate the transport coefficients of opal
structures. We estimate this changes as function of the neck size and the
mean-free path of the carriers. The theory presented is also applicable to the
diffusion problem in other periodic structures.Comment: Submitted to PR
Present status of the nonstrange and other flavor partners of the exotic Theta+ baryon
Given the existing empirical information about the exotic Theta+ baryon, we
analyze possible properties of its SU(3)F-partners, paying special attention to
the nonstrange member of the antidecuplet N*. The modified piN partial-wave
analysis presents two candidate masses, 1680 MeV and 1730 MeV. In both cases,
the N* should be rather narrow and highly inelastic. Our results suggest
several directions for experimental studies that may clarify properties of the
antidecuplet baryons, and structure of their mixing with other baryons. Recent
experimental evidence from the GRAAL and STAR Collaborations could be
interpreted as observations of a candidate for the Theta+ nonstrange partner.Comment: 4 pages, 1 figure, talk given at the Topical Group on Hadron Physics
(Fermilab, Oct. 24-26, 2004
The classification of static vacuum space-times containing an asymptotically flat spacelike hypersurface with compact interior
We prove non-existence of static, vacuum, appropriately regular,
asymptotically flat black hole space-times with degenerate (not necessarily
connected) components of the event horizon. This finishes the classification of
static, vacuum, asymptotically flat domains of outer communication in an
appropriate class of space-times, showing that the domains of outer
communication of the Schwarzschild black holes exhaust the space of
appropriately regular black hole exteriors.Comment: This version includes an addendum with a corrected proof of
non-existence of zeros of the Killing vector at degenerate horizons. A
problem with yet another Lemma is pointed out; this problem does not arise if
one assumes analyticity of the metric. An alternative solution, that does not
require analyticity, has been given in arXiv:1004.0513 [gr-qc] under
appropriate global condition
Resonant thermal transport in semiconductor barrier structures
I report that thermal single-barrier (TSB) and thermal double-barrier (TDB)
structures (formed, for example, by inserting one or two regions of a few Ge
monolayers in Si) provide both a suppression of the phonon transport as well as
a resonant-thermal-transport effect. I show that high-frequency phonons can
experience a traditional double-barrier resonant tunneling in the TDB
structures while the formation of Fabry-Perot resonances (at lower frequencies)
causes quantum oscillations in the temperature variation of both the TSB and
TDB thermal conductances and .Comment: 4 pages. 4 figure.
Large Thermoelectric Power Factor in TiS2 Crystal with Nearly Stoichiometric Composition
A TiS crystal with a layered structure was found to have a large
thermoelectric power factor.The in-plane power factor at 300 K is
37.1~W/Kcm with resistivity () of 1.7 mcm and
thermopower () of -251~V/K, and this value is comparable to that of the
best thermoelectric material, BiTe alloy. The electrical
resistivity shows both metallic and highly anisotropic behaviors, suggesting
that the electronic structure of this TiS crystal has a
quasi-two-dimensional nature. The large thermoelectric response can be ascribed
to the large density of state just above the Fermi energy and inter-valley
scattering. In spite of the large power factor, the figure of merit, of
TiS is 0.16 at 300 K, because of relatively large thermal conductivity,
68~mW/Kcm. However, most of this value comes from reducible lattice
contribution. Thus, can be improved by reducing lattice thermal
conductivity, e.g., by introducing a rattling unit into the inter-layer sites.Comment: 11 pages, 4 figures, to be published in Physical Review
Chiral Soliton Model vs Pentaquark Structure for \Theta (1540)
The exotic baryon (1540 MeV)\omega - \phi$ mixing.Comment: 11 pages, references added, final published versio
IUCF High Intensity Polarized Ion Source
This research was sponsored by the National Science Foundation Grant NSF PHY-931478
A Medium-Resolution Near-Infrared Spectral Library of Late Type Stars: I
We present an empirical infrared spectral library of medium resolution
(R~2000-3000) H (1.6 micron) and K (2.2 micron) band spectra of 218 red stars,
spanning a range of [Fe/H] from ~-2.2 to ~+0.3. The sample includes Galactic
disk stars, bulge stars from Baade's window, and red giants from Galactic
globular clusters. We report the values of 19 indices covering 12 spectral
features measured from the spectra in the library. Finally, we derive
calibrations to estimate the effective temperature, and diagnostic
relationships to determine the luminosity classes of individual stars from
near-infrared spectra.
This paper is part of a larger effort aimed at building a near-IR spectral
library to be incorporated in population synthesis models, as well as, at
testing synthetic stellar spectra.Comment: 34 pages, 12 figures; accepted for publication at ApJS; the spectra
are available from the authors upon reques
- …