60,592 research outputs found
Scaling analysis of Kondo screening cloud in a mesoscopic ring with an embedded quantum dot
The Kondo effect is theoretically studied in a quantum dot embedded in a
mesoscopic ring. The ring is connected to two external leads, which enables the
transport measurement. Using the "poor man's" scaling method, we obtain
analytical expressions of the Kondo temperature T_K as a function of the
Aharonov-Bohm phase \phi by the magnetic flux penetrating the ring. In this
Kondo problem, there are two characteristic lengths. One is the screening
length of the charge fluctuation, L_c=\hbar v_F/ |\epsilon_0|, where v_F is the
Fermi velocity and \epsilon_0 is the energy level in the quantum dot. The other
is the screening length of spin fluctuation, i.e., size of Kondo screening
cloud, L_K=\hbar v_F/ T_K. We obtain different expressions of T_K(\phi) for (i)
L_c \ll L_K \ll L, (ii) L_c \ll L \ll L_K, and (iii) L \ll L_c \ll L_K, where L
is the size of the ring. T_K is markedly modulated by \phi in cases (ii) and
(iii), whereas it hardly depends on \phi in case (i). We also derive
logarithmic corrections to the conductance at temperature T\gg T_K and an
analytical expression of the conductance at T\ll T_K, on the basis of the
scaling analysis.Comment: 21pages, 10 figure
Presymplectic current and the inverse problem of the calculus of variations
The inverse problem of the calculus of variations asks whether a given system
of partial differential equations (PDEs) admits a variational formulation. We
show that the existence of a presymplectic form in the variational bicomplex,
when horizontally closed on solutions, allows us to construct a variational
formulation for a subsystem of the given PDE. No constraints on the
differential order or number of dependent or independent variables are assumed.
The proof follows a recent observation of Bridges, Hydon and Lawson and
generalizes an older result of Henneaux from ordinary differential equations
(ODEs) to PDEs. Uniqueness of the variational formulation is also discussed.Comment: v2: 17 pages, no figures, BibTeX; minor corrections, close to
published versio
Discovery of the spectroscopic binary nature of three bright southern Cepheids
We present an analysis of spectroscopic radial velocity and photometric data
of three bright Galactic Cepheids: LR Trianguli Australis (LR TrA), RZ Velorum
(RZ Vel), and BG Velorum (BG Vel). Based on new radial velocity data, these
Cepheids have been found to be members of spectroscopic binary systems.
The ratio of the peak-to-peak radial velocity amplitude to photometric
amplitude indicates the presence of a companion for LR TrA and BG Vel. IUE
spectra indicate that the companions of RZ Vel and BG Vel cannot be hot stars.
The analysis of all available photometric data revealed that the pulsation
period of RZ Vel and BG Vel varies monotonically, due to stellar evolution.
Moreover, the longest period Cepheid in this sample, RZ Vel, shows period
fluctuations superimposed on the monotonic period increase. The light-time
effect interpretation of the observed pattern needs long-term photometric
monitoring of this Cepheid. The pulsation period of LR TrA has remained
constant since the discovery of its brightness variation.
Using statistical data, it is also shown that a large number of spectroscopic
binaries still remain to be discovered among bright classical Cepheids.Comment: 9 pages, 14 figure
RELATIONSHIPS BETWEEN MARKET PRICE SIGNALS AND PRODUCTION MANAGEMENT: THE CASE OF FED BEEF
The beef industry in the United States consists of several distinct production levels ranging from the cow-calf producer at the lowest level to the final consumer. These sectors face varying levels of profitability, degrees of market power, conflicting goals, and price signals. Environmental regulations involve questions of what costs are involved, who is in a position to pay these costs, and whether market prices are capable of signaling different environmental practices. Understanding the relationships within the beef industry may allow researchers to fine-tune analyses of environmental issues in the beef industry.Beef, BMP, Cattle, Pricing, Livestock Production/Industries, Marketing,
Millimeter and Submillimeter Survey of the R Corona Australis Region
Using a combination of data from the Antarctic Submillimeter Telescope and
Remote Observatory (AST/RO), the Arizona Radio Observatory Kitt Peak 12m
telescope and the Arizona Radio Observatory 10m Heinrich Hertz Telescope, we
have studied the most active part of the R CrA molecular cloud in multiple
transitions of Carbon Monoxide, HCO and 870\micron continuum emission.
Since R CrA is nearby (130 pc), we are able to obtain physical spatial
resolution as high as 0.01pc over an area of 0.16 pc, with velocity
resolution finer than 1 km/s. Mass estimates of the protostar driving the
mm-wave emission derived from HCO, dust continuum emission and kinematic
techniques point to a young, deeply embedded protostar of 0.5-0.75
M, with a gaseous envelope of similar mass. A molecular outflow is
driven by this source that also contains at least 0.8 M of molecular
gas with 0.5 L of mechanical luminosity. HCO lines show the
kinematic signature of infall motions as well as bulk rotation. The source is
most likely a Class 0 protostellar object not yet visible at near-IR
wavelengths. With the combination of spatial and spectral resolution in our
data set, we are able to disentangle the effects of infall, rotation and
outflow towards this young object.Comment: 29 pages, 9 figures. Accepted for publication in the Astrophysical
Journa
Synthetic 3D Spin-Orbit Coupling
We describe a method for creating a three-dimensional analogue to Rashba
spin-orbit coupling in systems of ultracold atoms. This laser induced coupling
uses Raman transitions to link four internal atomic states with a tetrahedral
geometry, and gives rise to a Dirac point that is robust against environmental
perturbations. We present an exact result showing that such a spin-orbit
coupling in a fermionic system always rise to a molecular bound state.Comment: 4 pages, 6 figure
A heuristic approach to the weakly interacting Bose gas
Some thermodynamic properties of weakly interacting Bose systems are derived
from dimensional and heuristic arguments and thermodynamic relations, without
resorting to statistical mechanics
Anomalous Nernst Effect in the Vortex-Liquid Phase of High-Temperature Superconductors by Layer Decoupling
Linear diamagnetism is predicted in the vortex-liquid phase of layered
superconductors at temperatures just below the mean-field phase transition on
the basis of a high-temperature analysis of the corresponding frustrated XY
model. The diamagnetic susceptibility, and the Nernst signal by implication, is
found to vanish with temperature as (T_c0 - T)^3 in the vicinity of the
meanfield transition at T_c0. Quantitative agreement with recent experimental
observations of a diamagnetic signal in the vortex-liquid phase of
high-temperature superconductors is obtained.Comment: 8 pages, 3 figure
The bottom of the white dwarf cooling sequence in the old open cluster NGC 2158
We use 10 orbits of Advanced Camera for Surveys observations to reach the end
of the white dwarf cooling sequence in the solar-metallicity open cluster NGC
2158. Our photometry and completeness tests show that the end falls at
magnitude m_F606W = 27.5 +/- 0.15, which implies an age between ~1.8 and ~2.0
Gyr, consistent with the age of 1.9 +/- 0.2 Gyr obtained from fits to the
main-sequence turn-off. The faintest white dwarfs show a clear turn toward
bluer colors, as predicted by theoretical isochrones.Comment: 12 pages, 4 figures (2 in low resolution, and 1 bonus for
astro-ph-only). ApJ Letter accepted on December 1, 200
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