28,204 research outputs found
Anisotropic spin Hall effect from first principles
We report on first principles calculations of the anisotropy of the intrinsic
spin Hall conductivity (SHC) in nonmagnetic hcp metals and in antiferromagnetic
Cr. For most of the metals of this study we find large anisotropies. We derive
the general relation between the SHC vector and the direction of spin
polarization and discuss its consequences for hcp metals. Especially, it is
predicted that for systems where the SHC changes sign due to the anisotropy the
spin Hall effect may be tuned such that the spin polarization is parallel
either to the electric field or to the spin current.Comment: Accepted for publication in Physical Review Letter
The POOL Data Storage, Cache and Conversion Mechanism
The POOL data storage mechanism is intended to satisfy the needs of the LHC
experiments to store and analyze the data from the detector response of
particle collisions at the LHC proton-proton collider. Both the data rate and
the data volumes will largely differ from the past experience. The POOL data
storage mechanism is intended to be able to cope with the experiment's
requirements applying a flexible multi technology data persistency mechanism.
The developed technology independent approach is flexible enough to adopt new
technologies, take advantage of existing schema evolution mechanisms and allows
users to access data in a technology independent way. The framework consists of
several components, which can be individually adopted and integrated into
existing experiment frameworks.Comment: Talk from the 2003 Computing in High Energy and Nuclear Physics
(CHEP03), La Jolla, Ca, USA, March 2003, 5 pages, PDF, 6 figures. PSN MOKT00
Propagation of relativistic charged particles in ultracold atomic gases with Bose-Einstein condensates
We study theoretically some effects produced by a propagation of the charged
particles in dilute gases of alkali-metal atoms in the state with Bose-Einstein
condensates. The energy change of the high-speed (relativistic) particle that
corresponds to the Cherenkov effect in the condensate is investigated. We show
that in the studied cases the particle can both loose and receive the energy
from a gas. We find the necessary conditions for the particle acceleration in
the multi-component condensate. It is shown that the Cherenkov effect in
Bose-Einstein condensates can be used also for defining the spectral
characteristics of atoms.Comment: 6 pages, 3 figure
Automated Classification of Periodic Variable Stars detected by the Wide-field Infrared Survey Explorer
We describe a methodology to classify periodic variable stars identified
using photometric time-series measurements constructed from the Wide-field
Infrared Survey Explorer (WISE) full-mission single-exposure Source Databases.
This will assist in the future construction of a WISE Variable Source Database
that assigns variables to specific science classes as constrained by the WISE
observing cadence with statistically meaningful classification probabilities.
We have analyzed the WISE light curves of 8273 variable stars identified in
previous optical variability surveys (MACHO, GCVS, and ASAS) and show that
Fourier decomposition techniques can be extended into the mid-IR to assist with
their classification. Combined with other periodic light-curve features, this
sample is then used to train a machine-learned classifier based on the random
forest (RF) method. Consistent with previous classification studies of variable
stars in general, the RF machine-learned classifier is superior to other
methods in terms of accuracy, robustness against outliers, and relative
immunity to features that carry little or redundant class information. For the
three most common classes identified by WISE: Algols, RR Lyrae, and W Ursae
Majoris type variables, we obtain classification efficiencies of 80.7%, 82.7%,
and 84.5% respectively using cross-validation analyses, with 95% confidence
intervals of approximately +/-2%. These accuracies are achieved at purity (or
reliability) levels of 88.5%, 96.2%, and 87.8% respectively, similar to that
achieved in previous automated classification studies of periodic variable
stars.Comment: 48 pages, 17 figures, 1 table, accepted by A
Spin-Dependent Hubbard Model and a Quantum Phase Transition in Cold Atoms
We describe an experimental protocol for introducing spin-dependent lattice
structure in a cold atomic fermi gas using lasers. It can be used to realize
Hubbard models whose hopping parameters depend on spin and whose interaction
strength can be controlled with an external magnetic field. We suggest that
exotic superfluidities will arise in this framework. An especially interesting
possibility is a class of states that support coexisting superfluid and normal
components, even at zero temperature. The quantity of normal component varies
with external parameters. We discuss some aspects of the quantum phase
transition that arises at the point where it vanishes.Comment: 9 pages, 7 figures; added/corrected references in [11] and [44
Cherenkov Radiation from Pairs and Its Effect on Induced Showers
We calculate the Cherenkov radiation from an pair at small
separations, as occurs shortly after a pair conversion. The radiation is
reduced (compared to that from two independent particles) when the pair
separation is smaller than the wavelength of the emitted light. We estimate the
reduction in light in large electromagnetic showers, and discuss the
implications for detectors that observe Cherenkov radiation from showers in the
Earth's atmosphere, as well as in oceans and Antarctic ice.Comment: Final version, with minor changes, to appear in PRD. 5 pages with 4
figure
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