12,544 research outputs found
Neutrinos, Weak Interactions, and r-process Nucleosynthesis
Two of the key issues in understanding the neutron-to-proton ratio in a
core-collapse supernova are discussed. One of these is the behavior of the
neutrino-nucleon cross sections as supernova energies. The other issue is the
many-body properties of the neutrino gas near the core when both one- and
two-body interaction terms are included.Comment: To be published in the Proceedings of "International Symposium on
Structure of Exotic Nuclei and Nuclear Forces (SENUF 06)", March 2006, Tokyo,
Japa
Quantum three-body system in D dimensions
The independent eigenstates of the total orbital angular momentum operators
for a three-body system in an arbitrary D-dimensional space are presented by
the method of group theory. The Schr\"{o}dinger equation is reduced to the
generalized radial equations satisfied by the generalized radial functions with
a given total orbital angular momentum denoted by a Young diagram
for the SO(D) group. Only three internal variables are
involved in the functions and equations. The number of both the functions and
the equations for the given angular momentum is finite and equal to
.Comment: 16 pages, no figure, RevTex, Accepted by J. Math. Phy
Entanglement of two atomic samples by quantum non-demolition measurements
This paper presents simulations of the state vector dynamics for a pair of
atomic samples which are being probed by phase shift measurements on an optical
beam passing through both samples. We show how measurements, which are
sensitive to different atomic components, serve to prepare states which are
close to being maximally entangled.Comment: 8 pages, 8 figures, REVTeX
One-dimensional transport in polymer nanofibers
We report our transport studies in quasi one-dimensional (1D) conductors -
helical polyacetylene fibers doped with iodine and the data analysis for other
polymer single fibers and tubes. We found that at 30 K < T < 300 K the
conductance and the current-voltage characteristics follow the power law: G(T)
~ T^alpha with alpha ~ 2.2-7.2 and I(V) ~ V^betta with betta ~ 2-5.7. Both G(T)
and I(V) show the features characteristic of 1D systems such as Luttinger
liquid or Wigner crystal. The relationship between our results and theories for
tunneling in 1D systems is discussed.Comment: 11 pages, 3 figures, accepted for publication in Phys. Rev. Letter
Can Hall drag be observed in Coulomb coupled quantum wells in a magnetic field?
We study the transresistivity \tensor\rho_{21} (or equivalently, the drag
rate) of two Coulomb-coupled quantum wells in the presence of a perpendicular
magnetic field, using semi-classical transport theory. Elementary arguments
seem to preclude any possibility of observation of ``Hall drag'' (i.e., a
non-zero off-diagonal component in \tensor\rho_{21}). We show that these
arguments are specious, and in fact Hall drag can be observed at sufficiently
high temperatures when the {\sl intra}layer transport time has
significant energy-dependence around the Fermi energy . The
ratio of the Hall to longitudinal transresistivities goes as , where
is the temperature, is the magnetic field, and .Comment: LaTeX, 13 pages, 2 figures (to be published in Physica Scripta, Proc.
of the 17th Nordic Semiconductor Conference
Nonlinear Response of Composite Panels Under Combined Acoustic Excitation and Aerodynamic Pressure
A finite element formulation is presented for the analysis of large deflection response of composite panels subjected to aerodynamic pressure- at supersonic flow and high acoustic excitation. The first-order shear deformation theory is considered for laminated composite plates, and the von Karman nonlinear strain-displacement relations are employed for the analysis of large deflection panel response. The first-order piston theory aerodynamics and the simulated Gaussian white noise are employed for the aerodynamic and acoustic loads, respectively. The nonlinear equations of motion for an arbitrarily laminated composite panel subjected to a combined aerodynamic and acoustic pressures are formulated first in structure node degrees-of-freedom. The system equations are then transformed and reduced to a set of coupled nonlinear equations in modal coordinates. Modal participation is defined and the in-vacuo modes to be retained in the analysis are based on the modal participation values. Numerical results include root mean square values of maximum deflections, deflection and strain response time histories, probability distributions, and power spectrum densities. Results showed that combined acoustic and aerodynamic loads have to be considered for panel analysis and design at high dynamic pressure values
Concatenating Decoherence Free Subspaces with Quantum Error Correcting Codes
An operator sum representation is derived for a decoherence-free subspace
(DFS) and used to (i) show that DFSs are the class of quantum error correcting
codes (QECCs) with fixed, unitary recovery operators, and (ii) find explicit
representations for the Kraus operators of collective decoherence. We
demonstrate how this can be used to construct a concatenated DFS-QECC code
which protects against collective decoherence perturbed by independent
decoherence. The code yields an error threshold which depends only on the
perturbing independent decoherence rate.Comment: 4 pages, no figures. Several changes. To appear in PR
Preparation of spin squeezed atomic states by optical phase shift measurement
In this paper we present a state vector analysis of the generation of atomic
spin squeezing by measurement of an optical phase shift. The frequency
resolution is improved when a spin squeezed sample is used for spectroscopy in
place of an uncorrelated sample. When light is transmitted through an atomic
sample some photons will be scattered out of the incident beam, and this has a
destructive effect on the squeezing. We present quantitative studies for three
limiting cases: the case of a sample of atoms of size smaller than the optical
wavelength, the case of a large dilute sample and the case of a large dense
sample.Comment: 18 page
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