14,657 research outputs found
Statistical Analysis of Spectral Line Candidates in Gamma-Ray Burst GRB870303
The Ginga data for the gamma-ray burst GRB870303 exhibit low-energy dips in
two temporally distinct spectra, denoted S1 and S2. S1, spanning 4 s, exhibits
a single line candidate at ~ 20 keV, while S2, spanning 9 s, exhibits
apparently harmonically spaced line candidates at ~ 20 and 40 keV. We evaluate
the statistical evidence for these lines, using phenomenological continuum and
line models which in their details are independent of the distance scale to
gamma-ray bursts. We employ the methodologies based on both frequentist and
Bayesian statistical inference that we develop in Freeman et al. (1999b). These
methodologies utilize the information present in the data to select the
simplest model that adequately describes the data from among a wide range of
continuum and continuum-plus-line(s) models. This ensures that the chosen model
does not include free parameters that the data deem unnecessary and that would
act to reduce the frequentist significance and Bayesian odds of the
continuum-plus-line(s) model. We calculate the significance of the
continuum-plus-line(s) models using the Chi-Square Maximum Likelihood Ratio
test. We describe a parametrization of the exponentiated Gaussian absorption
line shape that makes the probability surface in parameter space
better-behaved, allowing us to estimate analytically the Bayesian odds. The
significance of the continuum-plus-line models requested by the S1 and S2 data
are 3.6 x 10^-5 and 1.7 x 10^-4 respectively, with the odds favoring them being
114:1 and 7:1. We also apply our methodology to the combined (S1+S2) data. The
significance of the continuum-plus-lines model requested by the combined data
is 4.2 x 10^-8, with the odds favoring it being 40,300:1.Comment: LaTeX2e (aastex.cls included); 41 pages text, 10 figures (on 11
pages); accepted by ApJ (to be published 1 Nov 1999, v. 525
Current-induced spin polarization and the spin Hall effect: a quasiclassical approach
The quasiclassical Green function formalism is used to describe charge and
spin dynamics in the presence of spin-orbit coupling. We review the results
obtained for the spin Hall effect on restricted geometries. The role of
boundaries is discussed in the framework of spin diffusion equations.Comment: 10 pages, 5 figures, Submitted to Solid State Communications Special
Issue on "Fundamental Phenomena in Low Dimensional Electron Systems". Special
Issue Editors: Marco Polini, Michele Governale, Hermann Grabert, Vittorio
Pellegrini, and Mario Tos
Antiferro-quadrupole Ordering of CeB Studied by Resonant X-ray Scattering
Under zero magnetic field, a quadrupolar order parameter at q_Q=(1/2,1/2,1/2)
in a typical antiferro-quadrupole (AFQ) ordering compound CeB6 has been
observed for the first time by means of a resonant X-ray scattering (RXS) te\
chnique. The RXS is observed at the 2p->5d dipole transition energy of the Ce
L3-edge. Using this RXS technique to observe the pure order parameter of the
AFQ state, the magnetic phase diagram of Phase II is first determined.Comment: 7 pages, 4 figure
Distribution of Microscopic Energy Flux in Equilibrium State
The distribution function P(j) of the microscopic energy flux, j, in
equilibrium state is studied. It is observed that P(j) has a broad peak in
small j regime and a stretched-exponential decay for large j. The peak
structure originates in a potential advection term and energy transfer term
between the particles. The stretched exponential tail comes from the momentum
energy advection term.Comment: 5 pages, 2 figure
Generating high-order optical and spin harmonics from ferromagnetic monolayers
High-order harmonic generation (HHG) in solids has entered a new phase of
intensive research, with envisioned band-structure mapping on an ultrashort
time scale. This partly benefits from a flurry of new HHG materials discovered,
but so far has missed an important group. HHG in magnetic materials should have
profound impact on future magnetic storage technology advances. Here we
introduce and demonstrate HHG in ferromagnetic monolayers. We find that HHG
carries spin information and sensitively depends on the relativistic spin-orbit
coupling; and if they are dispersed into the crystal momentum space,
harmonics originating from real transitions can be -resolved and carry
the band structure information. Geometrically, the HHG signal is sensitive to
spatial orientations of monolayers. Different from the optical counterpart, the
spin HHG, though probably weak, only appears at even orders, a consequence of
SU(2) symmetry. Our findings open an unexplored frontier -- magneto-high-order
harmonic generation.Comment: 19 pages, 4 figure
Large thermoelectric figure of merit for 3D topological Anderson insulators via line dislocation engineering
We study the thermoelectric properties of three-dimensional topological
Anderson insulators with line dislocations. We show that at high densities of
dislocations the thermoelectric figure of merit ZT can be dominated by
one-dimensional topologically-protected conducting states channeled through the
lattice screw dislocations in the topological insulator materials with a
non-zero time-reversal-invariant momentum such as Bi_{1-x}Sb_x. When the
chemical potential does not exceed much the mobility edge the ZT at room
temperatures can reach large values, much higher than unity for reasonable
parameters, hence making this system a strong candidate for applications in
heat management of nano-devices.Comment: 4 pages, 3 figure
UV and X-ray Spectral Lines of FeXXIII Ion for Plasma Diagnostics
We have calculated X-ray and UV spectra of Be-like Fe (FeXXIII) ion in
collisional-radiative model including all fine-structure transitions among the
2s^2, 2s2p, 2p^2, 2snl, and 2pnl levels where n=3 and 4, adopting data for the
collision strengths by Zhang & Sampson (1992) and by Sampson, Goett, & Clark
(1984). Some line intensity ratios can be used for the temperature diagnostics.
We show 5 ratios in UV region and 9 ratios in X-ray region as a function of
electron temperature and density at 0.3keV < T_e < 10keV and . The effect of cascade in these line ratios and in the level
population densities are discussed.Comment: LaTeX, 18 pages, 10 Postscript figures. To appear in Physica Script
Excitation of spin waves on a cylindrical semiconductor heterostructure with Rashba spin-orbit interaction
Elementary excitations in a paramagnetic semiconductor quantum well confined
to a cylindrical surface are theoretically studied on the basis of coupled
spin-charge drift-diffusion equations. The electric-field-mediated eigenmodes
are optically excited by an oscillating interference pattern, which induces a
current in the outer circuit. For a cylinder with a given radius, sharp
resonances are predicted to occur in the steady-state current response, which
are due to weakly damped spin remagnetization waves.Comment: 7 pages, 1figur
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