613 research outputs found
Fold and thrust belts : structural style, evolution and exploration – an introduction
Peer reviewedPublisher PD
High Resolution Spectroscopy of the X-ray Photoionized Wind in Cygnus X-3 with the Chandra High Energy Transmission Grating Spectrometer
We present a preliminary analysis of the 1--10 keV spectrum of the massive
X-ray binary Cyg X-3, obtained with the High Energy Transmission Grating
Spectrometer on the Chandra X-ray Observatory. The source reveals a richly
detailed discrete emission spectrum, with clear signatures of
photoionization-driven excitation.
Among the spectroscopic novelties in the data are the first astrophysical
detections of a number of He-like 'triplets' (Si, S, Ar) with emission line
ratios characteristic of photoionization equilibrium, fully resolved narrow
radiative recombination continua of Mg, Si, and S, the presence of the H-like
Fe Balmer series, and a clear detection of a ~ 800 km/s large scale velocity
field, as well as a ~1500 km/s FWHM Doppler broadening in the source. We
briefly touch on the implications of these findings for the structure of the
Wolf-Rayet wind.Comment: 11 pages, 3 figures; Accepted for publication in ApJ Letter
Localized magnetoplasmon modes arising from broken translational symmetry in semiconductor superlattices
The electromagnetic propagator associated with the localized collective
magnetoplasmon excitations in a semiconductor superlattice with broken
translational symmetry, is calculated analytically within linear response
theory. We discuss the properties of these collective excitations in both
radiative and non-radiative regimes of the electromagnetic spectra. We find
that low frequency retarded modes arise when the surface density of carriers at
the symmetry breaking layer is lower than the density at the remaining layers.
Otherwise a doublet of localized, high-frequency magnetoplasmon-like modes
occurs.Comment: Revtex file + separate pdf figure
Nonlinear Spin Dynamics in Ferromagnets with Electron-Nuclear Coupling
Nonlinear spin motion in ferromagnets is considered with nonlinearity due to
three factors: (i) the sample is prepared in a strongly nonequilibrium state,
so that evolution equations cannot be linearized as would be admissible for
spin motion not too far from equilibrium, (ii) the system considered consists
of interacting electron and nuclear spins coupled with each other via hyperfine
forces, and (iii) the sample is inserted into a coil of a resonant electric
circuit producing a resonator feedback field. Due to these nonlinearities,
coherent motion of spins can develop, resulting in their ultrafast relaxation.
A complete analysis of mechanisms triggering such a coherent motion is
presented. This type of ultrafast coherent relaxation can be used for studying
intrinsic properties of magnetic materials.Comment: 1 file, LaTex, 23 page
Effects of Multi-Surface Modification on Curie temperature of ferroelectric films
Within the framework of mean field theory, we study the effects of
multi-surface modification on Curie temperature of ferroelectric films using
the transverse Ising model. The general nonlinear equations for Curie
temperature of multi-surface ferroelectric films with arbitrary exchange
constants and transverse fields are derived by the transfer matrix method. As
an example, we consider a film consisting of top surface layers, bulk layers
and bottom surface layers. Two types of surface modifications, modifications of
a surface exchange constant and a surface transverse field are taken into
account. The dependence of Curie temperature on the surface layer numbers, bulk
layer numbers, surface exchange constants, surface transverse fields and bulk
transverse fields is discussed.Comment: 11 pages, 5 figure
Resonant two-magnon Raman scattering in antiferromagnetic insulators
We propose a theory of two-magnon {\it resonant\/} Raman scattering from
antiferromagnetic insulators, which contains information both on the magnetism
and the carrier properties in the lighly doped phases. We argue that the
conventional theory does not work in the resonant regime, in which the energy
of the incident photon is close to the gap between the conduction and valence
bands. We identify the diagram which gives the dominant contribution to Raman
intensity in this regime and show that it can explain the unusual features in
the two-magnon profile and in the two-magnon peak intensity dependence on the
incoming photon frequency.Comment: 11 pages (REVTeX) + 3 figures in a single postscript file are
appended in uuencoded format, preprint TCSUH-94:09
Quantum Coherence Oscillations in Antiferromagnetic Chains
Macroscopic quantum coherence oscillations in mesoscopic antiferromagnets may
appear when the anisotropy potential creates a barrier between the
antiferromagnetic states with opposite orientations of the Neel vector. This
phenomenon is studied for the physical situation of the nuclear spin system of
eight Xe atoms arranged on a magnetic surface along a chain. The oscillation
period is calculated as a function of the chain constant. The environmental
decoherence effects at finite temperature are accounted assuming a dipole
coupling between the spin chain and the fluctuating magnetic field of the
surface. The numerical calculations indicate that the oscillations are damped
by a rate , where is the number of spins and is
the relaxation time of a single spin.Comment: 10 pages, Latex, two postscript figures; submitted to Phys. Rev.
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