593 research outputs found
Magnonic Crystal with Two-Dimensional Periodicity as a Waveguide for Spin Waves
We describe a simple method of including dissipation in the spin wave band
structure of a periodic ferromagnetic composite, by solving the Landau-Lifshitz
equation for the magnetization with the Gilbert damping term. We use this
approach to calculate the band structure of square and triangular arrays of Ni
nanocylinders embedded in an Fe host. The results show that there are certain
bands and special directions in the Brillouin zone where the spin wave lifetime
is increased by more than an order of magnitude above its average value. Thus,
it may be possible to generate spin waves in such composites decay especially
slowly, and propagate especially large distances, for certain frequencies and
directions in -space.Comment: 13 pages, 4 figures, submitted to Phys Rev
Intrinsic Energy Localization through Discrete Gap Breathers in One-Dimensional Diatomic Granular Crystals
We present a systematic study of the existence and stability of discrete
breathers that are spatially localized in the bulk of a one-dimensional chain
of compressed elastic beads that interact via Hertzian contact. The chain is
diatomic, consisting of a periodic arrangement of heavy and light spherical
particles. We examine two families of discrete gap breathers: (1) an unstable
discrete gap breather that is centered on a heavy particle and characterized by
a symmetric spatial energy profile and (2) a potentially stable discrete gap
breather that is centered on a light particle and is characterized by an
asymmetric spatial energy profile. We investigate their existence, structure,
and stability throughout the band gap of the linear spectrum and classify them
into four regimes: a regime near the lower optical band edge of the linear
spectrum, a moderately discrete regime, a strongly discrete regime that lies
deep within the band gap of the linearized version of the system, and a regime
near the upper acoustic band edge. We contrast discrete breathers in anharmonic
FPU-type diatomic chains with those in diatomic granular crystals, which have a
tensionless interaction potential between adjacent particles, and highlight in
that the asymmetric nature of the latter interaction potential may lead to a
form of hybrid bulk-surface localized solutions
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
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
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
Recommended from our members
CPP-603 underwater fuel storage facility site integrated stabilization management plan (SISMP). Volume I
The CPP-603 Underwater Fuel Storage Facility (UFSF) Site Integrated Stabilization Management Plan (SISMP) has been developed to describe the activities required for the relocation of spent nuclear fuel (SNF) from the CPP-603 facility. These activities are the only Idaho National Engineering Laboratory (INEL) actions identified in the Implementation Plan developed to meet the requirements of the Defense Nuclear Facilities Safety Board (DNFSB) remediation in the Defense Nuclear Facilities Complex. To date, 622 spent nuclear fuel units have been moved from the CPP-603 north and middle water basins, leaving 743 units in the south basin to be relocated from the facility by December 31, 2000. Besides moving fuels from the CPP-603, in 1993 and 1994 more than 300 fuel storage yokes in the north and middle basins were redundantly rigged because of corrosion problems. More than 200 fuel transfers within the north and middle basins were also made to ensure proper spacing of the fuels, and 104 corroded cans containing spent space reactor fuel were repackaged underwater to prevent potential release of their contents. This document is provided to address the relocation activities for the remaining 743 units in the south basin into wet storage pools at building CPP-666 or into dry storage at the Irradiation Fuel Storage Facility (IFSF)
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.
Matrix metalloproteinase 9 expression in primary human prostatic adenocarcinoma and benign prostatic hyperplasia.
Matrix metalloproteinase (MMP) expression was investigated in patients with prostatic adenocarcinoma and benign prostatic hyperplasia (BPH). Forty-one men were studied: 26 had histologically proven prostate cancer, with 14 (54%) showing metastatic disease; 15 patients had BPH. Prostatic tissue was obtained from transurethral resection and needle core biopsies; gelatinolytic activity was determined by zymography. Seven gelatinolytic bands were detected, with molecular weights ranging from > 100 kilodalton (kDa) to 29 kDa. Nine of 14 patients (64%) with skeletal metastases had 92 kDa activity, present in only two of 12 patients (17%) with a negative bone scan, and absent in BPH. The 92 kDa gelatinolytic activity was expressed in 73% of aneuploid tumours compared with 20% of diploid tumours. A 97 kDa gelatinase was expressed in 80% of BPH samples and 23% of carcinoma patients. Enzyme bands of 72, 66 and 45 kDa were equally expressed in malignant tissue, irrespective of metastatic status, but were expressed in fewer BPH patients. The 97, 92, 66 and 45 kDa enzymes were identified as being pro-MMP-9 sequences by Western blotting, using a specific antibody directed against the pro sequence of the mature protein. MMP activity appeared to be increased in malignant prostatic tissue compared with BPH. Pro-MMP-9, in its 92 kDa form, was shown to be exclusively expressed by malignant prostatic tissue, and in particular by tumours that exhibited the aggressive and metastatic phenotype
XMM-Newton study of the persistent X-ray source 1E1743.1-2843 located in the Galactic Center direction
We report the results of an XMM-Newton observation of the persistent X-ray
source 1E1743.1-2843, located in the Galactic Center (GC) direction. We
determine the position of the source at alpha_J2000=17h46m21.0s,
delta_J2000=-28deg43'44" (with an uncertainty of 1.5"), which is the most
accurate to date, and will enable cross-identifications at other wavelengths.
The source was bright during this observation (L_2-10keV ~ 2.7 x 10^36
d^2_10kpc erg/s for a power-law continuum), with no significant variability. We
propose that 1E1743.1-2843 may be explained in terms of a black hole candidate
in a low/hard state. There is an indication that the source exhibits different
states from a comparison of our results with previous observations (e.g.,
ART-P, BeppoSAX). However, the present spectral analysis does not rule out the
hypothesis of a neutron star low-mass X-ray binary as suggested previously. If
1E1743.1-2843 is actually located in the GC region, we might expect to observe
significant 6.4keV fluorescent iron line emission from nearby molecular clouds
(e.g., GCM+0.25+0.01).Comment: 6 pages; accepted for publication in A&
Resonant Raman Scattering in Antiferromagnets
Two-magnon Raman scattering provides important information about electronic
correlations in the insulating parent compounds of high- materials. Recent
experiments have shown a strong dependence of the Raman signal in
geometry on the frequency of the incoming photon. We present an analytical and
numerical study of the Raman intensity in the resonant regime. It has been
previously argued by one of us (A.Ch) and D. Frenkel that the most relevant
contribution to the Raman vertex at resonance is given by the triple resonance
diagram. We derive an expression for the Raman intensity in which we
simultaneously include the enhancement due to the triple resonance and a final
state interaction. We compute the two-magnon peak height (TMPH) as a function
of incident frequency and find two maxima at and . We argue that the
high-frequency maximum is cut only by a quasiparticle damping, while the
low-frequency maximum has a finite amplitude even in the absence of damping. We
also obtain an evolution of the Raman profile from an asymmetric form around
to a symmetric form around . We
further show that the TMPH depends on the fermionic quasiparticle damping, the
next-nearest neighbor hopping term and the corrections to the
interaction vertex between light and the fermionic current. We discuss our
results in the context of recent experiments by Blumberg et al. on
and and R\"{u}bhausen et al. on
and show that the triple resonance theory yields a qualitative
and to some extent also quantitative understanding of the experimental data.Comment: 19 pages, RevTeX, 16 figures embedded in the text, ps-file is also
available at http://lifshitz.physics.wisc.edu/www/morr/morr_homepage.htm
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