3,664 research outputs found
Competition of Color Ferromagnetic and Superconductive States in a Quark-Gluon System
The possibility of color ferromagnetism in an SU(2) gauge field model is
investigated. The conditions allowing a stable color ferromagnetic state of the
quark system in the chromomagnetic field occupying small domains are
considered. A phase transition between this state and the color superconducting
state is considered. The effect of finite temperature is analyzed.Comment: 21 pages, 4 Postscript figure
Surface Electronic Structures and Field Emission Currents at Sodium Overlayers on Low-Index Tungsten Surfaces
The total energy distributions (TEDs) of the emission currents in field
emission and surface photofield emission and the overlayer-induced
modifications in the surface electronic structures from the technologically
important W surfaces with the commensurate W(100)/Na c(2x2), W(110)/Na (2x2)
and W(111)/Na (1x1) overlayers are calculated. The TEDs obtained by our recent
numerical method that extends the full-potential linear augmented plane wave
method for the electronic structures to the study of field and photofield
emission are used to interpret the shifts of the peaks in the experimental TEDs
in field emission and photofield emission from the W(100) and W(110) surfaces
at sub-monolayer and monolayer Na coverage. Hybridization of the 3s Na states
with the pairs of dz2-like surface states of the strong Swanson hump in clean
W(100) and surface resonances in clean W(111) below the Fermi energy shifts
these W states by about -1.2 eV and -1.0 eV, thus stabilizing these states, to
yield new strong peaks in the TEDs in field emission and photofield emission
from W(100)/Na c(2x2) and W(111)/Na (1x1) respectively. The effect of Na
intralayer interactions are discussed and are shown to shift the strong s- and
p-like peaks in the surface density of states of W(110) below and above the
Fermi energy respectively to lower energy with increased Na coverage, in
agreement with experiments.Comment: 12 page
Molecular hydrogen absorption systems in Sloan Digital Sky Survey
We present a systematic search for molecular hydrogen absorption systems at
high redshift in quasar spectra from the Sloan Digital Sky Survey (SDSS) II
Data Release 7 and SDSS-III Data Release 9. We have selected candidates using a
modified profile fitting technique taking into account that the Ly
forest can effectively mimic H absorption systems at the resolution of SDSS
data. To estimate the confidence level of the detections, we use two methods: a
Monte-Carlo sampling and an analysis of control samples. The analysis of
control samples allows us to define regions of the spectral quality parameter
space where H absorption systems can be confidently identified. We find
that H absorption systems with column densities
can be detected in only less than 3% of SDSS quasar spectra. We estimate the
upper limit on the detection rate of saturated H absorption systems () in Damped Ly- (DLA) systems to be about 7%. We
provide a sample of 23 confident H absorption system candidates that would
be interesting to follow up with high resolution spectrographs. There is a
1 color excess and non-significant extinction excess
in quasar spectra with an H candidate compared to standard DLA-bearing
quasar spectra. The equivalent widths (EWs) of C II, Si II and Al III (but not
Fe II) absorptions associated with H candidate DLAs are larger compared to
standard DLAs. This is probably related to a larger spread in velocity of the
absorption lines in the H bearing sample.Comment: 17 pages, 17 figures, accepted for publication in MNRA
Counting Berg partitions
We call a Markov partition of a two dimensional hyperbolic toral automorphism
a Berg partition if it contains just two rectangles. We describe all Berg
partitions for a given hyperbolic toral automorphism. In particular there are
exactly (k + n + l + m)/2 nonequivalent Berg partitions with the same
connectivity matrix (k, l, m, n)
Size effects in radiospectroscopy spectra of ferroelectric nanopowders
The theoretical and experimental investigation of ferroelectric nanopowders
is performed. The manifestation in radiospectroscopy spectra of size driven
ferroelectric-paraelectric phase transition at some critical particle average
size was the main goal of the consideration. In theoretical part the size
effect for the materials with ferroelectric tetragonal phase and cubic
paraelectric phase was considered allowing for the spontaneous polarization
inhomogeneity inside a particle and distribution of particle sizes. In ESR the
transformation of the spectra from tetragonal symmetry to cubic symmetry with
decreasing of nanoparticle sizes was calculated. Measurements of Fe3+ ESR
spectra in nanopowder of BaTiO3 were carried out at room temperature. The
decrease of intensity of tetragonal symmetry ESR lines of Fe3+ and appearance
of cubic symmetry line with asymmetry of the shoulders was observed with the
average sizes decrease with complete disappearance of tetragonal spectrum at
average size less or equal 40 nm. The comparison of the theory with experiment
was carried out. The value of critical size Rc = 40 nm was extracted from ESR
data. The asymmetry and broadening of right hand side shoulder of ESR cubic
symmetry line was shown to be related to contribution of paramagnetic centers
in the vicinity of the particles surface. The deconvolution of the cubic line
allowed to show, that this region size is about 3 nm.Comment: 10 pages, 8 figure
Partial covering of emission regions of Q 0528-250 by intervening H clouds
We present an analysis of the molecular hydrogen absorption system at z = 2.811 in the spectrum of the blazar Q0528-250. We demonstrate that the
molecular cloud does not cover the background source completely. The partial
coverage reveals itself as a residual flux in the bottom of saturated H_2
absorption lines. This amounts to about (2.220.54)% of the continuum and
does not depend on the wavelength. This value is small and it explains why this
effect has not been detected in previous studies of this quasar spectrum.
However, it is robustly detected and significantly higher than the zero flux
level in the bottom of saturated lines of the Ly-alpha forest,
(-0.210.22)%. The presence of the residual flux could be caused by
unresolved quasar multicomponents, by light scattered by dust, and/or by
jet-cloud interaction. The H absorption system is very well described by a
two-component model without inclusion of additional components when we take
partial coverage into account. The derived total column densities in the H
absorption components A and B are logN(H)[cm] = 18.100.02 and
17.820.02, respectively. HD molecules are present only in component B.
Given the column density, logN(HD)= 13.330.02, we find
N(HD)/2N(H)=(1.480.10)x10, significantly lower than previous
estimations. We argue that it is crucial to take into account partial coverage
effects for any analysis of H bearing absorption systems, in particular
when studying the physical state of high-redshift interstellar medium.Comment: Accepted for MNRA
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