14,731 research outputs found
Different Methods of Forming Cold Fronts in Non-Merging Clusters
Sharp edges in X-ray surface brightness with continuous gas pressure called
cold fronts have been often found in relaxed galaxy clusters such as Abell 496.
Models that explain cold fronts as surviving cores of head-on subcluster
mergers do not work well for these clusters and competing models involving gas
sloshing have been recently proposed. Here, we test some concrete predictions
of these models in a combined analysis of density, temperature, metal
abundances and abundance ratios in a deep Chandra exposure of Abell 496. We
confirm that the chemical discontinuities found in this cluster are not
consistent with a core merger remnant scenario. However, we find chemical
gradients across a spiral "arm" discovered at 73 kpc north of the cluster
center and coincident with the sharp edge of the main cold front in the
cluster. Despite the overall SN Ia iron mass fraction dominance found within
the cooling radius of this cluster, the metal enrichment along the arm,
determined from silicon and iron abundances, is consistent with a lower SN Ia
iron mass fraction (51% +- 14%) than that measured in the surrounding regions
(85% +- 14%). The "arm" is also significantly colder than the surroundings by
0.5-1.6 keV. The arm extends from a boxy colder region surrounding the center
of the cluster, where two other cold fronts are found. This cold arm is a
prediction of current high resolution numerical simulations as a result of an
off-center encounter with a less massive pure dark matter halo and we suggest
that the cold fronts in A496 provide the first clear corroboration of such
model, where the closest encounter happened ~ 0.5 Gyr ago. We also argue for a
possible candidate dark matter halo responsible for the cold fronts in the
outskirts of A496.Comment: 11 ApJ pages, 1 Table, 16 Figures, accepted for publication in the
Astrophysical Journal. For full version with all hi-res figures click on
http://www.astro.lsa.umich.edu/~rdupke/a496sub.pd
Oblique triangular antiferromagnetic phase in CsCuCoCl
The spin-1/2 stacked triangular antiferromagnet CsCuCoCl with
undergoes two phase transitions at zero field. The
low-temperature phase is produced by the small amount of Co doping. In
order to investigate the magnetic structures of the two ordered phases, the
neutron elastic scattering experiments have been carried out for the sample
with . It is found that the intermediate phase is identical to
the ordered phase of CsCuCl, and that the low-temperature phase is an
oblique triangular antiferromagnetic phase in which the spins form a triangular
structure in a plane tilted from the basal plane. The tilting angle which is
42 at K decreases with increasing temperature, and becomes
zero at K. An off-diagonal exchange term is proposed as the
origin of the oblique phase.Comment: 6 pages, 7 figure
The Effect of Changes in the ASCA Calibration on the Fe-Kalpha Lines in Active Galaxies
The ASCA calibration has evolved considerably since launch and indeed, is
still evolving. There have been concerns in the literature that changes in the
ASCA calibration have resulted in the Fe-Kalpha lines in active galaxies (AGN)
now being systematically narrower than was originally thought. If this were
true, a large body of ASCA results would be impacted. In particular, it has
been claimed that the broad red wing (when present) of the Fe-Kalpha line has
been considerably weakened by changes in the ASCA calibration. We demonstrate
explicitly that changes in the ASCA calibration over a period of about eight
years have a negligible effect on the width, strength, or shape of the
Fe-Kalpha lines. The reduction in both width and equivalent width is only ~8%
or less. We confirm this with simulations and individual sources, as well as
sample average profiles. The average profile for type 1 AGN is still very
broad, with the red wing extending down to ~4 keV. The reason for the claimed,
apparently large, discrepancies is that in some sources the \fekalfa line is
complex, and a single-Gaussian model, being an inadequate description of the
line profile, picks up different portions of the profile with different
calibration. Single-Gaussian fits do not therefore model all of the line
emission in some sources, in which case they do not compare old and current
calibration since the models do not then describe the data.Comment: Accepted for publication in the Astrophysical Journal, Vol. 569, 10
April, 2002. 22 pages, 4 figure
Black String Perturbations in RS1 Model
We present a general formalism for black string perturbations in
Randall-Sundrum 1 model (RS1). First, we derive the master equation for the
electric part of the Weyl tensor . Solving the master equation
using the gradient expansion method, we give the effective Teukolsky equation
on the brane at low energy. It is useful to estimate gravitational waves
emitted by perturbed rotating black strings. We also argue the effect of the
Gregory-Laflamme instability on the brane using our formalism.Comment: 14 pages, Based on a talk presented at ACRGR4, the 4th Australasian
Conference on General Relativity and Gravitation, Monash University,
Melbourne, January 2004. To appear in the proceedings, in General Relativity
and Gravitatio
Nonlinear Pseudo-Supersymmetry in the Framework of N-fold Supersymmetry
We recall the importance of recognizing the different mathematical nature of
various concepts relating to PT-symmetric quantum theories. After clarifying
the relation between supersymmetry and pseudo-supersymmetry, we prove
generically that nonlinear pseudo-supersymmetry, recently proposed by Sinha and
Roy, is just a special case of N-fold supersymmetry. In particular, we show
that all the models constructed by these authors have type A 2-fold
supersymmetry. Furthermore, we prove that an arbitrary one-body quantum
Hamiltonian which admits two (local) solutions in closed form belongs to type A
2-fold supersymmetry, irrespective of whether or not it is Hermitian,
PT-symmetric, pseudo-Hermitian, and so on.Comment: 10 pages, no figures; typos correcte
Методи інтенсифікації виробництва неконцентрованої азотної кислоти
З'ясовано, що азотна кислота є стратегічним продуктом, виробництво якого необхідно для розвитку країни. Наведено аналіз можливих варіантів одержання продукту та обґрунтування способу виробництва в Україні. Розглянуто екологічні аспекти виробництва азотної кислоти. Установлено недоліки виробництва. Запропоновано спосіб виробництва.It was found out that nitric acid is a strategic product, the production of which is necessary for the development of the country. The analysis of possible variants of obtaining a product and the substantiation of the method of production in Ukraine is given. The environmental aspects of production of nitric acid are considered. The defects of production are established. The method of production is offered
Upper Bound on the First Star Formation History
Our understanding of the nature of the extragalactic background light (EBL)
has improved with the recent development of gamma-ray observation techniques.
An open subject in the context of the EBL is the reionization epoch, which is
an important probe of the formation history of first stars, the so-called
Population III (Pop III) stars. Although the mechanisms for the formation of
Pop III stars are rather well understood on theoretical grounds, their
formation history is still veiled in mystery because of their faintness. To
shed light into this matter, we study jointly the gamma-ray opacity of distant
objects and the reionization constraints from studies of intergalactic gas. By
combining these studies, we obtain a sensitive upper bound on the Pop III star
formation rate density as at
, where and are the escape fraction of ionizing
photons from galaxies and the clumping factor of the intergalactic hydrogen
gas. This limit is a times tighter constraint compared with previous
studies that take into account gamma-ray opacity constraints only. Even if we
do not include the current gamma-ray constraints, the results do not change.
This is because the detected gamma-ray sources are still at where
the reionization has already finished.Comment: 5 pages, 2 figures, accepted for publication in ApJ
Well-being of Pensioners. A Subjective Assessment of the Life's Quality (By the Example of China and Russia)
The well-being of pensioners depends on not only objective factors, but also subjective. Subjective assessment of the life's quality occupies an irreplaceable position in the welfare of pensioners. This study is limited by the following restrictions: results of the survey (80 profiles in Russia, 154 questionnaires in China): 18 questions for both objective and subjective assessments; deviation of the quality of life of pensioners in Russia and China; recommendations for improving pension policy (from the standpoint of the interests of the person and the state).We proved hypothesis that, despite the significant differences assessment of the life's quality and welfare of older persons in China and Russia, subjective assessment is important. A key way of the well-being of older persons is a union of state support, personal and corporate resources
Coherent Acoustic Perturbation of Second-Harmonic-Generation in NiO
We investigate the structural and magnetic origins of the unusual ultrafast
second-harmonicgeneration (SHG) response of femtosecond-laser-excited nickel
oxide (NiO) previously attributed to oscillatory reorientation dynamics of the
magnetic structure induced by d-d excitations. Using time-resolved x-ray
diffraction from the (3/2 3/2 3/2) magnetic planes, we show that changes in the
magnitude of the magnetic structure factor following ultrafast optical
excitation are limited to = 1.5% in the first 30 ps. An
extended investigation of the ultrafast SHG response reveals a strong
dependence on wavelength as well as characteristic echoes, both of which give
evidence for an acoustic origin of the dynamics. We therefore propose an
alternative mechanism for the SHG response based on perturbations of the
nonlinear susceptibility via optically induced strain in a spatially confined
medium. In this model, the two observed oscillation periods can be understood
as the times required for an acoustic strain wave to traverse one coherence
length of the SHG process in either the collinear or anti-collinear geometries.Comment: 26 pages, 7 figure
Coherent quasi-particles-to-incoherent hole-carriers crossover in underdoped cuprates
In underdoped cuprates, only a portion of the Fermi surface survives as Fermi
arcs due to pseudogap opening. In hole-doped LaCuO, we have deduced
the "coherence temperature" of quasi-particles on the Fermi arc above
which the broadened leading edge position in angle-integrated photoemission
spectra is shifted away from the Fermi level and the quasi-particle concept
starts to lose its meaning. is found to rapidly increase with hole
doping, an opposite behavior to the pseudogap temperature . The
superconducting dome is thus located below both and , indicating
that the superconductivity emerges out of the coherent Fermionic
quasi-particles on the Fermi arc. remains small in the underdoped
region, indicating that incoherent charge carriers originating from the Fermi
arc are responsible for the apparently metallic transport at high temperatures
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