6,330 research outputs found
The cluster of galaxies Abell 376
We present a dynamical analysis of the galaxy cluster Abell 376 based on a
set of 73 velocities, most of them measured at Pic du Midi and Haute-Provence
observatories and completed with data from the literature. Data on individual
galaxies are presented and the accuracy of the determined velocities is
discussed as well as some properties of the cluster. We obtained an improved
mean redshift value z=0.0478^{+0.005}_{-0.006} and velocity dispersion
sigma=852^{+120}_{-76}km/s. Our analysis indicates that inside a radius of
900h_{70}^{-1}kpc (15 arcmin) the cluster is well relaxed without any
remarkable feature and the X-ray emission traces fairly well the galaxy
distribution. A possible substructure is seen at 20 arcmin from the centre
towards the Southwest direction, but is not confirmed by the velocity field.
This SW clump is, however, kinematically bound to the main structure of Abell
376. A dense condensation of galaxies is detected at 46 arcmin (projected
distance 2.6h_{70}^{-1}Mpc) from the centre towards the Northwest and analysis
of the apparent luminosity distribution of its galaxies suggests that this
clump is part of the large scale structure of Abell 376. X-ray spectroscopic
analysis of ASCA data resulted in a temperature kT = 4.3+/-0.4 keV and metal
abundance Z = 0.32+/-0.08 Z_solar. The velocity dispersion corresponding to
this temperature using the T_X-sigma scaling relation is in agreement with the
measured galaxies velocities.Comment: 11 pages, 10 figures, accepted for publication in A&
Numerical Simulation of Magnetic Interactions in Polycrystalline YFeO3
The magnetic behavior of polycrystalline yttrium orthoferrite was studied
from the experimental and theoretical points of view. Magnetization
measurements up to 170 kOe were carried out on a single-phase YFeO3 sample
synthesized from heterobimetallic alkoxides. The complex interplay between
weak-ferromagnetic and antiferromagnetic interactions, observed in the
experimental M(H) curves, was successfully simulated by locally minimizing the
magnetic energy of two interacting Fe sublattices. The resulting values of
exchange field (H_E = 5590 kOe), anisotropy field (H_A = 0.5 kOe) and
Dzyaloshinsky-Moriya antisymmetric field (H_D = 149 kOe) are in good agreement
with previous reports on this system.Comment: 26 pages, 9 figure
Embedded interdigital transducers for high frequency surface acoustic waves on GaAs
We investigate high-performance, high-frequency interdigital transducers (IDTs) for the generation of surface acoustic waves(SAWs) on GaAs substrates, where the metal fingers are embedded in the substrate. We demonstrate that the acoustic reflections and the scattering of the surface modes into the substrate become considerably reduced in these transducers, leading to an increased output power. The finger embedding process is particularly relevant for the generation of powerful beams of high-frequency SAWs on weak piezoelectric substrates (such as most of the semiconducting materials) using long IDTs. We also show that the reflection reduction is important for the design of focusing single-finger IDTs, since it minimizes the effects of the finger grating on the angular dependence of the phase velocit
Multimodal imaging analyses of hyperreflective dot-like lesions in acute syphilitic posterior placoid chorioretinopathy
Background: Retrospective review of one acute syphilitic posterior placoid chorioretinitis (ASPPC) case with serological evidence of syphilis who had ocular signs and symptoms not attributable to other diseases. Enface and spectral-domain optical coherence tomographySD-OCT were analyzed at the time of presentation and at 1-month visit following initiation of treatment. The study patient underwent standard treatment for neurosyphilis. Results: Ophthalmic examination and imaging studies were consistent with the diagnosis of ASPPC. The patient age was 33 year-old and the baseline visual acuity was 20/400 and 20/80 in the right and left eyes, respectively. At presentation, SD-OCT scans showed disruption and loss of the ellipsoid zone (EZ), small nodular elevations on retinal pigment epithelium (RPE) and punctate hyperreflectivity in the choroid. Enface OCT at the level of RPE and EZ demonstrated multiple hyperreflective dot-like lesions simmetrically distributed within the macular area. These dot-like lesions corresponded to the small nodular elevations on RPE and to disruption/loss of EZ observed with SD-OCT. One month after neurosyphilis therapy, the visual acuity improved and the outer retinal changes partially reversed in both eyes. Conclusions: We report the outer retinal findings and its correlation using both en-face and SD-OCT in a patient with ASPPC. En-face OCT imaging provides a more precise outer retinal layers analyses allowing a better understanding of the ASPPC pathophysiology.Univ Fed Sao Paulo, Dept Ophthalmol, Sao Paulo, BrazilFed Univ Sao Paulo UNIFESP, Rua Botucatu,821,Vila Clementino, BR-04023062 Sao Paulo, SP, BrazilUniv Fed Sao Paulo, Dept Ophthalmol, Sao Paulo, BrazilFed Univ Sao Paulo UNIFESP, Rua Botucatu,821,Vila Clementino, BR-04023062 Sao Paulo, SP, BrazilWeb of Scienc
Effect of angular momentum on equilibrium properties of a self-gravitating system
The microcanonical properties of a two dimensional system of N classical
particles interacting via a smoothed Newtonian potential as a function of the
total energy E and the total angular momentum L are discussed. In order to
estimate suitable observables a numerical method based on an importance
sampling algorithm is presented. The entropy surface shows a negative specific
heat region at fixed L for all L. Observables probing the average mass
distribution are used to understand the link between thermostatistical
properties and the spatial distribution of particles. In order to define a
phase in non-extensive system we introduce a more general observable than the
one proposed by Gross and Votyakov [Eur. Phys. J. B:15, 115 (2000)]: the sign
of the largest eigenvalue of the entropy surface curvature. At large E the
gravitational system is in a homogeneous gas phase. At low E there are several
collapse phases; at L=0 there is a single cluster phase and for L>0 there are
several phases with 2 clusters. All these pure phases are separated by first
order phase transition regions. The signal of critical behaviour emerges at
different points of the parameter space (E,L). We also discuss the ensemble
introduced in a recent pre-print by Klinko & Miller; this ensemble is the
canonical analogue of the one at constant energy and constant angular momentum.
We show that a huge loss of informations appears if we treat the system as a
function of intensive parameters: besides the known non-equivalence at first
order phase transitions, there exit in the microcanonical ensemble some values
of the temperature and the angular velocity for which the corresponding
canonical ensemble does not exist, i.e. the partition sum diverges.Comment: 17 pages, 11 figures, submitted to Phys. Rev.
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