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.