7,327 research outputs found

    Alignments of the Dominant Galaxies in Poor Clusters

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    We have examined the orientations of brightest cluster galaxies (BCGs) in poor MKW and AWM clusters and find that, like their counterparts in richer Abell clusters, poor cluster BCGs exhibit a strong propensity to be aligned with the principal axes of their host clusters as well as the surrounding distribution of nearby (< 20/h Mpc) Abell clusters. The processes responsible for dominant galaxy alignments are therefore independent of cluster richness. We argue that these alignments most likely arise from anisotropic infall of material into clusters along large-scale filaments.Comment: 8 pages, 5 figure

    The Ellipticity and Orientation of Clusters of Galaxies from N-Body Experiments

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    In this study we use simulations of 1283^3 particles to study the ellipticity and orientation of clusters of galaxies in N-body simulations of differing power-law initial spectra (P(k) \propto k^n ,n = +1, 0, -1, -2),anddensityparameters(), and density parameters (\Omega_0 = 0.2to1.0).Furthermore,unlikemosttheoreticalstudieswemimicmostobserversbyremovingallparticleswhichlieatdistancesgreaterthan21/hMpcfromtheclustercenterofmass.Wecomputedtheaxialratioandtheprincipalaxesusingtheinertiatensorofeachcluster.Themeanellipticityofclustersincreasesstronglywithincreasing to 1.0). Furthermore, unlike most theoretical studies we mimic most observers by removing all particles which lie at distances greater than 2 1/h Mpc from the cluster center of mass. We computed the axial ratio and the principal axes using the inertia tensor of each cluster. The mean ellipticity of clusters increases strongly with increasing n.Wealsofindthatclusterstendtobecomemoresphericalatsmallerradii.Wecomparedtheorientationofaclustertotheorientationofneighboringclustersasafunctionofdistance(correlation).Inaddition,weconsideredwhetheraclustersmajoraxistendstoliealongthelineconnectingittoaneighboringcluster,asafunctionofdistance(alignment).Bothalignmentsandcorrelationswerecomputedinthreedimensionsandinprojectiontomimicobservationalsurveys.Ourresultsshowthatsignificantalignmentsexistforallspectraatsmallseparations(. We also find that clusters tend to become more spherical at smaller radii. We compared the orientation of a cluster to the orientation of neighboring clusters as a function of distance (correlation). In addition, we considered whether a cluster's major axis tends to lie along the line connecting it to a neighboring cluster, as a function of distance (alignment). Both alignments and correlations were computed in three dimensions and in projection to mimic observational surveys. Our results show that significant alignments exist for all spectra at small separations (D < 15 h^{-1}Mpc)butdropsoffatlargerdistanceinastrongly Mpc) but drops off at larger distance in a strongly n-$dependent way.Comment: 22 pages, requires aaspp4.sty, flushrt.sty, and epsf.sty Revised manuscript, accepted for publication in Ap

    AAV-mediated and pharmacological induction of Hsp70 expression stimulates survival of retinal ganglion cells following axonal injury.

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    We evaluated the effect of AAV2- and 17-AAG (17-N-allylamino-17-demethoxygeldanamycin)-mediated upregulation of Hsp70 expression on the survival of retinal ganglion cells (RGCs) injured by optic nerve crush (ONC). AAV2-Hsp70 expression in the retina was primarily observed in the ganglion cell layer. Approximately 75% of all transfected cells were RGCs. RGC survival in AAV2-Hsp70-injected animals was increased by an average of 110% 2 weeks after the axonal injury compared with the control. The increase in cell numbers was not even across the retinas with a maximum effect of approximately 306% observed in the inferior quadrant. 17-AAG-mediated induction of Hsp70 expression has been associated with cell protection in various models of neurodegenerative diseases. We show here that a single intravitreal injection of 17-AAG (0.2 ug ul(-1)) results in an increased survival of ONC-injured RGCs by approximately 49% compared with the vehicle-treated animals. Expression of Hsp70 in retinas of 17-AAG-treated animals was upregulated approximately by twofold compared with control animals. Our data support the idea that the upregulation of Hsp70 has a beneficial effect on the survival of injured RGCs, and the induction of this protein could be viewed as a potential neuroprotective strategy for optic neuropathies

    Superconducting gap structure of the 115's revisited

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    Density functional theory calculations of the electronic structure of Ce- and Pu-based heavy fermion superconductors in the so-called 115 family are performed. The gap equation is used to consider which superconducting order parameters are most favorable assuming a pairing interaction that is peaked at (\pi,\pi,q_z) - the wavevector for the antiferromagnetic ordering found in close proximity. In addition to the commonly accepted dx2y2d_{x^2-y^2} order parameter, there is evidence that an extended s-wave order parameter with nodes is also plausible. We discuss whether these results are consistent with current observations and possible measurements that could help distinguish between these scenarios.Comment: 8 pages, 4 figures; Accepted for publication in JPC

    Boundary effects on the scaling of the superfluid density

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    We study numerically the influence of the substrate (boundary conditions) on the finite--size scaling properties of the superfluid density ρs\rho_s in superfluid films of thickness HH within the XY model employing the Monte Carlo method. Our results suggest that the jump ρsH/Tc\rho_s H/T_c at the Kosterlitz--Thouless transition temperature TcT_c depends on the boundary conditions.Comment: 2 pages, 1 Latex file, 1 postscript figure, 2 style file
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