8,334 research outputs found

    IC Design for the TV Receiver

    Get PDF
    Not listed

    Boundary effects on the scaling of the superfluid density

    Full text link
    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

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

    Get PDF
    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

    Race at the Pivot Point: The Future of Race-Based Policies to Remedy De Jure Segregation After Parents Involved in Community Schools

    Get PDF
    This article examines the perhaps unintended consequences of changing legal doctrine. Most commentary on the U.S. Supreme Court Parents Involved in Community Schools (“PICS”) decision explores PICS’ impact upon voluntary race-based policies to remedy unintentional de facto racial segregation. In contrast, this analysis explores PICS’ impact upon mandatory race-based policies to remedy government-sponsored de jure racial segregation. After PICS, the Fourteenth Amendment’s essence and character can turn on a finding of unitary status, a purely factual and somewhat subjective determination reviewable only for clear error. Under the Equal Protection Clause, a school district found to operate a de jure segregated school system may be forced to use race-based policies to undo the effects of such segregation. The instant, however, that a district judge signs the court order granting that school district unitary status, the Equal Protection Clause then forbids the school district from using the identical race-based policies to address the effects of de facto segregation. PICS thus has injected into the Equal Protection Clause’s schizophrenic identity a never-before-seen wrinkle called a pivot point.The pivot point arises when school systems constitutionally required to use race-based policies to remedy de jure segregation become constitutionally prohibited from using the same race-based policies to address de facto segregation voluntarily. After exploring PICS’ effect on de jure school systems’ legal obligations, we explore the ramifications of a constitutional standard that abruptly transforms legal obligations on the basis of a subjective factual determination. This pivot point may induce bizarre effects in familiar legal processes, with unpredictable consequences. In its zeal to alter Brown v. Board of Education’s legacy, the PICS majority overlooked the structural impact of its decision on de jure systems governed by a very different vision of the Equal Protection Clause. The resulting pivot point is a testament to the dangers of parsing individual rights too finely at the expense of maintaining stability in legal structure and process

    First Results from the Large Area Lyman Alpha Survey

    Get PDF
    We report on a new survey for z=4.5 Lyman alpha sources, the Large Area Lyman Alpha (LALA) survey. Our survey achieves an unprecedented combination of volume and sensitivity by using narrow-band filters on the new 8192x8192 pixel CCD Mosaic Camera at the 4 meter Mayall telescope of Kitt Peak National Observatory. Well-detected sources with flux and equivalent width matching known high redshift Lyman alpha galaxies (i.e., observed equivalent width above 80 Angstroms and line+continuum flux between 2.6e-17 and 5.2e-17 erg/cm^2/sec in an 80 Angstrom filter) have an observed surface density corresponding to 11000 +- 700 per square degree per unit redshift at z=4.5. Spatial variation in this surface density is apparent on comparison between counts in 6561 and 6730 Angstrom filters. Early spectroscopic followup results from the Keck telescope included three sources meeting our criteria for good Lyman alpha candidates. Of these, one is confirmed as a z=4.52 source, while another remains consistent with either z=4.55 or z=0.81. We infer that 30 to 50% of our good candidates are bona fide Lyman alpha emitters, implying a net density of about 4000 Lyman alpha galaxies per square degree per unit redshift.Comment: 10 pages, 2 figures (3 .ps files), uses AASTeX 4. Submitted to The Astrophysical Journal Letter

    Cluster Ellipticities as a Cosmological Probe

    Full text link
    We investigate the dependence of ellipticities of clusters of galaxies on cosmological parameters using large-scale cosmological simulations. We determine cluster ellipticities out to redshift unity for LCDM models with different mean densities Ωm\Omega_m and amplitudes of mass fluctuation σ8,0\sigma_{8,0}. The mean ellipticity increases monotonically with redshift for all models. Larger values of σ8,0\sigma_{8,0}, i.e., earlier cluster formation time, produce lower ellipticities. The dependence of ellipticity on Ωm\Omega_m is relatively weak in the range 0.2Ωm0.50.2 \leq \Omega_m \leq 0.5 for high mass clusters. The mean ellipticity eˉ(z)\bar{e}(z) decreases linearly with the amplitude of fluctuations at the cluster redshift zz, nearly independent of Ωm\Omega_m; on average, older clusters are more relaxed and are thus less elliptical. The distribution of ellipticities about the mean is approximated by a Gaussian, allowing a simple characterization of the evolution of ellipticity with redshift as a function of cosmological parameters. At z=0z=0, the mean ellipticity of high mass clusters is approximated by eˉ(z=0)=0.2480.069σ8,0+0.013Ωm,0\bar{e}(z=0) = 0.248-0.069 \sigma_{8,0} + 0.013 \Omega_{m,0}. This relation opens up the possibility that, when compared with future observations of large cluster samples, the mean cluster ellipticity and its evolution could be used as a new, independent tool to constrain cosmological parameters, especially the amplitude of mass fluctuations, σ8,0\sigma_{8,0}.Comment: 16 pages, 4 figure

    Alignments of Voids in the Cosmic Web

    Get PDF
    We investigate the shapes and mutual alignment of voids in the large scale matter distribution of a LCDM cosmology simulation. The voids are identified using the novel WVF void finder technique. The identified voids are quite nonspherical and slightly prolate, with axis ratios in the order of c:b:a approx. 0.5:0.7:1. Their orientations are strongly correlated with significant alignments spanning scales >30 Mpc/h. We also find an intimate link between the cosmic tidal field and the void orientations. Over a very wide range of scales we find a coherent and strong alignment of the voids with the tidal field computed from the smoothed density distribution. This orientation-tide alignment remains significant on scales exceeding twice the typical void size, which shows that the long range external field is responsible for the alignment of the voids. This confirms the view that the large scale tidal force field is the main agent for the large scale spatial organization of the Cosmic Web.Comment: 10 pages, 4 figures, submitted to MNRAS, for high resolution version, see http://www.astro.rug.nl/~weygaert/tim1publication/voidshape.pd

    The dynamics of Abell 2634

    Get PDF
    We have amassed a large sample of velocity data for the cluster of galaxies Abell 2634 which contains the wide-angle tail (WAT) radio source 3C 465. Robust indicators of location and scale and their confidence intervals are used to determine if the cD galaxy, containing the WAT, has a significant peculiar motion. We find a cD peculiar radial velocity of 219 plus or minus 98 km s(exp -1). Further dynamical analyses, including substructure and normality tests, suggest that A 2634 is an unrelaxed cluster whose radio source structure may be bent by the turbulent gas of a recent cluster-subcluster merger
    corecore