8,334 research outputs found
Boundary effects on the scaling of the superfluid density
We study numerically the influence of the substrate (boundary conditions) on
the finite--size scaling properties of the superfluid density in
superfluid films of thickness within the XY model employing the Monte Carlo
method. Our results suggest that the jump at the
Kosterlitz--Thouless transition temperature 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
In this study we use simulations of 128 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\Omega_0 = 0.2nD < 15 h^{-1}n-$dependent way.Comment: 22 pages, requires aaspp4.sty, flushrt.sty, and epsf.sty Revised
manuscript, accepted for publication in Ap
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Role of appetitive phenotype trajectory groups on child body weight during a family-based treatment for children with overweight or obesity.
ObjectiveEmerging evidence suggests that individual appetitive traits may usefully explain patterns of weight loss in behavioral weight loss treatments for children. The objective of this study was to identify trajectories of child appetitive traits and the impact on child weight changes over time.MethodsSecondary data analyses of a randomized noninferiority trial conducted between 2011 and 2015 evaluated children's appetitive traits and weight loss. Children with overweight and obesity (mean age = 10.4; mean BMI z = 2.0; 67% girls; 32% Hispanic) and their parent (mean age = 42.9; mean BMI = 31.9; 87% women; 31% Hispanic) participated in weight loss programs and completed assessments at baseline, 3, 6,12, and 24 months. Repeated assessments of child appetitive traits, including satiety responsiveness, food responsiveness and emotional eating, were used to identify parsimonious grouping of change trajectories. Linear mixed-effects models were used to identify the impact of group trajectory on child BMIz change over time.ResultsOne hundred fifty children and their parent enrolled in the study. The three-group trajectory model was the most parsimonious and included a high satiety responsive group (HighSR; 47.4%), a high food responsive group (HighFR; 34.6%), and a high emotional eating group (HighEE; 18.0%). Children in all trajectories lost weight at approximately the same rate during treatment, however, only the HighSR group maintained their weight loss during follow-ups, while the HighFR and HighEE groups regained weight (adjusted p-value < 0.05).ConclusionsDistinct trajectories of child appetitive traits were associated with differential weight loss maintenance. Identified high-risk subgroups may suggest opportunities for targeted intervention and maintenance programs
Race at the Pivot Point: The Future of Race-Based Policies to Remedy De Jure Segregation After Parents Involved in Community Schools
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
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
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 and amplitudes of mass fluctuation
. The mean ellipticity increases monotonically with redshift for
all models. Larger values of , i.e., earlier cluster formation
time, produce lower ellipticities. The dependence of ellipticity on
is relatively weak in the range for high mass
clusters. The mean ellipticity decreases linearly with the
amplitude of fluctuations at the cluster redshift , nearly independent of
; 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 , the mean
ellipticity of high mass clusters is approximated by . 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, .Comment: 16 pages, 4 figure
Alignments of Voids in the Cosmic Web
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
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
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