89 research outputs found
The velocity and mass distribution of clusters of galaxies from the CNOC1 cluster redshift survey
In the context of the CNOC1 cluster survey, redshifts were obtained for
galaxies in 16 clusters. The resulting sample is ideally suited for an analysis
of the internal velocity and mass distribution of clusters. Previous analyses
of this dataset used the Jeans equation to model the projected velocity
dispersion profile. However, the results of such an analysis always yield a
strong degeneracy between the mass density profile and the velocity dispersion
anisotropy profile. Here we analyze the full (R,v) dataset of galaxy positions
and velocities in an attempt to break this degeneracy. We build an `ensemble
cluster' from the individual clusters under the assumption that they form a
homologous sequence. To interpret the data we study a one-parameter family of
spherical models with different constant velocity dispersion anisotropy. The
best-fit model is sought using a variety of statistics, including the overall
likelihood of the dataset. Although the results of our analysis depend slightly
on which statistic is used to judge the models, all statistics agree that the
best-fit model is close to isotropic. This result derives primarily from the
fact that the observed grand-total velocity histogram is close to Gaussian,
which is not expected to be the case for a strongly anisotropic model. The
best-fitting models have a mass-to-number-density ratio that is approximately
independent of radius over the range constrained by the data. They also have a
mass-density profile that is consistent with the dark matter halo profile
advocated by Navarro, Frenk & White, in terms of both the profile shape and the
characteristic scale length. This adds important new weight to the evidence
that clusters do indeed follow this proposed universal mass density profile.
[Abridged]Comment: 37 pages, LaTeX, with 11 PostScript figures. Accepted by the
Astronomical Journal, to appear in the May 2000 issue. This replacement
version contains an additional Appendix and one additional Figure with
respect to the version submitted to astro-ph originall
The Apparent and Intrinsic Shape of the APM Galaxy Clusters
We estimate the distribution of intrinsic shapes of APM galaxy clusters from
the distribution of their apparent shapes. We measure the projected cluster
ellipticities using two alternative methods. The first method is based on
moments of the discrete galaxy distribution while the second is based on
moments of the smoothed galaxy distribution. We study the performance of both
methods using Monte Carlo cluster simulations covering the range of APM cluster
distances and including a random distribution of background galaxies. We find
that the first method suffers from severe systematic biases, whereas the second
is more reliable. After excluding clusters dominated by substructure and
quantifying the systematic biases in our estimated shape parameters, we recover
a corrected distribution of projected ellipticities. We use the non-parametric
kernel method to estimate the smooth apparent ellipticity distribution, and
numerically invert a set of integral equations to recover the corresponding
distribution of intrinsic ellipticities under the assumption that the clusters
are either oblate or prolate spheroids. The prolate spheroidal model fits the
APM cluster data best.Comment: 8 pages, including 7 figures, accepted for publication in MNRA
The mass function of the Las Campanas loose groups of galaxies
We have determined the mass function of loose groups of galaxies in the Las
Campanas Redshift Survey. Loose groups of galaxies in the LCRS range in mass
from M \sim 10^{12} {\rm M}_{\sun} to 10^{15} {\rm M}_{\sun}. We find that
the sample is almost complete for masses in the interval 5\cdot 10^{13}-8\cdot
10^{14} {\rm M}_{\sun}. Comparison of the observed mass function with
theoretical mass functions obtained from N-body simulations shows good
agreement with a CDM model with the parameters ,
and the amplitude of perturbations about
. For smaller masses the mass function of LCRS loose groups
flattens out, differing considerably from the group mass function found by
Girardi and Giuricin (2000) and from mass functions obtained by numerical
simulations.Comment: 9 pages, 7 figures, AA accepte
Influence of nitrogen on diamond growth in oxyacetylene combustion chemical vapor deposition
Shapes and Alignments of Galaxy Cluster Halos
We present distribution functions and spatial correlations of the shapes of
dark matter halos derived from Hubble Volume simulations of a LambdaCDM
universe. We measure both position and velocity shapes within spheres
encompassing mean density 200 times the critical value, and calibrate small-N
systematic errors using Poisson realizations of isothermal spheres and higher
resolution simulations. For halos more massive than 3x10^{14} Msun/h, the shape
distribution function peaks at (minor/major, intermediate/major) axial ratios
of (0.64,0.76) in position, and is rounder in velocity, peaking at (0.72,0.82).
Halo shapes are rounder at lower mass and/or redshift; the mean minor axis
ratio in position follows (M,z) = c_{15,0} [1-\alpha\ln(M/10^{15}Msun/h)]
(1+z)^{-\epsilon}, with c_{15,0}=0.631 \pm 0.001, \alpha=0.023 \pm 0.002 and
\epsilon=0.086 \pm 0.004. Position and velocity principal axes are well aligned
in direction, with median alignment angle , and the axial ratios in
these spaces are correlated in magnitude. We investigate mark correlations of
halo pair orientations using two measures: a simple scalar product shows alignment extending to 30 \hinv \mpc while a filamentary statistic
exhibits non-random alignment extending to scales \sims 200 \hinv \mpc, ten
times the sample two-point correlation length and well into the regime of
negative two-point correlation. Cluster shapes are unaffected by the
large-scale environment; the shape distribution of supercluster members is
consistent with that of the general population.Comment: 12 pages, 8 figures, submitted to Ap
The Potential of Stem Cell Therapy to Repair White Matter Injury in Preterm Infants: Lessons Learned From Experimental Models
Diffuse white matter injury (dWMI) is a major cause of morbidity in the extremely preterm born infant leading to life-long neurological impairments, including deficits in cognitive, motor, sensory, psychological, and behavioral functioning. At present, no treatment options are clinically available to combat dWMI and therefore exploration of novel strategies is urgently needed. In recent years, the pathophysiology underlying dWMI has slowly started to be unraveled, pointing towards the disturbed maturation of oligodendrocytes (OLs) as a key mechanism. Immature OL precursor cells in the developing brain are believed to be highly sensitive to perinatal inflammation and cerebral oxygen fluctuations, leading to impaired OL differentiation and eventually myelination failure. OL lineage development under normal and pathological circumstances and the process of (re)myelination have been studied extensively over the years, often in the context of other adult and pediatric white matter pathologies such as stroke and multiple sclerosis (MS). Various studies have proposed stem cell-based therapeutic strategies to boost white matter regeneration as a potential strategy against a wide range of neurological diseases. In this review we will discuss experimental studies focusing on mesenchymal stem cell (MSC) therapy to reduce white matter injury (WMI) in multiple adult and neonatal neurological diseases. What lessons have been learned from these previous studies and how can we translate this knowledge to application of MSCs for the injured white matter in the preterm infant? A perspective on the current state of stem cell therapy will be given and we will discuss different important considerations of MSCs including cellular sources, timing of treatment and administration routes. Furthermore, we reflect on optimization strategies that could potentially reinforce stem cell therapy, including preconditioning and genetic engineering of stem cells or using cell-free stem cell products, to optimize cell-based strategy for vulnerable preterm infants in the near future
Increased Myogenic and Protein Turnover Signaling in Skeletal Muscle of Chronic Obstructive Pulmonary Disease Patients With Sarcopenia
Transforming matters: sustaining gold lifeways in artisanal and small-scale mining
Growth strategies in mining regions promote gold extraction basedonindustrial mining, associating Artisanal and Small-scale Gold Mining (ASGM) with persistent informality. Against this background, we consider how to approach transformations to sustainability in ASGM. Acknowledging how problematic this topic is for sustainability debates,given howASGM is associated with a host of environmental and social problems,we argue that a justice lens demands we confront such challenges within the global politics of sustainability. This leads us to review advances inthe study of ASGM, linked to debates on extractivism, resource materialities, and informality. We use the notion of gold lifeways to capture how the matter of mining shapes different worlds of extraction. We argue that consideration of the potential for transformations to sustainability needs to be grounded within the realities of ASGM. This necessitates giving value to miners’ knowledge(s), perspectives and interests, while recognising the plurality of mining futures. Nevertheless, we conclude that between the immediacy of precarious work and the structural barriers to change in ASGM, the challenges for transformation cannot be underestimated.NWOGlobal Challenges (FSW
Sex Differences in the Brain: A Whole Body Perspective
Most writing on sexual differentiation of the mammalian brain (including our own) considers just two organs: the gonads and the brain. This perspective, which leaves out all other body parts, misleads us in several ways. First, there is accumulating evidence that all organs are sexually differentiated, and that sex differences in peripheral organs affect the brain. We demonstrate this by reviewing examples involving sex differences in muscles, adipose tissue, the liver, immune system, gut, kidneys, bladder, and placenta that affect the nervous system and behavior. The second consequence of ignoring other organs when considering neural sex differences is that we are likely to miss the fact that some brain sex differences develop to compensate for differences in the internal environment (i.e., because male and female brains operate in different bodies, sex differences are required to make output/function more similar in the two sexes). We also consider evidence that sex differences in sensory systems cause male and female brains to perceive different information about the world; the two sexes are also perceived by the world differently and therefore exposed to differences in experience via treatment by others. Although the topic of sex differences in the brain is often seen as much more emotionally charged than studies of sex differences in other organs, the dichotomy is largely false. By putting the brain firmly back in the body, sex differences in the brain are predictable and can be more completely understood
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