272 research outputs found
A New Halo Finding Method for N-Body Simulations
We have developed a new halo finding method, Physically Self-Bound (PSB)
group finding algorithm, which can efficiently identify halos located even at
crowded regions. This method combines two physical criteria such as the tidal
radius of a halo and the total energy of each particle to find member
particles. Two hierarchical meshes are used to increase the speed and the power
of halo identification in the parallel computing environments. First, a coarse
mesh with cell size equal to the mean particle separation is
used to obtain the density field over the whole simulation box. Mesh cells
having density contrast higher than a local cutoff threshold
are extracted and linked together for those adjacent to each other. This
produces local-cell groups. Second, a finer mesh is used to obtain density
field within each local-cell group and to identify halos. If a density shell
contains only one density peak, its particles are assigned to the density peak.
But in the case of a density shell surrounding at least two density peaks, we
use both the tidal radii of halo candidates enclosed by the shell and the total
energy criterion to find physically bound particles with respect to each halo.
Similar to DENMAX and HOP, the \hfind method can efficiently identify small
halos embedded in a large halo, while the FoF and the SO do not resolve such
small halos. We apply our new halo finding method to a 1-Giga particle
simulation of the CDM model and compare the resulting mass function
with those of previous studies. The abundance of physically self-bound halos is
larger at the low mass scale and smaller at the high mass scale than proposed
by the Jenkins et al. (2001) who used the FoF and SO methods. (abridged)Comment: 10 pages, 8 figs, submitted to Ap
BOSS Great Wall: morphology, luminosity, and mass
We study the morphology, luminosity and mass of the superclusters from the
BOSS Great Wall (BGW), a recently discovered very rich supercluster complex at
the redshift . We have employed the Minkowski functionals to quantify
supercluster morphology. We calculate supercluster luminosities and masses
using two methods. Firstly, we used data about the luminosities and stellar
masses of high stellar mass galaxies with .
Secondly, we applied a scaling relation that combines morphological and
physical parameters of superclusters to obtain supercluster luminosities, and
obtained supercluster masses using the mass-to-light ratios found for local
rich superclusters. We find that the BGW superclusters are very elongated
systems, with shape parameter values of less than . This value is lower
than that found for the most elongated local superclusters. The values of the
fourth Minkowski functional for the richer BGW superclusters (
and ) show that they have a complicated and rich inner structure. We
identify two Planck SZ clusters in the BGW superclusters, one in the richest
BGW supercluster, and another in one of the poor BGW superclusters. The
luminosities of the BGW superclusters are in the range of , and masses in the range of . Supercluster luminosities and masses obtained
with two methods agree well. We conclude that the BGW is a complex of massive,
luminous and large superclusters with very elongated shape. The search and
detailed study, including the morphology analysis of the richest superclusters
and their complexes from observations and simulations can help us to understand
formation and evolution of the cosmic web.Comment: Comments: 10 pages, 2 figures, A&A, in pres
Numerical Methods for the Simulation of Dynamical Mass Transfer in Binaries
We describe computational tools that have been developed to simulate
dynamical mass transfer in semi-detached, polytropic binaries that are
initially executing synchronous rotation upon circular orbits. Initial
equilibrium models are generated with a self-consistent field algorithm; models
are then evolved in time with a parallel, explicit, Eulerian hydrodynamics code
with no assumptions made about the symmetry of the system. Poisson's equation
is solved along with the equations of ideal fluid mechanics to allow us to
treat the nonlinear tidal distortion of the components in a fully
self-consistent manner. We present results from several standard numerical
experiments that have been conducted to assess the general viability and
validity of our tools, and from benchmark simulations that follow the evolution
of two detached systems through five full orbits (up to approximately 90
stellar dynamical times). These benchmark runs allow us to gauge the level of
quantitative accuracy with which simulations of semi-detached systems can be
performed using presently available computing resources. We find that we should
be able to resolve mass transfer at levels per
orbit through approximately 20 orbits with each orbit taking about 30 hours of
computing time on parallel computing platforms.Comment: 34 pages, 20 eps figures, submitted to ApJ
Diagnostic accuracy of Doppler ultrasound technique of the penile arteries in correlation to selective arteriography
In 63% of 265 patients with erectile dysfunction a relevant arterial inflow disturbance was found by Doppler ultrasound examination. Correlation between Doppler and arteriography in 58 patients showed an accuracy of 95% in detecting penile arteries and an accuracy of 91% in discovering a pathological arterial pattern (arterial anomaly or arteriosclerotic obstruction). In 15 patients the arterial inflow was measured additionally by Doppler ultrasound technique after intracavernosal injection of vasoactive drugs (IIVD) (7.5 mg papaverine and 0.25 mg phentolamine). This technique proved to be more reliable than in the flaccid state and markedly facilitated localization and assessment of pathological changes of the cavernosal arteries
Skin microvascular vasodilatory capacity in offspring of two parents with Type 2 diabetes
Aims<br/> Microvascular dysfunction occurs in Type 2 diabetes and in subjects with fasting hyperglycaemia. It is unclear whether this dysfunction relates to dysglycaemia. This study investigated in normogylcaemic individuals whether a genetic predisposition to diabetes, or indices of insulin resistance including endothelial markers, were associated with impaired microvascular function.<br/> Methods<br/> Maximum microvascular hyperaemia to local heating of the skin was measured using laser Doppler flowmetry in 21 normoglycaemic subjects with no family history of diabetes (Group 1) and 21 normoglycaemic age, sex and body mass index-matched offspring of two parents with Type 2 diabetes (Group 2). <br/>Results<br/> Although Group 2 had normal fasting plasma glucose and glucose tolerance tests, the 120-min glucose values were significantly higher at 6.4 (5.3-6.6) mmol/l (median (25th-75th centile)) than the control group at 4.9 (4.6-5.9) mmol/l (P=0.005) and the insulinogenic index was lower at 97.1 (60.9-130.8) vs. 124.0 (97.2-177.7) (P=0.027). Skin maximum microvascular hyperaemia (Group 1: 1.56 (1.39- 1.80) vs. Group 2: 1.53 (1.30-1.98) V, P=0.99) and minimum microvascular resistance which normalizes the hyperaemia data for blood pressure (Group 1: 52.0 (43.2-67.4) vs. Group 2: 56.0 (43.7-69.6) mmHgN, P=0.70) did not differ in the two groups. Significant positive associations occurred between minimum microvascular resistance and indices of the insulin resistance syndrome; plasminogen activator inhibitor type 1 (R-s=0.46, P=0.003), t-PA (R-s=0.36, P=0.03), total cholesterol (R-s=0.35, P=0.02), and triglyceride concentration (R-s=0.35, P=0.02), and an inverse association with insulin sensitivity (R-s=-0.33, P=0.03).<br/> Conclusions<br/> In normoglycaemic adults cutaneous microvascular vasodilatory capacity is associated with features of insulin resistance syndrome, particularly with plasminogen activator inhibitor type 1. A strong family history of Type 2 diabetes alone does not result in impairment in the maximum hyperaemic response
Topology of structure in the Sloan Digital Sky Survey: model testing
We measure the three-dimensional topology of large-scale structure in the
Sloan Digital Sky Survey (SDSS). This allows the genus statistic to be measured
with unprecedented statistical accuracy. The sample size is now sufficiently
large to allow the topology to be an important tool for testing galaxy
formation models. For comparison, we make mock SDSS samples using several
state-of-the-art N-body simulations: the Millennium run of Springel et al.
(2005)(10 billion particles), Kim & Park (2006) CDM models (1.1 billion
particles), and Cen & Ostriker (2006) hydrodynamic code models (8.6 billion
cell hydro mesh). Each of these simulations uses a different method for
modeling galaxy formation. The SDSS data show a genus curve that is broadly
characteristic of that produced by Gaussian random phase initial conditions.
Thus the data strongly support the standard model of inflation where Gaussian
random phase initial conditions are produced by random quantum fluctuations in
the early universe. But on top of this general shape there are measurable
differences produced by non-linear gravitational effects (cf. Matsubara 1994),
and biasing connected with galaxy formation. The N-body simulations have been
tuned to reproduce the power spectrum and multiplicity function but not
topology, so topology is an acid test for these models. The data show a
``meatball'' shift (only partly due to the Sloan Great Wall of Galaxies; this
shift also appears in a sub-sample not containing the Wall) which differs at
the 2.5\sigma level from the results of the Millennium run and the Kim & Park
dark halo models, even including the effects of cosmic variance.Comment: 13 Apj pages, 7 figures High-resolution stereo graphic available at
http://www.astro.princeton.edu/~dclayh/stereo50.ep
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