2,218 research outputs found
Pharmacologic counter measures minimizing post-space flight orthostatic intolerance
The effect of bed rest on drug disposition and physiological function was investigated as part of a project to determine the cardiovascular effects of space flight. One group of subjects was given doses of lidocane, penicillin-G, and ICG during a control period and following seven days of bed rest. Cardiac function was evaluated by echo-cardiography. Renal function was evaluated in a second group before and after several days of bed rest. Inulin, para-aminohippurate, and dextran clearances were studied. In the first group, the post-bed rest parameters were not statistically different from the pre-bed rest valves. In the second study, renal function did not change significantly after seven days of bed rest. Plans for future research are reviewed
Hydrodynamical simulations of galaxy properties: Environmental effects
Using N-body+hydro simulations we study relations between the local
environments of galaxies on 0.5 Mpc scale and properties of the luminous
components of galaxies. Our numerical simulations include effects of star
formation and supernova feedback in different cosmological scenarios: the
standard Cold Dark Matter model, the Broken Scale Invariance model (BSI), and a
model with cosmological constant (LCDM).
In this paper, we concentrate on the effects of environment on colors and
morphologies of galaxies, on the star formation rate and on the relation
between the total luminosity of a galaxy and its circular velocity. We
demonstrate a statistically significant theoretical relationship between
morphology and environment. In particular, there is a strong tendency for
high-mass galaxies and for elliptical galaxies to form in denser environments,
in agreement with observations. We find that in models with denser environments
(CDM scenario) ~ 13 % of the galactic halos can be identified as field
ellipticals, according to their colors. In simulations with less clustering
(BSI and LCDM), the fraction of ellipticals is considerably lower (~ 2-3 %).
The strong sensitivity of morphological type to environment is rather
remarkable because our results are applicable to ``field'' galaxies and small
groups. If all galaxies in our simulations are included, we find a
statistically significant dependence of the galaxy luminosity - circular
velocity relation on dark matter overdensity within spheres of radius 0.5 Mpc,
for the CDM simulations. But if we remove ``elliptical'' galaxies from our
analysis to mimic the Tully-Fisher relation for spirals, then no dependence is
found in any model.Comment: 44 pages, 21 figures (17 included). Submitted to New Astronomy. GIFF
color plots and the complete paper in Postscript (including color figures)
can be found at http://astrosg.ft.uam.es/~gustavo/newas
Large-scale structure formation for power spectra with broken scale invariance
We have simulated the formation of large-scale structure arising from
COBE-normalized spectra computed by convolving a primordial double-inflation
perturbation spectrum with the CDM transfer function. Due to the broken scale
invariance ('BSI') characterizing the primordial perturbation spectrum, this
model has less small-scale power than the (COBE-normalized) standard CDM model.
The particle-mesh code (with cells and particles) includes a
model for thermodynamic evolution of baryons in addition to the usual
gravitational dynamics of dark matter. It provides an estimate of the local gas
temperature. In particular, our galaxy-finding procedure seeks peaks in the
distribution of gas that has cooled. It exploits the fact that ``cold"
particles trace visible matter better than average and thus provides a natural
biasing mechanism. The basic picture of large-scale structure formation in the
BSI model is the familiar hierarchical clustering scenario. We obtain particle
in cell statistics, the galaxy correlation function, the cluster abundance and
the cluster-cluster correlation function and statistics for large and small
scale velocity fields. We also report here on a semi-quantitative study of the
distribution of gas in different temperature ranges. Based on confrontation
with observations and comparison with standard CDM, we conclude that the BSI
scenario could represent a promising modification of the CDM picture capable of
describing many details of large-scale structure formation.Comment: 15 pages, Latex using mn.sty, uuencoded compressed ps-file with 15
figures by anonymous ftp to ftp://ftp.aip.de/incoming/mueller/bsi.u
Hydrodynamical simulations of galaxy formation: effects of supernova feedback
We numerically simulate some of the most critical physical processes in
galaxy formation: The supernova feedback, in conjunction with gasdynamics and
gravity, plays a crucial role in determining how galaxies arise within the
context of a model for large-scale structure. Our treatment incorporates a
multi-phase model of the interstellar medium and includes the effects of
cooling, heating and metal enrichment by supernovae, and evaporation of cold
clouds. The star formation happens inside the clouds of cold gas, which are
produced via thermal instability. We simulate the galaxy formation in standard
biased CDM model for a variety of parameters and for several resolutions in the
range 2--20kpc. In our picture, supernova feedback regulates the
evolution of the gas components and star formation. The efficiency of cloud
evaporation by supernova strongly influences star formation rates. This
feedback results in a steady rate of star formation in large galaxies (mass
larger than 2-3x10^{11}\Msun) at a level of (1-10)\Msun\yr for .
Supernova feedback has an even stronger effect on the evolution of dwarf
galaxies, most of which have a small fraction of stars and extremely low
luminosities: . In the case of both large and small galaxies, the
distribution of luminous matter (stars) is strongly BIASED with respect to the
dark matter. We find an approximate biasing measure of the form for z=0 and overdensities exceeding 1000. Deviations
from this relation (a factor 2-3) depend on the environment. For halo masses
exceeding 2x10^{10}\Msun, the dependence of the absolute magnitude on the
total mass can be approximated as M_V=-18.5-4\log(M_{tot}/10^{11}\Msun), with
a scatter of less than 0.5mag.Comment: 17 pages LATEX (uses mn.sty). 12 PostScript figures and the text are
available at ftp://charon.nmsu.edu/pub/aklypin/HYDRO Corrected ftp adderes
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Notational analysis of goals scored from open play in international field hockey
Dynamical effects of the neutrino gravitational clustering at Planck angular scales
We study the CMB anisotropy induced by the non-linear perturbations in the
massive neutrino density associated to the non-linear gravitational clustering
proceses. Our results show that for the neutrino fraction in agreement with
that indicated by the astroparticle and nuclear physics experiments and a
cosmological accreting mass comparable with the mass of known clusters, the
angular resolution and the sensitivity of the CMB anisotropy measurements from
the Planck surveyor will allow the detection of the dynamical effects of the
neutrino gravitational clustering.Comment: 40 pages and 12 figures, submitted to ApJ (14 March 2002
The Neural Correlates of Non-Spatial Working Memory in Velocardiofacial Syndrome (22q11.2 Deletion Syndrome)
Velocardiofacial syndrome (VCFS), also known as 22q11.2 deletion syndrome, is a neurogenetic disorder that is associated with both learning disabilities and a consistent neuropsychological phenotype, including deficits in executive function, visuospatial perception, and working memory. Anatomic imaging studies have identified significant volumetric reductions in the parietal lobe of individuals with VCFS, but several studies have reported that the frontal lobe is relatively preserved. We used functional magnetic resonance imaging to investigate the neural correlates of non-spatial working memory in 17 youths with VCFS, 10 of their unaffected siblings, and 10 community controls (with the same proportion of learning disabilities as the VCFS youths). Task performance of siblings tended to be more accurate than children with VCFS, who did not differ from community controls. All three-study groups recruited parietal regions that were equivalent in location and magnitude. Whereas the sibling group also recruited the dorsolateral prefrontal cortex (DLPFC), Broca\u27s area, and anterior cingulate, DLPFC activation was absent in the whole brain analyses of children with VCFS and controls. Moreover, the magnitude of frontal activation in VCFS participants was restricted relative to both siblings and controls. These findings suggest that VCFS participants exhibit frontal hypoactivation that is not attributable to performance. In addition, VCFS children and controls (many with idiopathic learning disabilities) appear to rely on phonological rehearsal to hold information on line instead of the DLPFC. Despite previous anatomic MRI reports of preserved frontal lobe volumes in VCFS therefore, these fMRI findings suggest that the frontal component of the distributed network subserving executive function and working memory may be disrupted in youth with this disorder
Luminosity- and morphology-dependent clustering of galaxies
How does the clustering of galaxies depend on their inner properties like
morphological type and luminosity? We address this question in the mathematical
framework of marked point processes and clarify the notion of luminosity and
morphological segregation. A number of test quantities such as conditional
mark-weighted two-point correlation functions are introduced. These descriptors
allow for a scale-dependent analysis of luminosity and morphology segregation.
Moreover, they break the degeneracy between an inhomogeneous fractal point set
and actual present luminosity segregation. Using the Southern Sky Redshift
Survey~2 (da Costa et al. 1998, SSRS2) we find both luminosity and
morphological segregation at a high level of significance, confirming claims by
previous works using these data (Benoist et al. 1996, Willmer et al. 1998).
Specifically, the average luminosity and the fluctuations in the luminosity of
pairs of galaxies are enhanced out to separations of 15Mpc/h. On scales smaller
than 3Mpc/h the luminosities on galaxy pairs show a tight correlation. A
comparison with the random-field model indicates that galaxy luminosities
depend on the spatial distribution and galaxy-galaxy interactions. Early-type
galaxies are also more strongly correlated, indicating morphological
segregation. The galaxies in the PSCz catalog (Saunders et al. 2000) do not
show significant luminosity segregation. This again illustrates that mainly
early-type galaxies contribute to luminosity segregation. However, based on
several independent investigations we show that the observed luminosity
segregation can not be explained by the morphology-density relation alone.Comment: aastex, emulateapj5, 20 pages, 13 figures, several clarifying
comments added, ApJ accepte
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