2,397 research outputs found
Approximate analysis of thermal convection in a crystal-growth cell for Spacelab 3
The transient and steady thermal convection in microgravity is described. The approach is applicable to many three dimensional flows in containers of various shapes with various thermal gradients imposed. The method employs known analytical solutions to two dimensional thermal flows in simpler geometries, and does not require recourse to numerical calculations by computer
The Role of Parked Cars in Content Downloading for Vehicular Networks
When it comes to content access using Inter-Vehicle Communication (IVC),
data will mostly flow
through Road Side Units (RSUs), deployed in our cities. Unfortunately, the RSU
coverage is expected to be rather scattered. Instead of relying on RSUs only,
the paper investigate the possibility of
exploiting parked vehicles to extend the RSU service coverage. Our
approach leverages optimization models aiming at maximizing the
freshness of content that downloaders retrieve, the efficiency in
the utilization of radio resources, and the fairness in exploiting the
energy resources of parked vehicles. The latter is constrained so as not to
excessively drain parked vehicle batteries.
Our approach provides an estimate of the system
performance, even in those cases where users may only be willing
to lease a limited amount of their battery capacity to extend RSU coverage.
Our optimization-based results are validated by comparing them against ns-3
simulations. Performance evaluation highlights that the use of parked
vehicles enhances the efficiency of the content downloading process by
25%-35% and can offload more than half the data traffic from RSUs,
with respect to the case where only moving cars are used as relays. Such gains
in performance come at a small cost in terms of battery utilization for
the parked vehicles, and they are magnified when a backbone of parked
vehicles can be formed
Galaxy Harassment and the Evolution of Clusters of Galaxies
Disturbed spiral galaxies with high rates of star formation pervaded clusters
of galaxies just a few billion years ago, but nearby clusters exclude spirals
in favor of ellipticals. ``Galaxy harassment" (frequent high speed galaxy
encounters) drives the morphological transformation of galaxies in clusters,
provides fuel for quasars in subluminous hosts and leaves detectable debris
arcs. Simulated images of harassed galaxies are strikingly similar to the
distorted spirals in clusters at observed by the Hubble Space
Telescope.Comment: Submitted to Nature. Latex file, 7 pages, 10 photographs in gif and
jpeg format included. 10 compressed postscript figures and text available
using anonymous ftp from ftp://ftp-hpcc.astro.washington.edu/pub/hpcc/moore/
(mget *) Also available at http://www-hpcc.astro.washington.edu/papers
The Fundamental Plane of Radio Galaxies
We collected photometrical and dynamical data for 73 low red-shift (z<0.2)
Radio Galaxies (LzRG) in order to study their Fundamental Plane (FP). For 22
sources we also present new velocity dispersion data, that complement the
photometric data given in our previous study of LzRG (Govoni et al. 2000a). It
is found that the FP of LzRG is similar to the one defined by non-active
elliptical galaxies, with LzRG representing the brightest end of the population
of early type galaxies. Since the FP mainly reflects the virial equilibrium
condition, our result implies that the global properties of early--type
galaxies (defining the FP) are not influenced by the presence of gas accretion
in the central black hole. This is fully in agreement with the recent results
in black hole demography, showing that virtually all luminous spheroidal
galaxies host a massive black hole and therefore may potentially become active.
We confirm and extend to giant ellipticals the systematic increase of the
mass-to-light ratio with galaxy luminosity.Comment: 8 pages, 3 figures, accepted for publication in A&
Normics: Proteomic Normalization by Variance and Data-Inherent Correlation Structure
Several algorithms for the normalization of proteomic data are currently available, each based on a priori assumptions. Among these is the extent to which differential expression (DE) can be present in the dataset. This factor is usually unknown in explorative biomarker screens. Simultaneously, the increasing depth of proteomic analyses often requires the selection of subsets with a high probability of being DE to obtain meaningful results in downstream bioinformatical analyses. Based on the relationship of technical variation and (true) biological DE of an unknown share of proteins, we propose the “Normics” algorithm: Proteins are ranked based on their expression level–corrected variance and the mean correlation with all other proteins. The latter serves as a novel indicator of the non-DE likelihood of a protein in a given dataset. Subsequent normalization is based on a subset of non-DE proteins only. No a priori information such as batch, clinical, or replicate group is necessary. Simulation data demonstrated robust and superior performance across a wide range of stochastically chosen parameters. Five publicly available spike-in and biologically variant datasets were reliably and quantitively accurately normalized by Normics with improved performance compared to standard variance stabilization as well as median, quantile, and LOESS normalizations. In complex biological datasets Normics correctly determined proteins as being DE that had been cross-validated by an independent transcriptome analysis of the same samples. In both complex datasets Normics identified the most DE proteins. We demonstrate that combining variance analysis and data-inherent correlation structure to identify non-DE proteins improves data normalization. Standard normalization algorithms can be consolidated against high shares of (one-sided) biological regulation. The statistical power of downstream analyses can be increased by focusing on Normics-selected subsets of high DE likelihood
CTQ 414: A New Gravitational Lens
We report the discovery and ground based observations of the new
gravitational lens CTQ 414. The source quasar lies at a redshift of z = 1.29
with a B magnitude of 17.6. Ground based optical imaging reveals two point
sources separated by 1.2 arcsec with a magnitude difference of roughly 1 mag.
Subtraction of two stellar point spread functions from images obtained in
subarcsecond seeing consistently leaves behind a faint, residual object. Fits
for two point sources plus an extended object places the fainter object
collinear with the two brighter components. Subsequent HST/NICMOS observations
have confirmed the identification of the fainter object as the lensing galaxy.
VLA observations at 8.46 GHz reveal that all components of the lensing system
are radio quiet down to the 0.2 mJy flux level.Comment: Latex, 18 pages including 2 ps figures; accepted for publication in
A
Does environment affect the star formation histories of early-type galaxies?
Differences in the stellar populations of galaxies can be used to quantify
the effect of environment on the star formation history. We target a sample of
early-type galaxies from the Sloan Digital Sky Survey in two different
environmental regimes: close pairs and a general sample where environment is
measured by the mass of their host dark matter halo. We apply a blind source
separation technique based on principal component analysis, from which we
define two parameters that correlate, respectively, with the average stellar
age (eta) and with the presence of recent star formation (zeta) from the
spectral energy distribution of the galaxy. We find that environment leaves a
second order imprint on the spectra, whereas local properties - such as
internal velocity dispersion - obey a much stronger correlation with the
stellar age distribution.Comment: 5 pages, 2 figures. Proceedings of JENAM 2010, Symposium 2:
"Environment and the formation of galaxies: 30 years later
An XMM and Chandra view of massive clusters of galaxies to z=1
The X-ray properties of a sample of high redshift (z>0.6), massive clusters
observed with XMM-Newton and Chandra are described, including two exceptional
systems. One, at z=0.89, has an X-ray temperature of T=11.5 (+1.1, -0.9) keV
(the highest temperature of any cluster known at z>0.6), an estimated mass of
(1.4+/-0.2)x10^15 solar masses and appears relaxed. The other, at z=0.83, has
at least three sub-clumps, probably in the process of merging, and may also
show signs of faint filamentary structure at large radii,observed in X-rays. In
general there is a mix of X-ray morphologies, from those clusters which appear
relaxed and containing little substructure to some highly non-virialized and
probably merging systems. The X-ray gas metallicities and gas mass fractions of
the relaxed systems are similar to those of low redshift clusters of the same
temperature, suggesting that the gas was in place, and containing its metals,
by z=0.8. The evolution of the mass-temperature relation may be consistent with
no evolution or with the ``late formation'' assumption. The effect of point
source contamination in the ROSAT survey from which these clusters were
selected is estimated, and the implications for the ROSAT X-ray luminosity
function discussed.Comment: 9 pages, in Carnegie Observatories Astrophysics Series, Vol. 3:
Clusters of Galaxies: Probes of Cosmological Structure and Galaxy Evolution,
ed. J. S. Mulchaey, A. Dressler, and A. Oemler. See
http://www.ociw.edu/ociw/symposia/series/symposium3/proceedings.html for a
full-resolution versio
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