1,278 research outputs found
FAM13A and POM121C are candidate genes for fasting insulin: functional follow-up analysis of a genome-wide association study
Aims/hypothesis: By genome-wide association meta-analysis, 17 genetic loci associated with fasting serum insulin (FSI), a
marker of systemic insulin resistance, have been identified. To define potential culprit genes in these loci, in a cross-sectional
study we analysed white adipose tissue (WAT) expression of 120 genes in these loci in relation to systemic and adipose tissue
variables, and functionally evaluated genes demonstrating genotype-specific expression in WAT (eQTLs).
Methods: Abdominal subcutaneous adipose tissue biopsies were obtained from 114 women. Basal lipolytic activity was measured
as glycerol release from adipose tissue explants. Adipocytes were isolated and insulin-stimulated incorporation of
radiolabelled glucose into lipids was used to quantify adipocyte insulin sensitivity. Small interfering RNA-mediated knockout
in human mesenchymal stem cells was used for functional evaluation of genes.
Results: Adipose expression of 48 of the studied candidate genes associated significantly with FSI, whereas expression of 24, 17
and 2 genes, respectively, associated with adipocyte insulin sensitivity, lipolysis and/or WAT morphology (i.e. fat cell size relative
to total body fat mass). Four genetic loci contained eQTLs. In one chromosome 4 locus (rs3822072), the FSI-increasing allele
associated with lower FAM13A expression and FAM13A expression associated with a beneficial metabolic profile including
decreased WAT lipolysis (regression coefficient, R = −0.50, p = 5.6 × 10−7). Knockdown of FAM13A increased lipolysis by ~1.5-
fold and the expression of LIPE (encoding hormone-sensitive lipase, a rate-limiting enzyme in lipolysis). At the chromosome 7
locus (rs1167800), the FSI-increasing allele associated with lower POM121C expression. Consistent with an insulin-sensitising
function, POM121C expression associated with systemic insulin sensitivity (R = −0.22, p = 2.0 × 10−2), adipocyte insulin sensitivity
(R = 0.28, p = 3.4 × 10−3) and adipose hyperplasia (R = −0.29, p = 2.6 × 10−2). POM121C knockdown decreased expression
of all adipocyte-specific markers by 25–50%, suggesting that POM121C is necessary for adipogenesis.
Conclusions/interpretation: Gene expression and adipocyte functional studies support the notion that FAM13A and POM121C
control adipocyte lipolysis and adipogenesis, respectively, and might thereby be involved in genetic control of systemic insulin
sensitivity
The impact of the dark matter-gas interaction on the collapse behaviour of spherical symmetric systems
If the gas in the evolving cosmic halos is dissipating energy (cooling) then
due to the variation of the gravitational potential the dark matter halo also
undergoes a compactification. This is well-known as Adiabatic contraction (AC).
Complementary to the AC we investigate the resulting dynamical behaviour of the
whole system if the backreaction of the AC of DM onto the gas is taken into
account. In order to achieve sufficient high resolution also within the central
halo region, we use a crude fluid approximation for the DM obeying the
adiabatic contraction behaviour. Further, we restrict ourself to spherical
symmetry and vanishing angular momentum of the studied matter configurations.
The computations are done using a first-order Godunov type scheme. Our results
show that the dynamical interaction between gas and DM may lead to significant
shorter collapse times. If the gas cools the dynamical behaviour of the whole
system depends strongly on the shape of the initial density profile. Our
findings indicate that for a certain mass range of halo configurations the
dynamical interaction between gas and DM might be important for the halo
evolution and must be taken into account.Comment: 9 pages, 13 figures, accepted for publication in A&A, added
reference
SPH Simulations of Counterrotating Disk Formation in Spiral Galaxies
We present the results of Smoothed Particle Hydrodynamics (SPH) simulations
of the formation of a massive counterrotating disk in a spiral galaxy. The
current study revisits and extends (with SPH) previous work carried out with
sticky particle gas dynamics, in which adiabatic gas infall and a retrograde
gas-rich dwarf merger were tested as the two most likely processes for
producing such a counterrotating disk. We report on experiments with a cold
primary similar to our Galaxy, as well as a hot, compact primary modeled after
NGC 4138. We have also conducted numerical experiments with varying amounts of
prograde gas in the primary disk, and an alternative infall model (a spherical
shell with retrograde angular momentum). The structure of the resulting
counterrotating disks is dramatically different with SPH. The disks we produce
are considerably thinner than the primary disks and those produced with sticky
particles. The time-scales for counterrotating disk formation are shorter with
SPH because the gas loses kinetic energy and angular momentum more rapidly.
Spiral structure is evident in most of the disks, but an exponential radial
profile is not a natural byproduct of these processes. The infalling gas shells
that we tested produce counterrotating bulges and rings rather than disks. The
presence of a considerable amount of preexisting prograde gas in the primary
causes, at least in the absence of star formation, a rapid inflow of gas to the
center and a subsequent hole in the counterrotating disk. In general, our SPH
experiments yield stronger evidence to suggest that the accretion of massive
counterrotating disks drives the evolution of the host galaxies towards earlier
(S0/Sa) Hubble types.Comment: To appear in ApJ. 20 pages LaTex 2-column with 3 tables, 23 figures
(GIF) available at this site. Complete gzipped postscript preprint with
embedded figures available from http://tarkus.pha.jhu.edu/~thakar/cr3.html (3
Mb
A solar cycle of spacecraft anomalies due to internal charging
International audienceIt is important to appreciate how the morphology of internal charging of spacecraft systems, due to penetrating electrons, differs from that of the more common surface charging, due to electrons with lower energy. A specific and recurrent anomaly on a geostationary communication satellite has been tracked for ten years so that solar cycle and seasonal dependencies can be clearly established. Concurrent measurements of sunspot number, solar wind speed and 2-day >2 MeV electron fluence are presented to highlight pertinent space weather relationships, and the importance of understanding the complex particle interaction processes involved
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An Eddy Current Tube Testing Technique Using a Hybrid Coil Configuration With Sequential Sampling.
The Ellipticity of the Disks of Spiral Galaxies
The disks of spiral galaxies are generally elliptical rather than circular.
The distribution of ellipticities can be fit with a log-normal distribution.
For a sample of 12,764 galaxies from the Sloan Digital Sky Survey Data Release
1 (SDSS DR1), the distribution of apparent axis ratios in the i band is best
fit by a log-normal distribution of intrinsic ellipticities with ln epsilon =
-1.85 +/- 0.89. For a sample of nearly face-on spiral galaxies, analyzed by
Andersen and Bershady using both photometric and spectroscopic data, the best
fitting distribution of ellipticities has ln epsilon = -2.29 +/- 1.04. Given
the small size of the Andersen-Bershady sample, the two distribution are not
necessarily inconsistent. If the ellipticity of the potential were equal to
that of the light distribution of the SDSS DR1 galaxies, it would produce 1.0
magnitudes of scatter in the Tully-Fisher relation, greater than is observed.
The Andersen-Bershady results, however, are consistent with a scatter as small
as 0.25 magnitudes in the Tully-Fisher relation.Comment: 19 pages, 5 figures; ApJ, accepte
NGC 4138 - A Case Study in Counterrotating Disk Formation
The Sa(r) galaxy NGC 4138 has been recently found to contain an extensive
counterrotating disk which appears to be still forming. Up to a third of the
stars in the disk system may be on retrograde orbits. A counterrotating ring of
H II regions, along with extended counterrotating H I gas, suggests that the
retrograde material has been recently acquired in the gas phase and is still
trickling in. Using numerical simulations, we have attempted to model the
process by which the counterrotating mass has been accreted by this galaxy. We
investigate two possibilities: continuous retrograde infall of gas, and a
retrograde merger with a gas-rich dwarf galaxy. Both processes are successful
in producing a counterrotating disk of the observed mass and dimensions without
heating up the primary significantly. Contrary to our experience with a
fiducial cold, thin primary disk, the gas-rich merger works well for the
massive, compact primary disk of NGC 4138 even though the mass of the dwarf
galaxy is a significant fraction of the mass of the primary disk. Although we
have restricted ourselves mainly to coplanar infall and mergers, we report on
one inclined infall simulation as well. We also explore the possibility that
the H-alpha ring seen in the inner half of the disk is a consequence of
counterrotating gas clouds colliding with corotating gas already present in the
disk and forming stars in the process.Comment: To appear in ApJ, 21 pages, LaTeX (aaspp4) format, 17 figs (gzipped
tar file) also available at ftp://bessel.mps.ohio-state.edu/pub/thakar/cr2/
or at http://www-astronomy.mps.ohio-state.edu/~thakar
Robust, data-driven inference in non-linear cosmostatistics
We discuss two projects in non-linear cosmostatistics applicable to very
large surveys of galaxies. The first is a Bayesian reconstruction of galaxy
redshifts and their number density distribution from approximate, photometric
redshift data. The second focuses on cosmic voids and uses them to construct
cosmic spheres that allow reconstructing the expansion history of the Universe
using the Alcock-Paczynski test. In both cases we find that non-linearities
enable the methods or enhance the results: non-linear gravitational evolution
creates voids and our photo-z reconstruction works best in the highest density
(and hence most non-linear) portions of our simulations.Comment: 14 pages, 10 figures. Talk given at "Statistical Challenges in Modern
Astronomy V," held at Penn Stat
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