1,651 research outputs found
The environmental dependence of clustering in hierarchical models
In hierarchical models, density fluctuations on different scales are
correlated. This induces correlations between dark halo masses, their formation
histories, and their larger-scale environments. In turn, this produces a
correlation between galaxy properties and environment. This correlation is
entirely statistical in nature. We show how the observed clustering of galaxies
can be used to quantify the importance of this statistical correlation relative
to other physical effects which may also give rise to correlations between the
properties of galaxies and their surroundings. We also develop a halo model
description of this environmental dependence of clustering.Comment: 11 pages, 6 figures, MNRAS in pres
Designing hollow nano gold golf balls.
Hollow/porous nanoparticles, including nanocarriers, nanoshells, and mesoporous materials have applications in catalysis, photonics, biosensing, and delivery of theranostic agents. Using a hierarchical template synthesis scheme, we have synthesized a nanocarrier mimicking a golf ball, consisting of (i) solid silica core with a pitted gold surface and (ii) a hollow/porous gold shell without silica. The template consisted of 100 nm polystyrene beads attached to a larger silica core. Selective gold plating of the core followed by removal of the polystyrene beads produced a golf ball-like nanostructure with 100 nm pits. Dissolution of the silica core produced a hollow/porous golf ball-like nanostructure
Why Do Stars Form In Clusters? An Analytic Model for Stellar Correlation Functions
Recently, we have shown that if the ISM is governed by super-sonic turbulent
flows, the excursion-set formalism can be used to calculate the statistics of
self-gravitating objects over a wide range of scales. On the largest
self-gravitating scales ('first crossing'), these correspond to GMCs, and on
the smallest non-fragmenting self-gravitating scales ('last crossing'), to
protostellar cores. Here, we extend this formalism to rigorously calculate the
auto and cross-correlation functions of cores (and by extension, young stars)
as a function of spatial separation and mass, in analogy to the cosmological
calculation of halo clustering. We show that this generically predicts that
star formation is very strongly clustered on small scales: stars form in
clusters, themselves inside GMCs. Outside the binary-star regime, the projected
correlation function declines as a weak power-law, until a characteristic scale
which corresponds to the characteristic mass scale of GMCs. On much larger
scales the clustering declines such that star formation is not strongly biased
on galactic scales, relative to the actual dense gas distribution. The precise
correlation function shape depends on properties of the turbulent spectrum, but
its qualitative behavior is quite general. The predictions agree well with
observations of young star and core autocorrelation functions over ~4 dex in
radius. Clustered star formation is a generic consequence of supersonic
turbulence if most of the power in the velocity field, hence the contribution
to density fluctuations, comes from large scales. The distribution of
self-gravitating masses near the sonic length is then imprinted by fluctuations
on larger scales. We similarly show that the fraction of stars formed in
'isolated' modes should be small (\lesssim10%).Comment: 8 pages, 3 figures, accepted to MNRAS (minor revisions to match
accepted version
The nature of assembly bias - I. Clues from a LCDM cosmology
We present a new proxy for the overdensity peak height for which the
large-scale clustering of haloes of a given mass does not vary significantly
with the assembly history. The peak height, usually taken to be well
represented by the virial mass, can instead be approximated by the mass inside
spheres of different radii, which in some cases can be larger than the virial
radius and therefore include mass outside the individual host halo. The sphere
radii are defined as r = delta_t + log_10(M_vir/M_nl), where delta_t is
the age relative to the typical age of galaxies hosted by haloes with virial
mass M_vir, M_nl is the non-linear mass, and =0.2 and =-0.02 are the free
parameters adjusted to trace the assembly bias effect. Note that depends on
both halo mass and age. In this new approach, some of the objects which were
initially considered low-mass peaks belong to regions with higher
overdensities. At large scales, i.e. in the two-halo regime, this model
properly recovers the simple prescription where the bias responds to the height
of the mass peak alone, in contrast to the usual definition (virial mass) that
shows a strong dependence on additional halo properties such as formation time.
The dependence on the age in the one-halo term is also remarkably reduced. The
population of galaxies whose "peak height" changes with this new definition
consists mainly of old stellar populations and are preferentially hosted by
low-mass haloes located near more massive objects. The latter is in agreement
with recent results which indicate that old, low-mass haloes would suffer
truncation of mass accretion by nearby larger haloes or simply due to the high
density of their surroundings, thus showing an assembly bias effect. The change
in mass is small enough that the Sheth et al. (2001) mass function is still a
good fit to the resulting distribution of new masses.Comment: 13 pages, 10 figures, submitted to MNRAS, comments welcom
Event Horizons in Numerical Relativity I: Methods and Tests
This is the first paper in a series on event horizons in numerical
relativity. In this paper we present methods for obtaining the location of an
event horizon in a numerically generated spacetime. The location of an event
horizon is determined based on two key ideas: (1) integrating backward in time,
and (2) integrating the whole horizon surface. The accuracy and efficiency of
the methods are examined with various sample spacetimes, including both
analytic (Schwarzschild and Kerr) and numerically generated black holes. The
numerically evolved spacetimes contain highly distorted black holes, rotating
black holes, and colliding black holes. In all cases studied, our methods can
find event horizons to within a very small fraction of a grid zone.Comment: 22 pages, LaTeX with RevTeX 3.0 macros, 20 uuencoded gz-compressed
postscript figures. Also available at http://jean-luc.ncsa.uiuc.edu/Papers/
Submitted to Physical Review
Fitting the incidence data from the city of Campinas, Brazil, based on dengue transmission modellings considering time-dependent entomological parameters
FAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOFour time-dependent dengue transmission models are considered in order to fit the incidence data from the City of Campinas, Brazil, recorded from October 1st 1995 to September 30th 2012. The entomological parameters are allowed to depend on temperature and precipitation, while the carrying capacity and the hatching of eggs depend only on precipitation. The whole period of incidence of dengue is split into four periods, due to the fact that the model is formulated considering the circulation of only one serotype. Dengue transmission parameters from human to mosquito and mosquito to human are fitted for each one of the periods. The time varying partial and overall effective reproduction numbers are obtained to explain the incidence of dengue provided by the models.Four time-dependent dengue transmission models are considered in order to fit the incidence data from the City of Campinas, Brazil, recorded from October 1st 1995 to September 30th 2012. The entomological parameters are allowed to depend on temperature and precipitation, while the carrying capacity and the hatching of eggs depend only on precipitation. The whole period of incidence of dengue is split into four periods, due to the fact that the model is formulated considering the circulation of only one serotype. Dengue transmission parameters from human to mosquito and mosquito to human are fitted for each one of the periods. The time varying partial and overall effective reproduction numbers are obtained to explain the incidence of dengue provided by the models113FAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO2009/15098-
The baryonic Tully-Fisher relation and galactic outflows
Most of the baryons in the Universe are not in the form of stars and cold gas
in galaxies. Galactic outflows driven by supernovae/stellar winds are the
leading mechanism for explaining this fact. The scaling relation between galaxy
mass and outer rotation velocity (also known as the baryonic Tully-Fisher
relation, BTF) has recently been used as evidence against this viewpoint. We
use a LCDM based semi-analytic disk galaxy formation model to investigate these
claims. In our model, galaxies with less efficient star formation and higher
gas fractions are more efficient at ejecting gas from galaxies. This is due to
the fact that galaxies with less efficient star formation and higher gas
fractions tend to live in dark matter haloes with lower circular velocities,
from which less energy is required to escape the potential well. In our model
the intrinsic scatter in the BTF is 0.15 dex, and mostly reflects scatter in
dark halo concentration. The observed scatter, equal to 0.24 dex, is dominated
by measurement errors. The best estimate for the intrinsic scatter is that it
is less than 0.15 dex, and thus our LCDM based model (which does not include
all possible sources of scatter) is only just consistent with this. In our
model, gas rich galaxies, at fixed virial velocity (V_vir), with lower stellar
masses have lower baryonic masses. This is consistent with the expectation that
galaxies with lower stellar masses have had less energy available to drive an
outflow. However, when the outer rotation velocity (V_flat) is used the
correlation has the opposite sign, with a slope in agreement with observations.
This is due to scatter in the relation between V_flat and V_vir. In summary,
contrary to some previous claims, we show that basic features of the BTF are
consistent with a LCDM based model in which the low efficiency of galaxy
formation is determined by galactic outflows.Comment: 7 pages, 4 figures, accepted to MNRA
Cosmological Constraints from a Combination of Galaxy Clustering and Lensing -- I. Theoretical Framework
We present a new method that simultaneously solves for cosmology and galaxy
bias on non-linear scales. The method uses the halo model to analytically
describe the (non-linear) matter distribution, and the conditional luminosity
function (CLF) to specify the halo occupation statistics. For a given choice of
cosmological parameters, this model can be used to predict the galaxy
luminosity function, as well as the two-point correlation functions of
galaxies, and the galaxy-galaxy lensing signal, both as function of scale and
luminosity. In this paper, the first in a series, we present the detailed,
analytical model, which we test against mock galaxy redshift surveys
constructed from high-resolution numerical -body simulations. We demonstrate
that our model, which includes scale-dependence of the halo bias and a proper
treatment of halo exclusion, reproduces the 3-dimensional galaxy-galaxy
correlation and the galaxy-matter cross-correlation (which can be projected to
predict the observables) with an accuracy better than 10 (in most cases 5)
percent. Ignoring either of these effects, as is often done, results in
systematic errors that easily exceed 40 percent on scales of \sim 1
h^{-1}\Mpc, where the data is typically most accurate. Finally, since the
projected correlation functions of galaxies are never obtained by integrating
the redshift space correlation function along the line-of-sight out to
infinity, simply because the data only cover a finite volume, they are still
affected by residual redshift space distortions (RRSDs). Ignoring these, as
done in numerous studies in the past, results in systematic errors that easily
exceed 20 perent on large scales (r_\rmp \gta 10 h^{-1}\Mpc). We show that it
is fairly straightforward to correct for these RRSDs, to an accuracy better
than percent, using a mildly modified version of the linear Kaiser
formalism
Interaction of pregnancy-specific glycoprotein 1 with integrin Α5β1 is a modulator of extravillous trophoblast functions
Human pregnancy-specific glycoproteins (PSGs) serve immunomodulatory and pro-angiogenic functions during pregnancy and are mainly expressed by syncytiotrophoblast cells. While PSG mRNA expression in extravillous trophoblasts (EVTs) was reported, the proteins were not previously detected. By immunohistochemistry and immunoblotting, we show that PSGs are expressed by invasive EVTs and co-localize with integrin α5. In addition, we determined that native and recombinant PSG1, the most highly expressed member of the family, binds to α5β1 and induces the formation of focal adhesion structures resulting in adhesion of primary EVTs and EVT-like cell lines under 21% oxygen and 1% oxygen conditions. Furthermore, we found that PSG1 can simultaneously bind to heparan sulfate in the extracellular matrix and to α5β1 on the cell membrane. Wound healing assays and single-cell movement tracking showed that immobilized PSG1 enhances EVT migration. Although PSG1 did not affect EVT invasion in the in vitro assays employed, we found that the serum PSG1 concentration is lower in African-American women diagnosed with early-onset and late-onset preeclampsia, a pregnancy pathology characterized by shallow trophoblast invasion, than in their respective healthy controls only when the fetus was a male; therefore, the reduced expression of this molecule should be considered in the context of preeclampsia as a potential therapy
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