30,777 research outputs found
On Perturbation Spectra of N-flation
In this note we study the adiabatic perturbation spectrum of N-flation with
power law potential. We show that the scalar spectrum of N-flation is generally
redder than that of its corresponding single field. The result obtained for
that with unequal massive fields is consistent with the recent numerical
investigation of Kim and Liddle.Comment: 3 pages, refs. added, comments added, typos corrected, abstract
changed, to publish in PRD brief repor
An asymptotic sampling formula for the coalescent with Recombination
Ewens sampling formula (ESF) is a one-parameter family of probability
distributions with a number of intriguing combinatorial connections. This
elegant closed-form formula first arose in biology as the stationary
probability distribution of a sample configuration at one locus under the
infinite-alleles model of mutation. Since its discovery in the early 1970s, the
ESF has been used in various biological applications, and has sparked several
interesting mathematical generalizations. In the population genetics community,
extending the underlying random-mating model to include recombination has
received much attention in the past, but no general closed-form sampling
formula is currently known even for the simplest extension, that is, a model
with two loci. In this paper, we show that it is possible to obtain useful
closed-form results in the case the population-scaled recombination rate
is large but not necessarily infinite. Specifically, we consider an asymptotic
expansion of the two-locus sampling formula in inverse powers of and
obtain closed-form expressions for the first few terms in the expansion. Our
asymptotic sampling formula applies to arbitrary sample sizes and
configurations.Comment: Published in at http://dx.doi.org/10.1214/09-AAP646 the Annals of
Applied Probability (http://www.imstat.org/aap/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Radio and Far-Infrared Emission as Tracers of Star Formation and AGN in Nearby Cluster Galaxies
We have studied the radio and far-infrared (FIR) emission from 114 galaxies
in the 7 nearest clusters (<100 Mpc) with prominent X-ray emission to
investigate the impact of the cluster environment on the star formation and AGN
activity in the member galaxies. The X-ray selection criterion is adopted to
focus on the most massive and dynamically relaxed clusters. A large majority of
cluster galaxies show an excess in radio emission over that predicted from the
radio-FIR correlation, the fraction of sources with radio excess increases
toward cluster cores, and the radial gradient in the FIR/radio flux ratio is a
result of radio enhancement. Of the radio-excess sources, 70% are early-type
galaxies and the same fraction host an AGN. The galaxy density drops by a
factor of 10 from the composite cluster center out to 1.5 Mpc, yet galaxies
show no change in FIR properties over this region, and show no indication of
mass segregation. We have examined in detail the physical mechanisms that might
impact the FIR and radio emission of cluster galaxies. While collisional
heating of dust may be important for galaxies in cluster centers, it appears to
have a negligible effect on the observed FIR emission for our sample galaxies.
The correlations between radio and FIR luminosity and radius could be explained
by magnetic compression from thermal ICM pressure. We also find that simple
delayed harassment cannot fully account for the observed radio, FIR, and mid-IR
properties of cluster galaxies.Comment: 21 pages, 15 figures, Accepted by Ap
Hepatitis C virus 3'UTR regulates viral translation through direct interactions with the host translation machinery.
The 3' untranslated region (3'UTR) of hepatitis C virus (HCV) messenger RNA stimulates viral translation by an undetermined mechanism. We identified a high affinity interaction, conserved among different HCV genotypes, between the HCV 3'UTR and the host ribosome. The 3'UTR interacts with 40S ribosomal subunit proteins residing primarily in a localized region on the 40S solvent-accessible surface near the messenger RNA entry and exit sites. This region partially overlaps with the site where the HCV internal ribosome entry site was found to bind, with the internal ribosome entry site-40S subunit interaction being dominant. Despite its ability to bind to 40S subunits independently, the HCV 3'UTR only stimulates translation in cis, without affecting the first round translation rate. These observations support a model in which the HCV 3'UTR retains ribosome complexes during translation termination to facilitate efficient initiation of subsequent rounds of translation
Effects of interorbital hopping on orbital fluctuations and metal-insulator transitions: Extended linearized dynamical mean-field theory
We study the effects of interorbital hopping on orbital fluctuations and
Mott-Hubbard metal-insulator transition (MIT) in the two-orbital Hubbard model
within the extended linearized dynamical mean-field theory. By mapping the
model onto an effective model with different bandwidths through the canonical
transformation, we find that at half-filling, the increases of the interorbital
Coulomb interaction and the Hund's coupling drive the MIT, and
the critical for MIT increases with the lift of the inter-orbital
hopping integral . Meanwhile at quarter filling and in the strong
correlation regime, the system without exhibits MIT with the
decreasing of , and favors the orbital liquid ground state. However, the
system transits from metal to insulator with the increasing of t,
accompanied with the rising of the orbital order parameter. These results show
the important role of the interorbital hopping in the orbital fluctuation and
orbital ordering.Comment: 7 pages, 6 figure
Model-Independent Measurement of the Primordial Power Spectrum
In inflationary models with minimal amount of gravity waves, the primordial
power spectrum of density fluctuations, , together with the basic
cosmological parameters, completely specify the predictions for the cosmic
microwave background (CMB) anisotropy and large scale structure. Here we show
how we can strongly constrain both and the cosmological parameters
by combining the data from the Microwave Anisotropy Probe (MAP) and the galaxy
redshift survey from the Sloan Digital Sky Survey (SDSS). We allow
to be a free function, and thus probe features in the primordial power spectrum
on all scales. MAP and SDSS have scale-dependent measurement errors that
decrease in opposite directions on astrophysically interesting scales; they
complement each other and allow the measurement of the primordial power
spectrum independent of inflationary models, giving us valuable information on
physics in the early Universe, and providing clues to the correct inflationary
model.Comment: 4 pages including 4 figures. To appear in "Particle Physics and the
Early Universe (COSMO-98)", editor David O. Caldwell (American Institute of
Physics
Tractable diffusion and coalescent processes for weakly correlated loci
Widely used models in genetics include the Wright-Fisher diffusion and its
moment dual, Kingman's coalescent. Each has a multilocus extension but under
neither extension is the sampling distribution available in closed-form, and
their computation is extremely difficult. In this paper we derive two new
multilocus population genetic models, one a diffusion and the other a
coalescent process, which are much simpler than the standard models, but which
capture their key properties for large recombination rates. The diffusion model
is based on a central limit theorem for density dependent population processes,
and we show that the sampling distribution is a linear combination of moments
of Gaussian distributions and hence available in closed-form. The coalescent
process is based on a probabilistic coupling of the ancestral recombination
graph to a simpler genealogical process which exposes the leading dynamics of
the former. We further demonstrate that when we consider the sampling
distribution as an asymptotic expansion in inverse powers of the recombination
parameter, the sampling distributions of the new models agree with the standard
ones up to the first two orders.Comment: 34 pages, 1 figur
Multivariate Decomposition for Hazard Rate Models
We develop a regression decomposition technique for hazard rate models, where the difference in observed rates is decomposed into components attributable to group differences in characteristics and group differences in effects. The baseline hazard is specified using a piecewise constant exponential model, which leads to convenient estimation based on a Poisson regression model fit to person-period, or split-episode data. This specification allows for a flexible representation of the baseline hazard and provides a straightforward way to introduce time-varying covariates and time-varying effects. We provide computational details underlying the method and apply the technique to the decomposition of the black-white difference in first premarital birth rates into components reflecting characteristics and effect contributions of several predictors, as well as the effect contribution attributable to race differences in the baseline hazard.Poisson regression, hazard rates, decomposition, piecewise constant exponential model
- …