628 research outputs found
Non-Gaussianity from Step Features in the Inflationary Potential
We provide analytic solutions for the power spectrum and bispectrum of
curvature fluctuations produced by a step feature in the inflaton potential,
valid in the limit that the step is short and sharp. In this limit, the
bispectrum is strongly scale dependent and its effective non-linearity attains
a large oscillatory amplitude. The perturbations to the curvature power
spectrum, on the other hand, remain a small component on top of the usual
spectrum of fluctuations generated by slow roll. We utilize our analytic
solutions to assess the observability of the predicted non-Gaussian signatures
and show that, if present, only very sharp steps on scales larger than ~ 2 Gpc
are likely to be able to be detected by Planck. Such features are not only
consistent with WMAP7 data, but can also improve its likelihood by 2 Delta ln L
~ 12 for two extra parameters, the step location and height. If this
improvement were due to a slow roll violating step as considered here, a
bispectrum or corresponding polarization power spectrum detection would provide
definitive checks as to its primordial origin.Comment: Typos fixed, supersedes journal versio
Hormone Receptor and ERBB2 Status in Gene Expression Profiles of Human Breast Tumor Samples
The occurrence of large publically available repositories of human breast tumor gene expression profiles provides an important resource to discover new breast cancer biomarkers and therapeutic targets. For example, knowledge of the expression of the estrogen and progesterone hormone receptors (ER and PR), and that of the ERBB2 in breast tumor samples enables choice of therapies for the breast cancer patients that express these proteins. Identifying new biomarkers and therapeutic agents affecting the activity of signaling pathways regulated by the hormone receptors or ERBB2 might be accelerated by knowledge of their expression levels in large gene expression profiling data sets. Unfortunately, the status of these receptors is not invariably reported in public databases of breast tumor gene expression profiles. Attempts have been made to employ a single probe set to identify ER, PR and ERBB2 status, but the specificity or sensitivity of their prediction is low. We enquired whether estimation of ER, PR and ERBB2 status of profiled tumor samples could be improved by using multiple probe sets representing these three genes and others with related expression
Evolution of dispersion in the cosmic deuterium abundance
Deuterium is created during Big Bang Nucleosynthesis, and, in contrast to the
other light stable nuclei, can only be destroyed thereafter by fusion in
stellar interiors. In this paper we study the cosmic evolution of the deuterium
abundance in the interstellar medium and its dispersion using realistic galaxy
evolution models. We find that models that reproduce the observed metal
abundance are compatible with observations of the deuterium abundance in the
local ISM and z ~ 3 absorption line systems. In particular, we reproduce the
low astration factor which we attribute to a low global star formation
efficiency. We calculate the dispersion in deuterium abundance arising from
different structure formation histories in different parts of the Universe. Our
model also predicts an extremely tight correlation between deuterium and metal
abundances which could be used to measure the primordial deuterium abundance.Comment: 6 pages, 5 figures. Accepted for publication in MNRAS Letters.
Figures rearranged to match published versio
The origin of dispersion in DLA metallicities
Recent chemical abundance measurements of damped Ly-alpha absorbers (DLAs)
revealed an intrinsic scatter in their metallicity of ~0.5 dex out to z~5. In
order to explore the origin of this scatter, we build a semi-analytic model
which traces the chemical evolution of the interstellar matter in small regions
of the Universe with different mean density, from over- to underdense regions.
We show that the different histories of structure formation in these regions,
namely halo abundance, mass and stellar content, is reflected in the chemical
properties of the protogalaxies, and in particular of DLAs. We calculate mean
metallicity-redshift relations and show that the metallicity dispersion arising
from this environmental effect amounts to ~0.25 dex and is an important
contributor to the observed overall intrinsic scatter.Comment: 6 pages, 2 figures. Accepted for publication in MNRAS Letter
Optimal Carbon Taxes for Emissions Targets in the Electricity Sector
The most dangerous effects of anthropogenic climate change can be mitigated
by using emissions taxes or other regulatory interventions to reduce greenhouse
gas (GHG) emissions. This paper takes a regulatory viewpoint and describes the
Weighted Sum Bisection method to determine the lowest emission tax rate that
can reduce the anticipated emissions of the power sector below a prescribed,
regulatorily-defined target. This bi-level method accounts for a variety of
operating conditions via stochastic programming and remains computationally
tractable for realistically large planning test systems, even when binary
commitment decisions and multi-period constraints on conventional generators
are considered.
Case studies on a modified ISO New England test system demonstrate that this
method reliably finds the minimum tax rate that meets emissions targets. In
addition, it investigates the relationship between system investments and the
tax-setting process. Introducing GHG emissions taxes increases the value
proposition for investment in new cleaner generation, transmission, and energy
efficiency; conversely, investing in these technologies reduces the tax rate
required to reach a given emissions target
Reaching within a dynamic virtual environment
This is an Open Access article distributed under the terms of the Creative Commons Attribution Licens
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