4,992 research outputs found
Quantum slow-roll and quantum fast-roll inflationary initial conditions: CMB quadrupole suppression and further effects on the low CMB multipoles
Quantum fast-roll initial conditions for the inflaton which are different
from the classical fast-roll conditions and from the quantum slow-roll
conditions can lead to inflation that last long enough. These quantum fast-roll
initial conditions for the inflaton allow for kinetic energies of the same
order of the potential energies and nonperturbative inflaton modes with nonzero
wavenumbers. Their evolution starts with a transitory epoch where the redshift
due to the expansion succeeds to assemble the quantum excited modes of the
inflaton in a homogeneous (zero mode) condensate, and the large value of the
Hubble parameter succeeds to overdamp the fast-roll of the redshifted inflaton
modes. After this transitory stage the effective classical slow-roll epoch is
reached. Most of the efolds are produced during the slow-roll epoch and we
recover the classical slow-roll results for the scalar and tensor metric
perturbations plus corrections. These corrections are important, both for
scalar and for tensor perturbations, if scales which are horizon-size today
exited the horizon by the end of the transitory stage and as a consequence the
lower CMB multipoles get suppressed (fast-roll) or enhanced (precondensate).
These two types of corrections can compete and combine in a scale dependent
manner. They arise as natural consequences of the quantum nonperturbative
inflaton dynamics, and provide a consistent and contrastable model for the
origin of the suppression of the quadrupole and for other departures of the low
CMB multipoles from the slow-roll inflation-LambdaCMB model which are to be
contrasted to the TE and EE multipoles and to the forthcoming and future CMB
data.Comment: LaTeX, 14 pages, 3 figure
Two component dark matter
We explain the PAMELA positron excess and the PPB-BETS/ATIC e+ + e- data
using a simple two component dark matter model (2DM). The two particle species
in the dark matter sector are assumed to be in thermal equilibrium in the early
universe. While one particle is stable and is the present day dark matter, the
second one is metastable and decays after the universe is 10^-8 s old. In this
model it is simple to accommodate the large boost factors required to explain
the PAMELA positron excess without the need for large spikes in the local dark
matter density. We provide the constraints on the parameters of the model and
comment on possible signals at future colliders.Comment: 6 pages, 2 figures, discussion clarified and extende
Structure Formation, Melting, and the Optical Properties of Gold/DNA Nanocomposites: Effects of Relaxation Time
We present a model for structure formation, melting, and optical properties
of gold/DNA nanocomposites. These composites consist of a collection of gold
nanoparticles (of radius 50 nm or less) which are bound together by links made
up of DNA strands. In our structural model, the nanocomposite forms from a
series of Monte Carlo steps, each involving reaction-limited cluster-cluster
aggregation (RLCA) followed by dehybridization of the DNA links. These links
form with a probability which depends on temperature and particle
radius . The final structure depends on the number of monomers (i. e. gold
nanoparticles) , , and the relaxation time. At low temperature, the
model results in an RLCA cluster. But after a long enough relaxation time, the
nanocomposite reduces to a compact, non-fractal cluster. We calculate the
optical properties of the resulting aggregates using the Discrete Dipole
Approximation. Despite the restructuring, the melting transition (as seen in
the extinction coefficient at wavelength 520 nm) remains sharp, and the melting
temperature increases with increasing as found in our previous
percolation model. However, restructuring increases the corresponding link
fraction at melting to a value well above the percolation threshold. Our
calculated extinction cross section agrees qualitatively with experiments on
gold/DNA composites. It also shows a characteristic ``rebound effect,''
resulting from incomplete relaxation, which has also been seen in some
experiments. We discuss briefly how our results relate to a possible sol-gel
transition in these aggregates.Comment: 12 pages, 10 figure
Angiotensin II induction of PDGF-C expression is mediated by AT1 receptor-dependent Egr-1 transactivation
Platelet-derived growth factors are a family of mitogens and chemoattractants comprising of four ligand genes (A-, B-, C-, D-chains) implicated in many physiologic and pathophysiologic processes, including atherosclerosis, fibrosis and tumorigenesis. Our understanding of the molecular mechanisms, which regulate PDGF-C transcription remains incomplete. Transient transfection analysis, conventional and quantitative real-time PCR revealed the induction of PDGF-C transcription and mRNA expression in smooth muscle cells (SMCs) exposed to the peptide hormone angiotensin (ATII), which induces Egr-1. Occupancy of a G + C-rich element in the proximal region of the PDGF-C promoter was unaffected by ATII. Instead we discovered, using both nuclear extracts and recombinant proteins with EMSA and ChIP analyses, the existence of a second Egr-1-binding element located 500 bp upstream. ATII induction of PDGF-C transcription is mediated by the angiotensin type 1 receptor (AT1R) and Egr-1 activation through this upstream element. DNAzyme ED5 targeting Egr-1 blocked ATII-inducible PDGF-C expression. Moreover, increased PDGF-C expression after exposure to ATII depends upon the differentiation state of the SMCs. This study demonstrates the existence of this novel ATII-AT1R-Egr-1-PDGF-C axis in SMCs of neonatal origin, but not in adult SMCs, where ATII induces Egr-1 but not PDGF-C
Intrinsic Morphology of Ultra-diffuse Galaxies
With the published data of apparent axis ratios for 1109 ultra-diffuse
galaxies (UDGs) located in 17 low-redshift (z~ 0.020 - 0.063) galaxy clusters
and 84 UDGs in 2 intermediate-redshift (z~ 0.308 - 0.348) clusters, we take
advantage of a Markov Chain Monte Carlo approach and assume a ubiquitous
triaxial model to investigate the intrinsic morphologies of UDGs. In contrast
to the conclusion of Burkert (2017), i.e., the underlying shapes of UDGs are
purely prolate (), we find that the data favor the oblate-triaxial
models () over the nearly prolate ones. We also find that the
intrinsic morphologies of UDGs are relevant to their stellar
masses/luminosities, environments, and redshifts. First, for the low-redshift
UDGs in the same environment, the more-luminous ones are always thicker than
the less-luminous counterparts, possibly due to the more voilent internal
supernovae feedback or external tidal interactions for the progenitors of the
more-luminous UDGs. The UDG thickness dependence on luminosity is distinct from
that of the typical quiescent dwarf ellipticals (dEs) and dwarf spheroidals
(dSphs) in the local clusters and groups, but resembles that of massive
galaxies; in this sense, UDGs may not be simply treated as an extension of the
dE/dSph class with similar evolutionary histories. Second, for the low-redshift
UDGs within the same luminosity range, the ones with smaller cluster-centric
distances are more puffed-up, probably attributed to tidal interactions.
Finally, the intermediate-redshift cluster UDGs are more flattened, which
plausibly suggests a `disky' origin for high-redshift, initial UDGs.Comment: Accepted for publication in ApJ; new versio
The potential of hematopoietic growth factors for treatment of Alzheimer's disease: a mini-review
There are no effective interventions that significantly forestall or reverse neurodegeneration and cognitive decline in Alzheimer's disease. In the past decade, the generation of new neurons has been recognized to continue throughout adult life in the brain's neurogenic zones. A major challenge has been to find ways to harness the potential of the brain's own neural stem cells to repair or replace injured and dying neurons. The administration of hematopoietic growth factors or cytokines has been shown to promote brain repair by a number of mechanisms, including increased neurogenesis, anti-apoptosis and increased mobilization of bone marrow-derived microglia into brain. In this light, cytokine treatments may provide a new therapeutic approach for many brain disorders, including neurodegenerative diseases like Alzheimer's disease. In addition, neuronal hematopoietic growth factor receptors provide novel targets for the discovery of peptide-mimetic drugs that can forestall or reverse the pathological progression of Alzheimer's disease
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