1,955 research outputs found
Deflationary Universe Scenario
We show that it is possible to realize an inflationary scenario even without
conversion of the false vacuum energy to radiation. Such cosmological models
have a deflationary stage in which is decreasing and radiation produced
by particle creation in an expanding Universe becomes dominant. The preceding
inflationary stage ends since the inflaton potential becomes steep. False
vacuum energy is finally (partly) converted to the inflaton kinetic energy ,
the potential energy rapidly decreases and the Universe comes to the
deflationary stage with a scale factor . Basic features
and observational consequences of this scenario are indicated.Comment: 18p, KUNS-1201 Plain TeX, phyzzx. Reference file is included which
previously was misse
Phase space geometry in scalar-tensor cosmology
We study the phase space of spatially homogeneous and isotropic cosmology in
general scalar-tensor theories. A reduction to a two-dimensional phase space is
performed when possible-in these situations the phase space is usually a
two-dimensional curved surface embedded in a three-dimensional space and
composed of two sheets attached to each other, possibly with complicated
topology. The results obtained are independent of the choice of the coupling
function of the theory and, in certain situations, also of the potential.Comment: 18 pages, 9 figures, latex, to appear in Ann. Phys. (NY
Potential-density pairs for axisymmetric galaxies: the influence of scalar fields
We present a formulation for potential-density pairs to describe axisymmetric
galaxies in the Newtonian limit of scalar-tensor theories of gravity. The
scalar field is described by a modified Helmholtz equation with a source that
is coupled to the standard Poisson equation of Newtonian gravity. The net
gravitational force is given by two contributions: the standard Newtonian
potential plus a term stemming from massive scalar fields. General solutions
have been found for axisymmetric systems and the multipole expansion of the
Yukawa potential is given. In particular, we have computed potential-density
pairs of galactic disks for an exponential profile and their rotation curves.Comment: 8 pages, no figures, corrected version to the one that will appear in
Gen. Relativ. Gravit., where a small typo in eq. (13) is presen
Interplay between Stellar Spirals and the ISM in Galactic Disks
We propose a new dynamical picture of galactic stellar and gas spirals, based
on hydrodynamic simulations in a `live' stellar disk. We focus especially on
spiral structures excited in a isolated galactic disk without a stellar bar.
Using high-resolution, 3-dimensional N-body/SPH simulations, we found that the
spiral features of the gas in galactic disks are formed by essentially
different mechanisms from the galactic shock in stellar density waves. The
stellar spiral arms and the interstellar matter on average corotate in a
galactic potential at any radii. Unlike the stream motions in the galactic
shock, the interstellar matter flows into the local potential minima with
irregular motions. The flows converge to form dense gas clouds/filaments near
the bottom of the stellar spirals, whose global structures resemble dust-lanes
seen in late-type spiral galaxies. The stellar arms are non-steady; they are
wound and stretched by the galactic shear, and thus local densities of the arm
change on a time scale of ~ 100 Myrs, due to bifurcating or merging with other
arms. This makes the gas spirals associated with the stellar arms non-steady.
The association of dense gas clouds are eventually dissolved into inter-arm
regions with non-cirucular motions. Star clusters are formed from the cold,
dense gases, whose ages are less than ~30 Myrs, and they are roughly associated
with the background stellar arms without a clear spatial offset between gas
spiral arms and distribution of young stars.Comment: 13 pages, 12 figures, accepted by ApJ. Higher resolution of ms.pdf is
available at http://d.pr/Nvjk A targzipped Supplementary movies is available
at http://d.pr/TV6
Involvement of HTLV-I Tax and CREB in aneuploidy: a bioinformatics approach
BACKGROUND: Adult T-cell leukemia (ATL) is a complex and multifaceted disease associated with human T-cell leukemia virus type 1 (HTLV-I) infection. Tax, the viral oncoprotein, is considered a major contributor to cell cycle deregulation in HTLV-I transformed cells by either directly disrupting cellular factors (protein-protein interactions) or altering their transcription profile. Tax transactivates these cellular promoters by interacting with transcription factors such as CREB/ATF, NF-κB, and SRF. Therefore by examining which factors upregulate a particular set of promoters we may begin to understand how Tax orchestrates leukemia development. RESULTS: We observed that CTLL cells stably expressing wild-type Tax (CTLL/WT) exhibited aneuploidy as compared to a Tax clone deficient for CREB transactivation (CTLL/703). To better understand the contribution of Tax transactivation through the CREB/ATF pathway to the aneuploid phenotype, we performed microarray analysis comparing CTLL/WT to CTLL/703 cells. Promoter analysis of altered genes revealed that a subset of these genes contain CREB/ATF consensus sequences. While these genes had diverse functions, smaller subsets of genes were found to be involved in G2/M phase regulation, in particular kinetochore assembly. Furthermore, we confirmed the presence of CREB, Tax and RNA Polymerase II at the p97Vcp and Sgt1 promoters in vivo through chromatin immunoprecipitation in CTLL/WT cells. CONCLUSION: These results indicate that the development of aneuploidy in Tax-expressing cells may occur in response to an alteration in the transcription profile, in addition to direct protein interactions
Subterahertz gyrotron developments for collective Thomson scattering in LHD
Collective Thomson scattering (CTS) is expected to provide the spatially resolved velocity
distribution functions of not only thermal and tail ions but also alpha particles resulting from fusion
reactions. CTS using gyrotrons with frequency higher than the conventional ones used for plasma
heating would have advantages to alleviate refraction, cutoff effects, and background electron
cyclotron emission noise. Therefore, a high-power pulse gyrotron operating at approximately 400
GHz is being developed for CTS in Large Helical Device (LHD). A single-mode oscillation with a
frequency greater than 400 GHz, applying the second-harmonic resonance, was successfully
demonstrated in the first stage. At the same time, concrete feasibility study based on ray tracing,
scattering spectra, and electron cyclotron emission calculations has been conducted
Phantom crossing, equation-of-state singularities, and local gravity constraints in f(R) models
We identify the class of f(R) dark energy models which have a viable
cosmology, i.e. a matter dominated epoch followed by a late-time acceleration.
The deviation from a LambdaCDM model (f=R-Lambda) is quantified by the function
m=Rf_{,RR}/f_{,R}. The matter epoch corresponds to m(r=-1) simeq +0 (where
r=-Rf_{,R}/f) while the accelerated attractor exists in the region 0<m<1. We
find that the equation of state w_DE of all such ``viable'' f(R) models
exhibits two features: w_DE diverges at some redshift z_{c} and crosses the
cosmological constant boundary (``phantom crossing'') at a redshift z_{b}
smaller than z_{c}. Using the observational data of Supernova Ia and Cosmic
Microwave Background, we obtain the constraint m<O(0.1) and we find that the
phantom crossing could occur at z_{b}>1, i.e. within reach of observations. If
we add local gravity constraints, the bound on m becomes very stringent, with m
several orders of magnitude smaller than unity in the region whose density is
much larger than the present cosmological density. The representative models
that satisfy both cosmological and local gravity constraints take the
asymptotic form m(r)=C(-r-1)^p with p>1 as r approaches -1.Comment: 8 pages, 3 figures, version to appear in Physics Letters
Surface and Temporal Biosignatures
Recent discoveries of potentially habitable exoplanets have ignited the
prospect of spectroscopic investigations of exoplanet surfaces and atmospheres
for signs of life. This chapter provides an overview of potential surface and
temporal exoplanet biosignatures, reviewing Earth analogues and proposed
applications based on observations and models. The vegetation red-edge (VRE)
remains the most well-studied surface biosignature. Extensions of the VRE,
spectral "edges" produced in part by photosynthetic or nonphotosynthetic
pigments, may likewise present potential evidence of life. Polarization
signatures have the capacity to discriminate between biotic and abiotic "edge"
features in the face of false positives from band-gap generating material.
Temporal biosignatures -- modulations in measurable quantities such as gas
abundances (e.g., CO2), surface features, or emission of light (e.g.,
fluorescence, bioluminescence) that can be directly linked to the actions of a
biosphere -- are in general less well studied than surface or gaseous
biosignatures. However, remote observations of Earth's biosphere nonetheless
provide proofs of concept for these techniques and are reviewed here. Surface
and temporal biosignatures provide complementary information to gaseous
biosignatures, and while likely more challenging to observe, would contribute
information inaccessible from study of the time-averaged atmospheric
composition alone.Comment: 26 pages, 9 figures, review to appear in Handbook of Exoplanets.
Fixed figure conversion error
General Scalar Fields as Quintessence
We study the cosmological evolution of scalar fields with arbitrary
potentials in the presence of a barotropic fluid (matter or radiation) without
making any assumption on which term dominates. We determine what kind of
potentials V(phi) permits a quintessence interpretation of the scalar field phi
and to obtain interesting cosmological results. We show that all model
dependence is given in terms of lambda= - V'/V only and we study all possible
asymptotic limits: lambda approaching zero, a finite constant or infinity. We
determine the equation of state dynamically for each case. For the first class
of potentials, the scalar field quickly dominates the universe behaviour, with
an inflationary equation of state allowing for a quintessence interpretation.
The second case gives the extensively studied exponential potential. While in
the last case, when lambda approaches infinity, if it does not oscillate then
the energy density redshifts faster than the barotropic fluid but if lambda
oscillates then the energy density redshift depends on the specific potential.Comment: 14 pages, LaTeX, 4 postscript figure
P-wave excited baryons from pion- and photo-induced hyperon production
We report evidence for , , ,
, , and , and find
indications that might have a companion state at 1970\,MeV. The
controversial is not seen. The evidence is derived from a
study of data on pion- and photo-induced hyperon production, but other data are
included as well. Most of the resonances reported here were found in the
Karlsruhe-Helsinki (KH84) and the Carnegie-Mellon (CM) analyses but were
challenged recently by the Data Analysis Center at GWU. Our analysis is
constrained by the energy independent scattering amplitudes from either
KH84 or GWU. The two amplitudes from KH84 or GWU, respectively, lead to
slightly different branching ratios of contributing resonances but the
debated resonances are required in both series of fits.Comment: 22 pages, 28 figures. Some additional sets of data are adde
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