4,773 research outputs found
Nuclear Propelled Vessels and Neutrino Oscillation Experiments
We study the effect of naval nuclear reactors on the study of neutrino
oscillations. We find that the presence of naval reactors at unknown locations
and times may limit the accuracy of future very long baseline reactor-based
neutrino oscillation experiments. At the same time we argue that a nuclear
powered surface ship such as a large Russian ice-breaker may provide an ideal
source for precision experiments. While the relatively low reactor power would
in this case require a larger detector, the source could be conveniently
located at essentially any distance from a detector built at an underground
location near a shore in a region of the world far away from other nuclear
installations. The variable baseline would allow for a precise measurement of
backgrounds and greatly reduced systematics from reactor flux and detector
efficiency. In addition, once the oscillation measurement is completed, the
detector could perform geological neutrino and astrophysical measurements with
minimal reactor background.Comment: 4 pages, 2 figure
Astrophysical factors:Zero energy vs. Most effective energy
Effective astrophysical factors for non-resonant astrophysical nuclear
reaction are invariably calculated with respect to a zero energy limit. In the
present work that limit is shown to be very disadvantageous compared to the
more natural effective energy limit. The latter is used in order to modify the
thermonuclear reaction rate formula so that it takes into account both plasma
and laboratory screening effects.Comment: 7 RevTex pages. Accepted for publication in Phys.Rev.
Selection and validation of reference genes for quantitative RT-PCR expression studies of the non-model crop Musa
Gene expression analysis by reverse transcriptase real-time or quantitative polymerase chain reaction (RT-qPCR) is becoming widely used for nonmodel plant species. Given the high sensitivity of this method, normalization using multiple housekeeping or reference genes is critical, and careful selection of these reference genes is one of the most important steps to obtain reliable results. In this study, reference genes commonly used for other plant species were investigated to identify genes displaying highly uniform expression patterns in different varieties, tissues, developmental stages, fungal infection, and osmotic stress conditions for the non-model crop Musa (banana and plantains). The expression stability of six candidate reference genes was tested on six different sample sets, and the results were analyzed using the publicly available algorithms geNorm and NormFinder. Our results show that variety, plant material, primer set, and gene identity can all influence the robustness and outcome of RT-qPCR analysis. In the case of Musa, a combination of three reference genes (EF1, TUB and ACT) can be used for normalization of gene expression data from greenhouse leaf samples. In the case of shoot meristem cultures, numerous combinations can be used because the investigated reference genes exhibited limited variability. In contrast, variability in expression of the reference genes was much larger among leaf samples from plants grown in vitro, for which the best combination of reference genes (L2 and ACT genes) is still suboptimal. Overall, our data confirm that the stability of candidate reference gene
New Mechanism for Electronic Energy Relaxation in Nanocrystals
The low-frequency vibrational spectrum of an isolated nanometer-scale solid
differs dramatically from that of a bulk crystal, causing the decay of a
localized electronic state by phonon emission to be inhibited. We show,
however, that an electron can also interact with the rigid translational motion
of a nanocrystal. The form of the coupling is dictated by the equivalence
principle and is independent of the ordinary electron-phonon interaction. We
calculate the rate of nonradiative energy relaxation provided by this mechanism
and establish its experimental observability.Comment: 4 pages, Submitted to Physical Review
W+jets Matrix Elements and the Dipole Cascade
We extend the algorithm for matching fixed-order tree-level matrix element
generators with the Dipole Cascade Model in Ariadne to apply to processes with
incoming hadrons. We test the algoritm on for the process W+n jets at the
Tevatron, and find that the results are fairly insensitive to the cutoff used
to regularize the soft and collinear divergencies in the tree-level matrix
elements. We also investigate a few observables to check the sensitivity to the
matrix element correction
A study to define meteorological uses and performance requirements for the Synchronous Earth Observatory Satellite
The potential meteorological uses of the Synchronous Earth Observatory Satellite (SEOS) were studied for detecting and predicting hazards to life, property, or the quality of the environment. Mesoscale meteorological phenonmena, and the observations requirements for SEOS are discussed along with the sensor parameters
Strong lensing constraints on the velocity dispersion and density profile of elliptical galaxies
We use the statistics of strong gravitational lensing from the CLASS survey
to impose constraints on the velocity dispersion and density profile of
elliptical galaxies. This approach differs from much recent work, where the
luminosity function, velocity dispersion and density profile were typically
{\it assumed} in order to constrain cosmological parameters. It is indeed
remarkable that observational cosmology has reached the point where we can
consider using cosmology to constrain astrophysics, rather than vice versa. We
use two different observables to obtain our constraints (total optical depth
and angular distributions of lensing events). In spite of the relatively poor
statistics and the uncertain identification of lenses in the survey, we obtain
interesting constraints on the velocity dispersion and density profiles of
elliptical galaxies. For example, assuming the SIS density profile and
marginalizing over other relevant parameters, we find 168 km/s < sigma_* < 200
km/s (68% CL), and 158 km/s < sigma_* < 220 km/s (95% CL). Furthermore, if we
instead assume a generalized NFW density profile and marginalize over other
parameters, the slope of the profile is constrained to be 1.50 < beta < 2.00
(95% CL). We also constrain the concentration parameter as a function of the
density profile slope in these models. These results are essentially
independent of the exact knowledge of cosmology. We briefly discuss the
possible impact on these constraints of allowing the galaxy luminosity function
to evolve with redshift, and also possible useful future directions for
exploration.Comment: Uses the final JVAS/CLASS sample, more careful choice of ellipticals,
added discussion of possible biases. Final results essentially unchanged.
Matches the MNRAS versio
Bouncing cosmological solutions and their stability
In the present paper we consider the bouncing braneworld scenario, in which
the bulk is given by a five-dimensional charged AdS black hole spacetime with
matter field confined in a brane. Then, we study the stability of
solutions with respect to homogeneous and isotropic perturbations.
Specifically, the AdS black hole with zero ADM mass and charge, and open
horizon is an attractor, while the charged AdS black hole with zero ADM mass
and flat horizon, is a repeller.Comment: 9 pages, 1 figur
Imaging the Earth's Interior: the Angular Distribution of Terrestrial Neutrinos
Decays of radionuclides throughout the Earth's interior produce geothermal
heat, but also are a source of antineutrinos. The (angle-integrated)
geoneutrino flux places an integral constraint on the terrestrial radionuclide
distribution. In this paper, we calculate the angular distribution of
geoneutrinos, which opens a window on the differential radionuclide
distribution. We develop the general formalism for the neutrino angular
distribution, and we present the inverse transformation which recovers the
terrestrial radioisotope distribution given a measurement of the neutrino
angular distribution. Thus, geoneutrinos not only allow a means to image the
Earth's interior, but offering a direct measure of the radioactive Earth, both
(1) revealing the Earth's inner structure as probed by radionuclides, and (2)
allowing for a complete determination of the radioactive heat generation as a
function of radius. We present the geoneutrino angular distribution for the
favored Earth model which has been used to calculate geoneutrino flux. In this
model the neutrino generation is dominated by decays in the Earth's mantle and
crust; this leads to a very ``peripheral'' angular distribution, in which 2/3
of the neutrinos come from angles > 60 degrees away from the downward vertical.
We note the possibility of that the Earth's core contains potassium; different
geophysical predictions lead to strongly varying, and hence distinguishable,
central intensities (< 30 degrees from the downward vertical). Other
uncertainties in the models, and prospects for observation of the geoneutrino
angular distribution, are briefly discussed. We conclude by urging the
development and construction of antineutrino experiments with angular
sensitivity. (Abstract abridged.)Comment: 25 pages, RevTeX, 7 figures. Comments welcom
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