1,902 research outputs found
Universe acceleration and fine structure constant variation in BSBM theory
In this work we investigate the utility of using SNe Ia observations in
constraining the cosmological parameters in BSBM theory where a scalar field is
responsible for both fine structure constant variation and late time universe
acceleration. The model is discussed in the presence of an exponential self
potential for the scalar field. Stability and phase space analysis of the
solutions are studied. The model is tested against observational data for
Hubble parameter and quasar absorption spectra. With the best fitted model
parameters, the theory predicts a good match with the experimental results and
exhibits fine structure constant variation. The analysis also shows that for
the equation of state parameter, recent universe acceleration and possible
phantom crossing in future is forecasted.Comment: 14 pages, 10 figures, final version with minor modification accepted
to be published in JCA
A methodology for determining amino-acid substitution matrices from set covers
We introduce a new methodology for the determination of amino-acid
substitution matrices for use in the alignment of proteins. The new methodology
is based on a pre-existing set cover on the set of residues and on the
undirected graph that describes residue exchangeability given the set cover.
For fixed functional forms indicating how to obtain edge weights from the set
cover and, after that, substitution-matrix elements from weighted distances on
the graph, the resulting substitution matrix can be checked for performance
against some known set of reference alignments and for given gap costs. Finding
the appropriate functional forms and gap costs can then be formulated as an
optimization problem that seeks to maximize the performance of the substitution
matrix on the reference alignment set. We give computational results on the
BAliBASE suite using a genetic algorithm for optimization. Our results indicate
that it is possible to obtain substitution matrices whose performance is either
comparable to or surpasses that of several others, depending on the particular
scenario under consideration
Ideal stoichiometric technetium nitrides under pressure: a first-principles study
Technetium nitrides with various ideal stoichiometries have been investigated with the first-principle method at the pressures between 0–60 GPa. It have been found that there could be many stable technetium nitrides including Tc₃N, Tc₂N, TcN, Tc₂N₃, TcN₂, TcN₃, and TcN₄, among which Tc₃N and Tc₂N sub-nitrides are synthesizable at zero pressure and could be applied to nuclear waste management, such as separate radioactive 99Tc from nuclear fuel cycle. Moreover, N-rich TcN₃ and TcN₄ exhibit remarkable bulk properties and can be potential ultrastiff and hard materials.Нітриди технеція з різною ідеальної стехіометрією досліджені із застосуванням методу перших принципів при тисках від 0 до 60 ГПа. Встановлено, що може бути багато стабільних нітридів технеція, включаючи Tc₃N, Tc₂N, ТКС, Tc₂N₃, TcN₂, TcN₃ і TcN₄, серед яких субнітриди Tc₃N і Tc₂N синтезуються при нульовому тиску і можуть бути використані для обробки ядерних відходів, таких як виділений при ядерному паливному циклі радіоактивний 99Tc. Більш того, TcN₃ і TcN₄, збагачені N, демонструють чудові об’ємні властивості і можуть бути потенційними ультражорсткими і твердими матеріалами.Нитриды технеция с различной идеальной стехиометрией исследованы с применением метода первых принципов при давлениях от 0 до 60 ГПа. Установлено, что может быть много стабильных нитридов технеция, включая Tc₃N, Tc₂N, ТКС, Tc₂N₃, TcN₂, TcN₃ и TcN₄, среди которых субнитриды Tc₃N и Tc₂N синтезируются при нулевом давлении и могут быть использованы для обработки ядерных отходов, таких как выделенный при ядерном топливном цикле радиоактивный 99Tc. Более того, TcN₃ и TcN₄, обогащенные N, демонстрируют замечательные объемные свойства и могут быть потенциальными ультражесткими и твердыми материалами
Influence of Carbon Concentration on the Superconductivity in MgCxNi3
The influence of carbon concentration on the superconductivity (SC) in
MgCNi has been investigated by measuring the low temperature specific
heat combined with first principles electronic structure calculation. It is
found that the specific heat coefficient of the
superconducting sample () in normal state is twice that of the
non-superconducting one (). The comparison of measured
and the calculated electronic density of states (DOS) shows that the
effective mass renormalization changes remarkably as the carbon concentration
changes. The large mass renormalization for the superconducting sample and the
low (7K) indicate that more than one kind of boson mediated
electron-electron interactions exist in MgCNi.Comment: 4 pages, 4 figure
Pharmacogenetic variants influence tamoxifen's estrogenic effect on bone density
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/109849/1/cptclpt200586.pd
Search for Gamma-Ray Emission from AE Aquarii with Seven Years of Fermi-LAT Observations
AE Aquarii (AE Aqr) is a cataclysmic binary hosting one of the fastest
rotating (P = 33.08 s) white dwarfs known. Based on seven years of
Fermi Large Area Telescope (LAT) Pass 8 data, we report on a deep search for
gamma-ray emission from AE Aqr. Using X-ray observations from ASCA, XMM-Newton,
Chandra, Swift, Suzaku, and NuSTAR, spanning 20 years, we substantially extend
and improve the spin ephemeris of AE Aqr. Using this ephemeris, we searched for
gamma-ray pulsations at the spin period of the white dwarf. No gamma-ray
pulsations were detected above 3 significance. Neither phase-averaged
gamma-ray emission nor gamma-ray variability of AE Aquarii is detected by
Fermi-LAT. We impose the most restrictive upper limit to the gamma-ray flux
from AE Aqr to date: erg cm s in the 100
MeV-300 GeV energy range, providing constraints on models.Comment: 16 pages, 4 figures, 1 table, Accepted for publication in Ap
Compressive Properties of SiC Particle-Reinforced Aluminum Matrix Composites under Repeated Impact Loading
Under repeated impact loading, SiC particle-reinforced aluminum matrix composites (SiCp/Al) experience severe plastic strains, which can lead to local changes in their microstructure. Microstructure variations have a significant effect on the dynamic behavior of SiCp/Al composites under subsequent impact loading. Their microstructure was analyzed by scanning electron microscopy (SEM). Then the dynamic compressive properties of SiCp/Al composites were studied using the split Hopkinson pressure bar (SHPB), and the dynamic compression stress–strain curve for each impact was plotted.В условиях повторного ударного нагружения композиционные материалы с алюминиевой матрицей, упрочненные частицами SiC (SiCp/Al), испытывают действие высоких пластических деформаций, что может приводить к локальным изменениям их микроструктуры. Изменения микроструктуры оказывают существенное влияние на динамическое поведение композиционных материалов SiCp/Al при последующем ударном нагружении. Их микроструктура проанализирована с использованием сканирующей электронной микроскопии. Динамическую сжимаемость композиционных материалов изучали с помощью разрезного стержня Гопкинсона, была построена зависимость деформации от динамического сжимающего напряжения для каждого ударного воздействия
Temporal build-up of electromagnetically induced transparency and absorption resonances in degenerate two-level transitions
The temporal evolution of electromagnetically induced transparency (EIT) and
absorption (EIA) coherence resonances in pump-probe spectroscopy of degenerate
two-level atomic transition is studied for light intensities below saturation.
Analytical expression for the transient absorption spectra are given for simple
model systems and a model for the calculation of the time dependent response of
realistic atomic transitions, where the Zeeman degeneracy is fully accounted
for, is presented. EIT and EIA resonances have a similar (opposite sign) time
dependent lineshape, however, the EIA evolution is slower and thus narrower
lines are observed for long interaction time. Qualitative agreement with the
theoretical predictions is obtained for the transient probe absorption on the
line in an atomic beam experiment.Comment: 10 pages, 9 figures. Submitted to Phys. Rev.
Motion-Induced Radiation from a Dynamically Deforming Mirror
A path integral formulation is developed to study the spectrum of radiation
from a perfectly reflecting (conducting) surface. It allows us to study
arbitrary deformations in space and time. The spectrum is calculated to second
order in the height function. For a harmonic traveling wave on the surface, we
find many different regimes in which the radiation is restricted to certain
directions. It is shown that high frequency photons are emitted in a beam with
relatively low angular dispersion whose direction can be controlled by the
mechanical deformations of the plate.Comment: 4 pages, 2 eps figues included, final version as appeared in PR
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