4,011 research outputs found
Large collection of astrophysical S-factors and its compact representation
Numerous nuclear reactions in the crust of accreting neutron stars are
strongly affected by dense plasma environment. Simulations of superbursts, deep
crustal heating and other nuclear burning phenomena in neutron stars require
astrophysical S-factors for these reactions (as a function of center-of-mass
energy E of colliding nuclei). A large database of S-factors is created for
about 5000 non-resonant fusion reactions involving stable and unstable isotopes
of Be, B, C, N, O, F, Ne, Na, Mg, and Si. It extends the previous database of
about 1000 reactions involving isotopes of C, O, Ne, and Mg. The calculations
are performed using the Sao Paulo potential and the barrier penetration
formalism. All calculated S-data are parameterized by an analytic model for
S(E) proposed before [Phys. Rev. C 82, 044609 (2010)] and further elaborated
here. For a given reaction, the present S(E)-model contains three parameters.
These parameters are easily interpolated along reactions involving isotopes of
the same elements with only seven input parameters, giving an ultracompact,
accurate, simple, and uniform database. The S(E) approximation can also be used
to estimate theoretical uncertainties of S(E) and nuclear reaction rates in
dense matter, as illustrated for the case of the 34Ne+34Ne reaction in the
inner crust of an accreting neutron star.Comment: 13 pages, 2 figures, Phys. Rev. C, accepte
Molecular Identification of Eimeria Species in Broiler Chickens in Trinidad, West Indies
Coccidiosis is an intestinal disease of chickens of major economic importance to broiler industries worldwide. Species of coccidia found in chickens include Eimeria acervulina, Eimeria brunetti, Eimeria maxima, Eimeria mitis, Eimeria necatrix, Eimeria praecox, and Eimeria tenella. In recent years, polymerase chain reaction (PCR) has been developed to provide accurate and rapid identification of the seven known Eimeria species of chickens. The aim of this study was to use species-specific real-time PCR (qPCR) to identify which of the seven Eimeria species are present in Trinidad poultry. Seventeen pooled fecal samples were collected from 6 broiler farms (2–5 pens per farm) across Trinidad. Feces were also collected from birds showing clinical signs of coccidiosis in two live bird markets (pluck shops). qPCR revealed the presence of five species of Eimeria (E. acervulina, E. maxima, E. mitis, E. necatrix, and E. tenella), but not E. brunetti or E. praecox. Mixed infections were detected on all broiler farms, and DNA of two highly pathogenic Eimeria species (E. tenella and E. necatrix) was detected in feces taken from clinically sick birds sampled from the two pluck shops
Air Conditions Close to the Ground and the Effect on Airplane Landings
This report presents the results of an investigation undertaken to determine the feasibility of making glide landings in gusty air. Wind velocities were measured at several stations between the ground and a height of 51 feet, and flight tests were made to determine the actual influence of gusts on an airplane gliding close to the ground
Crab cavities for linear colliders
Crab cavities have been proposed for a wide number of accelerators and
interest in crab cavities has recently increased after the successful operation
of a pair of crab cavities in KEK-B. In particular crab cavities are required
for both the ILC and CLIC linear colliders for bunch alignment. Consideration
of bunch structure and size constraints favour a 3.9 GHz superconducting,
multi-cell cavity as the solution for ILC, whilst bunch structure and
beam-loading considerations suggest an X-band copper travelling wave structure
for CLIC. These two cavity solutions are very different in design but share
complex design issues. Phase stabilisation, beam loading, wakefields and mode
damping are fundamental issues for these crab cavities. Requirements and
potential design solutions will be discussed for both colliders.Comment: 3 pages. To be published in proceedings of LINAC 2008, Victoria,
Canad
New Experimental limit on Optical Photon Coupling to Neutral, Scalar Bosons
We report on the first results of a sensitive search for scalar coupling of
photons to a light neutral boson in the mass range of approximately 1.0
milli-electron volts and coupling strength greater than 10 GeV using
optical photons. This was a photon regeneration experiment using the "light
shining through a wall" technique in which laser light was passed through a
strong magnetic field upstream of an optical beam dump; regenerated laser light
was then searched for downstream of a second magnetic field region optically
shielded from the former. Our results show no evidence for scalar coupling in
this region of parameter space.Comment: pdf-file, 10 pages, 4 figures, submitted to Physical Review Letter
Formation scenarios and mass-radius relation for neutron stars
Neutron star crust, formed via accretion of matter from a companion in a
low-mass X-ray binary (LMXB), has an equation of state (EOS) stiffer than that
of catalyzed matter. At a given neutron star mass, M, the radius of a star with
an accreted crust is therefore larger, by DR(M), than for usually considered
star built of catalyzed matter. Using a compressible liquid drop model of
nuclei, we calculate, within the one-component plasma approximation, the EOSs
corresponding to different nuclear compositions of ashes of X-ray bursts in
LMXB. These EOSs are then applied for studying the effect of different
formation scenarios on the neutron-star mass-radius relation. Assuming the SLy
EOS for neutron star's liquid core, derived by Douchin & Haensel (2001), we
find that at M=1.4 M_sun the star with accreted crust has a radius more than
100 m larger that for the crust of catalyzed matter. Using smallness of the
crust mass compared to M, we derive a formula that relates DR(M) to the
difference in the crust EOS. This very precise formula gives also analytic
dependence of DR on M and R of the reference star built of catalyzed matter.
The formula is valid for any EOS of the liquid core. Rotation of neutron star
makes DR(M) larger. We derive an approximate but very precise formula that
gives difference in equatorial radii, DR_eq(M), as a function of stellar
rotation frequency.Comment: 6 pages, 4 figures. Accepted for publication in Astronomy and
Astrophysic
The Physical Origins of Entropy Production, Free Energy Dissipation and their Mathematical Representations
A complete mathematical theory of nonequilibrium thermodynamics of stochastic
systems in terms of master equations is presented. As generalizations of
isothermal entropy and free energy, two functions of states play central roles:
the Gibbs entropy and the relative entropy , which are related via the
stationary distribution of the stochastic dynamics. satisfies the
fundamental entropy balance equation with entropy production
rate and heat dissipation rate , while . For
closed systems that satisfy detailed balance: . For open system
one has where the housekeeping heat
was first introduced in the phenomenological nonequilibrium steady state
thermodynamics. Entropy production consists of free energy dissipation
associated with spontaneous relaxation, , and active energy pumping that
sustains the open system . The amount of excess heat involved in the
relaxation .Comment: 4 pages, no figure
- …