7,537 research outputs found
IUE ultraviolet observations of W UM a Stars
International Ultraviolet Explorer observations of four W UMa eclipsing binary systems (44 Boo, VW Cep, W UMa, and epsilon) are discussed. The stars generally show large surface fluxes of high temperature lines (C II, C IV, N V, Si IV) which may result from the high rotational velocities forced by synchronous rotation. High dispersion spectra of the 44 Boo system in the Mg II line enable the individual stellar components to be identified. The line widths and phase variations are consistent with the optically determined spectroscopic orbit. Circumstellar absorption of Mg II may be presented at selected phases
Feshbach Resonances and Limiting Thermodynamics of Strongly Correlated Nucleons
A finite temperature model of strongly correlated nucleons with underlying
isospin symmetries is developed. The model can be used to study the role of
bound states and Feshbach resonances on the thermal properties of a spin 1/2,
isospin 1/2 system of protons and neutrons by varying the proton fraction. An
analysis of features associated with a universal thermodynamic limit or unitary
limit is given. In the limit of very large scattering length, the effective
range to quantum thermal wavelength appears as a limiting scale in an
interaction energy and equation of state.Comment: 8 pages, 4 figure
Solution of the Bohr hamiltonian for soft triaxial nuclei
The Bohr-Mottelson model is solved for a generic soft triaxial nucleus,
separating the Bohr hamiltonian exactly and using a number of different
model-potentials: a displaced harmonic oscillator in , which is solved
with an approximated algebraic technique, and Coulomb/Kratzer,
harmonic/Davidson and infinite square well potentials in , which are
solved exactly. In each case we derive analytic expressions for the
eigenenergies which are then used to calculate energy spectra.
Here we study the chain of osmium isotopes and we compare our results with
experimental information and previous calculations.Comment: 13 pages, 9 figure
Bacterial leaching: biotechnology in the mining industry
Bacterial leaching is the extraction of metals from their ores using microorganisms. Microbial technology offers an economic alternative for the mining industry, at a time when high-grade mineral resources are being depleted
A supersymmetric model of gamma ray bursts
We propose a model for gamma ray bursts in which a star subject to a high
level of fermion degeneracy undergoes a phase transition to a supersymmetric
state. The burst is initiated by the transition of fermion pairs to sfermion
pairs which, uninhibited by the Pauli exclusion principle, can drop to the
ground state of minimum momentum through photon emission. The jet structure is
attributed to the Bose statistics of sfermions whereby subsequent sfermion
pairs are preferentially emitted into the same state (sfermion amplification by
stimulated emission). Bremsstrahlung gamma rays tend to preserve the
directional information of the sfermion momenta and are themselves enhanced by
stimulated emission.Comment: published versio
Calculation of Timber Yields From North Queensland Rainforests
Calculation of timber yields from north Queensland rainforests indicate that the long term average yield is in the vicinity of 63 000 cubic metres per year, and that an allowable cut of 60 000 cubic metres per year should apply for the period 1986-1991. These calculations apply to the 158 000 hectares of Crown land managed for timber production between Townsville and the Daintree River. Estimates were prepared using cutting cycle analysis, and incorporated a number of innovations made possible by advances in computing technology. These included simulating the growth of individual plots rather than of stratum averages, and the use of a dynamic growth model which accommodated stand density, composition and site quality
Utility of Landsat Thematic Mapper Data for Mapping Site Productivity in Tropical Moist Forests
Regression analysis was used to develop a relationship between Landsat 5 Thematic Mapper data and site quality of permanent sample plots. The thermal band (6) produced misleading results, but the ratio of band 4 on 5 showed promise when combined with geological information. Best results were obtained when regression analysis was restricted to ensure that at least one each of the visible (1 to 3), mid-infrared (5 and 7) and near-infrared (4) bands were included. Results suggest that Landsat TM may be useful for mapping site quality in tropical moist forest in north Queensland. Interpolation of site productivity within a single pass seems feasible, but attempts to extrapolate results to other passes or to imagery obtained on different dates may be unreliable
A study of Feshbach resonances and the unitary limit in a model of strongly correlated nucleons
A model of strongly interacting and correlated hadrons is developed. The
interaction used contains a long range attraction and short range repulsive
hard core. Using this interaction and various limiting situations of it, a
study of the effect of bound states and Feshbach resonances is given. The
limiting situations are a pure square well interaction, a delta-shell potential
and a pure hard core potential. The limit of a pure hard core potential are
compared with results for a spinless Bose and Fermi gas. The limit of many
partial waves for a pure hard core interaction is also considered and result in
expressions involving the hard core volume. This feature arises from a scaling
relation similar to that for hard sphere scattering with diffractive
corrections. The role of underlying isospin symmetries associated with the
strong interaction of protons and neutrons in this two component model is
investigated. Properties are studied with varying proton fraction. An analytic
expression for the Beth Uhlenbeck continuum integral is developed which closely
approximates exact results based on the potential model considered. An analysis
of features associated with a unitary limit is given. In the unitary limit of
very large scattering length, the ratio of effective range to thermal
wavelength appears as a limiting scale. Thermodynamic quantities such as the
entropy and compressibility are also developed. The effective range corrections
to the entropy vary as the cube of this ratio for low temperatures and are
therefore considerably reduced compared to the corrections to the interaction
energy which varies linearly with this ratio. Effective range corrections to
the compressibility are also linear in the ratio.Comment: 39 pages, 15 figures, 2 table
Fat transforms ascorbic acid from inhibiting to promoting acid-catalysed N-nitrosation
<b>Background</b>: The major potential site of acid nitrosation is the proximal stomach, an anatomical site prone to
a rising incidence of metaplasia and adenocarcinoma. Nitrite, a pre-carcinogen present in saliva, can be
converted to nitrosating species and N-nitroso compounds by acidification at low gastric pH in the presence
of thiocyanate.
<b>Aims</b>: To assess the effect of lipid and ascorbic acid on the nitrosative chemistry under conditions simulating
the human proximal stomach.
<b>Methods</b>: The nitrosative chemistry was modelled in vitro by measuring the nitrosation of four secondary
amines under conditions simulating the proximal stomach. The N-nitrosamines formed were measured by gas
chromatography–ion-trap tandem mass spectrometry, while nitric oxide and oxygen levels were measured
amperometrically.
<b>Results</b>: In absence of lipid, nitrosative stress was inhibited by ascorbic acid through conversion of nitrosating
species to nitric oxide. Addition of ascorbic acid reduced the amount of N-nitrosodimethylamine formed by
fivefold, N-nitrosomorpholine by .1000-fold, and totally prevented the formation of N-nitrosodiethylamine
and N-nitrosopiperidine. In contrast, when 10% lipid was present, ascorbic acid increased the amount of Nnitrosodimethylamine,
N-nitrosodiethylamine and N-nitrosopiperidine formed by approximately 8-, 60- and
140-fold, respectively, compared with absence of ascorbic acid.
<b>Conclusion</b>: The presence of lipid converts ascorbic acid from inhibiting to promoting acid nitrosation. This
may be explained by nitric oxide, formed by ascorbic acid in the aqueous phase, being able to regenerate
nitrosating species by reacting with oxygen in the lipid phase
Local Projections of Low-Momentum Potentials
Nuclear interactions evolved via renormalization group methods to lower
resolution become increasingly non-local (off-diagonal in coordinate space) as
they are softened. This inhibits both the development of intuition about the
interactions and their use with some methods for solving the quantum many-body
problem. By applying "local projections", a softened interaction can be reduced
to a local effective interaction plus a non-local residual interaction. At the
two-body level, a local projection after similarity renormalization group (SRG)
evolution manifests the elimination of short-range repulsive cores and the flow
toward universal low-momentum interactions. The SRG residual interaction is
found to be relatively weak at low energy, which motivates a perturbative
treatment
- …