6,042 research outputs found
Light-cone coordinates based at a geodesic world line
Continuing work initiated in an earlier publication [Phys. Rev. D 69, 084007
(2004)], we construct a system of light-cone coordinates based at a geodesic
world line of an arbitrary curved spacetime. The construction involves (i) an
advanced-time or a retarded-time coordinate that labels past or future light
cones centered on the world line, (ii) a radial coordinate that is an affine
parameter on the null generators of these light cones, and (iii) angular
coordinates that are constant on each generator. The spacetime metric is
calculated in the light-cone coordinates, and it is expressed as an expansion
in powers of the radial coordinate in terms of the irreducible components of
the Riemann tensor evaluated on the world line. The formalism is illustrated in
two simple applications, the first involving a comoving world line of a
spatially-flat cosmology, the other featuring an observer placed on the axis of
symmetry of Melvin's magnetic universe.Comment: 11 pages, 1 figur
Health Behaviors Among College Students: The Influence of Future Time Perspective and Basic Psychological Need Satisfaction
Health behavior change may prevent many fatal diseases, and may be influenced by social and motivational constructs. We assessed the interaction effect of future time perspective and basic psychological need fulfillment on positive and negative health behaviors. Future time perspective was associated with more positive, and less negative, health behaviors. Need fulfillment was associated with only positive health behaviors. In moderation analyses, individuals reporting both high need fulfillment and future perspective reported greater positive health behaviors, and were especially unlikely to smoke. Enhancing future-mindedness and supporting need satisfaction in interventions targeting modifiable health behaviors is encouraged
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
Emperical Tests of Acceptance Sampling Plans
Acceptance sampling is a quality control procedure applied as an alternative to 100% inspection. A random sample of items is drawn from a lot to determine the fraction of items which have a required quality characteristic. Both the number of items to be inspected and the criterion for determining conformance of the lot to the requirement are given by an appropriate sampling plan with specified risks of Type I and Type II sampling errors. In this paper, we present the results of empirical tests of the accuracy of selected sampling plans reported in the literature. These plans are for measureable quality characteristics which are known have either binomial, exponential, normal, gamma, Weibull, inverse Gaussian, or Poisson distributions. In the main, results support the accepted wisdom that variables acceptance plans are superior to attributes (binomial) acceptance plans, in the sense that these provide comparable protection against risks at reduced sampling cost. For the Gaussian and Weibull plans, however, there are ranges of the shape parameters for which the required sample sizes are in fact larger than the corresponding attributes plans, dramatically so for instances of large skew. Tests further confirm that the published inverse-Gaussian (IG) plan is flawed, as reported by White and Johnson (2011)
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
Probabilistic Requirements (Partial) Verification Methods Best Practices Improvement. Variables Acceptance Sampling Calculators: Empirical Testing
The NASA Engineering and Safety Center was requested to improve on the Best Practices document produced for the NESC assessment, Verification of Probabilistic Requirements for the Constellation Program, by giving a recommended procedure for using acceptance sampling by variables techniques as an alternative to the potentially resource-intensive acceptance sampling by attributes method given in the document. In this paper, the results of empirical tests intended to assess the accuracy of acceptance sampling plan calculators implemented for six variable distributions are presented
Probabilistic Requirements (Partial) Verification Methods Best Practices Improvement. Variables Acceptance Sampling Calculators: Derivations and Verification of Plans
The NASA Engineering and Safety Center was requested to improve on the Best Practices document produced for the NESC assessment, Verification of Probabilistic Requirements for the Constellation Program, by giving a recommended procedure for using acceptance sampling by variables techniques. This recommended procedure would be used as an alternative to the potentially resource-intensive acceptance sampling by attributes method given in the document. This document contains the outcome of the assessment
Stress in Swine
Stress appears to be increasing in swine and its toll ranges from death of animals to undesirable meat characteristics. The authors review the problem and list some preventive measures you can take
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
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