21,435 research outputs found
Nuclear weak interaction rates in primordial nucleosynthesis
We calculate the weak interaction rates of selected light nuclei during the
epoch of Big Bang Nucleosynthesis (BBN), and we assess the impact of these
rates on nuclear abundance flow histories and on final light element abundance
yields. We consider electron and electron antineutrino captures on 3He and 7Be,
and the reverse processes of positron capture and electron neutrino capture on
3H and 7Li. We also compute the rates of positron and electron neutrino capture
on 6He. We calculate beta and positron decay transitions where appropriate. As
expected, the final standard BBN abundance yields are little affected by
addition of these weak processes, though there can be slight alterations of
nuclear flow histories. However, non-standard BBN scenarios, e.g., those
involving out of equilibrium particle decay with energetic final state
neutrinos, may be affected by these processes.Comment: 10 pages, 6 figure
Big Bang Nucleosynthesis with Independent Neutrino Distribution Functions
We have performed new Big Bang Nucleosynthesis calculations which employ
arbitrarily-specified, time-dependent neutrino and antineutrino distribution
functions for each of up to four neutrino flavors. We self-consistently couple
these distributions to the thermodynamics, the expansion rate and scale
factor-time/temperature relationship, as well as to all relevant weak,
electromagnetic, and strong nuclear reaction processes in the early universe.
With this approach, we can treat any scenario in which neutrino or antineutrino
spectral distortion might arise. These scenarios might include, for example,
decaying particles, active-sterile neutrino oscillations, and active-active
neutrino oscillations in the presence of significant lepton numbers. Our
calculations allow lepton numbers and sterile neutrinos to be constrained with
observationally-determined primordial helium and deuterium abundances. We have
modified a standard BBN code to perform these calculations and have made it
available to the community.Comment: 9 pages, 5 figure
Weak Interaction Rate Coulomb Corrections in Big Bang Nucleosynthesis
We have applied a fully relativistic Coulomb wave correction to the weak
reactions in the full Kawano/Wagoner Big Bang Nucleosynthesis (BBN) code. We
have also added the zero temperature radiative correction. We find that using
this higher accuracy Coulomb correction results in good agreement with previous
work, giving only a modest 0.04 percent increase in helium mass fraction over
correction prescriptions applied previously in BBN calculations. We have
calculated the effect of these corrections on other light element abundance
yields in BBN and we have studied these yields as functions of electron
neutrino lepton number. This has allowed insights into the role of the Coulomb
correction in the setting of the neutron-to-proton ratio during the BBN epoch.
We find that the lepton capture processes' contributions to this ratio are only
second order in the Coulomb correction.Comment: 8 pages, 3 figure
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Sceloporus cautus
Number of Pages: 5Integrative BiologyGeological Science
One year of monitoring the Vela pulsar using a Phased Array Feed
We have observed the Vela pulsar for one year using a Phased Array Feed (PAF)
receiver on the 12-metre antenna of the Parkes Test-Bed Facility. These
observations have allowed us to investigate the stability of the PAF
beam-weights over time, to demonstrate that pulsars can be timed over long
periods using PAF technology and to detect and study the most recent glitch
event that occurred on 12 December 2016. The beam-weights are shown to be
stable to 1% on time scales on the order of three weeks. We discuss the
implications of this for monitoring pulsars using PAFs on single dish
telescopes.Comment: 6 pages, 4 figures, 2 tables. Accepted for publication in PAS
Computation of aircraft component flow fields at transonic Mach numbers using a three-dimensional Navier-Stokes algorithm
A computer analysis was developed for calculating steady (or unsteady) three-dimensional aircraft component flow fields. This algorithm, called ENS3D, can compute the flow field for the following configurations: diffuser duct/thrust nozzle, isolated wing, isolated fuselage, wing/fuselage with or without integrated inlet and exhaust, nacelle/inlet, nacelle (fuselage) afterbody/exhaust jet, complete transport engine installation, and multicomponent configurations using zonal grid generation technique. Solutions can be obtained for subsonic, transonic, or hypersonic freestream speeds. The algorithm can solve either the Euler equations for inviscid flow, the thin shear layer Navier-Stokes equations for viscous flow, or the full Navier-Stokes equations for viscous flow. The flow field solution is determined on a body-fitted computational grid. A fully-implicit alternating direction implicit method is employed for the solution of the finite difference equations. For viscous computations, either a two layer eddy-viscosity turbulence model or the k-epsilon two equation transport model can be used to achieve mathematical closure
Environmental Hedonism or, Securing the Environment Through the Common Law
This Article investigates whether a right to environmental hedonism can be claimed and compensated for when the environment is degraded. Building upon the economic and mathematical uncertainties in assessing any claim for loss of enjoyment of the environment, the Article considers the evaluation of environmental harms ex post through use of restorative damages allowed under the Restatement (Second) of Torts - and concludes that because of the ambiguities in public policy for not only determining what is an appropriate case for an award of restorative damages but also evaluating the nature and the scope of environmental injuries, these damages are deficient as a tool for protecting environmental degradations. The Article then studies the parens patriae powers of the government to manage and to protect the environment as a source for securing the environment and finds justification for its exercise through the application and use of the Doctrine of Public Trust. It concludes by examining the Common Law of nuisance - and especially anticipatory and aesthetic nuisance - concluding, as such, this body of law provides the strongest remedial base for protecting assaults on the environment
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