22,916 research outputs found
Cryogenic combustion laboratory
The objective is to establish a major experimental laboratory for studying fundamental processes such as mixing and combustion under liquid rocket engine conditions. The capability of this laboratory will include operation using a variety of fuel and oxidizer systems including liquid oxygen and liquid hydrocarbons. In addition to providing the proper facilities for supplying and controlling these fuels and oxidizers, a specific effort is being made to provide a state-of-the-art diagnostic capability for combustion measurements. In particular, optical and laser-based techniques are being emphasized for measurements of species, velocities, and spray characteristics
Monthly mean forecast experiments with the GISS model
The GISS general circulation model was used to compute global monthly mean forecasts for January 1973, 1974, and 1975 from initial conditions on the first day of each month and constant sea surface temperatures. Forecasts were evaluated in terms of global and hemispheric energetics, zonally averaged meridional and vertical profiles, forecast error statistics, and monthly mean synoptic fields. Although it generated a realistic mean meridional structure, the model did not adequately reproduce the observed interannual variations in the large scale monthly mean energetics and zonally averaged circulation. The monthly mean sea level pressure field was not predicted satisfactorily, but annual changes in the Icelandic low were simulated. The impact of temporal sea surface temperature variations on the forecasts was investigated by comparing two parallel forecasts for January 1974, one using climatological ocean temperatures and the other observed daily ocean temperatures. The use of daily updated sea surface temperatures produced no discernible beneficial effect
Shell model description of the 14C dating beta decay with Brown-Rho-scaled NN interactions
We present shell model calculations for the beta-decay of the 14C ground
state to the 14N ground state, treating the states of the A=14 multiplet as two
0p holes in an 16O core. We employ low-momentum nucleon-nucleon (NN)
interactions derived from the realistic Bonn-B potential and find that the
Gamow-Teller matrix element is too large to describe the known lifetime. By
using a modified version of this potential that incorporates the effects of
Brown-Rho scaling medium modifications, we find that the GT matrix element
vanishes for a nuclear density around 85% that of nuclear matter. We find that
the splitting between the (J,T)=(1+,0) and (J,T)=(0+,1) states in 14N is
improved using the medium-modified Bonn-B potential and that the transition
strengths from excited states of 14C to the 14N ground state are compatible
with recent experiments.Comment: 4 pages, 5 figures Updated to include referee comments/suggestion
Low-momentum ring diagrams of neutron matter at and near the unitary limit
We study neutron matter at and near the unitary limit using a low-momentum
ring diagram approach. By slightly tuning the meson-exchange CD-Bonn potential,
neutron-neutron potentials with various scattering lengths such as
and are constructed. Such potentials are renormalized
with rigorous procedures to give the corresponding -equivalent
low-momentum potentials , with which the low-momentum
particle-particle hole-hole ring diagrams are summed up to all orders, giving
the ground state energy of neutron matter for various scattering lengths.
At the limit of , our calculated ratio of to that of
the non-interacting case is found remarkably close to a constant of 0.44 over a
wide range of Fermi-momenta. This result reveals an universality that is well
consistent with the recent experimental and Monte-Carlo computational study on
low-density cold Fermi gas at the unitary limit. The overall behavior of this
ratio obtained with various scattering lengths is presented and discussed.
Ring-diagram results obtained with and those with -matrix
interactions are compared.Comment: 9 pages, 7 figure
Supernova neutrinos in the light of FCNC
We study the effect of including flavor changing neutral currents (FCNC) in
the analysis of the neutrino signal of a supernova burst. When we include the
effect of the FCNC which are beyond the standard model (SM) in the study of the
MSW resonant conversion, we obtain dramatic changes in the \Delta
m^2-sin^2(2\theta) probability contours for neutrino detection.Comment: 8 pages in ReVTeX,3 figures. Revised manuscript submitted to Phys.
Rev.
Quantifying flow and stress in ice mélange, the world’s largest granular material.
Tidewater glacier fjords are often filled with a collection of calved icebergs, brash ice, and sea ice. For glaciers with high calving rates, this “m ́elange” of ice can be jam-packed, so that the flow of ice fragments is mostly determined by granular interactions. In the jammed state, ice m ́elange has been hypothesized to influence iceberg calving and capsize, dispersion and attenuation of ocean waves, injection of freshwater into fjords, and fjord circulation. However, detailed measurements of ice m ́elange are lacking due to difficulties in instrumenting remote, ice-choked fjords. Here we characterize the flow and associated stress in icem ́elange, using a combination of terrestrial radar data, laboratory experiments, and numerical simulations. We find that, during periods of terminus quiescence, ice m ́elange experiences laminar flow over timescales of hours to days. The uniform flow fields are bounded by shear margins along fjord walls where force chains between granular icebergs terminate. In addition, the average force per unit width that is transmitted to the glacier terminus, which can exceed 107N/m, increases exponentially with them ́elange length-to-width ratio. These “buttressing” forces are sufficiently high to inhibit the initiation of large-scale calving events, supporting the notion that ice m ́elange can be viewed as a weak granular ice shelf that transmits stresses from fjord walls back to glacier termini.Ye
Hot new directions for quasi-Monte Carlo research in step with applications
This article provides an overview of some interfaces between the theory of
quasi-Monte Carlo (QMC) methods and applications. We summarize three QMC
theoretical settings: first order QMC methods in the unit cube and in
, and higher order QMC methods in the unit cube. One important
feature is that their error bounds can be independent of the dimension
under appropriate conditions on the function spaces. Another important feature
is that good parameters for these QMC methods can be obtained by fast efficient
algorithms even when is large. We outline three different applications and
explain how they can tap into the different QMC theory. We also discuss three
cost saving strategies that can be combined with QMC in these applications.
Many of these recent QMC theory and methods are developed not in isolation, but
in close connection with applications
Low Momentum Nucleon-Nucleon Interactions and Shell-Model Calculations
In the last few years, the low-momentum nucleon-nucleon (NN) interaction
V-low-k derived from free-space NN potentials has been successfully used in
shell-model calculations. V-low-k is a smooth potential which preserves the
deuteron binding energy as well as the half-on-shell T-matrix of the original
NN potential up to a momentum cutoff Lambda. In this paper we put to the test a
new low-momentum NN potential derived from chiral perturbation theory at
next-to-next-to-next-to-leading order with a sharp low-momentum cutoff at 2.1
fm-1. Shell-model calculations for the oxygen isotopes using effective
hamiltonians derived from both types of low-momentum potential are performed.
We find that the two potentials show the same perturbative behavior and yield
very similar results.Comment: 8 pages, 8 figures, to be published in Physical Review
- …