1,023 research outputs found
SNAP-8 corrosion program Quarterly progress report, period ending 31 May 1965
Differences in corrosion and mass transfer rates in corrosion loops for SNAP-8 system and effectiveness of cold trapping in reducing hydrogen concentratio
Snap-8 corrosion program quarterly progress report, period ending 28 feb. 1965
SNAP-8 corrosion program - hydrogen solubility in sodium-potassium, permeability of hydrogen and deuterum through stainless steel, and phase equilibri
Smoothing effect and delocalization of interacting Bose-Einstein condensates in random potentials
We theoretically investigate the physics of interacting Bose-Einstein
condensates at equilibrium in a weak (possibly random) potential. We develop a
perturbation approach to derive the condensate wavefunction for an amplitude of
the potential smaller than the chemical potential of the condensate and for an
arbitrary spatial variation scale of the potential. Applying this theory to
disordered potentials, we find in particular that, if the healing length is
smaller than the correlation length of the disorder, the condensate assumes a
delocalized Thomas-Fermi profile. In the opposite situation where the
correlation length is smaller than the healing length, we show that the random
potential can be significantly smoothed and, in the meanfield regime, the
condensate wavefunction can remain delocalized, even for very small correlation
lengths of the disorder.Comment: The word "screening" has been changed to "smoothing" to avoid
confusions with other effects discussed in the literature. This does not
affect the content of paper, nor the results, nor the physical discussio
Hadronic Annihilation Decay Rates of P-wave Heavy Quarkonia with Both Relativistic and QCD Radiative Corrections
Hadronic annihilation decay rates of P-wave heavy quarkonia are given to
next-to-leading order in both and . They include ten
nonperturbative parameters, which can be rigorously defined as the matrix
elements of color-singlet and color-octet operators in NRQCD. We expect these
papameters will be determined from lattice calculations in future.Comment: 5 Pages RevTex. The paper is withdraw
Atom cooling and trapping by disorder
We demonstrate the possibility of three-dimensional cooling of neutral atoms
by illuminating them with two counterpropagating laser beams of mutually
orthogonal linear polarization, where one of the lasers is a speckle field,
i.e. a highly disordered but stationary coherent light field. This
configuration gives rise to atom cooling in the transverse plane via a Sisyphus
cooling mechanism similar to the one known in standard two-dimensional optical
lattices formed by several plane laser waves. However, striking differences
occur in the spatial diffusion coefficients as well as in local properties of
the trapped atoms.Comment: 11 figures (postscript
Disorder-induced trapping versus Anderson localization in Bose-Einstein condensates expanding in disordered potentials
We theoretically investigate the localization of an expanding Bose-Einstein
condensate with repulsive atom-atom interactions in a disordered potential. We
focus on the regime where the initial inter-atomic interactions dominate over
the kinetic energy and the disorder. At equilibrium in a trapping potential and
for small disorder, the condensate shows a Thomas-Fermi shape modified by the
disorder. When the condensate is released from the trap, a strong suppression
of the expansion is obtained in contrast to the situation in a periodic
potential with similar characteristics. This effect crucially depends on both
the momentum distribution of the expanding BEC and the strength of the
disorder. For strong disorder, the suppression of the expansion results from
the fragmentation of the core of the condensate and from classical reflections
from large modulations of the disordered potential in the tails of the
condensate. We identify the corresponding disorder-induced trapping scenario
for which large atom-atom interactions and strong reflections from single
modulations of the disordered potential play central roles. For weak disorder,
the suppression of the expansion signals the onset of Anderson localization,
which is due to multiple scattering from the modulations of the disordered
potential. We compute analytically the localized density profile of the
condensate and show that the localization crucially depends on the correlation
function of the disorder. In particular, for speckle potentials the long-range
correlations induce an effective mobility edge in 1D finite systems. Numerical
calculations performed in the mean-field approximation support our analysis for
both strong and weak disorder.Comment: New Journal of Physics; focus issue "Quantum Correlations in Tailored
Matter - Common perspectives of mesoscopic systems and quantum gases"; 30
pages, 10 figure
Orbitally excited and hybrid mesons from the lattice
We discuss in general the construction of gauge-invariant non-local meson
operators on the lattice. We use such operators to study the - and -wave
mesons as well as hybrid mesons in quenched QCD, with quark masses near the
strange quark mass. The resulting spectra are compared with experiment for the
orbital excitations. For the states produced by gluonic excitations (hybrid
mesons) we find evidence of mixing for non-exotic quantum numbers. We give
predictions for masses of the spin-exotic hybrid mesons with $J^{PC}=1^{-+},\
0^{+-}2^{+-}$.Comment: 31 pages, LATEX, 8 postscript figures. Reference adde
Thermoluminescence of zircon: a kinetic model
The mineral zircon, ZrSiO4, belongs to a class of promising materials for geochronometry by means of thermoluminescence (TL) dating. The development of a reliable and reproducible method for TL dating with zircon requires detailed knowledge of the processes taking place during exposure to ionizing radiation, long-term storage, annealing at moderate temperatures and heating at a constant rate (TL measurements). To understand these processes one needs a kinetic model of TL. This paper is devoted to the construction of such amodel. The goal is to study the qualitative behaviour of the system and to determine the parameters and processes controlling TL phenomena of zircon. The model considers the following processes: (i) Filling of electron and hole traps at the excitation stage as a function of the dose rate and the dose for both (low dose rate) natural and (high dose rate) laboratory irradiation. (ii) Time dependence of TL fading in samples irradiated under laboratory conditions. (iii) Short time annealing at a given temperature. (iv) Heating of the irradiated sample to simulate TL experiments both after laboratory and natural irradiation.
The input parameters of the model, such as the types and concentrations of the TL centres and the energy distributions of the hole and electron traps, were obtained by analysing the experimental data on fading of the TL-emission spectra of samples from different geological locations. Electron paramagnetic resonance (EPR) data were used to establish the nature of the TL centres. Glow curves and 3D TL emission spectra are simulated and compared with the experimental data on time-dependent TL fading. The saturation and annealing behaviour of filled trap concentrations has been considered in the framework of the proposed kinetic model and comparedwith the EPR data associated with the rare-earth ions Tb3+ and Dy3+, which play a crucial role as hole traps and recombination centres. Inaddition, the behaviour of some of the SiOmn− centres has been compared with simulation results.
Application of remote sensor data to geologic analysis of the Bonanza test site Colorado
Research activities on geologic remote sensing applications for Colorado are summarized. Projects include: regional and detailed geologic mapping, surficial and engineering geology, fracture studies, uranium exploration, hydrology, and data reduction and enhancement. The acquisition of remote sensor data is also discussed
A Bayesian palaeoenvironmental transfer function model for acidified lakes
A Bayesian approach to palaeoecological environmental reconstruction deriving from the unimodal responses generally exhibited by organisms to an environmental gradient is described. The approach uses Bayesian model selection to calculate a collection of probability-weighted, species-specific response curves (SRCs) for each taxon within a training set, with an explicit treatment for zero abundances. These SRCs are used to reconstruct the environmental variable from sub-fossilised assemblages. The approach enables a substantial increase in computational efficiency (several orders of magnitude) over existing Bayesian methodologies. The model is developed from the Surface Water Acidification Programme (SWAP) training set and is demonstrated to exhibit comparable predictive power to existing Weighted Averaging and Maximum Likelihood methodologies, though with improvements in bias; the additional explanatory power of the Bayesian approach lies in an explicit calculation of uncertainty for each individual reconstruction. The model is applied to reconstruct the Holocene acidification history of the Round Loch of Glenhead, including a reconstruction of recent recovery derived from sediment trap data.The Bayesian reconstructions display similar trends to conventional (Weighted Averaging Partial Least Squares) reconstructions but provide a better reconstruction of extreme pH and are more sensitive to small changes in diatom assemblages. The validity of the posteriors as an apparently meaningful representation of assemblage-specific uncertainty and the high computational efficiency of the approach open up the possibility of highly constrained multiproxy reconstructions
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