13,398 research outputs found
Design, development, and fabrication of a prototype ice pack heat sink subsystem. Flight experiment physical phenomena experiment chest
The concept of a flight experiment physical phenomena experiment chest, to be used eventually for investigating and demonstrating ice pack heat sink subsystem physical phenomena during a zero gravity flight experiment, is described
High-spin intruder states in the fp shell nuclei and isoscalar proton-neutron correlations
We perform a systematic shell-model and mean-field study of fully-aligned,
high-spin f_{7/2}^{n} seniority isomers and d_{3/2}^{-1} f_{7/2}^{n+1} intruder
states in the A~44 nuclei from the lower-fp shell. The shell-model calculations
are performed in the full sdfp configuration space allowing 1p-1h cross-shell
excitations. The self-consistent mean-field calculations are based on the
Hartree-Fock approach with the Skyrme energy density functional that reproduces
empirical Landau parameters. While there is a nice agreement between
experimental and theoretical relative energies of fully-aligned states in N>Z
nuclei, this is no longer the case for the N=Z systems. The remaining deviation
from the data is attributed to the isoscalar proton-neutron correlations. It is
also demonstrated that the Coulomb corrections at high spins noticeably depend
on the choice of the energy density functional.Comment: 4 pages. submitted to Phys. Rev. Let
Perturbation theory for the effective diffusion constant in a medium of random scatterer
We develop perturbation theory and physically motivated resummations of the
perturbation theory for the problem of a tracer particle diffusing in a random
media. The random media contains point scatterers of density uniformly
distributed through out the material. The tracer is a Langevin particle
subjected to the quenched random force generated by the scatterers. Via our
perturbative analysis we determine when the random potential can be
approximated by a Gaussian random potential. We also develop a self-similar
renormalisation group approach based on thinning out the scatterers, this
scheme is similar to that used with success for diffusion in Gaussian random
potentials and agrees with known exact results. To assess the accuracy of this
approximation scheme its predictions are confronted with results obtained by
numerical simulation.Comment: 22 pages, 6 figures, IOP (J. Phys. A. style
On the Neutral Gas Content and Environment of NGC 3109 and the Antlia Dwarf Galaxy
As part of a continuing survey of nearby galaxies, we have mapped the neutral
gas content of the low surface brightness, Magellanic-type galaxy NGC 3109 ---
and its environment, including the Antlia dwarf galaxy --- at unprecedented
velocity resolution and brightness sensitivity. The HI mass of NGC 3109 is
measured to be (3.8 +/- 0.5) x 10^8 Msun. A substantial warp in the disk of NGC
3109 is detected in the HI emission image in the form of an extended low
surface brightness feature. We report a positive detection in HI of the nearby
Antlia dwarf galaxy, and measure its total neutral gas mass to be (6.8 +/- 1.4)
x 10^5 Msun. We show the warp in NGC 3109 to lie at exactly the same radial
velocity as the gas in the Antlia dwarf galaxy and speculate that Antlia
disturbed the disk of NGC 3109 during a mild encounter ~1 Gyr in the past. HI
data for a further eight galaxies detected in the background are presented.Comment: Accepted for publication in A
Non-ergodic transitions in many-body Langevin systems: a method of dynamical system reduction
We study a non-ergodic transition in a many-body Langevin system. We first
derive an equation for the two-point time correlation function of density
fluctuations, ignoring the contributions of the third- and fourth-order
cumulants. For this equation, with the average density fixed, we find that
there is a critical temperature at which the qualitative nature of the
trajectories around the trivial solution changes. Using a method of dynamical
system reduction around the critical temperature, we simplify the equation for
the time correlation function into a two-dimensional ordinary differential
equation. Analyzing this differential equation, we demonstrate that a
non-ergodic transition occurs at some temperature slightly higher than the
critical temperature.Comment: 8 pages, 1 figure; ver.3: Calculation errors have been fixe
Shell Model Monte Carlo Investigation of Rare Earth Nuclei
We utilize the Shell Model Monte Carlo (SMMC) method to study the structure
of rare earth nuclei. This work demonstrates the first systematic ``full
oscillator shell plus intruder'' calculations in such heavy nuclei. Exact
solutions of a pairing plus quadrupole hamiltonian are compared with mean field
and SPA approximations in several Dysprosium isotopes from A=152-162, including
the odd mass A=153. Basic properties of these nuclei at various temperatures
and spin are explored. These include energy, deformation, moments of inertia,
pairing channel strengths, band crossing, and evolution of shell model
occupation numbers. Exact level densities are also calculated and, in the case
of 162 Dy, compared with experimental data.Comment: 40 pages; 24 figures; 2 tables. Update includes correction of figure
labe
Effective diffusion constant in a two dimensional medium of charged point scatterers
We obtain exact results for the effective diffusion constant of a two
dimensional Langevin tracer particle in the force field generated by charged
point scatterers with quenched positions. We show that if the point scatterers
have a screened Coulomb (Yukawa) potential and are uniformly and independently
distributed then the effective diffusion constant obeys the
Volgel-Fulcher-Tammann law where it vanishes. Exact results are also obtained
for pure Coulomb scatterers frozen in an equilibrium configuration of the same
temperature as that of the tracer.Comment: 9 pages IOP LaTex, no figure
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