26,188 research outputs found
The probability distribution of a trapped Brownian particle in plane shear flows
We investigate the statistical properties of an over-damped Brownian particle
that is trapped by a harmonic potential and simultaneously exposed to a linear
shear flow or to a plane Poiseuille flow. Its probability distribution is
determined via the corresponding Smoluchowski equation, which is solved
analytically for a linear shear flow. In the case of a plane Poiseuille flow,
analytical approximations for the distribution are obtained by a perturbation
analysis and they are substantiated by numerical results. There is a good
agreement between the two approaches for a wide range of parameters.Comment: 5 pages, 4 figur
Influence of gaseous hydrogen on metals Interim report
Gaseous hydrogen embrittlement in Inconel 718, Inconel 625, AISI 321 stainless steel, Ti-5Al-25Sn ELI, and OFHC coppe
Chiral dynamics in few-nucleon systems
We report on recent progress achieved in calculating various few-nucleon
low-energy observables from effective field theory. Our discussion includes
scattering and bound states in the 2N, 3N and 4N systems and isospin violating
effects in the 2N system. We also establish a link between the nucleon-nucleon
potential derived in chiral effective field theory and various modern
high-precision potentials.Comment: 12 pp, uses aipproc style files, 4 figures, contribution to the
conference on "Mesons and Light Nuclei", Prag, July 2001, to appear in the
proceeding
Chiral dynamics in few-nucleon systems
We employ the chiral nucleon-nucleon potential derived using the method of
unitary transformation up to next-to-next-to-leading order (NNLO) to study
bound and scattering states in the two-nucleon system. The predicted partial
wave phase shifts and mixing parameters for higher energies and higher angular
momenta beyond the ones which are fitted are mostly well described for energies
below 300 MeV. Various deuteron properties are discussed. We also apply the
next-to-leading order (NLO) potential to 3N and 4N systems. The resulting 3N
and 4N binding energies are in the same range what is found using standard NN
potentials. Experimental low-energy 3N scattering observables are also very
well reproduced like for standard NN forces. Surprisingly the long standing
Ay-puzzle is resolved at NLO. The cut-off dependence of the scattering
observables is rather mild.Comment: LaTeX2e, 8 pages; invited talk presented at the XVIIth European
Conference on Few-Body Problems in Physics, Evora, Portugal, September 2000;
to be published in the Proceeding
The radial variation of HI velocity dispersions in dwarfs and spirals
Gas velocity dispersions provide important diagnostics of the forces
counteracting gravity to prevent collapse of the gas. We use the 21 cm line of
neutral atomic hydrogen (HI) to study HI velocity dispersion and HI phases as a
function of galaxy morphology in 22 galaxies from The HI Nearby Galaxy Survey
(THINGS). We stack individual HI velocity profiles and decompose them into
broad and narrow Gaussian components. We study the HI velocity dispersion and
the HI surface density, as a function of radius. For spirals, the velocity
dispersions of the narrow and broad components decline with radius and their
radial profiles are well described by an exponential function. For dwarfs,
however, the profiles are much flatter. The single Gaussian dispersion profiles
are, in general, flatter than those of the narrow and broad components. In most
cases, the dispersion profiles in the outer disks do not drop as fast as the
star formation profiles, derived in the literature. This indicates the
importance of other energy sources in driving HI velocity dispersion in the
outer disks. The radial surface density profiles of spirals and dwarfs are
similar. The surface density profiles of the narrow component decline more
steeply than those of the broad component, but not as steep as what was found
previously for the molecular component. As a consequence, the surface density
ratio between the narrow and broad components, an estimate of the mass ratio
between cold HI and warm HI, tends to decrease with radius. On average, this
ratio is lower in dwarfs than in spirals. This lack of a narrow, cold HI
component in dwarfs may explain their low star formation activity.Comment: Accepted for publication in The Astronomical Journal, 13 pages, 10
figures, 4 table
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