123 research outputs found
Chiral Symmetry Breaking with the Curtis-Pennington Vertex
We study chiral symmetry breaking in quenched QED, using a vertex Ansatz
recently proposed by Curtis and Pennington. Bifurcation analysis is employed to
establish the existence of a critical coupling and to estimate its value. The
main results are in qualitative agreement with the ladder approximation, the
numerical changes being minor.Comment: 19 pages, LaTe
Critical coupling for dynamical chiral-symmetry breaking with an infrared finite gluon propagator
We compute the critical coupling constant for the dynamical chiral-symmetry
breaking in a model of quantum chromodynamics, solving numerically the quark
self-energy using infrared finite gluon propagators found as solutions of the
Schwinger-Dyson equation for the gluon, and one gluon propagator determined in
numerical lattice simulations. The gluon mass scale screens the force
responsible for the chiral breaking, and the transition occurs only for a
larger critical coupling constant than the one obtained with the perturbative
propagator. The critical coupling shows a great sensibility to the gluon mass
scale variation, as well as to the functional form of the gluon propagator.Comment: 19 pages, latex, 3 postscript figures, uses epsf.sty and epsf.tex. To
be published in Phys. Lett.
On the behavior of micro-spheres in a hydrogen pellet target
A pellet target produces micro-spheres of different materials, which are used
as an internal target for nuclear and particle physics studies. We will
describe the pellet hydrogen behavior by means of fluid dynamics and
thermodynamics. In particular one aim is to theoretically understand the
cooling effect in order to find an effective method to optimize the working
conditions of a pellet target. During the droplet formation the evaporative
cooling is best described by a multi-droplet diffusion-controlled model, while
in vacuum, the evaporation follows the (revised) Hertz-Knudsen formula.
Experimental observations compared with calculations clearly indicated the
presence of supercooling, the effect of which is discussed as well.Comment: 22 pages, 8 figures (of which two are significantly compressed for
easier download
X-ray scattering from stepped and kinked surfaces: An approach with the paracrystal model
A general formalism of X-ray scattering from different kinds of surface
morphologies is described. Based on a description of the surface morphology at
the atomic scale through the use of the paracrystal model and discrete
distributions of distances, the scattered intensity by non-periodic surfaces is
calculated over the whole reciprocal space. In one dimension, the scattered
intensity by a vicinal surface, the two-level model, the N-level model, the
faceted surface and the rough surface are addressed. In two dimensions, the
previous results are generalized to the kinked vicinal surface, the two-level
vicinal surface and the step meandering on a vicinal surface. The concept of
crystal truncation rod is generalized considering also the truncation of a
terrace by a step (yielding a terrace truncation rod) and a step by a kink
(yielding a step truncation rod).Comment: 33 pages, 18 figure
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Numerical modeling of shock-sensitivity experiments
The Forest Fire rate model of shock initiation of heterogeneous explosives has been used to study several experiments commonly performed to measure the sensitivity of explosives to shock and to study initiation by explosive-formed jets. The minimum priming charge test, the gap test, the shotgun test, sympathetic detonation, and jet initiation have been modeled numerically using the Forest Fire rate in the reactive hydrodynamic codes SIN and 2DE
Dynamics of Cryogenic Jets: Non-Rayleigh Breakup and Onset of Nonaxisymmetric Motions
We report development of generators for periodic, satellite-free fluxes of
mono-disperse drops with diameters down to 10 mikrometers from cryogenic
liquids like H_2, N_2, Ar and Xe (and, as reference fluid, water). While the
breakup of water jets can well be described by Rayleigh's linear theory, we
find jet regimes for H_2 and N_2 which reveal deviations from this behavior.
Thus, Rayleigh's theory is inappropriate for thin jets that exchange energy
and/or mass with the surrounding medium. Moreover, at high evaporation rates,
axial symmetry of the dynamics is lost. When the drops pass into vacuum, frozen
pellets form due to surface evaporation. The narrow width of the pellet flux
paves the way towards various industrial and scientific applications.Comment: 4 pages, 4 figures, 1 table; final version to appear in Phys.Rev.Lett
(minor changes with respect to v1
High-resolution LEED profile analysis and diffusion barrier estimation for submonolayer homoepitaxy of Ag/Ag(100)
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A semigroup for Lagrangian 1D isentropic flow
This paper discusses a system of Lagrangian equations used to describe 1D isentropic flow. This paper covers the approximate differential equations, the Banach space re-metrization and semigroup generation. 10 refs
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