6,782 research outputs found
Profiles of inflated surfaces
We study the shape of inflated surfaces introduced in \cite{B1} and
\cite{P1}. More precisely, we analyze profiles of surfaces obtained by
inflating a convex polyhedron, or more generally an almost everywhere flat
surface, with a symmetry plane. We show that such profiles are in a
one-parameter family of curves which we describe explicitly as the solutions of
a certain differential equation.Comment: 13 pages, 2 figure
Nucleon polarizabilities in the perturbative chiral quark model
The nucleon polarizabilities alpha(E) and beta(M) are studied in the context
of the perturbative chiral quark model. We demonstrate that meson cloud effects
are sufficient to explain the electric polarizability of nucleon. Contributions
of excite quark states to the paramagnetic polarizability are dominant and
cancel the diamagnetic polarizability arising from the chiral field. The
obtained results are compared to data and other theoretical predictions.Comment: 25 pages, 18 figures, 2 table
Non-equilibrium statistical mechanics of classical nuclei interacting with the quantum electron gas
Kinetic equations governing time evolution of positions and momenta of atoms
in extended systems are derived using quantum-classical ensembles within the
Non-Equilibrium Statistical Operator Method (NESOM). Ions are treated
classically, while their electrons quantum mechanically; however, the
statistical operator is not factorised in any way and no simplifying
assumptions are made concerning the electronic subsystem. Using this method, we
derive kinetic equations of motion for the classical degrees of freedom (atoms)
which account fully for the interaction and energy exchange with the quantum
variables (electrons). Our equations, alongside the usual Newtonian-like terms
normally associated with the Ehrenfest dynamics, contain additional terms,
proportional to the atoms velocities, which can be associated with the
electronic friction. Possible ways of calculating the friction forces which are
shown to be given via complicated non-equilibrium correlation functions, are
discussed. In particular, we demonstrate that the correlation functions are
directly related to the thermodynamic Matsubara Green's functions, and this
relationship allows for the diagrammatic methods to be used in treating
electron-electron interaction perturbatively when calculating the correlation
functions. This work also generalises previous attempts, mostly based on model
systems, of introducing the electronic friction into Molecular Dynamics
equations of atoms.Comment: 18 page
Compton Scattering from the Deuteron and Extracted Neutron Polarizabilities
Differential cross sections for Compton scattering from the deuteron were
measured at MAX-lab for incident photon energies of 55 MeV and 66 MeV at
nominal laboratory angles of , , and . Tagged
photons were scattered from liquid deuterium and detected in three NaI
spectrometers. By comparing the data with theoretical calculations in the
framework of a one-boson-exchange potential model, the sum and difference of
the isospin-averaged nucleon polarizabilities, and (in units of fm),
have been determined. By combining the latter with the global-averaged value
for and using the predictions of the Baldin sum rule for
the sum of the nucleon polarizabilities, we have obtained values for the
neutron electric and magnetic polarizabilities of (total) (model) and (total) (model), respectively.Comment: 4 pages, 2 figures, revtex. The text is substantially revised. The
cross sections are slightly different due to improvements in the analysi
Role of the mean curvature in the geometry of magnetic confinement configurations
Examples are presented of how the geometric notion of the mean curvature is
used for general magnetic field configurations and magnetic surfaces. It is
shown that the mean magnetic curvature is related to the variation of the
absolute value of the magnetic field along its lines. Magnetic surfaces of
constant mean curvature are optimum for plasma confinement in multimirror open
confinement systems and rippled tori.Comment: PDFLaTeX, 10 pages, 5 figure
Prospects for SIMPLE 2000: A large-mass, low-background Superheated Droplet Detector for WIMP searches
SIMPLE 2000 (Superheated Instrument for Massive ParticLE searches) will
consist of an array of eight to sixteen large active mass ( g)
Superheated Droplet Detectors(SDDs) to be installed in the new underground
laboratory of Rustrel-Pays d'Apt. Several factors make of SDDs an attractive
approach for the detection of Weakly Interacting Massive Particles (WIMPs),
namely their intrinsic insensitivity to minimum ionizing particles, high
fluorine content, low cost and operation near ambient pressure and temperature.
We comment here on the fabrication, calibration and already-competitive first
limits from SIMPLE prototype SDDs, as well as on the expected immediate
increase in sensitivity of the program, which aims at an exposure of 25
kg-day during the year 2000. The ability of modest-mass fluorine-rich detectors
to explore regions of neutralino parameter space beyond the reach of the most
ambitious cryogenic projects is pointed out.Comment: 19 pages, 10 figures included. New Journal of Physics, in pres
Fragmentation channels of relativistic Be nuclei in peripheral interactions
Nuclei of Li were accelerated at the JINR Nuclotron. After the
charge-exchange reaction involving these nuclei at an external target a second
Be beam of energy 1.23A GeV was formed. This beam was used to expose
photo-emulsion chambers. The mean free path for inelastic Be interactions
in emulsion =14.00.8 cm coincides within the errors with those
for Li and Li nuclei. More than 10% of the Be events are associated
with the peripheral interactions in which the total charge of the relativistic
fragments is equal to the charge of the Be and in which charged mesons are
not produced. An unusual ratio of the isotopes is revealed in the composition
of the doubly charged Be fragments: the number of He fragments is twice
as large as that of He fragments. In 50% of peripheral interactions, a
Be nucleus decays to two doubly charged fragments. The present paper gives
the channels of the Be fragmentation to charged fragments. In 50% of
events, the Be fragmentation proceeds only to charged fragments involving
no emission of neutrons. Of them, the He+He channel dominates, the
He+d+p and Li+pchannels constitute 10% each. Two events involving no
emission of neutrons are registered in the 3-body He+t+p and He+d+d
channels. The mean free path for the coherent dissociation of relativistic
Be nuclei to He+He is 71 m. The particular features of the
relativistic Be fragmentation in such peripheral interactions are explained
by the He+He 2-cluster structure of the Be nucleus.Comment: 10 pages, 3 figures, 3 tables, conference: Conference on Physics of
Fundamental Interactions, Moscow, Russia, 5-9 Dec 200
On the Conductivity of a Magnetoactive Turbulent Plasma
The problem of determining the effective conductivity tensor of a
magnetoactive turbulent plasma is considered in the approximation of isolated
particles. Additional gyrotropicterms are shown to appear in the conductivity
tensor in the presence of mean, nonzero magnetic helicity. The dispersion of
propagating electro- magnetic waves changes, additional modes and additional
rotation of the polarization plane appear, and the waves can be amplified. The
properties acquired by plasma with helicity are similar those observed in
chiral and bianisotropic electrodynamic media.Comment: 15 page
Role of the Nuclear and Electromagnetic Interactions in the Coherent Dissociation of the Relativistic Li Nucleus into the H + He Channel
The differential cross section in the transverse momentum and a total
cross section of mb for the coherent dissociation of a 3-A-GeV/
Li nucleus through the HHe channel have been measured on emulsion
nuclei. The observed dependence of the cross section is explained by the
predominant supposition of the nuclear diffraction patterns on light (C, N, O)
and heavy (Br, Ag) emulsion nuclei. The contributions to the cross section from
nuclear diffraction ( MeV/) and Coulomb MeV/)
dissociations are calculated to be 40.7 and 4 mb, respectively.Comment: ISSN 0021-3640, Pleiades Publishing, Ltd., 200
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