496 research outputs found
Noble Gas Clusters and Nanoplasmas in High Harmonic Generation
We report a study of high harmonic generation from noble gas clusters of
xenon atoms in a gas jet. Harmonic spectra were investigated as a function of
backing pressure, showing spectral shifts due to the nanoplasma electrons in
the clusters. At certain value of laser intensity this process may oppose the
effect of the well-known ionization-induced blueshift. In addition, these
cluster-induced harmonic redshifts may give the possibility to estimate cluster
density and cluster size in the laser-gas jet interaction range.Comment: 5 pages, 4 figure
Space-time extensions II
The global extendibility of smooth causal geodesically incomplete spacetimes
is investigated. Denote by one of the incomplete non-extendible causal
geodesics of a causal geodesically incomplete spacetime . First, it
is shown that it is always possible to select a synchronised family of causal
geodesics and an open neighbourhood of a final segment
of in such that is comprised by members of ,
and suitable local coordinates can be defined everywhere on
provided that does not terminate either on a tidal force tensor
singularity or on a topological singularity. It is also shown that if, in
addition, the spacetime, , is globally hyperbolic, and the
components of the curvature tensor, and its covariant derivatives up to order
are bounded on , and also the line integrals of the
components of the -order covariant derivatives are finite along the
members of ---where all the components are meant to be registered with
respect to a synchronised frame field on ---then there exists a
extension so that for each , which
is inextendible in , the image, , is
extendible in . Finally, it is also proved that
whenever does terminate on a topological singularity
cannot be generic.Comment: 42 pages, no figures, small changes to match the published versio
What does a strongly excited 't Hooft-Polyakov magnetic monopole do?
The time evolution of strongly exited SU(2) Bogomolny-Prasad-Sommerfield
(BPS) magnetic monopoles in Minkowski spacetime is investigated by means of
numerical simulations based on the technique of conformal compactification and
on the use of hyperboloidal initial value problem. It is found that an
initially static monopole does not radiate the entire energy of the exciting
pulse toward future null infinity. Rather, a long-lasting quasi-stable
`breathing state' develops in the central region and certain expanding shell
structures -- built up by very high frequency oscillations -- are formed in the
far away region.Comment: 4 pages, 6 figure
Derivation of the Matalon-Packter law for Liesegang patterns
Theoretical models of the Liesegang phenomena are studied and simple
expressions for the spacing coefficients characterizing the patterns are
derived. The emphasis is on displaying the explicit dependences on the
concentrations of the inner- and the outer-electrolytes. Competing theories
(ion-product supersaturation, nucleation and droplet growth, induced sol-
coagulation) are treated with the aim of finding the distinguishing features of
the theories. The predictions are compared with experiments and the results
suggest that the induced sol-coagulation theory is the best candidate for
describing the experimental observations embodied in the Matalon-Packter law.Comment: 9 pages, 7 figures, RevTe
A Note on Hartle-Hawking Vacua
The purpose of this note is to establish the basic properties--- regularity
at the horizon, time independence, and thermality--- of the generalized
Hartle-Hawking vacua defined in static spacetimes with bifurcate Killing
horizon admitting a regular Euclidean section. These states, for free or
interacting fields, are defined by a path integral on half the Euclidean
section. The emphasis is on generality and the arguments are simple but formal.Comment: 5 pages, LaTe
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