113 research outputs found
Pressure dependence of the dielectric loss in semi-conducting polypyrrole aged at room temperature
The effect of physical aging of semi-conducting polypyrrole at ambient
temperature for two years duration on the dielectric loss at various pressures
is investigated. Changes of the dielectric loss spectra and the modification of
the values of the activation volume for relaxation are interpreted through the
division of chain clusters into smaller components and the reduction of the
size of the conductive grains.Comment: Synthetic Metals (in print
Recoil correction to the ground state energy of hydrogenlike atoms
The recoil correction to the ground state energy of hydrogenlike atoms is
calculated to all orders in \alpha Z in the range Z = 1-110. The nuclear size
corrections to the recoil effect are partially taken into account. In the case
of hydrogen, the relativistic recoil correction beyond the Salpeter
contribution and the nonrelativistic nuclear size correction to the recoil
effect, amounts to -7.2(2) kHz. The total recoil correction to the ground state
energy in hydrogenlike uranium (^{238}U^{91+}) constitutes 0.46 eV.Comment: 16 pages, 1 figure (eps), Latex, submitted to Phys.Rev.
QED theory of the nuclear recoil effect on the atomic g factor
The quantum electrodynamic theory of the nuclear recoil effect on the atomic
g factor to all orders in \alpha Z and to first order in m/M is formulated. The
complete \alpha Z-dependence formula for the recoil correction to the
bound-electron g factor in a hydrogenlike atom is derived. This formula is used
to calculate the recoil correction to the bound-electron g factor in the order
(\alpha Z)^2 m/M for an arbitrary state of a hydrogenlike atom.Comment: 17 page
Long aging time thermal degradation of the ac conductivity and complex permittivity of conducting polypyrrole
The modification of the ac conductivity and the complex permittivity of
conducting polypyrrole was monitored throughout a two years thermal aging at
343K. Reduction of the cross-over frequency is correlated with the degradation
of dc-conductivity, while the ac conductivity region corresponding to the
so-called 'universal' dielectric relaxation remains practically invariant
during the first year of ageing, which implies a collective co-operativity
among multiple degradation processes that yield a practically time-independent
effective disordered environment. A broad dielectric loss peak recorded in
fresh specimens splits into two distinct relaxations for intermediate stages of
the annealing process. The ageing-time evolution of the dc component and the
relaxations are qualitatively analysed and time constants are determined.Comment: Synth. metals (2011) in prin
Spectral analysis and zeta determinant on the deformed spheres
We consider a class of singular Riemannian manifolds, the deformed spheres
, defined as the classical spheres with a one parameter family of
singular Riemannian structures, that reduces for to the classical metric.
After giving explicit formulas for the eigenvalues and eigenfunctions of the
metric Laplacian , we study the associated zeta functions
. We introduce a general method to deal with some
classes of simple and double abstract zeta functions, generalizing the ones
appearing in . An application of this method allows to
obtain the main zeta invariants for these zeta functions in all dimensions, and
in particular and . We give
explicit formulas for the zeta regularized determinant in the low dimensional
cases, , thus generalizing a result of Dowker \cite{Dow1}, and we
compute the first coefficients in the expansion of these determinants in powers
of the deformation parameter .Comment: 1 figur
Notes on a paper of Mess
These notes are a companion to the article "Lorentz spacetimes of constant
curvature" by Geoffrey Mess, which was first written in 1990 but never
published. Mess' paper will appear together with these notes in a forthcoming
issue of Geometriae Dedicata.Comment: 26 page
Heart rate as an indicator for exercise prescription for normal, overweight, and obese adolescents
Gravitational Lensing by Black Holes
We review the theoretical aspects of gravitational lensing by black holes,
and discuss the perspectives for realistic observations. We will first treat
lensing by spherically symmetric black holes, in which the formation of
infinite sequences of higher order images emerges in the clearest way. We will
then consider the effects of the spin of the black hole, with the formation of
giant higher order caustics and multiple images. Finally, we will consider the
perspectives for observations of black hole lensing, from the detection of
secondary images of stellar sources and spots on the accretion disk to the
interpretation of iron K-lines and direct imaging of the shadow of the black
hole.Comment: Invited article for the GRG special issue on lensing (P. Jetzer, Y.
Mellier and V. Perlick Eds.). 31 pages, 12 figure
Estabilidade de agregados e resistência à penetração em Latossolos adubados por cinco anos com biossólido
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