152 research outputs found
Lithium Ionization by a Strong Laser Field
We study ab initio computations of the interaction of Lithium with a strong
laser field. Numerical solutions of the time-dependent fully-correlated
three-particle Schroedinger equation restricted to the one-dimensional
soft-core approximation are presented. Our results show a clear transition from
non-sequential to sequential double ionization for increasing intensities. Non
sequential double ionization is found to be sensitive to the spin configuration
of the ionized pair. This asymmetry, also found in experiments of
photoionization of Li with synchrotron radiation, shows the evidence of the
influence of the exclusion principle in the underlying rescattering mechanism
Nonlinear resonance reflection from and transmission through a dense glassy system built up of oriented linear Frenkel chains: two-level models
A theoretical study of the resonance optical response of assemblies of
oriented short (as compared to an optical wavelength) linear Frenkel chains is
carried out using a two-level model. We show that both transmittivity and
reflectivity of the film may behave in a bistable fashion and analyze how the
effects found depend on the film thickness and on the inhomogeneous width of
the exciton optical transition.Comment: 26 pages, 9 figure
Estimation of (co)variance components and genetic parameters for tick resistance in beef cattle measured by counting in two different body regions.
Transferring orbital and spin angular momenta of light to atoms
Light beams carrying orbital angular momentum, such as Laguerre-Gaussian
beams, give rise to the violation of the standard dipolar selection rules
during the interaction with matter yielding, in general, an exchange of angular
momentum larger than hbar per absorbed photon. By means of ab initio 3D
numerical simulations, we investigate in detail the interaction of a hydrogen
atom with intense Gaussian and Laguerre-Gaussian light pulses. We analyze the
dependence of the angular momentum exchange with the polarization, the orbital
angular momentum, and the carrier-envelope phase of light, as well as with the
relative position between the atom and the light vortex. In addition, a
quantum-trajectory approach based on the de Broglie-Bohm formulation of quantum
mechanics is used to gain physical insight into the absorption of angular
momentum by the hydrogen atom
Observation of spontaneous self-channelling of light in air below the collapse threshold
We report the observation of the self-guided propagation of 120 fs, 0.56 mJ
infrared radiation in air for distances greater than one meter. In contrast to
the known case of filamentation, in the present experiment the laser power is
lower than the collapse threshold. Therefore the counter balance between Kerr
self focussing and ionization induced defocussing as the stabilizing mechanism
is ruled out. Instead, we find evidences of a process in which the transversal
beam distribution reshapes into a form similar to a Townes soliton. We include
numerical support for this conclusion
Three-dimensional numerical simulation of 1GeV/Nucleon U92+ impact against atomic hydrogen
The impact of 1GeV/Nucleon U92+ projectiles against atomic hydrogen is
studied by direct numerical resolution of the time-dependent wave equation for
the atomic electron on a three-dimensional Cartesian lattice. We employ the
fully relativistic expressions to describe the electromagnetic fields created
by the incident ion. The wave equation for the atom interacting with the
projectile is carefully derived from the time-dependent Dirac equation in order
to retain all the relevant terms.Comment: 12 pages and 7 figures included in the tex
Distribuição de rhipicephalus (boophilus) microplus em diferentes regiões corporais de bovinos resistentes e suscetíveis ao carrapato.
Objetivou-se investigar diferenças na distribuição de carrapatos sobre regiões corporais de bovinos geneticamente resistentes ou sensíveis ao parasito. Participaram das avaliações 40 fêmeas da raça Braford previamente classificadas quanto à resistência e expostas a quatro infestações artificiais. Os dois grupos foram eficientes em limitar a frequência de larvas na região mediana, concentrando a quantidade de carrapatos na região posterior. Animais resistentes foram mais eficientes que os sensíveis em limitar a frequência dos carrapatos na região anterior e apresentaram maior frequência de carrapatos na região posterior que os hospedeiros suscetíveis
Goodness of fit comparisons among five bayesian models in genome-wide association of tick resistance in brazilian Hereford and Braford beef cattle.
This study aimed to compare five models fitness and top effect SNPs obtained with three different Bayesian GWAS methods applied to cattle tick resistance in Braford and Hereford
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