Nonsequential Double Recombination in Intense Laser Fields

A second plateau in the harmonic spectra of laser-driven two-electron atoms is observed both in the numerical solution of a low-dimensional model helium atom and using an extended strong field approximation. It is shown that the harmonics well beyond the usual cut-off are due to the simultaneous recombination of the two electrons, which were emitted during different, previous half-cycles. The new cut-off is explained in terms of classical trajectories. Classical predictions and the time-frequency analysis of the ab initio quantum results are in excellent agreement. The mechanism corresponds to the inverse single photon double ionization process in the presence of a (low frequency) laser field.Comment: 4 pages, RevTeX, v2 with an extended strong field approximation treatment of the process; instead, v1 describes an attosecond control scheme to enhance the proces

Método de obtenção qualificada de fenótipos visando à avaliação de genótipos bovinos resistentes ao carrapato Rhipicephalus (Boophilus) microplus.

Formação de grupos de manejo; Determinação correta do momento da mensuração da carga parasitária; Controle parasitário durante o período de avaliação; Padronização da técnica de contagem de carrapatos; Registro de dados; Análise dos dados.bitstream/item/31735/1/CO-75-online.pd

Cognitive-behavioral therapy in social phobia

OBJETIVO: Este artigo revisa aspectos relevantes da fobia social e os estágios de tratamento através da terapia cognitivo-comportamental em crianças, adolescentes e adultos. MÉTODO: A partir do banco de dados Medline, realizou-se revisão da literatura publicada a respeito do tratamento da fobia social por meio da terapia cognitivo-comportamental. RESULTADOS: Revisão da literatura sugere que a fobia social é uma condição prevalente e crônica, caracterizada por inibição social e timidez excessiva. Tanto o diagnóstico como o tratamento desse transtorno são comumente determinados pelo nível de incômodo e pelo prejuízo funcional. Estudos populacionais indicam taxas de prevalência ao longo da vida para a fobia social entre 2,5 e 13,3%. As principais técnicas utilizadas na terapia cognitivo-comportamental para a fobia social são descritas e exemplificadas em um relato de caso. CONCLUSÕES: Há consenso geral na literatura de que a terapia cognitivo-comportamental é eficaz tanto para o tratamento de jovens como de adultos com fobia social. Uma vez que a fobia social com freqüência tem início precoce, a identificação de crianças com risco acentuado para o desenvolvimento de fobia social deve ser priorizada em investigações futuras.OBJECTIVE: This article reviews relevant aspects of social phobia and the stages of treatment within cognitive-behavioral therapy in children and adolescents, as well as in adults. METHOD: A review of the literature published on the treatment of social phobia using cognitive-behavioral treatments was performed using the Medline database. RESULTS: A review of the literature suggests that social phobia is a chronic and prevalent condition, characterized by social inhibition and excessive shyness. Diagnosis and treatment of the disorder are usually determined by distress level and functional impairment. Population studies indicate that lifetime prevalence rates for social phobia range from 2.5 to 13.3%. The main techniques used in cognitive-behavioral therapy for social phobia are described and exemplified in a case report. CONCLUSIONS: There is a general consensus in the literature that cognitive-behavioral therapy is efficacious in the treatment of youth and adults with social phobia. Because of the early onset associated with social phobia, the identification of children at high risk for the development of social phobia should be prioritized in future investigations

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

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

Spatial Modulation of linear and quadratic susceptibilities in Lithium Niobate crystals by using femtosecond laser pulses

In this work we present the spatial control of the linear susceptibility (χ1) in Lithium Niobate crystals by means of infrared (800 nm) femtosecond interaction. Diffraction gratings have been performed on the surface (relief) and inside (phase) of these samples by femtosecond laser writing. Also we have performed a spatial control of the quadratic susceptibility (χ 2 ) by direct writing of a pattern of ferroelectric domains on the surface of z cut substrates by using the second harmonic femtosecond pulses (400 nm). Finally, efficient photonic devices for second harmonic generation via quasi phase matching could be obtained following the experimental procedure presented in this work