Collisions of low-energy antiprotons with molecular hydrogen: ionization, excitation and stopping power

A time-dependent coupled-channel approach was used to calculate ionization, excitation, and energy-loss cross sections as well as energy spectra for antiproton and proton collisions with molecular hydrogen for impact energies 8 keV < E < 4000 keV.Comment: 4 pages, 4 figures, conference LEAP0

Sums of products of Coulomb wave function over degenerate states

The sums of products of Coulomb wave function over degenerate states are expressed in terms of quadratic forms that depend on the wave function of only one state with zero orbital angular momentum l = m = 0. These sums are encountered in many fields in the physics of atoms and molecules, for example, in investigations of the perturbation of degenerate atomic energy levels of a small potential well, a delta-function potential. The sums were found in an investigation of the limit of the Coulomb Green's function G(r, r', E), where the energy parameter E approaches an atomic energy level: E --> E-n, E-n = -Z(2)/2n(2). The Green's function found by L. Hostler and R. Pratt in 1963 was used. The result obtained is a consequence of the degeneracy of the Coulomb energy levels, which in turn is due to the four-dimensional symmetry of the Coulomb problem. (C) 2000 MAIK "Nauka/Interperiodica"

New summation rules for Coulomb wave functions

Sums of products of the Coulomb wave functions over degenerate manifolds have been obtained in a closed form. These sums appear in many atomic and molecular problems. The sums have been obtained making use of the properties of the Coulomb Green's function G(r, r', E), in the limit E --> E-n, where E-n, is the eigenenergy of the hydrogenlike atomic ion. The closed Hostler-Pratt form of G in the coordinate representation has been used. The sums calculated are a consequence of the n degeneracy of the Coulomb atomic energy levels. This itself, as is well known, follows from the four-dimensional symmetry of the Coulomb problem for the hydrogen atom

Invasive leafminers on woody plants: a global review of pathways, impact, and management

Leafminers are a taxonomically diverse group of endophagous insects. A number of them are pests in forestry, horticulture and agriculture, and some of them have become important invasive species. Here, we discuss the characteristics of invasive leafminers of woody plants. We first present 12 cases of invasive leaf-mining species belonging to four different insect orders. For each of them, we briefly describe their invasion, including pathways of introduction, their impact and management methods and their ecology. We then discuss various aspects of these invasions. Leafminers are introduced to new continents and spread through various pathways such as horticultural trade and accidental transport of adults and pre-imaginal stages in containers and vehicles. They may also spread long distances with air currents. A few species have serious economic impacts as orchard pests, such as the citrus leafminer, Phyllocnistis citrella, or as pests of ornamental plants, such as the horse-chestnut leafminer, Cameraria ohridella. The ecological impact of these species should be better studied, especially those killing native trees, such as the birch leaf-mining weevil, Orchestes fagi, in Canada. Compared to other insect groups, invasive leafminers are usually recruited by a range of native parasitoids, which may or may not succeed in controlling the invasive species. Biological control by introduction of parasitoids from the native range has often been successful to control invasive leafminers. The review ends by short discussions on taxonomic issues and on the use of leafminers as models to study invasion ecology

Factores de riesgo asociados a las conductas compulsivas en el uso de las tecnologías de la información y la comunicación (TIC).

Determina la relación que existe entre determinados factores de riesgo y las conductas compulsivas en el uso de las Tecnologías de la Información y la Comunicación – TIC. La investigación se realizó la Escuela de Ciencias Psicológicas de la Universidad de San Carlos de Guatemala, ubicada en el Centro Universitario Metropolitano –CUM- durante el ciclo 2011. Para seleccionar la muestra se utilizó la técnica de muestreo no aleatoria y estuvo integrada por 102 estudiantes de la jornada matutina, comprendidos entre los 17 a 25 años de edad. Para recopilar información se utilizó un cuestionario de 20 preguntas, que evaluaron en primer lugar la prevalencia de las conductas compulsivas y en segundo la participación de diez factores de riesgo relevantes previamente detectados en otros estudios previos al presente. Analiza los resultados en tablas y gráficas con porcentajes que permitieron concluir, que la prevalencia de las conductas compulsivas hacia las TIC detectadas en la muestra sobrepasa el 22% y que los tres factores más críticos son: la dependencia al chat, correo electrónico y redes sociales, el bajo control parental y el desbalance en el conocimiento de las TIC entre padres e hijos