Some peculiarities of motion of neutral and charged test particles in the field of a spherically symmetric charged object in General Relativity

We propose the method of investigation of radial motions for charged and neutral test particles in the Reissner-Nordstr\"{o}m field by means of mass potential. In this context we analyze special features of interaction of charges and their motions in General Relativity and construct the radial motion classification. For test particles and a central source with charges $q$ and $Q$, respectively, the conditions of attraction (when $qQ>0$) and repulsion (when $qQ<0$) are obtained. The conditions of motionless test particle states with respect to the central source are investigated and, in addition, stability conditions for such static equilibrium states are found. It is shown that stable states are possible only for the bound states of weakly charged particles in the field of a naked singularity. Frequencies of small oscillations of test particles near their equilibrium positions are also found.Comment: 15 pages, 9 figure

Dipole model for double meson production in two-photon interactions at high energies

In this work the double vector meson production in two-photon interactions at high energies is investigated considering saturation physics. We extend the color dipole picture for this process and study the energy and virtuality dependence of the forward differential cross section. Comparison with previous results is presented and the contribution of the different photon polarizations is estimated.Comment: 20 pages, 8 figures, 1 table. Version to be published in European Physical Jornal

Causes of morphological discontinuities in soils of Depressão Central, Rio Grande do Sul State, Brazil

Morphological, particularly textural, discontinuities between horizons increase soil erodibility in Depressão Central, Rio Grande do Sul State (Brazil). Characterization of such discontinuities would help to understand landscape evolution and to model near-surface hydrology. The objective of this research was to explore the relationship between morphological discontinuity and deposition of transported materials during pedogenesis. Transported material was meant to be mineral particles found in the soil profile, transported probably by water or gravity, that were not present neither in the parent material nor derived from it. Five soils of this region (two Alfisols, two Ultisols and one Mollisol) were sampled and morphological, sand grain size statistics, chemical and mineralogical analyses were used to search for evidences of deposition of transported materials. Two soils had abrupt textural change but no evidence of deposition of transported materials, two soils had less contrasting morphology and some characteristics that are possibly related to deposition, and one soil had no morphological discontinuity, but had deposition of material enriched in magnetite-maghemite in the sand fraction of the A horizon. Therefore, there were no relationship between morphological discontinuity and deposition of transported materials for these profiles in the Depressão Central.Contrastes morfológicos entre horizontes, e particularmente os contrastes texturais, aumentam a erodibilidade do solo na Depressão Central do Rio Grande do Sul (Brasil). A caracterização destes contrastes contribui para a compreensão da evolução da paisagem e para a modelagem da hidrologia de superfície. Cinco solos desta região foram amostrados e a morfologia, distribuição do tamanho de grãos da fração areia, análises químicas e mineralógicas foram usadas para tentativamente relacionar o contraste textural e morfológico com materiais transportados durante a pedogênese. Por materiais transportados entendem-se as partículas minerais presentes no perfil do solo, transportadas provavelmente por água ou gravidade, e que não estavam presentes nem no material de origem e nem foram derivadas deste. Dois solos apresentaram mudança textural abrupta sem evidências de deposição, dois solos apresentaram menor contraste morfológico e evidências que sustentam a possibilidade de deposição e um solo não apresentou contraste morfológico, porém as características indicam deposição de material rico em magnetita-maghemita na fração areia do horizonte A. Portanto, não foi encontrada relação entre descontinuidades morfológicas e deposição de materiais transportados, na Depressão Central