914 resultados para Functions of covariance


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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

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Chromatoid body (CB) is a typical cytoplasmic organelle of germ cells, and it seems to be involved in RNA/protein accumulation for later germ-cell differentiation. Despite most of the events in mammals spermatogenesis had been widely described in the past decades and the increase in the studies related to the CB molecular composition and physiology, the origins and functions of this important structure of male germ cells are still unclear. The aims of this study were to describe the nucleolar cycle and also to find some relationship between the nucleolar organization and the CB assembling during the spermatogenesis in mammals. Cytochemical and cytogenetics analysis showed nucleolar fragmentation in post-pachytene spermatocytes and nucleolar reorganization in post-meiotic spermatids. Significant difference in the number and in the size of nucleoli between spermatogonia and round spermatids, as well as differences in the nucleolar position within the nucleus were also observed. Ultrastructural analysis showed the CB assembling in the cytoplasm of primary spermatocytes and the nucleolar fragmentation occurring at the same time. In conclusion our results suggest that the CB may play important roles during the spermatogenesis process in mammals and that its origin may be related to the nucleolar cycle during the meiotic cell cycle.

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Chauliocheilos saxatilis, new genus and species, is described from headwater streams of the rio Itamarandiba, upper rio Jequitinhonha basin, southeastern Brazil. The new genus is diagnosed from all other Loricariidae members by having a unique labial appendix at laterodorsal portion of lower lip, associated to the proximal region of insertion of the maxillary barbel. From all Hypoptopomatinae genera, Chauliocheilos can be distinguished by having two additional series of lateral plates, one between the dorsal and mid-dorsal series, and the other between the mid-ventral and ventral series. In addition, the great number of lateral plates, the absence of the iris operculum, and the posterior dorsal-fin insertion contacting the neural spine of eighth vertebra, are other useful features to recognize the genus. The phylogenetic position of Chauliocheilos among the Hypoptopomatinae, as well as the morphology and possible functions of the labial appendix, are discussed.

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Most work on supersingular potentials has focused on the study of the ground state. In this paper, a global analysis of the ground and excited states for the successive values of the orbital angular momentum of the supersingular plus quadratic potential is carried out, making use of centrifugal plus quadratic potential eigenfunction bases. First, the radially nodeless states are variationally analyzed for each value of the orbital angular momentum using the corresponding functions of the bases; the output includes the centrifugal and frequency parameters of the auxiliary potentials and their eigenfunction bases. In the second stage, these bases are used to construct the matrix representation of the Hamiltonian of the system, and from its diagonalization the energy eigenvalues and eigenvectors of the successive states are obtained. The systematics of the accuracy and convergence of the overall results are discussed with emphasis on the dependence on the intensity of the supersingular part of the potential and on the orbital angular momentum.

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