Symmetry Groups
Mostrando 37-48 de 93 artigos, teses e dissertações.
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37. Espectroscopia de multicoincidencia aplicada ao estudo de moleculas
The main purpose of this thesis is to study selective photo-fragmentation processes of free molecules excited by synchrotron radiation using multi-coincidence spectros-copy. Below are summarized some original and important contributions of this work: 1) We show for the first time experimental evidences of ultrafast dissociation in water molecule after O1s ®
Publicado em: 2002
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38. Preparation and characterization of V2O5 catalyst supported TiO2. / Preparação e caracterização de catalisadores de V2O5 suportados em TiO2.
A series of samples of the catalytic system V2O5/TiO2 was prepared by the sol-gel method with different proportions of the active phase (from 0 to 9% in mass of V2O5) and calcined in different temperatures (from 250 to 6000C). A similar system was obtained by the impregnation method for comparison. The catalyst were characterized by their textural and struct
Publicado em: 2001
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39. Polinização por morcegos Glossophaginae versus Phyllostominae em floresta de terra firme na Amazonia Central
The aim of this study is to contrast attributes between plants pollinated by Glossophaginae and Phyllostominae bats in the "terra-fmne" Amazonian forest. The study was conducted in three habitats: "floresta de baixio" (BAl), "floresta de platô" (PLA) and "floresta de vertente" (VER). Thirty four individuaIs of bat-pollinated plants belonging to nine tree sp
Publicado em: 2000
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40. Sobre simetrias e ornamentos
This objective of this work is to study symmetries and the groups of symmetries of ornaments. Firstly, the isometries of the plane (translation, rotation, reflection and glide reflection), the cyclical and dihedral groups and the translation s group are studied. After, the classification of the discrete symmetry groups of the plane is presented: Cn and Dn, t
Publicado em: 1999
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41. Análise de simetrias nos grupos do tipo Dm usando conceitos de sistemas dinâmicos. / Dynamical analysis of symmetry groups Dm trough dynamical systems concepts.
O entendimento de quebra espontânea de simetria é um problema importante para o estudo de fenômenos na evolução de sistemas abertos, tanto em física quanto em química, como também na biologia. Aqui estudamos um método a mais para este tipo de análise, usando conceitos de sistemas dinâmicos com simetria. O sistema dinâmico escolhido é discreto, i
Publicado em: 1999
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42. Electrooptic characterization of organic crystals / Caracterização eletroóptica de cristais orgânicos
This work reports on the electrooptical characterization of organic crystals, namely: L-arginine phosphate monohidrate, Lalanine and L-threonine. We describe the theoretical aspect in these crystals discussing how the effect occurs according to the symmetry groups of each one. Furthermore, we discuss and observe the occurrence of piezoelectric effects during
Publicado em: 1998
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43. Maximal Sub-algebras of Semi-simple Lie Algebras, Symmetry Breaking and the Genetic Code / Subalgebras maximais das álgebras de Lie semisimples, quebra de simetria e o código genético
O propósito deste trabalho é dar uma contribuição ao projeto iniciado por Hornos &Hornos que visa explicar as degenerescências do código genético como resultado de sucessivas quebras de simetria ocorridas durante sua evolução. O modelo matemático usado requer a construção de todas as representações irredutíveis de dimensão 64 das álgebras de
Publicado em: 1998
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44. Estudo de materiais a base de bismuto (III) : sistema Bi2O3-V2O5 modificado pela incorporação de metais alcalinos terrosos
In the present work, we have studied a material with unusual properties, bismuth vanadate, BiVO4. The synthesis of this material was performed through the oxide method and the non-hydrolytic sol-gel method. This was done, in order to obtain information about the influence of these methods on the structural, thermal, compositional, morphological, and color ch
Publicado em: 1995
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45. Acetilacetona, diacetamida e N-(2-piridil)-acetamida imobilizadas na superficie de silica gel - preparação, caracterização, adsorção, termoquimica e espectroscopia de complexos suportados
The ligands acetyIacetone(ac), diacetamide(da) and N-(2-pyridyl)acetamide(pa) were immobilized on siIica gel surface, giving the products Si-ac, Si-da and Si-pa, respectively. These materiaIs were characterized through elemental analyses, infrared spectroscopy, surface area measurement, solid state carbon-13 NMR, thermogravimetry and differencial scanning ca
Publicado em: 1993
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46. An introduction to the methodology of structure determination by single crystal x-ray diffraction: applications to some complexes of lanthanides and transition metals with organic ligands / Introdução aos métodos de determinação de estruturas por difração de raios-X em monocristais: aplicação a alguns complexos de lantanídeos e metais de transição com ligantes orgânicos
The crystal structure of the complexes Ln(ClO4)3.6[PONH2(C6H5)2] where Ln=Eu, La, Cu[NH2(CH3)2CCO2]2, NiBr2.4[AsO(C6H5)3].8H2O (green), NiBr2.4[AsO(C6H5)3.1,5(CH3C6H5).H2O (orange) and of the ligand PONH2(C6H5)2 have been determined by X-ray diffraction. The complexes involving lanthanide ions refined to final R factors of R(Eu)=0.125 and R(La)=0.133 and the
Publicado em: 1983
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47. Symmetry arguments in chemistry
The use (and misuse) of symmetry arguments in constructing molecular models and in the interpretation of experimental observations bearing on molecular structure (spectroscopy, diffraction, etc.) is discussed. Examples include the development of point groups and space groups for describing the external and internal symmetry of crystals, the derivation o
The National Academy of Sciences of the USA.
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48. Screw rotations and glide mirrors: Crystallography in Fourier space
The traditional crystallographic symmetry elements of screw axes and glide planes are subdivided into those that are removable and those that are essential. A simple real-space criterion, depending only on Bravais class, determines which types can be present in any space group. This terminological refinement is useful in expressing the complementary relation
The National Academy of Sciences.