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Search Results: 1 - 10 of 602969 matches for " Campos Elvio A. de "
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Crystallization Mechanism and Kinetics of BaO-Li2O-ZrO2-SiO2 Glasses
Silveira, Cristian Berto da;Campos, Sílvia Denofre de;Campos, Elvio A. de;Oliveira, Ant?nio Pedro Novaes de;
Materials Research , 2002, DOI: 10.1590/S1516-14392002000100004
Abstract: differential thermal analysis and scanning electron microscopy were used to determine the influence of the addition of bao on the crystallization mechanism of li2o-zro2-sio2 systems. as the concentration of bao in the samples increased, a transition occurred in the predominant crystallization mechanism, which passed from superficial to volumetric. to determine the maximum nucleation rate, the crystallization kinetics of the sample containing 20 mole % bao, which showed the most uniform crystallization, was studied by counting the nuclei with an image analyzer. the first nuclei appeared at the first endothermic inflection point (at the start of tg, at 440 °c), while the maximum number of nuclei was counted at the midpoint of the glass transition region (446 °c). these results are similar to those observed for other materials that crystallize in volume, and confirm scanning electron microscopy data.
Crystallization Mechanism and Kinetics of BaO-Li2O-ZrO2-SiO2 Glasses
Silveira Cristian Berto da,Campos Sílvia Denofre de,Campos Elvio A. de,Oliveira Ant?nio Pedro Novaes de
Materials Research , 2002,
Abstract: Differential thermal analysis and scanning electron microscopy were used to determine the influence of the addition of BaO on the crystallization mechanism of Li2O-ZrO2-SiO2 systems. As the concentration of BaO in the samples increased, a transition occurred in the predominant crystallization mechanism, which passed from superficial to volumetric. To determine the maximum nucleation rate, the crystallization kinetics of the sample containing 20 mole % BaO, which showed the most uniform crystallization, was studied by counting the nuclei with an image analyzer. The first nuclei appeared at the first endothermic inflection point (at the start of Tg, at 440 °C), while the maximum number of nuclei was counted at the midpoint of the glass transition region (446 °C). These results are similar to those observed for other materials that crystallize in volume, and confirm scanning electron microscopy data.
Cobalt(II) Hematoporphyrin IX immobilized in a cellulose acetate niobium(V) oxide composite membrane: preparation and oxygen reduction study
Gushikem, Yoshitaka;Campos, Elvio A.;
Journal of the Brazilian Chemical Society , 1998, DOI: 10.1590/S0103-50531998000300011
Abstract: hematoporphyrin ix [8,13,-bis(1-hydroxyethyl)-3,7,12,17-tetramethyl-21h-porphyrin-2,18-dipropionic acid] was adsorbed on the organic-inorganic composite membrane cel/nb2o5 surface. the porphyrin is strongly adhered on the nb2o5 surface by reaction of the porphyrin co2h groups with nb2o5 forming the -coo-nb chemical bond. metallation of the porphyrine ring was made very easily by immersing the membrane in co(ii) solution and allowing to rest for a few hours. the electronic absorption bands due to the q bands indicated the symmetry change from d2h to d4h upon metallation of the porphyrin ring. the chemical analyses of the material confirmed that the metallation yield was practically 100%. oxygen was reduced on a electrode surface made with the material under a cathodic peak potential of -390 mv, in 1 m kcl solution at ph 1, temperature of 298 k and at ambient pressure. the oxygen reduction was proposed to occur by a two electron transfer mechanism. a linear cathodic peak current response was obtained for dissolved oxygen concentrations between 1.5 and 15 ppm.
Cobalt(II) Hematoporphyrin IX immobilized in a cellulose acetate niobium(V) oxide composite membrane: preparation and oxygen reduction study
Gushikem Yoshitaka,Campos Elvio A.
Journal of the Brazilian Chemical Society , 1998,
Abstract: Hematoporphyrin IX [8,13,-bis(1-hydroxyethyl)-3,7,12,17-tetramethyl-21H-porphyrin-2,18-dipropionic acid] was adsorbed on the organic-inorganic composite membrane Cel/Nb2O5 surface. The porphyrin is strongly adhered on the Nb2O5 surface by reaction of the porphyrin CO2H groups with Nb2O5 forming the -COO-Nb chemical bond. Metallation of the porphyrine ring was made very easily by immersing the membrane in Co(II) solution and allowing to rest for a few hours. The electronic absorption bands due to the Q bands indicated the symmetry change from D2h to D4h upon metallation of the porphyrin ring. The chemical analyses of the material confirmed that the metallation yield was practically 100%. Oxygen was reduced on a electrode surface made with the material under a cathodic peak potential of -390 mV, in 1 M KCl solution at pH 1, temperature of 298 K and at ambient pressure. The oxygen reduction was proposed to occur by a two electron transfer mechanism. A linear cathodic peak current response was obtained for dissolved oxygen concentrations between 1.5 and 15 ppm.
Influence of the zirconium and titanium oxides on bioactivity of materials constituted by Na2O-CaO-P2O5-SiO2 Estudo da bioatividade de materiais constituídos por Na2O-CaO-P2O5-SiO2: Influência da adi o dos óxidos de zirc nio e de titanio
Silvia Denofre de Campos,Elvio Ant?nio de Campos,Wagner Alex Jann Favre,Leandro de Bispo Carneiro
Orbital : the Electronic Journal of Chemistry , 2012,
Abstract: In this work were synthesized by conventional fusion, biomaterials based on Na2O-CaO-P2O5-SiO2 with titanium oxide and zirconium oxide at different concentrations. The bioglasses, when submitted to the heat treatment in the crystallization temperatures, obtained by Differential Thermal Analysis (DTA) showed an internal reorganization indicated by the presence of different crystalline phases observed in X-ray diffraction patterns of the samples. These crystalline phases, rich in calcium phosphates and calcium silicates, are probably the actives sites useful to the ion exchange process between solid and solution to apatite and hydroxyapatite formation, being responsible by bioactive behavior. Biocompatibility tests for the synthesized materials were made by placing the samples in contact with a solution simulating the blood plasma (SBP). There was a variation of the initial pH of this solution to the more basic pH (from 8.5 to 12.0), indicating the interaction between the solid and the SBP solution. This effect was more pronounced to materials with TiO2 that can be understood as a greater bioactivity and compatibility on these materials. Para este trabalho foram sintetizados, pelo método de fus o convencional, biomateriais baseados em Na2O-CaO-P2O5-SiO2 com óxido de titanio e óxido de zirc nio em diferentes concentra es. Os biovidros quando submetidos ao tratamento térmico nas respectivas temperaturas de cristaliza o, obtidas por Análise Térmica Diferencial (DTA), mostraram uma reorganiza o interna evidenciada pela presen a de fases cristalinas distintas, observadas nos difratogramas de raio-X das amostras. Estas fases cristalinas, ricas em fosfatos de cálcio e silicatos de cálcio, servem de sítios ativos para o processo de troca i nica entre o sólido e a solu o, propiciando a forma o de apatita e de hidroxiapatita, responsáveis pelo comportamento bioativo. Testes de biocompatibilidade dos materiais sintetizados foram feitos colocando-se as amostras em contato com uma solu o que simula o plasma sanguíneo (SPS). Observou-se um deslocamento do pH inicial desta solu o para pHs mais básicos (de 8,5 a 12,0) o que indica intera o entre o sólido e a solu o SPS. Este efeito foi mais intenso para materiais com TiO2 atribuindo-se a eles, maior bioatividade e compatibilidade.
An Inexact Restoration Package for Bilevel Programming Problems  [PDF]
Elvio A. Pilotta, Germán A. Torres
Applied Mathematics (AM) , 2012, DOI: 10.4236/am.2012.330181
Abstract: Bilevel programming problems are a class of optimization problems with hierarchical structure where one of the con-straints is also an optimization problem. Inexact restoration methods were introduced for solving nonlinear programming problems a few years ago. They generate a sequence of, generally, infeasible iterates with intermediate iterations that consist of inexactly restored points. In this paper we present a software environment for solving bilevel program-ming problems using an inexact restoration technique without replacing the lower level problem by its KKT optimality conditions. With this strategy we maintain the minimization structure of the lower level problem and avoid spurious solutions. The environment is a user-friendly set of Fortran 90 modules which is easily and highly configurable. It is prepared to use two well-tested minimization solvers and different formulations in one of the minimization subproblems. We validate our implementation using a set of test problems from the literature, comparing different formulations and the use of the minimization solvers.
Existence of a Walrasian Equilibrium in Locally Convex Topological Vector Spaces, with Interdependent Utility Functions  [PDF]
Elvio Accinelli, Aramando García, Marisol Torres
Theoretical Economics Letters (TEL) , 2017, DOI: 10.4236/tel.2017.71005
Abstract: In this paper we extend the well known result of existence of Walrasian equilibrium given in Debreu (1952) to economies modeled over topological vector spaces. Our work is closely related to the previous results of Yannelis-Pranhakar (1983), and Tan and Yuan (1999), but unlike these papers we prove the existence of a Walrasian equilibrium in infinite dimensional economies with interdependent and price-dependent utilities.
Experimental poisoning of goats by Ipomoea carnea subsp. fistulosa in Argentina: a clinic and pathological correlation with special consideration on the central nervous system
Ríos, Elvio E.;Cholich, Luciana A.;Gimeno, Eduardo J.;Guidi, María G.;Acosta de Pérez, Ofelia C.;
Pesquisa Veterinária Brasileira , 2012, DOI: 10.1590/S0100-736X2012000100007
Abstract: ipomoea carnea subsp. fistulosa, aguapei or mandiyura, is responsible for lysosomal storage in goats. the shrub contains several alkaloids, mainly swansonine which inhibits lysosomal α-mannosidase and golgi mannosidase ii. poisoning occurs by inhibition of these hydrolases. there is neuronal vacuolation, endocrine dysfunction, cardiovascular and gastrointestinal injury, and immune disorders. clinical signs and pathology of the experimental poisoning of goats by ipomoea carnea in argentina are here described. five goats received fresh leaves and stems of ipomoea. at the beginning, the goats did not consume the plant, but later, it was preferred over any other forage. high dose induced rapid intoxication, whereas with low doses, the course of the toxicosis was more protracted. the goats were euthanized when they were recumbent. cerebrum, cerebellum, medulla oblongata, pons and colliculi, were routinely processed for histology. in nine days, the following clinical signs developed: abnormal fascies, dilated nostrils and abnormal postures of the head, cephalic tremors and nystagmus, difficulty in standing. subsequently, the goats had a tendency to fall, always to the left, with spastic convulsions. there was lack in coordination of voluntary movements due to purkinje and deep nuclei neurons damage. the cochlear reflex originated hyperreflexia, abnormal posture, head movements and tremors. the withdrawal reflex produced flexor muscles hypersensitivity at the four legs, later depression and stupor. abnormal responses to sounds were related to collicular lesions. thalamic damage altered the withdrawal reflex, showing incomplete reaction. the observed cervical hair bristling was attributed to a thalamic regulated nociceptive response. depression may be associated with agonists of lysergic acid contained in ipomoea. these clinical signs were correlated with lesions in different parts of the cns.
Niklas Luhmann: La compleja incertidumbre de un mundo secularizado
Tell,Elvio A.;
Ciencia, docencia y tecnolog?-a , 2007,
Abstract: niklas luhmann's work invites us to think over society in a new way, leaving behind old habits and traditional thoughts built by the western intellectual heritage since the illustration. lukhmann's reluctance to sustain the basic postulates of the ancient european thought and his concern about proposing an illustration of the illustration are no more that forewords to approaching the requirements of a new theory more suitable to modern times. thus, it could be said that he requires to go beyond modernity tempting to create new intellectual categories. as an example, his work implies a constant concern to conceive a new concept of subject independent from his/her context meant in terms of social systems, and while the analysis of social communication traditionally implies subjects, for the studied author that represents a chimera. even when communication assumes the participation of either several or many people, that is the very reason why it cannot be attributed to any particular one.
Niklas Luhmann: la compleja incertidumbre de un mundo secularizado
Elvio A. Tell
Ciencia, Docencia y Tecnología , 2007,
Abstract: La obra de Niklas Luhmann es una invitación a pensar de un modo nuevo la sociedad, abandonando viejos hábitos y tradiciones de pensamiento que ha forjado la herencia intelectual de Occidente desde la Ilustración. El rechazo de Luhmann a mantener los postulados del pensamiento veteroeuropeo y su preocupación en formular una ilustración de la ilustración no son más que preámbulos para abordar la exigencia de una nueva teoría más acorde con los tiempos modernos. En este sentido, bien puede decirse que exige ir más allá de la modernidad tendiendo a crear nuevas categorías intelectuales. Por ejemplo, su obra es una constante preocupación por pensar un nuevo concepto de sujeto independiente de su entorno que son los sistemas sociales. Tradicionalmente el análisis de la comunicación social supone sujetos. Para el autor, esto representa una quimera. Si bien es cierto que la comunicación presupone la participación de muchas personas, precisamente por eso, no puede ser atribuida a ningún individuo en particular.
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