Dos genios, dos épocas: lectura comparativa de ‘La Sonata a Kreutzer’ de Tolstoi y ‘El Túnel’ de Sábato

Aquest treball té l'objectiu d'analitzar de manera detallada dues grans obres de la literatura universal: ‘La Sonata a Kreutzer’ de León Tolstoi i ‘El Túnel’ d'Ernesto Sábato. El nostre segle es distingeix dels d'antany pel valor de la comunicació. És per això, que la literatura ha de cobrar més importància. No ens referim a una mera lectura d'uns llibres, sinó a un estudi a fons del que signifiquen les paraules que estan escrites en les obres. Es realitzarà una anàlisi partint d'aquestes novel·les, amb la utilització de vària bibliografia, amb la finalitat d'abastar algunes de les qüestions relevants i així, poder conèixer les similituds i diferències entre dues obres de diferents autors.

La ceguera como motivo en Ensayo sobre la ceguera de José Saramago e Informe sobre ciegos de Ernesto Sábato

El trabajo de investigación, El motivo de la ceguera en el Ensayo sobre la ceguera de José Saramago e Informe sobre ciegos de Ernesto Sábato, analiza desde el área y la metodología de la literatura comparada el uso del motivo literario de la ceguera en los dos textos mencionados, resaltando las similitudes y diferencias del tratamiento del motivo dentro de las dos obras y como éste sostiene una serie de obsesiones e ideas sobre el estado actual del mundo que comparten los autores de las dos novelas.

El abismo lógico (Borges y los filósofos de las ideas)

Este libro explora un fenómeno que se repite en algunos textos del escritor argentino Jorge Luis Borges (1899-1986). Está compuesto por nueve capítulos, que corresponden al análisis de la reescritura de nueve distintas propuestas filosóficas. Las propuestas están cobijadas bajo la misma doctrina: el idealismo. Es un libro que se escribe para validar la propuesta de un método de lectura que cuenta a la vez con una dosis de ingenio y con planteamientos rigurosos, permitiendo así un tipo de análisis que, siendo sistemático, es también lúdico, conservando de este modo las funciones fundamentales de la literatura. No pocas conjeturas ha habido acerca de las intenciones de Borges o de sus creencias.El texto propone análisis novedosos de los cuentos de Borges y reevalúa y critica algunos análisis existentes elaborados por diferentes comentaristas. El tipo de análisis propuesto se haría extensivo a otros cuentos de Borges y a otros autores. Es un texto que se esfuerza por tomar distancia de las interpretaciones existentes que hay sobre la obra de Borges y de proponer nuevas lecturas siguiendo un cierto rigor interpretativo. Las conclusiones finales sitúan la propuesta del libro en el centro de debates contemporáneos de la literatura como la muerte del autor, los límites de la interpretación y la intertextualidad. La misma propuesta se encarga de establecer su relación y su distancia con los comentaristas reconocidos y se aparta de propuestas interpretativas pasadas de moda. La aproximación al tema, además, vincula el análisis literario con la historia de la filosofía, haciéndolo interesante para un público más amplio.El texto propone análisis novedosos de los cuentos de Borges y reevalúa y critica algunos análisis existentes elaborados por diferentes comentaristas. El tipo de análisis propuesto se haría extensivo a otros cuentos de Borges y a otros autores. Es un texto que se esfuerza por tomar distancia de las interpretaciones existentes que hay sobre la obra de Borges y de proponer nuevas lecturas siguiendo un cierto rigor interpretativo. Las conclusiones finales sitúan la propuesta del libro en el centro de debates contemporáneos de la literatura como la muerte del autor, los límites de la interpretación y la intertextualidad. La misma propuesta se encarga de establecer su relación y su distancia con los comentaristas reconocidos y se aparta de propuestas interpretativas pasadas de moda. La aproximación al tema, además, vincula el análisis literario con la historia de la filosofía, haciéndolo interesante para un público más amplio.

Princípios fundamentais e modelos de transferência de energia inter e intramolecular

This work outlines the historic development of the concept and main theories of energy transfer, as well as the principal experiments carried out to confirm or refute the proposed theories. Energy transfer in coordination compounds is also discussed with a focus on rare earth systems.

Co-eletrodeposição oscilatória de cobre e estanho

It is investigated in the present contribution the oscillatory co-electrodeposition of CuSn on a polycrystalline gold surface in the presence of Triton X-100 surfactant and citric acid as additive, in acidic media. The experiments were conducted under potentiostatic control and the system dynamics characterized in terms of the morphology and stability of the current oscillations. Besides modulations in the frequency and amplitude of the current oscillations, several patterned states were observed, including relaxation-like and mixed mode oscillations. The oscillations were found to be very robust and some time series presented regular motions up to about two hours.

Efeito dos dióxidos de enxofre e de nitrogênio no desempenho de uma célula a combustível de membrana de intercâmbio de prótons

There is presently much interest in the clean and efficient generation of energy by proton exchange membrane fuel cells (PEMFC), using hydrogen as fuel. The generation of hydrogen by the reforming of other fuels, anaerobic fermentation of residual waters and other methods, often produce contaminants that affect the performance of the cell. In this work, the effect of gaseous SO2 and NO2 on the performance of a H2/O2 single PEMFC is studied. The results show that SO2 decreases irreversibly the performance of the cell under operating conditions, while NO2 has a milder effect that allows the recovery of the system.

Effect of temperature on the electro-oxidation of ethanol on platinum

We present in this work an experimental investigation of the effect of temperature (from 25 to 180 ºC) in the electro-oxidation of ethanol on platinum in two different phosphoric acid concentrations. We observed that the onset potential for ethanol electro-oxidation shifts to lower values and the reaction rates increase as temperature is increased for both electrolytes. The results were rationalized in terms of the effect of temperature on the adsorption of reaction intermediates, poisons, and anions. The formation of oxygenated species at high potentials, mainly in the more diluted electrolyte, also contributes to increase the electro-oxidation reaction rate.

Temperature effects on the oscillatory electro-oxidation of methanol on platinum

We report in this paper the effect of temperature on the oscillatory electro-oxidation of methanol on polycrystalline platinum in aqueous sulfuric acid media. Potential oscillations were studied under galvanostatic control and at four temperatures ranging from 5 to 35 degrees C. For a given temperature, the departure from thermodynamic equilibrium does not affect the oscillation period and results in a slight increase of the oscillation amplitude. Apparent activation energies were also evaluated in voltammetric and chronoamperometric experiments and were compared to those obtained under oscillatory conditions. In any case, the apparent activation energies values fell into the region between 50 and 70 kJ mol(-1). Specifically under oscillatory conditions an apparent activation energy of 60 +/- 3 kJ mol(-1) and a temperature coefficient q(10) of about 2.3 were observed. The present findings extend our recently published report (J. Phys. Chem. A, 2008, 112, 4617) on the temperature effect on the oscillatory electro-oxidation of formic acid. We found that, despite the fact that both studies were carried out under similar conditions, unlike the case of formic acid, only conventional, Arrhenius, dynamics was observed for methanol.

The role of the steps in the cleavage of the C-C bond during ethanol oxidation on platinum electrodes

Ethanol oxidation has been studied on stepped platinum single crystal electrodes in acid media using electrochemical and Fourier transform infrared (FTIR) techniques. The electrodes used belong to two different series of stepped surfaces: those having (111) terraces with (100) monoatomic steps and those with (111) terraces with (110) monoatomic steps. The behaviors of the two series of stepped surfaces for the oxidation of ethanol are very different. On the one hand, the presence of (100) steps on the (111) terraces provides no significant enhancement of the activity of the surfaces. On the other hand, (110) steps have a double effect on the ethanol oxidation reaction. At potentials below 0.7 V, the step catalyzes the C-C bond cleavage and also the oxidation of the adsorbed CO species formed. At higher potentials, the step is not only able to break the C-C bond, but also to catalyze the oxidation of ethanol to acetic acid and acetaldehyde. The highest catalytic activity from voltammetry for ethanol oxidation was obtained with the Pt(554) electrode.

Surface structure effects on the electrochemical oxidation of ethanol on platinum single crystal electrodes

Ethanol oxidation has been studied on Pt(111), Pt(100) and Pt(110) electrodes in order to investigate the effect of the surface structure and adsorbing anions using electrochemical and FTIR techniques. The results indicate that the surface structure and anion adsorption affect significantly the reactivity of the electrode. Thus, the main product of the oxidation of ethanol on the Pt(111) electrode is acetic acid, and acetaldehyde is formed as secondary product. Moreover, the amount of CO formed is very small, and probably associated with the defects present on the electrode surface. For that reason, the amount of CO(2) is also small. This electrode has the highest catalytic activity for the formation of acetic acid in perchloric acid. However, the formation of acetic acid is inhibited by the presence of specifically adsorbed anions, such as (bi) sulfate or acetate, which is the result of the formation of acetic acid. On the other hand, CO is readily formed at low potentials on the Pt(100) electrode, blocking completely the surface. Between 0.65 and 0.80 V, the CO layer is oxidized and the production of acetaldehyde and acetic acid is detected. The Pt(110) electrode displays the highest catalytic activity for the splitting of the C-C bond. Reactions giving rise to CO formation, from either ethanol or acetaldehyde, occur at high rate at any potential. On the other hand, the oxidation of acetaldehyde to acetic acid has probably the lower reaction rate of the three basal planes.

Estabilidade de agregados em argissolo sob diferentes usos, comparado com mata

A estrutura exerce grande importância no comportamento agrícola do solo, pela sua influência em propriedades do solo. Assim, objetivou-se avaliar a estabilidade de agregados e relacioná-la com diferentes frações orgânicas de um ARGISSOLO Vermelho-amarelo distrófico sob mata, seringueira, laranjeira e pastagem degradada. A amostragem foi realizada em trincheiras, de 0 a 10, 10 a 20 e 20 a 30 cm. Foram analisadas textura, argila dispersa em água, grau de floculação, densidade do solo, carbono orgânico total (COT), nitrogênio total (NT), ácidos fúlvicos (AF), húmicos (AH) e humina (HN), carbono da biomassa microbiana (C-Micr) e matéria orgânica leve (MOL). Foi determinada a estabilidade de agregados em água e calculados índices de estabilidade. Os resultados mostram diferenças de densidade do solo, seguindo a ordem mata < seringueira < laranjeira < pastagem. A estabilidade de agregados não se altera entre os usos nas profundidades de 0 a 10 e 10 a 20 cm, enquanto de 20 a 30 cm nota-se a ordem mata > seringueira > laranjeira > pastagem. No solo sob mata, seringueira e laranjeria a estabilidade de agregados está relacionada aos maiores teores de COT, NT,AF, AH, HN, C-Micr e MOL, enquanto na pastagem está relacionada principalmente a ciclos de umedecimento e secagem.

Valoración del estudio vesical y del tracto urinario superior en pacientes con citología urinaria positiva y pruebas de imagen negativas

Introducció: La citologia urinària positiva en context de cistoscopia sense evidència de tumor macroscòpic obliga a continuar el seu estudi. En el nostre centre es realitzen biòpsies vesicals múltiples normatitzades (BMN) i citologia ureteral selectiva en aquest casos. Material i mètodes: Estudi retrospectiu de 70 pacients amb citologia urinària positiva en absència de tumor macroscòpic. Es van avaluar els resultats de totes les biòpsies vesicals múltiples i les citologies ureterals selectives realitzades. Resultats: Es va diagnosticar CIS vesical em 45 (64,3%) pacients. Es va detectar citologia ureteral positiva em 12: cinc (7,2%) en el costat esquerre i set (10%) en el dret. Es va observar CIS vesical concomitant em 2 de 5 pacients amb PAP ureteral positiu esquerra i em 5 de 7 amb PAP ureteral positiu dret. Conclusions: La biòpsia múltiple normatitzada (BMN) és útil per a aquest casos. Els pobres resultats obtinguts en citologia ureteral selectiva posen en dubte la rendibilitat de la seva utilització sistemàtica.

Preparação e caracterização de eletrodos monocristalinos

Studies of the kinetics of electrocatalytic reactions on well oriented single crystal surfaces have demonstrated the influence of surface structure on the rate and mechanisms of many electrochemical processes. The preparation and characterization of these surfaces is the first step in this type of studies. In this paper, a methodology employed in order to ensure the quality and cleanliness of single crystals and their utilization as rotating electrodes is described.

Metodologia para o crescimento de esferas monocristalinas de metais nobres

This paper describes in detail a technique employed to grow quasi-spherical single crystals of noble metals for electrochemical applications, using platinum as an example. The metal beads were formed by melting the extremity of a wire in an oxygen / butane flame. X-ray techniques were used to check the crystallization and to determine the orientation of the crystals. Treatment with a pure hydrogen flame followed by a cooling procedure in a hydrogen / argon atmosphere were used for conditioning the well-defined platinum single crystal surfaces. Finally, electrochemical characterization of the Pt(111), Pt(110) and Pt(100) surfaces was done in diluted sulfuric acid solution in the hydrogen adsorption / desorption potential region.