Aplicação de Modelos Matemáticos para Previsão de Recalques do Aterro de Nova Iguaçu – RJ, Brasil

O presente trabalho versa sobre uma análise de recalques em longo prazo à luz de cinco modelos teóricos de compressibilidade, os modelos de Sowers, Gandola et al., Ling et al., Meruelo e Oweis. Os valores dos recalques medidos durante 960 dias foram utilizados para prever recalques em 50 anos. O estudo foi realizado no aterro sanitário (CTR-NI) que está localizado na região metropolitana do Rio de Janeiro, sudeste do Brasil. O aterro recebe diariamente entre 3.500 e 6.000 toneladas de resíduos sólidos urbanos e industriais classe II, segundo classificação da ABNT NBR 10.004. Os recalques obtidos com o monitoramento variaram na faixa de 0,48% a 1,30% indicando que sob carga constante os recalques foram pouco significativos. Os modelos de previsão apresentaram curvas de recalques a curto prazo aproximadas, já a longo prazo destacam-se as previsões de Gandola et al. e Oweis que apresentaram valores consideravelmente maiores que os modelos de Sowers, Ling et al. e Meruelo.  Os valores de previsão de recalques em 50 anos variaram entre 150 mm e 1000 mm aproximadamente, sendo mais significativos as previsões obtidas através do modelo de Oweis

Cathodic Corrosion: A Quick, Clean, and Versatile Method for the Synthesis of Metallic Nanoparticles**

A simple and effective method for the synthesis of nanoparticles is reported based on extreme cathodic polarization of a metal, formation of cation-stabilized metal anions, and their agglomeration (see picture). The improved catalytic activity of these nanoparticles in the oxidation of carbon monoxide as well as methanol is shown using platinum.<br/

Solid-state reference electrodes based on carbon nanotubes and polyacrylate membranes

A novel potentiometric solid-state reference electrode containing single-walled carbon nanotubes as the transducer layer between a polyacrylate membrane and the conductor is reported here. Single-walled carbon nanotubes act as an efficient transducer of the constant potentiometric signal originating from the reference membrane containing the Ag/AgCl/Cl− ions system, and they are needed to obtain a stable reference potentiometric signal. Furthermore, we have taken advantage of the light insensitivity of single-walled carbon nanotubes to improve the analytical performance characteristics of previously reported solid-state reference electrodes. Four different polyacrylate polymers have been selected in order to identify the most efficient reservoir for the Ag/AgCl system. Finally, two different arrangements have been assessed: (1) a solid-state reference electrode using photo-polymerised n-butyl acrylate polymer and (2) a thermo-polymerised methyl methacrylate:n-butyl acrylate (1:10) polymer. The sensitivity to various salts, pH and light, as well as time of response and stability, has been tested: the best results were obtained using single-walled carbon nanotubes and photo-polymerised n-butyl acrylate polymer. Water transport plays an important role in the potentiometric performance of acrylate membranes, so a new screening test method has been developed to qualitatively assess the difference in water percolation between the polyacrylic membranes studied. The results presented here open the way for the true miniaturisation of potentiometric systems using the excellent properties of single-walled carbon nanotubes

Single-Molecule Electrochemical Transistor Utilizing a Nickel-Pyridyl Spinterface

Using a scanning tunnelling microscope break-junction technique, we produce 4,4′-bipyridine (44BP) single-molecule junctions with Ni and Au contacts. Electrochemical control is used to prevent Ni oxidation and to modulate the conductance of the devices via nonredox gatingthe first time this has been shown using non-Au contacts. Remarkably the conductance and gain of the resulting Ni-44BP-Ni electrochemical transistors is significantly higher than analogous Au-based devices. Ab-initio calculations reveal that this behavior arises because charge transport is mediated by spin-polarized Ni <i>d</i>-electrons, which hybridize strongly with molecular orbitals to form a “spinterface”. Our results highlight the important role of the contact material for single-molecule devices and show that it can be varied to provide control of charge and spin transport

Modification cathodique du platine (suivi par microscopie à champ proche " SPM ")

Le traitement cathodique du platine en milieu organique en présence d'électrolytes supports, organiques et inorganiques conduit à une modification de la structure et des propriétés du matériau de platine. Ces changements morphologiques, au cours du traitement électrochimique, ont été analysés par la microscopie à force atomique couplée à l'électrochimie EC-AFM. L'insertion du sel dans le matériau de platine conduit à la formation de grains sur la surface, ces derniers recouvrent totalement la surface quand la charge injectée au platine augmente. Le processus de la modification est complètement réversible après ré-oxydation. Ces nouvelles phases organométalliques présentent un pouvoir réducteur important. Cette propriété a été utilisée pour conduire au greffage de groupements aryle sur la surface du platine modifié. Enfin, l'usage de la microscopie électrochimique à balayage SECM a permis à la fois d'induire et de suivre la modification locale du platine par l'intermédiaire d'un radical anion, ainsi que la détermination des propriétés de la phase organométallique.RENNES1-BU Sciences Philo (352382102) / SudocSudocFranceF

Scanning electrochemical microscopy in nonusual solvents: inequality of diffusion coefficients problem.

Scanning electrochemical microscopy offers interesting possibilities for investigating both transport properties in room-temperature ionic liquids (RTILs) and reactions occurring at the ionic liquid/substrate interface. Besides the expected difficulties related to the lower diffusion coefficients for species dissolved in RTILs arising from the higher viscosity of RTILs, the major problem comes from the inequality of the diffusion coefficients between the oxidized and reduced forms of the redox mediator used to probe the interfaces. This question was treated by an extension of the model originally presented by Martin and Unwin (Martin, R. D.; Unwin, P. R. J. Electroanal. Chem. 1997, 439, 123) and was adapted to the specific aspects of SECM in ionic liquids. The inequalities of diffusion coefficients lead to large anomalies in the current responses, which in extreme cases impede the recording of stationary approach curves. Conditions for recording steady-state approach curves into ionic liquids and consequences of erroneous data treatment were examined. These discrepancies with the simple models (when diffusion coefficients have been taken as equal), could be transformed in a convenient method for characterizing the transport properties of species dissolved in RTIL. The analysis is based on transient SECM experiments and determinations from nonambiguous dimensionless parameters. Experimental examples based on SECM in common RTILs, using the O2/ O2*- couple, were analyzed taking into account the presented model