The effect of constituent metal ions on the electrokinetics of chalcopyrite

Chalcopyrite in contact with water is thermodynamically unstable in the presence of oxygen. Oxidation of chalcopyrite may take place due to various factors, e.g., geological environment, mining/comminution, and storage. In this work oxidation of chalcopyrite has been investigated through interfacial electrokinetics. The characteristics of samples obtained from different geological locations as well as the effects of ageing and laboratory oxidation have been delineated. Variation of the solid-liquid ratio was found to have a significant effect on the zeta-potential characteristics of chalcopyrite. The role of constituent metal ions, namely copper and iron, has been studied in the absence and presence of externally added metal ions. The results indicated that the ratio of Cu/Fe on the surface of oxidized chalcopyrite determines the Stern layer potential and under appropriate solution chemistry conditions influences charge reversals. The mineral surfaces, thus, could be either copper-rich or iron-rich as reflected by a shift in pH(iep),,(s). The observed charge reversals have been explained on the basis of a model proposed by James and Healy. (C) 1997 Academic Press.

Electrocatalytic efficiency of polyaniline by cyclic voltammetry and electrochemical impedance spectroscopy studies

Electrochemical redox reactions of ferrous/ferric (Fe2+/Fe3+) and hydroquinone/quinone (H(2)Q/Q) were studied on Pt and polyaniline (PANI)-deposited Pt electrodes in 0.5 M H2SO4-supporting electrolyte by cyclic voltammetry and ac impedance spectroscopy. A comparison of the experimental data obtained with the Pt and PANI/Pt electrodes suggested that the reactions were catalyzed by the PANI. Based on a relative increase in peak currents of cyclic voltammograms, catalytic efficiency (gamma(cv)) of the PANI was defined. There was an increase in gamma(cv) with an increase of scan rate and a decrease of concentration of Fe2+/Fe3+ or H(2)Q. The complex plane impedance spectrum of the electrode consisted of a semicircle in high frequency range and a linear spike in low frequency range. The exchange current density (i(0)) calculated using the semicircle part of the impedance showed Butler-Volmer kinetics with respect to concentration dependence. From a relative increase of i(0) on the PANI/Pt electrode, catalytic efficiency (gamma(eis)) was evaluated. (C) 2002 Elsevier Science B.V. All rights reserved.

Kinetics of hydrogen evolution on submicron size Co, Ni, Pd and CoNi alloy powder electrodes by d.c. polarization and a.c. impedance studies

Submicron size Co, Ni and Co-Ni alloy powders have been synthesized by the polyol method using the corresponding metal malonates and Pd powder by reduction of PdOx in methanol. The kinetics of the hydrogen evolution reaction ( HER) in 6 M KOH electrolyte have been studied on electrodes made from the pressed powders. The d.c. polarization measurements have resulted in a value close to 120 mV decade(-1) for the Tafel slope, suggesting that the HER follows the Volmer-Heyrovsky mechanism. The values of exchange current density (i(o)) are in the range 1-10 mA cm(-2) for electrodes fabricated in the study. The a.c. impedance spectra measured at several potentials in the HER region showed a single semicircle in the Nyquist plots. Exchange current density (i(o)) and energy transfer coefficient (alpha) have been calculated by employing a nonlinear least square-fitting program.

Copolyesters from Soybean Oil for Use as Resorbable Biomaterials

A family of soybean oil (SO) based biodegradable cross-linked copolyesters sourced from renewable resources was developed for use as resorbable biomaterials. The polyesters were prepared by a melt condensation of epoxidized soybean oil polyol and sebacic acid with citric acid (CA) as a cross-linker. D-Mannitol (M) was added as an additional reactant to improve mechanical properties. Differential scanning calorimetry revealed that the polyester synthesized using only CA as the cross-linker was semicrystalline and elastomeric at physiological temperature. The polymers were hydrophobic in nature. The water wettability, elongation at break and the degradation rate of the polyesters decreased with increase in M content or curing time. Modeling of release kinetics of dyes showed a diffusion controlled mechanism underlies the observed sustained release from these polymers. The polyesters supported attachment and proliferation of human stem cells and were thus cytocompatible. Porous scaffolds induced osteogenic differentiation of the stern cells suggesting that these polymers are well suited for bone tissue engineering. Thus, this family of polyesters offers a low cost and green alternative as biocompatible, bioresobable polymers for potential use as resorbable biomaterials for tissue engineering and controlled release.

Lmlk seal impressions once again : a second rejoinder to Oded Lipschits

Abstract: This article deals in the main with claims made by Lipschits et al. that the lmlk stamps were partly manufactured after Sennacherib’s campaign in 701 BCE. It forms specifically a rejoinder to Lipschits’ claims published recently. Finally, in the epilogue, are presented the data dealing with the suggestions of Lipschits, which have already been published by Stern, Grena and Van der Veen.

Technological status and development prospects of small-scale fishing crafts in Nigerian coastal water

A study of fishing crafts was conducted in some coastal states of Nigeria to elucidate findings on the existing crafts as the baseline for further developments. Based on the technical designs, three types of fishing crafts were identified; planked, dug-out and half dug-out canoes. The planked canoes have the largest cubic number and dug-out canoes the least. At loadwater line, the ratio of freeboard to draft was 2 : 1 for planked canoes, indicating reserved buoyancy. Trim of planked canoe is by stern; the beam-length ratio for dug-out canoes showed high drag. Most of the sea-going canoes have U-shaped bottom hull profile capable of withstanding the rigours of surf landing and displayed good stability against longitudinal water wave. Gunwale and thwarts provided respectively the longitudinal and transverse strength of planked and half dug-out canoes. With its characteristics 'weight low down' construction, planked canoe represent the climax of small scale fishing crafts developments in Nigerian coastal waters. It's only draw back is durability. Further improvement in this canoe should be aimed at increasing the hull size and stiffness, water tightness of deck by coating, caulking, fastening, increasing level of motorization and installation of deck working equipments. Experimental design and use of fibre glass, aluminium and ferrocement hulls, together with improved planked canoe is highly advocated

Trapped ion magnetic resonance: concepts and designs

A novel spectroscopy of trapped ions is proposed which will bring single-ion detection sensitivity to the observation of magnetic resonance spectra. The approaches developed here are aimed at resolving one of the fundamental problems of molecular spectroscopy, the apparent incompatibility in existing techniques between high information content (and therefore good species discrimination) and high sensitivity. Methods for studying both electron spin resonance (ESR) and nuclear magnetic resonance (NMR) are designed. They assume established methods for trapping ions in high magnetic field and observing the trapping frequencies with high resolution (<1 Hz) and sensitivity (single ion) by electrical means. The introduction of a magnetic bottle field gradient couples the spin and spatial motions together and leads to a small spin-dependent force on the ion, which has been exploited by Dehmelt to observe directly the perturbation of the ground-state electron's axial frequency by its spin magnetic moment.

A series of fundamental innovations is described m order to extend magnetic resonance to the higher masses of molecular ions (100 amu = 2x 10^5 electron masses) and smaller magnetic moments (nuclear moments = 10^(-3) of the electron moment). First, it is demonstrated how time-domain trapping frequency observations before and after magnetic resonance can be used to make cooling of the particle to its ground state unnecessary. Second, adiabatic cycling of the magnetic bottle off between detection periods is shown to be practical and to allow high-resolution magnetic resonance to be encoded pointwise as the presence or absence of trapping frequency shifts. Third, methods of inducing spindependent work on the ion orbits with magnetic field gradients and Larmor frequency irradiation are proposed which greatly amplify the attainable shifts in trapping frequency.

The dissertation explores the basic concepts behind ion trapping, adopting a variety of classical, semiclassical, numerical, and quantum mechanical approaches to derive spin-dependent effects, design experimental sequences, and corroborate results from one approach with those from another. The first proposal presented builds on Dehmelt's experiment by combining a "before and after" detection sequence with novel signal processing to reveal ESR spectra. A more powerful technique for ESR is then designed which uses axially synchronized spin transitions to perform spin-dependent work in the presence of a magnetic bottle, which also converts axial amplitude changes into cyclotron frequency shifts. A third use of the magnetic bottle is to selectively trap ions with small initial kinetic energy. A dechirping algorithm corrects for undesired frequency shifts associated with damping by the measurement process.

The most general approach presented is spin-locked internally resonant ion cyclotron excitation, a true continuous Stern-Gerlach effect. A magnetic field gradient modulated at both the Larmor and cyclotron frequencies is devised which leads to cyclotron acceleration proportional to the transverse magnetic moment of a coherent state of the particle and radiation field. A preferred method of using this to observe NMR as an axial frequency shift is described in detail. In the course of this derivation, a new quantum mechanical description of ion cyclotron resonance is presented which is easily combined with spin degrees of freedom to provide a full description of the proposals.

Practical, technical, and experimental issues surrounding the feasibility of the proposals are addressed throughout the dissertation. Numerical ion trajectory simulations and analytical models are used to predict the effectiveness of the new designs as well as their sensitivity and resolution. These checks on the methods proposed provide convincing evidence of their promise in extending the wealth of magnetic resonance information to the study of collisionless ions via single-ion spectroscopy.

Investigations of charge-carrier dynamics at semiconductor/liquid interfaces

Theoretical and experimental investigations of charge-carrier dynamics at semiconductor/liquid interfaces, specifically with respect to interfacial electron transfer and surface recombination, are presented.

Fermi's golden rule has been used to formulate rate expressions for charge transfer of delocalized carriers in a nondegenerately doped semiconducting electrode to localized, outer-sphere redox acceptors in an electrolyte phase. The treatment allows comparison between charge-transfer kinetic data at metallic, semimetallic, and semiconducting electrodes in terms of parameters such as the electronic coupling to the electrode, the attenuation of coupling with distance into the electrolyte, and the reorganization energy of the charge-transfer event. Within this framework, rate constant values expected at representative semiconducting electrodes have been determined from experimental data for charge transfer at metallic electrodes. The maximum rate constant (i.e., at optimal exoergicity) for outer-sphere processes at semiconducting electrodes is computed to be in the range 10^-17-10^-16 cm⁴ s^-1, which is in excellent agreement with prior theoretical models and experimental results for charge-transfer kinetics at semiconductor/liquid interfaces.

Double-layer corrections have been evaluated for semiconductor electrodes in both depletion and accumulation conditions. In conjuction with the Gouy-Chapman-Stern model, a finite difference approach has been used to calculate potential drops at a representative solid/liquid interface. Under all conditions that were simulated, the correction to the driving force used to evaluate the interfacial rate constant was determined to be less than 2% of the uncorrected interfacial rate constant.

Photoconductivity decay lifetimes have been obtained for Si(111) in contact with solutions of CH₃OH or tetrahydrofuran containing one-electron oxidants. Silicon surfaces in contact with electrolyte solutions having Nernstian redox potentials > 0 V vs. SCE exhibited low effective surface recombination velocities regardless of the different surface chemistries. The formation of an inversion layer, and not a reduced density of electrical trap sites on the surface, is shown to be responsible for the long charge-carrier lifetimes observed for these systems. In addition, a method for preparing an air-stable, low surface recombination velocity Si surface through a two-step, chlorination/alkylation reaction is described.

Energy efficiency in trawling operations

Diurnal variation in trawl catches and its influence on energy efficiency of trawler operations are discussed in this paper, based on data on landings of a Japanese factory trawler which operated in the Indian waters during 1992-93. The factory vessel equipped for stern trawling had a length overall of 110 m, GT of 5460 and installed engine power of 5700 hp. Operations were conducted off west coast of India between 31 and 278 m depth contours, using a 80.4 m high opening bottom trawl with an adjusted vertical opening of 7.60.9 m. The catch data was grouped according to the median towing hour, by the time of the day. CPUE obtained was 3713.4 kg.h-1 for day time operations and 1536.6 kg.h-1 for night-time operations. Mean daily catches were 31367 kg.day-1 (SE: 2743) for day time operations and 9430 kg.day-1 (SE: 966) for night-time operations. Fuel consumption were 0.399 and 0.982 kg fuel.kg fish-1, respectively for day and night-time operations. Total catch and catch components such as threadfin bream, bulls eye, hairtails, trevelly, lizard fish showed significant improvement during day-time operations while swarming crabs showed a significant improvement in the night-time operations. The difference in catch rates between day and night could be attributed to diurnal variation in the spatial distribution and schooling behaviour of the catch categories, their differential behaviour in the vicinity of trawl systems under varying light levels of day and night and consequent effect on catching efficiency and size selectivity at different stages in the capture process. The results obtained in addition to its importance in the operational planning of trawling in order to realise objectives of maximising catch per unit effort and minimising fuel consumption per unit volume of fish caught, has added significance in the use of bottom trawl surveys in stock abundance estimates.

Transferências produtivas e consultas terapêuticas: afeto e intensidade na experiência psicanalítica

O presente trabalho procura examinar a experiência psicanalítica através das consultas terapêuticas de Winnicott, levando-se em conta sua realização em instituições públicas de saúde brasileiras e buscando uma leitura não-ortodoxa da construção do dispositivo psicanalítico. Para isto, propõe-se, em um primeiro momento, o estudo sobre a questão do afeto e da intensidade na experiência analítica a partir das teorizações iniciais sobre transferência na obra freudiana. Em seguida discute-se a contribuição ferencziana com relação à noção de tato e a intensidade própria de sua prática clínica, priorizando-se a fase final de sua obra, momento em que o foco de seu trabalho dirigia-se mais agudamente às questões referentes ao lugar do analista, aos sentimentos contra-transferenciais e à elasticidade da técnica. Num terceiro momento, propõe-se um exame das idéias de Winnicott a respeito do manejo e o uso do objeto e as suas implicações na teorização sobre a transferência. Finalmente, pretende-se pensar o campo de afetação que se dá na clínica psicanalítica a partir dos conceitos de introjeção em Ferenczi, o surgimento dos sensos de eu e afetos de vitalidade na teoria de Stern e a relação de tais conceitos com alguns dos pressupostos winnicottianos, para fundamentar a possibilidade de transferências produtivas nas consultas terapêuticas.

Construção da maternidade contemporânea e a participação em um grupo de suporte online no Facebook

Este estudo buscou contribuições da psicologia do desenvolvimento, pela perspectiva da psicologia evolucionista e sociocultural, para compreender a construção da maternidade contemporânea com uso do Facebook como suporte online. No último século ocorreram muitas transformações no papel social da mulher, o mercado de trabalho a incorporou, o nível de escolaridade aumentou, a taxa de natalidade caiu. Entretanto, a diminuição no número de filhos não reduziu o trabalho materno. Em contextos urbanos de grandes cidades, as famílias estendidas são menos frequentes. Em contraste, o uso de redes sociais, tipo Facebook, aumenta. O percentual de brasileiras (30-39 anos) que utiliza a internet supera 50%. Hipotetizou-se que redes sociais online podem complementar o apoio demandado pelas mães. Desse modo, entendendo que mulheres precisam de apoio para cuidar das crianças e que o mundo atual está interconectado através da internet, buscou-se abordar a maternidade contemporânea em sociedade urbana e a internet no contexto do suporte online à parentalidade. Foram feitos dois estudos com amostra de um grupo de suporte online para gestantes/mães no Facebook: 1) Análise de postagens coletadas (30 meses), objetivando compreender discurso materno e principais temas abordados; 2) Investigação da percepção sobre rede de apoio geral e online, como o apoio online pode ser conseguido, o que interessa às mães neste tipo de apoio e perfil sociodemográfico. O Estudo 1, analisou conteúdo de 2.510 postagens apontando dois grupos de categorias: psicológicas (45%) e não-psicológicas (55%). No primeiro, o discurso enquadra-se na teoria da constelação da maternidade de Daniel Stern: 1) vida crescimento (50%); 2) relacionar-se primário (8%); 3) matriz de apoio (40%); 4) reorganização da identidade (2%). O segundo indicou quatro categorias: 5) negócios/divulgação (54%); 6) desenvolvimento gestacional/parto (9%); 7) pós-parto (5%); 8) indicações/pedidos práticos (32%). O Estudo 2 apontou que as participantes têm idade média de 31,86 anos, 88,6% possui graduação completa, a maioria mora com companheiro, exerce atividade profissional remunerada e tem renda familiar mensal superior a 10 salários mínimos (48%). Os principais interesses estão nos temas relacionados à saúde e cuidados com bebê. A maioria indica que lê as postagens com mais frequência do que expõem suas dúvidas. Grande parte percebe o grupo online como uma ajuda importante no exercício da sua maternidade. A escala de apoio social (presencial) apresenta escores maiores do que a escala de apoio social online com diferença em todas as dimensões. A escala de apoio social online aponta que as dimensões apoio informacional e emocional apresentam escores maiores, revelando que a troca de informações e o encorajamento em momentos difíceis da vida parecem ser os mais relevantes, apontando, principalmente, que há diferença significativa entre a dimensão emocional e as demais dimensões da escala. Resumindo, o grupo de suporte online se mostrou uma importante ferramenta para compartilhar informações entre mulheres que estão passando pelo mesmo momento do ciclo vital, e o suporte online um instrumento relevante ao suporte à parentalidade, prestando-se a um serviço que não poderia ser imaginado décadas atrás. Novos estudos poderão aprofundar e ampliar os resultados desta investigação

An experiment conducted with a floating trawl net off Cochin

The paper deals with an experiment with a floating trawl net off Cochin, using a pair of curved otter boards and a transducer mounted on the head rope of the net. 32 hauls were made with different towing speeds and warp length keeping one factor constant for varying parameters of the other factor. The working data for 32 hauls are presented and the effect in the fishing depth of the net due to the variation in one factor is mentioned. The 'fishing depth' is indicated in this paper as the distance between the head rope and the bottom. The usefulness of similar experiments with added information on the angle of leading warp at the stern for the exploitation of column fishes in Indian waters is indicated.

Comparison of model predictions and speed trial results for a group of 32' wooden trawlers

Speed trial results of six 32' wooden stern, trawlers built to the same design are analyzed to determine the EHP ship Froude number curves in each case and are compared with the model test results of the same design and for the corresponding, displacement, conditions.

The Pearl Banks inspection: April, 1970

The last major pearl fishery in the Gulf of Mannar was held in February-March, 1958, when about 4.5 million oysters were collected from the south-west Cheval Paar by dredging. (Sivalingam 1961). Subsequently, two smaller fisheries, one in 1960 and another in 1961 took place. In these two fisheries one million oysters and four hundred thousand oysters respectively were collected from the Cheval paar by dredging. (De Fonselm 1953). Inspections of the Banks were carried out in 1962, 1963, 1964 and 1965. (Balasuriya 1964 and Silva 1965 and 66). Since then inspections were not possible due to one of two reasons or both the non-availability of operational dredges and a suitable vessel for this type of work.The "Pesalai" a 235-ton stern trawler was made available by the Ceylon Fisheries Corporation management for the 1970 inspection. Two new 6-foot dredges turned out by the Government Factory were also available for this work. However, the survey was limited to 3 days-the period for which the vessel had been released. It was further limited to those areas of the banks over 6 fathoms in depth because of the risk in operating a large vessel in shallower depths.