Microcrystalline silicon is a two-phase material. Its composition can be interpreted as a series of grains of crystalline silicon imbedded in an amorphous silicon tissue, with a high concentration of dangling bonds in the transition regions. In this paper, results for the transport properties of a μc-Si:H p-i-n junction obtained by means of two-dimensional numerical simulation are reported. The role played by the boundary regions between the crystalline grains and the amorphous matrix is taken into account and these regions are treated similar to a heterojunction interface. The device is analyzed under AM1.5 illumination and the paper outlines the influence of the local electric field at the grain boundary transition regions on the internal electric configuration of the device and on the transport mechanism within the μc-Si:H intrinsic layer.

Microcrystalline silicon is a two-phase material. Its composition can be interpreted as grains of crystalline silicon imbedded in an amorphous silicon tissue, with a high concentration of danglind bonds in the transition regions. In this paper, results obtained by means of numerical simulations about the transport properties of a μc-Si:H p-i-n junction are reported. The role played by the boundary regions between the crystalline grains and the amorphous matrix is taken in account, and these regions are treated similarly to a heterojunction interface. The influence of the local electric field at the grains boundary transition regions on the internal electric configuration of the device is outlined under illumination and applied external bias. © 1999 Elsevier Science S.A. All rights reserved.

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Fuscoredoxin is a unique iron containing protein of yet unknown function originally discovered in the sulfate reducers of the genus Desulfovibrio. It contains two iron-sulfur clusters: a cubane [4Fe-4S] and a mixed oxo- and sulfide-bridged 4Fe cluster of unprecedented structure. The recent determination of the genomic sequence of Escherichia coli (E. coli) has revealed a homologue of fuscoredoxin in this facultative microbe. The presence of this gene in E. coli raises interesting questions regarding the function of fuscoredoxin and whether this gene represents a structural homologue of the better-characterized Desulfovibrio proteins. In order to explore the latter, an overexpression system for the E. coli fuscoredoxin gene was devised. The gene was cloned from genomic DNA by use of the polymerase chain reaction into the expression vector pT7-7 and overexpressed in E. coli BL21(DE3) cells. After two chromatographic steps a good yield of recombinant protein was obtained (approximately 4 mg of pure protein per liter of culture). The purified protein exhibits an optical spectrum characteristic of the homologue from D. desulfuricans, indicating that cofactor assembly was accomplished. Iron analysis indicated that the protein contains circa 8 iron atoms/molecule which were shown by EPR and Mossbauer spectroscopies to be present as two multinuclear clusters, albeit with slightly altered spectroscopic features. A comparison of the primary sequences of fuscoredoxins is presented and differences on cluster coordination modes are discussed on the light of the spectroscopic data. (C) 1999 Academic Press.

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An air-stable formate dehydrogenase (FDH), an enzyme that catalyzes the oxidation of formate to carbon dioxide, was purified from the sulfate reducing organism Desulfovibrio gigas (D. gigas) NCIB 9332. D. gigas FDH is a heterodimeric protein [alpha (92 kDa) and beta (29 kDa) subunits] and contains 7 +/- 1 Fe/protein and 0.9 +/- 0.1 W/protein, Selenium was not detected. The UV/visible absorption spectrum of D, gigas FDH is typical of an iron-sulfur protein. Analysis of pterin nucleotides yielded a content of 1.3 +/- 0.1 guanine monophosphate/mol of enzyme, which suggests a tungsten coordination with two molybdopterin guanine dinucleotide cofactors. Both Mossbauer spectroscopy performed on D. gigas FDH grown in a medium enriched with Fe-57 and EPR studies performed in the native and fully reduced state of the protein confirmed the presence of two [4Fe-4S] clusters. Variable-temperature EPR studies showed the presence of two signals compatible with an atom in a d(1) configuration albeit with an unusual relaxation behavior as compared to the one generally observed for W(V) ions.

The soluble methane monooxygenase system from Methylococcus capsulatus (Bath) catalyzes the oxidation of methane to methanol and water utilizing dioxygen at a non-heme, carboxylate-bridged diiron center housed in the hydroxylase (H) component. To probe the nature of the reductive activation of dioxygen in this system, reactions of an analogous molecule, nitric oxide, with the diiron(II) form of the enzyme (H-red) Were investigated by both continuous and discontinuous kinetics methodologies using optical, EPR, and Mossbauer spectroscopy. Reaction of NO with H-red affords a dinitrosyl species, designated H-dinitrosyl, with optical spectra (lambda(max) = 450 and 620 nm) and Mossbauer parameters (delta = 0.72 mm/s, Delta E-Q = 1.55 mm/s) similar to those of synthetic dinitrosyl analogues and of the dinitrosyl adduct of the reduced ribonucleotide reductase R2 (RNR-R2) protein. The H-dinitrosyl species models features of the H-peroxo intermediate formed in the analogous dioxygen reaction. In the presence of protein B, H-dinitrosyl builds up with approximately the same rate constant as H-peroxo (similar to 26 s(-1)) at 4 degrees C. In the absence of protein B, the kinetics of H-dinitrosyl formation were best fit with a biphasic A –> B –> C model, indicating the presence of an intermediate species between H-red and H-dinitrosyl. This result contrasts with the reaction of H-red with dioxygen, in which the H-peroxo intermediate forms in measurable quantities only in the presence of protein B. These findings suggest that protein B may alter the positioning but not the availability of coordination sites on iron for exogenous ligand binding and reactivity.

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We consider the Banach algebra \(\mathfrak{A}\) of singular integral operators with matrix piecewise continuous coefficients in the reflexive Orlicz space \(L_M^n(\Gamma)\). We assume that \(\Gamma\) belongs to a certain wide subclass of the class of Carleson curves; this subclass includes curves with cusps, as well as curves of the logarithmic spiral type. We obtain an index formula for an arbitrary operator from the algebra \(\mathfrak{A}\) in terms of the symbol of this operator.

The paper is devoted to some only recently uncovered phenomena emerging in the study of singular integral operators (SIO's) with piecewise continuous (PC) coefficients in reflexive rearrangement-invariant spaces over Carleson curves. We deal with several kinds of indices of submultiplicative functions which describe properties of spaces (Boyd and Zippin indices) and curves (spirality indices). We consider some ``disintegration condition{''} which combines properties of spaces and curves, the Boyd and spirality indices. We show that the essential spectrum of SIO associated with the Riemann boundary value problem with PC coefficient arises from the essential range of the coefficient by filling in certain massive connected sets (so-called logarithmic leaves) between the endpoints of jumps. These results combined with the Allan-Douglas local principle and with the two projections theorem enable us to study the Banach algebra \(\mathfrak{A}\) generated by SIO's with matrix-valued piecewise continuous coefficients. We construct a symbol calculus for this Banach algebra which provides a Fredholm criterion and gives a basis for an index formula for arbitrary SIO's from \(\mathfrak{A}\) in terms of their symbols.

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As a Norwegian sociologist pointed out recently at the Encontro Internacional de Vilamoura on Fishing, “the fisheries management is the management of people, not fish" This statement may surprise many specialists, but it puts once again a series of questions and problems in their true place: society, social relationships, individuals. It is necessary to adopt a new attitude, a new type of intervention, a new vision, which may mean “community management”, a system of co-management, new models of business organisation and consumer behaviour. Towards this end, sociology can and should contribute with its analytical instruments, with its set of scientific reflections and controversies, to the enrichment of the knowledge about a complex reality in profound change, such as that of the socio-economic fisheries system.

Most known teaching experiences focus on parallel computing courses only, but some teaching experiences on distributed computing courses have also been reported. In this paper we describe a course on Parallel and Distributed Processing that is taught at undergraduate level in the Computer Science degree of our University.This course presents an integrated approach concerning concurrency, parallelism, and distribution issues. It’s a breadth-first course addressing a wide spectrum of abstractions: the theoretical component focus on the fundamental abstractions to model concurrent systems, including process cooperation schemes, concurrent programming models, data and control distribution, concurrency control and recovery in transactional systems, and parallel processing models; the practical component illustrates the design and implementation issues involved in selected topics such as a data and control distribution problem, a distributed transaction-based support system and a parallel algorithm.We also discuss how this approach has been contributing to prepare the student to further actions regarding research and development of concurrent, distributed, or parallel systems.

The electrochemical behavior of the species [Co(eta(5)-C5H5)(eta(3)-2-MeC3H4)I] and [Co(eta(5)-C5H5)(eta(3)-2-MeC3H4)(ACN)](+) in ACN solutions, at 25 degrees C, is described. The kinetic analysis of the cyclic voltammetry curves indicates that the introduction of one electron in the former complex is concerted with the dissociation of the Co-I bond. The ensuing radical undergoes fast solvation to yield the solvato complex [Co(eta(5)-C5H5)(eta(3)-2-MeC3H4)(ACN)](.), which then acts as an efficient electron donor toward the starting material with the formation of[Co(eta(5)-C5H5)(eta(3)-2-MeC3H4)(ACN)](+); finally, the cation is electroreduced at the working potentials to conclude an overall autocatalytic sequence. The solvato complex [Co(eta(5)-C5H5)(eta(3)-2-MeC3H4)(ACN)](.), formed as a product of the above reduction process, can be reversibly reduced to the corresponding anion at more negative potentials. Confirmation of the above mechanism and of the fact that the solvato complex can act as a solution electron donor toward the starting material was obtained by studying the electrochemical behavior of the solvato complex itself and through calculations aimed to better define the dissociative electron-transfer process to [Co(eta(5)-C5H5)(eta(3)-2-MeC3H4)I]. The dissociation of the metal-halide bond in the neutral complex [Co(eta(5)-C5H5)(eta(3)-2-MeC3H4)I], with the formation of[Co(eta(5)-C5H5)(eta(3)-2-MeC3H4)(ACN)](+), was also found to occur spontaneously, in the bulk, through the observation of a progressive change of the cyclic voltammetric pattern. Support for the occurrence of the reaction between the starting complex and the solvent was confirmed by conductivity and spectroscopic measurements, which allowed the rate constant for the homogeneous solvolysis to be determined.

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