Reactive oxygen species (ROS), when in excess, are among the most deleterious species an organism can deal with. The physiological effects of ROS include amino acid chain cleavage, DNA degradation and lipid oxidation, among others. They can be formed in the cytoplasm in a variety of ways, including autooxidation reactions (FMN- and FAD-containing enzymes) and Fenton reactions as a result of the cytoplasmatic pool of iron ions. The superoxide anion (021, despite its short half-life in solution, is particularly pernicious as it can form other reactive ROS (such as the strong oxidant peroxynitrite) or oxidize and/or reduce cellular components. For strict anaerobic or microaerophilic bacteria it is of particular importance to be able to dispose of ROS in a controlled manner, especially if these organisms are temporarily exposed to air. This review aims to describe the structural characteristics of superoxide reductases (SORs) and mechanistic aspects of biological superoxide anion reduction. SORs can be considered the main class of enzymes behind the oxygen detoxification pathway of anaerobic and microaerophilic bacteria. The geometry of the active site (three classes have been described), the possible electron donors in vivo and the current hypothesis for the catalytic mechanism will be discussed. Some phylogenetic considerations are presented, regarding the primary structure of SORs currently available in genome databases. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007).

Cobalt compounds of the general formula [COX2(alpha-diimine)], where X = Cl or I and the alpha-diimines are 1,4-diaryl-2,3-dimethyl-1,4-diaza-1,3-butadiene (Ar-DAB) and bis(aryl)acenaphthenequinonediimine (Ar-BIAN) were synthesized by the direct reaction of the anhydrous cobalt salts CoCl2 or CoI2 and the corresponding alpha-diinline ligand in dried CH2Cl2. The synthesized compounds are [Co(Ph-DAB)Cl-2] (1a), [Co(o,o',p-Me3C6H2-DAB)Cl-2] (1b), and [Co(o,o'iPr(2)C(6)H(3)-DAB)Cl-2] (1c) with the ligands Ar-DAB, and also [Co(o,o',p-Me3C6H2-BIAN)I-2] (2'b) with the ligand Ar-BIAN. The crystal structures of all the compounds were solved by single-crystal X-ray diffraction. In all cases the cobalt atom is in a distorted tetrahedron, which is built up of two halide atoms and two nitrogen atoms of the alpha-dimune ligand. X-band EPR measurements of polycrystalline samples performed on compounds 1b, 1c, and 2'b indicate a high-spin Col, ion (S = 3/2) in an axially distorted environment. Single-crystal EPR experiments on compounds 1b and 1c allowed us to evaluate the orientation of the g tensor in the molecular frame. (c) Wiley-VCH Verlag GmbH & Co.

The bacterial cytochroine c peroxidases contain an electron-transferring haem c (E) and a peroxidatic haem c (P). Many are isolated in an inactive oxidised state. Reduction of the E baem promotes Ca2+-dependent spin state and coordination changes at the P haem rendering it accessible to ligand. Recent crystallographic work on the oxidised and mixed valence enzymes has suggested a mechanism by which an electron entering the E haem remotely triggers this activation of the P haem. Binding of hydrogen peroxide at the activated P haem leads to an intermediate catalytic form containing two oxidising equivalents, one of which is a ferryl oxene. This form of the enzyme is then reduced by two single electron transfers to the E haem delivered by small redox proteins such as cytochromes or cupredoxins. The binding of these small redox proteins is dominated by global electrostatic forces but the interfaces of the electron transfer complexes that are formed are largely hydrophobic and relatively non-specific. These features allow very high electron transfer rates in the steady state. (c) 2006 Elsevier Inc. All rights reserved.

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Structural design relies essentially on tests made on cylinders of small size to estimate the probability of failure of prototype members, since full-scale testing of structures to determine their strength is not feasible. The confidence that such scale modeling deserves in terms of representation of actual behavior needs careful examination, due to such factors as material nonlinearities, difficulties of scale representation of particulate materials, and sometimes the impossibility of simultaneously satisfying independent dimensionless parameters. Some failures explained by linear fracture mechanics are associable with strong size effects, as opposed to the cases where small cracks are a material property. Besides research centered on these problems, a number of studies of scale effects have been associated with the increased probability of finding a flaw in larger objects. In fact, geometric similitude may coexist with microscopic randomness of flaws that cause size effects to appear. The type of material of the object under study may also be a decisive factor. For example, scatter of the mechanical properties in unidirectional fiber-reinforced polymers (FRPs) is much larger than in metals due to a larger density of flaws. Thus the strength of FRP laminates may depend on the volume of material involved. Strengthening reinforced concrete columns with FRP wraps leads to new constitutive laws for the overall response of the columns and requires small-scale testing followed by extrapolation for design use. The present paper focuses on the difficulties of this step, based on the experimental data obtained. The questions mentioned above are addressed, and the relevance of the adequate representation of the lateral stiffness of the FRP jacket in the scaled cylinders is emphasized. The paper also addresses the problem of testing confined cylinders with a given slenderness ratio H/D=height/diameter, within the range usually characteristic of short columns, and extrapolating the results for columns of different H/D. The importance of the parameter (thickness of jacket/diameter of column, representative of stiffness of jacket/stiffness of concrete core) is also examined. The influence of the parameter is shown to be relatively minor, whereas the nonscaling of the relative stiffness of the core and jacket would be a major cause of error. The experimental data, in terms of strain and strength, are also compared with numerical models proposed in the literature, and the quality of the approximations is analyzed.

This paper addresses the design and planning of supply chains with product return. A graph approach is used as the modelling methodology. Commonly, the application of graph approaches to the design of supply chains, considers nodes as chain entities and arcs as connections between them. These assumptions are extended in the present work where products may also be associated with both nodes and arcs. A multi-product network formulation is obtained which is further generalised to consider the modelling of time, resulting in a dynamic multi-product network model with product return. This generalisation assumes that any node is a transformation point which allows inbound and outbound products to differ. Considering four different kinds of entities (factories, warehouses, sorting centres and customers), proper functions are defined for each one: production, postponement, usage and selection. An example, base on a Portuguese industry case, is applied in order to corroborate the model applicability and adequacy to real world problems.

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The effect of rigid inclusions on the densification during isothermal sintering of glass matrix composites was investigated. Mixtures containing borosilicate glass powder and 0, 5, 10 and 25 vol. % alumina (Al 2O3) particles were prepared and powder compacts isostatically pressed at 200 MPa have been used. The sintering behaviour of the samples heated at 800°C during various times was investigated through density measurement, axial and radial shrinkage measurements. The microstructure was analysed by SEM and the crystalline phases present in the sintered composites were identified by XRD. The relative density of the isothermally treated borosilicate glass-Al2O3 composites decreased significantly with the increase in Al2O3 content because the presence of rigid inclusions retarded the densification of the compacts. The borosilicate glass exhibited anisotropic shrinkage behaviour, showing a radial shrinkage higher than the axial shrinkage and isotropic shrinkage was favoured by Al2O3 additions. Sintered glass showed a dense microstructure with some spherical closed pores. The microstructure of composites with 5 vol. % Al2O3 revealed that most of the pores were filled by capillary flow of the glass. The microstructure of composites with higher Al2O3 additions showed dense areas together with interconnected pores, which appeared at the sites of large glass particles in the green compacts.

Diphasic silicon films (nc-Si/a-Si:H) have been prepared by a new regime of plasma enhanced chemical vapour deposition in the region adjacent of phase transition from amorphous to microcrystalline state. Comparing to the conventional amorphous silicon (a-Si:H), the nc-Si/a-Si:H has higher photoconductivity (σph), better stability, and a broader light spectral response range in the longer wavelength range. It can be found from Raman spectra that there is a notable improvement in the medium range order. The blue shift for the stretching mode and red shift for the wagging mode in the IR spectra also show the variation of the microstructure. By using this kind of film as intrinsic layer, a p-i-n junction solar cell was prepared with the initial efficiency of 8.51% and a stabilized efficiency of 8.01% (AM1.5, 100 mw/cm2) at room temperature. © 2006.