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The transition probabilities of Kα hypersatellite lines and energy shifts with respect to the corresponding diagram lines are computed using the Dirac–Fock model for several values of atomic number Z throughout the periodic table. The influence of the Breit interaction on the Kα₁^h/Kα₂^h line intensity ratio, Kα₁^h and Kα₂^h line energy shifts and Kα₁^h to Kα₂^h line energy splitting is evaluated. Double-K shell hole threshold values for selected elements with 23 ⩽Z⩽ 30, calculated within the same approach, are compared with available experimental results.

The transition probabilities of K&alpha; hypersatellite lines and energy shifts with respect to the corresponding diagram lines are computed using the Dirac&ndash;Fock model for several values of atomic number <I>Z</I> throughout the periodic table. The influence of the Breit interaction on the K&alpha;<SUB>1</SUB><SUP>h</SUP>/K&alpha;<SUB>2</SUB><SUP>h</SUP> line intensity ratio, K&alpha;<SUB>1</SUB><SUP>h</SUP> and K&alpha;<SUB>2</SUB><SUP>h</SUP> line energy shifts and K&alpha;<SUB>1</SUB><SUP>h</SUP> to K&alpha;<SUB>2</SUB><SUP>h</SUP> line energy splitting is evaluated. Double-K shell hole threshold values for selected elements with 23 &les;<I>Z</I>&les; 30, calculated within the same approach, are compared with available experimental results.

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This paper aims to discuss the effect of order and disorder on the electrical performances of covalent silicon semiconductors and ZnO based ionic oxide semiconductors used as active channel layers in thin film transistors. The effect of disorder on covalent semiconductors directly affects their electrical transport properties due to the asymmetric behaviour of sp states, while in ionic oxide semiconductors it is found that this effect is small due to the fact that angular disorder has no effect on the spherical symmetry of s states. To this we must add that the mobility of carriers in both systems is quite different, being also affected by electron-phonon interactions (weak in silicon and strong in ionic oxides leading to formation of polarons). Besides, the impurity doping effect and the presence of vacancies in disordered silicon and in ionic oxides behave differently, which will influence the thin film properties and so, the performances of the devices produced. © 2007 Springer-Verlag.

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The role of order and disorder on the electronic performances of n -type ionic oxides such as zinc oxide, gallium zinc oxide, and indium zinc oxide used as active (channel) or passive (drain/source) layers in thin film transistors (TFTs) processed at room temperature are discussed, taking as reference the known behavior observed in conventional covalent semiconductors such as silicon. The work performed shows that while in the oxide semiconductors the Fermi level can be pinned up within the conduction band, independent of the state of order, the same does not happen with silicon. Besides, in the oxide semiconductors the carrier mobility is not bandtail limited and so disorder does not affect so strongly the mobility as it happens in covalent semiconductors. The electrical properties of the oxide films (resistivity, carrier concentration, and mobility) are highly dependent on the oxygen vacancies (source of free carriers), which can be controlled by changing the oxygen partial pressure during the deposition process and/or by adding other metal ions to the matrix. In this case, we make the oxide matrix less sensitive to the presence of oxygen, widening the range of oxygen partial pressures that can be used and thus improving the process control of the film resistivity. The results obtained in fully transparent TFT using polycrystalline ZnO or amorphous indium zinc oxide (IZO) as channel layers and highly conductive poly/nanocrystalline ZGO films or amorphous IZO as drain/source layers show that both devices work in the enhancement mode, but the TFT with the highest electronic saturation mobility and on/off ratio 49.9 cm2 V s and 4.3× 108, respectively, are the ones in which the active and passive layers are amorphous. The ZnO TFT whose channel is based on polycrystalline ZnO, the mobility and on/off ratio are, respectively, 26 cm2 V s and 3× 106. This behavior is attributed to the fact that the electronic transport is governed by the s -like metal cation conduction bands, not significantly affected by any type of angular disorder promoted by the 2p O states related to the valence band, or small amounts of incorporated metal impurities that lead to a better control of vacancies and of the TFT off current. © 2007 American Institute of Physics.

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Cross-linked polyethylene (XLPE) is currently widely used as an insulating material for power cables due to its good physical properties, however when in use it undergoes an electrical ageing process. Its ability to trap electric charge can give rise to space charge accumulation in the bulk of the polymer and produce localised electric stresses that can lead to cable failure, since the electric field will be increased above the design stress in some regions favouring the initiation of degradation there. In this work the PEA (pulsed electro-acoustic) method was used to compare the charge dynamics in three samples (XLPE cable peelings) aged in different ways (electrothermally in the laboratory, field aged in service and thermally aged in the laboratory). Very different transient behavior was found depending upon the ageing history. This is related to differences in the migration of chemical species in the insulation layer, which are known to act as charge traps. All materials showed heterocharge peaks when the space charge reached stability, the magnitude of which seems to be related to the severity of the ageing. (c) 2007 Elsevier B.V. All rights reserved.

Cross-linked polyethylene (XLPE) is currently widely used as an insulating material for power cables due to its good physical properties, however when in use it undergoes an electrical ageing process. Its ability to trap electric charge can give rise to space charge accumulation in the bulk of the polymer and produce localised electric stresses that can lead to cable failure, since the electric field will be increased above the design stress in some regions favouring the initiation of degradation there. In this work the PEA (pulsed electro-acoustic) method was used to compare the charge dynamics in three samples (XLPE cable peelings) aged in different ways (electrothermally in the laboratory, field aged in service and thermally aged in the laboratory). Very different transient behavior was found depending upon the ageing history. This is related to differences in the migration of chemical species in the insulation layer, which are known to act as charge traps. All materials showed heterocharge peaks when the space charge reached stability, the magnitude of which seems to be related to the severity of the ageing.

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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).

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In this work (Al,Ti) and (Al,Ti,N) films with composition gradient in depth starting either with pure Al or pure Ti were deposited on Si, glass and Au at room temperature in a DC magnetron discharge without bias. The plasma parameters, for both custom made cathodes, were determined and the process was real-time controlled to obtain in the plasma the necessary deposition changes in relative metal abundances to get the desired depth profile composition on the films. In this work the process was designed to get a constant gradient for the composition depth profile. The morphology of the films was analysed by SEM while the composition gradients were measured by SIMS, XPS and RBS, confirming preset nominal depth composition profile of the films. To obtain (Al,Ti,N) thin films with gradient depth composition, N2 must be supplied to the discharges. The plasma behaviour is modified in the presence of N2 and the influence on the film characteristics is studied using the same techniques referred above. The (Al,Ti) and (Al,Ti,N) film properties are compared. We succeed in validating the coating technique opening new application possibilities.

A requirement of many surface science studies is the capability to alter a sample temperature in a controlled mode. Sample preparation procedures such as heating or cooling ramps, high temperature spikes, fast annealing, or simply maintaining a sample at a very high, or very low, temperature are common. To address these issues, we describe the design and the construction of a multipurpose sample holder. Key points of this design are operation in an extended temperature range from liquid nitrogen (LN(2)) temperature to approximately 1300 K, temperature control during heating and cooling, low thermal inertia with rates up to 50 K s(-1) (heating) and -20 K s(-1) (cooling), and small heated volume to minimize background problems in thermal desorption spectroscopy (TDS) spectra. With this design the sample can be flash heated from LN(2) temperature to 1300 K and cooled down again in less than 100 s. This sample holder was mounted and tested in a multitechnique apparatus and adds a large number of sample preparation procedures as well as TDS to the list of already available surface analysis techniques.

To achieve highly accurate controlled depositions a specially designed vapour source, for metals with low to medium melting temperature, was developed. A quartz crystal microbalance is fitted inside the evaporation chamber to provide real-time rate and thickness monitoring. A carefully planned geometry allows maintaining a small deposition area centred on the sample without compromising flow rate measurements. Dosing rates as low as 0.02 ML/min are easily achieved, therefore providing true sub-monolayer control. This source was tested and calibrated for Ag and is being successfully used to study the growth of Ag clusters on TiO2.

We report the 98% assignment of the apo-form of an orange protein, containing a novel Mo-Cu cluster isolated from Desulfovibrio gigas. This protein presents a region where backbone amide protons exchange fast with bulk solvent becoming undetectable. These residues were assigned using C-13-detection experiments.

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If indicators of international competitivity of the Portuguese industry reveal very strong weaknesses in the field of education and vocational training, the achievement of a solution is not based only (and should not!) in a decisive increase of investment and support in the education and training system. It seem not logical to think in that way, once normally when one tries to solve a problem that is done in the context of that same problem. Eventually there are other strategies. Which are, then, the fields where is necessary to orient the investiment to improve an industrial competitivity? To try to answer this question, we analise one of the sectors that have contributed the most for an improvement of the Portuguese economical performance, and for a true innovative process as in terms of industrial product, or in terms of manufacturing and distribution processes. Is the automotive sector where that happens, taken in its two most important sub-sectors: the one of automobile manufacturing and assembly, and the one of components manufacturing.

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No abstract is available for this item.