III-V nitrides for electronic and optoelectronic applications

Recent developments in III-V nitride thin-film materials for electronic and optoelectronic applications are reviewed. The problems that are limiting the development of these materials and devices made from them are discussed. The properties of cubic boron nitride, aluminum nitride, gallium nitride, AlN/GaN solid solutions and heterostructures, and indium nitride are discussed. It is pointed out that the lack of a suitable substrate, with the possible exception of SiC for AlN, is a problem of considerable magnitude. This is compounded by the presence of shallow donor bands in GaN and InN which are apparently caused by N vacancies. The question of whether these vacancies occur (if they do) as a result of intrinsic or extrinsic (as a result of deposition) nonstoichiometry has not been answered. However, the recent advances in the fabrication of p-type GaN and a p-n junction light emitting diode via the electron beam stimulation of the Mg dopant are very encouraging and may considerably advance the technology of this material. This would indicate that self-compensation effects, similar to those observed in ZnO and ZnSe, may not be present in the III-V nitrides, since cubic BN (cBN) AlN and now GaN have been reportedly doped both n- and p-type     

Segmented force plate (SFP) software package for clinical use

A gait analysis system is described. It is designed for clinical use as well as research purposes. The system is simple to operate and can be used by non-computer specialist. The design philosophy is straightforward and allows for easy adaptation to other systems. Samples of the output are presented.     

Empirical assessment of a threshold model for sylvatic plague.

Plague surveillance programmes established in Kazakhstan, Central Asia, during the previous century, have generated large plague archives that have been used to parameterize an abundance threshold model for sylvatic plague in great gerbil (Rhombomys opimus) populations. Here, we assess the model using additional data from the same archives. Throughout the focus, population levels above the threshold were a necessary condition for an epizootic to occur. However, there were large numbers of occasions when an epizootic was not observed even though great gerbils were, and had been, abundant. We examine six hypotheses that could explain the resulting false positive predictions, namely (i) including end-of-outbreak data erroneously lowers the estimated threshold, (ii) too few gerbils were tested, (iii) plague becomes locally extinct, (iv) the abundance of fleas was too low, (v) the climate was unfavourable, and (vi) a high proportion of gerbils were resistant. Of these, separate thresholds, fleas and climate received some support but accounted for few false positives and can be disregarded as serious omissions from the model. Small sample size and local extinction received strong support and can account for most of the false positives. Host resistance received no support here but should be subject to more direct experimental testing.     

Anion Sensing Porphyrin Functionalized Nanoparticles

Disulfide and dithiocarbamate functionalized porphyrins have been synthesized and used as protecting ligands for gold nanoparticle formation either via ligand substitution reactions or by direct synthesis. These nanoparticles have been shown to recognize anions via changes in the absorbance spectrum of the surface adsorbed porphyrin moieties. Association constants, derived from quantitative titrations, indicate a remarkable surface enhancement effect where the surface bound porphyrins bind anions much more strongly than the free receptor in solution.     

Perils of Using Hurricane Katrina to Teach Engineering Ethics

Katrina is a case the complexity of which makes it hard to use. It is also a case unlikely to repay the trouble of using it. According to IPET's current understanding of what happened, probably the final word, the engineering decision-making was probably too diffuse to make an interesting ethics case.     

Prophylactic effects of recombinant human superoxide dismutase in neonatal lung injury

To determine if recombinant human Cu-Zn superoxide dismutase (rhSOD) would prevent acute lung injury caused by hyperoxia and barotrauma, 26 newborn piglets were studied. Ten piglets were hyperventilated (arterial PCO2 15-20 Torr) with 100% O2 for 48 h. A second group received identical treatment for 4 h (n = 2) or 48 h (n = 8) but was given 5 mg/kg of rhSOD intratracheally at time 0. Six piglets were normally ventilated (arterial PCO2 40-45 Torr) for 48 h with 21% O2. Pulmonary function and tracheal aspirates were examined at time 0 and at 24 and 48 h, and bronchoalveolar lavage was performed at 48 h. In piglets treated with hyperoxia and hyperventilation, lung compliance decreased 42%, and tracheal aspirates showed an increase in neutrophil chemotactic activity (32%), total cell counts (135%), elastase activity (93%), and albumin concentration (339%) over 48 h (P < 0.05). All variables were significantly lower in rhSOD-treated piglets and comparable to normoxic control values. Surfactant remained active in all groups. Immunohistochemistry demonstrated that at 48 h significant rhSOD was distributed homogeneously in terminal airways. Adding rhSOD to tracheal aspirates of hyperoxic hyperventilated piglets did not alter neutrophil chemotaxis, suggesting that rhSOD protected the lung by reducing the production of chemotactic mediators. Results indicate that acute lung injury caused by 48 h of hyperoxia and hyperventilation is significantly ameliorated by prophylactic intratracheal administration of rhSOD.     

Design, synthesis, and characterization of a photoactivatable flavocytochrome molecular maquette

We report the construction of a synthetic flavo-heme protein that incorporates two major physiological activities of flavoproteins: light activation of flavin analogous to DNA photolyase and rapid intramolecular electron transfer between the flavin and heme cofactors as in several oxidoreductases. The functional tetra-alpha-helix protein comprises two 62-aa helix-loop-helix subunits. Each subunit contains a single cysteine to which flavin (7-acetyl-10-methylisoalloxazine) is covalently attached and two histidines appropriately positioned for bis-his coordination of heme cofactors. Both flavins and hemes are situated within the hydrophobic core of the protein. Intramolecular electron transfer from flavosemiquinone generated by photoreduction from a sacrificial electron donor in solution was examined between protoporphyrin IX and 1-methyl-2-oxomesoheme XIII. Laser pulse-activated electron transfer from flavin to meso heme occurs on a 100-ns time scale, with a favorable free energy of approximately -100 meV. Electron transfer from flavin to the lower potential protoporphyrin IX, with an unfavorable free energy, can be induced after a lag phase under continuous light illumination. Thus, the supporting peptide matrix provides an excellent framework for the positioning of closely juxtaposed redox groups capable of facilitating intramolecular electron transfer and begins to clarify in a simplified and malleable system the natural engineering of flavoproteins.     

An autoantibody to C1-inhibitor recognizes the reactive center of the inhibitor

Immunohistochemistry was applied to AMeX-fixed sections of twelve cases of gastric carcinoma obtained at surgical resection to explore the occurrence and distribution of fibrin deposits in situ. Fibrinogen was distributed in abundance throughout perivascular zones and in the connective tissue of the tumor stroma. Fibrin II (des-fibrinopeptide B-type fibrin) was easily identified in a direct apposition to the surface membranes of viable carcinoma cells, predominantly at the host-tumor interface and in the regions immediately adjacent to the zones of angiogenesis. Further studies are required to identify the triggers of the coagulation reactions as well as fibrinolytic system components in the gastric cancer tissue.