Preliminary,space focused,reliability tests on European GaN HEMTs

ESA is investing significant efforts towards developing a European, space qualified, GaN supply chain for microwave components. Numerous R&D projects have been completed, or are ongoing, that focus on areas such as epitaxial growth, transistor electrical performance and reliability enhancement, e.g. in projects such as GREAT². In order to perform independent verification and validation, ESA has also begun to modernise and re-equip its microwave component laboratory to augment the well established materials and component test capabilities. This paper describes the laboratory capabilities and provides some preliminary results and lessons learned from performing high temperature storage, hydrogen poisoning and DC step stress tests on European sourced GaN samples.     

The non-linear viscoelastic behaviour of human hair at moderate extensions

We report the results of experiments carried out on the stress relaxation of slightly stretched human hair. The results show that human hair is viscoelastic, and that when quickly extended to a moderate degree (0.5-6.5%) and held, the force generated will fall to half its original value in about 15 h. However, the relaxation process is also dependent on extension, so that iso-chronous (constant time) data is non-Hookean. We show that the iso-chronous stress/strain behaviour departs from linearity at about 1% extension and the modulus progressively decreases thereafter according to a power-law relationship with strain.     

The metabolism and analysis of isoflavones and other dietary polyphenols in foods and biological systems

Polyphenols in dietary and botanical matrices are usually present as simple and complex O-glycosides. In fermented dietary materials, the glycosidic moiety is removed and accompanied in some cases by more complex changes to the polyphenol. As for most xenobiotics, polyphenols undergo phase II conjugation in the intestinal wall during their absorption from the gut. In contrast, a few polyphenols, such as puerarin in the kudzu vine, are C-glycosides and are stable in the gut and during absorption, distribution and excretion. Large bowel bacteria reduce polyphenol aglycones, causing opening of the heterocyclic B-ring and ring cleavage. The products are mostly absorbed and enter the bloodstream. Phase I and II metabolism events occur in the intestine and the liver - most polyphenols predominantly circulate as β-glucuronides and sulfate esters with very little as the aglycones, the presumed active forms. In addition, metabolism can occur in non-hepatic tissues and cells including breast tumor cells that have variable amounts of cytochrome P450s, sulfatase and sulfotransferase activities. Inflammatory cells produce chemical oxidants (HOCl, HOBr, ONO(2)(-)) that will react with polyphenols. The isoflavones daidzein and genistein and the flavonol quercetin form mono- and dichlorinated products in reaction with HOCl. Genistein is converted to 3'-nitrogenistein in the lung tissue of lipopolysaccharide-treated rats. Whereas polyphenols that can be converted to quinones or epoxides react with glutathione (GSH) to form adducts, chlorinated isoflavones do not react with GSH; instead, they are converted to β-glucuronides and are excreted in bile. Analysis of polyphenols and their metabolites is routinely carried out with great sensitivity, specificity and quantification by LC-tandem mass spectrometry. Critical questions about the absorption and tissue uptake of complex polyphenols such as the proanthocyanins can be answered by labeling these polyphenols with (14)C-sucrose in plant cell culture and then purifying them for use in animal experiments. The (14)C signature is quantified using accelerator mass spectrometry, a technique capable of detecting one (14)C atom in 10(15) carbon atoms. This permits the study of the penetration of the polyphenols into the interstitial fluid, the fluid that is actually in contact with non-vascular cells.     

Scientific quality of original research articles on environmental tobacco smoke

OBJECTIVE: To evaluate the scientific quality of original research articles on the health effects of environmental tobacco smoke; to determine whether poor article quality is associated with publication in non-peer-reviewed symposium proceedings or with other article characteristics. DESIGN: Cross sectional study of original research articles on the health effects of environmental tobacco smoke published in peer reviewed journals and non-peer-reviewed symposium proceedings from 1980 to 1994. Article quality was assessed by two independent reviewers who used a valid and reliable instrument, were unaware of study hypotheses, were blinded to identifying characteristics of articles, and had no disclosed conflicts of interest. PARTICIPANTS: All symposium articles (n = 68) and a random sample of peer reviewed journal articles (n = 68) that satisfied inclusion/exclusion criteria. MAIN OUTCOME MEASURE: Mean quality scores, which could range from 0 (lowest quality) to 1 (highest quality). RESULTS: Using multivariate regression analysis, symposium articles were of poorer scientific quality than peer reviewed journal articles when controlling simultaneously for the effects of study design, article conclusion, article topic, and source of funding acknowledged (P = 0.027). Article quality was not associated with either source of funding acknowledged or article conclusion in multivariate analyses. CONCLUSIONS: In published reports on environmental tobacco smoke, non-peer-reviewed symposium articles tend to be of poor quality. These articles should not be used in scientific, legal, or policy settings unless their quality has been independently assessed.


     

Untapped Knowledge about Water Reuse: the Roles of Direct and Indirect Educational Messaging

Water Resources Management - Public awareness of water quality concerns has increased since the Flint, MI crisis, but knowledge about water resources management remains low. Consequently,...     

The influence of grain size on the creep of uranium dioxide

The creep of uranium dioxide has been investigated as a function of grain size. At high stresses, when creep is controlled by dislocation movement, grain boundaries exert a strengthening effect and this strengthening is correlated with the Hall-Petch equation. The degree of strengthening diminishes with increases in temperature. At lower stresses, when creep is controlled by mass transport, grain boundaries exert a weakening effect owing to the reduction in diffusion path length as grain size is reduced. In this range behaviour is correlated with the Nabarro-Herring equation with stress replaced by an effective stress _E=–₀ where ₀ is a threshold stress for diffusional creep associated with the limitation of the ability of boundaries to emit and absorb vacancies. ₀ appears to decrease as grain size is increased.