Plasma etch-induced conduction changes in gallium nitride

The effect of plasma-etching damage on carrier transport properties in GaN has been studied under various plasma conditions by monitoring the changes in sheet resistivity (ρ _s) and mobility (μ _s) or the resistivity (R). All the etching experiments were performed in an electron cyclotron resonance microwave plasma reactive ion etching (ECR-RIE) system. Consistent changes in the transport properties have been observed with increasing dc bias (ion energy) in all plasmas except in those containing chlorine. With noble gas plasmas, the largest change in conductance was created when Ar, the heaviest ion, was accelerated to its highest voltage. In these Ar sputtering cases, substantial surface micro-roughening has been observed. These surfaces also display considerable nitrogen deficiency as measured by Auger electron spectroscopy. These observations suggest that preferential sputtering of nitrogen from the surface of GaN is one form of ion damage. The other is displacement damage. Both of these forms of ion damage are considered to be the direct cause of the observed changes in the electrical properties.     

Polybrominated diphenyl ethers in birds of prey from Northern China

Birds of prey from Northern China (Beijing area) were examined for polybrominated diphenyl ethers (PBDEs). A total of 47 specimens from eight different species were analyzed. Muscle and liver were analyzed separately for each bird. Kidneys were pooled by species. Common kestrels exhibited the highest PBDE levels (mean muscle and liver concentrations of 12300 and 12200 ng/g lipid weight, respectively), with maxima in an individual bird of 31700 in muscle and 40900 ng/g lw in liver. Congener profiles differed between some species, but were generally dominated by the more brominated congeners (e.g., BDE-153, -209, -183, -207). BDE-209 was especially elevated compared to other published reports. Interspecies differences in congener concentrations and profiles may be due to diet, behavior, or biotransformation capacities. BDE-209 was detected in 79.4% of the samples. Common kestrels contained the highest BDE-209 levels (mean/maxima of 2150/6220 in muscle and 2870/12200 ng/g lw in liver). BDE-209 was the dominant congener in tissues from some buzzards, scops owls, and long-eared owls. It was the second most abundant congener in common kestrels. The remarkable levels and dominance of BDE-209 may relate to significant production, usage, or disposal of deca-containing products in China. These observations reinforce the growing view that organisms using terrestrial food chains may have greater exposure to BDE-209.     

Persistent halogenated hydrocarbons in consumer fish of China: regional and global implications for human exposure

Concentrations of persistent halogenated hydrocarbons (PHHs) were determined in 13 consumer fish species (a total of 390 individuals) collected from a major fish-farming region of China. The potential health risks of PHHs associated with consumption of fish from China was also systematically assessed regionally and globally. In all fish samples, DDTs, HCHs, PCBs, and PBDEs were the predominant PHH residues, with the median levels (ranges) being 6.0 (0.14-698.9), 0.50 (0.13-24.06), 0.10 (< 0.02-7.65), and 0.15 (< 0.0012-3.85) ng/g wet weight, respectively. The upper-bound (90th percentile) values of estimated daily intakes of DDT, HCHs, PCBs, and PBDEs via fish consumption were 45.5, 1.35, 0.46, and 0.30 ng/kg bw/d (urban), and 15.9, 0.47, 0.16, and 0.10 ng/kg bw/d (rural). Globally, the upper-bound outflows via fishery exportation of DDT, HCHs, PCBs, and PBDEs were 185, 5.51, 1.86, and 1.22 kg, respectively, in 2005. Japan was the largest recipient of PHHs, followed by Korea and the United States. Fish consumption assessments indicated that consumption of freshwater farmed and wild marine fish generally does not subject consumers to significant health risk as far as PHHs are concerned, while limited consumption of seawater farmed fish is advised.     

Development of a rapid method based on front face fluorescence spectroscopy for the monitoring of egg freshness: 1—evolution of thick and thin egg albumens

In this preliminary study, the intrinsic fluorescence of thick and thin egg albumens was evaluated as a possible rapid method for the monitoring of egg freshness. The fluorescence emission spectra of tryptophan residues (excitation: 290 nm; emission: 305–430 nm) of proteins and fluorescent Maillard reaction products (excitation: 360; emission: 380–580 nm) were recorded directly on thick and thin albumen samples within 2–3, 4, 5, 9, 10, 12, 16, 18, 23, 25 and 29 days of storage. Principal component analysis (PCA) and factorial discriminant analysis (FDA) were applied to the spectra data sets. Considering tryptophan fluorescence spectra recorded on thick egg albumen, correct classification was observed for 62.8 and 54.3% for the calibration and the validation sets, respectively. Better classification was obtained from thin egg albumen since 67.3 and 69.1% of samples were correctly classified. Considering fluorescent Maillard reaction products, the similarity map determined by the principal components (PCs) 1 and 2 showed a discrimination of eggs as a function of their storage time on both thick and thin albumens. The percentage of samples correctly classified into four groups by the FDA was 97.4 and 91.4% for the calibration and validation thick albumen samples, respectively. It was concluded that fluorescent Maillard reaction products could be considered as fingerprints that may allow the discrimination between fresh and aged eggs.     

Effect of Decarburization on the Residual Stresses Produced by Shot Peening in Automotive Leaf Springs

The shot peening is used in the leaf springs manufacturing process for producing a compressive residual stress field (CRSF) at and near the surface that improves the fatigue resistance. The resulting CRSF is influenced by the surface ferrite thickness associated with the decarburization. Hence, this work aims to extend the knowledge on the influence of the decarburization on the CRSF for the given shot peening conditions. A study on the laboratory scale was conducted for an SAE 5160 steel grade used in the automotive industry. Next, specimens with different decarburization depths were treated using industrial shot peening, and the resulting CRSF was characterized. The CRSF was found to be influenced by the decarburization depth. It is assumed that the elastic deformation mechanism is predominant at low decarburization depths, followed by a zone in which both the elastic and plastic deformation have competing mechanisms that contribute to the CRSF, and at higher decarburization depths, the dominant mechanism is plastic deformation. The values for σ_srs and σ_mcrs decrease as the decarburized depth increases, and suitable CRSFs were obtained below a decarburization depth of 120 µm in industrial leaves. Furthermore, the prediction based on expressions correlating the measured variables was good in these leaves.     

PU elastomers comprising spherical nanosilicas: Balancing rheology and properties

For polyurethane (PU) engineering elastomers, although urethane chemistry allows tailoring of elastomer properties, there is an inherent correlation between increasing strength and decreasing elongation-to-break. The ability to break this correlation provides great potential for creating high-performance materials that possess attractive combined properties. The incorporation of nanofillers is one of the promising approaches. However, while property enhancement is achieved, nanocomposite systems often experience significant increase in viscosity leading to process difficulty. In this paper, the use of nanospherical particles to mitigate the rheology was explored. We were able to achieve significant property enhancement in the ultimate mechanical properties and thermal stability while maintaining low viscosity during process. By first forming well dispersed nanosilica in polyol, followed by elastomer casting, material with significantly higher strength, elongation-to-break, thus, toughness, and degradation temperature than one without nanosilica was obtained. The performance improvement is attributed to the ability to form a low viscosity, stable nanofluid where the nanosilicas are present as primary nanoparticles in the polyol. The morphology of the formed elastomers was studied. It is hypothesized that nanoparticles reduce defects that contribute to premature failure of the elastomer, thus improving ultimate properties.     

Measured performance at 77 K of superconducting microstripresonators and filters

Results on three types of passive microwave devices fabricated and tested using epitaxial thin films of Tl₂CaBa₂Cu ₂O₈ grown on LaAlO₃ are reported. A microstrip ring resonator with unloaded Q of 2740 at 77 K and 33 GHz is described. A superconducting 4.6 GHz band-reject filter with unloaded Q greater than 15000 when operated at 77 K is reported. In addition, results on a multiple microstrip bandpass filter are presented     

Profile hidden Markov models

The recent literature on profile hidden Markov model (profile HMM) methods and software is reviewed. Profile HMMs turn a multiple sequence alignment into a position-specific scoring system suitable for searching databases for remotely homologous sequences. Profile HMM analyses complement standard pairwise comparison methods for large-scale sequence analysis. Several software implementations and two large libraries of profile HMMs of common protein domains are available. HMM methods performed comparably to threading methods in the CASP2 structure prediction exercise.