The generation of point defects in GaAs by electron-hole recombination at dislocations

The degradation of GaAs heterojunction lasers results in the formation of long dislocation dipoles which grow by a climb process involving point defect concentrations of the order of 10¹⁹ cm⁻³. The driving force for this climb process is not understood and it has been suggested that the material contains a supersaturation of native interstitials which condense on the dislocation during device operation. An alternative model proposed that the driving force is related to the energy released by electron-hole recombination on the dislocation which is partially dissipated by the dislocation emitting vacancies into the surrounding lattice.Gallium arsenide substrates containing greater than 2 × 10¹⁸ tellurium atoms cm⁻³ contain interstitial concentrations of the order of 10¹⁷ cm⁻³ which condense out to form small dislocation loops during an anneal at 880°C. The presence of these loops indicates that the annealed material does not contain excess interstitials in solution. This annealed material was optically pumped and examined by transmission electron microscopy. It was found that the loops developed into dipoles typical of degraded lasers. The number of point defects involved in this climb process increased with increasing pumping power and time. These results are discussed in terms of the two mechanisms listed above and it is concluded that the energy released by electron-hole recombination at the dislocation provides the driving force for the climb process.     

Microwave Backscatter Dependence on Surface Roughness, Soil Moisture, And Soil Texture: Part III-Soil Tension

Results are presented of an experimental program to determine the impact of soil texture on radar response to soil moisture present within nonvegetated soil surfaces. These findings extend previous reports which document the experimental relationship between the radar backscattering coefficient ?° and soil moisture for bare soil [1] and soil under crop canopies [2]. In confirmation of previous results [1] and [2], the sensitivity of ?° to surface gravimetric or volumetric soil moisture is shown to be inversely related to clay content of the soil. As a result, gravimetric or volumetric moisture indicators exhibit poor performance in moisture estimation algorithms for complex multitextured soils. However, estimation algorithms incorporating some knowledge of soil water retention as a function of soil matric potential, or tension, display strong correlation with radar response, typically r ? 0.8, and are shown to be relatively independent of soil texture. These findings are shown to be consistent with soil dielectric properties [3]-[5].     

Altered metabolism of the methionine methyl group in the leukocytes of patients with schizophrenia

Previous work has indicated that abnormal methylation processes may be associated with schizophrenia. In this study, leukocytes from patients with schizophrenia were incubated with methyl-14C-L-methionine and the evolved 14CO2 measured. With increasing concentration of methionine, the evolved 14CO2 was lower in the patients than in normal control subjects. The incorporation of 14C into protein was the same in both groups, and when carboxyl-14C-L-methionine was used the evolved 14CO2 was the same in both groups, thus excluding the possibility that altered incorporation into protein or oxidation of the methionine molecule as a whole were responsible. The observed differences in methionine-methyl metabolism suggest that an abnormality in transmethylation processes or in oxidation of the methyl group to CO2 is associated with schizophrenia. That this occurs in a peripheral tissue indicates that the abnormality is not restricted to the central nervous system.     

Central and peripheral influences on retention of postural asymmetry in rats.

Four studies with 94 Long-Evans rats examined potential neural processes involved in retention of a peripherally induced postural asymmetry. In Exp I, dorsal and ventral spinal root section following varying intervals of stimulation successfully abolished peripherally induced hindlimb asymmetry. Exp II revealed that 50 min of ventral root stimulation, in the absence of central connection, was not effective in producing asymmetry persistence. Exp III attempted to more closely delineate the time parameters involved in peripherally induced asymmetry retention. Asymmetry was found to consistently outlast a spinal transection if 40 min of stimulation was given. In Exp IV, possible modulatory higher brain center influences on the retention processes were demonstrated. Asymmetry persistence was consistently observed in Ss that received 10, 20, 30, 40, or 50 min of hindlimb stimulation if 50 min were allowed to elapse between the onset of stimulation and spinal section. Results (1) suggest an active involvement of spinal reflex centers in the fixation process, (2) indicate that the manner in which reflex activity is altered is not crucial as long as underlying time parameters are adhered to, and (3) demonstrate that higher center influences can modulate retention of a postural asymmetry in a complex manner. (14 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Immunological regulation of Angiostrongylus cantonensis infections in rats: modulation of population density and enhanced parasite growth following one or two superimposed infections

Rats acquired a degree of protective immunity to reinfection with Angiostrongylus cantonensis after a single infection with 50 infective larvae. Infected rats resisted the establishment of most challenging larvae and protective immunity increased with subsequent reinfections. Part of the primary infection was lost after a superimposed second and also following a superimposed third infection, but the total size of the concurrent adult worm populations remained the same as that from a primary infection. Worms surviving from the primary infection showed enhanced growth after each reinfection but their fecundity was impaired.     

A simple method for high yield fabrication of sharp silicon tips

A simple, high yield, method for the fabrication of sharp silicon tips is described. A triangular etch mask design is used to ensure that the tip forms with a single point. An anisotropic wet etch gives rise to a tip that continues to “self-sharpen” after the etch mask is released. The tip geometry comprises three converging {1 1 3} planes towards the apex with {3 1 3} planes forming at the base. The apex of each tip typically has a radius of curvature of <5 nm, which can be reduced to <2 nm by a subsequent oxide sharpening process. Tips of this kind have been successfully integrated into the fabrication of atomic force microscopy probes.     

Plant-derived polyphenols attenuate lipopolysaccharide-induced nitric oxide and tumour necrosis factor production in murine microglia and macrophages

Lipopolysaccharides released during bacterial infections induce the expression of pro-inflammatory cytokines and lead to complications such as neuronal damage in the CNS and septic shock in the periphery. While the initial infection is treated by antibiotics, anti-inflammatory agents would be advantageous add-on medications. In order to identify such compounds, we have compared 29 commercially available polyphenol-containing plant extracts and pure compounds for their ability to prevent LPS-induced up-regulation of NO production. Among the botanical extracts, bearberry and grape seed were the most active preparations, exhibiting IC(50) values of around 20 mug/mL. Among the pure compounds, IC(50) values for apigenin, diosmetin and silybin were 15, 19 and 12 muM, in N-11 murine microglia, and 7, 16 and 25 muM, in RAW 264.7 murine macrophages, respectively. In addition, these flavonoids were also able to down-regulate LPS-induced tumour necrosis factor production. Structure-activity relationships of the flavonoids demonstrated three distinct principles: (i) flavonoid-aglycons are more potent than the corresponding glycosides, (ii) flavonoids with a 4'-OH substitution in the B-ring are more potent than those with a 3'-OH-4'-methoxy substitution, (iii) flavonoids of the flavone type (with a C2=C3 double bond) are more potent than those of the flavanone type (with a at C2-C3 single bond).     

Polyphenol and vitamin C contents in European commercial blackcurrant juice products

Vitamin C and polyphenol contents (anthocyanins, proanthocyanidins, phenolic acids and flavonols) were analysed in commercial blackcurrant juice products purchased from various European countries (Finland, Poland, Germany, United Kingdom) using HPLC methods. The aim was to study variation between countries, as well as evaluate the intake of polyphenols from commercial juices. There was significant variation in the contents of polyphenols and vitamin C between countries. Expressed as the ready-to-drink beverages, German, Polish, Finnish and British products averaged anthocyanin contents of 38, 32, 12 and 7.5 mg/2.5 dl, proanthocyanidin contents of 27, 24, 10 and 1.2 mg/2.5 dl, flavonol contents of 16, 15, 5.2 & 1.9 mg/2.5 dl and phenolic acid contents of 12, 8.9, 3.7 and 1.5 mg/2.5 dl, respectively. The mean vitamin C content was highest in British (70 mg/2.5 dl) and lowest in Finnish products (15 mg/2.5 dl). The intake of polyphenols from German and Polish ready-to-drink beverages was clearly higher than that from Finnish, and especially, British beverages.     

Channel microband electrode arrays for mechanistic electrochemistry. Two-dimensional voltammetry: transport-limited currents

A channel electrode array, with electrodes ranging in size from the millimeter to the submicrometer scale, is used for the amperometric interrogation of mechanistically complex electrode processes. In this way, the transport-limited current, measured as a function of both electrode size and electrolyte flow rate (convection), is shown to provide a highly sensitive probe of mechanism and kinetics. The application of "two-dimensional voltammetry" to diverse electrode processes, including E, ECE, ECEE, EC', and DISP2 reactions, is reported.