Photoconductivity null apparatus for the determination of minority carrier lifetime

A variable time constant exponential pulse generator used to null exponential photoconductivity decay signals is described. Circuitry using this generator for the direct readout of minority carrier lifetime of semiconductors is also presented.     

Evidence that GABA transmission mediates context-specific extinction of learned fear

Recent evidence has suggested that molecular chaperones participate in the conformational change between the normal cellular prion protein (PrPC) and its scrapie isoform (PrPSc). To study a role of PrPC in the regulation of expression of heat shock proteins (HSPs), a group of molecular chaperones, heat-induced expression of major HSPs (HSP105, HSP90alpha, HSP72, HSC70, HSP60, and HSP25) was investigated in cultured skin fibroblasts isolated from the mice homogeneous for a disrupted PrP gene (PrP-/- mice) by Western blot analysis and immunocytochemistry. Two lines of fibroblasts were established and designated SFK derived from the PrP-/- mice and SFH derived from the PrP+/+ mice, respectively. In both SFK and SFH cells, HSP105, HSP72, and HSP25 were expressed at low levels under unstressed conditions but they were induced markedly following exposure to heat stress (43 degreesC/20 min) at 3-72 h postrecovery. In both cell types, HSC70 and HSP60 were expressed at high levels under unstressed conditions and their levels remained unchanged after heat shock treatment. HSP90alpha was undetectable in both cell types under any conditions examined. The pattern of expression, induction, and subcellular location of HSP105, HSP72, HSC70, HSP60, and HSP25 was not significantly different between SFK and SFH cells under unstressed and heat-stressed conditions. Furthermore, the levels of constitutive expression of HSP105, HSC70, HSP60, and HSP25 were similar between the brain tissues isolated from the PrP-/- and PrP+/+ mice. These results indicate that HSP induction is not affected by either the existence or the absence of PrPC in the cells.     

Shock tube studies of methyl butanoate pyrolysis with relevance to biodiesel

Methyl butanoate pyrolysis and decomposition pathways were studied in detail by measuring concentration time-histories of CO, CO₂, CH₃, and C₂H₄ using shock tube/laser absorption methods. Experiments were conducted behind reflected shock waves at temperatures of 1200–1800 K and pressures near 1.5 atm using mixtures of 0.1%, 0.5%, and 1% methyl butanoate in Argon. A novel laser diagnostic was developed to measure CO in the ν₁ fundamental vibrational band near 4.56 μm using a new generation of quantum-cascade lasers. Wavelength modulation spectroscopy with second-harmonic detection (WMS-2f) was used to measure CO₂ near 2752 nm. Methyl radical was measured using UV laser absorption near 216 nm, and ethylene was monitored using IR gas laser absorption near 10.53 μm. An accurate methyl butanoate model is critical in the development of mechanisms for larger methyl esters, and the measured time-histories provide kinetic targets and strong constraints for the refinement of the methyl butanoate reaction mechanism. Measured CO mole fractions reach plateau values that are the same as the initial fuel mole fraction at temperatures higher than 1500 K over the maximum measurement time of 2 ms or less. Two recent kinetic mechanisms are compared with the measured data and the possible reasons for this 1:1 ratio between MB and CO are discussed. Based on these discussions, it is expected that similar CO/fuel and CO₂/fuel ratios for biodiesel molecules, particularly saturated components of biodiesel, should occur.     

Obesogenic Diet Cycling Produces Graded Effects on Cognition and Microbiota Composition in Rats

Scope

The effects of diet cycling on cognition and fecal microbiota are not well understood.

Method and Results

Adult male Sprague-Dawley rats were cycled between a high-fat, high-sugar “cafeteria” diet (Caf) and regular chow. The impairment in place recognition memory produced by 16 days of Caf diet was reduced by switching to chow for 11 but not 4 days. Next, rats received 16 days of Caf diet in 2, 4, 8, or 16-day cycles, each separated by 4-day chow cycles. Place recognition memory declined from baseline in all groups and was impaired in the 16- versus 2-day group. Finally, rats received 24 days of Caf diet continuously or in 3-day cycles separated by 2- or 4-day chow cycles. Any Caf diet access impaired cognition and increased adiposity relative to controls, without altering hippocampal gene expression. Place recognition and adiposity were the strongest predictors of global microbiota composition. Overall, diets with higher Caf > chow ratios produced greater spatial memory impairments and larger shifts in gut microbiota species richness and beta diversity.

Conclusion

Results suggest that diet-induced cognitive deficits worsen in proportion to unhealthy diet exposure, and that shifting to a healthy chow for at least a week is required for recovery under the conditions tested here.     

A high pressure shock tube study of n-propylbenzene oxidation and its comparison with n-butylbenzene

Ignition delay times have been measured for mixtures of n-propylbenzene in air (≈21% O₂, ≈79% N₂) at equivalence ratios of 0.29, 0.48, 0.96 and 1.92 and at reflected shock pressures of 1, 10 and 30 atm in a heated high-pressure shock tube over a wide temperature range (1000–1600 K). The effects of reflected shock pressure and of equivalence ratio on ignition delay time were determined and common trends highlighted. Simulations were carried out using the n-propylbenzene sub-mechanism contained in an n-butylbenzene reaction mechanism available in the literature. This kinetic model was improved by including pressure dependent reactions which were not in place previously and the addition of the NUI Galway C₀–C₄ sub-mechanism. These simulations showed very good agreement with the experimental data. Additionally a comparison is made with experimental data previously obtained and published for n-butylbenzene over the same range of conditions and common trends are highlighted.     

Effects of systemic, intracerebral, or intrathecal administration on an N-methyl-D-aspartate receptor antagonist on associative morphine analgesic tolerance and hyperalgesia in rats.

A flavor paired with morphine shifted to the right the function relating morphine dose to tail-flick latencies and provoked hyperalgesic responses when rats were tested in the absence of morphine. These learned increases in nociceptive sensitivity were not mediated by alterations in tail-skin temperature. Microinjection of the competitive N-methyl-D-aspartate (NMDA) receptor antagonist D,L-2-amino-5-phosphonopentanoic acid (AP-5) into the lateral ventricle reversed the hyperalgesic responses but spared the tolerance to morphine analgesia. By contrast, systemic administration of the noncompetitive NMDA receptor antagonist MK-801 or intrathecal infusion of AP-5 reversed the hyperalgesic responses as well as the tolerance to morphine analgesia. The results demonstrate that associatively mediated tolerance to morphine analgesia can co-occur with hyperalgesic responses and are discussed relative to learned activation of endogenous pronociceptive mechanisms. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dispersion of linewidth-broadening factor in 1.5 ?m laser diodes

Measurements which demonstrate the strong dependence of the linewidth-broadening factor ? on photon energy in 1.5 ?m lasers are reported, ? was found to vary between 3 and 11 over a 40 meV energy range. The consequences for the linewidth and transient wavelength chirping in 1.5 ?m DFB lasers, where the operating wavelength may be different from the peak gain wavelength, are examined.