Novel strained quantum well laser grown by MOVPE

Strained-layer broad-area lasers have been grown by MOVPE. The structures contain 3.5 nm-wide Ga/sub 0.3/In/sub 0.7/As quantum wells. They emit close to 1.5 mu m and have been made to lase under current injection. These structures were compared with similar lasers containing unstrained 7.0 nm-wide Ga/sub 0.47/In/sub 0.53/As quantum wells also emitting at 1.5 mu m. No improvement has been found in J/sub th/ (933 A cm/sup -2/) or T/sub 0/ (47 K) in the case of the strained structure, despite the expected band structure modification.<>     

Effects of a microinjection of morphine into the amygdala on the acquisition and expression of conditioned fear and hypoalgesia in rats.

A unilateral microinjection of morphine into the amygdala impaired the acquisition of fear and hypoalgesic responses in rats exposed to a heated floor in a hot-plate apparatus. This impairment was dose dependent, receptor specific, and not observed in rats microinjected with morphine into the caudal basolateral amygdala. A microinjection of morphine into the amygdala reduced the expression of fear responses and of naloxone-sensitive hypoalgesic responses, but did not reduce the expression of naloxone-insensitive hypoalgesic responses. The results document an involvement of opioidergic mechanisms in the amygdala in learned danger and of the amygdala in the control of opioid hypoalgesic responses. They also suggest that learned danger can activate antinociceptive mechanisms independently of the amygdala. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of benzodiazepine microinjection into the amygdala or periaqueductal gray on the expression of conditioned fear and hypoalgesia in rats.

Four experiments studied the effects of an intracranial microinjection of a benzodiazepine (midazolam) on the expression of conditioned fear (measured as passive avoidance) and conditioned hypoalgesia in rats. Unilateral microinjection of midazolam into the basolateral amygdala reduced both hypoalgesic and avoidance responses, whereas unilateral microinjection of midazolam into the ventrolateral region of the periaqueductal gray (vPAG) reduced the hypoalgesic response but not the avoidance response. The results are discussed in terms of gamma-aminobutyric acid–ergic inhibition of antinociceptive mechanisms in the vPAG and of the activation of these mechanisms by amygdala-based fear processes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Use of chemical kinetics to predict critical parameters of gaseous detonations

Computational modeling of chemical kinetics of fuel oxidation under conditions similar to those encountered in detonation waves is described. Sample applications to predicting critical detonation parameters are described, including lean and rich limits to detonation in linear tubes, direct initiation of unconfined spherical detonations by means of high explosive charges or by transition from a linear tube, and kinetic inhibition of detonation.     

An infusion of bupivacaine into the nucleus accumbens disrupts the acquisition but not the expression of contextual fear conditioning.

An infusion of the local anesthetic bupivacaine into the nucleus accumbens (Acb) impaired the acquisition but not the expression of fear responses (freezing) to a shocked context but spared both the acquisition and expression of these responses to an auditory conditioned stimulus (CS) paired with the shock. In contrast, an infusion of bupivacaine into the amygdala impaired the acquisition and the expression of fear responses to both the CS and the context. The results demonstrate a critical role for the Acb in the acquisition but not the expression of contextual fear conditioning and are consistent with the view that this structure is involved in the processes by which rats represent a context (Westbrook, Good, & Kiernan, 1997). (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Reinstatement of extinguished fear by β-adrenergic arousal elicited by a conditioned context.

Five experiments examined the reinstatement of fear (freezing) produced by recent reexposure to a dangerous context. Rats were trained to fear a conditioned stimulus (CS) and a distinctive context with shock. The CS was then extinguished. A 2-min interval between reexposure to the dangerous context and presentation of the extinguished CS in a different context reinstated freezing when the CS was tested the next day. Propranolol (a β-adrenergic antagonist) blocked reinstatement of extinguished fear without decreasing freezing to a nonextinguished CS. Administration of epinephrine (an adrenergic agonist) reinstated extinguished fear without reexposure to the dangerous context. The results suggest a role for β-adrenergic activity elicited by exposure to a conditioned context in the reinstatement of extinguished fear. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dynamic post dispersion optimization at 40 Gb/s using a tunablefiber Bragg grating

A compact tunable fiber Bragg grating that uses distributed thin-film heaters on the surface of the fiber is used to dynamically optimize the post dispersion compensation of a multi-span 40-Gb/s nonreturn-to-zero (NRZ) transmission system. Dynamic post dispersion compensation with this device enables the system to operate over a much wider range of launch power than is otherwise possible with simple, fixed compensation using dispersion compensating fiber     

Randomized competitive algorithms for the list update problem

We prove upper and lower bounds on the competitiveness of randomized algorithms for the list update problem of Sleator and Tarjan. We give a simple and elegant randomized algorithm that is more competitive than the best previous randomized algorithm due to Irani. Our algorithm uses randomness only during an initialization phase, and from then on runs completely deterministically. It is the first randomized competitive algorithm with this property to beat the deterministic lower bound. We generalize our approach to a model in which access costs are fixed but update costs are scaled by an arbitrary constantd. We prove lower bounds for deterministic list update algorithms and for randomized algorithms against oblivious and adaptive on-line adversaries. In particular, we show that for this problem adaptive on-line and adaptive off-line adversaries are equally powerful.A preliminary version of these results appeared in a joint paper with S. Irani in theProceedings of the 2nd Symposium on Discrete Algorithms, 1991 [17].This research was partially supported by NSF Grants CCR-8808949 and CCR-8958528.This research was partially supported by NSF Grant CCR-9009753.This research was supported in part by the National Science Foundation under Grant CCR-8658139, by DIMACS, a National Science Foundation Science and Technology center, Grant No. NSF-STC88-09648.     

A comparative experimental and computational study of methanol, ethanol, and n-butanol flames

Laminar flame speeds and extinction strain rates of premixed methanol, ethanol, and n-butanol flames were determined experimentally in the counterflow configuration at atmospheric pressure and elevated unburned mixture temperatures. Additional measurements were conducted also to determine the laminar flame speeds of their n-alkane/air counterparts, namely methane, ethane, and n-butane in order to compare the effect of alkane and alcohol molecular structures on high-temperature flame kinetics. For both propagation and extinction experiments the flow velocities were determined using the digital particle image velocimetry method. Laminar flame speeds were derived through a non-linear extrapolation approach based on direct numerical simulations of the experiments. Two recently developed detailed kinetics models of n-butanol oxidation were used to simulate the experiments. The experimental results revealed that laminar flame speeds of ethanol/air and n-butanol/air flames are similar to those of their n-alkane/air counterparts, and that methane/air flames have consistently lower laminar flame speeds than methanol/air flames. The laminar flame speeds of methanol/air flames are considerably higher compared to both ethanol/air and n-butanol/air flames under fuel-rich conditions. Numerical simulations of n-butanol/air freely propagating flames, revealed discrepancies between the two kinetic models regarding the consumption pathways of n-butanol and its intermediates.