Tunneling injection quantum-dot lasers with polarization-dependent photon-mediated carrier redistribution and gain narrowing

A theoretical and experimental study of a particular transverse-electric (TE) mode lasing mechanism of a tunneling injection InP quantum-dot (QD) laser is reported. In the experiment, the TE mode lasing action takes place at the first excited state of InP biaxially compressively strained QDs. This QD state is coupled to the ground state of two tensile-strained InGaP quantum wells (QWs) although the tensile-strained QW structure favors the transverse-magnetic (TM) polarization light emission. The measured TE and TM modal gain spectra show a typical QW gain evolution behavior at low injection currents, which can be theoretically modeled by the quasi-equilibrium of carrier distribution. When the injection current is increased near threshold, a TE gain narrowing and a simultaneous TM gain pinning are observed in the measured modal gain spectra, which cannot be explained via the quasi-equilibrium model. We propose a polarization-dependent photon-mediated carrier redistribution in the QD-coupled-QW structure to explain this TE and TM gain evolution behavior. When the injection current is just below threshold, the strong carrier depletion via stimulated emission due to coupling between the InP QD and InGaP QW states plays an important role in carrier redistribution, which depends on the optical transition energy and polarization. This concept of the polarization-dependent photon-mediated carrier redistribution explains the TE gain narrowing and TM gain pinning behavior. In addition, a coupled rate equation model is established, and the calculated polarization power ratio based on the coupled rate equations explains the experimental observation.     

The gill calcium transport cycle in rainbow trout is correlated with plasma levels of bioactive, not immunoreactive, stanniocalcin

The aims of this study were to determine the most appropriate duration for the measurement of the maximal accumulated O2 deficit (MAOD), which is analogous to the anaerobic capacity, to ascertain the effects of mass, fat free mass (FFM), leg volume (Vleg) and lower body volume (V1b) on anaerobic test performance, to examine the reproducibility for peak power output (Wpeak) or maximal anaerobic power using an air-braked cycle ergometer and to produce approximations for the percentages of aerobic and anaerobic metabolism during exercise of short duration but high intensity. A group of 12 endurance trained cyclists [mean age 25.1 (SD 4.6) years; mean body mass 73.43 (SD 7.12) kg; mean maximal oxygen consumption 5.12 (SD 0.35) l.min-1; mean body fat 12.5 (SD 4.1) %] accordingly performed four counterbalanced treatments of 45, 60, 75 and 90 s of maximal cycling on an air-braked ergometer. The mean O2 deficit of 3.52 l for the 45-s treatment was significantly less (P < 0.01) than those for the 60 (3.75 l), 75 (3.80 l) and 90-s (3.75 l) treatments. These data therefore indicate that in predominantly aerobically trained subjects the O2 deficit attains a plateau after 60 s of maximal cycling on an air-braked ergometer. Statistically significant interclass correlation coefficients (P < 0.05) between the anthropometric variables (mass, FFM, Vleg and Vlb) and Wpeak or maximal anaerobic power (0.624-0.748) and MAOD (ml) or anaerobic capacity (0.666-0.772) furthermore would suggest the relevance of taking into account muscle mass during anaerobic tests.(ABSTRACT TRUNCATED AT 250 WORDS)     

Neocortical ectopias in BXSB mice: effects upon reference and working memory systems

BXSB mice have an approximately 40-60% incidence of neocortical ectopias in layer I of the prefrontal/motor cortex. Prior studies have found major behavioral differences between those with ectopias and their non-ectopic littermates. Some of these findings indicate that the two groups differ with respect to spatial reference and working memory. The purpose of this study was to measure reference and working memory in the same animals to test the hypothesis that the ectopics would have better reference memory but less effective working memory. The Lashley III maze has cul-de-sacs which must be eliminated, and T-choices where the animal has to decide whether to go left or right. Ectopic and non-ectopic mice were equally able to learn the maze and did not differ on cul-entry or T-choice errors. Then the maze was inverted and the animals were retested. Turning the maze upside down did not change the relative status of the blind alleys. Therefore, the reference memory knowledge from the prior week's training could be used to avoid entering the culs. However, inverting the maze caused a left-right mirror image reversal of the T-choices. Therefore, prior reference memory information would interfere with learning the new path through the maze, whereas working memory would enable the mouse to eliminate T-choice errors. Ectopic mice made less cul-entry errors and more T-choice errors than their non-ectopic littermates, as predicted.     

Differential c-fos expression in the nucleus of the solitary tract and spinal cord following noxious gastric distention in the rat

c-Fos has been used as a marker for activity in the spinal cord following noxious somatic or visceral stimulation. Although the viscera receive dual afferent innervation, distention of hollow organs (i.e. esophagus, stomach, descending colon and rectum) induces significantly more c-Fos in second order neurons in the nucleus of the solitary tract and lumbosacral spinal cord, which receive parasympathetic afferent input (vagus, pelvic nerves), than the thoracolumbar spinal cord, which receives sympathetic afferent input (splanchnic nerves). The purpose of this study was to determine the contribution of sympathetic and parasympathetic afferent input to c-Fos expression in the nucleus of the solitary tract and spinal cord, and the influence of supraspinal pathways on Fos induction in the thoracolumbar spinal cord. Noxious gastric distention to 80 mmHg (gastric distension/80) was produced by repetitive inflation of a chronically implanted gastric balloon. Gastric distension/80 induced c-Fos throughout the nucleus of the solitary tract, with the densest labeling observed within 300 microns of the rostral pole of the area postrema. This area was analysed quantitatively following several manipulations. Gastric distension/80 induced a mean of 724 c-Fos-immunoreactive nuclei per section. Following subdiaphragmatic vagotomy plus distention (vagotomy/80), the induction of c-Fos-immunoreactive nuclei was reduced to 293 per section, while spinal transection at T2 plus distention (spinal transection/80) induced a mean of 581 nuclei per nucleus of the solitary tract section. Gastric distension/80 and vagotomy/80 induced minimal c-Fos in the T8-T10 spinal cord (50 nuclei/section), but spinal transection/80 induced 200 nuclei per section. Repetitive bolus injections of norepinephrine produced transient pressor responses mimicking the pressor response produced by gastric distension/80. This manipulation induced minimal c-Fos in the nucleus of the solitary tract and none in the spinal cord. It is concluded that noxious visceral input via parasympathetic vagal afferents, and to a lesser extent sympathetic afferents and the spinosolitary tract, contribute to gastric distention-induced c-Fos in the nucleus of the solitary tract. The induction of c-Fos in the nucleus of the solitary tract is significantly greater than in the viscerotopic segments of the spinal cord, which is partially under tonic descending inhibition, but is not subject to modulation by vagal gastric afferents. Distention pressures produced by noxious gastric distention are much greater than those produced during feeding, suggesting that c-Fos induction in the nucleus of the solitary tract to noxious distention is not associated with physiological mechanisms of feeding and satiety. The large vagal nerve-mediated induction of c-Fos in the nucleus of the solitary tract following gastric distension suggests that parasympathetic afferents contribute to the processing of noxious visceral stimuli, perhaps by contributing to the affective-emotional component of visceral pain.     

Potentially avoidable hospitalizations: inequalities in rates between US socioeconomic groups

OBJECTIVES: The National Hospital Discharge Survey (NHDS) was used to evaluate potentially avoidable hospital conditions as an indicator of equity and efficiency in the US health care system. METHODS: With the use of 1990 data from the NHDS, the National Health Interview Survey, and the census, national rates of hospitalization were calculated for avoidable conditions by age, race, median income of zip code, and insurance status. RESULTS: An estimated 3.1 million hospitalizations were for potentially avoidable conditions. This was 12% of all hospitalizations in 1990 (excluding psychiatric admissions, women with deliveries, and newborns). Rates of potentially avoidable hospitalizations were higher for persons living in middle- and low-income areas than for persons living in high-income areas, and were higher among Blacks than among Whites. These class and racial differences were also found among the privately insured. Differences among income and racial groups for persons aged 65 and over were not significant. CONCLUSIONS: Inequalities in potentially avoidable hospitalizations suggest inequity and inefficiency in the health care delivery system. Avoidable hospital conditions are a useful national indicator to monitor access to care.     

North sea oil: Responses to employment opportunities

Britain's new offshore oil industry might have generated much additional employment especially in the building, manning and supply of rigs. But there was a failure at first to take proper advantage; little was done to train people in new skills. Consequently the oil companies brought in equipment and skilled personnel from abroad. Eventually efforts were made to improve matters and the paper examines the steps taken to bring more of the employment benefits to Britain, but finds only partial success.