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At least 253 records · Page 14Linked to original sources
PubMed1997

Triton's distorted atmosphere.

A stellar-occultation light curve for Triton shows asymmetry that can be understood if Triton's middle atmosphere is distorted from spherical symmetry. Although a globally oblate model can explain the data, the inferred atmospheric flattening is so large that it could be caused only by an unrealistic internal mass distribution or highly supersonic zonal winds. Cyclostrophic winds confined to a jet near Triton's northern or southern limbs (or both) could also be responsible for the details of the light curve, but such winds are required to be slightly supersonic. Hazes and clouds in the atmosphere are unlikely to have caused the asymmetry in the light curve.

Atmosphere↗
PubMed1969

Lipid synthesis by isolated Chlamydia psittaci.

The isolated cells of the host-dependent meningopneumonitis agent, Chlamydia psittaci, were shown to incorporate radioactive carbon from aspartate, isoleucine, and glucose-6-phosphate into cell lipids. The nature of this incorporation was investigated. Radioactivity was found only in the fatty acids and primarily in the phosphatidyl ethanolamine, and, to a lesser extent, in the phosphatidyl choline fractions. Branched-chain fatty acids, not found in host lipid, were shown to constitute a large proportion of the fatty acid content of phosphatidyl ethanolamine. The reasons why only fatty acid synthesis took place under the conditions of our experiments with isolated meningopneumonitis agent cells remain obscure.

Aspartic Acid↗
PubMed1968

Influence of gas environment on catabolic activities and on reoxidation of reduced nicotinamide adenine dinucleotide phosphate in Chlamydia.

We investigated the effect of the gas environment on the enzymatic reactions of intact isolated cells of the agents of trachoma and of meningopneumonitis of the host-dependent genus Chlamydia. In comparison with the reactions taking place in a gas phase of air, O(2) depressed CO(2) production from pyruvate and glutamate by trachoma and from glutamate by meningopneumonitis. O(2) enhanced the degradation of pyruvate by meningopneumonitis, but this effect was due to increased H(2)O(2), and was reversed by added catalase. Both dehydrogenation of alpha-ketoglutarate and was reversed by added catalase. Dehydrogenation of alpha-ketoglutarate by both agents and production of CO(2) from C(1) of glucose-6-phosphate were stimulated by O(2) and depressed in N(2). The latter activity was stimulated in air, O(2), and N(2) by nicotinamide adenine dinucleotide phosphate (NADP) in relation to the amount added, and also in air or O(2), but not in N(2), by moderate amounts of NADP and an excess of oxidized glutathione with concomitant formation of H(2)O(2). A small but significant amount of O(2) was consumed during the course of these reactions. It is suggested that glutathione reductase activity can occur only when accompanied by an oxidative reaction, and that this close link between the two reactions represents a mechanism of electron transport which transfers hydrogen to molecular O(2).

Air↗
PubMed2006

Does unilateral pedaling activate a rhythmic locomotor pattern in the nonpedaling leg in post-stroke hemiparesis?

Recent investigation in persons with clinically complete spinal cord injury has revealed that locomotor activity in one limb can activate rhythmic locomotor activity in the opposite limb. Although our previous research has demonstrated profound influences of the nonparetic limb on paretic limb motor activity poststroke, the potency of interlimb pathways for increasing recruitment of the paretic limb motor pattern is unknown. This experiment tested whether there is an increased propensity for rhythmic motor activity in one limb (pedaling limb) to induce rhythmic motor activity in the opposite limb (test limb) in persons poststroke. Forty-nine subjects with chronic poststroke hemiparesis and twenty controls pedaled against a constant mechanical load with their pedaling leg while we recorded EMG and pedal forces from the test leg. For the experimental conditions, subjects were instructed to either pedal with their test leg (bilateral pedaling) or rest their test leg while it was either stationary or moved anti-phased (unilateral pedaling). In persons poststroke, unilateral pedaling activated a complete pattern of rhythmic alternating muscle activity in the nonpedaling, test leg. This effect was most clearly demonstrated in the most severely impaired individuals. In most of the control subjects, unilateral pedaling activated some muscles in the nonpedaling leg weakly, if at all. We propose that, ipsilateral excitatory pathways associated with contralateral pedaling in control subjects are increasingly up-regulated in both legs in persons with hemiparesis as a function of increased hemiparetic severity. This enhancement of interlimb pathways may be of functional importance since contralateral pedaling induced a complete motor pattern of similar amplitude to the bilateral pattern in both the paretic and nonparetic leg of the subjects with severe hemiparesis.

Aged↗
PubMed2006

Anterior-posterior ground reaction forces as a measure of paretic leg contribution in hemiparetic walking.

BACKGROUND AND PURPOSE: Walking after stroke is characterized by slow gait speed, poor endurance, reduced quality and adaptability of walking patterns, and an inability to coordinate the legs. Estimates based on mechanical work calculations have suggested that the paretic leg does 30% to 40% of the total mechanical work over the gait cycle, regardless of hemiparetic severity, but these work estimates may not describe the contribution of each leg to forward propulsion. The purpose of this study was to establish a quantifiable link between hemiparetic severity and paretic leg contribution to propulsion during walking, which we propose to quantify using a measure based on the anterior-posterior ground reaction forces (A-P GRFs). METHODS: A total of 47 participants with chronic hemiparesis walked at self-selected speeds to collect spatiotemporal parameters and 3D GRFs. A 16-person subset also participated in a pedaling protocol to compare A-P GRF measures to established measures of paretic leg output. RESULTS: A-P GRF measures were correlated with both walking speed and hemiparetic severity. These measures were also strongly correlated with positive work and net work values obtained during the pedaling task. The percentage of total propulsion generated by the paretic leg (PP) was calculated and found to be 16%, 36%, and 49% for those with high, moderate, and low hemiparetic severity, respectively. CONCLUSIONS: PP was found to provide a quantitative measure of the coordinated output of the paretic leg. Further research on this measure of forward propulsion may lead to the provision of an effective tool for distinguishing functional compensation from physiological restitution.

Aged↗