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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

Opposing actions of dibutyryl cyclic AMP and GMP on temperature in conscious guinea-pigs

It is shown that the intracerebroventricular administration of dibutyryl cyclic AMP (Db-cAMP) induced hyperthermia in guinea pigs which was not mediated through prostaglandins or norepinephrine since a prostaglandin synthesis inhibitor and an alpha-adrenergic receptor blocking agent did not antagonize the hyperthermia. However, the hyperthermic response to Db-cAMP was attenuated by the central administration of a beta-adrenergic receptor antagonist, which indicates that cAMP may be involved, through beta-adrenergic receptors, in the central regulation of heat production and conservation. The central administration of Db-cGMP produced hypothermia which was not mediated via histamine H1 or H2 receptors and serotonin. The antagonism of hypothermia induced by Db-cGMP and acetylcholine + physostigmine by central administration of a cholinergic muscarine receptor antagonist and not by a cholinergic nicotinic receptor antagonist suggests that cholinoceptive neurons and endogenous cGMP may regulate heat loss through cholinergic muscarine receptors. It is concluded that these results indicate a regulatory role in thermoregulation provided by a balance between opposing actions of cAMP and cGMP in guinea pigs.

Kandasamy, S. B.↗
NASA NTRS1983

Photoelectrochemical electrodes

The surface of a moderate band gap semiconductor such as p-type molybdenum sulfide is modified to contain an adherent film of charge mediating ionene polymer containing an electroactive unit such as bipyridimium. Electron transport between the electrode and the mediator film is favorable and photocorrosion and recombination processes are suppressed. Incorporation of particles of catalyst such as platinum within the film provides a reduction in overvoltage. The polymer film is readily deposited on the electrode surface and can be rendered stable by ionic or addition crosslinking. Catalyst can be predispersed in the polymer film or a salt can be impregnated into the film and reduced therein.

Williams, R. M.↗
NASA NTRS1983

Lack of correlation between mycoplasma induced IFN-gamma production in vitro and natural killer cell activity against FLD-3 cells

The role of interferon (IFN) in the normal-killer-cell (NK) mediated lysis of tumor cells in vitro is investigated experimentally. Normal mouse spleen cells and spleen cells treated with anti-Thy-1.2 serum are cultured for 24 h with Friend erythroleukemia (FLD-3) cells in RPMI 1640 medium; supernatant fluid from cultures with FLD-3 lysis are assayed for IFN-gamma, and it is found that pretreatment with anti-Thy-1.2 suppresses IFN-gamma generation without affecting the ability of NK to mediate the lysis of FLD-3. Further tests indicate that the generation of IFN-gamma is stimulated by the presence of Mycoplasma arginini in the FLD-3 cells.

Kumar, V.↗
NASA NTRS1985

Anatomy of the Vestibulo-automatic Outflow to the Gut

Motion sickness can be induced by vestibular effects on the sympathetic portion of the autonomic nervous system. However, the pathways linking the vestibular and autonomic pathways are unknown. As a first step in this analysis, the locations of preganglionic sympathetic neurons (PSN) and dorsal root afferent ganglionic neurons (DRG) which supply sympathetic innervation to major portions of the gastrointestinal tract in rabbits were identified. The objective of a second series of experiments is to determine which of the brainstem nuclei project to the autonomic regions of the spinal cord that control gastrointestinal motility. To achieve this goal, a trans-synaptic retrograde tracer (3H-tetanus toxoid) is applied to the greater splanchnic nerve. This method allows the labeling of neurons within the brainstem that project only to the preganglionic synpathetic neurons. One structure that has been strongly implicated in mediating vestibulo-autonomic control is the cerebellum (i.e., nodulus and uvula). The outflow of these lobules to the autonomic regions of the brainstem is mediated by the fastigial nucleus. To determine the precise projections of the fastigial nucleus to the brainstem nuclei involved in emesis, anterograde tracer (3H-leucine) was injected into the fastigial nucleus in a third series of experiments.

Torigoe, Y.↗
NASA NTRS1985

Role of interferon in resistance and immunity to protozoa

Production of interferon (I) in response to protozoan infection, and the interferon-mediated inhibition of parasite replication were studied in order to determine if these effects may be related to immunologic-mediated resistance of the hosts. Two extracellular parasites-Trypanosoma brucei rhodesiense and Naegleria fowlei were used. Upon infection with the trypanosome, only resistant strains of mice produced I. An early peak of alpha/beta I is followed by appearance of gamma I, which coincided with antibody production and a drop in parasitemia. In case of the amoeba, pretreatment of its suspension with alpha/beta I inhibits its replication in vitro, and appears to protect mice from the infection and the disease. It is proposed that production of interferon, with its regulatory effect on the immune responses, may play a major role in regulating the processes of protozoan-caused diseases.

Sonnenfeld, G.↗
NASA NTRS1987

Electron tunneling through covalent and noncovalent pathways in proteins

A model is presented for electron tunneling in proteins which allows the donor-acceptor interaction to be mediated by the covalent bonds between amino acids and noncovalent contacts between amino acid chains. The important tunneling pathways are predicted to include mostly bonded groups with less favorable nonbonded interactions being important when the through bond pathway is prohibitively long. In some cases, vibrational motion of nonbonded groups along the tunneling pathway strongly influences the temperature dependence of the rate. Quantitative estimates for the sizes of these noncovalent interactions are made and their role in protein mediated electron transport is discussed.

Beratan, David N.↗
NASA NTRS1986

Dexamethasone regulates glutamine synthetase expression in rat skeletal muscles

The regulation of glutamine synthetase by glucocorticoids in rat skeletal muscles was studied. Administration of dexamethasone strikingly enhanced glutamine synthetase activity in plantaris and soleus muscles. The dexamethasone-mediated induction of glutamine synthetase activity was blocked to a significant extent by orally administered RU38486, a glucocorticoid antagonist, indicating the involvement of intracellular glucocorticoid receptors in the induction. Northern blot analysis revealed that dexamethasone-mediated enhancement of glutamine synthetase activity involves dramatically increased levels of glutamine synthetase mRNA. The induction of glutamine synthetase was selective in that glutaminase activity of soleus and plantaris muscles was not increased by dexamethasone. Furthermore, dexamethasone treatment resulted in only a small increase in glutamine synthetase activity in the heart. Accordingly, there was only a slight change in glutamine synthetase mRNA level in this tissue. Thus, glucocorticoids regulate glutamine synthetase gene expression in rat muscles at the transcriptional level via interaction with intracellular glutamine production by muscle and to mechanisms underlying glucocorticoid-induced muscle atrophy.

Max, Stephen R.↗
NASA NTRS1990

The human factors of workstation telepresence

The term workstation telepresence has been introduced to describe human-telerobot compliance, which enables the human operator to effectively project his/her body image and behavioral skills to control of the telerobot itself. Major human-factors considerations for establishing high fidelity workstation telepresence during human-telerobot operation are discussed. Telerobot workstation telepresence is defined by the proficiency and skill with which the operator is able to control sensory feedback from direct interaction with the workstation itself, and from workstation-mediated interaction with the telerobot. Numerous conditions influencing such control have been identified. This raises the question as to what specific factors most critically influence the realization of high fidelity workstation telepresence. The thesis advanced here is that perturbations in sensory feedback represent a major source of variability in human performance during interactive telerobot operation. Perturbed sensory feedback research over the past three decades has established that spatial transformations or temporal delays in sensory feedback engender substantial decrements in interactive task performance, which training does not completely overcome. A recently developed social cybernetic model of human-computer interaction can be used to guide this approach, based on computer-mediated tracking and control of sensory feedback. How the social cybernetic model can be employed for evaluating the various modes, patterns, and integrations of interpersonal, team, and human-computer interactions which play a central role is workstation telepresence are discussed.

Smith, Thomas J.↗
NASA NTRS1991

Rhesus monkey (Macaca mulatta) complex learning skills reassessed

An automated computerized testing facility is employed to study basic learning and transfer in rhesus monkeys including discrimination learning set and mediational learning. The data show higher performance levels than those predicted from other tests that involved compromised learning with analogous conditions. Advanced transfer-index ratios and positive transfer of learning are identified, and indications of mediational learning strategies are noted. It is suggested that these data are evidence of the effectiveness of the present experimental apparatus for enhancing learning in nonhuman primates.

Washburn, David A.↗
NASA NTRS1991

Language Research Center's Computerized Test System (LRC-CTS) - Video-formatted tasks for comparative primate research

Automation of a computerized test system for comparative primate research is shown to improve the results of learning in standard paradigms. A mediational paradigm is used to determine the degree to which criterion in the learning-set testing reflects stimulus-response associative or mediational learning. Rhesus monkeys are shown to exhibit positive transfer as the criterion levels are shifted upwards, and the effectiveness of the computerized testing system is confirmed.

Rumbaugh, Duane M.↗
NASA NTRS1992

Short-duration spaceflight impairs human carotid baroreceptor-cardiac reflex responses

The effect of a spaceflight on the vagally mediated baroreceptor-cardiac reflex responses of humans were investigated by measuring the responses (provoked by neck pressure changes) in supine position and the heart rate and blood pressure in the supine and standing positions in 16 astronauts before and after 4- to 5-day long Space Shuttle missions. The results showed that exposures to spaceflight resulted in reduced baseline levels of the vagal-cardiac outflow and the vagally mediated responses to changes of the arterial baroreceptor input and that these changes contribute to postflight reductions of astronauts' ability to maintain standing arterial pressures.

Fritsch, Janice M.↗
NASA NTRS1992

Role of atrial natriuretic peptide in systemic responses to acute isotonic volume expansion

A hypothesis is proposed that a temporal relationship exists between increases in cardiac filling pressure and plasma artrial natriuretic peptide (ANP) concentration and also between ANP elevation and vasodilation, fluid movement from plasma to interstitium, and increased urine volume (UV). To test the hypothesis, 30 ml/kg isotonic saline were infused in supine male subjects over 24 min and responses were monitored for 3 h postinfusion. Results show that at end infusion, mean arterial pressure (RAP), heart rate and plasma volume exhibited peak increases of 146, 23, and 27 percent, respectively. Mean plasma ANP and UV peaked (45 and 390 percent, respectively) at 30 min postinfusion. Most cardiovascular variables had returned toward control levels by 1 h postinfusion, and net reabsorption of extravascular fluid ensued. It is concluded that since ANP was not significantly increased until 30 min postinfusion, factors other than ANP initiate responses to intravascular fluid loading. These factors include increased vascular pressures, baroreceptor-mediated vasolidation, and hemodilution of plasma proteins. ANP is suggested to mediate, in part, the renal response to saline infusion.

Watenpaugh, Donald E.↗
NASA NTRS1992

Effects of acute exercise on attenuated vagal baroreflex function during bed rest

We measured carotid baroreceptor-cardiac reflex responses in six healthy men, 24 h before and 24 h after a bout of leg exercise during 6 deg head-down bed rest to determine if depressed vagal baroreflex function associated with exposure to microgravity environments could be reversed by a single exposure to acute intense exercise. Baroreflex responses were measured before bed rest and on day 7 of bed rest. An exercise bout consisting of dynamic and isometric actions of the quadriceps at graded speeds and resistances was performed on day 8 of bed rest and measurements of baroreflex response were repeated 24 h later. Vagally-mediated cardiac responses were provoked with ramped neck pressure-suction sequences comprising pressure elevations to +40 mm Hg, followed by serial, R-wave triggered 15 mm Hg reductions, to -65 mm Hg. Baroreceptor stimulus-cardiac response relationships were derived by plotting each R-R interval as a function of systolic pressure less the neck chamber pressure applied during the interval. Compared with pre-bed rest baseline measurements, 7 d of bed rest decreased the gain (maximum slope) of the baroreflex stimulus-response relationship by 16.8 +/- 3.4 percent (p less than 0.05). On day 9 of bed rest, 24 h after exercise, the maximum slope of the baroreflex stimulus-response relationship was increased (p less than 0.05) by 10.7 +/- 3.7 percent above pre-bed rest levels and 34.3 +/- 7.9 percent above bed rest day 7. Our data verify that vagally-mediated baroreflex function is depressed by exposure to simulated microgravity and demonstrate that this effect can be acutely reversed by exposure to a single bout of intense exercise.

Convertino, Victor A.↗
NASA NTRS1992

Potential health hazards from thermal degradation events - Particulate vs. gas phase effects

The effect of instillation of ultrafine TiO2 particles (10-nm anatase-TiO2 and 12-nm rutile-TiO2 (administered in doses from 60 to 1000 microg/rat and 500 microg/rat, respectively) on the respiratory tract of exposed rats was compared to the effects of larger (250 nm anatase-TiO2 and 220-nm rutile-TiO2 particles (given in doses 500 or 1000 microg/rat and 500 microg/rat, respectively). These effects were also compared to the effects of inhalation of 20-nm and 250-nm anatase-TiO2 particles and inhalation with surrogate gas phase components (HF and HCl). It was found that ultrafine TiO2 particles induced greater inflammatory reaction in the lung, had greater adverse effect on alveolar macrophage-mediated clearance function, and had a greater potential to induce mediators which can adversely affect other lung cells than did larger-sized particles. Inhalation of surrogate gas phase components caused injury only to the upper respiratory tract, in contrast to the ultrafine particles, which affected the deep lung.

Oberdorster, Gunter↗
NASA NTRS1994

Momentum transport near a magnetic X line in collisionless reconnection

Plasma dynamics and momentum transport near an X line during time-dependent magnetic reconnection in a collisionless plasma are investigated based on two-dimensional particle simulations. We find that a weakly skewed velocity distribution is formed near the magnetic X line, leading to the presence of off-diagonal elements of the plasma pressure tensor. Let the reconnection electric field be in the y direction. The gradients of the off-diagonal elements of the pressure tensor can provide a transport of the y momentum. During the normal magnetic reconnection, the momentum transport associated with the off-diagonal terms of the pressure tensor mediates a transfer of the y momentum from the region near the X line to regions outside the X line. A period of 'reverse magnetic reconnection,' during which the plasma kinetic energy is converted into magnetic energy, is also observed in the simulation. When reverse reconnection occurs, the gradients of the off-diagonal pressure tensor elements can mediate a transfer of y momentum into the X line. It is found that the inertial term also plays a significant role in the force balance near the magnetic X line. An explanation for the origin of the off-diagonal pressure terms is also given in this paper.

Cai, H. J.↗
NASA NTRS1995

Solar radiation, phytoplankton pigments and the radiant heating of the equatorial Pacific warm pool

Recent optical, physical, and biological oceanographic observations are used to assess the magnitude and variability of the penetrating flux of solar radiation through the mixed layer of the warm water pool (WWP) of the western equatorial Pacific Ocean. Typical values for the penetrative solar flux at the climatological mean mixed layer depth for the WWP (30 m) are approx. 23 W/sq m and are a large fraction of the climatological mean net air-sea heat flux (approx. 40 W/sq m). The penetrating solar flux can vary significantly on synoptic timescales. Following a sustained westerly wind burst in situ solar fluxes were reduced in response to a near tripling of mixed layer phytoplankton pigment concentrations. This results in a reduction in the penetrative flux at depth (5.6 W/sq m at 30 m) and corresponds to a biogeochemically mediated increase in the mixed layer radiant heating rate of 0.13 C per month. These observations demonstrate a significant role of biogeochemical processes on WWP thermal climate. We speculate that this biogeochemically mediated feedback process may play an important role in enhancing the rate at which the WWP climate system returns to normal conditions following a westerly wind burst event.

Siegel, David A.↗
NASA NTRS1993

Steady state and dynamical structure of a cosmic-ray-modified termination shock

A hydrodynamic model is developed for the structure of a cosmic-ray-modified termination shock. The model is based on the two-fluid equations of diffuse shock acceleration (Drury and Volk, 1981). Both the steady state structure of the shock and its interaction with outer heliospheric disturbances are considered. Under the assumption that the solar wind is decelerated by diffusing interstellar cosmic rates, it is shown that the natural state of the termination shock is a gradual deceleration and compression, followed by a discontinuous jump to a downstream state which is dominated by the pressure contribution of the cosmic rays. A representative model is calculated for the steady state which incorporates both interstellar cosmic ray mediation and diffusively accelerated anomalous ions through a proposed thermal leakage mechanism. The interaction of large-scale disturbances with the equilibrium termination shock model is shown to result in some unusual downstream structure, including transmitted shocks and cosmic-ray-modified contact discontinuities. The structure observed may be connected to the 2-kHz outer heliospheric radio emission (Cairns et al., 1992a, b). The time-dependent simulations also demonstrate that interaction with solar wind compressible turbulence (e.g., traveling interplanetary shocks, etc.) could induce the termination shock to continually fluctuate between cosmic-ray-dominated and gas-dynamic states. This fluctuation may represent a partial explanation of the galactic cosmic ray modulation effect and illustrates that the Pioneer and Voyager satellites will encounter an evolving shock whose structure and dynamic properties are strongly influence by the mediation of interstellar and anomalous cosmic rays.

Donohue, D. J.↗
NASA NTRS1993

Acute Cutaneous Microvascular Flow Responses to Whole-Body Tilting in Humans

The transition from upright to head-down tilt (HDT) posture in humans increases blood pressure superior to the heart and decreases pressure inferior to the heart. Consequently, above heart level, myogenic arteriolar tone probably increases with HDT, in opposition to the withdrawal of baroreceptor-mediated sympathetic tone. We hypothesized that due to antagonism between central and local controls, the response of the facial cutaneous microcirculation to acute postural change will be weaker than that in the leg, where these two mechanisms reinforce each other. Cutaneous microvascular flow was measured by laser Doppler flowmetry simultaneously at the shin and the neck of 7 male and 3 female subjects. Subjects underwent a stepwise tilt protocol from standing control to 54 deg head-up tilt (HUT), 30 deg, 12 deg, O deg, -6 deg (HDT), -12 deg, -6 deg, O deg, 12 deg, 30 deg, 54 deg, and standing, for 30-sec periods with 10-sec transitions between postures. Flows at the shin and the neck increased significantly (P less than 0.05) from standing baseline to 12 deg HUT (252 +/- 55 and 126 +/- 9% (bar X +/- SE) of baseline, respectively). From 12 deg to -12 deg tilt, flows continued to increase at the shin (509 +/- 71% of baseline) but decreased at the neck to baseline levels (100 +/- 15% of baseline). Cutaneous microvascular flow recovered at both sites during the return to standing posture with significant hysteresis. Flow increases from standing to near-supine posture are attributed at both sites to baroreceptor-mediated vasodilation. The great dissimilarity in flow response magnitudes at the two measurement sites may be indicative of central/local regulatory antagonism above heart level and reinforcement below heart level.

Breit, Gregory A.↗