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At least 235 records · Page 13

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NASA NTRS1979

Laboratory simulations of the Viking Labeled Release experiment - Kinetics following second nutrient injection and the nature of the gaseous end product

Injection of (C-14)-labeled nutrient onto Mars soil produced an evolution of C-14 gas in the Viking Labeled Release (LR) experiment. However, a second injection of nutrient seven days later was followed by an abrupt diminution of the amount of radioactive gas in the test cell. Simulation experiments performed in the LR Test Standards Module (TSM) have yielded a plausible explanation for this diminution. Radioactive carbon gases were injected into the TSM test cell in the presence and absence of two Mars analog soils. After equilibration, water was injected and its effect observed. The results indicate that the flight data following second nutrient injection can be explained on a physico-chemical basis involving a carbon dioxide/water/soil equilibrium in the test cell. The results also suggest that the gaseous end product of the Labeled Release reaction on Mars is more likely carbon dioxide than carbon monoxide.

Levin, G. V.↗

NASA NTRS1982

Moving-Surface Follower Aids Microsurgery

Novel manipulator follows movements of arteries and muscles, enabling precise placement of probe or other microsurgical tool in moving tissue. Microprobe assembly is mounted on output of pneumatic servo of commercial noncontracting thickness gage. Pulsations of tissue surface to be penetrated by probe are sensed by gage and followed by servo, eliminating relative motion between tissue and probe.

Feldstein, C.↗

NASA NTRS1982

Aircraft sampling of the sulfate layer near the tropopause following the eruption of Mount St. Helens

Twenty-three filter sampling flights of the NASA Lewis F-106 aircraft, were conducted in the Great Lakes region between June 4 and Dec. 23, 1980, following the major eruption of Mount St. Helens on May 18. The IPC-1478 filters were exposed over an altitude range spanning the local tropopause. A filter sample exposed above the tropopause on June 5 indicated a sulfate level 50 times the baseline measurements, which is consistent with the trajectory predictions of the leading edge of the cloud on its second transit around the earth. Subsequent measurements over a period of 7 months revealed the existence of a layer of sulfate above the tropopause that decayed to a level of about 4 times previously measured background levels by the beginning of August. Concentration of nitrate above the tropopause exhibited considerable variability and showed some enhancement compared with previously measured concentration levels. On the basis of the null results of X ray fluorescence measurements, there is no evidence of ash particle concentrations of greater than 3.4 microns/cu m persisting in the layer above the tropopause following the second transit of the cloud.

Lezberg, E. A.↗

NASA NTRS1982

Time variations of aerosols in the stratosphere following Mount St. Helens eruptions

Samples of stratospheric aerosols collected with U-2 aircraft for several months following the first three major eruptions of Mount St. Helens were analyzed for ash and liquid acid content. Ash grain sizes and compositions vary depending on collection altitude, location within the drifting cloud, and days following their injection. s computers Size distributions of ash particles vary with altitude. Generally small particles are depleted more rapidly at low altitudes (12 km) than at higher altitudes (17-18 km). Although samples collected 1 day after the first eruption of May 18, 1980, were dry, flow marks on the aircraft indicated parts of the cloud contained heavy acid concentrations. Indeed, all other samples obtained within 1 to 4 days after later eruptions (May 25 and June 12, 1980) were covered with copious amounts of liquid acid. Proportions of liquid to ash varied considerably depending on sampling location and cloud age. Because the acid-coated ash globules were large, they rapidly fell from the stratosphere until, by late June 1980, only a residue of acid droplets remained. Size distributions and concentrations of these droplets varied considerably.

Farlow, N. H.↗

NASA NTRS1982

A direct observation of solar neutrons following the 0118 UT flare on 1980 June 21

The Gamma Ray Spectrometer on the Solar Maximum Mission satellite has observed energetic solar neutrons (greater than 50 MeV) at the earth following a solar flare that occurred on the west limb on June 21, 1980 at 01:18:20 UT. Impulsive photon emission from 10 keV to greater than 65 MeV lasting over a period of about 66 s was followed by a transient flux of 50-600 MeV neutrons incident over a 17 minute period. The peak counting rate corresponds to an average flux at the earth of (3.8 + or - 0.6) x 10 to the -2nd neutrons/sq cm s at 130 MeV. These observations indicate the emission of 3 x 10 to the 28th neutrons/sr with energies greater than 50 MeV, requiring the rapid acceleration (much less than 60 s) of protons to GeV energies during the impulsive phase of the flare.

Chupp, E. L.↗

NASA NTRS1982

VO2 kinetics during submaximal exercise following simulated weightlessness

A study is presented of the effects of deconditioning following 7 days of continuous head-down (-6 degrees) bedrest on changes in steady-state VO2, O2, and recovery VO2 during the performance of constant-load exercises. The deconditioning effects of bedrest on the physical working capacity were manifested in the subjects by significant changes in VO2 kinetics following the 7 days of head-down bedrest. While the subjects demonstrated the ability to attain similar steady-state VO2, simulated weightlessness using head-down bedrest resulted in a reduction of total VO2 capacity and an increase in the O2 deficit and VO2 halftime during submaximal constant-load exercise. It is concluded that this change in VO2 kinetics was induced by reexposure of the cardiovascular system to the +1 Gz (upright) environment.

Convertino, V. A.↗

NASA NTRS1983

Quantitative histochemistry of rat lumbar vertebrae following spaceflight

The histochemical effects of the return to gravity immediately and 6 and 29 days following spaceflight on the bone of rat vertebral bodies were investigated. No significant change in the calcium salt content of the vertebrae was found immediately postflight, although 6 days later it was significantly decreased. The calcium content was found to have returned to normal by 29 days postflight. While postflight collagen content was not significantly altered, keratosulfate was found to be significantly higher in trabecular bone of rats immediately postflight and 6 days postflight. In addition, chondroitin sulfate was found to be increased in vertebral bone on days 6 and 29 postflight. These findings indicate that bone turnover slows in vertebrae during spaceflight allowing bone aging, which support the contention that a form of osteolysis begins immediately upon return to gravity to remove components of old bone at which time mineral levels decrease and levels of chondroitin and keratkosulfates shift. It was found that the osteolysis phase was quickly followed by new bone replacement which was completed before 29 days postspaceflight.

Eurell, J. A.↗

NASA NTRS1984

Modeling to predict pilot performance during CDTI-based in-trail following experiments

A mathematical model was developed of the flight system with the pilot using a cockpit display of traffic information (CDTI) to establish and maintain in-trail spacing behind a lead aircraft during approach. Both in-trail and vertical dynamics were included. The nominal spacing was based on one of three criteria (Constant Time Predictor; Constant Time Delay; or Acceleration Cue). This model was used to simulate digitally the dynamics of a string of multiple following aircraft, including response to initial position errors. The simulation was used to predict the outcome of a series of in-trail following experiments, including pilot performance in maintaining correct longitudinal spacing and vertical position. The experiments were run in the NASA Ames Research Center multi-cab cockpit simulator facility. The experimental results were then used to evaluate the model and its prediction accuracy. Model parameters were adjusted, so that modeled performance matched experimental results. Lessons learned in this modeling and prediction study are summarized.

Sorensen, J. A.↗

NASA NTRS1984

Nitrate in the Greenland ice sheet in the years following the 1908 Tunguska event

The Tunguska event on June 30, 1908 has been subjected to much speculation within different fields of research. Publication of the results of the 1961 expedition to the Tunguska area (Florensky, 1963) supports the view that a cometary impact caused the event. Based on this interpretation, calculations of the impactor energy release and explosion height have been reported by Ben-Menahem (1975), and velocity, mass, and density of the impactor by Petrov and Stulov (1975). Park (1978) and Turco et al. (1981, 1982) used these numbers to calculate a production of ca. 30,000,000 tons of NO during atmospheric transit. This paper presents a high-resolution study of nitrate concentration in the Greenland ice sheet in ca. 10 years covering the Tunguska event. No signs of excess nitrate are found in three ice cores from two different sites in Greenland in the years following the Tunguska event. By comparing these results with results for other aerosols generally found in the ice, the lack of excess NO3(-) following the Tunguska event can be interpreted as indicating that the impactor nitrate production calculated by Park (1978) and Turco et al. (1981, 1982) are 1-2 orders of magnitude too high. To explain this, it is suggested, from other lines of reasoning, that the impactor density determined by Petrov and Stulov (1975) probably is too low.

Rasmussen, K. L.↗

NASA NTRS1984

Optimal state-rate feedback explicit model-following

The development of optimal explicit model-following control laws which include the use of state-rate signals is described. By formulating the control problem to consider both state and state-rate errors, some generalization of previous results is obtained. For special cases in which 'perfect' model-following is possible, the form of the resulting control law is particularly simple and leads to clear understanding of the direct influences of the weighting matrices used in the problem formulation. In addition the use of state-rate feedback permits the solution to be expressed in terms of gains on state an state-rate errors between model and controlled element, thereby obviating any requirement that perturbation signals be used for feedback.

Buethe, S.↗

NASA NTRS1984

Investigation of Satellite Measurements in the Presence of Clouds, Forcing Influences on Clouds and Feedback to the Large Scale Following Convection

Satellite measurements during cloudy conditions, forces influencing clouds and large scale feedback following convection were investigated. The following conditions were studied: (1) passing marked thermal features aloft near the northern Bay of Bengal at the time of formation of the July 1979 monsoon depression; (2) recognition of regions of dense high overcast clouds in satellite radiances; (3) evolution of monsoon cloud systems and controlling factors on the clouds, and the effects of the clouds on thermodynamic and wind structures for improvements for numerical models are suggested.

Warner, C.↗

NASA NTRS1984

VO2 kinetics of constant-load exercise following bed-rest-induced deconditioning

Previous studies have shown that the oxygen uptake kinetics during exercise and recovery may be changed by alterations in work intensity, prior exercise, muscle group involvement, ambient conditions, posture, disease state, and level of physical conditioning. However, the effects of detraining on oxygen uptake kinetics have not been determined. The present investigation has the objective to determine the effects of deconditioning following seven days of continuous head-down bed rest on changes in steady-state oxygen uptake, O2 deficit, and recovery oxygen uptake during the performance of constant-load exercise. The obtained results may provide support for previous proposals that submaximal oxygen uptake was significantly reduced following bed rest. The major finding was that bed-rest deconditioning resulted in a reduction of total O2 transport/utilization capacity during the transient phase of upright but not supine exercise.

Convertino, V. A.↗

NASA NTRS1985

Simulation evaluation of display/FLIR concepts for low-altitude, terrain-following helicopter operations

Trials were run on a six degree of freedom combat helicopter simulator to evaluate head-down displays with integrated FLIR imagery for terrain-following, course-steering, and transition to approach and hover helicopter pilot tasks. Three display formats were tested, providing varying levels of symbology for, e.g., the flight path angle, pitch-attitude data, vertical speed, altitude, etc. The pilots were also furnished flight director guidance, i.e., terrain-following, course steering, airspeed hold, and approach to hover. All the displays permitted the pilots to fly satisfactory mission in the CGI scenarios. The results revealed that the pilots preferred a nonconformal FLIR display superposition.

Swenson, H. N.↗

NASA NTRS1986

A nitric oxide increase observed following the July 1982 solar proton event

Following the solar proton event (SPE) of July 13, 1982, an increase in the strength of nitric oxide Gamma bands was observed in spectral scans of the atmospheric albedo made by the solar backscattered ultraviolet instrument on Nimbus 7. Analysis of the (10), (01), and (02) Gamma band strengths allow an estimate to be made of the cumulative amount of nitric oxide above an altitude of 50 km. An increase in nitric oxide in southern hemisphere high latitudes following the SPE amounting to about 5 x 10 to the 14th molecules per sq cm above an altitude of approximately 50 km is observed. The observed increase persists until the middle of September. A similar increase is not observed in the northern hemisphere, indicating that under summer conditions the mesospheric/thermospheric NO distribution returns to normal within a few days after the end of an SPE.

Mcpeters, R. D.↗

NASA NTRS1987

The significance of error dynamics in model-following for flight control design

The role of the system error dynamics in model-following control systems is discussed, along with the use of handling quality specifications, actuation bandwidth constraints, stability, and closed-loop performance requirements in flight control design. The model-following problem is formulated using both direct state-space and linear, quadratic, optimization techniques. The results are then demonstrated using several examples involving a generic forward-swept-wing vehicle and a conventional flight vehicle with large parameter uncertainty in order to illustrate the trade-off in closed-loop performance and control law complexity.

Schmidt, David K.↗

NASA NTRS1988

Leg vascular responsiveness during acute orthostasis following simulated weightlessness

The effect of weightlessness on vascular response to orthostatic stress was investigated in human subjects by measuring changes in the arterial pulse volume (APV) of the legs during exposure to lower body negative pressure (LBNP) applied before and after 10 days of continuous 6-deg head-down bed rest. Heart rate, mean arterial blood pressure (MAP), and impedance rheographic indices of APV were measured during rest and at 1 min of -30 mm Hg LBNP. Bed rest was found not to alter the responses of MAP to LBNP. Resting APV was decreased after bed rest; however, APV was reduced upon transfer from rest to 1-min LBPN by the same relative magnitude before and after bedrest. It is concluded that peripheral arterial vasoconstriction, as indicated by reduction in APV during LBNP, is not affected by bedrest. The results suggest that there was no apparent alteration in responsiveness of the leg vasculature following simulated weightlessness, and that the control mechanisms of peripheral resistance do not contribute significantly to reduced orthostatic tolerance following spaceflight.

Blamick, Cynthia A.↗

NASA NTRS1987

Nitrogen transformations following tropical forest felling and burning on a volcanic soil

Nitrogen transformations and loss were measured following forest clearing in a relatively fertile tropical forest site. Nitrogen mineralization, nitrification, and amounts of ammonium and nitrate increased substantially in surface soils during the 6 mo following burning, then returned to background levels. The nitrogen content of microbial biomass declined to half its original value 6 mo after clearing and remained low in the cleared sites. Plant uptake of nitrogen was substantial on cleared plots (50 g/sq m), but it accounted for only 18 percent of N-15 label added to field plots. MIcrobial immobilization of N-15 was small relative to that in a cleared temperate site, and measurements of denitrification potentials suggested that relatively little mineralized nitrogen was lost to the atmosphere. Substantial amounts of nitrogen (40-70 g/sq m) were retained as exchangeably bound nitrate deep in the soils of a cleared plot on which revegetation was prevented; this process accounted for 12 percent of the N-15 label added to field plots.

Matson, Pamela A.↗

NASA NTRS1989

Terrain-Following/Terrain-Avoidance System For Helicopters

Report describes early stages of development of control system enabling helicopter to follow automatically contours of terrain below and avoid collisions with terrain. Focuses on optimization of algorithm for generation of flightpath with respect to several variables, development of controller to position helicopter precisely along terrain-following/terrain-avoidance (TF/TA) flightpath, and integration of flightpath-trajectory software with flightpath-control software.

Dorr, Dan W.↗