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Davis, H.

Publications and source records attributed to Davis, H..

5 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Evaluation of medical treatments to increase survival of ebullism in guinea pigs

Spaceflight carriers run a constant risk of exposure to vacuum. Above 63,000 ft (47 mmHg), the ambient pressure falls below the vapor pressure of water at 37 C, and tissue vaporization (ebullism) begins. Little is know about appropriate resuscitative protocols after such an ebullism exposure. This study identified injury patterns and mortality rates associated with ebullism while verifying effectiveness of traditional pulmonary resuscitative techniques. Male Hartley guinea pigs were exposed to 87,000 ft for periods of 40 to 115 sec. After descent, those animals that did not breathe spontaneously were given artificial ventilation by bag and mask for up to 15 minutes. Those animals surviving were randomly assigned to one of three treatment groups--hyperbaric oxygen (HBO), ground-level oxygen (GLO2), and ground-level air (GLAIR). The HBO group was treated on a standard treatment table 6A while the GLO2 animals received O2 for an equivalent length of time. Those animals in the GLAIR group were observed only. All surviving animals were humanely sacrified at 48 hours. Inflation of the animal's lungs after the exposure was found to be difficult and, at times, impossible. This may be due to surfactant disruption at the alveolar lining. Electron microscopy identified a disruption of the surfactant layer in animals that did not survive initial exposure. Mortality was found to increase with exposure time: 40 sec--0 percent; 60 sec--6 percent; 70 sec--40 percent; 80 sec--13 percent; 100 sec--38 percent; 110 sec--40 percent; and 115 sec--100 percent. There was no difference in the delayed mortality among the treatment groups (HBO--15 percent, GLO2--11 percent, GLAIR--11 percent). However, since resuscitation was ineffective, the effectiveness of any post-exposure treatment was severely limited. Preliminary results indicate that reuscitation of guinea pigs following ebullism exposure is difficult, and that current techniques (such as traditional CPR) may not be appropriate.

Stegmann, Barbara J.↗
NASA NTRS1992

Coarse-fine residual gravity cancellation system with magnetic levitation

Aircraft flight along parabolic trajectories have been proposed and executed in order to achieve low cost, near free fall conditions of moderate duration. This paper describes a six degree of freedom experiment isolation system designed to cancel out residual accelerations due to mechanical vibrations and errors in aircraft trajectory. The isolation system consists of a fine motion magnetic levitator whose stator is transported by a conventional coarse motion stage. The levitator uses wide gap voice coil actuators and has the dual purpose of isolating the experiment platform from aircraft vibrations and actively cancelling residual accelerations through feedback control. The course motion stage tracks the levitated platform in order to keep the levitator's coils centered within their matching magnetic gaps. Aspects of system design, an analysis of the proposed control strategy and simulation results are presented. Feasibility experiments are also discussed.

Salcudean, S. E.↗
NASA NTRS1982

Space transportation

The physical laws governing launch vehicles are reviewed, together with the performance of launch vehicles thus far used and expected developments in space transportation systems. Launches are generally made in the direction of earth rotation to take advantage of the initial velocity in that direction, which can amount to about 0.46 km/sec at the equator. Spacecraft usually attain a parking orbit, where spacecraft conditions are assessed before moving on to final orbit or interplanetary trajectory. Rocket batteries were first used in a battle near Beijing in 1232, and manned space flight began with the Vostok flight in 1961, followed by the Apollo lunar landings in the later 1960s. Rocket thrust performance is analyzed, together with the thrust/mass ratio for ascent and descent. The Shuttle, capable of placing 29.5 t in LEO, will be or is equipped to also carry IUS and PAM engines for transferring payloads from LEO to GEO. Parallel burn boosters may be added to increase the payload capability, and Shuttle-derived launch vehicles may be developed to carry construction materials to space and return to earth for a runway landing. Alternatively, the Shuttle engines may be modularized in order to develop a heavy-lift launch vehicle for unmanned cargo ascents.

Davis, H.↗
NASA NTRS1966

Computation research

Least squares method used in linearizing roots of polynomial and to derive approximations

APPROXIMATION METHOD↗