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At least 829 records · Page 46

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NASA NTRS1977

Determination of constant-volume balloon capabilities for aeronautical research

The proper application of constant-volume balloons (CVB) for measurement of atmospheric phenomena was determined. And with the proper interpretation of the resulting data. A literature survey covering 176 references is included. the governing equations describing the three-dimensional motion of a CVB immersed in a flow field are developed. The flowfield model is periodic, three-dimensional, and nonhomogeneous, with mean translational motion. The balloon motion and flow field equations are cast into dimensionless form for greater generality, and certain significant dimensionless groups are identified. An alternate treatment of the balloon motion, based on first-order perturbation analysis, is also presented. A description of the digital computer program, BALLOON, used for numerically integrating the governing equations is provided.

Tatom, F. B.↗

NASA NTRS1977

Effect of prolonged space flight on cardiac function and dimensions

By taking advantage of the capabilities of echocardiography to measure noninvasively left ventricular volume, stroke volume, and ejection fraction, and of the fact that the astronauts were routinely subjected to lower body negative pressure (whereby cardiac filling is progressively decreased), it was possible to construct classic ventricular function curves noninvasively, thereby obviating the difficulties encountered in comparing cardiac function at different end-diastolic volumes preflight and postflight. In this manner, the effect of an 84-day period of weightlessness on cardiac structure and function was evaluated in the Skylab 4 astronauts.

Henry, W. L.↗

NASA NTRS1978

Measurement of the time-temperature dependent dynamic mechanical properties of boron/aluminum composites

A flexural vibration test and associated equipment were developed to accurately measure the low strain dynamic modulus and damping of composite materials from -200 C to over 500 C. The basic test method involves the forced vibration of composite bars at their resonant free-free flexural modes in a high vacuum cryostat furnace. The accuracy of these expressions and the flexural test was verified by dynamic moduli and damping capacity measurements on 50 fiber volume percent boron/aluminum (B/Al) composites vibrating near 2000 Hz. The phase results were summarized to permit predictions of the B/Al dynamic behavior as a function of frequency, temperature, and fiber volume fraction.

Dicarlo, J. A.↗

NASA NTRS1978

CO2 laser-driven Stirling engine

A 100-W Beale free-piston Stirling engine was powered remotely by a CO2 laser for long periods of time. The engine ran on both continuous-wave and pulse laser input. The working fluid was helium doped with small quantities of sulfur hexafluoride, SF6. The CO2 radiation was absorbed by the vibrational modes of the sulfur hexafluoride, which in turn transferred the energy to the helium to drive the engine. Electrical energy was obtained from a linear alternator attached to the piston of the engine. Engine pressures, volumes, and temperatures were measured to determine engine performance. It was found that the pulse radiation mode was more efficient than the continuous-wave mode. An analysis of the engine heat consumption indicated that heat losses around the cylinder and the window used to transmit the beam into the engine accounted for nearly half the energy input. The overall efficiency, that is, electrical output to laser input, was approximately 0.75%. However, this experiment was not designed for high efficiency but only to demonstrate the concept of a laser-driven engine. Based on this experiment, the engine could be modified to achieve efficiencies of perhaps 25-30%.

Lee, G.↗

NASA NTRS1977

Fast but accurate techniques for calculating radiative terms in numerical atmospheric models and in remote sensing applications

Methods were developed for calculating radiative terms with relatively high accuracy but with sufficient speed, so that they can be used in numerical atmospheric models or in high volume processing of satellite measured radiances for remote sensing of atmospheric and surface parameters. Comparison with commonly used methods in both types of applications indicate improvements in calculating transmittances of factors between two and three, and in calculating radiances and cooling rates of factors between two and seven.

Arking, A.↗

NASA NTRS1981

Modified MEE Industries static thermal gradient diffusion cloud chamber

The experiments performed at the Workshop were undertaken to confirm the calculated sample volume, determine the usable range of supersaturation, and minimum detectable size. Comparison of absolute CCN concentrations with other state-of-the-art continuous flow diffusion chambers at supersaturations near 1 percent indicated that the volume used produced CCN concentrations well within the range of CCN concentrations determined at the workshop. This agreement is interpreted to mean the sample volume was correct. Direct measurements of the beam geometry done in the laboratory indicated a factor of 4-5 error. This error is apparently due to the larger apparent visible beam diameter versus the actual usable beam diameter given the droplet illumination, chamber optical geometry, microscope optics and film characteristics.

Borys, R. D.↗

NASA NTRS1986

Fuel Gage for Sloshing Tanks

New gage accurately measures fuel remaining in moving, or sloshing, tank. Measures tank air (or other gas) pressure and time required for pressure to change from one preselected level to another. Time measurement directly proportional to volume of air. Data processor computes relative volumes of air and fuel in tank.

Garner, H. D.↗

NASA NTRS1988

Evaluating Solid-Lubricant Films

Report describes experimental techniques for measuring properties of solid-lubricant films. Discusses experimental parameters. Reviews basic pin-on-disk configurations and methods of preparing disks and applying solid lubricants. Techniques for constant-temperature testing, low-contact-stress testing, and temperature-versus-time testing presented. Suggests methods of measuring pin-wear volume and recommends ways of presenting data.

Fusaro, Robert L.↗

NASA NTRS1990

Small domes on Venus - Probable analogs of Icelandic lava shields

On the basis of observed shapes and volumetric estimates, small, dome-like features on radar images of Venus are interpreted to be analogs of Icelandic lava-shield volcanoes. Morphometric data for Venusian domes in Aubele and Slyuta as well as measurements of representative dome volumes and areas from Tethus Regio are used to demonstrate that the characteristic aspect ratios and flank slopes of these features are consistent with a subclass of low Icelandic lava-shield volcanoes (LILS).

Garvin, James B.↗

NASA NTRS1991

Aerosol backscatter measurements at 10.6 microns with airborne and ground-based CO2 Doppler lidars over the Colorado High Plains. II - Backscatter structure

Measurements of tropospheric aerosol volume backscatter coefficients at 10.6-microns wavelength were obtained with airborne continuous wave and ground-based pulsed CO2 Doppler lidars over the Colorado High Plains during a 20-day period in summer 1982. A persistent 'background' layer was found between 6- and 10-km altitude, with a generally uniform backscatter mixing ratio of about 10 to the -10th sq m/kg per sr. The upper boundary of this background layer varied with the tropopause height; the lower boundary varied with the strength and diurnal cycle of convective mixing in the planetary boundary layer (PBL). For quiescent meteorological conditions, the transition from the PBL to the background layer was usually very sharp, with backscatter decreases sometimes as large as 3 decades in about 70 m. Sharp gradients were also found at the boundaries of shallow (tens of meters) subvisible cirrus clouds. For less stable conditions, associated with vertical aerosol transport by deep cumuliform clouds, backscatter tended to decrease exponentially with altitude.

Bowdle, David A.↗

NASA NTRS1991

Pulmonary function in men after oxygen breathing at 3.0 ATA for 3.5 h

A complete description of pulmonary measurements obtained after continuous O2 exposure of 13 healthy men at 3.0 ATA for 3.5 h is presented. Measurements included flow-volume loops, spirometry, and airway resistance(n = 12); CO diffusing capacity (n = 11); closing volumes (n= 6); and air vs. HeO2 forced vital capacity maneuvers (n = 5). The average difference in maximum mid expiratory flows at 50 percent vital capacity on air and HeO2 was found to be significantly reduced postexposure by 18 percent. Raw and CO diffusing capacity were not changed postexposure. It is concluded that the relatively large change in forced expiratory flow at 25-75 percent of vital capacity compared with the mean forced expiratory volume in 1 s, the reduction in density dependence of flow, and the normal Raw postexposure are all consistent with flow limitation in peripheral airways as a major cause of the observed reduction in expiratory flow.

Clark, J. M.↗

NASA NTRS1992

The future of spaceborne altimetry. Oceans and climate change: A long-term strategy

The ocean circulation and polar ice sheet volumes provide important memory and control functions in the global climate. Their long term variations are unknown and need to be understood before meaningful appraisals of climate change can be made. Satellite altimetry is the only method for providing global information on the ocean circulation and ice sheet volume. A robust altimeter measurement program is planned which will initiate global observations of the ocean circulation and polar ice sheets. In order to provide useful data about the climate, these measurements must be continued with unbroken coverage into the next century. Herein, past results of the role of the ocean in the climate system is summarized, near term goals are outlined, and requirements and options are presented for future altimeter missions. There are three basic scientific objectives for the program: ocean circulation; polar ice sheets; and mean sea level change. The greatest scientific benefit will be achieved with a series of dedicated high precision altimeter spacecraft, for which the choice of orbit parameters and system accuracy are unencumbered by requirements of companion instruments.

Koblinsky, C. J.↗

NASA NTRS1993

Atomizing-gas temperature effect on cryogenic spray dropsize

Correlating expressions for two-phase flow breakup of liquid nitrogen, LN2, jets in sonic velocity nitrogen gasflows were obtained for an atomizing-gas temperature range of 111 to 442 K. The correlations were based on characteristic dropsize measurements obtained with a scattered-light scanner. The effect of droplet vaporization on the measurements of the volume-median dropsize was calculated by using previously determined heat and momentum transfer expressions for droplets evaporating in high-velocity gasflow. Finally, the dropsize of the originally unvaporized spray was calculated, normalized with respect to jet diameter and correlated with atomizing-gas flowrate and temperature.

Ingebo, Robert D.↗

NASA NTRS1993

Atomizing-gas temperature effect on cryogenic spray dropsize

Ingebo, Robert D.↗

NASA NTRS1991

Jet ejecta mass upon oblique impact

Theoretical models in the jetting regime for symmetric and asymmetric impact of thin plates predict the mass and velocity of jetted material upon oblique impact. However, experimental constraints on the amount of material which form jets upon oblique impact are not known. A series of preliminary experiments were conducted in which tungsten (W) flyer plates at speeds of 1.5 to 2.0 km/s were obliquely impacted into carbon targets at 30 deg in the regime of jetting, yielding radiation temperatures in the about 3200 K range. Both framing-camera and flash X-ray imaging were conducted. Broad cm-sized craters induced by jet ejecta on 2024 Al witness plates were used to infer jet mass. We infer, from measured witness plate crater volumes, that jet masses in the range of 0.01 to 0.06 g are produced by a 32 mm diameter, 6 mm thick W impactor. This is about one to two orders of magnitude less than those calculated from present theoretical models. In contrast, in refractory material experiments, the mass of gabbro ejecta trapped in styrofoam is 0.52 g, which is similar to that calculated.

Yang, W.↗

NASA NTRS1993

A marine sedimentary model for the evolution of the northern plains

For the purpose of focusing the following discussion, we begin with the reasonable assumption that landforms interpreted to be shorelines can be considered to be as diagnostic of former water levels within the northern plains of Mars as lava flows are of former volcanism. Once (or if) this interpretation of these features becomes more generally accepted and the compositional and topographic datasets for Mars improve, their distribution can be used to make valuable independent estimates of the planet's water budget by providing quantitative measures of surface reservoir volumes at specific instances in Martian history. The problem is approached from a consideration of the basin's volume and its implied requirement on juvenile water sources and channel discharges, rather than the other way around.

Parker, T. J.↗

NASA NTRS1993

First height comparison of noctilucent clouds and simultaneous PMSE

On the night of August 9-10, 1991, two rocket payloads were launched into simultaneously occurring noctilucent clouds (NLC) and polar mesospheric summer echoes (PMSE) above Esrange, a third rocket payload was launched into a NLC where a PMSE was detected 5 minutes later above Esrange, in Sweden as part of the NLC-91 campaign. An aim of this experiment was to compare the vertical structures and locations of the NLC and PMSE events. To this end, in-situ optical photometers and particle impact sensors were used to measure the altitude and vertical structure of the NLC layer, while the Cornell University portable radar interferometer (CUPRI) was used to probe the PMSE. Although this comparison is complicated by the horizontal separations between the in-situ measurements and the radar volume, and low electron densities which reduced the overall radar reflectivity, we conclude that the PMSE layer in the CUPRI radar volume remained above the NLC layer detected by the in-situ instruments by 300 to 2000 m throughout the experiment. We interpret this result as supporting the view that PMSE are more likely to result from the presence of aerosols smaller than the ones optically detectable as NLCs.

Waelchli, Urs↗

NASA NTRS1995

In situ phytoplankton absorption, fluorescence emission, and particulate backscattering spectra determined from reflectance

An inverse model was developed to extract the absortion and scattering (elastic and inelastic) properties of oceanic constituents from surface spectral reflectance measurements. In particular, phytoplankton spectral absorption coefficients, solar-stimulated chlorophyll a fluorescence spectra, and particle backscattering spectra were modeled. The model was tested on 35 reflectance spectra obtained from irradiance measurements in optically diverse ocean waters (0.07 to 25.35 mg/cu m range in surface chlorophyll a concentrations). The universality of the model was demonstrated by the accurate estimation of the spectral phytoplankton absorption coefficents over a range of 3 orders of magnitude (rho = 0.94 at 500 nm). Under most oceanic conditions (chlorophyll a less than 3 mg/cu m) the percent difference between measured and modeled phytoplankton absorption coefficents was less than 35%. Spectral variations in measured phytoplankton absorption spectra were well predicted by the inverse model. Modeled volume fluorescence was weakly correlated with measured chl a; fluorescence quantum yield varied from 0.008 to 0.09 as a function of environment and incident irradiance. Modeled particle backscattering coefficients were linearly related to total particle cross section over a twentyfold range in backscattering coefficents (rho = 0.996, n = 12).

Roesler, Collin S.↗