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At least 595 records · Page 33
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Improving survival after tissue vaporization (Ebullism)

Exposure of unprotected humans to altitudes above 63,000 ft results in ebullism. Ebullism occurs when the vapor pressure of tissues is less than the ambient pressure and the tissues spontaneously 'boil'. This may result in rapid unconsciousness, cardiac vaporlock, pulmonary collapse, cerebral anoxia, and sometimes even death. Potential places for this include EVA accidents in space, aircraft experiencing rapid decompression at high altitudes with cabin or pressure suit failure, and accidents during pressure suit training exercises. The pathophysiology of ebullism was studied in the 40's to 60's using animal models. There is one report of a prolonged, unprotected human exposure and several anecdotal of unprotected short term exposures to near vacuum. In addition to pulmonary and neurologic concerns, unprotected exposure of the head may result in freezing of the corneal surface of the eye. Surface eye freezing may impair vision and significantly impact mission completion. At this time, little data are available on the effectiveness of conventional treatment protocols, such as hyperbaric oxygen, for ebullism induced injuries. Research is needed to assess the efficacy of other adjunctive therapies such as high frequency ventilation and cerebral protective drugs that are still under development.

Stegmann, Barbara J.↗
NASA NTRS1992

Digital data registration and differencing compression system

A process for x ray registration and differencing results in more efficient compression is discussed. Differencing of registered modeled subject image with a modeled reference image forms a differential image for compression with conventional compression algorithms. Obtention of a modeled reference image includes modeling a relatively unrelated standard reference image upon a three dimensional model, which three dimensional model is also used to model the subject image for obtaining the modeled subject image. The registration process of the modeled subject image and modeled reference image translationally correlates such modeled images for resulting correlation thereof in spatial and spectral dimensions. Prior to compression, a portion of the image falling outside a designated area of interest may be eliminated, for subsequent replenishment with a standard reference image. The compressed differenced image may be subsequently transmitted and/or stored, for subsequent decompression and addition to a standard reference image so as to form a reconstituted or approximated subject image at either remote location and/or at a later moment in time. Overall effective compression ratios of 100:1 are possible for thoracic x ray digital images.

Ransford, Gary A.↗
NASA NTRS1992

Hollow fiber clinostat for simulating microgravity in cell culture

A clinostat for simulating microgravity on cell systems carried in a fiber fixedly mounted in a rotatable culture vessel is disclosed. The clinostat is rotated horizontally along its longitudinal axis to simulate microgravity or vertically as a control response. Cells are injected into the fiber and the ends of the fiber are sealed and secured to spaced end pieces of a fiber holder assembly which consists of the end pieces, a hollow fiber, a culture vessel, and a tension spring with three alignment pins. The tension spring is positioned around the culture vessel with its ends abutting the end pieces for alignment of the spring. After the fiber is secured, the spring is decompressed to maintain tension on the fiber while it is being rotated. This assures that the fiber remains aligned along the axis of rotation. The fiber assembly is placed in the culture vessel and culture medium is added. The culture vessel is then inserted into the rotatable portion of the clinostat and subjected to rotate at selected rpms. The internal diameter of the hollow fiber determines the distance the cells are from the axis of rotation.

Rhodes, Percy H.↗
NASA NTRS1991

Assessment of surface penetration with polarimetric radar

An airborne P-, L-, and C-band polarimetric radar dataset acquired over the Atchafalaya Bay study site was used to assess its surface penetration capabilities. The dataset was decompressed and reformatted to form a three-wavelength and three-polarization nine-channel dataset. All nine channels were filtered for speckle noise removal, using the 7-by-7 local-statistics moving-window filtering. Significant smoothing of data was obtained so that the data can be classified using the SRCH and M234 ELAS programs. Preliminary assessment of the PLC images indicated that the radar waves penetrated muddy water. Therefore the radar can measure the water depth and can be used to map the submerged sediments. A statistical analysis of the digital data provided insight on the depth of muddy water penetration.

Wu, Shih-Tseng↗
NASA NTRS1992

Validation of a dual-cycle ergometer for exercise during 100 percent oxygen prebreathing

A study has been designed to determine if exercise, while prebreathing 100 percent oxygen prior to decompression, can reduce the current resting-prebreathe time requirements for extravehicular activity and high altitude reconnaissance flight. For that study, a suitable exercise mode was required. Design considerations included space limitations, cost, pressure suit compatibility, ease and maintenance of calibration, accuracy of work output, and assurance that no significant mechanical advantage or disadvantage would be introduced into the system. In addition, the exercise device must enhance denitrogenation by incorporation of both upper and lower body musculature at high levels of oxygen consumption. The purpose of this paper is to describe the specially constructed, dual-cycle ergometer developed for simultaneous arm and leg exercise during prebreathing, and to compare maximal oxygen uptake obtained on the device to that obtained during leg-only cycle ergometry and treadmill testing. Results demonstrate the suitability of the dual-cycle ergometer as an appropriate tool for exercise research during 100 percent oxygen prebreathing.

Wiegman, Janet F.↗
NASA NTRS1992

Features on Venus generated by plate boundary processes

Various observations suggest that there are processes on Venus that produce features similar to those associated with plate boundaries on earth. Synthetic aperture radar images of Venus, taken with a radar whose wavelength is 12.6 cm, are compared with GLORIA images of active plate boundaries, obtained with a sound source whose wavelength is 23 cm. Features similar to transform faults and to abyssal hills on slow and fast spreading ridges can be recognized within the Artemis region of Venus but are not clearly visible elsewhere. The composition of the basalts measured by the Venera 13 and 14 and the Vega 2 spacecraft corresponds to that expected from adiabatic decompression, like that which occurs beneath spreading ridges on earth. Structures that resemble trenches are widespread on Venus and show the same curvature and asymmetry as they do on earth. These observations suggest that the same simple geophysical models that have been so successfully used to understand the tectonics of earth can also be applied to Venus.

Mckenzie, Dan↗
NASA NTRS1993

Methods of evaluating the effects of coding on SAR data

It is recognized that mean square error (MSE) is not a sufficient criterion for determining the acceptability of an image reconstructed from data that has been compressed and decompressed using an encoding algorithm. In the case of Synthetic Aperture Radar (SAR) data, it is also deemed to be insufficient to display the reconstructed image (and perhaps error image) alongside the original and make a (subjective) judgment as to the quality of the reconstructed data. In this paper we suggest a number of additional evaluation criteria which we feel should be included as evaluation metrics in SAR data encoding experiments. These criteria have been specifically chosen to provide a means of ensuring that the important information in the SAR data is preserved. The paper also presents the results of an investigation into the effects of coding on SAR data fidelity when the coding is applied in (1) the signal data domain, and (2) the image domain. An analysis of the results highlights the shortcomings of the MSE criterion, and shows which of the suggested additional criterion have been found to be most important.

Dutkiewicz, Melanie↗
NASA NTRS1993

High-performance compression of astronomical images

Astronomical images have some rather unusual characteristics that make many existing image compression techniques either ineffective or inapplicable. A typical image consists of a nearly flat background sprinkled with point sources and occasional extended sources. The images are often noisy, so that lossless compression does not work very well; furthermore, the images are usually subjected to stringent quantitative analysis, so any lossy compression method must be proven not to discard useful information, but must instead discard only the noise. Finally, the images can be extremely large. For example, the Space Telescope Science Institute has digitized photographic plates covering the entire sky, generating 1500 images each having 14000 x 14000 16-bit pixels. Several astronomical groups are now constructing cameras with mosaics of large CCD's (each 2048 x 2048 or larger); these instruments will be used in projects that generate data at a rate exceeding 100 MBytes every 5 minutes for many years. An effective technique for image compression may be based on the H-transform (Fritze et al. 1977). The method that we have developed can be used for either lossless or lossy compression. The digitized sky survey images can be compressed by at least a factor of 10 with no noticeable losses in the astrometric and photometric properties of the compressed images. The method has been designed to be computationally efficient: compression or decompression of a 512 x 512 image requires only 4 seconds on a Sun SPARCstation 1. The algorithm uses only integer arithmetic, so it is completely reversible in its lossless mode, and it could easily be implemented in hardware for space applications.

White, Richard L.↗
NASA NTRS1992

Dissemination and fractionation of projectile materials in the impact melts from Wabar Crater, Saudi Arabia

Results are presented from the analyses of small ballistically dispersed melt samples (occurring in the form of aerodynamically shaped spheres, dumbbells, and teardrops) from the Wabar Crater (Saudi Arabia) and of melts from the Wabar and Nejed meteorites. On the basis of the data obtained and of models for crater forming processes it is concluded that the ballistically-dispersed glasses were formed from material at shallow levels in the target zone where temperatures were higher and where intimate physical contact with the disrupting impactor was achieved. Siderophile element fractionation was completed early, while the impactor was undergoing decompression and prior to mixing with the target glasses.

Mittlefehldt, David W.↗
NASA NTRS1992

Neurology of microgravity and space travel

Exposure to microgravity and space travel produce several neurologic changes, including SAS, ataxia, postural disturbances, perceptual illusions, neuromuscular weakness, and fatigue. Inflight SAS, perceptual illusions, and ocular changes are of more importance. After landing, however, ataxia, perceptual illusions, neuromuscular weakness, and fatigue play greater roles in astronaut health and readaptation to a terrestrial environment. Cardiovascular adjustments to microgravity, bone demineralization, and possible decompression sickness and excessive radiation exposure contribute further to medical problems of astronauts in space. A better understanding of the mechanisms by which microgravity adversely affects the nervous system and more effective treatments will provide healthier, happier, and longer stays in space on the space station Freedom and during the mission to Mars.

Fujii, M. D.↗
NASA NTRS1990

Explosive volcanism and associated pressures - Implications for models of endogenically shocked quartz

The nature of explosive volcanic phenomena and associated pressures, both from field and theoretical perspectives, is discussed. An endogenic origin for shocked quartz at the K/T boundary requires impulsive pressures greater than 60 kbars to be generated during explosive volcanism. Explosive volcanic eruptions which are events of sustained decompression may be initiated by impulsive explosions while the magnitudes of the overpressures are small. These maximum overpressures can be controlled mainly by the tensile strength of the rock surrounding the magma chamber-conduit system. Thus maximum overpressures in the volcanic environment are limited to less than 500 bars which are orders of magnitude less than those required for shock quartz (greater than 60 kbars). This observation is found to be consistent with the complete lack of field or petrographic evidence in support of shock metamorphism associated with volcanic eruptions and their products.

De Silva, S. L.↗
NASA NTRS1994

Algorithm For Integer Cosine Transforms

Algorithm computes coefficients of integer cosine transforms, containing only integer coefficients approximately proportional to floating-point coefficients of discrete cosine transforms. Used in compression of image data in blocks of N x N pixels, discrete cosine transforms involve large amounts of computation, typically amounting to 80 percent of computational load in data-compression scheme. In constructing integer approximations, competing requirements are to obtain data-compression and data-decompression performances comparable to those of corresponding descrete cosine transforms while taking advantage of simplicity afforded by integer arithmetic to reduce complexity and amount of computation.

Pollara, Fabrizio↗
NASA NTRS1994

Safety-Valve Mechanism For Pressure-Vessel Window

Pressure-activated valve mechanism seals small window in pressure chamber if window cracks or breaks, thereby preventing continued leakage or sudden decompression. Window used in experiments involving optical observation of processes in chamber. Valve mechanism activated by pressure from gas leaking through window.

Mccoomb, E. J.↗
NASA NTRS1993

Metabolic rate measurements comparing supine with upright upper-body exercises

The ground-based study that tested the hypothesis that metabolic rates during supine and upright upper-body exercises are similar (mean value of 200 kcal/h) is presented. Six subjects each performed supine or upright exercise at three exercise stations, a hand-cycle ergometer, a rope-pull device, and a torque wrench. After a baseline measurement of the metabolic rate at rest, the metabolic rate was measured twice at each exercise station. The mean metabolic rates (kcal/h) during supine (n = 6) and upright control (n = 4) exercise stations were not significantly different except for the rope-pull station, 153.5 +/- 16.6 (supine) as compared to 247.0 +/- 21.7 (upright), p is less than 0.05. This difference may be due in part to an increased mechanical efficiency of supine exercises (15.0 +/- 0.7 percent) as compared to that of upright exercises (11.0 +/- 1.08 percent), p is less than 0.05. The net energy input was significantly smaller for the supine rope-pull exercise (64 +/- 18) as compared to upright (176 +/- 20). The relationship between best-rest exercises, metabolic rates, and the incidence of decompression sickness (DCS) should be examined to determine the true risk of DCS in spaceflight extravehicular activities.

Fortney, Suzanne M.↗
NASA NTRS1993

Computer networking at SLR stations

There are several existing communication methods to deliver data from the satellite laser ranging (SLR) station to the SLR data center and back: telephonmodem, telex, and computer networks. The SLR scientific community has been exploiting mainly INTERNET, BITNET/EARN, and SPAN. The total of 56 countries are connected to INTERNET and the number of nodes is exponentially growing. The computer networks mentioned above and others are connected through E-mail protocol. The scientific progress of SLR requires the increase of communication speed and the amount of the transmitted data. The TOPEX/POSEIDON test campaign required to deliver Quick Look data (1.7 kB/pass) from a SLR site to SLR data center within 8 hours and full rate data (up to 500 kB/pass) within 24 hours. We developed networking for the remote SLR station in Helwan, Egypt. The reliable scheme for data delivery consists of: compression of MERIT2 format (up to 89 percent), encoding to ASCII Me (files); and e-mail sending from SLR station--e-mail receiving, decoding, and decompression at the center. We do propose to use the ZIP method for compression/decompression and the UUCODE method for ASCII encoding/decoding. This method will be useful for stations connected via telephonemodems or commercial networks. The electronics delivery could solve the problem of the too late receiving of the FR data by SLR data center.

Novotny, Antonin↗
NASA NTRS1993

A CAM-based LZ data compression IC

A custom CMOS processor is introduced that implements the Data Compression Lempel-Ziv (DCLZ) standard, a variation of the LZ2 Algorithm. This component presently achieves a sustained compression and decompression rate of 10 megabytes/second by employing an on-chip content-addressable memory for string table storage.

Winters, K.↗
NASA NTRS1993

The Communication Link and Error ANalysis (CLEAN) simulator

During the period July 1, 1993 through December 30, 1993, significant developments to the Communication Link and Error ANalysis (CLEAN) simulator were completed and include: (1) Soft decision Viterbi decoding; (2) node synchronization for the Soft decision Viterbi decoder; (3) insertion/deletion error programs; (4) convolutional encoder; (5) programs to investigate new convolutional codes; (6) pseudo-noise sequence generator; (7) soft decision data generator; (8) RICE compression/decompression (integration of RICE code generated by Pen-Shu Yeh at Goddard Space Flight Center); (9) Markov Chain channel modeling; (10) percent complete indicator when a program is executed; (11) header documentation; and (12) help utility. The CLEAN simulation tool is now capable of simulating a very wide variety of satellite communication links including the TDRSS downlink with RFI. The RICE compression/decompression schemes allow studies to be performed on error effects on RICE decompressed data. The Markov Chain modeling programs allow channels with memory to be simulated. Memory results from filtering, forward error correction encoding/decoding, differential encoding/decoding, channel RFI, nonlinear transponders and from many other satellite system processes. Besides the development of the simulation, a study was performed to determine whether the PCI provides a performance improvement for the TDRSS downlink. There exist RFI with several duty cycles for the TDRSS downlink. We conclude that the PCI does not improve performance for any of these interferers except possibly one which occurs for the TDRS East. Therefore, the usefulness of the PCI is a function of the time spent transmitting data to the WSGT through the TDRS East transponder.

Ebel, William J.↗
NASA NTRS1994

Vulnerability of manned spacecraft to crew loss from orbital debris penetration

Orbital debris growth threatens the survival of spacecraft systems from impact-induced failures. Whereas the probability of debris impact and spacecraft penetration may currently be calculated, another parameter of great interest to safety engineers is the probability that debris penetration will cause actual spacecraft or crew loss. Quantifying the likelihood of crew loss following a penetration allows spacecraft designers to identify those design features and crew operational protocols that offer the highest improvement in crew safety for available resources. Within this study, a manned spacecraft crew survivability (MSCSurv) computer model is developed that quantifies the conditional probability of losing one or more crew members, P(sub loss/pen), following the remote likelihood of an orbital debris penetration into an eight module space station. Contributions to P(sub loss/pen) are quantified from three significant penetration-induced hazards: pressure wall rupture (explosive decompression), fragment-induced injury, and 'slow' depressurization. Sensitivity analyses are performed using alternate assumptions for hazard-generating functions, crew vulnerability thresholds, and selected spacecraft design and crew operations parameters. These results are then used to recommend modifications to the spacecraft design and expected crew operations that quantitatively increase crew safety from orbital debris impacts.

Williamsen, J. E.↗