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NASA NTRS1999

An X-Ray Study of Grain Evolution behind Non-Radiative Shock

We model the dynamics, the destruction by sputtering, and the infrared (IR) emission from collisionally heated dust grains in fast (>/= 400 km s(exp -1)) astrophysical shocks in order to develop IR diagnostics for the destruction of grains in these environments. The calculations take into account the feedback from sputtering and IR emission on the gas-phase abundances, the cooling, and the ionization and thermal structure of the shock. Sputtering changes the initial grain size distribution, creating a deficiency of small (radius <50 A) grains compared to their preshock abundances. The altered grain size distribution depends on shock velocity and the density of the interstellar medium. Dust particles with sizes below approximately equal 300 A are stochastically heated, undergo temperature fluctuations, and radiate an excess of near-infrared emission (i </= 40 (micron)meter) over that expected for grains in thermal equilibrium. This near-infrared excess is a measure of the abundance of small grains and therefore a powerful diagnostic for the amount of destruction the grains were subjected to in the shock. We present here IR spectra from collisionally heated dust for a variety of shocks, and depict the changes in the spectra as a function of postshock column density. Our studies compliment those of Vancura et at. that examined the effects of the release of the sputtered refractory elements on the ultraviolet and X-ray emission. Multiwavelength observations at X-ray, Ultraviolet (UV), and IR wavelengths are therefore essential in piecing together a comprehensive picture of the physics of grain destruction in fast astrophysical shocks.

Vancura, Olaf↗

NASA NTRS2000

A Simulation of Bromoform's Contribution to Stratospheric Bromine

Many chlorinated and brominated compounds that are inert in the troposphere are destroyed in the stratosphere and act as an in-situ source of stratospheric reactive chlorine and bromine. Other halogenated compounds that are reactive in the troposphere might contribute to the stratosphere's halogen budget in two ways. First, like their unreactive companions, rapid convective transport might carry them to the upper troposphere and make them available for subsequent advection by the mean circulation into the stratosphere before they are oxidized or photolyzed. Second, it is more likely that they are destroyed in the troposphere, and the chlorine and bromine that is released might then be transported to the stratosphere. We evaluate the relative influence of these processes on stratospheric bromine in a three-dimensional chemistry and transport model which simulates the distribution of bromoform (CHBr3). CHBr3 is parameterized as a short-lived, ocean-surface source gas whose destruction by photolysis and reaction with hydroxyl (OH) in the troposphere and stratosphere yields inorganic bromine (Br(sub y)). Many of the observed features of CHBr3 are simulated well, and comparisons with observations are used to show that the model represents aspects of transport in the upper troposphere and lower stratosphere that are critical to the evaluation. In particular, the model maintains the observed troposphere-stratosphere distinctness in transport pathways and reproduces the observed seasonal dependence of the mixture of air in the middle- and high-latitude lowermost stratosphere. We estimate that adding CHBr3 to models which already include the long-lived organic brominated compounds (halons and methyl bromide) will increase the simulated stratospheric mass of Br(sub y) by about 15 percent. In-situ stratospheric destruction of CHBr3 produces Br(sub y) in amounts which are comparable to that transported into the stratosphere after photolysis and oxidation of CHBr3 in the troposphere. In our simulations the mass of Br(sub y) produced from the destruction of CHBr3 does not exceed the mass of Br(sub y) produced from the destruction of the long-lived compounds at any level in the stratosphere. However, Br(sub y) from the loss of CHBr3 accounts for approximately one-third of the total Br(sub y) in the lowest kilometer of the stratosphere.

Nielsen, J. Eric↗

NASA NTRS1999

Streptomycin ototoxicity and hair cell regeneration in the adult pigeon utricle

OBJECTIVE: The purpose of this study was to develop a technique to investigate the regeneration of utricular hair cells in the adult pigeon (Columba livia) following complete hair cell loss through administration of streptomycin. STUDY DESIGN: Experimental animal study. METHODS: Animals were divided into four groups. Group 1 received 10 to 15 days of systemic streptomycin injections. Animals in Groups 2 and 3 received a single direct placement of a 1-, 2-, 4-, or 8-mg streptomycin dose into the perilymphatic space. Animals in Groups 1 and 2 were analyzed within 1 week from injection to investigate hair cell destruction, whereas Group 3 was investigated at later dates to study hair cell recovery. Group 4 animals received a control injection of saline into the perilymphatic space. Damage and recovery were quantified by counting hair cells in isolated utricles using scanning electron microscopy. RESULTS: Although systemic injections failed to reliably achieve complete utricular hair cell destruction, a single direct placement of a 2-, 4-, or 8-mg streptomycin dose caused complete destruction within the first week. Incomplete hair cell loss was observed with the 1-mg dose. Over the long term, regeneration of the hair cells was seen with the 2-mg dose but not the 8-mg dose. Control injections of saline into the perilymphatic space caused no measurable hair cell loss. CONCLUSIONS: Direct placement of streptomycin into the perilymph is an effective, reliable method for complete destruction of utricular hair cells while preserving the regenerative potential of the neuroepithelium.

Non-NASA Center↗

NASA NTRS2009

Using GPS to Detect Imminent Tsunamis

A promising method of detecting imminent tsunamis and estimating their destructive potential involves the use of Global Positioning System (GPS) data in addition to seismic data. Application of the method is expected to increase the reliability of global tsunami-warning systems, making it possible to save lives while reducing the incidence of false alarms. Tsunamis kill people every year. The 2004 Indian Ocean tsunami killed about 230,000 people. The magnitude of an earthquake is not always a reliable indication of the destructive potential of a tsunami. The 2004 Indian Ocean quake generated a huge tsunami, while the 2005 Nias (Indonesia) quake did not, even though both were initially estimated to be of the similar magnitude. Between 2005 and 2007, five false tsunami alarms were issued worldwide. Such alarms result in negative societal and economic effects. GPS stations can detect ground motions of earthquakes in real time, as frequently as every few seconds. In the present method, the epicenter of an earthquake is located by use of data from seismometers, then data from coastal GPS stations near the epicenter are used to infer sea-floor displacements that precede a tsunami. The displacement data are used in conjunction with local topographical data and an advanced theory to quantify the destructive potential of a tsunami on a new tsunami scale, based on the GPS-derived tsunami energy, much like the Richter Scale used for earthquakes. An important element of the derivation of the advanced theory was recognition that horizontal sea-floor motions contribute much more to generation of tsunamis than previously believed. The method produces a reliable estimate of the destructive potential of a tsunami within minutes typically, well before the tsunami reaches coastal areas. The viability of the method was demonstrated in computational tests in which the method yielded accurate representations of three historical tsunamis for which well-documented ground-motion measurements were available. Development of a global tsunami-warning system utilizing an expanded network of coastal GPS stations was under consideration at the time of reporting the information for this article.

Song, Y. Tony↗

NASA NTRS2011

Two Catalysts for Selective Oxidation of Contaminant Gases

Two catalysts for the selective oxidation of trace amounts of contaminant gases in air have been developed for use aboard the International Space Station. These catalysts might also be useful for reducing concentrations of fumes in terrestrial industrial facilities especially facilities that use halocarbons as solvents, refrigerant liquids, and foaming agents, as well as facilities that generate or utilize ammonia. The first catalyst is of the supported-precious-metal type. This catalyst is highly active for the oxidation of halocarbons, hydrocarbons, and oxygenates at low concentrations in air. This catalyst is more active for the oxidation of hydrocarbons and halocarbons than are competing catalysts developed in recent years. This catalyst completely converts these airborne contaminant gases to carbon dioxide, water, and mineral acids that can be easily removed from the air, and does not make any chlorine gas in the process. The catalyst is thermally stable and is not poisoned by chlorine or fluorine atoms produced on its surface during the destruction of a halocarbon. In addition, the catalyst can selectively oxidize ammonia to nitrogen at a temperature between 200 and 260 C, without making nitrogen oxides, which are toxic. The temperature of 260 C is higher than the operational temperature of any other precious-metal catalyst that can selectively oxidize ammonia. The purpose of the platinum in this catalyst is to oxidize hydrocarbons and to ensure that the oxidation of halocarbons goes to completion. However, the platinum exhibits little or no activity for initiating the destruction of halocarbons. Instead, the attack on the halocarbons is initiated by the support. The support also provides a high surface area for exposure of the platinum. Moreover, the support resists deactivation or destruction by halogens released during the destruction of halocarbons. The second catalyst is of the supported- metal-oxide type. This catalyst can selectively oxidize ammonia to nitrogen at temperatures up to 400 C, without producing nitrogen oxides. This catalyst converts ammonia completely to nitrogen, even when the concentration of ammonia is very low. No other catalyst is known to oxidize ammonia selectively at such a high temperature and low concentration. Both the metal oxide and the support contribute to the activity and selectivity of this catalyst.

Wright, John D.↗

NASA NTRS2015

Survival Times of Meter-Sized Rock Boulders on the Surface of Airless Bodies

This study considers the survival times of meter-sized rock boulders on the surfaces of several airless bodies. As the starting point, we employ estimates of the survival times of such boulders on the surface of the Moon by[1], then discuss the role of destruction due to day-night temperature cycling, consider the meteorite bombardment environment on the considered bodies in terms of projectile flux and velocities and finally estimate the survival times. Survival times of meter-sized rocks on lunar surface: The survival times of hand specimen-sized rocks exposed to the lunar surface environment were estimated based on experiments modeling the destruction of rocks by meteorite impacts, combined with measurements of the lunar surface meteorite flux, (e.g.,[2]). For estimations of the survival times of meter-sized lunar boulders, [1] suggested a different approach based on analysis of the spatial density of boulders on the rims of small lunar craters of known absolute age. It was found that for a few million years, only a small fraction of the boulders ejected by cratering process are destroyed, for several tens of million years approx.50% are destroyed, and for 200-300 Ma, ~90 to 99% are destroyed. Following [2] and other works, [1] considered that the rocks are mostly destroyed by meteorite impacts. Destruction of rocks by thermal-stress. However, high diurnal temperature variations on the surface of the Moon and other airless bodies imply that thermal stresses may also be a cause of surface rock destruction. Delbo et al. [3] interpreted the observed presence of fine debris on the surface of small asteroids as due to thermal surface cycling. They stated that because of the very low gravity on the surface of these bodies, ejecta from meteorite impacts should leave the body, so formation there of fine debris has to be due to thermal cycling. Based on experiments on heating-cooling of cm-scale pieces of ordinary and carbonaceous chondrites and theoretical modeling of expansion of the cracks formed they concluded that thermal fragmentation breaks up rocks larger than a few centimeters more quickly than do micrometeoroid impacts. According to them at 1 AU distance from the Sun the lifetime of 10 cm rock fragments on asteroids with a period of rotation from 2.2 to 6 hours should be only ~103 to 104 years and the larger the rock the faster it gets destroyed. But although [3] are obviously correct stating that impact ejecta should leave small asteroids, the low-velocity part of escaping ejecta will mostly stay in orbits close this given asteroid and part of them will eventually return to it. Moreover, directly beneath the impact point the target rock should be fractured and crushed but may not leave the body (Figure 1). These two points question the conclusions of [3].

Basilevsky, A. T.↗

NASA NTRS1971

Sterilization of space hardware.

Discussion of various techniques of sterilization of space flight hardware using either destructive heating or the action of chemicals. Factors considered in the dry-heat destruction of microorganisms include the effects of microbial water content, temperature, the physicochemical properties of the microorganism and adjacent support, and nature of the surrounding gas atmosphere. Dry-heat destruction rates of microorganisms on the surface, between mated surface areas, or buried in the solid material of space vehicle hardware are reviewed, along with alternative dry-heat sterilization cycles, thermodynamic considerations, and considerations of final sterilization-process design. Discussed sterilization chemicals include ethylene oxide, formaldehyde, methyl bromide, dimethyl sulfoxide, peracetic acid, and beta-propiolactone.

Pflug, I. J.↗

NASA NTRS1978

Carbon fiber study. A compilation of an intergovernmental committee study

Carbon fibers have opened a wealth of new structural engineering and consumer product opportunities. The potential benefits are higher strength, and lighter weight military and commercial products, which portend energy savings and increases safety. Unfortunately, these benefits are not realized without risk. Inadvertent fiber release, during manufacture or by destruction of the resin binder in fire, is the major hazard associated with composites. The carbon (or graphite) fibers are finer than human hair and if released into the air, they can be easily transported by winds or currents. In contact with electrical devices, they can create resistive loading, short circuits, and arcing, resulting in stoppages or destruction. Their health impact is not fully known and requires careful research and analysis before any firm conclusions can be reached; however, based upon current available information, they are primarily an irritant to the eyes and skin, like fiberglass, rather than carcinogenic or destructive to lung tissue. Major manufacturers are aware of the unique problems associated with these materials and have successfully applied controls to avoid the inplant problems.

Source record↗

NASA NTRS1986

Why do interstellar grains exist?

There exists a discrepancy between calculated destruction rates of grains in the interstellar medium and postulated sources of new grains. This problem was examined by modelling the global life cycle of grains in the galaxy. The model includes: grain destruction due to supernovae shock waves; grain injection from cool stars, planetary nebulae, star formation, novae, and supernovae; grain growth by accretion in dark clouds; and a mixing scheme between phases of the interstellar medium. Grain growth in molecular clouds is considered as a mechanism or increasing the formation rate. To decrease the shock destruction rate, several new physical processes, such as partial vaporization effects in grain-grain collisions, breakdown of the small Larmor radius approximation for betatron acceleration, and relaxation of the steady-state shock assumption are included.

Seab, C. G.↗

NASA NTRS1988

Workshop on the Growth of Continental Crust

Constraints and observations were discussed on a fundamental unsolved problem of global scale relating to the growth of planetary crusts. All of the terrestrial planets were considered, but emphasis was placed on the Earth's continental crust. The title of each session is: (1) Extraterrestrial crustal growth and destruction; (2) Constraints for observations and measurements of terrestrial rocks; (3) Models of crustal growth and destruction; and (4) Process of crustal growth and destruction.

Ashwal, Lewis D.↗

NASA NTRS1989

Ozone budgets from the Dynamics and Chemistry of Marine Stratocumulus experiment

Measurements from the Dynamics and Chemistry of marine Stratocumulus experiment have been used to study components of the regional ozone budget. The surface destruction rate is determined by eddy correlation of ozone and vertical velocity measured by a low-flying aircraft. Significant variability is found in the measured surface resistance; it is partially correlated with friction velocity but appears to have other controlling influences as well. The mean resistance is 4190 s/m which is higher (slower destruction) than most previous estimates for seawater. Flux and mean measurements throughout the marine boundary layer are used to estimate the net rate of in situ photochemical production/destruction of ozone. Averaged over the flights, ozone concentration is found to be near steady state, and a net of photochemical destruction of 0.02-0.07 ng/cu m per sec is diagnosed. This is an important confirmation of photochemical model results for the remote marine boundary layer. Ozone vertical distributions above the boundary layer show a strongly layered structure with very sharp gradients. These distributions are possibly related to the stratospheric ozone source.

Kawa, S. R.↗

NASA NTRS1991

Chemical waste disposal in space by plasma discharge

An inductively coupled plasma discharge apparatus operating at 13.56 MHz and with electrical power up to 2.5 kW was constructed. The efficiency of this device to destroy various gases expected to be carried aboard the Space Station was tested. By expressing the efficiency of the device in terms of G-value (the number of molecules decomposed per 100 eV of energy absorbed), the results are compared with known efficiencies of ionizing radiation to destroy these same gases. In the case of ammonia, it was found that in the inductively coupled device, the destruction efficiency, G(-NH3) varied from 6.0 to 32.0 molecules/100 eV, depending on conditions. It was also found that capacitatively coupled discharges were less efficient in destroying NH2 than the inductively coupled discharge. In the case NH2 destruction, it was found that the G(-NH3) was a qualitative guide to the efficiencies of plasmas. The plasma device was also used to destroy nitrous oxide and methane. It is shown how the G-value for the destruction of any gas can be computed theoretically from a knowledge of the electron velocity distribution, the various electron molecule scattering cross sections, and the rate constants for the reactions of secondary species.

Baird, James K.↗

NASA NTRS1991

The relative importance of prebiotic synthesis on the Earth and input from comets and meteorites

The prebiotic synthesis of hydrogen cyanide and formaldehyde was studied by the action of electric discharges on various model primitive atmospheres containing CH4, CO, and CO2. Photochemical production rates would also have been important and were calculated for HCN and H2CO. A reasonable rate of synthesis of amino acids from these sources is about 10 n moles/(sq cm yr) or 0.10 moles/sq cm in 10(exp 7) yrs. This would give a concentration of 3 x 10(exp -4) M in an ocean of the present size (300 liters/sq cm). The amino acids cannot accumulate over a longer period because the entire ocean passes through the 350 C submarine vents in 10(exp 7) yrs, which decomposes all the organic compounds. A number of workers have calculated the influx of comets and meteorites on the primitive earth, both as a destructive process for organic compounds and for any life that was present, as well as a source of organic compounds. Some of the amino acids from the meteorite proposed to have hit the earth 65 x 10(exp 6) yrs ago were detected at the Cretaceous/Tertiary boundary sediments. The problem with proposing a large scale input of organic compounds from meteorites and comets is that they must survive passage through the atmosphere and impact. There are some processes that would allow survival such as showers of centimeter to meter sized meteorites and various aerodynamic braking processes for larger objects. Even if a significant amount of the organic material survived impact, the destructive processes in the hydrothermal vents would remove these compounds on the average in 10(exp 7) yrs or less. If it is assumed that the input rate was sufficient to overcome these destructive processes, then too much carbon and water, especially from comets, would have been added to the surface of the earth. It was concluded that while some organic material was added to the earth from comets and meteorites, the amount available from these sources at a given time was only a few percent of that from earth based syntheses.

Miller, S. L.↗

NASA NTRS1992

Lumley's energy cascade dissipation rate model for boundary-free turbulent shear flows

True dissipation occurs mainly at the highest wavenumbers where the eddy sizes are comparatively small. These high wavenumbers receive their energy through the spectral cascade of energy starting with the largest eddies spilling energy into the smaller eddies, passing through each wavenumber until it is dissipated at the microscopic scale. However, a small percentage of the energy does not spill continuously through the cascade but is instantly passed to the higher wavenumbers. Consequently, the smallest eddies receive a certain amount of energy almost immediately. As the spectral energy cascade continues, the highest wavenumber needs a certain time to receive all the energy which has been transferred from the largest eddies. As such, there is a time delay, of the order of tau, between the generation of energy by the largest eddies and the eventual dissipation of this energy. For equilibrium turbulence at high Reynolds numbers, there is a wide range where energy is neither produced by the large eddies nor dissipated by viscosity, but is conserved and passed from wavenumber to higher wavenumbers. The rate at which energy cascades from one wavenumber to another is proportional to the energy contained within that wavenumber. This rate is constant and has been used in the past as a dissipation rate of turbulent kinetic energy. However, this is true only in steady, equilibrium turbulence. Most dissipation models contend that the production of dissipation is proportional to the production of energy and that the destruction of dissipation is proportional to the destruction of energy. In essence, these models state that the change in the dissipation rate is proportional to the change in the kinetic energy. This assumption is obviously incorrect for the case where there is no production of turbulent energy, yet energy continues to cascade from large to small eddies. If the time lag between the onset on the energy cascade to the destruction of energy at the microscale can be modeled, then there will be a better representation of the dissipation process. Development of an energy cascade time scale equation is discussed.

Duncan, B. S.↗

NASA NTRS1989

Residual mode filters and adaptive control in large space structures

One of the most difficult problems in controlling large systems and structures is compensating for the destructive interaction which can occur between the reduced-order model (ROM) of the plant, which is used by the controller, and the unmodeled dynamics of the plant, often called the residual modes. The problem is more significant in the case of large space structures because their naturally light damping and high performance requirements lead to more frequent, destructive residual mode interaction (RMI). Using the design/compensation technique of residual mode filters (RMF's), effective compensation of RMI can be accomplished in a straightforward manner when using linear controllers. The use of RMF's has been shown to be effective for a variety of large structures, including a space-based laser and infinite dimensional systems. However, the dynamics of space structures is often uncertain and may even change over time due to on-orbit erosion from space debris and corrosive chemicals in the upper atmosphere. In this case, adaptive control can be extremely beneficial in meeting the performance requirements of the structure. Adaptive control for large structures is also based on ROM's and so destructive RMI may occur. Unfortunately, adaptive control is inherently nonlinear, and therefore the known results of RMF's cannot be applied. The purpose is to present the results of new research showing the effects of RMI when using adaptive control and the work which will hopefully lead to RMF compensation of this problem.

Davidson, Roger A.↗

NASA NTRS1994

The formation of small grains in shocks in the ISM

Carbonaceous and silicate grains swept up, and betatron accelerated, by supernova-generated shock waves in the interstellar medium are exposed to grain destructive processing. The degree of grain destruction is determined by the differential gas-grain and grain-grain velocities, which lead to sputtering of the grain surface and grain core disruption (deformation, vaporization and shattering), respectively. The threshold pressure for grain shattering in grain-grain collisions (100 k bar) is considerably lower than that for vaporization (approximately 5 M bar). Therefore, collisions between grains shatter large grains into smaller fragments (i.e., small grains and PAH's). Using a new algorithms for the destructive processes, it was possible to model the formation fo small grain fragments in grain-grain collisions in the warm phase of the interstellar medium. It was found that in one cycle through the warm medium (approximately 3 x 10(sup 6) years) of order 1-2% of the total grain mass is shattered into particles with radii of less than 50 A.

Jones, Anthony P.↗

NASA NTRS1995

Enhanced alkaline hydrolysis and biodegradability studies of nitrocellulose-bearing missile propellant

Large amounts of energetic materials which have been accumulated over the years in various manufacturing and military installations must be disposed of in an environmentally sound manner. Historically, the method of choice for destruction of obsolete or aging energetic materials has been open burning or open detonation (OB/OD). This destruction approach has become undesirable due to air pollution problems. Therefore, there is a need for new technologies which will effectively and economically deal with the disposal of energetic materials. Along those lines, we have investigated a chemical/biological process for the safe destruction and disposal of a double base solid rocket propellant (AHH), which was used in several 8 inch projectile systems. The solid propellant is made of nitrocellulose and nitroglycerin as energetic components, two lead salts which act as ballistic modifiers, triacetin as a plasticizer and 2-Nitrodiphenylamine (2-NDPA) as a stabilizer. A process train is being developed to convert the organic components of the propellant to biodegradable products and remove the lead from the process stream. The solid propellant is first hydrolyzed through an enhanced alkaline hydrolysis process step. Following lead removal and neutralization, the digested liquor rich in nitrates and nitrites is found to be easily biodegradable. The digestion rate of the intact ground propellant as well as the release of nitrite and nitrate groups were substantially increased when ultrasound were supplied to the alkaline reaction medium compared to the conventional alkaline hydrolysis. The effects of reaction time, temperature, sodium hydroxide concentration and other relevant parameters on the digestion efficiency and biodegradability have been studied. The present work indicates that the AHH propellant can be disposed of safely with a combination of physiochemical and biological processes.

Sidhoum, Mohammed↗

NASA NTRS1994

A study of X-ray and infrared emissions from dusty nonradiative shock waves

We have constructed models that predict the dynamic evolution and infrared (IR) emission of grains behind nonradiative shock waves. We present a self-consistent treatment of the effect of grain destruction and heating on the ionization structure and X-ray emission of the postshock gas. Incorporating thermal sputtering, collisional heating, and deceleration of grains in the postshock flow, we predict the IR and X-ray fluxes from the dusty plasma as a function of swept-up column density. Heavy elements such as C, O, Mg, S, Si and Fe are initially depleted from the gas phase but are gradually returned as the grains are destroyed. The injected neutral atoms require some time to 'catch up' with the ionization state of the ambient gas. The nonequilibrium ionization state and gradient in elemental abundances in the postshock flow produces characteristic X-ray signatures that can be related to the age of the shock and amount of grain destruction. We study the effects of preshock density and shock velocity on the X-ray and IR emission from the shock. We show that the effects of graindestruction on the X-ray spectra of shock waves are substantial. In particular, temperatures derived from X-ray spectra of middle-aged remnants are likely to be overestimated by approximately 15% if cosmic abundances are assumed. Due to the long timescales for grain destruction in X-ray gases over a wide range of temperatures, we suggest that future X-ray spectra studies of supernova remnants be based on depleted abundances instead of cosmic abundances. Our model predictions agree reasonably well with IRAS and Einstein IPC observations of the Cygnus Loop.

Vancura, Olaf↗