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At least 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
NASA NTRS1999

Prebiotic Nitrogen Fixation by FeS Reduction of Nitrite Under Acidic Conditions

Theories for the origin of life require the availability of reduced nitrogen for the formation of such species as amino acid and nucleic acids. In a strongly reducing atmosphere, compounds essential to the chemical evolution of life, such as amino acids, can form by reactions between HCN, NH3, and carbonyl compounds produced in spark discharges. However, under non-reducing atmospheres, electric discharges produced NO rather than HCN or NH3. This raises the questions of; how ammonia can be formed under a neutral atmosphere, and what conditions are needed such formation to occur? On possibility is the conversion of NO into nitric and nitrous acids (through HNO) and rained into the oceans. The reduction of nitrite by aqueous Fe(II) (6 Fe(+2) + 7 H(+) + NO2(-) yields 6 Fe(III) + 2 H2O + NH3) such as was present on the early Earth could then have produced ammonia. However, this reaction does not proceed at pHs less than 7.3. An alternative is reduction by other forms of Fe(II), such as FeS. We will present results that show that FeS can reduce nitrite to ammonia at pHs as low as pH 5 under a variety of conditions.

Summers, David P.↗
NASA NTRS1971

Welded polypropylene liners for large descaling tanks

Liners for nitric and hydrofluoric acid tanks show no sign of deterioration after 18 months of continuous use. Each side of each edge of the polypropylene sheets is chamfered, and sheets are welded from both sides with polypropylene filler rod and a special hot-air welding torch.

Abel, H. P.↗
NASA NTRS1983

Etchant for HgxCd1-xTe Crystals

Preferential etching by mixture of nitric and hydrochloric acids reveals crystal dislocation defects (type D) and impurity-dislocation defects (type S) in these crystals, which have optical and electrical applications.

Irene, E. A.↗
NASA NTRS1983

Observation of defects in mercury cadmium telluride crystals grown by chemical vapor transport

A mixture of nitric and hydrochloric acids was found to yield etch pits on mercury cadmium telluride crystals grown by chemical vapor transport using iodine or mercuric iodide as the transport agent. Two types of pits were observed by optical microscopy: triangular pyramidal and round saucer shaped pits. Transmission electron microscopy confirmed that two types of defects were present: dislocations and second phase occlusions. The present study suggests that the defects are near the crystal surface and therefore will probably not significantly affect the electrical characteristics.

Irene, E. A.↗
NASA NTRS1988

Antarctic polar stratospheric aerosols: The roles of nitrates, chlorides and sulfates

Nitric and hydrochloric acids have been postulated to condense in the winter polar stratosphere to become an important component of polar stratospheric clouds. One implication is that the removal of NO(y) from the gas phase by this mechanism allows high Cl(x) concentrations to react with O3, because the formation of ClNO3 is inhibited. Contributions of NO3 and Cl to the stratospheric aerosol were determined during the 1987 Airborne Antarctic Ozone Experiment by testing for the presence of nitrates and chlorides in the condensed phase. Aerosol particles were collected on four 500 micron diameter gold wires, each pretreated differently to give results that were specific to certain physical and chemical aerosol properties. One wire was carbon-coated for concentration and size analyses by scanning electron microscopy; X-ray energy dispersive analyses permitted the detection of S and Cl in individual particles. Three more wires were coated with Nitron, barium chloride and silver nitrate, respectively, to detect nitrate, sulfate and chloride in aerosol particles. All three ions, viz., sulfates, nitrates and chlorides were detected in the Antarctic stratospheric aerosol. In terms of number concentrations, the aerosol was dominated by sulfates, followed by chlorides and nitrates. An inverse linear regression can be established between nitrate concentrations and ozone mixing ratio, and between temperature and nitrates.

Pueschel, R. F.↗
NASA NTRS2003

New Method Developed To Purify Single Wall Carbon Nanotubes for Aerospace Applications

Single wall carbon nanotubes have attracted considerable attention because of their remarkable mechanical properties and electrical and thermal conductivities. Use of these materials as primary or secondary reinforcements in polymers or ceramics could lead to new materials with significantly enhanced mechanical strength and electrical and thermal conductivity. Use of carbon-nanotube-reinforced materials in aerospace components will enable substantial reductions in component weight and improvements in durability and safety. Potential applications for single wall carbon nanotubes include lightweight components for vehicle structures and propulsion systems, fuel cell components (bipolar plates and electrodes) and battery electrodes, and ultra-lightweight materials for use in solar sails. A major barrier to the successful use of carbon nanotubes in these components is the need for methods to economically produce pure carbon nanotubes in large enough quantities to not only evaluate their suitability for certain applications but also produce actual components. Most carbon nanotube synthesis methods, including the HiPCO (high pressure carbon monoxide) method developed by Smalley and others, employ metal catalysts that remain trapped in the final product. These catalyst impurities can affect nanotube properties and accelerate their decomposition. The development of techniques to remove most, if not all, of these impurities is essential to their successful use in practical applications. A new method has been developed at the NASA Glenn Research Center to purify gram-scale quantities of single wall carbon nanotubes. This method, a modification of a gas phase purification technique previously reported by Smalley and others, uses a combination of high-temperature oxidations and repeated extractions with nitric and hydrochloric acid. This improved procedure significantly reduces the amount of impurities (catalyst and nonnanotube forms of carbon) within the nanotubes, increasing their stability significantly. The onset of decomposition of the purified nanotubes (determined by thermal gravimetric analysis in air) is more than 300 C higher than that of the crude nanotubes. Transmission electron microscopy analysis of nanotubes purified by this method reveals near complete removal of iron catalyst particles. Analysis of the nanotubes using inductively coupled plasma spectroscopy revealed that the iron content of the nanotubes was reduced from 22.7 wt% in the crude nanotubes to less than 0.02 wt%. X-ray photoelectron spectroscopy revealed a decrease in iron content after purification as well as an increase in oxygen content due to the formation of carboxylic acid groups on the surface of the nanotubes. Nanotubes purified by this improved method can be readily dispersed in common organic solvents, in particular N,N-dimethylformamide, using prolonged ultrasonic treatment. These dispersions can then be used to incorporate single wall carbon nanotubes into polymer films.

Lebron, Marisabel↗
NASA NTRS1973

Neutron activation analysis for antimetabolites

Determination of metal ion contaminants in food samples is studied. A weighed quantity of each sample was digested in a concentrated mixture of nitric, hydrochloric and perchloric acids to affect complete solution of the food products. The samples were diluted with water and the pH adjusted according to the specific analysis performed. The samples were analyzed by neutron activation analysis, polarography, and atomic absorption spectrophotometry. The solid food samples were also analyzed by neutron activation analysis for increased sensitivity and lower levels of detectability. The results are presented in tabular form.

Source record↗
NASA NTRS1999

Portable fiber-coupled diode-laser-based sensor for multiple trace gas detection

Tunable narrowband mid-infrared radiation from 3.25 to 4.4 micrometers is generated by a compact fiber-coupled, difference-frequency-based spectroscopic source. A 20-mW external cavity diode laser (with a tuning range from 814 to 870 nm) and a 50-mW distributed-Bragg-reflector diode-laser-seeded ytterbium-doped fiber amplifier operating at 1083 nm are difference-frequency mixed in a multi-grating, temperature-controlled periodically poled LiNbO3 crystal. A conversion efficiency of 0.44 mW/(W2cm) (corresponding to a power of approximately equal to 3 microW at 3.3 micrometers) represents the highest conversion efficiency reported for a portable device. Performance characteristics of such a sensor and its application to spectroscopic detection of CO2, N2O, H2CO, HCl, NO2, and CH4 will be reported in this work.

Non-NASA Center↗
NASA NTRS1991

Organic acids and selected nitrogen species for ABLE-3

The NASA Global Tropospheric Experiment (GTE) executed airborne science missions aboard the NASA Wallops Electra (NA429) in the North American high latitude (greater than 45 deg North) atmosphere during Jul. to Aug. 1988 and Jul. to Aug. 1990. These missions were part of GTE's Atmospheric Boundary Layer Experiment (ABLE). The 1988 mission , ABLE-3A, examined the ecosystems of Alaska as a source and/or sink for important tropospheric gases and particles, and gained new information on the chemical composition of the Arctic atmosphere during the summertime. During 1990 the second high latitude mission, ABLE-3B, focused on the Hudson Bay Lowland and Labrador regions of Canada. Both of these missions provided benchmark data sets on atmosphere biosphere exchange and atmospheric chemistry over largely uninhabited regions of North America. In support of the GTE/ABLE-3A and -3B field missions, the University of New Hampshire flew instrumentation aboard the Wallops Electra research aircraft to provide measurements of the trace gases nitric (HNO3), formic (HCOOH), and acetic (CH3COOH) acid. In addition, measurements were conducted to determine the major water soluble ionic composition of the atmospheric aerosol. For ABLE-3B, groundbased measurements of the acidic trace gases were also performed from the NASA micrometerological tower situated at Schefferville, Laborador. These measurements were aimed at assessing dry deposition of acidic gases to the taiga ecosystem in the Laborador region of Canada.

Talbot, Robert W.↗
NASA NTRS1994

Active chlorine and nitric oxide formation from chemical rocket plume afterburning

Chlorine and oxides of nitrogen (NO(x)) released into the atmosphere contribute to acid rain (ground level or low-altitude sources) and ozone depletion from the stratosphere (high-altitude sources). Rocket engines have the potential for forming or activating these pollutants in the rocket plume. For instance, H2/O2 rockets can produce thermal NO(x) in their plumes. Emphasis, in the past, has been placed on determining the impact of chlorine release on the stratosphere. To date, very little, if any, information is available to understand what contribution NO(x) emissions from ground-based engine testing and actual rocket launches have on the atmosphere. The goal of this work is to estimate the afterburning emissions from chemical rocket plumes and determine their local stratospheric impact. Our study focuses on the space shuttle rocket motors, which include both the solid rocket boosters (SRB's) and the liquid propellant main engines (SSME's). Rocket plume afterburning is modeled employing a one-dimensional model incorporating two chemical kinetic systems: chemical and thermal equilibria with overlayed nitric oxide chemical kinetics (semi equilibrium) and full finite-rate chemical kinetics. Additionally, the local atmospheric impact immediately following a launch is modeled as the emissions diffuse and chemically react in the stratosphere.

Leone, D. M.↗
NASA NTRS2001

Novel effects of nitric oxide

Nitric oxide (NO), a simple free radical gas, elicits a surprisingly wide range of physiological and pathophysiological effects. NO interacts with soluble guanylate cyclase to evoke many of these effects. However, NO can also interact with molecular oxygen and superoxide radicals to produce reactive nitrogen species that can modify a number of macromolecules including proteins, lipids, and nucleic acids. NO can also interact directly with transition metals. Here, we have reviewed the non--3',5'-cyclic-guanosine-monophosphate-mediated effects of NO including modifications of proteins, lipids, and nucleic acids.

Non-NASA Center↗
NASA NTRS2000

Fluid shear stress stimulates prostaglandin and nitric oxide release in bone marrow-derived preosteoclast-like cells

Bone is a porous tissue that is continuously perfused by interstitial fluid. Fluid flow, driven by both vascular pressure and mechanical loading, may generate significant shear stresses through the canaliculi as well as along the bone lining at the endosteal surface. Both osteoblasts and osteocytes produce signaling factors such as prostaglandins and nitric in response to fluid shear stress (FSS); however, these humoral agents appear to have more profound affects on osteoclast activity at the endosteal surface. We hypothesized that osteoclasts and preosteoclasts may also be mechanosensitive and that osteoclast-mediated autocrine signaling may be important in bone remodeling. In this study, we investigated the effect of FSS on nitric oxide (NO), prostaglandin E(2) (PGE(2)), and prostacyclin (PGI(2)) release by neonatal rat bone marrow-derived preosteoclast-like cells. These cells were tartrate-resistant acid phosphatase (TRAP) positive, weakly nonspecific esterase (NSE) positive, and capable of fusing into calcitonin-responsive, bone-resorbing, multinucleated cells. Bone marrow-derived preosteoclast-like cells exposed for 6 h to a well-defined FSS of 16 dynes/cm(2) produced NO at a rate of 7.5 nmol/mg protein/h, which was 10-fold that of static controls. This response was completely abolished by 100 microM N(G)-amino-L-arginine (L-NAA). Flow also stimulated PGE(2) production (3.9 microg/mg protein/h) and PGI(2) production (220 pg/mg protein/h). L-NAA attenuated flow-induced PGE(2) production by 30%, suggesting that NO may partially modulate PGE(2) production. This is the first report demonstrating that marrow derived cells are sensitive to FSS and that autocrine signaling in these cells may play an important role in load-induced remodeling and signal transduction in bone. Copyright 2000 Academic Press.

NASA Discipline Cell Biology↗
NASA NTRS2001

Simulated microgravity upregulates an endothelial vasoconstrictor prostaglandin

Endothelial nitric oxide contributes to the vascular hyporesponsiveness to norepinephrine (NE) observed in carotid arteries from rats exposed to simulated microgravity. The goal of the present study was to determine whether a cyclooxygenase product of arachidonic acid also influences vascular responsiveness in this setting. Microgravity was simulated in rats by hindlimb unweighting (HU). After 20 days of HU, carotid arteries were isolated from control and HU-treated rats, and vascular rings were mounted in tissue baths for the measurement of isometric contraction. Two cyclooxygenase inhibitors, indomethacin and ibuprofen, and the selective thromboxane A(2) prostanoid-receptor antagonist, SQ-29548, had no effect on the contraction to NE in control vessels but markedly reduced contraction to NE in HU vessels. When the endothelium was removed, indomethacin no longer had any effect on the NE-induced contraction in HU vessels. In endothelium-intact vessels in the presence of indomethacin, the addition of the nitric oxide synthase inhibitor, N(G)-L-nitro-arginine methyl ester, to the medium bathing HU vessels increased the contraction to NE to the level of that of the control vessels. These results indicate that HU treatment induced two endothelial changes in carotid artery that opposed each other. Nitric oxide activity was increased and was responsible for the vascular hyporesponsiveness to NE. The activity of a vasoconstrictor prostaglandin was also increased, and attenuated the vasodilating effect of nitric oxide.

Non-NASA Center↗
NASA NTRS1995

Aqueous nitrite ion determination by selective reduction and gas phase nitric oxide chemiluminescence

An improved method of flow injection analysis for aqueous nitrite ion exploits the sensitivity and selectivity of the nitric oxide (NO) chemilluminescence detector. Trace analysis of nitrite ion in a small sample (5-160 microL) is accomplished by conversion of nitrite ion to NO by aqueous iodide in acid. The resulting NO is transported to the gas phase through a semipermeable membrane and subsequently detected by monitoring the photoemission of the reaction between NO and ozone (O3). Chemiluminescence detection is selective for measurement of NO, and, since the detection occurs in the gas-phase, neither sample coloration nor turbidity interfere. The detection limit for a 100-microL sample is 0.04 ppb of nitrite ion. The precision at the 10 ppb level is 2% relative standard deviation, and 60-180 samples can be analyzed per hour. Samples of human saliva and food extracts were analyzed; the results from a standard colorimetric measurement are compared with those from the new chemiluminescence method in order to further validate the latter method. A high degree of selectivity is obtained due to the three discriminating steps in the process: (1) the nitrite ion to NO conversion conditions are virtually specific for nitrite ion, (2) only volatile products of the conversion will be swept to the gas phase (avoiding turbidity or color in spectrophotometric methods), and (3) the NO chemiluminescence detector selectively detects the emission from the NO + O3 reaction. The method is free of interferences, offers detection limits of low parts per billion of nitrite ion, and allows the analysis of up to 180 microL-sized samples per hour, with little sample preparation and no chromatographic separation. Much smaller samples can be analyzed by this method than in previously reported batch analysis methods, which typically require 5 mL or more of sample and often need chromatographic separations as well.

NASA Discipline Environmental Health↗
NASA NTRS1987

Bolide impacts, acid rain, and biospheric traumas at the Cretaceous-Tertiary boundary

Two plausible projectiles are considered: an ice-rich long-period comet and a much smaller rock-metal asteroid. In the framework of a proposal addressed by Lewis et al. (1982), it is shown that, while the impact projectiles themselves do not shock-heat the atmosphere very extensively, the supersonic plume of water vapor and rock produced on impact does shock the atmosphere up to global scales and the shock is of sufficient intensity to produce abundant nitric oxide. For example, an ice-rich long-period comet with a mass of 1.25 x 10 to the 16th kg and a velocity of 65 km/s striking the earth would produce about 7 x 10 to the 40th molecules NO through shock-heating of the atmosphere by the high-velocity ejecta plume fragments. Specific attention is given to the fraction of the atmosphere shock-heated, the global circulation of the nitrogen oxides, the effects of the ejecta plume water on acid rain (AR) predictions, the effects of AR on continental soils, the relationship between AR production rates and the total amount of acid needed to acidify the surface oceans, and the longevity of the oceanic acidity event and the exhaled CO2 event and their implications for the environment in the first millenia or so after the impact.

Prinn, Ronald G.↗
NASA NTRS2005

Review of HxPyOz-Catalyzed H + OH Recombination in Scramjet Nozzle Expansions; and Possible Phosphoric Acid Enhancement of Scramjet Flameholding, from Extinction of H3PO4 + H2 - Air Counterflow Diffusion Flames

Recent detailed articles by Twarowski indicate that small quantities of phosphorus oxides and acids in the fuel-rich combustion products of H2 + phosphine (PH3) + air should significantly catalyze H, OH and O recombination kinetics during high-speed nozzle expansions -- to reform H2O, release heat, and approach equilibrium more rapidly and closely than uncatalyzed kinetics. This paper is an initial feasibility study to determine (a) if addition of phosphoric acid vapor (H3PO4) to a H2 fuel jet -- which is much safer than using PH3 -- will allow combustion in a high-speed scramjet engine test without adverse effects on localized flameholding, and (b) if phosphorus-containing exhaust emissions are environmentally acceptable. A well-characterized axisymmetric straight-tube opposed jet burner (OJB) tool is used to evaluate H3PO4 addition effects on the air velocity extinction limit (flame strength) of a H2 versus air counterflow diffusion flame. Addition of nitric oxide (NO), also believed to promote catalytic H-atom recombination, was evaluated for comparison. Two to five mass percent H3PO4 in the H2 jet increased flame strength 4.2%, whereas airside addition decreased it 1%. Adding 5% NO to the H2 caused a 2% decrease. Products of H-atom attack on H3PO4 produced an intense green chemiluminescence near the stagnation point. The resultant exothermic production of phosphorus oxides and acids, with accelerated H-atom recombination, released sufficient heat near the stagnation point to increase flame strength. In conclusion, the addition of H3PO4 vapor (or more reactive P sources) to hydrogen in scramjet engine tests may positively affect flameholding stability in the combustor and thrust production during supersonic expansion -- a possible dual benefit with system design / performance implications. Finally, a preliminary assessment of possible environmental effects indicates that scramjet exhaust emissions should consist of phosphoric acid aerosol, with gradual conversion to phosphate aerosol. This is compared to various natural abundances and sources.

Pellett, Gerald↗
NASA NTRS1999

Role of Inflammatory Reponse in Experimental Decompression Sickness

Decompression to altitude can result in gas bubble formation both in tissues and in the systemic veins. The venous gas emboli (VGE) are often monitored during decompression exposures to assess risk for decompression sickness (DCS). Astronauts are at risk for DCS during extravehicular activities (EVA), where decompression occurs from the Space Shuttle or Space Station atmospheric pressure of 14.7 pounds per square inch (PSI) to that of the space suit pressure of 4.3 PSI. DCS symptoms include diffuse pain, especially around joints, inflammation and edema. Pathophysiological effects include interstitial inflammatory responses and recurring injury to the vascular endothelium. Such responses can result in vasoconstriction and associated hemodynamic changes.The granulocyte cell activation and chemotaxin release results in the formation of vasoactive and microvascular permeability altering mediators, especially from the lungs which are the principal target organ for the venous bubbles, and from activated cells (neutrophils, platelets, macrophages). Such mediators include free arachidonic acid and the byproducts of its metabolism via the cyclooxygenase and lipoxygenase pathways (see figure). The cyclooxygenase pathway results in formation of prostacyclin and other prostaglandins and thromboxanes that cause vasoconstriction, bronchoconstriction and platelet aggregation. Leukotrienes produced by the alternate pathway cause pulmonary and bronchial smooth muscle contraction and edema. Substances directly affecting vascular tone such as nitric oxide may also play a role in the respose to DCS. We are studying the role and consequent effects of the release inflammatory bioactive mediators as a result of DCS and VGE. More recent efforts are focused on identifying the effects of the body's circadian rhythm on these physiological consequences to decompression stress. al

Butler, B. D.↗
NASA NTRS1979

Oxides of nitrogen and the clouds of Venus

Nitric oxide may be produced in the atmosphere of Venus by lightning storms in the clouds. The paper suggests that the odd nitrogen thus formed may play an important part in the chemistry of the clouds. Specifically, production rates for NO2 in the limiting case of high NO concentrations are estimated. If the NO density is high, it is suggested that NO2 may catalyse the production of sulfuric acid aerosol from sulfur dioxide and water vapor, and may also form nitrogen-sulfur compounds such as nitrosyl sulfuric acid, NOHSO4. The large partricles seen by the Pioneer Venus sounder probe may contain considerable quantities of NOHSO4. If this is the case, odd nitrogen must be present in the atmosphere in at least a parts-per-million mixing ratio.

Watson, A. J.↗