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At least 1,081 records · Page 60

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NASA NTRS1980

Comparison of inlet suppressor data with approximate theory based on cutoff ratio

This paper represents the initial quantitative comparison of inlet suppressor far-field directivity suppression with that predicted using an approximate liner design and evaluation method based upon mode cutoff ratio. The experimental data was obtained using a series of cylindrical point-reacting inlet liners on an Avco-Lycoming YF102 engine. The theoretical prediction program is based upon simplified sound propagation concepts derived from exact calculations. These indicate that all of the controlling phenomenon can be approximately correlated with mode cutoff ratio which itself is intimately related to the angles of propagation within the duct. The objective of the theory-data comparisons is to point out possible deficiencies in the approximate theory which may be corrected. After all theoretical refinements have been made, then empirical corrections can be applied.

Rice, E. J.↗

NASA NTRS1979

Synthesis of perfluoroalkylether oxadiazole elastomers

A method for the simultaneous chain extension and crosslinking of perfluoroalkylethers which yields a thermally stable perfluoroalkylether oxadiazole elastomer crosslinked by trifunctional perfluoroalkylether-1,3,5-triazine is reported. In the preparation, hydroxylamine crystals prepared from hydroxylamine hydrochloride to which sodium butoxide had been added is mixed with perfluoroalkylether dinitrile to obtain the monomer, as the nitrile is converted to amidoxime. Monomers are heated at 140 to 200 C to form poly(perfluoroalkylether oxadiazole) with a 1,2,4-oxadiazole structure by a step-growth polymerization reaction. Simultaneous chain extension and crosslinking are observed to occur when the purified monomer is heated directly and when the remaining nitrile in the monomer is allowed to react with excess ammonia to form the corresponding amidine, which is then heated. Weight loss studies show the thermal stability of the perfluoroalkylether elastomer to be generally better than fluorosilicone or polyester elastomers, especially in air, indicating its potential usefulness for high-performance elastomeric applications.

Rosser, R. W.↗

NASA NTRS1980

A model for dust cloud autoignition

The paper deals with the problem of autoignition of a cloud of solid particles uniformly dispersed in a gas with one component of which it can react exothermally. Energy equations are derived similar to those of Rumanov and Khaikin (1969) but using methods of a phase-plane representation to describe ignition conditions resulting from these equations.

Krishna, C. R.↗

NASA NTRS1980

Photosensitized oxidation of unsaturated polymers

A review of the photosensitized oxidation of singlet oxygenation of unsaturated hydrocarbon polymers and of their model compounds is presented. The cis and trans forms of 1,4-polyisoprene, 1,4-polybutadiene and 1,2-poly(1,4-hexadiene) are studied, and their microstructural changes which occur on reaction with (IO2) in solution were investigated by infrared, (H-1) and (C-13) NMR spectroscopy. The polymers yielded allylic hydroperoxides with shifted double bonds according to the 'ene' mechanism of simple olefins. It was shown that single oxygenation of unsaturated polymers is similar to their low molecular weight analogs, and that the differences are due to secondary processes affecting the (IO2)-reacted polymers.

Golub, M. A.↗

NASA NTRS1979

Silicon material task - Low cost solar array project /JPL/DOE/

The paper describes the silicon material task of the low-cost solar array project, which has the objective of establishing a silicon production capability equivalent to 500 mW per year at a price less than 10 dollars/kg (1975 dollars) in 1986. The task program is divided into four phases: technical feasibility, scale-up studies (the present phase), experimental process system development units, and implementation of large-scale production plants, and it involves the development of processes for two groups of materials, that is, semiconductor grade and solar cell grade. In addition, the effects of impurities on solar cell performance are being investigated. Attention is given to problem areas of the task program, such as environmental protection, material compatibility between the reacting chemicals and materials of construction of the equipment, and waste disposal.

Lutwack, R.↗

NASA NTRS1979

A model of Martian surface chemistry

Alkaline earth and alkali metal superoxides and peroxides, gamma-Fe2O3 and carbon suboxide polymer, are proposed to be constituents of the Martian surface material. These reactive substances explain the water modified reactions and thermal behaviors of the Martian samples demonstrated by all of the Viking Biology Experiments. It is also proposed that the syntheses of these substances result mainly from electrical discharges between wind-mobilized particles at Martian pressures; plasmas are initiated and maintained by these discharges. Active species in the plasma either combine to form or react with inorganic surfaces to create the reactive constituents.

Oyama, V. I.↗

NASA NTRS1980

Nitridation of silicon /111/ - Auger and LEED results

Clean silicon (111) (7x7) surfaces at up to 1050 C have been reacted with nitrogen ions and neutrals produced by a low energy ion gun. The LEED patterns observed are similar to those previously reported for reaction of silicon (111) (7x7) with NH3. The nitrogen KLL peak exhibits no shift or change in shape with nitride growth. At the same time the magnitude of the elemental silicon LVV peak at 92 eV decreases progressively as a new peak at 84 eV increases. The position of both peaks appears to be independent of the degree of nitridation. Since the Auger spectra are free of oxygen and other impurities, these features can be attributed only to silicon, nitrogen, and their reaction products. Characteristic features of the Auger spectra are related to LEED observations and to the growth of microcrystals of Si3N4.

Delord, J. F.↗

NASA NTRS1980

Silicon oxidation in fluoride solutions

Silicon is produced in a NaF, Na2SiF6, and Na matrix when SiF4 is reduced by metallic sodium. Hydrogen is evolved during acid leaching to separate the silicon from the accompanying reaction products, NaF and Na2SiF6. The hydrogen evolution reaction was studied under conditions simulating leaching conditions by making suspensions of the dry silicon powder in aqueous fluoride solutions. The mechanism for the hydrogen evolution is discussed in terms of spontaneous oxidation of silicon resulting from the cooperative effects of (1) elemental sodium in the silicon that reacts with water to remove a protective silica layer, leaving clean reactive silicon, and (2) fluoride in solution that complexes with the oxidized silicon in solution and retards formation of a protective hydrous oxide gel.

Sancier, K. M.↗

NASA NTRS1980

Immunomicrospheres - Reagents for cell labeling and separation

Immunomicrospheres are specially designed microscopic particles that have antibodies or similar molecules chemically bound to their surfaces. The antibody-coated microspheres react in a highly specific way with target cells, viruses, or other antigenic agents. Immunomicrospheres may be synthesized so that they incorporate compounds that are highly radioactive, intensely fluorescent, magnetic, electron opaque, highly colored, or pharmacologically active. These various types of microspheres may be coated with pure, highly specific monoclonal antibodies obtained by the new hybridoma cell cloning techniques or with conventional antibody preparations. Some of the many present and potential applications for these new reagents are (1) new types of radioimmune or immunofluorescent assays, (2) improved fluorescence microscopy, (3) separation of cells on the basis of the fluorescent, electrophoretic, or magnetic properties of bound immunomicrospheres, (4) markers for use in several types of electron or standard light microscopy, and (5) delivery of lethal compouds to specific undesirable living cells. The combination of the various new types of synthetic microspheres and the newly available homogeneous antibodies offers new opportunities in research, diagnosis, and therapy.

Rembaum, A.↗

NASA NTRS1982

Silicone/Acrylate Copolymers

Two-step process forms silicone/acrylate copolymers. Resulting acrylate functional fluid is reacted with other ingredients to produce copolymer. Films of polymer were formed by simply pouring or spraying mixture and allowing solvent to evaporate. Films showed good weatherability. Durable, clear polymer films protect photovoltaic cells.

Dennis, W. E.↗

NASA NTRS1980

A two-dimensional model of odd nitrogen in the thermosphere and mesosphere

Satellite measurements of the global nitric oxide distribution demonstrating the need for a two dimensional model of odd nitrogen photochemistry and transport in the thermosphere and mesosphere are reviewed. The main characteristics of a new code solving the transport equation for N(4S), N(2D), and N0 are given. This model extends from pole to pole between 75 and 275 km and reacts to the magnetic activity, the ultraviolet solar flux, and the neutral wind field. The effects of ionization and subsequent odd nitrogen production by high latitude particle precipitation are also included. Preliminary results are illustrated for a magnetically quiet solar minimum period with no neutral wind.

Gerard, J. C.↗

NASA NTRS1980

Formulation and evaluation of C-Ether fluids as lubricants useful to 260 C

Three base stocks were evaluated in bench and bearing tests to determine their suitability for use at bulk oil temperatures (BOT) from -40 C to +260 C. A polyol ester gave good bearing tests at a bulk temperature of 218 C, but only a partially successful run at 274 C. These results bracket the fluid's maximum operating temperature between these values. An extensive screening program selected lubrication additives for a C-ether (modified polyphenyl ether) base stock. One formulation lubricated a bearing for 111 hours at 274 C (BOT), but this fluid gave many deposit related problems. Other C-ether blends produced cage wear or fatigue failures. Studies of a third fluid, a C-ether/disiloxane blend, consisted of bench oxidation and lubrication tests. These showed that some additives react differently in the blend than in pure C-ethers.

Clark, F. S.↗

NASA NTRS1980

Graphite fiber surface treatment to improve char retention and increase fiber clumping

Composites containing carbon and graphite fibers can release fibers into the atmosphere during a fire. This release can potentially cause failure in some types of electrical equipment. Reduced fiber dispersion during and after combustion will reduce risks. Epoxidized char forming systems were synthesized which will react with commercially available surface treated carbon fiber. Fibers modified with these char formers retained adhesion in a specific epoxy matrix resin. Small scale combustion testing indicates that using these char former modified fibers in laminates will help to reduce the dispersement of fibers resulting from exposure to fire without sacrificing resin to fiber adhesion.

Paul, J. T., Jr.↗

NASA NTRS1978

Membrane consisting of polyquaternary amine ion exchange polymer network interpenetrating the chains of thermoplastic matrix polymer

An ion exchange membrane was formed from a solution containing dissolved matrix polymer and a set of monomers which are capable of reacting to form a polyquaternary ion exchange material; for example vinyl pyride and a dihalo hydrocarbon. After casting solution and evaporation of the volatile component's, a relatively strong ion exchange membrane was obtained which is capable of removing anions, such as nitrate or chromate from water. The ion exchange polymer forms an interpenetrating network with the chains of the matrix polymer.

Rembaum, A.↗

NASA NTRS1980

Continuous coal processing method

A coal pump is provided in which solid coal is heated in the barrel of an extruder under pressure to a temperature at which the coal assumes plastic properties. The coal is continuously extruded, without static zones, using, for example, screw extrusion preferably without venting through a reduced diameter die to form a dispersed spray. As a result, the dispersed coal may be continuously injected into vessels or combustors at any pressure up to the maximum pressure developed in the extrusion device. The coal may be premixed with other materials such as desulfurization aids or reducible metal ores so that reactions occur, during or after conversion to its plastic state. Alternatively, the coal may be processed and caused to react after extrusion, through the die, with, for example, liquid oxidizers, whereby a coal reactor is provided.

Ryason, P. R.↗

NASA NTRS1980

Responses of the frog primary vestibular afferents to direct vibration of the semicircular canal

Responses of primary afferents (PA) of lateral semicircular canal to sinusoidal vibration of the canal wall within the range 0.05-200 Hz (mean amplitudes 5-15 microns) in immobilized frogs were studied. Dynamic characteristics (gain, phase) of relative linear velocity of the vibrator (micron X/s) were examined. At 0.2 Hz, the gain was 5.35 + or - 3.19 imp X/s /micron X/s (mean; S.D.; n=14) and linearly decreased if the frequency rose. Phase lag of relative velocity at 0.05 Hz was 49.8 deg + or - 16.5 deg (n=13) and at 1 Hz 97 deg + or - 9.4 deg (n=22). At 100 Hz phase lag was about 240 deg. Three groups of PA are described: wide range PA reacting in the range from 0.05 up to 60-180 Hz; high frequency PA responding in the range from 20-40 up to 100-150 Hz; and low frequency PA responding in the range from 0.05 up to 2-20 Hz.

Orlov, I. V.↗

NASA NTRS1980

Improved refractory coatings

The adhesion, friction and wear properties of sputtered refractory coatings on substrates of materials that form stable nitrides are enhanced by placing each substrate directly below a titanium carbide target of a commercial radiofrequency diode apparatus in a vacuum chamber. Nitrogen is bled into the system through a nozzle resulting in a small partial pressure of about 0.5% to 2.5% during the first two minutes of deposition. The flow of nitrogen is then stopped, and the sputtering ambient is reduced to pure argon through a nozzle without interrupting the sputtering process. When nitrogen is deliberately introduced during the crucial interface formation, some of the titanium at the interface reacts to form titanium nitride while the metal of the substrate also forms the nitride. These two nitrides atomically mixed together in the interfacial region act to more strongly bond the growing titanium carbide coating as it forms on the substrate.

Brainard, W. A.↗

NASA NTRS1980

A mechanism for the compressive ignition of liquid monopropellants

Possible mechanisms for compressive ignition of liquid monopropellants are discussed. These mechanisms all involve the collapse of a gas filled bubble imbedded in the liquid. A model of the collapse of a gas bubble in an incompressible liquid and the combustion of the surrounding liquid after ignition occurs is presented. The effect of gas covolume, liquid density, the adiabatic exponent, rate of pressurization and prepressurization are investigated. Calculations for finite and infinite liquid volumes are also presented. Gas generation in the bubble is shown to have a significant effect on its evolution and the introduction of a surface enhancement factor leads to a runaway reaction. For the conditions considered, the reacting bubble oscillates at a frequency of about 35 kHz over the first 0.5 milliseconds. This frequency decreases as the surface enhancement factor is increased. The implication is that a one dimensional model of this process may be tractable from the standpoint of computer time.

Morrison, W. F.↗