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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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Single integral representations for the resistive and reactive components of the radiation impedance appropriate to a rectangular piston are established, thereby enabling a systematic refinement of estimates at both short and long wave lengths. Comparisons with previous analyses are made explicit as well as extensions and corrections thereto.
The energy savings and reactive power reduction functions initiated by the power factor controller (PFC) are discussed. A three-phase PFC with soft start is examined analytically and experimentally to determine how well it controls the open loop instability and other possible modes of instability. The detailed mechanism of the open loop instability is determined and shown to impose design constraints on the closed loop system. The design is shown to meet those constraints.
The condensation of a diol with a silane in toluene yields a silphenylene-siloxane polymer. The reaction of stiochiometric amounts of the diol and silane produced products with molecular weights in the range 2.0 - 6.0 x 10 to the 5th power. The molecular weight of the product was greatly increased by a multistep technique. The methodology for synthesis of high molecular weight polymers using a two step procedure was refined. Polymers with weight average molecular weights in excess of 1.0 x 10 to the 6th power produced by this method. Two more reactive silanes, bis(pyrrolidinyl)dimethylsilane and bis(gamma butyrolactam)dimethylsilane, are compared with the dimethyleminodimethylsilane in ability to advance the molecular weight of the prepolymer. The polymers produced are characterized by intrinsic viscosity in tetrahydrofuran. Weight and number average molecular weights and polydispersity are determined by gel permeation chromatography.
Alternatives to the traditional concepts for real time health and safety operations were examined. The pitfalls of the conventional contingency planning for health and safety are highlighted. The Solar Maximum Mission (SMM) contingency planning and operations provides the evolution from the conventional people intensive health and safety operation, toward a night watchman mode of operations. The SMM spacecraft health and safety operations were budget constrained to the point that one operator was responsible for the health and safety of the entire spacecraft one week after launch. The spacecraft was a protoflight with brand new subsystem configurations, software and procedures. To manage the risks associated with this one man SMM health and safety operation, the real time contingency planning and operations centered around unambiguously identifying a system level problem, and reactively safing components susceptible to unrecoverable damage. The methodology applied to both analyzing and implementing this approach of SMM is shown.
The development of an iron-base alloy that combines the normally divergent properties of high toughness and high strength at cryogenic temperatures is discussed. Specifically, alloy properties were sought which at -196 C would exhibit a fracture toughness of 220 MPa-m(1/2) with a corresponding yield strength of 1.4 GPa (200 ksi). Early work showed that high toughness could be achieved in Fe-12Ni alloys containing reactive metal additions such as Al, Nb, Ti, and V. Further research emphasized strengthening of these tough alloys by thermomechanical processing and the addition of Cu. Results showed that high strength and high toughness could be achieved in a single alloy at temperatures as low as -196 C. An alloy with composition Fe-12Ni-9.5Al-2Cu exhibited a yield strength of 1.65 GPa with a corresponding fracture toughness of 220 MPa-m(1/2) at -196 C. Strengthening due to Cu additions to the Fe-12Ni base alloys results primarily from precipitation of Cu-rich epsilon particles approximately 20 nm in diameter. Strengthening mechanisms are discussed in terms of an elastic modulus hardening model and are supported by transimission electron microscopy examinations of selected test specimens.
A program for investigating the grain enlargement resulting from the laser recrystallization of a thin gallium arsenide film on a patterned substrate, a technique known as graphoepitaxy was evaluated. More specifically, the effects of recrystallizing an uncapped gallium arsenide film using a continuous wave neodymium YAG laser operating at 1.06 microns were studied. In an effort to minimize arsenic loss from the film, the specimens were held in an arsine atmosphere during recrystallization. Two methods for fabricating patterned substrates were developed, one using reactive ion etching of a molybdenum film on both sapphire and silicon substates and another by preferential wet etching of a silicon substrate onto which a film of molybdenum was subsequently deposited.
A 120 day limited mobility experiment with young male rats and its results, including retarded growth and degenerative changes in the cardiac muscle, are described. A 120 day strict bedrest experiment with 10 human volunteers and its results are described and discussed. Early subjective complaints, subsequent adaptation and eventual progressive changes in excitability and reactivity, reduction in functional capability of the cerebral cortex, and disturbances in water-salt, protein and fat metabolism, including development of precursors of atherosclerosis, as well as poor results of the orthostatic test after 4 months, are presented. These results are explained as applied to sedentary workers and recommendations are given for such persons to exercise in the morning, at work and in the evening in order to prevent hypokinesis and its physical, mental and physiological effects.
Silicon nitride and hafnium nitride coatings were deposited by reactive RF sputtering on oxidized and unoxidized 440C stainless steel substrates. Sputtering was done in mixtures of argon and nitrogen gases from pressed powder silicon nitride and from hafnium metal targets. Depositions were at two background pressures, 8 and 20 mtorr, and at two different fractions (f) of nitrogen in argon, 0.25 and 0.60, for hafnium nitride and at f = 0.25 for silicon nitride. The coatings and the interface between the coating and substrates were investigated by X-ray diffractometry, scanning electron microscopy, energy dispersive X-ray analysis and Auger electron spectroscopy. A Knoop microhardness of 1650 + or - 100 kg/sq mm was measured for hafnium nitride and 3900 + or - 500 kg/sq mm for silicon nitride. The friction coefficients between a 440C rider and the coatings were measured under lubricated conditions. Scratch test results demonstrate that the adhesion of hafnium nitride to both oxidized and unoxidized 440C is superior to that of silicon nitride. Oxidized 440C is found to have increased adhesion, to both nitrides, over that of unoxidized 440C.
A rubber-toughened addition-type polyimide composition is disclosed which has excellent high temperature bonding characteristics in the fully cured state, and improved peel strength and adhesive fracture resistance physical property characteristics. The process for making the improved adhesive involves preparing the rubber containing amic acid prepolymer by chemically reacting an amine-terminated elastomer and an aromatic diamine with an aromatic dianhydride with which a reactive chain stopper anhydride was mixed, and utilizing solvent or mixture of solvents for the reaction.
A flexible, porous battery separator includes a coating applied to a porous, flexible substrate. The coating comprises: (1) a thermoplastic rubber-based resin which is insoluble and unreactive in the alkaline electrolyte, (2) a polar organic plasticizer which is reactive with the alkaline electrolyte to produce a reaction product which contains a hydroxyl group and/or a carboxylic acid group, and (3) a mixture of polar particulate filler materials which are unreactive with the electrode. The mixture comprises at least one first filler material having a surface area of greater than 25 sq meters/gram, at last one second filler material having a surface area of 10 to 25 sq meters/gram. The volume of the mixture of filler materials is less than 45% of the total volume of the fillers and the binder. The filler surface area per gram of binder is about 20 to 60 sq meters/gram, and the amount of plasticizer is sufficient to coat each filler particle.
A repository for critical and important detailed design data and information, hitherto unpublished, along with significant data on oxygen reactivity phenomena with metallic and nonmetallic materials in moderate to very high pressure environments is documented. This data and information provide a ready and easy to use reference for the guidance of designers of propulsion, power, and life support systems for use in space flight. The document is also applicable to designs for industrial and civilian uses of high pressure oxygen systems. The information presented herein are derived from data and design practices involving oxygen usage at pressures ranging from about 20 psia to 8000 psia equal with thermal conditions ranging from room temperatures up to 500 F.
The Defense Research Establishment Ottawa (DREO) has been studying the nickel-cadmium system, both vented and sealed, since the early 1950's. Reasonable success has been achieved in a wide variety of applications covering: military vehicle use under Arctic conditions; high performance military aircraft; manpacked communications sets; remote standby power and small portable instrumentation. Early studies on the vented system for high rate vehicle and aircraft cranking applications proved useful in later studies on the sealed NiCd system. This was especially true in the areas of plate loading and electrolyte composition. To achieve high rate cranking currents of 20C to 30C, it was necessary to have light to moderate plate loadings, a large reactive surface area, and electrolyte of optimum conductivity. DREO undertook some fundamental studies to understand the system from the inside out rather than test cells from the outside and then analyze their components. The conclusions of these studies were incorporated into the Procurement Specification for Ni-Cd cells ISISA Spec S615-P-2. A brief comment will be made on the choice of cell design and how some of the factors of cell manufacture could affect cell performance.
A thin film field emission cathode array and an electron gun based on this emitter array are summarized. Fabricating state of the art cathodes for testing at NASA and NRL, advancing the fabrication technology, developing wedge shaped emitters, and performing emission tests are covered. An anistropic dry etching process (reactive ion beam etching) developed that leads to increasing the packing density of the emitter tips to about 5 x 10 to the 6th power/square cm. Tests with small arrays of emitter tips having about 10 tips has demonstrated current densities of over 100 A/sq cm. Several times using cathodes having a packing density of 1.25 x 10 to the 6th power tips/sq cm. Indications are that the higher packing density achievable with the dry etch process may extend this capability to the 500 A/sq cm range and beyond. The wedge emitter geometry was developed and shown to produce emission. This geometry can (in principle) extend the current density capability of the cathodes beyond the 500 A/sq cm level. An emission microscope was built and tested for use with the cathodes.
Experimental results are presented for the autothermal reforming (ATR) of n-hexane, n-tetradecane, benzene and benzene solutions of naphthalene. The tests were run at atmospheric pressure and at moderately high reactant preheat temperatures in the 800-900 K range. Carbon formation lines were determined for paraffinic and aromatic liquids. Profiles were determined for axial bed temperature and composition. Space velocity efforts were assessed, and the locations and types of carbon were recorded. Significant reactive differences between hydrocarbons were identified. Carbon formation characteristics were hydrocarbon specific. The differing behavior of paraffinic and aromatic fuels with respect to their carbon formation may be important in explaining the narrow range of carbon-free operating conditions found in the ATR of number two fuel oil.
Electron beam pulse radiolysis (600 KeV, 3 nsec) experiments have been carried out on epoxy-based matrix materials. Time and wavelength resolved emission and transient absorption techniques as well as ESR studies have been utilized to identify and monitor short lived reactive intermediates resulting from energetic electron impact. An energy deactivation model based on the results of this work has been developed. Recombination of primary charged species is found to be fast, resulting in the formation of longer lived excited electronic states and radicals which control the subsequent energy deactivation.
An assessment is presented of current knowledge concerning the role and importance of neutral and charged clusters in atmospheric heterogeneous catalysis, with a view to the recommendation of future studies needed for progress in the quantification of aerosol formation and catalytic reactivity. It is established that nucleation from the gaseous to the aerosol state commences via the formation of clusters among molecules participating in the phase-transformation process. Nucleation may proceed in some cases by way of the formation of prenucleation embryos, which then evolve through the energy barrier and undergo phase transformation. In other cases, cluster-cluster interaction among neutral particles or stagewise building of alternate-sign ion clusters may be important in the gas-to-particle conversion process.
The kinetics of formation of the N-blocked dipeptide, N-acetylglycylglycine, from N-acetylglycyl adenylate anhydride and glycine in aqueous solution at 25 C, and at various PH's are reported. The reaction is of interest in that over a physiologically relevant pH range (6-8), peptide synthesis proceeds more rapidly than hydrolysis, even at those pH's at which this compound becomes increasingly susceptible to base-catalyzed hydrolysis. Under similar conditions, the corresponding unblocked aminoacyl adenylate anhydrides are considerably more unstable, and undergo appreciable hydrlysis in the presence of free amino acid. Because N-blocked aminoacyl adenylate anhydrides serve as model compounds of peptidyl adenylate anhydrides, these results suggest that primitive amino acid polymerization systems may have operated by cyclic reactivation of the peptidyl carboxyl group, rather than that of the incoming amino acid.
Cometary ice mixtures are studied in a laboratory experiment designed to simulate the temperature, pressure and radiation environments of the interstellar Oort cloud region, in order to test the hypothesized radiation synthesis mechanism for changing the characteristics of the outer few meters of a comet stored in the Oort cloud for 4.6 billion years. All experiments conducted confirm the synthesis of new molecular species in solid phase mixtures at 20 K. When CH4 is present in the irradiated ice mixture, long chained, voltaile hydrocarbon and CO2 are synthesized together with high molecular weight C compounds present in the room temperature residue. Due to radiation synthesis, about 1 percent of the ice was converted into a nonvolatile residue containing complicated C compounds not present in the blank samples. These results suggest that initial molecular abundances can be altered, and new species created, as a result of radiation synthesis. Irradiated mixtures exhibited thermoluminescence and pressure enhancements during warming, showing the synthesis of reactive species. Outbursts in new comets resulting from similar irradiation-induced exothermic activity would be expected to begin occurring at distances of the order of 100 AU.