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At least 289 records · Page 16

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NASA NTRS1975

The Kinetics of the Trimethoxyboroxine-Induced Thermal Polymerization of Phenyl Glycidyl Ether

The kinetics of the bulk thermal polymerization of phenyl glycidyl ether induced by trimethoxyboroxine were investigated. Infrared absorption spectroscopy and gel permeation chromatography were used to follow the course of polymerization, while proton and boron-2 NMR spectroscopy were used to support the kinetic model developed. The postulated mechanism involves a fast-initiated, non-stationary cationic polymerization with five elementary steps, including spontaneous and monomer transfer as well as a termination reaction. The trimethoxyboroxine was found to be incorporated into the structure of the cured polymer. Tile polymerization was followed at several temperatures and with several ratios of initial concentrations of trimethoxyboroxine to phenyl glycidyl ether.

Lopata, Eugene S.↗

NASA NTRS1999

Petrology and Geochemistry of a Mg- and Al-Rich Orthopyroxenite Xenolith in the EETA79001 Shergottite: Implications for Mars Crustal Evolution

EETA79001 is a Mars meteorite (SNC) consisting of multiple rock types, including two basalt types, olivine and pyroxene xenocrysts, and ultramafic xenoliths. This study is focused on the petrology and geochemistry of one orthopyroxenite xenolith in PTS 68, designated X-1. It consists of chemically homogeneous orthopyroxene cores with exceptionally high Mg/Fe (mg#=85) and Al. Cores are permeated by minute high-Si+Al glassy inclusions, some with augite microlites. Magnesian core areas are mantled by more Fe-rich orthopyroxene rims grading to pigeonite away from cores. The xenolith is transected by cross-cutting shear planes, some of pre-incorporation origin. Major and minor element composition and variation suggest that core areas are primarily igneous, crystallized from a high temperature mafic melt. However, nearly constant mg# across cores suggest metamorphic equilibration. Si+Al inclusions may result from, among other processes, exsolution of feldspathic material during subsolidus cooling, or may be solid materials (alkali feldspar) poikilitically enclosed by growing igneous orthopyroxene crystals. Late reaction with more fractionated melts produced Fe-rich mantles, the whole assemblage later cut by tectonic micro-shear planes. Raw electron microprobe data produced during this study are available on request from the author.

Berkley, John L.↗

NASA NTRS1998

Diffusive Gas Loss from Silica Glass Ampoules at Elevated Temperatures

Changes in the pressure of hydrogen, helium and neon due to diffusion through the wall of silica crystal growth ampoules at elevated temperatures were determined experimentally. We show that, while both He- and Ne-losses closely follow conventional model of diffusive gas permeation through the wall, hydrogen losses, in particular at low fill pressures, can be much larger. This is interpreted in terms of the high solubility of hydrogen in silica glasses.

Palosz, W.↗

NASA NTRS1999

New RTM/RI Resins for the HSCT

In the first portion of this work, 1,2,3,3,4,4-hexafluoro-1,2-bis[4-(dimethylhydroxysilyl)phenoxy]cyclobutane and 1,2,3,3,4,4-hexafluoro-1,2-bis[3-(dimethylhydroxysilyl)phenoxy]cyclobutane were prepared and homopolymerized to afford polymers with excellent thermal stability and Tgs of 27 C and -12 C, respectively. Despite the moderately high wt% of fluorin in the polymer structure (23.8%), these polymers had poor fuel resistance. In fact, swelling measurements indicate that these polymers had apparent solubility parameters of about 18.2 J (exp 1/2) m (exp -3/2) (toluene). Copolymerization of the disilanol monomers with fluorosilicone monomers afforded copolymers containing 20-30 wt% of the perfluorocyclobutane-containing structure displayed adequate fuel resistance, enhanced thermal stability, and a Tg low enough to meet the requirements of a High Speed Civil Transport (HSCT) fuel tank sealant. In the second part of this work, trifluorovinylether-terminated oligomers were prepared and polymerized via cyclodimerization. Initially, an alpha, omega-silanol-terminated fluorosilicone was endcapped with trifluorovinylether end groups via a two-step synthetic sequence. The oligomer was thermally cyclodimerized to a polymer that displayed thermal stability similar to that of a fluorosilicone homopolymer. Second, 1,3-bis[4-trifluorovinyl(oxy)phenyl]-1,3-(3,3,3-trifluoropropyl)dimethyldisiloxane and 1,3-bis{3-trifluorovinyl(oxy)phenyl]-1,3-(3,3,3-trifluoropropyl)dimethyldisiloxane were prepared and cyclodimerized to afford polymers that contained pendant trifluoropropyl groups. The pendant trifluoropropyl groups did enhance solvent resistance in aliphatic hydrocarbon solvents, however, no improvement was observed in aromatic hydrocarbon solvents. These polymers also displayed excellent thermal stability. In the last part of this work, a series of monomers was prepared by the DCC-promoted esterification of 4-[trifluorovinyl(oxy)benzoic acid with alpha, omega-functionalized hydrogenated and partially fluorinated alcohols. The monomers were cyclodimerized to the corresponding polymers. The polymers that did not contain beta hydrogens displayed significantly higher thermal stability than the fully hydrogenated polymers. A commercially-available alpha,omega-hydroxy-terminated perfluoropolyether was then functionalized with 4-[trifluorovinyl(oxy)benzoylchloride. An attempt was made to polymerize the resulting oligomer via the cyclodimerization of the terminal trifluorovinylether moieties. Although the viscosity of the oligomer increased significantly during polymerization, Gel Permeation Chromatography (GPC) analysis revealed that the Tetrahydrofuran (THF) soluble portion of the polymer did not have high molecular weight.

Harris, Frank W.↗

NASA NTRS1999

Carbon Nanotubules: Building Blocks for Nanometer-Scale Engineering

Sinnott, Susan B.↗

NASA NTRS1999

Carbon Nanotubules: Building Blocks for Nanometer-Scale Engineering

The proposed work consisted of two projects: the investigation of fluid permeation and diffusion through ultrafiltration membranes composed of carbon nanotubules and the design and study of molecular transistors composed of nanotubules. The progress made on each project is summarized and also discussion about additional projects, one of which is a continuation of work supported by another grant, is included. The first project was Liquid Interactions within a Nanotubule Membrane. The second was the design of nanometer-scale hydrocarbon electronic devices. The third was the investigation of Mechanical properties of Nanotubules and Nanotubule bundles. The fourth project was to investigate the growth mechanisms of Carbon Nanotubules.

Sinnott, Susan B.↗

NASA NTRS1999

A New View of the Origin of the Solar Wind

This paper uses white-light measurements made by the SOHO LASCO coronagraph and HAO Mauna Loa Mk III K-coronameter to illustrate the new view of solar wind structure deduced originally from radio occultation measurements. It is shown that the density profile closest to the Sun at 1.15 Ro, representing the imprint of the Sun, is carried essentially radially into interplanetary space by small-scale raylike structures that permeate the solar corona and which have only been observed by radio occultation measurements. The only exception is the small volume of interplanetary space occupied by the heliospheric plasma sheet that evolves from coronal streamers within a few solar radii of the Sun. The radial preservation of the density profile also implies that a significant fraction of field lines which extend into interplanetary space originate from the quiet Sun, and are indistinguishable in character from those emanating from polar coronal holes. The white-light measurements dispel the long-held belief that the boundaries of polar coronal holes diverge significantly, and further support the view originally proposed that the fast solar wind originates from the quiet Sun as well as polar coronal holes.

Woo, Richard↗

NASA NTRS2000

Development and Application of Tools to Characterize the Oxidative Degradation of AP/HTPB/Al Propellants in a Propellant Reliability Study

The oxidative thermal aging of a crosslinked hydroxyl-terminated polybutadiene (HTPB)/isophorone diisocyanate (IPDI) polyurethane rubber was studied at temperatures between 25 C and 125 C. Changes in tensile elongation, mechanical hardening, polymer network properties, density, O2 permeation, and molecular chain dynamics were investigated as a function of age. The techniques used include solvent swelling, detailed modulus profiling, and NMR relaxation measurements. The Arrhenius methodology, which normally assumes a linear extrapolation of high temperature aging data, is critically evaluated by using extensive data superposition and highly sensitive oxygen consumption measurements. Significant curvature in the Arrhenius diagram of these oxidation rates is observed to be similar to previous results found for other rubber materials that have been evaluated by this technique. Preliminary gel/network properties suggest that crosslinking is the dominant process at higher temperatures. The effect on the oxidation rate of the binder when other constituents found in propellants are present, such as ammonium perchlorate, plasticizer and aluminum powder, is presented.

Celina, Mathew↗

NASA NTRS2001

Innovative Method for Developing a Helium Pressurant Tank Suitable for the Upper Stage Flight Experiment

The AFRL USFE project is an experimental test bed for new propulsion technologies. It will utilize ambient temperature fuel and oxidizers (Kerosene and Hydrogen peroxide). The system is pressure fed, not pump fed, and will utilize a helium pressurant tank to drive the system. Mr. DeLay has developed a method for cost effectively producing a unique, large pressurant tank that is not commercially available. The pressure vessel is a layered composite structure with an electroformed metallic permeation barrier. The design/process is scalable and easily adaptable to different configurations with minimal cost in tooling development 1/3 scale tanks have already been fabricated and are scheduled for testing. The full-scale pressure vessel (50" diameter) design will be refined based on the performance of the sub-scale tank. The pressure vessels have been designed to operate at 6,000 psi. a PV/W of 1.92 million is anticipated.

DeLay, Tom K.↗

NASA NTRS1995

A Network Model for the Effective Thermal Conductivity of Rigid Fibrous Refractory Insulations

A procedure is described for computing the effective thermal conductivity of a rigid fibrous refractory insulation. The insulation is modeled as a 3-dimensional Cartesian network of thermal conductance. The values and volume distributions of the conductance are assigned to reflect the physical properties of the insulation, its constituent fibers, and any permeating gas. The effective thermal conductivity is computed by considering the simultaneous energy transport by solid conduction, gas conduction and radiation through a cubic volume of model insulation; thus the coupling between heat transfer modes is retained (within the simplifications inherent to the model), rather than suppressed by treating these heat transfer modes as independent. The model takes into account insulation composition, density and fiber anisotropy, as well as the geometric and material properties of the constituent fibers. A relatively good agreement, between calculated and experimentally derived thermal conductivity values, is obtained for a variety of rigid fibrous insulations.

Marschall, Jochen↗

NASA NTRS2000

Atmosphere of Freedom: Sixty Years at the NASA Ames Research Center

Throughout Ames History, four themes prevail: a commitment to hiring the best people; cutting-edge research tools; project management that gets things done faster, better and cheaper; and outstanding research efforts that serve the scientific professions and the nation. More than any other NASA Center, Ames remains shaped by its origins in the NACA (National Advisory Committee for Aeronautics). Not that its missions remain the same. Sure, Ames still houses the world's greatest collection of wind tunnels and simulation facilities, its aerodynamicists remain among the best in the world, and pilots and engineers still come for advice on how to build better aircraft. But that is increasingly part of Ames' past. Ames people have embraced two other missions for its future. First, intelligent systems and information science will help NASA use new tools in supercomputing, networking, telepresence and robotics. Second, astrobiology will explore lore the prospects for life on Earth and beyond. Both new missions leverage Ames long-standing expertise in computation and in the life sciences, as well as its relations with the computing and biotechnology firms working in the Silicon Valley community that has sprung up around the Center. Rather than the NACA missions, it is the NACA culture that still permeates Ames. The Ames way of research management privileges the scientists and engineers working in the laboratories. They work in an atmosphere of freedom, laced with the expectation of integrity and responsibility. Ames researchers are free to define their research goals and define how they contribute to the national good. They are expected to keep their fingers on the pulse of their disciplines, to be ambitious yet frugal in organizing their efforts, and to always test their theories in the laboratory or in the field. Ames' leadership ranks, traditionally, are cultivated within this scientific community. Rather than manage and supervise these researchers, Ames leadership merely guided them, represents them to NASA headquarters and the world outside, then steps out of the way before they get run over.

Bugos, Glenn E.↗

NASA NTRS2000

Integrated Design and Analysis Overview

The objectives of the project this viewgraph presentation summarizes (integrated design and analysis) include the following: (1) Develop methodology for assessing the effects of manufacturing defects; (2) Develop damage tolerance criteria and damage tolerance database for reusable launch vehicle cryogenic tank structures, including impact, pressure leakage, cryogenic permeation, and validated damage prediction tools; and (3) Develop repair technology.

Gates, Tom S.↗

NASA NTRS2001

The Magnetic Free Energy in Active Regions

The magnetic field permeating the solar atmosphere governs much of the structure, morphology, brightness, and dynamics observed on the Sun. The magnetic field, especially in active regions, is thought to provide the power for energetic events in the solar corona, such as solar flares and Coronal Mass Ejections (CME) and is believed to energize the hot coronal plasma seen in extreme ultraviolet or X-rays. The question remains what specific aspect of the magnetic flux governs the observed variability. To directly understand the role of the magnetic field in energizing the solar corona, it is necessary to measure the free magnetic energy available in active regions. The grant now expiring has demonstrated a new and valuable technique for observing the magnetic free energy in active regions as a function of time.

Metcalf, Thomas R.↗

NASA NTRS2001

Autofrettage to Counteract Coefficient of Thermal Expansion Mismatch in Cryogenic Pressurized Pipes with Metallic Liners

Composite feedlines with metal liners have the potential to reduce weight/cost while providing the same level of permeation resistance and material compatibility of all-metal feedlines carrying cryogenic propellants in spacecraft. The major technical challenges are the large difference in Coefficient of Thermal Expansion between the liner and the composite, and the manufacturing method required to make a very thin liner with the required strength and dimensional tolerance. This study investigates the use of autofrettage (compressive preload) to counteract Coefficient of Thermal Expansion when pre-pressurization procedures cannot be used to solve this problem. Promising materials (aluminum 2219, Inconel 718, nickel, nickel alloy) and manufacturing techniques (chemical milling, electroplating) are evaluated to determine the best liner candidates. Robust, autofrettaged feedlines with a low Coefficient of Thermal Expansion liner (Inconel 718 or nickel alloy) are shown to successfully counteract mismatch at LOX temperature. A new concept, autofrettage by temperature, is introduced for high Coefficient of Thermal Expansion materials (aluminum and pure nickel) where pressure cannot be used to add compressive preload.

Wen, Ed↗

NASA NTRS1998

Seal the Deal

AvanTeco Corporation has developed a moisture/contaminant sensor chip. This newly developed chip rapidly responds to the presence of moisture, especially in condensed form and in presence of ionic impurities. It determines whether moisture has permeated a hermetically sealed package or a plastic encapsulated microcircuit. The sensor chip was designed as a "go/no go" chip, which is assembled with other chips in a multi-chip module to assess the risk of failure for the entire module. It has been commercialized and is sold by Revtek, Inc.

Source record↗

NASA NTRS2003

Numerical Simulation of Waves Driven by Plasma Currents Generated by Low-Frequency Alfven Waves in a Multi-Ion Plasma

When multi-ion plasma consisting of heavy and light ions is permeated by a lowfrequency Alfien (LFA) wave, the EXB and the polarization drifts of the different ion species and the electrons could be quite different. The relative drifts between the charged-particle species drive waves, which energize the plasma. Using 2.5-D particle-in-cell simulations, we study this process of wave generation and its nonlinear consequences in terms of acceleration and heating plasma. Specifically we study the situation for LFA wave frequency being lower than the heavyion cyclotron frequency in a multi-ion plasma. We impose such a wave to the plasma assuming that its wavelength is much larger than that of the waves generated by the relative drifts. For better understanding, the LFA-wave driven simulations are augmented by those driven by initialized ion beams.

Singh, Nagendra↗

NASA NTRS2003

Facesheet Delamination of Composite Sandwich Materials at Cryogenic Temperatures

The next generation of space transportation vehicles will require advances in lightweight structural materials and related design concepts to meet the increased demands on performance. One potential source for significant structural weight reduction is the replacement of traditional metallic cryogenic fuel tanks with new designs for polymeric matrix composite tanks. These new tank designs may take the form of thin-walled sandwich constructed with lightweight core and composite facesheets. Life-time durability requirements imply the materials must safely carry pressure loads, external structural loads, resist leakage and operate over an extremely wide temperature range. Aside from catastrophic events like tank wall penetration, one of the most likely scenarios for failure of a tank wall of sandwich construction is the permeation of cryogenic fluid into the sandwich core and the subsequent delamination of the sandwich facesheet due to the build-up of excessive internal pressure. The research presented in this paper was undertaken to help understand this specific problem of core to facesheet delamination in cryogenic environments and relate this data to basic mechanical properties. The experimental results presented herein provide data on the strain energy release rate (toughness) of the interface between the facesheet and the core of a composite sandwich subjected to simulated internal pressure. A unique test apparatus and associated test methods are described and the results are presented to highlight the effects of cryogenic temperature on the measured material properties.

Gates, Thomas S.↗

NASA NTRS1998

Use of Novel Light Sources and Melatonin Delivery Systems in the Maintenance of Temporal Organization of Physiological and Behavioral Circadian Rhythms

The synchronization of physiological and behavioral rhythms are controlled by an endogenous biological clock. It is generally accepted that environmental lighting is the strongest entrainer of this clock. The pineal gland is an important physiological transducer of environmental lighting via systemic melatonin secretion. We have used a novel light source using light emitting diode (LED) technology to entrain circadian rhythms in rats, and propose a novel percutaneous exogenous melatonin delivery system to entrain rat rhythms. We used 5 groups of Sprague-Dawley rats (175-350 g; N = 8/group) and showed normal entrainment of gross locomotor activity, feeding, and drinking circadian rhythms at light intensities varying from 80 lux to 0.1 lux (22.4 to 0.03 sq cm). To improve the delivery of melatonin across the skin stratum corneum it was formulated in a suitable vehicle in a transdermal drug delivery system. Various saturated and unsaturated fatty acids were used E, akin penetration enhancers. Our best vehicle formulation was achieved with a combination-of ethano1:water (60:40) along with 5% oleic acid as the enhancer. This formulation mixture was studied using Franz diffusion cell (0.636 sq cm diffusional area) and 1 cu cm dorsal skin isolated from Sprague Dawley rats. Our results showed that oleic acid in combination with the water ethanol mixture improved the flux of melatonin by more than 18 fold. The lag time for melatonin permeation was 2-3 hrs and the peak concentrations were achieved in 8-10 hrs. Our approaches in the future will involve the use of our transdermal melatonin delivery system and under the influence of LED light and microgravity.

Winget, C. M.↗