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  • Polymer and Materials Science  (6)
  • CYBERNETICS  (4)
  • Astrophysics
  • 1990-1994  (10)
  • 1
    Digitale Medien
    Digitale Medien
    Synthesis and characterization of oligocyclosiloxanes via the hydrosilation of vinylsilanes and vinylsiloxanes with heptamethylcyclotetrasiloxane (1993)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 31 (1993), S. 891-900 
    Details
    ISSN: 0887-624X
    Schlagwort(e): oligocyclosiloxanes ; hydrosilation ; heptamethylcyclotetrasiloxane ; siloxane redistribution ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The preparation of oligocyclosiloxanes via hydrosilation reactions has been investigated. Hydrosilation reactions employing heptamethylcyclotetrasiloxane and vinyl-containing silanes and siloxanes yielded a variety of oligocyclosiloxanes with various numbers of cyclosiloxane rings connected through tri-, tetra-, penta-, hexa-, hepta-, or octafunctional junctions. The oligocyclosiloxanes were characterized by gas chromatography, IR spectroscopy, 29Si-, 1H-, and 13C-NMR spectroscopy, elemental analysis, and vapor phase osmometry. The polycyclics were redistributed with hexamethyldisiloxane and the resulting fragments analyzed by gas chromatography. All results were consistent with the formation of isomeric oligocyclosiloxanes due to a lack of absolute regioselectivity of the hydrosilation reaction. © 1993 John Wiley & Sons, Inc.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pola.1993.080310407
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  • 2
    Digitale Medien
    Digitale Medien
    PBI powder processing to performance parts (1994)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 53 (1994), S. 485-496 
    Details
    ISSN: 0021-8995
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: A new route (“direct forming”) was developed for forming dense PBI shapes from PBI powder. The new process affords the possibility of automated PBI powder shaping (“cold compaction”) and densification in batches of multiple parts by a “powder-assisted hot isostatic pressing” process. Direct forming is a more productive alternative to hot compression molding. Two developments enable PBI direct forming: (1) the discovery that PBI powders that are porous and plasticized with moisture can be shaped by compaction at ambient temperatures (cold-compacted), and (2) a finding that cold-compacted shapes can be densified in large batches by a powder-assisted hot isostatic pressing. The porous PBI powder is formed from PBI in solution by a spray-precipitation process. When plasticized with moisture, this powder is cold-compactible to PBI shapes with densities up to 94% of that of ultimate density of PBI. These shapes, which have sufficient strength to be handled, are then further consolidated via powder-assisted hot isostatic pressing to shapes with excellent thermal and mechanical properties and densities of about 99% of the ultimate. © 1994 John Wiley & Sons, Inc.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/app.1994.070530503
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  • 3
    Digitale Medien
    Digitale Medien
    Torsional properties of healed canine diaphyseal defects grafted with a fibrillar collagen and hydroxyapatite/tricalcium phosphate composite (1994)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Biomaterials 5 (1994), S. 277-283 
    Details
    ISSN: 1045-4861
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Medizin , Technik allgemein
    Notizen: The need for alternatives to autogenous bone grafts is widely recognized. This study compared the torsional strength of canine femora 1 year after grafting with one of three forms of a collagen/hydroxyapatite/tricalcium phosphate bone grafting material (COLLAGRAFT15), autogenous bone, or no graft. The groups were compared to each other and to the unoperated contralateral femora. Results of torsional testing were evaluated for torsional strength, torsional displacement, total energy to fracture and White fracture mode. Data analysis showed lower torsional strength of the operated vs. unoperated femora with the exception of morsellized COLLAGRAFT15 material, which had higher strength. However, the only difference in the operated groups was that the morsellized COLLAGRAFT15 had greater strength than several groups including the autogenous bone group. There was no difference found in angular displacement between any of the groups. However, there was a difference in the energy to fracture in both strip forms of the COLLAGRAFT15. The final conclusion is that in this model, grafting with COLLAGRAFT15 provided torsional properties at one year postoperatively at least equivalent to autogenous bone. © 1994 John Wiley & Sons, Inc.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jab.770050402
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  • 4
    Digitale Medien
    Digitale Medien
    The effects of heat treatments and bead size on the corrosion of porous F75 in saline and serum (1990)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 24 (1990), S. 79-94 
    Details
    ISSN: 0021-9304
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Medizin , Technik allgemein
    Notizen: An accelerated anodic corrosion method was used to study the effects of heat treatment and bead size on corrosion and metal ion release of porous coated F75 cylinders in saline and serum. Three heat treatments were used: a standard process for F75 implants (HTA), the standard plus an additional hour in air to produce a thin oxide film (HTA′), and a sintering in high vacuum to produce a chromium-depleted surface (HTB). Three bead sizes of similar composition were used, with approximate sizes of 215, 300, and 560 μm. The results demonstrated that HTA′ had the lowest corrosion rate and that of HTB was significantly greater than either HTA or HTA′. The corrosion rates of HTA and HTA′ were significantly greater in serum as compared with saline, whereas that of HTB was not affected by the presence of serum, suggesting an interaction between chromium and serum proteins. Bead size had a minimal effect on the corrosion rate of HTA′. For HTA, the small beads had the highest corrosion rate; the lowest was with the medium-sized beads. Bead size had the most significant effect with HTB, with that of the smaller beads having the higher corrosion rates. The effects of bead size were less consistent in serum, suggesting that protein adsorption may mask some of the surface area effects. It is concluded that the oxide film does reduce corrosion, that proteins do have an influence on the corrosion of F75, and that this method can be a suseful tool for studying the effects of improved heat treatment methods on the corrosion rate of F75 implants.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jbm.820240108
    Standort Signatur Erwartet Verfügbarkeit
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  • 5
    Digitale Medien
    Digitale Medien
    Tissue response and in vivo degradation of selected polyhydroxyacids: Polylactides (PLA), poly(3-hydroxybutyrate) (PHB), and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHB/VA)The opinions or assertions about specific products identified by brand name contained herein are the private views of the authors (JGD, MKH) and are not to be construed as conveying either an official endorsement or criticism by the U.S. Department of Health and Human Services or the Food and Drug Administration. (1993)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 27 (1993), S. 1135-1148 
    Details
    ISSN: 0021-9304
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Medizin , Technik allgemein
    Notizen: The tissue response and in vivo molecular stability of injection-molded polyhydroxyacids - polylactides (PLA), poly(3-hydroxybutyrate) (PHB), and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHB/VA, 5-22% VA content) - were studied. Polymers were implanted subcutaneously in mice and extirpated at 1, 3, and 6 month in order to study tissue response and polymer degradation.All polymers were well tolerated by the tissue. No acute inflammation, abscess formation, or tissue necrosis was observed in tissues adjacent to the implanted materials. Furthermore, no tissue reactivity or cellular mobilization was evident remote from the implant site. Mononuclear macrophages, proliferating fibroblasts, and mature vascularized fibrous capsules were typical of the tissue response. Degradation of the polymers was accompanied by an increase in collagen deposition. For the polylactide series, the inflammatory response after 1 month of implantation was less for materials containing the D-unit in the polymer chain, whereas in the case of the polyhydroxybutyrate/valerates, the number of inflammatory cells increased with increasing content of the valerate unit in the polymer chain. Between 1-3 months, there was slightly more tissue response to the PHB and PHB/VA polymers than to PLA. This response is attributed to the presence of leachable impurities and a low molecular weight soluble component in the polyhydroxybutyrate/valerates. At 6 months, the extent of tissue reaction was similar for both types of polymers.All polylactides degraded significantly (56-99%) by 6 months. For a poly(L-lactide) series, degradation rate in vivo decreased with increasing initial molecular weight of the injection-molded polymer. Several samples showed pronounced bimodal molecular weight distributions (MWD), which may be due to differences in degradation rate, resulting from variability in distribution of crystalline and amorphous regions within the samples. This may also be the result of two different mechanisms, i.e., nonenzymatic and enzymatic, which are involved in the degradation process, the latter being more extensive at the later stage of partially hydrolyzed polymer. The PHB and PHB/VA polymers degraded less (15-43%) than the polylactides following 6 months of implantation. Generally, the polymer with higher valerate content (19%, 22% degraded most. The decrease in molecular weight was accompanied by a narrowing of the MWD for PHB and copolymers; there was no evidence of a bimodal MWD, possibly indicating that the critical molecular weight that would permit enzyme/polymer interaction had not been reached. Weight loss during implantation ranged from 0-50% for the polylactides, whereas for the PHB polymers weight loss ranged from 0-1.6%. © 1993 John Wiley & Sons, Inc.
    Zusätzliches Material: 13 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jbm.820270904
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  • 6
    Digitale Medien
    Digitale Medien
    Improved fire safety of composites for naval applications (1992)
    New York, NY [u.a.] : Wiley-Blackwell
    Fire and Materials 16 (1992), S. 119-125 
    Details
    ISSN: 0308-0501
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Architektur, Bauingenieurwesen, Vermessung , Maschinenbau
    Notizen: This study is based on the use of integral, hybrid thermal barrier to protect the core of the composite structure. Thermal barrier treatments evaluated in this study include ceramic fabric, ceramic coating, intumescent coating, hybrid of ceramic and intumescent coating, silicone foam, and phenolic skin. The composite systems evaluated in combination with thermal barrier treatments included glass/vinyl ester, graphite/epoxy, graphite/bismaleimide, and graphite/phenolic. All configurations were tested for flammability characteristics. These included smoke density and combustion gas generation (ASTM E-662), residual flexural strength (ASTM D-790), heat release rate, and ignitability (ASTM E-1354). ASTM E-662 test method covers the determination of specific optical density of smoke generated by solid materials. ASTM D-790 test method covers the determination of flexural properties of composite materials in the form of rectangular bars. ASTM E-1354 (cone calorimeter) covers the measurement of the response of materials exposed to controlled levels of radiant heating with or without an external ignitor, and is used to determine the ignitability, heat release rates, mass loss rates, effective heat of combustion, and visible smoke development. Without any fire barrier treatments, all composite systems evaluated in this study failed to meet ignitability and peak heat release requirements of MIL-STD-2031 (SH) at radiant heat fluxes of 75 and 100 kW m-2, respectively. Intumescent coating and a hybrid system consisting of intumescent coating over ceramic coating were the most effective fire barrier treatments for composite systems evaluated in this study. Using either of these treatments, all composite systems met the ignitability requirements of 90 and 60 at 75 and 100 kW m-2, respectively. Except for glass/vinyl ester, all systems also met the peak and average heat release requirements of MIL-STD-2031 (SH) at radiant heat fluxes of 25, 75, and 100 kW m-2, respectively.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/fam.810160303
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  • 7
    facet.materialart.
    Unbekannt
    The Generic Spacecraft Analyst Assistant (GenSAA): A tool for automating spacecraft monitoring with expert systems (1991)
    In:  CASI
    Details
    Publikationsdatum: 2013-08-31
    Beschreibung: Flight Operations Analysts (FOAs) in the Payload Operations Control Center (POCC) are responsible for monitoring a satellite's health and safety. As satellites become more complex and data rates increase, FOAs are quickly approaching a level of information saturation. The FOAs in the spacecraft control center for the COBE (Cosmic Background Explorer) satellite are currently using a fault isolation expert system named the Communications Link Expert Assistance Resource (CLEAR), to assist in isolating and correcting communications link faults. Due to the success of CLEAR and several other systems in the control center domain, many other monitoring and fault isolation expert systems will likely be developed to support control center operations during the early 1990s. To facilitate the development of these systems, a project was initiated to develop a domain specific tool, named the Generic Spacecraft Analyst Assistant (GenSAA). GenSAA will enable spacecraft analysts to easily build simple real-time expert systems that perform spacecraft monitoring and fault isolation functions. Lessons learned during the development of several expert systems at Goddard, thereby establishing the foundation of GenSAA's objectives and offering insights in how problems may be avoided in future project, are described. This is followed by a description of the capabilities, architecture, and usage of GenSAA along with a discussion of its application to future NASA missions.
    Schlagwort(e): CYBERNETICS
    Materialart: The 1991 Goddard Conference on Space Applications of Artificial Intelligence; p 129-139
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 8
    facet.materialart.
    Unbekannt
    Group-oriented coordination models for distributed client-server computing (1994)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: This paper describes group-oriented control models for distributed client-server interactions. These models transparently coordinate requests for services that involve multiple servers, such as queries across distributed databases. Specific capabilities include: decomposing and replicating client requests; dispatching request subtasks or copies to independent, networked servers; and combining server results into a single response for the client. The control models were implemented by combining request broker and process group technologies with an object-oriented communication middleware tool. The models are illustrated in the context of a distributed operations support application for space-based systems.
    Schlagwort(e): CYBERNETICS
    Materialart: NASA. Goddard Space Flight Center, The 1994 Goddard Conference on Space Applications of Artificial Intelligence; p 305-318
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 9
    facet.materialart.
    Unbekannt
    Ultrasonic robot localization using Dempster-Shafer theory (1992)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-08-28
    Beschreibung: A localization algorithm for ultrasonic robot described is based on range readings from wide beam ultrasonic transducers to built a model of the empty regions in the room. The method is incorporated into a move-to-station behavior which was demonstrated on the Georgia Tech mobile robot. A belief model of the range of readings that was based on Dempster-Shafer theory was used to compute the belief of points in the environment being empty, occupied, or unknown. The current belief in the empty space was used to construct a weighted centroid of the empty space after each move of the robot. By moving toward this center of mass and continually adding to the beliefs of the point in the environment the robot iteratively moved to the center of the open space.
    Schlagwort(e): CYBERNETICS
    Materialart: In: Neural and stochastic methods in image and signal processing; Proceedings of the Meeting, San Diego, CA, July 20-23, 1992 (A93-32905 12-63); p. 2-11.
    Format: text
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    NASA TECHNICAL REPORTS
  • 10
    facet.materialart.
    Unbekannt
    GenSAA - Advancing satellite monitoring with expert systems (1991)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-07-13
    Beschreibung: During numerous contacts with a satellite each day, spacecraft analysts must closely monitor real time data watching for combinations of telemetry parameter values, trends, and other indications that may signify a problem or failure. At the NASA Goddard Space Flight Center, fault-isolation expert systems are currently in operation supporting this data monitoring task. Based on the lessons learned during these initial efforts in expert system automation, a new domain-specific expert system development tool is being developed to facilitate the rapid development and reuse of real-time expert systems to serve as fault-isolation assistants for spacecraft analysts.
    Schlagwort(e): CYBERNETICS
    Materialart: AIAA PAPER 91-3948 , AIAA Computing in Aerospace Conference; Oct 21, 1991 - Oct 24, 1991; Baltimore, MD; United States
    Format: text
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    NASA TECHNICAL REPORTS
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