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  • Physics  (73)
  • BIOTECHNOLOGY  (60)
  • STRUCTURAL MECHANICS  (57)
  • ASTROPHYSICS
  • 1970-1974  (190)
  • 1960-1964
  • 1972  (190)
Collection
Keywords
Publisher
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  • 1970-1974  (190)
  • 1960-1964
Year
  • 1
    Electronic Resource
    Electronic Resource
    EPR studies of mechanically induced bond rupture in elastomersPaper presented at the Symposium on Mechano-Chemistry of Polymers, American Chemical Society National Meeting, Washington, D. C., September 16, 1971. (1972)
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-2: Polymer Physics 10 (1972), S. 599-606 
    Details
    ISSN: 0449-2978
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Electron paramagnetic resonance (EPR) spectroscopy was used to compute the surface bond rupture density in polyurethane and to determine the phase experiencing fracture in styrene-butadiene block copolymers when these elastomers are subjected to mechanical degradation by grinding. The polyurethane grinding was done at temperatures above and below the glass transition Tg; 0.155 × 1013 radicals/cm2 of fracture surface area were formed above the Tg and 4.42 × 1013 radicals/cm2 for grinding below the Tg. These values are essentially equal to those found earlier for spherulitic polymers. In all cases the fracture appears able to progress along preferential paths so as to rupture significantly fewer molecular chains than one would expect on the basis of calculations of the number of chains passing through each square centimeter of cross section. Comparison of EPR spectra formed by grinding styrene-butadiene copolymer with those of styrene and butadiene above indicated that at cryogenic temperature, the fracture in the copolymer takes place in the butadiene phase.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1972.160100403
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Fracture behavior in nylon 6 fibers (1972)
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-2: Polymer Physics 10 (1972), S. 1415-1445 
    Details
    ISSN: 0449-2978
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A reaction rate model of fracture in polymer fibers is described. This model assumes that bond rupture is governed by absolute reaction rate theory with a stress-aided activation energy. It is demonstrated that the key in obtaining good agreement between the model and experiment lies in taking proper account of the variation of stress on the tie-chain molecules. The more taut chains rupture first, and the load is redistributed among the remaining unruptured tie chains. The effect of varying the temperature both in the model and in experiments on fracture in fibers is explored. Good agreement between predictions of the model and experiment is possible only with an undeterstanding of the distribution in stress on the tie chains. The distribution in stress on the chains was experimentally determined by monitoring the kinetics of bond rupture with electron paramagnetic resonance (EPR) spectroscopy. Temperature is found to have two effects on macroscopic strength. (1) The thermal energy aids the atomic stress in breaking the atomic bonds; as a consequence the rate of bond rupture of a family of bonds under a given molecular stress is increased. In this respect temperature might be viewed as decreasing the “strength” of a bond. (2) Temperature also serves to “loosen” the molecular structure and in this way modify the distribution in stress on the tie chains. To explain bond rupture and macroscopic fracture behavior quantitatively, account must be taken of both effects.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1972.160100802
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    (Diethoxyphosphato)- and (π-cyclopentadienyl)-(diethoxyphosphato)-oxotitanium (IV) polynuclear complexes (1972)
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-1: Polymer Chemistry 10 (1972), S. 1559-1562 
    Details
    ISSN: 0449-296X
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1972.150100527
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  • 4
    Electronic Resource
    Electronic Resource
    Chromocene catalysts for ethylene polymerization: Scope of the polymerization (1972)
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-1: Polymer Chemistry 10 (1972), S. 2621-2637 
    Details
    ISSN: 0449-296X
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chromocene deposited on silica supports of high surface area forms a highly active catalyst for polymerization of ethylene. Polymerization is believed to occur by a coordinated anionic mechanism previously outlined. The catalyst formation step liberates cyclopentadiene and leads to a new divalent chromium species containing a cyclopentadienyl ligand. The catalyst has a very high chain-transfer response to hydrogen which permits facile preparation of a full range of molecular weights. Catalyst activity increases with an increase in silica dehydration temperature, chromium content on silica, and ethylene reaction pressure. The temperature-activity profile is characterized by a maximum near 60°C, presumably caused by a deactivation mechanism involving silica hydroxyl groups. A value of 72 was estimated for the ethylene-propylene reactivity ratio (r1). Linear, highly saturated polymers are normally prepared below 100°C. By contrast with other commercial polyethylenes, the chromocene catalyst produces polyethylenes of relatively narrow molecular weight distribution. Above 100°C, unsaturated, branched polymers or oligomers are formed by a simultaneous polymerization-isomerization process.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1972.150100910
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  • 5
    Electronic Resource
    Electronic Resource
    Ethylene polymerization with supported bis(triphenylsilyl) chromate catalysts (1972)
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-1: Polymer Chemistry 10 (1972), S. 2609-2620 
    Details
    ISSN: 0449-296X
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Bis(triphenylsilyl) chromate is an active catalyst for ethylene polymerization without further treatment or additives. Catalytic activity is markedly increased when the compound is deposited on silica-alumina and is further increased if it is deposited on silica and then treated with an aluminum alkyl. Polymer molecular weight can be controlled by reaction temperature, hydrogen addition, support type, and reducing agent structure to give polymers ranging in melt index from essentially zero to 〉 100. In the supported catalysts the bis(triphenylsilyl) chromate appears to be bound to the support and to undergo a reduction step either by reaction with ethylene or with aluminum alkyl prior to polymerization. The active site is envisioned as chromium alkyl, bound to the support, with propagation occurring by insertion of the monomer into a Cr—C bond. Chain termination is by chain transfer to monomer.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1972.150100909
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  • 6
    Electronic Resource
    Electronic Resource
    Stereochemistry of alternating isobutene-maleic anhydride, isobutene-dimethyl fumarate, and isobutene-dimethyl maleate copolymersPresented in part at the XXIIIrd International Congress of Pure and Applied Chemistry, Boston, Massachusetts, July 1971. (1972)
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-1: Polymer Chemistry 10 (1972), S. 1297-1310 
    Details
    ISSN: 0449-296X
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The stereochemical composition of the free radical alternating isobutene-maleic anhydride (IB/MA), isobutene-dimethyl fumarate (IB/DMF), and isobutene-dimethyl maleate (IB/DMM) copolymers was investigated by proton magnetic resonance. In contrast to the singlet gem-dimethyl resonance found in polyisobutene or in the alternating isobutene/acrylonitrile copolymer, the gem-dimethyl resonance of IB/MA, hydrolyzed IB/MA, and esterified IB/MA is a quadruplet with peaks of approximately equal intensity. The multiplicity of the spectra is consistent with the presence of equal amounts of threo-di-isotactic and threo-di-syndiotactic triads, disproving previous claims that such copolymers are predominantly threo-di-isotactic. The spectrum of the analogous IB/DMF indicates that the copolymer is composed entirely of erythro-di- isotactic and erythro-di-syndiotactic triads. This result is consistent with the exclusive trans opening of the dimethyl fumarate double bond and provides the first example for the stereospecific double bond opening of a noncyclic monomer in free radical polymerization. In contrast, the spectrum of IB/DMM shows that the dimethyl maleate double bond opens approximately 93% cis and 7% trans during copolymerization. Since the stereochemical composition of IB/DMF and IB/DMM is not the same, it is concluded that the radicals formed from dimethyl maleate and/or dimethyl fumarate do not equilibrate freely among all the possible configurations before isobutene addition.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1972.150100502
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  • 7
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    Simulation of a steady-state integrated human thermal system. (1972)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: The mathematical model of an integrated human thermal system is formulated. The system consists of an external thermal regulation device on the human body. The purpose of the device (a network of cooling tubes held in contact with the surface of the skin) is to maintain the human body in a state of thermoneutrality. The device is controlled by varying the inlet coolant temperature and coolant mass flow rate. The differential equations of the model are approximated by a set of algebraic equations which result from the application of the explicit forward finite difference method to the differential equations. The integrated human thermal system is simulated for a variety of combinations of the inlet coolant temperature, coolant mass flow rate, and metabolic rates.
    Keywords: BIOTECHNOLOGY
    Type: Computers in Biology and Medicine; 2; 1972
    Format: text
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    NASA TECHNICAL REPORTS
  • 8
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    Residual strength and crack propagation tests on C-130 airplane center wings with service-imposed fatigue damage (1972)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Fourteen C-130 airplane center wings, each containing service-imposed fatigue damage resulting from 4000 to 13,000 accumulated flight hours, were tested to determine their fatigue crack propagation and static residual strength characteristics. Eight wings were subjected to a two-step constant amplitude fatigue test prior to static testing. Cracks up to 30 inches long were generated in these tests. Residual static strengths of these wings ranged from 56 to 87 percent of limit load. The remaining six wings containing cracks up to 4 inches long were statically tested as received from field service. Residual static strengths of these wings ranged from 98 to 117 percent of limit load. Damage-tolerant structural design features such as fastener holes, stringers, doublers around door cutouts, and spanwise panel splices proved to be effective in retarding crack propagation.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-2075 , ER-11178
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 9
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    Skin and muscle components of forearm blood flow in directly heated resting man. (1972)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: Changes in forearm muscle blood flow (FMBF) during direct whole-body heating were measured in 17 normal subjects using three different methods. We conclude that FMBF is not increased by direct whole-body heating. Since renal and splanchnic blood flow fall 30% under these conditions, maximal total skin blood flow in 12 previously studied subjects can be estimated from the rise in cardiac output to be 7.6 L/min (3.0-11.1 L/min).
    Keywords: BIOTECHNOLOGY
    Type: Journal of Applied Physiology; 32; Apr. 197
    Format: text
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    NASA TECHNICAL REPORTS
  • 10
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    Simulation of a steady-state integrated human thermal system. (1972)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: The mathematical model of an integrated human thermal system is formulated. The system consists of an external thermal regulation device on the human body. The purpose of the device (a network of cooling tubes held in contact with the surface of the skin) is to maintain the human body in a state of thermoneutrality. The device is controlled by varying the inlet coolant temperature and coolant mass flow rate. The differential equations of the model are approximated by a set of algebraic equations which result from the application of the explicit forward finite difference method to the differential equations. The integrated human thermal system is simulated for a variety of combinations of the inlet coolant temperature, coolant mass flow rate, and metabolic rates. Two specific cases are considered: (1) the external thermal regulation device is placed only on the head and (2) the devices are placed on the head and the torso. The results of the simulation indicate that when the human body is exposed to hot environment, thermoneutrality can be attained by localized cooling if the operating variables of the external regulation device(s) are properly controlled.
    Keywords: BIOTECHNOLOGY
    Type: Computers in Biology and Medicine; 2; Feb. 197
    Format: text
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    NASA TECHNICAL REPORTS
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