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  • Polymer and Materials Science  (3)
  • AIRCRAFT DESIGN, TESTING AND PERFORMANCE  (2)
  • 1990-1994  (4)
  • 1970-1974  (1)
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  • 1
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-2: Polymer Physics 8 (1970), S. 555-570 
    ISSN: 0449-2978
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Four equations, relating the glass transition temperatures Tg of homopolymers and copolymers to invariant additive temperature parameters (ATP) associated with their constituent groups, but weighted in different ways, have been applied to the calculation of the Tg of seven series of polymers having alkyl side chains. It is shown that the Tg of the 32 polymers considered may be calculated, within 7°K of the observed values, without the use of interaction coefficients from 15 independent variables, representing summations of the ATP's. The present calculations are confined to those structures which may be formed by a recombination of the structures corresponding to these independent variables. It is an essential feature of the approach that a distinction is made between groups with different nearest neighbors. Alternative methods of calculation are considered. The temperature parameter for a sequence of three or more methylene groups is estimated as 141°K, in conformity with the transition in polyethylene at 148°K. Nearest-neighbor interactions, stereoregularity, and crystallinity effects are discussed.
    Zusätzliches Material: 12 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 40 (1990), S. 1177-1194 
    ISSN: 0021-8995
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: In recent years, tetraethyl orthosilicate (TEOS) has been used as a precursor in preparing inorganic glasses. The technique, known as the sol-gel process involves a two step poly(hydrolysis-condensation)reaction sequence. The work presented here is concerned with the utilization of a suitably functionalized oligomeric “glassy” organic polymeric component in this two step sequence. In particular, an amine terminated amorphous poly(arylene ether) ketone, (PEK), end capped with isocyantonropyl triethoxy silane was used to synthesize a hybrid network with TEOS. Low incorporation of the PEK oligomers into the network caused by early vitrification can be eliminated by carrying out reactions at elevated temperatures. A systematic change in mechanical and physical properties of the hybrid glass has been found with TEOS content and the annealing temperatures. A model for the network has been proposed based on structural and morphological evidence.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 25 (1991), S. 1417-1429 
    ISSN: 0021-9304
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Medizin , Technik allgemein
    Notizen: Physical characteristics of a Ti-6Al-4V implant were evaluated following fabrication using a new electrodischarge compaction technique. Ti-6Al-4V atomized powders were loaded into Pyrex tubes (3.3 mm ID) and subjected to a highvoltage, high-current-density pulse in air for a period of less than 300 μs. Single pulses (1.0, 1.5, 2.0 and 2.5 KJ/grampowder) were applied from a capacitor bank (240, 480 or 720 μF) to produce solid core implants with porous surface layers. Implants were evaluated microscopically for core size, neck size, pore size, grain structure, and incorporated oxide film. Hardness was also evaluated. Implants were compared with Ti-6Al-4V commercial powders. Core size increased and pore size decreased with increases in energy and capacitance. The cores were composed of equiaxed grains which were free of oxide at the grain boundary. Porous layers, consisting of particles connected in three dimensions by necks, were free of oxide films at the connecting interfaces. Neck size increased with increases in input energy and capacitance. Hardness readings of the core, necks, and porous particles resulted in readings higher than or similar to control materials. Electrodischarge compaction did not alter the physical characteristics during compaction.
    Zusätzliches Material: 12 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 4
    Publikationsdatum: 2019-07-13
    Beschreibung: Data, tables, and graphs relative to the optimal trajectories for an aerospace plane are presented. A single-stage-to-orbit (SSTO) configuration is considered, and the transition from low supersonic speeds to orbital speeds is studied for a single aerodynamic model (GHAME) and three engine models. Four optimization problems are solved using the sequential gradient-restoration algorithm for optimal control problems: (1) minimization of the weight of fuel consumed; (2) minimization of the peak dynamic pressure; (3) minimization of the peak heating rate; and (4) minimization of the peak tangential acceleration. The above optimization studies are carried out for different combinations of constraints, specifically: initial path inclination that is either free or given; dynamic pressure that is either free or bounded; and tangential acceleration that is either free or bounded.
    Schlagwort(e): AIRCRAFT DESIGN, TESTING AND PERFORMANCE
    Materialart: NASA-CR-187848 , NAS 1.26:187848 , AAR-248-PT-2 , 1990 American Control Conference; May 23, 1990 - May 25, 1990; San Diego, CA; United States
    Format: application/pdf
    Standort Signatur Erwartet Verfügbarkeit
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  • 5
    Publikationsdatum: 2019-07-13
    Beschreibung: The optimization of the trajectories of an aerospace plane is discussed. This is a hypervelocity vehicle capable of achieving orbital speed, while taking off horizontally. The vehicle is propelled by four types of engines: turbojet engines for flight at subsonic speeds/low supersonic speeds; ramjet engines for flight at moderate supersonic speeds/low hypersonic speeds; scramjet engines for flight at hypersonic speeds; and rocket engines for flight at near-orbital speeds. A single-stage-to-orbit (SSTO) configuration is considered, and the transition from low supersonic speeds to orbital speeds is studied under the following assumptions: the turbojet portion of the trajectory has been completed; the aerospace plane is controlled via the angle of attack and the power setting; the aerodynamic model is the generic hypersonic aerodynamics model example (GHAME). Concerning the engine model, three options are considered: (EM1), a ramjet/scramjet combination in which the scramjet specific impulse tends to a nearly-constant value at large Mach numbers; (EM2), a ramjet/scramjet combination in which the scramjet specific impulse decreases monotonically at large Mach numbers; and (EM3), a ramjet/scramjet/rocket combination in which, owing to stagnation temperature limitations, the scramjet operates only at M approx. less than 15; at higher Mach numbers, the scramjet is shut off and the aerospace plane is driven only by the rocket engines. Under the above assumptions, four optimization problems are solved using the sequential gradient-restoration algorithm for optimal control problems: (P1) minimization of the weight of fuel consumed; (P2) minimization of the peak dynamic pressure; (P3) minimization of the peak heating rate; and (P4) minimization of the peak tangential acceleration.
    Schlagwort(e): AIRCRAFT DESIGN, TESTING AND PERFORMANCE
    Materialart: NASA-CR-187868 , NAS 1.26:187868 , AAR-247 , American Control Conference; May 23, 1990 - May 25, 1990; San Diego, CA; United States
    Format: application/pdf
    Standort Signatur Erwartet Verfügbarkeit
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