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61.
62.
Timothy J. Bunning Hong G. Jeon Ajit K. Roy Kristen M. Kearns Barry L. Farmer Walter W. Adams 《应用聚合物科学杂志》2003,87(14):2348-2355
The thermal and mechanical properties of polyurethane‐infiltrated carbon foam of various densities were investigated. By combining the high thermal conductivity of the carbon foam with the mechanical toughness of the pure polyurethane, a mechanically tough composite (relative to the unfilled foam) that could be used at higher temperatures than the polyurethane's degradation was formed. Both the tensile strength and the modulus increased by an order of magnitude for the composites compared to unfilled foam, while the compressive and shear strengths and moduli of the composites approached values exhibited by pure polyurethane. At both 300 and 400°C, the rectangular blocks of pure polyurethane lost their mechanical integrity due to decomposition in air. Thermogravimetric analysis confirms substantial initial weight loss above 290°C. Filled carbon foam blocks, however, maintain their mechanical integrity at both 300 and 400°C indefinitely, although the bulk of the rectangular block mass is polyurethane. Three different carbon foam densities are examined. As expected, the higher density foams show greater heat transfer. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 2348–2355, 2003 相似文献
63.
The glass transition temperatures (Tg's) of several polystyrenes and styrene–alkyl methacrylate copolymers and terpolymers were measured using thermomechanical analysis (TMA) and differential scanning calorimetry (DSC). The polymers studied had number-average molecular weights from 3000 to 250,000 g/mole. The results indicate that the composition dependence of the Tg's for the copolymers and terpolymers can be satisfactorily described by a general Fox equation. In general, the measured Tg's of the copolymer and terpolymer samples depend more on the steric effects of the constituent pendent groups than on their molecular weights. The chain flexibility rather than the size of the pendent group is the determining factor in the glass transition properties of the styrene polymers. 相似文献
64.
Walter Soares Leal Antônio Ricardo Panizzi Cintia Carla Niva 《Journal of chemical ecology》1994,20(5):1209-1216
The alarm pheromone system ofLeptoglossus zonatus (Dallas) adults was shown to be composed of hexyl acetate, hexanol, hexanal, and hexanoic acid. Single components tested in the field elicited dispersive behavior of over 70% of adults. 2-(E)-Hexenal, found in the secretion of nymphs, but not in the exudates of adults, was also active against adults. In addition, first-instar nymphs responded to the four components of the alarm pheromone of adults as well as to 2-(E)-hexenal, a component of their own alarm pheromone system. Adults and nymphs possess different alarm pheromone systems, which are not specific to their own life stage. That hemipteran alarm pheromone systems are not species-specific was supported by the fact that both adult and nymphL. zonatus responded to butanoic acid, an alarm pheromone of Alydidae, which was not found in this Coreidae species. 相似文献
65.
The crystal structure and molecular conformation of 2-cyano-4-bromo-4′-N,N-diethylaminoazobenzene (C17H17N4Br, mol. wt. = 357·2 a.m.u) has been determined from X-ray diffraction data; triclinic, P (No. 2), a = 10·132(11) Å, b = 12·216(16) Å, c = 6·966(11) Å, α = 104·21(9)°, β = 92·67(12)°, γ = 97·22(7)°, V = 826·5(9) Å3, Z = 2, Dc = 1·436 g cm?3, F(000) = 378, λ(MoKα) = 0·71069 Å, μ(MoKα) = 26·0 cm?1. The structure was solved by the multiple solution direct method and refined by full-matrix least-squares to R = 0·059 for 1538 independent observed reflections. The azobenzene skeleton is planar to within 0·06 Å. Most significant bonding data are: NN, 1·290(8) Å; BrC, 1·866(6) Å; mean CN (azo) 1·380(8) Å; NNC, 113·6(4) and 115·3(4)°; NCC (cis relative to NN) 125·9(4)° and 126·7(4)°; NCC (trans) 116·8°(5)° and 116·1(4)°. 相似文献
66.
Nuclear magnetic resonance spectroscopy has been used to study the dissociation and reaction of N,N′-(2-propyloximino)-4,4′-methylenebis(phenylcarbamate), as a crosslinking agent for polymers containing labile hydrogens. The crosslinking of poly(acrylic acid), polyacrylamide, and poly(vinyl alcohol) was found to result upon heating each to 150°C for 10 min with this component at 2–10 wt %. 相似文献
67.
Walter J. Thomas Mohamed A. El-Sawy Edward W. Palmer 《Chemical Engineering Communications》1982,16(1):53-78
Two published theoretical models are examined and applied to experimental results for absorption and desorption. The system used was CO2/H2O and studies were made for liquid film flow down inclined planes. Experimental results give “Reduced” values of mass ransfer rates.
Interferometric studies give interfacial concentration, penetration and film depths, and take-up of carbon dioxide. In the case of desorption the interferograms are distorted by “deflections.”
All the experimental values for absorption and desorption differ from those calculated from theoretical models.
Desorption is not a mirror image of absorption, and it is approximately 75% of the transfer rate of absorption over a wide operating range.
A comparison is made of the behaviour of static pools and flowing liquid films. 相似文献
Interferometric studies give interfacial concentration, penetration and film depths, and take-up of carbon dioxide. In the case of desorption the interferograms are distorted by “deflections.”
All the experimental values for absorption and desorption differ from those calculated from theoretical models.
Desorption is not a mirror image of absorption, and it is approximately 75% of the transfer rate of absorption over a wide operating range.
A comparison is made of the behaviour of static pools and flowing liquid films. 相似文献
68.
We present a model of spatial navigation based on the non-convergent dynamics of brain activity. The system includes a hippocampal module that processes global spatial information and a cortical module that deals with local sensory information. We test the model using several spatial navigation paradigms: goal finding, shortcutting and detouring. Computer simulations show that the performance of the agent qualitatively matches that of animals and related models. This new approach provides a novel interpretation of how the brain accomplishes spatial navigation. 相似文献
69.
70.