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991.
992.
993.
Jeffrey T. Fong 《Nuclear Engineering and Design》1978,51(1):45-54
To cope with uncerainties in mechanical and structural design, enigineers exercise their judgement through the use of safety factors based on service experience and laboratory data on relevant design parameters. Using the problem of fatigue life prediction as a vehicle, the relationship between the size of a safety factor and the associated risk and cost-benefit estimates of the engineering judgement based on new technical information, is demonstrated. The subtle influence of the choice of a distribution function for a given set of data is exhibited by comparing the gaussian with the three-parameter Weibull fits of a set of fatigue life data on 6061-T6 aluminum. A system of ranking the importance of different sources of uncertainties based on an analysis of service data is proposed along with an example to “refine” the system using up-to-date laboratory and field measurements. The concept of a rational definition of safety factors as a tool for engineers who design under uncertainty is discussed. 相似文献
994.
The effect of filler particle size and orientation on the impact fracture toughness of a highly filled plasticized polymeric material 总被引:1,自引:0,他引:1
The effect of particle size and orientation on the inherent fracture toughness of a filled plasticized polymeric material
has been determined by application of linear elastic fracture mechanics. Testing was caried out in a three-point bend mode
under impact conditions. The material was a triple base gun propellant consisting of a matrix of nitrocellulose plasticized
with nitroglycerine and filled with particles of nitroguanidine (NQ). The crystalline NQ was used in the “as-received” form
of needles and in a “ground” state. The material containing as-received NQ consistently had a higher fracture toughness than
the material with ground NQ, and the toughness was a maximum when the fillers were aligned perpendicularly to the fracture
surface. The impact fracture toughness was found to be virtually independent of strain rate over the range from 3 to 90 sec−1.
Seven-perforated cylindrical grains of the material containing as-received and ground NQ crystals, and the grains were tested
in a pneumatic gas gun and a Hopkinson bar apparatus. The grains containing the ground NQ have been shown to be generally
less resistant to fracture than the grains containing as-received NQ. 相似文献
995.
F. H. C. Kelly Mak Fong Keng Chua Gek Sim 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1972,22(7):857-862
A study of the size distribution of calcium carbonate particles obtained by precipitation in a sucrose medium containing different polar additives has been made, including a series of tests to determine the polar property of the precipitate surface via electrophoresis and measurements of heat of adsorption. A mechanism of polar growth has also been suggested to explain the present results. 相似文献
996.
The hydrogen belts of membranes are defined as the regions consisting of hydrogen bond acceptors, i.e., the C=O groups of
glycero- and sphingolipids, and hydrogen bond donors, i.e., cholesterol-OH, sphingolipid-OH, proteins, and water. Lipid-lipid
hydrogen bonding in these belts has been suggested. The connection of such hypothetical bonding with the condensation effect,
i.e., the apparent reduction of surface area occupied by phospholipids in mixed monolayers with cholesterol, has been tested
with lipids possessing and lacking C=O groups: diester, diether, and dialkyl phosphatidylcholine, and analogous polyoxyethylene
diglycerides. Condensation by cholesterol was observed for all lipids. Consequently, the hypothetical lipid-C=O-cholesterol
hydrogen bonding is not a prerequisite for the condensation effect. 相似文献
997.
998.
999.
Although solar energy is able to power the heat-driven refrigeration, its contribution is quite limited due to the conventional cooling requirement. In building air-conditioning, it is common to supply low temperature chilled water, usually in 5–7 °C. If this temperature can be elevated, it would enhance the effectiveness to harness solar energy and minimize auxiliary heating. Solar refrigeration would then be more effective through high temperature cooling, by providing 15–18 °C chilled water instead. In such provision, radiant ceiling cooling can be coupled to handle the space cooling load, particularly space sensible load. And the space latent load and ventilation load are handled by a separate dehumidification provision, like the heat-driven desiccant dehumidification. Therefore, a solar hybrid air-conditioning system is formulated, using adsorption refrigeration, chilled ceilings and desiccant dehumidification. In this study, the year-round performances of the proposed solar hybrid air-conditioning systems were evaluated for two typical office types. The performance metrics include the solar fraction, coefficient of performance, solar thermal gain, primary energy consumption and indoor conditions. Comparative study was conducted for the hybrid air-conditioning system worked with the three common types of chilled ceilings, namely the chilled panels, passive chilled beams and active chilled beams. The solar hybrid air-conditioning system was also benchmarked with the conventional vapour compression refrigeration for office use. It is found that the proposed solar hybrid air-conditioning system is technically feasible through high temperature cooling. Among the three types of chilled ceilings, the passive chilled beams is the most energy-efficient option to work with the solar adsorption refrigeration for space conditioning in the subtropical city. 相似文献
1000.
Lawrence S. Giles C.L. Fong S. 《Knowledge and Data Engineering, IEEE Transactions on》2000,12(1):126-140
This paper examines the inductive inference of a complex grammar with neural networks and specifically, the task considered is that of training a network to classify natural language sentences as grammatical or ungrammatical, thereby exhibiting the same kind of discriminatory power provided by the Principles and Parameters linguistic framework, or Government-and-Binding theory. Neural networks are trained, without the division into learned vs. innate components assumed by Chomsky (1956), in an attempt to produce the same judgments as native speakers on sharply grammatical/ungrammatical data. How a recurrent neural network could possess linguistic capability and the properties of various common recurrent neural network architectures are discussed. The problem exhibits training behavior which is often not present with smaller grammars and training was initially difficult. However, after implementing several techniques aimed at improving the convergence of the gradient descent backpropagation-through-time training algorithm, significant learning was possible. It was found that certain architectures are better able to learn an appropriate grammar. The operation of the networks and their training is analyzed. Finally, the extraction of rules in the form of deterministic finite state automata is investigated 相似文献