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101.
The failure mechanisms of several epoxy polymers (including pure, rubber- and particulatemodified, as well as rubber/particulate hybrid epoxies) were investigated over a wide range of strain rates (10–6 to 102 sec–1) and temperatures (–80 to 60° C). A substantial variation in fracture toughness, GIc, with rate was observed at both very high and very low strain rates. Under impact testing conditions, GIc for both pure and rubber-modified epoxies displayed peaks at about 23 and –80° C which appeared to correlate with the corresponding size of the crack tip plastic zone. In order to explain these rate and temperature-dependent GIc results, two separate crack blunting mechanisms were proposed: thermal blunting due to crack tip adiabatic heating and plastic blunting associated with shear yield/flow processes. Thermal blunting was found to occur in the pure- and rubber-modified epoxies under all impact testing conditions and temperatures above 0° C. For temperatures below –20° C under impact conditions, the fracture toughness is dependent on viscoelastic loss processes and not thermal blunting. Plastic blunting was predominant at very slow strain rates less than 10–2 sec–1 for the pure- and rubber-modified epoxies and at impact strain rates for the fibre and hybrid epoxies. Microstructural studies of fracture surfaces provided some essential support for the two proposed crack blunting mechanisms. 相似文献
102.
Integrating communication services 总被引:3,自引:0,他引:3
The need for communication services which span multiple communication technologies is growing. Communication services are being developed in three areas: in the public switched telephony networks, on the Internet in the form of integrated multimedia including voice-over-Internet, and in private switched telephony networks in the form of enterprise computer-telephony integration applications. This article shows it is plausible to create unified services which span the Internet and public switched telephony networks, and goes on to describe Nexus, an architecture and prototype for integrated communication services 相似文献
103.
Chor Ping Low Ning Wang Jim Mee Ng 《International Journal of Communication Systems》2002,15(8):655-682
Multicasting refers to the transmission of data from a source node to multiple destination nodes in a network. Group multicasting is a generalization of multicasting whereby every member of a group is allowed to multicast messages to other members that belong to the same group. The routing problem in this case involves the construction of a set of low cost multicast trees with bandwidth requirements, one for each member of the group for multicasting messages to other members of the group. In this paper, we examine this routing problem with an additional requirement that member nodes are allowed to join and leave the multicasting group anytime during a session. We call this problem, the dynamic group multicast routing problem (DGMRP). In this paper, we proposed three heuristic algorithms to generate a set of low cost multicast trees with dynamic group membership. Results from our empirical study shows that the one of the proposed algorithms, called Maximum bandwidth bottleneck path selection algorithm (MBBPS), achieves better utilization of bandwidth resources as compared with the other two algorithms which are based on a greedy approach. In addition MBBPS performs better in terms of cost when the bandwidth is not sufficient in the network. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
104.
105.
Peiling Hou Peng Zou Min-Yong Low Eli Chan Hwee-Ling Koh 《Food Additives & Contaminants》2006,23(9):870-875
An analogue of acetildenafil was detected in an extract of pre-mixed bulk powder. To our knowledge, the powder was destined to be encapsulated and sold as a dietary supplement. The structure was identified by NMR, HR-ESI-MS, ESI-MSn and FTIR analyses. Owing to the inclusion of a hydroxyl group in acetildenafil, the detected compound was called 'hydroxyacetildenafil'. With increasing use of dietary supplements marketed for penile erectile dysfunction, the detection of analogues of sexual performance enhancers is important and timely. 相似文献
106.
A G Low 《Journal of the science of food and agriculture》1977,28(11):980-982
A simple stainless steel urine and faeces separator for use with female pigs is described. The equipment fits into a standard Shinfield metabolism cage for pigs. The separator has been used in metabolism trials with pigs from 20 to 90 kg liveweight. 相似文献
107.
Jeffery D.R. Low G.C. Barnes M. 《IEEE transactions on pattern analysis and machine intelligence》1993,19(5):529-532
Effective management of the software development process requires that management be able to estimate total development effort and cost. One of the fundamental problems associated with effort and cost estimation is the a priori estimation of software size. Function point analysis has emerged over the last decade as a popular tool for this task. Criticisms of the method that relate to the way in which function counts are calculated and the impact of the processing complexity adjustment on the function point count have arisen. SPQR/20 function points among others are claimed to overcome some of these criticisms. The SPQR/20 function point method is compared to traditional function point analysis as a measure of software size in an empirical study of MIS environments. In a study of 64 projects in one organization it was found that both methods would appear equally satisfactory. However consistent use of one method should occur since the individual counts differ considerably 相似文献
108.
109.
A method for determining the thermal coefficients in electrical machines based upon a new linear lumped parameter model and accurate measurement of temperature and loss densities within the machine is presented. The thermal network is reduced to a system of simultaneous equations. The equivalent thermal coefficients are determined by solving the equations using a singular value decomposition (SVD) method. Results obtained for a 4 kW totally enclosed fan cooled (TEFC) induction motor are presented and compared with established data. The technique is suitable for establishing more accurate thermal coefficients for composite materials and combinations of complex geometrical form 相似文献
110.
The regulation of translation frequently involves protein-RNA interactions. An intriguing example of this is the alternative decoding of UGA, typically a stop codon, as selenocysteine. Two RNA structures, the mRNA selenocysteine insertion sequence (SECIS element) and a unique selenocysteyl-tRNA, are required for this process. In prokaryotes, a single RNA-binding protein, a selenocysteine-specific elongation factor, interacts with both the tRNA and mRNA to confer decoding. Whether eukaryotes use a similar mechanism is currently the subject of intense investigation. 相似文献