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排序方式: 共有451条查询结果,搜索用时 15 毫秒
61.
This paper presents a quantitative economic analysis and a qualitative constructability analysis of three-dimensional fiber-reinforced plastic (FRP) reinforcement cages for concrete beams. Material, labor, and life-cycle costs are provided, and construction practice aspects are discussed. The results of the analyses indicate that prefabricated FRP cages can offer benefits to the construction industry. Although the initial costs of the FRP materials are likely to be higher than those of steel rebar, there is a significant potential for cost savings due to reduced maintenance and labor costs, as a result of the corrosion resistance of the FRP and the increased construction productivity. When direct life-cycle costs are considered, FRP reinforcements already constitute, in many cases, an economically competitive alternative to conventional steel reinforcement in adverse environments. If, in addition, the indirect cost savings as well as quality and safety issues are considered, the FRP reinforcement may be even more competitive. 相似文献
62.
Selection of equipment for construction projects, a key factor in the success of the project, is a complex process. Current models offered by the literature fail to provide adequate solutions for two major issues: the systematic evaluation of soft factors, and the weighting of soft benefits in comparison with costs. This paper presents a selection model based on analytic hierarchy process (AHP), a multiattribute decision analysis method, with a view to providing solutions for these two issues. The model has the capacity to handle a great number of different criteria in a way that truly reflects the complex reality, to incorporate the context and unique conditions of the project, and to allow for manifestation of user experience and subjective perception. The model was implemented in an in-house developed system that was improved and validated through testing by senior professionals. The main academic contribution of the study is in the modification of AHP to correspond with the nature of equipment selection and in its utilization as an effective means for the formalization of knowledge possessed by competent, experienced practitioners. On the practical side, the proposed model offers an efficient, convenient tool that forces the users into orderly, methodical thinking, guides them in making logical, consistent decisions, and provides a facility for all necessary computations. 相似文献
63.
64.
Repeated communication and Ramsey graphs 总被引:2,自引:0,他引:2
Alon N. Orlitsky A. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》1995,41(5):1276-1289
We study the savings afforded by repeated use in two zero-error communication problems. We show that for some random sources, communicating one instance requires arbitrarily many bits, but communicating multiple instances requires roughly 1 bit per instance. We also exhibit sources where the number of bits required for a single instance is comparable to the source's size, but two instances require only a logarithmic number of additional bits. We relate this problem to that of communicating information over a channel. Known results imply that some channels can communicate exponentially more bits in two uses than they can in one use 相似文献
65.
The selectins, a family of Ca(2+)-dependent lectins, are expressed on inflamed vascular endothelium and some leukocyte subsets, and mediate adhesive contacts between blood cells and vessel walls. These interactions are loose and reversible, operate under conditions of shear flow, and result in leukocyte rolling along the vessel wall. The structure of the selectins and their ligands makes them uniquely suited for supporting the type of bond formation and dissociation that must prevail in order for a cell to be able to roll under conditions of flow. Because rolling precedes (and appears to be essential for) the integrin-mediated firm arrest before extravasation in response to inflammatory or infectious stimuli, inhibition of selectin function has potential for anti-inflammatory therapy, but also presents some significant challenges because of the complexity of the processes involved. 相似文献
66.
A Ariel R Hershkoviz L Cahalon DE Williams SK Akiyama KM Yamada C Chen R Alon T Lapidot O Lider 《Canadian Metallurgical Quarterly》1997,27(10):2562-2570
The putative effects of interleukin (IL)-7, operating in the context of extracellular matrix (ECM), on the adhesion of human T cells were examined. Recombinant human, IL-7 was found to bind ECM or fibronectin (FN) with IC50 values of 10-100 nM. Nanogram amounts of both soluble and, especially, FN- or ECM-bound IL-7, which differentially affected the morphologies of FN-adherent T cells, induced the adhesion of resting CD4+ and CD8+ T cells in dose-dependent and beta 1 integrin-dependent manners. Under static and flow conditions, soluble IL-7 also induced the binding of unstimulated T cells to vascular cell adhesion molecule-1, suggesting that this cytokine can also modulate integrin binding to endothelial cell ligands. The effects of affinity modulation by IL-7 of FN-specific beta 1 integrins depend on the presence of soluble FN, which inhibited T cell adhesion to FN induced by FN-bound IL-7 or by an integrin-specific affinity-modulating monoclonal antibody, but not by soluble IL-7 or phorbol 12-myristate 13-acetate. These findings provide an example of a major ECM integrin ligand, FN, which is capable of modulating its adhesive interactions with specific immune cells by associating with and presenting a cytokine in a bio-active state. 相似文献
67.
Y Shapira R Hirsch R Jortner M Nili B Vidne A Sagie 《Canadian Metallurgical Quarterly》1997,133(5-6):169-73, 246
A series of 12 patients with 16 episodes of prosthetic heart-valve thrombosis over 3 years is presented. Most episodes affected mitral or tricuspid bileaflet prostheses. All patients were inadequately anticoagulated at the time of thrombosis. The clinical presentation was acute and severe in 6 patients, and subacute or chronic in the rest. Physical examination was suggestive of stuck valves in most cases. Transthoracic echocardiography revealed increased transvalvular gradients in most. However, clearer evidence of valve thrombosis was obtained from transesophageal echocardiography or fluoroscopy. 9 patients eventually had their valves re-replaced successfully, and the preoperative diagnosis was confirmed in all. 5 patients were operated as soon as the diagnosis was established. and an additional 4 were operated after failure of anticoagulation. In 4 patients the valve leaflets became completely mobile after a course of thrombolysis. Prosthetic valve thrombosis is a severe and potentially fatal complication in patients with mechanical heart valves. Alertness of physicians at all levels- the general practitioner, the internist and the cardiologist- to the possibility of valve thrombosis and to its clinical presentation may lead to prompt and earlier diagnosis and to comprehensive therapy. 相似文献
68.
Aviad Shapira 《工程教育杂志》1995,84(1):81-85
Recognizing that civil engineering students, as part of their construction training, must have closer contact with the real-world construction arena, a construction engineering laboratory has recently been set up at the Civil Engineering Department, Technion—Israel Institute of Technology. The laboratory is gradually being integrated into the curriculum of the Civil Engineering Department's Construction Engineering and Management Program. This paper describes the laboratory and its operation, and illustrates the laboratory's effectiveness in fulfilling its assigned role. 相似文献
69.
WW Fisher LG Bowman RH Thompson SA Contrucci L Burd G Alon 《Canadian Metallurgical Quarterly》1998,31(3):493-496
Transcutaneous electrical nerve stimulation is used to reduce pain but also may be useful for self-injurious behavior (SIB). In the current investigation, a microcurrent electromedical device, classified as a transcutaneous electrical nerve stimulator (TENS), was applied with a man with Down syndrome who displayed SIB that persisted in the absence of social contingencies. Although clinically significant results were not maintained, a clear difference in the rates of SIB during active and inactive TENS was observed. 相似文献
70.
E. A. Katz D. Faiman S. Goren S. Shtutina B. Mishori Yoram Shapira 《Fullerenes, Nanotubes and Carbon Nanostructures》1998,6(1):103-111
A heterojunction was prepared by depositing a thin film of C60 on a p-Si substrate. Photovoltaic properties were observed using a UV-filtered solar simulator and natural sun light. Surface Photovoltage Spectroscopy was employed to distinguish between the nature of photoconversion in the C60 and Si layers. 相似文献