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21.
Experiments show that the strength of nanostructures can be very high and that strength statistics are dominated by surface
flaws. To understand the dependence of strength on the surface morphology, a series of fracture mechanics based Monte-Carlo
simulations were performed. The surfaces of previously tested Si nanobeams were measured, statistically characterized and
equivalent surfaces were generated. The surface profiles consist of bunched steps with varying heights and widths. At the
root of each step, there is a stress singularity defined by a stress intensity factor. The beams were assumed to fail when
the stress intensity factor anywhere on the surface exceeds the fracture toughness. In agreement with experiments, simulations
show that even a small increase in the surface roughness results in a significant reduction in the strength of nanostructures.
Thus, careful attention to the surfaces is essential for optimum strength and reliability at the nanoscale. 相似文献
22.
This study proposes to use genetic algorithms for defining the topic boundaries in search of engine transaction logs. Users are interested in multiple topics during a search session, and genetic algorithms are used in this study to determine whether a search engine user has changed topics during a session. Sample data logs from FAST and Excite search engines were analyzed. The findings show that genetic algorithms are fairly successful in identifying topic continuations and shifts in search engine transaction logs. 相似文献
23.
24.
R. Ulusay E. Tuncay N. Hasancebi 《Bulletin of Engineering Geology and the Environment》2010,69(3):397-410
Peats consist of the partly decomposed remains of vegetation, which have accumulated in waterlogged areas. They are often
unsuitable for supporting structures of any kind due to their high water content, high compressibility, low shear strength
and high degree of spatial variability. The paper reports a preliminary study on peats from industrial sites in the city of
Kayseri, Turkey. The soils in the study area are classified as peat to muck. The peats are fibrous at shallow depth and become
amorphous as they extend to some 8 m depth. The ranges of geo-engineering properties are generally consistent with those reported
in the literature, with some variation due to their higher mineral soil contents. The behavior of the peats is essentially
frictional, with high friction and relatively small cohesion. The direct shear tests yielded higher shear strengths than those
from the triaxial tests, due to the fact that the peat specimens used in the direct shear tests were rich in fibers and mineral
soils. Back analysis of the settlement of heavy rolls of metal wires laid on the peat generally confirmed the consolidation
properties of the soil determined in laboratory. 相似文献
25.
Seda Bekin Acar Mustafa Ozcelik Tamer Uyar Mehmet Atilla Tasdelen 《Iranian Polymer Journal》2017,26(6):405-411
A series of hybrid networks based on polyhedral oligomeric silsesquioxane (POSS) were prepared by thiol-epoxy click reaction using commercially available octakis-glycidyl-POSS (G-POSS), trimethylolpropane triglycidyl ether, and trimethylolpropane tris(3-mercaptopropionate) as monomers. The click reaction was simply catalyzed by lithium hydroxide which proceeded readily at ambient conditions in very good yields. The incorporation of G-POSS into the network was clearly determined by transmission electron microscopy, FTIR, and 1H-NMR spectroscopy techniques performed with a model study using 1-butane thiol and G-POSS molecules. The homogeneous distribution of G-POSS up to 5 wt% in the hybrid network was apparently confirmed by morphological investigations. By increasing G-POSS content higher than 5 wt%, the heterogeneous dispersion of G-POSS was determined from the tensile strength measurements. The significant decrease in tensile strength was possible due to the agglomeration of G-POSS. On the other hand, thermal properties of hybrid networks were compared together by thermogravimetric analyses, where all samples exhibited one-step degradation in the range of 220–500 °C. The thermal decomposition of hybrid network led to complete degradation of the organic part and favored the formation of stable carbonaceous and inorganic residues as char. Thus, the char yields of hybrid networks were increased to 6.2, 7.8, 10.1, 12.7, and 15.1% by G-POSS loadings from 0 to 15 wt%. This improvement was also a proof of the incorporation of G-POSS into the hybrid networks that resulted in high heat-resistant POSS-based hybrid networks compared to a sample without G-POSS. 相似文献
26.
A GIS-Based Optimization Framework for Competitive Multi-Facility Location-Routing Problem 总被引:1,自引:1,他引:0
In a dynamic market setting, firms need to quickly respond to shifting demographics and economic conditions. In this paper,
we investigate the problem of determining the optimum set of locations for a firm, which operates a chain of facilities under
competition. We consider the objective of maximizing profit, defined as gross profit margin minus logistics costs. We propose
a location-routing model where revenue is realized according to probabilistic patronization of customers and routing costs
are incurred due to vehicles serving the open facilities from a central depot. We propose a hybrid heuristic optimization
methodology for solving this model. The optimal locations are searched for by a Genetic Algorithm while an integrated Tabu
Search algorithm is employed for solving the underlying vehicle routing problem. The solution approach is tested on a real
dataset of a supermarket chain. The results show that the location decisions made by the proposed methodology lead to increased
market share and profit margin, while keeping logistics costs virtually unchanged. Finally, we present a GIS-based framework
that can be used to store, analyze and visualize all data as well as model solutions in geographic format. 相似文献
27.
Tuncay Saydam 《Journal of Network and Systems Management》1997,5(3):233-255
A multimedia service architecture is constructedby using a generic component model. In order to derivespecific components, a generic service agent and genericservice component architectures are developed. Using generic agent and the service components,a TINA-C conformant object-oriented hierarchical genericservice component is developed and presented. As anexample, a multimedia QoS service and management architecture is presented. 相似文献
28.
Energy is one of the indispensable factors regarding the assurance of social prosperity and economic development of a country. The developing countries struggle to obtain energy sources reliable in the long term to complete their economic development, and the developed countries struggle to get them to keep their present prosperity levels. Coal seems to continue its indispensable position among the other energy sources for many years because of its production in more than 50 countries, the least effect it has from the price fluctuation and its usage lifespan of more than 200 years. The countries that are aware of it have investments in mining fields in the countries rich in coal reserves, and they continue investing considerable amount of money. 相似文献
29.
Comprising 65–70% of the world's oil reserves, the Gulf States (Saudi Arabia, Iran, Iraq, Kuwait, UAE and Qatar) are key countries for the solutions to the energy supply matters of the world. Free flow of oil to the world markets from Gulf region is an indispensable part of the major security issues. The Middle East has had mainly security related problems such as Arab–Israeli wars and conflicts, Arab–Iranian war and conflicts, Arab–Arab war and conflicts, US–Gulf wars and conflicts and more recently radicalism and terrorist attacks. Energy supply security requires the enhancement of the peace and cooperation between countries instead of competition. Preventive policy approaches are more suitable to address energy supply matters. Preventive strategy might be possible with the active participation of NATO within the “out of area” type operations to the Middle East and quite possibly indirectly to the Asia-Pacific regions. Religious and ethnic radicalism and terrorist attacks has also direct effects over oil supply security matters. 相似文献
30.
FA Atik GJ Lopes Filho Mde M Linhares J Seda Neto NS Mansur 《Canadian Metallurgical Quarterly》1998,116(4):1781-1783
The authors report a case of a 25 year old Brazilian man with a history of crampy abdominal pain in the left iliac fossa for 2 weeks, abdominal distention, mucous diarrhea and anorexia. The patient presented signs of hemodynamic instability and a hard mass palpated in the left iliac fossa presented peritoneal irritation. At laparotomy, fecal peritonitis and a punched-out perforation of the midsigmoid colon were found. A left hemicolectomy was performed with terminal colostomy. Specimen examination revealed a thickened rectosigmoid wall, narrow lumen and multiple mucosal polyps. Microscopically, chronic granulomatous colitis with Schistosoma mansoni eggs confirmed the etiology. To the authors' knowledge, this is the first case of obstruction complicated with perforation due to mansoni schistosomiasis reported in the literature. 相似文献