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排序方式: 共有1371条查询结果,搜索用时 16 毫秒
41.
Moon-Sung Cho Ki-Seob Sim Ho Chun Suk Seok-Kyu Chang 《Nuclear Engineering and Design》2000,200(3):407-419
A static analysis, finite-element (FE) model was developed to simulate out-reactor fuel–string strength tests with use of the well-known, structural analysis computer code ABAQUS. The FE model takes into account the deflection of fuel elements, and stress and displacement in endplates subjected to hydraulic drag loads. It was adapted to the strength tests performed for CANFLEX 43-element bundles and the existing 37-element bundles. The FE model was found to be in good agreement with experiment results. With use of the FE model, the static behavior of the fuel bundle string, such as load transfer between ring elements, endplate rib effects, hydraulic drag load incurring plastic deformation in fuel string and hydraulic flow rate effects were investigated. 相似文献
42.
Small package delivery companies offer services where packages are guaranteed to be delivered within a given time-frame. With variability in travel time, the configuration on the hub-and-spoke delivery network is vital in ensuring a high probability of meeting the service-level guarantee. We present the stochastic p-hub center problem with chance constraints, which we use to model the service-level guarantees. We discuss analytical results, propose solution heuristics, and present the results from computational experiments. 相似文献
43.
The application of object oriented concepts (OO) to the requirements phase of information systems (IS) and software development
has been adopted by many proponents of IS and software development methodologies. Although many claims have been made about
the effectiveness of OO techniques for improving requirements analysis, very few experimental studies have been done to substantiate
these claims. This paper addresses this gap in the literature by conducting an experimental study that attempts to validate
the effectiveness of object-oriented analysis (OOA) by comparing it to structured analysis (SA) for producing requirements.
We argue that the quality of the requirements specification can be measured and that measurement can be used to compare the
effectiveness of OOA and SA. We present an overview of the basic models and principles associated with OOA and SA, a discussion
of quality in requirements definition, and a detailed discussion of the research methodology used. A review of relevant research
is also presented and directions for further research are suggested. Our findings suggest that the OOA methodology does not
necessarily produce better requirements statements. 相似文献
44.
Hydrogen‐Bonding‐Driven Enantioselective Resolution against the Kazlauskas Rule To Afford γ‐Amino Alcohols by Candida rugosa Lipase 下载免费PDF全文
Bora Min Jeemin Park Yong‐Kyun Sim Dr. Suhyun Jung Seong‐Ho Kim Dr. Jae Kwang Song Dr. Bum Tae Kim Prof. Sang Youn Park Prof. Jaesook Yun Prof. Seongsoon Park Dr. Hyuk Lee 《Chembiochem : a European journal of chemical biology》2015,16(1):77-82
Most lipases resolve secondary alcohols in accordance with the “Kazlauskas rule” to give the R enantiomers. In a similar manner to other lipases, Candida rugosa lipase (CRL) exhibits R enantioselectivity towards heptan‐2‐ol, although the enantiomeric ratio (E) is low (E=1.6). However, unexpected enantioselectivity (i.e., S enantioselectivity, E=58) of CRL towards 4‐(tert‐butoxycarbonylamino)butan‐2‐ol, which has a similar chain length to heptan‐2‐ol, has been observed. To develop a deeper understanding of the molecular basis for this unusual enantioselectivity, we have conducted a series of molecular modeling and substrate engineering experiments. The results of these computational and experimental analyses indicated that a hydrogen bond between the Ser450 residue and the nitrogen atom of the carbamate group is critical to stabilize the transition state of the S enantiomer. 相似文献
45.
46.
Filiberto González Garcia Maria Elena Leyva Marcia Gomes Oliveira Alvaro Antonio Alencar De Queiroz Alexandre Zirpoli Simões 《应用聚合物科学杂志》2010,117(4):2213-2219
The mechanical and adhesive properties of epoxy formulations based on diglycidyl ether of bisphenol A cured with various aliphatic amines were evaluated in the glass state. Impact and uniaxial compression tests were used to determine the impact energy, elastic modulus and yield stress, respectively. The adhesion tests were carried out in steel–steel joints using single‐lap shear, T‐peel, and impact adhesive joints geometry. The better mechanical and adhesive behavior of the networks is obtained when exists high flexibility of chain between crosslink and/or high elastic modulus. The 1‐(2‐aminoethyl)piperazine epoxy network presents the best adhesive properties, high flexibility, and the largest impact energy. However, it possesses low elastic modulus and yield stress. Also, exhibits increases in peel strength and impact energy while reductions in lap shear strength. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 相似文献
47.
A.Z. Simões C.R. Foschini F. Moura J.A. Varela E. Longo 《Ceramics International》2012,38(5):3841-3849
Bi0.85La0.15FeO3 (BLFO015) thin films were deposited by the polymeric precursor solution on La0.5Sr0.5CoO3 substrates. For comparison, the films were also deposited on Pt bottom electrode. X-ray diffraction data confirmed the substitutions of La into the Bi site with the elimination of all secondary phases under a substitution ratio x = 15% at a temperature of 500 °C for 2 h. A substantial increase in the remnant polarization (Pr) with La0.5Sr0.5CoO3 bottom electrode (Pr ≈ 34 μC/cm2) after a drive voltage of 9 V was observed when compared with the same film deposited on Pt substrate. The leakage current behavior at room temperature decreased from 10?8 (Pt) to 10?10 A/cm2 on (La0.5Sr0.5CoO3) electrode under a voltage of 5 V. The fatigue resistance of the Au/BLFO015/LSCO/Pt/TiO2/SiO2/Si (1 0 0) capacitors with a thickness of 280 nm exhibited no degradation after 1 × 108 switching cycles at a frequency of 1 MHz. 相似文献
48.
Chern-Horng Sim Ekambaram Rajmadhan Surendra Ranganath 《Machine Vision and Applications》2012,23(2):243-253
We propose a scheme to detect individuals in any image frame of a video sequence showing densely crowded scenes against cluttered
backgrounds. The method uses only spatial information, and in an initial pass through the image a trained Viola–Jones-type
local detector is used to locate individuals in the densely crowded scene. This yields a large number of false alarms. Hence,
in a second step, we seek to reduce the false alarms, and propose two methods for this. In the first, color information from
the initially detected windows is passed to a classifier to reduce the false alarms. This classifier consists of a cascade
of boosted classifiers with Haar-like features as input and is trained with color information from local windows. In the second
method, a weak perspective model of an uncalibrated camera is used to further reduce the false alarm rate while maintaining
the detection rate. This is based on the size and locations of the detections in the image frame, without the use of any 3D
world information. Results are presented in the form of receiver operating characteristic curves. For instance, at a 79.0%
detection accuracy, the false alarm rate is 20.3%. 相似文献
49.
Hoi Sim Wong Tat-Jun Chin Jin Yu David Suter 《Computer Vision and Image Understanding》2013,117(12):1755-1769
In many robust model fitting methods, obtaining promising hypotheses is critical to the fitting process. However the sampling process unavoidably generates many irrelevant hypotheses, which can be an obstacle for accurate model fitting. In particular, the mode seeking based fitting methods are very sensitive to the proportion of good/bad hypotheses for fitting multi-structure data. To improve hypothesis generation for the mode seeking based fitting methods, we propose a novel sample-and-filter strategy to (1) identify and filter out bad hypotheses on-the-fly, and (2) use the remaining good hypotheses to guide the sampling to further expand the set of good hypotheses. The outcome is a small set of hypotheses with a high concentration of good hypotheses. Compared to other sampling methods, our method yields a significantly large proportion of good hypotheses, which greatly improves the accuracy of the mode seeking-based fitting methods. 相似文献
50.
Ana Dolores Santiago de Freitas Everardo Valadares Sá Barretto de Sampaio Bárbara Laine Ribeiro da Silva Jarcilene Silva de Almeida Cortez R?mulo Sim?es Cezar Menezes 《Nutrient Cycling in Agroecosystems》2012,94(2-3):181-192
Although biological nitrogen fixation (BNF) is considered the main input of N in mature and regenerating native tropical vegetation, it has seldom been quantified. Biomass and N accumulation and fixation were determined for spontaneously occurring herbaceous species in caatinga areas in four regeneration stages (2, 17, 39 and >50?years after abandonment from agricultural use). BNF was estimated using the 15N natural-abundance method. The 2-year regeneration area had the highest total herb (6,355?kg?ha?1) and legume (262?kg?ha?1) biomass production, N stocks (82?kg?ha?1) and fixed N (5.0?kg?ha?1). N2-fixing legumes (nine species in the sampled area) contributed over 97?% of legume biomass in all areas. Macroptilium gracile added the largest amount of N (3.9?kg?ha?1 in the 2-year regeneration area) because of its large biomass production (205?kg?ha?1), although it was not the species with the highest proportion of fixed N (76?%). All of the N2-fixing species obtained large proportions of their N from symbiosis, most of them more than 50?%.However, the amounts of fixed N per unit area were relatively low (0.22?C5.00?kg?ha?1) because the biomass of N2-fixing species was always less than 5?% of the total herb biomass. 相似文献