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排序方式: 共有2738条查询结果,搜索用时 15 毫秒
1.
Abstract: This paper presents an approach to the preliminary design of simple span precast pretensioned highway bridge girders using mathematical optimization methods. This type of bridge system is competitive for short and medium spans but also can accommodate long-span bridges if girder splicing and continuity are introduced. The bridge design problem is formulated as a nonlinear programming problem and is solved by the projected lagrangian algorithm. Several design objectives are investigated either separately or simultaneously with the aim of achieving cost-efficient bridge designs. The approach is used to generate a new set of five optimal girder sections and then to determine the girder spacing and span length capability of each precast girder. The five sections types (A, B, C, D, and E) proposed herein are more cost-effective than the corresponding Canadian standard sections because for similar depths they achieve greater span length and girder spacing while requiring less concrete and prestressing steel. This study also enables identification of the governing design requirements (serviceability and/or ultimate limit states active constraints) that may be adopted as optimality criteria when simplified preliminary designs of this bridge type for different design codes and girder sections are required. 相似文献
3.
Jeremy M. Rathfon Zoha M. AL‐Badri Raja Shunmugam Scott M. Berry Santosh Pabba Robert S. Keynton Robert W. Cohn Gregory N. Tew 《Advanced functional materials》2009,19(5):689-695
The chemical sensing of nerve gas agents has become an increasingly important goal due to the 1995 terrorist attack in a Tokyo subway as well as national security concerns in regard to world affairs. Chemical detection needs to be sensitive and selective while being facile, portable, and timely. In this paper, a sensing approach using a pyrene imine molecule is presented that is fluorimetric in response. The detection of a chloro‐Sarin surrogate is measured at 5 ppmv in less than 1 second and is highly selective towards halogenated organophosphates. The pyrene imine molecule is incorporated into polystyrene films as well as micrometer and sub‐micrometer fibers. Using both a direct drawing approach and electrospinning, micrometer and nanofibers can be easily manufactured. Applications for functional sensing micrometer and nanofibers are envisioned for optical devices and photonics in addition to solution and airflow sensing devices. 相似文献
4.
JS Kim I Lopez PL DiPatre F Liu A Ishiyama RW Baloh 《Canadian Metallurgical Quarterly》1999,52(1):40-44
Immunocytochemical examination for mitochondrial protein and cytochrome oxidase was performed to demonstrate oncocytes in normal adenohypophysis obtained from 28 patients of various age. A small number of solitary large epithelial cells showed intense cytoplasmic granular immunoreactivities for mitochondrial protein and cytochrome oxidase. The proportions of the cells positive for the former and the latter ranged from 0% to 5.9% (mean+/-SD; 1.5+/-1.7%) and from 0% to 4.9% (1.4+/-1.6%), respectively. These cells were either absent or extremely rare in young patients (under 10 years) but tended to increase in number with age (P < 0.0001). On the other hand, the mirror section technique showed that most of these cells were negative for adenohypophysial hormones, but a few of them were faintly positive for: alpha-subunit (8.0%), beta-subunits of follicle-stimulating hormone (4.8%), luteinizing hormone (2.5%), thyroid-stimulating hormone (1.0%), and growth hormone (0.5%), and were negative for prolactin and adrenocorticotropic hormone. We considered that these cells represent oncocytes that exist in varying numbers in normal adenohypophysis. It was suggested that oncocytes in normal adenohypophysis share various common features with tumorous oncocytes of pituitary oncocytomas. 相似文献
5.
This article reviews issues concerning the training and credentialing of vascular surgeons in the use of endovascular techniques in the peripheral vascular system. These guidelines update a prior document that was published in 1993. They have been rewritten to accommodate the rapid evolution that has occurred in the field and to provide the appropriate requirements that a vascular surgeon should fulfill to be competent in the basic skills needed to safely and effectively perform all presently accepted diagnostic and therapeutic endovascular procedures. 相似文献
6.
Matthias Delafontaine Anthony G. Cohn Nico Van de Weghe 《Expert systems with applications》2011,38(5):5187-5196
Due to recent technological advances in position-aware devices, data about moving objects is becoming ubiquitous. Yet, it is a major challenge for spatial information systems to offer tools for the analysis of motion data, thereby evolving from static to dynamic frameworks. This paper aims to contribute to this area by introducing an implementation prototype for an information system based on the Qualitative Trajectory Calculus, a spatiotemporal calculus to represent and reason about moving point objects. 相似文献
7.
Gregory D. Breetzke Karina Landman Ellen G. Cohn 《Journal of Housing and the Built Environment》2014,29(1):123-139
Gated communities have long been seen as a rational response to rising crime levels, yet very little is known about the extent to which residing in a gated community actually reduces an individuals’ risk of criminal victimisation. In this study, we use location quotients to compare the extent of burglary in gated communities with burglary across the entire city of Tshwane, South Africa, as well as compare burglary in gated communities with burglary occurring within a series of buffer intervals immediately surrounding these communities. Finally, we identify what physical characteristics of gated communities differentiate between high and low burglary in these enclaves. Prior to expectations, we found that gated communities (and their immediate surrounding areas) are associated with increased levels of burglary. There are, however, a number of physical characteristics of gated communities which are associated with much lower burglary levels. The implications of our work from a crime prevention and development planning perspective are discussed. 相似文献
8.
Crystal structure of TNF-alpha mutant R31D with greater affinity for receptor R1 compared with R2 总被引:2,自引:0,他引:2
Reed C; Fu ZQ; Wu J; Xue YN; Harrison RW; Chen MJ; Weber IT 《Protein engineering, design & selection : PEDS》1997,10(10):1101-1107
Crystal structures have been determined of recombinant human tumor necrosis
factor-alpha (TNF-alpha) and its R31D mutant that preferentially binds to
TNF receptor R1 with more than seven times the relative affinity of binding
to receptor R2. Crystals of the wild-type TNF were of space group
P4(1)2(1)2 and had unit cell dimensions of a = b = 94.7 and c = 117.4 A.
Refinement of the structure gave an R-factor of 22.3% at 2.5 A resolution.
The crystals of TNF R31D mutant diffracted to 2.3 A resolution, and were of
identical space group to the wild type with unit cell dimensions of a = b =
95.4 and c = 116.2 A, and the structure was refined to an R-factor of
21.8%. The trimer structures of the wild-type and mutant TNF were similar
with a root mean square (r.m.s.) deviation of 0.56 A for Calpha atoms;
however, the subunits within each trimer were more variable with an average
r.m.s. deviation of 1.00 A on Calpha atoms for pairwise comparison of
subunits. Model complexes of TNF with receptors R1 and R2 have been used to
predict TNF-receptor interactions. Arg31 in all three subunits of wild-type
TNF is predicted to form an ionic interaction with the equivalent glutamic
acid in both receptors R1 and R2. Asp31 of the TNF R31D mutant is predicted
to interact differently with the two receptors. The side chain of Asp31 in
two subunits of the TNF mutant is predicted to form hydrogen bond
interactions with Ser59 or Cys70 of R1, while it has no predicted
interactions with R2. The loss of three strong ionic interactions of Arg31
and the electrostatic repulsion of Asp31 with Glu in the receptors is
consistent with the reduced binding of the R31D mutant to both receptors
relative to wild-type TNF. The replacement of these ionic interactions by
two weaker hydrogen bond interactions between Asp31 of the R31D mutant and
R1, compared with no interactions with R2, is in agreement with the
observed preferential binding of the R31D mutant to R1 over R2. Analysis of
the structure and function of receptor-discriminating mutants of TNF will
help understand the biological role of TNF and facilitate its use as an
antitumor agent.
相似文献
9.
There is a vast literature on the problem of how to sequence products in a blocking flow shop so as to minimise makespan. It is often the case, however, that problem instances have multiple optima, and that within the set of optimal (or near optimal) solutions, other characteristics of importance vary substantially. Thus, the solution found by an approach that solely minimises makespan may be inferior to alternate solutions that have comparable makespan but superior value with regard to other criteria. In this paper, we demonstrate this by considering makespan and customer responsiveness, the potential that a sequence has for modification so as to incorporate customer order changes after production has begun. We consider the relationship between these two metrics and present computational results to show how different approaches to making trade-offs between them can change the solution characteristics substantially. 相似文献
10.
C Eder P Proksch V Wray K Steube G Bringmann RW van Soest Sudarsono E Ferdinandus LA Pattisina S Wiryowidagdo W Moka 《Canadian Metallurgical Quarterly》1999,62(1):184-187
Two samples of the marine sponge Stylissa carteri collected in Indonesia yielded two new bromopyrrole alkaloids: debromostevensine (1) and debromohymenin (2), as well as nine other known congeners (3-11). The structures of the new compounds were unambiguously established on the basis of their NMR and mass spectra. 相似文献