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排序方式: 共有640条查询结果,搜索用时 15 毫秒
51.
Pascale Nouchi Bruno Dany Jean -Florent Campion Louis -Anne de Montmorillon Pierre Sillard Alain Bertaina 《电信纪事》2003,58(11-12):1586-1602
Optical fiber has evolved from a not-so-transparent glass tube to an extraordinarily efficient transmission medium. It is now acknowledged as a central element of modern telecommunication being part of the whole optimization process to further improve transmission system performance and cost. In this paper, we briefly introduce transmission system optimization problematics as well as key fiber characteristics. We then review the elements of fiber design for optimized optical communication networks, including metropolitan, long and ultra-long haul applications and show how fibers have evolved over the last ten years to keep pace with more and more demanding requirement of transmission system. 相似文献
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53.
Considerable improvement in the processing techniques of superconductors is necessary to control the reactivity of cuprates towards potential substrate materials. In this study, the reactivity of YBa2Cu2Ox, melt with nickel was assessed. YBa2Cu3Ox was partly melted in nickel at 1080°C under argon. Crystallized compounds indicated that a significant reduction of cuprates occurred due to a low oxygen potential which changes the formal copper valency (Cu2+→Cu+). A substantial nickel contamination of the melt by the attack of the nickel took place with the formation of a nickel oxide skeleton which was selectively infiltrated by a Ba-Cu-O rich liquid. Such a selective mass transport produced a significant chemical demixing and an important modification in the stoichoimetry of the melt. This preferential mass transport, fractional crystallization as well as nickel contamination caused the formation of phases which resulted from an extensive evolution of the compositional path as well as the formation of Ni-doped cuprates. 相似文献
54.
Fortin Claudette; Bédard Marie-Claude; Champagne Julie 《Canadian Metallurgical Quarterly》2005,31(2):276
Duration and location of breaks in time interval production were manipulated in various conditions of stimulus presentation (Experiments 1-4). Produced intervals shortened and then stabilized as break duration lengthened, suggesting that participants used the break as a preparatory period to restart timing as quickly as possible at the end of the break. This interpretation was supported in Experiment 5, in which similar results were obtained with a reaction time response executed at the end of the break. In all experiments, produced intervals lengthened as the break occurred later during the interval. The authors conclude that varying break location and duration reveal, respectively, the influence of attentional time-sharing before the interruption and of preparatory processes taking place during the break. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
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Martin Me Court Eric Imbert Pascale Vincensini-fort Jérôme Mars Hervé Ribot Dominique Persegol Thierry Jacquemin Josette Toussan-berger Denis Trystram José Camargo da Costa Mahmoud Helal Atman Guerchaoui Noureddine Mhaya Ignacio Jesus Ania de Briseno Chien Nguyen Duc Laurent Chety 《电信纪事》1989,44(3-4):194-197
57.
Mikal Ziane Ph.D. Mohamed Zaït Ph.D. student Projet Rodin Pascale Borla-Salamet Ph.D. 《The VLDB Journal The International Journal on Very Large Data Bases》1993,2(3):277-301
In this article, we describe our approach to the compile-time optimization and parallelization of queries for execution in DBS3 or EDS. DBS3 is a shared-memory parallel database system, while the EDS system has a distributed-memory architecture. Because DBS3 implements a parallel dataflow execution model, this approach applies to both architectures. Using randomized search strategies enables the exploration of a search space large enough to include zigzag trees, which are intermediate between left-deep and right-deep trees. Zigzag trees are shown to provide better response time than right-deep trees in case of limited memory. Performance measurements obtained using the DBS3 prototype show the advantages of zigzag trees under various conditions. 相似文献
58.
Freret Thomas; Chazalviel Laurent; Roussel Simon; Bernaudin Myriam; Schumann-Bard Pascale; Boulouard Michel 《Canadian Metallurgical Quarterly》2006,120(6):1285
The assessment of both histological and functional long-term outcomes after cerebral ischemia is increasingly recommended for preclinical studies. Whereas correlations between behavioral impairments and primary ischemic lesion are documented, little is known about their relationships with remote nonischemic regions that undergo secondary degeneration, such as the thalamus. Anesthetized rats were subjected to mild (30 min) or severe (60 min) occlusion of the middle cerebral artery. Two months after ischemia, sensorimotor behavior was assessed according to the neurological score, limb-placing, adhesive-removal, and staircase tests; the final histological lesion was measured after this assessment. Cortical damage was correlated to all transient and long-lasting sensorimotor deficits, whereas striatal lesion was more consistently reflected by the forelimb-placing reflexes and adhesive-removal motor deficits. By contrast, the thalamic atrophy was not correlated to early neurological impairment, but rather to the late sensory deficit at the adhesive-removal test and to the skilled forepaw reaching alteration at the staircase test. This suggests that thalamus contributes, albeit moderately, to the ischemia-induced long-lasting sensorimotor deficits, some of which represent relevant targets for therapeutic interventions. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
59.
Technical-term translation represents one of the most difficult tasks for human translators since (1) most translators are not familiar with terms and domain-specific terminology and (2) such terms are not adequately covered by printed dictionaries. This paper describes an algorithm for translating technical words and terms from noisy parallel corpora across language groups. Given any word which is part of a technical term in the source language, the algorithm produces a ranked candidate match for it in the target language. Potential translations for the term are compiled from the matched words and are also ranked. We show how this ranked list helps translators in technical-term translation. Most algorithms for lexical and term translation focus on Indo-European language pairs, and most use a sentence-aligned clean parallel corpus without insertion, deletion or OCR noise. Our algorithm is language- and character-set-independent, and is robust to noise in the corpus. We show how our algorithm requires minimum preprocessing and is able to obtain technical-word translations without sentence-boundary identification or sentence alignment, from the English–Japanese awk manual corpus with noise arising from text insertions or deletions and on the English–Chinese HKUST bilingual corpus. We obtain a precision of 55.35% from the awk corpus for word translation including rare words, counting only the best candidate and direct translations. Translation precision of the best-candidate translation is 89.93% from the HKUST corpus. Potential term translations produced by the program help bilingual speakers to get a 47% improvement in translating technical terms. 相似文献
60.
Many river rehabilitation projects to enhance the aquatic habitat focus on the creation of pool and riffle habitat by the implementation of flow deflectors, with various degrees of successes and failures. A more comprehensive understanding of the complex three‐dimensional flow dynamics that induces scour around instream structures is required for a more effective design. The objective of this study is to examine the three‐dimensional mean and turbulent flow characteristics around paired flow deflectors for various types of deflector design in a laboratory flume. Three deflector angles (45°, 90° and 135°) and two deflector heights (with flow under and over the deflector height) were tested over a smooth (plexiglas) bed and a sand bed. Three‐dimensional velocity measurements were taken with an acoustic Doppler velocimeter at several planform positions at two heights above the bed. Results show that the 90° deflectors create the most important disturbance in the mean flow field, in turbulence intensity and bed shear stress. There is, however, a marked difference in the spatial distribution of the mean and turbulent parameters over a mobile bed and over a smooth, fixed bed. This stresses the importance of understanding the feedback between bed topography and flow dynamics and limits the applicability of conclusions drawn from plane bed experiments to natural rivers. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献