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排序方式: 共有473条查询结果,搜索用时 328 毫秒
31.
In this paper, a performance analysis of a metal hydride based hydrogen storage container with embedded cooling tubes during absorption of hydrogen is presented. A 2-D mathematical model in cylindrical coordinates is developed using the commercial software COMSOL Multiphysics 4.2. Numerical results obtained are found in good agreement with experimental data available in the literature. Different container geometries, depending upon the number and arrangement of cooling tubes inside the hydride bed, are considered to obtain an optimum geometry. For this optimum geometry, the effects of various operating parameters viz. supply pressure, cooling fluid temperature and overall heat transfer coefficient on the hydriding characteristics of MmNi4.6Al0.4 are presented. Industrial-scale hydrogen storage container with the capacity of about 150 kg of alloy mass is also modeled. In summary, this paper demonstrates the modeling and the selection of optimum geometry of a metal hydride based hydrogen storage container (MHHSC) based on minimum absorption time and easy manufacturing aspects. 相似文献
32.
Response surface methodology (RSM) based on a D-optimal design was employed to investigate the tribological characteristics of journal bearing materials such as brass, bronze, and copper lubricated by a biolubricant, chemically modified rapeseed oil (CMRO). The wear and friction performance were observed for the bearing materials tested with TiO2, WS2, and CuO nanoadditives dispersed in the CMRO. The tests were performed by selecting sliding speed and load as numerical factors and nano-based biolubricant/bearing materials as the categorical factor to evaluate the tribological characteristics such as the coefficient of friction (COF) and specific wear rate. The results showed that RSM based on a D-optimal design was instrumental in the selection of suitable journal bearing materials for a typical system, especially one lubricated by nano-based biolubricant. At a sliding speed of 2.0 m/s and load of 100 N, the bronze bearing material with CMRO containing CuO nanoparticles had the lowest COF and wear rate. In addition, scanning electron microscopy (SEM) examination of the worn bearing surfaces showed that the bronze bearing material lubricated with CMRO containing CuO nanoadditive is smoother than copper/brass bearing material. 相似文献
33.
Bernd Finkbeiner Sriram Sankaranarayanan Henny Sipma 《Electronic Notes in Theoretical Computer Science》2002,70(4)
By collecting statistics over runtime executions of a program we can answer complex queries, such as “what is the average number of packet retransmissions” in a communication protocol, or “how often does process P1 enter the critical section while process P2 waits” in a mutual exclusion algorithm. We present an extension to linear-time temporal logic that combines the temporal specification with the collection of statistical data. By translating formulas of this language to alternating automata we obtain a simple and efficient query evaluation algorithm. We illustrate our approach with examples and experimental results. 相似文献
34.
Processing, physical and thermal properties of BlackglasTM matrix composites reinforced with NextelTM fabric 总被引:5,自引:0,他引:5
Sriram Rangarajan Roland Belardinelli Pranesh B. Aswath 《Journal of Materials Science》1999,34(3):515-533
The cure and pyrolysis behavior of a BlackglasTM resin and NextelTM 440 impregnated with BlackglasTM resin were studied. Cure of the BlackglasTM resin is an exothermic process and DSC studies indicate that with an increase of catalyst content from 0.1 to 1.0%, the onset and peak temperature of cure are decreased coupled with an increase in the enthalpy of cure indicating a greater extent of cross linking. However, pyrolysis char yield of the pyrolyzate is relatively insensitive to cure conditions.Cure pressure and pyrolysis environment are variables in the processing of BlackglasTM matrix composite reinforced with NextelTM 440 Plain weave fabric. Variations in cure pressure from 30 to 80 psi had no discernible effect on the chemistry of the pryrolyzate. However, the higher cure pressure resulted in top and bottom ply damage. Pyrolysis in an Ar environment resulted in incorporationj of up to 12 wt % C of which 8 wt % as graphitic in nature in the ceramic matrix. Pyrolysis in NH3 resulted in 3.9 wt % nitrogen and 1.5 wt % carbon in the matrix, with all the nitrogen and carbon bonded to Si. The cured panels have to be pyrolyzed/densified between 6–7 times to achieve required density and porosity content. Oxidation behavior of the composites at 1000°C indicate that the argon pyrolyzed CMC's lose more weight due to decomposition of the pyrolytic carbon, whereas, NH3 pyrolyzed CMC's are stable as both the N and C are bonded to Si in the matrix. Dielectric constants K and K measured at 1 GHz in the as-processed condition are high in the argon pyrolyzed CMC, (K = 11–28) due to the presence of pyrolytic carbon. On the other hand NH3 pyrolyzed CMC exhibit low dielectric constant (K = 4). On oxidation, the dielectric constant in both the Ar and NH3 pyrolyzed panels is approximately 4.0. 相似文献
35.
Measurements of small-signal forward conductance vs temperature at a constant bias current, and the reverse conductance vs temperature at a constant bias voltage have been carried out on ion-implanted n-GaAs Schottky barrier diodes fabricated on semi-insulated substrates, for the temperature range of 97–340 K. The results obtained have been interpreted in terms of diode ideality factors and compared with those calculated using the thermionic field emission model for the forward bias case and the pure field emission model for the reverse bias case. 相似文献
36.
The minimum -small partition problem is the problem of
partitioning a given simple polygon into subpolygons, each with diameter
at most , for a given > 0.
This paper considers the version of this problem that disallows Steiner
points.
This problem is motivated by applications in mesh generation and collision detection.
The main result in the paper is a polynomial-time algorithm that
solves this problem, and either returns an optimal partition or
reports the nonexistence of such a partition.
This result contrasts with the recent NP-completeness result for the
minimum -small partition problem for polygons with
holes (C. Worman, 15th Canadian Conference on Computational Geometry, 2003).
Even though the running time of our algorithm is a polynomial in the input size,
it is prohibitive for most real applications and we seek faster algorithms
that approximate an optimal solution.
We first present a faster 2-approximation algorithm for the
problem for simple polygons and
then a near linear-time
algorithm for convex polygons that
produces, for any > 0, an (+)-small
partition with no more polygons than in an optimal
-small partition.
We also present an exact polynomial-time algorithm for the minimum
-small partition problem with the additional constraint that
each piece in the partition be convex. 相似文献
37.
Lipyeow Lim Min Wang Sriram Padmanabhan Jeffrey Scott Vitter Ramesh Agarwal 《World Wide Web》2007,10(1):37-69
Recent work on incremental crawling has enabled the indexed document collection of a search engine to be more synchronized
with the changing World Wide Web. However, this synchronized collection is not immediately searchable, because the keyword
index is rebuilt from scratch less frequently than the collection can be refreshed. An inverted index is usually used to index
documents crawled from the web. Complete index rebuild at high frequency is expensive. Previous work on incremental inverted
index updates have been restricted to adding and removing documents. Updating the inverted index for previously indexed documents
that have changed has not been addressed. In this paper, we propose an efficient method to update the inverted index for previously
indexed documents whose contents have changed. Our method uses the idea of landmarks together with the diff algorithm to significantly reduce the number of postings in the inverted index that need to be updated. Our experiments verify
that our landmark-diff method results in significant savings in the number of update operations on the inverted index. 相似文献
38.
The possible impact of technological advancement on video games' effects—particularly in the case of violent games—has often been discussed but has not been thoroughly explored by empirical research. The present investigation employed a 2 × 2 between-subjects factorial experiment to examine the interplay of technological advancement and violence by exposing participants ( N = 120) to either a newer or older version of a violent or nonviolent game and measuring these factors' effects on players' sense of presence, involvement, physiological arousal (measured by skin conductance), self-reported arousal, and affective and cognitive aggression. The results indicate that technological advancement increased participants' sense of presence, involvement, and physiological and self-reported arousal. Neither advancement nor violence had statistically significant effects on accessibility of players' aggressive thoughts, but there is some tentative evidence that violent game content increased players' state hostility. Theoretical and practical implications of findings are discussed, and recommendations are made for future research. 相似文献
39.
Nawab Ali Sriram Krishnamoorthy Mahantesh Halappanavar Jeff Daily 《International journal of parallel programming》2013,41(3):469-493
Faults are expected to play an increasingly important role in how algorithms and applications are designed to run on future extreme-scale systems. Algorithm-based fault tolerance is a promising approach that involves modifications to the algorithm to recover from faults with lower overheads than replicated storage and a significant reduction in lost work compared to checkpoint-restart techniques. Fault-tolerant linear algebra algorithms employ additional processors that store parities along the dimensions of a matrix to tolerate multiple, simultaneous faults. Existing approaches assume regular data distributions (blocked or block-cyclic) with the failures of each data block being independent. To match the characteristics of failures on parallel computers, we extend these approaches to mapping parity blocks in several important ways. First, we handle parity computation for generalized Cartesian data distributions with each processor holding arbitrary subsets of blocks in a Cartesian-distributed array. Second, techniques to handle correlated failures, i.e., multiple processors that can be expected to fail together, are presented. Third, we handle the colocation of parity blocks with the data blocks and do not require them to be on additional processors. Several alternative approaches, based on graph matching, are presented that attempt to balance the memory overhead on processors while guaranteeing the same fault tolerance properties as existing approaches that assume independent failures on regular blocked data distributions. Evaluation of these algorithms demonstrates that the additional desirable properties are provided by the proposed approach with minimal overhead. 相似文献
40.
In this two-part paper, we present a model for the solidification of semicrystalline thermoplastic polymers that links the microscopic and macroscopic length scales. The model accounts for the important physical phenomena occurring during spherulitic cyrstallization and predicts microstructural evolution. In this first part, we concentrate on the growth of individual spherulites. We present a fast and accurate model that predicts the shape of a spherulite as well as the path of its constitutive lamellae in any thermal situation. In part II of this paper we shall couple this new model for spherulite growth with a nucleation law and a macroscopic heat flow computation, thus enabling us to model realistic crystallization conditions. 相似文献