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101.
基于遗传算法的分布式异构数据库的查询优化 总被引:2,自引:1,他引:2
对于分布武异构数据库,查询优化问题是其核心问题。本文用基于位、值结构树型编码的遗传算法对分布武异构数据库进行查询优化,取得了很好的效果。 相似文献
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104.
Fatigue of bituminous mixtures 总被引:1,自引:0,他引:1
H. Di Benedetto C. de La Roche H. Baaj A. Pronk R. Lundström 《Materials and Structures》2004,37(3):202-216
This paper presents an interlaboratory test campaign organized by the RILEM 182-PEB Technical Committee. In the campaign,
11 different test methods, comprising uniaxial tension/compression, 2-, 3- and 4-point bending and indirecttension tests,
were utilized in order to investigate fatigue characteristics of a dense graded asphalt concrete mixture. The testing conditions
specified were sinusoidal excitation at 10Hz and 10°C using controlled strain and stress modes. In total, more than 150 fatigue
tests were carried out during the investigation. The fatigue test results were analyzed using both classical as well as continuum
damage mechanics approaches. The fatigue test results obtained using the classical fatigue approach are considerably influenced
by test type and mode of loading (controlled stress or strain) used. Consequently, this approach has limited use in realistic
fatigue characterization of bituminous materials and pavement structures. In contrast to the classical approach, models founded
on continuum damage theory may serve to isolate intrinsic fatigue characteristics from the influence of so-called biased effects,
which are largely caused by the accelerated laboratory testing. The continuum damage models investigated may constitute steps,
towards a rational mechanistic fatigue characterization model, which are important for effective future pavement design. 相似文献
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106.
This 6-year longitudinal study examined girls' peer-nominated social preference and aggression in childhood as predictors of self- and parent-reported externalizing symptoms, substance use (i.e.. cigarette, alcohol, and marijuana use), and sexual risk behavior in adolescence. Participants were 148 girls from diverse ethnic backgrounds, who were initially assessed in Grades 4-6 and again in Grades 10-12. Results supported a moderator model, indicating that social preference changed the nature of the association between childhood aggression and adolescent outcomes. When accompanied by peer rejection, aggressive behavior was moderately stable over time and significantly associated with adolescent girls' substance use and sexual risk behavior. However, under conditions of peer acceptance, no significant association between childhood aggression and adolescent outcomes emerged. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
107.
Accounting for light that is diffusely scattered from a surface is one of the practical challenges in reflectance measurement. Integrating spheres are commonly used for this purpose in point measurements of reflectance and transmittance. This solution is not directly applicable to a spectral imaging application for which diffuse reflectance measurements are desired. In this paper, an imaging spectrophotometer design is presented that employs a uniform light source to provide diffuse illumination. This creates the inverse measurement geometry to the directional illumination/diffuse reflectance mode typically used for point measurements. The final system had a spectral range between 400 and 1000 nm with a 5.2 nm resolution, a field of view of approximately 0.5 m by 0.5 m, and millimeter spatial resolution. Testing results indicate illumination uniformity typically exceeding 95% and reflectance precision better than 1.7%. 相似文献
108.
We analyze the behavior of a dense granular aggregate made by identical, elastic spheres, uni-axially compressed at constant pressure. Our goal is to predict the evolution of the effective moduli along the loading path when small perturbations are applied to stressed states. The analytical model is based upon the average strain theory. We show that the moduli in the anisotropic state normalized with the corresponding initial isotropic value, are captured by a so crude model. Numerical simulations support this result. 相似文献
109.
The purpose of this study was to develop regression equations to predict manual arm strength for a wide variety of hand locations within the reach envelope. Maximum voluntary manual arm strength was determined from 71 female participants in six exertion directions (superior, inferior, anterior, posterior, medial and lateral), in a total of 28 hand locations. Forces ranged from 51.3 to 164.4 N, and had a pooled coefficient of variation of 29.9%. Across all 168 combinations of hand locations and exertion directions, the multivariate regression equations explained 92.5% of the variance and had a root mean square error (RMSE) of only 6.4 N, using only the anterior, lateral and vertical location of the hand relative to the active shoulder joint as inputs. These equations provide a proof-of-principle for our novel regression approach, and represent a first step towards a more comprehensive equation to estimate maximum acceptable forces for occupational tasks. 相似文献
110.
In this work the effect of spent diatomaceous earth (SDE), as pore forming or silica carrier, on the properties of clay ceramic bricks was investigated. Mixtures of clay and SDE waste were, compacted, dried and fired at 950°C during 6?h. The technological properties of waste-clay bricks were analysed to evaluate the influence of the waste incorporation. The SDE (1–5?wt-%) addition in the clay matrix causes a reduction between 6 and 12% of the bulk density compared with the control samples (only clay) which implies good insulating characteristics. In addition, the waste incorporation increases the water absorption within the range 4–31% and decreases the compressive strength between 12 and 26%. However, the incorporation of the waste is beneficial as no remarkable changes in the technological properties are observed. These results indicate that the waste has a predominant pore forming effect over a pore filling effect. 相似文献