共查询到20条相似文献,搜索用时 125 毫秒
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研究了应用于广泛温度范围内的氮化硅及二氧化锆陶瓷的机械性状。着重探索了在周围介质条件下的抗裂性。查明,认为采用维氏硬度试验压头压痕法对试样进行试验的结果是可信的。根据分析结果,对材料的组织断面做了研究,并参照了二氧化锆模拟材料的试验数据。 相似文献
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基于橡胶试样单轴拉伸试验得到的拉力和变形量等试验数据,利用最小二乘法拟合求得橡胶材料的Mooney-Rivlin模型及Yeoh模型常数。基于有限元方法,用得到的模型常数对试样变形量进行计算并与试验结果对比。结果表明,Mooney-Rivlin模型在小应变和中等应变时可以较好地描述材料的力学行为,Yeoh模型适合模拟大应变时材料的力学行为。利用得到的模型常数计算分析异形密封圈的静态性能,最大变形量计算值与试验值的相对误差为2.74%,表明了所选模型常数的准确性。 相似文献
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准确地标定参数是使用商用离散元软件PFC合理建模的前提和关键步骤。采用PFC3D对砂土线性模型试样共进行了80次三轴压缩试验模拟,分别改变颗粒间摩擦系数、颗粒有效模量、颗粒刚度比和试样初始孔隙率等细观参数,探究不同围压下细观参数的变化对试验结果(最大偏应力)的敏感性。结果表明,颗粒间摩擦系数对试验结果有明显影响,初始孔隙率在>0.32%时对试验结果有明显影响。 相似文献
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《Sequential Analysis》2013,32(2):239-256
Abstract In this paper we consider the problem of testing for a parameter change based on the cusum test (cf. Lee, S.; Ha, J.; Na, O.; Na, S. The cusum test for parameter change in time series models. Scand. J. Statist. 2003, 30, 651–739) utilizing the maximum likelihood estimator. The issue is handled in iid random samples, and then special attention is paid to hidden Markov models. It is shown that the limiting distribution of the cusum test statistic is the sup of a standard Brownian bridge under regularity conditions. A simulation result is provided for illustration. 相似文献
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莫来石基透气性陶瓷—金属复合材料的制备工艺 总被引:2,自引:0,他引:2
本文研究在以硅酸乙脂水解液为粘结剂情况下,莫来石和铁粉的粉浆浇注成型工艺对坯体质量及其烧结体性能的影响。结果表明,采用真空混浆、振动成型,能获得高质量的坯体;莫来石、铁粉在整个坯体中均匀分布,坯体表面及心部消除了空气中混浆产生的气孔。同时,提高了烧结体的强度,而透气系数和空气中混浆试样的几乎一致。 相似文献
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The asymptotic distribution of the residual autocovariance matrices in the class of periodic vector autoregressive time series models with structured parameterization is derived. Diagnostic checking with portmanteau test statistics represents a useful application of the result. Under the assumption that the periodic white noise process of the periodic vector autoregressive time series model is composed of independent random variables, we demonstrate that the finite sample distributions of the Hosking‐Li‐McLeod portmanteau test statistics can be approximated by those of weighted sums of independent chi‐square random variables. The quantiles of the asymptotic distribution can be computed using the Imhof algorithm or other exact methods. Thus, using the (single) chi‐square distribution for these test statistics appears inadequate in general, although it is often recommended in practice for diagnostic methods of that kind. A simulation study provides empirical evidence. 相似文献
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断裂韧性测试程序的开发 总被引:1,自引:0,他引:1
根据国家标准在MTS疲劳机上开发了断裂韧性测试的卸载柔度法试验程序 ,该程序将试验过程和数据采集、结果处理于一体 ,大大方便了试验的进行。通过试验验证满足标准要求 相似文献
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经检测 ,重组人胰岛素注射液生物学效价为 2 8.2U mg。按 0 .5、1.0和 2 .0U kg皮下注射 ,对小鼠正常血糖、葡萄糖型高血糖以及大鼠四氧嘧啶型高血糖均有明显的降低作用。重组人胰岛素对雄性小鼠LD5 0 为 2 1.6 9± 2 .46U kg,雌性为 47.5 6± 6 .10U kg。犬长期毒性试验表明 ,未出现任何毒性。 相似文献
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This paper examines the distribution of the overlapping variance ratio (OVR) statistic when the errors are distributed with thick tails as described by the family of stable Paretian distributions. The asymptotic distribution of the OVR statistic, which depends on the characteristic exponent, can be estimated using simulation. It is found that the convergence of the distribution of the OVR statistic to its asymptotic limit is extremely slow. Thus, the asymptotic results will not be able to provide any useful approximation in finite samples. To facilitate the OVR statistic as a test for the random walk hypothesis, the tail quantiles are estimated for several finite sample sizes. 相似文献
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A subset of colors often needs to be selected to represent a full set. In one such application, a multi‐band color sensor is used to measure reflective color samples, and a matrix transformation method is used to recover the reflectance spectrum of the measured sample. To achieve this, a group of training colors needs to be selected to calculate the transformation matrix. A genetic algorithm (GA) has been developed to optimize the selection of the subset of training colors, and the result is compared with those obtained using random selection or a traditional culling algorithm. In a simulation study, the GA gives better results. 相似文献