混凝土构件检测样本容量的确定方法

混凝土构件检测时,一般采用百分比抽样的方式.以回弹法中对混凝土强度进行检测时采用百分比抽样的抽样方式为例,从绝对误差限和相对误差限的角度分析了不同构件总量均采用此方法抽取样本的不合理性,并提出在不同混凝土强度等级、不同构件总数的情况下,通过控制一定的误差限来确定样本数量的方法.通过理论和实例分析,提出在抽样过程中,采用分层抽样技术对检测构件进行合理分层,降低总体方差,可减少样本数量.这种方法也适用于其它检测问题的样本容量的确定.     

Interval estimation of mean response time for a G/M/1 queueing system: empirical Laplace function approach

Mean response time is an important performance measure for a queueing system. In this paper, we propose a consistent and asymptotically normal (CAN) estimator of the mean response time for a G/M/1 queueing system, which is based on the fixed point of empirical Laplace function. The confidence interval for the mean response time can be constructed by applying the proposed CAN estimator and its estimated variance. And we carried out a simulation study to perform the accuracy of the constructed confidence interval by calculating the coverage percentage and the relative average length of confidence interval. Detailed discussions of all simulation results for three various models of G/M/1‐type system are presented and some valuable conclusions are provided. Copyright © 2006 John Wiley & Sons, Ltd.     

关于二元混合物体系的偏摩尔吉布斯自由能的表达式

利用Gibbs-Duhem方程证明了偏摩尔自由能的一个计算公式.     

Stopping rules,permutation invariance and sufficiency principle

In the context of sequential (point as well as interval) estimation, a general formulation of permutation-invariant stopping rules is considered. These stopping rules lead to savings in the ASN at the cost of some elevation of the associated risk—a phenomenon which may be attributed to the violation of the sufficiency principle. For the (point and interval) sequential estimation of the mean of a normal distribution, it is shown that such permutation-invariant stopping rules may lead to a substantial saving in the ASN with only a small increase in the associated risk.Work partially supported by (i) Office of Naval Research, Contract Number N00014-85-K-0548, and (ii) Office of Naval Research, Contract Number N00014-83-K-0387.     

The distribution and the exact percentage points for Wilks'L mvc criterion

Summary Wilks'L _mvc is the likelihood ratio criterion for testing the hypothesis that the mean values are equal, the variances are equal and the covariances are equal, in ap-variate normal population. In this article the exact null distribution as well as the exact percentage points are given for the first time. The distribution is obtained for the most general cases and the inverse tables, namely, the values ofu for given values ofF(u) are computed for the values ofF(u)=0.01, 0.02, 0.05 and for the various values ofn andp whereF(u) is the exact distribution function of the test statistic,n=N−1 andN is the sample size. The exact tables are given forp=2, 3, 4, 5, 6, 7, 8, 9.     

The distribution of the sphericity test criterion

The exact distribution of Mauchly's sphericity test criterion W = |S|/[trS/p]^p, when S is the sum of product matrix from a sample of size N taken from a p-variate normal population, is obtained using contour integration and methods similar to those of Nair and Box. Tables of percentage points for p = 4(1)10, α = 0.01 and 0.05, and various values of N (including small) are given and comparisons made with approximate percentage points using methods of Box, Mauchly, Tukey and Wilks, and Davis.     

稳幅范围,稳幅精度与De—Qing电路的设计

De—Qing电路的设计历来都是从它的稳定工作的必要条件出发,求得网络元件参数。本文从理论分析证明De-Qing工作有一限制的范围,这一范围既决定于所选元件参数,更大程度上取决于设计者所期望的稳幅精度。     

Percentage Points of the Largest Among Student's T Random Variable

Let us consider k( 2) independent random variables U₁, . . . ,U_k where U_i is distributed as the Student's t random variable with a degree of freedom m_i, i=1, . . . ,k. Here, m₁, . . . ,m_k are arbitrary positive integers. We denote m=(m₁, . . . ,m_k) and U_k:k=max {U₁, . . . ,U_k}, the largest Student's t random variable. Having fixed 0< <1, let a a(k,) and h_m h_m (k,) be two positive numbers for which we can claim that (i) ^k(a)–^k(–a)=1–, and (ii) P{–h_m U_k:k h_m}=1–. Then, we proceed to derive a Cornish–Fisher expansion (Theorem 3.1) of the percentage point h_m. This expansion involves a as well as expressions such as _i=1 ^k m_i ^–1, _i=1 ^km_i ^–2, and _i=1 ^k m_i ^–3. The corresponding approximation of h_m is shown to be remarkably accurate even when k or m₁, . . . ,m_k are not very large.     

再燃煤粉的NO还原特性研究

实验研究了原煤、煤焦以及煤在不同气氛下受热得到的气体产物对NO的还原特性。结果表明，原煤的NO还原能力不仅与其挥发分含量有关，还与煤中的矿物质有关；制焦气氛中的O2能改变煤焦对NO的还原能力，其改变与煤种有关。高挥发分煤所释放的挥发性产物对NO的还原率也高， 但Tongchuan(TC)煤除外。TC煤的挥发分含量不高，但由TC煤得到的挥发物对NO的还原率与高挥发分的Sanxie(SX)和Shenmu(SM)煤释放的挥发物相当。煤在N2环境下所释放的气体产物对NO的还原能力比CO2气氛下释放的气体产物对NO的还原能力强，但TC煤除外。同样，制气气氛中的氧对燃煤挥发物的NO还原能力的影响也很大，这种影响与煤种有关。     

Metal arene complexation of polybenzyl: Preparation and methylation

Polybenzyl has been complexed with the chromium tricarbonyl moiety by thermal treatment with chromium hexacarbonyl. The aryl rings of the product were complexed with the chromium tricarbonyl moiety to the extent of 41–63%. Assessment of the degree of complexation was satisfactorily carried out by elemental chromium analysis or by ¹³C-NMR methods which agreed within 5%. GPC was less satisfactory. TGA analysis of the complexed polymers suggested the possibility of cross-linking on thermal treatment. The benzylic groups of the polymer complex were methylated with base and methyl iodide in up to 88% of the complexed arene activated methylene groups. © 1992 John Wiley & Sons, Inc.