FAAS法测定硫酸中的铁和锌

本文建立了火焰原子吸收光谱法测定硫酸中铁和锌的方法。确定了最佳仪器工作条件和样品处理方法。在选择好的实验条件下,测定铁的特征浓度为0.014μg/mL/1％吸收;测定锌的特征浓度为0.002μg/mL/1％吸收。回收率分别为铁98.8％—103.4％,锌92.5％—98.6％。     

Quantitative convergence assessment for Markov chain Monte Carlo via cusums

Yu (1995) provides a novel convergence diagnostic for Markov chain Monte Carlo (MCMC) which provides a qualitative measure of mixing for Markov chains via a cusum path plot for univariate parameters of interest. The method is based upon the output of a single replication of an MCMC sampler and is therefore widely applicable and simple to use. One criticism of the method is that it is subjective in its interpretation, since it is based upon a graphical comparison of two cusum path plots. In this paper, we develop a quantitative measure of smoothness which we can associate with any given cusum path, and show how we can use this measure to obtain a quantitative measure of mixing. In particular, we derive the large sample distribution of this smoothness measure, so that objective inference is possible. In addition, we show how this quantitative measure may also be used to provide an estimate of the burn-in length for any given sampler. We discuss the utility of this quantitative approach, and highlight a problem which may occur if the chain is able to remain in any one state for some period of time. We provide a more general implementation of the method to overcome the problem in such cases.     

The problem of multiple causation in population analysis, with particular reference to the poplygamy-fertility hypothesis

The hypothesis that polygyny is associated with higher fertility than monogamy was evaluated. An assessment of previous studies and of the results of a 1966-1967 study comparing the fertility levels of polygynously and monogamously married women in a rural and an urban population in Nigeria lead to the conclusion that the hypothesis was useless. The hypothesis was judged to be useless because 1) fertility rates are the product of multiple influences; 2) it is too difficult to separate out these multiple influences, given the variability involved in polygynous practices and the inadequates of the data; and 3) the influence of polygyny on fertility is too slight to take into account. In the Nigerian study, the fertility of 2742 monogamously married women was compared with the fertility of 1261 polygynously married women. Preliminary analysis revealed that the fertility rate was higher for polygynously married women; however, when marriage duration was controlled, there was no significant differences between the fertility rates observed for the polygynously and monogamously married women living in rural areas nor those living in urban area.     

The quincunx: history and mathematics

Received: December 30, 1999; revised version: July 19, 2000     

Maximum entropy sampling and optimal Bayesian experimental design

When Shannon entropy is used as a criterion in the optimal design of experiments, advantage can be taken of the classical identity representing the joint entropy of parameters and observations as the sum of the marginal entropy of the observations and the preposterior conditional entropy of the parameters. Following previous work in which this idea was used in spatial sampling, the method is applied to standard parameterized Bayesian optimal experimental design. Under suitable conditions, which include non-linear as well as linear regression models, it is shown in a few steps that maximizing the marginal entropy of the sample is equivalent to minimizing the preposterior entropy, the usual Bayesian criterion, thus avoiding the use of conditional distributions. It is shown using this marginal formulation that under normality assumptions every standard model which has a two-point prior distribution on the parameters gives an optimal design supported on a single point. Other results include a new asymptotic formula which applies as the error variance is large and bounds on support size.     

On some probability distributions associated with random walks

The probability distribution of the total number of games to ruin in a gambler's ruin random walk with initial position n, the probability distribution of the total size of an epidemic starting with n cases and the probability distribution of the number of customers served during a busy period M/M/1 when the service starts with n waiting customers are identical. All these can be easily obtained by using Lagrangian expansions instead of long combinatorial methods. The binomial, trinomial, quadrinomial and polynomial random walks of a particle have been considered with an absorbing barrier at 0 when the particle starts its walks from a point n, and the pgfs. and the probability distributions of the total number of jumps (trials) before absorption at 0 have been obtained. The values for the mean and variance of such walks have also been given.     

Facilitating the Transition from Student to Social Worker: Challenges of the Younger Student

Abstract

The transition from student to social worker is a process which social work educators cannot control but can facilitate. Through classroom and field instruction faculty assumer responsibility of preparing students' professional knowledge, skills, and values; however, our responsibilities should extend beyond curriculum delivery. Drawing on Schlossberg's (1984) model of transitions, this article discusses two primary factors which affect the younger student in transition—developmental needs and the external environment—and strategies for assisting in the transition through intervention in academic advising and teaching roles.     

The behavior of estimated measures of association in small and moderate sample sizes for 2×3 tables

We consider the distributions of Goodman and Kruskal's G, Kendall's tau-b, and correlation coefficients rho and rho-s for sample sizes 10‘10’40 from 2×3 tables. The results are compared with asymptotic theory. It is found that the convergence of G to its asymptotic normal distribution is much slower than the convergence of the other measures to theirs, and that G is more likely to be significantly biased. However, the variances and biases of all four measures come close to their asymptotic values for quite moderate sample sizes.     

The pitman nearness criterion and its determination

A general method for determining Pitman Nearness is given In the case of univariate estimators. This method is then applied to some estimation problems. The concept of Pitman Nearness is also generalized to the multivariate case. The James-Stein estimators are used to illustrate the multivariate comparison.