Research papers

Rapid colorimetric assay for cellular growth and survival: Application to proliferation and cytotoxicity assays

Tim R. Mosmann

Probability and Statistics With Reliability, Queuing, and Computer Science Applications.

W. A. Thompson, Kishor S. Trivedi

Probability and Statistics with Reliability, Queuing and Computer Science Applications, Second Edition, offers a comprehensive introduction to probabiliby, stochastic processes, and statistics for students of computer science, electrical and computer engineering, and applied mathematics. Its wealth of practical examples and up-to-date information makes it an excellent resource for practitioners as well.

Low-temperature physics: Knudsen effects in liquid helium

P. V. E. McClintock

Floral biology in relation to hand pollination of white yam

M. O. Akoroda

Comparison of simple potential functions for simulating liquid water

William L. Jorgensen, Jayaraman Chandrasekhar, Jeffry D. Madura, Roger Impey, Michael L. Klein

Classical Monte Carlo simulations have been carried out for liquid water in the NPT ensemble at 25 °C and 1 atm using six of the simpler intermolecular potential functions for the water dimer: Bernal–Fowler (BF), SPC, ST2, TIPS2, TIP3P, and TIP4P. Comparisons are made with experimental thermodynamic and structural data including the recent neutron diffraction results of Thiessen and Narten. The computed densities and potential energies are in reasonable accord with experiment except for the original BF model, which yields an 18% overestimate of the density and poor structural results. The TIPS2 and TIP4P potentials yield oxygen–oxygen partial structure functions in good agreement with the neutron diffraction results. The accord with the experimental OH and HH partial structure functions is poorer; however, the computed results for these functions are similar for all the potential functions. Consequently, the discrepancy may be due to the correction terms needed in processing the neutron data or to an effect uniformly neglected in the computations. Comparisons are also made for self-diffusion coefficients obtained from molecular dynamics simulations. Overall, the SPC, ST2, TIPS2, and TIP4P models give reasonable structural and thermodynamic descriptions of liquid water and they should be useful in simulations of aqueous solutions. The simplicity of the SPC, TIPS2, and TIP4P functions is also attractive from a computational standpoint.

A technique for radiolabeling DNA restriction endonuclease fragments to high specific activity

Andrew P. Feinberg, Bert Vogelstein

Some aspects of the biology of Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae), a pest of stored groundnuts in Nigeria

George N. Mbata, FABIAN N. C. OSUJI

Software engineering: A practitioner's approach

Optimization by Simulated Annealing

Scott Kirkpatrick, C. D. Gelatt, M.P. Vecchi

There is a deep and useful connection between statistical mechanics (the behavior of systems with many degrees of freedom in thermal equilibrium at a finite temperature) and multivariate or combinatorial optimization (finding the minimum of a given function depending on many parameters). A detailed analogy with annealing in solids provides a framework for optimization of the properties of very large and complex systems. This connection to statistical mechanics exposes new information and provides an unfamiliar perspective on traditional optimization problems and methods.

The Iron Cage Revisited: Institutional Isomorphism and Collective Rationality in Organizational Fields

Paul DiMaggio, Walter W. Powell

Instead of examining why organizations are dissimilar, this study explores why organizations tend to be increasingly and inevitably homogenous in their forms and practices. Organizations in a similar line of work are structured into an organizational field by powerful forces that lead them to become similar. Rather than the causes of rationalization and bureaucratization suggested by Max Weber, including competition and the need for efficiency, institutional similarity is due to the structuration of organizational fields, a process caused largely by the state and the professions, which are the great rationalizers of the late 20th century. In highly structured organizational fields, rational efforts of individuals aggregately lead to structural, cultural, and output homogeneity. Homogenization is best captured by the concept of isomorphism, the process whereby one element in a population resembles others that confront the same environmental conditions. The two types of isomorphism are competitive and institutional. Three processes lead to organizational similarity: (1) coercive isomorphism stemming from political influence and the problem of legitimacy; (2) mimetic isomorphism resulting from uniform responses to uncertainty; and (3) normative isomorphism associated with professionalism. While these isomorphic processes improve organizational transactions, they do not necessarily increase internal efficiency. Twelve hypotheses are offered for further research about which organizational fields will be most homogenous. These hypotheses relate the impact of resource centralization and dependency, goal ambiguity and technical uncertainty, and professionalism and structuration on isomorphic change. Finally, useful implications of the study for theories of organizations and social change are offered. (TNM)

Empirical exchange rate models of the seventies

Richard Meese, Kenneth Rogoff

The biology of Carangidae (Teleostei) in Natal estuaries

S. J. M. Blaber, D. P. Cyrus

The occurrence and abundance of 17 species of Carangidae in Natal estuaries are described. The following six species are of significance in the estuarine community: Caranx ignobilis, C. melampygus, C. papuensis, C. sexfasciatus, Lichia amia and Scomberoides lysan . Only juveniles and subadults utilize estuaries. The time of recruitment, growth rates and feeding biology of the six species were investigated. Among the juveniles, C. ignobilis and C. sexfasciatus are mainly piscivorous on a variety of small estuarine fishes and estuarine dependent juveniles of marine species, while C. melampygus, C. papuensis and S. lysan filter feed on mysids and juvenile penaeids. Subadults of all species are piscivorous, although C. papuensis and S. lysan retain a suitable gill raker structure for filter feeding and a proportion of their diet consists of mysids and penaeids. The salinity and turbidity preferences of each species were investigated. All are euryhaline but C. melampygus, C. papuensis and 5. lysan are only found in clear water. It is suggested that the more widespread estuarine distribution of juvenile C. sexfasciatus and C. ignobilis may be related to their turbidity tolerances. The role of carangids in Natal estuaries is discussed in relation to their ecological significance in estuaries as predators and their degree of estuarine dependence.

The central role of the propensity score in observational studies for causal effects

Paul R. Rosenbaum, Donald B. Rubin

The propensity score is the conditional probability of assignment to a particular treatment given a vector of observed covariates. Both large and small sample theory show that adjustment for the scalar propensity score is sufficient to remove bias due to all observed covariates. Applications include: (i) matched sampling on the univariate propensity score, which is a generalization of discriminant matching, (ii) multivariate adjustment by subclassification on the propensity score where the same subclasses are used to estimate treatment effects for all outcome variables and in all subpopulations, and (iii) visual representation of multivariate covariance adjustment by a two- dimensional plot.

Stages and processes of self-change of smoking: Toward an integrative model of change.

James O. Prochaska, Carlo C. DiClemente

An integrative model of change was applied to the study of 872 Ss (mean age 40 yrs) who were changing their smoking habits on their own. Ss represented the following 5 stages of change: precontemplation, contemplation, action, maintenance, and relapse. 10 processes of change were expected to receive differential emphases during particular stages of change. Results indicate that Ss (a) used the fewest processes of change during precontemplation; (b) emphasized consciousness raising during the contemplation stage; (c) emphasized self-reevaluation in both contemplation and action stages; (d) emphasized self-liberation, a helping relationship, and reinforcement management during the action stage; and (e) used counterconditioning and stimulus control the most in both action and maintenance stages. Relapsers responded as a combination of contemplaters and people in action would. Results are discussed in terms of developing a model of self-change of smoking and enhancing a more integrative general model of change. (14 ref) (PsycINFO Database Record (c) 2006 APA, all rights reserved). © 1983 American Psychological Association.

The Practice of English Language Teaching

Jeremy Harmer

A guide to teaching the English language covers such topics as English as world language, methodologies, grouping students, educational technology, lesson planning, testing and evaluation, and learner autonomy.

Simulating physics with computers

Richard P. Feynman

Efficacious Form for Model Pseudopotentials

Leonard Kleinman, D. M. Bylander

A simple way has been discovered to put model pseudopotentials, $V(\stackrel{\ensuremath{\rightarrow}}{\mathrm{r}})={\ensuremath{\Sigma}}_{\mathrm{lm}}|{Y}_{\mathrm{lm}}〉{V}_{l}(r)\ifmmode\times\else\texttimes\fi{}〈{Y}_{\mathrm{lm}}|$, into a form which reduces the number of integrals of $V(\stackrel{\ensuremath{\rightarrow}}{\mathrm{r}})$ required for an energyband calculation from $\frac{\mathrm{mn}(n+1)}{2}$ to $\mathrm{mn}$ for each $l$ in the sum (where $n$ is the number of plane waves used in the expansion and $m$ the number of points in the Brillouin zone at which the calculation is performed). The new form may be chosen to improve the accuracy of the pseudopotential when used in other chemical environments.

Accents of English

J. C. Wells

Accents of English is about the way English is pronounced by different people in different places. Volume 1 provides a synthesizing introduction, which shows how accents vary not only geographically, but also with social class, formality, sex and age; and in volumes 2 and 3 the author examines in greater depth the various accents used by people who speak English as their mother tongue: the accents of the regions of England, Wales, Scotland and Ireland (volume 2), and of the USA, Canada, the West Indies, Australia, New Zealand, South Africa, India, Black Africa and the Far East (volume 3). Each volume can be read independently, and together they form a major scholarly survey, of considerable originality, which not only includes descriptions of hitherto neglected accents, but also examines the implications for phonological theory. Readers will find the answers to many questions: Who makes 'good' rhyme with 'mood'? Which accents have no voiced sibilants? How is a Canadian accent different from an American one, a New Zealand one from an Australian one, a Jamaican one from a Barbadian one? What are the historical reasons for British-American pronunciation differences? What sound changes are currently in progress in New York, in London, in Edinburgh? Dr Wells his written principally for students of linguistics, phonetics and English language, but the motivated general reader will also find the study both fascinating and rewarding.

Studies on the Biology of the Grasshopper Pest Zonocerus Variegatus (L.) (Orthoptera: Pyrgomorphidae) in Nigeria: 1911–1981

S. Afolabi Toye

A full coupled-cluster singles and doubles model: The inclusion of disconnected triples

George D. Purvis, Rodney J. Bartlett

The coupled-cluster singles and doubles model (CCSD) is derived algebraically, presenting the full set of equations for a general reference function explicitly in spin–orbital form. The computational implementation of the CCSD model, which involves cubic and quartic terms, is discussed and results are reported and compared with full CI calculations for H2O and BeH2. We demonstrate that the CCSD exponential ansatz sums higher-order correlation effects efficiently even for BeH2, near its transition state geometry where quasidegeneracy efforts are quite large, recovering 98% of the full CI correlation energy. For H2O, CCSD plus the fourth-order triple excitation correction agrees with the full CI energy to 0.5 kcal/mol. Comparisons with low-order models provide estimates of the effect of the higher-order terms T1T2, T21T2, T31, and T41 on the correlation energy.

Principles of Artificial Intelligence

Nils J. Nilsson

Solar engineering of thermal processes

Structural Equation Models with Unobservable Variables and Measurement Error: Algebra and Statistics

Claes Fornell, David F. Larcker

Claes Fornell, David F. Larcker, Structural Equation Models with Unobservable Variables and Measurement Error: Algebra and Statistics, Journal of Marketing Research, Vol. 18, No. 3 (Aug., 1981), pp. 382-388

Structural Equation Models with Unobservable Variables and Measurement Error: Algebra and Statistics

Claes Fornell, David F. Larcker

Several issues relating to goodness of fit in structural equations are examined. The convergence and differentiation criteria, as applied by Bagozzi, are shown not to stand up under mathematical or statistical analysis. The authors argue that the choice of interpretative statistic must be based on the research objective. They demonstrate that when this is done the Fornell-Larcker testing system is internally consistent and that it conforms to the rules of correspondence for relating data to abstract variables.