Spatial prediction of crystalline defects observed in molecular dynamic simulations of plastic damage

Molecular dynamic computer simulation is an essential tool in materials science to study atomic properties of materials in extreme environments and guide development of new materials. We propose a statistical analysis to emulate simulation output with the ultimate goal of efficiently approximating the computationally intensive simulation. We compare several spatial regression approaches including conditional autoregression (CAR), discrete wavelets transform (DWT), and principle components analysis (PCA). The methods are applied to simulation of copper atoms with twin wall and dislocation loop defects, under varying tilt tension angles. We find that CAR and DWT yield accurate results but fail to capture extreme defects, yet PCA better captures defect structure.     

A small sample confidence interval for autoregressive parameters

This paper is concerned with interval estimation of an autoregressive parameter when the parameter space allows for magnitudes outside the unit interval. In this case, intervals based on the least-squares estimator tend to require a high level of numerical computation and can be unreliable for small sample sizes. Intervals based on the asymptotic distribution of instrumental variable estimators provide an alternative. If the instrument is taken to be the sign function, the interval is centered at the Cauchy estimator and a large sample interval can be created by estimating the standard error of this estimator. The interval proposed in this paper avoids estimating this standard error and results in a small sample improvement in coverage probability. In fact, small sample coverage is exact when the innovations come from a normal distribution.     

Remembrance of things not past

Lawrence L. Langer, Holocaust Testimonies: the Ruins of Memory (New Haven, CT and London: Yale University Press, 1991). Pp.xv + 216. £20 (hardback); £9.95 (paperback). ISBN 0 300 04 96 68 and 05 24 72.

Debórah Dwork, Children With a Star: Jewish Youth in Nazi Europe (New Haven, CT and London: Yale University Press, 1991). Pp.xlvi + 354; illus. £19.95 (hardback); (paperback forthcoming). ISBN 0 300 05 0542 and 05 44 75.

Dalia Ofer, Escaping the Holocaust: Illegal Immigration to Israel (New York and Oxford: Oxford University Press, 1991). Pp.xiii + 408; illus. £30. ISBN 019 506 3406.     

MAPPING CULTURAL/POLITICAL DEBATES IN LATIN AMERICAN STUDIES

The theorization of postmodernism as the cultural logic of late capitalism has generated a number of debates among Latinos in the US and among Latin American critics in particular. This article examines a number of writings published between 1989 and 1994 by Latin American critics focusing on the viability of seeing Latin America as postmodern. We argue that in the rush to accept First World theoretical frameworks, there has been much confusion and a collapsing of economic, political and cultural categories. Conflating market growth and shifts with social change and the availability of a plurality of consumer goods with the distribution of goods and services, some critics have been quick to label cultural production in Latin America as ‘postmodern’. What is needed is a delimitation of the categories used, an examination of the cultural debate in relation to other debates on development, social movements, democratization and alliance politics, as well as an examination of local intellectual debates within the global context of restructuring and transnational capital.     

A machine learning analysis of drought and rural population change on the North American Great Plains since the 1970s

Population and Environment - Machine learning techniques have to date not been widely used in population-environment research, but represent a promising tool for identifying relationships between...     

Markov models of mite movements

Continuous time Markov models were used to analyse data from two bioassays to investigate the influence of β-fraction, a by-product of hop processing, on the two-spotted spider mite. The models were fitted to aggregate counts of the numbers of live and dead mites on treated and untreated halves of discs cut from leaves of hop and French bean plants. Some of the rate parameters were time dependent. Although not all parameters could be estimated precisely, the analysis enabled the quantitative effects of treatment over time to be estimated with reasonable precision. The estimated treatment effects were largely insensitive to the assumed values of other parameters. The first bioassay showed a progressive initial response to increasing concentration of β-fraction, although data at the intermediate concentration appeared anomalous. The second bioassay showed similar responses on hop and French bean leaves, with a stronger repellent effect on the lower leaf surface than on the upper surface.     

Qualitative Research: Valuable or Irrelevant?

This paper evaluates qualitative research methods in relation to the emancipatory research model. It identifies the main reasons why researchers opt for qualitative research, describes the principal data collection techniques used by them, and discusses some of the problems associated with these procedures. Drawing on insights gained from doing qualitative research in day centres for disabled young adults, I argue that these methodologies are fundamental to the emancipatory research paradigm; but their relevance can only be determined by researchers' willingness to challenge the institutions which control disability research production.     

Strategic thinking with computers

The author describes the development of a system of cognitive mapping as a strategic management tool. Strategic Options Development and Analysis (SODA) has been used extensively by project teams working on strategic issues. A typical programme is described and the procedure is based on attention to the ownership of data as the basic material, and on the design of strategy workshops using the owned data. This appendix describes the use of the system in practice and the benefits and drawback perceived in running the strategy workshop.     

Managing organizational change—A strategic approach

Developing the competence, commitment and capacity for change of people is a vital element in the creation and maintenance of competitive advantage and should be an integral part of the strategic equations and business plans of any firm. This theme, examples of ‘good’ practice, and strategies to implement a strategic approach to people have been explained and developed in a brief case ‘action pack’ produce by the authors of this article for the MSC and NEDO. Key factors identified in the development of the three ‘C’s are effective leadership, involvement and good employee communications, stress on performance management, appropriate reward systems and training and development.