Simulation model of a predator-prey system comprised ofPhytoseiulus persimilis andTetranychus urticae. II. Model sensitivity to variations in the life history parameters of both species and to variations in the functional response and components of the numerical response

Summary A detailed sensitivity analysis of a model of a predator-prey system comprised ofTetranychus urticae andPhytoseiulus persimilis was performed. The aim was to assess the relative importance of the life history parameters of both species, the functional response, and the components of the numerical response. In addition, the impact of the initial predator-prey ratio and the timing of predator introduction were tested. Results indicated that the most important factors in the system were relative rates of predator and prey development, the time of onset of predator oviposition, and the mode of the predator's oviposition curve. The total oviposition of the predator, the effect of prey consumption on predator oviposition, and predator searching were important under some conditions. Factors of moderate importance were the adult female predator's functional response, total prey oviposition, the mode of the prey's oviposition curve, abiotic mortality of the pre-adult predator, and the effect of prey consumption on predator development and on the immature predator's mortality. Factors of least importance were the variances of the predator's and prey's oviposition curves, the abiotic mortality of the adult predator, the abiotic mortality of the pre-adult and adult prey, the functional response of the nymphal and adult male predators, and the effect of prey consumption on adult predator mortality. The sex ratios had little effect, except when the proportion of female predators was very low. The initial predator-prey ratio and time of predator introduction had significant impacts on system behavior, though the patterns of impact were different.     

Variable selection for survival data with a class of adaptive elastic net techniques

The accelerated failure time (AFT) models have proved useful in many contexts, though heavy censoring (as for example in cancer survival) and high dimensionality (as for example in microarray data) cause difficulties for model fitting and model selection. We propose new approaches to variable selection for censored data, based on AFT models optimized using regularized weighted least squares. The regularized technique uses a mixture of \(\ell _1\) and \(\ell _2\) norm penalties under two proposed elastic net type approaches. One is the adaptive elastic net and the other is weighted elastic net. The approaches extend the original approaches proposed by Ghosh (Adaptive elastic net: an improvement of elastic net to achieve oracle properties, Technical Reports 2007) and Hong and Zhang (Math Model Nat Phenom 5(3):115–133 2010), respectively. We also extend the two proposed approaches by adding censoring observations as constraints into their model optimization frameworks. The approaches are evaluated on microarray and by simulation. We compare the performance of these approaches with six other variable selection techniques-three are generally used for censored data and the other three are correlation-based greedy methods used for high-dimensional data.     

Modelling the management of underground water assets

Central to the activities of any industry is the modernization of its assets. This paper describes the application of statistical methods to the asset management plan of a large water company. A model for the underground assets is given in detail, and the extensive computations required are illustrated. A Bayesian model shows the consequences of various policy options and provides realistic measures of the uncertainty connected with them.     

Singapore's Malay-Muslim minority: Social identification in a post-‘9/11’ world

Fundamental within Singapore's modernisation push ‘From Third World to First’ was the long-term strategy of establishing a Singapore identity based on multiracialism, multilingualism, multiculturalism and multireligiousity (the ‘4Ms’). But while wholesale landscape changes have largely removed earlier associations between ethnicity and residence, government promotion of a shared Singapore identity has been frustrated by the lagging educational and socio-economic achievements of Singapore's Malay minority. Prior to the events of ‘9/11’ government concern had centred on the growing popularity of private Islamic schools, or madrasahs, which in the government's view could affect educational standards in the city-state. However, following the destruction of the World Trade Center government attention was quickly shifted to the promotion of ‘racial harmony’ and Singaporeans were urged to ‘get to know your neighbours’ in a tacit admission that 40 years of ‘racial’ assimilation had yet to produce ethnically integrated, cross-cultural community spirit. Subsequent events, particularly the arrest of local Jemaah Islamiyah operatives and the destruction in Iraq, have impacted most strongly upon Singapore's Malay-Muslim community and posed challenges to its identity within a multicultural society.     

Social Policy in South Korea: Cultural and Structural Factors in the Emergence of Welfare

There are a number of features that make South Korea an interesting place to study social policy. First, it has experienced rapid economic development with the associated changes in urbanization and demography. This change has created social problems, which the state has had to address. Second, the country retains a strong cultural tradition and repeated affirmation of the values and practices of Confucianism. In this paper, these two features are considered in relation to the way social policy has been addressed. The thrust of the paper will be on the policy responses to perceived social problems and the way in which other social problems are individualized within families. These policies are informed and shaped by Korean politics and culture.     

Skills,control, and the mass professions

Since members of the mass professions are employed mainly by large organisations in the public sector, they are increasingly ‘managed’. What is happening to their skills, their control over their own work, and their professionalism, are matters of concern as revealed by recent disputes. These are precisely questions at the heart of the labour process debate relaunched by Braverman. The insights generated by this stream of writing, already profitably applied beyond blue collar work to clerical occupations may be extended to embrace elements of the service class. There the notion of indetermination goes beyond the notion of discretion. Changes in public ideology have effects analogous to those arising from technological innovation in manufacturing. Yet professionals, whilst attending to technological aspects of their work, typically ignore the wider social issues. In this respect they are vulnerable to deskilling and erosion of control over their work.     

The implementation of the bayesian paradigm

Routine implementation of the Bayesian paradigm requires an efficient approach to the calculation and display of posterior or predictive distributions for given likelihood and prior specifi- cations. In this paper we shall review some of the analytic and numerical approaches currently available, describing in detail a numerical integration strategy based on Gaussian quadrature, and an associated strategy for the reconstruction and display of distributions based on spline techniques.     

A note on cost-return calculations and decisions to migrate

In the notions of the aggregative cost-benefit migration models, this paper questions the assumption that prospective migrants behave as if they are not only concerned with, but are able to calculate expected pecuniary and non-pecuniary returns to re-location. Results of a survey which evaluates the role of cost-return calculations in decisions to migrate suggest that there may be population sub-groups who either do not care to make cost-returns calculations to migration, or who are unable to do so.