Look before you leap : a confidence-based method for selecting species criticality while avoiding negative populations in τ-leaping

The stochastic simulation algorithm was introduced by Gillespie and in a different form by Kurtz. There have been many attempts at accelerating the algorithm without deviating from the behavior of the simulated system. The crux of the explicit τ-leaping procedure is the use of Poisson random variables to approximate the number of occurrences of each type of reaction event during a carefully selected time period, τ. This method is acceptable providing the leap condition, that no propensity function changes “significantly” during any time-step, is met. Using this method there is a possibility that species numbers can, artificially, become negative. Several recent papers have demonstrated methods that avoid this situation. One such method classifies, as critical, those reactions in danger of sending species populations negative. At most, one of these critical reactions is allowed to occur in the next time-step. We argue that the criticality of a reactant species and its dependent reaction channels should be related to the probability of the species number becoming negative. This way only reactions that, if fired, produce a high probability of driving a reactant population negative are labeled critical. The number of firings of more reaction channels can be approximated using Poisson random variables thus speeding up the simulation while maintaining the accuracy. In implementing this revised method of criticality selection we make use of the probability distribution from which the random variable describing the change in species number is drawn. We give several numerical examples to demonstrate the effectiveness of our new method.

Sociopathic attitudes to road safety

Injuries and deaths due to unsafe driving practices are a substantial health and socioeconomic burden to the community. Young socially disadvantaged males who are involved in a lifestyle of risky behaviour, crime and motor vehicle accidents seem unaffected by educational campaigns to improve safer driving. The aim is to develop a driving and social behavioural profile that may explain the lack of effectiveness of road safety advertising and suggest ways to refine educational strategies to reduce the risky lifestyle and associated harms among those most vulnerable, the 15-25 year olds. The procedure involved a quantitative and qualitative analysis through questionnaires, surveys and focus groups involving a comparison of populations (n = 668) by age, gender and socioeconomic status in three discrete Australian sites. Information gathered included issues related to road safety awareness, knowledge of advertising, personal and peer group attitudes as well as driving and life style history. The results indicate that within the community a highly visible profile of strong anti-social road safety activities by an educationally and economically disadvantaged sub-culture exists and this group seem impervious to road safety advertising and education initiatives. As the overall unsafe driving and risky antisocial behaviour is significant among 15-25 year olds within the community the solution is seen to be community based. A long-term (five to ten year) program has been posited; promoting community partnerships through consultative and local action committees at all levels creating locally designed formal and informal educational and mutual support programs.

Identifying parent perspectives to guide active travel intervention with small populations : case study in Denver, Colorado

This paper investigates a strategy for guiding school-based active travel intervention. School-based active travel programs address the travel behaviors and perceptions of small target populations (i.e., at individual schools) so they can encourage people to walk or bike. Thus, planners need to know as much as possible about the behaviors and perceptions of their target populations. However, existing strategies for modeling travel behavior and segmenting audiences typically work with larger populations and may not capture the attitudinal diversity of smaller groups. This case study used Q technique to identify salient travel-related attitude types among parents at an elementary school in Denver, Colorado; 161 parents presented their perspectives about school travel by rank-ordering 36 statements from strongly disagree to strongly agree in a normalized distribution, single centered around no opinion. Thirty-nine respondents' cases were selected for case-wise cluster analysis in SPSS according to criteria that made them most likely to walk: proximity to school, grade, and bus service. Analysis revealed five core perspectives that were then correlated with the larger respondent pool: optimistic walkers, fair-weather walkers, drivers of necessity, determined drivers, and fence sitters. Core perspectives are presented—characterized by parents' opinions, personal characteristics, and reported travel behaviors—and recommendations are made for possible intervention approaches. The study concludes that Q technique provides a fine-grained assessment of travel behavior for small populations, which would benefit small-scale behavioral interventions

Models of collective cell motion for cell populations with different aspect ratio : diffusion, proliferation and travelling waves

Continuum, partial differential equation models are often used to describe the collective motion of cell populations, with various types of motility represented by the choice of diffusion coefficient, and cell proliferation captured by the source terms. Previously, the choice of diffusion coefficient has been largely arbitrary, with the decision to choose a particular linear or nonlinear form generally based on calibration arguments rather than making any physical connection with the underlying individual-level properties of the cell motility mechanism. In this work we provide a new link between individual-level models, which account for important cell properties such as varying cell shape and volume exclusion, and population-level partial differential equation models. We work in an exclusion process framework, considering aligned, elongated cells that may occupy more than one lattice site, in order to represent populations of agents with different sizes. Three different idealizations of the individual-level mechanism are proposed, and these are connected to three different partial differential equations, each with a different diffusion coefficient; one linear, one nonlinear and degenerate and one nonlinear and nondegenerate. We test the ability of these three models to predict the population level response of a cell spreading problem for both proliferative and nonproliferative cases. We also explore the potential of our models to predict long time travelling wave invasion rates and extend our results to two dimensional spreading and invasion. Our results show that each model can accurately predict density data for nonproliferative systems, but that only one does so for proliferative systems. Hence great care must be taken to predict density data for with varying cell shape.

Exceptional teachers for disadvantaged schools

This article reports on the first year of the Exceptional Teachers for Disadvantaged Schools project, a teacher education approach designed to prepare high quality teachers for low socio-economic schools. The Exceptional Teachers for Disadvantaged Schools (ETDS) project is an innovative way to prepare high-quality teachers for employment in low-SES schools. The program, based at Queensland University of Technology (QUT), offers a specialised curriculum, designed to equip high-achieving pre-service teachers for work in the schools that need them most. Selected pre-service teachers at QUT are invited to take part in the trial course, based on their academic performance over the first two years of their four-year Bachelor of Education degree, and on a demonstrated commitment to social justice. These participants undertake a modified version of QUT's B Ed on-campus curriculum. They have their practicum/field experience at one of a range of disadvantaged schools throughout Queensland which have agreed to partner with QUT in the program. In the past, teacher education for disadvantaged schools has been described as applying a 'missionary' or deficit model (Larabee, 2010; Comber and Kamler, 2004; Flessa, 2007). The principals of schools participating in the ETDS react strongly against such an approach, and have explicitly asked project staff not to send them anyone who 'thinks they can save the world'. The ETDS project has moved well away from such a model, towards a position that is explicitly centred on notions of academic excellence. The project is now at the end of its first trial year.

Exceptional teachers for disadvantaged schools

A major issue facing Australia is addressing an education system that OECD’s data from the Programme for International Student Assessment (PISA) show is of high quality, but low equity. In other words, while Australian schools score relatively high in terms of international benchmarks related to quality, the same cannot be said in relation to indicators of social background or socioeconomic status (SES). The federal and state responses to this dilemma can be found in a coordinated national agenda targeting social inclusion. Two key policy areas within this agenda relate directly to the Exceptional Teachers for Disadvantaged Schools Project (ETDS). These are the Higher Education Participation and Partnerships Program (HEPPP) and the National Partnership Agreements on Low Socio-economic Status School Communities and Improving Teacher Quality.

How does the size and shape of local populations in China compare to general anthropometric surveys currently used for product design?

Anthropometry has long been used for a range of ergonomic applications & product design. Although products are often designed for specific cohorts, anthropometric data are typically sourced from large scale surveys representative of the general population. Additionally, few data are available for emerging markets like China and India. This study measured 80 Chinese males that were representative of a specific cohort targeted for the design of a new product. Thirteen anthropometric measurements were recorded and compared to two large databases that represented a general population, a Chinese database and a Western database. Substantial differences were identified between the Chinese males measured in this study and both databases. The subjects were substantially taller, heavier and broader than subjects in the older Chinese database. However, they were still substantially smaller, lighter and thinner than Western males. Data from current Western anthropometric surveys are unlikely to accurately represent the target population for product designers and manufacturers in emerging markets like China.

The moderator effect of cognitive modifiability on a traditional undergraduate admissions test for disadvantaged Black students in South Africa

Contends that South African universities must find admissions criteria, other than high school grades, that are both fair and valid for Black applicants severely disadvantaged by an inferior school education. The use of traditional intellectual assessments and aptitude tests for disadvantaged and minority students remains controversial as a fair assessment; they do not take account of potential for change. In this study, therefore, a measure of students' cognitive modifiability, assessed by means of an interactive assessment model, was added as a moderator of traditional intellectual assessment in predicting 1st-yr university success. Cognitive modifiability significantly moderated the predictive validity of the traditional intellectual assessment for 52 disadvantaged Black students. The higher the level of cognitive modifiability, the less effective were traditional methods for predicting academic success and vice versa.

Addressing quality teaching in hard to staff settings : the Exceptional Teachers for Disadvantaged Schools Project

This Exceptional Teachers for Disadvantaged Schools (ETDS) project sets out to design a new model of Australian teacher education responding to recent demands for quality education in low SES and disadvantaged schools. The project moves teacher education from the ‘missionary’ (Larabee, 2010) or deficit (Comber and Kamler 2004; Flessa, 2007) approaches, towards a focus on notions of quality and academic excellence. Rice (2008, p.1) argues for a need to place more of the “very best teachers into the most challenging schools”, yet the problem is not merely one of training more teachers, for disadvantaged schools already receive disproportionate numbers of beginning teachers (Connell, 1994; Vickers & Ferfolja, 2006). Rather, Grossman and Loeb (2010, p. 245) argue the problem centers on the common practice of “[p]lacing the least experienced teachers with the most needy students”. This paper reports on the first year trial of the project. The ETDS project is at present, the only mainstream Australian teacher education model that targets cohorts of academically high achieving pre-service teachers with the overt aim of preparing graduates of the program to teach in disadvantaged schools. At the end of its first year, the ETDS program graduated 20 new teachers, each of whom had over the previous 18 months engaged with a specialized curriculum and carefully monitored/scaffolded practicum placements in disadvantaged schools around Brisbane, Australia.