Uncertainty of flow in porous media

The problem posed to the Study Group was, in essence, how to estimate the probability distribution of f(x) from the probability distribution of x. Here x is a large vector and f is a complicated function which can be expensive to evaluate. For Schlumberger's applications f is a computer simulator of a hydrocarbon reservoir, and x is a description of the geology of the reservoir, which is uncertain

Promoting reflection in asynchronous virtual learning spaces: tertiary distance tutors' conceptions

Increasingly, universities are embedding reflective activities into the curriculum. With the growth in online tertiary education, how effectively is reflection being promoted or used in online learning spaces? Based on the notion that teachers’ beliefs will influence their approaches to teaching, this research sought to understand how a group of distance tutors at the UK Open University conceptualised reflection. It was hoped that these findings would illuminate their approaches to promoting reflection as part of their online pedagogies. Phenomenographic analysis indicated that these tutors conceptualised reflection in four qualitatively different ways. Furthermore, the data suggested that these educators held a combination of two conceptions: one that understood the origin of being reflective and one that understood the purpose of reflection. Analysis of structural aspects of these conceptions offered insight into tutors’ own perspectives for what is needed to make online learning environments fertile territory for reflective learning

The role of gender in students’ ratings of teaching quality in computer science and environmental engineering

Students’ ratings of teaching quality on course units in computer science and environmental engineering at a large Swedish university were obtained using the Course Experience Questionnaire; 8,888 sets of ratings were obtained from men and 4,280 sets were obtained from women over ten academic years. There were differences in the ratings given by students taking the two programs; in particular, teachers tended to receive higher ratings in subjects that were less typical for their gender than in subjects that were more typical for their gender. There were differences in the ratings given to male and female teachers, differences in the ratings given by male and female students, and interactions between these two effects. There was no systematic trend for students to give different ratings to teachers of the same gender as themselves compared with teachers of the other gender. Nevertheless, without exception even the statistically significant effects were small in magnitude and unlikely to be of theoretical or practical importance. It is concluded that the causes of differences in the career progression of male and female teachers in engineering education need to be sought elsewhere.   

Bayesian regression discontinuity designs: Incorporating clinical knowledge in the causal analysis of primary care data

The regression discontinuity (RD) design is a quasi-experimental design that estimates the causal effects of a treatment by exploiting naturally occurring treatment rules. It can be applied in any context where a particular treatment or intervention is administered according to a pre-specified rule linked to a continuous variable. Such thresholds are common in primary care drug prescription where the RD design can be used to estimate the causal effect of medication in the general population. Such results can then be contrasted to those obtained from randomised controlled trials (RCTs) and inform prescription policy and guidelines based on a more realistic and less expensive context. In this paper we focus on statins, a class of cholesterol-lowering drugs, however, the methodology can be applied to many other drugs provided these are prescribed in accordance to pre-determined guidelines. NHS guidelines state that statins should be prescribed to patients with 10 year cardiovascular disease risk scores in excess of 20%. If we consider patients whose scores are close to this threshold we find that there is an element of random variation in both the risk score itself and its measurement. We can thus consider the threshold a randomising device assigning the prescription to units just above the threshold and withholds it from those just below. Thus we are effectively replicating the conditions of an RCT in the area around the threshold, removing or at least mitigating confounding. We frame the RD design in the language of conditional independence which clarifies the assumptions necessary to apply it to data, and which makes the links with instrumental variables clear. We also have context specific knowledge about the expected sizes of the effects of statin prescription and are thus able to incorporate this into Bayesian models by formulating informative priors on our causal parameters.Comment: 21 pages, 5 figures, 2 table

A theoretical treatment of void electromigration in the strip geometry

The void electromigration process in the strip geometry is investigated analytically and numerically. The void is assumed to travel either along the axis of symmetry of the metal strip or at the boundary. In each case, the shape, the velocity of the void and the characteristic electrical current are predicte

Models of void electromigration

We study the motion of voids in conductors subject to intense electrical current densities. We use a free-boundary model in which the flow of current around the insulating void is coupled to a law of motion (kinematic condition) for the void boundary. In the first part of the paper, we apply a new complex variable formulation of the model to an infinite domain and use this to (i) consider the stability of circular and flat front travelling waves, (ii) show that, in the unbounded metal domain, the only travelling waves of finite void area are circular, and (iii) consider possible static solutions. In the second part of the paper, we look at a conducting strip (which can be used to model interconnects in electronic devices) and use asymptotic methods to investigate the motion of long wavelength voids on the conductor boundary. In this case we derive a nonlinear parabolic PDE describing the evolution of the free boundary and, using this simpler model, are able to make some predictions about the evolution of the void over long times.<br/

Stress-Based IS Security Compliance: Towards a Conceptual Model

This study extends current behavioural information security compliance research by adapting the “work-stress model” of the Job Demands-Resources model to security behaviour. The paper proposes that users’ compliance burnout and security engagement are results of coping with security demands and receiving resources respectively. Compliance burnout would reduce security compliance while security engagement would increase it. The security compliance model developed in this study emphasises developing emotional and cognitive resources from IS users through effective provision of organisational resources and security requirements to promote desired security practice

Stopping the Leak: Retaining Beginning Teachers

The need for teacher retention has prompted numerous American states to provide programs for training mentors. The goal of mentor training is to offer a support mechanism that will retain novice teachers and assist them in developing their teaching skills. Such a program is the Texas Beginning Educator Support System (TxBESS) which has supported over 10,000 beginning teachers since its implementation in 1999 (State Board for Educator certification, 2004). A group of TxBESS supported interns was surveyed and the data suggest that both retention rates and teacher satisfaction were. high. The interns reported satisfaction particularly with regard to the effectiveness of the mentors