Critical Behavior of the Widom-Rowlinson Lattice Model

We report extensive Monte Carlo simulations of the Widom-Rowlinson lattice model in two and three dimensions. Our results yield precise values for the critical activities and densities, and clearly place the critical behavior in the Ising universality class.Comment: 6 pages, LaTeX, 5 figures available upon reques

Phase Diagram of the Lattice Restricted Primitive Model

We present a comprehensive study of the lattice restricted primitive model, i.e., a lattice gas consisting of an equal number of positively and negatively charged particles interacting via on-site exclusion and a 1/r potential. On the cubic lattice, Monte Carlo simulations show a line of Neel points separating a disordered, high-temperature phase from a phase with global antiferromagnetic order. At low temperatures the (high-density) ordered phase coexists with the (low-density) disordered phase. The Neel line meets the coexistence curve at a tricritical point, T_t \simeq 0.14, rho_t \simeq 0.4. A simple mean-field analysis is in qualitative agreement with simulations.Comment: Contribution to the AIP Conference on Treatment of Electrostatic Interactions in Computer Simulations of Condensed Media 25 pages, 16 figure

Advanced security infrastructures for grid education

This paper describes the research conducted into advanced authorization infrastructures at the National e-Science Centre (NeSC) at the University of Glasgow and their application to support a teaching environment as part of the Dynamic Virtual Organisations in e-Science Education (DyVOSE) project. We outline the lessons learnt in teaching Grid computing and rolling out the associated security authorisation infrastructures, and describe our plans for a future, extended security infrastructure for dynamic establishment of inter-institutional virtual organisations (VO) in the education domain

Supporting the clinical trial recruitment process through the grid

Patient recruitment for clinical trials and studies is a large-scale task. To test a given drug for example, it is desirable that as large a pool of suitable candidates is used as possible to support reliable assessment of often moderate effects of the drugs. To make such a recruitment campaign successful, it is necessary to efficiently target the petitioning of these potential subjects. Because of the necessarily large numbers involved in such campaigns, this is a problem that naturally lends itself to the paradigm of Grid technology. However the accumulation and linkage of data sets across clinical domain boundaries poses challenges due to the sensitivity of the data involved that are atypical of other Grid domains. This includes handling the privacy and integrity of data, and importantly the process by which data can be collected and used, and ensuring for example that patient involvement and consent is dealt with appropriately throughout the clinical trials process. This paper describes a Grid infrastructure developed as part of the MRC funded VOTES project (Virtual Organisations for Trials and Epidemiological Studies) at the National e-Science Centre in Glasgow that supports these processes and the different security requirements specific to this domain

Automated Measurement of Adherence to Traumatic Brain Injury (TBI) Guidelines using Neurological ICU Data

Using a combination of physiological and treatment information from neurological ICU data-sets, adherence to traumatic brain injury (TBI) guidelines on hypotension, intracranial pressure (ICP) and cerebral perfusion pressure (CPP) is calculated automatically. The ICU output is evaluated to capture pressure events and actions taken by clinical staff for patient management, and are then re-expressed as simplified process models. The official TBI guidelines from the Brain Trauma Foundation are similarly evaluated, so the two structures can be compared and a quantifiable distance between the two calculated (the measure of adherence). The methods used include: the compilation of physiological and treatment information into event logs and subsequently process models; the expression of the BTF guidelines in process models within the real-time context of the ICU; a calculation of distance between the two processes using two algorithms (“Direct” and “Weighted”) building on work conducted in th e business process domain. Results are presented across two categories each with clinical utility (minute-by-minute and single patient stays) using a real ICU data-set. Results of two sample patients using a weighted algorithm show a non-adherence level of 6.25% for 42 mins and 56.25% for 708 mins and non-adherence of 18.75% for 17 minutes and 56.25% for 483 minutes. Expressed as two combinatorial metrics (duration/non-adherence (A) and duration * non-adherence (B)), which together indicate the clinical importance of the non-adherence, one has a mean of A=4.63 and B=10014.16 and the other a mean of A=0.43 and B=500.0

Trust realisation in multi-domain collaborative environments

In the Internet-age, the geographical boundaries that have previously impinged upon inter-organisational collaborations have become decreasingly important. Of more importance for such collaborations is the notion and subsequent nature of trust - this is especially so in Grid-like environments where resources are both made available and subsequently accessed and used by remote users from a multitude of institutions with a variety of different privileges spanning across the collaborating resources. In this context, the ability to dynamically negotiate and subsequently enforce security policies driven by various levels of inter-organisational trust is essential. In this paper we present a dynamic trust negotiation (DTN) model and associated prototype implementation showing the benefits and limitations DTN incurs in supporting n-tier delegation hops needed for trust realisation in multi-domain collaborative environments

Comparison of advanced authorisation infrastructures for grid computing

The widespread use of grid technology and distributed compute power, with all its inherent benefits, will only be established if the use of that technology can be guaranteed efficient and secure. The predominant method for currently enforcing security is through the use of public key infrastructures (PKI) to support authentication and the use of access control lists (ACL) to support authorisation. These systems alone do not provide enough fine-grained control over the restriction of user rights, necessary in a dynamic grid environment. This paper compares the implementation and experiences of using the current standard for grid authorisation with Globus - the grid security infrastructure (GSI) - with the role-based access control (RBAC) authorisation infrastructure PERMIS. The suitability of these security infrastructures for integration with regard to existing grid technology is presented based upon experiences within the JISC-funded DyVOSE project