Entity

Time filter

Source Type

Haarlem, Netherlands

Fitzgerald J.,Newcastle University | Pierce K.,Newcastle University | Verhoef M.,Chess
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2010

This paper presents initial results of research aimed at developing methods and tools for multidisciplinary collaborative development of dependable embedded systems. We focus on the construction and analysis by co-simulation of formal models that combine discrete-event specifications of computer-based controllers with continuous-time models of the environment with which they interact. Basic concepts of collaborative modelling and co-simulation are presented. A pragmatic realisation using the VDM and Bond Graph formalisms is described and illustrated by means of an example, which includes the modelling of both normal and faulty behaviour. Consideration of a larger-scale example from the personal transportation domain suggests the forms of support needed to explore the design space of collaborative models. Based on experience so far, challenges for future research in this area are identified. © 2010 Springer-Verlag Berlin Heidelberg. Source


Van Vlaenderen I.,Chess | Van Bellinghen L.-A.,Chess | Meier G.,Glaxosmithkline | Nautrup B.P.,EAH Consulting
BMC Infectious Diseases | Year: 2013

Background: Indirect herd effect from vaccination of children offers potential for improving the effectiveness of influenza prevention in the remaining unvaccinated population. Static models used in cost-effectiveness analyses cannot dynamically capture herd effects. The objective of this study was to develop a methodology to allow herd effect associated with vaccinating children against seasonal influenza to be incorporated into static models evaluating the cost-effectiveness of influenza vaccination.Methods: Two previously published linear equations for approximation of herd effects in general were compared with the results of a structured literature review undertaken using PubMed searches to identify data on herd effects specific to influenza vaccination. A linear function was fitted to point estimates from the literature using the sum of squared residuals.Results: The literature review identified 21 publications on 20 studies for inclusion. Six studies provided data on a mathematical relationship between effective vaccine coverage in subgroups and reduction of influenza infection in a larger unvaccinated population. These supported a linear relationship when effective vaccine coverage in a subgroup population was between 20% and 80%. Three studies evaluating herd effect at a community level, specifically induced by vaccinating children, provided point estimates for fitting linear equations. The fitted linear equation for herd protection in the target population for vaccination (children) was slightly less conservative than a previously published equation for herd effects in general. The fitted linear equation for herd protection in the non-target population was considerably less conservative than the previously published equation.Conclusions: This method of approximating herd effect requires simple adjustments to the annual baseline risk of influenza in static models: (1) for the age group targeted by the childhood vaccination strategy (i.e. children); and (2) for other age groups not targeted (e.g. adults and/or elderly). Two approximations provide a linear relationship between effective coverage and reduction in the risk of infection. The first is a conservative approximation, recommended as a base-case for cost-effectiveness evaluations. The second, fitted to data extracted from a structured literature review, provides a less conservative estimate of herd effect, recommended for sensitivity analyses. © 2013 Van Vlaenderen et al.; licensee BioMed Central Ltd. Source


Poulsen Nautrup B.,EAH Consulting | Van Vlaenderen I.,Chess | Gasper S.M.,Zoetis Inc. | Holland R.E.,Chess
Journal of Animal Science | Year: 2013

The goal of this study was to determine the clinical and economic impact of using tulathromycin as first line treatment for bovine respiratory disease (BRD) compared with other commonly used antimicrobials. Two decision trees were developed simulating the consequences of treating cattle at high risk of developing BRD [control model (CM)] or cattle with first clinical BRD episode [treatment model (TM)]. As comparators florfenicol and tilmicosin were considered in both models whereas enrofloxacin was included in the TM because it was only labeled for treatment of BRD at the time of development of the calculators. A total of 5 (CM) and 10 (TM) comparative clinical studies that reported efficacy data for the selected drugs and indications were identified as suitable for model population. The following outcomes were considered: first treatment success, number of subsequent BRD treatments, chronics, and mortalities. Cost parameters were considered from the perspective of the producer and included treatment costs (first treatment and retreatments) and costs of chronics and deaths derived from published sources for 2010 (default). The models allowed the estimation of clinical and economic consequences according to each individual trial outcomes. Treatment with tulathromycin resulted in more first treatment successes and fewer removals (chronics and deaths) in all comparisons. The average total number of antimicrobial treatments required for the management of BRD was also least with tulathromycin as first treatment option. Because of better efficacy, total costs over the entire study periods were always lowest with tulathromycin. Depending on the study selected as the basis for the efficacy evaluation, cost savings with tulathromycin were calculated in the CM between US$21.00 and $47.86 (vs. florfenicol) and $11.37 and $72.64 (vs. tilmicosin); cost savings in the TM ranged between $28.47 and $143.87 (vs. florfenicol) and $7.75 and $84.91 (vs. tilmicosin) as well as between $23.22 and $47.82 (vs. enrofloxacin), with the ranges reflecting a variety of settings in different trials. Thus, the higher drug costs of tulathromycin were more than offset by reduced BRD treatments, chronics, and mortalities in the herd. Fewer BRD episodes in cattle treated with tulathromycin not only contributes to overall savings in BRD management but also reduces the necessity of repeated antibiotic treatment, supporting prudent use of antimicrobials in livestock. © 2013 American Society of Animal Science. All rights reserved. Source


Hooman J.,Embedded Systems Institute | Hooman J.,Radboud University Nijmegen | Verhoef M.,Chess
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2010

To support model-based development and analysis of embedded systems, the specification language VDM++ has been extended with asynchronous communication and improved timing primitives. In addition, we have defined an interface for the co-simulation of a VDM++ model with a continuous-time model of its environment. This enables multi-disciplinary design space exploration and continuous validation of design decisions throughout the development process. We present an operational semantics which formalizes the precise meaning of the VDM extensions and the co-simulation concept. © 2010 Springer. Source


Das Mahapatra S.,Jadavpur University | Saha D.,Jadavpur University | Saha R.,Jadavpur University | Sanyal D.,Jadavpur University | And 2 more authors.
2016 IEEE 1st International Conference on Control, Measurement and Instrumentation, CMI 2016 | Year: 2016

A Stewart platform that is a 6-DOF parallel manipulator with a moveable frame for three linear and three angular motions has been designed with electrohydraulic actuation for achieving maneuverability of heavy load. A popular application is the motion simulator for an aircraft or a ship that could be used for training by generating specific motions within the confine of a laboratory. The main contribution of this work is the design and realization of a high-precision simulator with low-cost proportional valves using a simple PI controller for achieving basic motions. A pose-feedback controller has been conceived for the system constructed on the basis of the feedback of the leg lengths and a linearized inverse kinematic model about the neutral position. A number of real-time experiments have shown the design to be quite satisfactory. © 2016 IEEE. Source

Discover hidden collaborations