Reduction of prosthetic vascular graft thrombogenicity by phosphorylcholine containing lipids and polymers. The thrombogenicity of arterial grafts can be modified by coating with new polymers that mimic haemocompatible blood cell membranes

This thesis reviews the clinical problems associated with atheromatous arterial disease, its treatment with prosthetic bypass biomaterials, and considers the development and assessment of these materials. The thesis tests the hypothesis that coating existing biomaterials with biological membrane phospholipids, which mimic the good haemocompatibility of erythrocyte membranes, may be a step towards the solution of the problem of biomaterial thrombogenicity. Twelve phospholipids from the RBC membrane are evaluated as haemocompatible surface coatings by two in vitro assays; 1) material thrombelastography (MTEG), and 2) fibrinopeptide A generation. The technique of MTEG is presented in detail and important developments of this methodology are described. The underlying mechanisms of haemocompatibility of these phospholipids are examined by incubation of lipid liposomes with human plasma using individual clotting factor assays. Phospholipids and polymers containing phosphorylcholine (PC), namely sphingomyelin and dipalmitoylphosphatidylcholine (DPPC), very significantly reduce the activation of platelets and clotting factors. They are considerably better than the biomaterials Dacron and PTFE. The stability of DPPC, sphingomyelin and the PC-polymers during sterilisation with steam, ethylene oxide and irradiation are studied. Marked decomposition is documented using the techniques of chromatography, FTIR and MTEG. Despite radiation induced changes, sphingomyelin and some PC-polymers remain less thrombogenic than PTFE or Dacron to both platelets and clotting factors. Untreated Dacron vascular grafts are compared with grafts coated with sphingomyelin and two PC-polymers in a double blind randomised in vivo trial, using a modified sheep arteriovenous fistula preparation. The end points are indium-111 platelet imaging and uptake, platelet survival times, iodine-125 fibrinogen uptake and graft histology. Sphingomyelin significantly reduces platelet uptake by 66% and the cross sectional area of graft thrombus by 90% compared to the control grafts. All three materials prolong platelet survival, but do not reduce fibrinogen activation significantly. The original hypothesis is supported and further investigation of these materials should be undertaken

Evidence-based medicine and progress in the medical sciences

The question what scientific progress means for a particular domain such as medicine seems importantly different from the question what scientific progress is in general. While the latter question received ample treatment in the philosophical literature, the former question is hardly discussed. I argue that it is nonetheless important to think about this question in view of the methodological choices we make. I raise specific questions that should be tackled regarding scientific progress in the medical sciences and demonstrate their importance by means of an analysis of what evidence-based medicine (EBM) has, and has not, to offer in terms of progress. I show how critically thinking about EBM from the point of view of progress can help us in putting EBM and its favoured methodologies in the right perspective. My conclusion will be that blindly favouring certain methods because of their immediately tangible short-term benefits implies that we parry the important question of how best to advance progress in the long run. This leads us to losing sight of our general goals in doing research in the medical sciences

Reflections on Mira : interactive evaluation in information retrieval

Evaluation in information retrieval (IR) has focussed largely on noninteractive evaluation of text retrieval systems. This is increasingly at odds with how people use modern IR systems: in highly interactive settings to access linked, multimedia information. Furthermore, this approach ignores potential improvements through better interface design. In 1996 the Commission of the European Union Information Technologies Programme, funded a three year working group, Mira, to discuss and advance research in the area of evaluation frameworks for interactive and multimedia IR applications. Led by Keith van Rijsbergen, Steve Draper and myself from Glasgow University, this working group brought together many of the leading researchers in the evaluation domain from both the IR and human computer interaction (HCI) communities. This paper presents my personal view of the main lines of discussion that took place throughout Mira: importing and adapting evaluation techniques from HCI, evaluating at different levels as appropriate, evaluating against different types of relevance and the new challenges that drive the need for rethinking the old evaluation approaches. The paper concludes that we need to consider more varied forms of evaluation to complement engine evaluation

Making molecules by mergoassociation: two atoms in adjacent nonspherical optical traps

Mergoassociation of two ultracold atoms to form a weakly bound molecule can occur when two optical traps that each contain a single atom are merged. Molecule formation occurs at an avoided crossing between a molecular state and the lowest motional state of the atom pair. We develop the theory of mergoassociation for pairs of nonidentical nonspherical traps. We develop a coupled-channel approach for the relative motion of the two atoms and present results for pairs of cylindrically symmetrical traps as a function of their anisotropy. We focus on the strength of the avoided crossing responsible for mergoassociation. We also develop an approximate method that gives insight into the dependence of the crossing strength on aspect ratio

Assessing the modelling approach and datasets required for fault detection in photovoltaic systems

Reliable monitoring for photovoltaic assets (PVs) is essential to ensuring uptake, long term performance, and maximum return on investment of renewable systems. To this end this paper investigates the input data and machine learning techniques required for day-behind predictions of PV generation, within the scope of conducting informed maintenance of these systems. Five years of PV generation data at hourly intervals were retrieved from four commercial building-mounted PV installations in the UK, as well as weather data retrieved from MIDAS. A support vector machine, random forest and artificial neural network were trained to predict PV power generation. Random forest performed best, achieving an average mean relative error of 2.7%. Irradiance, previous generation and solar position were found to be the most important variables. Overall, this work shows how low-cost data driven analysis of PV systems can be used to support the effective management of such assets

Making molecules by mergoassociation: Two atoms in adjacent nonspherical optical traps

Mergoassociation of two ultracold atoms to form a weakly bound molecule can occur when two optical traps that each contain a single atom are merged. Molecule formation occurs at an avoided crossing between a molecular state and the lowest motional state of the atom pair. We develop the theory of mergoassociation for pairs of nonidentical nonspherical traps. We develop a coupled-channel approach for the relative motion of the two atoms and present results for pairs of cylindrically symmetrical traps as a function of their anisotropy. We focus on the strength of the avoided crossing responsible for mergoassociation. We also develop an approximate method that gives insight into the dependence of the crossing strength on aspect ratio