Advanced Material Concepts for Luminescent Solar Concentrators

Sunlight that is incident on the front surface of a luminescent solar concentrator (LSC) is absorbed and subsequently re-emitted by luminescent materials. The resulting luminescence is transported to the edge of the LSC sheet and concentrated onto photovoltaic devices. Despite its potential for generating low-cost solar power, LSC development faces numerous challenges, the majority of which are related to the luminescent materials used in their design. Earlier LSC research focused on organic dyes, and while several of the shortcomings with these materials have been solved over time, some major challenges remain. This paper outlines the loss mechanisms that limit conversion efficiency of the LSC and highlights the role that advanced materials can play. Losses include nonunity fluorescence quantum yield (FQY), reabsorption losses, incomplete utilization of the solar spectrum, and escape cone losses. Long-term photostability is also discussed as it is essential for commercial feasibility of any solar technology. Past and current techniques, designed to reduce these losses, are described and their experimental achievements are discussed.     

Neutron reflectometry investigation of polymer-polymer reactions at the interface between immiscible polymers

Primary amine end functionalised deuteropolystyrene has been mixed with unmodified hydrogenous polystyrene and a thin film placed on top of a film of an acrylic polymer that either has carboxylic acid groups located at one end of each molecule or as substituents on each repeat unit. After holding at 453 K for defined times, the interfacial excess layer at the interface between the two polymers has been quantitatively analysed using neutron reflectometry and the extent of grafting of the deuteropolymer at the interface determined. Whilst maintaining the concentration of carboxylic acid units constant (fixed reacting groups) the extent of grafting increases with concentration of the functionalised deuteropolystyrene in the polystyrene layer. On changing the molecular weight of the functionalised deuteropolystyrene but maintaining the molar concentration of reactive end groups constant, the extent of grafting is larger for the lower molecular weight polymer. Although, the qualitative variation of the extent of grafting with time is in agreement with theories for interfacial grafting, exact correspondence cannot be obtained. The initial rate of grafting corresponds to second order rate constants of ∼0.1-0.2 l mol⁻¹ s⁻¹ but saturation of grafting is evident at far lower values (and hence earlier in the reaction process) than predicted by theory. Moreover, this saturation extent of grafting is at a level much lower than anticipated if brush-like layer formation is encouraged by interfacial grafting.     

Long-term fairness with bounded worst-case losses

How does one repeatedly choose actions so as to be fairest to the multiple beneficiaries of those actions? We examine approaches to discovering sequences of actions for which the worst-off beneficiaries are treated maximally well, then secondarily the second-worst-off, and so on. We formulate the problem for the situation where the sequence of action choices continues forever; this problem may be reduced to a set of linear programs. We then extend the problem to situations where the game ends at some unknown finite time in the future. We demonstrate that an optimal solution is intractable, and present two good approximation algorithms.     

A multi-institutional, multinational study of programming concepts using card sort data

Abstract: This paper presents a case study of the use of a repeated single‐criterion card sort with an unusually large, diverse participant group. The study, whose goal was to elicit novice programmers' knowledge of programming concepts, involved over 20 researchers from four continents and 276 participants drawn from 20 different institutions. In this paper we present the design of the study and the unexpected result that there were few discernible systematic differences in the population. The study was one of the activities of the National Science Foundation funded Bootstrapping Research in Computer Science Education project (2003).     

Morphology of peripheral airways in current smokers and ex-smokers

To investigate the effect of smoking status on pulmonary function and pathologic changes in the peripheral airways, we studied 97 patients who underwent thoracotomy for coin lesions. The patients were divided into 4 groups: nonsmokers (n = 9), current smokers (n = 51), and those who had ceased smoking for less than (n = 18) or more than (n = 19) 2 yr prior to surgery. We found that current smokers had evidence of air-flow obstruction with abnormal lung volumes when compared with nonsmokers. Ex-smokers had lung volumes similar to those of nonsmokers, but showed evidence of obstruction, with the FEV1/FVC between the values found for nonsmokers and current smokers. Examination of the small airways showed that the membranous bronchioles of current smokers and ex-smokers displayed only increased goblet cell metaplasia when compared with those in nonsmokers; the respiratory bronchioles of current and ex-smokers showed increases in intraluminal and airway wall inflammatory cells, wall fibrosis, and pigment deposition. We conclude that patients who currently smoke cigarettes have reduced lung function that is associated with abnormalities of airway structure. Although those who have stopped smoking have function that is closer to the nonsmoking group, there is no apparent difference in structural change between current and ex-smokers.     

Three-dimensional motion and reconstruction of coronary arteries from biplane cineangiography

A new approach is described for reconstructing coronary arteries from two sequences of projection images. The estimation of motion is performed on three-dimensional line segments (or centrelines), and is based on a ‘predictionprojection-optimization’ loop. The method copes with time varying properties, deformations and superpositions of vessels. Experiments using simulated and real data have been carried out. and the results found to be robust over a full cycle of a human heart. Local and global kinetic features can then be derived to obtain a greater insight on the cardiac functional state     

Fatigue crack growth behavior of X2095 Al–Li alloy

Microstructures and micro-textures of X2095 Al–Li alloy in as-received/superplastic state were characterized by means of SEM/BDS, X-ray diffraction and orientation imaging microscopy (OIM). It was observed that the microstructure of the alloy was typical of a particulate-reinforced composite material, consisting of aluminum matrix and homogeneously distributed T_B(Al₇Cu₄Li) particles with a volume fraction of about 10%. Brass-type texture was the dominant texture component. Both constant amplitude and near-threshold fatigue crack growth rates of the alloy in the L–T and T–L orientations were determined at different stress ratios. Particular attention was paid to the role of the T_B phase in the fatigue crack growth. When a fatigue crack approached a T_B particle, the crack basically meandered to avoid the particle. The T_B particles thus provided a strong resistance to the propagation of fatigue crack by promoting crack deflection and the related crack closure effects. The fatigue crack propagation behavior has been explained by the microstructural features, micro-textures, cracking characteristics and crack closure effects.     

The impact of pain in spinal cord injury: A case–control study.

Objective: To examine the impact of pain on functioning across multiple quality of life QOL) domains among individuals with spinal cord injury (SCI). Design: A case–control design that matched 2 groups (i.e., extreme pain interference and no pain interference) case for case on age (i.e., within 10 years), education, gender, race, marital status, primary occupation, and impairment level. Etiology of SCI and injury duration, although not specifically matched, were the same in 84% and 91% of the cases, respectively. Participants: Individuals with traumatic-onset SCI from the National Spinal Cord Injury database (n?=?86 matched pairs). Outcome Measures: Satisfaction With Life Scale, Craig Handicap Assessment and Reporting Technique, and Short Form SF-12. Results: The extreme pain interference group reported a significantly lower overall QOL and had higher total handicap scores than the no pain interference group. Areas of handicap most influenced by pain were mobility, social integration, and economic self-sufficiency. The extreme pain interference group also reported significantly lower physical and mental health than the no pain interference group. Conclusions: Pain has a consistent detrimental impact on functioning across multiple QOL domains even after controlling for multiple demographic and medical characteristics known to be associated with self-reported QOL. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Analytical performance prediction for robust constrained model predictive control

This paper presents a new analysis tool for predicting the closed-loop performance of a robust constrained model predictive control (MPC) scheme. Currently, performance is typically evaluated by numerical simulation, leading to an extensive computation when investigating the effect of controller parameters, such as the horizon length, the cost weightings and the constraint settings. The analytic method, in this paper, avoids this computational burden, thus enabling a rapid study of the trades between the design parameters and the performance. Previous work developed an MPC formulation employing constraint tightening to achieve robust feasibility and constraint satisfaction despite the action of an unknown but bounded disturbance. This paper shows that the expected performance of that controller can be predicted using a combination of the gains of two linear systems, the optimal control for the unconstrained system, and a candidate policy used in performing the constraint tightening. The method also accounts for the possible mismatch between the predicted level of disturbance and the actual level encountered. The analytic results are compared with simulation results for several examples and are shown to provide accurate predictions of performance and its variation with the system parameters.     

Cognitive and learning difficulties and how they affect access to IT systems

In October 2005, the IBM Human Ability and Accessibility Center and T.J. Watson Research Center hosted a symposium on “cognitive and learning difficulties and how they affect access to IT systems”. The central premise of the symposium was the recognition that cognitive and learning difficulties have a profound impact on a person’s ability to interact with information technology (IT) systems, but that little support is currently being offered by those systems. By bringing together internationally renowned experts from a variety of different, but complementary, research fields, the symposium aimed to provide a complete overview of the issues related to this topic. This paper summarises the discussions and findings of the symposium.