On the equivalence of Bayesian and dominant strategy implementation in a general class of social choice problems

We consider a standard social choice environment with linear utilities and independent, one-dimensional, private values. We provide a short and constructive proof that for any Bayesian incentive compatible mechanism there exists an equivalent dominant strategy incentive compatible mechanism that delivers the same interim expected utilities for all agents. We demonstrate the usefulness and applicability of our approach with several examples. Finally, we show that the equivalence between Bayesian and dominant strategy implementation breaks down when utilities are non-linear or when values are interdependent, multi-dimensional, or correlated.

A geometric approach to mechanism design

We develop a novel geometric approach to mechanism design using an important result in convex analysis: the duality between a closed convex set and its support function. By deriving the support function for the set of feasible interim values we extend the wellknown Maskin-Riley-Matthews-Border conditions for reduced-form auctions to social choice environments. We next refine the support function to include incentive constraints using a geometric characterization of incentive compatibility. Borrowing results from majorization theory that date back to the work of Hardy, Littlewood, and Polya (1929) we elucidate the "ironing" procedure introduced by Myerson (1981) and Mussa and Rosen (1978). The inclusion of Bayesian and dominant strategy incentive constraints result in the same support function, which establishes equivalence between these implementation concepts. Using Hotelling's lemma we next derive the optimal mechanism for any social choice problem and any linear objective, including revenue and surplus maximization. We extend the approach to include general concave objectives by providing a fixed-point condition characterizing the optimal mechanism. We generalize reduced-form implementation to environments with multi-dimensional, correlated types, non-linear utilities, and interdependent values. When value interdependencies are linear we are able to include incentive constraints into the support function and provide a condition when the second-best allocation is ex post incentive compatible.Mechanism design, convex set, support function, duality, majorization, ironing, Hotelling's lemma, reduced-from implementation, BIC-DIC equivalence, concave objectives, interdependent values, second-best mechanisms

Simulating and Modelling Adaptive Walks with the NK Model

This presentation outlines results obtained by simulating adaptive walks using the NK model. We were interested in how the mutation bias affects the distribution of fitness effects and how we could use our results to form theoretical equations to model the behaviour of a walk. Necessary biological background is also described

An on-line solid phase extraction procedure for the routine quantification of urinary methylmalonic acid by liquid chromatography-tandem mass spectrometry

Background: The goal of this study was to develop and to validate an improved isotope-dilution-liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the quantification of methylmalonic acid (MMA) in urine. Methods: A previously described sample preparation protocol requires two solvent extraction steps, including evaporation. The first extraction is to extract the analyte from the sample, and second occurs following derivatization of the extract. In the method described here, the second evaporation step was substituted by on-line solid phase extraction employing column-switching and a permanent co-polymer based extraction cartridge. A standard validation protocol was applied to investigate the performance of the method. Results: The method was found to be linear in the clinically relevant range of concentrations (6-100 mu mol/L). Total coefficients of variation were below 10% and inaccuracy was <10% for quality control samples at three concentrations. Conclusions: By omitting one evaporation step, the semi-automated method described in this article enables for more convenient work-flow in the quantification of urinary MMA compared to the previous protocol. This is of relevance for MMA measurement in the routine clinical laboratory setting. Validation demonstrated acceptable analytical performance. Clin Chem Lab Med 2010;48:1647-50

Identification of histoplasma -specific peptides in human urine

pre-printHistoplasmosis is a severe dimorphic fungus infection, which is often difficult to diagnose due to similarity in symptoms to other diseases and lack of specific diagnostic tests. Urine samples from histoplasma-antigen-positive patients and appropriate controls were prepared using various sample preparation strategies including immunoenrichment, ultrafiltration, high-abundant protein depletion, deglycosylation, reverse-phase fractions, and digest using various enzymes. Samples were then analyzed by nanospray tandem mass spectrometry. Accurate mass TOF scans underwent molecular feature extraction and statistical analysis for unique disease makers, and acquired MS/MS data were searched against known human and histoplasma proteins. In human urine, some 52 peptides from 37 Histoplasma proteins were identified with high confidence. This is the first report of identification of a large number of Histoplasma-specific peptides from immunoassay-positive patient samples using tandem mass spectrometry and bioinformatics techniques. These findings may lead to novel diagnostic markers for histoplasmosis in human urine

Moving the Needle on Literacy: Lessons Learned from a School Where Literacy Rates Have Improved Over Time

Literacy is the most important skill children are required to master during their early school life. At the same time, much has been written about both the inadequate preparation of teachers to teach reading and the ever-increasing number of poor readers in our schools. In this study, we examined teachers’ perceptions of the factors that have contributed to their school’s success in improving children’s literacy scores. We used a sequential explanatory mixed methods research design where Phase 1 involved collecting quantitative data to document the improvement in reading and asking the teachers to fill out a questionnaire, while Phase 2 comprised gathering qualitative data where the principal and a language arts teacher commented on the findings from Phase 1. The results revealed three important themes that teachers perceive contributing to their school’s success. First, teachers collaborate weekly on their own learning, plan instruction together, and provide support for each other. Second, formative assessments are shared within each grade and data are used to inform areas of growth, not to evaluate teachers’ performance. Third, the school focuses on improving reading and believes in the child’s continuous growth. Taken together, the findings of our study suggest that teachers perceive success to be a team effort grounded on theory and the principles of collaborative learning. Keywords: children, literacy, mixed methods, reading, professional development. La littératie constitue l’habileté la plus importante que les enfants doivent maitriser pendant leurs premières années à l’école. Parallèlement, on a beaucoup écrit sur la préparation inadéquate des enseignants en matière d’enseignement de la lecture et sur le nombre croissant d’élèves avec des compétences insuffisantes en lecture. Dans cette étude, nous avons examiné les perceptions qu’ont les enseignants des facteurs ayant contribué à la réussite de leur école dans l’amélioration des compétences des élèves en lecture. Nous avons employé un modèle exploratoire et séquentiel de recherche à méthodes mixtes. Pendant la première phase, nous avons recueilli des données quantitatives afin de documenter l’amélioration en lecture et avons demandé aux enseignants de compléter un questionnaire. La deuxième phase a consisté en la cueillette de données qualitatives ou le directeur de l’école et l’enseignant de langue ont commenté les résultats de la première phase. Les résultats ont révélé trois thèmes importants relatifs aux perceptions des enseignants quant à la réussite de leur école. En premier lieu, les enseignants collaborent de façon hebdomadaire sur leur propre développement, planifient les cours ensemble et s’appuient mutuellement. Deuxièmement, on partage les évaluations formatives entre enseignants de la même année et on étudie les données pour identifier les aspects à améliorer, pas pour évaluer la performance des enseignants. Troisièmement, l’école mise sur l’amélioration de la lecture et croit en l’épanouissement continu des élèves. Globalement, les résultats de notre étude indiquent que les enseignants perçoivent la réussite comme découlant d’un effort collectif ancré dans la théorie et les principes de l’apprentissage collaboratif. Mots clés : enfants, littératie, méthodes mixtes, lecture, développement professionne

Delayed ipsilateral intestinal perforation after endoscopic gastrojejunostomy: A perspective on underlying mechanisms

The endoscopic management for malignant gastric outlet obstruction has expanded with the advent of endoscopic ultrasound-guided gastrojejunostomy. Delayed perforation after endoscopic ultrasound-guided gastrojejunostomy is an important yet rarely reported adverse event, and it is unclear why some patients may suffer this complication. We present a case of intestinal perforation occurring one month after endoscopic ultrasound-guided gastrojejunostomy and discuss potential mechanisms which may contribute to this outcome

Crossfit as modern means of physical education

Physical education is a pedagogical process aimed at physical development, functional improvement of organism, studies of basic efferent skills of vital importance and knowledge related to them for the future successful professional activities