Amélioration du débit d'évènements, de la qualité des données et de la puissance consommée d'un circuit intégré de photodiodes avalanches monophotoniques

De nos jours, les médecins reposent de plus en plus sur différentes formes d'imagerie médicale pour fournir des diagnostics rapides et fiables aux patients. La tomographie d'émission par positrons (TEP) et la tomodensitométrie (TDM) sont deux modalités d'imagerie largement utilisées en médecine moderne. La TEP permet de suivre le déplacement d'un radiotraceur injecté au patient afin d'observer le métabolisme d'une substance ciblée. La TDM, quant à elle, permet d'imager la densité des différents tissus du corps afin de reconstruire une image structurelle des organes du patient. Bien que ces modalités d'imageries apportent une aide considérable aux médecins, certaines limitations persistent notamment quant à la dose de rayons X utilisés en TDM, ou encore à la durée importante des reconstructions d'images en TEP. Différents groupes de recherches à travers le monde travaillent à l'amélioration de tels scanners notamment quant à l'augmentation du contraste des images ou à la réduction de la dose à laquelle les patients sont exposés. L'utilisation du temps de vol (TDV) des photons constitue une approche prometteuse pour atteindre ces deux objectifs. Le Groupe de recherche en imagerie médicale de Sherbrooke (GRAMS) travaille depuis quelques années au développement de matrices de photodiodes avalanches monophotoniques (PAMP) capables d'atteindre une résolution temporelle de 10 ps. L'approche utilisée consiste à superposer la matrice de PAMP sur le circuit de lecture, ce qui permet d'intégrer des circuits de traitement numérique directement dans le détecteur. Le présent projet consiste à développer la section numérique d'un circuit de lecture optimisé pour une utilisation en TDM à temps de vol. Comme la TDM-TDV en est encore à ses débuts, le circuit de lecture doit extraire le compte de photons reçus à l'intérieur d'une fenêtre temporelle pour chaque pixel du détecteur, et ce, sans perte d'information. Pour s'y faire, les circuits requis seront ajoutés à un circuit intégré optimisé pour la TEP-TDV développé et testé en 2017. Les tests effectués sur ce circuit ont permis de mettre en évidence certains problèmes quant à la linéarité des convertisseurs temps-numérique (CTN). Comme l'algorithme implémenté dans le circuit intégré ne s'attendait pas à des non-linéarités aussi importantes, la conversion des codes de CTN en étampe de temps ne peut être effectuée sans introduire une erreur importante. Ainsi, le projet consiste dans un premier temps à ajouter les fonctionnalités requises pour que le circuit intégré puisse être utilisé dans un scanner TDM-TDV. Dans un second temps, des corrections seront apportées à l'algorithme de conversion en temps de manière à compenser pour les non-linéarités du CTN et ainsi tirer pleinement avantage des fonctionnalités implémentées dans la dernière révision du circuit intégré. Finalement, vu la maturité du circuit de lecture pour la TEP, un effort de réduction de puissance du circuit intégré permettra de le rapprocher d'une intégration dans un scanner complet

Modélisation d'une situation d'apprentissage en termes de connaissances et de règles pour rendre compte de l'activité de l'élève: Etude dans le contexte de l'apprentissage de la lecture en classe

International audienceIn this article, we note that an activity cannot be only defined by its effective form and knowledge of the field concerned which is brought into play. We propose to define an activity by knowledge of the field of training brought into play, by its form but also in what it can influence the state of knowledge of learning and the means that one has to check this impact. We propose here our results of multi-field research carried out around the specification and the modeling of teaching activities in the field of the reading with an aim of building an environment of follow-up of learning. We present the methodology of work practised in the team, the structure of the specifications of activities, the computational models deduced and finally their implementation in an environment from follow-up from learning.Dans cet article, nous constatons qu'une activité ne peut pas être définie uniquement par sa forme effective et les connaissances du domaine visé qui sont mises en jeu. Nous proposons de définir une activité par les connaissances du domaine d'apprentissage mises en jeu, par sa forme mais également en ce qu'elle peut influer l'état de connaissance de l'apprenant et les moyens que l'on a de vérifier cet impact. Nous proposons ici nos résultats de recherche pluridisciplinaire menés autour de la spécification et la modélisation d'activités pédagogiques dans le domaine de la lecture dans le but de construire un environnement de suivi de l'apprenant. Nous présentons la méthodologie de travail pratiquée dans l'équipe, la structure des spécifications d'activités, les modèles computationnels déduits et finalement leur mise en œuvre dans un environnement de suivi de l'apprenant

Multi-core fibre-fed integral-field unit (MCIFU):Overview and first-light

The Multi-Core Integral-Field Unit (MCIFU) is a new diffraction-limited near-infrared integral-field unit for exoplanet atmosphere characterization with extreme adaptive optics (xAO) instruments. It has been developed as an experimental pathfinder for spectroscopic upgrades for SPHERE+/VLT and other xAO systems. The wavelength range covers 1.0 um to 1.6um at a resolving power around 5000 for 73 points on-sky. The MCIFU uses novel astrophotonic components to make this very compact and robust spectrograph. We performed the first successful on-sky test with CANARY at the 4.2 meter William Herschel Telescope in July 2019, where observed standard stars and several stellar binaries. An improved version of the MCIFU will be used with MagAO-X, the new extreme adaptive optics system at the 6.5 meter Magellan Clay telescope in Chile. We will show and discuss the first-light performance and operations of the MCIFU at CANARY and discuss the integration of the MCIFU with MagAO-X.</p

VATs in Federal States: Experiences and Emerging Possibilities

The biggest tax story of the last third of the 20 th century was the value-added tax (VAT). From its tentative beginnings in the reform of the French production tax in the early 1950s, by August 2000 some form of VAT existed in at least 123 countries. Few fiscal innovations have been adopted so widely and so quickly. Towards the close of the century, another striking trend was the increasing decentralization of the public sector in many countries around the world. In this process, increasing responsibility for delivering such important and expensive public services as education and health has been devolved to sub-national governments, often to regional governments such as states or provinces. Such decentralization may make good sense in many respects, but experience suggests that it is essential to devolve responsibility not only for expenditures but also for some significant revenues if adequate fiscal accountability is to be maintained.The traditional literature on tax assignment suggests that the best form of taxation for intermediate-level governments is a sales tax. Some form or another of sales tax does in fact constitute the major source of finance for intermediate governments in many countries. Indeed, in developing countries in which income taxes do not play a major role, it is hard to see what other major revenue sources such governments could utilize. The retail sales tax once favored as a regional tax, and still in place in most U.S. states (and some Canadian provinces) is now an aberrationfrom a worldwide perspective. The only good sales tax is now generally considered to be a VAT.There appear to be at least three reasons why the question of sub-national consumption VATs needs to bereconsidered, particularly in federal countries with important regional governments. First, there are few other major revenue options open to countries in which, for whatever reason, substantial expenditure responsibilities have been shifted to lower levels of government, if those governments are to behave in a fiscally responsible manner. Second, sub-national VATs have now in fact been successfully operating in Canada for a decade and have also existed, if to less general acclaim, in Brazil for over 30 years. Finally, several novel proposals have recently been made to overcome certain problems that some see with applying the system used in Canada to other countries in which tax administration is less well developed.Working Paper Number 01-04

VAT Treatment of public sector bodies: the Canadian model

This paper examines alternatives to the exempt VAT treatment of public bodies, non-profit organizations and charitable organizations (public service bodies). It focuses in particular on the Canadian VAT (the federal Goods and Services Tax) and its treatment of transactions involving public service bodies, including government to government transactions. Under the Canadian Goods and Services Tax rebate system, most supplies made by public service bodies are exempt but such bodies may claim a rebate for GST paid on purchases made to render such supplies. The rebate schedule is flexible and rebate rates may vary according to the nature of the activities and jurisdiction of operation (in the case of subnational VATs such as the Harmonized Sales Tax). The Canadian system therefore provides some compensation for VAT paid in purchases made in the course of providing exempt supplies and mitigates some of the inefficiencies and distributional impacts of a blanket exemption. Tax expenditure data for Canada suggest that this support is important. When compared to alternatives to exemption, the Canadian system lies between the extremes of the New Zealand and EU models. In New Zealand, nearly all transactions involving public service bodies are subject to VAT in the normal way, whereas nearly all such transactions are exempt in the EU, subject to an array of complex rules. The paper closes by arguing that the Canadian rebate system is more efficient and predictable than the EU system and should be given serious consideration as an alternative to that system, assuming that applying a New Zealand-style solution in the EU is far too radical a reform to contemplate

Essays on corporate taxation and the firm

grantor: University of TorontoThree essays treat various issues in understanding and evaluating firm behaviour in response to taxation. Essay I analyzes capital taxation in a dominant firm model. Essay II analyzes corporate tax refunds in an oligopolistic supergame model. Essay III analyzes the impact of tax asymmetries on investment decisions in a neoclassical model. Essay I proposes a two-stage dominant firm model which allows for cost-reducing investment by the dominant firm prior to quantity competition. Market structure is endogenous, and accommodated and impeded entry equilibria with and without underinvestment are characterized. Tax effects are generally consistent with economic theory but special cases arise: for example, (i) small tax changes alter market structure through entry or exit; (ii) some tax changes have no impacts on market variables; and (iii) a subsidy to non-producing fringe is welfare-improving. The analysis emphasizes the importance of market discontinuities. Essay II proposes a particular collusive equilibrium in a repeated oligopoly model with homogeneous quantity-setting firms. The industry sustains tacit collusion by using credible and severe punishments of deviations. The paper focuses on the impact of changing the refundability of tax losses. The analysis of the most collusive equilibrium with losses indicates that a tax policy which increases refundability reduces industry output, increases market price, and therefore strengthens tacit collusion. In addition, the policy increases government revenue and reduces social welfare. Essay III develops theoretical expressions for the user cost of capital in the presence of tax asymmetries. An empirical model is developed to estimate the probability of a given tax status on the basis of firm characteristics. A structural switching regression model of the firm's demand for capital goods is developed next. This model uses estimated probabilities as inputs and is utilized to investigate the potential endogeneity of the cost of capital using a balanced panel of Canadian companies. Results suggest that tax status affects the firms' capital acquisition behaviour.Ph.D

Value-Added Tax Treatment of Public Sector Bodies and Non-Profit Organizations: A Developing Country Perspective

The application of the value-added tax to public sector bodies, non-profit organizations and charitable organizations substantially departs from full taxation in most VAT regimes around the world. The problems with the mostly exempt regime for those organizations are reviewed. Options to modify or replace the regimes are reviewed and assessed from the perspective of developing and transitional economies. The Australian-New Zealand model, where all goods and services supplied by those organizations are within the scope of the tax, emerges as the preferred option. Nevertheless, a gradualist policy may be better suited to the circumstance of many developing and transitional economies.value-added tax, public sector bodies, government, non profit organizations, charitable organizations

Corporation Tax Asymmetries and Cartel Unity

This paper examines the impact of changing the extent to which tax losses are refunded to firms in a model of imperfect competition. It proposes a particular collusive equilibrium in a repeated oligopoly with homogeneous quantity-setting firms. The industry sustains tacit collusion by using credible and severe punishments of deviations. The analysis of the most collusive equilibrium with losses indicates that a tax policy which increases refunds reduces output, increases market price, and therefore strengthens tacit collusion. In addition, the policy increases government revenue. An increase in the corporation tax rate has similar effects. Copyright Kluwer Academic Publishers 2001tax asymmetries, collusive equilibrium, losses, punishment,