High-contrast imaging in polychromatic light with the self-coherent camera

Context. In the context of direct imaging of exoplanets, coronagraphs are commonly proposed to reach the required very high contrast levels. However, wavefront aberrations induce speckles in their focal plane and limit their performance. Aims. An active correction of these wavefront aberrations using a deformable mirror upstream of the coronagraph is mandatory. These aberrations need to be calibrated and focal-plane wavefront-sensing techniques in the science channel are being developed. One of these, the self-coherent camera, of which we present the latest laboratory results. Methods. We present here an enhancement of the method: we directly minimized the complex amplitude of the speckle field in the focal plane. Laboratory tests using a four-quadrant phase-mask coronagraph and a 32x32 actuator deformable mirror were conducted in monochromatic light and in polychromatic light for different bandwidths. Results. We obtain contrast levels in the focal plane in monochromatic light better than 3.10^-8 (RMS) in the 5 - 12 {\lambda}/D region for a correction of both phase and amplitude aberrations. In narrow bands (10 nm) the contrast level is 4.10^-8 (RMS) in the same region. Conclusions. The contrast level is currently limited by the amplitude aberrations on the bench. We identified several improvements that can be implemented to enhance the performance of our optical bench in monochromatic as well as in polychromatic light.Comment: 4 pages, 3 figures, accepted in Astronomy & Astrophysics (02/2014

Dynamic Incentive Contracts with Uncorrelated Private Information and History Dependent Outcomes

In existing papers on dynamic incentive contracts, the dynamic structure of the principal-agent relationship arises exclusively from the ability of the principal to learn about the hidden information over time. In this paper we deal with a different source of dynamics, which is considered standard in all areas of economics other than the information literature: we study situations where current opportunities depend on past and current actions, notwithstanding any information conveyed by the actions. Standard examples include investment, Learning by doing , and R&D. In order to focus on this neglected source of dynamics, we restrict our attention to situations involving asymmetric information in each period, but without any intertemporal informational correlation, so that no dynamic effect arises from informational asymmetries directly. This makes comparisons with static results both easier and more interesting. La dynamique des modèles actuels de contrats incitatifs provient de la capacité du principal, à partir des actions observées dans le présent, d'apprendre quelque chose sur l'information qui ne lui sera pas directement accessible dans le futur. Nous étudions ici une autre source de dynamique, négligée dans la littérature sur l'information0501s standard dans toutes les autres branches de la science économique, et qui résulte du fait que les actions courantes définissent les opportunités futures. C'est ce qui se passe lorsqu'il y a investissement, apprentissage, R-D, etc. Pour bien identifier les propriétés dynamiques résultant de ce type de situations dans les modèles de principal-agent avec information asymétrique, nous nous en tenons à des modèles où il n'y a aucune corrélation entre information présente et information future, si bien qu'aucun effet dynamique ne résulte directement de l'asymétrie d'information.Incentive contracts, Dynamic, Asymmetric information, Principal agent relationship, Investment, Learning by doing, Contrats incitatifs, Dynamique, Information asymétrique, Relation principal-agent, Investissement, Learning by doing.

Real Investment Decisions Under Adjustment Costs and Asymmetric Information

We study the cost-of-adjustment model of investment when there is asymmetry of information between owners (the principal) and managers (the agent). Information asymmetry distorts the relationship between investment and the cost of capital for all agent types, and a regime of inaction appears over a certain cost range, in an observationnally different way than when fixed adjustment costs, or irreversibilities, cause a similar phenomenon. Uncertainty, in the form of an increase in the spread of agents' types, tends to reduce investment despite symmetric adjustment cost and perfect competition. The model gives a new interpretation of Tobin's q under asymmetric information, explaining some results of the mergers and acquisition literature.Investment, information asymmetry, adjustment cost, mergers and acquisition

The Taxation of Nonrenewable Natural Resources

We provide an analytical overview of the distortionary eff ects of some common forms of taxes faced by the nonrenewable resources sector of the economy. In the category of taxes meant speci fically to capture the resource rent, we look at a speci c severance tax, an 'ad valorem' severance tax, a profi t tax and a 'lump-sum' tax, with emphasis on their e ffects on the extraction decisions over time and on the initial reserves to be developed. In the category of taxes meant for all sectors of the economy, we look at the corporate income tax and its special provision for the resource sector in the form of a depletion allowance, with emphasis on the eff ects on the intra-industry resource extraction decisions and on the inter-industry allocation of investment

Dynamiques comparées des effets de la taxation minière

Ce texte étudie l’effet de la taxation sur le sentier d’extraction d’une ressource naturelle non renouvelable en situation de concurrence parfaite. Il s’agit d’une synthèse de travaux récents sur le sujet. Quoique le cadre d’analyse soit défini de façon générale, on y traite de façon plus particulière d’une taxe forfaitaire, d’une redevance spécifique, d’une redevance ad valorem, d’une taxe sur les profits et d’ une taxe sur la valeur de la propriété. L’analyse est faite dans un premier temps sous l’hypothèse simplificatrice qu’il n’y a pas d’effet de stock sur les coûts d’extraction, puis reprise pour le cas plus complexe où les coûts d’extraction dépendent de l’extraction cumulée. Un traitement séparé est fait de l’impôt sur le revenu des sociétés, qui nécessite l’introduction explicite du capital dans le modèle.This paper deals with the effect of taxation on the extraction path of a nonrenewable natural resource. It presents a synthesis of some recent papers on the subject. Although the analytical framework is designed to study the effect of quite general forms of taxes, the emphasis is put in the paper on a lump sum or franchise tax, a specific severance tax, an ad valorem severance tax, a profit tax and a tax on the value of the reserves. The analysis is first carried out under the assumption that extraction costs are independent of the stock of the resource; it is then repeated for the more complicated case where extraction costs depend on the remaining reserves. The corporate income tax is treated separately, since it requires the introduction of capital in the model

The Efficient Use of Multiple Sources of a Nonrenewable Resource under Supply Cost Uncertainty

Uncertainties as to future supply costs of nonrenewable natural resources, such as oil and gas, raise the issue of the choice of supply sources. In a perfectly deterministic world, an efficient use of multiple sources of supply requires that any given market exhausts the supply it can draw from a low cost source before moving on to a higher cost one; supply sources should be exploited in strict sequence of increasing marginal cost, with a high cost source being left untouched as long as a less costly source is available. We find that this may not be the efficient thing to do in a stochastic world. We show that there exist conditions under which it can be efficient to use a risky supply source in order to conserve a cheaper non risky source. The benefit of doing this comes from the fact that it leaves open the possibility of using it instead of the risky source in the event the latter’s future cost conditions suddenly deteriorate. There are also conditions under which it will be efficient to use a more costly non risky source while a less costly risky source is still available. The reason is that this conserves the less costly risky source in order to use it in the event of a possible future drop in its cost

Le régime juridique des langues dans l'administration publique au Nouveau-Brunswick

Linguistic rights in New Brunswick have progressed since the enactment of the Official Languages of New Brunswick Act of 1969. The Canadian Charter of Rights and Freedoms has caused the entrenchment of some linguistic guarantees in the Constitution and has provided for judicial enforcement. Collective rights have also been given legislative sanction through the passing, in 1981, of An Act Recognizing the Equality of the Two Official Linguistic Communities in New Brunswick, and new legislation to replace the 1969 Act has now been proposed in a recent government-sponsored study. This paper looks at the legal consequences of these enactments in relation to public administration in New Brunswick