49,089 research outputs found

    The calibration of interferometric visibilities obtained with single-mode optical interferometers. Computation of error bars and correlations

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    I present in this paper a method to calibrate data obtained from optical and infrared interferometers. I show that correlated noises and errors need to be taken into account for a very good estimate of individual error bars but also when model fitting the data to derive meaningful model parameters whose accuracies are not overestimated. It is also shown that under conditions of high correlated noise, faint structures of the source can be detected. This point is important to define strategies of calibration for difficult programs such as exoplanet detection. The limits of validity of the assumptions on the noise statistics are discussed

    Brief Announcement: Wait-Free Universality of Consensus in the Infinite Arrival Model

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    In classical asynchronous distributed systems composed of a fixed number n of processes where some proportion may fail by crashing, many objects do not have a wait-free linearizable implementation (e.g. stacks, queues, etc.). It has been proved that consensus is universal in such systems, which means that this system augmented with consensus objects allows to implement any object that has a sequential specification. In this paper, we consider a more general system model called infinite arrival model where infinitely many processes may arrive and leave or crash during a run. We prove that consensus is still universal in this more general model. For that, we propose a universal construction based on a weak log that can be implementated using consensus objects

    Book review: activating human rights and peace

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    Activating Human Rights and Peace is an enlightening collection of well thought through cases aimed at academics and students of human rights, political science, law and justice, peace and conflict studies and sociology. It argues that we need to appreciate that cultivating a human rights and peace consciousness is choice-less: there is a moral imperative to engender and sustain an ethical praxis that is motivated by a concern and commitment for how we live with each other. Kristen Perrin notes that each chapter gives a glimpse into the diverse range of ideas encompassing contemporary human rights issues

    Small codimension subvarieties in homogeneous spaces

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    We prove Bertini type theorems for the inverse image, under a proper morphism, of any Schubert variety in an homogeneous space. Using generalisations of Deligne's trick, we deduce connectedness results for the inverse image of the diagonal in X2X^2 where XX is any isotropic grassmannian. We also deduce simple connectedness properties for subvarieties of XX. Finally we prove transplanting theorems {\`a} la Barth-Larsen for the Picard group of any isotropic grassmannian of lines and for the Neron-Severi group of some adjoint and coadjoint homogeneous spaces.Comment: 20 page

    Rational curves on minuscule Schubert varieties

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    Let X be a minuscule Schubert variety and α\alpha a class of 1-cycle on X. In this article we describe the irreducible components of the scheme of morphisms of class α\alpha from a rational curve to X. The irreducible components are described in the following way : the class α\alpha can be seen as an element of Pic(X)∗Pic(X)^* the dual of the Picard group. Because any Weil-divisor need not to be a Cartier-divisor, there is (only) a surjective map s:A1(X)∗→Pic(X)∗s:A^1(X)^*\to Pic(X)^* from the dual of the group of codimension 1 cycles to the dual of the Picard group. The irreducible components are given by the effective elements β\beta in A1(X)∗A^1(X)^* such that s(β)=αs(\beta)=\alpha. The proof of the result uses the Bott-Samelson resolution Y of X. We prove that any curve on X can be lifted in Y (after deformation). This is because any divisor on minuscule Schubert variety is a moving one. Then we prove that any curve coming from X can be deformed so that it does not meet the contracted divisor of Y→XY\to X. This is possible because for minuscule Schubert variety there are lines in the projectivised tangent space to a singularity. It is now sufficient to deal with the case of the orbit of Stab(X)Stab(X) the stabiliser of X and we can apply results of our previous paper math.AG/0003199.Comment: In english, 29 page
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