Detection of brown dwarfs by the micro-lensing of unresolved stars

The presence of brown dwarfs in the dark galactic halo could be detected through their gravitational lensing effect and experiments under way monitor about one million stars to observe a few lensing events per year. We show that if the photon flux from a galaxy is measured with a good precision, it is not necessary to resolve the stars and besides more events could be observed.Comment: 14 p., LaTeX, 4 figures available on request, PAR-LPTHE 92 39/LPC 92 1

Beam mismatch effects in Cosmic Microwave Background polarization measurements

Measurement of cosmic microwave background polarization is today a major goal of observational cosmology. The level of the signal to measure, however, makes it very sensitive to various systematic effects. In the case of Planck, which measures polarization by combining data from various detectors, the beam asymmetry can induce a temperature leakage or a polarization mode mixing. In this paper, we investigate this effect using realistic simulated beams and propose a first-order method to correct the polarization power spectra for the induced systematic effect.Comment: Accepted by Astronomy & Astrophysic

Some sources of systematic errors on CMB polarized measurements with bolometers

Some sources of systematic errors, specific to polarized CMB measurements using bolometers, are examined. Although the evaluations we show have been made in the context of the Planck mission (and more specifically the Planck HFI), many of our conclusions are valid for other experiments as well.Comment: Contribution to the International workshop "Background Polarized Emission from Radio to Microwave Wavelengths" October 9-12, 2001, Bologna, Ital

Fast Quantum Algorithm for Solving Multivariate Quadratic Equations

In August 2015 the cryptographic world was shaken by a sudden and surprising announcement by the US National Security Agency NSA concerning plans to transition to post-quantum algorithms. Since this announcement post-quantum cryptography has become a topic of primary interest for several standardization bodies. The transition from the currently deployed public-key algorithms to post-quantum algorithms has been found to be challenging in many aspects. In particular the problem of evaluating the quantum-bit security of such post-quantum cryptosystems remains vastly open. Of course this question is of primarily concern in the process of standardizing the post-quantum cryptosystems. In this paper we consider the quantum security of the problem of solving a system of {\it $m$ Boolean multivariate quadratic equations in $n$ variables} (\MQb); a central problem in post-quantum cryptography. When $n=m$, under a natural algebraic assumption, we present a Las-Vegas quantum algorithm solving \MQb{} that requires the evaluation of, on average, $O(2^{0.462n})$ quantum gates. To our knowledge this is the fastest algorithm for solving \MQb{}

Metadata and Open Access: Reliably Finding Content and Finding Reliable Content

Metadata and open access publishing continue to be topics of debate and discussion in the popular media, blogs, and listservs. Different points of view exist among librarians, researchers, publishers, and others, and several examples will be presented regarding open access journals and articles and digital data from the perspective of metadata and accessibility. Open access content is the utmost accessible content, if students and researchers know how to find it and know how to judge whether what they find is worthy of inclusion in their research. The discussion will focus on how to make open access publications and articles more accessible. Questions the paper will strive to answer are: What metadata elements would help academic librarians and researchers find these resources within the larger databases, institutional repositories, and/or discovery services? How do librarians vet open access publications for research by students and faculty? How do they determine which titles to include in their catalogs and how to catalog them? What additional information would be helpful? What role could publishers of directories and providers of link, search, and discovery services play to that would lead to open access content? How can metadata better describe digital data and make it more accessible to researchers

XMOISE: A Logical Spreadsheet to Elicit Didactic Knowledge

International audienceKnowledge elicitation is a critical problem in computerized learning environments that make use of a knowledge base. Fortunately, contrary to usual expertise elicitation situations, didactic scientific knowledge is quite often well formalized, and authors are used to deal with the logical organization of the domain they teach. We want to propose here an original tool, a logical spreadsheet which, if included in an authoring package, will help authors organize concepts and at the same time make both conception and maintenance of didactic knowledge bases much easier