234 research outputs found
Behind the Scenes of the Discovery of Two Extrasolar Planets: ESO Large Programme 666
No full textThis is the story of the Large Programme 666, dedicated to discover sub-stellar objects (extrasolar planets and brown dwarfs), and to measure their masses, radii, and mean densities. We hunt selected OGLE transit candidates using spectroscopy and photometry in the ‘twilight zone’, stretching the limits of what is nowadays possible with the VLT.Fil: Minniti, Dante. Pontificia Universidad Católica de Chile; ChileFil: Melo, Claudio. European Southern Observatory; ChileFil: Naef, Dominique.Fil: Udalski, Andrzej. Warsaw University; PoloniaFil: Pont, Frédéric. Observatoire de Genève; SuizaFil: Moutou, Claire. Laboratoire d’Astrophysique de Marseille; FranciaFil: Santos, Nuno. Universidad de Porto; PortugalFil: Queloz, Didier. Universidad de Porto; PortugalFil: Mazeh, Tsevi. Tel Aviv University; IsraelFil: Gillon, Michel. Observatoire de Genève,; SuizaFil: Mayor, Michel. Observatoire de Genève,; SuizaFil: Udry, Stephane. Observatoire de Genève,; SuizaFil: Diaz, Rodrigo Fernando. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Hoyer, Sergio. Universidad de Chile; ChileFil: Ramírez, Sebastian. Pontificia Universidad Católica de Chile; ChileFil: Pietrzynski, Grzegorz. Warsaw University Observatory; PoloniaFil: Gieren, Wolfgang. Universidad de Concepción; ChileFil: Ruíz, María Teresa. Universidad de Chile; ChileFil: Zoccali, Manuela. Pontificia Universidad Católica de Chile; ChileFil: Tamuz, Omar. Tel Aviv University; IsraelFil: Shporer, Avi. Tel Aviv University; IsraelFil: Kubiak, Marcin. Warsaw University; PoloniaFil: Soszynski, Igor. Warsaw University; PoloniaFil: Szewczyk, Olaf. Warsaw University; PoloniaFil: Szymanski, Michal. Warsaw University; PoloniaFil: Ulaczyk, Krzysztof. Warsaw University; PoloniaFil: Wyrzykowski, Lukasz. University of Cambridge; Reino Unid
Book Reviews
No full text'Searching for a Better Society: The Peruvian Economy from 1950'; Author: by John Sheahan; Reviewer:Raul Hopkins; 'Democratisation in Africa'; Editors: Larry Diamond and Marc F. Plattner; Reviewer: Jan Kees van Donge; 'Exchange Rate Misalignment: Concepts and Measurement for Developing Countries'; Editors: Lawrence E. Hinkle and Peter J. Montiel; Reviewer: Christopher Tsoukis; 'Orangi Pilot Project, Reminiscences and Reflections'; Author: Akhtar Hameed Khan; Reviewer: Jo Beall; 'Whey Governments Waste Natural Resources: Policy Failures in Developing Countries'; Author: William Ascher; Reviewer: Julio Pena-Torres; 'Evaluating Development Aid - Issues, Problems and Solutions'; Author: Basil Cracknell; Reviewer: Mike Faber; 'Development Microeconomics'; Authors: Pranab Bardhan and Christopher Udry; Reviewer: Scott McDonald; 'Economic and Social Changes in Czech Society After 1989: An Alternative View'; Authors: Lubomir Mlcoch, Pavel Machonin and Milan Sojka; Reviewer: Alasdair MacBean; 'Resistance to the Shah: Landowners and Ulama in Iran'; Author: Mohammad Gholi Majd; Reviewer: Rodney Wilson; 'Corruption and Democratisation'; Editors: Alan Doig and Robin Theobald; Reviewer: Heather A. Marquette;Review Books,
Recherche de compagnons de faible masse par optique adaptative
No full textAu cours de cette dernière décennie, le domaine de la recherche et l'étude de compagnons froids autour des étoiles du voisinage solaire s'est beaucoup accéléré. L'étude des compagnons stellaires de faible masse et des compagnons naines brunes apportent d'importantes contraintes sur la compréhension de la formation stellaire. L'étude des systèmes planétaires, quant à elle, permet de comprendre la for-mation de notre propre système solaire. Jusqu'à présent, la technique des vitesses radiales a permis de découvrir la plupart des nouveaux systèmes. Il s'agit d'une méthode indirecte qui ne permet pas l'analyse des photons du compagnon froid. La prochaine étape consiste à analyser directement les photons de compagnons. Pour ce faire, de nombreux projets d'instruments imageurs à haut contraste ont vu le jour récemment. Cette thèse s'inscrit dans la préparation scientifique et le développement de l'un de ces projets: l'instrument SPHERE qui sera installé au Very Large Telescope au Chili en 2012. Dans une première partie, je présente les questions astrophysiques qui motivent la recherche de compagnons d'étoiles ainsi que les deux techniques observationnelles que j'ai utilisé au cours de ma thèse: l'imagerie à haut contraste et la technique des vitesses radiales. Un état des lieux de la recherche des compagnons planétaires, naines brunes et stellaires est également fait. Dans la deuxième partie, je développe les techniques observationnelles ainsi que l'analyse de donnés utilisées. La troisième partie présente une étude sur le désert des naines brunes autour d'étoiles de type solaires sélectionnées dans un échantillon d'étoiles à dérives en vitesses radiales. La quatrième partie développe un travail observationnel qui consiste à essayer de détecter les compagnons planétaires ou naines brunes autour de naines rouges. La dernière partie est consacrée à la présentation de l'instru-ment SPHERE et à ma contribution personnelle à l'étude de cet instrument.ln the last decade, the field of the search and study of cold companions around solar neighborhood stars has greatly improved. The study of low mass stellar compani?ns and brown dwarf companions brings important constraints in the unclerstanding of stellar formation. The study of planetary sys tems allows us to understand the formation of our own solar system. Up to now, most systems were cliscovered with the radial velocities technique. This technique is an indirect method that prevents from analysing the photons of a cold companion. The next step consists in detecting and analysing the photons of such companions. Many projects of high contrast imaging instruments have been re cently cleveloped in orcier to fulfil this task. This thesis was inspired by the scientific preparation and the development of such a project : the SPHERE instrument that will be installed at the Very Large Telescope in Chile in 2012. ln the first part, 1 introduce the astrophysical questions that motivate the search for star companions and de scribe the two observation techniques that 1 used during my PhD : high contrast imaging and radial velocities techniques. A state of art about the status of the search for low mass stellar compa nions, brown clwarf companions and planetary companions is also done. ln the second part, 1 clescribe the observation, data reduction and analysis techniques 1 used. The third part presents a study on the brown dwarf desert around around solar type stars that were selected from a sample of stars with radial velocity drift. ln the fourth part, 1 clevelop an observation work that consists in detecting the planetary or brown dwarf companions around red dwarfs. The last part is devoted to the description of the SPHERE instrument and to my own contribution into this instrumental project.GRENOBLE1-BU Sciences (384212103) / SudocSudocFranceF
Gender, Agricultural Production, and the Theory of the Household.
No full textVirtually all models of the household assume that the allocation of resources is Pareto efficient. Within many African households, agricultural production occurs on many plots controlled by different members of the household. Pareto efficiency implies that factors should be allocated efficiently across these plots. The author finds, in contrast, that plots controlled by women are farmed much less intensively than similar plots within the household controlled by men. The estimates imply that about 6 percent of output is lost because of inefficient factor allocation within the household. The paper suggests a new approach to modeling intrahousehold allocation consistent with the empirical results. Copyright 1996 by University of Chicago Press.
Risk and Insurance in a Rural Credit Market: An Empirical Investigation in Northern Nigeria.
No full textCredit contracts play a direct role in pooling risk between households in northern Nigeria. Repayments owed by borrowers depend on realizations of random shocks by both borrowers and lenders. The paper develops two models of state-contingent loans. The first is a competitive equilibrium in perfectly enforceable contracts. The second permits imperfect information and equilibrium default. Estimates of both models indicate that quantitatively important state-contingent payments are embedded in these loan transactions but that a fully efficient risk-pooling equilibrium is not achieved. The research is based on a year-long survey in Zaria, Nigeria, conducted by the author. Copyright 1994 by The Review of Economic Studies Limited.
Mind the gap
No full textAlthough research offers valuable perspectives on educational practice, the transfer from findings to teaching is reportedly limited. This article explores reasons for this disparity and considers evidence-based teacher education in light of teacher learning. Drawing on personal experience as both teacher trainer and researcher, the author examines how research can be accessible by linking it to teacher inquiry and context, and argues for shifting focus from the perceived research-practice gap towards an approach that seeks to bridge teacher thinking, acting, and becoming
Risk and Saving in Northern Nigeria
No full textThis paper uses data collected by the author to examine the extent to which households in northern Nigeria use asset stocks to smooth their consumption over time in the face of production shocks. The primary question is simple: do households dissave when their farms suffer from negative production shocks? Evidence is presented in support of the thesis that households use their assets as buffer stocks against the receipt of idiosyncratic shocks. Households reduce their saving by economically significant amounts when they receive an adverse shock on their upland plots. In this agricultural economy, asset stocks are used directly in production. A standard model of intertemporal choice is modified in order to account for these direct linkages between saving and production and the consequent implications of consumption-smoothing behavior for households' portfolio choices. In accordance with the model, it is saving in the form of grain stocks (rather than livestock) which is reduced when households are affected by adverse shocks. Moreover, a significant portion of this response is increased net sales of grain contingent upon the realization of an adverse shock. Finally, it is shown that households forecast the receipt of near-future adverse shocks and that they increase current savings in anticipation
An Earth-mass planet orbiting alpha Centauri B
No full textInternational audienceExoplanets down to the size of Earth have been found, but not in the habitable zone--that is, at a distance from the parent star at which water, if present, would be liquid. There are planets in the habitable zone of stars cooler than our Sun, but for reasons such as tidal locking and strong stellar activity, they are unlikely to harbour water-carbon life as we know it. The detection of a habitable Earth-mass planet orbiting a star similar to our Sun is extremely difficult, because such a signal is overwhelmed by stellar perturbations. Here we report the detection of an Earth-mass planet orbiting our neighbour star α Centauri B, a member of the closest stellar system to the Sun. The planet has an orbital period of 3.236 days and is about 0.04 astronomical units from the star (one astronomical unit is the Earth-Sun distance)
Periodicities in the high-mass X-ray binary system RXJ0146.9+6121/LSI+61 235
No full textThe high-mass X-ray binary RX J0146.9+6121, with optical counterpart LS I+61°235 (V831 Cas), is an intriguing system on the outskirts of the open cluster NGC 663. It contains the slowest Be type X-ray pulsar known with a pulse period of around 1400 s and, primarily from the study of variation in the emission line profile of Hα, it is known to have a Be decretion disc with a one-armed density wave period of approximately 1240 d. Here we present the results of an extensive photometric campaign, supplemented with optical spectroscopy, aimed at measuring short time-scale periodicities. We find three significant periodicities in the photometric data at, in order of statistical significance, 0.34, 0.67 and 0.10 d. We give arguments to support the interpretation that the 0.34 and 0.10 d periods could be due to stellar oscillations of the B-type primary star and that the 0.67 d period is the spin period of the Be star with a spin axis inclination of 23+10−8 degrees. We measured a systemic velocity of −37.0 ± 4.3 km s−1 confirming that LS I+61°235 has a high probability of membership in the young cluster NGC 663 from which the system's age can be estimated as 20–25 Myr. From archival RXTE All Sky Monitor (ASM) data we further find ‘super’ X-ray outbursts roughly every 450 d. If these super outbursts are caused by the alignment of the compact star with the one-armed decretion disc enhancement, then the orbital period is approximately 330 d
Happiness as a Driver of Risk-Avoiding Behavior
No full textUnderstanding the reasons why individuals take risks, particularly unnecessary risks, remains an important question in economics. We provide the first evidence of a powerful connection between happiness and risk-avoidance. Using data on 300,000 Americans, we demonstrate that happier individuals wear seatbelts more frequently. This result is obtained with five different methodological approaches, including Bayesian model-selection and an instrumented analysis based on unhappiness through widowhood. Independent longitudinal data corroborate the finding, showing that happiness is predictive of future motor vehicle accidents. Our results are consistent with a rational-choice explanation: happy people value life and thus act to preserve it.risk preferences, seatbelt usage, vehicle accidents, subjective well-being, happiness
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