Discovery of high proper motion ancient white dwarfs: nearby massive compact halo objects?

We present the discovery and spectroscopic identification of two very high proper motion ancient white dwarf stars, found in a systematic proper motion survey. Their kinematics and apparent magnitude clearly indicate that they are halo members, while their optical spectra are almost identical to the recently identified cool Halo white dwarf WD0346+246. Canonical stellar halo models predict a white dwarf volume density of two orders of magnitude less than the approx 7*10^{-4} Solar masses per pc^{-3} inferred from this survey. With the caveat that the sample size is very small, it appears that a significant fraction, about 10%, of the local dark matter halo is in the form of very old, cool, white dwarfs.Comment: 8 pages, 2 figures, accepted for publication in ApJL; references adde

Perceptions et stratégies d’adaptation aux changements climatiques : le cas des communes d’Adjohoun et de Dangbo au Sud-Est Bénin

La présente étude met en exergue la variable humaine, responsable des perturbations climatiques suite aux actions anthropiques. Elle a été conduite dans deux communes de la vallée de l’Ouémé, compte tenu de leurs nombreuses potentialités hydro‑agricoles et de leur vulnérabilité aux intenses activités agricoles. La méthodologie de recherche comprend : une étude exploratoire permettant de choisir les villages sur la base de critères tels que la toposéquence et l’importance des activités agricoles, une phase d’enquêtes approfondies avec l’administration de questionnaires structurés auprès de 70 producteurs, des entretiens semi-structurés, informels individuels et de groupes, des transects participatifs et une triangulation de sources d’informations complémentaires. Les analyses de perceptions et stratégies d’adaptation ont été faites avec les populations et SAS a été utilisé pour l’analyse en composantes principales. Les résultats révèlent que les producteurs perçoivent et vivent les effets des changements climatiques avec pour conséquences de profonds bouleversements socio-économiques ces quinze dernières années. Ces bouleversements concernent les précipitations caractérisées par des séquences d’inondation, de sècheresse prolongée, de fortes températures et une fréquence élevée des vents violents. Les causes de ces changements sont attribuées aux bouleversements des normes sociales et les petits producteurs sont les plus vulnérables. Diverses stratégies développées comprennent l’adoption de variétés à cycles plus courts, la mise en valeur de différentes unités de paysage, l’intensification de l’utilisation des engrais chimiques, la diversification des sources de revenus.Perceptions and strategies of adaptation to climate changes : the cases of Adjohoun and Dangbo districts in South-East BeninThis study focuses on human variable as responsible for climate change. It was carried out in two districts of Ouémé Valley based on its numerous hydro-agricultural potentialities and their vulnerability to intensified agricultural activities. The research methodology includes an exploratory study which enabled to choose villages based on criteria such as toposequence, and the importance of agricultural activities ; in-depth survey with the administration of a structured questionnaire to 70 small-scale individual farmers ; semi structured, informal individual and focus group interviews, participatory transect walks and triangulation of complementary information sources. The analysis of perceptions and adaptation strategies were jointly made with interviewed farmers and SAS was used to analyse main components. The results revealed that farmers perceived and acknowledged climate change effects, which brought about serious socio-economic upheavals the last fifteen years. These upheavals relate to erratic precipitations characterized with sequences of flooding, lengthened drought, higher temperature and increased frequency of violent wind. The causes of this climate change were attributed to the disruption of social norms and values and small-scale farmers are the most vulnerable. Various developed strategies include : use of extra early maturing varieties, cultivation of different toposequences, application of additional chemical fertilisers, diversification sources of income

Long Period Variables in the Magellanic Clouds: OGLE + 2MASS + DENIS

(abridged) The 68000 I-band light curves of variable stars detected by the OGLE survey in the Large and Small Magellanic Clouds (MCs) are fitted by Fourier series, and also correlated with the DENIS and 2MASS databases and with lists of spectroscopically confirmed M-, S- and C-stars. Lightcurves and the results of the lightcurve fitting (periods and amplitudes) and DENIS and 2MASS magnitudes are presented for 2277 M-,S-,C-stars in the MCs. The following aspects are discussed: the K-band period-luminosity relations for the spectroscopically confirmed AGB stars, period changes over a timespan of about 17 years in a subset of about 400 LPVs, and candidate obscured AGB stars.Comment: Astronomy and Astrophysics, accepte

An automated system for fast transfer and injection of hyperpolarized solutions

Dissolution dynamic nuclear polarization (dDNP) has become a hyperpolarization method of choice for enhancing nuclear magnetic resonance (NMR) signals. Nuclear spins are polarized in solid frozen samples (in a so-called polarizer) that are subsequently dissolved and transferred to an NMR spectrometer for high sensitivity detection. One of the critical challenges of dDNP is that it requires both a fast transfer to limit nuclear spin relaxation losses as well as stability to guarantee high resolution (no bubbles nor turbulences). Here we describe the design, construction and performances of such a transfer and injection system, that features a 5 m/s speed and sub-Hz spectral resolution upon arrival at the detection spot. We demonstrate the use of such a system for inter-magnet distances of up to 10 m

Enumeration of permutations sorted with two passes through a stack and D_8 symmetries

We examine the sets of permutations that are sorted by two passes through a stack with a $D_8$ operation performed in between. From a characterization of these in terms of generalized excluded patterns, we prove two conjectures on their enumeration, that can be refined with the distribution of some statistics. The results are obtained by generating trees.On étudie les ensembles de permutations qui sont triées par deux passages dans une pile séparés par une opération du groupe $D_8$. À partir d'une caractérisation de ces ensembles en termes de motifs exclus généralisés, on démontre deux conjectures sur leur énumération, qui peuvent être raffinées par la distribution de certaines statistiques. Ces résultats sont obtenus à l'aide d'arbres de génération

Doubly alternating Baxter permutations are Catalan

The Baxter permutations who are alternating and whose inverse is also alternating are shown to be enumerated by the Catalan numbers. A bijectio

Doubly alternating Baxter permutations are Catalan

The Baxter permutations who are alternating and whose inverse is also alternating are shown to be enumerated by the Catalan numbers. A bijection to complete binary trees is also given