Wavefront sensing with a brightest pixel selection algorithm

Astronomical adaptive optics systems with open-loop deformable mirror control have recently come on-line. In these systems, the deformable mirror surface is not included in the wavefront sensor paths, and so changes made to the deformable mirror are not fed back to the wavefront sensors. This gives rise to all sorts of linearity and control issues mainly centred on one question: Has the mirror taken the shape requested? Non-linearities in wavefront measurement and in the deformable mirror shape can lead to significant deviations in mirror shape from the requested shape. Here, wavefront sensor measurements made using a brightest pixel selection method are discussed along with the implications that this has for open-loop AO systems. Discussion includes elongated laser guide star spots and also computational efficiency.Comment: 10 pages, 12 figures, accepted by MNRA

Research notes: Aluminum tolerance in soybean germplasm

Aluminum in the soil solution is a severe growth limiting factor in certain acid soils (Foy, 1964; Long and Foy, 1970). This problem is particularly serious in acid subsoils (Adams and Lund, 1966; Foy, 1964) which are difficult to lime. Recent research has centered on selecting those plant cultivars which demonstrate a degree of tolerance to soil aluminum

In situ monitoring of corrosion processes by coupled micro-XRF/micro-XRD mapping to understand the degradation mechanisms of reinforcing bars in hydraulic binders from historic monuments

International audienceHistoric monuments have been partly built since antiquity with iron or steel reinforcements sealed in mortars or hydraulic binders. But the presence of chloride in the environment can weaken the structures due to the corrosion of these metallic parts, leading to the cracking of the binder. In this context, in order to better understand the first steps of these corrosion mechanisms a chemical cell was designed to operate in situ analyses of the phases precipitated when a chlorinated solution is introduced in the vicinity of the bar. The chemical and structural characterization (micro-XRF and micro-XRD respectively) was performed under synchrotron radiation at the SOLEIL-DiffAbs beamline. Moreover, complementary SEM-EDS analyses were carried out before and after the in situ cell experiment in order to determine the final localisation of the corrosion products inside the crack network. The results show that iron can spread up to 1 mm away from the metallic bar inside the pores of the binder after 44 h of corrosion. Moreover, in accordance with laboratory experiments conducted in solution in the presence of Fe2+ and Cl- ions the reaction pathways conduct to the successive formation of an intermediate Fe(ii)-Fe(iii) chlorinated green rust which transforms into ferric oxyhydroxides such as akaganeite or goethite depending on the local concentration of iron

Mexico City basin wind circulation during the MCMA-2003 field campaign

International audienceMCMA-2003 was a major field campaign investigating the atmospheric chemistry of the Mexico City Metropolitan Area (MCMA) in April of 2003. This paper describes the wind circulation patterns during the campaign both within the Mexico City basin and on the regional scale. ''Time roses'' are introduced to concisely analyze the diurnal wind patterns. Three episode types were identified that explain the conditions encountered: ''O3-South'', ''Cold Surge'' and ''O3-North''. These can be diagnosed from a combination of synoptic and basin observations based on whether the day was predominantly cloudy, or whether the O3 peak was in the north or south of the basin. O3-South days have weak synoptic forcing due to an anti-cyclone over the eastern Pacific. Strong solar heating leads to northerly flows in the basin and an evening shift due to a gap flow from the south-east. Peak ozone concentrations are in the convergence zone in the south of the city. Cold Surge days are associated with ''El Norte'' events, with strong surface northerlies bringing cold moist air and rain. Stable conditions lead to high concentrations of primary pollutants and peak ozone in the city center. O3-North days occur when the sub-tropical jet is closer to Mexico City. With strong westerlies aloft, the circulation pattern is the same as O3-South days except for a wind shift in the mid-afternoon leading to ozone peaks in the north of the city. This classification is proposed as a means of understanding pollutant transport in the Mexico City basin and as a basis for future meteorological and chemical analysis. Furthermore, model evaluation and design of policy recommendations will need to take into account the three episode types

The Locomotion and Energetics of Hatchling Squid, Illex illecebrosus

Although never seen in nature, gelatinous egg masses up to 1 m in diameter containing 10,000 to 100,000 eggs have been produced in captivity by female Illex illecebrosus swimming in mid-water in the 15 m diameter Aquatron pool. When incubated at temperatures between 13 and 26°C these masses produced viable hatchlings whose behaviours were observed and recorded. The hatchlings sink at 5 mm s-1, swim vertically at speeds up to 26 mm s-1, hover and avoid both the surface and the bottom. Metabolie rates estimated from rates of yolk utilization and calculated values for swimming costs were used to predict " critical periods'' or survival times for unfed hatchlings in various temperature and activity regimes. Theseare discussed in relation to the hypothesized role of the Gulf Stream in distribution of the hatchlings of this commercially important but still poorly understood squid species. Potential benefits from vertical migration are suggested and a comparison with Loligo opalescens made

Les objets en plomb découverts sur le site portuaire médiéval de Taillebourg – port d’Envaux

Des prospections subaquatiques menées dans la Charente, sur le site de Taillebourg – Port d’Envaux (17), ont révélé la présence de nombreux témoins d’activités liés au fleuve Charente, datés principalement des périodes mérovingienne et carolingienne. Parmi l’abondant mobilier découvert figure un lot d’objets en plomb.Ces plombs ont été trouvés dans un contexte de pratiques halieutiques. Les premières interprétations les définissent comme des lests d’engins de pêche. La découverte d’un tel corpus est déjà en soi un fait intéressant. En effet, la facilité de recyclage de ce matériau de plaide pas pour sa conservation. L’étude de ce matériel a porté à la fois sur la définition de leur typologie et une première interprétation de leur fonction. En plus des méthodes de classement habituellement utilisées, une approche expérimentale a été menée pour mieux appréhender les techniques de mise en forme utilisées. Des analyses de surface par fluorescence X ont pu être également réalisées. Enfin, le contexte chronologique plaçant cette collection au haut Moyen Âge et la découverte de ce matériel dans la zone d’influence de l’atelier monétaire de Melle nous ont conduit à poser la question de l’origine du plomb métal. Pour répondre à cette interrogation, une série d’analyses isotopique du plomb a été réalisée à partir de la série des plombs naviformes.Subaquaeous surveys carried out in the Charente, on the site Taillebourg – Port Envaux (dept. Charente-Maritime, France) revealed the presence of many evidences in activities related to river Charente, dating mainly from Merovingian and Carolingian periods. A lot of lead objects is found among the abundant furniture.These leads were found in a context of fishing practices. The first interpretations defined as fishing gear. The discovery of such a corpus is itself an interesting fact. Indeed, the tendency of recycling this material does not plead for its preservation. The study of these sinkers has focused both on the definition of their type and initial interpretation of their function. In addition to classified methods usually used, an experimental approach was undertaken to better understand the techniques of production. Surface analysis by X-ray fluorescence were also performed. Finally, the historical context, placing the collection in the High Middle Ages and the discovery of this material in the zone of influence of the mint of Melle led us to the question of the origin of lead metal. To answer this question, a series of lead isotope analysis was carried out from the series of boat-form leads

Dosages par fluorescence X portable d’ateliers médiévaux de production des métaux non-ferreux

La difficulté liée à la détection des ateliers de métallurgie des non-ferreux a conduit à tester un nouveau mode de prospection par spectrométrie de fluorescence X portable. Après une phase de calibration qui a donné de très bons résultats pour les métaux recherchés dans cette étude, trois approches ont été tentées sur le site de Castel-Minier (site minier et pluri métallurgique du second Moyen Âge, Ariège, France). Grâce à un travail interdisciplinaire incluant à la géochimie, l’archéologie, l’histoire et la géophysique, les résultats ont été particulièrement positifs. Ils ont conduit à une meilleure perception chronologique du site, à la localisation d’ateliers de traitement de scorie et la sériation des anomalies géochimiques.Difficulties related to non-ferrous metal workshops detection led to test a new way of survey by a real portable x-ray spectrometer. After a calibration phase which yielded very good results for lead, zinc and cooper, three approaches were tried in south-west of France at the site of Castel-Minier, (mining and multi metallurgical site from the second Middle Ages). Thanks to an interdisciplinary work that include geochemistry, archeology, history and geophysic, the results were particularly positive. They led to a better understanding of chronological phases. They give the location of slag processing workshops and classification of geochemical anomalies

In situ measurements of speciated atmospheric mercury and the identification of source regions in the Mexico City Metropolitan Area

In order to expand the currently limited understanding of atmospheric mercury source-receptor relationships in the Mexico City Metropolitan Area, real time measurements of atmospheric mercury were made at a downtown urban site, and a rural site on the outskirts of Mexico City, during March 2006. Numerous short-lived increases in particulate mercury (PHg) and reactive gaseous mercury (RGM) concentrations were observed at the urban site during the 17 day study, and less frequent increases in gaseous elemental mercury (GEM) concentrations were measured at both the urban and rural sites. The episodic increases observed were attributed to plume impacts from industrial point source emissions in and around Mexico City. Average concentrations and standard deviations measured during the study were as follows: i) urban site; PHg=187±300 pg m−3 [m superscript -3], RGM=62±64 pg m−3 [m superscript -3], GEM=7.2±4.8 ng m−3 [m superscript -3], and; ii) rural site; GEM=5.0±2.8 ng m−3 [m superscript -3]. Several source regions of atmospheric mercury to the urban and rural sites were determined using Concentration Field Analysis, in which atmospheric mercury measurements were combined with back trajectory data to determine source regions. Only some source regions correlated to mercury emission sources listed in the Federal Pollutant Release and Transfer Register, leaving the rest unaccounted for. Contributions of anthropogenic mercury point sources in and around Mexico City to concentration averages measured at the urban site during the study were estimated to be: 93±3% of reactive mercury (PHg and RGM), and; 81±0.4% of GEM. Point source contributions to GEM measured at the rural site were 72±1%. GEM and reactive mercury (PHg+RGM) were not found to correlate with biomass burning at either of the measurement sites.National Science Foundation (U.S.) (Grant 0514280)National Science Foundation (U.S.) (Grant 0511803)Science to Achieve Results Program (U.S.) (Grant R829798)United States. Environmental Protection Agenc

A New Strategy for Deep Wide-Field High Resolution Optical Imaging

We propose a new strategy for obtaining enhanced resolution (FWHM = 0.12 arcsec) deep optical images over a wide field of view. As is well known, this type of image quality can be obtained in principle simply by fast guiding on a small (D = 1.5m) telescope at a good site, but only for target objects which lie within a limited angular distance of a suitably bright guide star. For high altitude turbulence this 'isokinetic angle' is approximately 1 arcminute. With a 1 degree field say one would need to track and correct the motions of thousands of isokinetic patches, yet there are typically too few sufficiently bright guide stars to provide the necessary guiding information. Our proposed solution to these problems has two novel features. The first is to use orthogonal transfer charge-coupled device (OTCCD) technology to effectively implement a wide field 'rubber focal plane' detector composed of an array of cells which can be guided independently. The second is to combine measured motions of a set of guide stars made with an array of telescopes to provide the extra information needed to fully determine the deflection field. We discuss the performance, feasibility and design constraints on a system which would provide the collecting area equivalent to a single 9m telescope, a 1 degree square field and 0.12 arcsec FWHM image quality.Comment: 46 pages, 22 figures, submitted to PASP, a version with higher resolution images and other supplementary material can be found at http://www.ifa.hawaii.edu/~kaiser/wfhr