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81.
Suzanna Randall Gilles Fontaine Elizabeth Green Dave Kilkenny Lisa Crause Oliver Cordes Simon O’Toole Lázló Kiss Bi-Qing For Pierre-Olivier Quirion 《Astrophysics and Space Science》2004,291(3-4):465-471
We report on the outcome of the first major multi-site campaign on a long-period variable subdwarf B star. The target PG 1627+017 was observed for a total of 334 h during April/May/June 2003 from the lynchpin observatory at Mt. Bigelow, Arizona, with important contributions coming from co-observations at SAAO, Calar Alto and Siding Spring. Preliminary analysis indicates the presence of 8–10 probable periods in the range ~4500 to ~8900 s with relative amplitudes between 0.1 and 0.5%;. The range over which the periods are found is in qualitative agreement with theoretical predictions and the number of periods found shows potential for an in-depth asteroseismological analysis. Multi-colour observations show that the relative amplitudes of pulsation are larger in the U-band than in the R, which again is in agreement with theory. However, more multi-colour observations are needed to be able to make statements at the quantitative level. 相似文献
82.
Andrew Steele David t. Goddard Dave Stapleton Jan k. w. Toporski Vanessa Peters Virginia Bassinger George Sharples David d. Wynn‐Williams David s. Mckay 《Meteoritics & planetary science》2000,35(2):237-241
Abstract— Examination of fracture surfaces near the fusion crust of the martian meteorite Allan Hills (ALH) 84001 have been conducted using scanning electron microscopy (SEM) and atomic force microscopy (AFM) and has revealed structures strongly resembling mycelium. These structures were compared with similar structures found in Antarctic cryptoendolithic communities. On morphology alone, we conclude that these features are not only terrestrial in origin but probably belong to a member of the Actinomycetales, which we consider was introduced during the Antarctic residency of this meteorite. If true, this is the first documented account of terrestrial microbial activity within a meteorite from the Antarctic blue ice fields. These structures, however, do not bear any resemblance to those postulated to be martian biota, although they are a probable source of the organic contaminants previously reported in this meteorite. 相似文献
83.
Lauren Hutchison Paul Montagna Dave Yoskowitz Damion Scholz Jace Tunnell 《Estuaries and Coasts》2015,38(1):67-80
The goal of the current study was to document local stakeholder perceptions of ecosystem services provided by coastal habitats and to incorporate values of ecosystem services into an ecosystem-based management plan. A second goal was to identify and quantify ecosystem service supply at the local level, which is a knowledge gap identified by the Millennium Ecosystem Assessment. Ecosystem services were quantified as stakeholder perceptions of values. To identify local stakeholder perceptions of coastal habitat ecosystem services, a workshop was conducted at which stakeholders were asked to complete surveys. Data from the surveys were used to create a spatial representation of the number of ecosystem services provided by habitats in the form of a heat map. Results of the study were incorporated into an ecosystem-based management plan to enable stakeholders and managers to make better-informed decisions regarding priority areas for conservation, preservation, and restoration. The methods used in this study can be expanded to develop future ecosystem-based management plans. 相似文献
84.
85.
John M. Zachara Ravi K. Kukkadapu Tanya Peretyazhko Mark Bowden Chongmin Wang Dave W. Kennedy Dean Moore Bruce Arey 《Geochimica et cosmochimica acta》2011,75(21):6330-6349
Bioreduced anthraquinone-2,6-disulfonate (AH2DS; dihydro-anthraquinone) was reacted with a 2-line, Si-substituted ferrihydrite under anoxic conditions at neutral pH in PIPES buffer. Phosphate (P) and bicarbonate (C); common adsorptive oxyanions and media/buffer components known to effect ferrihydrite mineralization; and Fe(II)aq (as a catalytic mineralization agent) were used in comparative experiments. Heterogeneous AH2DS oxidation coupled with Fe(III) reduction occurred within 0.13-1 day, with mineralogic transformation occurring thereafter. The product suite included lepidocrocite, goethite, and/or magnetite, with proportions varing with reductant:oxidant ratio (r:o) and the presence of P or C. Lepidocrocite was the primary product at low r:o in the absence of P or C, with evidence for multiple formation pathways. Phosphate inhibited reductive recrystallization, while C promoted goethite formation. Stoichiometric magnetite was the sole product at higher r:o in the absence and presence of P. Lepidocrocite was the primary mineralization product in the Fe(II)aq system, with magnetite observed at near equal amounts when Fe(II) was high [Fe(II)/Fe(III)] = 0.5 and P was absent. P had a greater effect on reductive mineralization in the Fe(II)aq system, while AQDS was more effective than Fe(II)aq in promoting magnetite formation. The mineral products of the direct AH2DS-driven reductive reaction are different from those observed in AH2DS-ferrihydite systems with metal reducing bacteria, particularly in presence of P. 相似文献
86.
Hugh Davies Paul Weber Phil Lindsay Dave Craw Barrie Peake James Pope 《Applied Geochemistry》2011,26(12):2121-2133
The Mangatini Stream drains a coal mining area in the mountains of northwestern South Island of New Zealand. Abundant rainfall on pyritic rocks yields acid mine drainage (AMD) to the stream, which flows through a steep gorge at discharges that rapidly increase from <1 to >100 m3/s during frequent rain events. The AMD is treated with finely ground limestone, which is discharged as a slurry at a point in the middle of the gorge. The limestone slurry mixes and reacts with the AMD during flow ∼4 km downstream over ∼12 h. Neutralisation reactions increase stream pH from near 3 (untreated Mangatini Stream water impacted by AMD) to 5–6 in the first 250 m downstream, although mixing is commonly incomplete in this zone. Large stream discharge volumes in rain events dilute the neutralising material input, thus driving the pH back towards 4 downstream of treatment. More complete neutralisation is achieved 4 km downstream, even in major rain events, and pH can rise to >7. Partial neutralisation is sufficient to remove most of the dissolved Fe(III) (typically ∼30 mg/L) from the Mangatini Stream in the first 10 m, and remaining dissolved Fe is essentially all Fe(II), which decreases over time as it oxidises and precipitates. Dissolved Al in the Mangatini Stream (typically ∼50 mg/L) decreases steadily downstream over ∼100 m in the limestone mixing zone. Precipitated Fe and Al form amorphous oxyhydroxides that are transported as suspended solids and deposited on the stream bed with excess limestone in zones of low flow velocity. Dissolved Zn is removed from solution by adsorption to Fe oxyhydroxide when pH reaches ∼5, but dissolved Ni remains in solution despite the neutralisation process. Gypsum precipitation occurs throughout the limestone mixing zone, resulting in at least 30% decrease in dissolved . Minor ettringite forms in the first 100 m, but then probably redissolves. The limestone dosing system is an effective method of neutralising the effects of AMD and removing most dissolved metals in a steep mountain stream with frequent rain events where this dynamic environment places many constraints on treatment options. 相似文献
87.
The DigitalOcean (DO) Project is designed to bring essential Web 2.0 capabilities to an open-source software platform built
for scientific collaboration and publishing. The DO platform is being built using the Drupal content management system (CMS).
The following are some of the core features of the proposed platform: social networking, media/data sharing/publishing, and
collaboration spaces for scientific virtual organizations (VO); active support for VO governance and reputation systems for
members and objects; Creative Commons licensing, support for preprint archives and micro-articles, and; professional user-profiles
that can be saved as well formatted biosketches. The DO platform serves as a collaboration environment for active research
teams, a personal repository for individual researchers, an aggregation/filter for science information, and a scientific publishing
tool. This article will outline the history and goals of the DO Project, the core technology concerns and solutions, and the
opportunities that this new platform will bring to scientists across the planet. 相似文献
88.
Richard Dekany Roger Angel Keith Hege Dave Wittman 《Astrophysics and Space Science》1994,212(1-2):299-319
Traditional astrometric methods are limited in accuracy by the atmosphere in a way that does not show much improvement with increased telescope aperture. However, there is the potential for very high accuracy with large telescopes if advantage can be taken of these factors: First, the differential atmospheric distortion of images of closely adjacent stars is less with larger aperture; second, the diffraction limit is sharper, and third, photon statistics are improved. In this paper we analyze and give experimental tests of techniques that could be applied to the detection of planets with the mass of Jupiter or Uranus, if they are present in nearby binary star systems.The atmospheric perturbation of the relative position of the energy centroids measured in short exposure images of binary stars depends on the effective height of the turbulent distortion. For a 4-meter telescope, the error in centroid determination of a 4-arcsec binary can be as small as 20 milliarcsec (mas) in a single 20-millisecond (msec) exposure. The relative position measured by cross-correlation of short exposure speckle images, as suggested by McAlister (1977b), may give even higher accuracy. In this case, Roddier (Roddieret al., 1980) has shown that the atmospheric error depends on the thickness rather than the height of the layers that make the dominant contribution to the turbulence. Through Monte Carlo analysis we show that on occasions when the turbulence arises largely in a thin layer, a single 20-msec exposure of a 4-arcsec binary taken with a 4-m aperture can yield an astrometric accuracy of order 0.5 mas.We report on experiments made at the Steward Observatory 2.3-m telescope which achieved accuracies corresponding to 1.7 mas in a 2.24-arcsec binary and 16.1 mas in a 6.0-arcsec binary with only 15 and 18 specklegram pairs respectively. We plan to use the 6.5-m converted MMT to obtain much higher performance, between 4.0 mas and 0.40 masper independent specklegram pair, depending upon atmospheric conditions, for binaries of 4-arcsec separation. By cycling rapidly through perhaps 100 binaries, thus calibrating systematic errors through the average change in binary separation, Jupiter-mass planets may be detectable with small but regular access to the telescope.Paper presented at the Conference onPlanetary Systems: Formation, Evolution, and Detection held 7–10 December, 1992 at CalTech, Pasadena, California, U.S.A. 相似文献
89.
Ralph Spencer Roshene Mccool Bryan Anderson Dave Brown Mike Bentley 《Experimental Astronomy》2004,17(1-3):221-228
ALMA, EVLA and e-MERLIN use high data rate optical fibre links based on commercially available 10 Gbps opto-electronics. This paper describes the systems designed by NRAO and JBO staff to be used in ALMA and e-MERLIN. ALMA has a requirement for a 120 Gbps data rate per telescope, requiring the use of 12 lasers in the 1550 nm telecommunication band, with maximum link lengths around 20 km. e-MERLIN has a lower bandwidth and requires 30 Gbps links per telescope and therefore three lasers per telescope; however, the link lengths reach up to around 400 km, and amplification, de-dispersion and regeneration are required. Dense wavelength division multiplexing is used to avoid fibre management problems and save fibre costs. The design criteria and experience gained in these projects is very relevant to SKA as the proposed configuration of the antenna elements maps well to the link lengths used here. The chosen data rate will be a major cost driver. 相似文献
90.
Lithologically controlled invisible gold,Yukon, Canada 总被引:1,自引:0,他引:1