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341.
Z. Martins J. S. Watson M. A. Sephton O. Botta P. Ehrenfreund I. Gilmour 《Meteoritics & planetary science》2006,41(7):1073-1080
Abstract— We have analyzed an important fraction of the free carboxylic acids present in water extracts of the CM2 chondrite Murchison and the CI1 chondrite Orgueil using gas chromatographymass spectrometry (GC‐MS). The free nature of the carboxylic acids analyzed was ensured by employing a single‐step water extraction. Analyses revealed the presence of a structurally diverse suite of both aliphatic and aromatic acids in Murchison, while Orgueil exhibits a simpler distribution of exclusively aromatic acids. Within the Murchison aromatic acids, there are previously unreported phthalic acids, methyl phthalic acids, and hydroxybenzoic acids. In Orgueil, benzoic acid and very small amounts of methylbenzoic acids and methylhydroxybenzoic acids were detected. For the aromatic acids in both Murchison and Orgueil, most structural isomers were identified, suggesting an origin by abiotic processes. Quantitative differences are evident between acids in the two meteorites; carboxylic acids are much more abundant in Murchison than in Orgueil. The data suggest that differing levels of aqueous alteration on the meteorite parent body(ies) has produced dissimilar distributions of carboxylic acids. 相似文献
342.
Source subtraction for the extended Very Small Array and 33-GHz source count estimates 总被引:1,自引:0,他引:1
Kieran A. Cleary † Angela C. Taylor ‡ Elizabeth Waldram Richard A. Battye Clive Dickinson § Rod D. Davies Richard J. Davis Ricardo Genova-Santos Keith Grainge Michael E. Jones ¶ Rüdiger Kneissl G. G. Pooley Rafael Rebolo José Alberto Rubiño-Martín Richard D. E. Saunders Paul F. Scott Ane Slosar David Titterington Robert A. Watson 《Monthly notices of the Royal Astronomical Society》2005,360(1):340-353
We describe the source subtraction strategy and observations for the extended Very Small Array (VSA), a cosmic microwave background interferometer operating at 33 GHz. A total of 453 sources were monitored at 33 GHz using a dedicated source subtraction baseline. 131 sources brighter than 20 mJy were directly subtracted from the VSA visibility data. Some characteristics of the subtracted sources, such as spectra and variability, are discussed. The 33-GHz source counts are estimated from a sample selected at 15 GHz. The selection of VSA fields in order to avoid bright sources introduces a bias into the observed counts. This bias is corrected and the resulting source count is estimated to be complete in the flux-density range 20–114 mJy. The 33-GHz source counts are used to calculate a correction to the VSA power spectrum for sources below the subtraction limit. 相似文献
343.
344.
A thermobarometer for sphene (titanite) 总被引:9,自引:0,他引:9
Leslie A. Hayden E. Bruce Watson David A. Wark 《Contributions to Mineralogy and Petrology》2008,155(4):529-540
Sphene and zircon are common accessory minerals in metamorphic and igneous rocks of very different composition from many different
geological environments. Their essential structural constituents, Ti and Zr, are capable of replacing each other to some degree.
In this paper we detail the results of high pressure–temperature experiments as well as analyses of natural sphene crystals
that establish a systematic relationship between temperature, pressure and Zr concentration in sphene. Calibrations of the
temperature and pressure relationships are presented as a thermobarometer. Synthetic sphene crystals were crystallized in
the presence of zircon, quartz and rutile at 1–2.4 GPa and 800–1,000°C from hydrothermal solutions. Crystals were analyzed
for Zr by electron microprobe (EMP). The experimental results define a log-linear relationship between equilibrium Zr content
(ppm by weight), pressure (GPa) and reciprocal absolute temperature:
The incorporation of Zr into sphene was found to be rather sensitive to pressure effects and also to the effects of kinetic
disequilibrium and growth entrapment that result in sector zoning. The Zr content of sphene is relatively insensitive to the
presence of both REEs and F-Al substitutions in sphene. To supplement and test the experimental data, sphenes from seven rocks
of well-constrained origin were analyzed for Zr by both EMP and ion microprobe (IMP). The sphene thermobarometer records crystallization
temperatures that are consistent with independent thermometry. When applied to natural sphene of unknown origin or growth
conditions, this thermobarometer has the potential to estimate temperatures with an approximate uncertainty of ±20°C over
the temperature range of interest (600–1,000°C). The Zr-in-sphene thermobarometer can also be used in conjunction with the
Zr-in-rutile thermobarometer to estimate both pressure and temperature of crystallization.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.
相似文献
Leslie A. HaydenEmail: |
345.
346.
L. Ignacio Vilchis Lisa T. Ballance William Watson 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(1):125-140
Considerable evidence exists, showing an accelerated warming trend on earth during the past 40–50 years, attributed mainly to anthropogenic factors. Much of this excess heat is stored in the world's oceans, likely resulting in increased environmental variability felt by marine ecosystems. The long-term effects of this phenomenon on oceanic tropical ecosystems are largely unknown, and our understanding of its effects could be facilitated by long-term studies of how species compositions change with time. Ichthyoplankton, in particular, can integrate physical, environmental and ecological factors making them excellent model taxa to address this question. While on eight (1987–1990, 1992 and 1998–2000) NOAA Fisheries cruises to the eastern Pacific warm pool, we characterized the thermal and phytoplankton pigment structure of the water column, as well as the neustonic ichthyoplankton community using CTD casts and Manta (surface) net tows. Over the 13-year period, 852 CTD and Manta tow stations were completed. We divided the study area into three regions based on regional oceanography, thermocline depth and productivity, as well as a longitudinal gradient in species composition among stations. We then analyzed temporal trends of ichthyoplankton species composition within each region by pooling stations by region and year and making pairwise comparisons of community similarity between all combinations of the eight cruises within each region. We also identified environment-specific species assemblages and station groupings using hierarchical clustering and non-metric multi-dimensional scaling (MDS). Our analyses revealed a longitudinal gradient in community structure and temporal stability of ichthyoplankton species composition. Over the 13 years ichthyoplankton assemblages in the two westernmost regions varied less than in the eastern region. MDS and cluster analyses identified five ichthyoplankton assemblages that corresponded to oceanographic habitats and a gradient in community composition. We hypothesize that the changes in thermocline depth during the El Niños of 1987–1988, 1997–1998 and the extended period of warmth during 1990–1994 altered productivity sufficiently to cause a shift in the abundances of foundation species of the upwelling systems of the eastern Pacific warm pool. Our study suggests that ichthyoplankton assemblages in oligotrophic waters are more resilient to changes in the thermocline than assemblages in upwelling regions; or that oligotrophic regions simply have less physical variation compared to upwelling regions. 相似文献
347.
Stephen J. Brooks Vivienne J. Jones Richard J. Telford Peter G. Appleby Emily Watson Suzanne McGowan Stuart Benn 《Journal of Paleolimnology》2012,47(4):631-644
Loch Ruthven holds the largest British population of the rare water-bird Podiceps auritus, the Slavonian or horned grebe. The breeding success of this bird has fluctuated annually since records began in 1970. To
investigate whether these trends are linked to the abundance of chironomid midges, which are an important food-source for
the grebe chicks, we analysed a sediment core from the lake, which was sliced at 2.5-mm intervals and provided near-annual
sampling resolution. We also analysed diatoms and algal pigments in the lake sediments and inferred changes in total phosphorus
from the diatom assemblage to determine whether changes in lake productivity have influenced the abundance of chironomids.
Trends in grebe productivity, chironomid abundance and algal assemblages were compared against climate data to determine whether
climate, specifically, the North Atlantic Oscillation, was the ultimate driver of the trends we recorded. Our results show
that grebe breeding success is positively correlated with chironomid abundance and chironomid abundance is positively correlated
with diatom-inferred total phosphorus. Lake productivity and chironomid abundance began to rise early in the twentieth century
and continued to rise on a steeper trajectory from the mid-twentieth century to the present. Since the mid-1960s, chironomid
abundance began to fluctuate erratically and since 1970 was in phase with grebe productivity, with the grebe trends most plausibly
lagging by 1 year. These trends appear to correlate with inter-annual fluctuations in diatom-inferred total phosphorus. No
correlation was found between grebe productivity or chironomid abundance and climate variables, suggesting that the size of
the chironomid population and breeding success of Podiceps auritus at Loch Ruthven is resource-linked. 相似文献
348.
Jun-Ji Cao Chong-Shu Zhu Judith C. Chow John G. Watson Yong-Ming Han Ge-hui Wang Zhen-xing Shen Zhi-Sheng An 《Atmospheric Research》2009,94(2):194-202
Aerosol black carbon (BC) was measured every 5 min at Xi'an, China from September 2003 to August 2005. Daily BC concentrations ranged from 2 to 65 μg m− 3, averaging 14.7 ± 9.5 μg m− 3 and displayed clear summer minima and winter maxima. BC typically peaked between 0800 and 1000 LST and again between 2000 and 2200 LST, corresponding with morning and evening traffic combined with nighttime residential cooking and heating. The nocturnal peak was especially evident in winter, when more domestic heating is used and pollutant-trapping surface-inversions form earlier than in summer. BC frequency distributions the most commonly occurring concentrations occurred between 5 and 10 μg m− 3 in all four seasons. BC ranged from 1.6% and 15.6%, and averaged 8.3% of PM2.5. A clear inverse relationship between BC and wind speed (WS) was found when WS was below 2.5 to 3.0 m s− 1, implying a local origin for BC. Mixed layer depths (MLDs) were shallower during BC episodes compared to cleaner conditions. 相似文献
349.
Judith C. Chow John G. Watson Douglas H. Lowenthal Karen L. Magliano 《Atmospheric Research》2008,90(2-4):243-ICNAA07
Aerosol size distributions were measured with Micro Orifice Uniform Deposit Impactor (MOUDI) cascade impactors at the rural Angiola and urban Fresno Supersites in California's San Joaquin Valley during the California Regional PM10/PM2.5 Air Quality Study (CRPAQS) winter campaign from December 15, 2000 to February 3, 2001. PM2.5 filter samples were collected concurrently at both sites with Sequential Filter Samplers (SFS). MOUDI nitrate (NO3−) concentrations reached 66 μg/m3 on January 6, 2001 during the 1000–1600 PST (GMT-8) period. Pair-wise comparisons between PM2.5 MOUDI and SFS concentrations revealed high correlations at the Angiola site (r > 0.93) but more variability (r < 0.85) at the Fresno site for NO3−, sulfate (SO4=), and ammonium (NH4+). Correlations were higher at Fresno (r > 0.87) than at Angiola (r < 0.7) for organic carbon (OC), elemental carbon (EC), and total carbon (TC). NO3− and SO4= size distributions in Fresno were multi-modal and wider than the uni-modal distributions observed at Angiola. Geometric mean diameters (GMD) were smaller for OC and EC than for NO3− and SO4= at both sites. OC and EC were more concentrated on the lowest MOUDI stage (0.056 µm) at Angiola than at Fresno. The NO3− GMD increased from 0.97 to 1.02 µm as the NO3− concentration at Angiola increased from 43 to 66 µg m− 3 during a PM2.5 episode from January 4–7, 2001. There was a direct relationship between GMD and NO3− and SO4= concentrations at Angiola but no such relationships for OC or EC. This demonstrates that secondary aerosol formation increases both concentration and particle size for the rural California environment. 相似文献
350.
D. Heath Jones Mike A. Read Will Saunders Matthew Colless Tom Jarrett Quentin A. Parker Anthony P. Fairall † Thomas Mauch Elaine M. Sadler Fred G. Watson Donna Burton Lachlan A. Campbell Paul Cass Scott M. Croom John Dawe † Kristin Fiegert Leela Frankcombe Malcolm Hartley John Huchra Dionne James Emma Kirby Ofer Lahav John Lucey Gary A. Mamon Lesa Moore Bruce A. Peterson Sayuri Prior Dominique Proust Ken Russell Vicky Safouris Ken-ichi Wakamatsu Eduard Westra Mary Williams 《Monthly notices of the Royal Astronomical Society》2009,399(2):683-698
We report the final redshift release of the 6dF Galaxy Survey (6dFGS), a combined redshift and peculiar velocity survey over the southern sky (| b | > 10°) . Its 136 304 spectra have yielded 110 256 new extragalactic redshifts and a new catalogue of 125 071 galaxies making near-complete samples with ( K , H , J , r F , b J ) ≤ (12.65, 12.95, 13.75, 15.60, 16.75) . The median redshift of the survey is 0.053. Survey data, including images, spectra, photometry and redshifts, are available through an online data base. We describe changes to the information in the data base since earlier interim data releases. Future releases will include velocity dispersions, distances and peculiar velocities for the brightest early-type galaxies, comprising about 10 per cent of the sample. Here we provide redshift maps of the southern local Universe with z ≤ 0.1 , showing nearby large-scale structures in hitherto unseen detail. A number of regions known previously to have a paucity of galaxies are confirmed as significantly underdense regions. The URL of the 6dFGS data base is http://www-wfau.roe.ac.uk/6dFGS . 相似文献