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排序方式: 共有835条查询结果,搜索用时 31 毫秒
821.
Mapping ideas from cyberspace to realspace: visualizing the spatial context of keywords from web page search results 总被引:1,自引:0,他引:1
Ming-Hsiang Tsou Ick-Hoi Kim Sarah Wandersee Daniel Lusher Li An Brian Spitzberg 《International Journal of Digital Earth》2014,7(4):316-335
We introduce a new method for visualizing and analyzing information landscapes of ideas and events posted on public web pages through customized web-search engines and keywords. This research integrates GIScience and web-search engines to track and analyze public web pages and their web contents with associated spatial relationships. Web pages searched by clusters of keywords were mapped with real-world coordinates (by geolocating their Internet Protocol addresses). The resulting maps represent web information landscapes consisting of hundreds of populated web pages searched by selected keywords. By creating a Spatial Web Automatic Reasoning and Mapping System prototype, researchers can visualize the spread of web pages associated with specific keywords, concepts, ideas, or news over time and space. These maps may reveal important spatial relationships and spatial context associated with selected keywords. This approach may provide a new research direction for geographers to study the diffusion of human thought and ideas. A better understanding of the spatial and temporal dynamics of the ‘collective thinking of human beings’ over the Internet may help us understand various innovation diffusion processes, human behaviors, and social movements around the world. 相似文献
822.
Mohammad Z. Al-Hamdan William L. Crosson Sigrid A. Economou Maurice G. Estes Jr Sue M. Estes Sarah N. Hemmings 《国际地球制图》2014,29(1):85-98
We describe a remote sensing and geographic information system (GIS)-based study that has three objectives: (1) characterize fine particulate matter (PM2.5), insolation and land surface temperature (LST) using NASA satellite observations, Environmental Protection Agency (EPA) ground-level monitor data and North American Land Data Assimilation System (NLDAS) data products on a national scale; (2) link these data with public health data from the REasons for Geographic And Racial Differences in Stroke (REGARDS) national cohort study to determine whether these environmental risk factors are related to cognitive decline, stroke and other health outcomes and (3) disseminate the environmental datasets and public health linkage analyses to end users for decision-making through the Centers for Disease Control and Prevention (CDC) Wide-ranging Online Data for Epidemiologic Research (WONDER) system. This study directly addresses a public health focus of the NASA Applied Sciences Program, utilization of Earth Sciences products, by addressing issues of environmental health to enhance public health decision-making. 相似文献
823.
We present a study of water vapour in the Venus troposphere obtained by modelling specific water vapour absorption bands within the 1.18 μm window. We compare the results with the normal technique of obtaining the abundance by matching the peak of the 1.18 μm window. Ground-based infrared imaging spectroscopy of the night side of Venus was obtained with the Anglo-Australian Telescope and IRIS2 instrument with a spectral resolving power of R ~ 2400. The spectra have been fitted with modelled spectra simulated using the radiative transfer model VSTAR. We find a best fit abundance of 31 ppmv (?6 +9 ppmv), which is in agreement with recent results by Bézard et al. (Bézard, B., Fedorova, A., Bertaux, J.-L., Rodin, A., Korablev, O. [2011]. Icarus, 216, 173–183) using VEX/SPICAV (R ~ 1700) and contrary to prior results by Bézard et al. (Bézard, B., de Bergh, C., Crisp, D., Maillard, J.P. [1990]. Nature, 345, 508–511) of 44 ppmv (±9 ppmv) using VEX/VIRTIS-M (R ~ 200) data analyses. Comparison studies are made between water vapour abundances determined from the peak of the 1.18 μm window and abundances determined from different water vapour absorption features within the near infrared window. We find that water vapour abundances determined over the peak of the 1. 18 μm window results in plots with less scatter than those of the individual water vapour features and that analyses conducted over some individual water vapour features are more sensitive to variation in water vapour than those over the peak of the 1. 18 μm window. No evidence for horizontal spatial variations across the night side of the disk are found within the limits of our data with the exception of a possible small decrease in water vapour from the equator to the north pole. We present spectral ratios that show water vapour absorption from within the lowest 4 km of the Venus atmosphere only, and discuss the possible existence of a decreasing water vapour concentration towards the surface. 相似文献
824.
Craig L. Hebert Alan J. Kaufman Sarah C. Penniston-Dorland Aaron J. Martin 《Precambrian Research》2010
Radiometric constraints on mid-Ediacaran Period glaciation (Gaskiers) in Newfoundland narrowed the known temporal gap between widespread ice ages and the evolution of complex metazoans to several million years. To further evaluate this claim we studied an Ediacaran glacial diamictite at the base of the Fauquier Formation of northern Virginia, and discovered a conformable relationship between the post-glacial cap carbonate and overlying volcanic rocks of the Catoctin Formation. U/Pb zircon age constraints for the rift-related volcanic flows suggest initial emplacement around 571 million years ago. Application of the Catoctin age to the Fauquier succession indicates the occurrence of an ice age about 10 million years younger than the 582 Ma Gaskiers event, supporting the view of multiple Ediacaran Period glaciations. Furthermore, the age constraint from eastern Laurentia falls within radiometric uncertainty of fossiliferous strata in Avalonia, indicating that the Fauquier glaciation was coincident with early metazoan evolution. 相似文献
825.
Hydrous partial melting in the sheeted dike complex at fast spreading ridges: experimental and natural observations 总被引:5,自引:1,他引:4
Lydéric France Juergen Koepke Benoit Ildefonse Sarah B. Cichy Fabien Deschamps 《Contributions to Mineralogy and Petrology》2010,160(5):683-704
In ophiolites and in present-day oceanic crust formed at fast spreading ridges, oceanic plagiogranites are commonly observed
at, or close to the base of the sheeted dike complex. They can be produced either by differentiation of mafic melts, or by
hydrous partial melting of the hydrothermally altered sheeted dikes. In addition, the hydrothermally altered base of the sheeted
dike complex, which is often infiltrated by plagiogranitic veins, is usually recrystallized into granoblastic dikes that are
commonly interpreted as a result of prograde granulitic metamorphism. To test the anatectic origin of oceanic plagiogranites,
we performed melting experiments on a natural hydrothermally altered dike, under conditions that match those prevailing at
the base of the sheeted dike complex. All generated melts are water saturated, transitional between tholeiitic and calc-alkaline,
and match the compositions of oceanic plagiogranites observed close to the base of the sheeted dike complex. Newly crystallized
clinopyroxene and plagioclase have compositions that are characteristic of the same minerals in granoblastic dikes. Published
silicic melt compositions obtained in classical MORB fractionation experiments also broadly match the compositions of oceanic
plagiogranites; however, the compositions of the coexisting experimental minerals significantly deviate from those of the
granoblastic dikes. Our results demonstrate that hydrous partial melting is a likely common process in the root zone of the
sheeted dike complex, starting at temperatures exceeding 850°C. The newly formed melt can either crystallize to form oceanic
plagiogranites or may be recycled within the melt lens resulting in hybridized and contaminated MORB melts. It represents
the main MORB crustal contamination process. The residue after the partial melting event is represented by the granoblastic
dikes. Our results support a model with a dynamic melt lens that has the potential to trigger hydrous partial melting reactions
in the previously hydrothermally altered sheeted dikes. A new thermometer using the Al content of clinopyroxene is also elaborated. 相似文献
826.
The extent to which leaf water D-enrichment (transpiration) and soil water D-enrichment (evaporation) affect the D/H ratio of plant leaf waxes remains a contentious issue, with important implications for paleohydrologic reconstructions. In this study we measure δD values of precipitation (δDp), groundwater (δDgw), plant xylem water (δDxw) and leaf water (δDlw) to understand their impact on the δD values of plant leaf wax n-alkanes (δDwax) in an arid ecosystem. Our survey includes multiple species at four sites across an aridity gradient (80-30% relative humidity) in southern California.We find that many species take up groundwater or precipitation without significant fractionation. D-enriched soil water is a minor source even in species known to perform and utilize waters from hydraulic lift, such as Larrea tridentata (+10‰). Measurements of leaf water isotopic composition demonstrate that transpiration is an important mechanism for D-enrichment of leaf waters (+74 ± 20‰, 1σ), resulting in the smallest net fractionation yet reported between source water and leaf waxes (L. tridentata −41‰; multi-species mean value is −94 ± 21‰, 1σ). We find little change in leaf water D-enrichment or net fractionation across the climatic gradient sampled by our study, suggesting that a net fractionation of ca. −90‰ may be appropriate for paleohydrologic reconstructions in semi-arid to arid environments. Large interspecies offsets in net fractionations (1σ = 21‰) are potentially troublesome, given the observed floristic diversity and the likelihood of species assemblage changes with climate shifts. 相似文献
827.
New 40Ar/39Ar thermochronology results and thermal modeling support the hypothesis of Hollister et al. (2004), that reheating of the mid-Cretaceous Ecstall pluton by intrusion of the Coast Mountains Batholith (CMB) was responsible for spatially variable remagnetization of the Ecstall pluton. 40Ar/39Ar ages from hornblende and biotite from 12 locations along the Skeena River across the northern part of the Ecstall pluton decrease with proximity to the Quottoon plutonic complex, the nearest member of the CMB to the Ecstall pluton. The oldest 40Ar/39Ar ages are found farthest from the Quottoon plutonic complex, and are 90 ± 3 Ma for hornblende, and 77.9 ± 1.2 Ma for biotite. The youngest 40Ar/39Ar ages are found closest to the Quottoon plutonic complex, and are 51.6 ± 1.2 Ma for hornblende, and 45.3 ± 1.7 Ma for biotite. No obvious relationship between grain size and age is seen in the Ecstall pluton biotites. Spatial trends in 40Ar/39Ar ages are consistent with model results for reheating by a thermal wall at the location of the Quottoon plutonic complex. Although no unique solution is suggested, our results indicate that the most appropriate thermal history for the Ecstall pluton includes both reheating and northeast side up tilting of the Ecstall pluton associated with intrusion of the Quottoon plutonic complex. Estimates of northward translation from shallow paleomagnetic inclinations in the western part of the Ecstall pluton are reduced to ∼3000 km, consistent with the Baja-BC hypothesis, when northeast side up tilting is accounted for. 相似文献
828.
Sarah K. Appleby Martin R. Gillespie Colin M. Graham Richard W. Hinton Grahame J. H. Oliver Nigel M. Kelly 《Contributions to Mineralogy and Petrology》2010,160(1):115-132
In contrast to I-type granites, which commonly comprise infracrustal and supracrustal sources, S-type granites typically incorporate
predominantly supracrustal sources. The initial aim of this study was to identify the sources of three Scottish Caledonian
(~460 Ma) S-type granites (Kemnay, Cove and Nigg Bay) by conducting oxygen, U–Pb and Hf isotope analyses in zircon in order
to characterise one potential end-member magma involved in the genesis of the voluminous late Caledonian (~430–400 Ma) I-type
granites. Field, whole-rock geochemical and isotopic data are consistent with the generation of the S-type granites by melting
their Dalradian Supergroup country rocks. While Hf isotope compositions of magmatic zircon, U–Pb data of inherited zircons,
and high mean zircon δ18O values of 9.0 ± 2.7‰ (2SD) and 9.8 ± 2.0‰ for the Kemnay and Cove granites support this model, the Nigg Bay Granite contains
zircons with much lower δ18O values (6.8 ± 2.1‰), similar to those found in Scottish I-type granites. This suggests that the Nigg Bay Granite contains
low-δ18O material representing either altered supracrustal material, or more likely, an infracrustal source component with mantle-like
δ18O. Mixing trends in plots of δ18O vs. εHf for S-type granite zircons indicate involvement of at least two sources in all three granites. This pilot study
of Scottish Caledonian S-type granites demonstrates that, while field and whole-rock geochemical data are consistent with
local melting of only supracrustal sources, the oxygen isotopic record stored in zircon reveals a much more complex petrogenetic
evolution involving two or more magma sources. 相似文献
829.
Sarah?K.?FortnerEmail author Martyn?Tranter Andrew?Fountain W.?Berry?Lyons Kathleen?A.?Welch 《Aquatic Geochemistry》2005,11(4):391-412
We have investigated the geochemistry of supraglacial streams on the Canada Glacier, Taylor Valley, Antarctica during the
2001–2002 austral summer. Canada Glacier supraglacial streams represent the link between primary precipitation (i.e. glacier
snow) and proglacial Lake Hoare. Canada Glacier supraglacial stream geochemistry is intermediate between glacier snow and
proglacial stream geochemistry with average concentrations of 49.1 μeq L−1 Ca2+, 19.9 μeq L−1 SO42−, and 34.3 μeq L−1 HCO3−. Predominant west to east winds lead to a redistribution of readily soluble salts onto the glacier surface, which is reflected
in the geochemistry of the supraglacial streams. Western Canada Glacier supraglacial streams have average SO42−:HCO3− equivalent ratios of 1.0, while eastern supraglacial streams average 0.5, suggesting more sulfate salts reach and dissolve
in the western supraglacial streams. A graph of HCO3− versus Ca2+ for western and eastern supraglacial streams had slopes of 0.87 and 0.72, respectively with R2 values of 0.84 and 0.83. Low concentrations of reactive silicate (> 10 μmol L−1) in the supraglacial streams suggested that little to no silicate weathering occurred on the glacier surface with the exception
of cryoconite holes (1000 μmol L−1). Therefore, the major geochemical weathering process occurring in the supraglacial streams is believed to be calcite dissolution.
Proglacial stream, Anderson Creek, contains higher concentrations of major ions than supraglacial streams containing 5 times
the Ca2+ and 10 times the SO42−. Canada Glacier proglacial streams also contain higher concentrations (16.6–30.6 μeq L−1) of reactive silicate than supraglacial streams. This suggests that the controls on glacier meltwater geochemistry switch
from calcite and gypsum dissolution to both salt dissolution and silicate mineral weathering as the glacier meltwater evolves.
Our chemical mass balance calculations indicate that of the total discharge into Lake Hoare, the final recipient of Canada
Glacier meltwater, 81.9% is from direct glacier runoff and 19.1% is from proglacial Andersen Creek. Although during a typical,
low melt ablation season Andersen Creek contributes over 40% of the water added to Lake Hoare, its overall chemical importance
is diluted by the direct inputs from Canada Glacier during high flow years. Decadal warming events, such as the 2001–2002
austral summer produce supraglacial streams that are a major source of water to Lake Hoare. 相似文献
830.
Variability in dissolved organic matter fluorescence and reduced sulfur concentration in coastal marine and estuarine environments 总被引:1,自引:0,他引:1
Sarah G.S. DePalmaW. Ray Arnold James C. McGeerD. George Dixon D. Scott Smith 《Applied Geochemistry》2011,26(3):394-404
Fluorescence characterization of dissolved organic matter (DOM) and measurements of Cr-reducible sulfide (CRS) are presented for 72 coastal marine and estuarine water samples obtained from the USA and Canada. Each sample is identified according to source: terrigenous, autochthonous, wastewater or mixed. Fluorescence data are resolved into contributions from humic, fulvic, tyrosine and tryptophan-like fluorophores. Humic and fulvic-like fluorophores correlate well with dissolved organic C (DOC) (r2 = 0.73 and 0.71, respectively) but tyrosine and tryptophan-like fluorophores show no correlation with DOC. Quality factors are identified by normalization of fluorescence contributions to DOC. Humic and fulvic components show no statistical differences between sources but the amino acid-like fluorescence quality factors show significant variations between source, with highest values for autochthonous sources (0.07 ± 0.01 arbitrary fluorescence units per mg of C) versus low values (0.015 ± 0.005) for terrigenous source waters. CRS concentrations are highly variable from 0.07 ± 0.01 to 7703 ± 98 nM and do no correlate with DOC except when terrigenous source waters (n = 13) are separated out from the total sample set (r2 = 0.55). There is an open question in the literature; does DOC source matter in terms of protective effects towards metal toxicity? Here is shown that DOC molecular-level quality does vary and that this variation is mostly in terms of the contributions of amino acids to total fluorescence. 相似文献