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111.
MUHAMMAD SHARAF GARY ARROY RON PERKINS Spectra-Physics Inc. North First Street San Jose CA U.S.A. 《地理学报(英文版)》1991,(3)
Ratio measurements are commonly used to address a variety of analytical problems in environmental,forensic and pharmaceutical laboratories.In absorbance ratioing techniques,analytical chemists rely onthe spectral features of the analyte(s)of interest.The absorbances at two wavelengths are monitored andthe ratio of these two absorbances is computed.This ratio is then used to confirm the identity of theanalyte(s)of interest,the purity of a product or the overlap of chromatographic peaks.These decisionsoften have far-reaching consequences(e.g.the identification of the source,biogenic or petrogenic,ofhydrocarbons in biological tissues or water).Given the cost and the liabilities associated with suchdecisions,it is unfortunate that these ratios are seldom reported with any statistical confidence.Thepurpose of this study is to delineate the parameters that affect absorbance ratio measurements.Themodels that can be used to estimate the statistical confidence in these measurements are derived andevaluated experimentally.The results show that these models can estimate the relative standard deviationsin absorbance ratios accurately.They can also estimate the effect of signal-to-noise ratio and the choiceof wavelengths on the precision of absorbance ratios. 相似文献
112.
Ronald?GoldbergEmail author Beth?Phelan Jose?Pereira Stacy?Hagan Paul?Clark Allen?Bejda Anthony?Calabrese Anne?Studholme Kenneth?W.?Able 《Estuaries and Coasts》2002,25(2):215-226
We compared distribution and abundance by habitat for age-0, young-of-the-year (YOY) winter flounder,Pseudopleuronectes americanus, in three estuaries (Hammonasset River, Navesink River, and Great Bay-Little Egg Harbor) in the northeastern United States to better define essential fish habitat (EFH). Two replicates of five representative habitats were sampled in most estuaries: eelgrass (Zostera marina), unvegetated areas adjacent to eelgrass, macroalgae, (primarilyUlva lactuca), unvegetated areas adjacent to macroalgae, and tidal marsh creeks. Fish were sampled every two weeks, May through October 1995 and 1996, with a beam-trawl (1-m width, 3-mm mesh net). Abundance of YOY winter flounder was highest in the Navesink River estuary and similar between years, but was significantly lower and differed between years in the Great Bay-Little Egg Harbor and Hammonasset River estuaries. Annual temperature differences appear to influence estuary use by YOY. In the years and estuaries studied, where habitat-related differences in abundance were significant, YOY were found in higher densities in unvegetated areas adjacent to eelgrass. The exception was in the Hammonasset River in 1995 when densities were higher in eelgrass. We conclude that the type of habitat most important to YOY winter flounder varies among estuaries and as a result, care should be taken in defining EFH, based only on limited spatial and temporal sampling. 相似文献
113.
114.
Paulina Montero Giovanni Daneri Humberto E. González Jose Luis Iriarte Fabián J. Tapia Lorena Lizárraga Nicolas Sanchez Oscar Pizarro 《Continental Shelf Research》2011,31(3-4):202-215
We characterized the seasonal cycle of productivity in Reloncaví Fjord (41°30′S), Chilean Patagonia. Seasonal surveys that included measurements of gross primary production, community respiration, bacterioplankton secondary production, and sedimentation rates along the fjord were combined with continuous records of water-column temperature variability and wind forcing, as well as satellite-derived data on regional patterns of wind stress, sea surface temperatures, and surface chlorophyll concentrations. The hydrography and perhaps fjord productivity respond to the timing and intensity of wind forcing over a larger region. Seasonal changes in the direction and intensity of winds, along with a late-winter improvement in light conditions, may determine the timing of phytoplankton blooms and potentially modulate productivity cycles in the region.Depth-integrated gross primary production estimates were higher (0.4–3.8 g C m?2 d?1) in the productive season (October, February, and May), and lower (0.1–0.2 g C m?2 d?1) in the non-productive season (August). These seasonal changes were also reflected in community respiration and bacterioplankton production rates, which ranged, respectively, from 0.3 to 4.8 g C m?2 d?1 and 0.05 to 0.4 g C m?2 d?1 during the productive and non-productive seasons and from 0.05 to 0.6 g C m?2 d?1 and 0.05 to 0.2 g C m?2 d?1 during the same two periods. We found a strong, significant correlation between gross primary production and community respiration (Spearman, r=0.95; p<0.001; n=12), which suggests a high degree of coupling between the synthesis of organic matter and its usage by the planktonic community. Similarly, strong correlations were found between bacterioplankton secondary production and both gross primary production (Spearman, r=0.7, p<0.05, n=9) and community respiration (Spearman, r=0.8, p<0.05, n=9), indicating that bacterioplankton may be processing an important fraction (8–59%) of the organic matter produced by phytoplankton in Reloncaví Fjord. In winter, bacterial carbon utilization as a percentage of gross primary production was >100%, suggesting the use of allochthonous carbon sources by bacterioplankton when the levels of gross primary production are low. Low primary production rates were associated with a greater contribution of small cells to autotrophic biomass, highlighting the importance of small-sized plankton and bacteria for carbon cycling and fluxes during the less productive winter months. Fecal pellet sedimentation was minimal during this period, also suggesting that most of the locally produced organic carbon is recycled within the microbial loop. During the productive season, on the other hand, the area exhibited a great potential to export organic matter, be it to higher trophic levels or vertically towards the bottom. 相似文献
115.
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117.
Taras Agryzkov Jose L. Oliver Leandro Tortosa 《International journal of geographical information science》2014,28(3):479-495
Urban researchers and planners are often interested in understanding how economic activities are distributed in urban regions, what forces influence their special pattern and how urban structure and functions are mutually dependent. In this paper, we want to show how an algorithm for ranking the nodes in a network can be used to understand and visualize certain commercial activities of a city. The first part of the method consists of collecting real information about different types of commercial activities at each location in the urban network of the city of Murcia, Spain. Four clearly differentiated commercial activities are studied, such as restaurants and bars, shops, banks and supermarkets or department stores, but obviously we can study other. The information collected is then quantified by means of a data matrix, which is used as the basis for the implementation of a PageRank algorithm which produces a ranking of all the nodes in the network, according to their significance within it. Finally, we visualize the resulting classification using a colour scale that helps us to represent the business network. 相似文献
118.
Oligotrophic areas harbour low macrofaunal abundance and patchy distribution. In these areas it is necessary to test the reliability of biological indicators, especially those based on taxonomic sufficiency where the level of identification is balanced against the need for ecological information and could affect the efficiency of bioindicators. The BOPA (benthic opportunistic polychaetes and amphipods) index was applied in five coastal areas subjected to different perturbations (aquaculture, harbour, brine, sewage, and thermal pollution) in the Canary archipelago, an oligotrophic area of the Atlantic Ocean. Significant differences in the BOPA index between impact and control sites were only found in the area affected by a harbour. Perturbations such as aquaculture, brine or sewage discharge produce only a weak response of the BOPA index, whereas no effects were observed at thermal pollution‐impacted locations. The BOPA index should be used with caution to establish the ecological status of coastal water bodies in the Canary Islands, since it was only reliable in strongly impacted regions (enlargement harbour works), but did not respond clearly to other man‐induced perturbations. 相似文献
119.
GPS-derived orbits for the GOCE satellite 总被引:5,自引:4,他引:1
Heike Bock Adrian Jäggi Ulrich Meyer Pieter Visser Jose van den IJssel Tom van Helleputte Markus Heinze Urs Hugentobler 《Journal of Geodesy》2011,85(11):807-818
The first ESA (European Space Agency) Earth explorer core mission GOCE (Gravity field and steady-state Ocean Circulation Explorer)
was launched on 17 March 2009 into a sun-synchronous dusk–dawn orbit with an exceptionally low initial altitude of about 280 km.
The onboard 12-channel dual-frequency GPS (Global Positioning System) receiver delivers 1 Hz data, which provides the basis
for precise orbit determination (POD) for such a very low orbiting satellite. As part of the European GOCE Gravity Consortium
the Astronomical Institute of the University of Bern and the Department of Earth Observation and Space Systems are responsible
for the orbit determination of the GOCE satellite within the GOCE High-level Processing Facility. Both quick-look (rapid)
and very precise orbit solutions are produced with typical latencies of 1 day and 2 weeks, respectively. This article summarizes
the special characteristics of the GOCE GPS data, presents POD results for about 2 months of data, and shows that both latency
and accuracy requirements are met. Satellite Laser Ranging validation shows that an accuracy of 4 and 7 cm is achieved for
the reduced-dynamic and kinematic Rapid Science Orbit solutions, respectively. The validation of the reduced-dynamic and kinematic
Precise Science Orbit solutions is at a level of about 2 cm. 相似文献
120.
Chris B. Folkes Heather M. Wright Raymond A. F. Cas Shanaka L. de Silva Chiara Lesti Jose G. Viramonte 《Bulletin of Volcanology》2011,73(10):1427-1454
From detailed fieldwork and biotite 40Ar/39Ar dating correlated with paleomagnetic analyses of lithic clasts, we present a revision of the stratigraphy, areal extent
and volume estimates of ignimbrites in the Cerro Galán volcanic complex. We find evidence for nine distinct outflow ignimbrites,
including two newly identified ignimbrites in the Toconquis Group (the Pitas and Vega Ignimbrites). Toconquis Group Ignimbrites
(~5.60–4.51 Ma biotite ages) have been discovered to the southwest and north of the caldera, increasing their spatial extents
from previous estimates. Previously thought to be contemporaneous, we distinguish the Real Grande Ignimbrite (4.68 ± 0.07 Ma
biotite age) from the Cueva Negra Ignimbrite (3.77 ± 0.08 Ma biotite age). The form and collapse processes of the Cerro Galán
caldera are also reassessed. Based on re-interpretation of the margins of the caldera, we find evidence for a fault-bounded
trapdoor collapse hinged along a regional N-S fault on the eastern side of the caldera and accommodated on a N-S fault on
the western caldera margin. The collapsed area defines a roughly isosceles trapezoid shape elongated E-W and with maximum
dimensions 27 × 16 km. The Cerro Galán Ignimbrite (CGI; 2.08 ± 0.02 Ma sanidine age) outflow sheet extends to 40 km in all
directions from the inferred structural margins, with a maximum runout distance of ~80 km to the north of the caldera. New
deposit volume estimates confirm an increase in eruptive volume through time, wherein the Toconquis Group Ignimbrites increase
in volume from the ~10 km3 Lower Merihuaca Ignimbrite to a maximum of ~390 km3 (Dense Rock Equivalent; DRE) with the Real Grande Ignimbrite. The climactic CGI has a revised volume of ~630 km3 (DRE), approximately two thirds of the commonly quoted value. 相似文献