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排序方式: 共有347条查询结果,搜索用时 31 毫秒
51.
Lozach S Dauvin JC Méar Y Murat A Davoult D Migné A 《Marine pollution bulletin》2011,62(12):2753-2760
Sampling the sea bottom surface remains difficult because of the surface hydraulic shock due to water flowing through the gear (i.e., the bow wave effect) and the loss of epifauna organisms due to the gear’s closing mechanism. Slow-moving mobile epifauna, such as the ophiuroid Ophiothrix fragilis, form high-density patches in the English Channel, not only on pebbles like in the Dover Strait or offshore Brittany but also on gravel in the Bay of Seine (>5000 ind m−2). Such populations form high biomasses and control the water transfer from the water column to the sediment. Estimating their real density and biomass is essential for the assessment of benthic ecosystem functioning using trophic web modelling. In this paper, we present and discuss the patch patterns and sampling efficiency of the different methods for collecting in the dense beds of O. fragilis in the Bay of Seine. The large Hamon grab (0.25 m−2) highly under-estimated the ophiuroid density, while the Smith McIntyre appeared adequate among the tested sampling grabs. Nowadays, diving sampling, underwater photography and videos with remote operated vehicle appear to be the recommended alternatives to estimate the real density of such dense slow-moving mobile epifauna. 相似文献
52.
Hans Romang Massimiliano Zappa Nadine Hilker Matthias Gerber François Dufour Valérie Frede Dominique Bérod Matthias Oplatka Christoph Hegg Jakob Rhyner 《Natural Hazards》2011,56(2):509-527
IFKIS-Hydro is an information and warning system for hydrological hazards in small- and medium-scale catchments. The system
collects data such as weather forecasts, precipitation measurements, water level gauges, discharge simulations and local observations
of event-specific phenomena. In addition, IFKIS-Hydro incorporates a web-based information platform, which serves as a central
hub for the submission and overview of data. Special emphasis is given to local information. This is accomplished particularly
by human observers. In medium-scale catchments, discharge forecast models have an increasing importance in providing valuable
information. IFKIS-Hydro was developed in several test regions in Switzerland and the first results of its application are
available now. The system is constantly extended to additional regions and may become the standard for warning systems in
smaller catchments in Switzerland. 相似文献
53.
Alain Genty Christophe Le Potier Stéphane Gounand 《Geotechnical and Geological Engineering》2011,29(4):537-554
Numerical simulations of the transport of radionuclide from high-level radioactive waste stored in geological repositories
often do not take into account construction defects in the repository. The potential impact of drilling and excavation deviation
from the engineer planned design is a priori considered negligible. We conducted computations on repository geometries that
contain deviations from horizontal of a few degrees. The analysis of the results shows that the impact of deviation defects
varies from 9 to 16%. A perfect control of the galleries and waste repository cell orientations is then of concern for radioactive
waste repository construction, failing which numerical simulations must be conducted on the worst geometric configuration
or margin errors added. On the other hand, if the orientation control is precise enough, a modification of the repository
design including controlled deviations from the horizontal may be of interest. 相似文献
54.
Combining in situ isotopic, trace element and textural analyses of quartz from four magmatic-hydrothermal ore deposits 总被引:2,自引:0,他引:2
Dominique Tanner Richard W. Henley John A. Mavrogenes Peter Holden 《Contributions to Mineralogy and Petrology》2013,166(4):1119-1142
This study couples in situ 16O, 17O and 18O isotope and in situ trace element analyses to investigate and characterize the geochemical and textural complexity of magmatic-hydrothermal quartz crystals. Euhedral quartz crystals contemporaneous with mineralization were obtained from four magmatic-hydrothermal ore deposits: El Indio Au–Ag–Cu deposit; Summitville Au–Ag–Cu deposit; North Parkes Cu–Au deposit and Kingsgate quartz-Mo–Bi–W deposit. The internal features of the crystals were imaged using cathodoluminescence and qualitative electron microprobe maps. Quantitative isotopic data were collected in situ using 157 nm laser ablation inductively coupled plasma mass spectrometry (for 40 trace elements in quartz) and sensitive high-resolution ion microprobe (for 3 isotopes in quartz). Imaging revealed fine oscillatory zoning, sector zoning, complex “macromosaic” textures and hidden xenocrystic cores. In situ oxygen isotope analyses revealed a δ18O range of up to 12.4 ± 0.3 ‰ in a single crystal—the largest isotopic range ever ascribed to oscillatory zonation in quartz. Some of these crystals contain a heavier δ18O signature than expected by existing models. While sector-zoned crystals exhibited strong trace element variations between faces, no evidence for anisotropic isotope fractionation was found. We found: (1) isotopic heterogeneity in hydrothermal quartz crystals is common and precludes provenance analysis (e.g., δD–δ18O) using bulk analytical techniques, (2) the trace element signature of quartz is not an effective pathfinder toward noble metal mineralization and (3) in three of the four samples, both textural and isotopic data indicate non-equilibrium deposition of quartz. 相似文献
55.
Wafa Abouchami Stephen J. G. Galer Tristan J. Horner Mark Rehkämper Frank Wombacher Zichen Xue Myriam Lambelet Melanie Gault‐Ringold Claudine H. Stirling Maria Schönbächler Alyssa E. Shiel Dominique Weis Philip F. Holdship 《Geostandards and Geoanalytical Research》2013,37(1):5-17
Research into natural mass‐dependent stable isotope fractionation of cadmium has rapidly expanded in the past few years. Methodologies are diverse with MC‐ICP‐MS favoured by all but one laboratory, which uses thermal ionisation mass spectrometry (TIMS). To quantify the isotope fractionation and correct for instrumental mass bias, double‐spike techniques, sample‐calibrator bracketing or element doping has been used. However, easy comparison between data sets has been hampered by the multitude of in‐house Cd solutions used as zero‐delta reference in different laboratories. The lack of a suitable isotopic reference material for Cd is detrimental for progress in the long term. We have conducted a comprehensive round‐robin assay of NIST SRM 3108 and the Cd isotope offsets to commonly used in‐house reference materials. Here, we advocate NIST SRM 3108 both as an isotope standard and the isotopic reference point for Cd and encourage its use as ‘zero‐delta’ in future studies. The purity of NIST SRM 3108 was evaluated regarding isobaric and polyatomic molecular interferences, and the levels of Zn, Pd and Sn found were not significant. The isotope ratio 114Cd/110Cd for NIST SRM 3108 lies within ~ 10 ppm Da?1 of best estimates for the Bulk Silicate Earth and is validated for all measurement technologies currently in use. 相似文献
56.
57.
We studied zooplankton contribution to the total particulate phosphatase activity, the kinetics of this activity, the relation to the different taxonomic groups and the role of particle-bound bacteria. The activity of total particulate material collected from a liter of seawater was more elevated in May, June and August than during the rest of the year. These high activities resulted from a high contribution of the >90 microm fraction which account then for more than 60% of the total particulate activity. Two Michaelian processes with high and low V(max) were disclosed on this fraction. The high V(max) component was responsible for the high summer activities. During these periods, high densities of cirriped Cypris were found which were statistically correlated with this high V(max) component as with its specific activity. Moreover, the contribution of attached bacteria to these high activities was low. In return, this contribution was predominant during the periods of low activity. A simple method was developed to characterise this bacterial activity. 相似文献
58.
We study two asymptotic regimes of unstable miscible displacements in porous media, in the two limits, where a permeability-modified aspect ratio, RL=L/H(kv/kh)1/2, becomes large or small, respectively. The first limit is known as transverse (or vertical) equilibrium, the second leads to the problem of non-communicating layers (the Dykstra–Parsons problem). In either case, the problem reduces to the solution of a single integro-differential equation. Although at opposite limits of the parameter RL, the two regimes coincide in the case of equal viscosities, M=1. By comparison with high-resolution simulation we investigate the validity of these two approximations. The evolution of transverse averages, particularly under viscous fingering conditions, depends on RL. We investigate the development of a model to describe viscous fingering in weakly heterogeneous porous media under transverse equilibrium conditions, and compare with the various existing empirical models (such as the Koval, Todd–Longstaff and Fayers models). 相似文献
59.
J. Zender D. Berghmans D. S. Bloomfield C. Cabanas Parada I. Dammasch A. De Groof E. D’Huys M. Dominique P. Gallagher B. Giordanengo P. A. Higgins J.-F. Hochedez M. S. Yalim B. Nicula E. Pylyser L. Sanchez-Duarte G. Schwehm D. B. Seaton A. Stanger K. Stegen S. Willems 《Solar physics》2013,286(1):93-110
The PROBA2 Science Centre (P2SC) is a small-scale science operations centre supporting the Sun observation instruments onboard PROBA2: the EUV imager Sun Watcher using APS detectors and image Processing (SWAP) and Large-Yield Radiometer (LYRA). PROBA2 is one of ESA’s small, low-cost Projects for Onboard Autonomy (PROBA) and part of ESA’s In-Orbit Technology Demonstration Programme. The P2SC is hosted at the Royal Observatory of Belgium, co-located with both Principal Investigator teams. The P2SC tasks cover science planning, instrument commanding, instrument monitoring, data processing, support of outreach activities, and distribution of science data products. PROBA missions aim for a high degree of autonomy at mission and system level, including the science operations centre. The autonomy and flexibility of the P2SC is reached by a set of web-based interfaces allowing the operators as well as the instrument teams to monitor quasi-continuously the status of the operations, allowing a quick reaction to solar events. In addition, several new concepts are implemented at instrument, spacecraft, and ground-segment levels allowing a high degree of flexibility in the operations of the instruments. This article explains the key concepts of the P2SC, emphasising the automation and the flexibility achieved in the commanding as well as the data-processing chain. 相似文献
60.
We analyze the light curves of the recent solar eclipses measured by the Herzberg channel (200?–?220 nm) of the Large Yield RAdiometer (LYRA) onboard Project for OnBoard Autonomy (PROBA2). The measurements allow us to accurately retrieve the center-to-limb variations (CLV) of the solar brightness. The formation height of the radiation depends on the observing angle, so the examination of the CLV provide information about a broad range of heights in the solar atmosphere. We employ the 1D NLTE radiative transfer COde for Solar Irradiance (COSI) to model the measured light curves and corresponding CLV dependencies. The modeling is used to test and constrain the existing 1D models of the solar atmosphere, e.g. the temperature structure of the photosphere and the treatment of the pseudo-continuum opacities in the Herzberg continuum range. We show that COSI can accurately reproduce not only the irradiance from the entire solar disk, but also the measured CLV. Hence it can be used as a reliable tool for modeling the variability of the spectral solar irradiance. 相似文献