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91.
Luis Manuel de Vries Jesus Carrera Oriol Falivene Oscar Gratacós Luit Jan Slooten 《Mathematical Geosciences》2009,41(1):29-42
Simulation of flow and solute transport through aquifers or oil reservoirs requires a precise representation of subsurface
heterogeneity that can be achieved by stochastic simulation approaches. Traditional geostatistical methods based on variograms,
such as truncated Gaussian simulation or sequential indicator simulation, may fail to generate the complex, curvilinear, continuous
and interconnected facies distributions that are often encountered in real geological media, due to their reliance on two-point
statistics. Multiple Point Geostatistics (MPG) overcomes this constraint by using more complex point configurations whose
statistics are retrieved from training images. Obtaining representative statistics requires stationary training images, but
geological understanding often suggests a priori facies variability patterns. This research aims at extending MPG to non-stationary
facies distributions. The proposed method subdivides the training images into different areas. The statistics for each area
are stored in separate frequency search trees. Several training images are used to ensure that the obtained statistics are
representative. The facies probability distribution for each cell during simulation is calculated by weighting the probabilities
from the frequency trees. The method is tested on two different object-based training image sets. Results show that non-stationary
training images can be used to generate suitable non-stationary facies distributions. 相似文献
92.
Spatial assessment of fishing effort around European marine reserves: implications for successful fisheries management 总被引:7,自引:0,他引:7
Stelzenmüller V Maynou F Bernard G Cadiou G Camilleri M Crec'hriou R Criquet G Dimech M Esparza O Higgins R Lenfant P Pérez-Ruzafa A 《Marine pollution bulletin》2008,56(12):2018-2026
We examined the spatial dynamic of artisanal fishing fleets around five European marine protected areas (MPAs) to derive general implications for the evaluation of MPAs as fisheries management tools. The coastal MPAs studied were located off France, Malta and Spain and presented a variety of spatial designs and processes of establishment. We developed a standardized methodology to define factors influencing effort allocation and to produce fishing effort maps by merging GIS with geostatistical modelling techniques. Results revealed that in most cases the factors “distance to the no-take”, “water depth”, and “distance to the port” had a significant influence on effort allocation by the fishing fleets. Overall, we found local concentration of fishing effort around the MPA borders. Thus, neglecting the pattern of fishing effort distribution in evaluating MPA benefits, such as spillover of biomass, could hamper sound interpretation of MPAs as fisheries management tools. 相似文献
93.
In Bahia Samborombon (SW Atlantic; 35°30′–36°22′S; 56°45′–57°23′W) migratory American golden plover (Pluvialis dominica), black-billed plover (P. squatarola), ruddy turnstone (Arenaria interpres), and whimbrel (Numenius phaeopus) forage on fiddler crabs (Uca uruguayensis). These shorebirds have distinct patterns of feeding behavior and capture different proportions of each sex and size. P. dominica made short runs, capturing mostly juvenile crabs, which are eaten whole. P. squatarola use a similar feeding strategy but capture females primarily. A. interpres walks continuously, capturing almost exclusively large male crabs (71%). N. phaeopus walk in the Uca patch and probe burrows by inserting the bill; they primarily capture females. The feeding rate of A. interpres is higher than that of P. dominica, P. squatarola, and N. phaeopus. Handling time shown by P. dominica and A. interpres was greater than the other two species for all categories of crabs. In all cases, handling time of male crabs was greater than those of either females or juveniles. All the evidences suggest that U. uruguayensis is an important food source for all these species and should be accounted in any conservation endeavor. *** DIRECT SUPPORT *** A01BY085 00006 相似文献
94.
The fundamental frequency of a rectangular isotropic plate having a linear thickness variation is computed using the method of eigensensitivity analysis. The approach incorporates eigen derivatives to evaluate a Maclaurin series representation of the desired eigenvalue, here the fundamental frequency. Comparison with published results, for various taper ratios, aspect ratios, and support conditions, demonstrates the accuracy and utility of the expression and methodology. 相似文献
95.
This paper aims to develop an improved understanding of the critical response of structures to multicomponent seismic motion characterized by three uncorrelated components that are defined along its principal axes: two horizontal and the vertical component. An explicit formula, convenient for code applications, has been derived to calculate the critical value of structural response to the two principal horizontal components acting along any incident angle with respect to the structural axes, and the vertical component of ground motion. The critical response is defined as the largest value of response for all possible incident angles. The ratio rcr/rsrss between the critical value of response and the SRSS response—corresponding to the principal components of ground acceleration applied along the structure axes—is shown to depend on three dimensionless parameters: the spectrum intensity ratio γ between the two principal components of horizontal ground motion characterized by design spectra A(Tn) and γA(Tn); the correlation coefficient α of responses rx and ry due to design spectrum A(Tn) applied in the x‐ and y‐directions, respectively; and β = ry/rx. It is demonstrated that the ratio rcr/rsrss is bounded by 1 and . Thus the largest value of the ratio is , 1.26, 1.13 and 1.08 for γ = 0, 0.5, 0.75 and 0.85, respectively. This implies that the critical response never exceeds times the result of the SRSS analysis, and this ratio is about 1.13 for typical values of γ, say 0.75. The correlation coefficient α depends on the structural properties but is always bounded between −1 and 1. For a fixed value of γ, the ratio rcr/rsrss is largest if β = 1 and α = ±1. The parametric variations presented for one‐storey buildings indicate that this condition can be satisfied by axial forces in columns of symmetric‐plan buildings or can be approximated by lateral displacements in resisting elements of unsymmetrical‐plan buildings. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
96.
Weijie FENG Marco Y.-T. LEUNG Dongxiao WANG Wen ZHOU Oscar Y. W. ZHANG 《大气科学进展》2022,39(10):1637-1649
An extreme drought appeared in South China from October 2020 to March 2021. During that time, sea surface temperatures exhibited an unprecedented warm center over the northwest Pacific (NWP) and a cold center over the tropical eastern Pacific (La Ni?a). This study demonstrates the combined effects of an exceptionally warm NWP and a moderate La Ni?a are closely linked to the anomalous drought in South China. The sea surface temperature anomaly in these two regions induced a steeper horizontal geopotential height gradient over South China. As a result, anomalous northeasterly winds prevailed over South China, altering water vapor transport and moisture convergence. A simplified atmospheric general circulation model also verifies the influence of the NWP warm anomaly on South China precipitation. This study points out that the sea surface temperature variation in the NWP was important to the occurrence of extreme drought in South China from October 2020 to March 2021. 相似文献
97.
The Monin–Obukhov similarity theory (MOST) functions fε and fT, of the dissipation rate of turbulent kinetic energy (TKE). ε, and the structure parameter of temperature, CT2, were determined for the stable atmospheric surface layer using data gathered in the context of CASES-99. These data cover
a relatively wide stability range, i.e. ζ=z/L of up to 10, where z is the height and L the Obukhov length. The best fits were given by fε = 0.8 + 2.5ζ and fT= 4.7[ 1+1.6(ζ)2/3], which differ somewhat from previously published functions. ε was obtained from spectra of the longitudinal wind velocity
using a time series model (ARMA) method instead of the traditional Fourier transform. The neutral limit fε =0.8 implies that there is an imbalance between TKE production and dissipation in the simplified TKE budget equation. Similarly,
we found a production-dissipation imbalance for the temperature fluctuation budget equation. Correcting for the production-dissipation
imbalance, the ‘standard’ MOST functions for dimensionless wind speed and temperature gradients (φm and φm) were determined from fε and fT and compared with the φm and φh formulations of Businger and others. We found good agreement with the Beljaars and Holtslag [J. Appl. Meteorol. 30, 327–341 (1991)] relations. Lastly, the flux and gradient Richardson numbers are discussed also in terms of fε and fT. 相似文献
98.
Rhythmic movements in response to tidal cycles are characteristic of infaunal inhabitant of intertidal soft-bottoms, allowing
them to remain in the area with best living conditions. The effect of bioturbators as modifier of local environmental conditions
and thus of gradients in intertidal habitats, has not been investigated yet. The Atlantic estuarine intertidal areas are dominated
by the burrowing crabChasmagnathus granulatus that generates strong environmental heterogeneity by affecting the physical-chemical characteristics of the sediment. The
comparison between intertidal areas with and without crab shows that sediments in the crab beds remain more humid, softer,
and homogeneous across the intertidal and along the tidal cycle than areas without crabs. The densities of infauna were higher
at high intertidal zones in crab beds than in similar areas without crabs. Infaunal organisms performed vertical movements
into the sediment following the tidal cycle that were always of higher magnitude in habitats without crabs. Infaunal species
tend to spend most of the time buried into the sediment in the crab bed. Migratory shorebirds use the Atlantic estuarine environments
as stopover or wintering sites. They feed (mainly on polychaetes) in the low intertidal zones of both habitats (with and without
crabs), but they also feed in the upper intertidal of the crab bed; polychaete per capita mortality rate is higher in the
upper part of the crab bed. Environmental heterogeneity produced by crab disturbance has an effect on the infaunal behavior,
risk of mortality, and the zonation pattern. This is another example of the ecosystem engineering ability of a burrowing intertidal
species. 相似文献
99.
A discussion is presented that highlights the growing utilization of composite structures for marine applications. Important to this trend is an understanding of the buckling response of marine panels under hygroscopic loads. Consideration are presented for the use of eigensensitivity analysis as a means of developing an approximate closed-form expression for computing the critical buckling response in the absense of an exact solutions 相似文献
100.
Oscar E. Romero Dierk Hebbeln Gerold Wefer 《Deep Sea Research Part I: Oceanographic Research Papers》2001,48(12):46
Flux of siliceous plankton and taxonomic composition of diatom and silicoflagellate assemblages were determined from sediment trap samples collected in coastal upwelling-influenced waters off northern Chile (30°S, CH site) under “normal” or non-El Niño (1993–94) and El Niño conditions (1997–98). In addition, concentration of biogenic opal and siliceous plankton, and diatom and silicoflagellate assemblages preserved in surface sediments are provided for a wide area between 27° and 43°S off Chile. Regardless of the year, winter upwelling determines the maximum production pattern of siliceous microorganisms, with diatoms numerically dominating the biogenic opal flux. During the El Niño year the export is markedly lower: on an annual basis, total mass flux diminished by 60%, and diatom and silicoflagellate export by 75%. Major components of the diatom flora maintain much of their regular seasonal cycle of flux maxima and minima during both sampling periods. Neritic resting spores (RS) of Chaetoceros dominate the diatom flux, mirroring the influence of coastal-upwelled waters at the CH trap site. Occurrence of pelagic diatoms species Fragilariopsis doliolus, members of the Rhizosoleniaceae, Azpeitia spp. and Nitzschia interruptestriata, secondary components of the assemblage, reflects the intermingling of warmer waters of the Subtropical Gyre. Dictyocha messanensis dominates the silicoflagellate association almost year-around, but Distephanus pulchra delivers ca. 60% of its annual production in less than three weeks during the winter peak. The siliceous thanatocoenosis is largely dominated by diatoms, whose assemblage shows significant qualitative and quantitative variations from north to south. Between 27° and 35°S, the dominance of RS Chaetoceros, Thalassionema nitzschioides var. nitzschioides and Skeletonema costatum reflects strong export production associated with occurrence of coastal upwelling. Both highest biogenic opal content and diatom concentration at 35° and 41°–43°S coincide with highest pigment concentrations along the Chilean coast. Predominance of the diatom species Thalassiosira pacifica and T. poro-irregulata, and higher relative contribution of the silicoflagellate Distephanus speculum at 41°–43°S suggest the influence of more nutrient-rich waters and low sea surface temperatures, probably associated with the Antarctic Circumpolar Water. 相似文献