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411.
412.
María del Carmen Martínez Juan F. Navarro José Manuel Ferrándiz 《Celestial Mechanics and Dynamical Astronomy》2007,99(1):59-68
The efficiency in the computation of circular functions, such as cos(u) or sin(u), where u is a Poisson series, is important to derive accurate solutions of many problems of Celestial Mechanics, for instance, the
orbital or rotational perturbed motion of natural or artificial bodies, since expansions in terms of Legendre functions and
multiple Fourier series appear almost everywhere. Therefore, it is worth searching for alternative algorithms with lower computational
cost. In this article, we propose a method based on the idea of elimination, which was originally applied to solve numerical
problems, mainly in the case of matrix functions. Our comparisons with the traditional Taylor expansion prove that this new method can be more efficient when applied to compute the sine and cosine of a Poisson series. 相似文献
413.
Eduard Salvador-Solé Alberto Manrique Andreu Raig Gullermo González-Casado José María Solanes Gustavo A. Bruzual 《Astrophysics and Space Science》2001,276(2-4):1065-1071
We present an analytical model of galaxy formation and evolution. After giving a rapid overview of the strategy employed and
the main ingredients included in the model, we focus on describing the main differences between this model and other similar
ones available.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
414.
Néstor A. Gabellone Lía Solari María Claps Nancy Neschuk 《Environmental Geology》2008,53(6):1353-1363
The main ions were measured seasonally during two years at 13 sampling stations in the Salado River and its main tributaries.
The importance of each ion was assessed by standard methods used to examine ionic composition and by multivariate methods.
The K-means clustering and Principal Component Analysis were applied to the percentages of the major ions. The concentration of
the major cations are in the order Na+ > Mg2+ > Ca2+ > K+ and the major anions, Cl− > SO42− > HCO3− > CO32−, and the salinity was high (mean TDS 2,691 mg l−1) due to sodium chloride. Using the proportions of the ions was possible to identify seven types of water within the basin
related to discharges of different river sub-catchments and from endorheic catchments (in a sand dune region) actually connected
with the basin by canals. The chemical composition of the basin is consequence of surface waters receiving salts from groundwater,
evaporation and weathering of Post-Pampeano materials, and of anthropogenic impact by diversion between subcatchments for
flood control. These results allowed us to test the marked effects on the ionic balance of basin at the base of a diversion
management from endorheic catchments characterized by high salinity waters. 相似文献
415.
D. Sabina D’Ambrosio Adriana García Analía R. Díaz Allan R. Chivas María C. Claps 《Journal of Paleolimnology》2017,58(2):101-117
Ecological and biogeographical studies of Neotropical non-marine ostracods are rare, although such information is needed to develop reliable paleoecological and paleoclimatic reconstructions for the region. An extensive, yet little explored South American area of paleoclimatic interest, is the arid-semiarid ecotone (Arid Diagonal) that separates arid Patagonia from subtropical/tropical northern South America, and lies at the intersection of the Pacific and Atlantic atmospheric circulation systems. This study focused on the Laguna Llancanelo basin, Argentina, a Ramsar site located within the Arid Diagonal, and was designed to build a modern dataset using ostracods (diversity, spatial distribution, seasonality, habitat preferences) and water chemistry. Cluster and multivariate analysis of the data indicated that salinity is the most significant variable segregating two ostracod groups. Limnocythere aff. staplini is the only species that develops abundant populations in the saline ephemeral Laguna Llancanelo during almost all seasons, and is accompanied by scarce Cypridopsis vidua in summer. The latter species is abundant in freshwater lotic sites, where Ilyocypris ramirezi, Herpetocypris helenae, and Cyprididae indet. are also found in large numbers. Darwinula stevensoni, Penthesilenula incae, Heterocypris incongruens, Chlamydotheca arcuata, Chlamydotheca sp., Herpetocypris helenae, and Potamocypris smaragdina prefer freshwater lentic conditions (springs), with C. arcuata and Chlamydotheca sp. found only in the Carapacho warm spring, which has a year-round constant temperature of ~20 °C. Seasonal sampling was necessary because some taxa display a highly seasonal distribution. Species that were recorded have either subtropical or Patagonian affinities, although a few taxa are endemic or common to both regions. These data can serve as modern analogues for reconstructing the late Quaternary history of the area, and to investigate the extent and position of the arid/semiarid ecotone (Arid Diagonal) during past glacial/interglacial cycles. 相似文献
416.
Contributions of different time scales to extreme Paraná floods 总被引:1,自引:0,他引:1
417.
418.
M. Alazard A. Boisson J-C. Maréchal J. Perrin B. Dewandel T. Schwarz M. Pettenati G. Picot-Colbeaux W. Kloppman S. Ahmed 《Hydrogeology Journal》2016,24(1):35-57
The recharge flow paths in a typical weathered hard-rock aquifer in a semi-arid area of southern India were investigated in relation to structures associated with a managed aquifer recharge (MAR) scheme. Despite the large number of MAR structures, the mechanisms of recharge in their vicinity are still unclear. The study uses a percolation tank as a tool to identify the input signal of the recharge and uses multiple measurements (piezometric time series, electrical conductivity profiles in boreholes) compared against heat-pulse flowmeter measurements and geochemical data (major ions and stable isotopes) to examine recharge flow paths. The recharge process is a combination of diffuse piston flow and preferential flow paths. Direct vertical percolation appears to be very limited, in contradiction to the conceptual model generally admitted where vertical flow through saprolite is considered as the main recharge process. The horizontal component of the flow leads to a strong geochemical stratification of the water column. The complex recharge pattern, presented in a conceptual model, leads to varied impacts on groundwater quality and availability in both time and space, inducing strong implications for water management, water quality evolution, MAR monitoring and longer-term socio-economic costs. 相似文献
419.
420.
Marçal Ximenes Brendan Duffy Mafaldo J. Faria Kate Neely 《Environmental Earth Sciences》2018,77(19):711
The management of groundwater quality is a critical issue in developing nations where sanitation and drinking water targets are commonly addressed by facilitating access to groundwater, which is then managed as a common-pool resource. We investigate the quality of the shallow unconfined groundwater in Dili’s alluvial fan system, which 50% of Dili’s rapidly growing population use for all their water requirements. Using the basic chemical and microbiological analyses that are locally available (sulfate, total hardness, fluoride, manganese, iron, ammonia, nitrite, nitrate, total coliform and E. coli) we show that the shallow wells commonly contain enhanced concentrations of dissolved solids and microbiological contaminants (total coliform and E. coli), relative to deeper wells. Cool, shallow wells are worse than warm equivalents. Elevated nitrate and nitrite pollution in the embassy district are tentatively attributed to affluence factors, such as lawn cultivation and water filtration equipment. Microbiological contamination, and associated manganese contamination of groundwater, mimic population patterns, but are concentrated in the finer grained sediments of the small fans and low-slope interdistributary areas. We suggest that rapid development and successful implementation of appropriate sanitation policy in Dili (and elsewhere) is required to address the problematic features of the shallow groundwater system. Success will be predicated on (1) the establishment of baseline data, and (2) development of a systems-thinking approach to holistic water resource management. 相似文献