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101.
102.
Evaluation of total load sediment transport formulas using ANN 总被引:2,自引:0,他引:2
The calculated results from various sediment transport formulas often differ from each other and from measured data. Some parameters in the sediment transport formulas are more effective than others to estimate total sediment load. In this study, an Artificial Neural Network (ANN) model is trained using four dominant parameters of sediment transport formulas. ANN models are able to reveal hidden laws of natural phenomena such as sediment transport process. The results of ANN and some total bed material load sediment transport formulas have been compared to indicate the importance of variables which can be used in developing sediment transport formulas. To train ANN, average flow velocity, water surface slopes, average flow depth, and median particle diameter are used as dominant parameters to estimate total bed material load. Two hundreds and fifty samples are used to train the ANN model. Twenty-four sets of field data not used in the training nor calibration of ANN are used to compare or verify the accuracy of ANN and some well-known total bed material load formulas. The test results show that the ANN model developed in this study using minimum number of dominant factors is a reliable and uncomplicated method to predict total sediment transport rate or total bed material load transport rate. Results show that the accuracy of formulas in descending order are those by Yang (1973), Laursen (1958), Engelund and Hansen (1972), Ackers and White (1973), and Toffaleti (1969). These results are similar to those made by ASCE (1982) based on laboratory and field data not used in this paper. Study results also show that the formulas based on physical laws of sediment transport, like those formulas that were developed based on power concept, are more accurate than other formulas for estimating total bed material sediment load in rivers. 相似文献
103.
Didier?LaporteEmail author Michael?J.?Toplis Monique?Seyler Jean-Luc?Devidal 《Contributions to Mineralogy and Petrology》2004,146(4):463-484
A new technique that allows extraction of liquids from peridotite at degrees of melting as low as 0.2 wt% is presented. Microfractures that formed in the graphite sample container at the beginning of the experiments were used as traps for the liquid phase. Glass-filled cracks (or 'microdikes') unaffected by quench crystallisation were produced in all experiments and were analysed using standard electron microprobe techniques. Reversal experiments demonstrated that, at moderate degrees of melting (4.4 and 6.5 wt%), the segregated liquid was in equilibrium with the neighbouring peridotite. At very low degrees of melting (0.3 wt%), the liquid in the microdikes failed to fully equilibrate with the peridotite after 5 days and the sandwich technique was used in combination with the microdike technique to approach more closely the equilibrium composition of near-solidus partial melts. The microdike technique was used to study melting of a depleted peridotite at 1 GPa and 1,220 to 1,360 °C.Editorial responsibility: T.L. Grove 相似文献
104.
We perform Monte Carlo simulations of synthetic EMSS cluster samples, to quantify the systematic errors and the statistical uncertainties on the estimate of Ω0 derived from fits to the cluster number density evolution and to the X-ray temperature distribution up to z =0.83 . We identify the scatter around the relation between cluster X-ray luminosity and temperature to be a source of systematic error, of the order of Δsyst Ω0 =0.09 , if not properly taken into account in the modelling. After correcting for this bias, our best Ω0 is 0.66. The uncertainties on the shape and normalization of the power spectrum of matter fluctuations imply relatively large uncertainties on this estimate of Ω0 , of the order of Δstat Ω0 =0.1 at the 1 σ level. On the other hand, the statistical uncertainties due to the finite size of the high-redshift sample are twice as small. Therefore, what is needed in order to improve the accuracy of Ω0 estimates based on cluster number density evolution is a more reliable measure of the local temperature function and a better understanding of the cluster observed properties both in the local Universe and at high redshift, that is the relation between cluster mass, temperature and luminosity. This requires detailed observations of X-ray selected cluster samples, in comparison with hydrodynamic simulations including refined physics. 相似文献
105.
Marta Fort J. Antoni Sellarès 《International journal of geographical information science》2014,28(9):1877-1903
Data analysis and knowledge discovery in trajectory databases is an emerging field with a growing number of applications such as managing traffic, planning tourism infrastructures or better understanding wildlife. In this paper, we study the problem of finding flock patterns in trajectory databases. A flock refers to a large enough subset of entities that move close to each other for, at least, a given time interval. We present parallel algorithms, to be run on a Graphics Processing Unit, for reporting three different variants of the flock pattern: (1) all maximal flocks, (2) the largest flock and (3) the longest flock. We also provide their complexity analysis together with experimental results showing the efficiency and scalability of our approach. 相似文献
106.
Influence of bioturbation by the polychaete Nereis diversicolor on the structure of bacterial communities in oil contaminated coastal sediments 总被引:1,自引:0,他引:1
Cuny P Miralles G Cornet-Barthaux V Acquaviva M Stora G Grossi V Gilbert F 《Marine pollution bulletin》2007,54(4):452-459
Patterns of change in the structure of bacterial communities monitored by ribosomal intergenic spacer analysis (RISA) in oil contaminated sediments inhabited or not by the marine polychaete Nereis diversicolor were studied during 45 days under laboratory conditions. Results supported by principal component analysis showed a marked response of the bacterial communities to the oil contamination and to the presence of N. diversicolor. Phylogenetic affiliation of specific RISA bands showed that, in the contaminated sediments, the presence of the marine polychaetes favoured the development of bacteria which may play an active role in natural bioremediation processes of oil polluted environments. 相似文献
107.
La présente étude a pour objectif d’analyser la variabilité spatiale multi-échelles de l’équivalent en eau de la neige (EEN). Dans un premier temps, la variabilité spatiale de l’EEN par rapport à la latitude et à la longitude a été analysée. Des indices locaux ont été utilisés pour caractériser les différentes structures spatiales. Par la suite, les structures spatiales homogènes ont été délimitées à l’aide de l’approche de segmentation spatiale multi-résolutions en utilisant des méta-variables physiographiques. La segmentation a été validée à l’aide du test non paramétrique de Kruskal-Wallis appliqué aux données de l’EEN de chaque paire de zones adjacentes. À l’échelle régionale, la segmentation spatiale a permis d’identifier six zones géographiques différenciées par leur position par rapport aux modes de circulations atmosphériques et la disposition du relief. À l’échelle locale, la segmentation spatiale montre le rôle de la pente, de la courbure, etc. dans la variabilité spatiale du couvert nival.
Editeur Z. W. Kundzewicz; Editeur associé E. Gargouri 相似文献