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Bougrain Laurent Gonzalez Maria Bouchot Vincent Cassard Daniel Lips Andor L. W. Alexandre Frédéric Stein Gilbert 《Natural Resources Research》2003,12(3):173-181
This study is concerned with understanding of the formation of ore deposits (precious and base metals) and contributes to the exploration and discovery of new occurrences using artificial neural networks. From the different digital data sets available in BRGM's GIS Andes (a comprehensive metallogenic continental-scale Geographic Information System) 25 attributes are identified as known factors or potential factors controlling the formation of gold deposits in the Andes Cordillera. Various multilayer perceptrons were applied to discriminate possible ore deposits from barren sites. Subsequently, because artificial neural networks can be used to construct a revised model for knowledge extraction, the optimal brain damage algorithm by LeCun was applied to order the 25 attributes by their relevance to the classification. The approach demonstrates how neural networks can be used efficiently in a practical problem of mineral exploration, where general domain knowledge alone is insufficient to satisfactorily model the potential controls on deposit formation using the available information in continent-scale information systems. 相似文献
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Urmas Haud 《Astrophysics and Space Science》1981,76(2):477-490
The systemic velocity of M31, rotation and expansion velocities as functions of galactocentric distance have been derived from all data available on the radial velocity field of the Andromeda galaxy. The bending of the outer parts of the M31 disk has been considered. The calculations confirm the existence of gas outflow from the central parts of the galaxy. The obtained rotation curve is rather flat from 5 to 37 kpc. The spiral arms cause the waves both in the rotation and expansion curve. The new rotation curve is given in Table III. 相似文献
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Consequences of coastal upwelling events on physical and chemical patterns in the central Gulf of Finland (Baltic Sea) 总被引：1，自引：0，他引：1
The consequences of a coastal upwelling event on physical and chemical patterns were studied in the central Gulf of Finland. Weekly mapping of hydrographical and -chemical fields were carried out across the Gulf between Tallinn and Helsinki in July–August 2006. In each survey, vertical profiles of temperature and salinity were recorded at 27 stations and water samples for chemical analyses (PO43−, NO2−+NO3−) were collected at 14 stations along the transect. An ordinary distribution of hydrophysical and -chemical variables with the seasonal thermocline at the depths of 10–20 m was observed in the beginning of the measurements in July. Nutrient concentrations in the upper mixed layer were below the detection limit and nutriclines were located just below or in the lower part of the thermocline. In the first half of August, a very intense upwelling event occurred near the southern coast of the Gulf when waters with low temperature and high salinity from the intermediate layer surfaced. High nutrient concentrations were measured in the upwelled water – 0.4 μmol l−1 of phosphates and 0.6 μmol l−1 of nitrates+nitrites. We estimated the amount of nutrients transported into the surface layer as 238–290 tons of phosphorus (P)-PO43− and 175–255 tons of N-NOx for a 12 m thick, 20 km wide and 100 km long coastal stretch. Taking into account a characteristic along-shore extension of the upwelling of 200 km, the phosphate-phosphorus amount is approximately equal to the average total monthly riverine load of phosphorus to the Gulf of Finland. It is shown that TS-characteristics of water masses and vertical distribution of nutrients along the study transect experienced drastic changes caused by the upwelling event in the entire studied water column. TS-analysis of profiles obtained before and during the upwelling event suggests that while welled up, the cold intermediate layer water was mixed with the water from the upper mixed layer with a share of 85% and 15%. We suggest that the coastal upwelling events contribute remarkably to the vertical mixing of waters in the Gulf of Finland. Intrusions of nutrient-rich waters along the inclined isopycnal surfaces in the vicinity of upwelling front were revealed. The upwelling event widened the separation of phosphocline and nitracline which in turn prevented surfacing of nitrate+nitrite-nitrogen during the next upwelling event observed a week after the upwelling relaxation. A suggestion is made that such widening of nutricline separation caused by similar upwelling events in early summer could create favourable conditions for late summer cyanobacterial blooms. 相似文献
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Vertical dynamics of summer phytoplankton in a stratified estuary (Gulf of Finland,Baltic Sea) 总被引：1，自引：1，他引：0
Urmas Lips Inga Lips Taavi Liblik Villu Kikas Kristi Altoja Natalja Buhhalko Nelli Rünk 《Ocean Dynamics》2011,61(7):903-915
We present the results of multiparametric observations designed to follow the phytoplankton dynamics and interrelated physical,
chemical and biological processes in the Gulf of Finland (Baltic Sea). Data were acquired by an autonomous moored water column
profiler, an acoustic Doppler current profiler, a flow-through system installed aboard a ferry and by profiling and discrete
water sampling aboard research vessels in July and August 2009. The main aim of the study was to investigate the processes
responsible for the formation and maintenance of sub-surface maxima of phytoplankton biomass. We suggest that the environmental
conditions caused by the prevailing atmospheric and oceanographic forcing (wind; vertical stratification; basin-wide, mesoscale
and sub-mesoscale processes) are preferred by certain species/taxonomic groups and explain the migration patterns of phytoplankton.
Nocturnal downward migration of phytoplankton with a swimming speed up to 1.6 m h−1 occurred when the community was dominated by the dinoflagellate Heterocapsa triquetra. The observed splitting of the population into two vertically separated biomass maxima suggests that the H. triquetra cells, which reached the sub-surface layers with high nutrient concentrations, experienced bi-diurnal or asynchronous (when
swimming upwards) vertical migration. The most intense sub-surface biomass maxima, on some occasions with the biomass much
higher than that in the surface layer, were detected in connection to the sub-mesoscale intrusions below the depth of the
strongest vertical density gradient. 相似文献
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Seven intrathermocline lenses (ITLs) of Mediterranean origin have been found during three cruises of the R/VArnold Veimer in the eastern north Atlantic Ocean. As ITL moved off its source, relative conservativity of some thermohaline characteristics such as the density range occupied by the lenses, theT, S indices, the core's vertical structure, and the form of the thermohaline front were observed. In the region of mixing, the intensity of the finestructure intrusion stratification increases with the age of lenses when they propagate to the colder freshened background waters. The systems of the step-like structures below the ITL core are formed at a considerable distance between the lenses and the source.Translated by Mikhail M. Trufanov. 相似文献
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The Gulf of Finland is a 400-km long and 48–135-km wide tributary estuary of the Baltic Sea featuring the longitudinal two-layer estuarine flow modified by transverse circulation. Longitudinal volume transport in the deep layer is investigated by decomposing it into an averaged, slowly changing estuarine component (due to large-scale density gradients, river discharge and mean wind stress) and wind-driven fluctuating component. The derived expression relates the total deep-layer transport to the projection of wind stress fluctuation to a site-specific direction. The relationship is tested and calibrated by the results from numerical experiments carried out with the three-dimensional baroclinic circulation model. For the entrance to the Gulf of Finland, winds from northeast support standard estuarine circulation and winds from southwest work against the density-driven and riverine flow. The deep estuarine transport may be reversed if the southwesterly wind component exceeds the mean value by 4–5.5 m s−1. According to the data from hydrographic observations in the western Gulf of Finland, an event of advective halocline disappearance was documented in August 1998. Comparison of the deep-water transport estimates calculated from the wind data in 1998 with the observed salinity variations showed that the events of rapid decay of estuarine stratification were coherent with the estimated reversals of deep-layer volume transport, i.e. events of salt wedge export from the gulf. 相似文献
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Urmas Haud 《Astrophysics and Space Science》1984,104(2):337-345
It is shown that the rise of rotation velocities in the outer regions of our Galaxy may be illusive, and is caused by an excessive simplification of the methods of processing the observational data. Taking into consideration the possibility of the radial motions of the gas, we demonstrate that the existing observational data do not conflict with the hypothesis of the flat rotation curve of our Galaxy. The bending of the outer regions of the galactic disk has no significant effect on the observed radial velocities of the gaseous complexes. It is also shown that the wavy form of the rotation curve may be evoked by the spiral density waves in the Galaxy. 相似文献
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