Local and Target Exploration of Conglomerate-Hosted Gold Deposits Using Machine Learning Algorithms: A Case Study of the Witwatersrand Gold Ores,South Africa     

Nwaila  Glen T.  Zhang  Steven E.  Frimmel  Hartwig E.  Manzi  Musa S. D.  Dohm  Christina  Durrheim  Raymond J.  Burnett  Mark  Tolmay  Leon 《Natural Resources Research》2020,29(1):135-159

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A method for seafloor classification using directional variograms, demonstrated for data from the western flank of the Mid-Atlantic Ridge     

Ute Christina Herzfeld 《Mathematical Geology》1993,25(7):901-924

Seafloor classification is aimed at quantitatively characterizing seafloor properties such as roughness and anisotropy, and at using such spatial characteristics to distinguish geological provinces automatically. From geostatistical principals, a variogram method is developed for seafloor classification and it is demonstrated for data from the western flank of the Mid-Atlantic Ridge at 25°45N to 26°40N. This study uses HYDROSWEEP bathymetric data which have been ping-edited to flag erroneous data records, and navigation corrected. The classification method can handle the resultant data gaps inside the survey swaths as well as interpret data from several swaths. For a suite of test areas representative of different geological provinces, directional variograms are calculated, and characteristic parameters are extracted for the classification. Examples include a sediment pond, abyssal hill terrain in several segments and of variable spacing, inside and outside corners of ridge discontinuities, and mixed morphological forms. The dependency of the results on random or regular subsampling and on the size of the test area is investigated.  相似文献   

Accuracy of the spatial representation of the seafloor with bathymetric sidescan sonars     

Pierre Cervenka  Ute Christina Herzfeld  Christian De Moustier 《Marine Geophysical Researches》1994,16(6):407-425

When isobath maps of the seafloor are constructed with a bathymetric sidescan sonar system the position of each sounding is derived from estimates of range and elevation. The location of each pixel forming the acoustic backscatter image is calculated from the same estimates. The accuracy of the resulting maps depends on the acoustic array geometry, on the performances of the acoustic signal processing, and on knowledge of other parameters including: the platform's navigation, the sonar transducer's attitude, and the sound rays' trajectory between the sonar and the seafloor. The relative importance of these factors in the estimation of target location is assesed. The effects of the platform motions (e.g. roll, pitch, yaw, sway, surge and heave) and of the uncertainties in the elevation angle measurements are analyzed in detail. The variances associated with the representation (orientation and depth) of a plane, rectangular patch of the seafloor are evaluated, depending on the geometry of the patch. The inverse problem is addressed. Its solution gives the lateral dimensions of the spatial filter that must be applied to the bathymetric data to obtain specified accuracies of the slopes and depths. The uncertainty in the estimate of elevation angle, mostly due to the acoustic noise, is found to bring the main error contribution in across-track slope estimates. It can also be critical for along-track slope estimates, overshadowing error contributions due to the platform's attitude. Numerical examples are presented.On leave at the Naval Research Laboratory, Code 7420, Washington D.C. 20375-5350, U.S.A.  相似文献   

中国湖北钉螺(腹足纲:圆口螺科)分类现状   总被引：1，自引：0，他引：1  

George M.Davis  张儀  郭源华  Christina Spolsky 《海洋科学集刊》1997,(39):89-95

本文对采自中国境内不同水域、不同螺壳类型的14个螺群的同工酶数据进行了遗传分化研究,探讨中国湖北钉螺的分类现状。结果表明,中国钉螺存在重要的遗传分化及与遗传分化相关的可分辨的类型。对此进行研究后还发现了县城交叉传播和亚种间可能存在3个例外杂合螺群的依据;此外,螺群遗传分化类型与地理分布、螺壳刻纹和形态特征相一致。以此为基础,湖北钉螺(Oncomelania hupensis)再分成3个独立的亚种:滇川亚种(O.h. robertsoni )、福建亚种(O.h. tangi )和湖北亚种(O,h. hupensis).  相似文献   

Contaminant exposure and effects in Baltic ringed and grey seals as assessed by biomarkers   总被引：3，自引：0，他引：3  

Nyman M  Bergknut M  Fant ML  Raunio H  Jestoi M  Bengs C  Murk A  Koistinen J  Bäckman C  Pelkonen O  Tysklind M  Hirvi T  Helle E 《Marine environmental research》2003,55(1):73-99

The Baltic Sea ecosystem has suffered from a heavy pollutant load for more than three decades. Persistent organic pollutants (POPs) and heavy metals have been of most concern due to their persistence and toxic properties. Ringed seals (Phoca hispida baltica) and grey seals (Halichoerus grypus) living in the Baltic Sea have been suffering from pathological impairments, including reproductive disturbances, which have resulted in a depressed reproductive capacity. We investigated several biochemical parameters as potential biomarkers for exposure to and effects of the contaminant load in the Baltic seals. Seals from less polluted areas were used as reference material in terms of the pollution load. In both Baltic seal populations, the levels of some biochemical parameters diverged from those in the reference seals, and some of these showed a clear correlation with the individual contaminant load. Of the potential bioindicators, we propose cytochrome P4501A activity and vitamin E levels, in blubber or plasma, as exposure biomarkers for polychlorinated biphenyls (PCBs) and dichlorodiphenyltrichloroethane (DDT) in both species. The arylhydrocarbon receptor-mediated chemical-activated luciferase gene expression (CALUX) response reflects the whole PCB and DDT burden in ringed seals. Retinyl palmitate (vitamin A) levels showed a negative correlation with the individual POP load, and is proposed as potential effect biomarkers for the depletion of the vitamin A stores. As the nutritional levels of both vitamin A and E have an impact on the vitamin levels in the seals, more information on the dietary vitamin levels is needed before any conclusions can be drawn. As the relationship between biochemical parameters and contaminants varied between the two species, species-specific characteristics has to be considered when monitoring the health status and possible toxic effects of the contaminant load in ringed and grey seals.  相似文献   

Assessing the sustainability factors of traditional olive groves on Lesvos Island,Greece (Sustainability and traditional cultivation)     

Christina Giourga  Angeliki Loumou  Iris Tsevreni  Assimina Vergou 《GeoJournal》2008,73(2):149-159

In Europe the process of agricultural engagement or disengagement is attributed to the economic factor and mainly on the level of alternative employment source development. It is the relational quality of economic, social and environmental factors that determine sustainability of agricultural holdings and, hence, households. In regions of poor agricultural structures and of many employment opportunities as well as in regions suffering from agricultural depression, households exhibit stronger tendencies towards agricultural disengagement. Remarkably in southern Europe a stable agricultural engagement and not disengagement is observed, even though in recent years there are limited possibilities of alternative income sources and prevailing agricultural depression. This article highlights the factors which lead households to stable engagement with agriculture in a region of southern Europe, the island of Lesvos. The island is characterised by traditional olive grove mono-culture, poor agricultural structures and limited employment opportunities. The investigation of the economic, social and environmental farm household characteristics concluded that in regions where poor agricultural infrastructure and lack of employment prevail, all three factors of sustainability contribute to stability and/or low agricultural disengagement. Among these, the economic factor is the most sensitive and hence highly influential. The social factor is highlighted as a quality and consistent factor due to the respect for tradition. The environmental factor, finally, is characterised by mild cultivation practices, contributing to environment conservation.  相似文献   

Continental rifting as a function of lithosphere mantle strength     

Frdric Gueydan  Christina Morency  Jean-Pierre Brun 《Tectonophysics》2008,460(1-4):83-93

The role of the uppermost mantle strength in the pattern of lithosphere rifting is investigated using a thermo-mechanical finite-element code. In the lithosphere, the mantle/crust strength ratio (S_M/S_C) that decreases with increasing Moho temperature T_M allows two strength regimes to be defined: mantle dominated (S_M > S_C) and crust dominated (S_M < S_C). The transition between the two regimes corresponds to the disappearance of a high strength uppermost mantle for T_M > 700 °C. 2D numerical simulations for different values of S_M/S_C show how the uppermost mantle strength controls the style of continental rifting. A high strength mantle leads to strain localisation at lithosphere scale, with two main patterns of narrow rifting: “coupled crust–mantle” at the lowest T_M values and “deep crustal décollement” for increasing T_M values, typical of some continental rifts and non-volcanic passive margins. The absence of a high strength mantle leads to distributed deformations and wide rifting in the upper crust. These numerical results are compared and discussed in relation with series of classical rift examples.  相似文献   

Climate change projections for Greek viticulture as simulated by a regional climate model     

Lazoglou  Georgia  Anagnostopoulou  Christina  Koundouras  Stefanos 《Theoretical and Applied Climatology》2018,133(1-2):551-567

Theoretical and Applied Climatology - Viticulture represents an important economic activity for Greek agriculture. Winegrapes are cultivated in many areas covering the whole Greek territory, due to...  相似文献   

Analysis of agro-climatic parameters and their influence on maize production in South Africa     

Omolola?M.?AdisaEmail author  Christina?M.?Botai  Joel?O.?Botai  Abubeker?Hassen  Daniel?Darkey  Eyob?Tesfamariam  Alex?F.?Adisa  Abiodun?M.?Adeola  Katlego?P.?Ncongwane 《Theoretical and Applied Climatology》2018,134(3-4):991-1004

This study analyzed the variability of the agro-climatic parameters that impact maize production across different seasons in South Africa. To achieve this, four agro-climatic variables (precipitation, potential evapotranspiration, minimum, and maximum temperatures) were considered for the period spanning 1986–2015, covering the North West, Free State, Mpumalanga, and KwaZulu-Natal (KZN) provinces. Results illustrate that there is a negative trend in precipitation for North West and Free State provinces and positive trend in maximum temperature for all the provinces over the study period. Furthermore, the results showed that among other agro-climatic parameters, minimum temperature had the most influence on maize production in North West, potential evapotranspiration (combination of the agro-climatic parameters), minimum and maximum temperature influenced maize production in KZN while maximum temperature influenced maize production in Mpumalanga and Free State. In general, the agro-climatic parameters were found to contribute 7.79, 21.85, 32.52, and 44.39% to variation in maize production during the study period in North West, Free State, Mpumalanga, and KZN, respectively. The variation in maize production among the provinces under investigation could most likely attribute to the variation in the size of the cultivated land among other factors including soil type and land tenure system. There were also difference in yield per hectare between the provinces; KZN and Mpumalanga being located in the humid subtropical areas of South Africa had the highest yield per hectare 5.61 and 4.99 tons, respectively, while Free State and North West which are in the semi-arid region had the lowest yield per hectare 3.86 and 3.03 tons, respectively. Understanding the nature and interaction of the dominant agro-climatic parameters discussed in the present study as well as their impact on maize production will help farmers and agricultural policy makers to understand how climate change exerts its influence on maize production within the study area so as to better adapt to the major climate element that either increases or decreases maize production in their respective provinces.  相似文献   

Assessing the effects of forest biomass reductions on forest health and streamflow     

Ryan R. Bart  Ram L. Ray  Martha H. Conklin  Mohammad Safeeq  Philip C. Saksa  Christina L. Tague  Roger C. Bales 《水文研究》2021,35(3):e14114

Forest biomass reductions in overgrown forests have the potential to provide hydrologic benefits in the form of improved forest health and increased streamflow production in water-limited systems. Biomass reductions may also alter evaporation. These changes are generated when water that previously would have been transpired or evaporated from the canopy of the removed vegetation is transferred to transpiration of the remaining vegetation, streamflow, and/or non-canopy evaporation. In this study, we combined a new vegetation-change water-balance approach with lumped hydrologic modelling outputs to examine the effects of forest biomass reductions on transpiration of the remaining vegetation and streamflow in California's Sierra Nevada. We found that on average, 102 mm and 263 mm (8.0% and 20.6% of mean annual precipitation [MAP]) of water were made available following 20% and 50% forest biomass-reduction scenarios, respectively. This water was then partitioned to both streamflow and transpiration of the remaining forest, but to varying degrees depending on post-biomass-reduction precipitation levels and forest biomass-reduction intensity. During dry periods, most of the water (approximately 200 mm [15.7% on MAP] for the 50% biomass-reduction scenario) was partitioned to transpiration of the remaining trees, while less than 50 mm (3.9% on MAP) was partitioned to streamflow. This increase in transpiration during dry periods would likely help trees maintain forest productivity and resistance to drought. During wet periods, the hydrologic benefits of forest biomass reductions shifted to streamflow (200 mm [15.7% on MAP]) and away from transpiration (less than 150 mm [11.8% on MAP]) as the remaining trees became less water stressed. We also found that streamflow benefits per unit of forest biomass reduction increased with biomass-reduction intensity, whereas transpiration benefits decreased. By accounting for changes in vegetation, the vegetation-change water balance developed in this study provided an improved assessment of watershed-scale forest health benefits associated with forest biomass reductions.  相似文献