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51.
An important task in modern geostatistics is the assessment and quantification of resource and reserve uncertainty. This uncertainty
is valuable support information for many management decisions. Uncertainty at specific locations and uncertainty in the global
resource is of interest. There are many different methods to build models of uncertainty, including Kriging, Cokriging, and
Inverse Distance. Each method leads to different results. A method is proposed to combine local uncertainties predicted by
different models to obtain a combined measure of uncertainty that combines good features of each alternative. The new estimator
is the overlap of alternate conditional distributions. 相似文献
52.
The origin of accretionary lapilli 总被引:1,自引:0,他引:1
Experimental investigations in a recirculating wind tunnel of the mechanisms of formation of accretionary lapilli have demonstrated that growth is controlled by collision of liquid-coated particles, due to differences in fall velocities, and binding as a result of surface tension forces and secondary mineral growth. The liquids present on particle surfaces in eruption plumes are acid solutions stable at 100% relative humidity, from which secondary minerals, e.g. calcium sulphate and sodium chloride, precipitate prior to impact of accretionary lapilli with the ground. Concentric grain-size zones within accretionary lapilli build up due to differences in the supply of particular particle sizes during aggregate growth. Accretionary lapilli do not evolve by scavenging of particles by liquid drops followed by evaporation — a process which, in wind tunnel experiments, generates horizontally layered hemispherical aggregates. Size analysis of particles in the wind tunnel air stream and particles adhering to growing aggregates demonstrate that the aggregation coefficient is highly grain-size dependent. Theoretical simulation of accretionary lapilli growth in eruption plumes predicts maximum sizes in the range 0.7–20 mm for ash cloud thicknesses of 0.5–10 km respectively. 相似文献
53.
A. Feldmeier 《Astrophysics and Space Science》1994,221(1-2):393-408
Due to the instability of the radiation line force, the winds of hot, luminous stars should show a pronounced time-dependence resulting from the nonlinear growth of initially small perturbations. Following the method of Owocki, Castor & Rybicki (1988), we describe the time-dependent wind structure obtained with an independently developed code. Under the central assumption ofisothermality, our results are in very good agreement with the ones by Owocki et al. We find that the response of the wind to periodic base perturbations remains largely periodic, at least up tor 2...3R
*
, with no clear evidence of stochastic behaviour.In order to test the foregoing assumption of isothermality and to compute the X-ray emission from models of structured winds, we have also incorporated theenergy equation into our simulations. We encountered the numerical problem that all radiative cooling zones collapse because of the oscillatory thermal instability (cf. Langer et al. 1981). We present a method to hinder this collapse by changing the cooling function at low temperatures. The resulting wind showsresolved cooling zones; but, for a supergiant wind relatively close to the star (r 10R
*
), the macroscopic wind structure is very similar to isothermal calculations. Most of the hot material is caused by shell-shell collisions. 相似文献
54.
利用2017年6—8月的FNL再分析资料分析了新疆地区夏季平流层低层风场的时空演变特征,开展了平流层低层风场的高分辨率数值模拟和检验。结果表明:新疆地区夏季平流层纬向风随时间的变化存在经向差异,同时准零风层开始和结束的时间也存在经向差异,准零风层开始时间南部地区早于北部地区,而准零风层结束时间则相反。整个夏季新疆地区上空的准零风层处于70~40 hPa之间,其高度随时间呈先降低而后升高的变化趋势。准零风层数值模拟结果表明,模拟的准零风层参数与探空资料分析结果相比二者存在一致的变化趋势,准零风层起始高度的平均绝对误差为467 m,该高度对应的风速均方根误差为1.75 m/s。 相似文献
55.
Local food is championed as one alternative response to industrial systems of food production and supply. While advocacy for local food is high, there is a lack of empirical evidence about the actual shape and scale of such food supply chains, especially from a retail perspective. Using supply chain diagrams, this paper presents a summary of ‘new’ agro-food geographies for five different retail types—farm shops, butchers, caterers, specialist shops, supermarkets/department stores—that all source local food from suppliers in the Scottish-English borders. Presented as five separate ‘shopping trips’, the paper examines where, how and why retailers source local food. Results reveal the complex nature of local food systems, especially in terms of intra-sector competitive dynamics (with a notable tension between direct forms of retail and established (independent) retailers), links and overlaps with ‘normal’ food retail systems and elastic notions of the ‘local’. The paper also draws a key distinction between locally produced and locally supplied food products. 相似文献
56.
Guillermo Booth-Rea Jos Fernando Simancas Antonio Azor Jos Miguel Azan Francisco Gonzlez-Lodeiro Paulo Fonseca 《Comptes Rendus Geoscience》2006,338(16):1260-1267
Multi-equilibrium thermobarometry shows that low-grade metapelites (Cubito-Moura schists) from the Ossa–Morena Zone underwent HP–LT metamorphism from 340–370 °C at 1.0–0.9 GPa to 400–450 °C at 0.8–0.7 GPa. These HP–LT equilibriums were reached by parageneses including white K mica, chlorite and chloritoid, which define the earliest schistosity (S1) in these rocks. The main foliation in the schists is a crenulation cleavage (S2), which developed during decompression from 0.8–0.7 to 0.4–0.3 GPa at increasing temperatures from 400–450 °C to 440–465 °C. Fe3+ in chlorite decreased greatly during prograde metamorphism from molar fractions of 0.4 determined in syn-S1 chlorites down to 0.1 in syn-S2 chlorites. These new data add to previous findings of eclogites in the Moura schists indicating that a pile of allochtonous rocks situated next to the Beja-Acebuches oceanic amphibolites underwent HP–LT metamorphism during the Variscan orogeny. To cite this article: G. Booth-Rea et al., C. R. Geoscience 338 (2006). 相似文献
57.
Heavy metals in freshly deposited sediments of the river Subernarekha, India: an example of lithogenic and anthropogenic effects 总被引:1,自引:0,他引:1
A. K. Upadhyay K. K. Gupta J. K. Sircar M. K. Deb G. L. Mundhara 《Environmental Geology》2006,50(3):397-403
Heavy metal distribution patterns in river sediments aid in understanding the exogenic cycling of elements as well as in assessing the effect of anthropogenic influences. In India, the Subernarekha river flows over the Precambrian terrain of the Singhbhum craton in eastern India. The rocks are of an iron ore series and the primary rock types are schist and quartzite. One main tributary, the Kharkhai, flows through granite rocks and subsequently flows through the schist and quartzite layers. The Subernarekha flows through the East Singhbhum district, which is one of India’s industrialised areas known for ore mining, steel production, power generation, cement production and other related activities. Freshly deposited river sediments were collected upstream and downstream the industrial zone. Samples were collected from four locations and analysed in <63-μm sediment fraction for heavy metals including Zn, Pb, Cd and Cu by anodic stripping voltammetry. Enrichment of these elements over and above the local natural concentration level has been calculated and reported. Sediments of the present study are classified by Muller’s geo-accumulation index (I
geo) and vary from element to element and with climatic seasons. During pre-monsoon period the maximum I
geo value for Zn is moderately to highly polluted and for Cu and Pb is moderately polluted, respectively, based on the Muller’s standard. Anthropogenic, lithogenic or cumulative effects of both components are the main reasons for such variations in I
geo values. The basic igneous rock layer through which the river flows or a seasonal rivulet that joins with the main river may be the primary source for lithogenic components. 相似文献
58.
Porous fence is a kind of artificial windbreak that has many practical applications. The threshold wind velocities at different distances downwind from porous fences were measured and the corresponding characteristics of particle movement observed to assess their shelter effect. It is found that the fence’s porosity is the key factor that determines the resulting shelter effect. The area near a fence can be typically classified into five regions, each with a different mode of particle movement. Dense fences, and especially solid fences, favor the accumulation of sand upwind of the fences. Fences with porosities of 0.3–0.4 produce the maximum threshold wind velocity; those with porosities of 0.3–0.6 (depending on the fence height) provide the maximum effective shelter distance. It is confirmed that the fence porosities of 0.3–0.4 that have been proposed for practical application in previous research are the most effective for abating wind erosion. 相似文献
59.
Scott W. White 《Natural Resources Research》2006,15(4):271-281
This paper updates a life-cycle net energy analysis and carbon dioxide emissions analysis of three Midwestern utility-scale
wind systems. Both the Energy Payback Ratio (EPR) and CO2 analysis results provide useful data for policy discussions regarding an efficient and low-carbon energy mix. The EPR is
the amount of electrical energy produced for the lifetime of the power plant divided by the total amount of energy required
to procure and transport the materials, build, operate, and decommission the power plants. The CO2 analysis for each power plant was calculated from the life-cycle energy input data.
A previous study also analyzed coal and nuclear fission power plants. At the time of that study, two of the three wind systems
had less than a full year of generation data to project the life-cycle energy production. This study updates the analysis
of three wind systems with an additional four to eight years of operating data.
The EPR for the utility-scale wind systems ranges from a low of 11 for a two-turbine system in Wisconsin to 28 for a 143-turbine
system in southwestern Minnesota. The EPR is 11 for coal, 25 for fission with gas centrifuge enriched uranium and 7 for gaseous
diffusion enriched uranium. The normalized CO2 emissions, in tonnes of CO2 per GWeh, ranges from 14 to 33 for the wind systems, 974 for coal, and 10 and 34 for nuclear fission using gas centrifuge and gaseous
diffusion enriched uranium, respectively. 相似文献
60.
对改进初始强迫风场后的Zebiak-Cane海气耦合模式预报性能进行了全面评估。结果表明:1)耦合模式在20世纪90年代预报能力小于80年代;提前0~5个月的耦合模式预报能力小于同期持续预报能力,之后则相反;耦合模式对Nino3区指数预报能力最强。2)在1997/1998年El Nino事件期间,耦合模式对东太平洋SSTA场预报能力大于其对中西太平洋SSTA场的预报能力,且提前0~2个月之后的耦合模式对东太平洋SSTA场预报能力远远大于持续预报。 相似文献