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91.
Several two-equation turbulence models using isotropic eddy viscosity and wall functions are assessed by solution of the neutral atmospheric boundary layer over a flat surface and wind flow over two- and three-dimensional models and real terrain. Calculations are presented for wind flow over the Sirhowy Valley in Wales, an embankment along the Rhine in Germany and the Askervein Hill in Scotland. Comparisons of predictions with previous work, and laboratory and field data, show that the RNG-based k–p68/xxlarge8712.gif" alt="isin" align="MIDDLE" BORDER="0"> model gives the best agreement with respect to the flow profiles and length of the separated flow region. The results of this model are analyzed with a non-linear stress-strain relation to gauge the potential effect of turbulence anisotropy. 相似文献
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本文给出了一类p(x)-Laplace方程的正径向解在单位球上的1个唯一性定理,文章中假定p(x)是径向的单调函数.并且非线性项满足某种单调性条件。 相似文献
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The 17 Sustainable Development Goals (SDGs) aim to end extreme poverty and create a healthy, sustainable world by the year 2030. Goal 7 is of interest to this study as it targets access to clean and affordable energy. However, in this study we show that the energy created in South Africa is not necessary clean. South Africa has numerous coal-fired power station located in the Mpumalanga (MP), Gauteng (GP) and Limpopo (LP) provinces. These power station produce tons of toxic pollutants including sulphur dioxide (SO2), nitrogen dioxide (NO2) and sulphates (SO4). These pollutants are known to have a negative impact on human health, climate and the environment. In this study we use the sequential Mann-Kendall test to investigate the 39 year (1980–2019) trends of SO2, NO2 and SO4 from these source areas. We also report for the first time on the observations of SO2 and NO2 from the Sentinel-5 P sensor over South Africa. Increasing trends of SO2 were observed in the MP, LP and GP regions. The increase was mostly due to the emissions from coal-fired power stations. Moreover, the increase of SO2 over the years could be due to the increasing demand in electricity, aging power stations and the low quality of coal used. Sentinel-5 P observations of SO2 and NO2 over South Africa were observed in the MP, GP and LP regions as a result of coal-fired power stations. Dispersion of SO2 and NO2 over South Africa were observed in the winter months, while confined SO2 and NO2 in the source region were observed in the summer months. 相似文献
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Aquaculture, like terrestrial farming, cannot achieve economic and sustainable production without high performing genetic stocks tailored to the conditions under which they are grown. It is essential, therefore, that aquaculture investment includes genetics and biotechnology to adapt marine livestock to the novel conditions of intensive aquaculture and to the demanding markets into which they are sold. The return on investment in well-structured breeding programmes can be very high, and significant performance and economic gains have been demonstrated in multiple species. Many factors must be considered in designing a genetic improvement programme, including the reproductive biology of the species and the identification of realistic and commercially relevant breeding goals based on the resources and facilities available. This paper reviews the options available to aquaculturists and provides examples of how these are being applied to six aquaculture species in New Zealand: king salmon, hāpuku, kingfish, Greenshellp>TM p> mussels, Pacific oysters and pāua (abalone). 相似文献
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家庭联产承包责任制实现了土地所有权和使用权的初步分离,使农民获得了相对独立的承包经营权,极大地调动了农民的生产积极性。然而,随着农村经济社会的发展,人地矛盾日益激化,土地的边际生产力已出现明显的递减趋势,土地小规模家庭经营,农业的比较利益大大下降;同时,农村的剩余劳动力涌向经济较发达的大中城市,城市化进程骤然加剧等,使得土地家庭承包经营这一土地制度逐渐显露出自身的缺陷。在稳定农村土地承包关系的前提下,促进农村土地流转,可以在一定程度上发挥土地的规模效益,促进农村经济社会的健康持续发展。 相似文献
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针对不同方法提取面波基模式频散曲线精度问题,笔者分别采用τ-p变换、频率分解法、F-K变换、高分辨率线性拉东变换(High-Resolution Linear Radon Transform,简称HRLRT)对六层递增型地质模型合成瑞雷波记录进行频散能量成像,并按频散能量最大值拾取基模式频散曲线。为定量评价理论模型基模式频散曲线提取解与解析解的接近程度,引入了均方差与相关系数两种评价参数。评价结果表明,高分辨率线性拉东变换提取基模式频散曲线精度最高,均方差为11.167 8,相关系数为0.994 9;F-K变换提取基模式频散曲线精度最低,均方差为195.274,相关系数为0.515 2。 相似文献