The Tilt between Acretion Disk and Stellar Disk     

Shiyin Shen  Zhengyi Shao  Minfeng Gu 《Journal of Astrophysics and Astronomy》2011,32(1-2):197-201

The orientations of the accretion disk of active galactic nuclei (AGN) and the stellar disk of its host galaxy are both determined by the angular momentum of their forming gas, but on very different physical environments and spatial scales. Here we show the evidence that the orientation of the stellar disk is correlated with the accretion disk by comparing the inclinations of the stellar disks of a large sample of Type 2 AGNs selected from Sloan Digital Sky Survey (SDSS, York et al. 2000) to a control galaxy sample. Given that the Type 2 AGN fraction is in the range of 70–90 percent for low luminosity AGNs as a priori, we find that the mean tilt between the accretion disk and stellar disk is ~ 30 degrees (Shen et al. 2010).  相似文献   

长江河口近底层悬沙和沉积物的交换过程研究     

林益帆  戴志军  谢华亮  魏稳  葛振鹏  高近娟 《海洋学报》2014,36(7):99-110

大河河口的动力沉积过程一直是陆海相互作用研究的核心内容,其中水体泥沙的垂向交换是河口动力-沉积机制分析中的关键环节。基于2011年12月对长江河口及其邻近海湾采集的大范围、高密度的近底层悬沙、海床表层1~2cm(表层沉积物)和垂向向下约2~10cm的沉积物(次表层沉积物)同步3组303个样品,利用经验正交函数方法,对河口地区的悬沙和沉积物交换过程进行研究。结果表明:近底层水体悬沙的空间分布模式主要以粉砂粒级为主,空间分布差异性不大;表层及次表层沉积物的空间分布模式相似,但较近底层水体悬沙的分布复杂,存在明显的区域性特征,其中南汇边滩水域中部辐散区的沉积物表现为粗粉砂-细砂模式,其他区域由粉砂组分模式组成。近底层水体悬沙、表层和次表层沉积物的第一模态主要反映了粒径较细的泥沙运动,第二模态主要反映了粒径较粗的泥沙运动。在近底层水体悬沙与表层沉积物的垂向交换中,主要交换粒级为粉砂组分粒级。在表层沉积物与次表层沉积物的垂向交换中,南汇边滩中部辐散区的主要交换粒级为粗粉砂-细砂组分粒级,其他区域主要为粉砂组分粒级。  相似文献   

阵风及其谱模拟   总被引：3，自引：0，他引：3  

张云彩  姚美旺  王敏声  顾海粟 《海洋工程》1996,(2)

作用于海洋工程结构物的风力一般可分为恒定分量和变动分量两部分，认为前者是由于稳定风速所致，后者是由于风速脉动引起的。在实验室中为了恰当地模拟海上环境，不但要实现稳定风速的模拟，而且变动风速也要满足一定要求，这即是阵风谱的模拟。本文在风速的脉动是随机的，并服从高斯分布，且是由无限多正弦风叠加而成的基础上，叙述了海洋工程模型试验中如何实现阵风谱的模拟，并给出了模拟实例。  相似文献   

6000m深海拖曳系统动力响应计算   总被引：4，自引：3，他引：4  

廖世俊  顾云冠  朱继懋 《海洋工程》1995,(2)

本文数值计算了６０００ｍ深海单拖体和双拖体拖曳系统的动态响应，特别是研究了拖船的垂荡运动对拖体定高性的影响。对于双拖体系统，本文对第二拖体在水中的重量、联接两拖体的缆索长度及其在水中重量等因素对第二拖体定高性的影响进行了详细的计算、分析。计算表明，采用双拖体系统可大大提高系统的定高性。  相似文献   

中国数字创意上市挂牌企业空间格局及其影响因素     

展亚荣  谷人旭 《地理科学》2022,42(8):1370-1380

基于中国数字创意上市企业、新三板挂牌企业数据,运用核密度估计、标准差椭圆、基尼系数、负二项回归模型等方法探究其空间分布特征及影响因素。研究发现：① 数字创意上市挂牌企业总体呈“东密西疏”的空间结构特征,集聚与扩张共存并以集聚为主,且始终保持京津冀、长三角、珠三角等多核心空间集聚形态,空间分布高度不均衡且区域重心北向迁移显著。② 数字创意上市挂牌企业空间分布具有行业异质性,其集聚区域、集聚强度因产业特性和所有制性质不同而存在差异。③ 数字创意上市挂牌企业的空间分异受到集聚经济、基础设施、正式制度、非正式制度因素中的文化活跃度与企业家创新精神、宏观经济环境因素中的全球连通性、金融集聚水平等因素影响,具有明显“高等级城市偏好”。企业空间分异影响因素因产业特性和所有制不同存在差异。  相似文献   

Neural networks and their derivatives for history matching and reservoir optimization problems     

Jérémie Bruyelle  Dominique Guérillot 《Computational Geosciences》2014,18(3-4):549-561

In geosciences, complex forward problems met in geophysics, petroleum system analysis, and reservoir engineering problems often require replacing these forward problems by proxies, and these proxies are used for optimizations problems. For instance, history matching of observed field data requires a so large number of reservoir simulation runs (especially when using geostatistical geological models) that it is often impossible to use the full reservoir simulator. Therefore, several techniques have been proposed to mimic the reservoir simulations using proxies. Due to the use of experimental approach, most authors propose to use second-order polynomials. In this paper, we demonstrate that (1) neural networks can also be second-order polynomials. Therefore, the use of a neural network as a proxy is much more flexible and adaptable to the nonlinearity of the problem to be solved; (2) first-order and second-order derivatives of the neural network can be obtained providing gradients and Hessian for optimizers. For inverse problems met in seismic inversion, well by well production data, optimal well locations, source rock generation, etc., most of the time, gradient methods are used for finding an optimal solution. The paper will describe how to calculate these gradients from a neural network built as a proxy. When needed, the Hessian can also be obtained from the neural network approach. On a real case study, the ability of neural networks to reproduce complex phenomena (water cuts, production rates, etc.) is shown. Comparisons with second polynomials (and kriging methods) will be done demonstrating the superiority of the neural network approach as soon as nonlinearity behaviors are present in the responses of the simulator. The gradients and the Hessian of the neural network will be compared to those of the real response function.  相似文献   

Gold enrichment characteristics and exploration prospects in Zambia: Based on 1∶1000000 geochemical mapping     

Jun-ping Ren  Jie Wang  A-lei Gu  Li-bo Zuo  Hong-wei Sun  Kang-kang Xu  Fu-Qing He  Chipilauka Mukofu  Alphet Phaskani Dokowe  Ezekiah Chikambwe 《China Geology》2022,5(1):60-70

The 1∶1000000 geochemical mapping of Zambia provides catchment sediment geochemical data for 58elements including Au from 746 sediment samples at 736 sampling sites,corresponding to a sampling density of about one site per 1000 km2.Under strict quality control using field duplicates,certified reference materials,and analytical replicate samples,the Au was determined by Inductively Coupled Plasma Mass Spectrometry(ICP-MS).The detection limit of Au was 0.20×10^-9.The 95%range(2.5%–97.5%)of Au concentrations was from 0.24×10^-9 to 1.36×10^-9,and the median value was 0.40×10^-9.The most noticeable Au distribution patterns shown on the map are mainly located between Lusaka and Ndola(Lufilian Arc Belt).In addition,several high Au value areas occurred in Mansa,Muyombe,Chipata,and Livingstone.The spatial distribution patterns of Au in tectonic units,drainage basins,and geomorphological landscapes could be related to the Lufilian Arc Belt and Bangweulu Block.The Au concentrations show metallogenic belts between Muyombe and Mbala areas,between Mansa and Ndola areas,and between Lusaka and Kasempa areas.  相似文献   

Estimation of internal nutrient release in large shallow Lake Taihu,China   总被引：1，自引：0，他引：1  

Qin Boqiang  Zhu Guangwei  Zhang Lu  Luo Liancong  Gao Guang  Gu Binhe 《中国科学D辑(英文版)》2006,49(1):38-50

Based on field investigation of wave, sediment suspension and the changes in nutrient concentration of the water column in Lake Taihu, China, we proposed two release models to quantify nutrient release under static and dynamic conditions, respectively. Under static conditions, nutrient release from sediments to the overlying water mainly depends on chemical diffusion induced by concentration gradient, in which the nutrient release is controlled by the temperature, dissolved oxygen concentration in the sediment-water interface, oxidation-reduction potential and the concentration difference between porewater and overlying water. Under dynamic condition (or disturbed condition), both dissolved and particulate nutrients in sediments are released into the water column because of wind-induced sediment suspension. The amount of nutrient release under dynamic conditions is larger than that under the static condition. The release of dissolved nutrients, however, does not increase because the wind induced turbulence made oxidation of metallic elements such as Fe (ferric iron), Mn which are capable of precipitating soluble reactive phosphate (SRP). Under dynamic conditions, therefore, the release of total phosphorus (TP) increases dramatically but the release of SRP is close to those under static conditions. In sediments of Lake Taihu, high Fe content leads to a high ratio of Fe to P contents in sediments (Fe:P ratio). Under dynamic conditions, therefore, nutrient release is controlled by the intensity of disturbance, sediment consolidation and nutrient content in sediments. As for dissolved nutrients, especially SRP, the release is also controlled by the intensity of dynamic re-oxidation, Fe content in sediments and nutrient concentration gradient between porewater and overlying water. Based on these two release modes, the release flux in Lake Taihu has been estimated. In the static condition (i.e. laboratory experimental condition), total release of NH₄ ⁺-N for whole lake is ca. 10,000 ton/a, and PO₄ ^3?-P is ca. 900 ton/a. In the dynamic condition, nutrient release following sediment suspension was estimated according to three different intensities of wind forcing which were defined as “calm” (wind speed is less than 2 m/s), “gentle” (wind speed is greater than 2 m/s and less than 6 m/s) and “gust” (wind speed is greater than 6 m/s). The release rate in the condition of “calm” was estimated in terms of the nutrient release in the laboratory experimental static condition; whereas the release rate in conditions of “gentle” and “gust” was estimated in terms of measurement during sediment resuspension conducted in flume experiments. With the observation of wind velocity and frequency in 2001, each type of wind forcing took the frequency of 12%, 82% and 6% for “calm”, “gentle” and “gust”, respectively. The yearly release of nitrogen was 81,000 ton and phosphorus was 21,000 ton, which is about 2–6 folds of annual external loading, respectively.  相似文献   

Diversity and zonal distribution of arbuscular mycorrhizal fungi on the northern slopes of the Tianshan Mountains     

Shi ZhaoYong  Chen ZhiChao  Zhang LiYun  Feng Gu  Christie Peter  Tian ChangYan  Li XiaoLin 《中国科学D辑(英文版)》2007,50(1):135-141

The arbuscular mycorrhizal (AM) fungal status of the 20 most common plant species distributed in 4 vegetation types (meadow steppe, desert steppe, steppe desert and typical desert) on the northern slopes of the Tianshan Mountains was investigated. Samples of the plant species and their rhizosphere soils were collected from the 4 vegetation zones and examined to compare their mycorrhizal status, AM fungal spore densities, biovolumes, and community structures. 28 AM fungal species were isolated from the rhizosphere soils: of these, 5 belonged to Acaulospora, 1 to Archaeospora and 22 to Glomus. 5 AM fungi, Glomus aggregatum, G. claroideum, G. deserticola, G. etunicatum and G. sinuosum, were observed in all 4 zonal types. No significant differences were observed in mean proportion of root length colonized by AM fungi among the plant species within each zonal type. Comparing the 4 zonal types, Plantago minuta (84.5%) in steppe desert and Eremopyrum orientale (83.1%) in typical desert showed the highest root colonizatsion rates. AM fungal spore densities and biovolumes were significantly different in the different zonal types. AM fungal spore densities and biovolumes, species richness and diversity were highest in meadow steppe and lowest in typical desert.  相似文献   

Uniform asymptotic Green's functions for efficient modeling of cracks in elastic layers with relative shear deformation controlled by linear springs     

Anthony P. Peirce  Hongren Gu  Eduard Siebrits 《国际地质力学数值与分析法杂志》2009,33(3):285-308

We present a uniform asymptotic solution (UAS) for a displacement discontinuity (DD) that lies within the middle layer of a three‐layer elastic medium in which relative shear deformation between parallel interfaces is controlled by linear springs. The DD is assumed to be normal to the two interfaces between the elastic media. Using the Fourier transform method we construct a leading term in the asymptotic expansion for the spectral coefficient functions for a DD in a three‐layer‐spring medium. Although a closed‐form solution will require a solution in terms of an infinite series, we demonstrate how this UAS can be used to construct highly efficient and accurate solutions even in the case in which the DD actually touches the interface. We compare the results using the Green's function UAS solution for a crack crossing a soft interface with results obtained using a multi‐layer boundary element method. We also present results from an implementation of the UAS Green's function approach in a pseudo‐3D hydraulic fracturing simulator to analyze the effect of interface shear deformation on the fracture propagation process. These results are compared with field measurements. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献