The lower limit of the Doppler factor for a Fermi blazar sample     

Jun-Hui Fan  Denis Bastieri  Jiang-He Yang  Yi Liu  Tong-Xu Hua  Yu-Hai Yuan  De-Xiang Wu 《中国天文和天体物理学报》2014,(9)

We selected 457 blazars(193 flat spectrum radio quasars, 61 lowsynchrotron peaked blazars, 69 intermediate-synchrotron peaked blazars and 134high-synchrotron peaked blazars) from the second Fermi-LAT catalog(2FGL) of γ-ray sources, which have X-ray observations. We calculated the lower limits for their Doppler factors, δγ, and compared the lower limits with the available Doppler factors and the apparent superluminal velocities in the literature.  相似文献   

1980—2020年中国九大流域蒸散发及其组分时空评估     

杨泽龙  李艳忠  白鹏  杜深文  郝奕  钱畅  李超凡 《地球信息科学学报》2022,24(5):889-901

蒸散发是地表陆气水分交换的纽带,准确量化蒸散发的时空演变格局对于水资源规划与管理至关重要。本文基于GLEAM模型的蒸散发及其组分数据集,借助7个通量观测站数据、120个流域的流域水量平衡及PML_V2蒸散发产品,在中国九大流域系统评估了GLEAM-ET产品,分析了植被恢复背景下,蒸散发（ET）及其组分（植被蒸腾Ec,截留蒸发Ei,土壤蒸发Es）在1980—2020年的时空演变格局。本文主要得到以下结论：① GLEAM-ET产品在中国九大流域具有较好的适用性,其性能与气候类型有关,干旱区效果优于湿润区。此外,GLEAM与PML_V2模型在九大流域相关性较好（R>0.7）,分布格局与变化趋势整体保持一致。② 全国尺度上,ET均值为416.88 mm,增长速率为1.21 mm/a。Ec与ET均呈自东南向西北递减的分布格局,而Es与其相反。Ec、ET在九大流域均呈显著增加趋势（p<0.001）。Ei、Es在季风区流域分别呈显著增加和显著减小趋势;在内陆区流域呈不显著减小（p>0.05）和显著增加趋势。③在植被恢复背景下,ET组分比例发生了变化。Ec占比变化存在南北差异,南方流域Ec占比均减小,北方流域均增加。Ei占比在各流域均增加,Es占比均减小。黄河流域ET组分对植被恢复的响应最为明显,Ec占比增加了5.21%,Es占比减小了5.56%。  相似文献   

An efficient and adaptive approach for modeling gravity effects in spherical coordinates     

Zhiwei Li  Tianyao Hao  Ya Xu  Yi Xu 《Journal of Applied Geophysics》2011,73(3):221-231

The need to obtain more reliable Earth structures has been the impetus for conducting joint inversions of disparate geophysical datasets. For seismic arrival time tomography, joint inversion of arrival time and gravity data has become an important way to investigate velocity structure of the crust and upper mantle. However, the absence of an efficient approach for modeling gravity effects in spherical coordinates limits the joint tomographic analysis to only local scales. In order to extend the joint tomographic inversion into spherical coordinates, and enable it to be feasible for regional studies, we develop an efficient and adaptive approach for modeling gravity effects in spherical coordinates based on the longitudinal/latitudinal grid spacing. The complete gravity effects of spherical prisms, including gravitational potential, gravity vector and tensor gradients, are calculated by numerical integration of the Gauss–Legendre quadrature (GLQ). To ensure the efficiency of the gravity modeling, spherical prisms are recursively subdivided into smaller units according to their distances to the observation point. This approach is compatible with the parameterization of regional arrival time tomography for large areas, in which both the near- and far-field effects of the Earth's curvature cannot be ignored. Therefore, this approach can be implemented into the joint tomographic inversion of arrival time and gravity data conveniently. As practical applications, the complete gravity effects of a single anomalous density body have been calculated, and the gravity anomalies of two tomographic models in the Taiwan region have also been obtained using empirical relationships between P-wave velocity and density.  相似文献   

广州市美丽乡村空间分异特征及其影响因素   总被引：1，自引：0，他引：1  

张晨  肖大威  黄翼 《热带地理》2020,40(3):551-561

以广州市已公布的4批美丽乡村建设试点数据为基础，通过最邻近指数、基于Riple’s函数的多距离空间聚类分析、核密度分析和叠置分析等方法，探讨了广州市美丽乡村的发展现状、空间分布格局及其影响因素。结果表明：1）自2013年起，广州市美丽乡村数量逐年递增且增长率呈现上升趋势；2）广州市美丽乡村空间分布呈明显的集聚型分布；3）Ripley’s函数分析表明美丽乡村要素点空间分布格局随距离变化略有不同，在0.14 km处集聚强度达到最大；4）核密度分析显示美丽乡村高密度区域主要分布在广州南部和西北部，包括番禺－南沙1个热点主核心区和从化、花都－白云2个热点副核心区，密度分布呈现多核心不均衡特点；5）乡村的地形水文、人文历史、交通区位和政策规划为美丽乡村空间分布的主要影响因素，其中，政策规划因素对“美丽乡村群”空间格局的形成起决定性影响。空间分布特征总体反映出广州市美丽乡村规划建设初见成效，并逐步形成以热点核心区为基础的“美丽乡村群”。最后，在乡村选点、空间优化、价值提升以及乡村治理等方面提出若干建议。  相似文献   

对流层折射对超视距雷达信号定位的影响     

梁毅  王忠 《成都信息工程学院学报》2007,22(1):18-21

超视距雷达信号的精确定位对于提高超视距探测能力有十分重要的意义。但由于对流层中的折射效应，定位系统所测目标的仰角、距离等参量均存在一定的折射误差。主要分析对流层的折射效应对超视距雷达信号定位的影响，并且给出相应的折射误差图（仰角误差和距离误差）；此外，还针对3种不同的大气折射指数模型进行比较，得出折射误差对比图。  相似文献   

Study on low‐strain integrity testing of pipe‐pile using the elastodynamic finite integration technique     

Zhi Tang Lu  Zhi Liang Wang  Dong Jia Liu 《国际地质力学数值与分析法杂志》2013,37(5):536-550

This study focuses on the three‐dimensional (3‐D) characteristics of wave propagation in pipe‐pile using elastodynamic finite integration technique. First, a real 3‐D pile‐soil model in cylindrical coordinate system is presented. Then, the governing equations are established. With the boundary and initial conditions, the numerical solution is obtained. The accuracy and feasibility of the self‐written code are further verified via comparing with the measured data. Velocity histories at different angles of pile top and pile tip are illustrated, and the snapshots reflecting the 3‐D characteristics of wave propagation are given. It shows that the interferences of Rayleigh waves can confuse the result interpretation for pile integrity testing. The increase of hammer contact time can effectively mitigate the interferences, and the interferences of Rayleigh waves are weakest at an angle of 90° from where hammer hits. Besides, surrounding soil can partly mitigate the wave interferences. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

河西地区重力动态变化的二维离散小波多尺度分解   总被引：7，自引：5，他引：2  

朱桂芝  祝意青  唐文  程宏宾 《大地测量与地球动力学》2004,24(1):46-49

采用二维离散小波的多尺度分解技术，对1994～1995年和2002～2003年的河西地区重力动态变化进行分解，提取该地区不同层次的重力动态变化异常，结果反映了不同深度在一定尺度意义上的介质密度的动态变化分布。  相似文献   

全球纬向平均的海气耦合一维模式分析     

唐佑民 《成都信息工程学院学报》1991,(1)

本文从能量平衡角度,考虑海气相互作用和纬向间的差异,设计了一个纬向平均的海气耦合一维模式,进行了模式平衡态求解、敏感性试验以及随机分析。并对模式部分计算结果进行了与实测资料的比较,验证了模式的合理性和可信性。  相似文献   

深层地下水SPD人工补给系统     

贺屹  彭翠华  刘燕 《地球科学与环境学报》2006,28(1):47-50

提出了一种新的深层地下水回灌方法———SPD人工补给系统,并通过室内沙槽模拟试验,对该系统和常规的直接井回灌法作了比较。研究表明,利用该系统补给深层地下水,具有回灌水质要求低、补给速度快、补给量多、不易淤堵等特点,是深层地下水人工补给的一条有效的新途径。  相似文献   

On the spectral lags of the short gamma-ray bursts     

Tingfeng Yi  Enwei Liang  Yiping Qin  Ruijing Lu 《Monthly notices of the Royal Astronomical Society》2006,367(4):1751-1756

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