Weak lensing of the CMB: extraction of lensing information from the trispectrum     

《New Astronomy》2003,8(3):231-253

We discuss the four-point correlation function, or the trispectrum in Fourier space, of CMB temperature and polarization anisotropies due to the weak gravitational lensing effect by intervening large scale structure. We discuss the squared temperature power spectrum as a probe of this trispectrum and, more importantly, as an observational approach to extracting the power spectrum of the deflection angle associated with the weak gravitational lensing effect on the CMB. We extend previous discussions on the trispectrum and associated weak lensing reconstruction from CMB data by calculating non-Gaussian noise contributions, beyond the previously discussed dominant Gaussian noise. Non-Gaussian noise contributions are generated by lensing itself and by the correlation between the lensing effect and other foreground secondary anisotropies in the CMB such as the Sunyaev–Zel’dovich (SZ) effect. When the SZ effect is removed from temperature maps using its spectral dependence, we find these additional non-Gaussian noise contributions to be an order of magnitude lower than the dominant Gaussian noise. If the noise-bias due to the dominant Gaussian part of the temperature squared power spectrum is removed, then these additional non-Gaussian contributions provide the limiting noise level for the lensing reconstruction. The temperature squared power spectrum allows a high signal-to-noise extraction of the lensing deflections and a confusion-free separation of the curl (or B-mode) polarization due to inflationary gravitational waves from that due to lensed gradient (or E-mode) polarization. The small angular scale temperature and polarization anisotropy measurements provide a novel approach to weak lensing studies, complementing the approach based on galaxy ellipticities.  相似文献   

Response of the radiation belt electron flux to the solar wind velocity: Parameterization by radial distance and energy     

《Journal of Atmospheric and Solar》2008,70(14):1810-1828

The solar wind velocity is the primary driver of the electron flux variability in Earth's radiation belts. The response of the logarithmic flux (“log-flux”) to this driver has been determined at the geosynchronous orbit and at a fixed energy [Baker, D.N., McPherron, R.L., Cayton, T.E., Klebesadel, R.W., 1990. Linear prediction filter analysis of relativistic electron properties at 6.6 RE. Journal of Geophysical Research 95(A9), 15,133–15,140) and as a function of L shell and fixed energy [Vassiliadis, D., Klimas, A.J., Kanekal, S.G., Baker, D.N., Weigel, R.S., 2002. Long-term average, solar-cycle, and seasonal response of magnetospheric energetic electrons to the solar wind speed. Journal of Geophysical Research 107, doi:10.1029/2001JA000506). In this paper we generalize the response model as a function of particle energy (0.8–6.4 MeV) using POLAR HIST measurements. All three response peaks identified earlier figure prominently in the high-altitude POLAR measurements. The positive response around the geosynchronous orbit is peak P₁ (τ=2±1 d; L=5.8±0.5; E=0.8–6.4 MeV), associated with high-speed, low-density streams and the ULF wave activity they produce. Deeper in the magnetosphere, the response is dominated by a positive peak P₀ (0±1 d; 2.9±0.5R_E; 0.8–1.1 MeV), of a shorter duration and producing lower-energy electrons. The P₀ response occurs during the passage of geoeffective structures containing high IMF and high-density parts, such as ICMEs and other mass ejecta. Finally, the negative peak V₁ (0±0.5 d; 5.7±0.5R_E; 0.8–6.4 MeV) is associated with the “D_st effect” or the quasiadiabatic transport produced by ring-current intensifications. As energies increase, the P₁ and V₁ peaks appear at lower L, while the D_st effect becomes more pronounced in the region L<3. The P₀ effectively disappears for E>1.6 MeV because of low statistics, although it is evident in individual events. The continuity of the response across radial and energy scales supports the earlier hypothesis that each of the three modes corresponds to a qualitatively different type of large-scale electron acceleration and transport.  相似文献   

三亚市季节性旅游移民社会融合对主观幸福感的影响     

赵臣  陈扬乐  张凯  申文灿 《地理科学》2020,40(12):2064-2072

以旅游消费移民的代表性群体——季节性旅游移民为对象,构建季节性旅游移民社会融合对主观幸福感影响的概念模型,并提出相关假设;以典型的旅居城市三亚为案例地,运用结构方程模型对假设进行验证。研究表明：季节性旅游移民的文化融合对主观幸福感的影响较小,仅对正面情绪有显著的正向影响;而心理融合和身份融合均正向显著作用于主观幸福感的生活满意和正面情绪2个维度,且对负面情绪有显著抑制作用。基于实证分析,从文化融合、身份融合、心理融合等层面提出季节性旅游移民主观幸福感的提升策略。  相似文献   

基于碎屑锆石的黄土高原—毛乌素交界区石峁黄土粉尘物源估算^*          下载免费PDF全文

安宇  范念念  徐志伟  刘兴年 《古地理学报》1999,24(4):802-812

对于黄土高原粉尘物质的来源以及沙漠和河流对粉尘的贡献,仍未达成一致的认识。本研究以毛乌素东神木市石峁剖面为研究对象,利用碎屑锆石年龄谱,对末次冰消期以来的风成粉尘堆积和河流沉积物展开源区分析,并使用逆蒙特卡罗模型进行物源的定量计算。结果显示,粒径分布和阴极发光(CL)图像显示石峁黄土为典型风成沉积。其粗颗粒碎屑锆石(>40 μm)年龄峰值集中在190~300 Ma、300~600 Ma、1700~1900 Ma和2300~2600 Ma,年龄谱显示近源(局地基岩碎屑)、中源(黄河河沙)和远源(阿拉善地区沙漠)均有贡献; 定量计算表明,三者分别贡献71%、21%和8%的风成粗颗粒。中、近源中,黄河及其支流侵蚀基岩后搬运沉积的漫滩物质成为粉尘输移的中转站,为黄土的形成提供了主要的物源。光释光测年结果表明,石峁剖面河流沉积物及其上覆的黄土物质分别形成于倒数第2次冰消期和末次冰消期,两者之间的沉积间断可能指示了末次冰期至冰消期的侵蚀事件,导致了河滩物质暴露,从而形成了潜在的局地尘源。这些结果表明,包括黄河干支流在内的河流系统对黄土粉尘有重要的物源贡献。  相似文献   

A study on landscape mosaic structure in urban-rural area in Northwest of China with RS and GIS   总被引：4，自引：0，他引：4  

Jian-hua Xu  Yan Lu  Nan-shan Ai  Wen-ze Yue 《中国地理科学(英文版)》2001,11(4):366-376

At the study area of Xigu District in Lanzhou City, using RS & GIS as tools we apply Diversity, Dominance, Fragmentation, Isolation and so on to study the quantitative, fractal and spatial characters of landscapes structures in the four sub-regions divided by the morphological features. Using the Fractal Theory to establish the fractal structure models, we analyze the complexity and stability of various landscapes distribution with fractal dimension value. The spatial distribution characteristics of landscape mosaic structure are also expounded. At the end of the paper we discuss the relevant problems on the main factors which control and effect on the spatial pattern of landscapes as well as on landscape optimization and management. Foundation item: Under the auspices of the National Natural Science Foundation of China (No. 40171069). Biography: XU Jian-hua (1965 - ), male, a native of Gansu province, professor. His research interest includes Geo-computation and GIS.  相似文献   

一种新ⅡR分数阶微分滤波器     

邹杰  吴晓红  王正勇  罗代升 《成都信息工程学院学报》2008,23(2):169-173

从频域角度出发,分析了几种基于典型微分算子的ⅡR分数阶微分滤波器的数字实现,提出一种频率响应更接近理想微分的新算子,在此基础上运用连续分数扩充方法实现了分数阶微分滤波器的设计,并详细推导基于新算子的ⅡR分数阶微分滤波器的数字实现。实验证明,基于新算子的ⅡR分数阶微分滤波器频率响应整体上优于Tustin和Simpson等其他ⅡR分数阶滤波器。  相似文献   

视频监视系统中运动目标检测的新方法     

吴嵘  段文锋  钟诚 《成都信息工程学院学报》2008,23(1):25-29

运动目标检测是计算机视觉监视系统的核心。对于采用固定摄像机监控视频运动目标的检测,利用Affine Lucas Kanade特征跟踪算法的图像金字塔模型,根据模型的不同层数,将对应不同层数分辨率下的差分图像与Susan算子结合,通过形态学处理实现对复杂背景下运动目标的检测。仿真实验结果表明,采用的算法有效地抑制了噪声对运动目标检测效果的影响,且计算量随金字塔层数的增加而成倍减少。  相似文献   

分数阶微积分在医学图像处理中的应用     

晏祥玉  周激流 《成都信息工程学院学报》2008,23(1):38-41

简要介绍了分数阶微积分和医学图像的概念,然后从分数阶微分基本定义出发,得到了可以作用于二维医学图像的分数阶微分掩模,掩模可以根据对图像的需求进行增强,最后通过实验证明,这个方法可以有效完成对医学图像的处理,并且弥补了传统方法不能连续改变处理效果的缺点,是一种简单可行并且效果较好的图像增强方法。  相似文献   

严格逐段单调函数迭代根的不存在性     

刘鎏 《成都信息工程学院学报》2009,24(2):198-200

对于严格逐段单凋函数,前人证明在函数自身迭代后非单调点个数增加的情况下不存在次数大于函数非单调点个数的迭代根,这里进一步证明在一定条件下函数小存在次数等于函数非单调点个数的迭代根.  相似文献   

结合逆向工程和fuzz技术的Windows软件漏洞挖掘模型研究   总被引：1，自引：0，他引：1  

刘坤 《成都信息工程学院学报》2008,23(2):178-181

Windows软件漏洞挖掘已经成为网络安全技术一个重要的组成部分。结合逆向工程和fuzz技术,提出了一个全新的Windows软件漏洞挖掘模型：首先分别介绍了逆向工程和fuzz技术主要特点和研究内容,接着介绍了结合逆向工程和fuzz技术的软件漏洞挖掘模型原理,最后展示了利用这个模型进行漏洞挖掘的实例演示。  相似文献