Flux contribution of coherent structures and its implications for the exchange of energy and matter in a tall spruce canopy

The flux contribution of coherent structures to the total exchange of energy and matter is investigated in a spruce canopy of moderate density in heterogeneous, complex terrain. The study deploys two methods of analysis to estimate the coherent exchange: conditional averages in combination with wavelet analysis, and quadrant analysis. The data were obtained by high-frequency single-point measurements using sonic anemometers and gas analysers at five observation heights above and within the canopy and subcanopy, and represent a period of up to 2.5 months. The study mainly addresses the momentum transfer and exchange of sensible heat throughout the roughness sublayer, while results are provided for the exchange of carbon dioxide and water vapour above the canopy. The magnitude of the flux contribution of coherent structures largely depends on the method of analysis, and it is demonstrated that these differences are attributed to differences in the sampling strategy between the two methods. Despite the differences, relational properties such as sweep and ejection ratios and the variation of the flux contribution with height were in agreement for both methods. The sweep phase of coherent structures is the dominant process close to and within the canopy, whereas the ejections gain importance with increasing distance to the canopy. The efficiency of the coherent exchange in transporting scalars exceeds that for momentum by a factor of two. The occurrence of coherent structures results in a flux error less than 4% for the eddy-covariance method. Based on the physical processes identified from the analysis of the ejection and sweep phases along the vertical profile in the roughness sublayer, a classification scheme for the identification of exchange regimes is developed. This scheme allows one to estimate the region of the canopy participating in the exchange of energy and matter with the above-canopy air under varying environmental conditions.     

Bulk-rock geochemistry and plagioclase zoning in lavas exposed along the northern flank of the Western Blanco Depression (Northeast Pacific): Insight into open-system magma chamber processes

The present study is based on a set of lavas and crosscutting dikes collected by dives along detailed vertical transects on the northern flank of the western part of the Blanco Transform Fault, Northeast Pacific. The studied area consists of a small basin, the Western Blanco Depression (WBD), extending from the southern end of the Juan de Fuca ridge to a pseudofault trace 60 km eastward. The Northern Scarp of the WBD comprises a volcanic unit overlying a sheeted-dike complex. Major and trace element data, coupled with Sr–Nd isotope ratios, reveal a two-component mantle source, composed by an isotopically depleted matrix variably veined by more enriched material. One chemical group (NS2), indistinguishable from the other Northern Scarp samples on the basis of trace element data, has an unusually depleted isotopic composition typical of a nearly pure mantle end-member. Some cogenetic samples of the Northern Scarp have been used to constrain the differentiation modalities. Anorthite and MgO content profiles in plagioclase xenocrysts and phenocrysts reveal (i) the existence of H₂O-bearing evolved melts in the mushy zones and (ii) the occurrence of mixing process between these melts and anhydrous mafic liquids. The hydration is supported by other petrographic features such as high magmatic fO₂ values, calculated from Fe–Ti oxide pairs, and the presence of pyroxene inclusions in plagioclase phenocrysts. Mixing, consistent with the existence of Ni-rich ferrobasalts, is interpreted to be the consequence of the reservoir refilling by mafic liquids (Mg# = 70). These petrological and geochemical evidences are combined with the evolution of Mg# with depth to suggest a periodic open-system magma chamber evolution beneath the southern end of the Juan de Fuca ridge.     

基于中值滤波和小波变换的天气雷达回波图像处理

本文提出了一种中值滤波和小波变换相结合的天气雷达回波图像处理方法,分别从目标回波的视觉角度和统计量的客观角度对处理后图像进行了分析。实验结果表明,本文算法实现了去除回波图像中高斯和脉冲混合噪声的目的,有效的保留了回波图像边缘细节,视觉效果好,层次感较为丰富,处理效果明显优于传统图像处理方法,为自动识别回波种类的研究提供了良好的基础。     

小波分析若干应用模型及在测绘中的应用和展望＊

小波分析是８０年代中期发展起来的应用数学理论,在众多学科领域取得了广泛的应用。文中首先对小波分析的发展作了简要概述,然后介绍了小波分析在测绘中的应用,对小波分析若干与测绘相关的应用模型进行了分析和讨论,并对小波分析在测绘中的应用前景作了展望。     

利用小波包算法实现快速近似K-L变换

分析了 K-L变换的不足 ,研究了利用小波包算法实现快速近似 K-L变换的问题 ,并对两种算法的复杂度进行了比较。实验结果表明 :提出的快速近似 K-L变换算法在精度和速度两个方面都具有明显的优势。     

基于多分辨分析的滤波算法在SAR图像斑点噪声消除中的应用

合成孔径雷达 (SAR)图像一般都存在相干噪声 ,对地物信息的提取及 SAR图像应用的干扰非常严重 ,对此许多人提出了不少处理方法 ,并分析对比了多种滤波算法 ,认为改良 K -均值自适应滤波效果最佳。本文中分析了改良 K -均值自适应滤波法的数学基础的局限性 ,并采用了一种基于多分辨分析的滤波算法 ,该算法通过将噪声 (或较小的结构特征 )与较大的结构特征相分离 ,然后滤出噪声 (或较小的结构特征 ) ,从而达到消除斑点噪声的目的。实验结果证明 ,基于多分辨分析的滤波算法在消除 SAR图像的斑点噪声方面优于改良 K -均值自适应滤波法。     

OFDM基带处理系统的设计与实现

阐述了适合高速无线数据传输的正交频分复用(OFDM)调制方式的基本原理及调制解调的快速傅立叶变换(FFT)实现,并给出OFDM基带处理系统的结构图和硬件模块框图。     

基于傅里叶变换质谱的烃源岩成熟度评价方法及地质意义

<正>伴随非常规油气资源的勘探开发,油气资源开采的广度和深度进一步扩大,一定程度上缓解了我国油气供需矛盾、保障了我国能源安全,同时有力推动了能源结构战略转型。但同时也对能源地质研究工作提出了新的挑战。有机质成熟度是油气评价的重要参数之一,不同成熟阶段的有机质会对应产出不同成因、不同性质、不同质量的油气,如何准确评价沉积有机质成熟度是当前油气资源勘探开发工作的关键问题之一。前人在科研实践工作中从光学、化学、谱学等角度提出了适用条件各异的成熟度评价方法,在部分地质环境中获得了良好的应用效果,但已有的成熟度指标多受测定方法原理的制约导致其适用性不同程度受限(肖贤明等,2020),制约了油气资源的高质量勘探开发。     

Improvement of pseudo-static method for slope stability analysis

traditional In this paper, two drawbacks pseudo-static method （vertical of the slice method） in the slope stability evaluation have been studied. First, the sliding mass is divided into vertical slices according to this method, which is irrational to some extent in the seismic design of slope. Second, only peak ground acceleration （PGA） is considered, and the effects of shaking frequency and duration on slope stability are neglected. And then, based on the theory of elastic wave and the summarized geological model, this paper put forwards an improved method of pseudo-method by using the theory of elastic wave and Hilbert-Huang transform. The improved pseudostatic method gives reasonable considerations to the time-frequency effects of seismic wave and its rationality has been verified by the shaking table test. This method can evaluate the safety of a slope, the happening time and the scale of landslides. At the same time, this method also can improve the high accuracy of the evaluation of the safety of the slope.     

Multi-Time Scale Analysis of Runoff at the Yangtze Estuary Based on the Morlet Wavelet Transform Method

Runoff series of the Yangtze River presents an intricate variation tendency under the reinforced influence of human activities.The Morlet Wavelet Transform method has been applied to analyze the annual runoff data from 1950 to 2011 at the Yangtze River Estuary.It can clearly reveal the multi-time scales structure,break point,change and distribution of periodic variation in the different time scales of the runoff series.The main conclusions are that：1） Repeated periodic oscillations accompanied by an extremely large fluctuation are presented in the runoff series with an obvious difference between wet and dry years,and the major periods of the time series are about 3,8,16 and 23 years respectively.Among them,the presented maximum periodic oscillation is 23 years scale.2） In the 23-year time scale,the wet periods are 1950-1958,1969-1980 and 1992-2003,and the dry periods are 1959-1968,1981-1991 and 2004-2011.3） It can be predicted from the view of long time scales that the low annual runoff will likely occur in the near future.