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211.
212.
数字原稿色域的定量分析与比较 总被引:1,自引:0,他引:1
提出了一种科学、准确地定量分析数字原稿色域的方法,通过相关实验比较了各种成像环境对数字原稿色域的影响,并获得了一些有价值的成果。 相似文献
213.
晴空与有云大气辐射分布的数值模拟及其对全天空图像云识别的应用 总被引:5,自引:0,他引:5
全天空图像自动云识别的研究相对来说是一项较新的研究领域。当前国际上较为通用的全天空图像云识别方法主要依靠图像蓝红灰度值对比的阈值方法进行判断。然而非洁净大气中气溶胶的增多给云识别增加了难度,同时太阳高度角不同天空色度分布情况也不同。文中利用Libradtran辐射传输模式,计算了不同能见度不同太阳高度角情况下3个典型波长(450,550,650nm;蓝/绿/红)无云及有云大气的天空辐亮度分布情况,并进行了比较分析。结果表明,相同太阳高度角情况下,无云及有云大气中蓝红比值随能见度的下降呈单调下降趋势。在特定的云光学厚度和能见度情况下,天空色度彼此呈现出类似的分布状况。全天空图像阈值判断云识别自适应算法的建立需要与太阳高度角、地面能见度联系起来。当前尚无法建立一个判断阈值随太阳高度角以及能见度变化的函数关系式。较为可行的办法是建立典型能见度、典型太阳高度角情况下的辐射信息库,在具体云识别时,首先确定太阳高度角,而后根据天空辐射比情况确定天空能见度,并利用辐射信息标准库做云或非云判别。该工作为全天空云识别算法提供判别依据,同时建立云识别随能见度和太阳高度角变化的判别信息库。 相似文献
214.
215.
Juan Carlos Bergmann 《Boundary-Layer Meteorology》2006,119(1):171-179
Precision measurements indicate that the stability capping of the neutral planetary boundary layer (PBL) that leads to a reduced
PBL height is caused by the very stable upper part of the PBL, rather than by an overlying inversion. Radiative processes
related to liquid water in boundary-layer clouds seem to play the key role for the formation of the stable upper PBL. The
famous Leipzig Profile – generally considered as an example of a neutral PBL – has been included in Hess’s analysis because
its PBL height is considerably lower than the ca. 3000 m to be expected by numerical models in truly neutral conditions. An
analysis of the original observations reveals that the Leipzig PBL was stable and that it can be consistently treated as a
‘normal’ stable PBL with a height of ca. 700 m. A further finding is that the super-geostrophic PBL wind speed maxima predicted
by almost all models are not observed in near-steady-state conditions. For the ‘ranking’ of analytical models versus numerical
models, the comparisons with measurements show that the analytical models perform comparably well and even partially better
than the numerical models. 相似文献
216.
Juan Manuel Arbona 《Geoforum》2007,38(1):127-137
In October 2003, hundreds of thousands of Bolivians took to the streets demanding the resignation of President Gonzalo Sánchez de Lozada. After 20 years of neo-liberal policies - and the failures to improve the living conditions of the majority - the proposal to export natural gas via Chile was taken by the population as yet another step to sustain an unjust political order. Facing a direct challenge by the population the Sánchez de Lozada administration responded with indiscriminate military force. The result was 63 dead and over 300 wounded, which deepened and extended the social rage and eventually forced the resignation of the President. The neo-liberal project - promoted and defended by Sánchez de Lozada - collapsed. The city of El Alto was the epicentre of the challenges to the legitimacy of this political order. This article focuses on the role of local political entities and neighbourhood networks from El Alto in articulating political spaces that challenged the legitimacy of the institutional infrastructure and led to the October 2003 ruptures in the neo-liberal project. Furthermore, I make the case that the particular histories and memories (of “relocalized” miners and indigenous/peasants) that converged in and defined this city were pivotal in the organization of a “political subsoil” that surged to the surface during the October 2003 events. 相似文献
217.
218.
实践证明,桩网复合地基同时具备竖向增强体复合地基与水平向增强体复合地基的加固优点,能很好地提高地基土体承载力,减小不均匀沉降,特别是桥头过渡段地基处理中能有效控制“桥头跳车”现象的产生。本文主要对桩网复合地基的加固机理进行分析,并结合自然平衡拱理论和加筋垫层拉膜效应理论推导出路堤下桩网复合地基桩土应力比计算公式,同时分析了各设计参数变化对桩土应力比的变化规律。工程实体试验表明,本文所推导的桩土应力比计算公式具有较好的适用性。 相似文献
219.
Ruth Soto Antonio M. Casas-Sainz Juan J. Villalaín Beln Oliva-Urcia 《Tectonophysics》2007,445(3-4):373-394
In this work we analyse and check the results of anisotropy of magnetic susceptibility (AMS) by means of a comparison with palaeostress orientations obtained from the analysis of brittle mesostructures in the Cabuérniga Cretaceous basin, located in the western end of the Basque–Cantabrian basin, North Spain. The AMS data refer to 23 sites including Triassic red beds, Jurassic and Lower Cretaceous limestones, sandstones and shales. These deposits are weakly deformed, and represent the syn-rift sequence linked to basins formed during the Mesozoic and later inverted during the Pyrenean compression. The observed magnetic fabrics are typical of early stages of deformation, and show oblate, triaxial and prolate magnetic ellipsoids. The magnetic fabric seems to be related to a tectonic overprint of an original, compaction, sedimentary fabric. Most sites display a NE–SW magnetic lineation that is interpreted to represent the stretching direction of the Early Cretaceous extensional stage of the basin, without recording of the Tertiary compressional events, except for sites with compression-related cleavage.Brittle mesostructures include normal faults, calcite and quartz tension gashes and joints, related to the extensional stage. The results obtained from joints and tension gashes show a dominant N–S to NE–SW, and secondary NW–SE, extension direction. Paleostresses obtained from fault analysis (Right Dihedra and stress inversion methods) indicate NW–SE to E–W, and N–S extension direction. The results obtained from brittle mesostructures show a complex pattern resulting from the superposition of several tectonic processes during the Mesozoic, linked to the tectonic activity related to the opening of the Bay of Biscay during the Early Cretaceous. This work shows the potential in using AMS analysis in inverted basins to unravel its previous extensional history when the magnetic fabric is not expected to be modified by subsequent deformational events. Brittle mesostructure analysis seems to be more sensitive to far-field stress conditions and record longer time spans, whereas AMS records deformation on the near distance, during shorter intervals of time. 相似文献
220.
水能是清洁安全的能源。但如果对水能资源进行竭泽而渔地过度开发,必将引起地质生态环境方面的负面影响,甚至引发生态灾难。文章列举了岷江上游流域水能开发中的大量事例,呼吁应科学、合理、有序地开发利用河流水能资源,岷江上游流域水能资源的开发现状,应给人们以警醒和反思。 相似文献