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101.
The short-term (2 years) influence of fire burning with the wind (head fire) and against the wind (back fire) on the productivity (above-ground phytomass and litter) and fire behaviour were determined over seven growing seasons (1995/96–2001/02) in a semi-arid rangeland. The results showed that head fires had significantly greater flame height and rate of spread than back fires. Fire caused a decrease of 40.5% and 22.5% in basal cover for the first and second seasons after burning respectively. The seasonal above-ground phytomass production and litter were significantly decreased by fire over all growing seasons. Seasonal production losses due to fire varied between 225 and 430 kg ha−1. The relation between above-ground phytomass production loss due to fire, and two independent variables namely seasonal rainfall and fuel load (above-ground phytomass plus litter) before burning, were investigated. The multiple linear regression equations obtained for one (r=0.89) and 2 years (r=0.86) after a fire, can be used with great success in estimating seasonal production losses due to fire in semi-arid rangeland. 相似文献
102.
利用中子活化及PIXE和可见光灰度仪, 对青海瓦里关大气本底基准监测站的大气气溶胶样品进行了测量。通过元素相对浓度、富集因子和主因子分析等数据统计分析, 并结合同期的气团后退轨迹分布资料, 讨论了瓦里关大气气溶胶元素的组成及来源。结果表明, 位于青藏高原偏远地区的瓦里关大气气溶胶以土壤及地壳等自然来源为主, 因子分析的方差百分数给出瓦里关气溶胶中自然源的贡献率平均在70%以上。燃煤、交通及冶炼等人为源也占有一定比例。大气黑碳气溶胶的观测也表明人类活动影响的存在。人为源的影响多与来自东部及河西走廊等经济发达地区的气流有关。 相似文献
103.
NI Jinren MENG Xiaogang Center for Environmental Sciences Peking University Beijing China The Key Laboratory of Water Sediment Sciences Ministry of Education Beijing . 《国际泥沙研究》2001,16(2)
1 INNDUCTIONMes on prtcles are of significance to understand the motion of pwhcles in solid-liquid two-Phaseflows (Ni, et aI, l991). Early in l85l, Stokes (l85l) stUdied the simple harmonic linear motion of a singlesphere using a cylinder and a long flat plate. As a result, a simPle mathematical expression was given.Later on, Boussineaq (l885), Basset (1888), and Oseen (1927) stUdied the Iinear motion of a singIesphere that was accelotd in viscous fluid. It was fOund that the forces … 相似文献
104.
在论述猫岩崩滑体基本特征的基础上,对该崩滑体的成因进行了初步探讨;采用反分析优化参数计算,评价了崩滑体在各工况下的稳定性,研究结果为深溪沟水电站厂房布置方案的选择,提供了重要依据。 相似文献
105.
Deformability of rock masses influencing their behavior is an important geomechanical property for the design of rock structures. Due to the difficulties in determining the deformability of jointed rock masses at the laboratory-scale, various in-situ test methods such as pressuremeter, dilatometer, plate loading tests etc. have been developed. Although these techniques are currently the best and direct methods, they are time-consuming and expensive, and present operational difficulties. In addition, the influence of the test volume on deformation modulus depending on the method employed is also important. For these reasons empirical equations to indirectly estimate the deformation modulus have also been recommended by several investigators as an alternative approach. In this study; the geomechanical quality of weak, heavily jointed, sheared and/or blocky greywacke rock masses, on which very concentrated civil works are continuing at the southern and southwestern parts of Ankara (Turkey), was assessed. The deformation modulus was determined by pressuremeter tests, the possible effects of variables on the derived deformation modulus from the pressuremeter test were evaluated by numerical methods, and the comparisons between the deformation modulus of the greywackes obtained from the pressuremeter tests and their geomechanical quality (GSI and RMR) were made. Numerical simulations revealed that the presence of a disturbed annulus around the borehole causes underestimation of the deformation modulus, while the effect of length to diameter ratio of the pressuremeter probe on the deformation modulus is minor. Based on the geo-engineering characterization assessments, mainly two greywacke rock masses with different geomechanical qualities were identified. Geotechnical quality of one of these rock masses was verified by the back analysis of two slope failures. The empirical equations to indirectly estimate the deformation modulus of the greywackes using their GSI and RMR values yielded high coefficients of correlation. 相似文献
106.
Two artificial neural network models for the prediction of elastic modulus of jointed rock mass from the elastic modulus of
corresponding intact rock and joint parameters have been demonstrated in this paper. The data collected from uniaxial and
triaxial compression tests on different rocks with different joint configurations and different confining pressure conditions,
reported in the literature are used as input for training the networks. Important joint properties like joint frequency, joint
inclination and roughness of joints are considered separately for making the network more versatile. Two different techniques
of artificial neural networks namely feed forward back propagation (FFBP) and radial basis function (RBF) are used to predict
the elastic modulus ratio. 相似文献
107.
108.
Different ways of framing the nexus between climate change and migration have been advanced in academic, advocacy and policy circles. Some understand it as a state-security issue, some take a protection (or human security) approach and yet others portray migration as an adaptation or climate risk management strategy. Yet we have little insight into how these different understandings of the ‘problem’ of climate change-related migration are beginning to shape the emergence of global governance in the climate regime. Through a focus on the UNFCCC Task Force on Displacement we argue that these different framings of climate change migration shape how actors understand the appropriate role of the TFD, including the substantive scope of its mandate; its operational priorities; the nature of its outputs and where it should be situated in the institutional architecture. We show that understanding the different framings of the nexus between climate change and migration – and how these framings are contested within the UNFCCC – can help to account for institutional development in this area of climate governance. 相似文献
109.
基于前后张驰逼近(Back and Forth Nudging,简称BFN)和集合卡尔曼滤波(EnKF)方法,构建了一种新的同化方法HBFNEnKF(Hybrid Back and Forth Nudging EnKF)混合同化方法,并将此同化系统分别与通道浅水模式(shallow water model)和全球浅水模式对接,检验了HBFNEnKF同化方法的有效性。同时,对比了集合均方根滤波(EnSRF)、HNEnKF (Hybrid Nudging EnKF)、HBFNEnKF三种方法在有误差模式中的同化效果。试验结果表明:HBFNEnKF同化方法保留了HNEnKF方法的同化连续性,解决了EnKF同化不连续不平滑的问题,同时还有着更快的收敛速度;当采用单变量分析试验时,HBFNEnKF方法的优势最为明显,表明HBFNEnKF能够较好地保持不同模式变量间的平衡。此外,增量场尺度分析结果表明:相比EnSRF,HBFNEnKF在大尺度范围有更好的同化效果,同时能够避免在中小尺度范围内出现大量的虚假增量。 相似文献
110.
2001年昆仑山口西MS8.1地震经历了一个复杂的破裂过程,其破裂长、幅度大、破裂速度多变,成为大陆型地震研究的典型地震。本文融合近场高精度大地测量观测(4幅InSAR影像,34个GPS点位同震位移)和高信噪比远震波形记录,基于有限断层反演理论,联合反演得到该地震同震破裂时空过程的统一模型;同时,基于欧洲区域台网波形数据,利用反投影方法获得高频破裂的时空展布。联合反演结果表明,破裂自西向东传播的过程中走向有所变化,破裂尺度达400km,最大滑移量达8m,地震矩大小为6.1×1020Nm,对应的矩震级MW为7.78。主断层破裂经历了3个阶段,其中,超剪切破裂阶段对应最大位错区域,破裂到达西大滩段与昆仑山口断层交叉处时,破裂速度与尺度迅速下降。反投影结果同样显示破裂的3个阶段空间上对应大地测量反演的3个最大破裂区,最大破裂区的扩展速度达6km/s,但超剪切破裂终止在断层交叉口东部约30km处断层走向发生转变的位置。 相似文献