The effects of rock uplift and rock resistance on river morphology in a subduction zone forearc,Oregon, USA

Relationships between riverbed morphology, concavity, rock type and rock uplift rate are examined to independently unravel the contribution of along-strike variations in lithology and rates of vertical deformation to the topographic relief of the Oregon coastal mountains. Lithologic control on river profile form is reflected by convexities and knickpoints in a number of longitudinal profiles and by general trends of concavity as a function of lithology. Volcanic and sedimentary rocks are the principal rock types underlying the northern Oregon Coast Ranges (between 46°30′ and 45°N) where mixed bedrock–alluvial channels dominate. Average concavity, θ, is 0·57 in this region. In the alluviated central Oregon Coast Ranges (between 45° and 44°N) values of concavity are, on average, the highest (θ = 0·82). South of 44°N, however, bedrock channels are common and θ = 0·73. Mixed bedrock–alluvial channels characterize rivers in the Klamath Mountains (from 43°N south; θ = 0·64). Rock uplift rates of ≥0·5 mm a⁻¹, mixed bedrock–alluvial channels, and concavities of 0·53–0·70 occur within the northernmost Coast Ranges and Klamath Mountains. For rivers flowing over volcanic rocks θ = 0·53, and θ = 0·72 for reaches crossing sedimentary rocks. Whereas channel type and concavity generally co-vary with lithology along much of the range, rivers between 44·5° and 43°N do not follow these trends. Concavities are generally greater than 0·70, alluvial channels are common, and river profiles lack knickpoints between 44·5° and 44°N, despite the fact that lithology is arguably invariant. Moreover, rock uplift rates in this region vary from low, ≤0·5 mm a⁻¹, to subsidence (<0 mm a⁻¹). These observations are consistent with models of transient river response to a decrease in uplift rate. Conversely, the rivers between 44° and 43°N have similar concavities and flow on the same mapped bedrock unit as the central region, but have bedrock channels and irregular longitudinal profiles, suggesting the river profiles reflect a transient response to an increase in uplift rate. If changes in rock uplift rate explain the differences in river profile form and morphology, it is unlikely that rock uplift and erosion are in steady state in the Oregon coastal mountains. Copyright © 2006 John Wiley & Sons, Ltd.     

Mantle heat flow and thermal structure of the northern block of Southern Granulite Terrain, India

Continental shield regions are normally characterized by low-to-moderate mantle heat flow. Archaean Dharwar craton of the Indian continental shield also follows the similar global pattern. However, some recent studies have inferred significantly higher mantle heat flow for the Proterozoic northern block of Southern Granulite Terrain (SGT) in the immediate vicinity of the Dharwar craton by assuming that the radiogenic elements depleted exposed granulites constitute the 45-km-thick crust. In this study, we use four-layered model of the crustal structure revealed by integrated geophysical studies along a geo-transect in this region to estimate the mantle heat flow. The results indicate that: (i) the mantle heat flow of the northern block of SGT is 17 ± 2 mW/m², supporting the global pattern, and (ii) the lateral variability of 10–12 mW/m² in the surface heat flow within the block is of crustal origin. In terms of temperature, the Moho beneath the eastern Salem–Namakkal region appears to be at 80–100 °C higher temperature than that beneath the western Avinashi region.     

大功率电法勘查铝土矿的效果

简要地阐述了河南省西部铝土矿形成的地质背景、矿体特征、地球物理特性;探讨利用大功率电法勘查铝土矿的方法技术;举例说明大功率电法的找矿效果,客观地指出了目前存在的问题,对今后工作提出了自己的看法。     

云南地热资源及其开发前景

云南地热异常多且显著。滇西高温水热活动区是藏滇水热带的南延，滇东断陷盆地中低温水热活动区的形成得益于独特的地质结构，滇西、滇南花岗岩地热系统则主要吸收地层中K^40同位索放射热而成。开发前景极为广阔。     

一个简单的雪晶辐射参数化方案及雪晶辐射对中尺度降水的影响

文章提出一个简单的雪晶辐射性质参数化方案, 并利用1998年6月8日华南暴雨资料研究了雪晶的辐射性质对于中尺度降水的影响。结果表明:雪晶的辐射性质对中尺度降水的影响是不可忽略的, 白天尤为显著; 它能够明显地改变中尺度降水的局部特征, 特别是降水中心的强度和位置, 而对降水的分布影响不大。因此, 建立独立的雪晶辐射参数化对提高中尺度模式对中尺度降水的预报能力是必要的。     

Angular resolution of terrestrial laser scanners

Knowledge of a laser scanner's spatial resolution is necessary in order to prevent aliasing and estimate the level of detail that can be resolved from a scanned point cloud. Spatial resolution can be decoupled into range and angular components. The latter is the focus of this paper and is governed primarily by sampling interval and laser beamwidth. However, emphasis is often placed on one of these—typically sampling interval—as an indicator of resolution. Since both affect the resolution of a scanned point cloud, consideration of only one factor independent of the other can lead to a misunderstanding of a system's capabilities. This will be demonstrated to be inappropriate except under very specific conditions. A new, more appropriate resolution measure for laser scanners, the effective instantaneous field of view (EIFOV), is proposed. It is derived by modelling the shift variance of the equal angular increment sampling process, laser beamwidth-induced positional uncertainty and observed angle quantisation with ensemble average modulation transfer functions (AMTFs). Several commercially available terrestrial laser scanner systems are modelled and analysed in terms of their angular resolution capabilities using the EIFOV.     

基于现行抗震规范的胡聿贤模型参数研究

回顾了地震地面加速度随机过程模型,根据随机振动理论采用迭代方法求解出与我国现行《建筑抗震设计规范》(GB50011-2001)设计反应谱相对应的功率谱密度函数,选用胡聿贤功率谱密度函数拟合上述功率谱密度函数,运用非线性拟合技术给出了与规范对应的胡聿贤功率谱参数,可供这种模型作为地震地面运动输入时选用。     

大跨度钢桁架转换结构振动台试验研究

以某带高位大跨钢桁架转换结构高层建筑为工程背景,进行了1/25缩尺比例的模型振动台试验,通过粘贴在钢桁架杆件上的应变片,测试了输入不同加速度峰值地震波作用下钢桁架的地震响应。在加速度峰值0.9g地震波作用下,两端支承钢桁架筒体剪力墙才出现裂缝,表明连接部位剪力墙受力性能较好;人工波作用下结构的地震响应最大,层地震作用力在钢桁架转换结构层有突变;试验中随模型结构裂缝发展和抗侧刚度衰减,层地震作用力分布发生变化,其中钢桁架转换结构层承担地震力相对减小,钢桁架应变反应也相对趋缓;钢桁架两端杆件受力较大,表明支承剪力墙对钢桁架的约束作用较大。     

Threat level green: Conceding ecology for security in eastern Europe and the former Soviet Union

Following the collapse of the Soviet Union, the predicted scenarios of Central Asian water wars and catastrophic nuclear accidents have failed to materialize. However, the Aral Sea continues to shrink apace, and dangerous Soviet-built nuclear reactors have since proliferated in the former eastern bloc. These seemingly paradoxical outcomes can in part be attributed to the framing of these environmental issues as security matters by leading international regulatory, aid and lending institutions. Integrating these environmental concerns with the realist worldview of security studies systematically emphasized security dimensions at the expense of ecological concerns even amongst organizations distant from traditional defense affairs. This article proposes that international security strategy in this period is one of environmental appeasement defined as the systematic granting of ecologically unfriendly concessions in order to reduce short-term security risks. The article presents evidence that this appeasement strategy generated seemingly impressive results in terms of ameliorating short-term security risks, while actually exacerbating the underlying ecological situation. The article argues that while the foundational environmental risks remain unaddressed, the associated security threats have likewise not been ultimately resolved.     

PHC管桩荷载传递的试验研究和数值分析

通过在预应力高强混凝土管桩(PHC桩)的桩顶、桩端及桩周各主要土层的分界面埋设应变计的静荷载试验，研究了PHC管桩的荷载传递机理，分析了轴力和桩侧摩阻力的变化规律。并以工程中PHC管桩的竖向抗压静载试验为基础，运用有限单元法对软土地区的PHC管桩桩-土相互作用进行模拟，在分析中采用弹塑性模型，引入了非线性接触面单元，并且考虑了土体的材料非线性。分析结果表明，计算值和实测值有一定的差别，但是变化趋势基本一致。