Energy Expenditure and Geomorphic Work of the Cataclysmic Missoula Flooding in the Columbia River GGorge,USA     

Gerardo Benito 《地球表面变化过程与地形》1997,22(5):457-472

Cataclysmic releases from the glacially dammed Lake Missoula, producing exceptionally large floods, have resulted in significant erosional processes occurring over relatively short time spans. Erosional landforms produced by the cataclysmic Missoula floods appear to follow a temporal sequence in many areas of eastern Washington State. This study has focused on the sequence observed between Celilo and the John Day River, where the erosional features can be physically quantified in terms of stream power and geomorphic work. The step-backwater calculations in conjunction with the geologic evidence of maximum flow stages, indicate a peak discharge for the largest Missoula flood of 10 × 10⁶m³s⁻¹. The analysis of local flow hydraulics and its spatial variation were obtained calculating the hydrodynamic variables within the different segments of a cross-section. The nature and patterns of erosional features left by the floods are controlled by the local hydraulic variations. Therefore, the association of local hydraulic parameters with erosional and depositional flood features was critical in understanding landform development and geomorphic processes. The critical stream power required to initiate erosion varied for the different landforms of the erosional sequence, ranging from 500 W m⁻² for the streamlined hills, up to 4500 W m⁻² to initiate processes producing inner channels. Erosion is possible only during catastrophic floods exceeding those thresholds of stream power below which no work is expended in erosion. In fact, despite the multiple outbursts which occurred during the late Pleistocene, only a few of them had the required magnitude to overcome the threshold conditions and accomplish significant geomorphic work. © 1997 by John Wiley & Sons, Ltd.  相似文献   

供电网络系统的可靠性分析     

杜景林  杨亚弟 《世界地震工程》2005,21(4):133-138

研究了生命线工程系统中供电网络系统的可靠性分析方法。在元件可靠性分析的基础上,进行供电网络系统工程地震可靠性分析,提出了供电网络系统功能失效分级及失效等级的判定方法,并建立了功能失效系数的概念,给出了供电网络系统功能失效系数的计算方法,从而实现了供电网络系统功能失效分析的定量化。  相似文献   

生产连结相关之理论比较:从"权力关系"取径研究生产网络的重要性   总被引：2，自引：0，他引：2  

杨道宁 《世界地理研究》2005,14(1):9-14

近十年来,国际上已有许多学者从“权力关系”的角度加以研究生产网络的过程,如：Dicken所提出的生产链之概念,及Gereffi的全球商品链,与Henderson et al．提出之全球生产网络……等理论,皆开始重视探讨生产过程中各阶段关键作用者(agent)之间互动的重要性。近今这些不同但核心概念相似的理论,让我们意识到一个问题：到底从权力关系取径的角度,对于生产链接过程或产业聚集的研究,有何重要意义?对于一般讨论产品生产过程的地理研究,又可以多补足哪些观点?本文即从一般常用处理产品生产链接的两个相关理论——价值链与产品周期理论的意涵内容出发,比较其与“权力关系”取径二者之间解释生产链接过程的差异与优劣,并试图了解从“权力关系”观点,对于地理学研究产业之生产过程的重要性与意义,此为本文目的。  相似文献   

适用于海洋动态观测设备嵌入式系统的低功耗管理预测模型          下载免费PDF全文

李昌硕  周伟  杨群慧  季福武 《海洋技术学报》2024,(2)

能耗是制约海洋设备在水下工作时长的关键因素。为进一步降低海洋动态观测设备嵌入式系统的动态功耗, 本文针对前人提出的用于预测空闲时间的指数平滑算法所存在的权重系数基于凑数法确定、算法难以适应大波动等问题, 设计了一种新的权重系数, 并构建了一种自适应的低功耗管理预测模型。当模型检测到预测的空闲时间超过工作和休眠状态切换的时间阈值后, 中央处理器关停系统的部分外设, 使系统进入低功耗休眠状态。仿真和单片机实验均表明,本文提出的低功耗管理预测模型能够有效地提高对处理器工作的空闲时间预测的准确性, 且面对突发状况具有良好的自适应性, 可显著降低嵌入式系统的功耗, 有效延长设备的工作时间。  相似文献   

INVESTIGATION ON FUNDAMENTAL CHARACTERISTICS OF HYDROCHEMISTRY IN HEAD AREA OF THE CANGJIANG RIVER     

邓伟 《中国地理科学(英文版)》1991,1(3):272-283

The results of water sample analyses and investigation in the head area of the Changjiang River reveal that the characteristics of hydrochemistry of the river vary with drainage basins. In the drainage basin of the Tuotuo River, the mineral concentration of water is generally high, ions of Cl and Na are obviously dominant. The water tends to be salty, and the type of hydrochemistry is rather complex. In the drainage basin of the Dam River, the mineral concentration is mainly in a low and middle level, ions of HCO3- and Ca2 are higher than others, and the type of hydrochemistry is relatively simple. The ground water in deep layers plays an important role in recharging surface water, and the stable recharging results in little change in chemical composition of surface water.  相似文献   

20kv激光器电源的一种新型稳流电路的C.A.D.设计     

吴桓基 《成都信息工程学院学报》1988,(2)

本文提出了可用于光外差多普勒激光测风雷达或激光外差通信设备中的一个新电路——20KV高压稳流电路,用以稳定激光光频,使光外差探测后所获得的中间频率恒定。一般进口C.A.D.软件均需在高档计算机上运行,本文给出了自行设计的能在廉价微型计算机TRS-80,APPLE-Ⅱ上运行的C.A.D.软件。  相似文献   

Evaluation of the effect of equal power spectrum filtering in image restoration     

Yang Xu-hai  Zheng Xing-wu 《Chinese Astronomy and Astrophysics》2001,25(4):506-514

The effectiveness of equal power spectrum filtering in image restoration is analyzed via digital simulation. We start with a gray-scale map of concentric rings with different grey values. To obtain a dirty image, the original image is first transformed via a linear space-invariant system. Then, white noise is mixed into the image. The equal power spectrum filter is then used for the image restoration. The signal to noise ratio (SNR) and a defined steepness of the steps, together with the visual impression, are accepted to characterize the performance of the image restoration. It is concluded that a satisfactory restoration can be realized when the SNR > 15. When SNR < 5, the image is completely un-restorable. The effect of system's transfer function on image restoration is also discussed. The effectiveness of the presented model of equal power spectrum filter is confirmed by applying it to the restoration of an actual astronomical image. Finally, a typical application of the equal power spectrum filter is given.  相似文献   

Defining equivalent stationary PSDF to account for nonstationarity of earthquake ground motion   总被引：1，自引：0，他引：1  

I.D. Gupta  M.D. Trifunac 《Soil Dynamics and Earthquake Engineering》1998,17(2):89-99

This paper presents three approaches to defining the stationary power spectrum density function (PSDF) of strong ground acceleration, for prediction of structural response corresponding to the strong-motion stationary part of the input excitation. The first approach defines the PSDF in terms of the Fourier amplitude spectrum and a stationary duration of ground acceleration. The PSDF obtained by this approach predicts accurately the response of structures with low to intermediate natural periods. In the second approach, we introduce the concept of stationary duration of response, which is defined as a function of the natural period and damping ratio of the oscillator. Using this approach, it is possible to get accurate estimates of response amplitudes for the broad range of natural periods. However, it is not convenient in practical applications to deal with several stationary durations for a given input excitation. Further, to evaluate these durations it is necessary to specify both the Fourier and the response spectra of ground accelerations; whereas the common engineering practice is to specify the response spectrum only. Therefore, the third approach suggests the use of the response ‘spectrum compatible’ PSDF. The paper presents several improvements in the general methodology used for this purpose. The improvements mainly relate to using more accurate peak factors and to using the transient nature of response. The spectrum compatible PSDFs, as evaluated in the present study, provide realistic specification of strong ground motion for stochastic seismic response analyses of structures.  相似文献   

福建数字地震台网台址背景噪声分析   总被引：9，自引：3，他引：6  

陈祥熊  陈文明 《地震地磁观测与研究》1998,19(5):13-22

在使用福建区数字地震台网选台过程中,用１２个台址得到的背景噪声数字记录,计算分析了其背景噪声地动速度均方根值（ＲＭＳ）,有效测量动态范围、噪声功率谱及功率谱密度。所得结果可作为供评价仪器性能,台址安静程度的参考。对利用仪器所提供的动态范围,根据区域台网周围地震环境和台网记录地震的目的及任务设置适当的增益量程是也是有用的 。  相似文献   

历史时期广东省旱涝变化及其层次分析   总被引：1，自引：0，他引：1  

薛积彬  钟巍 《云南地理环境研究》2006,18(4):10-14

根据历史时期广东的旱涝灾害史料建立了该地区1480～1939年间旱涝指数序列,并采用小波分析、功率谱分析对该序列进行了研究。分析认为,从历史时期来看,广东的旱涝变化主要存在准7年、15年、23年左右的准周期,不同的历史时期主要影响周期不尽相同。旱涝指数的多尺度分析表明,广东在本世纪整体上将处于偏涝期,但自2000(±5)年已开始进入偏旱期,2010(±5)年左右达到最旱,这种偏旱状况将一致持续到2040(±5)左右,期间也会有较小强度的偏涝期出现。预计2040(±5)年之后广东将有较大强度的偏涝期出现,而且在未来几十甚至百年内的旱涝变化幅度有增大的趋势。由于高层次上的偏旱(涝)期常常包含有若干个低层次上的偏旱和偏涝期,因此在对未来气候变化趋势进行预测时,离开具体的时间尺度谈气候变化是没有意义的。  相似文献