Channel change,bankfull and effective discharges on a vertically accreting,meandering, gravel‐bed river     

B. Gomez  S. E. Coleman  V. W. K. Sy  D. H. Peacock  M. Kent 《地球表面变化过程与地形》2007,32(5):770-785

Along the lower reaches of the Waipaoa River, New Zealand, cross‐section survey data indicate there was a 23 per cent decrease in bankfull width and a 22 per cent reduction in channel cross‐section area between 1948 and 2000, as the channel responded to increased inputs of fine (suspended) sediment following deforestation of the headwaters in late C19 and early C20. We determined the bankfull discharge within a ～39 km long reach by routing known discharges through the one‐dimensional MIKE 11 flow model. The model runs suggest that the bankfull discharge varies between ～800 and ～2300 m³ s^?1 and that the average recurrence interval is 4 ± 2 years on the annual maximum series; by contrast, the effective flow (360 m³ s^?1) is equaled or exceeded three times a year. The variability in bankfull discharge arises because the banks tend to be lower in places where flood flows are constricted than in reaches where overbank flow is dispersed over a wide area, and because scour has counteracted aggradation in some locations. There is no downstream variation in Shields stress, or in relative shear stress, within the study reach. Bankfull shear stress is, on average, five times greater than the shear stress required to initiate motion. At the effective discharge it is more than twice the threshold value. The effective discharge probably has more relevance than the bankfull discharge to the overall picture of sediment movement in the lower reaches of the Waipaoa River but, because width is constrained by the stability and resistance of the bank material to erosion during high flows that also scour the bed, the overall channel geometry is likely determined by discharges at or near bankfull. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

2007年7月16日日本新溻地震对柏崎刈羽核电站的影响   总被引：1，自引：0，他引：1  

潘华李金臣  吴迪忠 《国际地震动态》2007,(11):21-32

2007年7月16日日本新溻县柏崎市附近海域发生Mw6．6地震（日本气象局震级MJMA6．8）。该地震引发世界最大核电厂——柏崎刈羽核电站多起核安全事件，是世界范围内有记载的对核电站影响最为严重的一次地震。本文根据收集到的资料，详细介绍了该地震对柏崎刈羽核电站造成的影响，文章最后概述了日本、国际原子能机构对该地震的反思以及我们应该从中吸取的经验教训。  相似文献   

DWDM与光接入技术     

钱寿宇 《成都信息工程学院学报》2001,16(4):255-257

介绍了一个利用DWDM技术的高速接入网方案，使终端用户对因特网的访问速率可达到1－10Gb/s。  相似文献   

Parameter identification for a suction‐dependent plasticity model     

L. Simoni  B. A. Schrefler 《国际地质力学数值与分析法杂志》2001,25(3):273-288

In this paper, the deterministic parameter identification procedure proposed in a companion paper is applied to suction‐dependent elasto‐plasticity problems. A mathematical model for such type of problems is firstly presented, then it is applied to the parameter identification using laboratory data. The identification procedure is applied in a second example to exploitation of a gas reservoir. The effects of the extraction of underground fluids appear during and after quite long periods of time and strongly condition the decision to profit or not of the natural resources. Identification procedures can be very useful tools for reliable long‐term predictions. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

Role of eicosenoic and docosenoic fatty acids in fresh water and marine lipids     

R.G. Ackman  J-L. Sebedio  M.I.P. Kovacs 《Marine Chemistry》1980,9(3):157-164

The isomeric compositions of the eicosenoic and docosenoic fatty acids of four freshwater fish oils (from sheepshead Aplodinotus grunniens, tullibee Coregonus artedii, maria Lota lota and alewife Alosa pseudoharengus, respectively) were examined by open-tubular gas—liquid chromatography. The 22:1ω11 isomer, usually the dominant isomer in marine-fish oils, was unimportant relative to 22:1ω9. The unsaponifiables lacked fatty alcohols and pristane and were mostly cholesterol. The probability that the 22:1ω1 in marine fish oils is strictly of an exogenous origin (primarily originating as the fatty alcohol in copepod wax esters) is reviewed and it is proposed that docosenoic acids have no obligatory role in the lipid biochemistry of either marine or freshwater fish.  相似文献   

关于跨越式发展的理论思考   总被引：1，自引：0，他引：1  

曹毅哲 《吉林地质》2001,20(4):50-54

中国是世界上最大的发展中国家,经济的发展与发达国家存在一定的差距,为了赶超世界先进水平,利用现在的大好机遇,党的十五届五中全会明确提出中国要实现生产力的跨越式发展。本文从马克思主义理论出发,着重探讨了跨越式发展理论提出的理论来源和实践基础,阐明了实现跨越式发展的几大途径;要划清跨越式发展与“大跃进”的区别;要利用好和平与发展、知识经济、经济全球化等机遇;努力发展高科技;发展地方特色经济;建立配套机制和措施,保护生态环境;创新观念等等。  相似文献   

秦岭—桐柏—大别造山带深部构造及其与南北两侧陆块关系之探讨   总被引：3，自引：0，他引：3  

李炳华 《陕西地质》2001,19(1):59-70

秦岭－桐柏－大别,向西乃至昆仑山、祁连山绵延1000多千米,属统一的而又包含多期不同动力学机制与成因的多种构造叠加组合。通过对数条重力,航磁、地震测深、磁大地电流剖面等资料解释,认为华北陆块,秦岭（包括桐柏－大别）,扬子陆块之地壳均为上,中,下三层结构,华北陆块下部以高角度向南向秦岭俯冲,上部则向秦岭仰冲,扬子陆块总体向北向秦岭低角度俯冲,扬子陆块多呈楔形镶入秦岭地壳中部,使秦岭带南侧呈向南开口的“锷鱼咀”式构造特点,上、下部为秦岭上,下地壳,而中部则为扬子陆块物质成份。秦岭分北秦岭,中秦岭、南秦岭。北秦岭为一复杂构造带,形成向北反转的叠瓦状逆冲推覆构造。南秦岭自北向南产生低角度叠瓦状逆冲断裂。近南北向通渭－武都、南阳－襄樊两条深断裂带将秦岭分成了西秦岭、东秦岭、桐柏山－大别山三段。  相似文献   

地震近场记录中来自沉积盆地底部的S-P转换波震相c   总被引：1，自引：0，他引：1       下载免费PDF全文

王培德  S.Klaus 《地震学报》2002,24(5):470-478

在1989年10月和1991年3月大同地震余震的近场记录中,发现P波与S波到时之间还存在一个附加震相. 对地震的精确定位表明,有一些带有附加震相的地震记录是在临界角之内的台站得到的,因而可以排除附加震相为地表折射波的可能性. 用质点运动轨迹分析方法对附加震相的振动方向进行分析后认为,附加震相的运动特性与P波的运动特性一致,因而,可能是来自沉积盆地底部的S-P转换波. 设定一个低速的沉积层覆盖在速度较高的基岩之上的速度结构模型,用合成地震图技术模拟出这次地震的附加震相,从而确认该附加震相为盆地底部的S-P转换波. 调整传播路径上沉积基底的深度,可以得到一个概略性的盆地底部的图象,即大同盆地底部是一个沿桑干河河谷中部深、两側浅的V形盆底.   相似文献   

The response of climatic jump in summer in north china to global warming   总被引：1，自引：1，他引：0  

Huang Jiayou 《大气科学进展》2000,17(2):184-192

To reveal climatic variation over North China, the climatic jumps in summer in Beijing are analyzed using the data of precipitation of summer (June, July, August) during the period of 1841-1993, in which those missed before 1950 were reconstructed by the stepwise regression method with minimum forecast error. The climatic jumps at different scales are analyzed using different diagnostic methods with different decade (10-100 years) windows. Some new methods and ideas are proposed. The variance difference, the linear tendency difference, and the difference of power spectral distribution between the samples before and after the period at the moving point in the center of the series are compared with other methods (for example, Mann-Kendall test, t-test, and accumulative anomaly etc.). Considering the differences among the statistics above, a synthetic jump index is also proposed in order to get the definite jump points in the moving series. The results show that the climatic jumps in the area occurred in the 1890’s, the 1910s and the 1920s, and mostly in the 1920s, which suggests that the local climatic jumps in North China have a simultaneous response to the global warming in the hundred-year scales.  相似文献   

数值模拟估算低低卫-卫跟踪观测技术反演地球重力场的空间分辨率   总被引：12，自引：8，他引：12       下载免费PDF全文

周旭华  吴斌  许厚泽  彭碧波 《地球物理学报》2005,48(2):282-287

从两个方面模拟研究了低低卫-卫跟踪观测技术恢复地球重力场的空间分辨率. 利用重力位系数作为扰动量，积分30天的轨道，研究重力位系数变化引起低低卫-卫跟踪星间距离和速率变化，结果表明，对于地球重力场模型EGM96的前120阶，998%和97%的位系数扰动引起星间距离和速率变化的均方差大于1×１０-５m和１×１０-７m/s，并且星间距离观测值对地球重力场的反应更为敏感. 不考虑非保守力误差的影响，用随机误差为１×１０－５m和１×１０－６m/s的星间距离和速率变化作模拟观测量，恢复了78阶地球重力场位系数，结果表明，采用随机误差为１×１０－５m的星间距离恢复地球重力场的精度明显高于１×１０－６m/s的星间速率结果，但是如果考虑非保守力误差影响，则星间测速的优越性大大增强.  相似文献