锦屏电站深埋隧洞大理岩卸荷力学特性试验研究     

朱珍德  王战鹏  朱明礼 《岩土力学》2006,27(Z1):487-492

利用MTS 815.04电液压伺服可控制刚性试验机,对取自四川凉山雅砻江大河湾锦屏二级水电站的大理岩试样进行了不同方式的卸荷试验。试验结果表明：在保持主应力差不变的卸荷试验中,随着围压降低,轴向应变先降低后又增大,而弹性模量先增大,后又突然降低;在保持轴向位移不变的卸荷试验中,随着围压的降低,试样的弹性模量先增大,达到峰值后开始降低,而轴向应力则不断降低;在保持主应力和不变的卸荷试验中得到泊松比大于由常规三轴试验得到的泊松比,但两者的强度值相差不大。  相似文献   

农业干旱综合应变防御技术研究   总被引：9，自引：0，他引：9       下载免费PDF全文

安顺清  王馥棠  徐祥德  郭安红 《应用气象学报》2000,(Z1)

针对华北地区农业生产水平和农业干旱特点 ,于 1 996～ 1 998年进行了农业干旱监测预测、秸秆覆盖、底墒科学利用、有限水胁迫效应、深松、多功能防旱剂和有限灌溉等单项农业干旱防御技术试验研究 .在它们的防旱机理、功能和操作技术方面取得了较好的效果 .在此基础上 ,在干旱严重的 1 998～ 1 999年冬小麦生育期内 ,在河南郑州郊区、山东泰安郊区和河北固城 ,根据各地条件因地制宜地对上述技术进行组装配套集成示范试验 .结果表明 ,综合应用这些技术具有较显著的抗旱增产效能 ,小麦增产 1 0 .1 %～ 36.0 % ,耗水量减少 1 .0 %～ 1 9.0 % ,水分利用效率提高 1 0 .6%～ 60 .0 % .  相似文献   

Irregular structures of the F layer at high latitudes during ionospheric heating     

E. D. Tereshchenko  M. O. Kozlova  O. V. Evstafiev  B. Z. Khudukon  T. Nygrén  M. Rietveld  A. Brekke 《Annales Geophysicae》2000,18(9):1197-1209

Results on heating the ionospheric F region above Tromsø, Norway are presented. The ionosphere was monitored by satellite tomography and amplitude scintillation methods as well as the EISCAT incoherent scatter radar. No effect of heating was observed in the daytime. In the evening and in the pre-midnight sector, noticeable tilts of the F region were observed during heating periods. The tilts overlapped the heating cone, where the electron density decreased and irregularities exceeding 10 km in size appeared. Between the heating periods the F layer was restored to its horizontal shape. The anisotropic parameters of small-scale irregularities with scale lengths of hundreds of metres were also determined. It was found that the perpendicular anisotropy points in the direction of F region plasma flow. In some cases the results can be explained by assuming that the small-scale irregularities were generated within the heating cone and drifted out of the heating region where they were subsequently observed.  相似文献   

Diffusion Coefficients of Noble Gases in Natural Minerals: An Apparent Experimental Time Dependence Caused by Domain Size Spectra     

C. Fulda  H. J. Lippolt 《Mathematical Geology》2000,32(1):31-47

Noble gas diffusion coefficients in natural minerals are of use for evaluating geochronometric dates and other geochemical data. Usually, they are determined by degassing at elevated temperatures grain powders of natural samples containing radiogenic or cosmogenic noble gases. For conventional evaluations of diffusion parameters from degassing experiments, the grains should be uniform with respect to structure, composition, shape, and size. The shape and size prerequisites can hardly be fulfilled, because even two very narrowly meshed sieves produce spectra of domain sizes, partly because of the inhomogeneity of the minerals. Accurate determination of the actual spectrum is difficult and hardly practicable. Calculations of the fractional gas loss of a sample with a spectrum of domain sizes, presented in this study, show that almost any domain size spectrum leads to apparent diffusion coefficients that depend on the extent of degassing. The exception of this rule is given. The deviation from the physical diffusion coefficient can be several orders of magnitude as shown by examples. This effect, resulting from shape and width of the domain size spectra, possibly is responsible both for the large spread of Arrhenius parameters for the same mineral in the literature and for the deviation from linearity of some published Arrhenius lines. For limited domain size spectra and short degassing times, the formula for fractional gas loss is very similar to the formula of the fractional gas loss of a single domain size. An effective domain radius, which ensures that at least the measured diffusion coefficient for very short degassing times equals the physical diffusion coefficient, is given. In addition, the dimensionless treatment of the problem is presented that leads to a method to determine Arrhenius parameters without knowing the domain size spectrum. Accurate diffusion measurements of samples with a spectrum of domain sizes may also be possible if the domain size spectrum is taken into consideration. To this end the domain size spectra should be approximated by Taylor-expandable functions or by series of discrete domain sizes. For both cases, the formulae are given.  相似文献   

KSC-127型射流式冲击器应用于大陆科学深钻的试验研究   总被引：21，自引：0，他引：21  

朴成哲  殷琨  蒋荣庆  王茂森 《世界地质》2000,19(3):295-298

根据现场试验,评价了ＫＳＣ－１２７冲击器的性能,分析了其对大陆科学深钻的适应性,且对大直径全面破碎冲击回转钻进工艺进行了讨论。  相似文献   

EXPERIMENTAL INVESTIGATION AND ANALYSIS OF HEC-6 RIVER MORPHOLOGICAL MODEL     

TAWATCHAI TINGSANCHALI  SEREE SUPHARATID 《水文研究》1996,10(5):747-761

Only comparatively few experimental studies have been carried out to investigate the performance of the HEC-6 river morphological model. The model was developed by the Hydrologic Engineering Center of the US Army Corps of Engineers. In this study, experiments were carried out in a 20 m long concrete flume 0.6 m wide with varying rectangular cross-sections. The channel bed is paved with uniform sand of D₅₀ = 0.9 mm and D₉₀ = 1.2 mm within the test reach of 12 m. Two types of experiments were carried out with sediment transport, one under steady uniform flow and another under steady non-uniform flow conditions. Nine steady uniform flow experiments were carried out to compare the measured equilibrium relationship of flow and sediment transport rate with two bedload formulae, namely, Du Boys and Meyer–Peter and Muller, and with three total load formulae, namely, Toffaleti, Laursen and Yang. It was found that even though the sediment transport consists of a certain portion of bedload, the total load formulae give satisfactory results and better agreement than the two bedload formulae. Five steady non-uniform flow experiments were carried out under various conditions of varying bed profile and channel width and also with sediment addition and withdrawal. The measured transient water surface and bed profiles are compared with the computed results from the HEC-6 model. It was found that the Toffaleti and Yang total load formulae used in the HEC-6 model give the most satisfactory prediction of actual bed profiles under various conditions of non-uniform flow and sediment transport. The effects of Manning's n, variations of sediment inflow, various sediment transport formulae, sediment grain size and the model numerical parameters, i.e. distance interval Δx and numerical weighting factor, on the computed water surface and bed profiles were determined. It was found that the selection of the sediment transport formulae has the most significant effect on the computed results. It can be concluded that the HEC-6 model can predict satisfactorily a long-term average pattern of local scour and deposition along a channel with either a small abrupt change in geometry or gradually varying cross-sections. However, the accuracy of the model prediction is reduced in the regions where highly non-uniform flow occurs.  相似文献   

半连续培养下东海原甲藻和中肋骨条藻种群生长过程与种间竞争研究   总被引：17，自引：0，他引：17  

王宗灵  李瑞香  朱明远  陈炳章  郝彦菊 《海洋科学进展》2006,24(4):495-503

采用半连续培养方法研究了温度和营养盐(N和P)限制对中国东海2种重要赤潮生物东海原甲藻和中肋骨条藻生长及种间竞争的影响。结果表明,东海原甲藻在20℃和25℃时生长状态良好,具有明显的指数增长期,15℃时细胞生长明显受到影响;中肋骨条藻具有较广的温度适应性,15~25℃时均具有明显的指数增长期。东海原甲藻可以忍受低营养盐环境并种群增长,而中肋骨条藻细胞增长需要较丰富的营养盐。在营养盐充足的环境里中肋骨条藻具有竞争优势,相反,在营养盐限制的环境中,东海原甲藻是竞争的优胜者。实验结果与东海原甲藻赤潮爆发现场的环境调查结果基本一致,可以作为解释东海原甲藻赤潮形成原因的依据。  相似文献   

Circular time-domain reflectometry system for monitoring bridge scour depth     

Jung-Doung Yu  Jong-Sub Lee 《Marine Georesources & Geotechnology》2020,38(3):312-321

Abstract

Sediment has a severe effect on bridge stability, and time-domain reflectometry (TDR) is a suitable method for assessing scour depth. This paper presents a fundamental study to demonstrate the suitability of a circular TDR system to enhance the resolution when monitoring scour depth with consideration of detailed local changes over a wide area around piers. A total of 32 electrodes are vertically installed on a cylinder pier around the circumference at ～7.36?mm intervals. Scour depth is investigated through small-scale laboratory experiments, where a measured waveform reflects the artificially constructed scour depth with high resolution (≈5?mm). Different scour types including circular, mushroom, elliptical, and irregular shapes are developed to verify the application of circular TDR, and shapes are predicted through the detailed local distribution. The influences of the reflected waveform according to water level change, temperature variation, and salinity effect are investigated as additional considerations, and the relative deviation of scour depth is analyzed. This study demonstrates that the proposed circular TDR system achieves better resolution than existing single TDR systems and may provide a better alternative technique for monitoring scour depth.  相似文献   

Experimental studies on the role of planktivorous fishes in the elimination ofMicrocystis bloom from Donghu Lake using enclosure method     

Xie Ping 《中国海洋湖沼学报》1996,14(3):193-204

The hypertrophic subtropic Donghu Lake's dense water bloom (of mainlyMicrocystis, Anabaena andOscillatoria) that occurred annually from the beginning of the 1970s, has disappeared since 1985. The influence of planktivorous fishes (silver and bighead carps) on the water bloom was studied for three years using the enclosure method. The enclosures stocked densely with bighead and/or silver carp were free of water bloom during the experimental period. The water bloom that appeared in the fish-free enclosures was completely eliminated in 10–20 days by introduction of silver and/or bighead carp(grass carp was not effective in controlling water bloom). This study showed clearly that grazing pressure by planktivorous fishes is a key factor in eliminating water bloom from the lake. This work was supported by FEBL (State Key Laboratory for Freshwater Ecology and Biotechnology of China) funds and by the National Natural Science Foundation of China (Grant No., 3937014).  相似文献   

Salt tectonics in pull-apart basins with application to the Dead Sea Basin   总被引：1，自引：0，他引：1  

J. Smit  J.-P. Brun  X. Fort  S. Cloetingh  Z. Ben-Avraham 《Tectonophysics》2008,449(1-4):1-16

The Dead Sea Basin displays a broad range of salt-related structures that developed in a sinistral strike-slip tectonic environment: en échelon salt ridges, large salt diapirs, transverse oblique normal faults, salt walls and rollovers. Laboratory experiments are used to investigate the mechanics of salt tectonics in pull-apart systems. The results show that in an elongated pull-apart basin the basin fill, although decoupled from the underlying basement by a salt layer, remains frictionally coupled to the boundary. The basin fill, therefore, undergoes a strike-slip shear couple that simultaneously generates en échelon fold trains and oblique normal faults, trending mutually perpendicular. According to the orientation of basin boundaries, sedimentary cover deformation can be dominantly contractional or extensional, at the extremities of pull-apart basins forming either folds and thrusts or normal faults, respectively. These guidelines, applied to the analysis of the Dead Sea Basin, show that the various salt-related structures form a coherent set in the frame of a sinistral strike-slip shearing deformation of the sedimentary basin fill.  相似文献