Non-symmetrical levee breaching processes in a channel bend due to overtopping

A series of experiments were done to reveal the overtopping breaching process of non-cohesive and cohesive levees in a U-bend flume. The flood hydrograph and breaching geometry were measured and analyzed in detail. The results show that the levee breaching processes can be briefly divided into four stages: slope erosion, longitudinal headward gully-cutting, lateral erosion, and relative stabilization. For non-cohesive levees, non-symmetrical lateral development of the breach occurs throughout the four stages, and the final non-symmetrical coefficient is approximately 2.2–2.6. Larger flow discharge or higher water level can accelerate the breaching process, while coarser sands tend to accelerate the process initially but depress the process at the end. The fluvial erosion rate of a non-cohesive breach shows a power-function relation with the excess wall shear stress. For cohesive levees, a plateau forms in the breach partially blocking the flow in the first two stages. The breach flow is approximately perpendicular to the levee body, and, thus, the erosion rates of the two breach sides are almost the same. Non-symmetrical lateral development mainly occurs in the third stage when the deep gully forms. The final non-symmetrical coefficient is approximately 2.7–3.3. It is expected that these findings can provide a valuable experimental dataset and a theoretical basis for breach closure and flood alleviation.     

Mapping of sound scattering objects in the northern part of the Barents Sea and their geological interpretation

On cruises 25 (2007) and 28 (2011) of the R/V Akademik Nikolai Strakhov in the northern part of the Barents Sea, the Geological Institute, Russian Academy of Sciences, conducted comprehensive research on the bottom relief and upper part of the sedimentary cover profile under the auspices of the International Polar Year program. One of the instrument components was the SeaBat 8111 shallow-water multibeam echo sounder, which can map the acoustic field similarly to a side scan sonar, which records the response both from the bottom and from the water column. In the operations area, intense sound scattering objects produced by the discharge of deep fluid flows are detected in the water column. The sound scattering objects and pockmarks in the bottom relief are related to anomalies in hydrocarbon gas concentrations in bottom sediments. The sound scattering objects are localized over Triassic sequences outcropping from the bottom. The most intense degassing processes manifest themselves near the contact of the Triassic sequences and Jurassic clay deposits, as well as over deep depressions in a field of Bouguer anomalies related to the basement of the Jurassic–Cretaceous rift system     

新疆西南天山阿万达金矿区赋矿围岩物源及形成时代:碎屑锆石U-Pb年代学制约

阿万达金矿位于西南天山造山带内。此次研究在简要总结其矿床地质特征基础上,对与阿万达金矿成矿密切相关的阿克苏群中硅质片岩围岩分别进行了岩石地球化学分析和LA-ICP-MS碎屑锆石U-Pb定年研究,以期对围岩的沉积环境、物源及形成时代进行讨论。岩石地球化学分析结果显示,阿万达金矿赋矿围岩中硅质片岩的原岩可能为一套成熟度较低的泥岩或砂岩,物源主要为石英岩质沉积物,沉积环境可能处于活动大陆弧内的沉积盆地内。U-Pb定年结果显示,其碎屑锆石定年数据主要形成了加权平均年龄值为405 Ma或406 Ma的年龄峰,其谐和年龄最小峰值即405 Ma可以作为其最大沉积年龄。因此笔者认为阿克苏群中硅质片岩的沉积时代并不是前人所定的长城纪,而是不老于早泥盆世。另外,这一地层的物源组成具有多样性,～405 Ma碎屑锆石占主体,可能与哈尔克山北缘火山弧内的早泥盆世岩浆活动有关;～745Ma的碎屑锆石的出现,表明其物源有少部分来自新元古代岩石;极少数～2.50 Ga的碎屑锆石的出现,反映了华北地台对本地层有物源上的贡献。     

APPLICATION OF THE CLUSTERING METHOD IN ANALYSING SHALLOW WATER MASSES AND MODIFIED WATER MASSES IN THE HUANGHAI SEA AND EAST CHINA SEA

The existing various T-S diagram methods of analysing water masses have a good effect on the ocean water mass analysis, but they have many limitations in analysing water masses in the shallow sea. The main point is that it is difficult to determine the core of original water type in the shallow sea area, so a large error may be carried into the determination of the boundaries of water mass. For example, when water masses are analyzed with the conventional analysis method of concentration mixture, we usually obtain a very     

Tests and applications of an approach to absorbing reflected waves towards incident boundary

If the upstream boundary conditions are prescribed based on the incident wave only, the time-dependent numerical models cannot effectively simulate the wave field when the physical or spurious reflected waves become significant. This paper describes carefully an approach to specifying the incident wave boundary conditions combined with a set sponge layer to absorb the reflected waves towards the incident boundary. Incorporated into a time-dependent numerical model, whose governing equations are the Boussinesq-type ones, the effectiveness of the approach is studied in detail. The general boundary conditions, describing the down-wave boundary conditions are also generalized to the case of random waves. The numerical model is in detail examined. The test cases include both the normal one-dimensional incident regular or random waves and the two-dimensional oblique incident regular waves. The calculated results show that the present approach is effective on damping the reflected waves towards the incident wave boundary.     

Stability and phase relations of nonstoichiometric clinopyroxenes in the join diopside-Ca-Eskola component at high pressures

The stability of nonstoichiometric clinopyroxenes in the Di-CaEsk join was experimentally studied, and phase diagrams were constructed for this join at pressures of 2.0 and 3.0 GPa. It was found that melting in the diopside part of the join occurs at anomalously low temperatures, and nonstoichiometric clinopyroxene coexists with a phase approaching diopside in composition. Phase relations along the Di-CaEsk join can be described and consistently interpreted only assuming that the diopside phase (α-diopside) is thermodynamically stable. The following phase volumes were observed along the solidus of the join at a pressure of 3.0 GPa: Cpx, αDi+Cpx, αDi+Cpx+Qtz, αDi+Cpx+Grt+Qtz, Cpx+Grt+Qtz, Cpx+Grt+Ky+Qtz, Grt+Ky+Qtz. Melting occurs via the eutectic reaction αDi+Cpx+Grt+Qtz=L at a temperature of about 1200°C in the diopside part of the system and via the eutectic reaction Cpx+Grt+Ky+Qtz=L at a temperature of 1400°C in the calcium-rich part of the system. At a pressure of 2.0 GPa, melting occurs at temperatures of 1200–1300°C via the eutectic reaction αDi+Cpx+ An + Qtz=L. The invariant equilibrium (L, An, Cpx, Grt, αDi, Qtz) lies within the pressure range 2.0–3.0 GPa. Nonstoichiometric clinopyroxenes form complex solid solutions, the compositions of which are not strictly confined to the Di-CaEsk join and depend on temperature, pressure, and phase association. Grossular garnets coexist with nonstoichiometric clinopyroxenes and α-diopside.     

Modeling of deep-seated high-alumina parageneses on the basis of the stability fields of corundum- and spinel-normative assemblages of the system CaO–MgO–Al2O3–SiO2

To elaborate physicochemical models for the origin of crystalline rocks, experimental studies of the field of high-alumina assemblages of the system CaO–MgO–Al₂O₃–SiO₂ were carried out at 10–30 kbar and 1250–1535 °C. We have determined the phase relations between the melt (L) and An, Sp, Cpx, Cor, and Ga, the slope of the rays of the monovariant reactions An + Sp = Cpx + Cor + (Ga) and L = Cpx +Ga + Cor + Sp, the position of the nonvariant point (An, Sp, Cpx, Cor, Ga, L), and the compositions of phases participating in these reactions. Based on a topological analysis of the studied segment of the system CaO–MgO–Al₂O₃–SiO₂, we have substantiated that “eclogitization” must follow the reaction Opx + An + Sp = Cpx + Ga. A fundamental continuous series of eutectic monovariant equilibria was observed: L = Cpx + Opx + Fo + An, L = Cpx + Opx + An + Sp, L = Cpx (+ Ga) + An + Sp, and L = Cpx + Cor (+ Ga) + An. A change in the melt composition in this series of eutectic reactions depending on pressure must reflect the most likely magma genesis trend in nature. Comparision of the composition fields in which the above series of reactions is observed with the composition fields of the rocks of magmatic formations showed that this series is most similar to the alkali-earth series of rocks. The mineralogical compositions of cumulates and phenocrysts found in the effusive and dike varieties of these rocks correspond to unique sets of subsolidus phase associations and individual subsolidus phases crystallizing in this fundamental eutectic series.     

呼伦贝尔地区土地荒漠化动态变化

呼伦贝尔地区是中国重要的天然草原和畜牧基地, 随着该地区经济和社会的发展及人类对资源的不合理利用, 土地荒漠化现象加重。笔者应用RS和GIS技术, 以1970 年MSS、2000 年ETM和 2007年CBERS数据为数据源, 主要采用人工目视解译方法, 并辅助野外调查验证, 获得三期解译数据, 并利用空间分析、网格剖分方法, 对呼伦贝尔地区荒漠化的时空变化情况进行研究。结果表明: 近40年来, 该地区土地荒漠化总面积不断增加, 1970 年该地区土地荒漠化面积为7408.76 km2 , 2000年为7 539.52 km2 , 2007年增加到7 852.12 km2 , 共增加面积443.36 km2。1970-2000年间, 沙漠化减轻、盐碱化加重的面积为134.09 km2 , 沙漠化加重、盐碱化减轻的面积为53.35 km2 ; 2000- 2007年间, 沙漠化减轻、盐碱化加重的面积为41.71 km2 , 沙漠化加重、盐碱化减轻的面积为172.8 km2。     

Subpollen Particles as Atmospheric Cloud Condensation Nuclei

Izvestiya, Atmospheric and Oceanic Physics - Bioparticles constitute a significant fraction of atmospheric aerosol. Their size range varies from nanometers (macromolecules) to hundreds of...     

宁洱6.4级地震灾情信息特征分析

选取2007年宁洱6.4级地震发生后一周内政府收集和上报的灾情档案资料中的人员伤亡和财产损失两类主要信息为基础资料,对该次地震的灾情信息特征进行初步分析.结果表明:灾情信息来源的主体为县级政府部门,描述方式以定量为主.在地震发生后4h内以定性描述为主,4～12h期间定性描述与定量描述都有,12 h后以定量描述为主;单位时间内灾情信息获知和上报的数量随时间的推移先逐渐增加,到达峰值后逐渐减少,最后趋于平稳;从信息随时间变化情况来看,最先掌握死亡人员数量,接着是重伤人员数量,最后是受伤人员数量;与地震灾害直接经济损失评估结果比较,房屋损失信息更直接地反应本次地震损失.