Are flawed MPAs any good or just a new way of making old mistakes?     

Le Quesne  Will J. F. 《ICES Journal of Marine Science》2009,66(1):132-136

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SII型海洋重力仪稳定平台倒台故障分析与处理     

陈岳英  董庆亮  韩文华  曹建波  罗君  潘乐  陆高峰 《海洋测绘》2009,29(6):55-57

SⅡ型海洋重力仪凭借其动态测量精度高、系统可靠性强等优点已日益成为海洋调查中重力测量的重要仪器之一。从SⅡ型海洋重力仪在使用中出现的稳定平台倒台故障着手,分析了平台倒台故障的原因以及处理方法,并对仪器使用中的注意事项以及改进建议作了介绍。  相似文献   

An approach to the modeling of viscoelastic damage. Application to the long‐term creep of gypsum rock materials     

B. Nedjar  R. Le Roy 《国际地质力学数值与分析法杂志》2013,37(9):1066-1078

A three‐dimensional phenomenological model is developed to describe the long‐term creep of gypsum rock materials. The approach is based on the framework of continuum damage mechanics where coupling with viscoelasticity is adopted. Specifically, a local damage model based on the concept of yield surface is proposed and deeply investigated. Among the many possibilities, we choose in this work its coupling with a generalized Kelvin–Voigt rheological model to formulate the whole behavior. Long‐term as well as short‐term relaxation processes can be integrated in the model by means of as many as necessary viscoelastic processes. The numerical discretization is described for an easy integration within a finite element procedure. Finally, a set of numerical simulations is given to show the possibilities of the presented model. It shows good agreement with some experimental results found in the literature. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

The Holocene tephrostratigraphic record of Lake Shkodra (Albania and Montenegro)     

Roberto Sulpizio  Aurelien Van Welden  Benoit Caron  Giovanni Zanchetta 《第四纪科学杂志》2010,25(5):633-650

Two cores were recovered in the southeastern part of Lake Shkodra (Montenegro and Albania) and sampled for identification of tephra layers. The first core (SK13, 7.8 m long) was recovered from a water depth of 7 m, while the second core (SK19, 5.8 m long) was recovered close to the present‐day shoreline (water depth of 2 m). Magnetic susceptibility investigations show generally low values with some peaks that in some cases are related to tephra layers. Naked‐eye inspection of the cores allowed the identification of four tephra layers in core SK13 and five tephra layers in core SK19. Major element analyses on glass shards and mineral phases allowed correlation of the tephra layers between the two cores, and their attribution to six different Holocene explosive eruptions of southern Italy volcanoes. Two tephra layers have under‐saturated composition of glass shards (foiditic and phonolitic) and were correlated to the AD 472 and the Avellino (ca. 3.9 cal. ka BP) eruptions of Somma‐Vesuvius. One tephra layer has benmoreitic composition and was correlated to the FL eruption of Mount Etna (ca. 3.4 cal. ka BP). The other three tephra layers have trachytic composition and were correlated to Astroni (ca. 4.2 cal. ka BP), Agnano Monte Spina (ca. 4.5 cal. ka BP) and Agnano Pomici Principali (ca. 12.3 cal. ka BP) eruptions of Campi Flegrei. The ages of tephra layers are in broad agreement with eight ¹⁴C accelerator mass spectrometric measurements carried out on plant remains and charcoal from the lake sediments at different depths along the two cores. The recognition of distal tephra layers from Italian volcanoes allowed the physical link of the Holocene archive of Lake Shkodra to other archives located in the central Mediterranean area and the Balkans (i.e. Lake Ohrid). Five of the recognised tephra layers were recognised for the first time in the Balkans area, and this has relevance for volcanic hazard assessment and for ash dispersal forecasting in case of renewed explosive activity from some of the southern Italy volcanoes. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

Fluid-absent (dehydration) melting of biotite in metapelites in the early stages of crustal anatexis   总被引：48，自引：1，他引：48  

Nicole Le Breton  Alan Bruce Thompson 《Contributions to Mineralogy and Petrology》1988,99(2):226-237

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青海湖沉积物中的粘土矿物   总被引：5，自引：0，他引：5       下载免费PDF全文

徐昶  林乐枝 《地质科学》1989,5(4):348-354

本文对青海湖沉积物中的粘土矿物和沉积环境进行了初步研究。沉积物的粒度成分一般以粉砂级为主,湖周沉积物较粗,湖内沉积物较细。湖中粘土矿物以伊利石-绿泥石为主,含少量蒙脱石和高岭石等。沉积物表层未见蒙脱石,粘土中Al₂O₃、K₂O和MgO的相对百分含量的特征与海粘土的化学成分特征相似。  相似文献   

Subsidence, extension and thermal history of the West African margin in Senegal     

Marie Vronique Latil Brun  Francis Lucazeau 《Earth and Planetary Science Letters》1988,90(2)

The subsidence of the Atlantic margin in Senegal clearly shows two rapid stages related to the formation of (1) the Central Atlantic during the early Jurassic (around 200 Ma), and (2) the Equatorial Atlantic during the Cretaceous (100 Ma). A simple model of extension is used to interpret the subsidence history and to derive the thermal evolution of this basin. The present-day gravity, bathymetry, bottom hole temperatures (BHT) in oil exploration boreholes and heat flow density are used to control the validity of the model. Two cross sections from the outcropping basement to oceanic crust are used, one in Casamance and the other one at the south to latitude of Dakar. The model can fully explain the first-order subsidence history as well as the present-day observations, and therefore can provide valuable information about the thermal evolution of sediments and about the structure of the continental crust along the margin. Comparisons with the opposite margin in North America (Blake Plateau and Carolina trough) indicate a rather different evolution (the North American margin did not undergo the second stage of rifting) and a different crustal structure (crustal thinning is less important on the African margin).  相似文献   

A four-parameter,two degree-of-freedom block-spring model: Effect of the driver velocity     

Jose L. Brun  Javier B. Gomez 《Pure and Applied Geophysics》1994,143(4):633-653

We analyze the effect of tectonic plate velocities in the earthquake pattern using a simple mass-spring model of the Burridge and Knopoff type with two blocks and a velocity-weakening friction law. Previous versions of the two-block model assume a steady driver during slip events (limit of zero driver velocity), which, in some cases makes necessary the introduction of artificial parameters to start the numerical integration of the equations of motion at impending slip of any block. Still maintaining the condition of zero driver velocity during slip, we shall introduce a procedure to start the numerical integration without introducing artificial parameters and this will be done by using a linearized version of the equations of motion valid for small velocities and considering nonzero driver velocity. We also introduce a four parameter model in which the driver velocity enters the equations during the whole simulation, and analyze the effect of the new parameter, the driver velocity, in the displacement and time patterns of blocks motion, directly related to earthquake statistics such as coseismic slips and average repeat times.  相似文献   

Influence of bottom topography roughness on the jet and inertial recirculation of a mid-latitude gyre     

Bernard Barnier  Christian Le Provost 《Dynamics of Atmospheres and Oceans》1993,18(1-2)

Several numerical experiments are conducted to examine the influence of mesoscale, bottom topography roughness on the inertial circulation of a wind-driven, mid-latitude ocean gyre. The ocean model is based on the quasi-geostrophic formulation, and is eddy-resolving as it features high vertical and horizontal resolutions (six layers and a 10 km grid). An antisymmetrical double-gyre wind stress curl forces the baroclinic modes and generates a strong surface jet. In the case of a flat bottom, inertia and inverse energy cascade force the barotropic mode, and the resulting circulation features strong, barotropic, inertial gyres. The sea-floor roughness inhibits the inertial circulation in the deep layers; the barotropic component of the flow is then forced by eddy-topography interactions, and its energy concentrates at the scales of the topography. As a result, the baroclinicity of the flow is intesified: the barotropic mode is reduced with regard to the baroclinic modes, and the bottom flow (constrained by the mesoscale sea-floor roughness) is decoupled from the surface flow (forced by the gyre-scale wind). Rectified, mesoscale bottom circulation induces an interfacial form stress at the thermocline, which enhances horizontal shear instability and opposes the eastward penetration of the jet. The mean jet is consequently shortened, but the instantaneous jet remains very turbulent, with meanders of large meridional extent. The sea-floor roughness modifies the energy pathways, and the eddies have an even more important role in the establishment of the mean circulation: below the thermocline, rectification processes are dominant, and eddies transfer energy toward permanent mesoscale circulations strongly correlated with topography, whereas above the thermocline mean flow and eddy generation are influenced by the mean bottom circulation through interfacial stress. The topography modifies the vorticity of the barotropic and highest baroclinic modes. Vorticity accumulates at the small topographic scales, and the vorticity content of the highest modes, which is very weak in the flat-bottom case, increases significantly. Few changes occur in surface-intensified modes. In the deep layers of the model, the inverse correlation between relative vorticity and topography at small scales ensures the homogenization of the potential vorticity, which mainly retains the largest scales of the bottom flow and the scale of β.  相似文献   

长波稳定性的季节变化          下载免费PDF全文

吕克利  农尚尧  蒋乐 《热带气象学报》1993,9(2):105-113

利用多层模式导得了多层斜压大气中的斜压不稳定的必要条件,还利用迭代-还原法计算了春夏秋冬实际基流上不稳定波的增长率。结果显示,长波扰动的增长率及其不稳定波的波长范围有明显的季节变化,冬季增长率最大,不稳定波的波长范围也最宽,春季次之,夏季最弱;β参数对长波不稳定起稳定化作用,它减小不稳定波的增长率,缩小不稳定波的波长范围;Froude数的影响与β参数相反,它对长波起不稳定化作用.地形的存在,使不稳定波的波长范围缩小,对增长率的影响比较复杂。  相似文献