Study of Partial Coefficients for Design of Semicircular Breakwaters

In the present study,the reliability design of semicircular breakwater is based on the verification of the rules defined by standard specifications,where partial coefficients are introduced to ensure safety.The reliability of the semicircular breakwaters has been analyzed by using the Hasofer-Lind method to determine the reliability index of structure that has correlated loads,utilizing the long-term observed wave data at a given place.The relation curve between reliability index and safety factor in the traditional design method,as well as the relationships between reliability index and partial coefficients,have been obtained.This paper proposes values of partial coefficients for the design expression of semicircular breakwaters in the cases of anti-sliding and anti-overturning.     

核心筒部分悬挂结构抗震分析的简化力学模型

提出了核心筒部分悬挂结构体系,在已有该体系振动台试验基础上,建立了该体系的抗震分析简化力学模型及其理论公式。按小震、中震和大震3种不同的地震作用情况,分析了该结构体系力学模型和动力方程的差异。利用有限元分析程序SAP2000,对这种结构体系进行了小震和大震作用下的结构地震反应分析,计算结果与试验结果吻合较好。     

云量对祁连山老虎沟12号冰川表面能量平衡的影响

为探讨云量对冰川表面能量平衡(SEB)的影响,利用架设在老虎沟12号冰川(简称12号冰川)消融区(4550 m a.s.l.)的自动气象站资料,结合能量平衡模型计算各能量分量并分析其季节变化,通过云量参数化方案获取云量因子并量化其对冰川表面能量收支的影响.结果表明:净短波辐射为冰川表面主要的能量来源(92％),净长波辐...     

不纯碳酸盐岩的变质作用

不纯碳酸盐岩中的矿物共生组合与变质时的总压和二氧化碳分压密切相关。总压增高促使透闪石、透辉石和橄榄石等矿物生成温度增高。变质过程中岩石中流体成分的变化有两种极端情况,即渗滤作用和缓冲作用。渗滤作用下变质反应,变质矿物界线和变质矿物特征等均与缓冲作用下有所差异,以此可以区别它们。湖北宿松群和河北红旗营子群不纯大理岩是在渗滤作用下变质的。山西五台群板峪口组不纯大理岩是在缓冲加渗滤作用下变质的。     

熔体结构与酸性熔岩的某些特征

在流纹质岩浆中,存在两种不混溶的熔体,一种熔体富SiO_2贫FeO,另一种则相反。从熔体结构的角度看,前一种熔体富桥氧,后者则富自由氧。水的解聚作用可以改变流纹质岩浆的结构,即降低它的聚合程度,因此,含水流纹岩浆的粘度低于玄武岩浆的粘度,从而使流纹岩中流纹构造发育。 实际工作中应避免混淆流纹岩与酸性熔结凝灰岩。     

Attenuation of compressional waves in peridotite measured as a function of temperature at 200 MPa

A technique has been developed to determine attenuation in rocks at high temperature using a gas-media, high-pressure apparatus. A pulse transmission technique and a spectral ratio method are used to study compressional seismic properties of rocks. Seismic waves are transmitted to and from the sample through buffer rods of mullite. The effect of seismic wave reflections within the sample assembly are cancelled out by taking ratios of the spectra measured at different temperatures. In order to obtain good signal-to-noise ratio for resolving the attenuation at high pressure and temperature, special care is taken in the sample assembly and the ultrasonic coupling between the sample, buffer rods and transducers. A very tight connection of the sample-buffer rod-transducer is essential for obtaining high frequency signals (>300 kHz) at high temperature. A small mass is attached to each outside end of the transducer to drive low frequency signals (<250 kHz) into the sample. Before attenuation measurements, the sample and the buffer rods are tightly compacted in a platinum tube at high pressure and room temperature to ensure pressure seal of the sample assembly. The frequency range of measurement covers 50 to 450 kHz for the sample. Attenuation is very small in the buffer rod compared to the sample for the entire temperature range of the study. Because of the small attenuation, a wide frequency band of 50 kHz to 3.2 MHz can be covered for investigating the attenuation in the buffer rod. The technique has been used to measure attenuation at high confining pressure, and temperatures including sub- and hyper-solidus of upper mantle rocks. Therefore, effects of partial melting on attenuation can be studied.The method is applied to the attenuation measurement in a peridotite as a function of temperature to 1225°C at 200 MPa confining pressure. At high temperature, signal amplitude decays more rapidly at high frequency than at low frequency, from which attenuation (andQ) can be determined using a spectral ratio method. No frequency dependence ofQ is resolved for both the sample and the buffer rod over the entire temperature and frequency ranges of the measurement. The results show thatQ decreases rapidly with increasing temperature even in the temperature range below the solidus of peridotites. Such temperature sensitivity ofQ is probably more useful to probe thermal structure in the upper mantle than that of conductivity at temperatures below the solidus. The results in this study are compared with available seismic velocity, electrical conductivity and solidus data for peridotites, suggesting that there is no discontinuous change in both mechanical and electrical properties of peridotites at the solidus temperature. Even at hypersolidus temperatures, it appears that velocity drops and conductivity increases continuously (not abruptly) with increasing melt fraction. This implies that mechanical and electrical properties of the upper mantle will gradually change at the boundary where the geotherm crosses the solidus.     

The Partitioning of Tungsten bwtween Aqueous Fluids and Silicate Melts

An experimental study has been carried out to determine the partition coefficients of tungsten between aqueous fluids and granitic melts at 800 °C and 1.5 kb with natural granite as the starting material. The effects of the solutions on the partition coefficients of tungsten show a sequence of P > CO ₃ ²⁻ > B > H₂O. The effects are limited (generallyK _D < 0.3) and the tungsten shows a preferential trend toward the melt over the aqueous fluid. The value ofK _D increases with increasing concentration of phosphorus; theK _D increases first and then reduces with the concentration of CO ₃ ²⁻ when temperature decreases, theK _D between the solution of CO ₃ ²⁻ and the silicate melt increases, and that between the solution of B₄O ₇ ²⁻ and the silicate melt decreases. The partition coefficients of phosphorus and sodium between fluids and silicate melts have been calculated from the concentrations of the elements in the melts. TheK _D value for phosphorus is 0.38 and that for sodium is 0.56. Evidence shows that the elements tend to become richer and richer in the melts.     

非均匀温度场中熔体结晶作用与科马提岩结构成因

具有重要岩石学和构造学意义的科马提岩，最吸引人同时又最令人困惑的特征之一是它的鬣刺结构和分层构造。本文从喷出地表的岩桨冷凝时温度分布、熔体性质与结晶作用的密切联系，把科马提岩浆喷发形成的岩流作为一个冷凝整体。通过与金属铸锭浇注成形和矿石冶炼生产的比较，发现它们在冷凝固结过程中温度场特征、熔体的性质、结晶能力和结晶方式都有十分相似的特点，并以此为出发点详细解析了科马提岩的鬣刺结构和岩石分层构造的形成     

钨、锡流-熔分配实验结果及其矿床成因意义

本文用实验确定了钨、锡在成分不同的花岗质熔体相与共存水热流体相的流-熔分配系数(D_(Me)~(V/L))及其与介质溶液(NaF,KF,HF,NaCl等水溶液)摩尔浓度间的函数关系。实验结果表明,钨、锡的分配行为明显不同。在相同条件下,随体系的不同,D_W~(V/L)比D_(Sn)~(V/L)大几倍至二十倍。钠和钾对钨、锡的流-熔分配行为的影响基本相同,而氟和氯对钨、锡的分配行为的影响相差甚远,花岗质熔体的主成分对D_W~(V/L)和D_(Sn)~(V/L)有复杂的影响。利用这些结果探讨与花岗岩有关的钨、锡矿床的成矿机理,得出了一些与前人不同的新认识。     

The impact of the Laacher See Volcano (11 000 yr B.P.) on terrestrial vegetation and diatoms

Late-glacial lake sediments containing the Laacher See Tephra (LST, 11 000 yr B.P.) have been analyzed for their pollen and diatom content at three sites at varying distances from the volcano and on different bedrock geologies. The aim was to test the null hypothesis that this major volcanic eruption had no effect on terrestrial pollen or aquatic diatom assemblages. The pollen spectra at all sites show a short-lived increase in grass pollen following the LST. Partial redundancy analysis and associated Monte Carlo permutation tests suggest, however, that the LST had no statistically significant effect at two sites but it had a statistically significant impact on the pollen assemblages at the site nearest (60 km) to the volcano.The diatom assemblages at the three sites changed individualistically after the LST deposition, with increases inAchnanthes minutissima at one site, an expansion ofAulacoseira species at another, and an increase ofAsterionella formosa andFragilaria brevistriata at the third site. Partial redundancy analysis and associated permutation tests suggest a statistically significant change in diatoms in relation to the LST and associated changes in sediment lithology at the one site situated on acidic bedrock. No significant impacts were found at the sites on volcanic or calcareous rocks. Due to the interaction between tephra and sediment lithology, it is not possible to conclude if the statistically significant diatom changes were a direct result of the LST deposition or an indirect result of lithological changes following LST deposition.This is the first paper in a series of papers published in this issue on high-resolution paleolimnology. These papers were presented at the Sixth International Paeolimnology Symposium held 19–21 April, 1993 at the Australian National University, Canberra, Australia. Dr A. F. Lotter and Dr. M. Sturm served as guest editors for these papers.