桩网复合地基桩土应力比的确定

实践证明,桩网复合地基同时具备竖向增强体复合地基与水平向增强体复合地基的加固优点,能很好地提高地基土体承载力,减小不均匀沉降,特别是桥头过渡段地基处理中能有效控制“桥头跳车”现象的产生。本文主要对桩网复合地基的加固机理进行分析,并结合自然平衡拱理论和加筋垫层拉膜效应理论推导出路堤下桩网复合地基桩土应力比计算公式,同时分析了各设计参数变化对桩土应力比的变化规律。工程实体试验表明,本文所推导的桩土应力比计算公式具有较好的适用性。     

Mesozoic extension in the Basque–Cantabrian basin (N Spain): Contributions from AMS and brittle mesostructures

In this work we analyse and check the results of anisotropy of magnetic susceptibility (AMS) by means of a comparison with palaeostress orientations obtained from the analysis of brittle mesostructures in the Cabuérniga Cretaceous basin, located in the western end of the Basque–Cantabrian basin, North Spain. The AMS data refer to 23 sites including Triassic red beds, Jurassic and Lower Cretaceous limestones, sandstones and shales. These deposits are weakly deformed, and represent the syn-rift sequence linked to basins formed during the Mesozoic and later inverted during the Pyrenean compression. The observed magnetic fabrics are typical of early stages of deformation, and show oblate, triaxial and prolate magnetic ellipsoids. The magnetic fabric seems to be related to a tectonic overprint of an original, compaction, sedimentary fabric. Most sites display a NE–SW magnetic lineation that is interpreted to represent the stretching direction of the Early Cretaceous extensional stage of the basin, without recording of the Tertiary compressional events, except for sites with compression-related cleavage.Brittle mesostructures include normal faults, calcite and quartz tension gashes and joints, related to the extensional stage. The results obtained from joints and tension gashes show a dominant N–S to NE–SW, and secondary NW–SE, extension direction. Paleostresses obtained from fault analysis (Right Dihedra and stress inversion methods) indicate NW–SE to E–W, and N–S extension direction. The results obtained from brittle mesostructures show a complex pattern resulting from the superposition of several tectonic processes during the Mesozoic, linked to the tectonic activity related to the opening of the Bay of Biscay during the Early Cretaceous. This work shows the potential in using AMS analysis in inverted basins to unravel its previous extensional history when the magnetic fabric is not expected to be modified by subsequent deformational events. Brittle mesostructure analysis seems to be more sensitive to far-field stress conditions and record longer time spans, whereas AMS records deformation on the near distance, during shorter intervals of time.     

中国古代大地测量

古代测量是中国古代文明的重要组成部分，它是适应农耕与征战的需要最早发展起来的实用技术之一。中国大地测量源于距今近5000年的原始社会末期的三皇五帝时代。几千年来，中国大地测量经历了从步量、丈量到立杆测影、仪器观测的发展过程。距今2000年的西汉时期，发明了浑天仪，开始了使用仪器测量地面点地理坐标的新阶段。公元724年，僧人一行与南宫说在黄河中游的平坦地区进行了世界上最早的子午线测量。16世纪后期，意大利人利玛窦带来了西方的测量技术，从此开始了中国传统大地测量与西方测量方法并行、融合的进程。明末清初，利用天文测地的方法在全国范围内测定了几十个经纬度点，为地图绘制提供了控制基础。天圆地方是中国古代最典型宇宙观，是中国古代测量与制图中未能考虑地球曲率的认识根源。简言之，中国古代大地测量成就辉煌，特色明显，与西方古代测量并驾齐驱。     

北美五大湖水环境保护经验分析

介绍了位于美国和加拿大边界的世界上最大的淡水水体——北美五大湖的基本情况及水环境污染和治理历程,讨论美加两国政府在水环境保护方面合作的经验,概括了五大湖环境保护工作所取得的成就。实践证明,五大湖水资源综合管理体制、水环境保护策略是行之有效的。经过几十年的努力,五大湖的水质状况已有明显改善,尤其是在人群健康保障、富营养化治理和有毒物质消减方面取得了长足的进步。     

On the Correlation between Convective Plume Updrafts and Downdrafts,Lidar Reflectivity and Depolarization Ratio

We question the correlation between vertical velocity (w) on the one hand and the occurrence of convective plumes in lidar reflectivity (i.e. range corrected backscatter signal Pz ²) and depolarization ratio (Δ) on the other hand in the convective boundary layer (CBL). Thermal vertical motion is directly investigated using vertical velocities measured by a ground-based Doppler lidar operating at 2 μm. This lidar provides also simultaneous measurements of lidar reflectivity. In addition, a second lidar 200 m away provides reflectivities at 0.53 and 1 μm and depolarization ratio at 0.53 μm. The time series from the two lidars are analyzed in terms of linear correlation coefficient (ρ). The main result is that the plume-like structures provided by lidar reflectivity within the CBL as well as the CBL height are not a clear signature of updrafts. It is shown that the lidar reflectivity within the CBL is frequently anti-correlated (ρ (w, Pz ² )) with the vertical velocity. On the contrary, the correlation coefficient between the depolarization ratio and the vertical velocity ρ (w, Δ ) is always positive, showing that the depolarization ratio is a fair tracer of updrafts. The importance of relative humidity on the correlation coefficient is discussed. An erratum to this article can be found at     

STUDIES OF THE VERTICAL STRUCTURE MODEL AND THE MICROWAVE ATTENUATION OF CLOUDS AND PRECIPITATION OVER TROPICAL OCEAN AREA*

Using radiosonde data and other related observations in the TOGA-COARE IOP(from November 1,1992 to February 28,1993),the microwave attenuation of non-precipitating clouds is investigated based on microwave radiative transfer model(MRTM) at the specific frequencies of 6.8,10.65,13.9,19.35,22.235,37.0,85.5 and 90.0 GHz.Besides,utilizing the data of the airborne radar and radiometer at 13.8 GHz in the IOP(Intensive Observation Period),vertical structure models for different types of precipitating clouds are obtained,and also the microwave attenuation of precipitating cloud is studied.Some statistical characteristics of 13.8 GHz microwave path integrated attenuation for stratiform and convective precipitating clouds are presented.The results given here are valuable for the spaceborne microwave remote sensing of precipitation,and the cloud and precipitation attenuation corrections in the spaceborne microwave remote sensing of earth surface over tropical ocean area.     

Hydrodynamic effect of the regulation project of Yangtze River deepwater channel downstream of Nanjing

A two-dimensional flow numerical model of the tidal reaches, which total length is more than 700 km, is established from Datong to the Yangtze River estuary. The tidal levels, velocities, diversion ratios and dynamic axes before and after the separate regulation of each reach and combined regulation of all reaches are obtained. The comparative analysis shows that the regulation project of a separate reach basically has no impact on velocity distributions and variations of diversion ratios of upper and lower reaches, the variations of dynamic axes are only within the local scope of the project. The regulation project of a separate reach also has less impact on the water level in the lower adjacent reaches, but will make the water levels in the upper reaches rise. After the implementation of the regulation projects for all reaches, the rise of water level in the upstream reaches will have a cumulative impact.     

A new Late Holocene sea-level record from the Mississippi Delta: evidence for a climate/sea level connection?

A detailed relative sea-level (RSL) record was constructed for the time interval 600–1600 AD, using basal peat to track sea level and containing 16 sea-level index points that capture ～60 cm of RSL rise. The study area is in the Mississippi Delta where the spring tidal range is ～0.47 m, the impact of ocean currents on sea-surface topography is limited, and crustal motions are well constrained. Age control was obtained by AMS ¹⁴C dating and most ages represent weighted means of two subsamples. Sample elevations were determined by combining differential GPS measurements with optical surveying. All index points were plotted as error boxes using 2σ confidence intervals for the ages, plus all vertical errors involved in sampling and surveying, as well as the indicative range of the samples. A striking clustering of sea-level index points between ～1000 and ～1200 AD suggests a possible acceleration in the rate of RSL rise. Removal of the long-term trend (0.60 mm yr^?1) allows for the possibility of a sea-level oscillation with a maximum amplitude of ～55 cm. However, given the size of the error boxes the possibility that oscillations did not occur cannot be entirely ruled out. Comparison of the new RSL record with various proxy climate records suggests that sea level in this area may have responded to hemispheric temperature changes, including the Medieval Warm Period and the Little Ice Age. However, given the error margins associated with this reconstruction, it is stressed that this causal mechanism is tentative and requires corroboration by high-resolution sea-level reconstructions elsewhere.     

Low calcification rates and calcium carbonate production in Porites panamensis at its northernmost geographic distribution

Porites panamensis is a hermatypic coral present in the eastern Pacific Ocean. Skeletal growth parameters have been reported, but studies of the relationship between annual calcification rates and environmental controls are scarce. In this study, we investigated three aspects of the annual calcification rates of P. panamensis: growth parameters among three P. panamensis populations; the sea surface temperature as a calcification rate control spanning a latitudinal gradient; and calcium carbonate production among three sites. Growth parameters varied among the sites due to the colony growth form. Massive colonies in the north showed a higher calcification rate than encrusting colonies in the south (mean: 1.22–0.49 g CaCO₃ · cm^?2 · yr^?1), where variations in calcification rates were related to growth rate (0.91–0.38 cm · yr^?1) rather than to skeletal density differences (overall mean ± SD, 1.31 ± 0.04 g CaCO₃ · cm^?3). Our results showed a positive linear relationship between annual calcification rates and sea surface temperatures within these P. panamensis populations. Differences were related to distinct oceanographic environments (within and at the entrance of the Gulf of California) with different sea surface temperature regimes and other chemical properties. Different populations calcified under different environmental conditions. Calcium carbonate production was dependent upon the calcification rate and coral cover and so carbonate production was higher in the north (coral cover 12%) than in the south (coral cover 3.5). Thus, the studied sites showed low calcium carbonate production (0.25–0.43 kg CaCO₃ · m^?2 · yr^?1). Our results showed reduced calcification rates, regional temperature regime control over calcification rates, different growth forms, low coral cover and low calcium carbonate production rates in P. panamensis.