Magnetic properties of tidal flat sediments of the Yangtze Estuary and its relationship with particle size   总被引：6，自引：0，他引：6  

张卫国  俞立中 《中国科学D辑(英文版)》2003,46(9):954-966

Since the 1970s, environmental magnetism has found extensive applications in diverse research areas of geoscience[1]. In China, a lot of environmental magnetic studies have been carried out on loess, lake and marine sediments for the purpose of paleoclima…  相似文献   

Revising the paradigm of tidal analysis – the uses of non-stationary data     

David A.?JayEmail author  Tobias?Kukulka 《Ocean Dynamics》2003,53(3):110-125

Surface elevation and current records contain non-tidal variance, often dismissed as noise. The processes responsible for the non-tidal component may also modulate the tidal signal, altering its strength and frequency structure. Because of their manner of generation and propagation, internal tides are inherently irregular. The non-stationary character of these and other tidal processes provides an integral and useful property of tidal records, because it provides an opportunity to obtain insights into tidal dynamics and the interaction of tidal and non-tidal processes. It is, moreover, productive to use multiple approaches in analyzing coastal and estuarine tidal processes so that both the time-varying and average frequency content are determined. Only by confronting the causes of non-stationary behaviour in this way can some of the remaining challenges in tidal analysis and prediction be overcome, e.g. shelf and estuarine currents, river tides, internal tides, tide-surge interactions and tidally influenced ecological processes. Several examples illustrate the utility of non-stationary tidal analysis methods.Responsible Editor: Jens Kappenberg  相似文献   

Migrating sand waves     

Giovanni?BesioEmail author  Paolo?Blondeaux  Maurifio?Brocchini  Giovanna?Vittori 《Ocean Dynamics》2003,53(3):232-238

A simple mathematical model is described, which reproduces the major features of sand waves' appearance and growth and in particular predicts their migration speed. The model is based on the linear stability analysis of the flat configuration of the sea bottom subject to tidal currents. Attention is focused on the prediction of the complex growth rate that bottom perturbations undergo because of both oscillatory fluid motions and residual currents. While the real part _r of controls the amplification or decay of the amplitude of the bedforms, the imaginary part _i is related to their migration speed. Previous works on the migration of the sand waves (Németh etal. 2002) consider a forcing tide made up by the M2 constituent (oscillatory period equal to 12 h) plus the residual current Z0 and predict always a downcurrent migration of the bedforms. However, field cases exist of upcurrent-migrating sand waves (downcurrent/upcurrent-migrating sand waves mean bedforms moving in the direction of the steady residual tidal current or in the opposite direction, respectively). The inclusion of a tide constituent characterized by a period of 6 h (M4) is the main novelty of the present work, which allows for the prediction of the migration of sand waves against the residual current Z0. Indeed, the M4 tide constituent, as does also the residual current Z0, breaks the symmetry of the problem forced only by the M2 tide constituent, and induces sand-wave migration. The model proposed by Besio etal. (2003a) forms the basis for the present analysis. Previous works on the subject (Gerkema 2000; Hulscher 1996a,b; Komarova and Hulscher 2000) are thus improved by using a new solution procedure (Besio etal. 2003a) which allows for a more accurate evaluation of the growth rate for arbitrary values of the parameter r, which is the ratio between the horizontal tidal excursion and the perturbation wavelength. Responsible Editor: Jens Kappenberg  相似文献   

Lunisolar torque on the atmosphere and Earth's rotation     

C. Bizouard  S. Lambert 《Planetary and Space Science》2002,50(3):323-333

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基于等高线构建TIN模型的平三角形修正算法     

张立朝  郑海鹰  陈引川  赵鹏  孙婷 《测绘学院学报》2006,(6)

设计了一种平三角形修正算法来修正TIN模型中可能出现的平三角形区域。该算法通过对由平三角形组成的区域进行分类,并针对不同的平区域采用交换边、增加点甚至不处理的修正方法,同时对由于等高线数据错误产生的一些特殊情况进行了分析处理。实验结果表明,该算法能够去除约束型狄洛尼三角网中所有应修正的平三角形,并生成对地形描述更为精确的三角网。  相似文献   

钢筋混凝土扁梁柱节点抗震设计方法   总被引：1，自引：0，他引：1  

戴益华 《地震工程与工程振动》2006,26(1):122-128

为考虑扁梁柱节点内、外核心区的相互作用,对扁梁柱节点的内、外核心区进行了重新划分,认为内、外核心区有一个重叠的区域,给出了地震作用在扁梁柱节点内外核心区的分配方法,采用压杆模型和软化桁架模型,提出扁梁柱节点的设计方法。该方法可以考虑节点核心区钢纤维和扁梁中无粘结预应力对扁梁柱节点抗剪极限承载力的作用。该设计方法的可靠性得到四个钢筋混凝土扁梁柱节点试验数据的验证。  相似文献   

Progressive grain-size sorting along an intertidal energy gradient     

A. Bartholomä  B.W. Flemming 《Sedimentary Geology》2007,202(3):464-472

Along a 2 km NW-SE transect along the energy gradient of an intertidal sand body of the back-barrier tidal flats of Spiekeroog island (German Wadden Sea, southern North Sea), three sets of closely spaced surface sediment samples were taken at different times to investigate whether the effects of progressive size sorting could be identified in the textural parameters and size-frequency curves of the sediments. Grain-sizes analyses were carried out with a high-resolution settling tube having an internal resolution of 1/50-psi intervals. The settling velocity data were subsequently transformed numerically into equivalent settling diameters on the basis of a quartz sphere standard. At this high resolution, it was possible to visualize subtle changes in textural parameters which would not have been resolved by standard 0.25-phi sieve analyses. The first two sample sets of 1992 and 1994 show similar trends of progressive fining in the sediment, combined with a slight decrease in skewness and sorting in the direction of decreasing energy. Ten years later, in 2003, the sediments were slightly coarser but still reflected the hydrodynamic energy gradient by a distinct fining trend along the transect. However, in contrast to the former data sets, the skewness values now remained constant, whereas the sorting values revealed the existence of two overlapping hydrodynamic energy regimes on the tidal flat. The better sorting in the coarser size fractions and the general coarsening trend in the central part of the tidal flat are interpreted to reflect an increase in the hydrodynamic energy level since the first two sample sets were collected. This observation suggests that some of the finer particles in the grain-size spectrum on the tidal flat were winnowed out by wave action without, however, completely obliterating the former trend. This interpretation is supported by an increase in the frequency and duration of strong winds as recorded by the national weather bureau since the early 1990s. The results of the study demonstrate that the intertidal sediments of the Wadden Sea respond rapidly and sensitively to gradual changes in the hydrodynamic energy regime.  相似文献   

应用深层平板载荷试验选择桩端持力层     

张海峰  岳元元  娄志良 《岩土工程技术》2007,21(6):307-309

深层平板载荷试验是一种新兴的原位测试方法。通过安阳某工程人工挖孔扩底灌注桩深层平板载荷试验的现场实践,确定了不同土层地基土的承载力特征值,为设计单位选择持力层提供数据,并为甲方节省了大量建设资金。  相似文献   

福建省数字化钻孔体应变观测资料质量初步分析     

刘水莲  李祖宁  杨颍  沈健健  黄跃进  许书元 《华南地震》2007,27(4):79-87

对整个福建省的钻孔体应变仪器运行状况进行了综合评价,并对4个台站的观测资料质量进行了分析,用M2波潮汐因子及其相对中误差等来衡量其总体精度和稳定性,还分析了钻孔应变观测的干扰机理和特征,希望能够正确地认识以及排除观测资料中的非异常信息,提高观测精度,为地震分析预报提供可靠的前兆资料。  相似文献   

A new analytical solution of tidal water table fluctuations in a coastal unconfined aquifer     

Zhiyao Song  Ling Li  Jun Kong  Honggui Zhang   《Journal of Hydrology》2007,340(3-4):256-260

This paper presents a new perturbation solution of the non-linear Boussinesq equation for one-dimensional tidal groundwater flow in a coastal unconfined aquifer. Built upon the work of Parlange et al. [Parlange, J.-Y., Stagnitti, F., Starr, J.L., Braddock, R.D., 1984. Free-surface flow in porous media and periodic solution of the shallow-flow approximation, J. Hydrol., 70, 251–263], the solution adopts a new perturbation parameter that is by definition less than unit, and thus is applicable to a wider range of physical conditions within the constraint of the Boussinesq approximation. This approach avoids a secular term in the third-order perturbation equation of Parlange et al. (1984), enabling the derivation of the third- and higher-order solutions. In comparison with a numerical (“exact”) solution, the new perturbation solution is shown to be slightly more accurate than that of Parlange et al. (1984) with the second-order approximation. The obtained third-order solution exhibits considerable improvement in accuracy. In relatively simple analytical forms, the present perturbation solution will help to understand better the non-linear characteristics of tidal water table fluctuations in as modeled by the non-linear Boussinesq equation coastal unconfined aquifers.  相似文献