The western desert — an example for geodetic problems in arid areas

In this paper some methodical aspects concerning the construction of an accurate geodetic network in arid areas and the connection of the new points to an existing network are discussed. In this context special attention is rapid on the determination of the station heights above the geoid. For the Western Desert in Egypt, which can be regarded as an example of an arid, geodetically underdeveloped region, an observational program is outlined that combines Doppler-measurements with an astrogravimetric-levelling.     

Optimizing fixed observational assets in a coastal observatory

Proliferation of coastal observatories necessitates an objective approach to managing of observational assets. In this article, we used our experience in the coastal observatory for the Columbia River estuary and plume to identify and address common problems in managing of fixed observational assets, such as salinity, temperature, and water level sensors attached to pilings and moorings. Specifically, we addressed the following problems: assessing the quality of an existing array, adding stations to an existing array, removing stations from an existing array, validating an array design, and targeting of an array toward data assimilation or monitoring.     

考虑力组合效应的钢框架端板连接力学行为

为研究不同力组合效应对平齐端板连接力学行为的影响,采用ABAQUS程序建立不同受力情况下连接的非线性简化有限元模型,通过与国内外典型试验结果对比分析,验证了有限元模型的可靠性。基于此通过考虑8种力组合因素的影响,分析了2种不同钢等级的梁柱节点力学行为,进一步讨论了EC3 Part 1-8规范的适用性。结果表明:简化有限元模型在弯矩-转角曲线、破坏形态、初始刚度和塑性抗力等方面与试验结果吻合良好。框架梁轴力对节点的力学行为影响显著,当轴拉力为20%的框架梁轴向塑性抗力N_pl时,高强钢节点的刚度和强度分别降低68%和52%;当轴压力为-20%N_pl时,刚度和强度分别增加89%和42%。此外节点的滞回耗能能力、破坏模式以及分类属性与梁轴力水平密切相关。对于高强钢梁柱平齐端板节点,EC3规范对框架梁轴压力的限值仍过于保守。研究结果对于提高结构的抗倒塌能力和组合力作用下的理论研究具有重要参考价值。     

Analysis of the zoned plagioclase of different magmatic environments: A preliminary ion-microprobe study

A method for quantitative analysis of silicates with an ion microprobe has been developed which suppresses molecular ion interferences with an energy filtering technique based on the difference in the kinetic energy distributions between single-atom ion and molecular ion species.Using this technique, the distribution patterns (zoning) of the major and trace elements were compared in plagioclase crystals from different magmatic environments. The phenocryst of an ocean-ridge tholeiite (mid-Indian Ocean Ridge) is characterized by homogeneous distribution on all elements analyzed. The apparent partition coefficient for K is more than a factor of two higher than the value found in the literature. The plagioclase grain in a Lower Zone of the Skaergaard Intrusion consists of a cumulus part with uniform An content and an intercumulus part with normal major element zoning. The cumulus part shows an outward increase of Sr and a decrease of Mg and Fe. Potassium is uniform but high, giving an apparent partition coefficient close to unity. The phenocryst in an alkali basalt from Terceira, Azores, consists of an inner part of bytownite and an outer part of labradorite with a sharp transition in between.It is suggested that the distribution of K in the Skaergaard plagioclase could represent a steady-state crystallization and that uniformity of a phase with respect to an element may not be adequate as a criterion for equilibrium.     

Propagation of Electromagnetic Field Pulse in an Inhomogeneous Medium Based on the Results of an Analytical Continuation of the Field

The possibility of visually controlling the propagation of an electromagnetic pulse in an inhomogeneous medium based on an analytical continuation of the observed field is presented.     

Small Scale Kinematic Dynamos: Beyond the α-Effect

In geodynamo simulations which simulate the generation of an axial dipolar magnetic field, the generation mechanism appears to be adequately described as an α²-dynamo with an anisotropic α-effect. The anisotropy in the α-effect favors an equatorial dipole field, however, which calls into question the interpretation in terms of an α²-dynamo. It is shown in this article with kinematic dynamo calculations and exemplary velocity fields with an anisotropic α-effect that both types of dipolar magnetic field can be generated. Two examples of working dynamos in a sphere with flows with zero α-effect are also provided.     

Torsional vibrations of elastic foundations embedded in an elastic half-space

This paper examines the axisymmetric torsional vibrations of an elastic pile and a hemispherical foundation embedded in a homogeneous elastic half-space. The embedded foundation–half-space system is decomposed into an extended half-space and a fictitious foundation. The deformations of the fictitious system are specified by an admissible function containing a set of generalized coordinates. The Lagrangian equations of motion are used to determine these coordinates associated with the assumed displacement function. Numerical results are presented for torsional impedance of an elastic pile and a hemisphere to illustrate the effects of relative flexibility and geometry. By employing certain simplifications on the pile–half-space system an approximate closed form solution is presented for the torsional impedance of an elastic pile.     

Review paper: Virtual sources and their responses,Part II: data‐driven single‐sided focusing

In Part I of this paper, we defined a focusing wave field as the time reversal of an observed point‐source response. We showed that emitting a time‐reversed field from a closed boundary yields a focal spot that acts as an isotropic virtual source. However, when emitting the field from an open boundary, the virtual source is highly directional and significant artefacts occur related to multiple scattering. The aim of this paper is to discuss a focusing wave field, which, when emitted into the medium from an open boundary, yields an isotropic virtual source and does not give rise to artefacts. We start the discussion from a horizontally layered medium and introduce the single‐sided focusing wave field in an intuitive way as an inverse filter. Next, we discuss single‐sided focusing in two‐dimensional and three‐dimensional inhomogeneous media and support the discussion with mathematical derivations. The focusing functions needed for single‐sided focusing can be retrieved from the single‐sided reflection response and an estimate of the direct arrivals between the focal point and the accessible boundary. The focal spot, obtained with this single‐sided data‐driven focusing method, acts as an isotropic virtual source, similar to that obtained by emitting a time‐reversed point‐source response from a closed boundary.     

Multiple‐tuned liquid column dampers for torsional vibration control of structures: theoretical investigation

This paper presents a theoretical investigation on the performance of multiple‐tuned liquid column dampers (MTLCD) for reducing torsional vibration of structures in comparison with single‐tuned liquid column dampers (STLCD). The analytical model is first developed for torsional vibration of a structure with an MTLCD under either harmonic excitation or white noise excitation. The experimental results are then used to verify the analytical model for coupled MTLCD‐structure systems under harmonic excitation. The performance of an MTLCD and its beneficial parameters for achieving the maximum torsional response reduction to white noise excitation are finally investigated through an extensive parametric study in terms of the distance from the centre line of the MTLCD to the rotational axis of the structure, the ratio of the horizontal length to the total length of liquid column, frequency bandwidth, head‐loss coefficient, the number of TLCD units in an MTLCD, frequency‐turning ratio and the spectral level of excitation moment. The results show that there is an optimal head‐loss coefficient and an optimal frequency bandwidth for an MTLCD to achieve the maximum torsional response reduction. It is also demonstrated that the sensitivity of an optimized MTLCD to the frequency‐tuning ratio is less than that of an optimized STLCD, and it can be further improved by increasing the bandwidth but at the cost of less torsional vibration reduction. Copyright © 2002 John Wiley & Sons, Ltd.     

溞类(Daphnia)反捕食的表型可塑性及其研究进展

表型可塑性指的是生物体在生物或非生物环境发生变化时会呈现出不同的表型能力,是生物在不稳定的生活环境中维持生存的一种主要策略.在淡水生态系统,大量研究表明浮游动物能通过捕食者释放的化学信息物质感知捕食风险的存在,从而导致反捕食的表型可塑性反应的发生.溞类是一类很好的研究浮游动物对捕食者释放的信息素产生表型可塑性反应的模式生物.本文综述了捕食者释放的化学信息素对溞类的生活史、形态特征、行为活动以及生理指标等表型的影响,探讨了其形成机制和生态意义.溞类对捕食风险信息素的表型可塑性是特定种群与捕食者长期相互作用下适应性进化产生的.加强这些研究对了解物种的形成和生物的进化有非常重要的意义.     

断裂带内介质的软化特性和地震的非稳定模型

本文将地震过程看作是一个包含断裂带和围岩的力学系统在外界扰动下的一种失稳现象,用变形体力学方法给出了断层带介质软化的本构方程和地震非稳定模型的一般的数学表述.借助于均匀场的非稳定模型,本文讨论了弹性回跳概念,导出了地震效率公式和论证了能量形式失稳准则的普遍性,并指出了在刚性试验机上研究声发射现象的重要意义.本文还介绍了用于研究非均匀场的地震非稳定性的有限单元法的通用程序以及唐山地震的算例.      

Magneto-elasticSH-type of motion

Summary TheSH-type of motion in an isotropic elastic halfspace with infinite electrical conductivity subjected to an uniform magnetic field and disturbed by a buried source is investigated. Expressions for the surface displacements for various type of sources are obtained by an application of Cagniard technique. Numerical calculation has been performed for the case of a diapole source moving parallel to the surface of the halfspace with an uniform velocity.     

车辆荷载作用下山西路基重塑黄土的动力特性研究

针对车辆荷载对山西高速公路路基土体影响研究不足的现状,从试验角度出发,研究车辆荷载水平、波形、干密度和围压对路基土体的动力特性响应。研究表明:路基土体的体变随波形比的增大而增大,随车辆荷载的增大而增大;路基土体的动弹性模量随干密度的增大而增大,随围压的增大而增大,阻尼比随围压的增大而减小。     

A note on magnetic modelling with remanence

The general problem of magnetic modelling involves accounting for the effect of both remanent magnetization and the application of an external magnetic field. However, as far as the disturbing field of a magnetic body in a magnetic environment is concerned, there is an equivalence between the effects of these two causations that allows the remanence to be represented in terms of an equivalent primary magnetic H field. Moreover, due to the linearity of the magnetic field in terms of its causations, the general modelling problem involving an applied magnetic field in the presence of remanence can be simply and more efficiently dealt with in terms of an equivalent primary field acting in the absence of any remanent magnetization.     

Open Channel Waves that Form after the Removal of a Screen before Uneven Bed

The results of an experimental study of the gravity waves that form in an open channel at the decomposition of an initial discontinuity in the free surface level above an uneven bed in the form of a shelf are discussed. Self-similar solutions obtained in the context of the first approximation of the shallow-water theory are tested. It is shown that more complex mathematical models must be used to adequately describe the waves of level drop in the upper pool and undular hydraulic jumps.     

孕震区产生电磁辐射的电学模型

震前电磁辐射是一种与孕震活动有关的客观现象,通过讨论孕震区的力学性质和电学性质,提出了孕震区产生电磁辐射的电学模型,并对这个电学模型作了尝试性的探讨。     

Volcanic eruption clouds and the thermal power output of explosive eruptions

The maximum height attained by a volcanic eruption cloud is principally determined by the convective buoyancy of the mixture of volcanic gas + entrained air + fine-sized pyroclasts within the cloud. The thermal energy supplied to convection processes within an eruption cloud is derived from the cooling of pyroclastic material and volcanic gases discharged by an explosive eruption. Observational data from six recent eruptions indicates that the maximum height attained by volcanic eruption clouds is positively correlated with the rate at which pyroclastic material is produced by an explosive eruption (correlation coefficient r = + 0.97). The ascent of industrial hot gas plumes is also governed by the thermal convection process. Empirical scaling relationships between plume height and thermal flux have been developed for industrial plumes. Applying these scaling relationships to volcanic eruption clouds suggests that the rate at which thermal energy is released into the atmosphere by an explosive eruption increases in an approximately linear manner as an eruption's pyroclastic production rate increases.     

A two-layer primitive equation model of an idealized Strait of Gibraltar connected to an eastern basin

We describe the solutions of a numerical two-layer primitive equation model of an idealized Strait of Gibraltar and an adjacent eastward basin. The quasi-steady circulation pattern in the basin features an anticyclonic gyre southward of the strait exit and an eastward boundary current attached to the southern boundary of the basin. A variation of the initial upper-layer depth and the target interface height at the eastern boundary causes minor changes of the upper-layer circulation in a basin with rectangular coastline and larger changes when a cape is added to the coastline of the southern boundary.     

When Can Inverted Water Tables Occur Beneath Streams?

Decline in regional water tables (RWT) can cause losing streams to disconnect from underlying aquifers. When this occurs, an inverted water table (IWT) will develop beneath the stream, and an unsaturated zone will be present between the IWT and the RWT. The IWT marks the base of the saturated zone beneath the stream. Although a few prior studies have suggested the likelihood of an IWT without a clogging layer, most of them have assumed that a low‐permeability streambed is required to reduce infiltration from surface water to groundwater, and that the IWT only occurs at the bottom of the low‐permeability layer. In this study, we use numerical simulations to show that the development of an IWT beneath an unclogged stream is theoretically possible under steady‐state conditions. For a stream width of 1 m above a homogeneous and isotropic sand aquifer with a 47 m deep RWT (measured in an observation point 20 m away from the center of the stream), an IWT will occur provided that the stream depth is less than a critical value of 4.1 m. This critical stream depth is the maximum water depth in the stream to maintain the occurrence of an IWT. The critical stream depth decreases with stream width. For a stream width of 6 m, the critical stream depth is only 1 mm. Thus while theoretically possible, an IWT is unlikely to occur at steady state without a clogging layer, unless a stream is very narrow or shallow and the RWT is very deep.