非饱和土地基中复合多层波阻板对S波的隔离效应

基于弹性波在非饱和多孔介质与单相弹性介质中的传播理论,考虑在非饱和土地基中设置一定厚度的复合多层波阻板（复合多层波阻板以3层为例）,利用Helmholtz矢量分解定理,推导了非饱和土地基中S波通过复合多层波阻板的透射、反射振幅比的解析解。通过数值算例,分析了层间波阻板剪切模量和密度等物理力学参数对非饱和土地基中S波通过复合多层波阻板时传播特性的影响规律。结果表明：复合多层波阻板中层间波阻板材料的剪切模量和密度对透反射系数影响显著。复合多层波阻板是一种有效的隔振屏障,严格控制层间波阻板的剪切模量和密度可以获得最佳隔振效果,这为复合多层波阻板在地基振动控制领域中的应用提供理论指导。     

Shaking table tests of a resilient bridge system with precast reinforced concrete columns equipped with springs

This paper presents the shake table test results of a novel system for the design of precast reinforced concrete bridges. The specimen comprises a slab and four precast columns. The connections are dry and the columns are connected to the slab by an ungrouted tendon. One of the tendon ends is anchored above the slab, in series with a stack of washer springs, while the other end is anchored at the bottom of the column. The addition of such a flexible restraining system increases the stability of the system, while keeping it relatively flexible allowing it to experience negative post-uplift stiffness. It is a form of seismic isolation. Anchoring the tendon within the column, caps the design moment of the foundation, and reduces its size. One hundred and eighty-one shake table tests were performed. The first 180 caused negligible damage to the specimen, mainly abrasion at the perimeter of the column top ends. Hence, the system proved resilient. The 181^st excitation caused collapse, because the tendons unexpectedly failed at a load less than 50% of their capacity (provided by the manufacturer), due to the failure of their end socket. This highlights the importance of properly designing the tendons. The tests were used to statistically validate a rigid body model. The model performed reasonably well never underestimating the median displacement response of the center of mass of the slab by more than 30%. However, the model cannot predict the torsion rotation of the slab that was observed in the tests and is due to imperfections.     

双排隔振屏障对振动波的阻隔作用及动力响应分析

本文采用模拟试验的方法,对分层土地基中双排隔振屏障对振动波的动力响应进行了探讨,并研究了桩长与土层分界面位置关系、激振频率对其隔振效果的影响作用,得出结论:（1）屏障前振动强度远大于屏障后振动强度,并随着振源距、激振频率、桩长的增加而下降,且屏障前出现明显振动增强现象,在激振频率80 Hz时产生振动峰值,振动强度在高频时基本稳定,继续增加激振频率,振动强度并不会发生明显变化。（2）屏障后中线左右2倍桩长范围内为整个隔振区域的薄弱区,其他区域则由包络线围成一个封闭有效隔振区。（3）屏障对中频和高频有更好的隔振效果,且桩长越大有效隔振面积越大,当桩长超过土层分界面时,有效隔振面积可达到53.25%～69.78%,但此时有效隔振面积增幅由原来的14.29%下降到11.64%,增幅降低了约3%。（4）未设屏障区振动强度较小,随激振频率小范围内浮动,在激振频率为30 Hz和80 Hz时取得振动峰值,且随着屏障布置方向减小,即靠近屏障一侧振动强度较强,远离屏障一侧振动强度较弱。     

‘The magical operations of separation’: English elite schools’ on-line geographies,internationalisation and functional isolation

This paper examines the enduring separation and isolation of elite schools in England, in the face of increasing and substantial internationalisation. It presents the findings of a research project examining the geographical narratives produced by 30 elite schools on their websites and through their prospectuses, newsletters, blogs and twitter feeds. A critical visual and textual analysis was undertaken. Drawing on these data, the paper argues that elite schools remain highly focused on promoting and defending their separateness and isolation, despite extensive, documented international involvements. Work on institutional and carceral geographies and geographies of education have provided some theoretical justification for why this might be the case, and we explore these reasons here. The paper concludes with a plea for more work on the elite schooling sector in England, as their spatial practices (isolation and internationalisation) continue to have a weighty bearing upon society.     

Isolation and biological characteristics of aerobic marine magnetotactic bacterium YSC-1

1 INTRODUCTION Magnetotactic bacteria are able to respond and orient along the direction of terrestrial or artificial magnetic field, a behavior referred to as magneto- taxis. In the majority of magnetotactic bacteria, the magnetosomes are 25–120 nm in d…     

Bulk organic δ13C and C/N ratios as palaeosalinity indicators within a Scottish isolation basin

Microfossils in isolation basin sediments are frequently used to reconstruct sea‐level change, but preservation problems and non‐analogue situations can limit their usefulness. Here we investigate the potential of stable carbon isotopes (δ¹³C) and C/N ratios from bulk organic matter, as an alternative proxy of salinity within isolation basin sediments from a basin in northwest Scotland. Within the Holocene sediment δ¹³C and C/N are determined largely by the mean weighted values of the predominant source of the organic material. Analysis of modern materials and comparison with the diatom record shows that the marine parts of the sequence are dominated by high δ¹³C and variable C/N. In the fresh water sequences the organic material is a mixture of both freshwater aquatic and terrestrial plant input that have relatively low δ¹³C and high C/N. The application of δ¹³C and C/N ratios in the studied basin in general follow the environmental change recorded by the diatoms and shows the potential of bulk organic matter in the investigation of salinity change in isolation basins. Copyright © 2005 John Wiley & Sons, Ltd.     

Probabilistic seismic response and reliability assessment of isolated bridges

Bridge seismic isolation strategy is based on the reduction of shear forces transmitted from the superstructure to the piers by two means: shifting natural period and earthquake input energy reduction by dissipation concentrated in protection devices. In this paper, a stochastic analysis of a simple isolated bridge model for different bridge and device parameters is conducted to assess the efficiency of this seismic protection strategy. To achieve this aim, a simple nonlinear softening constitutive law is adopted to model a wide range of isolation devices, characterized by only three essential mechanical parameters. As a consequence of the random nature of seismic motion, a probabilistic analysis is carried out and the time modulated Kanai-Tajimi stochastic process is adopted to represent the seismic action. The response covariance in the state space is obtained by solving the Lyapunov equation for a stochastic linearized system. After a sensitivity analysis, the failure probability referred to extreme displacement and the mean value of dissipated energy are assessed by using the introduced stochastic indices of seismic bridge protection efficiency. A parametric analysis for protective devices with different mechanical parameters is developed for a proper selection of parameters of isolation devices under different situations.     

Nonlinear Dynamic Response of HDRB and Hybrid HDRB-Friction Sliders Base Isolation Systems

The isolation systems are usually made of rubber bearings that are sometimes coupled in hybrid combination with frictional devices; this is the case of an in-site experimental campaign, performed on a base isolated apartment building in Rapolla (south of Italy). Several dropout tests at initial displacements up to 17cm allowed to obtain in-site information on the true dynamic response of the isolation system (building and isolators). The tests carried out allow a comparison between the free vibration responses of a building, isolated by using a 28 HDRB isolation system only, or an HDRB-Friction Sliders Hybrid one. The paper highlights the main differences of the response in the superstructure (the structure over the isolation system) obtained by using only HDRB isolation system, or the Hybrid one (HDRB and Friction Sliders in parallel system). Analysis and comparisons of experimental data, show the influence of nonlinearities on structural higher modes amplification, especially observed by using the higher nonlinear Hybrid isolation system. Tests results confirm that, in the case of a regular superstructure, like the Rapolla building, the isolation system nonlinearities influence the structural response.     

系统自振对绝对重力仪的影响模式分析

隔振问题是绝对重力仪研制中的关键技术难题之一。在自主研制"小型mGal级绝对重力仪"过程中发现,除了需要克服地面振动的影响之外,系统自振的影响也不容忽视,最大能达到mGal量级。通过对研制样机实验观测结果的分析,研究了系统自振产生的原因以及对系统偏差与观测内符合精度的影响模式,并给出了改进方案,以消除"系统自振"的影响,提高研制仪器的观测精度。     

海藻中类胡萝卜素的提取及含量测定

许多研究已经表明，类胡萝卜素是分布最广泛、最重要的一类光辅助合成色素。类胡萝卜素具有多种生物学功能：作为化学保护剂可抵抗由植物自身叶绿素的光敏氧化作用引起的有害作用，给人体补充β-胡萝卜素可有效降低心血管疾病和癌症的发生概率，高摄入富含类胡萝卜素的饮食和降低白内障发生的危险之间有重要联系(Bendich，1993)。海藻中含有丰富的类胡萝卜素，从结构类型说，通常可以分为三类：胡萝卜素、叶黄素和类胡萝卜素酸。海藻中还含有多种特有的类胡萝卜素，如褐藻黄素、甲藻黄素、硅藻黄素等。直到目前为止，海藻中类胡萝卜素的组成与生理学功能尚没有明确的结论，因而对我国丰富的海藻资源中的类胡萝卜素进行较为系统和全面的化学及生物活性研究已成为摆在我们面前的一个重要课题。本研究选取我国青岛海滨三类大型经济海藻——红、绿、褐藻中资源量丰富的代表性种类作为实验材料，较系统地测定了其中类胡萝卜素的含量，并运用经典的柱层析法对各类胡萝卜素组分进行了分离，通过薄层分析和可见光谱扫描对各分离组分进行了定性、定量分析。