循环荷载作用下纤维水泥土动力特性

通过动三轴试验,研究水泥土中掺入不同掺量的聚丙烯纤维和玄武岩纤维条件下,其动应力 、动弹性模量 随动应变的变化规律。试验结果表明：水泥土的动强度和动弹性模量与围压、掺入纤维的种类和纤维掺量有关;随着纤维掺量的增多,水泥土的动强度和动弹性模量增大,动变形减小。从滞回曲线和微观的角度分析,掺入玄武岩纤维的水泥土动力性能最好,聚丙烯纤维水泥土次之,素水泥土（无纤维）较弱;最大动弹性模量 随着围压和纤维掺量的增大而增大。玄武岩纤维水泥土在不同围压下的 归一化曲线相互聚拢,表明 对围压的依赖程度降低。     

光纤布拉格光栅用于海水盐度监测初探

海水入侵问题已波及中国沿海的9个省份,其中海水入侵最为严重的山东、辽宁两省入侵面积超过2000 km2。在气 候变化和人类活动等作用因素的加剧影响下,海水入侵问题不可避免,因此,海水入侵的监测和防治是解决问题的关键, 具有十分重要的意义。本文针对目前海水入侵监测技术存在的问题,提出了一种可大范围实时原位监测海水盐度的光纤布 拉格光栅（FBG） 方法,并设计试验对三种FBG盐度测试方案的可行性进行了对比研究。试验结果表明：FBG技术应用于 海水盐度监测具有一定可行性;利用能量补偿技术的两点串FBG测试效果最佳,灵敏度及稳定性在三种方案中均最好。基 于FBG的海水盐度监测方法可以弥补目前常用的水化学法和物探法存在的不足,为海水入侵的监测和预防提供了一种先 进、高效的手段。     

光纤传感技术在覆岩“两带”高度探测中的应用

为准确地掌握工作面采动过程中顶板岩层破规律及其特征,获得相应的技术参数,消除突水威胁、保障煤层安全开采等煤矿防治水工作。运用分布式光纤监测技术可以在其长度范围内连续监测覆岩在开采过程中应力应变的分布及大小,获得煤层覆岩的变形规律。结果表明,这种监测方法的突出优点就是改变了传统的点式监测方式,弥补了点式监测的不足,实现了实时、长距离和分布式的监测目标。该技术在内蒙古某煤矿"两带"高度探测中取得结果和并行电法监测相互验证,证明了该方法的可行性。     

Development of a Ground-Based LIF Instrument for Measuring HOx Radicals: Instrumentation and Calibrations

An instrument for measuringtropospheric OH/HO₂ radicals by laser-inducedfluorescence developed in our laboratory is presentedin detail. It is based on FAGE (fluorescence assay bygas expansion) technique and OH is both excited anddetected at 308 nm corresponding to its A-X(0,0) band.The alignment of the laser beam, the design of thesample gas inlet, and the devices for the fluorescencedetection are optimized so as to reduce the backgroundsignal while keeping the OH sensitivity as high aspossible. A thermalized position of the expanding gasbeam is probed in our system and we did not observe asevere decrease of the HO_x sensitivities under humidconditions. An optical fiber is used for deliveringthe laser light to the fluorescence detection cellmounted outside at a high position. Thus the laserbeam alignment is by far simplified and is made highlyreproducible, once settled properly. For thecalibration, two methods are employed: a system withlaser absorption measurements of OH and a system ofsimultaneous photolysis of H₂O and O₂. Thecalibration factors are compared well within thecombined uncertainty. Using the latter system, theconversion efficiency of HO₂ to OH by NO additionis measured to be around 90%. The detection limitsfor OH and HO₂ (S/N = 2) are estimated to be3.3 × 10⁶ and 3.6 × 10⁶cm^–3 at noon,respectively, with an integration time of 1 min. Theresults of test observations at our institute are alsopresented.     

碳纤维布改善高强混凝土柱延性的试验研究

本文进行了8根高强混凝土柱在低周反复荷载作用下的试验，研究了使用碳纤维布横向包裹的高强混凝土柱来提高其延性这种加固方法的有效性。本文研究了碳纤维布横向包裹高强混凝土柱的受力特性，分析了加荷角度，碳纤维布拉伸强度以及碳纤维布的包裹层数等因素对构件抗震加效果的影响，并对碳纤维布加固高强混凝土柱使其延性提高的机理进行了探讨，试验结果表明，横向缠裹碳纤维布可显著提高高强混凝土柱的延性。     

棉纤维生长各阶段的土壤水分状况对其束强的影响

在纤维伸长前期、填充后期充足的土壤水分对提高束强有利，纤维生长扭曲期土壤干旱对提高束强有利，反之则不利。     

反复荷载下碳纤维布加固钢筋混凝土框架梁的试验研究

通过2个碳纤维布加固钢筋混凝土框架梁和1个未加固框架梁的对比试验，分析了低周反复荷载作用下碳纤维布加固框架梁的加固效果，提出了加固梁的正截面承载力计算方法。     

Seismic performance of laminated timber frames with fiber‐reinforced joints

A series of dynamic experiments was performed on two‐story glue‐laminated timber frames. The tests included sinusoidal sweeps in one direction, arbitrary signals simulating earthquake loads in two directions, and harmonic free vibration at the fundamental frequency. Two experimental frames were manufactured and tested: (1) a control with horizontal laminations and no reinforcement at joint areas, and (2) a new frame design with densified material in the joint area that was further reinforced by glass‐fiber composite material. Preliminary tests of scaled and full‐size beam‐to‐column connections were performed to obtain connection characteristics needed for subsequent analytical modeling. Copyright © 2004 John Wiley & Sons, Ltd.     

Analysis of tubular steel bridge piers

A one‐dimensional model is proposed for the static and dynamic analysis of tubular steel bridge piers subjected to strong ground motions. The present formulation does not require experimental results nor shell analysis to obtain the constitutive equation of the model, which shows strength deterioration. The material properties and dimensions of bridge piers are required for static and dynamic analysis of the present model. The present analysis consists of two steps. The first step is to obtain the stress and strain relationship of the base plastic‐hinge region, where local inelastic buckling is observed. The modified Shanley's model and fiber elements are used to establish the compressive skeleton curve. The strength deterioration is taken into account in the resulting constitutive model. The second step is to analyze static and dynamic responses of tubular steel bridge piers. For overall analysis, the base plastic‐hinge region is discretized in the circumferential direction by using fiber elements whose constitutive equation was obtained in the first step. The validity of the present model has been confirmed through comparisons with existing experimental results. Copyright © 2005 John Wiley & Sons, Ltd.     

International Competition Between Satellite and Fiber Optic Carriers: A Geographic Perspective*

International telecommunications traffic relies entirely on two modes of transmission, satellites and fiber optics, which exhibit considerable but not complete fungibility. This article explores the economic and geographic dimensions of these two industries in the context of the growing market in global data and telephony traffic. First, it summarizes the changing conditions that have accentuated competition between them, including deregulation, technological change, and globalization. Next, it examines the changing cost structures, transmission capacities, and traffic volumes for each technology in the critical transatlantic and transpacific markets. Throughout, it documents the steady encroachment by fiber optics firms that threatens the viability of commercial satellite operators, a challenge the latter hope to meet though the growth of the cellular telephone market.