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The vibro-acoustic response of an infinite, fluid-loaded and periodically supported Timoshenko beam under a convected harmonic loading has been obtained in a mathematical form. Instead of considering the dynamics of a single substructure alone, an essentially different technique named as wavenumber-harmonic method for the analysis of periodic structures is presented. The method involves the use of Fourier transform, then the associated wavenumber response is expressed in a series form that represents wave components of the flexural motion. This approach differs from the space-harmonic analysis which describes the beam motion in spatial domain. With this approach the periodic boundary conditions and the phase relation between two substructures are not required. Furthermore, incorporating the heavy fluid loading effect is easy. This method can be used conveniently to calculate the sound power radiated from a fluid-loaded infinite beam, which is subject to either a moving point or distributed loading. The influence of periodic supports on the sound radiation has also been examined for different speeds of convected loading. [S0739-3717(00)01002-3]

This study used data obtained from the Taiwan Environmental Protection Administration to measure the dioxin exposure and the body burden for residents living in the vicinity of 19 municipal waste incinerators (MWIs). A survey was conducted in 1999-2003 for the residents. Approximately 16 ambient air samples and a 60-ml blood samples of 84 to 92 residents aged 18-65 yr were collected randomly in four zones (A, B, C, D) for each MWI site based on the atmospheric dispersion model (ADM). Zone A was defined with the highest pollution level, followed by zones B and C, and zone D (background level). Congeners of 17 polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) were determined for each sample. We summarized the PCDD/Fs levels in air samples and serum specimens by zone for these 19 sites. The mean ambient levels of PCDD/Fs fitted the ADM, the highest from zone A and the lowest from zone D (2.74 vs. 0.13 pg I-TEQ/Nm3). However, the mean serum concentration in zones A was not distinct from that in zones D (18.7 vs. 19.0 pg WHO-TEQ/g lipid). The age-specific average serum concentration increased from 13.27 pg WHO-TEQ/g in 18- to 25-yr-old subjects to 23.46 pg WHO-TEQ/g lipid in 56- to 65-yr-old subjects. In conclusion, the serum PCDD/Fs levels among residents did not adhere to the dispersion model for incineration emissions. The dose-response of serum PCDD/Fs by age suggests that the body burden of the chemicals is mainly associated with other sources instead of with inhalation.

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The present study investigates the effect of serrated grain boundary with zigzag morphology on the high temperature creep deformation of IN718 superalloy. The experimental results have indicated that the morphology of grain boundary can be a function of heat-treatment condition. Experimental work includes XRD, DSC analysis, and SEM microstructure observations in order to investigate the underlying mechanism for the formation of zigzag grain boundary. Creep test under 650°C/625MPa has been conducted on samples of IN718 with and without zigzag grain boundaries in order to determine its effects on deformation mechanisms. In conclusions, an improvement of 400 hours creep rupture life has been attributed by the serrated grain morphology. IntroductionTraditional alloy development programmes with the addition of refractory elements have been reduced significantly in recent years due to the associated high costs of raw materials. A wide range of commercial alloys, with compositions tailored to particular applications, is readily available and advances in performance can be gained through improvements in processing to further explore the full benefit of its compositions [1-3]. Nickel-iron based superalloy, IN718, is the most widely used superalloy for its good strength, corrosion resistance and weldability as well as for its long-time stability up to 650°C. IN718 is a precipitation-strengthened superalloy with microstructure containing various phases such as γ, γ′′, γ′, δ, and MC carbides. Previous researches have proposed that heat treatment induced serrated grain boundary in IN718 and result improvement in its mechanical properties [4][5][6][7].The aim of present study is to investigate the underlying mechanism for the formation of zigzag grain morphology and its effect on the creep rupture behaviour of IN718 under 650°C/625MPa. Experimental ProcedureA cylindrical bar of IN718 with 2m in length and 12.8mm in diameter were obtained from Huntington Alloys. The average grain size of as-received sample is 25µm [8]. The chemical composition is given in