Generalization of the Lamé problem for three-stage decelerated corrosion process of an elastic hollow sphere

The paper presents an analytical solution to Lamé's problem for a hollow sphere with unknown evolving boundaries. The double-sided uniform corrosion of a linearly elastic thick-walled spherical shell under internal and external pressure is considered. It is assumed that the corrosion rates are piecewise linear functions of the maximum principal stress on the related surface, and exponentially decaying with time. The corrosion process is supposed to be divided into three successive stages: constant rate double-sided corrosive wear, a stage of corrosion accelerated on only one of the surfaces of the shell, and a double-sided mechanochemical corrosion. Closed-formed expressions for all the consecutive stages are obtained with their junction points (corresponding to stress corrosion thresholds) being taken into account.     

Propagation of guided waves in pressure vessel

Pressure vessels usually operate under extremes of high/low temperatures and high pressures. Defect, such as crack and corrosion, can result in leakage or rupture failures, even catastrophic incidents. Guided wave-based structural health monitoring (SHM) technology is one of the most prominent options in non-destructive evaluation and testing (NDE/NDT) techniques. Propagation of guided waves in a typical pressure vessel is systematically investigated in this study for the application of guided wave-based SHM. Shape of the pressure vessel is a cylinder with two end caps. Because of geometric similarity, theory of guided wave propagation in the cylinderical structure is analyzed to study dispersive features of guided waves in the pressure vessel. Dispersion curves of three different types of guided wave modes, viz. the longitudinal, torsional and flexural modes, are calculated using theoretical method. Based on the analyses and experimental wave signals, central frequency and wave parameters of incident wave are optimized. Effect of contained liquid on propagation of guided waves, especially the L(0, 2) mode, in the pressure vessel is further investigated to minimize energy leakage of the wave to the contained liquid. The analytical method, finite element analysis (FEA) and experiments are applied to study propagation characteristics of guided waves in the pressure vessel, so as to demonstrate the feasibility of guided wave-based non-destructive evaluation and testing (NDE/NDT) for such kind of complex structures.     

光谱技术检测鲜红斑痣病变程度的MC模拟

在分析鲜红斑痣病理的基础上,根据病变程度改变真皮上层血液层的厚度,并建立相应的光学模型,确定其组织光学参数.通过Monte Carlo模拟,得出：鲜红斑痣皮肤反射光谱与荧光光谱均可反映鲜红斑痣皮肤病变程度,特别是血管直径的变化;当血管直径增大时,鲜红斑痣皮肤反射光谱反射率与荧光光谱强度均明显下降.研究表明反射光谱和荧光光谱可能应用于判断或分析鲜红斑痣皮肤的病变程度,从而为鲜红斑痣的临床治疗方案及治疗效果提供参考.     

国内外液化天然气输运容器发展状态

液化天然气输运容器包括罐箱、罐车和车载储气瓶,普遍采用高真空多层绝热方式是国际发展趋势,其合理应用需要多项关键技术.由于产品种类型号相对较少,适合批量化生产以适应液化天然气工业的迅猛发展.液化天燃气输运容器产品发展趋势和技术发展趋势可为我国低温储运容器生产厂家提供一定的参考.     

密闭系统中微波辅助萃取机制探讨

通过与普通加热萃取虎杖中白藜芦醇的产率进行对比 ,对密闭系统中微波辅助萃取的机理进行了探讨。结果表明 ,微波辅助萃取与普通加热萃取二者的活化能相差不大 ,分别为30.06和30.32kJ·mol-1。但微波辅助萃取的表观速率常数约是普通加热萃取的20倍。并且还利用电子扫描显微镜对样品微结构进行了观察 ,研究表明 ,细胞内极性成分如水吸收了微波能后压力迅速增加导致细胞结构的破坏是MAE快速高效的关键 ,由于细胞的破坏 ,萃取剂和萃取目标化合物更容易通过细胞壁 ,加速了扩散速度 ,进而加速了萃取速度。     

储氢高压容器钢壁中氢的浓度分布规律研究

储氢高压容器中的氢通过渗透会进入容器钢壁并在钢壁中扩散,最终透过容器外表面进入容器存放环境中.在容器钢壁中的氢会引起材料力学性能变化,从而引起容器承载能力变化.要认识这些变化,首先就要了解氢在钢壁中的渗透、扩散规律和浓度的瞬态分布规律.针对球形高压容器外表面满足一般传质边界条件的情况,建立求解容器壁中氢浓度的解析理论模型,导出了容器壁中瞬态氢浓度和渗透到环境中的氢累积量的理论公式.通过解析计算,给出了器壁中氢浓度和氢在环境中的累积渗透量随时间的变化曲线,分析了相应的变化规律.这些公式和规律性认识为后续的容器壁材料力学性能分析和容器承载能力评估提供了前提.     

Effect of acid concentration on closed-vessel microwave-assisted digestion of plant materials

The efficiency of microwave-assisted acid digestion of plants using different concentrations of nitric acid (2.0, 3.0, 5.0, 7.0 and 14 mol l⁻¹) with hydrogen peroxide (30% v/v) was evaluated by measuring the residual carbon content (RCC) using inductively coupled plasma optical emission spectrometry (ICP-OES) with axial viewing. Certified reference materials were used for evaluating the accuracy attained when 2 mol l⁻¹ HNO₃ was employed for digestion. Under all experimental conditions RCC values were always lower than 13% w/v, and even the highest concentration did not cause any interference with element recovery. It seems that the high pressure reached for closed-vessel operation improved the oxidative action of nitric acid due to consequent temperature increase, even when this reagent was not used at high concentrations. According to acid–base titration data, residual acid in the digestates varied from 1.2 to 4.0 mol l⁻¹, depending on the acid concentration initially added. It can be concluded that for plant materials, microwave-assisted acid digestion can be carried out under mild conditions, which implies that digestates do not need extensive dilution before introduction by pneumatic nebulization to ICP-OES. An additional advantage is the lower amount of residue generated when working with less concentrated acid solutions.     

The dynamics of cavitation bubbles in a sealed vessel

A model of cavitation bubbles is derived in liquid confined in an elastic sealed vessel driven by ultrasound. In this model, an assumption that the pressure acting on the sealed vessel due to bubble pulsations is proportional to total volume change of bubbles is made. Numerical simulations are carried out for a single bubble and for bubbles. The results show that the pulsation of a single bubble can be suppressed to a large extent in sealed vessel, and that of two matched bubbles with same ambient radius can be further suppressed. However, when two mismatched bubbles have the same ambient radii, an interesting breathing phenomenon takes place, where one bubble pulsates inversely with the other one. Due to this breathing phenomenon the suppression effect becomes weak, so the maximum radii of two mismatched bubbles can be larger than that of a single bubble or that of two matched bubbles in sealed vessel. Besides that, for two mismatched bubbles with different ambient radii, the small one in sealed vessel under some certain parameters can pulsate as strong as or even stronger than that of a single bubble in an open vessel.     

Determination of Copper in Silicates Using Chelating Resin After Decomposition With Teflon Vessel

Abstract

By the combined use of a decomposition vessel, chelating resin, and atomic absorption spectrometry, a simple method for the determination of copper in silicate rocks was devised. A sample was digested overnight at room temperature with small amounts of hydrofluoric acid and aqua regia in the Teflon vessel having a sealing stopper. In the presence of citrate, only the supernatant of the digested sample solution was passed through a small column of the chelating resin, Dowex A-1, at pH 4. After elution with nitric acid, copper was determined by ordinary atomic absorption spectrometry. The recovery, reproducibility, and accuracy of the method were quite satisfactory. The analytical results obtained for the standard rocks agreed well with reported results.