Wear of metal stirring rods in molten aluminium and suspensions of alumina particles in molten aluminium

The wear of stainless steel and titanium stirring rods in molten aluminium and a suspension of alumina particles in molten aluminium was studied. The known characteristic of more rapid wear by stainless steel than titanium was confirmed and the suspension of alumina particles was found to accelerate wear of both metals. Examination of worn specimens revealed that the stainless steel rods were separated from the liquid aluminium by a layer of iron, chromium and aluminium. Wear proceeded by the shedding of projections that formed on the layer into the liquid aluminium. Alumina particles accelerated wear by abrasion of the projections. The titanium was surrounded by a much thinner layer of titanium and aluminium mixture with no projections into the molten aluminium. The distribution of wear around the blades was controlled by the flow of liquid metal and of the alumina particles around each blade.     

Daily intake of TBT, Cu, Zn, Cd and As for fishermen in Taiwan

The consumption of contaminated seafood has been reported as an important route of human exposure to metals in Taiwan. We consider the concentrations of TBT, Cu, Zn, Cd, As, and the consumption of oysters of Taiwanese to be the important information related to public health in Taiwan. Therefore, the aim of this study was to evaluate the public health risks associated with TBT, Cu, Zn, Cd and As from shellfish for the general population and fishermen of Taiwan. In general, TBT concentrations in various oysters ranging from 0.32 to 1.51 microg/g dry wt. varied with sampling locations. The highest TBT, Cu, and Zn geometric mean (GM) concentrations in oysters of 1.51, 1180 and 1567 microg/g dry wt. were obtained from the Hsiangshan coastal area. The values of oyster consumption for fishermen were 94.1 and 250 g/day for typically and maximally exposed individuals, respectively. In particular, the highest intake (250 g/day) from fishermen was almost two times greater than that of the general population (139 g/day). The THQ (target hazard quotient) values of Hsiangshan's fishermen are 3.87 and 20.50 for TBT and Cu for maximally exposed individuals are higher than other oyster culture areas. It is interesting that those consuming oysters from Hsiangshan, Lukang, Taishi caused abnormally high THQs of TBT and other metals (100% over 1.0), and TBT was attributed to only 3-21% of the total THQs in different fishermen of Taiwan. Our results suggest that current environmental levels of TBT and other metals are associated with a significant potential threat to human health for fishermen resident in coastal areas of Taiwan.     

Using ADABOOST and Rough Set Theory for Predicting Debris Flow Disaster

Debris flow resulting from typhoons, heavy rainfall, tsunamis or other natural disasters is a matter of particular importance to Taiwan owing to the country’s unique geographical environment and exacerbated by poor slope management and global warming. With regard to these types of natural occurrences, recent global events have attracted the attention of experts in various fields, such as civil engineering, environmental engineering and information management. These experts have developed several techniques to study the various factors of debris flow. The ADABOOST and rough set theory (RST) are two emerging methods with regard to classification and rule provision. The ADABOOST, an adaptive boosting machine learning algorithm, uses very little memory during computation and can obtain robust classification results. RST is able to deal with uncertainties and vague information in generating rules for decision makers. Thus, this study develops an ADARST model which uses the unique strengths of the ADABOOST and RST in classification and rule generation and applies the proposed ADARST to analyze debris flow. Specifically, data from previous studies were obtained and used for the purposes of this study. Experimental results have shown that the proposed ADARST model is able to generate better results than those in previous investigations in terms of prediction accuracy. In addition, the designed ADARST model can provide rules including forward and backward reasoning ways for decision makers. Therefore, the proposed ADARST model is shown to be an effective methodology with which to analyze debris flow.     

基于有限元法的E-K模型参数敏感性分析

模型参数的确定是数值分析过程中的重要环节,合理把握参数的选取原则,可大大提高结构分析的可靠度以及参数反分析的计算效率.本文借助有限单元法考察了E-K模型参数变化对一个均质堤坝的位移和应力值的影响程度.通过分析明确了E-K模型中各参数对计算结果的敏感程度,同时提出了模型参数的选取原则.     

A study of electrical discharge grinding using a rotary disk electrode

This study aims to investigate the electrical discharge grinding (EDG) using a rotary disk electrode. From a practical perspective, the electrode is designed to mimic the machining process of a surface grinder with horizontal spindles. First, the machining ability of cold working tool steel AISI D2 by EDG is investigated. Then, the optimal machining parameters are found through ANOVA analysis. The experimental results show that both the lower electrode wear rate and the higher materials removal rate are obtained when a rotary disk electrode with positive polarity is conducted on EDG. In addition, the roughness of machined surfaces using an electrode with negative polarity can reach about 2 μm Rt, and no incidence of concentrated discharge or short circuit are found in any machining conditions.     

Effect of internal cooling/heating coil on adsorption/regeneration of solid desiccant tray for controlling air humidity

Thermal performances of solid desiccant tray having internal cooling/heating coil for air humidity adsorption and desiccant regeneration are investigated. Three units of desiccant tray each of 48 cm × 48 cm cross‐sectional area and 2.5 cm thickness filled with silica gel are tested in a wind tunnel. For adsorption process, an air stream is flowing through the desiccant trays and the air humidity is captured by the silica gel. Approximately 10–40% of air humidity could be adsorbed more in case of the internal cooling. Besides, the outlet air temperature increases only slightly. In regeneration process, a hot air stream is used to repel the moisture in the silica gel. With the internal heating, the regeneration time is shorter compared with that without internal water heating. In addition, a correlation for calculating the adsorption/regeneration performance of the silica gel trays is developed and the results from the model agree well with the experimental data. Copyright © 2008 John Wiley & Sons, Ltd.     

Robust Adaptive Control of Linear Induction Motors With Unknown End-Effect and Secondary Resistance

This paper proposes a novel robust adaptive speed/ position tracking control for a linear induction motor (LIM) with both end-effect and secondary resistance unknown. The practical current-fed controlled LIM, with residual current error, is considered, i.e., the traditional ideal current-loop assumption is relaxed. More practical conditions, such as bounded primary voltage and a finite absolute-integral of current tracking error is considered. To overcome the high nonlinearity and nonzero current error, a backstepping method, combining virtual desired variable synthesis, is developed for the speed and position tracking. Then, the controller achieves asymptotic speed and position tracking even with unknown parameters and immeasurable secondary flux. Furthermore, the effect of the residual current error is attenuated in an L₂ -gain sense. The experiments for several scenarios are carried out to verify the theoretical result.     

Sliding‐mode control of a three‐degrees‐of‐freedom nanopositioner

This paper presents the sliding‐mode control of a three‐degrees‐of‐freedom nanopositioner (Z, θ_x, θ_y). This nanopositioner is actuated by piezoelectric actuators. Capacitive gap sensors are used for position feedback. In order to design the feedback controller, the open‐loop characteristics of this nanopositioner are investigated. Based on the results of the investigation, each pair of piezoelectric actuators and corresponding gap sensors is treated as an independent system and modeled as a first‐order linear model coupled with hysteresis. When the model is identified and the hysteresis nonlinearity is linearized, a linear system model with uncertainty is used to design the controller. When designing the controller, the sliding‐mode disturbance (uncertainty) estimation and compensation scheme is used. The structure of the proposed controller is similar to that of a proportional integral derivative controller. Thus, it can be easily implemented. Experimental results show that 3‐nm tracking resolution can be obtained. Copyright © 2008 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society     

Stress Required to Densify a Low-Fire NiCuZn Ferrite Under Constrained Sintering

The effect of uniaxial stress on the densification behavior of a low-fire NiCuZn ferrite during constrained sintering of a multilayer structure of a ferrite tape and a pure alumina tape has been investigated. Compared with free sintering, the densification of ferrite becomes significantly reduced and slowed down under pressure-less constrained sintering. To enhance the constrained densification of ferrite in the temperature range required for free sintering, uniaxial stress applied in the thickness direction is needed. The required uniaxial stress to densify ferrite under constrained sintering to reach a relative sintered density of >95% decreases from 1100–1300 kPa at 900°C to 250–450 kPa at 1000°C. Moreover, no significant grain growth is found when the ferrite is densified under pressure-assisted constrained sintering.