Robustness of alternative non‐linearity tests for SETAR models

In recent years there has been a growing interest in exploiting potential forecast gains from the non‐linear structure of self‐exciting threshold autoregressive (SETAR) models. Statistical tests have been proposed in the literature to help analysts check for the presence of SETAR‐type non‐linearities in an observed time series. It is important to study the power and robustness properties of these tests since erroneous test results might lead to misspecified prediction problems. In this paper we investigate the robustness properties of several commonly used non‐linearity tests. Both the robustness with respect to outlying observations and the robustness with respect to model specification are considered. The power comparison of these testing procedures is carried out using Monte Carlo simulation. The results indicate that all of the existing tests are not robust to outliers and model misspecification. Finally, an empirical application applies the statistical tests to stock market returns of the four little dragons (Hong Kong, South Korea, Singapore and Taiwan) in East Asia. The non‐linearity tests fail to provide consistent conclusions most of the time. The results in this article stress the need for a more robust test for SETAR‐type non‐linearity in time series analysis and forecasting. Copyright © 2004 John Wiley & Sons, Ltd.     

一种简易新型长光程薄层光谱电化学池

设计并制作了一种新型长光程薄层光谱电化学池，其具有光程长、灵敏度高、重现性好等特点，且组装简便，电极容易更换，溶液未补偿电阻小，溶液用量少．易清洗．电解池以石墨为工作电极，分别用循环伏安、交流阻抗技术、光谱恒电位技术对其性能进行测试，得到比较满意的结果．     

重庆市三峡库区医疗垃圾现状及无害化处理分析

医疗垃圾属于一类危险废物，必须进行无害化处理。文章论述了医疗垃圾的特性和危害性，对重庆市三峡库区目前医疗垃圾管理和处理的现状进行了分析，针对其特点，提出对三峡库区医疗垃圾有效的管理措施和进行分区集中处理，具体分析了医疗垃圾处理技术方案：分类收集、密闭运输、预处理、焚烧、完全填埋等。通过无害化处理后，杜绝医疗垃圾对环境的污染，以保护三峡库区生态环境和水资源。     

我国旅行社实施CRM的思考

介绍了客户关系管理(CRM)的概念及内涵，通过对我国旅行社客户关系管理现状的分析，提出了我国旅行社实施CRM系统的两种基本策略，即自行建设策略和外包策略，并探讨了实施CRM时应处理好的几个问题。     

A Simple Linear Regression Approach to Modeling and Forecasting Mortality Rates

Observing that a sequence of negative logarithms of 1‐year survival probabilities displays a linear relationship with the sequence of corresponding terms with a time lag of a certain number of years, we propose a simple linear regression to model and forecast mortality rates. Our model assuming the linearity between two mortality sequences with a time lag each other does not need to formulate the time trends of mortality rates across ages for mortality prediction. Moreover, the parameters of our model for a given age depend on the mortality rates for that age only. Therefore, whether the span of the study ages with the age included is widened or shortened will not affect the results of mortality fitting and forecasting for that age. In the empirical testing, the regression results using the mortality data for the UK, USA and Japan show a satisfactory goodness of fit, which convinces us of the appropriateness of the linear assumption. Empirical illustrations further show that our model's performances of fitting and forecasting mortality rates are quite satisfactory compared with the existing well‐known mortality models. Copyright © 2015 John Wiley & Sons, Ltd.     

WTI crude oil option implied VaR and CVaR: An empirical application

Using option market data we derive naturally forward‐looking, nonparametric and model‐free risk estimates, three desired characteristics hardly obtainable using historical returns. The option‐implied measures are only based on the first derivative of the option price with respect to the strike price, bypassing the difficult task of estimating the tail of the return distribution. We estimate and backtest the 1%, 2.5%, and 5% WTI crude oil futures option‐implied value at risk and conditional value at risk for the turbulent years 2011–2016 and for both tails of the distribution. Compared with risk estimations based on the filtered historical simulation methodology, our results show that the option‐implied risk metrics are valid alternatives to the statistically based historical models.     

基于无速度传感器的直接转矩控制系统优化

针对传统异步电机直接转矩控制系统在低速运行状态下存在磁链轨迹发生波动、转矩脉动大的问题,提出一种新型异步电机直接转矩控制策略。采用滑模控制和空间矢量脉宽调制技术(SVPWM: Space Voltage Pwlse-Width Modulation), 引入滑模控制器, 以提高系统对参数变化和外界干扰的鲁棒性。利用空间电压矢量脉宽调制技术产生系统所需要的任意期望空间电压矢量, 使磁链轨迹更趋近于圆形, 即降低了转矩和磁链脉动,又增强了系统的鲁棒性。同时引入无速度传感器技术, 以提高系统工程应用性。通过在Matlab/ Simulink软件仿真结果表明, 新型直接转矩控制系统改善了磁链轨迹波动并有效地降低了转矩脉动, 使转速估计具有较高精度。     

Silicon in the Earth's core

Small isotopic differences between the silicate minerals in planets may have developed as a result of processes associated with core formation, or from evaporative losses during accretion as the planets were built up. Basalts from the Earth and the Moon do indeed appear to have iron isotopic compositions that are slightly heavy relative to those from Mars, Vesta and primitive undifferentiated meteorites (chondrites). Explanations for these differences have included evaporation during the 'giant impact' that created the Moon (when a Mars-sized body collided with the young Earth). However, lithium and magnesium, lighter elements with comparable volatility, reveal no such differences, rendering evaporation unlikely as an explanation. Here we show that the silicon isotopic compositions of basaltic rocks from the Earth and the Moon are also distinctly heavy. A likely cause is that silicon is one of the light elements in the Earth's core. We show that both the direction and magnitude of the silicon isotopic effect are in accord with current theory based on the stiffness of bonding in metal and silicate. The similar isotopic composition of the bulk silicate Earth and the Moon is consistent with the recent proposal that there was large-scale isotopic equilibration during the giant impact. We conclude that Si was already incorporated as a light element in the Earth's core before the Moon formed.