ESTIMATION OF THE MULTIVARIATE AUTOREGRESSIVE MOVING AVERAGE HAVING PARAMETER RESTRICTIONS AND AN APPLICATION TO ROTATIONAL SAMPLING

Abstract. The vector autoregressive moving average model with nonlinear parametric restrictions is considered. A simple and easy-to-compute Newton-Raphson estimator is proposed that approximates the restricted maximum likelihood estimator which takes full advantage of the information contained in the restrictions. In the case when there are no parametric restrictions, our Newton-Raphson estimator is equivalent to the estimator proposed by Reinsel et al. (Maximum likelihood estimators in the multivariate autoregressive moving-average model from a generalized least squares view point. J. Time Ser. Anal. 13 (1992), 133–45). The Newton-Raphson estimation procedure also extends to the vector ARMAX model. Application of our Newton-Raphson estimation method in rotational sampling problems is discussed. Simulation results are presented for two different restricted models to illustrate the estimation procedure and compare its performance with that of two alternative procedures that ignore the parametric restrictions.     

Pd-Ag-Sn-In-Zn合金时效强化机制研究

通过硬度测试、X射线衍射（XRD）分析、扫描电镜（SEM）观察研究了Pd-Ag-Sn-In-Zn合金时效强化行为及相关的微观结构变化，从而很好地解释了该合金的时效强化机制。结果表明，时效前期合金硬度的增加与在晶界处形成中间过渡相有关。通过扫描电镜观察，可以清楚地看到基体相以及等温时效过程中在晶界处有类似珠光体的析出相。随着稳定第二相的长大，硬度持续下降。     

锂离子电池硅基负极材料研究进展

本文主要介绍近年来硅及含硅材料作为锂离子电池负极材料的研究进展，包括硅单质、硅的氧化物以及硅的金属化合物和其它硅基多元化合物；分析了硅基材料作为锂离子电池负极材料存在的问题；阐述了硅基材料作为锂离子电池负极材料的研究前景。     

不同形貌Ga2O3纳米材料可控合成工艺研究

通过研究基片种类、加热温度、保温时间、冷却速度及是否加入催化剂等不同工艺参数对低维Ga2O3，纳米材料形貌的影响，确定出合成5种不同形貌β-Ga2O3纳米材料的工艺条件。场发射扫描电镜（FE-SEM）表明5种不同形貌α-Ga2O3纳米材料分别为纳米线、纳米棒、纳米带、纳米环及纳米片。X射线衍射（X-ray）分析结果表明不同形貌纳米材料均为晶格常数日=1．223nm，b=0．304nm，c=0．58nm，a=90°，β=103．7°，γ=90°的单斜晶系β-Ga2O3晶体。     

镍基粉末冶金FGH95高温合金的拉伸及低周疲劳性能研究

在420～650℃的温度范围内,研究了PM FGH95高温合金在应变率0.0001～0.01 s-1范围内的拉伸性能及在不同应力比R=-1及R=0下的低周疲劳性能.拉伸试验结果表明:在此温度范围内,应变率对弹性模量、拉伸屈服强度及塑性模量的影响可以忽略不计;并且应变率自0.0001 s-1增大至0.01 s-1时,弹性模量、拉伸屈服强度及塑性模量受温度的影响也不明显.PM FGH95合金受材料微结构的影响很大,材料含有的微缺陷对其力学性能有非常不利的影响.LCF试验结果表明:PM FGH95合金是循环硬化材料.当应力比R=-1时,温度对LCF寿命的影响很小;但在应力比R=0时,LCF寿命受温度的影响很大,且随着温度的增加材料的低周疲劳寿命减小.SEM断口扫描发现,断裂表面有很多的解理面,但没有疲劳条带,且此断裂模式下没有明显的塑性变形,所以FGH95合金的低周疲劳寿命几乎是由裂纹萌生阶段决定的.     

Electrochemical behaviors of TiO2−x films synthesized by plasma-based ion implantation and deposition in fibrinogen containing PBS solution

TiO_2−x films were synthesized on carbon by plasma-based ion implantation and deposition (PBII-D). Electrochemical behaviors of the prepared films were investigated in phosphate buffer solution (PBS) and fibrinogen containing PBS solution (PBS(Fn)), to probe charge transfer phenomena between TiO_2−x film and fibrinogen. Electrochemical impedance spectroscopy (EIS) as well as simulated values of equivalent circuit units including reaction resistance and electric double layer has been obtained, indicating different charge transfer rate occurred across the interfaces. The shape of Mott-Schottky spectroscopy around the rest-open potential indicates that TiO_2−x films are typical n-type semiconductor. Donor density results calculated by Mott-Schottky theory show that TiO_2−x films exhibit higher donor density in PBS(Fn) than in PBS, indicating charge transfer from fibrinogen to TiO_2−x films, and the space charge layers bend lower.     

搅拌槽中固液悬浮及其放大的研究

研究了具有盘管、碟形底和斜叶涡轮固液悬浮搅拌槽的放大规律。试验用槽径（外径）分别为０．２ｍ、０．５ｍ和１．０ｍ的三个有机玻璃搅拌槽。用激光法测定悬浮液浓度。得出离底悬浮及均匀悬浮时搅拌转速和比功率的经验关联式，与测定槽内轴向速度分布所导出的均匀悬浮方程相吻合，并表明槽径的放大指数主要由循环流数所决定。     

加强科学管理延长转化器的使用寿命

简述了巨化电化厂对转化器加强科学管理，以减少漏损的作法，取得了良好的经济效益。     

Alternative hydrocarbon solvents for cottonseed extraction

Hexane has been used for decades to extract edible oil from cottonseed. However, due to increased regulations affecting hexane because of the 1990 Clean Air Act and potential health risks, the oil-extraction industry urgently needs alternative hydrocarbon solvents to replace hexane. Five solvents,n-heptane, isohexane, neohexane, cyclohexane, and cylopentane, were compared with commercial hexane using a benchscale extractor. The extractions were done with a solvent to cottonseed flake ratio of 5.5 to 1 (w/w) and a miscella recycle flow rate of 36 mL/min/sq cm (9 gal/min/sq ft) at a temperature of 10 to 45°C below the boiling point of the solvent. After a 10-min single-stage extraction, commercial hexane removed 100% of the oil from the flakes at 55°C; heptane extracted 100% at 75°C and 95.9% at 55°C; isohexane extracted 93.1% at 45°C; while cyclopentane, cyclohexane, and neohexane removed 93.3, 89.4, and 89.6% at 35, 55, and 35°C, respectively. Each solvent removed gossypol from cottonseed flakes at a different rate, with cyclopentane being most and neohexane least effective. Based on the bench-scale extraction results and the availability of these candidate solvents, heptane and isohexane are the alternative hydrocarbon solvents most likely to replace hexane. Presented in part at the AOCS Annual Meeting & Expo, Atlanta, Georgia, May 1994.     

大型锻件热处理过程的数值模拟研究

在对大型锻件传热分析的基础上 ,建立了大型锻件的物理模型 ,对其温度场的变化规律进行了模拟计算 ,同时将模拟结果和实验结果进行对比分析 ,最后利用模拟计算对材料为 2 6Cr2Ni4MoV的某一电机转子的调质处理进行了模拟计算 ,从而说明了热处理过程的数值模拟方法的准确性和优越性。为进一步分析此类工件的组织转变和应力应变等奠定了基础。