Chaotic behavior of gastric migrating myoelectrical complex

Nonlinear feedback induces oscillation, whereas dynamic equilibrium between positive and negative nonlinear feedback generates rhythm. Physiological rhythms are central to life. No absolutely stable or periodic rhythm exists in living tissues. It has been extensively reported that many rhythms in human and animal organs, such as the heart and brain, are, in fact chaotic. The aim of this paper is to investigate whether the migrating myoelectrical complex (MMC) of the stomach was chaotic. The study was performed in eight healthy female hound dogs (15-22 kg), implanted with four pairs of bipolar electrodes on the serosa of the stomach along the greater curvature. After the dogs were completely recovered from the surgery, one complete cycle of gastric MMC was recorded from the serosal electrodes. Using Takens' embedding theorem, two parameters reflecting chaotic behavior, the attractor and the Lyapunov exponent of the myoelectrical recording, were reconstructed and computed, respectively. Statistical analysis was performed to investigate the difference in the Lyapunov exponents among different phases of the MMC. The results show that the MMC of the stomach is chaotic. Different phases of the MMC are characterized with different shapes of the attractors and different values of Lyapunov exponents. The characteristic chaotic behavior of the gastric MMC may be utilized for the identification of different phases.     

两种载体上的光电催化降解气相环已烷的研究

通过高聚物固体电解质Nafion分隔阴、阳极,将TiO2光催化剂负载在活性碳/石墨载体和泡沫镍载体上,构成新型气相光电催化反应系统.制造的微多孔光催化层使催化剂活性大大增加.气相光电催化反应系统降解环己烷的效率比单独光催化、电催化都高.实验结果表明,当两种载体涂层数均为3层,水蒸气与环己烷比率为20:1,外加电压为20V时,反应降解效率最高.     

螺旋埋弧焊管成型若干技术问题的探讨

结合螺旋埋弧焊管成型技术的发展变化和生产实际,从工艺角度对成型稳定性和成型器设计提出了看法和建议。分析了常见成型缺陷产生的原因,指出了螺旋埋弧焊管成型技术中调整、维护时应注意的问题。     

一种非线性分形的时间序列模型表示法

提出了一种基于非线性映射的迭代函数系统（ Ｉ Ｆ Ｓ）,并以此作为一个时间序列的模型。为了保证模型成立,文中给出了映射收缩条件并进行了证明。非线性函数以分段函数形式给出,文中讨论了当非线性函数取为多项式形式时模型的求解方法,并对湖底回波进行了实验。实验结果表明,非线性 Ｉ Ｆ Ｓ产生的吸引子能够很好地逼近原信号。     

Relationship between structures of polyacrylonitrile (PAN)–copper gradient composite film and electrochemical-reaction conditions

In this article, the relationship between the morphological structure and electrochemical conditions, the crystal structure in the electrochemical deposited phase, and the thermal properties of polyacrylonitrile (PAN)–copper gradient composite films (GCF) were studied. The results showed that the morphology of the GCF depended very much on the electrochemical conditions used in the reactions. The percent area of the deposited phase on the cross section of the GCF decreases with increases of the predrying time of the solution coated on the cathode, the power voltage, and the temperature in the electrochemical reactor. According to the data of a differential scanning calorimeter and a scanning electronic microscope, PAN chains are physically crosslinked by a deposited phase. Under the electrochemical conditions used in this article, the components of PAN are not affected by the electrochemical reactions. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 1159–1165, 1998     

超音速火焰喷涂WC-17Co涂层的高速磨削机理试验研究

针对超音速火焰喷涂WC-17Co高硬涂层的加工难题,对WC-17Co涂层进行了高速/超高速磨削试验。通过考察不同金刚石砂轮和磨削工艺参数对磨削力、磨削温度和表面残余应力、表面/亚表面微观形貌和表面粗糙度的影响,讨论了最大未变形切屑厚度与比磨削能的内在关系,分析了磨削温度对表面残余应力的作用规律,探讨了法向磨削力对涂层亚表面损伤的作用规律。结果表明：WC-17Co涂层磨削去除是脆性和延性去除并存;提高砂轮线速度将使磨削力先快速减小后缓慢增大,磨削温度持续升高,涂层磨削从脆性去除转为延性去除的趋势也逐渐增强,表面残余应力由压应力逐渐转变为拉应力,而磨削高温引起涂层热塑性变形是表面残余应力状态转变的根本原因。涂层亚表面磨削损伤层平均深度随法向磨削力的增大而变大。提高砂轮线速度、降低工作台速度和减小磨削深度均能增大涂层磨削塑性去除的比例。     

金属薄壁筒体对轮旋压技术进展及应用探析

对轮旋压是成形大型高强金属薄壁筒体的关键技术。分别从塑变机理、成形精度影响与控制、组织演变与缺陷、对轮旋压设备等四方面概述了金属薄壁筒体对轮旋压技术的最新研究进展,指出时变非线性特点导致塑性流动控制困难是对轮旋压技术工程化应用的瓶颈。剖析了对轮旋压技术难点,分析探讨了其发展趋势,揭示出多源混动的对轮主动强力柔性旋压工艺对超高强金属、大尺寸薄壁筒体精密旋压成形的借鉴意义。     

负载型TiO2光电催化降解酸性红B

用泡沫镍负载TiO2制作的电极作为工作电极,铂电极为对电极,饱和甘汞电极为参比电极,建立三电极的光电催化体系,以酸性红B(ARB)为研究对象,考察了该光电催化体系对有机物的降解性能.实验结果表明,在室温(29℃)条件下,外加电压0.05 V、溶液pH=4.0时,紫外光照120 min降解率可达85.5%;动力学研究表明,该反应为一级反应,其活化能为32.75 kJ/mol;降解前后溶液的紫外-可见吸收光谱表明,ARB得到了破坏,基本分解成小分子物质.