Role of electron transfer of quinones in hydroxylation of phenol

It was found that at neutral pH the hydroxylation reaction rate of phenol was accelerated with an increase of the amounts of 1,4-quinone (1,4-BQ), This acceleration was ascribed to the formation of semiquinone from 1,4-BQ. The semiquinone and 1,4-BQ were suggested to play a role of actual oxidant (electron transfer) in the catalytic cycle. With further reaction, most 1,4-BQ was converted into 1,4-hydroquinone (HQ) and the corresponding mechanism was proposed.

A double logarithmic method for studying the adsorption effects in an irreversible electrochemical process

The adsorption of an electroinactive product greatly influences an irreversible electrochemical reaction in three ways, including self-block, self-inhibition, and self-acceleration, and changes not only the heterogeneous electron-transfer rate constant but also the modified formal potential and electron-transfer coefficient of the electrochemical reaction. In order to study these adsorption effects, a double logarithmic method was suggested to be used in processing the potential-controlled thin layer spectroelectrochemical data. The result shows three types of double logarithmic plots for three kinds of adsorption effects. These double logarithmic plots can be a diagnostic criterion of the adsorption effects and enable us to determine some thermodynamic and kinetic parameters. The combination of nonlinear regression with double logarithmic method is a convenient way to examine the suggested mechanism and to extract more information from the limited experimental data. Some examples are given to test the theoretical results. (C) 1999 The Electrochemical Society. S0013-4651(98)05-012-5. All rights reserved.

Biochemical characterization of selenium-containing catalytic antibody as a cytosolic glutathione peroxidase mimic

A selenium-containing catalytic antibody (Se-4A4), prepared by converting reactive serine residues of a monoclonal antibody (4A4) raised against a GSH derivative into selenocysteines, acts as a mimic of cytosolic glutathione peroxidase (cGPX). To clarify the mechanism of action of this catalytic antibody, detailed studies on kinetic behaviour and biological activity were carried out. A rate of acceleration (k(cat)/K-m/k(uncat)) 10(7)-fold that of the uncatalytic reaction is observed. Under similar conditions, the turnover number (k(cat)) of Se-4A4 is 42% of that of the natural rabbit liver cGPX. The Se-4A4 reaction involves a Ping Pong mechanism, which is the same as that of the natural cGPX. The selenocysteine residue is located in the binding site of the antibody and is shown to be crucial for this activity. Of the thiol compounds tested, only GSH is able to serve as substrate for Se-4A4. It was demonstrated, using the free-radical-damage system (hypoxanthine/xanthine oxidase) of cardiac mitochondria, that Se-4A4 can protect mitochondria from free-radical damage at least 10(4)-fold more effectively than the natural cGPX.

Ship-board measurements and estimations of air-sea fluxes in the western tropical Pacific during TOGA COARE

Direct air-sea flux measurements were made on RN Kexue #1 at 40 degrees S, 156 degrees E during the Tropical Ocean Global Atmosphere (TOGA) Coupled Ocean-Atmospheric Response Experiment (COARE) Intensive Observation Period (IOP). An array of six accelerometers was used to measure the motion of the anchored ship, and a sonic anemometer and Lyman-alpha hygrometer were used to measure the turbulent wind vector and specific humidity. The contamination of the turbulent wind components by ship motion was largely removed by an improvement of a procedure due to Shao based on the acceleration signals. The scheme of the wind correction for ship motion is briefly outlined. Results are presented from data for the best wind direction relative to the ship to minimize flow distortion effects. Both the time series and the power spectra of the sonic-measured wind components show swell-induced ship motion contamination, which is largely removed by the accelerometer correction scheme, There was less contamination in the longitudinal wind component than in the vertical and transverse components. The spectral characteristics of the surface-layer turbulence properties are compared with those from previous land and ocean results, Momentum and latent heat fluxes were calculated by eddy correlation and compared to those estimated by the inertial dissipation method and the TOGA COARE bulk formula. The estimations of wind stress determined by eddy correlation are smaller than those from the TOGA COARE bulk formula, especially for higher wind speeds, while those from the bulk formula and inertial dissipation technique are generally in agreement. The estimations of latent heal flux from the three different methods are in reasonable agreement. The effect of the correction for ship motion on latent heat fluxes is not as large as on momentum fluxes.

Rifting process and formation mechanisms of syn-rift stage prolongation in the deepwater basin, northern South China Sea

Based on the latest seismic and geological data, tectonic subsidence of three seismic lines in the deepwater area of Pearl River Mouth Basin (PRMB), the northern South China Sea (SCS), is calculated. The result shows that the rifting process of study area is different from the typical passive continental margin basin. Although the seafloor spreading of SCS initiated at 32 Ma, the tectonic subsidence rate does not decrease but increases instead, and then decreases at about 23 Ma, which indicates that the rifting continued after the onset of seafloor spreading until about 23 Ma. The formation thickness exhibits the same phenomenon, that is the syn-rift stage prolonged and the post-rift thermal subsidence delayed. The formation mechanisms are supposed to be three: (1) the lithospheric rigidity of the northern SCS is weak and its ductility is relatively strong, which delayed the strain relaxation resulting from the seafloor spreading; (2) the differential layered independent extension of the lithosphere may be one reason for the delay of post-rift stage; and (3) the southward transition of SCS spreading ridge during 24 to 21 Ma and the corresponding acceleration of seafloor spreading rate then triggered the initiation of large-scale thermal subsidence in the study area at about 23 Ma.

Probability distribution of random wave-current forces

Based on the second-order solutions obtained for the three-dimensional weakly nonlinear random waves propagating over a steady uniform current in finite water depth, the joint statistical distribution of the velocity and acceleration of the fluid particle in the current direction is derived using the characteristic function expansion method. From the joint distribution and the Morison equation, the theoretical distributions of drag forces, inertia forces and total random forces caused by waves propagating over a steady uniform current are determined. The distribution of inertia forces is Gaussian as that derived using the linear wave model, whereas the distributions of drag forces and total random forces deviate slightly from those derived utilizing the linear wave model. The distributions presented can be determined by the wave number spectrum of ocean waves, current speed and the second order wave-wave and wave-current interactions. As an illustrative example, for fully developed deep ocean waves, the parameters appeared in the distributions near still water level are calculated for various wind speeds and current speeds by using Donelan-Pierson-Banner spectrum and the effects of the current and the nonlinearity of ocean waves on the distribution are studied. (c) 2006 Elsevier Ltd. All rights reserved.

Corrosion failure of marine steel in sea-mud containing sulfate reducing bacteria

The corrosion failure behavior of marine steel is affected by stress, which exists in offshore structures at sea-mud region. The sulfate reducing bacteria (SRB) in the sea-mud made the steel more sensitive to stress corrosion cracking (SCC) and weaken the corrosion fatigue endurance. In this paper, a kind of natural sea-mud containing SRB was collected. Both SCC tests by slow strain rate technique and corrosion fatigue tests were performed on a kind of selected steel in sea-mud with and without SRB at corrosion and cathodic potentials. After this, the electrochemical response of static and cyclic stress of the specimen with and without cracks in sea-mud was analyzed in order to explain the failure mechanism. Hydrogen permeation tests were also performed in the sea-mud at corrosion and cathodic potentials. It is concluded that the effect of SRB on environment sensitive fracture maybe explained as the consequences of the acceleration of SRB on corrosion rate and hydrogen entry into the metal.

基于解耦控制的SCARA机器人轨迹跟踪控制器设计

SCARA型机器人的控制问题由于其动力学模型中没有重力矩项的作用而得以简化,由于在实际应用中经常要求其高速运动,则对具有强耦合的哥氏力与向心力的控制就成为制约其系统性能的重要问题。提出通过线性变换对机器人系统解耦,将高阶系统转化为解耦的低阶系统进行控制的方法,并且应用极点配置对解耦的系统求解机器人控制器。该方法无需测量关节速度和加速度,只需要测量关节位置信号。所提出的控制器既能保证闭环系统全局渐进稳定,又能通过对线性化系统闭环极点的配置来获得期望的闭环系统响应性能。仿真实验证明了所提出的控制器设计方法的可行性。

关于水面形状的分析

对以恒加速度沿光滑平面运动的无盖水箱中的水面形状进行了具体分析,并给出了计算水箱中水稳定时液面与水平面夹角的公式·

基于最小疼痛感的机器人操作臂轨迹规划方法

针对机器人操作臂跟踪运动目标的问题,从仿生学的角度提出一种新的轨迹规划方法。将关节加速度的增量进行编码,同时将疼痛感作为优化指标,利用遗传算法在操作臂的关节空间进行轨迹优化,得到操作臂在跟踪运动目标过程中的具有较小疼痛感的轨迹。仿真试验结果表明,所提出的方法是可行的,可以规划出正确的跟踪轨迹,同时有效的减小了操作臂运动过程中的疼痛感。

一种新的角加速度估计方法及其应用

首先提出了一种新的基于卡尔曼滤波及牛顿预测的角加速度估计方法,在已知电机驱动系统位置信息的情况下,利用卡尔曼滤波实时估计系统的角加速度;同时采用牛顿预测方法解决估计算法的滞后问题,进一步提高了估计加速度的响应频带．以此为基础,本文进一步分析了利用估计加速度进行反馈控制以增强系统对外扰动的鲁棒性问题,提出了加速度反馈控制策略的设计准则并分析了稳定性．在一个直接驱动机器人关节上针对上述加速度估计及控制方法进行了实验研究:将估计加速度的实验结果与实测加速度(利用加速度计)的实验结果进行了比较分析,从而定量地揭示出估计加速度及其反馈控制在实际系统中的可行性及有效性．

机器人操作臂跟踪动态目标的轨迹规划方法

针对机器人操作臂跟踪运动目标问题,提出一种基于遗传算法的轨迹规划方法。通过对关节加速度的增量进行编码,实现在操作臂的关节空间进行轨迹优化,得到操作臂在跟踪运动目标过程中所需要的轨迹。仿真计算的结果表明,所提出的方法是有效的。

加速度空间中基于线性规划的移动机器人路径规划方法

针对动态不确定环境下移动机器人的路径规划问题,提出了加速度空间中一种基于线性规划(Linear programming,LP)的方法.在机器人的加速度空间中利用相对信息,把机器人路径规划这一非线性问题,描述成满足一组线性约束同时使目标函数极小的线性规划问题,嵌入基于线性规划方法的规划器,得到一条满足性能要求的最优路径.仿真试验验证了算法的实用性及有效性,与势场引导进化计算的方法(Artificial potential guided evolution algorithm,APEA)相比更优化,更实时.

基于卡尔曼滤波及牛顿预测的角加速度估计方法试验研究

基于角位置测量的角加速度实时估计问题是机电系统控制中一个非常重要的问题,在分析现有的线性回归平滑牛顿法和卡尔曼滤波法的基础上,提出了一种新的基于卡尔曼滤波和牛顿预测相结合的角加速度估计方法。该方法旨在利用牛顿预测进一步增强卡尔曼滤波的预测能力,减小由于滤波造成的相位滞后,提高估计加速度与实测加速度的一致性。为了验证新方法的有效性,以直接驱动机器人作为试验对象,采用将估计加速度的频率特性与实测加速度相比较的方法,分别对上述三种估计算法进行了试验比较研究,从而为利用估计加速度(取代测量加速度)实现加速度反馈控制提供了试验依据。

动态未知环境下基于相对坐标系的移动机器人实时运动规划

提出了一种简单、新颖的在动态未知环境下的移动机器人运动规划方法．此方法基于相对坐标系，通过传感器信息实时调整机器人的行为来实现规划．在规划过程中，机器人有两种行为：向目标运动和避碰，且避碰行为具有优先权．机器人两种行为的切换是基于加速度空问的，首先解决的是避碰问题，而向目标运动是作为避碰的反问题来考虑的．仿真研究验证了此规划方法的有效性。