Why Phenolic Acids Are Unlikely Primary Allelochemicals in Rice

Allelopathy in rice (Oryza sativa, L.) effective against weeds has been found in about 3.5% of tested rice germplasm in both laboratory and field experimentation. However, the allelochemicals responsible for growth inhibition of rice-associated weeds have not yet been identified. In the literature, phenolic acids are often mentioned as putative allelochemicals. If phenolic acids commonly reach growth inhibitory concentrations in rice ecosystems, it must be expected that the degree of tolerance to phenolic acids will vary among traditional rice cultivars or plant species adapted to rice environments having inherently different phenolic acid concentrations. Phenolic acids concentrations are normally greater in submerged than in aerobic soils. A dose–response study, however, showed that seedlings of rice cultivars adapted to submerged anaerobic soils did not have higher level of tolerance against p-hydroxybenzoic acid than did seedlings of varieties adapted to aerobic upland soils. Moreover, traditional rice cultivars had no greater tolerance than did improved cultivars that were recently bred for traits other than tolerance of phenolic acids. Similarly, there were no differences in tolerance of p-hydroxybenzoic acid between two Echinochloa weed species adapted to either anaerobic or aerobic growth conditions. Thus, neither the rice cultivars nor weed species had evolved different tolerance levels against the phenolic acid. However, all rice cultivars had significantly greater tolerance of p-hydroxybenzoic acid than did either weed species. In a second experiment, the rates at which rice plants released phenolic acids into solution cultures were measured for at least one month, the time period of greatest allelopathic activity following planting under field conditions. The maximum release rate of phenolic acids during the first month of growth was approximately 10 g/plant/day. At a conventional plant density, the release rate of phenolic acids would be approximately 1 mg/m²day. This order of release rate cannot provide concentrations remotely close to phytotoxic levels determined for these rice cultivars and weed species. The results presented in this paper do not preclude the possibility that phenolic acids might be one component in a mixture of chemicals that, when present simultaneously, are allelopathic.     

On adaptive sliding mode control without switching gain overestimation

This paper presents some further results on adaptive sliding mode control (ASMC) for a class of nonlinear systems with bounded uncertain parameters. Given a large initial tracking error, current ASMC design generally produces an unnecessarily large switching gain, consequently leading to a serious chattering problem or a large‐amplitude control jump for the continuous counterpart. To solve such an overadaptation problem, the switching gain adaptation mechanism is first analyzed in this paper, and the adaptation induced by the initial tracking error is suggested to be removed. Then, by exploiting the global sliding mode feature of time‐varying sliding mode control and integral sliding mode control, we present two effective methodologies for ASMC design. The proposed ASMC algorithms ensure that there is no overestimation of the switching gain and the system response is not slowed down when a small switching gain is generated. The validity of the proposed methods is verified by both theoretical analysis and simulation results. Copyright © 2012 John Wiley & Sons, Ltd.     

基于力矩电机的复合材料缠绕机构张力控制系统

介绍了一个复合材料缠绕机构的张力控制系统,该系统研究了一种新的执行机构一力矩电机的工作特性和驱动电路,采用电阻应变式张力传感器结合三辊式结构测定张力,以力矩电机为执行机构,利用单片机实现对张力的PID控制,实验结果表明,该系统在各种缠绕过程中都具有较好的控制效果和鲁棒性。     

基于椭圆循环圆的轿车扁平液力变矩器设计

为设计叶形更为合理、性能更优的轿车扁平化液力变矩器,提出了基于椭圆的扁平循环圆设计方法。提出了全新的扁平率定义,使扁平率的变化能够反应循环圆整体形状的变化。在分析环量分配规律对变矩器性能影响的基础上,改进了传统的等环量分配叶片法,针对不同叶轮采用不同的二次函数环量分配规律进行叶片设计,得到了叶形更为合理的扁平变矩器叶片。将本文方法与传统方法进行了对比分析,结果表明,用本文方法设计的扁平变矩器性能更佳。     

基于转矩变化估算的无刷双馈电机直接转矩控制

在研究无刷双馈电机直接转矩控制调速系统的基础上,利用Matlab/Simulink软件建立无刷双馈电机的仿真模型。结合电机本身特性和直接转矩控制转矩脉动大等特点,运用一种通过估算转矩变化量来实现转矩估算的闭环控制方法进行控制。通过仿真验证该方法能有效地减少转矩脉动,具有良好的动、静态性能。     

Methane absorption and application of mixed organic aggregate prepared from Span80 and alkaline salt

The water-based materials for mine gas absorption and explosion suppression were prepared, in which the mixed organic aggregate of Span80 and alkaline salt can be used as methane absorbent. Methane was used as a model of mine gas, and the absorptions of methane with different complex materials were studied using head space gas chromatography. Then the state of aqueous material was characterized with laser light scattering instrument and the effects of different complex materials on explosion suppression were preliminarily studied in explosion chamber which can simulate mine gas explosion. The research results showed that complex material could absorb methane and there was some correlation between the mean diameter of organic aggregate in aqueous material and the absorption effect. Additionally, the aqueous material could suppress the methane explosion to some degree. The material can absorb mine gas in atomization condition, therefore, degrease mine gas concentration and influence the distribution of mine gas in the space, and then suppress the mine gas explosion to some extent.     

一种改进的异步电动机直接转矩控制方法

针对传统异步电动机直接转矩控制方法转矩及磁链脉动大、开关频率不固定的缺点,提出了一种改进的异步电动机空间矢量调制直接转矩控制方法。该方法通过转矩角闭环控制实现定子磁链幅值和相角的解耦,从而获得参考电压空间矢量,实现对磁链误差和转矩误差的控制。仿真结果表明,该方法有效地克服了传统直接转矩控制方法的缺陷,获得了良好的动态响应性能。     

ZYBG型矿用瓦斯输送管道自动抑爆装置研制

为了保障瓦斯输送管道的安全性,采用主动抑爆技术研制了ZYBG型矿用瓦斯输送管道自动抑爆装置。该装置利用火焰探测器探测瓦斯爆炸信号,并将信号通过光电转换传输给控制器,控制器对信号进行判定和分析,在爆炸接近防护区间的瞬间快速打开高压抑爆器,释放抑爆介质,熄灭火焰,阻断爆炸的进一步传播。抑爆性能试验结果表明,该抑爆装置能够在5ms内快速捕捉火焰信息,并在35ms内迅速喷洒抑爆介质。     

采用支持向量回归抑制噪声的经验模态分解方法

在实际信号分解中,经验模态分解（ EMD）是对噪声敏感的,往往会分离出一些虚假的本征模函数,对信号的分析产生一定影响。为了提高EMD分解的正确率,减少其出现虚假本征模函数的情况,文中提出了一种基于支持向量回归（ SVR）的去噪方法。先对一次EMD分解结果进行SVR逐层滤波并且对信号进行重组,然后利用EMD方法对重组信号进行二次分解。实验表明,二次分解结果已经非常接近于理想的分解结果,不会出现虚假IMF。这种分解方法对噪声不敏感,能有效提高EMD方法对噪声的容忍度。     

偏磁式消弧线圈在安钢220kV变电站的应用

分析偏磁式消弧线圈补偿装置的作用及工作原理,介绍偏磁式消弧线圈补偿装置在安钢某220kV变电站10kV系统的具体应用.