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991.
More acidic sulfated metal oxides (SMO) such as SO4
2-/ZrO2 and SO4
2-/TiO2 catalyzed the methoxymethylation of alcohols with dimethoxymethane at ambient temperature to achieve a product yield of greater than 90% within a few hours. The reaction displayed a significant steric effect on the product yield with a preferential order of primary alcohol > secondary alcohol tertiary alcohol. The observed steric effect might result from the repulsion between the bulky alkyl group in the alcohol and the two methoxy groups in the protonated dimethoxymethane (oxonium ion). 相似文献
992.
The performance of handheld wireless devices can be affected when they are held close to parts of the human body. Deterioration can vary from person to person or even different forms or types of use. One of the problems is antenna impedance mismatch in different situations. Reported is an adaptive matching antenna realised by combining a simple monopole antenna and an oscillator with a phase-locked loop (PLL). The PLL helps to monitor return loss and to adjust the matching network automatically. It is found that the antenna can operate in the whole 2.4 GHz ISM band no matter how close it is to the human body after the adaptive matching circuit is applied. 相似文献
993.
在8位单片机系统中使用NOR Flash存储器,可以实现用简单设计完成复杂任务的目标,从而有效地缩短产品的开发周期,降低产品的制造成本.本文以NOR Flash存储器SST39SF040和MCS-51系列单片机为例,详细介绍大容量NOR Flash存储器与8位单片机的接口技术,给出硬件连接电路和扇区擦除操作的源程序代码. 相似文献
994.
为了提高发射可靠性,未来的运载火箭拟采用牵制释放系统.以一种新型强制式牵制释放系统为例,应用结构分析软件MSC/Marc建立了分析该系统中减载缓释机构缓释特性的有限元模型.计算结果表明:缓释销选用应变率无关型材料时,该机构的缓释力-行程曲线受火箭起飞速度等因素的影响较小,运载火箭的缓释行程以及缓释力-行程曲线可由减载缓释机构的设计来准确的控制.该机构对机械加工精度的要求不苛刻,易于加工.在选择缓释销的材料时应注意缓释过程中销内部可能出现的中心破裂. 相似文献
995.
This study presents a novel classification method using a combination of pixel- and object-based classifications, which includes the pixel-based uncertainty classification, object-based classification, and combined pixel- and object-based classification. As the spatial resolution increases, the complexity of land covers and the degree of information uncertainty in remote-sensing imagery increase, making remote-sensing image classification more difficult. For high-resolution image classification, using the pixel-based method it is easy to misclassify the different components with characteristic variations within the same land cover as different categories, and with the object-based method it is easy to misclassify the different categories of land cover with a strong spatial correlation as the same category. By using the proposed method, the pixel- and object-based classifications are performed on the image respectively, and the pixel-based classification result is utilized to correct the object-based classification result to obtain the optimized synthesis classification result. The experiments indicate that the combined classification method not only makes full use of the advantages of the individual-level methods, but also overcomes their disadvantages and produces higher classification accuracy than the single pixel- or object-based method. The accuracy improvement with the combined classification in the three experiments is 8.3, 9.5, and 13.2% relative to the pixel-based classification, and 7.2, 6.1, and 8.1% relative to the object-based classification. 相似文献
996.
Luigi Sedda David W. Morley David Benz G. R. William Wint Zhengming Wan David J. Rogers 《International journal of remote sensing》2013,34(4):1220-1233
The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Terra and Aqua satellites conducts continuous monitoring of the Earth's land surface and oceans. Recently, a sharp discontinuity (averaging 1.9°C) has been noticed at 60° N in both MODIS daytime and night-time land surface temperature (LST) products. This linear artefact arises because the CO2 high cloud test in the operational code for the generation of the MODIS cloud mask product is used only in the non-polar region (between 60° N and 60° S). The resulting discontinuity clearly has negative implications for any statistical applications of these temperature data. In this technical note we present a new algorithm, which minimizes this discontinuity. The method uses edge detection and elimination based on a mixture of Sobel and non-linear Laplacian filters (edge detection and quantification), cubic splines (edge modelling), and a controllable power function for image restoration. The implementation of this algorithm is demonstrated on an image of average minimum night-time LST between 2001 and 2008. 相似文献
997.
This paper analyses an asymptotic stability of a digitally redesigned control system when the states of the analogue and the digital control systems are approximately matched at every sampling point. The digital redesign is a simple method of converting a given analogue controller to an equivalent digital controller in the sense of state-matching. The concerned state-matching technique is to minimise the norm distance between the discretised closed-loop system matrix of linear analogue control system and that of linear digital control system. It is shown that (i) there exists an upper bound of the norm distance to guarantee the asymptotic stability of the digitally redesigned control system and (ii) the trajectories of the linear analogue and the linear digital control systems coincide at every sampling point if the norm distance is zero. Also, a robustness result is provided in the case that nonlinear perturbations occur in the analogue and the digital control systems. Moreover, design conditions for the developed stability analysis are proposed in terms of linear matrix inequalities. 相似文献
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