Heterogeneous acid catalytic esterification by porous polyoxometalate-tantalum pentoxide nanocomposites

Polyoxometalates (POMs) are useful catalysts in both redox and acid catalysis reactions since its catalytic features can be controlled at a molecular level. We investigated POM (POM = H₃PW₁₂O₄₀) on tantalum pentoxide (Ta₂O₅) via hydrolysis of tantalum pentachloride (TaCl₅) in the presence of POM using the sol-gel method for acid catalytic reaction. All obtained amorphous materials have been characterized by inductively coupled plasma atomic emission spectroscopy (ICP-AES), Fourier transform infrared (FT-IR) spectra, Raman scattering spectroscopy, ³¹P magic-angle spinning (MAS) NMR, field emission scanning electron microscopy (FESEM), and nitrogen adsorption/desorption analysis, in order to confirm the structure integrity of the Keggin unit in as-prepared composites and investigate the morphology and surface textural property of the composites. Catalytic activity of the catalysts has been evaluated for esterification of acetic acid with ethanol as a model reaction with different catalytic reaction parameters such as POM loading, reaction time, catalyst dose, molar ratio of the reactants, etc. The conversion of ethanol reached 87.4 % and the turnover frequency (TOF) was 2.9×10³.Meanwhile, it is easy to separate and recover POM/Ta₂O₅ from the reaction system.     

基于二维安全防护体系的WAF系统

针对Web攻击,传统防火墙对应用层防护存在不足,而Web应用防火墙可利用其架构的技术优势,应对繁多的攻击方式。给出二维安全防护系统及Web服务器核心内嵌模型,进一步给出Web应用防火墙设计实现方案。实验表明,该系统能够解决Web应用安全问题,具有较高的网络性能,支持策略的定制与扩展。     

SoHyFIS-Yager: A self-organizing Yager based Hybrid neural Fuzzy Inference System

The Hybrid neural Fuzzy Inference System (HyFIS) is a multilayer adaptive neural fuzzy system for building and optimizing fuzzy models using neural networks. In this paper, the fuzzy Yager inference scheme, which is able to emulate the human deductive reasoning logic, is integrated into the HyFIS model to provide it with a firm and intuitive logical reasoning and decision-making framework. In addition, a self-organizing gaussian Discrete Incremental Clustering (gDIC) technique is implemented in the network to automatically form fuzzy sets in the fuzzification phase. This clustering technique is no longer limited by the need to have prior knowledge about the number of clusters present in each input and output dimensions. The proposed self-organizing Yager based Hybrid neural Fuzzy Inference System (SoHyFIS-Yager) introduces the learning power of neural networks to fuzzy logic systems, while providing linguistic explanations of the fuzzy logic systems to the connectionist networks. Extensive simulations were conducted using the proposed model and its performance demonstrates its superiority as an effective neuro-fuzzy modeling technique.     

自动提取化学分子结构静态图像的交点信息

化学结构式(图)是化学分子惟一、无二义的描述形式,其主要由原子和化学键构成,在静态图中一般以端点和交点表示原子,以直线表示化学键。本文重点研究了化学分子结构静态图中交点信息的自动提取,主要工作如下:(1)总结了化学分子结构中的3种交点类型,即2条直线的交点表示CH2,3条直线的交点表示CH,4条直线的交点表示C,规范的提出了交点的3个定义,为后续自动提取化学分子结构静态图像的交点信息奠定了基础;(2)基于hough变换,从图像空间映射到参数空间,再联合参数空间和图像空间信息来提取直线,解决了峰值扩散现象,避免了伪直线出现;(3)记下每条直线的(ρ,θ)值,判断直线间有无交点,有则根据交点类型的3个定义,分析交点的类型,提取交点的信息,记录交点间的链接关系。最后,通过对若干幅化学分子结构的BMP图做实验,统计得出交点提取的准确率在75%左右,结果表明此方法可行。本研究为自动提取静态化学分子结构图的信息提供了证据。     

Effect of Multi-Wall Carbon Nanotubes on the Mechanical Properties of Natural Rubber

Multi-walled carbon nanotubes (MWNTs) were used to prepare natural rubber (NR) nanocomposites. Our first efforts to achieve nanostructures in MWNTs/NR nanocomposites were formed by incorporating carbon nanotubes in a polymer solution and subsequently evaporating the solvent. Using this technique, nanotubes can be dispersed homogeneously in the NR matrix in an attempt to increase the mechanical properties of these nanocomposites. The properties of the nanocomposites such as tensile strength, tensile modulus, elongation at break and hardness were studied. Mechanical test results show an increase in the initial modulus for up to 12 times in relation to pure NR. In addition to mechanical testing, the dispersion state of the MWNTs into NR studied by Transmission Electron Microscopy (TEM) in order to understand the morphology of the resulting system     

An interpolation model to accelerate the frequency-domain response calculation of grounding systems using the method of moments

The transient characteristics of grounding systems are essential for their designs and related electromagnetic-compatibility problems in power systems. Although the method of moments (MoM) is a popular way to analyze the characteristics of grounding systems, it is time-consuming. In this paper, a two-stage method is presented to construct fitted models of the frequency-domain responses of grounding systems to accelerate the calculations of the MoM. In the first stage, the adaptive model-based parameter estimation is used to adaptively choose the most valuable frequency sampling points to construct the initial fitted functions, and then the fitted functions are adjusted in the second stage by comparing the fitted results with those computed by the first principle model at some points. The validation was achieved by a comparison of the numerical results and those obtained by inverse fast Fourier transformation.     

Low-power-consumption and high-gain CMOS distributed amplifiers using cascade of inductively coupled common-source gain cells for UWB systems

A distributed amplifier with new cascade inductively coupled common-source gain-cell configuration is presented. Compared with other existing gain-cell configurations, the proposed cascade common-source gain cell can provide much higher transconductance and, hence, gain. The new distributed amplifier using the proposed gain-cell configuration, fabricated via a TSMC 0.18-/spl mu/m CMOS process, achieves an average power gain of around 10 dB, input match of less than -20 dB, and noise figure of 3.3-6.1 dB with a power consumption of only 19.6 mW over the entire ultra-wideband (UWB) band of 3.1-10.6 GHz. This is the lowest power consumption ever reported for fabricated CMOS distributed amplifiers operating over the whole UWB band. In the high-gain operating mode that consumes 100 mW, the new CMOS distributed amplifier provides an unprecedented power gain of 16 dB with 3.2-6-dB noise figure over the UWB range.     

视频图像压缩处理的研究与应用

介绍了MPEG-4压缩标准,阐述了其编码结构和语法.在此基础上设计了一个以MAP-CA DSP芯片为核心的视频压缩系统.系统可同时完成两路MPEG-4视频压缩,支持视频图像实时预览,视频由它直接传送到显存,压缩的码流也由它直接传送到内存,无需主机CPU介入作任何操作,并通过PCI接口传送到内存中,不占用CPU资源.     

嵌入式移动数据库研究

嵌入式技术已在人们生活中得到广泛应用;移动计算更是给人们的生活带来了极大的方便。有移动计算技术推动发展的新的数据库技术让人耳目一新。嵌入式移动数据库技术因此产生。主要论述了嵌入式移动数据库的特点及应用,嵌入式移动数据库管理系统(EMDB)的功能需求及特点,嵌入式移动数据库的系统结构。     

采用HDPLD实现高速ⅡR数字滤波器

以ⅡR数字滤波器的基本理论为依据,利用查找表结构确定了ⅡR高速数字滤波器的硬件实现方案,按照层次化、模块化的设计思路,使用VHDL硬件描述语言,采用高密度可编程逻辑器件进行了高速ⅡR滤波器的这一应用技术问题的硬件设计并进行了仿真.