级连码和数据交织技术在数字HDTV中的应用

本文分析采用格状编码调制和自适应均衡技术对HDTV传输系统性能的影响以及HDTV同播传输的干扰环境,给出克服干扰的措施。设计一种适合于HDTV应用的级连格状编码和RS码方案,并对其进行计算机模拟,模拟结果表明:该方案具有较好的误码性能。     

煤气加压站自动控制系统的分析与改进

对煤气加压站自动控制系统进行了分析，依据现有的技术手段对其提出了改造措施，分析了煤气热值测量方法与热值控制回路组成。     

带附加流的多组分矩形级联的稳态算法

提供一种带附加流的多组分矩形级联的稳态算法,该算法基于对级联主方程的准线性化,通过对级联分离因子逐渐逼近来加速收敛过程。数值计算表明,由稳态法和瞬态法得到的计算结果吻合完好,但稳态法相对于瞬态法能大为缩短计算时间,适合于计算带附加流的矩形级联或其它诸如阶梯形级联等更为复杂的级联。     

Uranium (IV)-(VI) Electron Exchange Reactions in Anion Exchange Resin,Tri-n-Octyl Amine and Tri-Butyl Phosphate

A study has been made of the U(IV)-U(VI) electron exchange reactions taking place between natural U(IV) and depleted U(VI) in anion exchange resin, as well as in TnOA/benzene and TBP/benzene systems.

The exchange rate in the anion exchange resin was smaller than the corresponding rates in 8–10 M HCl, which might be explained by considering that the diffusion of the exchangeable species is much slower in the anion exchange resin than in 8–10 M HCl.

The exchange rates in TnOA/benzene and in TBP/benzene were accelerated by decreasing the concentration of TnOA or TBP in benzene. The reason may be that TnOA and TBP, including the exchangeable species, is more easily diffused in dilute than in concentrated solution.

Based on activation energy values, the mechanism of exchange in the anion exchange resin was estimated to be similar to that in 8–10 M HCl solution, and the corresponding mechanism for TBP/benzene similar to that for the cation exchange resin. In the case of TnOA/benzene, the exchange process was presumed to resemble that of the anion exchange resin, judging from the similarity of ionic species extracted thereinto.     

永磁同步电动机混沌系统的串级控制

根据永磁同步电动机的数学模型,研究如何运用串级PD控制器来控制混沌.首先在理论上运用劳斯(Routh)判据分析永磁同步电动机模型串级PD控制混沌的可行性,然后通过在平衡点处线性化的雅克比(Jacobian)矩阵来求取PD参数的值.最后在MATLAB/Simulink仿真平台上利用数值仿真实验验证其有效性.通过研究可知,运用串级PD控制可以较好地消除混沌使系统达到一个稳定的状态.该方法具有一定的参考实用性,为永磁同步电动机混沌运动分析或控制打下了研究基础.     

斩波串级调速系统换相失败的分析与仿真

换相失败是串级调速系统逆变器的常见故障,与许多因素有关。分析了串级调速系统换相失败的原因及其影响因素,并针对电源故障引起的换相失败,提出了控制方法,运用MATLAB/simulink对该方法进行仿真研究。结果表明该方法是准确的、可行的,便于工程上的应用研究。     

改进的快速行人检测方法

行人检测在视频监控以及智能车系统中有着广泛的应用前景,为了能够更有效地检测行人,将人脸检测中级联检测框架引入行人检测中,并对其进行改进,采用Gentle AdaBoost算法进行分类器训练,以提高训练效率,同时在训练前引入了特征预筛选,以减少训练时间和系统开销。实验表明,改进后的方法训练时间短,检测精度高,同时具有较快的检测速度。     

Experiment and simulation on the performance of an autocascade refrigeration system using carbon dioxide as a refrigerant

The main purpose of this study is to investigate the performance of an autocascade refrigeration system using zeotropic refrigerant mixtures of R744/134a and R744/290. One of the advantages of this system is the possibility of keeping the highest pressure of the system within a limit by selecting the composition of a refrigerant mixture as compared to that in the vapor compression system using pure carbon dioxide. Performance test and simulation have been carried out for an autocascade refrigeration system by varying secondary fluid temperatures at evaporator and condenser inlets. Variations of mass flow rate of refrigerant, compressor power, refrigeration capacity, and coefficient of performance (COP) with respect to the mass fraction of R744 in R744/134a and R744/290 mixtures are presented at different operating conditions. Experimental results show similar trends with those from the simulation. As the composition of R744 in the refrigerant mixture increases, cooling capacity is enhanced, but COP tends to decrease while the system pressure rises.

Résumé

The main purpose of this study is to investigate the performance of an autocascade refrigeration system using zeotropic refrigerant mixtures of R744/134a and R744/290. One of the advantages of this system is the possibility in keeping the highest pressure of the system within a limit by selecting the composition of a refrigerant mixture as compared to that in the vapor compression system using pure carbon dioxide. Performance test and simulation have been carried out for an autocascade refrigeration system by varying secondary fluid temperatures at evaporator and condenser inlets. Variations of mass flow rate of refrigerant, compressor power, refrigeration capacity, and coefficient of performance (COP) with respect to the mass fraction of R744 in R744/134a and R744/290 mixtures are presented at different operating conditions. Experimental results show similar trends with those from the simulation. As the composition of R744 in the refrigerant mixture increases, cooling capacity is enhanced, but COP tends to decrease while the system pressure rises.     

国内外大型低温冷藏库氨制冷系统和制冷设备节能及安全技术的发展趋势

近年来国内外冷冻冷藏行业针对不同的冷库形式和贮藏用户特点,在低温冷藏库氨制冷系统和制冷机器、设备采用一些节能及安全技术。本文根据我国的国情和国外先进国家氨制冷系统的发展趋势做出一些研究和对比。     

一种新型偏置电路的CMOS亚阈型电压基准源

文章设计了一种工作在亚闽值状态下的CMOS电压基准源,分析了MOSFET工作在亚闽区的电压和电流限定条件。电压基准源可提供与工艺基本无关近似零温度系数的基准电压。为了提高电路的电源抑制比,该电路采用了共源共栅电流镜结构。该结构采用了一种新型的偏置电路．使得电流镜各级联管均工作在饱和区边缘而不脱离饱和区,提高输出电压摆幅,得到有较高恒流特性的基准电流。该电路采用0,6μmCMOS工艺,通过Spectra仿真,可工作在2V电压下,输出基准电压1.4V,温度系数为17×10^-6（V／℃）。