多源遥感的中国NO2浓度在时空上的对比

鉴于研究NO2柱浓度的长时间变化趋势时,不同卫星数据之间是否存在一致性非常重要,且不同卫星数据在不同空间尺度和季节上的对比研究较少,对比了GOME、SCIAMACHY、GOME-2和OMI反演的中国地区对流层NO2柱浓度在栅格尺度、省尺度、区域尺度和4个季节间的差异。结果表明,不同传感器的对流层NO2柱浓度在不同空间尺度和不同季节间具有良好的一致性,但是也有差别。NO2柱浓度平均值在省尺度上最大,区域尺度次之,栅格尺度上最小。SCIAMACHY反演的NO2柱浓度值低于GOME,高于GOME-2A和OMI,平均NO2柱浓度的最大差异出现在冬季,最大差异为SCIAMACHY比GOME、GOME-2A和OMI分别高-10.16%、17.51%和72.8%。GOME-2A和GOME-2B对流层NO2柱浓度均高于OMI,平均NO2柱浓度较大差异在春季和夏季,GOME-2A和GOME-2B分别比OMI高48.5%和41.55%。最后,卫星NO2柱浓度和地面NO2浓度验证结果表明,OMI数据和地面NO2浓度拟合的R2（0.72）大于GOME-2A数据与地面数据拟合的R2（0.6）。     

高清蓝光读取头中聚焦原理对比分析

对目前新一代中国蓝光高密度数字光盘存储系统(CBHD:China Blue High-definition Disc)的光学读取头中主流的两种聚焦方案进行分析,通过实验验证两种方案的可选择标准,总结其工作原理,并进行对比研究。通过光路模拟,得到探测器上光强分布图,提出了方案选取的基本判断参数:盘片离焦量。     

接触式IC卡接口原理与不同实现方式对比

详细介绍接触式IC卡读写原理;结合一个基于不同读写芯片、可以同时操作6片接触式IC卡的系统,对包括并行通信、半双工串行通信和I2C通信的几种不同接口形式的IC卡读写芯片进行了详细的对比分析。     

变频器工作原理以及应用中的注意问题

近年来变频器在电气传动控制方面得到了越来越广泛的应用,但如何使用各种不同种类的变频是很多电气工程师面临的问题。本文通过对变频器的发展历史、分类和工作原理的介绍以及对实际应用中应注意的问题作出了总结归纳,对选择和安装、调试变频器时有一定的借鉴意义。     

Optimization of pulse frequency modulated control systems via modified maximum principle

The problem of finding the optimum control function for the pulse frequency modulated (PFM) system is considered in this paper. In the PFM systems discussed here, the control function consists of a series of standard pulses. The optimization procedure consists of determining the polarity and positions of the pulses which make up the control function. The performance index is assumed to be a linear combination of the final values of the state variables. This does not exclude the problem of optimizing a system with respect to an integral, provided that the integrand is linear with respect to the state variables, but not necessarily with respect to the control function. In the PFM systems considered, the control function is fixed for a period of time following the initiation of each pulse. This fact precludes the direct application of the existing standard optimizing techniques. The Modified Maximum Principle is presented. It is based on Pontryagin's Maximum Principle and is applicable to open-loop systems with linear plants with fixed operating time. The Modified Maximum Principle is valid for systems with and without final value constraints on the state variables.     

网格资源描述技术的比较研究

网格资源描述是网格应用的关键,本文在分析网格资源特点的基础上,对资源描述技术进行了讨论;着重分析了三种资源描述技术各自的特点与局限性;经过分析最后得出资源描述框架RDF更适合于网格资源描述的开发。     

The role of standards

The Data Base Systems Study Group of Accredited Standards Committee X3 has initiated efforts that will lead to an eventual international standard in object-oriented data base systems. This work will require the coordination of current X3 committees H2 Data Languages and H4 Information Resource Management Dictionary within X3 as well as coordination with other standards development committees outside X3 but included in the ANSI interface with ISO through the JTCI TAG.     

Coherent control of three-dimensional atom localization based on different coupled mechanisms

We present a new scheme for three-dimensional (3D) atom localization in a four-level atomic system based on different coupled mechanisms. Owing to the space-dependent atom–field interaction, the position probability distribution of the atom can be directly determined by measuring the probe absorption and gain spectra. It is found that, based on different coupled mechanisms, the probability of finding the atom in 3D space is increased from 25% to 100%. Our scheme may be helpful in optical microscopy, the atom nano-lithography, and measurement of the center-of-mass wave function of moving atoms, etc.     

基于频域反射法的便携式土壤水分检测仪研制

根据土壤墒情监测的具体要求,研制了一种新型便携式土壤水分检测仪。基于频域反射(FDR)原理采集土壤容积含水量,采用标准的烘干称重实验对测量结果进行校正,并同时获取检测点经度、维度信息及实时时间,通过GPRS/GSM及时传送给远程数据中心和责任人。实地测试表明:土壤水分测量误差<3%,数据传输无误。该仪器性价比高,操作简便,适合农技人员使用,对土壤墒情实时监测和智能决策具有重要现实意义。     

Three different modifications of the dead-beat principle in optimum control

The principle of dead-beat control gives a method of optimum control. It is shown that two other optimum control settings, viz,. that, of the minimum sum criterion and that of the minimum integral criterion, are closely related to dead-beat control, The latter has the additional advantage of being optimal regardless of the moment of appearance of the step disturbance.     

A comparative study of tactile paving design standards in different countries

Tactile paving is a system of textured ground surface indicators found on public environments to assist blind and visually impaired persons to distinguish locations and directions, identify potential hazards, and then to move and reach expected destinations. The design of tactile paving is different from those of many public facilities because tactile paving is mainly used by blind and visually impaired persons. Although tactile paving was invented several decades ago it is only recently that it has been widely implemented in many cities, yet criticism on its unsatisfactory design for its particular users as well as other people is still frequently heard. One of the critical comments is the lack of a good standard. This paper reviews the history and development of tactile paving. By reviewing particular characteristics of tactile paving and the needs of blind and visually impaired persons, this paper discusses the importance of a standard for tactile paving. This paper then compares different tactile paving design standards in several selected countries. Focusing on the factors of type, pattern and color in constituting the standards of tactile paving, this paper tries to identify the problems of tactile paving in China, and then gives some suggestions and insights for consideration and further investigation.     

最优控制的计算原理:评论最小值原理

提出连续最优控制计算原理和离散最优控制计算原理,两者都可用于最优控制的数值优化. Pontryagin最小值原理和离散最小值原理,由于其含有的信息不完整,形式特殊,所以都不能用于最优控制的数值优化.此外Pontryagin最小值原理和离散最小值原理分别为连续最优控制计算原理和离散最优控制计算原理的特殊情况.