峰值电流模升压转换器的动态斜坡补偿电路设计

基于HHNEC 0.35 μm BCD工艺设计了一种应用于峰值电流模升压转换器的动态斜坡补偿电路.该电路能够跟随输入输出信号变化,相应给出适当的补偿量,从而避免了常规斜坡补偿所带来的系统带载能力低及瞬态响应慢等问题.经Cadence Spectre验证,该电路能够达到设计要求.     

基于C8051F34x单片机的USB Bootloader设计

介绍了一种在Silicon Labs公司的C8051F34x系列单片机上实现USB Bootloader的设计方法,使应用程序可以通过USB或COM通信实现远程在线升级。首先,简述了USB Bootloader;然后,详细阐述了USB Bootloader程序的设计和APP固件程序的设计,以及设计中需要注意的问题;最后,用VC++开发上位机软件来完成该Bootloader的远程在线下载功能。该Bootloader可以很方便地在其他类似单片机上移植,通用性强。     

基于Linux的通用视频音频采集系统的设计与实现

该文阐述了在Linux下,利用V4L以及ALSA,在普通PC上组建视频音频采集系统以及远程传输的方法。     

HERMES: embedded file system design for A/V application

Embedded systems such as PVR, set-top box, HDTV put unique demand on I/O subsystem design. Underlying software, particularly file system, needs to be elaborately designed so that it can meet tight constraints of consumer electronics platform: performance, price, reliability, and etc. In this work, we develop state-of-art file system elaborately tailored for A/V workload. There are two design objectives in our file system: performance and support for logical level abstraction. For performance, we develop a number of novel features: extent based allocation, single level file structure with block index augmentation scheme, aggressive free block allocation to minimize disk fragmentation, elaborate file system meta data layout, separation of name space data and file data and etc. HERMES enables the user to view file as a collection of semantic units (frame or audio samples). HERMES file system encompasses most of state-of-the-art file system technologies published in preceding works. Via extensive physical experiment, we verify that HERMES file system successfully addresses the original issues: good scalability, predictable I/O latency (minimizing variability in I/O latency), efficient disk head movement and etc. This is the result of harmonious effort of large I/O size, aggressive free block allocation algorithm, data block placement strategy, file organization, layout of HERMES file system and etc. The result of performance experiments indicate that HERMES file system prototype successfully meets the file system constraints for high volume and high bandwidth multimedia application. HERMES file system exhibits superior performance to EXT2 file system (Linux) and XFS file system (SGI).

基于P89V51的两轴稳定平台控制器设计

船在海上航行时会随着海浪不停的晃动,船载天线跟随船体晃动则会产生通讯中断,因此采取船载两轴稳定平台来实现天线与船体晃动的隔离,保证船载天线间的通讯质量;文中两轴稳定平台系统采用双闭环控制和积分分离PID控制器实现;文章阐述了船载稳定平台控制系统的工作原理,设计了一款基于P89V51微处理器的两轴稳定平台控制器,并给出了控制器硬件电路的设计原理图;最后按功能实现对软件模块进行了划分和介绍;通过摇摆台模拟试验,该两轴稳定平台控制系统运行可靠,动态精度较高,能确保船载天线之间的正常通讯。     

Limitations of nonlinear discrete periodic control for disturbance attenuation and robust stabilization

This paper presents a performance analysis of nonlinear periodically time-varying discrete controllers acting upon a linear time-invariant discrete plant. Time-invariant controllers are distinguished from strictly periodically time-varying controllers. For a given nonlinear periodic controller, a time-invariant controller is constructed. Necessary and sufficient conditions are given under which the time-invariant controller gives strictly better control performance than the time-invariant controller from which it was obtained, for the attenuation of l_p exogenous disturbances and the robust stabilization of l_p unstructured perturbations, for all p[1,∞].     

A method of predicting the number of clusters using Rand's statistic

Distributional and asymptotic results on the moment of Rand's C_k statistic were derived by DuBien and Warde [1981. Some distributional results concerning a comparative statistic used in cluster analysis. ASA Proceedings of the Social Statistics Section, 309–313.]. Based on those results, a method to predict the number of clusters is suggested by applying various agglomerative clustering algorithms. In the procedure, the methods using different indexes are examined and compared based on the concept of agreement (or, disagreement) between clusterings generated by different clustering algorithms on the set of data. Our method having practical generality works better than the other methods and assigns statistical meaning to C_k values in determining the number of clusters from the comparison.     

Selective oxidation reactions over titanium and vanadium metallosilicate molecular sieves

Selective oxidation reactions like the oxyfunctionalization of alkanes, hydroxylation of aromatics and sulfoxidation of thioethers have been carried out with dilute hydrogen peroxide over titanium and vanadium metallosilicate molecular sieves with MEL topology, viz., TS-2 and VS-2. Though both the catalysts possess similar activities, substantial differences in the product distribution are observed. The oxyfunctionalization of the primary carbon atoms of the alkanes and the oxidation of the methyl substituents of the aromatic hydrocarbons distinguish VS-2 from TS-2. Both the catalysts are found to be equally active in the hydroxylation of phenol, though they possess different activities in different solvents. In general, the oxidations are deeper over VS-2 than on TS-2.     

1993: Axline's eight principles of play therapy revisited.

Examined V. Axlines's book, Play Therapy (1947) which includes 8 basic principles on non-directive play therapy. Student responses to learning these principles in play therapy classes were also examined. Each student was assigned a play therapy client and was observed and assisted directly by the instructor, a licensed clinical psychologist. Clients were mildly trouble children (aged 5–10 yrs) and were selected from a referral base by the instructor as appropriate for the course. As the semester progressed and students gained direct experience, weekly small (3–4 student) group discussions were held to explore in-depth understanding of play therapy principles and how these principles are put into practice. It is concluded that Axline's book remains a classic text and a foremost resource in the field. Coupling it with experiential learning is an invaluable basis for teaching play therapy. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The confused world of sulfate attack on concrete

External sulfate attack is not completely understood. Part I identifies the issues involved, pointing out disagreements, and distinguishes between the mere occurrence of chemical reactions of sulfates with hydrated cement paste and the damage or deterioration of concrete; only the latter are taken to represent sulfate attack. Furthermore, sulfate attack is defined as deleterious action involving sulfate ions; if the reaction is physical, then, it is physical sulfate attack that takes place. The discussion of the two forms of sulfate attack leads to a recommendation for distinct nomenclature. Sulfate attack on concrete structures in service is not widespread, and the amount of laboratory-based research seems to be disproportionately large. The mechanisms of attack by different sulfates—sodium, calcium, and magnesium—are discussed, including the issue of topochemical and through-solution reactions. The specific aspects of the action of magnesium sulfate are discussed, and the differences between laboratory conditions and field exposure are pointed out.Part II discusses the progress of sulfate attack and its manifestations. This is followed by a discussion of making sulfate-resisting concrete. One of the measures is to use Type V cement, and this topic is extensively discussed. Likewise, the influence of w/c on sulfate resistance is considered. The two parameters are not independent of one another. Moreover, the cation in the sulfate salt has a strong bearing on the efficiency of the Type V cement. Recent interpretations of the Bureau of Reclamation tests, both long term and accelerated, are evaluated, and it appears that they need reworking.Part III reviews the standards and guides for the classification of the severity of exposure of structures to sulfates and points out the lack of calibration of the various classes of exposure. A particular problem is the classification of soils because much depends on the extraction ratio of sulfate in the soil: there is a need for a standardized approach. Taking soil samples is discussed, with particular reference to interpreting highly variable contents of sulfates. The consequences of disturbed drainage of the soil adjacent to foundations and of excessive irrigation, coupled with the use of fertilizer, are described. Whether concrete has undergone sulfate attack can be established by determining the change in the compressive strength since the time of placing the concrete. The rejection of this method and the reliance on determining the tensile strength of concrete because of “layered damage” are erroneous. Scanning electron microscopy (SEM) should not be the primary, and certainly not the first, method of determining whether sulfate attack has occurred. Mathematical modeling will be of help in the future but, at present, cannot provide guidance on the sulfate resistance of concrete in structures.Part IV presents conclusions and an overview of the situation, with consideration of future improvements. Appendix A contains the classification of exposure to sulfate given by various codes and guides.