采用光反馈控制白光LED的降压稳压器

由于大功率、高效率白光（以及其它颜色）LED的实现,采用LED的照明更受关注（参考文献1）。由于LED是一种电流控制器件,典型控制电路是调节通过LED的电流来保持一致的亮度。为了最好地利用电能,用户经常将开关转换电路用于LED,根据输入直流电压的不同,可以是降压（Buck）或升压转换器。图1是典型的降压和升压转换器白光LED驱动电路的结构。白光LED增加了串接电阻R,     

Object-oriented modeling and simulation of neural networks

The field of neural networks is being investigated by many researchers in order to provide solutions to difficult problems in the area of manufacturing systems. Computer simulation of neural networks is an important part of this investigation. This paper applies concepts from an important trend in software engineering research, namely object-oriented programming, to model neural networks.The design and implementation of a software object library is crucial to obtaining the full benefits of object-oriented programming. In this paper we discuss the design and implementation of a foundation library of software objects for the purpose of simulating and validating different network architectures and learning rules. The library contains objects that implement various types of nodes and learning rules. We discuss the results of our experiments to illustrate the benefits of using an object-oriented approach to modeling neural networks.     

Investigation of thermal stability, phase formation, electrical, and microstructural properties of sputter-deposited titanium aluminide thin films

Titanium aluminide thin films are being considered as coating materials for high temperature applications due to their high melting points and high oxidation resistance. In this study, Ti₃₇Al₆₃ and Ti₅₃Al₄₇ thin films are deposited onto SiO₂ substrates by RF magnetron sputtering using compound targets and then annealed in vacuum to investigate the properties of the films. Rutherford backscattering spectrometry, X-ray diffractometry, transmission electron microscopy, and four-point probe measurements are used to analyze the characteristics of Ti₃₇Al₆₃ and Ti₅₃Al₄₇ thin films for high temperature electronics applications. The films show good thermal stability up to 700 °C for 1 h in vacuum. Reasonable resistivity is obtained when appropriate compositions and anneal conditions are used.     

Sediment Removal Efficiency of Vortex Chamber Type Sediment Extractor

Experimental results on sediment removal efficiency of vortex chamber type sediment extractors are reported. A geometric configuration of the extractor is identified that is able to remove even the fine sediment (0.055 ? d ? 0.22?mm) from flow with high efficiency. For the purpose of analysis, the experimental data of present study are compiled with the data from other laboratories and the field that were collected previously by other investigators. Since the existing relations are not found to produce satisfactory results, a new relationship is developed for determination of the sediment removal efficiency of the vortex chamber type sediment extractors.     

Hydrophobic properties of polytetrafluoroethylene thin films fabricated at various catalyzer temperatures through catalytic chemical vapor deposition using a tungsten catalyzer

Using the catalytic chemical vapor deposition (Cat-CVD) method, polytetrafluoroethylene (PTFE) thin films were fabricated on Si(100) substrates at various catalyzer temperatures, using a tungsten catalyzer, and Fourier transform infrared (FTIR) spectroscopy and X-ray photoemission spectroscopy (XPS) were used to confirm the fabrication of the films. An atomic-force microscope (AFM) and a scanning electron microscope (SEM) were employed to study the correlation between the wettability and surface morphology of the samples. It was found that the wettability of the PTFE thin films fabricated via Cat-CVD is strongly correlated with the sizes of the film surfaces' nanoprotrusions, and that superhydrophobic PTFE thin-film surfaces can be easily achieved by controlling the sizes of the nanoprotrusions through the catalyzer temperature. The comparison of the wettability values and surface morphologies of the films confirmed that nanoscale surface roughness enhances the hydrophobic properties of PTFE thin films. Further, the detailed analysis of the films' surface morphologies from their AFM images with the use of the Wenzel and Cassie models confirmed that the nanoscale surface roughness enhanced the hydrophobic property of the PTFE films. Further, the variations of the wettability of the PTFE thin films prepared via Cat-CVD are well explained by the Cassie model. It seems that the increase in the trapping air and the reduction of the liquid-solid contact area are responsible for the superhydrophobicity of the PTFE thin films prepared via Cat-CVD.     

A COS study of OSI interoperability

The goal of OSI is the interoperation of computer systems from multiple vendors. The possibility of interoperation is further enhanced through the use of standardized profiles and conformance testing of implementations. While conformance testing is the primary vehicle it employs, in pursuing its primary goal of accelerating the introduction of interoperable OSI and ISDN products, the Corporation for Open Systems has examined how interoperability testing may supplement conformance testing. In the course of COS' interoperability study, formal definitions of interoperability were made, important metrics were identified, and various interoperability test methods were examined. COS believes that there may be a role for explicit interoperability testing to improve the “quality of the breed” and will endeavour to facilitate testing through its I-Lab project and other cooperative testing efforts.     

Modified drift field model for high-low transition in solar cells

A theoretical discussion is presented for the understanding of the back surface pp⁺ transition used in solar cells. It is shown that quasi-neutrality of space charge is a good approximation if the back surface diffusion is fairly deep. The error involved in the drift field model developed by assuming a quasi-neutrality of the space charge is compared with that inherent in the abrupt high-low junction model. The analysis shows that the back surface boundary, when measured from the heavily doped p⁺ side, effectively exists at a distance much larger than the impurity diffusion depth and the recombination current in the base is always less than its value estimated from the abrupt junction model. The voltage in the pp⁺ transition is due to the change in electric field by the excess carriers injected by light and drops across those regions of the cell where the injected carrier density is appreciable.     

Low temperature dielectric studies of zinc oxide (ZnO) nanoparticles prepared by precipitation method

Using zinc nitrate as a precursor and NaOH starch as a stabilizing agent, hexagonal zinc oxide (ZnO) nanoparticles has been synthesized by precipitation method. The transmission electron microscopy (TEM) images show particles of nearly uniform spherical size of around 40 nm. The infrared spectroscopy (FT-IR) measurement reveals the peak at 500 cm^?1, corresponding to the Zn–O bond. Dielectric studies of ZnO nanoparticles show frequency dependence dielectric anomaly at low temperature (85–300 K). Results reveal that the capacitance and loss tangent decrease with the frequency while these parameters improve with the increasing of temperature. The increase of a.c. conductivity with the temperature indicates that the mobility of charge carriers is responsible for hopping and electronic polarization in ZnO nanoparticles.     

Encapsulation of yeast (Saccharomyces cereviciae) by spray drying for extension of shelf life

The objective of the present work was to encapsulate yeast using different carrier materials and examine their efficacy in retaining viability of cells after spray drying. Slurry containing yeast cells along with known amount of carrier material (maltodextrin, corn starch, gum arabic, acacia gum, polyethylene glycol 8000, β-cyclodextrin, and skimmed milk powder, one at a time) was added and served as feed. Among these carrier materials attempted, corn starch and maltodextrin showed the best results with respect to powder yield (59%, w/w) and cell survival (80.5%), respectively. However, considering both survival and powder yield (67 and 59% w/w, respectively), corn starch was observed to be the most suitable carrier material.