Emitter-coupled pair chaotic generator circuit

An emitter-coupled pair chaotic generator is proposed with a control parameter that can be tuned for distinct chaotic behaviors. The proposed circuit is a compact, high-speed implementation of the chaotic map based on the hyperbolic tangent function. It is demonstrated that the circuit and map parameters are analytically related. As an application, we design a random number generator that passes all NIST statistical tests by applying a post-processing to the balanced bit sequence generated by a quantization of the circuit output.     

Use of transportable test stations for measuring satellite coverage dependent parameters during IOT campaigns

The in-orbit tests of the satellite coverage dependent parameters require the rotation of the satellite around its pitch and roll axes in order to ‘bring’ the various coverage locations onto one fixed IOT station. Alternatively, several transportable test stations can be located at different sites in the coverage area in order to measure the satellite performances on site. Although the second technique does not provide enough measurement points to reconstruct the complete coverage of shaped beam antennas, it presents several advantages for which it is still used by EUTELSAT for the IOTs of its satellites in conjunction with measurements based on the satellite attitude movements. In particular, the transportable test stations are used to test the stability of satellite EIRP and IPFD at the edges of the coverage areas, where the performances are more sensitive to the pointing errors induced by thermal deformation or satellite attitude changes. This paper presents the common experience gained by EUTELSAT and ESA in testing the coverage dependent parameters of the first and second generation of EUTELSAT satellites. In particular, the paper deals with the use of the transportable test stations during the EUTELSAT II F1 to F3 acceptance tests and with the test campaigns performed at several sites in the eastern European countries. In the first case, the transportable test stations were used in conjunction with satellite rotations around the pitch axis in order to measure the coverage dependent parameters along several cuts parallel to the equatorial plane at different roll angles. In the second case, the transportable test stations were used to periodically repeat the EIRP measurements of many satellite channels over several hours in order to test the EIRP stability of the EUTELSAT II satellites. For both cases, the paper presents a synthesis of the most significant IOT results together with a comparison between these results and the values of the coverage dependent parameters predicted on the basis of the on-ground tests.     

Adaptive decorrelating detectors for CDMA systems

Multi-user detection allows for the efficient use of bandwidth in Code-Division Multiple-Access (CDMA) channels through mitigation of near-far effects and multiple-access noise limitations. Due to its inherent noise and multipath immunity, CDMA multi-access is being considered as a platform for personal communication systems (PCS). As CDMA based digital communication networks proliferate, the need to determine the presence of a new user and integrate knowledge of this new user into the detection scheme becomes more important. The decorrelating detector is a linear multi-user detector that is asymptotically optimal in terms of near far resistance; however, in the presence of a new unknown user, performance of the decorrelator is severely degraded. Adaptive decorrelators are constructed which adaptively augment an existing conventional decorrelator to demodulate a new active user in addition to existing users. Several likelihood ratio based schemes are employed. Both synchronous and asynchronous communication are investigated.This research was supported by the U.S. Army Research Office under Grant DAAH04-93-G-0219.     

电子技术实验教学中科学素质与创新能力的培养

分析了当前高校电子技术实验教学中存在的一些问题，总结和介绍了作者在电子技术实验教学改革中针对提高学生科学素质和创新能力所做的一些工作尝试，并对进一步改革电子技术实验教学提出了设想。     

在光阻材料中过滤器吸附机制的作用(英文)

近来尼龙过滤被广泛用于光刻工艺流程来改善良率,因为许多IC和光阻制造商有实验性证据表明尼龙滤膜能吸附杂质。然而,尼龙滤膜降低缺陷的机制尚不清楚。通过致力于特定的光阻成分来研究不同的缺陷发生机制是十分有用的。利用表面改性和不同的光阻成分进行了各种吸附试验来测量尼龙滤膜的耐受性,包括表面张力,光酸发生剂和光酸抑制剂。最后,研究希望通过致力于如何最佳贯彻尼龙过滤策略来确定最有效的方法提高良率。     

Oxidation-sulfidation behavior of Ni aluminide in oxygen-sulfur mixed-gas atmospheres

Oxidation-sulfidation studies were conducted on sheet samples of nickel aluminide, containing 23.5 at. % Al, 0.5 at. % Hf, and 0.2 at. % B in an annealed condition and after preoxidation treatments. Continuous weight-change measurements were made by a thermogravimetric technique in exposure atmospheres of air, a low- gas mixture, and low- gas mixtures with several levels of sulfur. Detailed scanning electron microscopy (SEM), X-ray, and electron microprobe analyses of the corrosion product scale layers were performed. The air-exposed specimens developed predominantly nickel oxide; the specimen exposed to a low- .     

Impact of power electronics packaging on the reliability of grid connected photovoltaic converters for outdoor applications

This paper deals with thermal and reliability aspects of converters for grid connected photovoltaic applications (rate power approximately 100 W) which can be integrated into solar modules. The use of these Module Integrated Converters (MIC) promises a reduction of costs due to mass production. It improves behaviour of the whole photovoltaic system, as there is no voltage mismatch caused by shading effects. The electronic components of the MIC are exposed to extreme environmental conditions. Lifetime limiting factors are described. Methods to increase the lifetime of the most crucial components in the MIC, electrolytic capacitors, are described. The presented 1st generation Low Profile MIC with “optimised design” is capable of running in very high ambient temperatures. This design maximises availability of the photovoltaic system, which consequently leads to a cost reduction of the electrical energy delivered to the grid. Different realisations of how to integrate the designed Low Profile MIC into the solar module are discussed. A detailed thermal simulation is used to optimise the MIC design according to temperature and reliability issues. The models used for thermal simulation are described.     

一种基于显著不相关检验的快速分形图像编码方法

针对分形编码计算量过大的缺点,本文提出一种基于显著不相关检验的分形编码方法。对于文中的测试图像（Lenn256×256×8ppb和Boat256×256×8ppb）,其编码速度比基于子块分类的分形编码方法快2～15倍,而解码图像质量（PSNR）没有明显下降,压缩比还有一定的提高。     

谈谈我校现代电工电子实验室的教学与开放

我校自动化学院电工电子实验中心相继建成了“ＥＤＡ开放实验室”,“ＣＡＤ／ＣＡＩ实验室”和“ＰＬＣ实验室”三个现代电工技术实验室,并于１９９７年相继投入教学与开放,本文结合我们参与现代电工技术实验室教学与开放的实践,谈谈我们的感受与体会．     

The Effect of He Implantation on the Tensile Properties and Microstructure of Cu/Fe Nano‐Bicrystals

In situ uniaxial tensile experiments on as‐fabricated and helium‐implanted 100 nm‐diameter Cu/Fe bicrystals unearth the effect of individual face‐centred‐cubic/body‐centred‐cubic (fcc‐bcc) interfaces on improving radiation‐damage tolerance and helium absorption. Arrays of nanotensile specimens, each containing a single Cu grain in the bottom half and a single Fe grain on top, were fabricated by templated electron‐beam lithography and electrodeposition. Helium is implanted at 200 keV to a dose of 10¹⁴ ion/cm² nominally into the interface region. High‐resolution, site‐specific transmission electron microscopy (TEM) and through‐focus analysis reveal that the interfaces are nonplanar and contain ≈5 nm‐spaced He bubbles with diameters of 1–2 nm. Nanomechanical experimental results show that the irradiated samples exhibit yield and ultimate tensile strengths more than 60% higher than the as‐fabricated ones, while they retain comparable ductility. Tensile failure always occurs gradually, along the interfaces, with no noticeable shape localization. The absence of brittle failure in He‐irradiated metals might be explained, in part, by the inability of the small He bubbles to serve as sufficient stress concentrators for cracking. In addition, the non‐orthogonal orientation of the interfaces with respect to the loading axes results in the development of both normal‐ and shear‐stress components. Tensile loading along the pillar axes may cause those interfacial regions subjected to normal stresses to detach, while the inclined regions, subjected to shear, to carry plastic deformation until final fracture.