A Pulsed Light Source with a 900Å to 6000Å Continuum

The design of a compact high colour temperature source with a substantially continuous wide range spectral emission may be approached in various ways. This paper describes such a source which is finding many applications in a wide variety of investigations.     

选择数字录像机格式(上)

详细地介绍了我国广播电视设备在从模拟复合、模拟分量格式转向采用数字分量格式时，出现的4种主流格式数字设备的技术特点。同时对如何选择适合自己的数字格式的摄、录、编、播设备，提出了几点看法。     

Comparing similar and dissimilar friction stir welds of 2017–6005A aluminium alloys

Abstract

Similar and dissimilar friction stir welds made of aluminium alloys 2017-T6 and 6005A-T6 are compared in terms of heat inputs, temperatures, material flow distributions and resulting local and overall tensile properties. Similar welds are systematically hotter and weaker than the dissimilar welds. Predictions of a three-dimensional finite element model of the tensile test transverse to the weldline are assessed towards local deformation fields measured by digital image correlation. Deformation systematically localises on the weakest heat affected zone, which is on the 6005A side in the dissimilar welds.     

24—THE RELATIONS BETWEEN THE FIBRE-LENGTH PARAMETERS OBTAINED FROM THE DIGITAL FIBROGRAPH,THE COMB SORTER,AND THE SHIRLEY PHOTO-ELECTRIC STAPLER

An account is given of an investigation in which linear relations, with varying degrees of correlation, were found between the span length (S.L.) from the Digital Fibrograph and (a) the upper-half mean length, (b) the upper-quartile length, and (c) the mean fibre length, respectively, from the comb sorter, and between S.L. and the staple length determined on the Shirley Photo-electric Stapler. Correlations were dependent on the span amount in the S.L. and reached their optimum value for 30% S.L. and comb-sorter parameters, and for 2.5–10% S.L. and staple length from the Shirley Photo-electric Stapler.     

Experimental studies on fracture of unidirectional glass-fibre-reinforced plastics composites with V-notch

Abstract

The digital speckle correlation method is used to study the deformation and fracture behaviour of glass-fibre-reinforced plastics (GFRP) composites with V-notch under tensile loading. The deformation images surrounding the notch tip at varying load levels were captured; both the horizontal and vertical displacement fields are acquired. At the same time, the strain evolution information at the notch tip during the whole damage and fracture process of the notched sample is recorded by a three-element strain gauge. The effects of notch angle and notch depth on deformation and fracture of notched GFRP are analyzed. Some microscopic fracture characteristics such as interfacial debonding, fibre fracture and matrix damage are shown.     

A Digital Input Shaper for Stable and Transparent Haptic Interaction

This paper presents frequency-dependent digital damping referred to a digital input shaper (DIS). Compared to the previously proposed analog input shaper, the DIS makes the implementation of damping much more flexible and significantly reduces the electrical noise. Moreover, the DIS incorporates a position control method at the initial contact to improve the perceived contact hardness. Then, through a series of simulations and benchmark virtual wall experiments, we show that the DIS can significantly increase the impedance range that a haptic interface can stably display and that the initial contact hardness that a user perceives can be noticeably improved by using the proposed position control method. Finally, the DIS is applied to scaled teleoperation using an atomic force microscope and through contact experiments it is shown that it can indeed increase the scaled impedance of a real environment that can be stably displayed. ©     

Enhancing the Signal-to-Interference Ratio in Digital Direct-Sequence Spread-Spectrum Receivers

Digital direct-sequence spread-spectrumreceivers are known to suffer from severe impairments indeterministic types of interference, due to inherentanalog-to-digital converter nonlinearities. In thepresent paper a noncoherent digital direct-sequencespread-spectrum receiver with an integrated adaptiveinterference reduction scheme is presented. Adaptiveinterference reduction is accomplished by exploring the nonlinearity of a 2-bit analog-to-digitalconverter with a pair of magnitude thresholds centeredaround a fixed sign threshold. The magnitude thresholdsare adjusted by means of a statistical control loop. The received signal's magnitudedistribution and zero crossings are used to estimate thecomposition of the interference. The performance of theproposed receiver in the presence of combined additive white Gaussian noise and continuous-waveinterference has been investigated and compared to thebehavior of ideal digital receivers of comparably lowcomplexity as the approach presented. The digitalreceivers studied for comparison use either single-bithard-limiters or 2-bit analog-to-digital converters withadaptive thresholds.     

Efficient sub-band coding in JPEG2000 for improved authentication and tamper-proofing

Abstract

The LL sub-band from the discrete wavelet transform in JPEG2000 is similar to a smaller image of the original in spatial domain. The proposed authentication and tamperproofing scheme is to extract and hide the entire LL sub-band into the first-level sub-bands, 1LH and 1HL. The hidden data are used later with a unique digital signature and a public key to prove the authenticity of the image. Tampered areas could be accurately detected and recovered to a quality that is visually acceptable. This scheme can be used to authenticate sensitive images, such as medical images, to prove rightful ownership and to recover images before originals are available.     

数字存储示波器噪声特性的分析

以TektronixTDS2 10为研究对象 ,对数字存储示波器噪声进行了多次时域采样和频域分析 ,结果表明 ,示波器噪声是一种非零均值的带限白噪声 ,频谱很宽 ,对示波器测量误差和谱分析影响显著 ,应在高电压测试和信号数字处理时采取措施