Optimization of the number and the positions of error sensors in adaptive active sound control

l.lntroductlonRcccntly,inthcapplicationoractivcsoundcontrol,thetcchniqucofadaptivcfiltcrhasbeenincommonuseforcontro1systcmandithasbccnrealizedbyfastDSP(digitalsignalproccssing).Espcciallyinthcactivcsoundcontro1inspace,thiskindofcontrolsystemcansurmountthcdiflicu1tywhichiscauscdbythecomplicatcdacoustica1cnvi-ronmentandthevariationofmanyphysica1parameters.ThcreIbrcitprovidesapossibiIi-tyforthepracticaluscsoractivcsoundcontrol.Thisdis1inguishingfcaturchasbccnprovcdbyboththeoryandcxperimentl'].T…     

Temperature-compensating multiple fiber Bragg grating strain sensors with a metrological grating

A novel approach based on multiple fiber Bragg gratings for measuring the distributed strain, which is temperature compensated, is demonstrated. Especially, in order to increase the measurement accuracy, a metrological grating is employed to read out the output of the system. The measurement resolution of the system is less than 0.5 μ.     

Quantum noise limits to terabaud communications

From a general model of fiber optics, we investigate the physical limits of soliton-based terabaud communication systems. In particular we consider Raman and initial quantum noise effects which are often neglected in fiber communications. Simulations of the position diffusion in dark and bright solitons show that these effects become increasingly important at short pulse durations, even over kilometer-scale distances. We also obtain an approximate analytic theory in agreement with numerical simulations, which shows that the Raman effects exceed the Gordon-Haus jitter for sub-picosecond pulses.     

A novel method for fabricating apodized fiber Bragg gratings

In this paper, a new implementation of the double exposure method for fabricating apodized fiber Bragg gratings by controlling the parameters of rotation stage and the number of UV-shots is presented. As a result, the average refractive index is kept nearly constant along the Bragg grating, and various apodized fiber Bragg grating with high reflectivity and high side lobe suppression ratio have been fabricated in single-mode hydrogen-loaded photosensitive fiber . The achieved side-lobe suppression ratio is larger than 25 dB.     

60keV质子辐照对TiNi记忆合金薄膜马氏体相变的影响

利用磁控溅射的方法在氧化后的单晶Si基片上制备了TiNi形状记忆合金薄膜，利用示差扫描量热法和原位X射线衍射研究了薄膜的马氏体相变特征。通过60keV质子注入（辐照）薄膜样品研究了H+离子对合金薄膜马氏体相变特征的影响，结果表明氢离子注入后引起了马氏体相变开始Ms和结束点Mf以及逆马氏体相变开始As和结束温度Af的下降，而对R相变开始Rs和结束温度Rf影响不大。掠入射X射线衍射表明H+离子注入后有氢化物形成。H+离子注入形成的氢化物是引起相变点的变化的主要因素。     

Long-gauge length embedded fiber optic ultrasonic sensor for large-scale concrete structures

A fiber optic ultrasonic sensor based on Fizeau interferometer has been developed and demonstrated. A helium–neon laser light source with wavelength 0.6328 μm is used in our experiment. A special feature is its Fizeau configuration, which enables one to eliminate much undesirable noise by combining both the reference arm and the sensing arm within the same length of fiber. The dynamic response model of photo-elastic effect of ultrasonic wave and optical fiber is established. The fiber optic ultrasonic sensor experimental results are obtained and compared with the convenient PZT transducer.     

Interfacial strength of joints between fibers and dispersedly filled epoxy matrices

The concentration dependences of adhesive strength are investigated for fiber/dispersedly filled epoxy matrix systems. The measurements were carried out using an improved model of adhesiometer under normal conditions at a constant rate of loading. It is shown that the adhesive strength as a function of filler concentration has a maximum, which is more or less pronounced. The location of the maximum depends on the nature of filler and particle geometry. The increase in the adhesive strength at the maximum reaches 20–30% in comparison with that for the unfilled epoxy matrix. Since the interfacial strength between steel wire and all the mineral powders investigated is zero, the growth in the adhesive strength upon introduction of a finely divided filler in polymer binders is rather un expected. The possible reasons for the phenomenon observed are discussed. __________ Translated from Mekhanika Kompozitnykh Materialov, Vol. 43, No. 1, pp. 3–14, January–February, 2007.     

双屈服法测定93W合金的屈服强度

 用组合飞片技术以实现对待测材料93W合金进行加载-再加载和加载-卸载，并用VISAR（Velocity Interferometer System for Any Reflector）测试方法和高速数值示波器记录样品-窗口界面的粒子速度，通过上下屈服面法对实验数据进行处理，从而推出93W在冲击压力分别为16、32和96 GPa三个压力点下的屈服强度为：1.8、2.6和4.9 GPa。得到了93W合金在高压下材料屈服强度随冲击压力的增大而增大，但其与冲击压力的比值则随冲击压力的增加而减小的变化规律。     

多孔材料在热击波压实下的本构方程

 通过引入描述多孔材料中非零压状态基体体积占有比的承压系数α_v，取代过去常用的多孔度α，对多孔材料的本构方程进行修正而得到p＝α_vF(α_v, E)，解决了多孔材料发生熔化时，本构方程不适用的问题。应用结果表明，这种修正是合理的和可行的，对多孔材料的数值模拟工作具有一定的参考价值。