峰值检测电路中过峰时刻判断方法研究

峰值检测电路提供了峰值电压保持的方法,采集峰值需要准确的判断出过峰时刻。文中分别从软件和硬件两方面介绍了两种过峰时刻判断方法,软件方法结合A/D转换器和单片机程序对采集的数值比较得出过峰时刻,硬件方法采用微分电路和过零电压比较器将过峰时刻转换为高低电平信号,试验表明这两种方法都有很好的实用性。

工务设备满足JSQ6车辆过峰的整治实践及思考

JSQ6车辆涂有“禁止溜放”标记需要经迂回线送车至编组场,影响作业效率。笔者依托集团公司《JSQ车辆驼峰溜放技术应用研究》科研计划项目,全程参与JSQ6车辆驼峰溜放工务设备相关试验方案制定和现场测试,积极研究制定工务线路设备纵断面调整方案与整治方法,在全路首次顺利实现了JSQ6车辆驼峰溜放,提出了工务线路设备满足JSQ6车辆过峰的日常检查方法、周期和标准。整治实践过程的启示和建议,对于驼峰线路设计与优化、竖曲线的养护与凹底车辆设计,有很好的指导意义。

基于S3C2410的多道脉冲幅度分析器硬件设计

该文介绍了多道脉冲幅度分析器各组成部分,重点阐述了脉冲检测电路、过峰检测电路、采样保持电路的工作原理及以S3C2410微处理器作为中心的接口控制电路。

Relationship between the transition frequency of local fluid flow and the peak frequency of attenuation

Local fluid flow（LFF） at the mesoscopic scale is the main dissipation mechanism of seismic waves in heterogeneous porous media within the seismic frequency band.LFF is easily influenced by the structure and boundary conditions of the porous media,which leads to different behaviors of the peak frequency of attenuation.The associated transition frequency can provide detailed information about the trend of LFF;therefore,research on the transition frequency of LFF and its relationship with the peak frequency of the corresponding attenuation（i.e.,inverse of quality factor） facilitates the detailed understanding of the effect of inner structures and boundary conditions in porous media.In this study,we firstly obtain the transition frequency of fluid flux based on Biot＇s theory of poroelasticity and the fast Fourier transform algorithm in a sample containing one repeating unit cell（RUC）.We then analyze changes of these two frequencies in porous media with different porous properties.Finally,we extend our analysis to the influence of the undrained boundary condition on the transition frequency and peak frequency in porous media with multiple RUCs.This setup can facilitate the understanding of the effect from the undrained boundary condition.Results demonstrate that these two frequencies have the same trend at low water saturation,but amplitude variations differ between the frequencies as the amount of saturation increases.However,for cases of high water saturation,both the trend and the amplitude variation of these two frequencies fit well with each other.

Observed typhoon wave spectrum in northern South China Sea

To describe both the way in which a wave spectrum grows and the growth processes of realistic wave conditions,the dependence relationship between the spectrum parameters and wind parameters must be obtained. Based on data measured in 2010 by a Wave Rider buoy,which was deployed in the South China Sea at coordinates 21.89°N,115.13°E,we evaluated the wave spectrum in the sea area when affected by three typhoons:Conson,Chanthu,and Megi. The Joint North Sea Wave Project spectrum was parameterized based on the observed wave spectrum. We proposed a spectrum with three parameters:the dimensionless lowest moment of the spectrum,dimensionless peak frequency,and spectrum width. The relationships between these spectral parameters and the dimensionless fetch were also discussed.

Surface effects on in-shoe plantar pressure and tibial impact during running

Purpose： This study aims to explore the effects of running on different surfaces on the characteristics of in-shoe plantar pressure and tibial acceleration. Methods： Thirteen male recreational runners were required to run at 12 km/h velocity on concrete, synthetic track, natural grass, a normal treadmill, and a treadmill equipped with an ethylene vinyl acetate （EVA） cushioning underlay （treadmill_EVA）, respectively. An in-shoe plantar pressure system and an accelerometer attached to the tibial tuberosity were used to record and analyze the characteristics of plantar pressure and tibial impact during running. Results： The results showed that there were no significant differences in the 1 st and 2nd peak plantar pressures （time of occurrence）, pressure-time integral, and peak pressure distribution for the concrete, synthetic, grass, and normal treadmill surfaces. No significant differences in peak positive acceleration were observed among the five tested surface conditions. Compared to the concrete surface, however, running on treadmillEVA showed a significant decrease in the 1st peak plantar pressure and the pressure time integral for the impact phase （p 〈 0.05）. These can be further ascribed to a reduced peak pressure observed at heel region （p 〈 0.05）. Conclusion： There may not be an inevitable relationship between the surface and the lower-limb impact in runners. It is, however, still noteworthy that the effects of different treadmill surfaces should be considered in the interpretation of plantar pressure performance and translation of such results to overground running.

Experimental Study on Thermal Interaction of LBE and Lead Droplet with Subcooled Water

Characteristics of thermal-hydraulic interaction of LBE （45w%Pb-55w%Bi） and lead with subcooled water in pool water were investigated experimentally. Two kinds of interaction zones （deformation and fragmentation） and three kinds of interaction zones （solidification, deformation and fragmentation） were observed during LBE droplet/water interaction and lead droplet/water interaction, respectively. The fragmentation zone （FZ） could be identified exactly by two border lines： spontaneous nucleation temperature and minimum film boiling temperature. Within fragmentation zone, 10% to 35% tiny debris （diameter 〈 1 mm） of LBE and 5 to 8 kPa peak pressure generated with increasing the LBE temperature and no effect with increasing the subcooling of water. Only 2%-4% tiny debris （diameter 〈 1 mm） of lead and 2 kPa peak pressure generated regardless of lead and water temperature.

牟定白马山考察记

云南楚雄的心佛林寺院遗址前有一块《牟定县山寺名僧纪念碑记》,记载关于白马山连城寺的情况。文中涉及建文帝入滇事: '建文帝入滇,隐于僧,法名过峰,曾遁连城寺多年'。我曾到过几座传说'建文帝曾在本寺出家'的佛教寺院,但都没有建文皇帝为僧时的法名、法号,这一记载引起我的极大兴趣,但又难辨真伪。

Statistical extremes and peak factors in wind-induced vibration of tall buildings

In the structural design of tall buildings, peak factors have been widely used to predict mean extreme responses of tall buildings under wind excitations. Vanmarcke＇s peak factor is directly related to an explicit measure of structural reliability against a Gaussian response process. We review the use of this factor for time-variant reliability design by comparing it to the conven- tional Davenport＇s peak factor. Based on the asymptotic theory of statistical extremes, a new closed-form peak factor, the so-called Gamma peak factor, can be obtained for a non-Gaussian resultant response characterized by a Rayleigh distribution process. Using the Gamma peak factor, a combined peak factor method was developed for predicting the expected maximum resultant responses of a building undergoing lateral-torsional vibration. The effects of the standard deviation ratio of two sway components and the inter-component correlation on the evaluation of peak resultant response were also investigated. Utilizing wind tunnel data derived from synchronous multi-pressure measurements, we carried out a wind-induced time history response analysis of the Common- wealth Advisory Aeronautical Research Council （CAARC） standard tall building to validate the applicability of the Gamma peak factor to the prediction of the peak resultant acceleration. Results from the building example indicated that the use of the Gamma peak factor enables accurate predictions to be made of the mean extreme resultant acceleration responses for dynamic service- ability performance design of modem tall buildings.