High-sensitivity methane monitoring based on quasi-fundamental mode matched continuous-wave cavity ring-down spectroscopy

Continuous-wave cavity ring-down spectroscopy (CW-CRDS) is an important technical means to monitor greenhouse gases in atmospheric environment. In this paper, a CW-CRDS system is built to meet the needs of atmospheric methane monitoring. The problem of mode matching is explained from the perspective of transverse mode and longitudinal mode, and the influence of laser injection efficiency on measurement precision is further analyzed. The results of cavity ring-down time measurement show that the measurement precision is higher when the laser is coupled with the fundamental mode. In the experiment, DFB laser is used to calibrate the system with standard methane concentration, and the measurement residual is less than ±4×10^-4 μs^-1. The methane concentration in the air is monitored in real time for two days. The results show the consistency of the concentration changes over the two days, which further demonstrates the reliability of the system for the measurement of trace methane. By analyzing the influence of mode matching, it not only assists the adjustment of the optical path, but also further improves the sensitivity of the system measurement.     

基于相位敏感型光时域反射仪的除尘器破袋检漏及定位技术

针对水泥生产行业中袋式除尘器破袋检漏定位问题,提出了基于分布式光纤振动传感的检漏定位方法。分布式光纤振动传感系统灵敏度高,可以检测到布袋破损后粉尘气流对光纤产生的微振动信号,以此判断布袋是否破损,并通过时域差分法来定位破袋。搭建了一套相位敏感型光时域反射仪(φ-OTDR),通过室内模拟得出该系统最大信噪比为10dB,实际空间分辨率为23.7m,同时验证了该系统能响应低频粉尘气流扰动信号。在现场平台实验基础上,结合支持向量机(SVM)算法对现场测试数据进行识别分类,平均破袋识别准确率可达97.8%。结合φ-OTDR分布式系统与SVM算法可有效解决袋式除尘器破袋检漏定位问题。     

"三层传输模型"在嵌入式系统与PC间通信中的实现

针对嵌入式系统与PC间通信的特点,基于tcp/ip通讯模型的思想,提出适合嵌入式系统与PC间通讯的"三层传输模型",把嵌入式系统的通信过程设计为数据传输层、数据控制层、数据应用层,每层利用下层提供的功能为上层服务,解决嵌入式系统与PC间数据传输的高效性、可靠性的问题,并通过实验得出相关数据进行分析说明.本模型的思想具备一定的通用性,适用串口,蓝牙,红外等各种接口或同类嵌入式系统与PC进行通信的问题.     

Novel method for correcting light intensity fluctuation in the TDLAS system

A novel method for online correction of light intensity fluctuation in a practical tunable diode laser ab-sorption spectroscopy(TDLAS)system with wavelength modulation is presented.The proposed method is developed according to the linear relation between peaks at multiple frequencies of sine modulation in the power spectral density of the demodulated second-harmonic(2f)signal and the incident light intensity.Those peaks are demonstrated experimentally and explained as residual power at the first-harmonic and third-harmonic frequencies after 2f demodulation of the residual amplitude modulation signal due to the limited integrating time constant of the lock-in-amplifier.This method can achieve real-time correction of light intensity fluctuations with only little calculation.It can work well in a very large range of light intensity and has great potential applications in the wavelength modulation spectroscopy system.     

室内回填土质量病害分析与控制

根据GB50202-2002及GB50209-2002规范中回填土质量验收的要求,对回填土施工中易出现的问题及控制方法进行简要分析探讨。     

M-ZSM-5催化α-蒎烯空气环氧化反应

采用不同的金属离子交换Na-ZSM-5型分子筛制备M-ZSM-5催化剂.以空气作为氧化剂,N,N-二甲基甲酰胺(DMF)作为溶剂,用M-ZSM-5催化环氧化α-蒎烯.采用XRD和IR对催化剂进行表征,结果表明ZSM-5经过离子交换后其基本骨架结构没有发生变化.结果表明Co-ZSM-5的催化活性最高,以1.2%Co-ZSM-5型分子筛为催化剂,空气作为氧化剂并用少量的TBHP作为引发剂,采用DMF作为溶剂,在90℃下反应5 h,α-蒎烯的转化率达84.5%,α-蒎烯环氧化物选择性达78.1%.催化剂经过回收利用,发现催化效果基本保持一致.     

参考光照射下的数字全息图频谱特点及应用

提出了一种在离轴数字全息再现过程中确定参考光角度和简化滤波器设计过程的方法。分析了模拟参考光照射下的离轴数字全息图的频谱特点。首先将数字全息图与计算机模拟的原参考光波相乘,然后做傅里叶变换,得到其频谱图。结果发现,含有被记录物体信息的物光波频谱始终处在频谱面的中央位置。依据这一特点,不仅可以实现模拟再现时最佳参考光的角度参数测定,而且还可以使滤波器的结构设计过程简化。借助于滤波技术,数字全息再现像中零级像和共轭像得到了有效的去除,再现物体实像质量得到了有效的改善。