[Research on On-Line Calibration Based Photoacoustic Spectrometry System for Monitoring the Concentration of CO2 in Atmosphere].

Resonate frequency and cell constant of photoacoustic spectrum system are usually calibrated by using standard gas in laboratory, whereas the resonate frequency and cell constant will be changed in-situ, leading to measurement accuracy errors, caused by uncertainties of standard gas, differences between standard and measured gas components and changes in environmental condition, such as temperature and humidity. As to overcome the above problems, we have proposed an on-line atmospheric oxygen-based calibration technology for photoacoustic spectrum system and used in measurement of concentration of carbon dioxide in atmosphere. As the concentration of atmospheric oxygen is kept as constant as 20.96%, the on-line calibration for the photoacoustic spectrum system can be realized by detecting the swept-frequency and peak signal at 763.73 nm. The cell of the PAS has a cavity with length of 100 mm and an inner diameter of 6 mm, and worked in a first longitudinal resonant mode. The influence of environmental temperature and humidity, gas components on the photoacoustic cell's performance has been theoretically analyzed, and meanwhile the resonant frequencies and cell constants were calibrated and acquired respectively using standard gas, indoor air and outdoor air. Compared with calibrated gas analyzer, concentration of carbon dioxide is more accurate by using the resonant frequency and cell constant calculated by oxygen in tested air, of which the relative error is less than 1%, much smaller than that calculated by the standard gas in laboratory. The innovation of this paper is that using atmospheric oxygen as photoacoustic spectrum system's calibration gas effectively reduces the error caused by using standard gas and environmental condition changes, and thus improves the on-line measuring accuracy and reliability of the photoacoustic spectrum system.

[Cadmium and zinc absorption and distribution in various tree species in a mining area].

The study on the characteristics of cadmium (Cd) and zinc (Zn) absorption and distribution in 11 tree species in a mining area of Nanjing showed that the absorption and accumulation of test heavy metals differed with tree species, their organs, and heavy metals themselves. Among the test tree species, Viburnum awabuki had the highest Cd absorption, accumulation, and translocation rates, which could be used for the remediation of polluted soils via phytoextraction. Cd was mainly accumulated in tree roots, and its accumulation in tree organs was generally in the order of root > leaf and shoot > bark > stem. Zn was generally accumulated in above-ground part, such as in leaf and shoot, but not in root. For the test 11 tree species, the accumulation coefficients of Cd and Zn were all less than 0.2, while the translocation coefficients differed markedly, with that of Zn being higher than that of Cd in general.

Design and characteristics of refractive index sensor based on thinned and microstructure fiber Bragg grating.

A refractive index sensor based on the thinned and microstructure fiber Bragg grating (ThMs-FBG) was proposed and realized as a chemical sensing. The numerical simulation for the reflectance spectrum of the ThMs-FBG was calculated and the phase shift down-peak could be observed from the reflectance spectrum. Many factors influencing the reflectance spectrum were considered in detail for simulation, including the etched depth, length, and position. The sandwich-solution etching method was utilized to realize the microstructure of the ThMs-FBG, and the photographs of the microstructure were obtained. Experimental results demonstrated that the reflectance spectrum, phase shift down-peak wavelength, and reflected optical intensity of the ThMs-FBG all depended on the surrounding refractive index. However, only the down-peak wavelength of the ThMs-FBG changed with the surrounding temperature. Under the condition that the length and cladding diameter of the ThMs-FBG microstructure were 800 and 14 mum, respectively, and the position of the microstructure of the ThMs-FBG is in the middle of grating region, the refractive index sensitivity of the ThMs-FBG was 0.79 nm/refractive index unit with the wide range of 1.33-1.457 and a high resolution of 1.2 x 10(-3). The temperature sensitivity was 0.0103 nm/ degrees C, which was approximately equal to that of common FBG.