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Three bias errors in the measurement of structural intensity

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Chinese Journal of Acoustics 1996年第4期15卷 341-349页

作者： MING Ruisen(Department of Architecture, Zhejiang University Hangzhou 310027)

There are many possible bias errors in the measurement of structural intensity and some of them have been theoretically examined. Attempting to analyse all the bias errors at the same time results in a very complicated analysis and makes it difficult to draw clear *** bias errors are usually analysed individually. In this paper a theoretical study of three bias errors in the measurement of structural intensity is presented by using the twor-accelerometer array technique. It is assumed that the physical and material properties of the test structure are known. The analysis will be restricted to one-dimensional beams, but it can be extended to two-dimensional plates.

关键词： Structural intensity Two-accelerometer array technique bias error

THE ESTIMATE AND MEASUREMENT OF LONGITUDINAL WAVE INTENSITY

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Acta Mechanica Sinica 1996年第3期12卷 251-262页

作者：明瑞森 Department of Architecture Zhejiang University Hangzhou 310027 China

Quasi-longitudinal waves are one type of structural waves, which are important at high frequencies. This paper studies the estimate theory and measurement technique of quasi-longitudinal waves, analyzes the bias error due to the effect of bending waves. In a two-dimensional quasi-longitudinal wave held, the intensity vector is the sum of the effective intensity vector and the intensity variation vector. Its axial component is proportional to two imaginary parts of cross spectral densities and in the measurement, it is measured by a pair of two-transducer arrays. In a one-dimensional quasi-longitudinal wave field, the intensity variation is zero, the intensity is proportional to only one imaginary part of a cross spectral density and it can be measured using a two-transducer array. If bending and quasi-longitudinal waves coexist and the contribution from bending waves cannot be eliminated or reduced to a certain extent, the measured quasi-longitudinal wave intensity will contain a large error. The results measured on the three-beam structure show that quasi-longitudinal wave intensity can be accurately measured using the intensity technique when bending waves are negligible in comparison with quasi-longitudinal waves.

关键词： quasi-longitudinal wave intensity power flow bias error measurement technique

Establishment and Evaluation of a Method for Analyzing Atmospheric Volatile Organic Compounds

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Advances in Atmospheric Sciences 2007年第4期24卷 679-687页

作者：孙扬王跃思修天阳王迎红徐新 Institute of Atmospheric Physics Chinese Academy of SciencesBeijing 100029

An automated cumulative sampling system and a method that combines a two-step cryo-concentrated system and gas chromatography/mass spectrometry （CCS-GC/MS） are introduced. The method is evaluated by a set of special experiments and the results are presented. The lowest measurement detection limit was expanded from 10^-6 nmol mol^-1 to 10^-12 nmol mol^-1 by using CCS-GC/MS instead of the simpler method of gas chromatography/mass spectrometry （GC/MS）, with the average responsible factor of 39 object compounds being 2.9 × 10^-12. When the volume of air sample reached 1000 cm^3, the lowest detection limit reached up to 7 × 10^-12-40 × 10^-12 nmol mol^-1. The CCS-GC/MS method can potentially identify all objective chemical species in an atmospheric sample, with an average 2.5 s bias error of retention time for 39 gas chromatography （GC） peaks. Within the range 0-400×10^-9 nmol mol^-1, the concentration of 39 kinds of objective compounds can be individually calculated very accurately by a standard curve [average r^2 （coefficient of determination） value of above 0.99]. The recovery efficiency was 88%-111%, with an average of 100.8% ±5.6%. The bias error of precision was 2%-14%, with an average of 6.6%.

关键词： atmosphere cryo-concentration volatile organic compounds (VOCs) evaluation bias error