Frequency Modulation Multiplexing for Simultaneous Detection of Multiple Gases by use of Wavelength Modulation Spectroscopy with Diode Lasers

Modulation frequency multiplexing provides a straightforward method, analogous to television or radio broadcasting, for performing simultaneous detection of multiple gases by use of wavelength modulation spectroscopy with diode lasers. When fiber-optic coupled lasers are used, our approach guarantees that all beams transit the same optical path and impinge on the same detector. Each laser is modulated at a different frequency and the detector output is processed by a set of lock-in amplifiers, one for each laser, to measure the absorbance encountered by each laser.     

Measurements of NH(3) and CO(2) with Distributed-Feedback Diode Lasers Near 2.0 mum in Bioreactor Vent Gases

Measurements of NH(3) and CO(2) were made in bioreactor vent gases with distributed-feedback diode-laser sensors operating near 2 mum. Calculated spectra of NH(3) and CO(2) were used to determine the optimum transitions for interrogating with an absorption sensor. For ammonia, a strong and isolated absorption transition at 5016.977 cm(-1) was selected for trace gas monitoring. For CO(2), an isolated transition at 5007.787 cm(-1) was selected to measure widely varying concentrations [500 parts per million (ppm) to 10%], with sufficient signal for low mole fractions and without being optically thick for high mole fractions. Using direct absorption and a 36-m total path-length multipass flow-through cell, we achieved a minimum detectivity of 0.25 ppm for NH(3) and 40 ppm for CO(2). We report on the quasi-continuous field measurements of NH(3) and CO(2) concentration in bioreactor vent gases that were recorded at NASA Johnson Space Center with a portable and automated sensor system over a 45-h data collection window.     

微量特种气体的FT-IR定量分析

利用傅立叶变换红外光谱法对微量一氧化氮、二氧化氮、氧化亚氮、氨气、氯化氢、二氧化硫、二氯氢硅、三氯氢硅、四氯化硅等使用常规方法分析难度大、灵敏度不足、操作复杂的气体样品进行了定量分析.在恒定实验条件下进样,分辨率为4 cm-1,扫描8次,可以得到理想的分析结果.以氨气、一氧化氮和二氧化氮为例的定量分析结果表明,该方法重...     

Experience of Measurements with a Vibrating-Wire Viscometer on Natural Gases

A vibrating-wire viscometer designed for high-precision measurements on gases was applied to determine the viscosity coefficient of natural gases. The experiments were carried out at nominal temperatures of 260, 280, 300, and 320 K up to pressures of 20 MPa. A suitable experimental procedure had to be developed in order to minimize the influence of the retrograde behavior and the effects of adsorption and desorption that have to be expected in the thermodynamic range under study. As a consequence, the series of measurements could successfully be performed starting from vacuum followed by successive points up to the maximum pressure. The densities were calculated according to the ISO 12213 standard using the AGA-8 detailed characterization equation. The isotherms could adequately be represented with power series in density restricted to the fourth power. The reproducibility of the measurements was ±0.2 %, whereas the uncertainty is estimated to be ±0.5 %.     

用傅立叶变换红外光谱法检测气体中微量乙硼烷

利用配备长光程气体池的傅立叶变换红外光谱仪对气体中微量乙硼烷进行了定量分析。在恒定实验条件下进样,分辨率为4 cm~(-1),扫描8次,可以得到理想的分析结果。定量分析结果表明,该方法重复性良好(相对标准偏差0.5%),在0~100×10~(-6)摩尔分数范围内线性良好(R~2=0.9996),扩展不确定度小(4%),可用于气体中微量乙硼烷的定量分析。     

Measurements of Particulate (PM2.5), BC and Trace Gases Over the Northwestern Himalayan Region of India

Ambient trace gases (NH₃, NO, NO₂ and SO₂) and black carbon (BC) were measured along with particulate matter (PM_2.5) over the northwestern Himalayan region (Palampur, Kullu, Shimla, Solan and Nahan) of Himachal Pradesh (HP), India in a campaign mode during 12–22 March 2013 to evaluate the ambient air quality of the region. The average mixing ratio of ambient NH₃, NO, NO₂ and SO₂ were recorded as 7.1 ± 2.6, 3.1 ± 1.3, 3.9 ± 1.4 and 1.7 ± 0.7 ppb respectively over the northwestern Himalayan region. The average concentration of BC was estimated as 2.2 ± 0.5 µg m^?3 over the region whereas average concentration of PM_2.5 mass was estimated as 41.8 ± 7.9 µg m^?3. The spatial variation of ambient trace gases (NH₃, NO, NO₂ and SO₂), BC and PM_2.5 over the northwestern Himalayan region, India reveals that the region is mainly influenced by local activities, i.e., tourism activities, agricultural activities, biomass burning and vehicular emission. A significant positive linear correlation of NH₃ and NH₄ ⁺ with SO₄ ^2?, NO₃ ^? and Cl^? (NH₄ ⁺ vs. SO₄ ^2? , r ² = 0.652; NH₄ ⁺ vs. NO₃ ^?, r ² = 0.701; and NH₄ ⁺ vs. Cl^?, r ² = 0.627) of the PM_2.5 indicates the possible formation of (NH₄)₂SO₄, NH₄NO₃ and NH₄Cl aerosols over the region.     

Diode-Laser Wavelength-Modulation Absorption Spectroscopy for Quantitative in situ Measurements of Temperature and OH Radical Concentration in Combustion Gases

The in situ quantitative profiles of temperature and OH radical concentration in a postflame region of methane-air premixed counterflow flames were measured by wavelength modulation spectroscopy with a 1.5-mum external cavity diode laser. The second harmonic (2f) signal was generated from absorption by overtone vibrational-rotational transitions of OH: the ?(3/2) (v?, v?) = (2, 0) P11.5e (nu(0) = 6421.35 cm(-1)) or the ?(3/2) (v?, v?) = (3, 1) P5.5f (nu(0) = 6434.61 cm(-1)) transitions. The absorption occurred in the postflame region between methane-air premixed twin flames stabilized in a two-dimensional laminar counterflow burner (Tsuji burner) with a 60-mm line-of-sight path length. The temperature and OH concentration profiles at an equivalence ratio of phi = 0.85 were determined by least-squares fitting of theoretical 2f line shapes to the experimental counterparts and by calculation of the ratio of the line intensities of the two different OH transitions (two-line thermometry). The measured temperature and OH concentration profiles were cross checked by Rayleigh scattering thermometry, thermocouple measurements, and two-dimensional numerical prediction of premixed combustion by use of a detailed chemical kinetic mechanism. The measurements and the prediction showed reasonable agreement.     

Quantitative Analysis of Trace Moisture in N(2) and NH(3) Gases with Dual-Cell Near-Infrared Diode Laser Absorption Spectroscopy

This paper demonstrates our optical measurement system based on near-infrared tunable diode laser absorption spectrometry and reports the results of trace moisture determination in nitrogen and ammonia gases. A near-infrared InGaAsP distributed feedback diode laser operating at room temperature was employed as the optical source. We used a dual-cell detection strategy to cancel common mode noise from the diode laser and remove the effect of the residual moisture absorption in the beam path outside the sample cell. We also used this method to successfully eliminate the interfering absorption of matrix gas molecules such as NH(3). The detection limit of H(2)O absorption of 4 ppb in nitrogen and 12 ppb in ammonia was obtained using a single-pass absorption cell of only 92 cm in length and the average results of 10 scan measurements. This system has characteristics of both the high sensitivity and capability of in situ and real-time measurement.     

Hybrid Measurements of Image Histograms,with an Application to Texture Discrimination

Histograms of images show frequencies of occurrence of different grey levels in an image. Uses of such histograms include image encoding, defocus measurements and texture discrimination. Our three aims are to simplify the determination of histograms by measuring only a few moments of the histogram, to achieve fast hybrid electro-optical measurement of the moments and other statistical features, and to apply these measurements to texture discrimination.     

红外吸收光谱（NDIR）检测混合气体中二甲醚含量分析法

利用非分光红外吸收光谱法（NDIR）,采用中红外光源（波长：2．5—25μm）和主要包括样品气气阻、样品泵、红外吸收池和电路模块技术建立了混合气体中二甲醚气体成分光谱检测系统,并使用该系统对混合气体中的二甲醚气体成分进行了测量,得到了1．0×10^-2的检测灵敏度。整个光谱检测系统具有很好的光谱分辨率、选择性以及测量灵敏度,适用于各种混合气体中二甲醚气体成分的检测。     

高压气体终端净化技术在标准气体配制中的应用

介绍了气体高压净化技术在标准气体制备中的应用,随着标准气体制备难度加大及市场竞争加剧,该技术将得到广泛的应用。多年的实验结果表明该技术具有广阔的市场空间。     

论平衡记分卡在全面质量管理中的应用

将现代的战略管理工具平衡记分卡与传统的全面质量管理思想进行了比较分析,结果表明两者在很大程度上具有相似性和互补性,因此可以采用平衡记分卡帮助组织成功地实施全面质量管理,最后对平衡记分卡如何在全面质量管理中的应用进行了探讨.     

Application of Precision Connectors to High-Frequency Measurements

The availability of precision coaxial connectors which meet the specifications of the IEEE Subcommittee on Precision Coaxial Connectors has removed an important obstacle to the development of higher accuracy measurements systems over the frequency range from audio to 18 GHz. Some of the advances in techniques and standards which have resulted or are presently possible for measurements of impedance, VSWR, attenuation, phase, power, and dielectric properties of materials are reviewed. Problems relating to the connection of unknowns and standards to the terminals of an instrument are discussed with respect to measurements at audio frequencies, radio frequencies, and microwave frequencies.     

Noncontact, Nondestructive Evaluation of Realistic Cracks with Surface Acoustic Waves by Scanning Excitation and Detection Lasers

Nondestructive evaluation of surface-breaking cracks with a scanning laser source, a scanning laser probe, or a scanning laser pump–probe setup is discussed. Multimode scattering of laser-excited surface acoustic wave pulses by artificial slots, realistic fatigue, or impulsive cracks is considered. This includes measuring the size of cracks in the micrometer-to-millimeter range by optical recording of the complete displacement or velocity field around the crack. Results obtained with a scanning pump–probe setup for a partially closed microcrack, generated by an elastic shock pulse in silica, are compared with those achieved with a scanning source or scanning probe for machined open notches. Crack size analysis based on the frequency spectrum of the reflected Rayleigh wave and the time lag of the transmitted Rayleigh wave is discussed. Signal enhancement effects observed in the displacement and velocity field near the crack are studied.     

Depth of Field Measurements Relevant to Single Photon Detection Using Image-intensified Microscopy

The problems of defining a depth of field d _p when individual photons emitted in a low-level luminescent process are recorded via an image-intensified microscope are discussed. Simulation studies of a self-luminous cylindrical volume source whose axis lies along the optical axis of the microscope were carried out by moving a uniformly-illuminated pinhole along the optical axis, and arranging for its in-focus image to fill exactly a circular light detector. The detector output plotted against pinhole position is approximately Gaussian in form for the objectives studied (from 10 2 /0·25 to 74 2 /0·65), and d _p is defined as the full width at half maximum. These values of d _p adequately fit the theoretical relation d _p = 2·45 R/tan sin^-1(NA/n), where NA is the numerical aperture of the objective and n is the refractive index of the immersion medium. With spherical, or near-spherical, volume sources d _p is usually significantly greater than the volume of the source. The problems of defining a depth of field p when individual photons emitted in a low-level luminescent process are recorded via an image-intensified microscope are discussed. Simulation studies of a self-luminous cylindrical volume source whose axis lies along the optical axis of the microscope were carried out by moving a uniformly-illuminated pinhole along the optical axis, and arranging for its in-focus image to fill exactly a circular light detector. The detector output plotted against pinhole position is approximately Gaussian in form for the objectives studied (from 10 2 /0·25 to 74 2 /0·65), and d _p is defined as the full width at half maximum. These values of d _p adequately fit the theoretical relation d _p = 2·45 R/tan sin^-1(NA/n), where NA is the numerical aperture of the objective and n is the refractive index of the immersion medium. With spherical, or near-spherical, volume sources d _p is usually significantly greater than the volume of the source.     

基于BSC和ANP的企业综合绩效评价应用研究

以平衡计分卡法为基础构建了企业三级综合绩效评价体系,根据BSC中的因果关系链选择网络分析法ANP作为评价方法,一改以往评价指标独立、忽视它们之间联系的评价方法,从而体现出综合绩效评价体系中各维度指标之间相互影响、相互作用,最后给出了基于SD软件的部门绩效评价的实证研究.     

自适应滤波在车用发电机噪声测试中的应用

介绍车用发电机噪声的测试方法和特点,应用自适应滤波方法对车用发电机试验过程中所测得的发电机噪声与试验台背景噪声的混合信号进行分离研究,同时与独立分量分析（ICA）方法进行了比较。实验结果表明,用自适应滤波的方法能很好地把发电机噪声和背景噪声分离开来,从而使发电机生产厂家不必为控制噪声测试过程中的背景噪声而对其发电机试验平台进行改造,有效地解决了其产品噪声测试的难题。     

Application of Hologram Interferometry to Plate Deformation and Translation Measurements

The results of measuring the correlation of intensity fluctuations from two independent monochromatic light sources are given. The experiment is carried out in the region of strong fluctuations. It is shown that in this case the assumption of a gaussian field distribution leads to results essentially different from experiment.     

微粒群算法在无线电干涉测距定位中的应用

节点定位是无线传感网络的重要支撑技术.无线电干涉测距虽然测距精度高,但用遗传算法和迭代最小二乘算法进行节点定位的误差较大,本文针对这一问题.提出了基于微粒群算法的节点定位.该算法能够解决连续空间多维函数的优化问题,满足了基于无线电干涉测距节点定位的需要.仿真证明:该算法具有实现简单,运行稳定,计算误差小等优点.与其他常用节点定位技术相比,无线电干涉测距定位技术具有定位精度高,传播距离远,所需硬件设备少等优点.     

太阳能相变蓄热应用于吸收式制冷的研究

介绍了一种将太阳能相变蓄热技术应用于两级吸收式制冷的新型空调系统,简要分析了该系统的装置结构、工作原理和使用优点.对相变蓄热装置放热过程中放热盘管出水温度随放热时间的变化关系进行了实验测量,并对两级吸收式制冷系统效率进行了分析.通过研究可知,该太阳能空调系统有效解决了以往系统不稳定性和间断性问题;太阳能相变蓄热装置具有体积小、蓄热量大、放热速率大、连续放热温度均匀、便于控制热源加热温度等特点,适合储存太阳能并为吸收式制冷系统提供加热热源.综合考虑系统设备简单,加工要求低的制造特点,所以吸收式制冷以太阳能等低品位热源驱动有着良好的发展前景.