2.0 μm处CO2高温谱线参数测量研究

研究高温下待测气体的谱线属性, 如谱线强度、自加宽系数、空气加宽系数、温度系数等, 为高温环境中可调谐半导体激光吸收光谱技术反演温度、浓度、速度及其场分布提高精度和可靠性起着十分重要的作用. HITEMP数据库中的数据基本上是理论计算结果, 与实际情况存在相当的误差. 为了获得所选2.0 μm处的可用于燃烧诊断的CO₂谱线参数, 本文采用半导体激光器作为光源, 结合实验室的高温测量系统, 记录了700–1300 K温度范围内所选谱线的高温吸收光谱, 获得了各谱线在相应温度下的谱线强度、自展宽系数及温度系数等谱线参数. 测量得到CO₂的5006.978 cm^-1和5007.7874 cm^-1谱线强度与理论计算值相对误差小于11%; 获得了现有数据库缺少的温度系数和高温下自展宽系数数据. 所有各项参数对以后将要进行的燃烧诊断中的CO₂浓度检测有很大帮助. 关键词： 可调谐半导体激光吸收光谱 高温光谱 自展宽系数 温度系数     

结合环境参数修正的高温气体光谱检测系统设计

随着工业化进程加快，大气污染监控已受到广泛关注，为实现工业过程痕量气体浓度的准确监测，采用可调谐半导体激光吸收光谱技术(TDLAS)搭建了气体浓度在线监测系统，并以LabVIEW为软件开发平台完成了可视化界面。重点设计了数据处理功能及浓度反演算法，通过同步获取的环境压力参数对特征吸收光谱的有效拟合范围进行修正，提高吸光度信号的准确性，再通过读取的环境温度参数修正气体吸收线强以获得精确的浓度结果。将该系统应用于高温氨浓度在线测量实验中，获得高温不同压力下的氨气浓度测量结果。实验结果表明，在500 K温度下，不经过压力、温度参数修正的最大氨浓度反演偏差为18.81%，通过参数判断后再进行光谱提取和修正，得到浓度最大偏差为3.96%。该系统能够准确反演不同环境参数(压力、温度)下的气体浓度，实现了工业高温现场气体的实时、精确在线测量。     

利用波长调制光谱技术测量高温环境中的气体压强、温度和H_2O组分浓度

利用基于可调谐半导体激光器的扫描波长调制光谱技术,实现了高温燃烧场内气体参数的测量。提出了基于迭代算法实现气体压强、温度和组分浓度同时测量的方法,迭代算法具有收敛速度快以及对初始值不敏感等优点。采用频分复用技术,利用两条H_2O吸收谱线(7 454.45和6 806.03cm-1)的谐波信号,对高温燃烧场进行了实验研究,并将气体压强、温度和H_2O组分浓度测量结果与压力传感器、热电偶和直接吸收光谱法的测量结果进行比较,结果表明,基于波长调制光谱技术测得的气体压强、温度和H_2O浓度与预测值基本符合,最大偏差分别在7.6%,8.1%和7.5%以内。此方法具有多参数同时测量、免标定等显著优势,但由于依赖的参数较多,容易对测量精度造成影响。     

基于时分复用技术的吸收光谱气体温度在线测量研究

可调谐半导体激光吸收光谱技术是一种具有高灵敏度、高选择性的非接触式气体在线测量技术。通过直接扫描多条H2O特征谱线并结合最小二乘算法实现对开放环境气体温度的在线测量。利用HITRAN光谱数据库详细讨论了边界效应对气体温度浓度测量的影响,计算结果表明,扫描多特征谱线并结合最小二乘算法可有效减小边界效应对开放环境气体温度测量的影响。实验中采用时分复用技术同时扫描了7 444.36,7 185.60,7 182.95和7 447.48cm-1四条H2O特征谱线,对管式炉573～973K范围内不同工况下的气体温度进行了测量。吸收光谱测量结果与热电偶信号的最大温差小于52.4K,温度测量最大相对误差为6.8%。     

基于TDLAS技术的水汽低温吸收光谱参数测量

精确的气体光谱参数对气体浓度、温度等的光谱精确反演测量具有十分重要的意义,针对当前主流光谱数据库(例如HITRAN)中数据与实际数值存在相当误差的问题,自主研制了一套基于静态冷却技术的低温光谱实验平台,用于精确测量低温下的气体吸收光谱参数.运用该低温光谱实验平台,采用可调谐二极管激光吸收光谱(TDLAS)技术测量了温度为230—340 K、压强为10—1000 Pa时7240—7246 cm~(-1)波段的纯水汽振转跃迁光谱.采用Voigt线型多峰拟合方法,获得了5条水汽振转跃迁谱在不同温度、不同压强下的积分吸光度值及洛伦兹展宽值,运用线性拟合的方法得到这5条吸收线的自展宽半峰全宽系数及参考温度下的线强值.运用不确定度传递公式,计算得到实验结果的不确定度,与HITRAN2012数据库中的线参数进行对比,所测的5条吸收线中实验结果与数据库值最大相差10.96%,且实验结果的不确定度为1.11%—2.98%(置信概率p=95%,包含因子k=2),小于HITRAN2012数据库值的不确定度.     

固定波长激光直接吸收方法同时测量高温CO气体的温度与浓度

针对可调谐半导体激光吸收光谱技术(TDLAS)需要在整个谱线上扫描导致扫描过程中可能存在其他谱线干扰以及测量速度较慢的问题,提出了固定波长激光直接吸收测量方法。该方法采用固定波长下的直接吸收计算气体浓度,完全避免了谱线干扰的问题,并且提高了测量速度,尤其适合于动态燃烧化学反应的研究。通过在气体吸收池中对不同工况下的CO气体的温度以及浓度进行了测量,验证了方法的准确性,说明这种固定波长激光直接吸收测量方法同TDLAS方法一样可以应用于气体浓度和温度的测量。     

6611-6618cm~(-1)之间氨气光谱线强的测量

在可调谐半导体激光吸收光谱(TDLAS)技术中,目标气体分子的吸收光谱参数,尤其是线强对温度、浓度的精确反演测量具有重要作用.HITRAN/GEISA/HITEMP等数据库中的光谱参数包含理论计算的结果,与实际情况存在相当的误差.本文采用TDLAS-波长扫描直.接吸收技术测量了室温下氨气在6611—6618 cm~(-1)之间的吸收光谱,利用Voigt线型多峰拟合方法获得了20条谱线在不同压强下的积分吸光度值,将获得的不同压强下的积分吸光度值进行线性拟合计算测量温度下的线强值,同时通过不确定度分析及误差传递计算了实验钱强值的不确定度.通过与HITR.AN 2012数据库中值进行对比,得出氨气在6611—6618 cm~(-1)波段实验线强值与数据库中值相差0.51%—17.28%,且实验线强值的不确定度在0.81%—3.3%范围,小于HITRAN2012中线强的不确定度5%—10%范围.     

可调谐二极管激光吸收光谱法测量气体温度

研究了一种新型的非接触式测温技术——可调谐二极管激光吸收光谱(TDLAS)测温技术。介绍了温度测量及调制吸收光谱技术原理,分析了调制幅度对气体温度测量的影响。优选了氧气吸收谱线对13163.78 cm-1和13164.18 cm-1,在搭建的高温实验系统上,实现了气体温度和浓度的同时测量。通过分析实测波形获得了谱线13164.18 cm-1在823~1323 K温度范围内的碰撞展宽系数和温度指数。实验结果表明,在823~1323 K温度范围内,系统温度测量的线性误差为0.65%,最大波动为±15 K。     

可调谐半导体激光吸收光谱法对高温甲烷的测量研究

可调谐半导体激光吸收光谱(TDLAS)是一种具有高灵敏度、高分辨率、快速检测特点的气体检测技术,已广泛用于大气中多种痕量气体的检测以及地面的痕量气体和气体泄漏的检测。研究了利用TDLAS技术测量高温下甲烷浓度的实验方法,使用可加热的静态吸收池对在1653.72nm波长附近R(3)支转动跃迁的吸收线进行了测量,并计算了吸收线强。分别在相同温度不同浓度和相同浓度不同温度的两种条件下进行了实验。结果表明,利用直接吸收的方法,在实验室可以得到370K时的最小可探测限为100×10-6,500K时的最小可探测限为245×10-6(吸收池长度为10cm),可以应用在燃烧控制及喷焰气体浓度测量等多个领域。     

大气中水汽柱浓度的直射太阳光红外吸收光谱遥测研究EI北大核心CSCD

研制了一种地基傅里叶变换红外光谱遥测系统,自动记录了晴天的太阳近红外吸收光谱,从该光谱中实时获得了整层大气透射率,进而采用最优化方法从该透射率中反演出了测量站点地区大气中2011年10月17日到2013年3月6日期间的整层水汽柱浓度含量。由该地基遥感技术获得的高时间分辨率整层水汽柱浓度与太阳辐射计的测量结果相比较,两者具有较好的一致性,相关系数达92%。测量站点地区的水汽柱浓度日变化很大并且没有明显周期性,日变化的复杂特征与多种因素有关。由于大气环流、季节温度变化等因素影响,测量站点地区水汽柱浓度呈现出明显季节周期特征,夏季明显高于冬季。这些结果对于水汽探测和分析方法的研究应用具有重要意义。     

Self-organization of five species in a cyclic competition game

Cyclic competition game models, particularly the “rock–paper–scissors” model, play important roles in exploring the problem of multi-species coexistence in spatially ecological systems. We propose an extended “rock–paper–scissors” game to model cyclic interactions among five species, and find that two of the five can coexistent when biodiversity disappears, which is different from the “rock–paper–scissors” game. As the number of fingers is five, we named the new model the “fingers” game, where the thumb, forefinger, middle finger, ring finger, and little finger cyclically dominate their subsequent species and are dominated by their former species. We investigate the “fingers” model in two ways: direct simulations and nonlinear partial differential equations. An important finding is that the number of species in a cyclic competition game has an influence on the emergence of biodiversity. To be specific, the “rock–paper–scissors” model is in favor of maintaining biodiversity in comparison with the “fingers” model when the variables (population size, reproduction rate, selection rate, and migration rate) are the same. It is also shown that the mobility and reproduction rate can promote or jeopardize biodiversity.     

Contrastive analysis on tone between Putonghua and Taiwan Mandarin

The differences of the pitch and duration of Chinese syllables between Putonghua （PTH） and Taiwan Mandarin （TM） were studied. The speech materials to be used are not only isolated syllables, but also sentences. The results reveal that： For the isolated syllables, T1 and T2 in TM are influenced by Minnan dialect, therefore their pitch are lower than those in PTH. T3 is fall-rise in PTH, while it is fall in TM. Moreover, the syllable duration sequence for different tone is T3〉T2〉T1〉T4 in PTH, while it is T1〉T2〉T3〉T4 in TM. For the syllables in sentences, T2 is mid-rise in PTH, while it is mid-level in TM. And the T3 is longer than T4 but shorter than T1 or T2 in PTH, while it is the shortest in TM. Furthermore the effects of prosodic phrase boundary on duration for different tones are almost the same in PTH, but the lengthening part of T1 or T2 is longer than that of T3 or T4 in TM.     

Experimental study on downstep in Chinese intonation

Downstep in pitch contour of Chinese Putonghua is examined using subtly designed sentences by controlling tone combinations. The results show both automatic and nonautomatic downstep phenomena exist in Chinese. In non-automatic downstep, low tones compress downwards the pitch range of the following syllables. and the main influence of downstep is on topline. Low tone not only lower the topline behind it, but also raise the high tones before it, the effects are compatible with each other. In automatic downstep, the topline of pitch contour in intonational phrase is presented as a linear downtrend, but it differs among speakers due to the effect of personal stress practice. In comparison with downstep phenomenon in other tone or non-tone languages, the downstep ratio in Chinese is not constant, and the domain of downstep is not limited within the adjacent tones.     

Abelian-Higgs phase of SU(2) QCD and glueball energy

It is shown that SU(2) QCD admits an dual Abelian-Higgs phase, with a Higgs vacuum of a type-Ⅱ superconductor. This is done by using a connection decomposition for the gluon field and the random-direction approximation. Using a bag picture with soft wall, we presented a calculational procedure for the glueball energy based on the recent proof for wall-vortices [Nucl. Phys. B 741(2006)1].     

Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

A multi-conjugate adaptive optics （MCAO） can offer a possibility of widening field of view （FOV） characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle＇s expressions of two deformable mirrors （DMs） MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.     

Quick single-photon detector with many avalanche photo diodes working on the time division

Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.     

Signal generation in an isotropic medium in scanning electron acoustic microscope

Based on the research in Ref. [5][Materials Science and Engineering, 1989; A122： 57 63], an improved model of heat source is set up, the different modes of Lamb wave in an isotropic sample generated by a chopped electron beam at frequency f are obtained with integral transform and normal function expansion method, and the output signal of PZT coupled at the back surface of the sample is found out. The generation mechanism of SEAM （Scanning Electron Acoustic Microscopy） signal is discussed. It shows that the SEAM is a near field imaging technique with high spatial resolution and its best lateral spatial resolution is about 2√2α （α is the radius of the focused electron beam）. Some of experimental results of SEAM images are presented in the paper and it shows that the spatial resolution of SEAM is better than 0.5 μm and smaller than the thermal diffusion length of the sample. Therefore the character of near field imaging in SEAM is also proved experimentally.     

High efficiency filtering using two-dimensional photonic crystal coupled cavity structures

Transmission spectra of coupled cavity structures (CCSs) in two-dimensional (2D) photonic crystals (PCs) are investigated using a coupled mode theory, and an optical filter based on CCS is proposed. The performance of the filter is investigated using finite-difference time-domain (FDTD) method, and the results show that within a very short coupling distance of about 3λ, where λ is the wavelength of signal in vacuum, the incident signals with different frequencies are separated into different channels with a contrast ratio of 20 dB. The advantages of this kind of filter are small size and easily tunable operation frequencies.