COMPARISON OF SINGLE AND DUAL-PHASE LOCK-IN AMPLIFIERS FOR PHOTOACOUSTIC SPECTROSCOPY

Dual phase lock-in is usually used in photoacoustic research because it allows precise projection of the measured spectra. In this article, double and single phase lock-in amplifiers were used and the advantages and disadvantages of both were compared. Two liquid crystals were studied in this work: ethylo- and penthylo-cyanobiphenyl in cyclohexane, tetrahydrofuran, and acetonitrile. The red-shift of the maximum related to the polarity of solvents and a bigger shift for 4-penthylo-4′-cyanobiphenyl relative to 4-ethylo-4′-cyanobiphenyl were observed. In order to investigate the usefulness of the single-phase device, compared to the more expensive double-phase device, the frequency dependence measurements and photoacoustic spectra were recorded and compared. Small differences were observed (within the limit of error) in spectra obtained using the single and the double lock-in amplifier. The simpler single-phase lock-in device can be used to reliably measure frequency spectra without any loss of information.     

IN VIVO PHOTOACOUSTIC SPECTROSCOPY OF LEAVES INFECTED BY FUNGAL AND VIRAL DISEASES

Abstract

The PA spectra of fungal and viral infected leaves were recorded at a modulation frequency of 17 Hz. The leaves of sugar cane (Saccharum officinarum L.), severely infected with a sheath blight, and the leaves of a mung bean (Vigna radiata L.), infected with yellow mosaic virus, exhibit a higher PA signal than the untreated, healthy leaves of same cultivars at all wavelengths examined. The ratio of photoacoustic signals obtained from diseased and healthy leaves in the UV region was higher, as compared to that in the visible region. In fungal infections, the higher PA signal was attributed to non-radiative de-excitation (heat emission). In case of viral infection, the signal appears affected by both O₂ evolution and heat emission. The PA spectra of leaves show that the heat emission due to non-radiative de-excitation exceeds the O₂ evolution. Additionally, the PA spectroscopy proved capable of differentiating between the healthy C-3 and C-4 leaves.     

MEASUREMENT OF RADIATION INDUCED LOCALIZED ABSORPTION IN CHROMATOGRAPHIC ELUENTS BY MEANS OF THE CO LASER AND THE PZT PYROELECTRIC DETECTOR

Abstract

Combined use of the CO laser and PZT piezoelectric detector is proposed as a sensitive and specific detector for gas chromatography. The feasibility of this detection scheme is demonstrated for a model mixture containing varying proportions of acetone in water. After separation on a GC column, spectra of both constituents were recorded in the 1600 cm^?1 to 1900 cm^?1 range that encompasses the characteristic frequency of C=O bond in acetone. Reasonably high sensitivity (mass concentration limit is 1.2x10^?8 g acetone) and a good degree (factor 530) of spectral discrimination was achieved by a proper selection of analytical wavelengths.     

DETECTION AND ANALYSIS OF WELD POOL SHAPE FOR CO2 SHORT CIRCUITING ARC WELDING

0 INTRODUCTIONIt is well known that skilled welding operatorscan estimate and control beam quality by mainlyobServing the weld POOl. This means the POOl im8gecontains abundant inforTnation during weldprocess. So that, sensing information from POOl imeqedirectly is becoming a new method to control the weldquality.Following the advances in computer vision andM camera tecbnoogy, more and more researchesusing weld opl image for sensing welding processeshave been carried out, usually in T…     

RAPID AND GROSS SCREENING FOR Pb3O4 ADULTERANT IN GROUND SWEET RED PAPRIKA BY MEANS OF PHOTOACOUSTIC SPECTROSCOPY

Abstract

The potential of photoacoustic (PA) spectroscopy as a candidate method for rapid detection of gross amounts of red lead (Pb₃O₄) adulterant in a ground sweet red paprika was demonstrated. Linear relationship between the magnitude of PA signal at 545 nm and the concentration of red lead was found within 10% (w/w) to 50% (w/w). The limit of detection of a present PA spectrometer is 2% w/w Pb₃O₄.     

金刚石砂轮的CO2脉冲激光修锐研究

利用CO2激光对树脂结合剂金刚石砂轮片的表面进行了扫描试验,对扫描前后砂轮片的表面三维形貌进行了测试分析,研究了激光脉冲频率和占空比等参数的影响。结果表明,尽管平均扫描能量密度一定,但频率和占空比对修锐效果均会产生影响,其中频率的影响更为显著。同时,通过使用铝工件和砂轮片的相对刻划试验,对不同扫描条件下刻划时的切向力与法向力之比进行了对比分析,发现由于该力比可以有效地反映出砂轮片的切削性能,因此可以用来对修锐效果进行定量评价。     

调Q脉冲CO2激光切割Si3N4工程陶瓷的机理研究

采用调Q脉冲CO2激光器对Si3N4工程陶瓷进行了切割试验.在计及切口烧蚀前沿形状和高斯光束空间能量分布的前提下,采用简化的二维模型,针对气化切割过程,在能量平衡基础上,建立了一个脉冲激光切割数学模型.试验结果表明,采用高速多次重复走刀工艺可实现无损伤激光切割.     

纳米Al2O3/PS复合材料选区激光烧结成形域及力学性能

在前期研究确认激光功率P和扫描速度v对成形粉末NH1的选区激光烧结(Selective laser sintering,SLS)成形性具有显著性影响的基础上,重点研究P和v对NH1粉末的SLS成形性的影响,研究发现当P较小、v较快时,SLS烧结件结构不致密,强度较低;当P较高、v较慢时,SLS试件容易着火和翘曲变形;只有合理匹配P和v(即处在成形区内),才能直接制备出变形较小、密度较高的烧结件.同时对相同工艺条件下的Al2O3/PS纳米复合材料与纯聚苯乙烯SLS试件的缺口冲击吸收功进行比较,结果表明纳米复合材料的缺口冲击吸收功提高20%～50%,其最大值达到10.5 kJ/m2.利用场发射扫描式电子显微镜(FE-SEM)对NH1和纯PS(Polystyrene)粉SLS试件的断面进行微观结构分析,结果表明核壳式纳米Al2O3/PS复合粒子改善纳米氧化铝表面与聚苯乙烯极性的差异,纳米Al2O3在基体中分散性良好,且很好地起着增强增韧的效果.     

ON LINE MONITORING OF BURNING THROUGH FOR SHORT CIRCUIT CO2 ARC WELDING BASED ON THE SELF-ORGANIZE FEATURE MAP NEURAL NETWORKS

0　ＩＮＴＲＯＤＵＣＴＩＯＮＡｍｏｎｇｔｈｅｖａｒｉｅｔｙｏｆｆｕｓｉｏｎｗｅｌｄｉｎｇｐｒｏｃｅｓｓｅｓａｖａｉｌａｂｌｅ,ｓｈｏｒｔｃｉｒｃｕｉｔＣＯ2 ａｒｃｗｅｌｄｉｎｇｉｓａｔｅｃｈｎｏｌｏｇｙｗｈｉｃｈｉｓｏｎｅｏｆｔｈｅｍｏｓｔｆｒｅｑｕｅｎｔｌｙｕｓｅｄｍｅｔｈｏｄｉｎａｗｉｄｅｒａｎｇｅｏｆａｐｐｌｉｃａｔｉｏｎｓａｎｄａｌｓｏａｕｔｏｍａｔｉｏｎｂｅｃａｕｓｅｏｆｉｔｓｖｅｒｓａｔｉｌｉｔｙａｎｄｃｏｓｔｅｆｆｅｃｔｉｖｅｎｅｓｓ.Ｔｈｅｒｅｆｏｒｅ ,ｓｔｕｄｙｏｎｔｈｅｐｒｉｎ…     

短路过渡CO2焊接熔滴形状数值模拟与控制

为了进一步提高短路过渡CO2气体保护电弧焊的工艺性能和焊接质量,根据高速CCD摄像获得的熔滴及其短路过渡图像,分析了熔滴与熔池短路前的形状对熔滴与熔池的短路、熔滴在熔池中的铺展及液桥缩颈形成的影响.采用熔滴静力平衡模型研究了电磁力(燃弧电流)、表面张力、重力与熔滴形状的关系,并通过对燃弧电流的精确控制实现了对熔滴形状的有效控制.当熔滴与熔池短路前为细长形状时,短路过渡过程稳定柔顺,而当熔滴为扁平形状时,则不利于熔滴的短路过渡,甚至产生瞬时短路.燃弧阶段的熔滴形状体现了各种力对熔滴的作用,而电磁力(燃弧电流)是决定熔滴形状的主要因素.根据燃弧电流对熔滴形状的影响规律,提出了采用前期大、后期小的燃弧电流控制原则,以在燃弧的不同阶段获得不同的熔滴形状.试验结果表明该控制方法获得了良好的适合于熔滴短路过渡的短路前熔滴形状,短路过渡过程柔顺稳定,消除了瞬时短路以及由此导致的飞溅,改善了熔滴的短路过渡行为,短路过渡结束后焊丝端部的残余液态金属具有良好的一致性.     

DETERMINATION OF COPPER(II) IN NATURAL WATERS BY EXTRACTION USING N-O-VANILLIDINE-2-AMINO-P-CRESOL AND FLAME ATOMIC ABSORPTION SPECTROMETRY

A simple and accurate solvent extraction method was developed for the separation and preconcentration of trace levels of copper(II) in water using N-o-vanillidine-2-amino-p-cresol prior to its determination using flame atomic absorption spectrometry. Analytical parameters such as the pH of the aqueous phase, extraction time, concentration of the reagent, concentration of the nitric acid back extraction agent, volumes of aqueous phase and back extraction agent, and concomitant ions on the extraction yield of the copper(II) were investigated and optimized. Under the optimal conditions, the detection limit (3σ) was 0.61 µ g L^?1 for a 25 mL blank solution, yielding a preconcentration factor of 12.5. The method was succesfully applied to the determination of copper(II) in tap water, river water, and seawater. The accuracy of the method was verified by analyzing two certified reference materials and spiked water samples. The results obtained were in agreement with the certified values and the recoveries for spiked water samples were between 98 and 112%.     

温度对X65管线钢CO2腐蚀产物膜结构和力学性能的影响

利用SEM、XRD、能谱仪对不同温度下形成的腐蚀产物膜的形貌、厚度、结构和成分进行分析,利用纳米压痕仪测量腐蚀产物膜的硬度和弹性模量.结果表明,温度对腐蚀产物膜的表面形貌没有明显影响.在65℃到90℃温度范围内,温度对腐蚀产物膜的晶粒尺寸影响不大;115℃时,膜表面的晶粒尺寸不均匀,差别较大.温度对腐蚀产物膜的厚度影响较大,在65℃到115℃温度范围内,随着温度的升高,腐蚀产物膜的厚度降低;温度对腐蚀产物膜的表面成分影响不大,不同温度下膜的表面成分均为(Fe,Ca)CO3复盐;在65℃到90℃温度范围内,随着温度的升高,腐蚀产物膜的硬度和弹性模量降低,在90℃时出现最低值,温度升高至115℃,膜的硬度和模量又明显升高.