天水仙人崖石窟壁画颜料层原位-无损分析研究

壁画是我国极为重要的文化遗产类型,具有极高的历史价值、艺术价值、科学价值、文化价值和社会价值。颜料层作为壁画的核心价值所在,包含古代历史文化、宗教信仰、政治经济、科学技术等多方面的信息内涵。常规的颜料层分析方法有原位无损和微损取样两种,取样分析方法虽能满足这类珍贵、脆弱文物的研究,但获取样品数量有限且会对本体造成不可逆转的损伤。综合运用数字成像以及光谱等分析技术对天水仙人崖石窟壁画颜料层进行工艺与制作材料研究。结果显示,正射影像图能够真实记录壁画当前纹理信息,色度仪可以量化表征壁画颜料的颜色,红紫外摄影可以提取可见光下不易探查的壁画绘制线稿、修复痕迹等隐含信息,高倍数码显微镜可观察壁画表面的微观形态及破损处的层次信息,便携式X射线荧光光谱仪可检测出颜料中的元素由此判断主要显色元素,高光谱采集所得数据与标准图谱比较后能够准确判定颜料的矿物种类。因此,多种原位无损分析方法的联合运用,可以减少对文物的直接干预,亦可达到对壁画颜料层认知的目的。这些非接触式的无损检测方法,可精细化研究壁画颜料层的色彩、物理、化学属性等内容,是壁画现场分析的重要手段,可在石窟寺、寺观殿堂、墓葬壁画的研究上进行推广,发挥其应有之用。     

Nondestructive discrimination of internal defects in jujube (Huizao) of Xinjiang based on visible and near-infrared spectroscopy

Abstract

During harvest and transport, defects are most likely to affect the interior of jujubes and thus shorten their storage period. This study applied visible and near-infrared transmission spectroscopy to detect such internal defects. Spectra were acquired on the equator area at 0, 90, 180, and 270 degrees of each sample, and a model was constructed to obtain three-dimensional damage and defect detection model. The first derivative, multiplicative scatter correction, standard normal variate, and median filtering were used for preprocessing. Modeling by mean spectra achieved a better effect than using unidirectional spectra. Then, naive Bayes classifier and support vector machine were employed for the model establishment at 600–950?nm and 680–950?nm bands, respectively, using mean spectra. Median filtering effectively improved the signal to noise ratio and the discrimination accuracy of the support vector machine model at 600–950?nm reached 96.77%, which was the best value among all models. This result indicates that the support vector machine model was the optimum model and 600–950?nm was a suitable data range for the detection of internal defects. This research confirms the feasibility of implementing visible and near-infrared spectroscopy for the detection of internal defects in jujubes.     

偏置磁场对磁致伸缩纵向导波换能器效能的影响研究

为提高磁致伸缩导波换能器的激励效能,本文研究了磁场结构参数对偏置磁场空间分布的影响。基于COMSOL有限元仿真平台,对磁致伸缩换能器磁场分布特性进行了数值计算,研究了磁路结构形式、磁路和永磁铁数量等对偏置磁场分布的影响,最后优化出适合纵向导波激励的磁场结构参数。检测实验结果表明,随着偏置磁场磁路数量的增加,偏置磁场强度增大,磁场径向均匀性更好,磁致伸缩换能器的效能也相应提高;在相同磁路数量的条件下,永磁体数量的改变对换能器效能影响较小,四磁路偏置磁场最优;轭铁中部增加永磁铁后的磁路结构的偏置磁场的轴向均匀性更高,其激励效能更好。     

Optical method for determining the hardness of metals and alloys

We present an optical method for determining the hardness of metals, based on the correlation between the thermal diffusion coefficient and the hardness of the material. Spatial and temporal modulation localized in the nonstationary thermal wave profiles is transferred to the surface of the metal, where the time evolution of the speckle images produced by a probing laser beam is recorded by a CCD camera. A special algorithm for processing the speckle images allows us to determine the thermal diffusion coefficient. Experimental studies on steel samples confirmed the workability of the proposed method. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 3, pp. 460–465, May–June, 2009.     

低温微波近场显微镜及其在材料研究中的应用

微波近场技术是研究材料表面区域电磁性质的有效手段,结合低温技术则可将这种技术的应用拓展到更广的范围.本文报道了我们研制的低温扫描微波近场显微镜系统,它由微波近场显微镜和与之配合的可变温样品台构成,可以在液氮温度和室温之间工作.利用该系统我们详细研究了YBaCuO超导薄膜、NdSrMnO磁性薄膜在不同温度条件下的电磁性质,给出了相关实验结果.研究表明微波近场技术与低温技术的结合为电子材料和器件低温下局域电磁性质的研究提供了有力的手段.     

基于导波技术的螺柱轴力无损检测

根据弹性动力学理论,采用纵向导波与弯曲导波相结合的方法对螺柱所受轴向应力进行无损检测。计算了M22螺柱中纵向导波和弯曲导波的群速度频散曲线。根据频散曲线,确定了采用导波对螺柱轴向应力进行无损检测的最优检测信号频率范围(50~80 kHz),此频率范围的纵向导波与弯曲导波模态单一,并且频散性较低。分别计算了不同轴向应力σ作用下,多种频率的纵向导波和和弯曲导波在螺柱中传播的群速度值cgσrL和cgσrF。结果表明,随着轴向应力的增大,同频率纵向导波和弯曲导波的群速度皆呈线性递减趋势。利用纵向导波和弯曲导波群速度与轴向应力的线性关系及纵向导波和弯曲导波在轴向应力作用螺柱端面的反射时间tLσ和tσF,可以迅速确定螺柱所受轴向应力值。     

Embedded optical fiber Bragg grating sensor in a nonuniform strain field: Measurements and simulations

This paper investigates the use of embedded optical fiber Bragg gratings to measure strain near a stress concentration within a solid structure. Due to the nature of a stress concentration (i.e., the strong nonuniformity of the strain field), the assumption that the grating spectrum in reflection remains a single peak with a constant bandwidth is not valid. Compact tension specimens including a controlled notch shape are fabricated, and optical fiber Bragg gratings with different gage lengths are embedded near the notch tip. The form of the spectra in transmission varies between gages that are at different distances from the notch tip under given loading conditions. This variation is shown to be due to the difference in the distribution of strain along the gage length. By using the strain field measured using electronic speckle pattern interferometry on the specimen surface and a discretized model of the grating, the spectra in transmission are then calculated analytically. For a known strain distribution, it is then shown that one can determine the magnitude of the applied force on the specimen. Thus, by considering the nonuniformity of the strain field, the optical fiber Bragg gage functions well as an embedded strain gage near the stress concentration.     

Stress evaluation by pulse-echo ultrasonic longitudinal wave

In this paper, an activity aimed at developing an ultrasonic technique for evaluation of states of stress, and in the presence of gradients deriving from local effects of concentrated stress, is presented. The approach is based on the acoustoelastic effect in which ultrasonic wave propagation speed is linked to the magnitude of the stresses present. The technique developed calls for the use of longitudinal waves in pulse-echo technique that propagate in a direction perpendicular to the surface of the work piece. The technique has been applied in different experimental configurations on test specimens with concentration of stresses deriving from notches and fatigue cracks and has furnished encouraging results that highlight the potentiality of the method.     

蓝色圆珠笔字迹色痕傅里叶变换显微红外光谱法的无损分析

利用傅里叶变换显微红外光谱法中的微区衰减全反射采样技术无损测定了纸张上圆珠笔油墨所形成的字迹色痕,获得了１０种不同圆珠笔字迹的显微红外光谱图。结果表明,笔迹色痕的微区衰减全反射谱图可明显地识别色料和溶剂的结构组成;快速地分辨各生产厂家油墨的差异。同时,纸张的不同,字迹书写的深浅均可快速,准确地进行无损分析。     

Synchrotron Radiation Tomography for Reconstruction of Layer Structures and Internal Defects of Composite Materials

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