Moiré topography in odontology

For several decades, measurement of optical techniques has been used in different branches of science and technology. One of these techniques is the so-called moiré topography (MT) that enables the accurate measurement of different parts of the human body topography. This investigation presents the measurement of topographies of teeth and gums using an automated system of shadow moiré and the phase shift method in an original way. The fringe patterns used to compute the shape and the shape matrix itself are presented in the article. The phase shift method ensures precisions up to the order of microns. Advantages and disadvantages of using the MT are included. Besides, some positive and negative aspects concerned with the implementation of this technique in odontology are shown in the article.     

Variations on the chemical shift of TMS

The chemical shift of TMS is commonly assumed to be zero. However, it varies by over 1 ppm for 1H and 4 ppm for 13C and shows a correlation with the physical properties of the solvent. Using the commonly accepted convention that TMS always resonates at zero leads to significant errors when comparing chemical shifts in different solvents. A new method for measuring absolute chemical shift with a conventional NMR spectrometer is demonstrated. The observed chemical shift is corrected by measuring and correcting for susceptibility and shape factor. Practical suggestions are made for modifying the current chemical shift standard while maintaining compatibility with earlier literature.     

直流磁化测量中样品长度修正因数的分析

本文基于磁化电流在空间中磁场分布的计算,对不同长度的超导样品在测量线圈中真正排磁通作了分析,导出简单、明瞭的由检测线圈参数和样品长度所决定的修正因数。并将BiPbSrCaCuO高温单相样品截成不同长度,进行实验验证,实验结果与本文中的分析符合得较好。为小截面超导样品绝对抗磁矩的测量和计算提供了一种准确的分析方法。 关键词：     

偏心测量系统驱动机构的改进设计

偏心距是弹箭飞行稳定性的重要影响因素,其精确测量是保证弹道计算正确性的关键。为了解决某些特殊外形的弹体,在利用偏心测量系统测量偏心时,驱动弹体精确转动的机构出现卡滞、打滑等现象,导致无法自动测量的问题。本文结合系统偏心距测量的原理和试验操作步骤,分析了测量过程设备存在的不足及产生原因,提出了改进支撑和用减速伺服电机增加旋转力矩的方案,并进行了详细地设计及计算。验证结果表明,改进后的系统可以有效解决电机直驱不规则弹体时出现的问题,测量精度提高了4.15倍。扩大了测量范围,提高了驱动精度和测量效率,具有很好的应用价值。     

High-accuracy determination of water vapor refractivity by length interferometry

Humidity is the most problematic parameter for the accurate determination of the refractive index of air. Besides the fact that the humidity measurement can be limiting, the existing empirical equations for the refractive index of moist air are either restricted to 20 degrees C or are based on insufficient knowledge of the refractivity of water vapor. To overcome this problem, a new kind of measurement method for the refractivity of water vapor is suggested that is based on the accurate measurement of the absolute length of a step length by interferometry under vacuum conditions and subsequent measurements at different well-defined absolute water vapor pressures.     

Accurate determination of anisotropic thermal conductivity for ultrathin composite film

Highly anisotropic thermal conductive materials are of significance in thermal management applications. However, accurate determination of ultrathin composite thermal properties is a daunting task due to the tiny thermal conductance, severely hindering the further exploration of novel efficient thermal management materials, especially for size-confined environments. In this work, by utilizing a hybrid measuring method, we demonstrate an accurate determination of thermal properties for montmorillonite/reduced graphene oxide (MMT/rGO) composite film with a thickness range from 0.2 μ m to 2 μ m. The in-plane thermal conductivity measurement is realized by one-dimensional (1D) steady-state heat conduction approach while the cross-plane one is achieved via a modified 3ω method. As-measured thermal conductivity results are cross-checked with different methods and known materials, revealing the high measurement accuracy. A high anisotropic ratio of 60.5, independent of composite thickness, is observed in our measurements, further ensuring the negligible measurement error. Notably, our work develops an effective approach to the determination of ultrathin composite thermal conductivity, which may promote the development of ultrathin composites for potential thermal-related applications.     

Scanning of skin gloss by a diffractive optical element-based handheld glossmeter

Skin specular gloss (referred to as “gloss’’) determination is important in dermatology and cosmetic industry as it gives an indication of the skin health and beauty. Its accurate determination is, therefore, necessary. Commercially available glossmeters typically employ large incidence angle geometry, large illumination area, and fixed point measurements making them impractical regarding measurement of curved and complex non-planar objects or surfaces as well as low gloss regime such as the skin. In this study, we have demonstrated the novel application of a diffractive optical element-based handheld glossmeter with scanning capability, overcoming the disadvantages of conventional glossmeters, in the accurate determination of skin gloss and gloss profile for different skin types under different measurement conditions. Different parts of the body (back of the hands, the inner part of the arm and the forehead) of four volunteers with light, dark and intermediate skin types were scanned (also in different directions) to obtain the skin gloss profile and the statistical average skin gloss. Additionally, the skin surface was modified by arm extension and scanned as well. Our preliminary results showed that the statistical average skin gloss reading increased with the increasing lightness of skin. Areas with higher sebaceous glands (forehead) showed higher gloss reading than the other body parts (inner arm and back of the hand). However, the roughness of the skin surface decreased the statistical average skin gloss reading. The handheld scanning skin glossmeter allows for the accurate determination of skin gloss with sensitivity to small variation in the skin surface roughness with high repeatability.     

J-modulated ADEQUATE (JM-ADEQUATE) experiment for accurate measurement of carbon-carbon coupling constants

A new method for the accurate determination of carbon-carbon coupling constants is described. The method is based on a modified ADEQUATE experiment, where a J-modulated spin-echo sequence precedes the ADEQUATE pulse scheme. The J-modulation and scaling of carbon-carbon couplings is based on simultaneous incrementation of 13C chemical shift and coupling evolution periods. The time increment for the homonuclear carbon-carbon coupling evolution can be suitably scaled with respect to the corresponding increment for the chemical shift evolution. Typically a scaling factor of 2 to 3 is employed for the measurement of one-bond coupling constants, while multiplication by a factor of 10 to 15 is applied when small long-range couplings are determined. The same pulse scheme with coupling evolution period optimized for one-bond or long-range couplings allows the determination of the corresponding carbon-carbon coupling constants. The splittings of the ADEQUATE crosspeaks in the F1 dimension yield the appropriately multiplied coupling constants.     

高精度数字式相位差测量系统设计

在测量各种双口网络电路的频率特性时,需要对它们的输入与输出信号之间的相位差进行准确测量,针对采用示波器测量相位差误差较大的问题,提出一种能对信号相位差进行高精度测量的设计方案;系统采用过零鉴相和填充计数的测量原理,利用可编程逻辑器件的高速运算能力对高速脉冲计数,由单片机对工作电路进行协调控制和数据处理显示;同时设计高精度相位差可调的直接数字频率合成信号源对系统进行测试,实际测试结果显示,系统对相位差的测量精度高,最小测量精度可达0.1o,并实现宽频率范围的相位差测量。系统在实际应用中测量结果准确、稳定、可靠。     

Nondestructive determination of film thickness with laser-induced surface acoustic waves

The application of surface acoustic waves(SAWs) for thickness measurement is presented. By studying the impact of film thickness h on the dispersion phenomenon of surface acoustic waves, a method for thickness determination based on theoretical dispersion curve v( fh) and experimental dispersion curve v( f) is developed. The method provides a series of thickness values at different frequencies f, and the mean value is considered as the final result of the measurement. The thicknesses of six interconnect films are determined by SAWs, and the results are compared with the manufacturer's data.The relative differences are in the range from 0.4% to 2.18%, which indicates that the surface acoustic wave technique is reliable and accurate in the nondestructive thickness determination for films. This method can be generally used for fast and direct determination of film thickness.     

Macroscopic background gradient and radiation damping effects on high-field PGSE NMR diffusion measurements

The effects of macroscopic background gradients due to susceptibility differences at the sample interfaces and of radiation damping on pulsed-gradient spin-echo (PGSE) experiments are examined. Both phenomena can lead to the seemingly strange effect of the echo signal growing as the gradient strength increases at low applied gradient strengths. For a freely diffusing species, background gradients manifest themselves as slight concave or convex inflections in the linearized PGSE attenuation curve, depending on the polarity of the applied gradient. The various means of overcoming macroscopic background gradient problems, including bipolar gradients, and their efficacy are examined experimentally and discussed. The effects of radiation damping can also result in the attenuation curve being nonlinear but, different from the effect of background gradients, the nonlinearity does not change with the polarity of the applied gradient. The vulnerability of the stimulated echo-based PGSE sequence and variations of Hahn-based PGSE sequences is investigated. Both background gradients and radiation damping have serious implications for accurate diffusion measurement determination.     

三半波带通滤光片的制作与膜厚分析

在光学薄膜镀制中, 比较片与样品片之间的厚度比例关系是间接监控法成功的重要参数. 计算表明, 三半波带通滤光片中心位置能大致推测出这一关系, 通带形状能粗略反映镀制过程中的变化以及不同膜料间的比例系数差别. 后期, 作者顺利制作出多个不同中心位置的带通滤光片.     

Theory of Z-scan technique using Gaussian-Bessel beams with a phase object

This paper reports the theoretical study of combining Z-scan technique with Gauss-Bessel (GB) beams beside a phase object (PO) to measure the third-order nonlinear susceptibility components.By using this method,the sign of refractive index which depends on the shape of the close aperture Z-scan curve can be easily determined.Meanwhile,the magnitude of nonlinear coefficients can also be deduced by theoretical fit.The proposed method is advantageous for high sensitivity and imposes a lower stress in the cases of fragile materials,since small pulse energy is enough for the measurement of nonlinear coefficients.Predictions of the models are compared with Gaussian Z-scan measurement and GB Z-scan measurement.By using GB beams with a PO,the sensitivity of Z-scan measurements is found to be a factor of over 60 times greater than for Gaussian beams and 2 times greater than for Gaussian-Bessel beams.     

不稳定锂同位素移位的高精度测量实验方案(英文)

对丰中子晕核11Li的核电荷均方根半径的实验确定 ,特别是其与9Li的半径的差值 ,将对各种核模型进行灵敏的检验 .选择锂的合适跃迁 ,利用激光光谱技术高精度测量该跃迁的同位素移位 ,并扣除精确理论计算的质量移位贡献值 ,可以用来确定有关同位素的核电荷均方根半径 .就目前能够提供的实验设备和手段 ,对于不稳定锂的同位素8,9Li和短寿命丰中子晕核11Li而言 ,这是能够得到与核模型相独立的电荷半径值的唯一可行的方法 .这类实验正在德国重离子研究中心 (GSI)和欧洲核子中心的ISOLDE/CERN上计划实施 .描述了锂原子的激光激发共振电离途径和进行锂的同位素移位测量的实验装置,并讨论了采用这种方法测量到的6,7Li的初步结果及其精度 ,以及使用该方法研究不稳定核的灵敏性. A high-resolution isotope shift measurement of lithium isotopes in a suitable transition, combined with an accurate theoretical evaluation of the mass-shift contribution in the corresponding transition, can be used to determine the root-mean-square nuclear charge radii of these isotopes. For the unstable 8,9Li and the short-lived halo nucleus 11Li, this is the only approach available for obtaining nuclear-model-independent values of the charge radii within the reach of present-day facilities...     

Rapid Simultaneous Measurement of Hydrogen Isotopes in Aqueous Solution by 31P NMR

Integration of the ³¹P spectrum of phosphite formed after reaction of phosphorus tricholoride with partially deuterated water is found to yield an accurate measurement of the percent of deuteration (or protonation) after correction for the kinetic isotope effect. A kinetic isotope effect favoring proton reaction by a factor of 3.2 ± .25 is found. The method is tested over the range of 10% to 90% deuterium. The results are found to be accurate to ± 6% relative, which is probably limited by experimental error in the determination of the integral. Measurements outside the 10 to 90% range are possible, but require longer acquisition times because of the low signal-to-noise ratio of the small peaks.     

油井样品NMR T2谱的影响因素及T2截止值的确定方法

T₂ 谱是核磁共振（NMR）测、录井技术应用与解释、评价的基础. 岩样T₂ 谱受仪器测量参数、样品性质（岩性、颗粒大小、样品粒度、样品干湿状态、孔隙流体含量及性质、磁化率、润湿性）及地层水矿化度等因素的影响. T₂ 截止值是T₂ 谱中最重要的参数之一,选取的科学性与准确性直接影响到核磁共振测量结果. 通过文献查询,对T2 谱的影响因素及T₂ 截止值的确定方法进行了分析.     

Ferron比色法中不同Ferron体系、溶解度和实验温度等因素对测定单核铝浓度的影响

Ferron比色法被广泛应用于铝形态分析检测中,但迄今为止可能影响其测量准确性的某些重要因素尚未进行过系统研究。以Al-Ferron显色体系摩尔吸光系数ε值为关键,系列考察了不同Ferron体系、Ferron溶解度、实验温度、离子强度和参比体系这五个因素对Ferron比色法测定单核铝浓度准确度的影响。研究结果表明：不同Ferron体系、Ferron的溶解度、实验温度是Ferron比色法中的重要因素,测定时应当予以高度重视,否则会影响测量结果的准确性;溶液的离子强度以及参比体系等则对测定基本无影响。通过实验结果以及相关文献的总结分析,优化了Ferron比色法的测定条件,从而为获得准确的单核铝浓度测量结果所需要采取的操作程序提供了标准规范。     

Chirp-coefficient bisection iteration method for phase-intensity reconstruction of chirped pulses

A new method is proposed to systematically measure the phase-intensity information of chirped pulses that is based on the chirp-coefficient bisection iteration (CBI) concept. Through the CBI procedure with measured spectrum and temporal intensity profiles (or intensity autocorrelations), spectral and temporal amplitude–phase information can be rapidly retrieved. We experimentally verified that our method has high precision for nanosecond- and picosecond-level pulses and low precision for femtosecond-level pulses. Our proposed method does not require a sophisticated setup and has the advantage of accurate determination of temporal and spectral chirp coefficients with various orders. It also has lower cost, simple operation, in particular covers a wider measurement range than the main current methods. Moreover, the retrieved waveforms can reveal both the pulse shape and the actual intensity with spectral and temporal chirped coefficients of various orders, which can be directly used in various pulse propagation analyses such as chirped pulse amplification.     

多普勒频移修正在测定直升机飞行噪声固有频率中的应用

对于噪声信号采集系统采集的某型直升机的飞行噪声信号,提出了结合机载GPS数据,进行多普勒频移修正,然后叠加多个多普勒频移修正结果,以得到直升机旋翼、尾桨和减速器噪声固有频率的新方法,可以大大减小单次多普勒频移修正的误差。这种方法为确定飞行器飞行噪声固有频率提供了有效的途径。