Acta Metrologica Sinica

Office Online

Manuscript Tracking

Editor-in-chief

Journal Online

Current Issue

Advanced Search

Archive

Read Articles

Download Articles

Traffic

Quick Search

2022 Vol. 43, No. 5 Published: 2022-05-28

	565	Benchmarking Analysis of Scientific Research Output of International Metrology Institutions Based on Bibliometrics
		DUAN Yu-ning,LIU Yi-tong,LI Xiao-meng,SHANG Xue-shen,ZHANG Yu,YANG Cai-jun,WANG Li-li,LI Liu
		DOI: 10.3969/j.issn.1000-1158.2022.05.01
		Based on the data of SCI papers collected by Web of Science (WOS) from 2013 to 2020, the scientific research output (including the quantity and impact indicators) of National Institute of Metrology were analysed by internationally accepted bibliometrics method. In the meantime, the benchmarking analysis of the output of scientific research papers was carried out with the metrology institutions in developed countries, such as the National Institute of Standards & Technology (NIST), the National Physical Laboratory (NPL) and the Physikalisch-Technische Bundesanstalt (PTB). We attempted to demonstrate the position and current situation of our institute in the field of metrology, and analyzed the main advantages and disadvantages of our institute's scientific and technological innovation. It is hoped that the trends and research conclusions behind the data can provide reference and support for our institute in the development of the 14th Five-Year Plan.
		2022 Vol. 43 (5): 565-570 [Abstract] ( 250 ) HTML (1 KB) PDF (2088 KB) ( 387 )

	571	Research on Calibration Method of Initial Incident Angle of Metrological Laser Ellipsometer
		LI Xiong-wei,LI Qi,JI Feng,LI Shi,LI Wei,HUANG Lu,SHI Yu-shu,PI Lei
		DOI: 10.3969/j.issn.1000-1158.2022.05.02
		To ensure the accuracy of the measurement results of the metrology-type laser ellipsometer, an initial incidence angle calibration method is investigated, the incident laser optical axis of the ellipsometer is calibrated at 90° to the optical axis of the self-collimator by means of a linear displacement stage driving the CCD camera in one-dimensional motion, and its motion axis is used as a spatial linear auxiliary reference quantity. The results show that the initial incidence angle of the metrology-type laser ellipsometer is calibrated by this method, and the deviation of the optical axis pitch angle is less than 0.05° and the deviation of the deflection angle is less than 0.09°. The calibration results show that the calibration error of the SiO₂ film thickness standard on Si with the nominal value of 102.10nm is less than 0.4nm. The research work has improved the accuracy of the measurement and calibration service of the metrology-type laser ellipsometer.
		2022 Vol. 43 (5): 571-577 [Abstract] ( 211 ) HTML (1 KB) PDF (3482 KB) ( 388 )

	578	Research on Measurement Comparison of Cryogenic Radiometers
		XU Nan,YU Bing,SHI Xue-shun,ZHANG Peng-ju,FAN Ji-hong,LIU Zhi-wei,LIN Yan-dong
		DOI: 10.3969/j.issn.1000-1158.2022.05.03
		Cryogenic radiometer is by far the most accurate measurement system of optical radiant power, which is the fundamental quantity of detector based radiometry. In order to verify the consistency of the measurement values among different laboratories, a measurement comparison of cryogenic radiometers was organized by National Institute of Metrology as pilot laboratory, participating laboratories include the 41st Research Institute of China Electronics Technology Group Corporation and Xian Institute of Applied Optics. The comparison method, transfer standard and measurement facilities are presented, and the comparison results are analyzed. The comparison results show that the deviation of each laboratory relative to the reference value is within ±0.02%, and the comparison results prove the consistency of scales realized from different types of cryogenic radiometers in each laboratory.
		2022 Vol. 43 (5): 578-582 [Abstract] ( 253 ) HTML (1 KB) PDF (1046 KB) ( 581 )

	583	Human Action Recognition Method Based on Event Camera
		ZHANG Yuan-hui,XU Lu-jun,XU Bai-rui,HE Yu-chen
		DOI: 10.3969/j.issn.1000-1158.2022.05.04
		The existing method of human action recognition was to divide event data as virtual frames with fixed time interval. However, these technologies did not take full advantage of the asynchronous output feature of the event camera. In order to solve the shortages, a method to deal with event data directly is proposed. First, event camera is used to obtain nine kinds of common human action data, then preprocessing include filtering and grid down sampling. The preprocess can not only remove noise but also reduce the amount of input data of the model. Second, the shared convolution is used to extract the action space features, which use parallel convolution operation. Finally, human actions are classified and recognized. The experimental results show that the average recognition accuracy is 91.3% under normal illumination, different illumination has little effect on the accuracy of this method, it also has the advantages of fast training time and small number of parameters.
		2022 Vol. 43 (5): 583-589 [Abstract] ( 267 ) HTML (1 KB) PDF (3360 KB) ( 983 )

	590	Calibration of Tungsten-Rhenium Thermocouple Based on High Temperature Blackbody Furnace
		NIU Xing-jun,ZHANG Ting-ting,FANG Li-de,LU Xiao-feng
		DOI: 10.3969/j.issn.1000-1158.2022.05.05
		A calibration method for high-temperature thermocouples, as tungsten-rhenium couples, was designed based on the high temperature blackbody furnace at the National Institute of Metrology(NIM). The axial uniformity of the optimally designed cavity in the temperature thermostat was measured less than 0.5℃ within 20mm depth. The radiance temperature difference between the selected cavity and the central one was less than 0.5℃. The calibration method based on the high temperature blackbody furnace was verified by Pt-10% Rh/Pt thermocouple. The calibration error from 800℃ to 1300℃ was less than 0.5℃, and the uncertainty was estimated 0.8~1.5℃, k=2. In the range of 800~1900℃, the electromotive force of tungsten-rhenium thermocouple from different manufactures was calibrated, and the uniformity of the wires before and after calibration was also tested. The calibration result showed that the relative error of the tungsten-rhenium thermocouple was kept within 1%, and the uncertainty was estimated 3.7~13.0℃, k=2 which was about 0.7%t in the relative uncertainty.
		2022 Vol. 43 (5): 590-596 [Abstract] ( 201 ) HTML (1 KB) PDF (2516 KB) ( 339 )

	597	A signal processing method of ultrasonic gas flowmeter based on peak point fitting of ultrasonic echo energy
		MA Jie,XU Ke-jun,JIANG Zhen,ZHANG Lun,XU Hao-ran
		DOI: 10.3969/j.issn.1000-1158.2022.05.06
		Aiming at the problem that it is difficult to find the stable feature point in the signal processing of ultrasonic gas flowmeters,from the angle of the energy of the echo signal,the change rule of the echo signal energy is studied.The middle part of the rising segment of the contour of the echo energy signal is relatively stable,and the slope of the envelope of the middle part is the largest,which is approximately a straight line.A signal processing method based on echo energy peak point fitting is proposed.That is,firstly,the adjacent peak points of the rising segment of the echo energy signal are connected and the slope of each connected line is obtained,then four connected lines with larger slope are selected as the characteristic straight lines,and the right end points corresponding to the four characteristic straight lines are taken as the characteristic peak points to fit a straight line.Finally,the intersection point between the fitted straight line and x-axis is taken as the feature point,so as to calculate the ultrasonic propagation time.This signal processing method is implemented on the dual core system based on FPGA and DSP,and the calibration test is executed in the qualified testing institution.The results show that: the dual-channel ultrasonic gas flowmeter system based on the signal processing method of echo energy peak fitting achieves the 1.0-level accuracy,and the flow measurement range is 30~1200m³/h.
		2022 Vol. 43 (5): 597-602 [Abstract] ( 154 ) HTML (1 KB) PDF (2991 KB) ( 567 )

	603	Gas Holdup Measurement of Gas-liquid Two-phase Flow Using Microwave Sensor Based on Cross-shaped Antenna
		YU Xiao-fei,ZHANG Tao,XU Ying,FANG Li-de
		DOI: 10.3969/j.issn.1000-1158.2022.05.07
		In order to overcome the influence of the two-phase flow pattern on the gas holdup of the gas-liquid two-phase flow, a microwave sensor based on a cross-shaped antenna structure is designed based on microwave technology. The sensor is composed of horizontal and vertical dual antennas, which can well sense the hold-up value on the cross-section and improve the measurement accuracy. At the same time, a large number of cross-section gas content models are studied, and with reference to the scientific and effective unified evaluation standard, the volumetric content is given by the standard device to obtain the reference true value of the cross-section gas content. The gas content formula is obtained by fitting the flow experiment data, and the accuracy of the formula is verified. The results show that the measured value of the sensor is in good agreement with the L-M model, and the average error of the cross-sectional gas content measured by the microwave sensor is 2%.
		2022 Vol. 43 (5): 603-608 [Abstract] ( 237 ) HTML (1 KB) PDF (1807 KB) ( 217 )

	609	Research of Phase Sensitive Optical Time Domain Reflectometer Based on Support Vector Machine
		MA Shi-yang,WANG Yu,WANG Peng-fei,LI Jun-chan,BAI Qing,LIU Xin,JIN Bao-quan
		DOI: 10.3969/j.issn.1000-1158.2022.05.08
		In order to solve the problems of false alarm rates of vibration signals in the actual laying environment of optical fibers, a pattern recognition method based on wavelet energy spectrum and support vector machine (SVM) is introduced in the optical fiber vibration sensing system based on phase sensitive optical time domain reflectometer. Firstly, the optimal decomposition layer of wavelet energy spectrum analysis is set as 5 layers to extract feature vectors from the original signals. Then the classification of vibrations events are carried out under the “one to one method” multi-classification strategy of support vector machine. Considering the influence of experimental environment, three vibration patterns are carried out including walking through the fiber, striking on the fiber and jogging along the fiber. Finally, the accuracy rate, precision rate, recall rate and F value are used to evaluate the performance of support vector machine. According to the experimental results, this method has achieved 84.9% classification accuracy for vibration events.
		2022 Vol. 43 (5): 609-616 [Abstract] ( 151 ) HTML (1 KB) PDF (2686 KB) ( 328 )

	617	Chatter Identification Method for Ultrasonic Milling of Thin Walled Parts Based on IMB-CNN
		WU Feng-he,LI Shen-ye,SUN Ying-bing,GUO Bao-su
		DOI: 10.3969/j.issn.1000-1158.2022.05.09
		Chatter in ultrasonic milling of thin-walled parts seriously affects the quality of workpiece and aggravates tool wear, so a chatter image monitoring system was built. Convolutional neural network (CNN) was used to identify chatter images and the advantages of magnetotactic bacteria algorithm (MB), hill climbing algorithm (HC) and tabu search algorithm (TS) were taken synthetically to improve MB algorithm for optimizing the parameters. Therefore, a chatter identification method based on the improved magnetic bacteria convolution neural network (IMB-CNN) for ultrasonic milling of thin-walled parts was proposed. Firstly, the global search was carried out by MB algorithm, and then neighborhood search was carried out by HC algorithm with the optimal solution as the initial point, so as to avoid the oscillation of MB algorithm near the optimal solution. At the same time, the tabu list was used to skip the searched nodes to reduce the calculation scale and speed up the calculation efficiency. Finally, the optimal hyperparameters were applied to the CNN to realize the accurate identification of flutter images. Compared with other methods, this method achieves 97.69% recognition rate, and the judgment time is 363ms. The chatter is identified effectively, and the overall performance is better than other algorithms.
		2022 Vol. 43 (5): 617-623 [Abstract] ( 212 ) HTML (1 KB) PDF (2199 KB) ( 257 )

	624	Dynamic Weighing System of Pneumatic Conveying Based on Extended Kalman Filter Algorithm
		WANG Qin-yue,QIAN Zhen-hua,HE Guan-li,CAI Zhi-duan,XU Yu-xiang,CHEN Li-qun
		DOI: 10.3969/j.issn.1000-1158.2022.05.10
		To improve the dynamic weighing accuracy of powder in pneumatic conveying process, there was a dynamic weighing method based on extended Kalman filter algorithm be proposed, which set up multiple weighing sensors to fuse and filter the collected data, so as to eliminate the influence of interference noise on the system measurement. At the same time, the weight reduction measurement method was used to adjust the switching degree of the unloading control valve through the intelligent controller to improve the accuracy of dynamic weighing. The experimental results show that the average error of weighing 30kg silica powder is less than 0.3%.
		2022 Vol. 43 (5): 624-628 [Abstract] ( 184 ) HTML (1 KB) PDF (1398 KB) ( 469 )

	629	Study on the Determination of Apparent Density ConversionStandard Density of Crude Oil at 15~80℃ by Comparing Oscillating Tube and Pycnometer Method
		HE Yun-teng,ZHANG Jian,LI Hua,LI Dong-hui,WU Ying-xiang
		DOI: 10.3969/j.issn.1000-1158.2022.05.11
		Crude oil standard density (20℃) is an important item in the physical and chemical indicators of crude oil. By using Anton Paar (Anton Paar) DMATM 35 V4 Ex Petrol explosion-proof portable density meter and other equipment, the density of crude oil samples from oil wells in multiple oilfields were detected by pyknometer method and vibrating-tube densitometer method respectively at 15~80 ℃, the density temperature curve was drawn, the empirical formula was deduced and improved, and a calculation formula with test density and temperature as parameters was given. The oscillating tube density test method and the petroleum meter were combined to calculate the crude oil standard density, and the relative error was controlled within ±0.5%. It is possible to quickly obtain crude oil standard density parameters on-site.
		2022 Vol. 43 (5): 629-635 [Abstract] ( 166 ) HTML (1 KB) PDF (3139 KB) ( 213 )

	636	Calculation and Measurement for Acoustic Characteristics of Baffle Sample under High Hydrostatic Pressure
		LI Shui,LUO Ma-qi,YI Yan
		DOI: 10.3969/j.issn.1000-1158.2022.05.12
		In order to develop a pressured, low-frequency and wide-band acoustic barrier which can shield the noise and improve the spatial gain of acoustic array in underwater sonar system, the acoustic tube sample was designed. According to the sound propagation theory in layered medium, the sound pressure reflection coefficient and transmission coefficient under the backing of air and water were calculated by using the transfer matrix method of multilayer uniform structure, and there were obvious different acoustic properties. A measured sample with a diameter of 206mm was made. The acoustic performance of the acoustic baffle sample in the frequency range of 100Hz～4kHz and the hydrostatic pressure range from normal pressure to 2MPa was tested by using the standing wave tube and traveling wave tube measurement system in Hangzhou Research Institute of Applied Acoustics. The measured results are basically agreed with the theoretical calculation value. The acoustic baffle sample has certain low-frequency and wide-band echo characteristics under hydrostatic pressure.
		2022 Vol. 43 (5): 636-642 [Abstract] ( 210 ) HTML (1 KB) PDF (2830 KB) ( 136 )

	643	Self-calibration Method of Inductive Voltage Divider Based on Improved Incremental Buildup Method
		FENG Jian,SUN Jian,PAN Yang
		DOI: 10.3969/j.issn.1000-1158.2022.05.13
		The design method of reference voltage transformer and null detection transformer was introduced. The influence of leakage current between shielding of the transformers was analyzed. The classic incremental buildup calibration method was improved. Both the reference voltage and voltage difference measurement circuit got equipotential protection in zero balance and section voltage balance measurement procedures. The process of self-calibration method was derived. Calibration result was only related to the voltage difference measured by the lock-in amplifier during two balance procedures. The influences of reference voltage transformer, null detection transformer, auxiliary transformer and leakage current between shielding were removed. The calibration results of 1kV inductive voltage divider was presented, and the measurement uncertainty was evaluated, the relative expanded uncertainty was 5.4 × 10^-8(k=2).
		2022 Vol. 43 (5): 643-648 [Abstract] ( 189 ) HTML (1 KB) PDF (731 KB) ( 115 )

	649	Joint Estimation of the Capacity and SOC of Lithium Battery Based on WOA-UKF Algorithm
		WU Zhong-qiang,WANG Guo-yong,XIE Zong-kui,HE Yi-lin,LU Xue-qin
		DOI: 10.3969/j.issn.1000-1158.2022.05.14
		The state of charge (SOC) and effective capacity of lithium batteries are important parameters to characterize the current remaining capacity and life of the battery. A joint estimation method for the effective capacity and SOC of lithium-ion batteries is proposed. During the battery life cycle, a two-variable polynomial description for the non-linear model of open circuit voltage to SOC and battery effective capacity is given; when the number of battery cycles exceeds a preset value, whale optimization algorithm is used to estimate the current battery capacity and battery model parameters, and then an unscented Kalman filter is used to estimate the SOC of battery according to the model parameters and capacity values. In the estimation process of SOC, the whale optimization algorithm is used to update the noise variance of unscented Kalman filter, furthermore, the estimation accuracy is improved. Experimental results test the effectiveness of the method and the feasibility of the joint estimation scheme.
		2022 Vol. 43 (5): 649-656 [Abstract] ( 196 ) HTML (1 KB) PDF (2379 KB) ( 815 )

	657	Research on On-wafer Open Method for Chip Capacitance Measurement
		LI Hao,QIAO Yu-e,DING Chen,DING Li-qiang,LIU Xia-mei,WU Ai-hua
		DOI: 10.3969/j.issn.1000-1158.2022.05.15
		To achieve the effective open operation during the chip capacitance measurement, and enhance the veracity and coherence of the results, the on-wafer open method was researched. By analyzing the principle and structure of the standard capacitor and open termination, combined with the actual needs of semiconductor technical measurement, the on-wafer open instrument was designed and manufactured. Based on constructing the on-wafer capacitance test system, measurements on 1pF chip capacitance were conducted using traditional hanging open method and on-wafer open method. Results show that, compared with hanging open method, the on-wafer open method improves the veracity and coherence of test data, while the measuring repeatability achieves 0.01%, which offers an effective open method for chip capacitance metrology and measurement.
		2022 Vol. 43 (5): 657-661 [Abstract] ( 221 ) HTML (1 KB) PDF (1438 KB) ( 150 )

	662	Design and Implementation of NIMDO Scheme with BeiDou Short Message Communication
		GU Yang-yi,CHEN Liang,LIANG Kun,YANG Zhi-qiang
		DOI: 10.3969/j.issn.1000-1158.2022.05.16
		As a backup communications on the ground, and also in order to provide a more reliable frequency transmission path, a NIMDO scheme based on Beidou short message communication is proposed, and a set of remote time traceability device using more reliable communication is designed. Beidou short message communication is used to transmit the time-frequency data of the reference end, and the client analyzes the time-frequency data and tames the client NIMDO. The experimental results show that under the condition of short baseline, the NIMDO scheme based on BeiDou short message communication can achieve the precise traceability of remote time, and the traceability deviation between the client and the reference terminal is better than ±4ns, and the traceability deviation is 3.6ns.
		2022 Vol. 43 (5): 662-666 [Abstract] ( 189 ) HTML (1 KB) PDF (1933 KB) ( 580 )

	667	High-precision Optical Fiber Microwave Time-frequency Transfer Technology
		QI Miao-miao,LIN Ping-wei,PAN Jia-rong,JIANG Zhi-yuan
		DOI: 10.3969/j.issn.1000-1158.2022.05.17
		Optical fiber microwave time-frequency transfer technology has the advantages of high reliability, high stability, high precision, and low loss, it can provide a high-precision time-frequency reference for aerospace, national defense construction, high-speed communications and other industries. How to overcome the problems of low time synchronization accuracy, immature networking and integration technology in the existing technology, and at the same time ensure that the system will not cause a significant decrease in synchronization accuracy during long-distance transmission, becoming a core research issues in the field of optical fiber time-frequency transmission. The research progress of optical fiber microwave time-frequency transmission is reviewed, start from the traditional time transfer and frequency transfer technology, the new technology of integrated time-frequency transfer is introduced, finally, the application prospects of optical fiber microwave time-frequency transfer technology are prospected.
		2022 Vol. 43 (5): 667-674 [Abstract] ( 205 ) HTML (1 KB) PDF (2752 KB) ( 385 )

	675	Intercomparison of Aerosol Extinction Measurement Based on Optical Cavity Spectroscopy
		ZHANG Jia-luo,DU Ying-ying,CHEN Jun,WANG Meng,SU Ming-xu,LI Ling,CHENG Yi,LOU Sheng-rong
		DOI: 10.3969/j.issn.1000-1158.2022.05.18
		To achieve the on-line measurement of the broad-band extinction coefficient of atmospheric aerosols, an incoherent broad-band cavity enhanced absorption spectroscopy (IBBCEAS) experimental instrument was established. Then, in order to evaluate the accuracy and stability of the system, a comparative measurement was carried out simultaneously with CAPS-ALB, a single wavelength Cavity Attenuation Phase Shift ALBedo monitor, in the Environmental Science Building of Fudan University. The comparison result show that the measured aerosol extinction coefficients at the wavelength of 532nm of above two instruments has a same trend with a correlation coefficient of 0.974, indicating the established IBBCEAS system has similar reliability and stability to the metrological certificated high-precision instrument. After calibrated with CAPS-ALB, the measurement accuracy of the IBBCEAS system was significantly improved, and the measurement differency between the two instruments was reduced from 7.08Mm^-1 to 2.4Mm^-1. And it was also found that the broad-band spectral measurement is of great significance for studying the wavelength dependency of aerosol extinction coefficient.
		2022 Vol. 43 (5): 675-681 [Abstract] ( 186 ) HTML (1 KB) PDF (2436 KB) ( 153 )

	682	Design and Optimization of Metastable Krypton Beam Diagnostic System in Structure
		ZHANG Jia-le,FENG Gao-ping,SONG Jun-ling,RAO Wei,ZHU Xiao-xiao,LIANG Jian-wei,JIN Xing
		DOI: 10.3969/j.issn.1000-1158.2022.05.19
		The metastable krypton atoms have high internal energy, and they will be de-excited to produce electrons when they collide with the metal surface. The electron lens is used to image and detect the de-excited electrons to realize the characterization of the intensity and spatial distribution of the metastable krypton atom beam. Based on this principle, a metastable krypton atom beam imaging system is designed, and the finite element analysis method is used to study the influence of electrode spacing, thickness and electric potential on the movement of the de-excited electron beam. The results show that the imaging dispersion decreases with the improvement of the focusing ability of the electronic lens. The imaging error of each object point of the metastable krypton beam is below 2mm, the imaging size is 16.5mm, the average error is 3.71%, and the maximum error is 9.38%.
		2022 Vol. 43 (5): 682-687 [Abstract] ( 175 ) HTML (1 KB) PDF (2433 KB) ( 138 )

	688	Dynamic Motor Imagery Classification with Decision Fusion Based on Linear Discriminant Analysis
		FU Rong-rong,LI Peng,LIU Chong,ZHANG Yang
		DOI: 10.3969/j.issn.1000-1158.2022.05.20
		The recognition and classification of electroencephalogram (EEG) signals has always been a hot topic in brain computer interface technology. Aiming at the problem that single classifier can not make good use of features and the adaptability of classifiers, it is difficult to further improve the recognition accuracy. A classification decision level fusion strategy based on linear discriminant analysis (LDA) is proposed to improve the classification accuracy of brain computer interface system. Firstly, the false test features of the two classifiers are separated, and the more likely correct decision is selected from the two methods to improve the classification accuracy; secondly, in order to measure the uncertainty of each decision, the maximum and the second largest correlation coefficient with the corresponding classifier is used to extract the feature vector. Based on this idea, a new decision selector is proposed, the method combines two LDA based algorithms to select more likely accurate decisions, so as to improve the classification accuracy of EEG signals. The experimental results show that this method can achieve better classification accuracy in motion imagery data classification by combining with the algorithm with similar accuracy.
		2022 Vol. 43 (5): 688-695 [Abstract] ( 215 ) HTML (1 KB) PDF (2931 KB) ( 424 )

	696	Evaluation of the Influence of Bioaerosol Atomizers on the Activity of E.coli
		TIAN Ying,ZHANG Guo-cheng,LI Jing-jing,LIU Jia-qi,PAN Yi-ting,WU Dan,SHEN Shang-yi,HUO Sheng-wei
		DOI: 10.3969/j.issn.1000-1158.2022.05.21
		The research of bioaerosol relies on a stable and reliable atomization process. The performances of different aerosol generators are evaluated from the aspects of particle concentration, particle size distribution, bacterial culturability and cell membrane damage, and the influence of inlet flow is discussed.The results show that the mechanical stress in the process of aerosol generation seriously damages the integrity of the cell membrane, which reduces the cultivable rate of bacteria by more than 90%, and with the increase of air flow, the proportion of cell debris increases, and the cell membrane damage becomes more serious. Since the research of bioaerosol not only requires high concentrations of microorganisms, but also ensures the integrity and cultivability of cells, the above study will provide a basis for the performance evaluation and selection of bioaerosol generators.
		2022 Vol. 43 (5): 696-700 [Abstract] ( 218 ) HTML (1 KB) PDF (1322 KB) ( 222 )

News

Download

Links

Copyright © Editorial Board of Acta Metrologica Sinica
Supported by:Beijing Magtech