Pub Date : 2012-04-23DOI: 10.1109/EFTF.2012.6502348
Kejia Zhao, A. Zhang, K. Liang
Network time service system is constructed in NIM based on network time protocol (NTP). The synchronization software programm based on NTP is run at the client side. The mathematical uncertainty model of time offset is established. The uncertainty is analyzed and evaluated. The uncertainty of time server and client are evaluated particularly by the synchronizing experiments using a time and frequency solutions TimeAcc-007. The data processing algorithms are proposed for improving synchronization precision based on the result of uncertainty evaluation.
{"title":"Research on the uncertainty evaluation of network time service system","authors":"Kejia Zhao, A. Zhang, K. Liang","doi":"10.1109/EFTF.2012.6502348","DOIUrl":"https://doi.org/10.1109/EFTF.2012.6502348","url":null,"abstract":"Network time service system is constructed in NIM based on network time protocol (NTP). The synchronization software programm based on NTP is run at the client side. The mathematical uncertainty model of time offset is established. The uncertainty is analyzed and evaluated. The uncertainty of time server and client are evaluated particularly by the synchronizing experiments using a time and frequency solutions TimeAcc-007. The data processing algorithms are proposed for improving synchronization precision based on the result of uncertainty evaluation.","PeriodicalId":6409,"journal":{"name":"2012 European Frequency and Time Forum","volume":"145 1","pages":"122-125"},"PeriodicalIF":0.0,"publicationDate":"2012-04-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89081582","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2012-04-23DOI: 10.1109/EFTF.2012.6502373
T. J. Pinkert, J. Morgenweg, I. Barmes, D. Kandula, C. Gohle, K. Eikema
The capability of frequency-comb (FC) lasers to precisely measure optical frequencies has been extended to the to the extreme ultraviolet (XUV, wavelengths shorter than 100 nm), corresponding to frequencies of multiple PHz. We demonstrate “broad frequency comb generation” for a wavelength range of 51–85 nm. Our method is based on amplification and coherent up-conversion of a pair of pulses originating from a near-infrared femtosecond FC laser. Excitation of argon, neon, and helium with these upconverted laser pulses in the XUV lead to Ramsey-like signals with up to 61% contrast. From these signals an accuracy of 6 MHz has been achieved in the determination of the ground state ionization energy of helium at 51 nm. Further improvement to a kHz-level accuracy is expected based on a new pump laser for the employed parametric amplification system.
{"title":"Direct frequency metrology Up To PHz frequencies","authors":"T. J. Pinkert, J. Morgenweg, I. Barmes, D. Kandula, C. Gohle, K. Eikema","doi":"10.1109/EFTF.2012.6502373","DOIUrl":"https://doi.org/10.1109/EFTF.2012.6502373","url":null,"abstract":"The capability of frequency-comb (FC) lasers to precisely measure optical frequencies has been extended to the to the extreme ultraviolet (XUV, wavelengths shorter than 100 nm), corresponding to frequencies of multiple PHz. We demonstrate “broad frequency comb generation” for a wavelength range of 51–85 nm. Our method is based on amplification and coherent up-conversion of a pair of pulses originating from a near-infrared femtosecond FC laser. Excitation of argon, neon, and helium with these upconverted laser pulses in the XUV lead to Ramsey-like signals with up to 61% contrast. From these signals an accuracy of 6 MHz has been achieved in the determination of the ground state ionization energy of helium at 51 nm. Further improvement to a kHz-level accuracy is expected based on a new pump laser for the employed parametric amplification system.","PeriodicalId":6409,"journal":{"name":"2012 European Frequency and Time Forum","volume":"23 9","pages":"235-237"},"PeriodicalIF":0.0,"publicationDate":"2012-04-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"91421015","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2012-04-23DOI: 10.1109/EFTF.2012.6502345
Xuejun Chen, Zongwen Wu, Wenhua Zhao
The method aimed at enhancing precision of the two-way satellite time transfer for a low-speed dynamic object is presented in this paper. Calculous and vector algebra are used to analysis the precision of two way satellite time transfer when one of the station is a low-rate dynamic object, such as one satellite-communication station on a vessel. Mathematic model of the precision is hence obtained. Experimental results show that the main factors which affect the precision of the two-way satellite time transfer mainly includes a velocity and a course of the vessel, an elevation of the antenna, measure periods, a rise-fall range and period, a measure starting time and a initialization phase.
{"title":"The error model and the method analysis of TWSSTT for a low-rate dynamic object","authors":"Xuejun Chen, Zongwen Wu, Wenhua Zhao","doi":"10.1109/EFTF.2012.6502345","DOIUrl":"https://doi.org/10.1109/EFTF.2012.6502345","url":null,"abstract":"The method aimed at enhancing precision of the two-way satellite time transfer for a low-speed dynamic object is presented in this paper. Calculous and vector algebra are used to analysis the precision of two way satellite time transfer when one of the station is a low-rate dynamic object, such as one satellite-communication station on a vessel. Mathematic model of the precision is hence obtained. Experimental results show that the main factors which affect the precision of the two-way satellite time transfer mainly includes a velocity and a course of the vessel, an elevation of the antenna, measure periods, a rise-fall range and period, a measure starting time and a initialization phase.","PeriodicalId":6409,"journal":{"name":"2012 European Frequency and Time Forum","volume":"4 1","pages":"109-112"},"PeriodicalIF":0.0,"publicationDate":"2012-04-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88585720","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2012-04-23DOI: 10.1109/EFTF.2012.6502435
T. Kersten, S. Schon, U. Weinbach
Group Delay Variations (GDVs) are azimuth and elevation dependent code delays that can limit the accuracy of the GNSS code observables. This contribution focuses on the GDV determination and discusses several solutions with respect to repeatability and separability. On-site tests at a laboratory network as well as simulations of several time links are discussed analyzing the stochastic processes apparently introduced by GDV. The stability of the P3 links are not effected. However, offsets up to 0.6 ns can occur. In a detailed study, GDVs are applied to an inter-continental Precise Point Positioning (PPP) time transfer link. This analysis shows that GDV are not an issue for the stability of the PPP links, since small weights reduce the impact of the P3 GDV. It can be shown that the stochastic process, induced by GDV in a PPP analysis, is similar to a random walk noise, well below the L3 carrier phase observation noise of σφ = 6 mm. Offsets for the receiver clock estimates of up to 0.4 ns are reported for the link WTZS (Wettzell) and Boulder (NIST).
{"title":"On the impact of Group Delay Variations on GNSS time and frequency transfer","authors":"T. Kersten, S. Schon, U. Weinbach","doi":"10.1109/EFTF.2012.6502435","DOIUrl":"https://doi.org/10.1109/EFTF.2012.6502435","url":null,"abstract":"Group Delay Variations (GDVs) are azimuth and elevation dependent code delays that can limit the accuracy of the GNSS code observables. This contribution focuses on the GDV determination and discusses several solutions with respect to repeatability and separability. On-site tests at a laboratory network as well as simulations of several time links are discussed analyzing the stochastic processes apparently introduced by GDV. The stability of the P3 links are not effected. However, offsets up to 0.6 ns can occur. In a detailed study, GDVs are applied to an inter-continental Precise Point Positioning (PPP) time transfer link. This analysis shows that GDV are not an issue for the stability of the PPP links, since small weights reduce the impact of the P3 GDV. It can be shown that the stochastic process, induced by GDV in a PPP analysis, is similar to a random walk noise, well below the L3 carrier phase observation noise of σφ = 6 mm. Offsets for the receiver clock estimates of up to 0.4 ns are reported for the link WTZS (Wettzell) and Boulder (NIST).","PeriodicalId":6409,"journal":{"name":"2012 European Frequency and Time Forum","volume":"13 1","pages":"514-521"},"PeriodicalIF":0.0,"publicationDate":"2012-04-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"72770170","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2012-04-23DOI: 10.1109/EFTF.2012.6502336
A. Baranov, S. Ermak, V. Semenov
This work presents analytical studies of the orientation and light frequency shifts in microwave standards with regard to tensor component. It was shown that modulation technique application not only allows eliminating light shift but also provides significant reduction of the frequency errors introduced by external magnetic field orientation fluctuations while pumping alkali atoms with either D1 or D2 line.
{"title":"Orientation light shift suppression in alkali atom microwave standards with laser pumping","authors":"A. Baranov, S. Ermak, V. Semenov","doi":"10.1109/EFTF.2012.6502336","DOIUrl":"https://doi.org/10.1109/EFTF.2012.6502336","url":null,"abstract":"This work presents analytical studies of the orientation and light frequency shifts in microwave standards with regard to tensor component. It was shown that modulation technique application not only allows eliminating light shift but also provides significant reduction of the frequency errors introduced by external magnetic field orientation fluctuations while pumping alkali atoms with either D1 or D2 line.","PeriodicalId":6409,"journal":{"name":"2012 European Frequency and Time Forum","volume":"29 1","pages":"72-73"},"PeriodicalIF":0.0,"publicationDate":"2012-04-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75028970","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2012-04-23DOI: 10.1109/EFTF.2012.6502350
A. Cernigliaro, I. Sesia
In Global Navigation Satellite Systems (GNSS) the role of atomic clocks is essential for the determination of the user position and due to their excellent stability they are fundamental to ensure the adequate performances required in the positioning service. Since a degradation of the clock stability would immediately impact the navigation performances, the on board clock behaviour has to be continuously monitored. In this work, we illustrate a software tool developed at INRIM, optimized for GNSS clock characterization and monitoring. Although some commercial software are available for clock characterization, special attention has to be paid when dealing with space clocks. In fact, the space clock behaviour analysis may be complicated by different aspects: data from satellite clocks often present gaps and outliers as well as periodic fluctuations. On the contrary, data from timing laboratories are equally spaced and usually not affected by many outliers. Hence, often, the typical methods for clock characterization currently used in timing laboratories are not sufficient for space applications: new approaches, more suitable for GNSS applications, are required. To overcome these limitations, we developed the Clock Analysis Tool: a software, developed in Matlab, for clock characterization to be used either in metrological laboratories or for space applications. To fulfill GNSS needs, the software has been enhanced and extended, including new routines and functionalities of particular interest when characterizing the space clock behaviour, such as the dynamic stability analysis, as well as the addition of the uncertainty evaluation in the clock parameter estimation, or the inclusion of the system noise estimate in the frequency stability analysis. Moreover, the algorithms commonly used for clock characterization, such as the Allan Deviation computation and the frequency drift estimation, have been adapted to deal with space clock features, namely data gaps and outliers, treating missing data with the best possible procedure to allow the estimate of the stability over long observation intervals. In addition, the software has been provided with a graphical user interface, allowing an easy handling of satellite clock data and permitting a quick estimate and graphic representation of the clock key parameters.
{"title":"INRIM tool for satellite clock characterization in GNSS","authors":"A. Cernigliaro, I. Sesia","doi":"10.1109/EFTF.2012.6502350","DOIUrl":"https://doi.org/10.1109/EFTF.2012.6502350","url":null,"abstract":"In Global Navigation Satellite Systems (GNSS) the role of atomic clocks is essential for the determination of the user position and due to their excellent stability they are fundamental to ensure the adequate performances required in the positioning service. Since a degradation of the clock stability would immediately impact the navigation performances, the on board clock behaviour has to be continuously monitored. In this work, we illustrate a software tool developed at INRIM, optimized for GNSS clock characterization and monitoring. Although some commercial software are available for clock characterization, special attention has to be paid when dealing with space clocks. In fact, the space clock behaviour analysis may be complicated by different aspects: data from satellite clocks often present gaps and outliers as well as periodic fluctuations. On the contrary, data from timing laboratories are equally spaced and usually not affected by many outliers. Hence, often, the typical methods for clock characterization currently used in timing laboratories are not sufficient for space applications: new approaches, more suitable for GNSS applications, are required. To overcome these limitations, we developed the Clock Analysis Tool: a software, developed in Matlab, for clock characterization to be used either in metrological laboratories or for space applications. To fulfill GNSS needs, the software has been enhanced and extended, including new routines and functionalities of particular interest when characterizing the space clock behaviour, such as the dynamic stability analysis, as well as the addition of the uncertainty evaluation in the clock parameter estimation, or the inclusion of the system noise estimate in the frequency stability analysis. Moreover, the algorithms commonly used for clock characterization, such as the Allan Deviation computation and the frequency drift estimation, have been adapted to deal with space clock features, namely data gaps and outliers, treating missing data with the best possible procedure to allow the estimate of the stability over long observation intervals. In addition, the software has been provided with a graphical user interface, allowing an easy handling of satellite clock data and permitting a quick estimate and graphic representation of the clock key parameters.","PeriodicalId":6409,"journal":{"name":"2012 European Frequency and Time Forum","volume":"36 1","pages":"133-135"},"PeriodicalIF":0.0,"publicationDate":"2012-04-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75086921","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2012-04-23DOI: 10.1109/EFTF.2012.6502337
S. Micalizio, C. Calosso, A. Godone, F. Levi
In this paper we describe two phenomena that may affect the medium-long term stability performance of the pulsed vapor cell Rb clock we implemented at INRIM. The first effect is an anomalously large temperature sensitivity of the clock frequency. This effect is related to the presence of large stems in the cell and the order of magnitude of the observed phenomenon may be explained in terms of a model based on the ideal gas law. The second phenomenon is related to losses in the microwave cavity induced by the presence of the dielectric material (the cell) in the cavity and by the deposition of metallic Rb on the inner walls of the clock cell.
{"title":"Cell-related effects in the pulsed optically pumped frequency standard","authors":"S. Micalizio, C. Calosso, A. Godone, F. Levi","doi":"10.1109/EFTF.2012.6502337","DOIUrl":"https://doi.org/10.1109/EFTF.2012.6502337","url":null,"abstract":"In this paper we describe two phenomena that may affect the medium-long term stability performance of the pulsed vapor cell Rb clock we implemented at INRIM. The first effect is an anomalously large temperature sensitivity of the clock frequency. This effect is related to the presence of large stems in the cell and the order of magnitude of the observed phenomenon may be explained in terms of a model based on the ideal gas law. The second phenomenon is related to losses in the microwave cavity induced by the presence of the dielectric material (the cell) in the cavity and by the deposition of metallic Rb on the inner walls of the clock cell.","PeriodicalId":6409,"journal":{"name":"2012 European Frequency and Time Forum","volume":"73 1","pages":"74-78"},"PeriodicalIF":0.0,"publicationDate":"2012-04-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75550572","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2012-04-23DOI: 10.1109/EFTF.2012.6502352
Hong Zhang, Huanxin Li
Two-way time and frequency transfer (TWSTFT) is a high precision time transfer because TWSTFT via the GEO satellite can eliminate path delay mostly. Many factors affect the time transfer precision, such as: the modem time delay, the uplink and downlink path delay, a satellite transponder delay and delay of Sagnac effect etc‥ These effects can be measured or calculated. However, Temperature and humidity will reduce the performance of time transfer[1]. Besides, it can not be measured and calculated. In this text, we analyzed several years' TWSTFT data including the temperature and humidity value between NTSC (National Time Service Center) earth station and international earth stations and discussed the correlation between the external environment and TWSTFT comparison result. On the other hand, we did the experiment using satellite simulation, measured the earth stations equipment time delay and recorded the temperature and humidity. In the last, we drew the conclusion with the external environment and TWSTFT comparison result and had the advice to compensate for it.
双向时频传输(TWSTFT)是一种高精度的时间传输方法，通过GEO卫星进行时频传输可以有效地消除路径延迟。影响时间传输精度的因素很多，例如:调制解调器的时间延迟、上行和下行路径的延迟、卫星转发器的延迟和Sagnac效应等。这些影响可以测量或计算。然而，温度和湿度会降低时间传递的性能[1]。此外，它是无法测量和计算的。本文分析了多年来的TWSTFT数据，包括NTSC (National Time Service Center)地面站与国际地面站的温湿度值，讨论了外部环境与TWSTFT比较结果的相关性。另一方面，我们利用卫星模拟进行了实验，测量了地面站的设备时延，记录了温度和湿度。最后结合外部环境和TWSTFT对比结果得出结论，并提出相应的补偿建议。
{"title":"Environment effect on two way satellite time and frequency transfer","authors":"Hong Zhang, Huanxin Li","doi":"10.1109/EFTF.2012.6502352","DOIUrl":"https://doi.org/10.1109/EFTF.2012.6502352","url":null,"abstract":"Two-way time and frequency transfer (TWSTFT) is a high precision time transfer because TWSTFT via the GEO satellite can eliminate path delay mostly. Many factors affect the time transfer precision, such as: the modem time delay, the uplink and downlink path delay, a satellite transponder delay and delay of Sagnac effect etc‥ These effects can be measured or calculated. However, Temperature and humidity will reduce the performance of time transfer[1]. Besides, it can not be measured and calculated. In this text, we analyzed several years' TWSTFT data including the temperature and humidity value between NTSC (National Time Service Center) earth station and international earth stations and discussed the correlation between the external environment and TWSTFT comparison result. On the other hand, we did the experiment using satellite simulation, measured the earth stations equipment time delay and recorded the temperature and humidity. In the last, we drew the conclusion with the external environment and TWSTFT comparison result and had the advice to compensate for it.","PeriodicalId":6409,"journal":{"name":"2012 European Frequency and Time Forum","volume":"16 1","pages":"140-143"},"PeriodicalIF":0.0,"publicationDate":"2012-04-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75274127","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2012-04-23DOI: 10.1109/EFTF.2012.6502412
R. Smíd, M. Čížek, Z. Buchta, J. Lazar, O. Cíp
The ultra low expansion cavities play a crucial role in laser stabilization, and they are essential in ion clocks. We present a method to measure absolute distance between mirrors of Fabry-Perot cavity (FPC) with a spacer from an ultra low expansion material and the changes of the distance caused by temperature variation with femtometer resolution. The FPC was placed into a temperature-stabilized vacuum stainless steel chamber.
{"title":"Long-term temperature stabilized measurement of ultra-low expansion Fabry-Perot cavity","authors":"R. Smíd, M. Čížek, Z. Buchta, J. Lazar, O. Cíp","doi":"10.1109/EFTF.2012.6502412","DOIUrl":"https://doi.org/10.1109/EFTF.2012.6502412","url":null,"abstract":"The ultra low expansion cavities play a crucial role in laser stabilization, and they are essential in ion clocks. We present a method to measure absolute distance between mirrors of Fabry-Perot cavity (FPC) with a spacer from an ultra low expansion material and the changes of the distance caused by temperature variation with femtometer resolution. The FPC was placed into a temperature-stabilized vacuum stainless steel chamber.","PeriodicalId":6409,"journal":{"name":"2012 European Frequency and Time Forum","volume":"385 1","pages":"404-408"},"PeriodicalIF":0.0,"publicationDate":"2012-04-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76531055","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2012-04-23DOI: 10.1109/EFTF.2012.6502359
Chien‐Ming Wu, Tze-Wei Liu, You-Huan Chen, Wang-Yau Cheng, Shinn-Yan Lin
We report on our measured frequencies of cesium 6S–8S two-photon transitions. We also point out our finding on the influence of different cesium cells from different producer to the measured values of absolute frequency.
{"title":"Absolute frequencies of 133Cs 6S1/2–8S1/2 two-photon transition stabilized diode lasers","authors":"Chien‐Ming Wu, Tze-Wei Liu, You-Huan Chen, Wang-Yau Cheng, Shinn-Yan Lin","doi":"10.1109/EFTF.2012.6502359","DOIUrl":"https://doi.org/10.1109/EFTF.2012.6502359","url":null,"abstract":"We report on our measured frequencies of cesium 6S–8S two-photon transitions. We also point out our finding on the influence of different cesium cells from different producer to the measured values of absolute frequency.","PeriodicalId":6409,"journal":{"name":"2012 European Frequency and Time Forum","volume":"66 1","pages":"166-168"},"PeriodicalIF":0.0,"publicationDate":"2012-04-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73772892","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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