Pub Date : 2014-06-23DOI: 10.1109/EFTF.2014.7331496
J. Miao, B. Wang, C. Gao, Y. Bai, X. Zhu, L. J. Wang
We demonstrate a new ultra-stable frequency dissemination scheme on L band over 100m atmosphere. By compensating phase noise actively and a series of frequency conversions, the phase fluctuation is well compensated. Two links disseminate different frequency signals phase locked to a common reference simultaneously, and recover the disseminated frequency respectively at remote site. The stability of dissemination with phase compensation in free space is 3×10-13/s and 4×10-17/day. The relationship between dissemination stability and propagating distance is also discussed.
{"title":"Progress of ultra-stable frequency dissemination and synchronization in free space","authors":"J. Miao, B. Wang, C. Gao, Y. Bai, X. Zhu, L. J. Wang","doi":"10.1109/EFTF.2014.7331496","DOIUrl":"https://doi.org/10.1109/EFTF.2014.7331496","url":null,"abstract":"We demonstrate a new ultra-stable frequency dissemination scheme on L band over 100m atmosphere. By compensating phase noise actively and a series of frequency conversions, the phase fluctuation is well compensated. Two links disseminate different frequency signals phase locked to a common reference simultaneously, and recover the disseminated frequency respectively at remote site. The stability of dissemination with phase compensation in free space is 3×10-13/s and 4×10-17/day. The relationship between dissemination stability and propagating distance is also discussed.","PeriodicalId":129873,"journal":{"name":"2014 European Frequency and Time Forum (EFTF)","volume":"13 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-06-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128238244","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 : 2014-06-23DOI: 10.1109/EFTF.2014.7331519
A. G. Utkin, A. Beliaev, Y. Pavlenko
We describe the design of an active hydrogen frequency standard for a long operation in space. Most important maser design elements are shown and its some features are reviewed.
{"title":"Main construction features of the on board active hydrogen maser for Radioastron mission","authors":"A. G. Utkin, A. Beliaev, Y. Pavlenko","doi":"10.1109/EFTF.2014.7331519","DOIUrl":"https://doi.org/10.1109/EFTF.2014.7331519","url":null,"abstract":"We describe the design of an active hydrogen frequency standard for a long operation in space. Most important maser design elements are shown and its some features are reviewed.","PeriodicalId":129873,"journal":{"name":"2014 European Frequency and Time Forum (EFTF)","volume":"64 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-06-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133122225","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 : 2014-06-23DOI: 10.1109/EFTF.2014.7331526
A. Battisti, A. Cosentino, A. Sapia, M. Gioia, A. Borella, A. Godone, F. Levi, C. Calosso, S. Micalizio
The POP clock is a vapor cell frequency standard operating in pulsed regime at the Rb ground-state hyperfine frequency (6834 MHz). Selex ES' interest in this technology relies on the possibility to implement a compact unit, with reduced mass, size and power consumption compared to the Passive Hydrogen Maser (PHM, the primary clock of Galileo Navigation Constellation), but similar frequency stability and less operation constraints. A first feasibility study [1] under an ASI contract, was concluded in 2009 with the definition of a preliminary design for space use. Further studies were carried out at INRIM under an ESA contract and with the partnership of Selex-ES (SES). It was demonstrated that the optical detection simplifies the design and improves the frequency stability to values fully compliant to the Galileo specifications for the PHM. This paper presents a summary of the main results achieved by INRIM [2], and the industrialization approach required to pass from the laboratory prototype of the clock to an engineering model designed for the use on navigation satellites. The first step of the development plan will address the realization of electronic and optical units based on commercial components with either space heritage or ability to be space qualified.
{"title":"Industrialisation approach of the pop atomic clock for application to GNSS","authors":"A. Battisti, A. Cosentino, A. Sapia, M. Gioia, A. Borella, A. Godone, F. Levi, C. Calosso, S. Micalizio","doi":"10.1109/EFTF.2014.7331526","DOIUrl":"https://doi.org/10.1109/EFTF.2014.7331526","url":null,"abstract":"The POP clock is a vapor cell frequency standard operating in pulsed regime at the Rb ground-state hyperfine frequency (6834 MHz). Selex ES' interest in this technology relies on the possibility to implement a compact unit, with reduced mass, size and power consumption compared to the Passive Hydrogen Maser (PHM, the primary clock of Galileo Navigation Constellation), but similar frequency stability and less operation constraints. A first feasibility study [1] under an ASI contract, was concluded in 2009 with the definition of a preliminary design for space use. Further studies were carried out at INRIM under an ESA contract and with the partnership of Selex-ES (SES). It was demonstrated that the optical detection simplifies the design and improves the frequency stability to values fully compliant to the Galileo specifications for the PHM. This paper presents a summary of the main results achieved by INRIM [2], and the industrialization approach required to pass from the laboratory prototype of the clock to an engineering model designed for the use on navigation satellites. The first step of the development plan will address the realization of electronic and optical units based on commercial components with either space heritage or ability to be space qualified.","PeriodicalId":129873,"journal":{"name":"2014 European Frequency and Time Forum (EFTF)","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-06-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130584137","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 : 2014-06-23DOI: 10.1109/EFTF.2014.7331512
Y. Vorokhovsky, Vladimir Lyaskovsky, Yaroslav E. Kolpakov, A. Nikonov, A. Kotyukov
In recent years low noisy precision 100 MHz oscillators for continuous operation up to 15 years became more and more important for modern telecommunication and measurement equipment. Often it is important to minimize both close-in phase noise (at 10, 100 and 1000 Hz from carrier) and noise floor (at 10, 100 and 1000 kHz from carrier). Requirements became tougher not only for phase noises and various kinds of frequency stabilities, but also for OCXOs' reliability. To meet modern requirements for 100 MHz precision quartz oscillators, it is necessary to undertake actions targeted for improvement of reliability, optimization of both design and electronics of oscillator and considerable improvement of performance of quartz crystal. Successful advancement in these directions was made by authors in Morion Inc. during Y 2013.
{"title":"Recent achievements in performance of 100 MHz crystals and OCXOs","authors":"Y. Vorokhovsky, Vladimir Lyaskovsky, Yaroslav E. Kolpakov, A. Nikonov, A. Kotyukov","doi":"10.1109/EFTF.2014.7331512","DOIUrl":"https://doi.org/10.1109/EFTF.2014.7331512","url":null,"abstract":"In recent years low noisy precision 100 MHz oscillators for continuous operation up to 15 years became more and more important for modern telecommunication and measurement equipment. Often it is important to minimize both close-in phase noise (at 10, 100 and 1000 Hz from carrier) and noise floor (at 10, 100 and 1000 kHz from carrier). Requirements became tougher not only for phase noises and various kinds of frequency stabilities, but also for OCXOs' reliability. To meet modern requirements for 100 MHz precision quartz oscillators, it is necessary to undertake actions targeted for improvement of reliability, optimization of both design and electronics of oscillator and considerable improvement of performance of quartz crystal. Successful advancement in these directions was made by authors in Morion Inc. during Y 2013.","PeriodicalId":129873,"journal":{"name":"2014 European Frequency and Time Forum (EFTF)","volume":"29 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-06-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116597374","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 : 2014-06-23DOI: 10.1109/EFTF.2014.7331531
P. Dubé, A. Madej, M. Tibbo, J. Bernard
We have reported recently a high-accuracy measurement of the differential static scalar polarizability, Δα0, of the clock transition of 88Sr+. In this paper, we review the method used to make this measurement and the results obtained. Δα0 is an essential parameter for the control of the systematic shifts in ion optical frequency standards as it determines the blackbody radiation shift coefficient and the scalar Stark shift caused by micromotion. The new experimental value of Δα0 reduces the uncertainty of the blackbody radiation shift coefficient by a factor of 24, from 2 × 10-17 to 8.3 × 10-19. In addition, Δα0 determines the trap rf frequency for optimum cancellation of the positive Stark shift with the negative time-dilation shift. A suppression factor of more than 200 is obtained with the new value of Δα0, resulting in a net micromotion shift fractional uncertainty at the 10-19 level.
{"title":"Measurement of the static scalar polarizability of the 88Sr+ clock transition","authors":"P. Dubé, A. Madej, M. Tibbo, J. Bernard","doi":"10.1109/EFTF.2014.7331531","DOIUrl":"https://doi.org/10.1109/EFTF.2014.7331531","url":null,"abstract":"We have reported recently a high-accuracy measurement of the differential static scalar polarizability, Δα<sub>0</sub>, of the clock transition of <sup>88</sup>Sr<sup>+</sup>. In this paper, we review the method used to make this measurement and the results obtained. Δα<sub>0</sub> is an essential parameter for the control of the systematic shifts in ion optical frequency standards as it determines the blackbody radiation shift coefficient and the scalar Stark shift caused by micromotion. The new experimental value of Δα<sub>0</sub> reduces the uncertainty of the blackbody radiation shift coefficient by a factor of 24, from 2 × 10<sup>-17</sup> to 8.3 × 10<sup>-19</sup>. In addition, Δα<sub>0</sub> determines the trap rf frequency for optimum cancellation of the positive Stark shift with the negative time-dilation shift. A suppression factor of more than 200 is obtained with the new value of Δα<sub>0</sub>, resulting in a net micromotion shift fractional uncertainty at the 10<sup>-19</sup> level.","PeriodicalId":129873,"journal":{"name":"2014 European Frequency and Time Forum (EFTF)","volume":"36 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-06-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127466119","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 : 2014-06-23DOI: 10.1109/EFTF.2014.7331525
Zetian Xu, Xiaoyi Zeng, Xiaohui Shi, H. Che, K. Deng, Jie Zhang, Zehuang Lu
Magnesium ion which acts as the logic ion in 27Al+ ion optical clock is trapped and laser cooled in a linear ion trap. Rabi oscillation between two hyperfine ground states of 25Mg+ ion is observed and resonant frequency between two hyperfine ground states of 25Mg+ ion is measured. Earth magnetic field is compensated with three pairs of mutually perpendicular Helmholtz coils. Light shift induced by the Raman cooling beams is measured. With the photo-ionization laser of Al, Al+ ion is trapped together with Mg+ ion. The linewidth of the clock laser of the 27Al+ ion is measured to be about 0.8 Hz. The Allan deviation of the beat note from two independent lasers is 6.5×10-15 at 1s.
{"title":"Towards an 27Al+ ions optical clock","authors":"Zetian Xu, Xiaoyi Zeng, Xiaohui Shi, H. Che, K. Deng, Jie Zhang, Zehuang Lu","doi":"10.1109/EFTF.2014.7331525","DOIUrl":"https://doi.org/10.1109/EFTF.2014.7331525","url":null,"abstract":"Magnesium ion which acts as the logic ion in <sup>27</sup>Al<sub>+</sub> ion optical clock is trapped and laser cooled in a linear ion trap. Rabi oscillation between two hyperfine ground states of <sup>25</sup>Mg<sup>+</sup> ion is observed and resonant frequency between two hyperfine ground states of <sup>25</sup>Mg<sup>+</sup> ion is measured. Earth magnetic field is compensated with three pairs of mutually perpendicular Helmholtz coils. Light shift induced by the Raman cooling beams is measured. With the photo-ionization laser of Al, Al<sup>+</sup> ion is trapped together with Mg<sup>+</sup> ion. The linewidth of the clock laser of the <sup>27</sup>Al<sup>+</sup> ion is measured to be about 0.8 Hz. The Allan deviation of the beat note from two independent lasers is 6.5×10<sup>-15</sup> at 1s.","PeriodicalId":129873,"journal":{"name":"2014 European Frequency and Time Forum (EFTF)","volume":"9 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-06-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129127039","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 : 2014-06-23DOI: 10.1109/EFTF.2014.7331529
D. Ruffieux, N. Scolari, T. Le, P. Beuchat, A. Jaakkola, T. Pensala, J. Dekker, P. Dixit, C. Manier, K. Zoschke, H. Oppermann
This paper presents a miniature timing microsystem based on a pair of wafer-level packaged co-integrated low and high frequency silicon resonators -430kHz and 26MHz respectively- so as to implement a μW-level accurate, low power, temperature-compensated real time clock (RTC) and to generate low noise, low jitter clocks at any frequency between 1-50MHz in a reconfigurable way at less than 10mW power dissipation. Singulated resonator dies were assembled on a CMOS wafer by thermo-compressive bonding on Au stud-bumps and the resulting system was characterized at wafer level.
{"title":"A compact, versatile, miniature timing microsystem using two co-integrated wafer-level packaged silicon resonators","authors":"D. Ruffieux, N. Scolari, T. Le, P. Beuchat, A. Jaakkola, T. Pensala, J. Dekker, P. Dixit, C. Manier, K. Zoschke, H. Oppermann","doi":"10.1109/EFTF.2014.7331529","DOIUrl":"https://doi.org/10.1109/EFTF.2014.7331529","url":null,"abstract":"This paper presents a miniature timing microsystem based on a pair of wafer-level packaged co-integrated low and high frequency silicon resonators -430kHz and 26MHz respectively- so as to implement a μW-level accurate, low power, temperature-compensated real time clock (RTC) and to generate low noise, low jitter clocks at any frequency between 1-50MHz in a reconfigurable way at less than 10mW power dissipation. Singulated resonator dies were assembled on a CMOS wafer by thermo-compressive bonding on Au stud-bumps and the resulting system was characterized at wafer level.","PeriodicalId":129873,"journal":{"name":"2014 European Frequency and Time Forum (EFTF)","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-06-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129286923","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 : 2014-06-23DOI: 10.1109/EFTF.2014.7331484
M. Knapp, P. Jager, Markus Hauser, U. Rosler, W. Ruile, G. Scheinbacher, M. Honal, I. Bleyl, L. Reindl
We have investigated the temperature dependent elastic constants of SiO2 and GeO2. For this purpose, the phase velocity of the layered system has to be calculated using surface acoustic wave (SAW) differential delay lines on LiNbO3 substrates. Both SiO2 and GeO2 have a positive temperature coefficient of velocity. The GeO2 layer shows a significant reduction of the phase velocity compared to SiO2 which yields to an improved energy trapping of the surface acoustic wave in the overlay. However, severe stability issues arise using the GeO2 layer.
{"title":"Investigation of GeO2 thin film properties for improvement of temperature coefficient of frequency of SAW devices","authors":"M. Knapp, P. Jager, Markus Hauser, U. Rosler, W. Ruile, G. Scheinbacher, M. Honal, I. Bleyl, L. Reindl","doi":"10.1109/EFTF.2014.7331484","DOIUrl":"https://doi.org/10.1109/EFTF.2014.7331484","url":null,"abstract":"We have investigated the temperature dependent elastic constants of SiO<sub>2</sub> and GeO<sub>2</sub>. For this purpose, the phase velocity of the layered system has to be calculated using surface acoustic wave (SAW) differential delay lines on LiNbO<sub>3</sub> substrates. Both SiO<sub>2</sub> and GeO<sub>2</sub> have a positive temperature coefficient of velocity. The GeO<sub>2</sub> layer shows a significant reduction of the phase velocity compared to SiO<sub>2</sub> which yields to an improved energy trapping of the surface acoustic wave in the overlay. However, severe stability issues arise using the GeO<sub>2</sub> layer.","PeriodicalId":129873,"journal":{"name":"2014 European Frequency and Time Forum (EFTF)","volume":"10 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-06-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129562957","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 : 2014-06-23DOI: 10.1109/EFTF.2014.7331534
G. Rovera, M. Abgrall, P. Uhrich, J. Torre, C. Courde, M. Laas-Bourez, R. Sherwood
We present a direct comparison between two different techniques for the relative calibration of time transfer between remote time scales when using the signals transmitted by the Global Positioning System (GPS). In the remote sites, the local measurements are driving either the computation of the hardware delays of the local GPS equipment with respect to a given reference GPS station, a “receiver” calibration, or the computation of a global hardware offset between two distribution reference points of the remote time scales, a “link” calibration. Both techniques do not require the same measurements on site, and we discuss the uncertainty budget computation differences. We report on one calibration campaign organized during Autumn 2013 between Observatoire de Paris (OP), Paris, France, Observatoire de la Côte d'Azur (OCA), Plateau de Calern, France, and NERC Space Geodesy Facility (SGF), Herstmonceux, United Kingdom. We show the different ways to compute uncertainty budgets, leading to improvement factors of 1.2 to 1.5 on the hardware delay uncertainties when comparing the relative link calibration to the relative receiver calibration.
{"title":"Link calibration against receiver calibration time transfer uncertainty when using the Global Positioning System","authors":"G. Rovera, M. Abgrall, P. Uhrich, J. Torre, C. Courde, M. Laas-Bourez, R. Sherwood","doi":"10.1109/EFTF.2014.7331534","DOIUrl":"https://doi.org/10.1109/EFTF.2014.7331534","url":null,"abstract":"We present a direct comparison between two different techniques for the relative calibration of time transfer between remote time scales when using the signals transmitted by the Global Positioning System (GPS). In the remote sites, the local measurements are driving either the computation of the hardware delays of the local GPS equipment with respect to a given reference GPS station, a “receiver” calibration, or the computation of a global hardware offset between two distribution reference points of the remote time scales, a “link” calibration. Both techniques do not require the same measurements on site, and we discuss the uncertainty budget computation differences. We report on one calibration campaign organized during Autumn 2013 between Observatoire de Paris (OP), Paris, France, Observatoire de la Côte d'Azur (OCA), Plateau de Calern, France, and NERC Space Geodesy Facility (SGF), Herstmonceux, United Kingdom. We show the different ways to compute uncertainty budgets, leading to improvement factors of 1.2 to 1.5 on the hardware delay uncertainties when comparing the relative link calibration to the relative receiver calibration.","PeriodicalId":129873,"journal":{"name":"2014 European Frequency and Time Forum (EFTF)","volume":"24 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-06-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127626877","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 : 2014-06-23DOI: 10.1109/EFTF.2014.7331452
K. Stroganov, Timofey Kronidov, Boris Luylin, V. Kalinin, V. Plessky
This work reviews the operation principle of wireless measurement of temperature based on surface acoustic wave (SAW) delay line for electric power transmission lines. The architecture of the SAW reader, algorithm of temperature measurements and anti-collision method are considered.
{"title":"SAW temperature sensors for electric power transmission lines","authors":"K. Stroganov, Timofey Kronidov, Boris Luylin, V. Kalinin, V. Plessky","doi":"10.1109/EFTF.2014.7331452","DOIUrl":"https://doi.org/10.1109/EFTF.2014.7331452","url":null,"abstract":"This work reviews the operation principle of wireless measurement of temperature based on surface acoustic wave (SAW) delay line for electric power transmission lines. The architecture of the SAW reader, algorithm of temperature measurements and anti-collision method are considered.","PeriodicalId":129873,"journal":{"name":"2014 European Frequency and Time Forum (EFTF)","volume":"73 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-06-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127883432","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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