Pub Date : 2015-04-12DOI: 10.1109/FCS.2015.7138848
Li Liu, Yigen Wang, Xiao-na Zhao, Yuxin Zhuang, Zhong Wang
We proposed a novel magnetic field measurement method extended from the CPT method. It is based on the coherent population beating (CPB) phenomenon. CPB occurs in a typical three-level system, when the frequency difference of the two pump laser fields have a detuning from the ground states splitting, and the CPB oscillation frequency is equal to the detuning. We are able to detect the beat frequency shift with the external magnetic field changing via digital processing, thus we can acquire the Zeeman frequency shift and then calculate external magnetic field intensity accurately.
{"title":"A magnetometer based on coherent population beating","authors":"Li Liu, Yigen Wang, Xiao-na Zhao, Yuxin Zhuang, Zhong Wang","doi":"10.1109/FCS.2015.7138848","DOIUrl":"https://doi.org/10.1109/FCS.2015.7138848","url":null,"abstract":"We proposed a novel magnetic field measurement method extended from the CPT method. It is based on the coherent population beating (CPB) phenomenon. CPB occurs in a typical three-level system, when the frequency difference of the two pump laser fields have a detuning from the ground states splitting, and the CPB oscillation frequency is equal to the detuning. We are able to detect the beat frequency shift with the external magnetic field changing via digital processing, thus we can acquire the Zeeman frequency shift and then calculate external magnetic field intensity accurately.","PeriodicalId":57667,"journal":{"name":"时间频率公报","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2015-04-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90048847","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 : 2015-04-12DOI: 10.1109/FCS.2015.7138881
S. Micalizio, F. Levi, A. Godone, C. Calosso, B. François, S. Guérandel, D. Holleville, E. de Clercq, L. de Sarlo, P. Yun, J. Danet, M. Langlois, R. Boudot, M. A. Hafiz, E. Şahin, C. Affolderbach, S. Kang, F. Gruet, M. Gharavipour, G. Mileti, B. Desruelle
Vapor cell atomic clocks are an interesting technology because they combine compactness, low power consumption and excellent relative frequency stability. Recently, due to better performing laser sources and innovative techniques to prepare and detect the atoms, several cell-based prototypes exhibiting unprecedented frequency stability have been developed. These techniques allow a reduction in the transfer of laser noise to the atoms, improvement of the signal-to-noise ratio and subsequently the clock's frequency stability. The project IND55 Mclocks funded by the European Metrological Research Programme (EMRP) proposes to develop high performances vapor cell clocks for industrial applications. Three technologies are investigated: 1) the pulsed optical pumping (POP) scheme; 2) the cold atoms approach, and 3) the Coherent Population Trapping (CPT). The results related to the first period of activity are presented.
{"title":"Compact clocks for industrial applications: The EMRP project IND 55 MClocks","authors":"S. Micalizio, F. Levi, A. Godone, C. Calosso, B. François, S. Guérandel, D. Holleville, E. de Clercq, L. de Sarlo, P. Yun, J. Danet, M. Langlois, R. Boudot, M. A. Hafiz, E. Şahin, C. Affolderbach, S. Kang, F. Gruet, M. Gharavipour, G. Mileti, B. Desruelle","doi":"10.1109/FCS.2015.7138881","DOIUrl":"https://doi.org/10.1109/FCS.2015.7138881","url":null,"abstract":"Vapor cell atomic clocks are an interesting technology because they combine compactness, low power consumption and excellent relative frequency stability. Recently, due to better performing laser sources and innovative techniques to prepare and detect the atoms, several cell-based prototypes exhibiting unprecedented frequency stability have been developed. These techniques allow a reduction in the transfer of laser noise to the atoms, improvement of the signal-to-noise ratio and subsequently the clock's frequency stability. The project IND55 Mclocks funded by the European Metrological Research Programme (EMRP) proposes to develop high performances vapor cell clocks for industrial applications. Three technologies are investigated: 1) the pulsed optical pumping (POP) scheme; 2) the cold atoms approach, and 3) the Coherent Population Trapping (CPT). The results related to the first period of activity are presented.","PeriodicalId":57667,"journal":{"name":"时间频率公报","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2015-04-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89655927","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 : 2015-04-12DOI: 10.1109/FCS.2015.7138895
S. Ghenna, F. Giraud, C. Giraud-Audine, M. Amberg, B. Lemaire-Semail
This paper presents a new method to produce and control the vibration amplitude and direction of a travelling wave in a finite beam, using multi-modal approach. A closed loop control of the transducer vibration is applied using vector control method. the modelling in rotating frame and the decoupling according to two-axis allows to obtain a double independent closed loop control. This allows to regulate the vibration amplitude of the travelling wave directly. An analytical modelling is presented, with experimental validation, showing good performances even in the presence of perturbations.
{"title":"Modelling and control of a travelling wave in a finite beam, using multi-modal approach and vector control method","authors":"S. Ghenna, F. Giraud, C. Giraud-Audine, M. Amberg, B. Lemaire-Semail","doi":"10.1109/FCS.2015.7138895","DOIUrl":"https://doi.org/10.1109/FCS.2015.7138895","url":null,"abstract":"This paper presents a new method to produce and control the vibration amplitude and direction of a travelling wave in a finite beam, using multi-modal approach. A closed loop control of the transducer vibration is applied using vector control method. the modelling in rotating frame and the decoupling according to two-axis allows to obtain a double independent closed loop control. This allows to regulate the vibration amplitude of the travelling wave directly. An analytical modelling is presented, with experimental validation, showing good performances even in the presence of perturbations.","PeriodicalId":57667,"journal":{"name":"时间频率公报","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2015-04-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77383596","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 : 2015-04-12DOI: 10.1109/FCS.2015.7138910
R. Szplet, P. Kwiatkowski, Z. Jachna, K. Rozyc
We present a design, FPGA-based implementation and test results of a new three-channel time interval counter developed for a project called Legal Time Distribution System (LTDS). The main aim of the counter is to gather information about time drift of clocks involved into the LTDS, then to evaluate their stability, and finally to select the most stable one as a local clock. The counter provides a high measurement precision (<; 15 ps) and wide range (> 1s) that are obtained by combining period counting with two-stage time interpolation. The time counter is implemented in a universally available and relatively cheap programmable device from family Spartan-6 (Xilinx).
{"title":"Precise three-channel integrated time counter","authors":"R. Szplet, P. Kwiatkowski, Z. Jachna, K. Rozyc","doi":"10.1109/FCS.2015.7138910","DOIUrl":"https://doi.org/10.1109/FCS.2015.7138910","url":null,"abstract":"We present a design, FPGA-based implementation and test results of a new three-channel time interval counter developed for a project called Legal Time Distribution System (LTDS). The main aim of the counter is to gather information about time drift of clocks involved into the LTDS, then to evaluate their stability, and finally to select the most stable one as a local clock. The counter provides a high measurement precision (<; 15 ps) and wide range (> 1s) that are obtained by combining period counting with two-stage time interpolation. The time counter is implemented in a universally available and relatively cheap programmable device from family Spartan-6 (Xilinx).","PeriodicalId":57667,"journal":{"name":"时间频率公报","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2015-04-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78504255","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 : 2015-04-12DOI: 10.1109/FCS.2015.7138864
D. Sergei
This paper presents the new balanced low-loss DMS filter with the narrowed passband and improved selectivity on 42° YX LiTaO3. The filter is realized as two-transducer scheme. A narrow passband of the filter is obtained by choosing a definite gap length between the input and output IDTs. Also the both long weighted input IDT and reflectors are used. A shape of the frequency response of the filter is determined by the weighting function of the input IDT, number of the electrodes in output IDT and reflectors, relationship between the electrode pitches in the input IDT, output IDT and reflectors. An optimization of the mentioned parameters with a computer simulation using equivalent circuit model allows to get a specified high selectivity of the filter with a fractional bandwidth of 0.5-0.6% under condition that the insertion losses are low and input and output impedances are close to the specified real values. To decrease the input and output impedances the parallel connection of the two filters in the different acoustic tracks is used. To improve the selectivity of the filter the cascaded connection and phase weighting the input IDT are employed. The 300 MHz sample of the balanced SAW filter has shown an insertion loss of 3 dB, 2-dB bandwidth of 1.5 MHz, stopband attenuation of 70 dB at ±12 MHz offsets from a center frequency in a 75-Ω balanced system. The filter did not require the matching elements and housed in the 9.1×7.1×2 mm SMD package.
{"title":"Balanced low-loss 2-IDT double mode SAW filter with narrowed passband and improved selectivity","authors":"D. Sergei","doi":"10.1109/FCS.2015.7138864","DOIUrl":"https://doi.org/10.1109/FCS.2015.7138864","url":null,"abstract":"This paper presents the new balanced low-loss DMS filter with the narrowed passband and improved selectivity on 42° YX LiTaO3. The filter is realized as two-transducer scheme. A narrow passband of the filter is obtained by choosing a definite gap length between the input and output IDTs. Also the both long weighted input IDT and reflectors are used. A shape of the frequency response of the filter is determined by the weighting function of the input IDT, number of the electrodes in output IDT and reflectors, relationship between the electrode pitches in the input IDT, output IDT and reflectors. An optimization of the mentioned parameters with a computer simulation using equivalent circuit model allows to get a specified high selectivity of the filter with a fractional bandwidth of 0.5-0.6% under condition that the insertion losses are low and input and output impedances are close to the specified real values. To decrease the input and output impedances the parallel connection of the two filters in the different acoustic tracks is used. To improve the selectivity of the filter the cascaded connection and phase weighting the input IDT are employed. The 300 MHz sample of the balanced SAW filter has shown an insertion loss of 3 dB, 2-dB bandwidth of 1.5 MHz, stopband attenuation of 70 dB at ±12 MHz offsets from a center frequency in a 75-Ω balanced system. The filter did not require the matching elements and housed in the 9.1×7.1×2 mm SMD package.","PeriodicalId":57667,"journal":{"name":"时间频率公报","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2015-04-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84603455","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 : 2015-04-12DOI: 10.1109/FCS.2015.7138915
S. Kundermann, S. Lecomte
Carrier envelope frequency (fCEO) stabilization of frequency combs is traditionally achieved via power modulation of the pump of the comb oscillator. A further possibility is to shift the laser fCEO using an external acousto-optic frequency shifter (AOFS). In this case the optical frequency comb spectrum is shifted exactly by the RF modulation frequency of the AOFS. In this work different stabilization schemes in self-referenced frequency comb system architecture are compared. It is shown that AOFS frequency shifting represents a high performance alternative to the standard feedback control via pump power modulation.
{"title":"Comparison of different carrier-envelope frequency stabilization methods for a high performance DPSSL frequency comb","authors":"S. Kundermann, S. Lecomte","doi":"10.1109/FCS.2015.7138915","DOIUrl":"https://doi.org/10.1109/FCS.2015.7138915","url":null,"abstract":"Carrier envelope frequency (fCEO) stabilization of frequency combs is traditionally achieved via power modulation of the pump of the comb oscillator. A further possibility is to shift the laser fCEO using an external acousto-optic frequency shifter (AOFS). In this case the optical frequency comb spectrum is shifted exactly by the RF modulation frequency of the AOFS. In this work different stabilization schemes in self-referenced frequency comb system architecture are compared. It is shown that AOFS frequency shifting represents a high performance alternative to the standard feedback control via pump power modulation.","PeriodicalId":57667,"journal":{"name":"时间频率公报","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2015-04-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83944649","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 : 2015-04-12DOI: 10.1109/FCS.2015.7138820
L. Yi, E. Burt, R. Tjoelker
The mercury linear ion trap frequency standard (LITS) [1] at JPL continues to advance with multiple applications. In particular, the outstanding long-term stability [2] and practicality of the ground-based clock have attracted significant interests for time-keeping and metrology. However, the mercury RF discharge lamp used for optical pumping and state detection may limit the ultimate stability performance of the clock [3-4], constraining even broader application. For mercury ion frequency standards, the operational lamp behavior is described by the ratio of useful light at 194nm and unwanted background light at 254nm (194/254). This ratio has been observed to depend on several factors Increasing the 194nm output decreases optical pumping times and an increase of the 194/254 ratio improves the clock signal-to-noise ratio (SNR). These improvements lead to an improvement in clock short-term stability and enable the use of an even broader range of local oscillators. We have carried out several experiments to unfold the relationship between the 194/254 and the fabrication factors: buffer gas pressure, lamp ID, and the quantity of mercury. The quantitative results may be used to improve the process of lamp fabrication for mercury ion frequency standards. The research here may also shed light on other lamp-based applications.
{"title":"Mercury lamp studies in support of trapped ion frequency standards","authors":"L. Yi, E. Burt, R. Tjoelker","doi":"10.1109/FCS.2015.7138820","DOIUrl":"https://doi.org/10.1109/FCS.2015.7138820","url":null,"abstract":"The mercury linear ion trap frequency standard (LITS) [1] at JPL continues to advance with multiple applications. In particular, the outstanding long-term stability [2] and practicality of the ground-based clock have attracted significant interests for time-keeping and metrology. However, the mercury RF discharge lamp used for optical pumping and state detection may limit the ultimate stability performance of the clock [3-4], constraining even broader application. For mercury ion frequency standards, the operational lamp behavior is described by the ratio of useful light at 194nm and unwanted background light at 254nm (194/254). This ratio has been observed to depend on several factors Increasing the 194nm output decreases optical pumping times and an increase of the 194/254 ratio improves the clock signal-to-noise ratio (SNR). These improvements lead to an improvement in clock short-term stability and enable the use of an even broader range of local oscillators. We have carried out several experiments to unfold the relationship between the 194/254 and the fabrication factors: buffer gas pressure, lamp ID, and the quantity of mercury. The quantitative results may be used to improve the process of lamp fabrication for mercury ion frequency standards. The research here may also shed light on other lamp-based applications.","PeriodicalId":57667,"journal":{"name":"时间频率公报","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2015-04-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83689144","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 : 2015-04-12DOI: 10.1109/FCS.2015.7138851
R. Piriz, D. Rodríguez, P. Roldan, A. Mudrak, A. Bauch, F. Riedel, E. Staliuniene, J. Galindo, H. Esteban, I. Sesia, G. Cerretto, K. Jaldehag, C. Rieck, P. Uhrich, G. Rovera
In the Galileo FOC phase (Full Operational Capability), GMV is the prime contractor for the Time and Geodetic Validation Facility (TGVF), a contract of the European Space Agency (ESA). Within the TGVF, the Time Validation Facility (TVF) is the subsystem in charge of steering Galileo System Time (GST) to UTC, among other duties. The new TVF is operated at GMV headquarters near Madrid, Spain. TVF operations rely on the contribution of five European timing laboratories, located at INRiM, OP, PTB, ROA, and SP. This paper provides a general description of the TVF element and its related activities for the FOC phase, and presents the main results and findings of the TVF operation until now.
{"title":"The Time Validation Facility (TVF): An all-new key element of the Galileo operational phase","authors":"R. Piriz, D. Rodríguez, P. Roldan, A. Mudrak, A. Bauch, F. Riedel, E. Staliuniene, J. Galindo, H. Esteban, I. Sesia, G. Cerretto, K. Jaldehag, C. Rieck, P. Uhrich, G. Rovera","doi":"10.1109/FCS.2015.7138851","DOIUrl":"https://doi.org/10.1109/FCS.2015.7138851","url":null,"abstract":"In the Galileo FOC phase (Full Operational Capability), GMV is the prime contractor for the Time and Geodetic Validation Facility (TGVF), a contract of the European Space Agency (ESA). Within the TGVF, the Time Validation Facility (TVF) is the subsystem in charge of steering Galileo System Time (GST) to UTC, among other duties. The new TVF is operated at GMV headquarters near Madrid, Spain. TVF operations rely on the contribution of five European timing laboratories, located at INRiM, OP, PTB, ROA, and SP. This paper provides a general description of the TVF element and its related activities for the FOC phase, and presents the main results and findings of the TVF operation until now.","PeriodicalId":57667,"journal":{"name":"时间频率公报","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2015-04-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85639474","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 : 2015-04-12DOI: 10.1109/FCS.2015.7138902
Hongbo Wang, Hang Yi, Shengkang Zhang, Haifeng Wang, F. Shi, Huaiying Shang, Yujie Yang, J. Ge, Zhiqi Li
This paper gives a test method of BeiDou timing receiver delay. A BeiDou System simulator and a time interval counter were used in the experiments. During the process, the most important step is to calibrate the delay of the simulator. The uncertainty of this method is analyzed to be less than 1.5ns. Using this method, some typical Chinese commercial timing receivers were tested, and the results are shown in figures. The receiver delay variations with temperature have been studied.
{"title":"The study of BeiDou timing receiver delay calibration","authors":"Hongbo Wang, Hang Yi, Shengkang Zhang, Haifeng Wang, F. Shi, Huaiying Shang, Yujie Yang, J. Ge, Zhiqi Li","doi":"10.1109/FCS.2015.7138902","DOIUrl":"https://doi.org/10.1109/FCS.2015.7138902","url":null,"abstract":"This paper gives a test method of BeiDou timing receiver delay. A BeiDou System simulator and a time interval counter were used in the experiments. During the process, the most important step is to calibrate the delay of the simulator. The uncertainty of this method is analyzed to be less than 1.5ns. Using this method, some typical Chinese commercial timing receivers were tested, and the results are shown in figures. The receiver delay variations with temperature have been studied.","PeriodicalId":57667,"journal":{"name":"时间频率公报","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2015-04-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89372528","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 : 2015-04-12DOI: 10.1109/FCS.2015.7138786
N. Wells, T. Driskell, J. Camparo
The concept of atomic thermometry is demonstrated in an experimental system consisting of two lasers frequency stabilized using FM spectroscopy. Utilizing the temperature insensitivity of the 87Rb D1 isoclinic point, a reference laser is beat against a second laser locked to an atomic transition whose frequency is strongly dependent on the vapor temperature. The data presented here indicates that thermal fluctuations down to the mK level could potentially be sensed. This concept may be useful to obtain improved long term performance in Rb vapor cell atomic clocks.
{"title":"87Rb isoclinic point thermometry","authors":"N. Wells, T. Driskell, J. Camparo","doi":"10.1109/FCS.2015.7138786","DOIUrl":"https://doi.org/10.1109/FCS.2015.7138786","url":null,"abstract":"The concept of atomic thermometry is demonstrated in an experimental system consisting of two lasers frequency stabilized using FM spectroscopy. Utilizing the temperature insensitivity of the 87Rb D1 isoclinic point, a reference laser is beat against a second laser locked to an atomic transition whose frequency is strongly dependent on the vapor temperature. The data presented here indicates that thermal fluctuations down to the mK level could potentially be sensed. This concept may be useful to obtain improved long term performance in Rb vapor cell atomic clocks.","PeriodicalId":57667,"journal":{"name":"时间频率公报","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2015-04-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77128195","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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