Pub Date : 2020-11-23DOI: 10.23919/ENC48637.2020.9317452
T. Schuldt, M. Gohlke, M. Oswald, J. Sanjuan, T. Wegehaupt, Tim Blomberg, Jan Wüst, Ludwig Blümel, V. Gualani, K. Abich, C. Braxmaier
Future GNSS architectures, such as the proposed Kepler system, foresee optical technologies. Optical frequency references in combination with optical inter-satellite links can improve satellite navigation with respect to intra-system synchronization, accuracy of orbit determination and system monitoring and integrity. We present the current status of our work on optical frequency references based on molecular iodine and on optical resonators. Several setups have been realized with respect to applications in space, being the basis for the Kepler system.
{"title":"Optical Clock Technologies Enabling Advanced GNSS","authors":"T. Schuldt, M. Gohlke, M. Oswald, J. Sanjuan, T. Wegehaupt, Tim Blomberg, Jan Wüst, Ludwig Blümel, V. Gualani, K. Abich, C. Braxmaier","doi":"10.23919/ENC48637.2020.9317452","DOIUrl":"https://doi.org/10.23919/ENC48637.2020.9317452","url":null,"abstract":"Future GNSS architectures, such as the proposed Kepler system, foresee optical technologies. Optical frequency references in combination with optical inter-satellite links can improve satellite navigation with respect to intra-system synchronization, accuracy of orbit determination and system monitoring and integrity. We present the current status of our work on optical frequency references based on molecular iodine and on optical resonators. Several setups have been realized with respect to applications in space, being the basis for the Kepler system.","PeriodicalId":157951,"journal":{"name":"2020 European Navigation Conference (ENC)","volume":"3 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-11-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128782004","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 : 2020-11-23DOI: 10.23919/ENC48637.2020.9317492
S. Lo, Yu‐Hsuan Chen
The Federal Aviation Administration (FAA) Alternative Position Navigation and Timing (APNT) program developed several possibilities for improving distance measuring equipment (DME) such as DME pseudolite (PL) systems to provide data and passive ranging in addition to traditional DME operations. These enhanced DME (eDME) were designed to serve as an operational back up to GPS/GNSS, particularly to support future airspace and Next Generation Air Transportation System (NextGen) operations. While eDME concepts are not part of the current upgrades to the US DME system, there is continued interested in the ideas as they can support other airspace needs and help meet federal directives to increase the resiliency of Positioning, Navigation, and Timing (PNT) services [1].
{"title":"Message Design for a Robust Time Signal using Distance Measuring Equipment (DME) Pulse Pair Position Modulated (PPPM) Pseudo lite","authors":"S. Lo, Yu‐Hsuan Chen","doi":"10.23919/ENC48637.2020.9317492","DOIUrl":"https://doi.org/10.23919/ENC48637.2020.9317492","url":null,"abstract":"The Federal Aviation Administration (FAA) Alternative Position Navigation and Timing (APNT) program developed several possibilities for improving distance measuring equipment (DME) such as DME pseudolite (PL) systems to provide data and passive ranging in addition to traditional DME operations. These enhanced DME (eDME) were designed to serve as an operational back up to GPS/GNSS, particularly to support future airspace and Next Generation Air Transportation System (NextGen) operations. While eDME concepts are not part of the current upgrades to the US DME system, there is continued interested in the ideas as they can support other airspace needs and help meet federal directives to increase the resiliency of Positioning, Navigation, and Timing (PNT) services [1].","PeriodicalId":157951,"journal":{"name":"2020 European Navigation Conference (ENC)","volume":"26 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-11-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134208183","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 : 2020-11-23DOI: 10.23919/ENC48637.2020.9317402
C. Ugé, Tina Scheidweiler, C. Jahn
The reduction of emissions is one of the main common goals all over the globe. Shipping, as the main impact source of global emissions, plays a vital role and can perceptibly contribute to decarbonisation. The objective of EmissionSEA is to develop a methodology for the quantitative determination of CO2 emissions from shipping. With the help of the data of the Automatic Identification System (AIS), motion information is set in relation to ship size, speed as well as meteorological and oceanographic environmental conditions. More than 300.000.000 daily AIS data records from hundreds of own and thousands of cooperative AIS base stations as well as detailed ship data including information on the main propulsion plant are conflated and allows a detailed target/actual comparison of ship emissions worldwide. ENC 2020 Topic: Aviation & Marine Navigation Challenges in safety and security of information, communication and navigation in relation to current emerging threats
{"title":"Estimation of worldwide ship emissions using AIS signals","authors":"C. Ugé, Tina Scheidweiler, C. Jahn","doi":"10.23919/ENC48637.2020.9317402","DOIUrl":"https://doi.org/10.23919/ENC48637.2020.9317402","url":null,"abstract":"The reduction of emissions is one of the main common goals all over the globe. Shipping, as the main impact source of global emissions, plays a vital role and can perceptibly contribute to decarbonisation. The objective of EmissionSEA is to develop a methodology for the quantitative determination of CO2 emissions from shipping. With the help of the data of the Automatic Identification System (AIS), motion information is set in relation to ship size, speed as well as meteorological and oceanographic environmental conditions. More than 300.000.000 daily AIS data records from hundreds of own and thousands of cooperative AIS base stations as well as detailed ship data including information on the main propulsion plant are conflated and allows a detailed target/actual comparison of ship emissions worldwide. ENC 2020 Topic: Aviation & Marine Navigation Challenges in safety and security of information, communication and navigation in relation to current emerging threats","PeriodicalId":157951,"journal":{"name":"2020 European Navigation Conference (ENC)","volume":"8 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-11-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134270380","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 : 2020-11-23DOI: 10.23919/ENC48637.2020.9317460
S. Glaser, G. Michalak, R. König, Benjamin Männel, H. Schuh
In this study, the expected improvement of the future GNSS infrastructure “Kepler” on global geodetic reference frames with the focus on the Earth rotation parameters (ERP: pole coordinates xp’ yp and UT1-UTC) is assessed by simulations. Kepler features a Medium Earth Orbit (MEO) and Low Earth Orbit (LEO) segment and is characterized by the innovative key technologies of optical inter-satellite links (ISL) and optical frequency references as proposed by the German Aerospace Center DLR. The standard deviations of the estimated pole coordinates from the Kepler constellation are below 1 µas compared to µas in xp and 15 µas in yp from the MEO-only solution. The standard deviation of the UT1-UTC estimates in case of the full Kepler constellation is 0.3 µs compared to 1.8µs in case of MEO-only. The highly precise Kepler technique with stable orbits together with the globally distributed station network is very beneficial for the estimation of the ERP, especially the pole coordinates. UT1-UTC cannot be absolutely estimated from any satellite technique alone and needs to get fixed to at least the first value to external data. UT1-UTC can only be estimated absolutely from the space technique Very Long Baseline Interferometry (VLBI) which was simulated as well in case of two different scenarios (classical and next generation) and combined with the MEO-only and the Kepler solution. VLBI lacks in the spatial and temporal resolution of observations limiting the accuracy of the pole coordinates compared to GNSS. In the combined Vl. Bl+Kepler solution the mean value of 50 µas in xp (VLBI-only) is reduced to −2 µas and the standard deviation from 62 µas (VLBI-only) reduced below 1 µas. The combination with Kepler leads to improved pole coordinate estimates of VLBI. The combination with VLBI allows the estimation of UT1-UTC for Kepler without external information. The standard deviation of the UT 1- UTC estimates is improved from 1.5 µs for MEO+ VLBI to 0.3 µs for Kepler+ VLBI. Further improvements can be noticed in case of the combination with a next generation VLBI solution.
{"title":"Future GNSS Infrastructure for Improved Geodetic Reference Frames","authors":"S. Glaser, G. Michalak, R. König, Benjamin Männel, H. Schuh","doi":"10.23919/ENC48637.2020.9317460","DOIUrl":"https://doi.org/10.23919/ENC48637.2020.9317460","url":null,"abstract":"In this study, the expected improvement of the future GNSS infrastructure “Kepler” on global geodetic reference frames with the focus on the Earth rotation parameters (ERP: pole coordinates xp’ yp and UT1-UTC) is assessed by simulations. Kepler features a Medium Earth Orbit (MEO) and Low Earth Orbit (LEO) segment and is characterized by the innovative key technologies of optical inter-satellite links (ISL) and optical frequency references as proposed by the German Aerospace Center DLR. The standard deviations of the estimated pole coordinates from the Kepler constellation are below 1 µas compared to µas in xp and 15 µas in yp from the MEO-only solution. The standard deviation of the UT1-UTC estimates in case of the full Kepler constellation is 0.3 µs compared to 1.8µs in case of MEO-only. The highly precise Kepler technique with stable orbits together with the globally distributed station network is very beneficial for the estimation of the ERP, especially the pole coordinates. UT1-UTC cannot be absolutely estimated from any satellite technique alone and needs to get fixed to at least the first value to external data. UT1-UTC can only be estimated absolutely from the space technique Very Long Baseline Interferometry (VLBI) which was simulated as well in case of two different scenarios (classical and next generation) and combined with the MEO-only and the Kepler solution. VLBI lacks in the spatial and temporal resolution of observations limiting the accuracy of the pole coordinates compared to GNSS. In the combined Vl. Bl+Kepler solution the mean value of 50 µas in xp (VLBI-only) is reduced to −2 µas and the standard deviation from 62 µas (VLBI-only) reduced below 1 µas. The combination with Kepler leads to improved pole coordinate estimates of VLBI. The combination with VLBI allows the estimation of UT1-UTC for Kepler without external information. The standard deviation of the UT 1- UTC estimates is improved from 1.5 µs for MEO+ VLBI to 0.3 µs for Kepler+ VLBI. Further improvements can be noticed in case of the combination with a next generation VLBI solution.","PeriodicalId":157951,"journal":{"name":"2020 European Navigation Conference (ENC)","volume":"6 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-11-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115706928","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 : 2020-11-23DOI: 10.23919/ENC48637.2020.9317339
Jan-Jöran Gehrt, Wenyi Liu, David Stenger, Shuchen Liu, D. Abel
Parameterization of global navigation satellite system (GNSS)-aided navigation filter is an active research topic, because it is crucial for the state estimation accuracy and there is little theoretical guidance. This publication presents parameterization for extended Kalman filter (EKF) with the help of Bayesian optimization. Different ways to model and parameterize the measurement noise are discussed. An adaptive parameterization scheme is proposed, which maps the environment according to the dilution of precision (DOP) and signal-to-noise ratio (SNR). The new adaptive parameterization approach is evaluated with a test car in Aachen, Germany. Results are compared to a sigma-epsilon variance model and show a remarkable improvement of position estimation accuracy and preciseness. In average, the mean error along the validation data set is reduced by 2.5 m and the standard deviation is halved.
{"title":"Environmentally Dependent Adaptive Parameterization of a GNSS-aided Tightly-Coupled Navigation Filter","authors":"Jan-Jöran Gehrt, Wenyi Liu, David Stenger, Shuchen Liu, D. Abel","doi":"10.23919/ENC48637.2020.9317339","DOIUrl":"https://doi.org/10.23919/ENC48637.2020.9317339","url":null,"abstract":"Parameterization of global navigation satellite system (GNSS)-aided navigation filter is an active research topic, because it is crucial for the state estimation accuracy and there is little theoretical guidance. This publication presents parameterization for extended Kalman filter (EKF) with the help of Bayesian optimization. Different ways to model and parameterize the measurement noise are discussed. An adaptive parameterization scheme is proposed, which maps the environment according to the dilution of precision (DOP) and signal-to-noise ratio (SNR). The new adaptive parameterization approach is evaluated with a test car in Aachen, Germany. Results are compared to a sigma-epsilon variance model and show a remarkable improvement of position estimation accuracy and preciseness. In average, the mean error along the validation data set is reduced by 2.5 m and the standard deviation is halved.","PeriodicalId":157951,"journal":{"name":"2020 European Navigation Conference (ENC)","volume":"27 23 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-11-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131968427","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 : 2020-11-23DOI: 10.23919/ENC48637.2020.9317471
Tan Truong-Ngoc, A. Khenchaf, F. Comblet, Pierre Franck, Jean-Marc Champeyroux, O. Reichert
GNSS brings more signals and more satellites to improve positioning services. This paper introduces data fusion from multiple Global Navigation Satellite System (GNSS) constellations. In fact, some failures in satellite's signals negatively impact the quality of positioning. For this purpose, this paper presents the robust Extended Kalman Filter (robust-EKF) to eliminate the outliers and de-noising method based on the Long Short-Term Memory (LSTM). The algorithms are tested using GPS, Galileo and GLONASS data corresponding to base station ABMF in Guadeloupe. Robust combination of GPS, Galileo, and GLONASS data improve the position accuracy from 41.0% to 95.0% compared to the use of independent systems and by about 84.0% compared to the non-robust combination of GPS, Galileo, and GLONASS data. In particular, the position precision improves significantly using the method LSTM-EKF by about 74.0% compared to the robust-EKF.
{"title":"Filter De-Noising Method Using Long Short-Term Memory","authors":"Tan Truong-Ngoc, A. Khenchaf, F. Comblet, Pierre Franck, Jean-Marc Champeyroux, O. Reichert","doi":"10.23919/ENC48637.2020.9317471","DOIUrl":"https://doi.org/10.23919/ENC48637.2020.9317471","url":null,"abstract":"GNSS brings more signals and more satellites to improve positioning services. This paper introduces data fusion from multiple Global Navigation Satellite System (GNSS) constellations. In fact, some failures in satellite's signals negatively impact the quality of positioning. For this purpose, this paper presents the robust Extended Kalman Filter (robust-EKF) to eliminate the outliers and de-noising method based on the Long Short-Term Memory (LSTM). The algorithms are tested using GPS, Galileo and GLONASS data corresponding to base station ABMF in Guadeloupe. Robust combination of GPS, Galileo, and GLONASS data improve the position accuracy from 41.0% to 95.0% compared to the use of independent systems and by about 84.0% compared to the non-robust combination of GPS, Galileo, and GLONASS data. In particular, the position precision improves significantly using the method LSTM-EKF by about 74.0% compared to the robust-EKF.","PeriodicalId":157951,"journal":{"name":"2020 European Navigation Conference (ENC)","volume":"30 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-11-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131972922","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 : 2020-11-23DOI: 10.23919/ENC48637.2020.9317332
O. John, M. Reimann
In the area of maritime rescue, the factor time in the event of an accident and the associated conduct of rescue operations is of fundamental importance. A difference in the arrival of the rescue forces from a few minutes can decide in the worst case between death or complete recovery of an injured person. First, this paper briefly addresses peculiarities of ship accidents and examines in particular communication-enhancing measures to avoid them. In this context, current developments in the field of automatic speech recognition by artificial intelligence are presented on the basis of the research project ARTUS - Automated Transcription of Maritime VHF Radio Communication for SAR Mission Coordination. Based on the technology used in the project to transcribe the content of maritime radio messages and to locate as well as identify vessels, its potential challenges and safety benefits are analyzed.
{"title":"Increasing Quality of Maritime Communication through Intelligent Speech Recognition and Radio Direction Finding","authors":"O. John, M. Reimann","doi":"10.23919/ENC48637.2020.9317332","DOIUrl":"https://doi.org/10.23919/ENC48637.2020.9317332","url":null,"abstract":"In the area of maritime rescue, the factor time in the event of an accident and the associated conduct of rescue operations is of fundamental importance. A difference in the arrival of the rescue forces from a few minutes can decide in the worst case between death or complete recovery of an injured person. First, this paper briefly addresses peculiarities of ship accidents and examines in particular communication-enhancing measures to avoid them. In this context, current developments in the field of automatic speech recognition by artificial intelligence are presented on the basis of the research project ARTUS - Automated Transcription of Maritime VHF Radio Communication for SAR Mission Coordination. Based on the technology used in the project to transcribe the content of maritime radio messages and to locate as well as identify vessels, its potential challenges and safety benefits are analyzed.","PeriodicalId":157951,"journal":{"name":"2020 European Navigation Conference (ENC)","volume":"28 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-11-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132153482","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 : 2020-11-23DOI: 10.23919/ENC48637.2020.9317349
G. Jo, J. Noh, J. Lee, D. Lim, Sang Jeong Lee
Recently, the GNSS signal has tended to utilize the data channel and the pilot channel, and the pilot channel uses a secondary code as well as a primary code. In general, a long secondary code is used for frame synchronization and a short secondary code is used for data symbol synchronization. So far, most of GNSS signals use NH code as the short secondary code. However, the NH code may decrease the ratio of the maximum peak to the side peak as the residual Doppler frequency increases. In this paper, we analyze the effect of residual Doppler frequency and propose a new secondary code candidate which has similar performance to NH code. Finally, the ratio of the maximum peak to the side peak according to the residual Doppler frequency is presented for each NH code and proposed secondary code candidate.
{"title":"A study on new secondary codes for GNSS","authors":"G. Jo, J. Noh, J. Lee, D. Lim, Sang Jeong Lee","doi":"10.23919/ENC48637.2020.9317349","DOIUrl":"https://doi.org/10.23919/ENC48637.2020.9317349","url":null,"abstract":"Recently, the GNSS signal has tended to utilize the data channel and the pilot channel, and the pilot channel uses a secondary code as well as a primary code. In general, a long secondary code is used for frame synchronization and a short secondary code is used for data symbol synchronization. So far, most of GNSS signals use NH code as the short secondary code. However, the NH code may decrease the ratio of the maximum peak to the side peak as the residual Doppler frequency increases. In this paper, we analyze the effect of residual Doppler frequency and propose a new secondary code candidate which has similar performance to NH code. Finally, the ratio of the maximum peak to the side peak according to the residual Doppler frequency is presented for each NH code and proposed secondary code candidate.","PeriodicalId":157951,"journal":{"name":"2020 European Navigation Conference (ENC)","volume":"49 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-11-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127248563","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 : 2020-11-23DOI: 10.23919/ENC48637.2020.9317521
M. Schönfeldt, Antoine Grenier, Anaïs Delépaut, P. Giordano, Richard Swinden, J. Ventura-Traveset, D. Blonski, J. Hahn
Today, deep space missions are navigated and tracked with Deep Space Tracking Stations. However, the navigation operations are relatively expensive and the accuracy is within kilometre range, which needs to be improved for human space exploration. This paper will present initial results of a system study about a Lunar Navigation Satellite System. The study contains investigations about the design of navigation transmitter satellites considering the characteristics of different lunar orbits, the resulting visibility conditions and approximate performances for user receivers on and around the Moon.
{"title":"A System Study about a Lunar Navigation Satellite Transmitter System","authors":"M. Schönfeldt, Antoine Grenier, Anaïs Delépaut, P. Giordano, Richard Swinden, J. Ventura-Traveset, D. Blonski, J. Hahn","doi":"10.23919/ENC48637.2020.9317521","DOIUrl":"https://doi.org/10.23919/ENC48637.2020.9317521","url":null,"abstract":"Today, deep space missions are navigated and tracked with Deep Space Tracking Stations. However, the navigation operations are relatively expensive and the accuracy is within kilometre range, which needs to be improved for human space exploration. This paper will present initial results of a system study about a Lunar Navigation Satellite System. The study contains investigations about the design of navigation transmitter satellites considering the characteristics of different lunar orbits, the resulting visibility conditions and approximate performances for user receivers on and around the Moon.","PeriodicalId":157951,"journal":{"name":"2020 European Navigation Conference (ENC)","volume":"21 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-11-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125388720","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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