Pub Date : 2015-04-12DOI: 10.1109/FCS.2015.7138809
Maryam Abedi, T. Jin
When crystal oscillator applied in high dynamic host vehicle, dynamic loads impact its short and medium-term stability. In order to suppression and/or reduction these impacts, gyroscopic mounting is proposed to install oscillator on it. One of the main parameters which affect dynamic loads impacts on oscillator output is crystal g-sensitivity vector. Therefore, at first, statistical study has been accomplished on this parameter for SC-cut crystals which used in high dynamic oscillators. This study reveals that the angle between this vector and crystal surface (φ) nearly follows Rayleigh distribution with 1σ=19°. Thus, this vector tends to be close to crystal surface not perpendicular to it. Furthermore the analysis results of using gyro-mounting shows the acceptable results for quartz crystals with |φ|<;2σ=38° (85%). To prove gyro efficiency, its effect on each dynamic load is analyzed separately. The results of related analyses reveal that gyro shows its best for attitude change of host vehicle, such that it totally suppresses relevant disturbances. In the case of steady state load, sinusoidal and random vibrations, gyro best effects appear for |φ|<;30° and β angles which are not too close to 90°. Totally when high dynamic crystal oscillator is installed on gyro-mounting, the probability of observing instability on its output is reduced.
{"title":"Novel gyroscopic mounting for crystal oscillator (payload) applied in high dynamic host vehicle (platform) to improve its output stability","authors":"Maryam Abedi, T. Jin","doi":"10.1109/FCS.2015.7138809","DOIUrl":"https://doi.org/10.1109/FCS.2015.7138809","url":null,"abstract":"When crystal oscillator applied in high dynamic host vehicle, dynamic loads impact its short and medium-term stability. In order to suppression and/or reduction these impacts, gyroscopic mounting is proposed to install oscillator on it. One of the main parameters which affect dynamic loads impacts on oscillator output is crystal g-sensitivity vector. Therefore, at first, statistical study has been accomplished on this parameter for SC-cut crystals which used in high dynamic oscillators. This study reveals that the angle between this vector and crystal surface (φ) nearly follows Rayleigh distribution with 1σ=19°. Thus, this vector tends to be close to crystal surface not perpendicular to it. Furthermore the analysis results of using gyro-mounting shows the acceptable results for quartz crystals with |φ|<;2σ=38° (85%). To prove gyro efficiency, its effect on each dynamic load is analyzed separately. The results of related analyses reveal that gyro shows its best for attitude change of host vehicle, such that it totally suppresses relevant disturbances. In the case of steady state load, sinusoidal and random vibrations, gyro best effects appear for |φ|<;30° and β angles which are not too close to 90°. Totally when high dynamic crystal oscillator is installed on gyro-mounting, the probability of observing instability on its output is reduced.","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":"87806987","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.2015.7138814
Y. Yano, S. Goka, M. Kajita
We both numerically and analytically investigate on the light shift in Ramsey-CPT resonance for compact atomic clocks. The numerical calculation of the light shift is based on a density matrix analysis in Λ-type three state model. And the analytical method leads to an estimation equation of light shift in the Raman-Ramsey scheme. The estimation equation expresses the relationship between light shift and all pulse parameters. The results show that the estimation equation was reproduced well as the numerical results.
{"title":"Estimation of the light shift in Ramsey-coherent population trapping","authors":"Y. Yano, S. Goka, M. Kajita","doi":"10.1109/FCS.2015.7138814","DOIUrl":"https://doi.org/10.1109/FCS.2015.7138814","url":null,"abstract":"We both numerically and analytically investigate on the light shift in Ramsey-CPT resonance for compact atomic clocks. The numerical calculation of the light shift is based on a density matrix analysis in Λ-type three state model. And the analytical method leads to an estimation equation of light shift in the Raman-Ramsey scheme. The estimation equation expresses the relationship between light shift and all pulse parameters. The results show that the estimation equation was reproduced well as the numerical results.","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":"87035452","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.2015.7138892
Yuanbo Du, Rong Wei, R. Dong, Fan Zou, Yu-zhu Wang
This work presents several advances in our 87Rb atomic fountain clock (AFC) at Shanghai Institute of Optics and Fine Mechanics (SIOM). We directly lock the local oscillator (LO) of AFC, and make some improvements on the physical system, including optimizing the coupling of microwave and adjusting down the working temperature of interrogation region, etc. A short-term fractional frequency stability of 2.7 × 10-13τ-1/2 is obtained by comparing the AFC with an H-maser. In accuracy evaluation of AFC, a self-comparison method is introduced, and an evaluation precision of 6 ×10-16 is obtained at the average time of 300 000 s. In addition, a GPS common view instrument is set up to compare AFC with frequency standards at other time-keeping laboratories.
{"title":"Advances in the atomic fountain clock at SIOM","authors":"Yuanbo Du, Rong Wei, R. Dong, Fan Zou, Yu-zhu Wang","doi":"10.1109/FCS.2015.7138892","DOIUrl":"https://doi.org/10.1109/FCS.2015.7138892","url":null,"abstract":"This work presents several advances in our 87Rb atomic fountain clock (AFC) at Shanghai Institute of Optics and Fine Mechanics (SIOM). We directly lock the local oscillator (LO) of AFC, and make some improvements on the physical system, including optimizing the coupling of microwave and adjusting down the working temperature of interrogation region, etc. A short-term fractional frequency stability of 2.7 × 10-13τ-1/2 is obtained by comparing the AFC with an H-maser. In accuracy evaluation of AFC, a self-comparison method is introduced, and an evaluation precision of 6 ×10-16 is obtained at the average time of 300 000 s. In addition, a GPS common view instrument is set up to compare AFC with frequency standards at other time-keeping laboratories.","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":"88034161","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.2015.7138795
Y. Yoon, H. Moyer, D. Kirby, R. Kubena, R. Joyce, R. Bowen, H. Nguyen, D. Chang
UHF quartz MEMS oscillators operating at 813 MHz, 920 MHz and 1.048 GHz carrier frequencies utilizing a push-pull topology based on MOSIS SiGe 7WL technology have been demonstrated. The 1048 MHz resonator has an unloaded Q of 6,920 and a motional resistance of 31.7 ohms, as measured in a vacuum. This yields an fxQ product of 7.25×1012, close to the expected limit for quartz devices of 1×1013. Device phase noise was measured showing a minimum phase noise of -100 dBc/Hz for an 813 MHz oscillator at 1 kHz offset. A tuning range of 80 ppm was demonstrated at 920 MHz.
{"title":"UHF SiGe push-pull VCO MEMS oscillators","authors":"Y. Yoon, H. Moyer, D. Kirby, R. Kubena, R. Joyce, R. Bowen, H. Nguyen, D. Chang","doi":"10.1109/FCS.2015.7138795","DOIUrl":"https://doi.org/10.1109/FCS.2015.7138795","url":null,"abstract":"UHF quartz MEMS oscillators operating at 813 MHz, 920 MHz and 1.048 GHz carrier frequencies utilizing a push-pull topology based on MOSIS SiGe 7WL technology have been demonstrated. The 1048 MHz resonator has an unloaded Q of 6,920 and a motional resistance of 31.7 ohms, as measured in a vacuum. This yields an fxQ product of 7.25×1012, close to the expected limit for quartz devices of 1×1013. Device phase noise was measured showing a minimum phase noise of -100 dBc/Hz for an 813 MHz oscillator at 1 kHz offset. A tuning range of 80 ppm was demonstrated at 920 MHz.","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":"89305112","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.2015.7138961
P. Yun, S. Mejri, François Tricot, D. Holleville, E. de Clercq, S. Guérandel
Spectroscopy studies of coherent population trapping (CPT) with constructive polarization modulation are presented. In these studies, the effects of modulation frequency and laser intensity on the CPT contrast of the clock transition are investigated. We experimentally show that no CPT transition with ΔmF=2 is excited. Moreover, the constructive polarization modulation CPT signals are observed in both cases, with excited levels F'=3 and F'=4 in the Dl line of Cesium. Our studies show that this scheme, with potential to implement a compact and high performance clock, could also be applied to high pressure buffer gas cell, e.g., chip scale atomic clock.
{"title":"Study on double-modulation coherent population trapping resonance","authors":"P. Yun, S. Mejri, François Tricot, D. Holleville, E. de Clercq, S. Guérandel","doi":"10.1109/FCS.2015.7138961","DOIUrl":"https://doi.org/10.1109/FCS.2015.7138961","url":null,"abstract":"Spectroscopy studies of coherent population trapping (CPT) with constructive polarization modulation are presented. In these studies, the effects of modulation frequency and laser intensity on the CPT contrast of the clock transition are investigated. We experimentally show that no CPT transition with ΔmF=2 is excited. Moreover, the constructive polarization modulation CPT signals are observed in both cases, with excited levels F'=3 and F'=4 in the Dl line of Cesium. Our studies show that this scheme, with potential to implement a compact and high performance clock, could also be applied to high pressure buffer gas cell, e.g., chip scale atomic clock.","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":"88093442","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.2015.7138871
A. Jaakkola, P. Pekko, J. Dekker, M. Prunnila, T. Pensala
We report quartz level temperature stability of piezoelectrically driven silicon MEMS resonators. Frequency stability of better than ±10 ppm is measured for 23 MHz extensional mode resonators over a temperature range of T = -40 ... + 85°C. The temperature compensation mechanism is entirely passive, relying on the tailored elastic properties of heavily doped silicon with a doping level of n > 1020cm-3, and on an optimized resonator geometry. The result highlights the potential of silicon MEMS resonators to function as pin-to-pin compatible replacements for quartz crystals without any active temperature compensation.
{"title":"Second order temperature compensated piezoelectrically driven 23 MHz heavily doped silicon resonators with ±10 ppm temperature stability","authors":"A. Jaakkola, P. Pekko, J. Dekker, M. Prunnila, T. Pensala","doi":"10.1109/FCS.2015.7138871","DOIUrl":"https://doi.org/10.1109/FCS.2015.7138871","url":null,"abstract":"We report quartz level temperature stability of piezoelectrically driven silicon MEMS resonators. Frequency stability of better than ±10 ppm is measured for 23 MHz extensional mode resonators over a temperature range of T = -40 ... + 85°C. The temperature compensation mechanism is entirely passive, relying on the tailored elastic properties of heavily doped silicon with a doping level of n > 1020cm-3, and on an optimized resonator geometry. The result highlights the potential of silicon MEMS resonators to function as pin-to-pin compatible replacements for quartz crystals without any active temperature compensation.","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":"90262641","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.2015.7138938
R. Schneider, T. Naing, T. Rocheleau, C. Nguyen
A voltage controlled resonance frequency tuning mechanism, capable of effecting 1,500 ppm frequency shifts or more, is demonstrated for the first time on an AlN capacitive-piezoelectric resonator. The key enabler here is a compliant top electrode suspension that moves with applied voltage to effectively vary capacitance in series with the device, hence changing its series resonance frequency. Capacitive-piezoelectric AlN micromechanical resonators, i.e., those with electrodes not directly attached to the piezoelectric material, already exhibit high Q-factors compared to attached-electrode counterparts, e.g., 8,800 versus 2,100 at 300 MHz; are on/off switchable; and, as shown in this work, can exhibit electromechanical coupling Cx=C0 of 1.0%. This new ability to tune frequency without the need for external components now invites the use of on-chip corrective schemes to improve accuracy or reduce temperature-induced frequency drift, making an even more compelling case to employ this technology for frequency control applications.
{"title":"Gap reduction based frequency tuning for AlN capacitive-piezoelectric resonators","authors":"R. Schneider, T. Naing, T. Rocheleau, C. Nguyen","doi":"10.1109/FCS.2015.7138938","DOIUrl":"https://doi.org/10.1109/FCS.2015.7138938","url":null,"abstract":"A voltage controlled resonance frequency tuning mechanism, capable of effecting 1,500 ppm frequency shifts or more, is demonstrated for the first time on an AlN capacitive-piezoelectric resonator. The key enabler here is a compliant top electrode suspension that moves with applied voltage to effectively vary capacitance in series with the device, hence changing its series resonance frequency. Capacitive-piezoelectric AlN micromechanical resonators, i.e., those with electrodes not directly attached to the piezoelectric material, already exhibit high Q-factors compared to attached-electrode counterparts, e.g., 8,800 versus 2,100 at 300 MHz; are on/off switchable; and, as shown in this work, can exhibit electromechanical coupling Cx=C0 of 1.0%. This new ability to tune frequency without the need for external components now invites the use of on-chip corrective schemes to improve accuracy or reduce temperature-induced frequency drift, making an even more compelling case to employ this technology for frequency control 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":"75054818","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.2015.7138874
J. Zou, Chih-Ming Lin, A. Pisano
The use of butterfly-shaped thin plates, formed by reducing the tether-to-plate angle, can raised the quality factor (Q) of aluminum nitride (AlN) Lamb wave resonators (LWRs) by eliminating the anchor loss. The finite element analysis (FEA) simulation results show that the butterfly-shaped plate can efficiently keep the vibration far from the edges at the tether-to-plate plane, so that the acoustic wave leaky through the supporting tethers is reduced. Specifically, the rounded butterfly-shaped resonators show more efficient suppression in the anchor loss compared to the beveled butterfly-shaped resonators. The measured frequency response for a 863-MHz AlN LWR with 45° beveled tether-to-plate transition yields a Q of 1,979 which upwards 30% over a conventional rectangular resonator; another AlN LWR on the butterfly-shaped plate with rounded tether-to-plate transition yields a Q of 2,531, representing a 67% improvement.
{"title":"Anchor loss suppression using butterfly-shaped plates for AlN Lamb wave resonators","authors":"J. Zou, Chih-Ming Lin, A. Pisano","doi":"10.1109/FCS.2015.7138874","DOIUrl":"https://doi.org/10.1109/FCS.2015.7138874","url":null,"abstract":"The use of butterfly-shaped thin plates, formed by reducing the tether-to-plate angle, can raised the quality factor (Q) of aluminum nitride (AlN) Lamb wave resonators (LWRs) by eliminating the anchor loss. The finite element analysis (FEA) simulation results show that the butterfly-shaped plate can efficiently keep the vibration far from the edges at the tether-to-plate plane, so that the acoustic wave leaky through the supporting tethers is reduced. Specifically, the rounded butterfly-shaped resonators show more efficient suppression in the anchor loss compared to the beveled butterfly-shaped resonators. The measured frequency response for a 863-MHz AlN LWR with 45° beveled tether-to-plate transition yields a Q of 1,979 which upwards 30% over a conventional rectangular resonator; another AlN LWR on the butterfly-shaped plate with rounded tether-to-plate transition yields a Q of 2,531, representing a 67% improvement.","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":"73752502","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.2015.7138894
Lei Shao, K. Pipe
In this work, amplification of surface acoustic waves (SAWs) by electron drift in a nanometer-scale two-dimensional electron gas (2DEG) is analyzed analytically. We compare the amount of acoustic power gain per SAW radian produced by electron drift in a bulk GaN thin film layer and in a GaN-based 2DEG layer. Calculations suggest that acoustic amplification in a 2DEG is independent on the SAW frequency while only a very narrow bandwidth of SAWs could be amplified in bulk. Furthermore, the peak power gain per SAW radian occurs at a more practical carrier density for a 2DEG than for a bulk material.
{"title":"Acoustic power gain induced by 2D electron drifting","authors":"Lei Shao, K. Pipe","doi":"10.1109/FCS.2015.7138894","DOIUrl":"https://doi.org/10.1109/FCS.2015.7138894","url":null,"abstract":"In this work, amplification of surface acoustic waves (SAWs) by electron drift in a nanometer-scale two-dimensional electron gas (2DEG) is analyzed analytically. We compare the amount of acoustic power gain per SAW radian produced by electron drift in a bulk GaN thin film layer and in a GaN-based 2DEG layer. Calculations suggest that acoustic amplification in a 2DEG is independent on the SAW frequency while only a very narrow bandwidth of SAWs could be amplified in bulk. Furthermore, the peak power gain per SAW radian occurs at a more practical carrier density for a 2DEG than for a bulk material.","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":"73791729","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.2015.7138781
Ruochen Lu, A. Gao, S. Gong
This work reports the first observation of parametric excitation in geometrically optimized Aluminum Nitride (AlN) contour mode resonators (CMRs). The concept of parametric excited AlN CMRs harnesses the fact that the resonant frequencies of extensional mode vibrations along transverse and longitudinal directions can both be determined by resonator dimensions. Therefore, by geometrically optimizing lateral dimensions, dual resonances can be engineered at f0 and 2f0 respectively for inputting parametric excitation and outputting fundamental oscillations. In operation, the parametric excitation amplifies an orthogonal oscillation at f0 by periodically modulating the stiffness constants of AlN piezoelectric thin film via straining the structure. The experimental results have shown quality factor (Q) enhancement from 50 ot 2708 for a parametrically excited resonance. Upon further scaling and optimizations, it is anticipated that this type of devices will lead to the development of GHz low noise frequency sources and nano-electro-mechanical logic.
{"title":"Parametric excitation in geometrically optimized AlN contour mode resonators","authors":"Ruochen Lu, A. Gao, S. Gong","doi":"10.1109/FCS.2015.7138781","DOIUrl":"https://doi.org/10.1109/FCS.2015.7138781","url":null,"abstract":"This work reports the first observation of parametric excitation in geometrically optimized Aluminum Nitride (AlN) contour mode resonators (CMRs). The concept of parametric excited AlN CMRs harnesses the fact that the resonant frequencies of extensional mode vibrations along transverse and longitudinal directions can both be determined by resonator dimensions. Therefore, by geometrically optimizing lateral dimensions, dual resonances can be engineered at f0 and 2f0 respectively for inputting parametric excitation and outputting fundamental oscillations. In operation, the parametric excitation amplifies an orthogonal oscillation at f0 by periodically modulating the stiffness constants of AlN piezoelectric thin film via straining the structure. The experimental results have shown quality factor (Q) enhancement from 50 ot 2708 for a parametrically excited resonance. Upon further scaling and optimizations, it is anticipated that this type of devices will lead to the development of GHz low noise frequency sources and nano-electro-mechanical logic.","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":"74040553","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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