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Ehsan Ahmadi - One of the best experts on this subject based on the ideXlab platform.
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Effects of forward directivity on the response of soil–structure systems
Proceedings of the Institution of Civil Engineers - Structures and Buildings, 2015Co-Authors: Faramarz Khoshnoudian, Reza Attarnejad, Farzane Paytam, Ehsan AhmadiAbstract:The effects of input parameters of Pulse-like ground motions on the response of soil–structure systems are investigated through employing an ensemble of 64 ground motions. The soil and superstructure are idealised as a semi-infinite cone and a non-linear multiple-degrees-of-freedom shear building, respectively. The results confirm that the location of the critical storey is significantly affected by the Pulse inputs and interacting parameters. Also, the Pulse Period ranges in which the critical storey complies with upper storeys are influenced considerably by interacting parameters. Moreover, there is a trade-off between Pulse Period and amplitude to determine the seismic demands of the structure.
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Effects of inertial soil–structure interaction on inelastic displacement ratios of SDOF oscillators subjected to Pulse-like ground motions
Bulletin of Earthquake Engineering, 2014Co-Authors: Faramarz Khoshnoudian, Ehsan AhmadiAbstract:This study is devoted to investigate the effects of inertial soil-structure interaction (SSI) on the constant-strength inelastic displacement ratios of elastoplastic single-degree-of- freedomsystemsusingasuitof91Pulse-likegroundmotions.Thesoilbeneaththefoundation is simulated based on the cone model. A local minimum for the inelastic displacement ratios around the interacting system-to-Pulse Period ratio of one is demonstrated. Moreover, the soil flexibility increases the inelastic displacement ratios at all interacting system-to-Pulse Period ratios. However, the aspect ratio has decreasing and increasing effects on the inelastic displacement ratios before and after a threshold interacting system-to-Pulse Period ratio, approximately very close to one. It is confirmed that for slender structures, the SSI effects are the lowest at small interacting system-to-Pulse Period ratios and as this ratio increases, the SSI effects on the inelastic displacement ratios increase. However, for squat structures, the SSI approximately has more significant effects on the inelastic displacement ratios at lower interacting system-to-Pulse Period ratios and the effects decrease for higher interacting system-to-Pulse Period ratios. It is noted that the equal displacement rule is not valid as the SSI effects are taken into account. In addition, a formula is proposed to estimate the inelastic displacement ratios of soil-structure systems using nonlinear regression analysis, which is desirable for the displacement assessment of existing structures. Besides, the mean ratios of approximate-to-analyticalvalues,veryclosetoone,emphasizewellaccuracyoftheproposed formula.
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effects of Pulse Period of near field ground motions on the seismic demands of soil mdof structure systems using mathematical Pulse models
Earthquake Engineering & Structural Dynamics, 2013Co-Authors: Faramarz Khoshnoudian, Ehsan AhmadiAbstract:SUMMARY In this paper, the effects of Pulse Period associated with near-field ground motions on the seismic demands of soil–MDOF structure systems are investigated by using mathematical Pulse models. Three non-dimensional parameters are employed as the crucial parameters, which govern the responses of soil–structure systems: (1) non-dimensional frequency as the structure-to-soil stiffness ratio; (2) aspect ratio of the superstructure; and (3) structural target ductility ratio. The soil beneath the superstructure is simulated on the basis of the Cone model concept. The superstructure is modeled as a nonlinear shear building. Interstory drift ratio is selected as the main engineering demand parameter for soil–structure systems. It is demonstrated that the contribution of higher modes to the response of soil–structure system depends on the Pulse-to-interacting system Period ratio instead of Pulse-to-fixed-base structure Period ratio. Furthermore, results of the MDOF superstructures demonstrate that increasing structural target ductility ratio results in the first-mode domination for both fixed-base structure and soil–structure system. Additionally, increasing non-dimensional frequency and aspect ratio of the superstructure respectively decrease and increase the structural responses. Moreover, comparison of the equivalent soil–SDOF structure system and the soil–MDOF structure system elucidates that higher-mode effects are more significant, when soil–structure interaction is taken into account. In general, the effects of fling step and forward directivity Pulses on activating higher modes of the superstructure are more sever in soil–structure systems, and in addition, the influences of forward directivity Pulses are more considerable than fling step ones. Copyright © 2013 John Wiley & Sons, Ltd.
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Effects of Pulse Period of near‐field ground motions on the seismic demands of soil–MDOF structure systems using mathematical Pulse models
Earthquake Engineering & Structural Dynamics, 2013Co-Authors: Faramarz Khoshnoudian, Ehsan AhmadiAbstract:SUMMARY In this paper, the effects of Pulse Period associated with near-field ground motions on the seismic demands of soil–MDOF structure systems are investigated by using mathematical Pulse models. Three non-dimensional parameters are employed as the crucial parameters, which govern the responses of soil–structure systems: (1) non-dimensional frequency as the structure-to-soil stiffness ratio; (2) aspect ratio of the superstructure; and (3) structural target ductility ratio. The soil beneath the superstructure is simulated on the basis of the Cone model concept. The superstructure is modeled as a nonlinear shear building. Interstory drift ratio is selected as the main engineering demand parameter for soil–structure systems. It is demonstrated that the contribution of higher modes to the response of soil–structure system depends on the Pulse-to-interacting system Period ratio instead of Pulse-to-fixed-base structure Period ratio. Furthermore, results of the MDOF superstructures demonstrate that increasing structural target ductility ratio results in the first-mode domination for both fixed-base structure and soil–structure system. Additionally, increasing non-dimensional frequency and aspect ratio of the superstructure respectively decrease and increase the structural responses. Moreover, comparison of the equivalent soil–SDOF structure system and the soil–MDOF structure system elucidates that higher-mode effects are more significant, when soil–structure interaction is taken into account. In general, the effects of fling step and forward directivity Pulses on activating higher modes of the superstructure are more sever in soil–structure systems, and in addition, the influences of forward directivity Pulses are more considerable than fling step ones. Copyright © 2013 John Wiley & Sons, Ltd.
Faramarz Khoshnoudian - One of the best experts on this subject based on the ideXlab platform.
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Effects of forward directivity on the response of soil–structure systems
Proceedings of the Institution of Civil Engineers - Structures and Buildings, 2015Co-Authors: Faramarz Khoshnoudian, Reza Attarnejad, Farzane Paytam, Ehsan AhmadiAbstract:The effects of input parameters of Pulse-like ground motions on the response of soil–structure systems are investigated through employing an ensemble of 64 ground motions. The soil and superstructure are idealised as a semi-infinite cone and a non-linear multiple-degrees-of-freedom shear building, respectively. The results confirm that the location of the critical storey is significantly affected by the Pulse inputs and interacting parameters. Also, the Pulse Period ranges in which the critical storey complies with upper storeys are influenced considerably by interacting parameters. Moreover, there is a trade-off between Pulse Period and amplitude to determine the seismic demands of the structure.
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Effects of inertial soil–structure interaction on inelastic displacement ratios of SDOF oscillators subjected to Pulse-like ground motions
Bulletin of Earthquake Engineering, 2014Co-Authors: Faramarz Khoshnoudian, Ehsan AhmadiAbstract:This study is devoted to investigate the effects of inertial soil-structure interaction (SSI) on the constant-strength inelastic displacement ratios of elastoplastic single-degree-of- freedomsystemsusingasuitof91Pulse-likegroundmotions.Thesoilbeneaththefoundation is simulated based on the cone model. A local minimum for the inelastic displacement ratios around the interacting system-to-Pulse Period ratio of one is demonstrated. Moreover, the soil flexibility increases the inelastic displacement ratios at all interacting system-to-Pulse Period ratios. However, the aspect ratio has decreasing and increasing effects on the inelastic displacement ratios before and after a threshold interacting system-to-Pulse Period ratio, approximately very close to one. It is confirmed that for slender structures, the SSI effects are the lowest at small interacting system-to-Pulse Period ratios and as this ratio increases, the SSI effects on the inelastic displacement ratios increase. However, for squat structures, the SSI approximately has more significant effects on the inelastic displacement ratios at lower interacting system-to-Pulse Period ratios and the effects decrease for higher interacting system-to-Pulse Period ratios. It is noted that the equal displacement rule is not valid as the SSI effects are taken into account. In addition, a formula is proposed to estimate the inelastic displacement ratios of soil-structure systems using nonlinear regression analysis, which is desirable for the displacement assessment of existing structures. Besides, the mean ratios of approximate-to-analyticalvalues,veryclosetoone,emphasizewellaccuracyoftheproposed formula.
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effects of Pulse Period of near field ground motions on the seismic demands of soil mdof structure systems using mathematical Pulse models
Earthquake Engineering & Structural Dynamics, 2013Co-Authors: Faramarz Khoshnoudian, Ehsan AhmadiAbstract:SUMMARY In this paper, the effects of Pulse Period associated with near-field ground motions on the seismic demands of soil–MDOF structure systems are investigated by using mathematical Pulse models. Three non-dimensional parameters are employed as the crucial parameters, which govern the responses of soil–structure systems: (1) non-dimensional frequency as the structure-to-soil stiffness ratio; (2) aspect ratio of the superstructure; and (3) structural target ductility ratio. The soil beneath the superstructure is simulated on the basis of the Cone model concept. The superstructure is modeled as a nonlinear shear building. Interstory drift ratio is selected as the main engineering demand parameter for soil–structure systems. It is demonstrated that the contribution of higher modes to the response of soil–structure system depends on the Pulse-to-interacting system Period ratio instead of Pulse-to-fixed-base structure Period ratio. Furthermore, results of the MDOF superstructures demonstrate that increasing structural target ductility ratio results in the first-mode domination for both fixed-base structure and soil–structure system. Additionally, increasing non-dimensional frequency and aspect ratio of the superstructure respectively decrease and increase the structural responses. Moreover, comparison of the equivalent soil–SDOF structure system and the soil–MDOF structure system elucidates that higher-mode effects are more significant, when soil–structure interaction is taken into account. In general, the effects of fling step and forward directivity Pulses on activating higher modes of the superstructure are more sever in soil–structure systems, and in addition, the influences of forward directivity Pulses are more considerable than fling step ones. Copyright © 2013 John Wiley & Sons, Ltd.
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Effects of Pulse Period of near‐field ground motions on the seismic demands of soil–MDOF structure systems using mathematical Pulse models
Earthquake Engineering & Structural Dynamics, 2013Co-Authors: Faramarz Khoshnoudian, Ehsan AhmadiAbstract:SUMMARY In this paper, the effects of Pulse Period associated with near-field ground motions on the seismic demands of soil–MDOF structure systems are investigated by using mathematical Pulse models. Three non-dimensional parameters are employed as the crucial parameters, which govern the responses of soil–structure systems: (1) non-dimensional frequency as the structure-to-soil stiffness ratio; (2) aspect ratio of the superstructure; and (3) structural target ductility ratio. The soil beneath the superstructure is simulated on the basis of the Cone model concept. The superstructure is modeled as a nonlinear shear building. Interstory drift ratio is selected as the main engineering demand parameter for soil–structure systems. It is demonstrated that the contribution of higher modes to the response of soil–structure system depends on the Pulse-to-interacting system Period ratio instead of Pulse-to-fixed-base structure Period ratio. Furthermore, results of the MDOF superstructures demonstrate that increasing structural target ductility ratio results in the first-mode domination for both fixed-base structure and soil–structure system. Additionally, increasing non-dimensional frequency and aspect ratio of the superstructure respectively decrease and increase the structural responses. Moreover, comparison of the equivalent soil–SDOF structure system and the soil–MDOF structure system elucidates that higher-mode effects are more significant, when soil–structure interaction is taken into account. In general, the effects of fling step and forward directivity Pulses on activating higher modes of the superstructure are more sever in soil–structure systems, and in addition, the influences of forward directivity Pulses are more considerable than fling step ones. Copyright © 2013 John Wiley & Sons, Ltd.
Nobuyuki Kawai - One of the best experts on this subject based on the ideXlab platform.
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Accurate Position of SGR 1900+14 by Bursts and Changes in Pulse Period and Folded Pulse Profile with ASCA
The Astrophysical Journal, 1999Co-Authors: Toshio Murakami, S. Kubo, Noriaki Shibazaki, T. Takeshima, Atsumasa Yoshida, Nobuyuki KawaiAbstract:The Advanced Satellite for Cosmology and Astrophysics (ASCA) observed the soft gamma repeater SGR 1900+14 on 1998 April 30-May 1 and discovered a pulsar with a Period of 5.1589715(8) s from the known X-ray source of RX J190714.2+0919.3. Four months later, on September 16-17, ASCA observed SGR 1900+14 again just after the giant burst on 1998 August 27. Comparing the observations in September with those in April, there are several changes in characteristics. The Pulse Period changed to 5.160295(3) s, and thus the long-term Period derivative is 1.1 × 10-10 s s-1. This strongly supports a magnetar model. The folded Pulse profile in 2-10 keV largely changed from three peaks in April to one simple peak, while the steady intensity increased by a factor of 2. Finally, we successfully determined the accurate location of SGR 1900+14 by the bursts with an accuracy of 15 in diameter.
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accurate position of sgr 1900 14 by bursts and changes in Pulse Period and folded Pulse profile with asca
The Astrophysical Journal, 1999Co-Authors: Toshio Murakami, S. Kubo, Noriaki Shibazaki, T. Takeshima, Atsumasa Yoshida, Nobuyuki KawaiAbstract:The Advanced Satellite for Cosmology and Astrophysics (ASCA) observed the soft gamma repeater SGR 1900+14 on 1998 April 30-May 1 and discovered a pulsar with a Period of 5.1589715(8) s from the known X-ray source of RX J190714.2+0919.3. Four months later, on September 16-17, ASCA observed SGR 1900+14 again just after the giant burst on 1998 August 27. Comparing the observations in September with those in April, there are several changes in characteristics. The Pulse Period changed to 5.160295(3) s, and thus the long-term Period derivative is 1.1 × 10-10 s s-1. This strongly supports a magnetar model. The folded Pulse profile in 2-10 keV largely changed from three peaks in April to one simple peak, while the steady intensity increased by a factor of 2. Finally, we successfully determined the accurate location of SGR 1900+14 by the bursts with an accuracy of 15 in diameter.
Andrea Santangelo - One of the best experts on this subject based on the ideXlab platform.
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Orbital Parameters and Spectroscopy of the Transient X-Ray Pulsar 4U 0115+63
2011Co-Authors: S. Mueller, D. Klochkov, Ruediger Staubert, Andrea Santangelo, Maria Obst, Ingo Kreykenbohm, Felix Fuerst, M. Kuehnel, Joern Wilms, Katja PottschmidtAbstract:We report on an outburst of the high mass X-ray binary 4U 0115+63 with a Pulse Period of 3.6s in spring 2008 as observed with INTEGRAL and RXTE. By analyzing the lightcurves we derive an updated orbital- and Pulse Period ephemeris of the neutron star. We also study the Pulse profile variations as a function of time and energy as well as the variability of the spectral parameters. We find clear evidence for at least three cyclotron line features. In agreement with previous observations of 4U 0115+63, we detect an anti-correlation between the luminosity and the fundamental cyclotron line energy.
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Monitoring of Pulse Period in Her X-1 with Swift/BAT: evidence of mass ejection
Proceedings of The Extreme sky: Sampling the Universe above 10 keV — PoS(extremesky2009), 2010Co-Authors: D. Klochkov, Ruediger Staubert, Konstantin Postnov, N. I. Shakura, Andrea SantangeloAbstract:Monitoring of Pulse Period variations in accreting binary pulsars is an important tool to study the interaction between the magnetosphere of the neutron star and the accretion disk. While the X-ray flux of the brightest X-ray pulsars have been successfully mo nitored over many years (e.g. with RXTE/ASM, CGRO/BATSE, Swift/BAT), the possibility to monitor their Pulse timing properties continuously has so far been very limited. In our work we use Swift/BAT observations to study one of the most enigmatic X-ray pulsars, Hercules X-1. For the first time, a quasi-continuous monitoring of the Pulse Period and the Pulse Period derivative of Her X-1, is achieved over a long time (> 4 yrs). We argue that together with the long-term decrease of the orbital Period in Her X-1 the measured Pulse Period behaviour requires the presence of mass ejection from the inner parts of the accretion disk along the open magnetic field lines. The mass ejection episodes probably take place during strong spin-down episodes which are associated with the low X-ray luminosity.
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continuous monitoring of Pulse Period variations in hercules x 1 using swift bat
Astronomy and Astrophysics, 2009Co-Authors: D. Klochkov, Ruediger Staubert, Konstantin Postnov, N. I. Shakura, Andrea SantangeloAbstract:Context. Monitoring of Pulse Period variations in accreting binary pulsars is an important tool to study the interaction between the magnetosphere of the neutron star and the accretion disk. While the X-ray flux of the brightest X-ray pulsars have been successfully monitored over many years (e.g. with RXTE/ASM, CGRO/BATSE, Swift/BAT ), the possibility to monitor their Pulse timing properties continuously has so far been very limited. Aims. In our work we show that the Swift/BAT observations can be used to monitor coherent pulsations of bright X-ray sources and use Swift archival data to study one of the most enigmatic X-ray pulsars, Hercules X-1. A quasi-continuous monitoring of the Pulse Period and the Pulse Period derivative of an X-ray pulsar, here Her X-1, is achieved over a long time (4 yr). We compare our observational results with predictions of accretion theory and use them to test different aspects of the physical model of the system. Methods. In our analysis we use the data accumulated with Swift/BAT starting from the beginning of 2005 (shortly after launch) until the present time. To search for pulsations and for their subsequent analysis we used the count rate measured by the BAT detector in the entire field of view. Results. The slope of the correlation between the locally determined spin-up rate and the X-ray luminosity is measured for Her X-1 and found to be in agreement with predictions of basic accretion torque theory. The observed behaviour of the Pulse Period together with the previously measured secular decrease of the system’s orbital Period is discussed in the framework of a model assuming ejection of matter close to the inner boundary of the accretion disk.
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Continuous monitoring of Pulse Period variations in Hercules X-1 using Swift/BAT
Astronomy & Astrophysics, 2009Co-Authors: D. Klochkov, Ruediger Staubert, Konstantin Postnov, N. I. Shakura, Andrea SantangeloAbstract:Context. Monitoring of Pulse Period variations in accreting binary pulsars is an important tool to study the interaction between the magnetosphere of the neutron star and the accretion disk. While the X-ray flux of the brightest X-ray pulsars have been successfully monitored over many years (e.g. with RXTE/ASM, CGRO/BATSE, Swift/BAT ), the possibility to monitor their Pulse timing properties continuously has so far been very limited. Aims. In our work we show that the Swift/BAT observations can be used to monitor coherent pulsations of bright X-ray sources and use Swift archival data to study one of the most enigmatic X-ray pulsars, Hercules X-1. A quasi-continuous monitoring of the Pulse Period and the Pulse Period derivative of an X-ray pulsar, here Her X-1, is achieved over a long time (4 yr). We compare our observational results with predictions of accretion theory and use them to test different aspects of the physical model of the system. Methods. In our analysis we use the data accumulated with Swift/BAT starting from the beginning of 2005 (shortly after launch) until the present time. To search for pulsations and for their subsequent analysis we used the count rate measured by the BAT detector in the entire field of view. Results. The slope of the correlation between the locally determined spin-up rate and the X-ray luminosity is measured for Her X-1 and found to be in agreement with predictions of basic accretion torque theory. The observed behaviour of the Pulse Period together with the previously measured secular decrease of the system’s orbital Period is discussed in the framework of a model assuming ejection of matter close to the inner boundary of the accretion disk.
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continuous monitoring of Pulse Period variations in her x 1 using swift bat
arXiv: High Energy Astrophysical Phenomena, 2009Co-Authors: D. Klochkov, Ruediger Staubert, Konstantin Postnov, N. I. Shakura, Andrea SantangeloAbstract:Context: Monitoring of Pulse Period variations in accreting binary pulsars is an important tool to study the interaction between the magnetosphere of the neutron star and the accretion disk. While the X-ray flux of the brightest X-ray pulsars have been successfully monitored over many years (e.g. with RXTE/ASM, CGRO/BATSE, Swift/BAT), the possibility to monitor their Pulse timing properties continuously has so far been very limited. Aims: In our work we show that the Swift/BAT observations can be used to monitor coherent pulsations of bright X-ray sources and use the Swift archival data to study one of the most enigmatic X-ray pulsars, Hercules X-1. A quasi-continuous monitoring of the Pulse Period and the Pulse Period derivative of an X-ray pulsar, here Her X-1, is achieved over a long time (<~ 4 yrs). We compare our observational results with predictions of accretion theory and use them to test different aspects of the physical model of the system. Methods: In our analysis we use the data accumulated with Swift/BAT starting from the beginning of 2005 (shortly after launch) until the present time. To search for pulsations and for their subsequent analysis we used the count rate measured by the BAT detector in the entire field of view. Results: The slope of the correlation between the locally determined spin-up rate and the X-ray luminosity is measured for Her X-1 and found to be in agreement with predictions of basic accretion torque theory. The observed behaviour of the Pulse Period together with the previously measured secular decrease of the system's orbital Period is discussed in the frame of a model assuming ejection of matter close to the inner boundary of the accretion disk.
Toshio Murakami - One of the best experts on this subject based on the ideXlab platform.
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Accurate Position of SGR 1900+14 by Bursts and Changes in Pulse Period and Folded Pulse Profile with ASCA
The Astrophysical Journal, 1999Co-Authors: Toshio Murakami, S. Kubo, Noriaki Shibazaki, T. Takeshima, Atsumasa Yoshida, Nobuyuki KawaiAbstract:The Advanced Satellite for Cosmology and Astrophysics (ASCA) observed the soft gamma repeater SGR 1900+14 on 1998 April 30-May 1 and discovered a pulsar with a Period of 5.1589715(8) s from the known X-ray source of RX J190714.2+0919.3. Four months later, on September 16-17, ASCA observed SGR 1900+14 again just after the giant burst on 1998 August 27. Comparing the observations in September with those in April, there are several changes in characteristics. The Pulse Period changed to 5.160295(3) s, and thus the long-term Period derivative is 1.1 × 10-10 s s-1. This strongly supports a magnetar model. The folded Pulse profile in 2-10 keV largely changed from three peaks in April to one simple peak, while the steady intensity increased by a factor of 2. Finally, we successfully determined the accurate location of SGR 1900+14 by the bursts with an accuracy of 15 in diameter.
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accurate position of sgr 1900 14 by bursts and changes in Pulse Period and folded Pulse profile with asca
The Astrophysical Journal, 1999Co-Authors: Toshio Murakami, S. Kubo, Noriaki Shibazaki, T. Takeshima, Atsumasa Yoshida, Nobuyuki KawaiAbstract:The Advanced Satellite for Cosmology and Astrophysics (ASCA) observed the soft gamma repeater SGR 1900+14 on 1998 April 30-May 1 and discovered a pulsar with a Period of 5.1589715(8) s from the known X-ray source of RX J190714.2+0919.3. Four months later, on September 16-17, ASCA observed SGR 1900+14 again just after the giant burst on 1998 August 27. Comparing the observations in September with those in April, there are several changes in characteristics. The Pulse Period changed to 5.160295(3) s, and thus the long-term Period derivative is 1.1 × 10-10 s s-1. This strongly supports a magnetar model. The folded Pulse profile in 2-10 keV largely changed from three peaks in April to one simple peak, while the steady intensity increased by a factor of 2. Finally, we successfully determined the accurate location of SGR 1900+14 by the bursts with an accuracy of 15 in diameter.
