太阳风暴会造成地球电离层剧烈扰动,影响导航定位性能.本文针对2024-05-08—16太阳风暴期间发生的电离层扰动事件,分析了东、西半球不同纬度台站的电离层总电子含量(total electron content,TEC)、电离层TEC变化率、电离层F_(2)层临界...太阳风暴会造成地球电离层剧烈扰动,影响导航定位性能.本文针对2024-05-08—16太阳风暴期间发生的电离层扰动事件,分析了东、西半球不同纬度台站的电离层总电子含量(total electron content,TEC)、电离层TEC变化率、电离层F_(2)层临界频率、卫星导航单点定位误差等.分析认为:电离层向日面会对X射线耀斑发生响应,但是扰动主要来源是太阳风南向磁场能量注入引起的地磁暴;太阳风暴期间电离层顶部和底部的响应并不是同步的;卫星导航单点定位误差在太阳风暴期间会有明显增大,尤其在垂直方向会增大至±10 m,且在电离层暴恢复相期间会持续存在,并随电离层状态趋于平静呈逐渐减弱趋势.展开更多
Possible ionospheric disturbances relating to the May 12, 2008, MsS.0 Wenchuan earthquake were identified by Global Positioning System （GPS）-derived total electron content （TEC）, ion- osonde observations, the glob...Possible ionospheric disturbances relating to the May 12, 2008, MsS.0 Wenchuan earthquake were identified by Global Positioning System （GPS）-derived total electron content （TEC）, ion- osonde observations, the global ionospheric map （GIM）, and electron density profiles detected by the Constellation Observation System for Meteorology Ionosphere and Climate （COSMIC）. We applied a statistical test to detect anomalous TEC signals and found that a unique enhancement in TEC, recorded at 16 GPS stations, appeared on May 9, 2008. The critical fre- quency at F2 peak （foF2）, observed by the Chinese ionosondes, and maximal plasma frequency, derived from COSMIC data, revealed a characteristic similar to GPS TEC variations. The GIM showed that the anomalous variations of May 9 were located southeast of the epicenter. Using GPS data from 13 stations near the epicenter, we analyzed the TEC variations of satellite orbit traces during 04：00-11：00 UT. We found that TEC decreased to the east and increased to the southeast of the epicenter during this period. Results showed that the abnormal disturbance on May 9 was probably an ionosphenc precursor of the Wenchuan earthquake of May 12, 2008.展开更多
This work presents the results of the exact computation of (180)<sup>3</sup> = 5,832,000 third-order mixed sensitivities of the leakage response of a polyethylene-reflected plutonium (PERP) experimental be...This work presents the results of the exact computation of (180)<sup>3</sup> = 5,832,000 third-order mixed sensitivities of the leakage response of a polyethylene-reflected plutonium (PERP) experimental benchmark with respect to the benchmark’s 180 microscopic total cross sections. This computation was made possible by applying the Third-Order Adjoint Sensitivity Analysis Methodology developed by Cacuci. The numerical results obtained in this work revealed that many of the 3<sup>rd</sup>-order sensitivities are significantly larger than their corresponding 1<sup>st</sup>- and 2<sup>nd</sup>-order ones, which is contrary to the widely held belief that higher-order sensitivities are all much smaller and hence less important than the first-order ones, for reactor physics systems. In particular, the largest 3<sup>rd</sup>-order relative sensitivity is the mixed sensitivity <img src="Edit_754b8437-dfdf-487d-af68-c78c637e6d4e.png" width="180" height="24" alt="" />of the PERP leakage response with respect to the lowest energy-group (30) total cross sections of <sup>1</sup>H (“isotope 6”) and <sup>239</sup>Pu (“isotope 1”). These two isotopes are shown in this work to be the two most important parameters affecting the PERP benchmark’s leakage response. By comparison, the largest 1<sup>st</sup>-order sensitivity is that of the PERP leakage response with respect to the lowest energy-group total cross section of isotope <sup>1</sup>H, having the value <img src="Edit_a5cfcc11-6a99-41ee-b844-a5ee84b454b3.png" width="100" height="24" alt="" />, while the largest 2<sup>nd</sup>-order sensitivity is <img src="Edit_05166a2b-97f7-43f1-98ff-b21368c00228.png" width="120" height="22" alt="" />. The 3<sup>rd</sup>-order sensitivity analysis presented in this work is the first ever such analysis in the field of reactor physics. The consequences of the results presented in this work on the uncertainty analysis of the PERP benchmark’s leakage response will be presented in a subsequent work.展开更多
This work extends to third-order previously published work on developing the adjoint sensitivity and uncertainty analysis of the numerical model of a <u>p</u>oly<u>e</u>thylene-<u>r</u...This work extends to third-order previously published work on developing the adjoint sensitivity and uncertainty analysis of the numerical model of a <u>p</u>oly<u>e</u>thylene-<u>r</u>eflected <u>p</u>lutonium (acronym: PERP) OECD/NEA reactor physics benchmark. The PERP benchmark comprises 21,976 imprecisely known (uncertain) model parameters. Previous works have used the adjoint sensitivity analysis methodology to compute exactly and efficiently all of the 21,976 first-order and (21,976)<sup>2</sup> second-order sensitivities of the PERP benchmark’s leakage response to all of the benchmark’s uncertain parameters, showing that the largest and most consequential 1<sup>st</sup>- and 2<sup>nd</sup>-order response sensitivities are with respect to the total microscopic cross sections. These results have motivated extending the previous adjoint-based derivations to third-order, leading to the derivation, in this work, of the exact mathematical expressions of the (180)<sup>3</sup> third-order sensitivities of the PERP leakage response with respect to these total microscopic cross sections. The formulas derived in this work are valid not only for the PERP benchmark but can also be used for computing the 3<sup>rd</sup>-order sensitivities of the leakage response of any nuclear system involving fissionable material and internal or external neutron sources. Subsequent works will use the adjoint-based mathematical expressions obtained in this work to compute exactly and efficiently the numerical values of these (180)<sup>3</sup> third-order sensitivities (which turned out to be very large and consequential) and use them for a third-order uncertainty analysis of the PERP benchmark’s leakage response.展开更多
et X=(X1,...,Xn )' have a multivariate normal distribution with mean μ and covariance matrix Σ. In the case μ=0, Karlin and Rinott[6] obtained a necessary and sufficient condition on Σ for |X|=(|X1|,...,|Xn|)&...et X=(X1,...,Xn )' have a multivariate normal distribution with mean μ and covariance matrix Σ. In the case μ=0, Karlin and Rinott[6] obtained a necessary and sufficient condition on Σ for |X|=(|X1|,...,|Xn|)' to be MTP2. In this paper we consider the case μ≠0, and give some conditions under which |X| is MTP2. A necessary and sufficient condition is given for |X| to be TP2 when n=2 and μ≠0. Some results about the TP2 stochastic ordering are also given. The results are applied to obtain positive dependence and associated inequalities for multinormal and related distributions.展开更多
In this paper,we develop an approach to study the effect of second-order ionospheric delay on GPS positioning based on the ionosphere-free combination (abbreviated to Lc) of GPS dual-frequency carrier phase observable...In this paper,we develop an approach to study the effect of second-order ionospheric delay on GPS positioning based on the ionosphere-free combination (abbreviated to Lc) of GPS dual-frequency carrier phase observables,in which the first-order ionospheric delay has been eliminated.GPS data from IGS WUHN tracking station during April 9 23,2003 is used to perform the above approach,and results show that the second-order ionospheric delay in GPS so-called ionosphere-free observables will result in the regular southward shift of GPS positioning solution.Additionally,the influence of the Earth's magnetic field on second-order ionospheric delay over the Wuhan area is discussed,and it indicates that the Earth's magnetic field is one of the main factors why second-order ionospheric delay results in the regular southward shift of GPS positioning solution over Wuhan area.展开更多
文摘太阳风暴会造成地球电离层剧烈扰动,影响导航定位性能.本文针对2024-05-08—16太阳风暴期间发生的电离层扰动事件,分析了东、西半球不同纬度台站的电离层总电子含量(total electron content,TEC)、电离层TEC变化率、电离层F_(2)层临界频率、卫星导航单点定位误差等.分析认为:电离层向日面会对X射线耀斑发生响应,但是扰动主要来源是太阳风南向磁场能量注入引起的地磁暴;太阳风暴期间电离层顶部和底部的响应并不是同步的;卫星导航单点定位误差在太阳风暴期间会有明显增大,尤其在垂直方向会增大至±10 m,且在电离层暴恢复相期间会持续存在,并随电离层状态趋于平静呈逐渐减弱趋势.
基金supported financially by Science for Earthquake Resilience(XH14064Y)the open foundation of the State Key Laboratory of Geodesy and Earth's Dynamics(SKLGED2014-5-2-E)
文摘Possible ionospheric disturbances relating to the May 12, 2008, MsS.0 Wenchuan earthquake were identified by Global Positioning System （GPS）-derived total electron content （TEC）, ion- osonde observations, the global ionospheric map （GIM）, and electron density profiles detected by the Constellation Observation System for Meteorology Ionosphere and Climate （COSMIC）. We applied a statistical test to detect anomalous TEC signals and found that a unique enhancement in TEC, recorded at 16 GPS stations, appeared on May 9, 2008. The critical fre- quency at F2 peak （foF2）, observed by the Chinese ionosondes, and maximal plasma frequency, derived from COSMIC data, revealed a characteristic similar to GPS TEC variations. The GIM showed that the anomalous variations of May 9 were located southeast of the epicenter. Using GPS data from 13 stations near the epicenter, we analyzed the TEC variations of satellite orbit traces during 04：00-11：00 UT. We found that TEC decreased to the east and increased to the southeast of the epicenter during this period. Results showed that the abnormal disturbance on May 9 was probably an ionosphenc precursor of the Wenchuan earthquake of May 12, 2008.
文摘This work presents the results of the exact computation of (180)<sup>3</sup> = 5,832,000 third-order mixed sensitivities of the leakage response of a polyethylene-reflected plutonium (PERP) experimental benchmark with respect to the benchmark’s 180 microscopic total cross sections. This computation was made possible by applying the Third-Order Adjoint Sensitivity Analysis Methodology developed by Cacuci. The numerical results obtained in this work revealed that many of the 3<sup>rd</sup>-order sensitivities are significantly larger than their corresponding 1<sup>st</sup>- and 2<sup>nd</sup>-order ones, which is contrary to the widely held belief that higher-order sensitivities are all much smaller and hence less important than the first-order ones, for reactor physics systems. In particular, the largest 3<sup>rd</sup>-order relative sensitivity is the mixed sensitivity <img src="Edit_754b8437-dfdf-487d-af68-c78c637e6d4e.png" width="180" height="24" alt="" />of the PERP leakage response with respect to the lowest energy-group (30) total cross sections of <sup>1</sup>H (“isotope 6”) and <sup>239</sup>Pu (“isotope 1”). These two isotopes are shown in this work to be the two most important parameters affecting the PERP benchmark’s leakage response. By comparison, the largest 1<sup>st</sup>-order sensitivity is that of the PERP leakage response with respect to the lowest energy-group total cross section of isotope <sup>1</sup>H, having the value <img src="Edit_a5cfcc11-6a99-41ee-b844-a5ee84b454b3.png" width="100" height="24" alt="" />, while the largest 2<sup>nd</sup>-order sensitivity is <img src="Edit_05166a2b-97f7-43f1-98ff-b21368c00228.png" width="120" height="22" alt="" />. The 3<sup>rd</sup>-order sensitivity analysis presented in this work is the first ever such analysis in the field of reactor physics. The consequences of the results presented in this work on the uncertainty analysis of the PERP benchmark’s leakage response will be presented in a subsequent work.
文摘This work extends to third-order previously published work on developing the adjoint sensitivity and uncertainty analysis of the numerical model of a <u>p</u>oly<u>e</u>thylene-<u>r</u>eflected <u>p</u>lutonium (acronym: PERP) OECD/NEA reactor physics benchmark. The PERP benchmark comprises 21,976 imprecisely known (uncertain) model parameters. Previous works have used the adjoint sensitivity analysis methodology to compute exactly and efficiently all of the 21,976 first-order and (21,976)<sup>2</sup> second-order sensitivities of the PERP benchmark’s leakage response to all of the benchmark’s uncertain parameters, showing that the largest and most consequential 1<sup>st</sup>- and 2<sup>nd</sup>-order response sensitivities are with respect to the total microscopic cross sections. These results have motivated extending the previous adjoint-based derivations to third-order, leading to the derivation, in this work, of the exact mathematical expressions of the (180)<sup>3</sup> third-order sensitivities of the PERP leakage response with respect to these total microscopic cross sections. The formulas derived in this work are valid not only for the PERP benchmark but can also be used for computing the 3<sup>rd</sup>-order sensitivities of the leakage response of any nuclear system involving fissionable material and internal or external neutron sources. Subsequent works will use the adjoint-based mathematical expressions obtained in this work to compute exactly and efficiently the numerical values of these (180)<sup>3</sup> third-order sensitivities (which turned out to be very large and consequential) and use them for a third-order uncertainty analysis of the PERP benchmark’s leakage response.
文摘et X=(X1,...,Xn )' have a multivariate normal distribution with mean μ and covariance matrix Σ. In the case μ=0, Karlin and Rinott[6] obtained a necessary and sufficient condition on Σ for |X|=(|X1|,...,|Xn|)' to be MTP2. In this paper we consider the case μ≠0, and give some conditions under which |X| is MTP2. A necessary and sufficient condition is given for |X| to be TP2 when n=2 and μ≠0. Some results about the TP2 stochastic ordering are also given. The results are applied to obtain positive dependence and associated inequalities for multinormal and related distributions.
基金supported by the National Science Foundation for Distinguished Young Scholars (Grant No. 40625013)the National Natural Science Foundation of China (Grant No. 40890160)+1 种基金the National High-Tech Research and Development Program of China (Grant No. 2007AA12Z311)the Knowledge Innovation Program of the Chinese Academy of Sciences (Grant No.0909141014)
文摘In this paper,we develop an approach to study the effect of second-order ionospheric delay on GPS positioning based on the ionosphere-free combination (abbreviated to Lc) of GPS dual-frequency carrier phase observables,in which the first-order ionospheric delay has been eliminated.GPS data from IGS WUHN tracking station during April 9 23,2003 is used to perform the above approach,and results show that the second-order ionospheric delay in GPS so-called ionosphere-free observables will result in the regular southward shift of GPS positioning solution.Additionally,the influence of the Earth's magnetic field on second-order ionospheric delay over the Wuhan area is discussed,and it indicates that the Earth's magnetic field is one of the main factors why second-order ionospheric delay results in the regular southward shift of GPS positioning solution over Wuhan area.
