The exact radar cross-section （RCS） measurement is difficult when the scattering of targets is low. Ful polarimetric cali-bration is one technique that offers the potential for improving the accuracy of RCS measurem...The exact radar cross-section （RCS） measurement is difficult when the scattering of targets is low. Ful polarimetric cali-bration is one technique that offers the potential for improving the accuracy of RCS measurements. There are numerous polarimetric calibration algorithms. Some complex expressions in these algo-rithms cannot be easily used in an engineering practice. A radar polarimetric coefficients matrix （RPCM） with a simpler expression is presented for the monostatic radar polarization scattering matrix （PSM） measurement. Using a rhombic dihedral corner reflector and a metal ic sphere, the RPCM can be obtained by solving a set of equations, which can be used to find the true PSM for any target. An example for the PSM of a metal ic dish shows that the proposed method obviously improves the accuracy of cross-polarized RCS measurements.展开更多
Geological studies indicate that Qinghai\|Tibet plateau crust has shortened at least 2500km and the thickness was increased to 60～70km in the past 45Ma. Different researchers advocate different views to explain the s...Geological studies indicate that Qinghai\|Tibet plateau crust has shortened at least 2500km and the thickness was increased to 60～70km in the past 45Ma. Different researchers advocate different views to explain the shortening according to their studies.( Tapponnier,1977;Chang et al,1986;England et al,1986;Murphy,1997;Y.Pan,1999),however it is still unresolved on how much shortening in upper crustal especially in Qiangtang terrain.Qiangtang terrain is located in the center of Qinghai\|Tibet plateau, the tectonic deformation has been resulted from intracontinental convergence and collision of India plate with Eurasian plate.The deformation style of Qiangtang terrain shows east\|west\|trending folds and thrusts which formed in the shallow tectonic level during collisional\|intracontinental period. The folds type is characterized by nonpenetrative\|foliation parallel fold, the hinges have the same trend with the thrusts. These traits are favourable for restoring the balanced cross\|section and measuring the shortening. The balanced reconstruction is based on line balancing on three different stratigraphic sections (A,B and C)across the Northern Qiangtang basin in the area between 85°E and 87°E.The sections are all north\|south\|trending in accordance with the moving direction of thrusts.展开更多
This paper studies the development on the first order sea clutter cross section for bistatic high frequency surface wave radar (HFSWR). Based on the received first order electric field expression, a closed-form of cro...This paper studies the development on the first order sea clutter cross section for bistatic high frequency surface wave radar (HFSWR). Based on the received first order electric field expression, a closed-form of cross sections is derived to account for the case of receiving antenna array being mounted on the shipborne platform. The uniform linear motion and sway motion components are assumed to be responsible for the observed differences in comparison with the bistatic fixed antenna case. Correspondingly, simulations are conducted to study the sea clutter spectral characteristics for these two cases versus different system parameters and sea state conditions. It is shown numerically that the forward motion component will spread the Bragg lines severely and the influence triggered by the sway motion can be explained as the Bessel function modulation of the ordinary sea clutter spectra. The obtained results have important implications in the application of shipborne HFSWR technology to ocean remote sensing and target detection.展开更多
A new method of calculating the radai cross section (RCS) for wing-body blended targets is presented and verified. The method utilizes a computer program for modeling targets' geometry in terms of small pieces. Th...A new method of calculating the radai cross section (RCS) for wing-body blended targets is presented and verified. The method utilizes a computer program for modeling targets' geometry in terms of small pieces. The calculation is based on physical optics approximation. Examples are given to show the validity of the method.展开更多
Analyzing the mass of behind-armor debris (BAD) generated by Rolled Homogeneous Armor (RHA) subjected to normal penetration of variable cross-section Explosively Formed Projectile (EFP) is the purpose of this paper. S...Analyzing the mass of behind-armor debris (BAD) generated by Rolled Homogeneous Armor (RHA) subjected to normal penetration of variable cross-section Explosively Formed Projectile (EFP) is the purpose of this paper. So theoretical analysis, numerical simulation and experimental data are combined to analyze the influence of variable cross-section characteristic on the time history of crater radius. Moreover the relationships between time history of crater radius (as well as mass of BAD) and the thickness of RHA (from 30mm to 70 mm) and the impact velocity of EFP (1650 m/s to 1860 m/s) are also investigated. The results indicate that: 1) being compared to the variable cross-section characteristic is ignored, the theoretical time history of crater radius is in better agreement with the simulation results when the variable cross-section characteristic is considered;2) being compared to the other three conditions of plug, the theoretical mass of BAD is in the best agreement with the simulation results when the shape of plug is frustum of a cone and the angle between generatrix and bottom is 45- and the axial length of mushroom is considered.展开更多
The aerodynamic characteristics of projectiles with triangular and circular cross sections are investigated respectively by use of free-flight experiment.Processed the experiment data,curves of flight velocity variati...The aerodynamic characteristics of projectiles with triangular and circular cross sections are investigated respectively by use of free-flight experiment.Processed the experiment data,curves of flight velocity variation and nutation of both projectiles are obtained,based on the curves,their aerodynamic force and moment coefficients are found out by data fitting,and their aerodynamic performances are compared and analyzed.Results show that the projectile with triangular cross section has smaller resistance,higher lift-drag ratio,better static stability,higher stability capability and more excellent maneuverability than those of the projectile with circular cross section,therefore it can be used in the guided projectiles;under lower rotation speed,the triangular section projectile has greater Magnus moment leading to bigger projectile distribution.展开更多
We develop an efficient method for polished metallic sphere’s scattering prediction in terahertz band when its frequency dispersion property is considered. By deducing scattering solution of the lossy metallic sphere...We develop an efficient method for polished metallic sphere’s scattering prediction in terahertz band when its frequency dispersion property is considered. By deducing scattering solution of the lossy metallic sphere, the radar cross section(RCS)of different metallic spheres is given at terahertz frequencies. The investigation of the RCS of polished metallic spheres shows the normalized RCS is always same to the metals’ normal incidence reflectivity when the sphere becomes electrically large. The metals which have high reflectivity(such as Al, Cu, Ag and Au) show that the corresponding RCS of the spheres is almost πa2 in terahertz band. The sphere’s RCS of the transition metal such as Fe begins to decrease obviously since the far infrared.展开更多
Based on a Pade approximation, a wide-angle parabolic equation method is introduced for computing the multiobject radar cross section （RCS） for the first time. The method is a paraxial version of the scalar wave equ...Based on a Pade approximation, a wide-angle parabolic equation method is introduced for computing the multiobject radar cross section （RCS） for the first time. The method is a paraxial version of the scalar wave equation, which solves the field by marching them along the paraxial direction. Numerical results show that a single wide-angle parabofic equation run can compute multi-object RCS efficiently for angles up to 45 ° . The method provides anew and efficient numerical method for computation electromagnetics.展开更多
The reduction of TE-scattering by a conducting cylinder with multiple surface impedance loads is investigated. Synthesis procedures are developed to find the optimal loading which result in zero scattering in the desi...The reduction of TE-scattering by a conducting cylinder with multiple surface impedance loads is investigated. Synthesis procedures are developed to find the optimal loading which result in zero scattering in the desired directions or at several frequencies. Numerical results of these procedures are presented. The theoretical predictions are confirmed with an experiment. The proposed synthesis procedure is completely general and can be applied to arbitrarily shaped conducting bodies.展开更多
In this paper, an improved approach is presented to reconstruct two dimensional conduc- tor profile illuminated by incident plane waves of multiple frequencies and directions via amplitudes of backscattered field in n...In this paper, an improved approach is presented to reconstruct two dimensional conduc- tor profile illuminated by incident plane waves of multiple frequencies and directions via amplitudes of backscattered field in near regions. Newton-Kantorovitch algorithm is adopted to cast the non- linear coupled integral equations into linearized form, method of moment is used to transform the above linearized integral equations into matrix form, the resulting ill-posed overdetermined linear equations are solved using pseudoinverse technique based on Gram-Schedmit orthogonal procedure. Initial values are determined by solving a nonlinear least aquare error problem to establish an equivat lent circular cylinder. The effects of various parameters on reconstruction quality are discussed with numerical results and analysis.展开更多
It is well known that the incorrect results will be given using either the electric or magnetic field integral equation to calculate the radar cross section (RCS) of a closed body at the interior resonance. In this pa...It is well known that the incorrect results will be given using either the electric or magnetic field integral equation to calculate the radar cross section (RCS) of a closed body at the interior resonance. In this paper, an effective iterative technique is used to correct the calculated surface current density from the electric field integral equation. The radar cross section is computed for an infinite conducting circular cylinder at the interior resonance, and the obtained results are in good agreement with the analytical results. The backscattering cross section of an infinite triangular cylinder in the vicinity of a resonant frequency is also calculated. It is shown that the presence method is efficient and accurate.展开更多
In this study,K and L shell photoeffect cross-sections were measured for the elements in the range of 50≤Z≤65at 59.5keV.These photoeffect cross-sections were measured by using the experimentalσKαproduction cross-s...In this study,K and L shell photoeffect cross-sections were measured for the elements in the range of 50≤Z≤65at 59.5keV.These photoeffect cross-sections were measured by using the experimentalσKαproduction cross-section values measured in this paper and two different K shell fluorescence yield values in the literature.The results were compared with the calculated theoretical values.The values were plotted versus atomic number.展开更多
A new method called multi-frequency holography (MFH) for two-dimensional radar cross-section imaging of rotating objects is introduced, in which a constant coherent reference signal from transmitted signal is added in...A new method called multi-frequency holography (MFH) for two-dimensional radar cross-section imaging of rotating objects is introduced, in which a constant coherent reference signal from transmitted signal is added into received signal over certain frequency-width. With the MFH only the intensity of received composite signals needs to be measured. Both imaging situations of far field and near field are considered in details. Special restrictions about the MFH are also discussed and simulated by numerical computation. Examples of numerical simulation show that the method is effective, applicable and perspective.展开更多
目的探讨维持性血液透析(maintenance hemodialysis,MHD)患者计时站立行走测试(time up and go test,TUG)时间延长的影响因素。方法采用横断面调查法,选取2023年6月1日至2024年1月31日于首都医科大学附属北京潞河医院规律血液透析、数...目的探讨维持性血液透析(maintenance hemodialysis,MHD)患者计时站立行走测试(time up and go test,TUG)时间延长的影响因素。方法采用横断面调查法,选取2023年6月1日至2024年1月31日于首都医科大学附属北京潞河医院规律血液透析、数据完整且可配合的患者,分别采用简易精神状态检查表(Minimum Mental State Examination,MMSE)、5次起坐试验(5 times sit to stand,STS-5)、TUG量表评估患者认知功能、下肢肌肉力量、平衡及步态功能;根据TUG结果进行分组,即TUG≤12 s,判定为TUG正常组;TUG>12 s判定为TUG延长组,采用多因素Logistic回归法分析患者TUG延长组的影响因素,以受试者工作特征(receiver operating characteristic,ROC)曲线分析影响因素对TUG延长患者的预测价值。结果本研究共纳入146例MHD患者,TUG延长组86例,TUG正常组60例,两组的性别、年龄、合并高血压、合并糖尿病、血糖、教育水平、MMSE评分、C反应蛋白、血白蛋白、血肌酐、血钠、全段甲状旁腺素、低密度脂蛋白胆固醇、血尿酸、STS-5、单次尿素氮清除指数(urea clearance index,Kt/V)差异具有统计学意义(P<0.05);进一步行多因素Logistic回归分析显示,高龄、女性、低MMSE评分、低Kt/V以及STS-5时间延长是发生TUG延长的独立危险因素(P<0.05);ROC曲线显示,年龄、性别、MMSE总分、STS-5时间预测MHD患者发生TUG延长的曲线下面积(area under the curve,AUC)分别为0.825、0.678、0.777、0.836(P<0.01),具有较高的预测价值,Kt/V预测患者发生TUG延长的AUC为0.602(P=0.037),有一定的预测价值;以上5项指标作为整体模型预测MHD患者发生TUG延长的AUC为0.923(P<0.01)结论MHD患者的年龄、性别、MMSE评分、STS-5时间延长、Kt/V的水平与合并TUG延长相关,是发生TUG延长的独立危险因素,可能成为预测TUG延长的生物学指标。展开更多
基金supported by the National Basic Research Program of China(973 Program)(2010CB731905)
文摘The exact radar cross-section （RCS） measurement is difficult when the scattering of targets is low. Ful polarimetric cali-bration is one technique that offers the potential for improving the accuracy of RCS measurements. There are numerous polarimetric calibration algorithms. Some complex expressions in these algo-rithms cannot be easily used in an engineering practice. A radar polarimetric coefficients matrix （RPCM） with a simpler expression is presented for the monostatic radar polarization scattering matrix （PSM） measurement. Using a rhombic dihedral corner reflector and a metal ic sphere, the RPCM can be obtained by solving a set of equations, which can be used to find the true PSM for any target. An example for the PSM of a metal ic dish shows that the proposed method obviously improves the accuracy of cross-polarized RCS measurements.
文摘Geological studies indicate that Qinghai\|Tibet plateau crust has shortened at least 2500km and the thickness was increased to 60～70km in the past 45Ma. Different researchers advocate different views to explain the shortening according to their studies.( Tapponnier,1977;Chang et al,1986;England et al,1986;Murphy,1997;Y.Pan,1999),however it is still unresolved on how much shortening in upper crustal especially in Qiangtang terrain.Qiangtang terrain is located in the center of Qinghai\|Tibet plateau, the tectonic deformation has been resulted from intracontinental convergence and collision of India plate with Eurasian plate.The deformation style of Qiangtang terrain shows east\|west\|trending folds and thrusts which formed in the shallow tectonic level during collisional\|intracontinental period. The folds type is characterized by nonpenetrative\|foliation parallel fold, the hinges have the same trend with the thrusts. These traits are favourable for restoring the balanced cross\|section and measuring the shortening. The balanced reconstruction is based on line balancing on three different stratigraphic sections (A,B and C)across the Northern Qiangtang basin in the area between 85°E and 87°E.The sections are all north\|south\|trending in accordance with the moving direction of thrusts.
基金supported by the National Natural Science Foundation of China(61471144)
文摘This paper studies the development on the first order sea clutter cross section for bistatic high frequency surface wave radar (HFSWR). Based on the received first order electric field expression, a closed-form of cross sections is derived to account for the case of receiving antenna array being mounted on the shipborne platform. The uniform linear motion and sway motion components are assumed to be responsible for the observed differences in comparison with the bistatic fixed antenna case. Correspondingly, simulations are conducted to study the sea clutter spectral characteristics for these two cases versus different system parameters and sea state conditions. It is shown numerically that the forward motion component will spread the Bragg lines severely and the influence triggered by the sway motion can be explained as the Bessel function modulation of the ordinary sea clutter spectra. The obtained results have important implications in the application of shipborne HFSWR technology to ocean remote sensing and target detection.
文摘A new method of calculating the radai cross section (RCS) for wing-body blended targets is presented and verified. The method utilizes a computer program for modeling targets' geometry in terms of small pieces. The calculation is based on physical optics approximation. Examples are given to show the validity of the method.
基金financially supported by the National Natural Science Foundation of China(Grant No.11372136)
文摘Analyzing the mass of behind-armor debris (BAD) generated by Rolled Homogeneous Armor (RHA) subjected to normal penetration of variable cross-section Explosively Formed Projectile (EFP) is the purpose of this paper. So theoretical analysis, numerical simulation and experimental data are combined to analyze the influence of variable cross-section characteristic on the time history of crater radius. Moreover the relationships between time history of crater radius (as well as mass of BAD) and the thickness of RHA (from 30mm to 70 mm) and the impact velocity of EFP (1650 m/s to 1860 m/s) are also investigated. The results indicate that: 1) being compared to the variable cross-section characteristic is ignored, the theoretical time history of crater radius is in better agreement with the simulation results when the variable cross-section characteristic is considered;2) being compared to the other three conditions of plug, the theoretical mass of BAD is in the best agreement with the simulation results when the shape of plug is frustum of a cone and the angle between generatrix and bottom is 45- and the axial length of mushroom is considered.
基金Sponsored by Foundation of National Defense Key Laboratory
文摘The aerodynamic characteristics of projectiles with triangular and circular cross sections are investigated respectively by use of free-flight experiment.Processed the experiment data,curves of flight velocity variation and nutation of both projectiles are obtained,based on the curves,their aerodynamic force and moment coefficients are found out by data fitting,and their aerodynamic performances are compared and analyzed.Results show that the projectile with triangular cross section has smaller resistance,higher lift-drag ratio,better static stability,higher stability capability and more excellent maneuverability than those of the projectile with circular cross section,therefore it can be used in the guided projectiles;under lower rotation speed,the triangular section projectile has greater Magnus moment leading to bigger projectile distribution.
基金supported by the National Science Fund for Young Scientists of China(6130214861571011)
文摘We develop an efficient method for polished metallic sphere’s scattering prediction in terahertz band when its frequency dispersion property is considered. By deducing scattering solution of the lossy metallic sphere, the radar cross section(RCS)of different metallic spheres is given at terahertz frequencies. The investigation of the RCS of polished metallic spheres shows the normalized RCS is always same to the metals’ normal incidence reflectivity when the sphere becomes electrically large. The metals which have high reflectivity(such as Al, Cu, Ag and Au) show that the corresponding RCS of the spheres is almost πa2 in terahertz band. The sphere’s RCS of the transition metal such as Fe begins to decrease obviously since the far infrared.
基金This project was partially supported by the National Natural Science Foundation of China (60371041).
文摘Based on a Pade approximation, a wide-angle parabolic equation method is introduced for computing the multiobject radar cross section （RCS） for the first time. The method is a paraxial version of the scalar wave equation, which solves the field by marching them along the paraxial direction. Numerical results show that a single wide-angle parabofic equation run can compute multi-object RCS efficiently for angles up to 45 ° . The method provides anew and efficient numerical method for computation electromagnetics.
文摘The reduction of TE-scattering by a conducting cylinder with multiple surface impedance loads is investigated. Synthesis procedures are developed to find the optimal loading which result in zero scattering in the desired directions or at several frequencies. Numerical results of these procedures are presented. The theoretical predictions are confirmed with an experiment. The proposed synthesis procedure is completely general and can be applied to arbitrarily shaped conducting bodies.
文摘In this paper, an improved approach is presented to reconstruct two dimensional conduc- tor profile illuminated by incident plane waves of multiple frequencies and directions via amplitudes of backscattered field in near regions. Newton-Kantorovitch algorithm is adopted to cast the non- linear coupled integral equations into linearized form, method of moment is used to transform the above linearized integral equations into matrix form, the resulting ill-posed overdetermined linear equations are solved using pseudoinverse technique based on Gram-Schedmit orthogonal procedure. Initial values are determined by solving a nonlinear least aquare error problem to establish an equivat lent circular cylinder. The effects of various parameters on reconstruction quality are discussed with numerical results and analysis.
基金This project was supported by the Foundation of MOE of China (No. 00179).
文摘It is well known that the incorrect results will be given using either the electric or magnetic field integral equation to calculate the radar cross section (RCS) of a closed body at the interior resonance. In this paper, an effective iterative technique is used to correct the calculated surface current density from the electric field integral equation. The radar cross section is computed for an infinite conducting circular cylinder at the interior resonance, and the obtained results are in good agreement with the analytical results. The backscattering cross section of an infinite triangular cylinder in the vicinity of a resonant frequency is also calculated. It is shown that the presence method is efficient and accurate.
文摘In this study,K and L shell photoeffect cross-sections were measured for the elements in the range of 50≤Z≤65at 59.5keV.These photoeffect cross-sections were measured by using the experimentalσKαproduction cross-section values measured in this paper and two different K shell fluorescence yield values in the literature.The results were compared with the calculated theoretical values.The values were plotted versus atomic number.
文摘A new method called multi-frequency holography (MFH) for two-dimensional radar cross-section imaging of rotating objects is introduced, in which a constant coherent reference signal from transmitted signal is added into received signal over certain frequency-width. With the MFH only the intensity of received composite signals needs to be measured. Both imaging situations of far field and near field are considered in details. Special restrictions about the MFH are also discussed and simulated by numerical computation. Examples of numerical simulation show that the method is effective, applicable and perspective.
基金国防科技重点实验室基金项目（51447070104252502） The author would like to thanks Academician Lu Jian-xun and Profs Yi Xue-qin and Song Dong-an for their useful help and suggestions.
文摘目的探讨维持性血液透析(maintenance hemodialysis,MHD)患者计时站立行走测试(time up and go test,TUG)时间延长的影响因素。方法采用横断面调查法,选取2023年6月1日至2024年1月31日于首都医科大学附属北京潞河医院规律血液透析、数据完整且可配合的患者,分别采用简易精神状态检查表(Minimum Mental State Examination,MMSE)、5次起坐试验(5 times sit to stand,STS-5)、TUG量表评估患者认知功能、下肢肌肉力量、平衡及步态功能;根据TUG结果进行分组,即TUG≤12 s,判定为TUG正常组;TUG>12 s判定为TUG延长组,采用多因素Logistic回归法分析患者TUG延长组的影响因素,以受试者工作特征(receiver operating characteristic,ROC)曲线分析影响因素对TUG延长患者的预测价值。结果本研究共纳入146例MHD患者,TUG延长组86例,TUG正常组60例,两组的性别、年龄、合并高血压、合并糖尿病、血糖、教育水平、MMSE评分、C反应蛋白、血白蛋白、血肌酐、血钠、全段甲状旁腺素、低密度脂蛋白胆固醇、血尿酸、STS-5、单次尿素氮清除指数(urea clearance index,Kt/V)差异具有统计学意义(P<0.05);进一步行多因素Logistic回归分析显示,高龄、女性、低MMSE评分、低Kt/V以及STS-5时间延长是发生TUG延长的独立危险因素(P<0.05);ROC曲线显示,年龄、性别、MMSE总分、STS-5时间预测MHD患者发生TUG延长的曲线下面积(area under the curve,AUC)分别为0.825、0.678、0.777、0.836(P<0.01),具有较高的预测价值,Kt/V预测患者发生TUG延长的AUC为0.602(P=0.037),有一定的预测价值;以上5项指标作为整体模型预测MHD患者发生TUG延长的AUC为0.923(P<0.01)结论MHD患者的年龄、性别、MMSE评分、STS-5时间延长、Kt/V的水平与合并TUG延长相关,是发生TUG延长的独立危险因素,可能成为预测TUG延长的生物学指标。
