It is well known that the sea return echo contains contributions from at least two scattering mechanisms. In addition to the resonant Bragg scattering, the specular point scattering plays an important role as the inci...It is well known that the sea return echo contains contributions from at least two scattering mechanisms. In addition to the resonant Bragg scattering, the specular point scattering plays an important role as the incidence angle becomes smaller （≥ 20°）. Here, in combination with the Kirchhoff integral equation of scattering field and the stationary phase approximation, analytical expressions for Doppler shift and spectral bandwidth of specular point scattering, which are insensitive to the polarization state, are derived theoretically. For comparison, the simulated results related to the two-scale method （TSM） and the method of moment （MOM） are also presented. It is found that the Doppler shift and the spectral bandwidth given by TSM are insufficient at small incidence angles. However, a comparison between the analytical results and the numerical simulations by MOM in the backscatter configuration shows that our proposed formulas are valid for the specular point scattering case. In this work, the dependences of the predicted results on incidence angle, radar frequency, and wind speed are also discussed. The obtained conclusions seem promising for a better understanding of the Doppler spectra of the specular point scattering fields from time-varying sea surfaces.展开更多
An interpolating reproducing kernel particle method for two-dimensional （2D） scatter points is introduced. It elim- inates the dependency of gridding in numerical calculations. The interpolating shape function in th...An interpolating reproducing kernel particle method for two-dimensional （2D） scatter points is introduced. It elim- inates the dependency of gridding in numerical calculations. The interpolating shape function in the interpolating repro- ducing kernel particle method satisfies the property of the Kronecker delta function. This method offers a mathematics basis for recognition technology and simulation analysis, which can be expressed as simultaneous differential equations in science or project problems. Mathematical examples are given to show the validity of the interpolating reproducing kernel particle method.展开更多
In the electron or x-ray scattering experiment,the measured spectra at larger momentum transfer are dominated by the electric dipole-forbidden transitions,while the corresponding selection rules for triatomic molecule...In the electron or x-ray scattering experiment,the measured spectra at larger momentum transfer are dominated by the electric dipole-forbidden transitions,while the corresponding selection rules for triatomic molecules have not been clearly elucidated.In this work,based on the molecular point group,the selection rules for the electric multipolarities of the electronic transitions of triatomic molecules are derived and summarized into several tables with the variation of molecular geometry in the transition process being considered.Based on the summarized selection rules,the electron energy loss spectra of H2O,CO2,and N2O are identified,and the momentum transfer dependence behaviors of their valence-shell excitations are explained.展开更多
The knowledge of the energy level structures of atoms and molecules is mainly obtained by spectroscopic experiments. Both photoabsorption and photoemission spectra are subject to the electric dipole selection rules （...The knowledge of the energy level structures of atoms and molecules is mainly obtained by spectroscopic experiments. Both photoabsorption and photoemission spectra are subject to the electric dipole selection rules （also known as optical selection rules）. However, the selection rules for atoms and molecules in the scattering experiments are not identical to those in the optical experiments. In this paper, based on the theory of the molecular point group, the selection rules are derived and summarized for the electric monopole, electric dipole, electric quadrupole, and electric octupole transitions of diatomic molecules under the first Born approximation in scattering experiments. Then based on the derived selection rules, the electron scattering spectra and x-ray scattering spectra of H2, N2, and CO at different momentum transfers are explained, and the discrepancies between the previous experimental results measured by different groups are elucidated.展开更多
A simpler and improved utility approximate point scattered function for thin-film converters currently used in neutron photographic devices is proposed as a correction method to produce clearer,more realistic images.T...A simpler and improved utility approximate point scattered function for thin-film converters currently used in neutron photographic devices is proposed as a correction method to produce clearer,more realistic images.The validity of the model was demonstrated through a simulation experiment.Based on the results,an error analysis was carried out,certain corrections were made to the original model,and the final model achieved a very low relative error in the simulation experiment.The model can also be optimized for quantitative neutron photographic analysis using iterative algorithms to obtain realistic neutron photographic images more quickly.At the end of the article,the model is extended to consider the case of energy spectrum hardening by introducing a temperature correction parameter.展开更多
A solvable model of lateral line of a fish based on a wave equation with additional boundary conditions on a set of isolated points is proposed.Within the framework of this model it is shown that the ratio of pressure...A solvable model of lateral line of a fish based on a wave equation with additional boundary conditions on a set of isolated points is proposed.Within the framework of this model it is shown that the ratio of pressures on lateral lines on different fish flanks,as well as the cross section of sound scattering on both the lines,strongly depends on angles of incidence of incoming sound waves.The strong angular dependence of the pressure ratio seems to be sufficient for the fish to determine the directions from which the sound is coming.展开更多
We study s-wave pion-pion scattering length in lattice QCD for pion masses ranging from 330 MeV to 466 MeV.In the "Asqtad" improved staggered fermion formulation,we measure full ππ four-point correlators f...We study s-wave pion-pion scattering length in lattice QCD for pion masses ranging from 330 MeV to 466 MeV.In the "Asqtad" improved staggered fermion formulation,we measure full ππ four-point correlators for isospin I = 0 and 2 channels,and use chiral perturbation theory at next-to-leading order to extrapolate our simulation results.Extrapolating to the physical pion mass yields scattering lengths as mπaI=2 0 = 0.041 6(2) and m π a I =0 0 = 0.186(2) for isospin I = 2 and 0 channels,respectively.Our lattice simulation for ππ scattering length in I = 0 channel is an exploratory study,where we include the disconnected contribution,and our preliminary result is near to its experimental value.These simulations are carried out with MILC 2 + 1 flavor gauge configurations at lattice spacing a ≈ 0.15 fm.展开更多
Image quality in positron emission tomography(PET)is affected by random and scattered coincidences and reconstruction protocols.In this study,we investigated the effects of scattered and random coincidences from outsi...Image quality in positron emission tomography(PET)is affected by random and scattered coincidences and reconstruction protocols.In this study,we investigated the effects of scattered and random coincidences from outside the field of view(FOV)on PET image quality for different reconstruction protocols.Imaging was performed on the Discovery 690 PET/CT scanner,using experimental configurations including the NEMA phantom(a body phantom,with six spheres of different sizes)with a signal background ratio of 4:1.The NEMA phantom(phantom I)was scanned separately in a one-bed position.To simulate the effect of random and scatter coincidences from outside the FOV,six cylindrical phantoms with various diameters were added to the NEMA phantom(phantom II).The 18 emission datasets with mean intervals of 15 min were acquired(3 min/scan).The emission data were reconstructed using different techniques.The image quality parameters were evaluated by both phantoms.Variations in the signal-to-noise ratio(SNR)in a 28-mm(10-mm)sphere of phantom II were 37.9%(86.5%)for ordered-subset expectation maximization(OSEM-only),36.8%(81.5%)for point spread function(PSF),32.7%(80.7%)for time of flight(TOF),and 31.5%(77.8%)for OSEM+PSF+TOF,respectively,indicating that OSEM+PSF+TOF reconstruction had the lowest noise levels and lowest coefficient of variation(COV)values.Random and scatter coincidences from outside the FOV induced lower SNR,lower contrast,and higher COV values,indicating image deterioration and significantly impacting smaller sphere sizes.Amongst reconstruction protocols,OSEM+PSF+TOF and OSEM+PSF showed higher contrast values for sphere sizes of 22,28,and 37 mm and higher contrast recovery coefficient values for smaller sphere sizes of 10 and 13 mm.展开更多
散射中心匹配是当前散射中心用于SAR图像目标识别的一个主要技术途径。散射中心匹配的难点在于散射中心特征存在的误差和缺失。Coherent Point Drift(CPD)方法从概率密度估计的角度解决点模式匹配问题,能够较好地考虑散射中心的误差和...散射中心匹配是当前散射中心用于SAR图像目标识别的一个主要技术途径。散射中心匹配的难点在于散射中心特征存在的误差和缺失。Coherent Point Drift(CPD)方法从概率密度估计的角度解决点模式匹配问题,能够较好地考虑散射中心的误差和缺失。本文将CPD方法用于散射中心匹配,并在此基础上引入车辆目标SAR图像方位角估计先验信息和散射中心属性信息,以提高散射中心匹配的准确性和稳健性。MSTAR数据实验说明了该方法的有效性。展开更多
基金Project supported by the Young Scientists Fund of the National Natural Science Foundation of China(Grant No.40906088)the Specialized Research Fund for the Doctoral Program of Higher Education,China(Grant No.200804231021)
文摘It is well known that the sea return echo contains contributions from at least two scattering mechanisms. In addition to the resonant Bragg scattering, the specular point scattering plays an important role as the incidence angle becomes smaller （≥ 20°）. Here, in combination with the Kirchhoff integral equation of scattering field and the stationary phase approximation, analytical expressions for Doppler shift and spectral bandwidth of specular point scattering, which are insensitive to the polarization state, are derived theoretically. For comparison, the simulated results related to the two-scale method （TSM） and the method of moment （MOM） are also presented. It is found that the Doppler shift and the spectral bandwidth given by TSM are insufficient at small incidence angles. However, a comparison between the analytical results and the numerical simulations by MOM in the backscatter configuration shows that our proposed formulas are valid for the specular point scattering case. In this work, the dependences of the predicted results on incidence angle, radar frequency, and wind speed are also discussed. The obtained conclusions seem promising for a better understanding of the Doppler spectra of the specular point scattering fields from time-varying sea surfaces.
基金supported by the National Natural Science Foundation of China(Grant No.11171208)the Natural Science Foundation of Shanxi Province,China(Grant No.2013011022-6)
文摘An interpolating reproducing kernel particle method for two-dimensional （2D） scatter points is introduced. It elim- inates the dependency of gridding in numerical calculations. The interpolating shape function in the interpolating repro- ducing kernel particle method satisfies the property of the Kronecker delta function. This method offers a mathematics basis for recognition technology and simulation analysis, which can be expressed as simultaneous differential equations in science or project problems. Mathematical examples are given to show the validity of the interpolating reproducing kernel particle method.
基金Project supported by the National Key Research and Development Program of China(Grant No.2017YFA0402300)the National Natural Science Foundation of China(Grant No.U1732133)the Science Fund from Chinese Academy of Sciences(Grant No.11320101003)
文摘In the electron or x-ray scattering experiment,the measured spectra at larger momentum transfer are dominated by the electric dipole-forbidden transitions,while the corresponding selection rules for triatomic molecules have not been clearly elucidated.In this work,based on the molecular point group,the selection rules for the electric multipolarities of the electronic transitions of triatomic molecules are derived and summarized into several tables with the variation of molecular geometry in the transition process being considered.Based on the summarized selection rules,the electron energy loss spectra of H2O,CO2,and N2O are identified,and the momentum transfer dependence behaviors of their valence-shell excitations are explained.
基金Financial support for this work,provided by the Key National Project(No.2008ZX05035)the State Science and Technology Support Program,the National Natural Science Foundation of China (Nos.40574057,40874054,40804026)the State Basic Research and Development Program of China(No.2007CB209406)
基金Project supported by the National Natural Science Foundation of China(Grant Nos.U1332204,11274291,and 11320101003)
文摘The knowledge of the energy level structures of atoms and molecules is mainly obtained by spectroscopic experiments. Both photoabsorption and photoemission spectra are subject to the electric dipole selection rules （also known as optical selection rules）. However, the selection rules for atoms and molecules in the scattering experiments are not identical to those in the optical experiments. In this paper, based on the theory of the molecular point group, the selection rules are derived and summarized for the electric monopole, electric dipole, electric quadrupole, and electric octupole transitions of diatomic molecules under the first Born approximation in scattering experiments. Then based on the derived selection rules, the electron scattering spectra and x-ray scattering spectra of H2, N2, and CO at different momentum transfers are explained, and the discrepancies between the previous experimental results measured by different groups are elucidated.
基金the College Foundation Project,the College of Engineering and Technology of Chengdu University of Technology(No.C122018029)。
文摘A simpler and improved utility approximate point scattered function for thin-film converters currently used in neutron photographic devices is proposed as a correction method to produce clearer,more realistic images.The validity of the model was demonstrated through a simulation experiment.Based on the results,an error analysis was carried out,certain corrections were made to the original model,and the final model achieved a very low relative error in the simulation experiment.The model can also be optimized for quantitative neutron photographic analysis using iterative algorithms to obtain realistic neutron photographic images more quickly.At the end of the article,the model is extended to consider the case of energy spectrum hardening by introducing a temperature correction parameter.
基金supported by the Ministry of Education and Science of Ukraine(Grant No.0115U003208)。
文摘A solvable model of lateral line of a fish based on a wave equation with additional boundary conditions on a set of isolated points is proposed.Within the framework of this model it is shown that the ratio of pressures on lateral lines on different fish flanks,as well as the cross section of sound scattering on both the lines,strongly depends on angles of incidence of incoming sound waves.The strong angular dependence of the pressure ratio seems to be sufficient for the fish to determine the directions from which the sound is coming.
基金Supported by Fundamental Research Funds for the Central Universities under Grant No. 2010SCU23002the Startup Grant fromthe Institute of Nuclear Science and Technology of Sichuan University
文摘We study s-wave pion-pion scattering length in lattice QCD for pion masses ranging from 330 MeV to 466 MeV.In the "Asqtad" improved staggered fermion formulation,we measure full ππ four-point correlators for isospin I = 0 and 2 channels,and use chiral perturbation theory at next-to-leading order to extrapolate our simulation results.Extrapolating to the physical pion mass yields scattering lengths as mπaI=2 0 = 0.041 6(2) and m π a I =0 0 = 0.186(2) for isospin I = 2 and 0 channels,respectively.Our lattice simulation for ππ scattering length in I = 0 channel is an exploratory study,where we include the disconnected contribution,and our preliminary result is near to its experimental value.These simulations are carried out with MILC 2 + 1 flavor gauge configurations at lattice spacing a ≈ 0.15 fm.
基金supported by the Tehran University of Medical Sciences under Grant No.36291PET/CT and Cyclotron Center of Masih Daneshvari Hospital at Shahid Beheshti University of Medical Sciences。
文摘Image quality in positron emission tomography(PET)is affected by random and scattered coincidences and reconstruction protocols.In this study,we investigated the effects of scattered and random coincidences from outside the field of view(FOV)on PET image quality for different reconstruction protocols.Imaging was performed on the Discovery 690 PET/CT scanner,using experimental configurations including the NEMA phantom(a body phantom,with six spheres of different sizes)with a signal background ratio of 4:1.The NEMA phantom(phantom I)was scanned separately in a one-bed position.To simulate the effect of random and scatter coincidences from outside the FOV,six cylindrical phantoms with various diameters were added to the NEMA phantom(phantom II).The 18 emission datasets with mean intervals of 15 min were acquired(3 min/scan).The emission data were reconstructed using different techniques.The image quality parameters were evaluated by both phantoms.Variations in the signal-to-noise ratio(SNR)in a 28-mm(10-mm)sphere of phantom II were 37.9%(86.5%)for ordered-subset expectation maximization(OSEM-only),36.8%(81.5%)for point spread function(PSF),32.7%(80.7%)for time of flight(TOF),and 31.5%(77.8%)for OSEM+PSF+TOF,respectively,indicating that OSEM+PSF+TOF reconstruction had the lowest noise levels and lowest coefficient of variation(COV)values.Random and scatter coincidences from outside the FOV induced lower SNR,lower contrast,and higher COV values,indicating image deterioration and significantly impacting smaller sphere sizes.Amongst reconstruction protocols,OSEM+PSF+TOF and OSEM+PSF showed higher contrast values for sphere sizes of 22,28,and 37 mm and higher contrast recovery coefficient values for smaller sphere sizes of 10 and 13 mm.
文摘散射中心匹配是当前散射中心用于SAR图像目标识别的一个主要技术途径。散射中心匹配的难点在于散射中心特征存在的误差和缺失。Coherent Point Drift(CPD)方法从概率密度估计的角度解决点模式匹配问题,能够较好地考虑散射中心的误差和缺失。本文将CPD方法用于散射中心匹配,并在此基础上引入车辆目标SAR图像方位角估计先验信息和散射中心属性信息,以提高散射中心匹配的准确性和稳健性。MSTAR数据实验说明了该方法的有效性。
