A gradient-based optimization method for producing a contoured beam by using a single-fed reflector antenna is presented. First, a quick and accurate pattern approximation formula based on physical optics(PO) is adopt...A gradient-based optimization method for producing a contoured beam by using a single-fed reflector antenna is presented. First, a quick and accurate pattern approximation formula based on physical optics(PO) is adopted to calculate the gradients of the directivity with respect to reflector's nodal displacements. Because the approximation formula is a linear function of nodal displacements, the gradient can be easily derived. Then, the method of the steepest descent is adopted, and an optimization iteration procedure is proposed. The iteration procedure includes two loops: an inner loop and an outer loop. In the inner loop, the gradient and pattern are calculated by matrix operation, which is very fast by using the pre-calculated data in the outer loop. In the outer loop, the ideal terms used in the inner loop to calculate the gradient and pattern are updated, and the real pattern is calculated by the PO method. Due to the high approximation accuracy, when the outer loop is performed once, the inner loop can be performed many times, which will save much time because the integration is replaced by matrix operation. In the end, a contoured beam covering the continental United States(CONUS) is designed, and simulation results show the effectiveness of the proposed algorithm.展开更多
为了使星载赋形波束天线远场方向图与服务区形状匹配良好,并且在波束覆盖区内具有较平坦的方向性系数,将表征反射面形状的Zernike多项式展开系数作为优化变量,建立基于最小P乘法和Minmax方法的适应度函数,利用进化算法进行赋形反射面天...为了使星载赋形波束天线远场方向图与服务区形状匹配良好,并且在波束覆盖区内具有较平坦的方向性系数,将表征反射面形状的Zernike多项式展开系数作为优化变量,建立基于最小P乘法和Minmax方法的适应度函数,利用进化算法进行赋形反射面天线优化。利用该方法设计了覆盖中国大陆和巴西的赋形波束反射面天线。仿真结果表明,天线远场方向图与服务区形状均匹配良好,服务区内的方向性系数波动量分别为2.31 d B和11.23 d B,该值比现有方法小,并且该方法具有较高自由度及收敛性好的特点。展开更多
The aim of this study was to evaluate the accuracy and reproducibility of a morphological contour interpolation(MCI)based segmentation method for the volumetric measurement of bone grafts around implants.Three 3D-prin...The aim of this study was to evaluate the accuracy and reproducibility of a morphological contour interpolation(MCI)based segmentation method for the volumetric measurement of bone grafts around implants.Three 3D-printed models(one with a cylinder and two with a geometrically-complex form)were fabricated to simulate implant placement with a simultaneous guided bone regeneration(GBR)procedure.All models were scanned using a cone beam computed tomography(CBCT)instrument with the same parameters.The true volumes of the bone grafts in the models were assessed using computer-aided calculation(controls).For the test measurements,both manual and MCI-based methods were used.A comparison between the measured and true volumes was performed to evaluate the accuracy.The coefficients of variation of repeated measurements were calculated to evaluate the reproducibility.In addition,the execution time was recorded and a comparison between the two methods was performed.The high accuracy of the MCI-based method was found with differences between the measured value and actual volume,which never exceeded 7.3%.Excellent reproducibility was shown,with coefficients of variation never exceeding 1.1%.A shorter execution time was observed for the MCI-based method than for the manual method.Within the confines of this study,the MCI-based method may be suitable for volumetric measurements of grafted bone around implants.展开更多
Ⅰ. INTRODUCTION Electron diffraction zone axis patterns are rich in crystallographic information. Crystal symmetry can readily be obtained from the symmetry of the patterns. Zone axis patterns can be generated by con...Ⅰ. INTRODUCTION Electron diffraction zone axis patterns are rich in crystallographic information. Crystal symmetry can readily be obtained from the symmetry of the patterns. Zone axis patterns can be generated by convergent-beam or bend contour techniques. Convergent-展开更多
This work was to reveal the residual stress profile in electron beam welded Ti-6Al-4V alloy plates（50 mm thick） by using finite element and contour measurement methods.A three-dimensional finite element model of 50-...This work was to reveal the residual stress profile in electron beam welded Ti-6Al-4V alloy plates（50 mm thick） by using finite element and contour measurement methods.A three-dimensional finite element model of 50-mmthick titanium component was proposed,in which a column–cone combined heat source model was used to simulate the temperature field and a thermo-elastic–plastic model to analyze residual stress in a weld joint based on ABAQUS software.Considering the uncertainty of welding simulation,the computation was calibrated by experimental data of contour measurement method.Both test and simulated results show that residual stresses on the surface and inside the weld zone are significantly different and present a narrow and large gradient feature in the weld joint.The peak tensile stress exceeds the yield strength of base materials inside weld,which are distinctly different from residual stress of the thin Ti-6Al-4V alloy plates presented in references before.展开更多
基金supported by the National Natural Science Foundation of China(51805399)the Fundamental Research Funds for the Central Universities(JB180403)+2 种基金the Chinese Academy of Sciences(CAS)"Light of West China" Program(2017-XBQNXZ-B-024)the National Basic Research Program of China(973 Program)(2015CB857100)the Operation,Maintenance and Upgrading Fund for Astronomical Telescopes and Facility Instruments,budgeted from the Ministry of Finance of China(MOF)and administrated by the CAS
文摘A gradient-based optimization method for producing a contoured beam by using a single-fed reflector antenna is presented. First, a quick and accurate pattern approximation formula based on physical optics(PO) is adopted to calculate the gradients of the directivity with respect to reflector's nodal displacements. Because the approximation formula is a linear function of nodal displacements, the gradient can be easily derived. Then, the method of the steepest descent is adopted, and an optimization iteration procedure is proposed. The iteration procedure includes two loops: an inner loop and an outer loop. In the inner loop, the gradient and pattern are calculated by matrix operation, which is very fast by using the pre-calculated data in the outer loop. In the outer loop, the ideal terms used in the inner loop to calculate the gradient and pattern are updated, and the real pattern is calculated by the PO method. Due to the high approximation accuracy, when the outer loop is performed once, the inner loop can be performed many times, which will save much time because the integration is replaced by matrix operation. In the end, a contoured beam covering the continental United States(CONUS) is designed, and simulation results show the effectiveness of the proposed algorithm.
文摘为了使星载赋形波束天线远场方向图与服务区形状匹配良好,并且在波束覆盖区内具有较平坦的方向性系数,将表征反射面形状的Zernike多项式展开系数作为优化变量,建立基于最小P乘法和Minmax方法的适应度函数,利用进化算法进行赋形反射面天线优化。利用该方法设计了覆盖中国大陆和巴西的赋形波束反射面天线。仿真结果表明,天线远场方向图与服务区形状均匹配良好,服务区内的方向性系数波动量分别为2.31 d B和11.23 d B,该值比现有方法小,并且该方法具有较高自由度及收敛性好的特点。
基金the Project of Science and Technology Commission of Shanghai Municipality(No.19411950100)the Multicenter Clinical Research Program of Shanghai Jiao Tong University School of Medicine(No.DLY201822)the Fundamental Research Program Funding of Ninth People’s Hospital affiliated to Shanghai Jiao Tong University School of Medicine(No.JYZZ102)。
文摘The aim of this study was to evaluate the accuracy and reproducibility of a morphological contour interpolation(MCI)based segmentation method for the volumetric measurement of bone grafts around implants.Three 3D-printed models(one with a cylinder and two with a geometrically-complex form)were fabricated to simulate implant placement with a simultaneous guided bone regeneration(GBR)procedure.All models were scanned using a cone beam computed tomography(CBCT)instrument with the same parameters.The true volumes of the bone grafts in the models were assessed using computer-aided calculation(controls).For the test measurements,both manual and MCI-based methods were used.A comparison between the measured and true volumes was performed to evaluate the accuracy.The coefficients of variation of repeated measurements were calculated to evaluate the reproducibility.In addition,the execution time was recorded and a comparison between the two methods was performed.The high accuracy of the MCI-based method was found with differences between the measured value and actual volume,which never exceeded 7.3%.Excellent reproducibility was shown,with coefficients of variation never exceeding 1.1%.A shorter execution time was observed for the MCI-based method than for the manual method.Within the confines of this study,the MCI-based method may be suitable for volumetric measurements of grafted bone around implants.
文摘Ⅰ. INTRODUCTION Electron diffraction zone axis patterns are rich in crystallographic information. Crystal symmetry can readily be obtained from the symmetry of the patterns. Zone axis patterns can be generated by convergent-beam or bend contour techniques. Convergent-
基金supported by the National Natural Science Foundation of China (No.50935008)
文摘This work was to reveal the residual stress profile in electron beam welded Ti-6Al-4V alloy plates（50 mm thick） by using finite element and contour measurement methods.A three-dimensional finite element model of 50-mmthick titanium component was proposed,in which a column–cone combined heat source model was used to simulate the temperature field and a thermo-elastic–plastic model to analyze residual stress in a weld joint based on ABAQUS software.Considering the uncertainty of welding simulation,the computation was calibrated by experimental data of contour measurement method.Both test and simulated results show that residual stresses on the surface and inside the weld zone are significantly different and present a narrow and large gradient feature in the weld joint.The peak tensile stress exceeds the yield strength of base materials inside weld,which are distinctly different from residual stress of the thin Ti-6Al-4V alloy plates presented in references before.
