为了拓展倾斜波束圆极化天线(Circularly Polarized Antenna with Tilted Beam,CPA-TB)的带宽,在分析了该天线结构及其特征的基础上,提出了一种花纹式螺旋臂(Flower-Spiral,FS)协同互补开口谐振环(complementary split ring resontor,CS...为了拓展倾斜波束圆极化天线(Circularly Polarized Antenna with Tilted Beam,CPA-TB)的带宽,在分析了该天线结构及其特征的基础上,提出了一种花纹式螺旋臂(Flower-Spiral,FS)协同互补开口谐振环(complementary split ring resontor,CSRR)的CSRR-FS结构.该结构通过FS增加了天线表面电流路径,实现了天线驻波比(voltage standing wave ratio,VSWR)的拓展;利用CSRR改变了低频点反射板的电流分布,实现反射板小型化的同时,减小了天线的交叉极化分量,增强了天线的辐射性能,拓展了天线的轴比带宽.仿真和实测结果表明:与普通的平面反射板相比,在保证圆极化、波束倾角30°的条件下,基于CSRR-FS结构的CPA-TB相对带宽为24%(5.5-7GHz),天线工作带宽拓展了1.8倍.CSRR-FS结构的提出为CPA-TB带宽的拓展提供了新的途径.展开更多
基于非对称结构设计思想,以表面倾斜的高介电常数介质谐振器为辐射单元,采用改进的正交不等长缝隙结构耦合馈电,设计制作了一种圆极化倾斜波束介质谐振天线。通过对介质谐振器表面倾斜角度和馈电缝隙的参数优化,扩展了天线的频带宽度,...基于非对称结构设计思想,以表面倾斜的高介电常数介质谐振器为辐射单元,采用改进的正交不等长缝隙结构耦合馈电,设计制作了一种圆极化倾斜波束介质谐振天线。通过对介质谐振器表面倾斜角度和馈电缝隙的参数优化,扩展了天线的频带宽度,实现了宽频带圆极化倾斜波束辐射。仿真结果表明:天线在同时满足S11<-10 d B、3 d B轴比和30°波束倾斜条件下的带宽为18.2%。同时,由于采用高介电常数介质谐振器,天线剖面高度降低到0.165λ。实测结果和仿真结果吻合较好,验证了该设计的有效性。展开更多
Geometric calibration is critical to the accurate SPECT reconstruction. In this paper, a geometric calibration method was developed for a dedicated breast SPECT system with a tilted parallel beam （TPB） orbit. The ac...Geometric calibration is critical to the accurate SPECT reconstruction. In this paper, a geometric calibration method was developed for a dedicated breast SPECT system with a tilted parallel beam （TPB） orbit. The acquisition geometry of the breast SPECT was firstly characterized. And then its projection model was established based on the acquisition geometry. Finally, the calibration results were obtained using a nonlinear optimization method that fitted the measured projections to the model. Monte Carlo data of the breast SPECT were used to verify the calibration method. Simulation results showed that the geometric parameters with reasonable accuracy could be obtained by the proposed method.展开更多
在太阳能系统的设计中常涉及倾斜面上日总直射辐射的计算。计算倾斜面上日总直射辐射最常用的方法是Liu and Jordan所提出的数学方法,该方法是在假设地球表面没有大气层的情况下得出的,是一个典型的近似计算方法。研究通过直接数值积分...在太阳能系统的设计中常涉及倾斜面上日总直射辐射的计算。计算倾斜面上日总直射辐射最常用的方法是Liu and Jordan所提出的数学方法,该方法是在假设地球表面没有大气层的情况下得出的,是一个典型的近似计算方法。研究通过直接数值积分和Collares-Pereira and Rabl辐射计算经验关系对Liu and Jordan计算方法的正确性进行分析。结果表明:Liu and Jordan所提出的计算倾斜面上日总直射辐射的方法存在明显的计算误差,误差的大小与倾斜面的倾角和方位角有关,且方位角越大,计算误差越大;对于垂直表面,计算误差随着方位角的增加迅速增加,当方位角偏离正南90度时,由Liu andJordan方法所计算出的年总直射辐射误差高达20%以上。展开更多
Background:Bite mark identification is based on the individuality of a dentition and helps in identifying the perpetrator.The use of three-dimensional(3D)analysis of forensic evidence is highlighted in comparison with...Background:Bite mark identification is based on the individuality of a dentition and helps in identifying the perpetrator.The use of three-dimensional(3D)analysis of forensic evidence is highlighted in comparison with traditional methods.CBCT has been used in registering bite mark on food material.To our knowledge this is the first study where CBCT is used to register bite mark from human forearm.Aims and Objective:To signify the potential of CBCT in registering and analysing the bite mark on human skin and to analyse various identifying parameters.Materials and Method:60 subjects of either sex were asked to bite their own forearm and alginate impression of the maxillary and mandible dentition was taken and cast was poured.Both bitemark and cast was subjected to CBCT scanning and parameters like arch shape,inter canine width,mesio distal dimension of anterior teeth,and individual characteristics like rotation,buccal/lingual tilting of teeth was noted and compared and assigned a score using simplified version ofABFO scoring system.Results:Highly significant result with 56.6%definite match,26.66%probable match and 16.66%possible match were obtained using CBCT.Conclusion:CBCT is a non-destructive,accurate,efficient,objective and reproducible method.Out of all parameter mesio-distal dimension of teeth is the best parameter to judge the bitemark on skin.展开更多
文摘基于非对称结构设计思想,以表面倾斜的高介电常数介质谐振器为辐射单元,采用改进的正交不等长缝隙结构耦合馈电,设计制作了一种圆极化倾斜波束介质谐振天线。通过对介质谐振器表面倾斜角度和馈电缝隙的参数优化,扩展了天线的频带宽度,实现了宽频带圆极化倾斜波束辐射。仿真结果表明:天线在同时满足S11<-10 d B、3 d B轴比和30°波束倾斜条件下的带宽为18.2%。同时,由于采用高介电常数介质谐振器,天线剖面高度降低到0.165λ。实测结果和仿真结果吻合较好,验证了该设计的有效性。
基金Supported by National Natural Science Foundation of China (118110117465)
文摘Geometric calibration is critical to the accurate SPECT reconstruction. In this paper, a geometric calibration method was developed for a dedicated breast SPECT system with a tilted parallel beam （TPB） orbit. The acquisition geometry of the breast SPECT was firstly characterized. And then its projection model was established based on the acquisition geometry. Finally, the calibration results were obtained using a nonlinear optimization method that fitted the measured projections to the model. Monte Carlo data of the breast SPECT were used to verify the calibration method. Simulation results showed that the geometric parameters with reasonable accuracy could be obtained by the proposed method.
文摘在太阳能系统的设计中常涉及倾斜面上日总直射辐射的计算。计算倾斜面上日总直射辐射最常用的方法是Liu and Jordan所提出的数学方法,该方法是在假设地球表面没有大气层的情况下得出的,是一个典型的近似计算方法。研究通过直接数值积分和Collares-Pereira and Rabl辐射计算经验关系对Liu and Jordan计算方法的正确性进行分析。结果表明:Liu and Jordan所提出的计算倾斜面上日总直射辐射的方法存在明显的计算误差,误差的大小与倾斜面的倾角和方位角有关,且方位角越大,计算误差越大;对于垂直表面,计算误差随着方位角的增加迅速增加,当方位角偏离正南90度时,由Liu andJordan方法所计算出的年总直射辐射误差高达20%以上。
文摘Background:Bite mark identification is based on the individuality of a dentition and helps in identifying the perpetrator.The use of three-dimensional(3D)analysis of forensic evidence is highlighted in comparison with traditional methods.CBCT has been used in registering bite mark on food material.To our knowledge this is the first study where CBCT is used to register bite mark from human forearm.Aims and Objective:To signify the potential of CBCT in registering and analysing the bite mark on human skin and to analyse various identifying parameters.Materials and Method:60 subjects of either sex were asked to bite their own forearm and alginate impression of the maxillary and mandible dentition was taken and cast was poured.Both bitemark and cast was subjected to CBCT scanning and parameters like arch shape,inter canine width,mesio distal dimension of anterior teeth,and individual characteristics like rotation,buccal/lingual tilting of teeth was noted and compared and assigned a score using simplified version ofABFO scoring system.Results:Highly significant result with 56.6%definite match,26.66%probable match and 16.66%possible match were obtained using CBCT.Conclusion:CBCT is a non-destructive,accurate,efficient,objective and reproducible method.Out of all parameter mesio-distal dimension of teeth is the best parameter to judge the bitemark on skin.
