Detail-preserving ring artifact correction method for cone-beam CT

Ring artifact is the major factor that seriously influence quality of computed tomography(CT)image reconstruction,especially in testing large-scale workpieces.To remove ring artifact quickly and efficiently,a kind of ring artifact correction method is improved based on the post-processing CT image reconstruction in this paper.At first,transform the CT image from the rectangular coordinates into polar coordinates.Next,design multidimensional filter to filter the image and calculate the mean and variance of each filtered pixel in polar coordinates.The location of artifact point is determined by the double precision.One is the comparison of calculated variance and variance threshold,and another is the comparison of pixel value and pixel value threshold.Then,process the artifact points in a reasonable manner and do details remain to CT image in particular.At last,convert corrected polar image into rectangular coordinates.The actual experiment shows that compared with the original method,improved method can better correct the ring artifacts and keep the image details for CT images.It is a kind of practical ring artifact correction methods for subsequent processing and quantitative analysis.

A unified analysis of a micro-beam,droplet and CNT ring adhered on a substrate:Calculation of variation with movable boundaries

In this study, we developed a general method to analytically tackle a kind of movable boundary problem from the viewpoint of energy variation. Having grouped the adhesion of a micro-beam, droplet and carbon nanotube （CNT） ring on a substrate into one framework, we used the developed line of reasoning to investigate the adhesion behaviors of these systems. Based upon the derived governing equations and transversality conditions, explicit solutions involving the critical parameters and morphologies for the three systems are successfully obtained, and then the parameter analogies and common characteristics of them are thor- oughly investigated. The presented method has been verified via the concept of energy release rate in fracture mechanics. Our analyses provide a new approach for exploring the mechanism of different systems with similarities as well as for understanding the unity of nature. The analysis results may be beneficial for the design of nano-structured materi- als, and hold potential for enhancing their mechanical, chemical, optical and electronic properties.

Intra-beam scattering and beam lifetime in a candidate lattice of the soft X-ray diffraction-limited storage ring for the upgraded SSRF

New-generation synchrotron light sources are being designed and operated worldwide to provide brighter radiation by reducing the beam emittance to X-ray diffraction limits.Intra-beam scattering(IBS)and Touschek scattering in such facilities are significant and require attention because of their ultra-low emittance.Therefore,cure strategies need to be carefully studied to obtain highquality photon beams.For the Shanghai Synchrotron Radiation Facility Upgrade(SSRF-U),a candidate lattice of the storage ring,reaching the soft X-ray diffraction limit,was designed and presented for the first time in this study.The emittance growth and beam lifetime in the SSRF-U storage ring were studied using particle simulations for a series of different machine configurations.The gains with RF frequencies of 100 MHz and 500 MHz were compared.Along with a better filling pattern,a more suitable RF frequency was adopted in the SSRF-U.The variations in the equilibrium beam emittance with beam coupling and bunch-lengthening were identified using simulations.Optimal beam coupling and required bunch-lengthening for the SSRF-U storage ring were thus determined.The fitness of the beam energy in the SSRF-U was subsequently assessed using the obtained parameters.Additionally,the Touschek scattering and beam lifetime were calculated,and an acceptable total beam lifetime was obtained.

Compact and broadband circularly polarized ring antenna with wide beam-width for multiple global navigation satellite systems

A compact and broadband circularly polarized （CP） annular ring antenna with wide beam-width is proposed for multiple global navigation satellite systems （GNSS） in the L1 band. The annular ring is excited by two modified L-probes with quadrature phase difference. It has a 36.3% 10-dB return loss bandwidth and a 13% 3-dB axial ratio bandwidth, because of the orthogonal L-probes with 90° phase difference. The measured peak gain of the antenna is 3.9 dBic. It can detect the satellites at lower elevation as its half power beam-width （HPBW） is 113° in both the x-z and y-z planes, achieving a cross-polarization level of larger than 25 dB. Noticeably, the antenna achieves 89% size reduction compared with the conventional half wavelength patch antennas. It can be used in hand-held navigation devices of multiple GNSS such as COMPASS, Galileo, GPS and GLONASS.

The Calibration and Use of a New Ring-Shaped Ionization Chamber for Monitoring and Dosimetry of X-Ray Beams

Today, dosimeters are used generally for dosimetry of the diagnostic X-ray beam. Ionization chambers are appropriate instruments for monitoring and also the dosimetry of X-ray beam in medical diagnostic equipment. The present work introduces design and investigation of a new ring-shaped monitor chamber with a PMMA body, graphite-coated PMMA windows (0.5 mm thick), a special graphite-foil central electrode (0.1 mm thick, 0.7 g/cm3 dense) that creating two sensitive volumes and a central hole for crossing the radiation beam with less attenuation. The results of performance tests conducted at the Nuclear Science and Technology Research Institute, AEOI in Karaj- Iran proved the high short and long-term stability, the very low leakage current, the low directional dependence and very high ion collection efficiency through the special design of the collecting electrode. Moreover, the FLUKA Monte Carlo simulations certified the negligible effect of central electrode on this new ring-shaped monitor chamber. According to the results of the performance tests, the new monitor chamber can be used as a standard dosimeter in order to monitor X-ray beam in primary standard dosimetry laboratories.

考虑环间接头影响的盾构隧道纵向变形简化解

为反映外荷载下盾构隧道相邻环间张开和错台,提出考虑环间接头影响的盾构隧道纵向变形简化解答。首先,引入纵向梁-弹簧模型模拟盾构隧道纵向受力变形,其中采用Timoshenko短梁考虑隧道环段变形,引入转动和剪切弹簧分别模拟环间接头转动与错台。其次,构建弹性地基上纵向梁-弹簧模型的有限差分方程,以解决环间接头-管环非连续变形求解问题,并推导外荷载下既有盾构隧道的纵向变形公式。最后,建立新建隧道上穿和下穿引起既有盾构隧道的纵向变形解答,并与新建隧道上、下穿越工程案例及现有理论方法对比验证。研究结果表明:所提方法预测的隧道位移与Timoshenko连续梁模型,协同变形模型和实测数据均具有较好的一致性,但所提方法得到的环间错台略低于Timoshenko梁模型和协同变形模型;所提方法可考虑环间接头的影响,得到的隧道位移曲线呈现既不光滑也不连续的特征,其中环段变形以刚体位移为主,而环间接头主要发生转动和错台;而基于现有理论所得盾构隧道纵向位移均为连续曲线,无法反映环间接头的真实转动与错台位移。

弹性环梁支撑下圆形深基坑支护结构变形解析解

将环梁和支护结构分别视为弹性圆环和弹性圆柱薄壳,基于环梁和圆柱壳的变形协调,得到了具有任意数目弹性环梁支撑圆形深基坑支护结构变形的解析解.在验证解析解合理性和可靠性的基础上,针对某一实际圆形基坑工程,比较了在刚性和弹性环梁支撑下支护结构变形和内力的差异,并分析了支护结构底部边界条件、环梁弹性模量、尺寸和数量以及位置等参数对支护结构变形和内力分布的影响.研究结果表明:相对于刚性环梁支撑,弹性环梁支撑处内力变化较小,环梁弹性模量和尺寸的改变只对基坑挖掘面以上支护结构变形和内力影响显著,而对挖掘面以下的支护结构变形和内力几乎没有影响.该研究成果为圆形基坑支护结构设计提供了理论依据和指导.

圆形基坑极正交各向异性支护结构变形解析分析

考虑圆形深基坑支护结构轴向和环向配筋的差异,将支护结构简化为极正交各向异性圆柱薄壳,研究了分层土体中具有弹性支撑环梁约束的支护结构轴对称变形和内力特征.首先,将弹性支撑环梁的约束解除,代之以沿环向分布的未知集中力,基于弹性环梁和圆柱壳的边界条件和变形协调条件,得到了分层土体中具有弹性支撑环梁支护结构轴对称变形的解析解.其次,以上海地区某一圆形深基坑支护结构为例,揭示了支护结构环向和纵向弹性模量、环梁刚度、土体重度和静止土压力系数等因素对支护结构内力和变形的影响,结果表明:支护结构以环向承压为主,轴向弯曲为辅,故其环向刚度对径向位移的影响要明显大于其轴向刚度的影响,但材料参数对内力分布影响较弱;环梁刚度的增加可有效限制支护结构的变形,但会引起支护结构在支撑环梁处内力的显著增大;土层性质相差不大区域的支护结构可按均质土中支护结构进行分析,而土层性质有较大突变区域的支护结构分析则需考虑土层的分层效应.

电力隧道渗漏水成因分析及治理措施研究

电力隧道内电缆数量较多,电缆及其他电力设施对水非常敏感,如果积水淹没电缆(尤其是电缆接头部位),可能会造成事故和损失。文章详细分析了暗挖、盾构等结构形式隧道的渗漏水成因,对管片、环梁、沉降缝、墙体及管孔等部位渗漏水治理措施进行研究,提出了针对性的治理建议并进行了试点应用,为电力隧道渗漏水治理工作提供参考。

非均质环形谐振子结构性能分析方法

传统环形谐振子结构特性分析方法是基于均质弹性力学理论的,无法准确描述非均质材料力学特性对环形谐振子结构静、动态性能的影响规律。基于圆弧形结构的欧拉梁理论,根据非均质本构关系,运用Hamilton原理,提出一种非均质环形谐振子结构性能分析方法。利用非均质环形谐振子理论和布勃诺夫-伽辽金法,获得非均质环形谐振子静态弯曲问题和动态转动问题的理论解。然后,分析了材料的非均质力学特性对环形谐振子弯曲挠度、二阶弯曲角频率及进动系数的影响规律。典型非均质材料性能分析结果表明,传统方法对于二阶弯曲角频率计算误差达59%以上,而所提方法能够精确预测非均质谐振子结构的静、动态响应,计算出二阶弯曲角频率。

多轨道角动量模式谐振环形行波天线设计

为解决目前轨道角动量(OAM)天线难以在同一频率下多模工作的问题,推动OAM在无线通信领域的实际应用,设计、加工并测量了一种基于单层板的谐振环形行波天线,引入4个馈电探针将不同相位差的信号馈入行波天线。经仿真分析和实际测量,该天线可以在3 GHz上谐振并分别产生了携带有OAM模式l=0,l=±1,l=-2的涡旋电磁波束。该天线结构简单并且可以在同一频率下产生多种模式OAM,能够有效增加无线通信的信道容量,具有一定的理论意义和实用价值。

双U型单环谐振陀螺热弹性阻尼分析

对于MEMS环形谐振陀螺而言,品质因数是一个关键的技术指标,在真空条件下热弹性阻尼是影响品质因数的主要因素。因此,针对带有拓扑梳齿的双U型环形陀螺,首先分析了其结构形式和工作原理。其次研究了热弹性阻尼机理,对双U型环形陀螺热弹性阻尼进行了理论研究。同时借助有限元方法对热弹性阻尼进行了仿真分析,探索了结构参数对环形陀螺品质因数的影响。对不同结构参数的陀螺进行实验测试。仿真分析与实验测试结果表明,增加单环内径,减小单环环宽,减小中央圆盘的半径和减小支撑梁梁宽方式都可以降低陀螺热弹性阻尼,从而提高陀螺的品质因数。合理调整陀螺结构参数可以使陀螺品质因数在一定参数条件下达到十万量级。所提分析方法对降低热弹性阻尼,提高陀螺品质因数具有指导意义。

圆形深基坑环梁径向等效刚度系数研究

弹性支点法是我国现行规范推荐的深基坑支护结构计算方法。在弹性支点法基础上,针对圆形深基坑环梁作为支护桩弹性支点的刚度系数提出明确算法,达到更合理地计算支护结构内力和位移的目的。通过弹塑性力学厚壁圆筒理论,得到环梁径向位移公式,进而推导出环梁径向等效刚度系数和环梁换算截面的等效材料抗力计算公式。将径向等效刚度系数和等效材料抗力作为弹性支点的参数,计算支护结构内力和位移。采用此方法计算沈阳某圆形深基坑支护结构的内力和位移。结果表明:采用等效刚度系数的二维弹性支点法计算得到的支护结构的内力与位移,与现场监测数据比较吻合,比三维有限元计算结果更安全,比常规刚度系数计算结果更经济合理。

圆环非线性恢复力的梁约束模型建模

圆环隔振器是一种以圆环结构为基础的非线性隔振器,圆环结构在压缩变形过程中会受到压力和环面拉伸的耦合作用,从而产生非线性恢复力,对圆环结构非线性恢复力的精确建模是研究隔振器性能的关键。将圆环结构等分为多段曲梁,利用梁约束模型对每段曲梁建立计及几何非线性的力-位移关系模型,结合曲梁间的力传递关系和几何约束关系,建立了圆环整体在压缩过程中的非线性恢复力模型,并计算了圆环变形过程中所有分段点处的正应力。通过电子伺服疲劳试验机对圆环结构在压缩过程中的恢复力进行了测量,验证了梁约束模型的建模精度。研究结果表明,利用梁约束模型可以表征圆环结构非线性恢复力特性,其建模精度与椭圆积分法相当,而模型表达式和求解过程都比椭圆积分法简洁。圆环在压缩量最大时正应力最大,此时最大正应力在圆环的上下端点。梁约束模型的建模精度随着分段数的增加而提高,当分段数大于12时,梁约束模型的恢复力计算误差小于2%。

合肥光源1 nm发射度的储存环初步物理设计研究

针对合肥光源未来升级为纳米级发射度储存环的计划,设计了一个紧凑的H6BA lattice物理方案。在800 MeV束流能量下,自然发射度为1.2 nm·rad,达到了所辐射的极紫外光的衍射极限发射度。考虑误差效应的6D动力学孔径在水平正方向上大于20 mm,可满足离轴注入的需要。由于束流能量和发射度均较低,束内散射和Touschek效应显著,考虑10%耦合情况下,平衡发射度增长了约50%,Touschek寿命为4.2 h,采用全耦合模式可较为有效地抑制这2种效应。

Highly coupled off-resonance lattice design in diffraction-limited light sources

The round-beam operation presents many benefits for scientific experiments regarding synchrotron radiation and the weak-ening influences of intra-beam scattering in diffraction-limited synchrotron light sources.A round-beam generation method based on the global setting of skew quadrupoles and the application of a non-dominated sorting genetic algorithm was pro-posed in this study.Two schemes,including large-emittance coupling introduced via betatron coupling and vertical disper-sion,were explored in a candidate lattice for an upgrade-proposal of the Shanghai synchrotron radiation facility.Emittance variations with lattice imperfections and their influence on the beam dynamics of beam optic distortions were investigated.The results demonstrated that a precise coupling control ranging from 10 to 100%was achieved under low optical distortion,whereas full-coupling generation and its robustness were achieved by our proposed method by adjusting the skew quadrupole components located in the dispersion-free sections.The Touschek lifetime increased by a factor of 2–2.5.

考虑齿圈柔性的内啮合齿轮时变啮合刚度计算分析

当前大多数内齿轮啮合刚度都是基于忽略齿圈基体变形的假设计算的,文中应用Weber能量法基于精确的齿廓曲线方程建立内齿轮悬臂梁等效模型,同时基于铁木辛柯(Timoshenko)曲梁理论计算齿圈基体的变形量,并将齿圈变形耦合到齿轮啮合刚度计算中。通过MATLAB GUI编程进行内啮合齿轮时变啮合刚度数值计算,分析了齿圈柔性对啮合变形的影响,研究了齿圈厚度、支撑数量及啮合力位置对啮合刚度的影响。结果表明:齿圈厚度和支撑数量的增加均有利于齿轮副啮合刚度的增大;啮合齿中线位于固定支撑点时,齿圈啮合刚度最大,在靠近支撑中间位置时,啮合刚度最小,齿圈啮合刚度对应于螺栓支撑呈周期性波动。

高功率VCSEL激光器光束发散角的测量方法

垂直腔面发射激光器(Vertical Cavity Surface Emitting Laser,简称VCSEL)由于其能发射出垂直于腔面光束的特性使得多个VCSEL激光器可以在同一片芯片上紧密集成,而不需要大量的空间;且VCSEL激光器使用共振腔的反射镜来增强光并放大,从而实现高效的光发射;通常情况下,VCSEL激光器的发光效率可以达到40至60之间,与传统的激光器相比,VCSEL激光器更容易实现高效率。由于VCSEL激光器的可集成性好、效率高等特点,使其广泛应用于3D感知、自动驾驶、光通信等领域。因此,VCSEL激光器的质量检测工作也显得越来越重要。随着VCSEL激光器进军高功率领域,其发光束的模式也经历了从基模变为高阶模的过程,光束已经从类高斯光束变为了类拉盖尔-高斯空心圆环光束。虽然传统的1/e^(2)、D86等算法在测量基模下的类高斯光束的发散角较为精确,但对于高阶模式下的类拉盖尔-高斯空心圆环光束,这些方法则出现了明显的误差。考虑到VCSEL激光器在自动驾驶等重要领域的广泛应用,其光束精确度的要求也随之提高。因此,本文采用了D4σ算法,针对类拉盖尔-高斯空心圆环光束进行发散角测量,与1/e^(2)、D86等传统算法进行了比较。结果显示,新方法在发散角测量准确度上最高提升了230。

复合改造方案在风机基础扩容中的应用研究

针对老旧风机基础难以承担上部结构技改增效后的增幅荷载的难题,深入研究了改造后基础的薄弱部分,确立了基础改造效果的评价指标。同时以湖南某风场老旧基础环式风机基础为研究对象,对其扩容升级改造进行可行性研究,提出了一种环梁抱箍,并在环梁区域处施加围压的复合方案。通过数值分析研究不同围压参数对扩容风机基础的力学性能影响,得出围压参数最优组合并进一步对环梁尺寸进行优化设计。分析结果表明,环梁-围压复合基础扩容升级方案使得塔筒侧壁与基础混凝土的接触面积增大,从而增强了二者之间的相互作用,有效缓解了基础环底部的受力情况。同时,该方案还减少了基础环的位移量,增强了钢混结构的协同运动,使得基础能够承担更大的上部荷载,进而支撑此次扩容升级改造的完成。

可变光阑对焦深影响的探究

传统的标量光场其偏振态空间均匀分布,而矢量光场相较于标量光场其偏振态是空间变化的。这个空域变化的偏振特性使得矢量光场具有更大的调控自由度,在焦场设计、光学微操纵、微加工、以及量子信息领域有着潜在的应用。本文基于Richards-Wolf矢量衍射理论,研究了可变光阑以及透镜数值孔径对双环角向偏振光束聚焦特性的影响。结果表明,通过改变光阑大小以及透镜数值孔径,不仅可以改变焦斑光强、焦斑大小,也可以显著改变焦场暗通道的长度,从而生成较长的暗通道。生成的可变焦场暗通道未来可用于光学微操纵以及微加工的应用中。