Enhancing Precision in Radiotherapy Delivery: Validating Monte Carlo Simulation Models for 6 MV Elekta Synergy Agility LINAC Photon Beam Using Two Models of the GAMOS Code

The most crucial requirement in radiation therapy treatment planning is a fast and accurate treatment planning system that minimizes damage to healthy tissues surrounding cancer cells. The use of Monte Carlo toolkits has become indispensable for research aimed at precisely determining the dose in radiotherapy. Among the numerous algorithms developed in recent years, the GAMOS code, which utilizes the Geant4 toolkit for Monte Carlo simula-tions, incorporates various electromagnetic physics models and multiple scattering models for simulating particle interactions with matter. This makes it a valuable tool for dose calculations in medical applications and throughout the patient’s volume. The aim of this present work aims to vali-date the GAMOS code for the simulation of a 6 MV photon-beam output from the Elekta Synergy Agility linear accelerator. The simulation involves mod-eling the major components of the accelerator head and the interactions of the radiation beam with a homogeneous water phantom and particle information was collected following the modeling of the phase space. This space was po-sitioned under the X and Y jaws, utilizing three electromagnetic physics mod-els of the GAMOS code: Standard, Penelope, and Low-Energy, along with three multiple scattering models: Goudsmit-Saunderson, Urban, and Wentzel-VI. The obtained phase space file was used as a particle source to simulate dose distributions (depth-dose and dose profile) for field sizes of 5 × 5 cm2 and 10 × 10 cm2 at depths of 10 cm and 20 cm in a water phantom, with a source-surface distance (SSD) of 90 cm from the target. We compared the three electromagnetic physics models and the three multiple scattering mod-els of the GAMOS code to experimental results. Validation of our results was performed using the gamma index, with an acceptability criterion of 3% for the dose difference (DD) and 3 mm for the distance-to-agreement (DTA). We achieved agreements of 94% and 96%, respectively, between simulation and experimentation for the three electromagnetic physics models and three mul-tiple scattering models, for field sizes of 5 × 5 cm2 and 10 × 10 cm2 for depth-dose curves. For dose profile curves, a good agreement of 100% was found between simulation and experimentation for the three electromagnetic physics models, as well as for the three multiple scattering models for a field size of 5 × 5 cm2 at 10 cm and 20 cm depths. For a field size of 10 × 10 cm2, the Penelope model dominated with 98% for 10 cm, along with the three multiple scattering models. The Penelope model and the Standard model, along with the three multiple scattering models, dominated with 100% for 20 cm. Our study, which compared these different GAMOS code models, can be crucial for enhancing the accuracy and quality of radiotherapy, contributing to more effective patient treatment. Our research compares various electro-magnetic physics models and multiple scattering models with experimental measurements, enabling us to choose the models that produce the most reli-able results, thereby directly impacting the quality of simulations. This en-hances confidence in using these models for treatment planning. Our re-search consistently contributes to the progress of Monte Carlo simulation techniques in radiation therapy, enriching the scientific literature.

Stiffness Matrix Derivation of Space Beam Element at Elevated Temperature

<Abstract>Element stiffness equation is very important in structural analysis,and directly influences the accuracy of the results.At present,derivation method of element stiffness equation is relatively mature under ambient temperature,and the elastic phrase of material stress-strain curve is generally adopted as physical equation in derivation.However,the material stress-strain relationship is very complicated at elevated temperature,and its form is not unique,which brings great diffculty to the derivation of element stiffness equation.Referring to the derivation method of element stiffness equation at ambient temperature,by using the continuous function of stress-strain-temperature at elevated temperature,and based on the principle of virtual work,the stiffness equation of space beam element and the formulas of stiffness matrix are derived in this paper,which provide basis for finite element analysis on structures at elevated temperature.

Light beams with orbital angular momentum for free space optics

The light＇s orbital angular momentum （OAM） is a consequence of the spiral flow of the electromagnetic energy. In this paper, an analysis of light beams with OAM used for free space optics （FSO） is conducted. The basic description and conception of light＇s OAM are reviewed. Both encoding information into OAM states of single light beam and encoding information into spatial structure of the mixed optical vortex with OAM are discussed, and feasibility to improve the FSO＇s performance of security and obstruction of line of sight is examined.

STEADY-STATE RESPONSE OF A TIMOSHENKO BEAM ON AN ELASTIC HALF-SPACE UNDER A MOVING LOAD

By introducing the equivalent stiffness of an elastic half-space interacting with a Timoshenko beam, the displacement solution of the beam resting on an elastic half-space subjected to a moving load is presented. Based on the relative relation of wave velocities of the half-space and the beam, four cases with the combination of different parameters of the half-space and the beam, the system of soft beam and hard half-space, the system of sub-soft beam and hard half- space, the system of sub-hard beam and soft half-space, and the system of hard beam and soft half-space are considered. The critical velocities of the moving load are studied using dispersion curves. It is found that critical velocities of the moving load on the Timoshenko beam depend on the relative relation of wave velocities of the half-space and the beam. The Rayleigh wave velocity in the half-space is always a critical velocity and the response of the system will be infinite when the load velocity reaches it. For the system of soft beam and hard half-space, wave velocities of the beam are also critical velocities. Besides the shear wave velocity of the beam, there is an additional minimum critical velocity for the system of sub-soft beam and hard half-space. While for systems of （sub-） hard beams and soft half-space, wave velocities of the beam are no longer critical ones. Comparison with the Euler-Bernoulli beam shows that the critical velocities and response of the two types of beams are much different for the system of （sub-） soft beam and hard half-space but are similar to each other for the system of （sub-） hard beam and soft half space. The largest displacement of the beam is almost at the location of the load and the displacement along the beam is almost symmetrical if the load velocity is smaller than the minimum critical velocity （the shear wave velocity of the beam for the system of soft beam and hard half-space）. The largest displacement of the beam shifts behind the load and the asymmetry of the displacement along the beam increases with the increase of the load velocity due to the damping and wave racliation. The displacement of the beam at the front of the load is very small if the load velocity is larger than the largest wave velocity of the beam and the half space. The results of the present study provide attractive theoretical and practical references for the analysis of ground vibration induced by the high-speed train.

Transport characteristics of space charge-dominated multi-species deuterium beam in electrostatic low-energy beam line

The transport characteristics of a space chargedominated multi-species deuterium beam consisting of D_1^+,D_2^+, and D_3^+ particles in an electrostatic low-energy beam line are studied. First, the envelope equations of the primary D_1^+ beam are derived considering the space charge effects caused by all particles. Second, the evolution of the envelope of the multi-species deuterium beam is simulated using the PIC code TRACK, with the results showing a significant effect of the unwanted beam on the transport of the primary beam. Finally, different injected beam parameters are used to study beam matching, and a new beam extraction system for the existing duoplasmatron source is designed to obtain the ideal injected beam parameters that allow a D_1^+ beam of up to 50 m A to pass unobstructed through the electrostatic low-energy beam transport line in the presence of an unwanted(D_2^+, D_3^+)beam of 20 m A; at the same time, distortions of the beam emittance and particle distributions are observed.

Space Charge Effect of Bunched Beam With Gaussian Distribution

The nonlinear space charge effect of a bunched beam with Gaussian distribu-tion in the longitudinal direction is discussed.Some useful formulae are derived for cal-culating the potential induced by a cylinder model of space charge in the waveguide of alinac with different combinations of density distribution:Gaussian distribution in thelongitudinal direction versus Kapchinskij Vladimirskij,waterbag,parabolic andGaussian distribution in the transverse direction,rcspectively.

Influence of two-stream relativistic electron beam parameters on the space-charge wave with broad frequency spectrum formation

We developed a cubic non-linear theory describing the dynamics of the multiharmonic spacecharge wave（SCW）, with harmonics frequencies smaller than the two-stream instability critical frequency, with different relativistic electron beam（REB） parameters. The self-consistent differential equation system for multiharmonic SCW harmonic amplitudes was elaborated in a cubic non-linear approximation. This system considers plural three-wave parametric resonant interactions between wave harmonics and the two-stream instability effect. Different REB parameters such as the input angle with respect to focusing magnetic field, the average relativistic factor value, difference of partial relativistic factors, and plasma frequency of partial beams were investigated regarding their influence on the frequency spectrum width and multiharmonic SCW saturation levels. We suggested ways in which the multiharmonic SCW frequency spectrum widths could be increased in order to use them in multiharmonic two-stream superheterodyne free-electron lasers, with the main purpose of forming a powerful multiharmonic electromagnetic wave.

DETERMINATION OF SPACE GROUP OF PrCo_(12)B_6 COMPOUND BY CONVERGENT BEAM ELECTRON DIFFRACTION

The space group of PrCo_(12)B_6,compound has been determined using the convergent beam elec- tron diffraction method.The space group is found to be R3m.

Space-charge limiting currents for magnetically focused intense relativistic electron beams

The self-consistent differential equations, which describe a laminar-flow equilibrium state in a magnetically focused intense relativistic electron beam propagating inside a conducting waveguide, are presented. The canonical angular momentum, Pe, defined under the conditions at the source, uniquely determines the possible solutions of these equations. By numerically solving these equations, the space-charge limited current and the externally applied magnetic field are obtained in a solid beam and a hollow beam in two cases of Pθ= 0 （magnetically shielded source） and Pθ= const. （immersed source） separately. It is shown that the hollow beam is more beneficial to the propagation of the intense relativistic beam through a drift tube than the solid beam.

Beam Pattern Scanning (BPS) versus Space-Time Block Coding (STBC) and Space-Time Trellis Coding (STTC)

In this paper, Beam Pattern Scanning (BPS), a transmit diversity technique, is compared with two well known transmit diversity techniques, space-time block coding (STBC) and space-time trellis coding (STTC). In BPS (also called beam pattern oscillation), controlled time varying weight vectors are applied to the antenna array elements mounted at the base station (BS). This creates a small movement in the antenna array pattern directed toward the desired user. In rich scattering environments, this small beam pattern movement creates an artificial fast fading channel. The receiver is designed to exploit time diversity benefits of the fast fading channel. Via the application of simple combining techniques, BPS improves the probability-of-error performance and network capacity with minimal cost and complexity. In this work, to highlight the potential of the BPS, we compare BPS and Space-Time Coding (i.e., STBC and STTC) schemes. The comparisons are in terms of their complexity, system physical dimension, network capacity, probability-of-error performance, and spectrum efficiency. It is shown that BPS leads to higher network capacity and performance with a smaller antenna dimension and complexity with minimal loss in spectrum efficiency. This identifies BPS as a promising scheme for future wireless communications with smart antennas.

基于双面平行带线的全空间扫描漏波天线

为了实现从后向端射到前向端射的连续波束扫描天线,该文基于双面平行带线结构提出了一种具有全空间扫描能力的漏波天线。天线单元由双面平行带线传输线和一对反向加载的开路枝节组成,两个开路枝节分别位于传输线的上导带和下导带。加载的反向开路枝节等效为一个偶极子,使得天线单元具有全向辐射性能,作为整个全空间扫描漏波天线的基础单元。为了抑制周期漏波天线中的开阻带问题,又在天线基础单元上加载了一对平衡槽以实现频率平衡条件,还加载了一对匹配槽以匹配周期结构的阻抗。最后实现了一款天线原型,经仿真与实验验证,该天线能够在7.6 GHz到14.0 GHz的频率范围内,实现从后向端射,经侧向辐射,然后到前向端射的全空间扫描能力。

结合电子束辐照与压电压力波法空间电荷分布实时测量的空间电荷包迁移行为的研究

空间电荷包现象是一种特殊的空间电荷现象,具体表现为空间电荷以包的形态沿着极化电场的方向进行迁移.目前针对空间电荷包现象的研究还存在一些不足,研究的对象通常集中在聚乙烯及其交联产物中的正极性空间电荷包.本文提出了一套用于负极性空间电荷包特性研究的一体化实验系统,可进行电子束辐照与压电压力波法空间电荷分布实时测量相结合的实验研究,并简要介绍了该系统的结构与功能.该系统适用于不同厚度范围的各类绝缘电介质样品在不同电场下的实验研究.本文使用该实验系统初步研究了在不同外加电场(15,20,2.5,30 kV/mm)下聚丙烯与聚甲基丙烯酸甲酯样品内负极性空间电荷包的迁移行为,并从实验结果中提取了负极性载流子;(电子)的迁移特性.聚丙烯与聚甲基丙烯酸甲酯样品中电子的迁移速率均存在随着电场的增加而减小的负微分迁移率现象,聚丙烯中该现象出现的阈值电场约为26.0 kV/mm,聚甲基丙烯酸甲酯中该现象出现的阈值电场约为19.5 kV/mm,消失的截止电场约为27.5 kV/mm.

混凝土芯水泥土复合桩竖向承载特性分析方法

基于Euler梁理论和状态空间法,建立了综合考虑非线性芯桩-水泥土-桩周土界面作用的双层叠合直梁分析模型及其状态方程,推导了成层土中不同组合形式的复合桩截面内力与变形的统一解析解,有效地考虑了复合桩分析中土与结构相互作用、结构局部参数发生变化等难点。通过与已有文献中现场试验和数值计算结果对比,验证了该方法的有效性,并讨论了桩径比、芯长比和水泥土弹性模量对桩承载特性的影响。研究结果表明:(1)桩径比增大,可提供的桩侧摩阻力和桩端阻力增大,复合桩竖向承载力基本呈线性增长;(2)芯长比增大,复合桩竖向承载力的增长幅度逐渐增大;(3)水泥土弹性模量对于桩竖向承载力影响较小。

基于空间馈电的高功率波束扫描螺旋透射阵列天线设计

传统的透射式空馈阵列存在功率容量低的缺点,不能直接应用于高功率微波领域。现有的高功率空馈阵列布局不够灵活,波束扫描速度较慢,不能充分发挥空馈阵列在系统集成方面的优势。提出并设计了一种新型的采用空间馈电的螺旋辐射单元,并构建了一种透射式空馈螺旋阵列天线,通过控制单个螺旋旋转可以实现二维波束扫描,在设计上更加灵活,可根据实际应用需求调整阵列布局,符合高功率微波天线紧凑化、模块化的发展趋势。仿真设计了包含324个单元的透镜阵列,数值模拟结果表明,单元反射系数S11≤-20 dB,功率容量0.35 MW,阵列口径效率0.68,可在±45°范围内扫描,最大增益下降3 dB。

基于波束空间交替投影极大似然的拖曳式诱饵分辨判别方法

机载平台在遭遇威胁时,通过释放拖曳式诱饵假目标干扰进行自卫.载机和拖曳式诱饵在雷达波束宽度内,且径向距离小于距离分辨率时,雷达无法通过常规方法对载机目标和拖曳式诱饵进行分辨测量.针对数字相控阵雷达同拖曳式诱饵对抗的问题,提出一种基于波束空间交替投影极大似然(BSAP-ML)方法.首先通过阵元空间到波束空间处理,减少数字相控阵维度;然后通过交替投影方法对目标和拖曳式诱饵的角度进行迭代测量;最后通过基于角度向量的判别方法对载机目标和诱饵进行判断识别.仿真结果表明,该方法可用于数字相控阵雷达,对载机和拖曳式诱饵进行有效的超分辨角度测量和判别.

双层大跨重型钢梁受限空间内逆序施工技术

基于丽水国际会展中心项目政务方厅钢结构施工策划实践,介绍双层交错式大跨重型钢梁在受限空间内采用逆序施工技术的具体应用情况。采用先上后下的逆序吊装施工顺序,并结合原有结构支撑反顶、楼板钢筋加密、双机抬吊等施工工艺措施,使得在多种受限工况下的双层交错式重型钢梁仍可以经地面拼装后进行整体吊装,避免因大型机械上楼板造成的楼板开裂以及重型钢梁高空对接导致的精度不足、焊接质量不合格等一系列严重质量问题,最终达到减少安装措施费用、保护成品结构、缩短工期的施工目标,实现工程施工效益最大化。

钢管混凝土叠合柱-RC梁空间节点耐火性能分析

目的 研究钢管混凝土叠合柱-RC梁空间节点耐火性能,为实际工程提供参考。方法 通过ABAQUS有限元分析软件建立ISO-834标准火灾下钢管混凝土叠合柱-RC梁空间节点的温度场模型和力学模型;在试验与有限元模拟相吻合的基础上,分析此类构件空间节点的温度场分布、破坏模态、变形和内力分布等工作机理。结果 由于梁板的保护作用,节点区温度远低于非节点区;当梁、柱火灾荷载比相同,梁由2根增加至3根、4根时,空间节点耐火极限分别降低了41.58%和43.75%;高温和轴向荷载的共同作用下,内部钢管混凝土承担内力从常温的43.27%增加至180 min的52.9%。结论 钢管混凝土叠合柱-RC梁空间节点具有较好的耐火性能,能够满足实际工程中对耐火性能的要求。

基于2 bit超表面的单阶谐波波束扫描

波束扫描是一种广泛应用于无线通信、雷达、卫星通信和其他相关领域的技术,它允许无线信号或射线束在空间中定向、聚焦。近年提出的智能超表面时空编码方式拓展了超表面在物理维度上的自由度,使得其可以在单音波激励下完成多个频点的波束扫描,但仍然面临着增益低、波束副瓣大等一系列问题。针对这些问题,提出了一种基于超表面的谐波波束扫描方法。设计并加工了一种在E面可以达到斜入射60°的角度不敏感2 bit超表面单元并组建32×32阵列。针对单元谐波状态做出精确的3 bit相位量化。通过针对不同的初始参考相位,使用多目标遗传算法进行优化,将正一阶谐波的波束副瓣压低在了-15 dB水平,完成了时空编码超表面在E面60°波束扫描,为未来在超表面时空编码谐波波束赋形提供了充分有力的方案。

一种多层组合梁自由振动分析的混合有限元法

基于截面等效,提出了多层组合梁的二维分析模型。使用混合能变分原理,以包含频率函数的节点位移及其能量对偶的应力分量为单元节点未知量,引入混合元对梁长方向进行离散,建立动力学状态空间控制方程;接着引入微分求积法(Differential Quadrature Method,DQM)对控制方程进行梁高度方向的离散,求得组合梁在不同轴力与边界条件下的动力学方程。以混凝土-木材组合梁、波形钢腹板梁和钢-混组合梁为例进行验证。该方法基于二维理论,可为梁理论提供假设依据和误差分析的基准。