Coin-structured tunable beam shaping assembly design for accelerator-based boron neutron capture therapy for tumors at different depths and sizes

In the past decade,boron neutron capture therapy utilizing an accelerator-based neutron source(ABNS)designed primarily for producing epithermal neutrons has been implemented in the treatment of brain tumors and other cancers.The specifications for designing an epithermal beam are primarily based on the IAEA-TECODC-1223 report,issued in 2001 for reactor neutron sources.Based on this report,the latest perspectives and clinical requirements,we designed an ABNS capable of adjusting the average neutron beam energy.The design was based on a 2.8 MeV,20 mA proton beam bombarding a lithium target to produce neutrons that were subsequently moderated and tuned through a tunable beam shaping assembly(BSA)which can modify the thicknesses and materials of the coin-shaped moderators,back reflectors,filters,and collimators.The simulation results demonstrated that epithermal neutron beams for deep seated tumor treatment,which were generated by utilizing magnesium fluoride with lengths ranging between 28 and 36 cm as the moderator,possessed a treatment depth of 5.6 cm although the neutron flux peak shifts from 4.5 to 1.0 keV.When utilizing a thinner moderator,a less accelerated beam power can meet the treatment requirements.However,higher powers reduced the treatment time.In contrast,employing a thick moderator can reduce the skin dose.In scenarios that required relatively low energy neutron beams,the removal of the thermal neutron filter can raise the thermal neutron flux at the beam port.And the depth of the dose rate peak could be adjusted between 0.25 and 2.20 cm by combining magnesium fluoride and polyethylene coins of different thicknesses.Hence,this device has a better adaptability for the treatment of superficial tumors.Overall,the tunable BSA provides greater flexibility for clinical treatment than common BSA designs that can only adjust the port size.

Seismic Behavior of Diaphragm-Through Connections of Concrete-Filled Square Steel Tubular Columns and H-Shaped Steel Beams

Based on the introductions of a type of diaphragm-through connection between concrete-filled square steel tubular columns (CFSSTCs) and H-shaped steel beams,a finite element model of the connection is developed and used to investigate the seismic behavior of the connection.The results of the finite element model are validated by a set of cyclic loading tests.The cyclic loading tests and the finite element analyses indicate that the failure mode of the suggested connections is plastic hinge at the beam with inelastic rotation angle exceeding 0.04 rad.The suggested connections have sufficient strength,plastic deformation and energy dissipation capacity to be used in composite moment frames as beam-to-column rigid connections.

Study on shape factor of the fusion-solidification zone of electron beam weld

The concept of shape factors of the fusion-solidification zone is proposed to describe the weld cross section geometry. According to these shape factors, the electron beam weld fusion-solidification zone is divided into four typical shapes and the classification criterion for these typical shapes is suggested. An integrated parameter n, combining the line power density of electron beam and material thermal properties is proposed to describe the relative power input, and another integrated parameter n2 combing the accelerating voltage and focusing current is proposed to reflect the power distribution in the keyhole. A series of new expressions, which can reflect the influence of focusing current, accelerating voltage, beam current, and material thermal properties, are developed to predict the fusion-solidification zone shape based on experimental results nonlinear fitting of n1 and n2.

Propagation of shaped beam through uniaxially anisotropic chiral slab

A general solution is obtained to a canonical problem of the reflection and refraction of an arbitrary shaped beam by using a uniaxially anisotropic chiral slab.The reflected,internal as well as refracted shaped beams are expanded in terms of cylindrical vector wave functions,and the expansion coefficients are determined by using the boundary conditions and method of moments procedure.As two typical examples,the normalized field intensity distributions are evaluated for a fundamental Gaussian beam and Hermite-Gaussian beam,and some propagation properties,especially the negative refraction phenomenon,are discussed briefly.

ELECTRON OPTICS OF VARIABLE RECTANGULAR SHAPED BEAM LITHOGRAPHY SYSTEM D J-2

The electron optical column for the variable rectangular-shaped beam lithographysystem DJ-2 is described,with emphasis on the analysis of the optical configuration and theshaping deflection compensation.In this column the variable spot shaping is performed with aminimum number of lenses by a more reasonable optical scheme.A high-sensitivity electrostaticshaping deflector with sequential parallel-plates is implemented for high-speed spot shaping.With a precise linear and rotational approach,the spot current density,the edge resolution aswell as the position of spot origin remain unchanged when the spot size varies.Experiments showthat the spot current density of over 0.4 A/cm^2 is obtained with a tungsten hairpin cathode,andthe edge resolution is better than 0.2μm within a 2×2 mm^2 field size.

Force-displacement characteristics of simply supported beam laminated with shape memory alloys

As a preliminary step in the nonlinear design of shape memory alloy（SMA） composite structures,the force-displacement characteristics of the SMA layer are studied.The bilinear hysteretic model is adopted to describe the constitutive relationship of SMA material.Under the assumption that there is no point of SMA layer finishing martensitic phase transformation during the loading and unloading process,the generalized restoring force generated by SMA layer is deduced for the case that the simply supported beam vibrates in its first mode.The generalized force is expressed as piecewise-nonlinear hysteretic function of the beam transverse displacement.Furthermore the energy dissipated by SMA layer during one period is obtained by integration,then its dependencies are discussed on the vibration amplitude and the SMA＇s strain（Ms-Strain） value at the beginning of martensitic phase transformation.It is shown that SMA＇s energy dissipating capacity is proportional to the stiffness difference of bilinear model and nonlinearly dependent on Ms-Strain.The increasing rate of the dissipating capacity gradually reduces with the amplitude increasing.The condition corresponding to the maximum dissipating capacity is deduced for given value of the vibration amplitude.The obtained results are helpful for designing beams laminated with shape memory alloys.

Terahertz shaping technology based on coherent beam combining

The generation of terahertz(THz) waves by focusing a femtosecond pulsed laser beam at a distance is able to overcome the strong absorption properties of air and has rapidly attracted the attention of industry. However, the poor directionality of the THz wave radiation generated by this method is not conducive to THz wave applications. By controlling the morphology of the ultrafast laser-excited plasma filament and its electron density distribution through coherent beam combining technology, we achieve direct THz beam shaping and are able to obtain THz wave radiation of Gaussian or arbitrary transverse distribution. The novel experimental approach proposed in this paper opens up the research field of direct THz wave shaping using plasma. Moreover, it innovates multi-parameter convergence algorithms and, by doing so, has the potential to find beam patterns with higher energy conversion efficiency and break the energy limit of THz waves emitted by lasers at high power.

DESIGN AND PERFORMANCE OF SHAPING DEFLECTORS FOR VARIABLY SHAPED ELECTRON BEAM LITHOGRAPHY

In order to obtain uniform exposure in variably shaped electron beam lithography,the beam current density and edge resolution on the target must not change for different spotshapes and sizes.The key to the goal is the appropriate design of shaping deflectors.A linearand rotation compensation approach is presented.Values of linear and rotation compensationfactors versus the distances between electron source image and centers of deflectors are measuredon an experimental electron beam column with variable spot shaping.The experimental resultsare in good agreement with the calculated ones.

EFFECT OF SUBMERGED ENTRY NOZZLE (SEN) PARAMETERS AND SHAPE ON 3-D FLUID FLOW IN MOULD FOR BEAM BLANK CONTINUOUS CASTING

According to turbulent theory and characteristics of beam blank continuous casting, 3-D model to represent the flow of beam blank mould is established. The predicted results indicate that the exit obliquity of up 15°(+15°) should be adopted, which will benefit the floatation of non-metallic inclusion and purification of the molten steel. When the nozzle angle is 120°, the flow pattern is reasonable. Proper nozzle depth can be 200mm. Turbulent kinetic of meniscus can be reduced by adopting the square nozzle and suitable area of side outlet when casting speed increases. The results are consistent with those of water model experiment, so the model is exact and reasonable. The model can provide important information for design of SEN and defining of immersion depth.

基于Arduino的SMA丝材智能修复损伤钢筋混凝土梁试验研究

为修复钢筋混凝土梁在使用阶段中由于材料老化、裂缝开展等原因造成的损伤,提出一种基于Arduino智能平台和形状记忆合金(Shape Memory Alloy,SMA,具有形状记忆效应和超弹性特性)的智能修复控制系统,根据挠度及裂缝控制原理,设计智能修复控制装置。该装置由输入模块、处理模块和输出模块组成,当检测到钢筋应变超过限值时,输出模块升高SMA丝材温度对梁体进行修复。为验证该智能修复装置的修复性能,设计对比梁A(无修复装置)与试验梁B(加装智能修复控制装置),在加载过程中对试验梁B进行3次修复,对2根梁的跨中挠度、钢筋应变及裂缝宽度等进行对比分析。结果表明:破坏时试验梁B的跨中挠度、裂缝宽度均小于对比梁A,并且在3次修复中试验梁B的跨中挠度、裂缝宽度和钢筋应变最大回复率分别为31.0%、47.0%和71.5%。说明该智能修复控制装置可以监测试验梁受损情况并激发SMA材料对试验梁实施修复,实现钢筋混凝土梁的智能修复。

Low Velocity Impact Response Analysis of Shape Memory Alloy Reinforced Composite Beam

The low velocity impact responses of shape memory alloy （ SMA ） reinforced composite beams were analyzed by employing the finite element method. The finite element dynamic equntion was solved by the Newmark direct integration method, the impact contact force was determined asing the Hertzian contact law, and the influence of SMA .fibers on stiffiwss matrix is studied. Numerical results show that the SMA fibers can effectively improve the low velocity impact response property of composite beam.

On the Innovation,Design,Construction,and Experiments of OMEGA-Based SSPS Prototype:The Sun-Chasing Project

This study systematically introduces the development of the world’s first full-link and full-system ground demonstration and verification system for the OMEGA space solar power satellite(SSPS).First,the OMEGA 2.0 innovation design was proposed.Second,field-coupling theoretical models of sunlight concentration,photoelectric conversion,and transmitting antennas were established,and a systematic optimization design method was proposed.Third,a beam waveform optimization methodology considering both a high beam collection efficiency and a circular stepped beam shape was proposed.Fourth,a control strategy was developed to control the condenser pointing toward the sun while maintaining the transmitting antenna toward the rectenna.Fifth,a high-efficiency heat radiator design method based on bionics and topology optimization was proposed.Sixth,a method for improving the rectenna array’s reception,rectification,and direct current(DC)power synthesis efficiencies is presented.Seventh,high-precision measurement technology for high-accuracy beam-pointing control was developed.Eighth,a smart mechanical structure was designed and developed.Finally,the developed SSPS ground demonstration and verification system has the capacity for sun tracking,a high concentration ratio,photoelectric conversion,microwave conversion and emission,microwave reception,and rectification,and thus satisfactory results were obtained.

考虑剪切变形的欧拉梁单元一致质量矩阵

为明确考虑剪切变形的欧拉梁单元一致质量矩阵推导方法,以形函数为基础,基于虚功原理,区分伸缩、扭转以及是否考虑剪切变形的弯曲受力状态,给出了欧拉梁单元一致质量矩阵表达式。研究表明:不考虑剪切变形时,欧拉梁受弯状态的一致质量分析中一般不计单元上微元体水平方向的惯性力,此时仅需弯曲变形引发的竖向位移形函数即可;考虑剪切变形时,则需计入水平方向的惯性力,且同时需要完整的竖向位移形函数和纯弯曲转角位移形函数;对于变截面欧拉梁单元,其一致质量矩阵表达式过于复杂,可在等截面梁的基础上,根据元素位置对矩阵元素匹配左右端或平均截面面积及截面极惯性矩近似给出实用的质量矩阵表达式;考虑剪切变形时,欧拉梁的刚度矩阵亦可经竖向位移和纯弯曲转角位移形函数计算得到,这一过程与使用纯弯曲竖向位移和纯剪切竖向位移形函数的过程在本质上是一致的。

采用T型钢连接的可拆换钢梁抗震性能试验与数值研究

提出了一种采用T型钢连接的可拆换钢梁,在地震作用下T型钢集中耗散地震能量,并在震后通过更换T型钢实现使用功能的恢复。通过合理设计T型钢连接、钢梁中间段和悬臂段的抗弯承载力关系,定义设计承载力削弱系数的取值范围,从而实现T型钢集中损伤耗能,钢梁中间段和悬臂段保持弹性的屈服机制。为了使T型钢连接件实现预期的损伤和最优的耗能效果,设计了4个腹板采用不同截面和材料的T型钢连接件,并对T型钢连接的可拆换钢梁试件进行了低周往复加载试验和有限元分析。结果表明:T型钢连接的可拆换钢梁可以实现预期的屈服机制,达到T型连接件集中耗能的目的;T型钢腹板的残余变形和螺栓应力可以满足拆换条件,拆换后结构功能不变,实现了较为理想的可更换机制。狗骨式腹板截面的T型钢连接件塑性变形更均匀,耗能区域更大,耗能效率提高约30%,拆换时间和残余变形与普通截面相差不大,建议腹板采用狗骨式截面;采用低屈服点钢材可以提高T型钢的耗能效率约40%,在设计承载力系数取值合理的情况下,T型钢腹板可以选择低屈服点钢材。最后,基于试验和有限元结果,考虑到T型钢连接件的可拆换性和钢梁材料利用率,建议设计承载力削弱系数取值为0.65~0.85。

工字形钢梁-矩形钢管柱单向螺栓节点抗弯承载力理论计算方法

针对工字形纯钢梁和钢-混凝土组合梁分别与矩形钢管柱和矩形钢管混凝土柱采用单向螺栓(也称单边拧紧螺栓)连接形成的4种节点形式,对其在弯矩作用下的受力机理及破坏模式进行分析,讨论导致节点失效的因素。总结节点在弯矩作用下的9种失效模式,包括:单向螺栓拉断、端板受弯屈服、矩形钢管柱壁翼板受拉屈服、矩形钢管柱壁翼板受压屈服、矩形钢管柱壁腹板受压屈曲、混凝土楼板局部压溃、钢筋屈服、矩形钢管柱内混凝土局部压溃、矩形钢管柱壁腹板受压屈服,进而基于破坏模式给出节点各组件承载力的计算公式。对4种节点在不同破坏模式下的正弯矩承载力和负弯矩承载力进行分析,给出节点承载力计算公式。将节点抗弯承载力的理论计算结果与试验结果进行对比,验证理论计算方法的可靠性。

基于动态模态分解的Π形梁涡振流场特征分析

为探索Π形桥梁断面的涡振机理及气动措施的抑振原理,采用动态模态分解方法,结合计算流体动力学数值模拟,对某Π形桥的不同工况进行流场解耦和对比分析.结果表明,主梁下表面方腔内的不稳定涡是导致Π形梁涡激振动的重要因素,增设2道四分点下稳定板将空腔分割成3个较小的区域,可减少下缘分离涡的形成空间并降低空腔内涡的强度和尺度,从而有效抑制涡振.第2阶分解模态与结构振动同频,是引起涡激振动的主导模态;此模态能够直观揭示流场中主涡的形成和发展,简化流场分析的复杂性.第3、4分解阶模态与结构的涡振频率存在明显的倍频关系,能够精确捕获涡激力中的高频成分,有利于深入理解涡激振动的瞬时变化特性,制定更为精细的抑振措施.

碳纤维板加固H型钢梁抗剥离夹具研制及应用试验

外贴碳纤维板是钢梁抗弯加固的常用方法,但其端部易因界面应力集中导致剥离破坏,严重影响高性能材料的有效利用,特别是结构加固后的安全服役.为此开发出一种适用于H型钢梁的简易夹具——C形槽板夹,以加强碳纤维板的端部锚固.通过多根带夹碳纤维板加固梁的静力加载试验,验证了此夹具的可靠性,并考察了碳纤维板伸入剪跨段长度与剪跨段长度之比及锚固方式(纯粘、端锚和混锚)对加固效果的影响.研究发现端锚加固不同于纯粘,只要梁的控制截面仍在夹具之间,碳纤维板的极限应力、加固效果及利用效率均随其长度缩短而提高,当碳纤维板长度分别为600、750 mm时,前者极限应变和承载力比后者分别高27.3%和8.1%.由于钢梁表面处理质量较差,混锚加固梁均发生突然剥离,后期退化为端锚加固梁,因而相比端锚加固梁加固效果改善不大,需要提高表面处理质量再做类似研究.尽管如此,相比纯粘加固梁,混锚加固梁采用C形槽板夹后剥离破坏被延迟,抗弯性能大为改善.试验过程中还用压电阻抗法对界面剥离情况进行了检测,结果符合实际.

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.

横向静载作用下轨道交通预应力混凝土U型梁裂缝开展研究

为探究轨道交通预应力混凝土U型梁结构在腹板横向受力情况下的裂缝开展状况,通过回顾总结其裂缝开展成因,并以实际工程中的某标准梁段为例,进行了横向静载破坏试验,分析了U型梁结构在横向受力下的应变、挠度变化规律以及裂缝发育和损伤状况。研究结果表明,在横向对称荷载作用下,随着加载级的增大,U型梁展现出良好的整体性能和横向抗裂性能;该梁的裂缝损伤首先出现在腹板和底板处,随后逐步扩展到底板与腹板的连接部位;在破坏加载级下,腹板与翼缘发生破坏性裂缝损伤和明显的外扩变形;在高于规范撞击力建议值2倍的横向静载作用范围内,试验梁能够保持弹性工作状态,验证了采用美国ACI规范中对于列车脱轨撞击力的建议值进行U型梁横向抗撞设计的合理性。该研究成果可为轨道交通预应力混凝土U型梁的力学性能研究和结构优化设计提供更多参考。

高斯与平顶光束纳秒脉冲激光物质蒸发烧蚀动力学仿真研究

基于建立的纳秒脉冲激光与金属铝相互作用的二维轴对称模型,仿真研究了光束整形对纳秒脉冲激光烧蚀金属铝过程中蒸发烧蚀动力学的影响.结果表明:等离子体屏蔽对靶材的烧蚀特性具有显著影响,屏蔽效应主要体现在脉冲的中后期.对于3种激光轮廓,高斯光束的屏蔽效果最强,随着整形后的平顶光束直径的增大,屏蔽效果逐渐减弱.平顶光束与高斯光束作用下,靶材温度的二维空间分布较为不同.高斯光束作用时,靶材中心最先升温,随后温度沿径向和轴向扩散.由于平顶光束的能量分布更加均匀,因此一定径向范围内的靶材同时升温.光束整形对靶材的蒸发烧蚀动力学影响较大.对于高斯光束,靶材中心先烧蚀,随后产生径向烧蚀.由于整形后平顶光束的能量密度降低,因此靶面蒸发时间较高斯光束延后,并且一定径向范围内的靶材同时发生蒸发烧蚀.3种激光轮廓下,靶材的蒸发烧蚀形貌与光束的强度分布类似,其中高斯光束的烧蚀坑呈中间深两边浅的特点,平顶光束的烧蚀坑较为平坦.