Hierarchical theories for the free vibration analysis of functionally graded beams

This work addresses a free vibration analysis of functionally graded beams via several axiomatic refined theories. The material properties of the beam are assumed to vary continuously on the cross-section according to a power law distribution in terms of the volume fraction of the material constituents. Young’s modulus, Poisson’s ratio and density can vary along one or two dimensions all together or independently. The three-dimensional kinematic field is derived in a compact form as a generic N-order polynomial approximation. The governing differential equations and the boundary conditions are derived by variationally imposing the equilibrium via the Principle of Virtual Displacements. They are written in terms of a fundamental nucleo that does not depend upon the approximation order. A Navier-type, closed form solution is adopted. Higher-order displacements-based theories that account for non-classical effects are formulated. Classical beam models, such as Euler–Bernoulli’s and Timoshenko’s, are obtained as particular cases. Bending, torsion and axial modes are investigated. Slender as well as short beams are considered. Numerical results highlight the effect of different material distributions on natural frequencies and mode shapes and the accuracy of the proposed models.     

Directed 2D-to-3D pattern transfer method for controlled fabrication of topologically complex 3D features in silicon

A process that allows control over the 3D motion of catalyst nanostructures during metal-assisted chemical etching by their local pinning prior to etching is demonstrated. The pinning material acts as a fulcrum for rotation of the catalyst structures resulting in etching of silicon features with rotational geometry.     

The thermal treatment effects of CrN buffer layer on crystal quality of Zn-polar ZnO films

We report on the annealing effects of CrN buffer layers on the crystal quality of Zn-polar ZnO films grown by plasma assisted molecular beam epitaxy. The high-temperature (HT) annealing of CrN buffer layer improved the crystallinity of ZnO films. The full width at half maximums of (0002) and (10-11) ZnO ω-scan X-ray diffraction show 574 and 1296 arcsec, respectively, which show the 3 and 2 times narrower values than those of ZnO films without the annealing process. Moreover, the HT annealing can be effective method to improve the surface smoothness of ZnO film and reduce the crystal tilting.     

基于片上PowerPC的Vxworks处理平台的波束控制设计

片上嵌入式系统凭借其诸多方面的优势,如成本低、功耗低、尺寸小、处理速度快、可靠性高、实时性强、灵活性、产品上市时间以及设计开发周期短等优势,将嵌入式实时多任务操作系统VxWorks和基于FPGA的片上PowerPC平台相结合,使产品体积更小、环境适应性更强、运行更可靠、扩展和升级更灵活、生产成本更低。必将成为将来雷达产品上的主流技术。本文提出了在其内嵌PowerPC440处理器上构建Vxworks操作系统平台的雷达的波束控制设计。     

荷电控制电子枪特性的测量

扫描电子显微镜在科研和实际工作中扮演着越来越重要的角色,在集成电路行业常常被用来测量器件的关键尺寸。集成电路器件在进行表征时容易形成电荷积累,电荷积累会严重干扰检测系统的图像质量而影响测量器件尺寸的精度。使用荷电控制电子枪是一种常见且有效消除电荷积累的方式,荷电控制电子枪的特性直接影响着成像质量和检测效率。目前国内缺少有效针对荷电控制电子枪性能评价的研究,本文提出了一种法拉第杯小孔扫描测量方法并搭建了一套测试平台,在该平台上对自主研制的电子枪进行了束斑大小、束流密度分布和发散角等电子束特性测量,这将为对荷电控制电子枪的优化设计和安装调试起到了指导作用。     

An integrated high-performance beam optics-nuclear processes framework with hybrid transfer map-Monte Carlo particle transport and optimization

An integrated beam optics-nuclear processes framework is essential for accurate simulation of fragment separator beam dynamics. The code COSY INFINITY provides powerful differential algebraic methods for modeling and beam dynamics simulations in absence of beam-material interactions. However, these interactions are key for accurately simulating the dynamics of heavy ion fragmentation and fission. We have developed an extended version of the code that includes these interactions, and a set of new tools that allow efficient and accurate particle transport: by transfer map in vacuum and by Monte Carlo methods in materials. The new framework is presented, along with several examples from a preliminary layout of a fragment separator for a facility for rare isotope beams.     

Monte carlo study on 6 MV photon beams of a CyberKnife stereotactic radiosurgery system

In this paper,the beam quality and percent depth dose curves for different field sizes of CyberKnife? system were investigated by Monte Carlo simulations using the PENELOPE code,which has been used to simulate 6 MV photon beam.In water phantom,the absolute doses were calculated for Φ10–60 mm collimators,and percent depth dose curves were evaluated for Φ30–60 mm collimators.The agreement of dose distributions of the calculation with measurement was within 3.0%.The mean energy of photon spectrum was 1.46 MeV,and the beam quality index was 0.632,which was slightly smaller than that of measurement.     

Development of a reference database for Ion Beam Analysis and future perspectives

Ion Beam Analysis (IBA) is a set of material characterization techniques using energetic ion beams. IBA provides information about composition and the depth profile of elements in the near-surface layers of a sample, from the energy spectra of backscattered primary particles, recoils, nuclear reaction products or emitted γ-radiation. All IBA methods presuppose knowledge of the differential cross-section data however, only for strict Rutherford scattering is the cross-section known exactly. In order to address the data needs of the IBA community, the IAEA initiated the Coordinated Research Project (CRP) “Development of a Reference Database for Ion Beam Analysis” in 2005 which will conclude in 2010. The project focuses on the measurement, assessment, evaluation and benchmarking of elastic scattering and reaction cross sections. Data measured in this work have been incorporated in the IBANDL database (http://www-nds.iaea.org/ibandl/), whereas the evaluated cross-sections (calculated from the fit to the data of a nuclear model) are made available to the community through the on-line calculator SigmaCalc (http://www-nds.iaea.org/sigmacalc/).A summary of the results of the CRP activity is presented, and ways to further develop nuclear data for IBA are indicated. In particular, a newly proposed CRP devoted to particle induced gamma-ray emission is described.     

Major parameter measurement of high-brightness injector in Hefei Light Source

A photocathode radio frequency gun,which is an S-band normal conducting 1.6 copper cell cavity with water cooling system,was installed in Hefei Light Source.In order to know its characteristics and get it into normal operation,continuous conditioning was conducted in the last few months.Beam charge and dark current charge were measured using integrating current transformer.The beam transverse size was determined as 1.63 mm in minimum using YAG screen and GigE Vision camera.Using multi-slits technique,the transverse emittance was measured and normalized at 1.95 mm·mrad with beam charge of 240 pC.The results provide a way to optimize the facility.     

强流质子加速器物理与技术关键问题

建造下一代散裂中子源,需要把质子加速器的束功率提高一个数量级。因此,明确其中的关键技术困难,并针对它们进行前期研究与开发,以求技术上有所突破,是建造价格昂贵的强流质子加速器的必经步骤。新的技术挑战主要源于束流流强的提高、加速器功率的提高以及对加速器可靠性、稳定性要求的提高。分别就这些难题进行了简略的说明,并讨论目前解决它们的技术途径和各主要技术环节的工艺水平。最后,还讨论了强流质子加速器架构的选择问题。