Hierarchical-genetic-algorithm-based design of a large scale Fresnel lens for a reading light system with multiple LED sources

A conventional Fresnel lens is suitable to be used in the reading light system due to its features of directing and collecting light rays, as well as its properties of being essentially flat, plastic, lightweight, and cost efficient. However, it is not suitable for a reading light system with multiple light sources. To a reading light system with multiple light sources, a Fresnel lens with suitably designed groove angles can be used to improve the performance of that system in both illuminance and uniformity. Nevertheless, suitable groove angles are rather difficult to find if a Fresnel lens consists of a lot of groove angles and each angle covers a wide range of degrees. We develop a hierarchical genetic algorithm (HGA) to search for a set of optimal groove angles to design a Fresnel lens for a reading light system with multiple light sources from an enormous searching space. In addition, the groove angles of the Fresnel lens are directly derived from a conventional Fresnel lens database. The design goal is to maximize the illuminance and simultaneously maintain the uniformity of light rays incident to a specified reading surface. As a result, we can demonstrate that a HGA really works better than a genetic algorithm and the optimally designed Fresnel lens, indeed, offers a better light-guiding performance than a conventional Fresnel lens for a multiple-LED reading light system.     

Comparison of lens and Fresnel null correctors

Fresnel null correctors are compared with classical Offner and Hindle null correctors for both optical performance and system sensitivities to errors of construction and placement in the test setup. Fresnel null correctors are closely related to circular diffractive null correctors, the main difference being that a Fresnel uses tilted grooves functioning like a blazed diffraction grating. The Fresnel has an advantage in that specific power terms can produce an aspheric wave front directly and not as the byproduct of bending lenses as in the traditional lens null correctors. The parametric relationships are summarized for a range of configurations of lens null correctors and for Fresnel null correctors. The sensitivities to construction and deployment errors are presented for each of these examples. The performance of two Fresnel correctors for an autocollimation test of a full three-mirror Cassegrain configuration is presented.     

Replacement tissue-equivalent proportional counter for the International Space Station

The tissue-equivalent proportional counter (TEPC)-based dosemeters used on the International Space Station have exceeded their planned useful lives, and are scheduled to be replaced with the new units taking advantage of improved technology. The original TEPC detectors used cylindrical geometry with field tubes to achieve good energy resolution and minimum sensitivity to noise created by vibration. The inside diameter of these detectors is 5.1 cm. The new detectors developed for this application produce the resolution and vibration resistance of the cylindrical detector with the isotropic response and compact size of a spherical detector. The cathode structure consists of conductive tissue-equivalent plastic A-150 layers separated by thin polyethylene layers perpendicular to the anode. Each conductive layer is held at the electrical potential needed to produce uniform electric field strength along the anode wire, and thus the same gas gain for electrons produced in different portions of the spherical volume. The new design contains the whole preamplifier inside the vacuum chamber to reduce electronic noise. Also the vacuum chamber has a novel design with a 0.020-inch-thick aluminium wall to allow a total wall thickness of 0.5 g cm(-2), which is typical of the shielding provided by a space suit. This feature will allow measuring the dose on the astronauts' skin due to low-energy electrons and protons produced during solar events. The vacuum chamber has a new bayonet clamping system that reduces the total detector weight to less than half that of the old TEPC.     

Spectral anomalies in focused waves of different Fresnel numbers

Light propagation induces remarkable changes in the spectrum of focused diffracted beams. We show that spectral changes take place in the vicinity of phase singularities in the focal region of spatially coherent, polychromatic spherical waves of different Fresnel numbers. Instead of the Debye formulation, we use the Kirchhoff integral to evaluate the focal field accurately. We find that as a result of a decrease in the Fresnel number, some cylindrical spectral switches are geometrically transformed into conical spectral switches.     

一种外部加翼的圆柱小目标声隐身结构设计

针对水下小型航行器日益增强的声隐身需求,基于菲涅耳(Fresnel)半波带理论,提出一种可提高目标声隐身性能的外部加翼结构。利用板块元方法计算并分析不同结构参数的优化翼型结构声隐身性能的提升效果。研究结果表明,外翼覆盖了圆柱散射贡献最大的半波带,加速相位变化,降低入射方向相同投影面积的散射贡献,使得圆柱正横方位的目标强度有效降低。当翼的开角为第一Fresnel半波带对应圆心角度且外翼与圆柱主体相切时,该结构在节约制造成本的同时可使声隐身性能的提升效果最好。文中进行了加翼模型声散射特性水池实验,优化结构的 0°方位目标强度下降约 7 dB,俯仰方向角检测概率显著降低,证明该类翼型结构可以有效提高目标声隐身性能。     

Intensity and Phase in Fresnel Diffraction by a Plane Screen Consisting of Parallel Strips

Using the Huygens-Fresnel principle the expressions for the intensity and the phase in Fresnel diffraction phenomena have been derived. The cases of spherical, cylindrical and plane scalar waves incident upon the plane diffraction screen have been investigated. The diffraction screen may consist of any number of parallel strips of different transmissivities and different phase shifts, the width of the individual strips being large compared with the wave-length. As special cases of the general formulae, the intensity and phase distributions in the diffraction patterns for the following forms of the diffraction screen have been calculated: opaque and partially transparent half-plane, slit, strip and double slit. By means of the derived expressions, the validity of Babinet's principle for Fresnel diffraction phenomena of this type has been verified.     

A Numerical Study Comparing The Effect on Residual Stresses of Two Different Types of Projectiles During Shot Peening

Shot peening is a widely used technique to improve fatigue life in metallic alloys. This processing technique introduces a subsurface compressive residual stress field through a plastic deformation of the surface caused by the impact of a large number of high-speed projectiles. There are a number of parameters that affect the residual stress field depth and magnitude. The effects of the impact angle, shot speed and shot geometry are currently being researched. In particular, substituting spherical cast shots by cylindrical cut wire shots is an attractive option, especially in terms of cost. The effect of shot geometry on residual stresses, however, needs to be further investigated. Because industrial-scale experimentation is costly and cumbersome, mathematical modeling offers a convenient alternative to carry out this type of research. The present work shows a comparison between the residual stresses generated by the impact of spherical and cylindrical projectiles on a steel substrate. This threedimensional model was developed using ABAQUS finite element commercial software (Release 6.12, Dassault Systémes, France). The results show that cylindrical shots generate residual stress fields that are higher in magnitude than those generated by a spherical shot. However, the residual stress field of cylindrical shots impacting the surface at an oblique angle shows an important degree of asymmetry. This effect is not found when spherical shots impact the surface at the same oblique angle.     

基于立体几何的模块化灯具设计研究

目的研究立体几何的形态构成方法,提出灯具的模块化设计新方法。方法从4类经典立体几何形态入手,重点从模块化设计角度分析它们作为基本形对灯具造型的启发应用。结论分析现代灯具模块化生产的必要性,以此达到灯具产品更新换代快、崇尚节能环保的理念发展要求,提出灯具模块化设计新方法和应用。     

Performance of fitting procedures in curved geometry for retrieval of the optical properties of tissue from time-resolved measurements

By use of the solution of the diffusion equation for cylindrical and spherical geometry, two fitting procedures for retrieval of the optical properties from time-resolved measurements have been implemented. The fitting procedures are based on the Levenberg-Marquardt algorithm, in which the fitting parameters are the absorption coefficient, the reduced scattering coefficient, and an amplitude factor. Monte Carlo data generated for cylindrical and spherical geometry were fitted by these fitting procedures, and the retrieved optical properties were compared with those obtained from the inversion procedure with a mismatched geometry of a semi-infinite medium. The effects of refractive-index mismatch and of different boundary conditions of the diffusion equation were also studied, together with the effects of several sources of error that are typically found in time-resolved measurements. The advantages and drawbacks of these fitting procedures, including many details in several situations of interest in the field of tissue optics, are discussed. The results also offer a guideline to understanding the effects of mismatching in curved geometry as functions of source-detector distance and radii of cylinders or spheres.     

PET/CT图像融合精度测试体模与测试方法研究

通过自主研制的体模,测试PET/CT图像融合精度,并验证体模的可行性和有效性。采集PET/CT融合图像数据,利用IDL和Matlab软件测量圆柱棒及试管在PET、CT图像中的坐标值,两坐标值的差值即为图像融合精度。自制体模通过模拟热区和冷区,可以准确、快速地测量PET/CT图像融合精度,该体模可对日常质量控制项目的体模进行测试。     

Concept and design procedure for cylindrical element monochromators for synchrotron radiation

The design of a new type of soft X-ray grating monochromator which utilizes cylindrical optical elements is proposed. This design is the outcome of a return to simplicity. If not only offers high resolving power and transmission, but also has other advantages over the conventional designs. A simple analytical design procedure (which has been raytracing justified) for designing such a monochromator is described. The raytracing results also confirm that replacement of the cylindrical figure by a spherical one will not degrade the overall monochromator performance.     

机构设计在大型柱面网壳结构施工中的应用

 将机械行业中的机构运动概念应用到大型柱面网壳结构的施工，提出一种“折叠展开式”整体提升施工技
术． 详细阐述了该项施工方法的基本思想，并推导机构运动过程的运动学和动力学公式． 通过一个工程算例的分
析，总结机构运动和动力特性．计算结果证明机构运动过程中产生的动力效应不明显，处于“折叠”状态的网壳能够
承受施工荷载．该项新技术在亚洲最大跨度的柱面网壳结构的施工中得到了成功应用，证明了它的实用性和优越性．     

Development of a geometry-based process planning system for surface micromachining

There are many CAD systems developed for the design and fabrication of MEMS (Micro-Electro Mechanical Systems). However, most of them simulate the construction process given the two-dimensional mask data, and few systems generate the fabrication process plan from a designed model. Furthermore, the current systems simulate the construction process based on the two-dimensional geometry data. In this paper, a new process planning technique that uses a three-dimensional surface micromachined structure as input is proposed. The system decomposes an imported surface micromachined model into a set of three-dimensional models, each of which has the geometry compatible with the fabrication process, and then groups them for efficient layer generation. Finally, it generates the fabrication order and the masks for all the layers of the structure.     

Improvement of time resolution in a TOF PET system with the use of BaF2 crystals

In the course of the construction of a new type of time-of-flight positron emission tomograph (TOF PET), the time resolution of a system with BaF₂ crystals has been tested. It was found that low-viscosity silicon oil is one of the best optical coupling media between the BaF₂ crystal and the photomultiplier tube, and that the time resolution is less sensitive to the geometry between the detector and the source position. The dependence of the time resolution on the size of the BaF₂ crystal has been determined as well. Absorption and attenuation of photons in the detector system are expected to be of particular importance for the better performance of the TOF PET.     

Ray tracing of Fresnel systems

In this study based on an original program of aberration calculations and automated optical lens design we try to increase ray tracing of a Fresnel system so that the original program not only contains the initial functions but also satisfies the calculations of a Fresnel or mixed system (both general and Fresnel lenses).     

Information-based optical design for binary-valued imagery

Applications such as optical data storage, optical computing, and optical interconnects require optical systems that manipulate binary-valued images. Such an optical system can be viewed as a two-dimensional array of binary communication channels. This perspective is used to motivate the use of pagewise mutual information as a metric for optical system analysis and design. Fresnel propagation and coherent imaging both are analyzed in terms of mutual-information transmission. An information-based space-bandwidth product is used to analyze the trade-off between the numerical aperture and the number of image pixels in a coherent 4f system. We propose a new merit function to facilitate information-based optical system design. Information maximization and bit-error-rate minimization both are possible with the new radially weighted encircled-energy merit function. We demonstrate the use of this new merit function through a design example and show that the information throughput is increased by 8% and the bit-error rate is reduced by 36% when compared with systems designed with traditional criteria.     

热拉伸比对PET/ PE 原位微纤化复合材料形态和拉伸性能的影响

采用熔融挤出2热拉伸2淬冷方法制备了聚对苯二甲酸乙二醇酯( PET) / 聚乙烯( PE) 原位微纤化复合材料。固定体系组成( PET/ PE 为15/ 85), 热拉伸比增加, PET 粒子相继从球状转变成椭球状、棒状和纤维状; 除了最小粒径保持基本不变外, 最大和平均粒径均逐渐减小。微纤化复合材料在PE 的加工温度下成型时, 纤维能够良好地保持在体系中, 但在PET 的加工温度下成型时, 纤维重新熔融, 形成球状粒子。复合材料的拉伸模量和拉伸强度随拉伸比增加显著增加, 表明微纤化对材料具有良好的增强效果; 而断裂伸长率随热拉伸比增加剧烈下降, 产生明显的韧-脆转变。比基本断裂功( we ) 先随热拉伸比( HSR) 增加而增加, 热拉伸比为19117 左右时达到最大值, 继续增加热拉伸比, we 降低。      

Damage-potential comparison of spherical and cylindrical projectiles impacting on a system of bumper plates

This paper describes a series of smooth particle hydrodynamics (SPH) simulations of tungsten cylindrical and spherical projectiles impacting steel bumper plates at different impact configurations. Comparisons of the destructive capabilities of the spherical and cylindrical projectiles for each impact configuration are presented. Cylindrical geometries were spatially rotated to cover a wide range of impact configurations. The incidence angle of the velocity vector and its magnitude were varied. A rational approach is proposed to quantify the level of damage inflicted on the bumper plates on each impact event. This damage measure is used to create a set of comparative damage matrixes for cylindrical and spherical projectiles that identify under which impact configurations a given geometry is more damaged than the other.     

Plasmonic Metamaterial Cloaking at Optical Frequencies

In this paper, we present the design of cylindrical and spherical electromagnetic cloaks working at visible frequencies. The cloak design is based on the employment of layered structures consisting of alternating plasmonic and nonplasmonic materials, and exhibiting the collective behavior of an effective epsilon-near-zero material at optical frequencies. The design of a cylindrical cloak to hide cylindrical objects is first presented. Two alternative layouts are proposed, and both magnetic and nonmagnetic objects are considered. Then, the design of spherical cloaks is also presented. The full-wave simulations presented throughout the paper confirm the validity of the proposed setup, and show how this technique can be used to reduce the observability of cylindrical and spherical objects. The effect of the losses is also considered.      

Effective Fresnel number and the focal shifts of focused partially coherent beams

We define the effective Fresnel number of the cylindrical lens illuminated by a plane wave or Schell-model beams. On the basis of the concept of the effective Fresnel number, the focusing properties of the cylindrical lens illuminated by the Schell-model beam are investigated in a simple way. It is shown that the relative focal shift can be evaluated by an analytical formulation, which is expressed as a function of the effective Fresnel number. To evaluate our approach, we make the comparison between the results obtained by our method and the numerical calculation based on the diffraction integral. The results indicate that we can simply and exactly evaluate the focal shifts with our method.