基于TDD的低轨卫星跳波束资源分配算法

低轨(LEO)卫星跳波束技术可以灵活分配系统资源,适用于业务分布不均匀的场景。时分双工(TDD)方式可以减少星载和地面终端设备的天线数量,有效降低其复杂度,并有利于开展上下行非对称业务。本文提出一种基于TDD的LEO卫星跳波束资源分配算法,在满足业务需求的基础上,以最小化时域资源消耗为目标,建立支持跳波束和多频时分多址接入(MF-TDMA)机制的LEO卫星反向链路资源分配模型;综合考虑星地动态时延补偿,采取一种多层次的跳波束时隙架构设计,以最大化可用时隙为目标,建立上下行时隙切换模型,并提出一种基于TDD的跳波束时隙排布优化方法。仿真结果表明,对比于传统的MF-TDMA资源分配方法或固定多波束均分算法,本文提出的算法能有效提高系统的时隙利用率和吞吐量。     

一种适用于集群无人机超分辨的波束域方位估计算法

为了提升对集群无人机目标的分辨能力,提出了一种波束域方位超分辨估计算法。该方法不仅可以避免传统的稀疏表示类测角方法的计算复杂度高和需要选取超参数问题,而且在单快拍数、入射信号空间角度间隔较小等非理想情况下都具备很好的分辨能力,与相控阵雷达波束形成、距离?多普勒域处理的流程相适配。通过仿真试验,可以说明：该方法可以帮助雷达提前将密集目标分辨开,进而实现对于集群的规模（个数）、轮廓等信息进行准确估计,具有很强的应用价值。     

利用偏光分束棱镜测定波片的延迟量

在文〔３〕的基础上,提出了波片延迟量测量精度较高的方法。     

Enabling Coarse X-ray Fluorescence Imaging Scans with Enlarged Synchrotron Beam by Means of Mosaic Crystal Defocusing Optics

Trace elements, functionalized nanoparticles and labeled entities can be localized with sub-mm spatial resolution by X-ray fluorescence imaging (XFI). Here, small animals are raster scanned with a pencil-like synchrotron beam of high energy and low divergence and the X-ray fluorescence is recorded with an energy-dispersive detector. The ability to first perform coarse scans to identify regions of interest, followed by a close-up with a sub-mm X-ray beam is desirable, because overall measurement time and X-ray dose absorbed by the (biological) specimen can thus be minimized. However, the size of X-ray beams at synchrotron beamlines is usually strongly dependent on the actual beamline setup and can only be adapted within specific pre-defined limits. Especially, large synchrotron beams are non-trivial to generate. Here, we present the concept of graphite-based, convex reflection optics for the one-dimensional enlargement of a 1 mm wide synchrotron beam by a factor of 5 to 10 within a 1 m distance. Four different optics are tested and characterized and their reflection properties compared to ray tracing simulations. The general shape and size of the measured reflection profiles agree with expectations. Enhancements with respect to homogeneity and efficiency can be expected with improved optics manufacturing. A mouse phantom is used for a proof-of-principle XFI experiment demonstrating the applicability of coarse and fine scans with the suggested optics design.     

Investigation of HgCdTe p-n device structures grown by liquid-phase epitaxy

The microstructure of p-n device structures grown by liquid-phase epitaxy (LPE) on CdZnTe substrates has been evaluated using transmission electron microscopy (TEM). The devices consisted of thick (∼21-μm) n-type layers and thin (∼1.6-μm) p-type layers, with final CdTe (∼0.5 μm) passivation layers. Initial observations revealed small defects, both within the n-type layer (doped with 8×10¹⁴/cm³ of In) and also within the p-type layer but at a much reduced level. These defects were not visible, however, in cross-sectional samples prepared by ion milling with the sample held at liquid nitrogen temperature. Only isolated growth defects were observed in samples having low indium doping levels (2×10¹⁴/cm³). The CdTe passivation layers were generally columnar and polycrystalline, and interfaces with the p-type HgCdTe layers were uneven. No obvious structural changes were apparent in the region of the CdTe/HgCdTe interfaces as a result of annealing at 250°C.     

两跨连续GFRP-混凝土空心组合板受力性能试验研究

为研究高延性混凝土(HDC)加固钢筋混凝土梁的受剪性能,该文对7根HDC加固梁及4根未加固梁进行静力试验,研究剪跨比、配箍率、加固层厚度和加固层附加箍筋对钢筋混凝土梁破坏形态、荷载-挠度曲线、受剪承载力以及裂缝的影响。结果表明：采用HDC面层对钢筋混凝土梁进行受剪加固,可以显著提高梁的受剪承载力;HDC面层可以代替部分箍筋的受剪作用,改善钢筋混凝土梁的剪切破坏形态;加固试件在达到极限位移之后,试件的完整性较好,剩余承载力较高。基于试验结果,利用桁架-拱模型,提出了HDC加固钢筋混凝土梁的受剪承载力计算公式,计算值与试验值吻合较好。     

RC框架梁柱组合件抗震性能试验研究

为提高钢筋混凝土(RC)梁的变形能力,考虑在其塑性铰区采用高延性混凝土(HDC)代替普通混凝土。共设计6个剪跨比为3.6的RC梁试件,包含5个塑性铰区采用HDC的试件和1个RC对比试件。考虑HDC区长度、纵筋配筋率以及配筋方式和梁端配箍率的影响,研究试件在低周反复荷载下的滞回特性、变形能力及耗能能力。结果表明：与RC梁相比,塑性铰区采用HDC后,试件的破坏形态由弯剪破坏向弯曲破坏转变,延性和耗能能力均得到显著提高;纵筋配筋率、配筋方式相同时,在梁端塑性铰区采用HDC,试件的位移延性系数和极限位移角分别提高30%和53%,而同时采用HDC和箍筋时分别相应提高33%和76%;梁端局部采用HDC替换混凝土可减少箍筋用量;梁端塑性铰区的HDC长度对试件延性的影响较小。分别计算塑性铰区采用HDC梁在开裂荷载、屈服荷载、峰值荷载、极限荷载时的顶点位移,其计算值与试验值吻合较好。     

Process window for electron beam melting of Ti-6Al-4V

Selective electron beam melting (EBM) is a powder-bed based additive manufacturing technique for the fabrication of dense metallic parts. As a free-form deposition process EBM offers a high degree of freedom in design and a highly efficient utilization of material. For a widespread industrial application the achievable build rate is a critical factor. In this paper the process window for Ti-6Al-4V is explored by varying beam current and scan speed in a wide range. The EBM specimens were characterized by their density, porosity size and distribution, chemical composition, microstructure, hardness and tensile strength. Key findings include: (1) the minimum line energy necessary to achieve full density, (2) parameter sets for increased build rates at full density, and (3) formation of α'-martensite at high scan rates.     

Fluorescence enhancement from plasmonic Au templates

We have fabricated sub-quarter-micron-patterned Au templates with electron beam lithography, and studied their effect on the fluorescence intensity of immobilized, anti-rabbit IgG antibody labeled with AlexaFluor® 546. Varying the geometry of the structured surface, the plasmon resonances are tuned to match the fluorescence wavelengths and achieve significant fluorescence enhancement. Full electrodynamic simulations were used to understand the optical response and access the quality of the fabricated structures for surface plasmon excitation.     

The orthogonal meshless finite volume method for solving Euler–Bernoulli beam and thin plate problems

In this paper a new method untitled “orthogonal meshless finite volume method” (OMFVM) is developed for solving elastostatic problems in Euler–Bernoulli beam and thin plate. In this method, the weak formulation of a conservation law is discretized by restricting it to a discrete set of test functions. In contrast to the usual finite volume approach, the test functions are not taken as characteristic functions of the control volumes in a spatial grid, but are chosen from a Heaviside step function. The present approach eliminates the expensive process of directly differentiating the OMLS interpolations in the entire domain. This method was evaluated by applying the formulation to a variety of patch test and thin beam problems. The formulation successfully reproduced exact solutions. Numerical examples demonstrate the advantages of the present methods: (i) lower-order polynomial basis can be used in the OMLS interpolations; (ii) smaller support sizes can be used in the OMFVM approach; and (iii) higher accuracies and computational efficiencies are obtained.