Quantum polarization fluctuations of partially coherent dark hollow beams in non-Kolmogorov turbulence atmosphere

Non-classical polarization properties of dark hollow beams propagating through non-Kolmogorov turbulence are studied. The analytic equation for the polarization degree of the quantization partially coherent dark hollow beams is obtained.It is found that the polarization fluctuations of the quantization partially coherent dark hollow beams are dependent on the turbulence factors and beam parameters with the detection photon numbers. Furthermore, an investigation of the changes in the on-axis propagation point and off-axis propagation point shows that the polarization degree of the quantization partially coherent dark hollow beams presents oscillation for a short propagation distance and gradually returns to zero for a sufficiently long distance.

Generation of diffraction-free vectorial elliptic hollow beams with space-varying inhomogeneous polarizations

Diffraction-free vectorial elliptic hollow beams(vEHBs)are generated by an optical system composed of a short elliptic hollow fiber(EHF)and an axicon.Each beam has a closed elliptic annular intensity profile and space-varying polarization states in its diffraction-free distance of more than 1 m.The generated beams have a counter-clockwise or clockwise periodically-rotated inhomogeneous polarization.And the spin angular momentum(SAM)of the vEHBs is 1ħor-1ħwhich is consistent with the type of dual-mode in the EHF and the periodic polarization rotations of the vEHBs.The vEHBs have potential applications in optically trapping and micromanipulating the micro-or nano-particles,quantum information transmission,and Bose-Einstein condensates,etc.

A dark hollow beam from a selectively liquid-filled photonic crystal fibre

This paper reports that, based on the electromagnetic scattering theory of the multipole method, a high-quality hollow beam is produced through a selectively liquid-filled photonic crystal fibre. Instead of a doughnut shape, a typical hollow beam is produced by other methods; the mode-field images of the hollow-beam photonic crystal fibre satisfy sixth-order rotation symmetry, according to the symmetry of the photonic crystal fibre （PCF） structure. A dark spot size of the liquid-filled photonic crystal fibre-generated hollow beam can be tuned by inserting liquid into the cladding region and varying the photonic crystal fibre structure parameters. The liquid-filled PCF makes a convenient and flexible tool for the guiding and trapping of atoms and the creation of all-fibre optical tweezers.

Flexural behavior of ECC hollow beams incorporating different synthetic fibers

Twelve ECC beams with three different fiber types,along with four normal concrete beams,were tested in this study to evaluate the influence of cross-sectional hollowing on their flexural performance.The fiber types used were nylon monofilament(NM),low-cost untreated polyvinyl alcohol(PVA),and polypropylene(PP).Three different square hole sizes of 60,80,and 100 mm with cross-sectional hollowing ratios of 0.16,0.28,and 0.44,respectively,were adopted for each group of beams in addition to a solid beam.All beams were tested under four-point loading using a displacement-controlled testing machine.The test results showed that ECC beams can mostly withstand higher cracking and ultimate loads compared to their corresponding normal concrete versions.The results also showed that both the ductility and toughness of the ECC beams are higher than those of the normal concrete beams and that the ductility values of the hollow beams with a hole size of 60 mm are higher than those of the corresponding solid beams.Moreover,hollow ECC beams with hole sizes of 60 and 80 mm exhibited a higher ductility than a solid normal concrete beam.

The degenerating diffraction far-field propagation properties of the conical double half-Gaussian hollow beams

The far-field propagation properties of conical double half-Gaussian hollow beams in the condition of Collins formula are studied. Because of the cone angle of this kind of hollow beams, the diffraction is compensated and the inner diameter is turning bigger by the rule of geometric optics as the propagation distance is increasing, whereas the degenerating diffraction phenomenon is turned out. The far-field intensity distribution of the conical double half-Gaussian hollow beams in the condition of in-Collins formula is researched, and the results show that the far-field propagation properties can be depicted by this model. In the experiment, this kind of hollow beams are obtained by means of the dual-reflecting splitting optical system, and the inner diameter of the hollow beams is tested. The results show good agreement with the propagation theory in the condition of in-Collins formula.

The research of propagation characteristic and formation of double half-Gaussian hollow beams

A new kind of hollow beams, double half-Gaussian hollow beams,was put forward. With the help of the Collins formula, the analytical equation of propagation and transformation of the hollow laser beams in free space was deduced. The simulation shows that the intensity exhibits the three-dimensional trap distribution in the near-field, while the double half-Gaussian hollow beams turn into solid laser beams when propagating a certain distance, which shows the characteristics of self-focus. The double half-Gaussian hollow beams were obtained by means of the dual-reflecting splitting optical system. The intensity of the vertical loop in different distances was tested, which shows that the analytical equation of propagation and transformation is in agreement with the result.

Hollow Gaussian beams in strongly nonlocal nonlinear media

The propagation of hollow Gaussian beams in strongly nonlocal nonlinear media is studied in detail. Two analytical expressions are derived. For hollow Gaussian beams, the intensity distribution always evolves periodically. However the second-order moment beam width can keep invariant during propagation if the input power is equal to the critical power. The interaction of two hollow Gaussian beams and the vortical hollow Gaussian beams are also discussed. The vortical hollow Gaussian beams with an appropriate topological charge can keep their shapes invariant during propagation.

Physico-Mechanical Characterizations of Sand Concrete: Prestressed Beams and Hollow Bricks

The use of the sand concrete makes it possible to carry out a concrete having physico-mechanical properties answering the structural exigences and having economic and environmental advantages compared to the classical concrete. The present study aims to connecting the parameters of a formulation based on an empirical formula of Caquot in order to optimize, on the one hand the couple compressive strength/absorption of water under various degrees of hygrometry, and on the other hand more precisely to use the concrete sand in the public works sector in the prefabrication of prestressed beams and hollow bricks. The results show the importance of the type of formulation used because it takes into account the percentages of fillers of sand which is a co-product (waste) of massive rock crushing. In addition, the use of fillerized sands, which are wastes of crushing basaltic rocks and containing a small percentage of fillers, is efficient in the manufacture of prestressed beams. As for the hollow bricks, a fillerized basalt sand, containing a high percentage of filler, as well as a sand dune, gives satisfactory results.

Effects of edge beams on mechanic behavior under lateral load in reinforced concrete hollow slab-column structure

In order to get the formulae for calculating the equivalent frame width coefficient of reinforced concrete hollow slab-column structures with edge beam,the finite element structural program was used in the elastic analysis of reinforced concrete hollow slab-column structure with different dimensions to study internal relationship between effective beam width and the frame dimensions.In addition,the formulas for calculating the increasing coefficient of edge beam were also obtained.

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。

市政宽幅空心板梁桥加固设计关键技术

针对当前普遍暴露出来的装配式空心板梁桥病害,以武汉市三环线地面层五座空心板梁桥维修加固工程为背景,进行维修加固设计,提出的主要设计方法包括:梁体横向分块依次整体顶升的施工方案;新支座垫块双层设计;可根据现场实际情况进行适时调整的三种不同的支座垫块与墩台帽梁连接方式;铰缝跨缝植筋处理。施工过程及运营情况表明,这些设计方法在增加了施工的便利性,缩短了工期的同时,起到了良好的加固效果,有效恢复并提高了结构的整体受力性能、恢复了结构耐久性。

分缝护栏致空心板梁桥L型裂缝预应力控制方法研究

为提高护栏分缝桥梁的耐久性和承载力,以台金高速公路杨司高架桥预制空心板梁桥为背景,研究通过施加预应力控制因护栏分缝引起L型裂缝的有效性,并针对既有桥梁加固和新建桥梁设计提出通用的有效方法。采用Abaqus软件建立既有桥梁和新建桥梁的有限元模型,研究车道荷载作用产生的应力放大效应;分析预应力筋布置高度和长度对边梁梁底应力的影响及对既有桥梁护栏分缝导致的预应力损失;在此基础上,提出L型裂缝的预应力控制方法。结果表明:边梁应力放大系数随桥梁跨径和护栏高度的增加而增大,其取值范围为[1.42,2.14];预应力筋布置高度越低,边梁跨中梁底应力越大;预应力筋布置长度越短,既有桥梁梁底应力越大,对新建桥梁应力没有影响;分缝护栏对既有桥梁施加预应力产生损失,对新建桥梁不会产生预应力损失;在边梁跨中施加相应的预应力,可有效抵消跨中的应力集中效应,防止主梁跨中产生L型裂缝。

高功率VCSEL激光器光束发散角的测量方法

垂直腔面发射激光器(Vertical Cavity Surface Emitting Laser,简称VCSEL)由于其能发射出垂直于腔面光束的特性使得多个VCSEL激光器可以在同一片芯片上紧密集成,而不需要大量的空间;且VCSEL激光器使用共振腔的反射镜来增强光并放大,从而实现高效的光发射;通常情况下,VCSEL激光器的发光效率可以达到40至60之间,与传统的激光器相比,VCSEL激光器更容易实现高效率。由于VCSEL激光器的可集成性好、效率高等特点,使其广泛应用于3D感知、自动驾驶、光通信等领域。因此,VCSEL激光器的质量检测工作也显得越来越重要。随着VCSEL激光器进军高功率领域,其发光束的模式也经历了从基模变为高阶模的过程,光束已经从类高斯光束变为了类拉盖尔-高斯空心圆环光束。虽然传统的1/e^(2)、D86等算法在测量基模下的类高斯光束的发散角较为精确,但对于高阶模式下的类拉盖尔-高斯空心圆环光束,这些方法则出现了明显的误差。考虑到VCSEL激光器在自动驾驶等重要领域的广泛应用,其光束精确度的要求也随之提高。因此,本文采用了D4σ算法,针对类拉盖尔-高斯空心圆环光束进行发散角测量,与1/e^(2)、D86等传统算法进行了比较。结果显示,新方法在发散角测量准确度上最高提升了230。

铰缝损伤及铺装层对空心板桥横向刚度的影响

铰缝损伤是空心板桥梁较易出现的病害。为研究铺装层在铰缝损伤后对空心板桥梁横向刚度的影响,根据铰接板法理论,采用梁格法和Midas civil软件建立其有限元模型,对铰缝损伤后空心板桥梁的横向受力性能进行计算分析。研究结果表明:铺装层在空心板桥梁铰缝损伤后可起荷载横向传递的作用,提高了桥梁的横向受力性能,并且在多铰缝出现损伤时,提升效果更为明显;同时当铺装层厚度为10~20 cm时,铺装层厚度越大,桥梁的横向刚度越大,但对结构横向刚度的提升效果并不明显。

钢筋混凝土桥梁裂缝预防与维护方案

分析了空心板梁的结构特点与功能,并针对空心板梁的病害,即渗水和泛碱问题,解析其形成机理和影响,提出了在桥梁设计、施工、运营维护阶段预防渗水泛碱病害的措施及处治方案,同时指出,利用现代化技术和方法能够有效识别和监测空心板梁内部的渗水和泛碱反应迹象,采用相应的修复措施可以取得良好的效果,能够确保桥梁的健康和安全。

G15公路嘉金段空心板梁拼宽设计

随着时代的发展,社会对桥梁结构的建设提出了越来越高的要求.为了缓解交通压力,提升经济发展,降低工程造价,减小社会影响,越来越多的现状桥梁会被拓宽改建,继续承担着社会责任.G15公路嘉金段改扩建工程存在大量的既有桥梁改建需求,其中空心板梁拼宽,采用上部结构连接,下部结构不连接的方式.对空心板梁三种拼宽方案进行比选,同时计算分析了新建结构的沉降对现状空心板梁以及拼缝的影响.为桥梁改扩建工程的设计提供了一定的参考.

老旧预应力空心板梁非常规裂缝产生机理分析

混凝土开裂是老旧预应力空心板梁典型病害之一,通常表现为跨中底板弯曲裂缝和近支座腹板剪切裂缝。在多榀简支空心板梁的小剪跨比区段,发现了非常规的弯剪裂缝。利用空间杆系模型和精细化实体有限元模型,对先张预应力空心板梁的开裂机理进行分析。结果表明,设计缺陷和重载车辆是板梁底板和腹板贯通开裂的主要原因。其中,预应力端部应力集中,诱发了非常规弯剪裂缝产生;车辆荷载则加剧了薄弱截面裂缝的扩展。

梁高受限空心板桥横向连接优化设计分析

以某梁高受限的空心板漫水桥加固工程为例,通过建立有限元实体模型,详细分析了旧桥空心板梁及铰缝的受力状态,结果显示原空心板间的铰缝截面小且受力复杂,在重载作用下易破坏且影响结构横向传力,原桥设计荷载低且配筋弱,在荷载和环境作用下出现大量病害。为彻底解决桥梁结构病害,对下部结构进行加固后更换了上部结构,在梁高受限条件下设计了一种横向湿接的预应力空心板梁。经对比分析可知,新空心板梁优化了横向连接,改善了接缝横向受力状态,提高了结构整体性、承载能力和耐久性,并且加快了施工速度,减少了河道占用,目前改造后的桥梁使用状态良好,该设计思路及加固方案可为类似工程提供借鉴。

预应力混凝土空心板桥梁加固方法研究

为解决预应力混凝土空心板桥梁应用环节存在的结构承载力下降、桥体老化严重问题,规避由此引发的桥梁受损、桥面裂缝困境,保证桥梁运行质量,对预应力混凝土空心板桥梁加固方法展开研究,以案例解剖的方式,基于三维有限元模型分析桥梁病害的具体形式和产生原因。在此基础上初步制定技术方案,并结合数值计算结果、经济性、可行性分析结果确定最终方案,梳理方案技术流程、评估方案应用效果,以提高预应力混凝土空心板桥梁建设质量。

基于选区激光熔化技术的空心变截面梁点阵建模与性能研究

针对点阵结构受力不均、材料分布不合理和功能性单一等问题,设计了一种空心变截面梁点阵。该点阵主要由空心变截面梁和无冠空心球体组成,优化了节点连接方式,改善了材料分布,相比于传统体心立方点阵更具优势。完成了空心变截面梁点阵结构几何分析,基于点阵的几何数据模型和铁木辛柯梁理论推导了点阵结构参数与相对密度和力学性能之间的函数关系。设计了单胞边长10 mm空心变截面梁点阵,在同一相对密度、不同曲率半径的变截面梁点阵进行了准静态压缩仿真模拟,采用选区激光熔化技术制备了变截面梁点阵,进行了形貌分析和准静态压缩试验。结果表明:压缩仿真结果与实验结果趋势吻合,空心变截面梁点阵相比于传统体心立方点阵性能更优,外轮廓曲率半径为4 mm时力学性能最优,相比于普通点阵承载能力提高43%;变截面梁外轮廓及内孔光洁度较高,扫描提取模型与原模型相比偏差在0.25 mm以内。