基于窗口傅里叶变换剪切干涉法波前检测

提出了一种利用二维窗口傅里叶变换从径向剪切干涉条纹中准确得到波前的重建技术。首先对剪切干涉条纹做二维窗口傅里叶变换,设置阈值和频率积分范围后,进行二维窗口傅里叶逆变换,然后对包裹相位做去载频和相位展开处理得到相位差分布,最后使用波前迭代算法从相位差中复原实际波前。模拟计算表明,使用该方法最大相位复原误差为0.82%,均方根值为0.020 9 rad,实验结果验证了该方法的有效性。同时也对窗口傅里叶变换的关键参数,如窗函数的选择、窗口大小的确定以及阈值的选取等进行了简要讨论。与传统傅里叶变换法(FFT)相比,基于窗口傅里叶变换的剪切干涉波前检测法有更高的精度和稳定性,为波前检测提供一种新的处理方法。     

激波冲击R22重气柱所导致的射流与混合研究

基于大涡模拟, 结合五阶加权基本无振荡格式与沉浸边界法对激波自左向右与R22重气柱作用过程进行了数值模拟. 数值结果清晰地显示了激波诱导Richtmyer-Meshkov不稳定性所导致的重气柱变形过程, 并与Haas 和 Sturtevant 的实验结果符合. 另外, 结果还揭示了入射激波在气柱内右侧边界发生聚焦并诱导射流的过程, 以及在Kelvin-Helmhotz 次不稳定性作用下两个主涡滑移层形成次级涡的过程, 并分析了气柱变形过程中与周围空气的混合机理. 最后, 通过改变反射距离对反射激波与不同变形阶段的气柱的再次作用过程进行了研究. 结果表明: 当激波反射距离较长时, 反射激波与充分变形后的气柱作用, 使其在流向方向上进一步被压缩; 而当激波反射距离较短时, 反射激波会在气柱内发生马赫反射, 两个三波点附近产生两个高压区, 当其传播至气柱左侧边界时对气柱边界造成冲击加速, 诱导两道向左传播的反向射流. 关键词： Richtmyer-Meshkov不稳定性 R22重气柱 反射激波 射流     

Evolution of three-dimensional coherent structures in compressible axisymmetric jet

A high order difference scheme is used to simulate the spatially developing compressible axisymmetric jet. The results show that the Kelvin-Helmholtz instability appears first when the jet loses its stability, and then with development of jet the increase in nonlinear effects leads to the secondary instability and the formation of the streamwise vortices. The evolution of the three-dimensional coherent structure is presented. The computed results verify that in axisymmetric jet the secondary instability and formation of the streamwise vortices are the important physical mechanism of enhancing the flow mixing and transition occurring.     

径向双折射滤波器的超分辨性能研究

超分辨技术因其可以超越经典的衍射极限而为人们所熟知．并且．在光存储和共焦扫描成像系统中有着广泛的应用。把由两个偏振器和一个圆对称的双折射元件组成的径向双折射滤波器引入超分辨技术,借助琼斯算法推导出其光瞳函数的表达式。由分析得出通过改变径向双折射滤波器中偏振器的偏振方向和双折射元件的主轴之间的夹角,即可实现光学系统的横向超分辨或轴向超分辨。同时对评价该器件超分辨性能的参量第一零点比、斯特尔比和旁瓣强度抑制比做了详细的讨论。该滤波器用于超分辨技术的优点在于其制作不涉及相位的变化而比较简单,且费用比较低。缺点是旁瓣能量过高,但可以通过采用共焦系统来抑制。     

脉冲敲击技术对PI微球表面粗糙度的影响

作为点火靶重要候选靶丸之一, 聚酰亚胺 (PI) 空心微球采用降解芯轴技术结合双单体气相沉积聚合法 (VDP) 制备. 在PI涂层过程中微球碰撞对表面质量影响较大, 为了减小碰撞提高表面质量, 选用筛网盘做样品盘, 激励方式由压电振动模式改为脉冲敲击模式进行对比. 实验数据表明微球运动过程中碰撞是引起表面质量变差的原因, 通过理论分析确认了筛网盘通过减少接触点可以减少微球与微球间、微球与样品盘间的碰撞, 并且将压电振动改为脉冲敲击模式可以减小微球碰撞次数. 脉冲敲击模式与压电振动模式相比, 其可控性、微球弹跳幅度、消除静电等方面均优于压电振动. 对于微球壁厚均匀性而言, 压电振动略好于脉冲敲击, 但相差较小. 单个微球的壁厚最大偏差前者为0.68 μm, 优于后者的0.73 μm; 单个微球壁厚平均值在同一批次内的最大起伏, 前者为0.26 μm, 优于后者0.57 μm. 白光干涉仪数据显示脉冲敲击起到了提高微球表面质量的作用, 其表面粗糙度Rq值由52–93 nm 减小到28–44 nm. 关键词： 脉冲敲击技术 聚酰亚胺靶丸 表面粗糙度 壁厚均匀性     

Three different low-temperature plasma-based methods for hydrophilicity improvement of polyethylene films at atmospheric pressure

Three different low-temperature plasma-based methods were used to improve the surface hydrophilicity of polyethy- lene （PE） films, and all the modification processes were carried out by employing an atmospheric pressure plasma jet （APPJ） system. （a） PE films were directly modified by APPJ using a gas mixture of He and 02. （b） Acrylic acid （AA） was introduced into the system and a polymer acrylic acid （PAA） coating was deposited onto the PE films. （c） AA was grafted onto the PE surface activated by plasma pre-treatment. It was found that the hydrophilicity of the PE films was significantly improved for all the three methods. However, the samples modified by Process （a） showed hydrophobicity recovery after a storage time of 20 days while no significant change was found in samples modified by Process （b） and Process （c）. The Fourier transform infrared spectroscopy （FTIR） results indicated that the most intensive C=O peak was detected on the PE surface modified by Process （c）. According to the X-ray photoelectron spectroscopy （XPS） analysis, the ratios of oxygen-containing polar groups for samples modified by Process （b） and Process （c） were higher than that modified by Process （a）.     

基于RBF神经网络的磨矿粒度软测量模型及实现

磨矿分级作业是选矿生产中的重要环节,磨矿粒度的好坏直接影响浮选的精矿品位和尾矿回收率;在实际生产中粒度的测量有在线粒度分析仪,但存在成本高、维修率高,离线实验室化验又有时间延迟大的问题;对实际磨矿分级作业过程进行了分析,提出用径向基函数(RBF)神经网络建立磨矿粒度软测量模型,采用正交最小二乘法(OLS)算法对网络进行训练学习,泛化校验;仿真结果表明,在较少训练数据下该网络非线性处理能力和逼近能力依然很强,学习时间短,模型基本符合要求;通过OPC技术将Matlab与PKS控制系统相结合,实现实时软测量磨矿粒度。     

In situ observations of domain wall motion in Mn–Zn and Ni–Zn ferrites by Lorentz microscopy and electron holography

Domain wall motion in Mn–Zn and Ni–Zn ferrites with applied magnetic fields is investigated by in situ observations with Lorentz microscopy and electron holography. It is found that both Mn–Zn and Ni–Zn ferrites have a mean grain size of approximately 10 μm and several pores with sizes ranging from 0.2 to 1.1 μm. In situ observations by Lorentz microscopy with an applied magnetic field reveals that in Mn–Zn ferrite, the domain walls move easily across the grain boundary, while in Ni–Zn ferrite, the domain walls move along the grain boundary but are pinned at the grain boundary and pores. From in situ observations of Ni–Zn ferrite by electron holography, it is clarified that domain wall pinning at the grain boundary retards a sensitive increase in magnetic flux parallel to the applied field direction, which is considered to result in high hysteresis loss.     

纵波速度径向层析成像分析

钻井会造成近井壁附近岩石的声学性质改变,为研究纵波径向探测特性,本文使用径向柱状分层模型,应用二维轴对称有限差分法详细考察了过渡带厚度、声源频率以及接收器源距变化下,单极子测井响应的变化特征,并采用慢度-时间相关法研究了不同条件下所测量到的声速变化。最后基于射线理论,分析了不同条件下的首波到时变化特征。基于地层速度逐渐增加的模型表明,纵波的径向探测特性受源距影响较大,通过不同源距信号的组合,可以实现对近井壁纵波速度进行层析成像。     

Magnetic properties of the Cr(0 0 1) surface studied by spin-polarized scanning tunneling spectroscopy

The magnetic properties of the Cr(0 0 1) surface have been studied by spin-polarized scanning tunneling spectroscopy (SP-STS). Spatially resolved mapping of the spectroscopic dI/dU signal at an energy close to the spin-polarized Cr(0 0 1) surface state allows the confirmation of the topological antiferromagnetic order of the Cr(0 0 1) surface. It is shown that the presence of screw dislocations leads to the formation of domain walls which exhibit a width of 120–170 nm. A long-period modulation of the SP-STS signal was not observed indicating that the bulk spin-density wave is modified at the surface due to symmetry breaking.