Mean velocity behaviour in the near wake of long slender cylinder with a sharp trailing edge at a high Reynolds number

A simple eddy viscosity model is applied to the governing equations to establish the behaviour of the mean velocity in the turbulent axisymmetric near wake. The near wake develops from a long slender cylinder which is kept parallel to the flow and is developing under zero streamwise pressure gradient. The upstream turbulent boundary layer on the body of revolution is fully developed. In the inner layer of the flow downstream of the trailing edge, the turbulent inner layer of the upstream boundary layer grows into the initial logarithmic layer, and as a consequence, the centreline velocity in the near wake is shown to increase logarithmically with streamwise distances for large streamwise distances. The analysis further leads to two regions of the near wake flow (the inner near wake and the outer near wake), similar to that of a fully developed turbulent boundary layer, for which the governing equations have been derived. The matching between these two regions leads to a logarithmic variation in the normal direction. Also shown is the variation of the square of the wake width which varies logarithmically with streamwise distance in the near wake. These features are validated by comparison with available experimental data.     

周期极化LiNbO3脉冲走离效应分析

建立了包含高阶群速色散的OPCPA 数值模拟程序,并以准相位匹配的周期极化的LiNbO3(PPLN)参量放大器为例,在信号光是中心波长1 053 nm,脉宽100 fs的飞秒脉冲经展宽器展宽800 ps的啁啾脉冲,输入能量约0.6 nJ,泵浦光波长527 nm,脉宽3 ns,初始输入泵浦光强300 MW/cmLiNbO2,PPLN晶体的非共线角1.49°,极化周期9.7 μm的条件下, 对OPCPA过程前级的高阶群速色散引起的走离效应对泵浦光、信号光频谱和脉冲形状的影响等具体特性进行了数值模拟。结果表明：在合适的晶体长度下,高阶群速色散对参量转换效率的影响不大,但它对输出信号光的时间波形和频谱有较大影响,会引起脉冲时间形状畸变和频谱漂移。     

线材无模拉拔成形力数学模型研究

采用上限法确定了钨合金线材无模拉拔成形速度场及力能参数物理模型.分析了钨合金线材无模拉拔成形的变形模型、速度场以及力能参数的影响因素及影响规律,无模成形力能参数的影响因素主要有冷热源间距、断面减缩率、变形温度、拉伸速度、冷热源移动速度以及材料种类等,为无模拉拔成形工艺工业化应用奠定基础.     

HL—1M装置器壁硅化对电子速率分布的影响

在欧姆加热和低混杂波电流驱动条件下,利用磺化汞半导体探测器和碘化钠和探测器测出了ＨＬ－１Ｍ装置的Ｘ射线能谱,研究了器壁硅化前后电子速率分布和电子温度变化的特点,给出了Ｘ射线辐射强度与ＬＨＣＤ能量沉积的关系。     

压力陡降及容积加热条件下气—液两相系统瞬态分析

用一种解析与数值相结合的方法预测饱和液体在压力陡降及具有内热源条件下的瞬态响应。     

A New Imaging Method with a Spatial Filter for Incoherent Stream

A new imaging method using an incoherent-type pupil filter: SFINCS (Spatial Filter for INCoherent Stream) is presented. The new filter divides the imaging beam into several incoherent beams at the pupil plane thereby enlarging the depth-of-focus (DOF). The capabilities of SFINCS are studied by simulations and several ways to realize the method are also discussed. The experimental results show that SFINCS has excellent DOF expanding capabilities for a point-image such as a hole pattern in VLSI lithography, and that 1.7 μm DOF is obtained with a 0.30 μm hole pattern by an i-line projection lens with 0.57 NA (numerical aperture).Presented at the International Commission for Optics Topical Meeting, Kyoto, 1994.     

193nm光刻曝光系统的现状及发展

投影曝光工艺是集成电路制造过程中的关键环节,曝光系统的工艺水平已成为衡量微电子制造技术的重要标志。重点介绍了目前193 nm光刻设备曝光系统的发展现状和趋势,以及为提高曝光质量所采用的相关分辨率增强技术;通过分析曝光系统的构成和其中的关键技术,探讨了国内研制相关曝光设备所面临的挑战。     

Effect of local variations of the laminar flame speed on the global finger-flame acceleration scenario

Numerous formulations describing the dynamics and morphology of corrugated flames, including the scenarios of flame acceleration, are based on a “geometrical consideration”, where the wrinkled-to-planar flame velocities ratio, S_w /S_L , is evaluated as the scaled flame surface area, while the entire combustion chemistry is immersed into the planar flame speed S_L , which is assumed to be constant. However, S_L may experience noticeable spatial/temporal variations in practice, in particular, due to pressure/temperature variations as well as non-uniform distribution of the equivalence ratio and/or that of combustible or inert dust impurities. The present work initiates the systematic study of the impact of the local S_L -variations on the global flame evolution scenario. The variations are assumed to be imposed externally, in a manner being a free functional of the formulation. Specifically, the linear, parabolic and hyperbolic spatial S_L -distributions are incorporated into the formulations of finger flame acceleration in pipes, and they are compared to the case of constant S_L . Both two-dimensional channels and cylindrical tubes are considered. The conditions promoting or moderating flame acceleration are identified, and the revisited equations for the flame shape, velocity and acceleration rate are obtained for various S_L -distributions. The theoretical findings are validated by the computational simulations of the reacting flow equations, with agreement between the theory and modelling demonstrated.     

Breakthrough of 2- to 3-μm scale U–Pb zircon dating using Cameca IMS-1280HR SIMS

A zircon U–Pb dating method with a high spatial resolution of 2- to 3-μm was successfully implemented by using Cameca IMS-1280HR SIMS in this study. Homemade cathode and modified intermediate pole were used to improve the intrinsic performance of duoplasmatron ion source. An O⁻ primary beam with intensity of approximately 3 μA and stability of 0.68% over 40 minutes was achieved and could be used continuously for more than 240 hours under high current conditions. Under Gaussian illumination mode, a 2- to 3-μm O⁻ primary beam was obtained with an intensity of approximately 200 pA. Four standard zircons, namely, 91500, Temora, Plešovice, and Qinghu, were dated using the 2- to 3-μm high spatial resolution U–Pb isotopic analysis, yielding U–Pb ages consistent with their recommended values, within errors. Our work shows that zircon U–Pb dating with high accuracy and spatial resolution can be achieved, on the basis of a series of duoplasmatron modification and instrumental optimization.