边缘场发射体的非正交有限差分算法模拟

对边缘场致发射三极管进行了模拟，采用的模型为“鸡尾酒怀”结构。在静电分析中引入了一种新的数值计算方法－非正交曲线坐标系下的有限差分算法。由于取的坐标轴与边界重合，所以该方法能有效地处理任间形状的场致发射体。     

铝基定向碳纳米管复合膜的场发射性能研究

研究了铝基定向碳纳米管复合膜的场发射性能,获得了开启场强为1.15V/μm、最大发射电流密度为1.25mA/cm2的铝基定向碳纳米管薄膜.F-N曲线呈线性关系证明电子发射确为场致发射.     

新型碳纳米管场致发射显示驱动电路的研究

采用碳纳米管作为发射源的场致发射显示器是一种新型的平板显示技术,文章研究一种碳纳米管场致发射显示器件的驱动方法。该方法灰度等级实现方法简单,大大降低了扫描电极频率,有效地解决了高压和高速度之间的矛盾,能够满足用丝网印刷制备碳纳米管阴极的场致发射显示器件驱动电压高的要求。     

蒸镀碳化铪(HfC)对单根碳纳米管场致发射性能的改善

采用双向电泳法,在原子力显微镜探针尖端组装了单根碳纳米管,在真空环境下对比测量了单根碳纳米管蒸镀低逸出功材料HfC前后场致发射电流曲线和电流噪声的特点。证明了HfC蒸镀在碳纳米管上能够显著降低发射体的逸出功,减少电流噪声,并且观察到单根碳纳米管蒸镀了HfC后7μA左右的稳定电流发射。通过分析电流噪声,认为碳纳米管场致发射噪声主要来自吸附气体的频繁吸附和脱附。在低电流下,空间电离的离子轰击发射体表面,对吸附状态的影响占主导地位。当单根碳纳米管的场致发射电流超过1μA量级以后,碳纳米管表面温度快速升高,温度对气体吸附的影响占主导地位,吸附的气体分子逐渐脱附后,电流噪声开始降低。     

场致发射阴极材料的研究与进展

场致发射显示器是一种新型的具有竞争力的平板显示器,场致发射阴极是场致发射显示器的重要组成部分.介绍了各种场致发射阴极材料及其特性,分析了场致发射机理及各种场致发射阴极材料最新进展,并简单讨论了场致发射材料国内外开发应用研究现状及差距.     

场致发射阴极材料的研究进展

场致发射显示是一种具有良好应用前景的新型显示技术,场致发射阴极材料是场致发射显示器的核心内容.综述了近年来场致发射材料的研发热点,对金属、硅、金刚石及类金刚石薄膜、GaAs和CaN等场致发射材料的研究做了简要的归纳,同时介绍了碳纳米管、表面传导型场致发射材料及采用定向凝固技术制备的Si-TaSi2共晶自生复合场致发射材料等新型场致发射材料的研究进展,并展望了场致发射材料的研究及应用前景.     

常开型后栅极场致发射显示板工作特性的研究

常开型后栅极场致发射显示板是一种新型的场致发射器件.它直接利用阳极使阴极产生场致电子发射,而通过埋在阴极之下的栅极上施加负电压来阻止阴极产生场致电子发射来调制显示所需的图像.为了研究该场致发射显示板的阴极发射特性,本文采用有限元法对场致发射区域内的电场分布进行了模拟计算,用Fowler-Nordheim(F-N)公式计算了阴极表面的发射情况.并研究了阳极电压、阴极电压、阴调距、阴极宽度和阴极厚度等参数的改变对阴极发射特性和栅极调制能力的影响.计算结果显示阴极发射特性和栅极调制能力与上述电参数和结构参数关系密切,从而为优化设计这种显示器件提供了方向.     

CVD法和丝印法制作的碳纳米管场致发射冷阴极的研究

本文研究了丝网印刷法和CVD生长法制备的碳纳米管冷阴极的场致发射性能.结果表明,在没有模板的情况下,通过CVD生长的碳纳米管的直径与催化剂颗粒的直径有关,随催化剂颗粒的直径变化而变化,生长方向是随机的,但大电流发射稳定性较差;用丝网印刷方法制作的碳纳米管致发射冷阴极,场发射电流发射较稳定.     

无氧铜基金刚石薄膜场致发射特性研究

采用微波等离子体方法在铜片上沉积了多晶金刚石薄膜,用该薄膜制成的场致发射体的开启电压较低,发射电流密度较高。利用自制的场致发射阵列阴极高真空测试台测试了1～100mA／cm     

场致发射体的局域功函数研究

实际场致发射体表面不可能绝对光滑 ,而具有原子尺度的微小凸起会导致发射电流大大增加。基于发射电流主要来自于原子尺度微小凸起的假设 ,提出了局域半球镜像电荷模型 ,研究了场致发射功函数的降低 ,发现微小凸起处场致发射的局域功函数会降低而场增强因子将增大。将它代入F N公式计算了一个典型的单尖Spindt阴极的发射电流 ,所得结果与实验符合。在只考虑Nottingham效应的情况下 ,计算了一些材料Spindt型阴极每微尖的最大稳定发射电流     

基于坐标反推法的偏心轮轴升程测量

采用极坐标测量仪、三坐标测量机等通用型测量仪对偏心轮轴进行坐标测量,其主要配备的都是球形测头,无法直接测得偏心轮轴从动件所对应的升程及升程误差。针对此问题提出了一种基于坐标反推法的偏心轮轴升程测量方法。详细介绍了偏心轮轴的结构、对应不同测头的理论升程计算方法。推导了偏心轮轴表面轮廓点坐标反推平面测头、滚子测头和刀口测头的升程模型公式,利用最小二乘圆圆心和回转中心点确定了偏心圆轮的“桃尖”位置。在一台极坐标测量仪上进行了偏心轮轴测量实验,实验结果表明：基于坐标反推法的升程测量方法是有效的,对应3种测头的坐标反推升程与理论升程的差值分别为0.87, 0.90及0.90μm,基于坐标反推的升程能够更准确反映从动件实际运动规律。     

Integral analysis of a magnetic field for an arbitrary geometry coil with rectangular cross section

The integral method can effectively analyze magnetic fields, but the traditional integral method can analyze only coils with regular geometries. Therefore, a new integral method was developed to calculate the three-dimensional (3-D) magnetic field created by an arbitrary geometry coil with a rectangular cross section using the local coordinate method and a 3-D coordinate transformation. However, when the field points are on the surface of the coil or the basic segment is the right angle trapezoidal prism, singularities occur that make the numerical analysis of the magnetic field more difficult. Thus, we present here some mathematical methods to eliminate the singularities to allow accurate numerical analysis of the magnetic field. We validate the integral method by comparing it with the analytical solutions for regular geometry coils.     

一种浮空器气囊体积测量装置的现场校准方法探讨

介绍一种浮空器气囊体积测量装置的现场校准方法,通过设定现场校准区域,构建地面控制点的局部三维坐标;在被测对象侧边的6个地面控制点设立测站,用激光全站仪和棱镜组件按照极坐标法观察得到被测对象侧边精密标定杆上所有准校点的局部三维坐标,建立校准参考坐标系,构建完整的现场校准场。测量装置对在校准参考坐标系中的精密标定杆上校准点进行拍摄获得图片,解算得到测量装置的每个相机的外方位元素,得到其位置和姿态,完成校准工作。本文提出的现场校准方法解决了测量装置在任意场景下浮空器囊体体积测量的应用问题和测量装置使用中需要搬动情况下的校准问题。     

有限元新型自然坐标方法研究进展

网格畸变敏感问题一直是当前有限元法难以解决的问题,而新型自然坐标方法的诞生可以在一定程度上对解决这个难题有所帮助。该文介绍了有限元新型自然坐标方法研究的新近进展。包括第一类四边形面积坐标及其应用(单元构造,解析刚度矩阵的建立,以及在几何非线性问题中的应用等);第二类四边形面积坐标及其应用;六面体体积坐标及其应用。数值算例表明:无论网格如何扭曲畸变,这些基于新型自然坐标方法的有限元模型仍然保持高精度,对网格畸变不敏感。这显示了新型自然坐标方法是构造高性能单元模型的有效工具。     

Identification of the Parameters of a Nested Cylindrical Heat Source under Stationary Self‐Heating of a Raw Material Mass of the Same Form

This paper describes a computer method for determining the coordinate of the center, the heatrelease power, and the sizes of a homogeneous internal cylindrical heat source in a stationary axially symmetric temperature field arising under selfheating of a plant raw material.     

基于坐标极差估算高炮立靶密集度的方法

本文提出了一种在靶场进行高炮自动机射击试验时的立靶密集度简易估算方法．用随机技术在计算机上进行立靶密集度试验模拟,得出密集度估算的理论依据．通过统计靶场射击试验数据,归纳出高炮自动机立靶密集度与其弹丸着靶坐标极差的经验公式．研究结果表明,高炮自动机200m立靶密集度与弹丸着靶坐标极差之比取值范围在0．9～1．5之间,其平均值为1．1左右．密集度试验时,用比例系数1．1分别与一组弹着靶方位和高低坐标极差相乘,就可以快速地估算出方位和高低立靶密集度．     

Modified linear estimation method for generating multi-dimensional multi-variate Gaussian field in modelling material properties

Although a number of methods have been developed to generate random fields, it remains a challenge to efficiently generate a large, multi-dimensional, multi-variate property field. For such problems, the widely used spectral representation method tends to require relatively longer computing time. In this paper, a modified linear estimation method is proposed, which involves mapping the linearly estimated field through a series of randomized translations and rotations from one realization to the next. These randomized translations and rotations enable the simulated property field to be stationary. The autocorrelation function of the simulated fields can be approximately described by a squared exponential function. The algorithms of the proposed method in both the rectangular and cylindrical polar coordinate systems are demonstrated and the results validated by Monte-Carlo simulations. Comparisons between the proposed method and spectral representation method show that the results from both methods are in good agreement, as long as the cut-off wave numbers of the spectral representation method are sufficiently large. However, the proposed method requires much less computational time than the spectral representation method. This makes it potentially useful for generating large multi-dimensional fields in random finite element analysis. Applications of the proposed method are exemplified in both rectangular and cylindrical polar coordinate systems.     

柱坐标系下浅海传播声场时域有限差分预报方法

直角坐标系下的时域有限差分方法在水声传播仿真时由于计算量太大而较少应用。文章利用时域有限差分方法推导了柱坐标系下的声波方程的近似表达式,结合复频移完全匹配层建立浅海声传播模型,在减少计算量的同时准确预报了传播信号声压的时域波形、传播声场的时空演变过程以及频域传播损失曲线。在柱坐标系下使用时域有限差分方法仿真Pekeris传播环境声场并与简正波和波数积分模型进行对比,分析了时域有限差分水声传播模型的适用范围。结果表明,时域有限差分方法仿真浅海中近程传播声场精度较高。模型的稳定性与时间和空间网格大小有关,声源频率越高,空间和时间网格划分越小,计算量越大。数值离散带来的频散误差累积会导致远场传播声场计算不准确,因此时域有限差分水声传播模型更适用于低频中近程声场计算。     

Multipole analysis of biomagnetic signals from the human leg

Computationally tractable solutions of the "inverse problem," the calculation of source currents from magnetic field data, are an essential component of biomagnetic studies. A multipole analysis suitable for any system that may be modeled as having all currents oriented along a given axis but not depending on the value of position coordinate on that axis is described. The lowest nonvanishing term is dipolar, and we specify a "best fit" criterion that estimates from data the dipole's magnitude and orientation together with its location in the transverse plane. The dipolar term is seen to give good fits to fields measured outside the normal relaxed lower human leg, even though the field data varies with position along the leg-axis. Reasons for this success are considered. The analysis is not specific to biomagnetic systems and may be useful in electrical engineering or geophysical problems.     

Reformulation of the coordinate transformation method through the concept of adaptive spatial resolution. Application to trapezoidal gratings

We reformulate the coordinate transformation method for profiles represented by parametric equations. Numerically, the eigenvalue problem is solved by expanding both the electromagnetic field and the periodic coefficients of Maxwell's equations into Fourier series. For trapezoidal gratings, it is shown that the convergence of the method is closely related to the representation of the profile. A proper choice of the representation permits handling profiles that previously had been out of reach owing to their sharp edges. From a practical point of view, we are now able to analyze gratings with two vertical facets by using the coordinate transformation method.