Shape stability of InAs self-assembled islands on vicinal GaAs(001) substrates

We have grown InAs self-assembled islands on vicinal GaAs( 001) substrates. Atomic force microscopy and photoluminescence studies show that the islands have a clear bimodal size distribution. While most of the small islands whose growth is limited by the width of one multi-atomic step have compact symmetric shapes, a large fraction of the large islands limited by the width of one step plus one terrace have asymmetric shapes which are elongated along the multi-atomic step lines. These results can be attributed to the shape-related energy of the islands at different states of their growth. (C) 2008 Elsevier B. V. All rights reserved.

基于感知的多方向在线手写笔迹文本行提取

提出一种多方向手写笔迹文本行的提取方法.该方法以视觉感知理论为基础,采取自底向上的策略,先将笔画组合成类比字符的笔画块,然后基于这些笔画块建立链接模型,最后采用分支限界搜索算法从链接模型中找出最优行排列.实验结果表明,该方法能有效地提取多方向笔迹行结构,并适用于弯曲文本行的提取.

Low-Microwave Loss Coplanar Waveguides Fabricated on High-Resistivity Silicon Substrate

Three kinds of coplanar waveguides （CPWs） are designed and fabricated on different silicon substrates---common low-resistivity silicon substrate （LRS）, LRS with a 3μm-thick silicon oxide interlayer, and high-resistivity silicon （HRS） substrate. The results show that the microwave loss of a CPW on LRS is too high to be used, but it can be greatly reduced by adding a thick interlayer of silicon oxide between the CPW transmission lines and the LRS.A CPW directly on HRS shows a loss lower than 2dB/cm in the range of 0-26GHz and the process is simple,so HRS is a more suitable CPW substrate.

Aging in EPDM used for outdoor insulation

The effect of accelerated weather aging an ethylene-propylene-diene monomer(EPDM) rubber used for outdoor insulation was studied by surface roughness measurement and X-ray photoelectron spectroscopy(xps). The surface roughness of EPDM rubber changed with aging time. The surface oxygen and aluminum content were found to increase and that of carbon, silicon and nitrogen to decrease with time. The detailed XPS analysis indicated that the concentration of carbon in C-C decreased and that of highly oxidized carbons in C-O, C=O and O=C-O increased with time, which was due to the oxidation of EPDM rubber polymer. The appearance of O=C-O on the surface of EPDM rubber was a signal that EPDM rubber became aged. The aging speed decreased with time. The aging mechanism is discussed also.

输电线巡检机器人越障机理与试验

分析超高压输电线路架空地线上的障碍物类型以及跨越这些障碍的过程。可以发现,巡检机器人采用双臂交替跨越障碍,越障过程简单。但是由于受巡检机器人自身重力偏矩的影响和手臂长度尺寸的限制,当单臂悬架在架空地线上时,导致巡检机器人本体倾斜,另一手臂完成脱线和上线任务变得十分困难,有时甚至造成越障失败。为了解决上述问题,提出质量调节的控制方法。该方法通过调节巡检机器人的质心,使巡检机器人的本体保持水平状态。为了验证质量调节控制方法的正确性,采用Lagrange方法建立巡检机器人动力学模型,通过仿真试验、实验室模拟实际架空地线试验以及超高压实际现场试验说明了提出方法的可行性。

超高压输电线路巡检机器人两种越障定位方法比较

将两种基于传感器信息的导线定位方法的特点和差异进行了分析和对比,得出方法Ⅱ的解算能力强于方法Ⅰ的解算能力,但由于方法Ⅱ的定位精度低于方法Ⅰ的定位精度,因此,选用方法Ⅰ进行野外作业。

输电线路巡检机器人越障控制研究

介绍了超高压输电线路巡检机器人越障控制方法。根据巡检作业任务的要求,采用遥控与局部自主控制相结合的方法,实现了巡检机器人沿线行走及跨越障碍的功能。采用基于单目摄像头定位和视觉伺服的方法,实现了巡检机器人的自主越障控制。实验结果表明,该机器人可沿线行走并自主跨越障碍,从而验证了控制系统设计的有效性与合理性。

超高压输电线路巡检机器人越障控制问题的研究

给出了一种超高压输电线路巡检机器人控制系统的设计与实现方法.根据机器人的作业任务,提出了基于传感器信息、约束信息以及动作反馈信息作为输入,产生式系统作为动作输出的越障控制方式.仿真结果表明此方法对于机器人的越障过程是有效的.

输电线路巡检机器人的机构、建模与实验研究

输电线路巡检机器人是一种特种作业机器人，具有广阔的输电线路巡检的应用背景，该项研究是机器人学研究领域的前沿课题之一，而越障机构又是巡检机器人的关键技术之一。本文在863课题《超高压输电线路巡检机器人》的资助下，系统地研究了输电线路巡检机器人的移动越障机构及其理论建模，目的是分析综合越障巡检机构，研制新型的越障巡检机构；通过结构优化减小能耗提高机器人巡检线路的实用性。 本文首先系统研究了巡检作业的典型工况，建立巡检目标障碍空间的数学模型，为巡检机器人的越障巡检机构研究与越障规划奠定基础。 第二、建立特殊工况下的设计原则，研究越障巡检机构的分析与综合方法。1、提出一种基于障碍空间分析的越障巡检机构综合方法，在分析多种越障机构的越障原理与越障性能的基础上，基于螺旋理论进行越障巡检机构的型综合与数综合，优化越障巡检机构的自由度与构型，并且设计两种新型越障巡检机构。2、用影响系数法，建立机器人运动学模型，探讨越障巡检机构的运动综合。3、提出线上操作的打滑稳定裕度与摆动稳定裕度，且给出相应的判据。在建立静力学与动力学模型、探讨越障巡检机构的动力性能、分析操作手夹持姿态的稳定性的基础上，拓展夹持稳定性量度，提出打滑裕度与摆动裕度。 第三、建立特殊风载荷工况下，结构参数受风向和风压影响的数学模型，得到不同风荷载的风压对尺寸参数的影响；由风载荷影响操作手夹持稳定性，从而影响行走轮包角参数，分析得到相应的行走轮外缘包络包角范围。根据风荷载阻力与尺寸参数的关系，基于最小能量理论采用积分有限元分析，对机器人的重要零件与部件进行了结构参数优化。 第四、根据环境模型制定越障流程；分析越障过程的三个难点：机构平衡、导线辨识与定位可知，导线定位是越障的关键；并就如何定位导线的越障关键问题，提出一种解析定位方法，对比搜索定位方法可知，解析定位方法优于搜索定位方法。 第五、通过实验验证越障原理、越障规划、定位方法、及系统性能等。在调试和考机合格的基础上，分别在实验环境下验证了线上行走巡检原理的有效性和连续越障的可行性；在野外现场实验验证了越障巡检机器人系统的原理可靠性与越障定位的有效性。

Computation of stress intensity factors by the sub-region mixed finite element method of lines

Based on the sub-region generalized variational principle, a sub-region mixed version of the newly-developed semi-analytical 'finite element method of lines' (FEMOL) is proposed in this paper for accurate and efficient computation of stress intensity factors (SIFs) of two-dimensional notches/cracks. The circular regions surrounding notch/crack tips are taken as the complementary energy region in which a number of leading terms of singular solutions for stresses are used, with the sought SIFs being among the unknown coefficients. The rest of the arbitrary domain is taken as the potential energy region in which FEMOL is applied to obtain approximate displacements. A mixed system of ordinary differential equations (ODEs) and algebraic equations is derived via the sub-region generalized variational principle. A singularity removal technique that eliminates the stress parameters from the mixed equation system eventually yields a standard FEMOL ODE system, the solution of which is no longer singular and is simply and efficiently obtained using a standard general-purpose ODE solver. A number of numerical examples, including bi-material notches/cracks in anti-plane and plane elasticity, are given to show the generally excellent performance of the proposed method.

Multi-channel 2-D pattern transfer model based on imaging optics for submarine laser uplink communication

An optical communication scheme of 2-D pattern transfer based on imaging optics for submarine laser uplink communication (SLUC) is suggested. Unlike the methods aiming at avoiding neighboring crosstalk used in traditional multi-channel optical beam transferring, we make full use of the overlapping of each spreading beam other than controlling divergence effect of each beam to avoid interference noise. The apparent parameters have been introduced to simplify theoretical analysis of optical pattern transfer problem involving underwater condition, with the help of which the complex beam propagation inside two kinds of mediums can be easily reduced to brief beam transfer only inside air medium. In this paper, optical transmission path and receiver terminal optics geometry have been described in detail. The link range equation and system uplink performance analysis have also been given. At last, results of a proof-of-concept experiment indicate good feasibility of the proposed SLUC model. © 2007 Elsevier GmbH. All rights reserved.

Design and properties analysis of multi-layer dielectric used in pulse compressor gratings

Used in chirped-pulse amplification system and based on multi-layer thin film stack, pulse compressor gratings (PCG) are etched by ion-beam and holographic techniques. Diffraction efficiency and laser-induced damage threshold rely on the structural parameters of gratings. On the other hand, they depend greatly on the design of multi-layer. A theoretic design is given for dielectric multi-layer, which is exposed at 413.1 nm and used at 1053 nm. The influences of coating design on optical characters are described in detail. The analysis shows that a coating stack of H3L (H2L) (boolean AND) 9H0.5L2.01H meets the specifications of PCG well. And there is good agreement of transmission between experimental and the theoretic design. (c) 2005 Elsevier GmbH. All rights reserved.

Silicon-on-insulating multi-layers for total-dose irradiation hardness

Silicon-on-insulating multi-layer (SOIM) materials were fabricated by co-implantation of oxygen and nitrogen ions with different energies and doses. The multilayer microstructure was investigated by cross-sectional transmission electron microscopy. P-channel metal-oxide-semiconductor (PMOS) transistors and metal-semiconductor-insulator-semiconductor (MSIS) capacitors were produced by these materials. After the irradiated total dose reaches 3 x 10(5) rad (Si), the threshold voltage of the SOIM-based PMOS transistor only shifts 0.07 V, while thin silicon-on-insulating buried-oxide SIMOX-based PMOS transistors have a shift of 1.2V, where SIMOX represents the separated by implanted oxygen. The difference of capacitance of the SOIM-based MSIS capacitors before and after irradiation is less than that of the thin-box SIMOX-based MSIS capacitor. The results suggest that the SOIM materials have a more remarkable irradiation tolerance of total dose effect, compared to the thin-buried-oxide SIMOX materials.

Oscillatory magneto-conductance in quantum waveguides with lateral multi-barrier structures

The magneto-transport properties of a narrow quantum waveguide with lateral multibarrier modulation are investigated theoretically. It is found that the magnetoconductance as a function of Fermi energy or magnetic field exhibits square-wave-like oscillations. In the presence of magnetic field, the edge states are formed near each barrier and the boundaries. Therefore, the number of edge states increases with the number of lateral barriers, leading to the increase of the propagating modes. On the other hand, owing to the tunneling effect a pair of edge states around the barrier region with opposite moving directions may be coupled and formed a circulating localized state, leading to the quenching of the related propagating states. The resulting dispersion relation exhibits oscillation structures superimposed on the bulk Landau levels. These novel conductance characteristics may provide potential applications to the fabrication of new quantum devices.