Laser-induced changes in titanium by femtosecond,picosecond and millisecond laser ablation

In order to realize the qualitative control of the laser-induced changes trend and the quantitative control of the laser-induced changes range in titanium upon laser irradiation with different pulse duration, comparative ablation experiments by femtosecond, picosecond and millisecond pulsed lasers were carried out on titanium in this study. Then the final surface morphology, aspect ratio, chemical composition and microstructural state of the ablated titanium were analyzed by laser scanning confocal microscopy, X-ray photoelectron spectroscopy and transmission electron microscopy, respectively. The dependency of the morphology, size, composition and microstructure of ablated titanium on laser pulse duration variation were emphatically discussed. It is found that, as the laser pulse duration increases from femtosecond to millisecond scale, surface morphology quality of ablated titanium gets worse, aspect ratio of microgroove decreases, proportion of titanium oxides in final ablation products becomes larger and the microstructural state of ablated titanium has a higher amorphization degree, which can be attributed to the decreased laser intensity per pulse and enhanced heat conduction effect in titanium with the pulse duration increasing.     

基于STC89C51的新型液氮低温微创冷冻控制系统设计

设计了一种新型液氮低温微创冷冻控制系统,详述了系统的控制原理及各功能模块的实现.采用热流平衡原理、PID技术与STC89C51单片机及外围控制电路对冷冻冻结面范围、液氮瓶压力及冷刀刀头温度进行实时控制和显示.应用结果表明:该系统运行稳定,可靠性高,操作简单.     

激光照明水下目标距离选通成像系统的研制

基于水下目标探测的应用需求,研制开发了一套激光水下距离选通成像系统。系统采用波长532 nm、最大单脉冲能量400 mJ的Nd:YAG脉冲激光器作为照明光源,采用最小选通门宽3 ns、像元10241024的ICCD相机作为门选通器件和图像记录器件,利用DG535型数字脉冲发生器作为精确延时和同步控制器件实现激光脉冲和ICCD相机选通门的同步以实现距离选通功能。利用该系统在某水库进行了水下目标探测实验,实验结果表明,该系统可在6.5倍的衰减长度上识别目标,在8倍衰减长度上发现目标。     

光子晶体光纤传输特性的研究

应用平面波展开法研究光子晶体光纤的传输特性,数值模拟得到了光子晶体光纤传播模式图,以及光子晶体光纤的频率和色散关系,研究结果为光子晶体光纤器件的开发提供了理论依据。     

重金属铅离子胁迫下玉米叶片光谱弱差信息的DSAT甄别模型

光谱间微弱信息测度是当今高光谱遥感研究难点之一,传统光谱测度方法难以区分光谱信息的微弱差异。研究设计了不同浓度的铅(Pb)污染实验,并测量了不同浓度铅离子(Pb2+)胁迫下玉米叶片的高光谱反射率、叶绿素含量及Pb2+含量,但是从所测结果得出,不同浓度Pb2+胁迫下的光谱相似性相关系数均达到0.999,难以区分不同浓度Pb2+胁迫引发的光谱间微弱信息差异和污染程度。针对这一情况,基于光谱微分处理、正切函数增强、光谱角量度与波谱分段检测等,提出了一种新型的相似光谱测度方法,即微分光谱角正切(derivative spectral angle tangent,DSAT)法。为了验证DSAT在区分相关系数达0.99以上相似光谱的可行性和有效性,将DSAT用于不同浓度Pb2+胁迫玉米叶片的整体波形与光谱区间子波形的信息差异性度量与检测。实验结果得到,波形差异信息与玉米叶片中叶绿素相对浓度与Pb2+含量显著相关。进而也证明DSAT法在甄别较高相似性光谱间差异上具有更好的实用性和优越性。     

Local discrimination scheme for some unitary operations

It has been shown that for two different multipartite unitary operations U_1 and U_2, when tr(U_1~?U_2) = 0, they can always be perfectly distinguished by local operations and classical communication in the single-run scenario. However, how to find the detailed scheme to complete the local discrimination is still a fascinating problem. In this paper, aiming at some U_1 and U_2 acting on the bipartite and tripartite space respectively, especially for U_1~?U_2 locally unitary equivalent to the high dimensional X-type hermitian unitary matrix V with trV = 0, we put forward the explicit local distinguishing schemes in the single-run scenario.     

一种新型无人机机载计算机同步策略研究

机载计算机是无人机的核心部件,其可靠性高低直接决定了系统的安全。余度技术作为机载计算机可靠性设计的一项重要手段,对提高系统的应变能力,实现故障隐蔽以消除故障,改善系统性能有十分重要的作用。但是在余度技术中不同通道之间会存在一定的时钟误差,如果不进行处理将会使其无法达到无缝切换,从而影响系统的安全。在对机载计算机内部通道间不同步的原因进行详细分析的基础上,提出了一种软、硬件相结合的同步算法,并以三余度机载计算机为例进行了实际测试。测试结果证明该策略实现简单、同步效果好,异步度完全满足系统要求且付出的软、硬件代价小,显著提高了全系统的可靠性及可维护性。     

双重网络嵌入对公司IPO后市场表现的影响研究

将社会网络嵌入理论从单一网络拓展至双重网络,分析上市公司同时嵌入风险投资网络和承销商网络对公司IPO上市后市场表现的影响。利用2004～2017年有风险投资支持的IPO公司数据,实证检验结果表明：(1)单独嵌入风险投资网络中心位置、单独嵌入承销商网络中心位置,均会提高公司IPO后市场表现;(2)同时嵌入风险投资网络中心位置和承销商网络中心位置,对公司IPO后短期市场表现的正向影响会相互替代;(3)同时嵌入风险投资网络中心位置和承销商网络中心位置,对公司IPO后长期市场表现的正向影响会互相补充。     

Two-Phase Image Segmentation by Nonconvex Nonsmooth Models with Convergent Alternating Minimization Algorithms

Two-phase image segmentation is a fundamental task to partition an image into foreground and background. In this paper, two types of nonconvex and nonsmooth regularization models are proposed for basic two-phase segmentation. They extend the convex regularization on the characteristic function on the image domain to the nonconvex case, which are able to better obtain piecewise constant regions with neat boundaries. By analyzing the proposed non-Lipschitz model, we combine the proximal alternating minimization framework with support shrinkage and linearization strategies to design our algorithm. This leads to two alternating strongly convex subproblems which can be easily solved. Similarly, we present an algorithm without support shrinkage operation for the nonconvex Lipschitz case. Using the Kurdyka-Łojasiewicz property of the objective function, we prove that the limit point of the generated sequence is a critical point of the original nonconvex nonsmooth problem. Numerical experiments and comparisons illustrate the effectiveness of our method in two-phase image segmentation.     

旋转对称非球面自动加工控制算法研究

介绍了计算机控制光学表面成型（ＣＣＯＳ） 技术的基本原理,对双旋转磨头的去除函数进行研究,研究了不同形状的磨头的去除函数特性,并在多次实验的基础上得到了最优的加工参数,在去除函数的基础上提出了模板函数的概念及算法。根据加工旋转对称非球面光学表面的特点,结合模板函数提出了一种基于同心圆磨头运动轨迹的控制算法。运用该算法对神光Ⅲ号打靶非球面透镜的一种工艺试样（ Φ３００ｍ ｍ ,Ｆ５－９ ,最大非球面度为４６μｍ） 进行自动加工,面型精度达到１λ（ＲＭＳ,λ＝ ６３２－８ｎｍ）,取得了满意的结果。