Zr-Al-Ni-Cu(Nb,Ti)大块非晶玻璃转变的动力学性质

以Zr-Al-Ni-Cu (Nb,Ti)大块非晶合金差示扫描量热分析实验为基础,利用Lasocka方程、Kissinger方程及Vogel-Fulcher-Tamman(VFT)方程对其玻璃转变的动力学性质从不同方面进行了研究.分析结果表明：玻璃转变表观激活能越小,则晶化转变激活能越大,表现出相反的难易程度,且玻璃转变表观激活能数值远较传统非晶要小,验证了大块非晶合金独特的结构特点及玻璃形成能力(GFA)强的原因.利用VFT方程对玻璃转变弛豫时间与升温速度的VFT曲线 进行了拟合,所算得的玻璃脆性参数m均在30左右,反映了Zr-Al-Ni-Cu (Nb,Ti)非晶合金强 的脆性属性.玻璃转变处Lasocka关系的B值、原子表观激活能及玻璃脆性参数均反映了相同的GFA大小趋势,从不同方面进一步揭示了非晶合金玻璃转变区间的动力学行为与GFA之 间的密切联系,可作为判断非晶合金GFA强弱的重要依据. 关键词： 玻璃转变 玻璃形成能力 表观激活能 玻璃脆性参数     

压力对Zr46.75Ti8.25 Cu7.5Ni10Be27.5大块非晶合金玻璃转变和晶化动力学的影响

利用X射线衍射和差示扫描量热分析研究了高温高压下Zr46.75Ti8.25Cu7.5Ni10Be27.5大块非晶合金的玻璃转变和晶化行为,结果发现压力降低了该大块非晶合金中的自由体积、热焓和晶化激活能.     

Nb添加对Cu-Zr非晶合金玻璃转变和晶化动力学的影响

采用铜模吸铸法制备出直径为2 mm的Cu_50.3Zr_49.7-xNb_x(x=0,2)大块非晶合金，利用示差扫描量热分析(DSC)研究了2at%Nb元素添加对Cu-Zr非晶合金玻璃转变动力学和晶化动力学的影响，发现含Nb合金具有较低的脆性指数，和较高的晶化激活能.这表明微量Nb的添加提高了该二元Cu基非晶合金过冷金属液相的热稳定性，从而有利于其非晶合金的形成. 关键词： Cu-Zr非晶合金 Nb添加 玻璃转变动力学 晶化动力学     

大块金属玻璃Zr41Ti14Cu12.5Ni10Be22.5的流变行为研究

采用静态拉伸方法在连续升温条件下动态地测量了大块金属玻璃Zr41 Ti14Cu12.5Ni10Be225(Vitl)的黏度随温度的变化关系.在应变速率与温度的关系曲线中,观测到了与玻璃转变和晶化过程相联系的多个应变速率峰.在玻璃转变温度Tg以上,大块金属玻璃Zr41Ti14Cu125Ni10Be225的过冷液体呈现Newton流体特征,其黏度与温度的关系符合Vogel-Fulcher-Tammann(VFT)关系式,拟合得到脆度D*=36,VFT温度T0=319K,脆度参数m=30,这说明Zr41 Ti14Cu12.5Ni10Be225的过冷液体是一种类似于硅酸盐类的"强"液体.在玻璃转变温度Tg以下,粘度与温度的关系偏离VFT关系,从结构弛豫的观点出发,借助金属玻璃的自由体积模型对其进行了分析和讨论.     

注入Mo 在Zr57Nb5Cu15.4Ni12.6Al10非晶合金中的扩散

通过二次离子质谱仪(SIMS)研究了Mo在Zr57Nb5Cu15.4Ni12.6Al10非晶合金中的扩散,并计算出其扩散激活能Q和前置系数D0分别为1.95 eV和1.13×10-5 m2s-1.根据Stokes-Einstern关系式研究了玻璃转变温度以下593-673 K之间Zr57Nb5Cu15.4Ni12.6Al10非晶合金的黏滞特性,得到的黏滞系数从593 K的1.07×1010Poise降到673 K的1.42×108 Poise.     

大块金属玻璃Zr41Ti14Cu12.5Ni10Be22.5的流变行为研究

采用静态拉伸方法在连续升温条件下动态地测量了大块金属玻璃Zr41Ti14Cu12.5Ni10Be22.5（Vit1）的黏度随温度的变化关系.在应变速率与温度的关系曲线中，观测到了与玻璃转变和晶化过程相联系的多个应变速率峰.在玻璃转变温度Tg以上，大块金属玻璃Zr41Ti14Cu12.5Ni10Be22.5的过冷液体呈现Newton流体特征，其黏度与温度的关系符合Vogel Fulcher-Tammann (VFT)关系式，拟合得到脆度D*＝36，VFT温度T0＝319K，脆度参数m＝30，这说明Zr41T 关键词： 大块金属玻璃 应变速率 剪切黏度 自由体积     

非晶合金结构演变影响玻璃形成能力的分子动力学研究

通过分子动力学方法模拟了Ti75Al25、Ni50Zr50和Cu50Zr50非晶合金的玻璃转变过程, 得到并分析了平均原子体积和双体分布函数等结构参数, 并应用Voronoi多面体指数分析法统计了玻璃转变过程中二十面体及类二十面体团簇的数量, 通过分析团簇在玻璃转变过程中种类和数量的涨落趋势, 研究了非晶原子由短程序连接至中程序再至长程无序的动力学演化过程. 结果表明, 非晶合金的玻璃形成能力以及塑性变形能力与动力学演化过程中Voronoi团簇的种类和数量密切相关. 在玻璃转变过程中局部五次对称性高的团簇倾向于连接在一起形成链,从而密排整个空间, 降低系统的动力学行为从而提高玻璃形成能力. 塑性形变倾向于发生在局部五次对称性较低的区域. 在玻璃转变温度附近团簇种类和数量的突变反映出非晶合金的自组织临界行为, 蕴含着丰富的非线性动力学现象.     

高压下Co在Zr46.755Ti8.25Cu7.5Ni10Be27.5大块金属玻璃过冷液相区中的扩散

通过离子注入结合二次离子质谱分析方法,研究了高压下Co在Zr46.75Ti8.25Cu7.5Ni1oBe27.5大块金属玻璃过冷液相区中的扩散行为.在603 K时,Co在Zr46.75Ti8.25Cu7.5Ni10Be27.5大块金属玻璃中的扩散系数随压力的增大而增大,其扩散激活体积ΔV*=-1.236Ω,Ω是合金的平均原子体积.结果表明,在热平衡状态下Co在Zr46.75Ti8.25Cu7.5Ni10Be27.5大块金属玻璃中的扩散是通过间隙机理进行的.     

高压下Co在Zr46．75Ti8．25Cu7．5Ni10Be27．5大块金属玻璃过冷液相区中的扩散

通过离子注入结合二次离子质谱分析方法 ,研究了高压下Co在Zr4 6 .75Ti8.2 5Cu7.5Ni1 0 Be2 7.5大块金属玻璃过冷液相区中的扩散行为 .在 6 0 3K时 ,Co在Zr4 6 .75Ti8.2 5Cu7.5Ni1 0 Be2 7.5大块金属玻璃中的扩散系数随压力的增大而增大 ,其扩散激活体积ΔV =- 1.2 36Ω ,Ω是合金的平均原子体积 .结果表明 ,在热平衡状态下Co在Zr4 6 .75Ti8.2 5Cu7.5Ni1 0Be2 7.5大块金属玻璃中的扩散是通过间隙机理进行的     

块体非晶合金 Zr55Cu30Al10Ni5 结构弛豫的研究

应用同步辐射小角x射线散射和差示扫描量热分析对块体非晶合金Zr55Cu30Al10Ni5结构弛豫进行了研究.实验结果表明:经340℃、不同时间退火后的非晶内部的电子密度涨落随退火时间的延长先增大而后减小;玻璃转变温度附近焓弛豫峰的表观激活能则随退火时间的延长先减小而后增大.结果反映了随退火时间的延长,块体非晶合金内部类液体区不断减少及类固体区不断增加的过程.     

Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

A multi-conjugate adaptive optics （MCAO） can offer a possibility of widening field of view （FOV） characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle＇s expressions of two deformable mirrors （DMs） MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.     

Quick single-photon detector with many avalanche photo diodes working on the time division

Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.     

Characterization of PolyA and PolyC mismatches by Raman spectroscopy

A.C mismatches are studied by Raman spectral characterization of PolyA, PolyC, and their equimolar complex in solution of 0.14 mol/L Na ,pH7.0.Experimental results show that A·C mismatches occur to be A/B (mainly A) conformers, and unlike Watson-Crick base pairing, this kind of mismatches is stabilized by only one hydrogen bond involving cytosine N4H2 and adenine N7.The formation of A·C complex makes the base stacking interactions much stronger, and conformation of the backbone more ordered, which leads to obvious Raman hypochromic effect with some shifts in corresponding bands.     

Improvement of four-wave mixing-based wavelength conversion efficiency in dispersion shifted fiber by 40-GHz clock pumping

40-GHz clock modulated signal as a pump to improve the efficiency of four-wave mixing (FWM)-based wavelength conversion in a 26.5-km dispersion shifted fiber (DSF) is investigated. The experimental results demonstrate that the conjugated FWM component has higher intensity with the clock pumping than that with the continuous-wave (CW) light pumping. The improvement of FWM-based wavelength conversion efficiency is negligible when the pump power is less than Brillouin threshold. But when the pump power is greater than Brillouin threshold, the improvement becomes significant and increases with the increment of pump power. The improvement can increase up to 9 dB if pump power reaches 17 dBm.     

Speech enhancement by array crosstalk resistant ANC and spectrum subtraction

Microphone array-based speech enhancement has great importance for speech communications and speech recognition. To reduce the aperture of the microphone array and to increase the effect of the speech enhancement will greatly broaden the application areas of the microphone array. An array crosstalk resistant adaptive noise cancellation method is therefore presented. And then an improved spectral subtraction algorithm is further cascaded to obtain better enhancement results. Theoretic analysis and experiments indicate that the proposed scheme needs only a very small microphone array while it simultaneously achieves a higher SNR improvement. Besides, the proposed scheme can be used in many noisy environments and is easy for real-time implementation.     

Multi-pulse operation of a Kerr-lens mode-locked femtosecond laser

Our experimental results show that the presence of a proper amount of negative group velocity dispersion is essential to multi-pulse operation of a Kerr-lens mode-locked femtosecond laser. We demonstrate that the pulse separations and the number of pulses contained within a cavity round trip are strongly dependent on the initial perturbations. The results allow us to get a better understanding on the influences of the convoluted self-phase modulation and intra-cavity dispersions on the stable multi-pulse oscillation in a Kerr-lens mode-locked femtosecond laser.     

Propagation of Helmholtz-Gauss beams in weak turbulent atmosphere

Based on the Rytov approximation of light propagation in weak turbulent atmosphere,the closed-form expressions of field and average irradiance of each one of the four fundamental families of Helmholtz-Gauss (HzG)beams:cosine-Gauss beams,stationary Mathieu-Gauss beams,stationary parabolic-Gauss beams,and Bessel-Gauss beams,which are propagating in weak turbulent atmosphere,are obtained.The results show that the field and average irradiance can be written as the product of four factors:complex amplitude depending on the z-coordinate only,a Ganssian beam.a factor of complex phase perturbation induced by atmospheric turbulence,and a complex scaled version of the transverse shape of the non-diffracting beam.The effect of weak atmospheric turbulence on irradiance distribution of the HzG beam can be ignored.     

An effective method for reducing speckle noise in digital holography

An effective method for reducing the speckle noise in digital holography is proposed in this paper.Different from the methods based on classical filtering technique,it utilizes the multiple holograms which are generated by rotating the illuminating light continuously.The intensity images reconstructed by a series of holograms generated by rotating the illuminating light possess different speckle patterns.Hence by properly averaging the reconstructed intensity fields,the speckle noises can be reduced greatly.Experimental results show that the proposed method is simple and effective to reduce speckle noise in digital holography.     

Influence of purity of HfO2 on reflectance of ultraviolet multilayer

The impurities in two kinds of HfO2 materials and in their corresponding single layer thin films were determined through glow discharge mass spectrum technology and secondary ion mass spectrometry(SIMS) equipment respectively.It was found that ZrO2 was the main impurity in the two kinds of HfO2 either in the original HfO2 materials or in the electron beam deposited films.In addition,the difference of Zr content in the two kinds of HfO2 single laver films was much laxger than that of the other impurities such as Ti and Fe.which showed that it was just ZrO2 that made the difference between the optical performance of the film products including the two kinds of HfO2.With these two kinds of HfO2 and the same kind of SiO2.we deposited HfO2/SiO2 multilayer reflective coatings at the wavelength of 266 nm.Experimental results showed that the reflectances of these two mirrors were about 99.85% and 99.15% respectively,which agreed well with the designed results what were based on the optical constants obtained from the corresponding single layer thin films.