SU(2)格点规范Monte-Carlo的非禁闭迹象

本文用蒙特卡罗模拟方法讨论了SU(2)纯格点规范场(8³×4点阵)的有限温度问题及其相应的零温问题(8⁴点阵).并计算了系统的能量密度、热容和熵密度.它们的温度行为均表明在T/Λ_L=40—50区域有非禁闭相变发生.     

空气放电非平衡等离子体的模拟计算

 基于空气放电非平衡等离子体动力学,对空气放电进行了数值计算,分析了放电后等离子体中的主要粒子（N₂(v6),N₂(A3),O₂(a1),O和O₃）数密度随起始温度、电子数密度和约化场强的变化趋势。计算结果表明,随着初始温度的升高,空气放电产生的粒子数密度增加。温度为300 K时,放电产生的O原子数密度最大值约为4.90×⁷ cm^-3,而当温度升高到400 K和500 K时,O原子数密度的最大值则相应地增加到5.2×10¹⁰ cm^-3和5.51×10¹⁰ cm^-3。约化场强的影响与温度类似,其中氮气的振动激发态N₂(v6)数密度随约化场强的变化幅度不明显。电子数密度增加,粒子数密度大幅增加,氮分子的激发态N₂(A3)粒子数密度与电子数密度保持严格的线性关系。     

原子核中存在多夸克集团的实验检验

实验上观察到的³He和³H电荷形状因子的类似性,以及³He电荷密度的中空现象是与传统的原子核结构理论的预言相矛盾的.我们认为这个矛盾是原子核中多夸克集团存在的一个明显的征兆.夸克强子混合核模型成功地解释了实验上所观察到的现象.     

2维SU(NC)格点规范理论中夸克真空凝聚

用改进的Wilson夸克格点哈密顿量和变分法研究2维SU(N_C)规范场中夸克真空凝聚〈ψψ〉与夸克质量m_q和Wilson参数r的依赖关系. 结果表明: 对于给定的r, 当N_C=2,3,4,5,6,7,时, 〈ψψ〉_suba/(gN_C^3/2)的值随m_q的增大而减小. 对于较大的N_C(如N_C>3), 当m_q很小时, 〈ψψ〉_suba(gN_C^3/2)对r的依赖性很小, 但随着m_q的增大, 〈ψψ〉_suba/(gN_C^3/2)对r的依赖性增大, 且〈ψψ〉_suba/(gN_C^3/2)的值随r的增大而增大; 特别是, 当m_q→0时, 本文的格点结果与Zhitnitsky的连续理论分析结果(在弱耦合相中)很好地一致, 这意味着本文在m_q≠0时所得到的结果是可靠的.     

金刚石薄膜中二次电子输运的蒙特卡罗模拟

本文通过编写的二维MATLAB蒙特卡罗程序, 对倍增的二次电子在金刚石薄膜中的输运特性进行了初步模拟. 研究表明: 二次电子的迁移率对温度和外加电场的大小很敏感, 在杂质浓度比较低时(<10¹⁷/cm^-3)受杂质浓度的影响不大. 模拟得到的 二次电子的饱和速度为1.88×10⁷ cm/s, 无外加电场时的迁移率为3732 cm² /V.s. 同时, 通过对二次电子束团在金刚石薄膜中的整体输运特性的模拟, 证明了束团电荷密度在应用要求的范围内时, 空间电荷力的影响可以忽略不计.     

Cl/HN3/I2全气相化学激光体系的化学动力学模拟计算

 对Cl/HN₃/I₂产生NCl(a)/I激光的过程进行了化学动力学计算，主要考察了Cl,HN₃和I₂的初始粒子数密度及其配比对小信号增益系数的影响。结果发现,当温度为400K, 初始Cl粒子数密度为1×10¹⁵，1×10¹⁶和1×10¹⁷cm^-3时,小信号增益系数分别达到1.6×10^-4,1.1×10^-3和1.1×10^-2cm^-1，获得最佳小信号增益系数的HN₃和I₂的初始粒子数密度分别为初始Cl粒子数密度的1～2倍和2%～4%。同时，对Cl，HN₃和I₂配比对小信号增益系数和增益持续时间的影响进行了讨论。     

Orion KL超水微波激射辐射的“宁静相”物理特征

利用紫金山天文台青海观测站的13.7m的射电望远镜,观测OrionKL分子云的水微波激射辐射发现这个区的微波激射活动处于”宁静”状态,峰值流量为3×10⁴Jy,大约比爆发相微波激射辐射低两个数量级宁静水微波激射处于完全饱和的辐射过程,微波激射活动区的亮温度为3×10¹³K,氢分子数密度为8×10¹⁴m^-3,微波激射辐射两能级之间的布居反转粒子数密度为5×10⁵(H₂O)m相似文献   

电子束在VO2薄膜中引起的价态、相结构和光学性能的改变

 利用能量为1.7MeV, 注量分别为1.25×10¹³/cm², 1.25×10¹⁴/cm², 1.25×10¹⁵/cm²的电子束辐照VO₂薄膜,采用XPS, XRD等测试手段对电子辐照前后的样品进行分析,并研究了电子辐照对样品相变过程中光透射特性的影响。结果表明电子辐照引起VO₂薄膜中V离子出现价态变化现象,并使薄膜的X射线衍射峰发生变化。电子辐照在样品中产生的这些变化显著改变了VO₂薄膜的热致相变光学特性。     

用电子散射对S核和Si核同位素的进一步研究

用相对论平均场计算了^26,28,30,32S和^22,24,26,28Si的结合能, 均方根半径, 质子皮厚度, 单粒子能级等. 两套参数TM2和NL-SH的计算结果与实验值比较符合. 用平均场与相对论Eikonal近似结合计算出³²S和²⁸Si的形状因子和微分截面的结果, 与实验值也符合得较好. 进一步研究了S和Si的同位素链的基本性质和电子散射, 讨论了电子散射的电荷形状因子对电荷密度变化的敏感性. 电荷形状因子在下一代电子--不稳定原子核对撞机上可以测量, 这将能精确测量不稳定核的电荷半径和电荷密度分布, 本文计算的结果可供未来实验参考.     

4H-SiC肖特基二极管γ射线探测器的模型与分析

 在研究反偏压4H-SiC肖特基二极管作为g射线探测器工作机理的基础上建立了数值模型，模拟了不同偏压和辐照剂量率下探测器的暗电流、工作电流和灵敏度。模拟结果表明:探测器的灵敏度随反向偏压的增加而上升;对于Au/SiC肖特基二极管，有源区掺杂数密度为2.2×10¹⁵ cm^-3时，0 V偏压下探测器的灵敏度为13.9×10^-9 C/Gy，100 V偏压下为24.5×10^-9 C/Gy。计算结果与实验数据符合得较好。     

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.