环四甲撑四硝胺(HMX)结构和性质的DFT研究

用密度泛函理论 (DFT)B3LYP方法 ,取 6 - 31G 基组 ,求得环四甲撑四硝胺分子的几何构型、电子结构、IR谱和 2 98～ 12 0 0K的热力学性质 .全优化几何构型和电子结构均具有Ci 对称性 .在相邻原子之间以N -NO2 键的Mulliken集居数最小 ,表明其间电子分布较少 ,预示其为热解和起爆的引发键 .IR谱与实验结果良好相符     

AunXm(n+m=4,X=Cu，Al，Y)混合小团簇的结构和稳定性研究

采用基于密度泛函理论的B3LYP方法，优化了Au_nX_m(n+m=4,X=Cu，A l，Y)二元混合团簇的稳定结构.计算了稳定结构的平均结合能、电离势、电子亲和势、最高占据轨道能级和最低空轨道能级及二者间的能隙.结合Mulliken集居数分析研究了二元混合团簇稳定存在的规律，得出掺杂可以增强团簇稳定性的结论. 关键词： 混合团簇 结合能 能隙 分子轨道集居数     

AunXm(n+m=4,X=Cu,Al,Y)混合小团簇的结构和稳定性研究

采用基于密度泛函理论的B3LYP方法,优化了AunXm(n+m=4,X=Cu,Al,Y)二元混合团簇的稳定结构.计算了稳定结构的平均结合能、电离势、电子亲和势、最高占据轨道能级和最低空轨道能级及二者间的能隙.结合Mulliken集居数分析研究了二元混合团簇稳定存在的规律,得出掺杂可以增强团簇稳定性的结论.     

稀土元素掺杂对VH2解氢性能的影响

采用密度泛函理论(DFT)的第一性原理的平面波超软赝势方法,研究了La, Ce和Pr掺杂对VH₂的 电子结构和解氢性能的影响.计算结果显示La, Ce和Pr掺杂VH₂后晶体模型的费米能级E_f处 电子浓度N (E_f)的增加,表明体系结构稳定性减弱,解氢能力增强; 电子密度计算也显示V-H之间相互作用减弱,解氢能力增强;同时Mulliken布居数计算结果还显示掺杂以后 解氢能力增强与V-d轨道Mulliken布居数减少, V-s轨道Mulliken布居数增加有关.     

α-BeH_2电子结构与光学性质的第一性原理研究

基于密度泛函理论,采用赝势平面波方法研究了α-BeH2的结构、电子和光学性质.基态下,α-BeH2晶格常数a和体积弹性模量B0计算值与实验值及其它理论值一致.根据能带理论研究了α-BeH2基态下的能带结构、总态密度(DOS)和分波态密度(PDOS).经过分析发现α-BeH2为直接能隙半导体材料,能隙为5.44eV,与文献相比,本文计算的结果偏低,这主要是利用第一性原理中的局域密度近似(LAD)或广义梯度近似(GGA)交换关联能函数计算材料的带隙宽度或者磁耦合的理论结果均会偏低.通过对基态α-BeH2的Mulliken电荷分布和集居数的分析发现:α-BeH2属于离子键和共价键所形成的混合键化合物;α-BeH2的电荷总数分别来源于H1s轨道,Be2s和2p轨道.同时本文还分析研究了α-BeH2的光学介电函数、吸收系数、复折射率、反射系数和能量损失等光学性质.     

丁酮异构化的势能面分析

用密度泛函理论计算研究了丁酮异构化的势能面. 通过IRC方法确定了丁酮异构化的6个主要反应路径,相应的产物分别为1-丁烯-2-醇、2-丁烯-2-醇、丁醛或1-丁烯-1-醇、丙烯基甲醚、甲基烯丙基醚和乙烯基乙醚. 其中3个路径经过环氧丁烷,表明环氧丁烷是丁酮异构化过程中重要的中间产物. 计算得到的反应物和产物的垂直电离能与现有的实验值吻合得很好. 通过过渡态的相对能量和高能垒的数目比较,认为最可行的丁酮异构化反应路径是丁酮→1-丁烯-2-醇→2-丁烯-2-醇.     

石墨表面吸附钾系统电子性质的理论研究

基于集团模型电荷自洽的EHT(Extended Hückel Tneory)方法对K在石墨(0001)表面吸附态进行了优化计算.在3种不同的覆盖度(Θ)下,对k-石墨系统的电荷转移量△Q、吸附能△E、态密度PDOS和TDOS、Mulliken集居数和成键性质进行了比较.认同K/石墨吸附系统是石墨插层化合物(GIC)的雏型.并用LMTO方法对KC₈完成电子结构的第一性原理研究,得到与EHT完全一致的结果:K4s-Ca杂化态主要位于低能区域远离费米能级,构成反键轨道其电子转移到费米能级附近K3d-Cπ成键的杂化轨道上.空的3d轨道在目前EHT方法和LMTO方法计算中扮演了关键角色.这与其他文献K-4s态处在EF能级的结果不同,但与早期Fischer(1984),Johnson(1986)XPS,ARUPS的实验结果吻合.     

对甲基苯磺酰化丝氨酸Nd(Ⅲ)配合物的合成、表征及热分解反应动力学

合成了对甲基苯磺酰化丝氨酸配体(L)和对甲基苯磺酰化丝氨酸Nd(Ⅲ)配合物。通过元素分析、热分析、红外光谱、紫外光谱和摩尔电导等分析技术,确定配合物的组成为NdL3。用非等温热重分析方法研究了Nd(Ⅲ)配合物的热分解反应动力学,分解反应一步进行,其分解的动力学方程为dα/dt=Aexp(-Ea/RT)(1-α)2,并计算出了该步热分解的活化熵ΔS#、活化吉布斯自由能ΔG#和活化焓ΔH#分别为-86.7674J/mol.K、219.3884kJ/mol、170.9938kJ/mol。     

α-BeH2电子结构与光学性质的第一性原理研究

基于密度泛函理论,采用赝势平面波方法研究了α-BeH2的结构、电子和光学性质。基态下,α-BeH2的晶格常数a和体积弹性模量B0计算值与实验值及其它理论值一致。根据能带理论研究了α-BeH2基态下的能带结构、总态密度(DOS)和分波态密度(PDOS)。经过分析发现α-BeH2为直接能隙半导体材料,能隙为5.44eV,与文献相比,本文计算的结果偏低,这主要是利用第一性原理中的局域密度近似(LAD)或广义梯度近似(GGA)交换关联能函数计算材料的带隙宽度或者磁耦合的理论结果均会偏低。通过对基态α-BeH2的Mulliken电荷分布和集居数的分析发现：α-BeH2属于离子键和共价键所形成的混合键化合物;α-BeH2的电荷总数分别来源于各自的H 1s轨道,Be 2s和2p轨道。同时本文还分析研究了α-BeH2的光学介电函数、吸收系数、复折射率、反射系数和能量损失等光学性质。     

多硝基六氮杂金刚烷结构和相对稳定性的理论研究

基于密度泛函理论,在B3LYP/6-31G*水平下分别计算了潜在高能量密度化合物(HEDC)多硝基六氮杂金刚烷(PNHAAs)的结构,包括总能量、几何结构、氧平衡、偶极矩等．通过研究PNHAAs的结构参数,如N-NO2最大键长、N-NO2键的最小Mulliken集居数、-NO2所带最小负电荷、氧平衡,预测了10个标题物的相对稳定性或感度(起爆的难易程度．感度越高,化合物的稳定性越低)．结果发现,这四个参数基本上能得到一致的结论:随着硝基数目的增加,标题物的稳定性降低．氧平衡不能判别同分异构体的相对稳定性,但总能量和偶极矩可较好地判别同分异构体的相对稳定性．     

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.     

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.     

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.