儿茶素与脱氧腺苷相互作用的理论研究

本文采用密度泛函理论的M05方法,在6-311+G**基组水平上对建模的儿茶素-脱氧腺苷复合物进行几何结构的优化,得到了13个稳定的儿茶素-脱氧腺苷复合物.应用了自然键轨道(NBO)理论和分子中的原子理论(AIM)进行研究,氢键临界点电荷密度,拉普拉斯值,糖基扭转角!,假扭转角P等数据进行辅助研究,对这13种复合物中氢键的特征与性质进行了分析,还考虑了溶剂化效应对儿茶素与脱氧腺苷相互作用的影响.计算结果表明氢键对于复合物的稳定性起着非常重要的作用,而氢键的类型以及键级的大小共同影响着复合物的稳定性.所有的复合物进行基组重叠误差(BSSE)校正,相互作用能主要来自氢键贡献.通过计算结果分析比较,进而在理论上为儿茶素类药物的设计、修饰﹑合成和筛选提供有价值的信息.     

木犀草素和鸟嘌呤间相互作用的理论研究

采用密度泛函理论中的B3LYP方法对木犀草素和鸟嘌呤之间的相互作用和机理进行研究,分别找到了十八种木犀草素和鸟嘌呤复合物. 结果表明这些复合物是通过氢键相互作用而稳定存在的. 利用分子中的原子理论(AIM)和自然键轨道理论(NBO)对体系中的氢键进行研究. 通过基组重叠误差校正的复合物间的相互作用能为6.04～56.94 kJ/mol,计算结果表明在木犀草素-鸟嘌呤复合物中有很强的氢键相互作用. 比较了木犀草素和四个DNA碱基间的相互作 用,发现木犀草素-胸腺嘧啶是最强的,木犀草素-腺嘌呤是最弱的.     

木犀草素与腺嘌呤相互作用的理论研究

本文采用密度泛函理论中的B3LYP方法,在6-31+G~*基组水平上对木犀草素—腺嘌呤复合物进行结构优化和振动频率分析,得到了16种稳定的木犀草素—腺嘌呤复合物.应用分子中的原子理论(AIM)分析、自然键轨道(NBO)理论分析得到复合物氢键性质和特征.通过基组重叠误差(BSSE)校正后的相互作用能、成键临界点电荷密度、二阶稳定化能综合分析,得出三氢键复合物C-11结构是最稳定的.综合比较DNA的四个碱基与木犀草素间的相互作用,木犀草素与胸腺嘧啶的相互作用最强,木犀草素-腺嘌呤相互作用最弱,DNA的四个碱基与木犀草素间的相互作用能均比木犀草素与水间相互作用能大,这说明木犀草素作为抗癌药物能有效的发挥作用.     

紫草素与胞嘧啶相互作用的理论研究北大核心CSCD

采用密度泛函理论的M06方法在6-311++G**基组水平下对紫草素-胞嘧啶复合物进行了结构优化,得到了14个稳定的紫草素-胞嘧啶复合物.我们还应用了分子中的原子(AIM)理论和自然键轨道(NBO)理论对这14个复合物中的氢键的性质和特征进行了分析.通过基组重叠误差(BSSE)校正后的相互作用能,成键临界点电荷密度,二阶稳定化能的计算和分析,发现复合物1的结构是最稳定的.     

SiH_4…Y(Y=He,Ne,Ar,Kr)体系中的分子间弱相互作用北大核心CSCD

在MP2/aug-cc-pvtz水平上对SiH4…Y(Y=He,Ne,Ar,Kr)复合物势能面上的4个构型进行优化,探讨了SiH4…Y(Y=Ar,Kr)复合物体系中的蓝移氢键结构和电子性质.含基组重叠误差(BSSE)校正的分子间相互作用能的相对大小可以判断复合物的相对稳定性递增顺序为:SiH4…He→SiH4…Ne→SiH4…Ar≈SiH4…Kr.且SiH4与Y(Y=He,Ne)体系之间的相互作用可归属为van der Waals力,而SiH4与Y(Y=Ar,Kr)之间的相互作用属弱氢键.NBO及电子行为分显示,SiH4…Y(Y=Ar,Kr)氢键复合物是一种非静电性质的弱氢键作用.另外,对各复合物中相关键鞍点处的电子密度拓扑性质分析也表明复合物中均存在非静电性质的分子间弱相互作用.     

SiH4…Y(Y=He,Ne,Ar,Kr)体系中的分子间弱相互作用

在MP2/aug-cc-pvtz水平上对SiH4…Y(Y=He,Ne,Ar,Kr)复合物势能面上的4个构型进行优化,探讨了SiH4…Y(Y=Ar,Kr)复合物体系中的蓝移氢键结构和电子性质.含基组重叠误差(BSSE)校正的分子间相互作用能的相对大小可以判断复合物的相对稳定性递增顺序为:SiH4…He→SiH4…Ne→SiH4 …Ar≈SiH4…Kr.且SiH4与Y(Y=He,Ne)体系之间的相互作用可归属为van der Waals力,而SiH4与Y(Y=Ar,Kr)之间的相互作用属弱氢键.NBO及电子行为分显示,SiH4…Y(Y=Ar,Kr)氢键复合物是一种非静电性质的弱氢键作用.另外,对各复合物中相关键鞍点处的电子密度拓扑性质分析也表明复合物中均存在非静电性质的分子间弱相互作用.     

紫草素与胞嘧啶相互作用的理论研究

采用密度泛函理论的M06方法在6-311++G**基组水平下对紫草素-胞嘧啶复合物进行了结构优化,得到了14个稳定的紫草素-胞嘧啶复合物。我们还应用了分子中的原子(AIM)理论和自然键轨道(NBO)理论对这14个复合物中的氢键的性质和特征进行了分析。通过基组重叠误差(BSSE)校正后的相互作用能、成键临界点电荷密度、二阶稳定化能的计算和分析,发现复合物1的结构是最稳定的。     

SiH4•••Y(Y=He, Ne, Ar, Kr)体系中的分子间弱相互作用

在MP2/aug-cc-pvtz水平上对SiH4•••Y(Y=He, Ne, Ar, Kr)复合物势能面上的4个构型进行优化, 探讨了SiH4…Y(Y=Ar, Kr)复合物体系中的蓝移氢键结构和电子性质. 含基组重叠误差(BSSE)校正的分子间相互作用能的相对大小可以判断复合物的相对稳定性顺序为： SiH4…He ˂ SiH4…Ne ˂ SiH4…Ar ≈SiH4…Kr. 且SiH4与Y（Y=He, Ne）体系之间的相互作用可归属为van der Waals力, 而SiH4与Y(Y=Ar, Kr）之间的相互作用属弱氢键. NBO及电子行为分显示, SiH4…Y（Y= Ar, Kr）氢键复合物是一种非静电性质的弱氢键作用. 另外, 对各复合物中相关键鞍点处的电子密度拓扑性质分析也表明复合物中均存在非静电性质的分子间弱相互作用.     

硝酸羟胺-(H_2O)_n复合物氢键相互作用的密度泛函研究

为研究硝酸羟胺-(H_2O)_n复合物的氢键作用,采用密度泛函B3LYP方法在6-311++G(d, p)基组水平上对硝酸羟胺-(H_2O)_n复合物的结构进行优化,采用MP2/6-311++G(d, p)方法,经基组叠加误差和零点能校正计算得到复合物的相互作用能.利用自然键轨道分析方法研究复合物氢键作用的本质,并对复合物中水分子的振动光谱进行分析.计算结果表明,硝酸羟胺-(H_2O)_n复合物存在着6个硝酸羟胺-H_2O稳定构型和8个硝酸羟胺-(H_2O)_2稳定构型,且最稳定构型的相互作用能分别为52.821 kJ·mol~(-1)和73.349 kJ·mol~(-1).在硝酸羟胺-(H_2O)_n复合物中,水中H-O伸缩振动频率明显红移,且红移增大的程度与复合物稳定化能的变化趋势基本一致.     

气相中HOCl和O3分子间氯键和氢键的结构和性质

在DFT-B3LYP/6-311 G**水平上分别求得O3…ClOH氯键复合物和O3…HOCl氢键复合物势能面上的稳定构型.频率分析表明,与单体HOCl相比,分别在两种复合物中,Cl4-O5和H6-O5键伸缩振动频率发生红移,红移值分别为5.70和76.44cm-1.经MP2/6-311 G**水平计算的含BSSE和零点振动能校正的气相中相互作用能分别为-2.102和-4.920 kJ·mol-1.NBO分析表明,在O3…ClOH氯键复合物中,引起Cl4-05键变长的因素包括2种电荷转移:(1)LP(O1)1→σ*(C14-05);(2)LP(O1)2→σ*(Cl4-O5),其中LP(O1)2→σ*((Cl4-O5)转移占主要作用,总的结果是使σ*(Cl10-O11)的自然布居数增加了14.44 me;在O3…HOCl氢键复合物中也存在类似的电荷转移,结果使σ*(H6-O5)的自然布居数增加了18.09 me.NRT理论进行键序分析表明,在氯键复合物和氢键复合物中,Cl4-O5和H6-O5键的键序都减小,与红外光谱频率计算分析和NBO分析的结论一致.AIM理论分析表明,分别在两种复合物中,O1…Cl4间和O1…H6间都存在键鞍点,而且O1…Cl4和O1…H6的P(r)都较小,分别为0.0111和0.0152 a.u.,说明复合物中的氯键和氢键相互作用较弱.另外,O1…Cl4氯键和O1…H6氢键的Laplacian量(△)ρP(r)分别为0.0479和0.0641 a.u.,都是较小的正值,说明这两种相互作用都以静电作用为主.     

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.