MgBn（n=1-17）团簇的密度泛函理论研究

本文从第一性原理出发,采用密度泛函理论（DFT）的杂化密度泛函B3LYP方法,在6-31G(d)全电子基组水平上对MgBn(n=1-17)团簇各种可能的构型进行结构优化和频率分析,预测了各团簇的最低能量结构。结果表明MgBn 团簇主要有两种生长模式。同时对各团簇最低能量结构的能隙、结合能等电子性质进行了分析,由二阶能量差分及能隙随团簇尺寸的变化规律可以得到MgB6、MgB9、MgB13是比较稳定的团簇。通过NBO对自然电荷布居及成键特性进行分析,得到Mg原子带正电,以s轨道参与成键,B原子主要带负电,一部分B原子之间以sp杂化形成离域π键,有利于增强稳定性,其他B原子主要以s、p轨道参与成键。     

X@Mg_8B_(14)(X=H,Li)团簇核壳结构与性质的密度泛函理论研究

运用杂化密度泛函B3LYP方法,在6-31G*水平上对X@Mg_8B_(14)(X=H,Li)两种团簇进行了几何结构优化,并计算了其电子结构、振动特性和成键特性.计算结果表明:优化后的X@Mg_8B_(14)(X=H,Li)团簇均为橄榄球状核壳结构,对称性点群均为D2h.用自然键轨道方法分析了成键性质,发现X@Mg8B14(X=H,Li)团簇中B原子主要是sp杂化轨道参与成键,Mg原子主要是s轨道参与成键.Mg原子和B原子之间发生了大量的电子转移,在B原子层堆积了大量的电子;尤其是封装Li原子后,B原子层得电子数量明显增加.     

笼状团簇Mg12B24结构与性质的密度泛函理论研究

运用杂化密度泛函B3LYP方法,在6-31G*水平上优化得到了一种Mg₁₂B₂₄团簇的笼状稳定结构,其IR最强吸收峰位于205.23 cm^-1,Raman谱的最强峰位于242.63 cm^-1. Mg₁₂B₂₄团簇笼状结构中B原子主要是sp杂化轨道参与成键,Mg原子主要是s轨道参与成键.团簇中B原子层堆积了大量的电子,表明MgB₂的超导作用主要发生在B原子层;B原子层电子存在较强的离域性,也为超导电性提供了条件;Mg原子起了提供电子的作用.     

第一性原理对SinMg(n=1-12)团簇结构、稳定性与电子性质的研究

运用密度泛函理论(DFT)的杂化密度泛函B3LYP方法,在6-311G基组水平上对 团簇进行了构型优化、频率分析与电子性质计算.同时讨论了团簇的平均结合能、能级间隙、二阶能量差分、自然电子布居、极化率.研究结果表明： 团簇的基态绝大多数为立体结构. 时,体系的基态为自旋三重度, 时,则为单重态.镁原子的掺入使得主团簇的电子性质发生了明显的变化,掺杂使体系的平均结合能降低,能隙减小,化学硬度减小,电子亲和能增大.电子总是从 原子向 原子转移.团簇中原子之间的成键相互作用随n的增大 而增强,团簇的电子结构随n的增大而趋于紧凑.     

Tin(n=2~7)团簇结构, 稳定性和电荷分布关系的密度泛函研究

利用密度泛函理论中的B3LYP方法, 选择LANL2DZ基组优化Tin(2~7)团簇得到各团簇的稳定结构,然后对稳定结构的束缚能及自然轨道进行分析. 研究结果表明: Tin(n=2~7)团簇都依带帽的形式在前一个团簇的结构基础上加一个原子变化而来; 通过自然轨道分析发现, 团簇原子的轨道存在sp-d杂化, 有大约一个电子从4s转移到了3d, 原子之间亦存在电子转移, 而且除Ti7外, 团簇键长由最外层4d轨道电子和3d轨道共同决定, 在Ti7中, 团簇键长由3d轨道决定.     

(XB2)2(X=Al, Be, Na, Mg)团簇结构与性质的密度泛函研究

用密度泛函理论(DFT)的杂化密度泛函B3LYP方法在6-31G·基组水平上对(XB2)2(X=Al,Be,Na, Mg)团簇各种可能的构型进行几何结构优化,预测了各团簇的最稳定结构.并对最稳定结构的电子结构、振动特性、成键特性和电荷特性等进行了理论研究.结果表明,团簇的几何结构大多是平面结构,通常是B-B键和B-X键共存,较少出现X-X键.团簇的稳定结构中通常是几个呈负电性的B原子形成一个负电中心,而其他B原子和X原子处在端位,且显正电性.     

(XB2)2(X=Al, Be, Na, Mg)团簇的密度泛函研究

用密度泛函理论(DFT)的杂化密度泛函B3LYP方法在6-31G*基组水平上对(XB2)2(X=Al,Be,Na,Mg)团簇各种可能的构型进行几何结构优化,预测了各团簇的最稳定结构.并对最稳定结构的电子结构、振动特性、成键特性和电荷特性等进行了理论研究.结果表明,团簇的几何结构大多是平面结构,通常是B-B键和B-X键共存,较少出现X-X键.团簇的稳定结构中通常是几个呈负电性的B原子形成一个负电中心,而其他B原子和X原子处在端位,且显正电性.     

(MgB2)n(n=1～3)团簇结构与性质的密度泛函研究

用密度泛函理论(DFT)的杂化密度泛函B3IJYP方法在6-31G*基组水平上对(MgB2)n(n=1～3)团簇各种可能的构型进行几何结构优化,预测各团簇的最稳定结构,并对其振动特性、成键特性、极化率和超极化率等性质进行理论研究.结果表明,团簇的几何结构大多是平面结构,团簇的稳定结构中通常是几个呈负电性的B原子形成一个负电中心,而其他B原子和Mg原子处在端位,且显正电性,Mg原子的自然电荷在 0.559e～ 0.920e之间,B原子的自然电荷在-0.724e～ 0.197e之间;团簇中通常是B-B键和B-Mg键共存,较少出现Mg-Mg键,计算得到的B-B键键长在0.153～0.182 nm之间,B-Mg键键长在0.218～0.231 nm之间.     

FeBN(N≤15)团簇结构、电子性质和磁性的密度泛函理论研究

采用密度泛函理论中的广义梯度近似(Generalized Gradient Approximation, GGA)方法, 对不同自旋多重度的FeBN(N≤15)团簇的平衡几何结构、电子性质和磁性进行了研究. 团簇基态结构的平均结合能、二阶能量差分和能隙均表明FeB8、FeB12和FeB14团簇较相邻团簇稳定. 团簇基态结构中Fe原子的d轨道和B原子的p轨道存在着明显的杂化. 团簇基态结构的总磁矩主要来自Fe原子3d轨道的贡献, 且总磁矩随团簇尺寸增大呈现奇偶振荡.     

Al_nCl(n=2-14)团簇结构与电子性质的理论研究

运用卡里普索(CALYPSO)结构预测方法,在杂化密度泛函B3LYP/6-311G+(d)基组水平上,对Al_nCl(n=2-14)团簇的几何结构与电子性质进行优化计算,并讨论了团簇的平均结合能、能隙、二阶能量差分、电离能、亲和能以及电子自然布居和极化率.研究结果表明:Al_nCl(n=2-14)团簇的基态构型由简单平面几何结构向立体结构演化,形成Cl原子戴帽Al_n-1Cl团簇结构;Cl原子的掺杂增大了Al_n团簇的平均结合能;二阶能量差分、能隙、电离能、亲和能的变化表明Al_7Cl是幻数团簇结构;团簇中的电荷总是由Al_原子向Cl原子转移,原子之间的成键作用随着团簇尺寸的增大而增强.     

Hybrid Wavelength and Code Division Multiple Access in Optical Networks

A review of schemes for multiple access in fiber optic networks shows that a hybrid of wavelength and code division multiple access (WCDMA) combines the best features of both. In particular, the hybrid scheme retains the large information carrying capacity of wavelength division multiple access (WDMA) and flexibility of code division multiple access (CDMA). In this paper WDMA, optical CDMA (OCDMA), and WCDMA networks are discussed. In OCDMA networks, concept of incoherent and coherent coding including inverse decoding and matched filter is introduced. The delay performance of both WDMA and WCDMA networks, under the simple suboptimum access protocols based on cyclic search, is computed. It has been shown quantitatively that tuning delay significantly affects the delay performance of both WDMA and WCDMA networks. Futhermore, delay performance of WCDMA networks is always better than the WDMA networks for the same tuning delay, load, and number of users.     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Femtosecond Transform-Limited Pulse Generation by Compensating for the Linear Chirp of SPM Spectra in Dispersion Shifted Fibers

A simple technique of pulse compression, based on the linear chirp compensation of self-phase modulation (SPM) spectra in dispersion shifted fibers, is demonstrated. The optimization procedure is carried out, for a short span of a single-mode fiber, using a parabolic law, which describes the behavior of the squared output pulse width versus the pump peak power in the case of Gaussian pulses. The experimental results give a minimum pulse duration of 233 fs, which is in good agreement with the model. Shorter and coherent pulses, down to 90 fs, have been obtained by inserting an interference filter at the optical output.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Research on beamforming method for dual-line array with space mismatch between the two line arrays

The performance of port/starboard discrimination of dual-line array will be seriously degraded when the space between the two line arrays of the dual-line array is mismatched. The directivity function of the delay-sum and delay-subtract beamforming is deduced and the port/starboard discrimination of the delay-sum and delay-subtract beamforming is also studied both under the ideal status and the status under which the space between the two line arrays of the dual-line array is mismatched. Analysis results show the delay-subtract beamforming has better performance of port/starboard discrimination. At last, the sea trial results demonstrate the theoretical results.     

Sorting of bending magnets for the SSRF booster

The Shanghai Synchrotron Radiation Facility(SSRF)booster ring,a full energy injector for the storage ring,is deigned to accelerate the electron beam energy from 150MeV to 3.5GeV that demands high extraction efficiency at the extraction energy with low beam loss rate when electrons are ramping.Closed orbit distortion(COD)caused by bending magnet field uniformity errors which affects the machine performance harmfully could be effectively reduced by bending magnet location sorting.Considering the affections of random errors in measurement,both ideal sorting and realistic sorting are studied based on measured bending magnet field uniformity errors and one reasonable combination of bending magnets which can reduce the horizontal COD by a factor of 5is given as the final installation sequence of the booster bending magnets in this paper.     

Retrieval of ultraviolet skylight radiances and O3 slant column densities from balloon-borne limb spectrometer

With a novel light-weight and absolutely calibrated ultraviolet （UV） spectrometer, UV skylight radiances and O3 slant column densities are measured by balloon-borne limb measurements in Xinjiang area, China. UV skylight radiances measured at the height of 31 km are compared with the results from Modtran in the wavelength range from 290 to 420 nm. O3 slant column densities are derived from radiance spectra in the Huggins bands （320 - 335 nm） using differential optical absorption spectroscopy method. And the parameter exhibits a good correlation with the same value simulated by radiative transfer model （Tracy）. The O3 profile simultaneously measured by an O3 sonde is used as input in Tracy calculations. The O3 sonde is launched on the same balloon.     

Design optimization of highly sensitive LSPR enhanced surface plasmon resonance biosensors with nanoholes

For breaking through the sensitivity limitation of conventional surface plasmon resonance (SPR) biosensors, novel highly sensitive SPR biosensors with Au nanoparticles and nanogratings enhancement have been proposed recently.But in practice, these structures have obvious disadvantages.In this study, a nanohole based sensitivity enhancement SPR biosensor is proposed and the influence of different structural parameters on the performance is investigated by using rigorous coupled wave analysis (RCWA).Electromagnetic field distributions around the nanohole are also given out to directly explain the performance difference for various structural parameters.The results indicate that significant sensitivity increase is associated with localized surface plasmons (LSPs) excitation mediated by nanoholes.Except to outcome the weakness of other LSP based biosensors, larger resonance angle shift, reflectance amplitude, and sharper SPR curves' width are obtained simultaneously under optimized structural parameters.     

Polymer gratings based on photopolymerization for low-order distributed feedback polymer lasers

Novel polymer distributed feedback(DFB)gratings are fabricated based on photopolymerization to reduce lasing threshold of polymer lasers.A photopolymer formulation sensitive to 355-nm ultraviolet(UV)light is proposed for the fabrication of polymer gratings and it can be used to form polymer films by spin-coating process.A very low surface-relief depth ranging from 12.5 to about 1.0 nm has been demonstrated with a refractive-index modulation of about 0.012.The experimental results indicate that such polymer gratings have promising potentials for the fabrication of low-order DFB organic semiconductor lasers.     

A novel methodology for photometric compensation of projection display on patterned screen

We propose a novel methodology based on the projector-camera (ProCam) system to address the photometric compensation issue for the projection display on the patterned screen.The patterned screen is treated as the combination of a perfect white screen and a color modulator.The perfect white screen is used to automatically and accurately characterize the ProCam system offline using the polynomial model,and the parameters of the color modulator can be efficiently recovered by employing only two gray images based on the linear reflectance model.The experimental results show that the color artifacts of the display image can be greatly improved with this methodology,which demonstrates its feasibility and validity in the photometric compensation.