磁场中环状碳纳米卷电子结构的紧束缚法研究

通过考虑波矢■周期性边界条件,在石墨烯紧束缚模型基础上,构造了磁场中环状碳纳米卷模型,研究了其电子结构性质.结果表明环状碳纳米卷的电子结构以磁通量子Φ_0为周期随磁通量Φ周期性变化,通过控制手性和磁场,可将其调制成金属或不同带隙的半导体,其中m=3I(I为整数)、θ=2π/3的锯齿型环状碳纳米卷的带隙受磁场的影响比较小,m=18时变化幅度仅为7 μeV.     

碳纳米卷电子结构的紧束缚法研究

利用石墨平面碳原子轨道作sp2杂化时π电子的紧束缚模型,通过限定波矢k周期性边界条件,构造了碳纳米卷模型,研究了其电子结构性质.结果表明碳纳米卷的电子结构与其几何结构密切相关,通过控制手性和结构参数,可将其调制成不同带隙的半金属或半导体.     

环状碳纳米卷中的持续电流

在环状碳纳米卷紧束缚模型的基础上,导出了相应的持续电流表达式,并系统地研究了环状碳纳米卷的几何结构、分离能级、温度及塞曼效应对持续电流的影响。结果表明,环状碳纳米卷内部的持续电流数量级仅为10~(-7)A,并且随着卷环周长增大而逐渐减小。费米能级附近的能级几乎承载了所有持续电流,而远离的能级贡献非常小。随着温度升高,持续电流急剧减小;且卷环周长越大,受温度影响越明显。对于较强的磁场,考虑塞曼效应后,持续电流出现了新的减小的越变,周期性结构遭到破坏。     

轴向磁场对锯齿型和扶手椅型碳纳米卷电子结构的影响

碳纳米卷作为一种新型的碳基纳米材料,其结构非封闭且内径大小容易调控,成为当今材料科学研究热点之一。利用石墨烯碳原子轨道作sp2杂化时π电子的紧束缚模型,考虑波矢k周期性边界条件及轴向磁场的影响,构造了磁场中碳纳米卷的紧束缚模型,并研究了其在轴向磁场中的能带、能隙及电子态密度等性质。结果表明,碳纳米卷的能量色散是以磁通量子Φ0为周期随磁通量Φ变化,最低未占据分子轨道也随之产生了明显移动,从而导致碳纳米卷发生金属-半导体连续转变,其中ZCNS(15,0)能隙最大为0.878 e V,而ACNS(12,12)为0.654 e V     

有限长碳纳米卷电子结构的紧束缚法研究

通过卷曲石墨烯,构造了有限长碳纳米卷模型.基于能带理论中紧束缚近似方法,推导并研究了与手性、结构参数及卷长相关的色散关系解析表达式.结果表明,随着几何结构的变化,碳纳米卷会呈现出金属-半导体转变,及与卷长有关的不同的渐近带隙行为:振荡型衰减、单调衰减和不变.     

低维硼碳纳米材料第一原理研究

介绍了近年来关于低维硼碳纳米材料结构和电子性质的研究工作.通过第一原理计算,从理论上预言了稳定的低维硼纳米结构,并系统研究了以稳定硼平面为基础的硼纳米管和硼纳米带的电子性质.对于硼碳复合纳米材料,以BC3,BC5和BC7有序结构的平面为基础,发现对其剪裁、氢化修饰之后,硼碳纳米结构具有丰富的电磁学性质,可能在未来电子学器件中得到广泛的应用.     

缺陷对单壁碳纳米管电子结构调制的第一性原理计算

用密度泛函理论计算不同浓度点空位缺陷对扶手型和锯齿型碳纳米管电子结构的调制, 并对其键长、 缺陷形成能、 带隙及电子态密度进行分析. 结果表明： 随着缺陷浓度的增加, 邻近碳原子间化学键键长减小, 扶手型碳纳米管带隙打开, 由金属性质变为半导体性质, 锯齿型碳纳米管带隙逐渐变小; 碳原子缺失使缺陷附近未成键的悬键电子局域在Fermi能级附近形成额外的电子态而改变了碳纳米管的电子结构.     

sp~2杂化三维碳材料构建研究进展

sp~2杂化是碳碳成键的重要方式之一,利用其三重对称空间构型可以得到稳定的石墨结构和亚稳定的富勒烯、纳米碳管、石墨烯等碳纳米结构;未参与杂化的电子形成游离的π键,使得以上材料具有较好的电子导电性或其他独特的电学性质.因其优异的物理、化学、生物等特性,sp~2杂化碳材料,尤其是sp~2杂化纳米碳材料引起了巨大关注,有望在电子、能源、生物医疗、制药、功能材料等领域得到广泛应用.在已经进行的众多研究中,经常需要把上述碳纳米材料进行组装、构建成三维材料,从而在更大的尺度和空间中体现纳米基元的优异特性.本文综述了基于sp~2杂化的三维碳材料的最新进展,以构建方式和构建基元之间的相互作用为出发点进行相关评述.     

不同宽度锯齿型石墨烯纳米带的第一原理研究

采用第一原理密度泛函理论,研究了不同宽度边缘饱和（氢原子）一维石墨片纳米带的电学性质。研究表明：对于所有宽度锯齿型纳米带,其几何结构和电子结构与碳纳米带的宽度密切相关。这为揭示纳米带尺寸效应提供了一条切实可行的道路。     

锂离子电池负极硅碳纳米复合纤维的储锂性能

为了实现硅纳米颗粒与一维碳纳米纤维的高效复合,提高硅材料作为锂离子电池负极的电化学性能,通过同轴静电纺丝法构造了硅碳复合结构(Si/C-C)的一维纳米纤维作为锂离子电池的负极材料.通过SEM、TEM、XRD和电化学性能测试对其结构、形貌、成分和电化学性能等进行分析.结果表明:Si/C-C纳米复合纤维的平均直径为500~700 nm,硅含量为22%~33%;在100 m A/g的电流密度下,经100圈循环后其可逆容量维持在1 000 m Ah/g,表现出较佳的循环稳定性和较高的可逆比容量.研究表明,一维复合纳米纤维电化学性能的提升主要归因于硅碳复合结构中一维纳米纤维为硅提供了保护层,一方面有效抑制了硅的体积膨胀,另一方面提升了硅的电子导电性并有效缩短了离子迁移路径.     

An Index mechanism for multi-scale view in spatial databases

There are numerous geometric objects stored in the spatial databases. An importance function in a spatial database is that users can browse the geometric objects as a map efficiently. Thus the spatial database should display the geometric objects users concern about swiftly onto the display window. This process includes two operations:retrieve data from database and then draw them onto screen. Accordingly, to improve the efficiency, we should try to reduce time of both retrieving object and displaying them. The former can be achieved with the aid of spatial index such as R-tree, the latter require to simplify the objects. Simplification means that objects are shown with sufficient but not with unnecessary detail which depend on the scale of browse. So the major problem is how to retrieve data at different detail level efficiently. This paper introduces the implementation of a multi-scale index in the spatial database SISP (Spatial Information Shared Platform) which is generalized from R-tree. The difference between the generalization and the R-tree lies on two facets: One is that every node and geometric object in the generalization is assigned with a importance value which denote the importance of them, and every vertex in the objects are assigned with a importance value,too. The importance value can be use to decide which data should be retrieve from disk in a query. The other difference is that geometric objects in the generalization are divided into one or more sub-blocks, and vertexes are total ordered by their importance value. With the help of the generalized R-tree, one can easily retrieve data at different detail levels.Some experiments are performed on real-life data to evaluate the performance of solutions that separately use normal spatial index and multi-scale spatial index. The results show that the solution using multi-scale index in SISP is satisfying.     

Characterization of Ordovician carbonate reservoirs, southeastern Saskatchewan, Canada

The discovery of the prolific Ordovician Red River reservoirs in 1995 in southeastern Saskatchewan was the catalyst for extensive exploration activity which resulted in the discovery of more than 15 new Red River pools. The best yields of Red River production to date have been from dolomite reservoirs. Understanding the processes of dolomitization is, therefore, crucial for the prediction of the connectivity, spatial distribution and heterogeneity of dolomite reservoirs.The Red River reservoirs in the Midale area consist of 3～4 thin dolomitized zones, with a total thickness of about 20 m, which occur at the top of the Yeoman Formation. Two types of replacement dolomite were recognized in the Red River reservoir: dolomitized burrow infills and dolomitized host matrix. The spatial distribution of dolomite suggests that burrowing organisms played an important role in facilitating the fluid flow in the backfilled sediments. This resulted in penecontemporaneous dolomitization of burrow infills by normal seawater. The dolomite in the host matrix is interpreted as having occurred at shallow burial by evaporitic seawater during precipitation of Lake Almar anhydrite that immediately overlies the Yeoman Formation. However, the low δ18O values of dolomited burrow infills (-5.9‰～ -7.8‰, PDB) and matrix dolomites (-6.6‰～ -8.1‰, avg. -7.4‰ PDB) compared to the estimated values for the late Ordovician marine dolomite could be attributed to modification and alteration of dolomite at higher temperatures during deeper burial, which could also be responsible for its 87Sr/86Sr ratios (0.7084～0.7088) that are higher than suggested for the late Ordovician seawaters (0.7078～0.7080). The trace amounts of saddle dolomite cement in the Red River carbonates are probably related to "cannibalization" of earlier replacement dolomite during the chemical compaction.     

A computer generator for randomly layered structures

AcomputergeneratorforrandomlylayeredstructuresYUJia shun1,2,HEZhen hua2(1.TheInstituteofGeologicalandNuclearSciences,NewZealand;2.StateKeyLaboratoryofOilandGasReservoirGeologyandExploitation,ChengduUniversityofTechnology,China)Abstract:Analgorithmisintrod…     

Perspherical Approaches for Electrons in Atoms and Charged Excitons in Quantum Wells

Instead of following Fock’s expansion,we solve the Schrodinger equation for some quantum mechanical manybody systems such as electrons in atoms and charged excitons in quantum wells in a similar way in hyperspherical coordinates by expanding the wave functions into orthonormal complete basis sets of the hyperspherical hannonics(HHs)of hyperangles and generalized Laguerre polynomials(GLPs)of the hyperradius.This leads the equation to     

Advances in broadband wireless communications under high-mobility scenarios

Future mobile communication systems aim at providing very high data transmission rates, even in high-mobility scenarios such as high-speed wheel-track trains, maglev trains, highway vehicles, airplanes, guided missiles or spacecraft. A particularly important commercial application is the strong and increasing worldwide demand for high- speed broadband wireless communications （up to 574.8 km/ h test speeds or 380 km/h commercial speeds） in railways, providing data, voice and video services for applications such as onboard entertainment services to passengers, train control, train dispatch, train sensor status handling and sur- veillance. In such high-mobility scenarios, there are a number of communication challenges, including fast hand- over, location updating, high-speed channel modeling, estimation and equalization, anti-Doppler spreading tech- niques, fast power control, and dedicated network architec- ture. Because signal transmission in very high-speed scenarios will inevitably experience serious deterioration, it is imperative to develop key broadband mobile communi- cation techniques for such high-speed vehicles.     

Wuhan University Journal of Natural Sciences TOTAL CONTENTS

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海南岛地体及其毗邻陆缘晚中生代—新生代古地磁研究和构造演化

本文叙述了对海南岛及其毗邻大陆边缘白垩纪到第四纪地层岩石进行古地磁研究的全部工作过程。通过分析岩石中剩余磁矢量的磁偏角及磁倾角的变化,提出海南岛白垩纪以来经历的构造演化模式如下:早期伴随顺时针旋转而向南迁移,后期伴随逆时针转动并向北运移。联系该地区及邻区的地质、地球物理资料,对海南岛上述的构造地体运动提出以下认识:北部湾内早期有一拉张作用,主要是该作用使湾内地壳显著伸长减薄,形成北部湾盆地。从而导致了海南岛的早期构造运动,而海南岛后期的构造运动则主要是受南海海底扩张的影响。海南地体运动规律的阐明对于了解北部湾油气盆地的形成演化有重要的理论和实际意义。     

Scale-based spatial data model for GIS

Being the primary media of geographical information and the elementary objects manipulated, almost all of maps adopt the layer-based model to represent geographic information in the existent GIS. However, it is difficult to extend the map represented in layer-based model. Furthermore, in Web-Based GIS, It is slow to transmit the spatial data for map viewing. In this paper, for solving the questions above, we have proposed a new method for representing the spatial data. That is scale-based model. In this model we represent maps in three levels: scale-view, block, and spatial object, and organize the maps in a set of map layers, named Scale-View, which associates some given scales.Lastly, a prototype Web-Based GIS using the proposed spatial data representation is described briefly.     

Exciton Seebeck in Molecular Systems

Various applications relevant to the exciton dynamics,such as the organic solar cell,the large-area organic light-emitting diodes and the thermoelectricity,are operating under temperature gradient.The potential abnormal behavior of the exicton dynamics driven by the temperature difference may affect the efficiency and performance of the corresponding devices.In the above situations,the exciton dynamics under temperature difference is mixed with     

Achieving Unusual States of Matter Under High Pressure

The elongation method,originally proposed by Imamura was further developed for many years in our group.As a method towards O(N)with high efficiency and high accuracy for any dimensional systems.This treatment designed for one-dimensional(ID)polymers is now available for three-dimensional(3D)systems,but geometry optimization is now possible only for 1D-systems.As an approach toward post-Hartree-Fock,it was also extended to