锯齿型硅纳米管不同手性下的电学与光学性质

本文用第一性原理中的局域密度近似方法,计算了锯齿型单壁硅纳米管(single-walled silicon nanotubes,SWSiNTs)的能带结构、态密度、吸收谱及反射谱.计算结果表明当n=6～9时,带隙为0,该组SWSiNTs具有金属性;当n=10～21时,能带图出现带隙,该组SWSiNTs具有半导体性;当n=13～21时,该组SWSiNTs的带隙以3组手性指数为周期减小;并在吸收谱和反射谱都会在一些相似频率值附近产生峰值.     

C0 FE model based on HOZT for the analysis of laminated soft core skew sandwich plates: Bending and vibration

Bending and free vibration behaviour of laminated soft core skew sandwich plate with stiff laminate face sheets is investigated using a recently developed C₀ finite element (FE) model based on higher order zigzag theory (HOZT) in this paper. The in-plane displacement fields are assumed as a combination of a linear zigzag function with different slopes at each layer and a cubically varying function over the entire thickness. The out of plane displacement is considered to be quadratic within the core and constant in the face sheets. The plate theory ensures a shear stress-free condition at the top and bottom surfaces of the plate. Thus, the plate theory has all of the features required for accurate modelling of laminated skew sandwich plates. As very few element model based on this plate theory (HOZT) exist and they possess certain disadvantages, an attempt has been made to check the applicability of the refined element model. The nodal field variables are chosen in such a manner that there is no need to impose any penalty stiffness in the formulation. Refined C₀ finite element model has been utilized to study some interesting problems on static and free vibration analysis of laminated skew sandwich plates.     

On two types of Z-monodromy in triangulations of surfaces

Let $\Gamma$ be a triangulation of a connected closed 2-dimensional (not necessarily orientable) surface. Using zigzags (closed left–right walks), for every face of $\Gamma$ we define the $z$-monodromy which acts on the oriented edges of this face. There are precisely 7 types of $z$-monodromies. We consider the following two cases: (M1) the $z$-monodromy is identity, (M2) the $z$-monodromy is the consecutive passing of the oriented edges. Our main result is the following: the subgraphs of the dual graph ${\Gamma }^1$ formed by edges whose $z$-monodromies are of types (M1) and (M2), respectively, both are forests. We apply this statement to the connected sum of $z$-knotted triangulations.     

自由立体显示器中锯齿状交错狭缝光栅的设计

光栅式自由立体显示由于易存在莫尔条纹和串扰的问题而影响其显示效果.利用斜光栅可减轻莫尔条纹但增加了视点间的串扰.本文提出一种减轻莫尔条纹的光栅设计方法,同时对可视区域影响较小.设计中对光栅进行分段,并将相邻两段狭缝错开一定距离.该方法能减小通过同一狭缝看到两相邻子像素之间的黑条的比例,获得较宽且较淡的莫尔条纹,从而减轻了视觉干扰.仿真结果表明该光栅相比传统垂直光栅,莫尔条纹亮度下降了108.1％,而可视区域仅减小32.8％,具有较高的实用价值.     

A density-functional-theory-based finite element model to study the mechanical properties of zigzag phosphorene nanotubes

In this paper, the density functional theory calculations are used to obtain the elastic properties of zigzag phosphorene nanotubes. Besides, based on the similarity between phosphorene nanotubes and a space-frame structure, a three-dimensional finite element model is proposed in which the atomic bonds are simulated by beam elements. The results of density functional theory are employed to compute the properties of the beam elements. Finally, using the proposed finite element model, the elastic modulus of the zigzag phosphorene nanotubes is computed. It is shown that phosphorene nanotubes with larger radii have larger Young's modulus. Comparing the results of finite element model with those of density functional theory, it is concluded that the proposed model can predict the elastic modulus of phosphorene nanotubes with a good accuracy.     

Coupled energy patterns in zigzag molecular chains

The contribution of both longitudinal and transversal nonlinear oscillations to energy localization is investigated in a zigzag molecular chain, which include simultaneously nearest- and next-nearest neighbor interactions. Coupled amplitude equations are found in the form of discrete nonlinear Schrödinger equations, whose plane wave solutions are found to be subjected to some instabilities. They are shown to be very sensitive to transverse and longitudinal couplings, which is confirmed via direct numerical simulations. The two available modes are found to be alternatively responsible for energy localization and transport. Thermal fluctuations effects bring about highly localized modes, along with narrow structures for efficient energy transport.     

Impact of Phosphorus superlattices on charge and spin dependent transport properties of zigzag silicene nanoribbons

To investigate charge and spin dependent conductance properties of Phosphorus doped zigzag silicene nanoribbons (ZSiNRs), we utilize recursive Green's function method and Landauer-Büttiker formalism. Our calculations are performed in the absence and presence of exchange magnetic fields with both parallel and antiparallel configurations. Considering a supperlattice of Phosphorus substituents in a periodic distribution at the edge of nanoribbon, the effect of increasing number of dopants and period of the distribution on transport properties are studied. It is found that transport properties of doped ZSiNRs vary with doping concentration according to being odd or even of number of dopants. For parallel configuration, doped ZSiNR with various concentrations works as a controllable spin filter with Fermi energy. Increasing doping concentration leads to increasing size of conductance gap and improvement of controlling quality of spin-filtering property while increasing period of Phosphorus atomic distribution has destructive effect on size of conductance gap and destroys spin-filtering property. Moreover, we show that although the same results are obtained for transport properties of doped ZSiNR with various concentrations of Phosphorus atoms in presence of antiparallel exchange magnetic fields, a completely controllable spin-filtering property cannot be achieved by Fermi energy changes.     

Structural and electronic properties of a single C chain doped zigzag BN nanoribbons

The effects of single C-chain on the stability, structural and electronic properties of zigzag BN nanoribbons (ZBNNRs) were investigated by first-principles calculations. C-chain was expected to dope at B-edge for all the ribbon widths _Nz$N_z$ considered. The band gaps of C-chain doped _Nz$N_z$-ZBNNR are narrower than that of perfect ZBNNR due to new localized states induced by C-chain. The band gaps of _Nz$N_z$-ZBNNR-C(n  ) are direct except for the case of C-chain position n=2$n=2$. Band gaps of BN nanoribbons are tunable by C-chain and its position n, which may endow the potential applications of BNNR in electronics.     

The preparation of CdO nanowires from solid-state transformation of a layered metal-organic framework

A new coordination polymer formulated as [C₈H₁₀CdO₇]_n·4H₂O has been prepared via a hydrothermal procedure by using 1,4-benzenedicarboxylic (p-BDC) and Cd^II salt as starting materials. The structure was determined by single-crystal X-ray diffraction and the result shows that the complex crystallizes in orthorhombic system, space group Pcca, with M_r=402.62, a=7.293(2) Å, b=9.980(3) Å, c=19.889(6) Å, V=1447.6(8) Å³, Z=4, D_c=1.847 g/cm³, F(000)=808, μ(MoKα)=1.559 mm⁻¹, R=0.0478, wR=0.1150, GOF=1.199. It displays a neutral layered framework along ab plane constructed by hydrogen-bonding interaction through infinite zigzag chains. Its thermal decomposition and solid-state transformation course between 30 and 550 °C was recorded by TG curve and XRD pattern, respectively. Interestingly, it is found that at higher temperature the crystal material was converted to uniform CdO nanowires, suggesting an effective and reasonable complex-precursor procedure for preparing one-dimensional crystalline nanomaterials.