用于光子晶体光纤研究的超格子构造法

提出应用“超格子构造法”研究光子晶体光纤(PCF)的传输特性。电场用正交完备的厄米 高斯(Hermite Gauss)函数展开,有中心缺陷的周期性分布的介电常数用两组不同周期的介电常数分布迭加构成超格子,每组介 电常数都用余弦函数展开,然后利用波动方程及厄米 高斯函数的正交性,得到光子晶体光纤的传输特性(模场分 布、双折射、色散)。模式双折射的大小可用以衡量该算法的精度。

利用超格子模型对布拉格光纤的研究

为了研究布拉格光纤的模式特征和传输特性,提出了超格子模型,利用傅里叶级数表示光纤横向折射率分布,利用平面波展开法分析布拉格光纤的能带结构,基于厄米-主斯函数的局域正交函数展开法,从全矢量耦合波动方程出发,得到关于模式传播常量和电场展开系数的本征方程,从而分析布拉格光纤的模式特征。以高折射率芯布拉格光纤为例,实现了该算法,得到基模与二次模的横向电场分布、基模色散曲线和模式双折射。基模的模式双折射可用于衡量算法的精度,结果表明该算法精度较高。超格子模型不仅可以用于研究高折射率芯布拉格光纤,而且同样可以研究低折射率区域导光的布拉格光纤。

具有压缩三角格子的高双折射色散补偿光子晶体光纤

设计了一种具有高双折射和高负色散特性的光子晶体光纤。在包层中,采用压缩三角格子和两种不同大小椭圆空气孔。基于超格子构造法,研究了光子晶体光纤的结构参数对双折射特性和色散特性的影响。数值研究结果表明:双折射在1.1~1.9μm的宽波段范围内达到10^(-2)的高数量级,色散在1.4~1.8μm的宽波段范围内实现了高负色散,而且在传输窗口波长1.55μm处,双折射可达到3.4×10^(-2),x-和y-偏振基模色散分别为-127 ps/(nm·km)和-428 ps/(nm·km)。此外,双折射、色散和有效面积特性随光子晶体光纤结构的变化也进行了详细的研究。基于其高双折射和高负色散特性,此种光纤可以广泛用于色散补偿光纤和偏振依赖型通讯系统。

一种高双折射高负平坦色散压缩型光子晶体光纤

设计了一种具有高负平坦色散特性的压缩型高双折射光子晶体光纤。为了获得高双折射特性,光纤包层采用压缩三角格子和椭圆空气孔的结构;为了提高控制色散的灵活性,在纤芯加入小的缺陷空气孔。基于超格子构造法,详细地模拟分析了光纤的双折射、色散特性。研究结果表明:在波长1.3~1.8μm的宽波段范围内,可获得高负平坦色散且色散值约为-667 ps·nm^(-1)·km^(-1),色散值在±7 ps·nm^(-1)·km^(-1)的范围内变化;双折射在波长研究范围内都实现了10^(-2)的高数量级,且在1.55μm处可达到2.21×10^(-2)。基于此种光纤的高负色散特性和高双折射在光传输系统及光纤传感有广泛应用。

压缩型光子晶体光纤的双折射特性

定义了压缩率的概念,提出了一个可以构建三角格子、压缩三角格子、正方格子和矩形格子光子晶体光纤的模型;基于此压缩率模型,应用超格子构造法研究了压缩对光子晶体光纤双折射特性的影响.结果表明,通过改变光子晶体光纤晶格的压缩率可以获得较大的双折射.另外,分析了光纤双折射随晶格常数和空气孔直径的变化规律,并报导了光纤双折射符号随着空气孔直径变化而发生多次改变的现象.

多维空间索引结构SHG-Tree(英文)

R-Tree及其变种的多维索引结构在数据的操作过程中通过对空间的分隔和不断调整将整个空间划分为大小不等的子空间以容纳足够的空间对象,这种方法能有效地实现多维空间对象的索引,但不能避免频繁的节点分裂与重组操作所造成的计算开销,也不能避免对叶子节点中的候选对象进行空间匹配所带来的计算开销。提出了一种能有效解决上述问题的索引结构:SHG-Tree。基于SHG-Tree的索引方法将多维空间划分为不同粒度的格子单元并将这些格子单元通过SHG-Tree按空间包含关系组织为层次树结构,同一层的格子互不相交且空间范围固定。空间对象通过文中提出的线性化方法转换为一系列不同粒度的互不相交的空间格子,进而将对象在其覆盖的格子中注册以实现空间对象至SHG-Tree的映射。查询操作只需将查询条件映射为相应的格子并取出这些格子中的对象作为查询结果。这种索引结构能有效减少节点的分裂和组合带来的计算开销,也解决了传统R-Tree索引中对于叶子节点中的候选对象进行区域匹配的计算开销。基于SHG-Tree的索引结构支持包括相交查询、区域查询、包含查询、top-N查询、k-NN查询等常用的多维查询,实验表明SHG-Tree能在毫秒级实现各种空间查询。

三洋电机公司大容量五号镍氢电池上市

日本三洋电机公司于2004年8月1日上市两款最新的,容量为2500mAh(Min.2300mAh)的5号镍氢充电电池和900mAh(Min.840mAh)的7号镍氢充电电池,同时上市的还有新的快速充电器套装系列N-M57S和M-MR57S(带放电功能).全球镍氢电池的竞争十分惨烈.

NEW ITERATIVE SUPER-TRELLIS DECODING WITH SOURCE A PRIORI INFORMATION FOR VLCS WITH TURBO CODES

A novel Joint Source and Channel Decoding (JSCD) scheme for Variable Length Codes (VLCs) concatenated with turbo codes utilizing a new super-trellis decoding algorithm is presented in this letter. The basic idea of our decoding algorithm is that source a priori information with the form of bit transition probabilities corresponding to the VLC tree can be derived directly from sub-state transitions in new composite-state represented super-trellis. A Maximum Likelihood (ML) decoding algorithm for VLC sequence estimations based on the proposed super-trellis is also described. Simu-lation results show that the new iterative decoding scheme can obtain obvious encoding gain especially for Reversible Variable Length Codes (RVLCs),when compared with the classical separated turbo decoding and the previous joint decoding not considering source statistical characteristics.

Superlattice Patterns in Coupled Turing Systems

In this paper, superlattice patterns have been investigated by using a two linearly coupled Brusselator model. It is found that superlattice patterns can only be induced in the sub-system with the short wavelength. Three different coupling methods have been used in order to investigate the mode interaction between the two Turing modes. It is proved in the simulations that interaction between activators in the two sub-systems leads to spontaneous formation of black eye pattern and/or white eye patterns while interaction between inhibitors leads to spontaneous formation of super-hexagonal pattern. It is also demonstrated that the same symmetries of the two modes and suitable wavelength ratio of the two modes should also be satisfied to form superlattice patterns.

ab initio CALCULATION FOR THE ELECTRONIC STRUCTURE OF GaAs/Al_xGa_(1-x) As SUPERLATTICES: CONJUGATE GRADIENT APPROACH

The electronic structure of GaAs/Al xGa 1-x As superlattices has been investigated by an ab initio calculation method—the conjugate gradient (CG) approach.In order to determine that,a conventional CG scheme is modified for our superlattices:First,apart from the former scheme,for the fixed electron density n(z),the eigenvalues and eigenfunctions are calculated,and then by using those,reconstruct the new n(z).Also,for every k z,we apply the CG schemes independently.The calculated energy difference between two minibands,and Fermi energy are in good agreement with the experimental data.

Chinese Scientists in Dubna(1956–1965)

The work of Chinese scientists conducted at the Joint Institute for Nuclear Research(JINR)(1956–1965)was inextricably linked to the Sino-Soviet relations in the 1950 s–1960 s.During the early stage of the JINR,with the aid of advanced equipment and the international cooperation mechanism,Chinese scientists yielded significant results,such as the discovery of the antisigma-minus hyperon and the proof of the law of partial conservation of axial current(PCAC).After the Sino-Soviet split,Chinese scientists’activities at the institute were hampered by political tensions,eventually resulting in China’s withdrawal from the JINR in 1965.But through the involvement at the JINR,Chinese scientists were trained in scientific practices and participated in international exchange and cooperation which turned them into a new force in China’s nuclear industry,boosting its nuclear weapons,particle physics theory,and accelerator technology.In the meantime,the scientists’activities extended the international influence of the JINR.The withdrawal of China from the institute impacted both the JINR and the development of science in China.

Frequency in Middle of Magnon Band Gap in a Layered Ferromagnetic Superlattice

The frequency in middle of magnon energy band in a five-layer ferromagnetic superlattice is studied by using the linear spin-wave approach and Green＇s function technique. It is found that four energy gaps and corresponding four frequencie in middle of energy gaps exist in the magnon band along Kx direction perpendicular to the superlattice plane. The spin quantum numbers and the interlayer exchange couplings all affect the four frequencies in middle of the energy gaps. When all interlayer exchange couplings are same, the effect of spin quantum numbers on the frequency wg1 in middle of the energy gap Δw12 is complicated, and the frequency wg1 depends on the match of spin quantum numbers in each layer. Meanwhile, the frequencies wg2, wg3, and wg4 in middle of other energy gaps increase monotonously with increasing spin quantum numbers. When the spin quantum numbers in each layer are same, the frequencies wg1, wg2, wg3, and wg4 all increase monotonously with increasing interlayer exchange couplings.

Elastic Constants of Superconducting MgB2 from Molecular Dynamics Simulations with Shell Model

The elastic constants of superconducting MgB2 are calculated using a molecular dynamics method (MD)with shell model. The lattice parameters, five independent elastic constants, equations of state (EOS), Debye temperature, and bulk modulus of MgB2 are obtained. Meanwhile, the dependence of the bulk modulus B, the lattice parameters a and c, and the unit cell volume V on the applied pressure are presented. It is demonstrated that the method introduced here can well reproduce the experimental results with a reasonable accuracy.

Atoms of Lattices of Supernilpotent and Special Radicals

In this paper we define pure-supernilpotent radical and show that the class of all pureaupernilpotent radicals forms a complete lattice. We discuss some open questions on lattices of supernilpotent and special radicals [5, 6] and obtain some new results.

ab initio CALCULATION FOR THE ELECTRONIC STRUCTURE OF GaAs/AlxGa1-x As SUPERLATTICES: CONJUGATE GRADIENT APPROACH

The electronic structure of GaAs/Al xGa 1-x As superlattices has been investigated by an ab initio calculation method—the conjugate gradient (CG) approach.In order to determine that,a conventional CG scheme is modified for our superlattices:First,apart from the former scheme,for the fixed electron density n(z),the eigenvalues and eigenfunctions are calculated,and then by using those,reconstruct the new n(z).Also,for every k z,we apply the CG schemes independently.The calculated energy difference between two minibands,and Fermi energy are in good agreement with the experimental data.

FABRICATION OF PHOTONIC CRYSTAL WITH SUPERLATTICES

A novel technique was used to fabricate three-dimensional photonic crystals with superlattices. The super structure was fabricated by assembling monodispersed microspheres in the grooves of the scales of morpho butterfly, which makes the photonic crystal being composed of two kinds of different photonic structures (natural groove structure of butterfly wing and artificial microspherical colloids arrangement). The superstructural photonic crystal exhibits some unique optical properties different from both the butterfly wing and the colloidal crystal. The approach exhibited here provides a new way for fabricate photonic crystals with superlattices.

Novel Quantum Phases of Ultracold Bosonic Atoms in Honeycomb Optical Lattice

We study the quantum phase transition of ultracold atoms in the honeycomb optical lattice. The Hamiltonian of ultracold bosonic atoms in the honeycomb optical lattice is derived. We take the mean-field approximation and further solve the Hamiltonian with the numerical diagonalization method. We obtain the phase diagram and find that the Mort-insulator （MI）, density wave （DW） and modulated superfluid （MS） phases appear. Furthermore, the phase diagram is analyzed according to the order parameter and the average number of particles.

On gl（2｜2）（2）k Current Superalgebra and Twisted Conformal Field Theory

Motivated by the recently discovered hidden symmetry of the type IIB Green-Schwarz superstring on certain background, the non-semisimple Kac-Moody twisted superalgebra gl（2｜2）（2）k is investigated by means of the vector coherent state method and boson-fermion realization. The free field realization of the twisted current superalgebra at general level k is constructed. The corresponding Conformai Field Theory （CFT） has zero central charge. According to the classification theory, this CFT is a nonunitary field theory. After projecting out a U（1） factor and an outer automorphism operator, we get the free field representation of psl（2｜2）（2）k, which is the a/gebra of gl（2｜2）（2）k modulo the Z4-outer automorphism, the CFT has central charge -2.

Quantum Phase Transition in Two Species of Cold Bosonic Atoms

In this letter, the superfluid-Mott-insulator phase transition of two-species cold bosonic atoms in an optical lattices is studied. The Hamiltonian of this model is diagonalized by means of Bogliubov transformations and by the inversion symmetry of the optical lattice, the energy spectrum of this system is obtained. From She energy gap of the excitation spectrum, the quantum phase transition condition is obtained and it is determined by the competition between the interatomic repulsions and the tunnel coupling. It is found that there exists an ordinary fluid phase when taking the zero wave-vector limit.