Structural and optical characterization of InAs nanostructures grown on high-index InP substrates

The structural and optical properties of InAs layers grown on high-index InP surfaces by molecular beam epitaxy are investigated in order to understand the self-organization of quantum dots and quantum wires on novel index surfaces. Four different InP substrate orientations have been examined, namely, (1 1 1)B, (3 1 1)A, and (3 1 1)B and (1 0 0). A rich variety of InAs nanostructures is formed on the surfaces. Quantum wire-like morphology is observed on the (1 0 0) surface, and evident island formation is found on (1 1 1)A and (3 1 1)B by atomic force microscopy. The photoluminescence spectra of InP (1 1 1)A and (3 1 1)B samples show typical QD features with PL peaks in the wavelength range 1.3-1.55 mu m with comparable efficiency. These results suggest that the high-index substrates are promising candidates for production of high-quality self-organized QD materials for device applications. (C) 1999 Elsevier Science B.V. All rights reserved.

Single-negative negative index metamaterials with broad bandwidth - art. no. 683109

The theoretical method to design negative refractive index metamaterials by single negative permittivity metamaterials is presented. By designing the electric and magnetic response metamaterials separately, the complexity of the design work can be simplified a lot. For the magnetic response metamaterials, the metallic post structure is adopted. Varying the height of the post, the response wavelength can be adjusted linearly. For electric metamaterials, wire-mesh structure is adopted. The effective material parameters, including refractive index, impedance, permittivity and permeability are given. Such a structure has negative refractive index during a broad frequency band and easy to design.

Design and Realization of Index-Coupled DFB Laser with Sampled Grating

An index-coupled distributed feedback laser with the sampled grating has been designed and fabricated. The +1(st) order reflection of the sampled grating is utilized for laser single mode operation, which is 1.5329 mu m in the experiment. The sampled grating is formed by a conventional holographic exposure combined with the usual photolithography. The typical threshold current of DFB laser with the sampled grating is 25mA, and the optical output is about 10mW at the injected current of 100mA.

MULTIPLE PERIODIC SOLUTIONS OF ASYMPTOTICALLY LINEAR HAMILTONIAN SYSTEMS VIA CONLEY INDEX THEORY

In this paper we study the existence of periodic solutions of asymptotically linear Hamiltonian systems which may not satisfy the Palais-Smale condition. By using the Conley index theory and the Galerkin approximation methods, we establish the existence of at least two nontrivial periodic solutions for the corresponding systems.

基于重叠分块的FM-index性能研究与分析

FM-index压缩查询方法结合压缩技术和索引技术,其最大优势是能够在不解开压缩文件的情况下对源文件进行查询。该文通过理论分析和详细的测试数据研究重叠分块对FM-index压缩查询性能的改善。对改进后的FM-index和压缩软件Winrar在压缩时间和文件占用空间上进行分析和比较,进一步证明了重叠分块对FM-index压缩查询性能的改善。

FM-index分块并行算法及其实现

查询海量数据有压缩和索引两种方法来提高速度,该文结合这两种方法提出了压缩查询的方法.FM-index是一种自索引的全文查询算法,存在内存占用过大的问题,对于复杂的查询效率也不理想.该文提出分块FM-index算法,在分块的基础上采用MPI对算法进行并行化,解决了内存占用过多的问题,达到了较好的并行效率.

A Structured Prediction Approach for Statistical Machine Translation

We propose a new formally syntax-based method for statistical machine translation. Transductions between parsing trees are transformed into a problem of sequence tagging, which is then tackled by a search- based structured prediction method. This allows us to automatically acquire transla- tion knowledge from a parallel corpus without the need of complex linguistic parsing. This method can achieve compa- rable results with phrase-based method (like Pharaoh), however, only about ten percent number of translation table is used. Experiments show that the structured pre- diction approach for SMT is promising for its strong ability at combining words.

Investigation of Interfacial Tensions for Carbon Dioxide Aqueous Solutions by Perturbed-Chain Statistical Associating Fluid Theory Combined with Density-Gradient Theory

The perturbed-chain statistical associating fluid theory and density-gradient theory are used to construct an equation of state (EOS) applicable for the phase behaviors of carbon dioxide aqueous solutions. With the molecular parameters and influence parameters respectively regressed from bulk properties and surface tensions of pure fluids as input, both the bulk and interfacial properties of carbon dioxide aqueous solutions are satisfactorily correlated by adjusting the binary interaction parameter (k(ij)). Our results show that the constructed EOS is able to describe the interfacial properties of carbon dioxide aqueous solutions in a wide temperature range, and illustrate the influences of temperature, pressure, and densities in each phase on the interfacial properties.

Trapping of low-refractive-index particles with azimuthally polarized beam

Azimuthally polarized beams, focused by a high-numerical-aperture (NA) objective lens, form a hollow intensity distribution near the focus, which is appropriate for trapping low-refractive-index particles, in contrast to common linearly polarized or radially polarized beams. In this paper, the field distribution of the azimuthally polarized beam focused by a high-NA objective is described by the vectorial diffraction integral, and then the radiation forces on spherical particles with different parameters such as radius and refractive index are calculated by the T-matrix method. Numerical results show that the azimuthally polarized beam not only can steadily trap low-refractive-index particles at the focus center but also can trap multiple high-refractive-index particles around the focus center by virtue of the hollow-ring configuration. The range of the sizes of low-refractive-index particles that can be trapped steadily are presented, corresponding to different parameters such as the NA of the objective and the relative refractive index, based on which the NA of the objective can be selected to trap the appropriate size of particles. (C) 2009 Optical Society of America

Spectral relationship of photoinduced refractive index and absorption changes in fulgide films

Fulgides are one kind of organic photochromic compound, which are famous for their thermal irreversibility. In this report, from the difference spectra of the absorption A() of one kind of pyrrylfulgide, the spectral refractive index change n() was calculated by the Kramers-Kronig relation (KKR), and a good correlation of theoretically derived values and the experimental values of the n measured by a modified Michelson interferometer was found. Further, it is demonstrated that it was possible to calculate the spectral dependence of diffraction efficiency from the easily accessible absorption changes. This method will be a useful tool for the characterization and optimization of fulgide films. The results show that the diffraction efficiency is high at 488 and 750 nm, where the absorption is very small, so we can realize non-destructive reconstruction.

Yb3+-doped 200 mu m diameter core, gain guided index-antiguided fiber

The lasing in an end-pumped gain guided index-antiguided (GG-IAG) Yb3+-doped silicate glass fiber with a 200 mu m diameter core is demonstrated. Laser beams with similar beam propagation factors M (2) and mode field diameters W (0) (> 160 mu m) were observed at the output end of the GG-IAG fibers under different pump powers, which indicated that single mode behavior and excellent beam quality were achieved during propagation. Furthermore, the laser amplifier characteristics in the present Yb3+-doped GG-IAG fiber were also evaluated.