A DERIVATIVE-FREE ALGORITHM FOR UNCONSTRAINED OPTIMIZATION

In this paper a hybrid algorithm which combines the pattern search method and the genetic algorithm for unconstrained optimization is presented. The algorithm is a deterministic pattern search algorithm,but in the search step of pattern search algorithm,the trial points are produced by a way like the genetic algorithm. At each iterate, by reduplication,crossover and mutation, a finite set of points can be used. In theory,the algorithm is globally convergent. The most stir is the numerical results showing that it can find the global minimizer for some problems ,which other pattern search algorithms don＇t bear.     

Physical mechanics calculations for the cohesive energies and elastic constants of alkali-halide crystals

The Gordon-Kim method of calculating the interatomic potentials is modified with corrections to the exchange and dispersion interactions, and the interionic potentials in alkali-halide crystals are calculated from Roothaan-Hartree-Fock ionic wavefunctions. The lattice constants, cohesive energies and elastic constants of NaCl, NaF, NaBr, KCl, KF, KBr, RbCl, RbF and RbBr crystals are evaluated using the calculated interionic potentials. The agreement of the results with the experimental data is good.     

An improved AUSM-family scheme with robustness and accuracy for all Mach number flows

With the increasing popularity of Computational Fluid Dynamics (CFD), the reliability of numerical scheme becomes prominent. The work presents a newly improved scheme more reliable in all Mach number regimes to circumvent some typical symptoms of the previous AUSM-family schemes observed in hypersonic and very low speeds. This scheme is facilitated by reconstructing pressure diffusion term in mass flux, velocity diffusion term in pressure flux and numerical sound speed. Then, a variety of benchmark test cases are selected to systematically assess the effects of these key ingredients and investigate the additional features in terms of robustness and accuracy. The proposed scheme attains stronger shock robustness against carbuncle instability, better low-speed accuracy and higher resolution of oblique shocks compared with many existing upwind schemes. Moreover, it can exactly resolve contact discontinuity, preserve positivity, damp numerical overshoots and avert the global cut-off strategy. Numerical results for a wide spectrum of Mach numbers indicate its potential and reliable application to all Mach number flows.     

时滞Hopfield神经网络模型渐进稳定性的新准则

在不考虑激励函数有界,可微和单调的情况下,利用Lyapunov泛函方法,得到了时滞Hopfield神经网络模型的平衡点存在性和全局渐近稳定性的新准则.研究结果改进和推广了以前相关文献的结果.     

Structural and spectroscopic studies of LaPO4:Ce/Tb@LaPO4@SiO2 nanorods: Synthesis and role of surface coating

Highly fluorescent LaPO₄:Ce/Tb@LaPO₄@SiO₂ (core/shell/Si) nanorods(NRs) were fabricated with an average length 100 nm by co-precipitation process at low temperature. X-ray diffraction (XRD), Transmission electron microscopy (TEM), energy dispersive X-ray analysis, Fourier transform infrared, optical absorption and photoluminescence spectral techniques were applied to investigate the crystal structure, phase purity, morphology, surface chemistry and optical properties of the as-prepared samples. XRD results confirmed the formation of highly crystalline with single phase, monoclinic type structure. TEM image illustrates the poly-dispersed, narrow size distributed, irregular size rod-shaped nanostructures, with mean diameters of 20 nm and average lengths up to 140 nm. FTIR spectral analysis confirmed the silica surface modification. The comparative emission spectral study shows highest luminescence intensity of core/shell NRs, due to a reduction in nonradiative transition rate. The emission intensity enhancement proves that growing of an inert LaPO₄ layer on the surface of luminescent core-NRs was an effective way to suppress surface related quenching mechanism. These well crystalline, highly aqueous soluble along with extraordinary colloidal stability core/shell/Si NRs were extremely suitable material in fluorescent bio-labeling applications.     

Synthesis and electro-optical properties of self-doped ionic conjugated polymers: poly[2-ethynyl-N-(4-sulfobutyl)pyridinium betaine]

A noble self-dopable conjugated polybetaine, poly[2-ethynyl-N-(4-sulfobutyl)pyridinium betaine] (PESPB) was synthesized by the activated polymerization of 2-ethynylpyridine with 1,4-butanesultone without any additional initiator or catalyst. This polymerization proceeded at the condition of high temperature (130 °C). The polymer yield and inherent viscosity were 82% and 0.13 dl/g, respectively. The chemical structure of PESPB was identified by various instrumental methods to have a conjugated ionic polymer bearing the sulfobetaine moieties. This poly(sulfobetaine) was found to be more soluble in salt solution than in salt-free solution. The photoluminescence peak is located at 530 nm corresponding to the photon energy of 2.34 eV. The photoluminescence intensity was increased as the temperature is increased. At 1 kHz and room temperature, the dielectric constant and electrical conductivity of PESPB were 5.7 and 3.5 × 10⁻⁹ S/cm, respectively.     

HGAH矩阵的逆特征值问题

In this paper, the inverse eigenvalue problem of Hermitian generalized anti-Hamihonian matrices and relevant optimal approximate problem are considered. The necessary and sufficient conditions of the solvability for inverse eigenvalue problem and an expression of the general solution of the problem are derived. The solution of the relevant optimal approximate problem is given.