Refractometer based on a tapered Mach–Zehnder interferometer with Peanut-Shape structure

A novel refractometer based on tapered Mach–Zehnder modal interferometer (MZI) is proposed and experimentally demonstrated. This sensor is composed of a pair of Peanut-Shape structures and an embedded taper – the former excites high-order cladding modes, while the latter enhances the evanescent field. As the effective refractive index (RI) of cladding is based on the changes of surrounding RI, thus extinction ratio will change due to the alteration of the distribution of power in the fiber which is induced by various differences of core and cladding for RI. As a result, the maximum RI sensitivity of 240.78 extinction ratio/RIU (refractive index unit) is achieved within the range from 1.3334 to 1.4081.     

Dynamics of a stochastic density dependent predator-prey system with Beddington-DeAngelis functional response

In this paper, we discuss a stochastic density dependent predator-prey system with Beddington-DeAngelis functional response. First, we show that this system has a unique positive solution as this is essential in any population dynamics model. Then, we investigate the asymptotic behavior of this system. When the white noise is small, the stochastic system imitates the corresponding deterministic system. Either there is a stationary distribution, or the predator population will die out. While if the white noise is large, besides the extinction of the predator population, both species in the system may also die out, which does not happen in the deterministic system. Finally, simulations are carried out to conform to our results.     

Partial extinction,permanence and global attractivity in nonautonomous <Emphasis Type="Italic">n</Emphasis>-species Lotka-Volterra competitive systems with impulses

In this paper, the qualitative properties of general nonautonomous Lotka-Volterra n-species competitive systems with impulsive effects are studied. Some new criteria on the permanence, extinction and global attractivity of partial species are established by used the methods of inequalities estimate and Liapunov functions. As applications, nonautonomous two species Lotka-Volterra systems with impulses are discussed.     

Study on optical properties of aggregated ultra-small metal nanoparticles

We study the optical properties of dimer and septamer aggregates (in forms of being separated or merged) of ultra-small silver nanoparticles (a few nanometers in diameter) by calculating their extinction spectra and optical field distributions using the discrete dipole approximation method. Characteristics of their extinction spectra are identified due to different resonance modes dependent on the incidence states of light. Specifically, as polarization of the incidence light is perpendicular to the center-to-center lines of the nanoparticles, interaction of neighboring nanoparticles is in the “repulsive coupling mode”, which results in blue-shift of the resonance peak with decrease of the nanoparticle interspacing. While, whenever there is a projection of the polarization of incident light on the center-to-center lines of the nanoparticles, the “attractive coupling mode” between the nanoparticles dominates in their resonant interaction, which results in red-shift of the resonance peak with decrease of the nanoparticle interspacing. It is also shown that optical interaction of the ultra-small nanoparticles is only effective when their interspacings are approximately less than 15 nm, and particularly prominent when Coulomb interactions of the electronic charges of plasmons are active within a few nanometers.     

具有时滞的非自治Lotka-Volterra竞争系统的持久与灭绝

本文研究具有纯时滞的一般Ｎ－种群非自治Ｌｏｔｋａ－Ｖｏｌｔｅｒｒａ竞争系统的持久性和灭绝性．一些新的判别准则被建立．文献［８－１０］中得到的关于无时滞非自治Ｌｏｔｋａ－Ｖｏｌｔｅｒｒａ竞争系统的结果被改进和推广．     

薄膜的光谱发射率

本文讨论了薄膜内的多次反射对低吸收薄膜光谱发射率的影响。这里推导出的薄膜发射率的表达式与薄膜厚度d和其光学常数n(λ）和k(λ）有关。在d→∞的特殊情况下，薄膜发射率与大块材料发射率相等。给出了实际数值评价及发射率与d、n(λ）和k(λ)相互关系的更为精确的数值结果。     

Microstructural characterization and optical polarization of glass with needle-like micro–nano silver oriented arrangement

Homogeneous glasses in the Na₂O–B₂O₃–Al₂O₃–SiO₂ system doped with proper amount of AgCl were obtained by melting at a temperature of 1450 °C. Then, with several steps of treatment, including crystallization, elongation and reduction, the glass with oriented arrangement of needle-like micro–nano silver particles was produced. The microstructure and the optical properties of the glass samples in different stages were studied by SEM-EDAX, FE-SEM and UV–Vis spectrum. The results showed that the glass after elongation and reduction exhibits excellent polarization performance in the wavelength range from 600 nm to 900 nm, with an extinction ratio larger than 45 dB. The glass only elongated shows also slight polarizing performance, which may result from the formation of filament structure of Ag during elongation processing.     

Dynamics of a two-species Lotka-Volterra competition system in a polluted environment with pulse toxicant input

In most models of population dynamics in a polluted environment, the emission of toxicant is generally considered to be continuous, but it is often the case that toxicant is emitted in regular pulses. This paper deals with the effects of pulse toxicant input with constant rate on two-species Lotka-Volterra competition system in a polluted environment. The thresholds between persistence and extinction of each population are obtained. Moreover, our results indicate that the release amount of toxicant and the pulse period will affect the fate of each population. Finally, the results are verified through computer simulations.     

Effect of layer structures of gold nanoparticle films on surface enhanced Raman scattering

Using a method of collecting nanoparticles at a water/hexane interface in a close-packed monolayer film and transferring such films onto a solid substrate, three-dimensional multilayer films of nanoparticles were formed. The packed nanoparticles were gold nanospheres (NS) with a 26 nm diameter or gold nanorods (NR) with a 31 nm diameter and 74 nm length. We investigated variations in the surface enhanced Raman scattering (SERS) intensities from such nanoparticle films as the layer compositions were changed. The films stacked with NR layers generated much higher SERS intensity than those of NS layers. The SERS intensities from both kinds of films increased as the number of layers were increased. However, when the NR layer and NS layer were stacked alternately, SERS intensity varied in a zigzag fashion. It was found that the structure of top layer plays a distinguishable role in generating strong SERS enhancement while the lower layers contribute to SERS with less dependency on structures. Interlayer coupling as well as intralayer coupling was considered in order to explain the observations.