Specular propagation over rough surfaces: numerical assessment of Uscinski and Stanek's mean Green's function technique

The purpose of this paper is to numerically evaluate the effectiveness and accuracy of Uscinski and Stanek's mean Green's function technique for computing the mean field of a wave scattered by a rough surface. We present here a direct comparison of this technique with a rigorous numerical method, the forward scattering integral equation method, and another analytical method, the first-order smoothing approximation. Furthermore, we compare the roughness generated equivalent admittance using the three methods. Numerical computations reveal that the scattered field calculated by this technique is not accurate particularly for the equivalent admittance at low grazing angles, even though the mean surface current density is recovered when the wave has traversed several correlation lengths on the surface.     

Interaction among Cadmium Sulfide Nanoparticles, Acridine Orange, and Deoxyribonucleic Acid in Fluorescence Spectra and a Method for Deoxyribonucleic Acid Determination

Some studies on quantum dots (QD) as donors that enhance the fluorescence of a dye as an acceptor through fluorescence resonance energy transfer (FRET) have been reported. However, in the present work we discovered that CdS quantum dots sharply quenched the fluorescence of acridine orange (AO). Also, DNA enhanced the fluorescent signals of AO quenched by CdS. The extents of enhancement were in good proportion to the DNA concentrations. Based on this, a sensitive method was employed to determine DNA with both good selectivity and sensitivity. The calibration curve was linear over 60-4,000 ng mL(-1) and the determination limit (3sigma) was 4.39 ng mL(-1).     

Influence of depressed-index outer ring on evanescent tunneling loss in tapered double-cladding fibers

A tapered fiber with a depressed-index outer ring is fabricated and dispersion engineered to generate a widely tunable (1250-1650 nm) fundamental-mode leakage loss with a high cutoff slope (-1.2 dB/nm) and a high attenuation for stop band (>50 dB) by modification of both waveguide and material dispersions. The higher cutoff slope is achieved with a larger cross angle between the two refractive index dispersion curves of the tapered fiber and surrounding optical liquids through the use of depressed-index outer ring structures in double-cladding fibers.     

Organic p-i-n solar cells

We introduce a p-i-n-type heterojunction architecture for organic solar cells where the active region is sandwiched between two doped wide-gap layers. The term p-i-n means here a layer sequence in the form p-doped layer, intrinsic layer and n-doped layer. The doping is realized by controlled co-evaporation using organic dopants and leads to conductivities of 10^-4 to 10^-5 S/cm in the p- and n-doped wide-gap layers, respectively. The photoactive layer is formed by a mixture of phthalocyanine zinc (ZnPc) and the fullerene C₆₀ and shows mainly amorphous morphology. As a first step towards p-i-n structures, we show the advantage of using wide-gap layers in M-i-p-type diodes (metal layer–intrinsic layer–p-doped layer). The solar cells exhibit a maximum external quantum efficiency of 40% between 630-nm and 700-nm wavelength. With the help of an optical multilayer model, we optimize the optical properties of the solar cells by placing the active region at the maximum of the optical field distribution. The results of the model are largely confirmed by the experimental findings. For an optically optimized device, we find an internal quantum efficiency of around 82% under short-circuit conditions. Adding a layer of 10-nm thickness of the red material N,N-dimethylperylene-3,4:9,10-dicarboximide (Me-PTCDI) to the active region, a power-conversion efficiency of 1.9% for a single cell is obtained. Such optically thin cells with high internal quantum efficiency are an important step towards high-efficiency tandem cells. First tandem cells which are not yet optimized already show 2.4% power-conversion efficiency under simulated AM 1.5 illumination of 125 mW/cm² . PACS 73.61.Ph; 78.30.Jw; 89.30.Cc     

Monostability,bistability, periodicity and chaos in gene regulatory network

This letter gives a general review on the monostability, bistability, periodicity and chaos in gene regulatory network. Some simple motifs that generate monostability, bistability, periodicity and chaos are analytically and numerically reported. Further research directions of the nonlinear dynamics of gene regulatory network are discussed.     

Matter and light wave interferometry in gravitational fields

We consider the problem of finding the quantum mechanical phase associated with the propagation of a particle in a given external gravitational field, and conclude that it ism ds. In weak fieldsh this allows us to calculate the gravitationally induced phase on a freely traveling particle as 1/2 h P dx whereP is the ordinary momentum. This formula has the expected Newtonian limit and is then used to calculate effects in matter wave interferometry such as those due to gravity waves and the dragging of the ether frame by rotating bodies. Light wave interferometry is then considered and is shown to be also described by 1/2 h K dx , whereK is the wave vector of the light, and the integral is along the path of the ray. Matter and light wave interferometry are compared in various cases.A preliminary version of this work was presented at the Grenoble Workshop on Neutron Interferometry, June 1978.     

Above-threshold ionization photoelectron spectrum from quantum trajectory

Many nonlinear quantum phenomena of intense laser-atom physics can be intuitively explained with the concept of trajectory. In this paper, Bohmian mechanics (BM) is introduced to study a multiphoton process of atoms interacting with the intense laser field: above-threshold ionization (ATI). Quantum trajectory of an atomic electron in intense laser field is obtained from the Bohm-Newton equation first and then the energy of the photoelectron is gained from its trajectory. With energies of an ensemble of photoelectrons, we obtain the ATI spectrum which is consistent with the previous theoretical and experimental results. Comparing BM with the classical trajectory Monte-Carlo method, we conclude that quantum potential may play a key role to reproduce the spectrum of ATI. Our work may present a new approach to understanding quantum phenomena in intense laser-atom physics with the image of trajectory.     

Numerical solution of the two-dimensional Poincaré equation

This paper deals with numerical approximation of the two-dimensional Poincaré equation that arises as a model for internal wave motion in enclosed containers. Inspired by the hyperbolicity of the equation we propose a discretisation particularly suited for this problem, which results in matrices whose size varies linearly with the number of grid points along the coordinate axes. Exact solutions are obtained, defined on a perturbed boundary. Furthermore, the problem is seen to be ill-posed and there is need for a regularisation scheme, which we base on a minimal-energy approach.     

An inequality for the group chromatic number of a graph

We give an inequality for the group chromatic number of a graph as an extension of Brooks’ Theorem. Moreover, we obtain a structural theorem for graphs satisfying the equality and discuss applications of the theorem.