B-C-N Compound Synthesized Under High Temperature and High Pressure

Crystalline hexagonal B(N 1 m x C x ) and cubic B-C-N compounds have been synthesized from a precursor produced from melamine and boric acid by application of high temperature and high pressure. The synthesized products were characterized by X-ray diffraction. The lattice parameters for the hexagonal crystal are a=2.506 Å, c=6.657 Å, and that for the cubic crystal is a=3.596 Å. The X-ray photoelectron spectra of the B-C-N compound indicate the presence of B-N, C-N, C-C, and B-C bonds, which suggests that boron, carbon, and nitrogen atoms all bond with one another and that the B-C-N crystal is a compound in which the three kinds of atoms are mixed atomically. The composition of the B-C-N compound is B 0.47 C 0.23 N 0.30 . A strong absorption band at 1000～1120 cm m 1 attributable to the cubic B-C-N phase is observed in the infrared spectrum. The photoluminescence spectrum of hexagonal B-C-N powder measured at room temperature features a broad peak centered at 374 nm, corresponding to the band-edge emission of h-B-C-N, and is similar to that of w-GaN.     

Theory of the Domino Dynamics Via Nonadiabatic Transitions

Photoinduced nucleation processes, called photoinduced domino processes, via excited electronic states are discussed theoretically for a one-dimensional arrangement of deformable molecules using a model composed of localized electrons and lattices. We show that the global structural transition by photoexcitation only at a molecule (site) is possible in the adiabatic and diabatic limits. An intermediate regime between these limits is investigated; an analytical treatment and a numerical calculation are presented taking into account the nonadiabatic electronic transition, i . e ., the Landau-Zener-type transition. In this regime, the domino dynamics can be terminated halfway ( i . e ., a finite - size domain appears) in contrast to the "all-or-nothing" domino dynamics ( i . e ., a photoinduced domain vanishes or grows up to the system size) in the adiabatic and diabatic limits.     

Modeling Structural and Magnetic Phase Transitions in Iron-Nickel Nanoparticles

Martensitic phase transformations and magnetovolume effects in iron-nickel alloys are intimately related. The term Invar is widely used to characterize the unusual physical properties accompanying structural and magnetic instabilities such as those observed in the vicinity of the critical composition Fe 65 Ni 35 . We discuss the crossover from bulk iron-nickel alloys to nanoparticles with respect to structural and magnetic behavior. By employing molecular-dynamics and Monte Carlo methods, we find the absence of structural instabilities in defect-free particles, a linear scaling of the austenitic transformation temperature with the reciprocal cluster radius, as well as a decrease of the magnetic transition temperature with decreasing particle size.     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Boundary Value Problems with Sign Changing Nonlinearities for Second Order Singular Ordinary Differential Equations

General existence criteria, based on upper and lower solution type arguments, are presented for the Dirichlet boundary value problem y " + f ( t , y , y ') = 0, 0 < t < 1 with y (0) = y (1) = 0. Our nonlinearity may be singular in its dependent variable and is allowed to change sign.     

Monotone Method for Second Order Periodic Boundary Value Problems and Periodic Solutions of Delay Difference Equations

In this article, we employ monotone iterative technique to study the existence of solutions for second order periodic boundary value problem and periodic solutions of delay difference equations.     

Necessary-Sufficient Conditions for Permanence and Extinction in Lotka-Volterra System with Discrete Delays

In this article, we give the necessary and sufficient conditions for permanence and extinction of a two-species Lotka-Volterra system with different discrete delays. We improve some previous results. Moreover, we show the permanence and extinction for this system is equivalent to that of its corresponding nondelayed system.     

Differential Inequalities with Initial Time Difference

Some comparison results are obtained for differential inequalities with initial time difference. They are useful to get existence and stability theorems for differential equations.     

Exponential Decay Rates for Structural Acoustic Model with an Overdamping on the Interface and Boundary Layer Dissipation

We study uniform stability properties of a strongly coupled system of Partial Differential Equations of hyperbolic/parabolic type, which arises from the analysis and control of acoustic models with structural damping on an interface. A challenging feature of the present model is the presence of additional strong boundary damping which is responsible for lack of uniform stability of the free system ( overdamping phenomenon). It has been shown recently that by applying full viscous damping in the interior of the domain and suitable static damping on the interface, then the corresponding feedback system is uniformly stable. In this article we prove that uniform decay rates of solutions to the system can be achieved even if viscous damping is active just in an arbitrary thin layer near the interface.     

Existence and Comparison Results for First Order Periodic Implicit Difference Equations with Maxima

In this paper, we establish comparison results (maximum principles) which allow us to use the monotone method and the method of upper and lower solutions in order to build convergent sequences to the solutions of difference equations of the type j u k = f k , u k +1 , max l ] { k m h +1,…, k +1} u l , k ] I , u 0 = u T , with j u k = u k +1 m u k , I ={0,1,…, T m 1} and f ] C ( I 2 R 2 R , R ).