Synthesis and Photochemistry of Novel 3,5-Diacetyl-1,4-dihydropyridines. II [1]

In continuation of previous work some novel 3,5-diacetyl-1,4-dihydropyridine derivatives were synthesized and their photochemical behavior was studied under oxygen and argon atmosphere. Oxidation of the dihydropyridine ring and formation of pyridine derivatives was the result of the reaction. The presence of oxygen affects not only on the rate of oxidation, but also the formation of some unidentified by-products was observed on irradiation under this atmosphere.     

On the coupled NBEM and FEM for a class of nonlinear exterior Dirichlet problem in R 2

In this paper, based on the natural boundary reduction advanced by Feng and Yu, we couple the finite element approach with the natural boundary element method to study the weak solvability and Galerkin approximation of a class of nonlinear exterior boundary value problems. The analysis is mainly based on the variational formulation with constraints. We prove the error estimate of the finite element solution and obtain the asymptotic rate of convergence. Finally, we also give a numerical example.

     

Measurement of the K α to L α and K β to L β intensity ratios of seven elements in the atomic number range 52≤ Z ≤62 using photoionization at 59.5 keV1

The Kα to Lα and Kβ to Lβ intensity ratios of seven elements have been measured following photoionization at 59.5 keV by using a Si (Li) detector (FWHM=155 eV at 5.96 keV). The intensity ratios were determined by measuring K and L x-rays emitted from a standard target of a given element. The theoretical values of the Kα to Lα and Kβ to Lβ intensity ratios were calculated using theoretically tabulated values of shell/subshell photoionization cross sections, fluorescence yields, Coster-Kronig transition probabilities, and radiative decay rates for ηKLi≠ and ηKLi=0. The measured values are in good agreement with theoretical results. From Optika i Spektroskopiya, Vol. 97, No. 2, 2004, pp. 186–189. Original English Text Copyright ? 2004 by A. Kü?ük?nder, S?ğüt, E. Kü?ük?nder, Büyükkasap. This article was submitted by the authors in English.     

Metallization of U3O8via catalytic electrochemical reduction with Li2O in LiCl molten salt

The concept of a novel electrochemical reduction process for the treatment of spent nuclear fuels in Li₂O-LiCl molten salt was proposed and fresh tests using U₃O₈ powder were carried out to elucidate the reaction mechanism and verify the feasibility of the process. Electrolysis of Li₂O and reduction of U₃O₈ powder took place simultaneously at the cathode part of the electrolysis cell via a catalytic EC mechanism and the conversion of U₃O₈ to U metal was more than 99%. This revised version was published online in June 2006 with corrections to the Cover Date.     

Combined intra-intermolecular criss-cross cycloaddition of a new fluorinated unsymmetrical allenylazine with alkynes

The reaction of a new fluorinated unsymmetrical allenylazine with dimethyl acetylenedicarboxylate and phenylacetylene affords the combined intra-intermolecular criss-cross cycloaddition products, 2,3-disubstituted-1,10-diazatricyclo[5.2.1.0^4,10]deca-2,6-diene derivatives. The products contain three fused five-membered rings with two nitrogen atoms within an unsaturated heterocyclic system. The structures were assigned using 2D NMR correlations and in the case of the phenylacetylene adduct by X-ray structure analysis.     

Orbital formal normal forms for general Bogdanov-Takens singularity

We solve completely the problem of classification of germs of complex planar vector fields with nilpotent singularity with respect to formal orbital equivalence.     

Brightness and decay time of Zn2SiO4:Mn phosphor particles with spherical shape and fine size

Green-light-emitting Zn₂SiO₄:Mn phosphor particles were synthesized by modified large-scale spray pyrolysis using a colloidal solution containing fumed silica particles. The particles had a fine size, filled morphology, spherical shape and non-aggregation characteristics even after post-treatment at 1150 °C. The luminescence characteristics of Zn₂SiO₄:Mn phosphor particles having spherical shape, such as brightness and decay time under VUV excitation light, were investigated as a function of Mn content. The luminescence intensity exhibits a maximum at 5 mol% Mn-doped powder. The decay time increases consistently with decreasing Mn content and more saturated color coordinates are obtained with the composition having 12 mol% Mn. As a consequence, the 10 mol% Mn-doped powder proved to provide a good combination of favorable luminance and acceptable decay time. The influence of post-treatment temperature on the decay time and photoluminescence characteristics of Zn₂SiO₄:Mn particles was also investigated. Particles post-treated at 1155 °C had the maximum photoluminescence intensity, which was identical to 113% that of the commercial product, and a comparable decay time of 5.8 ms. PACS 81.20.Rg; 78. 55.Hx; 78.40.Ha; 81.05.Hd; 81.40.Tv     

Asymptotic properties of computationally efficient alternative estimators for a class of multivariate normal models

Parameters of Gaussian multivariate models are often estimated using the maximum likelihood approach. In spite of its merits, this methodology is not practical when the sample size is very large, as, for example, in the case of massive georeferenced data sets. In this paper, we study the asymptotic properties of the estimators that minimize three alternatives to the likelihood function, designed to increase the computational efficiency. This is achieved by applying the information sandwich technique to expansions of the pseudo-likelihood functions as quadratic forms of independent normal random variables. Theoretical calculations are given for a first-order autoregressive time series and then extended to a two-dimensional autoregressive process on a lattice. We compare the efficiency of the three estimators to that of the maximum likelihood estimator as well as among themselves, using numerical calculations of the theoretical results and simulations.     

Lyapunov-type inequalities for nonlinear systems

In this paper, by using elementary analysis, we establish some new Lyapunov-type inequalities for nonlinear systems of differential equations, special cases of which contain the well-known equations such as Emden-Fowler-type and half-linear equations. The inequalities obtained here can be used as handy tools in the study of qualitative behaviour of solutions of the associated equations.