The effect of composition variables on precursor degradation and their consequence on Nb2O5 film properties prepared by the Pecchini Method

The calcination of Nb₂O₅ prepared by the Pecchini method was investigated using thermal analysis. The polymer precursor was prepared with different citric acid/ethylene glycol (CA/EG) and citric acid/niobium precursor (CA/Nb) molar ratios. The results suggest a strong influence of the CA/EG molar ratio, mainly on the polymerization degree. The CA/Nb ratio also modifies the degradation process of the precursor solution. The effect of the precursor compositional variation was also observed in the oxide structure, as well as in its electrochemical and electrochromic behavior. Films prepared using high CA/EG and a Nb salt precursor amount have the highest values of charge density and coloration efficiency. Moreover XRD data for this sample show a crystalline structure while the samples prepared with low CA/EG ratio are amorphous.     

A nonconvex separation property and some applications

In this paper we proved a nonconvex separation property for general sets which coincides with the Hahn-Banach separation theorem when sets are convexes. Properties derived from the main result are used to compute the subgradient set to the distance function in special cases and they are also applied to extending the Second Welfare Theorem in economics and proving the existence of singular multipliers in Optimization. This work was partially supported by FONDECYT, ICM Complex Engineering System, CEE-ECOS.     

Lowest-order mode transmission in multimode dielectric S-bends

This paper focuses on the problem of lowest-order mode (LOM) transmission in multimode S-bends given LOM input. Total loss calculations in S-bends using the finite difference beam propagation method (FDBPM) are compared with analytical results. Sine and cosine shaped slab S-bend geometries are studied to determine if mode conversion (to higher-order modes) can be controlled and/or suppressed altogether. Reduction of bending losses for the overall structure is also sought. It is also shown that loss rates for a fixed radius of curvature and total loss in an S-bend are not sensitive to the substrate index. Thus results determined in this paper are applicable to a range of substrate indices. Specifically, it is shown that the results are applicable to ion-exchange glass waveguides. This revised version was published online in November 2006 with corrections to the Cover Date.     

Characterization of g∞,σ‐integral operators

The application of the general tensor norms theory of Defant and Floret to the ideal of (p, σ)‐absolutely continuous operators of Matter, 0 < σ < 1, 1 ≤ p < ∞ leads to the study of g_p′,σ‐nuclear and g_p′,σ‐integral operators. Characterizations of such operators has been obtained previously in the case p > 1. In this paper we characterize the g_∞,σ‐nuclear and g_∞,σ‐integral operators by the existence of factorizations of some special kinds. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Complex powers of hypoelliptic pseudodifferential operators

Complex powers of a class of hypoelliptic pseudodifferential operators in Rn, as well as their heat kernels are studied. An application to the Schatten-von Neumann property of pseudodifferential operators is given.     

One-pot conversion of activated alcohols into terminal alkynes using manganese dioxide in combination with the Bestmann-Ohira reagent

The direct conversion of activated primary alcohols into terminal alkynes through a sequential one-pot, two-step process involving oxidation with manganese dioxide and then treatment with the Bestmann-Ohira reagent is described. This transformation proceeds efficiently (59-99% yield) under mild reaction conditions with a range of benzylic, heterocyclic and propargylic alcohols. A tandem variant is also described, which is successful only with highly activated substrates.     

Spectral projected gradient and variable metric methods for optimization with linear inequalities

A family of variable metric methods for convex constrained optimizationwas introduced recently by Birgin, Martínez and Raydan.One of the members of this family is the inexact spectral projectedgradient (ISPG) method for minimization with convex constraints.At each iteration of these methods a strictly convex quadraticfunction with convex constraints must be (inexactly) minimized.In the case of the ISPG method it was shown that, in some importantapplications, iterative projection methods can be used for thisminimization. In this paper the particular case in which theconvex domain is a polytope described by a finite set of linearinequalities is considered. For solving the linearly constrainedconvex quadratic subproblem a dual approach is adopted, by meansof which subproblems become (not necessarily strictly) convexquadratic minimization problems with box constraints. Thesesubproblems are solved by means of an active-set box-constraintquadratic optimizer with a proximal-point type unconstrainedalgorithm for minimization within the current faces. Convergenceresults and numerical experiments are presented.     

Supramolecular Assembling through Anionic Iodine Secondary Bonds: Synthesis and X‐ray Characterization of (Et4N)[PhTeI4] and (Et4N)[(β‐Naphthyl)TeI4]

[PhTe]₂ and [(β‐naphthyl)Te]₂ react with iodine and tetraethylammonium iodide in toluene/methanol to give (Et₄N)[PhTeI₄] and (Et₄N)[(β‐Naphthyl)TeI₄]. The complexes were analysed by single crystal X‐ray diffraction affording the centrosymmetric monoclinic space group P2₁/c. In the novel compounds only anionic interactions of the types Te···I and I···I take place, cation‐anion effective contacts do not occur. Both anions [PhTeI₄] and [(β‐naphthyl)TeI₄] exhibit square pyramidal coordination at tellurium, with the iodine atoms in the basal positions and the organic groups apical. The tellurium centers achieve an octahedral coordination in the whole lattices through Te···I secondary bonds with the adjacent ionic species. Only the Te–I‐ and I–I‐secondary bonds behave as structure‐forming interactions in the self‐organization of the supramolecular anionic gatherings. New evidences show that for organyltellurates (Q)[PhTeX₄] (Q = protonated amines, amides or amino acids; X = Cl, Br, I), NH···X hydrogen bondings are able to hinder the anionic halogen‐halogen secondary interactions. In case of the more frequent I···I interactions, they have been observed only in the absence of NH···I hydrogen bonds.     

Manifolds of idemopotent matrices

Let M_n be the set of n×n matrices and r a nonnegative integer with r ≤ n. It is known,from Lie groups, that the rank r idempotent matrices in M_n form an arcwise connected 2n (n-r)-dimensional analytic manifold. This paper provides an elementary proof of this result making it accessible to a larger audience.     

Characterization of the minimal and maximal operator ideals associated to the tensor norm defined by a sequence space

We characterize the minimal and maximal operator ideals associated, in the sense of Defant and Floret, to a wide class of tensor norms derived from a Banach sequence space. Our results are extensions of classical ones about tensor norms of Saphar [Studia Math. 38 (1972) 71-100] and show the key role played by the structure of finite-dimensional subspaces in this kind of problems.