A simple and general preparation of vinylic sulfides, selenides and tellurides

A general method for the synthesis of vinylic chalcogenides by nucleophilic and Ni-catalyzed vinylic substitution on vinylic halides by phenyl chalcogenolates is described. The reactions were regio and stereoselective for the nickel catalyzed substitution, and mixture of isomers was observed for some examples in the thermal process in DMF.     

Development of a model-based netsourcing decision support system using a five-stage methodology

Managers increasingly face netsourcing decisions of whether and how to outsource selected software applications over the Internet. This paper illustrates the development of a netsourcing decision support system (DSS) that provides support for the first netsourcing decision of whether to netsource or not to do so. The development follows a five-stage methodology focusing on empirical modeling with internal validation during the development. It begins with identifying potential decision criteria from the literature followed by the collection of empirical data. Logistic regression is then used as a statistical method for selecting relevant decision criteria. Applying the logistic regression analysis to the dataset delivers competitive relevance and strategic vulnerability as relevant decision criteria. The development concludes with designing a core and a complementary DSS module. The paper critiques the developed DSS and its underlying development methodology. Recommendations for further research are offered.     

Absolute and relative cut-off in adaptive approximation by wavelets

Given the wavelet expansion of a function v, a non-linear adaptive approximation of v is obtained by neglecting those coefficients whose size drops below a certain threshold. We propose several ways to define the threshold: all are based on the characterization of the local regularity of v (in a Sobolev or Besov scale) in terms of summability of properly defined subsets of its coefficients. A-priori estimates of the approximation error are derived. For the Haar system the asymptotic behavior of both the approximation error and the number of survived coefficients is thoroughly investigated for a class of functions having Hölder-type singularities.     

Enzyme-mediated synthesis of EEHP and EMHP,useful pharmaceutical intermediates of PPAR agonists

A new scaleable synthetic route to the title compounds has been developed. The reaction pathway is based on the α-chymotrypsin-catalysed hydrolysis of the racemic ethyl 2-ethoxy-3-(p-methoxyphenyl)propanoate or of the racemic ethyl 2-methoxy-3-(p-methoxyphenyl)propanoate to give the corresponding resolved (S)-esters with excellent ee. The acids were easily separated from the (S)-esters by a simple acid–base work-up. The overall yields of 1 and 2 were 16% and 17%, respectively.     

Some features of 2 and 4-aminopyridines anchored on silica gel: Properties and chemisorption of metal(II) chlorides in non-aqueous solutions

Silica gel surfaces modified with 2- or 4-aminopyridine groups were used to adsorb MCl₂ (M = Co, Ni, Cu, Zn) from ethanol and acetone solutions at 298 K. The chemisorption isotherms fitted a modified Langmuir equation very well and are similar for all cations. The capacity of anchored 4-aminopyridine (SIL4) in adsorbing the metallic ion is larger than that of the immobilized 2-aminopyridine (SIL2). The maximum retention capacity has the sequence Cu> Co> Zn in acetone for both surfaces, and Zn> Co> Cu> Ni for SIL2, and Zn> Cu> Co> Ni for SIL4 in ethanol. For a given cation, the variation in enthalpy of solvent-solute exchange on the surface is always larger in ethanol. This process seems to be related to the enthalpy of solvation of the cation involved in the exchange.     

Performance evaluation of a wave-front displacement system for vectorial shearing interferometer

We describe a wave-front displacement system using a novel configuration of a pair of wedge prisms. The wave-front propagation, through the displacement system, is analyzed using the exact ray trace. The main advantage, of this configuration, is that the shearing (direction and magnitude) is constant from the displacement system to the image plane. The direction of the shearing depends on the relative orientation of the prisms. The magnitude of the shearing is proportional to the distance between prisms. The proportionality constant depends on the wedge angle and the material of fabrication of the prisms, and it gives the sensitivity to the displacement of the system. The deviation of the shearing due to the difference between the wedge angles is larger than that the produced by the oblique incidence of the wave-front. The experimental results confirm the theoretical data.     

Lower bounds for resonance widths in potential and obstacle scattering

Explicit lower bounds are given for the size of the imaginary parts of resonances for Schrödinger operators with non-trapping or trapping potentials, and for the Dirichlet Laplacian in the exterior of a star-shaped obstacle, both acting in three dimensions.Work partially supported by DiUC/FONDECYT (Chile)Work partially supported by U.S. National Science Foundation grant DMS 8705610