Pseudospectral collocation methods for fourth-order differential equations

A multi-domain pseudospectral collocation scheme for the approximationof linear fourth-order differential equations in one and twodimensions is presented. A complete analysis of the scheme isprovided and error estimates are proved for the one-dimensionalproblem. An efficient preconditioner based on a low-order finite-differenceapproximation to the same differential operator is proposed.The extension of the method to the biharmonic equation in twodimensions is discussed and results are presented for a problemdefined in a non-rectangular domain. Present address: Department of Mathematics, Tarbiat ModarresUniversity, Tehran, iran     

Conforming Chebyshev Spectral Collocation Methods for the Solution of Laminar flow in a Constricted Channel

The numerical simulation of steady planar two-dimensional laminarflow of an incompressible fluid through an abruptly contractingchannel using spectral domain decomposition methods is described.The key features of the method are the decomposition of theflow region into a number of rectangular subregions and spectralapproximations that are pointwise C¹ continuous across subregioninterfaces. Spectral approximations to the solution are obtainedfor Reynolds numbers in the range [0, 500]. The size of thesalient corner vortex decreases as the Reynolds number increasesfrom 0 to around 45. As the Reynolds number is increased further,the vortex grows slowly. A vortex is detected downstream ofthe contraction at a Reynolds number of around 175 that continuesto grow as the Reynolds number is increased further.     

Describing one- and two-neutron halos in effective field theory

In this paper, the recent work our group has undertaken on effective field theory (EFT) analyses of experimental data pertaining to one- and two-neutron halo nuclei is discussed. The cases of ¹⁹C and ⁸Li (one-neutron halos) and ²²C (two-neutron halo) are considered. For ¹⁹C and ⁸Li electromagnetic processes, such as Coulomb dissociation and radiative capture are considered. In the ²²C system the way in which the measured matter radius can be used to derive constraints on the two-neutron separation energy of this very neutron-rich system is shown. In each case the ‘Halo EFT’ ability to correlate different experimental observables with one another, in a model-independent manner, and up to an accuracy that is determined by the separation of scales in the halo system is shown.     

ChemInform Abstract: Substitution Chemistry of Gallium for Titanium in Nonlinear Optical KTiOPO4: Syntheses and Single-Crystal Structures of KGaF1-δ(OH). delta.PO4 (δ ≈ 0.3) (I) and KGa0.5Ge0.5(F,OH)0.5O0.5PO4 ( II).

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.     

ChemInform Abstract: Theoretical versus Experimental Charge and Spin-Density Distributions in trans-(Ni(NH3)4(NO2)2).

A comparison of data from three different theoretical models (ab initio UHF and DVXα MO calculations as well as cellular ligand field analysis (clf)) with experimental charge and spin-density distributions, obtained from X-ray and polarized neutron diffraction results, leads to a consistent picture of the electronic structure and M-L bonding in the title complex.