Search results for " Geometry"

Ligand effects on the structures and magnetic properties of tricyanomethanide-containing copper(II) complexes.

2007

The preparation, crystal structure and magnetic properties of four heteroleptic copper(II) complexes with the tricyanomethanide (tcm(-)) and the heterocyclic nitrogen donors 3,6-bis(2-pyridyl)pyridazine (dppn), 2,5-bis(2-pyridyl)pyrazine (2,5-dpp), 2,3-bis(2-pyridyl)pyrazine (2,3-dpp) and 2,3-bis(2-pyridyl)quinoxaline (2,3-dpq) are reported, {[Cu(2)(dppn)(OH)(tcm)(2)] x tcm}(n) (1), {[Cu(2,5-dpp)(tcm)] x tcm}(n) (2), {[Cu(2)(2,3-dpp)(2)(tcm)(3)(H(2)O)(0.5)] x tcm x 0.5H(2)O}(n) (3) and [Cu(2,3-dpq)(tcm)(2)](n) (4). 1 has a ladder-like structure with single mu-1,5-tcm ligands forming the sides and a bis-bidentate dppn and a single mu-hydroxo providing the rung. Each copper atom in 1 exhibits…

Propyl substituted 4-arylimino-1,2,3-trihydroacridylnickel complexes: Their synthesis, characterization and catalytic behavior toward ethylene

2015

Propyl substituted 4-arylimino-1,2,3-trihydroacridylnickel dihalide complexes were designed and prepared by metal-induced template reaction with NiCl2 center dot 6H(2)O or (DME)NiBr2. They were characterized by infrared spectroscopy and elemental analysis. Single crystal X-ray crystallography of representative complex Ni3 revealed a distorted trigonal bipyramidal geometry around nickel. The catalytic activities of the title nickel complexes were negatively affected by propyl substituent on their backbone when comparing with the results by unsubstituted ones. With the activation of diethylaluminium chloride, all nickel complexes exhibited moderate activity (up to 5.10 x 10(5) g mol(-1)(Ni) h…

Seminararbeiten von Semester 71/72, 72, 72/73

1801

Multi-level contrast filtering in image difference metrics

2013

In this paper, we present a new metric to estimate the perceived difference in contrast between an original image and a reproduction. This metric, named weighted-level framework Δ E E (WLF-DEE), implements a multilevel filtering based on the difference of Gaussians model proposed by Tadmor and Tolhurst (2000) and the new Euclidean color difference formula in log-compressed OSA-UCS space proposed by Oleari et al. (2009). Extensive tests and analysis are presented on four different categories belonging to the well-known Tampere Image Database and on two databases developed at our institution, providing different distortions directly related to color and contrast. Comparisons in performance wi…

On the time function of the Dulac map for families of meromorphic vector fields

2003

Given an analytic family of vector fields in Bbb R2 having a saddle point, we study the asymptotic development of the time function along the union of the two separatrices. We obtain a result (depending uniformly on the parameters) which we apply to investigate the bifurcation of critical periods of quadratic centres.

Generalized finite difference schemes with higher order Whitney forms

2021

Finite difference kind of schemes are popular in approximating wave propagation problems in finite dimensional spaces. While Yee’s original paper on the finite difference method is already from the sixties, mathematically there still remains questions which are not yet satisfactorily covered. In this paper, we address two issues of this kind. Firstly, in the literature Yee’s scheme is constructed separately for each particular type of wave problem. Here, we explicitly generalize the Yee scheme to a class of wave problems that covers at large physics field theories. For this we introduce Yee’s scheme for all problems of a class characterised on a Minkowski manifold by (i) a pair of first ord…

Volumes of certain small geodesic balls and almost-Hermitian geometry

1984

Let D be the characteristic connection of an almost-Hermitian manifold, V D m (r) the volume of a small geodesic ball for the connection D and C C D 1 the first non-trivial term of the Taylor expansion of V D m (r). NK-manifolds are characterized in terms of C C D 1 and a family of Hermitian manifolds for which ∫ M C C D 1 dvol is a spectral invariant is given and one proves that C C D 1 and the spectrum of the complex Laplacian, together, determine the class in which a compact Hermitian manifold lines.

On a-semiaffine planes with invisible lines

1987

Translationsstrukturen, die weder axial noch zentral sind

1979

A topological obstruction to the geodesibility of a foliation of odd dimension

1981

Let M be a compact Riemannian manifold of dimension n, and let ℱ be a smooth foliation on M. A topological obstruction is obtained, similar to results of R. Bott and J. Pasternack, to the existence of a metric on M for which ℱ is totally geodesic. In this case, necessarily that portion of the Pontryagin algebra of the subbundle ℱ must vanish in degree n if ℱ is odd-dimensional. Using the same methods simple proofs of the theorems of Bott and Pasternack are given.