Numerical simulation of flow of viscoelastic fluids

The paper deals with the numerical calculation of highly viscous, non-newtonian fluid flows in apparatus of mechanical engineering. We use a differential constitutive equation to approximate the real behaviour of technical fluids like polymer melts. By means of calculated flow examples in two and three dimensional geometries we demonstrate the influence of the non-newtonian behaviour. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Hydrogen bonding in N,N,N′,N′‐tetra­methyl­ethyl­ene­di­ammonium bis­(benzene­selenol­ate)

The crystal structure of the title compound, [Me₂NHC₂H₄NHMe₂][SePh]₂ or C₆H₁₈N₂²⁺·2C₆H₅Se^?, reveals hydrogen bonding between the benzene­seleno­late anions and the tetra­methyl­ethyl­ene­di­ammonium cations. The asymmetric unit contains one formula unit of the title compound. The two Se?H distances are 2.22 (4) and 2.34 (4) Å.     

The monophosphino urea derivative PPh(2)NMeC(O)NMeH: a hemilabile ligand switching between P,O- and P,N-coordination

Treatment of N,N'-dimethyl urea with ClPPh(2) and NEt(3) as auxiliary base in thf affords the title compound PPh(2)NMeC(O)NMeH (1) in high yield. The monophosphino urea derivative 1 constitutes the first isolated and fully characterized representative of this class with a NH functional group. Evidence for a solvent effect in the synthesis of 1 is given and the X-ray crystal structure determined. The reaction of 1 with [Mo(CO)(4)(NCMe)(2)] and the hemilabile character of the ligand 1 in the obtained P,O-chelate complex cis-[Mo(CO)(4)(eta(2)-PPh(2)NMeC(O)NMeH)] (2) are described. Furthermore, synthesis of the known bisphosphino urea derivative CO(NMePPh(2))(2) (3) starting from 1 is reported.     

Endliche ableitbare affine Ebenen

Ohne Zusammenfassung     

A counterexample to a global optimization algorithm

A counterexample to an algorithm of Dien (1988) for solving a minimization problem with a quasiconcave objective function and both linear and a reverse-convex constraint shows that this algorithm needn't lead to a solution of the given problem.