Komplexchemie perhalogenierter Cyclopentadiene und Alkine, VII

Coordination Chemistry of Perhalogenated Cyclopentadienes and Alkynes, VII1). - Synthesis of Several Tetrachlorometalloles of Cobalt, Rhodium, and Iridium; Structure of a Iridacyclopentadiene Derivative The reaction of dichloroethyne with CpCo(PPh3)2, RhCl(EPh3)3 (E = P, As, Sb), and IrCl(N2)(PPh3)2 leads to the formation of complexes containing a tetrachloro-1-metallacyclopentadiene unit. The crystal-structure determination of (Ph3P)2(Cl)- is reported

Die Freien Berufe im Sozio-ökonomischen Panel - Systematische Berichtigung der kritischen Wechsel innerhalb der Selbständigengruppe

Das Diskussionspapier greift die problematische Datenerfassung der Freien Berufe im Sozioökonomischen Panel (SOEP) auf. Im Mittelpunkt stehen sogenannte „kritische Wechsel“ zwischen freiberuflichen und selbständigen Tätigkeiten innerhalb der Selbständigen-Gruppe des SOEP. Forschungsziel dieser Arbeit ist es, in einem ersten Schritt diese kritischen Wechsel zu überprüfen und mögliche Muster fehlerbehafteter Informationen herauszuarbeiten. In einem zweiten Schritt werden konkrete operative Lösungsvorschläge zur Berichtigung dieser „kritischen Wechsel“ erarbeitet und schließlich am Beispiel der Freien Berufe innerhalb der Selbständigen-Gruppe im SOEP-Datensatz zwischen 1992-2002 umgesetzt. Über die Berichtigung des Datensatzes hinaus werden Vorschläge für die zukünftige Fragestellung im SOEP-Fragebogen unterbreitet sowie neue strategische Ziele für eine Erweiterung des wissenschaftlichen SOEP-Nutzerkreises im Kontext der Gründungsforschung aufgezeigt. Der Anhang dokumentiert die umfassende retrospektive Berichtigung der kritischen Wechsel auf der Personenebene im SOEP

Macroscopic effects of microscopic roughness in suspensions

This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.We study a model suspension consisting of a monolayer of identical spheres in a viscous medium without Brownian effects. In the absence of inertia, and under the influence of finite forces, perfectly smooth spheres will never come into contact because of the strength of the lubrication interaction. Indeed, an interaction between two spheres is perfectly reversible. However, this ideal is not achieved in practice: careful experiments with just two spheres show that some irreversible interaction occurs. We treat this interaction as a simple contact between the spheres: we assume that they are microscopically rough and have surface asperities which are too sparse to affect the hydrodynamics of the system, but which prevent the particles from approaching beyond some nominal surface separation. For a dilute suspensions in steady shear flow, a calculation to order c(2) in the particle area concentration shows that roughness actually lowers the viscosity of the suspension relative to its value for smooth spheres; this is because the excluded parts of configuration space are those with very close particles, where the lubrication layers cause high dissipation. Negative normal stress differences are also introduced by the roughness. At higher concentrations we use Stokesian Dynamics to simulate the suspension dynamics. We find that rough- ness increases the viscosity above an area concentration of around 40% and the normal stress differences be- come very sensitive to particle configuration, and fluctuate strongly with time

The effect of polydispersity in a turbulent channel flow laden with finite-size particles

We study turbulent channel flows of monodisperse and polydisperse suspensions of finite-size spheres by means of Direct Numerical Simulations using an immersed boundary method to account for the dispersed phase. Suspensions with 3 different Gaussian distributions of particle radii are considered (i.e. 3 different standard deviations). The distributions are centered on the reference particle radius of the monodisperse suspension. In the most extreme case, the radius of the largest particles is 4 times that of the smaller particles. We consider two different solid volume fractions, 2% and 10%. We find that for all polydisperse cases, both fluid and particles statistics are not substantially altered with respect to those of the monodisperse case. Mean streamwise fluid and particle velocity profiles are almost perfectly overlapping. Slightly larger differences are found for particle velocity fluctuations. These increase close to the wall and decrease towards the centerline as the standard deviation of the distribution is increased. Hence, the behavior of the suspension is mostly governed by excluded volume effects regardless of particle size distribution (at least for the radii here studied). Due to turbulent mixing, particles are uniformly distributed across the channel. However, smaller particles can penetrate more into the viscous and buffer layer and velocity fluctuations are therein altered. Non trivial results are presented for particle-pair statistics.Comment: Under review in the European Journal of Mechanics/B - Fluid