Silanolato-Komplexe von Titan und Zirconium. Die Kristallstrukturen von Cp2TiCl(OSiPh3) und Cp2ZrCl(OSiPh3)

Silanolato Complexes of Titanium and Zirconium. The Crystal Structures of Cp₂TiCl(OSiPh₃) and Cp₂ZrCl(OSiPh₃) The title compounds have been prepared by the reaction of Cp₂MCl₂ (M = Ti, Zr) with triphenylsilanole in diethylether in the presence of piperidine. They form only sparingly moisture sensitive orange (Ti) or colourless (Zr) crystal needles, which were characterized by X-ray crystallography. Cp₂TiCl(OSiPh₃): Space group P2₁/n, Z = 4, structure solution with 3961 observed unique reflections, R = 0.057. Lattice dimensions at 20°C: a = 1029.6, b = 1719.3, c = 1388.9 pm, β = 100.69°. The compound forms monomeric molecules with bond lengths TiO of 184.2 pm, SiO of 161.5 pm, and a TiOSi bonding angle of 164.5°. Cp₂ZrCl(OSiPh₃): Space group P3 , Z = 18, structure solution with 2799 observed unique reflections, R = 0.047. Lattice dimensions at ?20°C: a = b = 3518, c = 1058.3 pm. The structure consists of three symmetry-independent monomeric molecules, which differ only slightly. The bond lengths are (in average): ZrO 196.4 pm, SiO 162.1 pm, the ZrOSi bond angle is 173.7°.     

Combining magnetic resonance measurements with numerical simulations – Extracting blood flow physiology information relevant to the investigation of intracranial aneurysms in the circle of Willis

Cerebral aneurysms in the region of the circle of Willis have an incidence of 3–6% in western populations and involve the risk of rupture with subsequent subarachnoidal bleeding. The patient specific blood flow patterns are of substantial importance for understanding the pathogenesis of the lesions and may eventually contribute to deciding on the most efficient treatment procedure for a specific patient.A non-invasive method for performing in vivo measurements on blood velocity is 4D phase-contrast magnetic resonance angiography (PC-MRA), on the basis of which a flow field with all its parameters can be simulated. We are using this approach to investigate the hemodynamic parameters in the circle of Willis and, by analyzing the values at common locations of aneurysms, trying to find potential parameters to predict the development of aneurysms. Methodologically, we are acquiring the artery geometry with 3D-time-of-flight magnetic resonance (TOF) measurements and the blood velocity in the feeding arteries with 4D PC-MRA measurements in a healthy volunteer. These measurements are combined with computational fluid dynamics (CFD) to describe detailed hemodynamic patterns within the circle of Willis.     

Fictitious play in coordination games

We study the Fictitious Play process with bounded and unbounded recall in pure coordination games for which failing to coordinate yields a payoff of zero for both players. It is shown that every Fictitious Play player with bounded recall may fail to coordinate against his own type. On the other hand, players with unbounded recall are shown to coordinate (almost surely) against their own type as well as against players with bounded recall. In particular, this implies that a FP player's realized average utility is (almost surely) at least as large as his minmax payoff in 2×2 coordination games. Received: December 1997/Final version: November 1998     

Synthesis,Reductive Cleavage,and Cellular Interaction Studies of Biodegradable,Polyglycerol Nanogels

In this paper we describe disulfide containing, polyglycerol nanogels as a new class of biodegradable materials. These nanoparticles are prepared in inverse miniemulsion via an acid catalyzed ring‐opening polyaddition of disulfide containing polyols and polyepoxides. Varying conditions allow us to tune particle size and disulfide content within the polymer network; particles can be prepared with narrow polydispersities and diameters in the range from 25 to 350 nm. Particle degradation under reductive intracellular conditions is studied by various analytical techniques. Gel permeation chromatography indicates that final degradation products have relatively low molecular weights (≤ 5 kDa). In addition, studies in cell culture show these nanoscale materials to be highly biocompatible. Dye‐labelled nanogels are shown by optical microscopy techniques to readily internalize into cells by endocytotic mechanisms. This study highlights the great potential of these particles to function as sophisticated nanotransporters that deliver cargo to a certain tissue or cell target and then biodegrade into smaller fragments which would be cleared from the body by the kidney. (with ≈ 30 kDa molecular weight cut off)