Syndiotactic Polymerization of Propylene: Single‐Site Vanadium Catalysts in Comparison with Zirconium and Nickel

The syndiotactic‐specific polymerization of propylene can be promoted by single‐site catalysts based on vanadium, nickel and group IV metals. The polymerization mechanisms are reasonably well established for nickel and group IV metals. For vanadium catalysts the polymerization mechanisms reported in the literature are still debatable, since the stereochemistry of the monomer insertion is well known, but the active species have never been isolated. In this paper the mechanisms concerning Ni and group IV metal catalysts are briefly summarized and proposed mechanisms concerning vanadium are compared within one another.     

Set Voronoi diagrams of 3D assemblies of aspherical particles

Abstract

Several approaches to quantitative local structure characterization for particulate assemblies, such as structural glasses or jammed packings, use the partition of space provided by the Voronoi diagram. The conventional construction for spherical mono-disperse particles, by which the Voronoi cell of a particle is that of its centre point, cannot be applied to configurations of aspherical or polydisperse particles. Here, we discuss the construction of a Set Voronoi diagram for configurations of aspherical particles in three-dimensional space. The Set Voronoi cell of a given particle is composed of all points in space that are closer to the surface (as opposed to the centre) of the given particle than to the surface of any other; this definition reduces to the conventional Voronoi diagram for the case of mono-disperse spheres. An algorithm for the computation of the Set Voronoi diagram for convex particles is described, as a special case of a Voronoi-based medial axis algorithm, based on a triangulation of the particles’ bounding surfaces. This algorithm is further improved by a pre-processing step based on morphological erosion, which improves the quality of the approximation and circumvents the problems associated with small degrees of particle–particle overlap that may be caused by experimental noise or soft potentials. As an application, preliminary data for the volume distribution of disordered packings of mono-disperse oblate ellipsoids, obtained from tomographic imaging, is computed.     

The mixing set with divisible capacities: A simple approach

We give a simple algorithm for linear optimization over the mixing set with divisible capacities, and derive a compact extended formulation from such an algorithm. The main idea is to apply a suitable unimodular transformation to obtain an equivalent problem that is easier to analyze.     

Äthylen/Propen—Copolymerisation mit dem homogenen Katalysatorsystem Ti(Oi-C3H7)4/Al(C2H5)2F

Ohne Zusammenfassung     

A project for an intelligent system: Vision and learning

One of the most critical aspects of a truly intelligent system is the ability to learn, that is, to improve its own functionality by interacting with the environment and exploring it. In this paper, we argue that learning from exploring the environment should be the main goal in developing artificial intelligence. We also argue in favor of an integrated system—combining several state-of-the-art aspects of artificial intelligence, such as speech, vision, natural language, expert systems—as the experimental platform with which to approach this problem. We then describe the main features of a project of this type, MAIA, which is under development at I.R.S.T. The vision components of the system will be discussed in some detail, especially the navigation architecture of the indoor robot available to MAIA. We will conclude outlining some initial learning problems that will be approached within the MAIA project, such as learning to recognize faces and learning to update the map of the Institute used for indoor navigation.     

Ein neues Glas zu chemischen Apparaten

Ohne Zusammenfassung     

Group 4 Cs symmetric catalysts and 1-olefin polymerization

Polymerization of propene and 1-butene promoted by group 4 C_s symmetric metallocene precursors has been tested in different reaction conditions. The stereochemical structure of the polymer is affected by the radius of the transition metal, the substituent of the olefin and in some cases the reaction temperature and the monomer concentration. The results are tentatively rationalized considering the possible catalytic cycles that may produce either syndiotactic or isotactic polymers. A sample of syndiotactic polypropylene melting at 170°C is also reported.     

Orientierung der Propylen-Einheiten im Polypropylen und in Äthylen/Propylen-Copolymeren

Ohne Zusammenfassung