Covalent and ionic crystal radii and Phillips ionicity

Correlating bond length, crystal structure and Phillips ionicity in simple binary compounds with covalent crystal radii shows that most oxides and some fluorides have to be regarded as covalent compounds with respect to their crystal radii. “Anomalous covalent” octahedral radii of oxygen and fluorine should be interpreted as ionic radii.     

A method for calculating the ground state properties of light closed-shell nuclei

A method for solving the reaction matrix equation in closed-shell nuclei using a spherical harmonic-oscillator representation is presented. The equation is transformed to an infinite algebraic system for the matrix elements, the exclusion operator being treated exactly. The system can be solved with arbitrary accuracy which depends only on the chosen truncation.     

Effect of Free Trimethylaluminum Content in Methylaluminoxane on Performances of Bis(salicylaldiminate)nickel(II)‐Based Catalysts for Ethylene Polymerization

Summary: The performances of ethylene polymerization catalysts based on III and commercial methylaluminoxane were investigated by reducing the content of free trimethylaluminum in methylaluminoxane by its reaction with 2,6‐di‐tert‐butylphenol. This allowed optimization of the formulation of the catalyst, affording a high‐molecular‐weight linear polyethylene (PE) with a productivity [(1 900 kg of PE/(mol of Ni × h)], ten‐fold higher than that previously achieved for the same system adopting commercial methylaluminoxane not pre‐treated with the above phenol derivative.

     

Iterative Algorithms for Multiscale State Estimation, Part 1: Concepts

The objective of the present investigation is to explore the potential of multiscale refinement schemes for the numerical solution of dynamic optimization problems arising in connection with chemical process systems monitoring. State estimation is accomplished by the solution of an appropriately posed least-squares problem. To offer at any instant of time an approximate solution, a hierarchy of successively refined problems is designed using a wavelet-based Galerkin discretization. In order to fully exploit at any stage the approximate solution obtained also for an efficient treatment of the arising linear algebra tasks, we employ iterative solvers. In particular, we will apply a nested iteration scheme to the hierarchy of arising equation systems and adapt the Uzawa algorithm to the present context. Moreover, we show that, using wavelets for the formulation of the problem hierarchy, the largest eigenvalues of the resulting linear systems can be controlled effectively with scaled diagonal preconditioning. Finally, we deduce appropriate stopping criteria and illustrate the characteristics of the solver with a numerical example.     

The Mass Programme at GANIL Using the CSS2 and CIME Cyclotrons

The mass-measurement programme at GANIL aims to measure the masses of heavy nuclei close to the N=Z line which is the ideal region to study neutron-proton pairing. An original direct time-of-flight mass-measurement method was developed at GANIL which uses the CSS2 cyclotron as a high-resolution spectrometer. The masses of ions of A=68,76,80 and 100 have been measured with a precision of a few 10⁻⁶. Mass measurements will be performed with the new CIME cyclotron of SPIRAL using a similar method based on the measurement of the phase of the accelerated ions for different radio-frequencies. A recently approved experiment will help develop this new technique and aims to measure the mass of ³¹Ar radioactive nuclei with a precision of 10⁻⁶. This revised version was published online in July 2006 with corrections to the Cover Date.     

Identification of the Li ground state

The proton-stripping reaction from a ¹¹Be radioactive beam incident on a beryllium target demonstrates that only (7±3)% of the ⁹Li residues in the reaction are in coincidence with the 2.7 MeV γ-ray corresponding to the ⁹Li first excited state. This implies that the previously observed low-energy neutrons from the decay of the unbound nucleus ¹⁰Li represent a direct l=0 transition to the ⁹Li ground state. Consequently, neutron-unbound ¹⁰Li is proven to have the same parity inversion as occurs in the case of ¹¹Be with a  intruder state below the natural parity state.