Interpolatory properties of best rationalL 1-approximations

In this paper the distribution of the zeros of the error function for bestL ₁-approximation by rational functions fromR _n,m is considered. It is shown that the maximal distance between such zeros isO(1/(n–m)), ifn > m.Communicated by Edward B. Saff.     

Stationary axisymmetric solutions in the vacuum Jordan-Brans-Dicke theory

It is shown that any stationary axisymmetric solution to the vacuum field equations of the Jordan-Brans-Dicke (JBD) theory may be obtained from a composition of any stationary axisymmetric vacuum Einstein spacetime with the Weyl class of metrics. Thus, generating solution techniques can be used to obtain any stationary axisymmetric JBD vacuum solution. In this manner, C. B. G. McIntosh's results concerning this topic are improved upon.     

Acoustic susceptibility of an insulating spin-glass

High frequency acoustic measurements have been performed at temperatures around the freezing pointT _c in a cobalt insulating spin-glass. Assuming a Waller coupling mechanism between the spins and the acoustic wave, the data are interpreted in the framework of a dynamical model which takes into account the modulation of the reaction field. As a result, at the freezing temperature the characteristic relaxation time has no anomaly while the relevant susceptibility presents a maximum. The peculiar frequency dependence (as ^1/2) atT _c of the complex elastic constant is experimentally put in evidence.Associated with the Centre National de la Recherche Scientifique (UA 789)     

Searching for optimal configurations by simulated tunneling

Optimization theory deals with algorithms finding the lowest cost (energy) configuration in a minimal number of steps. When the cost function has many local minima, the deterministic algorithms become easily trapped in suboptimal solutions. The simulated annealing method tries to overcome this difficulty by introducting thermal noise in the problem. Here we explore the possibility of implementing search procedures analogous to the quantum tunneling effect. The suggested dynamics is a guided diffusion process of an interactingpopulation of configurations. Different dynamical aspects of the search process are formulated first in a simple one-dimensional tight-binding model with a hierarchical potential. The new algorithm is then applied to the Traveling Salesman Problem. It is demonstrated that the use of interacting, evolving populations of tours representing our wave packet leads to systematic improvements and possibly, to the optimal tour. In addition, the structure of the cost function landscape for a given instance becomes locally accessible. The performance of the algorithm and its implications for parallel computing and genetic programming are briefly discussed.     

Effect of Xe ion irration of Fe/Sn bilayers

Films of Fe (20 nm) and Sn (40 nm) have been deposited by PVD onto Al supports and irradiated with 100 keV Xe ions at a dose of 5×10¹⁵ ions/cm². Scanning electron microscopy (SEM) shows that the irregular morphology of deposited Sn is considerably flattened by irradiation, which produces also a noticeable sputtering of Sn. Conversion electron Mössbauer spectroscopy (CEMS) reveals the formation at the interface of a variety of intermetallic phases which is enhanced by irradiation. These phases, seem to be insensible to prolonged (several months) room temperature aging. Their thermal stability under annealing at temperature up to 523 K has also been investigated.     

Forward-backward multiplicity correlations in σ+ p,K + p andpp collisions at 250 GeV/c

Forward-backward multiplicity correlations in σ⁺,K ⁺ p andpp collisions at 250 GeV/c ( \(\sqrt s \) =22 GeV) are given for all charges and for the different charge combinations. The correlations are found to be caused predominantly by centrally produced particles. It is demonstrated that this result is an agreement with observations at the ISR and the CERNp \(\bar p\) -Collider. The results are compared to expectations from LUND, DPM and FRITIOF Monte Carlo models and a geometrical picture relating correlations in hadron-hadron collisions toe ⁺ e ^? data in terms of impact parameters is tested.