Autoresonant excitation of antiproton plasmas

We demonstrate controllable excitation of the center-of-mass longitudinal motion of a thermal antiproton plasma using a swept-frequency autoresonant drive. When the plasma is cold, dense, and highly collective in nature, we observe that the entire system behaves as a single-particle nonlinear oscillator, as predicted by a recent theory. In contrast, only a fraction of the antiprotons in a warm plasma can be similarly excited. Antihydrogen was produced and trapped by using this technique to drive antiprotons into a positron plasma, thereby initiating atomic recombination.     

Evidence of a precursor superconducting phase at temperatures as high as 180 K in RBa2Cu3O(7-δ) (R=Y, Gd, Eu) superconducting crystals from infrared spectroscopy

We show that a multilayer analysis of the infrared c-axis response of RBa2Cu3O(7-δ) (R=Y, Gd, Eu) provides important new information about the anomalous normal-state properties of underdoped cuprate high temperature superconductors. In addition to competing correlations which give rise to a pseudogap that depletes the low-energy electronic states below T*?T(c), it enables us to identify the onset of a precursor superconducting state below T(ons)>T(c). We map out the doping phase diagram of T(ons) which reaches a maximum of 180 K at strong underdoping and present magnetic field dependent data which confirm our conclusions.     

Efficient generalized conjugate gradient algorithms,part 1: Theory

The effect of inexact line search on conjugacy is studied in unconstrained optimization. A generalized conjugate gradient method based on this effect is proposed and shown to have global convergence for a twice continuously differentiable function with a bounded level set.     

Aspiration Based Simulated Annealing Algorithm

An aspiration based simulated annealing algorithm for continuousvariables has been proposed. The new algorithm is similar to the one givenby Dekkers and Aarts (1991) except that a kind of memory is introduced intothe procedure with a self-regulatory mechanism. The algorithm has beenapplied to a set of standard global optimization problems and a number ofmore difficult, complex, practical problems and its performance comparedwith that of the algorithm of Dekkers and Aarts (1991). The new algorithmappears to offer a useful alternative to some of the currently availablestochastic algorithms for global optimization.     

Nitroxide radicals

The proton hyperfine constants have been measured, using N.M.R., for a series of sterically hindered alkyl aryl nitroxides. Computer reconstructions of the electron resonance spectra show that the coupling constants obtained from the pure radical are very similar to those obtained from the electron resonance spectra of dilute solutions. Comparison of methyl and proton splittings in identical positions suggests that the radicals are σ in character although the molecular-orbital calculations are unable to distinguish between σ or π radicals.     

Generalized Polak-Ribière algorithm

A new generalized Polak-Ribière conjugate gradient algorithm is proposed for unconstrained optimization, and its numerical and theoretical properties are discussed. The new method is, in fact, a particular type of two-dimensional Newton method and is based on a finite-difference approximation to the product of a Hessian and a vector.     

Magnetic sensors with good signal-to-interference discrimination

Summary Principles are established for the design of coil arrays which generate distant magnetic fields diminishing as a high inverse power of the distance. By a principle of reciprocity these arrays, when used as sensors in induction and SQUID magnetometers, have an inherently low sensitivity to distant sources of magnetic field. Paper presented at the ?IV International Workshop on Biomagnetism?, held in Rome, September 14–16, 1982.     

On orthogonal trajectories and optimization

This note discusses a generalization of the trapezoidal method for numerical integration of the differential equations of the orthogonal trajectories of a function as a means of finding maximum or minimum values of the function. Connections between the choice of a parameter in the integration scheme and various modifications of Newton's method are indicated.     

One-loop renormalisation of superfield Yang-Mills theories

We calculate the one-loop ultraviolet and infrared divergences in superfield Yang-Mills theories to fourth order in the gauge field. The ultraviolet divergences require a non-linear field renormalisation, and graphs with external ghost fields show that a non-linear renormalisation of the gauge-fixing function is also needed. These observations are confirmed by calculations incorporating matter fields, which are used to extend the result to all orders for the special case of SU(2). On the other hand the infrared divergences, which occur in general gauges, are apparently impossible to remove in any acceptable way.