Precipitation structure in an Al-2·0 at. % Zn-1·0 at. % Mg alloy within and close to the grain boundaries and its effects on mechanical properties

During ageing the Al-2·0 at. %Zn-1·0 at. % Mg alloy at elevated temperatures the width of the precipitation free zone (PFZ) at both sides of the grain boundaries (GB) is identical with that free of quenched-in dislocation loops (DL). After sufficiently long ageing a band of precipitates is growing inside the former PFZ and the DLs in the midgrain regions act as sites for the heterogeneous nucleation of the-phase. Two precipitation processes significantly affect the mechanical properties. TEM correlates grain boundary precipitate density and morphology with grain boundary misorientation.     

Wave propagation in quasi-one-dimensional quantum plasma in a magnetic field

A cold electron gas fills the lowest Landau level for high enough magnetic fields and for low enough densities. Such a situation is expected to occur for the Malmberg-O'Neil experiment and also for pulsar crusts and atmospheres. Such plasmas behave as a quasi-one-dimensional system and exhibit some peculiarities in their wave structure. We study the dispersion and damping of the low frequencies, i.e., the whistler mode, and the extraordinary mode for zero temperature. The behavior of the whistler mode depends critically on the filling number _Fc=_F/ , where _F is the Fermi energy and is the cyclotron frequency. The one-dimensional character of the system affects the pair excitation spectrum and thus the decay of modes. We find that, in contrast to the three-dimensional situation, the plasma mode and the extraordinary mode remain undamped, while the whistler mode is undamped for all but very highk values.     

Periodic solutions of some infinite-dimensional Hamiltonian systems associated with non-linear partial difference equations. II

This is our second paper devoted to the study of some non-linear Schrödinger equations with random potential. We study the non-linear eigenvalue problems corresponding to these equations. We exhibit a countable family of eigenfunctions corresponding to simple eigenvalues densely embedded in the band tails. Contrary to our results in the first paper, the results established in the present paper hold for an arbitrary strength of the non-linear (cubic) term in the non-linear Schrödinger equation.     

Three-body Coulomb effects in neutral-particle-exchange singularity

In a three-body model with Coulomb interactions the Faddeev equations for the Alt-Grassberger-Sandhas transition operators are used to find the leading term of the neutron-transfer amplitude near the exchange singularity in the cos plane. We derive formulae containing three-body Coulomb effects for the renormalization of the second-order exchange pole in the calculation of observables, such as the cross section and polarizations.     

The search for top quarks at hadron colliders: a realistic appraisal

We study means of identifying top quarks of mass in the range 70–120 GeV at the CERN and FNAL \(\bar pp\) colliders. We show that “W+dijet” production presents a serious background to the conventional “isolated electron+dijet” signature of top. We study an improved signature, calculate the expected event rates, and discuss the determination of the mass of the top quark.     

Production of light superpartners in π0 radiative decays

The production rate of light photinos in radiative pion decay \(\pi ^0 \to \gamma \tilde \gamma \tilde \gamma\) is calculated. Experimental constraints on masses and mass splittings of scalar quarks imply the following upper bound on the decay rate \(BR(\pi ^0 \to \gamma \tilde \gamma \tilde \gamma ) \lesssim 10^{ - 16}\) .     

On the origin of additional peaks in the photoelectron spectra of yttrium

Ultraviolet Photoemission analysis of yttrium metal reveals well defined features far below the conduction band. In order to elucidate their origin, we have used X-ray/Ultra violet photoelectron spectroscopy together with inverse photoemission. The comparison of the spectra of clean yttrium and of H exposed yttrium suggests that these structures are most probably due to hydrogen bands, hydrogen being either in a stable surface hydride form or as subsurface H.