Amorphization of armco iron by boron implantation and subsequent crystallization by heat treatment: A CEMS,X-ray and ultramicrohardness study

The phase compositon of the near-surface zone of armco iron implanted with B⁺ ions (100 keV) at 200 °C was analyzed by CEMS and X-ray diffraction. The existing phases (bcc iron, Fe₂B and an amorphous Fe-B phase) were subsequently modified by heat treatment at various temperatures. The influence of the phase modifications upon the mechanical properties was studied by ultramicohardness measurements.     

Wave attenuation model for dephasing and measurement of conditional times

Inelastic scattering induces dephasing in mesoscopic systems. An analysis of previous models to simulate inelastic scattering in such systems is presented and a relatively new model based on wave attenuation is introduced. The problem of Aharonov-Bohm (AB) oscillations in conductance of a mesoscopic ring is studied. We show that the conductance is symmetric under flux reversal and the visibility of AB oscillations decays to zero as a function of the incoherence parameter, signaling dephasing. Further the wave attenuation model is applied to a fundamental problem in quantum mechanics, that of the conditional (reflection/transmission) times spent in a given region of space by a quantum particle before scattering off from that region.     

Polarization and thickness effects in Mössbauer spectroscopy

The lattice sites of positive pions in gold have been determined as a function of temperature by means of π⁺/μ ⁺ channelling experiments. A blocking pattern in the <100> direction at low temperatures indicates that only octahedral interstitial sites are occupied. The vanishing of this pattern and the reduction of muon flux enhancement observed in <110> ifT is raised above the Debye temperature (165 K) may be interpreted in terms of muon dechannelling owing to the thermal vibrations of the lattice atoms. Time-differential π⁺/μ ⁺ channelling studies on α-iron showed between 20 K and 70 K a strong dependence of the channelling profiles on the time the pions spent in the sample. The ‘young’ pions are well localized on O- or T-sites whereas the ‘old’ pions either become delocalized or occupy sites with strongly reduced symmetry. A model accounting for these observations is suggested. It is argued that there is a close relationship to earlierμ ⁺ SR experiments.     

How Fast can a Subharmonic Function Decay Along a Ray?

Much is known about the connection between the growth and decayof subharmonic functions. The results indicate that there isa general principle: asubharmonic function cannot decay ‘toofast’ relative to its growth.Three theorems are provedwhich, together with work previously published elsewhere, givea fairly complete account of how this principle works out fora subharmonic function having extremal decay along a ray. 1991Mathematics Subject Classification: 30D20, 31A05.     

Qualitative properties of modified equations

Suppose that a consistent one-step numerical method of orderr is applied to a smooth system of ordinary differential equations.Given any integer m 1, the method may be shown to be of orderr + m as an approximation to a certain modified equation. Ifthe method and the system have a particular qualitative propertythen it is important to determine whether the modified equationsinherit this property. In this article, a technique is introducedfor proving that the modified equations inherit qualitativeproperties from the method and the underlying system. The techniqueuses a straightforward contradiction argument applicable toarbitrary one-step methods and does not rely on the detailedstructure of associated power series expansions. Hence the conclusionsapply, but are not restricted, to the case of Runge-Kutte methods.The new approach unifies and extends results of this type thathave been derived by other means: results are presented forintegral preservation, reversibility, inheritance of fixed points.Hamiltonian problems and volume preservation. The techniquealso applies when the system has an integral that the methodpreserves not exactly, but to order greater than r. Finally,a negative result is obtained by considering a gradient systemand gradient numerical method possessing a global property thatis not shared by the associated modified equations.     

A porosity-dependent inelastic criterion for engineering materials

Many criteria have been developed to describe the yielding condition, plastic potential, and failure strength of engineering materials. In this paper, the authors first review the characteristics of a few of the more common criteria used for porous materials. It is then shown that the main features of many criteria can be represented by a unique set of recently developed equations. The ensuing multiaxial criterion becomes applicable to a variety of materials and loading states. One of the advantages of the proposed criterion, named MSDP_u, is that it is explicitly porosity-dependent. The validity of this general inelastic criterion is demonstrated using experimental results obtained from various types of materials. A brief discussion follows on the advantages and limitations of the proposed equations.