IMPURITY TRAPPING EFFECTS IN THE LOCALIZATION OF MUONS IN SOLIDS

Muon spin rotation ( mu SR) experiments are now regularly used to study solids and solid-state processes. The interpretation of mu SR data is usually based on a 'standard' picture in which the muons localise randomly in the solid, and then diffuse, possibly encountering impurities. There remain some important cases where no satisfactory interpretation results. For some of these anomalous systems the authors propose an alternative picture in which the two different factors are the importance of metastable (free muon) excited states, and the role of impurities in causing localisation. They show this allows a possible explanation of results for Al:Mn and demonstrate that elastic strain fields of defects may be a major factor in influencing localisation. They also propose a new mechanism for delayed self-trapping

Interatomic potentials for condensed matter

This paper forms an introduction to a discussion of interatomic forces. As such, it comments on the basic principles, and on some of the problems which underly present formulations, the ways in which future work should develop, and the classes of physical problem for which difficulties remain

THEORY OF REGULAR ARRAYS OF DEFECTS - VOID LATTICE

Defects in crystals may form a regular array, rather than a random distribution. The lattice of voids produced in irradiated molybdenum is a remarkable example of this. We give a general method of calculating the energy per defect in the array which exploits the periodicity of the defect lattice. The existence of the void lattice depends on the elastic interaction between voids. The present approach can treat both arbitrarily anisotropic elastic continua and discrete lattices, and is readily extended to discuss the stability of the defect lattice. The results predict that a void lattice should occur in molybdenum, and compare a number of models for the void. Stability against shear of the void lattice is not discussed in the present paper. The ratio of the void lattice spacing to void radius predicted is 2.2 to 4.5 and is smaller than the value of about 10 observed. The results are in general agreement with the more approximate Malén-Bullough treatment

Non- classical diffusion processes

This paper surveys quantum effects in diffusion, with special emphasis on isotope effects for hydrogen isotopes in metals. The various possible contributions to the isotope effect are surveyed, and their importance assessed. The bcc metals (V, Nb, Ta) and fee metals (Cu, Ni, Pd) involve different mechanisms, and these are still doubts in detail about some aspects. A full understanding requires knowledge of the hydrogen-metal interactions. Recent theoretical work supports some of the qualitative ideas discussed, and offers promise for future analyses

Making tracks in metals

Swift heavy ions lose energy primarily by inelastic electronic scattering and, above an energy threshold, electronic losses result in damage to the lattice. Such high energy radiation is beyond the range of validity of traditional cascade simulations, and predictive damage calculations are challenging. We use a novel methodology, which combines molecular dynamics with a consistent treatment of electronic energy transport and redistribution to the lattice, to model how swift heavy ions form damage tracks. We consider a range of material parameters (electron-phonon coupling strength, thermal conductivity and electronic specific heat) and show how these affect the maximum lattice temperature reached and the extent of residual damage. Our analysis also suggests that fission tracks may form in alloys of archaeological interest

It's written in the cloud: The hype and promise of cloud computing

Purpose of paper: This viewpoint discusses the emerging IT platform of Cloud Computing and discusses where and how this has developed in terms of the collision between internet and enterprise computing paradigms – and hence why cloud computing will be driven not by computing architectures but more fundamental ICT consumption behaviours. Design/methodology/approach: The approach has been based upon the discussion and recent developments of Software as a Service (SaaS) and associated ICT computing metaphors and is largely based upon the contemporary discussion at the moment of the impact of social, open source and configurable technology services. Findings: It is suggested that whilst cloud computing and SaaS are indeed innovations within ICT, the real innovation will come when such platforms allow new industries, sectors, ways of doing business, connecting with and engaging with people to emerge. Thus looking beyond the technology itself. Research limitations/applications: Author viewpoint only, not research based. Practical applications: Brings together some of the recent discussions within the popular as well as business and computing press on social networking, open source and utility computing. Social implications: Suggests that cloud computing can potentially transform and change the way in which IS and IT are accessed, consumed, configured and used in daily life. Originality / value of paper: Author viewpoint on a contemporary subject

Realizing the business benefits of enterprise IT

The development and implementation of IT/IS systems inherently requires a deep understanding of user requirements. However, experience shows that a key barrier to the success of an IT/IS system, is the manner by which it is adopted by end users. As such, this viewpoint article presents an overview of those typical enterprise IT user traits as experience by the author. These traits are placed in the context of the steps that need to be taken in terms of a lifecycle approach to business systems implementation. Thus, the paper describes those drivers which inhibit the adoption of enterprise IT/IS projects from a user expectation point of view. By outlining key benefits of such systems, the author presents a 6-stage approach to benefits realisation, known as the acronym, ASSIST. By applying such an approach, the management of business process change and delivery of IT/IS should be more achievable, by addressing the specific needs and expectations of different types of users, as identified in the text of the article. In doing so, the definition of those key IT/IS benefits as outlined in the ASSIST phase approach described is therefore a useful addition to existing project management and business analysis tools and techniques, that can be utilised by enterprise IT system delivery managers as well as Senior IT/IS managemen

DISTRIBUTIONS OF RANDOM-FIELDS IN SOLIDS - CONTRIBUTION OF THE NEAREST DEFECT

Discusses the statistical distribution of internal fields due to random defects in solids. It extends previous discussions by separating explicitly the contribution of the nearest defect from that due to all others. Possible applications include those to preferential defect pairing, to hopping conduction in randomly doped crystals, and to questions of the existence of phase transitions in random dipole systems. As a by-product, it is noted that the random strains in solids have a statistically negligible probability of localising a muon (assumed not self-trapped) except at the sites of defects themselves

LINEWIDTHS WITH GAUSSIAN AND LORENTZIAN BROADENING

Spin resonance lines occur which are broadened both by mechanisms giving a lorentzian shape and by mechanisms giving a gaussian shape It is often important to separate these contributions to the peak-to-peak separation of the derivative of the lineshape A simple and accurate expression is obtained to achieve this..