Table of contents

The Wigner-function (WF) approach to quantum electron transport in semiconductors is reviewed in this paper. The main definitions and properties related to the WF are presented, with a discussion of the various forms of the dynamical equations that govern its evolution. Monte Carlo solutions of such equations are also discussed. Interactions of electrons with applied fields, potential profiles, and phonons are analysed in detail. Finally, several physical applications are presented. Each topic has been developed from basic principles for the benefit of interested readers who are not experts in the particular subjects discussed in this paper.

The unique aspects of neutron scattering in biology rely largely on the extraordinary parameters of interaction of neutrons with hydrogen nuclei. The origin of isotopic and spin incoherent scattering and its possible implication for neutron diffraction from protein crystals are described. The impact of a change in the coherent scattering length of hydrogen nuclei with isotopic substitution and spin polarization is illustrated by a number of applications in structural biology, which show clearly the complementarity to x-ray diffraction. A more detailed account is given of polarized neutron scattering from dynamically polarized spin systems. Experimental evidence for the existence of selectively polarized proton spin domains and their use in structural studies is presented.

This contribution considers recent developments in the computer modelling of amorphous polymeric materials. Progress in our capabilities to build models for the computer simulation of polymers from the detailed atomistic scale up to coarse-grained mesoscopic models, together with the ever-improving performance of computers, have led to important insights from computer simulations into the structural and dynamic properties of amorphous polymers. Structurally, chain connectivity introduces a range of length scales from that of the chemical bond to the radius of gyration of the polymer chain covering 2–4 orders of magnitude. Dynamically, this range of length scales translates into an even larger range of time scales observable in relaxation processes in amorphous polymers ranging from about 10⁻¹³ to 10⁻³ s or even to 10³ s when glass dynamics is concerned. There is currently no single simulation technique that is able to describe all these length and time scales efficiently. On large length and time scales basic topology and entropy become the governing properties and this fact can be exploited using computer simulations of coarse-grained polymer models to study universal aspects of the structure and dynamics of amorphous polymers. On the largest length and time scales chain connectivity is the dominating factor leading to the strong increase in longest relaxation times described within the reptation theory of polymer melt dynamics. Recently, many of the universal aspects of this behaviour have been further elucidated by computer simulations of coarse-grained polymer models. On short length scales the detailed chemistry and energetics of the polymer are important, and one has to be able to capture them correctly using chemically realistic modelling of specific polymers, even when the aim is to extract generic physical behaviour exhibited by the specific chemistry. Detailed studies of chemically realistic models highlight the central importance of torsional dynamics in all relaxation processes in polymer materials. Finally, the interplay between local energetics, both intramolecular and intermolecular, and the local packing governs the glass transition in polymer melts.

The limits of nuclear stability have not been reached for most elements. Only for the lightest elements are the minimum and maximum number of neutrons necessary to form an isotope for a given element known. The current limits, novel features of nuclei at these limits as well as the future possibilities of pushing these limits even further will be discussed.

Superionic conductors are compounds that exhibit exceptionally high values of ionic conductivity within the solid state. Indeed, their conductivities often reach values of the order of 1 Ω⁻¹ cm⁻¹, which are comparable to those observed in the molten state. Following Faraday's first observation of high ionic conductivity within the solids β-PbF₂ and Ag₂S in 1836, a fundamental understanding of the nature of the superionic state has provided one of the major challenges in the field of condensed matter science. However, experimental and theoretical approaches to their study are often made difficult by the extensive dynamic structural disorder which characterizes superionic conduction and the inapplicability of many of the commonly used approximations in solid state physics. Nevertheless, a clearer picture of the nature of the superionic state at the ionic level has emerged within the past few decades. Many different techniques have contributed to these advances, but the most significant insights have been provided by neutron scattering experiments and molecular dynamics simulations. This review will summarize the state of current knowledge concerning the crystal structures and conduction processes of superionic conductors, beginning with a comparison of the behaviour of two of the most widely studied binary compounds, AgI and β-PbF₂. Each can be considered a parent of two larger families of highly conducting compounds which are related by either chemical or structural means. These include perovskite-structured oxides and Li⁺ containing spinel-structured compounds, which have important commercial applications in fuel cells and lightweight batteries, respectively. In parallel with these discussions, the relative importance of factors such as bonding character and the properties of the mobile and immobile ions (charge, size, polarizability, etc) in promoting the extensive lattice disorder which characterizes superionic behaviour will be assessed and the possibilities for predicting a priori which compounds will display high ionic conductivity discussed.