Complex relativity and real solutions. I: Introduction

This is the first of a series of papers on complex spaces and their use in complex relativity. The basic aim is to develop the theory of complex relativity but only insofar as it helps in obtaining, and understanding, real solutions of Einstein's vacuum equations as slices of complex solutions. In this first paper, specific aims of the whole series are first presented. The basic equations and key entities, which are used later, are presented. The basic relativistic language used is that of Newman and Penrose. Included is a discussion of a number of important properties which arise in the development of the basic equations and key concepts, these properties being mainly ones which are not apparent in standard real formulations.     

Quality assessment in in vivo NMR spectroscopy: I. Introduction,objectives, and activities

By enabling noninvasive measurements of tissue biochemistry, nuclear magnetic resonance spectroscopy (MRS) provides a unique means of characterizing tissues. Differences in equipment, techniques, and methodology between different laboratories cause major difficulties when comparing results, whether from measurements of tissue metabolism, or from the effects of different therapies. This is of concern in critically evaluating work from different laboratories and centres, causing potential difficulties in reproducing results, limiting the establishment of MRS as a standard method of diagnosis and of characterising disease and response to therapy in the laboratory and clinic. It also poses particular problems in establishing the multicentre clinical trials of MRS that are now required to provide adequate statistical power in confirming the encouraging preliminary clinical observations. These difficulties arise principally from imperfect localization of signal from selected regions of interest in the body, and from the subsequent analyses of the MRS spectra. Improvement is possible by establishing agreed procedures for test measurements and for data analysis, and by using appropriate test objects and test substances to establish the quality of measurements. A concerted research project on characterisation of biological tissues by NMR, principally concerned with MR imaging (MRI), was activated in 1984 by the European Economic Community as part of its third Medical and Health Research Programme, under the auspices of the Biomedical Engineering Concerted Actions' Committee (COMAC-BME). In 1988, this project was prolonged for 5 years, when the programme was expanded to encompass MRS. A series of five accompanying papers describes (a) the test protocols and objects agreed for assessing the quality of volume selective MRS measurements; (b) the experimental trials performed for a multicentre evaluation of these procedures on experimental and clinical systems; and (c) the results of a joint quantitative data analysis study on in vivo NMR time-domain test signals.     

Sputtering of ordered nickel-aluminium alloys: I. Introduction and preferential sputtering of Ni3Al

A combination of several surface-sensitive microanalytical techniques have been applied to the study of selective or preferential sputtering by inert gas ion bombardment of aluminium from binary ordered nickel-aluminium alloys. Two discrete intermetallic compounds, Ni₃Al (this paper) and NiAl (the companion paper) have been examined in order to provide information regarding the contribution of surface binding states to sputter mechanisms. The use of atom-probe field-ion microscopy for analysis of ion-sputtered surfaces has permitted the depth of bombardment-induced composition profiles to be estimated and comparisons to be drawn between these depth profiles and those obtained by conventional surface analysis techniques. Studies of preferential sputtering in ordered structures have provided information through atom-probe analysis of fundamental and superlattice oriented specimens about composition profiles and bombardment-induced disordering processes. Consideration of these data have led to conclusions that two distinct “equilibria” may be involved in the formation of super-induced altered layers.     

Galaxies: A Very Short Introduction,by J. Gribbin

A brief outline of conventional symmetry studies of crystalline solids using Bravais lattices, point groups and space groups is presented, leading up to the recent development by Shubnikov of the idea of antisymmetry and the subsequent derivation of the black and white Bravais lattices and of the black and white point groups and space groups. These groups are also called magnetic groups or Shubnikov groups.

The results of neutron-diffraction experiments have made it clear that there are many crystals whose structures must be described by one of these Shubnikov groups rather than by one of the ordinary point groups or space groups. The relationship between a structure with the symmetry of one of the Shubnikov point groups and the magnetic properties, paramagnetism, diamagnetism, ferromagnetism, ferrimagnetism or anti-ferromagnetism, which it is able to exhibit is also considered.