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As phenomena that necessarily emerge from the collective behavior of interacting particles, phase transitions continue to be difficult to predict using statistical thermodynamics. A recent proposal called the topological hypothesis suggests that the existence of a phase transition could perhaps be inferred from changes to the topology of the accessible part of the configuration space. This paper instead suggests that such a topological change is often associated with a dramatic change in the configuration space geometry, and that the geometric change is the actual driver of the phase transition. More precisely, a geometric change that brings about a discontinuity in the mixing time required for an initial probability distribution on the configuration space to reach the steady state is conjectured to be related to the onset of a phase transition in the thermodynamic limit. This conjecture is tested by evaluating the diffusion diameter and ε-mixing time of the configuration spaces of hard-disk and hard-sphere systems of increasing size. Explicit geometries are constructed for the configuration spaces of these systems and numerical evidence suggests that a discontinuity in the ε-mixing time coincides with the solid-fluid phase transition in the thermodynamic limit.

Hard sphere systems are often used to model simple fluids. The configuration spaces of hard spheres in a three-dimensional torus modulo various symmetry groups are comparatively simple and could provide valuable information about the nature of phase transitions. Specifically, the topological changes in the configuration space as a function of packing fraction have been conjectured to be related to the onset of first-order phase transitions. The critical configurations for 1 to 12 spheres are sampled using a Morse-theoretic approach, and they are available in an online, interactive database. Explicit triangulations are constructed for the configuration spaces of the two sphere system, and their topological and geometric properties are studied. The critical configurations are found to be associated with geometric changes to the configuration space that connect previously distant regions and reduce the configuration space diameter as measured by the commute time and diffusion distances. The number of such critical configurations around the packing fraction of the solid-liquid phase transition increases exponentially with the number of spheres, suggesting that the onset of the first-order phase transition in the thermodynamic limit is associated with a discontinuity in the configuration space diameter.

Whereas knowledge of a crystalline material's unit cell is fundamental to understanding the material's properties and behavior, there are no obvious analogs to unit cells for disordered materials despite the frequent existence of considerable medium-range order. This article views a material's structure as a collection of local atomic environments that are sampled from some underlying probability distribution of such environments, with the advantage of offering a unified description of both ordered and disordered materials. Crystalline materials can then be regarded as special cases where the underlying probability distribution is highly concentrated around the traditional unit cell. The H_{1} barcode is proposed as a descriptor of local atomic environments suitable for disordered bond networks and is applied with three other descriptors to molecular dynamics simulations of silica glasses. Each descriptor reliably distinguishes the structure of glasses produced at different cooling rates, with the H_{1} barcode and coordination profile providing the best separation. The approach is generally applicable to any system that can be represented as a sparse graph.

Many physical systems are composed of polyhedral cells of varying sizes and shapes. These structures are simple in the sense that no more than three faces meet at an edge and no more than four edges meet at a vertex. This means that individual cells can usually be considered as simple, three-dimensional polyhedra. This paper is concerned with determining the distribution of combinatorial types of such polyhedral cells. We introduce the terms fundamental and vertex-truncated types and apply these concepts to the grain growth microstructure as a testing ground. For these microstructures, we demonstrate that most grains are of particular fundamental types, whereas the frequency of vertex-truncated types decreases exponentially with the number of truncations. This can be explained by the evolutionary process through which grain growth structures are formed and in which energetically unfavorable surfaces are quickly eliminated. Furthermore, we observe that these grain types are "round" in a combinatorial sense: there are no "short" separating cycles that partition the polyhedra into two parts of similar sizes. A particular microstructure derived from the Poisson-Voronoi initial condition is identified as containing an unusually large proportion of round grains. This microstructure has an average of 14.036 faces per grain and is conjectured to be more resistant to topological change than the steady-state grain growth microstructure.

Although random cell complexes occur throughout the physical sciences, there does not appear to be a standard way to quantify their statistical similarities and differences. The various proposals in the literature are usually motivated by the analysis of particular physical systems and do not necessarily apply to general situations. The central concepts in this paper-the swatch and the cloth-provide a description of the local topology of a cell complex that is general (any physical system that can be represented as a cell complex is admissible) and complete (any statistical question about the local topology can be answered from the cloth). Furthermore, this approach allows a distance to be defined that measures the similarity of the local topology of two cell complexes. The distance is used to identify a steady state of a model grain boundary network, quantify the approach to this steady state, and show that the steady state is independent of the initial conditions. The same distance is then employed to show that the long-term properties in simulations of a specific model of a dislocation network do not depend on the implementation of dislocation intersections.

Cellular networks may be found in a variety of natural contexts, from soap foams to biological tissues to grain boundaries in a polycrystal, and the characterization of these structures is therefore a subject of interest to a range of disciplines. An approach to describe the topology of a cellular network in two and three dimensions is presented. This allows for the quantification of a variety of features of the cellular network, including a quantification of topological disorder and a robust measure of the statistical similarity or difference of a set of structures. The results of this analysis are presented for numerous simulated systems including the Poisson-Voronoi and the steady-state grain growth structures in two and three dimensions.

The expansion of an orientation distribution function as a linear combination of the hyperspherical harmonics suggests that the analysis of crystallographic orientation information may be performed entirely in the axis-angle parameterization. Practical implementation of this requires an understanding of the properties of the hyperspherical harmonics. An addition theorem for the hyperspherical harmonics and an explicit formula for the relevant irreducible representatives of SO(4) are provided. The addition theorem is useful for performing convolutions of orientation distribution functions, while the irreducible representatives enable the construction of symmetric hyperspherical harmonics consistent with the crystal and sample symmetries.

Nanoindentation has become ubiquitous for the measurement of mechanical properties at ever-decreasing scales of interest, including some studies that have explored the atomic-level origins of plasticity in perfect crystals. With substantial guidance from atomistic simulations, the onset of plasticity during nanoindentation is now widely believed to be associated with homogeneous dislocation nucleation. However, to date there has been no compelling quantitative experimental support for the atomic-scale mechanisms predicted by atomistic simulations. Our purpose here is to significantly advance the quantitative potential of nanoindentation experiments for the study of dislocation nucleation. This is accomplished through the development and application of high-temperature nanoindentation testing, and the introduction of statistical methods to quantitatively evaluate data. The combined use of these techniques suggests an unexpected picture of incipient plasticity that involves heterogeneous nucleation sites, and which has not been anticipated by atomistic simulations.

The paper considers the status of the wrongful life action particularly in the light of the recent acceptance of such actions in continental Europe. It is considered that the hurdle of causation is still not adequately overcome in these cases and, in a search for an answer to the difficulty, the author re-examines the Canadian case of Cherry v Borsman. This case was originally thought of as one of wrongful life associated with a negligently performed abortion and the paper attempts to overcome the problems of causation by comparing and contrasting the roles of the genetic counsellor and the abortionist. While the attempt is by no means wholly successful, it also serves to draw attention to some significant differences between wrongful life actions based on physical and mental disability in the neonate.

It has been said that change is the only constant, and that certainly holds true for health care settings in the 1990s. Consolidation of two hospitals is one such change. To be successful, the organization and its managers must deal with these changes in a proactive, positive, opportunity-seeking way. Fostering positive relationships with others in the work setting is as important as the fine tuning of clinical skills.

The aircraft disaster of the first flight of Operation "Baby Lift", which departed from Saigon, Vietnam, April 4, 1975, was survived by 149 orphaned children on their way to adoptive homes in the West. It had 157 passenger fatalities. The aircraft disaster exposed the surviving children to a complex disaster environment in which subatmospheric decompression, hypoxia, and deceleration were experienced, many children suffered a transient unconsciousness. We examined 135 surviving children between 1978 and 1985. The U.S. resident children were examined in the years 1979 to 1982 at an average age of 8 years and 6 months. They displayed the following symptomatology: attention deficit (> 75%), hyperactivity (> 65%), impulse disorder (> 55%), learning disabilities (> 35%), speech and language pathology (> 70%), and soft neurological signs (> 75%). The European children were examined in the years 1983 to 1985. On arrival at the adoptive home, 2 weeks after the accident they displayed the following symptomatology: muscle hypotonia (26%), seizures (2.5%), and regressed developmental milestones (33%). At the time of the diagnostic evaluations (1983 to 1985) the average age was 11 years and 8 months. They displayed the following symptomatology: attention deficit (59%), hyperactivity (52%), impulse disorder (48%), learning disabilities (43%), soft neurological signs (43%), epilepsy (16%), and speech and language pathology (34%). We conclude that a complex disaster environment can cause brain damage in children without prolonged unconsciousness, and that victims of disasters require a thorough evaluation from a multidisciplinary team.

The paper is concerned, in the main, with selective non-treatment of those incapable of making treatment decisions of their own. It draws attention to the conflict between the law and the medical profession in this field which was predicted some ten years ago and traces the British case law from then until the present day. It concludes that there is no such legal threat to medical practice in Great Britain and that any doubtful practices are currently controlled through the concept of the health care team.

It is appreciated that there are national and jurisdictional variations in regard to post-mortem dissections following accidental death. The purpose of this paper is to plead that, since there will be nationals of many states involved in an aircraft disaster, there should be a uniform system of forensic investigation on a world wide basis. The justification for this recommendation is illustrated through the investigation of accident causes and through the solution of the many problems relating to the settlement of probate which arise in accidental death. The causes of accidents which may be discovered by autopsy include crew incapacitation and criminality of all types. The emergency status may also be revealed and the type of accident, particularly whether in a controlled or uncontrolled phase, may become clear. The medico-legal problems to be resolved include those concerning payment of insurance policies, including the degree of life expectancy, and especially the disposal of estates when members of a family apparently die together. The resulting payments to beneficiaries may be quite different depending on the quality of the autopsy. These investigations are complementary to, and do not interfere with, the identification process but they are time consuming and expensive.

The lungs of 136 persons dying as a result of road traffic accidents were studied retrospectively for the presence of fat and bone marrow emboli. Comparable investigations were made in 54 cases of acute myocardial failure reported to the medicolegal authorities and in 50 cases of fatal drug overdose. A further 50 cases of myocardial failure dying in hospital were studied for the presence of bone marrow embolism only. It was considered that despite occurrence of an occasional anomalous case, both fat and bone marrow emboli are related to injury but that the incidence and severity of bone marrow embolism in particular depends greatly upon the conditions of the accidental death. The occurrence of pulmonary embolic phenomena in cases of natural death was attributed to resuscitative measures rather than the underlying condition. The results indicated that the medicolegal significance attached to the findings should, by themselves, be limited to the positive identification of injuries sustained before or at the time of death in the individual case.

The paper describes the histological appearances in the lungs from 11 fatal cases of paraquat poisoning. The study originated as an attempt to define the sequential changes in the condition and, from them, to assess the mode of action of the herbicide in the human. The main features of the "paraquat lung" include haemorrhage, extrusion of macrophages, oedema, "honeycombing", fibrosis and, rarely, epithelial hyperplasia. The indications are that the changes are progressive once a threshold tissue concentration has been reached. The appearances are compared to those in poisoning by hyperbaric oxygen and it is hypothesized that the toxic action of paraquat is to sensitize the lungs to oxygen at atmospheric pressure.

This paper traces the development of parental rights to accept or to refuse treatment for a defective newborn infant in the United Kingdom and in the United States of America; its main purpose is to explore the common trends from which an acceptable policy may be derived. It is probable that the British law on parental decision-making in respect of infants suffering from Down's syndrome is to be found in the civil case of In Re B rather than in the criminal case of R v Arthur. United States court decisions are strongly influenced by constitutional law and reflect the right to personal privacy. The position on each side of the Atlantic seems very similar but this similarity includes a sense of uncertainty as to legal responsibility. There is a case for agreed guidelines and a suggested format is offered for consideration.

A small sample of general practitioners was questioned about non-accidental injury to children. Differences emerged between those qualifying before and after 1960. Differences were also found in management between the general practitioners and other workers in this field, health visitors, social workers and the police. The need to include this subject in the continuing education of general practitioners is stressed.

This review article discusses the role of previous disease in military, private, and commercial pilots under the headings of occurrence, accident causation, and accident prevention. The importance of minor disease in military flying is stressed as are psychiatric disorders and alcoholism in general aviation. Disease of the coronary arteries is considered with special reference to commercial operations, where the importance of double crewing is emphasized. While symptomatic disease must always be significant, some of the problems associated with increasingly severe selection on the basis of asymptomatic disease are discussed.

One hundred and twenty-six consecutive cases of sudden infant death syndrome (SIDS) in the Edinburgh area have been studied with particular reference to the interrelationship of feeding, associated biochemical changes, and social status. There was an excess of cases born to parents in Social Classes IV and V: the effect was maximal in children who dies beyond 12 weeks of age. A low-grade uraemia was discovered in approximately one-fifth of the cases; analysis showed this to be related most strongly to bottle-feeding. Feeding habits were found to be associated with social class and this accounted for the relationship between bottle-feeding and the youth of mothers and also for an apparent relationship between uraemia in the infant and social class of the mother. Mothers of SIDS children were younger than expected and SIDS was found to be electrolyte imbalance is common in SIDS cases, nor did the findings support the suggestion that cross-infection due to overcrowding is an important aetiological factor. The significant factors of young motherhood, low social status, bottle-feeding, and mild uraemia in the babies are interrelated and seem to focus attention on unwitting 'mothering problems'. It is, however, not easy to see how this, or any other hypothesis, can account for all cases of SIDS.