Extent of stacking disorder in diamond

Hexagonal diamond has been predicted computationally to display extraordinary physical properties including a hardness that exceeds cubic diamond. However, a recent electron microscopy study has shown that so-called hexagonal diamond samples are in fact not discrete materials but faulted and twinned cubic diamond. We now provide a quantitative analysis of cubic and hexagonal stacking in diamond samples by analysing X-ray diffraction data with the DIFFaX software package. The highest fractions of hexagonal stacking we find in materials which were previously referred to as hexagonal diamond are below 60%. The remainder of the stacking sequences are cubic. We show that the cubic and hexagonal sequences are interlaced in a complex way and that naturally occurring Lonsdaleite is not a simple phase mixture of cubic and hexagonal diamond. Instead, it is structurally best described as stacking disordered diamond. The future experimental challenge will be to prepare diamond samples beyond 60% hexagonality and towards the so far elusive 'perfect' hexagonal diamond

The static response characteristics of a carbon bolometer element

Electrical resistivity of carbon resistor material for calculating static response characteristics of carbon bolometer elemen

Habitat Associations and Movement Tracking of North American Black Terns (Chlidonias niger)

Black Tern (Chlidonias niger) populations are declining across their range in North America, but it is unknown at what point during the annual cycle populations may be limited. Although causes of decline remain largely unknown, past studies showed that conditions on stop-over and over-wintering locations may be important factors. Little is known about the migration timing, routes, stop-over sites, or the range and environmental conditions of over-wintering Black Terns. Furthermore, it is unclear what habitat qualities and attributes influence Black Tern colony occurrence in the core of their breeding range in the Canadian prairies. Breeding habitat selection is increasingly important in the face of continuing and potentially damaging anthropogenic land uses and climate change. My objectives were to 1) examine the influence of various habitat, land use, and geographic covariates on Black Tern occupancy and abundance in the core of the species range in Saskatchewan; and 2) examine full annual cycle movements and potential differences in migratory stop-over and over-wintering locations from Black Terns breeding across their range in central (Saskatchewan, Canada) and eastern (Ontario, Canada and Michigan, USA) North America, while providing a preliminary assessment of migratory connectivity. I assessed Black Tern occupancy and abundance at 68 wetlands compiled from historic waterbird databases and field surveys. I used aerial imagery to quantify four habitat covariates I predicted would influence Black Tern site suitability: total wetland area, the extent of emergent vegetation present at each wetland, wetland classification, and the degree of anthropogenic encroachment surrounding each wetland. I deployed 88 archival light-level geolocators on Black Terns across five colonies in Saskatchewan and Ontario, Canada, and Michigan, USA, during the breeding seasons of 2016-2019 to track their migratory movements, stop-over, and over-wintering locations. Habitat association results showed that colony occurrence was predicted by both geographic and habitat covariates, with wetlands at mid-latitudes and with more emergent vegetation associated with an increased likelihood of Black Tern colony occurrence. Abundance was best predicted by geographic patterns (latitude) alone. These results revealed that Black Terns are selecting breeding habitat at multiple scales primarily along a narrow latitudinal band across Saskatchewan. This suggests that individuals may first be locating breeding sites based on large-scale landscape features driven by latitude, and then selecting specific wetland locations for breeding based on small-scale features such as emergent aquatic vegetation. The highest abundances corresponded with the boreal transition zone between the prairies to the south and boreal forest to the north, an area that might be preferred by Black Terns due to its abundance of wetland habitat. The migratory routes used by Black Terns varied among individuals, but some geographic patterns emerged; Black Terns from central and eastern regions used different migratory routes. All tagged individuals spent some or most of the wintering period at or off the coast of Panama, highlighting the importance of this location during the wintering period. These results suggest Panama might be a key location of population mixing on the wintering grounds. Additionally, migratory connectivity was stronger between breeding sites and the first migratory stopover location than it was between breeding sites and wintering locations, indicating that individuals from different breeding colonies generally remained more closely linked to other individuals from their same breeding colony during the fall migration, but that subsequent mixing of the populations occurred among individuals from multiple breeding locations on the wintering grounds. Some interesting patterns of Black Tern breeding dispersal were also uncovered based on long-distance breeding region switching of one individual tracked over multiple years. Furthermore, preliminary insights into colony abandonment and short-distance breeding dispersal of Black Terns in Saskatchewan were also revealed. These results fill important data gaps that exist for the North American Black Tern. Although Black Tern populations are declining across their range, I demonstrate that colony occurrence and abundance can be predicted using both geographic and habitat models. These associations have revealed evidence that individuals are selecting habitat at multiple scales, both large and small. The quadratic relationship between the likelihood of colony occurrence and the latitude of a wetland suggests that large-scale landscape variables, such as variation in wetland density, may be driving this pattern. Very little was previously known about the Black Tern full annual cycle, and these migratory tracks are the first that have been collected for the species. Despite the use of different flyways across the breeding range, tracked individuals showed a high degree of mixing and weak migratory connectivity on the wintering grounds. A concentration of birds in Panama suggests that localized threats in this area could have an impact across the breeding range. In addition, evidence of long- and short-distance breeding dispersal suggest a lack of population structure and high levels of movement and gene flow. My results provide some of the first detailed migratory tracks for the Black Tern in North America, and reveal important habitat associations in the core of the species range, critical information that could benefit the conservation of the species

Discrete-valued Levy processes and low latency financial econometrics

Motivated by features of low latency data in finance we study in detail discrete-valued Levy processes as the basis of price processes for high frequency econometrics. An important case of this is a Skellam process, which is the difference of two independent Poisson processes. We propose a natural generalisation which is the difference of two negative binomial processes. We apply these models in practice to low latency data for a variety of different types of futures contracts.futures markets; high frequency econometrics; low latency data; negative binomial; Skellam distribution.

Explorations into the rare earth chemistry of biphenolates and superbulky cyclopentadienyl ligands, and a study of C-F activation by rare earth metals

Angus Shephard studied a range of alternative synthetic methods for accessing valuable rare earth metal complexes. He explored new and previously unused methods of synthesising rare earth biphenolate complexes, superbulky lanthanoid metallocene complexes, and lanthanoid formamidinate and pyrazolate species. His work has provided fundamental insight into the reactivity of free rare earth metals

Des coloriages de pavages super et superbes

II existe une vaste littérature sur le sujet des groupes de couleurs et des coloriages des motifs dans le plan [2, chapitre 8], [6], [8]. II est toutefois étrange qu’aucun de ces travaux ne semble porter directement sur les problèmes du coloriage des pavages comme tel. Plus particulièrernent, bien que les groupes de couleurs soient souvent présentés comme des groupes de symétrie de couleurs des pavages, un examen approfondi révélera que ce ne sont que les motifs des pavés du pavage qui sont considérés; d’autres propriétés essentielles d’un pavage tel que son type topologique et I’adjacence de certaines paires de pavés sont ignorées. Si, par contre, on en tient compte, plusieurs problèmes intéressants (et complexes) se présentent. Le but de cet article est d’aborder quelques-uns de ces problèmes. On s’intéressera plus particulièrement à ce qu’on appelle les super coloriages de pavages isoédriques. (On expliquera ci-dessous les termes essentiels.) Au-delà de I’intérêt mathématique, les super coloriages sont très attrayants d’un point devue esthétique et, à ce titre, ils ont été utilisés par des artistes comme M.C. Escher. En fait dans I’ensemble des collections publiées d’oeuvres d’Escher, tous les coloriages de pavages isoédriques sont super. (On peut consulter, par exemple, [ 1 , Planches E2-E23, E32-E31, E36-E51, E55, E62-E66, E70, E73-E79, E86, E88-E92, E94-E98, E l 02-E109, E116-E119, E124, E127, E128].) Ce fait fut à I’origine du présent article, il est la suite d’une présentation de I’auteur au Escher Symposium de Rome en mars 1985 (un rapport en a été donné dans les Comptes-rendus de cette rencontre [7]). Toutefois, dans I’intérêt du lecteur, on répétera ici la terminologie jugée essentielle et cette présentation sera auto-suffisante. L’auteurtient à exprimer sa reconnaissance à Marjorie Senechal et à Tom Wieting pour hi avoir suggéré les corrections à [6], et, plus particulièrement a Branko Grünbaum pour nos discussions utiles et les commentaires qu’il porta sur les versions préliminaires de cet article, commentaires qui menèrent à plusieurs améliorations.There exists an extensive literature concerning colour groups and the related colourings of the motifs of a plane pattern [2, Chapter 81, [6], [8]. It is strange that none of this work seems to refer directly to the problems of colouring tilings as such. To be more specific, though colour groups are often displayed as the colour symmetry groups of tilings, careful examination will show that it is only the patterns of the tiles in the tilings which are under consideration; other essential properties of a tiling such as its topological type, and the adjacencies of certain pairs of tiles, are ignored. If the latter are taken into account, several interesting (and difficult) problems emerge. It is the purpose of the present paper to consider some of these. In particular, we shall be concerned with what are called super colourings of isohedral tilings. (These words and other essential terminology, will be explained shortly.) Besides being mathematically interesting, super colourings are very attractive from an aesthetic point of view, and have been used by artists such as M.C. Escher. In fact, in the published collections of Escher’s works, all his colourings of isohedral tilings are super. (See, for example, [ l , Plates E2-E23, E32-E31, E36-E51, E55, E62-E66, E70, E73-E79, E86, E88-E92, E94-E98, E102-E109, E l 16-El 19, E 124, E 127, E 1281.) This fact motivated the present paper, which isasequel to the talkgiven bythe authoratthe ExherSymposium in Rome in March 1985, and reported in the Proceedings of that meeting [7]. However, for the convenience of the reader, essential terminology will be repeated here and the presentation will be self-contained. The author wishes to express his gratitude to Marjorie Senechal and Tom Wieting for supplying him with corrections to [6], and, more especially to Branko Grunbaum for helpful discussions and for his comments on preliminary versions of this paper which led to many improvements.Peer Reviewe

Hydrogen mean force and anharmonicity in polycrystalline and amorphous ice

The hydrogen mean force from experimental neutron Compton profiles is derived using deep inelastic neutron scattering on amorphous and polycrystalline ice. The formalism of mean force is extended to probe its sensitivity to anharmonicity in the hydrogen-nucleus effective potential. The shape of the mean force for amorphous and polycrystalline ice is primarily determined by the anisotropy of the underlying quasi-harmonic effective potential. The data from amorphous ice show an additional curvature reflecting the more pronounced anharmonicity of the effective potential with respect to that of ice Ih.Comment: 12 pages, 7 figures, original researc

Inhalation therapy during acute asthma : the role of a combined steroid and beta-stimulant preparation

CITATION: Joubert, J. R., Burger, G. & Shephard, E. 1985. Inhalation therapy during acute asthma : the role of a combined steroid and beta-stimulant preparation. South African Medical Journal, 68:381-384.The original publication is available at http://www.samj.org.zaA compound consisting of a β-stimulant, salbutamol (100 μg/puff), and a steroid, beclomethasone diproprionate (50 μg/puff), was studied to test the hypothesis that the corticosteroid could enhance the bronchodilator proporties of the β-stimulant during chronic asthma and simulated acute attacks (antigen challenge). Conventional doses (200 μg and 100 μg of salbutamol and beclomethasone respectively) were compared using a schedule which included a second administration 1 hour later. The results obtained on the baseline bronchial responsiveness of chronic asthmatics and during the delayed asthmatic response (simulated acute asthma) were similar. The compound was as effective as salbutamol alone but not more so. A significantly greater bronchodilator response was recorded in all patients after the second administration of both the compound and salbutamol alone. The practical advantages of having one rather than two inhalers are evident, but the appropriate application of this compound agent, probably in a prophylactic role, must be defined.Publisher’s versio