Architecture and evolution of a fjord‐head delta,western Vancouver Island,British Columbia

The architectural framework and Holocene evolution of the Zeballos fjord‐head delta on west‐central Vancouver Island was established through a multidisciplinary field‐based study. The Zeballos delta is a composite feature, consisting of an elevated, incised, late Pleistocene delta and an inset Holocene delta graded to present sea level. Both deltas have a classic Gilbert‐type tripartite architecture, with nearly flat topset and bottomset units and an inclined foreset unit. Time domain electromagnetic (TDEM) and ground‐penetrating radar (GPR) surveys, borehole data, and gravel pit exposures provided information on the internal form, lithologies and substrate of both deltas. Both sets of deltaic deposits coarsen upward from silt in the bottomset unit to gravel in the topset unit. The TDEM survey revealed a highly irregular, buried bedrock surface, ranging from 20 m to 190 m in depth, and it delineated saltwater intrusion into the deltaic sediments. Late Quaternary sea‐level change at Zeballos was inferred from delta morphology and the GPR survey. The elevated, late Pleistocene delta was constructed when the sea was about 21 m higher relative to the land than it is today. It was dissected when sea‐level fell rapidly as a result of glacio‐isostatic rebound. Relative sea‐level reached a position about 20 m below the present datum during the early Holocene. Foreset beds that overlap and progressively climb in a seaward direction and topset beds that thicken to 26 m landward imply that the delta aggraded and prograded into Zeballos Inlet during the middle and late Holocene transgression. Sea‐level may have risen above the present datum during the middle Holocene, creating a delta plain at about 4 m a.s.l. Remnants of this surface are preserved along the valley margins. Copyright © 2004 John Wiley & Sons, Ltd.     

High-resolution simulations of stellar collisions between equal-mass main-sequence stars in globular clusters

We performed high-resolution simulations of two stellar collisions relevant for stars in globular clusters. We considered one head-on collision and one off-axis collision between two 0.6-M_⊙ main-sequence stars. We show that a resolution of about 100 000 particles is sufficient for most studies of the structure and evolution of blue stragglers. We demonstrate conclusively that collision products between main-sequence stars in globular clusters do not have surface convection zones larger than 0.004 M_⊙ after the collision, nor do they develop convection zones during the 'pre-main-sequence' thermal relaxation phase of their post-collision evolution. Therefore, any mechanism which requires a surface convection zone (i.e. chemical mixing or angular momentum loss via a magnetic wind) cannot operate in these stars. We show that no disc of material surrounding the collision product is produced in off-axis collisions. The lack of both a convection zone and a disc proves a continuing problem for the angular momentum evolution of blue stragglers in globular clusters.     

Brown dwarf populations in open clusters

We present the results of multiple simulations of open clusters, modelling the dynamics of a population of brown dwarf members. We consider the effects of a large range of primordial binary populations, including the possibilities of having brown dwarf members contained within a binary system. We also examine the effects of various cluster diameters and masses. Our examination of a population of wide binary systems containing brown dwarfs, reveals evidence for exchange reactions whereby the brown dwarf is ejected from the system and replaced by a heavier main-sequence star. We find that there exists the possibility of hiding a large fraction of the brown dwarfs contained within the primordial binary population. We conclude that it is probable that the majority of brown dwarfs are contained within primordial binary systems which then hides a large proportion of them from detection.     

Planets in 47 Tuc

We consider the survivability of planetary systems in the globular cluster 47 Tucanae. We compute the cross-sections for the breakup of planetary systems via encounters with single stars and binaries. We also compute the cross-sections to leave planets on eccentric orbits. We find that wider planetary systems ( d ≳0.3 au) are likely to be broken up in the central regions of 47 Tucanae (within the half-mass radius of the cluster). However, tighter systems and those in less-dense regions may survive. Tight systems will certainly survive in less-dense clusters where subsequent surveys should be conducted.     

A model for rock interfacial behaviour

Summary A model is proposed to describe the frictional resistance offered by two sliding bodies, with application to rock mechanics. In the model, frictional resistance is attributed to three components. In addition to basic sliding and dilational components, which are widely accepted in geomechanics, a third component is introduced, due to plough resistance. This component is due to ploughing of the surface by asperities and wear particles. The dilation and plough components are functions of the interacting surface profiles (surface roughness), relative hardness between the sliding bodies, normal stress and sliding distance. Degradation of surface roughness, and hence reduction in dilation and plough resistance, is formulated using wear theory. The resulting model shows a peak behaviour followed by a postpeak softening response which is often observed in load transfer curves of rock socketed piles. Good agreement with published experimental data is obtained. The model demonstrates that wear theory can be applied to problems in geomechanics to describe the complex behaviour of two sliding bodies.     

Crustal structure from spectral ratio of short-period P waves

This study examines the method of spectral ratio response and verifies a structure beneath Umeå from short-period P waves of teleseismic events. Previously, researchers reported difficulty in interpreting observed ratios of short-period waves in terms of realistic models. Compatible results are returned here by restricting the length of analysis to a short duration (about 12 s) with the understanding that only the gross features of the crust may be modelled. Our results indicate a 42-km two-layer shield structure similar to that derived from long-period P waves. The structure so inferred is attributed to considerations of the observed and theoretical model truncated ratios in the frequency range 0.9–1.3 Hz, the dominant periods of the signals analysed, a short data window, analysis of records with a well-developed beat character and a relatively simple crust beneath the recording station.     

Statistical and cartographic methods of analysing spatial patterns of mortality

The health field concept is examined as a framework within which to analyse spatial patterns of mortality. Disease mapping and its problems are investigated with particular reference to ischaemic heart disease in the U.K.     

The aluminosilicate fraction of North Pacific manganese nodules

Nine nodules collected from throughout the deep North Pacific were analyzed for their mineralogy and major-element composition before and after leaching with Chester-Hughes solution. Data indicate that the mineral phillipsite accounts for the major part (> 75%) of the aluminosilicate fraction of all nodules. It is suggested that formation of phillipsite takes place on growing nodule surfaces coupled with the oxidation of absorbed manganous ion. All the nodules could be described as ternary mixtures of amorphous iron fraction (Fe-Ti-P), manganese oxide fraction (Mn-Mg Cu-Ni), and phillipsite fraction (Al-Si-K-Na), these fractions accounting for 96% of the variability of the chemical composition.     

Effects of coarse-grained materials on properties of residual soil

Residual soils are generally characterised by a low coefficient of permeability and high shrinkage potential. Several soil improvement methods can be applied to overcome these problems, including mixing the residual soil with coarse-grained soils. In order to study the effects of varying coarse-grained materials on the hydraulic properties and shrinkage characteristics of residual soils, a local residual soil was mixed with different percentages of a gravelly sand and a medium sand. The hydraulic properties and shrinkage potential of the residual soil and the soil mixtures were investigated. The measurements showed that increasing the amount of coarse-grained materials increased the saturated permeability and reduced the shrinkage potential of the residual soil mixture. Increasing the amount of coarse-grained materials in the residual soil produced changes in several key parameters of soil-water characteristic curve (e.g., the slope, the air-entry value, the residual matric suction, and the residual volumetric water content), as well as the unsaturated permeabilities of the soil mixtures.