Crinoid localities of the Silurian of the British Isles

The first monograph of the British Silurian crinoids was published as early as 1839 and identified 14 species; over 120 are now known. The most productive horizon for both diversity of species and numbers of well‐preserved specimens is the Much Wenlock Limestone Formation at Dudley (Lower Silurian, Wenlock), a site of international significance. Other localities have produced fewer, but different species. Herein, we introduce the most important crinoid localities in the Llandovery to Ludlow of the British Isles, and figure some of the many beautiful and significant specimens that they have produced.     

Ageing research in Australia: reflecting on Graeme Hugo’s four decades of contribution

ABSTRACT

Globally, population ageing is one of the most pressing social and policy issues faced today. Over the next two decades, Australian society will face dramatic increases in the proportion of the population aged 65 years and over, as the baby boomers move into older age and fertility levels remain low. Yet population ageing is not a surprising or new trend—demographic changes in the age profile of a population tend to occur incrementally rather than suddenly. As a demographer and geographer, Graeme Hugo drew attention to this trend in Australia’s population more than three decades ago. Throughout Graeme Hugo’s vast breadth of work over the past 40 years, there has been a consistent thread of demographic analysis and academic thought associated with the ageing of Australia’s population. This paper focuses on Hugo’s contributions to academic thought and policy on Australia’s ageing population and the challenges associated with this for both service delivery and health policy as Australian society moves into an unprecedented era of population ageing.     

Explanation of locking of four‐node plane element by considering it as elastic Dirichlet‐type boundary value problem

The aim of this study is to arrive at a better understanding of the phenomenon of locking of low‐order compatible displacement type of finite elements in particular for the hour‐glass mode of the plane four‐node element and dilative materials. To this end the properties of finite elements are investigated in an analytical way, where a finite element is considered as a plane boundary value problem with prescribed boundary displacement (Dirichlet problem). In this paper for the sake of simplicity the simplest possible linear comparison solid, namely isotropic linear elasticity, is applied, although recognizing fully that for a dilative material elasto‐plasticity would be more realistic. From the study described in this paper it is concluded that locking of the four‐node element is not due to any particular numerical formulation of this compatible finite element since, even the analytical solution suffers from this problem. The locking of this element is not related to incompressibility of the material either as the analytical solution shows locking to occur at a parameter set which differs significantly from the one in case of incompressibility. It is shown that locking is a consequence of the combination of the dilative material behaviour and the compatible displacement type of boundary conditions, which leads to infinite isotropic stresses in the element. These infinite isotropic stresses occur at the limit of uniqueness of the solution, which for this element is shown to occur outside the parameter range of the sufficiency of uniqueness. Copyright © 2000 John Wiley & Sons, Ltd.     

NanoSIMS isotopic analysis of small presolar grains: Search for Si3N4 grains from AGB stars and Al and Ti isotopic compositions of rare presolar SiC grains

We report isotopic ratio measurements of small SiC and Si₃N₄ grains, with special emphasis on presolar SiC grains of type Z, and new nucleosynthesis models for ²⁶Al/²⁷Al and the Ti isotopic ratios in asymptotic giant branch (AGB) stars. With the NanoSIMS we analyzed 310 SiC grains from Murchison (carbonaceous CM2 chondrite) separate KJB (diameters 0.25-0.45 μm) and 153 SiC grains from KJG (diameters 1.8-3.7 μm), 154 SiC and 23 Si₃N₄ grains from Indarch (enstatite EH4 chondrite) separate IH6 (diameters 0.25-0.65 μm) for their C and N isotopic compositions, 549 SiC and 142 Si₃N₄ grains from IH6 for their C and Si isotopic compositions, 13 SiC grains from Murchison and 66 from Indarch for their Al-Mg compositions, and eight SiC grains from Murchison and 10 from Indarch for their Ti isotopic compositions. One of the original objectives of this effort was to compare isotopic analyses with the NanoSIMS with analyses previously obtained with the Cameca IMS 3f ion microprobe. Many of the Si₃N₄ grains from Indarch have isotopic anomalies but most of these apparently originate from adjacent SiC grains. Only one Si₃N₄ grain, with ¹³C and ¹⁴N excesses, has a likely AGB origin. The C, N, and Si isotopic data show that the percentage of SiC grains of type Y and Z increase with decreasing grain size (from ∼1% for grains >2 μm to ∼5-7% for grains of 0.5 μm), providing an opportunity for isotopic analyses in these rare grains. Our measurements expand the number of Al-Mg analyses on SiC Z grains from 4 to 23 and the number of Ti analyses on Z grains from 2 to 11. Inferred²⁶Al/²⁷Al ratios of Z grains are in the range found in mainstream and Y grains and do not exceed those predicted by models of AGB nucleosynthesis. Cool bottom processing (CBP) has been invoked to explain the low ¹²C/¹³C ratios of Z grains, but this process apparently does not lead to increased ²⁶Al production in the parent stars of these grains. This finding is in contrast to presolar oxide grains where CBP is needed to explain their high ²⁶Al/²⁷Al ratios. The low ^46,47,49Ti/⁴⁸Ti ratios found in Z grains and their correlation with low ²⁹Si/²⁸Si ratios extend the trend seen in mainstream grains and confirm an origin in low-metallicity AGB stars. The relatively large excesses in ³⁰Si and ⁵⁰Ti in Z grains are predicted by our models to be the result of increased production of these isotopes by neutron-capture nucleosynthesis in low-metallicity AGB stars. However, the predicted excesses in ⁵⁰Ti (and ⁴⁹Ti) are much larger than those found. Even lowering the strength of the ¹³C pocket cannot solve this discrepancy in a consistent way.     

Large-scale dispersant leaching and effectiveness experiments with oils on calm water

The use of dispersants to treat oil spills in calm seas is discouraged because there is insufficient ‘mixing energy’ to cause immediate dispersion of the oil. However, dispersants might be applied while the seas are calm, in the expectation that they would work later when sea states increase. The present study examined the persistence of dispersants in treated oil slicks on calm water in a large outdoor wave tank. Test slicks, pre-mixed with dispersant, were allowed to stand on static and flowing water for up to six days, after which their dispersibility was tested by exposing them to breaking waves. Results showed that thicker slicks exposed to calm water for up to six days dispersed completely with the addition of breaking waves. Thinner slicks and slicks exposed to water movement became less dispersible within two days. The loss of dispersibility was caused by dispersant loss rather than by oil weathering.     

Characterization of pyroclastic fall and flow deposits from the 1815 eruption of Tambora volcano,Indonesia using ground-penetrating radar

Ground-penetrating radar (GPR) is used to image and characterize fall and pyroclastic flow deposits from the 1815 eruption of Tambora volcano in Indonesia. Analysis of GPR common-mid-point (CMP) data indicate that the velocity of radar in the sub-surface is 0.1 m/ns, and this is used to establish a preliminary traveltime to-depth conversion for common-offset reflection profiles. Common-offset radar profiles were collected along the edge of an erosional gully that exposed approximately 1–2 m of volcanic stratigraphy. Additional trenching at select locations in the gully exposed the contact between the pre-1815 eruption surface and overlying pyroclastic deposit from the 1815 eruption. The deepest continuous, prominent reflection is shown to correspond to the interface between pre-eruption clay-rich soil and pyroclastics that reach a maximum thickness of 4 m along our profiles. This soil surface is distinctly terraced and is interpreted as the ground surface augmented for agriculture and buildings by people from the kingdom of Tambora. The correlation of volcanic stratigraphy and radar data at this location indicates that reflections are produced by the soil-pyroclastic deposit interface and the interface between pyroclastic flows (including pyroclastic surge) and the pumice-rich fall deposits. In the thickest deposits an additional reflection marks the interface between two pyroclastic flow units.