Life-bearing primordial planets in the solar vicinity

The space density of life-bearing primordial planets in the solar vicinity may amount to ～8.1×10⁴?pc^?3 giving total of ～10¹⁴ throughout the entire galactic disk. Initially dominated by H₂ these planets are stripped of their hydrogen mantles when the ambient radiation temperature exceeds 3?K as they fall from the galactic halo to the mid-plane of the galaxy. The zodiacal cloud in our solar system encounters a primordial planet once every 26 My (on our estimate) thus intercepting an average mass of 10³ tonnes of interplanetary dust on each occasion. If the dust included microbial material that originated on Earth and was scattered via impacts or cometary sublimation into the zodiacal cloud, this process offers a way by which evolved genes from Earth life could become dispersed through the galaxy.     

The chemical evolution of dwarf spheroidal galaxies: dissecting the inner regions and their stellar populations

Using three-dimensional hydrodynamical simulations of isolated dwarf spheroidal galaxies (dSphs), we undertake an analysis of the chemical properties of their inner regions, identifying the respective roles played by Type Ia supernovae (SNe Ia) and Type II supernovae (SNe II). The effect of inhomogeneous pollution from SNe Ia is shown to be prominent within two core radii, with the stars forming therein amounting to ∼20 per cent of the total. These stars are relatively iron-rich and α-element depleted compared to the stars forming in the rest of the galaxy. At odds with the projected stellar velocity dispersion radial profile, the actual three-dimensional one shows a depression in the central region, where the most metal-rich (i.e. [Fe/H]-rich) stars are partly segregated. This naturally results in two different stellar populations, with an anticorrelation between [Fe/H] and velocity dispersion, in the same sense as that observed in the Sculptor and Fornax dSphs. Because the most iron-rich stars in our model are also the most α depleted, a natural prediction and test of our model is that the same radial segregation effects should exist between [α/Fe] and velocity dispersion.     

Mosquitoes in the mix: How transferable is creative city thinking?

This paper contributes to recent debates about whether urban policy discourses are transferable and what is at stake in their translation. It draws on discussion of Darwin (Northwest Territory, Australia), a tropical savanna location that the local government wants to promote as a 'creative city', without quite knowing what this might require. We discuss relevant debates on research knowledge construction, the creative city and the path-dependent character of neoliberal governmental objectives. We then turn to the geographical, demographic and cultural characteristics that make Darwin a challenging and distinct context for translation of global theories of creative city rejuvenation. As well as arguing a case for more nuanced, locationally specific, analysis of the capacity of places to embrace travelling policy discourses, we suggest ways in which creative city research can be refreshed through engaging with literatures on (post)colonial urban politics and intersections with policy initiatives other than those targeted at 'creative industries' per se . We systematically outline the particular challenges that tropical cities in remote locations provide to accepted wisdom about creativity-led urban planning.     

Assessment of Density‐Induced Tracer Movement in Groundwater Velocity Measurements with Point Velocity Probes (PVPs)

The concept of equivalent freshwater head was adapted to predict the conditions under which density‐driven flow would adversely impact measured groundwater velocities using point velocity probes (PVPs). Theoretically, vertical flow will result from any density contrast between the PVP tracer and the groundwater. However, laboratory testing of tracers with salinities ranging from 0 to 2000 mg NaCl/L showed that horizontal velocities could be determined with good accuracy with up to 60% of the total flow being vertical due to density effects in a gravel medium. The available data suggest that density effects are less likely to be pronounced in sandy sediments. The relative amount of vertical flow due to tracer density can be estimated from vertical and horizontal velocities measured with PVPs, or from the ratio of vertical to horizontal hydraulic gradients. The equivalent freshwater gradient produced from a given tracer salinity at 10 °C (a typical groundwater temperature at moderate latitudes) can be estimated from 7.80 × 10^?7 × (M_NaCl), where M_NaCl is the mass of NaCl added, in mg, to 1 L of site groundwater in the mixing of the tracer. Equations for other temperatures were also determined.     

Shock-induced kelyphite formation in the core of a complex impact crater

We present a compositional and textural analysis of shock-induced microtextures in garnet porphyroblasts in migmatitic garnet–cordierite–biotite paragneisses from the centre of the Vredefort impact structure, South Africa. Detailed imaging and major element analysis of deformation features in, and adjacent to, the garnet porphyroblasts record a complex, heterogeneous distribution of shock effects at the microscale. As the most competent silicate mineral in the assemblage, with the highest Hugoniot Elastic Limit and a wide pressure–temperature stability field, the porphyroblastic garnet preserves a more diverse shock deformation response compared to minerals such as quartz and feldspar, which underwent more comprehensive shock metamorphism and subsequent annealing. The garnet porphyroblasts display pre-impact fractures that are overprinted by later intra-granular Hertzian and distinctive planar fractures associated with the impact event. Shock-induced strain localization occurred along internal slip planes and defects, including pre-existing fractures and inclusion boundaries in the garnet. Symplectitic (kelyphitic) coronas commonly enclose the garnet porphyroblasts, and inhabit intra-granular fractures. The kelyphite assemblage in fractures with open communication beyond garnet grain boundaries is characterized by orthopyroxene—cordierite—sapphirine. Conversely, the kelyphite assemblage in closed-off intra-granular fractures is highly variable, comprising spatially restricted combinations of a secondary garnet phase with a majoritic component, Al-rich orthopyroxene, sapphirine and cordierite. The impedance contrast between garnet porphyroblasts and their inclusions further facilitated the formation of shock-induced features (Al-rich orthopyroxene coronas). Together, the textural and mineralogical data suggest that these features provide a record of oscillatory shock perturbations initiated under confining pressure beneath the transient crater floor. This occurred as the shocked rock volume underwent post-shock expansion, forming the core of the central uplift, and was followed by variable textural re-equilibration. This study thus provides a microtextural and mineralogical perspective of the shock regime within confined crust immediately prior to and during central uplift formation.     

Subversive sites: rave culture, spatial politics and the internet in Sydney, Australia

Summary 'Rave' subcultures have emerged over the last ten years in Sydney, mobilizing spatial practices and dance styles that originated in Europe and North America. As these dance cultures diversify and fragment, the internet is increasingly being used as a means of organizing rave activities, publishing information about artists, DJs and record labels, and, in more radicalized fragments of the scene, is imbued with meaning—as a 'web' to support illegal appropriations of urban space for dance venues. Hakim Bey's 'Temporary Autonomous Zone', a left-anarchist spatial philosophy, underlies this rhetorical use of new computer technology, and is central to debates about youth subcultures, music and space, which I examine throughout this paper.     

A REFRACTORY GLASS CHONDRULE IN THE VIGARANO CHONDRITE

Vigarano, a type 3 carbonaceous chondrite, contains a chondrule composed of highly refractory Ca and Al rich glass with minor spinel. The chondrule formed from material similar to the Ca, Al, Ti-rich aggregates that are common in Vigarano and other type 3 chondrites and formation of these refractory aggregates must predate formation of some Vigarano chondrules. Experiments with synthetic analogues and a comparison with studies in the system CaO-MgO-Al₂O₃-SiO₂ indicate a temperature for formation of the chondrule at or above 1700 °C followed by very rapid cooling.     

On Cryer's problem with large displacements

The consolidation of a porous saturated sphere under an isotropic pressure, and free to drain on its surface, is examined. It is shown that a Mandel—Cryer effect develops irrespective of the magnitude of the strains which occur. Surprisingly, the effect is found to be virtually independent of strain. However, the progress of consolidation is substantially faster in the presence of large strains.