Protostellar disks and the primitive solar nebula

The objective is to obtain quantitative information on the turbulent transport of mass, angular momentum, and energy under the conditions that characterize the solar nebula, by direct numerical calculations. These calculations were made possible by research conducted on supercomputers (Cray XMP and Cray 2) by the Ames Computational Fluid Dynamics Branch. Techniques were developed that permitted the accurate representation of turbulent flows over the full range of important eddy sizes. So far, these techniques were applied (and verified) primarily in mundane laboratory situations, but they have a strong potential for astrophysical applications. A sequence of numerical experiments were conducted to evaluate the Reynold's stress tensor, turbulent heat transfer rate, turbulent dissipation rate, and turbulent kinetic energy spectrum, as functions of position, for conditions relevant to the solar nebula. Emphasis is placed on the variation of these properties with appropriate nondimensional quantities, so that relations can be derived that will be useful for disk modeling under a variety of hypotheses and initial conditions

Meteor ablation spheres from deep-sea sediments

Spheres from mid-Pacific abyssal clays (0 to 500,000 yrs old), formed from particles that completely melted and subsequently recrystallized as they separated from their meteoroid bodies, or containing relict grains of parent meteoroids that did not experience any melting were analyzed. The spheres were readily divided into three groups using their dominant mineralogy. The Fe-rich spheres were produced during ablation of Fe and metal-rich silicate meteoroids. The glassy spheres are considerably more Fe-rich than the silicate spheres. They consist of magnetite and an Fe glass which is relatively low in Si. Bulk compositions and relict grains are useful for determining the parent meteoroid types for the silicate spheres. Bulk analyses of recrystallized spheres show that nonvolatile elemental abundances are similar to chondrite abundances. Analysis of relict grains identified high temperature minerals associated with a fine-grained, low temperature, volatile-rich matrix. The obvious candidates for parent meteoroids of this type of silicate sphere is a carbonaceous chondrite

Apollo 15 rake sample microbreccias and non-mare rocks: Bulk rock, mineral and glass electron microprobe analyses

Quantitative electron microprobe data of Apollo 15 nonmare rake samples are presented. Bulk analyses of lithic fragments in the nomare rocks (expressed in oxide weight-percent) and the corresponding CIPW molecular norms are given. The mineralogy of the rocks and lithic fragments are also given; structural formulae for complete analyses and molecular end-members for all mineral analyses are included. The mineral analyses include pyroxene, olivine, plagioclase, barian K-feldspar, spinel and ilmenite, cobaltian metallic nickel-iron as well as SiO2-K2O-rich residual glass. Electron micropobe analyses (oxide weight percent) of glasses in loose fines and microbreccia samples and their CIPW molecular norms are presented along with electron microprobe data on bulk, mineral, and matrix glass from chondrules

Nature and preservation of Late Jurassic breakup-related volcanism in the carnarvon basin, North West shelf, Australia

Funding This work was funded through a postgraduate scholarship from the University of Adelaide, Faculty of Engineering Computer and Mathematical Sciences, and also by ASEG Research Foundation Grant no. RF19P01. These funding sources had no involvement in study design; in the collection, analysis and interpretation of data; in the writing of the report; or in the decision to submit the article for publication. Acknowledgements We would like to thank Iain Campbell, formerly Chief Petroleum Geophysicist at the South Australian Department for Energy and Mining for arranging the stitching together of multiple SEGY component files for the Indian 3D seismic reflection survey which was instrumental for interpretation of the Toro Volcanic Complex. We would also like to thank both Simon Lang and particularly Victorien Paumard of the Centre for Energy Geoscience, University of Western Australia, for numerous discussions around the development of the Barrow Delta in the Exmouth Sub-Basin and Exmouth Plateau. We thank Tiago Alves for editorial guidance, and the constructive reviews provided by Victorien Paumard, Natasha Stanton, Gerome Calves, Chris Elders, Kamaldeen Omosanya and one anonymous referee.Peer reviewe

A model for simulating the deposition of water-lain sediments in dryland environments

International audienceA numerical process-imitating model, the Discrete Storm Event Sedimentation Simulator (DSESS), has been developed to represent the climatic and hydraulic conditions of drylands in modelling their geomorphological development and sedimentary facies distributions. The ultimate aim is to provide insights into the lateral variability of permeability in the Triassic Sandstone aquifers of the UK for the study of solute movement. DSESS employs discrete storm-flood automata, released across a cellular landscape, to model sediment transport: erosion, migration and deposition. Sediment classes with different grain sizes can be modelled. Empirical process-based equations are used to quantify the movement of the automata, their erosion potential, sediment-carrying capacity and interaction with the underlying sediments. The approach emphasises the sequence of dryland storm events and associated floods rather than their timing. Flood events are assumed to be discrete in time. Preliminary tests carried out with DSESS using simple systems and idealised initial conditions produce lithological and land surface features characteristic of dryland settings and indicate the potential of the model for large-scale, long-time modelling of sedimentary facies development. Markedly different results are observed across the range of tests carried out in response to the non-linear interactions between the different elements of the landscape and the floodwaters simulated with DSESS. Simulations show that sediment accumulations develop concave upward radial profiles, plano-convex cross-profiles and possess a general lateral grading of sediment with distance from source. The internal grain size architecture shows evidence of both persistent and rapidly changing flow conditions, with both lateral and longitudinal stepping of coarse bodies produced by ?scour and fill' events and random avulsions. Armoured layers form so that near-surface sediments have increased likelihood of preservation. Future developments will include representation of aeolian deposition, mass wasting and hyper-concentrated (debris) flows. Keywords: avulsion, channel, deposition, drylands, erosion, gravel armouring, modelling, sheet-flood, transport capacit

Spatiotemporal complexity of the universe at subhorizon scales

This is a short note on the spatiotemporal complexity of the dynamical state(s) of the universe at subhorizon scales (up to 300 Mpc). There are reasons, based mainly on infrared radiative divergences, to believe that one can encounter a flicker noise in the time domain, while in the space domain, the scaling laws are reflected in the (multi)fractal distribution of galaxies and their clusters. There exist recent suggestions on a unifying treatment of these two aspects within the concept of spatiotemporal complexity of dynamical systems driven out of equilibrium. Spatiotemporal complexity of the subhorizon dynamical state(s) of the universe is a conceptually nice idea and may lead to progress in our understanding of the material structures at large scalesComment: references update

Magnetic permeability of stainless steel for use in accelerator beam transport systems

High-vacuum beam transport tubes are being designed for use in an accelerator under development at Los Alamos. In areas such as weld-heat-affected zones, the tubes will require localized magnetic permeability of less than 1.02. Seven austenitic stainless steel candidates, 304L, 310, 316L, 317LN, 20Cb-3, Nitronic 33, and Nitronic 40, have been evaluated to determine their permeability in cold-worked, annealed, and weld-affected zones. 310 and 20Cb-3 showed permeability after welding of less than 1.01. 1 ref., 1 fig., 1 tab

Ultra-strong Adhesion of Graphene Membranes

As mechanical structures enter the nanoscale regime, the influence of van der Waals forces increases. Graphene is attractive for nanomechanical systems because its Young's modulus and strength are both intrinsically high, but the mechanical behavior of graphene is also strongly influenced by the van der Waals force. For example, this force clamps graphene samples to substrates, and also holds together the individual graphene sheets in multilayer samples. Here we use a pressurized blister test to directly measure the adhesion energy of graphene sheets with a silicon oxide substrate. We find an adhesion energy of 0.45 \pm 0.02 J/m2 for monolayer graphene and 0.31 \pm 0.03 J/m2 for samples containing 2-5 graphene sheets. These values are larger than the adhesion energies measured in typical micromechanical structures and are comparable to solid/liquid adhesion energies. We attribute this to the extreme flexibility of graphene, which allows it to conform to the topography of even the smoothest substrates, thus making its interaction with the substrate more liquid-like than solid-like.Comment: to appear in Nature Nanotechnolog

Universal Dynamic Conductivity and Quantized Visible Opacity of Suspended Graphene

We show that the optical transparency of suspended graphene is defined by the fine structure constant, alpha, the parameter that describes coupling between light and relativistic electrons and is traditionally associated with quantum electrodynamics rather than condensed matter physics. Despite being only one atom thick, graphene is found to absorb a significant (pi times alpha=2.3%) fraction of incident white light, which is a consequence of graphene's unique electronic structure. This value translates into universal dynamic conductivity G =e^2/4h_bar within a few percent accuracy

Young people and political action: who is taking responsibility for positive social change?

A human rights perspective suggests that we are all responsible for ensuring the human rights of others, which in turn ensures that our own human rights are respected and protected. A convenience sample of 108 young people (41 males and 67 females) aged between 16 and 25 completed a questionnaire which asked about (a) levels of involvement in political activity and (b) sense of personal responsibility for ensuring that the human rights of marginalised groups (e.g. ethnic minorities, immigrants, lesbians and gay men) are protected. Findings showed that most respondents supported (in principle) the notion of human rights for all, but tended to engage in low key political activity (e.g. signing petitions; donating money or goods to charity) rather than actively working towards positive social change. Qualitative data collected in the questionnaire suggested three main barriers to respondents viewing themselves as agents of positive social change: (1) "It’s not my problem", (2) "It’s not my responsibility", and (3) a sense of helplessness. Suggestions for how political action might best be mobilised among young people are also discussed.</p