ASTEC -- the Aarhus STellar Evolution Code

The Aarhus code is the result of a long development, starting in 1974, and still ongoing. A novel feature is the integration of the computation of adiabatic oscillations for specified models as part of the code. It offers substantial flexibility in terms of microphysics and has been carefully tested for the computation of solar models. However, considerable development is still required in the treatment of nuclear reactions, diffusion and convective mixing.Comment: Astrophys. Space Sci, in the pres

Precambrian non-marine stromatolites in alluvial fan deposits, the Copper Harbor Conglomerate, upper Michigan

Laminated cryptalgal carbonates occur in the Precambrian Copper Harbor Conglomerate of northern Michigan, which was deposited in the Keweenawan Trough, an aborted proto-oceanic rift. This unit is composed of three major facies deposited by braided streams on a large alluvial-fan complex. Coarse clastics were deposited in braided channels, predominantly as longitudinal bars, whereas cross-bedded sandstones were deposited by migrating dunes or linguoid bars. Fine-grained overbank deposits accumulated in abandoned channels. Gypsum moulds and carbonate-filled cracks suggest an arid climate during deposition. Stromatolites interstratified with these clastic facies occur as laterally linked drapes over cobbles, as laterally linked contorted beds in mudstone, as oncolites, and as poorly developed mats in coarse sandstones. Stromatolites also are interbedded with oolitic beds and intraclastic conglomerates. Stromatolitic microstructure consists of alternating detrital and carbonate laminae, and open-space structures. Radial-fibrous calcite fans are superimposed on the laminae. The laminae are interpreted as algal in origin, whereas the origin of the radial fibrous calcite is problematic. The stromatolites are inferred to have grown in lakes which occupied abandoned channels on the fan surface. Standing water on a permeable alluvial fan in an arid climate requires a high water table maintained by high precipitation, or local elevation of the water table, possibly due to the close proximity of a lake. Occurrence of stromatolites in the upper part of the Copper Harbor Conglomerate near the base of the lacustrine Nonesuch Shale suggests that these depositional sites may have been near the Nonesuch Lake.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72022/1/j.1365-3091.1983.tb00713.x.pd

Revealing microscale bulk structures in polymer–carbon nanocomposites using spin-echo SANS

We have used spin-echo small-angle neutron scattering (SESANS) to probe the hierarchy of structures present in polymer–carbon nanocomposites, with length scales spanning over three orders of magnitude, from 10 nm to 16 μm. The data processing and reduction show a unified approach across two SESANS instruments (TU Delft and Larmor at the ISIS neutron source) and yield consistent data that are able to be modelled using well-established hierarchical models in freely available software such as SasView. Using this approach, we are able to extend the measured length scales by over an order of magnitude compared to traditional scattering methods. This yields information about the structure in the bulk that is inaccessible with conventional scattering techniques (SANS/SAXS) and points to a way for interrogating and investigating polymer nanocomposites routinely across multiple length scales

A line-balancing strategy for designing flexible assembly systems

We present a rough-cut analysis tool that quickly determines a few potential cost-effective designs at the initial design stage of flexible assembly systems (FASs) prior to a detailed analysis such as simulation. It uses quantitative methods for selecting and configuring the components of an FAS suitable for medium to high volumes of several similar products. The system is organized as a series of assembly stations linked with an automated material-handling system moving parts in a unidirectional flow. Each station consists of a single machine or of identical parallel machines. The methods exploit the ability of flexible hardware to switch almost instantaneously from product to product. Our approach is particularly suitable where the product mix is expected to be stable, since we combine the hardware-configuration phase with the task-allocation phase.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/45513/1/10696_2004_Article_BF00167513.pd

Fluid dynamic induced break-up during volcanic eruptions

Determining whether magma fragments during eruption remains a seminal challenge in volcanology. There is a robust paradigm for fragmentation of high viscosity, silicic magmas, however little is known about the fragmentation behaviour of lower viscosity systems—the most abundant form of volcanism on Earth and on other planetary bodies and satellites. Here we provide a quantitative model, based on experiments, for the non-brittle, fluid dynamic induced fragmentation of low viscosity melts. We define the conditions under which extensional thinning or liquid break-up can be expected. We show that break-up, both in our experiments and natural eruptions, occurs by both viscous and capillary instabilities operating on contrasting timescales. These timescales are used to produce a universal break-up criterion valid for low viscosity melts such as basalt, kimberlite and carbonatite. Lastly, we relate these break-up instabilities to changes in eruptive behaviour, the associated natural hazard and ultimately the deposits formed

A facile route for rubber breakdown via cross metathesis reactions

A new approach towards reprocessing cross-linked rubbery materials by catalytic disassembly of polymer chains, which eliminates the need for energy intensive mechanical processes, is demonstrated. First and second generation (G1 and G2) Grubbs’ ruthenium catalysts break down polybutadiene (PBd) networks at their double bonds via cross-metathesis (CM) reactions to produce readily soluble molecules. A dramatic reduction in molecular weight to around 2000 g mol−1 was observed by size exclusion chromatography and the breakdown of cross-linked networks was confirmed by rheometry. This process was repeated with a styrene-butadiene rubber sheet, a common component of vehicle tyres, with a G2 catalyst and a diester to accelerate the breakdown. A sufficient amount of G2 catalyst and a diester were found to diffuse into the styrene-butadiene rubber sheet, to catalyse its breakdown into rubber crumb. This reaction can be achieved at room temperature within 2.5 h. Increasing the reaction time and temperature increased the extent of the breakdown and under these conditions some breakdown of rubber occurred with the addition of only the G2 catalyst, without the need for a diester. We speculate that, when present, pendant ethylene groups in the PBd chain structure can participate in CM reactions, enabling break-down of the cross-linked network into individual molecules with lasso-like structures

Association and Relaxation of Supra-Macromolecular Polymers

This paper describes the structures created by assembling functionalised entangled polymers and the effect these have on the rheology of the material. A polybutadiene (PBd) linear polymer precursor of sufficient molecular weight to be entangled is used. This is end functionalised with the self-associating group 2-ureido-4pyrimidinone (UPy). Interestingly, despite the relatively high molecular weight of the precursor diluting the UPy concentration, the effect on the material’s properties is significant. To characterise the assembled microstructure we present linear rheology, extensional non-linear rheology and small angle X-ray scattering (SAXS). The linear rheology shows that the functionalised PBd assembles into large macro-structures where the terminal relaxation time is up to seven orders of magnitude larger than the precursor. The non-linear rheology shows strain-hardening over a broad range of strain-rates. We then show by both SAXS and modelling of the extensional data that there must exist clusters of UPy associations and hence assembled polymers with branched architecture. By modelling the supra-molecular structure as an effective linear polymer, we show that this would be insufficient in predicting the strain-hardening behaviour at lower extension-rates. Therefore, in this flow regime the strain-hardening is likely to be caused by branching. This is backed up by SAXS measurements which show that UPy clusters larger than pair-pair groups exist

Distortion of Chain Conformation and Reduced Entanglement in Polymer–Graphene Oxide Nanocomposites

We study the conformations of polymer chains in polymer–graphene oxide nanocomposites. We show that the chains have a reduced radius of gyration that is consistent with confinement at a solid interface in the melt, as is expected for well-dispersed, high aspect ratio nanoparticles that are much larger than the polymer coil size. We show that confinement of the polymer chains causes a corresponding reduction in interchain entanglements, and we calculate a contribution to the plateau modulus from the distorted polymer network via a simple scaling argument. Our results are a significant step forward in understanding how two-dimensional nanoparticles affect global material properties at low loadings

Women's physical and psychological condition independently predict their preference for apparent health in faces

Physical condition (e.g., health, fertility) influences female mate preferences in many species, with females in good condition preferring "higher quality" (e.g., healthier) mates. In humans, condition may comprise both physical (e.g., health and fertility) and psychological factors (e.g., stress, anxiety, and depression). We found that women with low waist-to-hip ratios (indicating health and fertility) or who scored low on anxiety, depression, and stress measures expressed greater attraction to composite male (but not female) faces with color and texture cues associated with apparent health than did women with relatively high waist-to-hip ratios or who scored relatively high on the anxiety, depression, and stress measures. These effects of physical and psychological condition were independent and were not mediated by women's perceptions of their own attractiveness. Our findings indicate that women's physical and psychological conditions both contribute to individual differences in face preferences