Some effects of small-scale metallicity variations in cooling flows

In an attempt to reconcile recent spectral data with predictions of the standard cooling flow model, it has been suggested that the metals in the intracluster medium (ICM) might be distributed inhomogeneously on small scales. We investigate the possible consequences of such a situation within the framework of the cooling flow scenario. Using the standard isobaric cooling flow model, we study the ability of such metallicity variations to preferentially suppress low-temperature line emission in cooling flow spectra. We then use simple numerical simulations to investigate the temporal and spatial evolution of the ICM when the metals are distributed in such a fashion. Simulated observations are used to study the constraints real data can place on conditions in the ICM. The difficulty of ruling out abundance variations on small spatial scales with current observational limits is emphasized. We find that a bimodal distribution of metals may give rise to interesting effects in the observed abundance profile, in that apparent abundance gradients with central abundance drops and off-centre peaks, similar to those seen recently in some clusters, are produced. Different elements behave in different fashion as governed by the temperature dependence of their equivalent widths. Our overall conclusion is that, whilst this process alone seems unlikely to be able to account for the sharp reduction in low temperature emission lines seen in current spectral data, a contribution at some level is possible and difficult to rule out. The possibility of small-scale metallicity variations should be considered when analysing high resolution cluster X-ray spectra.Comment: 14 pages, 10 figures. Accepted for publication in MNRA

High-Temperature Processing of Solids Through Solar Nebular Bow Shocks: 3D Radiation Hydrodynamics Simulations with Particles

A fundamental, unsolved problem in Solar System formation is explaining the melting and crystallization of chondrules found in chondritic meteorites. Theoretical models of chondrule melting in nebular shocks has been shown to be consistent with many aspects of thermal histories inferred for chondrules from laboratory experiments; but, the mechanism driving these shocks is unknown. Planetesimals and planetary embryos on eccentric orbits can produce bow shocks as they move supersonically through the disk gas, and are one possible source of chondrule-melting shocks. We investigate chondrule formation in bow shocks around planetoids through 3D radiation hydrodynamics simulations. A new radiation transport algorithm that combines elements of flux-limited diffusion and Monte Carlo methods is used to capture the complexity of radiative transport around bow shocks. An equation of state that includes the rotational, vibrational, and dissociation modes of H$_2$ is also used. Solids are followed directly in the simulations and their thermal histories are recorded. Adiabatic expansion creates rapid cooling of the gas, and tail shocks behind the embryo can cause secondary heating events. Radiative transport is efficient, and bow shocks around planetoids can have luminosities $\sim$few$\times10^{-8}$ L$_{\odot}$. While barred and radial chondrule textures could be produced in the radiative shocks explored here, porphyritic chondrules may only be possible in the adiabatic limit. We present a series of predicted cooling curves that merit investigation in laboratory experiments to determine whether the solids produced by bow shocks are represented in the meteoritic record by chondrules or other solids.Comment: Accepted for publication in ApJ. Images have been resized to conform to arXiv limits, but are all readable upon adjusting the zoom. Changes from v1: Corrected typos discovered in proofs. Most changes are in the appendi

Implicit Large-Eddy Simulations of Hot and Cold Supersonic Jets in Loci-CHEM

This paper introduces a 4th-order accurate low-dissipation flux scheme for use on un- structured CFD codes, and compares this flux scheme with two others for LES calculations of hot and cold supersonic jets. The flux schemes are compared with experimental profiles of jet centerline Mach number, total temperature and total pressure, with jet spreading rate data, and with near- field acoustic measurements. The influence of grid resolution on these solution accuracy is also evaluated. The new low-dissipation flux scheme is shown to be stable on a high-speed compressible turbulent ow problem, and to be significantly more accurate than the existing baseline flux approach

Economic Evaluation of Breeding Objectives for Beef Cattle

Defining breeding objectives for beef cattle is a difficult task, especially for cattle under extensive grazing, as described by the authors in this Session. In considering economic aspects, Wilton points out the poor feedback among different sectors of the industry (such as among cow-calf producers, store cattle farmers and finishing operators; also between commercial and pedigree herds). Farmers with different breeds contributing to crossbred cattle also appear to receive poor market signals