Feeding Dairy Cattle

PDF pages: 4

Milking Sane Safe Sanitary

PDF pages: 1

Coronae & Outflows from Helical Dynamos, Compatibility with the MRI, and Application to Protostellar Disks

Magnetically mediated disk outflows are a leading paradigm to explain winds and jets in a variety of astrophysical sources, but where do the fields come from? Since accretion of mean magnetic flux may be disfavored in a thin turbulent disk, and only fields generated with sufficiently large scale can escape before being shredded by turbulence, in situ field production is desirable. Nonlinear helical inverse dynamo theory can provide the desired fields for coronae and outflows. We discuss the implications for contemporary protostellar disks, where the MRI (magneto-rotational instability) can drive turbulence in the inner regions, and primordial protostellar disks, where gravitational instability drives the turbulence. We emphasize that helical dynamos are compatible with the magneto-rotational instability, and clarify the relationship between the two.Comment: 12 pages, LaTeX (with figs); version in press for "Proceedings of the International Workshop on Magnetic Fields and Star Formation: Theory vs. Observation" Madrid, Spain; April 200

Star-forming accretion flows and the low luminosity nuclei of giant elliptical galaxies

The luminosities of the centers of nearby elliptical galaxies are very low compared to models of thin disc accretion to their black holes at the Bondi rate, typically a few hundredths to a few tenths of a solar mass per year. This has motivated models of inefficiently-radiated accretion that invoke weak electron-ion thermal coupling, and/or inhibited accretion rates due to convection or outflows. Here we point out that even if such processes are operating, a significant fraction of the accreting gas is prevented from reaching the central black hole because it condenses into stars in a gravitationally unstable disc. Star formation occurs inside the Bondi radius (typically ~100pc in giant ellipticals), but still relatively far from the black hole in terms of Schwarzschild radii. Star formation depletes and heats the gas disc, eventually leading to a marginally stable, but much reduced, accretion flow to the black hole. We predict the presence of cold (~100K), dusty gas discs, containing clustered H-alpha emission and occasional type II supernovae, both resulting from the presence of massive stars. Star formation accounts for several features of the M87 system: a thin disc, traced by H-alpha emission, is observed on scales of about 100pc, with features reminiscent of spiral arms and dust lanes; the star formation rate inferred from the intensity of H-alpha emission is consistent with the Bondi accretion rate of the system. Star formation may therefore help suppress accretion onto the central engines of massive ellipticals. We also discuss some implications for the fueling of the Galactic center and quasars.Comment: 13 pages, accepted to MNRA

Pedagogies of academic writing in teacher education: from epistemology to practice and back again

This paper discusses barriers to the development of academic writing, in the area of teacher education in UK higher education . We first situate these issues in a higher education context increasingly defined by new technologies and diverse cohorts of higher education students. Drawing on empirical data obtained from interviews with both students and teachers (N=21), we then critically examine a range of perspectives on the definition, role and function of academic literacy in this contemporary context. Findings include useful insights into the development of writing skills and teacher identity, but they also reveal fundamental differences in the epistemological presuppositions of those teaching academic writing. These accounts are reflected in significant differences in pedagogy, and raise important questions for practice which, although potentially irresolvable, may help to explain some of the difficulties which emerge when trying to teach academic writing. Such fundamental issues, we argue, need to be at least recognized if teachers hope to develop the writing capacity of trainee teachers in an academic context. 3rd International Conference on Higher Education Advances, HEAd'17. Universitat Politecnica de Valencia, Valencia

ESTIMATES OF DEMAND RELATIONSHIPS FOR APRICOTS AND APRICOT PRODUCTS

Apricots are a unique commodity in that they are used in four ways: for fresh markets and for canning, freezing, and drying. This article formulates a model of the demand system for this commodity and presents FIML and 2SLS estimates of the simultaneous components of the system. The empirical findings include estimates of price flexibilities and elasticities and equations that predict prices and allocations among product forms, given the annual production.Demand and Price Analysis,

Do We Need "Ionosorbed" Oxygen Species? (Or, "A Surface Conductivity Model of Gas Sensitivity in Metal Oxides Based on Variable Surface Oxygen Vacancy Concentration")

The author provides an opinion on direct experimental evidence available to support the "ionosorption theory" often employed to interpret "electrophysical" measurements made during a gas sensing experiment. This article then aims to provide an alternative framework of a "surface conductivity" model based on recent advances in theoretical and experimental investigations in solid state physics, and to use this framework as a guide toward design rules for future improvement of gas sensor performance

Two-temperature coronae in active galactic nuclei

We show that coronal magnetic dissipation in thin active sheets that sandwich standard thin accretion disks in active galactic nuclei may account for canonical electron temperatures of a few $\times 10^9$K if protons acquire most of the dissipated energy. Coulomb collisions transfer energy from the ions to the electrons, which subsequently cool rapidly by inverse-Compton scattering. In equilibrium, the proton energy density likely exceeds that of the magnetic field and both well exceed the electron and photon energy densities. The Coulomb energy transfer from protons to electrons is slow enough to maintain a high proton temperature, but fast enough to explain observed rapid X-ray variabilities in Seyferts. The $\sim 10^9$K electron temperature is insensitive to the proton temperature when the latter is $\ge 10^{12}$K.Comment: 5 pages LaTex, and 2 .ps figures, submitted to MNRAS, 4/9

Skull Flexure from Blast Waves: A Mechanism for Brain Injury with Implications for Helmet Design

Traumatic brain injury [TBI] has become a signature injury of current military conflicts, with debilitating, costly, and long-lasting effects. Although mechanisms by which head impacts cause TBI have been well-researched, the mechanisms by which blasts cause TBI are not understood. From numerical hydrodynamic simulations, we have discovered that non-lethal blasts can induce sufficient skull flexure to generate potentially damaging loads in the brain, even without a head impact. The possibility that this mechanism may contribute to TBI has implications for injury diagnosis and armor design.Comment: version in press, Physical Review Letters; 17 pages, 5 figures (includes supplementary material