On anisotropy function in crystal growth simulations using Lattice Boltzmann equation

In this paper, we present the ability of the Lattice Boltzmann (LB) equation, usually applied to simulate fluid flows, to simulate various shapes of crystals. Crystal growth is modeled with a phase-field model for a pure substance, numerically solved with a LB method in 2D and 3D. This study focuses on the anisotropy function that is responsible for the anisotropic surface tension between the solid phase and the liquid phase. The anisotropy function involves the unit normal vectors of the interface, defined by gradients of phase-field. Those gradients have to be consistent with the underlying lattice of the LB method in order to avoid unwanted effects of numerical anisotropy. Isotropy of the solution is obtained when the directional derivatives method, specific for each lattice, is applied for computing the gradient terms. With the central finite differences method, the phase-field does not match with its rotation and the solution is not any more isotropic. Next, the method is applied to simulate simultaneous growth of several crystals, each of them being defined by its own anisotropy function. Finally, various shapes of 3D crystals are simulated with standard and non standard anisotropy functions which favor growth in -, - and -directions

PDP4XL2: Personal Development Planning for Cross-Institutional Lifelong Learning. Final Report.

This collaborative project PDP4XL2 built on the strengths and successful outcomes of PDP4Life and took as its principal focus the use of personal development planning and e-portfolios to develop and sustain favourable learner attitudes towards lifelong learning and to understand the role that technology plays in supporting that process. Project objectives included identifying student and employer attitudes to and usage of PDP and e-portfolios in the creative industries and health cares. This final report documents the outcomes of the project

THE DETERMINANTS OF HAPPINESS AMONG RACE GROUPS IN SOUTH AFRICA

This paper tests for happiness differences among race groups in South Africa and also investigates the determinants of happiness for each race group. Using data from the 2008 National Income Dynamics Survey, the results indicate that reported happiness differs substantially among race groups, with Blacks being the least happy. The determinants of happiness also differ between race groups. While Whites attached greater importance to physical health, employment status and absolute income matter greatly for Blacks. For Coloureds and Blacks, relative income is an important determinant of happiness, with religious importance significantly contributing to the happiness of Indians/Asians.Happiness, race, determinants, South Africa, Health Economics and Policy, Institutional and Behavioral Economics, Public Economics, I31, D60,

Procreate and cherish: A note on Australia’s abrupt shift to Pro-Natalism

After a long history of arguing that Australian governments do not intervene in the bedrooms of the nation, in 2004 the Howard Government did exactly that. Under the enthusiastic choreographing of then Treasurer Peter Costello, it implemented an explicit and indirect fertility policy in the form of a maternity payment, commonly known as the ‘Baby Bonus’. Rising fertility in Australia since that time has been widely claimed as evidence of the policy’s success. Hailed as a mini ‘baby boom’, Costello was moved to describe the policy as a shift from ‘population or perish’ to ‘procreate and cherish’. Despite arguing against it while in Opposition, the policy has been continued with only a few changes by the incumbent Rudd Government, seemingly on the grounds that it may indeed be responsible for the recent ‘nudging up’ of birth rates. This paper traces the policy shift and concludes with a brief analysis of Australian trends across the period of the Baby Bonus (2004-2008), showing that one quarter of the increase in numbers is due to cohort size, but noting that fertility has also risen in many developed countries across the same period and thus trends in Australia may just be part of a broader trend – and/or in part an artifact of the index used to measure fertility. It also draws attention to the collateral effect of an increased dependency ratio, with the mini ‘boom’ reaching school age at the very moment the post war baby boomers reach retirement age – as forewarned by Costello in 2002 when initially rejecting the idea of a Baby Bonus

What can Gaia proper motions tell us about Milky Way dwarf galaxies?

We present a proper-motion study on models of the dwarf spheroidal galaxy Sculptor, based on the predicted proper-motion accuracy of Gaia measurements. Gaia will measure proper motions of several hundreds of stars for a Sculptor-like system. Even with an uncertainty on the proper motion of order 1.5 times the size of an individual proper-motion value of ~10 mas/century, we find that it is possible to recover Sculptor's systemic proper motion at its distance of 79 kpc.Comment: 5 pages, 1 figure; to appear in the proceedings of the GREAT-ITN conference on "The Milky Way Unravelled by Gaia", Barcelona (Dec 1-5 2014

A new fitting-function to describe the time evolution of a galaxy's gravitational potential

We present a new simple functional form to model the evolution of a spherical mass distribution in a cosmological context. Two parameters control the growth of the system and this is modelled using a redshift dependent exponential for the scale mass and scale radius. In this new model, systems form inside out and the mass of a given shell can be made to never decrease, as generally expected. This feature makes it more suitable for studying the smooth growth of galactic potentials or cosmological halos than other parametrizations often used in the literature. This is further confirmed through a comparison to the growth of dark matter halos in the Aquarius simulations.Comment: 5 pages, 4 figures; example figures replaced by their correct versions. Accepted for publication in A&

The time evolution of gaps in tidal streams

We model the time evolution of gaps in tidal streams caused by the impact of a dark matter subhalo, while both orbit a spherical gravitational potential. To this end, we make use of the simple behaviour of orbits in action-angle space. A gap effectively results from the divergence of two nearby orbits whose initial phase-space separation is, for very cold thin streams, largely given by the impulse induced by the subhalo. We find that in a spherical potential the size of a gap increases linearly with time for sufficiently long timescales. We have derived an analytic expression that shows how the growth rate depends on the mass of the perturbing subhalo, its scale and its relative velocity with respect to the stream. We have verified these scalings using N-body simulations and find excellent agreement. For example, a subhalo of mass 10^8 Msun directly impacting a very cold thin stream on an inclined orbit can induce a gap that may reach a size of several tens of kpc after a few Gyr. The gap size fluctuates importantly with phase on the orbit, and it is largest close to pericentre. This indicates that it may not be fully straightforward to invert the spectrum of gaps present in a stream to recover the mass spectrum of the subhalos.Comment: 4 pages, 4 figures, ApJ Letters in pres