Can giant planets form by gravitational fragmentation of discs?

Gravitational fragmentation has been proposed as a mechanism for the formation of giant planets in close orbits around solar-type stars. However, it is debatable whether this mechanism can function in the inner regions (R<40 AU) of real discs. We use a newly developed method for treating the energy equation and the equation of state, which accounts for radiative transfer effects in SPH simulations of circumstellar discs. The different chemical and internal states of hydrogen and the properties of dust at different densities and temperatures (ice coated dust grains at low temperatures, ice melting, dust sublimation) are all taken into account by the new method.We present radiative hydrodynamic simulations of the inner regions of massive circumstellar discs and examine two cases: (i) a disc irradiated by a cool background radiation field (T_bgr=10K)and (ii) a disc heated by radiation from its central star (T_bgr~1/R). In neither case does the disc fragment: in the former because it cannot cool fast enough and in the latter because it is not gravitationally unstable. Our results (a) corroborate previous numerical results using different treatments for the hydrodynamics and the radiative transfer, and (b) confirm our own earlier analytic predictions. We conclude that disc fragmentation is unlikely to be able to produce giant planets around solar-type stars at radii <40 AU.Comment: Accepted by A&A, 10 pages, high-resolution available at http://www.astro.cf.ac.uk/pub/Dimitrios.Stamatellos/publications

The Rise of the Small Investor in the US and the UK, 1895 to 1970

The role of the small shareholder has been largely ignored in the literature, which has tended to concentrate on controlling shareholders and family ownership. And yet, focus on the importance of small shareholders can capture significant aspects of financial development, since the more 'confident' the minority shareholders, the easier will capital flow to firms. Pre 1970, debates and policy conflicts linked to stock exchange development concentrated on shareholder democracy and diffusion as key indicators. The number of shareholders relative to the population was seen as a critical factor in explaining not only structures in corporate finance but also political and economic preferences, market developments and overall economic development. This paper explores the so-called democratisation of investment and the factors behind it through the lens of trends in estimates of the UK and US shareholding populations between 1895 and 1970. It covers three key periods: before World War I, before and after the stock market crash of 1929, and post-World War II. It identifies three periods in the US when shareholder numbers were paramount: in the boom years of the 1920s, as part of the inquest into the 1929 Crash, and post-World War II in an attempt to boost stock market activity. In the UK, although some concern was expressed during the 1920s and 1930s at the passive nature of small investors, who held diversified portfolios with small amounts in each holding, it was the fear of nationalisation after World War II which led to more in-depth shareholder estimates

Rebalancing the Euro Area: The Costs of Internal Devaluation

This paper investigates the economic costs of rebalancing current account positions in the Euro area by means of internal devaluation. Internal devaluation relies on wage suppression the deficit countries. Based on an old Keynesian model we estimate a current account equation, a wage-Phillips curve and an Okun’s Law equation. All estimations are carried out for a panel of twelve Euro area members. From the estimation results we calculate the output costs of reducing current account deficits. Greece, Ireland, Italy, Portugal and Spain (GIIPS) had, on average, current account deficits of 8.4% of GDP in 2007. To eliminate these current account deficits, a reduction of GPD by some 47% would be necessary. In principle there are two ways that trade imbalances could be resolved: deflationary adjustment in the deficit countries or inflationary adjustment in the surplus countries. Presently, the burden of adjustment is exclusively on the deficit countries. Our results indicate that the economic costs of this adjustment to those countries are equivalent to the output loss of the Great Depression. An adjustment of the surplus countries would increase growth and it would come with higher inflation, but it would allow rebalancing without a Great Depression in parts of Europe

The formation of brown dwarfs and low-mass stars by disc fragmentation

We suggest that a high proportion of brown dwarfs are formed by gravitational fragmentation of massive, extended discs around Sun-like stars. We argue that such discs should arise frequently, but should be observed infrequently, precisely because they fragment rapidly. By performing an ensemble of radiation-hydrodynamic simulations, we show that such discs typically fragment within a few thousand years to produce mainly brown dwarfs (including planetary-mass brown dwarfs) and low-mass hydrogen-burning stars. Subsequently most of the brown dwarfs are ejected by mutual interactions. We analyse the properties of these objects that form by disc fragmentation, and compare them with observations.Comment: 4 pages, 2 figures, to appear in the proceedings of the Cool Stars 15 conferenc

Validation of a magneto- and ferro-hydrodynamic model for non-isothermal flows in conjunction with Newtonian and non-Newtonian fluids

This work focuses on the validation of a magnetohydrodynamic (MHD) and ferrohydrodynamic (FHD) model for non-isothermal flows in conjunction with Newtonian and non- Newtonian fluids. The importance of this research field is to gain insight into the interaction of non-linear viscous behaviour of blood flow in the presence of MHD and FHD effects, because its biomedical application such as magneto resonance imaging (MRI) is in the centre of research interest. For incompressible flows coupled with MHD and FHD models, the Lorentz force and a Joule heating term appear due to the MHD effects and the magnetization and magnetocaloric terms appear due to the FHD effects in the non-linear momentum and temperature equations, respectively. Tzirtzilakis and Loukopoulos [1] investigated the effects of MHD and FHD for incompressible non-isothermal flows in conjunction with Newtonian fluids in a small rectangular channel. Their model excluded the non-linear viscous behaviour of blood flows considering blood as a Newtonian biofluid. Tzirakis et al. [2, 3] modelled the effects of MHD and FHD for incompressible isothermal flows in a circular duct and through a stenosis in conjunction with both Newtonian and non-Newtonian fluids, although their approach neglects the non-isothermal magnetocaloric FHD effects. Due to the fact that there is a lack of experimental data available for non-isothermal and non-Newtonian blood flows in the presence of MHD and FHD effects, therefore the objective of this study is to establish adequate validation test cases in order to assess the reliability of the implemented non-isothermal and non-Newtonian MHD-FHD models. The non-isothermal Hartmann flow has been chosen as a benchmark physical problem to study velocity and temperature distributions for Newtonian fluids and non-Newtonian blood flows in a planar microfluidic channel. In addition to this, the numerical behaviour of an incompressible and non-isothermal non-Newtonian blood flow has been investigated from computational aspects when a dipole-like rotational magnetic field generated by infinite conducting wires. The numerical results are compared to available computational data taken from literature