Radio Continuum Sources Associated with AB Aur

We present high angular resolution, high-sensitivity Very Large Array observations at 3.6 cm of the Herbig Ae star AB Aur. This star is of interest since its circumstellar disk exhibits characteristics that have been attributed to the presence of an undetected low mass companion or giant gas planet. Our image confirms the continuum emission known to exist in association with the star, and detects a faint protuberance that extends about $0\rlap.{''}3$ to its SE. Previous theoretical considerations and observational results are consistent with the presence of a companion to AB Aur with the separation and position angle derived from our radio data. We also determine the proper motion of AB Aur by comparing our new observations with data taken about 17 years ago and find values consistent with those found by Hipparcos.Comment: 6 pages, 1 figur

Competition between supersolid phases and magnetisation plateaux in the frustrated easy-axis antiferromagnet on a triangular lattice

The majority of magnetic materials possess some degree of magnetic anisotropy, either at the level of a single ion, or in the exchange interactions between different magnetic ions. Where these exchange interactions are also frustrated, the competition between them and anisotropy can stabilize a wide variety of new phases in applied magnetic field. Motivated by the hexagonal delafossite 2H-AgNiO 2, we study the Heisenberg antiferromagnet on a layered triangular lattice with competing first- and second-neighbour interactions and single-ion easy-axis anisotropy. Using a combination of classical Monte Carlo simulation, mean-field analysis, and Landau theory, we establish the magnetic phase diagram of this model as a function of temperature and magnetic field for a fixed ratio of exchange interactions, but with values of easy-axis anisotropy D extending from the Heisenberg (D =0) to the Ising (D=&#8734) limits. We uncover a rich variety of different magnetic phases. These include several phases which are magnetic supersolids (in the sense of Matsuda and Tstuneto or Liu and Fisher), one of which may already have been observed in AgNiO 2. We explore how this particular supersolid arises through the closing of a gap in the spin-wave spectrum, and how it competes with rival collinear phases as the easy-axis anisotropy is increased. The finite temperature properties of this phase are found to be different from those of any previously studied magnetic supersolid.Comment: 25 pages; 29 figures; minor revisions; accepted for publication in Phys. Rev.

Single Mothers and Poverty in Costa Rica

Despite increasing average real family incomes in Costa Rica in the late 1990s and early 2000s, poverty rates did not fall. In this paper, we argue that during this period economic growth in Costa Rica did not translate into reduced poverty because of changes in family structure and in the labor market, and that these changes had an important gender dimension. Specifically, an increase in the proportion of Costa Rican households headed by single mothers led to an increase in the number of women with children entering the labor force. Many of these mothers, new entrants to the labor force, were unable or unwilling to find full-time work in the high-paying formal sector, and ended up unemployed or working part-time as self-employed workers. These labor market phenomena, in turn, contributed to low incomes for households vulnerable to poverty, especially those households headed by single mothers.wages, Central America, poverty, employment, single mothers, Costa Rica

On the inconsistency of the Malmquist-Luenberger index

Apart from the well-known weaknesses of the standard Malmquist productivity index related to infeasibility and not accounting for slacks, already addressed in the literature, we identify a new and significant drawback of the Malmquist-Luenberger index decomposition that questions its validity as an empirical tool for environmental productivity measurement associated with the production of bad outputs. In particular, we show that the usual interpretation of the technical change component in terms of production frontier shifts can be inconsistent with its numerical value, thereby resulting in an erroneous interpretation of this component that passes on to the index itself. We illustrate this issue with a simple numerical example. Finally, we propose a solution for this inconsistency issue based on incorporating a new postulate for the technology related to the production of bad output