Charles A.,Saint Marys University, Halifax
Current Opinion in Environmental Sustainability | Year: 2012
This article explores several key ingredients for successful and sustainable interactions of people and oceans, based on an integrative social-ecological systems perspective. Several key themes are examined: governance and decision-making, livelihoods and well-being, and the modern challenge of adaptation to current and future climate change. Each of these applies at various scales, from the local to the global. While much attention in the literature lies on global and large-scale systems, the smaller scale is deserving of at least as much attention; this point is illustrated by a local-level example. Indeed, cross-scale linkages that connect scales of impacts and levels of decision-making are key elements in improving the governance of marine systems. © 2012 Elsevier B.V.
Sawicki M.,Saint Marys University, Halifax
Publications of the Astronomical Society of the Pacific | Year: 2012
This article describes SEDfit, the earliest-but continually upgraded-software package for spectral energy distribution fitting (SED fitting) of high-redshift photometric data, and the only one to properly treat nondetections. The principles of maximum-likelihood SED fitting are described, including formulae used for fitting both detected and undetected (upper limits) photometric data. The internal mechanics of the SEDfit package are presented and several illustrative examples of its use are given. The article concludes with a discussion of several issues and caveats applicable to SED fitting in general. © 2012. The Astronomical Society of the Pacific. All rights reserved.
Deupree R.G.,Saint Marys University, Halifax
Astrophysical Journal | Year: 2011
Zero-age main-sequence models of uniformly rotating stars have been computed for 10 masses between 1.625 and 8 M and for 21 rotation rates from zero to nearly critical rotation. The surface shape is used to distinguish rotation rather than the surface equatorial velocity or the rotation rate. Using the surface shape is close, but not quite equivalent, to using the ratio of the rotation rate to the critical rotation rate. Using constant shape as the rotation variable means that it and the mass are separable, something that is not true for either the rotation rate or surface equatorial velocity. Thus, a number of properties, including the ratio of the effective temperature anywhere on the surface to the equatorial temperature, are nearly independent of the mass of the model, as long as the rotation rate changes in such a way as to keep the surface shape constant. © 2011. The American Astronomical Society. All rights reserved..
Vorobyov E.I.,Saint Marys University, Halifax
Astrophysical Journal | Year: 2010
Motivated by a considerable scatter in the observationally inferred lifetimes of the embedded phase of star formation, we study the duration of the Class 0 and Class I phases in upper-mass brown dwarfs and low-mass stars using numerical hydrodynamic simulations of the gravitational collapse of a large sample of cloud cores. We resolve the formation of a star/disk/envelope system and extend our numerical simulations to the late accretion phase when the envelope is nearly totally depleted of matter. We adopt the classification scheme of André et al. and calculate the lifetimes of the Class 0 and Class I phases (τC0 and τCI, respectively) based on the mass remaining in the envelope. When cloud cores with various rotation rates, masses, and sizes (but identical otherwise) are considered, our modeling reveals a sub-linear correlation between the Class 0 lifetimes and stellar masses in the Class 0 phase with the least-squares fit exponent m = 0.8 0.05. The corresponding correlation between the Class I lifetimes and stellar masses in Class I is super-linear with m = 1.2 0.05. If a wider sample of cloud cores is considered, which includes possible variations in the initial gas temperature, cloud core truncation radii, density enhancement amplitudes, initial gas density and angular velocity profiles, and magnetic fields, then the corresponding exponents may decrease by as much as 0.3. The duration of the Class I phase is found to be longer than that of the Class 0 phase in most models, with a mean ratio τCI/τC0 1.5-2. A notable exception are young stellar objects that form from cloud cores with large initial density enhancements, in which case τC0 may be greater than τCI. Moreover, the upper-mass (≳1.0 M ⊙) cloud cores with frozen-in magnetic fields and high cloud core rotation rates may have the τCI/τC0 ratios as large as 3.0-4.0. We calculate the rate of mass accretion from the envelope onto the star/disk system and provide an approximation formula that can be used in semi-analytic models of cloud core collapse. © 2010. The American Astronomical Society. All rights reserved..
Clarke D.A.,Saint Marys University, Halifax
Astrophysical Journal, Supplement Series | Year: 2010
Recent and not-so-recent critiques of the widely used magnetohydrodynamics (MHD) code, ZEUS-3D, challenge its reliability and efficiency suggesting that its MHD algorithm is capable of "significant errors" in some simple one-dimensional shock-tube problems. I show that these concerns are either inapplicable in multi-dimensional astrophysical applications, or result from a misuse of the code rather than "flaws" in its design. I also describe a few multi-dimensional test problems including one for super-Alfvénic turbulence, and highlight some recent innovations and improvements to the code now available online. © 2010 The American Astronomical Society.