The sub-solar Initial Mass Function in the Large Magellanic Cloud

The Magellanic Clouds offer a unique variety of star forming regions seen as bright nebulae of ionized gas, related to bright young stellar associations. Nowadays, observations with the high resolving efficiency of the Hubble Space Telescope allow the detection of the faintest infant stars, and a more complete picture of clustered star formation in our dwarf neighbors has emerged. I present results from our studies of the Magellanic Clouds, with emphasis in the young low-mass pre-main sequence populations. Our data include imaging with the Advanced Camera for Surveys of the association LH~95 in the Large Magellanic Cloud, the deepest observations ever taken with HST of this galaxy. I discuss our findings in terms of the Initial Mass Function, which we constructed with an unprecedented completeness down to the sub-solar regime, as the outcome of star formation in the low-metallicity environment of the LMC.Comment: To appear in the Proceedings of IAU Symposium 256 "The Magellanic System: Stars, Gas, and Galaxies", 6 pages, 3 figure

"A Structural Approach to Hedonic Equilibrium Models"

This paper presents a quality theory for differentiated products. Analytical solutions for the equilibrium demand for quality and the equilibrium price equation are computed. The model is estimated and the willingness to pay for improvements in the air quality of Houston is computed. The empirical results show that the standard n on-structural approach would seriously underestimate benefits for non-marginal and small changes in air quality.

An Evaluation of Risk Attitudes and Risk Tolerance in Emergency Medicine Residents

An underlying issue to our current healthcare system is how decisions made in the emergency department affect patients. This is paramount for underserved populations, which are more likely to have poor physical and mental health, lack of primary care, greater use of health services, and be generally dissatisfied with their medical care.1,2 What should the emergency physician (EP) do for these patients? These decisions are largely based upon individual risk tolerance. While risk is a indelible part of emergency medicine (EM), a risk profile of EM residents has not been compiled. Knowledge of risk taking tendencies among this niche of medical professionals could be critical. If EM residents have great risk aversion, they might practice defensive medicine, thereby incurring crippling costs4. On the other hand, if emergency medicine residents are greatly risk tolerant, they may make decisions that lead to significant morbidity and mortality. It is essential to establish a baseline risk profile before any corrective measures can be advanced. This study attempted to accomplish precisely that using Risk Type CompassTM.https://jdc.jefferson.edu/cwicposters/1023/thumbnail.jp

Applications of a tight-binding total energy method for transition and noble metals: Elastic Constants, Vacancies, and Surfaces of Monatomic Metals

A recent tight-binding scheme provides a method for extending the results of first principles calculations to regimes involving $10^2 - 10^3$ atoms in a unit cell. The method uses an analytic set of two-center, non-orthogonal tight-binding parameters, on-site terms which change with the local environment, and no pair potential. The free parameters in this method are chosen to simultaneously fit band structures and total energies from a set of first-principles calculations for monatomic fcc and bcc crystals. To check the accuracy of this method we evaluate structural energy differences, elastic constants, vacancy formation energies, and surface energies, comparing to first-principles calculations and experiment. In most cases there is good agreement between this theory and experiment. We present a detailed account of the method, a complete set of tight-binding parameters, and results for twenty-nine of the alkaline earth, transition and noble metals.Comment: 24 pages (REVTEX), 6 figures (epsf.tex required). Several new results have been added. Re-submitted to Physical Review

From Neutron Star Observables to the Equation of State. I. An Optimal Parametrization

The increasing number and precision of measurements of neutron star masses, radii, and, in the near future, moments of inertia offer the possibility of precisely determining the neutron star equation of state. One way to facilitate the mapping of observables to the equation of state is through a parametrization of the latter. We present here a generic method for optimizing the parametrization of any physically allowed EoS. We use mock equations of state that incorporate physically diverse and extreme behavior to test how well our parametrization reproduces the global properties of the stars, by minimizing the errors in the observables mass, radius, and the moment of inertia. We find that using piecewise polytropes and sampling the EoS with five fiducial densities between ~1-8 times the nuclear saturation density results in optimal errors for the smallest number of parameters. Specifically, it recreates the radii of the assumed EoS to within less than 0.5 km for the extreme mock equations of state and to within less than 0.12 km for 95% of a sample of 42 proposed, physically-motivated equations of state. Such a parametrization is also able to reproduce the maximum mass to within 0.04 M_sun and the moment of inertia of a 1.338 M_sun neutron star to within less than 10% for 95% of the proposed sample of equations of state.Comment: Minor changes made to match published ApJ versio

Clustered Star Formation in the Small Magellanic Cloud. A Spitzer/IRAC View of the Star-Forming Region NGC 602/N 90

We present Spitzer/IRAC photometry on the star-forming HII region N 90, related to the young stellar association NGC 602 in the Small Magellanic Cloud. Our photometry revealed bright mid-infrared sources, which we classify with the use of a scheme based on templates and models of red sources in the Milky Way, and criteria recently developed from the Spitzer Survey of the SMC for the selection of candidate Young Stellar Objects (YSOs). We detected 57 sources in all four IRAC channels in a 6.2' x 4.8' field-of-view centered on N 90; 22 of these sources are classified as candidate YSOs. We compare the locations of these objects with the position of optical sources recently found in the same region with high-resolution HST/ACS imaging of NGC 602, and we find that 17 candidate YSOs have one or more optical counterparts. All of these optical sources are identified as pre-main sequence stars, indicating, thus, ongoing clustered star formation events in the region. The positions of the detected YSOs and their related PMS clusters give a clear picture of the current star formation in N 90, according to which the young stellar association photo-ionizes the surrounding interstellar medium, revealing the HII nebula, and triggering sequential star formation events mainly along the eastern and southern rims of the formed cavity of the parental molecular cloud.Comment: Accepted fro Publication in ApJ. 8 pages, 6 figures, 3 color figures submitted as JP

Foreign Exchange Intervention and Equilibrium Real Exchange Rates

Monetary authorities intervene in the currency markets in order to pursue a monetary rule and/or to smooth exchange rate volatility caused by speculative attacks. In the present paper we investigate for possible intervention effects on the volatility of nominal exchange rates and the estimated equilibrium behaviour of real exchange rates. The main argument of the paper is that omission of intervention effects -when they are significant- would bias the ability to detect any PPP-based behaviour of the real exchange rates in the long run. Positive evidence for this argument comes from the experience of six Central and Eastern European economies, whose exchange markets are characterised by frequent interventions.Foreign Exchange Market Intervention; Real Exchange Rates; PPP.

Coarse Molecular-Dynamics Determination of the Onset of Structural Transitions: Melting of Crystalline Solids

Using a coarse molecular-dynamics (CMD) approach with an appropriate choice of coarse variable (order parameter), we map the underlying effective free-energy landscape for the melting of a crystalline solid. Implementation of this approach provides a means for constructing effective free-energy landscapes of structural transitions in condensed matter. The predictions of the approach for the thermodynamic melting point of a model silicon system are in excellent agreement with those of ''traditional'' techniques for melting-point calculations, as well as with literature values