Line Ratios Reveal N2H+ Emission Originates Above the Midplane in TW Hydrae

Line ratios for different transitions of the same molecule have long been used as a probe of gas temperature. Here we use ALMA observations of the N2H+ J~=~1-0 and J~=~4-3 lines in the protoplanetary disk around TW Hya to derive the temperature at which these lines emit. We find an averaged temperature of 39~K with a one sigma uncertainty of 2~K for the radial range 0.8-2'', significantly warmer than the expected midplane temperature beyond 0.5'' in this disk. We conclude that the N2H+ emission in TW Hya is not emitting from near the midplane, but rather from higher in the disk, in a region likely bounded by processes such as photodissociation or chemical reprocessing of CO and N2 rather than freeze out.Comment: Accepted for publication in ApJ Letters, 5 pages, 1 figur

Health Transfers: An Application of Health-Health Analysis to Assess Food Safety Regulations

The authors apply a Health-Health Analysis to risks associated with harvesting Gulf oysters to evaluate that approach to managing health and safety risks

Tracing the Earliest Stages of Planet Formation through Modelling and Sub-mm Observations

This thesis explores the utility of molecular line emission as a tool to unravel the physical structures and processes involved in planet formation. Observations of molecular ions, HCO+ and DCO+, in the disk of DM Tauri allow for a study of the ionization structure. These constraints are an essential ingredient in modelling the physical and chemical evolution of a disk which directly impact the efficiency of planet formation. We also present the first spatially resolved direct measurement of turbulence in a protoplanetary disk using CO, CN and CS molecular line emission. Such a measurement is vital in identifying the physical mechanisms driving turbulence. In addition, we perform a thorough analysis of all uncertainties involved when determining turbulent velocities in disks and demonstrate that all measurements of turbulence will be ultimately limited by the precision to which the gas temperature can be derived. Finally, the CS emission profile from TW Hydrae displays a dip-like feature coincident with features observed in scattered light observations of the disk, suggesting a common origin. Extensive modelling demonstrates that this may be the first detection of a surface density perturbation through molecular line emission, potentially the manifestation of an embedded protoplanet or a strong magneto-rotational instability

On Wondering: The Epistemology of A Questioning Attitude

An emerging trend in contemporary epistemology departs from the traditional preoccupation with the nature of knowledge, belief, evidence, justification, and the problems of skepticism. This trend focuses instead on the nature of inquiry itself and especially on the role of questions and questioning attitudes that arise in and define that activity. Naturally, this emerging trend calls for a philosophical exploration of the nature of questioning attitudes like curiosity and wondering, and of the various epistemological considerations pertaining to them. Consequently, this project primarily addresses two questions: what does it mean to wonder? And what is required to wonder well? The project is thus both descriptive and normative, aiming to pin down the place that wondering has in our ontology of epistemologically significant mental states and to determine what kinds of prescriptive norms it is subject to in the course of rational inquiry