Accretion variability in young, low-mass stellar systems

Through the study of accretion onto the young, low-mass stars known as T Tauri Stars (TTS), we can better understand the formation of our solar system. Gas is funneled along stellar magnetic field lines into magnetospheric accretion columns where it reaches free-fall velocities and shocks at the stellar surface, generating emission that carries information about the inner regions of the protoplanetary disk. Accretion is a variable process, with characteristic timescales ranging from minutes to years. In this dissertation, I use simulations, models, and observations to provide insight into the driving forces of mass accretion rate variability on timescales of minutes to weeks and the structure of the inner disk. Using hydrodynamic simulations, I find that steady-state, transonic accretion occurs naturally in the absence of any other source of variability. If the density in the inner disk varies smoothly in time with roughly day-long time-scales (e.g., due to turbulence), traveling shocks develop within the accretion column, which lead to rapid increases in the accretion luminosity followed by slower declines. I present the largest Hubble Space Telescope (HST) spectral variability study of TTS to date. I infer mass accretion rates and accretion column surface coverage using newly updated accretion shock models. I find typical changes in the mass accretion rate of order 10% and moderate changes in the surface coverage for most objects in the sample on week timescales. Individual peculiar epochs are further discussed. I find that the inner disk is inhomogeneous and that dust may survive near the magnetic truncation radius. Next, I link 2-minute cadence light curves from the Transiting Exoplanet Survey Satellite (TESS) to accretion using ground-based U-band photometry. Additional HST observations for one target enable more detailed connections between TESS light curves and accretion. I also use the TESS light curves to identify rotation periods and patterns of quasi-periodicity. Finally, I connect hydrodynamic simulations, accretion shock models, and stellar rotation to predict signatures of a turbulent inner disk. I generate light curves from these models to make comparisons to previous month-long photometric monitoring surveys of TTS using metrics of light curve symmetry and periodicity

Assessment of motivation to control alcohol use: The motivational thought frequency and state motivation scales for alcohol control

publisher: Elsevier articletitle: Assessment of motivation to control alcohol use: The motivational thought frequency and state motivation scales for alcohol control journaltitle: Addictive Behaviors articlelink: http://dx.doi.org/10.1016/j.addbeh.2016.02.038 content_type: article copyright: © 2016 Elsevier Ltd. All rights reserved

Law, Liquor, and Love

This article discusses attempts at alcohol law reform in New Zealand between 2008 and 2017. First, it describes a major review of alcohol by the New Zealand Law Commission, headed by Sir Geoffrey Palmer, who had overseen liberalisation of alcohol regulation 25 years earlier. The main recommendations of the commission’s final report featured progressive reform of the alcohol laws regulating marketing, price, accessibility and age of purchase. Second, it outlines the response to the commission’s report by the Nationalled government, including an Alcohol Reform Bill that ignored the key recommendations of the commission. This ‘non-reform’ bill was the outcome of a political process of obfuscation, delay and inaction led by then prime minister, John Key. Third, the article describes the factors that have contributed to the lack of effective alcohol law reform, despite the review and high public support for change over the past decade. We conclude that ‘the love of money’ is at the heart of the barriers to change. Finally, we propose three main policies that would make a significant difference to reducing alcohol-related harm in New Zealand and suggest how these could be advanced

A transitional disk around an intermediate mass star in the sparse population of the Orion OB1 Association

We present a detailed study of the disk around the intermediate mass star SO 411, aiming to explain the spectral energy distribution of this star. We show that this is a transitional disk truncated at $\sim$11 au, with $\sim$0.03 lunar masses of optically thin dust inside the cavity. Gas also flows through the cavity, since we find that the disk is still accreting mass onto the star, at a rate of $\sim 5x10^{-9}$ Msun/yr. Until now, SO 411 has been thought to belong to the $\sim$3 Myr old {$\sigma$} Orionis cluster. However, we analyzed the second Gaia Data Release in combination with kinematic data previously reported, and found that SO 411 can be associated with an sparse stellar population located in front of the {$\sigma$} Orionis cluster. If this is the case, then SO 411 is older and even more peculiar, since primordial disks in this stellar mass range are scarce for ages $>$5 Myr. Analysis of the silicate 10$\mu$m feature of SO 411 indicates that the observed feature arises at the edge of the outer disk, and displays a very high crystallinity ratio of $\sim$0.5, with forsterite the most abundant silicate crystal. The high forsterite abundance points to crystal formation in non-equilibrium conditions. The PAH spectrum of SO 411 is consistent with this intermediate state between the hot and luminous Herbig Ae and the less massive and cooler T Tauri stars. Analysis of the 7.7$\mu$m PAH feature indicates that small PAHs still remain in the SO 411 disk.Comment: Accepted in the Astrophysical Journal (17 pages, 9 Figures

Improving Winter Road Maintenance in New Mexico

The New Mexico Department of Transportation’s (NMDOT) Intelligent Transportation Systems Bureau seeks to implement technological solutions to make the roads safer for drivers. The goal of this project was to improve NMDOT winter maintenance operations. We developed a tool to rank locations for Environmental Sensor Stations and compiled a list of several recommended locations within District 5. We also produced a list of recommendations for how the NMDOT can improve its resource management practices through implementing process and technological solutions