The post-infall evolution of a satellite galaxy

As galaxy simulations increase in resolution more attention is being paid towards the evolution of dwarf galaxies and how the simulations compare to observations. Despite this increasing resolution we are however, far away from resolving the interactions of satellite dwarf galaxies and the hot coronae which surround host galaxies. We describe a new method which focuses only on the local region surrounding an infalling dwarf in an effort to understand how the hot baryonic halo will alter the chemodynamical evolution of dwarf galaxies. Using this method we examine how a dwarf, similar to Sextans dwarf spheroidal, evolves in the corona of a Milky Way like galaxy. We find that even at high perigalacticons the synergistic interaction between ram pressure and tidal forces transform a dwarf into a stream, suggesting that Sextans was much more massive in the past in order survive its perigalacticon passage. In addition the large confining pressure of the hot corona allows gas that was originally at the outskirts to begin forming stars, initially forming stars of low metallicity compared to the dwarf evolved in isolation. This increase in star formation eventually allows a dwarf galaxy to form more metal rich stars compared to one in isolation, but only if the dwarf retains gas for a sufficiently long period of time. In addition, dwarfs which formed substantial numbers of stars post-infall will have a slightly elevated [Mg/Fe] at high metallicity ([Fe/H] -1.5).Comment: 29 pages, 26 figures, A&A accepte

The effect of gravitational tides on dwarf spheroidal galaxies

The effect of the local environment on the evolution of dwarf spheroidal galaxies is poorly understood. We have undertaken a suite of simulations to investigate the tidal impact of the Milky Way on the chemodynamical evolution of dwarf spheroidals that resemble present day classical dwarfs using the SPH code GEAR. After simulating the models through a large parameter space of potential orbits the resulting properties are compared with observations from both a dynamical point of view, but also from the, often neglected, chemical point of view. In general, we find that tidal effects quench the star formation even inside gas-endowed dwarfs. Such quenching, may produce the radial distribution of dwarf spheroidals from the orbits seen within large cosmological simulations. We also find that the metallicity gradient within a dwarf is gradually erased through tidal interactions as stellar orbits move to higher radii. The model dwarfs also shift to higher $\langle$[Fe/H]$\rangle$/L ratios, but only when losing $>$$20\%$ of stellar mass.Comment: A&A accepte

Exploring the immunosuppressive properties of various agents in the experimental autoimmune encephalomyelitis models of multiple sclerosis

One of the major focuses for our lab involves examining the immunosuppressive properties of various agents and receptors in the experimental autoimmune encephalomyelitis (EAE) model of multiple sclerosis (MS). This dissertation encompasses an investigation of cannabidiol in the EAE model, the endocannabinoid CB1 receptor in the EAE model, staphylococcal superantigens (SAgs) as immunosuppressive agents, and various aspects of the EAE model. The first chapter covers the existing literature pertinent to these studies, the second and third chapters cover the material, methods, and results from the studies, and the fourth chapter is a discussion of how those results fit into the existing body of literature. A fifth chapter has also been included which covers two additional studies designed to develop alternative EAE models for our lab; however, both studies turned out differently than expected. One of the most interesting developments from this final chapter was the discovery of an age dependent difference in the memory T cell response of older mice, which allows for more robust disease to be induced when cells from 6 month old mice are used in the passive EAE (P-EAE) model as opposed to mice 10 weeks of age

A Delphi Study Using Value-Focused Thinking for United States Air Force Mission Dependency Index Values

Recently, the Air Force Civil Engineer Center (AFCEC) identified that the Mission Dependency Index (MDI) had issues with reflecting the criticality of some mission sets. The MDI is a constructed value assigned to assets that reflects the consequence of failure. The primary mission sets having MDI issues were non-flightline assets. The current Air Force MDI metric relies on data collected using the Naval Facilities Engineering Command (NAVFAC) methodology and adapts the data by using facility categorization codes. The result is a method that compares alternatives to each other to develop an individual asset\u27s MDI value. As a corrective measure to this methodology, non-flightline centric mission sets have been allowed to adjust (i.e. increase) their asset MDI values. This modification in MDI values has led to inflation of the metric. To address the issue, this research focuses on how the MDI values should be assigned by examining both public and private methodologies. Leveraging the Delphi technique and Value Focused Thinking (VFT), three models are created to suggest the proper inputs that should be considered when producing the MDI values for the Air Force\u27s assets. The models inputs were interruptability, redundancy, replaceability and the number of missions affected

Disease surveillance and projected expansion in climatic suitability for Trypanosoma cruzi, the Etiological agent of Chagas disease, in Oklahoma.

The vector-borne hemoflagellate parasite Trypanosoma cruzi infects seven million people globally and causes chronic cardiomyopathy and gastrointestinal diseases. Historically, T. cruzi was endemic to Central and South America, but is now found throughout the southern United States and across 43 countries globally. There are three reports of T. cruzi in wild raccoons and dogs in Oklahoma, but its endemicity in the state is poorly studied. We suspect Mexican free-tailed bats (Tadarida brasiliensis) contribute to the endemicity of T. cruzi in Oklahoma by their annual migration from Central America to North American maternity roosts. During the summer of 2017, we sampled 361 Mexican free-tailed bats at three maternity roosts in Oklahoma for T. cruzi. We collected wing tissues and extracted DNA, amplified target T. cruzi DNA by PCR using the primers TCZ1/TCZ2, and observed amplification by gel electrophoresis. We detected T. cruzi DNA in one juvenile Mexican free-tailed bat resulting in a prevalence of 0.27% in the 361 sampled bats. The positive sample was sequenced at Eton Biosciences, confirmed as T. cruzi, and uploaded to GenBank (MG869732). This finding is the first reported detection of a wild bat naturally infected with T. cruzi in Oklahoma, suggests Mexican free-tailed bats can contribute to T. cruzi endemicity via migration between endemic foci, and provides insight on the endemicity of T. cruzi in underrepresented endemic areas. To better understand the potential impact of global climate change on the future epidemiology of T. cruzi in Oklahoma, we used the program MaxEnt to develop an ecological niche model for T. cruzi and five widespread Triatoma vectors based on 19 bioclimatic variables and 546 published localities within the United States. We modeled regions of current potential T. cruzi and Triatoma distribution, and regions projected to have suitable climatic conditions under a Representative Concentration Pathway (RCP 8.5) scenario by 2070. Regions with potential suitable climatic conditions for T. cruzi, T. indictiva, T. lecticularia, T. protracta, and T. sanguisuga are predicted to increase within the United States and Oklahoma by 2070. Regions with potential suitable climatic conditions for T. gerstaeckeri are predicted to increase within the United States but not in Oklahoma by 2070. Our findings agree with previous literature and confirm that climate change will influence the expansion of T. cruzi and important Triatoma vectors in Oklahoma and the United States

Computational issues in chemo-dynamical modelling of the formation and evolution of galaxies

Chemo-dynamical N-body simulations are an essential tool for understanding the formation and evolution of galaxies. As the number of observationally determined stellar abundances continues to climb, these simulations are able to provide new constraints on the early star formaton history and chemical evolution inside both the Milky Way and Local Group dwarf galaxies. Here, we aim to reproduce the low $\alpha$-element scatter observed in metal-poor stars. We first demonstrate that as stellar particles inside simulations drop below a mass threshold, increases in the resolution produce an unacceptably large scatter as one particle is no longer a good approximation of an entire stellar population. This threshold occurs at around $10^3\,\rm{M_\odot}$, a mass limit easily reached in current (and future) simulations. By simulating the Sextans and Fornax dwarf spheroidal galaxies we show that this increase in scatter at high resolutions arises from stochastic supernovae explosions. In order to reduce this scatter down to the observed value, we show the necessity of introducing a metal mixing scheme into particle-based simulations. The impact of the method used to inject the metals into the surrounding gas is also discussed. We finally summarise the best approach for accurately reproducing the scatter in simulations of both Local Group dwarf galaxies and in the Milky Way.Comment: 23 pages, 18 figures, accepted for publication in Astronomy and Astrophysic

The Smith Cloud and its dark matter halo: Survival of a Galactic disc passage

The current velocity of the Smith Cloud indicates that it has undergone at least one passage of the Galactic disc. Using hydrodynamic simulations we examine the present day structure of the Smith Cloud. We find that a dark matter supported cloud is able to reproduce the observed present day neutral hydrogen mass, column density distribution and morphology. In this case the dark matter halo becomes elongated, owing to the tidal interaction with the Galactic disc. Clouds in models neglecting dark matter confinement are destroyed upon disc passage, unless the initial cloud mass is well in excess of what is observed today. We then determine integrated flux upper limits to the gamma-ray emission around such a hypothesised dark matter core in the Smith Cloud. No statistically significant core or extended gamma-ray emission are detected down to a 95% confidence level upper limit of $1.4\times10^{-10}$ ph cm$^{-2}$ s$^{-1}$ in the 1-300 GeV energy range. For the derived distance of 12.4 kpc, the Fermi upper limits set the first tentative constraints on the dark matter cross sections annihilating into $\tau^{+}{\tau}^{-}$ and $b\bar{b}$ for a high-velocity cloud.Comment: 10 pages, 8 figures. Submitted to MNRA