Master of Science

thesisQuantifying deposition efficiency for fugitive dust on vegetation is essential for developing more accurate computational models. This work focuses on the role that turbulent motions play in deposition enhancement. This research combines field and wind tunnel experiments to study particle deposition onto vegetation resulting from small-scale interactions of turbulent flows. These experiments will help to optimize the design of vegetative windbreaks as a mitigation tool for fugitive dust removal from the atmosphere. The long-term goal is to use these data for model development and parameterization within the Quick Urban and Industrial Complex (QUIC) dispersion modeling system. Experimental testing in a full scale wind tunnel seeks to quantify deposition efficiencies by varying the relevant Stokes number parameters (i.e., wind speed, deposition area of substrate, and particle size). Experimental results indicated that grid induced turbulence enhances deposition in all six directions (x-upstream and downstream, y-right and left, z-up and down). Deposition was enhanced on the upstream impaction surface (-x direction) by a factor of two compared to the no-grid "laminar" case. Deposition on all other directional surfaces increased by about an order of magnitude. This work investigates the effect of isotropic turbulence on the enhancement of particle deposition to surfaces for inertial impaction dominated processes. Turbulence and particle deposition were quantified using hot-wire anemometry and fluorimetry measurement techniques, respectively. The contribution of turbulence on deposition is shown to scale with a dimensionless parameter formed from the combination of the classical Stokes number (Stk) and the Taylor-microscale Reynolds number (Rλ). This scaling helps to understand the role that the intermediate eddies (λ) and turbulent fluctuations (u') have on deposition fraction (DFλ). A modified Stokes number (Stk*=Stk·Rλ 0.3) parameterization for an empirical equation (DFλ = 100-100/(440.5·(Stk*)3.88+1)) was devised to utilize this new scaling and incorporate physically significant turbulent deposition parameters (i.e., λ and u') into the solution. Experimental results indicate that past impaction parameterizations substantially underestimate deposition in the presence of turbulence

The Role of Risk in Determining Liberalizing Trade

This paper seeks to extend the research done by Bates to the years 1985-’95 and ‘96-2001. Bates found that increased terms-of-trade instability leads to decreased openness. He also found that terms-oftrade instability led to a change in trade regimeii. This paper searches to see if these results have continued through 1995 in order to secure more legitimacy as a leading theory among the risk literature of today. Over that time period, the Soviet Union and the Apartheid regime broke down. These countries have experienced major political and economic reforms due to these events, which should make these countries extremely vulnerable to risk. LDCs were forced in the early 90s to open their borders without question in order to receive aide from intercontinental organizations. It may no longer be the case that risk determines openness with these various global shocks during the late 80s and early 90s, so this paper analyzes whether Bates’s empirical research on terms-of-trade instability continues through these risky times

A systematic study of the inner rotation curves of galaxies observed as part of the GASS and COLD GASS surveys

We present a systematic analysis of the rotation curves of 187 galaxies with masses greater than 10^10 M_sol, with atomic gas masses from the GALEX Arecibo Sloan Survey (GASS), and with follow-up long-slit spectroscopy from the MMT. Our analysis focuses on stellar rotation curves derived by fitting stellar template spectra to the galaxy spectra binned along the slit. In this way, we are able to obtain accurate rotation velocity measurements for a factor of 2 more galaxies than possible with the Halpha line. Galaxies with high atomic gas mass fractions are the most dark-matter dominated galaxies in our sample and have dark matter halo density profiles that are well fit by Navarro, Frenk & White profiles with an average concentration parameter of 10. The inner slopes and of the rotation curves correlate more strongly with stellar population age than with galaxy mass or structural parameters. At fixed stellar mass, the rotation curves of more actively star-forming galaxies have steeper inner slopes than less actively star-forming galaxies. The ratio between the galaxy specific angular momentum and the total specific angular momentum of its dark matter halo, R_j, correlates strongly with galaxy mass, structure and gas content. Low mass, disk-dominated galaxies with atomic gas mass fractions greater than 20% have median values of R_j of around 1, but massive, bulge-dominated galaxies have R_j=0.2-0.3. We argue that these trends can be understood in a picture where gas inflows triggered by disk instabilities lead to the formation of passive, bulge-dominated galaxies with low specific angular momentum.Comment: 10 pages, 12 figures, submitted to MNRA

Habitat selection by the relict leopard frog (Rana onca): Assessment of vegetation use at two scales

In recent years, two populations of the rare Relict Leopard Frog (Rana onca) have gone extinct. These population extinctions occurred concomitantly with the encroachment of native emergent vegetation into pools in which frogs were usually observed. In order to determine if adult Rana onca prefer more vegetatively open habitats, a radio-telemetry study was conducted. A total of 809 radio telemetry observations were made on 34 frogs from April 2 through December 7, 2004. Binary Logistic Regression was used with both macrohabitat and microhabitat data to compare habitat characteristics between low-use and high-use segments of the spring. A more traditional multiple analysis of variance (MANOVA) approach was also used at the macrohabitat scale to compare used segments to non-used segments. Both of these analyses supported the hypothesis that adult Rana onca select for areas with less vegetative cover

Environmental Effects in the Evolution of Galactic Bulges

We investigate possible environmental trends in the evolution of galactic bulges over the redshift range 0<z<0.6. For this purpose, we construct the Fundamental Plane (FP) for cluster and field samples at redshifts =0.4 and =0.54 using surface photometry based on HST imaging and velocity dispersions based on Keck spectroscopy. As a reference point for our study we include data for pure ellipticals, which we model as single-component Sersic profiles; whereas for multi-component galaxies we undertake decompositions using Sersic and exponential models for the bulge and disk respectively. Although the FP for both distant cluster and field samples are offset from the local relation, consistent with evolutionary trends found in earlier studies, we detect significant differences in the zero point of ~=0.2 dex between the field and cluster samples at a given redshift. For both clusters, the environmentally-dependent offset is in the sense expected for an accelerated evolution of bulges in dense environments. By matching the mass range of our samples, we confirm that this difference does not arise as a result of the mass-dependent downsizing effects seen in larger field samples. Our result is also consistent with the hypothesis that - at fixed mass and environment - the star formation histories of galactic bulges and pure spheroids are indistinguishable, and difficult to reconcile with the picture whereby the majority of large bulges form primarily via secular processes within spiral galaxies.Comment: 5 pages, 3 figures, accepted for publication in ApJ Letter

Spam-T5: Benchmarking Large Language Models for Few-Shot Email Spam Detection

This paper investigates the effectiveness of large language models (LLMs) in email spam detection by comparing prominent models from three distinct families: BERT-like, Sentence Transformers, and Seq2Seq. Additionally, we examine well-established machine learning techniques for spam detection, such as Na\"ive Bayes and LightGBM, as baseline methods. We assess the performance of these models across four public datasets, utilizing different numbers of training samples (full training set and few-shot settings). Our findings reveal that, in the majority of cases, LLMs surpass the performance of the popular baseline techniques, particularly in few-shot scenarios. This adaptability renders LLMs uniquely suited to spam detection tasks, where labeled samples are limited in number and models require frequent updates. Additionally, we introduce Spam-T5, a Flan-T5 model that has been specifically adapted and fine-tuned for the purpose of detecting email spam. Our results demonstrate that Spam-T5 surpasses baseline models and other LLMs in the majority of scenarios, particularly when there are a limited number of training samples available. Our code is publicly available at https://github.com/jpmorganchase/emailspamdetection

Evolution of the Stellar Mass--Metallicity Relation - I: Galaxies in the z~0.4 Cluster Cl0024

We present the stellar mass-stellar metallicity relationship (MZR) in the Cl0024+1654 galaxy cluster at z~0.4 using full spectrum stellar population synthesis modeling of individual quiescent galaxies. The lower limit of our stellar mass range is $M_*=10^{9.7}M_\odot$, the lowest galaxy mass at which individual stellar metallicity has been measured beyond the local universe. We report a detection of an evolution of the stellar MZR with observed redshift at $0.037\pm0.007$ dex per Gyr, consistent with the predictions from hydrodynamical simulations. Additionally, we find that the evolution of the stellar MZR with observed redshift can be explained by an evolution of the stellar MZR with their formation time, i.e., when the single stellar population (SSP)-equivalent ages of galaxies are taken into account. This behavior is consistent with stars forming out of gas that also has an MZR with a normalization that decreases with redshift. Lastly, we find that over the observed mass range, the MZR can be described by a linear function with a shallow slope, ($[Fe/H] \propto (0.16 \pm 0.03) \log M_*$). The slope suggests that galaxy feedback, in terms of mass-loading factor, might be mass-independent over the observed mass and redshift range.Comment: 22 pages, 10 figures. Accepted for publication in Ap