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College of Sciences

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School of Biological Sciences

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School of Chemistry and Biochemistry

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School of Earth and Atmospheric Sciences

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School of Mathematics

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School of Physics

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Understanding bioaerosols atmospheric lifecycle, abundance variability and impacts

(Georgia Institute of Technology, 2019-12-18) Negron, Arnaldo Andres

Bioaerosols are ubiquitous in the atmosphere and may have important impacts on human health, cloud formation, the hydrological cycles and biogeochemical cycles. Measuring and characterizing bioaerosols remains a challenge owing to their low atmospheric concentration. During this thesis, we have developed an approach to collect large amounts of bioaerosols (e.g., on ground-based or airborne platforms) in a liquid suspension over the sub-hour to multiple hour timescale using a modified high-volume wet cyclone. The bioaerosols are then subsequently characterized using flow cytometry and other biology tools, results leading to robust quantifications of bioaerosol populations. Together with the observations from rapid autofluorescence detection techniques, they can provide powerful insights on the concentration, composition, and activity of bioaerosol with rapid time resolution. The new characterization approach was applied to study bioaerosol populations in multiple, distinct environments: i) an urban environment in the Southeast United States surrounded by heavy forestation (Atlanta, GA), ii) the marine boundary layer, free troposphere, terrestrial environments near California during the BOAS 2015 aircraft campaign, and, iii) the remote Eastern Mediterranean sea influenced by the European continental outflow and Saharan dust events. In the Southeast United States, we observed that the bioaerosol population is highly dynamic and driven by the prevailing meteorology. We detect high concentrations of large bioaerosol population rich in nucleic acid (consistent with wet-ejected fungal spores) during humid and warm days after rain events, while other days are characterized by smaller bioaerosol (consistent with bacteria) that are low in nucleic acid content. During the airborne deployment at the California Coast, small bacterialike particles that are low in nucleic acid content are ubiquitous and tend to be enhanced in the marine free troposphere compared to the boundary layer thought to be the source. Concentrations of microbes in the marine boundary layer are about 10 times less than those found in the airmasses characterized by terrestrial emissions, while the cell types from flow cytometry and light induced fluorescence indicate very different populations. In the Eastern Mediterranean, bioaerosol is dominated by small bioaerosol with low nucleic acid content (consistent with bacterial cells). Interestingly, the highest concentration is not observed during periods where continental outflow airmasses are sampled, but during dust events. The observations carried out during this thesis show that bioaerosol associated with air masses influenced by terrestrial (and especially dust) emissions carry the largest bioaerosol concentrations. We also see that smaller bioaerosol consistent with microbes (with a diameter ~ 1 μm and low nucleic content) are ubiquitous at concentrations ranging between 104 m-3 and 105 m-3. Microbes in the marine boundary layer off the coast of California are about 10 times lower than that observed in terrestrial environments (103 m-3 to 104 m-3), although in the Eastern Mediterranean, bioaerosol concentrations can be as high as in terrestrial environments. Occasionally, we observe concentrations of larger nucleic acid-rich particles (consistent with fungal spores), especially after rain events. The extent to which the fungal spores travel is surprisingly large – given that they are observed at the remote Eastern Mediterranean, hundreds (and maybe thousands) of kilometers away from their terrestrial origin. The impacts of these concentrations and types of bioaerosol in all the environments sampled can be significant. We estimate for example that the phosphorous delivery from bioaerosol to the Eastern Mediterranean Sea, although much lower than recent model estimates, can still explain the concentrations that are associated with background levels of atmospheric phosphorus. In terms of their impacts on clouds, the concentration of marine bioaerosol is high enough to potentially influence ice nucleation in warm mixed-phase cloud, especially given that secondary ice processes are favored and can promote any initial low levels of primary ice. The above mentioned potential impacts of bioaerosol, however, may be modulated by atmospheric processing – very few studies of which exist. Towards this, we studied the response of microbes to simulated atmospheric acidification (a process that occurs everywhere in the atmosphere) by quantifying their cultivability and ability to express ice nucleation capacity as a function of pH levels observed for micron-sized particles in the atmosphere. For this, a droplet freezing assay was developed and used to study the effect of aerosol pH on an ice active P. syringae strain. Surprisingly, the microbes could resist considerable levels of acidification, as they retain their cultivability and ice nucleation capability to pH levels as low as 4. Upon increased acidification, however, (e.g., pH=2.5 or less), the ice active P. syringae lost cultivability and reduced their ice nucleation temperature close to -15oC, approaching the properties of Arizona test dust. Repeated freezing-thawing cycles over the same strains exhibit repeatable ice nucleation results. These results show that models of ice nucleation that consider the effects of bioaerosol need to consider the impacts of atmospheric acidification; the smooth dependence of ice nucleating characteristics (freezing temperature vs. pH) suggests that such effects can be parameterized using the approach developed during this thesis. The methods and scientific results produced during this thesis show that the simple yet powerful methods developed here can be readily used to sample bioaerosol, characterize their population characteristics, metabolic state, ice nucleation activity, and response to a variety of atmospheric stressors.
Signatures of the El Nino-southern oscillation on rainfall and cave dripwater oxygen isotopes in N. Borneo

(Georgia Institute of Technology, 2019-12-11) Ellis, Shelby Ann

Oxygen isotope (δ18O) records of speleothem carbonates are a critical terrestrial paleoclimate archive, providing insight into past hydroclimate variations and past changes in atmospheric circulation. Specifically, time series of rainfall and cave dripwater oxygen isotopes (δ18O) provide site-specific assessments of climate or non-climate related signals recorded in stalagmite δ18O used for such reconstructions. However, modern paired multi-year δ18O time series of rainwater and dripwater are limited in the tropical latitudes, an area known to contain regionally-specific atmospheric complexities acting on rainfall δ18O. Furthermore, karst drainage pathways vary significantly within the same cave system, altering the original climate-driven δ18O rainfall signal. In this thesis, I present an extended multi-year study of rainfall and cave dripwater δ18O time series from Gunung Mulu National Park in Northern Borneo to quantify the cloud-to-cave transformation process spatially and temporally across the Mulu karst, building on work previously presented by Moerman et al., 2013 and Moerman et al., 2014. Chapter 1 will broadly cover topics related to how stable water isotopes in rainfall, cave dripwaters, and stalagmites can detect ENSO-driven shifts in the hydrological cycle, building off almost a decade’s worth of modern (Cobb et al., 2007; Moerman et al., 2013; 2014; Partin et al., 2013a) and paleoclimate (Carolin et al., 2013; 2016; Chen et al., 2016; Meckler et al., 2012; Partin et al., 2007; 2013a) observations from a well-established research site in Northern Borneo, Sarawak, Malaysia. Chapter 2 quantifies the rainfall-to-cave dripwater transformation of isotopic climate-signals in the Mulu karst from continuous observations over the last ~12 years. These time series are the longest-running daily rainfall δ18O time series (2006 – 2018) and longest tropical biweekly dripwater δ18O time series (2007 – 2018) globally. Vadose zone mixing translates ENSO-related variations in rainfall δ18O to three monitored cave dripwater δ18O sites. Using two simple modeling techniques, we generated an ensemble of different modeled dripwater time series directly corresponding to local rainfall δ18O, estimating Mulu water takes ~3 to 18 months to transit through the karst. This transit time provides context for what resolution of climate signals can be potentially recorded in local stalagmites employed for hydroclimate reconstructions. Overall, this thesis supports previous interpretations of using the amount effect framework for Mulu stalagmite δ18O records through the multi-year, paired local rainfall and dripwater δ18O time series. This research clearly demonstrates paired rainfall and cave δ18O observations can support more minute interpretations of highly-resolved paleo-ENSO stalagmite records.
Surface Modification of Hard PVC by Molecules with Antibacterial Activity

(Georgia Institute of Technology, 2019-12-09) Pigliautile, Lucrezia

In this work, we present an analysis of different PVC surface modifications, attempted with the intention of attaching antibacterial small molecules, polymers, and oligomers on the plastic. These modifications allowed us to obtain intrinsically antibacterial PVC, which can be potentially applied in healthcare and medical devices. The modification was performed with two procedures, copper-catalyzed azide-alkyne cycloaddition, and nucleophilic substitution. In the first case, the surface of PVC was initially treated with sodium azide to obtain partially azidated PVC, followed by treatment with alkyne-bearing small molecules and polymers. In the second method, the surface was treated with amine-bearing small molecules and polymers, directly substituting the chlorine atoms on PVC. We concluded that the hydrophilicity, the size of the molecule, and the reaction conditions, are the main factors that influence the success of these modifications. Bacteria viability tests were performed on differently-substituted PVC samples, showing good antibacterial activities for PVC surfaces treated with quaternary ammonium salts and acceptable activities for samples modified with polyethyleneimine and oligoethylene glycol.
A study of a fit index for explanatory item response theory models

(Georgia Institute of Technology, 2019-12-05) Handy, Heather

Likelihood ratio chi square tests for nested models are typically used to determine model significance. Multiple correlations of item difficulties estimated with the explanatory predictors are often used to provide further information about model quality. However, the regression approach is not statistically justifiable, since the effective sample size becomes the number of items. Applying explanatory item response theory (IRT) models is advantageous when designing and selecting items. A simulation study was conducted to compare an explanatory item response theory fit statistic, Δ2 (Embretson, 1997; 2016), to traditionally used fit indices (nested model likelihoods and limited information multiple correlations) for assessing model quality. Simulation conditions include varying test length, item difficulty and the number of predictors.
Transforming the preparation of physics graduate teaching assistants

(Georgia Institute of Technology, 2019-12-02) Alicea-Munoz, Emily

Graduate Teaching Assistants (GTAs) are key partners in the education of undergraduate students. In large-enrollment intro physics classes, students spend roughly half of their in-class hours in labs and recitations under the supervision of GTAs. Since GTAs can have a large impact on their students' learning, it is important to provide them with appropriate preparation for teaching. But GTAs are also students themselves -- they have many demands on their time, and not all of them want to become professors after grad school. Therefore, it is crucial that GTA preparation not be a burden but rather be fully integrated into their professional development. The School of Physics at Georgia Tech has been offering a GTA prep course for first-year Ph.D. students since 2013. The majority of these first-time GTAs have no prior teaching experience but consider teaching to be an important part of their professional development as physicists. Through a cycle of implementation and revision, and guided by the 3P Framework we developed (Pedagogy, Physics, Professional Development), the course has evolved into a robust and comprehensive professional development program that is well-received by physics graduate students. We assessed the effectiveness of the course with a combination of surveys, pre/post tests, and student evaluations. We found that GTAs feel better prepared for teaching after going through the Orientation. GTAs consider most useful the course activities in which they can practice and get feedback on their teaching ("Microteaching", "Lab Simulation") and the lessons in which we discuss the pedagogical content knowledge necessary to teach intro physics labs and recitations ("Teaching Physics"). GTAs who participate in the GTA prep course adopt more learner-centered teaching approaches and increase their pedagogical knowledge. They also receive higher end-of-semester student evaluations than GTAs whose first teaching experience predated the establishment of the GTA prep course.
Using Polymorphic Microsatellites to Determine the Population Genetics of Vespula maculifrons

(Georgia Institute of Technology, 2019-12) Thompson, Veronica

Social insects have an interesting genetic history and are studied in order to discern how their social behaviors affects their genetic makeup. The eastern yellowjacket Vespula maculifrons is one such species whose altruistic behaviors and caste system should negatively affect their genetic diversity but instead has fluorished for many years as a dominant species in their ecosystem. We investigated whether V. maculifrons follows the pattern of other social insects in having a small genetic diversity and therefore, a small effective population size. We sequenced seventeen polymorphic microsatellites of V. maculifrons of three different years that were chosen in accordance to the temporal method. We performed a Fixation Index test on the data with the three years as subpopulations in order to determine the differences in allele frequency amongst the groups over time. This was done in order to support our theory that V. maculifrons has a low amount of genetic diversity, which correlates to low amounts of allele fixation, and therefore a low effective population size. We found that the fixation index was significantly low, which supported this idea that not many alleles have gone to fixation. This would indicate that the effective population size is low because the population is still affected by genetic drift. In the future, a concrete calculation of the effective population size will be performed with combinations of multiple equations that can account for the many unique social traits of Vespula maculifrons. This will then help in order to add more information to the gap of knowledge on the fascinating genetic makeup of these unique social organisms.
Testing how methods impact the results of interspecific competition research

(Georgia Institute of Technology, 2019-12) Woo, Esther

There are currently two methods that can be used to measure interspecific competition, pairwise and mutual invasion. Both can be used to generate niche difference (ND) and relative fitness difference (RFD) values, as well as determine if two species are able to coexist. Although the newer method, mutual invasion, has been in use for eight years, there has not yet been a study that compares the two. In order to determine if the method impacts the results found in a study, two simple experiments were conducted concurrently. The five-week long experiment involved determining whether Colpidium striatum and Tetrahymena pyriformis are able to coexist. Upon completion, both methods concluded that they could coexist. Despite reaching the same conclusion, it is still unknown if other species pairings or more complex experiments would alter these results.
Development of a Wireless, Commercial Electromyography System for Use in Athletics and Physical Therapy

(Georgia Institute of Technology, 2019-12) Brooksher, Riley

Electromyography is a muscle activity recording technique that is not often used in a clinical setting due to difficulties in reproducibility. In this paper I aim to create a wireless, wearable system for electromyography. This system is built into a pair of compression shorts, and sends both electromyography and positional data from inertial measurement units to users’ mobile devices. This system is primarily useful in physical therapy and athletic fields, as quantitative information on user gait can improve in the healing and training processes.
Effects of Acute and Chronic Inflammation on Vasopressin Expression in the Paraventricular Nucleus of the Hypothalamus

(Georgia Institute of Technology, 2019-12) Patel, Shivany

Inflammation can lead to a suite of behavioral changes known as sickness behaviors, which have been implicated in the etiology of chronic inflammatory disease. Here, we examine the role of acute and chronic induction of inflammation on vasopressin (AVP) expression in the paraventricular nucleus of the hypothalamus (PVN) of female mice. To test, adult female C57B6/J mice were injected with lipopolysaccharide (LPS) at two different dosages and schedules to induce acute (1.0mg/kg, once) and chronic (0.25mg/kg LPS, eight times) inflammatory responses. The acute dose has previously been demonstrated to induce sickness behaviors, as measured by the open field test and a social interaction test; however, these measures were unaffected by the chronic administration of LPS. AVP mRNA expression in the PVN was measured using fluorescent in situ hybridization (FISH) and fluorescent microscopy. Both the acute and chronic administration of LPS resulted in an increase in PVN AVP expression without a change in the area of this expression. This increase in AVP in the PVN occurred despite the lack of sickness behavior, suggesting that further work is necessary to characterize the role of AVP in the PVN in these chronic and acute inflammatory responses.
A Proposed Improvement for Measuring Hydroxylamine in Seawater

(Georgia Institute of Technology, 2019-12) Sandler, Lily R.

Hydroxylamine is a chemical intermediate in the nitrogen cycle that can quickly react via biotic and abiotic processes to yield nitrous oxide, a potent greenhouse gas. Because of its high reactivity, hydroxylamine tends to be present at low concentrations in aquatic ecosystems. High reactivity and low concentrations also make hydroxylamine difficult to measure. Our goal was to improve the method for measuring environmental concentrations of hydroxylamine. The current method involves converting hydroxylamine to nitrous oxide with ferric ammonium sulfate at low pH and analyzing the nitrous oxide produced by gas chromatography. This method requires a recovery curve because the conversion of hydroxylamine to nitrous oxide does not always go to completion. Here, we propose a new method using a manganese oxide mineral pyrolusite, which rapidly oxidizes hydroxylamine and completely converts it to nitrous oxide, thus eliminating the need for a recovery curve and sample acidification. The method involves (1) crushing and sieving commercial pyrolusite to increase reactive surface area; (2) adding crushed pyrolusite to airtight bottles containing hydroxylamine in artificial seawater at neutral pH; (3) incubating for two hours; and (4) analyzing of the oxidized product, nitrous oxide, by gas chromatography. Hydroxylamine concentrations are calculated from the concentration of nitrous oxide in headspace before and after pyrolusite addition. Addition of crushed pyrolusite resulted in complete conversion of hydroxylamine to nitrous oxide within two hours, whereas minimal conversion occurred without pyrolusite. This method has a shorter reaction time and goes to completion, allowing for more rapid and accurate measurements of hydroxylamine in aquatic environments.