High frequency oscillatory ventilation (HFOV) relies on low tidal volumes cycled at supraphysiologic rates, producing fundamentally different mechanisms for gas transport and exchange compared to conventional mechanical ventilation. Despite the appeal of using low tidal volumes to mitigate the risks of ventilator- induced lung injury (VILI), HFOV does not improve mortality in most clinical applications. One possible explanation for this is that HFOV distributes flows throughout the lung in a non-uniform and frequency-dependent manner, especially in the presence of mechanical heterogeneity. This thesis is a systematic investigation of the relationship between carbon dioxide elimination and frequency content during oscillatory ventilation, with emphasis on the frequency- dependent effects of mechanical heterogeneity and various gas transport mechanisms. A computational model consisting of an anatomically-structured airway network was used to simulate ventilation distribution and gas exchange in a canine lung. These simulations were validated against theoretical predictions and experimental data for eucapnic oscillatory ventilation. The model was also used to assess the impact of mechanical heterogeneity on ventilation distribution and gas transport. Simulations demonstrated a critical transition at the resonant frequency, above which the ventilation patterns became spatially clustered and frequency-dependent. Finally, the model demonstrated that pairs of oscillatory frequencies could yield eucapnic conditions with less potential for VILI compared to traditional single frequency HFOV. These results illustrate the importance of frequency selection in managing the distribution of ventilation and gas transport in the heterogeneous lung, and suggest that the frequency content in oscillatory waveforms may be optimized to achieve eucapnic gas exchange using less injurious ventilation. / 2017-10-27T00:00:00Z

Advancements in Li-ion batteries are needed especially for the development of electric vehicles and stationary energy storage. Prior research has shown mesoscale variations in electrode electronic conductive properties, which can cause capacity loss and uneven electrochemical behavior of Li-ion batteries. A micro-four-line probe (μ4LP) was used to measure electronic conductivity and contact resistance over mm-length scales in that prior work. This work describes improvements to overcome the challenge of unreliable surface contact between theμ4LP and the sample. Ultimately a second generation flexible probe called the micro-radial-surface probe (μ4LP) was designed and produced. The test fixture was also optimized to obtain consistent contact with the new measurement probe and to perform measurements at a lower force. The μ4LP was then used to study the effect of heterogeneity on calendering, which is the compression of electrode films to obtain a uniform thickness and desired porosity. The thickness, electronic conductivity and contact resistance of two cathodes and one anode were measured before and after calendering. The the spatial standard deviation divided by the mean was used as a measure of heterogeneity. The results show variability in conductive properties increased for two of the three samples after calendering, despite the increased uniformity in thickness of the electrodes. This suggests that additional quality control metrics are needed besides thickness to be able to identify uneven degradation and produce longer lasting batteries.

Leaders in the field of home visiting and family support research have indicated that the inclusion of home visiting in comprehensive services for low-income families with young children can play a key role in improving a wide variety of outcomes for at-risk children and their families. These recommendations have been based in part on selected empirical findings from the home visiting literature. However, synthesis of empirical findings has proven difficult, due to the heterogeneity of this population and the diverse applications of home visiting as a service delivery strategy. The present meta-analysis examined a representative sample of the peer-reviewed literature to provide a comprehensive, quantified description of the features and findings of this literature. The four research questions addressed by the meta-analysis provide a framework for this description. The first research question concerned a description of research designs and methodological features found in the literature. The second and third research questions concerned, respectively, descriptions of the samples and interventions employed in primary studies. The final research question concerned the examination of those domains in which primary studies measured outcomes, and the quantification of outcomes in terms of standardized mean difference effect sizes. Summarization of primary studies' methodological features illustrated specific issues that may be addressed in the design of future home visiting research, and laid a basis for the examination of meta-analysis findings. The composition of primary studies' samples reflected the heterogeneity expected from a population defined by a parameter as broad as "low-income," yet included lacunae that may represent subgroups among the poor that are not being studied. Data providing an assessment of several types of intervention features have implications for questions of treatment efficacy, and for future home visiting research. Mean effect sizes in several domains were found to have a magnitude of practical significance for child and family outcomes. Findings of this project provide a structure for continued meta-analysis of this body of literature, and highlight potential areas for further primary research. Meta-analysis data lend support to previous recommendations, as well as point out gaps in our knowledge.

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Understanding the relationship between heterogeneity, biodiversity and ecosystem function is an active focus of ecological research that has direct applications to the formulation of sustainable, science-based, watershed conservation plans. Here, I applied ecological theory on heterogeneity to the expansion of North American beaver to test hypotheses about physical habitat and fish biodiversity at a riverscape scale. To test these hypotheses (Chapter 4), I first addressed two methodological issues (Chapter 2, 3). By evaluating three types of gear at three levels of effort in a randomized block design over 4 replicate days, I show that 10 minnow traps, 2 hoop nets and 20 m of electrofishing captured most fish species within a 30-m sampling area (Chapter 2). Multiple statistical measures provided similar information, therefore I used general indices (richness, diversity), ecological guilds (flow based), and select multivariate analyses (DCA) to summarize fish communities (Chapter 3). I used these methodological insights to test ecological hypotheses by collecting habitat and fish data at all beaver dams (n = 15) and select control sites (n = 9) in Fish Brook, a coastal watershed in northeastern Massachusetts. From these data, I gained six basic and applied insights. First, beaver dams were distributed throughout the stream network. Second, at a local scale, beaver dams created more habitat heterogeneity than control sites. Specifically, beaver dams created four types of habitat alterations based on upstream-downstream differences in stream width, depth, velocity, and substrate. Third, richness and diversity of fish species around beaver dams were linked to habitat heterogeneity. Fourth, the mechanisms by which beaver dams altered fish biodiversity were mediated through habitat changes at the beaver dam patch boundary. Upstream of the dam macrohabitat guilds occupied the lentic areas, while below dams, fluvial fish guilds used shallow, faster water. Fifth, fluvial species responded the most dramatically to these habitat changes. Finally, in a system depauperate of lotic habitat, fluvial habitats created below beaver dams provided an important refuge for native stream fish. These source areas can increase resiliency and maintaining them may be useful for sustainable watershed conservation plans in these types of systems.

Thesis advisor: Stefano Anzellotti / Autism Spectrum Disorder (ASD) displays uniquely in every individual, creating disparities in symptom severity, genetics, and functional connectivity. Examining the relationship between genetic and functional connectivity variability could help to better understand individual differences in ASD. From this, improved diagnosis, treatment, and understanding of ASD can be developed. To resolve individual differences in symptom severity and presentation, I generated matrices of subject functional connectivity data and compared this to gene expression maps. Multivariate regression analysis was performed on the data to anticipate ASD symptoms from these correlation matrices and to establish which genes have the largest impact on these predictions. The ANOVAs ran on the data were not significant, but there were several genes implicated in specific aspects of ASD. STX1A, MVP, CDKL5, and RABEP2 were the only genes correlated across more than one subtype of ASD. These results pave the way for future research to investigate the roles of these genes in a larger size of ASD subjects. / Thesis (BS) — Boston College, 2023. / Submitted to: Boston College. College of Arts and Sciences. / Discipline: Departmental Honors. / Discipline: Psychology and Neuroscience.

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