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Speckle decorrelation-based techniques for measuring cerebral dynamics with ultrasound and optics
(2025) Liu, Bingxue; Boas, David A.
Cerebral hemodynamics and cellular dynamics are crucial for maintaining brain health and function. Dysregulation of these processes is implicated in various neurological conditions, such as stroke and neurodegenerative diseases. Non-invasive imaging techniques, including functional ultrasound (fUS) and laser speckle contrast imaging (LSCI), have shown great promise for monitoring cerebral blood flow (CBF) in preclinical animal studies, offering high spatiotemporal resolution over large field of view. However, both methods face limitations in their ability to accurately quantify physiological parameters. fUS, typically relying on power Doppler signals as an indicator of cerebral blood volume (CBV), is often affected by system noise and motion artifacts, while color Doppler-based fUS is limited to detecting axial blood flow, resulting in incomplete assessments of cerebral blood flow speed (CBFspeed). Similarly, conventional LSCI models assume that speckle dynamics arise solely from blood flow, neglecting the potential for measuring cellular dynamics in brain tissue. To address these limitations, this thesis focuses on applying speckle decorrelation-based methods in both fUS and LSCI to improve the quantitative measurement of brain dynamics. First, we introduce an ultrasound speckle decorrelation-based time-lagged functional ultrasound technique (tl-fUS) for the quantification of the relative changes in CBFspeed, CBV and CBF during functional stimulations. Numerical simulations, phantom validations, and in vivo mouse brain experiments were performed to test the capability of tl-fUS in accurately parsing and quantifying these hemodynamic parameters, demonstrating superior performance compared to conventional Doppler-based fUS techniques. Next, we developed a multi-dynamics laser speckle contrast model that incorporates both fast blood flow dynamics and slow tissue dynamics. To enhance the sensitivity to slow tissue dynamics, we built a short-separation speckle contrast optical spectroscopy (ss-SCOS) system with point illumination and point detection using linear fiber arrays. Finally, an epi-illumination-based wide-field LSCI system was developed to map both fast and slow speckle dynamics. The system was demonstrated in transient and permanent stroke models, indicating slow tissue dynamics as a novel and important biomarker for studying stroke evolution and recovery.
Advanced quantum structures for infrared detectors
(2025) Glennon, John; Bellotti, Enrico
Type-II superlattices (T2SLs) have emerged as promising alternatives to the more established bulk material systems for infrared (IR) photodetection. This is due to predicted fundamental advantages, such as the tunability of the band gap and theoretically reduced Auger recombination rates. However, the superiority of these materials has not been experimentally realized, prompting the need for further investigation. A bottleneck in the development of improved superlattice (SL) structures and devices is the cost in time and resources required to prototype and characterize these materials as well as incomplete knowledge of the material properties and physical phenomena that characterize these structures. Therefore, the field would greatly benefit from simulation methodologies that enable the development of advanced T2SL materials. In this work, the field of IR photodetection is reviewed highlighting the most common T2SLs structures currently being experimentally implemented. A quantum transport model that includes the necessary physical mechanisms to model carrier transport in these structures will be presented. The results of an investigation on the extraction of vertical carrier mobility, a property important for carrier collection, from quantum transport simulations is presented for an example T2SL. It is demonstrated thatcarrier transport in these structures can be highly coherent. In this case, the apparent mo-bility is suppressed due to ballistic resistance, requiring care when predicting the intrinsic mobility of these materials. The best method of mobility extraction is one that considers the dependence of the resistance on device length. This method was applied to predict the quantum efficiency (QE) in curved focal-plane arrays composed of n-type mid-wave InAs/InAsSb and InAs/GaSb structures subjected to the effects of superlattice disorder and external strain imposed by the curving procedure. It is demonstrated that the external strain has a minimal impact on the QE relative to disorder in both structures suggesting the device design could be viable. Additionally, it was found that large magnitudes of positive axisymmetric strain could result in enhanced hole transport. Finally, a comprehensive investigation is presented that probed for optimized n-type long-wave InAsSb/InAsSb SL
structures, a material known to result in low QE devices, for various substrate lattice constants. Several structures were found demonstrating hole mobilities with greater resilience to SL disorder providing potential candidates for future prototyping.
Impact of waves and storms on salt marsh erosion and sedimentation dynamics
(2024) Houttuijn Bloemendaal, Lucila J.; FitzGerald, Duncan
Salt marshes are dynamic coastal environments that continuously undergo lateral and vertical changes due to erosion and sedimentation dynamics that are mediated by physical and biological processes. This dissertation focuses on edge erosion and the drivers behind this form of marsh loss, as well as sedimentation of the marsh platform from storms and the potential sources of these sediment influxes. By studying these erosion and sedimentation dynamics in a variety of marshes, this dissertation contributes to our understanding of sediment movement in marsh systems and the drivers of marsh loss and resilience. The marsh edge is vulnerable to wave attack, which can dislodge sediment or induce mass failure through undercutting and destabilizing action of the edge. Vegetation and geotechnical properties affect the erodibility of the marsh edge, and all these factors interact to enhance or mitigate edge erosion and produce certain marsh edge morphologies. The first chapter of this dissertation investigates these different parameters and their relationship to the type and distribution of edge erosion occurring in the Great Marsh, Massachusetts. This work demonstrates that there is no clear relationship among wind fetch, geotechnical properties, and the type of edge erosion observed because of heterogeneity of the marsh. Marsh edges can erode in both exposed and sheltered areas, and the geotechnical characteristics of the marsh edge do not serve as indicators of edge erosion. Parameters and processes beyond those generally ascribed to be the drivers of edge erosion may therefore be responsible for marsh loss. The second chapter takes a closer look at the relationship between waves and marsh shoreline retreat, as the nature of this relationship can help predict marsh loss under varying wind and wave conditions, as well as have implications on the impact of storms on edge erosion and marsh loss. This study shows that there is no universal or generalizable linear relationship between wave power and retreat as previously suggested, but rather the relationships between these parameters are site-specific and are often not linear at all. As a result, in one marsh, storms may have an outsized impact on retreat, while in another marsh more moderate wind-wave conditions may contribute to most of the retreat. Thus, it is important to calibrate these relationships for each marsh to fully constrain marsh loss due to wave attack and predict future marsh erosion. This work further highlights the importance of utilizing statistically robust analyses and regressions to investigate these relationships.
Whereas storms contribute to marsh loss via edge erosion, they can also enhance vertical accretion and resilience of marshes to sea level rise (SLR) through storm-driven sediment transport and deposition. Major storms such as hurricanes can provide most of the inorganic sediment delivered to the marsh platform, though the source of these sediments is less understood for southeastern USA. Chapter 3 of this dissertation characterizes foraminifera communities in Hurricane Irma deposits in Sapelo Island, Georgia and compares them with the communities of surrounding sediment reservoirs to investigate the provenance of these storm-derived deposits. The foraminifera in the hurricane deposits resembled the foraminifera found in the surrounding marsh, rather than nearby sediment reservoirs such as tidal flats, channels, and offshore sediments. These similarities between the storm and marsh foraminifera assemblages are attributed to a mix of two processes: resilience of marsh foraminifera and rapid recolonization of these communities in the storm deposits following the passage of Hurricane Irma, and some reworking of marsh sediments into the storm deposits during the hurricane’s storm surge. The study also assesses the utility of foraminifera in identifying storm deposits, which has implications for the sensitivity of foraminifera paleostorm studies.
The broken book: reading and materializing Middle English literary compilations
(2024) Hertz, John J.; Appleford, Amy
This dissertation explores the multifaceted relationship between medieval books, their materiality, and the networks of human and non-human actors that shape their existence. Drawing from New Materialist studies and Bill Brown's "Thing Theory," it examines how medieval readers interacted with texts and material books, acknowledging the intricate web of people and objects involved in their production and reception. By focusing on the materiality of medieval books, this dissertation seeks to unveil the often-overlooked connections between various human and non-human actors involved in book production and reading. Each chapter delves into a specific case study, starting with the Auchinleck Manuscript, an early compilation of Middle English texts and romances. This chapter argues that the manuscript's composite nature reflects and encourages a similar mode of self-fashioning in its readers, linking English identity formation to the compilation of texts. The second chapter explores the Oxford Group Manuscripts and Chaucer's dream vision poems. It investigates how these manuscripts, produced in fascicles, parallel the imaginative process and recombination of sensory data in Chaucer's dream narratives. Chapter three examines the "compilation narratives" framing Thomas Hoccleve's poems, emphasizing their depictions of scribal labor and textual communion. Comparing these narratives to Hoccleve's holographs reveals the intersections between authorial self-fashioning and fifteenth-century bookmaking. The final chapter analyzes Sir Thomas Malory's Le Morte Darthur in its earliest forms, the Winchester Manuscript and William Caxton's printed edition. It argues that Malory's work is fundamentally a compilation, and that Caxton's edition represents a broader shift towards author-centric and commodified books. The chapter also explores the paratextual features of Le Morte Darthur in its manuscript and printed forms to discern the impact they would have had on the reception and interpretation of the text.
This dissertation challenges traditional notions of authorship and intentionality in book production, highlighting the agency of material objects and their role in shaping the meaning and reception of medieval texts. It offers new understandings of the dynamic interplay between human and non-human actors within the networks that shape late medieval English book culture.
The causal impact of user-centered counseling on women's reproductive health outcomes: evidence from Malawi
(2024) Kurt, Yunus E.; Fernandez-Val, Ivan
Nearly half of all pregnancies in the U.S. —and comparable numbers worldwide—are unintended, leading to adverse health outcomes for mothers and children, financial constraints and family instability, diminished educational and developmental outcomes for children, and worse labor market outcomes for women. Effective family planning counseling can mitigate these consequences by correcting misinformation and misconceptions around contraceptive methods, and improve overall contraceptive decision-making for women. User-centered counseling (UCC) refines the standard counseling approach by first eliciting women’s contraceptive preferences, then tailoring the session to discuss a subset of methods aligned with those preferences. We conduct a randomized controlled trial in Malawi involving over 700 women, where we evaluate the effects of UCC alongside partner invitation (PI), where women are encouraged to involve their partners in the counseling process. In the first chapter, we study the impacts of both interventions on several outcomes around contraceptive method use dynamics and fertility. We find that women encouraged to involve their partners tended to move from injectables to implants, suggesting a partner-driven preference. However, UCC appears to neutralize this effect. Contraceptive consistency, proxied by the maximum number of consecutive months women use same method or number of months women use any method, was significantly influenced by UCC, fostering more regular use of contraceptives, although it was somewhat mitigated when combined with PI. In terms of fertility outcomes, we observe that UCC seems to reduce pregnancies and births, but when combined with PI, the effect is the opposite. Finally, neither UCC nor PI significantly alter the likelihood of discontinuation. In the second chapter, we explore how women’s preferences over contraceptive methods evolve and whether method uses are concordant with these preferences or not. We first document that preferences vary significantly in both the short and long term. We then observe that both user-centered counseling and partner invitation interventions have minimal impact on aligning women’s contraceptive preferences with their actual usage, both in the short and long term. In the third chapter, we apply two methods to examine the heterogeneous impacts of UCC on a range of family planning outcomes. Firstly, we utilize the Sorted Effects method, which involves estimating and ordering partial effects based on covariates, graphically representing this variation, and also comparing the mean characteristics of the most with the least affected women. Secondly, we adopt the Generic Machine Learning method, suitable for our data’s high-dimensional nature, which helps estimate features (Best Linear Predictor (BLP) and Group Average Treatment Effects (GATES)) of the conditional average treatment effects without relying on predetermined covariates. Nonetheless, our experiment’s power to uncover meaningful heterogeneities in the impact of UCC is limited.
Population genetics, environmental tolerances, and natural variation in infection frequency of the parasitic anemone, Edwardsiella lineata
(2024) Lee, Joanna Claire; Finnerty, John R.
Mnemiopsis leidyi, the sea walnut, is one of the most destructive invasive species in the world. The ctenophore has broad environmental tolerances, a high rate of zooplankton consumption, extensive regeneration capabilities, and extraordinary fecundity. While there is a substantial body of research on M. leidyi’s role as a predator of zooplankton and as prey to the ctenophore Beroe ovata, only a few studies have examined M. leidyi’s relationship with its parasite, the lined sea anemone, Edwardsiella lineata. Previous research has shown that E. lineata may be exerting top-down control on the ctenophore in areas where present along the Northwestern Atlantic; the parasite has not established a population in M. leidyi’s invasive range. While a handful of studies have examined the ecological relationship between host and parasite, all studies have taken place at the same site, Woods Hole, and some failed to report key parameters such as host size and parasite number. More detailed examinations of this relationship are necessary to understand the parasite’s potential for controlling host populations in both native and European waters and how this control may be affected under various abiotic conditions. In my dissertation I performed three studies exploring the ecological relationship between M. leidyi and E. lineata. First, I profiled the variation in infection frequency in populations in Massachusetts and Rhode Island and examined the relationship between host size, parasite load, and seasonality. My results show that in natural populations, infected ctenophores are larger than non-infected conspecifics. The pattern of infection was also highly variable across sites and time. Second, I tested the temperature and salinity tolerances of E. lineata larvae to determine if certain conditions, such as those found in the invasive range of M. leidyi are refuges for the host from parasitism. My data indicate that temperature and salinity conditions alone will not prevent E. lineata from establishing a population in Europe. However, developmental outcomes and survival are both reduced at lower salinities and higher temperatures. Finally, using a RAD-seq approach I profiled population connectivity between juvenile parasite and adult polyp populations of E. lineata in Massachusetts and Rhode Island. E. lineata populations were found to be panmictic like host M. leidyi, though some structuring appeared between parasite and polyp populations. While asexual reproduction was seen in polyp mats, none was found within hosts.These data help contribute to the wider body of research on the M. leidyi-E. lineata system and also provide data on sea anemone genetic structure, which is currently understudied. I suggest that future studies examine cues for asexual reproduction in both the parasite and host and profile infection frequency and genetic structure in populations further south.
University housing, sense of belonging, and self-esteem
(2023-10-21) Culver, E.; Jumani, S.; Kuli, C.; Paquette, S.; Singhal, A.; Zeiler, L.; Mello-Goldner, D.
Birth order and personality: a comparative analysis
(2024-10-26) Fortner, Tabitha; Mello-Goldner, Diane
Conformity and its impact on purchasing decisions on social media
(2024-10-26) Weiss, Andre; Belyakov, A.; Chari, Y.S.; Mathew, A.; Pauly, T.; Perches, M.; Mello-Goldner, Diane
Harmony or tension: investigating the interconnected realms of Type A/Type B personalities, self-esteem, and fear of success
(2024-10-26) Anastacia, Anessa; Henson, Liam; Paredes, Manuel; Turabelidze, Stacey; Weiss, Stephanie; Mello-Goldner, Diane