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Spatiotemporal dynamics of groundwater flow and transport along Arctic coasts: exploring subterranean estuaries, fluxes, and seasonal drivers
Full text linkSubmarine groundwater discharge (SGD) along coastlines serves as a potent, but invisible conduit for materials and energy, and therefore, has significant implications for coastal biogeochemistry. SGD is particularly crucial in the Arctic subterranean estuaries (STEs), as it interacts with organically rich soils and thermally vulnerable ice-bounded permafrost before reaching the freshwater-saltwater mixing zone nearshore. Yet, its magnitude has been largely downplayed and its flow and transport dynamics remain understudied. The distinct hydrological and climatic processes imposed on Arctic STEs during thawing, summer, freeze-up, and winter periods differentiate these systems from well-studied STEs of temperate regions. With changing climate, altered thawing period onset, prolonged above-zero temperatures (i.e. extended summers), increased storm activities due to decreased sea-ice extent, and enhanced degradation of terrestrial and coastal permafrost are expected to cause major changes in groundwater storage, and potentially, discharge. Therefore, improved comprehension of coastal groundwater hydrology is essential for predicting future changes in Arctic hydrology and ecosystems. This dissertation investigates the spatiotemporal dynamics of groundwater flow and transport along the lagoon coasts of the Alaskan Beaufort Sea. Specifically, this work aims to constrain (1) how important in magnitude the fresh terrestrial SGD and organic-inorganic matter fluxes are for Arctic coastal water budgets and biogeochemistry in the summer, (2) how the hydro-thermal regime of coastal supra-permafrost aquifer evolves over short (hourly-daily) and seasonal timescales, and (3) how major climatic and oceanic factors influence variations in Arctic coastal groundwater availability and discharge. The chapters utilize geophysical, hydraulic, thermal, and chemical field data collected along shore-perpendicular piezometer transects installed in Kaktovik and Simpson Lagoons along the Beaufort Sea coast in the North Slope of the Alaska. Ex situ techniques including numerical (groundwater flow-transport) models (Chapters 2 and 3) and explainable artificial intelligence tools (Chapter 4), further supported our observations and elevated understanding in multi-dimensional system dynamics. The studies indicated that Arctic STEs deliver significant amounts of fresh SGD, dissolved organic carbon, organic nitrogen, and inorganic carbon (i.e. CO₂) in summer. Heat advection due to flow of groundwater was found significant for the thermal regime of STEs, and thus, the distribution of ice nearshore. Terrestrial fresh groundwater availability and discharge were sporadic, abundant, and absent in thawing, summer, and early freeze-up seasons, respectively. They were majorly influenced by potential evaporation in the daily and monthly time-scales, and by precipitation on the daily event-based scale. Easterly-westerly winds near coastlines were a major marine driver of SGD.Earth and Planetary Science
Development of a machine-learning platform for the autonomous analysis of 3D+T calcium imaging data
Full text linkThe role of live imaging within the biological sciences is to observe a system and its dynamic evolution over time. To understand neural pathways and signaling, Ca²⁺ imaging is a key technology as it allows for the non-invasive observation of neural activity. Advances in high-speed imaging has led to the creation of Ca²⁺ imaging systems that can capture all neurons in the nervous system of animal models such as Caenorhabditis elegans. While tens of minutes of continuous imaging can be performed, the manual analysis takes tens of hours and limits the throughput of functional Ca²⁺ imaging studies. This dissertation develops a machine learning platform specialized for the processing of volumetric videos. Enabled by work in low-rank 4D convolutions, our platform consists of two key technologies: a self-supervised video denoising method to increase the underlying data quality and a two-stage object detector for neuron recognition and tracking. We package these items in an interactive software such that advanced computational tools are accessible irrespective of computational experience. We develop and apply this platform to twenty-minute recordings of the model organism C. elegans. The raw volumetric video, acquired by a laser-scanning confocal microscope, is first restored with our self-supervised denoising method. For the dimmest neurons, our method increases the signal-to-background ratio by more than 30 times as compared to the raw data. This data is then processed by a novel-two stage object detector that identifies and segments objects in 3D. Further, a contrastive tracking loss is included as it allows for this model to learn both segmentation and tracking in an end-to-end fashion. Applied in this fashion to twenty-minute recordings, our platform accurately detects 245 of the 302 neurons in the C. elegans. Requiring no human intervention, approximately 80% of the nervous system can be detected and extracted in 6-8 hours on a local desktop.Biomedical Engineerin
Relating GNSS and VLBI antenna positions through co-observation of radio frequency sources
Full text linkTerrestrial References Frames (TRFs) underpin all modern navigational techniques, which depend on the accuracy and stability of these reference frames to derive consistent positions that can be related to each other at different epochs and locations. Many important areas of science also depend on the long-term stability of station positions such as studies of sea level rise, ice mass balance, glacial isostatic adjustment, and tectonic plate motion. The most precise and accurate TRFs consist of observations submitted by multiple geodetic techniques that are combined through local tie vectors. These local tie vectors are high accuracy vector differences in position between the reference points of instruments that contribute to each of these techniques individually, occurring at specialized locations called collocation sites where the instruments are placed close to each other.
For many years, these local tie vectors have been produced primarily through one technique–laser ranging between reflectors placed near the reference points of the instruments with a total station. This dissertation lays out the necessary measurement theory, digital signal processing techniques, high-fidelity models, and experiment setup to realize an entirely new methodology of producing these local tie vectors via co-observation of radio frequency sources with a Global Navigation Satellite Systems (GNSS) antenna and receiver and a Very Long Baseline Interferometry (VLBI) radio telescope. The technique is then thoroughly demonstrated through a series of experiments with GNSS antennas colocated with telescopes of the Very Long Baseline Array (VLBA). In preliminary experiments, it is demonstrated that a GNSS antenna and receiver that can produce baseband samples can co-observe with a radio telescope to detect natural radio sources more than 5 billion light years from the Earth in addition to GNSS satellites. Using GNSS processing techniques to account for clock variation, it is also shown that coherent accumulations of up to 20 minutes are possible with a rubidium frequency standard that is much cheaper than the typical H maser used in
VLBI processing.
A second set of experiments intended for precision geodesy includes the estimation of the first GNSS-VLBI tie vectors directly through the reference points of the participating instruments with both GNSS and VLBI analysis techniques. Preliminary results suggest that on the sub-100 m baselines used in these experiments, the technique may yield ties of mm-level accuracy and precision. Upcoming experiments in late 2025 promise to bring this technique to each telescope in the Very Long Baseline Array and to produce the first repeatability measurements for these tie vectors. Through GNSS analysis via correlation of the samples recorded by the radio telescope with the pseudorandom noise sequence of an observed GNSS satellite, we have shown that any radio telescope with an L band feed can use this technique to produce tie vectors with any colocated GNSS receiver, including International GNSS Service (IGS) stations. This technique is thus easily extensible, and the software developed for this effort can be used to produce many more ties worldwide at geodetic colocation sites.
The technique also serves as a direct comparison between the signal processing and data analysis techniques used in the GNSS and VLBI communities. This inter-comparison has yielded a robust phase wind-up model applicable to both radio telescopes and GNSS antennas and observations of both natural radio sources and transmitting satellites. In addition, for the first time rigorous and automated integer ambiguity resolution techniques are adapted from the GNSS community to
consistently resolve the phase ambiguity in both satellite observations and traditional geodetic VLBI observations of natural radio sources. This methodology can be adopted in the wider VLBI community to make the use of phase delay measurements a routine part of geodetic processing.Aerospace Engineerin
Microwave impedance microscopy for the characterization of dielectrics, ferroelectrics, and amorphous semiconductors
Full text linkThe invention of field-effect transistors in the last century has led to substantial technological advances, which greatly changed our daily life over the past few decades. As we enter the era of artificial intelligence, the quest of ever-increasing computing power has set high demands for new materials, new architectures, and new characterization tools. The traditional way of characterizing device performance is electrical transport, such as the measurements of current-voltage relation or capacitance-voltage relation. However, this type of method may suffer from contact issues, making it difficult to obtain the intrinsic properties. In this dissertation, I will use three examples to show how we implement microwave impedance microscopy (MIM) to extract material information that is less likely accessible by conventional techniques. The first example is to evaluate the dielectric constant of ultrathin dielectric flakes. By combining MIM scanning and COMSOL simulation, we successfully extracted the permittivity values of several high-κ oxides and low-κ polymers. The thinnest flake we measured is about 2 nm. The second one is to image the coexistence of polar and non-polar BiFeO₃ phases. The contrast in MIM-Im and MIM-Re channels can be attributed to the difference in permittivity and AC conductivity between the two phases, respectively. The extracted permittivity values match well with results from other independent experiments. The AC conductivity is almost unchanged for a broad range of frequencies, confirming that it is electronic in nature. The last one is to study the charge transport of amorphous InGaZnO (a-IGZO) thin film transistors. We studied the equilibrium and transient states of the devices by applying constant and pulsed gate bias, respectively. Through the analysis of MIM images and transient signals, we visualized the potential landscape, identified two transport mechanisms, and extracted the characteristic length and time scales. All results provide new insights into the properties of these advanced materials, which are important for their future applications in nanoscale transistors, memories, and displays. The ideology can be generalized to the characterization of other newly discovered materials and devices as well.Physic
InSb-based dilute-bismide alloys for long-wave infrared sensing
Full text linkDilute-bismide alloys have received significant attention over the past few decades due to the rather dramatic bandgap reductions caused by the incorporation of small concentrations of bismuth into traditional III-V alloys. This presents unique opportunities in strain and bandgap engineering for optoelectronic devices; in fact, bismuth-induced bandgap reductions can be leveraged to access technologically significant wavelength ranges for sources and emitters with III-V-Bi materials. In particular, dilute-bismide alloys have the potential to enable access to the long-wave infrared (LWIR), a spectral region with numerous applications in gas sensing, astronomical imaging, and thermography. Currently, LWIR devices continue to be dominated by the material system mercury cadmium telluride (Hg[subscript 1-x]Cd[subscript x]Te). As this material system not only suffers from numerous growth and fabrication challenges but is also comprised of highly toxic constituent elements, there is strong motivation for developing a direct transition, lattice-matched III-V alloy with tunable bandgap energies across the LWIR. Since InSb possesses the narrowest bandgap energy of any traditonal III-V binary alloy, InSb-based dilute-bismide alloys can be expected to span the entire LWIR with minimal bismuth incorporation. As compared to wider bandgap host matrices, InSb and III-Bi materials boast relatively similar properties including bond strengths, electronegativities, and optimal growth temperatures. In turn, this may enable significant bismuth incorporation into InSb without the extreme material and optical degradation often seen in other dilute-bismide alloys. Despite these advantages, InSb[subscript 1-x]Bi[subscript x] and antimony-rich InAs[subscript y]Sb[subscript 1-x-y]Bi[subscript x] remain relatively underexplored and many fundamental material properties have yet to be experimentally investigated for these InSb-based dilute-bismide alloys. This work seeks to optimize the growth window for InAs[subscript y]Sb[subscript 1-x-y]Bi[subscript x] and gain a deeper understanding of the alloy's structural and optical properties to evaluate the material system's potential for high-performance optoelectronic devices. In particular, this work demonstrates, for the first time, InSb[subscript 1-x]Bi[subscript x] with unity-sticking bismuth incorporation as a route to photoluminescence at extended wavelengths beyond that of InSb. Building on this, the additional incorporation of small amounts of arsenic is shown to restore lattice-matching to InSb substrates, which is of paramount importance for photodetectors. To wholly evaluate the potential of this material system for optoelectronic devices, prototype photodetectors are designed, fabricated, and characterized showcasing extension in cutoff wavelength beyond that of InSb photodetectors.Electrical and Computer Engineerin
Emission and dispersion models to assess impacts of unconventional oil and gas development on air quality and community exposures
Full text linkThe rapid expansion of unconventional oil and gas development (UOGD) in the United States has resulted in detrimental impacts on climate, air quality and human health. To comprehensively assess the impacts of UOGD on air quality and community exposures, better characterization of emissions from UOGD is needed. However, the complexity and heterogeneity of UOGD operations make the characterization of emissions difficult and limited. UOGD operations emit various pollutants, including several criteria air pollutants and hazardous air pollutants, with sources and characteristics varying significantly between and within sites. Transport and transformation of these pollutants further complicates source attribution and exposure assessment. To accurately estimate impacts of UOGD emissions and attribute ambient concentrations of pollutants to sources, fine scale spatial and temporal characterization of these emissions is required. This dissertation describes the development of spatially and temporally resolved emissions of Nitrogen oxides (NOx) from a highly localized and transient UOGD source, hydraulic fracturing. These fine scale emissions are coupled with a chemical transport model to assess their impacts on regional air quality. Accurate spatial and temporal allocation of NOx emissions from hydraulic fracturing leads to increased predicted ozone formation in Eagle Ford Shale of Texas, a NOx-limited region. Frameworks to simplify atmospheric dispersion models for use in exposure assessment and measurement reconciliation are also developed. In Eagle Ford Shale, modeling dispersion from oil and gas sources within a 50-100 km radius of a receptor site is necessary to fully explain concentrations at that site. A space-weighted source aggregation method within this radius can reduce the number of sources by an order of magnitude, while maintaining accuracy in exposure predictions. Finally, a nested modeling domain for dispersion modeling is proposed, which aims to capture local effects and regional trends. These frameworks will contribute to a community model predicting exposures from UOGD.Chemical Engineerin
On neural mechanisms for relaying sensory inputs
Full text linkSensory systems must maintain sensitivity and selectivity across a broad range of environments and behavioral contexts to compute meaningful representations of the world. The relay of sensory information from peripheral receptors to central brain areas is a dynamic process, as the neural code shifts with both environmental and internal states. While these adaptations allow organisms to navigate the range of contexts which they encounter, dynamic sensory relay also raises the question of how cortical areas construct reliable sensory representations across conditions.
The clearest example of the dual challenges of maintaining sensitivity and selectivity in sensory systems comes from luminance adaptation in the visual system. To maintain sensitivity across the massive range of luminance intensities encountered between midnight and midday, the retina transitions between rod and cone-mediated phototransduction. This adaptation is known to shift the selectivity of retinal ganglion cells, which relay the output of the retina to central brain areas. In the first part of this dissertation, I show how thalamic and cortical populations encode features of the visual world across luminance conditions. I present data from large populations of simultaneously recorded neurons in the mouse to show that visual cortex generates a representation that is invariant to the absolute intensity of peripheral signals. I show how a physiologically constrained model of the visual pathway provides a mechanism by which visual cortex generates a luminance-invariant code despite changing receptive fields and interneuronal correlations at the periphery.
In addition to exploring sensory relay across environmental conditions, in the second part of this dissertation I explore how sensory relay is disrupted in disease. Typical thalamocortical relay is characterized by two distinct firing modes- burst and tonic. These two firing modes are hypothesized to function in tandem to relay distinct sensory information to cortex. Using population recordings in mouse thalamus, I quantify the distribution of firing modes and synchrony across neurons. I also show how firing mode is modulated by behavioral state. Finally, I show that in Fragile X mutant mice, the typical distribution of thalamic firing modes is disrupted, which may contribute to the abnormal cognitive phenotype of individuals with FX.Psycholog
Intricate interaction of dietary saturated fat intake and plasma triglycerides on memory performance in middle-aged adults
Full text linkAlzheimer's disease and related dementias are projected to triple by 2050. Addressing modifiable health and lifestyle factors is crucial for prevention and reducing the associated public health burden. This study investigates the interaction between triglyceride levels and dietary intake and quality on memory performance in middle-aged adults at heightened risk for metabolic health issues. Community-dwelling adults aged 40-65 participated in this cross-sectional study. Participants were excluded if they had a history of neurological or psychiatric disease, or were smokers. Dietary intake was self-reported via a 3-day food record. Serum triglyceride levels were measured. Neuropsychological testing assessed memory performance. Cross-sectional regression analyses examined the interactions between dietary intake and quality with triglyceride levels on memory performance in 146 middle aged adults with heightened cardiometabolic risk. The analysis revealed a significant interaction between triglyceride levels and the ratio of dietary saturated fat to total caloric intake on memory performance (β = -0.087, p = 0.022). Participants with elevated triglyceride levels and a higher ratio of saturated fat in their diet performed worse on memory tests. Conversely, those with elevated triglycerides but a lower ratio of saturated fat in their diet exhibited better memory performances. Higher adherence to USDA dietary guidelines, indicated by higher Healthy Eating Index 2020 scores, was associated with better memory performance (β = 0.018, p < 0.002), regardless of triglyceride levels. Thus, diet quality, measured by adherence to dietary guidelines, is broadly beneficial for cognitive health. Although, the combination of elevated triglyceride levels with a high ratio of dietary saturated fat intake is significantly associated with poorer memory performance in midlife adults. Precision nutrition strategies to reduce the ratio of saturated fat to total caloric intake guided towards midlife adults with elevated triglyceride levels may mitigate memory-related cognitive decline and improve brain health.Psycholog
From hobby to side hustle : fan artist professionalization in the post-network era
Full text linkIn the U.S. broadcast industries, there exists a long history of commodifying fan art and co-opting fan labor for promotional purposes, whether to increase market penetration, lower advertising cost, demonstrate audience value, leverage subcultural capital, or all of the above. However, in the wake of post-Fordist production practices, neoliberal market logics, and post-exposure marketing challenges, that commodification has escalated. Industrial perceptions of and approaches toward fan art have made a telling transition, from strange hobby to side hustle, pastime to profession. Fan artists are no longer just used for free labor or increased access to key demographics; they are now being hired as contingent workers and touted as such. Between 2008 and 2018, broadcast networks, cable channels, and streaming platforms have evolved their marketing strategy from appropriation to professionalization—enclosing the artist, not just the art. In so doing, they are able to leverage the affective labor and aspirational labor of fan artists, mobilizing their economic precarity and fannish subjectivity for television promotion. This project uses historical research, as well as content and discourse analysis, to evidence these changes in the mechanics and motivations of fan art promotion within the U.S. post-network era television industry. But the professionalization of fan artists is only a microcosm of a larger labor ecosystem. At the bleeding edge of contemporary media employment models, labor laws, professionalization processes, and union jurisdictions, these professionalized fan artists are artifacts of the post-recession era. They are both actor and archive, in many ways the only record of the shifting strategies, transitory norms, ephemeral ideologies, and lived realities of media work. As they are professionalized, their identity and productivity are enclosed and formalized, monetized and commodified. However, given the state of flexible labor markets and waning labor organizations, that commodification comes without the protections historically afforded media professionals. By situating professional fan artists as a case study of post-recessional, post-network era television promotional labor, this project explores both structural problems of and potential solutions to contemporary contingent media work.Radio-Television-Fil
Guards at the games: the International Olympic Committee and security, 1972-1996
Full text linkThe 1972 Munich Olympic Games marked a pivotal moment in Olympic history. An attack by Palestinian terrorists on Israeli athletes and coaches in the Olympic Village marred the image of the Olympic Games as a mere sporting event. In the ensuing decades, the task of providing security at the Olympics evolved as Organizing Committees sought to nullify all threats, real and perceived. Yet, outside of one two-decade old manuscript, sport historians have virtually ignored this topic. While initially lackluster in their efforts, the International Olympic Committee (IOC) eventually played an important, yet rarely discussed role in the preparation and provision of security at Olympic events. This dissertation examines the evolution of IOC policy towards security from the Munich Olympics in 1972 to the last attack at an Olympic competition, the 1996 Centennial Park bombing in Atlanta. In the years prior to the attack in Munich, the IOC attempted to side-step political problems existing in the larger world. Following the massacre, the IOC initially forced the various Organizing Committees for the Olympic Games to provide security with their own resources (ie. without any monetary or logistical aid from the IOC). A change in leadership and one dynamic IOC member altered the course of this policy. Consequent to these developments, IOC leaders were forced to finally admit, at least internally, that politics mattered greatly. By applying transnational relations theory from the field of political science, this study explores the IOC’s role as a non-state actor that, at times, coordinated the security efforts of national governments, non-governmental organizations, and national sporting bodies.Kinesiology and Health Educatio