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NEURAL REPRESENTATIONS OF LANDMARKS AND GOALS IN THE HIPPOCAMPAL FORMATION
No full textWhen exploring an environment, landmarks play a key role in orientating an animal and providing information on how to navigate to various goals in the world. Within the hippocampus, place cells represent an animal’s current location in a given environment. This feature can be used to decode an animal’s absolute position in space and at a population level is theorized to represent an internal map of the environment. Place cells are stable across multiple days but readily accommodate changes within the environment. In this thesis, I focus on how the system represents features of the external environment, focusing on landmarks and goal locations. Chapter 2 examines landmark vector cells, neurons whose receptive fields are tied to a fixed distance and angle to multiple landmarks in space. Using CA1 recordings performed in darkness, I find that landmark vector representations continue to fire relative to these landmark positions, indicating that the position of these landmarks is maintained in the animal’s memory. Furthermore, I find that place cells and landmark vector cells spontaneously drift in concert with one another, suggesting that a common directional input may be used in their computation. The results support a unified model of place cell and landmark vector cell computation that utilizes egocentric bearing cells from the lateral entorhinal cortex as a necessary input. To further investigate how points in the world can be utilized as anchors for egocentric bearing cells, I trained animals on a goal-directed task and recorded from the lateral entorhinal cortex. These animals were implanted with custom microdrives with Neuropixels probes, described in Chapter 3, to help attain a larger sample of neurons from the region. Chapter 4 describes these results, where I find neurons that represent the position of an animal to these changing goal locations indicating that any goal position can be flexibly used as an anchor point from trial to trial. Together, these studies expand our understanding of how the hippocampal network, with inputs from the lateral entorhinal cortex, can function to represent the external world in relationship to an animal’s position in space
ON A MOUNTAIN-PASS THEOREM IN HYPERBOLIC SPACE AND ITS APPLICATION
Get PDFIn hyperbolic space, the problem of finding minimal hypersurfaces with prescribed asymptotic behaviors is called the asymptotic Plateau problem. In this thesis, we record the min-max theory in hyperbolic space developed in YaoMountainPass. More precisely, we show that given two low energy solution to the asymptotic Plateau problem that are local minima, there is a high energy solutions between the two. As a corollary, we prove a topological uniqueness result under assumptions on the asymptotic geometry.
The thesis is divided into three parts. In the first part, we establish a relative version of area functional. This is necessary because the usual area functional is infinite valued for minimal hypersurfaces with asymptotic boundaries. The variational theory for this new relative functional also gives minimal hypersurfaces and thus can serve as a substitute for the original area functional.
In the second part, we run the min-max procedure using the functional from the first part. We also discuss the asymptotic regularity of the newly constructed minimal hypersurface. This is based on the work of Schoen--Simon combined with the work of Hardt--Lin.
In the end, we prove a topological uniqueness result for asymptotic Plateau problem. This uses mean curvature flow to deform minimal hypersurfaces with the same asymptotic boundaries into each other. The assumption on the asymptotic boundaries is needed to guarantee no singularities occur and so there is no topology change along the flow
SUPERVISED AND SELF-SUPERVISED APPROACHES FOR VIDEO UNDERSTANDING
Get PDFVideos serve as a powerful medium for communication, offering a dynamic and engaging way to present information that often surpasses the effectiveness of static images or text. The field of video understanding, which involves the automatic analysis and interpretation of video content by machines, is becoming increasingly important as the volume of video data generated and shared online continues to grow. This field has a wide array of applications, including surveillance, media, healthcare, and autonomous vehicles, where it can provide critical insights and support decision-making.
The goal is to develop techniques to enable video understanding with or without labels, explore modalities beyond RGB and develop approaches which can work with limited computing resources and data. The dissertation provides both modeling contributions and empirical evidence on a variety of video understanding tasks.
We first present an approach for supervised pose-based action recognition with a novel architecture and pose-aware data augmentation strategy. Use of pose instead of RGB helps us better capture motion information and avoid scene and object biases. Next, we investigate self-supervised learning of pose encoders using contrastive learning. A new module called HaLP is presented to increase the number of positives used in contrastive learning by hallucinating in the latent space. When integrated into contrastive learning frameworks, HaLP consistently improves performance on skeleton-based action recognition tasks. Third, an approach is presented for self-supervised key step extraction from unlabeled procedural videos by using multiple modalities like appearance, motion, and depth. A novel loss function enforces temporal and cross-modal consistency to learn discriminative representations, which are then clustered to obtain key steps. This approach demonstrates superior performance on multiple tasks including key-step localization and phase classification. Finally, a new max-margin contrastive learning objective is formulated based on support vector machines. By optimally selecting negatives as support vectors, faster convergence and higher-quality representations are achieved across various modalities including images, videos, and graphs
Kant, Incongruent Counterparts, and the Priority of Space
Get PDFKant, Incongruent Counterparts, and the Priority of Space examines Kant’s three main arguments from incongruent counterparts. Incongruent counterparts are objects that are perfectly similar in size and shape, but which differ in their left- or right-orientation, making it impossible to place one object into the space the other occupies. This phenomenon is most apparent in how a left hand cannot fit into a right-handed glove. Kant argues in 1768 that this phenomenon shows that absolute space is real, in 1770, that space is the form of intuition, and in 1783, that space and time are mere forms of intuition and not representations of things in themselves.
This dissertation argues that Kant consistently appealed to incongruent counterparts to support the claim that space is prior to the objects and relations in it. Chapter one overviews previous interpretations of the arguments from incongruent counterparts and identifies core disagreements in the interpretation of Kant’s arguments: it is unclear whether there is any continuity in what the arguments appeal to and whether, in its final version, it is consistent with Kant’s mature philosophy. The chapter articulates a guiding hypothesis for the dissertation: bringing to bear recent literature on Kant’s notions of ground can show that the priority of space remains what incongruent counterparts establish but that other changes in the argument can be understood in terms of Kant’s changing views on metaphysical dependence.
Chapter two gives an interpretation of Kant’s 1768 argument for the reality of absolute space from incongruent counterparts. On the view defended in this chapter, Kant claims that absolute space is real because absolute space must be presupposed as prior to the objects and relations in it to explain the determination of objects as left- or right-oriented. The chapter examines if and how Kant’s pre-critical views about metaphysical reasoning feature in establishing the reality of absolute space.
The third chapter examines how Kant changed his focus in 1770 to examining objects in space as sensible objects. It argues that the argument from incongruent counterparts now establishes that sensibility is a cognitive faculty that operates independently of the understanding because, in incongruent counterparts, it is apparent how sensible things are arranged: incongruent counterparts can appear in different places because space is the form of sensibility and because space is prior to how sensible objects are embedded in space. The understanding cannot make the difference between left and right intelligible because embedding is not how the understanding considers the dependence between things as grounds and consequences.
Chapter four proposes to read the argument that occurs in Kant’s Prolegomena as an extension of a longer argument for idealism in the first part of the Prolegomena. Within this context, incongruent counterparts establish that space is the form of sensibility and that we can have no a priori conceptual representation of a thing in itself as spatial. The understanding cannot represent space a priori because it is mereologically - “formally” - prior to the things in it, which runs counter to how the understanding organizes objects of thought in discursive thinking. The chapter defends the view that Kant did not argue in ways that are not consistent with his mature philosophy, because what is stated in the Prolegomena can be unambiguously mapped onto Kant’s concerns about illegitimate transgressions of the pure understanding.
The chapters jointly support the thesis that Kant consistently held on to the view that space is, in some sense, prior to the objects and relations in it. Overall, the view is supported by an examination of the changes in Kant’s views on legitimate metaphysical reasoning about space. While his notion of space in 1768 was originally considered to be the ultimate ground of how to differentiate left- and right-oriented objects, this view became inconsistent with how Kant regarded how things were organized in sensibility. Ultimately, in the critical philosophy, Kant used the illegitimate operations of the understanding, including reasoning that sought to reduce the composition of objects to their grounds, to show that the understanding cannot by itself represent space and time a priori
ESTIMATING LOGISTICS AND COSTS OF DECOMMISSIONING OFFSHORE WIND FARMS
Get PDFOffshore wind is a relatively young and growing industry worldwide. OWFs have a typical lifespan between 25 to 30 years and will require decommissioning when the project reaches its end-of-life. Over 700 offshore wind turbines will reach their end-of-life in the next decade and it is essential that operators have accurate estimates for the resources and costs associated with decommissioning. To date, only seven OWFs have been decommissioned, providing little real-world experience or data for operators to use when planning future decommissioning projects.
This research aims to establish if offshore wind companies are underestimating the resources, time, and costs to decommission an OWF. This was accomplished through a qualitative comparison of literature review with subject interviews and surveys. Interview subjects and survey participants were asked the same nine questions. Their responses were then compared to information found in literature review
INTO THE DIGITAL ABYSS: EXPLORING THE DEPTHS OF DATA COLLECTED BY IOT DEVICES
Get PDFThe proliferation of interconnected smart devices, once ordinary household appliances, has led to an exponential increase in sensitive data collection and transmission. The security and privacy of IoT devices, however, have lagged behind their rapid deployment, creating vulnerabilities that can be exploited by malicious actors. While security attacks on IoT devices have garnered attention, privacy implications often go unnoticed, exposing users to potential risks without their awareness. Our research contributes to a deeper understanding of user privacy concerns and implications caused by data collection within the vast landscape of the Internet of Things (IoT). We uncover the true extent of data accessible to adversarial individuals and propose a solution to ensure data privacy in precarious situations. We provide valuable insights, paving the way for a more informed and comprehensive approach to studying, addressing, and raising awareness about privacy issues within the evolving landscape of smart home environments
Dealing with the Correlation Structures in Functional Genomics Data
No full textTraditional statistical methods treats the genes and samples as independent. However, making use of the correlation structures between genes or between samples could provide insights on the biology.
In this thesis, we introduced statistical methods for modeling gene expression data that accounts for correlation structures at either gene level or sample level.
For gene-level correlation, we introduced Spatial Quantile Normalization (SpQN), that adjusts for the confounding effect of gene expression level to the observed gene-gene correlations. Our method has been shown to enhance the signals of transcription factor associated gene co-expression signals.
For sample-level correlation that comes from spatial locations, we introduced multi-sample non-negative spatial factorization (mNSF), that allows the factorization of spatial data accounting for the spatial dependencies of the factors. Our method has been shown to reveal spatial patterns that are associated with anatomical structure or biological process.
For sample-level correlation that comes from disease severity, we introduced integrative pseudotime analysis of single cell at sample level (IPASS), that uses the dependency between samples of similar disease severity stage, to model the gradient change of gene expression levels as well as gene regulation activities on the chromosome along the disease progression process
Depressive Symptoms, Sleep Disturbance, and Quality of Life Among Middle-Aged and Older Adults Living With Chronic Physical Health Conditions: A Comparative Study in South Africa and The United States
No full textINTRODUCTION: In the era of global health challenges, physical illnesses (i.e., diabetes, hypertension, and cardiovascular disease) threaten well-being and healthcare systems. Informing care approaches encompassing these conditions and their associated outcomes is crucial to addressing these challenges. Depression, a leading cause of disease burden, and sleep disturbance, an underreported public health problem, intricately influence the quality of life (QoL) of individuals with physical illnesses. Despite their significance, associations among depressive symptoms, sleep disturbances, and QoL remain poorly understood, particularly among individuals with physical illnesses. This dissertation aims to unravel this complexity in South Africa (SA) and the United States (US).
OBJECTIVES: (1) Investigate the extent to which sleep disturbance moderates the depressive symptom-QoL relationship in SA vs. the US; (2) Examine temporal-bidirectional associations among depressive symptoms, sleep disturbances, and QoL in SA; (3) Investigate these temporal-bidirectional associations in the US.
METHODS: The study involved participants aged 50+ with at least one physical illness, analyzing data from the Health and Retirement International Family of Studies (N=21,519). Pre-statistical harmonization aligned common items across the datasets and country-specific regression analyses were conducted due to measurement non-invariance. Cross-lagged models examined temporal-bidirectional associations. Moderation by demographic factors was also explored.
RESULTS: Sleep disturbances moderated the depressive symptom–QoL association in SA and the US, with greater moderation in SA and variations by sex, age, and race. Individual-level analyses in SA revealed higher sleep disturbances predicted lower depressive symptoms and lower QoL. In the US, findings indicated reciprocal relationships between higher sleep disturbances and higher depressive symptoms, as well as lower QoL and higher sleep disturbances. In the US, QoL functioned as a mediator.
CONCLUSIONS: Sleep disturbances moderate the depressive symptom–QoL relationship in both countries, with sleep disturbances being protective in SA. This underscores the need to screen/treat depressive symptoms and sleep problems in populations with physical illnesses. Temporal findings in SA suggest sleep disturbances predict lower depressive symptoms, warranting further research into their potential antidepressive function. Reciprocal relationships between depressive symptoms and sleep disturbances, and between QoL and sleep disturbances in the US, call for multifaceted interventions targeting all three conditions to enhance well-being
Particle Friction, Breakage, and Damage: Deformation Mechanisms of Brittle Granular Materials
Get PDFUnderstanding the mechanics of granular materials is essential in geophysics and for a
broad range of industries and for defense-related applications. However, predicting
the mechanical behavior of granular materials is still challenging, and even their
most basic micromechanics remain poorly understood. This thesis sheds light on
the micromechanics of granular materials by examining their friction, breakage, and
damage. The friction between grains constituting a granular material was examined
using a new micromechanical testing apparatus to study smooth and rough soda lime
glass particles in carefully controlled dry, humid, and lubricated environments during
normal compression and shearing. The breakage of granular particles was studied across
strain rates and pressure regimes using confined uniaxial strain experiments performed
in an oedometer, a drop tower, and a split-Hopkinson bar. These experiments
provided some of the first data quantifying particle breakage at stresses up to several
gigapascals. This study also used in-situ acoustic emissions measurements to study
deformation mechanisms active throughout the compaction process during low strain-
rate experiments. The mechanical response of Ottawa sand was further investigated
by studying the impact of projectiles into dry and wet sand targets. We specifically
examined depth of penetration, breakage, and in-situ displacement fields reconstructed
using a novel method. Damage of inter-particle bonds was examined by studying
sintered soda-lime glass at the microscale using inter-particle bond tensile testing
and at the macroscale using unconfined uniaxial compression testing of cylindrical
core-drilled samples
SCHOOL INFORMATION GAPS AMONG PARENTS AND THE ROLE OF ONLINE SOURCES
No full textSocial media is an increasingly important platform for parents to gather and exchange information to develop opinions on the quality of school options for their children. Ratings and comments on online platforms offer subjective but direct evaluations of school performance and school quality.
These sources of information have not been studied sufficiently. The existing literature does not identify the factors that influence ratings and comments, nor clarify whether comments and ratings can be compared across different school types. The extent to which online comments reflect schools’ actual situation has also not been studied.
The dissertation presents three empirical studies. The first study examines the relationship between online word-of-mouth regarding students’ learning and the actual academic performance of schools. The second study investigates the determinants of the “star” ratings provided by parents. The third study compares the commenting and rating behaviors of parents across public, charter, and private schools.
The findings reveal that online comments and ratings largely reflect schools’ average test scores rather than their improvement in scores. Strong correlations are also present between “star” ratings and perceptions of teacher quality, student learning, and school climate. In these areas, parents’ negative experiences have a greater influence on their ratings than positive experiences. The findings also reveal differences across school types. While charter schools receive similarly favorable online ratings and comments as traditional public and private schools, charter schools receive more comments on average, suggesting that online platforms are particularly relevant for shaping patterns of school choice. As with other schools, charter schools with high test scores receive more favorable comments and ratings than do those with high test score gains. Thus, online comments and ratings do not appear to steer parents toward those charter schools that have stronger claims for greater actual learning gains, and they instead suggest that parents should choose charter schools just like they choose traditional public schools, favoring those with the highest performance.
Altogether, the findings clarify the potential impact of online comments and ratings for educational equity among schools, as it is shaped by how parents encourage each other to approach school choice decisions