VictorJuiz/thesis huggingface dataset:
Two mechanisms of human contingency learning [electronic resource]
Keywords: Psychology

Understanding how we learn the relationships between events in the world, and how we learn to respond appropriately to those events has been an important focus of research in psychology and the cognitive sciences for many years. While many different theories have been proposed, two broad classes of accounts have been particularly popular. Findings from studies of animal conditioning and tasks requiring humans learners to make very fast responses have led to proposals that learning in these tasks is based on a process of gradual adjustments to pathways linking representations of cue events to representations of their outcomes and appropriate responses to those outcomes. However, many of the same findings can also be explained as a process of making explicit inferences about the likely causal relationships between events. Findings from human contingency learning tasks have been argued to support the idea that learners in these tasks rely on an inference-based reasoning process. This has led some to doubt that both types of processes necessarily exist. The experiments presented in this thesis set out to look for evidence that both processes exist, and that they are preferentially involved in different kinds of learning situations. In the presented experiments, participants saw displays containing single or paired objects and learned which displays were usually followed by the appearance of a dot shortly afterward. Some participants predicted whether the dot would appear and then saw the outcome, while others were required to respond very quickly if the dot appeared shortly after the objects. For prediction participants, instructions that guided them to infer which objects had the power to cause the dot outcome determined whether contingencies associated with one object affected predictions about its pair mate. For fast-paced responding participants, contingencies associated with one object affected responses to the pair-mate, even when more neutral instructions were provided. These results challenge single-mechanism accounts and support the proposal that the mechanisms underlying performance in the two tasks are distinct. The remainder of the thesis focuses on the development of computational models of the different kinds of processes thought to underlie responding in these tasks.
Two-phase flow phenomena in fuel cell microchannels [electronic resource]
Keywords: Mechanical Engineering

Proton exchange membrane (PEM) fuel cells show promise as CO2-free energy-conversion devices. Predictions show that reducing the size of the gas delivery channels could improve the efficiency and power density of PEM fuel cells, however the expected benefits of reduced channel sizes have not been realized due to flooding by water generated at the cathode. Channels with small dimensions exhibit an increased propensity toward flooding as surface tension forces become significant when compared with viscous, inertial, and pressure forces. This study characterizes the distinct two-phase flow profiles that result from the interplay of these forces. We investigate fundamental water-gas interactions in silicon channels of various hydraulic diameters and cross-sectional aspect ratios using a high-contrast fluorescent imaging technique. Then, we develop a test structure to study the evolution of two-phase flow structures in a microchannel geometry designed to mimic conditions in a fuel cell channel -- a 60-cm long channel with distributed water introduction through a porous gas diffusion layer (GDL) on one wall. Finally, we present considerations for the implementation of spinning-disk confocal microscopy to provide three-dimensional (3D) visualization of two-phase flow structures which may provide insight into key flow transitions that were observed during high-speed fluorescent flow visualization. By characterizing and modeling two-phase flow in various microchannel geometries and under a large range of flow conditions, these studies provide insight that enables the improved design of microchannels for two-phase flow in fuel cells and other practical devices.
Uncovering the organization of semantic structure with similarity and inductions [electronic resource]
Keywords: Psychology

Can semantic representations be captured by explicit structures? While connectionist models have long presented a challenge to rigidly structured models, recent work using structured probabilistic models have reintroduced such representations. For example, it has been proposed that trees are an appropriate choice of structure for capturing semantic judgments about blank biological properties of animals. In this work, we call this claim into question. We examine three models that have been explored in recent work on semantic cognition, including a structured probabilistic model, a neural network model, and a null model based on the raw covariance matrix. The models are compared to property induction judgments and similarity ratings across several sets of studies. First, we replicate a previous success of the structured model on a two-premise induction over mammals, but show that the connectionist model can also succeed at modeling this task. Second, we demonstrate that the structured model rapidly loses effectiveness when tested on sets of mammals which include cross-tree similarities such as living in water. Third, we examine the influence of question context on induction performance, by asking about diet, habitat, and behavior as well as blank biological properties. Finally, we extend beyond mammals to include birds and fish, gathering a rich set of similarity judgments, and demonstrate that these similarity judgments include systematic structure which no tree could capture. These results confirm that tree structures can serve as a good first-order representation of animal similarities and property induction judgments. However, they also show that these highly structured representations fail to capture subtle, yet important, effects in semantic judgments, specifically those that are not consistent with the tree structure. Other models which do not impose specific inductive biases on their training data, such as connectionist models or the null model, can capture these subtler effects as well.
Understanding and preventing anterior cruciate ligament injuries using novel motion analysis systems [electronic resource]
Keywords: Mechanical Engineering

The overall goal of this dissertation is to use novel motion analysis systems to investigate the underlying mechanisms that cause an anterior cruciate ligament (ACL) injury and then to explore movement modification methods that might prevent ACL injuries from occurring. Additionally, novel motion analysis systems can provide new information about ACL injuries and therefore should be used to help analyze these injuries from a different perspective. This thesis provides the results from multiple experimental studies that used two novel motion analysis systems to investigate the underlying causes of ACL injury and potential injury prevention methods. Using a markerless motion capture system, the first investigation determined that increasing the coefficient of friction of the shoe-surface condition will change a subject's movement strategies during a sidestep cutting task in specific ways that may increase the risk of ACL injury. This investigation provides a biomechanical basis for the increased incidence of ACL injuries on high friction surfaces, and suggests that females are more at risk for ACL injury when cutting on high friction surfaces. In terms of novel motion analysis systems, there is a need for simple, cost effective methods to identify athletes at a higher risk for ACL injury during jumping tasks. As such, the second study assessed the capacity of a wearable inertial-based system to evaluate ACL injury risk during jumping tasks. The proposed system measured the knee flexion angle and the trunk lean, and demonstrated good concurrent validity and discriminative performance in terms of the known risk factors for ACL injury. This study also reported the angular velocity of the thigh and shank segments during bilateral and unilateral drop jumps for the first time. Furthermore, this study illustrated that there is an association between the coronal segment angular velocity and knee abduction moment, and that the coronal segment angular velocity can differentiate between subjects at higher risk for ACL injury. Recent studies have shown that the incidence of ACL injury can be decreased through the use of intervention programs. Therefore, the objective for the final study was to determine if an independent inertial-based system can be used to modify jump landing mechanics in order to decrease the risk for ACL injury by providing real-time feedback based on known kinematic and kinetic injury risk factors. This study found that the subjects reduced their risk for ACL injury after training with the system because there were significant increases in the maximum knee flexion angle and the maximum trunk lean. The subjects also reduced their risk for injury by decreasing their thigh coronal angular velocity, which was correlated with a decrease in their knee abduction moment. This study suggests that an inertial-based system could be used for interventional training aimed at reducing the risk for ACL injury.
Understanding hematopoietic stem cells [electronic resource] : from macro to micro
Keywords: Chemical and Systems Biology.

Recent technological advances in high throughput technology, sample preparation and data analysis have made whole genome mRNA and miRNA analysis of purified hematopoietic cell populations much more accessible. The high throughput analysis of the hematopoietic stem cell (HSC) population has yielded massive amounts of data and now we are in the process of biologically validating these targets. Esam1 is one target yielded from microarray analysis of the HSC population. We found Esam1 to be highly and selectively expressed by HSC from mouse bone marrow. Esam1 is also a viable positive HSC marker in fetal, young and aged mice, as well as in mice of several different strains. In addition, we find robust levels of Esam1 transcripts in purified human HSC. Esam1-/- mice do not exhibit severe hematopoietic defects, however, Esam1-/- BM has an increased frequency of HSC and fewer T cells. HSC from Esam1-/- mice give rise to more granulocyte/monocytes in culture and a higher T cell:B cell ratio upon transplantation into congenic mice. These studies identify Esam1 as a novel, widely applicable HSC-selective marker and suggest that Esam1 may play roles in both HSC proliferation and lineage decisions. MicroRNA-125b (miR-125b) is a target yielded from miRNA profiling of the HSC population. We show that miR-125b is highly expressed in HSC and its expression decreases in committed progenitors. Overexpression of miR-125b in mouse HSC enhances their function, demonstrated through serial transplantation of highly purified HSC, and enriches for the previously described Slamf1lo CD34- lymphoid balanced and the Slamf1negCD34- lymphoid biased cell subsets within the multipotent HSC [CD34-KLS] fraction. This enrichment of HSC subsets occur via an anti-apoptotic mechanism, reducing the mRNA expression levels of two pro-apoptotic targets, Bmf and KLF13. The anti-apoptotic effect of miR-125b is more pronounced in the lymphoid biased HSC subset because of their intrinsic higher baseline levels of apoptosis. Together, these data reveal that miR-125b regulates hematopoietic stem cell survival and can promote lymphoid fate decisions at the level of the HSC by preferentially expanding lymphoid balanced and lymphoid biased HSC.
Understanding microstructure and charge transport in semicrystalline polythiophenes [electronic resource]
Keywords: Materials Science and Engineering

Semiconducting polymers are a promising class of organic electronic materials, with the potential to have a large impact in the field of macroelectronics. In this thesis, we focus on understanding the relationship between microstructure and charge transport in semicrystalline polythiophenes. A method is presented for the measurement of complete pole figures of polymer thin films using an area detector, allowing for the first time quantitative characterization of crystalline texture and degree of crystallinity. Thin film transistors are used to measure electrical characteristics, and charge transport behavior is modeled according to the Mobility Edge (ME) model. These characterization methods are first used to investigate the effect of substrate surface treatment and thermal annealing on the microstructure of polythiophene thin films, and the effect of microstructural details on charge transport. Next, we investigate the semicrystalline microstructure in confined polythiophene films. Pole figures are used to quantify a decrease in the degree of crystallinity of films with decreasing thickness, accompanied by an improvement in crystalline texture. Next, we investigate the influence of the degree of regioregularity, molecular weight and the processing solvent on microstructure (degree of crystallinity and texture) and charge transport in high mobility P3HT thin films. Surprisingly, when processing conditions are optimized, even a polymer with moderate regioregularity can form a highly textured film with high charge carrier mobility. Finally, we use films of P3HT with engineered, anisotropic in-plane microstructure to understand the importance and mechanism of transport across grain boundaries in these semicrystalline films. Results from this study provide the first experimental evidence for the application of a percolation model for charge transport in high molecular weight semicrystalline polymer semiconductors. Understanding how characteristics of the polymer as well as details of the processing conditions can affect the film microstructure and device performance is important for future materials design and device fabrication.
Understanding of NiO-based unipolar resistive switching from first principle simulations to macroscopic models [electronic resource]
Keywords: Electrical Engineering

As NAND Flash memory technology is facing challenging issues such as electronic coupling between adjacent cells and high coupling of the control gate with floating gate in scaling down to and beyond 16nm technology node, new functional devices or materials has been explored to continue consecutive development of memory technology beyond 16nm technology node. One of the new emerging non-volatile memories is resistance change random access memory(ReRAM) possibly meeting the requirements to replace NAND Flash; i.e., low cost, simple structure, promising 8nm technology node, low power dissipation, high endurance, possible integration in crossbar arrays in 3D on top of silicon base CMOS ICs. In ReRAM, understanding the switching mechanism was very complicated because there have been many different phenomena co-existing under circumstances when ultimate electrical stress is applied. One of them, oxidation/reduction of transition metals is generally accepted to results in the unipolar switching. In this switching mode, both thermal and chemical processes are associated with the effect of electric field. For clearer understanding of mechanism of the unipolar switching, defect states in NiO are investigated, which is closely related to electrical conductivity of the transition metal-based resistive switching materials. Study on feasible "ON" and "OFF" states in atomic scale gave an insight into atomic structure of conductive filament, role of oxygen (or oxygen vacancies) and its migration. With these first principle modeling results, a quantitative model for reset/retention and filament formation was proposed. Experimental results for reduction of reset current and long retention time of RON by inserting interfacial layer between a metal electrode and resistive switching material can be explained based on the quantitative model.
Understanding radical breaks [electronic resource] : media and behavior in small teams engaged in redesign scenarios
Keywords: Mechanical Engineering

In this study, I present an empirically supported framework for understanding how and under what conditions small horizontally organized design teams perform radical redesigns or radical breaks. This is done in the context of how incremental improvements as well as mid-level redesigns are made. The notion of radical breaks captures what is often thought of as "thinking outside of the box", and reframing problems to find new and unique solutions. A radical break occurs in the course of a redesign when designers make a major departure from the provided artifact. Observations based on case studies of small design teams in a redesign task, suggest three closely bound concepts as a mechanism for understanding how design process determines design outcomes: Dimensions of Engagement; the quality of enactment subjects made while working, Media Response and Interaction; how subjects responded to and interacted with media, and Path Determination; how and when designers determine what they will do.
Understanding the role of lipids in tear-film stability [electronic resource]
Keywords: Chemical Engineering

The tear film is the thin layer of fluid that covers the surface of the eye. While the functions of the tear film are numerous, the primary role is to protect the corneal surface. When an individual has dry eye disease the tear film breaks up and exposes the corneal epithelial cells, which leads to ocular irritation. The primary components of the outermost layer of the tear film are meibomian lipids, a mixture of long chain nonpolar lipids. Although this lipid layer is thought to play an important role in tear film stability, little is known about the structure and viscoelasticity of meibum, or how these properties relate to tear film stability in dry eye disease. The primary focus of this work was to understand how meibum behaves at an air-water interface to mimic the in vivo conditions of the tear film lipid layer. At room temperature meibum was found to form a predominantly elastic interfacial film, although the film became more fluid as it was heated to body temperature. Interfacial x-ray scattering at room temperature revealed ordered lattices and multilayers at high levels of compression that contributed to high elasticity. In bulk samples, small angle x-ray scattering identified two populations of lipid lamellar phases with unique melt behavior. Meibum collected from patients with meibomian gland dysfunction, a form of dry eye disease, contained the same crystalline phases; however, the prevalence of those phases was reduced indicating a quantifiable change in lipid composition. To ascertain whether meibum viscoelastic properties are relevant to tear film performance, the effects of surface elasticity on an advancing droplet were studied. While droplets covered with a Newtonian monolayer followed classical hydrodynamics, meibum and other insoluble surfactants with surface shear elasticity induced periodic stick-release of the contact line at low advancing velocities and non-ideal behavior at higher velocities. Finally, to explore how a water soluble surfactant may be used to repair a compromised lipid layer, the interactions between a poly(ethylene oxide)-poly(butylene oxide) block copolymer (EOBO) and a model phospholipid monolayer were studied. The lipids and EOBO remained phase separated at the interface, yet EOBO was able to restore the native lattice spacing and mechanical properties of the lipid monolayer, which could make it a valuable tool for a number of biological applications. Meibomian lipids are a complex natural extract with a number of remarkable properties. Although the lipids present in meibum are diverse, meibum can form an elastic interfacial film with ordered phases in bulk material or at an interface. We have shown a link between meibum structure and elasticity, which both depend on temperature. Major composition changes that occur with disease could alter meibum melt temperature and viscoelasticity, which will ultimately modulate the ability of meibum to stabilize the tear film.
Unifying the divide [electronic resource] : effects of the division of labor on person-to-group attachment
Keywords: Sociology.

This dissertation examines the processes by which the intragroup division of labor structurally influences the development of group attachment. It specifically addresses a classic sociological issue over whether specialization in the division of labor is beneficial or detrimental to the development of person-to-group bonds and group cohesion. I propose that that solely looking at the independent effects of task specialization in isolation is problematic. Instead, I suggest that it is more beneficial to characterize the division of labor in terms of the different relational aspects that underline micro-interactional task structure. Towards this aim, my project proposes that interdependence in the division of labor is organized around three relational dimensions (task coordination, task differentiation, and skill specialization), which in combination exert complex influences on the development of person-to-group bonds. The first part of my dissertation research proposes a new original theory that specifies how these three relation dimensions differentially impact three independent processes by which group cohesion can endogenously grow from task structure. The second part of my dissertation centers around two major empirical analyses derived from data collected from a large-scale laboratory experiment. The first empirical study asks whether group bonding is higher in specialized teams? The second empirical study asks whether the impact of specialization changes when task specialization is no longer equally differentiated among group members, but is instead unequally divided amongst group members such that only a few group members possess unique skills important for team success? This project provides three major theoretical contributions: First, it addresses a fundamental issue that lies at the heart of sociology by asking what structural aspects of social interaction encourage individuals to become more attached to a group? Second, it re-conceptualizes the division of labor on an interpersonal level by breaking the concept down into its constituent parts to analyze how the division of labor actually works in real social interaction. Third, it brings insight to a major debate over whether organizational division of labor inhibits or enhances group solidarity by suggesting that the impact of task dimensions like specialization is not straightforward, but is complex and can only be examined while in simultaneous combination with other task dimensions.
Unsupervised learning and reverse optical flow in mobile robotics [electronic resource]
Keywords: Electrical Engineering

As sensor resolution increases and costs decrease, the amount of data available on mobile robotics platforms is exploding. Unsupervised machine learning algorithms, and their ability to produce useful information without large labeled training sets, are an important tool for benefiting from this abundance. In this thesis the application of unsupervised learning to three subfields of mobile robotics is discussed. Tracking multiple moving objects from an unmanned aerial vehicle, road following in loosely-structured environments, and autonomous offroad navigation. The thesis focuses on building dynamic activity-based ground models for multi-object tracking, the combination of optical flow techniques and dynamic programming to estimate the location of a road, and the use of optical flow techniques to improve the quality of an autonomous robot's obstacle classification.