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Reconstructing Dynamical Systems From Time Series Using Statistical Learning and Takens' Delay Embedding Theorem
Get PDFThe field of dynamical systems studies how systems evolve in time according to deterministic, probabilistic, or hybrid rule sets. Embedding theorems can be used to describe how observations of these systems can be used to reconstruct their dynamics. However, these theorems do not provide a backmapping to the full-dimensional descriptions of these dynamics. The recovery of these full-dimensional descriptions from time series observations, such as those furnished by experiments, is central to the study of dynamical systems. In this work we propose and validate a pipeline that combines embedding theorems and statistical learning to represent dynamics from time series in a mathematically rigorous way and learn backmappings to full dimensional descriptions with universal function approximators in the context of molecular dynamics. We demonstrate that this framework is robust under noise and extend it for use with arbitrary dynamical systems. We introduce the TAkens Reconstruction (TAR) software package to perform univariate, multivariate and multi-temporal Takens' reconstructions of arbitrary time series and apply the work beyond physics, in the context of economic systems. Lastly, we investigate optimization of observable choice to maximize reconstruction quality. This work provides a theoretical and computational framework with which we can reconstruct and analyze the dynamics of arbitrary dynamical systems. It constitutes a contribution to a broader class of techniques bridging the gap between experimental observation and theoretical understanding of dynamics
Building Evidence of Dark Pattern Effects on User Attention and Behavior
No full textDesign choices on digital platforms significantly influence user behavior and experience. Rather than prioritizing user well-being, many platforms employ tactics that steer user choices to their advantage, a platform tendency that is all too familiar. While all design can influence user behavior, many online platforms employ design elements beyond neutral influence and engage with coercion, manipulation, and deception, commonly referred to as "dark patterns." This dissertation addresses open questions regarding dark patterns, including: 1) What are end-user experiences with dark patterns specifically designed to capture and steer user attention?2) What behavioral changes do attention-capturing designs induce? 3) Lastly, what areas of consensus or tension exist regarding dark patterns' effects on user behavior more broadly? Accordingly, the dissertation comprises three studies:1) A qualitative interview study exploring user experiences with dark patterns designed to capture and steer user attention, revealing how features like Netflix's autoplay and intrusive recommendations can undermine user autonomy.2) A quantitative experimental study measuring the reduction in Netflix consumption when autoplay is disabled, suggesting increased user autonomy.3) A systematic literature review synthesizing existing quantitative research on dark patterns, highlighting scholarly consensus on the impact of dark patterns on user behavior and identifying areas needing further investigation. Collectively, these studies provide empirical evidence on how design choices can manipulate user attention and behavior, offering insights to inform designers, policymakers, and users about the ethical implications of such design patterns.</p
Exploring the Limits of Size-Selectivity in Nanoscale Solute Transport Using Block Copolymer Nanolithography
Get PDFA thorough understanding of water and particle transport in the ultrafiltration regime, where the species to be separated range from 1 to 100 nm, is crucial for both scientific research and technological applications, including water treatment, electrochemical energy conversion, and biosensors. Fundamental studies on size-exclusion-based separation in this regime require a precisely controlled experimental platform that enables systematic manipulation of pore size with high spatial resolution. Additionally, designing a filtration process that supports large-scale operation and prolonged usage time enhances separation efficiency. We developed a nanofabrication process based on block copolymer (BCP) self-assembly and sequential infiltration synthesis (SIS) to fabricate silicon nitride (SiNx) membranes. The process was optimized to achieve thick perpendicular cylinder BCP films, fine-tuned etching environments for transferring the SIS-enhanced porous mask into SiNx, and protective strategies for successfully releasing 100-nm-thick porous structures. Quantitative pore-size distribution analysis of individual membranes, as well as multiple membranes produced across a 4-inch wafer, confirmed high reproducibility and reliability at the wafer level. The fabricated SiNx membranes serve as model ultrafiltration membranes, exhibiting good mechanical properties, large-area coverage, and high-aspect-ratio pores with sub-20 nm resolution. The fabricated membranes were validated through flow rate measurements, which showed good agreement with the predicted values based on the Hagen-Poiseuille equation. Filtration experiments using dextran molecules were conducted in a crossflow filtration system, revealing a time-dependent rejection behavior, where the sharpness of the rejection curve increased with prolonged filtration time. More importantly, the rejection profile was sharper than that predicted by the hindered transport model, fundamentally overcoming the selectivity limit. Bimodal membranes, featuring a binary pore size distribution, provide a unique platform for studying size-selective transport, flow partitioning, and fouling dynamics in ultrafiltration. Building upon isoporous membranes, a second population of pores was fabricated using electron beam lithography. These systems enable precise control over the population of “defects” (i.e., pores much larger than the targeted/mean pore size). A systematic simulation, analyzing how binary distribution and the number of interactions affect the rejection profile, revealed a direct pathway to correlate selectivity with permeability. The permeability of large-pore and bimodal membranes was studied and compared to three different theoretical models. Notably, bimodal membranes exhibited higher flow rates than the sum of their nanoporous and large-hole subcomponents, suggesting enhanced permeability. A solute size-dependent rejection profile exhibited an S-shaped transition for smaller solutes, followed by a plateau, confirming that small pores governed solute rejection, while large pores facilitated transport. Over time, the rejection plateau increased while flow rates decreased, indicating a progressive shift in effective membrane morphology. This dissertation provides new insights into the interplay between membrane morphology, flow transport, and filtration performance. The fabricated model membranes, with precisely controlled pore-size distributions, establish a robust platform for systematically investigating key factors influencing size-selective ultrafiltration, including solute-pore interactions, pore size distribution effects, and rejection dynamics
Discovering Dark Matter with the MUonE Experiment
Get PDFThe MUonE experiment aims to extract the hadronic contribution to the muon anomalous magnetic moment from a precise measurement of the muon-electron differential scattering cross section. We show that MUonE can also discover thermal relic dark matter using only its nominal experimental setup. Our search strategy is sensitive to models of dark matter in which pairs of pseudo-Dirac fermions are produced in muon-nucleus scattering in the target, and the heavier state decays semivisibly to yield dilepton pairs displaced downstream from the interaction point. This approach can probe sub-GeV thermal-relic dark matter whose cosmological abundance is governed by the same model parameters that set the MUonE signal strength. Furthermore, our results show that the downstream electron calorimeter plays a key role in rejecting backgrounds for this search, thereby providing strong motivation for the MUonE to keep this component in the final experimental design
Hypoxia Induces Extensive Protein and Proteolytic Remodeling of the Cell Surface in Pancreatic Adenocarcinoma (PDAC) Cell Lines
Get PDFThe tumor microenvironment (TME) plays a crucial role in cancer progression. Hypoxia is a hallmark of the TME and induces a cascade of molecular events that affect cellular processes involved in metabolism, metastasis, and proteolysis. In pancreatic ductal adenocarcinoma (PDAC), tumor tissues are extremely hypoxic. Here, we leveraged mass spectrometry technologies to examine hypoxia-induced alterations in the abundance and proteolytic modifications to cell surface and secreted proteins. Across four PDAC cell lines, we discovered extensive proteolytic remodeling of cell surface proteins involved in cellular adhesion and motility. Looking outward at the surrounding secreted space, we identified hypoxia-regulated secreted and proteolytically shed proteins involved in regulating the humoral immune and inflammatory response, and an upregulation of proteins involved in metabolic processing and tissue development. Combining cell surface N-terminomics and secretomics to evaluate the cellular response to hypoxia enabled us to identify significantly altered candidate proteins which may serve as potential biomarkers and therapeutic targets in PDAC. Furthermore, this approach provides a blueprint for studying dysregulated extracellular proteolysis in other cancers and inflammatory diseases
Untangling stability and gain modulation in cortical circuits with multiple interneuron classes
Get PDFSynaptic inhibition is the mechanistic backbone of a suite of cortical functions, not the least of which are maintaining network stability and modulating neuronal gain. In cortical models with a single inhibitory neuron class, network stabilization and gain control work in opposition to one another – meaning high gain coincides with low stability and vice versa. It is now clear that cortical inhibition is diverse, with molecularly distinguished cell classes having distinct positions within the cortical circuit. We analyze circuit models with pyramidal neurons (E) as well as parvalbumin (PV) and somatostatin (SOM) expressing interneurons. We show how, in E – PV – SOM recurrently connected networks, SOM-mediated modulation can lead to simultaneous increases in neuronal gain and network stability. Our work exposes how the impact of a modulation mediated by SOM neurons depends critically on circuit connectivity and the network state
Trends in parallel application to emergency medicine residency between 2009 and 2023
Get PDFObjectives: The residency match can be a stressful and costly period for applicants. A notable portion of applicants choose to apply to multiple specialties during the residency match process, known as “parallel applying.” This study investigated the trends in parallel applications among emergency medicine (EM) residency applicants from 2009 to 2023. Methods: This is a retrospective analysis on data obtained from the Association of American Medical Colleges (AAMC) Electronic Residency Application System (ERAS). The data set comprised applicants who applied either exclusively to EM or to EM in combination with other specialties. Variables analyzed included the number of applications submitted and the frequency of parallel applications across different applicant groups including international medical graduates (IMGs), U.S. international medical graduates (USIMGs), and graduates from U.S. allopathic and osteopathic institutions. Results: The study included 64,095 applicant records corresponding to 57,572 unique individuals. The percentage of applicants to EM residency parallel applying decreased between 2009 (62.0%) and 2020 (43.0%) but subsequently increased through 2023 (62.6%). The total number of applications submitted by both single-specialty and parallel applicants increased over the same period. The mean number of applications to EM programs by parallel applicants rose significantly, reflecting a broader trend of increasing application volumes across all applicant groups while the proportion of applications that were to EM programs decreased, especially following 2021. Conclusions: The trend of parallel applying among EM residency applicants slowly decreased from 2009 to 2021 and then increased through 2023, with the trend largely driven by an increase in the proportion of IMG applicants who were parallel applying. Understanding the motivations and impacts of parallel applications is crucial for developing strategies to support applicants and improve the matching process. Further research is needed to explore the factors influencing these trends and to inform policy and advising practices in medical education.</p
Essays on the Economic Analysis of Liability Insurance
Get PDFThis dissertation consists of essays exploring the microeconomic implications of liability insurance in three distinct domains: signaling, bargaining, and externalities. Each essay is dedicated to a separate topic. The first essay, Reliability Insurance, concentrates on signaling. Aside from deterring carelessness and guaranteeing compensation to victims, tort liability communicates willingness to bear any loss that results from imprudence. In so doing, tort liability counterintuitively serves the interest of injurers, allowing them to signal quality and substantiate credible commitment to careful behavior. In many market interactions, liability thus serves as a quintessential warranty, establishing injurers’ reliability. Yet the purchasing of liability insurance, at least on the surface, directly contradicts the credibility signal communicated by tort liability: instead of committing to self-incur the cost of any loss generated by their risky activity, tortfeasors choose to transfer this cost to an insurer. Insurance, in simple terms, seems to erode the skin-in-the-game message that injurers often wish to convey. The essay delves into this conundrum, studying the insurance-credibility interface both descriptively and normatively. The second essay, Insurance Settlements and the Perpetuation of Legal Risks, spotlights the unique bargaining strategies deployed by liability insurance carriers and identifies their profound legal implications. Against the anti-settlement tendencies routinely attributed to insurers, the essay identifies that under certain circumstances, it might be in insurers’ best interest to settle and avoid socially desirable litigation. This emanates from the fact that insurers are better off with legal uncertainty: ambiguity preserves injurers’ liability risks, thus enhancing their demand for insurance. The essay explores insurers’ strategic use of settlement to maintain legal risks, discusses concrete realms in which this behavior is observable, offers a normative discussion on the social costs and benefits of insurance, and considers potential mechanisms that may eliminate the ascribed problem. The third essay, Risk Allocation in a General-Equilibrium Model of Liability Insurance, offers a general-equilibrium analysis of externalities and risk allocation within the triangle of the insured, the insurer, and a third party. To date, both legal and economic literature on insurance has confined its focus to risk externalities that arise from the bilateral relationship between the insured and the insurer. Canonic accounts have introduced the problem of moral hazard, whereby the insured externalizes risk on the insurer. More modern contributions have highlighted insurer monitoring, which may induce the insured to reinternalize those risks. It was not until the last few years that commentators incorporated third parties into the equation, maintaining that they, too, tend to externalize risks on insurers. My proposed analysis completes the picture, demonstrating that the presence of third parties may actually generate multiple equilibria. The essay makes two main contributions to existing understanding of insurance dynamics. First, it shows that any actor within the triangle of insurer, insured, and a third party may act opportunistically and exhibit moral hazard that facilitates excessive risk. Second, any actor within this triangle may be the one who ultimately bears the cost of such excessive risk
Negotiating Asexual Identity in r/asexuality
Get PDFWith asexual (“ace”) people making up a minority even within queer communities, the internet has become a vital space for ace people to interact with the asexual community. In recent years, the Reddit forum r/asexuality has become the most active discursive space surrounding asexual identity, with over 230,000 members. Existing literature has theorized asexual identity formation through the lens of “discovery,” wherein individuals come to identify as ace after “discovering” the label (often via online spaces) and using it to understand their deviant experiences and desires—or, more precisely, their lack thereof. However, identity formation is a process that stretches beyond discovery of the asexual label as people negotiate complex experiences of doubt, reaffirmation, and validation. I argue that emergent online spaces such as r/asexuality play a key role in mediating these processes of identity negotiation. Through qualitative interviews with members of the r/asexuality community, I examine how ace people make sense of their role(s) in r/asexuality as they engage with the community over time and how these roles facilitate identity negotiation. I find that individuals who are new to r/asexuality see their primary role in the community as observing and learning from others, while members who have spent more time in the subreddit described their role as supporting others and building community. Acting within their respective roles facilitated the identity negotiation processes of both groups in divergent ways. This study broadens scholarly understanding of asexual online communities, which remain understudied in social scientific research
Problematic internet use as an age-related multifaceted problem: Evidence from a two-site survey
Get PDFBackground and aims: Problematic internet use (PIU; otherwise known as Internet Addiction) is a growing problem in modern societies. There is scarce knowledge of the demographic variables and specific internet activities associated with PIU and a limited understanding of how PIU should be conceptualized. Our aim was to identify specific internet activities associated with PIU and explore the moderating role of age and gender in those associations. Methods: We recruited 1749 participants aged 18 and above via media advertisements in an Internet-based survey at two sites, one in the US, and one in South Africa; we utilized Lasso regression for the analysis. Results: Specific internet activities were associated with higher problematic internet use scores, including general surfing (lasso β: 2.1), internet gaming (β: 0.6), online shopping (β: 1.4), use of online auction websites (β: 0.027), social networking (β: 0.46) and use of online pornography (β: 1.0). Age moderated the relationship between PIU and role-playing-games (β: 0.33), online gambling (β: 0.15), use of auction websites (β: 0.35) and streaming media (β: 0.35), with older age associated with higher levels of PIU. There was inconclusive evidence for gender and gender × internet activities being associated with problematic internet use scores. Attention-deficit hyperactivity disorder (ADHD) and social anxiety disorder were associated with high PIU scores in young participants (age ≤ 25, β: 0.35 and 0.65 respectively), whereas generalized anxiety disorder (GAD) and obsessive-compulsive disorder (OCD) were associated with high PIU scores in the older participants (age > 55, β: 6.4 and 4.3 respectively). Conclusions: Many types of online behavior (e.g. shopping, pornography, general surfing) bear a stronger relationship with maladaptive use of the internet than gaming supporting the diagnostic classification of problematic internet use as a multifaceted disorder. Furthermore, internet activities and psychiatric diagnoses associated with problematic internet use vary with age, with public health implications.</p