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Scalable Methods for Modeling Dynamic Spatio-Temporal Data
Get PDFHierarchical spatio-temporal models have been developed to model complex datasets exhibiting spatio-temporal (ST) autocorrelation; however, many of these models are purely descriptive and do not explicitly model the underlying dynamic processes. Animal movement or general movement behaviors are examples of such dynamic processes; that is, animals, or agents, move from one place to another over time, and their migration behavior can change with time and as well as their current (and past) locations. The motivating example for this thesis aims to model the spatio-temporal movement of the Eurasian collared-dove within the continental United States from 2001-2010. Existing studies have modeled animal movement using a reaction-diffusion equation or other systems of differential equation. Recently, dynamic spatio-temporal models (DSTMs) have incorporated these physical processes into a Bayesian hierarchical modeling framework. While DSTMs are extremely flexible, they can be computationally costly to fit and do not scale well to high-dimensional observations. In this thesis, I propose a computationally-efficient method to fit DSTMs to large spacetime count-valued datasets. The proposed scalable DSTM utilizes spatial basis functions to summarize the high-dimensional data as well as a spatial interpolator to assimilate observations at irregularly-spaced locations. I demonstrate the approach on simulated examples as well as a real-world dataset that tracks the prevalence of the Eurasian collared dove. Through a comparative analysis, the proposed approach is evaluated against a competing method with respect to goodness-of-fit and uncertainty quantification. In addition, I compare the model-fitting walltimes to assess the associated computational costs. The thesis concludes with a summary of the main contributions, discussion of key limitations, and directions for future research
Shame
No full textThis talk begins with the complexities of defining shame, as both an individual and social emotion that is variously contested in many contemporary societies. It discusses the extensive reliance on shame of most if not all traditional societies, and the various devices used to enforce it. It emphasizes the strong deterrent effect that resulted -- shame was more important as deterrent than punishment. The lecture then turns to the attack on shame as an affront to individual dignity and a cruel punishment, that resulted from the new values of the Enlightenment in Western societies on both sides of the Atlantic. Traditional shaming devices, like pillories, were outlawed, and efforts were made to reduce shame in childrearing and in schools. This effort has continued into recent decades, with campaigns against various forms of individual and group shaming. However, it has proved impossible fully to eliminate shaming, and new shaming impulses have arisen in various contemporary situations -- further spurred, recently, by the shaming potential of social media. The lecture closes with the resultant tensions over shaming in contemporary society and the possibility of using the historical record to take a more nuanced approach to the emotion
COOPERATION AND COMPETITION IN THE U.S. AIRLINE INDUSTRY: ESSAYS ON RELATIONAL CONTRACTS AND COMMON OWNERSHIP
Get PDFThis dissertation comprises three empirical essays exploring the themes of cooperation and competition within the U.S. airline industry.Chapter 1 looks at how informal agreements called relational contracts impact how well airlines operate. Relational contracts are used when parties need to work together over a long time, be flexible, and adapt to changes. In the U.S. airline industry, major airlines hire smaller regional airlines to operate some of their flights. The contracts they have for this outsourcing don’t work well when there’s bad weather and quick changes to those operations are needed. To handle these situations better, major airlines make informal agreements with their regional partners. These agreements help them adjust their operations quickly, which is important for how well they perform. The study examines whether the extent of these agreements by a major airline at an airport affects the delays and cancellations of their flights. The results show that these relational contracts improve airlines’ performance by lowering delays and cancellations, especially when the weather is bad, because they allow for quick adjustments to be made. In Chapter 2, I investigate how the ownership of shares by institutional investors in competing companies affects competition in the market. This ownership, known as common ownership, raises concerns that it might harm competition because the managers of these companies may prioritize the profits of their rivals and take into account the impact of their pricing decisions. To test this idea, I examine how common ownership influences pricing practices that could be anticompetitive. I use tests proposed by (Ciliberto et al., 2019) to analyze whether common ownership reduces price differences between firms and makes prices less responsive to market changes. By studying data from the U.S. airline industry, I find no evidence to support the claim that common ownership leads to anticompetitive pricing strategies. In fact, my analysis challenges previous studies that focused only on price levels and suggests that common ownership does not necessarily result in behavior that harms competition. In the third chapter of my research, I explore the question of whether common ownership leads to higher prices using structural modeling analysis. To begin, I look at the relationship between prices and common ownership by comparing them in a series of price regressions. This comparison shows a small, but marginally significant, link between common ownership and lower prices. This suggests that common ownership might have a slight effect on reducing prices. Next, I use a structural model to estimate the impact of common ownership on pricing behavior. This model considers both the demand for airline services and how airlines decide on prices. In this model, I take into account how firms think about their rivals’ profits when setting prices. To better understand the results, let’s talk about two pricing models. The first one is called the ”Bertrand pricing model.” In this model, airlines compete with each other by independently setting prices to make the most profit. The second model is the ”common ownership pricing model.” In this model, airlines consider their rivals’ profits when deciding on prices. Based on my analysis, I find that the influence of common ownership on pricing behavior is slightly positive, but not statistically significant. This means that common ownership does not lead to higher prices compared to what we would expect in a competitive market where airlines set prices independently
Self-management Interventions among Students with Disabilities: A Systematic Review and Meta-analysis
Get PDFStudents with disabilities often present social, emotional, and/or behavioral problems that can adversely impact their educational progress. As a result, interventions that are effective in addressing these non-academic challenges are needed. Self-management is an intervention that has demonstrated effectiveness across individual studies and systematic reviews. However, few studies have examined how participant characteristics or intervention characteristics may influence the intervention’s effectiveness. Educators need this information to successfully support the social, emotional, and behavioral needs of students. As such, this study consists of a systematic review and meta-analysis designed to answer the following questions. 1. What is the average treatment effect of self-management interventions among individuals with disabilities? 2. Is there a difference in treatment effect for (a) social, (b) academic, or (c) behavioral outcomes? 3. Do student characteristics (e.g., age, gender, grade, race, cognitive ability, disability) moderate the intervention effect? 4. Do intervention characteristics (e.g., implementer, setting, proportion of self-managed components) moderate the intervention effect? This systematic review and meta-analysis provides an update of the current literature regarding the effectiveness and implementation of self-management intervention among school-age students with disabilities and provides evidence that may help guide educators in the selection of interventions that best match their students. Compared to previous reviews, this study includes a broader range of disability categories and learning contexts. Additionally, the current study used multilevel modeling and robust variance estimation, which allowed for the investigation of within-study and between-study differences in student outcomes. Results from 41 studies and 117 participants yielded an overall positive effect indicating that all participants displayed some benefit from self-management interventions. Results, however, revealed significant variability between and within studies, suggesting that participants benefited differently, even when provided the same intervention. Further analyses suggest that participant characteristics have a greater influence on outcomes than intervention characteristics
Advanced Materials with Fine-Tuned Surface Modifications for Water Desalination and Biomedical Applications
No full textThis work is embargoed by the author and will not be publicly available until July 17, 2027.The adhesion resulting from bonding strength plays a vital role in material performance, affecting electrochemical adsorption, ions storage and physical attachment existing at the surface of varieties of materials, with broader implications for water treatment, energy, and biomedical areas. In this thesis, I have successfully demonstrated two strategies to achieve fine-tuned surfaces to obtain higher attractive forces among ions-charged surface in liquid environments and among solid interfaces connection. The tight bonding between ions from a saline liquid and a charged carbon electrode is critical in water desalination by capacitive deionization, where the surface of porous carbon has an immediate impact on salt adsorption behavior. Surface modification between carbon and an activating agent result in tunable surface and electrical properties of natural wood converted carbon electrode, further enhancing its water desalination performance. On the other hand, the adhesion between the hook and main body of a pacemaker is important to its safety usage, while the release of bonding is also significant during components replacement. Thus, a dual-crosslinked liquid crystal elastomer (LCE) film with reversible shape deformation property was successfully designed and synthesized. Due to the special mechanical property, the LCE film is applied as an easy-detachable component in a novel pacemaker. In summary, the adhesion between solid-liquid surface and physical connections between components ensure the successful application of surface-modified advanced materials in environmental and biomedical areas.2025-05-1
INVESTIGATING DUAL ENROLLMENT POLICY TO ENHANCE ACCESS AND SUCCESS: AN INSTRUMENTAL MULTICASE STUDY
Get PDFThis qualitative instrumental multicase study described and explored dual enrollment policies in three states: Colorado, Indiana, and Virginia. Student outcomes from dual enrollment participation are positive, yet access to these programs is uneven within and across states. Colorado, Indiana, and Virginia have similar educational governance structures, and each has received attention from national organizations due to positive aspects of their dual enrollment policies. This research included both documents and interviews as data, and integrated a policy lens, differentiating it from the current scholarly literature investigating dual enrollment. Participants included key stakeholders representing relevant state agencies in each state. Incorporating a policy process framework, strategies for conducting policy-relevant research, and an adapted document analysis tool contributed to the research methods. This multicase study included attention to each case followed by cross-case analysis. Four global themes emerged: policy, finances, people, and data reporting. Variations within and between states were explored to better understand what contributed to or inhibited dual enrollment opportunities. As an instrumental study, recommendations to help stakeholders and policymakers seeking to leverage dual enrollment policies to support and improve higher education access and college attainment are to establish clear and directive policies, dedicate finances, value and support the people engaged in the work, and prioritize disaggregated data reporting
DETERMINING THE BETTI NUMBERS OF R/(X^P^E,Y^P^E,Z^P^E) FOR MOST EVEN DEGREE HYPERSURFACES IN ODD CHARACTERISTIC
Get PDFLet k be a field of odd characteristic p. Fix an even number d < p + 1 and a power q ≥ d+3 of p. For most choices of degree d standard graded hypersurfaces R = k[x, y, z]/(f) with homogeneous maximal ideal m, we can determine the graded Betti numbers of R/m^[q]. In fact, given two fixed powers q_0, q_1 ≥ d+3, for most choices of R the graded Betti numbers in high homological degree of R/m^[q_0] and R/m^[q_1] are the same up to a constant shift. This thesis shows this fact by combining our results with the work of Miller, Rahmati, and R.G on link-q-compressed polynomials. We show that link-q-compressed polynomials are indeed fairly common in many polynomial rings
Probabilistic Generative Models for Learning with Hypergraphs
Get PDFHypergraphs extend conventional graphs by allowing hyperedges to connect any number of nodes. Despite increasing interest in hypergraphs and numerous attempts to exploit their higher-order connections, existing hypergraph analytics solutions have been limited in their effectiveness, primarily due to the complexity arising from the exponential hyperedge space. This dissertation first examines the efficacy of previous hypergraph analytics methods by developing two network anomaly detection approaches: one based on regular graphs and the other leveraging existing hypergraph analytics techniques. While experimental results demonstrate the effectiveness of the former approach, the latter proves to be less successful, indicating a demand for more advanced hypergraph-based frameworks. To address this demand, this dissertation introduces Hypergraph Simultaneous Generators (HySGen), a versatile probabilistic hypergraph model that formulates its generative process by conditioning the distribution of hyperedges on the nodes' community affiliations. Distinguishing itself from previous models, HySGen does not alter the nature of the hyperedges or constrain their size, and provides a novel method for detecting overlapping communities by effectively utilizing the higher-order connection information in hypergraphs. To tackle the intractable complexity associated with representing the entire state space of the hyperedges, this dissertation introduces a complexity reduction method that reduces the super-exponential inference time to linear without sacrificing any significant precision. Additionally, an algorithmic solution is presented for a runtime issue arising in situations requiring extremely high precision. To objectively assess detected overlapping communities, this dissertation introduces a novel performance measure that addresses the limitations of existing metrics. Experimental results demonstrate the effectiveness, scalability, and superiority of the introduced models and methods compared to current state-of-the-art techniques. The implementations of these models and methods have been incorporated into a popular open-source network analysis and graph mining library. This dissertation lays the foundation for a new line of future research and establishes a framework for developing innovative and effective hypergraph analytics algorithms, addressing the challenges and complexities associated with this field
Accelerating Polynomial Multiplication for Lattice-based Post-Quantum Cryptography
Get PDFCryptography plays an important part in today’s security and privacy. With the threat of Quantum Computers, modern cryptography will soon be extended with a new Post- Quantum Cryptography (PQC) standard. The new cryptography standard will bring new challenges: larger keys and certificates, more time-consuming operations, the need for novel and effective side-channel protection, and more.In this work, we focus on one aspect of the challenge – high-speed implementations in hardware and software – and one family of PQC algorithms - lattice-based cryptography. In investigating various approaches to speed up post-quantum cryptography, we observe that Number Theoretic Transform (NTT), Fast Fourier Transform (FFT), and Toom-Cook (TC) are crucial algorithms for the major operation of lattice-based cryptography - polynomial multiplication. This thesis discusses two proposed solutions: compact and efficient Number Theoretic Transform in hardware and high-speed Single Instruction, Multiple Data (SIMD)- based approach to implementing polynomial multiplication in software. In the hardware part, we present a conflict-free memory access for Radix-2×2, a variant of Radix-4 NTT implementation. In addition, our proposed solution addresses the disadvantages of the Radix-4 architecture, which only works for N = 4n. Instead, our design works for any N = 2n, with n ≥ 4. Our design is simple and versatile. It supports three major operations of polynomial mul- tiplication in the same circuit: Forward NTT, point-wise multiplication, and Inverse NTT. Compared to related work, our design uses fewer FPGA resources, such as Digital Signal Processing (DSP) units and Block RAMs (BRAMs). In the software part, we focus on optimized constant-time software implementations of three NIST PQC Key Encapsulation Mechanisms (KEMs) - CRYSTALS-Kyber, NTRU, and Saber - and three Digital Signature schemes - Falcon, SPHINCS+, and XMSS, tar- geting ARMv8 microprocessor cores. All optimized implementations include explicit calls to Advanced Single-Instruction Multiple-Data instructions (a.k.a. NEON instructions). Benchmarking is performed using two platforms: 1) MacBook Air, based on an Apple M1 System on Chip (SoC), including four high-performance ’Firestorm’ ARMv8 cores, running with the frequency of around 3.2 GHz, and 2) Raspberry Pi 4, a single-board computer based on the Broadcom SoC, BCM2711, with four 1.5 GHz 64-bit Cortex-A72 ARMv8 cores. We tailored the Toom-Cook algorithm by selecting optimal settings for NTRU and Saber. We demonstrated the advantages of our signed arithmetic implementation of NTT in Falcon and Kyber compared to the unsigned arithmetic NTT. We also improved the performance of hash-based signatures significantly by using the Crypto Instructions of the Apple M1 processor. Overall, our high-speed NEON implementations achieve considerable speed-up compared to the corresponding reference implementations in C. The obtained algorithm rankings are similar to those reported for the Advanced Vector Extensions 2 (AVX2)-based implementations developed by the respective submission teams, running on Intel and AMD processor cores
Characterizing AU Microscopii Planets with Transit Timing Variations
No full textExoplanetary sciences is a relatively new field of study that has grown beyond just detection method to include, among other things, planetary and atmospheric characterizations. Recent missions such as Kepler, K2, and TESS has resulted in more than 5 000 planets being validated or confirmed, allowing us to delve deeply into studying the properties of these planets and their host systems. In this thesis, I present the Transit Timing Variations (TTVs) of AU Mic b and c and the validation of the candidate planet AU Mic d. AU Mic is a young (22 Myr) nearby exoplanetary system that exhibits excess TTVs that cannot be accounted for by the two known transiting planets b and c nor stellar activity. 37 transit observations (including one ASTEP, one Brierfield, 23 LCOGT, one PEST, three Spitzer, and eight TESS), three Rossiter-McLaughlin (R-M) observations (ESPRESSO, iSHELL, and SPIRou), and nine CHEOPS transit midpoint times are included in our TTV analyses. First, we use EXOFASTv2 to jointly model the transit light curves to obtain the transit midpoint times. We then construct an O–C diagram and model the TTVs with Exo-Striker. Second, we reproduce our results with an independent photodynamical analysis. We recover a TTV mass for AU Mic c of 10.8+2.3−2.2 M⊕. We compare the TTV-derived constraints to a recent radial-velocity (RV) mass determination. We also observe excess TTVs that do not appear to be consistent with the dynamical interactions of b and c alone, and do not appear to be due to spots or flares; therefore, we hypothesize the existence of a third planet AU Mic d that is driving the observed excess TTVs. I calculate d’s potential orbital periods by modeling the observed super-period in AU Mic b’s TTVs. Next, we explore several possible configurations for planet d, including having d be interior to b and having d be between b and c. We generate TTV log-likelihood periodograms to explore possible solutions for the orbital period of planet d and then follow those up with detailed TTV and RV MCMC modeling and stability tests. We find several candidate periods for AU Mic d, all of which are near resonances with AU Mic b and c of varying order. Based on our model comparisons, AU Mic b’s TTV super-period, stability tests, and Occam’s razor arguments regarding near-mean motion orbital resonance (MMR) chains and coplanarity of AU Mic system, the most-favored orbital period of AU Mic d is 12.73812 ± 0.00128 days (T_C,d = 2458333.32110 ± 0.35836 BJD), which puts the three planets near a 4:6:9 MMR. The mass for d from the most plausible case is M_d = 1.013 ± 0.146 M⊕, making this planet Earth-like in mass. This would make AU Mic the first known young star to host an Earth-mass planet. Lastly, I characterize AU Mic b’s atmosphere with Transit Depth Variations and found the effective radius of AU Mic b to be significantly smaller at 4.5 μm than at optical range, a phenomenon that is similarly seen in another young planet K2-33 b. The mass-radius analysis of AU Mic b indicates that it is comparable to that of a 10% H + He planet; however, since it’s atmosphere is known to be evaporating, AU Mic b is evolving into a smaller and denser planet over the next several Myrs or Gyrs. The presence of near-MMRs in a very young system implies that compact planetary systems can develop resonant chains very early on, which can quickly establish the stability of the systems. Additional TTV observations of the AU Mic system are needed to further constrain the planetary masses, search for possible transits of AU Mic d, and detect possible additional planets beyond AU Mic c. If AU Mic d does transit, it will serve as an incredibly valuable case study for characterizing the atmosphere of young terrestrial planets and understanding its evolution