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Simplicial Decomposition and Realization
Full text linkIn simplicial decomposition, we define two invariants --- V_Z and V_Q --- which represent notions of integral and rational volume of a certain class of simplicial complexes. We prove V_Z and V_Q are additive under disjoint union and connected sum, and investigate `integrality gaps\u27 between the two quantities. We apply the theory to establish a conjecture of Sleator, Thurston, and Tarjan on tetrahedral fillings, and, as a corollary, obtain a new proof of Pournin\u27s 2012 result on the diameter of the associahedron. In simplicial realization, we provide practical sufficient conditions and computer code to prove the existence of Euclidean embeddings of simplicial complexes with specified edge lengths. Example applications include proving the existence of specified edge-length graph embeddings in the plane, or specified edge-length embeddings of polyhedra in space. We apply this work to prove that every triangulation of the 2-sphere with maximum degree \u3c =6 and at most 23 vertices may be embedded in Euclidean 3-space with unit length edges
APPLICATIONS OF LANGUAGE-THEORETIC SECURITY TOWARDS SYSTEM SECURITY
Full text linkLanguage-theoretic security (or LangSec) research lies at the intersection of computer security research and formal language theory. In addition to investigating novel approaches for secure input handling in software systems, LangSec research also investigates novel conceptions of software exploitability derived from insights of formal language theory. This thesis advances this line of research by presenting:
(1) A survey of parser differential antipatterns (Chapter 3)
(2) A formal grammar backed secure parser generation framework for microcontrollers (Chapter 4)
(3) A toolkit for securing software module boundaries from crafted-input attacks (Chapter 5) (
4) An analysis which demonstrates latent functionality in complex package management systems and its security implications (Chapter 8)
(5) A framework for testing parser correctness via grammar-based input synthesis (Chapter 6)
(6) A novel fuzzing method for discovering parser differentials (Chapter 7)
Anatomy of an AI Arms Race: U.S. and China Technological Dispute for AI Leadership
No full textThe history of societies and the emergence of powerful states have been marked by cycles of conflict and war, followed by periods of cooperation that foster international stability. Similarly, the Cold War era saw a significant rise in military and economic capabilities, which highlighted a security dilemma as the former USSR and the United States sought to protect their national interests. Currently, artificial intelligence has expanded the scope of invisible warfare beyond the atomic bomb. Some scholars like Paul Scharre advocate that there is no arms race in place, and others support the idea of a healthy competition and collaboration that pushes innovation of AI among states. This thesis aims to investigate whether an AI Arms Race is presently unfolding between China and the United States. To support the idea that there’s an ongoing arms race and the U.S. is leading it, the argument will be built around the analogy of human anatomy to demonstrate a complete functional structure of the current warfare crisis. The skeletal system refers to the semiconductor production that drives AI systems, as well as the securitization of the supply chain. The nervous system represents the approach of AI regulations between government institutions. It explores the quid pro quo measures taken to balance political power as AI emerges as a powerful development and defense strategy. The muscular system acts as a military mechanism and autonomous weapons capabilities that both the US and China are developing to enhance security, but this also raises the risk of war escalation. Lastly, the cardiovascular system symbolizes the heart of artificial intelligence, representing the technology that fuels innovation and advanced LLMs.
This thesis concludes that the United States remains technologically superior in the securitization of supply chains and military AI systems. However, China\u27s rise, with its ambitious strategic plans, demonstrates resilience and progress despite export controls, positioning itself as a major competitor capable of closing the gap with the United States if the opportunity arises
Books and Media
Full text linkReviews of: The Lions of Winter, by Ty Gagne; 109° Below, a film directed by Nick Martini; Losing the Garden, by Laura Waterman; Ditch Memory, by Todd Davis; Shinrin-Yoku, by Marcyn Del Clements; You Are Here: Poetry in the Natural World, edited by Ada Limón
Appalachia Summer/Fall 2025: Complete Issue
Full text linkSummer/Fall 2025 - Volume LXXVI, Number 2 - Issue #260. On the Ground and Screen: Stories of smartphones in wild places
Property Testing AI: An Efficient Frontier
Full text linkIn this dissertation, we take a step towards addressing the major problem of a lack of standardized and rigorous approaches to testing and evaluation of AI systems. Taking inspiration from both the fields of Property Testing and Property Based Testing (for programs), we develop a novel taxonomy of partially overlapping classes of properties of AI systems, including simple properties, compound properties, higher order properties, data relation properties, and architecture-utility properties. We argue that this taxonomy categorizes a diverse set of AI traits -- including accuracy, fairness, robustness, monotonicity, point-wise and global privacy properties, sensitivity, and more -- according to the methods required to test for them. Through a series of four case studies, we investigate some of the peculiarities and challenges of testing for each of these types of properties. We show that, for these examples of complex AI properties, we must go beyond confidence intervals and I.I.D. sampling, and turn to additional theoretical and engineering tools such as property testing (case studies 1 and 2), Membership Inference Attacks (case study 3), and Adversarial Risk Analysis (case study 4). In addition, our case studies have intellectual merit on their own, including a new generalization bound for transformers based on two key complexity properties, a new theoretical perspective on Membership Inference Attacks as property tests, and a novel approach to evaluating overall risk of Multimodal Foundation Models in an adversarial context. Taken together, this work proposes property testing not only as a practical method but also as a unifying theoretical lens for building more principled and reliable AI evaluation strategies
PI4-Kinase Fwd in trafficking and cell surface expansion during early Drosophila embryogenesis
No full textCongenital birth deformities often arise during epithelial morphogenesis, displaying the need to understand the mechanisms underlying this process. Cell shape changes that mediate morphogenesis often require cell surface expansion to accommodate shifts in 3D tissue geometry. Previous work has identified Four Wheel Drive (Fwd), a Golgi-localized phosphatidylinositol 4-kinase (PI4K) IIIβ ortholog, as a regulator for cell surface expansion during Drosophila ventral furrow formation, a well-characterized model for epithelial folding.
Intracellular trafficking affects the cell’s capacity for surface expansion, which influences tissue properties such as membrane tension. This research will investigate the potential colocalization between Fwd and Rab11, a marker for recycling endosomes. We hypothesize that Fwd and Rab11 coordinate the trans-Golgi network and recycling endosomes to promote vesicle trafficking. We will evaluate the colocalization of Fwd and Rab11 through live imaging of embryos expressing Fwd-GFP and Rab11-mCherry, image segmentation and mask creation using ilastik, and identification of Fwd and Rab11 puncta that overlap in the masks.
In parallel, the project will investigate the potential function of Fwd in regulating membrane tension through the design of a membrane tension sensor. The sensor is a fusion protein consisting of a mechanosensitive channel linked to GFP, where the fluorescence intensity of GFP is inversely correlated with membrane tension. The effects of Fwd depletion on membrane tension dynamics will be visualized by live imaging of wild-type and fwd RNAi embryos. These experiments will provide key information about the molecular role of Fwd in cell surface expansion and its effects on the tissue’s mechanical properties.https://digitalcommons.dartmouth.edu/wetterhahn_2025/1015/thumbnail.jp
Dragon Guitars and Sexy Zombies: Tracing the Meta-Motion of the Naga Motif in Northeast Thailand
Full text linkAbstract
This thesis traces the evolving symbolism of the Naga motif (a mythic water serpent) in Northeast Thailand through a framework I call meta-motion, which maps symbolic persistence of this cultural signifier and boundary marker across four cultural horizons—animist (Z), Hindu–Khmer (B), Buddhist (A), and modern/global (C). Like electrons in quantum super position, symbolic motifs circulate as overlapping “waves” of potential meaning and are concretized into cultural “particles” only when recruited for specific ritual, commercial, or political purposes. I add a bookend extension to Chang’s Hindu-Buddhist (B/A) typology with the addition of Horizons Z and C in order to make visible the accumulative logic by which cultural symbols persist.
Based on sixteen months of multilingual archival study and ethnographic fieldwork in Northeast Thailand and Laos, the analysis draws on Barth’s cultural boundary theory, Watanabe’s idea of cultural shibboleths and recombinant forms, and Tambiah’s fieldwork in Thailand during the 1960s where he observed layered ritual and religious fields. I show that the Naga phin acts simultaneously as boundary marker and bridge: its carved Naga head along with the intrinsically Lao tonal contour of Mo Lam assert Isan distinctiveness, while its amplified form and artistic stage presence invite cosmopolitan participation.
Reframing syncretism as strategic calibration rather than passive blending, the meta-motion framework provides a transferable lens for analyzing resilience of cultural motifs and symbols under globalization. It shifts the conversation from rupture-centric post-colonial narratives toward an agentive, locally driven model of cultural persistence, and explains how motifs such as the Naga remain “good to think with” (Lévi-Strauss 1963) in new epistemic terrains
IMPROVING THE FIGURE OF MERIT IN IRON-VANADIUM-ALUMINIUM THERMOELECTRIC ALLOY SYSTEM GUIDED BY COMPUTATIONAL MODELING
Full text linkThermoelectric materials can convert a thermal gradient to electricity. Currently, commercialized Bi2Te3 is brittle and expensive, which restricts the usage of this material. Compared to other thermoelectric materials, Fe2VAl is cost-effective, stable and more robust mechanically. However, the figure of merit (zT) had been much lower than Bi2Te3. In this thesis, our main goal is to improve the figure of merit in Fe2VAl system guided by computational modeling. We will start the discussion by presenting the Ge doped Fe2VAl sample with record thermoelectric figure of merit value. Then, we analyze the system via computational modeling and explore the underlying mechanism for high zT in Ge doped Fe2VAl. The theoretical analysis has three parts. In the first part, we discuss the impact of substitutional defects (or doping) on the phase stability. We compare several possible dopants and find that Ge defect helps to stabilize the metastable B2* and L21* phases, which have a flatter band and provides more available electrons in the thermal excitation process. The trade-off in carrier mobility is compensated by a significant increase in free carrier density such that the overall electrical conductivity still increases by 3-4 times compared to that in the base alloy. We also discuss the Fe vacancies, which will work as phonon scattering centers and reduce the lattice thermal conductivity. In the second part, we use cluster expansion to study the phase transition temperature and meta-stable phases in Fe2VAl, including the effect of Ge dopants. For n-type alloys, modeling shows that Ge-doping would reduce the order-disorder transition temperature. Furthermore, calculations show that the Al-rich and V-rich samples both have a lower order-disorder phase transition temperature, so we expect a better performance in these samples than the base alloy by enhancing the atomic disorder. In the third part, we explore the bandgap engineering in Fe2VAl. We present the previous bandgap engineering work first (especially Garmroudi’s work), focusing on opening the effective bandgap to reduce the undesirable bipolar effect at \u3e400 K. Currently, most experimental and theoretical results support that Fe2VAl is a semimetal at 0 K, while the \u3c 0.1 eV bandgap observed at room temperature can be attributed to three factors: finite temperature disordering, off-stoichiometry compositional fluctuations of Al and V, and Burstein-Moss shift. Corresponding to these three factors, we propose three strategies to open the bandgap in Fe2VAl: incorporating meta-stable phases, creating disorder and involving external doping.
The above computational analysis serves as insightful guidance for experiments. Based on these results, we fabricated Al-rich p-type Fe2VAl sample, which is confirmed to be the best p-type sample with record figure of merit values. The theoretical prediction coincides with the experiments quite well in this off-stoichiometric system.
In summary, this dissertation provides a systematic computational analysis of Fe2VAl material system. The theoretical modeling provides insight to understand strongly enhanced thermoelectric performance in Ge-doped n-type alloys and directly inspired the development of Al-rich p-type alloys, both breaking the record of figure of merit in Fe2VAl material system. The new record for n-type alloys is now comparable to that in Bi2Te3. These results demonstrate the importance of computational modeling in guiding the design of new thermoelectric materials
PARTICLE-BASED HIGH-FIDELITY INTERFACE TRACKING ALGORITHMS
No full textAccurate interface tracking is essential in simulating multiphase flows, material deformation, and other physical phenomena involving evolving geometries. In this thesis, we present an adaptive dual-particle representation for high-fidelity interface tracking. By combining two types of particles—feature particles and sample particles—we construct an implicit representation that captures fine geometric details. This representation is evolved explicitly using a velocity flow field, enabling accurate and adaptive tracking of dynamic interfaces. We further propose a particle level set method on the flow map, leveraging the state-of-the-art accuracy of particle-based advection. By integrating this approach with the particle level set framework, we achieve fourth-order accuracy in interface representation and advection. Our method tracks both gradients and Hessians of the level set, allowing it to resolve sub-cell features beyond the reach of traditional techniques. Extensive numerical experiments and comparisons demonstrate that our method consistently outperforms existing interface tracking approaches in terms of accuracy, volume preservation, and feature fidelity