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대사이상으로 유발되는 간세포암 발병 기전 연구
No full text학위논문(박사) - 한국과학기술원 : 의과학대학원, 2025.2,[xii, 78 p. :]The mechanism of hepatocarcinogenesis driven by metabolic stress remains unclear, despite the increasing burden of metabolic dysfunction-associated steatotic liver disease. This study aimed to investigate the role of metabolic stress and its cooperating factor in promoting hepatocarcinogenesis using a mouse model. C57BL/6J mice at 7 weeks of age streptozotocin (STZ) injection followed by high-fat diet (HFD) feeding (STZHFD), resulting in a 100% tumor incidence after one year of HFD feeding. In contrast, neither STZ nor HFD alone induced tumor formation. Whole-genome sequencing of non-tumor hepatocytes from STZHFD and control mice revealed that HFD or aging had minimal effect on mutation rates, with STZ serving as the primary cause of somatic mutations. Mutation rates increased in lipid-laden light hepatocytes from STZHFD mice as disease progressed, indicating a lineage shift towards a highly mutated population. Bipotent transient liver progenitor cells differentiating from biliary epithelial cells (BECs), appeared following STZ injection, which differentiated and proliferated into mature hepatocytes only with subsequent HFD. Lineage tracing confirmed that this BEC-derived lineage developed into hepatocellular carcinoma. Somatic mutations in BECs and BEC-derived hepatocytes were significantly higher than in non-BEC-derived hepatocytes, suggesting the explanation for hepatocarcinogenesis in this lineage. Increased WNT ligand secretion from endothelial cells promoted this process in STZHFD mice. These results indicate that BECs are more susceptible to somatic mutation accumulation from alkylating agents compared to pre-existing hepatocytes, and that HFD fosters a tumor-promoting environment by promoting the differentiation and proliferation of BEC-derived hepatocytes, ultimately leading to HCCs originating from the BEC-lineage.한국과학기술원 :의과학대학원
일체형 가압경수로 적용 나선형 증기발생기의 나선관 밀도파 진동 연구
No full text학위논문(박사) - 한국과학기술원 : 원자력및양자공학과, 2025.2,[vii, 147 p. :]Helical steam generators are critical components in the design of small modular reactors, offering good heat transfer performance and compact design characteristics that enhance spatial efficiency. These features make helical steam generators viable options for both light-water and non-light-water reactors. However, they pose significant design and operational challenges, particularly with respect to two-phase flow instabilities such as density wave oscillation (DWO). DWO arises from complex thermal-hydraulic interactions within the helical tubes, and failure to clearly define stability boundaries can adversely impact the safety and performance of steam generators and reactor operations. This study provides an in-depth experimental and computational analyses of DWO in helical steam generators, aiming to deepen the understanding of the thermal-hydraulic characteristics and DWO mechanisms in helical tubes. Using experimental data obtained under various pressure and temperature conditions, the study compares and analyzes DWO trends based on the MARS-KS code. The analysis focuses on DWO characteristics observed in two configurations: two identical helical tubes and three helical tubes with differing geometries. This comparison evaluates the validity of deriving DWO stability boundaries for helical steam generators. To achieve these objectives, an experimental facility utilizing R245fa as the working fluid was designed and constructed. The experimental results provided detailed insights into the two-phase flow pressure drop and DWO characteristics in helical steam generators. The data were further used for the validation and enhancement of the MARS-KS code, contributing to the establishment of stability boundaries that can represent complex helical steam generators. This study is expected to serve as foundational data for the design and safety assessment of helical steam generators in the future.한국과학기술원 :원자력및양자공학과
각분해광전자분광법을 통한 물질 표면에서의 이차원 전자계 형성과 조절 연구
No full text학위논문(박사) - 한국과학기술원 : 물리학과, 2025.2,[ix, 64 p. :]This dissertation investigates the controlled manipulation of Rashba states in a topological material and polaronic behavior in an oxide material, highlighting their potential for advanced quantum applications. Rashba states, known for their promise in spintronics and topological quantum computing, are typically confined to specific material groups, and methods for their reliable control remain limited. In the first part of this study, Rashba states are revealed on the (001) surface of KZnBi, a topological Dirac semimetal, using angle-resolved photoemission spectroscopy (ARPES) and first-principles calculations. By altering surface conditions with alkali metal deposition, we demonstrate that restoring surface order enables the Rashba state, which is absent on a freshly cleaved surface. Additionally, continued deposition modifies the Rashba state’s dispersion from a parabolic form to a Dirac-like linear dispersion, providing a strategy for tailoring Rashba properties in topological systems. The second part of the dissertation focuses on the formation and stability of polarons in a high-density two-dimensional electron gas (2DEG) on the (001) surface of WO₃. Polaronic states typically collapse at high electron densities due to electronic screening, limiting their exploration in high-density regimes. Here, an unscreened polaronic state is observed, facilitated by oxygen vacancies and stabilized in a c(2×2) surface reconstruction. Using ARPES and scanning tunneling microscopy/spectroscopy, signatures of this stable polaronic state are identified at densities reaching 2.6×10¹⁴ cm⁻². This ordered polaron phase not only remains resilient to screening but also introduces possibilities for studying high-density polaron interactions, such as bipolaron formation and collective polaron behaviors, which may even include bipolaron superconductivity.This work presents novel methods for surface-state manipulation and stabilization in topological and oxide materials, offering significant insights for applications in spintronic devices, quantum computing, and correlated electron systems.한국과학기술원 :물리학과
준결정에서의 초공간 기하학과 이색적인 양자 현상
No full text학위논문(박사) - 한국과학기술원 : 물리학과, 2025.2,[xxii, 182 p. :]Quasicrystals exhibit unique physical properties distinct from conventional crystals and amorphous materials due to their aperiodic long-range atomic order. The study of these properties has required novel theoretical approaches, as traditional band-based methods rooted in periodicity cannot be applied. This dissertation introduces the concept of "hyperspace geometry," closely tied to the tiling patterns of quasicrystals, aiming to theoretically elucidate the exotic quantum phenomena that arise in various quasicrystal structures, while exploring their experimental applicability and controllability. Specifically, this dissertation addresses anomalous quantum transport, strong correlation effects over mesoscopic distances, the presence of multipolar magnetism, and pattern-dependent superconductivity, all grounded in the high-order symmetry and geometrical features of hyperspace. In addition, the existence and nature of the critical states that are driving these unique quantum phenomena are clarified, proposing methods to experimentally manipulate them. Through this, it deepens the theoretical understanding of properties of quasicrystals and presents the potential for experimental applications of quasicrystalline materials based on hyperspace geometry.한국과학기술원 :물리학과
박막 리튬 나이오베이트 기반 비선형 및 양자 포토닉스 연구
No full text학위논문(박사) - 한국과학기술원 : 물리학과, 2025.2,[viii, 76 p. :]The ability to manipulate light through the interaction with matter is fundamental for applications such as phase and intensity modulation and the generation of new wavelengths, enabling key technologies in telecommunications and quantum optics. However, for these capabilities to transition from laboratory research to commercial products, it is essential to achieve chip-scale integration. The thesis addresses this challenge by investigating nonlinear and quantum photonics using an integrated lithium niobate platform with strong second-order nonlinearity, demonstrating a versatile approach for miniaturized photonic devices.
We first present a wide-spectral electro-optic modulator that operates from the visible to the mid-infrared wavelengths using a novel two-point coupling method. This platform achieves precise control of coupling strength and high extinction ratios, overcoming spectral bandwidth limitations in conventional modulators.
Next, we conduct comprehensive analysis of the mid-infrared optical losses in thin-film lithium niobate micro-resonators, revealing that surface contamination and bulk defects are the main contributors to optical loss.
We also demonstrate ultra-bright spontaneous parametric down-conversion photon pair generation in a compact X-cut PPLN racetrack micro-resonator, establishing a highly efficient source for on-chip quantum photonic circuits.
These results lay a strong foundation for advancing scalable, high-performance LN-based photonic devices, opening new avenues for next-generation applications in quantum information processing, optical communications, and advanced spectroscopy.한국과학기술원 :물리학과
인류세에서의 친환경 태도와 행동: 디지털 시대의 순환 경제를 중심으로
No full text학위논문(박사) - 한국과학기술원 : 과학기술정책대학원, 2025.2,[iv, 138 p. :]This dissertation aims to explore environmnetal attitudes and behaviors in the Anthropocene, with a focus on smartphone disposal practices within the context of the circular economy in the digital age. Online survey data collected in South Korea (n = 1,668, age range = 19-90n = 943, age range = 19-78) were analyzed. In Chapter 2, the Anthropocene Awareness scale was developed to complement existing scales. Reliability tests, factor analyses, and correlation analyses revealed that the scale is a single, reliable dimension that demonstrates a strong correlation with envrionmental behaviors. Chapter 3 investigate individual smartphone disposal behaviors, classifying them into responsible disposal types—such as trade-in programs, second-hand sales, and transfers to family or friends—and non-disposal behaviors. Motivations and barriers for each type of behavior were analyzed using ordered logistic regression. In Chapter 4, factors influencing awareness, experiences, and behavioral intentions toward AI-based smartphone trading platforms, Mintit ATMs were examined through binary and ordered logistic regression analyses. The findings indicate that promoting responsible smartphone disposal requires targeted interventions addressing challenges such as emotional attachment, response efficacy, and behavioral knowledge while enhancing public awareness of disposal systems beyond general environmental education. The dissertation also emphasizes the need for further research on the circular economy, particularly concerning the older population, who not only face significant challenges in smartphone disposal but also hold the potential to be key agents in addressing these issues. Through the development of the Anthropocene Awareness scale and the analysis of smartphone disposal behaviors in South Korea, this study contributes valuable insights into individual environmental behaviors in the Anthropocene and provides practical policy recommendations to support circular economy practices in the digital age.한국과학기술원 :과학기술정책대학원
IT 기반 정보 집약적 서비스의 도입 요인, 사용자 역량, 그리고 가치 창출에 관한 연구: 의료 및 에너지 분야를 중심으로
No full text학위논문(박사) - 한국과학기술원 : 경영공학부, 2025.2,[iv, 113 p. :]The proliferation of information technology has paved the way for an array of information-intensive services. Notably, in domains characterized by high information utilization, such as the healthcare and energy sectors, IT-enabled information-intensive services exhibit considerable potential to yield benefits for individuals and society. To realize their intended value, these newly introduced services require user adoption and utilization based on appropriate capabilities. This dissertation encompasses three studies that explore the adoption factors, user capabilities, and value creation associated with IT-enabled information-intensive services. The initial essay delves into the health protection motivation and health information systems underpinning health protection behaviors, examining personal, social, and technological factors as well as system characteristics. The subsequent two essays investigate the effects of providing users with information about their energy consumption and reduction in energy appliance purchases, usage patterns, and consumption curtailment. Through these investigations, this dissertation offers specific and comprehensive insights that contribute to the design of IT-enabled information-intensive services aimed at enhancing individual and social utility, developing adoption promotion strategies, and assessing anticipated outcomes.한국과학기술원 :경영공학부
금융 및 커머스 산업에서 딥러닝을 통한 예측 및 최적화에 관한 연구
No full text학위논문(박사) - 한국과학기술원 : 경영공학부, 2025.2,[vi, 87p :]This dissertation addresses four critical prediction and optimization problems in finance and commerce, aiming to create value through efficient management by leveraging state-of-the-art deep learning technologies. This research presents novel methodologies based on advanced deep learning techniques to solve practical industrial challenges.
First, we propose a novel approach to stock portfolio optimization by connecting deep reinforcement learning with Modern Portfolio Theory. Second, we develop a GenAI-based multimodal stock prediction model that integrates textual data from analyst reports with stock price data. Third, we propose a representation-degeneration-based multimodal contrastive learning approach to predict initial sales of new products. Fourth, we introduce a text-to-outfit retrieval method for fashion item recommendations.
Each study validates its proposed methodology through empirical analysis using real-world data, demonstrating both theoretical contributions and practical applicability in their respective domains.한국과학기술원 :경영공학부
테일시터 드론의 데이터 기반 증분 비행 동역학 및 무게중심 제어 연구
No full text학위논문(박사) - 한국과학기술원 : 항공우주공학과, 2025.2,[v, 80 p. :]This paper presents a novel design to enhance the performance of a tailsitter flying wing during its transition phase by adjusting the center of gravity (CG) location and employing temporal index Gaussian process-based derivative incremental nonlinear dynamic inversion (TIGPD INDI) control to address uncertainties arising from CG shifts. In the forward and backward transition phases, the tailsitter relies on elevon and thrust control to manage its pitch axis control. During the forward and backward transition, pitch moment must be generated to rotate large pitch angle range under low dynamic pressures. If restoring pitch moment is too high or too low, the static stability hinders the transitions and flight maneuvers. By adjusting the CG location, the restoring pitching moment relative to the angle of attack is effectively manipulated. The tilt-rotor, tilt-wing and hybrid VTOL integrate rotating structural mechanism or motors for transitions, creating mechanical complexity and increasing mass and energy consumption due to redundancy. There exists extended flap, propeller pitch control, double wing configurations for tailsitter to solve lack of pitching moment issue. Taking an innovative approach, the proposed approach eliminates the need for additional multiple actuators or motors typically required for these configurations by employing simple battery moving mechanism with single actuator without any structural changes at the external frame. To address the complex moment dynamics introduced by CG shifts, a robust TIGPD-INDI control is employed, treating the effects of the CG shift in the model as uncertainties. This controller design requires state derivative terms, for which Gaussian process regression—a data-driven model estimation method—is proposed. Simulation results demonstrate that the proposed CG control integrated tailsitter enables smoother transitions and maintains a narrower angle of attack range compared to a tailsitter without static margin adjustments. Also, the proposed TIGPD INDI controller showed robustness and better estimation performance than other methods.한국과학기술원 :항공우주공학과
Oscillating scalar potential and its implications for cosmic neutrino background searches
No full textWe propose a novel mechanism in which the mass-squared term of a scalar potential periodically switches sign due to an external oscillatory wave. As a result of this "potential oscillation," the vacuum transitions between symmetry-broken and symmetry-restored phases. This repeated toggling leads to a time-varying vacuum state that, through the scalar field's couplings to other sectors, gives rise to interesting phenomenological consequences. As a concrete illustration, we demonstrate how these oscillations can open a new avenue for probing the cosmic neutrino background.