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Recent Applications of Generalized Instrumental Variable Models
No full textThis study comprehensively reviews recent developments in the
application of the generalized instrument variable (GIV) framework
introduced by Chesher and Rosen (2017, Econometrica). The GIV
framework effectively derives sharp bounds (equivalent to identified
sets) in incomplete models. Focusing on limited dependent variable
models with endogeneity, this study demonstrates the application of
general identification results to obtain the identified set in specific
settings. Moreover, practical implementation challenges that may
arise are discussed, and potential strategies for overcoming them
are highlighted in empirical research
Associations between social frailty, use of digital device and depression among community-dwelling older adults: A population-based cross-sectional study
No full textAimSocial frailty is prevalent among community-dwelling older adults, and it is a leading factor associated with depression in this population. Digital devices can provide opportunities to engage in social or recreational activities, helping to reduce depression in older adults, regardless of their level of social frailty. However, little is known about which specific activities older adults engage in with such devices can lower depression. Therefore, this study aimed to examine which activities are associated with a lower likelihood of developing depression after adjusting for social frailty.MethodsA secondary data analysis was carried out using the 2020 National Survey of Older Koreans, which includes a nationally representative sample of community-dwelling older adults in Korea (n = 9920). Depression was measured using the Geriatric Depression Scale, social frailty was measured with the Social Frailty Index and digital device use was measured using 11 items from the survey. The 11 items included sending and receiving text messages, searching for information, taking pictures or videos, watching videos, playing games, and more. The data were analyzed using weighted logistic regressions.ResultsIn this study, 13% of participants showed depression. After adjusting for social frailty, the following activities were significantly related to lower odds of depression: playing games (OR 0.618, 95% CI 0.438-0.872, P = 0.006), and searching for and installing applications (OR 0.590, 95% CI 0.372-0.937, P = 0.025).ConclusionsOlder adults engaging in activities using digital devices are less likely to develop depression. Educational programs should be developed to teach older adults about various activities they can perform with digital devices. Geriatr Gerontol Int 2025; 25: 434-441.Y
Effect of porcine oviductal fluid-derived extracellular vesicle supplementation on in vitro embryonic developmental competence and the production efficiency of cloned pigs
No full textExtracellular vesicles (EVs) derived from oviductal epithelial cells help with fertilization and embryo development. Although the effects of EVs on the developmental competence of somatic cell nuclear transfer (SCNT) embryos are known, their impact on the production efficiency of cloned pigs in surrogate mothers is unclear. We evaluated the effects of porcine oviductal fluid-derived EVs (oEVs) on the in vitro development of SCNT embryos and production efficiency in cloned pigs. Embryos were treated with isolated and characterized oEVs for 48 h, corresponding to the residence time of fertilized embryos in the oviduct. In both parthenogenetic activation (PA) and SCNT embryos, oEV-treated groups exhibited higher rate of blastocyst formation than the controls. Gene expression analysis revealed increased expression of genes essential for early embryonic development in four-cell stage SCNT embryos, including those involved in pluripotency (POU5F1; POU class 5 homeobox 1), genome stability (Zinc finger and SCAN domain containing 4), and DNA damage response (Checkpoint kinase 1). Additionally, gene expression analysis of blastocysts from SCNT embryos showed increased expression of pluripotency (POU5F1) and Wnt signal transduction (Axis inhibition protein 2). Transfer of day-2 in vitro cultured SCNT embryos into surrogate mothers revealed no significant difference in production efficiencies between the control and experimental groups. Thus, enhanced early embryonic developmental competence observed in vitro following oEV treatment of PA or SCNT embryos did not translate into improved production efficiency of cloned pigs following embryo transfer to surrogate mothers. Hence, the impact of oEV treatment on live birth outcomes requires further investigation.N
Revision of subfamily Calonecrinae (Coleoptera: Cucujoidea: Nitidulidae) systematics and natural history of a mysterious group
No full textCalonecrinae represent a unique but small subfamily of Nitidulidae that is endemic to South Asia. Their habitats, the South Asian lowland forests, are under the imminent threat of degradation, posing a risk of rapid extinction for these species in their specific locales. Despite the looming threat to their existence, our understanding of this enigmatic group remains limited. We conducted an examination of museum and newly collected specimens, alongside a review of the literature, which led to the discovery of a new species, Calonecrus mindanaoensis sp. nov., from Mindanao, Philippines. Additionally, we provide detailed illustrations of various type specimens of the genus Calonecrus Thomson. For the first time, the immature stages of Calonecrinae were described based on Calonecrus jendeki, with detailed photographs including scanning electron microscopy images. Additionally, their natural history was uncovered, revealing that all life stages are uniquely adapted to complete their entire life cycle in sticky sap. We reevaluate the phylogenetic placement of the Calonecrinae based on phylogenetic analyses of mitochondrial genomes. Calonecrinae positioned within the Epuraeinae clade and are phylogenetically related to the epuraeine genus Trimenus. Consequently, this study proposes reclassifying Calonecrinae as Calonecrini stat. nov., an extremely modified tribe within the Epuraeinae. This research significantly broadens our understanding of the ecology of Calonecrini. Along with the taxonomic and phylogenetic results, we provide a solid foundation for the conservation of this group and further research into their unique habitat preferences and evolutionary behaviour.N
In-situ fabrication of GaN/short-range ordered BN heterostructure light-emitting diodes
No full textWe fabricated GaN/BN double heterostructure light-emitting diodes (LEDs) where the BN layer exhibited an amorphous-like short-range order and facilitated the in-situ epitaxial lateral overgrowth (ELOG) of GaN films. Using an identical metal-organic chemical vapor deposition, the BN layer was reliably formed on the GaN film and then served as a growth mask during the high-temperature growth of the GaN overlayer. The BN layers were well dispersed over the entire surface with a partial coverage of 40-60% and a thickness of a few nm. The laterally overgrown GaN was epitaxially related to the initial GaN film exhibiting single crystallinity with flat and smooth surface morphology. Meanwhile, the in-situ-formed BN layer effectively blocked the threading dislocations where its density reductions were comparable to those of typical ex-situ ELOG processes. Furthermore, the BN-assisted ELOG reduced the mosaic of the practical single crystalline GaN grains and drastically improved crystallographic alignment and internal quantum efficiency. More importantly, the BN-assisted ELOG yielded high device performance of the GaN LEDs demonstrating that the benefits of ELOG were fully achieved with the fast and instant fabrication process.Y
Analysis of Discrepancies Between Textbook Descriptions and Experimental Observations of Water Cooling and Suggestions for Improvement
No full text본 연구에서는 중학교 과학 교과서에서 제시된 물의 냉각 곡선 실험과 실제 실험 결과 간의 불일치를 분석하고, 이를 해결하기 위한 개선 방안을 제안하였다. 교과서에서는 물이 냉각될 때 온도가 일정하게 감소하다가 0 ℃에서 응고가 일어나며 온도가 변하지 않는다고 설명하지만, 실제 실험에서는 과냉각 현상으로 인해 온도가 0 ℃ 이하로 떨어졌다가 갑작스럽게 상승하며 응고가 진행되었다. 또한, 실험에 소요되는 시간이 길어 수업 시간 내에 완료하기 어려운 점도 확인되었다. 이에 본 연구에서는 교과서의 실험 방법을 재현하고 불일치 현상의 원인을 탐구한 뒤, 개선된 실험 방법을 설계하였다. 이를 위해 냉각제의 온도를 –10 ℃ 이하로 유지하고, 물의 초기 온도를 높이며, 교반 자석을 사용해 대류를 촉진하여 과냉각을 최소화하고 실험 시간을 단축하였다. 이러한 개선을 통해 실제 실험 결과와 교과서의 설명 사이의 일치도를 높였으며, 교육 현장에서 보다 효과적으로 실험을 수행할 수 있게 되었다.N
Skill dependencies uncover nested human capital
No full textModern economies require increasingly diverse and specialized skills, many of which depend on the acquisition of other skills first. Here we analyse US survey data to reveal a nested structure within skill portfolios, where the direction of dependency is inferred from asymmetrical conditional probabilities—occupations require one skill conditional on another. This directional nature suggests that advanced, specific skills and knowledge are often built upon broader, fundamental ones. We examine 70 million job transitions to show that human capital development and career progression follow this structured pathway in which skills more aligned with the nested structure command higher wage premiums, require longer education and are less likely to be automated. These disparities are evident across genders and racial/ethnic groups, explaining long-term wage penalties. Finally, we find that this nested structure has become even more pronounced over the past two decades, indicating increased barriers to upward job mobility.Y
고분자 유체의 고체-액체 계면에서의 분자층 형성에 대한 유변학적 연구
No full text학위논문(박사) -- 서울대학교 대학원 : 자연과학대학 물리·천문학부(물리학전공), 2025. 2. 제원호.유체의 유변학적 특성은 일상생활에서 경험하는 파괴, 마찰, 젖음과 같은 기계적 현상을 설명한다. 과학과 기술의 발전과 함께, 더 작은 규모에서 물리적 특성을 이해하는 것이 점점 중요해지고 있다. 그러나 크기가 유사하고 연속족 모델이 더 이상 유효하지 않은 나노스케일에서는 이러한 이해가 여전히 도전 과제로 남아있다. 이에 따라 나노와 벌크 스케일 사이의 유변 모듈러스를 연속적으로 이해하기 위해 우리는 멀티스케일 레올로지를 성공적으로 수행할 수 있는 수정 진동자 기반-원자힘 현미경 (QTF-AFM) 기반 레오미터를 제시한다.
또한, 우리는 고분자 유체가 나노스케일 계면에서 비정질 상태에서 층상 구조로 구조적 전이를 할 수 있음을 관찰했다. 다양한 고체 표면에서 고분자 유체의 구조를 실험적으로 시각화하고 복소 모듈러스를 정량화했다. 인력 상호작용하는 표면에서 고분자의 분자량이 증가함에 따라 층상 구조가 강화되다가 얽힘이 발생하면 얽힘으로 인한 분자 간 상관관계로 인해 층상 구조가 억제되는 것을 발견했다. 더불어, 층상 구조는 손실 모듈러스 (loss modulus)를 현저히 감소시키는 동시에, 표면과의 거리에 대해 진동하는 저장 모듈러스 (storage modulus)를 나타낸다.
결과적으로, 층상 계면 유체에서는 거리의 변화에 따라 고체적 성질과 유체적 성질이 번갈아 나타나는 특성이 관찰된다. 이러한 고체와 유체상의 공존은 계면에서의 유체의 구조와 물성 관계에 대한 오랜 질문에 대한 실마리를 제공한다. 우리의 연구 결과는 나노스케일부터 벌크스케일까지 복잡한 유체의 마찰-유변학적 (tribo-rheology) 특성을 종합적으로 이해할 수 있는 기초를 제공한다.The rheological characteristics of fluids describe mechanical phenomena encountered in daily life, such as fracture, friction, and wetting. With advancements in science and technology, understanding physical properties at smaller scales has become increasingly important. However, this remains challenging, as the continuum description applicable at the bulk- and micro- does not hold at the nanoscale, where structures are comparable in size and the continuum model for fluids breaks down. Therefore, to bridge the gap between nano- and bulk-scale rheological moduli, we present a quartz tuning fork-atomic force microscope (QTF-AFM) based rheometer for successfully performing multiscale rheology.
Also, we observe that polymeric fluids can undergo a structural transition from the amorphous to the layered state at nanoscale interfaces. We experimentally visualize the structure and quantify the complex modulus of polymeric fluids on various solid substrates. We find that the layering enhances with increasing molecular weight of the polymer on attractive surfaces until entanglement occurs. Once entanglement takes place, the layering is suppressed due to intermolecular correlation. Furthermore, the layering substantially reduces the loss modulus while exhibiting an oscillatory storage modulus with respect to the distance from the substrate.
Consequently, alternating properties of solidity and fluidity depending on the distance emerge in the layered interfacial fluids. This coexistence of solid-like and fluid-like phases may provide clues to longstanding questions about the structure-property relations in fluids at interfaces. Our results provide a comprehensive understanding of the tribo-rheological properties of complex fluids across from nano- to bulk-scales.Abstracts i
List of Figures vii
1. Introduction 1
1.1 Motivation 1
1.2 Outline of this work 3
2. QTF-AFM based rheometer 5
2.1 System overview – Atomic force microscopy 5
2.2 Theory of shear-mode AFM 10
2.3 QTF as a quantitative force sensor 11
2.4 Preamplifier of QTF 18
2.5 Response time of QTF sensor 21
2.6 Tapered stiffness for measuring shear force 25
2.7 DC supply for controlling piezoelectric-transducer 27
3. Theoretical background 31
3.1 Introduction 31
3.2 Modeling viscoelastic fluids 34
3.3 Maxwell relaxation time 41
3.4 Complex modulus calculation 43
3.5 Free energy analysis of polymer-wall interaction 49
4. Multiscale rheology 52
4.1 Introduction 52
4.2 Experimental process 54
4.3 Rheology across the scale 61
4.4 Conclusion 70
5. Interfacial structure of polymeric fluids 71
5.1 Introduction 71
5.2 Structure of interfacial polymeric fluids 73
5.3 Free energy theory 81
5.4 Rheological properties of interfacial polymeric fluids 85
5.5 Relaxation time of interfacial polymeric fluids 92
6. Aging effects of layered structures 101
6.1 Introduction 101
6.2 Time dependence of layered structures 104
6.3 Rheological studies of nanoscale aging effects 106
6.4 Nanoscale aging effects analyzed by Maxwell relaxation time 110
7. Conclusions 113
Appendix 116
Appendix A. 116
Appendix B. 119
Bibliography 125
Abstract in Korean 138
Publication list 140박
First- and Second-Person Pronoun Use by East Asian EFL Learners: Corpus-Based Study of Argumentative Essays
No full textBased on the ICNALE corpus, this study investigates the use of first- and second-person pronouns in argumentative essays by Chinese, Korean, and Japanese leaners of English as a foreign language (EFL) across four proficiency levels. The findings indicate that higher-proficiency learners use these pronouns less frequently, which aligns with prior studies on Western EFL learners. Additionally, Korean and Japanese learners show stronger preference for I over we, whereas Chinese learners exhibit the opposite pattern. These differences may stem from various factors, such as cultural influences or first-language (L1) rhetorical conventions. Statistical analyses suggest that L1 background exerts a stronger effect on pronoun usage than proficiency level. This challenges the prescriptive English for Academic Purposes guidelines, which discourage first-person pronouns for novice writers regardless of their linguistic background. Meanwhile, pedagogical approaches that emphasize the rhetorical functions of pronouns may better equip learners in making informed lexical choices based on their communicative intent
Electrolyte-free potassium ions intercalated in 2D layered metal oxide for imitating spatiotemporal biological neural dynamics
No full textAlkali ions are crucial to physiological neural activitiesand their dynamics can be implemented in various iontronics. For the host materials for al preferred choice thanks to their facilitating ion Nevertheless, challenges such as the need for exte and thermodynamic stability during ion movem understanding of the electrical dynamics associated with alkali ion movement has rarely been demonstrated in 2D layered materials so far. Here, layered MnO2 nanoplate with potassium ions combination of potassium ions and layered MnO2 with a subsequent phase transition, resulting in material's distinct hybrid plasticity, driven by its i sequential motion recognition, valuable for ass kali ions, 2D layered materials have become the accommodation and movement between layers. r nal electrolytes, pre-fabrication for ion intercalation, ents still persist. Consequently, the comprehensive we engineered an electrolyte-free high-crystalline 2D by metal-organic chemical vapor deposition. The exhibits electrically induced ion migration coupled negative differential resistance. Furthermore, the on dynamics, provides a sophisticated platform for essing continuous motion across varied subjects. Finally, we demonstrate the broad applicability spatiotemporal ion modulation within three-t advancements. of our 2D K-MnO2 and highlight its versatility in erm inal structures, showing potential for futureN