Understanding Contrastive Learning Through the Lens of Margins

Contrastive learning, along with its variations, has been a highly effective self-supervised learning method across diverse domains. Contrastive learning measures the distance between representations using cosine similarity and uses cross-entropy for representation learning. Within the same framework of cosine-similarity-based representation learning, margins have played a significant role in enhancing face and speaker recognition tasks. Interestingly, despite the shared reliance on the same similarity metrics and objective functions, contrastive learning has not actively adopted margins. Furthermore, decision-boundary-based explanations are the only ones that have been used to explain the effect of margins in contrastive learning. In this work, we propose a new perspective to understand the role of margins based on gradient analysis. Based on the new perspective, we analyze how margins affect gradients of contrastive learning and separate the effect into more elemental levels. We separately analyze each and provide possible directions for improving contrastive learning. Our experimental results demonstrate that emphasizing positive samples and scaling gradients depending on positive sample angles and logits are the keys to improving the generalization performance of contrastive learning in both seen and unseen datasets, and other factors can only marginally improve performance

Hydrothermally treated coral scaffold promotes proliferation of mesenchymal stem cells and enhances segmental bone defect healing

Introduction: Synthetic hydroxyapatite (HAp) scaffolds have shown promising therapeutic outcomes in both animals and patients. In this study, we aim to evaluate the chemical and physical phenotype, biocompatibility, and bone repair effects of hydrothermally treated coral with natural coral and synthetic HAp.Methods: The phase composition, surface pattern, 3D structures, and porosity of the scaffolds were characterized, and cell viability, proliferation, and osteogenic differentiation of mesenchymal stem cells (MSCs) after seeding onto the scaffold were determined. The scaffolds were implanted into rats to assess their bone repair effects using micro-CT analysis, mechanical testing, and histological staining.Results: The results showed that the phase composition, porous structure, and porosity of hydrothermally treated coral were comparable to pure HAp scaffold. While only the natural coral happens to be dominantly calcium carbonate. Higher cell proliferation and osteogenic differentiation potential were observed in the hydrothermally treated coral scaffold compared to natural coral and pure HAp. Histological results also showed increased new bone formation in the hydrothermally treated coral group.Discussion: Overall, our study suggests that hydrothermal modification enhances the cytocompatibility and therapeutic capacity of coral without altering its physical properties, showing superior effectiveness in bone repair to synthetic HAp

The First Very Long Baseline Interferometry Image of 44 GHz Methanol Maser with the KVN and VERA Array (KaVA)

We have carried out the first very long baseline interferometry (VLBI) imaging of 44 GHz class I methanol maser (7_{0}-6_{1}A^{+}) associated with a millimeter core MM2 in a massive star-forming region IRAS 18151-1208 with KaVA (KVN and VERA Array), which is a newly combined array of KVN (Korean VLBI Network) and VERA (VLBI Exploration of Radio Astrometry). We have succeeded in imaging compact maser features with a synthesized beam size of 2.7 milliarcseconds x 1.5 milliarcseconds (mas). These features are detected at a limited number of baselines within the length of shorter than approximately 650 km corresponding to 100 Mlambda in the uv-coverage. The central velocity and the velocity width of the 44 GHz methanol maser are consistent with those of the quiescent gas rather than the outflow traced by the SiO thermal line. The minimum component size among the maser features is ~ 5 mas x 2 mas, which corresponds to the linear size of ~ 15 AU x 6 AU assuming a distance of 3 kpc. The brightness temperatures of these features range from ~ 3.5 x 10^{8} to 1.0 x 10^{10} K, which are higher than estimated lower limit from a previous Very Large Array observation with the highest spatial resolution of ~ 50 mas. The 44 GHz class I methanol maser in IRAS 18151-1208 is found to be associated with the MM2 core, which is thought to be less evolved than another millimeter core MM1 associated with the 6.7 GHz class II methanol maser.Comment: 19 pages, 3 figure

The Age of Geopolitics: Japan, Russia, and the United States in the Far East, 1895-1905

The central intellectual problem of this dissertation is geopolitics. In particular, it is driven by three closely related questions: What is geopolitics? How does geopolitics work? What value does geopolitics have? Drawing from the classics, this study recasts geopolitics as an international theory concerned with the geographic orientation of foreign policy. It examines the relationship between two conceptual variables: geopolitics and geostrategy. A state’s geopolitical position, or “geopolitics,” is defined by “interest”—economic and military objectives—and “accessibility”—the ability to relocate resources and men—vis-à-vis different regions; this in turn is reflected in the direction of expansion, “geostrategy.” The crux of its argument is that accessibility is a more reliable predictor of geostrategy than interest. The empirical section is centered around three historical cases of Japan, Russia, and the United States with focus on their Far Eastern policies during the critical decade (1895-1905) demarcated by the Sino-Japanese War (1894-1895) and the Russo-Japanese War (1904-1905). Geopolitics brings back space and time to international relations theory and the craft of international history. From the policy standpoint, it also helps anticipate where today’s emerging powers will expand—thus where strategic competition will occur. In this way, this study ultimately attempts to bridge the gap between the history, theory, and practice of international politics

THE INTEGRATED DESIGN PROCESS OF A REHABILITATION EXERCISE SYSTEM: ELBOW JOINT REHABILITATION DEVICE AND SERVICE

Department of Creative Design EngineeringThis study employed a design agenda based on an integrated design process for a new rehabilitation exercise device and service system as a potential solution for treating upper-limb rehabilitation confronting the Korean rehabilitation treatment industry. For generating the design agenda, adopting a mixed design process consisting of both the main design process treating the overall process and the sub design process treating the phase process. Activities were conducted to define the design requirements while carrying out the design process. These activities included interviews with rehabilitation medical specialists at Kyungpook National University Hospital and Ulsan National University Hospital, visits to the occupational rehabilitation therapy room, and reviewing prior research surveys. This activity made it possible to understand the design requirements and trends in the design of upper-limb rehabilitation devices in Korea by extracting keywords and analyzing the collected information. A specialist in rehabilitation medicine at Kyungpook National University Hospital/Ulsan University, a company specializing in precision control, and a professor of design at Ulsan Institute of Science and Technology provided assistance and professional knowledge required in determining design the elements during the design process. The final result is divided into the interview result, the service system???s design and the device???s design within the service system. Several reasons were identified from interview results as to why a rehabilitation robot is not easily introduced and used in the Korean rehabilitation hospital based on four categories: medical environment, existing products, exercise, and hospital systems. The service system completed the concept design level. The device design was completed at the system-level design and partially the detail design. The device design???s specific results include establishing the type of product, drawings, IF design contest entries, and patent applications. The expected effectiveness of the design agenda in this research is the introduction of Smart rehabilitation methods, improvement of medical welfare, reduction of work burden, quantification of diagnosis and prescription, and provision of customized training for patients. Rehabilitation medical professionals and precision control service providing companies showed the willingness to study further and commercialize the device design outcome. Through this study, one example is presented to designers in the Korean upper-limb rehabilitation device design field to employ design leadership to attract engineers or other groups of experts so that post-product concept design may be further studied.clos

Rethinking Geopolitics: Geography as an Aid to Statecraft (Fall 2023)

Geopolitics has become marginalized in modern international relations scholarship despite its foundational role. This essay seeks to bring geopolitics back to the mainstream of international relations through conceptual, historical, and theoretical analyses. I make three arguments. First, definitional confusion about geopolitics comes from an overly broad understanding of geography. Notwithstanding various uses, however, geography itself should be re-centered as the analytical core of geopolitics. Second, classical geopolitics sought to inform grand strategy using geography as an explanatory variable and was thus institutionalized in U.S. strategic education. To wit, geography was used as “an aid to statecraft.” Finally, although largely ignored in mainstream international relations, the basic premise of geopolitics still undergirds much of its research. But the asymmetry, relativity, and comprehensiveness of geography have not been well explored. Drawing from classical geopolitical works, I offer some suggestions for future research on how to use geography in international relations scholarship.LBJ School of Public Affair

A Physically Unclonable Function Combining a Process Mismatch Amplifier in an Oscillator Collapse Topology

1