Atlas of Science Collaboration, 1971-2020

The evolving landscape of interinstitutional collaborative research across 15 natural science disciplines is explored using the open data sourced from OpenAlex. This extensive exploration spans the years from 1971 to 2020, facilitating a thorough investigation of leading scientific output producers and their collaborative relationships based on coauthorships. The findings are visually presented on world maps and other diagrams, offering a clear and insightful portrayal of notable variations in both national and international collaboration patterns across various fields and time periods. These visual representations serve as valuable resources for science policymakers, diplomats and institutional researchers, providing them with a comprehensive overview of global collaboration and aiding their intuitive grasp of the evolving nature of these partnerships over time.Comment: 6+121 pages, many figures, 49 M

A half-century of international research collaboration dynamism: Congregate or disperse?

The past decades have witnessed a dramatic change in researchers' collaboration mode across borders. In addition to purely academia-driven collaborations, various state-led initiatives have also been developed and are underway, reflecting the rapidly changing geopolitical situation of the contemporary world. In such multilayered cooperative and competitive relationships among countries, it is of great interest to leaders in academia and the policy arena to grasp the full scope of international research collaboration and their country's place within it, along with its change over time. However, evidence for such world-scale dynamism is scarce to date. This paper provides unique evidence of how international collaboration clusters have formed and evolved over the past half-century for a broad set of scientific publications. Our analyses are based on data retrieved from OpenAlex, a large-scale Open Bibliometrics platform launched in 2022. The science and technology areas of focus include Quantum Science, Artificial Intelligence, Biotechnology and others, totalling 15. We first review the top-tier countries' global presence change for each discipline, measured by publication volumes and international collaboration rates. Notably, the US and China are shown to have rapidly moved closer together for decades but have started moving apart after 2019. Subsequently, we analyse and visualise the international collaboration clusters for each discipline and period based on a hierarchical clustering method. Finally, we provide global-scale quantitative evidence for a 'Shrinking World' of the past half-century's research collaboration. These results provide valuable insights into the big picture of past, present and future international collaboration.Comment: 2+19 pages (5 figures) for Main Text; 21 pages (7 figures, 1 table) for Supplementary Material

Large Winding Sector of AdS/CFT

We study a family of classical strings on R x S^3 subspace of the AdS_5 x S^5 background that interpolates between pulsating strings and single-spike strings. They are obtained from the helical strings of hep-th/0609026 by interchanging worldsheet time and space coordinates, which maps rotating/spinning string states with large spins to oscillating states with large winding numbers. From a finite-gap perspective, this transformation is realised as an interchange of quasi-momentum and quasi-energy defined for the algebraic curve. The gauge theory duals are also discussed, and are identified with operators in the non-holomorphic sector of N=4 super Yang-Mills. They can be viewed as excited states above the ``antiferromagnetic'' state, which is ``the farthest from BPS'' in the spin-chain spectrum. Furthermore, we investigate helical strings on AdS_3 x S^1 in an appendix.Comment: 1+52 pages, 10 figures, v2: references and comments added, v3: minor changes and a reference adde

Evolving landscape of US-China science collaboration: Convergence and divergence

International research collaboration among global scientific powerhouses has exhibited a discernible trend towards convergence in recent decades. Notably, the US and China have significantly fortified their collaboration across diverse scientific disciplines, solidifying their status as a national-level duopoly in global scientific knowledge production. However, recent reports hint at a potential decline in collaboration between these two giants, even amidst the backdrop of advancing global convergence. Understanding the intricate interplay between cooperation and disparity within the US-China relationship is vital for both academia and policy leaders, as it provides invaluable insights into the potential future trajectory of global science collaboration. Despite its significance, there remains a noticeable dearth of quantitative evidence that adequately encapsulates the dynamism across disciplines and over time. To bridge this knowledge gap, this study delves into the evolving landscape of interaction between the US and China over recent decades. This investigation employs two approaches, one based on paper identifiers and the other on researcher identifiers, both obtained from bibliometric data sourced from OpenAlex. From both approaches, our findings unveil the unique and dynamic nature of the US-China relationship, characterised by a collaboration pattern initially marked by rapid convergence, followed by a recent phase of divergence.Comment: Main Text: 15 pages (4 figures); Supplementary Materials: 3 pages (3 figures

Dynamics of moire trion and its valley polarization in microfabricated WSe2/MoSe2 heterobilayer

The moire potential, induced by stacking two monolayer semiconductors with slightly different lattice mismatches, acts as periodic quantum confinement for optically generated excitons, resulting in spatially ordered zero-dimensional quantum systems. However, there are limitations to exploring intrinsic optical properties of moire excitons due to ensemble averaged and broadened emissions from many peaks caused by the inhomogeneity of the moire potential. In this study, we proposed a microfabrication technique based on focused Ga+ ion beams, which enables us to control the number of peaks originating from the moire potential and thus explore unknown moire optical characteristics of WSe2/MoSe2 heterobilayers. By taking advantage of this approach, we reveal emissions from a single moire exciton and charged moire exciton (trion) under electrostatic doping conditions. We show the momentum dark moire trion state above the bright trion state with a splitting energy of approximately 4 meV and clarify that the dynamics are determined by the initial trion population in the bright state. Furthermore, the degree of negative circularly polarized emissions and their valley dynamics of moire trions are dominated by a very long valley relaxation process lasting ~700 ns. Our findings on microfabricated heterobilayers could be viewed as an extension of our groundbreaking efforts in the field of quantum optics application using moire superlattices.Comment: 41 pages, 4 figure