Non-Abelian topological defects and strain mapping in 2D moir\'e materials

We present a general method to analyze the topological nature of the domain boundary connectivity that appeared in relaxed moir\'e superlattice patterns at the interface of 2-dimensional (2D) van der Waals (vdW) materials. At large enough moir\'e lengths, all moir\'e systems relax into commensurated 2D domains separated by networks of dislocation lines. The nodes of the 2D dislocation line network can be considered as vortex-like topological defects. We find that a simple analogy to common topological systems with an $S^1$ order parameter, such as a superconductor or planar ferromagnet, cannot correctly capture the topological nature of these defects. For example, in twisted bilayer graphene, the order parameter space for the relaxed moir\'e system is homotopy equivalent to a punctured torus. Here, the nodes of the 2D dislocation network can be characterized as elements of the fundamental group of the punctured torus, the free group on two generators, endowing these network nodes with non-Abelian properties. Extending this analysis to consider moir\'e patterns generated from any relative strain, we find that antivortices occur in the presence of anisotropic heterostrain, such as shear or anisotropic expansion, while arrays of vortices appear under twist or isotropic expansion between vdW materials. Experimentally, utilizing the dark field imaging capability of transmission electron microscopy (TEM), we demonstrate the existence of vortex and antivortex pair formation in a moir\'e system, caused by competition between different types of heterostrains in the vdW interfaces. We also present a methodology for mapping the underlying heterostrain of a moir\'e structure from experimental TEM data, which provides a quantitative relation between the various components of heterostrain and vortex-antivortex density in moir\'e systems.Comment: 15 pages with 11 figure

Local-level spatiotemporal dynamics of COVID-19 transmission in the Greater Seoul Area, Korea: a view from a Bayesian perspective

OBJECTIVES The purpose of this study was to enhance the understanding of the local-level spatiotemporal dynamics of COVID-19 transmission in the Greater Seoul Area (GSA), Korea, after its initial outbreak in January 2020. METHODS Using the weekly aggregates of coronavirus disease 2019 (COVID-19) cases of 77 municipalities in the GSA, we examined the relative risks of COVID-19 infection across local districts over 50 consecutive weeks in 2020. To this end, we employed a spatiotemporal generalized linear mixed model under the hierarchical Bayesian framework. This allowed us to empirically examine the random effects of spatial alignments, temporal autocorrelation, and spatiotemporal interaction, along with fixed effects. Specifically, we utilized the conditional autoregressive and the weakly informative penalized complexity priors for hyperparameters of the random effects. RESULTS Spatiotemporal interaction dominated the overall variability of random influences, followed by spatial correlation, whereas the temporal correlation appeared to be small. Considering these findings, we present dynamic changes in the spread of COVID-19 across local municipalities in the GSA as well as regions at elevated risk for further policy intervention. CONCLUSIONS The outcomes of this study can contribute to advancing our understanding of the local-level COVID-19 spread dynamics within densely populated regions in Korea throughout 2020 from a different perspective, and will contribute to the development of regional safety planning against infectious diseases

Spatiotemporal Associations between Local Safety Level Index and COVID-19 Infection Risks across Capital Regions in South Korea

This study aims to provide an improved understanding of the local-level spatiotemporal evolution of COVID-19 spread across capital regions of South Korea during the second and third waves of the pandemic (August 2020~June 2021). To explain transmission, we rely upon the local safety level indices along with latent influences from the spatial alignment of municipalities and their serial (temporal) correlation. Utilizing a flexible hierarchical Bayesian model as an analytic operational framework, we exploit the modified BYM (BYM2) model with the Penalized Complexity (PC) priors to account for latent effects (unobserved heterogeneity). The outcome reveals that a municipality with higher population density is likely to have an elevated infection risk, whereas one with good preparedness for infectious disease tends to have a reduction in risk. Furthermore, we identify that including spatial and temporal correlations into the modeling framework significantly improves the performance and explanatory power, justifying our adoption of latent effects. Based on these findings, we present the dynamic evolution of COVID-19 across the Seoul Capital Area (SCA), which helps us verify unique patterns of disease spread as well as regions of elevated risk for further policy intervention and for supporting informed decision making for responding to infectious diseases

A novel transparent and auditable fog-assisted cloud storage with compensation mechanism

© 1996-2012 Tsinghua University Press. This paper introduces a new fog-assisted cloud storage which can achieve much higher throughput compared to the traditional cloud-only storage architecture by reducing the traffics toward the cloud storage. The fog-storage service providers are transparency to end-users and therefore, no modification on the end-user devices is necessary. This new system is featured with (1) a stronger audit scheme which is naturally coupled with the proposed architecture and does not suffer from the replay attack and (2) a transparent and efficient compensation mechanism for the fog-storage service providers. We provide rigorous theoretical analysis on the correctness and soundness of the proposed system. To the best of our knowledge, this is the first paper to discuss about a storage data audit scheme for fog-assisted cloud storage as well as the compensation mechanism for the service providers of the fog-storage service providers

Simulation Study on Internal Short Circuits in a Li-Ion Battery Depending on the Sizes, Quantities, and Locations of Li Dendrites

The internal short circuit caused by the Li dendrite is well known to be a major cause for fire or explosion accidents involving state-of-the-art lithium-ion batteries (LIBs). However, post-mortem analysis cannot identify the most probable cause, which is initially embedded in the cell, because the original structure of the cell totally collapses after the accident. Thus, multiphysics modeling and simulation must be an effective solution to investigate the effect of a specific cause in a variety of conditions. Herein, we reported an electrochemical-thermal model to simulate the internal short circuit depending on Li dendrite's sizes (1, 3, 5, 7, and 9 mu m), quantities (1-9), relative locations (0, 25, 50, 100, and 150 mu m), and external temperature (-10, 10, 30, and 50 degrees C). Through monitoring the temperature change affected by the joule and reaction heats for each case, we suggested critical conditions that led to unavoidable thermal runaway. Thus, this model can be a steppingstone in understanding the correlation between internal short circuits and Li dendrites.TRU

A Thermo-Electrochemical Model of 18.5 V/50 Ah Battery Module for Railway Vehicles

We developed a thermo-electrochemical model of a 50 Ah pouch-type lithium-ion cell and utilized a cell model to build an 18.5 V/50 Ah module to analyze the thermal behavior under various operating conditions and design cooling systems for optimal operating temperature ranges. Specifically, the heat generated by electrochemical reactions was simulated through an electrochemical cell model, and then the calculated heat was coupled with a heat transfer model reflecting the actual 3D structure of the cell. By fitting two temperature-dependent parameters, i.e., the chemical diffusion coefficient and exchange current density, the model accurately estimated the electrochemical and thermal properties with errors less than 3%, even under wide temperature (25 degrees C, 35 degrees C, and 45 degrees C) and C-rate (0.5, 1, 2, and 5C) conditions. Based on this reliable cell model, we built an 18.5 V/50 Ah module model with five cells in series to simulate both the amount of heat generated and the required heat sink. Finally, both the cell and module models were used to predict the electrochemical and thermal behaviors under actual wireless tram operations in Turkey. The model results were compared with experimental results to confirm their reliability. © 2022 Song, Lee, Kim, Kang, Jung, Lee, Kwon and Lee.TRU

Unexpected pressure effects on sulfide-based polymer-in-ceramic solid electrolytes for all-solid-state batteries

Among the next-generation battery technologies, all-solid-state lithium batteries (ASLBs) are the most attractive because of the high safety and high energy density. The critical difference between ASLBs and conventional lithium-ion batteries (LIBs) is the replacement of the liquid electrolyte with a solid electrolyte (SE). Thus, for battery development, the investigation of ionic conductivities of SEs is essential. Sulfide-type ion conductors are representative SEs having high ionic conductivities and are ductile. However, sulfide-type SEs suffers from H2S gas release and degradation when exposed to the moisture in the air, and, as a result, the study and optimization of the fabrication parameters is challenging. In this study, we fabricated a polymer-in-ceramic SE as a thin, large-area, free-standing SE. Crucially, to optimize the fabrication conditions, we used a model inorganic particles that do not suffer from the moisture sensitivity typical of sulfide-based SEs. Interestingly, the ionic conductivity of the polymer-in-ceramic SE changed with applied pressure, behavior unlike that of a conventional pellet-type SEs prepared from sulfide powders. To understand this phenomenon, we carried out digital twinned 3D structure simulation analysis, which revealed changes in the specific contact area and distribution of ionic density in the polymer-in-ceramic SE. As a result, we propose a model composition that will facilitate the exploration of polymer-in-ceramic SEs and their characteristics and, thus, enhance the practical use of ASLBs. © 2022 Elsevier LtdFALS

Phosphokinase Antibody Arrays on Dendron-Coated Surface

Monitoring protein phosphorylation at the cellular level is important to understand the intracellular signaling. Among the phosphoproteomics methods, phosphokinase antibody arrays have emerged as preferred tools to measure wellcharacterized phosphorylation in the intracellular signaling. Here, we present a dendron-coated phosphokinase antibody array (DPA) in which the antibodies are immobilized on a dendron-coated glass slide. Self-assembly of conically shaped dendrons well-controlled in size and structure resulted in precisely controlled lateral spacing between the immobilized phosphosite-specific antibodies, leading to minimized steric hindrance and improved antigen-antibody binding kinetics. These features increased sensitivity, selectivity, and reproducibility in measured amounts of protein phosphorylation. To demonstrate the utility of the DPA, we generated the phosphorylation profiles of brain tissue samples obtained from Alzheimer’s disease (AD) model mice. The analysis of the profiles revealed signaling pathways deregulated during the course of AD progression.1331sciescopu

The Development of an IMU Integrated Clothes for Postural Monitoring Using Conductive Yarn and Interconnecting Technology

Spinal disease is a common yet important condition that occurs because of inappropriate posture. Prevention could be achieved by continuous posture monitoring, but most measurement systems cannot be used in daily life due to factors such as burdensome wires and large sensing modules. To improve upon these weaknesses, we developed comfortable “smart wear” for posture measurement using conductive yarn for circuit patterning and a flexible printed circuit board (FPCB) for interconnections. The conductive yarn was made by twisting polyester yarn and metal filaments, and the resistance per unit length was about 0.05 Ω/cm. An embroidered circuit was made using the conductive yarn, which showed increased yield strength and uniform electrical resistance per unit length. Circuit networks of sensors and FPCBs for interconnection were integrated into clothes using a computer numerical control (CNC) embroidery process. The system was calibrated and verified by comparing the values measured by the smart wear with those measured by a motion capture camera system. Six subjects performed fixed movements and free computer work, and, with this system, we were able to measure the anterior/posterior direction tilt angle with an error of less than 4°. The smart wear does not have excessive wires, and its structure will be optimized for better posture estimation in a later study