•Variable-step second order Alikhanov formula for time fractional Allen-Cahn equations.•Discrete maximum principle and sharp error estimates.•Graded/adaptive time meshes for long-term simulations.
In ...this work, we present a second-order nonuniform time-stepping scheme for the time-fractional Allen-Cahn equation. We show that the proposed scheme preserves the discrete maximum principle, and by using the convolution structure of consistency error, we present sharp maximum-norm error estimates which reflect the temporal regularity. As our analysis is built on nonuniform time steps, we may resolve the intrinsic initial singularity by using the graded meshes. Moreover, we propose an adaptive time-stepping strategy for large time simulations. Numerical experiments are presented to show the effectiveness of the proposed scheme. This seems to be the first second-order maximum principle preserving scheme for the time-fractional Allen-Cahn equation.
We applied the chemical transport model GEOS‐Chem to examine the changes in aerosols and tropospheric O3 in China from 2012–2017 and the associated radiative forcing and health impact. Simulated ...surface layer concentrations and column burdens of aerosols and O3 were evaluated by comparing with ground‐based and satellite‐retrieved measurements. Between 2012 and 2017, simulated annual mean concentrations of PM2.5 decreased by 21.0%, while O3 increased by 11.9% over eastern China (20–45°N, 105–122.5°E). Changes in aerosols and O3 over 2012–2017 jointly exerted a positive radiative forcing of 1.26 W/m2 over eastern China, which was dominated by the less cooling from PM2.5 reductions (1.18 W/m2). The Global Exposure Mortality Model predicted 268.3 (247.3–291.6) thousand (9.6%) fewer deaths in eastern China in 2017 relative to 2012. These results suggest an appreciable health benefit and a potential warming as a consequence of clean air actions.
Plain Language Summary
Stringent clean air actions have been implemented in China since 2013, aiming to improve air quality. As a result, observed concentrations of aerosols decreased while those of O3 increased in eastern China. In this work we assess the radiative forcing and health impact resulted from the changes in aerosols and O3 in China for the period of 2012–2017 by using a chemical transport model. The model reproduces the observed changes in PM2.5 and O3 in recent years and estimates a net positive radiative forcing of 1.26 W/m2 in 2017 relative to 2012 over eastern China. Further estimates from the mortality model show that approximately 270,000 deaths are avoided. Results from our study suggest an appreciable health benefit as well as a potential warming as a consequence of clean air actions over 2012–2017.
Key Points
Concentrations of PM2.5 decreased, and those of O3 increased as a result of air pollution control over 2012–2017
Changes in PM2.5 and O3 led to a positive radiative forcing of 1.26 W/m2 over eastern China (20–45°N, 105–122.5°E)
Changes in air pollution exposures are estimated to avoid 268.3 thousand deaths in eastern China
Scaled-YOLOv4: Scaling Cross Stage Partial Network Wang, Chien-Yao; Bochkovskiy, Alexey; Liao, Hong-Yuan Mark
2021 IEEE/CVF Conference on Computer Vision and Pattern Recognition (CVPR),
2021-June
Conference Proceeding
Odprti dostop
We show that the YOLOv4 object detection neural network based on the CSP approach, scales both up and down and is applicable to small and large networks while maintaining optimal speed and accuracy. ...We propose a network scaling approach that modifies not only the depth, width, resolution, but also structure of the network. YOLOv4-large model achieves state-of-the-art results: 55.5% AP (73.4% AP 50 ) for the MS COCO dataset at a speed of ~ 16 FPS on Tesla V100, while with the test time augmentation, YOLOv4-large achieves 56.0% AP (73.3 AP 50 ). To the best of our knowledge, this is currently the highest accuracy on the COCO dataset among any published work. The YOLOv4-tiny model achieves 22.0% AP (42.0% AP 50 ) at a speed of ~443 FPS on RTX 2080Ti, while by using TensorRT, batch size = 4 and FP16-precision the YOLOv4-tiny achieves 1774 FPS.
Liquid cell transmission electron microscopy (TEM) has attracted significant interest in recent years. With nanofabricated liquid cells, it has been possible to image through liquids using TEM with ...subnanometer resolution, and many previously unseen materials dynamics have been revealed. Liquid cell TEM has been applied to many areas of research, ranging from chemistry to physics, materials science, and biology. So far, topics of study include nanoparticle growth and assembly, electrochemical deposition and lithiation for batteries, tracking and manipulation of nanoparticles, catalysis, and imaging of biological materials. In this article, we first review the development of liquid cell TEM and then highlight progress in various areas of research. In the study of nanoparticle growth, the electron beam can serve both as the illumination source for imaging and as the input energy for reactions. However, many other research topics require the control of electron beam effects to minimize electron beam damage. We discuss efforts to understand electron beam-liquid matter interactions. Finally, we provide a perspective on future challenges and opportunities in liquid cell TEM.
Stability and convergence of the L1 formula on nonuniform time grids are studied for solving linear react ion-sub diffusion equations with the Caputo derivative. A discrete fractional Gronwall ...inequality is developed for the nonuniform L1 formula by introducing a discrete convolution kernel of Riemann-Liouville fractional integral. To simplify the consistency analysis of the nonuniform L1 formula, we bound the local truncation error in a discrete convolution form and consider a global convolution error involving the discrete Riemann-Liouville integral kernel. With the help of discrete fractional Gronwall inequality and global consistency error analysis, a sharp error estimate reflecting the regularity of solution is obtained for a simple L1 scheme. Numerical examples are provided to verify the sharpness of the error analysis.
Real-Time Imaging of Pt₃Fe Nanorod Growth in Solution Liao, Hong-Gang; Cui, Likun; Whitelam, Stephen ...
Science (American Association for the Advancement of Science),
05/2012, Letnik:
336, Številka:
6084
Journal Article
Recenzirano
The growth of colloidal nanocrystal architectures by nanoparticle attachment is frequently reported as an alternative to the conventional growth by monomer attachment. However, the mechanism whereby ...nanoparticle attachment proceeds microscopically remains unclear. We report real-time transmission electron microscopy (TEM) imaging of the solution growth of Pt₃Fe nanorods from nanoparticle building blocks. Observations revealed growth of winding polycrystalline nanoparticle chains by shape-directed nanoparticle attachment followed by straightening and orientation and shape corrections to yield single-crystal nanorods. Tracking nanoparticle growth trajectories allowed us to distinguish the force fields exerted by single nanoparticles and nanoparticle chains. Such quantification of nanoparticle interaction and understanding the growth pathways are important for the design of hierarchical nanomaterials and controlling nanocrystal self-assembly for functional devices.
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