Dual-step reduction of copper and formation mechanism of Cu pseudo-icosahedral microcrystals

W.S. wishes to thank University of St Andrews for a CSC-St Andrews scholarship.Pseudo-icosahedral Cu microcrystals have been synthesized in a solvothermal system containing CuSO4·5H2O as the precursor, polyvinylpyrrolidone (PVP) as a reductant/capping agent, and dimethylformamide as the solvent. The structural and morphological evolutions over the reaction time are investigated, which enable us to establish a novel formation mechanism of pseudo-icosahedral crystals of Cu. The first crystalline phase that appeared in the solution is Cu4SO4(OH)6·H2O in the form of microflakes. The microflakes are reduced and decomposed to Cu2O nanocrystallites, which assemble with PVP into spherulites. The Cu2O crystals are further reduced to Cu nanocrystallites, which aggregate with PVP again into spherical particles. An extraordinary phenomenon is that 20 separated (111) triangular plates form on each particle during surface recrystallization of Cu, and their locations match to the final facets of the pseudo-icosahedron. The plates extend to cover the whole surface of the sphere, forming a pseudo-icosahedral shell, followed by extension of the recrystallization from the surface to the core. This reversed crystal growth process increases the thickness of the plates until all the Cu nanocrystallites in the core are consumed. It is found that, during the surface recrystallization of polycrystalline spheres, the particles preferentially select the (111) planes of the face-centered cubic structure of Cu as the exposed faces because these planes have the minimum surface binding energy. The particles then try to keep as small as possible the specific surface area, and a pseudo-icosahedral shape consisting of 20 (111) plates, which has a specific surface area, about 10% lower than that of an octahedron, formed by eight (111) plates. Accordingly, the overall surface free energy of a pseudo-icosahedron is about 10% lower than that of an octahedron. The formation of tetrahedra as building units of icosahedra, as predicted previously, has not been observed. The formation of ideal icosahedra, the so-called perfect Platonic solid, and the formation of twin defects between neighboring (111) plates are not possible. The newly proposed formation mechanism of pseudo-icosahedra Cu sheds light on the understanding of formation of many other polyhedral crystals.Publisher PDFPeer reviewe

The Effect of School Organizational Support on Job Satisfaction of Primary and Secondary School Teachers: The Mediating Role of Teachers’ Engagement in Educational Research

The topic of teacher work satisfaction has long been a focus of educational study. This study examined the impact of school organizational support on teacher job satisfaction as mediated by teachers’ engagement in educational research, utilizing the findings of a survey on the academic quality of basic education students in Jiangsu Province in 2020 and analyzing the data of 21,154 primary and 16,585 secondary school teachers. In this work, the structural equation model is utilized. Significant favorable relationships are shown between school organization support, teachers’ participation in educational research, and teachers’ work happiness. The engagement of teachers in educational research somewhat mediates the relationship between school organization support and teacher job happiness. School organization support positively predicts teacher job satisfaction. The impact of school organization support on teachers’ participation in educational research and job satisfaction is greater at the primary level than at the junior secondary level

Structure and cleavage of monosodium urate monohydrate crystals

The structural study of monosodium urate monohydrate, as the principal component in gout stones, reveals that a simple and biocompatible way to breakdown the crystals into polymerised molecules at pH of 7.4 (the acidity of normal human blood) is to peel off them along the [001] direction by sonication.PostprintPeer reviewe

InceptionNeXt: When Inception Meets ConvNeXt

Inspired by the long-range modeling ability of ViTs, large-kernel convolutions are widely studied and adopted recently to enlarge the receptive field and improve model performance, like the remarkable work ConvNeXt which employs 7x7 depthwise convolution. Although such depthwise operator only consumes a few FLOPs, it largely harms the model efficiency on powerful computing devices due to the high memory access costs. For example, ConvNeXt-T has similar FLOPs with ResNet-50 but only achieves 60% throughputs when trained on A100 GPUs with full precision. Although reducing the kernel size of ConvNeXt can improve speed, it results in significant performance degradation. It is still unclear how to speed up large-kernel-based CNN models while preserving their performance. To tackle this issue, inspired by Inceptions, we propose to decompose large-kernel depthwise convolution into four parallel branches along channel dimension, i.e. small square kernel, two orthogonal band kernels, and an identity mapping. With this new Inception depthwise convolution, we build a series of networks, namely IncepitonNeXt, which not only enjoy high throughputs but also maintain competitive performance. For instance, InceptionNeXt-T achieves 1.6x higher training throughputs than ConvNeX-T, as well as attains 0.2% top-1 accuracy improvement on ImageNet-1K. We anticipate InceptionNeXt can serve as an economical baseline for future architecture design to reduce carbon footprint. Code is available at https://github.com/sail-sg/inceptionnext.Comment: Code: https://github.com/sail-sg/inceptionnex

MetaFormer Is Actually What You Need for Vision

Transformers have shown great potential in computer vision tasks. A common belief is their attention-based token mixer module contributes most to their competence. However, recent works show the attention-based module in Transformers can be replaced by spatial MLPs and the resulted models still perform quite well. Based on this observation, we hypothesize that the general architecture of the Transformers, instead of the specific token mixer module, is more essential to the model's performance. To verify this, we deliberately replace the attention module in Transformers with an embarrassingly simple spatial pooling operator to conduct only basic token mixing. Surprisingly, we observe that the derived model, termed as PoolFormer, achieves competitive performance on multiple computer vision tasks. For example, on ImageNet-1K, PoolFormer achieves 82.1% top-1 accuracy, surpassing well-tuned Vision Transformer/MLP-like baselines DeiT-B/ResMLP-B24 by 0.3%/1.1% accuracy with 35%/52% fewer parameters and 50%/62% fewer MACs. The effectiveness of PoolFormer verifies our hypothesis and urges us to initiate the concept of "MetaFormer", a general architecture abstracted from Transformers without specifying the token mixer. Based on the extensive experiments, we argue that MetaFormer is the key player in achieving superior results for recent Transformer and MLP-like models on vision tasks. This work calls for more future research dedicated to improving MetaFormer instead of focusing on the token mixer modules. Additionally, our proposed PoolFormer could serve as a starting baseline for future MetaFormer architecture design. Code is available at https://github.com/sail-sg/poolformer.Comment: CVPR 2022 (Oral). Code: https://github.com/sail-sg/poolforme

Photoluminescent nano-CsPbBr3 embedded in Cs4PbBr6 crystals : formation mechanism and properties

WS would like to thank the China Scholarships Council and the University of St Andrews for the CSC-St Andrews studentship. Part of this work was financially supported by the National Science and Technology Council in Taiwan (Contract No. NSTC 112-2113-M-002-020) for RSL.Luminescent crystalline cesium lead bromide has been synthesized by using an antisolvent method with the nominal ratio of Cs:Pb in the precursors varying in a wide range from 4.5:1 to 1:1. Although the powder X-ray diffraction patterns of all the specimens show Cs4PbBr6 as a pure phase or a main phase, high-resolution transmission electron microscopy images reveal a large amount of CsPbBr3 nanocrystallites embedded in all the Cs4PbBr6 crystals. A formation mechanism of these perovskite nanocrystallites serving as actual active centers of photoluminescence is proposed. The most crucial step in the crystal growth is the deposition of a noncrystalline coating layer containing polymerized PbBr64– linked by Cs+ with the Cs:Pb ratio of about 3:1, and therefore, the actual crystal growth sites are at the interface between the crystal and the coating layer, instead of the crystal/solution interface. The local lack of Cs during the formation of Cs4PbBr6 results in the formation of CsPbBr3 nanocrystallites inside the parent crystals of Cs4PbBr6. The photoluminescence quantum yield and stability of the embedded CsPbBr3 nanocrystallites are significantly improved in comparison with bare CsPbBr3 crystals. Such simultaneous growth of parent crystals and the embedded nanocrystallites sheds light on further development of cesium lead halide-based photoluminescent materials.Publisher PDFPeer reviewe