A semiclassical approach to surface Fermi arcs in Weyl semimetals

We present a semiclassical explanation for the morphology of the surface Fermi arcs of Weyl semimetals. Viewing the surface states as a two-dimensional Fermi gas subject to band bending and Berry curvatures, we show that it is the non-parallelism between the velocity and the momentum that gives rise to the spiral structure of Fermi arcs. We map out the Fermi arcs from the velocity field for a single Weyl point and a lattice with two Weyl points. We also investigate the surface magnetoplasma of Dirac semimetals in a magnetic field, and find that the drift motion, the chiral magnetic effect and the Imbert-Fedorov shift are all involved in the formation of surface Fermi arcs. Our work not only provides an insightful perspective on the surface Fermi arcs and a practical way to find the surface dispersion, but also paves the way for the study of other physical properties of the surface states of topological semimetals, such as transport properties and orbital magnetization, using semiclassical methods.Comment: 6 pages, 4 figures + Supplemental Material

How Graph Convolutions Amplify Popularity Bias for Recommendation?

Graph convolutional networks (GCNs) have become prevalent in recommender system (RS) due to their superiority in modeling collaborative patterns. Although improving the overall accuracy, GCNs unfortunately amplify popularity bias -- tail items are less likely to be recommended. This effect prevents the GCN-based RS from making precise and fair recommendations, decreasing the effectiveness of recommender systems in the long run. In this paper, we investigate how graph convolutions amplify the popularity bias in RS. Through theoretical analyses, we identify two fundamental factors: (1) with graph convolution (\textit{i.e.,} neighborhood aggregation), popular items exert larger influence than tail items on neighbor users, making the users move towards popular items in the representation space; (2) after multiple times of graph convolution, popular items would affect more high-order neighbors and become more influential. The two points make popular items get closer to almost users and thus being recommended more frequently. To rectify this, we propose to estimate the amplified effect of popular nodes on each node's representation, and intervene the effect after each graph convolution. Specifically, we adopt clustering to discover highly-influential nodes and estimate the amplification effect of each node, then remove the effect from the node embeddings at each graph convolution layer. Our method is simple and generic -- it can be used in the inference stage to correct existing models rather than training a new model from scratch, and can be applied to various GCN models. We demonstrate our method on two representative GCN backbones LightGCN and UltraGCN, verifying its ability in improving the recommendations of tail items without sacrificing the performance of popular items. Codes are open-sourced \footnote{https://github.com/MEICRS/DAP}.Comment: Accepted by Frontiers of Computer Scienc

Facile synthesis of chitosan-capped ZnS quantum dots as an eco-friendly fluorescence sensor for rapid determination of bisphenol A in water and plastic samples

This paper describes a novel eco-friendly fluorescence sensor for determination of bisphenol A (BPA) based on chitosan-capped ZnS quantum dots (QDs). By using safe and inexpensive materials, nontoxic ZnS QDs were synthesized via an environment-friendly method using chitosan as a capping agent. The as-prepared ZnS QDs exhibited characteristic absorption (absorbance edge at 310 nm) and emission (maxima at 430 nm) spectra with a relatively high fluorescence quantum yield of 11.8%. Quantitative detection of BPA was developed based on fluorescence quenching of chitosan-capped ZnS QDs with high sensitivity and selectivity. Under optimal conditions, the fluorescence response of ZnS QDs was linearly proportional to BPA concentration over a wide range from 0.50 to 300 mu g L-1 with a detection limit of 0.08 mu g L-1. Most of the potentially coexisting substances did not interfere with the BPA-induced quenching effect. The proposed analytical method for BPA was successfully applied to water and plastic real samples. The possible quenching mechanism is also discussed

On the seasonal variations of ocean bottom pressure in the world oceans

© The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Cheng, X., Ou, N., Chen, J., & Huang, R. X. On the seasonal variations of ocean bottom pressure in the world oceans. Geoscience Letters, 8(1), (2021): 29, https://doi.org/10.1186/s40562-021-00199-3.Seasonal variability of the ocean bottom pressure (OBP) in the world oceans is investigated using 15 years of GRACE observations and a Pressure Coordinate Ocean Model (PCOM). In boreal winter, negative OBP anomalies appear in the northern North Pacific, subtropical South Pacific and north of 40 °S in the Indian Ocean, while OBP anomaly in the Southern Ocean is positive. The summer pattern is opposite to that in winter. The centers of positive (negative) OBP signals have a good coherence with the mass convergence/divergence due to Ekman transport, indicating the importance of wind forcing. The PCOM model reproduces the observed OBP quite well. Sensitivity experiments indicate that wind forcing dominates the regional OBP seasonal variations, while the contributions due to heat flux and freshwater flux are unimportant. Experiments with daily sea level pressure (SLP) forcing suggest that at high frequencies the non-static effect of SLP is not negligible.This research was supported by the National Key R&D Program of China (2018YFA0605702), Natural Science Foundation of China (Grant nos. 41522601, 41876002, 41876224)

Biocompatibility of hydrophilic silica-coated CdTe quantum dots and magnetic nanoparticles

Fluorescent magnetic nanoparticles exhibit great application prospects in biomedical engineering. Herein, we reported the effects of hydrophilic silica-coated CdTe quantum dots and magnetic nanoparticles (FMNPs) on human embryonic kidney 293 (HEK293) cells and mice with the aim of investigating their biocompatibility. FMNPs with 150 nm in diameter were prepared, and characterized by high-resolution transmission electron microscopy and photoluminescence (PL) spectra and magnetometer. HEK293 cells were cultured with different doses of FMNPs (20, 50, and 100μ g/ml) for 1-4 days. Cell viability and adhesion ability were analyzed by CCK8 method and Western blotting. 30 mice were randomly divided into three groups, and were, respectively, injected via tail vein with 20, 60, and 100 μg FMNPs, and then were, respectively, raised for 1, 7, and 30 days, then their lifespan, important organs, and blood biochemical parameters were analyzed. Results show that the prepared water-soluble FMNPs had high fluorescent and magnetic properties, less than 50 μg/ml of FMNPs exhibited good biocompatibility to HEK293 cells, the cell viability, and adhesion ability were similar to the control HEK293 cells. FMNPs primarily accumulated in those organs such as lung, liver, and spleen. Lung exposed to FMNPs displayed a dose-dependent inflammatory response, blood biochemical parameters such as white blood cell count (WBC), alanine aminotransferase (ALT), and aspartate aminotransferase (AST), displayed significant increase when the FMNPs were injected into mice at dose of 100μg. In conclusion, FMNPs exhibit good biocompatibility to cells under the dose of less than 50 μg/ml, and to mice under the dose of less than 2mg/kg body weight. The FMNPs' biocompatibility must be considered when FMNPs are used for in vivo diagnosis and therapy

Inherent Safer Design for Chemical Process of 1,4-dioldiacetate-2-butene Oxidized by Ozone

PresentationOxidation reaction is the typical thermal runaway reaction. The reaction of 1,4-dioldiacetate-2- Butene oxidized by ozone was chosen to study the thermal hazards during the chemical process and the inherent safer designs (ISD) were proposed after analysis. The Qualitative Assessment for Inherently Safer Design (QAISD) was used to identify the risk during the chemical process. Meanwhile, the Reaction Calorimeter (RC1e) was used to analyze the thermal hazards of the chemical process. Two Inherent safer designs were proposed to increase the safe level of the process. ISD I is the improved reaction condition of reaction temperature at -5°C and ventilation rate of 200L•h-1, as well, ISDII is using a tubular reactor. The results indicate that the classification of the reaction hazard was lower with improvements of two ISDs, and the severity was reduced by 43%. Moreover, the inherent safety level of the reaction was increased by ISD I &IIof 63% and 43.4% respectively, which both have positive effects on inherent safety theories of "minimize", "substitute" and "moderate"

100G PAM-4 PON with 34 dB Power Budget Using Joint Nonlinear Tomlinson-Harashima Precoding and Volterra Equalization

We experimentally demonstrate 100G PAM-4 passive optical network using DML-based intensity modulation and direct detection with 3-dB system bandwidth of 15 GHz in O-band. Combining nonlinear Tomlinson-Harashima precoding at the transmitter and 2nd-order Volterra at the receiver enables 34-dB power budget for PON downstream

Diffuse benign inflammatory gastric polyps: A rare case in a young female: Case report and review of the literature

BackgroundGastric polyps are one of the most common clinical diseases arising from the mucosal surface of the stomach. The benign nature of the gastric polyp and its absence of symptoms have been widely accepted. Diffuse benign inflammatory polyps spanning the entire gastric mucosa are relatively rare in young people.Case presentationOur objective was to report a 20-year-old woman who presented with epigastric pain and vomiting; upper gastrointestinal barium contrast roentgenography demonstrated a huge defect in the filling of the stomach. Upper endoscopy also showed the presence of dense inflammatory polyps in the stomach that were the cause of the severe pylorus obstruction. The diffuse benign gastric polyps were diagnosed as inflammatory gastric polyps on the basis of findings on the histopathological examination. She was delivered as a result of the operating procedure of total gastrectomy and Roux-en-Y anastomosis of the esophagus and jejunum. Postoperative nutritional support therapy was also implemented. Postoperative pathological examination revealed inflammatory papillary and villous polyps distributed over the stomach, and eosinophilic infiltration was found in the local area of the polyp. Polyps move like tufts of coral. During the 16-month follow-up, patients with symptoms of malnutrition and anemia recovered.ConclusionNutritional support and a total gastrectomy were used to improve this patient's symptoms of malnutrition and anemia. Surgical intervention with appropriate nutritional support should be actively performed in these patients while strengthening the differential diagnosis of hereditary disease