基于扩展有限单元法的短纤维/橡胶复合材料裂纹扩展分析

为了研究短纤维/橡胶复合材料裂纹在拉伸载荷作用下的扩展演化规律,应用扩展有限元法对预制裂纹的短纤维/橡胶复合材料的裂纹扩展进行了数值模拟.采用随机顺序吸附算法在ABAQUS软件中生成短纤维分布模型,分析了失效准则参数(最大许用主应力和裂纹表面能)、短纤维细观参数(体积含量、长度和取向角)对裂纹扩展行为的影响规律,探究了短纤维的增韧机理,数值结果与试验结果吻合.研究结果表明:降低基体材料的损伤阈值可以实现裂纹的扩展,而不改变裂纹扩展特征;短纤维增强相的存在会改变裂纹的扩展方向,使裂纹的扩展路径呈现复杂性从而提高材料抗撕裂性能;裂纹扩展路径曲折度随短纤维含量、长度和取向角的增加而增大,试样拉断时所需要消耗的功增大,抗撕裂性提高.

Preparation and Characterization of Porous Carbon from Mixed Leaves for High-Performance Supercapacitors

With the increasing demand of sustainable and eco-friendly resources,it is very attractive to use waste leaves for activated carbon(AC)preparation that can be used in supercapacitors.Considering the practically collected leaves are commonly in mixed nature,and extra efforts are needed to sort these mixtures,we here report the first preparation of AC using mixed leaves from different plants,including Platanus acerifolia(PA),Firmiana platanifolia(FP)and Pistia stratiotes(PS),and compared the results with single leaves-derived AC materials.These leave-derived AC samples were characterized with FESEM,EDS,FTIR and Raman spectroscopy,and electrochemical tests.The AC derived from mixed leaves(PA3FP1PS2AC)showed a good specific capacitance of 246 F·g−1 at 1 A·g−1 in aqueous 3 mol·L^(-1)KOH.This sample further showed the largest specific capacitance of 201 F·g−1 at 5 A·g−1,as compared with the non-mixed AC samples,and a good stability of 100.0%capacitance retention over 1000 cycles.Utilizing mixed leaves for AC preparation is not only demonstrated to be a promising approach of low cost and high-performance AC production for supercapacitor applications,but may also help environmental protection by reducing the invasive species problem.

A Network Decomposition Model for Rubber-Like Materials Considering Topological Constraints

A molecular network constitutive model is proposed in this study.Based on the concept of molecular network decomposition,the molecular network was decomposed into a James-Guth 3-chain network model and an Arruda-Boyce 8-chain network model.Considering that the single molecular chain of rubber is constrained by the surrounding molecular networks, the 3-chain model and the 8-chain model were consequently modified using the tube theory.The proposed model contains four material parameters that were determined by fitting the uniaxial tensile test data from rubber-like materials,and the values of these parameters were utilized to determine the pure shear and the biaxial extension.The proposed model agrees well with the experimental data and can predict the test results of experiments performed under the conditions of pure shear and equi-biaxial deformation with acceptable accuracy.

Epidemiological characteristics and clinical manifestations of pediatric patients with COVID-19 in China: A multicenter retrospective study

Importance:The Coronavirus disease 2019(COVID-19)global pandemic poses a considerable challenge for pediatricians.Objective:This study aimed to identify the epidemiological characteristics and clinical features of pediatric patients with COVID-19 in China.Methods:This multicenter retrospective study included pediatric patients from 46 hospitals in China,covering 12 provinces and two municipalities.Epidemiological,demographic,clinical,laboratory,treatment,and outcome data were analyzed.Results:In total,211 pediatric patients with COVID-19 were included in this study.The median age was 7.0 years(range:22 days to 18 years).Approximately 16.3%of the patients exhibited asymptomatic infections,23.0%had upper respiratory tract infections,and 60.7%had pneumonia,including two with severe pneumonia and one with critical illness.Approximately 78.7%of the pediatric patients occurred in familial clusters.The most three common symptoms or signs at onset in children with COVID-19 were fever(54.5%),cough(49.3%),and pharyngeal congestion(20.8%).Only 17.6%of the patients presented with decreased lymphocyte count,whereas 13.6%had increased lymphocyte count.Among the patients with pneumonia who exhibited abnormal chest computed tomography findings,18.2%(23/127)of the patients had no other symptoms.Generally,the chest radiographs showed abnormalities that affected both lungs(49.6%);ground-glass opacity(47.2%)was the most common manifestation.The cure and improvement rates were 86.7%(183/211)and 13.3%(28/211),respectively.Only one patient with an underlying condition received invasive mechanical ventilation;none of the patients died.Interpretation:Similar to adults,children of all age groups are susceptible to COVID-19.Fortunately,most pediatric patients have mild symptoms or remain asymptomatic,despite the high incidence of pneumonia.Decreased proportions of white blood cells and lymphocytes are less frequent in children than in adults.

Isolation and characterization of mpox virus from the first mpox case in Shenzhen,China

Dear Editor,Unlike previous outbreaks of the mpox(previously known as monkeypox),which were localized in Africa and resulted in small numbers of infections due to limited human-to-human transmission,the current outbreak beginning in May 2022,has spread rapidly primarily through human-to-human transmission in non-endemic countries(Gong et al.,2022).As of 27 Sep 2023,115 countries and regions have reported cases of mpox to the World Health Organization(WHO),bringing the total number of confirmed cases to 90,618 including 125 deaths.Although the number of new cases has decreased in most WHO regions in the second half of 2022,the curves reveal a long outbreak tail in different subregions of the Americas.More worrying,106 mpox cases were reported in the mainland of China in June 2023.