Si和C的添加对Fe_(2.5)CoNiCu高熵合金显微组织和力学性能的影响

为了评估非金属元素(Si和C)对Fe_(2.5)CoNiCu高熵合金显微组织演变和力学性能的影响,采用真空感应熔炼法制备Fe_(2.5)CoNiCuSix(x=0.1~0.3,摩尔分数)和Fe_(2.5)CoNiCuCx(x=0.15~0.4,摩尔分数)两种系列高熵合金。结果表明,C和Si的加入显著促进BCC/FCC双相向单一FCC结构的转变,且添加C对BCC/FCC组织演变的影响更明显。Fe_(2.5)CoNiCuSi0.2高熵合金具有较高的硬度(HV439.5)和抗拉强度(868MPa),这与固溶强化和晶粒细化作用有关。随着C含量的增加,Fe_(2.5)CoNiCuCx高熵合金的硬度和强度均增加,这是碳化物的形成和固溶强化所致。这表明在高熵合金中添加非金属元素(C或Si)是提高合金强度和硬度的可行途径。

Particulate matter exposure exacerbates susceptibility to SARS-CoV-2 infection in humanized ACE2 mice

The global outbreak of coronavirus disease 2019(COVID-19),which is caused by severe acute respiratory syndrome coronavirus 2(SARS-CoV-2),as of 8 May 2021,has surpassed 150700000 infections and 3279000 deaths worldwide.Evidence indicates that SARS-CoV-2 RNA can be detected on particulate matter(PM),and COVID-19 cases are correlated with levels of air pollutants.However,the mechanisms of PM involvement in the spread of SARS-CoV-2 remain poorly understood.Here,we found that PM exposure increased the expression level of angiotensin-converting enzyme 2(ACE2)and transmembrane serine protease 2(TMPRSS2)in several epithelial cells and increased the adsorption of the SARS-CoV-2 spike protein.Instillation of PM in a hACE2 mouse model significantly increased the expression of ACE2 and Tmprss2 and viral replication in the lungs.Furthermore,PM exacerbated the pulmonary lesions caused by SARS-CoV-2 infection in the hACE2 mice.In conclusion,our study demonstrated that PM is an epidemiological factor of COVID-19,emphasizing the necessity of wearing anti-PM masks to cope with this global pandemic.

两仪聚合——拓扑结构聚合物合成新方法

两仪聚合(Janus polymerization)是在一条聚合增长链两端同时引发阳离子型和阴离子型开环聚合的聚合方法.两仪聚合可以一步从单体直接合成具有复杂拓扑结构的聚合物,包括两/多嵌段聚合物、超支化聚合物、杂臂星形聚合物和柱状聚合物刷等.本文总结了近年来本课题组有关两仪聚合方面的研究进展,介绍了两仪聚合特征与机理、两仪聚合在构筑拓扑结构聚合物上的应用、聚合产物独特而优异的性质、两仪聚合新体系等,并对两仪聚合发展作出了展望.

Effect of cooling rate upon the microstructure and mechanical properties of in-situ TiC reinforced high entropy alloy CoCrFeNi

Three types of in-situ TiC(5 vol%,10 vol%and 15 vol%)reinforced high entropy alloy CoCrFeNi matrix composites were produced by vacuum induction smelting.The effect of two extreme cooling conditions(i.e.,slow cooling in fu rnace and rapid cooling in copper crucible)upon the microstructure and mechanical properties was examined.In the case of slow cooling in the furnace,TiC was found to form mostly along the grain boundaries for the 5 vol%samples.With the increase of TiC reinforcements,fibrous TiC appeared and extended into the matrix,leading to an increase in hardness.The ultimate tensile strength of the composites shows a marked variation with increasing TiC content;that is,425.6 MPa(matrix),372.8 MPa(5 vol%),550.4 MPa(10 vol%)and 334.3 MPa(15 vol%),while the elongation-to-failure(i.e.,ductility)decreases.The fracture pattern was found to transit from the ductile to cleavage fracture,as the TiC content increased.When the samples cooled rapidly in copper crucible,the TiC particles formed both along the grain boundaries and within the grains.With the increase of TiC volume fraction,both the hardness and ultimate tensile strength of the resulting composites improved steadily while the elongation-to-failure declined.Therefore,the fast cooling can be used to drastically improve the strength of in-situ TiC reinforced CoCrFeNi.For example,for the 15 vol%TiC/CoCrFeNi composite cooled in the copper crucible,the hardness and ultimate tensile strength can reach as high as 595 HV and 941.7 MPa,respectively.

Facile Synthesis of Functional Poly (ε-caprolactone) via Janus Polymerization

Functionalized aliphatic polyesters attract increasing attentions as biocompatible and biodegradable polymers with broad applications in biological science. In this contribution, we propose a facile and controllable synthetic technique for functional poly(ε-caprolactone)(PCL) via Janus polymerization, which comprises cationic ring-opening copolymerization (ROP) of ε-caprolactone (CL) with 3,3-bis(chloromethyl)oxacyclobutane (CO) and (coordinated) anionic ROP of CL at a single propagating chain by rare earth metal triflates (RE(OTf)3)and propylene oxide, thus generating block copolymers in one step. The compositions of the copolymers of poly(CLb-(CL-r-CO)) can be modulated by various RE(OTf)3. Scandium triflate catalyzes Janus polymerization to yield the copolymers containing the highest CO contents among all the RE(OTf)3 catalysts used with complete conversion of CL. The chlorine in CO repeating units is ready to be transferred into azide group which affords the modification sites to react with 9-ethynyl-9-fluorenol and mPEG-alkyne, respectively, via copper(I)-catalyzed azide-alkyne cycloaddition reaction with quantitative conversions of azides, as confirmed by FTIR analyses. According to NMR and SEC analyses, copolymers (PCC-g-PEG) bearing a homo-PCL block and a PEG-grafted block of poly(CO-co-CL) demonstrate well-defined chemical structures. The investigations on thermal properties reveal the strong phase separation between PCL and PEG blocks. The amphiphilic PCC-g-PEG is able to sei住assemble into micelles in aqueous solution while cylindrical and lamellar morphologies are observed in bulk. We provide an efficient protocol to synthesize functional PCL combining onestep Janus polymerization and precise post-polymerization click reaction.

The preventive effect of vaccine prophylaxis on severe respiratory syncytial virus infection:A meta-analysis

Respiratory syncytial virus(RSV) is the key underlying cause of acute lower respiratory tract infection in infants; however, no licensed vaccine against RSV infection is currently available. This study was undertaken to assess the preventive effect of vaccine on RSV infection. In this metaanalysis, 1,792 published randomized clinical trials of RSV vaccines from Jan 1973 to Sep 2015 were examined. Among thirteen studies that met the inclusion criteria, eleven studies estimated the impact of RSV vaccines and four studies estimated the effect of adjuvants. The odds ratios(ORs) were 0.31(95% CI, 0.15–0.67) and 0.62(95% CI, 0.29–1.34), respectively. We found that RSV subunit vaccines can significantly reduce the incidence of RSV infection and that whether vaccination with adjuvant therapy was an effective strategy still remained to be studied. This analysis of the preventive effect of vaccines on RSV infection has direct applications for the prevention of RSV infections.

Janus Polymerization:A One-Shot Approach towards Amphiphilic Multiblock Poly(ester-acetal)s Directly from 1,3-Dioxolane withε-Caprolactone

Janus polymerization consists of anionic and cationic ring opening polymerizations(AROP and CROP)at the two ends of a single propagating polymer chain,followed by a self-triggered chain extension generating multiblock copolymers(MBCPs)in one step.In the contribution,Janus polymerization by Tm(OTf)_(3) or Er(OTf)_(3) catalyst with an epoxy initiator is applied to synthesize MBCPs of semi-crystalline poly(ε-caprolactone)(PCL)blocks from coordinated AROP and poly(1,3-dioxolane-co-ε-caprolactone)(P(DO-co-CL))blocks from CROP of DO with CL.Meanwhile,amorphous random copolymers[P(DO-r-CL)]are synthesized as control by employing other rare earth triflates[RE(OTf)_(3),RE=Y,Nd,Gd and Lu]as catalysts or in the absence of an initiator via CROP.On account of the distinguishable chemical structures and thermal properties between Janus MBCPs and cationic random copolymers,Janus features are confirmed including the CROP and AROP at a single propagating chain.The resultant amphiphilic copolymers self-assemble to nanoparticles in aqueous solution with designable diameters with the corresponding ratios of hydrophilic and hydrophobic seg-ments.MBCPs exhibit good shape memory properties with appropriate deformation temperature close to human body's,providing a prospect on the applications in biomedical devices.