In December 2019, an outbreak of an unknown cause of pneumonia (later named coronavirus disease 2019 [COVID-19]) occurred in Wuhan, China. This was found to be attributed to a novel coronavirus of zoonotic origin, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2; previously named 2019 novel coronavirus or 2019-nCoV). The SARS-CoV-2, a new type of highly pathogenic human coronavirus related to severe acute respiratory syndrome coronavirus (SARS-CoV), spread rapidly worldwide and caused 246,303,023 confirmed infections, including 4,994,160 deaths, by October 31, 2021. SARS-CoV-2 and SARS-CoV vary in their specific characteristics, regarding epidemics and pathogenesis. This article focuses on the comparison of the virology, epidemiology, and clinical features of SARS-CoV and SARS-CoV-2 to reveal their common and distinct properties, to provide an up-to-date resource for the development of advanced systems and strategies to monitor and control future epidemics of highly pathogenic human coronaviruses.

Multi-pass warm rolling with falling temperature was proposed and investigated to obtain AZ31 Mg alloy sheets with a fine-grained microstructure. The results indicated that the grain microstructure of AZ31 alloy sheets was successfully refined from 22.1 to 4.5 μm after multi-pass warm rolling with falling temperature and annealing. Compared to the as-received sheet, the multi-pass warm rolled sheets in annealed condition exhibited weaker (0001) basal texture intensity, which resulted in the significantly increased Schmid factor of 〈a〉 basal slip. After multi-pass warm rolling with falling temperature, the rolled sheets in annealed condition also exhibited much better mechanical properties, e.g., higher tensile strength, larger fracture elongation, and higher Erichsen value, especially the IE of 8-pass warm rolled sheet in annealed condition was significantly increased by ∼33% under the same thickness, which could be attributed to the refined grain microstructure and the weakened basal texture.

Bollobás and Scott (Random Struct. Alg.21 (2002) 414–430) asked for conditions that guarantee a bisection of a graph with m edges in which each class has at most (1/4+o(1))m edges. We demonstrate that cycles of length 4 play an important role for this question. Let G be a graph with m edges, minimum degree δ, and containing no cycle of length 4. We show that if (i) G is 2-connected, or (ii) δ ⩾ 3, or (iii) δ ⩾ 2 and the girth of G is at least 5, then G admits a bisection in which each class has at most (1/4+o(1))m edges. We show that each of these conditions are best possible. On the other hand, a construction by Alon, Bollobás, Krivelevich and Sudakov shows that for infinitely many m there exists a graph with m edges and girth at least 5 for which any bisection has at least (1/4−o(1))m edges in one of the two classes.

In present study, the semi-solid slurry of the AZ91–2Ca–1.5Ce alloy was firstly prepared by gas-bubbling processing and then was formed by die casting and squeeze casting, respectively. The influence of processing parameters on microstructure and mechanical properties of the alloy was investigated. The results show that increase of gas-flow rate and appropriate pouring temperature can improve the quality of the semi-solid slurry and change the morphology of primary α-Mg particles to rosette-like shape or roundness. Meanwhile, the addition of calcium and cerium refines the as-cast microstructure and dramatically improves the tensile properties, also the strengthening phase Al4Ce exists around the grain boundary. The peak ultimate tensile strength (UTS), yield strength, and elongation of rheo-die casting AZ91–2Ca–1.5Ce alloy are 202 MPa, 154 MPa, and 2.3%, respectively. Especially, compared with conventional liquid die-casting, the UTS and elongation of rheo-die casting AZ91–2Ca–1.5Ce alloy were improved by 8% and 64%, respectively. Meanwhile, the rheo-die casting alloy also showed higher mechanical properties than rheo-squeeze casting alloy, since the higher speed that die casting provided could induce more compact microstructure and remain the semi-solid characteristic better.

The new processing method of spark plasma sintering (SPS) followed by hot extrusion was developed to produce Mg–1Al–xCNTs composites. Microstructural characterization revealed that the reinforcement particles were distributed uniformly in Mg matrix. The results of mechanical properties indicated a fact that compared with monolithic Mg, all Mg–1Al–xCNTs composites, especially the Mg–1Al–0.15CNTs composite, fabricated by SPS followed by hot extrusion exhibited better tensile and compressive properties. Under tension, Mg–1Al–0.15CNTs composite exhibited higher 0.2% tensile yield strength (TYS) (157 MPa versus 98 MPa, increased by ∼60%) and ultimate tensile strength (271 MPa versus 188 MPa, increased by ∼44%) than monolithic Mg. In compression, Mg–1Al–0.15CNTs composite also obtained a great enhancement in 0.2% compressive yield strength (118 MPa versus 81 MPa, increased by ∼46%) and ultimate compressive strength (321 MPa versus 255 MPa, increased by ∼26%) compared to monolithic Mg. Meanwhile, Mg–1Al–0.15CNTs composite maintained a high tensile failure strain of ∼8.8% and a high compressive failure strain of ∼17.9%.