Background
To combat the COVID-19 pandemic, nonpharmaceutical interventions (NPI) were implemented worldwide, which impacted a broad spectrum of acute respiratory infections (ARI).
Methods
Etiologically diagnostic data from 142 559 cases with ARIs, who were tested for eight viral pathogens (influenza virus, IFV; respiratory syncytial virus, RSV; human parainfluenza virus, HPIV; human adenovirus; human metapneumovirus; human coronavirus, HCoV; human bocavirus, HBoV, and human rhinovirus, HRV) between 2012 and 2021, were analyzed to assess the changes of respiratory infections in China during the first COVID-19 pandemic year compared to pre-pandemic years.
Results
Test positive rates of all respiratory viruses decreased during 2020, compared to the average levels during 2012−2019, with changes ranging from -17·2% for RSV to -87·6% for IFV. Sharp decreases mostly occurred between February and August when massive NPIs remained active, although HRV rebounded to the historical level during the summer. While IFV and HMPV were consistently suppressed year round, RSV, HPIV, HCoV, HRV HBov resurged and went beyond historical levels during September, 2020−January, 2021, after NPIs were largely relaxed and schools reopened. Resurgence was more prominent among children younger than 18 years and in Northern China. These observations remain valid after accounting for seasonality and long-term trend of each virus.
Conclusions
Activities of respiratory viral infections were reduced substantially in the early phases of the COVID-19 pandemic, and massive NPIs were likely the main driver. Lifting of NPIs can lead to resurgence of viral infections, particularly in children.
The effects of different electromagnetic field and technological parameters on the microstructure and composition segregation of Pb-80%Sn alloy were studied. The results show that, both rotating and spiral magnetic field can improve the composition segregation ,refine grains of alloy. Moreover,the spiral magnetic field is more effective on improving composition homogenization and grain refining. The electromagnetic force distribution of spiral magnetic field is more helpful to form a well stirring in a larger zone and promote the formation of equiaxed grains, and the direction of the grain arrangement is much smaller. The technical parameters of spiral magnetic field have been optimized. It is found that, under the spiral magnetic field condition, when stirring time and exciting current exceeded a critical value, the size of the primary phase became larger. Therefore, there existed an optimum value of magnetic stirring parameters for the homogenization of component and refinement of grains.
Metal foams have both structural and functional properties, offer advantages in different fields such as automotive and aircraft etc., and thus gain more and more technical interest. In this study, a computational model is presented which allows the numerical simulation of the bubble expansion and solidification during metal foaming processes. Mathematical modelling of the different relevant physical properties and effects during the metal foam expansion and solidification is discussed in this paper. This model considers the broad variety of the complex boundary conditions, the simple and multiphase fluid flow with complex geometries, the stabilization of the foams, and the mutual interactions between the bubbles. The Navier-Stokes equation is applied to elucidate the fluid flows in the liquid and in the mushy zone. And the diffusion equation for the hydrogen transport, the distribution functions of the temperature, the density and kinetic equations are also be proposed and discussed.
The TiB2/AZ31 magnesium matrix composite was fabricated via self-propagating hightemperature synthesis (SHS) and then hot extruded. The influence of hot extrusion on the microstructure and property of TiB2/AZ31 composites was investigated. The results show that hot extrusion and synthesized TiB2 particles could refine the grain size obviously. The synthesized TiB2 particles are micro- and nano-sized, dispersing homogenously in the matrix. The interface between the matrix and the particles are good bonding. Meanwhile, slip and twinning are the main deformation modes during the hot extrusion. The fracture surface of hot-extruded TiB2/AZ31 magnesium matrix composite has more dimples than the as-cast AZ31 magnesium alloy. The improvement of microstructure seems to be beneficial for the fracture ductility of TiB2/AZ31 magnesium matrix composite.
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