Search

A coronavirus disease 2019 (COVID-19) model with quarantine and standard incidence rate is first developed, then a novel analysis approach for finding the ultimate lower bound of COVID-19 infectious individuals is proposed, which means that the COVID-19 pandemic is uniformly persistent if the control reproduction number $\mathcal{R}_{c}>1$. This approach can be applied to other related biomathematical models, and some existing works can be improved by using it. In addition, the COVID-19-free equilibrium $V^0$ is locally asymptotically stable (LAS) if $\mathcal{R}_{c}1$., 13 pages, 1 figure

Additional file 1. Fig. S1. Overall effect of historical grazing on the ln-based response ratios (i.e., ln (Xstranger/Xkin)) to neighbor identity for 13 indicators in Leymus chinensis offspring. OG-, clonal offspring of L. chinensis that have not experienced grazing, OG+, clonal offspring of long-term overgrazed L. chinensis. Fig. S2. Biomass allocations to leaf, stem, and root tissues in Leymus chinensis according to neighbor identity and grazing history. OG-, offspring of L. chinensis that have not experienced grazing, OG+, offspring of long-term overgrazed L. chinensis. Fig. S3. Effects of neighbor identity and grazing history of grazing on pot-scale tiller number and single of aboveground biomass in Leymus chinensis. OG-, offspring of L. chinensis that have not experienced grazing, OG+, offspring of long-term overgrazed L. chinensis. Fig. S4. Effects of neighbor identity and grazing history on leaf biomass of a single plant (SLBM), stem biomass of a single plant (SSBM), and aboveground biomass of a single plant (SABM) in Leymus chinensis. OG-, offspring of L. chinensis that have not experienced grazing, OG+, offspring of long-term overgrazed L. chinensis. Fig. S5. Temporal variation in the response of plant height to neighbor identity and grazing history in Leymus chinensis. OG–, offspring of L. chinensis that have not experienced grazing, OG+, offspring of long-term overgrazed L. chinensis. Table S1. The composition and concentration of each chemical substance used in the hydroponic experiment. Table S2. Results of linear models assessing the effects of neighbor identity and grazing-related maternal effects on biomass allocation.

Ni2P@C facilely prepared by microwave assisted combustion with phytic acid and nickel nitrate followed by reduction at 650 °C exhibits even higher activity for the hydrodechlorination of HCFC-22 than Pd/C. This method is also applicable for the synthesis of other metal phosphides, providing a versatile method for the fabrication of carbon encapsulated metal phosphide particles.

Interaction or lattice doping between Cr and Al contributes to the acidity and catalytic activity of Cr/Al catalysts, which is difficult to be achieved by the conventional preparation methods while maintaining nanostructures. We suggest that solution combustion synthesis (SCS) is one of the effective ways for this issue. Nanoscale Cr/Al composite catalysts of sheet structure with a thickness around 40–100 nm were fabricated via simple solution combustion method with Cr(NO3)3·9H2O and Al(NO3)3·9H2O as the precursors and glycine as the fuel. Following SCS and fluorination pretreatment, Cr species interact with Al species intimately forming an amorphous structure. The interaction provides relatively high amounts of defects and is favorable for the formation of active species, resulting in the enhanced Lewis acidity and catalytic activity. At 400 °C, a reaction rate of 33.9 mmol/h/g was achieved for the dehydrofluorination of HFC-152a over composite catalyst, which is 30–40% higher than that of Cr and Al cata...

With Al(NO3)3·9H2O as the Al precursor and PVDF as the fluorine source, freestanding AlF3 sub-microspheres were fabricated following calcination, without the involvement of corrosive HF solution. With the varying of Al(NO3)3·9H2O to PVDF weight ratio, θ-AlF3 and β-AlF3, α-AlF3 were obtained respectively. The formation mechanism, morphology, surface properties and catalytic activities for the dehydrofluorination of 1,1,1,2-tetrafluoroethane to trifluoroethylene were investigated. During the fabrication process, Al(NO3)3 interacts with O=C bond in DMF. Meanwhile, DMF further interacts with CH2 species in PVDF. Following calcination, PVDF decomposes to CO2 and HF fluorinating Al species to AlF3. The growth of AlF3 crystal and particle are confined by PVDF. Consequently, θ-AlF3, β-AlF3 and α-AlF3 are achieved. At 450 °C, HFC-134a conversion of 23% and reaction rate of 1.9 mmol g−1 h−1 are approached over θ-AlF3 catalyst. The reaction rate is almost 3 times higher than that of β-AlF3 and is 40% higher than that of high surface area α-AlF3 prepared by sol-gel method. No significant deactivation is observed in time on stream of 40 h. The stability is attributed to the interaction of AlF3 with carbon frame work. The present study provides a scalable and facile synthesis route for AlF3 spheres with controllable phase structures.

Metal-organic frameworks (MOFs) are promising platforms for the application of catalysis with hierarchical porous structures and high surface areas. However, the stability is one of the key challenges for the reactions at elevated temperatures. In the present work, we demonstrate the preparation of Quasi MIL-101 structures with high concentration of Cr2O3 molecular clusters (21.7 wt%˜54.2 wt%) via calcination in N2 atmosphere at temperatures between 350 °C and 500 °C. Cr2O3 clusters show high activity and stability for the dehydrofluorination of 1,1,1,3,3-pentafluoropropane (HFC-245fa) to 1,3,3,3-tetrafluoropropene (HFO-1234ze). Dehydrofluorination of HFC-245fa is an efficient route for the synthesis of HFO-1234ze. With calcination temperature of 450 °C, the reaction rate of Cr2O3 molecular clusters is almost 4 times higher than that of commercial Cr2O3 and no significant deactivation was observed. Therefore, this study provides a competitive strategy for the preparation of molecular clusters catalysts with high thermal stability.

Aims Adaptation of plants to their habitats through phenotypic plasticity in which they trade off various kinds of functional traits is an important ecological strategy. Whereas plant functional traits and its effects on grassland ecosystem functioning have received much attention, the importance of grazing effects on functional traits is poorly understood. This study, therefore, aimed to analyze the responding model of Leymus chinensis functional traits to long-term grazing in semi-arid grassland. Methods The study was conducted in a field experiment involving treatments with various grazing and enclosure schemes in Nei Mongol. We compared the effects of long-term enclosure, short-term enclosure (SE), moderate grazing (MG), and heavy grazing on plant functional traits in L. chinensis. Partial Least Squares Regression was used to analyze the contributions of controlling factors on changes in biomass in response to grazing. Important findings The size of L. chinensis became smaller in plots subject to long-term grazing compared with in the plots of enclosures. It had a significant conservative property of plant dwarf which can be found in the SE plot. Interestingly, the variability increased significantly with the increasing of plasticity index of different functional traits. Also, some functional traits, such as aboveground biomass, plant height, mean leaf length etc., were sensitive traits to grazing. However, other indicators, such as leaf numbers, stem diameter, mean leaf width etc., which were inert functional traits. Stem length, plant height and other traits were main factors which cased the decreasing of L. chinensis aboveground biomass. On the whole, phenotypic change is an important adaptive strategy of L. chinensis to long term grazing.