Evaluation of age-structured vaccination strategies for curbing the disease spread

Age structure is one of the crucial factors in characterizing the heterogeneous epidemic transmission. Vaccination is regarded as an effective control measure for prevention and control epidemics. Due to the shortage of vaccine capacity during the outbreak of epidemics, how to design vaccination policy has become an urgent issue in suppressing the disease transmission. In this paper, we make an effort to propose an age-structured SVEIHR model with the disease-caused death to take account of dynamics of age-related vaccination policy for better understanding disease spread and control. We present an explicit expression of the basic reproduction number R0 , which determines whether or not the disease persists, and then establish the existence and stability of endemic equilibria under certain conditions. Numerical simulations are illustrated to show that the age-related vaccination policy has a tremendous influence on curbing the disease transmission. Especially, vaccination of people over 65 is better than for people aged 21–65 in terms of rapid eradication of the disease in Italy

The complete mitochondrial genome of an economic sea anemone (Paracondylactis sinensis) in the East China Sea

Paracondylactis sinensis Carlgren, 1934 (Actiniidae, Actiniaria) is an edible sea anemone in China. Their wild population has intensively decreased in recent years due to overharvesting. In this study, the complete mitochondrial genome of this economic species collected in the coast of Zhejiang, China is sequenced and obtained using high throughput methods. The total length of this circular molecule is 20,786 bp. Thirteen protein coding genes, two ribosomal RNA genes, two transfer RNA (tRNATrp, tRNAMet) genes and a putative ORF are annotated in it. Phylogenetic analysis based on the amino acids of mitochondrial genomes indicates that this species belongs to the family of Actiniidae. This result is consistent with the previous work that identified the edible sea anemone as Paracondylactis sinensis although it has always been recognized as Calliactis sinensis (of family Hormathiidae) in most Chinese reports. Overall, the mitochondrial genome produced in this study assists in clarifying the phylogenetic status of this sea anemone and provides a molecular foundation for future protection and breeding work

Experimental and Numerical Investigation on the Effect of Scratch Direction on Material Removal and Friction Characteristic in BK7 Scratching

In order to study the influence of scratch direction on the deformation characteristics and material removal mechanism of optical glass BK7, nanoscratching experiments were conducted on a Nano indenter using Vickers indenter. Results indicate that the face-forward scratch is more likely to induce the initiation and propagation of lateral cracks, which is found to be more beneficial to material removal processes; in contrast, small chips and debris are released from the machined grooves without introducing lateral cracks in the edge-forward condition, leading to poor material removal efficiency. In addition, the choice of scratch direction can make differences to the elastic recovery rate of optical glass BK7. The results revealed that both the elastic recovery rate and the residual stresses of the material under the face-forward scratching are greater than those of the edge-forward scratching. A theoretical model for coefficient of friction (COF) under different scratch directions was established. It is found that the COF between indenter and workpiece in the edge-forward scratching is larger than the face-forward scratching under otherwise identical conditions, this finding is consistent with experimental results. A stress field analysis using finite element method (FEM) was conducted to understand the different crack initiation and propagation behaviors from different scratch directions. The current study discusses the significance of scratch direction on material removal behavior of optical glass BK7, and the results would encourage further research on investigating the connections between tool geometry and material removal mechanism

Effect of scratch direction on densification and crack initiation of optical glass BK7

© 2020 Elsevier Ltd and Techna Group S.r.l. It is known from nano-indentation studies that optical glass material undergoes a certain densification deformation during ductile scratching. In this study, nano-scratch experiments were conducted under different scratch directions (face-forward and edge-forward of the same indenter) and normal loads to explore the differences in densification of material in ductile removal mode. Furthermore, inherent differences in densification deformation were utilized to explore the effect of scratch direction on the crack resistance (CR) or ductile-to-brittle transition (DBT) of material under brittle removal mode. Based on quantitative evaluation of densification deformation induced by indentation and scratching, a high-temperature annealing procedure was employed to determine the changes of the scratch groove geometry and volume before and after the release of the scratch-induced densification deformation under different scratch directions (edge-forward and face-forward). The geometric parameters of scratch grooves under edge-forward and face-forward directions showed similar changes after annealing. It is found that in ductile removal mode, the densification ratio to the total scratching volume in edge-forward scratching is greater than that in face-forward scratching. It is likely that the greater densification deformation of edge-forward scratching led to stronger crack resistance and smaller tensile residual stress. Therefore, lateral cracks are more likely to initiate and propagate under face-forward scratching under brittle removal mode, which is consistent with the experimental results

Scratch with double-tip tool: Crack behavior during simultaneous double scratch on BK7 glass

© 2020 Elsevier Ltd Over the past decade, successive double-scratch tests have been extensively performed to study the grinding mechanism of brittle materials. However, the grits sometimes interact with the surface simultaneously. In this study, double tips with a tip separation of 0.6–1.8 μm are fabricated by focused ion beam. Subsequently, double-scratch tests on BK7 optical glass are conducted using the double-tip scratch tool with a scratch depth of 200–600 nm. The typical crack system and its evolution mechanism for double-tip scratch are discovered, before being explained using an analytical stress model. The ductile–brittle transition and the material-removal mechanism are discussed. An influential radius for the interference between cracks and the stress field in the double scratch is obtained, which can serve as a reference for the design of textured grinding wheels. Subsequently, the advantages and disadvantages of double-tip scratches are discussed considering different applications, such as microstructure fabrication and grinding

On the improvement of the ductile removal ability of brittle KDP crystal via temperature effect

Brittle KH2PO4 (KDP) crystal is difficult-to-machine because of its low fracture resistance whereby brittle cracks can be easily introduced in machining processes. To achieve ductile machining without any cracks, this type of materials is generally processed by some ultra-precision machining techniques at ambient temperature with nanoscale material removal, yielding low machining efficiency and high processing cost. Recently, thermal-assisted techniques have been used to successfully facilitate the machining of some difficult-to-machine materials, like superalloys, but little effort has been made to explore whether the temperature effect can contribute to the ductile machinability of brittle materials yet. Thus, the aim of this study is to figure out the specific role of temperature in the deformation behaviours of brittle KDP crystal by nano indentation/scratch methods. It is found that compared with those at ambient temperature (AT, i.e. 23 °C), the hardness and Elastic modulus of KDP crystal at elevated temperature (ET, i.e. 160 °C) decrease substantially by 21.4% and 32.5%, respectively, while the fracture toughness increases greatly by 15.5%, implying a higher ability of ductile deformation at ET. Meanwhile, the scratch length within ductile removal has been identified to be extended more than 4 times by increasing temperature from AT to ET. Both the quantity and size of brittle features (e.g., cracks and chunk removal) show a reducing trend with the increase of temperature. To uncover the underlying mechanism of this phenomenon, an updated stress field model is proposed to analyze the scratch-induced stress distribution by considering the evolution of material property at various temperature. These presented results are significant for the future design of specific thermal-assisted processing techniques for machining brittle materials efficiently

Novel lactotransferrin-derived synthetic peptides suppress cariogenic bacteria in vitro and arrest dental caries in vivo: [Novel lactotransferrin-derived anticaries peptides]

Objectives: The aim of the study was to design and synthesise novel lactotransferrin-derived antimicrobial peptides (AMPs) with enhanced antibacterial activity against cariogenic bacteria. Methods: We obtained the LF-1 (WKLLRKAWKLLRKA) and LF-2 (GKLIWKLLRKAWKLLRKA) AMPs, based on the N-terminal functional sequence of lactotransferrin, and characterised their physicochemical properties and secondary structure. Their antibacterial activity against caries-associated bacteria was evaluated using bacterial susceptibility and time-killing assays, as well as transmission electron microscopy (TEM). The antibiofilm activity against Streptococcus mutans biofilms was determined using biofilm susceptibility assays and confocal laser scanning microscopy (CLSM). A rodent model of dental caries was adopted to evaluate their anticaries effectiveness in vivo. Results: Both peptides possessed an α-helical structure with excellent amphipathicity. LF-1 was effective against S. mutans and Actinomyces species, whereas LF-2 showed more potent antibacterial activity than LF-1 against a broader spectrum of tested strains. Both peptides inhibited the formation of S. mutans biofilm starting at 8 μmol/L and exerted effective eradication of S. mutans in preformed biofilms. Both peptides exhibited satisfactory biocompatibility and exerted significant anticaries effects in a rodent model. Conclusions: Both lactotransferrin-derived peptides displayed strong antimicrobial activity against cariogenic bacteria and S. mutans biofilm in vitro and effectively inhibited dental caries in vivo

Experimental and Theoretical Investigations on Diamond Wire Sawing for a NdFeB Magnet

The normal processing of sintered NdFeB magnets, used in many applied fields, involves diamond wire sawing. Due to the fact of its relatively lower hardness and high brittleness, the surface roughness and periodic waviness of the sawed surface have become a serious problem, but the surface formation mechanism is still unknown. In this work, a diamond wire sawing experiment with a NdFeB magnet was conducted while both the cutting force and the diamond wire lateral displacement were monitored. The vibration, the lateral swing of the wire and the cutting force were thoroughly analyzed. After the experiment, the surface morphology was carefully inspected under both a white light interferometer and SEM. It was discovered that the lateral swing of the diamond wire was the main cause of the periodic waviness on the surface, the PV of which was positively proportional to the normal cutting force. The surface morphology and surface roughness along the saw mark revealed that the vibration impact of ploughing/rubbing grits can induce the NdFeB grain to loosen off and cause more brittle fractures when the feed rate was 0.05 mm/min under wet cutting