Search

Revealing the relationship among the machining parameters, surface topography, and functionality-related properties of the machined surface is crucial for obtaining micro-milling surfaces with good functional performance. In the present study, slot micro-milling Ti6Al4V was conducted to investigate the effect of machining parameters on the 3D surface topography, with an emphasis on surface defects, the 3D surface texture parameters, and functionality-related properties of the machined surface. The results show that the 3D surface topography of the machined surface presents obvious anisotropy in slot micro-milling Ti6Al4V. The 2D surface profile shows the non-uniformity along the slot width direction in slot micro-milling Ti6Al4V. The surface defects with different machining parameters are various, such as deep and large feed marks of single cutting, narrow and small feed marks of single cutting, feed marks of multi-cutting, scratch marks, scratch pit, surface tearing, tear pit, back-cutting marks, and metal debris. With the consideration of cutting processing efficiency and surface roughness Sa, it is suggested to adopt the high spindle speed and large depth of cut. At the same time, feed per tooth that is near the minimum cutting thickness is recommended to obtain the minimum surface roughness with the balance of chip thickness accumulation effect and chip removal or surface formation. Moreover, the functionality-related properties of the machined surface, e.g. friction or abrasion contact behaviors, load-bearing capacity, fluid retention properties, fatigue performance, and the machining parameter effect were evaluated with surface texture parameters, such as amplitude parameters, spatial parameters, hybrid parameters, and functional or volume parameters. Our findings are of great significance for shedding light on the relationship between the surface formation mechanism, surface topography, and functionality-related properties of machined surfaces in micro-milling Ti6Al4V. [ABSTRACT FROM AUTHOR]

Surface roughness and residual stress are related to the fatigue life of finished parts. However, experimental investigations lack a deep discussion about the cutting mechanism. Orthogonal cutting simulation for milling or two-dimensional finite element model is the simplification of the actual milling process, which makes it difficult to reflect the milling characteristic in the simulation. In the present study, a three-dimensional coupled thermo-mechanical simulation model was established to analyze the surface roughness and residual stress in milling 5083 aluminum alloy. Explicit dynamic analysis was used as the solution algorithm for the milling process. Implicit analysis was adopted to simulate the process of unloading and cooling. Mesh sensitivity analysis was conducted to identify the mesh size of the workpiece. Node displacement and stress information were output to calculate the surface roughness and residual stress. The effects of cutting parameters on surface roughness and residual stress were discussed by the simulation model. Moreover, milling experiments were conducted to validate the simulation results. It is observed that the surface roughness of the simulation and experiment shows the same trend with the increase of feed per tooth and depth of the cut, which verifies the simulation model. Moreover, the superficial residual stress of the machined surface is the result of the coupled thermo-mechanical with the compressed effect of the tool, the tensile effect of the tool, and thermal load. The superficial residual stress of the machined surface presents compressive stress at a different feed per tooth and spindle speeds. Current findings provide insights for understanding the formation mechanism of the surface topography and residual stress in milling aluminum alloy. [ABSTRACT FROM AUTHOR]

Micro-milling force and specific cutting energy play an important role in revealing the micro-milling mechanism. However, it is quite difficult to compare the micro-milling force values from different experiments due to the lack of a representative cutting force parameter to comprehensively evaluate the micro-milling force. Especially, there is no unified formula to accurately calculate the specific cutting energy in micro-milling due to variable chip cross-sectional area and periodically varying micro-milling force. In this work, the micro-milling force was systematically analyzed with fast Fourier transform spectrum analysis, curve shape, and representative parameter evaluation. The quasi-dynamic cutting force, which is represented by the P–V value of cutting force, was adopted to comprehensively evaluate the micro-milling force. The specific cutting energy was calculated with the ratio of quasi-dynamic cutting force and the average undeformed chip thickness. Moreover, the variable regularity of quasi-dynamic cutting force and specific cutting energy on cutting parameters were obtained with the micro-milling experiment. The results show that the quasi-dynamic cutting force first decreases and then increases with the increase of feed per tooth due to the chip accumulation effect. With the increase of spindle speed and depth of cut, the quasi-dynamic cutting force decreases and increases, respectively. The minimum undeformed chip thickness is between 0.3 and 0.5 μm, which is around 0.19 to 0.32 of tool edge radius in micro-milling Ti6Al4V. With the increase of spindle speed and depth of cut, the specific cutting energy shows a decreasing trend and changes a little, respectively. With the decrease of the feed per tooth, the specific cutting force shows a nonlinear increase. Our findings are of great significance for further scientific understanding the micro-milling mechanism from the perspective of cutting force and specific cutting energy. [ABSTRACT FROM AUTHOR]

Background: Rabies is a fatal zoonotic disease whose pathogenesis has not been fully elucidated, and vaccination is the only effective method for protecting against rabies virus infection. Most inactivated vaccines are produced using Vero cells, which are African green monkey kidney cells, to achieve large-scale production. However, there is a potential carcinogenic risk due to nonhuman DNA contamination. Thus, replacing Vero cells with human diploid cells may be a safer strategy. In this study, we developed a novel 2BS cell-adapted rabies virus strain and analysed its sequence, virulence and immunogenicity to determine its application potential as a human diploid cell inactivated vaccine. Methods and results: The 2BS cell-adapted rabies virus strain 2aG4-B40 was established by passage for 40 generations and selection of plaques in 2BS cells. RNA sequence analysis revealed that mutations in 2BS cell-adapted strains were not located at key sites that regulate the production of neutralizing antibodies or virulence in the aG strain (GQ412744.1). The gradual increase in virulence (remaining above 7.0 logLD50/ml from the 40th to 55th generation) and antigen further indicated that these mutations may increase the affinity of the adapted strains for human diploid cells. Identification tests revealed that the 2BS cell-adapted virus strain was neutralized by anti-rabies serum, with a neutralization index of 19,952. PrEP and PEP vaccination and the NIH test further indicated that the vaccine prepared with the 2aG4-B40 strain had high neutralizing antibody levels (2.24 to 46.67 IU/ml), immunogenicity (protection index 270) and potency (average 11.6 IU/ml). Conclusions: In this study, a 2BS cell-adapted strain of the 2aG4 rabies virus was obtained by passage for 40 generations. The results of sequencing analysis and titre determination of the adapted strain showed that the mutations in the adaptive process are not located at key sequence regions of the virus, and these mutations may enhance the affinity of the adapted strain for human diploid cells. Moreover, vaccines made from the adapted strain 2aG4-B40 had high potency and immunogenicity and could be an ideal candidate rabies virus strain for inactivated vaccine preparation. [ABSTRACT FROM AUTHOR]

Nanoindentation and nanoscratch tests of YAG single crystals were systematically performed. The mechanical properties including elastic recovery rate, elastic modulus, nano hardness and fracture toughness of YAG single crystals were obtained by the nanoindentation tests. The surface morphologies of the scratched grooves were analysed using scanning electron microscopy. The formation characteristics of YAG single crystals induced by varied-depth nanoscratch indicated that there was distinct brittle-to-ductile transition phenomenon during the scratching process. Surface radial cracks occurred prior to the edge-breaking phenomenon, and transverse cracks extending to the surface of the work material dominated the brittle removal of YAG single crystals. A theoretical model of the edge-breaking size during the nanoscratch process was developed by considering the stress intensity factor, elastic recovery rate, and residual force. This model indicated that the edge-breaking size increased as the normal force, average elastic recovery rate and elastic modulus increased, but decreased as the nanoindenter tip radius, fracture toughness and nano hardness increased. When the average elastic recovery rate was within 17.5%–20% (the maximum elastic recovery rate was within 35%–40%), the values predicted by the theoretical model agreed well with the experimental values, and the average error was less than 5%. The model could provide theoretical guidance for analysing the surface generation characteristics of brittle solid materials during the abrasive processing at brittle removal regime. [ABSTRACT FROM AUTHOR]

In recent years, geographically weighted regression (GWR) models have been widely used to address the spatial heterogeneity and spatial autocorrelation of PM2.5, but these studies have not fully considered the effects of all potential variables on PM2.5 variation and have rarely optimized the models for residuals. Therefore, we first propose a modified GWR model based on principal component analysis (PCA-GWR), then introduce five different spatial interpolation methods of radial basis functions to correct the residuals of the PCA-GWR model, and finally construct five combinations of residual correction models to estimate regional PM2.5 concentrations. The results show that (1) the PCA-GWR model can fully consider the contributions of all potential explanatory variables to estimate PM2.5 concentrations and minimize the multicollinearity among explanatory variables, and the PM2.5 estimation accuracy and the fitting effect of the PCA-GWR model are better than the original GWR model. (2) All five residual correction combination models can better achieve the residual correction optimization of the PCA-GWR model, among which the PCA-GWR model corrected by Multiquadric Spline (MS) residual interpolation (PCA-GWRMS) has the most obvious accuracy improvement and more stable generalizability at different time scales. Therefore, the residual correction of PCA-GWR models using spatial interpolation methods is effective and feasible, and the results can provide references for regional PM2.5 spatial estimation and spatiotemporal mapping. (3) The PM2.5 concentrations in the study area are high in winter months (January, February, December) and low in summer months (June, July, August), and spatially, PM2.5 concentrations show a distribution of high north and low south. [ABSTRACT FROM AUTHOR]

In this study, a novel β -1,3-glucan recognition protein gene (β-GRP) was identified from Melanotus cribricollis , and its potential role in the immune response was investigated. The full length of β-GRP cDNA (Accession Number: MT941530) was 1644 bp, encoding a protein composed of 428 amino acids. The theoretical molecular weight and the isoelectric point were 51.53 kDa and 6.17, respectively. The amino acid sequence of β -GRP from M. cribricollis was closely related to that of. β- GRP-like from Photinus pyralis , and was predicted to contain conserved GH16 domain without glucanase active site. The results of real-time quantitative PCR showed that fungal infection of Metarhizium pingshaense may significantly upregulated the expression level of β-GRP gene. The RNAi suppression of β-GRP gene expression significantly increased the corrected cumulative mortality. Meanwhile, antimicrobial peptide genes defensin and lysozyme were significantly downregulated after interference of β-GRP. Taken together, these results suggest that β-GRP of M. cribricollis probably participates in the host immune system by mediating the expression of antimicrobial peptides. This study provides comprehensive insights into the innate immune system of insect larvae. [ABSTRACT FROM AUTHOR]

The effect of titanium-alloying on microstructure and mechanical properties of Fe35Ni35Cr20Mn10 high-entropy alloy (HEA) was studied. The microstructure was characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The mechanical properties were examined by tensile and hardness tests. After the homogenization treatment at 1000 °C for 12 h, a great amount of thick/thin η flakes are observed to form at the grain boundaries, regularly intersect-arraying with specific directions that form η-locks. It is found that both the thick and thin η-Ni 3 Ti flakes are well coherent with face-centered cubic (FCC) matrix. Ti-alloying makes the homogenized Fe35Ni35Cr20Mn10 HEA possess high yield strength (331 MPa) and excellent ductility (47.2% in elongation), exhibiting a better strength-ductility. The remarkable rise in yield strength is from fine grain strengthening, dislocation hardening and second phase strengthening that are induced by Ti alloying. The refinement of grains induced by Ti alloying, the formation of a number of clear dislocation cells in FCC matrix and many stacking faults in FCC matrix and inside η flakes during the tensile deformation, and especially the coordinated deformation between η flakes and matrix, are thought to be responsible for the excellent ductility. The excellent strength-ductility in homogenized (Fe35Ni35Cr20Mn10) 95.3 Ti 4.7 HEA is, more importantly, due to the formation of regular intersect-arraying of η flakes (η-locks) with specific directions. The thick/thin η flakes are all along keeping the coherent relationship with FCC matrix during the total tensile deformation and hence can coordinately deform with the matrix. • Thick/thin η flakes are regularly intersect-arraying that form η-locks. • The thick/thin η flakes in η-locks are well coherent with FCC matrix. • The prepared HEA exhibits an excellent strength-ductility. • The η flakes keep the coherent relationship with FCC matrix during tensile deformation. • It is found that η flakes can coordinately deform with the matrix. [ABSTRACT FROM AUTHOR]

The sympathetic nervous system regulates bone formation and resorption under physiological conditions. However, it is still unclear how the sympathetic nerves affect stem cell migration and differentiation in bone regeneration. Distraction osteogenesis is an ideal model of bone regeneration due to its special nature as a self-engineering tissue. In this study, a rat model of mandibular distraction osteogenesis with transection of cervical sympathetic trunk was used to demonstrate that sympathetic denervation can deplete norepinephrine (NE) in distraction-induced bone callus, down-regulate β3-adrenergic receptor (adrb3) in bone marrow mesenchymal stem cells (MSCs), and promote MSC migration from perivascular regions to bone-forming units. An invitro Transwell assay was here used to demonstrate that NE can inhibit stroma-derived factor-1 (SDF-1)-induced MSC migration and expression of the migration-related gene matrix metalloproteinase-2 (MMP-2) and downregulate that of the anti-migration gene tissue inhibitor of metalloproteinase-3 (TIMP-3). Knockdown of adrb3 using siRNA abolishes inhibition of MSC migration. An in vitro osteogenic assay was used to show that NE can inhibit the formation of MSC bone nodules and expression of the osteogenic marker genes alkaline phosphatase (ALP), osteocalcin (OCN), and runt-related transcription factor-2 (RUNX2), but knockdown of adrb3 by siRNA can abolish such inhibition of the osteogenic differentiation of MSCs. It is here concluded that sympathetic denervation-induced MSC mobilization in rat mandibular distraction osteogenesis is associated with inhibition of MSC migration and osteogenic differentiation by NE/adrb3 in vitro. These findings may facilitate understanding of the relationship of MSC mobilization and sympathetic nervous system across a wide spectrum of tissue regeneration processes. [ABSTRACT FROM AUTHOR]

Generally running with frequent braking over short distances, the urban rail transit train generates great quantities of regenerative braking energy (RBE). The RBE feedback system can effectively recycle RBE and give it back to the AC grid. However, the lack of damp and inertia of generators makes conventional PWM RBE feedback system more sensitive to power fluctuations. To address this issue, a synchronverter-based RBE feedback system of urban rail transit is designed in this paper. First, the structure of the feedback system is presented. Then, the synchronverter-based control strategy with greater flexibility and higher stability is fully discussed. Furthermore, the parameter design of the system is analyzed in detail. Finally, simulation results and experimental results are provided to show the good dynamic performance of the system. Using this synchronverter-based approach, the system supplies traction power to the traction network when the train accelerates and gives the RBE back to the AC grid when the train brakes, in light of the variation of the DC bus voltage. Moreover, the system can be self-synchronized with the AC grid and make corresponding power management on the basis of changes in the voltage amplitude as well as the frequency of the grid. In this sense, the RBE feedback system becomes more flexible, effective and robust. [ABSTRACT FROM AUTHOR]