Magnetic-Field-Assisted Scratching Process of Single-Crystal Copper.

Energy-field-assisted cutting exhibits excellent ability to reduce cutting force and improve machining quality. In this study, a magnetic field was applied in an innovative way to aid in the cutting process, and magnetic-field-assisted scratching experiments of single-crystal copper were carried out. It was found that magnetic-field-assisted scratching increased the actual scratching force due to the additional Lorentz force in the cutting process. However, the friction coefficient of the magnetic-field-assisted scratching was reduced by 19.4% due to the tribological modification effect on tool/chip contact. Meanwhile, magnetic-field-assisted scratching was conducive to decreasing the degree of chip deformation, reducing microburrs on the machined surface, and obtaining a surface roughness reduction of an average of 26.8%. The possible reason for this effect was that the presence of a magnetic field in the cutting process promoted the dislocation slip of metal materials. The results indicated that magnetic-field-assisted cutting improves the machinability in the metal cutting process.

Adverse Effects of Prenatal Exposure to Oxidized Black Carbon Particles on the Reproductive System of Male Mice.

Ambient black carbon (BC), a main constituent of atmospheric particulate matter (PM), is a primary particle that is mainly generated by the incomplete combustion of fossil fuel and biomass burning. BC has been identified as a potential health risk via exposure. However, the adverse effects of exposure to BC on the male reproductive system remain unclear. In the present study, we explored the effects of maternal exposure to oxidized black carbon (OBC) during pregnancy on testicular development and steroid synthesis in male offspring. Pregnant mice were exposed to OBC (467 µg/kg BW) or nanopure water (as control) by intratracheal instillation from gestation day (GD) 4 to GD 16.5 (every other day). We examined the testicular histology, daily sperm production, serum testosterone, and mRNA expression of hormone synthesis process-related factors of male offspring at postnatal day (PND) 35 and PND 84. Histological examinations exhibited abnormal seminiferous tubules with degenerative changes and low cellular adhesion in testes of OBC-exposed mice at PND 35 and PND 84. Consistent with the decrease in daily sperm production, the serum testosterone level of male offspring of OBC-exposed mice also decreased significantly. Correspondingly, mRNA expression levels of hormone-synthesis-related genes (i.e., StAR, P450scc, P450c17, and 17ß-HSD) were markedly down-regulated in male offspring of PND 35 and PND 84, respectively. In brief, these results suggest that prenatal exposure has detrimental effects on mouse spermatogenesis in adult offspring.

[SP1 identified as a transcription factor of miR-122-5p].

OBJECTIVE: To study the transcription factors of the spermatogenesis-related promoter mir-122-5p. METHODS: SP1 and GATA4 were predicted as the possible transcription factors of the mir-122-5p promoter by bioinformatics analysis, followed by construction of the double luciferase pGL3-mir-122-5p promoter vector, pcDNA3.1 (+) -SP1 expression vector and pcDNA3.1 (+) -GATA4 expression vector, respectively. The pcDNA-SP1+pGL3-basic mixture plasmid and pcDNA-SP1+ pGL3-miR-122-5p promoter mixture plasmid, pcDNA-GATA4+pGL3-basic mixture plasmid and pcDNA-GATA4+pGL3-miR-122-5p promoter mixture plasmid were transferred into 293T cells. The enzyme activity was detected the Dual-Luciferase Reporter Assay System. RESULTS: The fluorescence value of the pcDNA3.1+pGL3-miR-122 promoter was 0.0362 ± 0.0004, significantly higher than that of the pcDNA3.1+pGL3-basic group (P < 0.05), indicating the successful construction of the mouse miR-122-5p promoter luciferase reporter plasmid. The fluorescence value was markedly higher in the pcDNA -SP1 + pGL3-miR-122-5p promoter than in the pcDNA -SP1+pGL3-basic group, suggesting that the transcription factor SP1 could promote the transcription of miR-122. There was no statistically significant difference in the fluorescence value between the pcDNA -gata4+pGL3-basic transfection and pcDNA -GATA4+pGL3-miR-122-5p promoter transfection groups, indicative of the inability of GATA4 to promote the transcription of miR-122-5p. CONCLUSIONS: The transcription factor SP1, rather than GATA4, can promote the transcription of miR-122-5p.

[Construction of RNA interfering lentiviral vector of occludin and its role in tight junctions].

OBJECTIVE: To investigate the role of occludin in tight junction (TJ) in vitro. METHODS: We constructed RNA interfering lentiviral vectors and transfected them into TM4 cells. Then we detected their inhibitory effect on occuldin by RT-PCR and Western blot and analyzed the role of occuldin in TJ using an in vitro TJ cell model. RESULTS: The pLenti 6.3-EGFP-occludin-miR expression vector was successfully constructed. The results of RT-PCR and Western blot showed that pLenti 6.3-EGFP-occludin-miR-3 significantly inhibited the expression of occludin (P < 0.05), which was remarkably lower than in the blank control and the pLenti 6.3- EGFP transfection group (0.7534 ± 0.089 vs 1.000 and 1.056 ± 0.025, P < 0.05). The expression of occludin was markedly suppressed and the tightness of tight junctions decreased in the TM4 cells transfected with pLenti 6.3-EGFP-occludin-miR-3. CONCLUSIONS: The pLenti 6.3-EGFP-occludin-miR expression vector was successfully constructed, and occludin is one of the functional proteins that maintain tight junctions.

Investigation on the Exit Burr Formation in Micro Milling.

The burr on micro part has harmful effect on the dimensional accuracy and service performance. The original control of exit burr formation during micro milling is desirable and advisable. In this paper, the formation mechanism of exit burr was studied based on the varying cutting direction during micro milling. Three exit burr control strategies were concluded, the material properties embrittlement, the support stiffness increasing and machining parameter optimizing operations. Then, micro milling experiments were carried out to investigate the exit burr morphology and size. It was found that the exit burr formation was attributed to the change of material flowing path at the exit surface, which was caused by the negative shear deformation zone that was induced by the discontinuous shape features. Different exit burr morphologies were classified; the triangle exit burr type was caused by the varying exit burr growing direction along the exit surface. The optimal machining parameters in micro milling to obtain a small exit burr were suggested.

miR-122-5p regulates the tight junction of the blood-testis barrier of mice via occludin : miR-122-5p can regulate the tight junction.

BACKGROUND: Occludin protein is the primary assembling protein of TJs and the structural basis for tight junction formation between Sertoli cells in the spermatogenic epithelium. The expression of miR-122-5p and occludin are negatively correlated. In order to investigate the regulation mechanism of miR-122-5p on occludin and TJ, the present study isolated primary Sertoli cells from C57BL/6 mice, identified a transcription factor of miR-122-5p in testicle, studied the modulating loci of miR-122-5p on occludin using a dual-luciferase reporter assay, analyzed the regulate of miR-122-5p on the expression of occludin with real-time RT-PCR and Western blot, and studied the effect of miR-122-5p on the tight junction using a Millicell Electrical Resistance System. RESULTS: The relative luciferase activity in the pcDNA-Sp1 + pGL3-miR-122-5p promoter group was significantly higher than that in the pcDNA-Sp1 + pGL3-basic group, which suggests that transcript factor Sp1 promotes the transcription of miR-122-5p. The relative luciferase activity in the occludin 3'-UTR (wt) + miR-122-5p mimic group was significantly lower than that in the other groups (p < 0.01), which indicates that miR-122-5p modulates the expression of occludin via the ACACTCCA sequence of the occludin-3'UTR. The levels of occludin mRNA and protein in the miR-122-5p mimic group were significantly lower than that in the other groups (p < 0.05), which indicates that miR-122-5p reduces the expression of occludin. The trans-epithelial resistance of the miR-122-5p mimic group was significantly lower than that of the blank control group after day 4 (p < 0.05), which indicates that miR-122-5p inhibited the assembly of the inter-Sertoli TJ permeability barrier in vitro. CONCLUSION: These results displayed that miR-122-5p could regulate tight junctions via the Sp1-miR-122-5p-occludin-TJ axis.

ABSTRAIT: CONTEXTE: La protéine occludine est. la principale protéine d'assemblage des jonctions serrées (JS), et la base structurelle pour la formation de ces jonctions entre les cellules de Sertoli dans l'épithélium séminifère. L'expression de miR-122-5p et de l'occludine sont négativement corrélées. Afin d'étudier le mécanisme de régulation de l'occludine et des TJ par miR-122-5p, nous avons, dans la présente étude, isolé des cellules primaires de Sertoli de souris C57BL/6, identifié un facteur de transcription de miR-122-5p dans le testicule, étudié les loci de miR-122-5p modulants l'occludine par le biais d'un système rapporteur à 2 luciférases, analysé la régulation de miR-122-5p sur l'expression de l'occludine par qRT-PCR et Western blot, et étudié l'effet de miR-122-5p sur les jonctions serrées à l'aide d'un Système de Résistance Electrique Millicell. RéSULTATS: L'activité relative de la luciférase dans le groupe du promoteur de pcDNA46 Sp1 + pGL3-miR-122-5p était significativement plus élevée que celle observée dans le groupe pcDNA-Sp1 + pGL3-basique, ce qui suggère que le facteur de transcription Sp1 favorise la transcription de miR-122-5p. L'activité relative de la luciférase dans le groupe 3'-UTR (wt) + miR-122-5p mimant l'occludine était significativement inférieure à celle des autres groupes (p < 0,01), ce qui indique que miR-122-5p module l'expression de l'occludine via la séquence ACACTCCA en 3' UTR de l'occludine. Les niveaux d'ARNm et de protéine occludine dans le groupe mimant miR-122-5p étaient significativement inférieurs à ceux des autres groupes (p < 0,05), ce qui indique que miR-122-5p inhibe l'expression de l'occludine. La résistance transépithéliale du groupe mimant miR-122-5p était significativement inférieure à celle du groupe témoin vierge après le jour 4 (p < 0.05), ce qui indique que miR-122-5p inhibe in vitro l'assemblage des jonctions serrées de la barrière de perméabilité inter-Sertolienne. CONCLUSIONS: Ces résultats montrent que miR-122-5p pourrait réguler les jonctions serrées via l'axe Sp1-miR-122-5p-occludine.

A 22-amino-acid peptide regulates tight junctions through occludin and cell apoptosis.

Occludin is a structural protein of tight junctions (TJ) in the blood-testis barrier (BTB). A 22-amino-acid peptide (22AA) in the second extracellular loop can reversibly regulate TJ, but its regulatory mechanism is unknown. In this study, a 22AA-induced TJ destruction animal model was constructed to investigate the effect of 22AA on Sertoli cells (SCs) and spermatid counts and cell apoptosis at different time points using a multiplex immunofluorescence technique. The effect of 22AA on the location and distribution of occludin was analyzed via dual confocal fluorescence microscope. Western blotting was used to analyze dynamic changes in occludin expression. Real-time RT-PCR was used to analyze miR-122-5p expression changes. Sperm density counts and mating methods were used to analyze the effect of 22AA on fertility in mice. The results showed that 22AA promoted SC and spermatid apoptosis, downregulated occludin, upregulated miR-122-5p, and decreased sperm density and litter size before 27 days (27D). After 27D, the expression of occludin increased again, miR-122-5p expression decreased again, both sperm density and litter size returned to normal, apoptosis stopped, and spermatogenesis began to recover. Therefore, it can be concluded that 22AA can destroy TJ by downregulating occludin and inducing cell apoptosis. After 27D, TJ and spermatogenesis functions return to normal.

Low-dose combined exposure of carboxylated black carbon and heavy metal lead induced potentiation of oxidative stress, DNA damage, inflammation, and apoptosis in BEAS-2B cells.

Black carbon (BC) and heavy metal lead (Pb), as typical components of atmospheric PM2.5, have been shown to cause a variety of adverse health effects. However, co-exposure to BC and Pb may induce pulmonary damage by aggravating toxicity via an unknown mechanism. This study aimed to investigate the combined toxicity of carboxylated black carbon (c-BC) and lead acetate (Pb) on human bronchial epithelial cells (BEAS-2B) at the no-observed-adverse-effect level (NOAEL). Cells were exposed to c-BC (6.25 µg/mL) and Pb (4 µg/mL) alone or their combination, and their combined toxicity was investigated by focusing on cell viability, oxidative stress, DNA damage, mitochondrial membrane potential (MMP), apoptosis, and cellular inflammation. Factorial analyses were also used to determine the potential interactions between c-BC and Pb. The results suggested that the combination of c-BC and Pb could significantly increase the production of reactive oxygen species (ROS), malondialdehyde (MDA), and lactate dehydrogenase leakage (LDH) and decrease the activities of glutathione (GSH) and superoxide dismutase (SOD). The excessive oxidative stress could increase the levels of inflammatory cytokine IL-6 and TNF-α, and induce oxidative DNA damage and dissipation of MMP. Moreover, the results also suggested that the combined group could enhance the cellular apoptotic rate and the activation of apoptotic markers like caspase-3, caspase-8, and caspase-9. The factorial analysis further demonstrated that synergistic interaction was responsible for the combined toxicity of c-BC and Pb co-exposure. Most noticeably, the co-exposure of c-BC and Pb could induce some unexpected toxicity, even beyond the known toxicities of the individual compounds in BEAS-2B cells at the NOAEL.

Experimental Study on the Minimum Undeformed Chip Thickness Based on Effective Rake Angle in Micro Milling.

Micro milling is widely used to manufacture micro parts due to its obvious advantages. The minimum undeformed chip thickness, the effective rake angle, and size effect are the typical characteristics and closely related to each other in micro milling. In this paper, the averaging method is proposed to quantitatively estimate the effective rake angle in the cutting process. The minimum undeformed chip thickness is explained based on the effective rake angle and determined to be 0.17 rn (tool cutting edge radius). Then, micro milling experiment was conducted to study the effect of the minimum undeformed chip thickness. It is found that the minimum undeformed chip thickness results in the unstable cutting process, the uneven peaks on cutting force signal, and the dense characteristic frequency distribution on frequency domain signal. The dominant ploughing effect induces the great specific cutting energy and the deteriorated surface roughness due to the minimum undeformed chip thickness.

Investigation on the Edge Chipping in Ultrasonic Assisted Sawing of Monocrystalline Silicon.

Monocrystalline silicon is an important semiconductor material and occupies a large part of the market demand. However, as a hard-brittle material, monocrystalline silicon is extremely prone to happen edge chipping during sawing processing. The edge chipping seriously affects the quality and performance of silicon wafers. In this paper, both conventional and ultrasonicassisted sawing tests were carried out on monocrystalline silicon to study the formation mechanism of edge chipping. The shape and size of edge chipping after sawing process were observed and measured. The experimental results demonstrated that different sawing processes present different material removal modes and edge quality. The mode of crack propagation was continuous cracks in conventional sawing process, while the expansion mode in ultrasonic assisted sawing was blasting microcracks. This results in the cutting force of ultrasonic assisted sawing becomes much smaller than that of conventional sawing process, which can reduce the size of edge chipping and improve the quality of machined surface.

Experimental Investigation on Direct Micro Milling of Cemented Carbide.

Cemented carbide is currently used for various precise molds and wear resistant parts. However, the machining of cemented carbide still is a difficult challenge due to its superior mechanical properties. In this paper, an experimental study was conducted on direct micro milling of cemented carbide with a polycrystalline diamond (PCD) micro end mill. The cutting force characteristics, surface formation, and tool wear mechanisms were systematically investigated. Experimental results show that cemented carbide can be removed with ductile cutting utilizing the PCD tool with a large tool tip radius. Micro burrs, brittle pits, and cracks are the observed surface damage mechanisms. The tool wear process presents microchipping on the cutting edge and exfoliating on the rake face in the early stage, and then severe abrasive and adhesive wear on the bottom face in the following stage.