Band gap characteristics of new composite multiple locally resonant phononic crystal metamaterial.

Locally resonant phononic crystal (LRPC) exhibit elastic wave band gap characteristics within a specific low-frequency range, but their band gap width is relatively narrow, which has certain limitations in practical engineering applications. In order to open a lower frequency band gap and broaden the band gap range, this paper proposes a new composite multiple locally resonant phononic crystal (CMLRPC). Firstly, the band structure of the CMLRPC is calculated by using the finite element method, and then the formation mechanism of the band gap of the CMLRPC is studied by analyzing its vibration mode, and the band gap width is expanded by adjusting the size of the single primitive cell in the supercell model of the CMLRPC. Secondly, an equivalent mass-spring system model for CMLRPC is established to calculate the starting frequency and cut-off frequency of the band gap, and the calculated results are in good agreement with the finite element calculation. Finally, the frequency response function of the CMLRPC is calculated and its attenuation characteristics are analyzed. Within the band gap frequency range, the attenuation values of the CMLRPC are mostly above 20 dB, indicating a good attenuation effect. Compared with traditional LRPC, this new CMLRPC opens multiple band gaps in the frequency range of 200 Hz, with a wider band gap width and better attenuation effect. In addition, considering both the contact between single primitive cell and the adjustment of their spacing in the supercell model of the CMLRPC, lower and wider band gap can be obtained. The research results of this paper provide a new design idea and method for obtaining low-frequency band gap in LRPC, and can provide reference for the design of vibration reduction and isolation structures in the field of low-frequency vibration control.

Laser Additive Manufacturing of Zinc Targeting for Biomedical Application.

Biodegradable zinc (Zn) is expected to be used in clinical application like bone tissue engineering scaffolds, since it possesses favorable biocompatibility and suitable degradation rate. Laser powder bed fusion (LPBF), which is a typical additive manufacturing technique, offers tremendous advantages in fabricating medical devices with personalized geometric shape and complex porous structure. Therefore, the combination of LPBF and biodegradable Zn has gained intensive attention and also achieved rapid development in recent years. However, it severely challenges the formation quality and resultant performance of LPBF-processed Zn-based materials, due to the evaporation and element loss during laser processing. In this study, the current research status and future research trends for LPBF of Zn-based implants are reviewed from comprehensive viewpoints including formation quality, microstructure feature, and performance. The influences of powder characteristics and process parameters on formation quality are described systematically. The microstructure evolution, mechanical properties, as well as the degradation behavior are also discussed. Finally, the research perspectives for LPBF of Zn are summarized, aiming to provide guideline for future study.

Nanometer effect promoting arsenic removal on α-MnO2 nano-surface in aqueous solution: DFT+U research.

The nanometer effect in the process of arsenic ions removal on α-MnO2 nano-surface is studied by the first-principle method through microfacet models. Several parameters, such as adhesion energy, electrostatic potential, and Mulliken population were calculated to illuminate the internal mechanism. The results show that the adsorption energies of As(OH)3 molecules on MnO2[(100×110)] nanostructure are smaller than that on the bulk surface with the same concentration, which means the nanometer effect is beneficial to enhance the adsorption ability of MnO2 nano-surface. In an aqueous solution, there exist two possible removal ways of As ions. One is the direct reaction of As(OH)3→As(OH)6-, which occurs both in bulk surface and nano-surface. However, to nanomaterials, there exists another removal way of As(OH)3→As(OH)4→As(OH)6- through an intermediate As(OH)4 molecule produced by nanometer effect. Furthermore the smaller electrostatic potential of As ions on [(100×110)] nano-surface is beneficial to enhance the removal capability of As ions. Then the reason why MnO2 nanomaterials have better catalytic activity than the bulk materials is originated from its much less adhesion energy, much more removal ways, and much smaller electrostatic potential. So this research provides a detailed understanding of the removal capability of toxic ions influenced by a nanometer effect.

Insight into the surface activity of defect structure in α-MnO2 nanorod: first-principles research.

The contribution of defect structure to the catalytic property of α-MnO2 nanorod still keeps mysterious right now. Using microfacet models representing defect structure and bulk models with high Miller index, several parameters, such as cohesive energy, surface energy, density of state, electrostatic potential, et al., have been used to investigate the internal mechanism of their chemical activities by first-principles calculation. The results show that the trend in surface energies of microfacet models follows as Esurface[(112 × 211)] > Esurface[(110 × 211)] > Esurface[(100 × 211)] > Esurface[(111 × 211)] > Esurface[(112 × 112)] > Esurface[(111 × 112)], wherein all of them are larger than that of bulk models. So the chemical activity of defect structure is much more powerful than that of bulk surface. Deep researches on electronic structure show that the excellent chemical activity of microfacet structure has larger value in dipole moments and electrostatic potential than that of bulk surface layer. And the microfacet models possess much more peaks of valent electrons in deformantion electronic density and molecular orbital. Density of state indicates that the excellent chemical activity of defect structure comes from their proper hybridization in p and d orbitals.

Xiao-Xu-Ming Decoction Reduced Mitophagy Activation and Improved Mitochondrial Function in Cerebral Ischemia and Reperfusion Injury.

We investigated whether Xiao-Xu-Ming decoction reduced mitophagy activation and kept mitochondrial function in cerebral ischemia-reperfusion injury. Rats were randomly divided into 5 groups: sham, ischemia and reperfusion (IR), IR plus XXMD (60 g/kg/day) (XXMD60), IR plus cyclosporin A (10 mg/kg/day) (CsA), and IR plus vehicle (Vehicle). Focal cerebral ischemia and reperfusion models were induced by middle cerebral artery occlusion (MCAO). Cerebral infarct areas were measured by triphenyl tetrazolium chloride staining. Cerebral ischemic injury was evaluated by hematoxylin and eosin staining (HE) and Nissl staining. Ultrastructural features of mitochondria and mitophagy in the penumbra of the ischemic cortex were observed by transmission electron microscopy. Mitophagy was detected by immunofluorescence labeled with LC3B and VDAC1. Autophagy lysosome formation was observed by immunofluorescence labeled with LC3B and Lamp1. The expression of LC3B, Beclin1, and Lamp1 was analyzed by Western blot. The rats subjected to MCAO showed worsened neurological score and cell ischemic damage. These were all significantly reversed by XXMD or CsA. Moreover, XXMD/CsA notably downregulated mitophagy and reduced the increase in LC3, Beclin1, and Lamp1 expression induced by cerebral ischemia and reperfusion. The findings demonstrated that XXMD exerted neuroprotective effect via downregulating LC3, Beclin1, Lamp1, and mitochondrial p62 expression level, thus leading to the inhibition of mitophagy.

Mitophagy is activated in brain damage induced by cerebral ischemia and reperfusion via the PINK1/Parkin/p62 signalling pathway.

This study examined the course of mitophagy following cerebral ischemia with reperfusion and the role of the PTEN-induced kinase 1 (PINK1)/Parkin/p62 signalling pathway. The middle cerebral artery of male Sprague-Dawley rats was occluded for 90 min and was followed by different time-points of reperfusion. Cerebral infarct areas were detected by 2,3,5-triphenyl tetrazolium chloride staining, while brain damage was observed by haematoxylin and eosin staining. Levels of LC3, Beclin1 and LAMP-1 were estimated by western blots. LC3B location was observed in various cells in the neurovascular unit. In addition, PINK1 accumulation in damaged mitochondria and Parkin/p62 mitochondrial translocation were investigated by double immunofluorescence staining. Finally, the levels of PINK1, Parkin and p62 expression in mitochondrial fractions were estimated by western blots. Cerebral ischemia with different time-points of reperfusion resulted in infarct in the territory of the middle cerebral artery accompanied by overall brain damage. In addition, we found up-regulation of LC3B, Beclin1, and LAMP-1, as well as mitophagy activation after reperfusion, with peak expression of these proteins at 24 h after reperfusion. Electron microscopy and immunofluorescence indicated that LC3B was primarily located in neurons, although lower levels of expression were found in astrocytes and even less in vascular endothelial cells. Moreover, significant increases in PINK1 accumulation in the outer membrane of mitochondria and increased Parkin/p62 mitochondrial translocation were shown at 24 h after reperfusion. These findings suggest that the PINK1/Parkin/p62 signalling pathway was involved in the pathophysiological processes following ischemia and reperfusion.

Research on the removal mechanism of antimony on α-MnO2 nanorod in aqueous solution: DFT + U method.

Although previous papers have reported the desorption process of antimony (Sb) ions adsorbed on α-MnO2 nanomaterials, some trace Sb(OH)4- molecular observed in experiments have not been understood clearly. Using two models as popular bulk surface and new microfacet, several parameters, such as adsorption energy, bond length, total density of state (TDOS) and activation energy, were calculated to research and analyze the catalytic reaction of Sb oxides on α-MnO2. The results show that the bulk surface model has the "mirror effect" in revealing the catalytic property of α-MnO2 nanorods. Using MnO2[(100 × 110)] microfacet model, a new molecular Sb(OH)4- molecular appears in the reaction process of Sb(OH)3 + H2O → Sb(OH)4- + H+. Further comparing the geometric morphology and TDOS of Sb(OH)4- with Sb(OH)6- molecular, it is found that their bonding length, dihedral and energy orbital of bonding peaks are too close to set the Sb(OH)4- as the precursor product of Sb(OH)6- molecular. Then the desorption process of Sb ions on α-MnO2 nanorods is virtually transformed into Sb(OH)3 → Sb(OH)4-  → Sb(OH)6- way in aqueous solution. Thus, our findings open an avenue for detailed and comprehensive theoretical studies of catalytic reaction by nanomaterials.

Synthesis of YSZ@Ni Nanoparticle by Modified Electroless Plating Process.

Ni-YSZ (Y2O3-stabilized ZrO2) composites with core-shell structure (YSZ@Ni) were produced by modified electroless plating process. It was found that YSZ nanoparticles were well encapsulated by nickel powders at 65 degrees C with pH = 12. The spherical nanopowders had core-shell structure and the shell layer was less than 20 nm. The X-ray diffraction (XRD) analysis inferred the production was composed of YSZ and Ni crystals. In the end, the formation mechanism was discussed.