Abstract Previous data demonstrate that traumatic brain injury (TBI) activates autophagy, and increases microtubule-associated protein 1 light chain 3 (LC3) immunostaining mainly in neurons. However, ...the role of autophagy in traumatic brain damage remains elusive. The aim of the present study was to investigate the autophagic mechanisms participating in traumatic brain injury. The autophagy inhibitors 3-methyladenine (3-MA) and bafliomycin A1 (BFA) were administered with a single i.c.v. injection before TBI. We first examined the protein levels of Beclin-1 and LC3 II, which have been found to promote autophagy previously. Immunoblotting analysis showed that 3-MA pretreatment reduced post-TBI Beclin-1 and LC3-II levels, and maintained p62/SQSTM1 (p62) levels. In addition, double immunolabeling showed that the increased punctate LC3-II dots colocalizing with Propidium Iodide (PI)-stained nuclei at 24 h after injury, were partially inhibited by 3-MA pretreatment. Furthermore, inhibition of autophagy could reduce TBI-induced cell injury assessed with i.p. injection of PI and lesion volume, and attenuate behavioral outcome evaluated by motor test and Morris water maze. The neuroprotective effects were associated with an inhibition on TBI-induced up-regulation of LC3, Beclin-1, cathepsin B, caspase-3 and the Beclin-1/Bcl-2 ratio. Taken together, these data imply that the autophagy pathway is involved in the pathophysiologic responses after TBI, and inhibition of this pathway may help attenuate traumatic damage and functional outcome deficits.
We have clearly discriminated the single-, bilayer-, and multiple-layer graphene (<10 layers) on Si substrate with a 285 nm SiO2 capping layer by using contrast spectra, which were generated from the ...reflection light of a white light source. Calculations based on Fresnel's law are in excellent agreement with the experimental results (deviation 2%). The contrast image shows the reliability and efficiency of this new technique. The contrast spectrum is a fast, nondestructive, easy to be carried out, and unambiguous way to identify the numbers of layers of graphene sheet. We provide two easy-to-use methods to determine the number of graphene layers based on contrast spectra: a graphic method and an analytical method. We also show that the refractive index of graphene is different from that of graphite. The results are compared with those obtained using Raman spectroscopy.
We show that graphene deposited on a substrate has a non-negligible density of atomic scale defects. This is evidenced by a previously unnoticed D peak in the Raman spectra with intensity of ∼1% with ...respect to the G peak. We evaluated the effect of such impurities on electron transport by mimicking them with hydrogen adsorbates and measuring the induced changes in both mobility and Raman intensity. If the intervalley scatterers responsible for the D peak are monovalent, their concentration is sufficient to account for the limited mobilities currently achievable in graphene on a substrate.
•The coatings showed a low roughness and a large thickness without defects when the overlap ratio was 70%.•Formation mechanism of the adhered powders during the EHLA cladding was proposed.•The ...response surface analysis was conducted to investigate the effect of parameters on the width of the single-track to keep the overlap ratio constant.•High-temperature wear properties of the H13 coatings and the 5CrNiMo substrate were compared.
Extreme high-speed laser (EHLA) cladding, which refers to metal deposition at speeds > 20 m/min, is the optimization for conventional laser cladding. Improving the surface properties of 5CrNiMo die steel has always been a research hotspot during engineering application. However, few research reported the enhancement of 5CrNiMo properties by EHLA cladding. The present study aims to optimize the surface roughness and analyze the high-temperature wear performance of the coatings produced by EHLA cladding. Results indicated that a laser power (4000 W), a reasonable scanning speed (376.8 mm/s) and a proper powder feeding rate (20.64 g/min) were essential for achieving the coatings with a low roughness and a large thickness without defects when the overlap ratio is 70%. In addition, the formation mechanism of the adhered powders during the EHLA cladding was discussed. The increase of the velocity and radius of the powders could reduce the adhered powders. Furthermore, the response surface analysis was conducted to investigate the effect of parameters on the width of the single-track to keep the overlap ratio constant. Additionally, friction and wear tests were carried out to discuss the tribological properties of the coatings and the 5CrNiMo substrate. The oxide film on the surface of the H13 coating enhanced the tribological property.
COVID-19 has emerged as the most serious international pandemic in early 2020 and the lack of comprehensive knowledge in the recognition and transmission mechanisms of this virus hinders the ...development of suitable therapeutic strategies. The specific recognition during the binding of the spike glycoprotein (S protein) of coronavirus to the angiotensin-converting enzyme 2 (ACE2) in the host cell is widely considered the first step of infection. However, detailed insights on the underlying mechanism of dynamic recognition and binding of these two proteins remain unknown. In this work, molecular dynamics simulation and binding free energy calculation were carried out to systematically compare and analyze the receptor-binding domain (RBD) of six coronavirus’ S proteins. We found that affinity and stability of the RBD from SARS-CoV-2 under the binding state with ACE2 are stronger than those of other coronaviruses. The solvent-accessible surface area (SASA) and binding free energy of different RBD subunits indicate an “anchor-locker” recognition mechanism involved in the binding of the S protein to ACE2. Loop 2 (Y473-F490) acts as an anchor for ACE2 recognition, and Loop 3 (G496-V503) locks ACE2 at the other nonanchoring end. Then, the charged or long-chain residues in the β-sheet 1 (N450-F456) region reinforce this binding. The proposed binding mechanism was supported by umbrella sampling simulation of the dissociation process. The current computational study provides important theoretical insights for the development of new vaccines against SARS-CoV-2.
The effects of ultrasonic impact peening (UIP) and laser shock peening (LSP) on 316L stainless steel were compared in terms of surface morphologies, microstructural evolutions and mechanical ...properties. The grain refinement mechanisms by mechanical and laser shock wave were subsequently analyzed. Experimental results showed that both UIP and LSP produced micro-grooves with the same depth (~48 μm) at the surface of 316L. The nano-grain size induced by double UIP treatment (10–90 nm) was much smaller than that by triple LSP treatment (>70 nm) because the impact numbers and total impact energy of UIP were much higher. The mechanical twinning was almost complete absence in the sample by UIP. On the contrary, the mechanical twinning was frequently observed in samples by LSP. The magnitude of peak pressure determined the transition from dislocation-dominated mechanism (~680 MPa for UIP) to twinning-dominated mechanism (~2200 MPa for LSP). The resultant dislocation cell size by UIP was much smaller than that by LSP due to the difference of dislocation density caused by different shock wave speed and impact numbers. Additionally, the compressive residual stress on the surface by UIP was higher than that by LSP in both measuring direction. Furthermore, both grain refinement and high dislocation density induced by UIP contributed to a significant increase in the hardness (~433 HV) and yield strength (~447 MPa). By contrast, the LSP induced mechanical twins which can act as dislocation blockers significantly improved the yield strength (~423 MPa).
•Surface work hardening takes place after implementation of single UIP/LSP treatment.•Large scale mechanical twins are not observed in the surface of 316L treated by UIP.•Compared with a shallow nano-grain layer (5-10 μm) in samples by LSP, UIP produced a well-defined layer (60-80 μm).•The surface compressive residual stress by UIP was much higher than that by LSP.•Compared with LSP, UIP shows a better strengthening effect on mechanical properties.
It is challenging to apply laser metal deposition (LMD) in underwater environment to realize on-site repair of marine equipment due to the potential impact of water. In the present work, we report an ...innovative underwater repair technique termed underwater laser metal deposition (ULMD) which can overcome the challenges. This new technique renders both technical and theoretical advancements from the following aspects: (1) A special in-house designed drainage nozzle was integrated with the laser cladding head to create local dry cavity which ensured the successful manufacturing of titanium alloy Ti-6Al-4V in underwater environment; (2) Unique microstructure formation/evolution mechanisms have been revealed for the ULMD process, which significantly differ from those of the in-air LMD process; (3) The hydrogen content has been well controlled during ULMD, which can effectively prevent the formation of hydrogen-induced cracks; (4) The mechanical properties of the ULMD Ti-6Al-4V parts were equal or even better than that fabricated by in-air LMD or SLM technique. In the meantime, a systematically parametric study was performed for this new technique and the experimental results showed that a high laser power (1600 W), a reasonable scanning velocity (800 mm/min) and a cross-hatching strategy were essential for achieving minimum metallurgical defects and full densification, which can provide very helpful guidance for the future research in this area. This research work opens a new avenue which makes underwater 3D-printing an applicable tool when coping with the fabrication and repair of customized components or complex shape parts in underwater environment.
•Powder feeding underwater laser metal deposition was firstly carried out on Ti-6Al-4V.•The quality of Ti-6Al-4V alloy by ULMD was equal or even better than that by in-air LMD.•How the underwater environment affects metallurgical behavior of the melt pool was studied.•Unique microstructure formation/evolution mechanisms were related with ULMD thermal process.•Influence mechanisms of the ULMD microstructure on tensile properties were revealed.
Underwater directed energy deposition (UDED) is a promising technology for on-site maintenance and repair of underwater structures. In this study, the damage zone on a Ti–6Al–4V plate was ...successfully repaired by UDED and no obvious internal defects were observed. The mechanisms of the special underwater thermal behaviors influencing the microstructural formation/evolution process and the resultant mechanical properties of Ti–6Al–4V repaired by UDED were systematically investigated by experimental and simulation methods. Compared with that prepared by in-air directed energy deposition (DED), the sample repaired by UDED presented the following differences: (1) The cooling rate was large and the heat accumulation of the sample was low during UDED due to the rapid heat dissipation by water and gas curtain gas. (2) The sample repaired by UDED was dominated by fine acicular martensite α′ with a high density of dislocations due to the weak intrinsic heat treatment (IHT), while the intensified IHT involved in DED provoked the significant decomposition of α′ into α and β film. (3) The weak IHT during UDED resulted in the formation of thin β films with a low vanadium content. The intensified IHT during DED promoted the diffusion of vanadium atoms and the coarsening of β films. (4) The average microhardness of the sample repaired by UDED (379 ± 15 HV) was higher than that repaired by DED (359 ± 11 HV). The sample repaired by UDED exhibited relatively poor ductility and low toughness due to the presence of acicular martensite α′. This work can provide an important foundation and useful guidance for tailoring the microstructure and properties of titanium alloys repaired by UDED in underwater environments.
The hydrogen economy has been identified as an alternative to substitute the non-sustainable fossil fuel based economy. Ongoing research is underway to develop environmentally friendly and economical ...hydrogen production technologies that are essential for the hydrogen economy. One of the promising ways to produce hydrogen is to use aluminum or its alloys to reduce water or hydrocarbons to hydrogen. This paper gives an overview on these aluminum-based hydrogen production methods, their limitations and challenges for commercialization. Also, a newly developed concept for cogeneration of hydrogen and electrical energy is discussed.
Underwater laser directed energy deposition (UDED) can be employed to repair and maintain the offshore engineering structures due to its advantages of flexible adjustment of feedstock materials and ...controllable heat input to the structures. For the first time, preprepared HSLA-100 steel plates were successfully remanufactured by UDED at an ambient pressure of 0.3 MPa (water depth of 30 m). The relationships between the hyperbaric underwater environment, solidification process, microstructures and mechanical properties of the HSLA-100 steel were clarified. The results show that the cooperation of surrounding water, central gases and gas curtain gas with large flow rates increased the cooling rates of the underwater melt pool. A lath martensitic microstructure with high dislocation densities and a number of inclusions was formed in the sample remanufactured by UDED. The in-situ precipitation of Cu-enriched nanoparticles was caused by the unique intrinsic heat treatment involved in the underwater deposition process. The average diameter of the Cu-enriched nanoparticles increased with increasing laser energy density. The microstructure of the sample remanufactured by UDED was harder than that of the sample remanufactured by in-air DED. The Charpy impact toughness and tensile properties of the samples remanufactured by UDED were close to those of the sample remanufactured by in-air DED. This work demonstrates the feasibility of high-quality remanufacturing of HSLA-100 steel via UDED in a hyperbaric underwater environment. The results obtained in this study could provide useful guidance for the application of UDED to offshore engineering structures.
•The HSLA-100 is firstly repaired by UDED in an underwater hyperbaric environment.•The high ambient pressure influences the metallurgical processes and microstructures.•In-situ precipitation of Cu is determined by the unique underwater thermal cycles.•HSLA-100 steel repaired by UDED possesses high strength and excellent toughness.•This work expands the applications of UDED to the hyperbaric underwater environments.
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