关键词： Mechanical activation   DTA   Raman spectroscopy   Sintering kinetics   Spinel  

摘要： Solid-state mechanical activation of MgO and alpha-Al2O3 powders was used to produce MgAl2O4. The cation site occupancy in the resulting MgAl2O4 spinel was investigated using different methods. Differential thermal analysis and thermal gravimetry showed that mechanical activation reduced the spinel formation temperature by around 200 degrees C, and the corresponding activation energy by about 25%. In addition, characteristic temperatures for evaporation of physisorbed water and decomposition of Mg(OH)(2) shifted to lower values, and peaks were more pronounced. Raman spectra were used to characterize the degree of inversion as a function of the sintering temperature for all of the sintered specimens, indicating that the breaking point for ordering of the crystal structure was around 1500 degrees C for non-activated samples, and 1400 degrees C for activated samples.

关键词： Grain boundaries  

摘要： Molecular dynamics simulations are performed to study the mechanical behaviors and microstructural evolution in nanocrystalline Cu films created by the phase field model under different strain rates and temperatures. The results indicate that grain boundaries' (GBs) migration caused by shear stress difference of GBs is found in the initial deformation stage. The migration on the site with a small curvature radius of curved GBs is large due to the high stress difference. The migration process of curved GBs in the initial stage is that atoms migrate from FCC structures to GBs along the (111) surface, which is different from the mechanism of atomic shuffling for the flat GBs. Meanwhile, the initial GBs migration can make curved GBs become flat. In addition to temperature and stress difference, the hexagonal-close-packed (HCP) structures including stacking faults and twin boundaries can accelerate GBs' migration. The influence of initial GB migration on mechanical properties is achieved by changing the fraction and distribution of HCP structures. Larger initial GB migration at a higher temperature significantly reduces stress concentration on GBs, which leads to the distribution of HCP changing from the grains with large initial GB migration to other grains. Therefore, the sites of crack nucleation at conditions of low and high temperatures are different due to different magnitudes of initial GB migration.

关键词： Boron  

摘要： We report the determination of diffusion paths and potential barriers of boron point defects in TiB2 calculated using the climbing image nudged elastic band method at T = 0 K, and ab initio molecular dynamics studies on the structural stabilities, diffusion behavior of boron point defects and mechanical strengths of TiB2 at elevated temperatures. In contrast to the previous conjecture that TiB2 with boron vacancies are thermodynamically unstable based on the calculations at T = 0 K that boron vacancies have positive formation energies and shift electronic Fermi energies from the pseudogap valleys to the bonding states, our results show that boron vacancies in TiB2 are very robust and they have negligible effects on the structural stabilities and mechanical strengths of TiB2 at least up to 2000 K within the vacancy concentration we studied (<2.5 at%). On the other hand, our results reveal that the boron interstitials can diffuse easily in TiB2 at a moderately high temperature (1000 K) or under large shear and tensile deformations, which give rise to significant deteriorations (more than 50% reduction) in the mechanical strength of TiB2 at a high temperature (2000 K) with a boron interstitial density below 2.5 at%. Under all the shear and tensile deformations we applied, the boron interstitials in TiB2 eventually diffuse into the boron layers, causing deformations of these boron layers, which weakens their interactions with metal layers nearby and consequently reduces the mechanical strengths of the materials as temperature and boron interstitial density increase. The present findings expand our understandings on the material strength of TiB2 at high temperatures with boron point defects, and offer new insights for its applications as a high-strength ultra-high temperature ceramic.

关键词： alternative splicing   molecular modeling   evolution   transcript phylogeny   kinase  

摘要： Alternative splicing and alternative initiation/termination transcription sites have the potential to greatly expand the proteome in eukaryotes by producing several transcript isoforms from the same gene. Although these mechanisms are well described at the genomic level, little is known about their contribution to protein evolution and their impact at the protein structure level. Here, we address both issues by reconstructing the evolutionary history of transcripts and by modeling the tertiary structures of the corresponding protein isoforms. We reconstruct phylogenetic forests relating 60 protein-coding transcripts from the c-Jun N-terminal kinase (JNK) family observed in seven species. We identify two alternative splicing events of ancient origin and show that they induce subtle changes in the protein's structural dynamics. We highlight a previously uncharacterized transcript whose predicted structure seems stable in solution. We further demonstrate that orphan transcripts, for which no phylogeny could be reconstructed, display peculiar sequence and structural properties. Our approach is implemented in PhyloSofS (Phylogenies of Splicing Isoforms Structures), a fully automated computational tool freely available at https://***/PhyloSofS-Team/PhyloSofS. (C) 2020 Elsevier Ltd. All rights reserved.

关键词： Phase synchronization   Collective phenomenon   Mechanical oscillators   Anti-synchronization  

摘要： Phase synchronization refers to a kind of collective phenomenon that the phase difference between two or more systems is locked, and it has widely been investigated between systems with the identical physical properties, such as the synchronization between mechanical oscillators and the synchronization between atomic ensembles. Here, we investigate the synchronization behavior between the mechanical oscillator and the atomic ensemble, the systems with different physical properties, and observe a novel synchronization phenomenon, i.e., the phase sum, instead of phase difference, is locked. We refer to this distinct synchronization as the phase anti-synchronization and show that the phase anti-synchronization can be achieved in both the classical and quantum level, which means this novel collective behavior can be tested in experiment. Also, some interesting connections between phase anti-synchronization and quantum correlation are found.

关键词： Cell biology   Neuroscience  

摘要： Neurons maintain axonal homeostasis via employing a unique organization of the microtubule (MT) cytoskeleton, which supports axonal morphology and provides tracks for intracellular transport. Abnormal MT-based trafficking hallmarks the pathology of neurodegenerative diseases, but the exact mechanism regulating MT dynamics in axons remains enigmatic. Here we report on a regulation of MT dynamics by AuTophaGy(ATG)-related proteins, which previously have been linked to the autophagy pathway. We find that ATG proteins required for LC3 lipid conjugation are dispensable for survival of excitatory neurons and instead regulate MT stability via controlling the abundance of the MT-binding protein CLASP2. This function of ATGs is independent of their role in autophagy and requires the active zone protein ELKS1. Our results highlight a non-canonical role of ATG proteins in neurons and suggest that pharmacological activation of autophagy may not only promote the degradation of cytoplasmic material, but also impair axonal integrity via altering MT stability.

关键词： Carbon nanotube   non-covalent functionalisation   biomolecules   buckling   molecular dynamics simulation  

摘要： The functionalisation of carbon nanotubes (CNTs) with biomolecules in an aqueous environment has found considerable potential applications in nanobiotechnology. To understand the structural properties under physical adsorption and mechanical characteristics of non-covalently functionalised CNTs with four important biomolecules in aqueous environment, i.e. l-alanine, guanine, thymine and uracil, molecular dynamics (MD) simulations are performed. It is demonstrated that, unlike l-alanine, the main factor of adsorption is pi-pi stacking together with van der Waals (vdW) interactions. Computation of gyration radius reveals that gyration radius increases linearly as the weight percentage of functional biomolecules increases. Also, it is shown that the presence of water molecules leads to more expansion of biomolecules around CNTs. Simulations show that Young's modulus of the adsorbed CNTs is slightly smaller than that of pure ones. Furthermore, it is demonstrated that the critical buckling force of functionalised CNT is higher than that of pure CNT. Also, for high aspect ratios, the critical strain of functionalised CNTs is found to be lower than that of pure ones and changes linearly by increasing the weight percentage of functional biomolecules. The buckling modes of functionalised CNTs in vacuum and aqueous environments are explored.

关键词： CNT   polymer   polyoxymethylene   molecular dynamics   composite  

摘要： Carbon Nanotubes (CNTs) are potential additives to polymeric materials as they can enhance the mechanical, structural, and electronic properties of the resulting polymeric composite. However, the improvement of different properties is not always guaranteed and the results usually depend on the specific polymer used, along with the quality and quantity of CNTs used in the polymer composite. In this work, a reactive force field (ReaxFF) is applied to perform molecular dynamics (MD) simulation to determine the change in mechanical properties of single-walled carbon nanotube (SWCNT)-reinforced Polyoxymethylene (POM) composite. We have varied the diameter of CNTs from 0.542 to 1.08 nm keeping the temperature constant at room temperature (300 K) and observed a significant change in the resulting mechanical property. Volume fraction of CNT and temperature are also varied and the results are presented through a stress-strain plot. After that, our Molecular Dynamics (MD) simulation result of CNT is compared with existing literature for code validation. Dependence of mechanical property on the interaction energy, fracture mechanism, and reasons behind it are discussed elaborately. It is clear from the results that the use of SWCNT in the polymer matrix of POM significantly improves the mechanical property of SWCNT-reinforced POM composite.

关键词： combustion performance   dynamics   fiber   MHSH   PBS  

摘要： Environmental problems caused by polymers and polymers have historically dominated both academic and industrial attention. Sustainable biodegradable wood-plastic composites (WPCs) as an optimum can solve the environmentally critical problems caused by petroleum-based polymers. However, they are flammable, prone to fire accidents, and often have a contradiction between mechanical performance and flame-retardant properties, which limits their range of applications. Here, we reported a flame-retarded poly(butylene succinate) (PBS) WPC prepared with modified natural fiber-magnesium hydroxide sulfate whisker (MHSH) hybrids and intumescent flame retardants (IFRs). The mechanical performance, flame-retardant properties, thermal stability, and actual fire simulation parameters of composites were investigated. Owing to the unique composition characteristics of modified cassava dregs-MHSH hybrids, the mechanical properties (70P/23I/5C/2M, flexural strength was 39.2 +/- 1.960/MPa, impact strength was 7.95 +/- 0.3975/ [KJ/m(2)]), flame retardant properties (70P/23I/5C/2M, the limiting oxygen index value was 39.6%, UL-94 was V0) and thermal stability of WPC have been improved. Thereby, the balance between mechanical performance and flame retardant properties of biocomposites has been achieved in the practical engineering requirements. Furthermore, cone calorimeter data indicated that modified cassava dregs-MHSH hybrids played a role in improving the fire safety of composites. The total heat release, total smoke produce, toxic gas release, and total oxygen consumed of 70P/23I/5C/2M were lowered compared with those of 70P/25I/5C. Dynamics analysis indicated that the addition of modified cassava dregs-MHSH hybrids increased the activation energy of composites. Based on the experimental and analyses data, especially the morphological characterization of char residue analysis, it illustrated that modified cassava dregs-MHSH hybrids have a reinforcement and flame-retardant effect. The