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The ingenious hierarchical structure of enamel composed of rods and protein produces excellent fracture resistance. However, the fracture resistance mechanism in the inner enamel is unknown. The micromechanical models of enamel are constructed to numerically analyze the mechanical behaviors of the inner enamel with different decussation angles and different decussation planes. The results show that the manner of crack propagation in the inner enamel, including crack bridging, crack deflection, and crack bifurcation, is determined by both the rod decussation angle and the decussation plane. In the case of the strong decussation plane, the fracture strength and the required energy dissipation with the decussation angles of 15° and 30° are much higher than those without decussation, demonstrating that decussation is an important mechanism in improving the fracture resistance of enamel. The maximum tensile stress of enamel with the decussation angle of 15° is slightly higher than that of enamel with the decussation angle of 30°, illustrating that an optimal decussation angle exists which balances the strength and toughness. The synergetic mechanism of the decussation angle and the decussation plane on the crack propagation provides a new design hint for bionic composites. [ABSTRACT FROM AUTHOR]

Enamel possesses ingenious hierarchical structure that gives rise to superior fracture resistance. Despite considerable efforts devoted to characterization of fracture behavior of enamel, the role of rod decussation in fracture of enamel is largely unknown. In this study, the features of rod decussation in the inner enamel are experimentally identified, and analyses of crack growth in enamel are carried out using a micromechanical model of enamel, in which the structural features of the outer enamel and rod decussation of the inner enamel are incorporated. We carry out calculations within a framework based on the extended finite element method, and the crack growth and crack path selection are natural outcomes of imposed loading. We show that crack deflection in enamel is controlled by rod decussation. For crack growth in the parazone, the crack path is oriented along the axis of enamel rods, leading to gross crack deflection. The microstructure of inner enamel with intermediate inclination angle enables multiple crack deflections, giving rise to enhanced toughness. For crack growth in the diazone, the transition in orientation of crack deflection occurs as inclination angle increases. The relatively straight crack path emerges in the case of the microstructure of enamel with intermediate inclination angle, leading to weak fracture resistance. It is further found that compared with the diazone, the gross crack deflection in the parazone provides greater contribution to fracture resistance of enamel. The findings of this study provide a good mechanistic understanding of the role of rod decussation in enamel. [ABSTRACT FROM AUTHOR]

Interest in the influence of musical training on executive functions (EFs) has been growing in recent years. However, the relationship between musical training and EFs remains unclear. By dividing EFs into inhibitory control, working memory, and cognitive flexibility, this study systematically examined its association with musical training in children, and further verified whether there was a sensitive period for the influence of music training on EFs. In Experiment 1, musically trained and untrained children were asked to complete the Go/No-go, Stroop, Continuous Performance, and Switching tasks. Results showed that musically trained children had an advantage in attention inhibition, response inhibition, and working memory, but not in cognitive flexibility. Moreover, the level of musical training was positively correlated with response inhibition and working memory abilities. In Experiment 2, results showed that early-trained musicians performed better on measures of attention inhibition, response inhibition, and working memory than did the age-matched control group, but late-trained musicians only performed better in attention inhibition. Thus, our findings suggest that music training is associated with enhanced EF abilities and provide the first evidence that early childhood is a sensitive period when musical training has a more powerful effect on the development of EFs. [ABSTRACT FROM AUTHOR]

In order to analyze and characterize the dynamic mechanical behavior and properties of TCI 8 alloy, the normal temperature quasi-static compression experiment was performed on the TC18 alloy using an electronic-universal testing machine to obtain the experimental data of the alloy under quasi-static condition. According to the experimental data, the dynamic mechanical properties of TC18 alloy at 298,523, 773, and 1 023 K with strain rates of 500, 1 000 and 1 500 s-1 were tested respectively using a Split Hopkinson Pressure Bar (SHPB). The stress-strain curves of the alloy under dynamic compression at high temperature were obtained. And the effects of temperature and strain rate on the dynamic mechanical behavior of TC18 alloy were analyzed. The results showed that the plastic strain of TC18 alloy increased obviously with the increase of strain rate at the same temperature, showing a certain strain-rate plasticizing effect. The (low stress of TC18 alloy decreased significantly with the increase of temperature under the same strain rate, and shows obvious thermal softening effect. The strain rate strengthening effect and thermal softening effect were carried out simultaneously in the process of plastic deformation at high slrain rate. The thermal softening effect was greater than the strain-rate strengthening effect when the temperature exceeds 773 K. [ABSTRACT FROM AUTHOR]