Rayleigh-Wave Dispersion Analysis and Inversion Based on the Rotation.

Rotational observation is essential for a comprehensive description of the ground motion, and can provide additional wave-field information. With respect to the three typical layered models in shallow engineering geology, under the assumption of linear small deformation, we simulate the 2-dimensional radial, vertical, and rotational components of the wave fields and analyze the different characteristics of Rayleigh wave dispersion recorded for the rotational and translational components. Then, we compare the results of single-component inversion with the results of multi-component joint inversion. It is found that the rotational component has wider spectral bands and more higher modes than the translational components, especially at high frequencies; the rotational component has better anti-interference performance in the noisy data test, and it can improve the inversion accuracy of the shallow shear-wave velocity. The field examples also show the significant advantages of the joint utility of the translational and rotational components, especially when a low-velocity layer exists. Rotational observation shall be beneficial for shallow surface-wave exploration.

Response of Woodpecker's Head during Pecking Process Simulated by Material Point Method.

Prevention of brain injury in woodpeckers under high deceleration during the pecking process has been an intriguing biomechanical problem for a long time. Several studies have provided different explanations, but the function of the hyoid bone, one of the more interesting skeletal features of a woodpecker, still has not been fully explored. This paper studies the relationship between a woodpecker head's response to impact and the hyoid bone. Based on micro-CT scanning images, the material point method (MPM) is employed to simulate woodpecker's pecking process. The maximum shear stress in the brainstem (SSS) is adopted as an indicator of brain injury. The motion and deformation of the first cervical vertebra is found to be the main reason of the shear stress of the brain. Our study found that the existence of the hyoid bone reduces the SSS level, enhances the rigidity of the head, and suppresses the oscillation of the endoskeleton after impact. The mechanism is explained by a brief mechanical analysis while the influence of the material properties of the muscle is also discussed.

Ultra-high sensitivity of super carbon-nanotube-based mass and strain sensors.

Based on the molecular structure mechanics method, the dynamic properties of super carbon nanotubes (STs), together with ST-based mass and strain sensors, are investigated. The following results are obtained: (a) the fundamental frequency of the STs is found to be lower than that of the single-wall carbon nanotube (SWCNT); (b) the STs may be a potential ultra-high sensitivity mass sensor with a sensitivity about 10(-24) g, which is much higher than that of SWCNT-based mass sensors (10(-21) g); (c) the ST-based strain sensor has a sensitivity as high as 887 Hz/nanostrain, which is also higher than that of SWCNT-based strain sensors. The obtained results suggest that the STs could be used to design the new generation of sensors due to its high sensitivity and ultra-low density.

The effective modulus of super carbon nanotubes predicted by molecular structure mechanics.

A super carbon nanotube (ST) is a kind of hierarchical structure constructed from carbon nanotubes (named as CNT arm tubes). With the detailed construction of a Y-junction considered, the effective mechanical properties of ST structures are studied by the molecular structure mechanics (MSM) method. The Young's modulus and shear modulus of STs are found to depend mainly on the aspect ratio of CNT arm tubes instead of the chirality of the ST. A scale law is adopted to express the relation between the effective modulus (Young's modulus or shear modulus) and the aspect ratio of the CNT arm tubes. The Poisson's ratio of the ST is affected by both the aspect ratio of the CNT arm tubes and the chirality of the ST. The deformation of the ST comes from both the bending and the stretching of the CNT arm tubes. The Y-junction acts as an reinforcement phase to make the bending and stretching couple together and induce large linearity in ST structures.

Mechanical properties of super honeycomb structures based on carbon nanotubes.

As a result of repeating carbon nanotube Y junctions periodically, super honeycomb structures have recently been proposed. In this paper, the mechanical properties of these structures are investigated by using the shell model of the finite element method. The study shows that the super honeycomb structures have great flexibility and outstanding capability in force transferring; the network configuration increases the ductility of the nanomaterials. Furthermore, it can be concluded that the equivalent tensile modulus and Poisson's ratio of super structures are dependent on the number of junctions in the width direction.