Wave characteristics of carbon nanotubes

AbstractThe research in the manuscript studies the wave characteristics in carbon nanotubes (CNTs) via beam theories. First, the material properties used in the beam models for the analysis of CNTs are proposed from the discrete atomic nature of CNTs. Secondly, the comparison of wave solution in a single walled carbon nanotube (SWNT) by Euler–Bernoulli beam model and Timoshenko beam model is conducted. The applicability of the two beam models is discussed from the numerical simulations. In addition, the difference of the two beam models on the terahertz frequency range is presented to show the significance of applying an appropriate continuum model in studying the wave propagation in CNTs. Thirdly, Timoshenko beam model is employed to study the wave propagation in a double walled carbon nanotube (DWNT) via a simple single beam theory by assuming co-axial motion of the two tubes, and a double beam theory accounting for van der Waals. The size effect of the DWNT on the wave solution by different beam theories is discussed as well. The feasibility of applying the simple single beam theory and the double beam theory is discussed through numerical simulations. It is hoped that the research in the manuscript may present a benchmark in the study of wave propagations in carbon nanotubes

Lattice instabilities of PbZrO3/PbTiO3 [1:1] superlattices from first principles

Ab initio phonon calculations for the nonpolar reference structures of the (001), (110), and (111) PbZrO_3/PbTiO_3 [1:1] superlattices are presented. The unstable polar modes in the tetragonal (001) and (110) structures are confined in either the Ti- or the Zr-centered layers and display two-mode behavior, while in the cubic (111) case one-mode behavior is observed. Instabilities with pure oxygen character are observed in all three structures. The implications for the ferroelectric behavior and related properties are discussed.Comment: 12 pages, 2 figures, 7 tables, submitted to PR

LOCAL/GLOBAL SAW SENSORS FOR TURBULENCE

Un nouveau détecteur utilisant une onde acoustique de surface (SAW) a été développé théoriquement et expérimentalement afin de permettre la détection de forces de surfaces telles que la pression et la friction, et aussi de déterminer la direction de courant turbulent eu tant que fonction de position et de temps par rapport à la structure concernée. Le détecteur est composé d'une paire de SAWs ayant une fréquence centrale identique dont les ondes de surface suffissent des stress transversaux de sens opposés. La différence entre les vitesses des deux SAWs est proportionnelle au stress transversal associé au courant turbulent. La différence entre la vitesse moyenne d'une paire de SAWs subjette à un courant turbulent et la vitesse de la SAW dans un fluide stationnaire est proportionnelle à la pression (stress perpendiculaire) du courant. La direction du courant du fluide peut aussi être déterminée grâce à un arrangement de trois paires de détecteurs SAW d'une manière similaire à une strain rosette. Selon la résolution spatiale et temporaire nécessaire, on peut mesurer simultanément les forces de surface fluctuantes et la direction du courant turbulent à la fois localement et globalement.A new surface acoustic wave (SAW) sensor is developed through theoretical and experimental investigation to detect the surface forces (wall pressure and wall friction) and the direction of the turbulent flow as a function of position and time on the structure. The sensor is composed of a pair of SAWs having an identical center frequency with surface waves experencing shear stresses in opposite directions. The difference in the two SAW velocities is proportional to the shear stress associated with the turbulent flow. The difference between the mean velocity of a pair of the SAWs subject to a turbulent flow and the velocity of the SAW in a stationary fluid is proportional to the pressure (normal stress) of the flow. The direction of fluid flow can also be determined through an arrangement of three pairs of SAW sensors in a manner similar to a strain rosette. Depending on the spatial and temporal resolution required, we can simultaneously measure the fluctuating surface forces and the direction of a turbulent flow both locally and globally

Wave propagation in piezoelectric coupled plates by use of interdigital transducer. Part 1. Dispersion characteristics

10.1016/S0020-7683(01)00243-8International Journal of Solids and Structures3951119-113

Longitudinal wave propagation in piezoelectric coupled rods

10.1088/0964-1726/11/1/305Smart Materials and Structures11148-54SMST

Wave propagation in piezoelectric coupled plates by use of interdigital transducer. Part 2: Wave excitation by interdigital transducer

10.1016/S0020-7683(01)00244-XInternational Journal of Solids and Structures3951131-114