We present an extension of the existing continuum theory for sound wave propagation in dilute gases in ‘‘narrow’’ two-dimensional channels to arbitrary Knudsen numbers; the theory provides predictions for the wavelength and attenuation coefficient as a function of the oscillation frequency. A channel is considered narrow in the context of wave propagation when its height is much smaller than th...

Submitted for the MAR14 Meeting of The American Physical Society Instability and Wave Propagation in Structured 3D Composites NARGES KAYNIA, NICHOLAS X. FANG, MARY C. BOYCE, Massachusetts Inst of Tech MIT — Many structured composites found in nature possess undulating and wrinkled interfacial layers that regulate mechanical, chemical, acoustic, adhesive, thermal, electrical and optical function...

For the wave equation, the Green’s function that describes the wave propagating between two receivers can be reconstructed by cross-correlation if the receivers are enclosed by sources on a closed surface. This technique is normally called interferometry. The ordinary operator used in this technique is cross-correlation. The same technique for Green’s function extraction can be applied to the s...

We present the temperature dependence of the growth rate of carbon nanofibers by plasma-enhanced chemical vapor deposition with Ni, Co, and Fe catalysts. We extrapolate a common low activation energy of 0.23-0.4 eV, much lower than for thermal deposition. The carbon diffusion on the catalyst surface and the stability of the precursor molecules, C2H2 or CH4, are investigated by ab initio plane w...

Vibrothermography is a promising technique that uses elastic ultrasonic wave excitation in solids for quality maintenance, e.g. in aerospace and automotive industry to monitor the integrity of surface or subsurface features. Vibrothermography allows for defect selective imaging using thermal waves that are generated by elastic sound or ultrasound waves. The mechanism involved is local friction ...

The microstructure of a composite material has an essential infl uence on its effective properties, and it can be used to regulate mechanical, chemical, acoustic, adhesive, thermal, electrical, and optical functions of the material. This research focused on purposely deploying the mechanics of instabilities to achieve sudden pattern transformations in the microstructure of a composite, and stud...

Laser-generated thermal wave diffraction theory is presented as a perturbative Born (or Rytav) approximation in a two-dimensional spatial domain for use with tomographic image reconstruction methodologies. The ranges of validity of the pertinent twodimensional spatial-frequencylthermal wavenumber domain complex plane contours are investigated in terms of the existence af inverse spatial Laplace...

Alfven waves are possible sources of turbulence in the interstellar medium. These waves are responsible for the transport of angular momentum and energy in the accretion discs. Such waves have been studied for last several decades in space plasmas. Most of the space plasmas are dusty. They contain charged grains and coupling of the grains to the magnetic field determines the wave propagation in...

Explicit finite difference and finite element schemes are constructed to solve wave propagation, shock, and impact problems. The schemes rely on exponential functions and the solution of linearised Rlemann problems in order to reduce the effects of numerical dispersion and diffusion. The relationship of the new schemes to existing explicit schemes is analysed and numerical results and compariso...

We study the effect of small, randomly distributed obstacles on wave propagation in two-dimensional (2D) and 3D excitable media described by the Aliev–Panfilov model. We find that increasing the number of obstacles decreases the conduction velocity of plane waves and decreases the effective diffusion coefficient in the eikonal curvature equation. The presence of obstacles also increases the ind...