Mathematical analysis of thermal diffusion shock waves

Thermal diffusion, also known as the Ludwig-Soret effect, refers to the separation of mixtures in a temperature gradient. For a binary mixture the time dependence of the change in concentration of each species is governed by a nonlinear partial differential equation in space and time. Here, an exact solution of the Ludwig-Soret equation without mass diffusion for a sinusoidal temperature field is given. The solution shows that counterpropagating shock waves are produced which slow and eventually come to a halt. Expressions are found for the shock time for two limiting values of the starting density fraction. The effects of diffusion on the development of the concentration profile in time and space are found by numerical integration of the nonlinear differential equation

On the sensitivity of an air pycnometer

Experimental DataSe

A kinetic and thermodynamic study of lac dye adsorption on silk yarn coated with microcrystalline chitosan

The coating of silk yarn with microcrystalline chitosan (MCCh) was carried out using the ultrasonic-assisted method at a pulsed wave frequency of 80 kHz, which only had a slight impact on the yarn as measured by changes in Young\u27s modulus and percentage of elongation compared with untreated silk. A significant enhancement of lac dye uptake onto MCCh-coated silk yarn compared with the untreated silk was observed. The rate of dye uptake at different temperatures onto silk yarn coated with MCCh was investigated. It was found that the adsorption rate constant and diffusion coefficient both increased with increasing temperature, as a result of a diffusion kinetically controlled process with a diffusion activation energy of 9.40 kJ mol −1 . This suggests that dye adsorption on silk yarn coated with MCCh is a physisorption process. The free energy change (∆G ○ ), enthalpy change (∆H ○ ) and entropy change for dye adsorption were also determined, and the negative values of ∆G ○ and ∆H ○ obtained indicated that the lac dye adsorption process is both spontaneous and exothermic

Three-dimensional imaging of biological cells with picosecond ultrasonics

We use picosecond ultrasonics to image animal cells in vitro-a bovine aortic endothelial cell and a mouse adipose cell-fixed to Ti-coated sapphire. Tightly focused ultrashort laser pulses generate and detect GHz acoustic pulses, allowing three-dimensional imaging (x, y, and t) of the ultrasonic propagation in the cells with similar to 1 mu m lateral and similar to 150 nm depth resolutions. Time-frequency representations of the continuous-wavelet-transform amplitude of the optical reflectivity variations inside and outside the cells show GHz Brillouin oscillations, allowing the average sound velocities of the cells and their ultrasonic attenuation to be obtained as well as the average bulk moduli

Observation and Simulation of Surface Acoustic Waves in Phononic Crystal

International audienc

Broadband evolution of phononic-crystal-waveguide eigenstates in real- and k-spaces

International audienceControl of sound in phononic band-gap structures promises novel control and guiding mechanisms. Designs in photonic systems were quickly matched in phononics, and rows of defects in phononic crystals were shown to guide sound waves effectively. The vast majority of work in such phononic guiding has been in the frequency domain, because of the importance of the phononic dispersion relation in governing acoustic confinement in waveguides. However, frequency-domain studies miss vital information concerning the phase of the acoustic field and eigenstate coupling. Using a wide range of wavevectors k, we implement an ultrafast technique to probe the wave field evolution in straight and L-shaped phononic crystal surface-phonon waveguides in real- and k-space in two spatial dimensions, thus revealing the eigenstate-energy redistribution processes and the coupling between different frequency-degenerate eigenstates. Such use of k-t space is a first in acoustics, and should have other interesting applications such as acoustic-metamaterial characterization