Shear waves in viscoelastic wormlike micellar fluids over a broad concentration range.

Low frequency (61 Hz) shear wave speeds have been measured in viscoelastic wormlike micellar (WM) fluids for a concentration range of 20/12-500/300 mM CTAB/NaSAL where CTAB is the surfactant and NaSAL is the salt and the concentration ratio was fixed at 0.6 for all experiments. The birefringent property of the WM fluids was exploited to visually track the the shear pulse using crossed optical polarizing filters and high speed video. Several scalings of shear wave speed as a function of concentration were discovered: c(s) ~ √C for 20-200 mM and c(s) ~ C for higher concentrations, but with a break in the slope at 400 mM CTAB. Over this full concentration range, the shear wave speed varied from 0.08-0.7 m/s. The shear wave speed was also found to be sensitive to the time between fluid synthesis and measurement indicating a long equilibrium time. Further, comparison with elastic and loss moduli obtained from rheology data show that shear wave propagation is dominated by the elastic modulus for this frequency range. Also briefly discussed are potential applications of this fluid in elastography.

Shear waves in viscoelastic wormlike micellar fluids.

Low frequency (61 Hz) shear wave speeds have been measured in viscoelastic wormlike micellar (WM) fluids for a concentration range of 20/12-160/96 mM CTAB/NaSAL. The strain induced birefringence of the WM fluids was exploited to optically track the shear pulse using crossed polarizing filters and high speed video. It was found that shear speed increases roughly linearly with concentration at a rate of 3.5 mm s(-1) mM(-1) CTAB. Further, comparison with elastic and loss moduli obtained from rheology data show that shear wave propagation is dominated by the elastic modulus for this frequency range.

Mild traumatic brain injury--the Fife perspective.

Results are reported from a study to identify patients residing in Fife with mild traumatic brain injury in the 16-65 year old age group, who attended an accident and emergency department following their brain injury. Over a two month period 161 such patients attended with minor head trauma, of which 33 entered our study. The major cause of mild traumatic brain injury was assault. We found that over two-thirds of patients in the study had persisting post-concussive symptoms six months post injury. Neuropsychological testing showed problems of concentration and memory, but not at a level that was significantly different from that expected in an average population. Other studies have shown that symptom rates are higher when patients get no explanation of their symptoms and we feel that better co-ordination of services for brain injured patients in Fife is required, to provide the necessary information, education and support.