X-ray vision.
Recent correspondence initiated by Dr. Cochrane Shanks' account of the sensation of light experienced during a CAT scan recalls an article on vision by X rays by R. R. Newell (1948).
Place of new contrast media in renal failure.
It was with great interest that I read “The effect of osmotic diuresis on urinary iodine concentration” (Webb et al., 1978) in your February issue. I believe some observations from our recent experiments and calculations may be of interest and cast some additional light on the place of contrast media of reduced osmolality in advanced renal failure.
Numerical analysis of surface crack propagation in flexible pavements using XFEM and cohesive zone model
Surface initiated (top-down) cracking in the longitudinal direction of pavements has become a predominant mode of failure in thick asphalt pavements. Most previous researchers studied crack propagation using the traditional Linear Elastic Fracture Mechanics (LEFM) method by calculating the stress intensity factor around the crack tip. In this paper, Extended Finite Element Method (XFEM) was used to study the key factors causing surface initiated crack propagation under surface tension and/or shear. A two-dimensional (2-D) finite element (FE) model for a two-lane flexible pavement was built to predict pavement responses and crack propagation potential under various scenarios. It was found that surface tension is the major driving force for crack propagation when the crack is at some distance away from tire loading. The results show that the distance from the location of crack to tire loading, the depth and direction of the crack, and the modulus ratio between the hot-mix asphalt (HMA) layer and the base layer have significant influences on crack propagation under surface tension. On the other hand, this study shows that shear stress can induce surface initiated crack propagation near the loading area as the shear resistance of material becomes low at the high temperature.