No abstract

No abstract

The effect of fiber loss, amplification, and sliding-frequency filters on the evolution of optical pulses in nonlinear optical fibers is considered, this evolution being governed by a perturbed nonlinear Schrödinger (NLS) equation. Approximate ordinary differential equations (ODE's) governing the pulse evolution are obtained using conservation and moment equations for the perturbed NLS equation together with a trial function incorporating a solitonlike pulse with independently varying amplitude and width. In addition, the trial function incorporates the interaction between the pulse and the dispersive radiation shed as the pulse evolves. This interaction must be included in order to obtain approximate ODE's whose solutions are in good agreement with full numerical solutions of the governing perturbed NLS equation. The solutions of the approximate ODE's are compared with full numerical solutions of the perturbed NLS equation and very good agreement is found.

No abstract

A method for segmentation of arteries in ultrasound Bmode images using a modified balloon model is presented. The external force which pulls the contour to the arterial boundary is the combination of the gradient and the second order derivative of the image. For 3D segmentation the contour of the first slice is found, and this is used as the initial position for the next slice. As the initial position of the contour may be outside the artery, the pressure term is decided by comparing the feature of texture inside and outside of the contour, allowing the contour to expand or shrink. The model has been tested on 55 images from carotid arteries. The 'gold standard' boundary drawn by a radiologist and the segmented boundary showed an average difference of 0.40 ± 0.30mm. 3D data was obtained using an anatomically correct carotid bifurcation flow phantom and gridded ready for CFD.