Effect of solvent plasticization on polypropylene microcellular foaming process and foam characteristics

In this research, the effect of crystalline fraction of polypropylene (PP) on cell nucleation behavior was overcome by an introduction of solvent‐plasticized step to the microcellular foaming in a solid‐state batch‐foaming process. Utilizing the plasticization performance of the solvent facilitated the PP to be foamed at the temperatures lower than its melting point with the dramatic development in the cellular morphology of the final foams. In consequence of the heterogeneous cell nucleation sites induction and the crystalline loss, which were induced by solvent, a high cell density (i.e., 10⁹–10¹⁰ cells/cm³) was promoted without the cell sacrificing at the elevated temperatures (155 and 165°C) and favorable PP microcellular foams were accomplished. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Effect of die geometry on foaming behaviors of high‐melt‐strength polypropylene with CO2

This article reports on a systematic study that was conducted to investigate the effects of die geometry (i.e., pressure and pressure drop rate) on the cell nucleation and growth behaviors of noncrosslinked high‐melt‐strength (HMS) polypropylene (PP) foams blown with supercritical CO₂. The experimental results showed that the cellular morphologies of PP foams were sensitive to the die geometry. Furthermore, the initial expansion behavior of the foam extrudate at the die exit was recorded using a high‐speed CCD camera. This enabled us to achieve a more thorough understanding of the effect of die geometry on both the initial expansion behavior and the final cellular morphology of HMS PP foams. The effect of die temperature on cell morphology was also studied. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Automatic initialization of active contours in ultrasound images of breast cancer

Gradient vector flow (GVF) snakes are an efficient method for segmentation of ultrasound images of breast cancer. However, the method produces inaccurate results if the seeds are initialized improperly (far from the true boundaries and close to the false boundaries). Therefore, we propose a novel initialization method designed for GVF-type snakes based on walking particles. At the first step, the algorithm locates the seeds at converging and diverging configurations of the vector field. At the second step, the seeds “explode,” generating a set of random walking particles designed to differentiate between the seeds located inside and outside the object. The method has been tested against five state-of-the-art initialization methods on sixty ultrasound images from a database collected by Thammasat University Hospital of Thailand (http://onlinemedicalimages.com). The ground truth was hand-drawn by leading radiologists of the hospital. The competing methods were: trial snake method (TS), centers of divergence method (CoD), force field segmentation (FFS), Poisson Inverse Gradient Vector Flow (PIG), and quasi-automated initialization (QAI). The numerical tests demonstrated that CoD and FFS failed on the selected test images, whereas the average accuracy of PIG and QAI was 73 and 87%, respectively, versus 97% achieved by the proposed method. Finally, TS has shown a comparable accuracy of about 93%; however, the method is about ten times slower than the proposed exploding seeds. A video demonstration of the algorithm is at http://onlinemedicalimages.com/index.php/en/presentations.