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Biomedical subjects

P J Dionne

Publications and source records attributed to P J Dionne.

5 recordsLinked to original sources
PubMed2005

NMR relaxation and pulsed-gradient diffusion study of polyethylene nanocomposites.

We performed pulsed-gradient spin-echo nuclear-magnetic-resonance (NMR) experiments on zinc oxide filled polyethylene. The molecular weights of the polyethylene samples ranged between 808 and 33,000 gmol, and four different zinc oxide samples were used: 27-, 33-, 51-, and 2500-nm-diameter particles. The results of these experiments showed that the diffusion coefficients of the polyethylene chains did not change with nanofiller content, but a drastic change is observed in the NMR relaxation spectrum in spin-spin-relaxation experiments. At fixed zinc oxide content and polyethylene molecular weight (close to entanglement), the system with the smallest zinc oxide showed the most rigid environment. At high polyethylene molecular weights, this effect was still observable but the difference between the three investigated systems was very small, suggesting that the system was dominated by entanglements.

Journal Article↗
PubMed1972

Epidemiology.

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Computers, Analog↗
PubMedDate not supplied

Three-dimensional coupled fluid-structure simulation of pericardial bioprosthetic aortic valve function.

A computational, three-dimensional coupled fluid-structure dynamics model was developed for a generic pericardial aortic valve in a rigid aortic root graft with physiologic sinuses. Valve geometry was based on that of the natural valve. Blood flow was modeled as pulsatile, laminar, Newtonian, incompressible flow. The structural model accounted for material and geometric nonlinearities and also simulated leaflet coaptation. A body fitted grid was used to subdivide the flow domain into computational finite volume cells. Shell finite elements were used to discretize the leaflet volume. A finite volume computational fluid dynamics code and finite element structure dynamics code were used to solve the flow and structure equations, respectively. The fluid flow and structural equations were coupled using an implicit "influence coefficient" technique. Physiologic ventricular and aortic pressure waveforms were prescribed as the flow boundary conditions. The aortic flow field, valve structural configuration, and leaflet stresses were computed at 2 msec intervals. Model predictions on aortic flow and transient variation in valve orifice area were in close agreement with corresponding experimental in vitro data. These findings suggest that the computer model has potential for being a powerful design tool for bioprosthetic aortic valves.

Algorithms↗