Photopolymerization of methacrylated dental resins at room temperature leads to the appearance of long-life free radicals because of system vitrification. These free radicals were observed by electronic paramagnetic resonance (EPR), and their characterization was undertaken by reference to the reactional mechanism, from the comparison with the model EPR signal and from theoretical simulation. Overlapping of two EPR signals assigned to two different kinds of radicals because of methacrylate end groups accounted for all the experimental and theoretical results.

We propose a new numerical technique, referred to as the Lagrangian Particle Method (LPM), for computing timedependent viscoelastic flows using either a differential constitutive equation (macroscopic approach) or a kinetic theory model (micro±macro approach). In LPM, the Eulerian finite element solution of the conservation equations is decoupled from the Lagrangian computation of the extra-stress at a number of discrete particles convected by the flow. In the macroscopic approach, the extra-stress carried by the particles is obtained by integrating the constitutive equation along the particle trajectories. In the micro±macro approach, the extra-stress is computed by solving along the particle paths the stochastic differential equation associated with the kinetic theory model. Results are given for the start-up flow between slightly eccentric rotating cylinders, using the FENE and FENE-P dumbbell models for dilute polymer solutions.

We aimed to study the performance of a parallel implementation of an intraoperative nonrigid registration algorithm that accurately simulates the biomechanical properties of the brain and its deformations during surgery. The algorithm was designed to allow for improved surgical navigation and quantitative monitoring of treatment progress in order to improve the surgical outcome and to reduce the time required in the operating room. We have applied the algorithm to two neurosurgery cases with promising results.High performance computing is a key enabling technology that allows the biomechanical simulation to be executed quickly enough for the algorithm to be practical. Our parallel implementation was evaluated on a symmetric multi-processor and two clusters and exhibited similar performance characteristics on each. The implementation was sufficiently fast to be used in the operating room during a neurosurgery procedure. It allowed a three-dimensional volumetric deformation to be simulated in less than ten seconds.

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