Advanced search algorithms for information-theoretic learning with kernel-based estimators

Recent publications have proposed various information-theoretic learning (ITL) criteria based on Renyi's quadratic entropy with nonparametric kernel-based density estimation as alternative performance metrics for both supervised and unsupervised adaptive system training. These metrics, based on entropy and mutual information, take into account higher order statistics unlike the mean-square error (MSE) criterion. The drawback of these information-based metrics is the increased computational complexity, which underscores the importance of efficient training algorithms. In this paper, we examine familiar advanced-parameter search algorithms and propose modifications to allow training of systems with these ITL criteria. The well known algorithms tailored here for ITL include various improved gradient-descent methods, conjugate gradient approaches, and the Levenberg-Marquardt (LM) algorithm. Sample problems and metrics are presented to illustrate the computational efficiency attained by employing the proposed algorithms.     

Propagation of fatigue cracks in acrylic bone cements containing different radiopaque agents

In this work three iodine-containing monomers were proposed as new radiopaque agents for acrylic bone cements. In previous studies the addition of iodine-containing methacrylate monomers provided a statistically significant increase in tensile stress, fracture toughness and ductility, with respect to the barium sulphate (BaSO4)-containing cement. However, since fatigue resistance is one of the main properties required to ensure a good long-term performance of permanent prostheses, it is important to compare the fatigue properties of these new bone cement formulations with the radiolucent and BaSO4-containing bone cements. Because the acrylic cements have initial cracks, fatigue crack propagation studies were performed. It can be observed that these acrylic cements followed the Paris-Erdogan model. The results showed that the addition of some organic radiopacifiers (DISMA, TIBMA) increased the fatigue crack propagation resistance as compared to the radiolucent cement, being similar to the BaSO4-containing cement. The radiolucent cement showed a low crack propagation resistance.