Modeling material stress using integrated Gaussian Markov random fields.

The equations of a physical constitutive model for material stress within tantalum grains were solved numerically using a tetrahedrally meshed volume. The resulting output included a scalar vonMises stress for each of the more than 94,000 tetrahedra within the finite element discretization. In this paper, we define an intricate statistical model for the spatial field of vonMises stress which uses the given grain geometry in a fundamental way. Our model relates the three-dimensional field to integrals of latent stochastic processes defined on the vertices of the one- and two-dimensional grain boundaries. An intuitive neighborhood structure of the said boundary nodes suggested the use of a latent Gaussian Markov random field (GMRF). However, despite the potential for computational gains afforded by GMRFs, the integral nature of our model and the sheer number of data points pose substantial challenges for a full Bayesian analysis. To overcome these problems and encourage efficient exploration of the posterior distribution, a number of techniques are now combined: parallel computing, sparse matrix methods, and a modification of a block update strategy within the sampling routine. In addition, we use an auxiliary variables approach to accommodate the presence of outliers in the data.

Influence of Attentional Focus Instructions on Motor Performance Among Adolescents With Severe Visual Impairment.

Substantial research has demonstrated that an external (vs. internal) attentional focus enhances motor performance among various populations. Interest has recently grown in examining the effects of attentional focus among individuals with visual impairments (VI), and, to date, research results have been conflicting with some studies supporting a potential benefit to an external focus among adults with VI, while a study of children with severe VI was inconclusive regarding this benefit. The present investigation compared the effects of an internal versus an external attentional focus on a discrete throwing task among adolescents with severe VI. We recruited 13 participants with a visual acuity score of less than 6/60 and had them throw a Goalball (25 cm ball with bells often used in competitive sports designed for people with VI) as fast as possible for three familiarization trials, three internal focus trials, and three external focus trials. These participants threw the ball with significantly higher velocity when using an external focus than in other conditions, indicating a benefit from an external focus for this population when performing this discrete task.