A Model to Predict the Density Profile of Particleboard

Certain mechanical properties of particleboard panels depend on the density variations that occur through the panel thickness (density profile). Particleboard density profiles result from the felting and hot pressing operations. Repeatedly altering a commercial particleboard manufacturing process to produce a predetermined density profile is undesirable from economic and production standpoints. An analytical tool to predict density profile as a function of the manufacturing processes was needed. Computer simulation modeling was employed to satisfy this need. A multilayer description of the density and moisture gradients resulting from the felting process provides input for this model. Inputs for the pressing process include platen temperature and press closing rate.The model simulates the physical and mechanical processes that occur in the press and mat system. Heat conduction, gas transport, layer compaction, and water phase changes were included in the model. Thermal properties were taken from the literature, and gas transport properties required approximation.A steeper density gradient with increasing platen temperature was predicted by the model. This result conforms to general expectations. Changes in press closing rates resulted in model-predicted density profiles that contradict the expected pattern. The probable reason for this effect is that the core layers remained at or near the ambient temperature, and the maximum mat resistance increased as closing rate increased. Simulation of an initially uneven moisture gradient resulted in increased heat penetration, as expected

The genetic architecture of the human cerebral cortex

The cerebral cortex underlies our complex cognitive capabilities, yet little is known about the specific genetic loci that influence human cortical structure. To identify genetic variants that affect cortical structure, we conducted a genome-wide association meta-analysis of brain magnetic resonance imaging data from 51,665 individuals. We analyzed the surface area and average thickness of the whole cortex and 34 regions with known functional specializations. We identified 199 significant loci and found significant enrichment for loci influencing total surface area within regulatory elements that are active during prenatal cortical development, supporting the radial unit hypothesis. Loci that affect regional surface area cluster near genes in Wnt signaling pathways, which influence progenitor expansion and areal identity. Variation in cortical structure is genetically correlated with cognitive function, Parkinson's disease, insomnia, depression, neuroticism, and attention deficit hyperactivity disorder