Computational studies on fragmentation of brittle materials

We study dynamic fragmentation of metallic structures using the cracking particles method with obscuration zone. The cracking particles method is an efficient meshfree method for modeling dynamic fracture. Fracture is modeled by a set of crack segments. The cracking particles method does not require the representation of the crack topology. To avoid numerical fracture observed in discrete approaches, we employ obscuration zones proposed by Mott in his analytical work of fragmentation theory. We also study the influence of initial imperfections with different stochastic input parameters on the results

You Need Guts to Make New Neurons

PURPOSE OF THE REVIEW: In the present review, we discuss the very recent findings that the gut microbiota composition can modulate cell-based plasticity in the brain, namely, adult hippocampal neurogenesis, and thereby alter hippocampal dependent behavior. RECENT FINDINGS: Absence of gut microbiota from birth or antibiotic-induced dysbiosis in adults leads to an aberrant metabolite production and immune functions. Both scenarios compromise a proper postnatal brain development, or brain wiring in adults, including aberrant neurogenesis. This in turn leads to a hippocampal mismanagement of environmental cues and renders the animals to be more susceptible to stress and less cognitively flexible which contribute to general impairments in learning and memory functions and social behavior. SUMMARY: Mounting evidence indicates that certain behavior aberrances in germ-free and dysbiotic mice are mediated by changes in neurogenesis. The mechanisms and the relevance of this complex regulation remain to be elucidated by future research

In contrast to many other mammals, cetaceans have relatively small hippocampi that appear to lack adult neurogenesis

The hippocampus is essential for the formation and retrieval of memories and is a crucial neural structure sub-serving complex cognition. Adult hippocampal neurogenesis, the birth, migration and integration of new neurons, is thought to contribute to hippocampal circuit plasticity to augment function. We evaluated hippocampal volume in relation to brain volume in 375 mammal species and examined 71 mammal species for the presence of adult hippocampal neurogenesis using immunohistochemistry for doublecortin, an endogenous marker of immature neurons that can be used as a proxy marker for the presence of adult neurogenesis. We identified that the hippocampus in cetaceans (whales, dolphins and porpoises) is both absolutely and relatively small for their overall brain size, and found that the mammalian hippocampus scaled as an exponential function in relation to brain volume. In contrast, the amygdala was found to scale as a linear function of brain volume, but again, the relative size of the amygdala in cetaceans was small. The cetacean hippocampus lacks staining for doublecortin in the dentate gyrus and thus shows no clear signs of adult hippocampal neurogenesis. This lack of evidence of adult hippocampal neurogenesis, along with the small hippocampus, questions current assumptions regarding cognitive abilities associated with hippocampal function in the cetaceans. These anatomical features of the cetacean hippocampus may be related to the lack of postnatal sleep, causing a postnatal cessation of hippocampal neurogenesis