The Effect of Arsenic on the Brittle-to-Ductile Transition in Si Single Crystals

The brittle-to-ductile transition (BDT) in arsenic doped (001) CZ silicon single crystals has been experimentally studied. The temperature dependence of apparent fracture toughness was measured by three-point bending tests at various strain rates. The BDT temperature in arsenic doped silicon was found to be lower than that in non-doped. The activation energy was obtained from the strain rate dependence of the BDT temperature. It was found that the value of the activation energy in the arsenic doped silicon is lower than that in non-doped, suggesting that the dislocation velocity in the silicon single crystal was increased by arsenic doping. The effect of increasing in dislocation velocity on the BDT temperature was also investigated by two-dimensional discrete dislocation dynamics simulations, indicating that the BDT temperature is decreased by increasing in dislocation velocity

Decreased expression of axon-guidance receptors in the anterior cingulate cortex in autism

<p>Abstract</p> <p>Background</p> <p>Axon-guidance proteins play a crucial role in brain development. As the dysfunction of axon-guidance signaling is thought to underlie the microstructural abnormalities of the brain in people with autism, we examined the postmortem brains of people with autism to identify any changes in the expression of axon-guidance proteins.</p> <p>Results</p> <p>The mRNA and protein expression of axon-guidance proteins, including ephrin (EFN)A4, eEFNB3, plexin (PLXN)A4, roundabout 2 (ROBO)2 and ROBO3, were examined in the anterior cingulate cortex and primary motor cortex of autistic brains (n = 8 and n = 7, respectively) and control brains (n = 13 and n = 8, respectively) using real-time reverse-transcriptase PCR (RT-PCR) and western blotting. Real-time RT-PCR revealed that the relative expression levels of EFNB3, PLXNA4A and ROBO2 were significantly lower in the autistic group than in the control group. The protein levels of these three genes were further analyzed by western blotting, which showed that the immunoreactive values for PLXNA4 and ROBO2, but not for EFNB3, were significantly reduced in the ACC of the autistic brains compared with control brains.</p> <p>Conclusions</p> <p>In this study, we found decreased expression of axon-guidance proteins such as PLXNA4 and ROBO2 in the brains of people with autism, and suggest that dysfunctional axon-guidance protein expression may play an important role in the pathophysiology of autism.</p