RESUMO
In solids, the response of the lattice to photoexcitation is often described by the inertial evolution on an impulsively modified potential energy surface which leads to coherent motion. However, it remains unknown if vibrational coherence is sustained through a phase transition, during which coupling between modes can be strong and may lead to rapid loss of coherence. Here we use coherent phonon spectroscopy to track lattice coherence in the structural phase transition of V_{2}O_{3}. In both the low and high symmetry phases unique coherent phonon modes are generated at low fluence. However, coherence is lost when driving between the low and high symmetry phases. Our results suggest strongly damped noninertial dynamics dominate during the phase transition due to disorder and multimode coupling.
RESUMO
BACKGROUND: Single and repeat concussions have a high prevalence in sport. However, there is limited research into longterm risks associated with single and repeat concussions. OBJECTIVES: To determine the effects of single and repeat historical concussions on the neuropsychological functioning and neurological reports of licensed jockeys. METHODS: Six hundred and ninety eight licensed jockeys in the UK were assessed for neurological and neuropsychological symptoms of concussion at least three months after potential episodes. RESULTS: Jockeys reporting multiple historical injuries versus a single injury showed reliable decrements on a measure of response inhibition and, to a less robust degree, on divided attention. Younger adults showed greater vulnerability. CONCLUSIONS: Repeated concussion is associated with reliable decrements in cognitive performance--even after a three month window for recent recovery.
