Fracture Diodes: Directional Asymmetry of Fracture Toughness.

Toughness describes the ability of a material to resist fracture or crack propagation. It is demonstrated here that fracture toughness of a material can be asymmetric, i.e., the resistance of a medium to a crack propagating from right to left can be significantly different from that to a crack propagating from left to right. Such asymmetry is unknown in natural materials, but we show that it can be built into artificial materials through the proper control of microstructure. This paves the way for control of crack paths and direction, where fracture-when unavoidable-can be guided through predesigned paths to minimize loss of critical components.

Verbal, visual, and spatio-sequential short-term memory: assessment of the storage capacities of children and teenagers with Down's syndrome.

BACKGROUND: It is recognized that individuals with Down's syndrome have a specific deficit in verbal short-term memory. On the other hand, non-verbal short-term memory seems to be preserved or even be a strong point for these persons. Nevertheless, the extent and specificity of the deficit must be determined. To do so, we carried out a research programme that allowed us to simultaneously assess various short-term memory systems in a developmental perspective, and to compare our participants' performance to that obtained by typically developing individuals of the same mental age. METHOD: Three span tasks are used (auditory word span/visual patterns test/Corsi blocks task) with 54 children and teenagers with Down's syndrome and 54 typically developing children as control group. Participants were matched according to their cognitive level. RESULTS: For the auditory word span task, participants with Down's syndrome obtained performances significantly lower than those of the typically developing participants. On the other hand, compared with typically developing children, children and teenagers with Down's syndrome have a spatio-sequential span significantly higher for the lowest developmental ages. No significant differences were found for visual span. CONCLUSIONS: Individuals with Down's syndrome exhibited a distinctive pattern of memory performance, in addition to their developmental specificities.

Differences in effective connectivity between dyslexic children and normal readers during a pseudoword reading task: an fMRI study.

PURPOSE: This fMRI study investigated phonological and lexicosemantic processing in dyslexic and in chronological age- and reading level-matched children in a pseudoword reading task. MATERIALS AND METHODS: The effective connectivity network was compared between the three groups using a structural model including the supramarginal cortex (BA 40; BA: Brodmann area), fusiform cortex (BA 37) and inferior frontal cortex (BA 44/45) areas of the left hemisphere. RESULTS: The results revealed differences in connectivity patterns. In dyslexic patients, in contrast with chronological age- and reading level-matched groups, no causal relationship was demonstrated between BA 40 and BA 44/45. However, a significant causal relationship was demonstrated between BA 37 and BA 44/45 both in dyslexic children and in the reading level-matched group. CONCLUSIONS: These findings were interpreted as evidence for a phonological deficit in developmental dyslexia.

[Clinical interest of fMRI and functional exploration methods of brain activity and interactivity: physical and neurophysiological considerations]. / Intérêt clinique de l'IRMf et des méthodes d'exploration fonctionnelle de l'activité et de l'interactivité cérébrales : considérations physiques et neurophysiologiques.

After having provided a brief reminder of the principle of the blood oxygen level-dependent (BOLD) contrast effect, the physiological bases of brain activity and the concepts of functional integration and effective connectivity, we describe the most recent approaches, which permit to explore brain activity and putative networks of interconnected active areas in order to examine the normal brain physiology and its dysfunctions. We present various methods and studies of brain activity analysis clinically applicable, and we detail the concepts of functional and effective connectivity, which allow to study the cerebral plasticity which occurs at the child's during the maturation (e.g., dyslexia), at the adult during the ageing (e.g., Alzheimer disease), or still in schizophrenia or Parkinson disease. The study of specific circuits in networks has to allow defining in a more realistic way the dynamic of the central nervous system, which underlies various cerebral functions, both in physiological and pathological conditions. This connectivity approach should improve the diagnostic and facilitate the development of new therapeutic strategies.