Direct observation and modelling of the crack–fibre interaction process in continuous fibre-reinforced ceramics: model experiment

The effect of the matrix–fibre interface bonding and debonding condition on the crack growth behaviour in a fibre-reinforced ceramic matrix composite was studied using a model glass fibre-reinforced PMMA matrix composite. The crack growth process from a centre notch is monitored using a compression splitting test. From direct observation three characteristic stages can be identified in the crack growth process of the composite, namely elastic constraint (stage I), matrix crack bowing (stage II) and crack bridging (stage III). Partial interface debonding occurs at the end of stage I and cylindrical interface debonding occurs at the end of stage II. The crack growth rate is accelerated just after the onset of interface partial debonding and this indicates that a debonded interface reduces the crack growth resistance. The partial interface debonding which occurs before fibre breaking plays an important role on the crack growth mechanism.     

Vitamin D inhibits angiogenesis in transgenic murine retinoblastoma

BACKGROUND: The objective of this study was to investigate whether luminal perfusion with glutamine or with oxygenated glutamine solutions prevents endotoxin-induced changes in mucosal permeability. METHODS: Three 15-cm segments of distal ileum were isolated in anesthetized 21-day-old piglets (n = 4) and perfused (50 mL/h) with Ringer's lactate solution, Ringer's lactate solution with 2% glutamine (wt/vol), glutamine, or glutamine purged with oxygen at 37 degrees C for 280 minutes. Plasma-to-lumen clearances of 51Cr-EDTA and urea were measured to assess mucosal permeability. At time 0 minutes, loading and maintenance IV infusions of markers were begun. Baseline permeabilities were obtained from time 60 to 80 minutes, and IV endotoxin (50 micrograms/kg) was introduced from time 80 to 140 minutes. RESULTS: Results are expressed as the ratio of the clearances of the two probes (CEDTA/CUREA). Permeability increased from baseline in loops perfused with Ringer's lactate solution vs loops perfused with glutamine purged with oxygen and with glutamine alone (p < .01). Saturation with oxygen was without effect inasmuch as glutamine alone negated permeability increases. Intestinal myeloperoxidase activity did not differ with perfusate (p > .05). CONCLUSIONS: These data suggest that endotoxin-induced permeability changes can be prevented or delayed by the supply of luminal glutamine at the time of insult.