RESUMO
A novel extrinsic method for the measurement of particle surface distribution in a carbon black-filled elastomer via nanoindentation is developed. This method is based on the measurement of the contact stiffness obtained from the continuous stiffness measurement mode. The proposed tip-particle model is held by two main hypotheses: the particles do not deform significantly during indentation so that only the elastomer matrix elastically deforms; particles are physically bounded with the surrounding matrix. Therefore, when the tip comes in contact with a particle, the latter becomes a hard extension of the tip, able to deform the elastomer matrix. Finally, the evolution of the measured contact stiffness is directly related to the increase of the contact area between the tip-particles set and the elastomer matrix. The proposed model is validated through a numerical and an experimental study. Moreover, an evaluation of the measurements bias allows to correct the particle surface distribution. A good agreement is found between the distribution measured from transmission electron microscopy observations and nanoindentation measurements.
RESUMO
A sample of 171 children and adolescents aged 3-17 years requiring venepuncture for blood sampling were asked to report on their pain and anxiety and were observed immediately before and during blood drawing. Depending on the measures used, 36-64% of children from 3 to 6 years old experienced moderate to severe distress from blood drawing. Multiple regression analysis revealed that age and the parents' prediction of how upset the child would feel before the blood test was a significant predictor of the observed distress and the self-report of pain. Experience with previous needle procedures did not add significantly to the prediction of distress. Identification of children at high risk to respond poorly to painful medical procedures is discussed.