RESUMO
Ultrasonic de-icing systems are energy-efficient solutions for ice protection. The systems generate high levels of stress in the ice by inducing vibrations in the substrate, resulting in bulk or adhesive ice failure and, ultimately, ice removal. For this purpose, two types of resonant modes can be excited: flexural and extensional modes. The extensional modes have the interesting ability to de-ice substantial areas of the underlying surface as long as they are pure and do not interfere with the flexural modes. However, the coupling between extensional and flexural modes occurs naturally for thin ice-covered substrates. The inertial effect that explains this coupling is demonstrated in this paper by means of the Euler-Lagrange approach. The Euler-Lagrange model also shows how the inertial effect can be eliminated by carefully adjusting the ratio of Young's modulus to substrate density to be close to that of ice. Finally, the paper details how multilayered or architectured materials can be used to design piezoelectric plate-like structures to achieve pure extensional modes for de-icing. The ultrasonic de-icing capabilities are demonstrated on prototypes covered with freezer ice.
RESUMO
Apolipoprotein E (protein: apo E; gene: APOE) plays an important role in the multifactorial etiology of both Alzheimer's disease (AD) and lipid level concentrations. The polymerase chain reaction (PCR) was used to investigate the APOE gene polymorphism in 446 unrelated Caucasians, among them 23 AD patients, and 100 Afro-Brazilians living in Porto Alegre, Brazil. The frequencies of the APOE*2, APOE*3 and APOE*4 alleles were 0.075, 0.810 and 0.115 in Caucasians and 0.075, 0.700 and 0.225 in Afro-Brazilians, respectively (c2 = 8.72, P = 0.013). A highly significant association was observed between the APOE*4 allele and AD in this population-based sample. The APOE*4 frequency in AD patients (39 percent) was about four times higher than in the general Caucasian population (11.5 percent). The influence of each of the three common APOE alleles on lipid traits was evaluated by the use of the average excess statistic. The E*2 allele is associated with lower levels of triglycerides and of total and non-HDL cholesterol in both men and women. Conversely, the E*4 allele is associated with higher levels of these traits in women only. The effect of APOE alleles was of greater magnitude in women.