RESUMO
The demand for lightweight aircraft structures has shifted from traditional metals like aluminum to composite materials such as carbon fiber reinforced polymers (CFRP) to achieve weight reduction. However, this transition has led to decreased lightning strike protection efficiency due to the dielectric nature of CFRP. To address this problem, two CFRP samples-one unprotected and the other shielded with carbon nanotube (CNT) sheets-were subjected to artificial lightning strike testing. The research employed a coupled thermal-electrical finite element analysis method to investigate the lightning strike's impact and damage mechanisms on both samples. The numerical results closely aligned with published experimental data, validating the simulation. Unprotected CFRP sustained damage through the thickness direction up to 8 composite plies and in-plane direction over a length of 110 mm. In contrast, the sample protected with CNT sheets exhibited damage limited to the surface of the first 4 plies, with in-plane damage reduced to 24 mm. Notably, the damage area in the CFRP protected with CNT sheets showed a substantial 78.1 % reduction compared to the unprotected CFRP sample. This suggests that CNT can enhance the electrical conductivity of CFRP when incorporated between interlayers in both in-plane and thickness directions. The study enhances understanding of CFRP damage behavior and failure modes under lightning strike conditions, emphasizing CNT sheets as an improved and viable lightning strike protection system for aerospace applications, warranting further investigation.
RESUMO
Objectives: To identify risk factors for severe disease and death among patients with diabetes and coronavirus disease 2019 (COVID-19) infection. Methods: This retrospective cohort study conducted at three hospitals included 733 consecutive patients with DM admitted with confirmed COVID-19 (March 1 - December 31, 2020). Multivariable logistic regression was performed to identify predictors of severe disease and death. Results: The mean age was 67.4 ± 14.3 years, 46.9% were males and 61.5% were African American. Among all patients, 116 (15.8%) died in the hospital. A total of 317 (43.2%) patients developed severe disease, 183 (25%) were admitted to an ICU and 118 (16.1%) required invasive mechanical ventilation. Increasing BMI (OR, 1.13; 95% CI, 1.02-1.25), history of chronic lung disease (OR, 1.49; 95% CI, 1.05-2.10) and increasing time since the last HbA1c test (OR, 1.25; 95% CI, 1.05-1.49) were the preadmission factors associated with increased odds of severe disease. Preadmission use of metformin (OR, 0.67; 95% CI, 0.47-0.95) or GLP-1 agonists (OR, 0.49; 95% CI, 0.27-0.87) was associated with decreased odds of severe disease. Increasing age (OR, 1.21; 95% CI, 1.09-1.34), co-existing chronic kidney disease greater than stage 3 (OR, 3.38; 95% CI, 1.67-6.84), ICU admission (OR, 2.93; 95% CI, 1.28-6.69) and use of invasive mechanical ventilation (OR, 8.67, 95% CI, 3.88-19.39) were independently associated with greater odds of in-hospital death. Conclusion: Several clinical characteristics were identified to be predictive of severe disease and in-hospital death among patients with underlying diabetes hospitalized with COVID-19.
