Smart beams with extension and thickness-shear piezoelectric actuators

Mechanical Engineering Department, King Saud UniversityAnalytical models and exact solutions for beams with thickness-shear and extension piezoelectric actuators are formulated and developed. The models are based on the first-order beam theory (FOBT) and higher-order beam theory (HOBT). The beam bending problem is solved by using the state-space approach along with the Jordan canonical form. Numerical examples of beams incorporating piezoelectric actuators with various boundary conditions are presented. In these examples, the validity of the proposed models and the feasibility of using shear-mode actuators in smart beams are investigated. For the extension-mode actuators there is slight difference between the deflections of the FOBT and that of the HOBT. For the shear-mode actuators there is pronounced difference between the deflections of the FOBT and that of the HOBT. The results of the FOBT are very sensitive to the value of the shear correction factor. The results of the present work are compared with the previously reported results in the literature, where available

Clinicodemographic characteristics and prognostic role of myasthenia gravis in thymoma: Experience from a Saudi population

OBJECTIVES: The objectives of the study were to determine the clinicodemographic characteristics and the prognostic role of myasthenia gravis (MG) in thymoma. METHODS: The records of patients who underwent surgical resection of thymoma at King Faisal Specialist Hospital and Research Center in the past 23 years were reviewed. Seventy thymoma patients were finally included and were then categorized based on MG status into the MG group (39 patients) and the non-MG group (31 patients). Collected data included patients' demographic characteristics, tumor characteristics, and postoperative clinical outcomes. All analyses were conducted using SPSS. The comparison between both groups was tested using the Student t-test and Chi-square test for continuous and categorical variables, respectively. A P = 0.05 or less indicated statistical significance. RESULTS: Patients' age ranged from 11 to 76 years, and female predominance was observed (55.7%). Compared to the non-MG group, no difference in patients' gender was observed (P = 0.058); however, MG patients had a younger age (39.30 vs. 48.77, P = 0.0095). No difference was noted between both groups based on the World Health Organization classification (P = 0.398), but MG patients tended to present with less-advanced tumors based on the TNM classification (P = 0.039) and lower stage based on the MASAOKA staging system (P = 0.017). No significant change in tumor size (P = 0.077), resectability (P = 0.507), and adjuvant therapy (P = 0.075) were observed. MG was not significantly associated with postoperative complications, morbidity, or mortality. However, it exhibited a prognostic protective role in terms of lower recurrence (2.56% vs. 35.48%, P = 0.0001) and longer survival duration (18.62 vs. 10.21 years, P < 0.001) as compared to non-MG patients. CONCLUSIONS: MG occurrence in thymoma patients is more likely to occur at a younger age, higher TNM classification, and advanced MASAOKA stage. Although no significant association was noted between MG and complications and mortality, MG exhibited a protective role in thymoma by providing a lower recurrence rate and longer survival duration