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In this article, an efficient numerical approach for weight optimisation of functionally graded (FG) beams in the presence of frequency constraints is presented. For the analysis purpose, a finite element (FE) solution based on the first order shear deformation theory (FSDT) is established to analyse the free vibration behaviour of FG beams. A four-parameter power law distribution and a five-parameter trigonometric distribution are used to describe the volume fraction of material constituents in the thickness direction. The goal is to tailor the thickness and material distribution for minimising the weight of FG beams while constraining the fundamental frequency to be greater than a prescribed value. The constrained optimisation problem is effectively solved by a novel differential evolution (DE) algorithm. The validity and efficiency of the proposed approach is demonstrated through two numerical examples corresponding to the four-parameter distribution and the five-parameter distribution.Keywords: FGM beam; lightweight design; frequency constraint; differential evolution.

Objective: Since the late 1980s, Vietnam has seen numerous social changes, likely leading to changes in adolescent sexual awareness. Adolescents are currently exposed to a plethora of sexual information without adequate sex education and knowledge. Globally, researchers have identified sexual knowledge and self-esteem as determinants of adolescent sexual awareness and behavior, but little is known about the role of social capital, especially in rural areas. This study aimed to clarify the relationship between sexual awareness and cognitive social capital among high school students in rural Vietnam. Materials and Methods: We conducted a questionnaire-based survey assessing sexual knowledge, sexual awareness, perceptions of peers' sexual experience, structural and cognitive social capital, and self-esteem (Rosenberg Self-Esteem Scale) in March 2017 among 1,583 11th graders at four public high schools in Hai Duong Province, Vietnam. Results: The final sample comprised 1,517 students (95.8% of total responses): 609 boys (40.1%) and 908 girls (59.9%). Multiple logistic regression analysis was performed with intolerance toward premarital sex as the dependent variable. In the first model, the independent variables were self-esteem, knowledge of proper timing for condom use, and perception that many peers are sexually experienced. The second model added an indicator of cognitive social capital. In the first model, self-esteem, knowledge of proper timing for condom use, and perception that many peers are sexually experienced were all significantly associated with intolerance toward premarital sex for both boys and girls. In the second model, for both boys and girls, only cognitive social capital was significantly associated with intolerance toward premarital sex. Conclusion: The results of this study regarding the effect of social capital in rural Vietnam are consistent with previous findings in urban areas. Social capital should be emphasized in efforts to improve sexual awareness and, in turn, sexual and reproductive health among adolescents in rural areas.