Selective frequency band filtration enables targeted acoustic wave attenuation, with applications in noise control, telecommunications, and vibro-acoustic systems. In passive noise cancellation earmuffs, selective frequency filtration can be used to address the challenge of workers needing to remove earmuffs for communication exposing them to harmful noise levels. By integrating periodic lattice structures, earmuffs can selectively allow safe low- to mid-frequency sounds to pass through while blocking harmful high-frequency noise. This study proposes a novel maltese-cross-honeycomb unit cell design, integrating Bragg scattering, and local resonance mechanisms through the Helmholtz resonator concept into a lattice structure to achieve broadband and selective sound filtration. Sound absorption and transmission loss were experimentally characterized using an impedance tube, analysing the effects of thickness, cell arrangement, and cell opening orientation. A validated finite element modelling model was used to study structural displacements and sound pressure levels (SPLs) within the impedance tube, correlating SPL values with absorption coefficients. The proposed metamaterial design exhibits a peak sound absorption coefficient of approximately 0.99 with high sound absorption retention across the frequency band of 3000–6400 Hz, with a transmission loss of 20–25 dB. On contrary, the published triangular reentrant honeycomb design could not exhibit retention of sound absorption across the frequency range, and the transmission loss value of only 10–12 dB was achieved. The optimized metamaterial design was then adopted as an insert for earmuff application demonstrating required hearing protection and speech intelligibility (up to 95 dB pink noise). Based on these findings, the maltese-cross-honeycomb unit cell metamaterial design is proposed to be adopted for earmuff applications to show selective frequency filtration by allowing low to mid-frequency waves (speech up to 3000 Hz) to pass through while blocking off the unwanted high-frequency sound waves.

Introduction: E-cigarette (EC) use is increasing among young adults in Malaysia. However, evidence on how EC-related behaviours and perceived physical activity barriers are associated with physical activity participation remains limited. This study examined the associations between EC-related behaviours and perceived physical activity barriers with physical activity status among Malaysian university students who use EC. Methods: A cross-sectional online survey was conducted between December 2023 and July 2024 across six Malaysian universities. Of 660 respondents, 564 met the age and International Physical Activity Questionnaire (IPAQ) criteria and were included in the analysis. Physical activity was classified as active and inactive. Exposures included EC use frequency, dual use, nicotine content, nicotine dependence, EC knowledge, motivations and perceptions for EC use, EC-related side effects, and perceived physical activity barrier items across personal, social and physical domains. Associations were analysed using chi-square tests and binary logistic regression, with odds ratios (ORs) and 95% confidence intervals. Results: Overall, 64.9% were classified as active. At the crude level, EC use frequency, nicotine content, and dual-use status were associated with physical activity. However, these variables were not retained in the multivariable model due to multicollinearity. Nicotine dependence emerged as one of the strongest behavioural correlates of physical inactivity, with higher dependence associated with greater odds of physical inactivity. Perceived barriers to physical activity, particularly personal and social barriers, demonstrated the strongest and most consistent associations, with substantially higher odds of inactivity across barrier levels. EC knowledge and perception variables were not independently associated after adjustment, although item-level patterns were observed. Reported EC related symptoms were mainly gastrointestinal, respiratory, and neurological but were not analysed in relation to physical activity. Conclusion: Physical activity among Malaysian university students who use EC is more consistently associated with nicotine dependence and perceived barriers, than with sociodemographic or knowledge variables. These findings suggest that interventions may benefit from addressing behavioural dependence and contextual constraints. Given the cross-sectional design, these results should be interpreted as hypothesis-generating. Implications: Physical activity among university students who use EC appears more closely associated with nicotine dependence and perceived barriers than with knowledge or sociodemographic factors. While some EC use patterns showed crude associations, nicotine dependence emerged as one of the strongest behavioural correlates of physical inactivity. Lower perceived barriers, particularly personal and social, were consistently linked to higher activity participation. These findings suggest that intervention strategies may benefit from addressing behavioural dependence alongside reducing personal and social barriers to physical activity, particularly factors related to motivation, self-confidence, and competing demands. Integrating accessible, context-specific physical activity opportunities within EC cessation or harm-reduction programmes may enhance engagement and promote healthier lifestyle behaviours among young adults.

Rare earth elements (REEs) are predominantly separated by using mixer–settler solvent extraction technology. While this method has been utilized in the industry, it does have a few setbacks, such as requirement of large module footprint to compensate for inefficient separation. Likewise, researchers have turned to membrane separation technology to address these challenges faced by mixer–settler solvent extraction. Supported liquid membranes (SLMs) are a viable alternative in membrane separation technology as they exhibit similar conceptual designs to that of solvent extraction, albeit requiring smaller amounts of organic carrier and lower module footprint compared to mixer settler solvent extraction. In this research, the application of an electrospun membrane was explored using SLMs for the separation between light REEs (LREEs) and heavy REEs (HREEs). To do this, the study initially employs the usage of neodymium (Nd) and dysprosium (Dy) as the baseline for LREEs and HREEs, and later using real REE leachate for the separation between LREEs and HREEs. This study also investigates the effects of different pH of feed solution, organic carrier loading, and stripping concentrations. Overall, to achieve higher selectivity of Nd/Dy, a higher pH of feed solution of 5, a low loading of organic carrier at 10 wt%, and a low stripping concentration of 1 M H₂SO₄ was recommended. For the separation of LREEs and HREEs, a separation factor of 2.38 was achieved with a recovery of 10.43% of LREEs in under 60 min by using a small-scale membrane of 4 cm² effective area. Long term operation indicates a stable LREE/HREE separation performance using the optimized condition.