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Background: Higher body mass index (BMI) and internalizing symptoms often codevelop with each other, and both of them have been widely linked to child later maladjustment. However, existing studies on the association between BMI and internalizing symptoms predominantly focus on the between-person association (i.e., the average association for a given group) and use continuous measures of BMI. To address these gaps, using approaches that can effectively partition within-person from between-person variation, this study aimed to delineate temporal dynamics (i.e., directionality) of the associations between BMI and internalizing symptoms (as continuous and clinical cut-off categorical measures for both of them). The trend of codevelopment between BMI and internalizing symptoms is also investigated. Methods: This study used data from the Early Childhood Longitudinal Studies, Kindergarten Class of 2010-2011 (ECLS:2011), a nationally representative birth cohort study in the United States. Participants were 17,552 children (48.78% female, M age = 5.6 years old at the first wave) who were assessed seven times from kindergarten through Grade 5. Results: Results of the random intercept, cross-lagged panel model suggested reciprocal within-person associations between BMI and internalizing symptoms from child 7.1 to 11.1 years old. Conclusions: Our findings highlight both the necessity of disaggregating between-person and within-person effects in cross-lagged associations between BMI and internalizing symptoms and the importance of interventions that target body weight and mental health issues in middle childhood to reduce the negative impact of both in the long run.

Friction stir welding with different pin-eccentric stir tools (the pin eccentricities were 0, 0.4, and 0.8 mm, respectively) was successfully utilized for joining dissimilar aluminum alloys AA5052 and AA6061, and the influences of pin eccentricity on the microstructural evolution and mechanical properties of joints were investigated. The results showed that sound joints could be obtained by placing the hard AA6061 in the advancing side, while the welding heat input led to both the coarsening of strengthening precipitates and dynamic recrystallization and softening of the nugget zone (NZ). The application of pin eccentricity promoted the material flow in the NZ and enlarged the area of the “onion ring”. Furthermore, the average grain size and fraction of recrystallized grain in the NZ decreased as the pin eccentricity increased. All joints failed in the NZ during tensile tests, and the joint produced by the 0.8 mm-pin-eccentric stir tool performed the highest tensile strength due to the enhanced grain-boundary and dislocation strengthening.