In this paper, molecular dynamics simulations are used to study the effect of molecular water and composition (Si/Al ratio) on the structure and mechanical properties of fully polymerized amorphous sodium aluminosilicate geopolymer binders. The X-ray pair distribution function for the simulated geopolymer binder phase showed good agreement with the experimentally determined structure in terms of bond lengths of the various atomic pairs. The elastic constants and ultimate tensile strength of the geopolymer binders were calculated as a function of water content and Si/Al ratio; while increasing the Si/Al ratio from one to three led to an increase in the respective values of the elastic stiffness and tensile strength, for a given Si/Al ratio, increasing the water content decreased the stiffness and strength of the binder phase. An atomic-scale analysis showed a direct correlation between water content and diffusion of alkali ions, resulting in the weakening of the AlO tetrahedral structure due to the migration of charge balancing alkali ions away from the tetrahedra, ultimately leading to failure. In the presence of water molecules, the diffusion behavior of alkali cations was found to be particularly anomalous, showing dynamic heterogeneity. This paper, for the first time, proves the efficacy of atomistic simulations for understanding the effect of water in geopolymer binders and can thus serve as a useful design tool for optimizing composition of geopolymers with improved mechanical properties.

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Objective There is little known about the demands of medical school on students’ sleep behavior. The study’s main goal was to examine the interplay between medical students’ sleep knowledge, personal attitudes towards sleep, and their sleep habits. Methods An anonymous online survey was created and emailed to all students enrolled at a large metropolitan medical school. Data on demographics, sleep perception and habits in addition to self-reported measures of students sleep knowledge, beliefs and sleepiness were collected. Results There were 261, out of a possible 720, responses to the survey. While 71.5% of respondents believed that they needed >7 hours of sleep only 24.9% of respondents stated they average >7 hours of sleep. During the week of an examination only 15.3% of students stated they averaged >7 hours of sleep. A comparison of pre-clinical and clinical students revealed that reported median sleep during a school or rotation night was significantly lower in clinical students as compared to pre-clinical students while mean sleep during examination weeks between the two groups was not statistically different. In regards to sleep knowledge, clinical students were more knowledgeable (65.53% correct) than pre-clinical students (39.83% correct) (t (1) = −8.9, p = .00). However, there was no difference in the assessment of dysfunctional beliefs between the two groups (66.0 for preclinical students, 64.7 for clinical students (t(1)= .37, p = .71) while clinical students had a higher score of sleepiness compared to pre-clinical students (9.12 to 7.83, t (1) = −2.3, p = .023). Conclusions A majority of medical students are sleeping an inadequate amount of time during their four years and as they progress from the pre-clinical to the clinical years the amount of time they sleep decreases even though their knowledge about sleep increases. Increased awareness around sleep health is required beyond sleep education, as medical students appear to need help translating knowledge into strategies to improve their own sleep and well-being.

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