No abstract

Nucleation of salt crystals in confined media occurs in many processes of high importance, such as injection of CO in geological formations for its sequestration. In particular, salt precipitation in clays, a main component of sedimentary rock, is an important phenomenon. The crystals precipitate on the pores' surface, modify the pore space morphology, and reduce its flow and transport properties. Despite numerous efforts to understand the mechanisms of nucleation of salt crystals in confined media, the effect of the clay's chemistry on the growth, distribution, and properties of the crystals is not well understood. We report the results of extensive molecular dynamics simulation of nucleation and growth of NaCl crystals in a clay pore using molecular models of two types of clay minerals, Na-montmorillonite and kaolinite. Clear evidence is presented for the nucleation of the salt crystals that indicates that the molecular structure of clay minerals affects their spatial distribution, although the nucleation mechanism is the same in both types of clays.

IntroductionYouTube is a popular social media used by youth and has electronic cigarette (e-cigarette) content. We used machine learning to identify the content of e-cigarette videos, featured e-cigarette products, video uploaders, and marketing and sales of e-cigarette products.MethodsWe identified e-cigarette content using 18 search terms (eg, e-cig) using fictitious youth viewer profiles and predicted four models using the metadata as the input to supervised machine learning: (1) video themes, (2) featured e-cigarette products, (3) channel type (ie, video uploaders) and (4) discount/sales. We assessed the association between engagement data and the four models.Results3830 English videos were included in the supervised machine learning. The most common video theme was ‘product review’ (48.9%), followed by ‘instruction’ (eg, ‘how to’ use/modify e-cigarettes; 17.3%); diverse e-cigarette products were featured; ‘vape enthusiasts’ most frequently posted e-cigarette videos (54.0%), followed by retailers (20.3%); 43.2% of videos had discount/sales of e-cigarettes; and the most common sales strategy was external links for purchasing (34.1%). ‘Vape trick’ was the least common theme but had the highest engagement (eg, >2 million views). ‘Cannabis’ (53.9%) and ‘instruction’ (49.9%) themes were more likely to have external links for purchasing (p<0.001). The four models achieved an F1 score (a measure of model accuracy) of up to 0.87.DiscussionOur findings indicate that on YouTube videos accessible to youth, a variety of e-cigarette products are featured through diverse videos themes, with discount/sales. The findings highlight the need to regulate the promotion of e-cigarettes on social media platforms.

No abstract