One of my nephews is working on his PhD in physics. So the following info may be useful to him besides just being interesting on its own.
Theory and research indicates that people with more positive emotions are better at attaining goals at work and in everyday life.
Does the expression of genuine positive emotions by scientists positively correlate with work-related accomplishments? Those accomplishments are the number of citations of their papers and the number of followers for their scholarly updates.
Using publicly available photographs of 440 scientists from a social networking site for researchers, multiple raters coded the smile intensities in the photos (full smile, partial smile, or no smile). The scientists with full smiles had the same quantity of publications but they had more citations per paper. The authors with full smiles attracted more followers to their updates compared to less positive emotionally expressive peers.
The results remained after controlling for age and sex. So no matter how serious you feel on the inside, if you want your work more widely distributed you should smile broadly in photos.