Using molecular dynamics and semi-empirical potentials, large scale transition metal dichalcogenides monolayers (TMDM) were examined. The focus of the study was the modification of the phonon spectrum of TMDMs by engineering substitutional defects to produce phononic resonators and waveguides on the atomic scale. The resonant frequencies of the aforementioned structures can be tuned by applying tensile or compressive stresses. The TMDMs exhibited wide phononic band gaps (PBG) in their phonon spectrum because they consist of atoms with quite different atomic masses. The PBG from the present semi-empirical calculations were found to be in reasonable agreement with previous ab initio calculations. The problem is very broad since many varieties of TMDMs (with or without defects) can be made. The present study focused on MX composites with M being Mo or W and X being S or Se. The most interesting behavior was found in WS with substitutional defects of either S ↔ Se or W ↔ Mo.

Background: Restrictions on movement and lockdown are measures taken in many nations, in response to the COVID-19 pandemic. University students are additionally burdened by the transition to distance e-learning. The aims of the study were to investigate the prevalence of anxiety and depression in university students and to identify associated risk factors.Design and Methods: An online questionnaire was administered to 2,009 students in the University of Patras, Greece, during the national lockdown. Socio-demographic, academic data, and the forced disruption of daily life were assessed along with the Greek version of the Hospital Anxiety and Depression Scale.Results: Anxiety and depression prevalence was 35.8% and 51.2% respectively. Age, school of study, financial status, self-perceived health status, level of satisfaction with the state's and university's response and specific aspects in the daily routine were associated with both anxiety and depression scores. At higher odds of both depression and anxiety were students with low income, bad health status, annoyed at staying home and those who encountered difficulties with the online education system. Additional risk factors for depression were studies in humanities and social sciences, and low satisfaction with the university's response, while for anxiety were studies in agricultural sciences and absence of information about COVID-19.Conclusions: The proportion of Greek students showing depression and anxiety, during the restrictive measures, is alarming. Mental health in university students should be monitored. Mitigation strategies should focus on specific personal, academic and social variables that have been identified as protective factors.

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