Relationship between mental health, sleep status and screen time among university students during the COVID-19 pandemic: a cross-sectional study.

OBJECTIVE: On 20 July 2021, after the outbreak of COVID-19 at Nanjing Lukou International Airport, several universities started closed management and online teaching. This had a large impact on students' daily life and study, which may lead to mental health problems. The purpose of this study is to study the effect of screen time on mental health status of university students and the possible mediating effect of sleep status. METHODS: This was a cross-sectional study. A web-based questionnaire survey was employed that included demographic characteristics, sleep status and mental health status (depression, anxiety and loneliness). The Pittsburgh Sleep Quality Index scale was used to assess sleep status, while the Centre for Epidemiologic Studies Depression (CES-D) scale, Generalised Anxiety Disorder-7 (GAD-7) scale and Emotional versus Social Loneliness Scale (ESLS) were used to assess depression, anxiety and loneliness, respectively. Linear and logistic regression models were developed and adjusted for confounding factors, and finally the mediating effects were tested using the Karlson-Holm-Breen method. RESULTS: Finally, 1070 valid questionnaires were included. Among these, 604 (56.45%) indicated depressive symptoms (CES-D score ≥16) and 902 (84.30%) indicated anxiety symptoms (GAD-7 score ≥10). The mean ESLS score (for loneliness) was 26.51±6.64. The relationship between screen time and depressive symptoms (OR 1.118, 95% CI 1.072 to 1.166) and anxiety symptoms (OR 1.079, 95% CI 1.023 to 1.138) remained significant after adjusting for confounding factors. Meanwhile, sleep status plays an intermediary role in screen time and mental health status (depression and anxiety) and accounts for 13.73% and 19.68% of the total effects, respectively. We did not find a significant association between screen time and loneliness. CONCLUSION: During the outbreak of COVID-19, screen time is inevitably prolonged among university students. There is a relationship between mental health and screen time, and sleep status plays a mediating role.

[The Research and Application of Transient Temperature Test Based on Apodized-Chirped FBG].

In order to quickly and accurately obtain the transient temperature field information of the barrel when the gun is firing, the transient temperature measurement system was designed with apodized-chirped fiber Bragg grating (FBG) probe. In the system, chirped fiber grating was used to modulate the bandwidth of echo light. The bandwidth of echo light had been greatly improved. So the number of apodized-chirped FBGs in one fiber could be greatly increased, and the energy of echo light was increased too. The performances of five common apodization functions were analyzed, and the super-Gaussian function was used to process the echo signals in the system. This function effectively suppressed sidelobe increases and spectral dispersion caused by chirp modulation, which indicated that it could meet the design requirements of the transient temperature measurement. 50 apodized-chirped FBGs, which evenly wound on the barrel, were used in the experiments, and they modulation range was from 1 532.0 to 1 548.0 nm. Transient temperature of a certain type of gun barrel was tested when it fired, and test data from the system were compared to WRP-130S high-speed temperature detector. Experimental results show that the two methods are similar ones with average error of less than 2%, and better than 1% in the region of temperature steady drop. 1 ℃ can cause 0.041 3 nm wavelength shift in temperature-wavelength data. Transient temperatures of 50 independent positions can be obtained in an acquisition, so the efficiency of the barrel temperature field reconstruction is greatly improving.