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Few studies have investigated stress in association with social and process smartphone use and how these types of use influence problematic smartphone use during the COVID-19 pandemic; furthermore, the moderation effects of resilience have been rarely tested in this model. For these, a cross-sectional survey was conducted involving 766 Chinese undergraduate students (74.4% female; M = 20.1 years, SD = 1.15) who were measured with their levels of stress, academic burnout, smartphone use types (social/process smartphone use), resilience, and problematic smartphone use. Based on the I-PACE theory, we built a structural equation model, and the results indicated that compared with social smartphone use, process smartphone use more related to problematic smartphone use; academic burnout fully mediated between stress and process smartphone use, and between stress and problematic smartphone use. Moreover, resilience moderated between stress and academic burnout, between academic burnout and process smartphone use, and between academic burnout and problematic smartphone use. We discuss the process smartphone use as a key indicator of problematic smartphone use and the role of academic burnout for linking stress and smartphone use behaviors. In addition, interventions for enhancing resilience should be launched in the future.

Two-dimensional carbon fiber reinforced silicon carbide (2D-C/SiC) composites are well-known for the high-temperature performance in aeronautical and aerospace fields, but they are susceptible to foreign object damage in service. Therefore, the high-temperature performance of pre-impacted 2D-C/SiC is closely connected with flight security. In this study, the pre-impact testing was conducted using a stress-reversal split Hopkinson bar, and the pre-impact energies were set from 0.1J to 0.9J. Subsequently, the pre-impacted specimens were heated for a period in the temperature-keeping procedure from 20 °C to 1600 °C. Oxidation kinetics of the pre-impacted 2D-C/SiC specimens were obtained based on the weight loss-temperature trends. Finally, the specimens were compressed under high temperatures at the strain rates from 10−4/s to 1000/s, so the residual compressive strength (RCS)-temperature trends were achieved. Hence, the correlation between the weight loss and the RCS was established. Interestingly, the pre-impact strengthening effect on the compressive strength was found. The results revealed that the RCS of 2D-C/SiC is affected by various parameters, providing new sights into the high-temperature damage tolerance of ceramic matrix composites.

Two-dimensional carbon fiber reinforced silicon carbide composites (2D-C/SiCs) exhibit excellent mechanical properties at high temperature. However, the weak interfacial performance limits range of their applications. In the present work, interlaminar shear strength (ILSS) of 2D-C/SiC was investigated. By using an industrial camera and an acoustic emission (AE) detection system, quasi-static tests at the shear strain rates from 10−5/s to 10−3/s were conducted. Strain contours revealed the damage evolution process. Peak frequencies of AE signals were clustered into three groups, corresponding to matrix damage, interfacial debonding and fiber fracture. Dynamic tests at the shear strain rates of 200/s and 600/s were conducted using a modified split Hopkinson bar (SHPB). The dynamic deformation phenomenon was captured by a high-speed camera. The high-speed images and digital image correlation (DIC) strain contours revealed the damage initiation under dynamic loading. Damage morphologies were observed by a scanning electron microscope (SEM). The real-time images and damage morphologies explained the mechanisms of shear strain-rate effect on ILSS. The proposed experimental method elicited a fresh perspective on designing dynamic interlaminar shear experiments. Moreover, the interlaminar shear performance over a wide range of shear strain rates enhanced our understanding of the strain-rate sensitivity of compressive strength and tensile strength of 2D-C/SiCs.

2D-C/SiC composites have widely been used in aeronautical and aerospace engineering, but their mechanical behaviors under small-mass and high-speed impact have not been thoroughly studied yet. In this paper, 2D-C/SiC beam specimens were impacted by a single-stage light-gas gun and the fracture processes were captured by a high-speed camera. Post-impact internal and surface damage morphologies were scanned by a CT and a SEM, respectively. Similar damage modes were revealed by high-speed images. Subsequently, quasi-static post-impact tension tests were conducted to understand the residual mechanical properties. Acoustic emission (AE) signals of specimens were detected during the tests and then classified by the K-means algorithm. Therefore, evolutions of matrix damage, interfacial delamination and fiber fracture were recognized. At the same time, strain value was obtained by digital image correlation (DIC) method and main crack propagations were obvious in strain contours. A combination of the AE and DIC methods very well monitored the real-time damage during post-impact testing, which further revealed the damage during impact phase.

Background: Academic burnout has been associated with problematic smartphone use. However, the mechanism underlying this relation has been inadequately explored during the COVID-19 pandemic.Materials and Methods: A total of 748 Chinese undergraduate students were recruited in the study who were measured with their levels of academic burnout, anxiety, resilience, and problematic smartphone use.Results: Our study showed that academic burnout significantly predicted problematic smartphone use both directly and indirectly via anxiety. By constructing a moderated mediation model, our study found that resilience moderated the direct impact and the second half of the indirect path (between anxiety and problematic smartphone use); however, with the moderation effects of resilience, both the indirect impact of academic burnout on problematic smartphone use via anxiety became insignificant.Conclusions: Our findings brought additional evidence on the association between academic burnout and problematic smartphone use and significantly suggested the potential solution to alleviate the influences.

Some researchers have pointed out the robust connection between alexithymia and mobile phone addiction. However, few studies have explored, in which way the mobile phone use patterns influenced this relationship. A survey was conducted and 847 Chinese undergraduate students (aged from 18 to 24) joined in this study. Students were tested with questionnaires for measuring their levels of mobile phone addiction, alexithymia and the frequencies of the categorized mobile phone use patterns. Results showed that alexithymia could positively predict mobile phone addiction directly and indirectly via use patterns of entertainment and transaction. Use pattern of interpersonal communication moderated the direct impact of alexithymia on mobile phone addiction. Findings brought new light on the research subject, presenting the relationship between alexithymia and mobile phone addiction and suggested the education authorities the ways of taking good advantage of mobile phones while minimizing their side effects.

COVID-19 epidemic has brought wide psychological impacts on the young adults. To investigate the depression and anxiety symptoms and their associations with problematic smartphone use under the COVID-19 epidemic, a total of 847 Chinese undergraduate students joined in this study and were measured with their levels of depression and anxiety symptoms, resilience, perceived social support, the sense of school belonging and problematic smartphone use. Results showed that among the Chinese undergraduate students, the disorder rates of depression and anxiety symptoms were 29.16% and 46.64% respectively, and their symptoms ranged from mild to extreme severe. Depression and anxiety symptoms both positively predicted problematic smartphone use. Resilience, perceived social support and the sense of school belonging partially mediated both associations; resilience and the sense of school belonging exerted buffering effects, while perceived social support exacerbated the impacts. The current study advanced our understanding of the COVID-19 impacts and furthermore, suggested the protective factors for mitigating these impacts.