To guarantee system stability, proportional capacitor-current-feedback (CCF) active damping control has been widely used in LCL -type grid-connected inverter. However, when digital control is adopted ...in a grid-side current-controlled inverter, proportional CCF active damping will show negative damping characteristic in frequency band higher than one-sixth of the sampling frequency ( f s /6), causing poor robustness in weak grid. In this article, an unstable second-order phase lead compensator is proposed to insert into the CCF path for eliminating the negative effect resulting from the digital control delay. In doing so, the positive damping region is extended to almost Nyquist frequency ( f s /2), which achieves high robustness against grid impedance variation. To ensure system stability, the discrete rule is investigated for the proposed compensator and system performance is analyzed when the LCL resonance frequency changes in the range of (0, f s /2) in discrete domain, a particularly simple and practical design is further presented for the proposed compensator and the current regulator. Finally, the effectiveness of the proposed strategy and parameters design is verified by the experimental results.
Abstract
Background
Cross-sectional and longitudinal studies have found that problematic mobile phone use, bedtime procrastination, sleep quality, and depressive symptoms are strongly associated. ...However, studies are inconsistent regarding whether problematic mobile phone use predicts depressive symptoms or vice versa, and sleep factors have been infrequently focused on in this regard. In addition, few studies have examined the longitudinal associations and directions of effects between these factors. Therefore, this study aims to explore the longitudinal relationship among problematic mobile phone use, bedtime procrastination, sleep quality, and depressive symptoms in college students.
Methods
Overall, 1181 college students completed questionnaires on problematic mobile phone use, bedtime procrastination, sleep quality, and depressive symptoms at two time points 12 months apart. A cross-lagged model was used to examine the longitudinal relationship between these factors.
Results
Cross-lagged analyses showed significant bidirectional relationships of problematic mobile phone use with bedtime procrastination and depressive symptoms. Additionally, there were also significant bidirectional relationships of sleep quality with bedtime procrastination and depressive symptoms. Problematic mobile phone use predicted subsequent sleep quality one-way, and bedtime procrastination predicted subsequent depressive symptoms one-way.
Conclusions
This study further expands our understanding of the longitudinal and bidirectional relationships among problematic mobile phone use, bedtime procrastination, sleep quality and depressive symptoms and helps school mental health educators design targeted interventions to reduce problematic mobile phone use, sleep problems, and depressive symptoms among college students.
Graphene is widely studied in various fields, due to its high electrical conductivity and thermal conductivity, as well as its large theoretical surface area. Graphene is used in batteries to improve ...the electronic conductivity of the material and to reduce the volume effect that the electrode material has during the charging and the discharging process. The graphene nanosheets (GNS) and the electrochemical properties of the composite of battery electrode material differ, due to the different preparation methods used for commercial GNS. Two types of commercial GNS were evaluated via XRD, Raman spectra, and HR-TEM. Li
4
Ti
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O
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/graphene nanosheet (LTO/GNS) composites were obtained with a sol-hydrothermal process with in situ additions of GNS. Both the LTO/GNS composites showed the same microstructure. The GNS in the composites provided conductive connections for LTO to establish a conductive network. The effect that GNS with low structural defects had on improving the electrical conductivity of the LTO/GNS was better than the GNS with additional structural defects. The LTO/GNS (with low structural defects) exhibited superior electrochemical performance than the LTO/GNS (with additional structural defects). Moreover, the LTO/GNS samples with additional structural defects obtained a lower specific capacity than the pure LTO samples, in terms of the rate performance measurements. The possible causes were analyzed throughout this study.
Emotions are attracting growing attention in second language acquisition (SLA), especially with the advent of positive psychology (PP). The fundamental role of emotions in affecting learners' second ...language (L2) achievement has been well-documented. Evidence also indicates that emotions can significantly influence learners' L2 learning engagement which profoundly impacts their academic performance. However, the links between emotions, engagement, and L2 achievement remain underexplored. To contribute to this research domain, the present study sought to unpack the relationships between learners' emotions, such as foreign language enjoyment (FLE), foreign language classroom anxiety (FLCA), and foreign language learning boredom (FLLB), and engagement as well as their English achievement. A total of 907 learners of English as a foreign language (EFL) from a university in China were recruited to complete an online questionnaire. Structural equation modeling (SEM) was performed to test the hypothesized relations among the variables. Results revealed correlations between learners' FLE, FLCA, and FLLB. Furthermore, learners' engagement was found to mediate the relationships between their emotions (FLE, FLCA, and FLLB) and English achievement. The findings broaden the nomological network of emotions and engagement in the EFL context, and provide evidence for the mechanism underlying the relationships between emotions, engagement, and achievement, thereby shedding light on EFL teaching and learning at the tertiary level in China.
Hydrous pyrolysis is a significant laboratory method to investigate oil generation with the presence of water. Generally, distilled water is utilized in hydrous pyrolysis but not natural formation ...water, which is ubiquitous in oilfields and has elevated salinities. To understand the influence of formation water on hydrocarbon generation and stable carbon isotopic ratios of expelled oils, two series of semi-closed hydrous pyrolysis experiments were conducted in a wide temperature range (250–550 °C) for the type I Green River Shale source rocks using distilled water and formation water with a salinity of 76 g/L. Oil generation peak occurred at a lower temperature (325 °C) in experiments using formation water compared to experiments using distilled water (375 °C), suggesting that the presence of formation water has facilitated the oil generation. The presence of formation water also promoted the hydrocarbon expulsion at lower temperatures in hydrous pyrolysis (325–350 °C). Stable carbon isotopic fractionation between unpyrolyzed kerogen and n-alkanes (n-C17 to n-C28) generated during the primary stage of oil generation (325–375 °C) is minor (<2.6‰) in the presence of formation water, but smaller relative to those in experiments using distilled water at individual temperature points. Positive correlations between pyrolysis temperatures and δ13C ratios of n-C17, n-C18 and n-C19 during oil generation were observed in the experiments using formation water, which is consistent with the knowledge that 12C–12C bonds are more readily to be cleaved than 13C–12C bonds. Outcomes of this study not only support that stable carbon isotopic analysis of n-alkanes is a powerful tool for fingerprinting oil source in sedimentary basins, but also highlight the significance of using formation water as a medium in hydrous pyrolysis to improve the understanding of chemical/isotopic variations during hydrocarbon generation.
•Minor carbon isotopic fractionation between kerogen and n-alkanes in pyrolysis.•Oil generation peak occurs earlier in experiments using formation water.•Formation water facilitated oil generation/expulsion in hydrous pyrolysis.•δ13C of n-C17 to n-C19 correlates temperature in experiments using formation water.
Background A negative school climate is an important factor affecting students’ mental health. However, few studies have focused on the mechanisms underlying the relationship. This study aimed to ...explore the mediating effect of school belonging on the association between negative school climate and depressive symptoms among Chinese adolescents, using a nationwide longitudinal survey. Methods We conducted a longitudinal study using data from the 2013 (T1) and 2014 (T2) waves of the China Education Panel Survey (CEPS). A negative school climate was assessed by school administrators’ reports. School belonging and depressive symptoms were evaluated using adolescents’ self-reports. We used a cross-lagged panel model to explore the mediating effect of school belonging on the association between negative school climate and depressive symptoms, adjusting for a set of covariates. Results In total, 7,049 Chinese adolescents with a mean age of 12.9 years were included in this study. The results of the cross-lagged model showed that negative school climate at T1 was significantly negatively associated with school belonging at T2 ( β = −0.089, 95%CI = −0.111–−0.067, p < 0.001), and was positively associated with depressive symptoms at T2 ( β = 0.032, 95%CI = 0.012–0.054, p = 0.002). In addition, school belonging at T1 was significantly negatively associated with depressive symptoms at T2 ( β = −0.025, 95%CI = −0.050–−0.001, p = 0.045). Mediation analysis showed that school belonging played a mediating role in the association between negative school climate and depressive symptoms ( β = 0.002, 95%CI = 0.001–0.005, p = 0.041). Conclusion Among Chinese adolescents, a negative school climate is associated with a greater risk of depressive symptoms. Improving school belonging may be helpful in decreasing the impact of a negative school climate on depressive symptoms in adolescents.
•This is the first to identify Mesoarchean (3.11–2.85 Ga) rocks in the southern Yangtze Block.•1.94 and 1.89 Ga granitic magmatism recorded in the Cuoke complex.•Multistage crustal growth and ...reworking occurred in the Cuoke complex.•The Yangtze Block experienced intense metamorphism and magmatism in the context of Nuna assembly.
The newly identified Cuoke Complex preserves voluminous early Precambrian granitoids, bearing key information for the early evolution of the Yangtze Block, South China. Here, we report new field observations, petrology, zircon U-Pb-Hf isotopes and trace elements for eight granitoids from this complex. The analyzed zircon domains are of magmatic origin, as evidenced by their oscillatory zoning, high Th/U ratios and magmatic rare earth element patterns. Three trondhjemitic gneisses yield crystallization ages of 3.11–3.06 Ga, documenting the oldest known rocks in the southern Yangtze Block. Their εHf(t) values vary from −3.2 to + 2.6 with depleted mantle two-stage (TDM2) model ages of 3.6–3.3 Ga, indicating reworking of Paleoarchean crustal materials. Three gneissic granitoids crystallized at 2.86–2.85 Ga and reveal a significant episode of granitoid magmatism in the late Mesoarchean. They possess positive εHf(t) values (+0.2 to +5.0) and slightly older TDM2 model ages (3.3–3.0 Ga), suggesting that these granitoids were most likely derived from remelting of juvenile continental crust. Two monzogranites with crystallization ages of 1.94 and 1.89 Ga display negative εHf(t) values (−13.0 to −8.1) and older TDM2 model ages (3.3–3.1 Ga), indicating substantial involvement of ancient crustal materials. Available zircon U-Pb-Hf isotopic data from the Cuoke Complex have revealed that the earliest crustal growth probably occurred in the early Paleoarchean, with significant crustal growth and reworking during the early Mesoarchean, followed by multistage crustal reworking during the late Mesoarchean to Paleoproterozoic. Integrating the results of this study with records from other Archean basement complexes in the Yangtze Block (i.e., Kongling, Zhongxiang, Douling, Yudongzi and Phan Si Pan), we propose that these complexes have diverse formation histories and generally experienced tectonothermal events at ca. 2.0–1.9 Ga, probably responding to the global-scale assembly of the Nuna supercontinent.
Abstract During rock drilling, a drill bit will wear as it breaks the rock. However, there is no uniform grading standard for rock abrasiveness. To solve this problem, the wear mechanisms of a ...polycrystalline diamond compact (PDC) bit and the formation it is drilling into are analyzed in depth, and an abrasiveness evaluation method based on the fractal dimension of the rock surface topography is established. Initially, a three-dimensional digital model is generated from a scanning electron microscope image of the rock after drilling; next, an evaluation of the irregularities on the rock surface is performed using an adapted Weierstrass–Mandelbrot (W-M) function to ascertain the fractal dimensionality. Then, the microcontact characteristics of the contact surface between the formation and the PDC bit are analyzed, and the distribution of the microconvex contact points of the two-body friction pair in a region is obtained. Because the sliding friction between the drill bit and the rock produces a large amount of heat, according to the contact area formula of the friction surface and heat conduction theory, the temperature rise and overall temperature distribution of the formation and PDC bit under the condition of sliding friction are revealed, and the real contact area between the formation and the drill bit within a certain temperature range is obtained. Finally, the evaluation index of rock abrasiveness under sliding conditions is established by adopting the wear weight loss of the rock cutting tool per unit volume as the index of rock abrasiveness, and the model is verified by a microdrilling experiment. The research in this paper is highly important for improving the rock-breaking efficiency and bit service life during drilling.
Financial protection is a key dimension of Universal Health Coverage (UHC), and social medical insurance is an effective measure to provide financial protection. The aim of this study is to examine ...the impact of urban-rural medical insurance integration on medical impoverishment in China. We collected the time of integration policy in 337 prefecture-level cities across China, combined with the longitudinal database of China Labor-force Dynamics Survey (CLDS) from 2012-2016, and used a difference-in-differences (DID) method with multiple time periods at the city level to study the effect of urban-rural medical insurance integration on the medical impoverishment. Besides, to explore the heterogeneity of policy effects across populations, we conducted subgroup analyses based on respondents' age, household registration, and whether they were rural-urban migrants. A total of 8,397 samples were included in the study. The integration policy has significantly reduced the incidence of medical impoverishment (average treatment effect on the treated (ATT) = - 0.055, p < 0.05). Subgroup analysis showed that the impacts on medical impoverishment varied by age group, and the integration policy has more effect on older people than on younger people (ATT for age 15-34 = - 0.018, p > 0.05; ATT for age 35-54 = - 0.042, p < 0.05; ATT for age 55-64 = - 0.163, p < 0.01). Moreover, the impacts also varied by household registration. The integration policy has a more significant impact on rural residents (ATT for rural = - 0.067, p < 0.05) compared to urban residents (ATT for urban = - 0.007, p > 0.05). Additionally, the policy has a bigger influence on rural-urban migrants (ATT for rural-urban migrated = - 0.086, p < 0.05) than on those who have not migrated (ATT for rural-urban unmigrated = - 0.071, p < 0.05). China's policy of integrating urban-rural medical insurance has been successful in reducing medical impoverishment, especially for older age, rural, and rural-urban migrated people. It can be speculated that the integrating policy may be adapted to other similar settings in developing countries to reduce medical impoverishment.
To explore the association between social capital and frailty and the mediating effect of health-promoting lifestyles among Chinese older adults, while providing scientific evidence for frailty ...intervention.
In May 2021, a cross-sectional study was conducted among 674 Chinese older adults in Changsha city. Data was collected using the Chinese Shortened Social Capital Scale (comprising structural social capital and cognitive social capital as two subscales), a simplified version of the Health-Promoting Lifestyle Profile and the Tilburg Frailty Indicator. Linear regression analysis was used to examine the association between social capital and frailty. Structural equation modeling was used to test the mediating effect of health-promoting lifestyles.
Cognitive social capital was significantly negatively associated with frailty and its three dimensions (physical, psychological, and social frailty), but structural social capital was not. Health-promoting lifestyles played a mediating role in the associations of cognitive social capital with frailty, physical and psychological frailty, but not with social frailty.
Higher cognitive social capital was associated with a reduced likelihood of frailty. The health-promoting lifestyles partially mediated the association between cognitive social capital and frailty. The use of health-promoting lifestyles or appropriate cognitive social capital interventions may reduce frailty among older adults.
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