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.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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.
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
5
O
12
/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.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
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.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
High-resolution and wide-swath (HRWS) multichannel synthetic aperture radar (SAR) provides extensive imaging coverage, playing a pivotal role in remote sensing applications. Although multichannel in ...azimuth SAR system has been proposed to deal with the contradiction problem between high resolution and low pulse repetition frequency, the channel errors caused by temperature, timing uncertainty and other factors may result in azimuth ambiguity and defocus. To address this issue, a deep learning-based channel calibration method is proposed in this article, in which multichannel errors can be simultaneously estimated to improve the performance of conventional separate channel estimation. Specifically, an end-to-end strategy over 3-D convolutional neural networks (CNNs) is proposed to estimate multichannel errors collaboratively by fully exploiting the correlation of both innerchannel and intrachannel signals. Furthermore, a simulation-based training data synthesis strategy is proposed to generate training samples with similar signal characteristics with the scene to be reconstructed, by which the proposed 3-D CNN can be well trained without real multichannel signals. Experiments over both simulated and real measured data demonstrate that the proposed deep learning-based channel calibration method can well estimate multichannel errors simultaneously to improve the performance of HRWS SAR imaging.
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.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Crystallization behavior of polylactic acid (PLA) under CO2 is meaningful due to its effect on foaming behavior during CO2 foaming, while present studies mainly concentrated on overall ...crystallization behavior. In this study, the effect of CO2 on nucleation and spherulite growth of PLA crystals was in situ investigated separately. During saturation, sorption of CO2 in PLA diluted the molecular chain density, thus increasing molecular chain mobility and weakening the interchain interaction, which reduced the amount of crystal nuclei in PLA. On the other hand, the spherulite growth rate reduced at high temperature and increased at low temperature attributed to the enhanced chain mobility under CO2. Thus, overall crystallization was controlled by the spherulite growth rate at low temperature and crystalline nucleation at high temperature under CO2. Besides, CO2 restricted lamella branching, resulting in an increased lamella thickness and z axis size. Current results revealed the effect of tunable molecular chain mobility and the interchain interaction adjusted by CO2 on nucleation and spherulite growth of PLA.
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IJS, KILJ, NUK, PNG, UL, UM
Palaeozoic petroleum systems in the South China craton are prospecting frontiers for unconventional oil/gas. Understanding the hydrocarbon generation/retention capacity of source rocks has critical ...implications for reserve evaluation and targeting, which yet remains ambiguous in this region. In this study, six representative lithological types of organic-rich, immature-low-mature source rocks (two shales, two carbonates, a coal, and a solid bitumen) taken from the South China craton were treated with semiclosed hydrous pyrolysis (300-550°C). Pyrolysis results show that shale and carbonate source rocks have great hydrocarbon generation capacities, and immature solid bitumen can also generate appreciable quantities of hydrocarbons, whereas coal has the least hydrocarbon generation capacity. Both oil and gas are important hydrocarbon products of thermal maturation of shales, whereas gas generation capacity of carbonate source rocks is relatively moderate compared to their oil generation capacity. Therefore, marine shale is an important exploration target for unconventional oil and gas, yet marine carbonate is an important target for unconventional oils. The presence of appreciable carbonate minerals in shales can facilitate oil and gas generation likely by (1) enhancing oil expulsion, (2) facilitating decarboxylation of organic acid, and (3) catalysis. Pyrolysis data also support that molecular composition of thermogenic gas is not dominantly controlled by lithofacies of source rocks but mainly affected by maturation. Outcomes of this study demonstrate that marine organic-rich rocks within the Palaeozoic strata in the South China craton are critical prospecting targets for unconventional oil and gas.
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