Intermediate polysulfides (Sn, where n = 2–8) play a critical role in both mechanistic understanding and performance improvement of lithium–sulfur batteries. The rational management of polysulfides ...is of profound significance for high‐efficiency sulfur electrochemistry. Here, the key roles of polysulfides are discussed, with regard to their status, behavior, and their correspondingimpact on the lithium–sulfur system. Two schools of thoughts for polysulfide management are proposed, their advantages and disadvantages are compared, and future developments are discussed.
Polysulfides (PS) play a vital role in lithium–sulfur batteries. The role of polysulfides is revisited with regard to their status, behavior, and critical impact on battery chemistry. Rational management of polysulfides including PS‐retain and PS‐bypass strategies are thoroughly discussed, and their future outlook is examined.
The flipped-classroom model is increasingly being adopted in competency-based medical education. However, it poses a major challenge to students who have not mastered self-regulated learning ...strategies. This study explores which self-regulated learning skills affect student learning performance in the first 2 years of medical school at a university in the midwestern United States.
Survey data were used to assess how 146 first- and second-year medical students' use of self-regulated learning strategies affected their performance on standardized tests.
Based on the results of regression analysis and content analysis, it was found that the use of peer learning and help-seeking positively affected the performance of first- and second-year students, respectively; whereas the use of rehearsal had a negative effect on student learning outcomes.
The study findings imply that during the transition period from traditional lecture-intensive learning to flipped-classroom learning, promoting peer learning and help-seeking could significantly improve students' academic achievement.
The large mode field area fiber can raise the tolerance of power, and high requirements for the bending characteristics of optical fibers are needed. In this paper, a fiber composed of a comb-index ...core, gradient-refractive index ring, and multi-cladding is proposed. The performance of the proposed fiber is investigated by using a finite element method at a 1550 nm wavelength. When the bending radius is 20 cm, the mode field area of the fundamental mode can achieve 2010 μm
, and the bending loss is reduced to 8.452 × 10
dB/m. Additionally, when the bending radius is smaller than 30 cm, there are two variations with low BL and leakage; one is a bending radius of 17 cm to 21 cm, and the other is from 24 cm to 28 cm (except for 27 cm). When the bending radius is between 17 cm and 38 cm, the highest bending loss is 1.131 × 10
dB/m and the lowest mode field area is 1925 μm
. It has a very important application prospect in the field of high-power fiber lasers and telecom applications.
It is of great significance to study the spatial network of the new energy vehicle (NEV) industry innovation efficiency and its factors to promote the rational allocation of innovative resources and ...the coordinated development of Chinese NEV industry. First, the Super Efficiency Data Envelope Analysis model is used to measure innovation efficiency in the NEV industry in Chinese provinces, and based on the results, the improved gravity model is applied to construct a spatial correlation network. Then, by applying social network analysis (SNA) to study NEV industry development node spatial correlations, we conclude that there is no overall hierarchical structure. The SNA are applied to examine spatial correlations with respect to NEV industry innovation efficiency in each province, and to analyze the role and position of each province in the spatial correlation network. Finally, the influencing factors of spatial correlation of the innovation efficiency of China's NEV industry has been discussed. The result shows that the difference in spatial distance and R&D investment has a significant impact on the spatial correlation of the NEV industry.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
It is necessary to build a proper theoretical method that can precisely describe isotope fractionation processes under super-cold (<200 K) conditions, because there have been many isotopic data ...obtained in our solar system that are related to such processes. However, current methods of isotope fractionation calculation, i.e., the Bigeleisen-Mayer equation and its higher-order energy corrections, may not be applicable to super-cold conditions. Here, we have checked important assumptions and higher-order corrections that can affect isotope fractionations of gas-phase molecules under super-cold conditions and developed a new theoretical method for calculating equilibrium isotope fractionation factors. Compared with previous works, we have added three new corrections into our calculation, i.e., nuclear-spin weights for quantum mechanical rotation, correction for Born-Oppenheimer approximation (BOA), and inversion splitting effect for non-planar molecules such as NH3. We further examined gaseous molecules of geochemistry and cosmochemistry relevance, e.g., H2, HF, HCl, H2O, H2S, HCHO, NH3, CH4 and their deuterated isotopologues. We found that the correction for BOA, which was rarely considered in previous studies, is important for those gaseous molecules under super-cold conditions. In case of D/H, 13C/12C and 18O/16O exchanges among organic molecules, BOA correction cannot be ignored even at ambient or higher temperature conditions. Most isotope fractionation trends at super-cold conditions reported here are quite different from their counterparts at ambient or higher temperature conditions. The method proposed here will extend our capability in interpreting equilibrium isotope fractionations to super-cold conditions in the solar system.
Students' active regulation of learning, through being motivated and a variety of cognitive and metacognitive strategies, is crucial to their online learning success. Despite the large numbers ...enrolled in online language courses, very little is known about students' motivation and strategy use in these learning environments, or how they may affect their online learning outcomes. This study helps fill this gap by examining students' motivation and learning-strategy use across a number of online language courses, and investigating the role of motivation and such strategies within the framework of self-regulated learning. Based on data about online language-learning strategies collected from 466 high-school-level online language students in a Midwestern virtual school, our findings indicated that online learning strategies operated at a moderate level in the process of foreign language-learning. Further analysis using structural equation modeling revealed that the use of online learning strategies predicted students’ online learning outcomes.
•Students used learning strategies in their online courses at a moderate level.•Online learning outcomes were not predicted by intrinsic or extrinsic motivation.•Learning strategy was the only predictor of the three learning outcomes.
One of the most important foundations of chemical geodynamics is that isotope anomalies of radiogenic isotopes observed in mantle-derived samples after correcting for natural and instrumental ...mass-dependent fractionations are mainly caused by radioactive decay of reservoirs with different parent-daughter ratios. It often denies the possibility of mass-independent fractionation processes at high temperatures. Therefore, isotope anomalies with very small magnitudes (ppm-level), such as 182W, has been used to identify different mantle reservoirs, the time scales of their formation and potential core-mantle interactions. 182W anomalies are generally considered as the sole consequences of radioactivity and nucleosynthesis that could be explained via simple mixing models of multiple reservoirs. However, the nuclear field shift effect (NFSE), has proved to be capable of producing the “anomalous mass effect” especially for heavy metal isotope systems even under very high temperatures. Therefore, it is necessary to test whether such small NFSE-induced mass-independent isotope fractionations can be magnified during unique mantle evolutionary processes, such as multi-stage melting and crystallization, to produce the observed isotope anomalies in mantle-derived rocks. Here we design a multistage closed-system melting and crystallization evolution model (denoted as MC2-model), combined with ab-initio calculations and Monte Carlo simulations to test our hypothesis. Multi-stage melting and crystallization evolution can occur in magma chambers, during tectonic movements in the early earth, in complex partial melting processes or plume and its surrounding mantle. Our simulation results show that there is an amplification effect during such multi-stage evolution process. The final isotope fractionations are scaled as aN, where N is the total number of melting or crystallization processes and a is a factor that related to the evolution path and detailed melting or crystallization behaviors, such as partition coefficient (D) and degree of melting or crystallization (F). In other words, if a mantle source region experienced multi-stage melting, melt extraction and crystallization processes, the isotope effect will probably linearly magnified. Taking O and W isotopes as examples, we conduct a statistical analysis for the results of such multi-stage simulation experiments and concluded that some of the ppm-level 182W anomalies, both positive and negative observed in Archean mantle-derived and modern plume-derived samples might be explained by this way, but our model seems to have difficulty in explaining 17O anomalies observed in anorthosite and basalts. This study provides another perspective for the origin of isotope anomalies that are observed in mantle-derived samples.
Rational design of highly active and durable electrocatalysts for oxygen reactions is critical for rechargeable metal–air batteries. Herein, we report the design and development of composite ...electrocatalysts based on transition metal oxide nanocrystals embedded in a nitrogen‐doped, partially graphitized carbon framework. Benefiting from the unique pomegranate‐like architecture, the composite catalysts possess abundant active sites, strong synergetic coupling, enhanced electron transfer, and high efficiencies in the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). The Co3O4‐based composite electrocatalyst exhibited a high half‐wave potential of 0.842 V for ORR, and a low overpotential of only 450 mV at the current density of 10 mA cm−2 for OER. A single‐cell zinc–air battery was also fabricated with superior durability, holding great promise in the practical implementation of rechargeable metal–air batteries.
Persephone's battery: Bifunctional electrocatalysts with pomegranate‐like architecture were designed and developed, exhibiting high catalytic activity for oxygen reduction and evolution reactions. These catalysts enabled the assembly of high‐performance zinc–air batteries with long cycling durability.
Flexible solid-state supercapacitors provide a promising energy-storage alternative for the rapidly growing flexible and wearable electronic industry. Further improving device energy density and ...developing a cheap flexible current collector are two major challenges in pushing the technology forward. In this work, we synthesize a nitrogen-doped graphene/MnO2 nanosheet (NGMn) composite by a simple hydrothermal method. Nitrogen-doped graphene acts as a template to induce the growth of layered δ-MnO2 and improves the electronic conductivity of the composite. The NGMn composite exhibits a large specific capacitance of about 305 F g–1 at a scan rate of 5 mV s–1. We also create a cheap and highly conductive flexible current collector using Scotch tape. Flexible solid-state asymmetric supercapacitors are fabricated with NGMn cathode, activated carbon anode, and PVA–LiCl gel electrolyte. The device can achieve a high operation voltage of 1.8 V and exhibits a maximum energy density of 3.5 mWh cm–3 at a power density of 0.019 W cm–3. Moreover, it retains >90% of its initial capacitance after 1500 cycles. Because of its flexibility, high energy density, and good cycle life, NGMn-based flexible solid state asymmetric supercapacitors have great potential for application in next-generation portable and wearable electronics.
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