This paper studies a new concept of using global navigation satellite system (GNSS) signals coherently reflected over relatively smooth ocean and ice surfaces from very low elevation angles (below ...∼8°) and received by low Earth orbit (LEO) satellites to retrieve the tropospheric information. This approach can provide horizontal profiles of tropospheric zenith delay and total column water vapor (TCWV) with centimeter‐level high precision and spatial resolutions of tens of km by ∼1 km, depending on the elevation angle, with a sampling spacing of ∼100 m. This approach can potentially be applied to most sea ice and calm ocean areas and provide tropospheric sensing data, which can complement and augment existing observation systems. A few case studies are conducted in this paper using the Spire grazing‐angle GNSS‐R data. The retrieved TCWV is compared to ERA5 products and the Sentinel‐3 Ocean and Land Color Instrument measurements and shows promising performances. The errors associated with the GNSS‐R tropospheric measurements are also discussed.
Plain Language Summary
The atmospheric water vapor is an important component for the weather and climate systems and is difficult to measure, especially over ocean and ice surfaces. This paper studies a new approach to measuring atmospheric water vapor using global navigation satellite system (GNSS) signals reflected off ocean and ice surfaces. If the reflection is from a low elevation angle (below ∼8°) and the reflected signal is coherent (all signal rays are reflected in the same direction), this approach can provide very high precision observation of the horizontal gradients of the tropospheric delay and the vertically integrated atmospheric water vapor with good spatial resolutions. This paper presents the methodology of the proposed approach and a few case studies to demonstrate the feasibility and performance by comparing the GNSS‐R retrieved water vapor measurements with models and the Sentinel‐3 satellite radiometry measurements. The errors associated with the GNSS Reflectometry (GNSS‐R) tropospheric measurements are also discussed.
Key Points
A new tropospheric sensing concept is studied that relies on coherent‐reflection global navigation satellite system (GNSS) signals off ocean and ice surfaces
Algorithms are developed and demonstrated using Spire grazing‐angle GNSS‐R data to retrieve tropospheric delay and water vapor
The presented approach provides high‐precision tropospheric delay and total column water vapor horizontal profiles, as validated using the Sentinel‐3 Ocean and Land Color Instrument data
Due to methodological difficulties and limitations of applicability, a quantitative bonding analysis based on the theory of resonance is presently not as convenient and popular as that based on the ...molecular orbital (MO) methods. Here, we propose an efficient quantitative resonance theory by expanding the DFT wave function in terms of a complete set of Lewis structures. By rigorously separating the resonance subsystem represented by a set of localized MOs, this approach is able to treat large molecules, nonplanar π-conjugate systems, and bonding systems mixing both σ and π electrons. Assessment in 2c-2e systems suggests a new projection-weighted symmetric orthogonalization method to evaluate the weights of resonance contributors, which overcomes the drawbacks of other weighting schemes. Applications to benzene, naphthalene and chlorobenzene show that the present method is insensitive to the basis set employed in the DFT calculations, and to the choices of the independent Lewis set determined by Rumer's rule. Advanced applications to diverse chemical problems provide unique and valuable insights into the understanding of hydrogen bonding, the π substituent effect on benzene, and the mechanism of Diels-Alder reactions.
An efficient quantitative resonance theory is devised on the basis of wave function expansion. Applications of the method provide valuable insights into diverse chemical problems such as hydrogen bonding, chemical selectivity and reaction mechanism.
High‐Ni layered oxide cathodes hold a great promise for fabricating high‐energy lithium‐ion batteries. However, the oxygen evolution during cycling is a crucial factor in the structure deterioration, ...potential change, and capacity decay of cathodes, limiting the commercial application of high‐Ni (Ni > 0.9) layered oxides in batteries. Herein, we demonstrate a feasible approach to enhance the stability of oxygen framework, through the surface oxygen immobilization with yttrium and bulk oxygen stabilization with aluminum in high‐Ni layered oxides. As expected, benefiting from the oxygen‐stabilized framework, the bulk structure deterioration, and interfacial parasitic reaction are mitigated obviously during battery operation, along with the improved thermal stability of cathode. Correspondingly, the as‐prepared high‐Ni oxide delivers high reversible capacity, impressive cycle ability, and low potential polarization upon cycling. Such significant improvement on the electrochemical performance is primarily attributed to the strong oxygen affinities of both yttrium at the surface layer and aluminum in the bulk, which synergistically stabilizes the oxygen framework of high‐Ni oxide via raising the energy barrier for oxygen evolution. Therefore, building the stable oxygen framework is critical for enhancing the energy density output, cycle operation, and thermal stability of high‐Ni oxide cathodes.
Introducing yttrium and aluminum with strong oxygen bonding onto the surface and into the bulk enables to build the stable oxygen framework on high‐Ni layered oxide. The oxygen‐stabilized framework is able to accommodate the internal stress and mitigate oxygen release, leading to the excellent cycle stability on capacity and mid‐point potential.
While the human transcriptome contains a large number of circular RNAs (circRNAs), the functions of most circRNAs remain unclear. Sequence annotation suggests that most circRNAs are generated from ...splicing in reversed orders across exons. However, the mechanisms of this backsplicing are largely unknown. Here we constructed a single exon minigene containing split GFP, and found that the pre-mRNA indeed produces circRNA through efficient backsplicing in human and Drosophila cells. The backsplicing is enhanced by complementary introns that form double-stranded RNA structure to bring splice sites in proximity, but such structure is not required. Moreover, backsplicing is regulated by general splicing factors and cis-elements, but with regulatory rules distinct from canonical splicing. The resulting circRNA can be translated to generate functional proteins. Unlike linear mRNA, poly-adenosine or poly-thymidine in 3' UTR can inhibit circular mRNA translation. This study revealed that backsplicing can occur efficiently in diverse eukaryotes to generate circular mRNAs.
This study explores how parametric uncertainties in the production affect failure tensile loads of reinforced thermoplastic pipes (RTPs) under combined loading conditions. The stress distributions in ...RTPs are examined with three-dimensional (3D) elasticity theory, and the analytical micromechanics of composites are evaluated. To evaluate the failure mechanisms for RTPs, 3D Hashin—Yeh failure criteria are combined with the damage evolution model to establish a progressive failure model. The theoretical model has been validated through numerical simulations and axial tensile tests data. To analyze how randomness of relevant parameters affects the first-ply failure (FPF) tensile load and final failure (FF) tensile load in RTPs, many samples are produced with the Monte—Carlo approach. The stochastic analysis results are statistically evaluated through the Weibull probability density distribution function. For the randomness of production parameters, the failure tensile load of RTPs fluctuates near the mean value. As the ply number at the reinforced layer increases, the dispersion of failure tensile load increases, with a high probability that the FPF tensile load of RTPs is lower than the mean value.
We propose two new models for human action recognition from video sequences using topic models. Video sequences are represented by a novel "bag-of-words" representation, where each frame corresponds ...to a "word". Our models differ from previous latent topic models for visual recognition in two major aspects: first of all, the latent topics in our models directly correspond to class labels; second, some of the latent variables in previous topic models become observed in our case. Our models have several advantages over other latent topic models used in visual recognition. First of all, the training is much easier due to the decoupling of the model parameters. Second, it alleviates the issue of how to choose the appropriate number of latent topics. Third, it achieves much better performance by utilizing the information provided by the class labels in the training set. We present action classification results on five different data sets. Our results are either comparable to, or significantly better than previously published results on these data sets.
Oxygen‐redox of layer‐structured metal‐oxide cathodes has drawn great attention as an effective approach to break through the bottleneck of their capacity limit. However, reversible oxygen‐redox can ...only be obtained in the high‐voltage region (usually over 3.5 V) in current metal‐oxide cathodes. Here, we realize reversible oxygen‐redox in a wide voltage range of 1.5–4.5 V in a P2‐layered Na0.7Mg0.2Fe0.2Mn0.6□0.2O2 cathode material, where intrinsic vacancies are located in transition‐metal (TM) sites and Mg‐ions are located in Na sites. Mg‐ions in the Na layer serve as “pillars” to stabilize the layered structure during electrochemical cycling, especially in the high‐voltage region. Intrinsic vacancies in the TM layer create the local configurations of “□–O–□”, “Na–O–□” and “Mg–O–□” to trigger oxygen‐redox in the whole voltage range of charge–discharge. Time‐resolved techniques demonstrate that the P2 phase is well maintained in a wide potential window range of 1.5–4.5 V even at 10 C. It is revealed that charge compensation from Mn‐ and O‐ions contributes to the whole voltage range of 1.5–4.5 V, while the redox of Fe‐ions only contributes to the high‐voltage region of 3.0–4.5 V. The orphaned electrons in the nonbonding 2p orbitals of O that point toward TM‐vacancy sites are responsible for reversible oxygen‐redox, and Mg‐ions in Na sites suppress oxygen release effectively.
Na0.7Mg0.2Fe0.2Mn0.6□0.2O2 with native transitional metal (TM) vacancies is designed as a novel cathode material for sodium‐ion batteries. The TM vacancies lead to nonbonding O 2p orbitals in this material, pointing toward these vacancies triggering reversible whole‐voltage‐range oxygen redox during charge and discharge processes. This work provides new ideals for design of cathode materials in anionic redox chemistry.
Understanding the role of teachers' facial expressions in students' learning is helpful to improve online teaching. Therefore, this study explored the effects of teacher's facial expressions on ...students' learning through analyzing three groups of video lectures. Participants were 78 students enrolled in three groups: one with an enhanced-expression teacher, one with a conventional-expression teacher, and one with the teacher's audio only. ANOVA was used to explore whether video lectures instructed by the enhanced-expression teacher were better than those instructed by the conventional-expression teacher and the audio-only teacher for facilitating students' learning, and what is the role of the teacher's emotions in students' perceived social presence, arousal level, cognitive load, and learning. The results showed that the video lecture by the enhanced-expression teacher was better than those with the conventional-expression teacher and with the audio-only for facilitating students' social presence, arousal level, and long-term learning. Interestingly, it was found that the teacher's emotions could relieve students' cognitive load. These results explained the inconsistency of existing studies by exploring the mechanism of teachers' emotions in students' learning. It also provides teachers with practical guidance for video lecture design.
Multivalent metal ion hybrid capacitors have been developed as novel electrochemical energy storage systems in recent years. They combine the advantages of multivalent metal ion batteries (
e.g.
, ...zinc-ion batteries, magnesium-ion batteries, and aluminum-ion batteries) with those of supercapacitors, and are characterized by good rate capability, high energy density, high power output and ultralong cycle life. Herein, after a brief introduction to supercapacitors and multivalent metal ion batteries, we reviewed the recent progress in research on multivalent metal ion hybrid capacitors, with a focus on zinc-ion hybrid capacitors, from the perspectives of design concept, configuration, electrochemical behavior and energy storage mechanism. An outlook of the future research regarding multivalent metal ion hybrid capacitors was also presented. This review will be beneficial for researchers around the world to have a better understanding of multivalent metal ion hybrid capacitors and develop novel electrochemical energy storage systems to meet the demands of rapidly developing electric vehicles and wearable/portable electronic products.
Multivalent metal ion hybrid capacitors are overviewed from the angle of design concept, configuration, electrochemical behavior and energy storage mechanism.
Increasing energy density of Li-ion batteries (LiBs) along with fast charging capability are two key approaches to eliminate range anxiety and boost mainstream adoption of electric vehicles (EVs). ...Either the increase of energy density or of charge rate, however, heightens the risk of lithium plating and thus deteriorates cell life. The trilemma of fast charging, energy density and cycle life are studied systematically in this work utilizing a physics-based aging model with incorporation of both lithium plating and solid-electrolyte-interphase (SEI) growth. The model is able to capture the key feature of temperature-dependent aging behavior of LiBs, or more specifically, the existence of an optimal temperature with the longest cycle life. We demonstrate that this optimal temperature is a result of competition between SEI growth and lithium plating. Further, it is revealed that either the increase of charge rate or of energy density accelerates lithium plating induced aging. As such, the optimal temperature for cell life increases from ∼20 °C for a high-power cell at 1C charge to ∼35–45 °C with the increase of charge rate and/or energy density. It would be beneficial to further increase the charge temperature in order to enable robust fast charging of high energy EV cells.
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•Temperature-dependent aging behavior of Li-ion battery is studied numerically.•Overall aging rate depends on the competition of lithium plating and SEI growth.•The optimal temperature for cycle life increases with charge rate & energy density.•Raising charging temperature is an effective method to eliminating lithium plating.
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