In the present Letter, we theoretically demonstrate that near-field radiative transport between one-dimensional periodic grating microstructures separated by nanometer vacuum gaps can be spectrally ...enhanced by exciting magnetic polaritons. Fluctuational electrodynamics that incorporates scattering matrix theory with rigorous coupled-wave analysis is employed to exactly calculate the near-field radiative flux between two metallic gratings. In addition to the well-known coupled surface plasmon polaritons, the radiative flux can be also spectrally enhanced due to the magnetic polariton, which is excited in the gap between the grating ridges. The mechanism of magnetic polaritons in the near-field radiative transport are elucidated in detail, while the unusual enhancement cannot be predicted by either Derjaguin's or the effective medium approximations. The effects of the vacuum gap distance and grating geometry parameters between the two gratings are investigated. The findings will open a new way to spectrally control near-field radiative transfer by magnetic polaritons with micro- or nanostructured metamaterials, which holds great potential for improving the performance of energy systems like near-field thermophotovoltaics.
Conspectus It is a permanent issue for modern society to develop high-energy-density, low-cost, and safe batteries to promote technological innovation and revolutionize the human lifestyle. However, ...the current popular Li-ion batteries are approaching their ceiling in energy density, and thus other battery systems with more power need to be proposed and studied to guide this revolution. Lithium–air batteries are among the candidates for next-generation batteries because of their high energy density (3500 Wh/kg). The past 20 years have witnessed rapid developments of lithium–air batteries in electrochemistry and material engineering with scientists’ collaboration from all over the world. Despite these advances, the investigation on Li–air batteries is still in its infancy, and many bottleneck problems, including fundamental and application difficulties, are waiting to be resolved. For the electrolyte, it is prone to be attacked by intermediates (LiO2, O2 –, 1O2, O2 2–) and decomposed at high voltage, accompanying side reactions that will induce cathode passivation. For the lithium anode, it can be corroded severely by H2O and the side products, thus protection methods are urgently needed. As an integrated system, the realization of high-performance Li–air batteries requires the three components to be optimized simultaneously. In this Account, we are going to summarize our progress for optimizing Li–air batteries in the past decade, including air-electrochemistry and anode optimization. Air-electrochemistry involves the interactions among electrolytes, cathodes, and air, which is a complex issue to understand. The search for stable electrolytes is first introduced because at the early age of its development, the use of incompatible Li-ion battery electrolytes leads to some misunderstandings and troubles in the advances of Li–air batteries. After finding suitable electrolytes for Li–air batteries, the fundamental research in the reaction mechanism starts to boom, and the performance has achieved great improvement. Then, air electrode engineering is introduced to give a general design principle. Examples of carbon-based cathodes and all-metal cathodes are discussed. In addition, to understand the influence of air components on Li–air batteries, the electro-activity of N2 has been tested and the role of CO2 in Li–O2/CO2 has been refreshed. Following this, the strategies for anode optimization, including constructing artificial films, introducing hydrophobic polymer electrolytes, adding electrolyte additives, and designing alloy anodes, have been discussed. Finally, we advocate researchers in this field to conduct cell level optimizations and consider their application scenarios to promote the commercialization of Li–air batteries in the near future.
2D materials have been attracting high interest in recent years due to their low structural symmetry, excellent photoresponse, and high air stability. However, most 2D materials can only respond to ...specific light, which limits the development of wide‐spectrum photodetectors. Proper bandgap and the regulation of Fermi level are the foundations for realizing electronic multichannel transition, which is an effective method to achieve a wide spectral response. Herein, a noble 2D material, palladium phosphide sulfide (PdPS), is designed and synthesized. The bandgap of PdPS is around 2.1 eV and the formation of S vacancies, interstitial Pd and P atoms promote the Fermi level very close to the conduction band. Therefore, the PdPS‐based photodetector shows impressive wide spectral response from solar‐blind ultraviolet to near‐infrared based on the multichannel transition. It also exhibits superior optoelectrical properties with photoresponsivity (R) of 1 × 103 A W−1 and detectivity (D*) of 4 × 1011 Jones at 532 nm. Moreover, PdPS exhibits good performance of polarization detection with dichroic ratio of ≈3.7 at 808 nm. Significantly, it achieves polarimetric imaging and hidden‐target detection in complex environments through active detection.
A wide spectral response photodetector and polarimetric image sensor based on 2D palladium phosphide sulfide (PdPS) are designed. The photoresponse range of PdPS is from solar‐blind ultraviolet to the near‐infrared. The PdPS‐based polarimetric imaging sensor achieves object imaging and hidden‐target detection in complex environments.
Piezoresistive sensor is a promising pressure sensor due to its attractive advantages including uncomplicated signal collection, simple manufacture, economical and practical characteristics. Here, a ...flexible and highly sensitive pressure sensor based on wrinkled graphene film (WGF)/innerconnected polyvinyl alcohol (PVA) nanowires/interdigital electrodes is fabricated. Due to the synergistic effect between WGF and innerconnected PVA nanowires, the as‐prepared pressure sensor realizes a high sensitivity of 28.34 kPa−1. In addition, the device is able to discern lightweight rice about 22.4 mg (≈2.24 Pa) and shows excellent durability and reliability after 6000 repeated loading and unloading cycles. What is more, the device can detect subtle pulse beat and monitor various human movement behaviors in real‐time.
The polyvinyl alcohol (PVA) nanowires serve as a dielectric layer between graphene film and interdigital electrode tuning the contact resistance. The wrinkled graphene films with hierarchical microstructures inside are used as active sensing material. The synergistic effect between wrinkled graphene films and innerconnected PVA nanowires makes the piezoresistive sensor realize a high sensitivity.
In recent years, the microstructure and physicochemical properties of high‐entropy ceramics have received much interest by the combination of multiple principal elements. Herein, ...(Ti0.2V0.2Cr0.2Nb0.2Ta0.2)2AlC–(Ti0.2V0.2Cr0.2Nb0.2Ta0.2)C high‐entropy ceramics (M2AlC‐MC HECs) were prepared by the spark plasma sintering (SPS) technique, attributing to the structural and chemical diversity of MAX phases. The microstructure of M2AlC‐MC HECs was characterized from micron to atomic scales, and the phase composition of M2AlC‐MC HECs was analyzed by a combination of Maud and Rietveld analysis. The results indicate the successful solid solution of Ti, V, Cr, Nb, and Ta atoms in the M‐site of the 211‐MAX configuration, and all the samples show a classic layered structure. The weight percentage of (Ti0.2V0.2Cr0.2Nb0.2Ta0.2)2AlC in the M2AlC‐MC HECs was more than 90%. Furthermore, the thermoelectric properties of M2AlC‐MC HECs were investigated for the first time in this study, and the electrical conductivity and thermal conductivity of HECs are 3278 S cm−1 and 2.78 W m−1 K−1at 298 K, respectively.
A convenient and rapid detection method for methanol in ethanol remains a major challenge due to their indistinguishable physical properties. Herein, a novel fluorescence probe based on perovskite ...was successfully designed to overcome this bottleneck. We report a new zero‐dimensional (0D) hybrid perovskite of MP2InxSb1−xCl7 ⋅ 6 H2O (MP=2‐methylpiperazine) displaying an unusual green light emission with near‐unity photoluminescence quantum yield. Remarkably, this 0D perovskite exhibits reversible methanol‐response luminescence switching between green and yellow color but fail in any other organic vapors. Even for blended alcohol solutions, the luminescent probe exhibits excellent sensing performance with multiple superiorities of rapid response time (30 s) and ultra‐low detection limit (40 ppm), etc. Therefore, this 0D perovskite can be utilized as a perfect fluorescence probe to detect traces of methanol from ethanol with ultrahigh sensitivity, selectivity and repeatability. To the best of our knowledge, this work represents the first perovskite as fluorescence probe for methanol with wide potential in environmental monitoring and methanol detection, etc.
0D hybrid lead‐free halide displays highly efficient broadband green light emission with a near‐unity photoluminescence quantum yield, and acts as a unique fluorescence sensor for methanol in ethanol with ultrahigh selectivity, sensitivity and repeatability as well as fast response time.
Rationally optimizing the photoluminescence performance via accurate structural modulation is one of most important and challenging issues for hybrid halides. Herein, a viable crystal dimensional ...reduction strategy is proposed to reasonably enhance the photoluminescence quantum yield (PLQY) of hybrid antimony halide. Specifically, a synthetic technique is developed and new 1D DMPZSbCl5 ∙ H2O (DP‐SbCl5) is sliced to 0D DMPZ2SbCl6 ∙ Cl ∙ (H2O)2 (DP‐SbCl6) with crystal dimensional reduction from infinite SbCl52− chain to discrete SbCl63− octahedron. Comparing with nonluminescent 1D DP‐SbCl5, 0D DP‐SbCl6 displays highly efficient broadband yellow light emission with enhanced PLQY up to 75.94%. First‐principles calculation demonstrates that 0D DP‐SbCl6 features more flat and narrow band structure, which promotes the photoelectron localization and increases the quantum confinement, and finally boosts the luminescence efficiency. Together highly efficient and ultra‐stable luminescence performance enable DP‐SbCl6 as excellent down‐conversion broadband yellow phosphor to successfully fabricate white light emitting diodes with a high color rendering index of 92. This work provides a novel structural modulation strategy of crystal dimensional reduction to rationally optimize the PL performance of hybrid metal halides.
With controllable structural evolution from 1D to 0D hybrid antimony halides, the photoluminescence quantum yield (PLQY) realizes a notable enhancement from <1% to 75.94% in yellow spectral region benefitting from more localized photoelectrons and increased quantum confinement. This work provides a structural platform to verify the feasibility of crystal dimensionality reduction strategy to rationally improve the PLQY of metal halides.
Sub‐freezing temperature presents a significant challenge to the survival of current Li‐ion batteries (LIBs) as it leads to low capacity retention and poor cell rechargeability. The electrolyte in ...commercial LIBs relies too heavily on ethylene carbonate (EC) to produce a stable solid electrolyte interphase (SEI) on graphite (Gr) anodes, but its high melting point (36.4 °C) severely restricts ion transport below 0 °C, causing energy loss and Li plating. Here, a class of EC‐free electrolytes that exhibits remarkable low‐temperature performance without compromising cell lifespan is reported. It is found that at sub‐zero temperatures, EC forms highly resistive SEI that seriously impedes electrode kinetics, whereas EC‐free electrolytes create a highly stable, low‐impedance SEI through anion decomposition, which boosts capacity retention and eliminates Li plating during charging. Pouch‐type LiCoO2 (LCO)|Gr cells with EC‐free electrolytes sustain 900 cycles at 25 °C with 1 C charge/discharge, and LiNi0.85Co0.10Al0.05O2 (NCA)|Gr cells last 300 cycles at −15 °C with 0.3 C charge, both among the best‐performing in the literature under comparable conditions. Even at −50 °C, the NCA|Gr cell with EC‐free electrolytes still delivers 76% of its room‐temperature capacity, outperforming EC‐based electrolytes.
A new class of ethylene carbonate (EC)‐free electrolytes, based on methyl acetate and fluorinated ethers, is proposed for Li‐ion batteries operating at sub‐freezing temperatures. The EC‐free electrolyte demonstrates all‐round performance advantages over the traditional EC‐based electrolyte and presents a viable solution to improve the capacity retention and rechargeability of metal‐ion batteries in cold climates.
Space-time correlation is a staple method for investigating the dynamic coupling of spatial and temporal scales of motion in turbulent flows. In this article, we review the space-time correlation ...models in both the Eulerian and Lagrangian frames of reference, which include the random sweeping and local straining models for isotropic and homogeneous turbulence, Taylor's frozen-flow model and the elliptic approximation model for turbulent shear flows, and the linear-wave propagation model and swept-wave model for compressible turbulence. We then focus on how space-time correlations are used to develop time-accurate turbulence models for the large-eddy simulation of turbulence-generated noise and particle-laden turbulence. We briefly discuss their applications to two-point closures for Kolmogorov's universal scaling of energy spectra and to the reconstruction of space-time energy spectra from a subset of spatial and temporal signals in experimental measurements. Finally, we summarize the current understanding of space-time correlations and conclude with future issues for the field.
Restricting human mobility is an effective strategy used to control disease spread. However, whether mobility restriction is a proportional response to control the ongoing COVID-19 pandemic is ...unclear. We aimed to develop a model that can quantify the potential effects of various intracity mobility restrictions on the spread of COVID-19.
In this modelling study, we used anonymous and aggregated mobile phone sightings data to build a susceptible–exposed–infectious–recovered transmission model for COVID-19 based on the city of Shenzhen, China. We simulated how disease spread changed when we varied the type and magnitude of mobility restrictions in different transmission scenarios, with variables such as the basic reproductive number (R0), length of infectious period, and the number of initial cases.
331 COVID-19 cases distributed across the ten regions of Shenzhen were reported on Feb 7, 2020. In our basic scenario (R0 of 2·68), mobility reduction of 20–60% within the city had a notable effect on controlling COVID-19 spread: a flattening of the peak number of cases by 33% (95% UI 21–42) and delay to the peak number by 2 weeks with a 20% restriction, 66% (48–75) reduction and 4 week delay with a 40% restriction, and 91% (79–95) reduction and 14 week delay with a 60% restriction. The effects of mobility restriction were increased when combined with reductions of 25% or 50% in transmissibility of the virus. In specific analyses of mobility restrictions for individuals with symptomatic infections and for high-risk regions, these measures also had substantial effects on reducing the spread of COVID-19. For example, the peak of the epidemic was delayed by 2 weeks if the proportion of individuals with symptomatic infections who could move freely was maintained at 20%, and by 4 weeks if two high-risk regions were locked down. The simulation results were also affected by various transmission parameters.
Our model shows the effects of various types and magnitudes of mobility restrictions on controlling COVID-19 outbreaks at the city level in Shenzhen, China. The model could help policy makers to establish the optimal combinations of mobility restrictions during the COVID-19 pandemic, especially to assess the potential positive effects of mobility restriction on public health in view of the potential negative economic and societal effects.
Guangdong Medical Science Fund, and National Natural Science Foundation of China.
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