Nanostructured metals have received a significant amount of attention in recent years due to their exciting plasmonic and photonic properties enabling strong field localization, light concentration, ...and strong absorption and scattering at their resonance frequencies. Resonant plasmonic and metamaterial absorbers are of particular interest for applications in a wide variety of technologies including photothermal therapy, thermophotovoltaics, heat-assisted magnetic recording, hot-electron collection, and biosensing. However, it is rather challenging to realize ultranarrow absorption bands using plasmonic materials due to large optical losses in metals that decrease the quality factor of optical resonators. Here, we theoretically and experimentally demonstrate an ultranarrow band absorber based on the surface lattice resonances (SLRs) in periodic nanowire and nanoring arrays on optically thick, reflecting metallic films. In experiments, we observed ultranarrow band resonant absorption peaks with a bandwidth of 12 nm and absorption amplitude exceeding 90% at visible frequencies. We demonstrate that the resonance absorption wavelength, amplitude of the absorption peak, and the bandwidth can be controlled by tuning the periodicity and the thickness of nanoring and nanowire arrays. Unlike conventional plasmonic absorbers utilizing common metal–insulator–metal stacks, our narrow band absorber consists solely of metals, facilitating stronger optical interaction between the SLR of periodic nanostructures and the highly reflective film. Moreover, by introducing asymmetry to the nanoring/nanowire hybrid system, we observe the spectral evolution of resonance splitting enabled by strong coupling between two individual SLRs arising from nanoring and nanowire arrays. Designing such all-metallic nanostructure arrays is a promising route for achieving ultranarrow band absorbers which can be used as absorption filters, narrow band thermal emitters in thermophotovoltaics, and plasmonic biosensors.
Nanostructured photonic materials enable control and manipulation of light at subwavelength scales and exhibit unique optical functionalities. In particular, plasmonic materials and metamaterials ...have been widely utilized to achieve spectral transmission, reflection, and absorption filters based on localized or delocalized resonances arising from the interaction of photons with nanostructured materials. Realization of visible-frequency, high-performance, large-area, optical filters based on nanoplasmonic materials is rather challenging due to nanofabrication related problems (cost, fabrication imperfection, surface roughness) and optical losses of metals. Here, we propose and demonstrate large-area perfect absorbers and transmission filters that overcome difficulties associated with the nanofabrication using a lithography-free approach. We also utilize and benefit from the optical losses in metals in our optical filter designs. Our resonant optical filter design is based on a modified, asymmetric metal–insulator–metal (MIM) based Fabry–Perot cavity with plasmonic, lossy ultrathin (∼30 nm) metallic films used as the top metallic layer. We demonstrated a narrow bandwidth (∼17 nm) super absorber with 97% maximum absorption with a performance comparable to nanostructure/nanoparticle-based super absorbers. We also investigated transmission (color) filters using ultrathin metallic films, in which different colors can be obtained by controlling the dielectric spacer thickness. With performance parameters of transmittance peak intensity reaching 60% and a narrow-band of ∼40 nm, our color filters exceed the performance of widely studied plasmonic nanohole array based color filters. Proposed asymmetric Fabry–Perot cavities using ultrathin metallic films could find applications in spectrally selective optical (color and absorber) filters, optoelectronic devices with controlled bandwidth such as narrow-band photodetectors, and light-emitting devices.
This study aimed to determine the effects of FeMn modified biochar composite (FMBC) treatment on the pH, redox properties, enzyme activities, and bacterial communities of As-polluted paddy soil. The ...two utilized FMBCs (FMBC1 and FMBC2) exhibited markedly different effects on soil pH, and treatment with biochar (BC) or FMBCs increased the soil redox potential and reduced the content of available As, facilitating the conversion of originally present non-specifically sorbed and specifically bound As forms to residual, amorphous hydrous oxide–bound, and crystalline hydrous oxide–bound ones. In general, the activities of soil enzymes increased after the above treatments, with the exception of that of alkaline phosphatase, which decreased upon supplementation with FMBC2. Supplementation with BC or FMBCs increased the abundance of Proteobacteria and Firmicutes, decreasing that of Bacteroidetes. Notably, FMBC1 and FMBC2 affected soil properties in different ways, although the mechanisms of the corresponding influence were similar. Thus, treatment with BC-based materials changed the distribution of As and the activities of soil enzymes, additionally affecting a variety of other physicochemical soil properties to make it suitable for microbial growth.
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•Added FMBCs could increase the soil redox potential and reduce the content of available As.•FMBCs could be facilitated the conversion of non-specifically sorbed As in paddy soil.•The addition of FMBCs increased the activity of soil enzymes.•Supplementation with FMBCs increased the abundance of Proteobacteria and Firmicutes.
Applied BC-based materials could change the As distribution and partial properties of soil to make it suitable for microbial growth.
Resonant absorbers based on nanostructured materials are promising for variety of applications including optical filters, thermophotovoltaics, thermal emitters, and hot-electron collection. One of ...the significant challenges for such micro/nanoscale featured medium or surface, however, is costly lithographic processes for structural patterning which restricted from industrial production of complex designs. Here, we demonstrate lithography-free, broadband, polarization-independent optical absorbers based on a three-layer ultrathin film composed of subwavelength chromium (Cr) and oxide film coatings. We have measured almost perfect absorption as high as 99.5% across the entire visible regime and beyond (400-800 nm). In addition to near-ideal absorption, our absorbers exhibit omnidirectional independence for incidence angle over ±60 degrees. Broadband absorbers introduced in this study perform better than nanostructured plasmonic absorber counterparts in terms of bandwidth, polarization and angle independence. Improvements of such "blackbody" samples based on uniform thin-film coatings is attributed to extremely low quality factor of asymmetric highly-lossy Fabry-Perot cavities. Such broadband absorber designs are ultrathin compared to carbon nanotube based black materials, and does not require lithographic processes. This demonstration redirects the broadband super absorber design to extreme simplicity, higher performance and cost effective manufacturing convenience for practical industrial production.
The estimation of the components which contain the characteristics of a signal attracts great attention in many real world applications. In this paper, we address the problem of the tracking of ...multiple signal components over discrete time series. We propose an algorithm to first detect the components from a given time-frequency distribution and then to track them automatically. In the first place, the peaks corresponding to the signal components are detected using the statistical properties of the spectral estimator. Then, an original classifier is proposed to automatically track the detected peaks in order to build components over time. This classifier is based on a total divergence matrix computed from a peak-component divergence matrix that takes account of both amplitude and frequency information. The peak-component pairs are matched automatically from this divergence matrix. We propose a stochastic discrimination rule to decide upon the acceptance of the peak-component pairs. In this way, the algorithm can estimate the number, the amplitude and frequency modulation functions, and the births and the deaths of the components without any limitation on the number of components. The performance of the proposed method, a post-processing of a time-frequency distribution is validated on simulated signals under different parameter sets. The method is also applied to four real-world signals as a proof of its applicability.
Directional emission of photoluminescence despite its incoherence is an attractive technique for light-emitting fields and nanophotonics. Optical metasurfaces provide a promising route for wavefront ...engineering at the subwavelength scale, enabling the feasibility of unidirectional emission. However, current directional emission strategies are mostly based on static metasurfaces, and it remains a challenge to achieve unidirectional emissions tuning with high performance. Here, we demonstrate quantum dots-hydrogel integrated gratings for actively switchable unidirectional emission with simultaneously a narrow divergence angle less than 1.5° and a large diffraction angle greater than 45°. We further demonstrate that the grating efficiency alteration leads to a more than 7-fold tuning of emission intensity at diffraction order due to the variation of hydrogel morphology subject to change in ambient humidity. Our proposed switchable emission strategy can promote technologies of active light-emitting devices for radiation control and optical imaging.
DNA programmable assembly has been combined with top-down lithography to construct superlattices of discrete, reconfigurable nanoparticle architectures on a gold surface over large areas. ...Specifically, the assembly of individual colloidal plasmonic nanoparticles with different shapes and sizes is controlled by oligonucleotides containing "locked" nucleic acids and confined environments provided by polymer pores to yield oriented architectures that feature tunable arrangements and independently controllable distances at both nanometer- and micrometer-length scales. These structures, which would be difficult to construct by other common assembly methods, provide a platform to systematically study and control light-matter interactions in nanoparticle-based optical materials. The generality and potential of this approach are explored by identifying a broadband absorber with a solvent polarity response that allows dynamic tuning of visible light absorption.
Gas diffusions in soil control all physical and biogeochemical processes in terrestrial ecosystems and correctly describing them is critical to numerical modelling of these processes. The movement of ...gases in soil needs to overcome the resistances caused by both gas-gas collision and gas-wall collision, and the relative significance of one resistance over another depends on the size and spatial distribution of the pores. Practical models often use the empirical dusty-gas formula to estimate the effective gas diffusion coefficient, assuming that all resistances are addable even after a volumetric average. Since it is impossible to separately measure the two resistances, the accuracy and reliability of this approach remains unknown. We investigate this using pore-scale modelling and tomography. Soil aggregates are acquired using X-ray computed tomography and the size and spatial distribution of their pores are calculated using a morphological model; each pore is associated with a bulk diffusion coefficient and a Knudsen diffusion coefficient, with the latter calculated based on the pore size. We then develop pore-scale models to simulate gas diffusion, and the diffusive flux and gas concentration simulated at pore scale are volumetrically averaged to calculate i) the effective Knudsen diffusion coefficient assuming the bulk diffusion coefficient is infinite, ii) the effective bulk diffusion coefficient assuming the Knudsen diffusion coefficient is infinite, and iii) the overall effective diffusion coefficient considering both the bulk and the Knudsen diffusions. The dusty-gas model estimates the effective diffusion coefficient using the effective bulk and the Knudsen diffusion coefficients, and its accuracy is tested against the effective diffusion coefficient directly calculated from the pore-scale simulations. The results indicate that the dusty-gas model is accurate when the diffusion is dominated by either bulk diffusion or Knudsen diffusion, whereas in the transition regime it systematically overestimates the effective diffusion coefficient. We also investigate the impact of saturation on the effective diffusion coefficients when the aggregates are either hydrophobic or hydrophilic, elucidating the significance of the Knudsen diffusion as the saturation of the aggregates increases.
•Microstructures of soil aggregates are acquired using X-ray micro-tomography.•Pore-scale models are developed to simulate gas diffusion in the aggregates.•Accuracy of the commonly used dusty-gas model is tested.•Impact of saturation on effective gas diffusion coefficient of the aggregates is studied.
Abstract
As the global aviation industry faces increasing pressure on the environment, the International Civil Aviation Organization (ICAO) has implemented increasingly strict requirements for ...aircraft carbon emissions. The adoption of innovative energy technologies, such as electric power, hydrogen fuel, and sustainable biofuels in the aviation sector, will enable us to achieve zero carbon emission targets and mitigate environmental pollution associated with air transportation. Drawing on statistical data of aviation accidents, this paper analyses the primary causes of flight mishaps and summarizes several safety issues faced by new energy aircraft. Based on these, the new energy aircraft is divided into several subsystems, including power system, energy system, flight control system and so on. Then, safety analysis tools and methods are then used to conduct an analysis of the aircraft’s safety, with the aim of improving overall safety.
•Pore-scale model is presented to simulate fluid flow in columns filled with two stratified media.•Volumetric average of the simulated results yields a pressure discontinuity at the strata ...interface.•The emerged discontinuous pressure reduced the combined ability of the media to conduct fluid.•Under certain circumstance the flow rate in the stratified media is even direction-dependant.
Water flow along or across the interfaces of contrasting materials is ubiquitous in hydrology and how to solve them in macroscopic models derived from volumetric average of the pore-scale processes remains elusive. While the change in the average velocity and pressure at water-sediment interface has been well established for channel flow over porous beds, whether a volumetric average alerts the pressure continuity when water flows across the interface of two porous materials is poorly understood despite its imperative implications in hydrological modelling. The primary purpose of this paper is to provide evidences via pore-scale simulations that volumetrically averaging the pore-scale processes indeed yields a discontinuous pressure when water flows across a material interface. We simulated two columns numerically reconstructed by filling them with stratified media: One is an idealised two-layer system and the other one is a 3D column filled by fine glass beads over coarse glass beads with their pore geometry acquired using x-ray computed tomography. The pore-scale simulation is to mimic the column experiment by driving fluid to flow through the void space under an externally imposed pressure gradient. Once fluid flow reaches steady state, its velocity and pressure in all voxels are sampled and they are then spatially averaged over each section perpendicular to the average flow direction. The results show that the average pressure drops abruptly at the material interface no matter which direction the fluid flows. Compared with the effective permeability estimated from the homogenization methods well established in the literature, the emerged discontinuous pressure at the interface reduces the combined ability of the two strata to conduct water. It is also found that under certain circumstances fluid flow is direction-dependant, moving faster when flowing in the fine-coarse direction than in the coarse-to-fine direction under the same pressure gradient. Although significant efforts are needed to incorporate these findings into practical models, we do elicit the emergence of discontinuous pressure at material interface due to volumetric average as well as its consequent implications in modelling of flow in heterogeneous and stratified media.
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