- 标题
- 摘要
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- 实验方案
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Modification of graphene oxide with titanium dioxide by alcoholic reduction
摘要： Graphene oxide (GO) nanocomposites doped with DEGUSSA (P25) was synthetized by (GO) alcoholic reduction at high temperatures, during the reduction the P25 anchored to the spaces left by carbonyls groups in the graphene network, this incorporation improved photocatalytic behavior by retarding the electro-hole pair (e? hC). Raman spectroscopy con?rms the anchorage, because the material with higher load of TiO2 presented a band at 1100 cm?1 belonging to Carbonate’s groups (CO3) and a total modi?cation of the bands D and G, also this material presents a band gap of 2.54 eV. The P25 incorporation into graphene three-dimensional arrangement is notorious in diffraction x ray patterns, because the graphene diffraction pattern shows a sharpened and smaller peak than the starting graphene oxide. The incorporation of TiO2 to graphene sheets, improved the band gap, which P25 being of 3.2 eV was reduced to almost 2.5 eV, naturally this allows it, to be an excellent material to be used as photoanodes, photovoltaic devices and photocatalysis, its demonstrated by a photodegradation of methylene blue at 60 ppm exposed to solar light and 25 ppm exposed to a sodium lamp that emits radiation close to 589 nm.
关键词： methylene blue degradation,Band gap,graphene oxide,titanium dioxide
更新于2025-09-23 15:22:29
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Stability Monitoring of the VIIRS Day/Night Band over Dome C with a Lunar Irradiance Model and BRDF Correction
摘要： The unique feature of the Visible Infrared Imager Radiometer Suite (VIIRS) day/night band (DNB) is its ability to take quantitative measurements of low-light scenes at night. In order to monitor the stability of the high gain stage (HGS) of the DNB, nighttime observations over the Dome C site under moonlight are analyzed in this study. The Miller and Turner 2009 (MT2009) lunar irradiance model has been used to simulate lunar illumination over Dome C. However, the MT2009 model does not differentiate the waxing and waning lunar phases. In this paper, the MT-SWC (SeaWiFS Corrected) lunar irradiance model differentiating the waxing and waning lunar phases is derived by correcting the MT2009 model using lunar observations made by the Sea-Viewing Wide Field-of-View Sensor (SeaWiFS). In addition, a top of atmosphere (TOA) bi-directional reflectance distribution function (BRDF) model during nighttime over Dome C is developed to remove the angular dependence from the nighttime TOA reflectance. The long-term stability monitoring of the DNB high-gain stage (HGS) reveals a lower reflectance factor in 2012 in comparison to the following years, which can be traced back to the change in relative spectral response (RSR) of National Oceanic & Atmospheric Administration's (NOAA's) Interface Data Processing Segment (IDPS) VIIRS DNB in April 2013. It also shows the radiometric stability of DNB data, with long-term stability of less than 1.58% over the periods from 2013 to 2016. This method can be used to monitor the radiometric stability of other low-light observing sensors using vicarious calibration sites under moonlight illumination.
关键词： visible infrared imaging radiometer suite (VIIRS),Miller and Turner 2009 (MT2009),Sea-Viewing Wide Field-of-View Sensor (SeaWiFS),Dome C site,day/night band (DNB),lunar observations,BRDF effect
更新于2025-09-23 15:22:29
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Identification of Wheat Yellow Rust Using Optimal Three-Band Spectral Indices in Different Growth Stages
摘要： Yellow rust, a widely known destructive wheat disease, affects wheat quality and causes large economic losses in wheat production. Hyperspectral remote sensing has shown potential for the detection of plant disease. This study aimed to analyze the spectral reflectance of the wheat canopy in the range of 350–1000 nm and to develop optimal spectral indices to detect yellow rust disease in wheat at different growth stages. The sensitive wavebands of healthy and infected wheat were located in the range 460–720 nm in the early-mid growth stage (from booting to anthesis), and in the ranges 568–709 nm and 725–1000 nm in the mid-late growth stage (from filling to milky ripeness), respectively. All possible three-band combinations over these sensitive wavebands were calculated as the forms of PRI (Photochemical Reflectance Index) and ARI (Anthocyanin Reflectance Index) at different growth stages and assessed to determine whether they could be used for estimating the severity of yellow rust disease. The optimal spectral index for estimating wheat infected by yellow rust disease was PRI (570, 525, 705) during the early-mid growth stage with R2 of 0.669, and ARI (860, 790, 750) during the mid-late growth stage with R2 of 0.888. Comparison of the proposed spectral indices with previously reported vegetation indices were able to satisfactorily discriminate wheat yellow rust. The classification accuracy for PRI (570, 525, 705) was 80.6% and the kappa coefficient was 0.61 in early-mid growth stage, and the classification accuracy for ARI (860, 790, 750) was 91.9% and the kappa coefficient was 0.75 in mid-late growth stage. The classification accuracy of the two indices reached 84.1% and 93.2% in the early-mid and mid-late growth stages in the validated dataset, respectively. We conclude that the three-band spectral indices PRI (570, 525, 705) and ARI (860, 790, 750) are optimal for monitoring yellow rust infection in these two growth stages, respectively. Our method is expected to provide a technical basis for wheat disease detection and prevention in the early-mid growth stage, and the estimation of yield losses in the mid-late growth stage.
关键词： yellow rust disease,three-band spectral index,different growth stages,hyperspectral remote sensing,wheat infection
更新于2025-09-23 15:22:29
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Design and Optimization of a Solar Power Conversion System for Space Applications
摘要： This manuscript details a design method for a 500kW solar power based microgrid system for space applications. The design method utilizes multi-objective optimization with the Genetic Algorithm considering four parameters that characterize solar power based microgrids (battery voltage, PV maximum power, PV maximum power point voltage, and number of panels per string). The final optimization metric is the ratio of daily average deliverable power to total system mass (W/kg) metric. The microgrid system is composed of a number of modular DC-DC micro-converters, of which four topologies (buck, boost, buck-boost and non-inverting buck-boost) are evaluated and compared. The non-inverting buck-boost converter is determined to be the best candidate, and the optimal system characteristics are provided and analyzed. The final system design achieves a specific power of 35.56W/kg, with optimized result of 743.7V battery voltage, 439.5W PV maximum power, 182.7V PV maximum voltage, and three panels per string. Based on the optimizations results, a prototype is designed, tested, and analyzed in terms of efficiency and low temperature reliability. The converter achieved a peak efficiency of 98.4%, a power density of 3.54W/cm3, a specific power of 3.76W/g, and operated for over 267 hours of 11-minute low temperature cycles from 0oC to -140oC.
关键词： low temperature testing,photovoltaic systems,wide band gap semiconductors,maximum power point trackers,design optimization,non-inverting buck-boost,space exploration,system-level design,DC-DC power converters,microgrids
更新于2025-09-23 15:22:29
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Hyperspectral Face Recognition with Patch-Based Low Rank Tensor Decomposition and PFFT Algorithm
摘要： Hyperspectral imaging technology with sufficiently discriminative spectral and spatial information brings new opportunities for robust facial image recognition. However, hyperspectral imaging poses several challenges including a low signal-to-noise ratio (SNR), intra-person misalignment of wavelength bands, and a high data dimensionality. Many studies have proven that both global and local facial features play an important role in face recognition. This research proposed a novel local features extraction algorithm for hyperspectral facial images using local patch based low-rank tensor decomposition that also preserves the neighborhood relationship and spectral dimension information. Additionally, global contour features were extracted using the polar discrete fast Fourier transform (PFFT) algorithm, which addresses many challenges relevant to human face recognition such as illumination, expression, asymmetrical (orientation), and aging changes. Furthermore, an ensemble classifier was developed by combining the obtained local and global features. The proposed method was evaluated by using the Poly-U Database and was compared with other existing hyperspectral face recognition algorithms. The illustrative numerical results demonstrate that the proposed algorithm is competitive with the best CRC_RLS and PLS methods.
关键词： spectral and spatial information,polar discrete fast Fourier transform,band fusion,ensemble classifier,global and local features,tensor decomposition,hyperspectral images
更新于2025-09-23 15:22:29
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A Coarse-to-Fine Optimization for Hyperspectral Band Selection
摘要： Hyperspectral band selection is a feature selection method that selects a most representative set of bands to achieve a good performance in several tasks such as classification and anomaly detection. It reduces the burden of storage, transmission, and computation. In this letter, a two-stage band selection algorithm is introduced. It selects bands and refines the result using a linear reconstruction error criterion. Then a coarse-to-fine band selection (CFBS) strategy is applied to the two-stage band selection in order to achieve a better result. CFBS selects bands group by group. Each group is selected based on bands that are not well represented by the previous groups, trying to minimize the linear reconstruction error. Experiments show that the proposed method has a significant advancement compared with other competitors.
关键词： Band selection,hyperspectral imaging.
更新于2025-09-23 15:22:29
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Evaluation of Signal Regeneration Impact on the Power Efficiency of Long-Haul DWDM Systems
摘要： Due to potential economic benefits and expected environmental impact, the power consumption issue in wired networks has become a major challenge. Furthermore, continuously increasing global Internet traffic demands high spectral efficiency values. As a result, the relationship between spectral efficiency and energy consumption of telecommunication networks has become a popular topic of academic research over the past years, where a critical parameter is power efficiency. The present research contains calculation results that can be used by optical network designers and operators as guidance for developing more power efficient communication networks if the planned system falls within the scope of this paper. The research results are presented as average aggregated traffic curves that provide more flexible data for the systems with different spectrum availability. Further investigations could be needed in order to evaluate the parameters under consideration taking into account particular spectral parameters, e.g., the entire C-band.
关键词： DWDM,phase shift keying,differential phase shift keying,power consumption,spectral efficiency,sub-band spacing,WDM networks,single-line rate,optical fibre networks,power efficiency,energy efficiency
更新于2025-09-23 15:22:29
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Time-order Phonon Scattering Processes are Responsible for the Asymmetric G* Raman Band in Graphene
摘要： Background: While most of the prominent features in the Raman spectrum of graphene are well understood as mentioned in patents within the Double Resonance (DR) picture, the origin of the peak at 2450 cm-1 (also called the G* band) still remains unclear. Method and Objective: In this work, we performed detailed Raman studies of single- and few-layer graphene using multiple laser excitations to unravel the origin of G* band. Results: Based on our analyses, we conclude that the G* band arises from a combination of Transverse Optical (iTO) and Longitudinal Acoustic (LA) phonons, and exhibits an asymmetric peak structure due to the presence of two different time-order phonon processes. The lower (higher) frequency sub-peak is ascribed to an LA-first (iTO-first) process. We provide three strong experimental evidences for the time-ordered scattering processes: the dependence of the G* band sub-peaks with (i) increasing laser energy, (ii) increasing defects, and (iii) increasing temperature. Finally, we attribute the enhanced asymmetry of the G* band in multi-layer graphene to multiple processes between electronic sub-bands, similar to the G’ band in multi-layer graphene. Conclusion: Our study uncovered the origin and nature of the G* peak in the Raman spectrum of graphene. We believe our results have important implications for processes such as graphene-enhanced Raman scattering, where the time-ordered scattering of optical and acoustic phonons can be very useful for sensing analytes.
关键词： second order,layer stacking,G* band,defects,graphene,Raman spectroscopy
更新于2025-09-23 15:22:29
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Novel Porous Boron Nitride Nanosheet with Carbon Doping: Potential Metal-Free Photocatalyst for Visible-Light-Driven Overall Water Splitting
摘要： The band gap of hexagonal boron nitride (h-BN) is far too wide for efficiently utilizing visible light, limiting its application in photocatalysis. The present study employs first principles calculations to demonstrate that the band gap energies of porous h-BN (p-BN) can be tuned by carbon doping to levels appropriate for the absorption of visible-light, and that the conduction band and valence band match well with the potentials of both hydrogen and oxygen evolution reactions. Importantly, a strategy of carbon doping to improve the energy level of valence band maximum is also proposed. Moreover, the carbon-doped p-BN exhibits good separation between photogenerated electrons/holes and structural stability at high temperatures. The DFT results help the design of high-performance two-dimensional photocatalysts that avoid the use of metals.
关键词： metal-free catalysts,photocatalyst,porous boron nitride nanosheets,overall water splitting,band structure engineering
更新于2025-09-23 15:22:29
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Polarization dependent five-band terahertz metamaterial using two resonators
摘要： In this paper, we present a multi-band terahertz metamaterial composed of two hexagonal shaped metallic resonators supported by a Teflon dielectric substrate. The performance characteristics of the proposed structure are evaluated numerically using CST Microwave Studio software. The design has polarization sensitive and angle independent operational nature. The designed structure resonates at five frequencies: 0.19 THz, 0.3 THz, 0.47 THz, 0.5 THz, and 0.61 THz in transverse electric mode. The underlying concept of multi-band resonances has been understood by obtaining the electric field.
关键词： multi-band,terahertz,metamaterial,imaging,polarization
更新于2025-09-23 15:22:29