Average Reflectance Research Articles

Упорядочение катионов в минералах сложного состава: P3-сергеванит — второй представитель группы эвдиалита с примитивной ячейкой

Sergevanite with idealized formula (Na12KH3O)[Ca3(Mn2Ca)](Na2Fe)Zr3Ti0.5Si25.5 O72OH2.(H2O)2 (Z = 3) — a low calcium eudialyte group mineral from Lovozero alkaline complex was investigated repeatedly using obtained earlier the X-ray diffraction data. Its crystal structure with 174 sites was refined in the frame of trigonal primitive cell to R = 4.7 % on the base of 5613 averaged independent reflections with F > 3(F). The unit-cell parameters were: a = 14. 2179(1), c = 30.3492(3) Å, V = 5313.1(1) Å3, space group P3. More detailed, close to real, cations distribution on sites was established. Studied sergevanite was the second mineral of eudialyte group with lowering symmetry from rhombohedral (R3) to trigonal (P3).

Pressure effect on the physical properties of 413-type MAX phase compound Nb4AlC3: Insights from DFT simulation

This article discusses the physical properties of the Nb4AlC3 MAX phase compound under the influence of pressure ranging from 0 to 100 GPa via the calculation of structural, mechanical, thermal, and optoelectrical properties by utilizing the density functional theory (DFT). Under the studied pressure range, the phase Nb4AlC3 is mechanically stable and various elastic moduli show a linear increase with pressure; while the machinability and dry lubricity show opposite cases. Nb4AlC3 shows brittle nature up to 20 GPa pressure, and after 20 GPa, Nb4AlC3 transits to ductile, and then the ductility increases with the further increase of pressure. Metallic feature is ensured from the band structure and density of states calculations as the valence band cross the Fermi level. The average reflectivity is more than 60% (from 0 to 100 GPa) which makes a capable solar heating reducing agent. The Debye temperature, minimum thermal conductivity, and melting point of the Nb4AlC3 compound have a linear increase response with pressure and the application of this compound as favorable thermal barrier coating (TBC) material.

Tailoring of the Structural, Optical, and Electrical Characteristics of Sol-Gel-Derived Magnesium-Zinc-Oxide Wide-Bandgap Semiconductor Thin Films via Gallium Doping.

The Ga-doped Mg0.2Zn0.8O (GMZO) transparent semiconductor thin films were prepared using the sol-gel and spin-coating deposition technique. Changes in the microstructural features, optical parameters, and electrical characteristics of sol-gel-synthesized Mg0.2Zn0.8O (MZO) thin films affected by the amount of Ga dopants (0-5 at%) were studied. The results of grazing incidence X-ray diffraction (GIXRD) examination showed that all as-prepared MZO-based thin films had a wurtzite-type structure and hexagonal phase, and the incorporation of Ga ions into the MZO nanocrystals refined the microstructure and reduced the average crystallite size and flatness of surface roughness. Each glass/oxide thin film sample exhibited a higher average transmittance than 91.5% and a lower average reflectance than 9.1% in the visible range spectrum. Experimental results revealed that the optical bandgap energy of the GMZO thin films was slightly higher than that of the MZO thin film; the Urbach energy became wider with increasing Ga doping level. It was found that the 2 at% and 3 at% Ga-doped MZO thin films had better electrical properties than the undoped and 5 at% Ga-doped MZO thin films.

Narrowband EUV Sc/Si Multilayer for the Solar Upper Transition Region Imager at 46.5 nm

The transition region is the key region between the lower solar atmosphere and the corona, which has been limitedly understood by human beings. Therefore, the Solar Upper Transition Region Imager (SUTRI) was proposed by Chinese scientists and launched in 2022 July. Right now, the first imaging observation of the upper transition region around 46.5 nm has been carried out by SUTRI. To ensure the spectral and temporal resolution of the SUTRI telescope, we have developed a narrowband Sc/Si multilayer. Based on the extreme ultraviolet (EUV) reflectivity measurements, the multilayer structure has been modified for ensuring the peak position of reflectivity was at 46.5 nm. Finally, the narrowband Sc/Si multilayer was successfully deposited on the hyperboloid primary mirror and secondary mirrors. The deviation of multilayer thickness uniformity was below than 1%, and the average EUV reflectivity at 46.1 nm was 27.8% with a near-normal incident angle of 5°. The calculated bandwidth of the reflectivity curve after primary and secondary mirrors was 2.82 nm, which could ensure the requirements of spectral resolution and reflectivity of SUTRI telescope to achieve its scientific goals.

Bacterial cellulose based three-dimensional porous composites with remarkable amphiphobic monolith properties for passive daytime radiative cooling

To tackle the daytime radiative cooling performance (DRCP) degradation of passive daytime radiative cooling materials (PDRCMs) due to contamination from aqueous or oily contaminants, modified three-dimensional porous composites of bacterial cellulose (BC) and barium sulfate (BaSO4) were fabricated by a unidirectional freeze-casting process and silanization modification. The modified BC/BaSO4 (M−BC/BaSO4) composites exhibited average reflectivity of 97.75%, average emissivity of 95.74%, and remarkable amphiphobic monolith properties with a water contact angle (WCA) and oily contact angle (OCA) of 154° and 145.5° for the surface and those of 153.5° and 143.5° for the internal section, respectively. They also exhibited insignificant changes in the DRCP before and after self-cleaning, achieving an average and maximum temperature drop of 10.40°C and 16.38°C before self-cleaning and those of 9.92°C and 16.40°C after self-cleaning, respectively. This work provides a new strategy for sustainable PDRCMs in practical applications.

Spectrally selective solar absorber and thermal infrared suppression based on hollow cylindrical microstructures

In recent decades, the world's environmental troubles have become increasingly serious. Seeking new and environmentally friendly energy sources to replace chemical fuels is the key to improving environmental problems. As a renewable energy source, solar energy is the most promising and viable alternative energy source. In this paper, we present a spectrally selective solar broadband absorber with a hollow cylindrical microstructure. The model uses Ti film-Al2O3 film-Cu film as the substrate and Ti–Al2O3–Ti–Al2O3 (in the order from top to bottom) materials stacked to form hollow cylinders as the microstructure. The model was simulated using the FDTD Solutions software from Lumerical Solutions. From the simulation results, it can be seen that the absorption rates of the model in the solar radiation band 280 nm–4000 nm are all above 90%, and the average absorption rate is 94.1%; under the light of AM 1.5, the weighted average absorption rate is 94.8%. In addition, the reflectivity of the model in the 6516 nm–20000 nm band is all higher than 80%, with an average reflectivity of 94.2%, and the average reflectivity in the non-solar radiation band of 4000 nm–20000 nm is 85.4%, which has good thermal infrared suppression ability. In addition, we discovered the physical mechanism of model broadband absorption by analyzing the electric field distribution maps at different wavelengths. At the same time, the model has polarization insensitivity and wide-angle absorption properties. The excellent spectral selectivity allows this solar broadband absorber to operate in high temperature environments, which is very meaningful for the research of both solar thermophotovoltaic technology and thermal insulation and cooling materials.

Homogeneous Nanostructured VO2@SiO2 as an Anti-Reflecting Layer in the Visible/Near Infrared Wavelength.

Low reflectivity is of great significance to photoelectric devices, optical displays, solar cells, photocatalysis and other fields. In this paper, vanadium oxide is deposited on pattern SiO2 via atomic layer deposition and then annealed to characterize and analyze the anti-reflection effect. Scanning electron microscope (SEM) images indicate that the as-deposited VOx film has the advantages of uniformity and controllability. After annealing treatment, the VO2@pattern SiO2 has fewer crevices compared with VO2 on the accompanied planar SiO2 substrate. Raman results show that there is tiny homogeneous stress in the VO2 deposited on pattern SiO2, which dilutes the shrinkage behavior of the crystallization process. The optical reflection spectra indicate that the as-deposited VOx@pattern SiO2 has an anti-reflection effect due to the combined mechanism of the trapping effect and the effective medium theory. After annealing treatment, the weighted average reflectance diminished to 1.46% in the visible near-infrared wavelength range of 650-1355 nm, in which the absolute reflectance is less than 2%. Due to the multiple scattering effect caused by the tiny cracks generated through annealing, the anti-reflection effect of VO2@pattern SiO2 is superior to that of VOx@pattern SiO2. The ultra-low reflection frequency domain amounts to 705 nm, and the lowest absolute reflectance emerges at 1000 nm with an astonishing value of 0.86%. The prepared anti-reflective materials have significant application prospects in the field of intelligent optoelectronic devices due to the controllability of atomic layer deposition (ALD) and phase transition characteristics of VO2.

Anti-reflection effect of high refractive index polyurethane with different light trapping structures on solar cells

The textured surfaces to reduce light reflectivity by using acid-alkali chemical etching and SiNx films are generally necessary for commercial crystalline silicon solar cells. However, this etching process requires a large amount of environmentally harmful acid-alkali solution and has limited options for texture and size. To overcome these disadvantages, a new anti-reflection strategy is proposed in this study, which is using soft nanoimprint lithography to prepare the textured structures on the outside of the SiNx films. The polyurethane with a high refractive index of 1.64 is selected as the texture material, and different templates are selected to prepare it into different light trapping structures, including positive-inverted pyramids, inverted lace cones, and positive-inverted moth-eye nanostructures allowing for easy customization of the textured structures. The finite element simulation and experiments demonstrate that these light trapping structures have a wide spectrum anti-reflection performance in visible and near-infrared bands. With the back surface of the commercial passivated emitter rear contact (PERC) bi-facial solar cells as the imprint substrates, some light trapping structures can reduce the surface weighted average light reflectivity (Rw) at the band of 300–1200 nm from 18.31% to less than 10% and the optimal structures can reduce Rw to 8.71%. This anti-reflection strategy can also be applied to thin-film solar cells and crystalline silicon solar cells of other structures, such as HIT, Topcon, Perovskite/c-Si tandem, and so forth, which shows great development potential.

Performance Analysis of STAR-IRS Aided NOMA Short-Packet Communications With Statistical CSI

We analyze the benefits of simultaneous transmitting and reflecting intelligent reflecting surfaces (STAR-IRSs) for short-packet communications (SPC) with non-orthogonal multiple access (NOMA) and statistical channel state information towards ultra-reliable and low-latency communications. Considering Rician fading and energy splitting protocol, we analyze the performance of STAR-IRS aided NOMA SPC systems with continuous and discrete phase shifts. We first derive new closed-form expressions for the average block error rate (BLER) and diversity order in the finite signal-to-noise ratio (SNR) regime. We then determine the relationship among the average BLER, power allocation, blocklength, and transmission and reflection coefficients. Finally, Monte Carlo simulations are used to verify our theoretical analysis and examine the optimal transmission and reflection coefficients that minimize the common blocklength in the considered system under reliability constraints.

Enhancing device efficiency using a reconfigurable terahertz wavefront modulator based on fermi level of graphene

This study investigates a Fermi-level-reconfigurable terahertz wavefront modulator composed of a hybrid material comprising graphene, silver metal, and silicon dioxide. Through theoretical simulation, analysis, and experimental investigations, it is found that graphene plays a crucial role in enhancing the performance of the modulator. Specifically, the presence of graphene increases the limiting factor of the modulator by 0.281, reduces the normalized modal field area by 0.15, decreases the transmission loss, and lowers the gain threshold by 30097 cm−1, thereby improving the efficiency, reliability, and stability of the device. The silicon dioxide and silver metal in the structure act as the primary reflective materials, achieving the effect of a metallic lens and validating the modulator's capability for efficient defocusing. Further investigations reveal that the carrier concentration of graphene can be easily controlled, allowing for manipulation of its physical properties through Fermi-level modulation. When incident light passes through the graphene array, it induces phase variations, altering the transmission path of light and thereby affecting the position of the defocused focal point, enabling dynamic adjustability. Under low Fermi-level control, the modulator achieves a 2πphase adjustment range with an average reflectivity of 75%. Thus, this provides potential for practical applications of more dynamic and tunable microdevices, particularly in the field of laser cutting technology and etching processes.

Vacuum-Packed Pork Sausages with Modified Casing Added with Orange Peel Extracts: Evaluating In Vitro Antioxidant Activity via Hyperspectral Imaging Coupled with Chemometrics

The antioxidant activities (in vitro) of vacuum-packaged dry-cured sausages stored for 1 year, which were treated with varying concentrations of extracts from orange peel (EFOP) in a modification solution, were evaluated using a central composite design. The individual variables: soy lecithin concentration, soy oil concentration, treated time, lactic acid addition, EFOP addition, and dependent variable [i.e., in vitro antioxidant activity] were analyzed by response surface methodology. Among the 32 treatment combinations, treatment 26 (central point) exhibited a higher 2,2-Diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity compared to the control group (natural hog casing without modification). Spectral pre-treatments were applied to enhance the robustness of the model, and a partial least squares regression model (PLSRM) was fitted. The results of the response surface methodology indicated that the interactive effects of a high [soy lecithin concentration] × a high [EFOP addition] yielded a DPPH assay result of over 35%. The determination coefficients (R2 value) of the second-order polynomial model for the simultaneous effects on in vitro antioxidant activity reached 65.28%. The PLSRM developed using average reflectance data after the first derivation pre-treatment demonstrated a higher R2 value in the calibration group compared to the untreated data. The first principal component accounted for 77.39% of the overall attributes and effectively differentiated the sausages’ antioxidant activity from 31.88%.

Constraints on metallogenic temperature and mineralization style from reflection color of sphalerite

The relationship between the color of sphalerite and trace elements has aroused the interest of researchers since a long time, but most of the study is still in the qualitative stage. In this contribution, we made attempt to reveal the relationship between the reflection color and its trace element, in order to discuss the genetic significance of various reflection colors of sphalerite through the quantitative study of reflection color of sphalerite. Based on LA-ICP-MS analysis and microspectrophotometer analysis of sphalerite samples in different types of deposits, the elements with significant correlation with the reflection color index were found and analyzed by factor analysis. Different genetic types of sphalerites have different color index, The average reflection color indices of each type sample are as follows, sphalerite from Mengya’a deposit: λd = 477.3 nm, Pe = 0.046, Rvis = 17.23%; sphalerite from Zhaxikang deposit: λd = 477.2 nm, Pe = 0.043, Rvis = 16.70%; sphalerite from Nanmushu deposit: λd = 476.4 nm, Pe = 0.038, Rvis = 16.55%. The reflection color index of sphalerite is correlated with the content of Mn, Fe, Ga, Ge, Ag, Cd, In, Tl, Pb. The results of factor analysis indicate that sphalerite with high reflectivity is more abundant in Fe, Mn and In, while the sphalerite with low reflectivity is more abundant in Ge, Tl, Pb and Ag. Furthermore, the reflection color index of sphalerite can be used to distinguish the genetic type of deposits. Based on an obvious linear relationship between the reflection color index of sphalerite and its mineralization temperature, we propose a new empirical equation: T(°C) = 61.4*Rvis + 1.1*λd + 6000*Pe-1533 which can be used as a geological thermometer.

Self-Adaptive Multistage Infrared Radiative Thermo-Optic Modulators Based on Phase-Change Materials

Phase-Change Materials (PCMs) are widely applied in dynamic optical modulation due to the dramatic changes in their complex refractive index caused by temperature variation. As the functionality varies, the application of a single PCM cannot meet the compact, efficient and broadband needs of optical modulators. In this work, we combine vanadium dioxide (VO2) and a chalcogenide (Ge2Sb2Te5 (GST) or In3SbTe2 (IST)) to obtain a VO2–GST/IST multiple-stack film that is optimized by a genetic algorithm. This film has a wide spectrum and high modulation properties with three self-switchable modes varied by temperature, including transmission, absorption and reflection. The optimal results are an average normal transmittance, absorbance, and reflectance of 0.76, 0.91, 0.86 in 3–5 μm and 0.72, 0.90, 0.90 in 8–14 μm under different temperature ranges. The film enhances the transmission and absorption properties due to the formation of anti-reflective coating and Fabry–Perot resonance. Compared with GST, the film maintains high reflectance due to the metal-like interface reflection of crystalline IST, which exhibits metallic properties. For different polarization states, the film demonstrates great directional insensitivity when the incidence angles vary from 0° to 60°. The designed self-adaptive multistage infrared radiative thermo-optic modulator has promising implications for optical fuse, fiber-optic communication and energy storage fields.

基于可见/近红外高光谱成像无损预测猕猴桃可溶性固形物含量

Soluble solid content (SSC) is a major quality index of kiwifruits. Visible near-infrared (Vis/NIR) hyperspectral imaging with the genetic algorithm (GA) was adopted in this study to realize the non-destructive prediction of kiwifruit SSC. A laboratory Vis/NIR hyperspectral imaging system was established to collect the hyperspectral imaging of 120 kiwifruit samples at a range of 400–1100 nm. The average reflectance spectral data of the region of interest of the kiwifruit hyperspectral imaging were obtained after different preprocessing method, namely, Savitzky–Golay smoothing (SG), multiplicative scatter correction (MSC), and their combination method. The prediction models of partial least squares regression, multiple linear regression, and least squares support vector machine (LS-SVM) were built for determining kiwifruit SSC by using the average reflectance spectral data and effective feature wavelength variables selected by GA, respectively. The results show that SG+MSC is the best preprocessing method. The precisions of the prediction models built using the effective feature wavelength variables selected by GA are higher than that established using full average reflectance spectral data. The GA-LS-SVM prediction model has a best performance with correlation coefficient for prediction (R=0.932) and standard error of prediction (SEP=0.536° Bx) for predicting kiwifruit SSC. The prediction accuracy has been improved by 5.6% compared with that of the prediction models established by using the full-band reflectance spectral data. This study provides an effective method for non-destructive detection of kiwifruit SSC.

Ultra-Wideband High-Efficiency Solar Absorber and Thermal Emitter Based on Semiconductor InAs Microstructures.

Since the use of chemical fuels is permanently damaging the environment, the need for new energy sources is urgent for mankind. Given that solar energy is a clean and sustainable energy source, this study investigates and proposes a six-layer composite ultra-wideband high-efficiency solar absorber with an annular microstructure. It achieves this by using a combination of the properties of metamaterials and the quantum confinement effects of semiconductor materials. The substrate is W-Ti-Al2O3, and the microstructure is an annular InAs-square InAs film-Ti film combination. We used Lumerical Solutions' FDTD solution program to simulate the absorber and calculate the model's absorption, field distribution, and thermal radiation efficiency (when it is used as a thermal emitter), and further explored the physical mechanism of the model's ultra-broadband absorption. Our model has an average absorption of 95.80% in the 283-3615 nm band, 95.66% in the 280-4000 nm band, and a weighted average absorption efficiency of 95.78% under AM1.5 illumination. Meanwhile, the reflectance of the model in the 5586-20,000 nm band is all higher than 80%, with an average reflectance of 94.52%, which has a good thermal infrared suppression performance. It is 95.42% under thermal radiation at 1000 K. It has outstanding performance when employed as a thermal emitter as well. Additionally, simulation results show that the absorber has good polarization and incidence angle insensitivity. The model may be applied to photodetection, thermophotovoltaics, bio-detection, imaging, thermal ion emission, and solar water evaporation for water purification.

Measuring optical reflectivity of graphene films using compensated Fabry-Perot interferometry

Graphene optical applications rely on its exceptional optical characteristics, for which accurate measurement of graphene reflectivity is critical. Fabry-Perot (F-P) interferometry is a standard reflectivity measurement method with a simple structure, fast measurement speed, and high system plasticity. However, a strong coupling relationship exists between the coupling coefficient and the reflectivity of graphene in the F-P interferometry measurements of graphene reflectivity. Therefore, a method for measuring the reflectivity of thin graphene films using F-P interferometry with a compensation factor is proposed and experimentally demonstrated. Four alternative graphene film reflectivity solution models are established within four different F-P cavity lengths. The experimental results of the solution model with cavity lengths of 50–100 μm show that the average reflectivity of single-layer, two-layer, five-layer, eight-layer, and ten-layer graphene films are 0.0131%, 0.101%, 0.793%, 1.335%, and 1.978% with the errors of 0.7%, 1.0%, 1.0%, 1.1%, and 1.1%, respectively. Meanwhile, the standard deviation of graphene reflectivity increases with the number of graphene layers. The highly consistent experimental data and comparative results confirmed the accuracy of our method. This method proposed in this paper could be further extended to measure the reflectivity of other 2-D materials.

Joint Collaboration on Comparing NOAA’s Ground-Based Weather Radar and NASA–JAXA’s Spaceborne Radar

Abstract The National Aeronautics and Space Administration (NASA) and National Oceanic and Atmospheric Administration (NOAA) have a long and successful history of weather radar research. The NOAA ground-based radars—WSR-88D network—provide nationwide precipitation observations and estimates with advanced polarimetric capability. As a counterpart, the NASA–JAXA spaceborne radar—the Global Precipitation Measurement Dual-Frequency Precipitation Radar (GPM DPR)—has global coverage and higher vertical resolution than ground-based radars. While significant advances from both NOAA’s WSR-88D network and NASA–JAXA’s spaceborne radar DPR have been made, no systematic comparisons between the WSR-88D network and the DPR have been done. This study for the first time generates nationwide comprehensive comparisons at 136 WSR-88D radar sites from 2014 to 2020. Systematic differences in reflectivity are found, with ground radar reflectivity on average 2.4 dB smaller than that of the DPR (DPR version 6). This research found the discrepancies between WSR-88D and DPR arise from different calibration standards, signal attenuation correction, and differences in the ground and spaceborne scattering volumes. The recently updated DPR version 7 product improves rain detection and attenuation corrections, effectively reducing the overall average WSR-88D and DPR reflectivity differences to 1.0 dB. The goal of this study is to examine the systematic differences of radar reflectivity between the NOAA WSR-88D network and the NASA–JAXA DPR and to draw attention to radar-application users in recognizing their differences. Further investigation into understanding and alleviating the systematic bias between the two platforms is needed.

A method to pan-sharpen SAR amplitude data via electromagnetic reflectance similarities

ABSTRACT For a long time, the idea of fusing synthetic radar imagery (SAR) and higher-resolution panchromatic imagery, with the aim of increasing the spatial resolution of radar imagery, has been conceived as impossible. The challenge is due to the different natures of microwave radiation and visible radiation, where the former is the spectrum of SAR imagery, and the latter is of panchromatic imagery. Average reflection amplitude, which constitutes pixel values on both panchromatic and SAR imagery, is taken as a common framework around which this study proposes a method that enables the translation of an array on a panchromatic spectrum into an array of C-band microwave spectrum in order to achieve a higher spatial resolution. In this regard, open-access Worldview-2 and Worldview-3 panchromatic and Sentinel-1 (amplitude-only) images are used. The outputs are qualified using spatial correlation coefficient (SCC), net histogram curve, and R2 difference, and Erreur relative globale adimensionnelle de synthese (ERGAS) as full-reference image quality assessment methods in various scenarios. The results are tenable enough to consider this method for ordinary earth observation and monitoring objectives.

Hierarchically structured stainless-steel surfaces with superior superhydrophobicity and anti-reflection

Superhydrophobicity and anti-reflection of stainless-steel surfaces have potential applications in the fields of solar energy absorption and conversion, stray light shielding, and optical stealth. Here, we propose an efficient method for fabricating hierarchically structured stainless-steel surface with superior superhydrophobicity and anti-reflection based on maskless electrochemical machining (maskless ECM) technology. The hierarchically structured surface not only had a contact angle of 154° without chemical modification, but also had an average reflectance of 1.44% in the wavelength range of 400–800 nm. The mechanism underlying optical properties was discussed. The hierarchical structure formed by maskless ECM is very suitable for mass production and large area fabrication.

Textured p-type crystalline silicon surfaces obtained by multi-step plasma process for SHJ solar cells

P-type monocrystalline silicon wafers were textured by means of a multi-step plasma etching technique with the aim of greatly reducing their reflectance and effectively exploiting the highest possible amount of solar radiation in heterojunction photovoltaic devices. Suitable surface morphologies, characterized by high light scattering, have to be obtained without damaging the c-Si electrical properties. For this reason, some aspects of the plasma etching process have been studied and improved. Modifications have been made to obtain both “cleaner” processes and energetically lower ion bombardment. By operating at high pressure (0.4 mbar), a process controlled by diffusion of reactive species towards the substrate was favoured. Another innovative aspect consisted in two “reconditioning” plasma processes of the Si surface before the actual silicon removal step with SF6 /O2 gas mixtures. A strong reduction in the average optical reflection down to 5% was obtained coupled with a minority carriers lifetime (τeff) of about 950 μs, value comparable to that of the untreated silicon. An interesting surface morphology, consisting in “U" shaped cavities, was obtained. Texture irregularities were easily removed by acid etching. The moderate depth of the cavities is very promising for an effective passivation with a-Si:H thin films.