Low Reflectance Values Research Articles

Electrodeposition of nano-Cu, Ni and binary Ni/Cu into nano-porous AAO layer for high-efficiency black spectrally selective coating

BackgroundAnodic aluminum oxide (AAO) template is widespread due to its diverse metal nanostructures. Various solar selective black coatings on aluminum oxide template were investigated. Spectrally selective nano-coating of nickel, copper and nickel–copper on anodized aluminum was produced.ResultsThe coatings were performed via electrodeposition and evaluated by measurement of coating thickness, hardness and optical properties. Also, these coatings were analyzed by scanning electron microscope, energy-dispersive X-ray spectroscopic and polarization studies in 3.5% NaCl solution. The anodized aluminum showed higher corrosion resistance (4.8284 KΩ) and lower corrosion rate (0.02189 mm/year). However, the electro-colored Al with Cu for 60 min showed the highest corrosion rate of 0.1942 mm/y, compared with other Al samples. The effect of anodizing time on the metal density and the optical efficiency of black copper coating was studied.ResultsThe obtained solar panels exhibit low values of solar reflectance within the visible range and high solar absorption efficiency. These coatings are highly efficient and adequate for any solar system.

Synthesis and Characterisation of Zinc-doped Antimony Selenide

Antimony selenide substituted with Sb0.4Se0.6 and doped with zinc at three doping ratios (x=0, 0.01 and 0.03) was prepared via the solid state reaction method. The three prepared compositions were reacted thermally at 400 °C for 3 h. The structure of specimens was characterised via X-ray powder diffractometer to obtain the type of crystalline structure and lattice parameters of the prepared specimens, which showed a polycrystalline, orthorhombic structure. Optical characterisation was then achieved via UV-visible spectroscopy to exhibit the transmittance and reflectance spectra and estimate the band gap values of the prepared compositions. The samples showed high absorption spectra at low wavelengths (from 60% to 90%) and low reflectance values (from nearly zero to 17%). The band gap measurement showed an indirect transition, with values ranging from 1.2 eV to 1.23 eV. The electrical characteristics were represented by DC resistivity measurement at low temperature and AC conductivity measurement against frequency. The compositions showed a semiconducting behaviour in DC resistivity and compatible results in AC conductivity.

Synthesis, characterization, and visible–near infrared properties of some perylene‐3,4,9,10‐tetracarboxylic bisimide derivatives

AbstractBACKGROUNDPerylene bisimide pigments are one of the high performance pigment categories that are utilized in near infrared reflective coatings. The relationship between structure and near infrared activity in the perylene pigments has been unknown to date.RESULTSSome of the factors suggested by previous researchers as affecting the near‐infrared (NIR) reflectance of perylene‐bisimide derivatives were investigated in this study and some are validated, while some others are rejected. In the visible region, there are substantial differences between the absorption spectra of the pigments in their solid‐state and dissolved form, indicating that crystallochromic phenomenon present in the pigments. The NIR properties of the synthesized pigments are investigated and the results exhibit an obvious correlation between the imide substitution structure and NIR properties of the pigments. However, a direct relationship cannot be established. Aliphatic substituted PDIs usually exhibit lower reflectance values in comparison to aromatic substituted ones but there are some exceptions in this regard. The results of UV‐visible–NIR reflectance spectra of each pigment were reported in both white and black substrates and, in this regard, the synthesized pigments were classified. All the PDIs fall into the absorbent‐transparent category in the NIR region. Thermogravimetric analysis indicates that all the PDIs have a heat resistance of at least 200 °C.CONCLUSIONThe structure‐NIR reflectance relationship of the five synthesized perylene pigments is evaluated and the results illustrate that the N‐substitution of the imide group can significantly influence the cool activity of the pigments. © 2021 Society of Chemical Industry (SCI).

ZnO thin films prepared by RF plasma chemical vapour transport for self-cleaning and transparent conducting coatings

ZnO thin films were prepared by chemical vapour transport method in inductively coupled plasma (ICP). The films were synthesized at different substrate positions and various oxygen/argon ratios. X-ray diffraction (XRD) revealed that all the synthesized films at different positions are mixture of hexagonal ZnO and hexagonal Zn phases. The relative peak integrated intensity (RPII) of the ZnO phase is 83.6, 25.3 and 45.3%, for positions 1, 2 and 3, respectively. Morphology of ZnO films was found to be sensitive to substrate position. Flat flakes, bended nanowires (NWs) and nanoparticles morphologies are observed for positions 1, 2 and 3, respectively. The sample synthesized at 1 is stoichiometric, whereas the samples prepared in positions 2 and 3 are sub-stoichiometric. The films prepared at positions 1 and 3 have relatively high transmittance and low reflectance values, whereas the film prepared at position 2 has low transmittance and high reflectance. The ZnO film prepared at position 2 is hydrophobic with water contact angle of 112.2°, which can be used as self-cleaning coating. For ZnO films prepared with various O2 ratios, the RPII was 83.2, 88.0, 96.4 and 100% for films prepared with 10, 20, 30 and 40%, respectively. With increasing O2 ratio, the nanograins became bigger and the stoichiometry improved. The transmittance and optical bandgap increased, whereas the reflectance and refractive index decreased with increase in O2 ratio. The ZnO film synthesized with 30% O2 ratio has the highest figure of merit (FOM) value; thus, this film may be considered as the best ZnO film for transparent conducting coating applications.

Improvement of absorption light of laser texturing on silicon surface for optoelectronic application

This work aim to achieving laser nano-textured Si structures by means of an ultra-fast ultra-violet femtosecond (fs) laser texturing technique. The evidences of the impact of the duration of irradiation of the femtosecond laser pulses on Silicon (Si) have been investigated experimentally. A Ti:Sapphire laser at 800 nm (130 fs pulse duration with 1 kHz rate of repetition) has been employed to create nano-textured surfaces in an n-type (111) Si wafer of 0.015 Ω.cm resistivity and 508 ± 5 μm thickness. The average sizes of diameters were estimated to be in the 25−45 nm. From PL measurements of Si nanostructures, size dependent shifts in the direction of the blue spectral region have been emphasized. A highly symmetrical band shape was recognized from the samples' Raman spectra after the irradiation, the phonon frequency (phonon peak shift) shifted below 520 cm−1. The surface nanostructured Si showed lower reflectance values compared with bulk Si (un-irradiated). The observed enhancement of the fabricated Si nanostructures broad spectral response, which is in the range between the visible to the near infrared (NIR) 400−1150 nm, was attributed to increasing light absorption within sub-nanostructures. Thus, the proposed technique could be a promising approach to enhance the performance of Si-based photo-detector.

Low reflectance of carbon nanotube and nanoscroll-based thin film coatings: a case study.

Research on carbon material-based thin films with low light reflectance has received significant attention for the development of high absorber coatings for stray light control applications. Herein, we report a method for the successful fabrication of stable thin films comprised of carbon nanotubes (CNTs) and nanoscrolls (CNS) on an aluminium (Al) substrate, which exhibited low reflectance of the order of 2–3% in the visible and near-infrared (NIR) spectral bands. Changes in the structural and chemical composition of pristine single-walled carbon nanotube (SWCNT) samples were analyzed after each processing step. Spectroscopy, microscopy and microstructural studies demonstrated emergence of CNS and multi-walled carbon nanotubes (MWCNTs) due to the sequential chemical processing of the sample. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) studies revealed the formation of CNS via curling and folding of graphene sheets. Microstructural investigations including SEM and atomic force microscopy (AFM) confirmed the presence of microcavities and pores on the surface of the film. These cavities and pores significantly contribute to the observed low reflectance value of CNTs, CNS compound films by trapping the incident light. Fundamental space environmental simulation tests (SEST) were performed on the coated films, that showed promising results with reflectance values almost unaltered in the visible and NIR spectral bands, demonstrating the durability of these films as potential candidates to be used in extreme space environmental conditions. This study describes the preparation, characterization, and testing of blended CNT and CNS coatings for low-light scattering applications.

Application of Micro-Raman Spectroscopy for the Quantitative Analysis of Vitrinite Reflectance in Medium and High Rank Colombian Coals

The structural changes and the degree of maturity of three Colombian coals from the Santander and Antioquia provinces were studied using a simple and fast curve fitting method of the RBS parameters (the distance between band G and band D), FWHM - G (total width at half the maximum of the G band) and AR (area of the Raman spectrum), obtained by deconvolution and band resolution of the Micro-Raman spectra. The results were compared by morphological and chemical analysis using a SEM scanning electron microscope coupled with a solid state X - ray EDS detector. A percentage of vitrinite reflectance (% Ro) of 4.3 %, 3.8 % and 0.07 % was obtained, a percentage of carbon by EDS analysis of 91.47 %, 87.78 %, 73.4 %, a morphological description by SEM analysis presenting smooth, rough surfaces and rough-lumpy and pore size between 0.7 µm - 0.8 µm, 1.3 µm - 1.5 µm and 0.2 µm - 0.7 µm for the anthracite, semi-anthracite and bituminous samples, respectively. The results showed that based on this method, it was possible to obtain a model that allows to rapidly analyze and characterize the coal. The results compare very well to those of Colombian coals normalized by other methods to improve the precision of the measurement. The modified method, however, did not offer an appropriate fit for the lower range coal and produced extremely low reflectance values. This effect is possibly related with the molecular structure of organic matter in coal or the presence of fluorescence interference.

Spectral characterization of the Batuga granite pluton, South Eastern Desert, Egypt: influence of lithological and mineralogical variation on ASD Terraspec data

The paper concerns with potential utilization of Landsat-8 data combined with TerraSpec spectro-radiometer and field studies for mapping and discriminating the different granitic varieties of Batuga pluton in the South Eastern Desert of Egypt. Integrated data of band combination, principal component analysis (PCA), band rationing, fusion technique, and TerraSpec measurements substantially improve visual interpretation to differentiate between granite varieties as well as basalt dikes traversing the pluton. Compilation of field, petrographic, and spectral data enables to distinguish three varieties of granite, namely alkali feldspar granite, garnet-bearing leucogranite, and two-mica granite (monzogranite). False color composite (FCC) image PC1, PC3, and PC4 in R, G, and B, respectively, is successful to discriminate the western part of Batuga pluton as mica granite (monzogranite) but it failed to discriminate the other two granite types. On the other hand, the band ratio combination 6/7, 5/6, and 2/4 successfully used to discriminate the three varieties of granite. Also, the image fusion technique of false color composite (7, 5, & 2) and band ratio (6/7, 5/6, & 2/4) combinations with the high spatial resolution band 2 of Sentinel-2 is applied using the Gram-Schmidt method. Regarding with TerraSpec measurements, the alkali feldspar granite displays two absorption features around 1.4 and 2.25 μm. Moreover, the garnet-bearing leucogranite shows four little absorption features at 1.4, 2.21, 2.25, and 2.33 μm, while the mica granite shows low reflectance values throughout the VNIR and SWIR regions compared to the other two varieties, and low four absorption features at 1.4, 2.21, 2.25, and 2.33 μm wavelengths. The basalt dikes show a low, nearly flat spectral profile in the VNIR and SWIR wavelength regions and small four absorption features also observed around the 0.65, 1.0, 1.2, and 2.32 μm wavelengths. Data materialized in the paper suggests the usefulness of Landsat-8 and TerraSpec spectroradiometer data as a powerful combination to discriminate the granitic rocks and the traversing basalt dikes as well.

Ga-Doped ZnO Nanostructured Powder for Cool-Nanopigment in Environment Applications.

Gallium (Ga) doped zinc oxide (ZnO) nanocrystals were successfully synthesized via a γ-radiation-assisted polymer-pyrolysis route. Ga doped ZnO samples with Ga and ZnO precursor salts with molar ratios of 0%, 3%, 5%, and 10% were produced. A γ-radiation dosage of 1.5 kGy was used for polymerization initiation during the sample preparation. The properties of the obtained nanocrystal samples were characterized using X-ray diffraction (XRD), Fourier transform infrared (FTIR), UV-visible absorption, NIR-VIS-UV diffused reflectance, and high-resolution transmission electron microscopy (HR-TEM) characterization techniques. XRD results revealed the formation of ZnO nanocrystals with wurtzite structure for both Ga-doped and undoped ZnO samples. Noticeable increasing in the line broadening of the XRD peaks as well as pronounced decreasing of crystallite size were observed with the increasing Ga ratio in the samples. Optical peaks around Ga:ZnO samples showed a blueshift in the optical absorption peaks with increasing Ga content. These results are in good agreement with the dependency of crystallites size as well as grain size on Ga ratio obtained from XRD and TEM images, which make them fit well for the powder cool-pigment applications. The doped samples showed high values of NIR reflectance () with percentage varied from 84.25% to 89.05% that enabled them to qualify for cool-nanopigment applications. Furthermore, such doped samples registered low values of visible reflectance () that enabled to reduce the glare from the reflected visible sunlight.

Reduction of Atmospheric Effects in Satellite Images During the COVID-19 Induced Lockdown

The quality of satellite images is affected due to the scattering and absorption of sunlight by atmospheric molecules and aerosols. Aerosols are small particles suspended in the atmosphere which affects the air quality. The concentration and characteristics of the atmospheric aerosols can vary from place to place. Aerosols are major constituents for the formation of haze and thus responsible for degradation in the satellite images. During the novel corona virus disease pandemic (COVID-19) countrywide lockdown in India, aerosols level significantly lowered in the north Indian cities in the Indo-Gangetic plain. In this paper, an analysis of image quality was done for Sentinel-2A/2B satellite images for different north Indian cities with respect to the impact of aerosols on image sharpness and surface reflectance values during the pre-lockdown and lockdown period. The image quality of the images was evaluated through the power spectrum, gradient, and reflectance values in the image. It was observed that the sharpness of the satellite images increased during the lockdown period due to the reduction in aerosols levels in the atmosphere. There was an increase in the power spectrum values from 5% (minimum) to 12% (maximum) in the blue band, 4% (minimum) to 10% (maximum) in the green band, and 1.7% (minimum) to 6% (maximum) in the red band in the satellite images of major cities in the Indo-Gangetic plain during the lockdown period. Since haze is an additive component in the images, thus it was also observed that surface reflectance values had decreased in visible bands for the features which have low surface reflectance values like water (30%), vegetation (21%) and barren land (17%) and surface reflectance values had increased in visible bands for the features which have high surface reflectance values like building (19%) during the lockdown period.

Low-phase spectral reflectance and equivalent “geometric albedo” of meteorites powders

Generally, the reflectance of a particulate surface depends on the phase angle at which it is observed. This is true for laboratory measurements on powders of natural materials as well as remote observations of Solar System surfaces. Here, we measured the dependences of reflectance spectra with phase angles, of a suite of 72 meteorites in the 400–2600 nm range. The 10–30° phase angle range is investigated in order to study the contribution of Shadow Hiding Opposition Effect (SHOE) to the phase behavior. The behavior is then extrapolated to phase angle of 0° using a polynomial fit, in order to provide grounds for comparison across meteorite groups (enabling to remove the contribution of shadows to reflectance) as well as to provide “equivalent albedo” values that should be comparable to geometric albedo values derived for small bodies. We find a general behavior of increasing strength of the SHOE with lower reflectance values (whether between samples or for a given samples with absorption features). This trend provides a first order way to correct any reflectance spectra of meteorite powders measured under standard conditions (g = 30°) from the contribution of shadows. The g = 0° calculated reflectance and equivalent albedos are then compared to typical values of albedos for main-belt asteroids. This reveals that among carbonaceous chondrites only Tagish Lake group, CI, and CM chondrites have equivalent albedo compatible with C- and D-type asteroids. On the other hand equivalent albedo derived with CO, CR and CK chondrites are compatible with L- and K-type asteroids. The equivalent albedo derived for ordinary chondrites is related to petrographic types, with low-grade petrographic type (type 3.6 and less) being generally darker that higher petrographic types. This works provides a framework for further understanding of the asteroids meteorite linkage in particular when combining with colors and spectroscopy.

Organic geochemical and petrographical characteristics of the lower part of Sarmord Formation, M-2 Well, Miran Oil Field, Kurdistan, NE Iraq: Implications for hydrocarbon generation potential and thermal maturation

The Lower Cretaceous Sarmord Formation (Hauterivian–Barremian) has been investigated in this study. The selected M-2 Well is one of the wells belonging to Miran block, Sulaimani Governorate, Kurdistan Region of Iraq. The area of interest is situated in the High Folded Zone, Western Zagros Fold-Thrust Belt, being approximately 30 km far from Sulaimani City towards the northwest direction. The selected samples were analyzed by Rock-Eval pyrolysis, infrared spectroscopy, and also studied microscopically to determine the quality and quantity of organic matter, the level of thermal maturity, as well as the hydrocarbon generation potentiality. Rock-Eval pyrolysis data show that the total organic carbon for Sarmord Formation is between 0.83 wt.% to 1.55 wt.%, with an average value of 1.27 wt.%. The average and range of S1, S2, and genetic potential (S1+S2) are: 0.76 (0.55–1.09) mg HC/g rock, 0.82 (0.65 – 1.28) mg HC/g rock, and 1.58 (1.21 -2.37) mg HC/g rock, respectively. The average value of pyrolysable carbon (PC) and residual carbon (RC) are of 0.23 wt.% and 1.04 wt.%, respectively. The hydrogen index (HI) is between 47 and 98, with an average value of 66. The obtained data indicate that the Sarmord Formation has a satisfiable range of total organic carbon content, but the organic matter by itself has poor potential to generate hydrocarbons because of low amount of S2, HI, and PC. The Rock-Eval maturity parameters (Tmax and PI ) are undependable in this study. Because they are out of the acceptable range. The cutting samples in this well have been contaminated by solid drilling additives, which were identified during the petrographiocal study by their structure and low reflectance values. The double peaks of S2, solid drilling additives, are affected of disturbing maturity parameters of Rock-Eval data. The petrographic study proved that the samples mostly contain bituminite, which is disseminated predominantly within the clayey particles, with minor amounts of alginite. Additionally, weathered and degraded humic particles are interpreted as content of drilling mud. The kerogen types are mostly of Type II kerogen, because the vitrinite macerals are absent and we have an indication of alginite; which is one of precursos of formation of bituminite. This result is controversial with the graphical presentation of kerogen type by Rock-Eval and infrared microscopy, as they are interpreted as Type III gas-prone kerogen. The equivalent vitrinite reflectance for the studied section ranges between 0.73-0.81%, with the values close to 0.80% being more accurate as were measured in homogenous solid bitumens. The obtained values indicate maturation within the oil window. While based on infra red spectroscopy, maturation is between 0.80 to 1.10, suggesting to higher maturation level compared to vitrinite reflectance values.

Impact of Se doping on optical and third-order nonlinear optical properties of spray pyrolysis fabricated CdS thin films for optoelectronics

Cadmium sulphide is known to have tremendous applications towards optoelectronic and nonlinear devices. Hence, here we have facilely casted the CdS films with diverse Se contents through low-cost spray pyrolysis technique. XRD study defends mono-phase formation of CdS having hexagonal system at all Se doping contents. Scherrer equation was employed to evaluate crystallite size in range of 15–25 nm. Vibrational study reveals the presence of fundamental modes of vibration of hexagonal CdS. EDX and SEM mapping studies approve the existence of Se and its homogeneous distribution all over the film. SEM micrographs shows the nanoscale grains formation on film surface and the size is increasing with Se doping. Optical study revealed that the grown films are of optimal quality with transparency in range of 60–75% with low absorbance and reflectance values. The refractive index values are noted to varied from 1 to 2.7 with wavelength and noticed to be reduced on Se content in UV–Vis region. The reduction in direct and indirect energy gap was found from 2.46 to 2.34 eV and 2.21 to 1.96 eV, correspondingly due to Se. PL emission profile contains an emission band at 528, 529, 529, 530 and 546 nm for 0.0, 0.5, 1.0, 2.5, 5.0 wt% Se:CdS films. Dielectric constant and loss were estimated. The nonlinear refraction (n2) and absorption coefficient (β) and third-order nonlinear susceptibility $$(\chi^{3} )$$ values were determined using Z-scan and observed in order of 10–8 cm2/W, 10–4 cm/W and 10–3 esu, correspondingly. The high values of $$\chi^{3}$$ propose the films for nonlinear applications.

Assessing the Effects of Microphysical Scheme on Convective and Stratiform Characteristics in a Mei-Yu Rainfall Combining WRF Simulation and Field Campaign Observations

Microphysics parameterization becomes increasingly important as the model grid spacing increases toward convection-resolving scales. Using observations from a field campaign for Mei-Yu rainfall in China, four bulk cloud microphysics schemes in the Weather Research and Forecasting (WRF) model were evaluated with respect to their ability to simulate precipitation, structure, and cloud microphysical properties over convective and stratiform regimes. These are the Thompson (THOM), Morrison graupel/hail (MOR_G/H), Stony Brook University (SBU_YLIN), and WRF double-moment six-class microphysics graupel/hail (WDM6_G/H). All schemes were able to predict the rain band but underestimated the total precipitation by 23%–35%. This is mainly attributed to the underestimation of stratiform precipitation and overestimation of convective rain. For the vertical distribution of radar reflectivity, many problems remain, such as lower reflectivity values aloft in both convective and stratiform regions and higher reflectivity values at middle level. Each bulk scheme has its advantages and shortcomings for different cloud regimes. Overall, the discrepancies between model output and observations mostly exist in the midlevel to upper level, which results from the inability of the model to accurately represent the particle size distribution, ice processes, and storm dynamics. Further observations from major field campaigns and more detailed evaluation are still necessary.

Relations between optical properties, dinoflagellates and zooplanktonic crustaceans in Antofagasta Bay (23°S, Chile)

Abstract Antofagasta Bay is characterized by a high primary productivity due to the presence of the cold Humboldt Stream that is associated with a high diversity in flora and fauna in the benthic and pelagial environments of the Chilean west coast. Nevertheless, due to the global climate changes, the existing biodiversity patterns change as well. The aim of the present study was to analyse Antofagasta Bay for determining the existence of patterns between optical properties of the water, and the phytoplankton and zooplankton. The results show that one site had high chlorophyll concentrations, high reflectance, a high abundance of the dinoflagellate genus Dinophysis, and a high abundance of copepodites, whereas five sites had low chlorophyll concentrations, a low reflectance value, low copepodite abundances, and high abundances of dinoflagellates of the genera Ceratium, Gymnodinium and Prorocentrum. These results are similar to earlier observations for the coastal waters along northern Chile.

Potential of active multispectral lidar for detecting low reflectance targets.

The calibration and sampling of the multispectral Light Detection and Ranging (lidar) intensity is still challenging because the data acquisition has to be optimized for simultaneous 3D measurement, and the intensity retrieval methods need to be fast to enable real-time detection. We have studied the spectral measurement of low reflectance targets with an 8-channel hyperspectral lidar with improved waveform sampling and sensitivity, which now allow the detection of spectral differences even at low reflectance values. Our initial analysis resulted in a classification accuracy greater than 80%, which indicates that the multispectral lidar is able to detect the small differences in target spectral properties when reflectance at two or more channels is compared at the same time.

Optical, structural, morphological, and compositional properties of cobalt doped tin oxide (CTO) thin films deposited by modified chemical bath method in alkaline medium

Tin oxide and cobalt doped tin oxide (CTO) thin films were successfully deposited using modified chemical bath method with tin (II) chloride dihydrate and cobalt chloride hexahydrate as precursors for Sn and Co ions respectively, in the presence of ammonium hydroxide as source of oxygen and pH adjuster. The samples obtained were annealed for 4 h at a temperature of 673 K and characterized for optical, structural, morphological and compositional analysis. The films exhibit low absorbance values (0.02–0.31) and low reflectance values (2.14%–20.10%) which varies directly with cobalt ion (Co2+) concentration. The transmittance values (48.64%–96.16%) of the films are high and varies inversely with cobalt ion (Co2+) concentration. The refractive index varies directly with increasing cobalt ion concentration and ranges from 2.60 to 1.49 for doped film and 1.34 for the undoped SnO2. Extinction coefficient of the films varies directly with cobalt ion concentration. The films have wide band gap, (2.90 eV–2.72 eV for doped films and 3.05 eV for undoped SnO2 thin film). Structural analysis revealed that the films are of tetragonal rutile phase of SnO2 with mineral name of cassiterite and confirmed that the grain sizes of the deposited films range from 10.99 nm to 9.40 nm. The dislocation density ranged between 8.28×10−3(line/nm2) and 11.32×10−3(line/nm2) while the microstrain obtained ranged between 6.07×10−3 to 12.03×10−3. The compositional results revealed the presence of the Sn, Co, O2 and some traces of other elements. The SEM images obtained show uniform surface without any voids or flaws. The micrographs show that the surfaces are composed of particles of slightly different sizes.

Ground albedo impacts on higher-order scattering spectral radiances of night sky

The contribution from ground reflected light to the night sky radiance is of increased interest because of constant modernization of street lighting systems that now efficiently eliminate light emissions above the horizontal plane, so the appreciable fraction of artificial light directed upwards is from ground reflection. Diffuse light of a night sky shows a positive correlation with ground albedo (α), but it seems there is no linear trend between α and the night sky brightness (NSB), at least not for all sky elements, and, the mechanism of this relationship becomes even more complicated due to multiple scattering effects. The extent to which the ground reflectance influences the higher-order scattering radiance of night sky, and, the factors that initiate the crossover from single- to multiple-scattering dominance of the sky glow has been virtually unexplored until now.We demonstrate here that albedo-induced effects in NSB exhibit an angular dependence, with amplitudes enhanced towards shorter wavelengths. For low values of ground reflectance and at short distances from a light source, the second-scattering radiance is found to be only a few percent of the first-order scattering radiance. However, the ratio of a higher- to the first-order scattering radiance gradually increases near horizon, specifically at the side opposite to the azimuthal position of the light source. Also the NSB in blue band has decreasing gradation tendency when increasing the altitude above sea level. The findings in this paper are significant in a proper incorporation of higher-order scattering in modeling the NSB under elevated reflectance conditions, and may be critical for saving computational time.

Evaluation of anti-soiling coatings for CSP reflectors under realistic outdoor conditions

Soiling of solar reflectors affects their reflectance and has a direct impact on the power output of concentrated solar power (CSP) plants. One way to minimize the efficiency losses is the implementation of anti-soiling coatings on the reflector surfaces. This method is being studied for the past decade, but has not been successfully commercialized yet. The purpose of the coatings is to reduce soiling and improve the washability of the reflectors. In this work results are presented from an extensive outdoor campaign of two potential anti-soiling coatings under realistic conditions at a representative CSP site in southern Spain. Nearly six years of outdoor data are available, which makes this campaign the longest published on this type of coatings. Regular cleaning and reflectance measurements were performed during the exposure and conclusions about the performance and durability of the coatings are drawn. It is shown that in the initial state the coatings show an advantageous behavior, resulting in higher reflectance during outdoor exposure due to less soiling and better cleaning of the reflectors. The second main finding is that durability is an important issue for the implemented coatings, as their properties degrade over time resulting in lower reflectance values after several years of exposure compared to conventional glass reflectors.

Functional sol-gel coated electrospun polyamide 6,6/ZnO composite nanofibers

Abstract Polymer-based nanofibers are good candidates for medical textiles due to their excellent properties including high surface area, breathability and flexibility. Doping polymer nanofibers with different nanoparticles enhances their existing properties. In this study, electrospun polyamide 6,6 (PA6,6) composite nanofibers containing ZnO nanoparticles (<50 nm) in different amounts (1%, 3% and 5%) were first produced by electrospinning technique; then, these nanofibers were coated with sol-gel ZnO solution (0.5 m) via dip coating method at 1000, 3000 and 5000 μm/s speeds. The sol-gel coating process increased the breaking strength of nanofiber mats, while the incorporation of ZnO nanoparticles into the polymer nanofibers reduced. Compared to pure PA6,6 nanofiber mats, the ZnO sol-gel coated samples and doped nanofibers had lower reflectance values. In addition, the reflection values decreased as the additive and coating speed increased.