Light Region Research Articles

Hyperspectral estimation of chlorophyll density in winter wheat using fractional-order derivative combined with machine learning

Chlorophyll density (ChD) can reflect the photosynthetic capacity of the winter wheat population, therefore achieving real-time non-destructive monitoring of ChD in winter wheat is of great significance for evaluating the growth status of winter wheat. Derivative preprocessing has a wide range of applications in the hyperspectral monitoring of winter wheat chlorophyll. In order to research the role of fractional-order derivative (FOD) in the hyperspectral monitoring model of ChD, this study based on an irrigation experiment of winter wheat to obtain ChD and canopy hyperspectral reflectance. The original spectral reflectance curves were preprocessed using 3 FOD methods: Grünwald-Letnikov (GL), Riemann-Liouville (RL), and Caputo. Hyperspectral monitoring models for winter wheat ChD were constructed using 8 machine learning algorithms, including partial least squares regression, support vector regression, multi-layer perceptron regression, random forest regression, extra-trees regression (ETsR), decision tree regression, K-nearest neighbors regression, and gaussian process regression, based on the full spectrum band and the band selected by competitive adaptive reweighted sampling (CARS). The main results were as follows: For the 3 types of FOD, GL-FOD was suitable for analyzing the change process of the original spectral curve towards the integer-order derivative spectral curve. RL-FOD was suitable for constructing the hyperspectral monitoring model of winter wheat ChD. Caputo-FOD was not suitable for hyperspectral research due to its insensitivity to changes in order. The 3 FOD calculation methods could all improve the correlation between the original spectral curve and Log(ChD) to varying degrees, but only the GL method and RL method could observe the change process of correlation with order changes, and the shorter the wavelength, the smaller the order, and the higher the correlation. The bands screened by CARS were distributed throughout the entire spectral range, but there was a relatively concentrated distribution in the visible light region. Among all models, CARS was used to screen bands based on the 0.3-order RL-FOD spectrum, and the model constructed using ETsR reached the best accuracy and stability. Its R2c, RMSEc, R2v, RMSEv, and RPD were 1.0000, 0.0000, 0.8667, 0.1732, and 2.6660, respectively. In conclusion, based on the winter wheat ChD data set and the corresponding canopy hyperspectral data set, combined with 3 FOD calculation methods, 1 band screening method, and 8 modeling algorithms, this study constructed hyperspectral monitoring models for winter wheat ChD. The results showed that based on the 0.3-order RL-FOD, combined with the CARS screening band, ETsR modeling has the highest accuracy, and hyperspectral estimation of winter wheat ChD can be realized. The results of this study can provide some reference for the rapid and nondestructive estimation of ChD in winter wheat.

Polymerized Small‐Molecule Acceptors with Linker Length‐Dependent Photocatalytic Activity for High‐Performance Solar Hydrogen Evolution

AbstractDeveloping organic semiconductor photocatalysts with alterable optical properties and excitonic behaviors for photocatalytic hydrogen evolution has received significant attention recently. Herein, three polymerized small‐molecule acceptors (PSMAs) with different linker lengths, namely PY‐1T, PY‐2T and PY‐3T, are designed and synthesized to construct nano‐photocatalysts. In comparison with small‐molecule YDT, these PSMAs exhibit broader absorption in both visible and near‐infrared (NIR) light region as well as enlarged exciton diffusion length. In the meanwhile, the intramolecular charge transfer and separation in PSMAs is promoted by varying the linker length, leading to enhanced light harvesting and charge utilization. As a result, the single‐component nano‐photocatalyst based on PY‐3T achieves an impressive average hydrogen evolution rate (HER) of 400.3 mmol h−1 g−1 under AM 1.5G sunlight (100 mW cm−2), which is ≈48 times greater than that of YDT NPs (8.3 mmol g−1 h−1). These results not only prove the potential that developing polymerized small‐molecule acceptors with extended chain length as efficient photocatalysts, but also elucidate the importance of regulating linker length in designing high‐performance photocatalysts.

Distribution Characteristic and Environment Response of DOM in Different Regions of Northern City

To explore the source information and composition characteristics of dissolved organic matter （DOM） in different regions of water bodies in northern cities, considering the urban water system of Shijiazhuang, Hebei Province as an example, ultraviolet-visible spectroscopy （UV-vis） and three-dimensional fluorescence parallel factor analysis （EEM-PARAFAC） were used to explain the optical parameters, abundance, and proportion of different components of DOM in water bodies of different regions. The results showed that： ① The concentrations of NO3--N, NO2--N, NH4+-N, TN, TP, and COD in the upstream were significantly lower than those in urban water bodies and downstream （P<0.01）, and TSIM increased after the water entered the city. ② The ultraviolet parameter a254 indicated that the concentration of DOM significantly increased after entering the city （P<0.001）. E2/E3 showed that the relative molecular weight of DOM in different regions was： upstream<urban water<downstream, and the SR of DOM in different regions was >1, indicating that the main source of DOM was endogenous input. ③ Three fluorescent components were identified, namely C1 （visible light region fulvic acid）, C2 （tryptophan）, and C3 （long wave humic substance）. The upstream and urban water bodies were mainly composed of protein-like components （C2）, while the downstream humic substances （C1+C3） accounted for a relatively high proportion （80.1%）. The PCA analysis showed significant spatial distribution differences. According to the results, SR>1, FI>1.8, and HIX<4 indicated that DOM exhibited low humification and strong autogenesis in different regions. ④ A significant correlation （P<0.01） was observed between C1 and C3 in the upstream and downstream. C1, C2, and C3 in urban water bodies were all significantly correlated （P<0.01）. In addition, C1 and C3 posed a significant correlation with NO3--N in different regional water bodies. RDA indicated that NO2--N, TDN, TDP, and COD were the main environmental driving factors for DOM distributions. In summary, the multiple pressures of the city exhibited a significant influence on the spectral properties of DOM in the flowing water system.

Characterization of structure and photoluminescence properties for LiZn(B1-xAlx)O3 (x=0-1) oxides

LiZn(B1-xAlx)O3 (x=0-1) oxide was prepared by calcining at 750 ℃ for 5h using a solid-state reaction method. Due to the difference in the ionic radii of B3+ and Al3+ ions, the lattice is distorted, and a bi-phase composed of ZnO and γ-LiAlO2 oxides are formed for x=1. As the Al3+ ion doping contents increasing, the bi-phase oxide powder particles transform from agglomerated irregular to flaky structure. Under an excitation wavelength of 367nm, two broad luminescence bands located at blue and yellow-green light regions are observed. The CIE chromaticity coordinates are located in the light blue light region for LiZnBO3, whereas the CIE coordinates are located in the white light region (x=0.33, y=0.34) for the bi-phase oxides, and it is quite close to the NTSC standard white light coordinates (x=0.33, y=0.33).

Characterization of Small Molecule-Based Organic Photodetectors for Non-Fullerene Bulk Heterojunction with Strong Response in the Visible Light Region

Characterization of Small Molecule-Based Organic Photodetectors for Non-Fullerene Bulk Heterojunction with Strong Response in the Visible Light Region

Enhanced Light Response Performance of Ceria-Based Composites with Rich Oxygen Vacancy.

Increasing the concentration of oxygen vacancies in ceria-based materials to solve the bottleneck of their applications in various fields has always been a research hotspot. In this paper, ceria-based cerium-oxygen-sulfur (Ce-O-S) composites that were composed of CeO2, Ce4O4S3, and Ce2(SO4)3 were synthesized by a precipitation method. The compositional, structural, morphological, and light response characteristics of prepared Ce-O-S composites were investigated by various characterization techniques. The molar ratio of oxygen vacancies to lattice oxygen can reach a maximum of 1.83 with Ce-O-S composites. The band gap values of the Ce-O-S composites were less than 3.00 eV, and the minimum value was 2.89 eV (at pH 12), which successfully extended the light response range from the ultraviolet light region to the short-wave blue light region. The remarkable light response performance of Ce-O-S composites can be mainly attributed to the high proportion of oxygen vacancy. Moreover, the higher proportion of oxygen vacancies can be attributed to the doping of Ce (+3) and S (-2) in the lattice of CeO2, and the synergistic effect of CeO2, Ce4O4S3, and Ce2(SO4)3. Moreover, the ceria-based Ce-O-S composites with rich oxygen vacancy in this research can be applied in light blocking, photocatalysis, and other related fields.

Phosphorus Doping Effects on the Optoelectronic Properties of K₂AgAsBr₆ Double Perovskites for Photovoltaic Applications

This work explores the modifications of optoelectronic properties in K₂AgAsBr₆ double perovskites induced by phosphorus doping. First-principles calculations using the CASTEP code with the PBE functional were carried out based on density functional theory (DFT). Our research investigates the electronic structure and optical behavior of the cubic Fm-3m phase of K₂AgAsBr₆, K₂AgAs₀.₈P₀.₂Br₆, and K₂AgAs₀.₆P₀.₄Br₆ to elucidate the impact of progressive phosphorus (P) substitution. P was chosen for its potential to modify the electronic structure due to its smaller atomic radius and different valence orbital energies compared to As. Our results reveal a systematic narrowing of the band gap with increasing P content, from 0.749 eV for the undoped compound to 0.587 eV for K₂AgAs₀.₈P₀.₂Br₆ and 0.424 eV for K₂AgAs₀.₆P₀.₄Br₆. This trend is attributed to the upward shift of the valence band maximum due to the higher energy of P 3p orbitals compared to As 4p orbitals. Analysis of the density of states confirms increased hybridization between P-p and As-p states at the valence band edge. Optical properties, including absorption coefficient, dielectric function, refractive index, and extinction coefficient, demonstrate a consistent red-shift and broadening of spectral features with P doping. Notably, P-substituted compounds exhibit enhanced absorption in the visible light region, with up to a 20% increase in the absorption coefficient at 550 nm for K₂AgAs₀.₆P₀.₄Br₆ compared to the undoped compound. This study reveals that elemental substitution offers a viable route to tailor optical and electronic properties of double perovskites, paving the way for the design of novel materials for next-generation photovoltaic and photoelectric devices.

Conjugated Polyvinyl Alcohol Modified SnO2 for Efficient Visible Light Photocatalytic Reduction of Cr(VI)

The photocatalytic activity of tin dioxide (SnO2) is limited due to its inadequate response to the solar spectrum, wide band gap, and low visible light photocatalytic activity. Here, we synthesized conjugated polyvinyl alcohol (CPVA) modified tin dioxide (CPVA/SnO2) through in-situ hydrothermal synthesis and evaluated its performance for photocatalytic reduction of hexavalent chromium Cr(VI). A series of testing and characterization results revealed that CPVA was uniformly coated on the surface of SnO2, forming a mesoporous CPVA/SnO2 heterojunction with enhanced crystallinity and reduced oxygen defects, which resulted in an expanded light absorption range towards the red light region. The reaction rate constant of CPVA/SnO2-A for photocatalytic reduction of Cr(VI) under visible light (0.060 min-1) was 6 times higher than that of homemade CPVA/TiO2 and 2.87 times higher than that of SnO2 for the photocatalytic reduction of Cr(VI) under UV light (0.0209 min-1). The photocatalytic mechanism indicates that CPVA/SnO2 exhibited significantly enhanced performance under UV-light irradiation by forming a type II heterojunction. When CPVA/SnO2 was exposed to visible light, photogenerated electrons on the lowest unoccupied molecular orbital (LUMO) of CPVA were efficiently transferred to the surface of SnO2 through the CPVA/SnO2 heterojunction, reducing electron-hole recombination while also photosensitizing the photocatalyst and promoting efficient photocatalysis under visible light illumination. Ultimately, this process effectively reduces Cr(VI) to Cr(III). Copyright © 2024 by Authors, Published by BCREC Publishing Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Effect of Bias Voltage on the Microstructure and Photoelectric Properties of W-Doped ZnO Films.

W-doped ZnO (WZO) films were deposited on glass substrates by using RF magnetron sputtering at different substrate bias voltages, and the relationships between microstructure and optical and electrical properties were investigated. The results revealed that the deposition rate of WZO films first decreased from 8.8 to 7.1 nm/min, and then increased to 11.5 nm/min with the increase in bias voltage. After applying a bias voltage to the substrate, the bombardment effect of sputtered ions was enhanced, and the films transformed from a smooth surface into a compact and rough surface. All the films exhibited a hexagonal wurtzite structure with a strong (002) preferred orientation and grew along the c-axis direction. When the bias voltage increased, both the residual stress and lattice parameter of the films gradually increased, and the maximum grain size of 43.4 nm was achieved at -100 V. When the bias voltage was below -300 V, all the films exhibited a high average transmittance of ~90% in the visible light region. As the bias voltage increased, the sheet resistance and resistivity of the films initially decreased and then gradually increased. The highest FOM of 5.8 × 10-4 Ω-1 was achieved at -100 V, possessing the best comprehensive photoelectric properties.

Determination of Three Metal Ions (Cu2+, Pb2+, Cd2+) by Ultraviolet-visible Spectroscopy

Abstract The objective of this article review is the determination of the concentration or amount of trace metal ions using Ultraviolet-visible spectrophotometry. The maximum absorption wavelength (λ-max) of the three metallic ions (Cu+2, Pb+2, and Cd+2) that I have highlighted are equivalent to (755 nm, 100-380 nm, and 323.9 nm) when they are alone, However, when these metal ions interact with a reagent, the λ-max of each metal ion differs. Ultraviolet-visible (UV-Vis) spectrophotometry is deemed an efficient method for both qualitative and quantitative analysis of pollutants in a water environment. This succinct statement outlines the focus of the article review, emphasizing the application of UV-Vis spectrophotometry for analyzing trace metal ions in water samples. Also, the analytical technique measures the amount of single-color lighting absorbed via a colorless substance in the close ultraviolet light region of a range (between 200 and 400 nm). The process required to ascertain the “identity, strength, quality and purity” of such chemicals is included in the pharmaceutical analysis. Using calibration curves and absorption band correlation with certain ions to find concentration metal ion or analyte in the sample. A bibliometric analysis classifies the top 10,000 cited UV-Vis papers (2016-2017) into four clusters: nanoparticles, photocatalysis, crystals, and biological interaction of Ag and Au nanoparticles.

Self-assembly of ZnO-Biochar/Kaolinite/Chitosan/GO with 1D/2D/3D heterojunctions for enhanced removal of estrogens and triclosan in water

This Study focuses on the preparation of sustainable and efficient Chitosan catalyst for the removal of three organic pollutants, 17β-Estradiol (E2), 17α-ethynyl estradiol (EE2) and triclosan (TCS) from water. The prepared nanocomposites were characterized by different techniques which confirmed the presence of the key components Chitosan, Carica Papaya seed and Kaolinite. The optical characterization proved the nanocomposite is photoactive with a band gap of 1.81 eV and 1.77 eV for Chitosan/kaolinite biochar (CS/KBC) and Chitosan/kaolinite biochar/GO (CS/KBC/GO) respectively, confirming the ability of the nanocomposite to be active in the visible light region of the spectrum. The degradation experiment using CS/KBC/GO was observed better with 100% removal for 5 mg/L E2 and EE2 over 60 min and 97.8% over 120 min for 10 mg/L TCS at optimum conditions (pH 3 for E2, and EE2 and pH 7). It was observed that the superoxide radical played a major role in the degradation of the contaminants. Furthermore, the CS/KBC/GO was efficient over four cycles without any decrease in performance, which rules out the question of catalyst deactivation proving the sustainability of the catalyst. The toxicity test shows that the water is safe as it does not harm cerio daphnia silvestrii organism.; CS/KBC/GO efficiently removed the micropollutants from real-life waste samples and the performance was very good with a slight decrease in performance for the wastewater due to the complex matrix of the water sample that competes for the active site.

Large π‐Conjugated Structure Strategy for Optimizing Polyimide Film‐Forming Properties and Developing Gas Fluorescence Sensors

ABSTRACTFour different amounts of anthracene groups were introduced into the polyimide (PI) backbone by one‐step polycondensation. This bulky and rigid polycyclic aromatic hydrocarbon structure effectively improved the solubility of the polyimide material. Therefore, the anthracene‐containing polyimides (ANPIs) were easily cast into the films at room temperature. The introduction of anthracene chromophores significantly developed the fluorescence performance of polyimides. It was found that the photoluminescence emission band of ANPIs migrated from the blue to the orange light region as the samples changed from solution to film. This is related to the aggregation of molecular chains in a solid state. Furthermore, ethanol and phenylethanol were selected to investigate the fluorescence response of the ANPI film. Interestingly, the sample displayed a noticeable luminescent “turn‐off” effect on the targets. It could be considered a convenient strategy for the detection of organic gases.

The Electronic Structure, Optical and Magnetic Properties of Cu, Fe, Mn, Ni, and V Doped Bi2WO6 in the Visible Light Region

Abstract The elastic and mechanical properties of intrinsic Bi2WO6 semiconductors, along with the electronic, optical, and magnetic properties of Cu-, Fe-, Mn-, Ni-, and V-doped Bi2WO6 at a uniform doping concentration of 6.25%, are studied using density functional theory (GGA+U). The study shows that intrinsic Bi2WO6 semiconductors exhibit good mechanical stability, anisotropy, and mixed ionic-covalent characteristics (Poisson's ratio ν = 0.17), classifying them as brittle oxide materials (B/G ≈ 0.8). Compared to intrinsic Bi2WO6, the doped Bi2WO6 exhibits a narrower bandgap, a broader absorption spectrum, and higher optical sensitivity. Their optical properties in the visible light range surpass those of intrinsic Bi2WO6, making them more promising for use as semiconductor catalysts. Notably, Cu- and V-doped Bi2WO6 exhibit higher absorption coefficients in the visible light region compared to other element-doped Bi2WO6, with a broader absorption spectrum and more pronounced photocatalytic effects. Furthermore, Cu-, Fe-, Mn-, Ni-, and V-doped Bi2WO6materials exhibit characteristics of diluted magnetic semiconductors, The total magnetic moments are 1.793 μB (Bi1.9375Cu0.0625WO6), 3.086 μB (Bi1.9375Fe0.0625WO6), 3.823 μB (Bi1.9375Mn0.0625WO6), 1.257 μB (Bi1.9375Ni0.0625WO6), and 1.859 μB (Bi1.9375V0.0625WO6). Bi1.9375Mn0.0625WO6 exhibits ferromagnetic ordering, while Bi1.9375Cu0.0625WO6, Bi1.9375Fe0.0625WO6, Bi1.9375Ni0.0625WO6, and Bi1.9375V0.0625WO6 exhibit Ferrimagnetic ordering. Compared to other element-doped Bi2WO6, Bi1.9375Mn0.0625WO6 shows a larger energy difference between the FM and NM ordering states(ΔE = 18.510 eV), demonstrating stronger magnetic ordering than Cu-, Fe-, Ni-, and V-doped Bi2WO6，and these materials hold potential for application in electronic spin-polarized devices.

Widespread distribution of chlorophyll f-producing Leptodesmis cyanobacteria.

Chlorophyll (Chl) f was reported as the fifth Chl in oxygenic photoautotrophs. Chlorophyll f production expanded the utilization of photosynthetically active radiation into the far-red light (FR) region in some cyanobacterial genera. In this study, 11 filamentous cyanobacterial strains were isolated from FR-enriched habitats, including hydrophyte, moss, shady stone, shallow ditch, and microbial mat across Central and Southern China. Polyphasic analysis classified them into the same genus of Leptodesmis and further recognized them as four new species, including Leptodesmis atroviridis sp. nov., Leptodesmis fuscus sp. nov., Leptodesmis olivacea sp. nov., and Leptodesmis undulata sp. nov. These cyanobacteria had absorption peaks beyond 700 nm due to Chl f production and red-shifted phycobiliprotein complexes under FR conditions. All but L. undulata produced phycoerythrin and showed varying degrees of a reddish-brown to dark green color under white light conditions. However, the phycoerythrin contents were sharply decreased under FR conditions, and these three Leptodesmis species appeared green. In summary, the Leptodesmis genus contains diverse species with the capacity to synthesize Chl f and is likely a ubiquitous group of Chl f-producing cyanobacteria.

Modifications and Applications of Metal-Organic-Framework-Based Materials for Photocatalysis.

Metal-organic frameworks (MOFs) represent a category of crystalline materials formed by the combination of metal ions or clusters with organic linkers, which have emerged as a prominent research focus in the field of photocatalysis. Owing to their distinctive characteristics, including structural diversity and configurations, significant porosity, and an extensive specific surface area, they provide a flexible foundation for various potential applications in photocatalysis. In recent years, researchers have tackled many issues in the MOF-based photocatalytic yield. However, limited light adsorption regions, lack of active sites and active species, and insufficient efficiency of photogenerated charge carrier separation substantially hinder the photocatalytic performance. In this review, we summarized the strategies to improve the photocatalytic performance and recent developments achieved in MOF and MOF-based photocatalysis, including water splitting, CO2 conversion, photocatalytic degradation of pollutants, and photocatalytic nitrogen fixation into ammonia. In conclusion, the existing challenges and prospective advancements in MOF-based photocatalysis are also discussed.

High-Stretchable and Transparent Ultraviolet-Curable Elastomer

This work introduces an ultraviolet (UV)-curable elastomer through the co-polymerization of aliphatic polyurethane acrylate and hydroxypropyl acrylate via UV irradiation. The UV-curable elastomer presents superior mechanical properties (elongation at a break of 2992%) and high transparency (94.8% at 550 nm in the visible light region). A robust hydrogel–elastomer stretchable sensor is fabricated by coating an ionic hydrogel on the surface of an elastomer, which enables real-time monitoring of human motion. In addition, the UV-curable elastomer can be used for 3D printing, as demonstrated by complex lattice structures using a digital light processing 3D printer.

The Study of Tunable Excitation Independent and Dependent Photoluminescence Behaviour of P-Functionalized Carbon Dots

In this article, excitation independent and dependent fluorescence properties of surface functionalized carbon dots were studied. The samples were synthesized using a biomass derived Indian gooseberry as carbon precursor via microwave irradiation technique. Concentrated phosphonic acid is utilized as a surface passivator for carbon dots. The formation of spherical carbon dots in the size range of 6 to 12 nm was shown by transmission electron microscopy images. Raman and Fourier transform IR spectroscopies suggest the creation of highly disordered sp3carbon atoms including presence of surface functional groups and interaction of phosphorus with surface of carbon core. From the UV-visible absorption study, absorbance bands at 231 nm and 283 nm attributed to π-π* molecular transitions from carbon core are found. From the photoluminescence measurements, both excitation independent and excitation dependent tunable fluorescence is obtained from ultraviolet to visible (yellow) region of light respectively. The involvement of carbon core electronic states and surface modifier states are responsible for the origin of luminescence and their distinguished nature. The mechanism is discussed and emitted colour are confirmed by CIE plot. The relative quantum yield of the P-functionalized carbon dots is found to be 18.9% with reference to quinine sulfate. The fluorescence in ultra-violet and visible regions is applicable for bioimaging and potential antimicrobial activities.

Mobility Prediction Algorithms for Handover Management in Heterogeneous LiFi and RF Networks: An Ensemble Approach

Light Fidelity (LiFi) is a communication technology that operates in the Visible Light (VL) region, using light as a medium to enable ultra-high-speed communication. The spectrum occupied by LiFi does not overlap with the Radio Frequency (RF) spectrum. Thus, they can be used in a hybrid manner to enhance the Quality of Service (QoS) for users. However, in a heterogeneous LiFi and RF network, users experience constant handovers due to the small coverage area of the LiFi and their frequent movement. This study proposes an intelligent handover scheme, where the network parameters of the users are used to train four machine learning models, namely an Artificial Neural Network (ANN), an Adaptive Neurofuzzy Inference System (ANFIS), a Support Vector Machine (SVM), and a Regression Tree (RT), to predict the mobility of the users, so that the central network can have a priori mobility information to ensure seamless connectivity. Furthermore, the performance of the standalone models was enhanced by integrating ensemble learning techniques such as the Simple Averaging Ensemble (SAE), Weighted Averaging Ensemble (WAE), and a Meta-Learning Ensemble (MLE). The results show that the ensemble algorithms improved prediction performance, with an average error decrease of 44.40%, 53.53%, and 61.03% for SAE, WAE, and MLE, respectively, which further demonstrated the effectiveness and robustness of using ensemble algorithms to predict user mobility.

Adaptation to visual sparsity enhances responses to isolated stimuli.

Sensory systems adapt their response properties to the statistics of their inputs. For instance, visual systems adapt to low-order statistics like mean and variance to encode stimuli efficiently or to facilitate specific downstream computations. However, it remains unclear how other statistical features affect sensory adaptation. Here, we explore how Drosophila's visual motion circuits adapt to stimulus sparsity, a measure of the signal's intermittency not captured by low-order statistics alone. Early visual neurons in both ON and OFF pathways alter their responses dramatically with stimulus sparsity, responding positively to both light and dark sparse stimuli but linearly to dense stimuli. These changes extend to downstream ON and OFF direction-selective neurons, which are activated by sparse stimuli of both polarities but respond with opposite signs to light and dark regions of dense stimuli. Thus, sparse stimuli activate both ON and OFF pathways, recruiting a larger fraction of the circuit and potentially enhancing the salience of isolated stimuli. Overall, our results reveal visual response properties that increase the fraction of the circuit responding to sparse, isolated stimuli.

Synthesis of silver-decorated titanium dioxide nanostructured films for enhanced visible light photocatalysis

Titanium dioxide (TiO2) has been extensively investigated for applications in photocatalysis due to its stability, nontoxicity, and robust photocatalytic properties. Although thin films of TiO2 are effective in wastewater treatment, their dense structure limits surface accessibility. The oblique angle deposition (OAD) technique can be used to create high surface area nanostructured thin films essential for photocatalytic applications. In this study, OAD was used to grow TiO2 thin films. To extend the activity to the visible light region, plasma-reduced silver (Ag) particles were coupled to the TiO2 surface. The Ag-decorated TiO2 (Ag-TiO2) nanostructured films were fabricated using a custom-built magnetron sputter deposition system with OAD technique capability. Different substrate angles of 0°, 35°, and 70° with respect to the target normal were used. The films were characterized for their structural, compositional, and optical properties. The photodegradation performance was evaluated using methylene blue (MB) as the test analyte under visible light irradiation. The results showed a significant improvement in degradation efficiency using plasma-reduced Ag-TiO2. Substrates tilted at 70° achieved the highest MB degradation efficiency of 89.84% after 5 h exposure. This tilt angle also revealed high surface roughness and high surface area. By tilting the substrate with respect to the target, high surface area thin films can be fabricated. This technique is ideal for applications that depend on the area of contact, such as photocatalysis.