Search Results (4,705)

Accurate bathymetric information is crucial for coastal management, navigation, and ecosystem monitoring, yet conventional hydrographic surveys are costly and logistically demanding. This study introduces a two-stage semiempirical model for satellite-derived bathymetry (SDB) based on log-ratio reflectance indices from atmospherically corrected Landsat 8 imagery. The approach combines the optical sensitivity of the green/blue band ratio and the attenuation properties of the red/blue ratio within a parametric regression framework, enhancing both stability and interpretability. The methodology was evaluated in two contrasting coastal environments: the turbid Magdalena-Almejas Lagoon System (Mexico) and the clear-water coral reef setting of Buck Island (U.S. Virgin Islands). Results demonstrated that the proposed model outperformed traditional semiempirical approaches (Lyzenga, Stumpf, Hashim), achieving $R^2=0.8155$ (RMSE = 1.16 m) in Magdalena-Almejas and $R^2=0.9157$ (RMSE = 1.38 m) in Buck Island. Performance was statistically superior to benchmark methods according to cross-validated confidence intervals and was comparable to an artificial neural network, while avoiding overfitting in data-scarce environments. These findings highlight the model’s suitability as a transparent, cost-efficient, and scalable alternative for SDB, particularly valuable in regions where in situ data are limited. Full article

Background: Retinal microvascular changes may serve as biomarkers for disease activity in multiple sclerosis (MS). This study evaluated macular and peripapillary vascular plexus densities using optical coherence tomography angiography (OCTA) in patients with relapsing MS (RMS) and healthy controls (HCs), exploring their association with disease activity based on the NEDA-3 concept. Methods: In a cross-sectional study, 117 RMS patients and 37 HCs underwent OCTA imaging. Parameters analyzed included superficial vascular plexus (SVP), deep vascular plexus (DVP), foveal avascular zone (FAZ), and radial peripapillary capillary (RPC) density. Images with artifacts were excluded. Associations between OCTA metrics and demographic, clinical, and MRI volumetrics, as well as NEDA-3 status, were evaluated using multivariate generalized estimating equations. Receiver operating characteristic (ROC) curves assessed predictive capacity. Results: Compared to HCs, MS eyes with prior optic neuritis showed significantly lower SVP density (p < 0.05). DVP and FAZ parameters did not differ between groups. SVP and DVP densities correlated with age, disease duration, relapse history, and MRI volumetrics, including gray matter and whole brain volume. SVP density predicted NEDA-3 status (AUC = 0.82), while DVP also showed predictive value (AUC = 0.64). FAZ FD (Foveal density) was associated with gray matter and whole brain atrophy (AUC = 0.62–0.61). Conclusions: Retinal vascular alterations correlate with clinical and MRI measures in MS. Reduced SVP and DVP densities may serve as markers of recent disease activity, and FAZ metrics reflect neurodegeneration. OCTA may be a valuable non-invasive tool for monitoring MS progression. Full article

The impact of wind on precipitation measurements from the OTT Parsivel² optical transmission disdrometer is quantified using computational fluid dynamics simulations. The numerical velocity field around the instrument body and above the instrument sensing area (the laser beam) shows significant disturbance that depends heavily on the wind direction. By computing the trajectories of raindrops approaching the instrument, the wind-induced bias is quantified for a wide range of environmental conditions. Adjustments are derived in terms of site-independent catch ratios, which can be used to correct measurements in post-processing. The impact on two integral rainfall variables, the rainfall intensity and radar reflectivity, is calculated in terms of collection and radar retrieval efficiency assuming a sample drop size distribution. For rainfall intensity measurements, the OTT Parsivel² shows significant bias, even much higher than the wind-induced bias typical of catching-type rain gauges. Large underestimation is shown for wind parallel to the laser beam, while limited bias occurs for wind perpendicular to it. The intermediate case, with wind at 45°, presents non negligible overestimation. Proper alignment of the instrument with the laser beam perpendicular to the prevailing wind direction at the installation site and the use of windshields may significantly reduce the overall wind-induced bias. Full article

In complex terahertz (THz) systems, multiple optical elements are often combined to achieve advanced functionalities. However, unwanted Fresnel reflections at their interfaces and between components lead to parasitic interference effects and signal losses. This study presents oil-based refractive-index-matching fillers integrated with additively manufactured assemblies to suppress Fresnel reflections and enhance overall optical system performance. The optical properties of 20 plant-based, synthetic, and mineral oils were investigated using terahertz time-domain spectroscopy (THz TDS). Furthermore, a multilayer structure was designed and experimentally verified, fabricated via fused deposition modeling (FDM) using highly transparent cyclic olefin copolymer (COC). The results demonstrate that the use of tailored oils reduces Fresnel reflection signal losses and also mitigates parasitic interference within the system, thereby improving the effective efficiency of the optical system. Additionally, THz TDS measurements on multilayer structures revealed that, in imaging configurations, the application of refractive-index-matched oils increases the signal gain by 2.33 times. These findings highlight the potential of oil-based index-matching fillers for imaging multilayered objects and mitigating delamination effects in optical elements. Full article

Many Global-South cities lack dense monitoring and suffer persistent cloud cover, hampering fine-scale trend detection. This study evaluates the potential of annual multi-sensor satellite embeddings from the AlphaEarth Foundations model in Google Earth Engine to predict and map major air pollutants in Quito, Ecuador, between 2017 and 2024. The 64-dimensional embeddings integrate Sentinel-1 radar, Sentinel-2 optical imagery, Landsat surface reflectance, ERA5-Land climate variables, GRACE terrestrial water storage, and GEDI canopy structure into a compact representation of surface and climatic conditions. Annual median concentrations of NO₂, SO₂, PM_2.5, CO, and O₃ from the Red Metropolitana de Monitoreo Atmosférico de Quito (REEMAQ) were paired with collocated embeddings and modeled using five machine learning algorithms. Support Vector Regression achieved the highest accuracy for NO₂ and SO₂ (R² = 0.71 for both), capturing fine-scale spatial patterns and multi-year changes, including COVID-19 lockdown-related reductions. PM_2.5 and CO were predicted with moderate accuracy, while O₃ remained challenging due to its short-term photochemical and meteorological drivers and the mismatch with annual aggregation. SHAP analysis revealed that a small subset of embedding bands dominated predictions for NO₂ and SO₂. The approach provides a scalable and transferable framework for high-resolution urban air quality mapping in data-scarce environments, supporting long-term monitoring, hotspot detection, and evidence-based policy interventions. Full article

This paper presents the growth and in situ optical characterization of silicon nanowires (Si NWs) on Al₂O₃(0001) substrates that are thermally faceted using the atomic low angle shadowing technique (ATLAS) method. Annealing Al₂O₃ substrates in air before surface faceting was used for the first time, as identified by atomic force microscopy (AFM). Planar Si NW arrays were subsequently deposited and characterized in real-time by reflectance anisotropy spectroscopy (RAS). RAS measurements detected irreversible spectral changes during growth, e.g., red-shift in peak energy for marking amorphous Si NW formation. Blue-shifts in RAS spectra following annealing post-growth at varied temperatures were found to be associated with structural nanowire development. AFM analysis following annealing detected dramatic changes in morphology, e.g., quantifiable differences in NW height and thickness and complete disappearance of nanowire structures at high temperatures. These results confirm the validity of in situ RAS as a monitoring tool for nanowire growth and illustrate Si NW morphology’s sensitivity to thermal processing. Full article

Copper nitride (Cu₃N) is gaining attention as an eco-friendly thin-film semiconductor in a myriad of applications, including storage devices, microelectronic components, photodetectors, and photovoltaic cells. This work presents a detailed optoelectronic study of Cu₃N thin films grown by reactive RF-magnetron sputtering under pure N₂. An overview of the state-of-the-art literature on this material and its potential applications is also provided. The studied films consist of Cu₃N polycrystals with a cubic anti-ReO₃ type structure exhibiting a preferential (100) orientation. Their optical properties across the UV-Vis-NIR spectral range were investigated using a combination of multi-angle spectroscopic ellipsometry, broadband transmission, and reflection measurements. Our model employs a stratified geometrical approach, primarily to capture the depth-dependent compositional variations of the Cu₃N film while also accounting for surface roughness and the underlying glass substrate. The complex dielectric function of the film material is precisely determined through an advanced dispersion model that combines multiple oscillators. By integrating the Tauc–Lorentz, Gaussian, and Drude models, this approach captures the distinct electronic transitions of this polycrystal. This customized optical model allowed us to accurate extract both the indirect (1.83–1.85 eV) and direct (2.38–2.39 eV) bandgaps. Our multifaceted characterization provides one of the most extensive studies of Cu₃N thin films to date, paving the way for optimized device applications and broader utilization of this promising binary semiconductor, and showing its particular potential for photovoltaic given its adequate bandgap energies for solar applications. Full article

Indirect lighting systems employing light-emitting diodes (LEDs) and diffuse reflective surfaces are prevalent in applications demanding stringent illumination uniformity. However, conventional diffuse reflection approaches exhibit inherent limitations (inevitable light loss from multiple diffuse reflections and trade-off between uniformity and efficiency). To overcome these constraints, we introduce a novel composite freeform surface illumination system that synergistically integrates total internal reflection (TIR) with diffuse reflection. This design leverages the inherent Lambertian radiation characteristics of LEDs and the properties of ideal diffuse reflectors. A rigorous mathematical model is derived based on the luminous intensity distribution of the LED chip, the prescribed illumination requirements on the target plane, the principle of energy conservation, and Snell’s law. The resulting system of nonlinear equations is solved to generate a series of two-dimensional profile curves, which are subsequently synthesized into an off-axis freeform surface. Simulated results demonstrate that the proposed system achieves higher optical efficiency and superior illumination uniformity compared to traditional diffuse reflector configurations. This universal and feasible methodology broadens the application potential of high-performance diffuse indirect lighting. Full article

Solution combustion-synthesized BaAl₂O₄: Eu²⁺, Nd³⁺, and Pr³⁺ blue–green long-afterglow phosphors are prepared and systematically investigated. First, XRD confirms the BaAl₂O₄ host and screens for trace residual features. SEM reveals the agglomerated granular morphology typical of combustion products. XPS verifies the valence states (Eu²⁺, Nd³⁺, Pr³⁺) and the chemical environment of the host lattice. UV-Vis diffuse reflectance spectra, transformed via the Kubelka–Munk function and analyzed using Tauc plots (indirect-allowed), indicate a wide band gap of the BaAl₂O₄ host with small, systematic shifts upon Nd³⁺/Pr³⁺ co-doping. PL measurements show Eu²⁺ 4f–5d emission and co-dopant-assisted excitation/defect pathways without altering the Eu²⁺ emission band shape. Afterglow lifetime and decay analyses correlate trap depth/distribution with the extended persistence. Finally, we demonstrate anti-counterfeiting by (i) snowflake printing and (ii) a binary 3 × 3 grid printed with two afterglow inks of different lifetimes to realize multi-level authentication. The sequential evidence links structure, chemistry, optical absorption, carrier trapping, and practical readout, providing a coherent basis for performance enhancement and application. Full article

External insulation of coastal power grids faces harsh conditions and is highly susceptible to flashover. Currently, technologies for online monitoring and flashover early warning are severely lacking. As a reflective passive sensing device, Fiber Bragg Grating (FBG) enables the monitoring of surface discharge and provides an early warning for flashover on external insulation. A 10 kV fiber-optic composite insulator was developed in this study. A linear relationship between the FBG central wavelength and interfacial temperature was established through temperature calibration experiments. Coastal salt fog conditions were simulated in an artificial fog chamber, where AC pollution flashover tests were performed on the fiber-optic composite insulator. FBG central wavelength and visible images of discharge were synchronously acquired during experimentation. Experimental results indicate that the interfacial locations on FBGs where the temperature increases during flashover coincide with the positions of visible discharge arcs, demonstrating the effectiveness of the monitoring method. A temperature rise rate of 4.88 × 10⁻² °C/s was found to trigger flashover warning, while a rate of 4.96 × 10⁻² °C/s initiated trip protection. A discharge-region ratio characteristic was proposed for visible discharge images based on highlight area ratio, R-channel deviation, and mean saturation features. This characteristic serves as a flashover warning when its value reaches 46.7%. This study provides a novel research approach for online monitoring and flashover early warning of external insulation in coastal salt fog environments. Full article

The organic/inorganic hybrid compound bis(2-amino-6-bromopyridinium) tetrachloridocuprate(II) (HABPy)₂[CuCl₄] was synthesized in crystalline form in a 77% yield from aqueous HCl solutions containing Cu(OAc)₂ and 2-amino-6-bromopyridine (ABPy). Single-crystal X-ray diffraction analysis revealed that the compound crystallizes in the monoclinic, centrosymmetric space group C2/c. The Cu atom shows a distorted tetrahedral coordination geometry with a τ₄ value of 0.69 (τ₄ = 1 for a perfect tetrahedron). The structure consists of organic (HABPy)⁺ cation layers at z = 0 and z = ½, alternating with inorganic [CuCl₄]²⁻ dianion layers at z = ¼ and z = ¾. These layers, parallel to the (001) plane, are interconnected by a plethora of supramolecular forces such as N–H···Cl hydrogen bonds, forming a three-dimensional network. Powder X-ray diffraction confirmed the purity of the synthesized bulk material. Fourier-transform infrared (FT-IR) spectroscopy and Raman spectroscopy support the protonation of the pyridine N atom. Hirshfeld surface analysis allowed us to further study the supramolecular forces in the crystal structure. The material shows purely paramagnetic behavior according to S = ½ with an effective magnetic moment µ_eff of 1.85 µB and a g factor of 2.14, in keeping with magnetically isolated [CuCl₄]²⁻ dianions. UV-vis diffuse reflectance spectroscopy of the orange-red material showed a tiny band at 314 nm and an intense band peaking at 622 nm. The optical gap was found to be 2.25 eV. The photoluminescence spectrum shows a partially structured band with maxima at 416 and 436 nm when irradiating at 370 nm, the wavelength of the maximum band found in the excitation spectrum. Full article

For large-scale measurement of microbubble parameters on the ocean surface beneath breaking waves, a buoy-type bubble sensor (BBS) is proposed. This sensor integrates a panoramic bubble imaging sub-sensor with a circular array fiber-optic sub-sensor. The sensitive unit of the latter sub-sensor is designed via theoretical modeling and experimental validation. Theoretical calculations indicate that the optimal cone angle for a quartz fiber-optic-based sensitive unit ranges from 45.2° to 92°. A prototype array element with a cone angle of 90° was fabricated and used as the core component for feasibility experiments in static and dynamic two-phase (gas and liquid) identification. During static identification, the reflected optical power differs by an order of magnitude between the two phases. For dynamic sensing of multiple microbubble positions, the reflected optical power varies from 13.4 nW to 29.3 nW, which is within the operating range of the array element’s photodetector. In theory, assembling conical quartz fiber-based sensitive units into fiber-optic probes and configuring them as arrays could overcome the resolution limitations of the panoramic bubble imaging sub-sensor. Further discussion of this approach will be presented in a subsequent paper. Full article

Recently, there has been significant progress in the area of semantic classification of water bodies at global scales with deep learning. For the key purposes of water inventory and change detection, advanced deep learning classifiers such as UNets and Vision Transformers have been shown to be both accurate and flexible when applied to large-scale, or even global, satellite image datasets from optical (e.g., Sentinel-2) and radar sensors (e.g., Sentinel-1). Most of this work is conducted with optical sensors, which usually have better image quality, but their obvious limitation is cloud cover, which is why radar imagery is an important complementary dataset. However, radar imagery is generally more sensitive to soil moisture than optical data. Furthermore, topography and wind-ripple effects can alter the reflected intensity of radar waves, which can induce errors in water classification models that fundamentally rely on the fact that water is darker than the surrounding landscape. In this paper, we develop a solution to the use of Sentinel-1 radar images for the semantic classification of water bodies that uses style transfer with multi-modal and multi-temporal image fusion. Instead of developing new semantic classification models that work directly on Sentinel-1 images, we develop a global style transfer model that produces synthetic Sentinel-2 images from Sentinel-1 input. The resulting synthetic Sentinel-2 imagery can then be classified with existing models. This has the advantage of obviating the need for large volumes of manually labeled Sentinel-1 water masks. Next, we show that fusing an 8-year cloud-free composite of the near-infrared band 8 of Sentinel-2 to the input Sentinel-1 image improves the classification performance. Style transfer models were trained and validated with global scale data covering the years 2017 to 2024, and include every month of the year. When tested against a global independent benchmark, S1S2-Water, the semantic classifications produced from our synthetic imagery show a marked improvement with the use of image fusion. When we use only Sentinel-1 data, we find an overall IoU (Intersection over Union) score of 0.70, but when we add image fusion, the overall IoU score rises to 0.93. Full article

Keratoacanthoma (KA) is a rapidly growing epithelial neoplasm characterized by clinical and histopathological features that often overlap with well-differentiated squamous cell carcinoma (SCC), posing diagnostic challenges. This review provides a comprehensive overview of KA, emphasizing advances in non-invasive diagnostic techniques such as dermoscopy, reflectance confocal microscopy (RCM), and line-field confocal optical coherence tomography (LC-OCT), which improve lesion characterization and differentiation from SCC. We discuss the histopathological phases of KA and highlight key features aiding in diagnosis. Furthermore, we explore the emerging role of human papillomavirus (HPV), particularly β-genus types, as a cofactor in KA carcinogenesis through modulation of apoptosis and DNA damage response pathways, especially under ultraviolet (UV) radiation exposure. Therapeutic strategies remain centered on complete surgical excision; however, alternative treatments, including radiotherapy, cryotherapy, topical agents, and systemic retinoids, are discussed with their respective benefits and limitations. Finally, we review current HPV vaccines and novel vaccine candidates targeting a broad spectrum of mucosal and cutaneous HPV types. This review underscores the importance of integrated diagnostic and therapeutic approaches to optimize KA management and highlights future directions in understanding its pathogenesis and treatment. Full article

Background/Objectives: Optical coherence tomography (OCT)-reflective drusen substructures (ODSs) are associated with the conversion of intermediate AMD to geographic atrophy (GA). However, ODSs must be manually identified, a laborious process introducing bias and variation. This study proposes objective radiomic metrics of drusen phenotypes and validates them for the prediction of GA development and GA growth rate. Methods: A total of 104 drusen with high-reflective cores (H-type), 105 with low-reflective cores (L-type), 129 conical drusen (C-type), and 101 normal drusen (N-type) were segmented from OCT images. Radiomic features were extracted from these drusen, and the most important features for drusen classification were extracted from the retinal pigment epithelium–Bruch’s membrane compartment of 743 OCT scans of eyes with dry AMD and used to predict GA conversion and fast growth. Results: Radiomic features classified drusen phenotypes with AUC = 0.87–0.95. H-type drusen have a higher reflectivity, greater variation in reflectivity, and coarser texture (p < 0.001). L-type drusen have a lower reflectivity and greater variation in reflectivity (p < 0.0001). C-type drusen have a less spherical shape and more disordered internal reflectivity (p < 0.001). N-type drusen have a more spherical shape and more uniform internal reflectivity (p < 0.001). These radiomic features predict the conversion from intermediate AMD to GA and top-quartile GA growth rate with AUC = 0.59–0.74 at years 1–3. Conclusions: These results demonstrate the potential of clinical phenotype-grounded radiomics for objective automated drusen analysis, GA risk stratification, and clinical prediction. Full article