Search Results (698)

Rapid and accurate quantification of residual guar gum in bauxite slurry flocculation is a critical bottleneck for closed-loop control of flocculant dosage. In this study, we systematically compared the anti-interference performance of the two UV-Vis spectrophotometer approaches, the single-wavelength absorbance method (A₂₆₃) and the peak-trough difference method (ΔA), in complex slurry matrices. Our results revealed that the two methods respond differently to pH and salt concentration variations, leading to the proposal of a dual-mode synergistic detection strategy. The A₂₆₃ method provides quantification under the specific conditions tested within the ranges of pH 3.0–8.0 and CaCl₂ concentration below 4.5 mmol/L. Beyond these boundaries, deviations from the Beer-Lambert law occurred, attributable to conformational transitions or salting-out aggregation of the polymer chains. In contrast, the ΔA method partially mitigated background drift through differential calculation and exhibited a more stable signal trend than A₂₆₃ across the tested ranges (pH 2.0–11.0, CaCl₂ 0–18 mmol/L), suggesting its potential utility as a semi-quantitative indicator in challenging matrices. However, its quantitative precision was constrained by small absolute signal values and systematic dependence on pH and salt conditions. Based on these findings, we propose a synergistic strategy-preferring the A₂₆₃ method under routine conditions while recommending the ΔA method for high-salinity or wide-pH scenarios- and accordingly define the preliminary applicability boundaries based on signal response observations at a single concentration. Flocculation–sedimentation tests confirmed that the method successfully determined the optimum dosage (5.0 g/kg dry slurry), at which the residual concentration in the supernatant correlated negatively with the sedimentation rate (R² > 0.95). The supernatant matrix after sedimentation (pH ≈ 7.1, low ionic strength) fell exactly within the safe window. This work provides a methodological reference for spectrophotometric quantification of trace organics in turbid, saline, and pH-variable slurry systems, and lays an analytical foundation for intelligent dosage control in bauxite slurry dewatering. Full article

Escalating track deterioration poses a significant challenge for infrastructure managers seeking to balance increasing capacity demands with long-term sustainability objectives. Although traffic loading is the primary driver of deterioration, existing deterioration models consider a wide range of additional factors whose representation varies across track forms. A comprehensive understanding of these factors is therefore necessary to support informed selection of railway track solutions. This study establishes a conceptual framework of deterioration factors for three railway track solutions: ballasted track, ballastless track, and combined track solutions (CTS). A systematic review of 30 deterioration models was conducted to identify deterioration factors and the mechanisms governing track degradation. Beyond synthesizing factors reported in existing deterioration models, the review identified five additional deterioration factors consistently associated with deterioration mechanisms in the broader railway engineering literature but not explicitly represented in the reviewed models. The review then evaluated the identified factors, grouped them by primary deterioration causes, and adapted them to reflect CTS-specific boundary conditions. The review revealed that existing deterioration models insufficiently address factors related to (i) properties of track subsystems and components, (ii) design characteristics of track forms, and (iii) design, location, and quantity of track transitions. Furthermore, deterioration-related parameters such as the elastic modulus of the track support and the amplitude and wavelength of differential settlement require specific consideration when assessing track form suitability within CTS. The resulting framework provides a structured conceptual representation of deterioration factors and their interrelationships, supporting future development of deterioration prediction models, life cycle cost assessments, and sustainability-oriented decision support methodologies for railway infrastructure. Full article

Characterizing gas–liquid boundaries in underwater high-speed images is complicated by optical propagation and interface effects that broaden intensity transitions. Whether narrower transitions also indicate more accurate boundary localization, however, remains unclear. We integrated broadband white and narrow-band blue, green, and yellow source conditions with configuration-specific RBW processing at nominal observation distances of 0.7 and 5.0 m. Each source-distance condition was represented by one acquisition run, from which 20 temporally separated frames were analyzed as frame-level subsamples. In the 5.0 m run, the observed mean RBW was 17.46% under the blue-source condition and 36.18% under the white-source condition, corresponding to a descriptive reduction of 51.73%. A sensitivity analysis based on the interquartile range (IQR) yielded a descriptive reduction of 33.42%, whereas the near-field means were similar across source conditions. Target-plane optical irradiance and camera spectral responsivity were not calibrated. These values therefore describe source-condition responses of the complete imaging chain rather than isolated wavelength effects. A 12-image near-field holdout set annotated by two observers was used to compare the proposed estimator with classical and learning-based edge detectors. This image-reference benchmark did not support a claim of superior localization, and RBW showed little monotonic association with normalized image-reference localization discrepancy within the holdout set. The results characterize within-run image responses rather than reproducible source-condition effects. They support RBW as a descriptor of processed transition width, but not as a measure of physical boundary-localization accuracy. Full article

Optical spectroscopy provides useful information about polymeric ultrathin films by combining interferometric and optical absorption data contained in the UV-Vis-NIR spectra. In particular, the UV-Vis-NIR spectrum of an ultrathin polymeric film contains information about the film thickness, structural disorder, bandgap energy, type of electron transition model (direct/indirect, allowed/forbidden), cutoff wavelength (i.e., the opaque/transparent switching wavelength), etc. Here, these properties have been determined for a model semi-crystalline polymer (polyethylene terephthalate, PET) in the form of ultrathin film before and after a mild mechanical deformation treatment (manual stretching). It has been found that E_U and E_g parameters are not strictly dependent on mechanical deformation due to their main dependence on the chemical composition/constitution of the polymer. Full article

A cyclometalated iridium(III) complex [Ir(ppy)₂(tpdp)]PF₆ ([1]PF₆; ppy = 2-phenylpyridinate, tpdp = 5,6,7,8-tetraphenyl-1,12-diazatripheneylene) was synthesized and structurally characterized by single-crystal X-ray diffraction analysis. In [1]⁺, two nitrogen atoms of tpdp coordinate to the iridium(III) ion with Ir-N distances of 2.131(4) and 2.114(4) Å. The peripheral phenyl substituents of tpdp are oriented nearly perpendicular to the enlarged π-conjugated plane of tpdp. [1]PF₆ exhibits shoulder bands at 472, 407, 368, and 337 nm, while the absorption increases continuously from ca. 520 nm toward shorter wavelengths. This spectral feature is similar to that of [Ir(ppy)₂(phen)]PF₆ ([2]PF₆), but the absorption intensity is much higher for [1]PF₆ in the UV region. The contribution from the π–π* transition of the tpdp ligand was considered to be the reason that [1]PF₆ exhibits such strong absorption in the UV region. Furthermore, [1]PF₆ exhibits an emission from ³MLLCT at 558 nm, whereas [2]PF₆ exhibits it at 560 nm. The luminescence lifetime (τ) of [1]PF₆ was 411 ns, shorter than that of [2]PF₆ (900 ns), and the absolute quantum yield (Φ) of [1]PF₆ was 4.8%, lower than that of [2]PF₆ (20.5%). Cyclic voltammetry (CV) analysis in degassed CH₃CN revealed redox waves both at the negative and positive sides (E_1/2 = 1.28 and −1.38 V vs. SCE) for [1]PF₆. In addition, DFT calculations were performed to discuss the electronic structures and photophysical properties of [1]⁺. Full article

We develop a reaction–diffusion–chemotaxis model for spatial tumour–immune–chemokine dynamics that couples logistic tumour growth, immune-mediated killing, chemokine-dependent immune recruitment, chemotactic migration, and signal production. For the non-dimensional system, we establish local classical solvability, nonnegativity, a uniform tumour-density bound, and global mass estimates for the immune and chemokine components. The tumour-free equilibrium is stable precisely when the baseline immune-control index satisfies ${\sigma }_0/\delta >1$, whereas positive homogeneous coexistence is characterized by a scalar nonlinear equation. Linearization in the Neumann Laplacian eigenbasis yields a mode-dependent cubic dispersion relation, showing that chemotaxis does not alter the tumour-invasion threshold but can destabilize homogeneous coexistence through a finite-wavelength oscillatory instability above a critical sensitivity ${\xi }_c$. A conservative finite-volume discretization with upwind chemotactic fluxes and implicit backward differentiation formula time integration is used to test these predictions. Numerical experiments recover the analytical equilibria and growth rates, identify the dominant unstable mode, reproduce the transition to spatial heterogeneity, and quantify the effects of immune recruitment, decay, and diffusion on the stability boundary. Grid-refinement, mass-balance, residual, and nonnegativity diagnostics support the computational reliability of the results. Full article

Deep exploration in mature gold districts requires subsurface alteration evidence that can be related quantitatively to three-dimensional (3D) geological architecture. This study develops a workflow for the Tudui–Shawang deposit in the Muping–Rushan metallogenic belt that integrates drill-core short-wave infrared (SWIR) spectroscopy, 3D alteration modeling, ore-controlling geological constraints, positive–unlabeled (PU) learning, and ensemble prospectivity prediction. A total of 2140 spectra from 10 drillholes were processed to identify mineral assemblages, extract spectral scalars and feature-shape attributes, classify alteration facies, and construct continuous 3D alteration evidence. Discrete smooth interpolation and indicator kriging were used for continuous and categorical attributes, respectively, and CatBoost, LightGBM, XGBoost, and Random Forest were evaluated within a spatially separated PU-bagging design. Quantitative analyses show that individual SWIR attributes have weak deposit-scale relationships with Au grade. Nevertheless, local IC minima, relatively lower pos2200 values near several mineralized intervals, alteration-facies transitions, and a broader shift toward longer pos2250 wavelengths characterize relevant parts of the mineralized system. FUSE performed best under 1 km × 1 km spatial holdout validation, with an ROC AUC of 0.8900 and a PRAUC of 0.8926. Prediction-area analysis and the 3D probability volume delineated three ranked exploration targets (T1–T3). The results show that drill-core SWIR-derived 3D alteration evidence, when integrated with ore-controlling geology and spatially validated machine learning, provides a practical basis for target prioritization in mature gold districts. Full article

While Thermal Infrared (TIR) sensors are standard for monitoring volcanic activity, their efficacy is severely compromised by meteorological clouds and dense volcanic ash. To overcome these optical limitations, we present the first ground-based application of a passive microwave radiometer for continuous volcano monitoring. Operating in the 10–12 GHz band, our Total Power Microwave Receiver is stationed 12 km from Mount Etna’s active craters to measure thermal emissions from eruptive hotspots. Unlike traditional TIR imaging, this low-cost, automated system exploits the atmospheric transparency of microwave wavelengths, enabling uninterrupted observation regardless of weather or solar illumination. We detail the system’s design and report its successful detection of volcanic phenomena during the 2023–2025 eruptive cycles, including the transit of a high-temperature ash cloud that triggered a significant radiometric peak. Our findings demonstrate that fixed-point microwave radiometry provides a reliable thermal signature of eruptive activity, offering a pioneering and highly accessible tool for the next generation of global volcanic early warning systems. Full article

Visible light communication (VLC) has emerged as a transformative optical wireless technology for sixth-generation (6G) networks, offering license-free spectrum access, inherent electromagnetic-interference immunity, high spatial confinement, and the unique ability to combine high-speed wireless connectivity with solid-state lighting infrastructure. However, the transition from conventional VLC links to practical 6G optical wireless systems requires far more than advanced modulation and signal processing. Future VLC performance will be strongly determined by the co-design of photonic front-ends, including high-speed transmitters, spectrally engineered emitters, reconfigurable optical interfaces, intelligent receivers, and energy-autonomous detection units. This article provides a comprehensive, device-centered review of photonic hardware and artificial intelligence (AI) enablers for next-generation 6G VLC systems. Particular attention is given to micro-LEDs, laser diodes, color-conversion materials, including perovskite quantum dots, advanced photodetectors, imaging receivers, wavelength-shifting fiber receivers, solar-cell-based receivers, optical reconfigurable intelligent surfaces (RISs), metasurfaces, beam-steering components, and optical wireless power transfer. This review discusses how AI can support inverse photonic design, transmitter and receiver calibration, nonlinear impairment mitigation, channel-aware beam control, and energy-aware resource management. Unlike broader VLC surveys that mainly emphasize network architecture, this article provides a device-centered perspective on AI-enabled photonic integration for 6G VLC, supported by a comprehensive survey of recent experimental demonstrations. Key challenges related to bandwidth, optical efficiency, receiver field of view, mobility, safety, standardization, and practical deployment are summarized, followed by a research roadmap for 2025–2032. Full article

Undular bores are classical shallow-water phenomena in which a sharp transition between two flow states is replaced, in a dispersive theory, by an oscillatory wave train. In non-dispersive shallow-water theory, the bore is associated with an apparent loss of mechanical energy. In dispersive models, this energy can be interpreted as being redistributed into the oscillatory tail. The aim of this short article is to formulate a possible extension of this interpretation when surface tension is included. The capillary contribution modifies the long-wave dispersion coefficient through a Bond-number-dependent term and adds an additional surface energy to the total energy functional. We derive the basic capillary-gravity KdV scaling, identify the modified energy density, and discuss how surface tension may affect the amplitude, wavelength, and energy flux of the trailing oscillations. The proposed direction is relevant for small-scale laboratory bores, tidal-bore fronts, and shallow tidal currents in which a rapid transition generates short dispersive oscillations. Special attention is paid to the critical value $Bo=1/3$, where the classical KdV dispersion vanishes, and a fifth-order correction is required. Full article

The ultrafast photochemical reaction dynamics of a cyclic(alkyl)(amino)carbene–carbon disulfide (CAAC–CS₂) dimer containing two adjacent S–S bonds were investigated using femtosecond time-resolved infrared spectroscopy in combination with multireference electronic structure calculations. Time-resolved vibrational spectra and global kinetic analysis reveal that photoexcitation of the S–S n → σ* transition at 375 nm induces subpicosecond (<0.3 ps) homolytic cleavage of one S–S bond, generating a bis-thiyl diradical intermediate. This intermediate undergoes two competing pathways: recombination to regenerate the parent dimer with a time constant of 5.7–8.5 ps, or secondary cleavage of the remaining S–S bond to yield two CAAC–CS₂ monomers with a time constant of 30–35 ps. Wavelength- and temperature-dependent kinetic measurements demonstrate that the branching between these pathways is governed by excess excitation energy and thermally driven radical-pair fluctuations. Multireference electronic structure calculations support a sequential S–S bond cleavage mechanism, in good agreement with the experimental observations. These findings provide direct spectroscopic evidence for a bis-thiyl diradical intermediate and offer new mechanistic insight into the ultrafast photochemistry of adjacent S–S bonds. Full article

In this work, a comprehensive analysis of the relationship between photoluminescent, thermo-oxidative, and photocatalytic (upon simulated sunlight exposure) properties of ZnO powders is performed. The correlation between the X-ray diffraction and microscopic data is studied. ZnO powders of various sizes and morphologies were used: pseudo-spherical nanoparticles (30–50 nm), submicron faceted crystallites (100–500 nm), and plate- and rod-like microstructures (up to 20 μm). The mean specific surface area values were 32 m²/g, 3.8 m²/g, and 2.6 m²/g for pseudo-spherical nanoparticles, submicron faceted crystallites, and plate- and rod-like microstructures, respectively. According to the XRD data, microstresses and carbon-based impurities were present in ZnO nanoparticles, which is characteristic of nanomaterials synthesized at low temperatures. According to the photoluminescence spectroscopy data, the emission in ZnO was reduced due to high defectiveness, and characteristic emission bands indicated the presence of organic impurities. Upon long signal registration times, an intensive luminescence band with an effective maximum at 579 nm occurred, which indicated the presence of long-term components exhibiting decay times τ ~300 μs. According to the XRD data, the crystal structure parameters of ZnO submicro- and microparticles were close, with no impurities present. In their photoluminescence spectra, pronounced UV and defect-related bands were present with intensity ratios of 11.6 and 6.88, respectively. The decrease in the UV and defect-related luminescence band intensity ratios indicates deviation from the stoichiometry toward an increased Zn over oxygen content. At long signal registration times, in submicron ZnO particles, a luminescence band with maxima at 425 and 490 nm is present, which decays rapidly. An emission band in the 530 nm region is also present, which decays for ≤80 μs, and a weak long-wavelength emission decaying for ~100 μs. At long delay and strobe times (up to milliseconds), only an emission in the 460 nm region is observed, which we connect to the triplet–singlet transition of a defect center (F*, F⁺*). At lower intensities, an emission connected to the surface contamination by organic impurities is observed. In photoluminescence spectra of ZnO microparticles, no long-wavelength emission components are observed. However, upon immersing into methylene blue solution, a modification of the surface and UV region of the spectra is observed with signs of charge carrier recombination rate acceleration. It is shown that the catalytic action of ZnO powders in polyethylene thermo-oxidation processes is determined by a combination of factors. In addition to dispersity and concentration, which are the key parameters, the morphology of ZnO particles, the presence of impurities, the surface state, and the distribution of active sites have a significant influence on catalysis. It has been experimentally demonstrated that these secondary factors can markedly affect the rate of radical formation in polyethylene films and alter their resistance to oxidation. ZnO nanoparticles exhibited low catalytic activity in both photocatalysis (rate constant 0.146 min⁻¹) and thermocatalysis due to the high defect density of the crystallites and the presence of carbon-containing impurities. Submicron ZnO particles, owing to a high carrier generation rate and suppressed recombination (via trapping), demonstrated the highest photoactivity (rate constant 0.729 min⁻¹). Submicron ZnO particles exhibit a catalytic effect on the thermo-oxidation of polyethylene (PE films); however, at concentrations above 8 wt.% a transition to an inhibiting effect is observed. ZnO microparticles catalyzed the oxidation of PE films over a broader concentration range (1–12 wt.%), with oxidation inhibition observed only at 18 wt.%. At the same time, they demonstrated moderate photocatalytic activity (rate constant 0.256 min⁻¹). These characteristics of the samples correlate with data obtained by microscopy, photoluminescence spectroscopy, and X-ray diffraction analysis. Full article

Garnet-structured compounds have long been recognized as versatile host platforms for luminescent phosphors, owing to their robust chemical stability and highly tunable cationic sublattices. Conventional aluminate and gallate garnets, however, generally face intrinsic limitations, including severe concentration quenching at high dopant levels, relatively high phonon energy, and unsatisfactory efficiency for long-wavelength near-infrared (NIR) emission. In recent years, sodium-based germanate garnets, constructed by introducing aliovalent Na⁺ into dodecahedral sites combined with Ge⁴⁺ substitution in tetrahedral frameworks, have emerged as a promising branch of garnet phosphors. The aliovalent Na+ incorporation brings unique structural effects, including energy migration blocking, coordination environment distortion, and defect level modulation, which endow the materials with advantages in mitigating concentration quenching, boosting energy transfer efficiency, and enhancing thermal stability. This review systematically summarizes the crystal structure classification and luminescence fundamentals of sodium-based germanate garnet systems, and introduces mainstream synthesis techniques represented by the high-temperature solid-state method. Focusing on representative host systems, the luminescence characteristics and energy transfer mechanisms of both rare earth- and transition metal-doped systems are elaborated in detail, followed by a summary of four representative performance regulation strategies: cationic disorder engineering, crystal field engineering, defect engineering and dual-site cooperative regulation. The multifunctional applications of these materials in white light-emitting diodes, plant growth lighting, fluorescence temperature sensing, NIR imaging, and information encryption are also presented. Finally, existing challenges and future research perspectives are proposed to provide guidance for the development of high-performance garnet phosphors. Full article

Equivalent black carbon (eBC) is a key component of fine particulate matter PM_2.5, originating from incomplete combustion processes and exerting significant impacts on air quality, human health, and climate. This study investigates the temporal variability and interannual changes in eBC in Kraków, Poland, in the context of Europe’s recent energy policy changes and ongoing energy transition. A one-year dataset (October 2023 to September 2024) based on multi-wavelength optical measurements was analysed to quantify total eBC and its fossil-fuel (eBC) and biomass-burning (eBC_bb) components and compared with 2020–2021 observations. Results show strong seasonal variability, with winter eBC concentrations averaging 4.0 µg m⁻³ and peaking at 5.5 µg m⁻³ in February, while summer minima reached 1.2–1.5 µg m⁻³. Biomass-burning contributions remained low throughout the year, ranging from 0.1–0.2 µg m⁻³ in summer to 0.4–0.5 µg m⁻³ in winter. PM_2.5 concentrations followed similar trends, with winter values of 24–31 µg m⁻³ and summer levels of 8–12 µg m⁻³. Extreme pollution episodes were observed during winter, with PM_2.5 exceeding 120 µg m⁻³ and eBC reaching 13 µg m⁻³. Despite the 2019 ban on coal and wood combustion, elevated wintertime eBC indicates a strong influence of regional emissions transported from surrounding areas. A clear weekly pattern was identified, with eBC concentrations approximately 40% higher on weekdays (3.1 µg m⁻³) compared to weekends (2.2 µg m⁻³), while eBC_bb showed minimal variation. The winter-to-summer eBC ratio (2.2) highlights the combined effects of heating demand and meteorological conditions. The findings demonstrate that the energy policy changes intensified winter pollution variability and weather events rather than increasing annual averages. The observed differences indicate that pronounced wintertime variability and episodic pollution remained important during 2023–2024 despite lower annual mean concentrations than in 2020–2021. While local policies effectively limit direct emissions within Kraków, regional contributions remain significant, emphasizing the need for coordinated emission reduction strategies and the inclusion of episodic extremes in air quality and health impact assessments. Full article

Wind power plays an important role in renewable energy generation, and the reliability of wind turbine gearboxes directly affects turbine operation and maintenance. Compound gear fault diagnosis remains challenging because multiple fault components may coexist and compound fault samples are often limited, leading to long-tailed data distributions. To address this problem, this study proposes a long-tailed multi-label diagnostic framework based on fiber Bragg grating (FBG) acceleration signals and multi-channel time-series imaging. Missing tooth, pitting, and tooth breakage faults are encoded as three independent labels to represent healthy, single-fault, double compound fault, and triple compound fault conditions. The one-dimensional FBG wavelength-shift signals are transformed into GASF-GADF-MTF three-channel images, which describe amplitude angular correlation, dynamic angular difference, and state transition information. A ResNet18-SE network trained with Focal Loss is developed to improve the recognition of minority compound fault samples. Experimental results show that the proposed method achieves an Exact Match Accuracy of 0.9950 and a Macro-F1 of 0.9980 on the Balanced dataset. Under the severe LT50 setting, it achieves an Exact Match Accuracy of 0.9739 and an F1₁₂₃ of 0.9469. These results demonstrate the effectiveness of the proposed framework for FBG-based long-tailed compound fault diagnosis. Full article