Search Results (249)

The dominant pores governing methane adsorption in coal are micropores (pore size < 2 nm). Their spatial heterogeneity can be quantitatively characterized using multifractal theory; however, the evolution patterns and mechanisms of microporous structures across different coalification degrees remain unclear. This research selected a series of coal samples from different ranks and identified the coalification degree using the maximum vitrinite reflectance (Rₒ_,max). By comprehensively employing low-temperature CO₂ adsorption experiments and multifractal analysis, the evolution patterns of the microporous structures and their multifractal spectral parameters were systematically revealed, and the underlying control mechanisms were explored. Results indicate that micropore volume (PV) and specific surface area (SSA) first exhibit a decrease and then increase as Rₒ_,max increases, with the trough occurring during the second coalification jump at Rₒ_,max = 1.2–1.4%. The pore sizes exhibit bimodal distributions, with the primary peak occurring in the range of 0.45–0.65 nm and the secondary peak occurring in the range of 0.8–0.9 nm. All microporous structures possess pronounced multifractal characteristics. The generalized dimension spectrum width (ΔD) and singularity spectrum width (Δα) exhibit an increasing–decreasing–increasing trend with Rₒ_,max, whereas the Hurst exponent (H) follows an inverted parabolic curve, first increases then decreases. This contrasts with the trends in PV and SSA, indicating that the evolution of pore-space heterogeneity and connectivity is independent of and lags the changes in micropore quantity. These patterns are governed by a structural phase transition within the coal macromolecular network. Marked by the second coalification jump, the microporous system shifts from a flexible degradation–polycondensation paradigm to a rigid ordering–construction paradigm. This transition drives the asynchronous, synergistic evolutions of pore quantity, spatial heterogeneity (ΔD and Δα), and topological connectivity (H). This research provides a theoretical basis for quantitatively evaluating pore heterogeneity in coal reservoirs. Full article

Voltage sags pose severe risks to sensitive equipment in modern industries, requiring power quality monitoring equipment to possess fast and accurate sag detection capabilities. The traditional second-order generalized integrator (SOGI) will have oscillation phenomena in the case of DC offset, low-frequency harmonics, and high-frequency impulse noise. This study introduces a strong detection algorithm that combines Adaptive Composite Morphological Filtering (ACMF) with an improved Mixed Second- and Third-Order Generalized Integrator (MSTOGI). First, the ACMF pre-filtering module dynamically adjusts the scale of composite structuring elements through periodic parameter optimization, effectively filtering high-frequency random impulses while preserving the sharp transitions of abrupt voltage changes. Second, MSTOGI eliminates DC offset, and optimizes the gain coefficient to achieve the best dynamic response speed. Ultimately, a cascaded notch filter (CNF) module focuses on and removes even-order harmonic ripples caused by the synchronous reference frame transformation. Simulation results indicate that under severe grid conditions involving multiple composite distortions, the proposed architecture reduces the sag detection time to within 1.0 ms under typical operating conditions, with steady-state phase errors strictly controlled within a ±2° range. This method provides a reliable solution for DVR and UPS. Full article

The properties of a Ca₉La(VO₄)₇ single crystal were studied using dielectric spectroscopy and second-harmonic generation. The crystal structure of Ca₉La(VO₄)₇ grown using the Czochralski technique was refined using single-crystal data. The distribution of Ca²⁺ and La³⁺ cations over structural positions was determined. The crystal structure refinement results were compared with those obtained previously from powder X-ray diffraction data. It was shown that the refinement carried out using two different data sets leads to approximately the same results for the distances in the polyhedra, but their distortion is significantly less in the case of using single-crystal data for calculation. Dielectric properties and conductivity measurements were performed on polished single-crystal wafers cut parallel and perpendicular to the c axis. Second-harmonic generation and dielectric temperature measurements revealed the presence of a reversible ferroelectric first-order phase transition at about 1224 K from the ferroelectric β-phase (space group R3c) to the paraelectric β′-phase. The ferroelectric–paraelectric phase transition is accompanied by a complex structural rearrangement, including a 60° rotation of the V1O₄ tetrahedron, as well as slight displacements of the Ca²⁺ and La³⁺ cations. It has been shown that the conductivity differs only slightly along the polar axis and perpendicular to it. Above the phase transition temperature, the activation energy of the conductivity is the same for all directions, E_a~1.2 eV. The influence of composition on the phase transition temperature and the formation of ferroelectric and nonlinear optical properties is discussed. Full article

We report the first examples of bent-shaped LC dimers based on a seven-membered bridged stilbene. We synthesized nonylene- and ether-linked cyano-terminated dimers (sC9-tCN and sOC7O-tCN, respectively) and a homologous series of nonylene-linked alkyl-terminated dimers (sC9-tCn) with alkyl carbon atoms n = 1–6. Polarizing optical microscopy, differential scanning calorimetry, and X-ray diffraction measurement were employed to investigate the phase-transition behavior and LC phase structures. sC9-tCN and sOC7O-tCN only exhibited a nematic (N) phase, whereas sC9-tCn (n = 1–5) formed both the N_TB and N phases. sC9-tC5 additionally formed an unidentified X phase from the N_TB phase and sC9-tC6 exhibited a smectic A phase from the N phase. The weak dispersion force and intermolecular affinity provided by the terminal alkyl chains are likely to be preferable to the large dipole–dipole interactions by the cyano termini for the N_TB phase formation of the present dimers. The isotropic points of sC9-tCn showed an odd–even oscillation with n, whereas the N–N_TB phase transition temperatures were comparable. Remarkably, the N_TB stripe textures of sC9-tCn appeared perpendicular to the rubbing direction, and the N–N_TB phase transitions exhibited their second-order nature. This study revealed the unique N_TB phase properties of the 7-membered bridged stilbene-based LC dimers. Full article

The Atlantic City–South Pass (ACSP) orogenic gold district, Wind River Mountains, Wyoming, occurs in the Archean South Pass Greenstone Belt primarily within greywackes and igneous rocks metamorphosed to the upper greenschist–lower amphibolite facies. Approximately 10 Mt of gold has been produced from pyrite and arsenopyrite-bearing quartz veins in deformation zones at the brittle–ductile transition. Multiple generations of primary and/or pseudosecondary fluid inclusions in gold-bearing quartz veins include one- and two-phase gaseous CO₂-CH₄ ± N₂ inclusions and two- and three-phase gaseous CO₂-CH₄-H₂O inclusions with rare NaCl daughter minerals. These primary/pseudosecondary inclusions show a broad range of homogenization temperatures (T_h) of 177.2 to 420.0 °C, with salinities of halite-bearing inclusions of >26 wt. % NaCl, with a high concentration of CaCl₂. Secondary aqueous inclusions formed at lower values of T_h (80.9 to 243.4 °C, with one outlier of 301.1 °C). Carbon from graphitic schists associated with gold-quartz veins yields values of δ¹³C = −28.5 to −19.1 per mil, suggesting that the light C isotope compositions of some carbonates (δ¹³C = −11.0 to −1.5 per mil) involved exchange reactions with graphite in the schists. Isotopic compositions of sulfur in sulfides (δ³⁴S = −1.0 to 3.6 per mil), oxygen in vein quartz (δ¹⁸O = 7.36 to 10.38 per mil), and hydrogen in fluid inclusions in vein quartz (δD = −125 to −55 per mil) are permissive of both magmatic-hydrothermal and metamorphic dehydration models for the origin of gold mineralization. However, a potential source of magmatic–hydrothermal fluids, the post-metamorphic Louis Lake granodiorite was unlikely to transport gold in a vapor state to become focused into shear zones as previously proposed. We favor a metamorphic dehydration model in which gold was derived from the South Pass supracrustal sequence and deposited in second-order shear zones that are spatially related to the first-order Roundtop Mountain Deformation Zone. Full article

Large density fluctuations near the QCD critical point can be probed via intermittency analysis, which involves measuring scaled factorial moments (SFMs) of multiplicity distributions in relativistic heavy-ion collisions. Intermittency reflects the emergence of scale invariance and self-similar structures, which are closely related to symmetry principles and their breaking near a second-order phase transition. We present a systematic model study of intermittency for charged hadrons in Au+Au collisions at $\sqrt{s_{\mathrm{NN}}}$ = 7.7, 11.5, 19.6, 27, 39, 62.4, and 200 $\mathrm{GeV}$. Using the cascade UrQMD model, we demonstrate that non-critical background effects can produce sizable SFMs and a large scaling exponent if they are not properly removed using the mixed-event subtraction method. To estimate the possible critical intermittency signal in experimental data, we employ a hybrid UrQMD+CMC model, in which fractal critical fluctuations are embedded into the UrQMD background. A direct comparison of the second-order SFM between the model and STAR experimental data suggests that a critical intermittency signal on the order of approximately $1.8\%$ could be present in the most central Au+Au collisions at RHIC energies. This study provides practical guidance for evaluating background contributions in intermittency measurements and offers a quantitative estimate for the critical signal fraction present in the STAR data. Full article

Background/Objectives: The transition to higher education is a critical phase of human development that makes adolescents and young adults particularly vulnerable to mental health problems, such as depression, anxiety, and stress. This study aimed to evaluate the psychometric properties of the Portuguese version of the Depression, Anxiety and Stress Scale-21 Items (DASS-21) among first-year undergraduate nursing students. Methods: A methodological study was conducted with 225 undergraduate nursing students, aged 17 to 18 years, from a higher education institution in central Portugal. Data were collected using the Google Forms platform. Confirmatory factor analysis was conducted to test three competing models: a single-factor model, a three-factor correlated model, and a second-order factor model. Reliability was assessed using composite reliability, and validity was evaluated using average variance extracted and the Fornell–Larcker criterion for discriminant validity. Results: Factor analyses revealed that the three-factor correlated model fit the data best overall, showing superior fit indices compared to the competing models (χ²/df = 2.37; CFI = 0.90; and RMSEA = 0.08; TLI = 0.88 and SRMR = 0.04). Composite reliability was high across all tested models, ranging from 0.84 to 0.94. The analysis of score distributions by category revealed a high prevalence of severe or extremely severe symptoms of anxiety, stress, and, to a lesser extent, depression. A statistically significant association was found between higher symptom severity and prior familiarity with mental illness. Conclusions: The DASS-21 proved to be a valid and reliable instrument for assessing psychological distress in higher education students. These findings underscore the urgent need for mental health programs in higher education institutions that focus on early detection and intervention, particularly for students initiating their studies and those with a history of mental health problems. Full article

The accurate determination of trace metals in aqueous matrices necessitates robust sample preparation techniques that enable selective preconcentration of analytes while ensuring compatibility with subsequent instrumental analysis. Dispersive solid-phase extraction (d-SPE), a suspension-based variant of conventional solid-phase extraction (SPE), facilitates rapid sorbent–analyte interactions and enhances mass transfer efficiency through direct dispersion of the sorbent in the sample solution. This approach offers significant advantages over traditional column-based SPE, including faster extraction kinetics and greater operational simplicity. When supported by appropriately engineered sorbents, d-SPE exhibits considerable potential for the selective enrichment of trace metal analytes from complex aqueous matrices. In this work, a fibrous silica-based chelating material, DSA-KCC-1, was synthesized by grafting 3,5-Di-tert-butylsalicylaldehyde (DSA) onto aminopropyl-modified KCC-1. The dendritic KCC-1 scaffold enables fast dispersion and short diffusion pathways, while the immobilized phenolate–imine ligand introduces defined binding sites for transition-metal uptake. Characterization by FTIR, TGA, BET, FESEM/TEM, XRD, and elemental analysis confirmed the successfulness of functionalization and preservation of the fibrous mesostructured. Adsorption studies demonstrated chemisorption-driven interactions for Pb(II) and Co(II) from water, with Langmuir-type monolayer uptake and pseudo-second-order kinetic behavior. The nano-adsorbent exhibited a markedly higher affinity for Pb(II) than for Co(II), with maximum adsorption capacities of 99.73 and 66.26 mg g⁻¹, respectively. Integration of the DSA-KCC-1 nanosorbent into a d-SPE–ICP-OES workflow enabled the reliable determination of trace levels of the target ions, delivering low limits of detection, wide linear calibration ranges, and stable performance over repeated extraction cycles. Analysis of NIST CRM 1643d yielded results in good agreement with the certified values, while the method demonstrated high tolerance toward common coexisting ions. The combined structural features of the KCC-1 support and the Schiff-base ligand indicate the suitability of DSA-KCC-1 for d-SPE workflows and demonstrate the potential of this SPE format for selective preconcentration of trace metal ions in aqueous matrices. Full article

In this study, the photocatalytic performance of natural clinoptilolite was enhanced through copper modification, achieved via ion exchange followed by KOH-induced precipitation, leading to materials with different copper speciation. Physicochemical characterization using WDXRF, PXRD, FTIR and N₂ physisorption revealed a transition from exchanged Cu²⁺ species at low loading to the formation of copper-bearing phases such as brochantite, Cu(OH)₂ and CuO at higher alkalinity. The Cu-modified samples were evaluated for the photocatalytic degradation of Congo red under UV irradiation. Among them, sample NZ-Cu3 exhibited the highest activity, achieving approximately 91% dye degradation within 30–40 min. Kinetic analysis demonstrated that the degradation process is better described by the pseudo-second-order model, indicating that chemisorption plays a dominant role. Radical scavenger experiments revealed that photogenerated holes (h⁺) are the primary reactive species responsible for dye degradation, while hydroxyl radicals contribute to a lesser extent. The enhanced photocatalytic performance is attributed to the synergistic effect of photocatalytic degradation, improved charge separation and the presence of surface copper species, highlighting Cu-modified clinoptilolite as a promising low-cost photocatalyst for wastewater treatment. Full article

The interfacial polymerization of fluorine-containing polyarylates (F-PAR) represents an important synthetic route for advanced polymeric materials. This work presents a comprehensive mechanistic investigation through integrated kinetic analysis and macromolecular characterization. The polymerization for both F-PAR and its non-fluorinated analogue (M-PAR) follows a two-stage, second-order kinetic profile, with the F-PAR system exhibiting a lower initial rate constant. Kinetic modeling revealed a dynamic reaction locus, transitioning from the bulk organic phase to an indistinguishable regime. The fluorinated system exhibits distinct stage-dependent behavior: initial retardation due to fluorine-induced “nucleophilicity penalty” on bisphenol monomer followed by a kinetic crossover where the growth rate of F-PAR surpasses M-PAR through enhanced oligomer electrophilicity. The terminal stage reveals fundamental divergence, while flexible M-PAR chains sustain accelerated growth via efficient chain-chain coupling, rigid F-PAR chains reach a molecular weight plateau. The incorporation of fluorine enhances thermal stability and optical transparency due to the low polarizability of C-F bonds. This study provides a complete mechanistic roadmap of fluorine’s dynamic role in polymer architecture control. Full article

In non-cooperative DSSS signal reception, the accurate estimation of the pseudo-noise (PN) sequence period is essential for successful despreading and information recovery. In this paper, we propose an average second-order-moment autocorrelation method based on the accumulated code difference function to enhance the estimation accuracy under low-signal-to-noise-ratio (SNR) conditions. The proposed approach involves three key aspects: First, a quadrature receiver is employed to mitigate the impact of the random initial phase on demodulation, enabling the full utilization of the signal energy. Second, a code difference function is constructed using transition information between adjacent spreading codes, and by leveraging the strong correlation between these functions, accumulated processing effectively suppresses the noise influence. Third, the autocorrelation result of the accumulated code difference function displays periodic peaks separated by intervals equal to the PN sequence period, allowing for period estimation through peak interval extraction. In addition, the introduced average-second-order-moment technique addresses the peak loss caused by information code randomness while further smoothing noise. Simulation and experimental results verify the effectiveness and practicality of the proposed method, which outperformed the average-second-order-moment method by about 1.5 dB and the accumulated-power-spectrum-reprocessing method by about 2 dB. Full article

Background/Objectives: All the industry standard methods for monitoring the freeze-drying process, from the single-vial assessment using temperature probes, such as thermocouples, to batch assessments using comparative pressure measurements, have poorly defined transitions marking the end of ice sublimation. In this study, through-vial impedance spectroscopy (TVIS) is used to characterise and validate the point on the Pirani curve that corresponds to the end of ice sublimation. The impact of the solution composition in relation to its propensity to form crystalline and amorphous domains and the impact of the batch size were investigated. Methods: Individual TVIS vials were placed at specific positions across the shelf, in order to represent the core and edge vials of the batch. The unique features of the high-frequency real part capacitance, with its precise sublimation endpoint-defining plateau, were then used to map the individual-vial sublimation endpoints onto the Pirani profile, with a view to predicting the batch sublimation endpoint. Results: TVIS vial endpoints enabled a key observation that the shape of the Pirani profile may be analysed in terms of two phases, the first being largely associated with ice sublimation and the second being associated with water desorption. Moreover, by identifying the transition point more precisely, even in the small to intermediate scale systems, we provide a scientific basis for predicting the sublimation endpoint for production-scale dryers, where Pirani sensors are already in place. Conclusions: Such qualification of batch sublimation endpoints would allow for earlier, confident switching to the secondary drying stage without unnecessary delay, leading to shorter cycles, reduced energy consumption, and improved utilisation of costly freeze-drying infrastructure. Full article

The transition toward a circular economy requires innovative strategies for valorizing industrial by-products. This study investigates the potential of steelmaking furnace slag (SFS) as a low-cost adsorbent for the removal and recovery of nickel and copper ions from aqueous systems. The slag was characterized using XRF, XRD, SEM, FTIR, and thermal analyses, confirming the presence of reactive phases such as lime, periclase, and calcium silicates. Batch adsorption experiments revealed high sorption capacities (up to 147 mg·g⁻¹) and were best described by the Langmuir isotherm and pseudo-second-order kinetic model, indicating chemisorption as the rate-limiting step. FTIR and SEM analyses demonstrated the formation of nickel and copper hydroxide/oxide phases, confirming surface precipitation mechanisms. Subsequent thermal treatment produced NiO- and CuO-enriched oxide systems with photocatalytic and antibacterial potential, while hydrometallurgical recovery using ammonia solutions achieved desorption efficiencies of 90–97%. The results highlight the dual role of SFS as an efficient sorbent for wastewater pre-treatment and as a secondary source of valuable metals, contributing to sustainable materials management and circular economy goals. Full article

A-site-ordered quadruple perovskite manganites, AMn₇O₁₂, show many interesting physical phenomena, including orbital and spin modulations, spin-induced multiferroic properties, and competitions between different magnetic ground states. Doping with Cu²⁺ can result in colossal magnetoresistance properties, ferrimagnetism, and additional structural modulations producing electric–dipole helicoidal textures. Many previous works have focused on large-concentration doping, reaching ACu₃Mn₄O₁₂ compositions. Small-concentration doping has been investigated in a limited number of systems, e.g., in BiCu_xMn_7−xO₁₂. In this work, we investigated solid solutions of NdCu_xMn_7−xO₁₂ with x = 0.1, 0.2, and 0.3, prepared at 6 GPa and 1500 K. Specific heat measurements detected three magnetic transitions at x = 0 (at T_N3 = 9 K, T_N2 = 12 K, and T_N1 = 84 K) and two transitions at x = 0.1 (at T_N2 = 10 K and T_N1 = 78 K), while only one transition was found at x = 0.2 (T_N1 = 72 K) and x = 0.3 (T_N1 = 65 K). Differential scanning calorimetry (DSC) measurements showed sharp and strong peaks near T_OO = 664 K at x = 0, corresponding to an orbital-order (OO) structural transition from I2/m to Im-3 symmetry. DSC anomalies were significantly broadened and their intensities were significantly reduced at x = 0.1–0.3, and structural transitions were observed near T_OO = 630 K at x = 0.1, T_OO = 600 K at x = 0.2, and T_OO = 570 K at x = 0.3. The x = 0.1 sample clearly showed double-peak features on the DSC curves near T_OO because of the presence of two close phases. High-resolution synchrotron powder X-ray diffraction studies gave strong evidence that phase separation phenomena took place in the x = 0.1–0.3 samples, where two I2/m phases with an approximate ratio of 1:1 were present (e.g., a = 7.47143 Å, b = 7.36828 Å, c = 7.46210 Å, and β = 90.9929° for one phase and a = 7.46596 Å, b = 7.37257 Å, c = 7.45756 Å, and β = 90.9328° for the second phase at x = 0.3). The Curie–Weiss temperature changed from negative (for x = 0, 0.1, and 0.2) to positive (for x = 0.3). T_OO, T_N1, the Curie–Weiss temperature, and magnetization (at 5 K and 70 kOe) changed almost linearly with x. Full article

In recent years, information propagation on social networks has attracted extensive attention, with psychological characteristics of individuals exerting a significant influence on the diffusion process. Our study investigates the role of regret psychology and its impact on information spreading and behavioral adoption. We categorize individuals into regretful and non-regretful groups and introduce regret intensity together with the proportion of regretful individuals as dynamic variables. Based on this, we construct a two-layer interactive model consisting of a psychological layer and a behavioral layer. Then we establish the behavioral adoption model for the heterogeneous population and study the propagation characteristics of the regretful individuals on social networks. Furthermore, we derive the propagation dynamics using edge-based compartmental theory to examine the transmission mechanism. Numerical simulations, which coincide nicely with our theoretical analyses, reveal the crossover phenomena in phase transitions: as the regret threshold increases, adoption dynamics shift from second-order continuous to first-order discontinuous transitions. More importantly, for a given propagation probability, there exists an optimal regret threshold that maximizes the final adoption size. These findings highlight the crucial role of regret psychology in reshaping the propagation mechanism and provide a new theoretical perspective for understanding symmetry transformations and group heterogeneity in social contagion dynamics. Full article