Search Results (5,287)

In recent years, the integration of renewable energy sources and the widespread use of nonlinear loads have increased dynamic uncertainties in modern power systems, making real-time and synchronized monitoring essential. Accurate M-class synchrophasor estimation under these nonstationary and spectrally uncertain conditions remains a challenging problem due to dynamic variations, harmonics/interharmonics, out-of-band interference, and measurement noise. This study proposes a suitably constrained optimization-based framework for M-class synchrophasor estimation, in which a hybrid structure integrating an ESPRIT-based subspace method with the Adaptive Fitness Distance Balance Artificial Rabbit Optimization (ES-AFDB-ARO) algorithm is employed. In this framework, the optimization stage is guided by spectral information obtained via the subspace stage to narrow the search space and improve convergence stability. Performance is evaluated under IEEE C37.118 steady-state and dynamic conditions via Monte Carlo simulations, showing that total vector error, frequency error, and rate-of-change-of-frequency error values remain within standard limits. Comparative analyses at 60 dB and 40 dB SNR demonstrate that the ES-AFDB-ARO method exhibits improved and more stable performance than the widely used interpolated discrete Fourier transform, Taylor weighted least squares and Taylor–Kalman filter methods. The results show that the proposed framework offers a reliable solution for synchrophasor estimation under dynamic operating conditions. Full article

BL Lacertae objects (BL Lacs) are active galactic nuclei notable for beamed emission generated in the relativistic jets, forming a small angle with respect to our line-of-sight. The broadband spectra of BL Lacs show a two-component spectral energy distribution (SED). The group of high-energy-peaked BL Lacs (HBLs) exhibit their lower-energy SED peak at the UV to X-ray frequencies. Consequently, these objects are generally bright in the 0.3–10 keV band (compared to other blazar subclasses) and allow us to carry out intense timing/spectral studies on the wide range of timescales (from years down to a few minutes). Although X-ray emission of HBLs is widely accepted to have a synchrotron origin (along with the occasional presence of the inverse-Compton component), many problems associated with the jet particle content, their acceleration up to ultra-relativistic energies and unstable mechanisms responsible for the extreme flux/spectral variability still remain to be solved. This review highlights the basic timing and polarimetric and spectral results obtained in the framework of the numerous studies of HBLs in the 0.3–10 keV band, which was covered by the X-ray instruments operating onboard the different space missions. Moreover, the plausible physical processes responsible for the observed HBL features (relativistic shocks, magnetic reconnection, turbulence etc.) are also addressed. Full article

Shock buffet is one of the critical issues affecting the aerodynamic performance, flight quality, and flight safety of large aircraft. To overcome the limitations of traditional experimental measurement methods, such as insufficient capability in capturing flow features and high cost, an integrated experimental system tailored for extreme cryogenic and high-Reynolds-number conditions is developed based on the conventional tuft technique. This system comprises “preparation of low-flow-disturbance fluorescent mini-tufts, high-efficiency large-area tuft taping, automatic generation of digital streamline, and flow topology analysis”. Furthermore, a technique for assessing the transonic shock buffet onset using dynamic flow visualization with fluorescent mini-tufts is proposed. This paper takes a typical supercritical airfoil as the research object. First, through high-precision numerical simulations, it reveals that low-energy, unstable boundary-layer separation is the core driving force for the development and maintenance of shock buffet, and that flow separation characteristics serve as an important basis for determining the shock buffet onset. Subsequently, experimental validation is conducted in a 0.3 m high-Reynolds-number transonic wind tunnel. Using a dual-excitation-band composite light source, simultaneous measurements of pressure-sensitive paint (PSP) and fluorescent mini-tuft patterns are realized. The experimental results show that under extreme conditions, characterized by a wide total temperature range of 110 K to 280 K and strong scouring at Mach numbers from 0.6 to 0.9, the fluorescent mini-tufts (approximately 0.05 mm in diameter) exhibit excellent flow-following capability without any detachment. The digitized flow patterns of the fluorescent mini-tufts, obtained via computer image recognition algorithms, clearly reveal the location and area of boundary-layer separation. The trends show good agreement with the cryogenic PSP results, providing an important reference for determining the shock buffet onset. Full article

PMSM-based flywheel energy storage systems require fast and robust speed regulation in the presence of parameter uncertainty, load disturbances, and measurement noise, while avoiding the cost and reliability limitations associated with mechanical encoders. This paper proposes a sensorless control framework that combines a fractional-order sliding-mode speed controller with a fractional-order sliding-mode observer. To improve dynamic performance, an improved hybrid Aquila Optimizer–African Vulture Optimization Algorithm (IHAOAVOA) is employed to tune the controller parameters, while the observer follows the proposed robust sensorless design. Simulation results show that at the 1000 rpm operating point under a 20 N·m load disturbance, the proposed method limits the startup overshoot to about 0.24%, compared with 8.02% for the PI control and 9.74% for the conventional sliding-mode control. After the disturbance is introduced at $\mathrm{t}=1.0$ s, the speed drop of the proposed method is limited to 2.80%, whereas those of the PI control and conventional sliding-mode control reach 7.20% and 5.60%, respectively. At the 8000 rpm operating point under an 80 N·m load disturbance, the proposed method maintains the same advantage, with an overshoot of about 0.04% and a speed drop of 1.88%, both lower than those of the two benchmark controllers. In sensorless operation, the sensorless scheme with the IHAOAVOA-tuned speed controller also improves transient estimation performance. At the 1000 rpm operating point, the maximum startup speed estimation error is reduced from 41.8 r/min to 34.8 r/min. At the 8000 rpm operating point, the estimation error enters the ±10 r/min band at 0.0671 s, compared with 0.0718 s for the PSO-tuned case. The electromagnetic torque responses further indicate that the proposed tuning strategy improves transient torque smoothness while maintaining comparable steady-state torque behavior. These results demonstrate that the proposed control framework provides an effective balance among fast dynamic response, disturbance rejection, sensorless estimation accuracy, and electromechanical transient smoothness for PMSM-based flywheel energy storage applications. Full article

The article presents the synthesis and characterization of double halide perovskites (DHPs) with the nominal composition Cs₂Ag_0.2Na_0.4In_0.6M_0.4Cl₆ (M = Si, Ti, Zr), including photoluminescence (PL), photoluminescence excitation (PLE) spectra measured over a range of temperatures and kinetics of luminescence. The materials were synthesized via a hydrothermal method. The phase purity and elemental composition of the synthesized perovskites were confirmed by X-ray diffraction (XRD), Rietveld refinement, scanning electron microscopy (SEM) equipped with energy-dispersive X-ray spectroscopy (EDS) and elemental analysis, which demonstrated that the samples showed a close match to the target stoichiometry. The PL spectra exhibit a systematic shift toward the lower-energy region with substitution from Si to Zr, correlating with the progressive increase in the ionic radii of the substituting cations. All samples display broad, asymmetric emission bands, characteristic of self-trapped excitonic (STE) states. Temperature-dependent PL measurements reveal a gradual decrease in emission intensity with increasing temperature for all samples. The maximum emission intensity is observed in the range of ~160–200 K, corresponding to optimal conditions for radiative recombination, whereas the lowest intensity is recorded at ~80–100 K, where thermal activation of radiative centers is minimal. An increase in temperature is accompanied by a red shift in the PL bands across all compositions. In the Ti-doped DHP, a pronounced blue shift at low temperatures is observed, which can be attributed to the involvement of Ti³⁺-related electronic states. An analysis of the activation energy of thermal luminescence quenching and the results of time-resolved spectroscopy revealed the activation of thermal processes in the titanium-containing sample and their rapid decay, whereas replacing titanium with silicon leads to more stable luminescence in the crystal under study. Thus, the enhanced luminescence characteristics of double halide perovskites doped with Ti, Si, and Zr highlight their potential for advanced photonic and optoelectronic applications. Full article

In this study, In_0.40Mn_0.15Co_3.85Sb₁₂ was synthesized by the ceramic method, using a traditional melting–annealing treatment (MA), followed by grinding and sintering via the hot-pressing (HP) technique. Rietveld refinement of the powder diffraction (PXRD) data confirms that the resulting phase has a cubic crystal structure in space group Im-3, which is isostructural with the pristine Co₄Sb₁₂ phase. The cell parameter a of the filled In_0.40Mn_0.15Co_3.85Sb₁₂ increases after hot pressing compared with the Co₄Sb₁₂ phase. This suggests that the partial substitution of cobalt atoms with manganese (Mn) alters the cell size of the resulting material. The PXRD pattern of the In_0.40Mn_0.15Co_3.85Sb₁₂ phase of the MA sample shows a low-intensity line (~30°), which is related to elemental antimony (~4%, by Rietveld refinement). Rietveld refinements support a second model which implies the pressure-induced self-insertion of remanent antimony from the (MA) phase into the void sites after (HP) treatment, leading to a new phase: In_0.30Sb_0.10Mn_0.15Co_3.85Sb_11.90 (HP). The vibrational Raman modes of the obtained phases, In_0.40Mn_0.15Co_3.85Sb₁₂ (MA and HP), are correlated with those of the pristine phase, Co₄Sb₁₂. A strong primary signal at 185 cm⁻¹ in the Raman spectrum of In_0.40Mn_0.15Co_3.85Sb₁₂ (MA) is associated with antimony impurities, which is confirmed by Rietveld refinement. Raman spectra of the HP sample are well correlated to the (SPS) Co₄Sb₁₂ phase, which reveals structural changes due to self-insertion of antimony into the voids. The band-gap energy values of both the In_0.40Mn_0.15Co_3.85Sb₁₂ (MA) phase and the (HP) phase are 0.750 ± 0.006 eV and 0.650 ± 0.004 eV, respectively. These values are higher than those of the Co₄Sb₁₂ phase, which has a band-gap energy of 0.55 eV. This indicates that the electronic band structure is modified by the partial substitution of cobalt with manganese and the introduction of indium in the icosahedral cages. Electrical transport properties at room temperature show that In_0.40Mn_0.15Co_3.85Sb₁₂ (MA) and In_0.30Sb_0.10Mn_0.15Co_3.85Sb_11.90 (HP) are n-type semiconductors. Full article

In this work, the atomic layer deposition (ALD) of an ultra-thin AlN film on the surface of monolayer EG grown on-axis 4H-SiC(0001) substrates has been investigated as a function of the number of ALD cycles. The formation of a homogeneous film with a 10 nm thickness and crystalline wurtzite structure was obtained after 320 cycles, as demonstrated by atomic force microscopy (AFM) mapping, X-ray photoelectron spectroscopy (XPS) and X-ray diffraction. Raman mapping revealed a significant reduction in the native compressive strain of as-grown EG (ε ≈ −0.36%) with increasing ALD cycles, down to a value of −0.16% after full coverage. Finally, Kelvin Probe Force Microscopy (KPFM) surface potential mapping allowed the evaluation of energy band alignment of the AlN/EG heterojunction, with a conduction band offset of ~2.6 eV between the crystalline AlN film and the underlying EG. Such a large offset confirms AlN as a promising gate dielectric for EG-based devices. Full article

Amid the ongoing acceleration of climate change over recent decades, extreme precipitation events have become more frequent and intense on a global scale, triggering severe natural hazards and considerable socioeconomic damage. Nevertheless, how extreme precipitation has evolved at the national level over long time spans, and what role atmosphere–ocean teleconnections play in driving regional differences, remains insufficiently explored. This study addresses that knowledge gap by conducting a comprehensive assessment of eight ETCCDI-based extreme precipitation indices (PRCPTOT, CWD, R20, R95p, R99p, RX1day, RX5day, and SDII) across six climatic sub-regions of China (Northeast, North, East, Central South, Northwest, and Southwest) over 1960–2020, drawing on daily records from 695 quality-controlled meteorological stations. Key atmospheric and oceanic circulation drivers were further diagnosed and their joint influence was quantified via multiple wavelet coherence (MWC). The analysis shows that five of the eight indices (CWD, R95p, R99p, RX1day, and RX5day) underwent statistically significant fluctuating changes (p < 0.05) throughout the 61-year record. Seven indices, all except CWD, demonstrated upward tendencies, with mutation points clustering after 2010, most notably between 2011 and 2016. Wavelet power spectra indicates elevated energy concentrations at multiple time scales, although only CWD exhibited a statistically significant periodicity of approximately 8–10 a (p < 0.05 against red noise). In terms of spatial patterns, index magnitudes generally increased along a northwest-to-southeast gradient. Stations registering significant upward shifts were concentrated in East and Central South China, whereas significant downward shifts appeared mainly in North China and the northern portion of East China. An altitude-dependent pattern was also detected: CWD rose with elevation, while the remaining indices declined sharply below 1288 m, fluctuated in the 1288–2090 m band, and dropped again above 2090 m. Wavelet coherence analysis uncovered significant resonance between extreme precipitation and four circulation indices—SCSMMI, WPSHI, PNA, and NAO. MWC further identified three driver combinations—ENSO-PNA, SCSMMI-WPSHI, and ENSO-NAO-EASMI—as the most influential, acting both individually and synergistically. These results furnish an empirical basis for forecasting, preventing, and managing precipitation-related disasters across China under future climate scenarios. Full article

Direct current (DC) surface flashover on polystyrene (PS) remains a critical bottleneck that impedes its reliable application in high-voltage insulation apparatus. To circumvent the protracted processing durations and stringent film-forming conditions inherent in conventional surface modification techniques, this study proposes a novel “liquid-film-assisted in situ rapid plasma curing” strategy. By harnessing atmospheric-pressure dielectric barrier discharge (DBD) technology within an argon ambient, the rapid (<6 min) and efficient deposition of a fluorosilane (FAS-13) functional coating onto the substrate was achieved. Microscopic characterizations coupled with isothermal surface potential decay (SPD) measurements reveal that this coating substantially mitigates the detrapping and surface migration of charge carriers. Macroscopic DC flashover testing corroborates that, under the optimal modification ratio, the surface breakdown voltage of PS is elevated to 14.04 kV, yielding an insulation gain of 26.94%. To elucidate the underlying physical mechanisms, density functional theory (DFT) calculations were conducted, revealing that the energy band misalignment between the wide-bandgap fluorinated layer and the substrate facilitates the construction of a high-density deep trap network (with a depth of ~0.8 eV) at the coating–substrate interface. By robustly anchoring primary electrons and inducing the formation of a homopolar space charge shielding layer, these deep traps physically arrest the evolution of the secondary electron emission avalanche (SEEA). Consequently, this work not only establishes a viable engineering framework for the rapid, large-scale surface reinforcement of DC insulation equipment but also provides profound quantum chemical insights into interfacial trap regulation within all-organic dielectrics. Full article

The Carajás Province, located in the southeastern Amazon, hosts some of the world’s largest high-grade iron deposits. Despite their economic importance, the processes linking lateritic weathering and iron enrichment remain incompletely understood. This study investigates the role of lateritic weathering in the evolution of the Serra Leste iron deposit through the characterization of a weathering profile and its parent rocks using drill-core samples. Analytical methods included X-ray diffraction (XRD), optical microscopy, scanning electron microscopy coupled with energy-dispersive spectroscopy (SEM-EDS), whole-rock geochemistry, and Mössbauer spectroscopy. Jaspilites weathered into ferruginous saprolite while preserving relic banding and mineral textures. Magnetite alteration produced pseudomorphic hematite with dissolution cavities progressively infilled by goethite, indicating iron remobilization during weathering. Weathering of chloritites generated clayey saprolite enriched in kaolinite and iron oxyhydroxides, with gibbsite occurring in more advanced stages. The uppermost horizon consists of a ferroaluminous duricrust composed of massive, spherulitic, and brecciated iron oxyhydroxides associated with gibbsite. Up-profile geochemical trends are marked by decreasing SiO₂ and increasing Fe₂O₃. The mineralogical, textural, and geochemical relationships indicate that the ferroaluminous duricrust was developed through contributions from both ferruginous and clayey saprolitic systems, particularly from the latter. These results support the interpretation that lateritic weathering played an important role in iron redistribution and supergene enrichment within the Serra Leste deposit, consistent with mature Amazonian lateritic systems. Full article

High-performance electromagnetic wave absorption materials are desperately needed due to the growing serious electromagnetic interference and pollution issues brought on by the quick growth of modern electronic technology and wireless communication. This work uses the organic–inorganic hybrid perovskite MAPbBr_xI_3−x as a model system to address the problem of restricted loss mechanisms and the challenges in changing the absorption bandwidth of single-component wave-absorbing materials. It achieves systematic tuning of electromagnetic wave absorption performance, especially within the effective working frequency spectrum, through accurate halogen site engineering. According to the study, MAPbI₃ (MPI), MAPbBr_1.5I_1.5 (MPIB), and MAPbBr₃ (MPB), which were synthesized using the anti-solvent approach, all demonstrated exceptional microwave absorption capability, with maximum reflection loss values exceeding −37 dB, among which MPB achieves a remarkable value of −42.41 dB at 16.60 GHz. More significantly, this work shows a distinct structure-property relationship between the effective absorption peak frequency range of this series of materials and their band structure: the strongest absorption peak shows a regular blue shift as the material bandgap widens and the bromine content rises. This finding suggests that focused tailoring of the operating frequency band in wave-absorbing materials can be achieved by manipulating the band structure of perovskites by varying the halogen concentration. In addition to confirming the significant application potential of organic–inorganic hybrid perovskites in the field of microwave absorption, this study offers a novel research perspective and material template for precisely and programmably controlling the absorption frequency band of wave-absorbing materials based on their basic electronic structures. Full article

Magnesium antimonide (Mg₃Sb₂) has emerged as a promising high-performance thermoelectric material, yet its efficiency is fundamentally determined by intrinsic point defects. In this study, we present a comprehensive investigation of defects in the intermetallic compound Mg₃Sb₂ using first laws of thermodynamics and density functional theory (DFT) within the generalized gradient approximation (GGA). By calculating the energy of defect formation and the charge transition energy between energy levels, it was determined how the change in chemical potential associated with phase synthesis affects the phase stability and carrier concentrations. Calculations show that donor defects dominate in Mg-rich alloys, primarily antimony vacancies and magnesium atoms in interstitial positions. This means that in a phase with a slight magnesium excess, e.g., Mg_3.01Sb_1.99 at 1400 K, n-type conductivity dominates. In the opposite case, i.e., in an Sb-rich alloy, magnesium vacancies spontaneously form in the Wyckoff 1a position. These ionized acceptors induce strong self-compensation, blocking the Fermi level about 0.38 eV above the valence band maximum. As a result of this process, the Mg₃Sb₂ phase, at elevated temperatures, becomes the non-stoichiometric Mg_2.99Sb_2.01 phase, which causes the material to retain p-type conductivity and actively block doping-induced n-type conductivity. The conducted studies demonstrate that the homogeneity range of the Mg-Sb system, although traditionally considered narrow, has a significant impact on the semiconducting properties of the material. Furthermore, they also point to the need for continued research on high temperature in the area of synthetic defect engineering, interface engineering, and optimization of the thermoelectric properties of materials based on Mg-Sb alloys. Full article

With the rapid development of rail transit, environmental vibrations caused by subway vehicle loads have garnered increasing attention. This study employs a three-dimensional finite element–infinite element coupling method to establish an integrated numerical model of the vehicle–track–tunnel–ground coupled system. The vehicle loads are obtained through the simulation of a physical vehicle model, incorporating the effects of track irregularities as excitation sources. Based on this model, the dynamic response characteristics of subway-induced vibrations within structural components and geological layers are systematically investigated. The results show that the vertical vibration response in the surrounding ground is most pronounced, with the vertical acceleration distribution following the pattern: tunnel bottom > tunnel crown > tunnel sides. Furthermore, high-frequency vibration components attenuate rapidly within one tunnel diameter. As vehicle speed increases, the vibration response in the surrounding ground significantly intensifies, indicating that dynamic effects are more pronounced under high-speed operation. Meanwhile, the vibration responses in far-field regions tend to converge. This study also finds that an acceleration amplification zone appears in the low-frequency band (0–5 Hz) during vibration propagation. Additionally, the near-field tunnel response exhibits energy concentration around 35 Hz before attenuation, which is significantly higher than the dominant frequency after propagation to the far field. These findings provide important insights for understanding the propagation mechanisms of subway-induced vibrations and offer a solid basis on which to develop effective vibration control strategies. Full article

Traditional taste evaluation relies heavily on manual sensory analysis, which is highly subjective and inefficient with poor cross-individual generalization, limiting its application in industrial flavor detection. To achieve accurate cross-subject taste recognition, this paper proposes an electroencephalogram (EEG) classification method based on a meta-learning wavelet graph convolutional neural network (ML-WGCNet) under sweet- and bitter-taste stimuli. Sucrose (sweetness) and quinine (bitterness) were used as stimulation sources, each prepared at six concentration gradients, including a water control. EEG signals were detected from 20 subjects. First, the Morlet wavelet transform was applied to decompose the EEG signals in the time–frequency domain, extracting the maximum and average energy values from five frequency bands as core features. A graph structure was then constructed using electrodes as nodes and Pearson correlation coefficients between electrodes as edge weights. A lightweight graph convolutional neural network (GCN) is employed to model spatial correlations among brain regions. Finally, by integrating a meta-learning framework and adopting leave-one-subject-out cross-validation, the model can rapidly adapt to new subjects. The experimental results show that the proposed method achieves average accuracies of 76.03% and 77.01% in cross-subject classification of sweet and bitter tastes, respectively. The corresponding precision values are 79.94% and 79.53%, the recall values are 75.77% and 78.51%, and the F1-scores are 78.24% and 78.08%, respectively, demonstrating that the proposed model significantly outperforms existing mainstream EEG classification methods. Full article

In this study, density functional theory (DFT)-based investigations are carried out using the CASTEP code. The plane-wave pseudopotential method is used to explore the multifunctional properties, including the structural, electronic spectra, thermo-mechanical and hydrogen storage properties, of hydrogen-rich mixed-anionic (Li₃H₄N₂X, where X = F, Cl, Br, and I) halides. The exchange–correlation interactions are treated within the generalized gradient approximation (GGA) using the Perdew–Burke–Ernzerhof (PBE) functional, while the hybrid HSE06 function is used for accurate band gap predictions. Moreover, the optical properties of the halides are analyzed under the influence of UV–Vis radiation instances. The band gap values of these orthorhombic-structured halides lie in the visible-to-UV regions of radiation, with values of 2.97 eV, 3.12 eV, 3.06 eV and 3.28 eV, respectively. Such band gap values allow these materials to absorb nearly 75% to 90% of incoming radiation, with absorption values around (10⁵ cm⁻¹). These favorable opto-electronic responses make these halides suitable for solar radiation energy conversion applications. Stable thermodynamic responses and the mechanical nature of the mixes (brittle for Li₃H₄N₂Br and ductile for the rest) reveal their practical applicability for flexible photonics. Moreover, due to the presence of rich hydrogen atoms, the Li₃H₄N₂F halide exhibits a gravimetric ratio of around 6.0 wt%, which is higher than the standard (5.5 wt%) value defined by the US DOE. Similarly, GHSC values of 2.5 wt% for Li₃H₄N₂I, 3.5 wt% for Li₃H₄N₂Br, and 5.0 wt% for Li₃H₄N₂Cl are reported; these values indicate that these compounds possess strong potential for use in the hydrogen fuel cells required in light-duty vehicles. Full article