Search Results (3,997)

Ultrasonic testing is a prevalent method for non-destructive evaluation of railway rails; however, conventional Time-of-Flight (ToF) approaches applied in practical dry-coupled inspections often rely on simplified assumptions regarding wave propagation velocity and neglect complex waveform characteristics. This paper presents a robust depth estimation framework for surface-breaking cracks that enhances sizing accuracy through effective velocity calibration and Hilbert envelope extraction. Unlike standard methods that assume the free-space speed of sound in air (343 m/s) for wave propagation within the air-filled gap of a surface-breaking crack, we propose an effective velocity model derived from in situ calibration to account for the boundary layer viscosity and thermal conduction effects within narrow crack geometries. The signal processing chain incorporates spectral analysis, band-pass filtering, and Hilbert Transform-based envelope detection to mitigate noise and resolve phase ambiguities. Experimental validation on steel specimens with controlled defects (0.2–10.0 mm) demonstrates that the proposed method achieves an exceptional linear correlation (R² ≈ 0.9976). The calibrated effective velocity was determined to be 289.3 m/s, approximately 15.6% lower than the speed of sound in air, confirming the significant influence of confinement effects. Furthermore, excitation parameters were optimized, identifying that high-voltage excitation (≥110 V) and a tuned pulse width (≈150 ns) are critical for maximizing the signal-to-noise ratio. The results confirm that combining physical model calibration with advanced signal analysis significantly reduces systematic errors, paving the way for portable, high-precision rail inspection systems. Full article

Historical masonry minarets are highly vulnerable to seismic actions due to their slender geometry, limited tensile capacity, and material heterogeneity. However, their response to near-fault ground motions characterized by velocity pulses remains insufficiently explored. This study investigates the seismic response of the historical Tavanlı Mosque Minaret (1894, Trabzon, Türkiye) subjected to pulse-like (PL) and non-pulse-like (NPL) near-fault ground motions. A three-dimensional finite element model (FEM) was developed in ANSYS Workbench and systematically calibrated using empirical formulations to represent the current dynamic condition of the structure. Seismic performance was evaluated through linear dynamic analyses in terms of displacement demands, principal stress distribution, and drift-ratio-based performance levels. The results indicate that model calibration significantly modifies the dynamic characteristics, increasing the fundamental frequency from 0.734 Hz to 1.126 Hz and reducing displacement demands by approximately 35–76% across the considered records. Despite this improvement, PL ground motions consistently generate more critical deformation demands than NPL motions, frequently exceeding Collapse Prevention (CP) limits even when Peak Ground Acceleration (PGA) values are relatively low. A key finding is that seismic demand cannot be reliably predicted by peak intensity measures or pulse-period ratios ($T_p/T_1$) alone; rather, velocity-related parameters and pulse coherence govern the structural response. These results demonstrate that integrating empirical model calibration with pulse-sensitive seismic analysis is essential for reliable seismic assessment and conservation planning of slender historical masonry structures located in near-fault regions. The study offers a systematic framework that integrates model calibration and pulse-sensitive seismic analysis for evaluating the drift-controlled response of slender historical masonry minarets in near-fault regions. Full article

Unmanned aerial vehicle Synthetic Aperture Radar (UAV SAR) is inevitably affected by hardware performance and complex electromagnetic environments, resulting in noise in the radar echo signal. This causes image blurring and loss of detail, severely limiting the detection performance and imaging quality of UAV SAR. High-repetition-rate UAV SAR can achieve high signal-to-noise ratio (SNR), but the SAR data volume grows exponentially, posing a challenge for large-scale data processing. Furthermore, in the case of high repetition rate, downsampling methods are needed to reduce the amount of raw data, which leads to a decrease in the echo SNR, thus significantly affecting SAR image details. Existing SAR signal processing methods typically involve a series of processing steps on the raw echo data, such as azimuth and range direction processing. However, these traditional methods still have limitations in improving the SNR, especially in complex environments or when the target signal is weak, where their effectiveness is often unsatisfactory. To address these issues, this paper first analyzes the SNR gain in SAR echo data processing and proposes a phase-compensated parameter-adjusted Chebyshev filtering algorithm to improve the SNR of SAR echoes. The algorithm first utilizes azimuth Chebyshev filtering to avoid spectral aliasing during downsampling and fully leverages navigation information provided by the airborne platform to accurately compensate for phase changes between pulses. Then, it employs parameter-adjusted Chebyshev filtering and coherent superposition techniques to combine multiple adjacent pulses into a single pulse with a higher SNR. Finally, the enhanced pulses are combined into a new two-dimensional matrix for subsequent pulse compression and imaging processing. This method can improve the echo SNR while reducing the amount of echo data, minimizing the loss of the original echo SNR and reducing the memory footprint of subsequent imaging processing, thus effectively improving data processing efficiency. The effectiveness of the algorithm is verified through simulation and actual measurement data. Full article

3D electrodeposition printing is an emerging process for fabricating metallic parts with controllable geometry, yet the coupled influences of electrochemical kinetics, ion transport, and tool motion on layer height remain difficult to interpret. This work presents a physics-based process model that links key process inputs, current density, electrolyte concentration, the inter-electrode gap, and tool scanning speed, to the resulting layer height in 3D electrodeposition printing of nickel-based structures. The model combines species transport in the inter-electrode gap with Butler–Volmer kinetics, under carefully stated assumptions regarding current efficiency, overpotential, and lateral spreading. Model predictions are validated against experimentally reported layer heights over a range of process conditions, yielding average errors (9–15%) and root-mean-square errors (0.13–0.28 µm) that demonstrate good agreement and highlight the impact of simplifying assumptions. Systematic parametric studies reveal how each process input monotonically influences layer height in ways consistent with Faraday’s law and diffusion-controlled growth, while also quantifying the relative sensitivity to different parameters. Building on these results, we introduce a dimensionless 3D Electrodeposition Printing Index that consolidates the key process and material parameters into a single scalar describing the geometric growth regime. The index enables construction of process maps that capture how combinations of current density, scan speed, concentration, and gap affect achievable layer height within the validated operating window. The scope and limitations of the proposed modeling framework and the index, particularly regarding other materials, more complex geometries, and pulsed or strongly convective regimes, are explicitly discussed, providing a basis for future model extensions and experimental validation. Full article

The development of high-efficiency energy dissipation devices is crucial for mitigating the significant threat posed by seismic loads to modern buildings. Therefore, the purpose of this work is to design a novel fluid viscous inerter damper (FVID) and systematically investigate its mechanical performance through theoretical derivations, experiments, and finite element simulations. Furthermore, the impact of FVIDs on the seismic performance of structures is comprehensively evaluated. The advantage of FVID is that under external excitation, the fluid can flow through multiple channels, thereby generating inertial and damping forces to dissipate energy. The theoretical model of FVID’s output force is determined based on FVID’s construction and fluid flow characteristics. The hysteresis performance of the FVID is evaluated through cyclic loading tests, and the influence of the cross-sectional radius and number of turns of the helical tube on its output force is analyzed. By performing finite element simulations of the internal flow field of FVID, the distributions of fluid pressure and velocity at different positions within FVID are analyzed. Based on Simulink, the focus is on investigating the control effect of FVID on structural responses under non-pulse near-field ground motions, pulse-type near-field ground motions, and far-field ground motions. The results indicate that the FVID has a strong energy-dissipation capacity and can effectively reduce structural responses under different types of earthquakes. The cross-sectional radius of the helical tube is a key design parameter that determines the damper’s output force. For highly destructive pulse-type near-field ground motions, FVIDs still exhibit excellent comprehensive performance in the structure. Full article

This study examines the combined effects of styrene–butadiene rubber (SBR) latex and fiber reinforcement on the mechanical and electrical properties of a high-performance fiber-reinforced composite (HPFRC). Mixtures incorporating steel fibers (SF, 0–4.5%), carbon fibers (CF, 0–1%), and hybrid SF/CF systems were evaluated, with 10–20% of the mixing water replaced by SBR. Electrical resistivity, rheological behavior, mechanical properties, and durability-related parameters were assessed and compared with plain and fiber-reinforced mixtures. Results showed that SBR significantly improved rheological behavior, flexural performance, durability, and interfacial bonding, while moderately enhancing compressive strength. The incorporation of fibers led to reduced electrical resistivity, with CF being more effective than SF, and the lowest resistivity of 4 Ω·m was achieved using a hybrid system of 0.25% CF and 1.5% SF. The addition of SF up to 1.5% increased compressive strength by up to 21%, whereas CF at 0.5% yielded the highest strength of 120 MPa. Durability indicators, including water absorption, sorptivity, and ultrasonic pulse velocity, were significantly improved at low SBR and fiber dosages. Interfacial treatment with SBR enhanced slant shear and pull-off strengths by up to 75% and 121%, respectively, confirming the effectiveness of polymer modification for multifunctional and repair-oriented HPFRC applications. Full article

The spatial response of rectangular pulse heterodyne phase-sensitive optical time-domain reflectometry ($\varphi$-OTDR) to an acoustic event is characterized by a windowing function rather than a point-like sensitivity. This effect degrades the system’s spatial resolution and introduces systematic errors in array signal processing. This work presents modeling analysis and a mitigation strategy for this fundamental limitation. The spatial windowing effect is modeled as a point spread function (PSF) derived from physical mechanisms and system parameters, including the pulse width, gauge length, and intra-pulse intensity dynamics. The PSF model is validated against measurements under near-ideal conditions using a fiber-coupled tuning fork. A Wiener filter-based deconvolution method is utilized to invert the windowed spatial response towards a point-like response. The effectiveness of this inversion is demonstrated through enhanced spatial resolution and accurate reconstruction of two-dimensional wavefront geometry. Furthermore, the impact of this effect on array signal processing is quantitatively evaluated. The results demonstrate that the proposed method effectively suppresses systematic errors in wavefield analysis, and specifically enhances the accuracy and confidence of steered response power—phase transform (SRP-PHAT) spatial spectrum estimation. This study provides a systematic framework for understanding, quantifying, and inverting the spatial response in $\varphi$-OTDR, enabling accurate and interpretable acoustic field sensing. Full article

The aim of this study was to model the inactivation of Bacillus coagulans vegetative cells subjected to thermal processing (60–90 °C, 1–30 min) and pulsed electric fields (PEF) (11, 15, and 20 kV/cm, up to 0.12 s, 20 Hz, 15 μs pulse width) at different pH environments (4.0 to 7.0) and in real food matrices (peach puree and carrot juice). Microbial survival data were successfully described using the Gompertz model. Thermal experiments confirmed the high heat resistance of B. coagulans, with maximum survival observed at pH 5.0–6.0. PEF treatments were effective in inactivating vegetative cells, with more intense PEF conditions leading to faster inactivation. Complete inactivation was achieved in less than 15 ms at low pH (4.5), while more than 120 ms was required at pH 6.0. Preheating samples to 50–60 °C prior to PEF significantly reduced the PEF processing time needed for full inactivation, by approximately 88%. In food matrices, the inactivation rate in peach puree was twice as high as in carrot juice, but up to 8 times lower than in buffer solutions. Cells were inactivated twice as fast in peach puree as in carrot juice. This study provides quantitative technical parameter references for optimizing non-thermal processing technologies for acidic/weakly acidic fruit and vegetable products. Full article

The partial discharge (PD) caused by insulation defects of gas-insulated switchgear (GIS) threatens the secure and stable operation of power systems. Traditional PD pattern recognition methods exhibit limitations due to incomplete information utilization and unresolved correlations among characteristic parameters. Based on the partial discharge mechanisms of GIS, this paper establishes a GIS partial discharge simulation model using the finite element time-domain (FETD) method. The propagation rules and influence factors of ultra-high-frequency (UHF) signals are studied. Furthermore, a PD pattern recognition method based on a deep convolutional neural network (CNN) is proposed. Research results indicate that UHF signals generated by GIS partial discharge are significantly influenced by pulse current waveforms and discharge quantity. The peak-to-peak amplitude of the electric field (Epp) increases linearly with the current amplitude, while it decreases nonlinearly with increasing pulse width. The UHF signal remains a certain value while the pulse width exceeds a critical threshold (4 ns). The proposed CNN-based approach, utilizing full-wave UHF signals, overcomes the shortcomings of traditional methods reliant on manually extracted discrete feature parameters. Compared to other network architectures and optimization algorithms, the ConvNeXt-AdamW model demonstrates superior performance, achieving an average PD pattern recognition accuracy exceeding 96%. Full article

This paper proposes a single-stage three-phase AC-DC converter based on an LLC resonant topology utilizing a front-end matrix switch. Unlike traditional two-stage solutions, the proposed topology synthesizes a fluctuating equivalent DC voltage from the three-phase input, achieving direct power conversion with high efficiency. To maintain a stable DC output voltage against the time-varying input, a trajectory-based Pulse Frequency Modulation (PFM) control strategy is developed. By employing State-Plane Analysis (SPA), the operational trajectory is divided into four calculation segments, allowing precise derivation of the switching frequency and duty cycles for both boost and buck modes within a single line cycle. Furthermore, to improve power density and reduce parasitic parameters, a high-frequency planar inductor with interleaved windings and a planar transformer are designed for 500 kHz operation. A pipeline control architecture based on a single DSP is implemented to handle the complex real-time computations. A 500 W prototype is built and tested under 100 V input and 130 V output conditions. Experimental results demonstrate that the converter achieves a peak efficiency of 97%, a power factor of 0.99, and a grid current Total Harmonic Distortion (THD) of 3.95%, validating the effectiveness of the proposed topology and control scheme. Full article

Regarding the problem of the accurate estimation of coherent parameters for the distributed coherent jamming system (DCJS) in active radar applications, this paper first establishes a transmit–receive signal model of the DCJS in the presence of coherent parameter estimation errors. Then, it analyzes and verifies that the generalized cross-correlation function weighting method causes a decrease in the estimation accuracy of coherent parameters due to whitening processing, which in turn impairs the synthesis efficiency of the DCJS. Finally, a coherent parameter estimation method based on frequency-domain feature matching is proposed. The weighting method based on frequency-domain feature matching can effectively preserve the intra-pulse features of signals, thereby improving the estimation accuracy of coherent parameters. The simulation results show that, compared with the existing algorithms, the proposed method improves the time delay estimation accuracy by 27.0% and the phase difference estimation accuracy by 8.3%. Full article

Photoelectrochemical (PEC) water splitting offers a sustainable route for solar-to-hydrogen conversion, yet its large-scale deployment is often hindered by energy-intensive and costly fabrication processes for semiconductor photoelectrodes. Electrodeposition provides an attractive alternative owing to its solution-based, low-temperature, and scalable nature; however, the relationship between electrochemical deposition parameters and photoelectrode functionality remains insufficiently understood. Herein, we systematically investigate system-level control in electrodeposition for photoelectrode synthesis using BiVO₄ photoanodes and CuO/Cu₂O photocathodes as model systems. By modulating deposition potential, current density, and electrical control modes, we elucidate how interfacial ion dynamics and growth kinetics govern film morphology, phase evolution, and PEC performance. DC electrodeposition establishes a baseline structure–performance relationship governed by precursor concentration and current density, while pulsed operation enables decoupling of nucleation and growth, leading to refined nanostructures and enhanced photocurrent responses. Further incorporation of reverse-pulsed potentials provides dynamic interfacial reset, enabling precise control over porosity and grain connectivity. The optimized BiVO₄ photoanodes fabricated under tailored reverse-pulsed conditions exhibit improved photocurrent density compared to continuously deposited counterparts. The insights presented here provide practical guidelines for rationally engineering high-performance, scalable, and environmentally benign photoelectrodes for PEC water splitting. Full article

Welding copper (Cu) and aluminum (Al) is highly demanded for lightweight and cost-effective manufacturing. However, it faces significant challenges. First, substantial differences in physical properties may lead to high residual stresses and distortion. Second, brittle intermetallic compounds (IMCs) readily form at the interface, severely compromising the joint’s mechanical properties and electrical conductivity. Third, the native oxide film on Al impedes effective wetting and bonding. Therefore, effective control over the interfacial microstructure of the welded joint is essential. This review provides a critical analysis and comparison of several typical welding techniques, including laser welding (LW), friction stir welding (FSW), ultrasonic welding (UW), brazing and soldering, and welding–brazing. These analyses focus on their process characteristics, joint microstructures, and corresponding formation mechanisms. Furthermore, this review synthesizes key strategies for enhancing joint quality, including process parameter optimization, introduction of functional interlayers, and external assistance, aimed at optimizing joint microstructure and minimizing defects. Based on the analysis, this work provides comparative insights into process selection and microstructure control, and highlights future directions: advancing novel methods such as magnetic pulse welding and transient liquid phase bonding; developing intelligent real-time process control to suppress brittle IMCs and associated defects; promoting sustainable practices and establishing standardized performance evaluation; and systematically investigating long-term reliability to support the industrial application of robust Cu/Al joints. Full article

This work investigated the structural, morphological, electrical and photovoltaic properties of n-ZnNiO/p-Si heterostructures. ZnNiO nanocomposite thin films were fabricated on p-Si (100) substrates using pulsed laser deposition, enabling the formation of n-type oxide/p-type silicon heterojunctions. The crystalline structure and surface morphology of the deposited thin films were examined using X-ray diffraction and scanning electron microscopy, revealing well-defined crystalline features and uniform surface morphology. The electrical characteristics were analyzed through current–voltage measurements, allowing the extraction of key diode parameters. In addition, the optoelectronic response under ultraviolet illumination was investigated, demonstrating pronounced photosensitivity in the UV spectral range. Several important electrical and optoelectronic parameters relevant to ultraviolet photodetection were determined and discussed. The obtained results indicate that ZnNiO-based heterostructures combined with silicon substrates constitute a promising material platform for advanced optoelectronic and ultraviolet applications. Full article

Background: Human immunodeficiency virus (HIV) and antiretroviral therapy (ART) are known to be involved in cardiovascular disease development. They act alongside systemic risk factors, which interact with both macrovascular and microvascular vessels to accelerate vascular damage. Therefore, the aim of this study was to investigate the cardiovascular risk factors and their relationship with retinal microvascular function in HIV-positive pregnant women on ART in Mthatha, South Africa. Methods: A cross-sectional study was carried out among 78 pregnant women (25 HIV-positive and 53 HIV-negative) in Mthatha, South Africa. Blood pressure (BP) parameters, including systolic BP (SBP), diastolic BP (DBP), and heart rate (HR), were measured, and mean arterial pressure (MAP) was calculated. Lipid profile parameters and fasting blood glucose were assessed. Markers for kidney function, such as albuminuria, were determined. Vascular biomarkers including asymmetric dimethyl arginine (ADMA) and human endothelial specific molecule-1 were quantified. Non-invasive vascular function parameters such as flow-mediated slowing (FMS), carotid-femoral pulse wave velocity (cfPWV), ankle-brachial index, central retinal arteriolar equivalent (CRAE), central retinal venular equivalent (CRVE), arteriolar venular ratio (AVR), uterine artery pulsatile index (UtA PI) were determined. Results: Diastolic BP, MAP, cfPWV, ADMA, low density lipoprotein (LDL-c) and UtA PI were higher in the HIV-positive group (p ≤ 0.05) compared to the HIV-negative group. The prevalence of prehypertension/hypertension was higher in the HIV-positive group (p ≤ 0.05). DBP, MAP, and cfPWV correlated positively with CRVE in the HIV-positive group (p ≤ 0.05), while AVR negatively correlated with the urinary creatinine (uCr) in the same group (p ≤ 0.05). Linear regression results demonstrated that DBP, cfPWV, ABI, and LDL-c were predictors of reduced AVR in the HIV-positive group. Conclusions: Increased cardiovascular risk was observed in HIV-positive pregnant women on ART. Further, increased cardiovascular risk such as hypertension and endothelial dysfunction due to ART predicted retinal microvascular dysfunction in the HIV-positive population. This implies a potential mechanistic link between macrovascular dysfunction due to cardiovascular risk factors and retinal microvascular impairment, highlighting the importance of assessing cardiovascular risk early and preserving overall vascular health in HIV-positive population. Full article