Search Results (802)

This study investigated the elevated-temperature deterioration of loess-containing concrete with different target strengths and evaluated ultrasonic-pulse-velocity (UPV)-based models for predicting residual compressive strength. Six mixtures combining target strengths of 30 and 45 MPa with loess replacement levels of 0, 15, and 30% were exposed to 23, 100, 200, 300, 500, and 700 °C. The dataset comprised 108 individual measurements representing 36 mixture-temperature conditions. Bulk density, UPV, and compressive strength were measured after natural cooling. Two normalization schemes were distinguished: a normal-concrete-based relative performance index, which retains both the initial penalty caused by loess replacement and subsequent thermal deterioration, and a mixture-specific residual ratio referenced to the initial value of each mixture. Experimental variability was quantified using standard deviations, coefficients of variation, and 95% confidence intervals. The effects of target strength, loess replacement, and temperature were examined using three-way ANOVA and Kruskal–Wallis tests. In addition, leakage-free condition-wise group cross-validation was performed so that the three replicates from each mixture-temperature condition were never divided between training and validation sets. UPV and compressive strength decreased markedly between 300 and 500 °C. Absolute compressive strength was significantly affected by all three factors, whereas exposure temperature was the dominant main effect for the mixture-specific residual strength ratio. Under condition-wise cross-validation, the normal-concrete-based relative model retained R² = 0.906, MAPE = 10.81%, and MPE = 0.60%, while the mixture-specific residual-ratio model achieved R² = 0.957 and MAPE = 7.94%. The proposed models are therefore suitable as preliminary screening-level tools within the investigated material and temperature ranges, but not as stand-alone bases for final structural safety decisions. Full article

With the growing complexity of electromagnetic environments, electronic systems suffer from prominent strong electromagnetic interference in practical service. As a key component implementing power amplification and transmission in communication systems, interference and damage effects of a GaN HEMT power amplifier under High-altitude Electromagnetic Pulse (HEMP) directly affect the regular operation of systems. In this paper, a physical device model and an injection source model are built first; injection simulations of different HEMP pulses are adopted to analyze internal temperature and current density distributions, predicting vulnerable positions of the device under gate injection. A GaN HEMT power amplifier based on CGH40010F is then established to investigate the failure mechanism under HEMP injection and the damage effect of different pulse parameters. An injection experiment system is conducted according to HEMP pulse standard; results indicate that power amplifier failure stems from GaN HEMT device destruction. The damage evolution is tightly associated with injected energy accumulation, and the gate–source channel is the susceptible region for GaN HEMT under gate injection. These conclusions can provide important references for the protective design of GaN HEMT power amplifiers. Full article

Predicting the long-term degradation of bioresorbable poly(L-lactide) (PLLA)–hydroxyapatite (HA) composites remains a critical challenge in orthopedic implant design. An artificial implant must support bone tissue and maintain its mechanical and elastic properties for a certain period of time, corresponding to the rate of regeneration of damaged tissue; the time can reach several months. This study investigates the evolution of elastic properties and bulk microstructure in highly filled PLLA–HA composites (5–20 wt.% HA) during 76 weeks of in vitro hydrolytic degradation at 37 °C. Using high-frequency pulsed scanning acoustic microscopy (100 MHz), microstructural transformations and local elastic moduli were monitored non-destructively, complemented by mechanical testing and density measurements. Results indicate a concentration-dependent degradation mechanism: while initial stiffness increased with HA content, filler concentrations exceeding 10 wt.% accelerated degradation via early interfacial debonding and cavity formation around filler agglomerates. Conversely, the 5 wt.% HA composite exhibited superior stability, maintaining an elastic modulus of 6.7 GPa over 64 weeks with minimal microstructural damage. High-frequency ultrasound effectively quantified internal void formation and degradation kinetics in a non-invasive manner. These findings identify 5 wt.% HA as the optimal concentration for balancing mechanical reinforcement with controlled resorption rates. This work provides fundamental insights into the structure–property–degradation relationships in biocomposites and validates ultrasonic diagnostics as a vital tool for predicting the service life of resorbable implantable devices. Full article

Fused silica–aluminum alloy dissimilar connections are in urgent demand in fields such as aerospace optoelectronic packaging, vacuum optical windows, and micro-electro-mechanical systems, yet the dramatic mismatch in thermal-expansion coefficient and thermophysical properties between the two materials has long been a bottleneck for reliable joining. Current ultrafast laser welding of such heterogeneous systems still suffers from prominent problems, including stringent optical contact requirements, high crack sensitivity on the fused silica side, and unclear coupling mechanism between clamping conditions and joint defects. This work systematically studies the joining process of femtosecond laser welding of fused silica and 6061 aluminum alloy dissimilar materials, focusing on the effects of scanning speed, pulse energy, scanning spacing, and fixture preload on the shear strength, microstructure, and elemental diffusion behavior of the joints. The results confirm that scanning speed and scanning spacing have a synergistic effect on heat input density; the magnitude of the fixture preload is a key factor determining the interfacial residual stress and crack sensitivity. By optimizing the scanning speed (6 mm/s) and combining it with a low preload and 140 μm scanning spacing, a high-strength heterogeneous joint with uniform elemental transition and no macroscopic cracks can be obtained. This study provides a detailed process-optimization approach for high-quality laser welding of dissimilar brittle/ductile materials. Full article

Current-driven manipulation of magnetic domain walls (DWs) in perpendicularly magnetized nanowires is promising for spintronic memory and logic applications. In this work, micromagnetic simulations are used to investigate the depinning of DMI-stabilized Néel domain walls from a stepped pinning site under unipolar square-pulse current excitation. The effects of current density, pulse frequency, duty cycle, Dzyaloshinskii–Moriya interaction (DMI), and temperature are examined. The results show that pulse frequency and duty cycle strongly influence the oscillatory response of the pinned DW and can promote depinning through efficient coupling with localized DW dynamics. Increasing the current density enhances the oscillation amplitude and facilitates escape from the pinning region, while variations in DMI produce marked changes in pinning stability and magnetic configuration. Thermal fluctuations further modify the depinning behavior, particularly for stronger DMI, where the system evolves from stable pinning to thermally assisted escape and, at higher temperatures, to less stable magnetic states. Overall, the results show that pulse parameters, DMI strength, and temperature jointly control DW depinning and stability, providing further insight into the tuning of current-driven DW transport in geometrically confined spintronic structures. Full article

This study investigates the responses in the resistance of polypyrrole (PPy) and titanium dioxide (TiO₂) single layers and PPy/TiO₂ heterostructures to rectangular pulses of monochromatic LED illumination under controlled relative humidity. Exposure to moisture increases the resistance of PPy while rapidly decreases that of TiO₂, reflecting opposite effects of electron donation from hydroxyl (–OH) groups in adsorbed H₂O on the majority carrier densities of the two materials. Under monochromatic illumination, the resistance of PPy decreases, whereas that of TiO₂ increases accompanied by a brief transient at excitation wavelengths near its optical edge (367 nm and 398 nm). This photoresponse is attributed to photoinduced modifications of carrier density through two opposing processes: photogeneration, which enhances charge carriers, and H₂O photodesorption, which reduces them. A combination of illumination and moisture exposure results in an intensified photoresponse of PPy, thereby enhancing its humidity response. The PPy/TiO₂ heterostructure demonstrates a mixed photoresponse arising from contrasting behaviors of its p-type PPy and n-type TiO₂ components, coupled with charge exchange across the p–n junction. When simultaneously exposed to moisture and monochromatic light, the heterostructure undergoes contrasting photoinduced carrier generation in its two components, which in turn modulates the depletion region in inverse phase with carrier density, thereby intensifying the overall photoresponse. This complementary “push–pull” interaction synergistically enhances both the photoresponse and the humidity response of the PPy/TiO₂ heterostructure. Full article

The article examines the use of pozzolanic cement and ground glass waste in mortar and their influence on physical and mechanical properties and resistance to the alkali–silica reaction (ASR). The materials used and the research methods used to determine the main properties of mortar are described. CEM II/A-P 52.5 N pozzolanic cement with ash additive, 0/4 fraction sand, and ground glass waste was used for the tests. The resistance of mortar to the ASR was determined according to the developments using the RILEM AAR-2 methodology. Seven mortar compositions were studied, in which cement was replaced with glass processing waste in the amounts of 5, 10, 15, 20, 25 and 30% of the cement mass. The effect of the amount of pozzolanic cement and glass waste on the following mortar properties was studied: density, ultrasonic pulse propagation velocity, compressive and flexural strengths, and ASR. A comparison of the physical and mechanical properties of mortar before and after ASR tests was performed. It was found that by modifying mortar with ground glass, i.e., by replacing pozzolanic cement with 5% to 10% ground glass waste, it is possible to reduce the amount of cement in the mortar, increase resistance to the alkali–silica reaction, and at the same time reduce CO₂ emissions associated with cement production and reuse ground glass waste. Full article

Photon-counting computed tomography (PCCT) represents a detector-level transformation in CT imaging. Unlike conventional energy-integrating detectors, photon-counting detectors directly convert individual X-ray interactions into electrical pulses and classify them according to energy. This architecture enables electronic-noise rejection, smaller detector pixels, improved geometric dose efficiency, and intrinsic spectral acquisition. However, the images available to radiologists are not produced directly by the detector; energy-resolved photon counts must first undergo calibration, correction, projection formation, reconstruction, and material decomposition. This narrative review provides an educational framework linking X-ray attenuation physics, detector materials and architectures, energy thresholds, and detector nonidealities to the resulting PCCT images. It describes conventional polyenergetic and ultra-high-resolution images, virtual monoenergetic imaging, iodine maps, virtual non-contrast imaging, calcium and bone subtraction, virtual non-calcium imaging, effective atomic number maps, electron-density maps, and emerging K-edge techniques. Particular emphasis is placed on the clinical purpose and limitations of each reconstruction, including noise, artifacts, partial-volume effects, misregistration, incomplete subtraction, calibration dependence, and limited cross-platform comparability. Practical considerations for protocol design, image selection, interpretation workflow, and spectral-data archiving are also discussed. Understanding the pathway from photon detection to image formation is essential for selecting the appropriate reconstruction, avoiding misinterpretation, and integrating PCCT effectively into clinical radiology. Full article

Porous multi-walled carbon nanotube (MWCNT) films combine strong optical absorption with thermal, Kerr-like, thermo-optical, and magneto-optical responses. However, these effects depend on film structure and may require different design conditions. In this work, a multiphysics model was used to analyze 12 MWCNT film configurations with dependance on thicknesses, porosity, and orientation parameters. The model included optical attenuation, transient heating, nonlinear refraction, thermo-optic modulation, magneto-optical response, and optical phase shift under irradiances of 7–20 MW cm⁻² and magnetic fields up to 1 T. Optical density ranged from approximately 0.4 to 2.8, while transmittance showed negligible variation with irradiance. Thin and porous films produced the highest temperature rises, approximately 4.5 K, and the largest total refractive-index changes. In contrast, thicker films generated larger accumulated phase shifts. The thermo-optic contribution is dominated under nanosecond laser irradiation. As the pulse duration approached the picosecond regime, the lower deposited energy reduced the photothermal response, so the Kerr-like and magneto-optical terms accounted for a larger total refractive-index change. This predictive parametric study identifies architecture- and pulse-dependent trends for future experimental evaluation of multifunctional MWCNT films. Full article

The physical, mechanical, and microstructural degradation that occurs in concrete elements exposed to high temperatures constitutes an important research topic in terms of the fire safety and service performance of structures. In this study, the behavior of plaster mortars produced with cement-based and ground granulated blast furnace slag (GGBFS)-based binders, as well as normal concrete (interior concrete) specimens coated with these mortars, under high-temperature exposure was experimentally investigated. After the prepared mortars and plastered concrete specimens were exposed to temperatures of 100, 300, 500, and 700 °C, changes in compressive strength, ultrasonic pulse velocity (UPV), water absorption, mass loss, and bulk density were evaluated. Analysis of the experimental results showed that high temperatures, particularly 300 °C and above, caused significant performance losses in all binder systems. Although calcium aluminate cement-based mortars developed high early-age strength, they exhibited more pronounced strength losses under elevated temperatures, whereas geopolymer-based binders demonstrated more stable performance at low and medium temperatures. Additionally, a strong correlation (R² ≈ 0.89) was observed between UPV and compressive strength in the plastered interior concrete specimens. At 500 and 700 °C, the plastered concrete specimens exhibited 9.8–13.3% and 10.4–18.1% higher residual compressive strength, respectively, compared with the unplastered control specimens. At 700 °C, the PC-based plaster provided the highest improvement in residual compressive strength (18.1%), while the G-Na system exhibited the lowest water absorption, which was 19.5% lower than that of the control concrete. Plastered concrete specimens retained their mechanical and physical properties better than the control (unplastered) concrete specimens at all temperature levels, and this finding was further supported by microstructural analyses. The results indicate that plaster systems produced with different binders are effective in limiting thermal damage to the interior concrete. Full article

Although the duty cycle is an important parameter in pulsed plasma nitriding, its role in simultaneously controlling the microstructure, mechanical performance, tribological behavior, and corrosion resistance of 12Kh18N10T stainless steel remains insufficiently understood. Therefore, this study systematically investigates these relationships under otherwise fixed nitriding conditions. The samples were nitrided at 500 °C, a pressure of 400 Pa, a voltage of 700 V, and a treatment duration of 5 h, with duty cycle (DC) values of 30, 60, and 90%. The surface microstructure and composition were characterized by scanning electron microscopy, energy-dispersive spectroscopy, and X-ray diffraction. The mechanical properties were evaluated by instrumented nanoindentation, the tribological properties were evaluated using the coefficient of friction and wear rate, and the corrosion resistance was investigated using potentiodynamic polarization. The maximum nitrided layer thickness of 91.29 μm was obtained at DC30, whereas the layer thickness at DC60 and DC90 was approximately 65.07 μm. Fe₄N and Cr₂N phases were identified in all samples. The DC60 regime provided the highest hardness of 740.6 HV, an elastic modulus of 215.9 GPa, the lowest coefficient of friction of 0.333, and the lowest corrosion current density of 0.000665 mA/cm². The minimum wear rate of 2.276 × 10⁻⁵ mm³/(N·m) was achieved at DC90. These results show that the optimal processing condition depends on the required combination of hardness, wear resistance, coefficient of friction, and corrosion resistance. The obtained results demonstrate that the functional properties of the steel can be effectively tailored by controlling the duty cycle. Full article

Polarity reversal changes not only the instantaneous electric field in a needle–plane air gap but also the subsequent field–particle coupling through the charged-particle distribution established before reversal. For a configuration in which the grounded needle and grounded lower plate share the same return path, it remains unclear to what extent this local history-dependent state is transferred to the complete grounded conductor and its externally measurable current. Here, a two-dimensional axisymmetric electrostatic model (ES) and a drift–diffusion–reaction–Poisson–discharge-fluid model (EDIS) were established for a 50 mm needle–plane air gap. Positive-to-negative (P2N)/negative-to-positive (N2P) reversals and history-retained/history-reset (H/R) controls were used to separate the effects of reversal path and pre-existing charged-particle state. Over the tested 0–2τ reset-hold range, the representative near-tip electron density in H remained approximately 15–16% higher than that in the corresponding R case, whereas the H/R conductor-integrated response of the complete common-ground assembly was indistinguishable at the present numerical resolution. Outer-domain analysis further showed that for the representative 15 kV case in the 300 mm reference domain, the EDIS and ES common-ground integrated responses differed by approximately 3.3%. Experimentally, P2N and N2P reversals were repeated at 5, 10, and 15 kV, yielding 120 events. The main common-ground current pulse increased with voltage magnitude and maximum voltage slew rate, and the median event-level Pearson correlation with signed dV/dt was approximately 0.989. Different capacitance-baseline constructions yielded central residual-integral levels of approximately 18–19%; after multiplicity correction, the 15 kV fixed-window absolute integral was the direction-sensitive terminal metric with the strongest statistical support. Under the investigated conditions—a nominal 0.5 mm tip radius, 50 mm gap, approximately 3 ms reversal time, and weak-discharge regime—the reversal path and particle history primarily reorganize the near-tip charged-particle state, whereas the dominant scale of the common-ground transient remains closely associated with the applied-voltage variation and the capacitive response of the system. Full article

5052 aluminum alloy has been widely used in aerospace, shipbuilding, automotive, and electronic industries due to its low density, high specific strength, and excellent corrosion resistance. Understanding its laser-induced damage behavior under combined continuous-wave (CW) and nanosecond (ns) pulse laser irradiation is essential for optimizing combined laser processing. In this study, the damage behaviors induced by individual CW laser, individual ns pulse laser, and combined pulse laser were systematically investigated using high-speed imaging, infrared thermography, and three-dimensional surface characterization. The results show that the combined pulse laser significantly enhances both damage depth and material removal efficiency compared with single laser irradiation. Although the peak surface temperature remains nearly unchanged under different processing conditions, the crater morphology and penetration depth vary substantially. High-speed imaging reveals that plasma evolution and molten metal ejection dominate the material removal process. Variations in processing parameters significantly modify molten pool dynamics and plasma behavior. In particular, enhanced plasma shielding or excessive energy dissipation reduces the effective laser energy coupling, leading to decreased material removal efficiency. The synergistic interaction among molten pool evolution, plasma expansion, and molten metal ejection governs the final damage morphology. This study provides new insights into the dynamic interaction mechanisms between combined pulse laser and aluminum alloys, offering guidance for parameter optimization in high-precision laser micromachining. Full article

In the present work, graphene-modified zinc oxide (ZnO-rGO) and fluorine-doped tin oxide (FTO) thin films were successfully fabricated using a simple, low-cost pulsed spray pyrolysis technique. The structural, morphological, optical, electrical, and surface electronic properties of the deposited films were systematically characterized. X-ray diffraction (XRD) analysis confirmed the formation of polycrystalline ZnO- and SnO₂-based phases with crystallite sizes in the nanometer range. The crystallographic parameters, microstrain, and dislocation density of the deposited films were found to be influenced by the incorporation of reduced graphene oxide (rGO) and fluorine dopants. Scanning electron microscopy (SEM) revealed compact and homogeneous surface morphologies with good film coverage and well-defined nanocrystalline features. Optical characterization demonstrated the wide-bandgap semiconducting behavior of the deposited films, with optical bandgap energies ranging from 3.262 to 3.312 eV for the ZnO-rGO films and from 3.91 to 4.01 eV for the FTO films. Kelvin probe measurements yielded work-function values in the range of approximately 5.0–5.2 eV, indicating favorable surface electronic characteristics suitable for optoelectronic applications. Furthermore, fluorine incorporation enhanced the dielectric response of the SnO₂ films, particularly in the low-frequency region owing to increased interfacial polarization effects. The obtained results demonstrate that pulsed spray pyrolysis provides a simple, cost-effective, and efficient route for fabricating ZnO-rGO and FTO thin films with desirable structural, optical, electrical, and surface electronic properties. These findings highlight the considerable potential of the developed materials for transparent electrodes and a wide range of optoelectronic applications. Full article

The Pulse Magneto Oscillation (PMO) solidification homogenization technique has been successfully applied in the continuous casting production of GCr15 bearing steel. To further investigate the effects of PMO technology on the precipitation mechanisms of primary carbides in GCr15 bearing steel, a series of directional solidification experiments were conducted under the influence of PMO. Characterization and analysis of the area proportion, number density, particle-size distribution, elemental distribution, and types of primary carbides in the as-cast bearing steel under various PMO parameters were conducted using Optical Microscopy (OM), Scanning Electron Microscopy (SEM), Electron Probe Microanalysis (EPMA), and Electron Backscatter Diffraction (EBSD). The findings reveal that the predominant carbide species precipitated in GCr15 bearing steel is M₃C type, characterized by a higher Cr content. As the PMO peak current and pulse frequency increase, there is a significant reduction in both the area proportion and number density of primary carbides. Compared to non-PMO conditions, the application of PMO results in a maximum decrease in carbide area proportion by up to 75.6% and a reduction in number density by up to 58.4%, leading to a more dispersed and uniform carbide distribution. Moreover, under the influence of PMO, the local solidification duration of the solution shortens, leading to an increase in the quantity of inclusions such as MnS, which undergo refinement. This facilitates the refinement of primary carbides that utilize inclusions as heterogeneous nucleation sites. Additionally, the reduction in dendritic arm spacing within the solidification structure and the enhancement of solute distribution near the solid–liquid interface, induced by PMO, also create favorable conditions for the reduction in size and quantity of primary carbides. Based on the distinctive characteristics of primary carbides under varying PMO parameters, an innovative dynamic model for the formation of primary carbides during the solidification process of GCr15 bearing steel has been proposed. Full article