Search Results (1,259)

Electromagnetic field-based stimulation has emerged as a promising noninvasive approach for enhancing bone fracture healing. Beyond conventional pulsed electromagnetic field (PEMF) therapies employing spatially uniform fields, dielectrophoretic-force-based (DEPF) stimulation exploits electromagnetic field non-uniformities to induce localized interactions to enhance fracture healing. However, the thermal behavior associated with DEPF-driven PEMF exposure in the presence of metallic orthopedic implants remains largely unexplored. In this study, the thermal response of tissue-like tibia phantoms with and without metallic implants is investigated using an integrated experimental and numerical framework. A custom-designed conical coil is employed to generate non-uniform DEPF excitation capable of affecting the fracture site. Surface temperature evolution is measured using infrared thermal imaging, while electromagnetic power absorption is quantified through specific absorption rate (SAR)-based thermal measurement coupled with a bio-heat formulation. Anatomically realistic tibia phantoms reconstructed from computed tomography data are fabricated via a 3D printer to represent clinically relevant fracture configurations. Experimental results show that the metallic implant exhibits a rapid temperature increase of approximately $0.4 °\mathrm{C}$ within the first few minutes of exposure, followed by thermal stabilization, corresponding to an effective absorbed power of ${\mathrm{SAR}}_{\mathrm{eff},\mathrm{implant}}\approx 2.2 \mathrm{W}/\mathrm{kg}$ inferred from the initial temperature slope. In contrast, the non-conductive resin phantom displays a temperature rise of only $0.05 °\mathrm{C}$ over the same interval, yielding ${\mathrm{SAR}}_{\mathrm{eff},\mathrm{resin}}\approx 0.8 \mathrm{W}/\mathrm{kg}$. These findings demonstrate that implant-related eddy-current losses dominate localized heating under DEPF excitation, while tissue-like media remain weakly affected. This work provides SAR-based experimental evaluation of DEPF stimulation in implanted tibia fracture models, offering new insight into implant-induced electromagnetic heating and its implications for the safety and optimization of DEPF-based bone-healing therapies. Full article

Detonation-based combustion has re-emerged as a promising pathway for enhancing the efficiency and compactness of future aerospace propulsion systems, motivated by the intrinsic pressure-gain characteristics of detonative heat release. This review provides a comprehensive synthesis of the physical foundations, technological progress, and practical limitations associated with pulse detonation engines, rotating detonation engines, and standing or oblique detonation wave concepts. By tracing the evolution from early theoretical models and laboratory-scale demonstrations to engine-relevant configurations, this article highlights how detonation physics, ignition mechanisms, wave stability, and flow–structure interactions collectively govern propulsion performance. Particular attention is paid to recent experimental and numerical studies, with the review focusing on their technological impact and on the feasibility of integrating detonation-based propulsion concepts into practical aerospace systems. The analysis evaluates these approaches’ potential to enhance system-level performance compared to conventional propulsion technologies, while highlighting key challenges associated with scalability, operability, and compatibility with existing aerospace architectures. The review further identifies emerging design strategies, including geometry tailoring, adaptive flow control, and hybrid architectures, as key enablers for extending operability and system integration. Overall, the findings indicate that future progress in detonation-based propulsion will depend less on demonstrating detonation itself and more on achieving robust, controllable, and scalable implementations suitable for realistic aerospace applications. Full article

Based on temperature–stress coupling simulation, a thermal source model for nanosecond pulsed hollow cathode electron beam surface modification is proposed. Dynamic thermal-stress changes from beam–surface interaction and their influence on micro–nano characteristics were systematically investigated. By analyzing maximum temperature/stress dynamics, cross-sectional remelted layer variations, and heating/cooling rates, the temperature and stress distribution in the micron-scale surface layer was comprehensively revealed, validating the model’s rationality. Combined with low, medium, and high pulse count experiments, the effects of thermal and stress factors on surface morphology and grain refinement were studied, elucidating underlying mechanisms through numerical correspondence. Results show irradiation effects confined to a 1.5–2 mm localized region, with extreme temperature changes (~10³ K) and stress variations (10³–10⁴ MPa) within tens of nanoseconds. Heating rates reached 10¹¹ K/s, cooling rates 10⁹–10¹⁰ K/s, exceeding microsecond pulsed beams by one to two orders. Simulated remelting zone diameter and thickness agreed well with experiments, confirming model validity. Grain refinement is primarily driven by rapid temperature distribution, generating instant solidification nucleation sites, with a secondary contribution from high-stress-induced plastic deformation forming sub-grains. 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

Multijunction laser power converters are demonstrated for the first time with high efficiencies for average optical irradiances exceeding 150 W/cm². The GaAs-based photovoltaic power converting III-V heterostructures are designed with six GaAs subcells having an area of 0.14 cm², receiving up to 22 W of input power at ~811 nm, delivering over 14 W of output power. The maximum efficiencies are obtained in the range of 30 to 75 W/cm², and efficiencies > 64% are still obtained at 160 W/cm². The efficiency reduction for higher irradiance values originates predominantly from residual heat generated in the active layers. For example, in 100% duty factor measurements, the bandgap voltage offset saturates to W_oc ~ 170 mV. However, in pulsed mode, W_oc values as low as 150 mV have been obtained for a device base temperature of 20 °C. For smaller 0.029 cm² devices, W_oc values around 137 mV are obtained at 240 W/cm². Full article

This study presents a detailed electrical analysis of AlGaN/GaN/Si HEMTs grown by molecular beam epitaxy, using direct and pulse current, small-signal microwave, and deep-level transient spectroscopy (DLTS) techniques to investigate transport characteristics and defect-related effects. DC measurements revealed self-heating effects and leakage currents, while RF analysis highlighted the devices’ high-frequency capabilities alongside parasitic effects linked to deep-level traps. Pulsed I–V characterization demonstrated gate-lag and drain-lag behaviors associated with dynamic charge trapping. DLTS identified electron traps, emphasizing their critical role in device degradation and switching performance. The strong correlation between trap states and electrical behavior underlines the importance of defect control for enhancing efficiency and reliability. Full article

Ice accretion along aircraft leading edges, particularly at stagnation line parting strips, remains difficult to remove using conventional electrothermal anti-icing systems. These systems require continuous high-power heating to maintain the stagnation region above the melting point, often exceeding 10–12 kW/m². This study introduces an Ice Cavitation Deicer (ICD) that removes ice through rapid, localized cavitation generated within a thin melt layer formed at the ice–surface interface. In the proposed approach, a short pulse of electric current melts a 1–10 µm interfacial layer and causes a cavitation impulse of approximately 1–10 MPa. This impulse ejects the stagnation-line ice in a direction normal to the surface, often against the external airflow, enabling the immediate aerodynamic removal of the remaining ice. Analytical modeling based on the energy conservation principle was used to determine the optimal foil geometry, thermal pulse parameters, thermal stress, and material selection. Experiments with various metallic foils and substrate materials validated the predicted ejection behavior. The impulses were sufficient to fracture and eject ice 1–10 mm thick. The observed ice fragment velocities varied from 1 m/s to 10 m/s. Compared with conventional thermal anti-icing, the ICD concept reduces power consumption by approximately two orders of magnitude while offering rapid and reliable leading-edge deicing. The low power requirements, rapid response, and compatibility with thin-foil heater architectures make ICD a promising technology for both conventional and electrified aircrafts, UAVs, rotorcrafts, and other platforms where power availability is limited. This manuscript presents the first theoretical and experimental research on the ICD method and is a concept-proof work. Further research and development are required before the ICD is ready to be tested in flight. Full article

Background/Objectives: Heated tobacco products (HTPs) are a gateway to nicotine addiction for non-smokers, especially young people. The short- and long-term health effects of using heated tobacco products are not yet fully understood. The study aimed to assess the effect of heated tobacco use on blood pressure and heart rate in young, healthy individuals aged 18–30. The study also assessed exposure to tobacco smoke by measuring salivary cotinine concentration. Methods: The case–control study was conducted in 2022–2025 among 200 healthy individuals aged 18–30 years: 70 I-Quit-Ordinary-Smoking users (IQOS), 65 daily traditional cigarette smokers (DS), and 65 non-smokers (NS). The research tool was a questionnaire containing information on the use of tobacco products. The participants completed a questionnaire and then underwent blood pressure measurements, anthropometric measurements, and saliva collection for cotinine levels. Results: The average age of initiation of IQOS use was 18.5 years, and smoking had continued for an average of 2.3 years. The average age of initiation of smoking traditional cigarettes was 16.3 years, and smoking had continued for 4.4 years. There were no statistically significant differences in median values between systolic blood pressure (SBP) and diastolic blood pressure (DBP) between the IQOS, DS, and NS groups (p > 0.05). High SBP values ≥ 140 mm Hg were observed in 10% of the IQOS users, 18.5% of the daily smokers of conventional cigarettes, and 12.3% of the non-smokers. High DBP values ≥ 90 mm Hg were observed in 11.4% of IQOS, 7.7% of DS, and 7.7% of NS. The cigarette smokers demonstrated significantly higher median cotinine levels compared to the IQOS users and non-smokers: 153.7 vs. 64.3 vs. 0.5 ng/mL (p < 0.01). Salivary cotinine levels were positively correlated (ρ = 0.38; p < 0.01) with the daily number of heated tobacco sticks among IQOS users (weak correlation), as well as among DS (ρ = 0.42; p < 0.01) with a higher daily number of cigarettes (moderate correlation). Conclusions: Long-term studies are needed to determine the health effects of heated tobacco products among young people in Poland. Furthermore, the potential impact of HTP aerosols on passive smokers should be examined. Further studies should consider the use of salivary cotinine as a biomarker. Full article

Carbon nanotube (CNT) cathode materials exhibit excellent electron emission performance and have become a key research focus in the field of vacuum electronics. However, their practical applications are still restricted by challenges, including emission instability and ambiguity in temporal resolution capability. This work investigated the thermal-assisted field emission characteristics of CNT and their application in pulsed X-ray imaging. Systematic characterization of the turn-on field strength, emission stability, pulse response characteristics, and pulsed X-ray imaging performance demonstrated that the thermal-assisted operating mode reduced current fluctuations to below 1%. Increasing the heating power further enhanced emission stability and lowered the turn-on field strength. In thermal-assisted pulsed emission mode, CNT cathodes exhibited reduced power consumption compared to conventional thermionic cathodes and achieved microsecond-scale pulse response. Further X-ray imaging experiments confirmed that the X-ray dose generated by CNT in this operational mode exhibited higher stability, enabling 100 μs pulsed imaging and clear visualization of rotating blades operating at 600 Hz. This study validated the feasibility of CNT cathodes for high-speed X-ray imaging and could provide a reference for the development of advanced pulsed X-ray sources and related technologies. Full article

This study investigates the impact of cavitation phenomena on heat and mass transfer in working fluids. To quantify the intensity of transport processes within cavitation bubble clusters, a numerical analysis of bubble dynamics was carried out with explicit consideration of fluid compressibility. The results demonstrate that physicochemical transformations induced by cavitation are governed not only by shock waves and pressure pulses generated during bubble collapse, but also by extreme thermal effects arising within collapsing cavitation clouds. Under conditions of maximum bubble compression, the vapor inside the bubbles and the surrounding liquid may undergo a transition to a supercritical state. The developed model elucidates the structure of microflows in the interbubble region and provides a quantitative evaluation of local velocity, pressure, and heat flux fields. The systematic assessment of cavitation-enhanced heat and mass transfer offers valuable insights for the advancement of conventional heat and mass transfer technologies and the design of innovative devices in mechanical and chemical engineering. Full article

Pulse thyristors are extensively utilized in pulsed plasma discharge applications. In this study, a pulse switch prototype is built using two parallel valve groups, each consisting of seven series-connected thyristors. Each thyristor is equipped with an anti-parallel protection diode, a static voltage-sharing resistor, and an RCD (resistor-capacitor-diode) dynamic voltage-sharing circuit. The prototype withstands 24 kV, delivers 150 kA peak current, operates at 10 Hz, and can run continuously for 1 s. Thermal analysis is essential under narrow-pulse high-current conditions to avoid failure from localized overheating. By investigating the expansion process of the conduction zone during thyristor turn-on, a single-thyristor turn-on model and a finite-element model of the multi-layer series thyristor module are established to analyze transient temperature distributions. Results show a non-uniform temperature profile across the silicon wafer, with the hottest zone near the gate ring. During repetitive pulses, the silicon temperature fluctuates rapidly, while the copper base heats up gradually. At a spreading speed of 30 m/s, the gate terminal temperature rises about 38 °C—within safe limits for now, but projected to exceed them under future operating conditions. Thus, improved thermal management will be critical in further development. Full article

Through Glass Via (TGV) technology has emerged as a promising solution for advanced packaging. While glass offers lower dielectric loss than silicon, its lower thermal conductivity raises concerns about electro-thermal coupling effects in high-power, high-frequency applications. Therefore, this study conducted an electro-thermal co-design of TGV grounded Coplanar Waveguide (CPW) and Radio Frequency (RF) TGV connected CPW structures. A high-power test platform was developed to investigate the electrical and thermal performance of these structures. The temperature distribution mechanism under high-power conditions was revealed. Under high power and high frequency, the decrease in surface conductivity affected by surface state and film layer composition leads to increased loss, triggering temperature rise and forming an electrothermal coupling loop. Under continuous wave operation (5–20 W), the temperature rise reaches 92.4 °C while insertion loss increases by only 0.4 dB. Under pulsed wave operation (25–100 W, 2.5% duty cycle), the temperature rise is merely 2.1 °C with insertion loss increasing by 0.3 dB. The quadruple-redundant design and reduces heat flux density, preventing localized hotspot formation. The pulse intervals suppress thermal accumulation, leading to lower temperature rise. Therefore, continuous wave applications should prioritize thermal management, while pulsed wave applications can focus on electrical performance optimization. Full article

Efficient apple orchard water management under climate variability requires understanding how fruit load and water supply regulate branch-scale water use to optimize irrigation, yield, and fruit quality. During the summer of 2014, sap flow (SF) and maximum daily shrinkage (MDS) were measured in one branch from six apple trees (Malus domestica Borkh. Cv. ‘Jazz™’) using the Compensation Heat Pulse method and diameter variation sensors in an orchard near Havelock North, New Zealand. One west-oriented branch per tree, with diameters of 1.5 to 2.3 cm, was monitored alongside midday stem (ψs) and leaf (ψl) water potentials, leaf gas exchanges, leaf area index (LAI), and fruit dry matter per branch at the end of the growing season. Half of the trees were subjected to irrigation withdrawal after day of year (DOY) 31 (non-irrigated treatment), resulting in a significantly lower midday stem water potential (ψs) by DOY 56 (−1.03 MPa). Pre-harvest, SF and MDS were tightly correlated (r² = 0.69), but this correlation decreased post-harvest (r² = 0.16) due to reduced fluctuations in both SF and branch variations (BV). SF was normalized per unit of leaf area, categorizing branches into high and low LAI: fruit dry matter ratio. SF values were approximately 2.2 times higher for FI pre-harvest and remained 2-fold higher post-harvest, associated with lower ψl and higher midday leaf transpiration for FI. MDS was identified as a better indicator of mild water deficit compared to SF, with both measurements responding effectively to midday vapor pressure deficit and reference evapotranspiration values. Overall, MDS proved to be a more sensitive indicator of mild water deficit than SF, while fruit load exerted a persistent influence on branch water use, highlighting the value of branch-scale measurements for improving irrigation management in apple orchards. Full article

Gas sensors based on metal oxide semiconductors (MOS) have attracted significant attention in monitoring of methane emission and leakage monitoring due to their high sensitivity, fast response time, simple structure and low cost. However, the high power consumption caused by long-term high-temperature operation of MOS sensors restricts their application in mobile and portable devices. In this study, MOF-derived Co₃O₄ dodecahedrons for low-concentration methane detection at room temperature was prepared using Zeolitic Imidazolate Framework-67 (ZIF-67) as a template and with various calcination temperatures. Among them, the Co₃O₄-350 calcined at 350 °C exhibited the optimal CH₄ sensing performance at room temperature, with a response of R_g/R_a = 1.53 to 2000 ppm CH₄. This enhanced gas sensing performance is attributed to the highest Co³⁺ proportions and the largest specific surface area in Co₃O₄-350 nanomaterials, which provided more active sites for gas adsorption and reaction. To address the challenge of slow response speed and irrecoverability during CH₄ detection at room temperature, the Co₃O₄ nanomaterials were printed onto a micro-heater plate (MHP) to form a MEMS gas sensor. By introducing a pulse heating mode to the MEMS sensor, the response and recovery time were significantly reduced to 26 s and 21 s, respectively. This enhancement improves both the efficiency and reliability of the MEMS gas sensor for early-stage detection of CH₄ leaks in various industrial applications. Full article

Permanent joints are commonly used in vehicle construction. The main methods used are gluing, welding and heat sealing. However, other joining methods that utilise plastic deformation of sheet metal are also becoming increasingly common. These methods include the sheet metal clinching joint. This is a joint that allows sheet metal to be joined, often in combination with bonding. Sheet metal of various thicknesses is used in vehicle construction and is subjected to plastic working. The main objective of the work was to assess the influence of plastic working of sheet metal on the strength of clinching joints. An additional objective was to determine the possibility of assessing the degree of aluminum sheet thickness reduction in a non-destructive manner using the ultrasonic (UT) method. The tests carried out showed that as the crumple increases, the strength of the clinched joint is reinforced. For sheet metal joints without crumpling, the strength was 608 N, and for 20% crumpling, the strength increased to 645 N, while for 47% crumpling, the strength increased to 671 N. For the largest crumpling of 60%, the strength was 712 N. In terms of non-destructive assessment of the degree of sheet thickness reduction, it was found that the best measure is the speed of the ultrasonic longitudinal wave. Other measures, such as decibel drops in pulse height for surface and longitudinal waves, show certain trends, but they are not conclusive. Full article