Search Results (1,940)

By employing graded-interfaces modeling, ~10 μm-emitting quantum cascade lasers (QCLs) are designed with previously found conditions for record-high wall-plug efficiency (WPE) operation of mid-infrared QCLs: direct resonant-tunneling injection from a prior-stage low-energy state into the upper-laser level, photon-induced carrier transport, and carrier-leakage suppression via the step-taper active-region (STA) approach. For devices with interface-roughness (IFR) parameters characteristic of optimized molecular-beam-epitaxy (MBE) growth, a maximum front-facet pulsed WPE value of 19.6% is projected for 60-stages STA-type devices. This results from several factors: 19 mV voltage defect at threshold, 72% voltage efficiency at the maximum WPE point, and ~93% injection efficiency due to strong carrier-leakage suppression. 2.7 W peak front-facet power is projected. For devices with our metal–organic chemical vapor deposition (MOCVD)-growth IFR parameters, the projected maximum pulsed WPE value is 17.1%, i.e., 1.7 times higher than the highest reported front-facet WPE value from ~10 μm-emitting MOCVD-grown QCLs. Studies regarding the WPE value variation with the stage number, while employing waveguide designs having the same empty cavity loss, reveal that the maximum WPE value remains almost the same for 50–60 stages devices. In turn, there is potential for obtaining significantly higher CW powers than from conventional ~10 μm-emitting QCLs. Full article

This paper proposes a long-period grating (LPG) based on double-clad fibers (DCFs) for multi-parameter sensing. The sensor consists of cascaded-input single-mode fibers (SMF), DCF, and output SMF. Multi-parameter detection is realized by utilizing the different sensing characteristics of the resonance peak under different physical parameters. The experiment results show that within the temperature range of 30–100 °C, the maximum sensitivity is 66.37 pm/°C. For the refractive index (RI) measurement, the tested range is 1.3309–1.3888 and the maximum sensitivity is −45.84 nm/RIU. Regarding curvature detection, the tested range is 0.6928–1.6971 m⁻¹ and the maximum sensitivity is −2.022 nm/m⁻¹. In addition, the sensor has a symmetrical structure, so its measurement is not restricted by the incident direction of light, thus having flexibility in practical use. This research not only contributes to the advancement of optical fiber sensor technology but also has significant implications for practical applications in industry, the environment, and healthcare. Full article

The dynamic characterization of historical buildings located in a complex geological and seismological context is essential to assess seismic vulnerability and to guide conservation strategies. This study presents a non-invasive, ambient vibration-based, investigation of the Norman Castle of Aci Castello (Sicily, Italy), applying Horizontal to Vertical Spectral Ratio (HVSR), Horizontal to Horizontal Spectral Ratio (HHSR), and Random Decrement Method (RDM) to evaluate the structure’s dynamic behavior and potential Soil–Structure Interaction (SSI) effects. The fundamental site frequency, estimated within a broad plateau in the range 2.05–2.70 Hz, does not overlap with the structural frequencies of the castle, which range approximately from 6.30 Hz to 9.00 Hz in the N–S structural direction and from 3.50 Hz to 8.50 Hz in the E–W direction, indicating absence of global SSI resonance. However, the structure exhibits a complex multimodal response, with direction-dependent behavior evident both in spectral peaks and in damping ratios, ranging from 2.10–7.73% along N–S and 0.90–5.84% along E–W. These behaviors can be interpreted as possibly linked to structural complexity and the interaction with the fractured volcanic substrate, characterized by shallow cavities, as well as to the material degradation of the masonry. In particular, the localized presence of subsurface voids may induce a perturbation of the low-frequency ambient vibration wavefield (e.g., microseisms), producing a localized increase in spectral amplitude observed at Level I. The analysis indicates the absence of global SSI resonance due to the lack of overlap between site and structural fundamental frequencies, while significant local SSI effects, mainly related to cavity-induced wavefield perturbation, are observed and may represent a potential vulnerability factor. These findings highlight the relevance of vibration-based diagnostics for heritage vulnerability assessment and conservation strategies. Full article

Power converters are essential for solar energy systems but achieving over 96% efficiency at 1 kW and 300 kHz with compact magnetic and EMC compliance remains challenging for high-power-density PV applications. This study presents the design, modeling, and experimental validation of a 1 kW two-phase interleaved boost converter operating from 12 V input to 48 V/20 A output, featuring a single EE32 Litz-wound coupled-core inductor with coupling coefficient k = −0.475 that reduces per-phase current ripple to just 120 mA (0.6% relative) at full load, a load-selective active zero-current switching (ZCS) circuit activated above 5 A threshold via DCR sensing to minimize switching losses without light-load penalties, and digital peak-current control with 2P2Z compensator implemented on an XMC4200 microcontroller, ensuring robust stability. Experimental results demonstrate peak efficiency of 98.6% at approximately 190 W load, full-load efficiency of approximately 96% with total losses limited to 40 W dominated by conduction rather than switching, thermal rise below 80 °C on key components, voltage regulation with less than 1% deviation down to 2 A minimum load, and full compliance with electromagnetic compatibility standards, including EN 55014-1/2 and EN 61000-4-2 ESD testing. The novel integration of selective ZCS, single-core magnetic, and high-frequency operation outperforms prior interleaved boost converters, which typically achieve 94–97% peak efficiency at lower switching frequencies of 20–100 kHz using multiple inductors or complex always-active resonant networks, making this solution particularly suitable for compact photovoltaic micro-converters, electric vehicles, and industrial power supplies requiring high efficiency, reliability, and regulatory compliance. Full article

Asymmetric and symmetric magnetoelectric (ME)-laminated composites with magnetostrictive layer FeNi and piezoelectric layer PZT are prepared. The longitudinal resonance ME voltage coefficient in the symmetric composite is approximately 1.57 times that in the asymmetric composite with same constituents due to the flexural deformation and asymmetric stress distribution in the asymmetric structure. By bonding an additional high-permeability FeSiB, combining FeSiB with FeNi forms magnetization-graded ferromagnetic materials. A stronger maximum ME voltage coefficient, a dual-peak phenomenon, and a self-bias ME effect are observed. The maximum ME voltage coefficients for asymmetric and symmetric composites reach 3.10 V/Oe and 5.67 V/Oe by adjusting the thickness of the FeCuNbSiB layer. The maximum zero-bias ME voltage coefficients for asymmetrical and symmetrical composite materials reach 2.19 V/Oe at 25 µm thickness of FeSiB and 2.87 V/Oe at 75 µm thickness of FeSiB. Such high performances enable the ME composites to possess ideal sensing and make them promising for self-bias current sensor applications. Full article

The increasing size and weight of deep-water topside modules necessitate reliable and efficient installation methods. The twin-barge float-over technique presents a viable alternative to conventional heavy-lift operations; however, its critical tri-vessel load transfer phase involves complex hydrodynamic interactions and continuous load redistribution that are not adequately captured by traditional staged analyses. This study develops a fully coupled time-domain dynamic model to simulate this process. The framework integrates multi-body potential flow hydrodynamics, mooring and fender systems, and Deck Support Units (DSUs). A novel continuous mass-point variation method is introduced to replicate progressive ballasting and the dynamic load transfer from single- to dual-barge support. Numerical simulations under representative sea states reveal significant narrow-gap resonance effects, direction-dependent motion amplification, and transient DSU load peaks that are overlooked in conventional quasi-static approaches. Beam-sea conditions are found to induce the largest lateral DSU loads and the highest risk of barge misalignment. The proposed framework demonstrates superior capability in predicting motion responses and load transitions, thereby providing critical technical support for the safe and efficient application of twin-barge float-over installations in complex marine environments. Full article

Chia seed oil, valued for its health-promoting omega-3 and omega-6 fatty acids, is highly susceptible to oxidation. This study employed a multi-technique approach based on electron spin resonance (ESR), low-field nuclear magnetic resonance (LF-NMR), and small-angle X-ray scattering (SAXS) to monitor its oxidative process. ESR identified alkyl (DMPO-•R) and peroxyl (DMPO-•OOR) radicals as primary species derived from unsaturated fatty acids. This was accompanied by a decrease in relaxation time of peak T₂₁, T₂₂, and T₂₃, and the peak area of S₂₁ gradually increased as the heating time increased. The SAXS intensity of chia seed oil at q = 3.4 nm⁻¹ increased markedly after heating for 20 h, and the peak shifted to the low q-region with Δq = 0.6 nm⁻¹, confirming the significant formation of nanoscale aggregates, which correlated with observed increases in oil turbidity. Our findings demonstrate the value of an integrated analytical strategy for a comprehensive understanding of oxidation in chia seed oil. Full article

Gold nanoparticles (AuNPs) are promising for biomedical applications, but their synthesis often requires toxic reagents. “Green” methods utilizing biopolymers offer a sustainable alternative. This study presents a novel synthesis of stable gold nanoparticles using a disulfide-crosslinked derivative of alginic acid (AA–S–S–AA) as both a reducing agent and stabilizer. The S–S-cross-linked alginate was synthesized with a degree of substitution of ~4.2% and reacted with HAuCl₄ in water at room temperature for just 10 min to give stable and polysaccharide in situ modified gold nanoparticles (AA-AuNPs). The resulting AA-AuNPs were characterized by a surface plasmon resonance peak at 539 nm and exhibited good colloidal stability over 14 days. Electron microscopy revealed spherical nanoparticles with a bimodal size distribution (10 nm and 75–100 nm) and a visible polysaccharide shell (5–9 nm), confirming effective stabilization. X-ray photoelectron spectroscopy confirmed the presence of metallic gold (Au⁰) and Au¹⁺. NMR analysis indicated the oxidation of disulfide groups to sulfonic acid during synthesis. The nanoparticles demonstrated a high negative zeta-potential of −53.9 mV, attributable to the polyanionic alginate corona, ensuring strong electrostatic stabilization. This work establishes sulfur-modified alginic acid as an efficient platform for the rapid synthesis of stable, hybrid nanoparticles for potential use in catalysis and biomedicine. Full article

This article presents the design of a dual-mode resonant, dual-band textile microstrip patch antenna for bent sensing applications. The antenna has a simple, slit-perturbed circular sector patch configuration. Unlike traditional single-mode resonant bending sensor antennas, dual-mode resonance brings a unique dual-band sensing characteristic to textile antennas. It effectively covers 2.45 GHz and 5.8 GHz Industrial, Scientific and Medical (ISM) frequency bands. Experimental results demonstrate that the proposed antenna achieves −10 dB impedance bandwidths of 1.4% (2.43–2.465 GHz) and 2.4% (5.775–5.915 GHz), with maximum peak gains of 8.8 dBi and 9.1 dBi, respectively. As experimentally validated on flannel substrates, the antenna achieves maximum bent sensing sensitivities of 1.1 MHz/mm and 1.78 MHz/mm at 2.45 GHz and 5.8 GHz bands, respectively. Furthermore, the antenna is able to provide stable E-plane broadside radiation patterns in bending situations. It would be an ideal candidate for radio frequency identification (RFID), health monitoring systems, and flexible communication applications. Full article

Introduction: Since COVID-19 primarily targets the respiratory system, it is essential to longitudinally monitor functional capacity and pulmonary function in individuals with post-COVID syndrome (PCS). This study aimed to evaluate the functional capacity of individuals with PCS during exercise using cardiopulmonary exercise testing (CPX) and examine its association with spirometry, impulse oscillometry (IOS), and lung ultrasound (LUS) parameters. Methods: Sixty individuals participated in this study. We assessed CPX, which measured peak oxygen consumption (VO₂peak), in addition to IOS, spirometry, and LUS. Results: The mean VO₂peak was 18.4 ± 5.9 mL/kg/min. Significant negative correlations were found between VO₂peak and the following parameters: age (r_s = −0.465, p = 0.0002), body mass index (BMI, r_s = −0.354, p = 0.0056), resonance frequency using IOS (r_s = −0.312, p = 0.0193), and LUS aeration score (rs = −0.261, p = 0.0439). Conclusions: Patients with PCS undergoing CPX demonstrated impaired functional capacity. In these individuals, higher age and BMI were associated with lower VO₂peak. Furthermore, alterations in LUS and IOS may also be linked to reduced VO₂peak. These findings are promising, as they were obtained using a low-cost device. Further studies are needed to investigate the factors that influence oxygen consumption in PCS. Full article

The design-related behaviour of structural dynamics for electric-assisted bicycle (e-bike) drive units significantly influences the mechanical system—e.g., vibrations and durability, stresses and loads, or functionality and comfort. Identifying the underlying mechanical principles opens up optimisation possibilities, such as improved e-bike design and user experience. Despite its potential to enhance the system, the structural dynamics of the drive unit have received little research attention to date. To improve the current situation, this paper uses a flexible multibody modelling approach, enabling new insights through virtual trials and analyses that are not feasible solely from measurements. The incorporation of the drive unit’s system-level topology regarding mass, moment of inertia, stiffness, and damping enables the analysis of critical system states. Experiments accompany the analysis and validate the model by demonstrating a load-dependent shift of the first torsional mode around 35 Hz to 60 Hz, capturing comparable resonance frequency ranges up to 6 kHz, and yielding qualitatively consistent peak positions in both steady-state and ramp-up analyses (mean deviations of 0.03% and 0.06%, respectively). Theoretical considerations of the multibody system highlight the effects, and the stated modelling restrictions make the method’s limitations transparent. The key findings are that the drive unit’s structural dynamic behaviour exhibits solely one structural mode until 0.5 kHz, and further 27 modes up to 10 kHz, solely originating due to the multibody arrangement of the drivetrain. These modes are also load-dependent and lead to resonances during operation. In summary, the approach enables engineers, for the first time, to significantly improve the structural dynamics of the e-bike drive unit using a full-scale system model. Full article

Traditional acoustic seabed classification methods, which are often sensitive to survey geometry and environmental conditions, have limitations in reliability and reproducibility. This study presents a novel physics-guided machine learning framework for automated sediment classification that leverages frequency-dependent acoustic reflection spectra. The framework, tested on two representative sediment types of poorly graded sand (SP) and poorly graded gravel (GP) in controlled laboratory conditions across a frequency range of 100–400 kHz, corrects water-column attenuation and isolates intrinsic sediment responses. Unlike earlier studies that focused solely on attenuation modeling or demonstrated spectral separability without statistical validation, this study embeds physics-guided corrections into a machine-learning pipeline, enabling automated, statistically validated sediment discrimination. Reflection spectra were acquired from 200 samples (100 per class) at 31 frequencies, forming a dataset for classifier evaluation. Random Forest (RF) and Logistic Regression (LR) were benchmarked under identical protocols. RF outperformed LR, achieving peak accuracy of 90% in optimal frequency windows (180–220, 310–350, and 330–370 kHz) and 84% across the full spectrum, compared to LR’s maxima of 82% and 80%. Feature importance revealed that discriminative bands align with wavelengths approximating grain sizes, indicating resonance-like mechanisms. The physics-guided approach demonstrated in this study offers reliable discrimination of sediments with similar grain sizes but different gradations, overcoming a limitation of intensity-only methods. The improved accuracy and interpretability of the classification results have significant implications for future marine survey methods, suggesting that the proposed framework could be a valuable tool for enhancing the efficiency and reliability of seabed characterization. Looking ahead, the potential practical applications of this research are significant, including field trials with autonomous sonar platforms and integration into remote sensing workflows. These applications will be essential to validate the robustness of the approach under real-world variability, paving the way for scalable, real-time seabed classification with implications for a wide range of marine research and applications. Full article

To broaden the operating bandwidth of the vibration energy harvester at low frequencies, this paper presents a cantilever beam piezoelectric energy harvester (PEH) based on the sloshing of a liquid-filled container. The harvester is designed to recover energy from the multi-order sloshing modes of the liquid in the container. A mathematical model of the coupled system comprising the liquid within the container and the PEH was established. Based on the fluid–structure interaction (FSI) theory, the coupling mechanism between the liquid natural sloshing frequency and the immersed natural frequency of the beam was revealed. Experimental validation shows that the resonance characteristics of the PEH are mainly dominated by the liquid antisymmetric sloshing mode. Through comparative experiments, the effect of liquid-filled container and cantilever beam parameters on the PEH’s peak output voltage and operating bandwidth was systematically analysed. The performance of the PEH was significantly improved when the first-order natural frequency of the partially immersed beam approached the liquid natural sloshing frequency, with the bandwidth coefficient increasing by nearly fourfold under this condition. This research provides new ideas for the design and optimisation of piezoelectric energy harvesters in liquid sloshing environments. Full article

The high-frequency and high-amplitude pyroshock environment during the use of spacecraft will cause damage to the equipment. To simulate this environment, a pyroshock environment simulator based on electromagnetic excitation is presented in this work. A multiphysics finite-element model with electromagnetic–force coupling is established to analyze field distributions during excitation and the acceleration response of a resonant plate under Lorentz loading. Parametric analyses examine coil structural parameters, coil current, and plate thickness and their effects on the SRS. It is suggested that the pyroshock environment excited by electromagnetic force has the characteristics of wide frequency band and high amplitude similar to the explosive-based pyrotechnical event, and compared with the single coil, the multi-coil combination can excite a higher peak acceleration without changing the SRS shape. At the same time, the structural parameters of the planar induction coil and the current in the coil only affect the SRS amplitude of the resonant plate, and the degree of influence of the parameters on the SRS peak amplitude is coil width > coil lift-off distance > coil thickness > coil turn-to-turn distance. Additionally, the experimental results are in good agreement with the simulated SRS, verifying the validity of the above-mentioned analysis. Full article

This paper presents a theoretical and experimental investigation of the amplitude–frequency response of a triple-microcantilever system designed for real-time ultra-low mass detection. The present study focuses on the unfunctionalized configuration to clarify the intrinsic electromechanical behavior of this system. Starting with analytical expressions, output voltage amplitude–frequency responses are derived for a Wheatstone-bridge-based readout circuit and used to analyze the relationship between the resonant frequencies and mechanical amplitude–frequency responses of the three microcantilevers and the resulting electrical response. The extrema and zero-crossing points of the output voltage do not trivially coincide with the individual resonance peaks or their intersection points; this offers more freedom for defining strong detection criteria. A specialized experimental setup has been developed and used to measure the frequency response of a fabricated triple-microcantilever prototype; good agreement with the theoretical predictions has been found within the operating range. Initial humidification tests confirm the high sensitivity of the microsystem against small added masses, corresponding to an estimated detection limit on the order of 10⁻¹⁶ kg for the unfunctionalized device. In this way, the present work confirms the validity of the proposed triple-microcantilever configuration for ultra-low mass sensing and outlines its potential for future application in pathogen detection upon surface functionalization. Full article