Search Results (1,858)

Pure Fe soft magnetic composites (SMCs) hold a prominent position in cost-sensitive 10–100 kHz medium-to-low-frequency power devices owing to their low raw-material expenditure and high saturation magnetisation. Nevertheless, the inherently poor interparticle electrical resistivity permits the formation of contiguous conduction paths under alternating magnetic fields, giving rise to marked eddy-current dissipation and localised thermal accumulation. To surmount this limitation, the present work introduces γ-mercaptopropyltriethoxysilane (KH580)-functionalised silicon nitride (Si₃N₄) nanosheets as a multifunctional interfacial regulating layer that simultaneously establishes an electrically insulating barrier and a thermally conductive network on the surface of Fe particles. The structural integrity, surface chemical speciation and deposition behaviour of Si₃N₄-s nanosheets on Fe particles were systematically examined, and correlations among lamellar coverage completeness, interfacial bonding robustness and the coupled electrical–magnetic–thermal response were elucidated. The findings reveal that KH580 silanisation introduces a surface functional layer while preserving the parent α-Si₃N₄ crystal structure, and XPS analysis suggests possible local N–Fe and Fe–S interfacial interactions between Si₃N₄-s and the Fe surface. At a loading of 4 wt.% Si₃N₄-s, a comparatively continuous and uniform lamellar coating develops on the Fe particle surfaces. The corresponding Fe/Si₃N₄ SMCs exhibit the highest volume resistivity and a peak thermal conductivity of approximately 12.1 W·m⁻¹·K⁻¹, while maintaining a core loss of approximately 600.2 kW·m⁻³ at 50 mT and 100 kHz. These results indicate that the 4 wt.% specimen provides the most favourable overall balance among electrical insulation, magnetic response, core-loss suppression and thermal transport within the investigated composition range, furnishing a functionalised lamellar interfacial engineering strategy for performance advancement of low-cost Fe-based SMCs. Full article

As the drone industry expands rapidly, the demand for high-performance propulsion systems with high power density, superior energy efficiency, and lightweight characteristics has grown significantly. Outer-rotor permanent magnet synchronous motors (OR-PMSMs) are particularly well-suited for drone propulsion, due to their superior torque density and efficient thermal management, compared to inner-rotor structures. However, achieving accurate performance prediction during the initial design phase remains challenging due to complex electromagnetic phenomena. This paper proposes an analytical methodology using the subdomain method to evaluate the electromagnetic performance of OR-PMSMs, specifically accounting for slotting effects caused by stator geometry. Rather than focusing on complex optimization algorithms, this study prioritizes comprehensive performance evaluation and experimental validation. Key electromagnetic parameters and circuit constants—including air-gap flux density, back-EMF, winding resistance, inductance, and electromagnetic torque—are calculated efficiently using the proposed analytical model. To complement the limitations of analytical formulation regarding core saturation and flux leakage, the finite element method (FEM) is conducted for comparative evaluation. Furthermore, a physical prototype of the OR-PMSMs for drone propulsion was fabricated, and experimental tests were performed to validate the analytical and numerical results. The analytical predictions demonstrate strong agreement with both the FEM simulations and experimental measurements, confirming the accuracy and reliability of the proposed framework. Consequently, this study addresses the inherent constraints of conventional analytical methods and provides a computationally efficient, yet precise, evaluation procedure, serving as valuable baseline data for the design and development of high-efficiency, lightweight drone propulsion motors. Full article

The static and dynamic magnetic responses of symmetric Fe/Al/Fe trilayers were investigated as a function of the thickness of the nonmagnetic spacer layer thickness, with t_Al ranging from 0 to 2 nm. Samples showed ferromagnetic coupling between Fe layers for all values of t_Al, despite presenting characteristics of low-quality thin films, including high roughness and low-saturation magnetic moments. However, it was demonstrated that inclusion of a thin nonmagnetic Al spacer is an effective method to reduce the effective apparent damping parameter (α_app) of the dominant acoustic mode of the multilayered system. Specifically, α_app was reduced from 0.030 to 0.013 when the Al spacer thickness exceeded the characteristic roughness of the layers (t_Al ≥ 1.4 nm). This reduction coincided with the appearance of distinct acoustic and optical resonance modes, indicating a transition from a direct exchange-coupled regime dominated by pinholes to a regime dominated by dipolar coupling. This suggests that decoupling the ferromagnetic layers is a viable strategy for developing low-damping Fe-based materials, even in systems with significant structural imperfections. Full article

Background/Objectives: In skull-base proton therapy, T2-weighted brain magnetic resonance (MR) imaging may be acquired with or without fat saturation (FS). The present study investigated the impact of this protocol variation on radiomics feature stability and brain radionecrosis (BRN) prediction. Methods: Paired T2-weighted FS and non-FS follow-up MR scans of proton-treated skull-base chordoma patients (n = 52) were used to assess feature stability. For BRN prediction (CTCAEv5 grade ≥ 1), baseline planning scans of chordoma and chondrosarcoma patients (n = 80) with mixed FS protocols were used. Following automated brain tissue segmentation, 1911 radiomics features were extracted from cerebrospinal fluid, gray, and/or white matter using PyRadiomics (v3.1.0). Feature stability was quantified using Lin’s concordance correlation coefficient (CCC). Several MR image- and feature-level processing configurations were explored, and the stability of combined gray and white matter features served as the reference for selecting the optimal configuration. Features were stratified based on CCC thresholds and were subjected to univariable feature selection using a Mann–Whitney U-test. Logistic regression was used for predictive modeling and its performance was measured using micro-averaged AUC within a repeated stratified cross-validation framework. Results: Radiomics features were highly sensitive to FS variations (median CCC range: 0.21–0.58). Combat harmonization without image-level processing was selected as the optimal configuration, under which 30% of features achieved CCC ≥ 0.70, and 10.7% demonstrated a CCC ≥ 0.85. Restricting modeling to a highly stable subset eliminated nearly 90% of the baseline features while significantly improving predictive performance (ΔAUC = 0.05, p < 0.001). Conclusions: A subset of radiomics features robust to FS variations was identified. Use of these stable features may mitigate the impact of protocol-induced variability in mixed-FS T2-weighted MR data while simultaneously improving BRN prediction performance. These findings are preliminary and should be interpreted cautiously, given the pilot nature of the study. Full article

Deep coalbed methane (CBM) represents a strategic successor field for unconventional oil and gas exploration and development in China, and fluid mobility is a key parameter determining CBM recovery rates. Existing NMR-based studies on coal rock pore structure and fluid mobility suffer from three deficiencies: a lack of coal rock classification based on T₂ spectral morphology, failure to incorporate fractal characteristics into pore classification, and insufficient understanding of fluid mobilization mechanisms in different pore types during gas-driven recovery. This study investigates deep coal rocks of the Taiyuan Formation in the Linxing Block, eastern Ordos Basin, using low-field nuclear magnetic resonance (LF-NMR), saturation gas displacement experiments, and fractal theory. Deep coal rocks were classified into three types based on T₂ spectral peak morphology under saturated conditions: Type I (central main peak), Type II (left-shifted main peak), and Type III (balanced bimodal peak). A fractal-based method was established to subdivide fluid-filled pores into four types: P1-1, P1-2, P1-3, and P2. Through multiple nitrogen displacement experiments, the fluid mobilization characteristics of each pore type at different displacement stages were quantitatively characterized. A fluid mobility index was proposed to comprehensively evaluate the overall fluid mobility of coal rocks. The results indicate that Type I coal rocks exhibit the highest fluid mobility (54.83% after three displacement cycles), with P1-3 pores as the primary mobile fluid reservoir, whereas Type II and Type III coal rocks show lower mobility (27.70% and 32.89%, respectively), with P1-2 pores as the dominant contributors. Pore structure complexity exhibits a significant nonlinear evolutionary relationship with fluid mobility. The fluid mobility index demonstrates a strong positive correlation with the degree of mobile fluid, validating its effectiveness in characterizing fluid mobility in deep coal rock reservoirs. These findings provide a theoretical foundation for sweet spot identification and development optimization in deep coal gas reservoirs. Full article

Hydrogen-bond organization plays a central role in determining the structure and properties of water from molecular to macroscopic scales. In this study, we propose a geometry-based descriptor for small hydrogen-bonded water clusters, (H₂O)_n, with n = 2–6. The central element of the proposed geometric framework is the dimensionless geometric index, S_n = d/l, where d is the center-to-molecule distance in a cluster configuration and l is the nearest-neighbor O···O distance associated with hydrogen-bonded water molecules. The geometric descriptor is not intended to replace quantum-chemical calculations or to provide a direct measurement of hydrogen-bond energy, lifetime, or number. Instead, it provides a compact geometric framework for describing the structural organization of small hydrogen-bonded water clusters. The obtained geometric trend is compared with selected Nuclear Magnetic Resonance (NMR), Møller–Plesset perturbation theory (MP2), and radial distribution function data as complementary qualitative and semi-quantitative references. The proposed geometric index S_n = ${\displaystyle \frac{d}{l}}$ was further compared with MP2 quantum-chemical O···O distances for (H₂O)_n clusters, n = 2–6, using the oxygen atoms as structural nodes of the hydrogen-bonded motifs. This comparison showed that the exponential increase in S_n is consistent with the characteristic O···O donor–acceptor length scale of approximately 2.8 Å, linking the geometric framework with calculated molecular geometries. Over the limited interval n = 2–6, the geometric index Sn increases monotonically and nonlinearly with cluster size. The quantum-chemical reference data previously reported in our study, comprising GIAO-DFT-calculated ¹H chemical shifts obtained for MP2-optimized water-cluster geometries, show a rapid nonlinear increase from the dimer to the pentamer, followed by the onset of saturation in the pentamer–hexamer range. The semi-empirical stabilization parameter evaluated in the present study indicates increasing relative stabilization, with a reduced incremental change around n ≈ 4–5. The qualitative consistency of these size-dependent trends supports the use of Sn as a compact geometric descriptor of hydrogen-bond organization in small water clusters, without interpreting it as a direct quantitative measure or mechanistic framework of hydrogen-bond cooperativity. Importantly, liquid water is not treated as a system of closed cyclic clusters; cyclic motifs are used only as frameworked geometric reference configurations for small hydrogen-bonded aggregates. The geometric trend is qualitatively compared with selected quantum-chemical, spectroscopic, and radial distribution function data and should be regarded as an empirical geometric approximation over the limited interval n = 2–6. These findings indicate that geometric, spectroscopic, and quantum-chemical descriptors reflect related, but not identical, aspects of hydrogen-bond organization. The proposed approach links cluster geometry, O···O intermolecular distances, and hydrogen-bond connectivity in a simplified geometric description. Full article

Understanding the anisotropic mechanical behavior and pore–fracture structure (PFS) evolution of bedded coal under mining disturbance is critical for gas extraction and hazard prevention in deep coal mining. This study employed low-field nuclear magnetic resonance (NMR) and fractal analysis to characterize the PFS of water-saturated coal samples with bedding angles of 0°, 30°, 45°, 60°, and 90°. The pore system was classified into adsorption and seepage pores according to pore size distribution. Real-time triaxial NMR tests were further conducted to reveal the coupled evolution of mechanical responses and PFS under different bedding orientations. Results show that bedding inclination controls pore distribution, connectivity, and structural complexity, while influencing coal strength, deformation, and failure through stress redistribution and bedding-plane activation. The mechanical response and PFS evolution exhibit strong anisotropic coupling during loading. A fractional-order porosity model was established by incorporating bedding orientation, anisotropy, and stress memory based on pore geometry and stress decomposition. Model verification confirms its effectiveness in describing anisotropic porosity and PFS evolution under varying bedding angles. This study provides theoretical support for permeability prediction, stability assessment, and hazard control in deep-bedded coal seams. Full article

Geomagnetically induced current (GIC) flowing through power transformers causes core saturation, leading to local hot-spot overheating, abnormal vibration, increased noise, and even irreversible transformer damage and forced outage. To prevent catastrophic GIC-induced failures, relay protection must isolate transformers in a timely and reliable manner, yet GIC has long been a critical challenge interfering with the correct operation of conventional transformer protection systems. This paper studies transformer excitation current characteristics under GIC impact, establishes a transformer model with extreme GIC injection, analyzes differential protection performance under varying GIC magnitudes, proposes a modified differential protection method, and verifies its effectiveness via simulations and experiments. Results demonstrate that GIC distorts transformer excitation current, introducing a second harmonic into differential current to trigger differential tripping blocking. The distinct second-harmonic features between magnetizing inrush and GIC injection enable reliable selective unblocking of harmonic restraint. To enable the differential protection to operate correctly under different GIC injection conditions, the operating threshold shall be adjusted according to the transformer parameters after the harmonic blocking is deactivated. The proposed strategy can potentially disable the harmonic blocker during GIC events, allowing relays to trip on demand, which is critical for ensuring transformer safety under extreme conditions. Full article

We reexamined the critical importance of water motion in measuring algal growth and photosynthetic rates, addressing a significant limitation in traditional static incubation approaches. It presents a comprehensive framework for dynamic measurement methods that better simulate natural hydrodynamic conditions experienced by both macroalgae and other benthic autotrophs. We considered the barrier effects of the diffusion boundary layer surrounding the algae on the fluxes of gases and nutrients across the cellular membrane, and integrates findings demonstrating that flow-enhanced mass transfer of nutrients, inorganic carbon and O₂ across diffusion boundary layers can increase photosynthetic performance in macroalgae including the tested Sargassum, Porphyra and Macrocystis species. We provide quantitative comparisons demonstrating that increased velocities of water current can enhance photosynthetic and/or nutrient uptake rates compared to stagnant conditions. The comparative analysis highlights the advantages of flowing water systems in reducing diffusion limitations and better simulating natural environments against the technical simplicity of static methods. We detailed practical methodologies including flow-through system setup and sealed chamber with magnetic stirring techniques for macroalgae, and brush substrate for benthic diatoms. These approaches enable diurnal physiological tracking and reveal saturation responses to increasing water velocities. The methodological framework provides researchers with robust protocols for more accurate assessment of algal photosynthesis and primary productivity in both experimental and applied contexts such as aquaculture, carbon sequestration, and ecological monitoring. Full article

The Co₄₀Fe₄₀B₂₀ alloy is a key magnetic material that combines high saturation magnetization with excellent soft magnetic properties, offering broad application prospects in fields such as spintronic devices, magnetic tunnel junctions, and tunnel magnetoresistive sensors. Hot pressing can be used to produce fine-grained, highly dense CoFeB alloys. However, there is currently a lack of systematic research on the intrinsic mechanisms by which the particle size of gas-atomized CoFeB powders and their non-equilibrium solidification microstructure regulate phase transformations, microstructural evolution, and densification behavior during hot pressing and sintering—particularly regarding the microstructural inheritance effects of powders with different particle sizes. To address this issue, this study used vacuum induction melting and gas atomization technology to prepare Co₄₀Fe₄₀B₂₀ pre-alloyed powders in three particle size ranges: <38 μm, 38–74 μm, and 74–154 μm. Under identical process parameters, corresponding bulk alloys were produced via vacuum hot-press sintering, and the effects of initial powder particle size on phase transformations and microstructural evolution in the sintered bodies were systematically investigated. Microstructural characterization revealed the complete phase evolution of the alloy from the non-equilibrium solidified powder state to the sintered equilibrium state. During hot-press sintering, the metastable (Fe,Co)₃B phase in the powder completely decomposed, transforming into a stable body-centered cubic bcc-(Fe,Co) phase and a bcc-(Fe,Co)₂B second phase. The dispersed (Fe,Co)₂B phase precipitated after sintering strongly inhibits grain boundary migration via the Zener pinning effect, effectively hindering grain growth and resulting in a uniform, fine-grained, equiaxed microstructure. In coarse powders, due to the presence of a portion of the (Fe,Co)₂B phase, this phase aggregates and grows during sintering, weakening the pinning effect and leading to abnormal grain growth. The Hall–Petch fine-grain strengthening effect resulting from grain refinement couples with and offsets the weakening of second-phase strengthening caused by second-phase coarsening, ultimately leading to sintered bodies prepared from powders of different particle sizes exhibiting similar macroscopic density and hardness properties. Full article

For scalable quantum networks and distributed quantum sensing, remote NV color-center spin ensembles require controllable long-range coherent connections. However, the magnetic dipole coupling between NV centers decays rapidly with distance, making direct stable coherent exchange difficult to achieve. Here, we propose an active-microwave-cavity-assisted scheme for long-range synchronization, in which traveling microwave photons establish a remote cavity–spin coupling channel, while saturable gain compensates cavity loss and propagation attenuation. The results show that the system exhibits collective superradiant emission under gain-off and forms a hysteretic synchronized state controlled by the propagation phase, separation distance, and optical cooling rate under gain-on. Moreover, the active cavity can mediate long-range phase synchronization between two remote NV ensembles, with local optical cooling enabling switching between in-phase and out-of-phase synchronized states. This scheme provides a theoretical route toward room-temperature, optically reconfigurable spin networks. Full article

The model predictive current control (MPCC) of an interior permanent magnet synchronous machine (IPMSM) requires an accurate motor parameter model to predict future currents and achieve high control performance. However, the inductance parameters of an IPMSM are easily affected by factors such as magnetic field saturation, leading to large current prediction errors, high current ripple, and poor stability. Therefore, an MPCC strategy for an IPMSM based on parameter adaptive feedback correction is proposed. First, based on the mathematical model of the IPMSM in the synchronous rotary coordinate, the cross-coupling relationship between the dq-axis inductance deviations and the current prediction error is derived to form an explicit prediction error model. Then, the influence of the d-axis and q-axis inductance parameter deviations of the IPMSM on the current prediction error is discussed in detail. Next, based on the established mathematical model of the prediction error, the recursive least squares scheme is adopted to identify the d-axis and q-axis deviations of the inductance parameters online. Finally, unlike conventional open-loop RLS correction, a PI-based closed-loop correction loop is designed that feeds the prediction error back to adjust the inductance deviations, thereby forcing the prediction error toward zero while inherently compensating for inverter dead-time effects. Simulations and experiments were conducted, and the results show that the proposed scheme greatly improves the accuracy of current prediction and inductance parameter estimation, and enhances robustness against parameter mismatch and dead-time disturbances. The key novelty lies in the PI-feedback-driven RLS closed-loop structure that simultaneously achieves error elimination and dead-time compensation. Full article

Permanent magnet synchronous motors (PMSMs) are widely used in AC drive systems, and their control performance depends strongly on accurate motor parameters. Conventional proportional-integral model reference adaptive system (PI-MRAS) observers use fixed adaptation gains, resulting in a trade-off between rapid convergence and low steady-state fluctuation. To address this limitation, this paper proposes a fuzzy proportional integral (Fuzzy-PI)-tuned MRAS observer for the simultaneous online identification of stator resistance (Rs) and stator inductance (Ls). The parameter-error dynamics are formulated from the PMSM model, and the adaptation laws are derived using Popov hyperstability theory. A fuzzy tuner uses the absolute identification error and its rate of change to schedule the proportional and integral gains online, thereby accelerating transient error convergence when the identification error is large and reducing estimation oscillations during steady-state operation. The method is evaluated through simulation and laboratory experiments involving rated operation, speed variation, parameter perturbation, and load disturbance. Under the investigated conditions, the identification errors of Rs and Ls are 3.8% and 0.18%, respectively. Compared with the conventional PI-MRAS, the reported Rs identification error decreases from 8.1% to 3.8% and the Ls identification error decreases from 0.91% to 0.18%. The results demonstrate an improved identification accuracy and disturbance recovery within the tested operating range. The implementation on an Infineon TC233 platform also demonstrates real-time feasibility, while broader validation under temperature variation, magnetic saturation, inverter nonlinearity, and measurement noise remains necessary. Full article

The complexity of micrometer-scale pore-throat structures in sandstone reservoirs strongly controls the occurrence state and mobilization degree of residual oil after water-flooding. To clarify the differences in residual oil occurrence between pure oil-zone and transition-zone reservoirs and their microscopic controlling mechanisms, sandstone samples were collected from the SII oil layer group, which belongs to the Upper Cretaceous Yaojia Formation, in the Nanqi area of the Daqing Oilfield, northern Songliao Basin, NE China, and were investigated. Mercury intrusion capillary pressure (MICP), two-dimensional nuclear magnetic resonance (2D NMR), laser scanning confocal microscopy (LSCM), micro-computed tomography (micro-CT), X-ray diffraction (XRD), wettability measurement and fractal analysis were integrated to systematically characterize the pore-throat architecture, mineral composition, seepage capacity, and residual oil occurrence of the two reservoir types. The results show that the pore-throat radius distributions are mainly unimodal. In the pure oil-zone samples, the pore-throat distribution is highly consistent with the corresponding permeability contribution curve, whereas evident deviations occur in some transition-zone samples. Large and medium pore throats exert the most significant control on seepage capacity, and the difference in fractal characteristics is mainly reflected by D1, the fractal dimension of large pore throats. The transition-zone reservoirs generally exhibit moderate to strong water-wet characteristics. Owing to the development of fine pore throats and strong capillary forces, water is prone to retention within pore-throat spaces, resulting in pronounced water-blocking and Jamin effects. After water-flooding, the pure oil-zone reservoirs exhibit lower residual oil saturation, with residual oil occurring mainly in a bound state; in contrast, the transition-zone reservoirs show higher residual oil saturation and relatively high proportions of free and semi-bound residual oil. Mineral composition further modifies pore-throat complexity and residual oil occurrence. D1 is negatively correlated with feldspar content, indicating that increased feldspar content helps improve the pore-throat structure, but positively correlated with clay mineral content, suggesting that clay minerals enhance structural complexity. In the transition-zone reservoirs, kaolinite and illite–smectite mixed-layer minerals are relatively well developed. Their velocity-sensitive and water-sensitive effects readily induce pore-throat blockage and increased flow resistance, which are important causes of residual oil enrichment and difficult oil mobilization in the transition zone. Full article

The detection of outer-wall defects in thick ferromagnetic structures by conventional pulsed eddy current testing is limited by the shallow penetration depth caused by the high magnetic permeability of ferromagnetic materials. In this study, a magnetic saturation pulsed eddy current testing method is proposed to improve the detectability of such defects. The analytical dependence of the eddy current skin depth on magnetic permeability was first clarified, and finite element simulations were carried out to visualize the effect of magnetic saturation on the magnetic field and eddy current distributions. Pulsed eddy current responses under different relative permeabilities were then numerically analyzed, followed by experimental validation using Q345B steel plates with different thicknesses and cubic Q345B specimens containing flat-bottom hole defects of different depths. The influence of the direction of the saturation magnetic field on testing performance was also investigated. The results demonstrate that magnetic saturation effectively increases eddy current penetration depth and significantly improves the sensitivity of pulsed eddy current testing to wall-thinning defects in thick ferromagnetic structures. Signal separation for different defect depths was markedly enhanced under saturated conditions. In addition, the optimal testing performance was achieved when the saturation magnetic field was parallel to the probe axis. These results, obtained on uncoated specimens under laboratory conditions, provide a validated physical basis and a preferred field-probe configuration for applying magnetic saturation pulsed eddy current testing to thick-walled ferromagnetic components. Full article