Search Results (72)

A low-profile tri-band metamaterial absorber is developed for microwave attenuation and electromagnetic shielding applications within the S-, C-, and X-band regions. The absorber employs a compact resonant topology comprising a square metallic ring and two nested decagonal resonators, fabricated on an FR-4 dielectric layer with a metallic backing. Numerical optimization results in three highly efficient absorption bands located at 3.6 GHz, 7.4 GHz, and 11 GHz, where the absorptivity exceeds 99%. The physical origin of the absorption response is examined through field localization, induced current distributions, constitutive parameter extraction, and impedance characteristics. The analysis demonstrates that the resonant modes generated by the coupled metallic elements promote strong confinement of electromagnetic energy within the structure, leading to dissipation of the incident power. The geometrical unit-cell symmetry further enables a nearly identical response for different polarization states, while maintaining stable operation for incoming angles up to 60° under both TE and TM excitations. To verify the simulation results, an array prototype was manufactured and tested using a free-space characterization technique. The measured absorption characteristics closely follow the simulated response, showing the effectiveness of the design methodology. Owing to its compact dimensions, near-unity absorption, angular stability, and strong shielding capability, the developed absorber offers significant potential for electromagnetic compatibility enhancement, microwave shielding, and radar-related applications. Full article

To address the challenge of simultaneously achieving broadband absorption, multi-mechanism tunability, and angular stability in terahertz multifunctional devices, this paper proposes a MoS₂/VO₂ composite terahertz metamaterial absorber based on an asymmetric multi-nested C-shaped structure. The device adopts a three-layer configuration consisting of a MoS₂/VO₂ composite plane–SiO₂ dielectric–Au reflector layer. Unlike conventional symmetric structures, which are limited by selection rules and symmetry-protected dark modes that hinder the excitation of higher-order resonances, this design effectively breaks structural symmetry protection through geometric asymmetry. This induces strong mode hybridization between originally orthogonal dark and bright modes, enabling broadband high absorption exceeding 96.7% across the 1.88–3.52 THz frequency range (61% RBW). Notably, the device demonstrates synergistic tuning advantages: the macroscopic on/off switching of broadband absorption characteristics via the phase transition of VO₂, combined with fine blind-spot compensation and enhancement in absorption peaks using the electrical tunability of MoS₂. Furthermore, thanks to its sub-wavelength unit cell design, the structure maintains excellent performance stability over a wide incident angle range from 0° to 60°. This study reveals a synergistic enhancement mechanism combining the asymmetric unit cell and hybrid materials, providing a systematic physical solution for resolving the trade-off between bandwidth extension and dynamic reconfigurability. Full article

This study reports the synthesis of low-defect Prussian blue analogues (PBAs) using a single iron-source method and systematically investigates the influence of atmospheric components, particularly water and oxygen, on their oxidative decomposition. Our findings demonstrate that the oxidative degradation of PBAs is governed synergistically by moisture and oxygen, with ambient humidity identified as the primary factor determining both the extent and kinetics of their decomposition. Notably, a pure oxygen environment by itself does not trigger material degradation, while oxygen markedly accelerates the decomposition only in the presence of moisture. As a result of the oxidation, enhanced Coulombic interaction between sodium ions and cyano groups induces structural modifications in the lattice framework, driving a phase transformation from monoclinic to cubic symmetry, accompanied by changes in its unit cell volume. Furthermore, in high-humidity environments, atmospheric moisture promotes the gradual deintercalation of sodium ions from the Prussian blue framework, resulting in the conversion of sodium-rich Prussian blue to the sodium-deficient form. Concurrently, an increase in lattice defect density leads to partial structural collapse, inducing the release of free ferrocyanide ions, which may subsequently react with the deintercalated sodium ions to form the sodium ferrocyanide impurity phase. We also find that the preferential decomposition of low-spin iron over high-spin iron within the framework leads to a further reduction in its electrochemical capacity. In contrast, potassium Prussian blue exhibits minimal interaction with water molecules and can effectively repel them through steric hindrance. Therefore, partial substitution of sodium with potassium ions is proposed as a viable strategy to enhance the structural stability of the Prussian blue framework, improve the storage performance of sodium Prussian blue (NaPB), and mitigate water ingress. This work offers fundamental insights into the storage characteristics and oxidative degradation mechanisms of PBAs. Full article

Background: Evidence on powered wearable exoskeleton gait training in patients with chronic hypoxic-ischemic encephalopathy (HIE) is virtually absent, and existing studies have focused on macroscopic functional outcomes while neglecting joint-level neuromuscular force-generation characteristics such as rate of force development (RFD). Objective: To examine the effects of a six-week powered exoskeleton gait training program on isometric hip strength and RFD, sit-to-stand (STS) performance, frontal-plane hip strength, and center-of-pressure (CoP) dynamics in a patient with chronic HIE-induced quadriparesis. Methods: A case report with pre- and post-intervention evaluation was conducted. A 47-year-old male with chronic HIE-induced quadriparesis (onset 2017) completed 18 sessions (three per week, six weeks) of powered lower-limb exoskeleton gait training. Outcomes included isometric hip peak force and RFD (DynaMo, Vald Performance), STS peak force and body mass-normalized RFD (ForceDecks, Vald Performance), frontal-plane hip strength (ForceFrame, Vald Performance), and CoP path length and mean velocity. Results: Hip extension peak force increased by 247–256% bilaterally, and hip extension RFD increased by 174–188%, whereas hip flexion peak force showed minimal change (+3.3–5.2%). Body mass-normalized STS RFD increased by 250% (10 to 35 N·s⁻¹·kg⁻¹), representing the largest relative gain. Hip abduction strength increased by 27.1–36.8% with improved bilateral symmetry; hip adduction imbalance reversed from right to left dominance. CoP path length and mean velocity each decreased by 3.7%. Conclusions: Six weeks of powered exoskeleton gait training selectively enhanced time-dependent neuromuscular output—particularly RFD—beyond maximal strength gains, with meaningful improvements in functional weight acceptance during STS. These findings support exoskeleton-based training as a promising rehabilitation strategy for patients with chronic CNS injury. Full article

In this work, the structural, electronic, charge-transfer, thermal, and magnetic properties of pristine and Fe-doped silicon carbide nanosheets (SiCNShs) were systematically investigated using spin-polarized density functional theory (DFT) within the Local Spin Density Approximation including Hubbard correction (LSDA + U). A 4 × 4 SiCNSh supercell containing 80 atoms was considered, where Fe atoms were substitutionally introduced at carbon sites to evaluate dopant-induced modifications in the nanosheet. Structural optimization, energy convergence, force minimization, and stress evolution analyses confirm that Fe incorporation preserves the structural integrity of the SiCNSh and leads to energetically stable configurations. The calculated defect formation energy (−7.44 eV/atom) demonstrates the thermodynamic feasibility of Fe substitution, while ab initio molecular dynamics (AIMD) simulations at 300 K verify the thermal stability of the energetically favorable Fe-doped configuration. Electronic-structure calculations reveal that pristine SiCNSh exhibits a nonmagnetic semiconducting nature with a band gap of approximately 2.4 eV, whereas Fe incorporation significantly modifies the electronic structure through pronounced Fe–3d/C–2p/Si–3p orbital hybridization. The band gap is reduced to approximately 1.1 eV for the single-Fe-doped system and further decreases to 0.53/0.51 eV (spin-up/spin-down) in the double-Fe configuration, while preserving semiconducting behavior. Spin-polarized band structure and density of states analyses demonstrate clear spin asymmetry near the Fermi level, indicating strong dopant-induced spin polarization and exchange interactions. Charge-density difference and Bader charge analyses reveal substantial dopant-induced charge redistribution characterized by electron depletion around Fe atoms, enhanced electron accumulation on neighboring carbon atoms, and partial charge neutralization of nearby Si atoms, resulting in a more localized covalent Si–C–Fe bonding environment. Mulliken spin population analysis further demonstrates robust ferromagnetic ordering, where the Fe dopant acts as the dominant magnetic center with strong induced spin polarization extending into neighboring Si and C atoms. Comparison between ferromagnetic (FM) and antiferromagnetic (AFM) configurations confirms that the 2Fe@C-doped SiCNSh stabilizes in a ferromagnetic ground state, exhibiting a favorable FM–AFM energy difference of 0.216 eV. Based on the mean-field approximation, the Curie temperature was estimated to be approximately 837 K, indicating strong magnetic stability significantly above room temperature. The present findings collectively demonstrate that Fe incorporation effectively tailors the electronic and magnetic properties of SiCNSh through band-gap engineering, spin-symmetry breaking, and stabilization of high-temperature ferromagnetism. These combined characteristics establish Fe-doped SiCNShs as promising candidates for spintronic devices, magnetic semiconductors, spin injectors, spin filters, and non-volatile magnetic memory applications. Full article

Graphene, with its excellent mechanical and electrical properties, is an ideal candidate material for constructing high-performance piezoresistive sensors. However, lattice defects inevitably introduced during its preparation and transfer processes can significantly alter its electronic structure, thereby affecting the sensing performance of the devices. Based on first-principles calculations, this work systematically investigates the effects of monovacancy defect concentrations ranging from 2% to 8% on the geometric structure, electronic structure, and piezoresistive performance of graphene. The results show that monovacancy defects induce local lattice distortions and bond reconstructions, forming 5–9 non-hexagonal ring structures at defect concentrations of 4% and 8%. In terms of electronic structure, the defects break the lattice symmetry and open a band gap. High concentrations of defects lead to severe overlapping of electronic states, causing the band gap to first increase and then decrease with increasing defect concentration, reaching a maximum value of 0.697 eV at a concentration of 6%. Meanwhile, the defects introduce localized electronic states, enhance the electron localization effect, and render the system p-type doped. Regarding piezoresistive performance, monovacancy defects significantly improve the gauge factor of graphene. At a defect concentration of 6%, the gauge factor reaches 118.23, which is approximately 36 times that of pristine graphene. These findings reveal the microscopic mechanism of strain-dependent electronic modulation in defective graphene and provide theoretical support for defect engineering design in high-performance graphene-based piezoresistive sensors. Full article

Stroke-related gait impairments are frequently associated with deficits in trunk control, movement coordination, and dynamic stability. Although robotic-assisted gait rehabilitation has shown promising clinical benefits, phase-specific biomechanical adaptations following rehabilitation remain incompletely understood. This study investigated phase-specific biomechanical adaptations following robotic-assisted gait rehabilitation in individuals with stroke using sensor-derived waveform analysis. Rehabilitation was performed three times per week over approximately 5–6 weeks using treadmill-based robotic gait training under dynamic body-weight support conditions. Pre- and post-intervention kinematic data were collected using a sensor-based motion analysis system. Joint kinematics, trunk motion, and center of gravity (COG) displacement were analyzed across the normalized gait cycle using waveform-based effect size analysis, statistical parametric mapping, principal component analysis, and k-means clustering to explore inter-individual adaptation patterns. Thirteen post-stroke hemiplegia patients (10 males; age = 63.9 ± 13.8 years), including six subacute and seven chronic stroke survivors, completed 16 rehabilitation sessions. The most prominent improvements were observed in trunk lateral flexion, particularly during loading response (d = 0.47, p < 0.01), indicating enhanced frontal plane trunk stability. Trunk flexion–extension showed reduced compensatory motion, whereas hip and knee adaptations were smaller and phase-dependent. COG displacement decreased across the gait cycle, reflecting improved dynamic stability. Step length increased significantly on both hemiplegic (Δ = +5.73 cm, p = 0.024) and intact sides (Δ = +8.83 cm, p = 0.007), while cadence and load symmetry remained unchanged. Clustering analysis revealed heterogeneous adaptation profiles rather than distinct responder groups. Chronic participants demonstrated greater variability within the Principal Component Analysis space compared to subacute participants, suggesting more variable and individualized biomechanical reorganization patterns rather than clearly separable recovery categories. Overall, robotic rehabilitation induced inter-individual biomechanical adaptations, predominantly involving proximal trunk control and stabilization strategies. Full article

Focusing on the self-powering demand of aircraft engine bladed disks (blisks), this paper investigates piezoelectric vibration energy-harvesting modeling and non-linear circuit performance. A multi-sector electromechanical coupled model is established to analyze the frequency splitting and vibration localization induced by minor structural mistuning. By breaking the cyclic symmetry, mistuning severely concentrates vibration energy into a specific sector, providing a localized high-energy concentration region for optimal energy extraction. To enhance recovery efficiency and load adaptability, three interface circuit topologies—Standard Energy-Harvesting (SEH), Parallel Synchronized Switch Harvesting on Inductor (P-SSHI), and Double Synchronized Switch Harvesting (D-SSHI)—are comparatively analyzed. Through wideband spatial–spectral dynamic response and steady-state impedance matching analyses, the non-linear energy conversion and transfer mechanisms are systematically characterized. Results demonstrate that synchronized switching circuits significantly improve energy transmission via forced voltage inversion, accompanied by a notable equivalent stiffness enhancement effect induced by electromechanical coupling. Furthermore, the D-SSHI topology not only exhibits substantial advantages in peak power extraction, but also, owing to its internal LC energy decoupling mechanism, forms a broad load-independent power plateau across an extremely wide impedance range. This research provides robust theoretical foundations for designing highly resilient self-powered intelligent blades under extreme operating conditions. Full article

To address fault-period DC-link overvoltage, the reduction in grid-side active-power regulation margin caused by reactive-current-priority operation, and the double-frequency current fluctuation induced by negative-sequence components under asymmetrical grid faults in a flywheel-assisted permanent-magnet direct-drive wind power system, this paper proposes a coordinated low-voltage ride-through (LVRT) strategy based on DC-link-voltage-threshold partitioning. According to the DC-link voltage level, the operating process is divided into a normal regulation region, a grid-side saturation region, and a flywheel activation region, thereby enabling coordinated regulation between grid-side reactive-current support and flywheel-side active-power absorption. To improve transient smoothness, an anti-windup mechanism together with a bumpless transfer scheme is incorporated into the coordinated control process to suppress integrator saturation and mitigate mode-transition disturbances. In addition, a grid-side proportional–integral–vector resonant controller (PI-VRC) is introduced to improve the suppression of double-frequency current fluctuation under asymmetrical faults and enhance converter capacity utilization. Simulation results show that the proposed strategy can effectively restrain fault-period DC-link voltage rise, improve three-phase current symmetry and grid power quality, and strengthen transient reactive-power support, thereby enhancing the asymmetrical-fault LVRT capability of the system. Full article

This study examines the determinants of bilateral trade asymmetries between Türkiye and its three main EU partners—Germany, Bulgaria, and Romania—over 2002–2024. Within the gravity framework, bilateral symmetry in trade data implies that reported exports should equal partner imports (Xᵢⱼ = Mⱼᵢ). Deviations from this condition reflect systematic distortions caused by valuation practices, institutional gaps, and crisis-induced disruptions. This study employs a fixed-effects panel framework to identify the structural and contextual determinants of mirror−data asymmetries in Türkiye–EU trade. Using HS2−level mirror statistics from TÜİK and Eurostat, three asymmetry measures—the Bilateral Asymmetry Index (BAI), Absolute Logarithmic Difference (ALD), and Relative Symmetry Index (RSI)—are estimated through a fixed-effects panel model. Results show that a one−unit improvement in logistics performance (LPI) reduces asymmetry by approximately 0.17 points (p < 0.01). Maritime connectivity (LSCI) shows a small but statistically significant positive coefficient, while exchange rate volatility remains insignificant. The effects of global crises are heterogeneous: the 2008 financial crisis significantly increases asymmetry (+0.07, p < 0.01), whereas COVID−19 is associated with a reduction in asymmetry (−0.04, p < 0.01). The interaction between LPI and crisis periods is negative and significant (−0.03, p < 0.05), confirming that a stronger logistics capacity buffers crisis-induced reporting gaps. Country-specific results reveal that Romania drives much of the variation (within−R² = 0.26), while Germany remains largely insulated from crisis effects. The findings highlight that deviations from bilateral symmetry are driven by structural and institutional factors rather than random error. Policy recommendations stress harmonized customs valuation, digital logistics integration, and enhanced Türkiye–EU statistical coordination to strengthen trade data reliability and crisis resilience. Full article

In ultra-wideband (UWB) synthetic aperture radar (SAR) imaging, in-band antenna standing waves (SW) can generate range ghosts, degrading image quality. To address this issue, an image-domain suppression method is proposed, leveraging the phase symmetry property (PSP) between the SW signal and its mirror SW (MSW) signal. Based on PSP, the MSW signal is rapidly constructed from the SW signal, ensuring that both share the same target region but exhibit different ghost regions. PSP is further extended to the image domain. Specifically, the SW-induced phase is extracted in the wavenumber domain. Based on the PSP, this phase is then used to construct the MSW signal, which exhibits a phase spectrum that is symmetric to that of the SW signal with respect to the origin. The MSW image is subsequently fused with the original SAR image, thereby effectively suppressing SW-induced ghosts. The experimental results demonstrate that the proposed method significantly mitigates ghosting while preserving the amplitude and structural integrity of the main signal, thereby enhancing overall imaging quality. Full article

Skeleton-based action recognition is a critical technology for intelligent sports analysis. Although the human skeletal structure exhibits inherent bilateral symmetry, sensor noise on resource-constrained edge devices frequently induces geometric distortion and topological asymmetry. Consequently, achieving a balance between high accuracy and real-time performance remains a significant challenge. To this end, we propose EMS-GCN, an Efficient Multi-scale Shift Graph Convolutional Network that integrates geometric priors. Specifically, we design a Gaussian kernel-driven topology refinement module to mitigate structural noise inherent in sensor data. By leveraging geometric symmetry and Gaussian distances among nodes, this module dynamically constrains graph topology learning, thereby effectively rectifying the structural asymmetry and ambiguity induced by noise. Furthermore, we construct a Multi-scale Shift Linear Attention (MSLA) module to replace computationally intensive temporal convolutions. Leveraging temporal shift invariance, this module captures multi-scale contexts via parameter-free shift operations. Furthermore, we introduce a linear temporal attention mechanism to model global temporal dependencies with linear complexity, effectively resolving the information asymmetry inherent in long-range interactions. Finally, EMS-GCN incorporates a dual-branch attention structure to adaptively calibrate feature responses. Extensive experiments demonstrate that our model maintains high recognition accuracy with only 0.56 M parameters, representing a reduction of over 60% compared to mainstream baselines. These results validate the efficacy of leveraging geometric and temporal symmetries to enhance real-time sports analysis. Full article

Birefringence, arising from the low-symmetry structure in orthorhombic LaFeO₃, limits the observation and utilization of magneto-optical effects. In this study, the pure-phase perovskite-typed La_1−xCe_xFe_1−xTi_xO₃/SiO₂ thin films were successfully fabricated via radio-frequency magnetron sputtering, where the co-doping of Ce³⁺ and Ti⁴⁺ ions effectively induced a structure transition from orthorhombic to a highly symmetric cubic phase, eliminating birefringence effect and thus reducing optical transmission loss. At the same time, the doped Ce³⁺ ions also effectively enhanced the magnetic and magneto-optical effects of the system due to their strong spin coupling effect and superexchange interaction with Fe³⁺ ions. The results show that the cubic-phase La_0.5Ce_0.5Fe_0.5Ti_0.5O₃/SiO₂ thin film exhibits excellent magnetic and magneto-optical performance. Their saturation magnetization reaches 180 emu/cm³ with an in-plane easy magnetic axis. And their magnetic circular dichroic ellipticity |ψ_F| reaches 3054 degrees/cm. Full article

Small rotorcraft unmanned aerial vehicles (UAVs) are highly susceptible to wind disturbances when performing tasks such as fixed-point hovering, low-altitude inspection, and aggressive maneuvers. Under complex, variable meteorological conditions, attitude stability and position-holding accuracy are particularly critical. Although quadrotor UAVs exhibit structural and dynamic symmetry, real wind disturbances are often asymmetric, disrupting the original balance and leading to intensified attitude oscillations, position drift, and degraded data quality. To effectively address the challenges of wind-induced oscillation and positional deviation, this paper proposes a fuzzy logic-based linear active disturbance rejection control (Fuzzy-LADRC) strategy. This approach employs a hybrid algorithm combining particle swarm optimization and gray wolf optimization to optimize controller parameters and incorporates fuzzy logic to enhance the adaptive capability of the linear active disturbance rejection controller (LADRC). Simulation experiments conducted in MATLAB/Simulink under complex wind-field conditions demonstrate that the proposed method significantly outperforms traditional PID controllers: in the regulation of roll and pitch angles, control performance improves by approximately 5%, while in yaw angle control, the improvement reaches up to 30%. Furthermore, this method can significantly suppress position deviation and fluctuation in the X and Y directions, and reduce the overshoot in the Z-axis during the UAV’s takeoff phase by 75%. Full article

To overcome the physical constraints during the miniaturization of conventional semiconductor devices, spintronics is playing an increasingly prominent role. The Rashba effect, characterized by spin–momentum locking, has emerged as a promising solution to address challenges. Two-dimensional (2D) Janus transition metal dichalcogenides (TMDCs) break spatial inversion symmetry, creating favorable conditions for the Rashba effect. Based on first-principles calculations, 2D Janus materials XMoYZ₂ (X = S/Se/Te; Y = Si/Ge; Z = N/P) were investigated, with strain, external electric field and charge doping employed to modulate the Rashba effect. The strain results reveal that the Rashba constants of XMoYZ₂ increase significantly with compressive strain. Specifically, after applying uniaxial strain, the Rashba constant of TeMoSiP₂ is enhanced to ~2.2 times its initial value. Compressive strain reduces atomic spacing, enhances orbital overlap, and increases spin–orbit coupling (SOC) strength. All the TeMoYZ₂ materials exhibit significant anisotropy under uniaxial strain, which is favorable for spin-oriented transport. SeMoGeP₂ shows an almost linear Rashba constant–electric field correlation, while TeMoGeP₂ and TeMoSiP₂ show non-monotonic variation. The Rashba constant of TeMoSiP₂ can be enhanced to ~2.7 times its intrinsic value under either positive or negative applied electric fields. Charge doping induces negligible changes in the SOC effect. Finally, the optical absorption properties of TeMoGeP₂, TeMoSiN₂, and TeMoSiP₂ were investigated. This study clarifies the mechanism underlying the enhancement of Rashba constants in XMoYZ₂ materials, enriching the research landscape of spintronics. Full article