Search Results (43)

The Vortex Ring State (VRS) poses a catastrophic aerodynamic threat to coaxial dual-rotor unmanned aerial vehicles (UAVs). Traditional reactive detection mechanisms provide insufficient altitude for recovery, while existing data-driven diagnostics are severely bottlenecked by data leakage, extreme class imbalance, and a lack of physical interpretability. To bridge these gaps, this paper proposes a physics-informed multimodal deep learning framework that transitions from post-occurrence detection to proactive early warning. We establish a 1.5 s precursor window—creating a three-class ordinal state space—to provide the flight control system with critical intervention time for differential rotor recovery. We developed a novel ViT-LSTM architecture (MTSF-Net) to fuse continuous seven-channel onboard-recorded data (comprising three-axis acceleration, three-axis angular velocity, and barometric vertical velocity), which are subsequently transformed into Continuous Wavelet Transform (CWT) spectrograms. To ensure real-time unidirectional inference while preserving absolute physical vibration scales across heterogeneous sensors, a Calibrated Benchmark Normalization (CBN) strategy is introduced. Furthermore, a Hybrid Ordinal Loss is proposed to mitigate the extreme sample imbalance (<0.5%) of the precursor state by penalizing asymmetric aerodynamic degradation. Evaluated under a strict sortie-based isolation protocol, the proposed system achieves an exceptional test accuracy of 98.26% and an unprecedented precursor recall of 100%. Notably, it completely eliminates fatal missed detections (VRS predicted as Normal) and false-positive VRS predictions triggered by precursor states. Finally, Gradient-weighted Class Activation Mapping (Grad-CAM) is utilized to verify that the multimodal sensor processing pipeline successfully anchors onto authentic physical vibration frequencies rather than artifactual noise, laying a rigorous, interpretable foundation for intelligent aviation safety systems. Full article

In this paper, a T-type buncher for a ridgetron accelerator is designed to further enhance the beam capture efficiency of a high-power ridgetron irradiation accelerator and reduce beam loss in the accelerator system. By incorporating a branch, the T-shaped buncher can reduce the required space compared with conventional coaxial bunchers at the same operating frequency. The physical design and electromagnetic field simulation of the T-type buncher were carried out using the CST frequency-domain solver and eigenmode solver. Subsequently, the bunching performance and its impact on beam transport in the ridgetron accelerator were further evaluated using the PIC solver. The results show that, within an input power range of 120–200 W, a 5 ns input pulse can be compressed to less than 0.6 ns, while the energy spread is maintained between 22% and 26%. At an input power of 140 W, the application of the buncher reduces beam loss after the first deflection by approximately 40%. When a 5 ns electron bunch is compressed to 2 ns (non-FWHM), the beam current increases by a factor of approximately 3.13 compared with the injection without the buncher. These results clearly demonstrate the effectiveness of the T-shaped buncher in improving beam capture efficiency and overall accelerator performance, providing a valuable reference for further power enhancement of ridgetron accelerators. Full article

The early stages of most particle accelerator chains produce sub-ns bunches with velocities in the range of 1% to 20% of the speed of light. Fast Faraday Cups (FFCs) are designed to measure the longitudinal charge distribution of these short bunches of free charges. Coaxial designs have been utilized at the GSI Helmholtz Centre for Heavy Ion Research (GSI)’s linear accelerator UNILAC to characterize ion bunches with bunch lengths ranging from a few hundred ps to a few ns. The typical design goals are to avoid the pre-field of the charges and to suppress secondary electron emission (SEE) while preserving the capability of bunch-by-bunch measurements. This contribution presents a novel FFC design manufactured using additive manufacturing, e.g., laser powder bed fusion (LPBF), and compares it with a traditionally produced FFC. The article highlights the design process, RF characterization, and selected measurements with ion beam carried out at GSI. Full article

We study thrust production in a single-fluid magnetohydrodynamic (MHD) thruster with Hall-type coaxial geometry and show how velocity–field alignment and magnetic topology set the operating regime. Starting from the momentum equation with anisotropic conductivity, the axial Lorentz force density reduces to $f_z={\sigma }_{\theta z}{E}_z{B}_r(\chi -1)$, with the motional-field ratio $\chi \equiv \left(u{B}_r\right)/E_z$. Hence, net accelerating force ($f_z>0$) is achieved if and only if the motional electric field $E_m=u{B}_r$ exceeds the applied axial bias $E_z$ ($\chi >1$), providing a compact, testable design rule. We separate alignment diagnostics (cross-helicity $h_c=\mathit{u}·\mathit{B}$) from the thrust criterion ($\chi$) and generate equation-only axial profiles for $\chi \left(z\right)$, $j_{\theta }\left(z\right)$, and $f_z\left(z\right)$ for representative parameters. In a baseline case $(E_z=150\mathrm{V}{\mathrm{m}}^{-1},{\sigma }_{\theta z}=50\mathrm{S}{\mathrm{m}}^{-1},u_0=12\mathrm{km}{\mathrm{s}}^{-1},B_{r0}=0.02\mathrm{T},L=0.10\mathrm{m})$, the $\chi >1$ band spans $\approx 21.2\%$ of the channel; a lagged correlation peaks at $\Delta z^{★}\approx 8.82\mathrm{mm}$$(C_{HU}=0.979)$, and ${\int }_0^L{f}_z\mathrm{d}z$ is slightly negative—indicating that enlarging the $\chi >1$ region or raising ${\sigma }_{\theta z}$ are effective levers. We propose a reproducible validation pathway (finite-volume MHD simulations and laboratory measurements: PIV, Hall probes, and thrust stand) to map $f_z$ versus $\chi$ and verify the response length. The framework yields concrete design strategies—$B_r\left(z\right)$ shaping where u is high, conductivity control, and modest $E_z$ tuning—supporting applications from station-keeping to deep-space cruise. Full article

The central role of heating and cooling in energy transition has been recognised in recent years, especially with geopolitical developments since February 2022 which demand an acceleration in deploying local energy sources to increase the resilience of the energy sector. Geothermal energy is a promising and vital option to optimize heating and cooling systems, promoting sustainability of urban environments. To this end, a proper design is of paramount importance to guarantee the energy performance of the whole system. This work deals with the optimization of the technical and geometrical characteristics of borehole heat exchangers (BHEs) as part of a shallow geothermal plant that is assumed to be integrated in an already operating gas-fired DH grid. Thermal performances of three different configurations were analysed according to the geological information that revealed an aquifer at −36 m overlying a poorly permeable marly succession. Numerical simulations validated the geological, hydrogeological, and thermo-physical models by back-analysing the experimental results of a thermal response test (TRT) on a pilot 150 m deep BHE. Five-year simulations were then performed to compare 150 m and 36 m polyethylene 2U, and 36 m steel coaxial BHEs. The coaxial configuration shows the best performance both in terms of specific power (74.51 W/m) and borehole thermal resistance (0.02 mK/W). Outcomes of the study confirm that coupling the best geological and technical parameters ensure the best energy performance and economic sustainability. Full article

This study investigates the impact of circumferential angle (φ) and interaction angle (θ) between hydrogen jets and diesel sprays in a co-axial hydrogen–diesel injector on combustion and emissions in a hydrogen–diesel dual-fuel engine using 3D CFD simulations. The results demonstrate that a co-axial dual-layer nozzle design significantly enhances combustion performance by leveraging hydrogen jet kinetic energy to accelerate fuel–air mixing. Specifically, a co-axial alignment (φ = 0°) between hydrogen and diesel sprays achieves optimal combustion characteristics, including the highest in-cylinder pressure (20.92 MPa), the earliest ignition timing (−0.3° CA ATDC), and the maximum indicated power of the high-pressure cycle (47.26 kW). However, this configuration also results in elevated emissions, with 29.6% higher NOx and 34.5% higher soot levels compared to a φ = 15° arrangement. To balance efficiency and emissions, an interaction angle of θ = 7.5° proves most effective, further improving combustion efficiency and increasing indicated power to 47.69 kW while reducing residual fuel mass. For applications prioritizing power output, the φ = 0° and θ = 7.5° configuration is recommended, whereas a φ = 15° alignment with a moderate θ (5–7.5°) offers a viable compromise, maintaining over 90% of peak power while substantially lowering NOx and soot emissions. Full article

The experimental and computational characterization of a cold model prototype designed to test the electromagnetic properties of a new RFQ (Radio-Frequency Quadrupole) cavity is reported. This cavity is intended to be an essential part of a compact, high-gradient proton accelerator for medical purposes. The RFQ’s design employs a novel RF power-coupler injection solution. One common way to couple the RF power in proton RFQs has been the use of loop-couplers inserted into the mid-section of the RFQ’s lobe sections. This technique has been demonstrated to be reliable and effective but introduces a significant perturbation into the lobe that can be more noticeable when dealing with compact structures. We propose a RF injection scheme that uses direct transition from a coaxial cable to the RFQ by connecting the inner coaxial conductor to the RFQ vane body. As a consequence, the lobe geometry is not perturbed, and the transversal electrical fields are directly excited through the vanes. Moreover, by using a pair of such couplers connected to opposite vanes at a given transversal plane of the RFQ, it is also possible to excite the desired quadrupolar TE210 modes while avoiding the excitation of dipolar TE110 modes. The resonances corresponding to different RFQ modes have been characterized, and the dependence of the amplitude of the modes on the relative phase of the field injected through the RF power ports has been demonstrated both by measurements and simulations. Full article

To address mass transport limitations in carbon nanofiber membrane electrodes for overall water splitting, a self-supporting nitrogen-doped hollow carbon nanofiber membrane embedded with Co/Co₂P heterojunctions (Co/Co₂P-NCNFs-H) was fabricated via continuous coaxial electrospinning. The architecture features uniform hollow channels (200–250 nm diameter, 30–50 nm wall thickness) and a high specific surface area (254 m² g⁻¹), as confirmed by SEM, TEM, and BET analysis. The Co/Co₂P heterojunction was uniformly dispersed on nitrogen-doped hollow carbon nanofibers through electrospinning, leverages interfacial electronic synergy to accelerate charge transfer and optimize the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). Electrochemical tests demonstrated exceptional catalytic activity, achieving current densities of 100 mA cm⁻² at ultralow overpotentials of 405.6 mV (OER) and 247.9 mV (HER) in 1.0 M KOH—surpassing most reported transition metal catalysts for both half-reactions. Moreover, the electrode exhibited robust long-term stability, maintaining performance for nearly 20 h at 0.6 V (vs. Ag/AgCl) (OER) and over 250 h at −1.5 V (vs. Ag/AgCl) (HER), attributed to the mechanical integrity of the hollow architecture and strong metal–carbon interactions. This work demonstrates that integrating hollow nanostructures (enhanced mass transport) and heterojunction engineering (optimized electronic configurations) creates a scalable strategy for designing efficient bifunctional catalysts, offering significant promise for sustainable hydrogen production via water electrolysis. Full article

This study systematically investigates the dynamic evolution of chemical regimes in pulsed coaxial dielectric barrier discharge (DBD) plasma under atmospheric pressure using mass spectrometry. An innovative real-time mass spectrometric monitoring methodology was established, enabling the dynamic tracking of the formation and consumption processes of key reactive species such as ozone (O₃) and nitrogen oxides (NO_x). Energy density was the critical parameter governing the evolution of gaseous chemical components, with a quantitative elucidation of the regulatory mechanisms of air flow rate and control voltage on plasma chemical regime transition kinetics. Experimental results revealed significant parametric correlations: Under a constant control voltage of 140 V, increasing the gas flow rate from 0.5 to 5.5 L/min prolonged the transition duration from O₃-NO_x coexistence regime to a NO_x-dominant regime from 408 s to 1210 s. Conversely, at a fixed flow rate of 3.5 L/min, elevating the control voltage from 120 V to 140 V accelerated this transition, reducing the required time from 2367 s to 718 s. Parametric sensitivity analysis demonstrated that control voltage exerts approximately 3.3 times greater influence on transition kinetics than flow rate variation. Through comprehensive analysis of the formation and consumption mechanisms of N, O, O₃, and NO_x species, we established a complete plasma chemical reaction network. This scheme provides fundamental insights into reaction pathways while offering practical optimization strategies for DBD systems. For aerospace applications, this work holds particular significance by demonstrating that the identified control parameters can be directly applied to plasma-assisted treatment of propellant wastewater at launch sites, where the efficient removal of nitrogen-containing pollutants is crucial. These findings advance both the fundamental understanding of atmospheric-pressure plasma chemistry and the engineering applications of plasma-based environmental remediation technologies in aerospace operations. Full article

This study investigates the hourglass–spindle-shaped trajectory of electron motion based on a model of electron and circularly polarized chirped laser pulse coaxial collision. The velocity, acceleration, and radiation distribution of the electron in this state of motion are systematically analyzed. The formation process of the hourglass–spindle-shaped trajectory is examined in detail. Four distinct stages of the electron–laser pulse collision process are proposed, with an in-depth analysis of the interaction dynamics and underlying mechanisms in each stage. The critical conditions for the formation of the hourglass–spindle-shaped trajectory are identified, along with the conditions for the emergence of two other possible trajectories resulting from the collision: the spiral-shaped and spindle-shaped trajectories. Additionally, a general model for analyzing electron–laser pulse collisions is proposed. Full article

Solar-driven catalytic oxidation processes for the removal of toxic gaseous pollutants have attracted considerable scientific attention, and there is a strong desire to improve the mass transfer, photogenerated charge separation, and O₂ activation by regulating the structure of the photocatalyst. Initially, functionalized graphene–TiO₂ mesoporous hollow nanofibers have been controllably fabricated by a coaxial electrospinning technique, in which functionalized graphene is controllably prepared through a sequential diazonium functionalization and silane modification and ensures its uniform distribution among TiO₂ nanoparticles (NPs). Subsequently, the ultrafine Ag NPs are primarily anchored onto the surface of graphene by an in situ frozen photodeposition strategy, producing Ag/functionalized graphene–TiO₂ mesoporous hollow nanofibers (Ag/SiG-TO MPHNFs). The optimal Ag/SiG-TO MPHNFs exhibit 3.9-fold and 4.6-fold enhancements in CO photooxidation compared with TO MPHNFs and P25 TiO₂, respectively. The enhanced photoactivity can be attributed to three factors: the creation of the mesoporous hollow structure accelerates mass transfer, the incorporation of graphene facilitates the transfer of photogenerated electrons from TiO₂ to graphene, and the anchoring of Ag NPs improves O₂ activation. Full article

This article presents an optimal tracking controller retrofitted with a nonlinear adaptive integral compensator, specifically designed to ensure robust and accurate positioning of Vertical Take-Off and Landing (VTOL) Unmanned Aerial Vehicles (UAVs) that utilize contra-rotating motorized propellers for differential thrust generation. The baseline position controller is synthesized by employing a fixed-gain Linear Quadratic Integral (LQI) tracking controller that stabilizes position by tracking both state variations and pitch-axis tracking error integral, which adjusts the voltage to control each coaxial propeller’s speed accurately. Additionally, the baseline tracking control law is supplemented with a rate-varying integral compensator. It operates as a nonlinear scaling function of the tracking-error velocity and the braking acceleration to enhance the accuracy of reference tracking without sacrificing its robustness against exogenous disruptions. The controller’s performance is analyzed by performing experiments on a tailored hardware-in-the-loop aero-pendulum testbed, which is representative of VTOL UAV dynamics. Experimental results demonstrate significant improvements over the nominal LQI tracking controller, achieving 17.9%, 61.6%, 83.4%, 43.7%, 35.8%, and 6.8% enhancement in root mean squared error, settling time, overshoot during start-up, overshoot under impulsive disturbance, disturbance recovery time, and control energy expenditure, respectively, underscoring the controller’s effectiveness for potential UAV and drone applications under exogenous disturbances. Full article

Due to the high viscosity and low fluidity of viscous crude oil, how to effectively recover spilled crude oil is still a major global challenge. Although solar thermal absorbers have made significant progress in accelerating oil recovery, its practical application is largely restricted by the variability of solar radiation intensity, which is influenced by external environmental factors. To address this issue, this study created a new composite fiber that not only possesses solar energy conversion and storage capabilities but also facilitates crude oil removal. PF@PAN@PEG was obtained by coaxial electrospinning processing, with PEG within PAN fibers, and a coating layer was applied to the fiber surface to impart oleophilicity and hydrophobicity. PF@PAN@PEG exhibited a high latent heat value (77.12 J/g), high porosity, and excellent photothermal conversion and oil storage capabilities, significantly reducing the viscosity of crude oil. PF@PAN@PEG can adsorb approximately 11.65 g/g of crude oil under sunlight irradiation. Notably, due to the encapsulation of PEG, PF@PAN@PEG can continuously maintain the crude oil at a phase change temperature by releasing latent heat under specific conditions, effectively reducing its viscosity with no PEG leakage at all. When solar light intensity varied, the crude oil collection efficiency increased by 21.99% compared to when no phase change material was added. This research offers a potential approach for the effective use of clean energy and the collection of viscous crude oil spill pollution. Full article

Skin, the largest organ of the human body, accounts for protecting against external injuries and pathogens. Despite possessing inherent self-regeneration capabilities, the repair of skin lesions is a complex and time-consuming process yet vital to preserving its critical physiological functions. The dominant treatment involves the application of a dressing to protect the wound, mitigate the risk of infection, and decrease the likelihood of secondary injuries. Pursuing solutions for accelerating wound healing has resulted in groundbreaking advancements in materials science, from hydrogels and hydrocolloids to foams and micro-/nanofibers. Noting the convenience and flexibility in design, nanofibers merit a high surface-area-to-volume ratio, controlled release of therapeutics, mimicking of the extracellular matrix, and excellent mechanical properties. Core-shell nanofibers bring even further prospects to the realm of wound dressings upon separate compartments with independent functionality, adapted release profiles of bioactive agents, and better moisture management. In this review, we highlight core-shell nanofibers for wound dressing applications featuring a survey on common materials and synthesis methods. Our discussion embodies the wound healing process, optimal wound dressing characteristics, the current organic and inorganic material repertoire for multifunctional core-shell nanofibers, and common techniques to fabricate proper coaxial structures. We also provide an overview of antibacterial nanomaterials with an emphasis on their crystalline structures, properties, and functions. We conclude with an outlook for the potential offered by core-shell nanofibers toward a more advanced design for effective wound healing. Full article

A coaxial helicopter with a maximum take-off weight of 600 kg was converted to an unmanned aerial vehicle. A minimally invasive robotic actuator system was developed, which can be retrofitted onto the copilot seat of the rotorcraft in a short period of time to enable automatic flight. The automatic flight control robot includes electromechanical actuators, which are connected to the cockpit inceptors and control the helicopter. Most of the sensors and avionic components were integrated into the modular robotic system for faster integration into the rotorcraft. The mechanical design of the control system, the development of the robot control software, and the control system architecture are described in this paper. Furthermore, the multi-body simulation of the robotic system and the estimation of the linear low-order actuator models from hover-frame flight test data are discussed. The developed technologies in this study are not specific to a coaxial helicopter and can be applied to the conversion of any crewed flight vehicle with mechanical controls to unmanned or fly-by-wire. This agile development of a full-size flying test-bed can accelerate the testing of advanced flight control laws, as well as advanced air mobility-related functions. Full article