Search Results (122)

The initiation of detonation is a critical yet challenging task for pulse and rotating detonation engines. Conventional approaches often rely on nanosecond repetitively pulsed discharges to generate nonequilibrium plasma for ignition assistance, but the complexity and high cost of the required power supplies limit practical applications. In this work, we experimentally investigate a simplified method using ordinary electrode breakdown discharge to produce an arc plasma that promotes jet-induced detonation initiation. Two ignition strategies are compared under the same total energy: dual-spark-plug ignition (energy concentrated at the jet tube head) and single-spark-plug coupled with electrode discharge (energy split between the jet tube head and an electrode pair placed near the detonation chamber inlet). High-speed schlieren measurements are performed to capture the dynamic flame evolution and shock wave structures. The results show that the electrode-discharge approach dramatically increases the detonation success rate from 13.33% to 66.67% over 30 repeated runs. The electrode discharge is found to occur after the emerging flame has already covered the electrodes. Therefore, the promoting mechanism is attributed not to the high temperature or free radicals generated in the already-burned products, but rather to the discharge-induced shock wave. This shock wave interacts with the corner expansion waves generated by the sudden area expansion, thereby delaying the unsteady decay of the leading shock and promoting re-initiation. This study provides the first experimental evidence that ordinary electrode breakdown discharge promotes jet-induced detonation via a shock-wave reinforcement mechanism. The findings enable a low-cost, compact plasma-assisted initiation strategy for practical detonation engines. Full article

Subauroral geospace is a dynamic region. Its various features include Subauroral Polarization Streams (SAPS), hot and cold zones, and storm enhanced densities (SED). Previous studies have covered the nightside, leaving the dayside largely unexplored and poorly understood. This study investigates the prenoon and midday sectors, based on multi-instrument, multipoint observations. In the inner magnetosphere, the observed dayside SAPS’ development was set off by solar-wind flow pressure increases compressing the dayside magnetosphere in the equatorial plane and triggering earthward-directed hot plasma surges or particle injections in the coupled Alfvenic solar wind and dayside magnetosphere. The dayside SAPS developed in an inner-magnetosphere voltage generator and appeared sometimes within the cold zone where the isotropic ion temperature (Ti_‖ ≈ Ti_⊥) minimized and sometimes within the hot zone fueled by whistler-mode chorus waves locally enhancing the field-aligned temperature anisotropy (T_‖ > T_⊥) and providing localized plasma heating both via Landau damping and implicitly. In the ionosphere, the observed dayside SAPS’ development was unfolding in a prenoon eastward auroral electrojet (AEJ) scenario on the dawnside and in a midday westward AEJ scenario on the duskside. The observed dayside SAPS mapped down to the noontime SED plume base depicted by the total electron content maps. Full article

During underwater laser welding, the coupling among water cooling, gas–liquid interface disturbances, and metal-vapor recoil pressure means that the relationships among plasma evolution, the thermal state of the keyhole, and spatter behavior remain insufficiently understood. In this study, 304NG stainless steel was welded in air and under local dry underwater conditions using a 10 kW continuous-wave fiber laser with a wavelength of 1070 nm to investigate the effects of laser power on the energy state and process stability of underwater welding. The underwater experiments were conducted in deionized water, with the workpiece positioned approximately 100 mm below the free water surface and without additional pressurization. High-speed imaging, infrared thermography, and spectroscopy were employed to characterize the transient evolution of the plasma and spatter, the apparent thermal state near the keyhole opening, and the spectral characteristics of the underwater plasma, respectively, while the plasma excitation temperature was calculated using the Boltzmann multi-line fitting method. The results showed that as the laser power increased from 2000 to 4000 W, the plasma size and temporal persistence increased significantly in both air and underwater environments; the transverse width of the underwater plasma at T₀ + 0.8 ms increased from approximately 2.7 to 5.8 mm, while the average maximum apparent temperature near the keyhole opening increased from approximately 2477 to 3071 °C. Meanwhile, the intensities of the characteristic Fe I lines increased overall, and the plasma excitation temperature increased from 5977 to 6510 K, consistent with the expansion of the plasma-emitting region, the enhanced persistence of the high-temperature core, and the increase in the apparent temperature near the keyhole opening. This study aims to provide a new systematic understanding and technical insights into plasma evolution during underwater laser welding. Full article

5052 aluminum alloy has been widely used in aerospace, shipbuilding, automotive, and electronic industries due to its low density, high specific strength, and excellent corrosion resistance. Understanding its laser-induced damage behavior under combined continuous-wave (CW) and nanosecond (ns) pulse laser irradiation is essential for optimizing combined laser processing. In this study, the damage behaviors induced by individual CW laser, individual ns pulse laser, and combined pulse laser were systematically investigated using high-speed imaging, infrared thermography, and three-dimensional surface characterization. The results show that the combined pulse laser significantly enhances both damage depth and material removal efficiency compared with single laser irradiation. Although the peak surface temperature remains nearly unchanged under different processing conditions, the crater morphology and penetration depth vary substantially. High-speed imaging reveals that plasma evolution and molten metal ejection dominate the material removal process. Variations in processing parameters significantly modify molten pool dynamics and plasma behavior. In particular, enhanced plasma shielding or excessive energy dissipation reduces the effective laser energy coupling, leading to decreased material removal efficiency. The synergistic interaction among molten pool evolution, plasma expansion, and molten metal ejection governs the final damage morphology. This study provides new insights into the dynamic interaction mechanisms between combined pulse laser and aluminum alloys, offering guidance for parameter optimization in high-precision laser micromachining. Full article

The dipole antenna is one of the oldest and most widely used devices in electromagnetic engineering, yet the behavior of its near-field during emission remains only partially captured by classical models. In the source-free region surrounding the arms, the vacuum Maxwell–Heaviside equations provide an insufficient number of configurations to describe the transient through which a bound signal becomes a freely propagating wave. We revisit the model equations, introducing an extended formulation in which an auxiliary velocity field complements the electromagnetic fields. Similarly to plasma physics, the outgoing signal is treated as an electromagnetic fluid carrying a charge density. As the far field is concerned, the resulting system admits an exact family of spherical free-wave solutions that follow the rules of geometrical optics. The near-to-far field transition also acquires a concrete dynamical description, thanks to the introduction of the pseudocharge, which is a charge-like density identified with the divergence of the electric field. In addition, a pressure-like potential, vanishing in the far field, tracks the conversion between bound and radiating energy. The approach is illustrated on a standard dipole antenna through direct numerical simulation of the full coupled system. The results suggest a unified analytical and computational pathway for antenna modeling, with natural extensions to more complex geometries and other radiating devices. Full article

Reservoir stimulation is essential in enhanced geothermal systems and unconventional reservoirs where low permeability, inadequate fracture connectivity, or near-wellbore damage restricts commercial injection or production. This review evaluates hydraulic fracturing, thermal stimulation, plasma-pulse stimulation, and selected dynamic stimulation technologies. It compares their physical mechanisms, fracture-network development, reservoir applications, permeability enhancement, operational maturity, deployment challenges, and future perspectives. Hydraulic fracturing remains the most mature method for reservoir-scale fracture creation, fracture conductivity, and reservoir connectivity. In enhanced geothermal systems, however, performance depends on the heat-exchange area, distributed flow, thermal sweep, long-term energy recovery, and induced-seismicity control rather than permeability enhancement alone. Thermal stimulation is integral to geothermal reservoir development. Cold-fluid injection generates thermoelastic stress redistribution, enlarges the fracture aperture, activates natural fractures, promotes thermally assisted fracture propagation, and influences thermal breakthrough. Plasma-pulse stimulation, also termed pulsed-power plasma, electrohydraulic, or shock-wave stimulation, provides a low-water method for near-wellbore permeability enhancement, damage bypass, fracture reactivation, and restimulation. Its broader deployment remains constrained by the limited treatment radius, scale-up uncertainty, energy-transfer efficiency, tool durability, completion integrity, and insufficient field validation. Liquid CO₂ phase-transition, propellant, and explosive stimulation provide additional dynamic-loading options with distinct fracture responses, controllability, safety, and technology readiness. Stimulation technologies should therefore be selected according to the dominant reservoir limitation and evaluated using sustained injectivity or productivity, effective reservoir contact, distributed flow, delayed thermal breakthrough, treatment durability, wellbore integrity, and a controlled geomechanical response. Future progress requires hybrid stimulation, coupled thermal–hydraulic–mechanical–chemical (THMC) modeling, integrated monitoring, adaptive control, physics-informed artificial intelligence, digital twins, standardized field validation, and techno-economic and life-cycle assessments. Full article

Sustaining human presence on the Moon depends on access to strategic metals, which can be achieved by directly utilizing extraterrestrial resources through in situ resource utilization (ISRU). This study presents novel insights and preliminary results into a previously unexplored strategy for metals extraction from the lunar regolith simulant Lunar Mare Soil (LMS-1) using deep eutectic solvents (DESs). Based on inductively coupled plasma–optical emission spectrometry (ICP-OES) measurements, the solubility of major oxide components of the regolith, SiO₂, Al₂O₃, TiO₂, Cr₂O₃, MgO and FeO_T, was investigated in ethaline (choline chloride:ethylene glycol, ChCl:EG) as well as reline (ChCl:Urea). Although both DESs enabled oxide dissolution, reline exhibited significantly higher dissolution efficiency, due to the additional hydrogen-bond donor sites, NH and CO groups from urea, as well as high chloride activity in the reline. Cyclic voltammetry (CV) and square wave voltammetry (SWV) revealed that dissolved metal species in the reline–regolith system undergo complex multivalent redox transitions. The equilibrium potentials of the metals were determined and correlated with the order in which the metals should be electrodeposited on the cathode from an electrolyte containing dissolved lunar regolith. Based on the data from electrochemical measurements, parameters for electrolysis were selected. At less negative overpotentials, the deposit consisted mainly of Si, while Al, Cr, and Fe, along with Si, were electrodeposited at more negative potentials. The results highlight the importance of considering the selective electrochemical extraction of metals from DESs using lunar regolith as the source. Full article

The laser irradiation effect on Charge-Coupled Devices (CCDs) has attracted wide attention in photoelectric countermeasures and imaging system hardening. This review provides a systematic analysis of the phenomena and mechanisms of laser-induced dazzling and damage effects on CCD sensors. It summarizes experimental and theoretical research progress with continuous-wave (CW), pulsed, and composite lasers, revealing distinct interaction mechanisms such as thermal effects, dielectric breakdown, and plasma ablation. The review also covers quantitative evaluation methods for assessing laser irradiation effects. This work provides a comprehensive reference for future studies. Full article

We propose a terahertz (THz) antenna-coupled wire-channel field-effect transistor—modified EdgeFET (m-EdgeFET), formed by combining single-gate FinFET and dual-side-gate EdgeFET concepts, which is used for THz detection. The proposed hybrid design was implemented on AlGaN/GaN high-electron-mobility transistor (HEMT) structures, demonstrating distinct response characteristics under 150 GHz and 300 GHz radiation at room temperature. The responsivity dependence on the channel length was determined, revealing that the peak responsivity reached up to 6.5 V/W at a gate voltage of −3 V, i.e., at a gate bias that is an order lower in magnitude than that required for EdgeFET to reach the maximum response. Meanwhile, the gate leakage current decreased by an order of magnitude (to about 1 nA) compared to a FinFET with similar geometry. The proposed geometry was shown to operate in two regimes: source-drain coupling (SD) and gate coupling (GG) of THz radiation with the transistor wire channel. The results confirm that the m-EdgeFET design is suitable for electrically controlled and fast THz detection. Full article

Combined pulse laser systems combining continuous-wave (CW) lasers and nanosecond pulsed lasers have shown clear advantages in metal ablation and surface modification. However, the plasma shielding effect induced by nanosecond pulses and the associated shock-wave phenomena in hybrid laser systems remain insufficiently investigated, particularly regarding their influence on CW laser energy coupling. In this study, the ablation behavior of metal targets under the combined irradiation of a 500 W CW laser and nanosecond pulsed lasers with pulse energies ranging from 0.4 J to 1.0 J was investigated. High-speed plasma imaging was employed to analyze laser–material interaction characteristics, including absorption behavior and molten material ejection, while high-speed infrared thermography was used to monitor transient temperature evolution during combined pulse laser processing. Macroscopic and microscopic analyses were conducted to characterize damage morphology, and a three-dimensional surface profilometer was used to quantitatively evaluate ablation efficiency. The results show that, under combined pulse laser irradiation, the removed volume increased from 0.05 mm³ to 0.618 mm³ and the ablation depth increased from 0.136 mm to 0.776 mm. Compared with CW laser processing alone, the ablation efficiency was markedly enhanced. This improvement is attributed to the combined effects of optimized energy deposition, thermal distribution, and material response. In addition, the plasma shielding effect was observed to vary with nanosecond pulse energy, indicating that precise energy control is critical for performance enhancement. This study demonstrates the potential of combined pulse laser technology for high-efficiency and high-precision metal surface processing and micro–nano fabrication. Full article

A comb model with periodic potential in side branches is introduced. A comb model is a model of geometrically constrained diffusion, such that the diffusion process along the comb’s main axis (backbone) is coupled to the diffusion process in fingers, the side branches of the comb. Here, we consider a generalized version of this complex process by enabling a periodic potential function in the fingers. We aim to understand how the potential function added affects the asymptotic transport scalings in the backbone. A set of exact results pertaining to the generalized model is obtained. It is shown that the relaxation process in fingers leads directly to the occurrence of a non-equilibrium stationary state (NESS) in comb geometry, provided that the total energy is zero. Also, it is shown that the spatial distribution of the probability density in proximity to NESS is given by the Mathieu distribution with zero energy. The latter distribution is found to be the direct result of relaxation towards stationarity of the Mathieu eigenspectrum. It is suggested that the generalized model can characterize anisotropic particle dispersion in beta-plane atmospheric (alternatively, electrostatic drift-wave plasma) turbulence and the subsequent formation of layered structures, zonal flows, and staircases. In this regard, the inherent interconnection between combs and staircases is discussed in some detail. Full article

Apatite is a widespread accessory mineral, which can provide information on the geochemical characteristics of magma and the conditions of hydrothermal alteration of the rocks in magmatic–hydrothermal deposits. This study aims to understand the relationships between the geochemical and textural features of apatites from diorite porphyries that have undergone different degrees of hydrothermal alteration in the Sharlo Dere area, Chelopech epithermal Cu-Au deposit, Bulgaria. The apatites were characterized by laser ablation–inductively coupled plasma mass spectrometry, scanning electron microscopy with energy-dispersive X-ray spectroscopy, electron probe microanalysis with wave-dispersive spectroscopy, optical cathodoluminescence and multi-element mapping. Magmatic apatites from “hematitic”, propylitic and propylitic-sericitic zones of alteration are distinguished by euhedral crystals with oscillatory zoning and brown luminescence in CL images. In quartz-sericitic alteration zones, apatite has a yellow CL response. Hydrothermally altered apatites in the diorite porphyries overprinted by advanced argillic alteration have corroded, irregular forms and pink-green luminescence. Apatite crystals of magmatic origin reveal high contents of chlorine, strontium, light rare earth elements (LREE), negative Eu anomalies and high La_N/Sm_N and Ce_N/Yb_N ratios. Hydrothermally altered or hydrothermal apatites are distinguished by their higher contents of Na₂O, F, SO₃, Y and middle rare earth elements (MREEs) and their low La_N/Sm_N and Ce_N/Yb_N ratios. The intensity of hydrothermal alteration affects the luminescence and major and trace element contents, including the rare earth element patterns in the apatites, implying apatite can be used as a geochemical indicator to study magmatic–hydrothermal ore deposits. Full article

In the field of acoustic wave detection, optical sensors have significant potential applications in numerous civilian and military fields due to their high sensitivity and immunity to electromagnetic interference. This study designed an undercoupled silica optical waveguide resonator (OWR) with a 2% refractive index contrast. Mode spot converters were introduced at both ends of the straight waveguide to achieve efficient optical transmission between the fiber and the waveguide. The resonator was fabricated using plasma-enhanced chemical vapor deposition (PECVD) and inductively coupled plasma (ICP) etching technologies. The results show that the quality factor (Q-factor) of the resonator reached 2.75 × 10⁶. Compared with a resonator with a refractive index difference of 0.75%, the Q-factor remained at the same order of magnitude while the sensor size was significantly reduced. To achieve high-sensitivity acoustic wave detection, this study employed an intensity demodulation method to realize acoustic wave detection with the resonator. Test results demonstrate that the OWR can detect acoustic signals in the frequency range of 25 Hz to 20 kHz, with a minimum detectable sound pressure of 1.58 μPa/Hz^1/2 @20 kHz and a sensitivity of 1.492 V/Pa @20 kHz. The sensor exhibits a good signal-to-noise ratio and stability. The proposed method shows broad application prospects in the field of acoustic sensing and is expected to enable large-scale applications in scenarios such as communication, biomedical monitoring, and precision industrial sensing. Full article

In this paper, we investigate the generalized coupled Zakharov system (GCZS), a fundamental model in plasma physics that describes the nonlinear interaction between high-frequency Langmuir waves and low-frequency ion-acoustic waves, including the influence of magnetic fields on weak ion-acoustic wave propagation. This research aims to achieve three main objectives. First, we uncover soliton solutions of the coupled system in hyperbolic, trigonometric, and rational forms, both in single and combined expressions. These results are obtained using the extended rational sinh-Gordon expansion method and the $\left({\displaystyle \frac{G^{\prime }}{G}},{\displaystyle \frac{1}{G}}\right)$-expansion method. Second, we analyze the dynamic characteristics of the model by performing bifurcation and sensitivity analyses and identifying the corresponding Hamiltonian function. To understand the mechanisms of intricate physical phenomena and dynamical processes, we plot 2D, 3D, and contour diagrams for appropriate parameter values. We also analyze the bifurcation of phase portraits of the ordinary differential equations corresponding to the investigated partial differential equation. The novelty of this study lies in the fact that the proposed model has not been previously explored using these advanced methods and comprehensive dynamical analyses. Full article

During the laser cladding process, the temperature, flow velocity, and element concentration of the molten pool will be affected by the plasma. Quantitative analysis of the mechanism by which the plasma affects heat and mass transfer during the laser cladding process is of great significance for improving the quality of the cladding layer. In this paper, a multi-field coupled numerical model of the laser cladding process of Fe60 using an ASTM 1045 disk laser was established. In the modeling, the interaction between the plasma cloud and the laser beam (the ionization process of metal vapor absorbing photon energy and the absorption and shielding effect of the plasma on laser energy), as well as the influence of surface tension, buoyancy, and shock waves generated by the expansion of the plasma cloud on the Marangoni flow of the liquid metal, was considered. A comparative analysis was performed on the transient evolution of the temperature field, flow field, and concentration field during the laser cladding process in the presence of the plasma cloud. The results show that the ionization process of metal vapor and the shielding effect of the plasma cloud cause a decrease in laser energy and the temperature of the cladding layer. The Marangoni flow is affected by the shock waves generated by the expansion of the plasma cloud, resulting in a decrease in the flow velocity of the melt. A slight decrease in the concentration of Fe, Cr, and Ni elements and a slight increase in the concentration of C element in the cladding layer are caused by melt evaporation. Full article