Search Results (99)

A pioneering detailed comparative study of the dynamics of plasma flows generated by high-power nanosecond and high-intensity femtosecond laser pulses with similar fluences of up to $3\times {10}^4$ J/cm² is presented. The experiments were conducted on the petawatt laser facility PEARL using two types of high-power laser radiation: femtosecond pulses with energy exceeding 10 J and a duration less than 60 fs, and nanosecond pulses with energy exceeding 10 J and a duration on the order of 1 ns. In the experiments, high-velocity (>100 km/s) flows of «femtosecond» (created by femtosecond laser pulses) and «nanosecond» plasmas propagated in a vacuum across a uniform magnetic field with a strength over 14 T. A significant difference in the dynamics of «femtosecond» and «nanosecond» plasma flows was observed: (i) The «femtosecond» plasma initially propagated in a vacuum (no B-field) as a collimated flow, while the «nanosecond» flow diverged. (ii) The «nanosecond» plasma interacting with external magnetic field formed a quasi-spherical cavity with Rayleigh–Taylor instability flutes. In the case of «femtosecond» plasma, such flutes were not observed, and the flow was immediately redirected into a narrow plasma sheet (or «tongue») propagating across the magnetic field at an approximately constant velocity. (iii) Elongated «nanosecond» and «femtosecond» plasma slabs interacting with a transverse magnetic field broke up into Rayleigh–Taylor «tongues». (iv) The ends of these «tongues» in the femtosecond case twisted into vortex structures aligned with the ion motion in the external magnetic field, whereas the «tongues» in the nanosecond case were randomly oriented. It was suggested that the twisting of femtosecond «tongues» is related to Hall effects. The experimental results are complemented by and consistent with numerical 3D magnetohydrodynamic simulations. The potential applications of these findings for astrophysical objects, such as short bursts in active galactic nuclei, are discussed. Full article

In this paper, an equation describing nonlinear wave phenomena on the surface of magnetically active plasma in the approximation of the complete homogeneity of processes along the direction of the constant magnetic field is obtained. One of its solutions, in the form of a pulse having the shape of rapidly decaying oscillations with a changing period, is found to essentially depend on the magnitude of the magnetic field and shown to be approximately described by a specially selected analytical function. A detailed analytical analysis of the properties of another solitary wave formation existing under conditions of resonant coincidence of its carrier frequency with the corresponding value of its eigen surface oscillations in the considered cold semi-infinite plasma, in which a constant magnetic field is directed along its boundary, is also carried out. The conditions for the excitation of wave disturbances are determined, and analytical expressions that adequately describe the space–time structure of nonlinear waves are proposed. Full article

This study aims to reduce pores, cracks, and other defects on the surface of laser powder bed fusion (LPBF)-fabricated 18Ni300 steel and improve its surface quality. Remelting was carried out on the surface with an argon arc as the heat source. Then, the surface layer was characterized using SEM, EDS, XRD, EBSD, and hardness testing. The results showed the following: When the pulse current $I$ increased from 16 A to 20 A, the surface hardness of LPBF 18Ni300 increased due to a decrease in defects and an increase in the martensite phase. The driving forces of convection in the molten pool (such as buoyancy, Lorentz magnetic force, surface tension, and plasma flow force) rose with an increase in current. When the current $I$ exceeded 20 A, the convection became more intense, making it easier for gas to be entrained into the melt pool, forming pores and introducing new defects, resulting in a decrease in surface hardness. The primary factors affecting the hardness of LPBF 18Ni300 after surface argon arc remelting were pore (defect) weakening and phase transformation strengthening, while the secondary factors included grain refinement strengthening and texture strengthening. The solidification mode of the remelted layer was: L → A → M + A′. The phase transition mode of the heat-affected zone was: M + A′ → A_reverse → M_temper. Compared with the base material and heat-affected zone, the grains in the remelted layer formed a stronger <001> texture with a larger average size (2.51 μm) and a lower misorientation angle. The content of the residual austenite A′ was relatively high in the remelted layer. It was distributed in the form of strips along grain boundaries, and it always maintained a shear–coherent relationship with martensite. Full article

Alzheimer’s disease (AD), the most prevalent form of dementia, is marked by progressive cognitive decline, affecting memory, language, orientation, and behavior. Pathological hallmarks include extracellular amyloid plaques and intracellular tau tangles, which disrupt synaptic function and connectivity. Neural oscillations, the rhythmic synchronization of neuronal activity across frequency bands, are integral to cognitive processes but become dysregulated in AD, contributing to network dysfunction and memory impairments. Targeting these oscillations has emerged as a promising therapeutic strategy. Preclinical studies have demonstrated that specific frequency modulations can restore oscillatory balance, improve synaptic plasticity, and reduce amyloid and tau pathology. In animal models, interventions, such as gamma entrainment using sensory stimulation and transcranial alternating current stimulation (tACS), have shown efficacy in enhancing memory function and modulating neuroinflammatory responses. Clinical trials have reported promising cognitive improvements with repetitive transcranial magnetic stimulation (rTMS) and deep brain stimulation (DBS), particularly when targeting key hubs in memory-related networks, such as the default mode network (DMN) and frontal–parietal network. Moreover, gamma-tACS has been linked to increased cholinergic activity and enhanced network connectivity, which are correlated with improved cognitive outcomes in AD patients. Despite these advancements, challenges remain in optimizing stimulation parameters, individualizing treatment protocols, and understanding long-term effects. Emerging approaches, including transcranial pulse stimulation (TPS) and closed-loop adaptive neuromodulation, hold promise for refining therapeutic strategies. Integrating neuromodulation with pharmacological and lifestyle interventions may maximize cognitive benefits. Continued interdisciplinary efforts are essential to refine these approaches and translate them into clinical practice, advancing the potential for neural oscillation-based therapies in AD. Full article

The microstructure, mechanical properties, corrosion behavior, cytocompatibility, and antibacterial properties of biodegradable Zn-3Cu-xMg (x = 0, 0.5, 1 wt.%) alloys with or without pulsed magnetic field treatment during casting were systematically investigated. Mg addition induced the formation of fine Mg₂Zn₁₁ precipitated along the matrix grain boundaries. With the increase in Mg content, the precipitation of the Mg₂Zn₁₁ phase increased, and the grain size became finer. Pulsed magnetic field treatment exacerbated the occurrence of this phenomenon. Under the combined action of the Mg₂Zn₁₁ phase and refined grain size, Zn3Cu0.5Mg alloy with pulsed magnetic field treatment had the best strength–ductility match (σ_UTS = 181.46 ± 1.06 MPa, δ = 3.95 ± 0.07%), moderate corrosion rate (i_corr = 5.69 ± 3.96 μA/cm²), positive cytocompatibility, and antibacterial properties. This study indicated that Zn3Cu0.5Mg alloy with pulsed magnetic field treatment had the greater potential to further improve its properties through subsequent conventional metal-forming processing and severe plastic deformation techniques to meet clinical requirements, compared to existing as-cast Zn alloys. Full article

This paper explores a recently proposed scalable z-pinch-based space propulsion engine in greater detail. This concept involves a “modified plasma focus with a tapered anode that transports current from a pulsed power source to a consumable portion of the anode in the form of a hypodermic needle tube continuously extruded along the axis of the device”. This tube is filled with a gas at a high pressure and also optionally with an axial magnetic field. The current enters the metal tube through its contact with the anode and returns to the cathode via the plasma sliding over its outer wall. The resulting rapid electrical explosion of the metal tube partially transfers current to a snowplough shock in the fill gas. Both the metal plasma and the fill gas form axisymmetric converging shells. Their interaction forms a hot and dense plasma of the fill gas surrounded by the metal plasma. Its ejection along the axis provides the impulse needed for propulsion. In a nonnuclear version, the fill gas could be xenon or hydrogen. Its unique energy density scaling could potentially lead to a neutron-deficient nuclear fusion drive based on the proton-boron avalanche fusion reaction by lining the tube with solid decaborane. In order to explore the inherent potential of this idea as a scalable space propulsion engine, this paper discusses its theoretical foundations and outlines the first iteration of a conceptual engineering design study for a proof-of-concept experiment based on the UNU-ICTP Plasma Focus facility at the Nanyang Technological University, Singapore. Full article

Butt welding experiments on 6061 Al alloy and Q235B steel of 2 mm thickness were conducted using an ER4047F flux-cored wire as the filler metal, after adding a pulsed magnetic field into the process of cold metal transfer (CMT) welding. The effect of the pulsed magnetic field intensity on the macro morphology, microstructure, tensile strength and corrosion resistance of the welding–brazing joint was analyzed. The results showed that when the pulsed magnetic field intensity increased from 0 to 60 mT, the wettability and spreadability of the liquid metal were improved. As a result, the appearance of the Al alloy/steel joint was nice. However, when the pulsed magnetic field intensity was 80 mT, the stability of the arc and the forming quality of the joint decreased, which resulted in a deterioration in the appearance of the joint. A pulsed magnetic field with different intensities did not alter the microstructure of the joint. All of the joint was composed of θ-Fe₂(Al,Si)₅ and τ₅-Al_7.2Fe_1.8Si at the interface and Al-Si eutectic phase and α-Al solid solution at the weld seam zone. Actually, with the pulsed magnetic field intensity increasing from 0 mT to 60 mT, the IMC thickness in the interfacial layer gradually reduced under the action of electromagnetic stirring. Also, the grain in the weld seam was refined, and elements were distributed uniformly. But when the pulsed magnetic field intensity was 80 mT, the grain in the weld seam began to coarsen, and the intermetallic compound (IMC) thickness was too small, which was unfavorable for the metallurgical bonding of Al alloy and steel. Therefore, with the increase in pulsed magnetic field intensity, the tensile strength of the joints first increased and then decreased, and it reached its maximum of 187.7 MPa with a pulsed magnetic field intensity of 60 mT. Similarly, the corrosion resistance of the joint first increased and then decreased, and it was best when the pulse magnetic field intensity was 60 mT. The Nyquist plot and Bode plot confirmed this result. The addition of a pulsed magnetic field caused less fluctuation in the anode current density, resulting in less localized corrosion of the joint using the scanning vibrating electrode technique (SVET). The XPS analysis showed the Al-Fe-Si compounds replacing the Fe-Al compounds in the joint was the main reason for improving its corrosion resistance under the action of a pulsed magnetic field. Full article

Recently, there has been a significant focus on developing various energy harvesting technologies to power remote electronic sensors, data loggers, and communication devices for smart grid systems. Among these technologies, magnetic energy harvesting stands out as one straightforward method to extract substantial power from current-carrying overhead lines. Due to the relatively small size of the harvester, the high currents in the distribution system quickly saturate its magnetic core. Consequently, the magnetic harvester operates in a highly nonlinear manner. The nonlinear nature of the downstream AC to DC converters further complicates the process, making precise analytical modeling a challenging task. In this paper, a clamped type overhead line magnetic energy harvester with a controlled active rectifier generating significant DC output power is investigated. A piecewise nonlinear analytical model of the magnetic harvester is derived and reported. The modeling approach is based on the application of the Froelich equation. The chosen approximation method allowed for a complete piecewise nonlinear analytical treatise of the harvester’s behavior. The main findings of this study include a closed-form solution that accounts for both the core and rectifiers’ nonlinearities and provides an accurate quantitative prediction of the harvester’s key parameters such as the transfer window width, optimal pulse location, average DC output current, and average output power. To facilitate the study, a nonlinear model of the core was developed in simulation software, based on parameters extracted from core experimental data. Furthermore, theoretical predictions were verified through comparison with a computer simulation and experimental results of a laboratory prototype harvester. Good agreement between the theoretical, simulation, and experimental results was found. Full article

Salmon, rich in protein and omega-3 fatty acids, has a short shelf life of 1 to 3 days when stored at 2 to 8 °C. Freezing, used for long-term preservation, often results in ice crystal formation. Ice crystals can cause structural damage, leading to cell wall rupture, which can affect the texture and cause nutrient loss. Ultimately, this process reduces the overall quality of the salmon. Supercooling, which cools food below its freezing temperature without forming ice crystals, offers an alternative. This study investigated the effects of oscillating magnetic fields (OMFs) and pulsed electric fields (PEFs) on ice crystal formation during salmon supercooling. The results showed that using OMFs and PEFs in supercooling reduced the storage temperature of salmon, maintaining a similar thiobarbituric acid reactive substances (TBARS) value to that of frozen and refrigerated samples. There was no significant difference in meat color between the fresh and frozen samples, and drip loss weight was comparable between the fresh and supercooled samples. The microbiological counts were the lowest in the supercooled samples compared to the frozen and refrigerated ones. These findings suggest that supercooling storage with OMFs and PEFs can mitigate quality degradation in salmon typically associated with freezing. Full article

Nanomagnetism and spintronics are currently active areas of research, with one of the main goals being the creation of low-energy-consuming magnetic memories based on nanomagnet switching. These types of devices could also be implemented in neuromorphic computing by crafting artificial neurons (ANs) that emulate the characteristics of biological neurons through the implementation of neuron models such as the widely used leaky integrate-and-fire (LIF) with a refractory period. In this study, we have carried out numerical simulations of a 120 nm diameter, 250 nm length ferromagnetic nanowire (NW) with the aim of exploring the design of an artificial neuron based on the creation and destruction of a Bloch-point domain wall. To replicate signal integration, we applied pulsed trains of spin currents to the opposite faces of the ferromagnetic NW. These pulsed currents (previously studied only in the continuous form) are responsible for inducing transitions between the stable single vortex (SV) state and the metastable Bloch point domain wall (BP-DW) state. To ensure the system exhibits leak and refractory properties, the NW was placed in a homogeneous magnetic field of the order of mT in the axial direction. The suggested configuration fulfills the requirements and characteristics of a biological neuron, potentially leading to the future creation of artificial neural networks (ANNs) based on reversible changes in the topology of magnetic NWs. Full article

Magnetic pulse welding (MPW) employs a strong pulsed magnetic field to accelerate parts against each other, thus forming an impact joint. Single-turn tool coils and field-shapers (FSs) used in MPW operate under the most demanding conditions, such as magnetic fields of 40–50 T with periods lasting tens of microseconds. With the use of conventional copper and bronze coils, intense thermo-mechanical stresses lead to the rapid degradation of the working bore. This work aimed to improve the efficiency of field-shapers and focused on the development of two- and four-slit FSs with a nanocomposite Cu 18Nb brazed wire acting as an inner current-carrying layer. The measured ratios of the magnetic field to the discharge current were 56.3 and 50.6 T/MA for the two- and four-slit FSs, respectively. FEM calculations of the magnetic field generated showed variations of 6–9% and 3% for the two- and four-slit FSs, respectively. The ovality percentages following copper tube compression were 27% and 7% for the two- and four-slit FSs, respectively. The measured deviations in the weld-joining length were 11% and 1.4% in the two- and four-slit FSs, respectively. Compared to the previous experiments on an entirely steel inductor, the novel FS showed significantly better results in terms of its efficiency and the homogeneity of its magnetic field. Full article

Beam stability and timing jitter in modern linear accelerators are becoming increasingly important. In particular, if a magnetic or radio-frequency (RF) compression regime is employed, the beam time of arrival jitter at the end of the linac can be strictly correlated with the phase noise of the accelerating fields of the RF structure working off-crest. For this reason, since 2008, an RF fast-feedback technique, which acts within each RF pulse, has been successfully employed at LNF-INFN (Laboratori Nazionali di Frascati dell’Istituto Nazionale di Fisica Nucleare) in the SPARC_LAB (Sources for Plasma Accelerators and Radiation Compton with Laser And Beam) facility on S-band (2856 MHz) klystrons powered by pulse-forming network (PFN) modulators, as reported in this paper. However, in order to meet the more stringent requirements of plasma wakefield acceleration schemes, some upgrades to this feedback system have been recently carried out. The first prototype has been experimentally tested on a C-band (5712 MHz) klystron, driven by a solid-state modulator, in order to investigate the possibility for additional improvement resulting from the inherently more stable power source. In this paper, the design, realization and the preliminary measurement results obtained at SPARC_LAB after such upgrades will be reviewed. Full article

The impact of a lightning electromagnetic pulse (LEMP) on a power line or power station produces an effect similar to that of switching between a significant power source and a power line circuit. This switch closure causes a sudden change in routing conditions, creating a transient state. This situation has been studied in terms of electrostatic and electromagnetic induction, as well as overvoltage changes. Appropriate mathematical models were used to analyze these changes. While vertical electric field analysis has been carried out in a few studies, magnetic field and horizontal electric field vectors have not been studied. In this study, the Rusck formulation and the Heidler current formulation are combined at the current level, developed and analyzed. This is because the Rusck expression can sometimes give incorrect results at the current level. Also, in the analysis, electromagnetic field formulations based on accelerating charges are used instead of the dipole approximation to eliminate the need for interpolation in the graphical results. In contrast to other studies in the literature, this study proposes the use of moving and accelerating load techniques to better understand the effects of LEMPs on power transmission lines. Also, in this study, the double exponential problem of the current form in Rusck’s formulation is addressed in order to obtain a close approximation of the physical form of the LEMP. Additionally, the field–line (coupling) relationship is studied according to a unique closed formulation, leading to important determinations about the overvoltages generated on a line depending on the propagation speed of the LEMP sprout and the electrical changes in the area where the LEMP first occurs. Full article

The rotation of cells is of significant importance in various applications including bioimaging, biophysical analysis and microsurgery. Current methods usually require complicated fabrication processes. Herein, we proposed an induced charged electroosmosis (ICEO) based on a chip manipulation method for rotating cells. Under an AC electric field, symmetric ICEO flow microvortexes formed above the electrode surface can be used to trap and rotate cells. We have discussed the impact of ICEO and dielectrophoresis (DEP) under the experimental conditions. The capabilities of our method have been tested by investigating the precise rotation of yeast cells and K562 cells in a controllable manner. By adjusting the position of cells, the rotation direction can be changed based on the asymmetric ICEO microvortexes via applying a gate voltage to the gate electrode. Additionally, by applying a pulsed signal instead of a continuous signal, we can also precisely and flexibly rotate cells in a stepwise way. Our ICEO-based rotational manipulation method is an easy to use, biocompatible and low-cost technique, allowing rotation regardless of optical, magnetic or acoustic properties of the sample. Full article

Reliable information about the properties of the processed materials has a significant impact on the effects of their processing. In induction heating processes, this also applies to information about the influence of temperature T on these properties. These are both thermal and electro-magnetic properties. Based on previous studies, a comprehensive experimental method is presented for estimating the temperature characteristics of thermal diffusivity, volumetric heat capacity and resistivity on one measurement station, with particular attention to ferromagnetic materials. The estimation process is carried out on an induction heating stand using forcing signals from an inverter generator. In a computer-controlled cycle that changes the base temperature level, basic measurements of thermal and electrical properties are carried out on a material sample in the form of a cylindrical disk. They are the results of the analysis of the temperature and electromagnetic responses of a material sample to short- and long-term step pulses of a sinusoidal excitation signal with a frequency of approximately 40 kHz. The presented estimation method can be treated as a final method or a preliminary procedure for radically narrowing the variability in decision variables inthe optimization process of simultaneous determination of the sought material characteristics. Full article