Longitudinal Magnetic Field Research Articles

Effect of an AC-DC composite longitudinal magnetic field on the microstructure and mechanical properties of WAAM Al-5 %Mg alloy

To address issues of poor forming accuracy, high porosity, and inadequate mechanical properties in wire arc additive manufacturing of aluminum alloys, this study applied external direct current (DC) and alternating current (AC) composite magnetic fields (ECMF) (AC+DC) in cold metal transition wire arc additive manufacturing (CMT-WAAM) of Al-5 % Mg alloys. The aim was to enhance the quality of forming and overall mechanical properties of the deposited specimens. Optimal ECMF (AC+DC) parameters-DC 3 A, AC 1 A, and alternating frequency 100 Hz-were determined through orthogonal experiments. Results showed that ECMF (AC+DC) facilitated arc expansion and stirred the molten pool via Lorentz force generation, thereby accelerating molten flow and improving forming precision. Compared to specimens without ECMF (AC+DC), those with ECMF (AC+DC) exhibited reduced porosity (1.07 % to 0.31 %, a decrease of 71.03 %) and finer grain size in the deposited layer (84.80 ±30.5μm to 69.10±25.1μm, an 18.51 % decrease). Additionally, average microhardness increased (83.83 HV to 96.70 HV, a 15.35 % increase), transverse tensile strength improved (239.66±1.6 MPa to 263.00± 1 MPa, a 9.86 % increase), and elongation at break enhanced from 25.50±3.8 % to 27.17±0.33 %. Longitudinal tensile strength also rose (232.33±14.33 MPa to 248.33±8.33 MPa, a 6.88 % increase), with elongation at break increasing from 19.00±7.5 % to 19.40±4.2 %. Moreover, the mechanical properties' anisotropy decreased. Consequently, ECMF (AC+DC) significantly enhanced the overall properties of CMT-WAAM Al-5 % Mg alloy deposition, providing valuable insights for extending engineering applications of Al-5 % Mg alloy WAAM.

Revealing and Manipulating Hidden Fine-Structure Coherence of Bright Excitons in CsPbI3 Perovskite Quantum Dots.

Observation and understanding of fine-structure splitting of bright excitons in lead halide perovskite quantum dots (QDs) are crucial to their emerging applications in quantum light sources and exciton coherence manipulation. Recent studies demonstrate that ensemble-level polarization-resolved transient absorption spectroscopy can reveal the quantum beats arising from the coherence between two fine-structure levels. Here we report the observation of an extra fine-structure quantum coherence hidden in previous studies by using cryo-magnetic quantum beat spectroscopy. In ∼6 nm CsPbI3 QDs, two splitting energies of 0.25 and 1.20 meV were observed at 1.7 K, which gradually increased to 0.74 and 1.55 meV, respectively, when a longitudinal magnetic field up to 7 T was applied. The field dependence allowed us to extract two distinct nominal Landé g-factors corresponding to QDs with different orientations with respect to the external field.

A SIMPLE SOURCE OF METAL AND GAS IONS FOR ION BEAM TECHNOLOGICAL INSTALLATIONS

At the stand of the Institute of Applied Physics of the National Academy of Sciences of Ukraine, a small-sized spattering source of metal and gas ions was developed, manufactured and tested. Ionization of sputtered atoms occurs by fast oscillating electrons in a longitudinal magnetic field. A beam containing ions of plasma-forming gas and metal is output through an emission hole in the anticathode. The source has high ion current stability, is easy to maintain, and can generate ions from any conductive solid. Modeling and manufacturing of an ion-optical system for this source, which is part of the injector of the implanter of the Institute of Applied Physics of the National Academy of Sciences of Ukraine, was carried out.

Numerical and experimental study of TIG welding arc in high frequency longitudinal magnetic field

The phenomenon of arc compression in TIG welding with high-frequency longitudinal magnetic field (HF-LMF) has been observed. However, its mechanism remains unclear, and there is a lack of numerical investigation. This work presents a two-dimension axisymmetrical model of arc plasma in high-frequency longitudinal magnetic field based on the magnetohydrodynamics (MHD). The distributions of temperature, velocity and pressure of arc plasma in HF-LMF are investigated at different applied LMF frequencies ranging from 0 to 5000 Hz. In order to make the simulation results more convincing, the induced current and the electric force were considered. The results show that the HF-LMF could generate a circumferential electric field, causing particles rotating. However, since HF-LMF is variable, the direction of the electric field also changes, which causes the arc to rotate back and forth. When the frequency of HF-LMF reaches 2000 Hz, the negative pressure zone above the center of the anode disappeared and the arc was compressed. Thus, as the frequency of LMF increases, the distribution of current density, anodic heat flux, and arc pressure changes from a bimodal distribution to a unimodal distribution, and the peak value increases. The theoretical predictions were in good agreement with the experimental results.

Global quantum discord in an Ising model with transverse and longitudinal magnetic fields

Global quantum discord in an Ising model with transverse and longitudinal magnetic fields

The magnetization in the lattice of quantum rings with rashba spin-orbit interaction

The magnetic properties of the lattice formed by noninteracting semiconductor quantum rings in a longitudinal magnetic field are investigated. It was shown that when the value of the Rashba parameter ξ = 1.5, the magnetization varies from positive to negative with changes in the Aharonov–Bohm flux and amplitude oscillations decrease.

Effect of a longitudinal magnetic field on streamer propagation in air: Numerical simulation

Two-dimensional numerical simulation of the negative streamer propagation in external electric and magnetic fields is performed for the case when applied electric and magnetic field vectors are parallel to the symmetry axis of the problem. The calculations are performed for air (a mixture of 80% N2 and 20% O2) with a concentration of gas molecules equal to Loshmidt's number. It is shown that the presence of a longitudinal field leads to a noticeable increase in the streamer propagation velocity associated with a decrease in its radius, which agrees with the known analytical estimates.

Enhancement of longitudinal magnetic field by interaction of heavy ion beams and plasma with strong magnetic field

Enhancement of longitudinal magnetic field by interaction of heavy ion beams and plasma with strong magnetic field

Mapping the Longitudinal Magnetic Field in the Atmosphere of an Active Region Plage from the Inversion of the Near-ultraviolet CLASP2.1 Spectropolarimetric Data

We apply the HanleRT Tenerife Inversion Code to the spectropolarimetric observations obtained by the Chromospheric Layer Spectropolarimeter. This suborbital space experiment measured the variation with wavelength of the four Stokes parameters in the near-ultraviolet spectral region of the Mg ii h and k lines over a solar disk area containing part of an active region plage and the edge of a sunspot penumbra. We infer the stratification of the temperature, the electron density, the line-of-sight velocity, the microturbulent velocity, and the longitudinal component of the magnetic field from the observed intensity and circular polarization profiles. The inferred model atmosphere shows larger temperature and electron density in the plage and the superpenumbra regions than in the quiet regions. The shape of the plage region in terms of its brightness is similar to the pattern of the inferred longitudinal component of the magnetic field in the chromosphere, as well as to that of the overlying moss observed by the Atmospheric Imaging Assembly in the 171 Å band, which suggests a similar magnetic origin for the heating in both the plage and the moss region. Moreover, this heating is particularly significant in the regions with larger inferred magnetic flux. In contrast, in the superpenumbra, the regions with larger electron density and temperature are usually found in between these regions with larger magnetic flux, suggesting that the details of the heating mechanism in the chromosphere of the superpenumbra may be different from those in the plage, but with the magnetic field still playing a key role.

Rapidly one-step fabrication of durable superhydrophobic graphene surface with high temperature resistance and self-clean

High temperature resistant and self-cleaning superhydrophobic flexible film has potential application value in lunar exploration. In this paper, a novel method of magnetic field-assisted ultrafast laser induced plasma was proposed to fabricate strongly superhydrophobic graphene on polyimide film with multi-level micro-nano structure. The longitudinal magnetic field contributed to constrain the induced plasma in the lateral direction so as to form a plasma plume with high temperature and high energy density. The multi-level micro-nano graphene structures with better ordering and superhydrophobicity were fabricated, which had a contact angle of 163.1° and a roll-off angle of 1.5°, as well as hydrophobic CC bond content of 72.82 %. The droplets can achieve obvious bouncing at different heights of 1 cm and 5 cm on surfaces at different angles of 0°, 5° and 10°. The contact angle was still greater than 160° after 25 days of aging treatment and heating at 300 °C for 40 min. The water droplets before and after the heating of the sample can push the dust off the surface, showing excellent high temperature resistance and self-cleaning performance.

Construction of Kinetic Model of Vacuum Arc Magnetic Fluid Under External Magnetic Field

The external magnetic field is an important control method of vacuum arc at present. Because of its high efficiency and economy, it has become an important method to study the kinetic model of vacuum arc magnetic fluid. Therefore, the kinetic model of vacuum arc magnetic fluid under the external magnetic field is constructed. Firstly, the mass conservation equation, radial momentum conservation equation, axial momentum conservation equation, energy conservation equation, electromagnetic equations are analyzed. The boundary conditions of the dynamic model are cathode boundary, anode boundary and fluid wall boundary. The fluid dynamics calculation software FLUENT is used as the calculation platform, and its secondary development is carried out. Combining VC++self-programming and self-defined macro functions, according to the boundary conditions, the kinetic model of vacuum arc magnetic fluid under external magnetic field is solved, and the kinetic model analysis of vacuum arc magnetic fluid under external magnetic field is realized. Experimental analysis shows under the action of longitudinal magnetic field, the intensity of longitudinal magnetic field increases, the maximum point of ion rotation speed in the magnetic fluid of vacuum arc moves outward along the edge of vacuum arc, the number density of electrons gradually moves from the central axis to the radial direction, and the high density area increases first and then decreases; Under the action of transverse magnetic field, the intensity of transverse magnetic field increases, the ion pressure in vacuum arc magnetic fluid gradually shifts and increases, and the ion number density also increases.

Magnetic Properties and Hysteresis Behavior of Mixed Spin Multilayer: A Monte Carlo Study

The hysteresis behavior and magnetic properties of the Ising multilayer system, consisting of spin − 1/2 and spin − 5/2, are examined by the use of the Monte Carlo simulation. We have reported the impact of the size and the exchange interactions, as well as the crystal field on the thermal total, partial magnetization and the phase diagram. We have found some interesting results such as first- and second-order phase transitions and critical end-points. To complete this study, we have illustrated and analyzed the effect of longitudinal magnetic field on the hysteresis behavior of the system.

Thin Ga(Sb,P)/GaP quantum wells with indirect band gap: Crystal structure, energy spectrum, exciton recombination and spin dynamics

Heterostructures with thin GaSb layers embedded in a GaP matrix are studied by transmission electron microscopy as well as steady-state and transient photoluminescence. For a single, one monolayer thick deposition with subsequent overgrowth, nonmonotonic Sb segregation results in self-organized Ga(Sb,P) double-quantum well (QW) formation. One QW is positioned deep in GaP at the designated place according to the heterostructure design, and the other QW is in the near surface region after 40 monolayers of GaP overgrowth. Both QWs are characterized by an indirect band gap. The band alignment in the QWs is identified as type I. In spite of the long (up to milliseconds) exciton lifetimes in the QWs in combination with the electron g factor of +2, the emission of the QWs demonstrates a low circular polarization degree in longitudinal magnetic fields as strong as 10 T. We demonstrate that the electron spin polarization in the Ga(Sb,P)/GaP heterostructure subject to a magnetic field occurs in the GaP layer, and spin-polarized charge carriers captured in the QWs store their spin orientation up to the millisecond time range, indicating very long spin relaxation times for the strongly localized electrons in the Ga(Sb,P)/GaP QWs.

Multi-kilogauss magnetic field driving the magnetospheric accretion process in EX Lupi

EX Lupi is the prototype of EX Lup-type stars, which are classical T Tauri stars (cTTSs) with luminosity bursts and outbursts of 1 to 5 magnitudes that last for a few months to a few years. These events are ascribed to an episodic accretion that can occur repeatedly, but whose physical mechanism is still debated. We aim to investigate the magnetically driven accretion of EX Lup in quiescence. We include for the first time a study of the small- and large-scale magnetic field. This allows us to characterise the magnetospheric accretion process of the system completely. We used spectropolarimetric times series acquired in 2016 and 2019 with the Echelle SpectroPolarimetric Device for the Observation of Stars and in 2019 with the SpectroPolarimètre InfraRouge at the Canada-France-Hawaii telescope during a quiescence phase of EX Lup. We were thus able to perform a variability analysis of the radial velocity, the emission lines, and the surface-averaged longitudinal magnetic field in different epochs and wavelength domains. We also provide a small-scale magnetic field analysis using Zeeman intensification of photospheric lines and a large-scale magnetic topology reconstruction using Zeeman-Doppler imaging. Our study reveals that typical magnetospheric accretion is ongoing on EX Lup. A main accretion funnel flow connects the inner disc to the star in a stable fashion and produces an accretion shock on the stellar surface close to the pole of the magnetic dipole component. We also measure one of the strongest fields ever observed on cTTSs. This strong field indicates that the disc is truncated by the magnetic field close to but beyond the corotation radius, where the angular velocity of the disc equals the angular velocity of the star. This configuration is suitable for a magnetically induced disc instability that yields episodic accretion onto the star.

Research of a 0.14 THz Dual-Cavity Parallel Structure Extended Interaction Oscillator.

This paper presents a method to enhance extended interaction oscillator (EIO) output power based on a dual-cavity parallel structure (DCPS). This stucture consists of two conventional ladder-line structures in parallel through a connecting structure, which improves the coupling efficiency between the cavities. The dual output power fusion structure employs an H-T type combiner as the output coupler, which can effectively combine the two input waves in phase to further increase the output power. The dispersion characteristics, coupling impedance, and field distribution of the DCPS are investigated through numerical and simulation calculations, and the optimal operating parameters and output structure are obtained by PIC simulation. At an operating voltage of 12.6 kV, current density of 200 A/cm2, and longitudinal magnetic field of 0.5 T, the DCPS EIO exhibits an output power exceeding 600 W at a frequency of 140.6 GHz. This represents a nearly three-fold enhancement compared with the 195 W output of the conventional ladder-line EIO structure. These findings demonstrate the significant improvement in output power and interaction efficiency achieved by the DCPS for the EIO device.

Characteristics of wave propagation in pre-stressed viscoelastic Timoshenko nanobeams with surface stress and magnetic field influences

The current investigation explores the behavior of pre-stressed viscoelastic Timoshenko nanobeams under the influence of surface effects and a longitudinal magnetic field. Utilizing a modified version of non-local strain gradient theory through the Kelvin–Voigt viscoelastic model, a closed-form dispersion relation using a suitable analytical approach has been derived. To account for surface stresses, Gurtin–Murdouch surface elasticity theory has been employed. Additionally, the study delves into the impact of a longitudinal magnetic field on a single-walled carbon nanotube, considering Lorentz magnetic forces. The validity of the findings is established by deriving results in the absence of surface effects and magnetic fields, aligning well with existing literature. The investigation indicates that pre-stress has marginal effects on flexural and shear waves, while surface effects, magnetic fields, non-locality, characteristic length, and nanotube diameter significantly influence the phase velocity. Additionally, the threshold velocity and blocking diameter are discussed for the model.

Analysis of the magnetic-thermal response of viscoelastic rotating nanobeams based on nonlocal theory and memory effect

Size-dependent effects in elastic deformation and thermal hysteresis effects in the heat transfer process are significant for small-size structures or devices. As an important component of micro- and nanoelectromechanical systems, the analysis of the thermodynamic properties of rotating nanobeams is crucial for the safe operation of the system. This work aims to construct a new nonlocal thermo-viscoelastic model and use this model to analyze the thermodynamic behavior of rotating nanobeams at the microscale. In this work, fractional order Kelvin-Voigt theory describes the viscoelasticity of materials. Moreover, the theory of continuous medium mechanics is improved by introducing nonlocal parameters to capture the size effect during deformation. Based on the generalized thermoelasticity theory, memory-dependent derivatives predict hysteresis effects during heat transfer. Nanobeams are placed in a longitudinal magnetic field. Graphene strips connected to a power supply are used as the nanobeam heat source. The effects of nonlocal parameters, damping coefficients, and fractional order parameters on the dynamic response of the system are analyzed. In addition, a new comparative study of the effects of voltage and resistance on the system is made in the context of the nonlocal generalized thermoelasticity theory.

Magneto-mechanical coupling in ferromagnetic shape memory alloys: Mechanical experimental investigation under magnetic field in NiMnGaCu alloy

Ferromagnetic shape memory alloys attracted increasing interest as multicaloric materials for solid state refrigeration. The most effective field coupling is achieved through the combination of the magnetic and mechanical induction of thermoelastic martensitic transformation. In the present work, we present an experimental investigation on NiMnGaCu polycrystalline cast alloy, by means of an experimental setup for compression tests in isothermal conditions under a longitudinal magnetic field. The setup has been ad hoc designed and developed specifically for this purpose. In this way, we can measure the elastocaloric and magnetocaloric effect at the same time. Moreover, the evolution of the entropy changes ΔS and the functional caloric parameters vs the magnetic field is evaluated. The application of magnetic field seems to act like a supplementary mechanical longitudinal stress. These preliminary results are fundamental to achieve a comprehensive understanding and modeling of coupled multicaloric phenomena.

Magnetic controlled arc welding technology: a review

PurposeThe purpose of this study is to optimize and improve conventional welding using EMF assisted technology. Current industrial production has put forward higher requirements for welding technology, so the optimization and improvement of traditional welding methods become urgent needs.Design/methodology/approachExternal magnetic field assisted welding is an emerging technology in recent years, acting in a non-contact manner on the welding. The action of electromagnetic forces on the arc plasma leads to significant changes in the arc behavior, which affects the droplet transfer and molten pool formation and ultimately improve the weld seam formation and joint quality.FindingsIn this paper, different types of external magnetic fields are analyzed and summarized, which mainly include external transverse magnetic field, external longitudinal magnetic field and external cusp magnetic field. The research progress of welding behavior under the effect of external magnetic field is described, including the effect of external magnetic field on arc morphology, droplet transfer and weld seam formation law.Originality/valueHowever, due to the extremely complex physical processes under the action of the external magnetic field, the mechanism of physical fields such as heat, force and electromagnetism in the welding has not been thoroughly analyzed, in-depth theoretical and numerical studies become urgent.

Resonant Absorption of Standing Magnetohydrodynamic Waves in Coronal Loops in the Absence of Directional Symmetry: The Effect of Plasma Flow

The oscillation properties of standing magnetohydrodynamic (MHD) waves in coronal loops have been investigated. The coronal loop is modeled as a straight cylinder with a purely longitudinal magnetic field and a field-aligned plasma flow. The loop model includes an inhomogeneous transitional layer that causes the wave to be resonantly damped. Our aim is to determine the damping rate of the standing MHD waves in flowing loops, in which the directional symmetry of the loop has been broken due to the presence of plasma flow. To do this, the standing wave has been considered as the superposition of two propagating waves with opposite directions of propagation but the same oscillation frequency and damping rate. Due to the absence of directional symmetry in the loop, it seems that the propagating components of the standing wave cannot have the same oscillation frequency and damping rate. To overcome this problem, in the perturbation method employed, we let both the oscillation frequency and damping rate be perturbed. As the flow speed increases the oscillation frequency of the standing wave decreases but its damping rate increases. As a result, the ratio of the oscillation frequency to the damping rate of the standing wave becomes a more decreasing function of the flow speed. The flow is an important quantity in determining the effectiveness of resonant absorption. In flowing loops even in the case of a thin transitional layer, resonant absorption can result in a damping rate on the order of the period time, which is in agreement with observations.