Combined Action Of Magnetic Field Research Articles

Microstructure Evolution of AZ91 Magnesium Alloy Welded Joint under Magnetic Field and NiCl2 Activated Flux

As the lightest engineering materials, magnesium alloys have been widely used. Because of the specific chemical and physical characteristics, the weldability of magnesium alloy is poor. Adopting suitable welding technology and improving the quality of magnesium alloy welded joints is key to their successful application. According to previous research data, it was found that the combined action of magnetic field and activated flux has a positive effect on improving-welding efficiency and improving the properties of a welded joint, butanalysis of microstructure evolution is insufficient. In this paper, AZ91 magnesium alloy was welded by TIG welding with activated flux and external longitudinal AC magnetic field. The phase composition and microstructure evolution were investigated. The experimental results revealed that the phase composition of welded joint was not changed due to the introduction of the magnetic field and activated flux, the growth patterns of grain in the weld seam and heat-affected zone were different. When the activated flux amount was 3 mg/cm2 with the effect of the magnetic field, the grain size of the weld seam was the finest, which was 18.96 μm. However, the grain size of the weld seam was larger than that of base metal. The crystallographic characteristics of grain boundaries in the weld seam and base metal were both LAGBs. The microstructure of the weld seam was messier than the base metal due to the larger misorientation angle. Under the combined action of the magnetic field and activated flux, the crystallization nucleation condition of the molten pool was changed, the formation of twins was promoted, and the crystal could selectively grow parallel with the (0001) basal plane.

Stability of Cracked Functionally Graded Graphene-Reinforced Beams under Magnetic Field

This paper studies linear dynamic stability of cracked functionally graded (FG) graphene platelet (GPL)-reinforced composite laminated beams subjected to the combined action of magnetic field and a periodic axial force. GPL weight fraction follows a layer-wise variation across the beam thickness. Effective material properties are estimated by micromechanics models, and the bending stiffness of the cracked section is evaluated by a rotational spring model. The governing equation is derived by Ritz method and Lagrange equation within the framework of the first-order shear deformation theory. The linear principle unstable regions of the cracked beams are determined by Bolotin method. Numerical results show that magnetic field intensity, GPL distribution pattern, boundary condition, crack depth and location have significant influence on the linear dynamic stability behaviors of the cracked beams.

Multicaloric effects in metamagnetic Heusler Ni-Mn-In under uniaxial stress and magnetic field

The world's growing hunger for artificial cold, on the one hand, and the ever more stringent climate targets, on the other, pose an enormous challenge to mankind. Novel, efficient, and environmentally friendly refrigeration technologies based on solid-state refrigerants can offer a way out of the problems arising from climate-damaging substances used in conventional vapor-compressors. Multicaloric materials stand out because of their large temperature changes, which can be induced by the application of different external stimuli such as a magnetic, electric, or a mechanical field. Despite the high potential for applications and the interesting physics of this group of materials, few studies focus on their investigation by direct methods. In this paper, we report on the advanced characterization of all relevant physical quantities that determine the multicaloric effect of a Ni-Mn-In Heusler compound. We have used a purpose-designed calorimeter to determine the isothermal entropy and adiabatic temperature changes resulting from the combined action of magnetic field and uniaxial stress on this metamagnetic shape-memory alloy. From these results, we can conclude that the multicaloric response of this alloy by appropriate changes of uniaxial stress and magnetic field largely outperforms the caloric response of the alloy when subjected to only a single stimulus. We anticipate that our findings can be applied to other multicaloric materials, thus inspiring the development of refrigeration devices based on the multicaloric effect.

Research for microstructure and mechanical properties of AZ91 magnesium alloy welded joint with magnetic field and activated flux

Although many experimental researches have been carried out on the effect of different fluxes and the mechanism responsible for the higher penetration in activated TIG welding of magnesium alloy, few works as reported in literatures are available concering the grain refinement and the improvement of mechanical properties of welding joints. This is because the activated flux has very limited or even negative effects on improving the mechanical properties of welded joints. In order to find a method that can improve welding efficiency and mechanical properties of welded joints, the longitudinal alternating magnetic field and NiCl2 activated flux were used during TIG welding of AZ91 magnesium alloy. The formation, mechanical properties, phase composition and crystal growth pattern of the weld seam were tested and analyzed to study the mechanism. The experimental results reveal that with proper parameter matching (magnetic field and activated flux), larger weld penetration and smaller form factor can be obtained, welding efficiency is improved accordingly, but the form factor with the magnetic field is bigger than that without magnetic field. When the activated flux amount is 3 mg cm−2 with the magnetic field, the optimal value of mechanical properties of welded joint is obtained, tensile strength is 385 MPa, elongation is 13.3%, micohardness is 67 HV, respectively. All of these are better than those without the magnetic field, the optimal activated flux amount is 2 mg cm−2. The application of magnetic field and activated flux has no noticeable effect on the phase composition of weld seam. Under the combined action of magnetic field and activated flux, the crystallization nucleation condition of molten pool was changed, the grain size was refined, the formation of twins was promoted, and the crystals selectively grew within the basal (0001) plane.

Domain wall depinning in Ni80Fe20/Pt bilayer nanostrips under the combined action of magnetic field and spin-orbit torque

Abstract We study the domain wall depinning from a triangle-shaped notch in Ni80Fe20/Pt bilayer nanostrips using electrical detection technique. It is found that for the 630 nm wide strip, the depinning fields are distributed in a narrow range. While for the 300 nm wide strip, the depinning fields are distributed in two distinctly separated ranges. Micromagnetic simulations show that for the 630 nm wide strip, the depinning corresponds to vortex domain wall, while for 300 nm wide strip, the depinnings of both the vortex wall and the transverse wall are observed. The chirality of vortex wall and the polarity of transverse wall have strong influence on the depinning field. Electrical current has a clear impact on the depinning, but its influence is different for different wall configuration. It can decrease or slightly increase the depinning field of the vortex domain wall depending on the wall chirality and the current direction. The depinning field of the transverse domain wall exhibits an oscillation variation with the current density. Compared to the depinning process of the domain wall in a control sample Ni80Fe20/Au, it can be inferred the current influence on the domain wall depinning is caused mainly by the current-induced spin-orbit torque.

The Effects of Various Chemical Agents on Priming of Neutrophils Exposed to Weak Combined Magnetic Fields

It has been shown that various chemical agents (ethylenediaminetetraacetic acid, zinc sulphate, ethyl alcohol, and rotenone) have different effects on preactivation (priming) of neutrophils that develop under weak combined collinear static and alternating magnetic fields (combined magnetic fields: a static field of 42 μT and an alternating field of 0.86 μT with the sum of frequencies 1.0, 4.4 and 16.5 Hz). Low concentrations (0.05%) of ethylenediaminetetraacetic acid decrease the intensity of luminol dependent chemiluminescence of neutrophils in response to an activator of the respiratory burst the peptide N-formyl-Met–Leu–Phe under the action of combined magnetic fields to a lesser extent than in the control. In contrast, ethyl alcohol (0.45%) and zinc sulphate (0.1 mM) have a greater effect on this process under the action of combined magnetic fields. Rotenone (1 μM) has a weak effect on neutrophil chemiluminescence both under the action of combined magnetic fields and in the control.

The role of lipid peroxidation and myeloperoxidase in priming a respiratory burst in neutrophils under the action of combined constant and alternating magnetic fields

The enhancement of lipid peroxidation in neutrophils (the content of malonic dialdehyde increased by 10.2%) has been shown after a 1-h exposure to a combined constant (42 μT) magnetic field and a weak low-frequency magnetic field (1.0, 4.4, and 16.5 Hz; 860 nT) collinear to it. No correlation was found between this effect and the process of functional pre-activation (priming) of neutrophils as a result of the combined action of magnetic fields detected by chemiluminescence enhancement in response to the introduction of the bacterial peptide N-formyl–Met–Leu–Phe in the presence of luminol, since ionol (10 μM), an inhibitor of lipid peroxidation, did not reduce the neutrophil priming index in this case. Preliminary addition of histidine (0.1 and 1.0 mM), a singlet oxygen scavenger, also did not decrease the priming index. A myeloperoxidase inhibitor, sodium azide (0.1 mM), exerted a significant inhibitory effect on the chemiluminescence intensity of the neutrophil suspension; priming did not develop in the presence of this inhibitor after the action of combined magnetic fields.

Highly Efficient Freestyle Magnetic Nanoswimmer.

The unique swimming strategies of natural microorganisms have inspired recent development of magnetic micro/nanorobots powered by artificial helical or flexible flagella. However, as artificial nanoswimmers with unique geometries are being developed, it is critical to explore new potential modes for kinetic optimization. For example, the freestyle stroke is the most efficient of the competitive swimming strokes for humans. Here we report a new type of magnetic nanorobot, a symmetric multilinked two-arm nanoswimmer, capable of efficient "freestyle" swimming at low Reynolds numbers. Excellent agreement between the experimental observations and theoretical predictions indicates that the powerful "freestyle" propulsion of the two-arm nanorobot is attributed to synchronized oscillatory deformations of the nanorobot under the combined action of magnetic field and viscous forces. It is demonstrated for the first time that the nonplanar propulsion gait due to the cooperative "freestyle" stroke of the two magnetic arms can be powered by a plane oscillatory magnetic field. These two-arm nanorobots are capable of a powerful propulsion up to 12 body lengths per second, along with on-demand speed regulation and remote navigation. Furthermore, the nonplanar propulsion gait powered by the consecutive swinging of the achiral magnetic arms is more efficient than that of common chiral nanohelical swimmers. This new swimming mechanism and its attractive performance opens new possibilities in designing remotely actuated nanorobots for biomedical operation at the nanoscale.

The action of combined magnetic fields with a very weak low-frequency alternating component on luminol-dependent chemiluminescence in mammalian blood

It is shown that the exposure of heparinized venous human blood diluted in phosphate buffer saline to extremely weak alternating magnetic fields of the ultralow-frequency (1 Hz, 600 nT; 4.4 Hz, 100 nT; 16.5 Hz, 160 nT) in combination with a collinear static magnetic field of 42 microT at physiological temperatures, causes a sharp 3-4 fold increase in its chemiluminescence after addition of luminol.

On the combined action of magnetic field and electric current on silicon plasticity

The specific features of the deformation behavior of low-resistivity p-type silicon single crystals have been studied using nontraditional methods of plastic deformation. Under the conditions of the combined action of a weak magnetic field and a direct electric current, a significant decrease in the plasticity of silicon is found during its active deformation when compared to the deformation in the absence of a magnetic field. An increase in the electrical conductivity of silicon samples subjected to active plastic deformation is found. The data that are obtained are compared with the previous data on single-crystal germanium. A possible explanation for the observed effects is given.

Research on the constant output force control system for giant magnetostrictive actuator disturbed by external force

In this paper, a constant output force control system for giant magnetostrictive actuator which is disturbed by external force continuously was developed. Based on the giant magnetostrictive actuator model related to the combined action of magnetic field and external force, a controller is designed. The controller is composed of giant magnetostrictive actuator model control algorithm and PID control algorithm to realize the output force reaching the constant force target quickly and finely adjustment. Control system’s hardware and related software were designed and software package was developed. Experiment results show that the control system has perfect response performance and stability, and favorable controllability. It can effectively realize the giant magnetostrictive actuator which is disturbed by external force continuously keeping outputting a constant force through adjusting the working current. It lays a certain theoretical foundation for giant magnetostrictive actuator being used in the fields of cutting with invariableness cutting force.

Quantum mechanical aspects of the effects of weak magnetic fields on biological objects

Possible mechanisms of action of weak combined magnetic fields on biological systems have been discussed in terms of quantum mechanics. The approaches proposed make it possible to solve the problem of the failure to compare the energy of active factors with the energy of thermal motion (kT problem). A mechanism of action of combined magnetic fields on biosystems has been proposed.

Ejection of magnetic-field-sensitive atoms from an optical dipole trap

Rubidium atoms prepared by evaporative cooling in an optical dipole trap are used in Stern-Gerlach type experiments. The analysis of the magnetic state distribution in the trap and during free fall demonstrates the possibility of ejecting all atoms with ${m}_{F}\ensuremath{\ne}0$ from the optical dipole trap. This is achieved by applying an appropriately located inhomogeneous magnetic field. We investigate the dynamics of this cleaning process, and record the temporal history of atom positions under the combined action of magnetic field and dipole-trap potential. The experimental findings are fully supported by realistic numerical simulations of the atomic dynamics. We show that analysis of the ejected atoms provides a means for nondestructive thermometry of a trapped atom cloud.

Action of combined magnetic fields on aqueous solution of glutamic acid: the further development of investigations

In the present work the results of the known investigation of the influence of combined static (40 μT) and alternating (amplitude of 40 nT) parallel magnetic fields on the current through the aqueous solution of glutamic acid, were successfully replicated. Fourteen experiments were carried out by the application of the combined magnetic fields to the solution placed into a Plexiglas reaction vessel at application of static voltage to golden electrodes placed into the solution. Six experiments were carried out by the application of the combined magnetic fields to the solution placed in a Plexiglas reaction vessel, without electrodes, within an electric field, generated by means of a capacitor at the voltage of 27 mV. The frequency of the alternating field was scanned within the bounds of 1.0 Hz including the cyclotron frequency corresponding to a glutamic acid ion and to the applied static magnetic field. In this study the prominent peaks with half-width of ~0.5 Hz and with different heights (till 80 nA) were registered at the alternating magnetic field frequency equal to the cyclotron frequency (4.2 Hz). The general reproducibility of the investigated effects was 70% among the all solutions studied by us and they arose usually after 40–60 min. after preparation of the solution. In some made-up solutions the appearance of instability in the registered current was noted in 30–45 min after the solution preparation. This instability endured for 20–40 min. At the end of such instability period the effects of combined fields action appeared practically every time. The possible mechanisms of revealed effects were discussed on the basis of modern quantum electrodynamics.

Some Problems in Modern Bioelectromagnetics

One of the main problems of bioelectromagnetics—the unbelievable narrow resonance peaks at the cyclotron frequency of the alternating magnetic field—was considered. Modern electrodynamics of condensed matter clearly brings out that the reason of this phenomenon is extremely low viscosity within coherence domains of aqueous electrolytic solutions. The electrochemical model of action of combined static and alternating magnetic fields on aqueous solutions of amino acids is proposed. The possibility of arising a succession of changes in ionic forms in these processes was revealed. The dipole ions (zwitterions) together with water molecules electrostatically forming joint groups in the solution, create favorable conditions for arising mixed coherence domains there. Simultaneously with evolution of the coherent processes in these domains, the amino acid zwitterions are transforming into the usual ionic form, fit for cyclotron resonance. The development of cyclotron resonance under action of combined magnetic fields increases the ion kinetic energy, and the ions leave the domains for the incoherent component of the solution according to Del Giudice pattern (Comisso et al., ; Del Giudice et al., ), creating the peak current through the solution. Then the ions are transforming little by little into zwitterionic form again; after that, the solution becomes ready to react on exposure of magnetic fields again. The possibilities for formation of coherence domains composed of water molecules together with peptide molecules or protein ones are discussed.

Fluid Flow and Solidification Under Combined Action of Magnetic Fields and Microgravity

Mathematical models, both 2-D and 3-D, are developed to represent g-jitter induced fluid flows and their effects on solidification under combined action of magnetic fields and microgravity. The numerical model development is based on the finite element solution of governing equations describing the transient g-jitter driven fluid flows, heat transfer, and solutal transport during crystal growth with and without an applied magnetic field in space vehicles. To validate the model predictions, a ground-based g-jitter simulator is developed using the oscillating wall temperatures where timely oscillating fluid flows are measured using a laser PIV (Particle Image Velocimetry) system. The measurements are compared well with numerical results obtained from the numerical models. Results show that a combined action derived from magnetic damping and microgravity can be an effective means to control the melt flow and solutal transport of single crystal growth in space environment.

Drift of Ions and Electrons in a Magnetic Field

Townsend's equations for the drift motion of ions under the combined action of magnetic field, concentration gradient and electric field are shown to be inconsistent with the Boltzmann equation. Other relations according to which a gradient contributes a perpendicular component to the drift are shown to be satisfactory in this respect. It is proved that such contributions exist and the fallacy in the demonstration that they do not exist is exposed. These equations lead to the simple result that the drift speed is the same as would occur if the components of concentration gradient and electric field perpendicular to it, as well as the magnetic field itself, did not exist. All of the equations are only semiquantitatively correct and are subject to refinement by a more adequate statistical treatment.