Values Of Magnetic Field Research Articles

Effect of the magnetic field on the electron kinetics under AC/DC electric fields: benchmark calculations and electron cyclotron resonance

This work presents a numerical study of the electron kinetics under AC/DC electric fields and DC magnetic fields crossed at arbitrary angles. The physical phenomena are studied both in model gases (Reid-ramp and Lucas–Saelee) and in real gases (N2 and Ar). The simulations are carried out with an upgraded version of the Monte Carlo open-source code LoKI-MC. The code is compared against several independent benchmark calculations available in the literature. In addition, new benchmark calculations for electron kinetics solvers are produced in conditions of coexistent AC electric and DC magnetic fields, accounting for the effect of the crossing angle between the fields and discriminating the evolution along the AC cycle. The role of the magnetic field is discussed, distinguishing the configurations with DC and AC electric fields. In DC electric fields, the oscillatory motion caused by the magnetic field decreases the efficiency of the electron acceleration, which manifests on the power absorbed by the electric field and on the electron mean energy. Notably, an exceptional behavior is found in Ar for small regions of and , where: for constant , the mean energy decreases with increasing ; and, for constant , it increases with increasing . These phenomena were firstly reported by Ness and Makabe in 2000 and are now confirmed by means of Monte Carlo simulations. In AC electric fields, when the magnetic field value is such that the electron cyclotron frequency is similar to the angular frequency of the electric field, the synchronization of the cyclotron motion with the electric field enhances electron acceleration, through the well-known electron cyclotron resonance. However, for conditions where the mean collision frequency is much higher than the cyclotron frequency, the synchronization tends to breakdown and the magnetic field is detrimental for the electron acceleration, as in the DC electric field case.

Enhancing the damping effect of MRF damper using an external magnetic excitation system

The magnetic field generated by the damper’s magnetic circuit governs the yield stress value of the Magnetroholgical Fluid (MRF) damper and hence its damping effect. This paper contributes to the literature on the development of MRF dampers by introducing a new design feature to improve the damper’s performance. The presented novel feature tends to amplify the magnetic field value and concentrate its flux within the MR fluid region. The excitation sources consist of 12 coils placed in radial directions surrounding the MRF to focus the energizing magnetic effects. However, the search for efficient solutions is not only focused on generating more energy but also on minimizing its loss. Therefore, a metallic ring was placed around the coils to close the magnetic circuit, guide the flux lines, and avoid any energy dispersion to the surrounding air. As a proof of concept, two materials were tested for the surrounding ring: plastic acrylonitrile butadiene styrene (ABS) and mild steel. The performance of both solutions was assessed experimentally with a Gaussmeter and numerically by using a model developed via COMSOL Multiphysics. Both techniques confirmed the efficiency of the solution based on a steel ring in preventing the flux dispersion into the surrounding air. In addition, an increase of the excitation current from 0 to 5A was found to elevate the magnetic field by 35%, compared with the ABS ring. In the second step, a test rig was designed and built to investigate the damping efficiency of the MRF experimentally. The testing apparatus consisted of a sliding-bearing mechanism connected to a variable speed motor. The damping effect was assessed based on the force and displacement data provided by a linear variable displacement transducer (LVDT) and a force cell. Damping forces were observed at a constant frequency of 0.36 Hz (22 rpm) when the testing system and the attached damper were functioning smoothly away from its resonant frequency. Moreover, the magnetic field excitation current was elevated from 0 A to 5 A with a 1 A step. Again, the metallic ring was found to produce a 112% greater damping coefficient than the case of the plastic ring when the excitation current reached 5A.

Impact of growth conditions on magnetic anisotropy and magnon Hanle effect in α-Fe2O3

The antiferromagnetic insulator α-Fe2O3 (hematite), widely used in spintronics and magnonics, features a spin-reorientation transition (Morin transition) at 263 K. Thin films, however, often lack this Morin transition, limiting their potential applications. Here, we investigate the impact of different growth conditions on the magnetic anisotropy in α-Fe2O3 films to tune the Morin transition temperature. To this end, we compare the structural, magnetic, and magnon-based spin transport properties of α-Fe2O3 films with different thicknesses grown by pulsed laser deposition in molecular and atomic oxygen atmospheres. We observe a finite Morin transition for those grown by atomic-oxygen-assisted deposition, interestingly even down to 19 nm thickness, where we find a Morin transition at 125 K. In easy-plane antiferromagnets, the nature and time-evolution of the elementary excitations of the spin system are captured by the orientation and precession of the magnon pseudospin around its equilibrium pseudofield, manifesting itself in the magnon Hanle effect. We characterize this effect in these α-Fe2O3 films via all-electrical magnon transport measurements. The films grown with atomic oxygen show a markedly different magnon spin signal from those grown in molecular oxygen atmospheres. Most importantly, the maximum magnon Hanle signal is significantly enhanced, and the Hanle peak is shifted to lower magnetic field values for films grown with atomic oxygen, suggesting changes in the magnetic anisotropy due to an increased oxygen content in these films. Our findings provide new insights into the possibility to fine-tune the magnetic anisotropy in α-Fe2O3 and thereby to engineer the magnon Hanle effect.

Influence of power-law index and hybrid-nanoparticles concentrations on the behavior of non-Newtonian hybrid nanofluid inside water solar collector

Nowadays, there is great attention given to solar collectors (SCs) for their important applications based on the advantages of nanotechnology and solar radiation. Hybrid nanofluid (HNF) is our first option due to its thermophysical properties that help in improving the overall performance, unlike other nanofluids. This paper gives a detailed novel analysis of SCs with the existence of Newtonian, power-law HNF in unsteady conditions and a three-dimensional model under the consideration of Brownian motion and thermophoresis parameter. In this research, the group transformation method (GTM) and similarity transformation steady state fluid dynamics are used to transform the mathematical model into a simpler system. This coupled system of ordinary differential equations with the related functions, dimensionless entropy generation and Bejan number is achieved at two cases of power-law index. The impact of involved parameters on velocity profile, temperature distribution, concentration field, entropy output of the system and Bejan number is depicted prominently by various graphs. The fluid velocity shows improvement with higher values of power-law index and shape factor, while it diminishes with magnetic parameter and Prandtl number. Enhancing the values of magnetic field and shape factor, results in increase of temperature characteristic which decreases with Prandtl number and power-law index. Increment in the concentration ratio parameter leads to maximize the entropy generation, whereas entropy generation diminishes with higher values of temperature ratio and magnetic parameter. The obtained results and the previously published work are compared qualitatively and quantitatively to each other to validate that the applied method is more efficient. It is predicted that the Nusselt number improves by 28.18% when the Prandtl number is taken range [Formula: see text]. The percentage of increasing in Sherwood number is noted to be 18.61% for range [Formula: see text] of Brownian motion parameter.

Electronic and optical properties of eccentric two dimensional quantum rings subjected to transverse tilted magnetic field

ABSTRACT Within the effective mass approximation framework, the electronic and optical properties of GaAs-based two-dimensional eccentric quantum rings subjected to a transverse magnetic field with an inclination θ-angle to the x-axis are investigated using a two-dimensional diagonalisation method. The results show that the electron energy spectra in concentric quantum rings reveal transparency to the action of magnetic field orientation, contrary to their optical properties, which turn out to be anisotropic with this later. In addition, the eccentricity preserves the absorption coefficient spectra for y-polarisation for all orientations of the magnetic field qualitatively, while those of x-polarisation are significantly modified by eccentricity and magnetic field. Specific peak transitions occurring at specific magnetic field values and θ-angle can be used as a signature of magnetic field orientation and eccentricity.

Entropy generation analysis on MHD flow of second-grade hybrid nanofluid over a porous channel with thermal radiation

The main objective of this research is to evaluate the Jeffery-Hamel model and entropy generation on the thermal radiation and magnetohydrodynamic flow of second-grade hybrid nanofluid between convergence and divergence channels in stretching and shrinking walls. We used blood as the base fluid and Cu and Fe3O4 as the nanoparticles in our model. The highly coupled nonlinear Partial differential equations are transformed into ordinary differential equations with the help of self-similarities transformation and solved using MATLAB solver by using the Bvp4c shooting technique. The Homotopy Perturbation Method (HPM) is compared to the Numerical Method (NM), and the results are reliable. The influences of velocity, temperature, entropy generation, and the Bejan number on nondimensional parameters like a magnetic field, the Reynolds number, thermal radiation, Deborah number, magnetic field, and the Brinkman number are discussed through graphs. The skin friction coefficients and heat transfer are also studied and portrayed as graphs and tables. The effect of a magnetic field on the velocity of stretching and shrinking through converging and diverging channels. When increasing the magnetic field, the velocity profile increases. As magnetic field values increase, the temperature profile decreases with the stretching and shrinking of converging channels. Also, the opposite behavior of stretching and shrinking for diverging channels is observed. As the Deborah number grows, the velocity reduces for the converging channel in the stretching and shrinking of the walls. It is observed that the opposite nature of the diverging channel occurs in the stretching and shrinking of the walls. In this model, biomedical applications in surgical procedures, nano-mediated atherosclerosis treatment, and several diseases with drug delivery systems.

New filamentary remnant radio emission and duty cycle constraints in the radio galaxy NGC 6086

Radio galaxies are a subclass of active galactic nuclei (AGN) in which accretion onto the supermassive black hole releases energy into the environment via relativistic jets. The jets are not constantly active throughout the life of the host galaxy and alternate between active and quiescent phases. Remnant radio galaxies are detected during a quiescent phase and define a class of unique sources that can be used to constrain the AGN duty cycle. We present, for the first time, a spatially resolved radio analysis of the radio galaxy associated with the galaxy NGC 6086 down to 144 MHz and constraints on the spectral age of the diffuse emission to investigate the duty cycle and evolution of the source. We used three new low-frequency, high-sensitivity observations; the first was performed with the Low Frequency Array at 144 MHz and the other two with the upgraded Giant Metrewave Radio Telescope at 400 MHz and 675 MHz, respectively. To these, we add two Very Large Array archival observations at higher frequencies (1400 and 4700 MHz). In the new observations in the frequency range 144–675 MHz, we detect a second pair of larger lobes and three regions within the remnant emission with a filamentary morphology. We analysed the spectral index trend in the inner remnant lobes and see systematically steeper values (αlow∼1.1–1.3) at the lower frequencies compared to the gigahertz frequencies (αhigh∼0.8–0.9). Steeper spectral indices are found in the newly detected outer lobes (up to αouter∼2.1), as expected if they trace a previous phase of activity of the AGN. However, the differences between the spectra of the two outer lobes suggest different dynamical evolutions within the intra-group medium during their expansion and/or different magnetic field values. Using a single-injection radiative model and assuming equipartition conditions, we place constraints on the age of the inner and outer lobes and derive the duty cycle of the source. We estimate that the duration of the two active phases was 45 Myr and 18 Myr and the duration of the two inactive phases was 66 Myr and 33 Myr. This results in a total active time of ton ∼ 39%. The filamentary structures have a steep spectral index (∼1) without any spectral index trend, and only one of them shows a steepening in the spectrum. Their origin is not yet clear, but they may have formed due to the compression of the plasma or due to magnetic field substructures.

Electromagnetic shielding properties of LPBF produced Fe2.9wt.%Si alloy

Ferromagnetic materials are used in various applications such as rotating electrical machines, wind turbines, electromagnetic shielding, transformers, and electromagnets. Compared to hard magnetic materials, their hysteresis cycles are featured by low values of coercive magnetic field and high permeability. The application of additive manufacturing to ferromagnetic materials is gaining more and more attraction. Indeed, thanks to a wider geometrical freedom, new topological optimized shapes for stator/rotor shapes can be addressed to enhance electric machines performances. However, the properties of the laser powder bed fusion (LPBF) processed alloy compared to conventionally produced counterpart must be still addressed. Accordingly, this paper presents for the first time the use of the LPBF for the manufacturing of Fe2.9wt.%Si electromagnetic shields. The process parameter selection material microstructure and the magnetic shielding factor are characterized.

Calculation of dipole matrix elements for the modeling of H-[formula omitted] Stark broadening in the presence of large magnetic field

B-spline basis sets are applied to the calculation of dipole matrix elements for the hydrogen atom placed in an intense magnetic field, in view of applications to the spectroscopic analysis of white dwarf atmospheres. A focus is put on the H-α line and magnetic field values in the kilotesla range are considered. The dipole matrix elements are shown to be significantly sensitive to the magnetic field. In the framework of plasma diagnostic, this means that the Stark broadening of the line, which is involved in density measurements, can be misinterpreted if the atomic structure is not well accounted for in numerical codes. As an illustration, we consider the H-ασ− component and apply a computer simulation method to the modeling of the Stark broadening of this line. The calculated dipole matrix elements are used therein as input.

An Optically Pumped Magnetometer with Omnidirectional Magnetic Field Sensitivity.

In mobile applications such as geomagnetic surveying, two major effects hamper the use of optically pumped magnetometers: dead zones, sensor orientations where the sensors signal amplitude drops; and heading errors, a dependence of the measured magnetic field value on the sensor orientation. We present a concept for an omnidirectional magnetometer to overcome both of these effects. The sensor uses two cesium vapor cells, interrogated by circularly-polarized amplitude-modulated laser light split into two beams propagating perpendicular to each other. This configuration is experimentally investigated using a setup wherein the laser beam and magnetic field direction can be freely adjusted relative to each other within a magnetically shielded environment. We demonstrate that a dead-zone-free magnetometer can be realized with nearly isotropic magnetic-field sensitivity. While in the current configuration we observe heading errors emerging from light shifts and shifts due to the nonlinear Zeeman effect, we introduce a straightforward approach to suppress these systematic effects in an advanced sensor realization.

Numerical Solutions of Casson-Nano Fluid Flow Past an Isothermal Permeable Stretching Sheet: MHD, Thermal Radiation and Transpiration Effects

The Runge-Kutta Shooting Technique may be used to discover numerical solutions by the absence of magnetic field, thermal radiation, then transpiration consequence for viscous, incompressible, electrically conducting with combination of Casson and Nano-fluids that approach an isothermal permeable non-linearly stretched sheet. The governing equations for this fluid flow were transformed keen on non-linear ODEs using the similarity quantities. Visualizations of velocities, temperatures, and concentrations illustrate the mathematics behind the issue. According to tabular data, these flow regulating factors affect the coefficient of friction for skin-friction, heat transfer, and mass flow coefficients. Program code validation literature has been compared to the new numerical findings. It has been shown that flow characteristics are greatly affected by the amount of air that is exhaled. The study’s applications include industrial Nano-technological manufacturing processes. In this current work, the speed profiles are diminishing growing values of Casson fluid limitation as well as decreases by growing values of Magnetic field & Suction/Injection parameters. With increasing effects Brownian motion and Thermophoresis temperature profiles are increase. As the values of Thermal radiation of limitation enhances, the temperature profiles are also increases. The concentration profiles are increasing with increasing values of Thermophoresis parameter and reverse effect observed in case of Brownian motion effect. Also, concentration profiles decreases with increasing values of Lewis number.

The role of plasma β in global coronal models: Bringing balance back to the force

Context. COolfluid COrona uNstrUcTured (COCONUT) is a global coronal magnetohydrodynamic (MHD) model that was recently developed and will soon be integrated into the ESA Virtual Space Weather Modelling Centre (VSWMC). In order to achieve robustness and fast convergence to a steady state for numerical simulations with COCONUT, several assumptions and simplifications were made during its development, such as prescribing filtered photospheric magnetic maps to represent the magnetic field conditions in the lower corona. This filtering leads to smoothing and lower magnetic field values at the inner boundary (i.e. the solar surface), resulting in an unrealistically high plasma β (greater than 1 in a large portion of the domain). Aims. We aim to examine the effects of prescribing such filtered magnetograms in global coronal simulations and formulate a method for achieving more realistic plasma β values and improving the resolution of electromagnetic features without losing computational performance. Methods. We made use of the newly developed COCONUT solver to demonstrate the effects of the highly pre-processed magnetic maps set at the inner boundary and the resulting high plasma β on the features in the computational domain. Then, in our new approach, we shifted the inner boundary to 2 R⊙ from the original 1.01 R⊙ and preserved the prescribed highly filtered magnetic map. With the shifted boundary, the boundary density and pressure were also naturally adjusted to better represent the considered physical location. This effectively reduces the prescribed plasma β and leads to a more realistic setup. The method was applied on a magnetic dipole, a minimum (2008) and a maximum (2012) solar activity case, to demonstrate its effects. Results. The results obtained with the proposed approach show significant improvements in the resolved density and radial velocity profiles, and far more realistic values of the plasma β at the boundary and inside the computational domain. This is also demonstrated via synthetic white light imaging (WLI) and with the validation against tomography data. The computational performance comparison shows similar convergence to a limit residual on the same grid when compared to the original setup. Considering that the grid can be further coarsened with this new setup, as its capacity to resolve features or structures is superior, the operational performance can be additionally increased if needed. Conclusions. The newly developed method is thus deemed as a good potential replacement of the original setup for operational purposes, providing higher physical detail of the resolved profiles while preserving a good convergence and robustness of the solver.

Uniform magnetic field on the relativistic spinless particles with constant rest mass in 2D polar space

We present a model for the interaction of relativistic spin-0 charged particles moving in a uniform magnetic field. In the absence of an improved perturbative approach, we solve Kummer's differential equation directly, including principal quantum numbers. As a functional approach to nuclear interaction, we consider relativistic particle bound states subject to a interaction without an antiparticle regime. Within the approximation line to , we have also improved the considerations of the and related to scalar and mass interactions. Moreover, we have found closeness in the introduced approximation scheme for a range of 0.5 to 1.0 fm. In this way, minimal coupling might also yield analytical energy spectra. Within the 2D spatial regime, we have also found that the energy levels of relativistic spin-0 particles increase with increasing interaction energy (i.e., the quantum well width decreases for given values). Additionally, energy levels increase with larger values of the uniform magnetic field. The charge distribution is also valid for the central interaction-confinement space.

Towards Resonantly Enhanced Acoustic Phonon-Exchange Magnon Interactions at THz Frequencies

Using valid experimental parameters, we quantify the magnitude of resonantly phonon-driven precession of exchange magnons in freestanding ferromagnetic nickel thin films on their thickness L. Analytical solutions of acoustically driven equations for magnon oscillators display a nonmonotonous dependence of the peak magnetization precession on the film thickness. It is explained by different L-dependence of multiple prefactors entering in the expression for the total magnetization dynamics. Depending on the ratio of acoustic and magnetic (Gilbert) damping constants, the magnetization precession is shown to be amplified by a Q-factor of either the phonon or the magnon resonance. The increase in the phonon mode amplitude for thinner membranes is also found to be significant. Focusing on the magnetization dynamics excited by the two first acoustic eigenmodes with p=1 and p=2, we predict the optimum thicknesses of nickel membranes to achieve large amplitude magnetization precession at multi 100 GHz frequencies at reasonably low values of an external magnetic field. By extending the study to the case of Ni-Si bilayers, we show that these resonances are achievable at even higher frequencies, approaching the THz range.

Recording the Magnetic Field Produced by an Undersea Energy Generating Device: A Low-Cost Alternative

This work describes the characteristics of a device capable of detecting the magnetic field generated by a submerged electrical conductor. This low-cost apparatus is based on the open-source Arduino platform and offers the possibility of monitoring magnetic fields generated by undersea cables. Measuring magnetic fields generated by undersea cables facilitates the development of technologies that will harness marine energy potential. The research is based on published parameters of magnetic field values generated by existing submarine cables. A coil was built to simulate an approximate magnetic field at 10 mT. The magnetic field generated by the coil was used as a reference standard. The device developed has a measurement probe built with an array of SS49E Hall effect sensors placed in a straight line and separated 5 cm from each other. A DS18B20 temperature sensor was added to make the necessary corrections and cancel the influence of temperature during the measurements. A microSD card module was attached to store continuous magnetic field measurements. The device was adjusted under strict laboratory conditions. The functionality of the device developed was confirmed by two samplings in the sea. In these samples, the magnetic field generated by the coil was measured in the entire water column from a depth of 3 m to 150 m. Results indicate that the prototype can successfully perform the necessary functions to quantify the underwater magnetic field accurately with about 10 µT accuracy.

Entropy generation for the MHD flow of a blood-based hybrid nanofluid by thermal radiation over converging and diverging channels

This study’s primary objective is to investigate the Jeffery–Hamel model and entropy generation in the magnetohydrodynamic (MHD) flow of hybrid nanofluid across stretching, shrinking, converging, and diverging channels. Aluminum oxide (Al2O3 ) and silver (Ag) are nanoparticles, using blood as the base fluid. The controlling nonlinear coupled partial differential equations (PDEs) are transformed into ordinary differential equations (ODEs) with similarity transformations and then solved using the Homotopy Perturbation Method (HPM) and shooting technique (Bvp4c). The HPM is compared to the numerical method (NM), and the results are more accurate and reliable. The effects of velocity, temperature, entropy generation, and the Bejan number on physical parameters like a magnetic field, the Reynolds number, magnetic field, and the Brinkman number are discussed through graphs. The heat transfer and skin friction coefficients are also studied and portrayed as graphs and tables. The influence of a magnetic field on the velocity profile of stretching and shrinking through converging and diverging channels. When increasing the magnetic field, the velocity profile increases. Physically, an increase in the magnetic field produces a higher Lorentz force, which improves fluid resistance and restricts fluid particle flow within the given topology. The temperature profile decreases in the stretching and shrinking of converging channels as magnetic field values rise. As well as the opposite behavior observed in stretching and shrinking for diverging channels. In this model, biomedical applications include studying physiological systems, surgical procedures, nano-pharmacological delivery systems, and nano-mediated treatment of atherosclerosis.

Efficiency of ferromagnetic shielding of superconducting coils of high-speed maglev crew

Background: Magnetic levitation transport with combined traction, suspension and guidance systems based on superconducting coils (SCC) allows reaching speeds of up to 500600 km/h with a very significant (up to 150200 mm) air gap, which is an important factor in ensuring the safety of high-speed transportation. However, SCC are a source of strong external magnetic fields, which, in conditions of limited crew dimensions, can have a harmful effect on both passengers and on-board auxiliary equipment.
 Aim: to analyze the external magnetic fields of the SCC systems for traction, suspension and direction of maglev vehicles and the effectiveness of ferromagnetic screens as a means of ensuring the electromagnetic safety of passengers and the electromagnetic compatibility of the SCC with other onboard equipment.
 Materials and methods: to achieve this goal, methods of analytical and numerical modeling of the magnetic fields of the SCC using modern software packages were used. As a prototype of the combined magnetic system of traction, suspension and direction, the system of the MLX-L0 maglev vehicle, which is undergoing pilot commercial operation at the Yamanashi test line (Japan), was adopted.
 Results: it is shown that the value of the external magnetic fields of the SCC of the traction and guiding systems in the passenger cabin of the prototype crew exceeds the maximum permissible levels established by domestic and foreign regulatory documents, both without shielding and with passive shielding with flat steel sheets.
 Conclusion: passive shielding of the SCC with steel sheets, including multilayer ones, does not provide the required reduction in the level of external magnetic fields for a given vehicle dimensions.

Stefan Blowing Impacts on Hybrid Nanofluid Flow over a Moving Thin Needle with Thermal Radiation and MHD

This investigation focuses on the impact of Stefan blowing on the flow of hybrid nanoliquids over a moving slender needle with magnetohydrodynamics (MHD), thermal radiation, and entropy generation. To facilitate analysis, suitable transformations are applied to convert the governing partial differential equations into a set of ordinary differential equations, which are then solved analytically using Homotopy Analysis Method (HAM) in Mathematica. This study investigates how varying the values of Stefan blowing, magnetic field, and thermal radiation parameters impact the profiles of velocity, temperature, and concentration. Additionally, the study analyzes the outcomes of the local skin friction, local Nusselt number, and local Sherwood number. Increasing the magnetic field reduces the velocity profile. The temperature profile is enhanced by a rise in the thermal radiation parameter. Also, the results reveal that an increase in the Stefan blowing number leads to higher profiles of velocity.

Convective heat and mass transfer rate on 3D Williamson nanofluid flow via linear stretching sheet with thermal radiation and heat absorption

A mathematical analysis is communicated to the thermal radiation and heat absorption effects on 3D MHD Williamson nanoliquid (NFs) motion via stretching sheet. The convective heat and mass boundary conditions are taken in sheet when liquid is motion. As a novelty, the effects of thermal radiation, heat absorption and heat and mass convection are incorporated. The aim is to develop heat transfer. Williamson NFs are most important source of heat absorption, it having many significant applications in “energy generation, HT, aircraft, missiles, electronic cooling systems, gas turbines” etc. The suitable similarity transformations have been utilized for reduce basic governing P.D. E’s into coupled nonlinear system of O.D. E’s. Obtained O.D. Es are calculated by help of R–K–F (“Runge–Kutta–Fehlberg”)4th order procedure with shooting technique in MATLAB programming. We noticed that, the skin friction coefficient is more effective in Williamson liquid motion when compared with NFs motion with higher numerical values of stretching ratio parameter, Williamson liquid motion is high when compared to NFs motion for large values of magnetic field. We compared with present results into previous results for various conditions. Finally, in the present result is good invention of previous results.

2.5D magnetohydrodynamic models of circumstellar discs around FS CMa post-mergers – I. Non-stationary accretion stage

ABSTRACT We investigate the dynamic evolution of the gaseous regions around FS CMa post-mergers. Owing to the slow rotation of the central B-type star, the dynamics is driven mainly by the magnetic field of the central star. Recent observations have allowed us to set realistic initial conditions, such as the magnetic field value ($B_\star \approx 6\times 10^{3}\, \mathrm{G}$), the mass of the central star ($M_\star =6\, \mathrm{M}_\odot$), and the initial disc density $\rho _{d0}\in [10^{-13}\, \mathrm{g\, cm^{-3}},10^{-11}\, \mathrm{g \, cm^{-3}}]$. We use the pluto code to perform 2.5D magnetohydrodynamic simulations of thin and thick disc models. Especially relevant for the interpretation of the observed properties of FS CMa post-mergers are the results for low-density discs, in which we find a jet emerging from the inner edge of the disc, as well as the formation of the so-called ‘hot plasmoid’ in the coronal region. Jets are probably detected as discrete absorption components in the resonance lines of FS CMa stars. Moreover, the magnetic field configuration in the low-density plasma region favours the appearance of magnetocentrifugal winds from the disc. The currents towards the star created by the magnetic field may explain accidentally observed material infall. The disc structure is significantly changed owing to the presence of the magnetic field. The magnetic field is also responsible for the formation of a hot corona, as observed in several FS CMa stars through the Raman lines. Our results are valid for all magnetic stars surrounded by a low-density plasma, that is, by some stars showing the B[e] phenomenon.