Magnetic Pressure Gradient Research Articles

INVESTIGATION OF PLASMA VISCOSITY AND MAGNETIC FORCES IN COAXIAL PLASMA DISCHARGE DEVICE

This paper investigates the axial plasma current sheath, PCS viscosity force, and its correlation with other magnetic forces acting on it at three different radial positions (2.625, 3.625, and 4.125 cm) within the annular space between the coaxial electrodes system of plasma discharge device (12 kV-56 kA) with positive central electrode. The rate of change of PCS momentum was also investigated at these axial and radial positions. The discharge processes are carried out with an argon gas pressure of 0.8 Torr. Experimental results of azimuthal magnetic induction as a function of axial and radial positions and Navier Stokes equation were employed to compute exactly, the rate of change of PCS momentum, axial magnetic force, magnetic pressure gradient force, and viscosity force.

MHD modeling of the molecular filament evolution

We perform numerical magnetohydrodynamic (MHD) simulations of the gravitational collapse and fragmentation of a cylindrical molecular cloud with the help of the FLASH code. The cloud collapses rapidly along it’s radius without any signs of fragmentation in the simulations without magnetic field. The radial collapse of the cloud is stopped by the magnetic pressure gradient in the simulations with parallel magnetic field. Cores with high density form at the cloud’s edges during further evolution. The core densities are n ≈ 1.7×108 and 2×10-7 cm–3 in the cases with initial magnetic field strengths B = 1.9×10-4 and 6×10-4 G, respectively. The cores move toward the cloud’s centre with supersonic speeds |vz| = 3.6 and 5.3 km/s. The sizes of the cores along the cloud’s radius and cloud’s main axis are dr = 0.0075 pc and dz = 0.025 pc, dr = 0.03 pc and dz = 0.025 pc, respectively. The masses of the cores increase during the filament evolution and lie in range of ≈(10-20)Me. According to our results, the cores observed at the edges of molecular filaments can be a result of the filament evolution with parallel magnetic field.

Evolution of current- and pressure-driven instabilities in relativistic jets

ABSTRACT Instabilities in relativistic magnetized jets are thought to be deeply connected to their energy dissipation properties and to the consequent acceleration of the non-thermal emitting relativistic particles. Instabilities lead to the development of small-scale dissipative structures, in which magnetic energy is converted in other forms. In this paper we present three-dimensional numerical simulations of the instability evolution in highly magnetized plasma columns, considering different kinds of equilibria. In fact, the hoop stresses related to the azimuthal component of magnetic field can be balanced either by the magnetic pressure gradient (force-free equilibria, FF) or by the thermal pressure gradient (pressure-balanced equilibria, PB) or by a combination of the two. FF equilibria are prone to current-driven instabilities (CDI), while PB equilibria are prone to pressure-driven instabilities (PDI). We perform a global linear stability analysis, from which we derive the different instability properties in the two regimes, showing that PDI have larger growth rates and are also unstable for high wavenumbers. The numerical simulations of the non-linear instability evolution show similar phases of evolution in which the formation of strong current sheets is followed by a turbulent quasi-steady state. PDI are however characterized by a faster evolution, by the formation of smaller scale dissipative structures and larger magnetic energy dissipation.

Neural network architecture to optimize the nanoscale thermal transport of ternary magnetized Carreau nanofluid over 3D wedge

SignificanceIncorporation of nanoparticles in base fluid water is significant for analysis of thermal behavior of nanofluid mixtures, which has various applications in materials science and thermal engineering, and supervised neural scheme predicts the thermal behavior by solving Carreau nanofluid model. MotiveThis article brings the investigation related to prediction of thermal transport of a ternary magnetized hybrid nanofluid [(Al2O3, CuO, TiO2)/H2O] with a three-dimensional Carreau nanofluid model over a wedge. Three nanoparticles dispersed in water (H2O). Inclined magnetic field is considered for judgement of velocity profile and thermal radiation is utilized to scrutinize the temperature distribution of nanofluid. The Carreau mathematical model is chosen to depict the rheological characteristics of non-Newtonian fluids at very high and very low shear rate. MethodologyPhysical assumptions creates the system of Partial differential equations (PDEs) and these are converted into ordinary differential equations (ODEs) by similarity tool. Further ODEs are dealt with bvp4c scheme and further prediction of solution is made by Levenberg-Marquardt neural network (LM-NN) supervised neural scheme. FindingsIncreased volume friction coefficients of nanoparticles increases the transport of heat. High inclined magnetic effect, thermal radiation, pressure gradient and shear strain parameter predict higher thermal transport.

Outflows Driven from a Magnetic Pseudodisk

Outflows play a pivotal role in star formation as one of its most visible markers and a means of transporting mass, momentum, and angular momentum from the infalling gas into the surrounding molecular cloud. Their wide reach (at least thousands of astrnomical units) is a contrast to typical disk sizes (∼10–100 au). We employ high-resolution three-dimensional nested-grid nonideal magnetohydrodynamic (MHD) simulations to study outflow properties in the Class 0 phase. We find that no disk wind is driven from the extended centrifugal disk that has weak magnetic coupling. The low-velocity winds emerge instead from the infalling magnetic pseudodisk. Much of the disk actually experiences an infall of matter rather than outflowing gas. Some of the pseudodisk wind (PD-wind) moves inward to regions above the disk and either falls onto the disk or proceeds upward. The upward flow gives the impression of a disk wind above a certain height even if the gas is originally emerging from the pseudodisk. The PD-wind has the strongest flow coming from a disk interaction zone that lies just outside the disk and is an interface between the inwardly advected magnetic field of the pseudodisk and the outwardly diffusing magnetic field of the disk. The low-velocity wind exhibits the features of a flow driven by the magnetic pressure gradient force in some regions and those of a magnetocentrifugal wind in other regions. We interpret the structure and dynamics of the outflow zone in terms of the basic physics of gravity, angular momentum, magnetic fields, and nonideal MHD.

Cardiovascular magnetic resonance imaging-derived intraventricular pressure gradients in ST-segment elevation myocardial infarction: a long-term follow-up study.

Recently, novel post-processing tools have become available that measure intraventricular pressure gradients (IVPGs) on routinely obtained long-axis cine cardiac magnetic resonance (CMR) images. IVPGs provide a comprehensive overview of both systolic and diastolic left ventricular (LV) functions. Whether IVPGs are associated with clinical outcome after ST-elevation myocardial infarction (STEMI) is currently unknown. Here, we investigated the association between CMR-derived LV-IVPGs and major adverse cardiovascular events (MACE) in a large reperfused STEMI cohort with long-term outcome. In this prospectively enrolled multi-centre cohort study, 307 patients underwent CMR within 14 days after the first STEMI. LV-IVPGs (from apex-to-base) were estimated on the long-axis cine images. During a median follow-up of 9.7 (5.9-12.5) years, MACE (i.e. composite of cardiovascular death and de novo heart failure hospitalisation) occurred in 49 patients (16.0%). These patients had larger infarcts, more often microvascular injury, and impaired LV-IVPGs. In univariable Cox regression, overall LV-IVPG was significantly associated with MACE and remained significantly associated after adjustment for common clinical risk factors (hazard ratio (HR) 0.873, 95% confidence interval (CI) 0.794-0.961, P = 0.005) and myocardial injury parameters (HR 0.906, 95% CI 0.825-0.995, P = 0.038). However, adjusted for LV ejection fraction and LV global longitudinal strain (GLS), overall LV-IVPG does not provide additional prognostic information (HR 0.959, 95% CI 0.866-1.063, P = 0.426). Early after STEMI, CMR-derived LV-IVPGs are univariably associated with MACE and this association remains significant after adjustment for common clinical risk factors and measures of infarct severity. However, LV-IVPGs do not add prognostic value to LV ejection fraction and LV GLS.

On modeling the in vivo ventricular passive mechanical behavior from in vitro experimental properties in porcine hearts

Myocardium passive mechanical response has been a major topic of study for decades due to its major impact on cardiac physiology. Here, we propose a novel modeling methodology that integrates both in vivo and in vitro data to estimate the tissue mechanical parameters for a particular orthotropic hyperelastic model as those proposed by Costa and by Holzapfel & Ogden, although it can be easily extended to any other. In vitro biaxial and triaxial shear extension tests were conducted in biopsied samples and in vivo pressure-volume recordings were obtained. Left ventricle (LV) geometry was reconstructed using magnetic resonance imaging (MRI) and pressure gradients during ventricular inflation were recorded with the Catheter Conductance Method (CCM). Finally, a Finite Element (FE) in vivo LV model was implemented to get the material model parameters using an inverse approach that uses a minimization process combining both the in vivo and in vitro available data. Our results demonstrate that the parameters obtained solely from in vitro testing (IVT), or from in vivo passive inflation (IVV) do not provide satisfactory fits for both responses simultaneously (R2IVTtests=0.977,R2IVTPV=0.697 and R2IVVtests=0.687,R2IVVPV=0.995). On the contrary, the proposed combined in vitro &in vivo optimization process (MIN) converges to a solution that effectively captures both the in vivo and in vitro behaviors (R2MINtests=0.815,R2MINPV=0.992). Thus, this novel combined approach offers a comprehensive framework for accurately characterizing myocardial mechanical behavior. The obtained parameters can serve as a basis for further cardiac simulations and contribute to a better understanding of cardiac mechanics and function.

Complex structure of turbulence across the ASDEX Upgrade pedestal

The theoretical investigation of relevant turbulent transport mechanisms in H-mode pedestals is a great scientific and numerical challenge. In this study, we address this challenge by global, nonlinear gyrokinetic simulations of a full pedestal up to the separatrix, supported by a detailed characterisation of gyrokinetic instabilities from just inside the pedestal top to the pedestal centre and foot. We present ASDEX Upgrade pedestal simulations using an upgraded version of the gyrokinetic, Eulerian, delta-f code GENE (genecode.org) that enables stable global simulations at experimental plasma $\beta$ values. The turbulent transport is found to exhibit a multi-channel, multi-scale character throughout the pedestal with the dominant contribution transitioning from ion-scale trapped electron modes/micro-tearing modes at the pedestal top to electron-scale electron temperature gradient modes in the steep gradient region. Consequently, the turbulent electron heat flux changes from ion to electron scales and the ion heat flux reduces to almost neoclassic values in the pedestal centre. $E\times B$ shear is found to strongly reduce heat flux levels in all channels (electron, ion, electrostatic, electromagnetic) and the interplay of magnetic shear and pressure gradient is found to locally stabilise ion-scale instabilities.

Increased Relative Velocity due to Enhanced Magnetic Pressure Gradient for the Collision Experiment of High-Beta Plasmoids

Increased Relative Velocity due to Enhanced Magnetic Pressure Gradient for the Collision Experiment of High-Beta Plasmoids

Understanding the Deflection of the “Cartwheel CME”: Data Analysis and Modeling

We study the low corona evolution of the “Cartwheel” coronal mass ejection (CME; 2008 April 9) by reconstructing its three-dimensional path and modeling it with magnetohydrodynamic simulations. This event exhibited a double deflection that has been reported and analyzed in previous works but whose underlying cause remained unclear. The Cartwheel CME traveled toward a coronal hole (CH) and against the magnetic gradients. Using a high-cadence, full-trajectory reconstruction, we accurately determine the location of the magnetic flux rope (MFR) and, consequently, the magnetic environment in which it is immersed. We find a pseudostreamer (PS) structure whose null point may be responsible for the complex evolution of the MFR at the initial phase. From the preeruptive magnetic field reconstruction, we estimate the dynamic forces acting on the MFR and provide a new physical insight into the motion exhibited by the 2008 April 9 event. By setting up a similar magnetic configuration in a 2.5D numerical simulation we are able to reproduce the observed behavior, confirming the importance of the PS null point. We find that the magnetic forces directed toward the null point cause the first deflection, directing the MFR toward the CH. Later, the magnetic pressure gradient of the CH produces the reversal motion of the MFR.

Mechanism of double diffusive convection due to magnetized Williamson nanofluid flow in tapered asymmetric channel under the influence of peristaltic propulsion and radiative heat transfer

PurposeThe purpose of this study, thermal radiation and viscous dissipation impacts on double diffusive convection on peristaltic transport of Williamson nanofluid due to induced magnetic field in a tapered channel is examined. The study of propulsion system is on the rise in aerospace research. In spacecraft technology, the propulsion system uses high-temperature heat transmission governed through thermal radiation process. This study will help in assessment of chyme movement in the gastrointestinal tract and also in regulating the intensity of magnetic field of the blood flow during surgery.Design/methodology/approachThe brief mathematical modelling, along with induced magnetic field, of Williamson nanofluid is given. The governing equations are reduced to dimensionless form by using appropriate transformations. Numerical technique is manipulated to solve the highly nonlinear differential equations. The roll of different variables is graphically analyzed in terms of concentration, temperature, volume fraction of nanoparticles, axial-induced magnetic field, magnetic force function, stream functions, pressure rise and pressure gradient.FindingsThe key finding from the analysis above can be summed up as follows: the temperature profile decreases and concentration profile increases due to the rising impact of thermal radiation. Brownian motion parameter has a reducing influence on nanoparticle concentration due to massive transfer of nanoparticles from a hot zone to a cool region, which causes a decrease in concentration profile· The pressure rise enhances due to rising values of thermophoresis and thermal Grashof number in retrograde pumping, free pumping and copumping region.Originality/valueTo the best of the authors’ knowledge, a study that integrates double-diffusion convection with thermal radiation, viscous dissipation and induced magnetic field on peristaltic flow of Williamson nanofluid with a channel that is asymmetric has not been carried out so far.

Heat and mass transport in an electrically conducting nanofluid flow over two-dimensional geometries

Engineering equipment in medicine, chemical and power engineering, electronics, and other human endeavours use nanofluids. The ability to improve mass and heat transport because of the low concentration of nanoparticles is the primary driver behind the vast array of nanofluid applications. Thus, the famous problems of viscous, incompressible, Newtonian, and 2-D laminar flow are revisited to investigate the mass and heat transmission rates for water-based carbon nanotubes (CNTs) with variable magnetic fields and external pressure gradients. Flow cases considered with varying pressure gradients are the flows upon a flat plate, flow in a planar diverging and converging channel, flow over a wedge, and plane stagnation flows, which are investigated. The impressions of thermophoresis and Brownian motion parameters are examined through the Buongiorno model. Using the Görtler transformation, the leading boundary layer (BL) equations are converted into dimensionless forms of ordinary differential equations (ODEs). Runge-Kutta Fehlberg Method (RKF45) is operated to tackle the ensuing ODEs to find the mass, heat, and skin friction rates. It has been found that the rates of shear stress, mass, and heat transport slow down with an escalating magnetic field. Although mass transport rates are decreased, shear stress and heat transport (HT) rates escalate due to the solid volume portion of carbon nanotubes. Furthermore, the pressure gradient parameter facilitates faster heat and shear stress transmission rates.

Statistical Survey of Magnetic Forces Associated With Earthward Bursty Bulk Flows Measured by MMS 2017–2021

AbstractWe investigate the magnetic forces (the magnetic pressure gradient force, the curvature force, and their sum the j × B‐force) associated with earthward bursty bulk flows (BBFs) using Magnetospheric Multiscale (MMS) data from five tail seasons (2017–2021). For the first time, the magnetic forces are inferred downtail of XGSM = −20 RE and in the GSM XY and YZ planes. The results suggest that BBFs tend to be accelerated earthward by the magnetic pressure gradient force tailward of ∼19 RE and decelerated closer to that distance in the 2017–2018 data. The force magnitudes increase with distance. This is in accordance with earlier Cluster results. In the 2019–2021 data, the pressure gradient force magnitudes are generally smaller and no clear distance for the acceleration reversal can be determined. The curvature forces for both 2017–2018 and 2019–2021 BBFs indicate earthward acceleration independent of distance, consistent with the Cluster measurements. The sum, the j × B‐force, suggests for the 2017–2018 BBFs earthward acceleration tailward of XGSM ∼15 RE and deceleration within that distance, also consistent with Cluster. In contrast, the 2019–2021 BBFs show general earthward acceleration by j × B independent of distance. In the GSM XY plane, the average (j × B)xy vectors are earthward, and in the premidnight and postmidnight dawnward for the 2017–2018 BBFs. For 2019–2021, the average (j × B)xy vectors have components toward the tail center. In the GSM YZ plane, the average (j × B)yz vectors are toward the neutral sheet.

The force density in electrical machines modeled as tension and pressure gradients of magnetic field lines

This paper shows how to model the force density in electrical machines based on the field lines of the magnetic flux density. The force density is written as two vector components: the magnetic tension force and the magnetic pressure gradient force. This approach has been applied in physics but never to forces in engineering problems. The magnetic tension force acts to straighten bent field lines, based on the curvature of the flux density. The magnetic pressure gradient force acts from regions of high flux density to regions of low flux density. Both force densities are derived from the Lorentz force using the tnb-frame of Frenet–Serret formulas and shown to be equivalent to the divergence of the Maxwell stress tensor. It is shown how the force density could describe the forces in a synchronous machine, including both the angular torque of the load and the radial forces between the rotor and the stator. It could also be linked to the power flow and thereby to the energy flux of Poynting’s vector. The force densities could be used to improve the understanding of the Maxwell stress tensor, since they are easier to illustrate as vectors compared to the matrix form of the Maxwell stress tensor. It also shows the location of the force density, which could improve the use of enclosing volumes when calculating the force based on the divergence theorem with the Maxwell stress tensor.

Transient MHD flow of fractional Burger's fluid model through a parallel microchannel with heat transfer and slip boundary condition

The combined influence of magnetic field, electro-osmotic flow (EOF), and pressure gradient on the unsteady magnetohydrodynamic fluid flow through a parallel microchannel is investigated. The Burger's liquid model is used for the fractional partial differential equation, which allows us to study the behavior of viscoelastic liquid velocity profile in the parallel microchannel. The Laplace transform (LT) in concert with the Fourier cosine transform are used to obtain the analytical solution of the velocity profile. Furthermore, using the method of separation of variables, the energy equation, Joule heating, energy dissipation, and electromagnetic effects are calculated to obtain the temperature within the microchannel. The influence of some relevant parameters like heat transfer, temperature distribution, Hartmann number (Ha), and Brinkman number (Br) on fluid flow velocity are presented graphically and discussed. The results obtained show that temperature decreases with Ha and Br of the transverse electric field for slip flow. Close to the middle of the microchannel, fluid flow velocity increases with decrease in the delay time parameter value and increase in the Burger's parameter value, while the opposite trend is found for the velocity near to the middle of the microchannel. In addition, Burger's liquid is quite general, such that Oldroyd-B, Maxwell, and Newtonian liquids are readily obtained as limiting cases. The study is significant in the application fields of chemical analysis and biological analysis, drug delivery, bacteria detection, and some others.

Numerical treatment of thermal and concentration convection along with induced magnetic field on peristaltic pumping of a magnetic six-constant Jeffrey nanofluid through a vertical divergent channel

This article presents a computational study for the peristaltic pumping within vertical irregular divergence channels filled with magnetic six-constant Jeffrey nanofluids. Various configurations of the outer boundaries are considered, namely, square wave, trapezoidal wave, multisinusoidal wave, and triangular wave. An induced magnetic field together with nanoparticles and mass concentration are considered. Influences of the Dufour and Soret numbers are examined, and the cases of long wavelength and low Reynolds number are applied. All the computations are obtained numerically via MATHEMATICA symbolical software (built-in command ND-Solve), and the obtained results are presented in terms of the axial velocity current density the function of magnetic force axially induced magnetic field nanoparticle fraction profile concentration profile temperature profile extra stress tensor pressure gradient pressure rise and stream function The major outcomes revealed that the square wave shape gives higher pressure gradients near the inlet and outlet parts while the multisinusoidal wave gives periodic behaviors of Also, higher axial-induced magnetic fields are given at the higher values of the magnetic Reynolds number.

Impact of an MHD Cattaneo-Christov model for a Williamson fluid flow across a wedge with a convective boundary condition: Homotopy Analysis Method

The present study aims to scrutinise the influence of the Cattaneo-Christov (CC) heat flux model on magnetohydrodynamic (MHD) laminar boundary-layer flow through a wedge in a non-Newtonian Williamson fluid along with convective boundary condition embedded in a porous medium. Significantly, the presence of the CC model explores the heat transfer characteristics which forecast the effect of thermal relaxation time on the boundary-layer phenomenon. The governing equations are formulated and modified into non-linear, coupled ODEs by utilising similarity transformations and then tackled by Homotopy Analysis Method (HAM). The obtained results are discussed and presented graphically for various values of emerging parameters on velocity and temperature distributions. The results reveal that the velocity is an enhancing function of the magnetic parameter, permeability parameter and Hartree pressure gradient parameter whereas decreasing with larger values of the Williamson fluid parameter. It is evident that the temperature upsurges due to the Biot number and decays with the relaxation parameter. The numerical values of skin-friction and Nusselt number are tabulated. Comparative reviews between the formerly published literature and the current data are made for specific cases, which are inspected to be in tremendous agreement. Abbreviations: BLF: Boundary layer flow; MHD Magnetohydrodynamic; CC model: Cattaneo-Christov model; NNF: non-Newtonian fluid; ODEs: Ordinary differential equations; PDEs: Partial differential equations

Spectroscopic observation of super-Alfvénic field-reversed configuration merging process by mixing of tracer ions.

Visualization of the collisional merging formation process of field-reversed configuration (FRC) has been attempted. In the collisional merging formation process, two initial FRC-like plasmoids are accelerated toward each other by a magnetic pressure gradient. The relative speed of the collision reaches several times the typical ion sonic speed and Alfvénic speed. The magnetic structure of the initial-FRCs is disrupted in the collision process, but the FRC-like magnetic structure is reformed in ∼30 µs after the collision. Magnetic reconnection should occur in this process; however, general theoretical models in magnetohydrodynamics approximation cannot be applied to this process because of the high-beta nature of FRC and super-Alfvénic/sonic relative speed. In this work, the spectroscopic observation of the collisional merging FRC formation was conducted to evaluate the timescale and geometry of merging. A slight amount of tracer element (e.g., helium) was mixed into one of two initial-FRCs. Mixing of the tracer did not cause serious adverse effects on the performance of the initial-FRC in the collision and merging processes. The collision and merging processes were visualized successfully and observed using a fast-framing camera with a bandpass filter. The timescale of merging and the outflow speed in the collisional merging process of FRCs were optically evaluated for the first time.

Dynamics of Magnetized Accretion Disks of Young Stars

We investigate the dynamics of the accretion disks of young stars with fossil large-scale magnetic field. The author’s magnetohydrodynamic (MHD) model of the accretion disks is generalized to take into account the dynamical influence of the magnetic field on gas rotation speed and vertical structure of the disks. With the help of the developed MHD model, the structure of an accretion disk of a solar mass T Tauri star is simulated for different accretion rates $$\dot {M}$$ and dust grain sizes $${{a}_{d}}$$ . The simulations of the radial structure of the disk show that the magnetic field in the disk is kinematic, and the electromagnetic force does not affect the rotation speed of the gas for typical values $$\dot {M} = {{10}^{{ - 8}}}$$ $${{M}_{ \odot }}$$ /yr and $${{a}_{d}} = 0.1$$ µm. In the case of large dust grains, $${{a}_{d}} \geqslant 1$$ mm, the magnetic field is frozen into the gas and a dynamically strong magnetic field is generated at radial distances from the star $$r \gtrsim 30$$ AU, the tensions of which slow down the rotation speed by $$ \lesssim {\kern 1pt} 1.5$$ % of the Keplerian velocity. This effect is comparable to the contribution of the radial gradient of gas pressure and can lead to the increase in the radial drift velocity of dust grains in the accretion disks. In the case of high accretion rate, $$\dot {M} \geqslant $$ 10–7 $${{M}_{ \odot }}$$ /yr, the magnetic field is also dynamically strong in the inner region of the disk, $$r < $$ 0.2 AU. The simulations of the vertical structure of the disk show that, depending on the conditions on the surface of the disk, the vertical gradient of magnetic pressure can lead to both decrease and increase in the characteristic thickness of the disk as compared to the hydrostatic one by 5–20%. The change in the thickness of the disk occurs outside the region of low ionization fraction and effective magnetic diffusion (“dead” zone), which extends from $$r = 0.3$$ to 20 AU.

Improvement of Plasmoid Acceleration Performance by Increased Magnetic Pressure Gradient for High-Mach Number Shock Generation

Improvement of Plasmoid Acceleration Performance by Increased Magnetic Pressure Gradient for High-Mach Number Shock Generation