Effect Of Lorentz Force Research Articles

The dynamics of charged dust in magnetized molecular clouds

We study the dynamics of large, charged dust grains in turbulent giant molecular clouds (GMCs). Massive dust grains behave as aerodynamic particles in primarily neutral dense gas, and thus are able to produce dramatic small-scale fluctuations in the dust-to-gas ratio. Hopkins & Lee (2016) directly simulated the dynamics of neutral dust grains in super-sonic MHD turbulence, typical of GMCs, and showed that the dust-to-gas fluctuations can exceed factor ~1000 on small scales, with important implications for star formation, stellar abundances, and dust behavior and growth. However, even in primarily neutral gas in GMCs, dust grains are negatively charged and Lorentz forces are non-negligible. Therefore, we extend our previous study by including the effects of Lorentz forces on charged grains (in addition to drag). For small charged grains (sizes <0.1 micron), Lorentz forces suppress dust-to-gas ratio fluctuations, while for large grains (sizes >1 micron), Lorentz forces have essentially no effect, trends that are well explained with a simple theory of dust magnetization. In some special intermediate cases, Lorentz forces can enhance dust-gas segregation. Regardless, for the physically expected scaling of dust charge with grain size, we find the most important effects depend on grain size (via the drag equation) with Lorentz forces/charge as a second-order correction. We show that the dynamics we consider are determined by three dimensionless numbers in the limit of weak background magnetic fields: the turbulent Mach number, a dust drag parameter (proportional to grain size) and a dust Lorentz parameter (proportional to grain charge); these allow us to generalize our simulations to a wide range of conditions.

A comparative study of wall jet flow containing carbon nanotubes with convective heat transfer and MHD

PurposeThe purpose of this study is to conduct a comparative investigation for incompressible electrically conducting nanofluid fluid through wall jet. Single-walled carbon nanotubes (SWCNTs) and multiple-walled carbon nanotubes (MWCNTs) are considered as the nanoparticles. To record the effect of Lorentz forces, a magnetic field is applied normally with the assumption that the induced magnetic field is negligible.Design/methodology/approachBoundary layer approximation is used to convert governing equations into ordinary differential equations along with appropriate boundary conditions. To obtain the results, used homotopy analysis method (HAM) has been used as an analytical technique and to validate the obtained results a famous numerical Runge–Kutta–Fehlberg method is also exploited. It has been observed that the results obtained through both of the methods are in excellent agreement with exact solution.FindingsThe Hartmann number is used as controlling parameter for velocity and temperature profile. That can be recorded as its extended values help to normalize the velocity, whereas it controls the rapid increase in temperature. The temperature profile is boosted by increasing the value of the Biot number, a physical parameter. Similarly, it also increases for an increased percentage of volume fraction of particles (SWCNTs/MWCNTs). The Hartmann number plays an important role in decreasing local skin friction coefficient. The influence of the Biot number and volume fraction of nanoparticles caused similar increasing effects on the local Nusselt number. Nanoparticles of the form SWCNT provide better heat transfer as compared to MWCNTs. Influence of the Biot number and volume fraction of nanoparticles caused similar increasing effects on the local Nusselt number. Nanoparticles of the form SWCNT provide better heat transfer as compared to MWCNTs.Originality/valueTo gain insight into the problem, the effects of various emerging parameters and physical quantities such as Biot number, Nusselt number and skin friction coefficient, have been explored.

Lorentz force effect on mixed convection micropolar flow in a vertical conduit

The present work provides a simulation of control and filtration process of hydromagnetic blood flow with Hall current under the effect of heat source or sink through a vertical conduit (pipe). This work meets other engineering applications, such as nuclear reactors cooled during emergency shutdown, geophysical transport in electrically conducting and heat exchangers at low velocity conditions. The problem is modeled by a system of partial differential equations taking the effect of viscous dissipation, and these equations are simplified and solved analytically as a series solution using the Differential Transformation Method (DTM). The velocities and temperature profiles of the flow are plotted and discussed. Moreover, the conduit wall shear stress and heat flux are deduced and explained.

Localized currents generated by simultaneous ultrasound and oscillating magnetic fields

Introduction: The goal of this work is to use the Lorentz force effect to generate localized currents in an ionic medium by applying ultrasound in the presence of oscillating magnetic fields. We expect to generate low frequency currents from the high frequency oscillations of ultrasound and magnetic fields. The duration of one complete, active cycle of the induced currents will be similar to that in TMS. This study aims to develop a theoretical framework, conduct numerical simulations and validate the results experimentally. This framework will be used in future work to develop a novel Magnetic Ultrasound Stimulation (MUS) system which can achieve highly focused, non-invasive, deep brain stimulation.

Effect of Lorentz force on the electrochemical performance of lithium-ion batteries

Lorentz force theory demonstrates that electric current density and magnetic force are proportional, indicating that they compensate each other. In a battery operated at high magnetic forces, the electrons in the active material move fast in a specific magnetic field. γ-Fe2O3, a highly magnetic material, is used to prepare LiFePO4 electrodes to study the effect of the Lorentz force on lithium-ion battery performance. The magnetic field created by γ-Fe2O3 induces magnetic forces on the charged LiFePO4 particles, accelerating electron movement. Superconducting quantum interference measurements reveal that saturation magnetization and remanence are prominent when γ-Fe2O3 is added to the LiFePO4 electrodes. The LiFePO4 electrode containing 15wt% γ-Fe2O3 led to superior battery capacity (69.8mAhg−1 at 10C) compared with the pure LiFePO4 electrode (1.8mAhg−1 at 10C). In this study, Lorentz force theory is applied to improve the specific capacity and cycle life at high current rates of a battery containing LiFePO4 cathode materials, suggesting that incorporating γ-Fe2O3 into the cathode is an easy and cheap strategy for increasing the power density and cycle life of lithium-ion batteries.

A proposed method for measurement of cosmic-ray mass composition based on geomagnetic spectroscopy

The effect of the geomagnetic Lorentz force on the muon component of extensive air shower (EAS) has been studied in a Monte Carlo generated simulated data sample. This geomagnetic field affects the paths of muons in an EAS, causing a local contrast or polar asymmetry in the abundance of positive and negative muons about the shower axis. The asymmetry can be approximately expressed as a function of transverse separation between the positive and negative muons barycentric positions in the EAS through opposite quadrants across the shower core in the shower front plane. In the present study, it is found that the transverse muon barycenter separation and its maximum value obtained from the polar variation of the parameter are higher for Iron primaries than protons for highly inclined showers. Hence, in principle, these parameters can be exploited to the measurement of primary cosmic-ray chemical composition. Possibility of practical realization of the proposed method in a real experiment is briefly discussed.

Mechanism analysis of Magnetohydrodynamic heat shield system and optimization of externally applied magnetic field

As a novel thermal protection technique for hypersonic vehicles, Magnetohydrodynamic (MHD) heat shield system has been proved to be of great intrinsic value in the hypersonic field. In order to analyze the thermal protection mechanisms of such a system, a physical model is constructed for analyzing the effect of the Lorentz force components in the counter and normal directions. With a series of numerical simulations, the dominating Lorentz force components are analyzed for the MHD heat flux mitigation in different regions of a typical reentry vehicle. Then, a novel magnetic field with variable included angle between magnetic induction line and streamline is designed, which significantly improves the performance of MHD thermal protection in the stagnation and shoulder areas. After that, the relationships between MHD shock control and MHD thermal protection are investigated, based on which the magnetic field above is secondarily optimized obtaining better performances of both shock control and thermal protection. Results show that the MHD thermal protection is mainly determined by the Lorentz force's effect on the boundary layer. From the stagnation to the shoulder region, the flow deceleration effect of the counter-flow component is weakened while the flow deflection effect of the normal component is enhanced. Moreover, there is no obviously positive correlation between the MHD shock control and thermal protection. But once a good Lorentz force's effect on the boundary layer is guaranteed, the thermal protection performance can be further improved with an enlarged shock stand-off distance by strengthening the counter-flow Lorentz force right after shock.

CuO-water nanofluid free convection in a porous cavity considering Darcy law

The natural convection of a CuO-water nanofluid in a permeable cavity is simulated using the Darcy law. The Brownian motion impact on the properties of the nanofluid is taken into account using the KKL model. The effect of Lorentz forces on the nanofluid hydrothermal behavior are considered. The control volume based finite element method is applied to solve the final equations. Roles of CuO-water volume fraction ( $\phi$ ), Rayleigh (Ra) and Hartmann (Ha) numbers for a porous medium are reported. Results show that the Nusselt number decreases with increasing Ha but it increases with increasing $\phi$ , Ra.

A model to predict the ultrasonic field radiated by magnetostrictive effects induced by EMAT in ferromagnetic parts

An Electro-Magnetic Acoustic Transducer (EMAT) is a non-contact source used in Ultrasonic Testing (UT) which generates three types of dynamic excitations into a ferromagnetic part: Lorentz force, magnetisation force, and magnetostrictive effect. This latter excitation is a strain resulting from a magnetoelastic interaction between the external magnetic field and the mechanical part. Here, a tensor model is developed to transform this effect into an equivalent body force. It assumes weak magnetoelastic coupling and a dynamic magnetic field much smaller than the static one. This approach rigorously formulates the longitudinal Joule’s magnetostriction, and makes it possible to deal with arbitrary material geometries and EMAT configurations. Transduction processes induced by an EMAT in ferromagnetic media are then modelled as equivalent body forces. But many models developed for efficiently predicting ultrasonic field radiation in solids assume source terms given as surface distributions of stress. To use these models, a mathematical method able to accurately transform these body forces into equivalent surface stresses has been developed. By combining these formalisms, the magnetostrictive strain is transformed into equivalent surface stresses, and the ultrasonic field radiated by magnetostrictive effects induced by an EMAT can be both accurately and efficiently predicted. Numerical examples are given for illustration.

Anisotropic magneto-transport properties of electron gases at SrTiO3 (111) and (110) surfaces

Electron gases at the surfaces of insulating (111)- and (110)-oriented SrTiO3 (STO) single crystals have been created using Ar+-irradiation and their magneto-transport properties are characterized. Fully metallic behaviors with sheet carrier density of ∼1014 cm−2 and low-temperature-mobilities as large as 8600 cm2 V−1 s−1 are obtained. Intrinsic in-plane anisotropic magnetoresistance (AMR) has been obtained by applying current along different crystal axes to subtract the Lorentz force effect. The results yield nearly 6-fold and 2-fold components for the (111)-and (110)-surfaces. A symmetry breaking in AMR for the (111)-surfaces with ordering temperature TO ∼ 30 K is also observed. In contrast, the out-of-plane AMR does not show anisotropy associated with crystal axes, suggesting a two-dimensional nature of the effect. Our results demonstrate that electron gases at (111)- and (110)-oriented STO surfaces are a promising playground for both fundamental research and all-oxide device applications.

Direct numerical simulation analysis of spanwise oscillating Lorentz force in turbulent channel flow at low Reynolds number

Direct numerical simulations of a turbulent channel flow at low Reynolds number (Re_{tau } = 180, based on the driving pressure gradient and channel half width) are performed. Some results are also presented for Re_{tau } = 400. In this work we apply an idealized spanwise Lorentz force near the lower wall of the channel and compare the results for the applied force and no-force cases in both the upper half and the lower half of the channel. We have studied two-point correlations to explain the effect of the Lorentz force on streamwise vortices and streaky structures. Despite the observation of clear stabilization of the streaky structures in the vicinity of the wall, the existence of the streamwise vortices is explained by the well-known turbulence regeneration cycle, which improves the understanding of streaky and streamwise vortex structure formation on turbulence generation. Spanwise oscillating Lorentz force effects on the Rankine vortex structures are investigated. Our results lead us to establish an explanation on the effect of sweep and ejection events on the mean vortex structures in the flow field. A mean vortex structure is defined by the time-averaged location of the local minimum and maximum of the streamwise r.m.s. vorticity. We also depict turbulence production rates for both cases and compared the lower and upper half of the channel.

The effects of radiation optical properties on the unsteady 2D boundary layer MHD flow and heat transfer over a stretching plate

In this work, the effects of radiation optical properties and Lorentz force on the 2D unsteady laminar boundary magnetohydrodynamic (MHD) fluid flow and heat transfer along a semi-infinite stretching plate are numerically investigated, the Joule heating effect and viscous dissipation are considered. The heat flux caused by the thermal radiation is obtained by solving the radiation transfer equation (RTE) instead of the Rosseland approximation. All the governing equations, including continuous equation, momentum equation, energy equation, and RTE subject to the boundary radiative emission, are transformed into dimensionless forms. The dimensionless governing equations together with the corresponding boundary conditions are solved numerically via Chebyshev collocation spectral method (CCSM). The effects of various physical parameters, say, Ha, Pr, Ec and Pl, especially the optical properties such as the optical thickness, the scattering albedo, and the wall emissivity of the plate, on the flow and heat transfer are depicted graphically and analyzed in detail. It is found that, due to the thermal radiation, the overall average temperature within the boundary layer becomes much higher and the boundary layer becomes thicker. The magnetic force can suppress the fluid flow significantly and stop the convective heat transfer effectively. Viscous dissipation and Joule heating greatly enhance the temperature distribution with the help of the magnetic field.

Large enhancement of positive magnetoresistance by Ce doping in Si epitaxial thin films

We report the investigation into a large enhancement of the magnetoresistance (MR) by Ce doping in Si epitaxial thin films at room temperature. The positive MR is proportional to the square of the magnetic field at low magnetic fields below 5 T, while it increases linearly with regards to the strength of the magnetic field above 5 T. Based on the experimental finding that the change in the donor level corresponds to that of the MR ratio as a function of Ce concentration, the electronic state turns out to be influenced by Ce doping and strongly correlate the magnetotransport characteristics. It is concluded that this MR effect appears via the Lorentz force effect on the carrier motion, which is enhanced by the random scattering potential distribution arising from the Ce doping.

Emergence of nontrivial magnetic excitations in a spin-liquid state of kagomé volborthite

When quantum fluctuations destroy underlying long-range ordered states, novel quantum states emerge. Spin-liquid (SL) states of frustrated quantum antiferromagnets, in which highly correlated spins fluctuate down to very low temperatures, are prominent examples of such quantum states. SL states often exhibit exotic physical properties, but the precise nature of the elementary excitations behind such phenomena remains entirely elusive. Here, we use thermal Hall measurements that can capture the unexplored property of the elementary excitations in SL states, and report the observation of anomalous excitations that may unveil the unique features of the SL state. Our principal finding is a negative thermal Hall conductivity [Formula: see text] which the charge-neutral spin excitations in a gapless SL state of the 2D kagomé insulator volborthite Cu3V2O7(OH)2[Formula: see text]2H2O exhibit, in much the same way in which charged electrons show the conventional electric Hall effect. We find that [Formula: see text] is absent in the high-temperature paramagnetic state and develops upon entering the SL state in accordance with the growth of the short-range spin correlations, demonstrating that [Formula: see text] is a key signature of the elementary excitation formed in the SL state. These results suggest the emergence of nontrivial elementary excitations in the gapless SL state which feel the presence of fictitious magnetic flux, whose effective Lorentz force is found to be less than 1/100 of the force experienced by free electrons.

On the separation of Lorentz and magnetization forces in the transduction mechanism of Electromagnetic Acoustic Transducers (EMATs)

Electromagnetic Acoustic Transducers (EMATs) are widely used in Nondestructive Evaluation (NDE) of metals, including the inspection of ferritic steels. Optimization of EMATs in ferromagnetic materials is often accomplished using computational simulations that account for the three main types of transduction mechanism, namely the effects of Lorentz forces, magnetization forces, and magnetostriction. The extensive literature on the Lorentz and magnetization mechanisms of EMATs has been historically scattered with alternative notations causing conflicting interpretations of the fundamental governing equations that often led to erroneous implementations of these equations in computational simulations. The purpose of this paper is to clarify this issue. The confusion is caused by the arbitrary nature of the separation of electromagnetic transduction force into Lorentz and magnetization components. This paper shows that apparently contradicting models are actually equivalent if the Lorentz and magnetization forces are chosen to correctly match each other, while mixing otherwise acceptable but mutually incompatible terms leads to unacceptable modelling errors. This paper also provides guidelines for the implementation of these transduction mechanisms in computational models for EMATs.

The effect of manganese incorporation in Bi2Se3 on the thermal, electrical transport and magnetic properties

Thermal, electrical transport, and magnetic measurements have been made on polycrystalline Mnx(Bi2Se3) where Mn was incorporated by melting Mn metal with pre-synthesized Bi2Se3. We find that, unlike Cux(Bi2Se3), this process leads to significant partial substitution of the 3d transition metal ion onto the Bi site rather than the interstitial site in the van der Waals gaps. Mn incorporation led to a systematic reduction in the magnitude of the thermopower and an increase in phonon scattering that resulted in a decrease in the thermal conductivity. The electronic contribution to the thermal conductivity at 300 K is 0.51 W m−1 K−1 for pure Bi2Se3, 0.75 W m−1 K−1 for the 3% Mn sample, but only 0.07 W m−1 K−1 for the 6% Mn incorporated sample. We find that the thermoelectric figure of merit, ZT, is enhanced in the 3% Mn sample by a factor of 1.7 at 300 K and a factor of 1.2 at 200 K. The pure compound has a susceptibility that can be modeled in terms of antiferromagnetic exchange between 0.13% half-filled (single electron) Se vacancies. Mn incorporation does not lead to magnetic order but there are antiferromagnetic interactions that become weaker with increasing Mn concentration. A positive power-law magnetoresistance is observed and it reaches 5.2% at low temperatures for the 3% Mn sample. The magnetoresistance is likely to arise from a Lorentz force effect. A lower magnetoresistance is measured for the 6% Mn sample and attributed to a shorter carrier mean free path from Mn impurity scattering.

Magnetic flux distortion in two-phase liquid metal flow: Model experiment

In this paper, we present the model experiments in order to study the magnetic flux distortion of a two-phase liquid metal flow excited by an AC magnetic field in a range of pulsation where Faraday induction and Lorentz force effects are significant. These experiments realized with solid aluminum rods allow to characterize the effects of flow velocity (0 ≲ U≤1 ms−1), void fraction (0≤α≤6.9 %), pulsation of the AC magnetic field (1.5×103≤ω≤12.5×103 rad s−1), and of two different void geometries. The results are analyzed on the basis of a first order expansion of magnetic flux in U and α. Despite the strong coupling between Faraday induction and Lorentz force effects, the results show that the contributions of U and α on a magnetic flux distortion can be well separated at both low magnetic Reynolds number and α values. These results are independent of void geometry.

Numerical investigation of three-dimensional hybrid Cu–Al2O3/water nanofluid flow over a stretching sheet with effecting Lorentz force subject to Newtonian heating

This work compares the heat transfer characteristics of traditional nanofluid with that of emerging hybrid nanofluid. Hybrid nanofluid, a new type of conventional fluid, has been used toward the enhancement of heat transfer in the boundary layer flow. A new model of thermophysical properties is employed to investigate the effects of Lorentz force over a three-dimensional stretching surface subject to Newtonian heating. Comparisons are obtained through the numerical parametric study, which has been carried out to explore the effects of various physical parameters involved in the problem. From this study it is observed that the heat transfer rate of hybrid nanofluid (Cu–Al2O3/water) is higher than nanofluid (Cu/water) even in the presence of a magnetic field environment. By opting to use different and appropriate nanoparticle proportions in hybrid nanofluid, the desired heat transfer rate can be achieved.

Effect of Lorentz forces on forced-convection nanofluid flow over a stretched surface

Magnetic nanofluid hydrothermal analysis over a plate is studied that includes consideration of thermal radiation. The Runge–Kutta (RK4) method is utilized to get solution of ODEs which are obtained from similarity solution. In considering the impacts of Brownian motion, we applied Koo–Kleinstreuer–Li correlation to simulate the properties of CuO–water. The influence is discussed of important parameters such as the temperature index, magnetic, radiation, and velocity ratio parameters and volume fraction of nanoparticle on hydrothermal behavior. Results illustrate that the coefficient of skin friction enhances with enhancing magnetic parameter while reduces with enhancing velocity ratio parameter. Also the Nusselt number was found to directly depend on the velocity ratio and temperature index parameters but has an inverse dependence on the magnetic and radiation parameters.

Comparison of Therapeutic Magnetic Stimulation With Electric Stimulation of Spinal Column Vertebrae

Electrical bone growth stimulators improve patient outcomes following the spinal fusion surgery, particularly important in high-risk patient populations. The therapeutic electromagnetic field (EMF) effects in tissue were modeled for two Food and Drug Administration (FDA) approved magnetic stimulation devices: 1) Coil A (SpinaLogic, DJO LLC, Vista, CA) and 2) Coil B system (Spinal-Stim, Orthofix Inc., Lewisville, TX). The electric current density induced in the target tissue (spinal vertebra) was compared with that of an FDA approved electric stimulation device (SpinalPak, Biomet, Warsaw, IN). For Coil A and Coil B, the EMF source was current-carrying coils that differed in the design (single coil versus two coaxial coil system) and the current characteristics (continuous 76.6 Hz sinusoid, biased versus intermittent 3850 Hz rectangular pulse bursts repeated at 1.5 Hz, unbiased). The local maximum induced electric field and current density were over 700-fold higher for Coil B system than for Coil A but only half of the values calculated for the reference electric stimulation device. The interaction of the magnetic field and the induced current in the tissue gives rise to local Lorentz force effects expressed as magnetoacoustic pressure (MAP) that for Coil B system reached 5 dB relative to $1~\mu $ Pa of sound pressure level in bone (SPL) (compared with −45 dB for Coil A and absent for capacitive coupling reference device). The analysis broadens the range of possible mechanisms of therapeutic EMF action to include the MAP.