External Uniform Magnetic Field Research Articles

Magnetically Controlled Modular Cubes With Reconfigurable Self-Assembly and Disassembly

Reconfigurable modular robots, which can actively assemble and disassemble on command, offer the possibility of mesoscale (milliscale and microscale) manufacturing with robustness and controllability. In this study, we present a design of a scalable modular subunit with embedded permanent magnets in a 3-D printed cubic body. The subunit can be wirelessly controlled by an external uniform magnetic field. We also present controlled assembly–disassembly techniques for these subunits. Our modular robotic platform is highly reconfigurable and can create programmable, predetermined patterns based on open-loop control. The 2-D motion planner computes all reachable polyomino shapes from an arbitrary initial configuration and provides the shortest movement sequences to form each shape. Experimental results match computational modeling, demonstrating robust and reproducible behavior of the modular robotic platform that is promising for mesoscale manufacturing applications. Two cube sizes were tested: 10-mm edge lengths and 2.8-mm edge lengths.

Modelling tippers on a sphere

SUMMARY In the past three decades, an immense amount of magnetic field data (with periods of measurements from months to years) has been collected worldwide, either inland or at the sea bottom. This makes it tempting to estimate from these data magnetotelluric (MT) vertical transfer functions—tippers—and further probe with them the 3-D distribution of electrical conductivity on a continental or even global scale. Such a problem setup requires modelling tippers in spherical geometry. It is known that MT impedances in spherical coordinates can be modelled using different polarizations of a uniform external magnetic field. As for tippers, one needs another type of excitation because the uniform external magnetic field of any polarization contains a non-zero radial component. In the paper, we elaborate a source model, which leads to valid tippers on a whole sphere. We also present a novel, accurate and computationally efficient solver to calculate the electromagnetic field in a spherical shell or a part thereof. To illustrate the workability of both the introduced source model and the developed new solver, we present the results of modelling the ocean induction effect in tippers on a global scale. We performed computations in the models with and without oceanic sediments and show that the sediments substantially influence the results in the coastal regions where the thickness of sediments is comparable with or even exceeds the ocean’s bathymetry.

Analyzing the Behavior of Spin Phases in External Magnetic Fields by Means of Spin-Constrained States.

During molecular dissociation in the presence of an external uniform magnetic field, electrons flip their spin antiparallel to the magnetic field because of the stabilizing influence of the spin Zeeman operator. Although generalized Hartree-Fock descriptions furnish the optimal mean-field energetic description of such bond-breaking processes, they are allowed to break Ŝz symmetry, leading to intricate and unexpected spin phases and phase transitions. In this work, we show that the behavior of these molecular spin phases can be interpreted in terms of spin phase diagrams constructed by constraining states to target expectation values of projected spin. The underlying constrained states offer a complete electronic characterization of the spin phases and spin phase transitions, as they can be analyzed using standard quantum chemical tools. Because the constrained states effectively span the entire phase space, they could provide an excellent starting point for post-Hartree-Fock methods aimed at gaining more electron correlation or regaining spin symmetry.

Self-Focusing of Gaussian Laser Beam in an Axially Magnetized Plasma

A well established parabolic equation approach to study the evolution of self-focusing of Gaussian laser beam in underdense, magnetized plasma has been presented. The uniform external magnetic field is assumed to be applied along (forward) as well as opposite (reverse) to the direction of propagation of laser beam. The nonlinear differential equation governing dimensionless beam-width parameter is derived under WKB and paraxial approximations. It is observed that forward (reverse) magnetic field increases (decreases) the self-focusing of Gaussian laser beam as compared to the unmagnetized case of reference.

Dust–ion acoustic solitary waves in a collisionless magnetized five components plasma

Abstract We have derived a Korteweg–de Vries–Zakharov–Kuznetsov (KdV-ZK) equation to study the nonlinear behavior of dust–ion acoustic waves in a collisionless magnetized five components dusty plasma consisting of warm adiabatic ions, nonthermal hot electrons, isothermal cold electrons, nonthermal positrons and static negatively charged dust particulates. It is found that the coefficient of the nonlinear term of the KdV-ZK equation vanishes along different family of curves in different compositional parameter planes. In this situation, to describe the nonlinear behavior of dust–ion acoustic waves, we have derived a modified KdV-ZK (MKdV-ZK) equation. When the coefficients of the nonlinear terms of both KdV-ZK and MKdV-ZK equations are simultaneously equal to zero, then we have derived a further modified KdV-ZK (FMKdV-ZK) equation which effectively describes the nonlinear behavior of dust–ion acoustic waves. Analytically and numerically, we have investigated the solitary wave solutions of different evolution equations propagating obliquely to the direction of the external static uniform magnetic field. We have seen that the amplitude of the KdV soliton strictly increases with increasing β e, whereas the amplitude of the MKdV soliton strictly decreases with increasing β e, where β e is the nonthermal parameter associated with the hot electron species. Also, there exists a critical value β r ( c ) ${\beta }_{\text{r}}^{(\text{c})}$ of β e such that the FMKdV soliton exists within the interval β r ( c ) < β e ≤ 4 7 ${\beta }_{\text{r}}^{(\text{c})}< {\beta }_{\text{e}}\le \frac{4}{7}$ , whereas the FMKdV soliton does not exist within the interval 0 < β e < β r ( c ) $0< {\beta }_{\text{e}}< {\beta }_{\text{r}}^{(\text{c})}$ . We have also discussed the effect of different parameters of the system on solitary waves obtained from the different evolution equations.

Proton wave function in a water molecule: Breakdown of degeneration caused by interactions with the magnetic field of a Magnetic Resonance Imaging device

The concept of a Magnetic Resonance Imaging (MRI) device is based on the emission of radio waves produced by the protons of the hydrogen atoms in water molecules when placed in a constant magnetic field after they interact with a pulsed radio frequency (RF) current. When the RF field is turned on, the protons are brought to a spin excited state. When the RF field is turned off, the MRI sensors are able to detect the energy released as the protons realign their spins with the magnetic field. In this work we provide a simple model to describe the basic physical mechanism responsible for the operation of MRI devices. We model the water molecule in terms of a central force problem, where the protons move around the (unstructured) doubly negatively charged oxygen atom. First, we employ an analytical treatment to obtain the system's wave function as well as its energy levels, which we show are degenerate. Next, the energy levels from the water molecule are studied in the presence of a uniform external magnetic field. As a result, they get shifted and the degeneration is lifted. We provide numerical results for a magnetic field strength commonly used in MRI devices.

A spin 1/2 particle with anomalous magnetic and electric dipole moments

It is Petras who first developed the P-symmetric theory for a spin 1/2 particle with an anomalous magnetic moment within the general Gel’fand – Yaglom approach. Recently, similarly it was introduced a P-asymmetric wave equation for a spin 1/2 particle which describes a particle with an electric dipole moment. In this paper, we study solutions of the equation for the P-asymmetric particle in presence of external magnetic fields. It turns out that the energy spectra are the same for P-asymmetric and P-symmetric particles. To clarify this coincidence, we demonstrate that there exists a simple transformation relating these two models, by which one wave equation can be reduced to the form of the other. Meanwhile, expressions for wave functions and P-reflection operators are different in these two theories. We extend this approach to the model in which both P-symmetric and P-asymmetric sectors are presented. The main result is the same, namely, there exists a simple, more general as compared with the mentioned above transformation relating the P-symmetric model and the model with two sectors, and expressions for wave functions and P-reflection operators are different in these two bases. We demonstrate that in the presence of an external uniform magnetic field, the energy spectra in the model with two sectors coincide with those in the P-symmetric theory. Thus, we develop a general theory for the P-asymmetric model and the model with two sectors within the Petras approach.

Diffraction by a Perfect Electromagnetic Conductor Half-Plane in an Anisotropic Plasma: An Integral Theory Approach

The diffraction of plane electromagnetic waves by a perfect electromagnetic conductor (PEMC) semi-infinite sheet which is embedded in an anisotropic medium is examined. The anisotropic region is modeled by a dielectric matrix. The external uniform magnetic field is taken as parallel to the edge of the semi-infinite sheet. Upon considering the H-polarized incident wave, the total scattered fields are obtained with the diffracted waves by using an integral theory which is associated with the scattered fields. The results are expressed in terms of the Fresnel functions. Thus, the wave behaviors at the transition boundaries are uniform. The solutions are compared numerically with the literature including limit values.

Considerations on anomalous photon and Z-boson self-couplings from the Born–Infeld weak hypercharge action

We investigate the effects of the Born–Infeld action on the Abelian sector of the electroweak model. The consequence of this approach is the emergence of anomalous couplings in the neutral sector of the Z-gauge boson and photon. These new couplings consist of quartic interactions of the photon with the Z-particle, as for example, three-photon-and-one-Z vertex. With that, we obtain the decay width of Z rightarrow 3,gamma from which we impose a bound on the Born–Infeld parameter. Other bounds are also obtained from the photon quartic couplings. Subsequently, we consider the presence of an external uniform magnetic field in connection with this Born–Infeld weak hypercharge model. The magnetic background field yields new kinematic effects, like the kinetic mixing between the photon and the Z-boson, and we obtain thereby the corresponding dispersion relations for the mixed photon-Z-particle system. Finally, we calculate the lowest-order modifications to the interaction energy for the anomalous coupling 3gamma -Z, within the framework of the gauge-invariant but path-dependent variables formalism. Our results show that the interaction energy contains a linear term leading to the confinement of static probe charges. With the help of the potential that comes out, interparticle forces are estimated.

Monte Carlo study of site disordered [formula omitted] Heisenberg models in the presence of a magnetic field and a weak random anisotropy

We study the 3d Heisenberg site disordered model with and without weak random anisotropy D in the presence of a uniform external longitudinal magnetic field using Monte Carlo methods. The spin and the chirality correlation lengths are measured. We provide evidence that the ”mixed chiral” phase is a chiral glass at a finite temperature transition TCG>0, whereas the spin glass temperature transition is at TSG=0 for D=0. In the anisotropic case we find that the model exhibited a strong evidence the occurrence of finite temperature transitions in the both sectors the spin and the chirality. Our estimate of the spin and chirality correlation-length exponents are compatible with our previous values obtained for the same model without anisotropy and the 3d Heisenberg spin glass.

Modulating thermal robustness and entanglement distribution in a two-dimensional dissipative spin system using impurities

We consider a finite two-dimensional Heisenberg triangular spin lattice coupled to a dissipative Markovian environment at finite temperature in the presence of an external uniform magnetic field. We show how inserting a magnetic impurity in the spin system can be used to effectively control the dynamics and asymptotic state of the system. A strong impurity, at a border or central site, was found to enhance its entanglement with the other spins and their thermal robustness to the dissipative environment reaching an asymptotic state that is independent of the system initial state. However, it reduces the entanglement among the other spins in the lattice and their thermal robustness and may diminish them depending on its strength and the environment temperature. Moreover, the effect of the impurity increases significantly as the degree of anisotropy of the spin system increases. Therefore, the entanglement distribution over the different sites of the lattice can be modulated by tuning the impurity strength, system anisotropy and environment temperature. The impurity can be used as a switch that turns the entanglement on among specific spins and off among others simultaneously.

All-Atom Simulation Method for Zeeman Alignment and Dipolar Assembly of Magnetic Nanoparticles.

Magnetic nanoparticles (MNPs) can organize into novel structures in solutions with excellent order and unique geometries. However, studies of the self-assembly of smaller MNPs are challenging due to a complicated interplay between external magnetic fields and van der Waals, electrostatic, dipolar, steric, and hydrodynamic interactions. Here, we present a novel all-atom molecular dynamics simulation method to enable detailed studies of the dynamics, self-assembly, structure, and properties of MNPs as a function of core sizes and shapes, ligand chemistry, solvent properties, and external field. We demonstrate the use and effectiveness of the model by simulating the self-assembly of oleic acid ligand-functionalized magnetite (Fe3O4) nanoparticles, with spherical and cubic shapes, into rings, lines, chains, and clusters under a uniform external magnetic field. We found that the long-range electrostatic interactions can favor the formation of a chain over a ring, the ligands promote MNP cluster growth, and the solvent can reduce the rotational diffusion of the MNPs. The algorithm has been parallelized to take advantage of multiple processors of a modern computer and can be used as a plugin for the popular simulation software LAMMPS to study the behavior of small MNPs and gain insights into the physics and chemistry of different magnetic assembly processes with atomistic details.

Study of melting of paraffin dispersed with copper nanoparticles in square cavity subjected to external magnetic field

The addition of high thermal conductivity nanoparticles in a phase change material (PCM) is an effective way to improve the thermal performance of the latent heat energy storage system. The present work uses paraffin wax as a PCM, and copper (Cu) nanoparticles are added for thermal conductivity enhancement. The thermal performance of the PCM dispersed with Cu nanoparticles in a square cavity during the melting process is numerically investigated. The enthalpy porosity approach is used to capture the melting of the PCM in the enclosure. The effect of orientation of the heated wall of the square cavity and volume fraction of the Cu nanoparticles on the melting rate and energy storage capacity is evaluated. Subsequently, a uniform external magnetic field in the horizontal direction is imposed on the square cavity filled with nano-enhanced PCM. Further, a parametric study on the strength of the magnetic field based on Hartmann number is performed to analyze the heat transfer and fluid flow characteristics of the PCM during the melting process. The melting rate of PCM and the energy storage capacity of nano-enhanced PCM are found maximum at 2% and 0.5% concentration of Cu nanoparticles, respectively. Additionally, with the increase in the strength of the external magnetic field, a decline in the melting rate and energy storage capacity is observed.

Effect of horizontal aspect ratio on magnetoconvective instabilities in liquid metals

Three-dimesional direct numerical simulations are performed to investigate the effect of the horizontal aspect ratio on magnetoconvective instabilities using plane layer Rayleigh-B\'enard geometry in the presence of an external uniform horizontal magnetic field. The onset of oscillatory instability is found to scale with magnetic field strength with two distinct scaling laws. The scaling exponent gradually decreases with the increment in the aspect ratio. Different transition routes to chaos have been found depending on the aspect ratio and the magnetic field strength. We find that transient chaotic flow reversals eventually lead to persistent chaotic flow reversals.

Numerical and experimental investigation of a magnetic micromixer under microwires and uniform magnetic field

With the development in biomedical and biotechnological areas, novel and efficient microfluidic devices integrated with sufficient and rapid mixing function have been attracting enormous scientific attention as versatile and robust platform for low cost and non-contact biological analysis and diagnose. Here, we design and fabricate a magnetic micromixer integrated with special designed microwires, a Y-shaped microchannel and uniform magnetic field for realizing rapid mixing between ferrofluid and deionized water. A comprehensive analysis on the dynamic behavior of ferrofluid is performed by using 3D Eulerian-Eulerian model. Good consistency between experiment and numerical results demonstrates that the enhanced mixing in the presence of longitudinally arranged microwires is due to the introduction of eddies, whose impacts are strengthened with the increase of the number of microwires (nw). However, increasing nw requires a long microchannel and long time to complete mixing. In order to further improve the mixing performance of our micromixer, a horizontally arranged microwire combined with a particular uniform magnetic field is proposed to provide enough magnetic force for enhancing the mixing of ferrofluid and deionized water, receiving optimal mixing efficiency 99.06%. The flexible tunability of external uniform magnetic field enables desired performance of our designed system.

Heat transfer analysis and entropy generation in the nanofluids composed by Aluminum and [formula omitted] Aluminum oxides nanoparticles

A porous rotating disk is used to study the second law of thermodynamics in relation to an electrically conducting, incompressible γ− alumina nanofluid. An external uniform vertical magnetic field. Base fluids are ethylene glycol and water. Alumina nanofluids make use of the experimentally derived viscosity and thermal conductivity models, as well as Brinkman viscosity and Maxwell's thermal conductivity models. Nuclear propulsion space vehicles can use the results of this research in rotating magnetohydrodynamic (MHD) energy generators and also thermal conversion processes. With shooting approach, fourth order Runge–Kutta method is used to solve the governing boundary layer equations numerically. The entropy generation equation can be obtained from the velocity and temperature gradients, respectively. There is a high level of agreement between the current study's findings and those of previously published studies. Using geometric and physical flow field-dependent parameters, this equation is nondimensional. Researchers have discovered that there are three types of velocity profiles that can be obtained: radial (or circumferential) velocity profiles, and tangential velocity profiles (radial velocity profiles). The influence of nanofluid type on fluid velocity, temperature, entropy generation, Bejan number, skin friction coefficient, and Nusselt number has been investigated. The same nanoparticles are expected to behave differently in temperature profiles with water and ethylene glycol. As well as demonstrating the potential of using magnetic rotating disk motors in revolutionary nuclear space propulsion engines, this model is valuable for increasing heat transfer in renewable energy systems and industrial thermal management.

Holographic Abrikosov lattice: Vortex matter from black hole

The $\mathrm{AdS}/\mathrm{CFT}$ correspondence provides a unique way to study the vortex matter phases in superconductors. We solve the dynamical evolution of a superconductor in $2+1$ dimensions at a finite temperature subjected to a magnetic field quench in terms of a gravitational ``hairy black hole'' dual living in an asymptotic ${\mathrm{AdS}}_{4}$ space. We exploit this to determine the nature of the equilibrium states realized at long times after the quench of this two dimensional type II superconductor in a perpendicular external uniform magnetic field ${B}_{0}$. This holographic superconductor exhibits the generic lower (${B}_{c1}(T)$) and upper (${B}_{c2}(T)$) critical fields. For ${B}_{0}<{B}_{c1}(T)$ the magnetic field is completely expelled revealing the Meissner phase, while the superconductivity is destroyed when ${B}_{0}>{B}_{c2}(T)$. Abrikosov lattices appear in the range ${B}_{c1}(T)<{B}_{0}<{B}_{c2}(T)$ that realize various configurations in the form of hexagonal, square and slightly irregular square lattices pending the magnetic field strength and the influence of finite size boundaries. We show this to be consistent with the expectations of Ginzburg-Landau theory where the upper and lower critical fields are associated with the inverse squares of the coherence length and magnetic penetration depth, respectively.

An Implicit, Conservative and Asymptotic-Preserving Electrostatic Particle-in-Cell Algorithm for Arbitrarily Magnetized Plasmas in Uniform Magnetic Fields

We introduce a new electrostatic particle-in-cell algorithm capable of using large timesteps compared to particle gyro-period under a uniform external magnetic field. The algorithm extends earlier electrostatic fully implicit PIC implementations with a new asymptotic-preserving particle-push scheme that allows timesteps much larger than particle gyroperiods. In the large-timestep limit, the integrator preserves all the averaged particle drifts, while recovering the full orbit for small timesteps. The scheme allows for a seamless, efficient treatment of particles with coexisting magnetized and unmagnetized species, and conserves energy and charge exactly without spoiling implicit solver performance. We demonstrate by numerical experiment with several problems of variable species magnetization (diocotron instability, modified two-stream instability, and drift instability) that orders of magnitude wall-clock-time speedups vs. the standard fully implicit electrostatic PIC algorithm are possible without sacrificing solution accuracy.

Синтез и свойства полиакриламидных феррогелей, наполненных магнитными наночастицами гексаферрита стронция

Ferrogels based on polyacrylamide with embedded magnetic particles of strontium hexaferrite SrFe12O19 with their content up to 17.9 wt. % have been synthesized and studied. The enthalpy of adhesion of polyacrylamide to the surface of particles was determined by the calorimetric method using a thermochemical cycle. Its negative values indicate good adhesion. This leads to a significant decrease in the degree of swelling of ferrogels with increasing particle content. The modulus of elasticity of ferrogels was measured under uniaxial compression with and without an external uniform magnetic field of 27.5 mT. The effect of a uniform magnetic field of 420 mT on the magnetostriction of ferrogels has been studied. It has been shown that ferrogels based on polyacrylamide filled with strontium hexaferrite underwent universal stretching in a magnetic field, leading to an increase in their volume and additional swelling.

Performance Analysis of Magnetic Nanoparticles during Targeted Drug Delivery: Application of OHAM

In recent years, the emergence of nanotechnology experienced incredible development in the field of medical sciences. During the past decade, investigating the characteristics of nanoparticles during fluid flow has been one of the intriguing issues. Nanoparticle distribution and uniformity have emerged as substantial criteria in both medical and engineering applications. Adverse effects of chemotherapy on healthy tissues are known to be a significant concern during cancer therapy. A novel treatment method of magnetic drug targeting (MDT) has emerged as a promising topical cancer treatment along with some attractive advantages of improving efficacy, fewer side effects, and reduce drug dose. During magnetic drug targeting, the appropriate movement of nanoparticles (magnetic) as carriers is essential for the therapeutic process in the blood clot removal, infection treatment, and tumor cell treatment. In this study, we have numerically investigated the behavior of an unsteady blood flow infused with magnetic nanoparticles during MDT under the influence of a uniform external magnetic field in a micro-tube. An optimal homotopy asymptotic method (OHAM) is employed to compute the governing equation for unsteady electromagnetohydrodynamics flow. The influence of Hartmann number (Ha), particle mass parameter (G), particle concentration parameter (R), and electro-osmotic parameter (k) is investigated on the velocity of magnetic nanoparticles and blood flow. Results obtained show that the electro-osmotic parameter, along with Hartmann’s number, dramatically affects the velocity of magnetic nanoparticles, blood flow velocity, and flow rate. Moreover, results also reveal that at a higher Hartman number, homogeneity in nanoparticles distribution improved considerably. The particle concentration and mass parameters effectively influence the capturing effect on nanoparticles in the blood flow using a micro-tube for magnetic drug targeting. Lastly, investigation also indicates that the OHAM analysis is efficient and quick to handle the system of nonlinear equations.