Magnetic Fields Of Order Research Articles

Pre-earthquake magnetic pulses

Abstract. A semiconductor model of rocks is shown to describe unipolar magnetic pulses, a phenomenon that has been observed prior to earthquakes. These pulses are suspected to be generated deep in the Earth's crust, in and around the hypocentral volume, days or even weeks before earthquakes. Their extremely long wavelength allows them to pass through kilometers of rock. Interestingly, when the sources of these pulses are triangulated, the locations coincide with the epicenters of future earthquakes. We couple a drift-diffusion semiconductor model to a magnetic field in order to describe the electromagnetic effects associated with electrical currents flowing within rocks. The resulting system of equations is solved numerically and it is seen that a volume of rock may act as a diode that produces transient currents when it switches bias. These unidirectional currents are expected to produce transient unipolar magnetic pulses similar in form, amplitude, and duration to those observed before earthquakes, and this suggests that the pulses could be the result of geophysical semiconductor processes.

Effect of magnetic field during the liquid – solid phase transition of some thermoplastic polymers

Application of external fields on a polymer is common physical treatment for modifying the polymer properties. The field is applied on the final polymeric object or during synthesising or polymerization. In this work, the magnetic field from powerful permanent magnets was applied during the phase transition from liquid to solid phase, where the polymer chain inter-attraction forces are minimal. So, magnetic fields with less strength may perform valuable structural variations. It is found that magnetic field of 355 mT accelerated the spherulite growth in polyethylene glycol (PEG) films. High density polyethylene (HDPE) of zigzag chain, polypropylene (PP) of chains with side group and polystyrene (PS) as glassy polymer with ring, were magnetically treated with different field strength during their phase transition. Treated and untreated film samples were tested physically. IR- spectroscopy, X-ray diffraction, DTA, DSC and tensile stress – strain testing techniques were used in order to characterize, quantitatively, most types of the occurred variations if any. PS samples were casted by hot pressing and from dilute solution in magnetic field in order to detect the effect of solidification time on the size of the magnetic induced variations. Properties of treated HDPE showed little swinging about the untreated value in the field strength up to 160 mT. PP properties showed serious variations in the same range of field strength. PS films casted from dilute solution showed stronger variations than the films casted by hot pressing of the melted PS. All data are presented in coloured graphs. Spherulites images are extracted from a video clip that is used in measuring the rate of PEG spherulite growth in magnetic fields.

Structural and magnetic properties of iron nanowires and iron nanoparticles fabricated through a reduction reaction.

The main goal of this work is to study the structural and magnetic properties of iron nanowires and iron nanoparticles, which have been fabricated in almost the same processes. The only difference in the synthesis is an application of an external magnetic field in order to form the iron nanowires. Both nanomaterials have been examined by means of transmission electron microscopy, energy dispersive X-ray spectrometry, X-ray diffractometry and Mössbauer spectrometry to determine their structures. Structural investigations confirm that obtained iron nanowires as well as nanoparticles reveal core–shell structures and they are composed of crystalline iron cores that are covered by amorphous or highly defected phases of iron and iron oxides. Magnetic properties have been measured using a vibrating sample magnetometer. The obtained values of coercivity, remanent magnetization, saturation magnetization as well as Curie temperature differ for both studied nanostructures. Higher values of magnetizations are observed for iron nanowires. At the same time, coercivity and Curie temperature are higher for iron nanoparticles.

Mechanical behaviour of magnetic Silly Putty: Viscoelastic and magnetorheological properties

In this work the mechanical and viscoelastic properties of magnetic Silly Putty are investigated. Silly Putty is a non-Newtonian material whose response depends on the rate at which it is deformed. For a rapid deformation, it behaves as an elastic solid, while over a relatively long time scale, the polymer molecules can be untangled and it flows as a fluid. The purpose of this article is to study the behaviour of this material firstly under a quasi-static compression and shear loading, and secondly under dynamic shear loading. The Silly Putty under study has a volume fraction of ferromagnetic particles. Hence, both quasi-static and dynamic stress are coupled with several strengths of magnetic field in order to assess the influence of the magnetisation on the mechanical and viscoelastic properties of the material. The approach adopted in this work followed the Design of Experiment method so that evaluating the influence of the variables and their interactions on the system response is possible. The results highlight a strong dependence on the deformation rate, while the influence of the magnetic field is weak, especially under dynamic shear tests in which the viscous components are predominant.

Asymmetric magnetoimpedance effect in ferromagnetic multilayered biphase films

We investigate the magnetoimpedance effect in ferromagnetic multilayered biphase films. We verify that the films present asymmetric magnetoimpedance behavior and, by playing with the number of the repetitions of the base structure of the multilayer and the probe current frequency, we explore the possibility of tailoring the linear region around zero magnetic field in order to achieve higher sensitivity values. The highest sensitivity is observed for the thicker film, reaching ∼15mΩ/Oe at ∼0.52GHz. Thus, the results open the possibilities for application of ferromagnetic multilayered biphase films with asymmetric magnetoimpedance effect in sensors devices.

Can One Hear Whistler Waves?

The aim of this article is to propose a mathematical framework giving access to a better understanding of whistler-mode chorus emissions in space plasmas. There is presently a general agreement that the emissions of whistler waves involve a mechanism of wave-particle interaction which can be described in the framework of the relativistic Vlasov-Maxwell equations. In dimensionless variables, these equationsinvolve a penalized skew-symmetric term where the inhomogeneity of the strong exterior magnetic field plays an essential part. The description of the related phenomena is achieved in two stages. The first is based on a new approach allowing to extend in longer times the classical insights on fast rotating fluids; it justifies the existence and the validity of long time gyro-kinetic equations; it furnishes criterions to impose on a magnetic field in order to obtain the long time dynamical confinement of plasmas. The second stage is based on a study of oscillatory integrals implying special phases; it deals with the problem of the creation of light inside plasmas.

Use of anisotropy of light transmittance in a system to measure the frequency of nanowires' rotation in a viscous liquid

Fe nanowires with diameters of ca. 80nm and lengths ranging from 1 to 3μm were immersed in a viscous liquid and exposed to a static magnetic field in order to orient them in a specific direction. The nanowire suspension was illuminated with a laser beam. The light intensity was measured at the input and output. It was observed that the light transmittance of the nanowire system was strongly dependent on the nanowires' orientation in relation to the laser beam. The phenomenon was applied to measure the rotation frequency of the nanowires immersed in a liquid with a viscosity of 2Pa·s. Rotation of the nanowires was enforced by a rotating magnetic field generated by a rotating magnet. On the basis of the obtained results it was observed that the highest frequency of the nanowires' rotation in the applied liquid, in a rotating magnetic field with induction of 46mT, exceeded 382Hz.

Von Zeipel’s theorem for a magnetized circular flow around a compact object

We analyze a class of physical properties, forming the content of the so-called von Zeipel theorem, which characterizes stationary, axisymmetric, non-selfgravitating perfect fluids in circular motion in the gravitational field of a compact object. We consider the extension of the theorem to the magnetohydrodynamic regime, under the assumption of an infinitely conductive fluid, both in the Newtonian and in the relativistic framework. When the magnetic field is toroidal, the conditions required by the theorem are equivalent to integrability conditions, as it is the case for purely hydrodynamic flows. When the magnetic field is poloidal, the analysis for the relativistic regime is substantially different with respect to the Newtonian case and additional constraints, in the form of PDEs, must be imposed on the magnetic field in order to guarantee that the angular velocity $\Omega$ depends only on the specific angular momentum $\ell$. In order to deduce such physical constraints, it is crucial to adopt special coordinates, which are adapted to the $\Omega={\rm const}$ surfaces. The physical significance of these results is briefly discussed.

Continuous-wave lasing between Landau levels in graphene

We predict the general feasibility and demonstrate the specific design of the THz laser operating between Landau levels in graphene placed on a polar substrate in a magnetic field of order 1 T. Steady state operation under a continuous wave optical pumping is possible due to an interplay between Auger and surface-phonon mediated relaxation of carriers. The scheme is scalable to other materials with massless Dirac fermions, for example surface states in 3D topological insulators such as Bi$_2$Se$_3$ or Bi$_2$Te$_3$.

Applying the cold plasma dispersion relation to whistler mode chorus waves: EMFISIS wave measurements from the Van Allen Probes.

Most theoretical wave models require the power in the wave magnetic field in order to determine the effect of chorus waves on radiation belt electrons. However, researchers typically use the cold plasma dispersion relation to approximate the magnetic wave power when only electric field data are available. In this study, the validity of using the cold plasma dispersion relation in this context is tested using Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) observations of both the electric and magnetic spectral intensities in the chorus wave band (0.1–0.9 fce). Results from this study indicate that the calculated wave intensity is least accurate during periods of enhanced wave activity. For observed wave intensities >10−3 nT2, using the cold plasma dispersion relation results in an underestimate of the wave intensity by a factor of 2 or greater 56% of the time over the full chorus wave band, 60% of the time for lower band chorus, and 59% of the time for upper band chorus. Hence, during active periods, empirical chorus wave models that are reliant on the cold plasma dispersion relation will underestimate chorus wave intensities to a significant degree, thus causing questionable calculation of wave-particle resonance effects on MeV electrons.

Control over electronic components by their magnetic field

We show the results of our studies related to control over objects by the magnetic field they generate. We propose a model to compute the current and its magnetic field in a conductor with a rectangular defect. We describe the developed and produced anisotropic magnetoresistive gradiometer head to measure surface magnetic fields in order to control the functionality of electronic components by the magnetic field they generate. We describe the operation of a testbed with a test circuit in the plotter.

T 1 relaxation measurement of ex-vivo breast cancer tissues at ultralow magnetic fields.

We investigated T 1 relaxations of ex-vivo cancer tissues at low magnetic fields in order to check the possibility of achieving a T 1 contrast higher than those obtained at high fields. The T 1 relaxations of fifteen pairs (normal and cancerous) of breast tissue samples were measured at three magnetic fields, 37, 62, and 122 μT, using our superconducting quantum interference device-based ultralow field nuclear magnetic resonance setup, optimally developed for ex-vivo tissue studies. A signal reconstruction based on Bayesian statistics for noise reduction was exploited to overcome the low signal-to-noise ratio. The ductal and lobular-type tissues did not exhibit meaningful T 1 contrast values between normal and cancerous tissues at the three different fields. On the other hand, an enhanced T 1 contrast was obtained for the mucinous cancer tissue.

Instrument for in-situ orientation of superconducting thin-film resonators used for electron-spin resonance experiments

When used in electron-spin resonance measurements, superconducting thin-film resonators must be precisely oriented relative to the external magnetic field in order to prevent the trapping of magnetic flux and the associated degradation of resonator performance. We present a compact design solution for this problem that allows in-situ control of the orientation of the resonator at cryogenic temperatures. Tests of the apparatus show that when proper alignment is achieved, there is almost no hysteresis in the field dependence of the resonant frequency.

Planar Alignment of Isolated Magnetic Disks in Newtonian Fluids by a Rotating Field

Magnetic anisotropy can be induced in soft magnetic composites by aligning constituent anisotropic magnetic particles. While the uniaxial alignment by a constant field has been extensively investigated, reported studies on alignment of magnetic particles in a rotating field lack experimental validation. In this effort, we present a systematic experimental and theoretical investigation of the alignment dynamics of isolated disk-shaped magnetic particles in a planar rotating magnetic field in order to fabricate composites with planar anisotropy. The theoretical model is developed assuming: 1) quiescent flow field, 2) low-Reynolds-number Stokes flow, 3) negligible Brownian motion, and 4) oblate-ellipsoid approximation for the magnetic disks. The model is experimentally verified by optical microscopy of disk suspensions for varied rotating field strength and frequency, fluid viscosity, and disk size. Good agreement is obtained between the predicted and measured results, yielding insight to parameters important for the control of anisotropy of composite magnetic materials.

EFFECTS OF MAGNETIC FIELDS ON SOLITON MEDIATED CHARGE TRANSPORT IN BIOLOGICAL SYSTEMS

In this paper, we analyze biological effects produced by magnetic fields in order to elucidate the physical mechanisms, which can produce them. We show that there is a chierarchy of such mechanisms and that the mutual interplay between them can result in the synergetic outcome. In particular, we analyze the biological effects of magnetic fields on soliton mediated charge transport in the redox processes in living organisms. Such solitons are described by nonlinear systems of equations and represent electrons that are self-trapped in alpha-helical polypeptides due to the moderately strong electron-lattice interaction. They represent a particular type of disssipativeless large polarons in low-dimensional systems. We show that the effective mass of solitons in the is different from the mass of free electrons, and that there is a resonant effect of the magnetic fields on the dynamics of solitons, and, hence, on charge transport that accompanies photosynthesis and respiration. These effects can result in non-thermal resonant effects of magnetic fields on redox processes in particular, and on the metabolism of the organism in general. This can explain physical mechanisms of therapies based on applying magnetic fields.

Airfoil Linear Wind Generator (ALWG): As A Novel Wind Energy Extraction Approach

Linear wind generator (LWG) is a sufficient way of wind energy harnessing process. However, complicated LWG energy extraction mechanism such as complex system for transferring linear motion to rotational motion and problems related to changing the angle of attack is resulted to energy dissipation. In the other hand the linear generator that delivers ocean wave energy to electricity has been developed as a new renewable energy extraction method. Some of the problems associated with this technology are corrosion, high cost of manufacturing, high requirement for installation and construction, economical consideration, etc. In the most recent works, low dissipation energy in mechanism, low cost, simplicity and high performance are highly regarded as environmentally friendly methods for wind energy extraction mechanisms. In the current study, we would like to introduce a new and efficient method to extract wind energy using airfoil linear wind generator(ALWG). ALWG is a new method that produces liner reciprocating motion via attached airfoils to a mover in a magnetic field in order to generate electricity. The most important advantage of ALWG is its simplicity and its compatibility to all wind situations that can be more controllable relative to ocean-based and also relative to LWG that become challengeable problem.

The Next Generation BLAST Experiment

The Balloon-borne Large Aperture Submillimeter Telescope for Polarimetry (BLASTPol) was a suborbital experiment designed to map magnetic fields in order to study their role in star formation processes. BLASTPol made detailed polarization maps of a number of molecular clouds during its successful flights from Antarctica in 2010 and 2012. We present the next-generation BLASTPol instrument (BLAST-TNG) that will build off the success of the previous experiment and continue its role as a unique instrument and a test bed for new technologies. With a 16-fold increase in mapping speed, BLAST-TNG will make larger and deeper maps. Major improvements include a 2.5-m carbon fiber mirror that is 40% wider than the BLASTPol mirror and ~3000 polarization sensitive detectors. BLAST-TNG will observe in three bands at 250, 350, and 500 μm. The telescope will serve as a pathfinder project for microwave kinetic inductance detector (MKID) technology, as applied to feedhorn-coupled submillimeter detector arrays. The liquid helium cooled cryostat will have a 28-day hold time and will utilize a closed-cycle 3 He refrigerator to cool the detector arrays to 270 mK. This will enable a detailed mapping of more targets with higher polarization resolution than any other submillimeter experiment to date. BLAST-TNG will also be the first balloon-borne telescope to offer shared risk observing time to the community. This paper outlines the motivation for the project and the instrumental design.

Closed-Loop Control of a Self-Positioning and Rolling Magnetic Microrobot on 3D Thin Surfaces Using Biplane Imaging

We propose a control methodology to precisely manipulate a self-positioning and rolling magnetic microrobot (SPRMM) along a complex moving path on a 3D thin surface. We introduce a closed-loop algorithm to control an external rotating magnetic field in order to precisely manipulate the SPRMM along a predefined arbitrary moving path. We also construct a biplane, vision-based image processing procedure to obtain the real-time 3D position of the SPRMM. We then construct an experimental setup to demonstrate precise rolling locomotion of the SPRMM on a 3D, complex thin surface.

Particle modelling of low-pressure radio-frequency magnetron discharges including the effects of self-induced electromagnetic fields

Modelling of radio-frequency (RF) magnetron discharges is performed using a particle-in-cell/Monte Carlo technique in the case of low-pressure argon gas at 4 mTorr and high external magnetic field in order to self-maintain the discharge and to generate an energetic quasi-ion beam required for cathode sputtering applications. An emphasis is made, for the first time in the literature in the case of low-pressure RF discharges, on the development of a particle model coupled with the full set of electromagnetic field equations. The aim is to analyse the effect on the RF plasma features of the plasma-induced magnetic field resulting from the coupling of the Maxwell–Ampere equation. We also analysed the effect of the electric field due to the time variation of magnetic field resulting from the coupling of the Maxwell–Faraday equation. For the present asymmetrical plasma reactor, the mean relative difference on, for instance, the ion density with and without the consideration of plasma-induced magnetic and electric fields due to the time variation of the magnetic field can reach about 2.5% in the region of the plasma bulk and about 10% in the lateral sheath. The effects of these two induced electromagnetic fields are in fact higher in the regions where the radial magnetic field generated by the external magnets belonging to the magnetron configuration is low. These non-negligible relative differences clearly show the importance of rigorously taking into account, beyond the usual Poisson's equation for the space charge electric field, the full set of electromagnetic Maxwell equations for a more accurate modelling of these low-pressure discharges, particularly when the total current density reaches a few mA cm−2.

TIDALLY DRIVEN DYNAMOS IN A ROTATING SPHERE

Large-scale planetary or stellar magnetic fields generated by a dynamo effect are mostly attributed to flows forced by buoyancy forces in electrically conducting fluid layers. However, these large-scale fields may also be controlled by tides, as previously suggested for the star $\tau$-boo, Mars or the Early Moon. By simulating a small local patch of a rotating fluid, \cite{Barker2014} have recently shown that tides can drive small-scale dynamos by exciting a hydrodynamic instability, the so-called elliptical (or tidal) instability. By performing global magnetohydrodynamic simulations of a rotating spherical fluid body, we investigate if this instability can also drive the observed large-scale magnetic fields. We are thus interested by the dynamo threshold and the generated magnetic field in order to test if such a mechanism is relevant for planets and stars. Rather than solving the problem in a geometry deformed by tides, we consider a spherical fluid body and add a body force to mimic the tidal deformation in the bulk of the fluid. This allows us to use an efficient spectral code to solve the magnetohydrodynamic problem. We first compare the hydrodynamic results with theoretical asymptotic results, and numerical results obtained in a truely deformed ellipsoid, which confirms the presence of the elliptical instability. We then perform magnetohydrodynamic simulations, and investigate the dynamo capability of the flow. Kinematic and self-consistent dynamos are finally simulated, showing that the elliptical instability is capable of generating dipole dominated large-scale magnetic field in global simulations of a fluid rotating sphere.