Increasing Field Strength Research Articles

Reddening and darkening trends of on/off swirls and the relationship with magnetic field strength

AbstractLunar swirls are albedo features associated with magnetic anomalies, and their formation mechanism has long been debated. Because spectral properties of lunar swirls provide information on space weathering environments and surface compositions, differences in the spectra between swirls and background regions can give a clue to their formation. We analyze space weathering for swirls in the lunar highlands and maria using the VIS-NIR spectral slope, 1550 nm reflectance, and 950 nm band depth. We find that highland swirls show lower reddening-to-darkening ratios than off-swirl regions, implying more decreases of nanophase iron relative to microphase iron on swirls. We also use magnetic field data to investigate the influence of the crustal magnetic field on the space weathering of a few selected swirls. The Reiner Gamma swirl becomes more immature as the magnetic field strength increases, although the entire swirl has a high albedo. Especially, the Reiner Gamma tail shows that the stronger magnetic field makes the surface undergo less spectral reddening. Our results support the solar wind stand-off hypothesis, which is that the solar wind deflected by the crustal field determines the optical property of the surface.

A New Reconstruction of the Sun’s Magnetic Field and Total Irradiance since 1700

Abstract We model the Sun’s large-scale magnetic field and total solar irradiance (TSI) since 1700 by combining flux transport simulations with empirical relationships between facular brightening, sunspot darkening, and the total photospheric flux. The photospheric field is evolved subject to the constraints that (1) the flux emergence rate scales as the yearly sunspot numbers, and (2) the polar field strength at solar minimum is proportional to the amplitude of the following cycle. Simulations are performed using both the recently revised sunspot numbers and an average of these numbers and the Hoyt–Schatten group numbers. A decrease (increase) in the polar field strength from one cycle to the next is simulated either by increasing (decreasing) the poleward flow speed, or by decreasing (increasing) the average axial tilts of active regions; the resulting photospheric field evolution is very similar whichever parameter is varied. Comparisons between irradiance data and both the simulated and observed photospheric field suggest that TSI and facular brightness increase less steeply with the field strength at solar minimum than at other phases of the cycle, presumably because of the dominance of small-scale ephemeral regions when activity is very low. This relative insensitivity of the irradiance to changes in the large-scale field during cycle minima results in a minimum-to-minimum increase of annual TSI from 1700 to 1964 (2008) of 0.2 (0.06) W m−2, a factor of 2–3 smaller than predicted in earlier reconstructions where the relation between facular brightness and field strength was assumed to be independent of cycle phase.

Effects of Gradient Magnetic Field on Charge Behavior and Electrical Tree Growth in Epoxy Resin

In this paper, a high-field magnet experimental system is setup to investigate the dielectric properties of epoxy resin in the presence of high magnetic field. An asymmetric ferromagnetic electrode system is used to build gradient magnetic field and investigate its effect on tree characteristics of epoxy resin. Influence mechanisms of gradient magnetic field on dielectric properties and tree characteristics of epoxy resin are discussed through combining experimental results and simulation calculation. Experimental results show that electrical trees are more easily to be initiated and spread more rapidly in gradient magnetic field. The conductivity of the epoxy resin increases with the increase of magnetic field strength due to energy level splitting, which is analyzed through electrodynamics calculation. The relative permittivity decreases, and the dielectric loss tangents increase when high magnetic field is applied. Changes of conductivity and relative permittivity affect the charge behavior and electric field distribution in epoxy resin, resulting in the particular electrical tree.

Effect of plaque geometry on targeted delivery of stem cells containing magnetic particles in a rigid and elastic curved artery with stenosis

Magnetic drug targeting (MDT) is a new and effective therapeutic technique to treat some diseases. In this method, the transfer of magnetic particles labeled with therapeutic agents in the presence of a magnetic field increases the efficiency of treatment. In this study, targeted delivery of endothelial cells containing magnetic particles in a stenosed curved artery for solid and elastic wall states was investigated, using an external magnetic field. The Eulerian-Lagrangian approach and the Eulerian-Lagrangian coupled FSI technique were employed to solve the continuum equations and track the trajectory of cells in a rigid and elastic artery, respectively. The influence of parameters was investigated, such as the mass of magnetic particles injected in each cell, the magnetic field strength, the injection time, the occlusion percentage, and the chord length of stenosis on the capture efficiency (CE). The effect of wall elasticity on CE was also studied. The results reveal that by increasing the mass of magnetic particles injected in each cell from 20 pg to 300 pg, the cells absorption at the target site is enhanced from 17% to 43%. Also, a slight increase in the magnetic field strength has a significant effect on increasing the CE. The injection of cells in a complete period of the cardiac cycle provides greater CE than other systole and diastole intervals. Examining the stenosis morphology shows that reducing the occlusion percentage from 40% to 20% and the chord length of stenosis from 70° to 30° results in an increase in the CE about 6% and 3% for 300 pg of magnetic particles in each cell, respectively. The trend of CE changes is the same for elastic artery and the rigid artery. However, in all cases, the elastic artery has a higher CE than the rigid artery. The obtained results can be useful for the treatment of atherosclerosis in curved vessels using targeted cell delivery.

Investigation on the evolution and distribution of plasma in magnetic field assisted laser-induced plasma micro-machining

Magnetically Controlled Laser-induced Plasma Micro-Machining (MC-LIPMM), compared to traditional direct laser ablation, has the ability of achieving better machining characteristics including larger aspect ratios of machined features, a smaller heat affected zone and more diverse micro-structures. To reveal the process mechanisms affected by the magnetic field, this paper studies the evolution and distribution of plasma in MC-LIPMM by analytical and experimental methods. An analysis of the confinement effect and enhanced collision of electrons-ions in the plasma in the presence of a magnetic field is performed for revealing the influence of the magnetic field on its diffusion and geometric size. To validate our theoretical predictions, experiments were conducted to analyze the effects of key process parameters on the geometrical size, shape and fluence of the plasma. Edge contour extracting and elliptic formula fitting algorithms were applied for quantitatively evaluating the changes. The experimental results show that transverse magnetic fields generate a larger plasma plume and change its shape from spherical to ellipsoidal compared to that without a magnetic field. The eccentricity of the ellipsoidal plasma exhibits a parabolic growth while the cross-sectional area of the fitted ellipse shows a linear growth as the transverse magnetic field strength increases. Greater growth in geometric size and intensity of the plasma was obtained under a longitudinal compared to a transverse magnetic field, and its shape changed into an elongated ellipsoid. Moreover, a two-dimensional magnetic field, combining both the transverse and the longitudinal magnetic field component, was shown to produce a larger area and intensity of spherical plasma under an appropriate transverse and longitudinal magnetic field strength compared to that without a magnetic field.

Effect of external static magnetic field on the particle distribution, the metallurgical process and the microhardness of Sn3.5Ag solder with magnetic Ni particles

PurposeThis paper aims to investigate the mechanism of Ni particles distribution in the liquid Sn3.5Ag melt under the external static magnetic field. The control steps of Ni particles and the Sn3.5Ag melt metallurgical process were studied. After aging, the microhardness of pure Sn3.5Ag, Sn3.5Ag containing randomly distributed Ni particles and Sn3.5Ag containing columnar Ni particles were compared.Design/methodology/approachPlace the sample in a crucible for heating. After the sample melts, place a magnet directly above and below the sample to provide a magnetic field. Sn3.5Ag with the different morphological distribution of Ni particles was obtained by holding for different times under different magnetic field intensities. Finally, pure Sn3.5Ag, Sn3.5Ag with random distributed Ni particles and Sn3.5Ag with columnar Ni particles were aged and their microhardness was tested after aging.FindingsThe experimental results show that with the increase of magnetic field strength, the time for Ni particle distribution in Sn3.5Ag melt to reach equilibrium is shortened. After aging, the microhardness of Sn3.5Ag containing columnar nickel particles is higher than that of pure Sn3.5Ag and Sn3.5Ag containing randomly distributed nickel particles. A chemical reaction is the control step in the metallurgical process of nickel particles and molten Sn3.5Ag.Originality/valueUnder the action of the magnetic field, Ni particles in Sn3.5Ag melt will be arranged into columns. With the increase of magnetic field strength, the shorter the time for Ni particles in Sn3.5Ag melt to arrange in a column. With the extension of the service time of the solder joint, if Sn3.5Ag with columnar nickel particles is used as the solder joint material, its microhardness is better than Sn3.5Ag with arbitrarily distributed nickel particles and pure Sn3.5Ag.

Nanostructuring of Mn(II)Pc thin films by vacuum deposition in a weak magnetic field

Manganese phthalocyanine, Mn(II)Pc, is a disc-like paramagnetic molecule whose unusual electronic structure have been studied for decades. However, no credible results on the direct impact of intrinsic molecular magnetism on the solid state properties of Mn(II)Pc are known. In this work, the Mn(II)Pc films were deposited by thermal vacuum evaporation with and without applying an external static magnetic field with a strength of a few tenths of a Tesla to the growth zone. Evolution of the microstructure of the thus formed films was documented using XRD, SEM, AFM and optical methods. In the field-free conditions, the Mn(II)Pc films deposited on the hot substrate are rather smooth, continuous and strongly textured. Large needle-like crystals (whiskers) grow when magnetic field is turned on, without noticeable correlation with the direction of field lines. However, the density of whiskers per unit area increases with increasing field strength. Possible explanations of the growth mechanism include molecular surface diffusion, adsorption energy lowering and Lorentz force but none of them is yet internally consistent.

Numerical investigation of internal plasma currents in a magnetic nozzle

Two-dimensional fully kinetic particle-in-cell simulations of an electrodeless plasma thruster, which uses a magnetic nozzle, were conducted to investigate the thrust generation induced by the internal plasma current. The results clearly show that the E×B and diamagnetic current densities are the major components of the internal plasma current. The simulated pressure structures reproduced the experimentally observed structures well. The results for various magnetic field strengths reveal that the E×B effect decreases, and the diamagnetic effect becomes dominant with an increase in the magnetic field strength; this demonstrates the significant contribution of the diamagnetic effect in thrust generation.

A Modified Approach to Dissipative Particle Dynamics for Simulating Magnetorheological Suspensions in Couette and Poiseuille Flows

In this paper, an improved dissipative particle dynamics (DPD) model is proposed to simulate magnetorheological (MR) suspension by using the cubic spline function to represent the interactions between magnetic and fluid particles. The model’s accuracy has been verified and validated through carrying out a number of simulations on simple fluids and MR fluids, in which both qualitative and quantitative agreements are observed between the DPD simulation results and the experimental findings and theoretical models in the existing literature. A series of numerical experiments are then conducted on MR fluids, thereby the microstructure evolution and flow properties of MR fluids in Couette and Poiseuille flows are investigated and the effects of some critical factors are particularly explored. Simulation results reveal that the plug region size, which relates to the yield stress of MR fluids, shows an increasing trend with the increase of magnetic field strength, particle volume fraction, particle mass but a decreasing trend with the increase of Mason number and pressure gradient; however, it remains almost unchanged with varying temperature.

Supersonic Flow of Vacuum Arc Plasma in a Magnetic Field

We have investigated the supersonic flow of dense plasma, formed by a pulsed vacuum arc, in a magnetic field of about 1 T using probe and optical diagnostics. Two separate magnetic field configurations were examined—an axial field with either converging or diverging lines of force. We find that for a low-current arc of from 0.4 to 1 kA and pulse duration of 270 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{s}$ </tex-math></inline-formula> , the diverging magnetic field leads to increased plasma flow velocity by about a factor of 2.5, whereas the converging magnetic field reduces the velocity by about the same amount. For a high-current arc of from 5 to 30 kA and pulse duration of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$40~\mu \text{s}$ </tex-math></inline-formula> , the plasma flow velocity increases, although the effect of increased field strength on flow velocity is less significant. Here, we describe these observations and other effects of magnetic field on the parameters of the vacuum arc plasma flow.

Space-time distribution characteristic of electric field in oil of oil-pressboard insulation structure oil under impulse voltage

The space electric field distribution in oil under impulse voltage is very important for the design of transformer insulation. The existing research only focused on the characteristics of the electric field at a certain point in oil-pressboard insulation structure. To in-depth study of the space electric field distribution in oil under impulse voltage changes with time and space, the measurement platform for the space electric field in oil under impulse voltage was built. The space electric field distribution in transformer oil under lightning impulse voltage was measured, and its changes with time and space were analysed. The results indicate that: As the applied voltage increases, the measured field strength begins to be lower than the applied, and the difference between the maximum measured and applied field strength increase. The space electric field distribution in oil in the wavefront time stage gradually becomes uniform with the increase of time. In the tail time stage, the weakening effect of the space charge on the electric field in oil gradually weakens with the increase of time and the applied field strength is first higher than the measured and then gradually lower than it.

Structure evolution of suspensions under time-dependent electric or magnetic field

The effect of time-dependent external fields on the structures formed by particles with induced dipoles dispersed in a viscous fluid is investigated by means of Brownian Dynamics simulations. The physical effects accounted for are thermal fluctuations, dipole-dipole and excluded volume interactions. The emerging structures are characterised in terms of particle clusters (orientation, size, anisotropy and percolation) and network structure. The strength of the external field is increased in one direction and then kept constant for a certain amount of time, with the structure formation being influenced by the slope of the field-strength increase. This effect can be partially rationalized by inhomogeneous time re-scaling with respect to the field strength, however, the presence of thermal fluctuations makes the scaling at low field strength inappropriate. After the re-scaling, one can observe that the lower the slope of the field increase, the more network-like and the thicker the structure is. In the second part of the study the field is also rotated instantaneously by a certain angle, and the effect of this transition on the structure is studied. For small rotation angles (theta le 20^{{circ }}) the clusters rotate but stay largely intact, while for large rotation angles (theta ge 80^{{circ }}) the structure disintegrates and then reforms, due to the nature of the interactions (parallel dipoles with perpendicular inter-particle vector repel each other). For intermediate angles (20<theta <80^{{circ }}), it seems that, during rotation, the structure is altered towards a more network-like state, as a result of cluster fusion (larger clusters). The details provided in this paper concern an electric field, however, all results can be projected into the case of a magnetic field and paramagnetic particles.

Relativistic ionization probabilities and photoelectron distributions of hydrogenlike ions in superstrong electromagnetic fields

The ionization probabilities and photoelectron distributions of the hydrogen atom and hydrogenlike ions ${\mathrm{He}}^{+}$ and ${\mathrm{Ne}}^{9+}$ in superstrong electromagnetic fields are obtained by solving the time-dependent Dirac equation with the help of the generalized pseudospectral method in spherical coordinates. A simple transformation of the original radial Dirac Hamiltonian is suggested that removes the spurious states. The ionization probabilities are calculated both within and beyond the dipole approximation for two pulse durations and various peak field strengths scaled with respect to the nuclear charge for each target. Performance of two analytic parameters previously suggested to estimate the nondipole effects is assessed against the numerical data obtained in this study. The photoelectron energy and angular distributions exhibit the above-threshold ionization peaks as well as the low-energy structure. In the superstrong field regime, the low-energy structure builds up with increasing field strength while the above-threshold ionization peaks decrease. The nondipole effects in the photoelectron distributions are also revealed and analyzed.

Topological Analysis of Magnetically Induced Current Densities in Strong Magnetic Fields Using Stagnation Graphs

Stagnation graphs provide a useful tool to analyze the main topological features of the often complicated vector field associated with magnetically induced currents. Previously, these graphs have been constructed using response quantities appropriate for modest applied magnetic fields. We present an implementation capable of producing these graphs in arbitrarily strong magnetic fields, using current-density-functional theory. This enables us to study how the topology of the current vector field changes with the strength and orientation of the applied magnetic field. Applications to CH4, C2H2 and C2H4 are presented. In each case, we consider molecular geometries optimized in the presence of the magnetic field. The stagnation graphs reveal subtle changes to this vector field where the symmetry of the molecule remains constant. However, when the electronic state and symmetry of the corresponding equilibrium geometry changes with increasing field strength, the changes to the stagnation graph are extensive. We expect that the approach presented here will be helpful in interpreting changes in molecular structure and bonding in the strong-field regime.

Numerical analysis of collision characteristics between charged drop and neutral droplet under uniform electric field

Dissipatingfog and fog water collection have been of great concern recently. Corona discharge can produce charge and electric field, and accelerate the above process by promoting fog droplets collision. Collision efficiency and kernel are introduced toanalyze the effect of electric charge and electric field on fog droplets collision in this paper. For fog droplets, the efficiency and kernel represent the probability and rate of collision, respectively. In addition, an extended trajectorymodel, including drag force, gravity, electrostatic force and applied electric field force, is proposed. The results indicate that the charge promotes the efficiency and kernel significantly. However, the collision efficiency between charged drop and neutral droplet under uniform electric field is reduced. When the applied electric field strength increases, the collision efficiency first decreases and then increases to 1.0, whereas the collision kernel increases at all times. This is because the electrostatic force, hydrodynamic force and inertial force vary with electric field. The calculatedresults can be used to optimize the efficiency of fog dissipation and fog water collection.

Intensity of the Earth's magnetic field: Evidence for a Mid-Paleozoic dipole low

The Mesozoic Dipole Low (MDL) is a period, covering at least ∼80 My, of low dipole moment that ended at the start of the Cretaceous Normal Superchron. Recent studies of Devonian age Siberian localities identified similarly low field values a few tens of million years prior to the Permo-Carboniferous Reverse Superchron (PCRS). To constrain the length and timing of this potential dipole low, this study presents paleointensity estimates from Strathmore (∼411 to 416 Ma) and Kinghorn (∼332 Ma) lava flows, United Kingdom. Both localities have been studied for paleomagnetic poles (Q values of 6 to 7), and the sites were assessed for their suitability for paleointensity from paleodirections, rock magnetic analysis, and microscopy. Thermal and microwave experiments were used to determine site mean paleointensity estimates of ∼3 to 51 μT (6 to 98 ZAm2) and 4 to 11 μT (9 to 27 ZAm2) from the Strathmore and Kinghorn localities, respectively. These, and all the sites from 200 to 500 Ma from the (updated) Paleointensity database (PINT15), were assessed using the Qualitative Paleointensity criteria (QPI). The procurement of reliable (QPI ≥ 5) weak paleointensity estimates from this and other studies indicates a period of low dipole moment (median field strength of 17 ZAm2) from 332 to 416 Ma. This "Mid-Paleozoic Dipole Low (MPDL)" bears a number of similarities to the MDL, including the substantial increase in field strength near the onset of the PCRS. The MPDL also adds support to the inverse relationship between reversal frequency and field strength and a possible ∼200-My cycle in paleomagnetic behavior relating to mantle convection.

Impacts of the horizontal swirl and axial tumble on the turbulent kinetic energy and combustion process of a natural gas engine

ABSTRACT Natural gas (NG) engines are restricted by slow combustion rates. An appropriate flow condition is considered to be the most promising way to improve the combustion rate of NG. In this study, decoupling analysis of the impacts of swirl and tumble on turbulent kinetic energy (TKE) and combustion process of a spark ignition (SI) NG engine was conducted by simulation. A 3D model was established and boundary conditions of the most economical operating point (1200 r/min, 100% load) were obtained through tests, and the rationality of the case was verified. Then, the flow field of the original engine was decoupled at the intake valve closing time to obtain the decoupled swirl field and the decoupled tumble field. Finally, the swirl field and the tumble field were amplified and applied to the SI NG engine. The results showed that high swirl or tumble can obtain high TKE, but the contribution mechanism of them to TKE is significantly different. According to the analysis of the spatial motion structure and energy conversion, the TKE in tumble field is much higher than that in swirl field with the same intensity. In addition, the impacts of swirl and tumble on the combustion process of the SI NG engine are both divided into two phases, and high swirl or tumble can obtain higher thermal efficiency. The combustion rate of NG first increased with the increase in initial flow field strength. When the swirl ratio at intake valve closing time (SR0) and the tumble ratio at intake valve closing time (TR0) exceeded 2.0 and 1.25, respectively, the combustion rate is kept in a fluctuating equilibrium state. At this time, the improvement of swirl and tumble on NG combustion process was brought into full play, the maximum indicated thermal efficiency reached 43.18% and 44.39%, respectively. Finally, the conclusion was drawn by comparing swirl and tumble in different aspects where high tumble shows greater potential in achieving super-high thermal efficiency.

Balmer-series spectral lines for hydrogen atoms in parallel magnetic and electric fields of white dwarfs

ABSTRACT We extended the two-dimensional B-spline approach recently developed to investigate the influence of a strong electric field on atomic structures and spectra for hydrogen atoms in magnetic fields of white dwarfs. Spectral lines for hydrogen in parallel magnetic and electric fields have been calculated. Wavelengths and oscillator strengths are presented for 14 Balmer α transitions as a function of magnetic and electric fields. The magnetic and electric field strengths involved span a scope, respectively, from around 23.5 to 2350 MG, and from 0 to 108 V/m. Our calculations show that the shift of Balmer-series spectral lines induced by a strong electric field reduces as the magnetic field strength increases. The obtained energy levels, wavelengths, and oscillator strengths are compared to available results in the literature, and excellent agreement was discovered. The spectral data reported in this paper can be applied to interpret the shifts of spectral lines of hydrogen in magnetic white dwarfs due to the presence of electric fields, and to predict additional spectral lines dipole-forbidden in a pure magnetic field.

Modeling nonlinear dielectric properties of laminated composites

sThe article is devoted to the development of a method for predicting the nonlinear dielectric properties of layered composites with complex dependences of the dielectric constant on the electric field strength, which consider the effects of a sharp increase and subsequent decrease in the dielectric constant with increasing field strength. The method is based on the use of the theory of asymptotic averaging proposed by N.S. Bakhvalov, E. Sanchez-Palencia, in relation to the nonlinear problem of electrostatics in a layered medium. As a result of applying this method, local nonlinear problems of electrostatics on a periodicity cell are formulated, and an algorithm for calculating effective nonlinear dielectric constants is proposed. It is shown that a layered composite is a transversely isotropic nonlinear dielectric material if its layers are isotropic materials. A numerical example of calculating the nonlinear properties of a 2-layer composite based on barium titanate and ferroelectric ceramic varicond VK4 is considered. Calculations have shown that the developed method for calculating the nonlinear-dielectric ratios of composites is quite effective and makes it possible to predict the dielectric properties of composites at various values of the electric field strength, including the regions where the dielectric permittivities of the layer materials are saturated. The developed technique can serve as a basis for designing new nonlinear dielectric composite materials with unusual properties.

Magnetic field sensor based on S-shaped and core-offset fusion splicing structure of single-mode fiber coated with magnetic fluid

Tunable refractive index characteristics of magnetic fluid have important research value in magnetic field sensing. In this paper, a magnetic field sensor based on S-shaped and core-offset fusion splicing structure of single-mode fiber coated with magnetic fluid is proposed and demonstrated. The proposed sensing structure is based on Mach-Zehnder interference principle and is coated with magnetic fluid. The basic idea of structural design is to first excite the fiber cladding mode by using an S-shaped fusion splicing structure, and then use the core-offset fusion splicing structure to achieve the interference between the cladding mode and the core mode. The refractive index of the magnetic fluid changes with the magnetic field strength, resulting in the variation in the transmission spectrum of the sensor. The experimental results show that the sensitivity of the sensor is 33.14 pm/Oe in the range of the magnetic field strength of 0–75 Oe, and the interference valley wavelength increases linearly with the increase of the magnetic field strength. Therefore, the fabricate process of the sensing structure only requires two simple fusion splicing operations of ordinary single-mode fiber, which has the characteristics of low cost, simple structure, easy processing, and high sensitivity, so it has broad application prospects.