Effect Of Gradient Magnetic Field Research Articles

Effects of Gradient Magnetic Field on Electrical Tree Growth of SiR/Graphene Nanocomposites

In this paper, an unevenly distributed gradient magnetic field is constructed. The electrical tree characteristics in silicone rubber (SiR) under a gradient magnetic field are investigated. The cumulative damage is increased by 365% under Δ1.5 T and by 411% under Δ-1.5 T gradient magnetic field. A modification method based on graphene nanosheet doping is proposed to improve the insulation performance of the SiR under a gradient magnetic field. With the introduction of an appropriate amount of graphene nanoparticles, the damage area of the SiR/Graphene nanocomposites is reduced to 19.9% in the nonmagnetic field, and is reduced to 17.4% and 14.0% under Δ±1.5 T gradient magnetic field respectively. The time to breakdown is extended by 40-84%. The experimental results show that the magnetic field can affect the charge behavior and enhance the electric field near the electrode. The growth of the electrical tree is accelerated due to the enhanced partial discharges. The graphene nanosheets reduce the interface electric field and inhibit the growth of electrical trees by capturing the injected charges.

Effects of Gradient Magnetic Field on Electrical Tree Growth Characteristics in Silicone Rubber

In this article, the positive and inverse gradient symmetric magnetic field and the asymmetric magnetic field with different angles are constructed. The influence of the magnetic field distribution on the electrical tree characteristics is investigated. The experimental results show that both the positive and the inverse gradient magnetic fields can promote the deterioration of the electrical trees. Under the symmetrical <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta 1.5$ </tex-math></inline-formula> T gradient magnetic field, the tree initiation probability increases from 55% to 100%, and the breakdown time decreases by 67.5%. Under the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta $ </tex-math></inline-formula> -1.5 T, the tree initiation probability increases from 55% to 75%, and the breakdown time declines by 57.5%. The morphology of the electrical trees is largely affected by the distribution of the magnetic field. The dispersion of the degradation channels increases with the enhancement of the magnetic field. Under the asymmetric magnetic field, the deterioration process is also accelerated, with the increase of the magnetic field. More importantly, the growth direction of the electric trees shifts to the side with the higher magnetic flux density. The magnetic field enhances the local electric field and promotes the occurrence of partial discharge by exerting a deflection force on the charges. Consequently, the growth rate and morphology of electrical trees are affected.

Effect of gradient magnetic field on corrosion of carbon steel pipes in seawater pumped storage power plants

Effect of gradient magnetic field on corrosion of carbon steel pipes in seawater pumped storage power plants

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.

Computational study of the effect of gradient magnetic field in navigation of spherical particles

The use of spherical magnetic nanoparticles that are coated with drugs and can be navigated in arteries to attack tumors is proposed as an alternative to chemotherapy. Navigation of particles is due to magnetic field gradients that may be produced in an MRI device. In the present work, a computational study for the evaluation of the magnitude of the gradient magnetic field for particles navigation in Y bifurcations is presented. For this purpose, the presented method solves for the fluid flow and includes all the important forces that act on the particles in their discrete motion. The method is based on an iteration algorithm that adjusts the gradient magnetic field to minimize the particles’ deviation from a desired trajectory. Using the above mentioned method, the appropriate range of the gradient magnetic field for optimum navigation of nanoparticles’s aggregation is found.

Effects of exposure to gradient magnetic fields emitted by nuclear magnetic resonance devices on clonogenic potential and proliferation of human hematopoietic stem cells.

This study investigates effects of gradient magnetic fields (GMFs) emitted by magnetic resonance imaging (MRI) devices on hematopoietic stem cells. Field measurements were performed to assess exposure to GMFs of staff working at 1.5 T and 3 T MRI units. Then an exposure system reproducing measured signals was realized to expose in vitro CD34+ cells to GMFs (1.5 T-protocol and 3 T-protocol). CD34+ cells were obtained by Fluorescence Activated Cell Sorting from six blood donors and three MRI-exposed workers. Blood donor CD34+ cells were exposed in vitro for 72 h to 1.5 T or 3 T-protocol and to sham procedure. Cells were then cultured and evaluated in colony forming unit (CFU)-assay up to 4 weeks after exposure. Results showed that in vitro GMF exposure did not affect cell proliferation but instead induced expansion of erythroid and monocytes progenitors soon after exposure and for the subsequent 3 weeks. No decrease of other clonogenic cell output (i.e., CFU-granulocyte/erythroid/macrophage/megakaryocyte and CFU-granulocyte/macrophage) was noticed, nor exposed CD34+ cells underwent the premature exhaustion of their clonogenic potential compared to sham-exposed controls. On the other hand, pilot experiments showed that CD34+ cells exposed in vivo to GMFs (i.e., samples from MRI workers) behaved in culture similarly to sham-exposed CD34+ cells, suggesting that other cells and/or microenvironment factors might prevent GMF effects on hematopoietic stem cells in vivo. Accordingly, GMFs did not affect the clonogenic potential of umbilical cord blood CD34+ cells exposed in vitro together with the whole mononuclear cell fraction.

Effects of gradient magnetic fields on CO2 sublimation in dry ice

A process of CO2 sublimation in a fragment of dry ice was observed under static gradient magnetic fields of up to 7 Tesla. Results indicated that Tesla order magnetic fields enhanced the release of CO2 gas from solid matter containing carbon dioxide. Paramagnetic oxygen molecules transported the sublimated particles containing carbon dioxide to a higher magnetic field.

EFFECTS OF GRADIENT MAGNETIC FIELDS ON THE MAGNETO-THERMAL MIXED CONVECTION OF AIR IN A HORIZONTAL PIPE

Effects of gradient magnetic fields on the mixed convection of air in a gravity field are numerically studied with 3-D model equations. The detailed characteristics of the magneto-thermal wind in a pipe are computed for the length ratios L (pipe length divided by pipe diameter) of 20, 30, 62, and 100, with diameter ratios N (diameter of an electric coil versus that of the pipe) from 2 to 200. It is found that there exists a best diameter ratio N to maximize the airflow rate for a channel with a fixed length. Detailed flow and temperature profiles are graphically presented for various values of N.

Formation of aligned two-phase microstructure in Fe-0.25 mass%C alloy under gradient high magnetic fields

Abstract The effect of uniform and gradient high magnetic fields on the microstructures of Fe-0.25 mass%C steel was investigated by optical microscopy. The results show that aligned two-phase microstructure was formed when uniform magnetic fields are imposed during the austenite to ferrite transformation. Such aligned two-phase microstructure became more distinct when gradient magnetic fields are imposed. The pearlite colonies are small and the space between columns is reduced in the specimen treated under gradient magnetic fields compared with those in the specimen treated under a uniform magnetic field. The mechanism on effect of gradient magnetic field is discussed from the viewpoint of dipolar interaction and the effect of magnetic force on ferrite grains.

Experimental investigation on possibility of oxygen enrichment by using gradient magnetic fields

This paper presents a novel method that uses the interception effect of gradient magnetic field on oxygen molecules to realize enrichment. The use of two opposite magnetic poles of two magnets at a certain distance forms a magnetic space having a field intensity gradient near its borders. When air injected into the magnetic space outflows from the magnetic space via its borders, oxygen molecules in the air will experience the interception effect of the gradient magnetic field, but nitrogen molecules will outflow from the magnetic space without hindrance. Thus, continuous oxygen enrichment is realized. The enrichment degree of oxygen reaches 0.65% when the inlet and outlet air flows are 40 mL/min and 20 mL/min, respectively, and the gas temperature is 298 K and the maximal product of magnetic flux density and its gradient is 563 T2/m (the distance between two magnetic poles is 1 mm). When the gas temperature rises to 343 K, the enrichment degree drops to 0.32%; and when the maximal product of magnetic flux density and field intensity gradient drops to 101 T2/m (the distance between two magnetic poles is 4 mm), the enrichment degree drops to 0.23%. The experimental results show that there is an optimal ratio between the inlet air flow and the outlet air flow. Under the experimental conditions in this paper, the value is about 2.0. It is demonstrated that the method presented in this paper can continuously enrich oxygen and has a higher enrichment degree than other oxygen-enrichment methods using magnetic separation.

Oxygen enrichment from air by using the interception effect of gradient magnetic field on oxygen molecules

This Letter reports a novel method to enrich oxygen from air by using the interception effect of gradient magnetic field on oxygen molecules. The effect of oxygen enrichment is relevant to the inlet air flow and the outlet air flow. The experimental results indicate that there is an optimal ratio between the inlet air flow and the outlet air flow. Under the conditions in this study, it should be about 2.0. Both too high and too low ratio result in a low increment of oxygen concentration. This phenomenon can be explained by considering the balance between the inertia force and the magnetizing force. Different ratio makes that the gas crossing the gradient magnetic field has a different macroscopic velocity of flow, namely, inertia force. The further experimental research shows that the effect of oxygen enrichment can be improved by extending the length of the borders of the gradient magnetic field under the constant inlet air flow and outlet air flow.

Application of multiple magnetic coils to drive the air flow in a long pipe

The laminar air flow in a pipe is studied with application of multiple magnetic fields at the point of uniform heat flux heating from the wall as the first boundary conditions. As the second boundary condition, after a coil, uniform heat flux heating and then uniform heat flux cooling from the wall is applied. Numerical computations are successfully carried out by solving transient 2-D equations with pressure gradient boundary condition for three lengths of pipe and two boundary conditions. The first one is for a ratio of pipe length and diameter L = 10 with a single electric coil. The second one is for L = 20 with two electric coils and the third one is for L = 30 with three electric coils to generate the magnetic field. A parameter ξ is from 0 to 2 × 10 7, which represents the strength of the magnetic field and the uniform heat flux from the pipe wall. The results show that the volume flow rate increases with the strength of magnetic field. Magnetic fields generated by the multi-coils can drive the air flow in the corresponding longer pipe almost equally to the shorter one with a single coil. From the distributions of the cross-sectional magnetic force along the pipe length, the effect of pressure, pressure gradient distribution along the pipe length, and the effect of gradient magnetic field and temperature field on the overall air flow rate can be analyzed and compared on the effect of wall cooling.

Paramagnetic artifact and safety criteria for human brain mapping

Biological effects of magnetic field and their safety criteria, especially effects of gradient magnetic field on the cerebral and pulmonary circulation during functional brain mapping are still unclear. Here we estimated that magnetically induced artifacts for the blood oxygenation level- and flow- based functional magnetic resonance imaging are less than 0.1%, and disturbance in the pulmonary circulation is less than 1.3% even if the field strength of magnetic resonance system is risen up to 10 tesla. These paramagnetic effects are considered to be small and harmless during human brain mapping.

Strong static magnetic field effects on yeast proliferation and distribution

The present study focuses on the effects of gradient magnetic fields on the behavior of yeast, such as its proliferation and mass distribution, and evaluates the effects of magnetism on materials in the yeast culture system. Yeast, Saccharomyces cerevisiae, was incubated in a liquid medium under magnetic fields (flux density B=14 T). When yeast in a tube was exposed to 9–14 T magnetic fields with a maximum flux density gradient of d B/d x=94 T/m, where x is the space coordinate, the rate of yeast proliferation under the magnetic fields decreased after 16 h of incubation compared to that of the control group. The physical properties of the yeast culture system were investigated to discover the mechanism responsible for the observed deceleration in yeast proliferation under magnetic fields. Gas pressure inside the yeast culture flask was compared with and without exposure to a magnetic field. The results suggested that the gas pressure inside a flask with 6 T, 60 T/m slowly increased in comparison to the pressure inside a control tube. Due to the diamagnetism of water (medium solution) and yeast, the liquid surface distinctly inclined under gradient magnetic fields, and the hydrostatic force in suspension was strengthened by the diamagnetic forces. In addition, magnetophoresis of the yeast cells in the medium solution exhibited localization of the yeast sedimentation pattern. The roles of magnetically changed gas-transport processes, hydrostatic pressures acting on the yeast, and changes in the distribution of the yeast sedimentation, as well as the possible effects of magnetic fields on yeast respiratory systems in the observed disturbance of the proliferation are discussed.

傾斜磁場が血流分配に与える影響

傾斜磁場が血流分配に与える影響

Effects of gradient magnetic fields on diffusion process of glycine in water

We studied diffusion processes of organic materials in water under gradient magnetic fields. We used two liquid chromatographic systems to observe diffusion processes of glycine and albumin under magnetic fields of up to 8 T. We measured the absorbance of glycine solution from an outlet of the column using low pressure liquid chromatography. The peak intensity in the chromatogram of glycine changed 10%-500% depending on the strength and direction of the magnetic field gradient. The retention time in the chromatogram of glycine was significantly prolonged when the direction of magnetic forces opposed the direction of the flow. We also measured the retention times of glycine and albumin under magnetic fields of up to 8 T using an HPLC system. The retention times of the two solutes under gradient magnetic fields increased by 100%-370%.

Dissolution of thrombus under high gradient magnetic fields

This study focused on the mechanism of effects of strong magnetic fields on a process of of fibrin clots. We measured the rate of fibrinolysis using a fibrin column as a model of a thrombus, and investigated the effects of gradient magnetic fields. Fibrin clots in glass tubes were digested by plasmin under magnetic fields of up to 8 T which were produced by a horizontal type of superconducting magnet at 37/spl deg/C. When a fibrin gel and a plasmin solution were exposed to magnetic fields where a product of magnetic fields and field gradients, B/spl middot/dB/dz, was 370 T/sup 2//m, dissolution of fibrin was enhanced by 34 %. However, we obtained no distinct effects when B/spl middot/dB/dz was less than 150 T/sup 2//m. As a mechanism, we proposed a model in which fibrin polymers in water magnetophoresically drifted in the direction of increasing magnetic fields, and digestions of fibrin polymers by plasmin were accelerated.

Book reviews

The authors of this paperback book are well known for many publications on the subject of safety of magnetic resonance and have gathered their very extensive experience into a comprehensive book of nearly 300 pages. The first chapter covers the bio-effects of static magnetic fields which are generally insignificant at the field strengths of up to 2.0 Tesla that are usually employed for imaging at present. The effects of gradient magnetic fields are dealt with in chapter 2 and of radiofrequency electro-magnetic fields in chapter 3 and again the hazards at the normally used imaging levels are of little significance.