Analysis of the Demagnetization Process of Nd-Fe-B Sintered Magnets at Elevated Temperatures by Magnetic Domain Observation Using a Kerr Microscope

Magnetization reversal and its propagation in sintered Nd–Fe–B magnets were clearly observed at elevated temperatures up to 150 °C using a Kerr microscope, image processing, and photo editing. Simultaneous magnetization reversal in several grains along the easy axis direction occurred at elevated temperature, and the extent of simultaneous magnetization reversal increased with temperature. This indicates that reduction in the coercivity of Nd–Fe–B sintered magnets at elevated temperatures is attributable to decrease in anisotropy and insufficient pinning of domain walls at grain boundaries

Analysis of Magnetization Reversal Process of Nd-Fe-B Sintered Magnets by Magnetic Domain Observation Using Kerr Microscope

We used a Kerr microscope, image processing, and photo editing to clarify magnetization reversal and its propagation in a sintered Nd-Fe-B magnet. Magnetic domain change was observed when a dc field from +20 to 20 kOe was applied to a sintered Nd-Fe-B magnet. Simultaneous magnetization reversal in several grains along the easy axis direction and its propagation to neighboring grains occurred. This indicates that the nucleation field in a grain and magnetic interaction between grains are important controlling factors of the coercivity of sintered Nd-Fe-B magnets

Relationship Between Output of a Fluxgate Sensor and Magnetization Process of Its Core

Motivated by the need to miniaturize fluxgate sensors, we investigated the dependence of the sensitivity of fluxgate sensors on the saturation flux density and magnetostriction of an amorphous ribbon core. In addition, the relationship between the sensing properties and the magnetization process of its core was investigated with a Kerr microscope. We found that the sensitivity decreased with an increase in magnetostriction. Highly magnetostrictive amorphous ribbons exhibited maze domains that were difficult to move by applying a low magnetic field of a few hundred amperes per meter. This effect caused a decrease in the sensitivity of the sensors

Magnetic domain observation of hydrogenation disproportionation desorption recombination processed Nd－Fe－B powder with a high-resolution Kerr microscope using ultraviolet light

A Kerr microscope that uses ultraviolet (UV) light for high-resolution domain observation was built, and the domain structure and magnetization process of hydrogenation disproportionation desorption recombination (HDDR) powder were examined. The UV Kerr microscope could observe nanometer-sized domain patterns. Applying a dc field of 1.0 kOe to HDDR powder at a desorption recombination (DR) time of 12 min produced abrupt wall motion. The pinning force exerted by the grain boundaries is inadequate for producing high coercivity because the Nd-rich phase layers along these boundaries are absent at a DR time of 12 min. For HDDR powder at a DR time greater than 14 min, changing the magnetic field by up to 1.0 kOe produced no observable wall motion. It follows that the high coercivity of HDDR powder is due to domain wall pinning at the grain boundaries

Domain Observation of Amorphous Wire with Large Diameter for Micro-Sensor and Micro-Motor Application

Domain structures of Fe-Si-B-Nb amorphous wires with a large diameter were investigated. A 10% increase of pulse output voltage due to large Barkhausen jumps in the Fe-Si-B-Nb wire at the diameter of 200 μm has been obtained which is less than expected due to decreased saturation and small domain size. Domain observation results indicate that the increase of the domain size in the inner core of the wire is important for high sensor output

Design methodology using topology optimization for anti- vibration reinforcement of generators in a ship’s engine room

Structural optimization for reinforcing the anti-vibration characteristics of the generators in the engine room of a ship is presented. To improve the vibration characteristics of the structures, topology optimization methods can be effective because they can optimize the fundamental characteristics of the structure with their ability to change the topology of the target structure. Topology optimization is used to improve the characteristics of the anti-vibration reinforcement of the generators in the engine room. First, an experimentally observed vibration phenomenon is simulated using the finite element method for frequency response problems. Next, the objective function used in topology optimization is set as the dynamic work done by the load based on the energy equilibrium of the structural vibration. The optimization problem is then constructed by adding the volume constraint. Finally, based on finite element analysis and the optimization problem, topology optimization is performed on several vibration cases to improve their performance and reduce weight.This work was supported by the JSPS KAKENHI Grant Numbers 24360356 and 25820422

Renal pericytes: regulators of medullary blood flow

Regulation of medullary blood flow (MBF) is essential in maintaining normal kidney function. Blood flow to the medulla is supplied by the descending vasa recta (DVR), which arise from the efferent arterioles of juxtamedullary glomeruli. DVR are composed of a continuous endothelium, intercalated with smooth muscle-like cells called pericytes. Pericytes have been shown to alter the diameter of isolated and in situ DVR in response to vasoactive stimuli that are transmitted via a network of autocrine and paracrine signalling pathways. Vasoactive stimuli can be released by neighbouring tubular epithelial, endothelial, red blood cells and neuronal cells in response to changes in NaCl transport and oxygen tension. The experimentally described sensitivity of pericytes to these stimuli strongly suggests their leading role in the phenomenon of MBF autoregulation. Because the debate on autoregulation of MBF fervently continues, we discuss the evidence favouring a physiological role for pericytes in the regulation of MBF and describe their potential role in tubulo-vascular cross-talk in this region of the kidney. Our review also considers current methods used to explore pericyte activity and function in the renal medulla

Temperature dependence and mechanisms for vortex pinning by periodic arrays of Ni dots in Nb films

Pinning interactions between superconducting vortices in Nb and magnetic Ni dots were studied as a function of current and temperature to clarify the nature of pinning mechanisms. A strong current dependence is found for a square array of dots, with a temperature dependent optimum current for the observation of periodic pinning, that decreases with temperature as (1-T/Tc)3/2. This same temperature dependence is found for the critical current at the first matching field with a rectangular array of dots. The analysis of these results allows to narrow the possible pinning mechanisms to a combination of two: the interaction between the vortex and the magnetic moment of the dot and the proximity effect. Moreover, for the rectangular dot array, the temperature dependence of the crossover between the low field regime with a rectangular vortex lattice to the high field regime with a square configuration has been studied. It is found that the crossover field increases with decreasing temperature. This dependence indicates a change in the balance between elastic and pinning energies, associated with dynamical effects of the vortex lattice in the high field range.Comment: 12 text pages (revtex), 6 figures (1st jpeg, 2nd-6th postscript) accepted in Physical Review