The present study demonstrates the effect of magnetic pulse compaction and spark plasma sintering on the microstructure and mechanical property of a sintered W body. The relative density of green specimens prepared by magnetic pulse compaction increases with increase in applied pressure, but when the applied pressure is 3.4 GPa or more, some cracks in the specimen are observed. The pressureless-sintered W shows neck growth between W particles, but there are still many pores. The sintered body fabricated by spark plasma sintering exhibits a relative density of above 90 %, and the specimen sintered at 1,600 oC after magnetic pulse compaction shows the highest density, with a relative density of 93.6 %. Compared to the specimen for which the W powder is directly sintered, the specimen sintered after magnetic pulse compaction shows a smaller crystal grain size, which is explained by the reduced W particle size and microstructure homogenization during the magnetic pulse compaction process. Sintering at 1,600 oC led to the largest Vickers hardness value, but the value is slightly lower than that of the conventional W sintered body, which is attributed mainly to the increased grain size and low sintering density.

The magnetocaloric effect (MCE), which is the reversible temperature change of magnetic materials due to an applied magnetic field, occurs largely in the vicinity of the magnetic phase transition temperature. This phenomenon can be used to induce magnetic refrigeration, a viable, energy-efficient solid-state cooling technology. Recently, Metal-organic frameworks (MOFs), due to their structural diversity of tunable crystalline pore structure and chemical functionality, have been studied as good candidates for magnetic refrigeration materials in the cryogenic region. In cryogenic cooling applications, MCE using MOF can have great potential, and is even considered comparable to conventional lanthanum alloys and magnetic nanoparticles. Owing to the presence of large internal pores, however, MOF also exhibits the drawback of low magnetic density. To overcome this problem, therefore, recent reports in literature that achieve high magnetic entropy change using a dense structure formation and ligand tuning are introduced.

A magnetic abrasive finishing process was proposed for improving the surface accuracy of microscale -diameter STS 304 bar used in many applications such as, medical, aerospace, and nuclear industries. Most of the previous research has already explored the conventional finishing technique to improve the accuracy of material in terms of the surface roughness. However, their results are still not good enough for the requirement in the today’s engineering industry. Especially, when the workpiece is a material of microscale-diameter, use of such conventional processes becomes impossible because they entail the application of high pressures that may damage the surface to be finished. Moreover, less control is available over these conventional finishing processes. In this study, an ultra-high-precision magnetic abrasive finishing process was applied to the precision machining of microscale-diameter STS 304 bar and the experimental work are performed with many critical parameters such as, different workpiece revolution speeds, abrasive grain sizes, different finishing temperatures, and pole vibrations. The results showed that in The initial surface roughness of 0.20 μm (Ra) was decreased to 0.025 μm with 0.5 μm of abrasive grain size and pole vibration 12Hz at 40,000 rpm.

sesses the finishing capabilities for application to high-precision machining. Because Ti-6AL-4V (Eli) is widely used in applications where it is exposed to the human body, the industrial grinding oil that is commonly used in the magnetic abrasive finishing process was replaced by vegetable oils; the processing performances of these different grinding oils were compared and verified. The characteristics of magnetic abrasive finishing were also investigated according to the temperature of the material. The experimental results show that olive oil yields a surface roughness improvement of 87%. Also, in terms of the roundness and the amount of material removal, the performance was excellent. This demonstrates the possibility of replacing the conventional industrial oil for grinding. Furthermore, when olive oil was used at different temperatures, the finishing characteristics at room temperature were the most excellent. SEM and EDX analyses of the machined components (before and after processing) showed that the material composition was not changed. Additionally, the magnetic abrasive tool composition was not found on the surface of the finished samples. In conclusion, the possibility of using vegetable oil as the grinding oil for high-precision machining of Ti-6Al-4V (Eli) bars via a magnetic abrasive finishing process at room temperature conditions was verified.

Synthesis of composite powders for the Fe2O3-Zn system by mechanical alloying (MA) has been investigated at room temperature. Optimal milling and heat treatment conditions to obtain soft magnetic composite with fine microstructure were investigated by X-ray diffraction, differential scanning calorimetry (DSC) and vibrating sample magnetometer (VSM) measurement. It is found that α-Fe/ZnO composite powders in which ZnO is dispersed in α-Fe matrix can be obtained by MA of Fe2O3 with Zn for 4 hours. The change in magnetization and coercivity also reflects the details of the solid-state reduction process of hematite by pure metal of Zn during MA. Densification of the MA powders was performed in a spark plasma sintering (SPS) machine at 900 ~ 1,000 ℃ under 60 MPa. Shrinkage change after SPS of sample MA'ed for 5 hrs was significant above 300 ℃ and gradually increased with increasing temperature up to 800 ℃. X-ray diffraction results show that the average grain size of α-Fe in the α-Fe/ZnO composite sintered at 900 ℃ is in the range of 110 nm.

Iron oxides currently attract considerable attention due to their potential applications in the fields of lithiumion batteries, bio-medical sensors, and hyperthermia therapy materials. Magnetite (Fe3O4) is a particularly interesting research target due to its low cost, good biocompatibility, outstanding stability in physiological conditions. Hydrothermal synthesis is one of several liquid-phase synthesis methods with water or an aqueous solution under high pressure and high temperature. This paper reports the growth of magnetic Fe3O4 particles from iron powder (spherical, <10 μm) through an alkaline hydrothermal process under the following conditions: (1) Different KOH molar concentrations and (2) different synthesis time for each KOH molar concentrations. The optimal condition for the synthesis of Fe3O4 using Fe powders is hydrothermal oxidation with 6.25 M KOH for 48 h, resulting in 89.2 emu/g of saturation magnetization at room temperature. The structure and morphologies of the synthesized particles are characterized by X-ray diffraction (XRD, 2θ = 20°–80°) with Cu-kα radiation and field emission scanning electron microscopy (FE-SEM), respectively. The magnetic properties of magnetite samples are investigated using a vibrating sample magnetometer (VSM). The role of KOH in the formation of magnetite octahedron is observed.

Fe3O4/SiO2/YVO4:Eu3+ multifunctional nanoparticles are successfully synthesized by facile stepwise sol-gel processes. The multifunctional nanoparticles show a spherical shape with narrow size distribution (approximately 40 nm) and the phosphor shells are well crystallized. The Eu3+ shows strong photoluminescence (red emission at 619 nm, absorbance at 290 nm) due to an effective energy transfer from the vanadate group to Eu. Core-shell structured multifunctional nanoparticles have superparamagnetic properties at 300 K. Furthermore, the core-shell nanoparticles have a quick response time for the external magnetic field. These results suggest that the photoluminescence and magnetic properties could be easily tuned by either varying the number of coating processes or changing the phosphor elements. The nanoparticles may have potential applications for appropriate fields such as laser systems, optical amplifiers, security systems, and drug delivery materials.

목적 : 뇌졸중 후 연하장애 중재에 포함된 임상가의 조기 접근을 위해 신경근전기자극(Neuromuscular Electronic Stimulation; NMES)와 비 침습성 뇌자극(Non-Invasive Brain Stimulation; NIBS)를 적용한 무작위 대조실험(Randomized Controlled Trials; RCTs) 연구의 메타분석을 통해 구체적인 효과와 방안을 제시하고자 한다. 연구방법 : Pubmed, CINAHL(EBSCOhost), Psycinfo, 한국학술정보원(Korean Studies Information Service System; KISS), 학술연구정보서비스(Research Information Sharing Service; RISS)를 통하 여 2008년부터 2019년까지의 논문을 검색하였다. 주요 용어는 “stroke OR CVA OR cerebrocascular accident OR vascular accident” AND “dysphagia OR swallowing disorder OR deglutition disorder” AND “tDCS OR transcranial direct current stimulation OR rTMS OR repetitive transcranial magnetic stimulation OR NMES OR neuromuscular electronic stimulation” AND “RCT OR randomized control trial”, “뇌졸중” 그리고 “연하장애 또는 삼킴곤란” 그리고 “경두개 자기자극 또는 경두개 직류자극 또는 신경근 전기자극” 그리고 “무작위대조실험”을 사용하였다. 포함기준과 배제기준을 적용하여 총 11개의 연구가 분석 대상으로 사용되었다. 결과 : 경두개 직류자극(Transcranial Direct Current Stimulation; tDCS)의 전기자극 강도는 1mA, 경 두개 자기자극(Repetitive Transcranial Magnetic Stimulation; rTMS)의 전기자극 강도는 3~5Hz, 신 경근 전기자극(Neuromuscular Electronic Stimulation; NMES)의 전기자극 강도는 8~15mA로 다양했으며, tDCS와 rTMS는 큰 효과크기, NMES는 중간 효과크기로 나타났다. 결론 : 본 연구는 메타분석을 통해 3가지 치료에 대한 효과를 확인하고 환자 특성과 중재 방향에 따라 다양한 결과를 확인할 수 있었다. 3가지 치료는 국내 뇌졸중 후 연하장애 회복에 효과가 있으며 안전하다고 판단한다. 향후 연하장애 회복을 이끄는 다양한 요인에 대한 명확한 연구가 활발히 이루어져야 할 것이다.

Information and communication technologies are developing rapidly as IC chip size becomes smaller and information processing becomes faster. With this development, digital circuit technology is being widely applied to mobile phones, wireless LANs, mobile terminals, and digital communications, in which high frequency range of GHz is used. In highdensity electronic circuits, issues of noise and EMC(Electro-Magnetic Compatibility) arising from cross talk between interconnects or devices should be solved. In this study, sheet-type electromagnetic wave absorbers that cause electromagnetic wave attenuation are fabricated using composites based on soft magnetic metal powder and silicon rubber to solve the problem of electromagnetic waves generated in wireless communication products operating at the frequency range of 2.4 GHz. Sendust(Fe-Si-Al) and carbonyl iron(Fe-C) were used as soft magnetic metals, and their concentrations and sheet thicknesses were varied. Using soft magnetic metal powder, a sheet is fabricated to exhibit maximum electromagnetic attenuation in the target frequency band, and a value of 34.2dB(99.9 % absorption) is achieved at the target frequency.

The purpose of this study is to investigate the ELF-MF emissions from UCLs and to compare the ELF-MF emission levels of HVTLs and UCLs. In addition, this study proposes a method and management plan to investigate the effects of exposure to ELF-MF emissions from UCLs. The ELF-MF emissions from the 154 kV UCL were 15.4±24.4 (GM: 7.8)mG, while from the 345 kV line they were 6.0±2.4 (GM: 5.7)mG. Through the comparison between ELF-MF emissions of 154 kV UCL and HVTL, at about 20 m distance from an overhead line the emissions level is 4 mG, while from an underground line at about 10 m distance the emission level was recorded as less than 4 mG. Through comparing the ELF-MF emission amount of the UCL according to the burial method, it was found that the direct ELF-MF emission levels are 15.3±7.4 (GM: 13.9)mG at the direct point, in the conduit type 21.0±30.4 (GM: 10.8)mG, and in the buried form 8.5±12.3 (GM:5.1)mG. In this study, ELF-MF emissions were about 37.0% and 47.5% lower, respectively, compared with the direct power and conduit type. The correlation between ELF-MF emission (mG) and power load (A) was analyzed. The higher the power load, the higher the ELF-MF emission. The correlation between ELF-MF emission at the direct point and depth of the UCL was also analyzed, and it was found that as the depth of line burial increased, ELF-MF emissions decreased.

We develop forecast models of daily probabilities of major flares (M- and X-class) based on empirical relationships between photospheric magnetic parameters and daily flaring rates from May 2010 to April 2018. In this study, we consider ten magnetic parameters characterizing size, distribution, and non-potentiality of vector magnetic fields from Solar Dynamics Observatory (SDO)/Helioseismic and Magnetic Imager (HMI) and Geostationary Operational Environmental Satellites (GOES) X-ray flare data. The magnetic parameters are classified into three types: the total unsigned parameters, the total signed parameters, and the mean parameters. We divide the data into two sets chronologically: 70% for training and 30% for testing. The empirical relationships between the parameters and flaring rates are used to predict flare occurrence probabilities for a given magnetic parameter value. Major results of this study are as follows. First, major flare occurrence rates are well correlated with ten parameters having correlation coefficients above 0.85. Second, logarithmic values of flaring rates are well approximated by linear equations. Third, using total unsigned and signed parameters achieved better performance for predicting flares than the mean parameters in terms of verification measures of probabilistic and converted binary forecasts. We conclude that the total quantity of non-potentiality of magnetic fields is crucial for flare forecasting among the magnetic parameters considered in this study. When this model is applied for operational use, it can be used using the data of 21:00 TAI with a slight underestimation of 2–6.3%.

We demonstrate the subsurface origin of the observed evolution of the solar active region 10930 (AR10930) associated with merging and breakup of magnetic polarity regions at the solar surface. We performed a magnetohydrodynamic simulation of an emerging magnetic flux tube whose field-line twist is asymmetrically distributed along its axis, which is a key to merging and fragmentation in this active region. While emerging into the surface, the flux tube is subjected to partial splitting of its weakly twisted portion, forming separate polarity regions at the solar surface. As emergence proceeds, these separate polarity regions start to merge and then break up, while in the corona sigmoidal structures form and a solar eruption occurs. We discuss what physical processes could be involved in the characteristic evolution of an active region magnetic field that leads to the formation of a sunspot surrounded by satellite polarity regions.

The curvature of spacetime represented by Einstein field equation has many physical implications, including gravity. As light is deflected by the curvature of spacetime, a magnetic field will also be influenced by the curved spacetime. A permanent magnet is generally known to maintain its persistent magnetic field on the ground as long as there is no external magnetic interference. However, a series of experiments find that there are noticeable changes in the magnetic fields distribution while the permanent magnet rotates. The magnetic field lines of the permanent magnet are deflected towards Earth’s centre, implying a possibility that we can use magnetic field, a more efficient tool than a satellite, to measure the curvature of spacetime. However, comparing the experimental results of this study with theoretically obtained values of the curvature of spacetime remains a vast area of research for future studies.