• 산업기술연구
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• 제15권
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• pp.175-185
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• 1995

Under the new environmental regulations announced by the government, utilities will have to cut their sulfur dioxide emissions by 60% from 1991 levels by the year of 1999. Sulfur dioxide emissions can be reduced prior to combustion by physical, chemical or biological coal cleaning. The new technology of high gradient magnetic separation (HGMS) offers the potential of economic separatoins of a variety of fine, weakly magnetic minerals including inorganic sulfur and many ash-forming minerals from coals. In the present paper, magnetic separation tests have been conducted on Korean anthracite and high-sulfur Chinese coal to investigate the feasibility of these techniques for reducing sulfur content from coals. In wet magnetic separation, the studied operating parameters include particle size, pH, matrix types, feed solids content, feed rate, number of cleaning stages and etc. The results shows that for wet separation, 60~70% of total sulfur was removed from coals with over 80% combustible recovery, on the other hand, for dry separation, 47.6% of total sulfur was removed from coals with 75% recovery.

• Journal of Magnetics
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• 제3권3호
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• pp.69-73
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• 1998

A drum type magnetic separator was designed and optimized by computer simulation. The separator consisted of rotating outer shell of drum, magnetic flux generator drum which was assembled with numbers of disk type magnet holders, and drum axis around which the magnet holders were fixed. NdFeB magnet blocks were inserted into the disks, and the disks were assembled layer by layer along the drum axis. Magnetic circuits of the separator were simulated on the basis of highest magnetic strength, least cost, and high yield of separation by using a Vector Field S/W employing the Opera-2D program. The separator proved a separation yield of 95% in removing fine iron-base particles, and installed at Hot Rolling Mill of Pohang Iron & Steel Co. In Korea.

• 한국우주과학회:학술대회논문집(한국우주과학회보)
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• 한국우주과학회 2011년도 한국우주과학회보 제20권1호
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• pp.26.3-27
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• 2011

Formation of a steep plasma density gradient in the middle-latitude ionosphere during geomagnetic storms and the latitudinal migration of its location depending on the storm phase are suggested to be associated with the ionospheric signature of the plasmapause. We test this idea by using the satellite and ground observation data during the 11 April 2001 storm. The locations of the steep plasma density gradient identified by TOPEX/Poseidon (2001 LT) and DMSP (1800 and 2130 LT) satellites coincide with the ionospheric footprints of the plasmapause identified by the IMAGE satellite. This observation may support the dependence of the middle-latitude plasma density gradient location on the plasmapause motion, but does not explain why the steep density gradient whose morphology is largely different from the morphology of the middle-latitude ionization trough during quiet period is formed in association with the plasmapause. The ionospheric disturbances in the total electron content (TEC) maps shows that the steep TEC gradient is formed at the boundary of the positive ionospheric storm in low-middle latitudes and the negative ionospheric storm in middle-high latitudes. We interpret that the thermospheric neutral composition disturbance in the dayside is confined within the middle-high latitude ionospheric convection zone. The neutral composition latitudes and, therefore, the locations of the steep plasma density gradient coincide with the footprints of the plasmapause. The TEC maps show that the appearance of the steep plasma density gradient in the pre-midnight sector during the recovery phase is related to the co-rotation of the gradient that is created during the main phase.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제12권4호
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• pp.1760-1778
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• 2018

For image segmentation with intensity inhomogeneity, many region-based level set methods have been proposed. Some of them however can't get the relatively ideal segmentation results under the severe intensity inhomogeneity and weak edges, and without use of the image gradient information. To improve that, we propose a new level set method combined with local direction gradient in this paper. Firstly, based on two assumptions on intensity inhomogeneity to images, the relationships between segmentation objects and image gradients to local minimum and maximum around a pixel are presented, from which a new pixel classification method based on weight of Euclidian distance is introduced. Secondly, to implement the model, variational level set method combined with image spatial neighborhood information is used, which enhances the anti-noise capacity of the proposed gradient information based model. Thirdly, a new diffusion process with an edge indicator function is incorporated into the level set function to classify the pixels in homogeneous regions of the same segmentation object, and also to make the proposed method more insensitive to initial contours and stable numerical implementation. To verify our proposed method, different testing images including synthetic images, magnetic resonance imaging (MRI) and real-world images are introduced. The image segmentation results demonstrate that our method can deal with the relatively severe intensity inhomogeneity and obtain the comparatively ideal segmentation results efficiently.

• Advances in nano research
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• 제9권4호
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• pp.221-235
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• 2020

The following composition establishes a nonlocal strain gradient plate model that is essentially related to mass sensors laying on Winkler-Pasternak medium for the vibrational analysis from graphene sheets. To achieve a seemingly accurate study of graphene sheets, the posited theorem actually accommodates two parameters of scale in relation to the gradient of the strain as well as non-local results. Model graphene sheets are known to have double variant shear deformation plate theory without factors from shear correction. By using the principle of Hamilton, to acquire the governing equations of a non-local strain gradient graphene layer on an elastic substrate, Galerkin's method is therefore used to explicate the equations that govern various partition conditions. The influence of diverse factors like the magnetic field as well as the elastic foundation on graphene sheet's vibration characteristics, the number of nanoparticles, nonlocal parameter, nanoparticle mass as well as the length scale parameter had been evaluated.

• Structural Engineering and Mechanics
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• 제66권2호
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• pp.237-248
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• 2018

This study presents the investigation of wave dispersion characteristics of a magneto-electro-elastic functionally graded (MEE-FG) nanosize beam utilizing nonlocal strain gradient theory (NSGT). In this theory, a material length scale parameter is propounded to show the influence of strain gradient stress field, and likewise, a nonlocal parameter is nominated to emphasize on the importance of elastic stress field effects. The material properties of heterogeneous nanobeam are supposed to vary smoothly through the thickness direction based on power-law form. Applying Hamilton's principle, the nonlocal governing equations of MEE-FG nanobeam are derived. Furthermore, to derive the wave frequency, phase velocity and escape frequency of MEE-FG nanobeam, an analytical solution is employed. The validation procedure is performed by comparing the results of present model with results exhibited by previous papers. Results are rendered in the framework of an exact parametric study by changing various parameters such as wave number, nonlocal parameter, length scale parameter, gradient index, magnetic potential and electric voltage to show their influence on the wave frequency, phase velocity and escape frequency of MEE-FG nanobeams.

• Investigative Magnetic Resonance Imaging
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• 제2권1호
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• pp.1-13
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• 1998

MR 영상을 획득하기 위해서 사용하고 있는 가장 기본적인 펄스파형(pulse sequense)은 스핀반향(spin echo)과 경사자계반향(gradient echo)이며, 최근 다방면으로 응용되고 있는 고속영상기법들은 이 두가지 펄스파형을 기보능로 하고 있다. 펄스파형의 종류와 펄스파형의 변수(TR, TE TI등의 펄스 상이의 시간 간격 및 flip angle 등)에 따라서 MR영상의 특징(대조도, SNR, artifact 등)이 달라지므로 임상응용시에는 목적에 따라 적절한 펄스파혀의 선택과 함께 변수값을 결정해야 한다. 이를 위하여 펄스파형에 관한 기본적인 지식과 함게 간단한 임상응용에 관하여 기술하고자 한다.

• 한국자기공명학회논문지
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• 제16권2호
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• pp.122-132
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• 2012

The effects of the sample viscosity and volume on the convective flows induced by temperature gradient in PGSE-NMR self-diffusion measurements at high temperature have been investigated. The experimental results showed that the viscosity of the liquid sample strongly affects the magnitude of the convective flows as well as the diffusion coefficient itself. It was also found that the convective flows increase as the sample volume increase.

• 한국수학교육학회지시리즈B:순수및응용수학
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• 제13권1호
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• pp.1-10
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• 2006

The unsteady Hartmann flow of an electrically conducting, viscous, incompressible fluid bounded by two parallel non-conducting porous plates is studied with heat transfer. An external uniform magnetic field and a uniform suction and injection are applied perpendicular to the plates while the fluid motion is subjected to a constant pressure gradient. The two plates are kept at different but constant temperatures while the Joule and viscous dissipations are included in the energy equation. The effect of the magnetic field and the uniform suction and injection on both the velocity and temperature distributions is examined.

• Smart Structures and Systems
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• 제12권1호
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• pp.1-22
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• 2013

Magnetic nanoparticle based bioseparation in microfluidics is a multiphysics phenomenon that involves interplay of various parameters. The ability to understand the dynamics of these parameters is a prerequisite for designing and developing more efficient magnetic cell/bio-particle separation systems. Therefore, in this work proof-of-concept experiments are combined with advanced numerical simulation to design and optimize the capturing process of magnetic nanoparticles responsible for efficient microfluidic bioseparation. A low cost generic microfluidic platform was developed using a novel micromolding method that can be done without a clean room techniques and at much lower cost and time. Parametric analysis using both experiments and theoretical predictions were performed. It was found that flow rate and magnetic field strength greatly influence the transport of magnetic nanoparticles in the microchannel and control the capturing efficiency. The results from mathematical model agree very well with experiments. The model further demonstrated that a 12% increase in capturing efficiency can be achieved by introducing of iron-grooved bar in the microfluidic setup that resulted in increase in magnetic field gradient. The numerical simulations were helpful in testing and optimizing key design parameters. Overall, this work demonstrated that a simple low cost experimental proof-of-concept setup can be synchronized with advanced numerical simulation not only to enhance the functional performance of magneto-fluidic capturing systems but also to efficiently design and develop microfluidic bioseparation systems for biomedical applications.