비전도성 벽과의 상호작용에 따른 단일 입자의 직류 유전영동 운동

강상모(Sangmo Kang) 대한기계학회 2015 大韓機械學會論文集B Vol.39 No.5

본 논문에서는 외부에서 균일한 직류전기장이 인가될 때 점성유체에 자유롭게 잠겨있는 단일 입자가 근처의 비전도성 평면 벽과의 상호작용 때문에 유발되는 2차원 유전영동 운동에 대하여 수치연구를 수행하였다. 특히 입자-유체 경계면에서 불연속적으로 급격히 변화하는 전기전도도를 가진 Maxwell 방정식을 해석하고 전기장을 구한 후 Maxwell 응력텐서를 적분하여 입자에 작용하는 유전영동 힘을 계산하였다. 해석 결과 전기장이 벽과 평행하게 인가될 때 입자는 항상 반발력이 유도되어 벽으로부터 멀어지는 방향으로 유전영동 운동이 발생하였으며, 그 운동특성은 입자와 벽 사이 간격과 입자의 전도도에 따라 크게 달라졌다. 운동 강도는 입자와 유체의 전도도가 서로 같으면 사라지나, 전도도가 서로 다르면 그 차이가 클수록 강도는 증가하였다. In this paper, we have numerically investigated two-dimensional dielectrophoretic (DEP) motions of a single particle suspended freely in a viscous fluid, interacting with a nearby nonconducting planar wall, under an externally applied uniform direct-current electric field. Particularly, we solve the Maxwell equation with a large sharp jump in the electric conductivity at the particle-fluid interface and then integrate the Maxwell stress tensor to compute the DEP force on the particle. Results show that, under an electric field parallel to the wall, one particle is always repelled to move far away from the wall and the motion depends strongly on the particle-wall spacing and the particle conductivity. The motion strength vanishes when the particle is as conductive as the fluid and increases as the conductivity deviates further from that of the fluid.

Electrodeless Conductivity Tensor Imaging (CTI) using MRI: Basic Theory and Animal Experiments

Saurav ZK Sajib,권오인,김형중,우응제 대한의용생체공학회 2018 Biomedical Engineering Letters (BMEL) Vol.8 No.3

The electrical conductivity is a passive material property primarily determined by concentrations of charge carriers andtheir mobility. The macroscopic conductivity of a biological tissue at low frequency may exhibit anisotropy related with itsstructural directionality. When expressed as a tensor and properly quantified, the conductivity tensor can provide diagnosticinformation of numerous diseases. Imaging conductivity distributions inside the human body requires probing it byexternally injecting conduction currents or inducing eddy currents. At low frequency, the Faraday induction is negligibleand it has been necessary in most practical cases to inject currents through surface electrodes. Here we report a novelmethod to reconstruct conductivity tensor images using an MRI scanner without current injection. This electrodelessmethod of conductivity tensor imaging (CTI) utilizes B1 mapping to recover a high-frequency isotropic conductivity imagewhich is influenced by contents in both extracellular and intracellular spaces. Multi-b diffusion weighted imaging is thenutilized to extract the effects of the extracellular space and incorporate its directional structural property. Implementing thenovel CTI method in a clinical MRI scanner, we reconstructed in vivo conductivity tensor images of canine brains. Depending on the details of the implementation, it may produce conductivity contrast images for conductivity weightedimaging (CWI). Clinical applications of CTI and CWI may include imaging of tumor, ischemia, inflammation, cirrhosis,and other diseases. CTI can provide patient-specific models for source imaging, transcranial dc stimulation, deep brainstimulation, and electroporation.

Reconstruction of inhomogeneous conductivities via the concept of generalized polarization tensors

Ammari, H.,Deng, Y.,Kang, H.,Lee, H. Gauthier-Villars 2014 Annales de l'Institut Henri Poincaré. Analyse non Vol.31 No.5

This paper extends the concept of generalized polarization tensors (GPTs), which was previously defined for inclusions with homogeneous conductivities, to inhomogeneous conductivity inclusions. We begin by giving two slightly different but equivalent definitions of the GPTs for inhomogeneous inclusions. We then show that, as in the homogeneous case, the GPTs are the basic building blocks for the far-field expansion of the voltage in the presence of the conductivity inclusion. Relating the GPTs to the Neumann-to-Dirichlet (NtD) map, it follows that the full knowledge of the GPTs allows unique determination of the conductivity distribution. Furthermore, we show important properties of the the GPTs, such as symmetry and positivity, and derive bounds satisfied by their harmonic sums. We also compute the sensitivity of the GPTs with respect to changes in the conductivity distribution and propose an algorithm for reconstructing conductivity distributions from their GPTs. This provides a new strategy for solving the highly nonlinear and ill-posed inverse conductivity problem. We demonstrate the viability of the proposed algorithm by preforming a sensitivity analysis and giving some numerical examples.

경상분지 백악기 화강암 암반에 대한 삼차원 수리전도텐서 추정사례

엄정기,이다혜 대한지질공학회 2022 지질공학 Vol.32 No.1

A workflow is presented to estimate the size of a representative elementary volume and 3-D hydraulic conductivity tensor based on fluid flow analysis for a discrete fracture network (DFN). A case study is considered for a Cretaceous granitic rock mass at Gijang in Busan, Korea. The intensity and size of joints were calibrated using the first invariant of the fracture tensor for the 2-D DFN of the study area. Effective hydraulic apertures were obtained by analyzing the results of field packer tests. The representative elementary volume of the 2-D DFN was determined to be 20 m square by investigating the variations in the directional hydraulic conductivity for blocks of different sizes. The directional hydraulic conductivities calculated from the 2-D DFN exhibited strong anisotropy related to the hydraulic behavior of the study area. The 3-D hydraulic conductivity tensor for the fractured rock mass of the study area was estimated from the directional block conductivities of the 2-D DFN blocks generated for various directions in 3-D. The orientations of the principal components of the 3-D hydraulic conductivity tensor were found to be identical to those of delineated joint sets in the study area. 본 연구는 부산 기장지역에 분포하는 백악기 흑운모 화강암에 대한 사례연구를 통하여 DFN(discrete fracture network) 유동해석 기반의 REV(representative elementary volume) 크기 및 삼차원 수리전도 텐서 추정을 위한 워크플로우를 제시하였다. 연구지역을 대표하는 이차원 DFN에 대하여 절리텐서의 일차불변량을 이용하여 절리의 빈도 및 길이가 보정되었다. 현장수압시험을 수행하여 선형의 등가유로관으로 취급된 현장의 절리에 대한 유효수리간극이 추정되었다. 연구지역의 이차원 DFN 블록에 대한 REV의 크기는 블록 크기에 따른 지향적 블록수리전도도의 변화를 분석하여 20 m × 20 m으로 결정하였다. 연구지역의 이차원 DFN에 대하여 산정된 지향적 블록수리전도도는 현장의 수리적 거동과 관련하여 강한 이방성을 지시한다. 다양한 방향으로의 이차원 DFN에서 산정된 지향적 블록수리전도도를 바탕으로연구지역의 절리성 암반에 대한 삼차원 수리전도텐서가 추정되었다. 삼차원 수리전도텐서의 주성분 방향은 현장에서 구분된 주 절리군의 방향과 일치한다.

구리-흑연 복합소재의 열전도계수 특성 모델링

박현준 ( Hyeon Jun Park ),이석호 ( Seok Ho Rhi ),이지수 ( Ji Su Lee. ) 충북대학교 산업과학기술연구소 2023 산업과학기술연구 논문집 Vol.37 No.1

In this study, a Cu-graphite composite is proposed as a solution to the reliability problem caused by the difference in the coefficient of thermal expansion (CTE) between chips and substrates. The thermal characteristics of the composite were investigated through the aspect ratio, arrangement, and volume fraction of fillers. ANSYS Material Designer was used to simulate the thermal conductivity (TC) of the composite material, varying the filler aspect ratio, tensor in the A11 direction, and volume fraction from 1 to 3, 0.3 to 0.6, and 0.1 to 0.3, respectively. The simulation was based on a Hot press specimen from a previous study. The results showed that increasing the content of copper filler decreased TC in the K1 and K2 directions, while it increased TC in the K3 direction. Furthermore, the study revealed the following insights: (1) decreasing the volume fraction improved TC in the K1 direction, regardless of the aspect ratio and tensor in the K1 direction; (2) low volume fraction and aspect ratio, and high tensor in the A11 direction improved TC in the K2 direction; (3) high volume fraction and aspect ratio, and low A11 tensor improved TC in the K3 direction. This study demonstrated the effectiveness of a Cu-graphite composite in improving the reliability of chips and substrates by controlling the thermal characteristics through the aspect ratio, arrangement, and volume fraction of fillers. The findings offer valuable insights for material designers to develop composite materials with improved thermal properties.

절리텐서의 성분 및 일차불변량이 2-D DFN 시스템의 블록수리전도 특성에 미치 는 영향

엄정기 대한자원환경지질학회 2019 자원환경지질 Vol.52 No.1

In this study, the effects of fracture tensor component and first invariant on block hydraulic behaviors are evaluated in the 2-D DFN(discrete fracture network) systems. A series of regression analysis is performed between connected fracture tensor components and block hydraulic conductivities estimated at every 30° hydraulic gradient directions for a total of 36 DFN systems having various joint density and size distribution. The directional block hydraulic conductivity seems to have strong relation with the fracture tensor component estimated in direction perpendicular to it. It is found that an equivalent continuum approach could be acceptable for the 2-D DFN systems under condition that the first invariant of fracture tensor is more than 2.0~2.5. The first invariant of fracture tensor seems highly correlated with average block hydraulic conductivity and can be used to evaluate hydraulic characteristics of the 2-D DFN systems. Also, a possibility of upscaling using the first invariant of fracture tensor for the DFN system is addressed through this study.

Doped Two-dimensional Semiconductor Superlattice: Photo-stimulated Quantum Thermo-magnetoelectric Effects under the Influence of a Confined Phonon

Bau Nguyen Quang,Quynh Nguyen Thi Lam,Ba Cao Thi Vi,Hung Le Thai 한국물리학회 2020 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.77 No.12

Photo-stimulated quantum thermo-magnetoelectric effects in doped two-dimensional semiconductor superlattices, including the photo-stimulated quantum Ettingshausen effect and the photo-stimulated quantum Peltier effect, have been theoretically studied by using the quantum kinetic equation method. In this work, we assume that the electron-confined acoustic phonon scattering is essential. Moreover, the presence of the laser radiation (LR) is also taken into account to determine the influence of confined phonons on the aforementioned effects. We have defined the analytical expressions for the kinetic tensors and the Ettingshausen and the Peltier coefficients, presented the numerically calculated the theoretical results for the GaAs:Si/GaAs:Be doped semiconductor superlattice and compared them with these for the case of an unconfined acoustic phonon. The results obtained indicated that the formulas for the kinetic tensors, the Ettingshausen coefficient (EC) and the Peltier coefficient (PC) contain the quantum number m specifying the confinement of a phonon and approach the results for an unconfined phonon as m goes to zero. We found that the kinetic tensors, the EC and the PC oscillate with changing magnetic field and that the confinement of a phonon causes a shift of the peaks in these oscillations to lower energy. The dependences of both EC and PC on the temperature were found to be nonlinear. Moreover, all the coefficients level off when the temperature was less than 4.5 K or greater than 5.5 K. The EC also depended on the doping concentration in a nonlinear way and reaches a positive constant value when the semiconductor superlattice was doped with a high concentration. Most of the numerical results showed that the magnitude of the tensors, the EC as well as the PC, within a confined acoustic phonon varie significantly in comparison with the unconfined phonon case. This means that the confinement of the phonon affects the thermo-magnetoelectric effect quantitatively and qualitatively. These results contribute to completing the theory of the thermo-magnetoelectric effects in the low-dimensional semiconductor systems.

비전도성 벽과의 상호작용에 따른 한 쌍 입자의 직류 유전영동 운동

강상모(Sangmo Kang) 대한기계학회 2015 大韓機械學會論文集B Vol.39 No.10

본 연구에서는 외부에서 균일한 직류전기장이 벽과 평행하게 인가될 때 점성유체 안에 자유롭게 잠겨있는 한 쌍의 입자들이 근처의 비전도성 평면 벽과의 상호작용 때문에 유발되는 2차원 유전영동운동에 대하여 수치연구를 수행하였다. 해석 결과 운동 특성은 입자들이 가지는 전기전도도 부호 조합과 입자들과 벽 사이 간격에 따라 크게 달라졌다. 두 입자가 서로 같은 전도도 부호를 가지면 입자들은 공전을 하다가 최종적으로 전기장과 평행하게 정렬한다. 반면에 서로 다른 부호를 가지면 입자들은 반대방향으로 공전하다 결국 전기장과 수직하게 정렬한다. 동시에 입자들은 전도도 조합과 무관하게 반발력을 받아 벽으로부터 멀어지는 쪽으로 이동한다. 입자들이 벽으로부터 멀리 떨어져 있을수록 입자들과 벽 사이 유전영동 상호작용 효과는 서서히 사라지며 대신 입자와 입자 사이 효과가 점점 두드러진다. The present study numerically investigated two-dimensional dielectrophoretic motions of a pair of particles suspended freely in a viscous fluid, interacting with a nearby nonconducting planar wall, under an external uniform electric field. The results show that the motions depend strongly on the set of two electric conductivity signs and the particles-wall separation gap. When both particles have the same sign, they revolve and finally align parallel to the electric field. In contrast, with different signs, they revolve in the opposite direction and finally align perpendicular to the field. Simultaneously, they are repelled to move farther away from the wall regardless of their conductivity set. With further separation from the wall, the particles-wall interaction effect diminishes and tthe particle-particle effect dominates.

Corticospinal Tract and Pontocerebellar Fiber of Central Pontine Myelinolysis

Yong Min,박성희,황승배 대한재활의학회 2012 Annals of Rehabilitation Medicine Vol.36 No.6

Central pontine myelinolysis is a rare neurologic disorder that is defined by demyelination of longitudinally descending tracts and transversly crossing fibers in the basis pontis. Frequently observed clinical manifestations of this disorder include sudden weakness, dysphagia, loss of consciouness and locked-in syndrome. However, there have been a few studies that reported a benign course of this disease, which include cerebellar signs, such as ataxia, intention tremor, and dysarthria. Here we report on a 53-year-old male with a history of liver cirrhosis who showed the cerebellar type of central pontine myelinolysis. The patient was diagnosed with central pontine myelinolysis based on clinical presentations and magnetic resonance imaging findings after a liver transplantation. Conventional magenetic resonance imaging (MRI) revealed the preservation of the corticospinal tract and abnormal pontocerebellar fibers. However, these findings were not sufficient to define the pathophysiology of our patient. Electrophysiologic analysis and diffusion tensor imaging (DTI) were performed to investigate cerebellar signs in this case. Delayed central motor conduction time (CMCT) to the tibialis anterior muscle with transcranial magnetic stimulation (TMS) was observed, which indicated demyelination of the corticospinal tract. Also, diffusion tensor imaging showed abnormal pontocerebellar fibers, which might have been caused by cerebellar dysfunction in our patient. A combination of TMS and DTI was also used to determine the pathophysiology of this disease.

평면 벽 근처에 있는 단일 입자가 벽면과 수직으로 인가된 균일 전기장 하에서 겪는 유전영동 운동

강상모(Sangmo Kang) 대한기계학회 2018 大韓機械學會論文集B Vol.42 No.2

본 논문에서는 직접수치모사를 수행하여 평면 벽과 유체가 서로 접촉해 있고 그 경계와 수직으로 외부 직류 전기장이 균일하게 인가되었을 때 벽 근처에 매달려 있는 단일 입자가 겪는 2차원 유전영동(DEP) 운동을 연구하였다. 따라서 Taylor & Melcher의 leaky-dielectric 모델을 풀어 전기장을 해석한 후 Maxwell 응력텐서를 적분하여 입자에 작용하는 DEP 힘을 계산하였으며, 반면에 연속방정식과 Stokes 방정식을 풀어 유동장을 예측하였다. 전기장과 유동장을 해석하기 위해 각각 예면경계법과 가상경계법으로 구성된 유한체적법을 개발하여 수치모사를 수행하였다. 결과에 따르면 근처에 평면 벽이 존재함으로써 벽-유체 경계와 수직방향으로 입자 DEP 운동이 발생하였으며, 이 운동은 입자와 벽의 전기전도율 조합과 그들 사이의 간격에 따라 그 특성이 크게 달라졌다. In this paper, we use a direct numerical simulation to investigate the two-dimensional dielectrophoretic (DEP) motion of a single particle in the vicinity of a planar wall under a uniform direct-current electric field imposed externally at a right angle to the wall-fluid interface. Accordingly, we solve the leaky dielectric model of Taylor and Melcher for the electric potential, and then integrate the Maxwell stress tensor to compute the DEP force. Further, we solve the continuity and Stokes equations for the flow field. For the simulations, we employ a finite volume approach, comprising a sharp interface method for the electric potential and an immersed boundary method for the flow field. The results show that the particle motion is initiated only in a direction perpendicular to the wall-fluid interface by the nearby wall, and depends strongly on the conductivity set of the particle and the wall, and their separation gap.