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Seonghoon Choi,Taehee Yoo,Seul-Ki Bac,Hakjoon Lee,Sangyeop Lee,Sanghoon Lee,Liu, X.,Furdyna, J. K. IEEE 2016 IEEE transactions on magnetics Vol.52 No.7
<P>Tunneling magnetoresistance (TMR) phenomena in hybrid Fe/GaAlAs/GaMnAs magnetic tunnel junctions (MTJs) were investigated by rotating a magnetic field of constant strength in the film plane. When a strong field (e.g., 4000 G) is used, the magnetization in GaMnAs and Fe coherently rotates in both layers, resulting in a smooth angular dependence of TMR. In contrast, abrupt transition steps and plateaus are observed in TMR, when a weak field (below 100 G) is rotated. The behavior observed in strong fields is ascribed to tunneling anisotropic magnetoresistance, an effect that occurs when magnetizations in both magnetic layers in the MTJ are aligned parallel to each other. The tunneling behavior observed in weak fields, on the other hand, is caused by differences in relative magnetization alignments in the two layers that arise from differences in their magnetocrystalline anisotropies. The latter behavior provided the anisotropic TMR that involved with parallel and antiparallel alignments at specific crystallographic directions.</P>
Lee, Kyungsub,Lee, Seonghoon Elsevier 2018 ELECTROCHIMICA ACTA Vol.289 No.-
<P><B>Abstract</B></P> <P>The growth rate of TiO<SUB>2</SUB> nanotubes depends on temperature, etchant concentration, and the strength of electric field. Under the typical fast hard anodization condition such as the strong electric field at 120 V, the flow of current is concentrated through the thin layer of TiO<SUB>2</SUB>, resulting in the bent or collapsed TiO<SUB>2</SUB> nanotubes or a break-down, called ‘burning’. To prevent the adverse effects, top etching and ’burning’, we introduced formamide of a high dielectric constant as an additive in the electrolyte. The organic acids were electrochemically generated from the decomposition of formamide on TiO<SUB>2</SUB>. The organic acids rapidly stabilized anodization current and thus, the highly ordered 17 μm-long TiO<SUB>2</SUB> nanotube arrays were obtained just in 5 min anodization. During the anodization with pure formamide mixed with 1.3 vol% water under the strong electric field, cyanides, ammonium ions, and fatty acids, originated from the decomposition of formamide adsorbed on the TiO<SUB>2</SUB>, were found by ion chromatograph and gas chromatograph–mass spectrometer (GC-MS) equipped with a pyrolyzer. The major roles of fatty acids such as oleic acids etc. generated from formamide are the current stabilization, the prevention of burning, and the delicate balancing of speed of etching with oxide layer growth.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
An Intelligent New Dynamic Load Redistribution Mechanism in Distributed Environments
Seonghoon Lee 한국콘텐츠학회(IJOC) 2007 International Journal of Contents Vol.3 No.1
Load redistribution is a critical resource in computer system. In sender-initiated load redistribution algorithms, the sender continues to send unnecessary request messages for load transfer until a receiver is found while the system load is heavy. These unnecessary request messages result in inefficient communications, low CPU utilization, and low system throughput in distributed systems. To solve these problems, we propose a genetic algorithm based approach for improved sender-initiated load redistribution in distributed systems. Compared with the conventional sender-initiated algorithms, the proposed algorithm decreases the response ime and task processing time.
Lee, Hyun Su,Choi, Chansoo,Kim, Chan Hyeong,Han, Min Cheol,Yeom, Yeon Soo,Nguyen, Thang Tat,Kim, Seonghoon,Choi, Sang Hyoun,Lee, Soon Sung,Kim, Jina,Hwang, JinHo,Kang, Youngnam The Korean Association for Radiation Protection 2019 방사선방어학회지 Vol.44 No.3
Background: Four-dimensional computed tomographic (4DCT) images are increasingly used in clinic with the growing need to account for the respiratory motion of the patient during radiation treatment. One of the reason s that makes the dose evaluation using 4DCT inaccurate is a change of the patient respiration during the treatment session, i.e., intrafractional uncertainty. Especially, when the amplitude of the patient respiration is greater than the respiration range during the 4DCT acquisition, such an organ motion from the larger respiration is difficult to be represented with the 4DCT. In this paper, the method to generate images expecting the organ motion from a respiration with extended amplitude was proposed and examined. Materials and Methods: We propose a method to generate extra-phase images from a given set of the 4DCT images using deformable image registration (DIR) and linear extrapolation. Deformation vector fields (DVF) are calculated from the given set of images, then extrapolated according to respiratory surrogate. The extra-phase images are generated by applying the extrapolated DVFs to the existing 4DCT images. The proposed method was tested with the 4DCT of a physical 4D phantom. Results and Discussion: The tumor position in the generated extra-phase image was in a good agreement with that in the gold-standard image which is separately acquired, using the same 4DCT machine, with a larger range of respiration. It was also found that we can generate the best quality extra-phase image by using the maximum inhalation phase (T0) and maximum exhalation phase (T50) images for extrapolation. Conclusion: In the present study, a method to construct extra-phase images that represent expanded respiratory motion of the patient has been proposed and tested. The movement of organs from a larger respiration amplitude can be predicted by the proposed method. We believe the method may be utilized for realistic simulation of radiation therapy.
An Enhanced Response Time Mechanism in Grid Systems
SeongHoon Lee 한국콘텐츠학회(IJOC) 2010 International Journal of Contents Vol.6 No.2
For applications that are grid enabled, the grid can offer a resource balancing effect by scheduling grid jobs on machines with low utilization. When jobs communicate with each other, the internet, or with storage resources, an advanced scheduler could schedule them to minimize communications traffic or minimize the distance of the communications. We propose an intelligent load distribution algorithm to minimize communications traffic and distance of the communications using genetic algorithm. The experiments show the proposed load redistribution algorithm performs efficiently in the variance of load in grid environments.
SeongHoon Lee 한국콘텐츠학회(IJOC) 2008 International Journal of Contents Vol.4 No.2
A load sharing algorithm is one of the important factors in computer system. In sender-initiated load sharing algorithms, when a distributed system becomes to heavy system load, it is difficult to find a suitable receiver because most processors have additional tasks to send. The sender continues to send unnecessary request messages for load transfer until a receiver is found while the system load is heavy. Because of these unnecessary request messages it results in inefficient communications, low cpu utilization, and low system throughput. To solve these problems, we propose a self-adjusting evolutionary algorithm for improved sender-initiated load sharing in distributed systems. This algorithm decreases response time and increases acceptance rate. Compared with the conventional sender-initiated load sharing algorithms, we show that the proposed algorithm performs better.
Antiferromagnetic Interlayer Exchange Coupling in Ferromagnetic GaMnAs/GaAs:Be Multilayers
Lee, Hakjoon,Lee, Sangyeop,Choi, Seonghoon,Yoo, Taehee,Lee, Sanghoon,Liu, Xinyu,Furdyna, Jacek K. IEEE 2015 IEEE transactions on magnetics Vol.51 No.11
<P>Interlayer exchange coupling (IEC) between the GaMnAs layers in GaMnAs/GaAs:Be multilayer systems has been investigated using magnetotransport experiments. The observation of a stable antiparallel magnetization alignment state from the systems indicates the presence of antiferromagnetic (AFM) IEC between the GaMnAs layers. The transitions between parallel and antiparallel alignments of GaMnAs magnetic layers in the system were carefully investigated by measuring resistance change with increasing temperature under various bias magnetic fields. From the dependence of the transition temperature on bias fields, we have estimated the magnitude of AFM IEC and its temperature behavior of our GaMnAs/GaAs:Be multilayers.</P>
Lee, Myoung Jin,Jin, Seonghoon,Baek, Chang-Ki,Hong, Sung-Min,Park, Soo-Young,Park, Hong-Hyun,Lee, Sang-Don,Chung, Sung-Woong,Jeong, Jae-Goan,Hong, Sung-Joo,Park, Sung-Wook,Chung, In-Young,Park, Young IEEE 2007 IEEE transactions on electron devices Vol.54 No.12
<P> We have experimentally analyzed the leakage mechanism and device degradations caused by the Fowler–Nordheim (F–N) and hot carrier stresses for the recently developed dynamic random-access memory cell transistors with deeply recessed channels. We have identified the important differences in the leakage mechanism between saddle fin (S-Fin) and recess channel array transistor (RCAT). These devices have their own respective structural benefits with regard to leakage current. Therefore, we suggest guidelines with respect to the optimal device structures such that they have the advantages of both S-Fin and RCAT structures. With these guidelines, we propose a new recess-FinFET structure that can be realized by feasible manufacturing process steps. The structure has the side-gate form only in the bottom channel region. This enhances the characteristics of the threshold voltage (<TEX>$V_{\rm TH}$</TEX>), <SMALL>ON</SMALL>/<SMALL>OFF</SMALL> currents, and the retention time distributions compared with the S-Fin structure introduced recently. </P>