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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, 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>
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.
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>
Lee Je Seop,Cha Yong Sung,Yeon Seonghoon,Kim Tae Youn,Lee Yoonsuk,Choi Jin-Geul,Cha Kyoung-Chul,Lee Kang Hyun,Kim Hyun 대한의학회 2021 Journal of Korean medical science Vol.36 No.18
Background: It is difficult to diagnose patients with poisoning and determine the causative agent in the emergency room. Usually, the diagnosis of such patients is based on their medical history and physical examination findings. We aimed to confirm clinical diagnoses using systematic toxicological analysis (STA) and investigate changes in the diagnosis of poisoning. Methods: The Intoxication Analysis Service was launched in June 2017 at our hospital with the National Forensic Service to diagnose intoxication and identify toxic substances by conducting STA. Data were collected and compared between two time periods: before and after the initiation of the project, i.e., from June 2014 to May 2017 and from June 2017 to May 2020. Results: A total of 492 and 588 patients were enrolled before and after the service, respectively. Among the 588 after-service patients, 446 underwent STA. Among the 492 before-service patients, 69.9% were diagnosed clinically, whereas the causative agent could not be identified in 35 patients. After starting the service, a diagnosis was confirmed in 84.4% of patients by performing a hospital-available toxicological analysis or STA. Among patients diagnosed with poisoning by toxins identified based on history taking, only 83.6% matched the STA results, whereas 8.4% did not report any toxin, including known substances. The substance that the emergency physician suspected after a physical examination was accurate in 49.3% of cases, and 12% of cases were not actually poisoned. In 13.4% of patients who visited the emergency room owing to poisoning of unknown cause, poisoning could be excluded after STA. Poisoning was determined to be the cause of altered mental status in 31.5% of patients for whom the cause could not be determined in the emergency room. Conclusion: A diagnosis may change depending on the STA results of intoxicated patients. Therefore, appropriate STA can increase the accuracy of diagnosis and help in making treatment decisions.
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>
Manipulation of magnetization in GaMnAs films by spin-orbit-induced magnetic fields
Lee, Sangyeop,Yoo, Taehee,Bac, Seul-Ki,Choi, Seonghoon,Lee, Hakjoon,Lee, Sanghoon,Liu, X.,Furdyna, J.K.,Dobrowolska, M. Elsevier 2017 CURRENT APPLIED PHYSICS Vol.17 No.5
<P>We have investigated the effect of spin-orbit-induced (SOI) magnetic fields on magnetization switching in GaMnAs films. The sign of such SOI fields depends on the direction of the current flowing in the film, thus providing a handle for electrically manipulating magnetization in ferromagnetic GaMnAs films. Specifically, when an applied magnetic field is swept along the current direction, magnetization reversal occurs via rotations in opposite sense (i.e., clockwise (CW) or counterclockwise (CCW)) depending on the sign of the current, thus leading to opposite signs of the planar Hall resistance (PHR) measured on the film. The effect of SOI fields also manifests itself through hysteretic behavior of PHR for two opposite currents as a fixed magnetic field is rotated in the film plane. The width of the resulting hysteresis between two current directions then allows us to estimate the magnitude of the SOI field at current density of 1.0 x 10(5) A/cm(2) as similar to 1.2 Oe in our GaMnAs film. Such switching of magnetization between two magnetic easy axes induced by switching the sign of an applied current provides a means of electronically controlling the value of film resistance (in this case of PHR), a process that can be exploited in spintronic devices. (C) 2017 Elsevier B.V. All rights reserved.</P>