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Search Results: 1 - 10 of 20473 matches for " Bongjae Kim "
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Termination-dependent Electronic and Magnetic Properties of Ultrathin SrRuO$_{3}$ (111) Film on SrTiO$_{3}$
Bongjae Kim,B. I. Min
Physics , 2013, DOI: 10.1103/PhysRevB.89.195411
Abstract: We have investigated electronic and magnetic properties of ultrathin SrRuO$_{3}$ (SRO) film grown on (111) SrTiO$_{3}$ substrate using the {\it ab initio} electronic structure calculations. Ru-terminated SRO (111) film suffers from strong surface atomic relaxations, while SrO$_{3}$-terminated one preserves the surface structure of ideal perovskites. Both Ru- and SrO$_{3}$-terminated SRO (111) film show unexpected interlayer antiferromagnetic (AFM) structure at the surface, but with different characters and mechanisms. The AFM structure for the former results from the large surface atomic relaxation, whereas that for the latter results from the truncated film effect. Interestingly, for the SrO$_{3}$-termination case, the half-metallic nature emerges despite the interlayer AFM structure. Upon reducing the thickness, the collapsing behavior of magnetic anisotropy from out-of-plane to in-plane easy axis is found to occur for the Ru-termination case, which, however, does not pertain to SrO$_{3}$-termination case.
Universal metastability of the low-spin state in Co$^{2+}$ systems: non-Mott type pressure-induced spin-state transition in CoCl$_{2}$
Bongjae Kim,Kyoo Kim,B. I. Min
Physics , 2014, DOI: 10.1103/PhysRevB.89.115131
Abstract: We have investigated the pressure-induced spin-state transition in Co$^{2+}$ systems in terms of a competition between the Hund's exchange energy ($J$) and the crystal-field splitting ($\Delta_{CF}$). First, we show the universal metastability of the low-spin state in octahedrally coordinated Co$^{2+}$ systems. Then we present the strategy to search for a Co$^{2+}$ system, for which the mechanism of spin-state and metal-insulator transitions is governed not by the Mott physics but by $J$ vs. $\Delta_{CF}$ physics. Using CoCl$_{2}$ as a prototypical Co$^{2+}$ system, we have demonstrated the pressure-induced spin-state transition from high-spin to low-spin, which is accompanied with insulator-to-metal and antiferromagnetic to half-metallic ferromagnetic transitions. Combined with metastable character of Co$^{2+}$ and the high compressibility nature of CoCl$_{2}$, the transition pressure as low as 27 GPa can be identified on the basis of $J$ vs. $\Delta_{CF}$ physics.
Substrate-tuning of correlated spin-orbit oxides
Bongjae Kim,Beom Hyun Kim,Kyoo Kim,B. I. Min
Physics , 2015,
Abstract: We have systematically investigated substrate-strain effects on the electronic structures of two representative Sr-iridates, a correlated-insulator Sr$_2$IrO$_4$ and a metal SrIrO$_3$. Optical conductivities obtained by the \emph{ab initio} electronic structure calculations reveal that the tensile strain shifts the optical peak positions to higher energy side with altered intensities, suggesting the enhancement of the electronic correlation and spin-orbit coupling (SOC) strength in Sr-iridates. The response of the electronic structure upon tensile strain is found to be highly correlated with the direction of magnetic moment, the octahedral connectivity, and the SOC strength, which cooperatively determine the robustness of $J_{eff}$=1/2 ground states. Optical responses are analyzed also with microscopic model calculation and compared with corresponding experiments. In the case of SrIrO$_3$, the evolution of the electronic structure near the Fermi level shows high tunability of hole bands, as suggested by previous experiments.
A Smart Checkpointing Scheme for Improving the Reliability of Clustering Routing Protocols
Hong Min,Jinman Jung,Bongjae Kim,Yookun Cho,Junyoung Heo,Sangho Yi,Jiman Hong
Sensors , 2010, DOI: 10.3390/s101008938
Abstract: In wireless sensor networks, system architectures and applications are designed to consider both resource constraints and scalability, because such networks are composed of numerous sensor nodes with various sensors and actuators, small memories, low-power microprocessors, radio modules, and batteries. Clustering routing protocols based on data aggregation schemes aimed at minimizing packet numbers have been proposed to meet these requirements. In clustering routing protocols, the cluster head plays an important role. The cluster head collects data from its member nodes and aggregates the collected data. To improve reliability and reduce recovery latency, we propose a checkpointing scheme for the cluster head. In the proposed scheme, backup nodes monitor and checkpoint the current state of the cluster head periodically. We also derive the checkpointing interval that maximizes reliability while using the same amount of energy consumed by clustering routing protocols that operate without checkpointing. Experimental comparisons with existing non-checkpointing schemes show that our scheme reduces both energy consumption and recovery latency.
A Low-Cost EEG System-Based Hybrid Brain-Computer Interface for Humanoid Robot Navigation and Recognition
Bongjae Choi, Sungho Jo
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0074583
Abstract: This paper describes a hybrid brain-computer interface (BCI) technique that combines the P300 potential, the steady state visually evoked potential (SSVEP), and event related de-synchronization (ERD) to solve a complicated multi-task problem consisting of humanoid robot navigation and control along with object recognition using a low-cost BCI system. Our approach enables subjects to control the navigation and exploration of a humanoid robot and recognize a desired object among candidates. This study aims to demonstrate the possibility of a hybrid BCI based on a low-cost system for a realistic and complex task. It also shows that the use of a simple image processing technique, combined with BCI, can further aid in making these complex tasks simpler. An experimental scenario is proposed in which a subject remotely controls a humanoid robot in a properly sized maze. The subject sees what the surrogate robot sees through visual feedback and can navigate the surrogate robot. While navigating, the robot encounters objects located in the maze. It then recognizes if the encountered object is of interest to the subject. The subject communicates with the robot through SSVEP and ERD-based BCIs to navigate and explore with the robot, and P300-based BCI to allow the surrogate robot recognize their favorites. Using several evaluation metrics, the performances of five subjects navigating the robot were quite comparable to manual keyboard control. During object recognition mode, favorite objects were successfully selected from two to four choices. Subjects conducted humanoid navigation and recognition tasks as if they embodied the robot. Analysis of the data supports the potential usefulness of the proposed hybrid BCI system for extended applications. This work presents an important implication for the future work that a hybridization of simple BCI protocols provide extended controllability to carry out complicated tasks even with a low-cost system.
Anisotropic Magnetic Couplings and Structure-Driven Canted to Collinear Transitions in Spin-orbit Coupled Sr2IrO4
Peitao Liu,Sergii Khmelevskyi,Bongjae Kim,Martijn Marsman,Dianzhong Li,Xing-Qiu Chen,D. D. Sarma,Georg Kresse,Cesare Franchini
Physics , 2015, DOI: 10.1103/PhysRevB.92.054428
Abstract: We put forward a scheme to study the anisotropic magnetic couplings in Sr2IrO4 by mapping fully relativistic constrained noncollinear density functional theory including an on-site Hubbard U correction onto a general spin model Hamiltonian. This procedure allows for the simultaneous account and direct control of the lattice, spin and orbital interactions within a fully ab initio scheme. We compute the isotropic, single site anisotropy and Dzyaloshinskii-Moriya (DM) coupling parameters, and clarify that the origin of the canted magnetic state in Sr2IrO4 arises from the interplay between structural distortions and the competition between isotropic exchange and DM interactions. A complete magnetic phase diagram with respect to the tetragonal distortion and the rotation of IrO6 octahedra is constructed, revealing the presence of two types of canted to collinear magnetic transitions: a spin-flop transition with increasing tetragonal distortion and a complete quenching of the basal weak ferromagnetic moment below a critical octahedral rotation.
Design of Quantification Model for Ransom Ware Prevent  [PDF]
Donghyun Kim, Seoksoo Kim
World Journal of Engineering and Technology (WJET) , 2015, DOI: 10.4236/wjet.2015.33C030

The growth of ICT within the society has become increasingly digitized, thus, the overall activity has amounted to various researches for protecting any data from malicious threats. Recently, ransomware has been a rapidly propagated subject for social engineering techniques especially the ransomware. Users can delete a ransomeware code using an antivirus software code. However, the encrypted data would be impossible to recover. Therefore, ransomware must be prevented and must have early detection before it infects any data. In this paper, we are proposing a quantification model to prevent and detect any cryptographic operations in the local drive.

Trends of Noninvasive Radiofrequency and Minimally Invasive Treatment for the Management of Facial Aging  [PDF]
Sunghee Kim, Moonjong Kim
Journal of Cosmetics, Dermatological Sciences and Applications (JCDSA) , 2019, DOI: 10.4236/jcdsa.2019.91003
Abstract: Various treatments for the management of facial aging have been performed among which noninvasive radio-frequency (RF; i.e., thermage) treatment and minimally invasive treatments are on the rise. The purpose of this study was to analyze trends of the treatment of facial aging in Korea and to investigate relationships between the use of noninvasive RF and minimally invasive treatments. A retrospective analysis conducted on data from 4021 patients showed that thermage treatment increased by 134.9% over 5 years. As a person ages, the rate of facial treatment with both the botulinum toxin (for the masseter and lines of the glabella, lateral canthus, and forehead) and the PDO thread lift increases. The use of the treatments, nasolabial fold filler and Silhouette Soft Thread, however, was not associated with aging. The patients receiving thermage treatment were less likely to undergo any of the other treatments including PDO thread lift, Silhouette Soft Thread, nasolabial fold filler, or any of the botulinum toxin treatments. Overall, the results showed that patients who had received noninvasive RF tended to receive less minimally invasive treatment.
The Effect of Prunella on Anti-Inflammatory Activity in RAW264.7 Mouse Macrophage Cells  [PDF]
Meehye Kim
Food and Nutrition Sciences (FNS) , 2012, DOI: 10.4236/fns.2012.39170
Abstract: The extracts of Prunella vulgaris L. (Labiatae), a popular Western and Chinese herbal medicine, was shown to have anti-inflammatory properties, which might be due to partially, their rosmarinic acid content. Inhition of prostaglandine E2 (PGE2) production in lipopolysaccharide (LPS) stimulated RAW264.7 mouse macrophage cells was assessed with an enzyme immunoassay (EIA) following 8-hour treatments with Prunella vulgaris extracts or fractions. Results showed that 95% ethanol extracts from P. vulgaris significantly inhibited PGE2 production. In further studies, fraction 2 from the 95% ethanol extract of P. vulgaris significantly reduced PGE2 production at 66 µg/ml (72% reduction). Cytotoxic-ity did not play a role in the noted reduction of PGE2 seen in either the extracts or fractions from P. vulgaris. High performance liquid chromatography analysis showed that there was 1.4 mM rosmarinic acid in 95% ethanol Prunella extract (201 mg/ml crude extract). Our results suggest that rosmarinic acid may contribute toward the anti-inflammatory activity of Prunella in a dose-response manner. Prunella might have a potential to be used as a functional food for anti-inflammatory activity.
An Effect of the Elastic Energy Stored in the Muscle-Tendon Complex at Two Different Coupling-Time Conditions during Vertical Jump  [PDF]
Sukwon Kim
Advances in Physical Education (APE) , 2013, DOI: 10.4236/ape.2013.31002

A study was performed to evaluate effects of elastic energy stored pre-stretch on the mechanical work output while performing vertical jump. Eight male volunteers of age between 21-29 years old participated in the present study. The present study hypothesized that the vertical jump height during countermovement jumps (CMJ) would be higher than that during squat jump (SJ). During squat jump, a volunteer paused 0.5 sec before making upward movement. The results showed that ground reaction forces and vertical jump displacements were higher in CMJ in comparison to SJ. The study concluded that part of the positive work measured did derive from the recoil of the elastic component of the muscle-tendon complex.

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