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Search Results: 1 - 10 of 318742 matches for " Jong-Kyo Choi and Nack J Kim "
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Deformation behavior of duplex austenite and ε-martensite high-Mn steel
Ki Hyuk Kwon, Byeong-Chan Suh, Sung-Il Baik, Young-Woon Kim, Jong-Kyo Choi and Nack J Kim
Science and Technology of Advanced Materials , 2013,
Abstract: Deformation and work hardening behavior of Fe–17Mn–0.02C steel containing ε-martensite within the austenite matrix have been investigated by means of in situ microstructural observations and x-ray diffraction analysis. During deformation, the steel shows the deformation-induced transformation of austenite → ε-martensite → α'-martensite as well as the direct transformation of austenite → α'-martensite. Based on the calculation of changes in the fraction of each constituent phase, we found that the phase transformation of austenite → ε-martensite is more effective in work hardening than that of ε-martensite → α'-martensite. Moreover, reverse transformation of ε-martensite → austenite has also been observed during deformation. It originates from the formation of stacking faults within the deformed ε-martensite, resulting in the formation of 6H-long periodic ordered structure.
Effective Use of Sugammadex for Incomplete Pyridostigmine Reversal of Muscle Relaxation by Rocuronium: A Case Report  [PDF]
Hee Jong Lee, Kyo Sang Kim, Ji Seon Jeong, Sung Hwan Choi, Kyu Nam Kim
Open Journal of Anesthesiology (OJAnes) , 2013, DOI: 10.4236/ojanes.2013.39083
Abstract:

Anticholinesterase does not allow adequate reversal of the deep neuromuscular blockade (NMB) achieved using high doses of relaxants. A 71-year-old female patient (weight 70 kg, height 169 cm) was scheduled for a transurethral resection of a bladder tumor under general anesthesia. We administered rocuronium 30 mg (0.43 mg/kg) for tracheal intubation due to an estimated short surgical time. During the operation, an additional rocuronium 10 mg was injected. The surgical procedure ended abruptly 10 minutes after receiving the last dose of rocuronium. At the end of surgery, the patient received pyridostigmine as a reversal. However, residual NMB persisted, and neuromuscular monitoring did not show the expected degree of recovery. Sugammadex 2 mg/kg was used, and the patient experienced complete reversal from NMB in just 2 min.

A New Weighted Correlation Coefficient Method to Evaluate Reconstructed Brain Electrical Sources
Jong-Ho Choi,Min-Hyuk Kim,Luan Feng,Chany Lee,Hyun-Kyo Jung
Journal of Applied Mathematics , 2012, DOI: 10.1155/2012/251295
Abstract: Various inverse algorithms have been proposed to estimate brain electrical activities with magnetoencephalography (MEG) and electroencephalography (EEG). To validate and compare the performances of inverse algorithms, many researchers have used artificially constructed EEG and MEG datasets. When the artificial sources are reconstructed on the cortical surface, accuracy of the source estimates has been difficult to evaluate. In this paper, we suggest a new measure to evaluate the reconstructed EEG/MEG cortical sources more accurately. To validate the usefulness of the proposed method, comparison between conventional and proposed evaluation metrics was conducted using artificial cortical sources simulated under different noise conditions. The simulation results demonstrated that only the proposed method could reflect the source space geometry regardless of the number of source peaks.
Critical currents for vortex defect motion in superconducting arrays
Jong Soo Lim,M. Y. Choi,Beom Jun Kim,J. Choi
Physics , 2005, DOI: 10.1103/PhysRevB.71.100505
Abstract: We study numerically the motion of vortices in two-dimensional arrays of resistively shunted Josephson junctions. An extra vortex is created in the ground states by introducing novel boundary conditions and made mobile by applying external currents. We then measure critical currents and the corresponding pinning energy barriers to vortex motion, which in the unfrustrated case agree well with previous theoretical and experimental findings. In the fully frustrated case our results also give good agreement with experimental ones, in sharp contrast with the existing theoretical prediction. A physical explanation is provided in relation with the vortex motion observed in simulations.
Fe–Al–Mn–C lightweight structural alloys: a review on the microstructures and mechanical properties
Hansoo Kim, Dong-Woo Suh and Nack J Kim
Science and Technology of Advanced Materials , 2013,
Abstract: Adding a large amount of light elements such as aluminum to steels is not a new concept recalling that several Fe–Al–Mn–C alloys were patented in 1950s for replacement of nickel or chromium in corrosion resistance steels. However, the so-called lightweight steels or low-density steels were revisited recently, which is driven by demands from the industry where steel has served as a major structural material. Strengthening without loss of ductility has been a triumph in steel research, but lowering the density of steel by mixing with light elements will be another prospect that may support the competitiveness against emerging alternatives such as magnesium alloys. In this paper, we review recent studies on lightweight steels, emphasizing the concept of alloy design for microstructures and mechanical properties. The influence of alloying elements on the phase constituents, mechanical properties and the change of density is critically reviewed. Deformation mechanisms of various lightweight steels are discussed as well. This paper provides a reason why the success of lightweight steels is strongly dependent on scientific achievements even though alloy development is closely related to industrial applications. Finally, we summarize some of the main directions for future investigations necessary for vitalizing this field of interest.
Novel electronic behavior driving NdNiO3 metal-insulator transition
M. H. Upton,Yongseong Choi,Jian Liu,D. Meyers,S. Middey,J. Chakhalian,Jong-Woo Kim,Philip J. Ryan
Physics , 2014,
Abstract: We present evidence that the metal-insulator transition (MIT) in a tensile strained NdNiO3 (NNO) film is facilitated by a redistribution of electronic density and neither requires Ni charge disproportionation nor symmetry change [1, 2]. Given epitaxial tensile strain in thin NNO films induces preferential occupancy of the $e_g$ $d_{x^2-y^2}$ orbital ($s_{3z^2-r^2}$) we propose the larger transfer integral of this orbital state with the O 2p mediates a redistribution of electronic density from the Ni atom. A decrease in Ni $d_{x^2-y^2}$ orbital occupation is directly observed by resonant inelastic x-ray scattering below the MIT temperature. Furthermore, an increase in Nd charge occupancy is measured by x-ray absorption at the Nd L3 edge. Both spin-orbit coupling and crystal field effects combine to break the degeneracy of the Nd 5d states shifting the energy of the Nd $e_g$ $d_{x^2-y^2}$ orbital towards the Fermi level allowing the A site to become an active acceptor during the MI transition. This work identifies the relocation of electrons from the Ni 3d to the Nd 5d orbitals across the MIT. We propose the insulating gap opens between the Ni 3d and O 2p resulting from Ni 3d electron localization mediated by charge loss. The transition seems neither purely Mott-Hubbard nor simple charge transfer.
Optical spectroscopy study on the electronic structure of $Eu_{1-x} Ca_x B_6$
Jungho Kim,S. -J. Oh,Youngwoo Lee,E. J. Choi,C. C. Homes,Jong-Soo Rhyee,B. K. Cho
Physics , 2004, DOI: 10.1103/PhysRevB.71.075105
Abstract: The optical conductivity $\sigma_{1}(\omega)$ of Eu$_{1-x}$Ca$_{x}$B$_{6}$ has been obtained from reflectivity and ellipsometry measurements for series of compositions, $0\leq x\leq 1$. The interband part of $\sigma_{1}(\omega) $ shifts continuously to higher frequency as Ca-content $x$ increases. Also the intraband spectral weight of $\sigma_{1}(\omega)$ decreases rapidly and essentially vanishes for $x\geq x_{c}=0.35$. These results show that the valence band and the conduction band of Eu$_{1-x}$Ca$_{x}$B$_{6}$ move away from each other such that their band overlap decreases with increasing Ca-substitution. As a result, the electronic state evolves from the semimetallic structure of EuB$_{6}$ to the insulating CaB$_{6}$ where the two bands are separated to open a finite gap ($\simeq 0.25$ eV) at the X-point of the Brillouin zone.
Termination-dependent Surface In-gap States in a Mixed-valent Topological Insulator: SmB$_6$
Junwon Kim,Kyoo Kim,Chang-Jong Kang,Sooran Kim,Hong Chul Choi,J. -S. Kang,J. D. Denlinger,B. I. Min
Physics , 2014, DOI: 10.1103/PhysRevB.90.075131
Abstract: We have investigated the surface states of a potential mixed-valent topological insulator SmB$_6$ based on the first principles density functional theory slab band structure analysis. We have found that metallic surface states are formed in the bulk band gap region, providing evidence for the topological insulating nature of SmB$_6$. The obtained surface in-gap states are quite different from those in existing reports in that they are formed differently depending on the Sm or B$_6$ surface termination, and are composed of mainly Sm $4f$ state indicating the essentiality of including $f$ electrons in describing the surface states. We have obtained the spin chiral structures of the Fermi surfaces, which are also in accordance with the topological insulating nature of SmB$_6$.
Quantum Oscillations of the Metallic Triangular-lattice Antiferromagnet PdCrO2
Jong Mok Ok,Y. J. Jo,K. Kim,T. Shishidou,E. S. Choi,Han-Jin Noh,T. Oguchi,B. I. Min,Jun Sung Kim
Physics , 2013, DOI: 10.1103/PhysRevLett.111.176405
Abstract: We report the de Haas-van Alphen (dHvA) oscillations and first-principle calculations for triangular antiferromagnet PdCrO2 showing unconventional anomalous Hall effect (AHE). The dHvA oscillations in PdCrO2 reveal presence of several 2 dimensional Fermi surfaces of smaller size than found in nonmagnetic PdCoO2. This evidences Fermi surface reconstruction due to the non-collinear 120 antiferromagnetic ordering of the localized Cr, consistent with the first principle calculations. The temperature dependence of dHvA oscillations shows no signature of additional modification of Cr spin structure below TN. Considering that the 120 helical ordering of Cr spins has a zero scalar spin chirality, our results suggest that PdCrO2 is a rare example of the metallic triangular antiferromagnets whose unconventional AHE can not be understood in terms of the spin chirality mechanism.
Rolling Fatigue Test of Large-Sized UHPC Member for Cable Stayed Bridge  [PDF]
Jeong-Rae Cho, Young Jin Kim, Jong Sup Park, Eun Suk Choi, Won Jong Chin
Engineering (ENG) , 2012, DOI: 10.4236/eng.2012.410082
Abstract: Recently, research strives to apply Ultra High Performance Concrete (UHPC) to large-sized structures owing to its remarkable mechanical performance and durability compared to normal concrete. The Korea Institute of Construction Technology proposed SuperBridge800, an edge girder type UHPC cable stayed bridge with central span of 800 m, through its detailed design. The bridge is designed to be erected through the connection of precast UHPC segments. The precast UHPC segment is monolithically composed of one ribbed deck slab and edge girders at each side. The connection between the precast segments is achieved by steel bars at the edge girders and by UHPC cast-in-place wet joint at the slab. Despite of the outstanding mechanical performance of UHPC, the fabrication of large-sized members is a difficult task since UHPC hardens faster than normal concrete and requires a special curing process. Therefore, the constructability of large-sized UHPC segment should be secured to achieve SuperBridge800. Besides, the performance of the connection between segments should also be guaranteed, especially in terms of the fatigue performance of the UHPC cast-in-place joint, which constitutes a weak point. To that goal, two half-scaled UHPC segments are manufactured and the constructability is examined by fabricating a large-sized UHPC member connected with respect to the design conditions. This study conducts rolling fatigue test on the so-fabricated large-sized UHPC member. Rolling fatigue test is carried out up to 2 million cycles considering actual vehicle load at each center and quarter points of the member. The test results confirm that the service limit state is satisfied.
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