• The Korean Journal of Pain
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• v.22 no.2
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• pp.158-162
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• 2009

Background: The loss of resistance (LOR) method is most commonly used to identify the epidural space. This method is thought to rely on the penetration of the ligamentum flavum. Unfortunately the exact morphology of the ligamentum flavum is variable at different vertebral levels. Especially, it has been pointed out that the lower cervical ligamentum flavum may be discontinuous in the midline in up to 50% of patients. Thus, the LOR method may be inaccurate to confirm the cervical epidural space. The aim of this study is to determine which method is the safest and most exact for confirming the cervical epidural space. Methods: 100 adult, chronic renal failure patients who were undergoing an arteriovenous bridge graft for hemodialysis at the upper arm under cervical epidural anesthesia were recruited for this study. During the cervical epidural puncture, we identified the cervical epidural space by subjectively feeling the resistance with using a finger just through the ligamentum flavum, and we also used the drip infusion method, the loss of resistance method using air, and the hanging drop method. By using 5 grades, we classified the extent of whether or not the techniques were effective. Results: Using the drip infusion method, we identify the epidural space in all the patients as ＋/＋＋ grade. The catheter insertion method was also successful in identifying those epidural spaces over a ${\pm}$ grade. The pseudo LOR was over ${\pm}$ grade in 47 patients. Conclusions: The combined LOR/hanging drop with drip infusion method is useful for confirming the cervical epidural space.

• ETRI Journal
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• v.31 no.5
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• pp.576-584
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• 2009

A novel tunable transconductor is presented. Input transistors operate in the triode region to achieve programmable voltage-to-current conversion. These transistors are kept in the triode region by a novel negative feedback loop which features simplicity, low voltage requirements, and high output resistance. A linearity analysis is carried out which demonstrates how the proposed transconductance tuning scheme leads to high linearity in a wide transconductance range. Measurement results for a 0.5 ${\mu}m$ CMOS implementation of the transconductor show a transconductance tuning range of more than a decade (15 ${\mu}A/V$ to 165 ${\mu}A/V$) and a total harmonic distortion of -67 dB at 1 MHz for an input of 1 Vpp and a supply voltage of 1.8 V.

• Journal of the Korean Society of Safety
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• v.31 no.4
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• pp.64-74
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• 2016

Recently, the seismic stability evaluation of concrete gravity dams is raised due to the failure of dams occurred by the Izmit, Turkey and JiJi, Taiwan earthquake in 1999. Dams failure may incur loss of life and properties around the dam as well as damage to dam structure itself. Recently, there has been growing much concerns about "earthquake - resistance" or "seismic safety" of existing concrete gravity dams designed before current seismic design provisions were implemented. This research develops three evaluation levels for seismic stability of concrete gravity dams on the basis of the evaluation method of seismic stability of concrete gravity dams in U.S.A., Japan, Canada, and etc. Level 1 is a preliminary evaluation which is for purpose of screening. Level 2 is a pseudo-static evaluation on the basis of the seismic intensity method. And level 3 is a detail evaluation by the dynamic analysis. Evaluation results on existing concrete gravity dams on operation showed good seismic performance under designed artificial earthquake(KHC earthquake).

• Journal of the Korean Wood Science and Technology
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• v.41 no.2
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• pp.123-133
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• 2013

This paper presents experimental and numerical tests on a recently developed timber column concealed base joint. This joint was designed to replace the wood-wood connection found in the post-and-beam structure of Hanok, the traditional Korean timber house. The use of metallic connectors provides an increased ductility and energy dissipation for a better performance under reversed loading, especially seismic. In this study, we investigate the performance of the joint under pseudo-static reversed cyclic moment loading through the study of its ductility and energy dissipation. We first perform experimental tests. Results show that the failure occurs in the metallic connector itself because of stress concentrations, while no brittle fracture of wood occur. Subsequent numerical simulations using a refined finite element model confirm these conclusions. Then, using a practical modification of the joint configuration with limited visual impact, we improve the ductility and energy dissipation of the joint while retaining a same level of rotational strength as the originally designed configuration. We conclude that the joint has a satisfying behavior under reversed moment loading for use in earthquake resistant timber structure in low to moderate seismicity areas like Korea.

• Steel and Composite Structures
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• v.39 no.3
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• pp.337-352
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• 2021

The study presented experimental and numerical investigation on the seismic performance of steel reinforced concrete (SRC) L-shaped column- reinforced concrete (RC) beam joints. Various parameters described as steel configuration form, axial compressive ratio, loading angle, and the existence of slab were examined through 4 planar joints and 7 spatial joints. The characteristics of the load-displacement response included the bearing capacity, ductility, story drift ratio, energy-dissipating capacity, and stiffness degradation were analyzed. The results showed that shear failure and flexural failure in the beam tip were observed for planar joints and spatial joint, respectively. And RC joint with slab failed with the plastic hinge in the slab and bottom of the beam. The results indicated that hysteretic curves of spatial joints with solid-web steel were plumper than those with hollow-web specimens. The capacity of planar joints was higher than that of space joints, while the opposite was true for energy-dissipation capacity and ductility. The high compression ratio contributed to the increase in capacity and initial stiffness of the joint. The elastic and elastic-plastic story deformation capacity of L-shaped column frame joints satisfied the code requirement. A design formula of joint shear resistance based on the superposition theory and equilibrium plasticity truss model was proposed for engineering application.

• Corrosion Science and Technology
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• v.22 no.6
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• pp.478-483
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• 2023

This study examined the corrosion behavior of bimetal materials composed of Fe-Ni alloy and Fe-Ni-Mo alloy, both suitable for use in electromagnetic switches. Electrochemical polarization and weight loss measurements revealed that, in contrast to Fe-Ni alloy, which exhibited pseudo-passivity behavior, Fe-Ni-Mo alloy had higher anodic current density, displaying only active dissolution and greater weight loss. This indicated a lower corrosion resistance in the Fe-Ni-Mo alloy. Equilibrium calculations for the phase fraction of precipitates suggested that the addition of 1 wt% Mo may lead to the formation of second-phase precipitates, such as Laves and M₆C, in the γ matrix. These precipitates might degrade the homogeneity of the passive film formed on the surface, leading to localized attacks during the corrosion process. Therefore, considering the differences in corrosion kinetics between these bimetal materials, the early degradation caused by galvanic corrosion should be prevented by designing a new alloy, optimizing heat treatment, or implementing periodic in-service maintenance.

• Corrosion Science and Technology
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• v.23 no.2
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• pp.93-103
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• 2024

In the present work, a phase-field model for dendritic solidification is applied to hot-dip ZnAlMg coatings to elucidate the morphology of zinc dendrites and the solute segregation leading to the formation of eutectics. These aspects define the microstructure that conditions the corrosion resistance and the mechanical behaviour of the coating. Along with modelling phase transformation and solute diffusion, the implemented model is partially coupled with the tracking of crystal orientation in solid grains, thus allowing the effects of surface tension anisotropy to be considered in multi-dendrite simulations. For this purpose, the composition of a hot-dip ZnAlMg coating is assimilated to a dilute pseudo-binary system. 1D and 2D simulations of isothermal solidification are performed in a finite element solver by introducing nuclei as initial conditions. The results are qualitatively consistent with existing analytical solutions for growth velocity and concentration profiles, but the spatial domain of the simulations is limited by the required mesh refinement.

• Geomechanics and Engineering
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• v.39 no.1
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• pp.87-104
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• 2024

In practical engineering, the design process for most retaining walls necessitates careful consideration of seismic resistance. The prevention of retaining wall overturning is of paramount importance, especially in cases where the foundation's bearing capacity is limited. To research the seismic active earth pressure (ES) of a relieving retaining wall rotating around base (RB), the shear dissipation graphs across various operating conditions are analyzed by using Optum software, and the earth pressure in each region was derived by the inclined strip method combined with the limit equilibrium method. By observing shear dissipation graphs across various operating conditions, the distribution law of each sliding surface is summarized, and three typical failure modes are obtained. The corresponding calculation model was established. Then the resultant force and its action point were obtained. By comparing the theoretical and numerical solutions with the previous studies, the correctness of the derived formula is proved. The variation of earth pressure distribution and resultant force under seismic acceleration are studied. The unloading plate's position, the wall heel's length, and seismic acceleration will weaken the unloading effect. On the contrary, the length of the unloading plate and the friction angle of the filling will strengthen the unloading effect. The derived formula proposed in this study demonstrates a remarkable level of accuracy under both static and seismic loading conditions. Additionally, it serves as a valuable design reference for the prevention of overturning in relieving retaining walls.

• Korean Chemical Engineering Research
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• v.40 no.6
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• pp.729-734
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• 2002

In this study, the polyaniline films of emeraldine base(EB) and lucoemeraldine base(LEB) form chemically doping with poly(sodium-4 styrenesulfonate, PSS) were prepared by casting the mixed solution of chloroform and m-cresol on ITO(indium tin oxide) electrode. By analyzing UV-vis spectra of the mixed solutions, the effects of the secondary doping by m-cresol were obtained. And the conductivity of polyaniline film was increased with increasing m-cresol content. The results suggest that the improvement of conductivity obtained by secondary doping results primarily from interaction of polyaniline and m-cresol. As the results of analyzing cyclic voltammograms, it was known that the redox peak currents of polyaniline electrode prepared from LEB were larger and more reversible than those of polyaniline electrodes prepared from EB. The charge transfer resistances($R_{ct}$) of polyaniline electrodes were reduced with increasing m-cresol content, and LEB/PSS electrodes were smaller than EB/PSS electrodes. This result agrees to the analysis of the redox peak current of cyclic voltammograms. The solution resistance and the capacity of electrical double layer almost unchanged in all prepared polyaniline electrodes. It was confirmed that solution resistance was independent of frequency factor in AC impedance spectra. Also the polyaniline film doping with PSS was revealed pseudo n-type characteristics of conducting polymer.

• Korean Journal of Materials Research
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• v.10 no.6
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• pp.437-444
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• 2000

We investigated the effect of substrate temperature, chemical composition and post-deposition heat-treatment on the crystal structure and electrical transport of $La_{1-x}Sr_xMnO_{3-{\delta}}$(0.19${\leq}x{\leq}$0.31) thin films. As-prepared $La_{1-x}Sr_xMnO_{3-{\delta}}$ films grown at $500^{\circ}C$ by sputter techniques were found to have the pseudo-tetragonal system(a/c=0.97) and a highly preferential <001> orientation. The films were changed to be of the cubic system by post-deposition annealing at around $900^{\circ}C$. A main target of $La_{0.67}Sr_{0.33}MnO_3$ as well as auxliary targets of $La_{0.3}Sr_{0.7}MnO_3$ ceramics were co-sputtered to control the chemical composition of the film. The Sr content(x) of the film ranged from 0.19 to 0.31, depending on the number of the auxiliary target. When x increased from 0.19 to 0.31, the electrical resistivity of the film decreased and the transition temperature between metal and semiconductor shifted to higher temperature. With a magnetic field of 0.18 T, the magneto-resistance ratio (MR(%) = (${\rho}_o-{\rho}_H/{\rho}_H$) of the $La_{0.69}Sr_{0.31}MnO_3$ thin film was about 390%.