• Proceedings of the PSK Conference
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• 2000.04a
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• pp.155.1-155.1
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• 2000

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.26 no.4
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• pp.365-370
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• 2017

In this article, a 20 kHz Titanium (Ti) ultrasonic waveguide system for a nano-surface reformation process was designed and fabricated. First, finite element analysis using ANSYS software was performed to find the optimal dimensions. The obtained anti-resonance frequency for the Ti transducer with the piezoelectric device was 20.0 kHz, which value agreed well with the experiment result of 20.1 kHz (0.5% error). To test the system, chromium molybdenum steel (SCM) 435 was chosen as a test-piece. The result proved that the reformed depth was $36{\mu}m$. In addition, hardness was measured before and after the process. The value was changed from 14 HRC to 21 HRC, which is 50% increasing rate. Finally, the friction coefficient test result showed that the surface coefficient was reduced from 0.14 to 0.10 (28.6% reduction). Based on the results, the Ti ultrasonic equipment is regarded as a useful device for nano-scale surface reformation.

• Advances in materials Research
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• v.9 no.3
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• pp.189-202
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• 2020

The objective of the present work is to investigate the effect of cutting parameters (Vc, fz and ap) on tool life and the level of vibrations velocity in the machined part during face milling operation of hardened AISI 52100 steel. Dry-face milling has been achieved in the annealed (28 HRc) and quenched (55 HRc) conditions using multi-layer coating micro-grain carbide inserts. Statistical analysis based on the Response surface methodology (RSM) and ANOVA analysis have been conducted through a plan of experiments methodology using a reduced Taguchi table (L9) in order to obtain engineering models for tool life and vibration velocity in the workpiece for both heat treatment conditions. The results show that the cutting speed has a dominant influence on tool life for both soft and hard part. Cutting speed and feed per tooth is the most significant parameters for vibration levels. Comparing the experimental values with those predicted by the developed engineering models of tool life and levels of vibrations velocity, a good correlation has been obtained (between 97% and 99%) in annealed and hard conditions.

• Design & Manufacturing
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• v.16 no.1
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• pp.9-14
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• 2022

A lot of research is being done on metal materials to improve the lifespan of molded parts. As a result, excellent mold materials have been developed that withstand high hardness at high temperatures and frictional heat generated from high-speed cutting. In this study, the press mold life of powder high-speed tool steel and general high-speed tool steel was compared. Powdered high-speed steel is composed of alloying elements such as tungsten, maldividene, cobalt, chromium, and vanadium in steel, which improves wear resistance compared to high-hardness and high-speed tool steels. The mold parts of both steel types were manufactured in the same way from heat treatment to machining, and the powder high-speed tool steel was 66HRC and the high-speed tool steel was 61HRC. As a result of the experiment, it was observed that the number of punching of powder high-speed tool steel was improved by 40-50%, and powder high-speed tool steel had fewer impurities, uniform texture, and excellent surface structure. It has a microscopic structure.

• Journal of Institute of Control, Robotics and Systems
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• v.18 no.10
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• pp.977-987
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• 2012

One of the most significant errors in the pseudo-range measurement performance of GNSSes (Global Navigation Satellite Systems) is their multipath error for high-precision applications. Several schemes to mitigate this error have been studied. Most of them, however, have been focused on the GPS (Global Positioning System) L1 C/A (Coarse/Acquisition) signal that was designed in the 1970s and is still being used for civil navigation. Recently, several modernized signals that were especially conceived to more significantly mitigate multipath errors have been introduced, such as Time Multiplexed and Composite Binary Offset Carrier (TMBOC and CBOC, respectively) signals. Despite this advantage, however, a problem remains with the use of TMBOC and CBOC modulations: the ambiguity of BOC (Binary Offset Carrier)-modulated signal tracking. In this paper, a novel unambiguous multipath error mitigation scheme for these modernized signals is proposed. The proposed scheme has the same complexity as HRCs (High Resolution Correlators) but with low ambiguity. The simulation results showed that the proposed scheme outperformed or performed at par with the HRC in terms of their multipath error envelopes and running averages in the static and statistical channel models. The ranging error derived by the mean multipath error of the proposed scheme was below 1.8 meters in an urban area in the statistical channel model.

• Journal of the Korean Society for Precision Engineering
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• v.31 no.12
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• pp.1115-1119
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• 2014

In this article, a 20 kHz ultrasonic waveguide for nano-surface treatment was designed and manufactured. When designing the system, finite element analysis with ANSYS software was performed to find optimal dimensions of the waveguide, which can raise energy efficiency. Consequently an anti-resonance frequency of an Al waveguide with a piezoelectric actuator was 20 kHz, which predicted the experimentally obtained value of 18 kHz well. For the assessment of the performance, Steel Use Stainless (SUS) 304 and chromium molybdenum steel (SCM) 435 specimens were tested. Cross-sectional microscopies of SUS304 were taken and they showed that the treated thickness was $30{\mu}m$. Additionally, hardness tests of SCM435 were done and the hardness before the process was 14.0 Rockwell Hardness-C scale (HRC) and after the process was 20.5 HRC, respectively, which means 46% increase. Considering these results, the developed ultrasonic system is thought to be effective in the nano-surface treatment process.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2002.02a
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• pp.11-18
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• 2002

The STD11 and KP4 are important steels and applied to the manufacturing of the die and mold. The purpose of this study is to investigate the machinability of tool steels of STD11(HRC60) and KP4(HRC32) when machining them by using ball end milling tools coated with TiAlN. Cutting forces by using a Kistler piezo-cell type tool dynamometer, surface roughness and tool wear by using tool microscope are used in the tests. The results from the cutting tests of KP4 specimens show that 85m/min. of cutting speed and 0.32mm/rev. of feed per revolution are optimum conditions for the higher productivity and 0.26mm/rev. with the same cutting speed are optimum conditions for better surface finishing. The results from machining STD11 workpiece at 30m/min. of cutting speed and 0.17m/rev. of feed per revolution show recommended for the higher productivity. The KP4 shows relatively smaller cutting forces than STD11 and STD11 shows the better surface finish than KP4.

• Korean Journal of Materials Research
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• v.16 no.6
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• pp.341-345
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• 2006

[ $Ni_2Si$ ] mixed powders were mechanically alloyed by a ball mill and then processed by hot isostatic pressing (HIP) and spark plasma sintering (SPS). In the powder that was mechanically alloyed for 15minutes(MA 15 min), only Ni and Si were observed but in the powder that was mechanically alloyed for 30minutes(MA 30 min), $Ni_2Si$, Ni and Si were mixed together. Some of the MA 15 min powder and MA 30 min powder were processed by HIP under pressure of 150MPa at the temperature of $1000^{\circ}C$ for two hours and some of them were processed by SPS under pressure of 60 MPa at the temperature of $1000^{\circ}C$ for 60 seconds. Both methods completely compounded the powders to $Ni_2Si$. The maximum density of sintered lumps by HIP method was 99.5% and the maximum density of the sintered lump by SPS method was 99.3%. with the hardness of HRc 66 with the hardness of HRc 63. Therefore, the SPS method that can sinter in short time at low cost is considered to be more economical that the HIP method that requires complicated sintering conditions and high cost and the sintering can produce target materials in desired sizes and shapes to be used for thin film.

• Korean Journal of Microbiology
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• v.38 no.4
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• pp.306-311
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• 2002

PCR of the mecA gene for the rapid detection of methicillin-resistant staphylococci was perfomed and compared with the antibiotic sensitivity test. A total of 43 strains of staphylococi from clinical specimens were used in this study. An antibiotic sensitivity test by the agar dilution method of NCCLS (The National Commitee for Clinical Laboratory Standard) was performed for the strains. Among them, 39 isolates were methicillin-resistant (MRS), and 4 isolates were methicillin-susceptible (MSS). With the exception for one strain (Staphylococcus cohnii, HRC2-4), all MRS strains amplified the expected 533 bp fragments of the mecA gene by PCR, However, one strain (Staphylococcus aureus, HSA1-10) that was classified as a sensitive strain by the antibiotic sensitivity test was mecA positive by PCR. All 35 methicillin-resistant Staphylococcus aureus (MRSA) strains were mecA positive, but overall, concordance between the results of the mecA PCR and antibiotic sensitivity test was 95.6%.

• Science of Emotion and Sensibility
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• v.22 no.1
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• pp.45-54
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• 2019

Empathy has been observed to be pivotal in enhancing both social relations and the efficiency of task performance. Empathetic interaction has been shown to begin with individuals mirroring each other's facial expressions, vocal tone, actions, and so on. The internal responses of the cardiovascular activity of people engaged in empathetic interaction are also known to be synchronized. This study attempted to objectively and quantitatively define the rules of empathy with regard to the synchronization of cardiac rhythm between persons. Seventy-four subjects participated in the investigation and were paired to imitate the facial expressions of their partner. An electrocardiogram (ECG) measurement was taken as the participants conducted the task. Quantitative indicators were extracted from the heart rhythm pattern (HRP) and the heart rhythm coherence (HRC) to determine the difference of synchronization of heart rhythms between two individuals as they pertained to empathy. Statistical significance was confirmed by an independent sample t-test. The HRP and HRC correlation(r) between persons increased significantly with empathy in comparison to an interaction that was not empathetic. A difference of the standard deviation of NN intervals (SDNN) and the dominant peak frequency decreased. Therefore, significant parameters to evaluate empathy have been proposed through a step-wise discrimination analysis. Empathic interactions may thus be managed and monitored for high quality social interaction and communication.