• Transactions of the Korean Society of Mechanical Engineers A
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• v.30 no.4 s.247
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• pp.428-434
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• 2006

Pulse laser welding of AISI 304 stainless steel plate was simulated to find optimal welding conditions by using commercial finite element code MARC. Due to geometric symmetry, a half model of AISI 304 stainless steel plate was considered and user subroutines were applied to boundary condition for the heat transfer. Material properties such as conductivity, specific heat, mass density and latent heat were given as a function of temperature. A moving heat source was designed on the basis of experimental data. As a result, Nd:YAG laser welding for AISI 304 stainless steel was successfully simulated and it should be useful to determine optimal welding condition.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.20 no.4
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• pp.434-439
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• 2011

There are about 2.4million disabled in Korea, 2009. Also, Korean society entered into an aging society. Therefore disable and elderly are getting more involved in our society. This study proposes simple ramp design for wheel chair users and welding method and condition for manufacturing. In the middle of ramp, screw jack and motor are installed so that ramp can be moved left and right side. To make the ramp moves easily, ramp was fixed by installing LM guide on both sides. Ramp production for using Nd:YAG laser certain dissimilar welding in stainless steel sheet and cold reduced carbon steel. The output was fixed by 3kW, the speed was increased to 2~7m/min, Argon was used as shielding gas and the flow rate was changed to 10~30L/min. The proper welding condition is the output 3kW and welding speed 2~5m/min.

• Korean Journal of Child Studies
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• v.24 no.2
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• pp.79-92
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• 2003

Data were collected from teacher reports and from 529 1st to 6th grade students through questionnaires. Bullying was higher among boys than girls. Victimization was higher in 2nd, 3rd, 4th and 6th grade boys than girls. Acting out was highest in 2nd graders and lowest in 3rd graders. Shy-anxiousness was highest in 4th and 6th graders and lowest in 1st and 3rd graders. Learning problems were lowest among 3rd graders. Competencies were higher in 1st and 2nd grades. Boys had more problem behaviors; girls showed better competencies. Bullying was positively related to acting out, and negatively related to frustration tolerance and task orientation. Victimization was positively related to shy-anxiousness and learning problems, and negatively related to frustration tolerance, assertive social skills and task orientation.

• Transactions on Control, Automation and Systems Engineering
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• v.4 no.4
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• pp.283-288
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• 2002

This paper has shown that the impulse and the unit step responses of 2nd-order systems can be computed by an analytic method. Three different 2nd-order systems are investigated: the prototype system, the system with one LHP(left half plane) real zero and the system with one RHP(right half plane) real zero. It has also shown that the effects of the LHP or the RHP zero are very serious when the zero is getting closer to the origin on the complex plane. Based on these analytic results, this paper has presented two sufficient and necessary conditions for 2nd-order linear SISO(single-input/single-output) stable systems to have the nonovershooting and the monotone nondecreasing step response, respectively. The latter condition can be extended to the sufficient conditions for the monotone nondecreasing step response of high-order systems.

• Journal of Magnetics
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• v.3 no.4
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• pp.116-119
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• 1998

Influence of small additions ($\leq$2.0 at.%) of Al, Ti, Co, and Ni on the microstructural development and the magnetic properties of melt-spun Fe-Bd-C alloys was investigated. Addition of these elements tended to stabilize the crystallization of as-spun ribbons. Especially, Al and Ti preferred to stabilize$ Fe_{17}Nd_2C_x.$ The average grain size of Fe17Nd2Cx (0.1~0.3 ${\mu}{\textrm}{m}$), obtained by a proper annealing, in the ribbon treated with 0.5 at.% additive was much smaller than that of additive-free ribbons, which would be the major source of large increase in coercivity. Among the additives, Ni was very effective to increase the coercivity whereas Co had beneficial effect on $T_c.$ By adding 0.5 at.% Ni, intrinsic coercivities of more than 1.4 T, 40~50% higher than that (~1.0T) of additive-free ribbons, can be obtained after annealing at 750~80$0^{\circ}C$.

• Journal of Advanced Marine Engineering and Technology
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• v.32 no.4
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• pp.570-577
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• 2008

Magnesium alloys are potentially useful as structural materials due to higher strength/weight ratio, heat conductivity and recyclability compared to other alloys. These alloys have attracted the interest of modern manufacturing such as the automobile, computer, communication and consumer electronic appliances industries. Hence welding techniques are required to be developed for these applications. Laser are known to be an excellent tool for them. This paper presents the laser weldability of AZ31 magnesium alloy with CW Nd:YAG laser. The low viscosity and surface tension of the melt pool make magnesium more difficult to weld than steel. As a result of this study, optimal process parameters could be obtained without weld defects. Also it was certain that cutting methods had influence on butt weldability.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2008.11a
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• pp.105-106
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• 2008

Nanotube morphology change of Ti-Ta-Zr alloy as Zr content increase has been researched using various experimental methods. Ti-Ta-Zr(3, 7 and 15 wt%) alloys were prepared by arc melting and nano-structure controlled for 24 hr at $1000^{\circ}C$ in argon atmosphere. Formation of oxide nanotubes are conducted by anodizing a Ti-Ta-Zr alloy in $H_3PO_4$ electrolytes with small amounts of fluoride ions at room temperature. Electrochemical experiments were carried out with conventional three-electrode configuration with a platinum counter electrode and a saturated calomel reference electrode. The samples were embedded with epoxy resin, leaving a square surface area of $10mm^2$ exposed to the anodizing electrolyte, 1.0M $H_3PO_4$ containing 0.8wt% NaF.

• Journal of the Korean Society for Precision Engineering
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• v.14 no.2
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• pp.74-83
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• 1997

The non-periodic angular accelerations of engine are the major cause of gear rattle. This gear rattle is based on the existence of a backlash between the drive gear of input shaft and the free gear of output shaft in the gearbox. Especially, the neutral gear rattle have a very bad effect on the ride quality. Test-rig was constructed in order to evaluate the parameter influence upon the neutral gear rattle. Also, each different 4 type torsional characteristic of clutch was manufactured. Experimental conditions are the use of each different 4 type torsional characteristic of clutch and oil temperature variation in gearbox. In case of the same stiffiness of pre-damper type clutch at idling, the clutch of large hysteresis showed dam- ping effects at the 2nd input gear and the 2nd output gear. Also, the main-damper type clutch was shown to large resonance phenomenon at the 2nd input gear. Accordingly, main-damper type clutch was unapp- roriate at idling.

• Parasites, Hosts and Diseases
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• v.59 no.4
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• pp.355-362
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• 2021

A rumen fluke Fischoederius elongatus is assigned to the type species of genus Fischoederius, family Gastrothylacidae. However, the mitochondrial sequences recently published are thought to be of inconsistent species, suggesting that several morphologically similar but genetically distinct species might be classified as Fischoederius elongatus. Thus, mentions of F. elongatus from South, Southeast, and East Asia might unintentionally refer to different species. The present work describes morphology and a full mitochondrial genome sequence of one of these species. The fluke specimens were collected from 2 infected cattle in Thailand. An interesting finding was the presence of a second tRNA-Asp gene next to a partial ND1 gene. It is suggested that these duplicated sequences are the remnants of non-reciprocal recombination events caused by inverted repeats located between ND2 and ND1 mitochondrial genes.

• Journal of Life Science
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• v.26 no.7
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• pp.749-757
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• 2016

This study was carried out to reveal the genetic population structure of the Jeju Island population and the phylogenetic relationship of East Asian populations of the large-footed bat (Myotis macrodactylus) based on the genetic polymorphisms of mitochondrial cytochrome B (CYTB) and NADH dehydrogenase subunit 1 (ND1) gene sequences. A total of fourteen and nine haplotypes were found in the CYTB and ND1 sequences from East Asian bats, respectively. Haplotype distribution showed locality specific patterns. The results from ND1 haplotype analysis showed that the Jeju Island population has four haplotypes: the Mt. Halla and Western subpopulations have three ND1 haplotypes, but the Eastern subpopulation has just a single haplotype Nd03, which is commonly found on this island. The neighbor-joining (NJ) tree showed the closer relationship between Jeju Island and Japan rather than that between Jeju and Gangwon-do Province. The divergence time between the maternal ancestor lineages of Japanese and Chinese populations was estimated to be 0.789±0.063 MYBP. The secondary divergence between Jeju and Japanese bats was calculated about to be 0.168±0.013 MYBP. The Jeju population has immigrated to the island at least fifty thousand years ago. In addition, ND1 haplotype analysis suggested that the insular bats have experienced at least two further genetic differentiation events within this island. Consequently, these findings suggested that the results of this study may play a critical role in understanding the phylogenetic relationship among East Asian bat populations of M. macrodactylus. To prepare more explainable information on evolutionary correlation, analysis is still required to examine using expanded samples from China, Russia, and southern parts of the Korean Peninsula.