• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.1
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• pp.1-12
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• 1992

Generally, laser machines with high generated power can be developed by means of enhancing their mean power, since the enhancement of mean power exerts an influence on peripheral parameters and machining performance. In this research, we evaluate the various machining properties by the use of two machines which bear different mean power each other, so that we may study various effects of the enhancement of mean power. As a result, when the mean power comes to be enhanced to 75%, we obtain the increase of output energy up to 69% and of peak power more than 95%, and also obtain almost twice of the cutting speed. Moreover we find the fact that if the test pieces have enough thickness in contrast with output energy, the pulse frequency moves toward the frequency bandwidth which takes proportion to the cutting speed mas well as to the amount of material removal per unit time. In addition it is finally obtained that the laser machine with high output power yields small taper degrees at kerf parts, while it has large cutting widiths and dross lengths.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.10
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• pp.1940-1954
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• 1992

Fine grid computations were attempted to analyze the turbulent flows in the near wall low Reynolds number region and the numerical analyses were incorporated by a finite-volume discretization with full find grid system and low Reynolds number k-.epsilon. model was employed in this region. For the improvement of low Reynolds number k-.epsilon. model, modification coefficient of eddy viscosity $f_{\mu}$ was derived as a function of turbulent Reynolds number $R_{+}$ and nondimensional length $y^{+}$ from the concept of two length scales of dissipation rate of turbulent kinetic energy. The modification coefficient $f_{\epsilon}$ in .epsilon. transport equation was also derived theoretically. In the turbulent kinetic energy equation, pressure diffusion term was added in order to consider low Reynolds number region effect. The main characteristics of this low Reynolds number k-.epsilon. model were founded as : (1) In high Reynolds number region, the present model has limiting behavior which approaches to the high Reynolds number model. (2) Present low Reynolds number k-.epsilon. model dose not need additional empirical constants for the transport equations of turbulent kinetic energy and dissipation of turbulent kinetic energy in order to consider wall effect. Present low Reynolds number turbulence model was tested in the pipe flow and obtained improved results in velocity profiles and Reynolds stress distributions compared with those from other k-.epsilon. models.s.s.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.44 no.4
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• pp.373-381
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• 1999

Six soybean cultivars having different SDS susceptibility were planted with sorghum seedinoculum infested with F. solani isolate 171 in the greenhouse. First leaf symptoms appeared on unifoliar leaves at 9 days after inoculation and all cultivars showed the typical leaf symptoms at 13 days after inoculation, when trifoliar leaves emerged. Leaf symptoms development in susceptible cultivars was faster than in resistant cultivars. Leaf symptom severities during the period of 25 to 29 days after inoculation showed a significant difference between cultivars which had SDS resistance and sus ceptibility. In this period, area under the diseaseprogress curve (AUDPC) of Hartz 6686 was the highest and that of PI 520733 was the lowest. SDS caused serious damage to the growth of soybean in all cultivars. Average reductions of growth rate of root fresh weight and dry weight were greater than those of plant tops. Duyu-kong showed less severe leaf symptoms than that of SDS suscetible cultivars; however, average growth rate of plants top and roots of this cultivar was less but not significantly different than those of SDS susceptible cultivars. In all cultivars, as severity of leaf symptoms increased, plant top weight decreased. Root rot symptoms were observed in all cultivars before leaf symptoms appeared. Average proportions of tap root reddish-brown discoloration of all cultivars was up to 75 % at 15 days after inoculati on; however there was no significant differenc between cultivars at each rating date. Appearances of leaf symptoms on leaves varied in each cultivar. SDS resistant cultivars had a significantly higher level of crinkling than susceptible cultivars and SDS susceptible cultivars had a significantly higher level of necrosis than resistant cultivars. Further study will be needed to identify the relationships between the physiological growth rate and SDS severities in soybeans.

• Journal of the Korean Society for Nondestructive Testing
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• v.14 no.1
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• pp.7-15
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• 1994

The two-dimensional elastoplastic analysis was peformed to reveal a detail residual stress distribution of ceramic/metal joint specimen using finite element method and X-ray method. The highest tensile residual stress, ${\sigma}_x$ perpendicular to the interface appeared at the edge of the ceramic near the interface. In the vicinity of the interface, the high stress concentration occurs and residual stress distributes three-dimensionally. Therefore, the measured stress distribution differed remarkably from the result of the two-dimensional finite-element analysis. Especially at the center of the specimen near the interface, the residual stress, ox obtained from the finite element analysis was compressive, whereas X-ray measurement yielded tensile ${\sigma}_x$. Therefore, it is also attempted to investigate the finite element model for the prediction of residual stress ${\sigma}_x$ distributed nearly the interface of joint.

• Parasites, Hosts and Diseases
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• v.51 no.4
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• pp.441-448
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• 2013

This study describes the first record of Bourgelatia diducta (Nematoda: Chabertiidae) from wild boars in the Republic of Korea (=South Korea). Gastrointestinal tracts of 87 Korean wild boars (Sus scrofa coreanus) hunted in mountains in the south-western part of South Korea between 2009 and 2012 were examined for their visceral helminths. B. diducta, as identified by morphological characteristics of the head and tail, were recovered from the large intestine of 47 (54%) wild boars. The average length of adult female worms was $11.3{\pm}0.872$ mm and the thickest part of the body measured $0.54{\pm}0.04$ mm in maximum width, while those of males were $9.8{\pm}0.72$ and $0.45{\pm}0.03$ mm, respectively. The characteristic J-shaped type II ovejector was observed in females, and the type II dorsal ray with 2 rami on each side of the median fissure was uniquely seen in males. The buccal capsule was small, relatively thin-walled, cylindrical, very short, and ring-shaped. The externodorsal ray arose from a common stem with the dorsal ray. The cervical groove was absent. The anterior extremity was equipped with 20-22 external corona radiata, 4 cephalic papillae and 2 lateral amphids around the mouth. The eggs were $66.0{\times}38.9{\mu}m$ in average size. By the present study, B. diducta (Nematoda: Chabertiidae) is recorded for the first time in South Korea. Additionally, morphological characteristics and identification keys provided in the present study will be helpful in the faunistic or taxonomic studies for strongylid nematodes related.

• Parasites, Hosts and Diseases
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• v.55 no.1
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• pp.85-88
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• 2017

Toxoplasma gondii causes serious infection worldwide in humans and animals. In this study, the seroepidemiology of toxoplasmosis was investigated in wild boars (Sus scrofa) (n=377), wild rabbits (cape hare, Lapus capensis) (n=331), and wild chickens (red junglefwol, Gallus gallus) (n=571) in 4 forested and country sided area of Hubei province of China. For this, blood samples were collected and tested by indirect hemagglutination test (IHA). The seroprevalence was found to be 7.2%, 5.1%, and 12.6% in wild boars, rabbits, and chickens, respectively, with significant differences among these species. The prevalence of T. gondii infection in male and female wild boars was found to be 7.9% and 6.5% (P<0.01), in male and female rabbits was 5.6% and 4.9% (P<0.01), and in male and female chickens was 17.1% and 7.7% (P<0.01), respectively, with significant differences between 2 genders of chickens (P<0.01). The findings of this study may help in planning of the prevention measures against T. gondii infection in wild animals in this area.

• Journal of Advanced Navigation Technology
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• v.18 no.5
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• pp.415-420
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• 2014

Another crucial issue is a providing secondary user(SU) with the its guaranteed quality of service(QoS) in cognitive radio systems, from the SU view to be allowed to opportunistically utilize the primary user(PU) spectrum on non-interfering. In this paper, we propose a bandwidth reallocation scheme for reducing SU dropping rate through renegotiation of requested channel numbers when available bandwidth is not enough for accepting the spectrum handoff SUs. We categorize SU calls into two types : the first priority and the second priority SU, and the first SU' service is supported by bandwidth reservation based on ARMA prediction model for PU arrivals, while the second SU's bandwidth demands for spectrum handoff is to be reallocated through their renegotiation. Simulation results show that our scheme can improve SU dropping rate and system resource utilization efficiency by bandwidth reallocation.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.10
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• pp.639-647
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• 2017

This basic study is focused on the physically removal method of carbon dioxide from the decomposition of ammonium carbarmate to prevent the recombination of ammonium salts. A basic visual experimental set-up was designed and constructed to observe the recombination phenomena from the proper composition of ammonia gas, carbon dioxide gas, and compressed air dilution gas. To quantify the recombination phenomena, a simple device was designed to measure the weight change under severe cases for three different tube sizes. The temperature and pressure in the visual tube and the volumetric flow rates of the nitrogen dilution gas were studied and the conditions to avoid recombination were analyzed according to mean free path theory. Diffusivity values based on the Chapman-Enskog theory were calculated from the experimental data. These value may serve as an index for the prevention of recombination.

• 한국신재생에너지학회:학술대회논문집
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• 2011.05a
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• pp.125.1-125.1
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• 2011

빛 에너지를 전기에너지로 변환하는 발전소자인 태양전지는 청정 재생 에너지원으로 최근 Si 박막 태양전지의 고 효율화를 위해 여러 기술적인 면에서 개발되어지고 있다. 현재 박막형 태양전지는 실리콘계가 주류를 이루고 있으며, 유리 혹은 유연성기판(금속 or 고분자)에 비정질 실리콘 박막을 형성시킨 태양전지와 실리콘웨이퍼의 양면에 태양전지를 형성함으로써 효율을 극대화시킨 이종접합태양전지 등이 연구되고 있다. 특히 flexible 태양전지는 hard 기판에 비해 비교적 저가인 플라스틱 필름과 금속 foil을 기판으로 이용함으로서 저가화가 용이하며, 가볍고 유연성을 갖추고 있어 휴대와 시공에 있어 매우 우수한 장점을 가지고 있다. 본 연구에서는 flexible 기판(stainless steel)을 이용하여 태양전지 내 반사막 층이 미치는 영향을 알아보기 위하여 AZO/Ag 이중구조 박막의 특성을 연구하였다. RF magnetron sputtering system을 이용하였으며, 상온에서 Ag/AZO 이중구조 박막을 제조하였다. stainless steel 기판 위에 Ag층을 25nm 두께로 증착하였으며 연속공정으로 AZO 박막을 100~500nm의 두께경사를 가지도록 성장시켰다. 이 때의 AZO/Ag 이중구조 박막의 표면 morphology는 AFM 분석결과 7nm~3nm의 값을 나타내었으며, AZO 박막의 두께가 증가할수록 rms 값이 감소하는 경향을 보여주었다. 본 발표에서는 flexible 기판 상에 성장된 AZO/Ag 이중구조 박막의 전기적, 광학적 특성 등에 관하여 추가적으로 토론한 후 태양전지 효율 중 흡수층 내 반사막 층이 미치는 역할을 알아보겠다.

• Tribology and Lubricants
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• v.35 no.6
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• pp.362-368
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• 2019

In this study, mechanical and tribological properties were investigated by varying the process temperature (50, 100, 125 and 150℃) to reduce internal stress. The internal stress reduction by thermal dissociation ta-C coating film with increasing temperature is confirmed through the curvature radius of the ta-C coating according to the temperature of the SUS plate. As the coating temperature increased, the mechanical properties (hardness, modulus, toughness) deteriorated, which is in agreement with the Raman analysis results. As the temperature increased, the sp² phase ratio increased owing to the dissociation of the sp³ phase. The friction and wear properties are related to the process temperature during ta-C coating. Low friction and wear properties are observed in high hardness samples manufactured at 50℃, and wear resistance properties decreased with increasing temperature. The contact area is expected to increase owing to the decrease of hardness(72 GPa to 39 GPa) and fracture toughness with increasing temperature which accelerated wear because of the debris generated. It was confirmed that at process temperature of over than 100℃, the bond structure of the carbon film changed, and the effect of excellent internal stress was reduced. However, the wear resistance simultaneously decreased owing to the reduction in fracture toughness. Therefore, in order to increase industrial utilization, optimum temperature conditions that reduce internal stress and retain mechanical properties.