• Coupled systems mechanics
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• 제11권3호
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• pp.267-284
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• 2022

Due to the high usage of ABS in industries, such as aerospace, auto, recreational devices, boat, submarines, etc., the purpose of this project was to find a way to weld this material, which gives advantages, such as affordable, high speed, and good connection quality. In this experimental project, the friction welding method was applied with parameters such as numerical control (NC) machine with two different speeds and three cross-sections, including a flat surface, cone, and step. After the end of the welding process, samples were then applied for both tensile and bending tests of materials, and the results showed that, with increasing the machining velocity Considering of samples, the friction of the surface increased and then caused to increase in the surface temperature. Considering mentioned contents, the melting temperature of composite materials increased. This can give a chance to have a better combination of Nanomaterial to base melted materials. Thus, the result showed that, with increasing the weight percentage (wt %) of Nanomaterials contents, and machining velocity, the mechanical behavior of welded area for all three types of samples were just increased. This enhancement is due to the better melting process on the welded area of different Nano contents; also, the results showed that the shape of the welding area could play a significant role, and by changing the shape, the results also changed drastically.A better shape for the welding process was dedicated to the step surface.

• Journal of the korean society of oceanography
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• 제32권2호
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• pp.69-74
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• 1997

Depth profiles of organic carbon (C), biogenic silica (Si), and inorganic phosphorus (P) in Maxwell bay sediments were determined to investigate paleoclimatic changes during Holocene. Organic C and biogenic Si contents generally show a down-core decrease trend, which appears to be mostly controlled by their vertical fluxes through productivity in the surface waters, but it is uncertain that inorganic P contents are directly influenced by productivity changes with time. Before 4000 yr B.p. marine productivity seemed to be almost zero because ice permanently covered the surface waters of the study area. As the climate started to become relatively warm at 4000 yr B.p., ice was sporadically melted in the surface waters and thereby marine productivity gradually increased until 1500 yr B.p. For the last 1500 year, marine productivity must be high enough to overcome the dilution by high terrigenous sedimentation, thus that period was the warmest during the last 6000 year.

• Journal of Welding and Joining
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• 제21권2호
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• pp.70-75
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• 2003

Spot welding is a process that sheet metals are joined in one or more spot by heating at the faying interface. In this process, the spatter is dispersed from melted area. It has been reported that spatter generation has adverse effects on weld quality. However, no systematic study has been carried out to find out its effect on weld quality in resistance spot welding processes. In this study, specially designed specimen are used to perform experimental investigation of spatter generation and its effect. Major finding of this study show trends in tensile-shear strength for various amounts of spatter generated during spot welding process. Thus, optimum welding conditions are proposed in view of spatter generation and tensile-shear strength. (Received December 11, 2002)

• 대한기계학회논문집A
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• 제32권5호
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• pp.419-423
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• 2008

A new polymer replication technology using ultrasonic vibration is proposed and demonstrated. A commercial ultrasonic welder has been used in this experiment. Two different types of nickel molds have been fabricated: pillar type and pore type microstructures. Polymethyl methacrlylate (PMMA) has been used as the replication material and the optimal molding time was 2 sec and 2.5 sec for pillar-type and pore-type micromolds, respectively. Compared with the conventional polymer micromolding techniques, the proposed ultrasonic micromolding technique has the shortest processing time. In addition, only contact area between micromold and polymer substrate is melted so that the thermal shrinkage can be minimized. The fabricated PMMA microstructures have been very accurately replicated without vacuum. The proposed ultrasonic molding technique is a good alternative for high volume production.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
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• pp.152-153
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• 2006

We demonstrate the methodology of engineering the multi-component ceramic nanopowder with precise morphology by nanoblast calcinations decomposition of preliminary engineered nanoreactors. Multiple explosions of just melted $C_3H_6N_6O_6$ embedded into preliminary engineered nanoreactors break apart the agglomerates due to the highly energetic impacts of the blast waves. Also, the solid-solubility of one component into the other is enhanced by the extremely high local temperature generated during each nano-explosion in surrounding area. This methodology was applied for production of agglomeratefree nano-aggregates of $Gd_{20}Ce_{80}O_{1.95}$ with an average size of 42 nm and $LaSrGaMgO_{3-x}$ nanopowder with an average aggregate size of 83 nm.

• Journal of Welding and Joining
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• 제23권6호
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• pp.55-60
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• 2005

In part 1. optimal process parameters such as thickness of stopper and welding time are achieved to produce high strength ISB(Inner Structured and Bonded) panels. Developed process is different from the usual resistance welding process in the number of points welded at a time. In part 2, Numerical modeling for this new process is proposed and the variation of contact area with respect to the gap of electrodes is studied through FE analyses, Besides, it is tried to figure out the welding nugget formation and proper distance between welding points. FE analytic results show that inner structures are melted more than skin plate, and current distribution between points to be welded can be controlled by distance welding points. Comparison of some FE analytic results with corresponding experimental results could confirm the validity of the proposed numerical modeling.

• 대기
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• 제18권4호
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• pp.317-338
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• 2008

Analyses of observational data and numerical simulations were performed to understand the mechanism of MCSs (Mesoscale Convective Systems) occurred on 13-14 July 2004 over Jindo area of the Korean Peninsula. Observations indicated that synoptic environment was favorable for the occurrence of heavy rainfall. This heavy rainfall appeared to have been enhanced by convergence around the Changma front and synoptic scale lifting. From the analyses of storm environment using Haenam upper-air observation data, it was confirmed that strong convective instability was present around the Jindo area. Instability indices such as K-index, SSI-index showed favorable condition for strong convection. In addition, warm advection in the lower troposphere and cold advection in the middle troposphere were detected from wind profiler data. The size of storm, that produced heavy rainfall over Jindo area, was smaller than $50{\times}50km^2$ according to radar observation. The storm developed more than 10 km in height, but high reflectivity (rain rate 30 mm/hr) was limited under 6 km. It can be judged that convection cells, which form cloud clusters, occurred on the inflow area of the Changma front. In numerical simulation, high CAPE (Convective Available Potential Energy) was found in the southwest of the Korean Peninsula. However, heavy rainfall was restricted to the Jindo area with high CIN (Convective INhibition) and high CAPE. From the observations of vertical drop size distribution from MRR (Micro Rain Radar) and the analyses of numerically simulated hydrometeors such as graupel etc., it can be inferred that melted graupels enhanced collision and coalescence process of heavy precipitation systems.

• Journal of Periodontal and Implant Science
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• 제23권3호
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• pp.564-576
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• 1993

The purpose of this study was to evaluate the effects of Nd:YAG laser treatment on removal of smear layer and exposure of dentinal tubules. The experimental specimens were obtained from root planed surface of 30 human teeth which were extracted due to severe periodontal disease. The specimens were assigned randomly of three groups: root planed group, Tetracycline HCl(100mg/ml, 5min) group, and Nd:YAG laser ($Laser-35^{TM}$, U.S.A. 5 seconds )group. Nd:YAG laser group was divided into 4 subgroups according to 3.0W, 3.5W, 4.0W, 4.5W of power. The surface change of specimens were evaluated by scanning electron microscopy. The number of exposed dentinal tubules and percentage of area occupied by dentinal tubule orifices per unit area between each group was statistically analyzed by paired Student t-test. The results were as follows: 1. By root planing only, dentinal tubule was not exposed, but scale-like smear layer and parallel instrument tracks were resulted. 2. Tetracycline HCl treated surfaces exhibited the small number of partially exposed dentinal tubules with long orifices. The number($3.80{\pm}0.79$) of exposed dentinal tubules on Tetracycline HCl group was significantly less than that in laser groups above 3.5W of power(P<0.001), and the percentage ($0.68{\pm}0.19$) of area occufied by dentinal tubule orifices per unit area($192\;{\mu}m^2$) was significantly lower than that of any laser group(P<0.001). 3. The laser group irradiated with 4.5W of power showed both the most number($10.60{\pm}0.97$) of exposed dentinal tubules among the experimental groups, and the highest percentage($3.75{\pm}0.55\;%$) of area occupied by dentinal tubule orifices. 4. Energy Surge during laser pulsing and overlapping passes of the fiber resulted in melted and resolidified surface textures with lava-like appearance.

• 한국조경학회지
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• 제26권4호
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• pp.25-35
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• 1999

This thesis is to newly understand the value and the meaning of Chonju Palkyong(全州八景) by the specific gravity in making a counter-proposal in other to improve the landscape identity of modern city and at the same time. I intended to group the grafting device for the preservation and regeneration of modern history cultural environment through the interpretation of landscape construction. The meaning system of Chonju Palkyong showed the symbolic system which a landscape construction, four directions and two places has and exhibited the landscape shape possessing a luxuriant local feature peculiar to Chonju, preserving visual bound language of a classical Palkyong. Especially, it implies the use of the substantial landscape experienced factor, the expressions about natural phenomena and the matter which has melted human living circumstances. The landscape construction and it's form show the system which forms the different time field, a far landscape and a mid distance landscape and a near landscape, etc., under the visual, psychological, scenic influenced area, preserving the feature of the similar and typical type of Sosang Palkyoung（瀟湘八景) which intended to seek the local reappearance of the famous site experienced type and natural matter which famous place and local conduct were combined. The object space of Chonju Palkyong area representing the nature of historical landscape cultural assets, pushed by the greater part of the development based theory, shows injured aspects, but needs to play a part to seek such a up-to-date successive plan as the reconstruction of the destroyed historical landscape area which motivated Palkyong, the establishment of useful area, the embodiment of the cultural identity of Palkyong area and the becoming of the educational cultural life space. The analysis of the landscape construction of Chonju Palkyong and the grouping of the modern successive plan which I considered in this thesis, will be able to become a fundamental data to carry out the preservation of historical landscape and the landscape plan in the city.

• 암석학회지
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• 제10권1호
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• pp.1-12
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• 2001

경상분지 통남부에 위치하는 울산 철-사문암광산 지역에는 유일하게 국내에서는 초염기성암과 탄산염 암체가 공간적으로 연관성을 가지고 소규모로 분포하고 있다. 야외지질조사, 광상시추코아자료, 안정동위원소 분선 등의 연구결과는 울산의 탄산염암체는 용융체에서 형성된 카보내타이트의 가능성이 큰 것으로 나타났으며, 산출상태는 관입암상의 특징임을 반영하고 있다. 이번 연구에 의한 이곳의 지질은 중생대 퇴적암과 화산암, 이를 관입하고 있는 화강암류, 화강암을 관입하고 있는 초염기성암, 이 초염기성암을 관입하고 있는 카보내타이트로 이루어진다. 탄산염암체는 지표 상에서는 초염기성암과 함께 동심원상의 타원형으로, 수직단면도에서는 깔때기형태로 산출되고 있다. 탄소, 산소 안정동위원소비는 전형적인 맨틀기원의 카보내타이트로서의 특징이라기보다는 특이한 이원성형태(bimodal pattern)를 나타내었으며, 이는 울산의 카보내타이트를 형성한 마그마가 맨틀에서 직접적으로 상승한 마그마라기보다는 지각 내에서 형성된 2차적 카보내타이트 마그마임을 지시하는 것으로 해석된다. 즉, 초염기성암 마그마가 상승하면서 지각 내에 있던 석회질암이 용융되어, 탄산염마그마를 형성하고, 심부의 파쇄대가 발달한 현재의 장소에 사문암체를 형성한 초염기성 마그마와 그 뒤를 이어 탄산염마그마가 관입한 것으로 여겨진다. 또한 울산 철-사문암광산 지역은 심부파쇄대가 발달된 것이며, 탄산염암체내의 유체포유물의 유형, 안정동위원소의 패턴, 초염기성암과의 공간적 관계 등은 울산의 탄산염암체가 카보내타이트로 해석되는 것을 지지해주고 있다.