• Tribology and Lubricants
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• 제37권2호
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• pp.77-80
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• 2021

In this study, we investigated the effect of the spring constant on frictional behavior at a nanoscale through molecular dynamics simulation. A small cube-shaped tip was modeled and placed on a flat substrate. We did not apply the normal force to the tip but applied adhesive force between the tip and the substrate. The tip was horizontally pulled by a virtual spring to generate relative motion against the substrate. The controlled spring constant of the virtual spring ranged from 0.3 to 70 N/m to reveal its effect on frictional behavior. During the sliding simulation, we monitored the frictional force and the position of the tip. As the spring constant decreased from 70 to 0.3 N/m, the frictional force increased from 0.1 to 0.25 nN. A logarithmic relationship between the frictional force and spring constant was established. The stick-slip instability and potential energy slope increased with a decreasing spring constant. Based on the results, an increase in the spring constant reduces the probability of trapping in the local minima on the potential energy surface. Thus, the energy loss of escaping the potential well is minimized as the spring constant increases.

• Journal of Species Research
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• 제8권3호
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• pp.288-293
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• 2019

Herein, we report a new record of Arna bipunctapex (Hampson) and a new species, Euproctis fulvatus sp. nov. in Korea; both are Lymantriine moths. Arna bipunctapex is distinguished by a relatively large wingspan with two black dots and a small dot between these black dots in the apical region of a yellowish forewing. The male genitalia of A. bipunctapex can be distinguished by the lack of a process on the sacculus of valva while the female genitalia can be distinguished by an antrum that is basally flat with two lateral digitate arms. Euproctis fulvatus is distinguished by yellowish wings with a medially curved central fascia of the forewing. The male genitalia can be distinguished by the bifid, digitate uncus and the simple, square-shaped valva with a distal strong invaginated margin. The female genitalia can be distinguished by the long, medially twisted, ductus dursae with simple antrum posteriorly strongly sclerotized and ovate corpus bursae without signum. Larvae of E. fulvatus are distinguished by a black head with a pair of long, black, lateral tufts, dorsum with 10-11 white intersegmental dots and bright red setal warts on T2-A8, and bright red glands on A6 and A7.

• Structural Engineering and Mechanics
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• 제69권4호
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• pp.383-397
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• 2019

More than one longitudinal web stiffener may be economical in the design of plate girders that have considerably high width-to-thickness ratio of webs. In this study, the bend-buckling strength of relatively deep webs with two horizontal lines of flat plate-shaped single-sided stiffeners was numerically investigated. Linear eigenvalue buckling analyses were conducted for specially selected hypothetical models of stiffened web panels, in which top and bottom junctions of a web with flanges were assumed to have simply supported boundary conditions. Major parameters in the analyses were the locations of two longitudinal stiffeners, stress ratios in the web, slenderness ratios and aspect ratios of web panels. Based on the application of assumptions on the combined locations of the two longitudinal web stiffeners, simplified equations were proposed for the bend-buckling coefficients and compared to the case of one longitudinal stiffener. It was found that bend-buckling coefficients can be doubled by adopting two longitudinal stiffeners instead of one longitudinal stiffener. For practical design purposes, additional equations were proposed for the required bending rigidity of the longitudinal stiffeners arranged in two horizontal lines on a web.

• 한국기계가공학회지
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• 제18권6호
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• pp.26-32
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• 2019

Ball end mills used for high-speed and high-precision machining require longer machining time than flat end mills or face cutters, since the tool diameter is limited and the rigidity is reduced by the characteristics of the tool's cutting edge: at the top end of the tool, the cutting speed approaches zero and hardly removes any material. Because there is little material removal at the top end of the ball end mill, the outer cutting edge performs the majority of the work; this irregular cutting force deforms the tool and shortens its life. In this study, we attached an eddy-current sensor to a tool to measure the deformation from the cutting force and we used a tool dynamometer to measure the cutting force. We found that the change in cutting force is dependent on the change in feed rate during square-shaped processing and, as the feed rate is accelerated, the cutting force also increases. Higher cutting forces increase tool deformation.

• 헤리티지:역사와 과학
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• 제34권
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• pp.4-18
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• 2001

Paekche black potteries are earthenwares begun to be produced at the beginning of Paekche Dynasty, around 3-century. They have typical Paekche style. Representative Paekche earthenwares are burnished black pottery, long oval shaped pots and shoulder pots. Among these, burnished black potteries are limited to Paekche in the occurrence site and age. Their numbers are a few. To reproduce black pottery, their compositions were analyzed. As a result of X-Ray analysis, quarts, feldspar, illite, muscovite, and anorthite were found on their surfaces and imsides spinel and vermiculite were found on their surfaces. Since same constituent minerals were found on surfaces and their insides, special other materials were not added to make surface black. With the showing vermiculite, they were made higher than $800^{\circ}C$. As a result of analysis, fine grained clay bad been influenced by the black smoke. Its luster was appeared by polishing with a big flat wooden spoon. The black color was made of smoking when the hot pot taken off from burning oven was covered with the wet pine leaves.

• 한국의상디자인학회지
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• 제22권4호
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• pp.93-104
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• 2020

This paper focuses on the spatial changes that create a three-dimensional or deep feeling on the surface of a scarf centering on the cube shape. Through this, consumers with various tastes were able to satisfy their image presentation. The cube form has simplicity and order and is likely to be used as a formative object. The cube shapes can be expressed in various forms through visual and perceptual spatial changes by presenting various shape changes based on the viewpoint of the two-dimensional silk surface, that is, by changing the eyes' position and orientation. Various visual theorists' discussions about cube-shaped visual changes were discussed. In addition, the three-dimensional spatial illusion caused by the shape and color of Victor Bazaarelli's cube was examined. The cube shape was printed silk surfaces to give a three-dimensional sense of space on a two-dimensional scarf design using the size change, the difference in the length of the line, and the color change. As such, the cube shape has infinite possibilities as a method that can express three-dimensional depth and space on the flat surface of a scarf. Therefore, it is hoped that this study will be applied to various aspects as the basic data for the scarf design that expresses the spatial changes in the form of cubes.

• Journal of Species Research
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• 제11권4호
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• pp.253-265
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• 2022

A study on silica-scaled chrysophytes(Chrysophyceae and Synurophyceae) from Mt. Sinbul alpine wetland, South Korea was performed from January 2018 to March 2020 using scanning electron microscopy (SEM). We found a total of 19 taxa of silica-scaled chrysophytes; Mallomonas(13); Synura (3); Chromophysomonas (1); Chrysosphaerella (1); and Paraphysomonas(1), of which six taxa, including two new species(Mallomonas dimorphus sp. nov. and Mallomonas alpestris sp. nov.), were reported for the first time in Korea. All the species are illustrated with SEM micrographs and briefly described with regard to their taxonomy. Two new species were described based on the cell shape, size and ultrastructure of the scales and bristles. Mallomonas dimorphus sp. nov. belongs to the Sectio Heterospinae in that its scales have a flat dome, a reticulated secondary layer and needle shaped bristles. However, this species is distinguished from other taxa in the Sectio by two different patterns of shield ornamentation and a dome ornamentation. Mallomonas alpestris sp. nov. belongs to Series Torquatae (Sectio Torquatae) characterized elongated domed collar scales, domeless body scales and rear scales with a short spine. However, it is different from all other taxa in the Sectio Torquatae as well as Series Torquatae by shield ornamentation of the body and rear scales with evenly spaced transverse ribs and papillae.

• 환경생물
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• 제40권4호
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• pp.497-509
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• 2022

A strain of Amphidinium species was established from samples collected from the intertidal zone of a sandy beach of Jeju Island, Korea. Its cells were 13.0-15.0 ㎛ in length and 10.0-13.0 ㎛ in width. Its cell shape was round or oval and dorsoventrally flat. A pyrenoid was located in the center of the cell and a nucleus was posteriorly located. Its epicone was small and left-deflecting. Its cingulum had V-shape on the ventral side, forming a ventral ridge and extending to the sulcus. Polygonal amphiesmal vesicles and ring-shaped body scales not described previous were observed on the surface of the cell. Its morphological features were consistent with those of previously described Amphidinium fijiense. Phylogeny based on ITS region and LSU rDNA sequences revealed that this Amphidinium isolate was clearly clustered with other A. fijiense strains, but separated from other Amphidinium species. These results indicate that this Amphidinium isolate is A. fijiense. This study reports its presence for the first time in the intertidal zone of a sandy beach of Jeju Island, Korea.

• 한국정밀공학회지
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• 제10권3호
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• pp.198-204
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• 1993

The study is concerned with finite element analysis and design of axisymmetric deep drawing by local heating. When the bottom shape of a cup is not flat but in complex-shaped, i.e., hemispherical, the cup cannot be drawn in one or two processes in the conventional deep drawing process and the limit drawing ratio is limited as well. By introducing local heating selectively with regards to the heating position, the formability of the sheet metal can be greatly increased with the reduced number of processes. In the Process analysisthe rigid- viscoplastic finite element method is employed and the temperature effect is incorporated. Bishop's step-wise decoupled method is employed to analyze the thermomechanical interaction between deformation and heat transfer. Axisymmetric deep drawing of a hemisphere-bottomed cup has been analyzed for various combinations of heat application in the punch and the die. At the first stage of deep drawing stretch forming is practically carried out by firmly pressing the blankholder with the punch and the die heated at various levels of temperature. Then at the second stage the same cup is drawn for the saame or different combination of temperature. From the computation, it has thus been shown that the fromability of a cup is greatly increased in two-stage deep drawing with increased limet drawing ratio.

• 한국어류학회지
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• 제17권3호
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• pp.167-172
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• 2005

조간대와 강하구에 출현하는 미끈망둑 Luciogobius guttatus은 썰물 동안에 건조하기 쉬운 자갈 바닥 아래에서 서식하는 특징을 보인다. 이러한 서식처를 선호하는 미끈망둑의 호흡체계를 조사하기 위해 지느러미 및 흡반을 포함하는 5개의 부속지의 표피구조를 관찰하였다. 표피는 모두 맨바깥층(outermost layer), 중간층(middle layer), 기저층(stratum germinativum)으로 구성된다. 맨바깥층은 다형세포 또는 편평세포, 그리고 점액세포로 구성되었으며, 특히 단일세포성의 점액세포는 $11.1{\sim}16.1{\mu}m$의 크기로 1~2층으로 배열되어 있으며, 산성다당류로 확인되었다. 중간층은 이웃한 표피세포로 팽대해진 팽대세포 (swollen cell)로 구성되어 있으며, $12.3{\sim}15.2{\mu}m$의 크기로 1~11층으로 배열되어 마치 거미망구조를 보인다. 이러한 팽대세포로 인해 상피 두께의 대부분을 차지한다. 많은 모세혈관이 기저막 아래에 분포하고 있으며, 미뢰 (taste bud)가 표피에 존재한다. 이러한 표피의 특징은 미끈망둑이 이중호흡체계인 피부호흡 (cutaneous respiration)과 밀접한 관계가 있는 것으로 생각된다.