• Journal of Institute of Control, Robotics and Systems
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• v.5 no.5
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• pp.558-567
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• 1999

X-ray laminography and DT(digital tomosynthesis) that can form a cross-sectional image of 3-D objects promis to be good solutions for inspecting interior defects of industrial products. DT is a kind of laminography technique and the difference is in the fact that it synthesizes the several projected images by use of the digitized memory and computation. The quality of images acquired from the DT system varies according to image synthesizing methods, the number of images used in image synthesizing, and X-ray projection angles. In this paper, a new image synthesizing method named 'log-root method' is proposed to get clear and accurate cross-sectional images, which can reduce both artifact and blurring generated by materials out of focal plane. To evaluate the quality of cross-sectional images, two evaluating criteria : (1) shape accuracy and (2) clearness of the cross-sectional images are defined. Based on these criteria, a series of simulations are performed, and the results show the superiority of the new synthesizing method over the existing ones such as averaging and minimum methods.

• Korean Journal of Agricultural Science
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• v.42 no.3
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• pp.183-189
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• 2015

Plant root penetration through soil profile is restricted by compacted layer such as plow pan under conventional tillage. For detecting the compact layer, we made a graduated T-shape probe and measured compared between the depths with rapid change in feeling hardness of hand penetration using T-shape probe and with a rapid increase of penetrometer cone index. On upland crops, including red pepper, corn, soybean and cucumber, plow pan depth ranged from 10 cm to 25 cm depth. The effective rooting depth (ER) had significant correlation with the plow pan depth (PP) except soils with the shallow ground water and/or poorly drained soil. The regression equation was ER = 0.9*PP ($R^2=0.54^{**}$, N = 14) with the applicative PP range of 10-25 cm.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.7 s.238
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• pp.921-929
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• 2005

This paper presents an accelerated life test for burnout of tungsten filament of incandescent lamp. From failure analyses of field samples, it is shown that their root causes are local heating or hot spots in the filament caused by tungsten evaporation and wire sag. Finite element analysis is performed to evaluate the effect of vibration and impact for burnout, but any points of stress concentration or structural weakness are not found in the sample. To estimate the burnout life of lamp, an accelerated life test is planned by using quality function deployment and fractional factorial design, where voltage, vibration, and temperature are selected as accelerating variables. We assumed that Weibull lifetime distribution and a generalized linear model of life-stress relationship hold through goodness of fit test and test for common shape parameter of the distribution. Using accelerated life testing software, we estimated the common shape parameter of Weibull distribution, life-stress relationship, and accelerating factor.

• Steel and Composite Structures
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• v.26 no.1
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• pp.103-113
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• 2018

To study the effects of corner braces on fatigue performance of the U-rib and roof weld in steel bridge decks, the fatigue experiment was carried out to compare characteristics of the crack shape with and without corner braces. The improvement of fatigue life and stress variation after setting corner braces were also analysed. Different parameters of corner brace sizes, arrangements, and detail types were considered in the FEM models to obtain stress distribution and variation at the weld. Furthermore, enhancement of the fatigue performance by corner braces was evaluated. The results demonstrated that the corner brace could improve the fatigue life of the U-rib and roof weld, which exerted even no influence on the crack shape. Moreover, stress of the roof weld was decreased and the crack position was transferred from the root weld to U-rib and corner brace weld. It was suggested no weld scallop should be drilled on the corner brace. A transverse rib with lower height which was set between U-ribs was favourable for improvement of fatigue performance.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.6 s.249
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• pp.523-530
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• 2006

One of the fascinating prospects is the possibility of new hydrodynamics technology on micro-scale system since oscillations of micro-droplets are of practical and scientific importance. It has been widely conceived that the lowest oscillation mode of a pendant droplet is the longitudinal vibration, i.e. periodic elongation and contraction along the longitudinal direction. Nonlinear and forced oscillations of supported viscous droplet were focused in the present study. The droplet has a free contact line with solid plate and inviscid fluid. Natural frequencies of a pendant droplet have been investigated experimentally by imposing the acoustic wave while the frequency is being increased at a fixed amplitude. It is found that a pendant droplet shows the resonant behaviors at each mode similar to the theoretical analysis. The rotation of the droplet about the longitudinal axis is the oscillation mode of the lowest resonance frequency. This rotational mode can be invoked by periodic acoustic forcing and is analogous to the pendulum rotation. It is also found that the natural frequency of a pendant droplet is independent of the drop density and surface tension but inversely proportional to the square root of the droplet size.

• Transactions of Materials Processing
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• v.25 no.3
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• pp.182-188
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• 2016

Flexibly-reconfigurable roll forming (FRRF) is a novel sheet metal forming technology conducive to producing multi-curvature surfaces by controlling the strain distribution along longitudinal direction. In FRRF, a sheet metal is shaped into the desired curvature by using reconfigurable rollers and gaps between the rollers. As FRRF technology and equipment are under development, a simulation model corresponding to the physical FRRF would aid in investigating how the shape of a sheet varies with input parameters. To facilitate the investigation, the current study exploits regression analysis to construct a predictive model for the longitudinal curvature of the sheet. Variables considered as input parameters are sheet compression ratio, radius of curvature in the transverse direction, and initial blank width. Samples were generated by a three-level, three-factor full factorial design, and both convex and saddle curvatures are represented by a quadratic regression model with two-factor interactions. The fitted quadratic equations were verified numerically with R-squared values and root mean square errors.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.25 no.6
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• pp.401-409
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• 2016

The formation of micro-burrs in micro-milling processes causes several problems related to productivity and surface integrity. It should be minimized and suppressed by effective monitoring of the cutting conditions. This paper presents the correlation between the micro-burr length and cutting signals in the micro-milling process of an Al alloy (Al6061-T6). The acoustic emission (AE) signals and cutting force signals are acquired during the experiments. The characteristics of the cutting signals are obtained by analyzing the AE root mean square value and resultant cutting force. In addition, the micro-burr length is measured according to the cutting conditions by analyzing a scanning electron microscopy image of the machined surface. The results of this study can be used to enhance the surface quality of micro parts.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.47
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• pp.124-134
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• 2002

The sweetpotato, Ipomoea batatas L. (Lam.), is one of the important summer upland crops in Korea and has been used as human food, industrial yaw material and vegetable. Sweetpotato has been consumed for human foods such as boiled, roasted, fried or salad etc. It should be developed for higher quality as a snack or health food, primarily through improving the eating and marketing qualities as well as nutritional value. Its quality after cooking or processing is a complex one combining the aroma, taste, texture and fiber content. The other important qualities for consumers are root shape, size, skin color, flesh color, insect and disease resistance, nutritional components and safety from phytoalexins(toxic stress metabolites) etc. Korean people generally prefer to red skin color, round or elliptic shape and dry texture, yellow flesh color of sweetpotato which is high in starch content including vitamins and nutrients. The almost factors of quality components of sweetpotato are genetically controlled by breeder, but postharvest handlings and marketing management for making high quality goods should be done thoroughly according to the quality evaluation criteria of sweetpotato from the moment of harvest until shipping them to the market by farmers and the other users. This paper describes current status and prospects of the quality evaluations and researches in sweetpotato roots in Korea.

• Journal of Korean Academy of Oral and Maxillofacial Radiology
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• v.29 no.1
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• pp.55-63
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• 1999

The author observed and compared the radiographic features of 49 cases of the fibrous dysplasia and 14 cases of the ossifying fibroma in the osteoblastic or mature stage radiologically and histopathologically. The obtained results were as follows: 1. Fibrous dysplasia occurred most frequently in the 2nd decade, but ossifying fibroma in the 3rd and 4th decades, and both lesions occurred with slight predilection in females. 2. In most cases, chief complaints were painless facial swelling. And 61.1％ of fibrous dysplasia occurred in the maxilla, 92.9％ of ossifying fibroma in the mandible, and most of these lesions occurred in the premolar-molar region. 3. In the mandibular lesions, ossifying fibroma was shown more oval and round shape. but fibrous dysplasia was shown fusiform shape. 4. Fibrous dysplasia was shown homogeneously distributed. complete radiopaque shadow at 63％, and ossifying fibroma was shown concentric. mixed appearance of radiolucent and radiopaque shadow at 92.9％. 5. Fibrous dysplasia was entirely shown poorly outlined and blended to normal surrounding bone, but ossifying fibroma was shown well-defined border. 6. Cortical thinning and expansion were observed in these lesions. but degree of cortical expansion was more severe in ossifying fibroma than fibrous dysplasia. 7. Loss of lamina dura. tooth displacement. and displacement of mandibular canal were observed in both lesions. but root resorption was observed in ossifying fibroma only.

• Journal of Korean Association for Spatial Structures
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• v.18 no.3
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• pp.83-91
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• 2018

In this study, we investigated the dynamic stability of the system and the semi-analytical solution of the shallow arch. The governing equation for the primary symmetric mode of the arch under external load was derived and expressed simply by using parameters. The semi-analytical solution of the equation was obtained using the Taylor series and the stability of the system for the constant load was analyzed. As a result, we can classify equilibrium points by root of equilibrium equation, and classified stable, asymptotical stable and unstable resigns of equilibrium path. We observed stable points and attractors that appeared differently depending on the shape parameter h, and we can see the points where dynamic buckling occurs. Dynamic buckling of arches with initial condition did not occur in low shape parameter, and sensitive range of critical boundary was observed in low damping constants.