• Polymer(Korea)
• /
• v.36 no.1
• /
• pp.59-64
• /
• 2012

The impact strength of material is considered the most important design factor for small and light products. Impact strength is a unique material property, thus the impact strength should not depend upon the geometry of specimen. However it varies according to specimen thickness, notching method, and notch shape. In this study, the variations of impact strength have been investigated according to thickness, notch shape, and notching method of specimen. Engineering plastics such as PC, ABS and POM have been used in this study. Experimental results showed impact strength increased as thickness decreasesd. PC showed the highest increment of impact strength when the thickness was thin. Fractured section of PC showed brittle fracture behavior when the specimen was thick. However it showed ductile fracture behavior when it was thin. The impact strength of in-mold notched specimen showed higher than that of milling notched specimen. PC showed the highest notch sensitivity among the materials used in this experiment.

• Applied Microscopy
• /
• v.25 no.2
• /
• pp.53-64
• /
• 1995

This study was designed to investigate the morphological alterations of zonula occludens, macula adherences and gap junctions between the hepatocytes in the fasting conditions. Animals (Sprague Dawley, $250{\sim}280g$) were divided into two groups: normal and fasting. The latter were fasted for eight days prior to sampling. Liver tissues were sectioned and replicated after freeze fracturing for the transmission electron microscopy. In the normal rat liver, the interhepatocellular space at the area of some zonula occludens appeared to be widened in thin sections. On the freeze fracture replicas., the zonula occludens appeared as an anastomosing network of $2{\sim}4$ strands or grooves on P or E faces. Free ends and fragments of the strands were observed. In the rat fasted for eight days, the hepatocytes were diminished in size and the organelles were decreased in number and size. The intercellular space was wide at many areas of zonula occludens in thin section. On the freeze fracture replicas, the zonula occludens showed diminution or disappearence of anastomosing network of strands or grooves. Free ends and small fragments of the strands or grooves were frequently encountered. The macula adherens was markedly increased in number in thin sections, although they could not be found on the freeze fracture replicas. The gap junctions were increased in number in thin sections. Small aggregations of the intramembranous particles appeared with larger ones on the freeze fracture replica. The evidences may suggest the followings: (1) The disassembly of zonula occludens in the fasting states is led from the diminished mechanical stress on the luminal surface of bile canaliculus with the impaired secretion of bile components from the hepatocytes. (2) The increase of macula adherens is necessary to maintain the liver parenchyma integrity in the fasting state which leads the hepatocyte to be diminished and finally the intercellular space to be separated. (3) The rise in both number and size of gap junctions is owing to the need of increasing intercellular communication between the hepatocytes during the fasting. (4) The alteration of zonula occludens is easily led by the physiological condition of hepatocytes even in the normal ones.

• Journal of the Korean Society of Clothing and Textiles
• /
• v.32 no.4
• /
• pp.598-607
• /
• 2008

Bast fibers were applied for various usages from fabrics to household care products long time ago. In this study, we investigated the physical characteristrus of water retted & chemically rotted fibers of Yucca, New Zealand hemp, Corn, Kuzu vine, Indian mallow, and Mulberry paper that have been harvested by domestic cultivation. Water retting is more effective than chemical rotting for six kinds of plant fibers. When all fibers were rotted chemically with 1% sodium hydroxide, only Kuzu vine and Indian mallow were retted. Indian mallow, Yucca, New Zealand hemp, and Com fibers have higher tensile strength than any other fibers. The crystallinity of Kuzu vine, Indian mallow, Yucca, New Zealand hemp, and Corn was as low as 60% but Yucca, New Zealand hemp were flexible. Yucca had fewer lumina whereas New Zealand hemp more lumina in cross sectional shape. Especially com fibers have a structure like sponge, and Indian mallow had a net shape. The longitudinal section of New Zealand hemp showed smooth and long shape. Mulberry paper was proved to be short and thin, which is quite appropriate for making paper. In this study, we found that plant fibers for living material could be used for cloth materials.

• Maxillofacial Plastic and Reconstructive Surgery
• /
• v.12 no.3
• /
• pp.34-41
• /
• 1990

The pilomatricoma (calcifying epithelioma of Malherbe) is rare benign hard, spherical and freely movable cutaneous tumor, which was differentiated from hair cells, particulary hair cortex cells. It is usually occured as a single, asymptomatic, 0.5 cm to 3.0 cm sized, deep seated, firm nodule, covered by normal or pink skin. It arises chiefly in young people, including children, and most often in the head, neck and upper extrimites. The authers experienced a case of pilomatricoma which occured in preauricular region. This case was summarized as follows. 1. 10 years old female has suffered from hard subepidermal mass on preauricular area and she visited our out patient clinic. So we performed surgical extirpation and the excised specimen was pathologically examined. 2. Grossly the tumor measures 2.0 cm in diameter and firm, bosselated, spherical shaped which covered by a thin layer of fibrous tissue. On cut section, it shows spicular gritty surfaces, well encapsulation, interwoven and keratotic lamellae. 3. Histopathologically, the epithelial masses of the tumor are composed of two type of cells, basophilic cells and shodow cells. The basophilic cells resemble hair matrix cells which posses round or elogated, deeply basophilic nuclei and scanty cytoplasm. The shadow cells show a central, unstained shadow at the site of the lost nucleus. Gradual development of basophilic cells into shadow cells can be observed. Foci of calcification are present within the lobule of shadow cells. The stroma of the tumor shows a considerable foreign body giant cell reaction adjacent to the shadow cells. 4. No recurrence was observed until post-operative 40 months.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.11 no.4
• /
• pp.45-54
• /
• 1991

The closed forms of mass matrix with rotational inertia matrix are developed for free vibration analysis in space structures containing linearing tapered members with cross section of thin-walled tube. The exact displacement functions are used for formulating mass matrix. The very small slopes of the tapered member are used in usual practice, such that the series expansion forms of these are also developed to avoid numerical failure in vibration analysis. Significant improvements of accuracy and efficiency of free vibration analysis are achieved by using the mass matrices developed in this study. Frequencies of free vibration of tapered members are compared with solutions based upon stepped representation of beam element.

• The Plant Pathology Journal
• /
• v.26 no.2
• /
• pp.139-148
• /
• 2010

A virus causing stunt, yellowing, severe mosaic, malformation symptoms on leaves and uneven development and malformation on fruits of zucchini was prevalent around Goseong, Gyeongsangnam-do, Korea. A survey conducted (2004) in the Goseong area revealed about 20% virus infection rate. The disease causative identified as Cucumber mosaic virus (CMV-Z1) was further characterized. The isolate induces mosaic symptoms on Cucumis sativus, while severe mosaic, stunt and malformation on C. pepo. Thin section analyses have shown that virus inclusions are formed in the cuticle layers as well as epidermal, parenchyma and collenchymas cells in virus-infected Nicotiana tabacum. CMV-Z1 isolate induced specific cytoplasmic inclusion bodies such as irregular clumps (IC), crystal (Cr) and irregular chloroplasts (ICh). IC was made up of virus particles interspersed with a darkly stained amorphous material and found both in the cytoplasm and vacuoles, whereas ICh and Cr were rarely found in the vacuoles. The genome of CMV-Z1 RNA-1 consists of 3359 nucleotide (nt) encoding 1a protein of 993 amino acids (aa). The CMV-Z1 RNA-2 was 3050 nt in length containing 2a (857 aa) and 2b (110 aa), while RNA-3 encoding 3a movement protein (279 aa) and coat protein (218 aa) was 2215 nt in length. Phylogenetic analyses of nucleotide sequences of CMV-Z1 isolate appeared it is more closely related to subgroup IA than to subgroup IB or II.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.18 no.9
• /
• pp.937-942
• /
• 2008

This paper presents a case history on failures of impeller and shaft due to pressure pulsation at single stage feed water pumps in 700 MW nuclear power plant during commissioning operation. The pumps had been service and had run for approximately $40{\sim}50$ hours. For the most part, the failures of impeller occurred with the presence of a number of fatigue cracks. All cracks were associated with the deleterious surface layer of impeller by visual and metallurgical examination. On-site testing and analytical approach was performed on the systems to diagnose the problem and develop a solution to reduce the effect of exciting sources. A major concern at high-energy centrifugal pump is the pressure pulsation created from trailing edge of the Impeller blade, flow separation and recirculation at centrifugal pumps of partial load. Pressure pulsation due to the interaction generating between impeller and casing coincided with natural frequencies of the impeller and shaft system during 1ow load operation. It was identified that dynamic stress exceeding the fatigue strength of the material at the thin shroud section due to the hydraulic instability at running condition below BEP.

• Magazine of the Korea Concrete Institute
• /
• v.10 no.6
• /
• pp.261-268
• /
• 1998

Deflections due to shrinkage are frequently ignored in design calculation. Especially for thin member, shrinkage often causes considerable deformations as wellas appreciable stress changes. Several methods for computing shringkage curvature have been proposed by many researchers. Some of the approximte methods widely used in the recent years are the equivalent tensile force method, Miller's method and Branson's method. These methods were, however, somewhat oversimplified and could be too conservative in the case of well cured concrete structure. In this paper, an approximate method for computing shrinkage curvature and deflection is proposed. Curvature due to shrinkage is derived from the requirements of strain compatibility and equilibrium of a section and the age-adjusted effective modulus method. The proposed method is verified by comparison with several experimental measurements. The correlations between calculated and measured curvatures is very good.

• Journal of Ocean Engineering and Technology
• /
• v.30 no.3
• /
• pp.201-207
• /
• 2016

In this paper, an aluminum pressure vessel (cylinder) for a 200 m water depth is designed and analyzed. Because of their lack of usage in the deep sea, only a few papers about pressure vessels subjected to external pressures have previously been published. Moreover, the high level of imported external-pressure-vessel products limits the academic pursuit. Yet, research on internal pressure vessels is widely available because of their broad usage at onshore. This paper presents the process of basic designing and modelling of pressure vessels using the design rules of American Standard of Mechanical Engineering (ASME) Section VIII Division 1. To promote understanding, finite element analysis (FEA) result of an existing sample cylinder which was not designed by ASME code is compared with the design obtained in this paper. Several methodologies are used for the finite element analysis, including rectangular, cylindrical, and axisymmetric coordinate, to attain an accurate stress result. Same dimensions except the thickness of the cylinder and loading condition of 0.200 MPa was given for the current study. Finally, a rigorous design procedure is added for the bolt and boundary conditions of the cylindrical body and its ends. The obtained stress level satisfies the allowable design stress value specified in the ASME code.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.14 no.5
• /
• pp.2474-2480
• /
• 2013

A stress ribbon pedestrian bridge is the structure in which the axial force of prestressed deck, which is developed by introducing prestressed force into the thin deck with the very low value of span to deck-depth ratio which is installed on bearing cables with the specified sag, resists most of external loadings. Since the design of stress ribbon pedestrian bridges should be conducted by assuming the cross-section of deck, the area of bearing cables and post-tensioning cables, and the prestressed force of post-tensioning cables, it requires much more iterative processes than the design of general bridges. In this research, to minimize such iteration processes, regression equations which can reasonably assume the area of bearing cables and post-tensioning cables, and the prestressed force of post-tensioning cables, are suggested for the bridge length of 80m with the sag-span ratios of 1/30, 1/40, and 1/50.