• Korean Journal of Soil Science and Fertilizer
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• v.16 no.4
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• pp.343-346
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• 1983

This paper was prepared to characterize a physico-chemical and mineralogical examination on blast furnace slag as a source of silicate fertilizer, which was quenched with high pressure water stream in process of iron refinery at Pohang Iron and Steel Manufacturing Inc. Quenched slag was more coarse in particle size compared to present commercial silicate fertilizer milled from air-cooled slag and mostly generated in size of 1 to 2 mm. The total chemical composition of quenched and air-cooled slags was same but mineralogical composition was quite different. The former was composed of amorphous materials resulting in more soluble silica content, however, the latter contained dominantly crystalline minerals such as akermanite, gehlenite and wollastonite which meant less soluble ones. Latent cementing property and angular surface of gain of the slag made it difficult to apply the slag directly, however, it could be used as a source of silicate fertilizer and soil ammendment.

• Journal of Food Hygiene and Safety
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• v.3 no.3
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• pp.117-129
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• 1988

Packaged meal manufacturing establishments in Seoul city and Kyungkido province were assessed in terms of the sanitary conditions and practices, time and temperature, and microbiological quality. Sanitary check-lists were developed to evaluate the sanitary condition of sampled packaged meal manufacturing establishments. Microbiological tests on.food containers, equipments, and foods in various phases of product flow were done. The results of the study are summarized as follows; 1) Sanitary condition of kitchen.and sanitary practices of employees in.large and medium establishments were evaluated as the some improvement required in order to meet all standards. But sanitary practices of employees in small establishments were evaluated as the unsatisfactory state with negligence or ignorance of safe practice. 2) The microbiological quality of basic ingredients and food materials after pre-preparation were poor. 3) Time and temperature data indicated that phases of holding ingredients at room temperature after cooking, assembly and packaging before delivery were critical. 4) Microbiological test results for food containers, equipments indicated that sanitary conditions of stainless steel ware, knife, wiping clothes and cutting board should be improved promptly. 5) Critical control points identified were ingredients, pre-preparation, Holding, and assembly and packaging. 6) Guidelines were suggested for effective quality control of packaged meals production.

• The Journal of the Korean dental association
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• v.53 no.9
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• pp.644-655
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• 2015

Purpose: This study was conducted to evaluate the effect of the fixture abutment connection type and diameter on the screw joint stability in external butt joint for 2nd surgery and internal cone connected type implant system for 1st and 2nd surgery using ultimate fracture strength. Materials and Methods: USII system, SSII system and GSII system of Osstem Implant were used. Each system used the fixture with two different diameters and cement-retained abutments, and tungsten carbide / carbon coated abutment screws were used. Disc shaped stainless steel metal tube was attached using resin-based temporary cement. The experimental group was divided into seven subgroups, including the platform switching shaped specimen that uses a regular abutment in the fixture with a wide diameter in USII system. A static load was increased to the metal tube at 5mm deviated point from the implant central axis until it reached the compression bending strength at a rate of 1mm/min. Then the deformations and patterns of fracture in threaded connection were compared. Results and Conclusion: 1. In the comparison between the Regular diameter, compression bending strength of SSII system was higher than USII system and GSII system. There was no significant difference between USII system and GSII system. 2. In the comparison between wide diameter, compression bending strength was increased in the order of GSII system, USII system, and SSII system. 3. In comparison between the implant diameter, compression bending strength of the wide diameter was greater than the regular diameter in any system(P<0.05). 4. There was no significant difference between the platform switching (III group) and the regular diameter (I group) in USII system. 5. In USII system, fracture of abutment screw and deformation of both fixture and abutment were observed in I, II and III subgroups. 6. Failure pattern of SSII system, which was the fracture of abutment screw and deformation of the abutment and fixture, was observed in both IV and V subgroups. Fracture of some fixtures was observed in subgroup V. 7. Failure pattern of GSII system, which was the fracture of the abutment screw and deformation of the fixture and the abutment, was observed in both VI and VII subgroups. Apart from other subgroups, subgroup VII demonstrated no bending neither the fracture at the top of the fixture. The compressive deformation of internal slope in the fixture was the only thing observed in subgroup VII.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.8
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• pp.857-863
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• 2012

In this study, tailor-welded blanks(TWB) were formed between high-strength steel(SABC1470) and cold rolled steels(SPFH590 and SPFC980) to improve passenger safety and reduce the weight of cars. Multi-material TWB specimens were highly strengthened through the heat treatment of SABC1470. The change in tensile strength caused by the stand-by time until water cooling after stamping and the deformation behavior of high-speed bending in a statically indeterminate condition such as in the center-pillar were evaluated. Multi-material TWB specimens that were heat-treated at the same temperature tended to show a decrease in tensile and yield strength, depending on the stand-by time until water cooling. On the other hand, Multi-material TWB specimens(SABC1470+SPFH590) that were heat treated at $850^{\circ}C$ showed good properties that were suitable for ensuring passenger safety in car accidents. From the viewpoint of passenger safety, it is best to use SABC1470 and SPFH590 in the upper and lower area of the center-pillar, respectively.

• Journal of Korean Tunnelling and Underground Space Association
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• v.14 no.5
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• pp.453-467
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• 2012

Usage of underground space is increasing at metropolitan city. More than 90% of flood damages have occurred at downtown of metropolitan cities. In order to prevent and/or minimize the flood-induced damage, an underground rainwater detention cavern was proposed to be built underneath existing structures. As for underground caverns to be built for flood control, multi-caverns will be mostly adopted rather than one giant cavern because of stability problem. Because of the stress concentration occurring in the pillars between two adjacent caverns, the pillar-stability is the Achilles' heel in multi-caverns. So, a new pillar-reinforcing technology was proposed in this paper for securing the pillar-stability. In the new pillar-reinforcing technology, reinforced materials which are composed of a steel bar and PC strands are used by applying pressurized grouting, and then, by applying the pre-stress to the PC strands and anchor body. Therefore, this new technology has an advantage of utilizing most of the strength that the in-situ ground can exert, and not much relying on the pre-cast concrete structure. The main effect of the pressurized grouting is the increase of the ground strength and more importantly the decrease of stress concentration in the pillar; that of the pre-stress is the increase of the ground strength due to the increase of the internal pressure. In this paper, ground reinforcing effects were verified the stress change in pillar is obtained by numerical analysis at each construction stage. From these results, the effects of pressurized grouting and pre-stress are verified.

• Journal of the Korean Institute of Rural Architecture
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• v.16 no.1
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• pp.119-127
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• 2014

This study suggests institutional and methodological approaches for preservation of South Korea's registered cultural properties of modern architecture. The suggested approaches are as follows. First, in order to improve the current registration and preservation system for cultural properties, we need to employ both structure-based classification and style-based classification. Registration criteria for modern architecture properties need to include more detailed classification in terms of their structure: brick structure, steel concrete structure and post lintel structure. In terms of construction style, the properties need to be further classified into the western style, the traditional style and the Korean-western eclectic style. In addition, protection of registered cultural properties need to be achieved through legislation of a protection system. Second, while the current system sets out six methods for preservation of registered cultural properties of modern architecture, more specific preservation methods types and plans need to be continuously introduced. In particular, as for the method of partial preservation, the method needs to be further classified based on the usage of the relevant structure so as to allow for more diverse options. First, the 'Preservation by Interior Alteration' needs to be added to the category, where the exterior is preserved as it is and the interior is preserved through alteration. Also needs to be added the preservation method where the interior space is preserved as it is and the exterior space is altered, in case the finishing materials of the exterior has deteriorated. Third, if the records on registered cultural properties of modern architecture are to provide the functions of legal evidences regarding management of architectural cultural properties, sources of knowledge required for policy making and implementation and past management record for the future, each phase needs to be closely connected in an organic manner, and we need to establish a management system and plan that go beyond the relevant organizations. Fourth, in order to preserve South Korea's registered cultural properties of modern architecture in its original state, it is imperative to prepare separate criteria for registration of technicians with expertise on modern architecture, and train experts and technicians on modern architecture, which is distinguished from the traditional architecture.

• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.1
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• pp.100-108
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• 2015

The purpose of this study is to evaluate the effect of improvement on the impact resistance and strength properties of cement composites by surface modification of aramid fiber. For aramid fiber reinforced cement composites, therefore, dispersion capability and the bonding efficiency between the fibers and the cement composite material need to be improved. It is possible by modifying surface properties to hydrophobic, it is considered that oiling agent ratio of 1.2 % and improvement of performance is in need to be investigated. In this study, short aramid fibers were mixed by different fiber length and oiling agent ratio. And improvement of strength properties and impact resistance performance of hybrid cement composites were evaluated under the influence of steel fiber. As a result, strength properties of aramid fiber reinforced cement composites are different by mixing ratio of fiber, oiling agent ratio and length of fiber. In case of cement composites which have same volume fraction and fiber length, tensile strength and flexural strength were improved with increase of the emulsions throughput of the fiber surface. The results of evaluation on the static strength properties had effects on impact resistance performance by high-velocity impact. And it was observed that the scabbing of rear was suppressed with increase of the oiling agent ratio.

• Journal of the Korea Concrete Institute
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• v.18 no.4 s.94
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• pp.527-534
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• 2006

This paper outlines a new strengthening technique for concrete beams using externally unbended high-strength bars. The advantages of proposed method lie in speed and simplicity of construction compared to the alternative strengthening method. Externally unbended reinforcement retains many of the advantages over external unbended prestressed tendons. It eliminates time consuming stressing operations. Clearance requirements around anchorages are reduced as access is not required for prestressing jacks. Test results of eight specimens on reinforced concrete beams using different reinforcement materials such as carbon fiber sheet, steel plate and high-tension bar are reported. The beam strengthened by carbon fiber sheet showed a brittle failure mode due to the separation of fiber. As a result of draped profile of external bar, the maximum strength of the beam were increased by up to 212 percent and the deflections were reduced by up to 65 percent. Test results show that the beams reinforced with high-tension bar are superior to reference specimens, especially for the strength and deformation capacity.

• Design & Manufacturing
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• v.12 no.2
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• pp.40-45
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• 2018

Recently, in construction equipment machinery production, development has focused on environmentally-friendly functions to improve existing production capacity. For excavators as well, emphasis has been placed on response to environmental regulations, miniaturization, and noise reduction, while technology is being developed considering cost reduction and safety.Accordingly, the front support, an inner reinforcement part of the excavator, as well as high-strength steel plates to improve safety and reduce weight, are being applied.However, in the case of high-strength materials, Springback occurs in the final formed part due to high residual stress during product forming. Derivation of a forming or product shaping process to reduce springback is needed. Accordingly, regarding the front support, an inner reinforcement part of the excavator, this study derived a method to improve springback and secure shape stiffness through analysis of the springback occurrence rate and springback causes through a forming analysis.As for the results of analyzing the springback occurrence rate of existing products through forming analysis, springback of -22.6 mm < z < 27.35 mm occurred on the z-axis, and it was confirmed that springback occurred due to the stiffness reinforcing bead of the upper and middle parts of the product.To control product residual stress and springback, we confirmed a tendency of springback reduction through local pre-cutting and stiffness reinforcement bead relocation.In the local pre-cutting model, springback was slightly reduced by 5.3% compared with the existing model, an insignificant reduction effect. In the stiffness reinforcement bead relocation model, when an X-shaped stiffness reinforcement bead was added to each corner portion of the product, springback was reduced by at least 80%.The X-shaped bead addition model was selected as the springback reduction model, and the level of stiffness compared to the existing model was confirmed through a structural analysis.The X-shaped bead additional model showed a stress springback of 90% and springback reduction of 7.4% compared with the existing model, indicating that springback and stiffness will be reinforced.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.6
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• pp.573-579
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• 2016

Studies on the deformation behavior of materials subjected to impact loads have been carried out in various fields of engineering and industry. The deformation and fracture of members for these machines/structures are known to correspond to the intermediate strain-rate region. Therefore, for the structural design, it is necessary to consider the dynamic deformation behavior in these intermediate strain-rate ranges. However, there have been few reports with useful data about the deformation and fracture behavior at intermediate strain-rate ranges. Because the intermediate strain-rate region is located between quasi-static and high strain-rate regions, it is difficult to obtain the intermediate strain-rate using conventional reasonable test equipment. To solve this problem, in this study, the measurement reliability of the constructed drop-bar impact tensile test apparatus was established and the dynamic behavior at the intermediate strain-rate range of carbon steels was evaluated by utilizing the apparatus.