• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.44 no.1
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• pp.88-97
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• 2016

A closed loop thermal control system simulates space thermal environment to verify the satellites' functionality in extremely cold/hot temperature. It is composed of a cryogenic blower, thermal shroud, heater, cryogenic valves. This paper presents an overview of closed loop thermal control system's design parameter and test results for control parameter. A capacity of blower is calculated through energy balance equation and an advantage/disadvantage for a shroud material and a type was analysed. The thermal control system is controlled by a constant density of fluid in the system. A requested performance of closed loop thermal control system was verified by measuring a homogeneity and stability of shroud through control parameter such as density and RPM of blower.

• Transactions of Materials Processing
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• v.28 no.5
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• pp.257-265
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• 2019

Multi-axial forging (MAF), a severe plastic deformation technique, is known to be difficult to obtain materials with homogeneous microstructures. Recently, multi-axial diagonal forging (MADF) process has been developed to solve this problem. In this study, in order to compare the microstructural and mechanical homogeneities of the MAFed and MADFed samples, oxygen-free copper (OFC) cubes measuring 25 mm in length were deformed through MAF and MADF processes and the average grain size and hardness were measured at the edge, face, and center regions of the samples. In the MAFed samples, ultrafine grains were formed at the center region, but a considerable amount of coarse grains remain at the face region. Therefore, the MAFed samples showed a high inhomogeneity in regards to grain size and hardness. On the contrary, in the case of the MADFed sample, the grain sizes at the edge, face, and center regions were similar and the hardness in all the regions are almost similar. This indicates that the MADFed sample has a homogeneous microstructure and uniform mechanical properties, which can be attributed to the homogeneous distribution of the effective strain throughout the material. The results of this study suggests that the MADF is a suitable process in the fabrication of high-strength copper materials with a homogeneous and ultrafine grain structure.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.35 no.2
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• pp.101-107
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• 2022

This study proposes the deconvolution method for the nanoindentation test results of geopolymer employing the Gaussian mixture model. Geopolymer has been studied extensively as an alternative construction material because it emits relatively lower CO₂ compared to ordinary Portland cement. Geopolymer is made of aluminosilicate and alkaline solution, and the Si/Al molar ratio affects its mechanical properties. Previous studies revealed that the Si/Al molar ratio of 1.8~2.0 results in the highest compressive strength, and the Si/Al molar ratio over 1.8 degrades the compressive strength of geopolymer severely; however the reason for the compressive strength degradation is still unclear. To understand the effect of the Si/Al molar ratio on the geopolymer structure, this study exploits the nanoindentation. The phase deconvolution of the indent modulus data is successful using the Gaussian mixture model, and it is observed that the Si/Al molar ratio alters the homogeneity of the geopolymer. Geopolymer becomes more homogeneous up to an Si/Al molar ratio of 1.8 at which geopolymer exhibits the highest compressive strength. The examination of this study is assumed to be adopted as evidence of strength degradation by the Si/Al ratio higher than the optimum value.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.20 no.1
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• pp.63-70
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• 2015

An inter-laboratory comparison campaign on nutrient analysis in seawater was carried out in 2010. Sets of three sterilized seawater samples (Bottle 130, 131, 132) which have enough homogeneity and stability were distributed to 10 laboratories. Participants analyzed the nutrients in their own laboratories (nitrite, nitrate, phosphate, and silicate) at least 5 times and reported the results. Statistical treatments were applied to the results to assess the precision for each laboratory and the discrepancy among laboratories. Most laboratories show within 10% of precision in all nutrient results. Degrees of scattering described as discrepancy among laboratories and relative percent difference values were 4~63% and 0.04~2217%, respectively. The statistical analysis shows that the difference among the laboratories may due to the systematic error rather than random error. When the results were corrected by the results of bottle 130 as a reference material, the degrees of scattering and the relative percent difference were improved significantly. As a result, since most participants show satisfactory precision for nutrient analyses, a use of reference materials which have homogeneity and stability was strongly recommended to improve the comparability of nutrient data.

• Journal of the Korea Institute of Building Construction
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• v.11 no.6
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• pp.530-537
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• 2011

The purpose of this study is to examine material performance of fiber reinforced cement composite for mass production. It is necessary to manufacture SHCC(Strain Hardening Cement Composite) by batch plant for field application and mass production. For the study, a mock-up test of SHCC manufactured in the batch plant was conducted, and the performance was compared with SHCC manufactured in the laboratory. Assessment items were freshness and hardening properties. Specifically, direct tensile test machine was used for performance verification of SHCC. As a result, there was a tendency of less satisfactory fiber dispersion and performance of strain hardening compared with the performance of SHCC manufactured in the laboratory. To address this, dry mixing and mortar mixing time should be increased compared to laboratory mixing, and injection time of an agent such as a water reducing agent should be properly controlled according to mixing combination, or the capacity to secure dispersion and homogeneity of material.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.39 no.6
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• pp.42-48
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• 2002

The design, construction and performance test of a convenient multi-purpose irradiator is described. A multi-purpose irradiator using Cesium-137 has been developed for studies of low dose radiation effects in biology and for calibration of Thermo Luminescent dosimeter(TLD). During the operation, three rods of radioactive material which are 10cm in length revolve 180 degrees and irradiate biological samples, or TLD, and return to their shielded position, after the programmed time. A programmable Logic Controller(PLC) controls the sequence of operation, interlock, motor rotation and safety system. The rotation speed of biological samples can vary up to 20 RPM. A real time monitoring system was also incorporated to check and control the operation status of the irradiator. The capacity of the irradiation chamber was 4.5 liters. The isodose distribution at arbitrary vertical planes was measured by using film dosimetry. The dose-rate was 0.13 cGy/min in air and 0.11 cGy/min in water equivalent material in the case of Cesium-137. Range of activity was 2 Ci. The homogeneity of dose distribution in the chamber was ${\pm}$7%. The actual radiation level on the surface was within permissible levels. The irradiator had a maximum 0.35 mR/min radiation leakage on its surface.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.12
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• pp.363-373
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• 2018

In today's diversified society, it is hard to know which building style represents the architectural style of the time. The simplicity found in monolithic-style buildings forms a symmetrical point with fairly complex structure, and its value can be acknowledged. This study analyzes buildings made of insulating lightweight aggregate concrete in the early 21st century, defines the concept of monolithic expression, and examines how these characteristics are expressed in the space, forms, and structural methods in construction. Unlike a multi-layered exterior wall system, which features multiple layers composed of a variety of materials, the exterior walls built with insulating lightweight aggregate concrete comes in a lump form with a mold form that is tightly filled with concrete as a single material and is monolithic. This is attributed to the creation of spaces characterized by the homogeneity of inner and outer spaces with the use of the same material, continuity of the surface as solidity, spatial characteristics of the stereotomic construction, expression of materiality with the use of exposed concrete, and the contrast of the lump and the space. This not only reveals formal characteristics that expose a discourse about monolithic architecture in contemporary architecture but also provide an opportunity to extend the range of discussion to structures and materials and even to their effects on space.

• Journal of Conservation Science
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• v.37 no.6
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• pp.778-790
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• 2021

The Stone Seated Buddha Triad and Stone Standing Buddha in Bijung-ri are state-designated heritage (treasure) statues having the Buddha style of the Goryeo dynasty from the 6th century. Conservation scientific investigations were conducted to understand the preservation status of these stone Buddha statues and to establish a conservation plan. The Stone Seated Buddha Triad and Stone Standing Buddha are composed of fine-medium grained biotite granite, which is considered to be of the same origin owing to their low magnetic susceptibility distribution of less than 0.2 (×10^-3 SI unit) and similar mineral characteristics. The Stone Seated Buddha Triad has highly homogenous mineral composition and particle size, whole-rock magnetic susceptibility, and geochemical characteristics very similar to those of the nearby outcrop. It was confirmed that a combination of physical, chemical, and biological factors affects the Stone Buddha statues. In particular, both the Stone Seated Buddha Triad and Stone Standing Buddha tend to be chipped off from the front and cracked and scaled from the back. The Stone Standing Buddha located outdoors experiences granularity decomposition and black algae formation, which accelerate the weathering under unfavorable conservation environments. The result of non-destructive physical property diagnosis using ultrasonic velocity showed that both the Stone Seated Buddha Triad and Stone Standing Buddha have been completely weathered (CW), indicating very poor physical properties.

• Journal of the Korean Geotechnical Society
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• v.38 no.12
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• pp.113-123
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• 2022

The required density relationship according to the press pressure of the floating die method and the homogeneity of the density distribution in the buffer block was evaluated to analyze the manufacturing characteristics of engineering scale bentonite-sand buffer blocks. In addition, the thermal conductivity was measured and compared with that of the pure bentonite buffer block to evaluate the level of thermal conductivity performance improvement of the bentonite-sand buffer material. As a result, it was confirmed that the standard deviation of dry density decreased to 0.011 and showed a homogeneous density distribution under the condition of press pressure greater than 400 kg/cm². Furthermore, as a result of the thermal conductivity test, the thermal conductivity of the buffer with optimum moisture content conditions was 1.345 and 1.261 W/(m·K) under the press pressure of 400 and 600 kg/cm², respectively. It increased by 16.1% and 11.0% compared to the pure bentonite buffer material. Based on the results of this study, it is judged that it can be used as fundamental data for manufacturing a homogeneous bentonite-sand buffer block on an engineering scale.

• The Journal of Korean Society for Radiation Therapy
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• v.29 no.2
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• pp.9-17
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• 2017

Purpose: The tissue description and electron density indicated by the Computed Tomography(CT) number (also known as Hounsfield Unit) in radiotherapy are important in ensuring the accuracy of CT-based computerized radiotherapy planning. The internal metal implants, however, not only reduce the accuracy of CT number but also introduce uncertainty into tissue description, leading to development of many clinical algorithms for reducing metal artifacts. The purpose of this study was, therefore, to investigate the accuracy and the clinical applicability by analyzing date from SMART MAR (GE) used in our institution. Methode: and material: For assessment of images, the original images were obtained after forming ROIs with identical volumes by using CIRS ED phantom and inserting rods of six tissues and then non-SMART MAR and SMART MAR images were obtained and compared in terms of CT number and SD value. For determination of the difference in dose by the changes in CT number due to metal artifacts, the original images were obtained by forming PTV at two sites of CIRS ED phantom CT images with Computerized Treatment Planning (CTP system), the identical treatment plans were established for non-SMART MAR and SMART MAR images by obtaining unilateral and bilateral titanium insertion images, and mean doses, Homogeneity Index(HI), and Conformity Index(CI) for both PTVs were compared. The absorbed doses at both sites were measured by calculating the dose conversion constant (cCy/nC) from ylinder acrylic phantom, 0.125cc ionchamber, and electrometer and obtaining non-SMART MAR and SMART MAR images from images resulting from insertions of unilateral and bilateral titanium rods, and compared with point doses from CTP. Result: The results of image assessment showed that the CT number of SMART MAR images compared to those of non-SMART MAR images were more close to those of original images, and the SD decreased more in SMART compared to non-SMART ones. The results of dose determinations showed that the mean doses, HI and CI of non-SMART MAR images compared to those of SMART MAR images were more close to those of original images, however the differences did not reach statistical significance. The results of absorbed dose measurement showed that the difference between actual absorbed dose and point dose on CTP in absorbed dose were 2.69 and 3.63 % in non-SMRT MAR images, however decreased to 0.56 and 0.68 %, respectively in SMART MAR images. Conclusion: The application of SMART MAR in CT images from patients with metal implants improved quality of images, being demonstrated by improvement in accuracy of CT number and decrease in SD, therefore it is considered that this method is useful in dose calculation and forming contour between tumor and normal tissues.