• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2008년도 하계학술발표대회 논문집
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• pp.776-781
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• 2008

A ground heat exchanger in a GSHP system is an important unit that determines the thermal performance of a system and its initial cost. The Size and performance of this heat exchanger is highly dependent on the thermal properties. A proper design requires certain site-specific parameters, most importantly the ground effective thermal conductivity, the borehole thermal resistance and the undisturbed ground temperature. This paper is part of a research project aiming at constructing a database of these site-specific properties, especially ground effective thermal conductivity. The objective was to develop and evaluation method, and to provide this knowledge to design engineers. To achieve these goals, thermal response tests were conducted using a testing device at nearly 150 locations in Korea. The in-situ thermal response is the temperature development over time when a known heating load imposed, e.g. by circulating a heat carrier fluid through the test exchangers. The line-source model was then applied to the response test data because of its simplicity. From the data analysis, the range of ground effective thermal conductivity at various sites is $1.5{\sim}4.0\;W$/mK. The results also show that the ground effective thermal conductivity varies with grouting materials as well as regional geological conditions and groundwater flow.

• Imaging Science in Dentistry
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• 제37권2호
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• pp.93-102
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• 2007

Purpose: Cone beam computed tomography (CBCT) provides a lower dose and cost alternative to conventional CT, promising to revolutionize the practice of oral and maxillofacial radiology. The purpose of this study was to evaluate the absorbed and effective doses of Implagraphy and VCT (Vatech Co., Hwasung, Korea) and compare them with those of panoramic radiography. Materials and Methods: Thermoluminescent dosimeter (TLD) chips were placed at 27 sites throughout the layers of Female ART Head and Neck Phantom for dosimetry. Implagraphy, VCT units, and Planmeca Proline XC panoramic unit were used for radiation exposures. Radiation weighted doses and effective doses were measured and calculated using 1990 and 2005 ICRP tissue weighting factors. Results: Effective doses in Sv (ICRP 2005, ICRP 1990) were 90.19, 61.62 for Implagraphy at maxillay molar area, 123.20, 90.02 for Implagraphy at mandibular molar area, 183.55, 139.26 for VCT and 40.92, 27.16 for panoramic radiography. Conclusion: Effective doses for VCT and Implagraphy were only about 2.2 to 4.5 times greater than those for panoramic radiography. VCT and Implagraphy, CBCT machines recently developed in Korea, showed moderately low effective doses.

• 한국재료학회지
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• 제32권11호
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• pp.508-514
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• 2022

Piezoelectric composite films which are enabled by inorganic piezoelectric nanomaterials-embedded polymer, have attracted enormous attention as a sustainable power source for low powered electronics, because of their ease of fabrication and flexible nature. However, the absorption of applied stress by the soft polymeric matrices is a major issue that must be solved to expand the fields of piezoelectric composite applications. Herein, a flexible and porous piezoelectric composite (piezoelectric sponge) comprised of BaTiO₃ nanoparticles and polydimethylsiloxane was developed using template method to enhance the energy conversion efficiency by minimizing the stress that vanishes into the polymer matrix. In the porous structure, effective stress transfer can occur between the piezoelectric active materials in compression mode due to direct contact between the ceramic particles embedded in the pore-polymer interface. The piezoelectric sponge with 30 wt% of BaTiO₃ particles generated an open-circuit voltage of ~12 V and a short-circuit current of ~150 nA. A finite element method-based simulation was conducted to theoretically back up that the piezoelectric output performance was effectively improved by introducing the sponge structure. Furthermore, to demonstrate the feasibility of pressure detecting applications using the BaTiO₃ particles-embedded piezoelectric sponge, the composite was arranged in a 3 × 3 array and integrated into a single pressure sensor. The fabricated sensor array successfully detected the shape of the applied pressure. This work can provide a cost-effective, biocompatible, and structural strategy for realizing piezoelectric composite-based energy harvesters and self-powered sensors with improved energy conversion efficiency.

• 대한핵의학회지
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• 제34권3호
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• pp.207-221
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• 2000

목적: 우리 나라에서 관동맥질 환자에게 시행되는 치료방법의 빈도와 현행수가와 개정 발표될 수가를 바탕으로 검사 전 유병률에 따라 비용효과 분석을 하였다. 대상 및 방법: 심근관류 SPECT를 한 후 관동맥조영술을 하는 경우, 운동부하심전도 후에 관동맥조영술을 한 경우, 바로 관동맥조영술을 한 경우, 그리고 운동부하심전도 후에 심근 SPECT 후에 관동맥조영술을 한 각각의 경우에 따라 비용을 계산하고 삶의 질을 고려한 여명(Quality Adjusted Life Year: QALY)가 각 치료하거나 치료하지 않았을 때 획득되는 여명의 차이(${\Delta}QALY$)를 산출하여 비용/${\Delta}QALY$가 검사 전 유병률에 따라 달라지는 양상을 제시하였다. 결과: 검사 전 유병률이 0.6이상일 때는 관동맥조영술을 바로 실시하는 것이 가장 비용대비효과가 높았다. 검사 전 유병률이 $0.2{\sim}0.6$이었을 때는 운동부하심전도 후에 심근 SPECT 후에 관동맥조영술을 하는 것이 비용대비 효과가 높았다. 심근 SPECT 후에 관동맥조영술을 하는 것이 차선책이었다. 운동부하심전도의 개정수가와 개정희망수가를 근거로 산출하였을 때에도 비용효과의 순서는 비슷하였다. 운동부하심전도 후 바로 관동맥조영술을 시행하는 것은 언제나 비용대비효과가 가장 낮았다. 결론: 심근관류 SPECT는 우리나라의 현행수가체계에서나 변동된 수가체계에서나 검사 전 유병률에 상관없이 비용효과면에서 우수하고 꼭 필요한 검사로 나타났다.

• 한국전기전자재료학회논문지
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• 제34권4호
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• pp.262-268
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• 2021

For the past several decades, various next-generation patterning methods have been developed to obtain well-designed nano-to-micro structures, such as imprint lithography, nanotransfer printing (nTP), directed self-assembly (DSA), E-beam lithography, and so on. Especially, nTP process has much attention due to its low processing cost, short processing time, and good compatibility with other patterning techniques in achieving the formation of high-resolution functional patterns. To transfer functional patterns onto desirable substrates, the use of soft materials is required for precise replication of master mold. Here, we introduce a simple and practical nTP method to create highly ordered structures using various polymeric replica materials. We found that polymethyl methacrylate (PMMA), polystyrene (PS), and polyvinylpyridine (PVP) are possible candidates for replica materials for reliable duplication of Si master mold based on systematic analysis of pattern visualization. Furthermore, we successfully obtained well-defined metal and oxide nanostructures with functionality on target substrates by using replica patterns, through deposition and transfer process. We expect that the several candidates of replica materials can be exploited for effective nanofabrication of complex electronic devices.

• 한국재료학회지
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• 제33권10호
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• pp.422-429
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• 2023

High-strength low-alloy steel is one of the widely used materials in onshore and offshore plant engineering. We investigated the alloying effect of solute atoms in α-Fe based alloy using ab initio calculations. Empirical equations were used to establish the effect of alloying on the Vicker's hardness, screw energy coefficient, and edge dislocation energy coefficient of the steel. Screw and edge energy coefficients were improved by the addition of V and Cr solute atoms. In addition, the addition of trace quantities of V, Cr, and Mn enhanced abrasion resistance. Solute atoms and contents with excellent mechanical properties were selected and their thermal conductivity and thermal expansion behavior were investigated. The addition of Cr atom is expected to form alloys with low thermal conductivity and thermal expansion coefficient. This study provides a better understanding of the state-of-the-art research in low-alloy steel and can be used to guide researchers to explore and develop α-Fe based alloys with improved properties, that can be fabricated in smart and cost-effective manners.

• Asian Pacific Journal of Cancer Prevention
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• 제15권16호
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• pp.6919-6922
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• 2014

Background: The cytological analysis of serous effusions is a common investigation and yields important diagnostic information. However, the distinction of reactive mesothelial cells from malignant cells can sometimes be difficult for the cytopathologist. Hence cost-effective ancillary methods are essential to enhance the accuracy of cytological diagnosis. The aim of this study was to examine the utility of nuclear morphometry in differentiating reactive mesothelial cells from malignant cells in effusion smears. Materials and Methods: Sixty effusion smears consisting of 30 effusions cytologically classified as malignant (adenocarcinomas) and 30 benign effusions showing reactive mesothelial cells were included in the study. ImageJ was used to measure the nuclear area, perimeter, maximal feret diameter, minimal feret diameter and the circularity. A total of ten representative cells were studied in each case. Results: Significant differences were found between benign and malignant effusions for the nuclear area, perimeter, maximal feret diameter and minimal feret diameter. No significant difference was found for circularity, a shape descriptor. Receiver operating characteristic (ROC) curve analysis revealed that nuclear area, perimeter, maximal feret diameter, and minimal feret diameter are helpful in discriminating benign and malignant effusions. Conclusions: Computerised nuclear morphometry is a helpful ancillary technique to distinguish benign and malignant effusions. ImageJ is an excellent cost effective tool with potential diagnostic utility in effusion cytology.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2009년도 하계학술발표대회 논문집
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• pp.58-63
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• 2009

A ground-loop heat exchanger for the ground source heat pump system is the core equipment determining the thermal performance and initial cost of the system. The size and performance of the heat exchanger is highly dependent on the ground thermal properties - the ground effective thermal conductivity, the borehole thermal resistance and the undisturbed ground temperature. Nowadays, precast concrete piles using steel reinforced precast concrete piles - energy piles - are used to reduce the installing cost of the ground-loop heat exchanger. We were carried out some tests to investigate the effects of some parameters such as borehole length, grouting materials and U-tube configuration of the energy piles. 4 concrete piles, each measuring $250mm{\sim}400mm$ in diameter and approx. 10m in length, and rigged with single spiral and 3 U-tube loop of $16mm{\times}2.3mm$ PB piping. The thermal response tests were conducted using a testing device for 4-different ground-loop heat exchangers. During the heating period, the energy piles absorb the heat of 0.89kW to 1.37kW.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.415.2-415.2
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• 2014

Cost-effective, robust devices for solid-state lighting industry that converts electricity to light revolutionize the current lighting industry. Phosphor materials used in these devices should be synthesized in a low-cost and effective method for use in WLEDs. In this presentation, the synthesis of Eu3+ ions doped BaMoO4 phosphor samples by a facile synthesis process for red component of WLEDs will be shown. The tetragonal phase of the host lattice was substantiated by the X-ray diffraction patterns. The morphological studies were carried out by using a field-emission scanning electron microscope and transmission electron microscope. These confirmed the formation of a shuttle like particles with perpendicular protrusions in the middle of the particle. The photoluminescence (PL) properties exhibited good emission with a high asymmetry ratio when excited with ultraviolet B wavelengths (~ 280-315 nm). The cathodoluminescence (CL) spectra showed similar results to the PL spectra, indicating the rich red emission. The results suggest that this phosphor is a good material as red region component in the development of tri-band UV excitation based WLEDs.

• Journal of Electrochemical Science and Technology
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• 제7권4호
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• pp.316-326
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• 2016

Development and discovery of efficient, cost-effective, and robust electrocatalysts are imperative for practical and widespread implementation of water electrolysis and fuel cell techniques in the anticipated hydrogen economy. The electrochemical reactions involved in water electrolysis, i.e., hydrogen and oxygen evolution reactions, are complex inner-sphere reactions with slow multi-electron transfer kinetics. To develop active electrocatalysts for water electrolysis, the physicochemical properties of the electrode surfaces in electrolyte solutions should be investigated and understood in detail. When electrocatalysis is conducted using nanoparticles with large surface areas and active surface states, analytical techniques with sub-nanometer resolution are required, along with material development. Scanning electrochemical microscopy (SECM) is an electrochemical technique for studying the surface reactions and properties of various types of electrodes using a very small tip electrode. Recently, the morphological and chemical characteristics of single nanoparticles and bio-enzymes for catalytic reactions were studied with nanometer resolution by combining SECM with atomic force microscopy (AFM). Herein, SECM techniques are briefly reviewed, including the AFM-SECM technique, to facilitate further development and discovery of highly active, cost-effective, and robust electrode materials for efficient electrolysis and photolysis.