• Bulletin of the Korean Chemical Society
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• v.29 no.10
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• pp.1960-1964
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• 2008

The roles of coordinating ligands (TOPO, OA, HDA, and TDPA) for the synthesis of ZnO nanoparticles are investigated. Various shapes (hexagonal cone, hexagonal plate, and rod) and sizes (5-100 nm) of ZnO nanoparticles are prepared in relation to the coordinating ligands. The hexagonal shapes ($\leq$ 100 nm) are synthesized with TOPO and OA, while smaller size nanorods (5 ${\times}$ 30 nm) are with TOPO and TDPA. The relative intensities of two distinctive emission bands centered at 385 and 500 nm, which are related to the exciton and defect states, respectively, depend on the crystal qualities of ZnO nanoparticles affected by the coordinating ligands. The intense UV emissions with the reduced visible emissions are found in the monodisperse nanoparticles such as hexagonal cones and nanorods, suggesting that the monodispersity as well as the crystallinity is closely related to the coordinating ligands. The blue-shift of photoluminescence and absorption edge is observed in the nanorods, because the sizes of the nanorods are in the quantum confinement regime.

• Journal of Korean Society of Forest Science
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• v.99 no.2
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• pp.235-243
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• 2010

Picea jezoensis with several infraspecific taxa is indigenous to Eastern Asia and the Far East of Russia. Although these taxa are very common, the taxonomic confusion surrounding this complex is reflected in ambiguity of the various taxonomic treatments currently used. Patterns of intraspecific variations of cone morphology and recognition of taxa within the P. jezoensis complex were investigated from 175 individuals. Morphological variation of cone characters was determined by the univariate analysis to be insignificant in separating most previously recognized infraspecific taxa in Korea, China, Russia, and Japan. Our statistical analysis showed that cones from northern populations were larger and wider than those from southern populations. Individuals from South Korea were predominantly smaller even than those from Honshu of Japan which were previously recognized as var. hondoensis. All measured characters appeared to show some clinal variation with changes in latitude, and a distinctive trend was evident. Consequently var. hondoensis, var. koreana, and var. microsperma cannot retain their infraspecific state within the P. jezoensis complex.

• The Bulletin of The Korean Astronomical Society
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• v.42 no.2
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• pp.62.1-62.1
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• 2017

In space weather forecast, it is important to determine three-dimensional properties of CMEs. Using 29 limb CMEs, we examine which cone type is close to a CME three-dimensional structure. We find that most CMEs have near full ice-cream cone structure which is a symmetrical circular cone combined with a hemisphere. We develop a full ice-cream cone model based on a new methodology that the full ice-cream cone consists of many flat cones with different heights and angular widths. By applying this model to 12 SOHO/LASCO halo CMEs, we find that 3D parameters from our method are similar to those from other stereoscopic methods (i.e., a triangulation method and a Graduated Cylindrical Shell model). In addition, we derive CME mean density (${\bar{\rho}_{CME}}={\frac{M_{total}}{V_{cone}}}$) based on the full ice-cream cone structure. For several limb events, we determine CME mass by applying the Solarsoft procedure (e.g., cme_mass.pro) to SOHO/LASCO C3 images. CME volumes are estimated from the full ice-cream cone structure. For the first time, we derive average CME densities as a function of CME height for several CMEs, which are well fitted to power-law functions. We will compare densities (front and average) of geoeffective CMEs and their corresponding ICME ones.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.6 no.3
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• pp.98-104
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• 2007

The carbon fiber reinforced carbon composite (CFRC) materials are necessary for the advanced industries that require the thermal resistance. And the development and research for CFRC has been in progress in the field of aerospace and defense industry. CFRC have several advantages and special properties such as excellent anti ablation, outstanding strength retention at very high temperature, high heat capacity and thermal transport, high specific stiffness and strength, and high thermal shock resistance. They have been used as aircraft brake, rocket nozzle, nose cones, jet engine turbine wheels, and high speed craft. Since the technology related to CFRC was prohibited from importing and exporting, we developed our own technology to produce F-16 B32 brake disk made out of CFRC, and then we performed various tests to observe the characteristics of CFRC-based brake disk developed in this study in view of density, strength, friction, specific heat, and heat conductivity.

• Proceedings of the Korean Society of Medical Physics Conference
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• 2002.09a
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• pp.446-449
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• 2002

The video based electronic portal imaging device (EPID), which could display the portal image in near real time, was implemented to verify treatment position error in FSRT(Fractionated Stereotatic Radiation Therapy) instead of a portal film. Also, Developed FSRT system was composed of the stereotactic frame, frame mounting system and collimator cones. The verification of treatment position is very crucial in special therapies like FSRT. In general, the FSRT uses high dpse rate at small field size for treating small intracranial lesions. To evaluate quantitative positioning errors in FSRT, we used the first FSRT image as reference image and obtained the second FSRT image that was moved 2mm intentionally and detected intracranial contours after image processing. The generated 2mm error could be verified by overlapping only contours of two images. Through this study, the radiation treatment efficiency could be improved by performing precise radiation therapy with a developed video based EPID and FSRT.

• Restorative Dentistry and Endodontics
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• v.19 no.2
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• pp.611-620
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• 1994

The purpose of this study was to evaluate the effect of post space preparation on apical sealing according to the methods and time of gutta percha removal. Forty six extracted single rooted teeth were selected for this study. Forty teeth were used as experimental groups and six teeth as control groups. Forty teeth were routinely prepared by step-back method and obturated with gutta percha cones and zinc oxide-eugenol cement using lateral condensation. All obturated teeth were divided into 4 groups of 10 teeth each. In each group of 1, 2, 3, heated plugger, gate glidden drill and chloroform and K-file were used respectively for post space preparation by removing the gutta percha immediately after obturation. In group 4, post space were prepared with gate glidden drill one week after obturation. In all experimental groups, the post space were prepared so that 4mm of apical gutta percha remained. After post space preparation, apical leakage were measured with electrochemical method for 28 days and analyzed statistically. The following results were obtained ; 1. No statistically significant differences in apical leakage were occured among the experimental groups using heated plugger, gate glidden drill and chloroform and K-file to remove the gutta percha immediately after obturation. 2. No significant difference in apical leakage was found between the teeth prepared post space immediately after obturation and those prepared 1 week after obturation. 3. In all experimental groups, the apical leakage was increased with time passage regardless of the post space preparation time and the gutta percha removal techniques.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.840-840
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• 2003

Operational Modal Analysis (OMA) is a technique for identification of modal parameters by measurement of only the system's response. On many lightweight structures, such as load-speaker cones and disk drive read/write heads, is impossible or impractical to measure the input forces. Another characteristic of lightweight structure is their sensitivity to mass loading from sensors. The Scanning Laser Doppler Vibrometry(SLDV) allows response measurements to be taken without mass loading. One disadvantage of OMA testing compared to tradition input output modal testing is the OMA mode shapes are un-scaled. This means that the mode shape obtained from an OMA test can not used for analytical structural modification studies. However, the un-scaled mode shapes from an OMA test can be used to update a Finite Element Model (FEM). The updated FEM can then be used to analytically predict the effect of structural modifications. This paper will present the results of an OMA test performed on a simple plate and motor in operating conditions. The un-scaled mode shapes from this test will be used to update a FEM model of the system. The updated FEM model will be then be used to predict the effect of attaching a mass to the plate. The shapes predicted by the FEM for the modified system will be compared to a second OMA test on the modified system

• Korean Journal of Materials Research
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• v.16 no.1
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• pp.63-67
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• 2006

The characteristics of the wet-etching of ZnO thin films were investigated using hydrochloric and phosphoric acid solutions as etchants. The etch rate of ZnO films, using highly diluted hydrochloric acid solutions at a concentration of 0.25% in deionized water, was determined to be about 120 nm/min, and linearly increased with increasing the acid concentration, resulting in $1.17{\mu}m/min$ when a 2% HCl solution was used. The surface of ZnO etched by an HCl solution, observed by scanning electron microscopy, showed a rough morphology with a high density of hexagonal pyramids or cones with sidewall angles of about ${\sim}45^{\circ}C$. Moreover, the sidewall angles of the masked area were similar to those of the pyramids on the surface. In comparison, the surface of ZnO etched by a phosphoric acid had a smooth surface morphology. The origin of this difference is from the very initial stage of etching, indicating that the etch-mechanism is different for each solution. Furthermore, when $H_3PO_4$ was added to the HCl aqueous solution, the morphology of the etched surface was greatly enhanced and the sidewall angle was also increased to about $65^{\circ}C$.

• Proceedings of the Korean Society for Emotion and Sensibility Conference
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• 2002.05a
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• pp.266-269
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• 2002

This paper explores a fundamental study of acquiring the users' KANSEI information regarding the recognition of shape models. Since there are many differences such as background differences and knowledge differences among users, they will produce different evaluations based on their KANSEI even when an identical shape model is presented. Cluster analysis is proved to be available for catching a group tendency and for constructing a mapping relation between a description of the shape model and the HANSEl database. In order to investigate an analogical relation and a mutual influence in our consciousness, first, we made a questionnaire that asked subjects to represent images having different colors and shape cones by using 4 pairs of adjectives (KANSEI words). Next, based on the cluster analysis of the questionnaire using a fuzzy set theory, we proposed a hypothesis showing how the analogical relation and the mutual influence work in our mind while viewing the shape models. Furthermore, how the properties of KANSEI depend on their descriptions was also investigated by virtue of the cluster analysis. This work will be valuable to construct a personal KANSEI database regarding the Shape Model Processing System.

• Proceedings of the Korea Institute of Fire Science and Engineering Conference
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• 2010.04a
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• pp.429-432
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• 2010

본 연구에서는 산불발생 시 산림 내 연료들의 화재위험성을 분석하고자 산불에 취약한 소나무류(적송, 해송, 리기다소나무)의 솔방울을 대상으로 착화특성과 발연특성을 고찰하였다. 연료는 대형 산불이 빈번하게 발생하는 강원도 동해안 지역에서 채취하였다. 적송과 해송의 솔방울은 26%와 27%로서 함수율 차이가 크지 않았으며, 발화온도는 $380^{\circ}C$ 정도인 것으로 나타났다. 반면, 리기다소나무의 솔방울은 33%의 수분을 함유하였으며, 발화온도는 $352^{\circ}C$ 정도인 것으로 나타났다. 또한, 적송 솔방울의 최대연기밀도는 924Ds로서 해송의 599Ds와 리기다소나무의 605Ds 보다 상대적으로 높았으며, 690s~732s 시간영역에서 최대값을 보이는 것으로 나타났다.