나노인덴테이션을 이용한 Ti(C_0.7N_0.3)-NbC-Ni 써멧 구성상의 경도평가

김성원,김대민,강신후,류성수,김형태,Kim, Seong-Won,Kim, Dae-Min,Kang, Shin-Hoo,Ryu, Sung-Soo,Kim, Hyung-Tae 한국분말야금학회 2008 한국분말재료학회지 (KPMI) Vol.15 No.6

The indentation technique has been one of the most commonly used techniques for the measurement of the mechanical properties of materials due to its experimental ease and speed. Recently, the scope of indentation has been enlarged down to the nanometer range through the development of instrumentations capable of continuously measuring load and displacement. In addition to testing hardness, the elastic modulus of submicron area could be measured from an indentation load-displacement (P-h) curve. In this study, the hardness values of the constituent phases in Ti($C_{0.7}N_{0.3}$)-NbC-Ni cermets were evaluated by nanoindentation. SEM observation of the indented surface was indispensable in order to separate the hardness of each constituent phase since the Ti($C_{0.7}N_{0.3}$)-based cermets have relatively inhomogeneous microstructure. The measured values of hardness using nanoindentation were ${\sim}20$ GPa for hard phase and ${\sim}10$ GPa for binder phase. The effect of NbC addition on hardness was not obvious in this work.

실리콘 나노선/다중벽 탄소나노튜브 Core-Shell나노복합체의 합성

김성원,이현주,김준희,손창식,김동환,Kim, Sung-Won,Lee, Hyun-Ju,Kim, Jun-Hee,Son, Chang-Sik,Kim, Dong-Hwan 한국재료학회 2010 한국재료학회지 Vol.20 No.1

Si nanowire/multiwalled carbon nanotube nanocomposite arrays were synthesized. Vertically aligned Si nanowire arrays were fabricated by Ag nanodendrite-assisted wet chemical etching of n-type wafers using $HF/AgNO_3$ solution. The composite structure was synthesized by formation of a sheath of carbon multilayers on a Si nanowire template surface through a thermal CVD process under various conditions. The results of Raman spectroscopy, scanning electron microscopy, and high resolution transmission electron microcopy demonstrate that the obtained nanocomposite has a Si nanowire core/carbon nanotube shell structure. The remarkable feature of the proposed method is that the vertically aligned Si nanowire was encapsulated with a multiwalled carbon nanotube without metal catalysts, which is important for nanodevice fabrication. It can be expected that the introduction of Si nanowires into multiwalled carbon nanotubes may significantly alter their electronic and mechanical properties, and may even result in some unexpected material properties. The proposed method possesses great potential for fabricating other semiconductor/CNT nanocomposites.

OFDMA 시스템의 ARQ 기반 멀티캐스트 방법

김성원,Kim, Sung-Won 한국정보통신학회 2009 한국정보통신학회논문지 Vol.13 No.1

한 노드에서 다수의 노드로 데이터를 전달하는 one-hop 통신에 사용되는 매체접속제어(MAC)는 멀티캐스트 기반의 데이터 통신을 사용하는 것이 매우 효율적이다. 유니캐스트와 달리 멀티캐스트에서는 모든 노드들과의 통신에서 우수한 품질을 얻기 위해서는 여러 노드들과의 서로 다른 무선 채널환경과 노드 이동성에 따른 무전 채널환경 변화에 대응할 수 있어야 한다. 하지만, IEEE 802.11에서는 다수개의 노드들과 RTS, CTS, ACK을 교환하는 방법이 정의되어 있지 않아서 신뢰성 있는 멀티캐스트를 지원하지 않고 있다. 이러한 문제를 해결하기 위해서 몇 가지 MAC 계층 프로토콜들이 제안되었다. 하지만, 신뢰성 있는 멀티 캐스트를 구현하기 위해서는 추가적인 오버헤드가 필요하며, 이 오버헤드로 인해서 시스템 성능이 저하하게 된다. 본 논문에서는 OFDMA 시스템에서 신뢰성 있는 멀티 캐스트를 구현하기 위해 필요한 오버헤드를 줄이기 위하여 계층통합적 (cross-layer) 설계기법을 제안한다. 제안된 오버헤드와 시스템 성능간의 관계를 분석하는 방법도 제안한다. Multicast-based data communication is an efficient communication scheme in wireless networks where the Media Access Control (MAC) layer is based on one-hop broadcast from one source to multiple receivers. Compared with unicast, multicast over wireless channel should handle varying channel conditions of multiple users and user mobility to achieve good quality for all users. However, IEEE 802.11 does not support reliable multicast due to its inability to exchange RTS/CTS and ACK with multiple recipients. Thus, several MAC layer protocols have been proposed to provide reliable multicast. For the reliable multicast, an additional overhead is introduced and it degrades the system performance. In this paper, we propose a cross-layer design to reduce the control overhead for reliable multicast in OFDMA systems. We present an analytical formulation of the system throughput associated with the overhead.

열차폐코팅용 La₂(Zr_1-xHf_x)₂O₇ 산화물의 상형성과 열물성

김성원,이성민,오윤석,김형태,장병국,Kim, Seong-Won,Lee, Sung-Min,Oh, Yoon-Suk,Kim, Hyung-Tae,Jang, Byung-Koog 한국분말야금학회 2011 한국분말재료학회지 (KPMI) Vol.18 No.6

As operating temperatures of engines or turbines continually increase for higher efficiency, significant amounts of researches have been focused on finding new materials, which would be alternatives to conventional yttria-stabilized zirconia (YSZ) for thermal barrier coatings (TBCs). In this study, phase evolution and thermo-physical properties of $La_2(Zr_{1-x}Hf_x)_2O_7$ pyrochlore systems are investigated for TBC applications. $La_2(Zr_{1-x}Hf_x)_2O_7$ systems are comprised by selecting $La^{3+}$ as A-site ions and $Zr^{4+}/Hf^{4+}$ as B-site ions in $A_2B_2O_7$ pyrochlore structures. For the developed phases in $La_2(Zr_{1-x}Hf_x)_2O_7$ compositions, thermo-physical properties such as thermal conductivity, thermal expansion coefficient are examined. The potential of these $La_2(Zr_{1-x}Hf_x)_2O_7$ compositions for TBC application is also discussed.

의안(醫案)의 데이터베이스 구조화 연구 - 시수도명의 의안을 중심으로 -

김성원,김기욱,이병욱,Kim, Sung-Won,Kim, Ki-Wook,Lee, Byung-Wook 대한한의학방제학회 2017 大韓韓醫學方劑學會誌 Vol.25 No.1

Objectives : The contents of the literature associated with the medical records were entered into the database. We want to find the structure and search methods for efficient utilization of the database. Methods : The contents were entered into the database using the 'Access 2014 of the MS'. The Query Sentences were created and utilized for a search. Results : We could find information about the prescriptions, medical records and patients by the herbs and symptom combinations using the single table named 'Integrated Knowledge' and queries. Integrated Knowledge is a table that gathered patient information, prescription information and symptom information together. Conclusions : If you store patient, prescription and symptom information on a single table, you could search and use the results by various combinations of the various elements included in the table. These results could help curing patients on the basis of evidence-based treatment at the clinics.

국내 현생 심성암류의 방사성 물질의 농도 및 의미

김성원,Kim, Sung Won 대한자원환경지질학회 2020 자원환경지질 Vol.53 No.5

최근 생활용품 및 건축자재 등에서 검출된 자연 방사성 물질로 인해 사회적으로 다양한 문제가 발생하고 있으며, 이는 조속히 해결해야 될 사회현안으로 대두되고 있다. 우리나라에서도 토양이나 지하수 내 중금속 및 우라늄, 라돈 등의 자연방사성 물질에 대해서 환경부에 의해 지난 20년 이상 장기간 조사된 바 있고, 토양과 지하수 내 자연방사성 물질의 기원이 암석-성인-변형적 특성 등의 지질학적 요인들과 밀접한 상관관계를 보여주는 것으로 추정되고 있지만, 기반암, 기반암 상부토양 및 지하수가 발달한 단층계 내 자연방사성 물질의 국가배경농도가 수립되어 있지 않아 정확한 지질학적 상관관계 규명이 미흡한 실정이다. 본 연구에서는 국내 현생 심성암류의 성인과 천연 방사성(라돈, 우라늄, 토륨 등)물질 농도와의 상관관계에 대한 예비 연구를 수행하였다. 현생 심성암류 중 알칼리 화강암류(섬장암, 몬조니암, 몬조섬록암 및 알칼리화강암)는 높은 마그마 온도와 고알칼리성의 경향 때문에 U, Th, Zr, REE 및 Nb 등이 부화되는 특징을 보여주어 높은 U과 Th 농도를 가진다. 지각물질의 혼합에 의해 고분화된 화강암류(우백질 화강암, 복운모화강암, 고알루미형질 S-type 화강암 및 페그마타이트)는 고분화되지 않은 일반 화강암류(섬록암, 화강섬록암 및 화강암)보다 U, Th 및 K+Na이 더욱 부화되는 경향을 보여준다. 고알칼리성 화강암류들은 주로 판내부의 열개환경, 대륙충돌 조산작용과 해양판의 대륙판 아래 섭입 이후에 일어나는 확장환경에서 생성된다. 반면에 우리나라에서 주로 산출되는 아알칼리성 캘크알칼리 화강암류는 해양판의 대륙판 밑으로의 섭입에 의한 호환경에서 주로 생성된다. 결과적으로 국내 현생 심성암류의 U, Th 및 K 함량변화는 지구조 환경에 의한 암석성인과 밀접한 연관성을 가지는 것으로 추정되며, 현생화강암류 대한 감마분석 자연방사성 핵종(²²⁶Ra, ²³²Th 및 ⁴⁰K) 예비 결과들은 고알칼리성과 고분화된 화강암류에서 높은 값을 보여준다. In recent years, various social issues related to the natural radioactive elements detected in household goods and building materials are addressed, and should be solved promptly. In Korea, for more than 20 years, the Ministry of Environment has investigated the natural radioactive materials such as heavy metals, uranium, and radon in soil or groundwater. The origins of natural radioactive materials in them may have a close correlation with the geological factors including classification of rocks, petrogenetic origins, and deformation characteristics, but the exact geological correlations are not clarified because of the absence of the government policy preserved in the basement rocks, soils as well as groundwater in fault-related reservoirs. This study aims to perform a research on the correlation between the petrogeneses of the Phanerozoic plutonic rocks and natural radioactive concentrations in rocks (radon, uranium, thorium, potassium etc.) in Korea. Among the Phanerozoic plutonic rocks, alkaline plutonic rocks (syenite, monzonite and monzodiorite and alkali granite) show high U and Th concentrations by high solubilities of U, Th, Zr, REE, and Nb until the most extreme stages of magmatic fractionation (viz. crystal fractionation) due to high magma temperature and high alkalinity tendency. The highly fractionated high-K calalkaline and peraluminous granitic rocks (leucogranite, two-mica granite and leucocratic pegmatite are also U and Th concentrations compared with other less or medium fractionated granitic rocks (diorite, granodiorite and granite). The alkaline plutonic rocks are associated with intracontinental rifting and extensional environment after crustal thickening by collisional and subductional processes. In contrast, the dominant calc-alkaline granitic rocks in Korea are related to the arc environment of the subduction zone. In summary, the trends of the U, Th and K concentration from the Phanerozoic plutonic rocks in Korea are closely linked to the petrogenesis of the rocks in tectonic environment. The preliminary data for gamma-spectrometric mesurments of natural radionuclide contents (²²⁶Ra, ²³²Th and ⁴⁰K) in the Phanerozoic plutonic rocks show high values in the alkaline and highly fractionated granitic rocks.

신앙을 가진 어린이들이 코로나19 시기에 경험한 변화와 바람에 관한 질적연구

김성원,Kim, Sung Won 한국기독교교육학회 2021 기독교교육논총 Vol.- No.67

본 연구의 목적은 신앙을 가진 어린이들이 코로나19 시기에 경험한 변화와 바람에 관한 이야기를 탐색하여 교육적 방향을 제언하기 위함이다. 이러한 목적을 위해 코로나19 시기의 삶과 신앙생활에 대해 교회에 출석하는 초등학교 3-4학년 어린이 9명과 면담하였다. 분석 결과, 연구참여자 어린이들은 코로나19 시기에 일상의 변화, 학교생활의 변화, 대인관계의 변화, 신앙생활의 변화, 감정의 변화를 경험한 것으로 분석되었다. 일상의 변화에는 감염 예방을 위한 노력, 사라진 놀이, 여유로운 일상과 무기력함이, 그리고 학교생활의 변화에는 비대면 수업 실시와 다양한 규칙을 요구받음이 포함되었다. 친구·선생님·부모님·형제자매와의 어려움이 대인관계 변화에, 비대면 예배 실시와 가정예배 회복이 신앙생활의 변화에 포함되었다. 연구참여자들의 바람을 분석한 결과, 여행과 놀이의 회복을 포함하는 일상적 바람, 대면 예배로의 복귀·수련회의 회복·재미있는 프로그램 개발을 포함하는 신앙에 관한 바람, 그리고 코로나19 이전 학교생활로 복귀가 도출되었다, 이와 같은 어린이들의 경험과 바람을 토대로 본 연구는 교육자들이 코로나19 시기에 보여 준 어린이들의 노력을 인정하고 그들의 마음을 읽어주고 소통·공동체·즐거움의 요소가 포함된 교회 프로그램을 개발할 필요가 있음을 제안한다. The purpose of this study is to suggest educational directions by exploring the stories of changes and expectations experienced by Christian children during the COVID-19 pandemic. For this purpose, nine third- to fourth-grade elementary school children attending the church, were interviewed about their changes and expectations regarding COVID-19. The results identified five areas of experience: daily life changes, school life changes, interpersonal relationship changes, religious life changes, and emotional changes during the COVID-19 period. Daily changes included infection prevention, missing play, leisurely routine, and lethargy. Changes in school life included loss of face-to-face classes and various rule requirements. Interpersonal relationship changes included the difficulties in forming relationships with friends, teachers, parents, and siblings, and religious life changes included loss of face-to-face worship and the restoration of family worship. Various negative emotions were expressed. Analysis of the participants' expectations showed in daily life they wanted to travel and play, return to pre-corona school life, return to face-to-face worship, restore retreats, and develop fun programs as religious life expectations. Based on these children's experiences and wishes, the study suggests that educators need to recognize children's efforts during the COVID-19 period, read their hurt feelings, and develop church programs that include communication, community, and fun elements.

비금속 포스트 코어가 전부도재관에 미치는 광학적인 영향

김성원,조인호,임주환,임헌송,Kim Sung-Won,Cho In-Ho,Lim Ju-Hwan,Lim Heon-Song 대한치과보철학회 2002 대한치과보철학회지 Vol.40 No.5

Recently as the esthetic concerns about dental prosthesis have been increased, the nonmetallic post and core systems have been introduced clinically to improve the color and the low optical transmittance of conventional casting metal post and core systems. The purpose of this study was to compare and analyze the optical transmittance and the shade changes of all-ceramic crowns with two nonmetallic post and core systems. The experimental groups were classified as follows : Total 27 specimens(9 samples in each group) were evaluated. Group I : Natural teeth as a control group Group II : CosmoPost and $Empress^{(R)}$ core (Ivoclar-Vivadent, Liechtenstein) Group III : $LIGHT-POST^{TM}$ and $LIGHT-CORE^{TM}$ (Bisco, U.S.A.) In all group, all-ceramic crowns were fabricated with the same shade of IPS $Empress^{(R)}$ II (Ivoclar-Vivadent, Liechtenstein) after abutment preparation, and then two kinds of spectrophotometers, UV 3101 PC (Shimadzu, Japan) and CM 503i (Minolta Co. Ltd. Japan), were used to measure the optical transmittance and the color value. The following results were obtained : 1. The optical transmittance of each group without all-ceramic crowns, was siginificantly decreased in order of Group III, I and II (p<0.05). 2. The optical transmittance of each group with all-ceramic crowns cemented, were siginificantly decreased in order of Group I, II and III (p<0.05). 3. In comparison with the shade of all-ceramic crowns, there were no significant differences between groups regardless of the cementation. 4. In comparison with the shade changes in each group after the cementation of all-ceramic crowns, there were no significant differences between groups. From the above results, it is thought that the selection among materials used in this study doesn't influence greatly the esthetic restoration, because the differences of optical transmittance were so small that those were clinically insignificant.

ZrB₂-SiC 복합세라믹스의 미세구조와 열전도도에 미치는 SiC 크기와 첨가량의 영향

김성원,권창섭,오윤석,이성민,김형태,Kim, Seong-Won,Kwon, Chang-Sup,Oh, Yoon-Suk,Lee, Sung-Min,Kim, Hyung-Tae 한국분말야금학회 2012 한국분말재료학회지 (KPMI) Vol.19 No.5

This paper reports the microstructures and thermal conductivities of $ZrB_2$-SiC composite ceramics with size and amount of SiC. We fabricated sintered bodies of $ZrB_2$-x vol.% SiC (x=10, 20, 30) with submicron and nanosized SiC densified by spark plasma sintering. Microstructure retained the initial powder size of especially SiC, except the agglomeration of nanosized SiC. For sintered bodies, thermal conductivities were examined. The observed thermal conductivity values are 40~60 W/mK, which is slightly lower than the reported values. The relation between microstructural parameter and thermal conductivity was also discussed.

OFDM 기반 무선 네트워크의 전송률 제어 기법

김성원,Kim, Sung-Won 한국정보통신학회 2008 한국정보통신학회논문지 Vol.12 No.9

OFDM 기반 무선 네트워크 시스템에서 서브캐리어(subcarrier) 단위로 전송률을 제어하는 기법을 제안한다. 제안된 프로토콜은 IEEE 802.11 표준에 정의된 CTS 프레임에 하나의 OFDM 심벌을 추가하여 구현된다. 수신기는 RTS 프레임을 수신한 후 해당 서브캐리어에 적절한 전송률을 결정하고, 이 결과를 CTS에 추가된 OFDM 심벌을 통하여 전달한다. 송신기와 수신기 사이의 전송률을 일치시키기 위한 에러 복구 방법도 제안한다. 제안된 기법을 통하여 무선 네트워크 시스템의 성능 향상이 이루어짐을 보인다. A protocol is proposed to control the rate of each subcarrier in OFDM-based wireless network systems. The proposed protocol adds an OFDM symbol in CTS frame defined in IEEE 802.11 standard. A receiver determines the rate of its subcarrier after it receives the RTS frame. The determined rate is added to OFDM symbol in CTS frame. In order to synchronize the rate information between the sender and the receiver, error recovery process is proposed. The performance improvement of the proposed method is shown by numerical results.