• 한국전자파학회논문지
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• 제30권3호
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• pp.181-189
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• 2019

본 논문에서는 WLAN(Wireless Local Area Network) 대역의 2.4 GHz, 5.8 GHz와 5G 대역의 3.5 GHz에서 사용가능한 3중 대역 모노폴 안테나를 설계하였으며, 제안된 안테나의 크기는 $100{\times}75{\times}1.6mm^3$로 기생소자를 사용하여 3중 대역 모노폴 안테나를 구현하였다. 또한 제안된 안테나로부터 ${\lambda}/4$ 떨어진 거리에 반사판을 설치함으로써 각 동작주파수들에서의 이득 향상과 SAR(Specific Absorption Rate)을 저감시켰다. 제작한 안테나를 측정한 결과, 반사 계수 -10 dB 이하 기준으로 540 MHz(2.02~2.56 GHz), 390 MHz(3.39~3.78 GHz) 그리고 1,210 MHz(5.56~6.77 GHz)에 해당하는 대역폭을 얻었다. 국제기준에서 요구하는 SAR 기준대비 2.4 GHz에서는 85.12 % 감소했고, 3.5 GHz에서는 50.06 %, 5.8 GHz에서는 36.87 % 감소하였다. 그러므로 제안된 안테나는 국제기준 SAR을 만족하며, WLAN과 5G 대역의 통신에서 사용할 수 있다.

• Restorative Dentistry and Endodontics
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• 제17권1호
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• pp.222-234
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• 1992

The purpose of this study was to evaluate the systemic and local production of immunoglobulins and their levels in patients with periapical cysts using Enzyme - Linked Immunosorbent Assay. Streptococcus sanguis, Bacteroides gingivalis, and Bacteroides intermedius were grown for use as antigen and they were harvested by centrifugation. The patients were divided into two groups: patients of periapical cysts and normal control. 5 patients of each group were selected and their blood were obtained via intravenous puncture prior to surgical operation. Sera were prepared by centrifugation of each blood samples. Cyst fluid were aspirated from cystic cavity and cyst wall were excised at operation. Control tissue were also excised at extraction site of impacted wisdom teeth from normal control. Each tissue was prepared by homogenization and centrifugation. Then antibodies of each sample were measured by modified ELISA. The following results were obtained: 1. Serum IgG and IgM levels were not significantly different between patients with periapical cyst and normal control. 2. IgG and IgM levels of cyst fluid to Bacteroides gingivalis and Bacteroides intermedius were significantly higher than those of serum of patients with periapical cyst, but there was no significant difference to Streptococcus sanguis. 3. IgG and IgM levels of cyst wall to Bacteroides gingivalis and Bacteroides intermedius were significantly higher than those of control tissue, but there was no significant difference to Streptococcus sanguis. 4. IgG and IgM levels in cyst fluid and IgG levels in cyst wall were highest to Bacteroides gingivalis, and IgM levels in cyst wall were highest to Bacteroides intermedius.

• 한국대기환경학회지
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• 제32권1호
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• pp.21-31
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• 2016

Organic carbon (OC) and elemental carbon (EC) in $PM_{2.5}$ were measured with Sunset OC/EC Field Analyzer at Taehwa Research Forest (TRF) near Seoul metropolitan area from May 2013 to April 2014. During the study period, the mean concentrations of OC and EC were $5.0{\pm}3.2{\mu}gC/m^3$ and $1.7{\pm}1.0{\mu}gC/m^3$, respectively. They showed clear seasonality reaching their maximum in winter ($6.5{\mu}gC/m^3$ and $1.9{\mu}gC/m^3$) and minimum in wet summer ($2.5{\mu}gC/m^3$ and $1.4{\mu}gC/m^3$). While OC showed greater seasonal variation, the diurnal variation was more noticeable for EC through all seasons with a clear maximum in the morning, which reveals the influence of vehicle emissions. In contrast, OC exhibited a broad second peak in the afternoon during May~June, when biological activities were the highest. Using the morning peaks of EC and OC, primary OC/EC ratio was assessed, which was assumed to be anthropogenic origin. It was the greatest in winter followed by spring and the lowest in wet summer. The seasonal difference in primary OC/EC ratio implies the influence of non-local sources of OC at the Mt. Taehwa.

• 대한수학회보
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• 제48권5호
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• pp.1033-1039
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• 2011

Let R be a ring with identity 1, I(R) be the set of all idempotents in R and G be the group of all units of R. In this paper, we show that for any semiperfect ring R in which 2 = 1+1 is a unit, I(R) is closed under multiplication if and only if R is a direct sum of local rings if and only if the set of all minimal idempotents in R is closed under multiplication and eGe is contained in the group of units of eRe. In particular, for a left Artinian ring in which 2 is a unit, R is a direct sum of local rings if and only if the set of all minimal idempotents in R is closed under multiplication.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1998년도 봄 학술발표회논문집(II)
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• pp.427-432
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• 1998

The objective of this research is to observe the actual response of low-rise nonseismic moment-resisting reinforced frame subjected to varied levels of earthquake ground motions. First of all, the reduction scale for the model was determined as 1 : 5 considering the capacity of the shaking table to be used. This model was, then, subjected to the shaking table motions simulating Taft N21E component earthquake ground motions, whose peak ground accelerations(PGA's) were modified to 0.12g, 0.2g, 0.3g, and 0.4g. The global behavior and failure mode were observed. The lateral accelerations and displacements at each story and local deformations at the critical portions of structure were measured. The base shear was measured by using specially made load cells. Before and after each earthquake simulation test, free vibration tests were performed to find the changes in the natural period and damping ratio of the model.

• The Korean Journal of Ecology
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• 제25권6호
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• pp.379-382
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• 2002

The present study was to investigate Pb and Cd concentrations in tissues of feral pigeons in urban areas. The Pb levels in bones and livers did not differ between Seoul and Kwangju areas. However, there were significant differences in kidney and liver Cd concentrations between the study sites. These are thought to be a reflection of the metal exposure conditions in the local environment. In particular, metal levels from Seoul were compared with those obtained in the same area between 1991 and 2000 in terms of the long-term biomonitoring approaches. The mean Pb concentrations in bones decreased from 59.1 $\mu$g/wet g in 1991 to 29.5 $\mu$g/wet g in 2000, totaling a reduction in concentrations of approximately 50 percent. However, there were no significant differences in the liver Pb concentrations. Concentrations of Cd in livers and kidneys did not differ between 1991 and 2000.

• 한국통신학회논문지
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• 제22권10호
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• pp.2317-2328
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• 1997

본 논문은 융선의 방향정보를 사용하여 지문을 실시간 자동 인식하는 알고리즘을 제안한다. 융선의 방향정보는 웨이블렛 변환(WT) 그리고 경사 가우시안(gradient of Gaussian)과 코히리언스(coherence)로부터 얻어진 주된 국부 방향(dominant local orientation)을 사용하여 추출한다. 웨이블렛 변환의 적용은 기존에 제안된 알고리즘들에 포함되어 있는 평활화(smoothing), 이진화(binarization), 세션화(thinning) 및 보정(restoration)등 여러 전처리 과정의 생략을 의미하며, 따라서 제안하는 알고리즘의 실시간 처리를 가능하게 한다. 지문 인식은 웨이블렛 변환상에서 3개의 영역-크기가 1/4로 작아진 영역(LL), 수직 성분이 강조된 영역(LH), 그리고 수평 영역이 강조된 영역(HL)-에 나타나는 주된 국부 방향을 사용하여 빠르고 효율적으로 수행된다. 제안한 알고리즘은 SunSparc-2 워크 스테이션 환경의 X-window에서 구현되었으며, $256{\times}256$ 화소 크기의 지문 영상에 적용하여 성능을 평가하였다. 그 결과, 상이한 지문을 동일 지문으로 오인식하는 Type II 에러율을 0%로 했을때, 동일 지문을 상이한 지문으로 오인식 하는 Type I 에러율은 2.5%로서 매우 좋은 성능을 보였다.

• 사물인터넷융복합논문지
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• 제10권2호
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• pp.77-84
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• 2024

지난 몇 년 동안 5G와 같은 새로운 저 지연 통신 프로토콜을 기반으로 IoT 엣지가 등장하기 시작했다. 그러나, IoT 엣지는 막대한 이점에도 불구하고, 새로운 보완 위협을 초래하여 이를 해결하기 위한 새로운 보안 솔루션이 필요하다. 본 논문에서는 IoT 시스템을 보완하는 클라우드 환경기반의 IoT 엣지 아키텍처 모델을 제안한다. 제안 모델은 IoT 엣지 장치에서 추출한 네트워크 트래픽 데이터를 기계 학습에 작용하여 사전에 보안 위협을 예방한다. 또한, 제안 모델은 로컬 노드에서 보안 데이터 일부를 할당함으로써 액세스 네트워크(엣지)에서의 부하 및 보안을 보장한다. 제안 모델은 IoT 엣지 환경 중 로컬 노드에 데이터 처리 및 관리의 일부 기능을 할당함으로써 액세스 네트워크(엣지)의 부하를 더욱 줄이는 동시에 취약 부분을 안전하게 보호한다. 제안 모델은 다양한 IoT 기능을 네임 서비스로 가상화하고, 필요에 따라 하드웨어 기능과 충분한 계산 리소스를 로컬 노드에 배포한다.

• 대한토목학회논문집
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• 제14권6호
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• pp.1349-1356
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• 1994

본 연구에서는 3가지 교각형상에 대하여 국부적 정지상세굴에 대한 실험결과를 분석하였다. 실험결과에 의하면 교각의 세굴은 $V/V_c=0.4{\sim}0.5$, $Fr_p{\fallingdotseq}0.2$일 때 시작되었고 상대세굴심은 유속비와 교각푸르드수와의 관계에서 선형적으로 증가하였다. 또한 상대세굴심은 ${\tau}_r$ < $10^{-4}$일 때는 선형적으로 증가하지만 ${\tau}_r$ > $10^{-4}$이 되면 일정해지는 경향을 가지며 모래의 기하표준편차(${\sigma}_g$)와 교각형상과도 깊은 관계가 있었다.

• 한국해양공학회지
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• 제22권1호
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• pp.13-21
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• 2008

In this study a method to predict CHF(Critical heat flux) in vertical round tubes with axially non-uniform cosine heat flux distribution for water was examined. For this purpose a local condition hypothesis based CHF prediction correlation for uniform heat flux in vertical round tubes for water was developed from 9,366 CHF data points. The local correlation consisted of 4 local condition variables: the system pressure(P), tube diameter(D), mass flux of water(G), and 'true mass quality' of vapor($X_t$). The CHF data points used were collected from 13 different published sources having the following operation ranges: 1.01 ${\leq}$ P (pressure) ${\leq}$ 206.79 bar, 9.92${\leq}$ G (mass flux) ${\leq}$ 18,619.39 $kg/m^2s$, 0.00102 ${\leq}$ D(diameter) ${\leq}$ 0.04468 m, 0.0254${\leq}$ L (length) ${\leq}$ 4.966 m, 0.11 ${\leq}$ qc (CHF) ${\leq}$ 21.41 $MVW/m^2$, and -0.87 ${\leq}X_c$ (exit qualities) ${\leq}$ 1.58. The result of this work showed that a uniform CHF correlation can be easily extended to predict CHF in axially non-uniform heat flux heater. In addition, the location of the CHF in axially non-uniform tube can also be determined. The local uniform correlation predicted CHF in tubes with axially cosine heat flux profile within the root mean square error of 12.42% and average error of 1.06% for 297 CHF data points collected from 5 different published sources.