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무선랜 기반의 실내 측위 시스템을 위한 신호 세기 예측 모델에 관한 연구
최희동,안와나즐레이브,박용완,최정희 에스케이텔레콤 (주) 2008 Telecommunications Review Vol.18 No.2
본 논문은 무선랜 기반의 실내 측위 시스템에서 전파 지문 방식의 데이터베이스 구성을 위한 수신 신호 세기 예측 모델에 관한 연구이다. 기존의 알고리즘은 실내 환경의 모든 요인을 입력하여 신호 세기 예상값을 결정하기 때문에 신호 세기 예측 시간이 오래 걸리며, 특정한 지역에서 이루어진 실험치를 사용해 전파 환경을 모델링 함으로써 예측값이 실제 수집된 값과 큰 오차를 가지게 된다. 본 논문에서는 신호 세기 예측 정확도를 향상시키고, 신호 세기 예측 시간을 줄이는 알고리즘을 제안한다. 제안하는 알고리즘은 측위의 대상 지역에서 몇 개의 측위 기준점을 지정하여 수신 신호 세기를 측정하고, 이를 데이터베이스에 적용하여 신호 세기 예측 시 활용한다. 또한 불완전한 전파 환경에 대한 보상을 하기 위해 다수의 측위 기준점으로부터 수신된 평균적인 신호 세기를 사용함으로써 신호 세기 예측값의 신뢰도를 높여준다. 제안된 신호 세기 예측 알고리즘은 컴퓨터 모의 실험을 통해 향상된 수신 신호 세기 추정 및 우수한 측위 성능을 보임을 확인하였다.
Analysis of gene expression during mineralization of cultured human periodontal ligament cells
최희동,노우창,박진우,이재목,서조영 대한치주과학회 2011 Journal of Periodontal & Implant Science Vol.41 No.1
Purpose: Under different culture conditions, periodontal ligament (PDL) stem cells are capable of differentiating into cementoblast-like cells, adipocytes, and collagen-forming cells. Several previous studies reported that because of the stem cells in the PDL, the PDL have a regenerative capacity which, when appropriately triggered, participates in restoring connective tissues and mineralized tissues. Therefore, this study analyzed the genes involved in mineralization during differentiation of human PDL (hPDL) cells, and searched for candidate genes possibly associated with the mineralization of hPDL cells. Methods: To analyze the gene expression pattern of hPDL cells during differentiation, the hPDL cells were cultured in two conditions, with or without osteogenic cocktails (β-glycerophosphate, ascorbic acid and dexamethasone), and a DNA microarray analysis of the cells cultured on days 7 and 14 was performed. Reverse transcription-polymerase chain reaction was performed to validate the DNA microarray data. Results: The up-regulated genes on day 7 by hPDL cells cultured in osteogenic medium were thought to be associated with calcium/iron/metal ion binding or homeostasis (PDE1A, HFE and PCDH9) and cell viability (PCDH9), and the down-regulated genes were thought to be associated with proliferation (PHGDH and PSAT1). Also, the up-regulated genes on day 14 by hPDL cells cultured in osteogenic medium were thought to be associated with apoptosis, angiogenesis (ANGPTL4 and FOXO1A), and adipogenesis (ANGPTL4 and SEC14L2), and the down-regulated genes were thought to be associated with cell migration (SLC16A4). Conclusions: This study suggests that when appropriately triggered, the stem cells in the hPDL differentiate into osteoblasts/cementoblasts, and the genes related to calcium binding (PDE1A and PCDH9), which were strongly expressed at the stage of matrix maturation, may be associated with differentiation of the hPDL cells into osteoblasts/cementoblasts.
최희동,이명재,고동완,곽성관,김동식,정관수 慶熙大學校 레이저 工學硏究所 2002 레이저공학 Vol.13 No.-
In this work, we examined the electrical and mechanical characteristics of TFD devices for various top electrode materials by measuring barrier height and performing ASE depth profile. It was found that the shift of current-voltage(Ⅰ-Ⅴ) characteristics of TFD device depends on the top electrode material. The main reason of the asymmetry in Ⅰ-Ⅴ curve was the differences in barrier height of top and bottom electrodes, and chemical composition at the interface region between top electrode and insulator layer also was important reason. The barrier heights(φ_B) evaluated from temperature dependence of the Ⅰ-Ⅴ relation are 0.7795(Al) 1.0287(Ti) and 1.2928(Ta) eV.
COUNTING STATISTICS MODIFIED BY TWO DEAD TIMES IN SERIES
최희동 한국원자력학회 2011 Nuclear Engineering and Technology Vol.43 No.3
Counting statistics modified by introducing two dead times in series under a Poisson input distribution are discussed. A previous study examined the two cases of series combinations of nonextended-extended (NE-E) and extended-extended (EE)dead times. The present study investigated the remaining two cases of extended-nonextended (E-NE) and nonextendednonextended (NE-NE) dead times. For the three time origins of the counting processes - ordinary, equilibrium, and shifted processes - a set of formulae was newly developed from a general formulation and presented for the event time interval densities, total densities, and exact mean and variance of the counts in a given counting duration. The asymptotic expressions for the mean and variance of the counts, which are most convenient for applications, were fully listed. The equilibrium mean count rates distorted by the three dead times in series were newly derived from the information obtained in these studies. An application of the derived formulae is briefly discussed.
Basic characterization of uranium by high-resolution gamma spectroscopy
최희동,김준혁 한국원자력학회 2018 Nuclear Engineering and Technology Vol.50 No.6
A basic characterization of uranium samples was performed using gamma- and X-ray spectroscopy. Thestudied uranium samples were eight types of certified reference materials with 235U enrichments in therange of 1e97%, and the measurements were performed over 24 h using a high-resolution and highpurityplanar germanium detector. A general peak analysis of the spectrum and the XKa region of theuranium spectra was carried out by using HyperGam and HyperGam-U, respectively. The standardreference sources were used to calibrate the spectroscopy system. To obtain the absolute detection efficiency,an effective solid angle code, EXVol, was run for each sample. Hence, the peak activities andisotopic activities were determined, and then, the total U content and 234U, 235U, and 238U isotopiccontents were determined and compared with those of the certified reference values. A new method todetermine the model age based on the ratio of the activities of 223Ra and 235U in the sample was studied,and the model age was compared with the known true age. In summary, the present study developed amethod for basic characterization of uranium samples by nondestructive gamma-ray spectrometry in24 h and to obtain information on the sample age.