• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제42회 동계 정기 학술대회 초록집
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• pp.196-196
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• 2012

Graphene, two-dimensional one-atom-thick planar sheet of carbon atoms densely packed in a honeycomb crystal lattice, has grabbled appreciable attention due to its extraordinary mechanical, thermal, electrical, and optical properties. Based on the graphene's high carrier mobility, high frequency graphene field effect transistors have been developed. Graphene is useful for photonic components as well as for the applications in electronic devices. Graphene's unique optical properties allowed us to develop ultra wide-bandwidth optical modulator, photo-detector, and broadband polarizer. Graphene can support SPP-like surface wave because it is considered as a two-dimensional metal-like systems. The SPPs are associated with the coupling between collective oscillation of free electrons in the metal and electromagnetic waves. The charged free carriers in the graphene contribute to support the surface waves at the graphene-dielectric interface by coupling to the electromagnetic wave. In addition, graphene can control the surface waves because its charge carrier density is tunable by means of a chemical doping method, varying the Fermi level by applying gate bias voltage, and/or applying magnetic field. As an extended application of graphene in photonics, we investigated the characteristics of the graphene-based plasmonic waveguide for optical signal transmission. The graphene strips embedded in a dielectric are served as a high-frequency optical signal guiding medium. The TM polarization wave is transmitted 6 mm-long graphene waveguide with the averaged extinction ratio of 19 dB at the telecom wavelength of $1.31{\mu}m$. 2.5 Gbps data transmission was successfully accomplished with the graphene waveguide. Based on these experimental results, we concluded that the graphene-based plasmonic waveguide can be exploited further for development of next-generation integrated photonic circuits on a chip.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제11권11호
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• pp.5301-5323
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• 2017

Small cell deployment offers a low-cost solution for the boosted traffic demand in heterogeneous cellular networks (HCNs). Besides improved spatial spectrum efficiency and energy efficiency, future HCNs are also featured with the trend of network architecture convergence and feasibility for flexible mobile applications. To achieve these goals, dual connectivity (DC) is playing a more and more important role to support control/user-plane splitting, which enables maintaining fixed control channel connections for reliability. In this paper, we develop a tractable framework for the downlink SINR analysis of DC assisted HCN. Based on stochastic geometry model, the data-control joint coverage probabilities under multi-frequency and single-frequency tiering are derived, which involve quick integrals and admit simple closed-forms in special cases. Monte Carlo simulations confirm the accuracy of the expressions. It is observed that the increase in mobility robustness of DC is at the price of control channel SINR degradation. This degradation severely worsens the joint coverage performance under single-frequency tiering, proving multi-frequency tiering a more feasible networking scheme to utilize the advantage of DC effectively. Moreover, the joint coverage probability can be maximized by adjusting the density ratio of small cell and macro cell eNBs under multi-frequency tiering, though changing cell association bias has little impact on the level of the maximal coverage performance.

• 대기
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• 제30권3호
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• pp.257-276
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• 2020

Faithful evaluation of the meteorological input is a prerequisite for a better understanding of air quality model performance. Despite the importance, the preliminary meteorological assessment has rarely been concerned. In this study, we aim to evaluate the performance of the Weather Research and Forecasting (WRF) model conducting a year-long high-resolution meteorological simulation in 2016 over the Seoul metropolitan area. The WRF model was configured based on a series of sensitivity simulations of initial/boundary meteorological conditions, land use mapping data, reanalysis grid nudging method, domain nesting method, and urban canopy model. The simulated results of winds, air temperature, and specific humidity in the atmospheric boundary layer (ABL) were evaluated following statistical evaluation guidance using the surface and upper meteorological measurements. The statistical evaluation results are presented. The model performance was interpreted acceptable for air quality modeling within the statistical criteria of complex conditions, showing consistent overestimation in wind speeds. Further statistical analysis showed that the meteorological model biases were highly systematic with systematic bias fractions (f_SB) of 20~50%. This study suggests that both the momentum exchange process of the surface layer and the ABL entrainment process should be investigated for further improvement of the model performance.

• 대기
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• 제26권2호
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• pp.277-288
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• 2016

Polar lows are intense mesoscale cyclones that mainly occur over the sea in polar regions. Owing to their small spatial scale of a diameter less than 1000 km, simulating polar lows is a challenging task. At King Sejong station in West Antartica, polar lows are often observed. Despite the recent significant climatic changes observed over West Antarctica, adequate validation of regional simulations of extreme weather events such as polar lows are rare for this region. To address this gap, simulation results from a recent version of the Polar Weather Research and Forecasting model (Polar WRF) covering Antartic Peninsula at a high horizontal resolution of 3 km are validated against near-surface meteorological observations. We selected a case of high wind speed event on 7 January 2013 recorded at Automatic Meteorological Observation Station (AMOS) in King Sejong station, Antarctica. It is revealed by in situ observations, numerical weather prediction, and reanalysis fields that the synoptic and mesoscale environment of the strong wind event was due to the passage of a strong mesoscale polar low of center pressure 950 hPa. Verifying model results from 3 km grid resolution simulation against AMOS observation showed that high skill in simulating wind speed and surface pressure with a bias of $-1.1m\;s^{-1}$ and -1.2 hPa, respectively. Our evaluation suggests that the Polar WRF can be used as a useful dynamic downscaling tool for the simulation of Antartic weather systems and the near-surface meteorological instruments installed in King Sejong station can provide invaluable data for polar low studies over West Antartica.

• 한국건설관리학회논문집
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• 제10권2호
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• pp.121-131
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• 2009

본 연구에서는 우리나라에서 시행되었던 BTO 민간투자사업의 자료를 이용해 BTO 민간투자사업에 투자되는 민간자본에 대한 적정수익률을 추정하고자 한다. 과거 우리나라에서 진행되었던 민간투자사업의 경우 민간자본에 제공된 실질수익률은 대략 $6%\sim9%$ 수준이었는데, 본 연구의 결과에 따르면 정부가 최소운영수입을 보장해준 과거 민간투자사업의 경우, 민간자본에게 제공되었던 수익률은 적정 수준을 상당히 초과하는 것으로 나타났다. 특히 대부분의 민간투자사업에 있어 실제 운영 수입이 실시협약 당시 예측된 운영수입에 현저히 못 미친다는 점을 고려할 때, 민간자본에 대한 적정수익률은 더 낮아지게 되며 따라서 과거에 제공된 수익률의 적정수익률 대비 초과분은 더욱 커지게 된다. 본 연구결과는 향후 BTO방식 민간투자 사업을 진행할 때 정부와 민간사업자간의 실시협약조건에 민간 사업자가 부담하는 위험 대비 적정수익률이 반영될 수 있도록 하는데 도움을 줄 것으로 예상된다.

• Journal of Gastric Cancer
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• 제15권4호
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• pp.262-269
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• 2015

Purpose: Intraabdominal abscess is one of the most common reasons for re-hospitalization after gastrectomy. This study aimed to develop a model for estimating the probability of intraabdominal abscesses that can be used during the postoperative period. Materials and Methods: We retrospectively reviewed the clinicopathological data of 1,564 patients who underwent gastrectomy for gastric cancer between 2010 and 2012. Twenty-six related markers were analyzed, and multivariate logistic regression analysis was used to develop the probability estimation model for intraabdominal abscess. Internal validation using a bootstrap approach was employed to correct for bias, and the model was then validated using an independent dataset comprising of patients who underwent gastrectomy between January 2008 and March 2010. Discrimination and calibration abilities were checked in both datasets. Results: The incidence of intraabdominal abscess in the development set was 7.80% (122/1,564). The surgical approach, operating time, pathologic N classification, body temperature, white blood cell count, C-reactive protein level, glucose level, and change in the hemoglobin level were significant predictors of intraabdominal abscess in the multivariate analysis. The probability estimation model that was developed on the basis of these results showed good discrimination and calibration abilities (concordance index=0.828, Hosmer-Lemeshow chi-statistic P=0.274). Finally, we combined both datasets to produce a nomogram that estimates the probability of intraabdominal abscess. Conclusions: This nomogram can be useful for identifying patients at a high risk of intraabdominal abscess. Patients at a high risk may benefit from further evaluation or treatment before discharge.

• Imaging Science in Dentistry
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• 제41권4호
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• pp.155-159
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• 2011

Purpose : This study was performed to determine the prevalence of maxillary canine impaction on a basis of a single panoramic radiograph in Bangladeshi population. Materials and Methods : A random sample of seven hundred panoramic radiographs was collected from the patient record of a dental clinic. All the selected panoramic radiographs were taken from January 2009 to August 2010 by a single panoramic radiograph machine with the same exposure time (19 seconds) for all radiographs. One hundred and twenty panoramic radiographs were excluded to minimize the selection bias. In a dim lit room, an observer assessed the radiographs on a standard radiographic light box. The position of the impacted maxillary canine was recorded in line with the longitudinal axis of a tooth using the edge of a metal ruler. Data were subsequently put on SPSS 11.5 software and chi-square (${\chi}^2$) tests were applied to find out the association. Results : Among 580 panoramic radiographs it was found that impacted maxillary canines were present in only 7 (1.2%) radiographs. A statistical significant difference was found between the age of the patients and the vertical position of the impacted canines (p=0.000) and between the age of the patients and the horizontal position of the impacted canines (p=0.003). Conclusion : The prevalence was found to be low compared with the present study from the limitation of panoramic image. Further study needs to include three-dimensional imaging modality.

• 한국조리학회지
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• 제18권4호
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• pp.100-117
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• 2012

본 연구의 목적은 일선 호텔직원들의 개인자원으로서 핵심자기평가(자아존중감, 일반화된 자아효능감, 통제위치 및 정서적 안정성), 직무스트레스 요인으로서 고객언어폭력(직무스트레스 요인)과 직무결과로서 이직의도 간의 구조관계를 분석하는 것이었다. 자료는 부산시내에 소재하는 10개의 특급호텔에 근무하는 일선직원들을 표본으로 하여 자기기입식 조사법에 의하여 수집되었다. 총 405부의 설문지가 최종 분석에 이용되었다. 본 연구는 연구모형과 연구가설들을 검증하기 위하여 구조방정식모형분석을 적용하였다. 가설화된 것처럼, 분석결과는 핵심자기평가가 고객언어폭력에 대한 지각과 이직의도를 경감시키는 것을 보여주었다. 고객언어폭력은 이직의도를 증폭시킨다는 결과를 보여주었다. 마지막으로, 실무적 시사점을 논의하였으며, 본 연구의 한계점을 제시하였고 향후 연구방향을 제안하였다.

• 대한한방부인과학회지
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• 제31권4호
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• pp.39-53
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• 2018

Objectives: The purpose of this review was to overview and evaluate the efficacy of electroacupunture for women with polycystic ovarian syndrome (PCOS) Methods: Relevant randomized controlled studies (RCTs) were identified by database searches in PubMED, EMBASE, OASIS, and Google scholar, up to May 2018. Data were extracted regarding hyperandrogenism, obesity and hyperinsulinemia indices. The risk of bias was assessed. Results: Five RCTs were included for analysis. In one RCT, electroacupuncture group had significantly lower free testosterone and testosterone, compared to no treatment group. However, The other RCTs showed no significant difference between two groups. For LH/FSH, Ferriman Gallway score, anti-mullerian hormone, body mass index, weight and waist, and insulin, electroacupuncture group showed no significant difference, compared to physical exercise, no treatment, and sham acupuncture group. Conclusions: Only a limited number of RCTs have been reported. At present, there is insufficient evidence to support the use of electroacupuncture for treatment of PCOS.

• 정보화정책
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• 제27권1호
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• pp.36-54
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• 2020

본 연구에서는 디지털 기기 이용을 위한 동기와 운용 기술 차원에서의 디지털 정보격차가 온라인 정치참여에 미치는 영향에 대해 실증적으로 분석하였다. 한국정보화진흥원에서 2018년 9월부터 12월까지 실시한 2018 디지털 정보격차 실태조사 데이터를 사용하여, 인터넷 이용자와 비이용자 간에 발생할 수 있는 표본선택의 편의를 통제하기 위해 Heckman 선택모형을 이용한 분석을 수행하였다. 연구결과, 디지털 기기를 이용하여 개별 시민들이 원하는 활동을 하기 위한 동기와 기기 운용 기술에 있어서의 격차는 온라인 정치참여에 유의한 영향이 나타났다. 또한 사회경제적 수준에서 연령, 교육수준 및 지역적 요인은 온라인 정치참여에 유의한 영향을 나타내지만, 성별 및 소득수준에서는 유의한 영향이 나타나지 않았다. 본 연구에서는 디지털 기기간 정보격차의 양상에 차이가 있다는 것을 밝혀냈다는 것에 의의가 있다. 즉, 모바일 기기 이용자의 경우에는 디지털 기기 이용 동기가, 개인용 컴퓨터 이용자의 경우에는 기기 운용 기술이 중요한 요인으로 식별되었다.