• 천문학회보
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• 제42권1호
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• pp.53.1-53.1
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• 2017

The YONSEI (YOnsei Nearby Supernova Evolution Investigation) project is to investigate the luminosity evolution of Type Ia supernovae (SNe Ia) by using their early-type host galaxies. As a part of this project, we have constructed our own SN catalogue. SALT2 and MLCS2k2 light-curve fitters implemented in SNANA package are employed to analyze the light-curve data. The catalogue provides a rest-frame peak magnitude in B-band or distance modulus, a light-curve shape parameter, and a color or an extinction value of each SN in the redshift range from 0.01 to 1.4. In this poster, we will present our progress in the detailed systematic tests for this catalogue.

• Korean Journal of Mathematics
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• 제26권3호
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• pp.425-437
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• 2018

In this paper, we linked the motion of spherical images with the motion of their curves. Surfaces generated by the evolution of spherical image of a space curve are constructed. Also geometric proprieties of these surfaces are obtained.

• 정보처리학회논문지B
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• 제10B권5호
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• pp.521-526
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• 2003

본 논문에서는 영역의 경계를 추출하기 위해 영상의 밝기 정보와 곡선전개 방식을 이용한 기하 활성 모델을 제안한다. 영역의 경계를 추출하는 문제를 추출한 영역의 평균 밝기 값과 전개중인 폐곡선 영역의 밝기 값의 차론 최소화시키는 것으로 설정한다. 최적의 해를 구하는 방법으로 레벨세트 이론을 적용한 곡선전개 방법을 이용한다. 이 방식은 일반적인 활성 모델에 비해 초기 곡선 설정에 제약이 없고 동시에 여러 영역의 경계 추출이 가능하다. 제안 모델은 에지 정보가 충분치 못한 영상의 경우에도 일반적인 에지 기반 방식에 비해 추출 결과가 양호하였다. 비등방성 확산 필터를 사용하여 영상을 전처리 함으로써 보다 나은 추출이 수행되었다. CT나 MRI 영상을 이용하여 모델의 성능을 확인하였다.

• 천문학회보
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• 제38권2호
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• pp.56.1-56.1
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• 2013

Supernovae type Ia (SNe Ia) cosmology is providing the only direct evidence for the presence of dark energy. This result is based on the assumption that the look-back time evolution of SNe Ia luminosity, after light-curve shape correction, would be negligible. However, the most recent compilation of SNe Ia data shows systematic difference in the Hubble residual (HR) between the E and Sd/Irr galaxies, indicating that the light-curve fitters used by the SNe Ia community cannot quite correct for a large portion of the population age effect. In order to investigate this possibility more directly, we have obtained low-resolution spectra for 30 nearby early-type host galaxies. This data set is used to estimate the luminosity-weighted mean ages and metallicities of host galaxies by employing the population synthesis models. We found an interesting trend between the host galaxy age and HR, in the sense that younger galaxies have positive residuals (i.e., light-curve corrected SNe Ia luminosity is fainter). This result is rather independent of the choice of the population synthesis models employed. Taken at face value, this age (evolution) effect can mimic a large fraction of the HR used in the discovery of the dark energy. This result is significant at 1.4 - 3 sigma levels, depending on the light curve fitters adopted, and further observations and analyses are certainly required to confirm the trend reported here.

• 천문학회보
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• 제36권2호
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• pp.69.2-69.2
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• 2011

The discovery of dark energy from Type Ia supernovae (SN Ia) is based on the implicit assumption that the look-back time evolution of SN Ia luminosity, after light-curve corrections, would be negligible. A strong support for this assumption was the apparent insensitivity of SN Ia distances across the host galaxy morphologies. However, Hicken et al. 2009 (H09) shows a systematic difference in the Hubble residual (HR) of $0.144{\pm}0.070$ mag between the E-S0 and Scd/Sd/Irr galaxies, after light-curve corrections. If true, this indicates that the light-curve fitters used by the SN Ia community can not correct for the population age (and therefore the evolution) effect. In order to confirm this, we have combined nearby SN Ia samples and the first-year SDSS-II SN Survey. The SNANA package was used for analyzing SN Ia light-curve, both for the MLCS2k2 and SALT2 fitters. We find a systematic difference in the HR of $0.10-0.13{\pm}0.030$ mag between E-S0 and Scd/Sd/Irr galaxies, which is in agreement with the result of H09, but now at the 3-5 ${\sigma}$ level. Considering the significant difference in the mean age of stellar population between these morphological types, the difference in the HR reported here suggests that the evolution effect of SN Ia luminosity should be considered in the cosmological application of SN Ia data.

• International Journal of Fuzzy Logic and Intelligent Systems
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• 제13권1호
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• pp.39-49
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• 2013

This paper presents a method of improving the performance of a day-ahead 24-h load curve and peak load forecasting. The next-day load curve is forecasted using radial basis function (RBF) neural network models built using the best design parameters. To improve the forecasting accuracy, the load curve forecasted using the RBF network models is corrected by the weighted sum of both the error of the current prediction and the change in the errors between the current and the previous prediction. The optimal weights (called "gains" in the error correction) are identified by differential evolution. The peak load forecasted by the RBF network models is also corrected by combining the load curve outputs of the RBF models by linear addition with 24 coefficients. The optimal coefficients for reducing both the forecasting mean absolute percent error (MAPE) and the sum of errors are also identified using differential evolution. The proposed models are trained and tested using four years of hourly load data obtained from the Korea Power Exchange. Simulation results reveal satisfactory forecasts: 1.230% MAPE for daily peak load and 1.128% MAPE for daily load curve.

• 한국콘텐츠학회논문지
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• 제5권6호
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• pp.138-145
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• 2005

본 연구에서는 실명(loss of eyesight)의 원인 질병중 하나인 녹내장의 진행과 진단 등의 의료 정보제공을 목적으로 양방향 곡선 전개 방식을 이용하여 망막 영상에서 시신경 원판(optic disk)의 경계를 검출하는 방법을 제안한다. 정확한 경계 검출의 위하여 텍스처 병합(texture synthesis)기반의 이미지 인페인팅 방법으로 시신경 원판 위를 지나는 혈관을 제거하고 전처리 과정에서 발생하는 잡음제거와 경계의 보존을 위해 비등방성 확산 필터링(anisotropic diffusion filtering)을 행한다. 혈관이 제거된 망막 영상에서 시신경 원판의 경계 검출은 양방향 곡선 방식으로 검출한다. 실험 결과에서, 제안한 알고리즘은 복잡한 망막영상에도 효율적으로 시신경 원판을 검출한다는 것을 보여준다.

• 융합신호처리학회논문지
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• 제1권1호
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• pp.23-31
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• 2000

본 논문에서는 물체의 경계나 형태 추출을 위하여 레벨 세트 이론을 바탕으로 한 새로운 곡선 전개방법을 제안한다. 특히 전처리 과정에서 잡음의 효과적 처리를 위하여 기존의 필터 방식들이 가지는 단점인 경계 부분의 bluning 현상을 줄이고 정확한 에지 위치를 보존할 수 있는 비등방성 확산 필터(anisotropic diffusion filter)를 사용한다. 기존의 레벨 세트 방식이 수축이나 팽창 중 단지 한가지의 방식만 적용되어지는 반면, 제안한 방법은 물체의 경계 추출시 팽창과 수축이 통시에 가능하므로 특히 초기 곡선이 여러 물체에 걸쳐져 있는 경우에도 정확한 형태 추출이 가능하였다. 아울러 초기 곡선의 설정이 위치나 형태에 거의 제한을 받지 않기 때문에 추출을 원하는 영역이 아주 조금만 포함되어 있어도 정화한 형태 추출이 가능하였다.

• 천문학논총
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• 제30권2호
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• pp.485-486
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• 2015

We use light-curve fitting models (MLCS2k2, SALT2, and SNooPy) as implemented in SNANA to make the YOnsei Nearby Supernova Evolution Investigation (YONSEI) Supernova Catalogue. The catalogue consists of several hundred Type Ia supernovae (SNe Ia) in the redshift range from 0.01 to 1.35, and provides distance moduli, light-curve shape parameters, and color or extinction values for each supernova. This data set will be used to study the dependence of SNe Ia luminosities on the host galaxy morphologies. In this paper, we present the YONSEI Supernova Catalogue and preliminary systematic tests for the catalogue.

• 천문학회보
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• 제37권2호
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• pp.76.1-76.1
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• 2012

We have employed SNANA supernova analysis package to make YONSEI Supernova Catalogue 1, which contains distance modulus, light-curve shape parameters, and color or extinction values of each supernova. This database is used to study the dependence of Type Ia supernovae (SNe Ia) luminosities on the host-galaxy morphologies. The redshift range of this catalogue is 0.010 < z < 1.555, and we use three light-curve fitters: SALT2, MLCS2k2 (Rv = 3.1), and MLCS2k2 (Rv = 1.7). We find a systematic difference in the Hubble residual (HR) of $0.1{\pm}0.031$ mag between E-S0 and Scd/Sd/Irr host-galaxies, and of $0.16{\pm}0.044$ mag between passive and star-burst host-galaxies. This difference is significant over the $3{\sigma}$ level. Considering the significant difference in the mean age of stellar population between these morphological types, the difference in the HR reported here suggests that the evolution effect of SNe Ia luminosity should be considered in the cosmological application of SNe Ia data.