• 천문학회지
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• 제52권6호
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• pp.217-225
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• 2019

We apply a modified Convolutional Neural Network (CNN) model in conjunction with transfer learning to predict whether an active region (AR) would produce a ≥C-class or ≥M-class flare within the next 24 hours. We collect line-of-sight magnetogram samples of ARs provided by the SHARP from May 2010 to September 2018, which is a new data product from the HMI onboard the SDO. Based on these AR samples, we adopt the approach of shuffle-and-split cross-validation (CV) to build a database that includes 10 separate data sets. Each of the 10 data sets is segregated by NOAA AR number into a training and a testing data set. After training, validating, and testing our model, we compare the results with previous studies using predictive performance metrics, with a focus on the true skill statistic (TSS). The main results from this study are summarized as follows. First, to the best of our knowledge, this is the first time that the CNN model with transfer learning is used in solar physics to make binary class predictions for both ≥C-class and ≥M-class flares, without manually engineered features extracted from the observational data. Second, our model achieves relatively high scores of TSS = 0.640±0.075 and TSS = 0.526±0.052 for ≥M-class prediction and ≥C-class prediction, respectively, which is comparable to that of previous models. Third, our model also obtains quite good scores in five other metrics for both ≥C-class and ≥M-class flare prediction. Our results demonstrate that our modified CNN model with transfer learning is an effective method for flare forecasting with reasonable prediction performance.

• 천문학회지
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• 제40권4호
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• pp.99-106
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• 2007

Statistical analyses were performed to investigate the relative success and accuracy of daily maximum X-ray flux (MXF) predictions, using both multilinear regression and autoregressive time-series prediction methods. As input data for this work, we used 14 solar activity parameters recorded over the prior 2 year period (1989-1990) during the solar maximum of cycle 22. We applied the multilinear regression method to the following three groups: all 14 variables (G1), the 2 so-called 'cause' variables (sunspot complexity and sunspot group area) showing the highest correlations with MXF (G2), and the 2 'effect' variables (previous day MXF and the number of flares stronger than C4 class) showing the highest correlations with MXF (G3). For the advanced three days forecast, we applied the autoregressive timeseries method to the MXF data (GT). We compared the statistical results of these groups for 1991 data, using several statistical measures obtained from a $2{\times}2$ contingency table for forecasted versus observed events. As a result, we found that the statistical results of G1 and G3 are nearly the same each other and the 'effect' variables (G3) are more reliable predictors than the 'cause' variables. It is also found that while the statistical results of GT are a little worse than those of G1 for relatively weak flares, they are comparable to each other for strong flares. In general, all statistical measures show good predictions from all groups, provided that the flares are weaker than about M5 class; stronger flares rapidly become difficult to predict well, which is probably due to statistical inaccuracies arising from their rarity. Our statistical results of all flares except for the X-class flares were confirmed by Yates' $X^2$ statistical significance tests, at the 99% confidence level. Based on our model testing, we recommend a practical strategy for solar X-ray flare predictions.

• Clinical and Experimental Reproductive Medicine
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• 제34권3호
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• pp.189-196
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• 2007

목 적: 본 연구의 목적은 난소기능이 저하된 불임 환자에서 체외수정시술 시 그 결과의 예측인자로서 환자의 연령과 혈중 FSH 수치의 중요성 및 그 임상적인 의미를 알아보고자 하였다. 연구방법: 2000년 1월부터 2004년 12월까지 본원 불임센터에서 체외수정시술을 시행받은 환자 중 이전 체외수정시술주기에서 획득된 난자 수가 5개 이하이며 FSH 농도가 15 mIU/ml 이상 25 mIU/ml 이하로 그 연령이 42세 이하인 난소기능이 저하된 불임 환자 85명의 85 체외수정시술 주기를 연구대상으로 하였다. 남성요인의 불임이나 착상 전 유전진단인 경우는 제외시켰다. 과배란유도의 방법은 단기요법 (flare-up protocol)을 사용한 경우로 제한하였다. 결 과: 대상군을 환자의 나이에 따라 분류하여 분석하였을 때 환자의 연령이 낮은 군 (age < 35, n=35)에서 고령환자 군 (age $\geq$ 35, n=50)에 비해 통계적으로 의미 있게 높은 착상률 (19.0% versus 4.0%, p<0.05)과 높은 지속임신율(100% versus 14.3%, p<0.05)을 보였으며, 연구대상 군을 기저 혈중 FSH농도에 의해 두 군으로 비교하였을 때 낮은 기저 혈중 FSH를 가진 군 (basal serum FSH < 20 mIU/ml, n=58)에서 기저혈중 FSH가 높았던 군 (basal serum FSH $geq$ 20 mIU/ml, n=27)에 비해 획득된 난자 숫자는 통계적으로 의미 있게 높은 반면 (4.6$\pm$0.7 versus 2.2$\pm$0.5, p<0.05)주기 취소율은 의미 있게 낮은 (19.0% versus 55.6%, p<0.05) 결과를 보였다. 결 론: 난소반응이 저하된 불임 환자의 체외수정시술 시 그 예후에 관련된 인자로서 환자의 연령은 해당 주기의 임신성공 및 임신 지속여부에 대한 예후를 예측할 수 있는 인자로서 의미가 있는 반면 기저 혈중 FSH농도는 해당 주기에서의 난소의 반응에 대한 예측인자로써 활용이 가능 할 것으로 사료된다.