Stock Returns Predictable : Some New Evidence from the Korean Stock Market

Hoyoung Ryu,Van Hai Hoang,Hee-un Ko 한국재무학회 2016 한국재무학회 학술대회 Vol.2016 No.05

This paper makes three contributions to the literature on predictability stock returns in the Korean stock market. We focus on out-of-sample forecasting of returns based on industry portfolios are predictability. From the results, we discover that in-sample and out-of-sample test during from 2000 to 2015, predictability is not homogeneous. Furthermore, we examine the determinants of out-of-sample predictability for each sector using industry characteristics and find strong evidence that return predictability has links to certain industry characteristics, such as book-to-market ratio, dividend yield, size, price earnings ratio, and trading volume. We also discover a mean combination forecast approach which has significant out-of-sample performance.

Pelvic Lymph Node Metastases in Prostate Cancer

Hoyoung Ryu,Byeongdo Song,Jinho Hwang,Sung Kyu Hong,Seok-Soo Byun,Sang Eun Lee,Sangchul Lee 대한비뇨기종양학회 2017 대한비뇨기종양학회지 Vol.15 No.3

Purpose: The aim of this study is evaluating the accuracy of preoperative magnetic resonance imaging (MRI) in patients who underwent pelvic lymph node dissection (PLND). Materials and Methods: The medical records of 1,528 patients who underwent radical prostatectomy and PLND from 2003 to 2017 in Seoul National University Bundang Hospital were retrospectively reviewed. We evaluated the various clinicopathologic variables including preoperative MRI findings and pathologic lymph node (LN) metastasis. The prediction model for pathologic LN metastasis was assessed using univariate and multivariable logistic regression analyses and areas under receiver operating characteristic (ROC) curves. Results: The mean age of our cohort was 66.4±6.7 years. Positive LN finding of preoperative MRI finding was observed in 9.4% (145 of 1,528) of patients. 5.3% (81 of 1,528) of patients had confirmed final pathologic LN metastases. Sensitivity and specificity of preoperative MRI were 30.8% and 91.7%, respectively. Multivariable analysis showed that preoperative MRI findings, clinical stage and biopsy Gleason score were independent significant predictors for pathologic LN metastasis (p<0.001, p=0.002, and p<0.001, respectively). Prediction model using preoperative MRI findings and National Comprehensive Control Network risk stratification showed fair accuracy using ROC analysis. Conclusions: Preoperative MRI findings for pathologic LN metastasis showed limited prediction value. A large-scale, multicenter, prospective study is needed to fully evaluate the clinical significance of preoperative MRI.

Medium-driven forward osmosis for energy efficient dewatering of microalgae coupled with microalgae cultivation

Hoyoung Ryu,Kyochan Kim,Hoon Cho,Yong Keun Chang,Jong-In Han 대한환경공학회 2019 대한환경공학회 학술발표논문집 Vol.2019 No.-

A prospective randomized trial of povidone-iodine suppository before transrectal ultrasonography-guided prostate biopsy :

Ryu, Hoyoung,Song, Sang Hun,Lee, Sang Eun,Song, Kyoung-Ho,Lee, Sangchul Ovid Technologies (Wolters Kluwer) - Lippincott Wi 2019 Medicine Vol.98 No.12

도로 건설기계 차량용 SDPF PM/NOx 저감 및 배압 특성에 관한 연구

류호영(Hoyoung Ryu),이성욱(Seangwock Lee),박기영(Giyoung Park),정윤민(Yunmin Jeong) 한국자동차공학회 2020 한국자동차공학회 부문종합 학술대회 Vol.2020 No.7

도로 건설기계차량용 SDPF PM/NO<SUB>X</SUB> 저감 및 배압 특성에 관한 연구

류호영(Hoyoung Ryu),박기영(Giyoung Park),정윤민(Yunmin Jeong),정홍석(Hongseok Jung),이상경(Sangkyoung Yi),김용우(Yongwoo Kim),김기호(Kiho Kim),이정천(Jungcheon Lee),이성욱(Seangwock Lee) 한국자동차공학회 2020 한국 자동차공학회논문집 Vol.28 No.5

After-treatment devices have been introduced into construction equipment vehicles due to environmental regulations lately. Despite this, however, the air pollution is still getting worse due to the use of vehicles without post- processing devices, and of aging vehicles. In addition, during a cold start, the PM/NO<SUB>X</SUB> purification efficiency is lowered due to the low exhaust gas temperature. To solve this problem, SDPF(Selective Catalytic Reduction on Diesel Particulate Filter) was developed in this study by integrating SCR(Selective Catalytic Reduction) and DPF(Diesel Particulate Filter). To develop SDPF, a mixer, a diffuser angle, and a V-W/TiO₂ catalyst were used, among others. To verify the effectiveness of the developed SDPF in addressing the aforementioned problem, its back pressure and PM/NO<SUB>X</SUB> reduction efficiency were measured using an engine dynamometer and emission test devices. The measurements showed that the back pressure of SDPF is lower than that of DPF+SCR, and that it satisfies the EURO-5 regulation. Additional catalytic-activity studies and verifications, however, are necessary.

한국 금융시장의 군집행태의 특성과 상호작용에 관한 연구

류호영(Hoyoung Ryu),강상훈(Sang Hoon Kang) 한국자료분석학회 2023 Journal of the Korean Data Analysis Society Vol.25 No.4

본 연구는 한국 금융시장에 존재하는 군집행태의 특성을 분석하고, 군집행태의 상호작용에 관해 연구하였다. 먼저, Chiang, Zheng(2010)이 제시한 모형을 사용하여 한국 금융시장의 군집행태를 분석하였는데, 유가증권시장과 코스닥시장 모두 군집행태가 존재하며, 기업규모가 작을수록군집행태가 강하게 나타났다. 또한, 유가증권시장의 군집행태는 시장 하락기에서만 관찰되며, 코스닥시장 역시 시장 상승기보다 시장 하락기에 군집행태가 더 강하게 나타난다. 다음으로, 군집행태와 시장 컨센서스와의 상호작용을 분석하여, 투자자들이 참여하고 있는 시장뿐만 아니라 투자자들이 의사결정에 영향을 준다고 알려진 다른 시장과의 상호관계를 분석하였다. Diebold, Yilmaz(2012)가 제시한 전이지수를 사용하여 군집행태의 상호작용을 분석한 결과, 유가증권시장의 군집행태는 기업규모와 상관없이 다른 시장으로부터 전이되는 정보의 크기가 큰 것으로 나타났으며, 코스닥시장 역시 소형주를 제외한 대형주와 중형주의 군집행태에서 이러한 의존성을 발견할 수 있었다. 군집행태의 의존성은 시장 상승기보다 시장 하락기에 보다 뚜렷하게 나타나며,이는 시장 하락기에 투자자들의 맹목적인 추종이 더 강해진다는 것을 의미하는 결과이다. 이러한 결과는 군집행태와 시장 컨센서스 간 쌍별 순전이효과를 측정하여 도식화한 네트워크 구조분석에서도 명확하게 확인할 수 있다. This study analyzed the characteristics of herding behavior existing in the Korean financial market and examined the dynamics of herding behavior. First, we analyzed the herding behavior of the Korean financial market using the methodology of Chiang, Zheng (2010). According to the results, herding behavior existed in both the KOSPI market and the KOSDAQ market, and the smaller the company size, the stronger the herding behavior. In addition, the herding behavior appears stronger during the declining market than during the rising market. Next, we analyzed the dynamics between herding behavior and market consensus using the spillover index of Diebold, Yilmaz (2012). As a result of the analysis, the inflow spillover effect of the herding behavior was greater than the outflow spillover effect. This characteristic of herding behavior is stronger during the declining market than during the rising market. These results mean that investors' blind followings become stronger during the declining market. These results are also clearly confirmed in the network topology analyzed by measuring the net pairwise spillover effect.

투자자 심리와 차익거래 제약이 고유변동성 이상현상에 미치는 영향

류호영(Hoyoung Ryu),김태혁(Taehyuk Kim),정대성(Daesung Jung) 한국증권학회 2020 한국증권학회지 Vol.49 No.6

본 연구는 한국 주식시장에서 투자자 심리와 차익거래 제약이 고유변동성 이상현상에 미치는 영향에 대해 검증하였다. 먼저, 고유변동성을 기준으로 10분위 포트폴리오를 구성하여 분석한 결과, 한국 주식시장에 고유변동성 이상현상이 존재하는 것으로 나타났다. 또한, 한국 주식시장에서 관찰되는 고유변동성 이상현상은 시간에 따라 변화하는 경향을 보이며, 이러한 결과가 투자자 심리와 차익거래 제약에 의한 영향인지 밝혀내기 위해 투자자 심리-고유변동성 포트폴리오와 차익거래 제약-고유변동성 포트폴리오를 구성하여 검증을 시행하였다. 분석 결과, 모든 투자자 심리 포트폴리오에서 고유변동성의 음(-)의 프리미엄이 관찰되지만, 투자자 심리의 변동에 따른 고유변동성 이상현상의 유의미한 변화는 확인되지 않았다. 반면, 차익거래 제약의 경우, 차익거래 제약이 낮은 포트폴리오에서는 고유변동성 이상현상이 관찰되지 않지만, 차익거래 제약이 높은 포트폴리오에서는 고유변동성의 음(-)의 프리미엄이 존재하는 것으로 나타났을 뿐만 아니라, 차익거래 제약이 높아질수록 고유변동성의 음(-)의 프리미엄이 강해지는 경향을 가지는 것으로 밝혀졌다. 이러한 결과를 종합하여 볼 때, 한국 주식시장에 존재하는 고유변동성 이상현상은 투자자 심리보다는 차익거래 제약에 의하여 발생하며, 차익거래 제약이 강하게 나타나는 기간 동안 고유변동성 이상현상은 심화된다. This study examined the effects of investor sentiment and limits-to-arbitrage on the idiosyncratic volatility (IVOL) puzzle in the Korean stock market. The IVOL portfolio analysis revealed that IVOL is negatively associated with stock returns. It indicates the existence of the IVOL puzzle in the Korean stock market. Additionally, the IVOL puzzle observed in the Korean stock market is time-varying. Therefore, this study analyzed whether the IVOL return premium becomes stronger due to investor sentiment and limits-to-arbitrage. According to the results, all the investor sentiment portfolios had a negative IVOL return premium regardless of whether investor sentiment was high or low, and no patterns of the IVOL puzzle due to investor sentiment were found. On the other hand, the IVOL puzzle is observed when limits-to-arbitrage were high as compared to when they were low. Furthermore, the higher the limits-to-arbitrage, the higher the negative IVOL return premium. These results suggest that the IVOL puzzle is caused by stocks with high limits-to-arbitrage and is intensified when limits-to-arbitrage are high.

아비딘의 비특이적 결합에 대한 연구

류지은,정소희,김은혜,정희재,박호영,이인숙 서울여자대학교 2010 자연과학연구논문집 Vol.22 No.-

The major distinguishing feature of the avidin/biotin system is the extraordinary affinity (K_(a) = 10^(15) M^(-1)) that characterizes the complex formed between the vitamin, biotin and the egg white protein, avidin. Interaction is so strong that even biotin (or avidin) coupled to proteins is available for binding by avidin (or biotin). Thus avidin/biotin system has become so popular in biological sciences. This work proposed the possibility of non-specific binding of free avidin to protein such as bovine serum albumin.

Open Partial Nephrectomy vs. Robot-Assisted Partial Nephrectomy for a Renal Tumor Larger than 4 cm: a Propensity Score Matching Analysis

이상철,Ryu Hoyoung,Lee Jeong Woo 대한의학회 2021 Journal of Korean medical science Vol.36 No.20

Background: To compare open partial nephrectomy (OPN) and robot-assisted partial nephrectomy (RAPN) in the management of renal tumors larger than 4 cm. Methods: Clinical records of 220 patients who underwent OPN or RAPN for a single renal tumor ≥ 4.0 cm with a normal contralateral kidney were reviewed. After determining the propensity score, surgical parameters, functional outcomes, and oncological outcomes were compared between OPN (n = 67) and RAPN (n = 67) groups of patients. Results: The RAPN group had longer operation time (149.0 min vs. 173.3 min, P = 0.030) and longer ischemic time (20.3 min vs. 29.4 min, P = 0.001), but shorter hospital stay (8.2 days vs 6.0 days, P = 0.001) than the OPN group. Estimated blood loss (P = 0.053), pain visual analog score at 1 day postoperatively (P = 0.194), and complications of grade III or higher (P = 0.403) were similar between OPN and RAPN groups. There was no radical conversion or positive surgical margin in either group. Mean change in 6-month estimated glomerular filtration rate was significantly better in the RAPN group (−8.2 vs. −3.1, P = 0.027). There was no statistical difference in recurrence-free survival (P = 0.970) or cancer-specific survival (P = 0.345) between the two groups. Conclusion: RAPN is a safe and feasible surgical modality comparable to OPN for managing renal tumors larger than 4 cm in terms of surgical, functional, and oncological outcomes.