• The Korean Journal of Applied Statistics
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• v.36 no.5
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• pp.381-397
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• 2023

The most representative design used in clinical trials is randomization, which is used to accurately estimate the treatment effect. However, comparison between the treatment group and the control group in an observational study without randomization is biased due to various unadjusted differences, such as characteristics between patients. Propensity score weighting is a widely used method to address these problems and to minimize bias by adjusting those confounding and assess treatment effects. Inverse probability weighting, the most popular method, assigns weights that are proportional to the inverse of the conditional probability of receiving a specific treatment assignment, given observed covariates. However, this method is often suffered by extreme propensity scores, resulting in biased estimates and excessive variance. Several alternative methods including trimming, overlap weights, and matching weights have been proposed to mitigate these issues. In this paper, we conduct a simulation study to compare performance of various propensity score weighting methods under diverse situation, such as limited overlap, misspecified propensity score, and treatment contrary to prediction. From the simulation results overlap weights and matching weights consistently outperform inverse probability weighting and trimming in terms of bias, root mean squared error and coverage probability.

• Journal of Internet Computing and Services
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• v.24 no.6
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• pp.137-144
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• 2023

Cyberattack technology is evolving to an unpredictable degree, and it is a situation that can happen 'at any time' rather than 'someday'. Infrastructure that is becoming hyper-connected and global due to cloud computing and the Internet of Things is an environment where cyberattacks can be more damaging than ever, and cyberattacks are still ongoing. Even if damage occurs due to external influences such as cyberattacks or natural disasters, intelligent self-recovery must evolve from a cyber resilience perspective to minimize downtime of cyber assets (OS, WEB, WAS, DB). In this paper, we propose an intelligent self-recovery technology to ensure sustainable cyber resilience when cyber assets fail to function properly due to a cyberattack. The original and updated history of cyber assets is managed in real-time using timeslot design and snapshot backup technology. It is necessary to secure technology that can automatically detect damage situations in conjunction with a commercialized file integrity monitoring program and minimize downtime of cyber assets by analyzing the correlation of backup data to damaged files on an intelligent basis to self-recover to an optimal state. In the future, we plan to research a pilot system that applies the unique functions of self-recovery technology and an operating model that can learn and analyze self-recovery strategies appropriate for cyber assets in damaged states.

• Journal of Intelligence and Information Systems
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• v.29 no.4
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• pp.69-90
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• 2023

The purpose of this study is to evaluate the service attributes and consumer reactions of telemedicine apps in South Korea and visualize their differentiation by constructing positioning maps. We crawled 23,219 user reviews of 6 major telemedicine apps in Korea from the Google Play store. Topics were derived by BERTopic modeling, and sentiment scores for each topic were calculated through KoBERT sentiment analysis. As a result, five service characteristics in the application attribute category and three in the medical service category were derived. Based on this, a two-dimensional positioning map was constructed through principal component analysis. This study proposes an objective service evaluation method based on text mining, which has implications. In sum, this study combines empirical statistical methods and text mining techniques based on user review texts of telemedicine apps. It presents a system of service attribute elicitation, sentiment analysis, and product positioning. This can serve as an effective way to objectively diagnose the service quality and consumer responses of telemedicine applications.

• The Journal of the Acoustical Society of Korea
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• v.25 no.5
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• pp.246-256
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• 2006

The plane wave reflection coefficient is an acoustic property containing all the information concerning the ocean bottom and can be used as an input parameter to various acoustic propagation models. In this paper, we measure the plane wave reflection coefficient, the sound speed, thd the attenuation for saturated granular medium in the water tank. Three kinds of glass beads and natural sand are used as the granular medium. The reflection experiment is performed with the sinusoidal tone bursts of 100 kHz at incident angles from 28 to 53 degrees, and the sound speed and attenuation experiment are performed also with the same signal. From the measured reflection signal, the reflection coefficient is calculated with the self calibration method and the experimental uncertainties are discussed. The sound speed and the attenuation measurements are used for the estimation of the porosity and permeability, the main Biot parameters. The estimated values are compared to the directly measured values and used as input values to the Biot theory in order to calculate the theoretical reflection coefficient. Finally, the reflection coefficient predicted by Biot theory is compared to the measured reflection coefficient and their characteristics are discussed.

• Journal of Advanced Navigation Technology
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• v.28 no.1
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• pp.102-108
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• 2024

In the initial stages of urban air mobility (UAM) operations, compliance with existing visual flight rules and instrument flight regulations for conventional human-crewed aircraft is crucial. Additionally, voice communication between the on board pilot and relevant UAM stakeholders, including vertiports, is essential. Consequently, very high frequency (VHF) aviation voice communication must be consistently provided throughout all phases of UAM operations. This paper presents the results of the VHF communication coverage analysis for the initial UAM demonstration areas, encompassing the Hangang River and Incheon Ara-Canal corridors, as well as potential vertiport candidate locations. By considering the influence of terrain and buildings through the utilization of a digital surface model (DSM), communication quality prediction results are obtained for the analysis areas. The three-dimensional coverage analysis results indicate that stable coverage can be achieved within altitude corridors ranging from 300 m to 600 m. However, there are shaded areas in the low-altitude vertiport regions due to the impact of high-rise buildings. Therefore, additional research to ensure stable coverage around vertiports in the lower altitude areas is required.

• Economic and Environmental Geology
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• v.57 no.4
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• pp.353-362
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• 2024

This study examined the spectral characteristics of sediments according to moisture content using an unmanned aerial vehicle (UAV)-based hyperspectral sensor and evaluated the efficiency of moisture content detection at different flight altitudes. For this purpose, hyperspectral images in the 400-1000nm wavelength range were acquired and analyzed at altitudes of 40m and 80m for sediment samples with various moisture contents. The reflectance of the sediments generally showed a decreasing trend as the moisture content increased. Correlation analysis between moisture content and reflectance showed a strong negative correlation (r < -0.8) across the entire 400-900nm range. The moisture content detection model constructed using the Random Forest technique showed detection accuracies of RMSE 2.6%, R² 0.92 at 40m altitude and RMSE 2.2%, R² 0.95 at 80m altitude, confirming that the difference in accuracy between altitudes was minimal. Variable importance analysis revealed that the 600-700nm band played a crucial role in moisture content detection. This study is expected to be utilized in efficient sediment moisture management and natural disaster prediction in the field of environmental monitoring in the future.

• Journal of Distribution Research
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• v.17 no.4
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• pp.55-80
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• 2012

I. Introduction Developing the relationships between companies is very important issue to ensure a competitive advantage in today's business environment (Bleeke & Ernst 1991; Mohr & Spekman 1994; Powell 1990). Partnerships between companies are based on having same goals, pursuing mutual understanding, and having a professional level of interdependence. By having such a partnerships and cooperative efforts between companies, they will achieve efficiency and effectiveness of their business (Mohr and Spekman, 1994). However, it is difficult to expect these ideal results only in the B2B corporate transaction. According to agency theory which is the well-accepted theory in various fields of business strategy, organization, and marketing, the two independent companies have fundamentally different corporate purposes. Also there is a higher chance of developing opportunism and conflict due to natures of human(organization), such as self-interest, bounded rationality, risk aversion, and environment factor as imbalance of information (Eisenhardt 1989). That is, especially partnerships between principal(or buyer) and agent(or supplier) of companies within supply chain, the business contract itself will not provide competitive advantage. But managing partnership between companies is the key to success. Therefore, managing partnership between manufacturer and supplier, and finding causes of conflict are essential to improve B2B performance. In conclusion, based on prior researches and Agency theory, this study will clarify how business hazards cause conflicts on supply chain and then identify how developed conflicts have been managed by two control mechanisms. II. Research model III. Method In order to validate our research model, this study gathered questionnaires from small and medium sized enterprises(SMEs). In Korea, SMEs mean the firms whose employee is under 300 and capital is under 8 billion won(about 7.2 million dollar). We asked the manufacturer's perception about the relationship with the biggest supplier, and our key informants are denied to a person responsible for buying(ex)CEO, executives, managers of purchasing department, and so on). In detail, we contact by telephone to our initial sample(about 1,200 firms) and introduce our research motivation and send our questionnaires by e-mail, mail, and direct survey. Finally we received 361 data and eliminate 32 inappropriate questionnaires. We use 329 manufactures' data on analysis. The purpose of this study is to identify the anticipant role of business hazard (environmental dynamism, asset specificity) and investigate the moderating effect of control mechanism(formal control, social control) on conflict-performance relationship. To find out moderating effect of control methods, we need to compare the regression weight between low versus. high group(about level of exercised control methods). Therefore we choose the structural equation modeling method that is proper to do multi-group analysis. The data analysis is performed by AMOS 17.0 software, and model fits are good statically (CMIN/DF=1.982, p<.000, CFI=.936, IFI=.937, RMSEA=.056). IV. Result V. Discussion Results show that the higher environmental dynamism and asset specificity(on particular supplier) buyer(manufacturer) has, the more B2B conflict exists. And this conflict affect relationship quality and financial outcomes negatively. In addition, social control and formal control could weaken the negative effect of conflict on relationship quality significantly. However, unlikely to assure conflict resolution effect of control mechanisms on relationship quality, financial outcomes are changed by neither social control nor formal control. We could explain this results with the characteristics of our sample, SMEs(Small and Medium sized Enterprises). Financial outcomes of these SMEs(manufacturer or principal) are affected by their customer(usually major company) more easily than their supplier(or agent). And, in recent few years, most of companies have suffered from financial problems because of global economic recession. It means that it is hard to evaluate the contribution of supplier(agent). Therefore we also support the suggestion of Gladstein(1984), Poppo & Zenger(2002) that relational performance variable can capture the focal outcomes of relationship(exchange) better than financial performance variable. This study has some implications that it tests the sources of conflict and investigates the effect of resolution methods of B2B conflict empirically. And, especially, it finds out the significant moderating effect of formal control which past B2B management studies have ignored in Korea.

• The Korean Journal of Financial Management
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• v.12 no.1
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• pp.167-186
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• 1995

기업인수합병(M&A) 시장의 활성화에 따라 적대적 공개매수를 방어하기 위한 반인수조치(Antitakeover Techniques)들에 관한 관심도 고조되고 있다. 지금까지 널리 알려져 있는 대표적인 반인수 조치들은 Fair Price Amendment(FPA), Classified Board Amendment(CBA)와 Poison Pills(PP) 등이다. 이들 대표적 세 반인수조치들 중에서 FPA와 CBA 채택의 경우는 주주들의 사전 승인이 요구되는데 반하여 PP는 주주들의 사전 승인없이 채택이 가능한 반인수조치이다. 이처럼 상이한 반인수조치들의 채택은 채택기업의 가치에 상이한 부의 효과를 미치는데, 이 분야의 많은 실증적연구 결과들이 보고되고 있다. 본 연구에서는 표본기업으로 현재까지 상호개별적으로 연구되어 왔던 두가지 반인수조치(FTA, CBA)에 PP와 비채택기업도 포함시키고 있다. 지금까지의 반인수조치 채택에 따른 기업가치에 미치는 부의 효과에 관한 연구결과를 확인해보고, 반인수조치 채택에 관한 경영자의 의사결정과 경영자의 부 사이에 체계적인 관계가 존재하는지를 실증분석하고자 한다. 여기서 경영자의 부는 기업내부자 지분율과 기업내 경영자를 위한 Golden Parachute의 존재 유무로 측정한다. 본 연구에서는 3개의 가설을 설정하였다. 가설1: 만일 경영자가 주주의 이익을 희생하면서 자신의 이익을 위한 반인수조치를 채택한다면, 반인수조치 채택의 공표는 평균적으로 기업가치에 부(-)의 효과를 보일 것이다. 가설2: 경영자의 내부지분율이 낮을때 경영자들은 주주에게 가장 해로운 반인수조치를 선택할 것이다. 가설3: Golden Parachute가 존재하지 않을때 경영자들은 주주에게 가장 해로운 반인수조치를 채택할 것이다. 본 연구의 대상기업들중에서 반인수조치 채택 기업들은 IRRC 1990년도판에서 수집되었고, 대칭표본 기업으로 반인수조치를 채택하지 않은 기업들은 CRSP 파일에서 기업규모, SIC 코드를 대응시켜 선정하였다. 임원, 관계이사들과 친인척을 포함하는 내부자의 지분과 Golden Parachute 존재 여부는 이 연구의 표본기업들의 Proxy Statement에서 수집하였다. 최종 표본기업은 FPA 채택기업, CBA 채택기업, PP채택기업, 그리고 비채택기업으로 4개의 상호 배타적인 기업 그룹으로 구성되었다. 본 연구는 Event Study와 Multinomial Logistic Regession의 두가지 실증분석 방법을 사용하였다. Event Study방법론은 반인수조치 채택 공표시 초과수익률을 조사하기 위해 사용하였다. Multinomial Logistic Regession은 선택된 반인수조치 종류와 설명 변수들(내부자 지분율, Golden Parachute)간에 체계적인 관계가 존재하는지를 검증하기 위해 사용되었다. 반인수조치들을 채택하는 기업들은 반인수조치를 채택하고 있지 않은 기업들에 비해 내부자 지분율이 낮게 나타났으며, 반인수조치 중 PP를 채택한 기업에서 가장 낮은 내부지분율을 보이고 있다. GP 채택을 보면 PP를 선택한 기업의 50%가 GP를 채택하였다. 본 연구에서 반인수조치 채택 발표일 하루 전후의 초과수익률을 조사한 결과는 반인수조치 미채택기업, CBA, FPA 채택기업들의 초과수익률은 통계적으로 의미가 없었으나, PP채택에 따른 초과수익률은 의미 있는 부(-)의 값을 나타냈다. 이와같이 CBA와 FPA채택기업들은 주주의 부를 감소시키지 않았으나 PP채택기업들은 주주의 부를 감소시켰다. 따라서 경영자는 주주의 이익을 희생시키면서 자신의 이익을 위해 PP를 선택하고 있음을 보여 주고 있다. 연구결과는 내부자 지분율의 크기가 경영자와 주주간의 이해를 효과적으로 일치시키고 있음을 제시하고 있다. 즉, 내부자 지분율이 큰 기업일수록 반인수조치를 채택하지 않거나 반인수조치 채택시에 주주의 이익에 반하지 않은 반인수조치를 선택하는 경향이 높다. Golden Parachute이 존재하는 기업은 FPA를 채택하거나 반인수조치를 채택하지 않는 것보다 PP나 CBA를 채택하는 경향이 더 높다. 한편 기업에서의 GP의 존재가 경영자의 가장 해로운 반인수조치 선택을 억제하지 못함을 보여주고 있는데, 이는 GP가 비효과적인 계약메카니즘임을 제기한다. GP가 경영자와 주주간의 이해를 일치시키도록하는 계약이라기 보다는 차라리 기업방어전략이 비효과적일때 경영자 자신의 안전판으로 제공되고 있음을 보여준다. 이 논문의 주요공헌은 기업내부자 지분율의 크기와 GP의 존재가 반인수조치 선택에 체계적인 영향을 미치고 있음을 보여준 것이다. 여기서 사용된 Multinomial Logistic모델은 내부지분을 크기와 GP의 존재가 PP또는 CBA가 채택될 것인지를 예측할 수 있게 한다.

• Korean Journal of Plant Resources
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• v.31 no.5
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• pp.498-514
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• 2018

A statistical analysis for 3651 genetic resources collected from China (1,542), Japan (1,409), Korea (413), and India (287) was conducted using normal distribution, variability index value (VIV), analysis of variation (ANOVA) and Ducan's multiple range test (DMRT) based on a data obtained from NIRS analysis. In normal distribution, the average protein content was 8.0%, whereas waxy type amylose and common rice amylose were found to be 8.7% and 22.7%, respectively. The protein contents ranged from 5.4 to 10.6% at the level of 95%. The waxy amylose and common rice amylose ranged from 5.9 to 11.5%, and from 16.9 to 28.5% at 95% confidence level, respectively. The VIV was 0.59 for protein, 0.64 for low amylose, and 0.81 for high amylose contents. The average amylose contents were 18.85% in Japanese, 19.99% in Korean, 20.27% in Chinese, and 25.46% in Indian resources, while the average protein contents were found to be 7.23% in Korean, 7.73% in Japanese, 8.01% in Chinese, and 8.17% in Indian resources. The ANOVA of amylose and protein content showed significant differences at the level of 0.01. The F-test for amylose content was 158.34, and for protein content 53.95 compared to critical value 3.78. The DMRT of amylose and protein content showed significant difference (p<0.01) between resources of different countries. Japanese resources had the lowest level of amylose contents, whereas, the lowest level of protein content was found in Korean resources compared to other origins. Indian resources showed the highest level of amylose and protein contents. It is recommended these results should be helpful to future breeding experiments.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.64 no.2
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• pp.70-88
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• 2019

A statistical analysis of 4,380 non-glutinous landrace rice germplasm collected from four East Asian countries namely South Korea (1,032), North Korea (994), Japan (800), and China (528) was conducted using normal distribution, variability index value (VIV), analysis of variation (ANOVA), and Duncan's multiple range test (DMRT) based on a data obtained from Near-Infrared Reflectance Spectroscopy (NIRS) analysis. In normal distribution, the average protein content was 8.2%, and the non-glutinous rice amylose, ranging over 10%, was found to be 22.0%. Protein content in most gremplasm was between 5.4 and 10.9%, and amylose content was between 15.0 and 28.9%. The VIV was 0.50 for protein, and 0.81 for non-glutinous rice amylose content. The average amylose content was 23.34% in Chinese, 21.55% in South Korean, 21.45% in Japanese, and 20.48% in North Korean resources, while the average protein content was found to be 9.02% in Chinese, 8.06% in Japanese, 8.04% in North Korean, and 7.99% in South Korean resources. ANOVA of amylose and protein content showed significant differences at p=0.01. The F-test value for amylose content was 94.92, and for protein content was 81.82 compared to the critical value of 3.79. DMRT of amylose and protein content revealed significant differences (p<0.01). Among the various germplasm obtained from different countries, that from North Korean had the lowest level of amylose content, whereas that from South Korea had the lowest level of protein content than all other resources. Chinese resources had the highest level of amylose and protein content. It is recommended to use these results in breeding fields.