• Korean Journal of Materials Research
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• v.22 no.5
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• pp.259-273
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• 2012

Chalcogenide-based semiconductors, such as $CuInSe_2$, $CuGaSe_2$, Cu(In,Ga)$Se_2$ (CIGS), and CdTe have attracted considerable interest as efficient materials in thin film solar cells (TFSCs). Currently, CIGS and CdTe TFSCs have demonstrated the highest power conversion efficiency (PCE) of over 11% in module production. However, commercialized CIGS and CdTe TFSCs have some limitations due to the scarcity of In, Ga, and Te and the environmental issues associated with Cd and Se. Recently, kesterite CZTS, which is one of the In- and Ga- free absorber materials, has been attracted considerable attention as a new candidate for use as an absorber material in thin film solar cells. The CZTS-based absorber material has outstanding characteristics such as band gap energy of 1.0 eV to 1.5 eV, high absorption coefficient on the order of $10^4cm^{-1}$, and high theoretical conversion efficiency of 32.2% in thin film solar cells. Despite these promising characteristics, research into CZTS-based thin film solar cells is still incomprehensive and related reports are quite few compared to those for CIGS thin film solar cells, which show high efficiency of over 20%. The recent development of kesterite-based CZTS thin film solar cells is summarized in this work. The new challenges for enhanced performance in CZTS thin films are examined and prospective issues are addressed as well.

• Korean Journal of Ecology and Environment
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• v.50 no.1
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• pp.116-125
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• 2017

Alpine plants with a scarcity of pollinators in harsh environments have been believed to undergo selfing for reproductive assurance; however, contradictory evidence is also available. Snowmelt regimes in alpine areas function to change life history characteristics of alpine plants such as flowering time and duration; yet the effects of snowmelt regimes have never been tested in alpine plants in Korea. This study was conducted to investigate the dichogamy, mating systems, and flowering characteristics of Megaleranthis saniculifolia populations [early and late snowmelt plots (ESP and LSP, respectively)] in a subalpine area of Sobaeksan Mountain in Korea. M. saniculifolia exhibited incomplete protogyny in that despite early maturation of pistils, maturation times of pistils and stamens within flowers were partly overlapped. Control and hand-outcrossing treatments produced significantly higher number of follicles and seeds per flower than autonomous and hand-selfing treatments. Based on the aggregate fruit set, the auto-fertility index (AI) and self-compatibility index (SI) were 0.33 and 0.50, respectively. Snowmelt occurred 10 days earlier in ESP than in LSP, thereby ESP and LSP showed distinct differences with regard to flower longevity and season, but showing no difference in peak flowering dates. We concluded that M. saniculifolia is an incomplete protogynous and largely outcrossing plant requiring pollinator service. Temporal variation in snowmelt time and subsequent changes in flowering characteristics under climate change may further threaten the population persistence of M. saniculifolia which has already been designated as endangered species in Korea.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2018.06a
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• pp.62-62
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• 2018

Pt is still considered as one of the most active electrocatalysts for ORR in alkaline fuel cells. However, the high cost and scarcity of Pt hamper the widespread commercialization of fuel cells. As a strong candidate for the replacement of Pt catalyst, silver (Ag) has been extensively studied due to its high activity, abundance, and low cost. Ag is more stable than Pt in the pH range of 8~14 as the equilibrium potential of Ag/Ag+ being ${\approx}200mV$ higher than that of Pt/PtO. However, Ag is the overall catalytic activity of Ag for oxygen reduction reaction(ORR) is still not comparable to Pt catalyst since the surface Ag atoms are approximately 10 times less active than Pt atoms. Therefore, further enhancement in the ORR activity of Ag catalysts is necessary to be competitive with current cutting-edge Pt-based catalysts. We demonstrate the architectural design of Ag catalysts, synthesized using plasma discharge in liquid phase, for enhanced ORR kinetics in alkaline media. An attractive feature of this work is that the plasma status controlled via electric-field could form the Ag nanowires or dendrites without any chemical agents. The plasma reactor was made of a Teflon vessel with an inner diameter of 80 mm and a height of 80 mm, where a pair of tungsten(W) electrodes with a diameter of 2 mm was placed horizontally. The stock solutions were made by dissolving the 5-mM AgNO3 in DI water. For the synthesis of Agnanowires, the electricfield of 3.6kVcm-1 in a 200-ml AgNO3 aqueous solution was applied across the electrodes using a bipolar pulsed power supply(Kurita, Seisakusyo Co. Ltd). The repetition rate and pulse width were fixed at 30kHz and 2.0 us, respectively. The plasma discharge was carried out for a fixed reaction time of 60 min. In case of Ag nanodendrites, the electric field of 32kVcm-1 in a 200-ml AgNO3 aqueous solution was applied and other conditions were identical to the plasma discharge in water in terms of electrode configuration, repetition rate and discharge time. Using SEM and STEM, morphology of Ag nanowires and dendrites were investigated. With 3.6 kV/cm, Ag nanowire was obtained, while Ag dendrite was constructed with 32 kV/cm. The average diameter and legth of Ag nanowireses were 50 nm and 3.5 um, and thoes values of Ag dendrites were 40 nm and 3.0 um. As a results of XPS analysis, the surface defects in the Ag nanowires facilitated O2 incorporation into the surface region via the interaction between the oxygen and the electron cloud of the adjacent Ag atoms. The catalytic activity of Ag for oxygen reduction reaction(ORR) showed that the catalytic ORR activity of Ag nanowires are much better than Ag nanodendrites, and electron transfer number of Ag nanowires is similar to that of Pt (${\approx}4$).

• Korean Journal of Construction Engineering and Management
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• v.13 no.1
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• pp.140-147
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• 2012

Climate changes caused by fossil fuel energy usages have led to serious environmental damages and resource scarcity. Ever-increasing demand for energy causes harsh competition in international energy markets. Nuclear power, which once was regarded as a desirable clean energy, began to face public oppositions after the Japanese nuclear disaster in 2011. In this context, wind power is now considered to be an ever-more important recyclable energy source. Thus, this study intended to identify critical success factors for wind power construction projects. After a thorough literature review, two focus group interview sessions were conducted. A questionnaire-based survey, coupled with the two previous methods, resulted in the extraction of important factors for the success of wind power projects. Experts, including those working as constructors, designers, and owners, were paid a direct visit for the interview and survey. The critical success factors were categorized into feasibility study, right policies, equipment selection, and project financing issues. The proposed critical success factors are expected to be an effective guideline for future investors in wind powers.

• The Journal of the Korean bone and joint tumor society
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• v.8 no.3
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• pp.76-82
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• 2002

Purpose: Benign bone tumor of the talar body have rarely been evaluated according to the therapeutic methods because of the scarcity of their incidence. Here, we report our experience of 8 cases who were treated by using of posterior approach and curettage through the posterior process of the talus. Materials and Methods: Between February 1986 and October 2001, we experienced 8 cases of benign bone tumor occurring in the talar body. They included two osteoid osteomas, two giant cell tumors, one capillary hemangioma, one chondroblastoma, one simple bone cyst, and one osteochondroma. Their mean age was 22.1 years (ranging from 10 to 41 years). Mean follow-up period was 7.7 years (ranging from 1 to 16 years). All patients were treated by using of posterior approach. Two osteoid osteomas and one osteochondroma were treated by excision of tumors. Other cases were treated with curettage through the cortical window on the posterior process of the talus. Results: There was no recurrence during the follow-up period. one infection occurred. Except this case, all patients had no pain in weight-bearing, and complete range of movement at the ankle joint was reserved in each case. Conclusion: In this study, we suppose that posterior approach to the talar body may be a safe method with minimal damage of normal tissues and sufficient of curettage is capable through the cortical window on the posterior process of the talus.

• Journal of Korea Society of Industrial Information Systems
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• v.21 no.4
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• pp.67-78
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• 2016

Recently many countries around the world are actively promoting smart city projects to address various urban problems such as traffic congestion, housing shortage, and energy scarcity. Due to development of the Internet of Things (IoT), the development of a smart city with sustainability, convenience, and environment-friendliness was enabled through the effective control and reuse of urban resources. The purpose of this study is to analyze the technical trends of IoT and present a development plan for smart city which is one of the applications of the IoT. To this end, the news articles of the Electronic Times between 2013 and 2015were analyzed using the text mining technique and smart city development cases of other countries were investigated. The analysis results revealed the close relationships of big data, cloud, platforms, and sensors with smart city. For the successful development of a smart city, first, all the interested parties in the city must work together to create new values throughout the entire process of value chain. Second, they must utilize big data and disclose public data more actively than they are doing now. This study has made academic contribution in that it has presented a big data analysis method and stimulated follow-up studies. For the practical contribution, the results of this study provided useful data for the policy making of local governments and administrative agencies for smart city development. This study may have limitations in the incorporation of the total trends because only the news articles of the Electronic Times were selected to analyze the technical trends of the IoT.

• Journal of Distribution Science
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• v.12 no.6
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• pp.81-88
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• 2014

Purpose - Entrepreneurship promotion is emerging as an important economic growth agenda. However, in Korea, entrepreneurship has weakened because of the collapse of the venture bubbles of the 2000s and the global economic recession in 2008, which have induced the business community to choose stability over risk. The Korean government has been implementing several support projects to inspire and promote youth entrepreneurship through various means including financial assistance; however, the perpetuation rate of young entrepreneurship is still low as compared to advanced economies such as the US and EU. This case study focuses on the Youth Start-Up Business Support Program of the Small & Medium Business Corporation, and explores practical alternatives. Further, it aims to suggest managerial factors and a conceptual model for change management factors affecting the business performance creation of a startup company, based on the Small and medium Business Corporation's young venture startup fund. Research design, data, and methodology - Many studies examine the current progress and issues of startup firms, for example, a lack of systematic cultivation of entrepreneurship and startup business training, lack of commercialization funding for youth startup businesses, lack of mentoring, and inadequate infrastructure. From prior research, we address four factors, namely, personal managerial capabilities, innovative business model, sufficient cash flow, and social network, affecting startup companies' business performance. This study involved a sample survey of 200 young entrepreneurs to investigate casual relations between the four factors and business performance. A regression analysis was used to verify the hypotheses. Results - First, in relation to differences in the founder's personal characteristics, age, sales amount, and number of employees significantly impact business performance. Second, regarding the causal relation between the four factors for creating business performance, an innovative business model and social networking have supported the hypotheses, revealing that the more that a start-up founder has an innovative business model and social networking, the more the start-up firms are likely to have better performance (e.g., sales volume, employment, ROE, ROI, etc.). Although the founder's competency and sufficient cash flow have no significant relationship with business performance, the mean value was higher performance for high founder's competency and sufficient cash flow. Conclusions - This study provides basic data on policy support strategies of the Small and Medium Business Corporation, to help young entrepreneurs achieve their start-up business goals. It shows that young entrepreneurship startup firms should strive to explore ideas to satisfy customers' needs, and that changes in customer value and the continuous innovation of business model differentiation are required to actively respond to change management. Moreover, at the infant startup stage, they should activate social network programs to share information, thereby offsetting resource scarcity and managing business risk. Further, the establishment of a long-term vision and the implementation of training programs in related specific fields should be supported to strengthen founders' personal capabilities.

• The Journal of the Korea Contents Association
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• v.7 no.3
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• pp.140-151
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• 2007

In this study, we attempted to develop a watershed runoff index subject to main control points by dividing the Geum River basin into 14 sub-basins. The Yongdam multipurpose dam Daecheong multipurpose dam and Gongju gage station were selected to serve as the main control points of the Geum River basin, and the observed flow of each control point was calculated by the discharge rating curve, whereas the simulated flow was estimated using the Rainfall Runoff Forecasting System (RRFS), user-interfaced software developed by the Korea Water Corporation, based on the Streamflow Synthesis and Reservoir Regulation (SSARR) model developed by the US Army Corps of Engineers. This study consisted of the daily unit observed flow and the simulated flow of the accumulated moving average flow by daily, 5-days, 10-days, monthly, quarterly and annually, and normal monthly/annually flow. We also performed flow duration analysis for each of the accumulated moving average and the normal monthly/annually flows by unit period, and abundant flow, ordinary flow, low flow and drought flow estimated by each flow duration analysis were utilized as watershed runoff index by main control points. Further, as we determined the current flow by unit period and the normal monthly/annually flow through the drought and flood flow analysis subject to each flow we were able to develop the watershed runoff index in a system that can be used to determine the abundance and scarcity of the flow at the corresponding point.

• Korean journal of communication and information
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• v.46
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• pp.590-626
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• 2009

The limitation and scarcity of broadcasting waves provide important rationale behind the idea of public ownership of broadcasting waves which can facilitate communications among people with diverse backgrounds and values in the society. Independence of broadcasting industry from the regulatory organization is imperative for the broadcasting industry to serve the public interest that has been historically defined by each county. For the Korean broadcasting industry, history of modern Korea taught us that the broadcasting regulatory organizations such as Korea Communications Commission(KCC) should be kept from any political influence for the industry to best serve the public. Recent controversies on the role of the CEO of KBS and the appointment of the CEO of YTN by the president of the country provide evidence that the independence of broadcasting in Korean society is a critical topic. This study examined the corporate structures of broadcasting industry and the political independence of the industry in relation to the changes in the concept of public interest and the role of broadcasting. It is critically important to investigate the political independence of broadcasting in Korea because the core argument of independence of broadcasting which is about the freedom of expression protected by the constitution is still contested in the country. For the purpose of collecting diverse perspectives on broadcasting, survey method was adopted in this study. Three groups Abstracts 697 of participants were recruited: reporters, experts in the field, and regular citizens. The result indicated that the independence of broadcasting was in the process of deterioration. Also, the participants of the study understood that it was impossible for the broadcasting to serve the public interest when the broadcasting was not free from the influence of regulatory institutions such as KCC.

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.5
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• pp.165-172
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• 2013

Convergence is increasingly prevalent in the IT world which generally refers to the combination of two or more different technologies in a single device. Especially, the spectrum scarcity is becoming a big issue because there are exponential growth of broadcasting and communication systems in the spectrum demand. Cognitive radio (CR) is a convergence technology that is envisaged to solve the problems in wireless networks resulting from the limited available spectrum and the inefficiency in the spectrum usage by exploiting the existing wireless spectrum opportunistically. However, the very process of convergence is likely to expose significant security issues due to the merging of what have been separate services and technologies and also as a result of the introduction of new technologies. The main purpose of this research is focused on devising an adaptive security framework based on carousel for CR networks as a distinct telecommunication convergence application, which are still at the stage of being developed and standardized with the lack of security concerns. The framework uses a secure credential, named as carousel, initialized with the location related information from objects position, which is used to design security mechanisms for supporting privacy and various securities based on it. The proposed adaptive security framework could be used as a security building block for the CR network standards and various convergence applications.