• The Korean Journal of Applied Statistics
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• v.37 no.4
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• pp.525-539
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• 2024

Massive multiplayer online role playing game (MMORPG) is a common type of game these days. Predicting user churn in MMORPG is a crucial task. The retention rate of users is deeply associated with the lifespan and revenue of the service. If the churn of a specific user can be predicted in advance, targeted promotions can be used to encourage their stay. Therefore, not only the accuracy of churn prediction but also the speed at which signs of churn can be detected is important. In this paper, we propose methods to identify early signs of churn by utilizing the daily predicted user retention probabilities. We train various deep learning and machine learning models using log data and estimate user retention probabilities. By analyzing the change patterns in these probabilities, we provide empirical rules for early identification of users at high risk of churn. Performance evaluations confirm that our methodology is more effective at detecting high risk users than existing methods based on login days. Finally, we suggest novel methods for customized marketing strategies. For this purpose, we provide guidelines of the percentage of accessed users who are at risk of churn.

• Journal of Chest Surgery
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• v.38 no.10 s.255
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• pp.680-684
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• 2005

Background: With the increasing age of the population, coronary artery bypass grafting in the elderly patients is becoming common. Off-pump coronary artery bypass grafting (OPCAB) has been proven to be less morbidity and to facilitate early recovery. The elderly patients may have benefits by avoiding the adverse effects of the cardiopulmonary bypass. The purpose of this study is to evaluate our results of OPCAB in elderly patients. Material and Method: A retrospective chart review was carried out for 12 patients aged over 80 years who underwent isolated OPCAB from January 2001 and March 2004. Data were collected risk factors for disease, extent of coronary disease, and in-hospital outcomes. Postoperative graft patiency was evaluated in 9 patients by multi-slice computed tomography. Result: Eleven patients had triple vessel disease or left main disease. Four patients were suffered from preoperative CVA, and 4 patients had chronic obstructive pulmonary disease. Two patients had myocardial infarction (MI), among them 1 patient was suffered from pulmonary edema after preoperative MI. There was no perioperative death, perioperative MI, and no ventricular arrhythmia. Also there was no perioperative stroke and renal failure. But there was one deep sternal infection who recovered by treating of muscle flap. Atrial fibrillation was newly developed in 1 patient, but was well controlled by medication. Mean intubation time was $15.9\pm4.4(8\~20hrs)$ hrs and mean ICU stay was $2.9\pm0.8(2\~4 days)$ days. Mean hospital day was $21.6\pm14.3(13\~56 days)$ days. Postoperative mean CK-MS was $11.3\pm14.1\;ng/mL$. Early postoperative graft patency rate was $100\%(24/24)$. Follow-up was completed in all patients. In this time, there was no patients with angina or death. Conclusion: The results of this study suggest that OPCAB reduces morbidity and favors hospital outcomes. Therefore, OPCAB is safe, reasonable and might be preferable operative strategy in elderly patients.

• Journal of Technology Innovation
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• v.24 no.4
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• pp.277-307
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• 2016

Since 2011, DCF(Discounted Cash Flow) method has been used initiatively for valuating R&D technology assets in the agricultural food industry and recently technology valuation based on royalties comparison among technology transfer transactions has been also carried out in parallel when evaluating the technology assets such as new seed development technologies. Since the DCF method which has been known until now has many input variables to be estimated, sophisticated estimation has been demanded at the time of technology valuation. In addition, considering more similar trading cases when applying sales transaction comparison or industry norm method based on information of technology transfer royalty, it is an important issue that should be taken into account in the same way in the Agri-Food industry. The main input variables used for technology valuation in the Agri-Food industry are life cycle of technology asset, the financial information related to the Agri-Food industry, discount rate, and technology contribution rate. The latest infrastructure building and data updating related to technology valuation has been carried out on a regular basis in the evaluation organization of the Agri-Food segment. This study verifies the key variables that give the most important impact on the results for the existing technology valuation in the Agri-Food industry and clarifies the difference between the existing valuation result and the outcome by referring the support information that is derived through the latest input information applied in DCF method. In addition, while presenting the scheme to complement fragment information which the latest input data just influence result of technology valuation, we tried to perform comparative analysis between the existing valuation results and the evaluated outcome after the latest of reference data for making a decision the input values to be estimated in DCF. To perform these analyzes, it was first selected the representative cases evaluated past in the Agri-Food industry, applied a sensitivity analysis for input variables based on these selected cases, and then executed a simulation analysis utilizing the key input variables derived from sensitivity analysis. The results of this study is to provide the information which there are the need for modernization of the data related to the input variables that are utilized during valuating technology assets in the Agri-Food sector and for building the infrastructure of the key input variables in DCF. Therefore it is expected to provide more fruitful information about the results of valuation.

• Korean Journal of Environmental Biology
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• v.34 no.2
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• pp.63-72
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• 2016

The objective of this study was to identify the life form characteristics, naturalized degree and introduction period of naturalized plants on upland fields in South Korea. The survey sites were selected in 222 upland fields over 9 provinces where are relatively dry soil conditions and are disturbed continuously by farming practices. It seemed that these uplands maintain good condition for the invasion and settlement of alien plants. Field surveys were carried out twice from May to June and from August to September in 2013. The vascular plants of the upland fields were listed into 539 taxa which contain 103 families, 320 genera, 448 species, 2 subspecies, 74 varieties and 15 forms. Ninety nine taxa were naturalized plants composed of 23 families, 64 genera, 91 species and 8 varieties. The urbanization index and naturalized index is 30.65% and 18.37%, respectively. Among total 99 naturalized plants, Compositae (30 taxa) was the most dominant family, and followed by Gramineae (14 taxa). On the basis of dormancy form, 78 taxa were belong to Th (Therophyte). In radicoid form, $R_5$ plants (86 taxa) and $R_3$ plants (14 taxa) were dominantly distributed. In disseminule form, $D_4$ including 63 taxa and $D_2$ containing 26 taxa were dominant. On the basis of growth form, erect form (e) containing 26 taxa was dominant. In conclusion, life form spectrum was $Th-R_5-D_4-e$ type. According to life form analysis, naturalized degree and introduction period, alien plants with unique characteristics may have high ability to settle and spread nationwide after inflow into South Korea. It needs further to observe some plant species with or without ecological features such as widely disseminated seeds by wind or water, high seed productivity, long life-span seeds, high germination rate of seeds, or non-dormant germinable seed.

• Korean Journal of Remote Sensing
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• v.14 no.3
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• pp.213-222
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• 1998

Electro-Optical Camera(EOC) is the main payload of the KOrea Multi-Purpose SATellite(KOMPSAT) with the mission of cartography to build up a digital map of Korean territory including a Digital Terrain Elevation Map(DTEM). This instalment which comprises EOC Sensor Assembly and EOC Electronics Assembly produces the panchromatic images of 6.6 m GSD with a swath wider than 17 km by push-broom scanning and spacecraft body pointing in a visible range of wavelength, 510~730 nm. The high resolution panchromatic image is to be collected for 2 minutes during 98 minutes of orbit cycle covering about 800 km along ground track, over the mission lifetime of 3 years with the functions of programmable gain/offset and on-board image data storage. The image of 8 bit digitization, which is collected by a full reflective type F8.3 triplet without obscuration, is to be transmitted to Ground Station at a rate less than 25 Mbps. EOC was elaborated to have the performance which meets or surpasses its requirements of design phase. The spectral response, the modulation transfer function, and the uniformity of all the 2592 pixel of CCD of EOC are illustrated as they were measured for the convenience of end-user. The spectral response was measured with respect to each gain setup of EOC and this is expected to give the capability of generating more accurate panchromatic image to the users of EOC data. The modulation transfer function of EOC was measured as greater than 16 % at Nyquist frequency over the entire field of view, which exceeds its requirement of larger than 10 %. The uniformity that shows the relative response of each pixel of CCD was measured at every pixel of the Focal Plane Array of EOC and is illustrated for the data processing.

• Korean journal of applied entomology
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• v.58 no.2
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• pp.111-120
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• 2019

Riptortus pedestris (Fabricius) (Hemiptera: Alydidae) is an economically important insect pest of soybean and fruit trees. We investigated the temperature effects on the adult fecundity and longevity, and determined the parameters of oviposition models and life table at different constant temperatures 15.8, 19.7, 24.0, 27.8, 32.6, 34.0, and $35.5^{\circ}C$. R. pedestris females reproduced successfully from 19.7 to $35.5^{\circ}C$ except $15.8^{\circ}C$. The longevity of R. pedestris was longest at $15.8^{\circ}C$ and it decreased with increasing temperature (76.6 days at $19.7^{\circ}C$ and 20.6 days at $35.5^{\circ}C$). The number of total eggs and viable eggs was highest at $24.0^{\circ}C$ (193.5 and 151.2). Egg hatchability was highest at $27.8^{\circ}C$ (84.0%). We compared the results of oviposition models and life table parameters using both total eggs and viable eggs. The parameter value (c: the maximum reproductive capacity) (190 eggs) of temperature dependent total fecundity model using total eggs was higher than that of the model using viable eggs. When we analyzed the life table parameter the values of net reproductive rate and mean generation time using viable eggs were lower than those using total eggs. The oviposition models and life table analysis using viable eggs will be helpful to understand the real population transition of R. pedestris in agricultural system.

• Journal of Bio-Environment Control
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• v.28 no.2
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• pp.172-177
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• 2019

Lactuca indica L. ('Seonhyang') baby leaves were harvested after cultivation for 4 weeks (less than 10 cm plant height) and adults were cultivated for 8 weeks ($20{\pm}5cm$ plant height). The respiration rate and the ethylene production rate of Lactuca indica leaves were higher than those of the baby leaves but the DPPH radical scavenging ability was lower than baby leaves. The $L^*$, $a^*$ and $b^*$ values did not show any significant difference between baby leaves and adult leaves but the chlorophyll content was higher in adult leaves. All adult and baby leaves of Lactuca indica were stored at $2^{\circ}C$, $8^{\circ}C$, and $20^{\circ}C$, respectively. The higher the storage temperature, the higher the fresh weight loss rate and weight loss rate of adult leaves was lower at $2^{\circ}C$ and $8^{\circ}C$. The visual quality of Lactuca indica leaves were determined by the panel test during storage and it deteriorated faster as the storage temperature increased. The shelf life that calculated the period of maintaining higher than 3 points of visual quality was longer than 1.6 days at $2^{\circ}C$, 1.4 days at $8^{\circ}C$ and 1.5 days at $20^{\circ}C$. The oxygen and carbon dioxide concentrations within the package of Lactuca indica leaves were similar to those in atmosphere. The chlorophyll content was maintained higher at lower storage temperature in the last storage day and the off-odor was higher in baby leaves than in the adult leaves of Lactuca indica L.

• Journal of Intelligence and Information Systems
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• v.23 no.1
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• pp.23-46
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• 2017

Although there have been cases of evaluating the value of specific companies or projects which have centralized on developed countries in North America and Europe from the early 2000s, the system and methodology for estimating the economic value of individual technologies or patents has been activated on and on. Of course, there exist several online systems that qualitatively evaluate the technology's grade or the patent rating of the technology to be evaluated, as in 'KTRS' of the KIBO and 'SMART 3.1' of the Korea Invention Promotion Association. However, a web-based technology valuation system, referred to as 'STAR-Value system' that calculates the quantitative values of the subject technology for various purposes such as business feasibility analysis, investment attraction, tax/litigation, etc., has been officially opened and recently spreading. In this study, we introduce the type of methodology and evaluation model, reference information supporting these theories, and how database associated are utilized, focusing various modules and frameworks embedded in STAR-Value system. In particular, there are six valuation methods, including the discounted cash flow method (DCF), which is a representative one based on the income approach that anticipates future economic income to be valued at present, and the relief-from-royalty method, which calculates the present value of royalties' where we consider the contribution of the subject technology towards the business value created as the royalty rate. We look at how models and related support information (technology life, corporate (business) financial information, discount rate, industrial technology factors, etc.) can be used and linked in a intelligent manner. Based on the classification of information such as International Patent Classification (IPC) or Korea Standard Industry Classification (KSIC) for technology to be evaluated, the STAR-Value system automatically returns meta data such as technology cycle time (TCT), sales growth rate and profitability data of similar company or industry sector, weighted average cost of capital (WACC), indices of industrial technology factors, etc., and apply adjustment factors to them, so that the result of technology value calculation has high reliability and objectivity. Furthermore, if the information on the potential market size of the target technology and the market share of the commercialization subject refers to data-driven information, or if the estimated value range of similar technologies by industry sector is provided from the evaluation cases which are already completed and accumulated in database, the STAR-Value is anticipated that it will enable to present highly accurate value range in real time by intelligently linking various support modules. Including the explanation of the various valuation models and relevant primary variables as presented in this paper, the STAR-Value system intends to utilize more systematically and in a data-driven way by supporting the optimal model selection guideline module, intelligent technology value range reasoning module, and similar company selection based market share prediction module, etc. In addition, the research on the development and intelligence of the web-based STAR-Value system is significant in that it widely spread the web-based system that can be used in the validation and application to practices of the theoretical feasibility of the technology valuation field, and it is expected that it could be utilized in various fields of technology commercialization.

• Journal of the Korean Electrochemical Society
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• v.20 no.4
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• pp.67-74
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• 2017

Layered Ni-rich NCM cathode materials $Li[Ni_xCo_{(1-x)/2}Mn_{(1-x)/2}]O_2$ ($x{\geq}0.6$) have advantages of high energy density and cost competitive over $LiCoO_2$. The discharge capacity of NCM increases proportionally to the Ni contents. However, there is a problem that it is difficult to realize the stable electrochemical performance due to cation mixing. In this study, synthesis conditions for the layered Ni-rich NCMs are investigated to achieve deliver the ones having good electrochemical performances. Synthesis parameters are atmosphere, lithium source, synthesis time, synthesis temperature and Li/M (M=transition metal) ratio. The degree of cation mixing gets worse as the Ni content is increased from $Li[Ni_{0.6}Co_{0.2}Mn_{0.2}]O_2$ (NCM6) to $Li[Ni_{0.8}Co_{0.1}Mn_{0.1}]O_2$ (NCM8). It is confirmed that higher level of cation mixing affects negatively on the electrochemical performance of NCMs. Optimum synthesis conditions are explored for NCMx (x=6, 7, 8) in order to reduce the cation mixing. Under optimized conditions for three representative NCMx, a high initial discharge capacity and a good cycle life are obtained for $180mAh{\cdot}g^{-1}$, 96.2% (50 cycle) in NCM6, $187mAh{\cdot}g^{-1}$, 94.7% (50 cycle) in NCM7, and $201mAh{\cdot}g^{-1}$, 92.7% (50 cycle) in NCM8, respectively.

• The korean journal of orthodontics
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• v.28 no.2 s.67
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• pp.329-341
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• 1998

Sterilization has received much attention in orthodontic practices over the past several years. The present study was undertaken to investigate the effects of sterilization on the physical properties of orthodontic pliers-AEZ, Unitek, and Dentronix ligature cutters. This study was designed to examine the tips of ligature cutters before and after 200 and 400 sterilization cycles using the Bowmar RHT-1000, the Dentronix DDS-5000, and the Eschmann SES-2000. The tip surface and the fracture surface were observed with a scanning electron microscope. The microstructure was observed with an optical microscope. The hardness test was carried out with the mic개-Vickers hardness tester and the Rockwell C Scale hardness tester. The chemical composition was analyzed by energy dispersive X-ray spectrometer. The results of this study were as follows : 1. The number and the size of corrosion products on the tip surface and the proportion of cleavage planes in fractured specimen increased, but the hardness of the tip decreased in proportion to sterilization cycles. From these observations, it was considered that mechanical properities decreased in proportion to sterilization cycles. 2. The number and the size of chromium carbides increased in proportion to sterilization cycles. Coarse microstructure decreased mechanical properities. 3. The AEZ and Unitek ligature cutters were Fe-Cr stainless steels, but the Dentronix ligature cutter was Co-Cr alloy. There were many differences among manufactures, but the chemical composition was .not changed after sterilization cycles. 4. The tip edge of ligature cutter used in a clinic revealed microcracks with the SEM observation. Clinical experience confirmed that ligature cutters were gradually degraded by sterilization.