• Information Systems Review
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• v.22 no.2
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• pp.137-166
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• 2020

While South Koreans overseas travelling rate has been increased every year, domestic travelling rate has been at a standstill for several years. The purpose of this study is to analyze domestic traveling styles of Koreans according to their generations in order to provide generation-specific traveling services. For this purpose, we categorized the survey respondents into four different generations, which are Millennium (age 19~34), X generation (35~54), Baby Boomer (55~64) and senior by following the criterions of the Korea National Tourism Organization. After then, we analyze factors related to travel preparation process, the actual traveling activities and satisfaction after the travel. In this study, 16,713 data collected by the Ministry of Culture, Sports and Tourism are used. The results of this study show that Korean people tends to acquire domestic traveling information from their own or acquaintances past experiences. Also, they do not prefer the organized trip for domestic travels, thus do not buy package products a lot. In addition, natural scenery, rich in cultural heritage, and convenient accommodation are the most important determinant factors affecting the overall travel satisfaction of level for all generations. The traveling characteristics for each generation are as follows. Millennium get traveling information from the internet a lot, and more specifically, they refer portal sites and social network services (SNS) in many cases. Also, they tend to travel in summer peak season to popular destinations and pursues active traveling experiences. Generation X has similar traveling patterns with Millennium, however they major transportation method is using their own car. Also, transportation convenience and satisfactory leisure activity are important factors affecting the overall satisfaction level to Generation X. On the other hand, Baby boomer generation has a greater emphasis on appreciation of nature, visiting famous restaurants, and relaxation, rather than actively participating experiencing programs. They travel evenly in summer and spring/fall season to many different areas instead of focusing on popular tourist spots. In addition, shopping and eating delicious food are the important factors affecting the overall satisfaction level for them. Lastly, Senior generation has similar characteristics with Baby boomer in many ways, however, they travel a lot on the same day using public transportations or car rental service. They prefer spring and autumn trips rather than summer peak season, and tend to buy packaged travel products a lot compared with other generations. If these different traveling characteristics of each generation are considered for organizing and customizing tourism services, it is expected that domestic tourism satisfaction level will be ultimately increased.

• Journal of Industrial Convergence
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• v.22 no.6
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• pp.99-106
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• 2024

The author thought about how to explain visual functions in an easy-to-understand way to customers visiting the optical shops and provide easy customer consultation, and attempted to evaluate the usability and value of the educational webtoon for patient consultation by applying it to the optical shops's visitors. Survey study was conducted targeting 152 customers who visited optical shops A in Incheon from January to December 2023. In this study, consultation was conducted using educational webtoons to help the general public understand concepts that are difficult to understand, such as binocular vision function, the concept of heterophoria, prism lenses, and binocular balance. The areas of 'understanding', 'interest', 'usability', 'necessity', and 'expression of expertise' felt by the visitors who received counseling were scored and evaluated, and differences according to counseling method were evaluated using an independent sample t-test. Statistical verification was performed. When the optometrist only explained verbally, the score distribution was relatively low: 1.96 points for understanding, 2.06 points for interest, 2.96 points for usability, 4.20 points for necessity, and 3.19 points for expertise. When the optometrist provided explanations along with the book, understanding was 4.14 points, interest was 3.28 points, usability was 3.60 points, necessity was 4.17 points, and expertise was 3.55 points. When the optometrist explained with a webtoon, understanding was 4.57 points, interest was 4.96 points, usability was 4.18 points, necessity was 4.65 points, and expertise was 3.15 points. When explanations were given only verbally, all items showed the lowest scores, whereas consultations using webtoons showed 4 points or more (excellent) in all items except the 'expression of expertise' item. It is evaluated that actively using webtoons in various consultation situations that occur in optical shops will help increase customer interest and concentration.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.4 no.1
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• pp.31-71
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• 1968

To clarify the breeding behavior of the hybrids between tropical and temperate area rice varieties, investigations were made on heading days and grain sterility. In this study, crosses were made in half way diallel involving 7 varieties: 2 photoperied sensitive Indicas, 2 less sensitive intermediate Indicas, 1 Ponlai Japonica and 2 high temperature sensitive Japonicas. The parents and $F_1$s were grown under 10 hours and 14 hours daylength controlled conditions at both IRRI(International Rice Research Institute, N$14^{\circ}$17') and Suwon(N$37^{\circ}$16'). F2s with their parents were grown at IRRI in the short day season, and at Suwon under natural conditions. Fa lines with their parents were grown at Suwon under natural conditions. Observations were made for heading days and sterility. The results are summarized as follow; 1. Heading days : 1. For the $F_1$s, earliness showed dominance or overdominance to lateness under the 10 hours condition, and dominance or partial dominance under the 14 hours conditions, at both IRRI and Suwon. 2. For the $F_2$s grown at IRRI during the shortday season earliness appeared to be dominant over lateness and segregation was not distinct and continuous. In the early season culture of $F_2$s at Suwon earliness showed partial dominance or was intermediate. In the proper season culture of $F_2$s lateness showed partial dominance or was intermediate. 3. In the combinations between late parental varieties which do not head at Suwon, transgressive segregants bearing effective panicles were obtained. 4. The crosses of parental varieties having long basic vegetative growth duration showed bigger variance in heading days, and significant correlation was found between of parental varieties and the mean coefficient of variance for parental arrays. 5. The means of heading days of F2 populations were significantly correlated with those of $F_1$ or mid-parents. The means of F 8 lines were also highly correlated with the means of $F_2$s, but, the means of $F_3$ lines grown at Suwon and of their parental $F_2$ individual, grown at IRRI were not correlated. 6. A faint heritability was calculated from the regression of $F_3$ lines grown at Suwon on the $F_2$ individuals grown at IRRI for most combinations, especially in the combinations involving shortday sensitive varieties. This implies low efficiency for the selection of heading days of $F_2$ individuals at IRRI to be grown in lines at Suwon. 7. No significant reciprocal effects were measured for $F_1$ and $F_2$ mean heading days. 8. Partitioning the observed photoperiod sensitivity. into two components, parental array mean md the deviation from this array mean, the parental photoperiod sensitivity contributing to the hybrids was measured in terms of general and specific combining ability for photoperiod sensitivity. 9. The photoperiod sensitivity of $F_1$s was higher than that of the parents, and it decreased as the generation progressed in most combinations of tested varieties. 10. The response of heading days to difference of temperature was weaker for $F_1$ hybrids than for the parents. The differences of temperature responses between the longday and shortday treatments were specific for the variety. 2. Sterility : 1. The $F_1$ sterility was specific for the combinations and not correlated to the parental sterility. The sterility of $F_1$s grown under the 10 hours condition was higher than of those grown under 14 hours. These results were the same at both locations, IRRI and Suwon. 2. The high sterile combinations in $F_1$ showed high sterility in $F_2$. The combinations between a high photoperiod sensitive variety and a high temperature sensitive variety showed high sterility and wider variance. 3. The mean sterility of $F_2$s was lower than of $F_1$s and the mean of $F_3$ lines was lower than of $F_2$s. Sterility decreased as the generation progressed, and the differences of $F_3$ sterility of different combinations were not significant. 4. A faint correlation between grain sterility and pollen sterility was observed in $F_2$ populations. 5. No significant reciprocal effects were measured in $F_1$ and $F_2$ sterility. 6. Following Griffing's method, specific combining ability effects were higher than general combining ability effects, especially in the combinations between highly photoperiod sensitive varieties and highly temperature sensitive varieties. 7. No distinct correlations were found between $F_2$ individual sterility grown at IRRI and $F_3$ line sterility grown at Suwon. 8. No distinct correlations were observed between heading days and sterility of $F_2$ individuals.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.14
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• pp.1-40
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• 1973

There is a general tendency to increase nitrogen level in rice production to insure an increased yield. On the other hand, percentage of ripened grains is getting decreased with such an increased fertilizer level. Decreasing of the percentage is one of the important yield limiting factors. Especially the newly developed rice variety, 'Tongil' is characterized by a relatively low percentage of ripened grains as compared with the other leading varieties. Therefore, these studies were aimed to finding out of some measures for the improvement of ripening in rice. The studies had been carried out in the field and in the phytotron during the period of three years from 1970 to 1972 at the Crop Experiment Station in Suwon. The results obtained from the experiments could be summarized as follows: 1. The spikelet of Tongil was longer in length, more narrow in width, thinner in thickness, smaller in the volume of grains and lighter in grain weight than those of Jinheung. The specific gravity of grain was closely correlated with grain weight and the relationship with thickness, width and length was getting smaller in Jinheung. On the other hand, Tongil showed a different pattern from Jinheung. The relationship of the specific gravity with grain weight was the greatest and followed by that with the width, thickness and length, in order. 2. The distribution of grain weight selected by specific gravity was different from one variety to another. Most of grains of Jinheung were distributed over the specific gravity of 1.12 with its peak at 1.18, but many of grains of Tongil were distributed below 1.12 with its peak at 1.16. The brown/rough rice ratio was sharply declined below the specific gravity of 1.06 in Jinheung, but that of Tongil was not declined from the 1.20 to the 0.96. Accordingly, it seemed to be unfair to make the specific gravity criterion for ripened grains at 1.06 in the Tongil variety. 3. The increasing tendency of grain weight after flowering was different depending on varieties. Generally speaking, rice varieties originated from cold area showed a slow grain weight increase while Tongil was rapid except at lower temperature in late ripening stage. 4. In the late-tillered culms or weak culms, the number of spikelets was small and the percentage of ripened grains was low. Tongil produced more late-tillered culms and had a longer flowering duration especially at lower temperature, resulting in a lower percentage of ripened grains. 5. The leaf blade of Tongil was short, broad and errect, having light receiving status for photosynthesis was better. The photosynthetic activity of Tongil per unit leaf area was higher than that of Jinheung at higher temperature, but lower at lower temperature. 6. Tongil was highly resistant to lodging because of short culm length, and thick lower-internodes. Before flowering, Tongil had a relatively higher amount of sugars, phosphate, silicate, calcium, manganese and magnesium. 7. The number of spikelets of Tongil was much more than that of Jinheung. The negative correlation was observed between the number of spikelets and percentage of ripened grains in Jinheung, but no correlation was found in Tongil grown at higher temperature. Therefore, grain yield was increased with increased number of spikelets in Tongil. Anthesis was not occurred below 21$^{\circ}C$ in Tongil, so sterile spikelets were increased at lower temperature during flowering stage. 8. The root distribution of Jinheung was deeper than that of Tongil. The root activity of Tongil evaluated by $\alpha$-naphthylamine oxidation method, was higher than that of Jinheung at higher temperature, but lower at lower temperature. It is seemed to be related with discoloration of leaf blades. 9. Tongil had a better light receiving status for photosynthesis and a better productive structure with balance between photosynthesis and respiration, so it is seemed that tongil has more ideal plant type for getting of a higher grain yield as compared with Jinheung. 10. Solar radiation during the 10 days before to 30 days after flowering seemed enough for ripening in suwon, but the air temperature dropped down below 22$^{\circ}C$ beyond August 25. Therefore, it was believed that air temperature is one of ripening limiting factors in this case. 11. The optimum temperature for ripening in Jinheung was relatively lower than that of Tongil requriing more than $25^{\circ}C$. Air temperature below 21$^{\circ}C$ was one of limiting factors for ripening in Tongil. 12. It seemed that Jinheung has relatively high photosensitivity and moderate thermosensitivity, while Tongil has a low photosensitivity, high thermosensitivity and longer basic vegetative phase. 13. Under a condition of higher nitrogen application at late growing stage, the grain yield of Jinheung was increased with improvement of percentage of ripened grains, while grain yield of Tongil decreased due to decreasing the number of spikelets although photosynthetic activity after flowering was. increased. 14. The grain yield of Jinheung was decreased slightly in the late transplanting culture since its photosynthetic activity was relatively high at lower temperature, but that of Tonil was decreased due to its inactive photosynthetic activity at lower temperature. The highest yield of Tongil was obtained in the early transplanting culture. 15. Tongil was adapted to a higher fertilizer and dense transplanting, and the percentage of ripened grains was improved by shortening of the flowering duration with increased number of seedlings per hill. 16. The percentage of vigorous tillers was increased with a denser transplanting and increasing in number of seedlings per hill. 17. The possibility to improve percentage of ripened grains was shown with phosphate application at lower temperature. The above mentioned results are again summarized below. The Japonica type leading varieties should be flowered before August 20 to insure a satisfactory ripening of grains. Nitrogen applied should not be more than 7.5kg/10a as the basal-dressing and the remained nitrogen should be applied at the later growing stage to increase their photosynthetic activity. The morphological and physiological characteristics of Tongil, a semi-dwarf, Indica $\times$ Japonica hybrid variety, are very different from those of other leading rice varieties, requring changes in seed selection by specific gravity method, in milling and in the cultural practices. Considering the peculiar distribution of grains selected by the method and the brown/rough rice ratio, the specific gravity criterion for seed selection should be changed from the currently employed 1.06 to about 0.96 for Tongil. In milling process, it would be advisable to bear in mind the specific traits of Tongil grain appearance. Tongil is a variety with many weak tillers and under lower temperature condition flowering is delayed. Such characteristics result in inactivation of roots and leaf blades which affects substantially lowering of the percentage of ripened grains due to increased unfertilized spikelets. In addition, Tongil is adapted well to higher nitrogen application. Therefore, it would be recommended to transplant Tongil variety earlier in season under the condition of higer nitrogen, phosphate and silicate. A dense planting-space with three vigorous seedlings per hill should be practiced in this case. In order to manifest fully the capability of Tongil, several aspects such as the varietal improvement, culural practices and milling process should be more intensively considered in the future.he future.

• Korean journal of applied entomology
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• v.16 no.4 s.33
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• pp.199-208
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• 1977

Activities of various hydrolytic enzymes produced by three plant pathogenic fungi, Sclerotium rolfsii Sacc., Sclerotinia sclerotiorum (Lieb.) deBary and Helminthosporium sigmoideum var. irregulare Crallery et Tullius, were measured. Activties and amounts of the enzymes in mycelia, cultural filtrates, and sclerotia(except of sclerotia of H. sigmoideum var. irregulare) were estimated at various pH levels in order to find out optimal pH for their enzymatic activities. Enzymes such as cellulase (ex), invertase, xylanase, $\beta-amylase$, polymethylgalacturonase, polygalacturonase, phosphatase and protease were estimated. Culture solution for production of enzymes was prepared by adding of 10g, D-glucose, 1.3g $NH_4NO_3,\; 0.5g\; MgSO_4,\;7H_2O,\; and\; 1.0g\; KH_2PO_4$ into 1 liter of potato decoction plus 2ml of micro element solution consisting of 0.2mg. Fe, 0.2mg Zn, and 0.1mg Mn as the sulphates into 1 liter of distilled water. All tested mycelia and cultural filtrates were obtained from the cultures incubarted in previous solution for ten days at $25^{\circ}C$, and sclerotia were harvested from PDA plates of 3. days old, The crude enzyme solutions were prepared according to the method of Miyazaki etal. Ten days after incubation, activities of Cx produced by Scl. sclerotiorum were higher than those of the other fung and each of Cx from three fungi showed different pH optima, such as S. rolfsii and Scl. schlerotiorum in acid side (around pH 3.0), H. sigmoideum var. irregulare in neutral side (around pH 6.3). Invertase activities of S. rolfsii were 20 times higher than those of the other fungi in all samples. All tested fungi, however, showed no significant difference between the enzymatic activities of their cultural filtrate and mycelia and the activities in sclerotia of S. rolfsii and Scl. sclerotiorum were hardly recognized. There were multiple peaks on the xylanase activity curves of three fungi in terms of pH values. High activities of the xylanase were revealed in sclerotia of S. rolfsii and Scl. sclerotiorum, and in mycelia of H. sigmoideum var. irregulare. The highest activities of $\beta-amylase$ were shown both in mycelia and cultural filtrate of H. sigmoideum var. irregulae among the tested fungi, and their optimal pH was 6.2 in both mycelia and cultural filtrate. In the S. rofsii and Sel. sclerotiorum, however, the activities of cultural filtrates were higher than those of the other fungi, and optimal pH was 3.0 and 6.2 for cultural filtrate and both mycelia and sclerotia, respectively. Activities of PMG were high in cultural filtrates of all tested fungi, especially in Scl. sclerotiorum and H. sigmoideum var. irregulare. Mycelia of themalso showed the considerable activities. Optimal pH for enzymatic activities were variable with thekind of fungi or with the samples measured. The highest activities of PG were presented by mycelia of S. rolfsii and Scl. sclerotiorum. $9.l\mu /min.\; and\; 9.5\mu g/min.$, respectively. Optimal pH for activity of PG in mycelia was around 4.5 in S. rolfsii and around 3.0 in Scl. sclerotiorum. Phosphatase of S. rolfsii and Scl. sclerotiorum was more active in acid side (optimal PH3. 5) and that of H. sigmoideum var. irregulare showed one peak each in acid, neutral and alkaline side. But the highest peak was at pH 9.5. Protease of all tested fungi was more active at pH 10.0, especially that of the cultural filtrate of H. sigmoideum var. irregualre.

• Tuberculosis and Respiratory Diseases
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• v.44 no.5
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• pp.1114-1124
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• 1997

Background : Endothelin(ET) is a very potent vasoconstrictive peptide produced by endothelial cells of pulmonary artery. The endothelin level was increased in plasma of primary pulmonary hypertension and acute pulmonary thromboembolism and it was suggested that the endothelin might do a critical role in the cardiopulmonary dysfunction in these two conditions. But the exact mechanism of increase of ET has not been known. In these two conditions, platelet activation and thrombosis are the main pathophysiologic findings. So there is a possibility that the platelet might stimulate endothelin secretion from endothelial cells. Therefore, we performed this study to evaluate the role of platelet and its mediators on endothelin production in bovine pulmonary artery endothelial(BPAE) cells. Method : Bovine pulmonary artery endothelial cells, ATCC certified cell line 209, were cultured and treated with human platelets($10^6{\sim}10^8/ml$), thrombin (0.1~10u/ml), TGF-${\beta}1$(1~100uM), serotonin(1~100uM), and endotoxin(1ug/ml) in a final volume of 500ul for 18 hours. Levels of ir(immunoreactive)-ET in each conditioned medium were measured by a radioimmunoassay specific for ET. Result : The increase of ir-ET levels was platelet number and time dependent over 18 hours. When washed human platelets were added($10^8/ml$), the ir-ET levels were significantly higher than that of control(p<0.05) at 8 and 18 hours after culture. Subthreshold concentration of platelets($10^7/ml$) coincubated with endotoxin(1ug/ml) or subthreshold dose of thrombin(0.1u/ml) stimulated ir-ET secretion from BPAE cells significantly(p<0.05) compared with control. Thrombin(1ug/ml, 10ug/ml) and TGF-${\beta}1$(100pM, 1000pM) significantly increased ir-ET secretion from BP AE cells(p<0.05) compared with control, but serotoin(1~100uM) and endotoxin(1ug/ml) did not stimulate the ir-ET secretion. Conclusions : Platelets stimulate endothelin secretion from bovine pulmonary artery endothelial cells. The mechanism of increase of endothelin secretion seems to be a stimulation by platelet itself or by mediators, such as TGF-${\beta}1$, secreted from activated platelets. And, in this study, the priming effect of platelets on endothelin secretion from BPAE cells could be another possibility.

• Korean Journal of Human Ecology
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• v.14 no.2
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• pp.313-319
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• 2005

This survey was conducted in order to obtain the basic data for desirable consumption habits through investigation and analysis of university students' fast food consumption behaviors. Questionnaires were collected from a total of 374 male and female students living in big or small and medium-sized cities in August, 2004. The contents surveyed were utilization and expenses of fast foods, choice of fast foods, relationship between fast foods and a diet, and characteristics of fast food restaurants. The results obtained are summarized as follows: 1. The ratio of the surveyees varied according to gender, residence, and the size of a city they're living in. For example, males took up 48.66% of the surveyees, while females did 51.34%. The ratio of residents in apartments and stand-alone houses was 54.81% and 45.19% each. 47.33% of the respondents were living in big cities, while 52.67% of them in small and medium-sized cities. 2. 70.1% of the surveyees responded that they are with friends when having fast foods. There was a highly significant difference between male and female in the type of eating companions (p<0.001). The average number of days that they eat fast foods was 1 to 2 times a week, which accounted for 63.7% of the respondents. However, in the case of eating foods, there was no significant differences between two sexes. 3. 64.2% of the surveyees paid more than 20,000 won to buy fast foods for a week, which showed no significant differences between genders. They tend to split a bill, rather than one person pays all. There was a highly significant difference between genders in paying method (p<0.001). 4. 52.1 % of the respondents chose a menu themselves. Their most favored food was chickens (26.5%), which showed a statistically significant difference between genders (p<0.001). 46.8% of them preferred coke as a drink, which had no significant difference between genders. 42.2% of the surveyees had fast foods between lunch and dinner, which also had no significant difference between genders. The most important factor in choosing a menu was its taste (62.8%), which indicated a significant difference between males and females (p<0.05). 5. The preference to fast foods was due to the influence of western culture (36.4%) and eating-out habits (29.1%), which was significantly different between genders (p<0.05). Those who eat fast foods answered they have normal weight and normal body type (49.5%). 24.3% of them were relatively fat with significant difference between genders (p<0.05). 63.4% of the surveyees thought themselves not picky with foods, and there was a significant difference between genders (p<0.05). 78.3% of them mostly preferred franchise restaurants because they are convenient and cheap.

• Journal of Intelligence and Information Systems
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• v.21 no.2
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• pp.93-112
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• 2015

Depending on the change in consumer's consumption pattern, existing retail shop has evolved in hypermarket or convenience store offering grocery and daily products mostly. Therefore, it is important to maintain the inventory levels and proper product configuration for effectively utilize the limited space in the retail store and increasing sales. Accordingly, this study proposed proper product configuration and inventory level strategy based on RFM(Recency, Frequency, Monetary) model and SOM(self-organizing map) for manage the retail shop effectively. RFM model is analytic model to analyze customer behaviors based on the past customer's buying activities. And it can differentiates important customers from large data by three variables. R represents recency, which refers to the last purchase of commodities. The latest consuming customer has bigger R. F represents frequency, which refers to the number of transactions in a particular period and M represents monetary, which refers to consumption money amount in a particular period. Thus, RFM method has been known to be a very effective model for customer segmentation. In this study, using a normalized value of the RFM variables, SOM cluster analysis was performed. SOM is regarded as one of the most distinguished artificial neural network models in the unsupervised learning tool space. It is a popular tool for clustering and visualization of high dimensional data in such a way that similar items are grouped spatially close to one another. In particular, it has been successfully applied in various technical fields for finding patterns. In our research, the procedure tries to find sales patterns by analyzing product sales records with Recency, Frequency and Monetary values. And to suggest a business strategy, we conduct the decision tree based on SOM results. To validate the proposed procedure in this study, we adopted the M-mart data collected between 2014.01.01~2014.12.31. Each product get the value of R, F, M, and they are clustered by 9 using SOM. And we also performed three tests using the weekday data, weekend data, whole data in order to analyze the sales pattern change. In order to propose the strategy of each cluster, we examine the criteria of product clustering. The clusters through the SOM can be explained by the characteristics of these clusters of decision trees. As a result, we can suggest the inventory management strategy of each 9 clusters through the suggested procedures of the study. The highest of all three value(R, F, M) cluster's products need to have high level of the inventory as well as to be disposed in a place where it can be increasing customer's path. In contrast, the lowest of all three value(R, F, M) cluster's products need to have low level of inventory as well as to be disposed in a place where visibility is low. The highest R value cluster's products is usually new releases products, and need to be placed on the front of the store. And, manager should decrease inventory levels gradually in the highest F value cluster's products purchased in the past. Because, we assume that cluster has lower R value and the M value than the average value of good. And it can be deduced that product are sold poorly in recent days and total sales also will be lower than the frequency. The procedure presented in this study is expected to contribute to raising the profitability of the retail store. The paper is organized as follows. The second chapter briefly reviews the literature related to this study. The third chapter suggests procedures for research proposals, and the fourth chapter applied suggested procedure using the actual product sales data. Finally, the fifth chapter described the conclusion of the study and further research.

• The Korean Journal of Malacology
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• v.1 no.1
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• pp.24-50
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• 1985

Five different populations of Parafossarulus manchouricus (Chongpyung, Chinju and Kunsan, Korea; and Japan and Taiwan), a population of Bitbynia (Gabbia) misella (Gongju, Korea) and two different populations of Bithynta tentaculata (Michigan, U.S.A. and Bodensee, Germany) were compared in regard to eff-laying characteristics, morphology, chromosome cytology, natural infections of parasites and ecology of habitats. A satisfactory culture method was devised for laboratory rearing of the snails. Tropical fish food (Terra SML) and powdered green leaves (Ceralife) were used as the main food sources for the snails. Benthic diatoms such as Navicula and Gomphonema from the periphyton were also essential for satisfactory growth, especially for the baby snails. The aquaria were stabilized with small stones from a local stream. Young P. manchouricus snails grew to adult size in about 54 days after hatching. They laid eggs 150-156 days after hatching. The whole cycle (birth to egg-laying) took approximately 5 months. The three species of bithyniid snails are iteroparous and lay eggs once a year. There were no major morphological differences in the shells of genera or subgenera studied here. They did exhibit the following rather minor differences. The shell of Parafossarulus has spirally raised ridges, and its apex is usually eroded; the other two genera lack these characteristics. The shell of B. (Gabbia) misella is small, nor exceeding 7.5 mm in length, while the shells of the other two species are larger, being more than 10 mm in length. Scanning electron microscopy (SEM) of the protoconch of P. manchouricus reveals nearly smooth sculpture with small, low, spiral wrinkles. This sculpture is quite different from that of the Hydrobiidae, a family to which the bithyniids are frequently assigned. Scanning electron microscopy of the radulae of the three bithyniid species showed that their radular morphologies are very similar, but there are some small differences, which may be species-specific. There were some statistical differences in shell heights between the Korean and the other populations of P. manchouricus, and between this species and the other two bithyniids as well. The shell differences between the several populations of Korean P. manchouricus may be related to environment. Edtails of the chromosome cycle of these bithyniid snails are similar to those reported for other snails. No specific differences were observed in the chromosome cycle between the various species and populations of snails employed in this study. Reporred for the first time in molluscs are two darkly stained "nucleolar organizers" during pachyterne stages of meiosis. Two different chromosome numbers were observed in the three bithyniid species: n=17 in B. tentaculata and P. manchouricus, and n=18 in B. (G.) misella. no sex chromosomes or supernumerary chromosomes were seen. There were no morphological differences in karyotypes of three Korean strains of P. manchouricus. The infection rates of cercariae of Clonorchis sinensis in Chinju and Kunsan strains of P. manchouricus were 0.14% and 1.25%, respectively. However, Clonorchis cercariae were found in Chongpyung strain of P. manchouriceu and Gongju strain of B. (G.) misella. The habitats of P. manchouricus around Jinyang Lake were relatively clean without any heavy pollution of aquatic microorganisms and organic materials during the period of this study. The levels of dissolved oxygen (D.O.) and biochemical oxygen demand (B.O.D.) of the water specimens sampled from the study areas ranged from 6.0 to 9.6 ppm and from 0.4 to 1.6 ppm, respectively. Eight metalic constituents from the water samples were also assayed, and all metalic ions detercted were remarkably low below the legal criteria. However, calcium ion in the water samples from the habitats of P. manchouricus was considerably higher than others.

• Korean Journal of Weed Science
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• v.15 no.4
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• pp.254-261
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• 1995

The nationwide weed survey was conducted in lowland rice fields over whole country of Korea in 1992 in order to determine a change of weed community and to identify a major dominant weed species and/or problem weed. Based on morphological characteristics of weeds, population ratio of broad leaf weed was 42.6%, grasses weed-9.0%, sedges-33.4% and others were 15.0%. Annual weed was 33.4% while perennial weed was 66.6% in terms of life cycle of weeds. Meanwhile, there was different weed occurrence as affected by planting method of the rice plant. In hand transplanted paddy fields predominant weed species was Sagittaria trifolia L., Monochoria vaginalis Presl., and Aneilema japonica Kunth. In machine transplanted rice fields of infant and young rice seedling Eleocharis kuroguwai Ohwi. and S. trifolia L. were more predominant. There was high occurrence of M. vaginalis, Echinochloa crus-galli L., and Leesia japonica Makino in water seeding while E. crus-galli and Cyperus serotinus Rottb. were predominant weed species in dry seeded rice. Monoculture of the rice plant would cause to high occurrence of E. kuroguwai, S. trifolia, M. vaginalis, E. crus-galli, and Sagittaria pygmaea Miq and there was higher population of S. trifolia, S. pygmaea, M. vaginalis, E crus-galli, and E. kuroguwai in double cropping system based on rice culture. In particular, there was high different weed occurrence under different transplanting times. E. kuroguwai, S. trifolia, S. pygmaea, M. vaginalis, and C. serotinus were higher population at the transplanting of 25 May and S. trifolia, E crus-galli, C. serotinus, and M. vaginalis at 10 June and S. pygmaea, E. kuroguwai, M. vaginalis, S. trifolia, and E. crusgalli at 25 June in Korea, respectively. Autumn tillage in terms of tillage time would cause more predominant weed species such as S. trifolia, E. kuroguwai, M. vaginalis, and S. pygmaea while spring tillage was higher population of E. kuroguwai, S. trifolia, E. crusgalli, M. vaginalis, and S. pygmaea. In plain area of paddy field there was higher occurrence of E. kuroguwai, S. trifolia, M. vaginalis, E. crus-galli, and S. pygmaea and in mid-mountainous area S. trifolia, E. kuroguwai, M. vaginalis, E. crus-galli, and Ludwigia prostrate Roxb. while in mountainous area S. trifolia, M. vaginalis, Potamogeton distinctus Ben., E. kuroguwai, and E. crus-galli were. In 1992 the most ten predominant weed species at the rice field of Korea based on summed dominant ratio(SDR) were E. kuroguwai > S. trifolia > E. crus-galli > M. vaginalis > S. pygmaea > C. serotinus > L. prostrate > P. distinctus > A. japonica > Scirpus juncoides Roxb.