• Transactions of the Korean Society of Mechanical Engineers
• /
• v.18 no.12
• /
• pp.3326-3334
• /
• 1994

To theoretically predict knock occurrence in S. I. engine as a function of engine design and operating parameters, transient local temperature and pressure, mixture density of flame front in combustion period are calculated. We next determined normal combustion period and auto ignition period of end gas using the prediction method on occurrence of spark knock which we suggested. We predict knock occurrence in S. I. engine by comparing consecutively normal combustion period with the auto ignition period of end gas in combustion period. Engine design and operating parameters such as compression ratio, engine speed, spark timing, inlet temperature and pressure are taken into account in this calculations. The predicted result are well matched with the experimental results in turbocharged engine. Therefore, this method will provide the systematic guideline for designing engines in view of knocking limits.

• Journal of Forest and Environmental Science
• /
• v.32 no.2
• /
• pp.149-157
• /
• 2016

Understanding regional characteristics in forest fire occurrence is important to establish effective forest fire prevention policy in Korea. This study analyzed the characteristics of forest fires occurred in 16 administrative districts for recent 25 years (1990~2014) to examine regional characteristics in forest fire occurrence. Forest fire occurrence reflects regional characteristics depending on climatic factors as well as region's society-cultural factors. Results showed that the first cause of forest fire occurrence was carelessness by human activities throughout all administrative districts, however, the second cause depends on regional characteristics. As the results of forest fire occurrence period analyzed for 10 days, the most forest fires occurred in the southern region during January to March, while forest fires in the northern region occurred mostly during March to April. We classified forest fire occurrence patterns into three types (centralized: Gyeonggi-do, dispersal: Busan, horizontally distributed: Gyeongsangnam-do) by multi-temporal analysis for forest fire occurrence period.

• Proceedings of the Korean Institute of Building Construction Conference
• /
• 2022.04a
• /
• pp.29-30
• /
• 2022

Tile defects in apartment houses are caused by a combination of various factors. These factors cannot be specified, and it is difficult to determine the exact cause because a number of causes are intertwined. In addition, because the climate of Korea is different by season, the coefficient of thermal expansion between materials is different, which is a major cause of tile defects. Therefore, this study analyzed the difference between the construction location and the period of defect occurrence according to the types of tile defects caused by environmental differences between indoor and outdoor environments. Two-way ANOVA was used, indoor and outdoor spaces were selected, and defect types were selected accordingly to show the difference in the occurrence period of each defect.

• Proceedings of the Korean Institute of Building Construction Conference
• /
• 2022.11a
• /
• pp.67-68
• /
• 2022

The area inside the apartment building where tiles are installed is applied as a finishing material for walls and floors, including exterior walls, balconies, hallways, bathrooms, and kitchens. As it is constructed in various spaces, differences in the type and period of occurrence of tile defects may appear, which is caused by heterogeneous characteristics between materials and external causes. Therefore, in this study, two-way ANOVA was used to figure out the relationship between the defect occurrence type and the period depending on the type of tile construction in the apartment building.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2004.05b
• /
• pp.479-483
• /
• 2004

A new calculation method of expected overtopping probability of rubble mound breakwater considering real tide occurrence has been proposed. A calculation method of expected overtopping probability of rubble mound breakwater was proposed by Kweon and Suh (2003). In their calculation, the fluctuation of tidal elevation was expressed by the sinusoidal change that yields the uniform distribution of occurrence frequency. However, the realistic distribution of tidal elevation should influence on the overtopping chance. In this study, the occurrence frequency of tidal elevation obtained from the real sea is included. The tidal elevation used in this study is collected from the east coastal part of Korean peninsular. Analyzing the annual data of the tidal fluctuation measured hourly during 355 days, the distribution of occurrence frequency is formulated utilizing by the normal distribution with one peak. Among the calculation procedures of annual maximum wave height, wave height-period joint distribution, wave run-up height and occurrence frequency of tide, only the annual maximum wave height is again chosen randomly from normal distribution to consider the uncertainty. The others are treated by utilizing the distribution function or relationship itself, It is found that the inclusion of the variability of tidal elevation has great influence on the computation of the expected overtopping probability of rubble mound breakwater. The bigger standard deviation of occurrence frequency is, the lower the overtopping probability of rubble mound breakwater is.

• Atmosphere
• /
• v.18 no.4
• /
• pp.493-506
• /
• 2008

In order to examine the variational features of Asian dust outbreak in recent years, observed WMO synop data were employed for the period from 1996 to 2007. We first divided Asian dust source regions into four subregions; 1) Taklamakan, 2) Gobi, 3) Inner Mongolia-Manchuria and 4) Loess, and the meteorogical variables such as wind speed, precipitation and threshold wind speed observed during the Asian dust outbreak period were compared with those during non-Asian dust period. The results showed that temporal variation of occurrence frequency of dust outbreak had a strong positive correlation with the frequency of strong wind speed and low precipitation in each of the 4 source regions. Spatial distributions of frequency of dust occurrence after 2002 showed increasing trend in Gobi and Inner Mongolia-Manchuria but decreasing trend in Loess region. This is showing a shift in main source region toward Northwest, especially since 2003.

• Journal of the Korean Society of Hazard Mitigation
• /
• v.2 no.1 s.4
• /
• pp.161-167
• /
• 2002

Forest fire danger period in nine Provinces (Gangwondo, Kyonggido, Gyeongsangnamdo, Gyeongsangbukdo, Jeollanamdo, Jeollabukdo, Jejudo, Chungcheongnamdo, Chungcheongbukdo) has turned out to be similar to recognize whether there are some differences between each Provinces, we used correlation analysis with number of occurrence and damage area by an interval of ten-day period. Based on this analysis, there was significant numbers of occurrence at all areas wish serious burns except Gyeongsangnamdo and Jejudo Provinces. Since persuasive power is insufficient as danger period of forest fire applies equally to nine Provinces, statistical analysis using number of forest fire occurrence and burned area are executed. And then, a analysis of variance(ANOVA) test of significance by an interval of ten day period is carried out. As a result of this analysis, there showed significant at 1% level for number of occurrence except Jejudo, and is also showed significant at 1% level for burned area except Gangwondo and Chejudo. Through regional correlation analysis for danger period, we classified three parts of Middle region (Gangwondo, Kyonggido, Gyeongsangnamdo, Gyeongsangbukdo, Jeollabukdo, Chungcheongnamdo, Chungcheongbukdo) Southern region (Gyongsangnamdo, Jeollanamdo) and Jejudo region. With respect to forest fire occurrence time, Middle region showed from the middle of February to first of May that amounts to 81% of entire occurrence in this region, and Southern region begins with at the last of January to the middle of April covering 71%. In terms of forest fire burned areas, it appears at the middle of February to the first of May, occupying 98% in Middle region, and Southern region showed burned areas from the last of January to the middle of April amounting to 82% of total occurrences.

• The Journal of Korean Medical History
• /
• v.31 no.2
• /
• pp.41-52
• /
• 2018

In this study, we research the tendency of medical text publication by examining the period of the great measles outbreak and the period of the publication of specialized smallpox texts. Using the National Institute of Korean History database for the Annals of Joseon Dynasty, the Daily Records of Royal Secretariat of Joseon Dynasty and Bibyeonsadeunglok, we will compare all records of measles occurrence. Measles and smallpox (Majin in Korean) have similar symptoms and treatment methods. In East Asia, when measles occurred it spread to Joseon and Japan, which are verified by records of the Annals of Joseon Dynasty, the Daily Records of Royal Secretariat of Joseon Dynasty and Bibyeonsadeunglok. The medical books related to measles are; Ryuhasinbang, Majinpyeon, Geupyubang, Yimsinyeokbang, Eulmisinjeon, Majingbang, Jinyeokbang, Magwahoetong, Majingibang, Susengsingam, Hongjinsinbang. Measles and Majin are the same disease. During the period of measles occurrence, measles-related medical books were published, and this relation of measles occurrence and measles-related medical text publication is verified by several national records.

• Proceedings of the KSME Conference
• /
• 2007.05b
• /
• pp.3311-3316
• /
• 2007

To analyze the influence of valve overlap period on a backfire occurrence, the single cylinder research engine with MCVVT(Mechanical Continuous Variable Valve Timing) system is developed and backfire limit equivalence ratio defined as fuel-air ratio equivalence ratio at which backfire occurs is examined according to various valve overlap period. The MCVVT is the system to control valve overlap period by mechanical device. It is estimated that the lower valve overlap period has the higher backfire limit equivalence ratio though the same energy is supplied. When the valve overlap period is changed from 30$^{circ}$ CA to 0$^{circ}$ CA, backfire limit equivalence ratio is increased 74%, approximately. It means that valve overlap period is concern in backfire occurrence, and may be one of the methods for controlling back fire occurred in a $H_2$ engine.

• Journal of Intelligence and Information Systems
• /
• v.18 no.1
• /
• pp.23-38
• /
• 2012

There is a large difference between purchasing patterns in an online shopping mall and in an offline market. This difference may be caused mainly by the difference in accessibility of online and offline markets. It means that an interval between the initial purchasing decision and its realization appears to be relatively short in an online shopping mall, because a customer can make an order immediately. Because of the short interval between a purchasing decision and its realization, an online shopping mall transaction usually contains fewer items than that of an offline market. In an offline market, customers usually keep some items in mind and buy them all at once a few days after deciding to buy them, instead of buying each item individually and immediately. On the contrary, more than 70% of online shopping mall transactions contain only one item. This statistic implies that traditional data mining techniques cannot be directly applied to online market analysis, because hardly any association rules can survive with an acceptable level of Support because of too many Null Transactions. Most market basket analyses on online shopping mall transactions, therefore, have been performed by expanding the co-occurrence criteria of traditional association rule mining. While the traditional co-occurrence criteria defines items purchased in one transaction as concurrently purchased items, the expanded co-occurrence criteria regards items purchased by a customer during some predefined period (e.g., a day) as concurrently purchased items. In studies using expanded co-occurrence criteria, however, the criteria has been defined arbitrarily by researchers without any theoretical grounds or agreement. The lack of clear grounds of adopting a certain co-occurrence criteria degrades the reliability of the analytical results. Moreover, it is hard to derive new meaningful findings by combining the outcomes of previous individual studies. In this paper, we attempt to compare expanded co-occurrence criteria and propose a guideline for selecting an appropriate one. First of all, we compare the accuracy of association rules discovered according to various co-occurrence criteria. By doing this experiment we expect that we can provide a guideline for selecting appropriate co-occurrence criteria that corresponds to the purpose of the analysis. Additionally, we will perform similar experiments with several groups of customers that are segmented by each customer's average duration between orders. By this experiment, we attempt to discover the relationship between the optimal co-occurrence criteria and the customer's average duration between orders. Finally, by a series of experiments, we expect that we can provide basic guidelines for developing customized recommendation systems. Our experiments use a real dataset acquired from one of the largest internet shopping malls in Korea. We use 66,278 transactions of 3,847 customers conducted during the last two years. Overall results show that the accuracy of association rules of frequent shoppers (whose average duration between orders is relatively short) is higher than that of causal shoppers. In addition we discover that with frequent shoppers, the accuracy of association rules appears very high when the co-occurrence criteria of the training set corresponds to the validation set (i.e., target set). It implies that the co-occurrence criteria of frequent shoppers should be set according to the application purpose period. For example, an analyzer should use a day as a co-occurrence criterion if he/she wants to offer a coupon valid only for a day to potential customers who will use the coupon. On the contrary, an analyzer should use a month as a co-occurrence criterion if he/she wants to publish a coupon book that can be used for a month. In the case of causal shoppers, the accuracy of association rules appears to not be affected by the period of the application purposes. The accuracy of the causal shoppers' association rules becomes higher when the longer co-occurrence criterion has been adopted. It implies that an analyzer has to set the co-occurrence criterion for as long as possible, regardless of the application purpose period.