• Communications for Statistical Applications and Methods
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• v.23 no.1
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• pp.1-20
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• 2016

Causal inference methodologies have been developed for the past decade to estimate the unconfounded effect of an exposure under several key assumptions. These assumptions include, but are not limited to, the stable unit treatment value assumption, the strong ignorability of treatment assignment assumption, and the assumption that propensity scores be bounded away from zero and one (the positivity assumption). Of these assumptions, the first two have received much attention in the literature. Yet the positivity assumption has been recently discussed in only a few papers. Propensity scores of zero or one are indicative of deterministic exposure so that causal effects cannot be defined for these subjects. Therefore, these subjects need to be removed because no comparable comparison groups can be found for such subjects. In this paper, using currently available causal inference methods, we evaluate the effect of arbitrary cutoffs in the distribution of propensity scores and the impact of those decisions on bias and efficiency. We propose a tree-based method that performs well in terms of bias reduction when the definition of positivity is based on a single confounder. This tree-based method can be easily implemented using the statistical software program, R. R code for the studies is available online.

• Journal of Digital Contents Society
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• v.18 no.1
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• pp.191-195
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• 2017

In this study, a smartphone application for reporting trees infected with pine wilt disease was developed to prevent the spread of the disease by the disease-carrying pests/insects, which is most damning to the country's pine trees, South Korea's representative tree species, and to ensure the sustained maintenance of the country's forest trees. Such application for handling information on the infected pine trees has three key components, as shown below. (1) Explanation of the pine wilt disease pests/insects, (2) Image capture of the infected pine tree, and transmission of its GPS location, (3) Inquiry on the neighboring area infected with pine wilt disease. It is possible to promptly provide the spatial information of the areas infected with pine wilt disease by developing a dedicated application for reporting trees infected with the disease based on GPS information. If users participate actively in the application and integration with the forest service application is to be realized, the application would be more actively utilized.

• Journal of the Korea Society of Computer and Information
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• v.12 no.5
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• pp.1-10
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• 2007

Many types of information provided through the web including news contents contain unnecessary clutters. These clutters make it difficult to build automated information processing systems such as the summarization, extraction and retrieval of documents. We propose a system that extracts and summarizes news contents from the web. The extraction system receives news contents in HTML as input and builds an element tree similar to DOM tree, and extracts texts while removing clutters with the hyperlink attribute in the HTML tag from the element tree. Texts extracted through the extraction system are transferred to the summarization system, which extracts key sentences from the texts. We implement the summarization system using co-occurrence relation graph. The summarized sentences of this paper are expected to be transmissible to PDA or cellular phone by message services such as SMS.

• The Transactions of the Korea Information Processing Society
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• v.6 no.9
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• pp.2332-2342
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• 1999

Multicast is an important system-level one-to-many collective communication service. A key issue in designing software multicast algorithms is to consider the trade-off between performance and portability. Based on the LogP model, the proposed parameterized communication model can more accurately characterize the communication network of parallel platforms, Under the parameterized model, we propose an efficient architecture-independent method. OPT-tree algorithm, to construct optimal multicast trees and also investigate architecture-dependent tuning on performance of the multicast algorithm to achieve the truly optimal performance when implemented in real networks. Specifically, OPT-mesh which is the optimized version of the parameterized multicast algorithm for wormhole-switched mesh networks is developed and compared with two other well-known network-dependent algorithms.

• Nuclear Engineering and Technology
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• v.55 no.5
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• pp.1901-1910
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• 2023

The safety-class (1E) digital control system (DCS) of nuclear power plant characterized structural multiple redundancies, therefore, it is important to quantitatively evaluate the reliability of DCS in different degree of backup loss. In this paper, a reliability evaluation model based on T-S fuzzy fault tree (FT) is proposed for 1E DCS of nuclear power plant, in which the connection relationship between components is described by T-S fuzzy gates. Specifically, an output rejection control system is chosen as an example, based on the T-S fuzzy FT model, the key indicators such as probabilistic importance are calculated, and for a further discussion, the T-S fuzzy FT model is transformed into Bayesian Network(BN) equivalently, and the fault diagnosis based on probabilistic analysis is accomplished. Combined with the analysis of actual objects, the effectiveness of proposed method is proved.

• The KIPS Transactions:PartD
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• v.15D no.6
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• pp.755-766
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• 2008

Recently, NAND flash memory is becoming into the spotlight as a next-generation storage device because of its small size, fast speed, low power consumption, and etc. compared to the hard disk. However, due to the distinct characteristics such as erase-before-write architecture, asymmetric operation speed and unit, disk-based systems and applications may result in severe performance degradation when directly implementing them on NAND flash memory. Especially when a B-tree is implemented on NAND flash memory, intensive overwrite operations may be caused by record inserting, deleting, and reorganizing. These may result in severe performance degradation. Although ${\mu}$-tree has been proposed in order to overcome this problem, it suffers from frequent node split and rapid increment of its height. In this paper, we propose Log-Structured B-Tree(LSB-Tree) where the corresponding log node to a leaf node is allocated for update operation and then the modified data in the log node is stored at only one write operation. LSB-tree reduces additional write operations by deferring the change of parent nodes. Also, it reduces the write operation by switching a log node to a new leaf node when inserting the data sequentially by the key order. Finally, we show that LSB-tree yields a better performance on NAND flash memory by comparing it to ${\mu}$-tree through various experiments.

• Journal of the Korea Computer Industry Society
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• v.3 no.9
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• pp.1235-1244
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• 2002

This paper proposes a group key management protocol for a secure of all the multicast user in PIM-SM multicast group communication. With prosed architect, subgroups for multicast secure group management will be divided by RP (Rendezvous-Point) unit and each RP has a subgroup manager. Each subgroup manager gives a secure key to it's own transmitter md the transmitter compress the data with it's own secure key from the subgroup manager. Before the transmitter send the data to receiver, the transmitter prepare to encrypt a user's service by sending a encryption key to the receiver though the secure channel, after choking the user's validity through the secure channel. As the transmitter sending a data after then, the architecture is designed that the receiver will decode the received data with the transmitter's group key. As a result, the transmitting time is shortened because there is no need to data translation by group key on data sending and the data transmition is possible without new key distribution at path change to SPT (Shortest Path Tree) of the router characteristic. Additionally, the whole architecture size is samller than the other multicast secure architecture by using the conventional PIM-SIM routing structure without any additional equipment.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.13 no.5
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• pp.3-15
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• 2003

The secure group communication enables the members, which belong to the same group, to communicate each other in a secure and secret manner. To do so, it is the most important that a group key is securely distributed among them and also group membership is efficiently managed. In detail, the generation, the distribution and the refreshment of a group key would be highly regarded in terms of low communication and computation complexity. In this paper, we show you a new protocol to generate a group key which will be safely shared within a group, utilizing the 2-party Diffie-Hellman key exchange protocol and the complete binary tree. Our protocol has less complexity of computation per group member by substituting many parts of exponentiation computations for multiplications. Consequently, each group member needs constant computations of exponentiation and multiplication regardless of the group size in the protocol and then it has less complexity of the computation than that of any other protocols.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.4
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• pp.1911-1930
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• 2017

Overlay routing has emerged as a promising approach to improve reliability and efficiency of the Internet. The key to overlay routing is the placement and maintenance of the overlay infrastructure, especially, the selection and placement of key relay nodes. Spurred by the observation that a few relay nodes with high betweenness centrality can provide more optimal routes for a large number of node pairs, we propose a resilient routing overlay network construction method by introducing Super-Relay nodes. In detail, we present the K-Minimum Spanning Tree with Super-Relay nodes algorithm (SR-KMST), in which we focus on the selection and connection of Super-Relay nodes to optimize the routing quality in a resilient and scalable manner. For the simultaneous path failures between the default physical path and the overlay backup path, we also address the selection of recovery path. The objective is to select a proper one-hop recovery path with minimum cost in path probing and measurement. Simulations based on a real ISP network and a synthetic Internet topology show that our approach can provide high-quality overlay routing service, while achieving good robustness.

• Journal of the Korean Society for Railway
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• v.9 no.3 s.34
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• pp.264-270
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• 2006

In this paper we present a safety plan to be applied to the development of the TCS(Train Control System). The safety plan that can be applied to the life cycle of a system, from the conceptual design to the dismantlement, shows the whole process of the paper work in detail through the establishment of a goal, analysis and assessment, the verification. In this paper we study about the making a plan, the preliminary hazard analysis, the hazard identification and analysis to guarantee the safety of the TCS. The process far the verification of the system safety is divided into several steps based on the target system and the approaching method. The guarantee of the system safety and the improvement of the system reliability is fellowed by the recommendation of the international standards.