• Journal of the Korea Society of Computer and Information
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• v.22 no.11
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• pp.97-104
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• 2017

Location prediction has been successfully utilized to provide high quality of location-based services to customers in many applications. In its usual form, the conventional type of location prediction is to predict future locations based on user's past movement history. However, as location prediction needs are expanded into much complicated cases, it becomes necessary quite frequently to make inference on the locations that target user visited in the past. Typical cases include the identification of locations that infectious disease carriers may have visited before, and crime suspects may have dropped by on a certain day at a specific time-band. Therefore, primary goal of this study is to predict locations that users visited in the past. Information used for this purpose include user's demographic information and movement histories. Data mining classifiers such as Bayesian network, neural network, support vector machine, decision tree were adopted to analyze 6868 contextual dataset and compare classifiers' performance. Results show that general Bayesian network is the most robust classifier.

• Current Optics and Photonics
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• v.1 no.5
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• pp.440-455
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• 2017

In this paper, we carry out a performance analysis of a two-user free-space optical (FSO) communication system with photodetector multiplexing, in which the two users are defined as the primary user (PU) and secondary user (SU). Unlike common single-user FSO systems, our photodetector multiplexing FSO system deploys a shared detector at the receiver and enables PU and SU to send their own data synchronously. We conduct the performance analysis of this FSO system for two cases: (1) in the absence of background radiation, and (2) in the presence of background radiation. Decision strategies for PU and SU are presented according to the two scenarios above. Exact and approximate conditional symbol-error probability (SEP) expressions for both PU and SU are derived, in an ideal channel with no fading. Average SEP expressions are also presented in the no-background-radiation scenario. Additionally, in some particular cases where the power ratio tends to 0.5 or 1, approximate SEP expressions are also obtained. Finally, numerical simulations are presented under different conditions, to support the performance analysis.

• ETRI Journal
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• v.33 no.2
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• pp.283-286
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• 2011

Path loss plays fundamental roles in system design, spectrum management, and performance evaluation. The traditional path loss model has a slight inconvenience; it depends on the unknown distance. In this letter, we explore the probability distribution function (PDF) of path loss in an indoor office environment by randomizing out the distance variable. It is shown that the resulting PDF is not Gaussian-like but is skewed to the right, and both the PDF and the moments are related to the size of the office instead of the unknown distance. To be specific, we incorporate the IEEE 802.15.4a channel parameters into our model and tabulate the cumulative distribution function with respect to different room sizes. Through a simple example, we show how our model helps a cognitive spectrum user to infer path loss information of primary users without necessarily knowing their transmitter-receiver distance.

• The Journal of Information Systems
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• v.16 no.3
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• pp.133-159
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• 2007

The primary purpose of this study is to examine the effects of perceived characteristics on user satisfaction and continuous usage intention in personal communities. We developed a research model based on the literature reviews of personal communities, TAM, perceived risks, and satisfaction. The research model includes perceived playfulness, perceived ease of use, perceived usefulness, and perceived risk as perceived characteristics in personal communities. For validation of this theoretical model, we survey the users of 'Mini-hompy', one of the most popular personal communities in Korea. The research model was empirically verified by structural equation model analysis with data collected from 407 samples. Analysis of the results indicates that perceived ease of use is positively related perceived playfulness and perceived usefulness. Perceived playfulness, perceived ease of use, and perceived risks are significantly related to satisfaction. User's satisfaction has positive relationship with continuous usage intention in personal communities.

• Proceedings of the Korean Reliability Society Conference
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• 2006.05a
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• pp.158-164
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• 2006

The creep behavior of newly developed composite geogrids which consists of PET yarns sheathed in PP were evaluated using SIM. For the SIM procedure, three test parameters, the applied loads, temperature steps and number of ribs were investigated, The study confirmed that temperature steps of 10 and 14$^{\circ}C$ up to 80$^{\circ}C$ are applicable for composite geogrids due to the different transition temperatures between two materials. At applied loads of 40 and 50%, only primary creep state was measured, while secondary creep state appeared at the applied loads of 60%, The lifetimes of composite geogrids were estimated at each of loading level using statistical reliability analysis technique. The results show that the lifetimes longer than 100 years can be predicted within 16 hours. Therefore, SIM is very effective and economical accelerated creep test methods, especially for lifetime prediction. This gives guidelines for users to select the appropriate factor of safety against creep considering the field condition within shorter test times.

• Journal of Communications and Networks
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• v.15 no.6
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• pp.576-580
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• 2013

In this paper, we investigate the capacity of a multipoint-to-point cognitive radio network. In existing works, the asymptotic capacity is only obtained in the high peak power region at secondary transmitter (ST) or obtained without considering the interference from primary transmitter (PT) for easy analysis. Here, we analyze the asymptotic capacity by considering an arbitrary peak power at the ST and the interference from the PT based on extreme value theory. Simulation results show that our approximated capacity is well-matched to the exact capacity. Furthermore, the scaling law of our capacity is found to be double logarithm of the number of secondary users.

• Journal of electromagnetic engineering and science
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• v.12 no.2
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• pp.148-154
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• 2012

In this paper, we propose an algorithm to conserve resources of the common control channel in a cognitive radio network by rejecting the redundant users using cooperative spectrum sensing. The proposed scheme is investigated under the paradigm of active spectrum sensing and a sequential detection technique. The algorithm is based on the J-divergence between the hypotheses of non primary user operation and the otherwise case. We select the most significant eigenvalues, which primarily affect the global statistical test. For the case where interference is from a secondary system transmission, a match filter is first employed to remove the degradation, and then the proposed algorithm is employed to remove the cooperative sensing nodes. Numerical results are provided and compared with conventional cases in order to validate the performance of the proposed algorithm.

• Journal of Information Technology Applications and Management
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• v.17 no.2
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• pp.175-185
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• 2010

The primary objective of this paper is to examine post acceptance behavior model in UCC services. Based on the relevant literature reviews, this study posits six characteristics, that is, expectation confirmation, perceived usefulness, perceived enjoyment, satisfaction, and continuance intention as key variables to describe the post acceptance behavior model in UCC services. Then we constructed a research model and hypotheses about relationship between these variables. A total 286 usable survey responses of UCC service users have been employed in the analysis. The empirical results of this study are summarized as follows. Firstly, expectation confirmation has a positive effect on the perceived usefulness, perceived enjoyment, and satisfaction. Secondly, perceived enjoyment has a positive effect on the satisfaction. Lastly, perceived usefulness, perceived enjoyment, and satisfaction have a positive effect on the continuance intention. These results will be helpful for the UCC services sector to further develop service delivery strategies for strengthening the ongoing relationship with customers. Finally, some possible limits of the present research and future directions for such research were discussed.

• Journal of the Korean Society of Safety
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• v.24 no.1
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• pp.43-49
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• 2009

The primary focus of this study is to develop a practical safety management manual that can be served as a guideline for building deconstruction works over the entire deconstruction processes; say, pre- and during the deconstruction process. Built upon the analysis findings of domestic deconstruction codes and laws, deconstruction manuals from several countries, and actual deconstruction practices, a safety manual is proposed. Total of 940 safety items are included in the manual according to the predetermined 15 safety categories. To improve the efficiency of end users' utilization, the proposed manual is embodied in the form of e-safety manual. Detailed descriptions and discussions on research findings are elaborated. in the main text.

• Proceedings of the Korean Society of Toxicology Conference
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• 2002.11b
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• pp.195-195
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• 2002

In recent years, the safety of sunscreens has been challenged based on the reports of its adverse effect on users; dermatitis, allergic contact dermatitis, photoallergic contact dermatitis. To investigate a correlation between sun protection factor (SPF) and the safety of sunscreens, we measured in vitro SPF index using homosalate as a standard and examined the toxicity tests on cosmetics; primary skin irritation tests, ocular irritation test, and skin sensitization test.(omitted)