• The Transactions of the Korean Institute of Electrical Engineers D
• /
• v.51 no.12
• /
• pp.577-582
• /
• 2002

The objective of this paper is to produce a weighted graph map for path-planning of an autonomous mobile robot(AMR) based on the measurements from a single ultrasonic sensor, which are acquired when the autonomous mobile robot explores unknown indoor circumstance. The AMR navigates in th unknown space by following the wall and gathers the range data using the ultrasonic sensor, from which the occupancy grid map is constructed by associating the range data with occupancy certainties. Then, the occupancy grid map is converted to a weighted graph map suing morphological image processing and thinning algorithms. the path- planning for autonomous navigation of a mobile robot can be carried out based on the occupancy grid map. These procedures are implemented and tested using an AMR, and primary results are presented in this paper.

• 제어로봇시스템학회:학술대회논문집
• /
• 2001.10a
• /
• pp.138.4-138
• /
• 2001

The purpose of this research is to build a quality-improved occupancy grid map for path-planning of an autonomous mobile robot(AMR) based on the measurements from a single ultrasonic sensor, which are acquired when the autonomous mobile robot explores unknown indoor environment. The AMR navigates in the unknown space by following the wall and gathers the range data using the ultrasonic sensor, from which the occupancy grid map is constructed by associating the range data with occupancy certainties. In order to increase the quality of the map we modify the Bayesian probability updating rule, reject non-systematic measurement errors and correct the predictable error of the AMR itself. These procedures are implemented and tested using an AMR, and primary results are presented in this paper.

• Journal of the Korea Society for Simulation
• /
• v.9 no.4
• /
• pp.1-10
• /
• 2000

One of the primary goals of the simulation experiments is to understand the overall system behavior and to analyze the system, ultimately to optimize the system. Optimizing the system includes determining the optimum condition of the system parameters of interest. This paper is concerned with the simulation methodology for estimating the unknown objective function for the system of interest and optimizing the system with respect to the controllable factors. In the process of estimating the unknown objective function, which is assumed to be a second order spline function, we use common random numbers for different set of the controllable factors resulting in more accurate parameter estimation for the objective function. We will show some mathematical result for the benefit of using common random numbers.

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

• Journal of Information Processing Systems
• /
• v.8 no.3
• /
• pp.471-482
• /
• 2012

For disaster exploration and surveillance application, this paper aims to present a novel application of a multi-robot agent based on WSN and to evaluate a multi-hop communication caused by the robotics correspondingly, which are used in the uncertain and unknown subterranean tunnel. A Primary-Scout Multi-Robot System (PS-MRS) was proposed. A chain topology in a subterranean environment was implemented using a trimmed ZigBee2006 protocol stack to build the multi-hop communication network. The ZigBee IC-CC2530 modular circuit was adapted by mounting it on the PS-MRS. A physical experiment based on the strategy of PS-MRS was used in this paper to evaluate the efficiency of multi-hop communication and to realize the delivery of data packets in an unknown and uncertain underground laboratory environment.

• Journal of Communications and Networks
• /
• v.17 no.4
• /
• pp.406-418
• /
• 2015

Cognitive radio networks (CRNs) have emerged as a promising solution to the problem of spectrum under utilization and artificial radio spectrum scarcity. The paradigm of dynamic spectrum access allows a secondary network comprising of secondary users (SUs) to coexist with a primary network comprising of licensed primary users (PUs) subject to the condition that SUs do not cause any interference to the primary network. Since it is necessary for SUs to avoid any interference to the primary network, PU activity precludes attempts of SUs to access the licensed spectrum and forces frequent channel switching for SUs. This dynamic nature of CRNs, coupled with the possibility that an SU may not share a common channel with all its neighbors, makes the task of multicast routing especially challenging. In this work, we have proposed a novel multipath on-demand multicast routing protocol for CRNs. The approach of multipath routing, although commonly used in unicast routing, has not been explored for multicasting earlier. Motivated by the fact that CRNs have highly dynamic conditions, whose parameters are often unknown, the multicast routing problem is modeled in the reinforcement learning based framework of learning automata. Simulation results demonstrate that the approach of multipath multicasting is feasible, with our proposed protocol showing a superior performance to a baseline state-of-the-art CRN multicasting protocol.

• English Language & Literature Teaching
• /
• v.16 no.3
• /
• pp.161-182
• /
• 2010

The goals of this study were to identify differences in learners' and teachers' perspectives on EFL learners' language anxiety, to identify the differences among teachers coping with learners' language anxiety, and to find how learners cope with their language anxiety. The research was effectuated by means of a survey questionnaire and interviews. The data were collected from 92 teachers and 230 students in four different school settings. There were the $6^{th}$ grade 50 primary school learners, the $2^{nd}$ grade 60 middle school learners, the $11^{th}$ grade 60 high school learners of, and the $2^{nd}$ and $3^{rd}$ grade 60 university learners. There were also 26 primary school teachers, 22 middle school teachers, 21 high school teachers, and 23 university teachers. The findings reveal that there were differences in responses among the respondents. The findings suggest that teachers need to pay attention to their particular learners' anxiety sources: especially in the case of primary school setting, the activity of answering teachers' questions for teachers was the primary source of learner's anxiety, in the case of middle school settings, translating sentences in English into Korean, in the case of high school setting, checking unknown vocabulary, and in the case of university settings, university learners felt anxious when classmates spoke fluently. The implications of the study indicate that these aspects should be handled carefully to motivate certain group of learners.

• The Korean Journal of Cytopathology
• /
• v.9 no.1
• /
• pp.21-28
• /
• 1998

Cytologic evaluation of cerebrospinal fluid(CSF) is an effective tool in diagnosing many disorders involving the central nervous system(CNS). CSF examination has been found to be of particular value in the diagnosis of metastatic carcinoma, lymphomatous or leukemic involvement of CNS and certain primary CNS tumors. As a survey of metastatic tumors to CSF and an evaluation of the preparation techniques increasing cellular yield in our laboratory, 713 CSF specimens examined between July 1995 and April 1997(1 year 10 months), were reviewed. There were 75 positive and 5 suspicious cases, the latter have had no evidence of tumors clinically. Primary tumors of 75 positive cases were classified as follows; 4(5.3%) as primary brain tumors, 40(53.3%) as secondary carcinomas, 13(17.3%) as leukemias, and 18 (24.0%) as lymphomas. The most common primary site of metastatic carcinomas was the lung in 17 cases(42.5%) followed by the stomach in 13(32.5%), breast in 8 (20.0%), and unknown primary in 2(5.0%). Four primary brain tumors were 3 cerebellar medulloblastomas and a supratentorial primitive neuroectodermal tumor (PNET). All 40 metastatic carcinomas were adenocarcinoma presented as single cells or cell clusters. Although signet ring cells were frequent in the cases of gastric primary cancers, no significant cytologic differences according to the primary site were observed. The cytologic features of leukemia and lymphoma were characterized by hypercellular smears presenting as individual atypical cells with increased N/C ratio, presence of nucleoli, and nuclear protrusions. In medulloblastomas and PNET, the principal cytologic findings were small undifferentiated cells arranged singly or in loose clusters with occasional rosettoid features. This study suggests that the CSF cytology is useful in the diagnosis of malignancy, especially metastatic extracranial tumors and the diagnostic accuracy can be improved by increasing cellular yield using cytocentrifuge.

• Journal of Korean Society of Occupational and Environmental Hygiene
• /
• v.29 no.3
• /
• pp.271-277
• /
• 2019

Objectives: A 46-year-old woman who had worked on cleaning stainless steel containers with Initially unknown powders died from acute silicosis. To determine whether the acute silicosis was related to his work environment, we conducted exposure assessment the level of exposure to respirable crystalline silica(RCS) during cleaning stainless steel containers with unknown powders. Methods: The exposure assessment of RCS were undertaken according to the National Institute for Occupational Safety and Health(NIOSH) method 7500. The components of the unknown powder were analyzed using X-ray Diffraction. Results: The unknown powder was found to be natural diatomaceous earth, which contained 12% and 9% quartz and cristobalite, respectively, crystalline silica. In the case of cleaning stainless steel containers with diatomaceous earth powder, the primary measurement resulted in 1.3 times higher occupational exposure limit of MOEL(in sum of quartz and cristobalite concentration) and 3.9 times higher in secondary measurement. The workbench was equipped with a local exhaust system, but because there was no hood at the end of the duct, the wind speed at the opening of the duct was 12 m/sec, whereas the controlled wind speed at the working position was only 0.3 m/sec below the legal standard. Conclusions: There is an urgent need to install the hood, conduct safety and health education for employers and workers, and periodically monitoring and manage the working environment.

• Korean Journal of Head & Neck Oncology
• /
• v.11 no.1
• /
• pp.100-105
• /
• 1995