• Honam Mathematical Journal
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• v.31 no.2
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• pp.177-183
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• 2009

In this article, we study ruled surfaces in a Lorentzian space-time, which have finite type immersion. We give a condition for bi-finite type surfaces to be of finite type.

• Korean Institute of Interior Design Journal
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• v.26 no.3
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• pp.45-54
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• 2017

A social phenomenon that occurs in a physical space is said to be a complex system. However, space syntax, which is commonly employed by researchers to identify such social phenomena, has various limitations in interpreting their complexity. On the other hand, agent-based modeling considers a variety of factors including the personality of the agent, objective-oriented work flows, estimation according to time flows and better prediction of space use through diverse parameters depending the situation, as well as the characteristics of the space. The agent-based method thus has the potentials to be developed as an alternative to space syntax techniques. In particular, discrete event driven simulation(DEVS), which is part of the agent-based modeling method, embraces the concept of networks just like space syntax, which allows a possible theoretical linkage in the future. This study suggests a procedural model of agent-based DEVS reflecting two different connection methods, i.e. connections between adjacent areas and those of the entire space, and attempts to identify the relationship between the local and regional indices of space syntax. A number of spaces were selected as examples-one for a preliminary experiment and eight modified for the main experiment-and space syntax and DEVS were applied to each of them. The comparative analysis of the results led to the conclusions as follows: 1) Adjacent connections were closely related to local indices, while the whole-space approach to regional indices. Local integration shows both characteristics. 2) Observation of the time flow model indicated a faster convergence with the range of 1 to 3-fold of the total time of one lap, with the error of less than 10%. 3) The heat map analysis showed more obvious characteristics of using the space for the entire space rather than adjacent connections. 4) Space syntax shows higher eligibility than ABM.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.9
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• pp.2022-2028
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• 2015

SpaceWire is a standard for high-speed links and networks between spacecraft components, which was invented for better, cheaper and faster on-board data handling in spacecraft. The standard defines timecode and its distribution which can be used for time synchronization among the nodes in a SpaceWire network. A timecode output from the time master which provides standard time over a SpaceWire network travels through links and routers to reach every nodes. While traveling, a timecode suffers from transmission delay and jitter which cause some difference in time synchronization among nodes. In this work, a simulator was developed using OMNeT++ to simulate the operation of a SpaceWire network and some analyses were performed on the transmission delay and jitter accompanied with a transmission of a timecode. The result will be used in the near future for the research of a precise time synchronization technique over a SpaceWire network.

• Journal of Astronomy and Space Sciences
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• v.37 no.1
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• pp.43-50
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• 2020

We have developed an algorithm for tracking coronal mass ejection (CME) propagation that allows us to estimate CME speed and its arrival time at Earth. The algorithm may be used either to forecast the CME's arrival on the day of the forecast or to update the CME tracking information for the next day's forecast. In our case study, we successfully tracked CME propagation using the algorithm based on g-values of interplanetary scintillation (IPS) observation provided by the Institute for Space-Earth Environmental Research (ISEE). We were able to forecast the arrival time (Δt = 0.30 h) and speed (Δv = 20 km/s) of a CME event on October 2, 2000. From the CME-interplanetary CME (ICME) pairs provided by Cane & Richardson (2003), we selected 50 events to evaluate the algorithm's forecast capability. Average errors for arrival time and speed were 11.14 h and 310 km/s, respectively. Results demonstrated that g-values obtained continuously from any single station observation were able to be used as a proxy for CME speed. Therefore, our algorithm may give stable daily forecasts of CME position and speed during propagation in the region of 0.2-1 AU using the IPS g-values, even if IPS velocity observations are insufficient. We expect that this algorithm may be widely accepted for use in space weather forecasting in the near future.

• Restorative Dentistry and Endodontics
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• v.19 no.2
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• pp.611-620
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• 1994

The purpose of this study was to evaluate the effect of post space preparation on apical sealing according to the methods and time of gutta percha removal. Forty six extracted single rooted teeth were selected for this study. Forty teeth were used as experimental groups and six teeth as control groups. Forty teeth were routinely prepared by step-back method and obturated with gutta percha cones and zinc oxide-eugenol cement using lateral condensation. All obturated teeth were divided into 4 groups of 10 teeth each. In each group of 1, 2, 3, heated plugger, gate glidden drill and chloroform and K-file were used respectively for post space preparation by removing the gutta percha immediately after obturation. In group 4, post space were prepared with gate glidden drill one week after obturation. In all experimental groups, the post space were prepared so that 4mm of apical gutta percha remained. After post space preparation, apical leakage were measured with electrochemical method for 28 days and analyzed statistically. The following results were obtained ; 1. No statistically significant differences in apical leakage were occured among the experimental groups using heated plugger, gate glidden drill and chloroform and K-file to remove the gutta percha immediately after obturation. 2. No significant difference in apical leakage was found between the teeth prepared post space immediately after obturation and those prepared 1 week after obturation. 3. In all experimental groups, the apical leakage was increased with time passage regardless of the post space preparation time and the gutta percha removal techniques.

• The Transactions of the Korean Institute of Power Electronics
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• v.25 no.4
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• pp.303-310
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• 2020

Estimating the accurate internal state of lithium ion batteries to increase their safety and efficiency is crucial. Various algorithms are used to estimate the internal state of a lithium ion battery, such as the extended Kalman filter and sliding mode observer. A state-space model is essential in using algorithms to estimate the internal state of a battery. Two principal methods are used to express the state-space model, namely, continuous time and discrete time. In this work, the extended Kalman filter is employed to estimate the internal state of a battery. Moreover, this work presents and analyzes the estimation performance of algorithms consisting of a continuous time state-space model and a discrete time state-space model through static and dynamic profiles.

• Journal of Astronomy and Space Sciences
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• v.37 no.3
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• pp.209-218
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• 2020

This paper describes the initial operations and preliminary results of the Instrument for the study of Stable/Storm-time Space (ISSS) onboard the microsatellite Next Generation Small Satellite-1 (NEXTSat-1), which was launched on December 4, 2018 into a sun-synchronous orbit at an altitude of 575 km with an orbital inclination angle of 97.7°. The spacecraft and the instruments have been working normally, and the results from the observations are in agreement with those from other satellites. Nevertheless, improvement in both the spacecraft/instrument operation and the analysis is suggested to produce more fruitful scientific results from the satellite operations. It is expected that the ISSS observations will become the main mission of the NEXTSat-1 at the end of 2020, when the technological experiments and astronomical observations terminate after two years of operation.

• Korean Institute of Interior Design Journal
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• v.22 no.2
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• pp.194-202
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• 2013

Commercial spaces are very sensitive in terms of trend and uniqueness, and many elements expressing space coexist together with brilliant ideas aiming to attract consumer attention and even induce sudden desire of purchase. Coexistence in space is expressed in various ways and out of those ways, representation by material is especially apparent. The application of material does not individually influence the expression of space, but the characteristics of multiple materials applied contribute to the distinction of space through mutual communication. This study intends to analyze how conversion is centered to express the distinction of space through materials communicated in space. The detailed study results are as follows. First, the conversion expression method of material resulted as 'Substitution', 'Contrast', 'Assimilation', 'Creation'. These four was divided and analyzed into 'Time', 'Space', 'Genre'. As a result of this analysis, such significances were shown as 'Contrast' in 'Time', 'Substitution' in 'Space', and 'Assimilation' in 'Genre'. Second, the conflict due to heterogeneity by conversion of 'Contrast' in 'Time' through past and current materials appeared to induce interest amongst consumers. Third, within 'Space', 'Substitution' of natural/artificial materials was noticeably applied. This is evaluated as a constructive way of expressing natural forms into artificial forms further intending to provoke attention and stimulate emotion. Fourth, in conversion through 'Assimilation' in 'Genre', rather than using materials only from other areas, synchronizing it by combining architectural materials is an effective method. Such results are thought to be a distinctive design method that draws attention of customers by communicating disparate materials in commercial space. Thus, the study results are expected to be utilized as an elementary resource in designing commercial space with character and high satisfaction.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.5C
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• pp.506-513
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• 2003

Most existing space-time coding (STC) schemes have been developed for flat fading channels. To obtain antenna diversity gain, they rely on channel state information (CSI) required at the receiver through channel estimation techniques. This paper proposes a new decision feedback decoding scheme for Alamouti-based space-time block coding (STBC) transmission over time-selective fading channels. In wireless channels, time-selective fading effects arise mainly due to Doppler shift and carrier frequency offset, Modelling the time-selective fading channels as the first-order Gauss-Markov processes, we use recursive algorithms such as Kalman filtering, LMS and RLS algorithms for channel tracking. The proposed scheme consists of the symbol decoding stage and channel tracking algorithms. Computer simulations confirm that the proposed scheme shows the better performance and robustness to time-selectivity.

• Journal of the Economic Geographical Society of Korea
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• v.18 no.1
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• pp.87-102
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• 2015

This study attempts to introduce the methodology for accounting real-time population distribution in the urban areas. For the purpose, we utilize the media user's time-space information from the media users' media diaries in the media panel survey databases. We analyze the space-time population rate for each activity space related with everyday urban lifes. Seoul has been selected as a case study area, since space-time information are relatively rich there, and thus the comparisons are available. The space-time population rates have been verified by the comparative analysis with the T-card results. We propose a real time population measurement method by combination of the space-time population rate with geographical data. The real time population of each activity space at each dong in Seoul has been calculated by multiplying the space-time population rates to the numbers of employer of three categories of activity spaces(residential, working, and commercial). By utilizing GIS, we visualize the results of two time points (3AM and 3PM) and then analyze the spacio-temporal characteristics of real time population distribution in Seoul. The Day time population distribution pattern shows strong relationships with the distribution of business and commercial activities, while the night time population distribution pattern can be explained by resident population distribution almost perfectly.