• Journal of the Korean Society for Industrial and Applied Mathematics
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• v.12 no.2
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• pp.119-131
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• 2008

The paper considers the computation method in the performance evaluation of cellular network in the phase-type distribution assumptions that the channel holding times induced from mobility are modeled by well-fitted distributions to reflect an actual situation. When ww consider a phase-type distribution model instead of exponential distribution, the complexity of the computation increase exponential even though the accuracy is improved. We consider an efficient numerical algorithm to compute the performance evaluations in cellular networks such as a handoff call dropping probability, new call blocking probability, and handoff arrival rate. Numerical experiment shows that numerical analysis results are well approximated to the results of simulation.

• Journal of the Korean Society for Nondestructive Testing
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• v.21 no.3
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• pp.277-280
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• 2001

General source location method that use an arrival time differences among sensors is restricted to the composite material and the complex-shaped material. In this study, a bundle-type acoustic sensor composed of 6 pinducers was utilized to determine wave propagation direction and then to estimate source location of the unidirectional GFRP. For the purpose of the study, slowness curve for the material was obtained and made an assumption that the incident waves on pinducers are propagated as a plane wave. According to the results, measured propagation directions of the wave were coincide with theoretical background, however, it was a hassle to determine the source location exactly. But, it is expected that bundle-type sensor gives more accurate results for zone location than generally used acoustic sensors.

• Journal of Ocean Engineering and Technology
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• v.23 no.1
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• pp.24-30
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• 2009

The purpose of this study was to establish an assessment method for the estimation of the pollution risk by oil spill accidents. Various oil spill patterns were calculated based on past accidents in the study area and these results were analyzed statistically. Then the risk probability, the oil arrival time, risk range, and so on were calculated. These calculations were performed for sub area sectors, fisheries and aquaculture farms, based on information about environmentally sensitive resources. Finally, the risk to each sub area sector was assessed by comparing the calculated results. These consequences indicated the objective and general risks of oil spill accidents and the result of this method will be made more appropriate by integrating real time risk predictions.

• Journal of Chest Surgery
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• v.25 no.1
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• pp.66-72
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• 1992

From March 1986 to March 1991, 29 patients were operated due to cardiac tamponade at the Department of Thoracic and Cardiovascular Surgery, Masan Koryo General Hospital. Among them, 19cases were traumatic origin and 10 were Non traumatic origin. A] Traumatic cardiac tamponade Out of 19 cases, 12 cases were resulted from penetrating injury and 7 cases from trauma. Average time interval from arrival to operation was 91 minutes[15min.~8.5hr.] in penetrating injury group. On the other hand, average time of in cases of blunt trauma was more than 3hours because of the difficulties in diagnosis. Four deaths occured in 19 cases [mortality rate: 21.1%] 3 in blunt trauma group[42.9%] and 1 in penetrating group[8.3%]. In view of our experience, the prognosis was closely correlated with injury mode, initial vital sign and mental status. There was no close correlation between prognosis and cardiac injury site. B] Non traumatic cardiac tamponade The etiologies were malignancy[4], non-spesific pericarditis[3], tuberculosis[1], pyogenic[1] and cardiomyopathy[1]. All of the cases in which performed tube pericardiostomy were the cases that showed no response to conservative treatment and repeat per-icardiocentesis. There was one posoperative death.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.8 no.12
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• pp.4389-4410
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• 2014

Network coding is a promising technology that increases system throughput by reducing the number of packet transmissions from the source node to the destination node in a saturated traffic scenario. Nevertheless, some packets can suffer from end-to-end delay, because of a queuing delay in an intermediate node waiting for other packets to be encoded with exclusive or (XOR). In this paper, we analyze the delay according to packet arrival rate and propose two network coding schemes, iXOR (Intelligent XOR) and oXOR (Optimal XOR) with Markov Decision Process (MDP). They reduce the average delay, even under an unsaturated traffic load, through the Holding-${\chi}$ strategy. In particular, we are interested in the unsaturated network scenario. The unsaturated network is more practical because, in a real wireless network, nodes do not always have packets waiting to be sent. Through analysis and extensive simulations, we show that iXOR and oXOR are better than the Distributed Coordination Function (DCF) without XOR (the general forwarding scheme) and XOR with DCF with respect to average delay as well as delivery ratio.

• Economic and Environmental Geology
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• v.34 no.6
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• pp.573-581
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• 2001

110 earthquake parameters (origin time, epicentral location and magnitude) were determined from 533 event records between 1905 and 1942 using data mainly from the "Annual Report of the Meteorological Observatory of the Government General of Tyosen" We adopted epicentral coordinates from the original reports for 34 events and from the Japanese Central Meteorological Observatory far another .34 events. We determined epicenters for 37 events using arrival time information from the reports. We adopted 4 epicenters from the International Seismological Summary and I from the Chinese bulletin. To determine the magnitude, we applied Tsuboi (1954) formula which is currently employed by Korea Meteorological Administration (KMA) for 94 events. For 16 events, we determined magnitude from the reef)reed felt epicentral areal using the correlation equation between known magnitude and felt area.

• Industrial Engineering and Management Systems
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• v.1 no.1
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• pp.29-45
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• 2002

In this study, we consider infinite supply of raw materials and backlogged demands as given two boundary conditions. And we need not make any specific assumptions about the inter-arrival of external demand and service time distributions. We propose a numeric model and an algorithm in order to compute the first two moments of inter-departure process. Entropy enables us to examine the convergence of this process and to derive measurable relations of this process. Also, lower bound on the variance of inter-departure process plays an important role in proving the existence and uniqueness of an optimal solution for a numeric model and deriving the convergence order of augmented Lagrange multipliers method applied to a numeric model. Through these works, we confirm some structural properties and numeric examples how the validity and applicability of our study.

• Communications for Statistical Applications and Methods
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• v.6 no.3
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• pp.881-892
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• 1999

In this paper we consider a polling system with two classes of stations; high priority and low priority. High priority stations are polled more frequently than low priority stations. We derive an exact and explicit formula for computing the mean waiting times for a message when the arrival processes are batch Poisson. In general the formula requires to solve two sets of simultaneous equations By specializing them to the case of two priority classes we greatly reduce the number equations and provide a simple formula for mean waiting times. We apply the results to a data communication processing system and show that the overall mean waiting time can be reduced by using priority polling.

• East Asian Economic Review
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• v.25 no.2
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• pp.151-174
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• 2021

This paper empirically examines whether and how inward foreign direct investment (FDI) affected industrial productivity in Korea during the 2000-2016 period, based on dynamic panel data of inflow FDI on an arrival basis from 427 manufacturing industries. The paper adds to the literature by analyzing whether both technology spillovers and industrial restructuring from inward FDI can differ according to industrial characteristics such as capital intensity, imported intermediate inputs, and tariffs. The empirical results show that the overall effects of inward FDI on total factor productivity (TFP) were statistically insignificant in general. However, the positive effects of inward FDI on productivity became statistically significant for industries with lower tariffs. Capital intensity were not involved in the relationship between inward FDI and productivity. Thus, the paper highlights that the results in previous studies with inward FDI on a notification basis were overestimated and inward FDI policies in Korea should focus on channels such as trade liberalization and the redistribution of production factors rather than capital accumulation.

• The Bulletin of The Korean Astronomical Society
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• v.46 no.2
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• pp.35.4-35.4
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• 2021

The Double Asteroid Redirection Test (DART) is NASA's first planetary defense test mission, designed to test the kinetic deflector technique by crashing into an asteroid and changing its orbit. DART's launch window opens in November, 2021, with arrival at its target less than a year later in late September or early October 2022. The target of the DART spacecraft is the moonlet Dimorphos, a 150-m moonlet orbiting the 780-m asteroid Dimorphos. By changing the orbit of Dimorphos around Didymos, the results can be detected much more easily than changing the orbit of an asteroid around the Sun. I will discuss what we know about Didymos and Dimorphos, the plans for the DART mission, the expected results, and how DART is important for planetary defense in general.