• The Bulletin of The Korean Astronomical Society
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• v.36 no.1
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• pp.48.1-48.1
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• 2011

We utilize the jitter radiation, which is the emission of relativistic electrons in the random and small-scale magnetic field, to investigate the high-energy emissions of gamma-ray bursts (GRBs). Under the turbulent scenario, the random and small-scale magnetic field is determined by the turbulence. We also estimate the acceleration and cooling timescales. We identify that some GRBs are possible cosmic-ray sources.

• Proceedings of the KSRS Conference
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• v.1
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• pp.446-449
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• 2006

It is backscattering of solar radiation by water body that makes ocean color observable from above, either by airplanes or satellites. Given the very low direct contribution to backscattering by phytoplankton cells, it is curious why the retrieval of phytoplankton concentration from remotely observed ocean color is evidently successful. From semianalytical bio-optical models, a dataset is created of spectral absorption, scattering and backscattering coefficients as a function of chlorophyll concentration. Four scenarios are considered, 1) only molecular and no particle scattering, 2) random particle backscattering uncorrelated with chlorophyll concentration, 3) constrained random particle scattering with known backscattering ratio, and 4) constrained random scattering with random backscattering ratio. Scenario 1 only introduces moderate errors of -20% - 90%. And for scenarios 3 and 4, the errors are largely within 30% and 100%. Scenario 2 introduces the largest errors, with the retrieved chlorophyll concentration virtually uncorrelated with the true values, implying the backscattering must somehow be related to the trophic state. The results of the study suggested These 3 cases confirmed that while it is the absorption by phytoplankton that in large part decides the accuracy of chlorophyll concentration retrieval, for the success of monitoring of global ocean primary productivity we have to improve our knowledge on particle backscattering.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.7 no.2
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• pp.308-326
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• 2013

Mobility Model has drawn more and more attentions since its critical role in Mobile Wireless Networks performance evaluation. This paper analyzes the mobility patterns in the catastrophe rescue scenario, and proposes the Random Waypoint with Base Point mobility model to model these characteristics. We mathematically analyze the speed and spatial stationary distributions of the nodes and derive explicit expressions for the one dimensional case. In order to keep the stationary distribution through the entire simulation procedure, we provide strategies to initialize the speed, location and destination of the nodes at the beginning of the simulation. The simulation results verify the derivations and the proposed methods in this paper. This work gives a deep understanding of the properties of the Random Waypoint with Base Point mobility model and such understanding is necessary to avoid misinterpretation of the simulation results. The conclusions are of practical value for performance analysis of mobile wireless networks, especially for the catastrophe rescue scenario.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 1998.04a
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• pp.83-89
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• 1998

In case of Radar Simulator ,the target ships should be generated and displayed on the monitor to provide the trainee with the feeling of real situation. The scenario methodology, which has been developed and used in Korea so far, however, has a fixed scenario, in which target ships are generated in the same manner at all time. As a result, the Radar simulator developed in Korea so far was in lack of training efficiency, as the trainee can get earily familiarized with the fixed scenaio. The paper, therefore, suggests the target ship generating methodology using random variables to improve the training efficiency of the existing simulator. In generating the target ships using this methodology, the speed, distance between the ships , and time interval of ships and time of ships were considered as a major factors which dterminie the ship's movements. The new methodology suggested was examined and found to generate target ships successfully giving a trainee the feeling of real situation.

• Water Engineering Research
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• v.5 no.2
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• pp.81-99
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• 2004

Long term streamflow regime under virtual climate change scenario was examined. Rainfall forecast simulation of the Canadian Global Coupled Model (CGCM2) of the Canadian Climate Center for modeling and analysis for the IPCC SRES B2 scenario was used for analysis. The B2 scenario envisions slower population growth (10.4 billion by 2010) with a more rapidly evolving economy and more emphasis on environmental protection. The relatively large scale of GCM hinders the accurate computation of the important streamflow characteristics such as the peak flow rate and lag time, etc. The GCM rainfall with more than 100km scale was downscaled to 2km-scale using the space-time stochastic random cascade model. The HEC-HMS was used for distributed hydrologic model which can take the grid rainfall as input data. The result illustrates that the annual variation of the total runoff and the peak flow can be much greater than rainfall variation, which means actual impact of rainfall variation for the available water resources can be much greater than the extent of the rainfall variation.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.36 no.2
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• pp.75-83
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• 2023

In this paper, we present the analysis results on the vibration serviceability of a pedestrian bridge considering the effect of pedestrian moving mass inertia. Using dynamic finite element analysis, we considered different walking scenarios, including pedestrian density, walking speed, random walking, and synchronized walking, to analyze the acceleration response of a 40m long single-span bridge with a steel composite box cross section. We showed that the equivalent fixed mass analysis method did not significantly differ from the moving mass analysis in the random walk scenario and a wider frequency excitation band may be useful to consider when evaluating vibration serviceability in a random walk scenario.

• Journal of Korean Society on Water Environment
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• v.40 no.3
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• pp.121-129
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• 2024

Harmful cyanobacterial blooms (HCBs) are caused by the rapid proliferation of cyanobacteria and are believed to be exacerbated by climate change. However, the extent to which HCBs will be stimulated in the future due to increased temperature remains uncertain. This study aims to predict the future occurrence of cyanobacteria in the Nakdong River, which has the highest incidence of HCBs in South Korea, based on temperature rise scenarios. Representative Concentration Pathways (RCPs) were used as the basis for these scenarios. Data-driven model simulations were conducted, and out of the four machine learning techniques tested (multiple linear regression, support vector regressor, decision tree, and random forest), the random forest model was selected for its relatively high prediction accuracy. The random forest model was used to predict the occurrence of cyanobacteria. The results of boxplot and time-series analyses showed that under the worst-case scenario (RCP8.5 (2100)), where temperature increases significantly, cyanobacterial abundance across all study areas was greatly stimulated. The study also found that the frequencies of HCB occurrences exceeding certain thresholds (100,000 and 1,000,000 cells/mL) increased under both the best-case scenario (RCP2.6 (2050)) and worst-case scenario (RCP8.5 (2100)). These findings suggest that the frequency of HCB occurrences surpassing a certain threshold level can serve as a useful diagnostic indicator of vulnerability to temperature increases caused by climate change. Additionally, this study highlights that water bodies currently susceptible to HCBs are likely to become even more vulnerable with climate change compared to those that are currently less susceptible.

• Structural Engineering and Mechanics
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• v.66 no.1
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• pp.75-84
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• 2018

This study presents the reliability-based analysis of nonlinear structures using the analytical fragility curves excited by random earthquake loads. The stochastic method of ground motion simulation is combined with the random vibration theory to compute structural failure probability. The formulation of structural failure probability using random vibration theory, based on only the frequency information of the excitation, provides an important basis for structural analysis in places where there is a lack of sufficient recorded ground motions. The importance of frequency content of ground motions on probability of structural failure is studied for different levels of the nonlinear behavior of structures. The set of simulated ground motion for this study is based on the results of probabilistic seismic hazard analysis. It is demonstrated that the scenario events identified by the seismic risk differ from those obtained by the disaggregation of seismic hazard. The validity of the presented procedure is evaluated by Monte-Carlo simulation.

• Proceedings of the IEEK Conference
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• summer
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• pp.35-38
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• 2004

The MAC protocol of HIPERLAN/2 is based on TDMA/TDD and AP (Access Point) can dynamically allocate the number of RCHs (Random CHannels). We propose a dynamic random channel allocation scheme improved by limiting the number of minimum RCHs. On a simulated scenario adopted practical Internet traffic, the proposed scheme is shown to achieve over $19\%$ lower delay than previously studied algorithm. This study will be a first step towards designing scope of RCHs for high-performance wireless packet network

• Proceedings of the IEEK Conference
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• 2008.06a
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• pp.959-960
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• 2008

Recently, biometric authentication mechanism has been used to provide high level of security in cryptographic systems. In this paper, we propose an efficient method of generating invariant iris key to be applied in cryptographic systems. In order to generate iris key and improve the performance at the stolen token scenario, multiple random projection technique was combined with multiple linear transformation methods. From the experimental results, we proved that invariant iris keys were generated and the proposed method was robust to stolen token scenario.