• The Bulletin of The Korean Astronomical Society
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• v.43 no.1
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• pp.72.2-72.2
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• 2018

The Opposition Effect (OE) is an enhancement of the brightness of a reflecting light as the phase angle (the Sun-target-observer angle) approaches zero. The mechanisms have been studied both theoretically and experimentally and nowadays recognized that there are two major mechanisms, namely, coherent backscattering OE (CBOE) and shadow hiding OE (SHOE). From data analyses of an S-type asteroid Itokawa taken with the Hayabusa spacecraft onboard camera, it is suggested that the CBOE would be dominant at phase angle smaller than ~ 1.4 deg, while SHOE dominates at larger phase angles (M. Lee & M. Ishiguro, under review). The study on the physical parameters which affect the OE, such as size and composition, will lead us to find a way to disentangle each of them from observation. The experiments in lab, however, faces two major difficulties: (a) the detector blocks the incident light if phase angle is nearly zero and (b) incident and emission angles must be controlled with high angular resolution to prevent blurring of OEs at different phase angles in one measurement. In this presentation, we introduce a new apparatus which has been installed at Seoul National University to investigate the OE in our lab, and summarize the initial results. It will be a valuable starting point to establish infrastructure in Korea, and will shed light on the investigation of OE physics using laboratory simulants.

• Journal of computational fluids engineering
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• v.22 no.1
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• pp.95-102
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• 2017

Debris flow is a composition of solid objects of various sizes, suspension and water, which occurs frequently as the results of landslide following heavy rainfall. This often causes extensive damage in the form of socio-economic losses and casualties as witnessed during the incident around Mt. Umyeon, Seoul in 2011. There have been numerous investigation to mitigate the impacts from debris flow; however, the estimation as preparedness measure has not been successful due to nonlinear and multiphase characteristics of phenomena both in material and process inherent in the debris flow. This study presents a numerical approach to simulate the debris flow using open source code of computational fluid dynamics, OpenFOAM with non-Newtonian viscosity model for three phase material modeling. In order to validate the proposed numerical method, the quantitative evaluations were made by comparisons with experimental results and qualitative analysis for the dispersion characteristics was carried for the case of debris flow in the actual incident from Mt. Umyeon.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.5B
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• pp.301-312
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• 2012

This study investigates the wave height distributions in front of a perforated wall generated by obliquely incident monochromatic waves through laboratory experiments conducted in a wave basin. Attention is paid to the difference or similarity between a plain wall and a perforated wall. And the investigation is focused on the chamber width and side wall effects of a perforated wall on the propagation characteristics of waves. The main results of this study show that the normalized wave height along a perforated wall is a significant difference compare to a plain wall cases. The side wall in the chamber suppresses the growth of the stem waves.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.204-209
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• 2008

The interest in the mechanical behavior of materials at high strain rates has increased in recent years, and by now it is well known that mechanical properties can be strongly influenced by the speed of applied load. The split Hopkinson pressure bar (SHPB) has been widely used to determine mechanical properties of materials at high loading rates. However, to ensure test reliability, measurement error source must be accounted for and eliminated. During experiment, the specimens were located between the incident and the transmit bar. The presence of contact frictions between the test bars and specimen may cause errors. In this work, numerical experiments were carried out to investigate the effect of friction on test results. In SHPB test, the measured stress by the transmitted bar is assumed to be flow stress of the test specimen. Through the numerical experiments, however, it is shown that the measured stress by the transmit bar is axial stress components. When, the contact surface is frictionless, the flow stress and the axial stress of the specimen are about the same. When the contact surface is not frictionless, however, the flow stress and the axial stress are not the same anymore. Therefore, the measured stress by the transmitted bar is not flow stress. The effect of friction on the difference between flow stress and axial stress is investigated.

• Strategy21
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• s.34
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• pp.93-127
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• 2014

During the four years following the sinking of the Cheonan frigate in 2010, the South Korean public opinion has seen changes in four basic ways. First, public polls with respect to the cause of the sinking show that 70% of the people consider North Korea as the culprit, while 20% maintain that it was not an act carried out by North Korea. Second, the opinions relative to the cause of the incident seem to vary according to age difference, generational difference, and educational difference. From 2011, people in their 20s showed 10% increase in regarding North Korea as the responsible party. People in their 30s and 40s still have a tendency not to believe the result of the investigation carried out by the combined military and civilian group. Third, the most prominent issue that arose aftermath of the Cheonan incident is the fact that political inclination and policy preference are influencing the scientific determination of the cause. In other words, scientific and logical approach is lacking in the process of determining the factual basis for the cause. This process is compromised by the inability of the parties concerned in sorting out what is objective and what is personal opinion. This confused state of affairs makes it difficult to carry on a healthy, productive debate. Fourth, rumors, propaganda, and disinformation generated by pro-North Korea Labor Party groups in the internet and SNS are causing considerable impact in forming the public opinion. Proposed Strategy 1. The administration can ascertain public trust by accurately determining the nature of the provocation based on accurate information in the early stages of the incident. 2. Education in scientific, logical, rational methodologyis needed at home, school, and workplace in order toenhance the people's ability to seek factual truths. 3. In secondary education, the values of freedom, human rights, democracy, and market economy must be reinforced. 4. It is necessary for the educational system to teach the facts of North Korea just as they are. 5. Fundamental strength of free democratic system must be reinforced. The conservative, mainstream powers must recognize the importance of self-sacrifice and societal duties. The progressive political parties must sever themselves from those groups that take instructions from North Korea's Labor Party. The progressives must pursue values that are based on fundamental human rights for all. 6. Korean unification led by South Korea is the genuine means to achieve peace in a nuclear-free Korean peninsula. The administration must recognize that this unification initiative is the beginning of the common peace and prosperity in the Far East Asia, and must actively pursue international cooperation in this regard.

• Geomechanics and Engineering
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• v.11 no.5
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• pp.657-670
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• 2016

The energy dissipation of coal under dynamic loads is a major issue in geomechanics and arising extensive concerns recently. In this study, dynamic loading tests of coal were conducted using a split Hopkinson pressure bar (SHPB) system, the characteristics of dynamic behavior and energy dissipation of coal were analyzed, and the mechanism of energy dissipation was discussed based on the fracture processes of coal under dynamic loads. Experimental results indicate that the energy dissipation of coal under dynamic loads has a positive linear correlation with both incident energy and dynamic compressive strength, and the correlation coefficients between incident energy, dynamic compressive strength and the energy dissipation rate are 0.74 and 0.98, respectively. Theoretical analysis demonstrates that higher level of stress leads to greater energy released during unstable crack propagation, thus resulting in larger energy dissipation rate of coal under dynamic loads. At last, a semi-empirical energy dissipation model is proposed for describing the positive relationship between dissipated energy and stress.

• Journal of the Korean Society for Nondestructive Testing
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• v.18 no.6
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• pp.445-454
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• 1998

In order to establish a technical concept for the detection of defects in weldments in thin steel plate, an experimental and theoretical investigation was carried out for artificial defects in a steel plate having a thickness of 2.4mm by using the guided wave technique. In particular the goal was to find the most effective testing parameters paying attention to the relationship between the excitation frequency by a tone burst system and various incident angles. It was found that the test conditions that worked best was for a frequency of 840kHz and an incident angle of 30 or 85 degrees, most of the defects were detected with these conditions. Also, it was clear that a guided wave mode generated under an incident angle of 30 degrees was a symmetric mode, So, and that of 85 degrees corresponded to an antisymmetric mode, Ao. By using the two modes, most of all of the defects could be detected. Furthermore, it was shown that the antisymmetric mode was more sensitive to defects near the surface than the symmetric mode. Theoretical predictions confirmed this sensitivity improvement with Ao for surface defects because of wave structure variation and energy concentration near the surface.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.30 no.4
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• pp.745-756
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• 2020

An ICS(industrial control system) is a complex system that safely and efficiently monitors and controls industrial processes such as electric power, water treatment, transportation, automation plants and chemical plants. Because successful cyber attacks targeting ICS can lead to casualties or serious economic losses, it becomes a prime target of hacker groups sponsored by national state. Cyber campaigns such as Stuxnet, Industroyer and TRITON are real examples of successful ICS attacks, and were developed based on the deep knowledge of the target ICS. Therefore, for incident investigation of ICSs, inspectors also need knowledge of control processes and accident investigation techniques specialized for ICSs. Because there is no applicable technology, it is especially necessary to develop techniques and tools for embedded controllers located at cyber and physical boundaries. As the first step in this research, we reviewed logging capability of 4 PLC(Programmable Logic Controller)s widely used in an ICS area, and checked whether selected PLCs generate logs that can be used for digital investigation in the proposed cyber attack scenario.

• Journal of Advanced Navigation Technology
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• v.15 no.6
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• pp.1212-1219
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• 2011

As recently Privacy Acts in Korea enforced in domestic companies' personal information management needs of a growing obligation for the safety measures and the right of personal information collection, use, limitations, management, and destroyed specifically for handling personal information. Such this regulations should be required technical and policy supports. Accordingly, for the enterprise incident has occurred, the personal information management system behave correctly operating to verify that the safety measures taken, and be determined by the specific preparation to be done. So the first, preparation phase corresponds to the upcoming digital forensic investigation model. On the other hand, the response team also carried these measures out correctly, it needs to be done to check the compliance of Privacy Act. Thus a digital forensics investigation model is strictly related with the implementation of the Privacy Acts and improve the coping strategies are needed. In this paper, we suggest a digital forensic investigation model corresponding to Privacy Act.

• Journal of Korean Society of Transportation
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• v.29 no.5
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• pp.121-138
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• 2011

More affordable and available cutting-edge technologies (e.g., wireless vehicle communication) are regarded as a possible alternative to the fixed infrastructure-based traffic information system requiring the expensive infrastructure investments and mostly implemented in the uninterrupted freeway network with limited spatial system expansion. This paper develops an advanced decentralized traveler information System (ATIS) using vehicle-to-vehicle (V2V) communication system whose performance (drivers' travel time savings) are enhanced by three complementary functions (autonomous automatic incident detection algorithm, reliable sample size function, and driver behavior model) and evaluates it in the typical $6{\times}6$ urban grid network with non-recurrent traffic state (traffic incident) with the varying key parameters (traffic flow, communication radio range, and penetration ratio), employing the off-the-shelf microscopic simulation model (VISSIM) under the ideal vehicle communication environment. Simulation outputs indicate that as the three key parameters are increased more participating vehicles are involved for traffic data propagation in the less communication groups at the faster data dissemination speed. Also, participating vehicles saved their travel time by dynamically updating the up-to-date traffic states and searching for the new route. Focusing on the travel time difference of (instant) re-routing vehicles, lower traffic flow cases saved more time than higher traffic flow ones. This is because a relatively small number of vehicles in 300vph case re-route during the most system-efficient time period (the early time of the traffic incident) but more vehicles in 514vph case re-route during less system-efficient time period, even after the incident is resolved. Also, normally re-routings on the network-entering links saved more travel time than any other places inside the network except the case where the direct effect of traffic incident triggers vehicle re-routings during the effective incident time period and the location and direction of the incident link determines the spatial distribution of re-routing vehicles.