• Structural Engineering and Mechanics
• /
• 제73권4호
• /
• pp.367-379
• /
• 2020

In recent railway projects where the railway connects between cities, newly planned tunnels are often located close to, or beneath an existing tunnel. Many claims and petitions have voiced public concern about the vibration and noise resulting from the situation. Vibrations and noises are engineering issues as well as environmental problems, and have become more important as people have become more concerned with their the quality of life. However, it is unlikely that the effects of vibration in situations where trains simultaneously pass a multileveled tunnel crossing have been appropriately considered in the phase of planning and design. This study investigates the superposition characteristic of ground-born vibrations from a multileveled tunnel crossing. The results from model tests and numerical analysis show that the ground-born vibration can be amplified by a maximum of about 30% compared to that resulting from the existing single tunnel. Numerical parametric study has also shown that the vibration amplification effect increases as the ground stiffness, the tunnel depth, and the distance between tunnels decrease.

• Korean Journal of Optics and Photonics
• /
• 제22권3호
• /
• pp.122-128
• /
• 2011

The AWG-filtering effect was investigated on a bidirectional 100-GHz-channel-spacing WDM-PON link using spectrum-sliced and RSOA-amplified light sources for downstream signals and a wavelength reuse technique for upstream signals. Signal performances of three different filtering AWGs, including Gaussian, trapezoidal, and rectangular types, were compared on link transmission with fiber nonlinear effects. As an extinction ratio of a downstream signal varied, the effect for both directional signals was analyzed and optimized. It was found that there was an optimal pass bandwidth of an AWG for the balance between relative intensity noise decrement and cross phase modulation noise increment as the bandwidth got wider.

• Journal of Korea Multimedia Society
• /
• 제22권8호
• /
• pp.960-973
• /
• 2019

The increased use of smartphones has made it easier to plan travel. Especially for people travelling in Europe, it is common to move between cities by train, and reserving passes with a mobile app offers many advantages. The Czech Republic, which is a familiar destination for Koreans, is called the "heart of Europe" and it is in central Europe, so it is inevitable to use the railway when travelling. This study has been compared with the structural characteristics of the railway reservation service operated by the Czech and Korean railways. In general, when evaluating the usability of an app, we often use a method that allows a group of users or experts to spot problems. However, this study suggests an analytical method to obtain more reliable and objective results. Also, the analysis of the structural characteristics has an advantage that the problem can be predicted at the prototype stage. This, of course, comes with time and financial benefits. The purpose of this research is to contribute to the development of applications that are more convenient to use and efficiency of development.

• ETRI Journal
• /
• 제42권6호
• /
• pp.951-964
• /
• 2020

This paper presents a lightweight true random number generator (TRNG) using beta radiation that is useful for Internet of Things (IoT) security. In general, a random number generator (RNG) is required for all secure communication devices because random numbers are needed to generate encryption keys. Most RNGs are computer algorithms and use physical noise as their seed. However, it is difficult to obtain physical noise in small IoT devices. Since IoT security functions are required in almost all countries, IoT devices must be equipped with security algorithms that can pass the cryptographic module validation programs of each country. In this regard, it is very cumbersome to embed security algorithms, random number generation algorithms, and even physical noise sources in small IoT devices. Therefore, this paper introduces a lightweight TRNG comprising a thin-film beta-radiation source and integrated circuits (ICs). Although the ICs are currently being designed, the IC design was functionally verified at the board level. Our random numbers are output from a verification board and tested according to National Institute of Standards and Technology standards.

• Strategy21
• /
• 통권30호
• /
• pp.31-62
• /
• 2012

It is a commons sense that the Republic of Korea is a maritime state that depends its survival on International Trade and International Economy. Korea was a peninsula and do it can be both maritime and continental state by its choice. However, after the national division in 1945, South Korea had became a virtual island and pursue a maritime way for national development in the past 60 plus years. Now, South Korea is becoming a world's 12 th largest major trading and maritime state. South Korea has far more ships per capita than any other nations in the world and its economy is heavily depend upon the imports and exports with other nations in the world that pass through the oceans. Therefore, the Koreans regard the security of the sea lanes of communication as vital to the survival of the nation. The SLOC is the life line for Republic of Korea. Since the early 1990s, immediately after the Cold War was over, South Koreans began to recognize the importance of Sea Routes and thus began to build a navy that can handle with the new problems of the post Cold War era. However, the maritime security environments of the Republic of Korea today is shaky and dangerous. Almost every water near the Korean peninsula, some kind of international confrontations are going on. Territorial disputes on Dok do, Senkaku, Scarbrough, Shisha, Nansha and Eodo between and among Korea, Japan, China, Taiwan, Phillipines, Indonesia and Vietnam are the examples. In this essay, the author argues that the S. Korean efforts and capabilities to deal with these challenges are not enough and exhorts more efforts and more powerful navy for the Korean people.

• Korean Journal of Radiology
• /
• 제21권4호
• /
• pp.462-470
• /
• 2020

Objective: To demonstrate that human visual illusion can contribute to sub-endocardial dark rim artifact in contrast-enhanced myocardial perfusion magnetic resonance images. Materials and Methods: Numerical phantoms were generated to simulate the first-passage of contrast agent in the heart, and rendered in conventional gray scale as well as in color scale with reduced luminance variation. Cardiac perfusion images were acquired from two healthy volunteers, and were displayed by the same gray and color scales used in the numerical study. Before and after k-space windowing, the left ventricle (LV)-myocardium boarders were analyzed visually and quantitatively through intensity profiles perpendicular the boarders. Results: k-space windowing yielded monotonically decreasing signal intensity near the LV-myocardium boarder in the phantom images, as confirmed by negative finite difference values near the board ranging -1.07 to -0.14. However, the dark band still appears, which is perceived by visual illusion. Dark rim is perceived in the in-vivo images after k-space windowing that removed the quantitative signal dip, suggesting that the perceived dark rim is a visual illusion. The perceived dark rim is stronger at peak LV enhancement than the peak myocardial enhancement, due to the larger intensity difference between LV and myocardium. In both numerical phantom and in-vivo images, the illusory dark band is not visible in the color map due to reduced luminance variation. Conclusion: Visual illusion is another potential cause of dark rim artifact in contrast-enhanced myocardial perfusion MRI as demonstrated by illusory rim perceived in the absence of quantitative intensity undershoot.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
• /
• 한국해양공학회 2003년도 추계학술대회 논문집
• /
• pp.93-96
• /
• 2003

Laser beam welding process is a relatively new process in comparison with arc welding process, but it is expected to apply widely because of the many advantages, and research and development of that process is being progressed actively for the practical use. the application of this welding process has been restricted due to the high initial investment and the need of precise processing against the material, but cost reduction and thick plate welding in high speed have become practial by recent technological development, and this welding process to not only small parts in automobile, machinery and physicochemical field, but also a large structure and pipe line are being applied. In order to utilize this welding process appropriately to a steel structure, the properties of welding residual stresses and fracture toughness in welded joints are to be investigated for relibilty. On this study, after performing the finite element analysis, thermal and residual stress properties have been examined to the general structural steel (HT50) by laser beam welding. Besides, the property of fracture toughness has been investigated by the Charpy impact test and 3-points bending CTOD test carried out in the range of temperature between $-60^{\circ}C$ and $20^{\circ}C$. From the research results it is revealed that the maximum residual stress appears in the center of plate thickness and the fracture toughness is influenced by strength mis-match.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• 제17권7호
• /
• pp.673-683
• /
• 2006

In this paper, we investgate variation of phase and magnitude characteristics which become different as the variables of DGS are changed and propose the new method to easily decide the best optimum DGS pattern taking advantage of this trend. Generalized Chebyshev(GC) low pass filter(LPF) is designed by using DGS obtained from this method GC DGS LPF is more available for filter application than Chevyshev DGS LPF because GC LPF have parallel resonators as series circuits, therefore unlikely Chebyshev LPF, transform step of the series elements can be omitted. By using the proposed method, GC DGS LPF(N=5) and as a subject of comparison, conventional Chbyshev LPF(N=7) are designed and implementation. From the comparison of the measured data, we confirmed that the implemented GC DGS 5th order LPF have much better cutoff characteristics and reduce by 0.58 times size, on the other hand the stop bandwidth become widen about 1.57 times or more in comparison with the conventional Chevyshev 7th order LPF.

• Journal of Ocean Engineering and Technology
• /
• 제21권3호
• /
• pp.71-76
• /
• 2007

Recently, many industries have been employing the application of laser beam welding, due to the resulting high welding quality, such as smaller width of melting and heat affective zone, smaller welding deformation, and fine grains of weldment, compared to arc welding. However, in order to appropriately utilize this welding process with steel structure, the characteristics of welding residual stresses and fracture toughness in welded joints are to be investigated for reliability. Therefore, in this study, the mechanical properties of weldments by arc and laser welding are investigated using FEM to confirm the weldability of laser welding to the general structural steel (HT50). The Charpy impact test and 3-points bending CTOD test are carried out in the range of temperatures between $-60^{\circ}C\;and\;20^{\circ}C$, in order to understand the effect on the fracture toughness of weldments. From the research results, it has been found that the maximum residual stress appears at the center of plate thickness, and that the fracture toughness is influenced by strength mis-match.

• Journal of the Korean Society of Marine Environment & Safety
• /
• 제26권6호
• /
• pp.594-600
• /
• 2020

The identification of the risk of collision between ships and objects is vital for achieving navigation safety. The purpose of this study is to analyze the phenomenon of ship domain invasion by breakwaters when ships pass between breakwaters. A method for evaluating the domain-invaded area under the conditions of the breakwater was developed. Next, experimental data were obtained and processed using the Automatic Identification System (AIS) of ships sailing near the breakwater at Busan Port to establish a ship domain that could be formed between the breakwaters. The ship domain was then constructed using Fujii's domain. Finally, the phenomenon in which the constructed ship domain was invaded by the breakwater was analyzed. Based on the experimental results, the domain of the ship invaded by the breakwater was identified.