• The Journal of Korean Institute of Information Technology
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• v.17 no.10
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• pp.49-55
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• 2019

In this paper, we propose a simple precoding vector design scheme for multi-user multiple-input single-output (MISO) interference channel when there are multiple eavesdroppers. We aim to obtain a mathematical closed-form solution of the secrecy rate optimization problem. For this goal, we design the precoding vector based on the signal-to-leakage plus noise ratio (SLNR). More specifically, the proposed precoding vector is designed to completely eliminate a wiretap channel capacity for refraining the eavesdroppers from detecting the transmitted information, and to maximize the transmitter-receiver link achievable rate. We performed simulation for the performance investigation. Simulation results show that the proposed scheme has better secrecy rate than the conventional scheme over all signal-to-noise ratio (SNR) range even though the special condition among the numbers of transmit antennas, transmitter-receiver links, and eavesdroppers is not satisfied.

• Korean Journal of Optics and Photonics
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• v.16 no.3
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• pp.182-190
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• 2005

The fiber Raman amplifier(FRA) is a distinctly advantageous technology. Due to its wider, flexible gain bandwidth, and intrinsically lower noise characteristics, FRA has become an indispensable technology of today. Various FRA modeling methods, with different levels of convergence speed and accuracy, have been proposed in order to gain valuable insights for the FRA dynamics and optimum design before real implementation. Still, all these approaches share the common platform of coupled ordinary differential equations(ODE) for the Raman equation set that must be solved along the long length of fiber propagation axis. The ODE platform has classically set the bar for achievable convergence speed, resulting exhaustive calculation efforts. In this work, we propose an alternative, highly efficient framework for FRA analysis. In treating the Raman gain as the perturbation factor in an adiabatic process, we achieved implementation of the algorithm by deriving a recursive relation for the integrals of power inside fiber with the effective length and by constructing a matrix formalism for the solution of the given FRA problem. Finally, by adiabatically turning on the Raman process in the fiber as increasing the order of iterations, the FRA solution can be obtained along the iteration axis for the whole length of fiber rather than along the fiber propagation axis, enabling faster convergence speed, at the equivalent accuracy achievable with the methods based on coupled ODEs. Performance comparison in all co-, counter-, bi-directionally pumped multi-channel FRA shows more than 102 times faster with the convergence speed of the Average power method at the same level of accuracy(relative deviation < 0.03dB).

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.3
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• pp.257-268
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• 2018

We have studied the damage mechanism of a metallic thin plate by the highly energetic fragments generated from high explosive(HE) warhead. The penetration process has presumed that the velocity of a fragment is in the range of 350 m/s to 3353 m/s, the thickness of Aluminum 2024 target plate is in the range of 1 mm~6.3 mm thick. The mass of fragment with hemisphere nose shape is in the range of 0.32 g to 16 g. The analytical solution for penetration process has been derived by using the report of the project THOR. The results of analysis implied that the closed forms by an exponentially decay function well fit the change of the ballistic limit velocity, loss velocity and loss mass of fragment as the mass of fragment and the thickness of target plate increase.

• Journal of Korean Tunnelling and Underground Space Association
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• v.9 no.2
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• pp.205-217
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• 2007

The behavior characteristics of underground structures are reported as they are not affected by their dynamic characteristics such as surface structures, but by dynamic characteristics of soil and rock surrounding the underground structures. Therefore, dynamic behavior of surrounding soil and rock dominates the dynamic behavior of the underground structure. The purpose of this paper is to analyze the dynamic response (longitudinal deformation and ovaling deformation) of the underground structure under earthquake loading. The dynamic responses of the underground structures were evaluated with varying earthquake conditions, soil conditions, and structural conditions using conventional closed-form solution of seismic behavior of underground structure. In addition, shaking table tests were conducted to simulate the earthquake loading and the dynamic behavior of the model was analyzed.

• Environmental and Resource Economics Review
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• v.27 no.4
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• pp.613-637
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• 2018

Fuel cell power plant which has advantages as a distributed generation is influenced by high cost of investment and uncertainty of electricity price. This study suggests the model of real options which considers the irreversibility of investment in the fuel cell plant and the uncertainty of electricity price. Most models of real options assume the geometric Brownian motion for convenience, but this study develops the model for the feasibility analysis considering the mean reverting process of electricity price, with the closed form solution on the value of investment option. The result of the empirical analysis considering the data related to the fuel cell generation with the scale of 20MW and the domestic RPS circumstance represents that the investment is feasible without the uncertainty, and is not feasible with the uncertainty. This result implies that the political support as well as the improvement of profit system including revenue and cost are necessary for the activation of the fuel cell power plant.

• International Journal of Naval Architecture and Ocean Engineering
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• v.12 no.1
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• pp.755-767
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• 2020

A significant development has been made on a new fatigue damage model applicable to Gaussian wide band stress response spectra using numerical approximation methods such as data processing, time simulation, and regression analysis. So far, most of the alternative approximate models provide slightly underestimated or overestimated damage results compared with the rain-flow counting distribution. A more reliable approximate model that can minimize the damage differences between exact and approximate solutions is required for the practical design of ships and offshore structures. The present paper provides a detailed description of the development process of a new fatigue damage model. Based on the principle of the Gaussian wide band model, this study aims to develop the best approximate fatigue damage model. To obtain highly accurate damage distributions, this study deals with some prominent research findings, i.e., the moment of rain-flow range distribution MRR(n), the special bandwidth parameter μk, the empirical closed form model consisting of four probability density functions, and the correction factor QC. Sequential prerequisite data processes, such as creation of various stress spectra, extraction of stress time history, and the rain-flow counting stress process, are conducted so that these research findings provide much better results. Through comparison studies, the proposed model shows more reliable and accurate damage distributions, very close to those of the rain-flow counting solution. Several significant achievements and findings obtained from this study are suggested. Further work is needed to apply the new developed model to crack growth prediction under a random stress process in view of the engineering critical assessment of offshore structures. The present developed formulation and procedure also need to be extended to non-Gaussian wide band processes.

• Tunnel and Underground Space
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• v.22 no.2
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• pp.86-92
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• 2012

Point estimate method has a less accuracy than Monte Carlo simulation that is usually considered as an exact probabilistic method, but this method still remains popular in probability-based reliability assessment in geotechnical and rock engineering, because it significantly reduce the number of sampling points and produces the statistical moments of a performance function in a reasonable accuracy. In the present study, we investigated the accuracy and applicability of point estimate methods proposed by Rosenblueth and Zhou & Nowak by comparing the results of these two methods with those of Monte Carlo simulations. The comparison was carried out for the problem of a lined circular tunnel in an elastic medium where an closed-form analytical solution is given. The comparison results showed that despite the non-linearity of the analytical solution, the statistical moments calculated by the point estimate methods and the Monte Carlo simulations agreed well with an average error of roughly 1-2%. This average error demonstrates the applicability of the two point estimate methods for the probabilistic reliability assessment of underground structures in combination with numerical analysis.

• Journal of the Korean Society for Advanced Composite Structures
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• v.3 no.1
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• pp.21-28
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• 2012

In this paper, we present the analytical study results pertaining to the buckling of the orthotropic plates and local buckling of structural compression members composed of orthotropic plate components. Fiber reinforced polymeric plastic (FRP) materials, have many advantages over conventional structural materials such as steel and concrete. The advantages of the FRP materials are high specific strength and stiffness, high corrosion resistance, right weight, etc. Among the various manufacturing methods, pultrusion process is one of the best choices for the mass production of structural plastic members. Since the major reinforcing fibers are placed along the axial direction of the member, this material is usually considered as an orthotropic (tranversely isotropic, more specifically) material. However, pultruded fiber reinforced plastic structural members have low modulus of elasticity and are composed of orthotropic thin plate components the members are prone to buckle. Therefore, stability is an important issue in the design of the pultruded FRP structural members. In this paper, the buckling of orthotropic plates and the local buckling of pultruded FRP structural members are investigated by following the previous research results and the local buckling strength of the member produced in the domestic manufacturer is found.

• Toxicological Research
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• v.18 no.1
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• pp.13-22
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• 2002

In Korea, 2,320 tonnes of acetanilide were mostly wed as intermediates for synthesis in phar-maceuticals or additives in synthesizing hydrogen peroxide, varnishes, polymers and rubber. Only small amount of 120 kg were wed as a stabilizer for hydrogen peroxide solution for hair colouring agents in 1998. Readily available environmental or human exposure data do not exist in Korea at the present time. However, potential human exposures from drinking water, food, ambient water and in work places are expected to be negligible because this chemical is produced in the closed system in only one company in Korea and the processing factory is equipped with local ventilation and air filtering system. Acetanilide could be distributed mainly to water based on EQC model. This substance is readily biodegradable and its bioaccumulation is low. Acute toxicity of acetanilide is low since the L $D_{50}$ of oral exposure in rats is 1,959 mg/kg bw. The chemical is not irritating to skin, but slightly irritating to the eyes of rabbits. horn repeated dose toxicity, the adverse effects in rats were red pulp hyperplasia of spleen, bone marrow hyperplasia of femur and decreased hemoglobin, hematocrit and mean corpuscular hemoglobin concentration. The LOAEL for repeated dose toxicity in rats was 22 mg/kg/day for both sexes. Acetanilide is not considered to be genotoxic. In a reproductive/developmental toxicity study, no treatment-related changes in precoital time and rate of copulation, impregnation, pregnancy were shown in all treated groups. The NOAELs for reproduction and developmental toxicity (off-spring toxicity) are considered to be 200 mg/kg bw/day and 67 mg/kg bw/day, respectively. Ecotoxicity data has been generated in a limited number of aquatic species of algae (72 hr- $E_{b}$ $C_{50}$; 13.5 mg/l), daphnid (48hr-E $C_{50}$ > 100 mg/l) and fish (Oryzias latipes, 96hr-L $C_{50}$; 100 mg/l). Form the acute toxicity values, the predicted no effect concentration (PNEC) of 0.135 mg/1 was derived win an assessment factor of 100. On the basis of these data, acetanilide was suggested as currently of low priority for further post-SIDS work in OECD.in OECD.D.

• Tunnel and Underground Space
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• v.14 no.3
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• pp.167-174
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• 2004

This paper is to introduce an article published in Rock Mechanics and Rock Engineering, 2003. In this research, a fracture mechanics model is developed to illustrate the importance of time-dependence far brittle fractured rock. In particular a model is developed fer the time-dependent degradation of rock joint cohesion. Degradation of joint cohesion is modeled as the time-dependent breaking of intact patches or rock bridges along the joint surface. A fracture mechanics model is developed utilizing subcritical crack growth, which results in a closed-form solution for joint cohesion as a function of time. As an example, a rock block containing rock bridges subjected to plane sliding is analyzed. The cohesion is found to continually decrease, at first slowly and then more rapidly. At a particular value of time the cohesion reduces to value that results in slope instability. A second example is given where variations in some of the material parameters are assumed. A probabilistic slope analysis is conducted, and the probability of failure as a function of time is predicted. The probability of failure is found to increase with time, from an initial value of 5% to a value at 100 years of over 40%. These examples show the importance of being able to predict the time-dependent behavior of a rock mass containing discontinuities, even for relatively short-term rock structures.