• Journal of the Korean Solar Energy Society
• /
• v.32 no.1
• /
• pp.15-24
• /
• 2012

IEC 61400-1 requires design lifetime of wind turbines at least 20 years, thus wind turbine should be assured for structural safety through load assessment. DLCs have been defined with respect to the load assessment in IEC 61400-1. In addition, if the extreme design values for DLC1.3 are equal or exceed the extreme design value for DLC1.1, DLC1.1 may be omitted. To omit DLC1.1, scale factor (c) will be increased in DLC1.3. However, this particular adjustment is not specified guidelines. Thus, this study was conducted. DLC1.1 was calculated for extrapolation of 50 years-extreme events using several probability distribution functions and fitting methods. And DLC1.3 was calculated for up to seven different values of scale factor (c) with $2{\leq}c{\leq}5$ in steps of 0.5. Finally, in this study, scale factor (c) that was the value of 4.51 was determined.

• Journal of Communications and Networks
• /
• v.18 no.2
• /
• pp.218-226
• /
• 2016

Coordination among users is an inevitable but time-consuming operation in wireless networks. It severely limit the system performance when the data rate is high. We present FC-MAC, a novel MAC protocol that can complete a contention within one contention slot over a joint frequency-code domain. When a node takes part in the contention, it generates randomly a contention vector (CV), which is a binary sequence of length equal to the number of available orthogonal frequency division multiplexing (OFDM) subcarriers. In FC-MAC, different user is assigned with a distinct signature (i.e., PN sequence). A node sends the signature at specific subcarriers and uses the sequence of the ON/OFF states of all subcarriers to indicate the chosen CV. Meanwhile, every node uses the redundant antennas to detect the CVs of other nodes. The node with the minimum CV becomes the winner. The experimental results show that, the collision probability of FC-MAC is as low as 0.05% when the network has 100 nodes. In comparison with IEEE 802.11, contention time is reduced by 50-80% and the throughput gain is up to 200%.

• Journal of Forest and Environmental Science
• /
• v.27 no.2
• /
• pp.93-99
• /
• 2011

In this study, a total of 350 households contained 700 individuals in Iganzo village were surveyed to study their literate and poverty levels and their impacts to conservation of the Mbeya Range Forest Reserve. The study included 350 women and 350 men. The majority of respondents were between the ages of 31-40 years old (53%), while the rest were between 41-50 years old (25%) and 21-30 years old (22%). The total income per day per household was calculated and averaged to 4,570 Tanzanian shillings that is equal to about 3 U.S. dollars. The average number of members per household was seven. It was reported that, there is a tremendous decrease in biodiversity composition of the reserve mainly due to poverty (80%) and ignorance (76%) of the people on the importance of the reserve. Other causes for this decrease were reported to be grazing of livestock in the reserve (23%), poor farming systems (68%), which resulted in soil erosion, encroachment (64%) through expansion of farms towards the reserve boundary and charcoal burning (34%). Respondents from Mbeya Urban Water Supply Authority and District Forest Office mentioned lack of funds (49%) and lack of experts (56%) as challenges that face the conservation of the reserve. It was revealed that 25% of respondents had never gone to school, 53% had primary level of education as their highest level of education, 20% had secondary education and 2% had first degree. The null hypothesis that poverty and illiteracy have a positive correlation to forest degradation was accepted based on these findings at a probability of p>0.85. Thus, it was concluded that poverty and illiteracy among Iganzo village residents are the main causes for the degradation of biodiversity in Mbeya Range Forest Reserve.

• KIPS Transactions on Computer and Communication Systems
• /
• v.10 no.10
• /
• pp.269-276
• /
• 2021

Recently, smart sensors are used in various environments, and the implementation of ad-hoc sensor networks (ASNs) is a hot research topic. Unfortunately, traditional sensor network routing algorithms focus on specific control issues, and they can't be directly applied to the ASN operation. In this paper, we propose a new routing protocol by using the Q-learning technology, Main challenge of proposed approach is to extend the life of ASNs through efficient energy allocation while obtaining the balanced system performance. The proposed method enhances the Q-learning effect by considering various environmental factors. When a transmission fails, node penalty is accumulated to increase the successful communication probability. Especially, each node stores the Q value of the adjacent node in its own Q table. Every time a data transfer is executed, the Q values are updated and accumulated to learn to select the optimal routing route. Simulation results confirm that the proposed method can choose an energy-efficient routing path, and gets an excellent network performance compared with the existing ASN routing protocols.

• Journal of the Earthquake Engineering Society of Korea
• /
• v.23 no.2
• /
• pp.89-99
• /
• 2019

In order to increase the seismic safety of nuclear power plant (NPP) structures, a technique to reduce the seismic load transmitted to the NPP structure by using a seismic isolation device such as a lead-rubber bearing has recently been actively researched. In seismic design of NPP structures, three directional (two horizontal and one vertical directions) artificial synthetic earthquakes (G0 group) corresponding to the standard design spectrum are generally used. In this study, seismic analysis was performed by using three directional artificial synthetic earthquakes (M0 group) corresponding to the maximum-minimum spectrum reflecting uncertainty of incident direction of earthquake load. The design basis earthquake (DBE) and the beyond design basis earthquakes (BDBEs are equal to 150%, 167%, and 200% DBE) of G0 and M0 earthquake groups were respectively generated for 30 sets and used for the seismic analysis. The purpose of this study is to compare seismic responses and seismic fragility curves of seismically isolated NPP structures subjected to DBE and BDBE. From the seismic fragility curves, the probability of failure of the seismic isolation system when the peak ground acceleration (PGA) is 0.5 g is about 5% for the M0 earthquake group and about 3% for the G0 earthquake group.

• Nuclear Engineering and Technology
• /
• v.54 no.6
• /
• pp.2135-2146
• /
• 2022

A nuclear energy facility is one of the most critical facilities to be safely protected during and after operation because the physical destruction of its barriers by an external attack could release radioactivity into the environment and can cause harmful effects. The barrier walls of nuclear energy facilities should be sufficiently robust to protect essential facilities from external attack or sabotage. Physical protection system (PPS) vulnerability assessment of a typical small nuclear research reactor was carried out by simulating an external attack with a tri-nitro toluene (TNT) shaped charge and results are presented. The reinforced concrete (RC) barrier wall of the research reactor located at a distance of 50 m from a TNT-shaped charge was the target of external attack. For the purpose of the impact assessment of the RC barrier wall, a finite element method (FEM) is utilized to simulate the destruction condition. The study results showed that a hole-size of diameter 342 mm at the front side and 364 mm at the back side was created on the RC barrier wall as a result of a 143.35 kg TNT-shaped charge. This aperture would be large enough to let at least one person can pass through at a time. For the purpose of the PPS vulnerability assessment, an Estimate of Adversary Sequence Interruption (EASI) model was used, which enabled the determination of most vulnerable path to the target with a probability of interruption equal to 0.43. The study showed that the RC barrier wall is vulnerable to a TNT-shaped charge impact, which could in turn reduce the effectiveness of the PPS.

• The Korean Journal of Nuclear Medicine
• /
• v.34 no.3
• /
• pp.207-221
• /
• 2000

Purpose: Cost-effectiveness of myocardial SPECT for the diagnosis of coronary artery disease was investigated considering the present and amended costs of myocardial SPECT and exercise ECG in Korea. Materials and Methods: Four diagnostic tactics such as 1) coronary angiography (CAG) after exercise ECG, 2) CAG after myocardial SPECT, 3) direct CAG, and 4) CAG after myocardial SPECT following exercise ECG were chosen. Costs were calculated using the present costs of various tests and effects represented by Quality Adjusted Life Year (QALY) were estimated. Difference of QALY (${\Delta}QALY$) was calculated by subtracting QALY of diagnosed/treated cases from QALY of undiagnosed cases. $Cost/{\Delta}QALY$ was calculated and compared between four different tactics according to pre-test probability. Results: When pre-test probability was equal to or larger than 0.6, direct CAG was the most cost-effective. When pre-test probability was between 0.2 and 0.6, CAG after myocardial SPECT following exercise ECG was the most cost-effective. CAG after myocardial SPECT was the second most cost-effective. Cost-effectiveness was similar when the costs of exercise ECG were doubled or quadrupled. CAG after exercise ECG was always the least cost-effective. Conclusion: Myocardial SPECT with or without preceding exercise ECG was the most cost-effective method to diagnose coronary artery disease in the present or expected amended cost system.

• Journal of the Korean Institute of Gas
• /
• v.21 no.4
• /
• pp.92-102
• /
• 2017

Fischer-Tropsch synthesis reaction converts syngas (mixture of CO and H2) to valuable hydrocarbon products. Simulation of low temperature Fischer -Tropsch Synthesis reaction and heat transfer at intensified process condition using catalyst filled single and multichannel microchannel reactor is considered. Single channel model simulation indicated potential for process intensification (higher GHSV of $30000hr^{-1}$ in presence of theoretical Cobalt based super-active catalyst) while still achieving CO conversion greater than ~65% and $C_{5+}$ selectivity greater than ~74%. Conjugate heat transfer simulation with multichannel reactor block models considering three different combinations of reactor configuration and coolant type predicted ${\Delta}T_{max}$ equal to 23 K for cross-flow configuration with wall boiling coolant, 15 K for co-current flow configuration with subcooled coolant, and 13 K for co-current flow configuration with wall boiling coolant. In the range of temperature maintained (498 - 521 K), chain growth probability calculated is desirable for low-temperature Fisher-Tropsch Synthesis.

• The Journal of Engineering Geology
• /
• v.3 no.2
• /
• pp.125-148
• /
• 1993

Groundwater flow in fractured rock masses is controlled by combined effects of fracture networks, state of geostafic stresses and crossflow between fractures and rock matrix. Furthermore the scaie dependent, anisotropic properties of hydraulic parameters results mainly from irregular paftems of fracture system, which can not be evaluated properly with the methods available at present. The basic assumpfion of discrete fracture network model is that groundwater flows only along discrete fractures and the flow paths in rock mass are determined by geometric paftems of interconnected fractures. The characteristics of fracture distribution in space and fracture hydraulic parameters are represented as the probability density functions by stochastic simulation. The discrete fracture network modelling was aftempted to characterize the groundwater flow in the vicinity of existing large cavems located in Wonjeong-ri, Poseung-myon, Pyeungtaek-kun. The fracture data of $1\textrm{km}^2$ area were analysed. The result indicates that the fracture sets evaluated from an equal area projection can be grouped into 6 sets and the fracture sizes are distributed in longnormal. The conductive fracture density of set 1 shows the highest density of 0.37. The groundwater inflow into a carvem was calculated as 29ton/day with the fracture transmissivity of $10^{-8}\textrm{m}^2/s$. When the fracture transmissivity increases in an order, the inflow amount estimated increases dramatically as much as fold, i.e 651 ton/day. One of the great advantages of this model is a forward modelling which can provide a thinking tool for site characterization and allow to handle the quantitative data as well as qualitative data.

• Journal of Digital Convergence
• /
• v.12 no.7
• /
• pp.327-336
• /
• 2014

This study aims to identify factors to affect regular utilization status of medical care in cardio-cerebrovascular patients. The research selected 770 cardio-cerebrovascular patients among surveyees from the Korea Health Panel 2010. We analyzed states of medical care utilization using descriptive statistics. Logistic regression analysis was used to examine the main factors associated with regular utilization status of medical care in cardio-cerebrovascular patients. In result, the significant factors associated with regular utilization status of medical care in cardio-cerebrovascular patients were age, education level, household income level. CCI, presence or absence of high risk drinking, and presence or absence of obesity. There's a high probability that patients aged between 60 and 69, equal to and higher than those of high school graduate in education level, upper middle class in household income, the higher CCI, absence of high risk drinking, presence of obesity utilize medical care services more regularly. Therefore, it is necessary to develop effective program and individualized approach for patients using lesser periodical medical care and patients with high risk drinking problem. In the future, these findings can be used an important data for healthcare policy and assessment.