• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.12
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• pp.1327-1336
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• 2007

In this paper, we propose a reconfigurable antenna which operates as a disk-loaded dipole antenna and a folded dipole antenna alternatively using RF on/off switches. The antenna can change its effective length to achieve dual-band operation; operates as the folded dipole antenna for stepping up the radiation resistance in low frequency band of $20{\sim}300$ MHz, and as the disk-loaded dipole antenna for an omni-directional radiation pattern (horizontal plane) and a donut-shaped radiation pattern (vertical plane) in high frequency band of $300{\sim}1.3$ GHz. In the low band, the proposed antenna shows higher gain than a conventional dipole antenna with a reduced antenna size. In the high band, the antenna maintains a broad beamwidth of about $80^{\circ}$, thus the antenna can be applicable to antennas for direction finding applications.

• Journal of Magnetics
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• v.9 no.4
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• pp.116-120
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• 2004

Hexagonal barium-ferrite ($BaFe_{12}O_{19}$, magnetoplumbite structure; BaM) film with perpendicularly c-axis orientation was successfully deposited on (100) silicon substrates with an MgO (111) underlayer by rf diode sputtering and in-situ heating at $920^{\circ}C$. The magnetic and structural properties of 0.27 ${\mu}m$ thick BaM films on MgO (111) underlayers were compared to films of the same thickness deposited onto single-crystal MgO (111) and c-plane ($000{\ell}$) sapphire ($Al_2O_3$) substrates by vibrating sample magnetometry (VSM), x-ray diffractometer (XRD), and atomic force microscopy (AFM). The thickness dependence of MgO (111) underlayers on silicon wafer was found to have a large effect on both magnetic and structural properties of the BaM film. The thickness of 15 nm MgO (111) underlayers produced BaM films with almost identical magnetic and structural properties as the single-crystal substrates; this can be explained by the lower surface roughness for thinner underlayer thicknesses. The magnetization saturation ($M_s$) and the ratio $H_{cII}/H_{c{\bot}}$ for the BaM film with a 15 nm MgO (111) underlayer is 217 emu/cc and 0.24, respectively. This is similar to the results for the BaM films deposited on the single-crystal MgO (111) and sapphire substrates of 197 emu/cc and 0.10, 200 emu/cc and 0.12, respectively. Therefore, the proposed MgO (111) underlayer can be used in many applications to promote c-axis orientation without the cost of expensive substrates.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.30 no.3
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• pp.165-173
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• 2007

A space launch vehicle system represents a typical example of large-scale multi-disciplinary systems, consisting of subsystems such as mechanical structure, electronics, control, telecommunication, propulsion, material engineering etc. A lot of cost is required to develop the launch vehicle system. A precise planning of R&D cost is very essential to make a success of the launch vehicle development program. Especially in the early development phase of a new space launch vehicle system, cost estimation techniques and analogy from past similar development data are very useful methods to estimate a development cost of the launch vehicle system. Now Korea Aerospace Research Institute is in charge of the KSLV-I (Korea Space Launch Vehicle-I) Program that is a part of Korea National Space program. KSLV-I Program is a national undertaking to develop launch capabilities to deliver science satellites of a 100kg-class into a low earth orbit. It is hereafter, going to plan to develop a new korean space launch vehicle. In this paper, first the development costs of well-known launch vehicles in the world are presented to provide a reference to make a development plan of a new launch vehicle. Second this paper introduces the present status of cost estimation applications at NASA. Finally this paper presents the results from application of a TRANSCOST, a parametric cost model, to derive a cost estimate of a new launch vehicle development, as an example.

• Nuclear Engineering and Technology
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• v.46 no.6
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• pp.783-796
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• 2014

The coarse mesh finite difference (CMFD) method is applied to the discontinuous finite element method based discrete ordinate calculation for source convergence acceleration. The three-dimensional (3-D) DFEM-Sn code FEDONA is developed for general geometry applications as a framework for the CMFD implementation. Detailed methods for applying the CMFD acceleration are established, such as the method to acquire the coarse mesh flux and current by combining unstructured tetrahedron elements to rectangular coarse mesh geometry, and the alternating calculation method to exchange the updated flux information between the CMFD and DFEM-Sn. The partial current based CMFD (p-CMFD) is also implemented for comparison of the acceleration performance. The modified p-CMFD method is proposed to correct the weakness of the original p-CMFD formulation. The performance of CMFD acceleration is examined first for simple two-dimensional multigroup problems to investigate the effect of the problem and coarse mesh sizes. It is shown that smaller coarse meshes are more effective in the CMFD acceleration and the modified p-CMFD has similar effectiveness as the standard CMFD. The effectiveness of CMFD acceleration is then assessed for three-dimensional benchmark problems such as the IAEA (International Atomic Energy Agency) and C5G7MOX problems. It is demonstrated that a sufficiently converged solution is obtained within 7 outer iterations which would require 175 iterations with the normal DFEM-Sn calculations for the IAEA problem. It is claimed that the CMFD accelerated DFEM-Sn method can be effectively used in the practical eigenvalue calculations involving general geometries.

• Magazine of the Korean Society of Agricultural Engineers
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• v.29 no.2
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• pp.53-63
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• 1987

Due to their wide range of application, deterministic comprehensive hydrologic models using digital computers have been developed in all countries of the world and researches are being undertaken for their appropriate applications. The aim of this study has been to demonstrate the practical implementation of a physically based distributed hydrologic model, the USDAHL-74 model and to investigate its ability to simulate the long term estimate of water balance quantities in a Korean mountainous watershed. Application of the model to Dochuk watershed indicates the following results. 1.Since the USDAHL-74 model includes all the major components of the hydrologic cycle in agricultural watersheds, thus is comprehnsive, the model seems to have a wide range of application from the fact that simulation results obtained are not only runoff volumes m various time units but their spatial variation as well as even soil moisture within the watershed. 2.An approximate calibration to determine the parameter values in the model using various data obtained from D0chuk shed shows that the simulation error of yearly runoff volume is only 0.6 % and a correlation coefficient between observed daily runoff volume and simulated one is 0.91 in all calibrated period.3.As a verification test of the model, runoff volumes are simulated using 1986 year data without changing the parameter values determined by 1985 year data. The tests show that the USDAHL-74 model is a flexible tool and that realistic production to simulate the long term estimate of runoff in Korean mountainous watershed could be obtained using only a short period of calibration.4. Despite of the encouraging results, there still remain minor problems concerning the practical application of the model to improve the result of simulations. Some of these are the small descrepancies between observed and simulated daily runoff volume appeared in the vicinity of peaks and the recession of1 the daily hydrographs and the model performance for the frozen ground and melting process in the model. 5. Alough the use of parameter with physical significance and the ability to improve calibrations on the basis of physical reasoning represents advantages in the simulation for ungaged watersheds, further researches are needed to use the USDAHL-74 mode to simulate runoff in ungaged watersheds.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2016.11a
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• pp.156-156
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• 2016

The effect of nitrogen doping on the mechanical and tribological performance of single-layer tetrahedral amorphous carbon (ta-C:N) coatings of up to $1{\mu}m$ in thickness was investigated using a custom-made filtered cathode vacuum arc (FCVA). The results obtained revealed that the hardness of the coatings decreased from $65{\pm}4.8GPa$ to $25{\pm}2.4GPa$ with increasing nitrogen gas ratio, which indicates that nitrogen doping occurs through substitution in the $sp^2$ phase. Subsequent AES analysis showed that the N/C ratio in the ta-C:N thick-film coatings ranged from 0.03 to 0.29 and increased with the nitrogen flow rate. Variation in the G-peak positions and I(D)/I(G) ratio exhibit a similar trend. It is concluded from these results that micron-thick ta-C:N films have the potential to be used in a wide range of functional coating applications in electronics. To achieve highly conductive and wear-resistant coatings in system components, the friction and wear performances of the coating were investigated. The tribological behavior of the coating was investigated by sliding an SUJ2 ball over the coating in a ball-on-disk tribo-meter. The experimental results revealed that doping using a high nitrogen gas flow rate improved the wear resistance of the coating, while a low flow rate of 0-10 sccm increased the coefficient of friction (CoF) and wear rate through the generation of hematite (${\alpha}-Fe_2O_3$) phases by tribo-chemical reaction. However, the CoF and wear rate dramatically decreased when the nitrogen flow rate was increased to 30-40 sccm, due to the nitrogen inducing phase transformation that produced a graphite-like structure in the coating. The widths of the wear track and wear scar were also observed to decrease with increasing nitrogen flow rate. Moreover, the G-peaks of the wear scar around the SUJ2 ball on the worn surface increased with increasing nitrogen doping.

• Journal of Korean Society for Geospatial Information Science
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• v.14 no.3 s.37
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• pp.47-53
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• 2006

In this contribution, an integration of seamless navigation system for the pedestrian is introduced. To overcome the GPS outages in various situations, multi-sensor of GPS, INS, electronic barometer and compass are considered in one Extented Kalman filter. Especially, the integrated system is designed for low-cost for the practical applications. Therefore, a MEMS IMU is considered, and the low quality of the heading is compensated by the electronic compass. In addition, only the pseudoranges from GPS measurements are considered for possible real-time application so that the degraded height is also controlled by a barometer. The mathematical models for each sensor with systematic errors such as biases, scale factors are described in detail and the results are presented in terms of a covariance analysis as well as the position and attitude errors compared to the high-grade GPS/INS combined solutions. The real application scenario of GPS outage is also investigated to assess the feasible accuracy with respect to the outage period. The description on the current status of the development and future research directions are also stated.

• Journal of Korean Society for Geospatial Information Science
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• v.10 no.3 s.21
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• pp.107-114
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• 2002

The cadastral surveying is essential for the effective management of a country, the D/B building of NGIS. Many of GPS applications require a positioning accuracy of several centimeters for rover in real-times. But, to achieve higher positioning accuracies in real-time, the double differencing technique should be implemented using carrier phase data. Corrected observations at the reference station can be transmitted and used to form double difference observations at the rover using a data link. In this study, the area accuracy of cadastral survey using the RTK GPS will be assessed, and will produce area of parcel of land. As the result of comparison among area by TS, planer surveying and RTK GPS. parcels-register for site is analyzed by this data. The results show that mean error of area calculated min. $2.42m^{2}{\sim}\;max.\;13.69m^{2}$ and RMSE calculated min. $0.00329\;{\sim}\;max.\;0.01846$.

• The Transactions of the Korea Information Processing Society
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• v.4 no.3
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• pp.811-820
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• 1997

Disk arrays are using to enhance data trandfer rate and I/O performance in multimedia applications which need a high-performance storage device with large storage capacity and high-speed network.As performance varies with configuration and data layout scheme,disk array characteristic variables must be approrpriately deter-mined in desibning disk array archetecture for a speciffic applicatoin. In this paper,in order to design a disk array architecturte as a storage server of a small-scale VOD system,we evaluate performance of a disk array to chose the number of disks in the array,disk array cinfiguration,a degree of declustering for a given data block size of continous media file system and I/D request size through simulation.Simulation result shows that RAID level 5 with 5 disks ios a suitable candidate for the disk array architecture which privides MPEG-2 files with a rate of 6 Mbps,Moreover,we whow that stripe unit is 64 KB and a layout scheme is contigous placement.

• Journal of Haehwa Medicine
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• v.8 no.1
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• pp.625-641
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• 1999

Aging occurs as a part of maturation as the time progresses which manifests in the human body causing morphological and functional degeneration, eventually leading to death. This experimental study was conducted to investigate a herbal formula to fortify the heart with easy clinical applications. Sungshimsan was chosen to study its effects in heart lipid peroxide and metabolic enzyme system in senescence induced rats. After pre-treatment of Sungshimsan for 2 weeks at the dosage of A (100mg/kg), B (250mg/kg), C (350mg/kg), and D (500mg/kg), a lipid peroxide and metabolic enzyme system changes of the heart were meaured in 32 weeks old rats. The following results were obtained in this study: 1. The contents of lipid peroxide was significantly reduced in the experimental groups treated with greater than 2 weeks at 250mg/kg. 2. The enzymatic activity of cytochrome P-450, cytochrome b5, and NADPH-cytochrome P450 reductase were significantly decreased in the 250mg/kg, 350mg/kg, and 500mg/kg experimental groups. 3. The activity of glutathione and glutathione S-transferase were significantly increased in the 250mg/kg, 350mg/kg, and 500mg/kg experimental groups. 4. The activity of glutathione reductase and glutathione peroxidase were not influenced compared to the control group. 5. The activity of ${\gamma}$-glutamylcystein synthetase was significantly increased in the 250mg/kg, 350mg/kg, and 500mg/kg experimental groups. 6. The activity of enzymes detoxificatioon superoxide dismutase and catalase were not influenced compared to the control group. Summarizing above results suggest that the Sungshimsan has profound effects in the heart lipid peroxide, free radicals, and delaying the heart aging process. Further clinical researches and application can be anticipated on the topic of senility and gerontology.