• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.20 no.4
• /
• pp.344-350
• /
• 2009

This paper proposes a hybrid antenna with novel beam steering scheme. The antenna have a cassegrain structure composed of two reflectors. The main reflector is designed for high gain performance using parabola curvature, and the sub-reflector is plate and can be rotated by ${\pm}3^{\circ}$. Thus proposed antenna can steer a antenna beam using the inclination of sub-reflector. A feed array composed of 20 elements is adapted as a feeder for electrical beam steering, and the antenna can be possible to steer the beam by the feed array with sub-reflector. Proposed antenna was fabricated to be operated in Ka-band(30.085$\sim$30.885 GHz) for TX and K-band(20.355$\sim$21.155 GHz), which are the operation frequencies of the Korean satellite, Mugunhwa, to provide satellite multi-media service to vehicles. By the performance test, it can be known that the antenna has minimum gain of 47 dBi for TX and 44.4 dBi for TX and can steer the beam by ${\pm}2^{\circ}$ with sub-reflector.

• Journal of the Korean Electrochemical Society
• /
• v.17 no.2
• /
• pp.94-102
• /
• 2014

Cation exchange membrane (Nafion) was modified to reduce the vanadium ion permeation through the membrane and to increase the vanadium redox flow battery (VRB) system performance by coating the graphene oxide (GO) which has nano-plate like morphology. Modified membrane properties were studied by measuring the ion exchange capacity (I.E.C), water uptake and proton conductivity. The thickness of the coated layer on the surface of the Nafion membrane was observed as $0.93{\mu}m$ by SEM. Proton conductivity and vanadium ion permeability of the modified membrane were decreased to 27% and 25% compared to that of the commercial Nafion membrane respectively. VRB single cell performance test was performed to compare the system performance of the VRB applied with commercial Nafion membrane and modified membrane. VRB system applied with modified membrane showed higher coulombic efficiency and energy efficiency than the VRB system applied with the commercial Nafion membrane due to the reduction of the vanadium ion permeation. From these result, we could suggest that the membrane modification by coating the GO on the surface of the Nafion membrane could be one of the promising strategies to reduce the vanadium ion permeation and to increase the VRB system performance effectively.

• Journal of the Korean Society for Railway
• /
• v.16 no.5
• /
• pp.386-393
• /
• 2013

In this study, the so-called repeated plate load bearing test (RPBT) used to get $E_{v2}$ values in order to check the degree of compaction of subgrade, and to get design parameters for determining the thickness of the trackbed foundation, is investigated. The test procedure of the RPBT method is scrutinized in detail. $E_{v2}$ values obtained from the field were verified in order to check the reliability of the test data. The $E_{v2}$ values obtained from high-speed rail construction sites were compared to converted modulus values obtained from resonant column (RC) test results. For these tests, medium-size samples composed of the same soils from the field were used after analyzing stress and strain levels existing in the soil below the repeated loading plates. Finite element analyses, using the PLAXIS and ABAQUS programs, were performed in order to investigate the impact of the strain influence coefficient. This was done by getting newly computed $I_z$ to get the precise strain level predicted on the subgrade surface in the full track structure; under wheel loading. It was verified that it is necessary to use precise loading steps to construct nonlinear load-settlement curves from RPBT in order to get correct $E_{v2}$ values at the proper strain levels.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.28 no.2
• /
• pp.187-195
• /
• 2015

The gas explosions in offshore installations are known to be very severe according to its geometry and environmental conditions such as leak locations and wind directions, and a dynamic response of structures due to blast loads depends on the load profile. Therefore, a parametric study has to be conducted to investigate the effects of the dynamic response of structural members subjected to various types of load shapes. To do so, a series of CFD analyses was performed using a full-scale FPSO topside model including detail parts of pipes and equipments, and the time history data of the blast loads at monitor points and panels were obtained by the analyses. In this paper, we focus on a structural dynamic response subjected to blast loads changing the magnitude of positive/negative phase pressure and time duration. From the results of linear/nonlinear transient analyses using single degree of freedom(SDOF) and multi-degree-of freedom(MDOF) systems, it was observed that dynamic responses of structures were significantly influenced by the magnitude of positive and negative phase pressures and negative time duration.

• Journal of the Earthquake Engineering Society of Korea
• /
• v.13 no.5
• /
• pp.11-21
• /
• 2009

Considering that the weight of a biaxial hollow slab system is not increased with an incremental increase in its thickness, and that the flexural stiffness of a biaxial hollow slab is not significantly lower than that of a general solid slab, there has been a growing need for biaxial hollow slab systems, because long span structures are in great demand. In a long span structure, the problem of vibration of floor slabs frequently occurs, and the dynamic characteristics of a biaxial hollow slab system are quite different from the conventional floor systems. Therefore, in this study, the floor vibration of a biaxial hollow slab system subjected to walking load is investigated in comparison with a conventional floor slab system. For the efficiency of time history analysis, an equivalent plate slab model that can precisely represent the dynamic behavior of a biaxial hollow slab system is used. From the analytical results, it was determined that vibration of a biaxial hollow slab system subjected to walking load is evaluated as "office-level vibration," according to the classifications of the architectural institute of Japan and ANSI.

• Journal of Korean Society of Steel Construction
• /
• v.17 no.6 s.79
• /
• pp.673-679
• /
• 2005

According to continuous welded rails on a bridge, temperature changes bring about the expansion of the bridge deck,adding axial forces on the track. Moreover, the ballast on the bridge deck expansion joint is moved due to the bridge deck. The longer the bridge deck is, the greater the influence will be, loosening the ballast, causing track irregularities, and deteriorating passenger comfort. Considering the structure of the bridge itself and tolerance for track irregularities caused by the loosened ballast on the bridge, the maximum length of the deck should be less than 80 m, which is the same as the standard of French railways. In this study, the interaction between the expansion related to the bridge length and the irregularity in the longitudinal level, referring to measurements and maintenance work performed in high-speed railways, was analyzed. This research shows that the installation of a sliding plate or a vertical ballast stopper is not a good option, since it is difficult. On the other hand, the installation of a ZLR fastener or gluing is easy, but its influence is insignificant. In conclusion, switch tie tamping or manual tamping is more effective than other methods of what?

• Journal of the Korean Vacuum Society
• /
• v.22 no.5
• /
• pp.250-256
• /
• 2013

It is described that the proton beam induces micro-size defects and electronic deep levels in luminescence Thin Film. Coincidence Doppler Broadening Positron Annihilation Spectroscopy (CDBPAS) and Positron lifetime Spectroscopy were applied to study of characteristics of a poly crystal samples. In this investigation the numerical analysis of the Doppler spectra was employed to the determination of the shape parameter, S-parameter value. The samples were exposed by 3.0 MeV proton beams with the intensities ranging between 0 to ${\sim}10^{14}$ particles. The S-parameter values decreased as increased the proton beam, that indicates the protons trapped in vacancies. Lifetime ${\tau}_1$ shows that positrons are trapped in mono vacancies. Lifetime ${\tau}_2$ is not changed according to proton irradiation that indicate the cluster vacancies of the grain structure.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.21 no.11
• /
• pp.501-509
• /
• 2020

Earthwork in the construction field is a core process of construction, and it is used in almost all processes and is connected to the safety of the structure directly. Therefore, it is essential to analyze and confirm the road tamping through a plate bearing test and a field density test. The current analog measurement methods for road tamping measurement is difficult to check in real-time, accurate location information, time information, and the history management of workers in the field. Therefore, IoT (Internet of Things)-based DCPT (Dynamic Cone Penetration Test) was developed for a smart construction environment with a solution to the problem. The Smart DCPT system operated in a smartphone environment is IoT-based. The Smart DCPT system can apply various applications and has advantages of flexibility, low cost, and high efficiency. The IoT-based DCPT records the digital road tamping information, location information, time information, and worker information per measurement count. In addition, the various information is transmitted in real-time to the management center through a smartphone. This system is expected to contribute to the management of the construction process.

• Composites Research
• /
• v.13 no.2
• /
• pp.30-39
• /
• 2000

It is difficult for civil engineer to apply composite materials of laminated type to structure for civil construction because of complicated theory although those have much merit. A simple method by which one can predict "exact" values of the natural frequency of vibration of laminated plates is presented. Many laminates with particular orientations have negligible values of $B_{16}$ and $B_{26}$ as the number of plies increases. Such laminates, with $D_{16}$ = $D_{26}$ ->0 can be solved by the same equation as for the special orthotropic laminates(1991,1995). If the quasi-isotrpic constants are used, It is possible to simplify analysis procedure since the equations for isotropic plates can be used. Use of some coefficients can produce "exact" values for laminates with such configuration. This coefficient, in fact, represents the effect of the anisotropy of the laminate. D. H. Kim proposed to use a correction factor, he developed, to produce "exact" solution out of the approximate solution obtained by using the quasi-isotropic constants(1995). In this paper, the fiber orienation studied is [$\alpha$/$\beta$/$\beta$/$\gamma$/$\alpha$/$\alpha$/$\beta$]r, with $\alpha$=-$\beta$, and $\gamma$${\gamma}$=$0^{\circ}$ or $90^{\circ}$ and the above-mentioned method is used to obtain the natural frequencies of plates with such orientations, and detailed result is presented for the use of engineers.nted for the use of engineers.

• Korean Journal of Soil Science and Fertilizer
• /
• v.43 no.2
• /
• pp.180-187
• /
• 2010

The study was performed to investigate the property of rhizosphere microorganisms, and community structure during GMO, and Non-GMO rice cultivation. In the dilution plate technique, there were no significant differences in microbial populations of rhizosplane with genetically modified, and non-genetically modified rice cultivation, and rhizosphere were also the same results. Dominant bacterial genera were Afipia 12.5%, Spingomonas 10.0%, Ramlibacter 10.0%, Mycobacterium 7.5%, and Tetrasphaera 7.5% in rhizosphere soil of genetically modified rice plant, while Afipia 7.3%, Spingomonas 12.2%, Ramlibacter 7.3%, Mycobacterium 17.1%, Tetrasphaera 14.6% in non-genetically modified cultivated at Suwon test fields in 2006. Majorgenera isolated from root surface cultivated in Yesan fields were Arthrobacter 12.7% in rhizoplane of genetically modified plant, and Burkholderia 22.2% of non-genetically modified plant in 2007, Paucimonas 26.6% of genetically modified plant, Chryseobacterium 15.4% of non-genetically modified plant in 2008. Also the microbial communities in rhizosphere soils of genetically modified, and non-genetically modified plants were characterized using phospholipid fatty acid, and denaturing gradient gel electrophoresis. The phospholipid fatty acid profiles of soils in this condition showed different pattern, but did not show significant differences between soils cultivated with genetically or non-genetically modified rice plants.