• Journal of Korean Society of Steel Construction
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• v.27 no.1
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• pp.23-30
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• 2015

Developed in this study were Octagonal-hollow-section(OHS) struts, whose compressive strengths against flexural and local buckling is higher than H-shape or rectangular-hollow-section(RHS) struts with the same unit weight. OHS members are also advantageous in handling and storing compared to circular hollow sections(CHS). OHS members were fabricated from HR Plates by cold forming and fillet welding. 5 numbers of 20m long OHS struts were assembled, each of which consist of two 9.6m long OHS member and two end connection elements made of cast iron. The compressive strength of the OHS strut was evaluated by comparing the test results, design codes and FEM analysis each other. Test results show that all of the struts have almost same or larger compressive strength than Korean Road Bridge Design Code(KRBDC) (2012). The initial imperfections can be estimated by using measured strains and are turned out to be less than L/450 for all the struts tested. The results of FEM analysis show that the variation of initial imperfection has less effects on the compressive strength for struts with vertical surcharge than for those with self-weight only, while the strength decreases as the initial imperfection increases. As the result of this study, the allowable initial imperfection for 20m long OHS struts is recommended to be less than L/350 on job sites.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.4
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• pp.1327-1334
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• 2014

Linear form of public works such as roads, railways and rivers, generally used as long work crossing administrative districts, can be several hundreds km length and narrow. These linear forms use SCM sheets, which do not include the quadrangle shape, to make a public announcement of topographical drawing in order to get the work approval. the Integrated measurement channel investigation and cadastral act that are established in 2009 apply the ITRF for the composition of design and construction books and coordinates of topographical map in order to get the work approval. However according to the article 5 of additional clause, while the cadastre is maintaining local coordinates, if there is a technical error in the content of the Public Announcement of Topographical Drawing that used the SCM, the question of responsibility of land borders and the efficacy or not of the announcement is raised as an administrative measure. After analysing the causes and enforcing coordinate conversion and correction taking into account linear form work's features, the result was reflected in the existing SCM. As a conclusion, the present study proposes the improvement of the procedures of the Public Announcement of Topographical Drawing.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.4
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• pp.1227-1240
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• 2014

Abandoned mines often cause environmental problems, such as alteration of landscape, metal contamination, and landslides due to a heavy rainfall. Geotechnical and rheological tests were performed on waste materials corrected from Imgi waste rock dump, located in Busan Metropolitan City. Debris flow mobility was examined with the help of 1-D BING model which was often simulated in both subaerial and subaqueous environments. To determine flow curve, we used a vane-penetrated rheometer. The shear stress (${\tau}$)-shear rate (${\dot{\gamma}}$) and viscosity(${\eta}$)-shear rate (${\dot{\gamma}}$) relationships were plotted using a shear stress control mode. Well-known rheological models, such as Bingham, bilinear, Herschel-Bulkley, Power-law, and Papanastasiou concepts, were compared to the rheological data. From the test results, we found that the tested waste materials exhibited a typical shear shinning behavior in ${\tau}$-${\dot{\gamma}}$ and and ${\eta}$-${\dot{\gamma}}$ plots, but the Bingham behavior is often observed when the water contents increased. The test results show that experimental data are in good agreement with rheological models in the post-failure stage during shearing. Based on the rheological properties (i.e., Bingham yield stress and viscosity as a function of the volumetric concentration of sediment) of waste materials, initial flowing shape (5 m, 10 m, and 15 m) and yield stress (100 Pa, 200 Pa, 300 Pa, and 500 Pa) were input to simulate the debris flow motion. As a result, the runout distance and front velocity of debris flow are in inverse propositional to yield stress. In particular, when the yield stress is less than 500 Pa, most of failed masses can flow into the stream, resulting in a water contamination.

• Spatial Information Research
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• v.21 no.1
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• pp.45-52
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• 2013

Recently 3D surveying is recommended to manage underground facilities systematically before refilling of site operation. As the demand of realtime localization increases, cost reduction and consistent data construction which are realizable by using one man surveying method with unmanned target, are necessary for constructing DB of all sorts of the underground facilities with more speediness and correctness. This study sets a goal to develop a new type of surveying target which allows realtime localization to be performed by one man, through making an optimum reflector(triangle, quadrangle, and semispherical shape) by using the retro-reflection principle of optical prism which is being used for surveying currently. The new surveying target makes realtime surveying possible. To check reliability of its data, the accuracy is compared with surveying coordination of total station for each type in a quantitative method. In the result, the usefulness of the reflector for Underground Facilities localization is proved. Thus the foundation for underground DB construction conducted by one man is established for acquisition of 3D location information in more efficient way through using unmanned target.

• Structural Monitoring and Maintenance
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• v.2 no.1
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• pp.77-93
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• 2015

The idea of using measured dynamic characteristics for damage detection is attractive because it allows for a global evaluation of the structural health and condition. However, vibration-based damage detection for complex structures such as long-span cable-supported bridges still remains a challenge. As a suspension or cable-stayed bridge involves in general thousands of structural components, the conventional damage detection methods based on model updating and/or parameter identification might result in ill-conditioning and non-uniqueness in the solution of inverse problems. Alternatively, methods that utilize, to the utmost extent, information from forward problems and avoid direct solution to inverse problems would be more suitable for vibration-based damage detection of long-span cable-supported bridges. The auto-associative neural network (ANN) technique and the probabilistic neural network (PNN) technique, that both eschew inverse problems, have been proposed for identifying and locating damage in suspension and cable-stayed bridges. Without the help of a structural model, ANNs with appropriate configuration can be trained using only the measured modal frequencies from healthy structure under varying environmental conditions, and a new set of modal frequency data acquired from an unknown state of the structure is then fed into the trained ANNs for damage presence identification. With the help of a structural model, PNNs can be configured using the relative changes of modal frequencies before and after damage by assuming damage at different locations, and then the measured modal frequencies from the structure can be presented to locate the damage. However, such formulated ANNs and PNNs may still be incompetent to identify damage occurring at the deck members of a cable-supported bridge because of very low modal sensitivity to the damage. The present study endeavors to enhance the damage identification capability of ANNs and PNNs when being applied for identification of damage incurred at deck members. Effort is first made to construct combined modal parameters which are synthesized from measured modal frequencies and modal shape components to train ANNs for damage alarming. With the purpose of improving identification accuracy, effort is then made to configure PNNs for damage localization by adapting the smoothing parameter in the Bayesian classifier to different values for different pattern classes. The performance of the ANNs with their input being modal frequencies and the combined modal parameters respectively and the PNNs with constant and adaptive smoothing parameters respectively is evaluated through simulation studies of identifying damage inflicted on different deck members of the double-deck suspension Tsing Ma Bridge.

• Korean Chemical Engineering Research
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• v.44 no.5
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• pp.513-519
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• 2006

We developed two kinds of the microchip for application to electrophoresis based on both glass and quartz employing the MEMS fabrications. The poly-Si layer deposited onto the bonding interface apart from channel regions can play a role as the optical slit cutting off the stray light in order to concentrate the UV ray, from which it is possible to improve the signal-to-noise (S/N) ratio of the detection on a chip. In the glass chip, the deposited poly-Si layer had an important function of the etch mask and provided the bonding surface properly enabling the anodic bonding. The glass wafer including more impurities than quartz one results in the higher surface roughness of the channel wall, which affects subsequently on the microflow behavior of the sample solutions. In order to solve this problem, we prepared here the mixed etchant consisting HF and $NH_4F$ solutions, by which the surface roughness was reduced. Both the shape and the dimension of each channel were observed, and the electroosmotic flow velocities were measured as 0.5 mm/s for quartz and 0.36 mm/s for glass channel by implementing the microchip electrophoresis. Applying the optical slit with poly-Si layer provides that the S/N ratio of the peak is increased as ca. 2 times for quartz chip and ca. 3 times for glass chip. The maximum UV absorbance is also enhanced with ca. 1.6 and 1.7 times, respectively.

• Korean Chemical Engineering Research
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• v.44 no.5
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• pp.498-504
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• 2006

The etch rates of photoresist (PR) and the etch selectivity of $SiO_2$ to PR in a high density $CHF_3$ plasma were investigated at different ion-incident angles and bias voltages. A Faraday cage was employed for the accurate control of ion-incident angles. The ion energy was controlled by changing bias voltages. The etch rate of $SiO_2$ continuously decreased with ion-incident angles but the etch rate of PR remained constant up to the middle angle region and decreased afterwards. The etch rates of $SiO_2$ normalized to those at $0^{\circ}$ incident angle changed with the ion-incident angle following a cosine(${\theta}$) curve. On the other hand, the normalized etch rates of the PR changed showing a drastic over-cosine shape in the middle angle region. The etch selectivity of $SiO_2$ to PR decreased with an increase in the ion-incident angle because the etch yields of PR were enhanced by physical sputtering in the middle angle region compared to the case of $SiO_2$ etching. The etch selectivity of $SiO_2$ to PR decreased with an increase in the bias voltage at nearly all ion-incident angles.

• Journal of the Korean Institute of Landscape Architecture
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• v.39 no.6
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• pp.21-35
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• 2011

This study is basic research which aims to compare and analyze changes in rural areas in modern times. The main purpose of this study is to comprehend the characteristics of changes in the Korean rural landscape and to suggest the implications for preservation and maintenance of the rural landscape. To help in understanding the rural landscape systematically, it should be divided into six types: housing landscape, cultivation landscape, green landscape, waterside landscape, streetscape and symbolic and religious landscape. According to this step, the contents and the procedures of changes were analyzed generally. Based on the literature review and field survey, the styles of changes were deduced to be formation, alternation, relocation, damage and restoration on landscape elements. Lastly, it was concluded that complex changes of landscape in rural areas from the government's development policy have been continued from macroscopic changes like overall structure and system of landscape to microscopic changes like shape, material, size and color of each landscape element. Rural villages which have not had the government's development policy applied to them may not be appropriate for this study. However, this study has significance in that it can suggest the direction for desirable rural planning. Future studies need to consider landscape change through not only the development policy but also economic, social and cultural factors.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.6 no.2
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• pp.238-246
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• 1996

High-density SiC-AIN solid solutions were fabricated from powder mixtures of $\beta$-SiC and AIN by hot-pressing in the 1870 to $2030^{\circ}C$ temperature range. The reaction of AIN and $\beta$-SiC (3C) powder transformed to the 2 H (wurzite) structure appeared to depend on the temperature and SiC/A1N ratio and seeds present. The crystalline phases consisted of a SiC-rich solid-solution phase and an A1N-rich solid-solution phase. At $2030^{\circ}C$ for 1 h, for a composition of 50 % AIN/50 % SiC with a seeding of $\alpha$-SiC, the complete solid solution could be obtained and the microstructures are equiaxed with a relatively homogeneous grain size of 2 H phases. The variation of the seeding of $\alpha$-SiC in SIC-A1N solid solutions could be attributed to the transformation behaviour and differences in size and shape of the grains, as well as to other factors, such as grain size distributions, compositional inhomogeneity, and structural defects.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.20 no.6
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• pp.283-288
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• 2010

Nanosized NiO powder was prepared by mixing an acid nickel salt and a base nickel salt and their reduction behavior was studied. Ni formate was employed as an acid salt and nickel hydroxide and basic nickel carbonate as base salts. One equivalent acid salt was mixed with 9 equivalent base salt. The mixture of the formate and the carbonate produced ~100 run spherical NiO powder by heat treatment at $750^{\circ}C$/2 h, but the mixture of the formate and the hydroxide gave rise to ~100 nm pseudo spherical NiO powder by heat treatment at $600^{\circ}C$/2 h and grew fast to give pseudo cubic crystals of 100~600 run by heat treatment at $750^{\circ}C$/2 h. Reduction by hydrogen gas proceeded much faster for the one with the hydroxide than that with the carbonate to give porous body with well grown necks. Their behavior was studied by analysis of TG/DSC, XRD, and SEM.