• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.3
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• pp.75-83
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• 2018

In study, Structural stability was considered when applying the high strength strut method with improved general strut method. considered whether there is sufficient stiffness to so as not buckling to the maximum hypothetical earth pressure. also structure stability of the strut component was reviewed. The high strength strut method is a technique used in place of the general strut method. high strength prefabricated Strut method is a technique that has bolt holes drilled in the upper flange at regular intervals. As a result of the buckling analysis, it was considered that the safety factor increased by about 5 %. also Since the stress generated is below the allowable stress, it is judged that structural stability of the strut is ensured. In particular, the safety factor of axial compressive stress increases about 16 % with use of high strength steel when applying the high strength prefabricated strut method. the high strength strut method is construction method may shorten the construction period and there is no expense to purchase additional materials.

• Atmosphere
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• v.20 no.3
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• pp.229-238
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• 2010

The 1,000~500 hPa thickness and the $0^{\circ}C$ isotherm at 850 hPa have been used as the traditional predictors for wintertime precipitation-type forecasts. New approaches are taking on added significance as preexistence method of determination for wintertime precipitation-type exhibits more or less prevalent false alarms. Moreover thicknesses and thermodynamic profiles from ordinary upper-air observation were not adequate to monitor the atmospheric structure. In this regard, Microwave radiometric profiler microwave radiometer is useful in wintertime precipitation-type forecasts because radiometric measurements provide soundings at high temporal resolution. In this study, the determination and the predictability of wintertime precipitation-type were examined by using the calculated thicknesses, temperature of 850 hPa (T850) from a microwave radiometer, and surface observation at National Center for Intensive Observation of severe weather (NCIO) located at Haenam, Korea. The critical values for traditional predictors (thickness of 1000~500 hPa and T850) were evaluated and adjusted to Haenam region because snow rarely occurred with a 1000-500 hPa thickness > 5,300 m and T850 > $-10^{\circ}C$. Three thicknesses (e.g., 1,000~850, 1000~700, and 850~700 hPa thickness), T850, surface air temperature, and wet-bulb temperature were also evaluated as the additional predictors. A simple nomogram and a flow chart were finally designed to determine the wintertime precipitation-type using the microwave radiometer. The skill scores for the predictability of precipitation-type determination are considerably improved and the predictors showed the temporal variations in 12 hours before precipitation. We can monitor the hit and run snowfall in winter successful by realtime watch of the predictors, especially in commutes of big cities.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.8
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• pp.743-749
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• 2015

In this paper, we describe the dynamic tumble-stability analysis of a seabed-walking robot named Crabster (CR200) in forward-incident currents. CR200 is designed to be operated in tidal-current conditions, and its body shape is also designed to minimize hydrodynamic resistances considering hydrodynamics. To analyze its tumble stability, we adopt the dynamic stability margin of a ground-legged robot and modify the definition of the margin to consider tidal-current effects. To analyze its dynamic tumble stability, we use the estimated hydrodynamic forces that act on the robot in various tidal-current conditions, and analyze the dynamic tumble-stability margin of the robot using the estimated results obtained for the various tidal-current conditions. From the analyses, we confirm the improved tumble stability of the robot according to the movement of the tumble axis caused by the supporting points of the legs.

• Journal of Korean Society for Quality Management
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• v.46 no.1
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• pp.169-188
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• 2018

Purpose: The purpose of this study is to analyze low-temperature starting performance of the light attacker and to search and improve the aircraft system including battery and Battery Charge and Control Unit(BCCU). Methods: In order to improve the starting up performance of the light attacker at low-temp, various deficiency cause were derived and analyzed using Fault Tree Analysis method. As a result, it was confirmed there were drawbacks in the charging and discharging mechanism of the battery. The inactivation of the battery's electrolyte at low-temp and the premature termination of the battery charge were the main cause. After long error and trial, we improved these problems by improving performance of battery and optimizing the charging algorithm of BCCU. Results: It was confirmed that the problems of starting up failures were solved through the combined performance test of the battery and BCCU, the ground test using the aircraft system and the operation test conducted by Korea Airforce operating unit for 3 months in winter. Conclusion: This study showed that the improvement of quality reliability was achieved and thus the start-up performance issue of the light attacker has been resolved at low temperature. And it is expected that the design methodologies of temperature-affected electrical system of aircraft will contribute to the development of the aircraft industry in the future.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.32 no.4
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• pp.66-73
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• 2000

Alkaline sulfite-anthraquinone(AS-AQ) cooking process has been applied to unground pine bark. The properties of the spent liquor such as molecular weight distributions, sulfonic equivalent weights, degree of sulfonation, phenolic hydroxyl groups and kaolin dispersing ability have been investigated to evaluate the possibility of using this liquor as concrete additives or binders. In the case of ground bark meal, more than 90% delignification was achieved at the optimal cooking conditions. However, applying these conditions on unground bark the delignification was slightly retarded. The decrease in the degree of delignification may be attributed to less penetration and diffusion of chemicals during the cooking of the bark. Increasing the cooking temperature only by $5^{\circ}C$ improved the delignification of the bark and about 90% delignification can be achieved. These results indicate that bark can be used successfully during AS-AQ cooking without any mechanical or physical pretreatment. The properties of lignin or polyphenol sulfonates in the spent liquor after AS-AQ cooking of the bark were compared with Sunflo-R, which is commercial lignosulfonate(CLS) prepared from wood. The weight average molecular weights(Mws) estimated by gel-filteration chromatography was found to be ranging from 1,200~1,800. These are considerably lower than those in CLS. Lignin or polyphenol sulfonates in the spent liquor of bark and CLS have similar degree of sulfonation, but the phenolic hydroxyl group was 1.8 times higher than CLS. Moreover, the dispersing abilities of the spent liquors were better than that of CLS, especially after 0.1% addition to kaolin suspension.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.29 no.1
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• pp.7-12
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• 1997

This study was intended to investigate the proper shape and size of calcium carbonate for the improvement of paper properties and its end use performance. We loaded calcium carbonate of various shapes and size in the handsheet and measured their physical and optical properties. Results obtained from the study are summarized as follows : 1. Due to different particle shapes and sizes, precipitated calcium carbonate (PCC) contributed greater to bulk improvement than ground calcium carbonate (GCC). Scalenohedral form of PCC produced the bulkiest sheet, GCC made the sheet bulkier as average particle size increases. 2. Tensile strength increased as average particle size was increasing. GCC kept tensile strength more effectively than PCC. The effect of particle size on tensile strength was much more pronounced as filler addition level was increasing. 3. Over the average particle size of 6.99$\mu$m, GCC gave much higher burst strength and internal bond than PCC did. In the filler levels of 20% and 30%, GCC by using bigger size fillers showed 50~100% improvement in some cases than PCC at the same filler content. 4. Tear strength increased as average particle size was increasing. At the filler level of 30%, PCC decreased tear greatly. 5. Over the average particle size of 13.56$\mu$m, GCC kept bending stiffness greater than PCC. Due to its shape, Scalenohedral form of PCC showed higher stiffness than others at the same particle size. 6. Cubic and acicular form of PCC improved light scattering coefficient very effectively. Light scattering coefficient of GCC decreased as average particle size increased. 7. Both of particle shape and size of filler were important factor in developing optical properties and bending stiffness. Particle size was the only important factor in developing other strength properties

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.05a
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• pp.996-1001
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• 2006

Automatic washing machines have been improved and popularized steadily since the first electric washing machine was produced in the early 1900's. Appliance industry has tried to obtain the performance of washing machine with large capacity, high energy efficiency, low vibration and low noise levels. As the installation peace of a washer becomes closer to the living space, vibration and noise problems become more important challenges. In general, a washing machine has four legs to support its body. Four legs of the washing machine should be attached on a floor. If not so, it may cause severe vibration or walking in the spin-drying process. Unfortunately, the floor of an ordinary house is bumpy in general, and the consumers will not accept bolting washing machines to a foundation; moreover, sometimes they move the location of their washing machines to utility rooms or bath rooms or kitchens and don't care for leveling the legs exactly. In this study, we devise an auto-leg system that prevents the occurrence of abnormal vibration and walking of washing machines. It is simply composed of a spring and a friction damper. Some experiments are implemented to show the dynamic characteristics of the three-dimensional auto-legged washing machine model that is located on the even or uneven ground. A spring parameter is optimized to adjust the length of the auto-leg system automatically up to 10 mm irregularity, and the friction damper is designed to decrease a resonance induced by the spring of the auto-leg system. Some numerical results show that placing the proposed auto-leg system in a washing machine makes good performance with low vibration, as well as low noise, regardless of the unevenness of the floor.

• Journal of Korea Water Resources Association
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• v.34 no.3
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• pp.275-285
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• 2001

Since the majority of streamflow during dry periods is provided by groundwater storage, the streamflow depends on a basin moisture state recharged from rainfall during wet periods. This hydrologic characteristics dives good condition to predict long-term streamflow if the basin state like groundwater recharge is known in advance. The objective of this study is to examine groundwater recharge effect to monthly streamflow, and to attempt monthly streamflow prediction using estimated groundwater recharge. The ground water recharge is used as an independent variable with streamflow and precipitation to construct multiple regression models for the prediction. Correlation analysis was performed to assess the effect of groundwater carry-over to streamflow and to establish the associations among independent variables. The predicted streamflow shows that the multiple regression model involved groundwater recharge gives improved results comparing to the model only using streamflow and precipitation as independent variables. In addition, this paper shows that the prediction model with the effect of groundwater carry-over taken into account can be developed using only precipitation.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.388-388
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• 2011

Graphene, with its unique physical and structural properties, has recently become a proving ground for various physical phenomena, and is a promising candidate for a variety of electronic device and flexible display applications. The physical properties of graphene depend directly on the thickness. These properties lead to the possibility of its application in high-performance transparent conducting films (TCFs). Compared to indium tin oxide (ITO) electrodes, which have a typical sheet resistance of ~60 ${\Omega}/sq$ and ~85% transmittance in the visible range, the chemical vapor deposition (CVD) synthesized graphene electrodes have a higher transmittance in the visible to IR region and are more robust under bending. Nevertheless, the lowest sheet resistance of the currently available CVD graphene electrodes is higher than that of ITO. Here, we report an ingenious strategy, irradiation of MeV electron beam (e-beam) at room temperature under ambient condition,for obtaining size-homogeneous gold nanoparticle decorated on graphene. The nano-particlization promoted by MeV e-beam irradiation was investigated by transmission electron microscopy, electron energy loss spectroscopy elemental mapping, and energy dispersive X-ray spectroscopy. These results clearly revealed that gold nanoparticle with 10~15 nm in mean size were decorated along the surface of the graphene after 1.0 MeV-e-beam irradiation. The fabrication high-performance TCF with optimized doping condition showed a sheet resistance of ~150 ${\Omega}/sq$ at 94% transmittance. A chemical transformation and charge transfer for the metal gold nanoparticle were systematically explored by X-ray photoelectron spectroscopy and Raman spectroscopy. This approach advances the numerous applications of graphene films as transparent conducting electrodes.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.2
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• pp.106-112
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• 2005

Modern versions of supersonic jet fighter aircraft have several different weapon loading configuration to support air-to-air combat and air-to-ground delivery of weapon modes. These various aircraft loading conditions could result in asymmetric configurations to the aircraft once delivered. These asymmetric configurations could result in decreased handling qualities for the pilot maneuvering, stability, control issues and aerodynamic performance of the aircraft. In order to eliminate or decrease these adverse impacts on the pilot's ability, development of T-50 flight control law attempts to control the aircraft in both longitudinal and lateral-directional axes. Especially, the design of the lateral-directional roll axis control laws, utilizing a simple roll rate feedback structure and gains such as F-16, is developed for the T-50 aircraft to meet the aircraft's design requirements. Consequently, it is found that the improved control law decreases the roll-off phenomenon in lateral axes during pitch maneuver.