• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.7
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• pp.69-74
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• 2003

By employing vane tip concept, a new rotor blade (NRSB-I) has been designed to enhance the noise characteristics of BERP blade. Numerical analyses have been performed for hovering rotor and the results are compared with respect to those of original BERP blade. Although the thrust of designed rotor decreases by 6-7% due to cutout at the tip region, the results indicate that the actual performance loss is negligible because power reduction is greater than thrust loss. It is also found that aerodynamic fence is required at the outboard kink to obtain clearly separated twin-vortices because the vortex generated at kink is diffused during the convection over the blade surface.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.1
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• pp.18-24
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• 2003

A three node triangular element with drilling rotations incorporating improved higher-order zig-zag theory(HZZT) is developed to analyze the vibration of pretwisted composite plates with embedded damping layer. Shear force matching conditions are enforced along the interfaces between the embedded damping patch and the border patch by matching the shear forces of the embedded damping patch to the shear forces of the adjacent border patch. The natural frequencies and modal loss factors are calculated for cantilevered pretwisted composite blade with damping core with the present triangular element, and compared to experiments and MSC/NASTRAN using a layered combination of plate and solid elements.

• International Journal of Railway
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• v.8 no.1
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• pp.10-14
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• 2015

Due to the characteristics of the vehicle structure, the magnetic levitation train has a confined bottom space thus a study on miniaturization and weight reduction of auxiliary power unit is essential. This auxiliary power unit is an essential device used for illumination, air conditioning, heating and air brake equipment excluding the motor. The previous auxiliary power unit for magnetic levitation train has used the hard switching having a high switching frequency with heavy loss in order to reduce the size of filter reactor and transformer but the reduction in volume was not significant. In this paper, by reducing the loss, reducing the size of the cooling unit and by increasing the switching frequency using the soft switching of resonant converter, it has miniaturized and reduced the weight of filter reactor and transformer which occupy significant space in the auxiliary power unit. This study has verified the performance of 50KVA grade prototype through simulated interpretation and analysis, and compared the size and weight of auxiliary power unit of the previous magnetic levitation train.

• Journal of Astronomy and Space Sciences
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• v.38 no.1
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• pp.65-82
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• 2021

For the vast majority of geostationary satellites currently in orbit, station keeping activities including orbit determination and maneuver planning and execution are ground-directed and dependent on the availability of ground-based satellite control personnel and facilities. However, a requirement linked to satellite autonomy and survivability in cases of interrupted ground support is often one of the stipulated provisions on the satellite platform design. It is especially important for a geostationary military-purposed satellite to remain within its designated orbital window, in order to provide reliable uninterrupted telecommunications services, in the absence of ground-based resources due to warfare or other disasters. In this paper we investigate factors affecting the robustness of a geostationary satellite's orbit in terms of the maximum duration the satellite's station keeping window can be maintained without ground intervention. By comparing simulations of orbit evolution, given different initial conditions and operations strategies, a variation of parameters study has been performed and we have analyzed which factors the duration is most sensitive to. This also provides valuable insights into which factors may be worth controlling by a military or civilian geostationary satellite operator. Our simulations show that the most beneficial factor for maximizing the time a satellite will remain in the station keeping window is the operational practice of pre-emptively loading East-West station keeping maneuvers for automatic execution on board the satellite should ground control capability be lost. The second most beneficial factor is using short station keeping maneuver cycle durations.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• v.29 no.4
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• pp.245-248
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• 2003

The retraction of anterior teeth could be performed more easier by inducing of skeletal anchorage system rather than by conventional method on orthodontic treatment. But, we wonder how effective the system draws well without anchorage loss and draws anterior teeth aside posteriorly, and if the system can reduce the time, in comparison with the anchorage of posterior teeth. For that reason we have studied on the subject of patients, who were required the maximum anchorage on orthodontic treatment and the cases without crowding. The subjects of the experimental group are 35 areas of 20 people who were inserted miniscrews after Mx or Mn 1st premolar extracted. Also, the subjects of the control group are 81 areas of 45 people who were not inserted miniscrews. Compared the anchorage loss of experimental group with control one, we could get the result that the anchorage loss of experimental group is $1.034{\pm}0.891mm$ and control group is $2.790{\pm}1.882mm$(P<0.01). Compared the space closing time of experimental group with control one, we could get the result that the space closing time of experimental group is $369.40{\pm}110.81$days and control group is $406.56{\pm}231.63$days. But the result of comparing space closing time has no significance in statistics. We recognized that the experimental group is more faster than the control group in the canine retraction velocity from the result ; the speed of a experimental group has as much as $0.60{\pm}0.23mm/30days$ while the speed of a control group has $0.44{\pm}0.35mm/30days$(P<0.05). So, we could convince that orthodontic miniscrew is used effectively in the cases required the maximum anchorage.

• Tunnel and Underground Space
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• v.25 no.5
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• pp.397-407
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• 2015

Estimation of shield TBM tunnelling-induced volume loss is of great importance for ground settlement control. This study proposed a simple method for evaluation of volume loss during TBM tunnlling, which is able to take into account of shield machine configurations and main driving data in calculation. The method was applied to analyze the tunnelling cases with earth pressure balanced and slurry pressure balanced shiled TBM, and mostly, reasonable agreements with monitoring results were found. Additional discussions were made for some disagreements.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2005.11a
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• pp.163-168
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• 2005

Attenuation in vegetation is important, for both terrestrial and earth-space systems. However, the wide range of conditions and types of foliage makes it difficult to develop a generalized prediction procedure. Currently, there is also a lack of suitably prediction model and measured experimental data for vegetation loss. So in this paper, vegetation loss data for four different tree-species, including Dawn-redwood tree, Plane tree, Pine tree and Fir tree are obtained by measurement in the frequency range of 1.0 $\sim$ 6.0 GHz. The through or scattered component is calculated using a model based upon the theory of RET(Radiative Energy Transfer) and RET modeling parameters are extracted from the measured data.

• Journal of the korean academy of Pediatric Dentistry
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• v.21 no.2
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• pp.540-546
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• 1994

The authors treated three patients who chiefly complained functional anterior crossbite due to premature loss of primary molars by using removable space maintainer and functional appliances. In orthodontic practice, the mandibular rest position and the possibility of taking construction bite have been as the criteria for evaluation of functional factors involved in anterior crossbite. Functional anterior crossbites, if left untreated, may have deleterious effects on the development and function of craniofacial complex and TMJ. Objectives of the treatment were as follows: 1) to recover vertical dimension 2) to eliminate functional disharmony 3) to correct anterior reversed occlusion 4) to attain good facial esthetics 5) to prevent unfavorable growth of jaw & dentition Characterized craniofacial morphology resulting from the premature loss of deciduous molars could be recovered following the correction of crossbite. Therefore, it is recommended that in orthodontic diagnosis of functional anterior crossbite due to premature loss of deciduous molars, the craniofacial abnormality affected by that should be considered.

• Journal of the Korean Society of Clothing and Textiles
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• v.18 no.3
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• pp.287-297
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• 1994

The purpose of this study is to investigate the Improvement of fiber surface, tenacity & elogation, fabric counts, thickness, handle, moisture regain, static voltage, handle, dyeability when polyester fabrics are treated with NaOH solution adding quartemary ammonium salt (Benzyl dimetyl dodecyl ammonium chloride . BDMDAC) The results are as follows. I. In regard to the method of processing VET, when the PET fabrics are alkaline-hydrolyzed adding BDMDAC, the weight loss of PET fabrics increased remarkably to the increse of BDMDAC concentration than when they are treated only in NaOH solution. When PET fabrics are alkaline-hydrolyzed the amount of BDMDAC as the catalyst is proper lg/1 II. The change in physical & chemical properties of alkaline-hydrolyzed PET fabrirs. 1. As the amount of the weight loss on PET fabrics increased, the void space of the PET yale increased but tenacity & elongation and thickness decreased. 2. The fabric counts of PET increased due to shrinkage by alkaline-hydrolydzing. 3. As the amount of of the weight loss on PET fabrics increased. NUMERI, FUKURAMI, increaseed and KOSHI decreased and Total hand value(T.H.V) in all cases increaseed. When the weight Ioss is 30.9% T.H.V. is best. 4. Moisture regain of PET fabrics a little increased by alkaline-hydrolyzing treatment. As the weight loss increased, static voltage is decreased. 5. The last dye absorption is different according to the degree of the Affinity. In regard to the difference of dye color, the dyestuff of low molecular weight dyed for deep color.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.17 no.7
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• pp.1558-1563
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• 2013

In this paper, we analyze the radio propagation path loss characteristics for the vertical electric dipole radiation over the perfect electric conductor(PEC) ground plane. Most research have been performed about the electromagnetic analysis of vertical electric dipole in free space for time domain or frequency domain. But this paper present the radio propagation path loss over PEC ground plane in time domain under the assumption of the vertical electric dipole as a base station. From the simulated results, the ground plane effect can change the location of near field from transmitting antenna and the transient responses at mobile are calculated. The results of this paper can be applied to surface radar or signal processing applications.