• Journal of Korean Society of Transportation
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• v.27 no.6
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• pp.147-156
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• 2009

We present a methodology for modeling and solving the transit frequency design problem with variable demand. The problem is described as a bi-level model based on a non-cooperative Stackelberg game. The upper-level operator problem is formulated as a non-linear optimization model to minimize net cost, which includes operating cost, travel cost and revenue, with fleet size and frequency constraints. The lower-level user problem is formulated as a capacity-constrained stochastic user equilibrium assignment model with variable demand, considering transfer delay between transit lines. An efficient algorithm is also presented for solving the proposed model. The upper-level model is solved by a gradient projection method, and the lower-level model is solved by an existing iterative balancing method. An application of the proposed model and algorithm is presented using a small test network. The results of this application show that the proposed algorithm converges well to an optimal point. The methodology of this study is expected to contribute to form a theoretical basis for diagnosing the problems of current transit systems and for improving its operational efficiency to increase the demand as well as the level of service.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.6
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• pp.505-516
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• 2011

The concept of the IGC(Integrated Guidance and Control) has been introduced to overcome the performance limit of the SGC(Separated Guidance and Control) loop. A new type of IGC with impact angle constraint has been proposed in this paper. Angle of attack, pitch angle rate, pitch angle and line of sight angle are considered as state variables. A controllability analysis and equilibrium point analysis have been carried out to investigate the control characteristic of the prposed IGC. The LQR(Linear Quadratic Regulator) has been adopted for the control law and detailed explanations about the adoption has been provided. The performance comparison between the IGC and the SGC has been carried out. The result of numerical simulations shows that the IGC guarantees better guidance performance than the SGC when the agile maneuver is needed for a specific guidance geometry.

• The Journal of Engineering Geology
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• v.17 no.4
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• pp.545-554
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• 2007

Landslides is mainly induced by a heavy rainfall, earthquake ground motion, and some other factors like soil mechanics, morphological-geological factors etc. Since the starting point of the failure seemed to be originated at a construction site in the study, it is meaningful to find out the relationship between the landslide and the construction. For this study, the slope failure factor was examined carefully to see that the original natural slope had vulnerability and that the complex ground had unstability changed by construction. A field survey was conducted on the original ground surface and filled-up ground. A laboratory test was also conducted to determine the geomechanical properties of soil samples. 2D and 3D limit equilibrium analysis with changing groundwater level were conducted at the failure depth using a seismic refraction survey. The result shows that the factor of safety is similar stability under all condition, but unstable under saturated condition.

• Journal of the Korean Society for Heat Treatment
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• v.9 no.1
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• pp.1-11
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• 1996

Mechanical alloying is an effective process to finely distribute inert dispersoids in an Al-TM(TM is a transition metal) system. It has been considered that high melting point aluminides are formed by precipitation from supersaturated Al(Ti) powder. This analysis is based on the fact that much higher content of TM than the solubioity can be dissolved in alpha aluminum during the high energy ball milling. Thus, decomposition behavior of Ti in the Al(Ti) was considered very important. But it is confirmed that the higher portion of Ti than Al(Ti) solid solution is existed as nano-sized Ti particles in the MA powders by high energy ball nilling from the XRD spectrum and TEM analysis in this study. Therefore, the role of undissolved TM particles affect the formation of aluminides should be suitably considered. In this study, we present experimental observation on the formation of $Al_3Ti$ fron mechanical alloyed Al-Ti alloys in the hyperperitectic region. This study showed that, in the mechanically alloyed Al-20wt%Ti specimen, intermediate phase of cubic $Al_3Ti$ and tetragonal $Al_{24}Ti_8$ formed at $300{\sim}400^{\circ}C$ and $400{\sim}500^{\circ}C$, respectively, before the MA state reaches to equilibrium at higher temperatures. The formation behavior of $Ll_2-Al_3Ti$ is interpreted by interdiffusion of Al and Ti in solid state based on the fact that large amount of nano-sized Ti particles exist in the milled powder. Present analysis indicated undissolved Ti particles of nanosize should have played an important role initiation the formation of $Al_3Ti$ phase during annealing.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.7 no.2
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• pp.198-208
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• 1995

Combining Iwan-Blevin's model into the approximated form of the nonlinear model derived for the dynamic analysis of the riser system with the inclusion of internal flow, current-vortex model is developed to investigate the effect of internal flow on vortex-induced vibration due to inline current The riser system includes a steadly flow inside the pipe which is modeled as an extensible or inextensible tubular beam. Galerkin's finite element approximation are implemented to derive the matrix equation of equilibrium for the finite element system. The investigations of the effect of internal flow on vibration due to inline current are performed according to the change of various parameters such as top tension, infernal flow velocity. current velocity, and so on. It is found that the effect of internal flow on vibration due to vortex shedding can be controlled by the increase of top tension. However, careful consideration has to be given, in design point in order to avoid the resonance band occurding near vortex shedding frequency, particularly for the long riser.

• Textile Coloration and Finishing
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• v.13 no.2
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• pp.120-127
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• 2001

In order to make a microfiber fabric with PET/Co-PET Sea-Island Type microfiber, the optimum condition of extraction and elimination of Co-PET from the mocrofiber was examined. At the same time, the physical property change of the fabric with respect to the change of the relative amount of the Co-PET in the microfiber was also examined to provide a directly applicable data set to the industry. The sample fabric used was warp 75/36(DTY) and weft 0.05d(PET/Co-PET, Sea Island Type Microfiber) twill fabric of 36 separated yarns＋40/24(high shrinking yarn) with 130/48 ITY. The data set was made at various NaOH concentrations and steam temperatures with time as a main variable. The physical properties examined were the tensile properties. The results obtained were the tensile. The results obtained were 1. For a proper extraction of Co-PET (13.5%)from the microfiber with wet curing, it takes more than 5 min. in 8 and 12% of NaOH solutions but it takes only 3 min. in 18% of NaOH solution at 12$0^{\circ}C$. 2. For a proper extraction of Co-PET (13.5%) from the microfiber with wet curing, ti takes 3~5min. in 12 and 14% of NaOH solution and it takes less than 3 min. in 18% of NaOH solution at $130^\circ{C}$. 3. The increasing ratio of WT increased with increasing NaOH concentrations and the equilibrium point reached was 3 min. at $120^\circ{C}$. 4. The WT increasing ratio was greater in 14 and 18% NaOH solutions than in 8 and 12% of NaOH solutions at $130^\circ{C}$5. The RT ratio changes at $120^\circ{C}$ in 8 and 12% of NaOH solutions were indifferent from that at $130^\circ{C}$ in 12% of NaOH solution. However, the RT was apparently decreased with increasing NaOH concentration.

• Textile Coloration and Finishing
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• v.13 no.2
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• pp.34-34
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• 2001

In order to make a microfiber fabric with PET/Co-PET Sea-Island Type microfiber, the optimum condition of extraction and elimination of Co-PET from the microfiber was examined. At the same time, the physical property change of the fabric with respect to the change of the relative amount of the Co-PET in the microfiber was also examined to provide a directly applicable data set to the industry. The sample fabric used was warp 75/36(DTY) and weft 0.05d(PET/Co-PET, Sea Island Type Microfiber) twill fabric of 36 separated yarns＋40/24(high shrinking yarn) with 130/48 ITY. The data set was made at various NaOH concentrations and steam temperatures with time as a main variable. The physical properties examined were the tensile properties. The results obtained were the tensile properties. The results obtained were 1. For a proper extraction of Co-PET (13.5%)from the microfiber with wet curing, it takes more than 5 min. in 8 and 12% of NaOH solutions but it takes only 3 min. in 18% of NaOH solution at 120℃. 2. For a proper extraction of Co-PET (13.5%) from the microfiber with wet curing, it takes 3∼5 min. in 12 and 14% of NaOH solution and it takes less than 3 min. in 18% of NaOH solution at 130℃. 3. The increasing ratio of WT increased with increasing NaOH concentrations and the equilibrium point reached was 3 min. at 120℃. 4. The WT increasing ratio was greater in 14 and 18% NaOH solutions than in 8 and 12% of NaOH solutions at 130℃. 5. The RT ratio changes at 120℃ in 8 and 12% of NaOH solutions were indifferent from that at 130℃ in 12% of NaOH solution. However, the RT was apparently decreased with increasing NaOH concentration.

• Journal of fish pathology
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• v.1 no.2
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• pp.131-134
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• 1988

Radiocobalt was used as tracer to study the uptake of cobalt by fish either from water or food source, respectively. Four groups of goldfish were exposed to $^{57}Co$-labelled water under 4 different temperatures, while another four groups were fed labelled feed pellets at $15^{\circ}C$. Results indicate that water temperature has no significant effect on the uptake of cobalt from water. The uptake from water is quite a slow process since the cobalt uptaken from water reached 0.0006% of available activity at best on the 13th day of exposure. The uptake from a labelled feed source showed a linear increase with time over the period of ninety days. On the 90th day of experiment the percentage of available activity consumed seemed to be approaching an equilibrium point at roughly 12% of the total activity fed to the goldfish.

• Journal of Korean Association for Spatial Structures
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• v.12 no.2
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• pp.89-98
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• 2012

This study investigates the optimum structural design of space truss considering global buckling, and is to obtain the minimal weight of the structure. The mathematical programming method is used for optimization of each member by member force. Besides, dynamic programming method is adapted for consideration in snap-through buckling. The mathematical modeling for optimum design of truss members consists of objective function of total weight and constrain equations of allowable tensile (or compressive) stress and slenderness. The tangential stiffness matrix is examined to find the critical point on equilibrium path, and a ratio of the buckling load to design load is reflected in iteration procedures of dynamic programming method to adjust the stiffness of space truss. The star dome is examined to verify the proposed optimum design processor. The numerical results of the model are conversed well and satisfied all constrains. This processor is a relatively simple method to carry out optimum design with consideration in global buckling, and is viable in practice with respect to structural design.

• The Transactions of the Korean Institute of Electrical Engineers D
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• v.52 no.7
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• pp.393-400
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• 2003

In this paper we deal with the virtually zero power control for the rigid rotor with radial suspension by the permanent magnetic bearing and axial suspension by electromagnetic bearing. The purpose of the virtually zero power control is to reduce the power consumption of the electromagnetic bearings. The axial active force is expressed by the normal second order equation which has only one degree-of-freedom. The virtually zero power control structure has two schemes. One is the coil control current integrator which is used to make the convergence of the control current to a range which is very close to zero. By using the current integrator the DC component which is included in the control current is eliminated, thus the control current converges to a range which is close to zero. The other is normal PD control loop which is used to make the rotor reach to stable equilibrium point and to maintain air gap so that the axial force produced by radial permanent magnet always balances the total weight of the rotor and its load. First we show a simple mathematical plant model and the virtually zero power (VZP) control blocks. Second, we investigate the theoretical feasibility and the stability of the proposed virtually zero Power control levitation system with PD feedback loop by using linear control theory Finally we show the effectiveness of the proposed control method to reduce the power consumption by simulations.