• Journal of Korean Society of Transportation
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• v.20 no.2
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• pp.149-159
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• 2002

The performance of two single-barrier three-phase control systems at diamond interchanges was evaluated for various traffic conditions. To emulate the actuated signal control, hardware-in-the-loop system combined with CORSIM simulation program was used. Two performance measures, average delay and total stops, were used for the evaluation process. Results showed that the two three-phase systems gave similar performance in terms of average delay, but not stops. The delay performance of each phasing system was generally dependent on the traffic pattern and ramp spacing. However, there was a distinct movement preference for each phasing system. The total stops decreased as the spacing increased, and it was the most sensitive variable that can differentiate between the two three-phase systems. It was also shown that the hardware-in-the-loop control could be a good method to overcome the limitations of current simulation technology.

• Journal of Electrical Engineering and Technology
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• v.6 no.2
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• pp.215-225
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• 2011

In this paper, a buck DC-DC bridge converter is used as a power factor correction (PFC) converter for feeding a voltage source inverter (VSI) based permanent magnet brushless DC motor (PMBLDCM) drive. The front end of the PFC converter is a diode bridge rectifier (DBR) fed from single phase AC mains. The PMBLDCM is used to drive the compressor of an air conditioner through a three-phase voltage source inverter (VSI) fed from a variable voltage DC link. The speed of the air conditioner is controlled to conserve energy using a new concept of voltage control at a DC link proportional to the desired speed of the PMBLDC motor. Therefore, VSI operates only as an electronic commutator of the PMBLDCM. The current of the PMBLDCM is controlled by setting the reference voltage at the DC link as a ramp. The proposed PMBLDCM drive with voltage control-based PFC converter was designed and modeled. The performance is simulated in Matlab-Simulink environment for an air conditioner compressor load driven through a 3.75 kW, 1500 rpm PMBLDC motor. To validate the effectiveness of the proposed speed control scheme, the evaluation results demonstrate improved efficiency of the complete drive with the PFC feature in a wide range of speed and input AC voltage.

• Journal of Power Electronics
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• v.7 no.4
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• pp.278-285
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• 2007

Recently, plasma display panels (PDP) have become the most promising candidate in the market for large screen size flat panel displays. PDPs have many merits such as a fast display response time and wide viewing angle. However, there are still concerns about high cost because they require complex driving circuits composed of high power switching devices to generate various voltage waveforms for three operational modes of reset, scan, and sustain. Conventional PDP driving circuits use path switches for voltage separation and a scan switch to offer a scan voltage for reset and scan operations, respectively. In addition, there exist reset switches to initialize PDPs by regulating the wall charge conditions with ramp shaped pulses, which means the necessity of specific power devices for the reset operation. Because power for the plasma discharge accompanied by a large current is transferred to a panel via path switches, high power rating switches are used for path switches. Therefore, this paper proposes a novel low-cost PDP driving scheme achieved by not only eliminating path switches but also merging the function of reset switches into other switches used for sustain or scan operations. The simulated voltage waveforms of the proposed topology and experimental results implemented in a 42-inch panel to demonstrate the validity of using a new gate driver that merges the functions of power switches are presented.

• Journal of the Optical Society of Korea
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• v.18 no.6
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• pp.633-638
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• 2014

We report experimental behaviors of condensed $^{87}Rb$ atoms responding to changes in the trap potential of the atomchip. The two-types of adiabatic and non-adiabatic overall changes were implemented by changing the ramp-down speed of the chip-wire current, which can dominantly modify the one-axis magnetic field gradient. Under the adiabatic process, a pure condensate stayed in the initial spin state and collectively oscillated with both monopole and dipole modes, while an atomic cloud above the critical temperature exhibited sound waves in a dense ultracold gas. On the other hand, Bose-Einstein condensate atoms with non-adiabatic perturbation were split into spatially different positions by spin states through spin-flip. We investigated the split ratio among spin states depending on final evaporation frequency. Potential changes, of course, cause collective oscillations regardless of the changing process.

• 한국정보디스플레이학회:학술대회논문집
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• 2003.07a
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• pp.863-866
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• 2003

Multi-walled carbon nanotubes (CNTs) were synthesized on glass substrates in the different ramp-up heating ambient of vacuum, He, Ar, and $N_{2}$ by thermal chemical vapor deposition. CNTs with higher crystallinity were developed in the buffer gases with faster growth rates than in vacuum. Field emission characteristics were strongly related to the relative position of CNT emitters to the cathode electrodes. The areal-spread emission and instability were overcome by locating the emitters far away from the edges of cathode electrodes. The electrical conditioning of emitters improved their emission uniformity over a large area although it decreased the emission current. This study also discussed the long-term stability of CNT emitters.

• Progress in Superconductivity and Cryogenics
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• v.20 no.3
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• pp.15-20
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• 2018

No-insulation (NI) pancake magnets are fabricated using Rare earth-Barium-Copper Oxide (REBCO) coated conductor (CC) tapes, which enabled a very compact magnet in the aspects of high critical current density ($J_c$) and high mechanical strength by removing insulation and allowing thinner stabilizer. They have also advantages such as self-quench protection. Therefore, it does not need quench detection and protection that can be very challenging in a high critical temperature ($T_c$) superconducting magnet technology. Recently, it was reported that the NI REBCO CC magnets have some drawbacks of long charging time and high field ramp loss which will be a concern in the operation of cryocooled magnets. These issues are related to the turn-to-turn contact resistivity and can be released by managing it. This is also closely related to the activity of reducing the contact joint resistance in the case of CC joints for long length CC fabrication. Therefore, in this study, the turn-to-turn contact resistance ($R_c$) at the CC contact part of differently stabilized CC tapes was measured. The behaviors of $R_c$ at CC contact parts according to the applied contact pressure were investigated. The range of $R_c$ measured for CC tapes adopted will provide fundamental data for design and fabrication of the CC NI coils.

• Proceedings of the KSME Conference
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• 2000.04a
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• pp.433-439
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• 2000

Lots of semi-active control devices have been developed in recent years because they have the best features of passive and active system. Especially, controllable magneto-rheological(MR) fluid devices have received significant attention in these area of research. The MR fluid is the material that reversibly changes from a free-flowing, linear viscous fluid to a semisolid with a controllable yield strength in milliseconds when exposed to a magnetic field. If the magnetic field is induced by moving a permanent magnet instead of applying current to a solenoid, it is possible to design a MR damper consuming low power because the power consumption is reduced at steady state. This paper proposes valve mode MR damper using permanent magnetic circuit that has wide range of operation with low power consumption and small size. To design a MR damper that has a large maximum dissipating torque and a low damping coefficient, a design parameter is adopted. The magnetic circuit, material of choke and choke type are selected experimentally with the design parameter. The behaviors of the damper are examined and torque tracking control using PID feedback controller is performed for step, ramp and sinusoidal trajectories.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.24 no.5
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• pp.425-431
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• 2006

Recently, the government has adjusted the 4th National Master Plan in an effect to achieve balanced national land development. However, the current traffic accident index ranks among the lowest in OECD countries, ranking 25th out of 29 countries. Therefore, this study is aimed at indicating problems with National Expressway and local roads developing a solution by analyzing the problems and suggesting the most appropriate design speed for inter-changes where the traffic accidents occur frequently. With the results, it is to obtain a design speed decision formula at interchange branch points to prevent traffic accidents, secure safe and optimal road conditions and maximize traffic load capability.

• Progress in Superconductivity and Cryogenics
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• v.11 no.3
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• pp.1-5
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• 2009

It is important to predict AC loss in $Nb_3Sn$ and NbTi cable-in-conduit-conductor (CICC) reliably for the design and operation of large superconducting coils. The hysteresis loss in the superconducting filaments and coupling loss within strands and among strands in a cable or composite are dominant ac losses in superconducting magnets. The coupling loss in a superconductor can be characterized by identifying the coupling constant time $n{\tau}$. To reduce the coupling loss, all the strands (superconductor and Cu) in KSTAR (Korea Superconducting Tokamak Advance Research) are chromium plated with thickness of $l{\pm}0.5{\mu}m$. The ac losses of PF1, PF5 and PF6 coils has been measured by calorimetric method while applying trapezoidal current pulses with various ramp rate from 0.5 kA/s to 2 kA/s. The coupling time constants for $Nb_3Sn$ coils are $25{\sim}55$ ms and the values are not co-related with the coil size, the time constants for NbTi coil is 30 ms.

• Membrane and Water Treatment
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• v.15 no.4
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• pp.153-162
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• 2024

The current research project focuses on the feasibility of recycling and reusing utilized osmosis membranes from the Beni Saf water seawater desalination station in the province of Ain Temouchent. The composite Reverse Osmosis (RO) membrane, which is referenced BW30-400-FR and manufactured by Dow Filmtec TM, is used for all the tests. Three solvents are tested: potassium permanganate (KMnO₄), sodium hydroxide (NaOH), hydrogen peroxide (H₂O₂), and the mixture of NaOH with KMnO₄ for the degradation of the active layer of the RO membrane. A frontal filtration of wastewater using these modified membranes was carried out. An analysis of the physicochemical properties of the filtrate was performed using a spectrophotometer. The results of the frontal filtration performed under perpendicular pressure using a filtration ramp show that the membranes immersed in the NaOH and KMnO₄ mixture for 24 hours produced a higher hydraulic flux compared to those immersed in NaOH and H₂O₂. At the end of the proposed treatment, the samples are analyzed by scanning electron microscopy (SEM) in addition to analyzing the clogging powder by EDX. The obtained results show the effectiveness of the proposed treatment for the degradation of the active layer in order to transform it into microfiltration and/or ultrafiltration.