• Korean Journal of Materials Research
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• v.12 no.6
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• pp.442-446
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• 2002

Design of microwave absorbers using high frequency properties of fiber reinforced composites are investigated. Two kinds of composite materials (glass and carbon) are used and their complex permittivity and permeability are measured by transmission/reflection technique using network analyzer. Low dielectric constant and nearly zero dielectric loss are determined in glass fiber composite. However, carbon fiber composites show the high dielectric constant and large conduction loss which is increased with anisotropy of fiber arrangement. It is, therefore, proposed that the glass and carbon fiber composites can be used as the impedance transformer (surface layer) and microwave reflector, respectively. By inserting the foam core or honeycomb core (which can be treated as an air layer) between glass and carbon fiber composites, microwave absorption above 10 dB (90% absorbance) in 4-12 GHz can be obtained. The proposed fiber composites laminates with sandwitch structure have high potential as lightweight and high strength microwave absorbers.

• International Journal of Control, Automation, and Systems
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• v.1 no.2
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• pp.215-221
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• 2003

The education system in this paper is used to demonstrate and educate the effects of electromagnetic induction. Placing an aluminum ring over the core and switching on AC source causes the ring to jump in the air due to induced currents in the ring producing a magnetic field opposed to that produced in the core. To control the position of the ring by only the current, it is to require nonlinear control algorithm and control board that is composed of photo sensors, decode circuit, computer communication, and power electronics circuit. This paper provides the development for education system in detail and the effects of dynamic neural networks for nonlinear control with on line is studied.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2002.10a
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• pp.202-207
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• 2002

The soundness of honeycomb core sandwich and laminate structure used for commercial aircrafts is generally evaluated with ultrasonic inspection because the inspection is most sensitive to planar surfaces which are perpendicular to sound propagation pass and reflects sound almost 100％ to equipment. And most defects inherent in composite material curing process has good reflective surfaces. With all this advantage, unexpected obstruction to product and additional cost could be occurred when inappropriate accept/reject criteria is given. In this study the importance of inspection criteria will be discussed to show how inappropriate criteria cause unexpected results leading to high production cost and how much time must be spent to correct those improper criteria with an actual case occurred in Aerospace Division, Korean Air.

• Transactions of Materials Processing
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• v.14 no.6 s.78
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• pp.570-576
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• 2005

Powder Injection Molding(PIM) has recently been recognized as an advanced manufacturing technology for low-cost mass production of metal or ceramic parts of complicated geometry With this regards, design technology of dental scaler tip PIM mold, which has complex shape and small core pin (diameter=0.6mm), with the help of computer-aided analysis of powder injection molding process was developed. Computer-aided analysis for dental scaler tip mold was implemented by finite element method with non-Newtonian fluid, modified Cross model viscosity, PvT data of powder/binder mixture. Compter-aided analysis results, such as filling pattern, weldline formation, air vent position prediction were compared with experimental result, and eventually have been shown good agreement. The core pin (diameter=0.6mm) deflection analysis of dental scaler tip PIM mold during PIM filling process was also investigated before mold fabrication.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.31 no.4
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• pp.28-44
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• 2023

This study investigates aircraft lessor business models by studying cases and interviewing experts to analyze investors and business strategies of aircraft lessor. The results confirm that there is a wide range of investors including institutional investors, financial institutions, insurance companies, corporations, and wealthy individuals for aircraft lessor. Aircraft lessors can be categorized based on its required rate of return (cost of capital) into bank-investing core, institutional investor-investing value-added, and hedge fund-investing opportunistic. Aircraft lessor decides leasing rate by aircraft purchasing price and lessee's credit rating. Core aircraft lessors invest in new aircrafts for new placement or sale-and-leaseback strategy requiring little technical risk in aircraft, value-added lessors invest in middle-aged aircrafts for re-leasing, opportunistic lessors invest in old aircrafts for freighter conversion or part-out strategy requiring high level of expertise. This study provides insights for future Korean aircraft lessor establishment and investment.

• Journal of Power System Engineering
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• v.11 no.3
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• pp.29-34
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• 2007

Existent researches about indoor thermal environment have been focused on to seek human's comfort in daytime. Also researches about thermal comfort during the sleeping time that is important for resting and recharging to modern people have been seldom existed. At present, as global warming phenomenon is being continued, most people are going through inconvenience by sultriness during the sleeping hours in sweltering summer night. Therefore we need another control method of an air conditioner to keep human's thermal comfort. Ambient temperature is a common factor of the environment, but analysis of its effect on human body physiology is still unknown. The effect of ambient temperature on human sleep has been increasingly studied in the last decade. This research investigated about optimal indoor temperature to maintain proper skin temperature and comfortable sleep when indoor air is cooled by an air conditioner in sweltering summer night.

• Journal of international Conference on Electrical Machines and Systems
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• v.3 no.3
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• pp.241-247
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• 2014

The voltage source PWM inverter generally used to drive the air conditioning (A/C) fans has been posing a large issue that the bearings in air conditioning fan motors are highly possible to be corroded electrically. Potential difference called shaft voltage is generated between inner and outer rings of the bearings due to inverter switching. The shaft voltage causes bearing lubricant breakdown dielectrically. As a result, bearing current is caused. This current causes the bearing corrosion. In previous work, we demonstrated that the shaft voltage can be reduced by using an insulator inserted between the outer and inner cores of the rotor in an air conditioning fan motor without grounding. This paper proposes the other countermeasure for reducing the shaft voltage in fan motors. The countermeasure which adds a capacitor between the brackets and the stator core is effective even for fan motors with non-insulated rotor. The effectiveness is confirmed by both simulated and experimental results.

• 전기의세계
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• v.21 no.2
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• pp.5-8
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• 1972

The purpose of this paper is, as a preliminary step to study on the method of analysing the torque of toothed solid iron rotor, to make an inquiry into the torque calculation formula of homogenious solid iron rotor without slot. The starting point for its theoretical analysis on torque generated by eddy current in solid iron rotor is based on the maximum air gap flux density. In solid rotor induction motor, torque generated by rotor core is considerably large in the range of large slip. The calculated value and observed value on the test machine are also examined in this paper.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.05a
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• pp.1029-1034
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• 2003

The basic Physical properties, Slump, Slump Flow, Air content, Bleeding, and Settlement of concrete was investigateed to test Characteristic of Setting and to evaluate the relation between Model Specimen and Heat of hydration for construction Over the High Temperature (CFT). The objective of this study is to take the partial core after the cementation of Model Specimen, test the compression intensity and analyze the relation to Test Piece.

• Progress in Superconductivity and Cryogenics
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• v.6 no.4
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• pp.27-31
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• 2004

This paper describes the development and fabrication of a high temperature superconducting motor which consists of HTS rotor and air-core stator. The machine was designed for the rated power of 100hp at 1800 rpm. The HTS field windings are composed of the double-pancake coils wound with AMSC's SUS-reinforced Bi-2223 tape conductor. These were assembled on the support structure and fixed by a bandage of glass-fiber composite. The cooling system is based on the heat transfer mechanism of the thermosyphon by using GM cryocooler as cooling source. The cold head is in contact with the condenser of a Ne-filled thermosyphon. The rotor assembly was tested independently at the stationary state and combined with stator. Characteristic parameters such as reactances, inductances, and time constants were determined to obtain a consistent overview of the machine operation properties. This motor has met all design parameters by demonstrating HTS field winding, cryogenic refrigeration systems and an air-core armature winding cooled with air. The HTS field winding could be cooled down below 30K. No-load test of open-circuit characteristics(OCC) and short-circuit characteristics(SCC) and load test with resistive load bank were conducted in generator mode. Maximum operating current of field winding at 30K was 120A. From OCC and SCC test results synchronous inductance and synchronous reactance were 2.4mH, 0.49pu, respectively. Efficiency of this HTS machine was 93.3% in full load(100hp) test. This paper will present design, construction, and basic experimental test results of the 100hp HTS machine.