• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.16 no.4 s.95
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• pp.389-396
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• 2005

In this paper, we propose a pre-distortion method using the NLMS(Normalized Least Mean Square) algorithm to cope with hish PAPR(Peak to Average Power Ratio) problem in OFDM communication system. This proposed scheme estimates the distortion characteristics of HPA, and changes the characteristic against the distortion. Therefore, it can be shown that the adaptive characteristic of the NLMS pre-distorter is good to track the various nonlinear characteristic of HPA, even though HPA characteristic is changed by temperature variation or aging. From the performance analysis, SNR efficiency of NLMS pre-distorter is about $0.5\;\cal{dB}$ less than that of common numerical non-adaptive pre-distorter, when IBO(Input Back Off) is $0\;\cal{dB}$. However, the NLMS pre-distorter is better than the common numerical pre-distorter, because these two pre-distorters have similar performance in higher than $3\;\cal{dB}$ IBO, and the NLMS pre-distorter maintains the constant performance even though characteristic of HPA is changed.

• The KSFM Journal of Fluid Machinery
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• v.3 no.2 s.7
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• pp.31-35
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• 2000

In this research, the performance predictions of the submersible mixer were investigated. The variation of the performance characteristics by changing the impeller design parameters were discussed through the flow calculation results by using a commercial program, FLUENT. The performance of the submersible mixers is related to the velocity diffusion profiles downstream of the impeller and also the required input motor power to mix the fluid. In this study, the various design parameters such as the number of blade, the hub and tip diameters, the impeller blade profiles and revolution speed of the blades were taken for the fixed values. The blade sweep direction, the chord length distribution along with the radius of the blade and the inlet blade angle were changed to make different testing models. The flow calculation results show the effect of the changed design parameters on the performance of the submersible mixers and also give some helpful information for designing more efficient submersible mixers.

• Journal of the Korea Institute of Military Science and Technology
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• v.6 no.4
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• pp.22-28
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• 2003

In the conventional weapon system, such as gun and small arms, it Is a general trend that for maximization of its performance and enhancement of its effectiveness, the firing control system(FCS) is developed and applied with the guns and small arms in the world. The FCS of the small arms for infantry man is composed of a few of sensors for acquisition of input data of FCS, such as range measurement, position sensing of weapon, temperature, etc., computer, displayer and power pack, and also the air burst munition is developed in parallel for the maximization of FCS's effectiveness. Since the flight time setting fuze for the air burst munition is adapted for next me, the measuring device of the muzzle velocity is needed to overcome the variation of muzzle velocity due to producing procedures and the differences of the using temperatures and so maintain the burst position accuracy This paper contained the technical information on the development of the measuring device of muzzle velocity, which designed in compact & light weight configuration with reliability and accuracy.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.2
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• pp.585-593
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• 1996

According to the considerable increase of the length of belt conveyors, the dynamic analysis of systme becomes necessary to consider the variation of tensions and transient motion of components during starting and stopping of conveyor. The mathematical model of system is derived using the lumped parameter method. The input driving force is represented with two functions of time and pulley speed to count the characteristics of motor and fluid coupling. An example system was studied with 14 km in the distance of carrying. At head, it has two drivers and one gravity take-up and at tail ond driver and one power winch take-up. In the example, the transient tensions and responses, calculated using two cases of driving force, are mutually compared in starting mode. Also, the position of maximum tension and the braking force of take-up are obtained in stopping mode.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.23 no.6
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• pp.421-429
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• 2011

Experimental and theoretical studies on cooling performance of two-channel thermoelectric air-cooling system in parallel flow are conducted. The effects of operating temperature to physical properties of thermoelectric module (TEM) are experimentally examined and used in the analysis of an air-cooling system considering thermal network and energy balance. The theoretical predicted temperature variation and cooling capacity are in good agreement with measured data, thereby validating analytic model. The heat absorbed rate increases with increasing the voltage input and decreasing thermal resistance of the system. The power consumption of TEM is linearly proportional to mean temperature differences due to variations of the physical properties on operation temperature of TEM. Furthermore thermal resistance of hot side has greater effects on cooling performance than that of cold side.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2015.05a
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• pp.685-688
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• 2015

A phase-shift full-bridge converter is widely used conventional converter. If the input power change in the variation of the output voltage, there is a time interval freewheeling according to a duty change. This is a factor of reducing the efficiency. In this paper, we propose a method for improving the efficiency of the converter/inverter systems that require high efficiency in the ESS. The proposed method was used for the duty control for solving the fail problem ZVS(Zero Voltage Switching) in Freewheeling interval. The proposed method was verified by experiments.

• Journal of Welding and Joining
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• v.25 no.5
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• pp.51-57
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• 2007

The present work was aimed to examine the variation of microstructure and mechanical properties by annealing($100{\sim}620^{\circ}C$, $2{\sim}8hr$) in A3003 Al alloy welded pipes. The A3003 Al alloy pipes with 34 mm in external diameter and 1.3 mm in thickness were manufactured by high frequency induction welding with the V shaped convergence angle $6.7^{\circ}$ and power input 50 kW. The tensile and yield strength decreased with increasing the annealing temperature remarkably, but elongation increased remarkably. Vickers hardness in welds decreased with increasing the annealing temperature remarkably. The primary intermetallic compound of $Al_{12}(Fe,\;Mn)_2Si$ was precipitated in welds as the same base metal. In a certain experimental condition, the welds line in A3003 alloys disappeared at $450^{\circ}C$ for 2 hr because of the same mechanical property and structure between welds and base metal.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.8B
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• pp.1413-1423
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• 2000

Color distribution is changed according to the variation of illumination position and illumination color. Therefore, even if images are relevant each other, retrieval accuracy is degraded. In this paper, we propose the image retrieval method using color information excluded illumination component. The proposed dynamic range control method removes the shadow region generated by change of illumination position to increase the color discrimination power. To exclude the illuminant color, we use the diffuse reflection component of object and gray world assumption. The experimental results show that the color histogram method using color information excluded illuminant has higher retrieval accuracy than conventional color histogram using the color information of input image.

• ETRI Journal
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• v.33 no.6
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• pp.897-903
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• 2011

A hybrid ${\Delta}{\Sigma}$ modulator for audio applications is presented in this paper. The pulse generator for digital-to-analog converter alleviates the requirement of the external clock jitter and calibrates the coefficient variation due to a process shift and temperature changes. The input resistor network in the first integrator offers a gain control function in a dB-linear fashion. Also, careful chopper stabilization implementation using return-to-zero scheme in the first continuous-time integrator minimizes both the influence of flicker noise and inflow noise due to chopping. The chip is implemented in a 0.13 ${\mu}m$ CMOS technology (I/O devices) and occupies an active area of 0.37 $mm^2$. The ${\Delta}{\Sigma}$ modulator achieves a dynamic range (A-weighted) of 97.8 dB and a peak signal-to-noise-plus-distortion ratio of 90.0 dB over an audio bandwidth of 20 kHz with a 4.4 mW power consumption from 3.3 V. Also, the gain of the modulator is controlled from -9.5 dB to 8.5 dB, and the performance of the modulator is maintained up to 5 nsRMS external clock jitter.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2003.05a
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• pp.279-283
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• 2003

As the state of the art in recent years Laser-Arc Hybrid welding is tried actively because of its various economical and technical advantages. In this study, melting tendencies according to the variation of laser-arc distance are investigated in case of YAG laser-TIG Hybrid welding process of AH32 ship structural steel. Nd-YAG laser with a laser beam power of 3KW is used and varied laser-arc distance 0mm to 10mm with fixing the TIG current as l00A. There is certain distance between laser and TIG elecrode to improve welding heat input and also increase the penetration.