• Journal of the Korean Society of Manufacturing Process Engineers
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• v.15 no.5
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• pp.80-85
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• 2016

In recent years, work to improve the power of a tractor has been in development. This study, using the mid-PTO power of a compact tractor, attempted to develop a high-speed mid-mower by setting the rotation to more than 3,000 RPM designed/manufactured major components of the high speed mid-mower. The performance of high-speed mid-mower was evaluated by the precision of straight bevel gears, and durability, the noise of the gearbox, the gearbox internal temperature, the maximum rotation speed of the mid-mowers, and the grass cutting test. Through the performance test results, the maximum number of revolutions of the mid-mower was measured over 3,000RPM, the gearbox noise and gearbox internal temperature satisfied the performance requirements of a high speed mid-mower.

• Journal of the Korean Society for Nondestructive Testing
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• v.32 no.3
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• pp.296-301
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• 2012

This paper describes an analytic method for infrared thermography to detect surface cracks in thin plates. Traditional thermographic method uses the spatial contrast of a thermal field, which is often corrupted by noise in the experiment induced mainly by emissivity variations of target surfaces. This study developed a robust analytic approach to crack detection for thermography using the holomorphic function of a temperature field in thin plate under steady-state thermal conditions. The holomorphic function of a simple temperature field was derived for 2-D heat flow in the plate from Cauchy-Riemann conditions, and applied to define a contour integral that varies depending on the existence and strength of singularity in the domain of integration. It was found that the contour integral at each point of thermal image reduced the noise and temperature variation due to heat conduction, so that it provided a clearer image of the singularity such as cracks.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.26 no.9
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• pp.798-805
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• 2015

This paper proposes Relaxation Oscillator with Random Number Generator to minimize electromagnetic interference (EMI) noise. DC-DC Converter with Relaxation Oscillator is presented how much spurious noise effects to RF Receiver system. The main frequency of the proposed Relaxation oscillator is 7.9 MHz to operate it and add temperature compensation block to be applied to the frequency compensation in response to temperature changes. The DC-DC Converter Spurious noise is reduced up to 20 dB through changing frequency randomly. It is fabricated in $0.18{\mu}m$ CMOS technology. The active area occupies an area of $220{\mu}m{\times}280{\mu}m$. The supply voltage is 1.8 V and current consumption is $500{\mu}A$.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.564-571
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• 2003

This research investigates how characteristics of ball bearing affect non-repeatable runout(NRRO) in a HDD spindle system at elevated temperature. It shows that the elevated temperature results in the increase of bearing contact angle and the decrease of bearing deformation due to the different thermal expansion rate of the components of the HDD spindle system. The increase of contact angle at elevated temperature is so small that the variation of bearing frequencies is negligible. On the other hand, the decrease of bearing deformation at elevated temperature reduces the stiffness of ball bearing and the natural frequencies of HDD spindle system consequently, which changes the amplitude and the frequency distribution of NRRO.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.23 no.8
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• pp.110-115
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• 2009

Recently, there has been a growing global interest in environmental conservation, and the field of electric power equipment has been working to become more environment-friendly. Accordingly, the low noise cooling fan of power transformers was developed through the improvement of blade shape. These are expected to apply to existing power transformers and low noise transformers. It is essential for low noise fan to possess good cooling performance as well as low audible noises. But, there was not analysis on the audible noise level and the cooling performance for low noise cooling fans until present. In this paper, we measure the audible noise level and the flow rate of low noise cooling fans to inspect the performance, Also, we confirmed that the low noise cooling fan is available to apply to power transformers through temperature rise tests of power transformers.

• Publications of The Korean Astronomical Society
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• v.11 no.1
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• pp.109-123
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• 1996

We have developed a 5GHz continuum receiver system. The receiver is a direct type receiver. In order to reduce the noise due to the fluctuation of the gain in the amplifiers, the system employs the Dicke switching method. We made the 5GHz low-noise amplifier and the bandpass filter. The low-noise amplifier gives ${\sim}35dB$ gain and has ${\sim}210K$ noise temperature. The bandpass filter has a passband between 4.3 and 5.4GHz. We also made switch driver, video amplifiers, phase detector, and integrator. Using a 1.8 meter offset parabolic antenna, we measured the efficiency of the system. Since the antenna does not have a driver to track objects, observations were performed with the antenna fixed. The measured noise temperature of the system is ${\sim}650K$. From the observation of the blank sky, noise level was measured. It was found that the systematic noise(${\sim}0.5K$: peak to peak value) is much larger than the thermal noise. The systematic noise is possibly related to the stability of the DC power supplied to the receiver system. Besides the noise of the system, it was found that the airplanes are the very serious noise sources. We measured the radio flux of the Sun using the developed system. The observed radio flux of the Sun is ${\sim}10^6Jy$, which is close to the known value of the quiet Sun. The test observation of the Sun shows that the angular beam size of the antenna is ${\sim}2.2^{\circ}$.

• Proceedings of the KIEE Conference
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• 1999.07d
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• pp.1864-1866
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• 1999

The magnetic nondestructive test can be applied to evaluate the magnetic material characteristics and the fracture properties through the internal defects of SA-508 used in the pressure vessels of the nuclear power plants as the direct and accurate in-situ testing methods. The fracture toughness, yield strength and the stress distribution around the defects in the surface and sub-surface of magnetic materials can be directly estimated by Bark-hausen noise(BN) methods as NDT. The testing process of SA-508 by Barkhausen noise method was advanced by controlling the austenizing peak temperature and the time of maintenance at a constant austenizing peak temperature, therefore causing the variation of fracture toughness. Through above process. we can evaluate the variations of effective grain size and the correlation of effective grain size and FATT at each situation. And the stress distribution around the defects can be quantified nondestructively through Barkhausen method.

• Journal of Astronomy and Space Sciences
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• v.21 no.1
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• pp.29-38
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• 2004

A ultra low noise Q-band HEMT receiver for VLBI has been developed using a local oscillator with a very high phase stability. The performance of receiver was verified by comparison with receivers which were developed at the other countries. The receiver noise temperature shows 65 K in the frequency ragne from 42 ㎓ to 44 ㎓, less than 100 K from 39 ㎓ to 46 ㎓, respectively. A receiver noise temperature at SiO major line of 43㎓ which will be mainly observed by using this receiver has been optimized.

• Journal of the Korean Society for Heat Treatment
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• v.21 no.4
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• pp.199-204
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• 2008

The destructive method is reliable and widely used for evaluating the properties of material but it is time-consuming and difficult to prepare specimens from in-service industrial facilities. In the present research, Barkhausen Noise (BN) has been used to evaluate changes of mechanical properties due to heat treatment condition. The BN voltage (rms voltage) was measured with grain size. The rms voltage of BN increased with the heat treatment temperature ($870{\sim}1000^{\circ}C$) because the grain size increased with the temperature. The rms voltage of BN decreased with various heat treatment processes, such as quenched, tempered and PWHT. The BN can be used for the nondestructive evaluation of the forged reactor vessels. and moreover, it may be effectively used in the field application.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.22 no.12
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• pp.1184-1190
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• 2012

This study is focused on the experimental analysis of the noise induced by phase change of refrigerant at the entrance of capillary tube. The refrigerant is usually two-phase condition when it flowed into the capillary tube. At the entrance of capillary tube, the phase condition of refrigerant is formed by sub-cool control. If it has sufficient sub-cool temperature, all of the vapor refrigerants turned to liquid, which means there is only liquid. Otherwise, the gas is coexisted. Based on this theory, we experiment on each case by changing sub-cool temperature using refrigerant-supplying equipment. The noise level is measured for each case and compared.