• Journal of the Korean Institute of Navigation
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• v.15 no.1
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• pp.1-9
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• 1991

The coaxial sample holder with 20mm in diameter and the adaptor from type N connector-to-20mm${\phi}$ coaxial tube are designed and manufactured which have been used for designing and measuring the fabricated microwave absorber. In addition, the measure in method of material constants of the microwave absorbers is described, which is focused on minimizing the error due to the sample's shapes, the fitting conditions, etc. After describing the design method of a single-layed microwave absorber, the microwave absorbers for X-band, C-band and S-band RADARs are designed and fabricated, respectively, which are composed of ferrite, carborn, and binder and have good performance. Futhermore, we develop the high performance microwave absorber in extremely wide-band type for RADAR, which is composed of different material and its mixing ratio and which could cover nearly from 4 to 10 GHz.

• ETRI Journal
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• v.28 no.1
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• pp.119-122
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• 2006

We present an intelligent optical switching structure based on our lambda-group model along with a working scheme that can provide a distinctive approach for dividing complicated traffic into specific tunnels for better optical performance and grooming efficiency. Both the results and figures from our experiments show that the particular channel partition not only helps in reducing ports significantly, but also improves the average signal-to-noise ratio of the wavelength channel and the blocking performance for dynamic connection requests.

• Journal of Communications and Networks
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• v.10 no.1
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• pp.63-70
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• 2008

Narrow-band interference (NBI) from the coexisting narrow-band services affects the performance of ultra wideband (UWB) systems considerably due to the high power of these narrow-band signals with respect to the UWB signals. Specifically, IEEE 802.11a systems which operate around 5 GHz and overlap the band of UWB signals may interfere with UWB systems significantly. In this paper, we suggest a novel NBI suppression technique based on singular value decomposition (SVD) algorithm in time hopping UWB (TH-UWB) systems. SVD is used to approximate the interference which then is subtracted from the received signals. The algorithm precision and closed-form bit error rate (BER) expression are derived in the wireless multipath channel. Comparing with the conventional suppression methods such as a notch filter and a RAKE receiver, the proposed method is simple and robust and especially suitable for UWB systems.

• Journal of the Korean Institute of Telematics and Electronics B
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• v.33B no.8
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• pp.50-59
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• 1996

In this paper, a new hierarchical motion estiamtion scheme using the wavelet transformed multi-resolution image layers is proposed. Compared with the full search motion estimation method, the existing hierarchical methods remarkably reduce the amount of the computation but their efficiencies are depreciated by the local minima problem. In order to solve the local minima problem, the multi-resolution image layers are composed using the wavelet transform and the number of layers participated in the motion estimation for a block is determined by considering of its low band energy and higher band energy on the first wavelet transformed layer. The ratio between higher band energy and low band energy of each block is evaluated and in the case of the blocks which include relatively large higher band energy, the motion estimation is carried out in the high resolution layer. Otherwise, all layers are used. The final motion vectors are obtained in the first wavelet transformed layer. So less bits for motion vectors are transmitted, and the decomposition of received image using inverse wavelet transform decreases the blocking effect.

• Journal of the Korean Association of Geographic Information Studies
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• v.17 no.1
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• pp.80-90
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• 2014

The objective of this research is to estimate the stand volume of Pinus koraiensis, by using the investigated volume and the information of remote sensing(RS), in the research forest of Kangwon National University. The average volume of the research forest per hectare was $307.7m^3/ha$ and standard deviation was $168.4m^3/ha$. Before and after carrying out 3 by 3 majority filtering on TM image, eleven indices were extracted each time. Independent variables needed for linear regression equation were selected using mean pixel values by indices. The number of indices were eleven: six Bands(except for thermal Band), NDVI, Band Ratio(BR1:Band4/Band3, BR2:Band5/Band4, BR3:Band7/Band4), Tasseled Cap-Greeness. As a result, NDVI and TC G were chosen as the most suitable indices for regression before and after filtering, and R-squared was high: 0.736 before filtering, 0.753 after filtering. As a result of error verification for an exact comparison, RMSE before and after filtering was about $69.1m^3/ha$, $67.5m^3/ha$, respectively, and bias was $-12.8m^3/ha$, $9.7m^3/ha$, respectively. Therefore, the regression conducted with filtering was selected as an appropriate model because of low RMSE and bias. The estimated stand volume applying the regression was $160,758m^3$, and the average volume was $314m^3/ha$. This estimation was 1.2 times higher than the actual stand volume of Pinus koraiensis.

• Journal of Advanced Navigation Technology
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• v.14 no.1
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• pp.33-40
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• 2010

In this paper, the bit-error-ratio (BER) performances of Digital Radio Mondiale Plus (DRM+) system which stand for the European standard to bring analogue FM radio to digital radio in Band-II(30-170 MHz) are evaluated under multipath fading channel models used in Band-II and the adjacent channel interference (ACI) caused by FM signal. From the simulation results, the DRM+ system shows robust performances under time-varying channel environments even though the speed of a vehicle is equal to 300km/h. And it is shown that the frequency diversity, determined by delay spread of multipath fading channel, increases the coding gain of the DRM+ system with an increase of delay spread. In addition, to guarantee the BER performance of 10-4 for DRM+ system with ACI due to FM signal, the simulation results show that the desired signal-to-ACI power ratio must be more than -30 dB when the carrier frequency distance is 150 kHz.

• Journal of Mechanical Science and Technology
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• v.15 no.6
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• pp.699-708
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• 2001

This paper presents a new approach to the AFR (Air-to-Fuel Ratio) control problem, which is based on the wide-band oxygen sensor output. The dedicated nonlinear controller is based on the feedback lineaization technique. It is well known that the feedback linearizing control technique requires an exact model of the plant for the cancellation of plant nonlinearities. A sliding mode control scheme is applied which can effectively compensate the modeling uncertainties. The measurement time delay of an oxygen sensor limits the gain of the feedback controller. Hence, time delay compensation procedure is necessary for the improvement of control performance. The Smith predictor is adopted to compensate the effects of time delay. The simulation and experimental results show that the proposed controllers can effectively reduce the transient peaks of AFR in spite of fast tip-in and tip-out maneuvers of the throttle.

• Journal of the Korean Society of Combustion
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• v.20 no.4
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• pp.1-9
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• 2015

The object of this study is a deriving the relations according to the measuring locations between the chemiluminescence and the flame state at commercial burner. In this study, the flame chemiluminescence of the flame of commercial burner is measured using a photomultiplier tube and the optical band-pass filter. In addition, the contour of the chemiluminescence of the flame is measured using the common CCD camera and the optical band-pass filters, and the acquired images is converted by the simple image processing as a matrix form. The results showed that certain relationship between optical data and equivalence ratio exists, and the contour according to the measuring location of the flame chemiluminescence is different by equivalence ratio.

• Journal of the Korean institute of surface engineering
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• v.37 no.4
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• pp.191-195
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• 2004

Gallium or sulphur additions in $CuInSe_2$ were prepared using RF magnetron sputtering and pulsed laser deposition respectively. All of the observed thin films shows a chalcopyrite structure with the S and Ga addition increases the favourable (112) peak. The optical absorption coefficients were slightly decreased. The energy band gap of films could be shifted from 1.04 to 1.68 eV by adjusting the mole ratio of S/(S+Se) and Ga/(In+Ga). It is possible to obtain the optimum energy band gap by adding S or Ga solute at a certain ratio in favour of Se and In respectively. It is also necessary to control the ratio of Ga and S additions and to retain a certain portion of In and Se to provide better properties of thin films.

• The KSFM Journal of Fluid Machinery
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• v.13 no.1
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• pp.35-41
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• 2010

Experimental study on the flow field inside the nozzle for radial turbine was performed. At design point, the pressure is high and the Mach number is low at the pressure side of the nozzle inlet semi-vaneless space as the flow turns through the nozzle vanes. As the flow accelerates through the nozzle passage to the throat the pressure level at the pressure and suction sides becomes similar. The flow continued accelerating from the throat to the inlet of turbine wheel and the pressure field became uniform in the circumferential direction in the vaneless space. In high expansion ratio condition, strong favorable pressure gradient band region occurred just after the throat in the semi-vaneless space in the circumferential direction and the pressure became uniform in the circumferential direction after this band. In low expansion ratio condition, core flow acceleration is dominant after the throat and this non-uniform pressure field reached to the inlet of turbine wheel.