• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.11
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• pp.24-32
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• 2005

The object of this study is to design radar absorbing structures(RAS) with load-bearing ability in X-band. Glass/Epoxy plain-weave composites of excellent specific stiffness and strength, containing multi-walled carbon nanotubes(MWNT) added to induce dielectric loss were fabricated. The observation of microstructure and the permittivity of the composites confirmed that the materials are suitable to be used for radar absorbing material. Genetic algorithm and theory for reflection/transmission of electromagnetic waves in a multi-layered RAS were applied to conduct an optimal design of a RAS composed of the developed composites. We observed that the thickness per ply changes with the number of ply and MWNT contents. The fabrication process was proposed considering the problem and applied to fabricate a designed RAS and the theoretical and measured reflection loss of the RAS were also found in good agreement.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.21 no.10
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• pp.1999-2007
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• 2017

In this paper, we implement a multi-band network selection (MNS) system based on Linux operating system which determines the optimal communication link for given network conditions among the available LTE, very high frequency (VHF), and high frequency (HF). The implemented software consists of a network interface, an MNS server, and a user GUI. We perform indoor test to verify the function of the implemented MNS system using two sets of MNS system. To this end, two types of VHF communication links that follow ITU-R M.1842-1 Annex 1 and Annex 4 are emulated in software. In addition, the HF transmission (reception) port of one MNS is directly connected to the HF reception (transmission) port of another MNS. We demonstrate through indoor tests that the implemented MNS system can support seamless maritime communication service in spite of artificial disconnection or re-connection of LTE, VHFs, and HF. The implemented MNS system is applicable to various maritime communication services including e-navigation.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.42 no.1
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• pp.14-24
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• 2017

In this paper, we propose a new EIM(erasure insertion method) based on the average-minimal-noise-power for HOM(higher order modulation) over AWGN(additive white Gaussian noise) under PBJ(partial-band jamming). Then we design SFH/SS(slow-frequency-hopping spread-spectrum) system by applying this method and formulate the PER(packet error rate) of the system. Based on this formula, we propose a new method to set the optimal threshold of the EIM and verify it at the designed 16-QAM SFH/SS system.

• Journal of Korea Water Resources Association
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• v.54 no.2
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• pp.121-133
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• 2021

Suspended Solids (SS) generated in rivers are mainly introduced from non-point pollutants or appear naturally in the water body, and are an important water quality factor that may cause long-term water pollution by being deposited. However, the conventional method of measuring the concentration of suspended solids is labor-intensive, and it is difficult to obtain a vast amount of data via point measurement. Therefore, in this study, a model for measuring the concentration of suspended solids based on remote sensing in the Nakdong River was developed using Sentinel-2 data that provides high-resolution multi-spectral satellite images. The proposed model considers the spectral bands and band ratios of various wavelength bands using a machine learning model, Support Vector Regression (SVR), to overcome the limitation of the existing remote sensing-based regression equations. The optimal combination of variables was derived using the Recursive Feature Elimination (RFE) and weight coefficients for each variable of SVR. The results show that the 705nm band belonging to the red-edge wavelength band was estimated as the most important spectral band, and the proposed SVR model produced the most accurate measurement compared with the previous regression equations. By using the RFE, the SVR model developed in this study reduces the variable dependence compared to the existing regression equations based on the single spectral band or band ratio and provides more accurate prediction of spatial distribution of suspended solids concentration.

• Advanced Industrial SCIence
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• v.3 no.2
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• pp.31-37
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• 2024

This paper presents a single and 2-patch microstrip array antenna operated on a frequency of 10.3GHz(x-band). It outlines the process of designing a microstrip patch array antenna using CST MWS. Initially, a single microstrip antenna was designed, followed by optimization using CST MWS to attain optimal return losses and gain. Subsequently, the design was expanded to create a 2×1 microstrip inset-fed array antenna for the X-band applications. The construction material is Roger RO4350B, with specific dimensions (h=0.79mm, 𝜖_r = 3.54). The achieved results include an S11 of -18dB at the resonant frequency (10.3GHz), a gain of 9.82dBi, a bandwidth of 0.165GHz, and a 3-dB beamwidth of 30°, 121° in Az(𝜑=0) and El(𝜑=90) plane, respectively. The future plan involves the fabrication of this array antenna and further expansion to a 4×4 array of microstrip antennas. It is then incorporated on the X-band applications for practical uses.

• Journal of the Korean Institute of Telematics and Electronics S
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• v.34S no.7
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• pp.28-38
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• 1997

Previously, we have proposed the M-BECM(Modified-Band Edge Component Maximization), which is a symbol synchronization algorithm based on spectral line method for all-digital high speed digital communications. However, Until now, the characteristics of the timing detector based on the spectral line method including M-BECM was not analyzed, particularly the effect of a timing offset at the optimal convergence pont. In this paper, we analyze the timing dtector's characteristics of the M-BECM and present optimal design value. First, the expression for the timing detector's mean value(often called its S-Curver) as a function of the normalized symbol timing offset is derived. Next, the P $D_{bias}$, the value for compensating the timing offset at an optimal convergence point, and the bandwidth of bandpass filter in the timing detector are calculated. It is also shown and analyzed that the P $D_{bias}$ is affected by varuous factors such as the excess bandwidth of input signal, frequency offsets, noise and particularly, the excess bandwidth of input signal is a major parameter to decide P $D_{bias}$. Finally, analytic resutls are compared to simulation results.

• Journal of Communications and Networks
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• v.17 no.1
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• pp.1-11
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• 2015

In this paper, the transmission of an improper-complex second-order stationary data sequence is considered over a strictly band-limited frequency-selective channel. It is assumed that the transmitter employs linear modulation and that the channel output is corrupted by additive proper-complex cyclostationary noise. Under the average transmit power constraint, the problem of minimizing the mean-squared error at the output of a widely linear receiver is formulated in the time domain to find the optimal transmit and receive waveforms. The optimization problem is converted into a frequency-domain problem by using the vectorized Fourier transform technique and put into the form of a double minimization. First, the widely linear receiver is optimized that requires, unlike the linear receiver design with only one waveform, the design of two receive waveforms. Then, the optimal transmit waveform for the linear modulator is derived by introducing the notion of the impropriety frequency function of a discrete-time random process and by performing a line search combined with an iterative algorithm. The optimal solution shows that both the periodic spectral correlation due to the cyclostationarity and the symmetric spectral correlation about the origin due to the impropriety are well exploited.

• Journal of Life Science
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• v.8 no.2
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• pp.145-157
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• 1998

We isolated 100 Vobrio sp. from marine products and sea from July to September, 1997. We attemped on purification of hemolysin produced by Vibrio sp. The growth, hemolysin production patterns by the 100 strains of Vibrio sp. showed identical, in general. V. unlnificus ys-1 produced hemolysis as the higtest titer. The optimal culture conditions for the hemolysin production by the V. vunificus ys-1 are followings; 1. Hemolysin production was optimal dering the late exponetial phage. 2. Maximal growth, hemolysin production were in heart infusion broth. 3. Maximal yields of hemolysin was obtained when the heart infusion broth had an intial pH of 8.0, 3$0^{\circ}C$, 3% NaCL. Hemolysin was purified from culture filtrate of the strain by ammonium sulfate recipitation, ion exchange and hydrophobic interaction chromatography. The results were as follows; 1. Hemogeneity of the purified hemolysin was demonstrated by revealing single band on SDS-PAGE. The molecular weight of purified hemolysin was 45KDa. 2. The absorbance rattern in ultraviolet wsa typical of those seen with most proteinb with 280nm. 3. Purified hemolysin was atable at 5$0^{\circ}C$ but 7$0^{\circ}C$ of the acivity was lost by heating for 30 min at 6$0^{\circ}C$/ Optimal temperature of purified hemolysin was 35$^{\circ}C$. 4. Purified hemolysin was stable at the pH range of 6~9, but in the less the pH5.0. above the pH 9.0, the hemolysin activity was lost completely.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.10C
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• pp.929-936
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• 2009

In this paper, we consider designing a multi-input multi-output (MIMO) overlay system for fixed MIMO wireless link, where a frequency flat narrowband channel is shared by multiple transmitter and receiver pairs. Assuming the perfect knowledge of the second-order statistics of the received legacy signals and the composite channels from the overlay transmitter to the legacy receivers, the jointly optimal linear precoder and decoder matrices of the MIMO overlay system is derived to minimize the total mean squared error (MSE) of the data symbol vector, subject to total average transmission power and zero interference induced to legacy MIMO systems already existing in the frequency band of interest. Furthermore, the necessary and sufficient condition for the existence of the optimal solution is also derived.

• Proceedings of the KOSOMBE Conference
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• v.1995 no.05
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• pp.227-229
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• 1995

This paper attempts to examine an optimal method for the chromosome specific vector extraction. Usually, represented method are used with a line segmentation on a chromosome Image. It is not Inaccurate but also needs a long time for the analysis. This paper purpose to aquire specific vector in the image with a using optimal ellipse estimation method. Normally, shapes of chromosomes are curved and too difficult to analyze automatically. A chromosome has a lot of band which looks like an ellipse. If we can estimate their bands with an ellipse, we can reconstruct the sample Which Is straight and can be analyzed easily. We have rearranged a chromosome Image with above proposed. Result shows a reconstructed sample which Is simple for chromosome analysis.