• Korean Journal of Materials Research
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• v.9 no.8
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• pp.854-857
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• 1999

The properties of Fe-Se-Te system(FeSe(sub)1-xTe(sub)x, x=0.2, 0.5, 0.8) have been studied by means of the X-ray diffraction method and Mossbauer spectroscopy. The results of X-ray diffraction patterns show that three samples have the ixed structure of tetragonal PbO and a small amount of hexagonal NiAs structure respectively. For x=0.5 the lattice parameters of tetragonal PbO structure are a=3.795$\AA$, c=5.896$\AA$ and c/a=1.55. The Mossbauer spectra were obtained with the various temperature variation and than they do not exhibit magnetic hyperfine structure but show a strong doublet. The values of observed isomer shift and quadrupole splitting suggest that the irons of all samples exist in the +2 oxidation state with a major covalent contribution. The temperature dependence of isomer shift values for x=0.8 seems to be originated from the second order Doppler effect.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.2C
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• pp.238-245
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• 2010

For orthogonal frequency division multiplexing (OFDM) systems sharing the spectrum with narrow band primary devices, a fractional bandwidth (FBW) mode has been proposed recently to reduce the interference to the primary users. The FBW mode divides the total OFDM bandwidth into subbands and activates (or deactivates) a subset of the subbands according to the result of spectrum sensing. In this paper, we analyze the detection error probability of FBW mode information which is delivered by the sequence embedded in the preamble and evaluate the performance in wireless regional area network environments. The results show that the detection probability derived analytically estimates the actual value from simulation adequately and that a low detection error probability less than $10^{-3}$ is obtained at a low signal-to-noise power ratio.

• Polymer(Korea)
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• v.35 no.5
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• pp.395-401
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• 2011

MWNT/PMMA and MWNT/PDMAEMA nanocomposites were prepared using an atom transfer radical polymerization (ATRP). The FTIR and XRD analysis results showed that the nanocomposites were composed of MWNTs grafted by either PMMA(PMMA-g-MWNTs) or PDMAEMA(PDMAEMA-g-MWNTs). A controlled living radical polymerization of ATRP was characterized by the thermogram analysis for the nanocomposites. The morphologies of prepared nanocomposites were analyzed by transmission electron microscopy. Raman analysis results for the nanocomposites showed that there occurred covalent bonding between acrylic polymers and MWNTs.

• Journal of Digital Contents Society
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• v.8 no.4
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• pp.491-497
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• 2007

RPersonal area networking technology is becoming increasingly important in enabling useful wireless home applications. For example, Bluetooth and IEEE 802.11b standards are the most commonly deployed technologies for wireless home applications. However, because both standards share the same unlicensed ISM (Industrial, Scientific, Medical) radio spectrum, severe interference is inevitable and performance can be impaired significantly when heterogeneous devices using the two technologies come into close proximity. In this paper, we research Gaussian FSK Bluetooth system, which is an open specification technology for short-range wireless connectivity between electronic devices. In this paper, we analyzes the effects of co-channel interference on the performance of a Gaussian FSK Bluetooth system. Performance criteria used in the study are the signal to interference power ratio (SIR), interference index, and the bit error rate (BER) in the wireless channel. The effect of co-channel interference from various sources on the performance of a Gaussian FSK Bluetooth system is analyzed using an IGA(Impulsive Gaussian Approximation) method, and these quantities are plotted against Eb/No, $\rho$ and SIR for various channel conditions in figures.

• Journal of Satellite, Information and Communications
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• v.9 no.2
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• pp.28-32
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• 2014

In this paper, we analyzed the performance of cyclostationary signal detection scheme for LTE system. We applied the cyclostationary signal detection scheme to the cognitive radio(CR) technology, which improves the usage efficiency of spectrums and shares frequencies, and we detected the signal in the long term evolution(LTE) band. LTE system has been designated as the standard to improve the maximum data rate and provide the low latency in the 3rd generation partnership project(3GPP). In this paper, we generated the LTE signals based on the orthogonal frequency division multiple access(OFDMA) and analyzed the performance of signal detection in accordance with the segment and threshold of the generated signals. Gaussian channel was used in the simulation and we discussed the future studies to apply the CR to the LTE system.

• Analytical Science and Technology
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• v.34 no.3
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• pp.128-133
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• 2021

During titration, several chemical reactions result in changes not only in the potential of chemicals, but also in the colors of the indicator. In a potentiometric titration, a titration curve is obtained by measuring the abrupt change in the potential at the endpoint. Generally, acid-base titration is performed by observing the color change caused by an indicator to determine the endpoint. The method of determining the endpoint by measuring the potential difference has been well established and commercialized; however, the devices that can obtain the endpoint by observing the color change are limited. Consequently, in this study, a simple and precise spectral endpoint detector was manufactured using a drop-counter comprising an infrared emitter and a phototransistor, a white light LED as the light source and photodetector, and an analog-to-digital converter (Arduino). Spectrator, a new named, showed excellent results in terms of the reproducibility of acid-base titration using thymol blue as an indicator. Herein, we present the results of the Spectrator-manufacturing process as well as the experimental results.

• Journal of Advanced Navigation Technology
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• v.26 no.5
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• pp.350-357
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• 2022

With the recent prediction of 'Cycle 25', the importance of space weather research increases. Accordingly, the World Radiocommunication Conference (WRC)-23 has adopted Agenda Item 9.1a) and carried out sharing researches between active/passive space weather observation systems and existing services. Therefore, in this paper, in order to increase the precision of space weather environment data and secure the frequency spectrum for observation systems, the direct interference effect from the weather radar in Gosan, Jeju on the space weather observation receiver in Hallim, Jeju, and the indirect interference on the observation receiver by diffraction and scattering from the radar target have been analyzed. As a result, it can be known that the radar direction, the propagation direction diffracted and scattered from the target, and the Rradar Cross Section (RCS) of the radar target, the reception area of the space weather observation antenna, and the antenna off-boresight are important parameters for the interference effect analysis.

• Journal of IKEEE
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• v.26 no.4
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• pp.693-704
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• 2022

5G service uses mid-band (n78) than existing mobile communication frequencies, so it is necessary to improve 5G coverage by utilizing low-band frequencies below 2 GHz. To this end, the application of Dynamic Spectrum Sharing technology of LTE and 5G-NR system using most of the low-band frequencies is required. In this paper, signaling overhead factors for DSS application and RF issues for terminal implementation are derived, and signaling overhead ratios from the respective perspectives of 5G-NR and LTE for the 1.8GHz band (50MHz width) that can utilize wide-bandwidth among low-band frequencies are estimated. Also handset RF issues were analyzed. Based on the analysis results, if DSS technology using low band is applied, it is expected that excellent 5G service quality can be provided due to 5G coverage improvement when LTE traffic quickly migrates to 5G-NR.

• Journal of the Korean Chemical Society
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• v.55 no.3
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• pp.418-429
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• 2011

Novel chromium(III), manganese(II), iron(III), cobalt(II), nickel(II), copper(II), ruthenium(III), and zirconyl(II) complexes of $N^1,N^2$-bis(3-((3-hydroxynaphthalen-2-yl)methylene-amino)propyl)phthalamide ($H_4L$, 1) have been synthesized and characterized by elemental, physical, and spectral analyses. The spectral data showed that the ligand behaves as either neutral tridentate ligand as in complexes 2-5 with the general formula $[H_4LMX_2(H_2O)]{\cdot}nH_2O$ (M=Cu(II), Ni(II), Co(II), X = Cl or $NO_3$), neutral hexadentate ligand as in complexes 10-12 with the general formula $[H_4LM_2Cl_6]{\cdot}nH_2O$ (M=Fe(III), Cr(III) or Ru(III)), or dibasic hexadentate ligand as in complexes 6-9 with the general formula $[H_2LM_2Cl_2(H_2O)_4]{\cdot}nH_2O$ (M = Cu(II), Ni(II), Co(II) or Mn(II), and 13 with general formula $[H_4L(ZrO)_2Cl_2]{\cdot}8H_2O$. Molar conductance in DMF solution indicated the non-ionic nature of the complexes. The ESR spectra of solid copper(II) complexes 2, 5, and 6 showed $g_{\parallel}$ >g> $g_e$, indicating distorted octahedral structure and the presence of the unpaired electron in the $N^1,N^2$ orbital with significant covalent bond character. For the dimeric copper(II) complex $[H_2LCu_2Cl_2(H_2O)_4]{\cdot}3H_2O$ (6), the distance between the two copper centers was calculated using field zero splitting parameter for the parallel component that was estimated from the ESR spectrum. The antibacterial and antifungal activities of the compounds showed that, some of metal complexes exhibited a greater inhibitory effect than standard drug as tetracycline (bacteria) and Amphotricene B (fungi).

• Journal of the Korean Chemical Society
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• v.38 no.12
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• pp.873-879
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• 1994

A series of samples of solid solutions in the $Sr_xEu_{1-x}FeO_{3-y}(0.00{\leq}x{\leq}1.00)$ system has been prepared at $1200^{\circ}C$ under an atmospheric air pressure. The structures of solid solutions are studied by X-ray diffraction, thermal, Mohr salt, and Mossbauer spectroscopic analyses. Their physical properties are also discussed with the electrical conductivities. X-ray diffraction data for the compositions of x = 0.00, 0.25, and 1.00 are assigned to the orthorhombic and the compositions of x = 0.50 and 0.75 to the cubic systems. The lattice volume reduced to cubic cell increases with the x value. The mole ratio of $Fe^{4+}$ iometric chemical formulas of the system are formulated from the x, $\tau$, and y values. The mixed valency state of Fe ions, the oxygen coordination, and covalent bond character are discussed with the Mossbauer spectroscopic data. The activation enegy of the electrical conductivities depends on the $\tau$ value in the temperature range of -$100^{\circ}C$ to $600\circC$ under the air pressure. The Mossbauer spectrum and electrical conductivity of the solid solutions are discussed with nonstoichiometric chemical compositions.