• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.136-137
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• 2006

The stochiometric mix of evaporating materials for the $ZnGa_2Se_4$ single crystal thin films were prepared from horizental furnace. To obtains the single crystal thin films, $ZnGa_2Se_4$ mixed crystal were deposited on throughly etched Si(100) by the Hot Wall Epitaxy (HWE) system. The temperates of the source and the substrate were $590^{\circ}C$ and $450^{\circ}C$, respectively. The crystalline structure of single crystal thin films was investigated by the double crystal X-ray diffraction(DCXD). Hall effect on this sample was measured by the method of van der Pauw and studied on carrier density and mobility dependence on temperature.

• ETRI Journal
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• v.43 no.6
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• pp.978-990
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• 2021

This article presents techniques for improved estimation of symbol timing offset (STO) and carrier frequency offset (CFO) for dual-polarization (DP) orthogonal frequency division multiplex (DP-OFDM) systems. Recently, quaternion multiple-input multiple-output OFDM has been proposed for high spectral efficiency communication systems, which can flexibly explore different types of diversities such as space, time, frequency, and polarization. This article focuses on synchronization techniques for DP-OFDM systems using a cyclic prefix, where the application of quaternion algebra leads to new improved estimators. Simulations performed for DP system methods show faster reduction of STO estimator variance with a double-slope line in the logvariance line versus signal-to-noise ratio (SNR) plot compared with singlepolarization (SP) counterparts, and simulations for CFO estimates show a 3-dB gain of DP over SP estimates for same SNR values defined, respectively, for quaternion-valued or complex-valued signals. Cramer-Rao bounds for STO and CFO are derived for the synchronization methods, correlating with the observed gains of DP over SP OFDM systems.

• Journal of Power Electronics
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• v.19 no.1
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• pp.134-145
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• 2019

A single-phase step-up five-level inverter topology with a new phase-shifted pulse width modulation (PS-PWM) strategy is proposed in this paper. When compared with conventional single-phase five-level inverter topologies, the proposed topology can realize multilevel inversion with a double step-up ratio, a reduced number of switching devices and self-balanced capacitor voltages. When compared with the conventional PS-PWM strategy, the new PS-PWM strategy can be implemented with one carrier reduced, which makes it much easier to implement in a digital signal processor (DSP) system. Experimental results have been presented to verify the effectiveness of the proposed inverter and the PS-PWM strategy.

• Proceedings of the PSK Conference
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• 2002.10a
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• pp.231.1-231.1
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• 2002

The anaerobic pathway for unsaturated fatty acid biosynthesis was established in the 1960s in Escherichia coli. The double bond is introduced into the growing acyl chain by FabA., an enzyme capable of both the dehydration of ${\beta}$-hydroxdecanoyl-［acyl carrier protein］ (ACP) to trans-2-decenoyl-ACP. and the isomerization of trans-2 to cis-3-decenoyl-ACP. However. there are a number of anaerobic bacteria whose genomes do not contain a fabA homolog, but these organisms nonetheless produce unsaturated fatty acids. (omitted)

• Journal of Astronomy and Space Sciences
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• v.26 no.2
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• pp.229-236
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• 2009

KOorea Multi-purpose SATellite(KOMPSAT)-5 will be launched at 550km altitude in 2010. Accurate satellite position(20 cm) and velocity(0.03 cm/s) are required to treat highly precise Synthetic Aperture Radar(SAR) image processing. Ionosphere delay was eliminated using dual frequency GPS data and double differenced GPS measurement removed common clock errors of both GPS satellites and receiver. SAC-C carrier phase data with 0.1 Hz sampling rate was used to achieve precise orbit determination(POD) with ETRI GNSS Precise Orbit Determination(EGPOD) software, which was developed by ETRI. Dynamic model approach was used and satellite's position, velocity, and the coefficients of solar radiation pressure and drag were adjusted once per arc using Batch Least Square Estimator(BLSE) filter. Empirical accelerations for sinusoidal radial, along-track, and cross track terms were also estimated once per revolution for unmodeled dynamics. Additionally piece-wise constant acceleration for cross-track direction was estimated once per arc. The performance of POD was validated by comparing with JPL's Precise Orbit Ephemeris(POE).

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.9 no.6
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• pp.574-579
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• 1999

A counter-flow type horizontal reactor of metal organic chemical vapor deposition was designed with the Reynolds and the Rayleigh numbers of Re = 4.5 and Ra = 215.8, respectively. The GaN thin films were grown and characterized by Hall measurement, double crystal X-ray diffraction analysis and photoluminescence measurement. The Si and Mg were also used for doping of GaN films. The dislocation density of $2.6{\times}10^8/\textrm {cm}^2$ was included in GaN films representing the geometrical lattice mismatch between sapphire substrates and GaN films. The Si doped n-GaN films provide the electron carrier density and mobility in the regions of $10^{17}~10^{18}/\textrm{cm}^3$ and 200~400 $\textrm{cm}^2$/V .sec, respectively. Mg doped p-GaN films were post-annealed and activated with the hole carrier density of $8{\times}10^{17}/{\textrm}{cm}^3$.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.20 no.1
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• pp.67-74
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• 2009

In this paper, we investigate the performance limitations of SubCarrier Multiplexed(SCM) WDM systems using optical Double-Side Band(DSB) modulated 16 QAM signals. The Bit-Error Rate(BER) performance is evaluated under various optical transmission links including the effects of the dispersion and fiber nonlinearities such as SPM(Self-Phase Modulation) and XPM(cross-phase modulation). After simulation of SCM-WDM systems, the dominant factors determining the entire system performance are appeared to be the nonlinearity of MZ(Mach-Zehnder) modulator and the SCM channel spacing. The BER performance of subcarrier channels in the higher frequencies was degraded with the large dispersion effect only, however, the performance was improved a little with a combined effect of fiber dispersion and nonlinear effect when the hish fiber launching power was applied.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.07a
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• pp.273-280
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• 2002

The stochiometric mix of evaporating materials for the CuGaTe$_2$ single crystal thin films was prepared from horizontal furnance. For extrapolation method of X-ray diffraction patterns for the CuGaTe$_2$ polycrystal, it was found tetragonal structure whose lattice constant a$\_$0/ and c$\_$0/ were 6.025 ${\AA}$ and 11.931 ${\AA}$, respectively. To obtain the single crystal thin films, CuGaTe$_2$ mixed crystal was deposited on throughly etched semi-insulator GaAs(100) substrate by the Hot Wall Epitaxy (HWE) system. The source and substrate temperature were 670 $^{\circ}C$ and 410 $^{\circ}C$ respective1y, and the thickness of the single crystal thin films is 2.1 $\mu\textrm{m}$. The crystalline structure of single crystalthin films was investigated by the photoluminescence and double crystal X-ray diffraction (DCXD). Hall effect on this sample was measured by the method of van der Pauw and studied on carrier density and mobility dependence on temperature. The carrier density and mobility of CuGaTe$_2$ single crystal thin films deduced from Hall data are 8.72${\times}$10$\^$23/㎥, 3.42${\times}$10$\^$-2/㎡/V$.$s at 293K, respectively. From the photocurrent spectrum by illumination of perpendicular light on the c - axis of the CuGaTe$_2$ single crystal thin film, we have found that the values of spin orbit coupling Δs.o and the crystal field splitting Δcr were 0.0791 eV and 0/2463eV at 10K, respectively. From the PL spectra at 10K, the peaks corresponding to free bound excitons and D-A pair and a broad emission band due to SA is identified. The binding energy of the free excitons are determined to be 0.0470eV and the dissipation energy of the donor -bound exciton and acceptor-bound exciton to be 0.0490eV, 0.00558eV, respectively.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.42 no.10 s.340
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• pp.39-50
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• 2005

In this paper, we propose a performance improving MAC algerian for the IEEE 802.11 DCF. WLAN based IEEE 802.11 uses two control methods called 'Distributed Coordination Function(UF)' and 'Point Coordination Function(PCF)'. The nF controls the Urnsmission based on carrier sense multiple access with collision detection(CSMA/CA), that decides a random backoff time with the range of contention window for each terminal. Normally, each terminal the CW double after collision, and reduces the CW to the minimum after successful transmission. This paper proposes an enhanced DCF algorithm that decreases the CW smoothly after successful transmission in order to reduce the collision Probability by utilizing the current status information of WLAN. We also analyze the throughput and delay performance for the unsaturated case mathematically. Simulation results show that our algorithm enhances the saturation throughput of WLAN. They also coincide well with the analytical results.

• Journal of the Society of Naval Architects of Korea
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• v.28 no.1
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• pp.150-168
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• 1991

A practical procedure for the ultimate compressive strength-based safety and reliability assessment of the double skin upper deck structure is described. The external compressive stress acting on the upper deck structure which is due to the still water and wave-induced sagging moment is approximately estimated by using the existing rule of classification society. The ultimate compressive stress of double skin structure under the action of sagging moment is analyzed by using idealized structural unit method. Here an idealized plate element subjected to uniaxial load is formulated by idealizing the nonlinear behaviour of the actual element taking account of the initial imperfections in the form of initial deflection and welding residual stress. The interaction effect between the local and global failure in the structure is also taken into consideration. The accuracy of the present method is verified comparing with the present solution and the existing numerical and experimental results for unit member and welded box columns. The safety of the structure is evaluated using the concept of conventional central safety factor and the reliability assessment is made by using Cornel's MVFOSM method. The present procedure is then applied to upper deck structure of double skin product oil carrier. The influence of the initial imperfections and the yield stress of the material on the safety and reliability of the structure is investigated.