• Journal of the Korean Society of Safety
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• v.20 no.3 s.71
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• pp.27-33
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• 2005

The shape memory effect in Ti-50.4at.%Ni alloy after solution treatment at 1273K for 2h and aged at 350, 450, $550^{\circ}C$ for 0.5, 1, 1.5, 2, 4, 10hrs had been investigated by differential scanning calorimetry measurement. It was found that ageing in the temperature range of $350^{\circ}C{\sim}550^{\cric}C$ induced complex transformation behavior, involving the R-phase and multiple-stage martensitic transformation. Usually aged Ni-rich NiTi alloys undergo martensitic transformation on cooling from high temperatures in two step : Austenite to R-phase and then R-phase to Martensite (normal behavior). In sample aged at $350^{\circ}C$ two distinct DSC peaks arised giving evidence of intermediate stages of martensite transformation. This results in the nucleation and growth of coherent $Ni_4Ti_3$-precipitate. These explain all features of the evolution of DSC charts during ageing including the number of distinct DS peaks and their positions.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.10
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• pp.1193-1201
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• 2004

The effect of equivalence ratio and fuel/air mixing quality on the phase-resolved gas temperatures at different phases of the oscillating pressure cycle was experimentally investigated. An atmospheric pressure, optically accessible and laboratory-scale dump combustor operating on methane with heat release rate of 1.59kW was used. Temperature measurements were made using coherent anti-Stokes Raman spectroscopy (CARS) at several spatial locations fur typical unstable combustion conditions. Analysis was conducted using parameters such as phase-resolved averaged temperature, normalized standard deviation and temperature probability distribution functions (PDFs). Also the probability on the occurrence of high temperature (over 1900K) was investigated to get the information on the perturbation of equivalence ratio and NOx emission characteristics. It was shown that most of temperature histograms exhibit Gaussian profile which has short breadth of temperature fluctuation at equivalence ratio of 0.6, while beta profile was predominant for the cases of other equivalence ratios (${\Phi}$=0.55, 0.50). It was also shown that phase-resolved averaged temperature oscillated in phase with pressure cycle, while normalized standard deviations which represent temporal turbulent intensity of temperature showed nearly constant value around 0.1. The characteristics on the occurrence of high temperature also displayed periodic wave form which was very similar to the pressure signal. And the amplitude of this profile went larger as the fuel/air mixing quality became poorer. These also provided additional information on the perturbation of equivalence ratio at flame as well as NOx emission characteristics.

• Korean Journal of Materials Research
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• v.25 no.8
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• pp.410-416
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• 2015

Microstructural analysis of a (${\alpha}+{\beta}$) Ti alloy was investigated to consider phase transformation in each step of the thermo-mechanical process using by SEM and TEM EDS. The TAF (Ti-6Al-4Fe) alloy was thermo-mechanically treated with solid solution at $880^{\circ}C$, rolling at $880^{\circ}C$ and annealing at $800^{\circ}C$. In the STQ state, the TAF microstructure was composed of a normal hcp ${\alpha}$ and metastable ${\beta}$ phase. In a rolled state, it was composed of fine B2 precipitates in an ${\alpha}$ phase, which had high Fe segregation and a coherent relationship with the ${\beta}$ matrix. Finally, in the annealing state, the fine B2 precipitates had disappeared in the ${\alpha}$ phase and had gone to the boundary of the ${\alpha}$ and ${\beta}$ phase. On the other hand, in a lower rolling temperature of $704^{\circ}C$, the B2 precipitates were more coarse in both the ${\alpha}$ and the boundary of ${\alpha}$ and ${\beta}$ phase. We concluded that microstructural change affects the mechanical properties of formability including rolling defects and cracks.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.19 no.11
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• pp.1281-1286
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• 2008

The PSK carrier signal recovery circuit using a six-port phase correlator was analyzed and the circuit structure is proposed in this paper. The proposed carrier signal recovery circuit that is made of reflection element and six-port phase correlator, which is comprised of a power divider and three hybrid branch line couplers, give a simple structure and can be fabricated without no difficulty. The circuit recovers the carrier signal of BPSK and QPSK modulation signal. The proposed scheme can be utilized as a basis structure for high-mode PSK carrier signal recovery. By simulation results, the recovered signal by the proposed circuit shows a good carrier signal characteristic with CW signal of a constant phase($23.4^{\circ}$) and ${\pm}0.8^{\circ}$ phase error due to glitch conditions.

• Journal of the Institute of Electronics Engineers of Korea TE
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• v.37 no.5
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• pp.77-84
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• 2000

In this paper, we modelized the multipath fading to Nakagami-m distribution fading channel which can be applied to the extended mobile communication channel environment. We assumed that the phase difference with reference signal happened in the received signal and in the receiver PLL(Phase Locked Loop) is the phase error. To correct the error we propose new RAKE receiver using PLL. In addition, we analyze the performance of DS/SS(Direct Sequence/spread Spectrum) system according to the gain of PLL,$\gamma_n$, the number of RAKE receiver branch L and MIP(Multipath Intensity Profile)'s exponential decay $\delta$. As a result, when the proposed RAKE receiver L Is increased and the $\delta$ is decreased the performance of the system gets better. Futhermore when PLL gain was 30dB, phase is identified. That is when the PLL gain is 30dB, the performance equals with the perfect coherent system's. Therefore, we can correct the phase error by using the proposed RAKE receiver and we proved that the PLL's requested limit gain should be 30dB.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.21 no.10
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• pp.1973-1980
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• 2017

In the case of a small UUV operating an active synthetic aperture sonar, various velocity disturbances may occur on the path due to the influence of external underwater environment, and this causes phase errors in coherent synthetic aperture processing, which has a large influence on the detected image. In this paper, when a periodic sinusoidal velocity disturbance is generated in the traveling direction, the phase generated by the round trip slope range at each position is estimated the cross correlation coefficient for multiple received signals and compensated the position variation in the overlapped DPC by the average value within the maximum allowable width. Through simulations, it has been confirmed that the images degraded by the velocity disturbance amplitude and fluctuating frequency of the UUV are removed from the false targets and the performance of azimuth resolution is improved by the proposed phase compensation method.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.24 no.6
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• pp.437-449
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• 1991

Time series of barometrically adjusted sea level at Pusan, Izuhara and Hakada are analyzed to study the fluctuations of the Tsushima Current through the Korea Strait. Variability of sea levels and their differences is divided into two parts with respect to the frequency of 0.01 or 0.02 cycles per day(cpd) At lower frequency, both of sea levels and sea level difference(SLD) are coherent and in phase to each other. Pusan has smaller seasonal variations in sea level than other two stations because the effects of geostrophic current and prevailing wind have a negative influence on the seasonal thermosteric contribution to sea level change. Low frequency variability of SLD thus of the Tsushima Current is much greater in the western channel. For higher frequency parts, SLD in the eastern channel has larger variability and is not coherent with that of the western channel. Sea levels at Pusan and Izuhara are $180^{\circ}$ out of phase with SLD in the western and eastern channel respectively, whereas the Hakada level is in phase. This result indicates that eastern channel has a normal response to the along-channel winds and cross-channel geostrophy because Izuhara faces the eastern channel.

• Korean Journal of Materials Research
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• v.8 no.2
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• pp.165-172
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• 1998

Epitaxial ultrathin films of $CoSi_2$ and double heteroepitaxial structure of Si/$CoSi_2$/Si(lll) were prepared on Si(111)-$7\times{7}$ substrate by in situ solid-phase epitaxy in a ultrahigh vacuum(LHV). The phase, chemical composition, crystallinity, and the microsructure of the Si/$CoSi_2$/Si(lll) interface were investigated by 2-MeV $^4He^{++}$ ion backscattering spectrometry, X-ray diffraction, and high-resolution transmission electron microscopy. The growth mode of the Co film was the Stransky-Krastanov type with texture when the substrate temperature was room temperature. A-type $CoSi_2$ ultrathin film was grown by deposition of about 50A Co on Si(ll1)-$7\times{7}$ substrate followed by in situ annealing at $700^{\circ}C$ for 10 min. The matching face relationships were $CoSi_2$[110]//Si[110] and $CoSi_2$(002)//Si(002) with no misorientation angle. The A-type $CoSi_2$/Si(lll) interface was abrupt and coherent. The best epi-Si/epi-$CoSi_2$2(A-type)/Si(lll) structure was obtained by deposition of Si film on the CoSii at $500^{\circ}C$ followed by in situ annealing at $700^{\circ}C$ for 10 min in UHV.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.7
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• pp.685-691
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• 2003

This paper newly analyzes the effect of the phase noise in the frequency synthesizer on the performance of SFH/M-NCFSK system by standard frequency deviation(equation omitted) when noncoherent FSK demodulation of the square-law detector is considered. We derive the SER in the SFH system and analyze the effect of phase noise on the SFH/M-NCFSK system performance according to the hopping frequency spacing (1/T$\_$h/) and the variation of the standard frequency deviation (equation omitted). The required SNR is about 13.4 dB to meet Ps=10$\^$-3/ when the standard frequency deviation is about 4.0 Hz and the hopping frequency spacing (1/T$\_$h/) in the SFH/2-NCFSK system is 30. So, there is about 2.4 dB power penalty than the phase noise-free system. If the hopping frequency spacing 1/T$\_$h/ is under 30, the error floor may happen and SER considerably grows up. We show that the analytic results closely match with the simulation results.

• 한국연소학회:학술대회논문집
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• 2003.12a
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• pp.103-108
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• 2003

The effect of equivalence ratio and fuel/air mixing quality on the phase-resolved gas temperatures at different phases of the oscillating pressure cycle was experimentally investigated. An atmospheric pressure, optically accessible and laboratory-scale dump combustor operating on methane with heat release rate of 1.59kW was used. Temperature measurements were made using coherent anti-Stokes Raman spectroscopy (CARS) at several spatial locations for typical unstable combustion conditions. Analysis was conducted using parameters such as phase-resolved averaged temperature, normalized standard deviation and temperature probability distribution functions (PDFs). Also the probability on the occurrence of high temperature (over 1900K) was investigated to get the information on the perturbation of equivalence ratio and NOx emission characteristics. It was shown that most of temperature histograms exhibit Gaussian profile which has short breadth of temperature fluctuation at equivalence ratio of 0.6, while beta profile was predominant for the cases of other equivalence ratios (${\Phi}$=0.55, 0.50). The characteristics on the occurrence of high temperature also displayed periodic wave form which is very similar to the pressure signal. And the amplitude of this profile goes larger as the fuel/air mixing quality become poorer. These also provided additional information on the perturbation of equivalence ratio at flame as well as NOx emission characteristics.