• Proceedings of the Korean Society of Precision Engineering Conference
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• 2010.11a
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• pp.729-730
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• 2010

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.10 no.5
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• pp.125-130
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• 2011

The characteristics of unsteady combustion were experimentally investigated using confined premixed flames stabilized by a rearward-facing step. The unsteady combustion used in this experiment plays an important role in controlling self-excited combustion oscillations and it has usually desirable performance such as high load combustion and low pollutant emission. It is known that combustion oscillation is occurred if Rayleigh's criterion is satisfied. The pressure fluctuation and OH-emission fluctuation were measured using pressure transducer and OH optical fiber respectively and then cross-corelation and phase difference were calculated to apply Rayleigh's criterion.

• Korean Journal of Optics and Photonics
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• v.9 no.4
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• pp.227-230
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• 1998

The Strehl ratio(SR) expressions are derived from the diffration intensity distribution in a Gaussian pupil imaging system, and Marechal criterion is applied for the case of astigmatism aberration first and then to all the rest of the Seidel 1st order aberrations. The aberration criteria obtained are tabulated. In the case of Rayleigh's pupil, the same criteria are always smaller than Gaussian pupil, thus the latter is superior to the former.

• Current Optics and Photonics
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• v.3 no.5
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• pp.466-472
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• 2019

A system for continuous-wave coherent Doppler lidar (CW lidar), made up of all-fiber structures and a coaxial transmission telescope, was set up for wind measurement in Hefei (31.84 N, 117.27 E), Anhui province of China. The lidar uses a fiber laser as a light source at a wavelength of $1.55{\mu}m$, and focuses the laser beam on a location 80 m away from the telescope. Using the CW lidar, radial wind measurement was carried out. Subsequently, the spectra of the atmospheric backscattered signal were analyzed. We tested the noise and obtained the lower limit of wind velocity as 0.721 m/s, through the Rayleigh criterion. According to the number of Doppler peaks in the radial wind spectrum, a classification retrieval algorithm (CRA) combining a Gaussian fitting algorithm and a spectral centroid algorithm is designed to estimate wind velocity. Compared to calibrated pulsed coherent wind lidar, the correlation coefficient for the wind velocity is 0.979, with a standard deviation of 0.103 m/s. The results show that CW lidar offers satisfactory performance and the potential for application in wind measurement.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.4 no.3
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• pp.635-642
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• 2000

We have been derived theoretically the SER's and CLP's of Wireless ATM (WATM) cells employing an OFDM/16QAM modulation scheme in wireless channel modeled as a frequency selective Rayleigh fading channel. The amount of the performance improvement of WATM- OFDM/16QAM systems adopting various coding techniques has been evaluated. In frequency selective Rayleigh fading channel, considering CLP : $10^{-3}$ as a criterion, it is observed that the performance improvement of about 14 dB is obtained in terms of $E_b/N_o$ by employing an OFDM scheme. It is also confirmed that convolutional coding technique gives better performance than the other coding techniques. Especially, when the convolutional codes are adopted to WATM-OFDM/16QAM systems, voice transmission services are sufficiently available with 5 dB of $E_b/N_o$.

• Steel and Composite Structures
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• v.4 no.4
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• pp.281-301
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• 2004

The paper begins by presenting a unified variational approach to the lateral-torsional buckling (LTB) analysis of doubly symmetric prismatic and tapered thin-walled beams with open cross-sections, which accounts for the influence of the pre-buckling deflections. This approach (i) extends the kinematical assumptions usually adopted for prismatic beams, (ii) consistently uses shell membrane theory in general coordinates and (iii) adopts Trefftz's criterion to perform the bifurcation analysis. The proposed formulation is then applied to investigate the influence of the pre-buckling deflections on the LTB behaviour of prismatic and web-tapered I-section simply supported beams and cantilevers. After establishing an interesting analytical result, valid for prismatic members with shear centre loading, several elastic critical moments/loads are presented, discussed and, when possible, also compared with values reported in the literature. These numerical results, which are obtained by means of the Rayleigh-Ritz method, (i) highlight the qualitative differences existing between the LTB behaviours of simply supported beams and cantilevers and (ii) illustrate how the influence of the pre-buckling deflections on LTB is affected by a number of factors, namely ($ii_1$) the minor-to-major inertia ratio, ($ii_2$) the beam length, ($ii_3$) the location of the load point of application and ($ii_4$) the bending moment diagram shape.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.24 no.9A
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• pp.1276-1284
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• 1999

We have evaluated the BER's and CLP's of Wireless ATM (WATM) cells employing the concatenated FEC code with pilot symbols for fading compensation through the simulation in indoor wireless channel modeled as a Rayleigh and a Rician fading channel, respectively. The results of the performance evaluation are compared with those obtained by employing the convolutional code in the same condition. In Rayleigh fading channel, considering the maximum tolerance BER ( $10^-3$) as a criterion of the voice service, it is blown that the performance improvement of about 4 dB is obtained in terms of $E_b/N_o$ by employing the concatenated FEC code with pilot symbols rather than the convolutional code with pilot symbols.When the values of K parameter which means the ratio of the direct signal to scattered signal power in Rician fading channel are 6 and 10, it is shown that the performance improvement of about 4 dB and 2 dB is obtained, respectively, in terms of $E_b/N_o$ by employing the concatenated FEC code with pilot symbols considering the maximum tolerance BER of the voice service. Also in Rician fading channel of K=6 and K= 10, considering CLP = $10^-3$ as a criterion, it is observed that the performance improvement of about 3.5 dB and1.5 dB is obtained, respectively, in terms of $E_b/N_o$ by employing the concatenated FEC code with pilot symbols.

• Korean Journal of Optics and Photonics
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• v.8 no.1
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• pp.1-6
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• 1997

The amplitude impulse S(x) of an interferometric optical imaging system for λ=193 nm(ArF laser) and NA=0.5 is derived for the pupil with superposed three Gauss pupils $A_1$($\omega$), $A_{2-}$($\omega$) and $A_{2+}$($\omega$). It is shown that FWHM of S(x) can be far less than the Rayleigh's criterion of resolution $\frac{1}{2}{\epsilon}_R$, where ${\epsilon}_R$ is equal to λ=193 nm in the present case of NA=0.5. The three Gauss pupils are provided in an optical system which consists of a Twyman-Green interferometer and an imaging system. The system is proposed and relevent optical components are discussed. Siloxane polymer is suggested for fabrications of amplitude modulation plates. In the present work, we assumed the system is free from aberration and linear. The case that the system has residual aberrations is important, and further work is necessary.

• 한국연소학회:학술대회논문집
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• 2001.11a
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• pp.125-135
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• 2001

Aiming at a direct, also more realistic, prediction of unstable waves evolving in the combustion chamber, present paper introduces a new analytical method. Instability equations are freshly formulated, and solve the time-integrated ODEs for amplification factors to find the transients of pressure and velocity fluctuations. Present numerical approach requires no separate treatments for nonlinearities. Preliminary numerical experiments for unstable waves in quasi-one-dimensional rocket combustor, show validity and applicability of present model, and promise for its practical use. Study for the complex models for physics, especially velocity- and pressure-coupled responses, and inclusion of multi dimensionality remains as future tasks.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.43 no.1 s.343
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• pp.95-102
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• 2006

In this paper, we present the performance analysis and design of a multi-path searcher operating over Rayleigh fading channels when multiple transmit antennas are employed in the down-link of W-CDMA system. The simulation results for the receiver operating characteristics (ROC) for 1, 2, and 4 transmit antennas are presented to corroborate the theoretical analyses. We also propose a procedure to find the optimum parameters of double-dwell serial searcher according to the number of the multiple transmit antennas. Our analyses and simulations indicate that post-detection integration is not necessary when the number of transmit antennas is more than two. Finally, we found that increasing transmit diversity order does not necessarily improve the detection performance when the received pilot signal strength is relatively low. Therefore, this gives us a practical criterion on increasing transmit diversity order.