• Journal of the Korean Society of Safety
• /
• v.14 no.3
• /
• pp.84-92
• /
• 1999

The effects of air velocity and excess air on combustion characteristics were studied in a fluidized bed combustor. The domestic low-grade anthracite coal with heating value of 2010 kcal/kg and the imported bituminous coal from Australia with heating value of 6520 kcal/kg were used as coal samples. The combustion characteristics of mixed fuels in a fluidized bed combustor could be interpreted by pressure fluctuation properties, ash distribution and gas emission. The properties of the pressure fluctuations, such as the standard deviation, cross-correlation function, dominant frequency and the power spectral density function, were obtained from the statistical analysis. From this study, the combustion region increased with increasing air velocity but decreased with excess air due to combustion characteristics of anthracite and bituminous coal.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
• /
• v.25 no.1
• /
• pp.1-8
• /
• 2011

In this paper, the method to calculate chromaticity coordinate from spectral power distribution of LED is presented. Also, inverse tri-stimulus algorithm to find mixed luminance of red, green, blue LED from targeted luminance and chromaticity coordinate is proposed. Besides, digital light color control system of LED lamp applied this algorithm has been developed. In experiments, each chromaticity coordinate of red, green, blue LED calculated from this algorithm has relative percentage error of few % to measured values. Digital code is drawn from inverse tri-stimulus algorithm, and measured values of luminance and chromaticity coordinate of LED lamp digitally controlled by this code also have relative percentage error within a few % to targeted luminance and chromaticity coordinate.

• Structural Engineering and Mechanics
• /
• v.3 no.4
• /
• pp.313-324
• /
• 1995

Flexible cantilever pipes conveying fluids with high velocity are analysed for their dynamic response and stability behaviour. The Young's modulus and mass per unit length of the pipe material have a stochastic distribution. The stochastic fields, that model the fluctuations of Young's modulus and mass density are characterized through their respective means, variances and autocorrelation functions or their equivalent power spectral density functions. The stochastic non self-adjoint partial differential equation is solved for the moments of characteristic values, by treating the point fluctuations to be stochastic perturbations. The second-order statistics of vibration frequencies and mode shapes are obtained. The critical flow velocity is first evaluated using the averaged eigenvalue equation. Through the eigenvalue equation, the statistics of vibration frequencies are transformed to yield critical flow velocity statistics. Expressions for the bounds of eigenvalues are obtained, which in turn yield the corresponding bounds for critical flow velocities.

• Journal of Astronomy and Space Sciences
• /
• v.33 no.2
• /
• pp.69-73
• /
• 2016

We use the non-stationary three dimensional two-layer outer gap model to explain gamma-ray emissions from a pulsar magnetosphere. We found out that for some pulsars like the Geminga pulsar, it was hard to explain emissions above a level of around 1 GeV. We then developed the model into a non-stationary model. In this model we assigned a power-law distribution to one or more of the spectral parameters proposed in the previous model and calculated the weighted phase-averaged spectrum. Though this model is suitable for some pulsars, it still cannot explain the high energy emission of the Geminga pulsar. An Inverse-Compton Scattering component between the primary particles and the radio photons in the outer magnetosphere was introduced into the model, and this component produced a sufficient number of GeV photons in the spectrum of the Geminga pulsar.

• The Bulletin of The Korean Astronomical Society
• /
• v.41 no.2
• /
• pp.54.3-55
• /
• 2016

We model the spectral energy distribution (SED) of the Class 0 protostar L1527 IRS using a dust continuum radiative transfer code RADMC-3D to study the initial condition of gravitational collapse. To constrain the envelope structure, we use the data obtained by Herschel /PACS, which covers the far-infrared regime ($55-190{\mu}m$) where the SED of L1527 IRS peaks. According to our modeling, a more flattened density profile fits the far-infrared SED of L1527 IRS better than the density profile of a rotating and infalling envelope. Thus, we employ the density structure of a Bonnor-Ebert sphere, which consists of the inner flat-topped and the outer power-law regions and is often used for describing the density structure of the youngest sources in the low mass star formation process. A Bonnor-Ebert sphere fits very well the observed SED at ${\lambda}$ > $10{\mu}m$, suggesting that L1527 IRS might collapse from an unstable Bonnor-Ebert sphere rather than a singular isothermal sphere.

• 한국정보디스플레이학회:학술대회논문집
• /
• 2008.10a
• /
• pp.509-512
• /
• 2008

In this study, colorimetric characteristics of a 2.2-inch iriver MP4 based upon OLED was evaluated and compared with another MP4 based upon Liquid Crystal Display (LCD). According to IEC61966-4, the two displays were tested in terms of spectral power distribution, tone reproduction curve (TRC), luminance, contrast, correlated color temperature, 2D color gamut and spatial uniformity. Consequently, the OLED showed better performance for the first four aspects but a similar quality was observed for the rest.

• 제어로봇시스템학회:학술대회논문집
• /
• 2000.10a
• /
• pp.303-303
• /
• 2000

It is difficult to determine the static axle weight of a vehicle with weigh-in-motion systems which in absence measure instantaneous axle impact forces. The difficulty in determining a static axle weight results from dynamic effects induced by vehicle/road interactions. One method to improve the problem is to quantify a statistical confidence level for measured axle weight. The quarter-car model is used to simulate vehicle motion, Also, the road input to vehicle model can be characterized in statistical terms by PSD (power spectral density) of appropriate amplitude and frequency contents other than an exact spatial distribution. The confidence levels for the measured axle weight can be obtained by the random process analysis using both vehicle model and road input.

• 유체기계공업학회:학술대회논문집
• /
• 2004.12a
• /
• pp.641-647
• /
• 2004

Characteristics of the high frequency pulsatile flow have been investigated experimentally to understand the flow phenomena in the hydraulic system. The accumulator in high frequency hydraulic system but that is not effective all frequency zone. Therefore, a hydraulic damper used with accumulator is suggested to reduce the high frequency pulsatile where the accumulator is not effective. The pulsating pressure obtained by Pressure measurement system are analyzed to power spectral density distribution. According to the variations of pump input pressure and actuator acceleration frequency, the pressure is measured with or without an accumulator or pulsatile damper The amplitude of pressure with damper is very lower than those without accumulator or damper due to absorbing function of damper. As the frequency of actuator acceleration is increased, the effect of damper becomes very important to decrease the amplitude of pulsatile Pressure waveform with high frequencies.

• Journal of the Optical Society of Korea
• /
• v.20 no.3
• /
• pp.435-440
• /
• 2016

We developed a simple and real-time readout autocorrelator for several tens and sub-10fs pulses, based on the two photon absorption phenomena of a commercial GaP photodetector including a transimpedance amplifier. With a suitable gain adjustment, we demonstrated that the interferometric autocorrelation for sub-nJ pulses delivered as a high output voltage as to resolve all fringes in an autocorrelation trace with features of low noise and a low offset voltage. By fitting the measured quadratic power dependence of output voltages, we obtained the quantum efficiency of TPA for the GaP detector comparable with those of a GaAsP diode and an SHG with a thin BBO crystal. The autocorrelator of a TPA based GaP photodetector is highly suitable for sensitively measuring a few cycle pulses with a broad spectral distribution from 600 nm to 1100 nm.

• Proceedings of the IEEK Conference
• /
• 2000.07a
• /
• pp.113-116
• /
• 2000

Phase noise of oscillator gives the performance degradation significantly when a high carrier frequency and low transmission rate are used. The BER(Bit Error Rates) degradation of QPSK(Quadrature Phase Shift Keying) transmission is analyzed with the oscillator phase noise level specified in downstream physical interface of LMDS(Local Multipoint Distribution Services) which is described in DAVIC(Digital Audio Visual Council). The model used for the phase noise is a power-law model. We also investigated the effects of the various transmission rates on system performance. For the transmission rate below 0.5 Mbps, the BER performance is severely degraded and we verified that the transmission rate, 20 Mbps, is adequate for the downstream of LMDS systems.