• Journal of the Korean Society for Railway
• /
• v.3 no.4
• /
• pp.219-228
• /
• 2000

This paper presents an advanced approach to simulate AC electric railway system in steady-state. The algorithm consists of two parts. One is circuit modeling of elements of electric railway system, the other is an analysis on electric circuit. The modeling procedure has two steps, in the first step, proposed is the modeling method which is considered to be an internal impedance of the autotransformers and mutual impedances between the feeding systems. For the load(locomotives) modeling which is the second step, improved results are obtained as application to the proposed constant power model compared with constant impedance model. In the analysis on electric circuit, a generalized analysis method using the loop equation has been proposed and there is no limit in the number of trains between the ATs. In addition, the computer simulation by the proposed model was practiced. Simulation result seems very reasonable. It is therefore concluded that techniques for the electric circuit modeling and analysis have been established. Accuracy of the techniques will be further investigated.

• Journal of Korean Society of Water and Wastewater
• /
• v.27 no.4
• /
• pp.457-468
• /
• 2013

Based on the activated sludge model(ASM), a mathematical model which represents the aerobic sludge digestion by sequencing batch reactor(SBR) combined with ultrasonic treatment was composed and performed in this study. Aerobic digestion using sequencing batch reactor(SBR) equipped with ultrasound treatment was also experimented for the purpose of parameter calibration. Most of the presented kinetic parameters in ASM or ASM2 could be used for the aerobic digestion of sludge but the parameters related in hydrolysis and decay rate needed modification. Hydrolysis rate constant of organic matter in aerobic condition was estimated at $0.3day^{-1}$ and the maximum growth rate for autotrophs in aerobic condition was $0.618day^{-1}$. Solubilization reactions of particulate organics and nitrogen by ultrasonication was added in this kinetic model. The solubilization rate is considered to be proportional to the specific energy which is defined by specific ultrasound power and sonication time. The solubilization rate constant by ultrasonication was estimated at $0.202(W/L)^{-1}day^{-1}$ in this study. Autotrophs as well as heterotrophs also decomposed by ultrasonic treatment and the nitrification reaction was limited by the lack of autotrophs accumulation in the digester.

• Journal of the Korean Institute of Telematics and Electronics D
• /
• v.36D no.1
• /
• pp.15-21
• /
• 1999

A new design of RF automatic gain control amplifier with low phase shift attenuator is proposed. By using the RF AGC amplifier, the output level of amplifier becomes to be constant. The error is 0.1dB. In addition, for arbitrary RF input power, it is possible to design the gain of amplifier to be fixed. If the constant gain is maintained, it is more reliable to make wanted IMD(Intermodulation Distortion) characteeristic amplifier.

• Publications of The Korean Astronomical Society
• /
• v.13 no.1 s.14
• /
• pp.135-147
• /
• 1998

We have simulated the interaction of supernova remnants with constant ambient medium to explore the dynamics of Type Ia supernova remnant. We assumed the supernova ejecta density distribution of the central constant and the outer power-law density distribution$({\rho}{\propto}{\gamma}^{-n})$. We have calculated four different cases with different n. By scaling the length and time scales from the initial parameters-ejecta mass, ejecta energy, the ambient density, we could compare effects of the different density distribution of the ejecta on the dynamics of the SNRs. The radius of the outer forward shock converges the Sedov-Talyor solution at t' = 2.3 when the swept-up mass is 8 times of the ejecta mass. On the other hand, the motion of the reverse shock are largely affected by n. The ejecta with smaller n takes comparably long time to thermalize the whole ejecta at $t'{\simeq}5.3,\;M_{sw}{\simeq}18M_{ej}$. We have applied our calculated results to obtain the ejecta density distributions of Tycho and SN1006 with $n{\simeq}6$.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2003.11a
• /
• pp.465-472
• /
• 2003

Creep Poisson's ratio reported by previous experimental studies on multiaxial creep of concrete was controversial. The Poisson's ratio is very sensitive to small experimental error that is inevitably induced, and the sensitivity may cause the controversy. It is difficulty to find out the properties on multiaxial creep of concrete. Therefore, a new approach method to analyze the test results is needed to precisely understand the properties on multiaxial creep of concrete. In this study, microplane model is used as a new approach method in analyzing the multiaxial creep test data. The six data sets extracted from the literature are fitted from regression analysis. Double-power law as a model representing volumetric and deviatoric creep evolutions on microplane is used, and six parameters in volumetric and deviatoric compliances are determined on the assumption that the volumetric and deviatoric creep strains are linearly proportional to corresponding stresses. The optimum fits give very accurate description of the test data. The Poisson's ratio calculated from the optimum fits varies with time and does not depends on the stress states, namely, uniaxial, biaxial, and triaxial stress states. Regression analysis is also performed on the assumption that the Poisson's ratio remains constant with titre. The constant Poisson's ratio can be use in practice without serious error.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.4 no.2
• /
• pp.417-426
• /
• 2000

In this paper, CE-CPSK(Constant Envelope Continuous Phase Shift Keying) modulated DS/SS(Direct Sequence Spread Spectrum) transceiver with 908 MHz carrier frequency and 1.5 MHz PN clock rate is proposed. To overcome the effect of nun-linear power amplifier, CE-CPSK modulation method which has the constant envelope and continuous phase characteristics is proposed. To analyze the DS/SS receiver performance with respect to code tracking loop, multipath fading channel is characterized as a two-ray Rayleigh fading channel. To compensate the demerit of analog delay locked loop, digital delay locked loop is employed for code tracking loop. Simulation and experimental examination has been carried out in AWGN(Additive White Gaussian Noise) and Rayleigh fading channel environment in order to prove validity of the proposed method.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2000.05a
• /
• pp.470-473
• /
• 2000

The metal-oxide-semiconductor field-effect transistor(MOSFET) has undergone many changes in the last decade in response to the constant demand for increased speed, decreased power, and increased patting density. The devices are scaled down day by day. Therefore, This paper investigates how MOSFET structures influence on transport properties in according to change of channel length and bias and, observes impact ionization between the drain and the gate. This paper proposes three models, i.e., conventional MOSFET, LDD MOSFET and EPI MOSFET. The gate lengths are 0.3$\mu\textrm{m}$ 0.15$\mu\textrm{m}$, 0.075$\mu\textrm{m}$ and scaling factor is λ = 2. We have presented MOSFET's characteristics such as I-V characteristic, impart ionization, electric field, using the TCAD. We have analyzed the adaptive channel and doping influences

• Journal of Communications and Networks
• /
• v.7 no.4
• /
• pp.450-461
• /
• 2005

In this paper, we derive analytical expressions for the exact pairwise error probability (PEP) of a space-time coded system operating over spatially correlated fast (constant over the duration of a symbol) and slow (constant over the length of a code word) fad­ing channels using a moment-generating function-based approach. We discuss two analytical techniques that can be used to evaluate the exact-PEPs (and therefore, approximate the average bit error probability (BEP)) in closed form. These analytical expressions are more realistic than previously published PEP expressions as they fully account for antenna spacing, antenna geometries (uniform linear array, uniform grid array, uniform circular array, etc.) and scattering models (uniform, Gaussian, Laplacian, Von-mises, etc.). Inclusion of spatial information in these expressions provides valuable insights into the physical factors determining the performance of a space-time code. Using these new PEP expressions, we investigate the effect of antenna spacing, antenna geometries and azimuth power distribution parameters (angle of arrival/departure and angular spread) on the performance of a four-state QPSK space-time trellis code proposed by Tarokh et al. for two transmit antennas.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2008.11a
• /
• pp.148-148
• /
• 2008

Low-k dielectric materials are an alternative plan to improve the signal propagation delay, crosstalk, dynamic power consumption due to resistance and parasitic capacitance generated the decrease of device size. Now, various materials is studied for the next generation. Diethoxymethlysiliane (DEMS) precursor using this study has two ethoxy groups along with one methyl group attached to the silicon atoms. SiCOH thin films were deposited on p-type Si(100) substrate by Plasma Enhanced Chemical Vapor Deposition (PECVD) using DEMS. In this study, we studied the effect of oxygen($O_2$) flow rate for DEMS to characteristics of thin films. The characteristics of thin films deposited using DEMS and $O_2$ evaluated through refractive index, dielectric constant(k), surface roughness, I-V(MIM:Al / SiCOH / Ag), C-V(MIM), deposition rate.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.11 no.5
• /
• pp.772-780
• /
• 1987

The normal and tangential belt forces for two types of flat belts are measured and compared. From friction theory, ti was assumed that tangential friction is proportional to the actual contact area $A_{a}$ and $A_{a}$ is proportional to normal pressure P; i.e., $A_{a}$ .var.P$^{n}$ . For a flat belt with cloth backing, the n=2/3 is obtained for the constant of belt surface model. For a flat belt with rubber backing, the n=0.9 to n=1.0 is suggested as a surface model constant. The theoretical equation developed in this paper showed agood with the experimental results.