• Journal of The Korean Astronomical Society
• /
• v.50 no.6
• /
• pp.157-165
• /
• 2017

$H_2O$ maser emission at 22 GHz in the circumstellar envelope is one of the good tracers of detailed physics and kinematics in the mass loss process of asymptotic giant branch stars. Long-term monitoring of an $H_2O$ maser spectrum with high time resolution enables us to clarify acceleration processes of the expanding shell in the stellar atmosphere. We monitored the $H_2O$ maser emission of the semi-regular variable R Crt with the Kagoshima 6-m telescope, and obtained a large data set of over 180 maser spectra over a period of 1.3 years with an observational span of a few days. Using an automatic peak detection method based on least-squares fitting, we exhaustively detected peaks as significant velocity components with the radial velocity on a $0.1kms^{-1}$ scale. This analysis result shows that the radial velocity of red-shifted and blue-shifted components exhibits a change between acceleration and deceleration on the time scale of a few hundred days. These velocity variations are likely to correlate with intensity variations, in particular during flaring state of $H_2O$ masers. It seems reasonable to consider that the velocity variation of the maser source is caused by shock propagation in the envelope due to stellar pulsation. However, it is difficult to explain the relationship between the velocity variation and the intensity variation only from shock propagation effects. We found that a time delay of the integrated maser intensity with respect to the optical light curve is about 150 days.

• ETRI Journal
• /
• v.34 no.6
• /
• pp.858-868
• /
• 2012

In this paper, stochastic models for the cross-correlation of multiple channels are established based on measurement data collected using a wideband multiple-input multiple-output relay Band Exploration and Channel Sounder system at 3.7 GHz. We propose models for the cross-correlation characteristics of large-scale parameters (LSPs) between two links, that is, the base station and mobile station (MS) link and the relay station and MS link. The LSPs include shadow fading, Rician K-factor, delay spread, angle spread of arrival, and angle spread of departure. Furthermore, models are established for the cross-correlation of the small-scale fading in the impulse responses of two links. The statistics of these model parameters are investigated as functions of geometrical features of the multilink. They are extracted from a large amount of cross-correlation observations, which are obtained in three measurement sites along more than one hundred measurement routes. These models can be used together with the standard single-link channel models for the generation of correlated components, for example, path clusters, in two separate channels.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.44 no.11
• /
• pp.11-18
• /
• 2007

FFT(Fast Fourier Transform) processor is one of the key components in the implementation of OFDM systems such as WiBro, DAB and UWB systems. Most of the researches on the implementation of FFT processors have focused on reducing the complexities of multipliers, memory and control circuits. In this paper, to reduce the memory size required for IFFT(Inverse Fast Fourier Transform), we propose a new IFFT design method based on a mapping method. By simulations, it is shown that the reposed IFFT design method achieves more than 60% area reduction and much SQNR(Signal-to-Quantization-Noise Ratio) gain compared with previous IFFT circuits.

• Journal of Positioning, Navigation, and Timing
• /
• v.4 no.2
• /
• pp.73-77
• /
• 2015

Global Positioning System (GPS) Precise Point Positioning (PPP) has been extensively used for geodetic applications. Since December 2012, BeiDou navigation satellite system has provided regional positioning, navigation and timing (PNT) services over the Asia-Pacific region. Recently, many studies on BeiDou system have been conducted, particularly in the area of precise orbit determination and precise positioning. In this paper PPP method based on BeiDou observations are presented. GPS and BeiDou data obtained from Mokpo (MKPO) station are processed using the Korea Astronomy and Space Science Institute Global Navigation Satellite System (GNSS) PPP software. The positions are derived from the GPS PPP, BeiDou B₁/B₂ PPP and BeiDou B₁/B₃ PPP, respectively. The position errors on BeiDou PPP show a mean bias < 2 cm in the east and north components and approximately 3 cm in the vertical component. It indicates that BeiDou PPP is ready for the precise positioning applications in the Asia-Pacific region. In addition, BeiDou tropospheric zenith total delay (ZTD) is compared to GPS ZTD at MKPO station. The mean value of their difference is approximately 0.52 cm.

• 전자공학회논문지 IE
• /
• v.44 no.2
• /
• pp.14-20
• /
• 2007

This paper presents quaternary D flip-flop with advanced performance. Quaternary D flip-flop is composed of the components such as thermometer code output circuit, EX-OR gate, bias inverter, transmission gate and binary D flip-flop circuit. The designed circuit is simulated by HSPICE in $0.35{\mu}m$ one-poly six-metal CMOS process parameters with a single +3.3V supply voltage. In the simulations, sampling frequencies is measured around 100MHz. The PDP parameters and FOM we estimated to be 59.3fJ, 33.7 respectively.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.11 no.6
• /
• pp.155-163
• /
• 2003

As vehicles become more intelligent for convenience and safety of drivers, the in-vehicle networking(IVN) systems and smart modules are essential components for intelligent vehicles. However, for wider application of smart modules and IVN's, the following two problems should be overcome. Firstly, because it is very difficult that transducer manufacturers developed the smart module that supports all the existing IVN protocols, the smart module must be independent of the type of networking protocols. Secondly, when the smart module needs to be replaced due to its failure, only the transducer should be replaced these without the replacement of the microprocessor and network transceiver. To solve these problems, this paper investigates the feasibility of an IEEE 1451 based smart module. More specifically, a smart module for DC motor control has been developed. The module has been evaluated for its delay caused by the IEEE 1451 architecture. In addition, the time required for transducer replacement has been measured.

• IE interfaces
• /
• v.23 no.3
• /
• pp.246-256
• /
• 2010

As wireless and mobile technologies have advanced significantly, lots of large sized healthcare organizations have implemented so called mobile hospital (m-Hospital) which provides a location independent and point of care (POC) clinical environment. Implementation of m-Hospital enhances quality of care because health professionals such as physicians and nurses can use hospital information systems at the very place where patients are located without any delay. This paper presents a real-time patient monitoring system based on wireless network technologies. A general framework for the patient monitoring process is introduced and the architecture and components of the proposed monitoring system is described. The system collects and analyzes biometric signals of in-patients who suffer from cancer. Specifically, it continuously monitors oxygen saturation of patients in bed and alarms health professionals instantly when an abnormal status of the patient is detected. The monitoring system has been used and clinically verified in a university hospital.

• Proceedings of the KIEE Conference
• /
• 2008.11a
• /
• pp.12-15
• /
• 2008

A distance relay has been widely used for transmission line protection. The distance relay detects a fault based on the calculated impedance i.e. the ratio of the voltage to the current measured from a current transformer (CT) and a coupling capacitor voltage transformer (CCVT), respectively. When a fault occurs and a CT saturates due to the magnitude of fault current, dc component, primary time constant, and the remanent flux of the iron core, the secondary current of a CT is distorted On the other hand, non-fundamental components generated during a fault can increase the error of a CCVT, particularly when a fault distance is short. The distortion of the current and voltage can cause mal-operation or the operating time delay of a distance relay. This paper describes the response of a distance relay considering the errors of a CT and a CCVT. The results indicate that the severe distortion of a CT and a CCVT have noticeable effect to a distance relay.

• Journal of the Korea Computer Industry Society
• /
• v.2 no.12
• /
• pp.1533-1540
• /
• 2001

In this paper, we described extraction method of electrical parameters and modeling method of PCB nets on PCB design process. To analyze electrical characteristics of real PCB structure, we selected a cache memory system as an experimental board and designed 6 layer PCB substrate. For extraction of the electrical parameters, we divided circuit elements into the components of conductor types which are wires, via holes, BGA balls etc. and combined the calculated value by real net structure to modeling the PCB nets. We analyzed the electrical characteristics of the PCB nets with the simulation tools of SPICE and XNS. The simulation analysis has shown that the maximum signal delay was 2.6ns and the maximum crosstalk noise was 281 mV and we found that the designed substrate was adequate to system specification.

• Journal of the Korea Institute of Military Science and Technology
• /
• v.19 no.4
• /
• pp.517-525
• /
• 2016

In this research, the effect of the pressure control of cooperative control system with regenerative brake for a military series hybrid-electric vehicle was studied. A cooperative control system with regenerative brake was developed to maximize regenerative energy from electric traction motors of the vehicle. However, the pressure control method of the system was modified to solve a time delay problem and it deteriorates the performance of the system. A Simulink model including the hybrid-electric components, the cooperative control system with regenerative brake, and the vehicle dynamics was developed and used to find a solution. The regenerative energy ratio with respect to the whole brake energy was increased in this research from less than 60 % to over 80 %.