• International Journal of Aeronautical and Space Sciences
• /
• v.16 no.3
• /
• pp.339-346
• /
• 2015

Aerodynamic flow control phenomena were investigated with a low-current DC surface discharge plasma actuator. The plasma actuator was found to operate in three different discharge modes with similar discharge currents of about 1 mA or less. Stable continuous DC discharge without audible noise was obtained at higher ballast resistances and lower discharge currents. However, even with continuous DC power input, a low-frequency self-pulsed discharge was obtained at lower ballast resistances, and a high-frequency self-pulsed discharge was obtained at higher set-point currents and higher ballast resistances, both with audible noise. The Schlieren image reveals that the low-frequency self-pulsed mode produces a synthetic jet-like flow implying that a gas heating effect plays a role, even though the discharge current is small. The high-frequency self-pulsed mode produces pulsed jets in a tangent direction, and the continuous DC mode produces a steady straight pressure wave. Particle image velocimetry (PIV) images reveal that the induced flow field by the low-frequency self-pulsed mode has flow propagating in the radial direction and centered between the electrodes. The high-frequency self-pulsed mode and continuous DC mode produce flow from the anode to the cathode. The perturbed region downstream of the cathode is larger in the high-frequency self-pulsed mode with similar maximum speeds.

• Journal of the Korean Applied Science and Technology
• /
• v.19 no.4
• /
• pp.339-348
• /
• 2002

Self-diffusion coefficients of colloidal ass9Ciation structures in the aqueous solutions of anionic ammonium dodecyl sulfate (ADS) and cationic octadecyltrimethylammonium chloride (OTAC) surfactants were measured by pulsed-gradient spin echo NMR. The results were interpreted on the basis of the ADS/OTAC/water phase diagram. Crossing the phase boundaries, significant changes in self diffusion coefficients were observed and well correlated to the phase diagram. For the micelles their apparent radii were obtained from Stokes-Einstein equation. Their values were 15 for the ADS micelles and 54 ${{\AA}}$ for the OTAC micelles, respectively. For vesicles which were formed spontaneously at different relative amounts of the surfactants and total surfactant concentrations, the radius was measured as 50 to 200 nm. This result is in fair agreement with those by TEM and light scattering.

• Journal of Communications and Networks
• /
• v.15 no.3
• /
• pp.276-282
• /
• 2013

Self-encoded spread spectrum (SESS) is a novel modulation technique that acquires its spreading code from a random information source, rather than using the traditional pseudo-random noise (PN) codes. In this paper, we present our study of the SESS system performance under pulsed-noise jamming and show that iterative detection can significantly improve the bit error rate (BER) performance. The jamming performance of the SESS with correlation detection is verified to be similar to that of the conventional direct sequence spread spectrum (DSSS) system. On the other hand, the time diversity detection of the SESS can completely mitigate the effect of jamming by exploiting the inherent temporal diversity of the SESS system. Furthermore, iterative detection with multiple iterations can not only eliminate the jamming completely but also achieve a gain of approximately 1 dB at $10^{-3}$ BER as compared with the binary phase shift keying (BPSK) system under additive white gaussian noise (AWGN) by effectively combining the correlation and time diversity detections.

• 제어로봇시스템학회:학술대회논문집
• /
• 2005.06a
• /
• pp.352-355
• /
• 2005

This paper describes an engineering model development of a pulsed plasma thruster, which is capable of an impulse bit of 20uNs and a specific impulse of 800s. The solid fuel which is Teflon allows for a self-contained, inert and stable propellant system. And, the PPT technology makes it possible to consider a revolutionary attitude control system (ACS) concept providing stabilization and pointing accuracies previously obtainable only with reaction wheels, with reduced mass and power requirements.

• Journal of the Korean Ceramic Society
• /
• v.56 no.1
• /
• pp.1-23
• /
• 2019

Dielectric materials with inherently high power densities and fast discharge rates are particularly suitable for pulsed power capacitors. The ongoing multifaceted efforts on developing these capacitors are focused on improving their energy density and storage efficiency, as well as ensuring their reliable operation over long periods, including under harsh environments. This review article summarizes the studies that have been conducted to date on the development of high-performance dielectric ceramics for employment in pulsed power capacitors. The energy storage characteristics of various lead-based and lead-free ceramics belonging to linear and nonlinear dielectrics are discussed. Various strategies such as mechanical confinement, self-confinement, core-shell structuring, glass incorporation, chemical modifications, and special sintering routes have been adopted to tailor the electrical properties and energy storage performances of dielectric ceramics. In addition, this review article highlights the challenges and opportunities associated with the development of pulsed power capacitors.

• Macromolecular Research
• /
• v.11 no.6
• /
• pp.444-450
• /
• 2003

Hydrophobically End-capped polyethylene oxide Urethane Resin(HEUR)-associating polymers, HEUR 35(8), HEUR 35(12), and HEUR 35(18), comprise a polyethylene oxide (PEO) having a molecular weight of 35,000 that is end capped with two C$\_$8/H$\_$17/, C$\_$12/H$\_$25/, and C$\_$18/H$\_$37/ alkyl chains, respectively. These associating polymers were synthesized by condensation reactions with polyethylene oxides and alkyl isocyanates. The self-diffusion coefficients of HEUR-associating polymers were measured in aqueous solution by pulsed-gradient spin-echo (PGSE) nuclear magnetic resonance (NMR) spectroscopy. All polymers underwent a decrease in their mean diffusion coefficients as the concentration was increased. However, the dispersion of the diffusion coefficients, ${\beta}$, about the mean fluctuated with changes in concentration. The large dispersion at low concentrations of HEUR 35(8) and HEUR 35(12) is related to the interaction between hydrophobic end groups, and the large dispersion at high concentrations of HEUR 35(18) is correlated with transient network formation. These results are valuable for predicting the associating mechanism of the large aggregates before and after their critical micelle concentration.

• Proceedings of the KIEE Conference
• /
• 2009.07a
• /
• pp.1025_1026
• /
• 2009

This paper introduces the test a rapid pulsed power charging system for pulsed power application. The charger is designed based on three-phase series resonant inverter followed by air cooled step-up transformers. It has many advantages of lower weight, small size and high efficiency compared with large bulky traditional pulse power charging system. To apply 150kJ pulsed power system, detail test was carried out at various condition and its results shows 90% efficiency at full load condition. And additional experiments such as short, open, and self discharging during charging status are performed to verify reliable operation at abnormal condition and it was confirmed that developed capacitor charger showed very reliable operation all over the tests.

• The Journal of The Korea Institute of Intelligent Transport Systems
• /
• v.10 no.1
• /
• pp.42-48
• /
• 2011

In this paper, a passive load-pull using a GaN HEMT (Gallium Nitride High Electron Mobility Transistor) bare-chip in X-band is presented. To obtain operation conditions that characteristic change by self-heating was minimized, pulsed drain bias voltage and pulsed-RF signal is employed. An accuracy impedance matching circuits considered parasitic components such as wire-bonding effect at the boundary of the drain is accomplished through the use of a electro-magnetic simulation and a circuit simulation. The microstrip line length-tunable matching circuit is employed to adjust the impedance. The measured maximum output power and drain efficiency of the pulsed load-pull are 42.46 dBm and 58.7%, respectively, across the 8.5-9.2 GHz band.

• Proceedings of the Optical Society of Korea Conference
• /
• 2003.07a
• /
• pp.44-45
• /
• 2003

전자기 유도 투과란 매질 속을 진행하는 빛의 투과가 다른 강한 빛의 작용으로 증가하게 되는 결맞음 현상을 말한다. 이러한 전자기 유도 투과는 또한 굴절율의 변화를 동반하게 되며, 그 결과 매질을 진행해 나가는 레이저빔은 유도 집속 및 확산, 또는 자체집속 및 확산의 제거 등을 겪게 된다. 이러한 원리를 이용하여 M. Jain 등은 납 증기에서 원공명 조건의 결맞음 밀도 포획을 이용한 자체집속의 제거에 성공한바 있다. (중략)

• Proceedings of the Korean Magnetic Resonance Society Conference
• /
• 2002.01a
• /
• pp.13-13
• /
• 2002