• Journal of Institute of Control, Robotics and Systems
• /
• v.16 no.3
• /
• pp.249-255
• /
• 2010

The paper proposes a new type of robust speed control strategy for permanent magnet synchronous motor by using PD-sliding mode hybrid control. The PD control has a good performance in the transient region while the sliding mode controller provides the robustness against system uncertainties. Taking advantages of the two control strategies, the proposed control method utilizes the PD control in the approaching region to the sliding surface and the sliding mode control near at the sliding surfaces. The chattering problem of the sliding mode controller is eliminated by applying the saturation function for the switching function of the sliding mode control. The stability of the sliding mode control is verified by using Lyapunov function with the proper selection of variable gains. It is shown that with this simple switching algorithm, stability of the overall hybrid control system is ensured. Through the simulations, the PD-sliding mode algorithm is shown to have a good performance in the transient response as well as being robust against disturbances. The robustness of the PD-sliding mode algorithm is further demonstrated against various external disturbances in the real experiments of SPMSM motor control.

• Journal of Semiconductor Engineering
• /
• v.3 no.2
• /
• pp.161-167
• /
• 2022

Electrical characteristics of LDMOS power device with LDD(Lightly Doped Drain) structure is studied with variation of the region of channel and LDD. The channel in LDMOSFET encloses a junction-type source and is believed to be an important parameter for determining the circuit operation of CMOS inverter. Two-dimensional TCAD MEDICI simulation is used to study hot-carrier effect, on-resistance Ron, breakdown voltage, and transient switching characteristic. The voltage-transfer characteristics and on-off switching properties are studied as a function of the channel length and doping levels. The digital logic levels of the output and input voltages are analyzed from the transfer curves and circuit operation. Study indicates that drain current significantly depends on the channel length rather than the LDD region, while the switching transient time is almost independent of the channel length. The high and low logic levels of the input voltage showed a strong dependency on the channel length, while the lateral substrate resistance from a latch-up path in the CMOS inverter was comparable to that of a typical CMOS inverter with a guard ring.

• The Bulletin of The Korean Astronomical Society
• /
• v.44 no.2
• /
• pp.60.4-60.4
• /
• 2019

Small bodies in the solar system are pristine leftovers of planetesimals since the formation epoch (~4.6 Gyr ago). After the formation, icy planetesimals have been preserved in the distant cold place beyond 30 au (i.e., Trans-Neptunian region) until recently without any catastrophic processes but have just been injected into inner region (<~5 au from the Sun) to be observed as comets. On the contrary, asteroids are rocky primitive objects (although some of them contains icy volatiles) distributing in the mainbelt between Mars and Jupiter orbits. Because of frequent encounters in the mainbelt, asteroids have experienced a number of repeated impacts until the present day. Namely, it is important to investigate thermal alternation process of cometary volatiles and refractories in the solar radiation field, whereas collisional and subsequence phenomena of asteroidal bodies. Although recent spacecraft observations revealed the physical natures on the surfaces of comets and asteroids, their interiors still remain largely unexplored. It is likely that a sudden brightening of a comet is associated with rapid sublimation of internal CO and CO2 or phase transition of amorphous H2O. An episodic dust ejection from an asteroid is causally related to an impact among asteroids, sudden sublimation of remaining subsurficial volatiles, etc. Because these transient phenomena provide rare opportunities to investigate their interiors, immediate observations using any optical instruments are particular important. In my presentation, I will review some examples of such transient phenomena in the solar system and propose possible collaborative research using the Korean Small Telescope Network.

• Korean Journal of Veterinary Research
• /
• v.39 no.4
• /
• pp.772-777
• /
• 1999

The uncaped genomic RNA of bovine viral diarrhea virus (BVDV) initiates translation by recruitment of eukaryotic translation initiation factors at the internal ribosome entry site (IRES). N-terminal protease ($N^{pro}$) is the first translation product of the open reading frame (ORF). By using the vaccinia virus SP6 RNA polymerase transient expression system, we showed previously that deletion of $N^{pro}$ region reduced translation by 21%. To better understand the biological significance of $N^{pro}$ for translation, we carried out a mutational analysis of the $N^{pro}$ region of BVDV cloned in the intercistronic region of a bicistronic reporter plasmid. We constructed a bicistronic expression vector in which the entire 5 UTR and the mutated $N^{pro}$ region (${\Delta}386-901$, ${\Delta}415-901$ and ${\Delta}657-901$) was cloned between two reporter genes, chloramphenicol acetyltransferase (CAT) and luciferase (LUC). In vivo translation analyses showed that $N^{pro}$ region was dispensible for efficient translation. The results indicate that the $N^{pro}$ region is not essential for BVDV RNA translation and the 3' boundary of BVDV IRES is expanded into $N^{pro}$ region, suggesting that $N^{pro}$ may not play a major role in BVDV replication.

• Journal of the Korean Magnetic Resonance Society
• /
• v.6 no.1
• /
• pp.45-53
• /
• 2002

Objectives: This study investigated alterations in regional cerebral blood flow (rCBF) in patients with transient global amnesia (TGA) using statistical parametric mapping 99 (SPM99). Methods: Noninvasive rCBF measurements using 99mTc-ethyl cysteinate dimer (ECD) SPECT were performed on 8 patients with TGA who have ongoing symptoms and 17 age matched controls. The relative rCBF maps in patients with TGA and controls were compared. Results: In patients with TGA, significant decreased rCBF was found along the L superior temporal extending to L parietal region of the brain and L thalamus. There were areas of increased rCBF in the R temporal, R frontal region and R thalamus. Conclusion: We could demonstrate decreased perfusion in left cerebral hemisphere and increased perfusion in right cerebral hemisphere in patients with TGA using SPM99. The imbalanced change of rCBF between bilateral cerebral hemisphere in patients with TGA might suggest that imbalanced neuronal activity between the bilateral hemispheres may have strong relationship to the pathogenesis of the TGA. For quantitative SPECT analysis in TGA patients, we recommend SPM99 rather than the ROI method because of its definitive advantages.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.12 no.5
• /
• pp.19-24
• /
• 2004

Entrainment of ambient gas into a transient diesel spray is a crucial factor affecting the following preparation of combustible mixture. In this study, the entrainment characteristics of ambient gas for a non-evaporating transient diesel were investigated using a common-rail injection system. The effects of ambient gas density and nozzle hole geometry were assessed with entrainment coefficient. Laser Doppler Velocimetry (LDV) technique was introduced to measure the entrainment speed of ambient gas into a spray. There appeared a region where the entrainment coefficients remained almost constant while injection rates were still changing. The effect of common-rail pressure, which altered the slope of injection rate curve, was hardly noticed at this region. Entrainment coefficient increased with ambient gas density, that is, the effect of ambient gas density was greater than that of turbulent jet whose entrainment coefficient remained constant. The non-dimensional distance was defined to reflect the effect of nozzle hole diameter and ambient gas density together. The mean value of entrainment coefficient was found to increase with non-dimensional distance from the nozzle tip, which would be suggested as the guideline for the nozzle design.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.27 no.11
• /
• pp.1618-1629
• /
• 2003

The effects of the interaction between flow field and heat transfer caused by the longitudinal vortices are experimentally investigated using a five hole probe and a transient liquid crystal technique. The test facility consists of a wind tunnel with vortex generators protruding from a bottom surface and a mesh heater. In order to control the strength of the longitudinal vortices, the angle of attack of vortex generators used in the present experiment is 20$^{\circ}$, and the spacing between the vortex generators is 25mm. The height and cord length of the vortex generator is 20mm and 50mm, respectively. Three-component mean velocity measurements are made using a f-hole probe system, and the surface temperature distribution is measured by the hue capturing method using a transient liquid crystal technique. The transient liquid crystal technique in measuring heat transfer has become one of the most effective ways in determining the full surface distributions of heat transfer coefficients. The key point of this technique is to convert the inlet flow temperature into an exponential temperature profile using the mesh heater set up in the wind tunnel. The conclusions obtained in the present experiment are as follows: The two maximum heat transfer values exist over the whole domain, and as the longitudinal vortices move to the farther downstream region, these peak values show the decreasing trends. These trends are also observed in the experimental results of other researchers to have used the uniform heat flux method.

• Journal of Advanced Marine Engineering and Technology
• /
• v.10 no.2
• /
• pp.156-164
• /
• 1986

In the case of boiling on high temperature wall, vapor film covers fully or parcially the surface. This phenomenon, film boiling or transition boiling, is very important in the surface heat treatment of metal, design of cryogenic heat exchanger and emergency cooling of nuclear reactor. Mainly supposed hydraulic-thermal accidents in nuclear reactor are LCCA (Loss of Coolant Accident) and PCM (Power-Cooling Mismatch). Recently, world-wide studies on reflooding of high temperature rod bundles after the occurrence of the above accidents focus attention on wall temperature history and required time in transient cooling process, wall superheat at rewet point, heat flux-wall superheat relationship beyond the transition boiling region, and two-phase flow state near the surface. It is considered that the further systematical study in this field will be in need in spite of the previous results in ref. (2), (3), (4). The paper is the study about the fast transient cooling process following the wall temperature excursion under the CHF (Critical Heat Flux) condition in a forced convective subcooled boiling system. The test section is a vertically arranged concentric annulus of 800 mm long and 10 mm hydraulic diameter. The inner tube, SUS 304 of 400 mm long, 8 mm I.D, and 7 mm O.D., is heated uniformly by the low voltage AC power. The wall temperature measurements were performed at the axial distance from the inlet of the heating tube, z=390 mm. 6 chromel- alumel thermocouples of 76 .mu.m were press fitted to the inner surface of the heating tube periphery. To investigate the heat transfer characteristics during the fast transient cooling process, the outer surface (fluid side) temperature and the surface heat flux are computed from the measured inner surface temperature history by means of a numerical method for inverse problems of transient heat conduction. Present cooling (boiling) curve is sufficiently compared with the previous results.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2001.07a
• /
• pp.844-847
• /
• 2001

In this work, transient characteristics of the Non-Punch Through(NPT) Insulated Gate Bipolar Transistor(IGBT) has been studied. we has analyzed with lifetimes excess minority carrier injected into N-dirft, base region of IGBT's BJT part and accumulated charge of on-state which affected swiching characteristic. In this paper, excess minority carrier and charge distribution in active base region is expressed analytically. This analysis proposed optical trade-off between lifetimes and accumulated charge for decreasing switching losses because charge result in switching loss when device was tuned off.

• Proceedings of the International Microelectronics And Packaging Society Conference
• /
• 2003.11a
• /
• pp.118-121
• /
• 2003

The electrochemical behaviors of UBM nickel were investigated. Electrode potential has been changed with the surface composition. Zinc is dissolved into the solution immediately after immersion. Electrode potential has three distinct regions: Zinc dissolution region, transient region and nickel plating region. The effects additives on electrode potential and polarization curves were also investigated. The addition of suppressor lowered the current density which is related with deposition rate.