• Journal of Power Electronics
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• 제11권5호
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• pp.719-725
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• 2011

This paper describes a novel Direct Torque Control (DTC) method for adjustable speed Doubly-Fed Induction Machine (DFIM) drives which is supplied by a two-level Space Vector Modulation (SVM) voltage source inverter (DTC-SVM) in the rotor circuit. The inverter reference voltage vector is obtained by using input-output feedback linearization control and a DFIM model in the stator a-b axes reference frame with stator currents and rotor fluxes as state variables. Moreover, to make this nonlinear controller stable and robust to most varying electrical parameter uncertainties, a two layer recurrent Artificial Neural Network (ANN) is used to estimate a certain function which shows the machine lumped uncertainty. The overall system stability is proved by the Lyapunov theorem. It is shown that the torque and flux tracking errors as well as the updated weights of the ANN are uniformly ultimately bounded. Finally, effectiveness of the proposed control approach is shown by computer simulation results.

• Journal of Electrical Engineering and Technology
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• 제13권3호
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• pp.1185-1201
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• 2018

This paper presents a sensorless direct torque control (DTC) combined with sliding mode approach (SM) and space vector modulation (SVM) to achieve mainly a high performance and reduce torque and flux ripples of a parallel-connected two five-phase permanent magnet synchronous machine (PMSM) drive system. In order to increase the proposed drive robustness and decrease its complexity and cost, the rotor speeds, rotor positions, fluxes as well as torques are estimated by using a sliding mode observer (SMO) scheme. The effectiveness of the proposed sliding mode observer in conjunction with the sliding mode control based DTC is confirmed through the application of different load torques for wide speed range operation. Comparison between sliding mode control and proportional integral (PI) control based DTC of the proposed two-motor drive is provided. The obtained speeds, torques and fluxes responses follow their references; even in low and reverse speed operations, load torques changes, and machines parameters variations. Simulation results confirm also that, the ripples of the torques and fluxes are reduced more than 3.33% and 16.66 %, respectively, and the speed overshoots and speed drops are reduced about 99.85% and 92.24%, respectively.

• 생명과학회지
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• 제21권3호
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• pp.451-458
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• 2011

Cordycepin은 동충하초로부터 분리한 생리활성 물질로써 항암활성을 가진다고 보고되어 있다. 하지만 그 정확한 항암 기전은 아직 확실하게 밝혀져 있지 않다. 이에 인간 전립선 암 세포주인 PC-3 세포를 이용하여 apoptosis와 그에 관련한 경로를 조사함으로써 cordycepin의 항암효과를 연구하였다. MTT assay를 통해 세포독성을 알아보았고 Annexin-V/PI 염색과 $Ca^{2+}$ 농도, ROS의 생성, MMP의 변화를 관찰하여 apoptosis 경로를 확인하였다. 뿐만 아니라 Western blot analysis를 이용하여 apoptosis와 관련된 단백질의 발현 정도를 확인하였다. 본 연구의 결과에서 cordycepin은 apoptosis 관련 단백질의 발현을 조절함으로써 apoptosis와 관련이 있음을 확인할 수 있었고, 미토콘드리아 관련 apoptosis 경로를 확인한 결과, ROS의 생성, $Ca^{2+}$의 증가 그리고 미토콘드리아 막 전위의 붕괴를 통해 apoptosis 기전이 유도됨을 알 수 있었다. 이상의 결과로부터 cordycepin은 PC-3 세포에 대하여 ROS와 $Ca^{2+}$의 농도 증가를 통해 MMP를 변화시켜 미토콘드리아 관련 apoptosis 기전을 거쳐 caspase의 활성을 증가시킴으로써 apoptosis를 유도함을 알 수 있었다.

• Journal of international Conference on Electrical Machines and Systems
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• 제3권1호
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• pp.78-82
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• 2014

Power Transformers with more than one secondary winding are not uncommon in industrial applications. But new classes of applications where very large number of independent secondaries are used are becoming popular in controlled converters for medium and high voltage applications. Cascade H-bridge medium voltage drives and Pulse Step Modulation (PSM) based high voltage power supplies are such applications. Regulated high voltage power supplies (Fig. 1) with 35-100 kV, 5-10 MW output range with very fast dynamics (${\mu}S$ order) uses such transformers. Such power supplies are widely used in fusion research. Here series connection of isolated voltage sources with conventional switching semiconductor devices is achieved by large number of separate transformers or by single unit of multi-secondary transformer. Naturally, a transformer having numbers of secondary windings (~40) on single core is the preferred solution due to space and cost considerations. For design and simulation analysis of such a power supply, the model of a multi-secondary transformer poses special problem to any circuit analysis software as many simulation softwares provide transformer models with limited number (3-6) of secondary windings. Multi-Secondary transformer models with 3 different schemes are available. A comparison of test results from a practical Multi-secondary transformer with a simulation model using magnetic component is found to describe the behavior closer to observed test results. Earlier models assumed magnetising inductance in a linear loss less core model although in actual it is saturable core made-up of CRGO steel laminations. This article discusses a more detailed representation of flux coupled magnetic model with saturable core properties to simulate actual transformers very close to its observed parameters in test and actual usage.

• 한국응용약물학회:학술대회논문집
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• 한국응용약물학회 2001년도 추계학술대회 및 정기총회
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• pp.102-102
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• 2001

Taurine (2-ethaneaminosulfonic acid) is one of the major intracellular ${\beta}$ -amino acids in mammals and is required for a number of biological processes including membrane stabilization, osmoregulation, antioxidation, detoxification, modulation of calcium flux and neurornodulation. The taurine transporter (TAUT) which contains 12 hydrophobic membrane-spanning domains has been cloned from dog kidney, rat brain, mouse brain, human thyroid, placenta and retina. In this study, The TAUT cDNA from the human intestinal epithelial cell, HT-29 was cloned and sequenced. Reverse-transcription polymerase chain reaction (RT-PCR) was performed to amplify partial cDNA encoding human intestinal TAUT. The coding region of the PCR product was 732 bp long. The primers were designed to encode highly conserved amino acid sequences near the transmembrane domains III (IPYFIFLF) and Ⅵ (KYKYNSYR) both in human and mouse. The TAUT cDNA amplified was ligated into the pGEX 4T-1 expression vector. The resulting sequence of human intestinal TAUT cDNA (Accession number of NCBI Genebank is AF346763) was identical to the sequences of the TAUTs previously determined in the human placenta and retina except 3 base pairs from that of the reported human thyroid. TAUT specific antibodies were generated to use them as biological tools in the studies of the biological role of TAUT. Peptides of 149-162 amino acid residue (14 amino acids) of the TAUT were synthesized. The synthetic peptide used in this study was LFQSFQKELPWAHC. This region was chosen not only to avoid putative glycosylation sites but also to exclude regions of known homology with GABA transporters in the extracellular hydrophilic domains. The synthetic peptide, TAUT-1 was conjugated with carrier protein, kehole lympet hemocyanin (KLH) to use as an antigen. When used for immunization on a rabbit to produce polyclonal antiserum, the conjugates elicited high -titered specific anti-TAUT-1 antibodies, which reacted well with the ovalbumin (OVA) conjugated peptides in ELISA. The KLH-conjugated peptide was also used as immunizing antigen in BALB/c mice to produce TAUT specific monoclonal antibodies. From the culture supernatant of the hybridoma, the specificity of anti-TAUT-1 monoclonal antibodies was confirmed by ELISA. Further applications of more tools in TAUT expression analysis will be performed such as western blotting and flow cytometry.

• 천문학회지
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• 제36권3호
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• pp.81-87
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• 2003

It is suggested that a flying-by star in a hot accretion disk may cool the hot accretion disk by the Comptonization of the stellar emission. Such a stellar cooling can be observed in the radio frequency regime since synchrotron luminosity depends strongly on the electron temperature of the accretion flow. If a bright star orbiting around the supermassive black hole cools the hot disk, one should expect a quasi-periodic modulation in radio, or even possible an anti-correlation of luminosities in radio and X-rays. Recently, the unprecedentedly accurate infrared imaging of the Sagittarius A$\ast$ for about ten years enables us to resolve stars around it and thus determine orbital parameters of the currently closest star S2. We explore the possibility of using such kind of observation to distinguish two quite different physical models for the central engine of the Sagittarius A$\ast$, that is, a hot accretion disk model and a jet model. We have attempted to estimate the observables using the observed parameters of the star S2. The relative difference in the electron temperature is a few parts of a thousand at the epoch when the star S2 is near at the pericenter. The relative radio luminosity difference with and without the stellar cooling is also small of order $10^{-4}$, particularly even when the star S2 is near at the pericenter. On the basis of our findings we tentatively conclude that even the currently closest pass of the star S2 is insufficiently close enough to meaningfully constrain the nature of the Sagittarius A$\ast$ and distinguish two competing models. This implies that even though Bower et al. (2002)have found no periodic radio flux variations in their data set from 1981 to 1998, which is naturally expected from the presence of a hot disk, a hot disk model cannot be conclusively ruled out. This is simply because the energy bands they have studied are too high to observe the effect of the star S2 even if it indeed interacts with the hot disk. In other words, even if there is a hot accretion disk the star like S2 has imprints in the frequency range at v $\le$ 100 MHz.

• Nuclear Engineering and Technology
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• 제53권6호
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• pp.1942-1946
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• 2021

Gadolinium oxysulfide (GOS) is regarded as a novel scintillator for the realization of ultra-high spatial resolution in neutron imaging. Monte Carlo simulations of GOS scintillator show that the capability of its spatial resolution is towards the micron level. Through the time-of-flight method, the light output of a GOS scintillator was measured to be 217 photons per captured neutron, ~100 times lower than that of a ZnS/LiF:Ag scintillator. A detector prototype has been developed to evaluate the imaging solution with the GOS scintillator by neutron beam tests. The measured spatial resolution is ~36 ㎛ (28 line pairs/mm) at the modulation transfer function (MTF) of 10%, mainly limited by the low experimental collimation ratio of the beamline. The weak light output of the GOS scintillator requires an enormous increase in the neutron flux to reduce the exposure time for practical applications.