• Journal of Power Electronics
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• v.8 no.3
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• pp.248-258
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• 2008

The Voltage Source Converter (VSC) is replacing the conventional line commutated current source converters in High Voltage DC (HVDC) transmission systems. The control of a two-level voltage source converter and its design dealt with HVDC systems and various factors such as reactive power, power factor, and harmonics distortion are discussed in detail. Simulation results are given for the two-level converter and designed control is used for bidirectional power flow. The harmonics minimization is taken by extending the 6-pulse VSC to multipulse voltage source converters. The control is also tested and simulated for a 12-pulse voltage source converter to minimize the harmonic distortion in AC currents.

• Korean Journal of Cognitive Science
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• v.4 no.2
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• pp.115-143
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• 1994

In this paper,I present an extended two-level model using LR parsing techniques.The LR-based two-level model not only guarantees effcient morphological processing but also achieves a higher degree of descriptive adequacy than Koskenniemi's original model.The two-level model is augmented with an independent morphosyntactic module based on feature-based CF word grammar.By adopting a CF word grammar,our model is capable of dealing with complex words with discontinuous dependencies without having duplicate lexicons.It is shown how LR predictions manifested in the parsing table can help the morphological processor to minimize the dictionary lookup process.

• Korean Journal of Optics and Photonics
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• v.14 no.1
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• pp.103-106
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• 2003

The microscopic quantum Langevin equations for two-level atom electric dipole systems are derived. starting from the microscopic interaction Hamiltonian of the systems. By averaging those microscopic equations over a macroscopic region, the macroscopic quantum Langevin equations are derived and the effect of local-field corrections on the two-level systems is investigated.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.191.1-191.1
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• 2014

Crystallization has become the most popular technique for the separation of enantiomers since the Pasteur's discovery. To investigate mechanism of crystallization of chiral molecules, it is necessary to study self-assembled structures on two-dimensional surface. Here, we have studied two-dimensional self-assembled structures of an unnatural amino acid, (S)-${\beta}$-methyl naphthalen-1-${\gamma}$-aminobutyric acid (${\gamma}^2$-1-naphthylalanine) on Au(111) surface at 150 K using scanning tunneling microscopy (STM). At initial stage, we found two chiral honeycomb structures which are counter-clockwise and clockwise configurations in one domain. The molecules are arranged around molecular vacancies, dark hole. By further increasing the amounts of adsorbed ${\gamma}^2$-1-naphthylalanine, a well-ordered square packed structure was observed. In addition, we found the other structure that molecules were trapped in the pore of the hexagonal molecular assembly.

• Annual Conference on Human and Language Technology
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• 1999.10e
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• pp.491-496
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• 1999

한국어 형태소 분석 방법 중 좌우 최장일치법은 분석 모델은 단순하지만 분석 후보의 과생성과 backtracking 발생 문제 등으로 인하여 연구가 미진하였다. 또한 Two-level 모델은 최장일치법에서 나타나는 문제점, 많은 two-level 규칙의 필요성, 그리고 중간 결과의 이용 문제로 인하여 한국어에 거의 적용되지 못하고 있다. 본 논문에서는 형태소 분석의 일반적인 모델로 알려진 Two-level 모델의 단점인 backtracking 문제와 분석 후보의 과생성 문제 그리고 중간 결과의 미사용 문제를 좌우 최장일치법을 이용하여 처리하는 방법론을 제안하고 좌우 최장일치법이 한국어 형태소 분석 방법에 효율적으로 적용될 수 있음을 제시한다.

• Journal of Electrical Engineering and Technology
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• v.13 no.1
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• pp.133-142
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• 2018

Paper presents a comparative study of space vector pulse width modulation (SVPWM) switching sequences for Voltage Source Inverters (VSIs). Various SVPWM switching sequences are studied for two and three level VSIs in linear modulation index region. The computations of dwell times are presented for two and three level VSIs based on space vector geometry in a synchronized and optimized manner. The existing SVPWM switching sequences are implemented using Matlab / Simulink and in an experimental setup for three phase two and three level VSIs. The simulation and experimental waveforms of conventional SVPWM (CSVPWM) and bus clamped SVPWM (BCSVPWM) are demonstrated for two and three level inverter respectively. The performance of different SVPWM switching sequences are evaluated and presented based on weighted voltage total harmonic distortion (THD).

• The Journal of Korean Obstetrics and Gynecology
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• v.29 no.1
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• pp.116-126
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• 2016

Objectives: The purpose of these cases is to report the effects of oriental medicine on two patients with premature ovarian failure. Methods: Two patients who had amenorrhea and hot flashes caused by premature ovarian failure were treated by oriental medicine such as herb medication. We estimated the effects of treatments by follow-up measurements of serum hormone level, menstrual cycle and symptoms. Besides, follicle and endometrium were checked by ultrasonography for academic research.Results After treatments, their symptoms of premature ovarian failure were improved and the menstrual cycle resumed. And the level of serum Follicle Stimulating Hormone decreased and the level of serum E₂ increased.Conclusions Two cases shows that oriental medicine has effects on patients with premature ovarian failure by follow-up measurements of serum hormone level, menstrual cycle and symptoms.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.17 no.3
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• pp.158-165
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• 2005

In order to analyze incompressible two-phase flow, Level Set method was applied on pseudo-compressibility formulation. Level Set function is defined as a signed distance function from the phase interface, and gives the information of the each phase location and the geometric data to the flow. In this study, Level Set function transport equation was coupled with flow conservation equations, and owing to pseudo-compressibility technique we could solve the resultant vector equation iteratively. Two-phase flow analysis code was developed on general curvilinear coordinate, and numerical tests of bubble dynamics and surging wave problems demonstrate its capability successfully.

• Journal of Power Electronics
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• v.18 no.4
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• pp.1027-1036
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• 2018

In this paper a new generalized space vector pulse width modulation scheme is proposed based on the principle of reverse mapping to drive the switches of multilevel inverters. This projected scheme is developed based on the middle vector of the subhexagon which holds the tip of the reference vector, which plays a major role in mapping the reference vector. A new approach is offered to produce middle vector of the subhexagon which holds tip of the reference vector in the multilevel space vector plane. By using middle vector of the subhexagon, reference vector is linked towards the inner two level sub-hexagon. Then switching vectors, switching sequence and dwell times corresponding to a particular sector of a two-level inverter are determined. After that, by using the two level stage findings, the switching vectors related to exact position of the reference vector are directly generated based on principle of the reverse mapping approach and do not need to be found at n level stage. In the reverse mapping principle, the middle vector of subhexagon is added to the formerly found two level switching vectors. The proposed generalized algorithm is efficient and it can be applied to an inverter of any level. In this paper, the proposed scheme is explained for a five-level inverter and the performance is analyzed for five level and three level inverters through MATLAB. The simulation results are validated by implementing the propose scheme on a V/f controlled three-level inverter fed induction motor using dSPACE control desk.

• Journal of computational fluids engineering
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• v.9 no.3
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• pp.73-80
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• 2004

A LS(Level Set) formulation is developed for computing two-phase flows on non- orthogonal meshes. Compared with the VOF(Volume-of-Fluid) method based on a non-smooth volume-fraction function, the LS method can calculate an interfacial curvature more accurately by using a smooth distance function. Also, it is quite straightforward to implement for 3-D irregular meshes compared with the VOF method requiring much more complicated geometric calculations. The LS formulation is implemented into a general purpose program for 3-D flows and verified through several test problems.