• 전력전자학회:학술대회논문집
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• 전력전자학회 2015년도 전력전자학술대회 논문집
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• pp.441-442
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• 2015

This paper proposes a new single-phase seven-level grid-connected inverter. Operational principle with switching function are analyzed. A digital proportional-integral current-control algorithm was implemented in a TMS320F28335 DSP to keep the current injected into the grid sinusoidal. To verify the performance of the proposed inverter, PSIM simulation and experimental results are also shown in this paper.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제4권1호
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• pp.39-48
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• 2000

In this paper we define T-fuzzy integrals of set-valued mappings, which are extensions of fuzzy integrals of the single-valued functions defined by Sugeno. And we discuss their properties.

• 대한수학회논문집
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• 제37권1호
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• pp.75-89
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• 2022

In this paper, we prove new fixed point theorems for single-valued and multi-valued weakly Picard operators in complete metric spaces and give several examples. As applications, we give several results to Fredholm integral equation.

• Korean Chemical Engineering Research
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• 제58권3호
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• pp.430-437
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• 2020

본 연구에서는 다단제어(Cascade Control)를 위한 안티 와인드업(Anti-windup) 기술을 개발하였다. 다단제어는 외란을 보다 효과적으로 제어하기 위해 내부에 되먹임(Feedback) 제어루프를 추가한 제어구조이다. 단일루프제어(Single-loop Control)와는 다르게 두 개의 제어루프로 이루어져 내부의 종속제어루프(Secondary Control)가 외부의 주제어루프(Primary Control)에 영향을 미치는 특징을 가지고 있다. 산업현장에서 다단제어에 적용하는 기존의 안티 와인드업 기술은 주로 주제어기(Primary Controller)와 종속제어기(Secondary Controller)에 각각 로컬 역연산법(Back Calculation)을 적용하는 것이다. 하지만 이 방법은 종속제어기의 제어출력이 포화되었을 때 발생하는 주제어기의 적분누적(Integral-windup) 현상을 효과적으로 제거하지 못한다. 이를 해결하기 위해 기존 로컬 안티 와인드업 기술을 확대 적용한 두 가지의 다단제어용 안티 와인드업 기술을 제안한다. 첫 번째는 다단 조건부 적분법(Cascade Conditional Integration)이고 두 번째는 다단 역연산법(Cascade Back Calculation)으로 단일루프제어에 적용되어 왔던 로컬 조건부 적분법과 역연산법을 다단제어로 확대 적용하여 다단제어 시스템에서 PID제어기의 적분누적 현상을 방지하고자하였다. 개발한 다단 조건부 적분법과 다단 역연산법은 간단하고 직관적이면서도 종속제어기의 제어출력의 포화로 인해 발생한 적분누적현상을 효과적으로 방지할 수 있고 공정이나 제어기 형태에 상관없이 우수한 제어성능을 유지할 수 있었다. 향후 실제 공정 적용을 통해 신뢰성을 확보한다면 산업현장의 다단제어기 성능을 개선하는데 크게 기여를 할 수 있을 것이다.

• BMB Reports
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• 제54권10호
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• pp.505-515
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• 2021

Human pluripotent stem cells (hPSCs) include human embryonic stem cells (hESCs) derived from blastocysts and human induced pluripotent stem cells (hiPSCs) generated from somatic cell reprogramming. Due to their self-renewal ability and pluripotent differentiation potential, hPSCs serve as an excellent experimental platform for human development, disease modeling, drug screening, and cell therapy. Traditionally, hPSCs were considered to form a homogenous population. However, recent advances in single cell technologies revealed a high degree of variability between individual cells within a hPSC population. Different types of heterogeneity can arise by genetic and epigenetic abnormalities associated with long-term in vitro culture and somatic cell reprogramming. These variations initially appear in a rare population of cells. However, some cancer-related variations can confer growth advantages to the affected cells and alter cellular phenotypes, which raises significant concerns in hPSC applications. In contrast, other types of heterogeneity are related to intrinsic features of hPSCs such as asynchronous cell cycle and spatial asymmetry in cell adhesion. A growing body of evidence suggests that hPSCs exploit the intrinsic heterogeneity to produce multiple lineages during differentiation. This idea offers a new concept of pluripotency with single cell heterogeneity as an integral element. Collectively, single cell heterogeneity is Janus-faced in hPSC function and application. Harmful heterogeneity has to be minimized by improving culture conditions and screening methods. However, other heterogeneity that is integral for pluripotency can be utilized to control hPSC proliferation and differentiation.

• Nuclear Engineering and Technology
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• 제54권5호
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• pp.1835-1844
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• 2022

Single-orifice plate is wildly utilized in the piping system of the nuclear power plant to throttle and depressurize the fluid of the pipeline. The cavitation induced by the single-orifice plate may cause some serious vibration of the pipeline. This study aims to find the optimal designs of the single-orifice plates that may have weak cavitation possibilities. For this purpose, a new single-orifice plate with a convergent-flat-divergent hole was modeled, a multi-objective optimization method was proposed to optimize the shape of a single-orifice plate, while computational fluid dynamics method was adopted to obtain the fluid physical quantities. The reciprocal cavitation number and the developmental integral were treated as cavitation indexes (e.g., objectives for the optimization algorithm). Two non-dominant designs ultimately achieved illustrated obvious reduction in the cavitation indexes at a Reynolds number Re = 1 ×10⁵ defined based on fluid velocity. Besides, the sensitivity analysis and temperature effects were also performed. The results indicated that the convergent angle of the single-orifice plate dominants the cavitation behavior globally. The optimal designs of single-orifice plates result in lower downstream jet areas and lower upstream pressure. For a constant Reynolds number, the higher temperature of liquid water, the easier it is to undergo cavitation. Whereas there is a diametric phenomenon for a constant fluid velocity. Moreover, the regression models were carried out to establish the mathematical relation between temperature and cavitation indexes.

• 대한기계학회논문집B
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• 제20권11호
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• pp.3620-3629
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• 1996

In the free molecular flow range, the pumping performance of a turbomolecular pump has been predicted by calculation of the transmission probability which employs the integral method and the test particle Monte-Carlo method. Also, new approximate method combining the double stage solutions, so called double-approximation, is presented here. The calculated values of transmission probability for the single stage agree quantitatively with the previous known numerical results. For a six-stage pump, the Monte-Carlo method is employed to calculate the overall transmission probability for the entire set of blade rows. When the results of the approximate method combining the single stage solutions are compared with those of the Monte-Carlo method at dimensionless blade velocity ratio C=0.4, the previous known approximate method overestimates as much as 34% than does the Monte-Carlo method. But, the new approximate method gives more accurate results, whose relative error is 10% compared to the Monte-Carlo method, than does the previous approximate method.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 춘계학술대회논문집
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• pp.1062-1073
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• 2007

Acoustic Target Strength (TS) is a major parameter of the active sonar equation, which indicates the ratio of the radiated intensity from the source to the re-radiated intensity by a target. In developing a TS equation, it is assumed that the radiated pressure is known and the re-radiated intensity is unknown. This research provides a TS equation for polygonal plates, which is applicable to near field acoustics. In this research, Helmholtz-Kirchhoff formula is used as the primary equation for solving the re-radiated pressure field; the primary equation contains a surface (double) integral representation. The double integral representation can be reduced to a closed form, which involves only a line (single) integral representation of the boundary of the surface area by applying Stoke's theorem. Use of such line integral representations can reduce the cost of numerical calculation. Also Kirchhoff approximation is used to solve the surface values such as pressure and particle velocity. Finally, a generalized definition of Sonar Cross Section (SCS) that is applicable to near field is suggested. The TS equation for polygonal plates in near field is developed using the three prescribed statements; the redection to line integral representation, Kirchhoff approximation and a generalized definition of SCS. The equation developed in this research is applicable to near field, and therefore, no approximations are allowed except the Kirchhoff approximation. However, examinations with various types of models for reliability show that the equation has good performance in its applications. To analyze a general shape of model, a submarine type model was selected and successfully analyzed.

• 대한기계학회논문집
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• 제13권3호
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• pp.479-489
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• 1989

본 논문에서는 Ｊ$_{1}$,Ｊ$_{2}$ 적분과 Ｋ$_{I}$,Ｋ$_{II}$ 사이의 완전한 관계를 좁은 직사각형 경로를 택하여 간판하게 유도하였다. 그리고 유한요소의 해로 Ｊ$_{2}$적분을 효율적으로 계산하는 방법을 제시하였다.이미 해가 존재하는 문제 를 본 방법으로 다루어 그 결과를 비교하였고 일방향(unidirectional) 적층판 cantil- ever 평판 내의 single edge crack에 대한 해를 제시하였다.

• Journal of Power Electronics
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• 제11권5호
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• pp.655-661
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• 2011

This paper presents two topologies for single-stage single-phase double-buck type PFC converters, designed to operate at high power factor, near sinusoidal input currents and adjustable output voltage. Unlike the known buck type PFC topologies, in which the output voltage is always lower than the maximum input voltage, the proposed converters can operate at output voltages higher than the ac input peak voltage. A reduced number of switches on the main path of the current are another characteristic of the two proposed topologies. To shape the input line currents, a fast and robust controller based on a sliding mode approach is proposed. This active non-linear control strategy, applied to these converters allows high quality input currents. A Proportional Integral (PI) controller is adopted to regulate the output voltage of the converters. This external voltage controller modulates the amplitude of the sinusoidal input current references. The performances of the presented rectifiers are verified with experimental results.