• Journal of Communications and Networks
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• 제15권1호
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• pp.102-110
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• 2013

This paper considers a cooperative orthogonal frequency division multiple access (OFDMA)-based cognitive radio network where the primary system leases some of its subchannels to the secondary system for a fraction of time in exchange for the secondary users (SUs) assisting the transmission of primary users (PUs) as relays. Our aim is to determine the cooperation strategies among the primary and secondary systems so as to maximize the sum-rate of SUs while maintaining quality-of-service (QoS) requirements of PUs. We formulate a joint optimization problem of PU transmission mode selection, SU (or relay) selection, subcarrier assignment, power control, and time allocation. By applying dual method, this mixed integer programming problem is decomposed into parallel per-subcarrier subproblems, with each determining the cooperation strategy between one PU and one SU. We show that, on each leased subcarrier, the optimal strategy is to let a SU exclusively act as a relay or transmit for itself. This result is fundamentally different from the conventional spectrum leasing in single-channel systems where a SU must transmit a fraction of time for itself if it helps the PU's transmission. We then propose a subgradient-based algorithm to find the asymptotically optimal solution to the primal problem in polynomial time. Simulation results demonstrate that the proposed algorithm can significantly enhance the network performance.

• 대한한방부인과학회지
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• 제35권4호
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• pp.161-173
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• 2022

Objectives: This study was conducted to evaluate the effectiveness of acupuncture in patients with primary menstrual difficulties taking NSAIDs. Methods: 30 women with primary menstrual difficulties with NSAIDs were assigned to treatment groups (n=15) and control groups (n=15). On their first visit, both groups were provided with a menstrual diary and were required to record the intensity of pain and the dosage of painkillers during each menstrual cycle. The treatment group received two acupuncture treatments per cycle during two cycles, and the control group did not receive acupuncture. Pain strength during menstruation was evaluated using Visual Analogue Scale (VAS), and the total number of painkillers taken during menstruation and the average number of painkillers taken during a single dose was measured. Results: The treatment group had significant pain relief compared to the pre-test group and significant differences from the control group. In addition, there was a significant difference between the treatment group and the control group in the frequency of taking painkillers during the menstrual period and the dose in the test group was significantly lower than before treatment. Conclusions: This clinical trial showed that this acupuncture can help alleviate primary menstruation and reduce the use of nonsteroidal anti-inflammatory drugs.

• Current Research on Agriculture and Life Sciences
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• 제4권
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• pp.95-101
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• 1986

진동경운(振動耕耘)에 있어서 경운저항(耕耘抵抗) 및 동력(動力)을 최소(最小)로 하는 Computer에 의한 자동제어(自動制御) 시스템의 개발(開發)을 목적(目的)으로 3가지 Mode의 제어(制御) program을 작성(作成)하여 실험(實驗)과 Simulation을 통(通)하여 각 Mode의 제어성능(制御性能)을 조사(調査)하였다. 진동속도비(振動速度比)를 일정(一定)(1.5)하게 한 경우 3가지 Mode 모두 동일(同一) 진동조건(振動條件)에 수렴하였다. 그러나 흙의 전단주파수(剪斷周波數)에 Blade의 진동수(振動數)를 match 시키는 방법 즉 흙의 전단주파수(剪斷周波數)의 2배의 진동수(振動數)로 Blade를 진동(振動)시키는 제어(制御) Mode가 수렴 시간이 짧고, 견인저항 및 동력의 최적치(最適値)에 가장 가까웠다. 또 경심(耕深) 및 토양수분(土壤水分)의 변화(變化)와 같은 외란(外亂)에 대한 견인저항 감소율의 변동(變動)은 10%이하(以下)로 적었다. 이상(以上)과 같이 흙의 전단주파수(剪斷周波數)에 Blade의 진동수(振動數)를 match 시키는 제어(制御) Mode의 제어성능(制御性能)이 가장 우수함을 알았다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2015년도 제46회 하계학술대회
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• pp.179-180
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• 2015

High wind penetration might cause the frequency stability problem because a wind power plant (WPP) is operating in a maximum power tracking mode to extract the maximal energy from wind and thus does not react to the system frequency variation. Therefore, the system operators encourage a WPP to participate in frequency control, which includes inertia/orl and primary control. The frequency support capability of a WPP depends on the amount of kinetic energy (KE) and reserve. This paper formulates an optimization problem to maximize KE while retaining the required reserve. The proposed optimization problem would allow wind generators (WGs) with a smaller wind speed to retaine more KE. The performance of the proposed optimization problem was investigated in a 100-MW WPP consisting of 20 units of 5-MW permanent magnet synchronous generators using an EMTP-RV simulator. The results show that the proposed optimization problem successfully improves the frequency nadir more than a conventional reserve allocation that distributes WGs proportional to the current output.

• Earthquakes and Structures
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• 제3권5호
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• pp.749-766
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• 2012

Structural control through integration of passive damping devices within the building structure has been increasingly implemented internationally in the last years and has proven to be a most promising strategy for earthquake safety. In the present paper an alternative configuration of an innovative energy dissipation mechanism that consists of slender tension only bracing members with closed loop and a hysteretic damper is investigated in its dynamic behavior. The implementation of the adaptable dual control system, ADCS, in frame structures enables a dual function of the component members, leading to two practically uncoupled systems, i.e., the primary frame, responsible for the normal vertical and horizontal forces and the closed bracing-damper mechanism, for the earthquake forces and the necessary energy dissipation. Three representative international earthquake motions of differing frequency contents, duration and peak ground acceleration have been considered for the numerical verification of the effectiveness and properties of the SDOF systems with the proposed ADCS-configuration. The control mechanism may result in significant energy dissipation, when the geometrical and mechanical properties, i.e., stiffness and yield force of the integrated damper, are predefined. An optimum damper ratio, DR, defined as the ratio of the stiffness to the yield force of the hysteretic damper, is proposed to be used along with the stiffness factor of the damper's- to the primary frame's stiffness, in order for the control mechanism to achieve high energy dissipation and at the same time to prevent any increase of the system's maximum base shear and relative displacements. The results are summarized in a preliminary design methodology for ADCS.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제49권9호
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• pp.541-545
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• 2000

We propose a pulsed $CO_2$laser below 30W by the AC(60Hz) switching control of leakage transformer primary which has some advantages of cost and size compared to a typical pulsed power supply. Pulse repetition rate is adjusted from 5 Hz to 60 to Hz control laser output. In this laser a low voltage open loop control for high voltage pulse discharge circuit is employed to aviod the Hv sampling or switching and high voltage leakage transformer is used to convert low voltage pulse rectified from AC to high voltage one. A ZCS(Zero Crossing Switch) circuit and a PIC(programble one-chip microprocessor are used to control gate signal of SCR precisely. The pulse repetition rate is limited by 60Hz due to the frequency of AC line and a high leadkage inductance. The maximum laser output was about 23 W at pulse repetition rate of 60Hz total gas mixture of $CO_2$ : $N_2$ : He=1: 9: 15 and total pressure of 18 Torr

• 조명전기설비학회논문지
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• 제12권1호
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• pp.45-50
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• 1998

최근, 유도전동기 회전속도 제어용 구동 전원으로 인버터와 싸이크로컨버터가 널리 사용되고 있다. 싸이크로컨버터에 의한 전동기 구동은 일정 주파수의 교류전원에서 직접 주파수가 다른 교류로 변환함으로 하드웨어 구성이 인버터 보다 간단하다. 본 연구의 목적은 싸이크로컨버터에 의한 유도전동기 벡터제어 시스템의 제어방법 및 하드웨어 설계를 행하는 것이다. 본 연구에서는 교류 전동기 슬립 주파수형 벡터제어 알고리즘을 도출하고 이 원리에 기초하여 싸이크로컨버터를 이용한 벡터제어 시스템을 구성하였다. 싸이크로컨버터는 1차 입력전류 진폭 $li_1l$ 과 각주파수 $\omega_1$을 지령값으로 진폭변조 제어신호를 발생하여 SCR의 게이터를 트리거한다. 본 벡터제어 시스템은 교류 전동기를 구동한 결과 자속이 일정하게 유지되면서 정회전에서 역회전까지 연속적으로 양호한 운전을 할 수 있었다.

• 한국정밀공학회지
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• 제20권3호
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• pp.157-164
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• 2003

The pulse-echo method is one of the most widely used ultrasonic techniques for application of nondestructive evaluation. Particularly, quantitative nondestructive evaluation of defects has been considered more important to assure the reliability and the safety of structure. Frequency energy in adhesive joints is based on the ultrasonic wave analysis. The attenuation coefficient upon wave amplitude and the frequency energy that is expressed in the term of wave pressure amplitude were utilized for the primary wave experiment. By means of a control experiment, it was confirmed that the variation of the frequency energy in adhesive joints depends on transition by stress variation. In this paper, the ultrasonic characteristics were measured for single lap joint and Double Cantilever Beam specimen with different fracture modes that was subjected to stress. Consequently, the data that was obtained from the adhesive specimen was analytically compared to the fracture mechanics parameter

• 전력전자학회논문지
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• 제23권4호
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• pp.256-264
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• 2018

This paper proposes a three-bridge LLC resonant converter with auxiliary switches for a wide output voltage control range. This converter can be controlled in two ways to achieve a wide controllable output voltage control range of $V_o$ to $3V_o$. The first control mechanism is achieved through the pulse width modulation (PM) of the auxiliary switches and primary switching devices, while the second control mechanism is achieved through the frequency modulation (FM) of the primary switching devices that are configured to operate in the full-bridge switching mode when the auxiliary switches are turned off. The feasibility of using the proposed converter is verified by the results of an experiment with a 2kW prototype.

• 전기학회논문지
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• 제59권7호
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• pp.1248-1254
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• 2010

Authors conducted a deduction of some parameters using the magnetic equivalent circuit method and a verification study of the thrust force control algorithm of a rotary-typed small-scaled linear induction motor for a railway transit. In a LIM, it is possible to express the parameters of the magnetic equivalent circuit into a function of the shape of the secondary aluminium plate and the airgap between the LIM primary core and the secondary aluminium plate. It means that the LIM properties can be changed considerably by the shape of the secondary aluminium plate and the airgap between the LIM primary core and the secondary aluminium plate. So, authors analyzed a tendency of changes of the magnetic equivalent circuit parameters and the LIM characteristics by changing of the airgap of the secondary aluminium plate of a rotary-typed small-scaled LIM. And authors conducted a verification study of the indirect vector control algorithm with constant slip frequency by using the rotary-typed small-scaled LIM tester set on the basis of the calculated LIM parameters. Finally authors accomplished a research on applicability for LIM railway transit.