• 대한방사선기술학회지:방사선기술과학
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• 제32권3호
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• pp.277-283
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• 2009

임상에서 정확한 진단을 위해 양질의 초음파 영상을 얻는 것은 중요하다. 본 연구에서는 초음파 진단기의 주파수와 동적 영역(dynamic range, DR) 설정 및 프로브 유형에 따른 초음파 영상의 변화를 관찰하였다. 실험에서 고형 및 낭성 종괴 병변과 유사한 초음파 평가 팬텀(539,551, ATS, USA)의 6가지 LCS(low contrast sensitivity) 표적(-15, -6, -3, +3, +6, +15 dB)에 대한 영상을 대상으로 평가하였다. 초음파 영상은 볼록형(convex, C3-7IM) 및 선형(linear probe, L5-12IM) 두 가지 탐촉자(Probe)에 대해 SA-9900(Medison Ltd, Korea)을 이용하여 얻었다. 주파수는 4가지 방식(gen, pen, res, harmonic), 동적영역은 $40{\sim}100\;dB$ 범위에서 설정을 변화하면서 영상을 취득하였다. 취득한 영상의 질은 표적의 명목상 LCS 값과 영상에서 측정된 LCS을 비교하여 평가 하였다. 실험 결과 볼록형 탐촉자의 경우, 각 LCS 표적에 대해 주파수 방식 별로 동적영역 값을 40, 60, 80, 100 dB로 변화할 때, 초음파 영상의 질은 유의한 변화가 없었다. 그러나 낭종성 병변에 가까운 LCS 표적 -15 dB에서는 동적영역 60 dB과 하모닉 주파수 방식에서 LCS 값이 높게 나타났다. 선형 프로브에서는 -15 dB LCS 표적에서 동적영역 40 dB, 하모닉 방식에서 명목상 값에 근접하였다. LCS관점에서 정량화된 영상의 평가의 한계와 주관적인 평가 즉 심리적인 관점에서의 ROC(Receiver Operating Characteristic) 평가의 필요성에 대해 토의하였다.

• Bulletin of the Korean Chemical Society
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• 제24권12호
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• pp.1731-1736
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• 2003

The reaction of ${\alpha}$-Benzilmonoxime with palladium(II) produces a green complex in triton X-100 micellar media. Palladium has been determined using zero and first derivative spectrophotometric methods. The absorbances of Pd(II)- ${\alpha}$--benzilmonoxime complex at 441.8 and 677.0 nm in 0.10 M perchloric acid solution were monitored and linear working ranges of 0.3-12.0 and 0.7-20 ${\mu}$g mL$^{-1}$ with detection limits of 0.07 and 0.10 ${\mu}$g $mL^-1$ were obtained, respectively. Also, recoveries in the range of 92.8 to 100.1% and relative standard deviations in the range of 0.4 to 7.1% were obtained. First derivative spectrophotometry has also been applied for palladium determination under the optimum condition. The linear dynamic range of 0.2-24.0 ${\mu}$g $mL^{-1}$ palladium with relative standard deviations of 0.6-6.9% and recoveries in the range of 94.9-102.5% has been obtained by first derivative spectrophotometry. The method shows high selectivity because of the high concentration of acid used, which prevents formation of complexes of ${\alpha}$--benzilmonoxime with the other cations. The palladium complex formed was stable at least one day. The method was successfully applied to the determination of palladium in some synthetic palladium alloys and palladium-charcoal powder.

• 한국생산제조학회지
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• 제19권4호
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• pp.553-561
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• 2010

In flat panel display or semiconductor industries, they install the equipments with fine line width and high throughput for fabrication and inspection. The equipments are required to have the linear stage which can position the work-piece with high speed, fine resolution on wide range of motion. In this paper, a precision planar linear XY stage is proposed. The stage has a symmetric planar window configuration and is guided by air-bearings on granite plate. The symmetric planar window configuration makes the stage has robustness against dynamic and thermal disturbances. The air-bearings let the stage move smooth on straight guide bar and flat granite surface. The stage is actuated by linear motor with Halbach magnet array (HMA). HMA generates more confined magnetic flux than conventional array. The linear motors are optimized by using sequential quadratic programming (SQP) with the several constraints that are thermal dissipation, required power, force ripple and so on. The planar linear XY stage with the symmetric planar configuration and the linear motors is implemented and then the performance such as force ripple, resolution and stroke are evaluated.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2003년도 ICCAS
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• pp.525-530
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• 2003

This paper is concerned with a control allocation strategy using the dynamic inversion which generates the nominal control input trajectories, and autopilot design using the time-varying control technique which is time-varying version of pole placement of linear time-invariant system for an agile missile with aerodynamic fin and thrust vectoring control. Dynamic inversion can decide the amount of the deflection of each control effector, aerodynamic fin and thrust vectoring control, to extract the maximum performance by combining the action of them. Time-varying control technique for autopilot design enhance the robustness of the tracking performance for a reference command. Nonlinear simulations demonstrates the dynamic inversion provides the effective nominal control input trajectories to achieve the angle of attack command, and time-varying control technique exhibits good robustness for a wide range of angle of attack.

• 소음진동
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• 제9권2호
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• pp.317-323
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• 1999

Dynamic characteristics of catenary that supplies electrical power to high-speed trains are investigated. A simple catenary is composed of the contact and messenger wires connected by droppers possessing bi-directional stiffness properties. For slender, repeating structures such as catenary, both the wave propagation and vibration properties need to be understood. The influence of parameters that determine catenary dynamics are investiaged through numerical simulations involving finite element models. The effects of the tension and flexural rigidity of the contact wire is first investigated. The effects of dropper characteristics are then investigated. For linear droppers wave propagation as well as modal properties are determined. For large catenary motion, droppers can be modeled as bi-directional elements possessing low stiffness in compression and high stiffness in tension. For this case, impulse response is computed and compared with the cases of linear droppers. It is found that the catenary dynamics are primarily determined by contact wire tension and dropper properties, with large responses observed in 5∼40 Hz frequency range. In particular, the dropper stiffness and spacing are found to have dominant influence on the response frequency and the wave transmission characteristics.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2008년도 추계학술대회 논문집 Vol.21
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• pp.233-233
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• 2008

A piezoelectric ultrasonic linear motor shaped with 'Butterfly' wings has been developed for thin electronics such as cellular phone and PDA. The butterfly piezoelectric transducer is simply composed of an elastic plate, which includes a tip for energy transfer and two protrusions to fix it, and two piezoelectric ceramics. Contact materials, such as a brass, and steel and alumina can make it possible to improve dynamic properties of the motors over a wide range of tribological conditions. The dynamic properties of the motor have been intensively measured and analyzed according to the applied voltage wave forms at the various frequencies. The results of numerical study and experimental investigation will be used for the future optimization of the actuator and the realization of the advanced ultrasonic motor.

• Journal of Mechanical Science and Technology
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• 제20권1호
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• pp.51-58
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• 2006

To compensate for the motion errors in hydrostatic tables, a method to actively control the clearance of a bearing corresponding to the amount of error using actively controlled capillaries is introduced in this paper. The design method for an actively controlled capillary that considers the output rate of a piezo actuator and the amount of error that must be corrected is described. The basic characteristics of such a system were tested, such as the maximum controllable range of the error, micro-step response, and available dynamic bandwidth when the capillary was installed in a hydrostatic table. The tests demonstrated that the maximum controllable range was $2.4\;{\mu}m$, the resolution was 27 nm, and the frequency bandwidth was 5.5 Hz. Simultaneous compensation of the linear and angular motion errors using two actively controlled capillaries was also performed for a hydrostatic table driven by a ballscrew and a DC servomotor. An iterative compensation method was applied to improve the compensation characteristics. Experimental results showed that the linear and angular motion errors were improved to $0.12{\mu}m$ and 0.20 arcsec, which were about $1/15^{th}$ and $1/6^{th}$ of the initial motion errors, respectively. These results confirmed that the proposed compensation method improves the motion accuracy of hydrostatic tables very effectively.

• 지질공학
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• 제29권3호
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• pp.339-349
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• 2019

국내 40개 구조물 설계 시 수행된 1,646개의 실내 및 현장시험 결과를 활용하여 국내 암종에 따른 동탄성계수의 분포특성을 파악하기 위하여 암종별 P파 속도, 정탄성계수, 동탄성계수 간의 상관식을 도출하고 기존 연구사례와 비교하여 검증하였다. P파 속도와 정탄성계수의 관계를 살펴보면 편마암에서는 선형, 화강암과 사암에서는 지수 함수의 관계를 보인다. 결정계수($R^2$)는 0.491~0.642로 높지 않지만, 결정계수를 0.836~0.990로 제시하고 있는 기존의 연구사례와 유사한 분포범위를 보인다. 정탄성계수와 동탄성계수의 상관식은 모든 암종에서 선형적인 관계를 보이며, 결정계수는 0.543~0.676이다. P파 속도와 동탄성계수의 상관식은 지수함수의 관계를 보이며, 결정계수는 0.875~0.940으로 높게 나타난다.

• 대한기계학회논문집A
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• 제30권7호
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• pp.757-764
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• 2006

Isothermal cyclic stress-strain deformation and thermomechanical deformation (TMD) of 429EM stainless steel were analyzed using a rheological model employing a bi-linear model. The proposed model was composed of three parameters: elastic modulus, yield stress and tangent modulus. Monotonic stress-strain curves at various temperatures were used to construct the model. The yield stress in the model was nearly same as 0.2% offset yield stress. Hardening relation factor, m, was proposed to relate cyclic hardening to kinematic hardening. Isothermal cyclic stress-strain deformation could be described well by the proposed model. The model was extended to describe TMD. The results revealed that the hi-linear thermomechanical model overestimates the experimental data under both in-phase and out-of-phase conditions in the temperature range of $350-500^{\circ}C$ and it was due to the enhanced dynamic recovery effect.

• Journal of Electrical Engineering and Technology
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• 제5권1호
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• pp.28-35
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• 2010

This paper presents new Adaptive Linear Combination Structure (ADALINE) for tracking/estimating voltage-current phasor and frequency of power system. To estimate the phasors and frequency from sampled data, the algorithm assumes that orthogonal coefficients and speed of angular frequency of power system are unknown parameters. With adequate sampled data, the estimation problem can be considered as a linear weighted least squares (LMS) problem. In addition to determining the phasors (orthogonal coefficients), the procedure estimates the power system frequency. The main algorithm is verified through a computer simulation and data from field. The proposed algorithm is tested with transient and dynamic behaviors during power swing, a step change of frequency upon islanding of small generators and disconnection of load. The algorithm shows a very high accuracy, robustness, fast response time and adaptive performance over a wide range of frequency, from 10 to 2000 Hz.