• The Journal of the Acoustical Society of Korea
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• 제23권1E호
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• pp.19-23
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• 2004

This paper presents an experimental technique to generate and detect axisymmetric longitudinal waves in a pipe by using piezoelectric cylindrical transducers. Radial pulses transmitted by one transducer have propagated in two opposite directions along the pipe, and other two transducers have received the propagating waves. The difference of the transit times measured for the waves in two paths of known distance difference has yielded the phase speed of the wave propagation. Wave speed has been measured in an empty pipe and in a water-filled pipe.

• 천문학회지
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• 제36권spc1호
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• pp.7-12
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• 2003

We have studied the magnetic helicity of active regions by using the data from (1) the photo-electric magnetograph of the Okayama Observatory (1983-1995) and (2) the video magnetograph of NAOJ/Mitaka (1992-2000). The latitude distribution of helicity showed a tendency that the regions in the north (south) hemisphere have negative (positive) helicities, respectively, which is already known as the hemispheric sign rule. If we look into the sign of helicity as a function of time, the sign rule was less definite or was reversed sometimes in the sunspot minimum phase. We also studied the relation between the magnetic helicity and the sunspot tilt angles, and found that these two quantities are positively correlated, which is opposite to the expectation of a theoretical model. The implications of this cycle-phase dependence of helicity signs and the correlation between magnetic he Ii city and sunspot tilt angles are discussed.

• 한국주조공학회지
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• 제10권6호
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• pp.503-508
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• 1990

The effect of interlamellar spacing on tensile behavior and fracture mode at high temperatures has been studied for unidirectionally solidified $Al-CuAl_2$ eutectic composite. The tensile properties at room temperature in $Al-CuAl_2$ eutectic composite improved as the interlamellar spacing decreased due to the constraint effects of closely spaced lamellae, while the opposite behavior was observed at high temperatures due to the annihilation of the constraint effects by phase boundary sliding. The $Al-CuAl_2$ eutectic composite exhibited brittle fracture mode below the temperature at which the reinforcing phase softened but ductile fracture mode above the temperature.

• 대한의용생체공학회:학술대회논문집
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• 대한의용생체공학회 1992년도 춘계학술대회
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• pp.92-97
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• 1992

The pulsatile nature of blood flow makes artefacts in 2D Fourier transform image. Spatial presaturation is known to be effective in eliminating flow artefacts when the spin echo acquisition is employed. However. this method requires additional RF pulse and spoiling gradient for presaturation. In this paper a new flow saturation technique which does not require additional saturation-RF and gradient is proposed. The proposed technique is equivalent to the existing saturation technique but the elimination of the flow component is achieved by a pair of tailored $90^{\circ}-180^{\circ}$ RF pulses in tile spin echo sequence. By use of two tailored RF pulses with opposite phase polarity, a linear phase gradient is generated for those moving materials and consequently all the spins of moving materials become dephased thereby no signal is observable. Computer simulations and experimental results obtained using both a phantom and a human volunteer with a 2.0 T whole body system are also presented.

• 한국수산과학회지
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• 제4권2호
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• pp.66-74
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• 1971

The general morphological characteristics of scales on the body surface in Cyprininae fishes can be summarized as follows: 1) The lentic and lotic habitats have no relation to the phase of scales. 2) The scales in the anterior body parts have transverse diameters longer than their longi-tudinal diameters: in the posterior body parts, the opposite holds true. 3) The scales having the largest diameters, both longitudinal and transverse, are the lateral line scales. 4) The position of the focus on each scale move posteriorly as the scale grows. In other words, the forward growth of the scales exceeds the backward. 5) The number of ridges in each scale is in proportion to longitudinal diameter. 6) In Cyprinus, the scales on the middle part of the body surface have more grooves than those on the other parts. All scales on this species commonly show incompleted grooves on the anterior and posterior areas, but the lateral area lacks grooves entirely. 7) In Carassius, there are more completed grooves than incompleted grooves. All grooves are arranged in radial patterns on the scales.

• 산업경영시스템학회지
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• 제30권1호
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• pp.33-40
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• 2007

A multi-server queueing system with finite buffer is considered. The input flow is the BMAP (Batch Markovian Arrival Process). The service time has the PH (Phase) type distribution. Customers from the BMAP enter the system according to the discipline of partial admission. Besides ordinary (positive) customers, the Markovian flow (MAP) of negative customers arrives to the system. A negative customer can delete an ordinary customer in service if the state of its PH-service process belongs to some given set. In opposite case the ordinary customer is considered to be protected of the effect of negative customers. The stationary distribution and the main performance measures of the considered queueing system are calculated.

• 한국소음진동공학회논문집
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• 제11권6호
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• pp.223-232
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• 2001

Aiming at a small axial pump with a levitated rotor, an axial-type self-bearing motor is presented, which has a rotor wish four permanent magnets and two stators with two-pole three-phase windings. In this system, only the axial motion of rotor is actively controlled by two opposite self-bearing motors just like in the case of an axial magnetic bearing, while the other motions are passively stable. For rotation, It follows the theory of a four-pole three-phase synchronous motor. This paper Introduces schemes for design and control of the self-bearing motor and shows some experimental results to Prove the feasibility of application for the axial Pump.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2009년도 추계학술대회
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• pp.160-163
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• 2009

HPA(High Power Amplifier)는 무선통신 시스템에서 필수적으로 요구되는 요소 중의 하나다. 그러나 전력 증폭기는 비선형 특성을 가지고 있으며 신호의 비선형 왜곡을 유발 시키고 인접채널 간섭을 심화시켜 시스템의 효율을 떨어뜨린다. 이러한 문제점을 해결하기 위해 많은 선형화 기법들이 제시되어왔다. 다항식 사전왜곡 기법은 증폭기로 입력되는 신호가 미리 증폭기의 역 특성을 갖도록 하는 기법으로 다항식을 통하여 증폭기를 모델링하기 때문에 수렴 속도가 빠르고 다른 기법들에 비해 좋은 성능을 보인다. 하지만 다항식으로 역 비선형 특성을 구할 경우, 증폭기의 포화영역에서 역 비선형 특성이 거의 무한대가 되어야 하기 때문에 선형화기의 성능이 크게 떨어진다. 본 논문에서는 이러한 문제점을 해결하기 위하여 PAPR(Peak-to-Average Power Ratio) 기법을 적용하여 다항식 사전왜곡 기법의 성능을 향상 시켰다.

• 한국전자파학회논문지
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• 제24권1호
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• pp.55-63
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• 2013

디지털 역지향성 안테나 시스템은 사전 정보 없이 입사된 신호의 위상을 추적하고 위상을 반대로 돌려 수신된 방향으로 재전송을 할 수 있는 시스템으로써 아날로그 역지향성 안테나와 비교하여 수정과 업그레이드가 쉽다는 장점이 있다. 이러한 특성으로 디지털 역지향성 안테나는 고속 이동체 환경에서의 빠른 빔 추적이 가능할 것이다. 특히 빠르고 정확하게 빔을 추적하기 위해서는 설계된 디지털 역지향성 안테나 시스템의 디지털 PLL의 성능이 매우 중요하므로, 본 논문에서는 디지털 역지향 안테나 시스템에서 디지털 필터 설계에 따른 위상 추적의 동작시간과 BER 성능을 확인하였다. 1 MHz의 QAM 신호를 발생시켰으며, $30^{\circ}$의 위상 지연이 생겼을 경우의 시뮬레이션 결과, 필터의 동작이 안정할 경우 위상 공액 기법을 사용한 역지향성 안테나 시스템의 성능이 사용하지 않았을 경우의 역지향성 안테나 시스템보다 약 1 dB의 성능 차이가 나며, 필터의 동작이 불안정할 경우, 발진이 일어나 위상을 추적하지 못해 성능이 매우 나빠짐을 확인할 수 있다.

• Current Optics and Photonics
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• 제2권5호
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• pp.474-481
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• 2018

We propose a polarization phase-shifting technique to investigate the thickness of $Ta_2O_5$ thin films deposited on BK7 substrates, using a modified Sagnac interferometer. Incident light is split by a polarizing beam splitter into two orthogonal linearly polarized beams traveling in opposite directions, and a quarter-wave plate is inserted into the common path to create an unbalanced phase condition. The linearly polarized light beams are transformed into two circularly polarized beams by transmission through a quarter-wave plate placed at the output of the interferometer. The proposed setup, therefore, yields rotating polarized light that can be used to extract a relative phase via the self-reference system. A thin-film sample inserted into the cyclic path modifies the output signal, in terms of the phase retardation. This technique utilizes three phase-shifted intensities to evaluate the phase retardation via simple signal processing, without manual adjustment of the output polarizer, which subsequently allows the thin film's thickness to be determined. Experimental results show that the thicknesses obtained from the proposed setup are in good agreement with those acquired by a field-emission scanning electron microscope and a spectroscopic ellipsometer. Thus, the proposed interferometric arrangement can be utilized reliably for non-contact thickness measurements of transparent thin films and characterization of optical devices.