• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2000년도 추계학술대회논문집
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• pp.225-231
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• 2000

Nonlinear characteristics of piezoelectric-type micro actuator used for hard disk drives are experimentally analyzed using Hutchinson's Magnum acturator. The nonlinear effects include hysteresis, superharmonic resonance, jump phenomenon, and shifting of natural frequencies. The effects of exciting frequency and input voltage on the nonlinear phenomena are investigated. It is shown that the micro actuator has the typical 3 times superhamonic resonances coupled to both 1st torsional and sway modes of the suspension.

• 전자공학회논문지T
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• 제35T권2호
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• pp.1-5
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• 1998

$CaSnO_3$ 시편을 고상반응법에 의해 제작하고, 그의 감습특성에 대해 조사하였다. 커패시턴스는 상대습도가 증가함에 따라 증가하며, 저주파 영역에서 우수한 감습도를 나타냈다. 감습도는 온도변화에 안정되며, 흡습, 탈습에 따라 약간의 히스테리시스 현상이 나타났다. 대기중 노출에 의해 드리프트 현상이 나타나며, 가열클리닝에 의해 오염에 의한 감습도 저하를 방지할 수 있다.

• 한국소음진동공학회논문집
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• 제13권11호
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• pp.845-851
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• 2003

The nonlinear vibration of moving viscoelastic belts excited by the eccentricity of pulleys is investigated through experimental and analytical methods. Laboratory measurements demonstrate the nonlinearities in the responses of the belt particularly in the resonance region and with the variation of tension, The measurements of the belt motion are made using noncontact laser sensors. Jump and hysteresis phenomenon are observed experimentally and were studied with a model. which considers the nonlinear relation of belt stretch. An ordinary differential equation is derived as a working form of the belt equation of motion, Numerical results show good agreements with the experimental observations, which demonstrates the nonlinearity of viscoelastic moving belts.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1992년도 하계학술대회 논문집 B
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• pp.685-688
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• 1992

This paper studies the commutation phenomenon in the Brushless DC Motor with the trapezoidal BEMF waveform. It is shown that the torque ripple am the speed ripple due to the phase commutation depend on driving sytem, operating speed am load condition. The effects of resistance and BEMF flat width on torque ripple are considered. Speed - torque characteristics of the motor is presented considering the phase commutation. Uncommutating current control method can attenuate the torque ripple in the low speed region, and also minimize the switching loss am switching frequency. In this paper, the commutation phenomena are verified by analytical formulation and simulation.

• The Journal of the Acoustical Society of Korea
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• 제21권3E호
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• pp.126-131
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• 2002

Ultrasonic measurements are made in egg white to study the properties of the solution of the natural protein. The high-Q ultrasonic resonator method is used to get the ultrasonic absorption spectra over the range 0.2-10 ㎒ at 20℃. It is proportional to the 1.25th power of the frequency. The gelation process caused by heat is studied from the change in the velocity and the absorption. at 3 ㎒ using the pulse echo overlap technique over the range of 10-80℃. The absorption decreases with increasing temperature up to 60℃ where it turns up sharply and rapidly increases thereafter. The strong absorption in the gel region is described by the interaction between the solution and the network structure made of protein. Very slow variation in time elapse is observed after the temperature is quickly raised. It would be a real-time observation of the network building process and the characteristic time for the process is shown to be 400 min. A hysteresis phenomenon with respect to the temperature is observed. This phenomenon is associated with the memorizing effect of the network structure of protein of the gel.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 춘계학술대회논문집
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• pp.836-841
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• 2002

The nonlinear vibration of moving viscoelastic belts excited by the eccentricity of pulleys is investigated through experimental and analytical methods. Laboratory measurements demonstrate the nonlinearities in the responses of the belt, particularly in the resonance region and with the variation of tension. The measurements of the belt motion were made using a noncontact laser sensor Jump and hysteresis phenomenon are observed experimentally and are studied with a model which considers the nonlinear relation of belt stretch. An ordinary differential equation is derived as a working form of the belt equation of motion. Numerical results show good agreements with the experimental observations, which demonstrates the nonlinearity of viscoelastic moving belts

• 한국통신학회논문지
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• 제36권3A호
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• pp.240-249
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• 2011

본 논문은 펨토셀시스템(femtocell system)의 단말(mobile station)이 핸드오버(handover)하기 전에 이웃한 기지국(neighbor station)의 정보를 공유하는 셀 관리(cell management) 기법과 핸드오버 방법에 대해 제안한다. 펨토셀시스템에서는 셀관리를 위해 수많은 펨토셀의 정보를 MOB_NBR-ADV메시지에 포함하여 방송하는데, 단말과 기지국에서 MOB_NBR-ADV메시지를 처리할 때 일시적인 부하가 발생된다. 따라서 효율적인 동작과 핸드오버 성공률 개선을 위해 MOB_NBR-ADV메시지의 구성 및 전송방법을 제안한다. 또한, 셀 간 중첩된 영역에서 핸드오버의 핑퐁(ping-pong) 현상을 막기 위해 히스테리시스 범위(hysteresis margin)를 이용한다. 그러나 수많은 펨토셀이 도입된 경우 기존의 히스테리시스범위 만으로 핑퐁현상을 막을 수 없다. 본 논문에서는 중첩된 셀의 개수가 증가하는 경우 히스테리시스범위가 커지는 방법과, 차등적으로 셀을 관리하여 불필요한 핸드오버의 횟수를 최소화하는 방법 등을 제안하였다. 컴퓨터 모의실험을 통해 성능 검증한 결과, 제안한 방식이 기존의 펨토셀 시스템의 셀 관리 및 핸드오버 방식에 비해 성능을 개선시키는 것을 확인하였다.

• 대한기계학회논문집B
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• 제23권11호
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• pp.1473-1480
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• 1999

In the case of Impingement of plane moving shock wave over concave or convex double wedges (pseudo-stationary flow) and cylindrical walls (truly non-stationary flow), it Is expected that there are transitions from regular reflection to Mach reflection or vice versa In shock wave reflections. In these connections, it is necessary to verify the various of reflection process and transition angle for the reflection problems In double wedges, and to verify the transition angle, effects of curvature radius and initial wall angle on it for the reflection problems In cylindrical walls. Especially, we focused our attention to confirm the existence of hysteresis phenomenon induced by the different transition processes, and Neumann paradox, which is a small discrepancy between theoretical and experimental transition angles. Experiments were carried out by using the shock tube of $6{\times}6cm^2$, and high speed photographic technique consisted of delay unit, triggering system, light source of Xe lamp and so on was used for flow visualization.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2005년도 춘계 학술발표회 논문집
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• pp.362-369
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• 2005

Studying unsaturated soil mechanics, determination of soil water characteristic curve and permeability equation is an essential factor but it is not easy. In this research a new testing apparatus was developed to determine soil water characteristic curve and permeability equation. The testing to get saturated permeability coefficients and soil water characteristic curves for two soils was performed by using the developed testing apparatus. First, a saturated permeability testing was performed and then the testing to get soil water characteristic curve of a drying process was performed. Next, the testing to get soil water characteristic curve of a wetting process was performed. Testing results showed hysteresis phenomena between soil water characteristic curve of a drying process and soil water characteristic curve of a wetting process. The permeability equations were determined by a theoretical method where a saturated permeability coefficient and a soil water characteristic curve were used.

• 한국지하수토양환경학회:학술대회논문집
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• 한국지하수토양환경학회 2000년도 추계학술대회
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• pp.107-118
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• 2000

For the last several decades, the fate of organic pollutants has been extensively studied in natural environments with emphasis on sorption and desorption phenomena. Although the mechanisms involved are not clear yet there is a consensus about the existence of hysteresis in the sorption and desorption of organic pollutants. Furthermore, it is found that hysteresis is the outcome of slow nonequilibrium sorption of organic pollutants, which results in the formation of desorption-resistant fractions of the pollutants. Desorption-resistant fractions may increase as a function of the residence time of the pollutants in the environments. Field monitoring data show a slow but continuous decline of chemicals applied to soil, followed by little or no subsequent disappearance. One plausible explanation for such resistance to biodegradation, desorption, or extraction can be attributed the gradual movement of organic pollutants to less accessible remote sites inside the matrix with time. This phenomenon has been termed sequestration or aging. The fact that some pollutants are sequestered in soil with time may have a great impact on bioremediation and risk assessment, Some portion of the resistant pollutants may still be present in the environments after bioremediation. It requires vigorous means to completely remove the aged portion that may not be further bioavailable. However, precaution should be taken since aging is not always evident. Aging seems to be soil and chemical specific.