• 한국전자파학회논문지
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• 제27권6호
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• pp.577-580
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• 2016

모노펄스 레이더에 대한 효과적인 재밍은 전파를 왜곡시키는 것이다. 그 중 대표적인 전파왜곡 기법은 두 개의 송신기를 이용하는 크로스 아이 기법이다. 크로스 아이 기법은 모노펄스 레이더의 구현 구조에 관계없이 각도를 기만할 수 있지만, 충분한 각도기만 효과를 갖기 위해서는 두 송신기의 위상 및 진폭 정확도가 확보되어야 한다. 이러한 위상 및 진폭 정확도는 전파왜곡 시스템을 구현하는데 있어서 핵심적인 요구 성능 파라미터이고, 목표로 하는 각도 오차에 따라 그 요구값이 달라진다. 본 논문에서는 목표하는 각도 오차에 따라 필요한 최소 위상차 및 진폭비를 수식으로 유도하고 그 결과를 분석한다.

• The Korean Journal of Physiology and Pharmacology
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• 제10권1호
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• pp.7-11
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• 2006

Interstitial cells of Cajal (ICCs) are pacemakers in gastrointestinal tracts, regulating rhythmicity by activating nonselective cation channels (NSCCs). In the present study, we investigated the general characteristics and pH-mediated regulation of pacemaker activity in cultured interstitial cells of Cajal. Under voltage clamp mode and at the holding potential of -60 mV, the I-V relationships and difference current showed that there was no reversal potential and voltage-independent inward current. Also, when the holding potentials were changed from +20 mV to -80 mV with intervals of 20 mV, there was little difference in inward current. In pacemaker activity, the resting membrane potential (RMP) was depolarized (In pH 5.5, $23{\pm}1.5$ mV depolarized) and the amplitude was decreased by a decrease of the extracellular pH. However, in case of increase of extracellular pH, the RMP was slightly hyperpolarized and the amplitude was decreased a little. The melastatin type transient receptor potential (TRPM) channel 7 has been suggested to be required for intestinal pacemaking activity. TRPM7 produced large outward currents and small inward currents by voltage ramps, ranging from +100 to -100 mV from a holding potential of -60 mV. The inward current of TRPM7 was dramatically increased by a decrease in the extracellular pH. At pH 4.0, the average inward current amplitude measured at -100 mV was increased by about 7 fold, compared with the current amplitude at pH 7.4. Changes in the outward current (measured at +100 mV) were much smaller than those of the inward current. These results indicate that the resting membrane potential of pacemaking activity might be depolarized by external acidic pH through TRPM7 that is required for intestinal pacemaking activity.

• International Journal of Naval Architecture and Ocean Engineering
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• 제11권2호
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• pp.875-882
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• 2019

The effects of Triangle Groove Strips (TGS) on Vortex-induced Vibration (VIV) suppression of marine riser are numerically investigated using Computational Fluid Dynamics (CFD) method. The range of Reynolds number in simulations is 4.0 × 10⁴ < Re < 1.2 × 10⁵. The two-dimensional unsteady Reynolds-Averaged Navier-Stokes (RANS) equations and Shear Stress Transport (SST) k-ω turbulence model are used to calculate the flow around marine riser. The Newmark-β method is employed for evaluating the structure dynamics of marine riser. The effect of the height ratio (ε) of TGS on VIV suppression is evaluated. The amplitude responses, frequency responses, vortex patterns and the flow around the structures are discussed in detail. With the increase of the height ratio of TGS, the suppression effect of TGS on VIV suppression is improved firstly and then weakened. When ε=0.04, the suppression effect of TGS is the best. Compared with the VIV responses of smooth marine riser, the amplitude ratio is reduced by 38.9%, the peak of the lift coefficient is reduced by 69% and the peak of the drag coefficient is reduced by 40% when Re=6.0 × 10⁴. With the increase of Reynolds number, the suppression effect of TGS on VIV suppression is improved firstly and then weakened. When the Reynolds number is 7.0 × 10⁴, the amplitude ratio can be reduced by 40.1%. As to the large-amplitude vibration cases, the TGS show nice suppression effect on VIV.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2006년도 Asia Navigation Conference
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• pp.134-143
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• 2006

Out of all types of motions the critical motions leading to capsize is roll. The dynamic amplification in case of roll motion may be large for ships as roll natural frequency generally falls within the frequency range of wave energy spectrum typical used for estimation of motion spectrum. Roll motion is highly non-linear in nature. Den are various representations of non-linear damping and restoring available in literature. In this paper an uncoupled non-linear roll equations with three representation of damping and cubic restoring term is solved using a perturbation technique. Damping moment representations are linear plus quadratic velocity damping, angle dependant damping and linear plus cubic velocity dependant damping. Numerical value of linear damping coefficient is almost same for all types but non-linear damping is different. Linear and non-linear damping coefficients are obtained form free roll decay tests. External rolling moment is assumed as deterministic with sinusoidal form. Maximum roll amplitude of non-linear roll equation with various representations of damping is calculated using analytical procedure and compared with experimental results, which are obtained form forced tests in regular waves by varying frequency with three wave heights. Experiments indicate influence of non-linearity at resonance frequency. Both experiment and analytical results indicates increase in maximum roll amplitude with wave slope at resonance. Analytical results are compared with experiment results which indicate maximum roll amplitude analytically obtained with angle dependent and cubic velocity damping are equal and difference from experiments with these damping are less compared to non-linear equation with quadratic velocity damping.

• Structural Engineering and Mechanics
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• 제80권5호
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• pp.491-501
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• 2021

A difference in subgrade settlement between two rails of a track manifests as lateral differential subgrade settlement. This settlement causes unsteadiness in the motion of trains passing through the corresponding area. To illustrate the effect of lateral differential subgrade settlement on the dynamic response of a vehicle-track coupling system, a three-dimensional vehicle-track-subgrade coupling model was formulated by combining the vehicle-track dynamics theory and the finite element method. The wheel/rail force, car body acceleration, and derailment factor are chosen as evaluation indices of the system dynamic response. The effects of the amplitude and wavelength of lateral differential subgrade settlement as well as the driving speed of the vehicle are analyzed. The study reveals the following: The dynamic responses of the vehicle-track system generally increase linearly with the driving speed when the train passes through a lateral subgrade settlement area. The wheel/rail force acting on a rail with a large settlement exceeds that on a rail with a small settlement. The dynamic responses of the vehicle-track system increase with the amplitude of the lateral differential subgrade settlement. For a 250-km/h train speed, the proposed maximum amplitude for a lateral differential settlement with a wavelength of 20 m is 10 mm. The dynamic responses of the vehicle-track system decrease with an increase in the wavelength of the lateral differential subgrade settlement. To achieve a good operation quality of a train at a 250-km/h driving speed, the wavelength of a lateral differential subgrade settlement with an amplitude of 20 mm should not be less than 15 m. Monitoring lateral differential settlements should be given more emphasis in routine high-speed railway maintenance and repairs.

• Wind and Structures
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• 제6권6호
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• pp.451-470
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• 2003

The classical two-degree-of-freedom (2-d-o-f) "sectional model" is of common use to study the dynamics of suspension bridges. It takes into account the first pair of vertical and torsional modes of the bridge and describes well global oscillations caused by wind actions on the deck, yielding very useful information on the overall behaviour and the aerodynamic and aeroelastic response; however, it does not consider relative oscillations between main cables and deck. On the contrary, the 4-d-o-f model described in the two Parts of this paper includes longitudinal deformability of the hangers (assumed linear elastic in tension and unable to react in compression) and thus allows to take into account not only global oscillations, but also relative oscillations between main cables and deck. In particular, when the hangers go slack, large nonlinear oscillations are possible; if the hangers remain taut, the oscillations remain small and essentially linear: the latter behaviour has been the specific object of Part I (Sepe and Augusti 2001), while the present Part II investigates the nonlinear behaviour (coexisting large and/or small amplitude oscillations) under harmonic actions on the cables and/or on the deck, such as might be generated by vortex shedding. Because of the discontinuities and strong nonlinearity of the governing equations, the response has been investigated numerically. The results obtained for sample values of mechanical and forcing parameters seems to confirm that relative oscillations cannot a priori be excluded for very long span bridges under wind-induced loads, and they can stimulate a discussion on the actual possibility of such phenomena.

• Structural Engineering and Mechanics
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• 제21권1호
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• pp.53-66
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• 2005

When a large number of identical cylinders are placed in an array with equal separation distance, near-resonant phenomena may occur between cylinders at critical frequencies, and cause large wave forces on each element of the array. In this paper, 64 truncated circular cylinders arranged in 4 rows and 16 columns are considered to check occurrence of near-resonant phenomena and performance of theoretical predictions based on the potential flow. Experiments are conducted in head waves to measure the wave elevation along the longitudinal centerline of the model, and measured results are compared with numerical ones. Attention is focused on the spatial variation of the wave amplitude around the first near-trapped-mode frequency.

• 한국농공학회논문집
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• 제48권5호
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• pp.63-71
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• 2006

In the present study, the dynamic deformation characteristics of clay, including the effect of loading rate in large strain ranges, were examined by performing undrained cyclic triaxial test. The test results showed that the loading rate to failure decreased with increasing loading amplitude and decreasing loading frequency. While the stress-strain relationships was not affected by loading frequency, excess pore pressure was affected significantly with the change in loading frequency. The change for 0.1 Hz was larger for than that of 0.01 Hz, resulting in inclined effective stress paths. Furthermore, the lower the frequency was, the higher the excess pore pressure was in the first loading.

• 반도체디스플레이기술학회지
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• 제13권4호
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• pp.33-36
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• 2014

In this paper, a carbon strain gauge for large strain was developed. The carbon strain gauge was fabricated by forming PCB and antenna pattern using Cu/Ni/Au film and carbon resistor pattern using screen printing process on plastic film substrate. It was possible to develop low-cost disposable strain gauge since the carbon paste was cheap and the fabrication process was simple. The wireless communication type carbon strain gauge was fabricated by integrating signal processing circuit, antenna and power all together on the same substrate as a strain gauge. The wireless communication type carbon strain gauge has a merit of being available immediately at the spot without any particular system.

• 지구물리와물리탐사
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• 제4권4호
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• pp.115-123
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• 2001

탄성파 중합 단면도 상에서 천연가스 부존 여부를 지시하는 명점(bright spot)은 가스 층이외에 음향계수 차이가 큰 지층에서도 나타나므로 가스 층여부를 판단하기 위해서는 속도분석, AVO 분석, 탄성파 복소 트레이스 분석 등 추가적인 정밀 자료처리가 필요하다. 본 연구에서는 가스 층 추정을 위해 정밀 속도분석과 트레이스 복소분석 그리고 입사각에 따른 진폭변화 결과인 탄화수소 직접 지시 단면도(DHI)분석을 실시하였다. 트레이스 복소분석은 지층 상$\cdot$하간의 물성변화에 따른 지질정보를 제공하는것으로 여기에서는 순간 진폭, 순간 진폭에 대한 1차 및 2차 미분 값, 순간 위상, 순간 주파수, 가중평균 순간 주파수 값을 구하여 시추가 이루어진 국내 대륙붕 탄성파 자료에 적용하였다. 자료처리 결과 가스가 부존할 가능성이 높은 지역에서는 순간 진폭, 순간 주파수 단면도 그리고 AVO 분석에 의한 DHI 단면도에서 공통적으로 탄성파 진폭이상이 나타나며 정밀 자료처리 결과 중 어느 한 곳이라도 진폭이상이 나타나지 않으면 가스 부존 가능성이 낮다고 할 수 있다.