• Journal of Advanced Research in Ocean Engineering
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• 제3권4호
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• pp.165-173
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• 2017

This study aims at validating simulations of the forced and freely vibrating cylinders at Reynolds number of approximately 500 in order to identify the capability of the CFD code, and to establish the analysis process of the vortex-induced vibration (VIV). The direct numerical and large eddy simulations were employed to resolve the various length scales of the vortices, and the morphing technique was used to consider a motion of the circular cylinder. For the forced vibration case, both in- and anti-phase VIV processes were observed regarding the frequency ratio. Namely, when the frequency ratio approaches to unity, the synchronization/lock-in process occurs, leading to substantial increases in drag and lift coefficients. This is strongly linked with the switch in timing of the vortex formation, and this physical tendency is consistent with that of Blackburn and Henderson (J. Fluid Mech., 1999, 385, 255-286) as well as force coefficients. For the free oscillation case, the mass and damping ratio of 50.8 and 0.0024 were considered based on the study of Blackburn et al. (J. Fluid Struct., 2000, 15, 481-488) to allow the direct comparison of simulation results. The simulation results for a peak amplitude of the cylinder and a shedding mode are reasonably comparable to that of Blackburn et al. (2000). Consequently, based on aforementioned results, it can be concluded that numerical methods were successfully validated and the calculation procedure was well established for VIV analysis with reasonable results.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 춘계학술대회 논문집
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• pp.1223-1227
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• 2005

Fine microgroove is the key component to fabricate micro-grating, micro-grating lens and so on. Conventional groove fabrication methods such as etching and lithography have some problems in efficiency and surface integrity. This study deals with the creation of ultra-precision micro grooves using non-rotational diamond tool and CNC machining center. The shaping type machining method proposed in the study allows to produce V-shaped grooves of $40\mu{m}$ in depth with enough dimensional accuracy and surface. For the analysis of machining characteristics in micro V-grooving, three components of cutting forces and AE signal are measured and processed. Experimental results showed that large amplitude of cutting forces and AE appeared at the beginning of every cutting path, and cutting forces had a linear relation with the cross-sectional area of uncut chip thickness. From the results of this study, proposed micro V-grooving technique could be successfully applied to forming the precise optical parts like prism patterns on light guide panel of TFT-LCD.

• 한국정보처리학회논문지
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• 제7권12호
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• pp.3885-3895
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• 2000

디지털 이미지 기법과 디지털 네트웍의 출현으로 예술적 작품의 복사가 더욱 쉬워지고 있다. 이러한 창작품을 보호하기 위해 데이터 안에 저작권을 표시할 수 있는 표식이나 인식 가능한 데이터를 삽입하는 기술이 필요해지고 있고 지난 몇 년간 디지털 이미지나 오디오, 비디오 등의 멀티미디어 데이터에 저작권을 표시하기 위한 데이터나 기타 다른 정보를 삽입할 수 있는 많은 기법들이 제안되어 왔다. 본 논문에서는 이미지의 주파수 영역에 인식 가능한 패턴을 삽입하고 추출하는 워트마킹 기법을 제안한다. 또한 삽입된 워터마크를 원본이미지의 정보 없이 추출할 수 있도록 하여 임의의 사람이 워터마크 된 이미지로부터 가짜원본을 생성하는 것이 어렵도록 한다. 원본정보 없이 워터마크를 추출하기 위해서 화소의 원래 값을 예측하는 방법을 사용한다. 예측기법은 구하고자 하는 화소의 주위값을 평균한다는 것을 의미한다. 부가적으로 워터마크를 이미지 주파수 영역에 삽입함으로써 JPEG같은 손실압축바업에도 견딜 수 있도록 한다.

• Journal of Power Electronics
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• 제11권2호
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• pp.228-236
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• 2011

The ${\Delta}\;V_{10}$ or 10-Hz flicker index, as a common method of measurement of voltage flicker severity in power systems, requires a high computational cost and a large amount of memory. In this paper, for measuring the ${\Delta}\;V_{10}$ index, a new method based on the Adaline (adaptive linear neuron) system, the FFT (fast Fourier transform), and the PSO (particle swarm optimization) algorithm is proposed. In this method, for reducing the sampling frequency, calculations are carried out on the envelope of a power system voltage that contains a flicker component. Extracting the envelope of the voltage is implemented by the Adaline system. In addition, in order to increase the accuracy in computing the flicker components, the PSO algorithm is used for reducing the spectral leakage error in the FFT calculations. Therefore, the proposed method has a lower computational cost in FFT computation due to the use of a smaller sampling window. It also requires less memory since it uses the envelope of the power system voltage. Moreover, it shows more accuracy because the PSO algorithm is used in the determination of the flicker frequency and the corresponding amplitude. The sensitivity of the proposed method with respect to the main frequency drift is very low. The proposed algorithm is evaluated by simulations. The validity of the simulations is proven by the implementation of the algorithm with an ARM microcontroller-based digital system. Finally, its function is evaluated with real-time measurements.

• 한국전자파학회논문지
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• 제20권1호
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• pp.67-74
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• 2009

본 논문에서는 광 이중 측파대역 변조 방식과 16 QAM(Quadrature Amplitude Modulation) 신호를 이용한 부반송파/파장 분할 다중화 시스템의 성능을 부반송파 채널 간격, 누화 전력 량(crosstalk power), BER(Bit-Error Rate) 특성을 통해 연구하고 있다. 광 전송 링크에서 분산 특성과 자기 위상 변조, 상호 위상 변조와 같은 비선형 현상을 고려하였을 때 BER특성을 살펴보았다. 컴퓨터 시뮬레이션 결과, 부반송파/파장 분할 다중화 시스템의 성능을 결정짓는 주도적인 인자는 마흐-젠더 변조기의 비선형 특성과 부반송파 채널 간격으로 관찰되었다. 광섬유의 분산에 의한 영향만 고려했을 때는 전송거리가 증가함에 따라 높은 주파수에 있는 부반송파 채널의 BER 성능이 나빠졌으나, 분산과 비선형 효과를 함께 고려되었을 경우 광섬유에 입사하는 전력이 클 때 높은 주파수에 있는 부반송파 채널에서 약간의 BER 성능 향상을 확인할 수 있었다.

• Journal of Korean Neurosurgical Society
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• 제38권5호
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• pp.375-379
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• 2005

Objective : Papaverine has been used in treating vasospasm following subarachnoid hemorrhage[SAH]. However, its action mechanism for cerebral vascular relaxation is not clear. Potassium channels are closely related to the contraction and relaxation of cerebral smooth muscle. Therefore, to identify the role of potassium and calcium channels in papaverine-induced vascular relaxation, we examine the effect of papaverine on potassium channels in freshly isolated smooth muscle cells from rat basilar artery. Methods : The isolation of rat basilar smooth muscle cells was performed by special techniques. The whole cell currents were recorded by whole cell patch clamp technique in freshly isolated smooth muscle cells from rat basilar artery. Papaverine was added to the bath solution. Results : Papaverine of $100{\mu}M$ into bath solution increased the amplitude of the outward $K^+$ current which was completely blocked by BKCa[large conductance calcium dependent potassium channels]blocker, IBX[iberiotoxin], and calcium chealator, BAPTA[l,2-bis[o-aminophenoxy]ethane-N,N,N',N'-tetraacetic acid], in whole cell mode. Conclusion : These results strongly suggest that potassium channels may play roles in papaverine-induced vascular relaxation in rat basilar artery.

• 한국정보통신학회논문지
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• 제20권1호
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• pp.222-229
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• 2016

수중에서 운용되는 소형 무인정 탑재 능동 합성개구면소나는 외부에서 발생되는 수중환경의 영향으로 플렛품 진행시 여러 가지 궤적 교란이 발생하게 되고 개구면 합성처리에 있어서 많은 오차를 가져 온다. 본 논문에서는 진행현측방향으로 주기적 및 랜덤 궤적교란이 발생될 때 합성개구면 초점처리에 의한 위상차 부정합에 따른 방위해상도에 미치는 영향을 비교 분석하였다. 시뮬레이션 결과, 주기적 궤적교란은 발생 교란 크기가 $0.3{\lambda}$, 변동 주기가 $2L_{sa}$보다 커지면 허위표적이 발생되고 방위해상도가 매우 나빠지게 되며, 합성개구면처리에 의한 해저 소형물체 탐지성능은 플렛폼의 궤적변동 종류와 조건에 따라서 방위해상도에 많은 영향을 미치는 특성을 나타내었다.

• The Korean Journal of Physiology
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• 제29권2호
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• pp.233-241
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• 1995

The nonapeptide bradykinin has been shown to exhibit an array of biological activities including relaxation/contraction of various smooth muscles. In order to investigate the effects of bradykinin on the contractility and the electrical activity of antral circular muscle of guinea-pig stomach, the isometric contraction and membrane potential were recorded. Also, using standard patch clamp technique, the $Ca^{2+}-activated$ K currents were recorded to observe the change in cytosolic $Ca^{2+}$ concentration. $0.4 {\mu}M$ bradykinin induced a triphasic contractile response (transient contraction-transient relaxation-sustained contraction) and this response was unaffected by pretreatment with neural blockers (tetrodotoxin, atropine and guanethidine) or with apamin. Bradykinin induced hyperpolarization of resting membrane potential and enhanced the amplitude of slow waves and spike potentials. The enhancement of spike potentials was blocked by neural blockers. Both the bradykinin-induced contractions and changes in membrane potential were reversed by the selective $B_2$-receptor antagonist $(N{\alpha}-adamantaneacetyl-_{D}-Arg-[Hyp, Thy,_{D}-Phe]-bradykinin)$. In whole-cell patch clamp experiment, we held the membrane potential at -20 mV and spontaneous and transient changes of Ca-activated K currents were recorded. Bradykinin induced a large transient outward current, consistent with a calcium-releasing action of bradykinin front the intracellular calcium pool, because such change was blocked by pretreatment with caffeine. Bradykinin-induced contraction was also blocked by pretreatment with caffeine. From these results, it is suggested that bradykinin induces a calciumrelease and contraction through the $B_{2}$ receptor of guinea-pig gastric smooth muscle. Enhancement of slow wave activity is an indirect action of bradykinin through enteric nerve cells embedded in muscle strip.

• 대한의용생체공학회:의공학회지
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• 제29권6호
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• pp.436-442
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• 2008

Magnetic resonance electrical impedance tomography(MREIT) has been suggested to produce cross-sectional conductivity images of an electrically conducting object such as the human body. In most previous studies, recessed electrodes have been used to inject imaging currents into the object. An MRI scanner was used to capture induced magnetic flux density data inside the object and a conductivity image reconstruction algorithm was applied to the data. This paper reports the performance of a thin and flexible carbon-hydrogel electrode that replaces the bulky and rigid recessed electrode in previous studies. The new carbon-hydrogel electrode produces a negligible amount of artifacts in MR and conductivity images and significantly simplifies the experimental procedure. We can fabricate the electrode in different shapes and sizes. Adding a layer of conductive adhesive, we can easily attach the electrode on an irregular surface with an excellent contact. Using a pair of carbon-hydrogel electrodes with a large contact area, we may inject an imaging current with increased amplitude primarily due to a reduced average current density underneath the electrodes. Before we apply the new electrode to a human subject, we evaluated its performance by conducting MREIT imaging experiments of five swine legs. Reconstructed conductivity images of the swine legs show a good contrast among different muscles and bones. We suggest a future study of human experiments using the carbon-hydrogel electrode following the guideline proposed in this paper.

• Smart Structures and Systems
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• 제17권3호
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• pp.363-389
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• 2016

Deficient modes that cannot be always identified from different sets of measurement data may exist in the application of operational modal analysis such as the stochastic subspace identification techniques in large-scale civil structures. Based on a recent work using the long-term ambient vibration measurements from an instrumented cable-stayed bridge under different wind excitation conditions, a benchmark problem is launched by taking the same bridge as a test bed to further intensify the exploration of mode identifiability. For systematically assessing this benchmark problem, a recently developed SSI algorithm based on an alternative stabilization diagram and a hierarchical sifting process is extended and applied in this research to investigate several sets of known and blind monitoring data. The evaluation of delicately selected cases clearly distinguishes the effect of traffic excitation on the identifiability of the targeted deficient mode from the effect of wind excitation. An additional upper limit for the vertical acceleration amplitude at deck, mainly induced by the passing traffic, is subsequently suggested to supplement the previously determined lower limit for the wind speed. Careful inspection on the shape vector of the deficient mode under different excitation conditions leads to the postulation that this mode is actually induced by the motion of the central tower. The analysis incorporating the tower measurements solidly verifies this postulation by yielding the prevailing components at the tower locations in the extended mode shape vector. Moreover, it is also confirmed that this mode can be stably identified under all the circumstances with the addition of tower measurements. An important lesson learned from this discovery is that the problem of mode identifiability usually comes from the lack of proper measurements at the right locations.