• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2003년도 The Fifth Asian Computational Fluid Dynamics Conference
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• pp.294-298
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• 2003

The complex, unsteady, self-sustained pressure oscillations induced by supersonic flow past a rectangular cavity is investigated using numerical simulations. The present numerical study is performed using a parallel, multiblock solver for the two-dimensional, compressible Navier­Stokes equations. Open cavities with length-to-depth (L / D) ratio in the range 0.5 - 3.3 are considered. This paper sheds light on the cavity physics, cavity oscillatory mechanism, and the organisation of vortical structures inside the cavity. The vortex shedding phenomenon, the shear layer impingement event at the aft wall and the movement of the acoustic/compression wave within the cavity are well predicted. The vortical structures· and the source of the acoustic disturbances are found to be located near the aft wall of the cavity. With the increase in the cavity length, strong recompression of the flow near the aft wall leading to a sudden jump in the cavity form drag is observed. The estimated cavity tones are in good agreement with the available semi­empirical relation. Multiple peaks are noticed in deep and long cavities. For the present free­stream Mach number 1.71, it is observed that around L/D=2.0, the cavity oscillatory mechanism changes from the transverse to longitudinal oscillatory mode. The effects of this transition on various fluid dynamics and acoustic properties are also discussed.

• 한국수산과학회지
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• 제39권spc1호
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• pp.198-202
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• 2006

We investigated the fecundity, egg size, reproductive output, and breeding frequency and season of Neocaridina denticulata denticulata and Latreutes planirostris which inhabit extremely different habitats. The marine shrimp Latreutes planirostris produced more eggs had at a given carapace length than the freshwater shrimp N. d. denticulata. However, N. d. denticulata had a larger egg volume and greater reproductive output than L. planirostris. The monthly gonadosomatic index (GSI) of the freshwater shrimp began to increase in April and reached a maximum in May, suggesting a single breeding period. In contrast, the GSI of the marine shrimp exhibited two breeding peaks: May-June and September. In both shrimps, the regressions between carapace length and ovarian weight were significant at the non-eyed and eyed embryo stages. For both species, an analysis of covariance revealed significant difference between the two regressions in elevation, but not in slope. These results indicate the potential for multiple ovulations within the reproductive season.

• Journal of the Korean Wood Science and Technology
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• 제21권4호
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• pp.64-72
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• 1993

Mechanical properties of 15 mm thick, three-layer particleboard were studied by varying resin content, specific gravity, mat moisture content, pressing time and pressing temperature. Based on the results of the study, Multiple regression models were developed to estimate the mechanical properties of three-layer particleboard. The results of this study showed the mechanical properties of particleboard were highly related with resin content. specific gravity and mat moisture content in decending order. The mechanical properties were able to estimated as the linear function of resin content and specific gravity. However, the effects of change in mat moisture content on the mechanical properties showed a non-linear pattern. The mechanical properties curves over mat moisture content reached peaks at 15 %, and then decreased at 18 % and 21 % of mat moisture contents. On the other hand, the effects of pressing time and pressing temperature on the mechanical properties of particleboard were not significant.

• 한국통신학회논문지
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• 제31권6A호
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• pp.586-592
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• 2006

대역확산 시스템에서 나머지 도플러 주파수 오프셋이 (residual Doppler frequency offset, RDFO) 있으면 부호 동기가 정확히 맞을 때에도 표본화된 최고 상관값은 실제 상관값의 꼭지값보다 낮다. 이로 말미암아 기존 단일 주파수 셀 (single frequency cell, SFC) 검파기법의 성능은 떨어진다. 이 논문에서는 RDFO가 있을 때 실제 꼭지값 근처에 상관값이 큰 여러 표본이 존재하는 것에 착안하여 새로운 탐색기법을 제안한다. 이를 위해 먼저 대역 확산 시스템에서 RDFO가 성능을 떨어뜨리는지 분석한다. 그 뒤, 기존 기법과 제안한 기법의 검파확률과 오경보확률을 얻고, 모의실험을 수행하여 RDFO가 있을 때 제안한 기법이 기존 기법보다 성능이 뛰어남을 보인다.

• 약학회지
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• 제25권4호
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• pp.161-165
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• 1981

The binding of two cephalosporins, cephalothin and cefazoline to human serum albumin(HSA) was studied by difference spectrophotometry using a spectrophotometric probe, 2-(4'-hydroxybenzeneazo) benzoic acid. The probe is strong visible absorbing material which interacts with serum albumin to give characteristic spectrophotometric peaks and provides the basis for a convenient assay to measure free and bound amounts in the presence of serum albumin and competitive drugs. The results obtained showed that the probe and cephalosporin compete for the same binding site on human serum albumin; thus the probe can be used to gauge the displacement of cephalosporins from human serum albumin. The data were interpreted on the basis of theory of multiple equilibria. The number of binding sites of human serum albumin for 2-(4'-hydroxybenzeneazo) benzoic acid(HBAB), cephalothin and cefazoline appears to be 4. By using this technique the binding constants were found as follows: HSA-HBAB, $7.89{\times}10^{4}M^{-1}$; HSA-cephalothin, $1.09{\times}10^{3}M^{-1}$ ; HSA-cefazoline, $1.21{\times}10^{3}M^{-1}$.

• 한국산학기술학회논문지
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• 제7권6호
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• pp.1231-1236
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• 2006

영상의 화질을 개선하기 위한 많은 방법 중 비교적 간단하게 사용되는 방법 중 하나는 영상의 대비를 조절하는 것이다. 이러한 대비를 조절하는 방법 중 하나인 히스토그램 균등화는 영상 계조도 값의 분포를 균등 분포로 변환함으로써 화질을 개선한다. 그러나, 기존의 방법은 영상의 히스토그램 분포가 몇개의 계조도 값에 군집화되어 있다면 영상의 계조도가 과도하게 변하는 단점을 갖는다. 본 논문은 그레이스케일 영상에 대해 히스토그램의 형태를 고려해서 가우시안 함수에 기반한 히스토그램 매칭 방법을 제안한다. 제안된 방법은 영상이 과도하게 밝아지는 것을 제한하고 히스토그램의 분포가 몇 개의 계조도에 군집화되어 있는 영상에서의 에지 및 어두운 부분의 자세한 정보를 표현하는데 우수한 성능을 나타내었다.

• Journal of Power Electronics
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• 제19권5호
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• pp.1248-1258
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• 2019

This paper presents a moth-flame optimization (MFO)-based maximum power point tracking (MPPT) method for photovoltaic (PV) systems. The MFO algorithm is a new optimization method that exhibits satisfactory performance in terms of exploration, exploitation, local optima avoidance, and convergence. Therefore, the MFO algorithm is quite suitable for solving multiple peaks of PV systems under partial shading conditions (PSCs). The proposed MFO-MPPT is compared with four MPPT algorithms, namely the perturb and observe (P&O)-MPPT, incremental conductance (INC)-MPPT, particle swarm optimization (PSO)-MPPT and whale optimization algorithm (WOA)-MPPT. Simulation and experiment results demonstrate that the proposed algorithm can extract the global maximum power point (MPP) with greater tracking speed and accuracy under various conditions.

• International Journal of Naval Architecture and Ocean Engineering
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• 제13권1호
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• pp.65-74
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• 2021

A key factor that governs the wave interferences of a submerged body is the dimensionless Froude number. Computational Fluid Dynamics (CFD) is used to describe the resistance force coefficients and the generated waves of two SUBOFF submarine models. Grid independence studies are performed on two cases, totally and shallowly submerged cases, with four sets of computing meshes. The highest peaks are marked by red points at given wavelengths, a line is fitted to those points with a least-squares approximation, and the half wake angle at multiple Froude numbers is defined between the fitted line and the centerline of the free surface. The results show that when the depth of the target is 1.1D, constructive interferences occur at Fn = 0.3 and 0.5, while destructive interference occurs at Fn = 0.35 with distortion of the waveform. The half wake angle is less than 19.47° because of the interference between the bow and stern wave systems.

• ETRI Journal
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• 제45권2호
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• pp.267-276
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• 2023

R&D strategies of companies with low and high technological levels are discussed based on the concept of technology convergence and divergence. However, empirically detecting enterprise technology convergence in the distribution of enterprise technology (total productivity increase) over time and identifying key change factors are challenging. This study used a novel statistical indicator that captures the internal technology distribution change with a single number to clearly measure the technology distribution peak as a change in critical bandwidth for enterprise technology convergence and presented it as evidence of each technology convergence or divergence. Furthermore, this study applied the quantitative technology convergence identification method. Technology convergence appeared from the separation of total corporate productivity distribution of 69 IT companies in Korea in 2019-2020 rather than in 2015-2016. Results indicated that when the total technological level was separated from the technology leading and technology catch-up, IT companies were found to be pursuing R&D strategies for technology catch-up.

• 한국정보통신학회논문지
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• 제19권2호
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• pp.414-421
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• 2015

본 논문에서는 두 사람의 합쳐진 심전도 신호를 분리하여 개인의 심전도 신호로 복원하는 방법을 제안한다. 합쳐진 심전도 신호를 분리하기 위해, 두 사람의 평균 심전도 신호를 사전에 측정하여 가지고 있다고 가정한다. 평균 심전도 신호는 합쳐진 심전도 신호에서 개인의 심전도 신호를 식별하는데 활용될 수 있다. 심전도 신호는 거의 주기 신호의 특성을 가지고 있기 때문에, 자기상관성을 구하면 심박 수의 배수마다 높은 피크 값을 가진다. 이를 통해 각 개인의 심박 주기를 파악할 수 있다. 파악된 두 사람 각각의 주기와 평균 심전도 신호를 이용하여 각각의 R-peak가 어느 사람의 R-peak인지 분류할 수 있다. 즉, 각 사람의 평균심전도 신호를 찾아진 R-peak위치에 배치하여 각 사람의 심전도신호의 추정신호를 만든 뒤 각 신호에 가중치를 얼마나 줘야 하는지 LMSE 최적화를 통해 계산된다. 이 가중치를 기반으로 복원신호를 만들어낸다. 이 복원신호에 에러 신호를 각 복원신호의 비율만큼 더해주는 추가 보정작업을 거침으로써 보다 실질적인 신호로 복원한다. 실험 결과를 통해 합쳐진 심전도 신호가 성공적으로 개인의 심전도 신호로 분리되는 것을 알 수 있다.