• 한국정보통신학회:학술대회논문집
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• 한국정보통신학회 2017년도 추계학술대회
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• pp.671-673
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• 2017

그룹 속도 분산과 비선형 효과의 상호 작용에 의해 왜곡되는 WDM 신호의 보상을 위한 분산 제어에 광 위상 공액기 (OPC; optical phase conjugator)가 적용된 링크에서 OPC가 전체 전송 링크의 중간 (midway)가 아닌 다양한 곳에 위치하는 경우 각각의 최대 중계 수를 도출해보았다.

• Water Engineering Research
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• 제1권4호
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• pp.293-298
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• 2000

Optimal values of $\alpha$ characterizing the linear dispersion property in the modified Boussinesq equations are determined by minimizing the combined relative errors of the phase and group velocities. The value of $\alpha$ is fixed in previous studies, whereas it is varying in the present study. The phase and group velocities are calculated by using variable $\alpha$ and compared to those of the linear Stokes wave theory and previous studies. It is found that the present study produces the best match to the linear Stokes theory.

• 한국수자원학회논문집
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• 제48권4호
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• pp.291-298
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• 2015

본 연구의 목적은 하천에서 흐름방향 유속의 횡분포식에 기반하여 1차원 종분산계수를 이론적으로 유도하고 이들의 타당성을 검증하는 것이다. 이를 위해 본 논문의 전편 "I. 흐름방향 유속의 횡포식"에서는 Shiono-Knight Model (일명 SKM)을 도입하여 삼각형 단면수로에서 횡분포식을 해석적으로 유도하였다. 본 논문의 후편 "II. 종분산계수"에서는 전편에서 유도된 유속의 횡분포식을 Fischer (1968)의 삼중 적분식에 대입하여 1차원 종분산계수 이론식을 새롭게 개발하였다. 본래 SKM은 Navier-Stokes 방정식을 근간으로 개발되어 주로 직선수로이면서 사다리꼴 단면이나 복단면 수로에 적용되어 왔지만, 본 연구에서는 사행으로인한 최심선의 변동을 고려할 수 있는 삼각형을 단면형상으로 가정하였다. 유도된 해석해를 검증하기 위해 자연하천에서 실측된 유속자료와 비교 분석하였다. 또한 유도된 횡분포식을 이용하여 단면평균유속을 산정하고, 이를 Manning의 유속식의 결과와 비교 검증하였다. 본 연구에서 개발한 이론식은 비록 유속의 횡분포를 경우에 따라서 섬세하게 재현하지는 못하더라도 조도계수를 포함한 몇 가지 기본적인 수리 및 지형자료만 측량한다면 유속의 관측없이 비교적 정확한 유속분포를 산출해 낼 수 있는 장점이 있었다.

• 대한기계학회논문집B
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• 제23권2호
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• pp.218-225
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• 1999

Flow visualization study has been conducted to simulate the turbulent dispersion behavior of a crossflow jet physically under the conditions of various thermal stratification in a wind tunnel. A smoke jet with the constant ratio of the jet to freestream velocity is injected normally to the cross flow of the thermally stratified wind tunnel(TSWT) for flow visualization. The typical natures of the smoke dispersion under different thermal stratifications such as neutral, weakly stable, strongly stable, weakly unstable, strongly unstable and inversion layer are successfully reproduced in the TSWT. The Instantaneous velocity and temperature fluctuations are measured by using a cold and hot-wire combination probe. The time averaged dispersion behaviors, the centerline trajectories, the spreading angles and the virtual origins of the cross jet are deduced from the edge detected images with respect to the stability parameter. All the general characteristics of the turbulent dispersion behavior reveal that the definitely different dispersion mechanisms are inherent in both stable and unstable conditions. It is conjectured that the turbulent statistics obtained in the various stability conditions quantitatively demonstrate the vertical scalar flux plays a key role in the turbulent dispersion behavior.

• 한국시뮬레이션학회논문지
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• 제28권3호
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• pp.83-89
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• 2019

본 연구는 회전 비행체(Magnus rotor)를 탑재한 분산탄두의 분산 균일도에 미치는 요인 분석과 성능지표를 도출하기 위해 모탄의 속도 V와 회전속도 ${\omega}$, 비행경로각(flight path angle) ${\gamma}$ 그리고 고도 h의 변화에 따른 해석 결과를 기술했으며, 이때 모탄의 회전속도와 속도의 비를 새로운 변수로 정의했다. 자탄의 분산 해석에는 풍동실험을 통해 획득한 공력계수를 사용한 6 자유도 운동방정식을 이용했으며, 분산도 분석을 위해 회귀분석과 결정계수를 구해 분산도를 평가했다. 해석결과 최적의 회전속도와 낙하속도의 비, 비행경로각(flight path angle)을 구할 수 있었으며, 방출고도는 분산도에 회전속도와 낙하속도의 비, 비행경로각(flight path angle)의 영향에 비해 영향은 크지 않고, 자탄의 분산반경에 영향이 큰 것을 확인했다.

• 대한기계학회논문집B
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• 제27권8호
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• pp.1165-1173
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• 2003

The effects of (1) phonon dispersion on thermal conductivity model and (2) differentiation of group velocity and phase velocity are examined for germanium. The results show drastic change of thermal conductivity regardless of the same relaxation time model. Also the contribution of transverse acoustic (TA) phonon and longitudinal acoustic (LA) phonon on the thermal conductivity at high temperatures is reassessed by considering more rigorous dispersion model. Holland model, which is commonly used for modeling thermal conductivity, underestimates the scattering rate for TA phonon at high frequency. This leads the conclusion that TA is dominant heat transfer mode at high temperatures. But according to the rigorous consideration of phonon dispersion, the reduction of thermal conductivity is much larger than the estimation of Holland model, thus the TA at high frequency is expected to be no more dominant heat transfer mode. Another heat transfer mechanism may exist at high temperatures. Two possible explanations we the roles of (1) Umklapp scattering of LA phonon at high frequency and (2) optical phonon.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.1627-1632
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• 2003

The effect of (1) phonon dispersion in thermal conductivity model and (2) the differentiation of group velocity and phase velocity for Ge is examined. The results show drastic change of thermal conductivity regardless of using same relaxation time model. Also the contribution of transverse acoustic (TA) phonon and longitudinal acoustic (LA) phonon is changed by considering more rigorous dispersion model. Holland model underestimates the scattering rate for high frequency TA, so misleading conclusion, i.e. TA is dominant heat transfer mode at high temperature. But the actual reduction of thermal conductivity is much larger than the estimation by Holland model and high frequency TA is no more dominant heat transfer mode. Another heat transfer mechanism may exist for high temperature. Two possible explanations are (1) high frequency LA by Umklapp scattering and (2) optical phonon.

• 천문학회보
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• 제41권1호
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• pp.35.2-35.2
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• 2016

We present a census of AGN-driven gas outflows based on the kinematics of ionized gas and stars, using a large sample of ~11,000 emission line galaxies at z < 0.3, selected from SDSS. First, a broad correlation between gas and stellar velocity dispersions indicates that the bulge gravitational potential plays a main role in determining the ionized gas kinematics. However, the velocity dispersion of the [OIII] emission line is larger than stellar velocity dispersion by a factor of 1.3-1.4, suggesting that the non-gravitational (non-virial) component, i.e., outflows, is almost comparable to the gravitational component. Second, gas-to-stellar velocity dispersion ratio increases with both AGN luminosity and Eddington ratio, suggesting that non-gravitational kinematics are clearly linked to AGN accretion. The distribution in the [OIII] velocity - velocity dispersion diagram dramatically expands toward large values with increasing AGN luminosity, implying that the launching velocity of gas outflows increases with AGN luminosity. Third, the fraction of AGNs with a signature of the non-gravitational kinematics, steeply increases with AGN luminosity and Eddington ratio, while the majority of luminous AGNs presents the non-gravitational kinematics in the [OIII] profile. These results suggest that ionized gas outflows are prevalent among type 2 AGNs. On the other hand, we find no strong trend of the [OIII] kinematics with radio luminosity, once we remove the effect of the bulge gravitational potential, indicating that ionized gas outflows are not directly related to radio activity for the majority of type 2 AGNs. We will discuss the implication of these results for AGN feedback in the local universe.

• Journal of the Optical Society of Korea
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• 제18권3호
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• pp.207-216
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• 2014

In this work, we report detailed numerical analysis of the near-elliptic core index-guiding triangular-lattice and square-lattice photonic crystal fiber (PCFs); where we numerically characterize the birefringence, single mode, cut-off behavior and group velocity dispersion and effective area properties. By varying geometry and examining the modal field profile we find that for the same relative values of $d/{\Lambda}$, triangular-lattice PCFs show higher birefringence whereas the square-lattice PCFs show a wider range of single-mode operation. Square-lattice PCF was found to be endlessly single-mode for higher air-filling fraction ($d/{\Lambda}$). Dispersion comparison between the two structures reveal that we need smaller lengths of triangular-lattice PCF for dispersion compensation whereas PCFs with square-lattice with nearer relative dispersion slope (RDS) can better compensate the broadband dispersion. Square-lattice PCFs show zero dispersion wavelength (ZDW) red-shifted, making it preferable for mid-IR supercontinuum generation (SCG) with highly non-linear chalcogenide material. Square-lattice PCFs show higher dispersion slope that leads to compression of the broadband, thus accumulating more power in the pulse. On the other hand, triangular-lattice PCF with flat dispersion profile can generate broader SCG. Square-lattice PCF with low Group Velocity Dispersion (GVD) at the anomalous dispersion corresponds to higher dispersion length ($L_D$) and higher degree of solitonic interaction. The effective area of square-lattice PCF is always greater than its triangular-lattice counterpart making it better suited for high power applications. We have also performed a comparison of the dispersion properties of between the symmetric-core and asymmetric-core triangular-lattice PCF. While we need smaller length of symmetric-core PCF for dispersion compensation, broadband dispersion compensation can be performed with asymmetric-core PCF. Mid-Infrared (IR) SCG can be better performed with asymmetric core PCF with compressed and high power pulse, while wider range of SCG can be performed with symmetric core PCF. Thus, this study will be extremely useful for designing/realizing fiber towards a custom application around these characteristics.

• 천문학회보
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• 제42권2호
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• pp.51.4-52
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• 2017

We present the derived kinematic characteristics of low-${\alpha}$ thin-disk and high-${\alpha}$ thick-disk stars in the Milky Way, investigated with a sample of about 33,900 G- and K-type dwarfs from the Sloan Extension for Galactic Understanding and Exploration (SEGUE). Based on the level of ${\alpha}$-element enhancement as a function of [Fe/H], we separate our sample into thin- and thick-disk stars and then derive mean velocity, velocity dispersion, and velocity gradients for the U, V and W velocity components, respectively, as well as the orbital eccentricity distribution. There are notable gradients in the V velocity over [Fe/H] in both populations: -23 km s-1 dex-1 for the thin disk and +44 km s-1 dex-1 for the thick disk. The velocity dispersion of the thick disk decrease with increasing [Fe/H], while the velocity.