• 천문학회보
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• 제35권1호
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• pp.28.2-28.2
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• 2010

We have investigated seven Extreme-Ultraviolet (EUV) bright points in the active region (AR 10926) on 2006 December 2 by the EUV imaging spectrometer (EIS) onboard Hinode spacecraft. We determined their Doppler velocities and non-thermal velocities from 15 EUV spectral lines (log T=4.7-7.2) by fitting each line profile to a Gaussian function. We present the Doppler velocity map as a function of temperature which corresponds to a different height. As a result, these active region bright points show two different types of characteristics. Type 1 bright point shows a systematic increase of Doppler velocity from -68 km/s (blue shift) at log T=4.7 to 27 km/s (red shift) at log T=6.7, while type 2 bright points have Doppler velocities in the range of -20 km/s and 20 km/s. Using MDI magnetograms, we found that only type 1 bright point was associated with the canceling magnetic feature at the rate of $2.4{\times}10^{18}$ Mx/hour. When assuming that these bright points are caused by magnetic reconnection and the Doppler shift indicates reconnection out flow, the pattern of the Doppler shift implies that type 1 bright point should be related to low atmosphere magnetic reconnection. We also determined electron densities from line ratio as well as temperatures from emission measure loci using CHIANTI atomic database. The electron densities of all bright points are comparable to typical values of active regions (log Ne=9.9-10.4). For the temperature analysis, the emission loci plots indicate that these bright points should not be isothermal though background is isothermal. The DEM analysis also show that while the background has a single peak distribution (isothermal), the EUV bright points, double peak distributions.

• 한국수소및신에너지학회논문집
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• 제28권3호
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• pp.300-307
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• 2017

This study is to investigate particle size and velocity profile of gasoline port injector using Phase Doppler Particle Analyzer (PDPA). In this experiment, a GV 250 Delphi port injector used for motorcycles was used for liquid injection. The injector consists of four holes and has a static flow rate of 2.13 g/s. The fuel used in the injection was N-heptane, which is similar to gasoline, as an alternative fuel. The test fuel was injected at an atmospheric temperature of $20^{\circ}C$ and an open atmosphere of 1 atm. The injection time was 10 ms and the injection pressure was 3.5 bar in PDPA experiment. The experimental target position was fiexd at 30, 50 and 75 mm from the nozzle tip and data were collected for a total of 10,000 samples. The experimental results show that the length diameter (D10), the Sauter mean diameter ($D_{32}$), and the mean droplet velocity (MDV) are $45-54{\mu}m$, $99-115{\mu}m$ and 15-21 m/s, respectively.

• 전기전자학회논문지
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• 제22권2호
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• pp.309-315
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• 2018

계단 주파수 레이더(Stepped Frequency Radar: SFR)는 송신 펄스의 주파수를 점진적으로 증가시켜 넓은 합성 대역폭을 만듦으로써 높은 거리 해상도를 얻는 방식이다. 그런데 이동표적의 경우 거리-도플러 결합(range-Doppler coupling) 현상으로 정확한 거리 추정을 할 수 없게 되므로 정확한 속도 추정을 통한 보상이 필요하다. 본 논문에서는 코히어런트 펄스열(Coherent Pulse Train: CPT)을 갖는 계단 주파수 레이더 파형을 제안하고, 이를 이용한 속도 추정 및 파라미터에 따른 결과를 기존의 VMD(Velocity Measurement Data) 방식과 시뮬레이션을 통해 비교하고 분석하였다.

• 한국군사과학기술학회지
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• 제21권2호
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• pp.147-157
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• 2018

There are increasing demands to provide early warning against intruding drones and cope with potential threats. Commercial anti-drone systems are mostly based on simple target detection by radar reflections. In real scenario, however, it becomes essential to obtain drone radar signatures so that hostile targets are recognized in advance. We present experimental test results that micro-Doppler radar signature delivers partial information on multi-rotor platforms and exhibits limited performance in drone recognition and classification. Afterward, we attempt to generate high resolution profile of flying drone targets. To this purpose, wide bands radar signals are employed to carry out inverse synthetic aperture radar(ISAR) imaging against moving drones. Following theoretical analysis, experimental field tests are carried out to acquire real target signals. Our preliminary tests demonstrate that high resolution ISAR imaging provides effective measures to detect and classify multiple drone targets in air.

• 한국음향학회:학술대회논문집
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• 한국음향학회 1992년도 학술논문발표회 논문집 제11권 1호
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• pp.103-106
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• 1992

기존의 혈류 속도 측정 방법으로는 인체내에 반사 물질을 투입하는 Fick technique과 electromagnetic flowmeter등을 이용한 invasive method와 Ultrasonic Doppler method에 의한 noninvasive method가 이용되고 있다. 이 방법들은 혈과의 모양이나 혈관에서의 flow velocity profile등에 관한 정확한 정보를 얻을 수 없다. 이와같은 문제점들을 해결하기 위한 혈류속도 측정 방법으로 실험실 조건하에서 인체에서와 유사한 혈류측정 장치를 제작하여, vessel의 표본 체적내의 산란체로부터 후방산란되는 초음파 신호의 correlation을 이용한 Ultrasound Time Domain Correlation (UTDC) technique을 연구하였다. UTDC technique을 이용하여 유속을 측정한 결과, 12% 이하의 정밀도로 평균 유체 유속이 측정되었고, Ultrasonic Doppler method에서 측정할 수 없는 혈과의 모양과 혈관의 각 위치에서의 유속 및 혈관벽에 이물질의 존재여부를 명확히 판단할 수 있었다.

• 한국통신학회논문지
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• 제27권3A호
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• pp.205-210
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• 2002

In a Doppler weather radar, high resolution windspeed profile measurements are needed to provide the reliable detection of hazardous weather conditions. For this purpose, the pulse pair method is generally considered to be the most efficient estimator, However, this estimator has some bias errors due to asymmetric spectra and may yield meaningless results in the case of a multimodal return spectrum. Although the poly-pulse pair method can reduce the bias errors of skewed weather spectra, the modes of spectrum may provide more reliable information than the statistical mean for the case of a multimodal or seriously skewed spectrum. Therefore, the idea of relatively simple mode estimator for a weather radar is developed in this paper, Performance simulations show promising results in the detection of hazardous weather conditions.

• 한국항해학회지
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• 제20권3호
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• pp.85-95
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• 1996

In the velocimeter, the ultrasonic pulse signal is used for measuring the profile velocity of moving targets distributed in space because of the merits of its high distance resolution and harmless affect to the human body. The velocity reading in conventional ultrasonic pulsed velocimeter depends on the wave pattern reflecting the spatial distribution of scatters and includes observational error due to the signal processing of analyzing pulse signal. In this paper, we evaluate an influence of the received waveform of pulsed signal on the velocity information by setting a model. Subsequently, in order to improve the distance resolution and to obtain precise velocity information without the influence of the spatial distribution of scatterers, we propose a new method for the analysis of Doppler pulsed signal, in which the pulsed signal is transformed into a phase function with local data. Finally, it is confirmed that the performance of the velocimeter is more improved in the proposed method than in the conventional one.

• 설비공학논문집
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• 제13권12호
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• pp.1184-1195
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• 2001

Analysis of fluid flow in rectangular ducts has been conducted since it has a wide application. The purpose is to provide experimental data for the comparison with computational results. Velocity distributions inside a rectangular duct with $90^{\circ}$ mitered elbow are measured by 5W laser doppler velocity meter for Reynolds numbers of 4,049, 8,104, and 12,186. Flow rates obtained by the integration of measured velocity profile at three cross-sections, which are inlet, middle section after the elbow, and outlet, have errors less than 0.9% among them. Turbulent fluctuation components in two directions are found to have almost similar magnitude each other at a certain location due to the isotropic characteristic of turbulence.

• Bulletin of the Korean Chemical Society
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• 제13권2호
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• pp.162-165
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• 1992

The fine structure branching ratio and Doppler profiles of photofragment Cl ($^{2}P_{j}$) atoms from photodissociation of CINO around 236 nm in the A band have been measured by the two photon resonance enhanced multiphoton ionization technique. The measured branching ratio, $Cl^{\ast} (^{2}P_{1/2})/Cl (^{2}P_{3/2})$ is $0.18{\pm}0.02$. The Doppler profile of Cl is well reproduced assuming that one of the two components in the photofragment translational spectra reported by Haas, Felder, and Huber [Chem. Phys. Lett., 180, 293 (1990)] should correspond to Cl and that an anisotropy parameter $\beta$ for the angular distribution is 0.45. The results suggest that CINO dissociation in the A band should consist of at least two non-crossing electronic states which correlate to the formation of $Cl^* and Cl, respectively.

• 한국인터넷방송통신학회논문지
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• 제16권6호
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• pp.125-133
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• 2016

스펙트럼 자원의 효율적 이용을 위한 하나의 해법으로 GPS 시각 기반의 시간이동선형주파수변조(TSLFM)를 갖는 동일채널 다중국소 레이더 운용을 위한 방법을 제시한다. 준 독립적 특성에 근거한 제안된 알고리즘은 선택된 TSLFM 신호 중에 상호상관 특성으로부터 허용할 수 있는 최소상관 수준을 갖는 TSLFM 후보군을 찾는 것이다. 제안 방법의 검증을 위해 톱니 LFM 신호를 갖는 동일채널에 운용되는 수 개의 레이더에 대해 거리-도플러 처리에 의한 수치해석을 하였다. 속도 및 거리를 갖는 점 목표물에 대해 거리 윤곽 및 도플러 편이 관점에서 계산 결과를 제시하고 고찰하였으며, 도출된 결과는 해상도 범위 내에서 매우 일치함을 보였다.