• Geophysics and Geophysical Exploration
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• v.9 no.1
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• pp.102-107
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• 2006

Recently, rapid developments in computer hardware have enabled reverse-time migration to be applied to various production imaging problems. As a wave-equation technique using the two-way wave equation, reverse-time migration can handle not only multi-path arrivals but also steep dips and overturned reflections. However, reverse-time migration causes unwanted artefacts, which arise from the two-way characteristics of the hyperbolic wave equation. Zero-lag cross correlation with diving waves, head waves and back-scattered waves result in spurious artefacts. These strong artefacts have the common feature that the correlating forward and backward wavefields propagate in almost the opposite direction to each other at each correlation point. This is because the ray paths of the forward and backward wavefields are almost identical. In this paper, we present several tactics to avoid artefacts in shot-domain reverse-time migration. Simple muting of a shot gather before migration, or wavefront migration which performs correlation only within a time window following first arriving travel times, are useful in suppressing artefacts. Calculating the wave propagation direction from the Poynting vector gives rise to a new imaging condition, which can eliminate strong artefacts and can produce common image gathers in the reflection angle domain.

• Geophysics and Geophysical Exploration
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• v.6 no.3
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• pp.153-159
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• 2003

Using reciprocity theorem, one direction aperture of seismogram can be extended to full aperture seismogram. Modified seismogram is applied to reverse time migration only to acquire improved migration image. In this paper, we tested reverse time migration with the Marmousi velocity data to examine efficiency of modified seismogram. And linearly increasing velocity model is selected and examined for a case where velocity data is insufficient. When true velocity is applied, using modified seismogram enhances the reverse time migration image more than using original seismogram. In the case of using linearly increasing velocity model, migration image is distorted. So low frequency source is brought in migration process. Reverse time migration image with low frequency source and linearly increasing velocity model is improved when modified seismogram is used. From the result of study, seismogram modification by reciprocity theorem is useful and migration image can be enhanced.

• Journal of the Korean Society for Geothermal and Hydrothermal Energy
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• v.16 no.1
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• pp.1-8
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• 2020

In this study, a new shape of wind turbine with horizontal axis has been proposed. The proposed wind turbine has two pairs of 3 tiltable blades which minimizes air resistance during the reverse rotational direction. Under a given wind speed, 3D numerical simulations on tiltable blades were performed for various TSRs(tip-speed-ratios). Four cases of rotational position was considered to analyze the torque and wind power generated on the blade surfaces. The results show that the maximum wind power occurs at the TSR of 0.2. Due to the blade tilting, the wind passes through the blade without air resistance at the reverse rotational direction. The torque is mainly caused by pressure differences between the front and rear surface of the blade, and it becomes maximum when the blade is located at the azimuth angle of 330°.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.41 no.11
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• pp.81-86
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• 2004

Hybrid beamformer composed of Direction-of-Arrival (DOA) based scheme followed by Maximal Ratio Combining (MRC) is proposed to overcome the degradation due to inaccurate channel estimation caused by insufficient pilot power, which happens in conventional Single-Input Multiple-Output (SIMO) Code Division Multiple Access (CDMA) reverse link. The proposed scheme could provide more accurate channel estimation and interference reduction at the expense of diversity gam in the spatially correlated SIMO channel. As a result, hybrid scheme outperforms conventional MRC beamformer for six or more antennas in the channel environment, in which Angle-of-Spread (AOS) is within 30$^{\circ}$.

• 유체기계공업학회:학술대회논문집
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• 2002.12a
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• pp.131-136
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• 2002

A computational analysis using Reynolds stress model in FLUENT is conducted to give a clear understanding of the effect of blade loading on the structure of tip leakage flow in a forward-swept axial-flow fan at design condition ($\phi$=0.25) and off-design condition ($\phi$=0.21 and 0.30). The roll-up of tip leakage flow starts near the minimum static wall pressure position, and the tip leakage vortex developes along the centerline of the pressure trough within the blade passages. Near tip region, a reverse flow induced by tip leakage vortex has a blockage effect on the through-flow. As a result, high momentum region is observed below the tip leakage vortex. As the blade loading increases, the reverse flow region is more inclined toward circumferential direction and the onset position of the rolling-up of tip leakage flow moves upstream. Because the casing boundary layer becomes thicker, and the mixing between the through-flow and the leakage jet with the different flow direction is enforced, the streamwise vorticity decays more fast with blade loading increasing. The computational results show that a distinct tip leakage vortex is observed downstream of the blade trailing edge at $\phi$=0.30, but it is not observed at $\phi$=0.21 and 0.25.

• Korean Journal of Child Studies
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• v.6 no.1
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• pp.3-16
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• 1985

The purpose of this study was the application of sequential analysis to mother-infant interaction data, with particular reference to goodness of fit. The subjects of this study were 22 7- to 16-month-old infants(12 girls and 10 boys) and their mothers. Each mother-infant dyad was videotaped in a 5-min free-play session in the playroom. The videotaped data was transcribed on the behavioral checklist every 3 seconds. The recorded raw data were lagged by one time interval (3 sec.). Transitional probabilities from behavior at time t-1 to behavior at time t were gathered. The statistical analysis of frequency data and transitional probabilities consisted of Z test, t test, and sign test. It was found that regarding 1) direction of effect: the transitional probability of infant vocalization following maternal vocalization was significantly higher than the reverse; the transitional probability of a 'Coacting State' following a 'Mother Active State' was significantly higher than the reverse; the probability of a 'Mother Active State' following 'Quiescent State' was significantly higher than that of a 'Coacting State' following an 'Infant Active State'; 2) sex differences: male infants' transitional probability from an 'Infant Active State' to a 'Quiescent State' was significantly higher than that of female infants; 3) age differences: more than younger infants older infants had higher transitional probabilities from a 'Mother Active State' to a 'Coacting State', from a 'Parallel State' to a 'Coacting State', and from a 'Quiescent State' to a 'Parallel State'. These showed goodness of fit for sex and age differences, particularily for direction of effect.

• Journal of the Korean Magnetics Society
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• v.2 no.2
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• pp.132-139
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• 1992

We have designed a magnetic field gradient useful for cylindrical imaging in NMR-CT. The direc¬tion of the designed field is parallel to the axis and the gradient in the radial direction of cylindrical coordinate is monotonically increasing. The ratio of the gradient in the radial and axial direction is greater than 10 near the center of coordinate. This ratio depends on solenoid length, the number of reverse current turns at center, and the amount of the reverse current. We built a gradient coil based on the numerical simulation and tested the field generated by NMR-CT. The resulting image matches with the theoretical expectation within 10% error. Since the data acquisition time of 1-D imaging is significantly shorter than 2-D imaging, it becomes possible to image much more dynamic objects by the use of this gradient field.

• Journal of the Semiconductor & Display Technology
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• v.18 no.3
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• pp.72-76
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• 2019

A Q-switched diode-pumped neodymium-doped yttrium vanadate (YVO₄, λ =1064nm) laser was used for the direct patterning of indium tin oxide (ITO) films on glass substrate. During the laser direct patterning, the laser beam was incident on the two different directions of glass substrate and the laser ablated patterns were compared and analyzed. At a low scanning speed of laser beam, the larger laser etched lines were obtained by laser beam incident in reverse side of glass substrate. On the contrary, at a higher scanning speed, the larger etched pattern sizes were found in case of the beam incidence from front side of glass substrate. Furthermore, it was impossible to find no ablated patterns in some laser beam conditions for the laser beam from reverse side at a much higher scanning speed and repetition rate of laser beam. The laser beam is expected to be transferred and scattered through the glass substrate and the laser beam energy is thought to be also dispersed and much more influenced by the overlapping of each laser beam spot.

• Journal of the Korean Society for Nondestructive Testing
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• v.33 no.1
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• pp.69-72
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• 2013

In long-range ultrasonic testing, a phased array probe composed of multiple identical transducers with an uniform interval of one quarter wavelength is usually used for the transmission or reception directivity control. This paper shows that the propagation directions of individual echoes can be identified in real time by displaying the inputs of a process for summing the constitution reception signals after compensating the phase difference due to the transducer interval, together with the output of the process. A constructive interference of the constitution echoes indicates a forward direction echo propagating along an intended direction while a destructive interference implies a reverse direction echo propagating along the direction opposite to the intended one.

• Journal of the Korean Society of Costume
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• v.62 no.5
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• pp.73-87
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• 2012

The purpose of this study is to find the Dart Manipulation with good fitting and evaluate the aesthetics of Dart Manipulation that is used in the designs of the original tops for women in their 30's. Subsequently, it suggests dart manipulation with good body fitting and physical fitness when designing original tops. The findings of this study are as follows. First, in the fitting of Dart Manipulation for different body types, cross direction Dart Manipulation received good marks in the Square Body Type while mixed direction and diagonal direction Dart Manipulation received high evaluation in the Standard Body Type. Also, for the Reverse Triangle Body Type, mixed direction Dart Manipulation received high marks. Since there are only small changes in fitting for the Square Body Type, the position of Dart Manipulation should be determined in regards to the aesthetic view as well as the fitting of the Standard Body Type and Reverse Triangle Body Type. Second, in the fitness of Dart Manipulation for different body types, an approach from the aesthetic view should be considered for Square Body Types because of the differences in fitness according to the position of dart manipulation. The fitness should be considered when positioning Dart Manipulation for the Standard Body Type and Reverse Triangle Body Type because of these differences. Third, for the greater variance of drop for these different body types, the change of the amount of dart received lower evaluation in fitting since the amount of dart increased when the dart was located higher than B.P. The number of dart should likely increase when gathering or tucking is necessary when there is an excessive amount of dart in Dart Manipulation for the different body types. Fourth, as for the changes of wrinkles in accordance with the body type, wrinkles were likely to be formed at the breast or neck area when there was a larger difference in drop. To prevent such problems, one more dart should be made on the wrinkle. In conclusion, the study suggests designing the original top with a better look and comfort by setting the balance between aesthetics and fitting in the design stage.