• Journal of The Korean Astronomical Society
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• v.53 no.6
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• pp.161-168
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• 2020

We report the discovery of a giant exoplanet in the microlensing event OGLE-2017-BLG-1049, with a planet-host star mass ratio of q = 9.53 ± 0.39 × 10-3 and a caustic crossing feature in Korea Microlensing Telescope Network (KMTNet) observations. The caustic crossing feature yields an angular Einstein radius of θE = 0.52 ± 0.11 mas. However, the microlens parallax is not measured because the time scale of the event, tE ≃ 29 days, is too short. Thus, we perform a Bayesian analysis to estimate physical quantities of the lens system. We find that the lens system has a star with mass Mh = 0.55+0.36-0.29 M⊙ hosting a giant planet with Mp = 5.53+3.62-2.87 MJup, at a distance of DL = 5.67+1.11-1.52 kpc. The projected star-planet separation is a⊥ = 3.92+1.10-1.32 au. This means that the planet is located beyond the snow line of the host. The relative lens-source proper motion is μrel ~ 7 mas yr-1, thus the lens and source will be separated from each other within 10 years. After this, it will be possible to measure the flux of the host star with 30 meter class telescopes and to determine its mass.

• Journal of Oral Medicine and Pain
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• v.23 no.1
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• pp.45-55
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• 1998

The author assessed the sagittal relationships between glenoid fossa of the temporal bone and mandibular condyle from lateral transcranial views of 74 TMJ with disc displacement and 16 TMJ with normal disc-condyle complex by the magnetic resonance image findings. All the subjects were female and also in their 3rd decades. The disc displacement group was subdivided into anterior disc displacement with reduction (ADWR) group and anterior disc displacement without reduction (ADWOR) group. The anterior, superior, and posterior joint spaces as well as anterior/posterior (A/P) ratio of the space at the closed jaw position and vertical and horizontal components of the condyle position relative to the articular eminence at the open jaw position were measured from all the subjects and the data were compared among groups. The result were as follows : 1. The mean posterior joint space of ADWR group was smaller than ADWOR group, but there were no significant differences in anterior and superior joint spaces between two groups. 2. There showed a tendency of higher A/P ratio in ADWR group which meant the condyle of ADWR was likely to take posteriorly displaced position. 3. There were higher proportion of neutral condylar position in glenoid fossa in normal group, but higher proportion of posterior condylar position in ADWR group. 4. There were no significant differences in the degree of condyle-fossa concentricity among groups.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.12
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• pp.1180-1185
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• 2008

In-house code which simulates the performance of pre-burner in staged-combustion liquid-fueled rocket engine was developed and demonstrated. Chemical reaction of pre-burner was modeled based on analytic algorithm of CEA (Chemical Equilibrium with Applications) and gas dynamics model was incorporated with it. Comparison results between in-house code and CEA have shown small relative errors except at very high or very low O/F ratio. Also the performance curve obtained by in-house code revealed that the calculated values follow the overall trend of real engine (RD-8) performance quite well and at steady-state operation, the deviation became very small.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.62 no.2
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• pp.90-94
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• 2013

In this paper, we propose a new algorithm to improve the contrast ratio, to preserve information of bright regions and to maintain the color of backlight image that appears with a great relative contrast. Backlight images of the natural environment have characteristics for difference of local brightness; the overall image contrast improvement is not easy. To improve the contrast of the backlight images, MSR (Multi-Scale Retinex) algorithm using the existing multi-scale Gaussian filter is applied. However, existing multi-scale Gaussian filter involves color distortion and information loss of bright regions due to excessive contrast enhancement and noise because of the brightness improvement of dark regions. Moreover, it also increases computational complexity due to the use of multi-scale Gaussian filter. In order to solve these problems, a linear MSR is performed that reduces the amount of computation from the HSV color space preventing the color distortion and information loss due to excessive contrast enhancement. It can also remove the noise of the dark regions which is occurred due to the improved contrast through edge preserving filter. Through experimental evaluation of the average color difference comparison of CIELAB color space and the visual assessment, we have confirmed excellent performance of the proposed algorithm compared to conventional MSR algorithm.

• International Journal of Aeronautical and Space Sciences
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• v.18 no.1
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• pp.154-164
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• 2017

This work conducts a validation study for the XH-59A helicopter using a rigid coaxial rotor system in order to establish the techniques of the conceptual design and performance analysis for the lift-offset compound rotorcraft. As a tool for conceptual design and performance analysis, NDARC (NASA Design and Analysis of Rotorcraft) is used for the present study. An assumed mission profile is considered for the conceptual design of the XH-59A. As a validation result of the design, the dimensions and weight of the XH-59A are appropriately designed when compared to the target values since the relative error is less than 0.5%. Then, performance analyses are conducted for the designed XH-59A model with and without auxiliary propulsion in hover and forward flight conditions. The present analyses show good validity since the prediction results compare well with both the flight test and previous analyses. Therefore, the techniques for the conceptual design and performance analysis of the lift-offset compound helicopter are overall considered to be appropriately established. In addition, this study investigates the influence of the lift-offset on the rotor effective lift-to-drag ratio of the XH-59A helicopter with auxiliary propulsion. As a result, the improvement of the rotor effective lift-to-drag ratio can be obtained by appropriately increasing the lift-offset in high-speed flight.

• Advances in aircraft and spacecraft science
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• v.6 no.3
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• pp.225-238
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• 2019

A spike attached to a blunt nosed body significantly alters its flow field and influences the aerodynamic coefficients at hypersonic speed. The basic body is an axisymmetric, with a hemisphere nose followed by a cylindrical portion. Five different types of spikes, namely, conical aerospike, hemisphere aerospike, flat-face aerospike, hemisphere aerodisk and flat-face aerodisk are attached to the basic body in order to assess the aerodynamic characteristic. The spiked blunt body without the aerospike or aerodisk has been set to be a basic model. The coefficients of drag, lift and pitching moment were measured with and without blunt spike body for the length-to-diameter ratio (L/D) of 0.5, 1.0, 1.5 and 2.0, at Mach 6 and angle of attack up to 8 degrees using a strain gauge balance. The measured forces and moment data are employed to determine the relative performance of the aerodynamic with respect to the basic model. A maximum of 77 percent drag reduction was achieved with hemisphere aerospike of L/D = 2.0. The comparison of aerodynamic coefficients between the basic model and the spiked blunt body reveals that the aerodynamic drag and pitching moment coefficients decrease with increasing the L/D ratio and angle of attack but the lift coefficient has increasing characteristics.

• Publications of The Korean Astronomical Society
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• v.32 no.1
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• pp.189-191
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• 2017

We performed systematic observations of the H $\small{I}$ $Br{\alpha}$ line ($4.05{\mu}m$) in 51 nearby (z<0.3) ultraluminous infrared galaxies (ULIRGs), using AKARI near-infrared spectroscopy. The $Br{\alpha}$ line is predicted to be the brightest among the H ${\small{I}}$ recombination lines in ULIRGs with visual extinction higher than 15 mag. We detected the $Br{\alpha}$ line in 33 ULIRGs. In these galaxies, the relative contribution of starburst to the total infrared luminosity ($L_{IR}$) is estimated on the basis of the ratio of the $Br{\alpha}$ line luminosity ($L_{Br{\alpha}}$) to $L_{IR}$. The mean $L_{Br{\alpha}}/L_{IR}$ ratio in LINERs or Seyferts is significantly lower (~50%) than that in H $\small{II}$ galaxies. This result indicates that active galactic nuclei contribute significantly (~50%) to $L_{IR}$ in LINERs, as well as Seyferts. We also estimate the absolute contribution of starburst to $L_{IR}$ using the ratio of star formation rates (SFRs) derived from $L_{Br{\alpha}}$ ($SFR_{Br{\alpha}}$) and those needed to explain $L_{IR}$ ($SFR_{IR}$). The mean $SFR_{Br{\alpha}}/SFR_{IR}$ ratio is only 0.33 even in H $\small{II}$ galaxies, where starburst is supposed to dominate the luminosity. We attribute this apparently low $SFR_{Br{\alpha}}/SFR_{IR}$ ratio to the absorption of ionizing photons by dust within H $\small{II}$ regions.

• The Bulletin of The Korean Astronomical Society
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• v.40 no.1
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• pp.84.2-84.2
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• 2015

There are probabilistic forecast models for solar flare occurrence, which can be evaluated by various skill scores (e.g. accuracy, critical success index, heidek skill score, true skill score). Since these skill scores assume that two types of forecast errors (i.e. false alarm and miss) are equal or constant, which does not take into account different situations of users, they may be unrealistic. In this study, we make an evaluation of a probabilistic flare forecast model (Lee et al. 2012) which use sunspot groups and its area changes as a proxy of flux emergence. We calculate daily solar flare probabilities from 1996 to 2014 using this model. Overall frequencies are 61.08% (C), 22.83% (M), and 5.44% (X). The maximum probabilities computed by the model are 99.9% (C), 89.39% (M), and 25.45% (X), respectively. The skill scores are computed through contingency tables as a function of forecast probability, which corresponds to the maximum skill score depending on flare class and type of a skill score. For the critical success index widely used, the probability threshold values for contingency tables are 25% (C), 20% (M), and 4% (X). We use a value score with cost/loss ratio, relative importance between the two types of forecast errors. We find that the forecast model has an effective range of cost/loss ratio for each class flare: 0.15-0.83(C), 0.11-0.51(M), and 0.04-0.17(X), also depending on a lifetime of satellite. We expect that this study would provide a guideline to determine the probability threshold for space weather forecast.

• New & Renewable Energy
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• v.9 no.3
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• pp.14-19
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• 2013

Comparative evaluation of offshore wind retreival software, which use the satellite images taken by Synthetic Aperture Radar sensor; SARTools of CLS-SOPRONO, France and SpaceEye of London Research and Development Corporation, Canada is carried out. For a reference satellite image, ENVISAT ASAR imagery of Jeollanam-do Wan-do area when the winter-time northwestern wind prevails is processed by CMOD_IFR2, CMOD4, CMOD5 algorithms. Wind speed difference and its relative ratio are calculated to evaluate uncertainty of software selection.

• International Journal of Aeronautical and Space Sciences
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• v.9 no.2
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• pp.9-17
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• 2008

When the stagnation temperature of the combustion chamber or ambient air increases, the specific heats and their ratio do not remain constant any more, and start to vary with this temperature. The gas remains perfect, except, it will be calorically imperfect and thermally perfect. A new generalized form of the Prandtl Meyer function is developed, by adding the effect of variation of this temperature, lower than the threshold of dissociation. The new relation is presented in the form of integral of a complex analytical function, having an infinite derivative at the critical temperature. A robust numerical integration quadrature is presented in this context. The classical form of the Prandtl Meyer function of a perfect gas becomes a particular case of the developed form. The comparison is made with the perfect gas model for aim to present a limit of its application. The application is for air.