• International Journal of Aeronautical and Space Sciences
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• v.13 no.3
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• pp.361-368
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• 2012

This paper presents an approach on the design of a nonlinear controller to track a reference velocity for an air-breathing supersonic vehicle. The nonlinear control scheme involves an adaptation of propulsive and aerodynamic characteristics in the equations of motion. In this paper, the coefficients of given thrust and drag functions are estimated and they are used to approximate the equations of motion under varying flight conditions. The form of the function of propulsive thrust is extracted from a thrust database which is given by preliminary engine input/output performance analysis. The aerodynamic drag is approximated as a function of angle of attack and fin deflection. The nonlinear controller, designed by using the approximated nonlinear control model equations, provides engine fuel supply command to follow the desired velocity varying with time. On the other hand, the stabilization of altitude, separated from the velocity control scheme, is done by a classical altitude hold autopilot design. Finally, several simulations are performed in order to demonstrate the relevance of the controller design regarding the vehicle.

• Journal of Korean Society of Forest Science
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• v.94 no.2 s.159
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• pp.121-126
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• 2005

This study was carried out to construct a single diameter and a single height model that could localize Chamaecyparis obtusa stand grown in 3 Southern regions of Korea. Dummy variables, which convert qualitative information such as geographical regions into quantitative information by means of a coding scheme (0 or 1), were used to localize growth models. In results, modified form of Gompertz equation, $Y_2={\exp}({\ln}(Y_1){\exp}(-{\beta}(T_2-T_1)+{\gamma}({T_2}^2-{T_1}^2))+({\alpha}+{\alpha}_1Al+{\beta}_1k_1+{\beta}_2k_2)(1-{\exp}(-{\beta}(T_2-T_1)+{\gamma}({T_2}^2-{T_1}^2))$, for diameter and height was successfully disaggregated to provide different projection equation for each of the 3 regions individually. The use of dummy variables on a single equation, therefore, provides potential capabilities for testing the justification of having different models for different sub-populations, where a number of site variables such as altitude, annual rainfall and soil type can be considered as possible variables to explain growth variation across regions.

• Journal of Forest and Environmental Science
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• v.31 no.3
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• pp.149-163
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• 2015

The aim of the present study was to assess the variation in species composition and diversity of woody species at different altitudes (900 to 2600 m asl) in Kedarnath Wildlife Sanctuary (KWLS) and its adjoining areas in Garhwal Himalaya, India. A total of 94 woody plant species (including 44 tree and 50 shrub species) belonging to 72 genera and 44 families were reported. Density varied from $235{\pm}9$ to $505{\pm}21trees\;ha^{-1}$ and $4,730{\pm}474$ to $9,530{\pm}700shrubs\;ha^{-1}$. Total basal cover varied from $10.49{\pm}0.66$ to $42.92{\pm}2.57m^2ha^{-1}$ (trees) and $0.36{\pm}0.024$ to $0.62{\pm}0.047m^2ha^{-1}$ (shrubs). Shannon-Wiener Index fluctuated between 2.30 to 3.53 (trees) and 2.74 to 3.78 (shrubs). Analysis of variance (ANOVA) indicated that altitude and aspect had significant effect on the distribution of woody species. Taxonomically, Rosaceae with 15 species emerged as the dominant family. Low value of maturity index and contiguous distribution of species denoted the early successional status of the studied forests. The conservation assessment based on altitudinal regimes and the information on species structure and function can provide baseline information for monitoring and sustaining the biodiversity.

• The Korean Journal of Ecology
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• v.23 no.6
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• pp.453-460
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• 2000

The forest vegetation of Mt. seondal was classified into eight communities and one afforestation by the phytosocialogical method (Z-M method). In general, Quercus mongolica trees occupied most of the area, while afforestation forest was distributed on the lower slope, cultivated land, and at the vicinity of village. The vegetation on the top part of Mt. Seondal was comparatively well preserved, but that in the lower areas has been disturbed heavily by human activity and some had mixed forests composed of pine trees, oaks, ashes, and Rhododendron micrantum shrub. By cluster analysis method. nine groups were identified as follows : Quercus mongolica group, Q. mongolica - Pinus densiflora group, Q. mongolica - Rhododendron schlipen - bachii group, Q. mongolica - Symplocos chinensis for. pilosa group, P. densiflora group, Juglans mandshurica group, Fraxinus mandshurica group, Betula costata group and Larix leptolepis group. These groups showed differences in species composition, but Quercus mongolica, Q. mongolica - P. densiflora, Q. mongolica - R. schlippenbachii and Q. mongolica - S. chinensis for. pilosa groups among them showed very similar floristic composition to each other. In the relationship between polar ordination axes and environmental variables, altitude was the environmental factor determining variation in species composition along axis X and soil moisture was the environmental along axis Y. They were the main factors in determining forest vegetation. The result of cluster analysis and polar ordination for the forest vegetation were corresponded to those of phytosocialogical classification in classifying vegetation.

• Journal of the Korean Society of Visualization
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• v.10 no.1
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• pp.47-54
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• 2012

Single Stage To Orbit (SSTO) missions which require its engines to be operated at varying back pressure conditions, use engines operate at high combustion chamber pressures (more than 100bar) with moderate area ratios (AR 70~80). This ensures that the exhaust jet flows full during most part of the operational regimes by optimal expansion at each altitude. Aero-spike nozzle is a kind of altitude adaptation nozzle where requirement of high combustion chamber pressures can be avoided as the flow is adapted to the outside conditions by the virtue of the nozzle configuration. However, the thrust prediction using the conventional thrust equations remains to be a challenge as the nozzle plume shapes vary with the back pressure conditions. In the present work, the performance evaluation of a new aero-spike nozzle is being carried out. Computational studies are carried out to predict the thrust generated by the aero-spike nozzle in varying back pressure conditions which requires the unsteady pressure boundary conditions in the computational domain. Schlieren pictures are taken to validate the computational results. It is found that the flow in the aero-spike nozzle is mainly affected by the base wall pressure variation. The aerospike nozzle exhibits maximum performance in the properly expanded flow regime due to the open wake formation.

• Solar Energy
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• v.11 no.1
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• pp.3-15
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• 1991

In this study global radiation and global illumination are directly measured and diffuse radiation and diffuse illumination measured utilizing semi-circular shadow ring. By analyzing measured radiation data, clear and overcast sky are classified according to the sky classification method used in Mantes, France. Measured illumination data are analyzed and 1) Clear sky illumination on a horizontal surface as a function of solar altitude. 2) Overcast sky illumination on a horizontal surface as a function of solar altitude, 3) Monthly variation of illumination. 4) Cumulative percentage of illumination, 5) Daylight intensity as a function of hours in a typical day, 6) Average number hours per day of illumination above 10 and 20klx are presented as a climatic data for daylighting design for Seoul, Korea.

• Journal of The Korean Astronomical Society
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• v.34 no.1
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• pp.25-29
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• 2001

We have constructed a non-spherical model for the hot oxygen corona of Mars by including the effects of planetary rotation and diurnal variation of the Martian ionosphere. Exospheric oxygen densities are calculated by integrating ensemble of ballistic and escaping oxygen atoms from the exobase over the entire planet. The hot oxygen atoms are produced by dissociative recombination of $O^+_2$, the major ion in the Martian ionosphere. The densities of hot oxygen atoms at the exobase are estimated from electron densities which have been measured to vary with solar zenith angle. Our model shows that the density difference of hot oxygen atoms between noon and terminator is about two orders of magnitude near the exobase, but reduces abruptly around altitudes of 2000 km due to lateral transport. The diurnal variation of hot oxygen densities remains significant up to the altitude of 10000 km. The diurnal variation of the hot oxygen corona should thus be considered when the upcoming Nozomi measurements are analyzed. The non-spherical model of the hot oxy-gen corona may contribute to building sophisticate solar wind interaction models and thus result in more accurate escaping rate of oxygens from Mars.

• Journal of Life Science
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• v.19 no.10
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• pp.1382-1388
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• 2009

Rubus crataegifolius is a shrub species and is primarily distributed throughout Asia and Europe. We collected 550 representative samples of the eleven populations in Korea to estimate leaf variation within species. The 35 morphological characteristics allowed us to resolve well-supported fixed characteristics and variable characteristics. Sixteen of twenty-three quantitative characteristics and five of twelve qualitative characteristics showed significant differences among populations. We argued that the population differentiation can accounted for the variation in phenetic characteristics such as spine in this species, but were less successful in accounting for variation in other traits. Within a polystatistic leaf structure, their morphological differences could be modulated by ecological pressure such as temperature, altitude, duration of sunshine, and solar radiation. The phenogram showed two distinct clades. One was a group in central Korea and the other was a group in the southern regions of Korea. If morphological characteristics in R. crataegifolius populations reflect their ecological niche, morphology should be regarded with caution as the main criterion for population studies in R. crataegifolius.

• Journal of Aerospace System Engineering
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• v.9 no.4
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• pp.16-22
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• 2015

Korea Aerospace Research Institute(here after KARI) has a plan to launch experimental lunar orbiter in 2018, and lunar orbiter and lander in 2020. There are several ways to go to the moon. Which one is direct transfer trajectory and another one is phasing loop transfer trajectory and the other one is WSB trajectory. Regardless of the transfer trajectories, LOI maneuver is the most important maneuver of all mission sequences because if this burn is failed, it is too difficult to get into the lunar orbit in the future. This paper describes first LOI target value of foreign lunar orbiters and analyzes orbital variations of experimental lunar orbiter according to various target values. By analyzing the variation of orbiter parameter after first LOI, proper orbital period for LOI target value are recommended to meet the inclination, apoapsis and periapsis altitude constraints.

• Journal of Science Education
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• v.34 no.2
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• pp.432-439
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• 2010

The purpose of this study is to investigate the characteristics of the ionosphere by monitoring VLF radio wave. For this purpose, we set up the SID(Sudden Ionospheric Disturbance) monitoring station in Pohang($36.03^{\circ}N$, $129.35^{\circ}E$), Korea receiving VLF radio wave(22.2kHz) transmitted from Ebino($32.04^{\circ}N$, $130.81^{\circ}E$), Japan. The observed data of radio wave intensities are analyzed to interpret the condition of the ionosphere. We can summarize the results as follows: Radio waves show regular daily variation. We can confirm the daily variation as a result of the formation of D layer. In relation to formation or extinction of D layer, intensity of radio wave gets weak right after sunrise and sunset. Southing altitude also affects the intensity of day time radio wave. At night when D layer disappears, the radio waves shows very irregular changes. The observed radio waves also shows the influence of the seasonal ionospheric variation. Long term observation could provide more detailed interpretation of daily as well as seasonal variation of ionosphere.