• Bulletin of the Korean Space Science Society
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• 2008.10a
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• pp.33.1-33.1
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• 2008

As a part of the construction of Korean Space Weather Prediction Center (K-SWPC), Korea Astronomy and Space Science Institute (KASI) installed a Scintillation Monitor (SCINTMON) and an All-Sky Camera to observe upper atmospheric/ionospheric phenomena. The SCINTMON is installed in KASI building in Daejeon in cooperation with Cornell university and is monitoring the ionospheric scintillations on GPS L-band signals. All-Sky Camera is installed at Mt. Bohyun in Youngcheon in cooperation with Korea Polar Research Institute. It is used to take the photograph for upper atmospheric layer through appropriate filters with specific airglow or auroral emission wavelengths and to observe upper atmospheric disturbance, propagation of gravity wave and aurora. The integrated data from the instruments including SCINTMON and All-Sky Camera will be used for giving nowcast on the space weather and making confidential forecast based on some space weather prediction models.

• Elastomers and Composites
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• v.46 no.2
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• pp.125-131
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• 2011

The effects of chopped kenaf fiber concentration on mechanical property of polypropylene (PP) composite are investigated. The addition of kenaf increased the tensile strength, flexural modulus, impact strength, specific gravity, and HDT, while decreased the elongation%, flexural strength, and melt flow index. The increase of mechanical properties is due to increased surface area contacting between fiber and polymer matrix and fiber-fiber interaction. Volatile extractives in the kenaf seemed to decrease the interfacial adhesion between kenaf surface and PP.

• Journal of Institute of Control, Robotics and Systems
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• v.14 no.11
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• pp.1146-1154
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• 2008

This paper presents a method for the acceleration analysis of multi-legged walking robots in consideration of the frictional ground contact. This method is based on both unified dynamic equation for finding the acceleration of a robot's body and constraint equation for satisfying no-slip condition. After the dynamic equation representing relationship between actuator torques and body acceleration, is derived from the force and acceleration relationship between foot and body's gravity center, the constraint equation is formulated to reconfigure the maximum torque boundaries satisfying no-slip condition from given original actuator torque boundaries. From application of the reconfigured torques to the dynamic equation, interested acceleration boundaries are obtained. The approach based on above two equations, is adapted to the changes of degree-of-freedoms of legs as well as friction of ground. And the method provides the maximum translational and rotational acceleration boundaries of body's center that are achievable in every direction without occurring slipping at the contact points or saturating all actuators. Given the torque limits in infinite normsense, the resultant accelerations are derived as a polytope. From the proposed method, we obtained achievable acceleration boundaries of 4-legged and 6-legged walking robot system successfully.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.2
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• pp.43.3-43.3
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• 2016

We present a library of high-resolution (R~45,000) and high signal-to-noise ratio ($S/N{\geq}200$) near-infrared spectra of 147 standard stars. High quality spectra were obtained with Immersion GRating INfrared Spectrograph (IGRINS) covering the full range of H ($1.496-1.795{\mu}m$) and K ($2.080-2.460{\mu}m$) bands. The targets are mainly selected as MK standard stars which have well-defined spectral types and luminosity classes, and cover a wide range of effective temperatures and surface gravities. The spectra were corrected for telluric absorption lines and absolute flux calibrated using Two Micron All Sky Survey (2MASS) photometry. We find new spectral indices in H and K bands and provide their EWs. We describe empirical relations between the measured EWs and stellar atmosphere parameters such as effective temperature and surface gravity.

• Physical Therapy Korea
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• v.3 no.2
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• pp.42-48
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• 1996

Weight bearing training on the involved leg is impotant for ambulation and activities of daily living in ambulatory hemiplegic patients. Traditionally, physical therapists have relied on exercise therapy and subjective evaluation. The goal for this study was to measure lower extremity weight distribution in standing with ten hemiplegic pations(M:8, F:2) and to determine the traing effect on symmetrical standing posture using a "Limloader". The Limloader is a machine designed for training symmetrical weight bearing posture. The results showed that the ability to keep the center of gravity within the limits for balance was improved significantly but the ability to adjust weight bearing on the involved leg was not (p<0.05). This study demostrated that hemiplegics can improved their symmetrical weight bearing ability using sensory biofeedback.

• The Bulletin of The Korean Astronomical Society
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• v.35 no.1
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• pp.72.1-72.1
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• 2010

Gas materials in the inner Galactic disk continuously migrate toward the Galactic center (GC) due to interactions with the bar potential, magnetic fields, stars, and other gaseous materials. In case of the Milky Way, those in forms of molecules appear to accumulate around 200 pc from the center (the central molecular zone, CMZ) to form stars there and further inside. The bar potential in the GC is thought to be responsible for such acculmulation of molecules and subsequent star formation, which is believed to have been continous throughout the lifetime of the Galaxy. We present 3-D hydrodynamic simulations of the CMZ that consider self-gravity, radiative cooling, and supernova feedback, and discuss the efficiency and role of the star formation in that region. We find that the gas accumulated in the CMZ by a bar potential of the inner bulge effectively turns into stars, supporting the idea that the stellar cusp inside the central 200 pc is a result of the sustained star formation in the CMZ. The obtained star formation rate in the CMZ, 0.03-0.1 Msun, is consistent with the recent estimate based on the mid-infrared observations by Yusef-Zadeh et al. We discuss the secular evolution of nuclear bulges in general, based on our results.

• Aerospace Engineering and Technology
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• v.12 no.2
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• pp.180-185
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• 2013

In this study, preliminary design of human powered aircraft was performed by considering the aerodynamic performance. For this, overall weight including the aircraft and pilot was determined. Then, the main wing and horizontal/vertical tail were designed with appropriate selection of the airfoils and planform shapes. Based on these, three dimensional flow was calculated to obtain lift and drag coefficients and the position of center of gravity (CG). Consequently, it was shown that the lift and power of the aircraft satisfied the constraints of the minimum required lift and the pilot's available power. Also, the CG of the aircraft was located at aerodynamic center (AC) of the main wing, which guaranteed 26% of the static margin.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.9
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• pp.1272-1280
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• 2001

An experimental study has been conducted to elucidate the resonance of natural convection in a side-heated square enclosure having a mechanically oscillating bottom wall. Under consideration is the impact of the imposed oscillating frequency, amplitude and the system Rayleigh number on the fluctuation of air temperatures. The experimental results show that the magnitude of the fluctuation of air temperature is substantially augmented at a specific forcing frequency of the oscillating bottom wall. The resonant frequency is increased with the increase of the Rayleigh number and it is little affected by the amplitude of the oscillating wall. It is also found that the resonant frequency is relevant to the Brunt- V$\"{a}$iS$\"{a}$l$\"{a}$ frequency which represents the stratification degree of the system.

• Journal of Korea Foundry Society
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• v.32 no.1
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• pp.38-43
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• 2012

The effects of Mg and Cu amounts on the casting characteristics and tensile property of Al-Zn-Mg-Cu alloys were investigated for the development of high strength aluminium alloys for gravity mold casting. Increase of copper amounts in Al-6%Zn-3%Mgy% Cu alloys resulted in reduction of the fluidity of these alloys and had little effects on the tensile property of these alloys. Increase of magnesium amounts from 1.0wt% to 3.3wt% in Al-6%Zn-x%Mg-0.5%Cu alloys resulted in reduction of the elongation of these alloys from 12% to 3% and increase of the tensile strength of these alloys from 340MPa to 450MPa, but had little effects on the fluidity of these alloys.

• Journal of the Society of Naval Architects of Korea
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• v.48 no.4
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• pp.357-362
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• 2011

It has been often reported that a water-jet propelled high speed vessel lost the course keeping ability in seaway. In this study, model tests of a high speed vessel were performed to measure the running attitude and to check the course keeping ability. The model ship may lose the course keeping ability due to bad running attitudes such as bow drop. So model tests were carried out to improve the running attitude by changing the position of longitudinal center of gravity and using appendages at the bow and the stern of a model. The position of lateral center of pressure moved toward stern and the course keeping ability was improved by modifying the transom wedge angle.