• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.242-243
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• 2006

NiTiZrSiSn bulk metallic glass powder was produced using inert gas atomization and then was sprayed onto a SS 41 mild steel substrate using the kinetic spraying process. Through this study, the effects of thermal energy of in-flight particle and crystallization degree by powder preheating temperature were evaluated. The deformation behavior of bulk metallic glass is very interesting and it is largely dependent on the temperature. The crystalline phase formation at impact interface was dependent on the in-flight particle temperature. In addition, variations in the impact behavior need to be considered at high strain rate and in-flight particle temperature.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.68 no.1
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• pp.129-139
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• 2019

In order for a gun-launched guided projectile to glide to the maximum range, when to deploy the fin and start flight with guidance and control should be considered in range optimization process. This study suggests a solution to the optimal guidance problem for flight range maximization of the flight model of a guided projectile in vertical plane considering the aerodynamic properties. After converting the nonlinear Multi-Phase Optimal Control Problem to Two-Point Boundary Value Problem, the optimized guidance command and the best fin deployment timing are calculated by the proposed numerical method. The optimization results of the multiple flight rounds with various initial velocity and launch angle indicate that determining specific launch condition incorporated with the guidance scheme is of importance in terms of mechanical energy consumption.

• Journal of Ginseng Research
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• v.45 no.5
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• pp.539-545
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• 2021

Background: Red ginseng polysaccharides (RGPs) have been acknowledged for their outstanding immunomodulation and anti-tumor activities. However, their studies are still limited by the complexity of their structural features, the absence of purification and enrichment methods, and the rarity of the analytical instruments that apply to the analysis of such macromolecules. Thus, this study is an attempt to establish a new mass spectrometry (MS)-based analysis procedure for RGPs. Methods: Saponin pre-excluded powder of RG (RG-SPEP, 10 mg) was treated with 200 µL of distilled water and centrifuged for 5 h at 1000 rpm and 85 ℃. Ethanol-based precipitation and centrifugation were applied to obtain RGPs from the heated extracts. Further, endo-carbohydrase treatments were performed to produce specific saccharide fragments. Solid-phase extraction (SPE) processes were implemented to purify and enrich the enzyme-treated RGPs, while matrix-assisted laser desorption/ionization time-of-flight/time-of-flight (MALDI-TOF/TOF) MS was employed for the partial structural analysis of the obtained RGPs. Results: Utilizing cellulase, porous graphitized carbon (PGC), hydrophilic interaction chromatography (HILIC), and MALDI-TOF/TOF MS, the neutral and acidic RGPs were qualitatively analyzed. Hex_n and Hex_n-18 (cellulose analogs) were determined to be novel neutral RGPs. Additionally, the [Unknown + Hex_n] species were also determined as new acidic RGPs. Furthermore, HexA_n (H) was determined as another form of the acidic RGPs. Conclusion: Compared to the previous methods of analysis, these unprecedented applications of HILIC-SPE and MALDI-TOF/TOF MS to analyze RGPs proved to be fairly effective for fractionating and detecting neutral and acidic components. This new procedure exhibits great potential as a specific tool for searching and determining various polysaccharides in many herbal medicines.

• Korean journal of applied entomology
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• v.42 no.4
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• pp.367-381
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• 2003

Dispersal polymorphism in insects Is a kind of adaptive strategy of the life history together with the diapause, consisting of the “long-winged or alate forms” of migratory phase and the “short-winged or apterous forms” of stationary phase. Dispersal polymorphism is a polymorphism related with the flight capability, and has three categories ; the wing polymorphisms, flight muscle polymorphisms, and flight behavior variations. Phase variation is another type of dispersal polymorphism varying in morphology, physiology and wing forms in response to the density of the population. The dispersal migration is a very adaptive trait that enables a species to keep pace with the changing mosaic of its habitat, but requires some costs. In general, wing reduction has a positive effect on the reproductive potential such as earlier reproduction and larger fecundity The dispersal polymorphism is a kind of optimization in the evolutionary strategies of the life history in insects; a trade-off between the advantages and disadvantages of migration. Wing polymorphism is a phenotypically plastic trait. Wing form changes with the environmental conditions even though the species is the same. Various environmental factors have an effect on the dispersal polymorphisms. Density dependent dispersal polymorphism plays an important role In population dynamics, but it is not a simple function of the density; the individuals of a population may be different in response to the density resulting different outcomes in the population biology, and the detailed information on the genotypic variation of the individuals in the population is the fundamental importance in the prediction of the population performances in a given environment. In conclusion, the studies on the dispersal polymorphisms are a complicated field in relation with both physiology and ecology, and studies on the ecological and quantitative genetics have indeed contributed to understanding of its important nature. But the final factors of evolution; the mechanisms of natural selections, might be revealed through the studies on the population biology.

• Korean Journal of Applied Biomechanics
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• v.27 no.3
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• pp.171-179
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• 2017

Objective: The purpose of this study was to perform a kinematic and kinetic analysis of double-under jump rope technique according to skill level and sex. Method: Participants comprised a skilled group of 16 (9 males, 7 females), and an unskilled group of 16 with 6 months or less of experience (9 males, 7 females). Five consecutive double-under successes were regarded as 1 trial, and all participants were asked to complete 3 successful trials. The data for these 3 trials were averaged and analyzed after collecting the stable third jump in each trial. The variables used in the analysis included phase duration, total duration, flight time, vertical toe height, stance width, vertical center of mass displacement, and right lower limb ankle, knee, and hip joint angles in the sagittal plane during all events. Results: The skilled group had a shorter phase and total duration and a shorter flight time than the unskilled group. The vertical center of mass displacement and ankle dorsiflexion angle were significantly smaller in the skilled group. The male group had a shorter phase duration than the female group. The vertical toe height was greater, the stance width was smaller, and the ankle and hip flexion angles were smaller in the male group. Conclusion: Variables that can be used to distinguish between skill levels are phase and total duration, flight time, vertical center of mass displacement, and ankle dorsiflexion angle. Differences between sexes in double-under jump rope technique may be related to lower limb flexion angle control.

• Journal of the Korean Society of Propulsion Engineers
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• v.18 no.4
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• pp.74-80
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• 2014

This paper describes the development of the dual-thrust flight motor for enhancing the hit probability of unguided rockets. We designed dual-thrust flight motor by shape modification of the double base propellant with high burning rate, and confirmed the dual-thrust performance by static firing tests. The test results showed the thrust ratio of about 1:7.6 between sustaining phase and boosting phase, and had a quietly normal dual-thrust characteristics. And the results showed that there was not the fire extinction phenomenon of propellant due to the pressure drop.

• Journal of the Korea Institute of Military Science and Technology
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• v.12 no.2
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• pp.213-221
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• 2009

An aircraft collision accident is a disaster that causes great losses of inventories and lives. Though a collision avoidance warning function is provided automatically to pilots in the aircrafts by the enhancement of the aircraft capability, achieving fast decision-making to escape a collision situation is a complex and dangerous work for pilots. If an in-flight collision situation is controlled by the air traffic control system which monitors all airplanes in the air, it would be more efficient to prevent in-flight collisions because it can handle the emergency before the pilot's action. In this paper, we develop the collision avoidance warning function in the air traffic control system. Specifically, we design and implement the five stages of the collision avoidance function, and propose a visualization method which could effectively provide the operators with the trajectories and altitudes of the aircrafts in a collision situation. By developing an in-flight collision warning function in the air traffic control system that visualizes flight patterns through the state transition data of in-flight aircrafts on the flight path lines, it can effectively prevent in-flight collisions with traffic alerts. The developed function allows operators to effectively select and control the aircraft in a collision situation by providing the operators with the expected collision time, the relative distance, and the relative altitude while assessing the level of alert, and visualizing the alert information which includes the Attention-Warning-Alert phase via embodying the TCAS standard. With the developed function the air traffic control system could sense an in-flight collision situation before the pilot's decision-making moment.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.1586-1591
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• 2004

Flow visualization experiments have been performed to investigate the effects of phase lag, reduced frequency qualitatively by examining wake pattern on a dragonfly type wing. The model was built with a scaled-up, flapping wings, composed of paired wings with fore- and hindwing in tandem, that mimicked the wing form of a dragonfly. The present study was conducted by using the smoke-wire technique, and an electronic device was mounted to find the exact positional angle of wing below the tandem wings, which amplitude is ranged from $-16.5^{\circ}$ to $+22.8^{\circ}$. Phase lag applied on the wings is $0^{\circ}$, $90^{\circ}$, $180^{\circ}$ and $270^{\circ}$. The reduced frequency is 0.15, 0.3 and 0.45 to investigate the effect of reduced frequency. It is inferred through observed wake pattern that the phase lag clearly plays an important role in the wake structures and in the flight efficiency as changing the interaction of wings. The reduced frequency also is closely related to wake pattern and determines flight efficiency.

• Journal of the Korean Society of Propulsion Engineers
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• v.16 no.1
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• pp.64-71
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• 2012

While a conventional ECS mainly consisted of an air cycle machine and heat exchangers, a new concept of a phase change heat exchanger was added to improve the transient performance of the ECS. As a result, an ECS modeling program including the phase change heat exchanger is newly developed to estimate its effect in various flight conditions such as take-off, maneuver, cruise, and landing. The simulation result regarding a virtual flight profile has confirmed the new ECS fulfilled the requirement by showing the temperature of the cooling air returned from the bay was always kept below $80^{\circ}C$. Through this study, the new ECS concept with PCHE was verified successfully.

• Journal of Mechanical Science and Technology
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• v.17 no.8
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• pp.1234-1245
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• 2003

An experimental study was carried out to investigate the reduced frequency effect on the near-wake of an elliptic airfoil oscillating in pitch. The airfoil was sinusoidally pitched around the center of the chord between -5$^{\circ}$and ＋25$^{\circ}$angles of attack at an airspeed of 3.4 m/s. The chord Reynolds number and reduced frequencies were 3.3 ${\times}$10$^4$, and 0.1, 0.7, respectively Phase-averaged axial velocity and turbulent intensity profiles are presented to show the reduced frequency effects on the near-wake behind the airfoil oscillating In pitch. Axial velocity defects in the near-wake region have a tendency to increase in response to a reduced frequency during pitch up motion, whereas it tends to decrease during pitch down motion at a positive angle of attack. Turbulent intensity at positive angles of attack during the pitch up motion decreased in response to a reduced frequency, whereas turbulent intensity during the pitch down motion varies considerably with downstream stations. Although the true instantaneous angle of attack compensated for a phase-lag is large, the wake thickness of an oscillating airfoil is not always large because of laminar or turbulent separation.