• Journal of Ocean Engineering and Technology
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• v.25 no.1
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• pp.32-38
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• 2011

Galvanized steel has gone through a chemical process to keep it from corroding. The steel gets coated in layers of zinc because rust will not attack this protective metal. For countless outdoor, marine, or industrial applications, galvanized steel is an essential fabrication component. The reduction of the corrosion rate of zinc is an important topic. In the past, a very popular way to reduce the corrosion rate of zinc was to use chemical conversion layers based on $Cr^{+6}$. However, a significant problem that has arisen is that the use of chromium salts is now restricted because of environmental protection legislation. Therefore, it is very important to develop new zinc surface treatments that are environmentally friendly to improve the corrosion resistance of zinc and adhesion with a final organic protective layer. In this study, a Urethane solution (only Urethane 20 wt.%; S-700) and an organic/inorganic solution with Si (Si polysilicate 10 wt.% + Urethane 10 wt.%; LRO-317) are used. Based on the salt spray test of 72 h, S-700 and LRO-317 had a superior effect for the corrosion resistance on EGI and HDGI, respectively.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.42 no.7
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• pp.616-621
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• 2014

Consumption of the fuel on the satellite operating in low earth orbit, is increased due to the air resistance and the amount of increase makes the satellite lifetime decrease or the satellite mass risen. Therefore the prediction of drag force of the satellite is important. In the paper, drag force and drag coefficient analysis of the parabolic antenna satellite in low earth orbit using direct simulation monte carlo method (DSMC) is conducted according to the mission altitude and angle of attack. To verify the DSMC simulated rarefied air movement, Starshine satellite drag coefficient according to the altitude and gas-surface interaction are compared with the flight data. Finally, from the analysis results, it leads to appropriate satellite drag coefficient for orbit lifetime calculation.

• Microbiology and Biotechnology Letters
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• v.37 no.1
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• pp.24-32
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• 2009

The KNUC25 strain isolated from over-fermented whole Chinese cabbage kimchi was examined for its physiological characteristics using API 50 CHL system assay and identified as Lactobacillus paraplantarum by analysis of whole-cell protein SDS-PAGE pattern assay and similarity of 16S rDNA sequence. L. paraplantarum KNUC25 had a broad antimicrobial activity spectrum from Gram positive to Gram negative bacteria. Scanning electron micrograph analysis showed that KNUC25 might attack to cell surface of indicator cells and destruction can lead to inhibition of the cell growth. The antimicrobial substance of the KNUC25 strain was stable to various degrading enzymes and at high temperature and not a plasmid-born matter. Resistance to proteolytic enzymes showed that an antimicrobial activity of KNUC25 might not be caused by proteinous substance. Maximum production of antimicrobial substance was the exponential growth phase at $30^{\circ}C$.

• Applied Biological Chemistry
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• v.42 no.3
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• pp.181-187
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• 1999

For the selection of an effective antagonistic biocontrol agent, we have isolated an antagonistic bacterium which produced extracellular chitinase, from a local soil of Kyongju, Korea. The selected strain was identified as Serratia proteamaculans 3095. The chitinase produced from Serratia sp. 3095 showed antifungal activity which can attack the hypha surface of Fusarium oxysporum and F. solani. The carbon and nitrogen sources for chitinase production were 0.15% colloidal chitin and 0.1% ammonium sulfate, respectively. Glucose in the chitinase production medium might inhibit the production of chitinase by feed back repression. The antagonistic Serratia sp. 3095 also showed a powerful biocontrol activity against F. oxysporum through in vitro test and in vivo pot test.

• International Journal of Aeronautical and Space Sciences
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• v.18 no.1
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• pp.8-16
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• 2017

Most of small air vehicles with moving wing fly at low Reynolds number condition and the reduced frequency of the moving wing ranges from 0.0 to 1.0. The physical phenomena over the wing dramatically vary with the reduced frequency. This study examines experimentally the effect of the reduced frequency at low Reynolds number. The NACA0012 airfoil performs sinusoidal pitching motion with respect to the quarter chord with the four reduced frequencies of 0.1, 0.2, 0.4 and 0.76 at the Reynolds number $2.3{\times}10^4$. Smoke-wire flow visualization, unsteady surface pressure measurement, and unsteady force calculation are conducted. At the reduced frequency of 0.1 and 0.2, various boundary layer events such as reverse flow, discrete vortices, separation and reattachment change the amplitude and the rotation direction of the unsteady force hysteresis. However, the boundary layer events abruptly disappear at the reduced frequency of 0.4 and 0.76. Especially at the reduced frequency of 0.76, the local variation of the unsteady force with respect to the angle of attack completely vanishes. These results lead us to the conclusion that the unsteady aerodynamic characteristics of the reduced frequency of 0.2 and 0.4 are clearly distinguishable and the unsteady aerodynamic characteristics below the reduced frequency of 0.2 are governed by the boundary layer events.

• Journal of the Korean Society of Propulsion Engineers
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• v.3 no.4
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• pp.75-82
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• 1999

Theoretical analysis and performance test of Jet vane type Thrust Vector Control(TVC) were conducted using supersonic cold-flow system. The use of TVC Systems an in particular jet vanes, are currently being researched for use in air launch, ship launch, underwater launch and high altitude maneuvering of tactical missiles and rockets. The necessity to generate control forces to rapidly change the course of the missile is frequently required when traditional, exterior aerodynamic surfaces are unable to produce these forces, when the flow over the control surface is insufficient. This situation can occur at launch, or high angles of attack of the control surfaces. Jet vanes peformed well at all altitudes and environmental conditions, and jet vanes are extremely effective at deflection angles up to as high as $30^{\circ}$, make them ideal for the launch and maneuver applications. In this study, performance test of supersonic cold-flow system and visualization of supersonic jet was conducted, and shape and deflection angle effect of two types of jet vanes are investigated.

• The KSFM Journal of Fluid Machinery
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• v.4 no.3 s.12
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• pp.7-13
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• 2001

The present study investigates convective heat/mass transfer and flow characteristics inside a cooling passage of rotating gas-turbine blades. The rotating duct has staggered ribs with $70^{\circ}$ attack angle, which are attached on leading and trailing surfaces. Naphthalene sublimation technique is employed to determine detailed local heat transfer coefficients using the heat and mass transfer analogy. Additional numerical calculations are conducted to analyze the flow patterns in the cooling passage. The present experiments employ two-surface heating conditions in the rotating duct because the exposed surfaces to hot gas stream are pressure and suction side surfaces in the middle passages of an actual gas-turbine blade. Secondary flows are generated by Coriolis and centrifugal forces in the spanwise and streamwise directions. The ribs attached on the walls disturb the mainflow resulting in recirculation and secondary flows near the ribbed wall. The local heat transfer and flow patterns in the passage are changed significantly according to rib configurations and duct rotation speeds. Therefore, the geometry and arrangement of the ribs are important for the advantageous cooling performance. The experimental results show that the ribs enhance the heat transfer more than $70\%$ from that of the smooth duct. The duct rotation generates the heat transfer discrepancy between the leading and trailing walls due to the secondary flows induced by the Coriolis force. The overal heat transfer pattern on the leading and trailing walls for the first and second passes are depended on the rotating speed, but the local heat transfer trend is affected mainly by the rib arrangements.

• Journal of Korea Foundry Society
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• v.34 no.2
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• pp.54-59
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• 2014

In this study, the extruded Al-6.3Zn-2.4Mg alloys were selected among the 7000 series aluminum alloys sensitive to hydrogen environment in order to examine the effects of both the aging conditions and the length of hydrogen charging period on the mechanical properties of the alloy. The specimens were aged for 24hours at $100^{\circ}C$ (under aging (UA)), $120^{\circ}C$ (peak aging (PA)), and $160^{\circ}C$ (over aging (OA)), respectively. Charging tests were performed at RT for 12, 24, 36 hours under potentiostatic conditions (-2000 mV vs (Ag/AgCl)) for 12, 24 and 36 hours in 1M $H_2SO_4$ and 0.1%$NH_4SCN$ solution. The fracture surface was examined by scanning electron microscopy (SEM). X-ray diffraction (XRD) pattern in peak aged sample was obtained before and after hydrogen charging from extruded Al-6.3Zn-2.4Mg alloys. The decreasing rate of tensile strength and elongation is represented in order of over aging < under aging < peak aging, and it is believed that the hydrogen recharge is more sensitive to elongation than tensile strength. The formation of $AlH_3$ in hydrogen charged Al-6.3Zn-2.4Mg alloys has been confirmed by X-ray diffraction studies.

• 한국가시화정보학회:학술대회논문집
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• 2003.11a
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• pp.39-42
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• 2003

Leading edge extension(LEX) in a highly swept shape applied to a delta wing features the modern air-fighters. The LEX vortices generated upon the upper surface of the wing at high angle of attack enhance the lift force of the delta wing by way of increased negative suction pressure over the surfaces. The present 3-D stereo PIV includes the Identification of 2-D cross-correlation equation, stereo matching of 2-D velocity vectors of two cameras, accurate calculation of 3-D velocity vectors by homogeneous coordinate system, removal of error vectors by a statistical method followed by a continuity equation criterion and so on. A delta wing model with or without LEX was immersed in a circulating water channel. Two high-resolution, high-speed digital cameras$(1280pixel\times1024pixel)$ were used to allow the time-resolved animation work. The present dynamic stereo PIV represents the complicated vortex behavior, especially, in terms of time-dependent characteristics of the vortices at given measuring sections. Quantities such as three velocity vector components, vorticity and other flow information can be easily visualized via the 3D time-resolved post-processing to make the easy understanding of the LEX effect or vortex emerging and collapse which are important phenomena occurring in the field of delta wing aerodynamics.

• Korean journal of applied entomology
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• v.51 no.3
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• pp.215-222
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• 2012

Pupation site selection behavior of Plodia interpunctella (H$\ddot{u}$bner) in response to its larval parasitoid, Bracon hebetor Say, was evaluated. Under the presence of the parasitoid, more moth larvae pupated in a layer deeper than 5 mm. Because the parasitoid searched for the host mostly in the surface layer (< 5 mm), larvae in deeper layers were able to successfully escape attack by the parasitoid. However, this behavior did not affect the numerical response of the parasitoid. The parasitoid laid more eggs per host larvae when the number of attacked larvae decreased.