• Current Optics and Photonics
• /
• v.1 no.2
• /
• pp.107-112
• /
• 2017

An adaptive optics system can be simulated or analyzed to predict its closed-loop performance. However, this type of prediction based on various assumptions can occasionally produce outcomes which are far from actual experience. Thus, every adaptive optics system is desired to be tested in a closed loop on an optical test bench before its application to a telescope. In the close-loop test bench, we need an atmospheric simulator that simulates atmospheric disturbances, mostly in phase, in terms of spatial and temporal behavior. We report the development of an atmospheric turbulence simulator consisting of two point sources, a commercially available deformable mirror with a $12{\times}12$ actuator array, and two random phase plates. The simulator generates an atmospherically distorted single or binary star with varying stellar magnitudes and angular separations. We conduct a simulation of a binary star by optically combining two point sources mounted on independent precision stages. The light intensity of each source (an LED with a pin hole) is adjustable to the corresponding stellar magnitude, while its angular separation is precisely adjusted by moving the corresponding stage. First, the atmospheric phase disturbance at a single instance, i.e., a phase screen, is generated via a computer simulation based on the thin-layer Kolmogorov atmospheric model and its temporal evolution is predicted based on the frozen flow hypothesis. The deformable mirror is then continuously best-fitted to the time-sequenced phase screens based on the least square method. Similarly, we also implement another simulation by rotating two random phase plates which were manufactured to have atmospheric-disturbance-like residual aberrations. This later method is limited in its ability to simulate atmospheric disturbances, but it is easy and inexpensive to implement. With these two methods, individually or in unison, we can simulate typical atmospheric disturbances observed at the Bohyun Observatory in South Korea, which corresponds to an area from 7 to 15 cm with regard to the Fried parameter at a telescope pupil plane of 500 nm.

• Korean Journal of Agricultural Science
• /
• v.13 no.2
• /
• pp.255-264
• /
• 1986

The objectives of this study were to examine the viscoelastic behaviour of stem samples of rice in force-relaxation and rheological model to represent its relaxation behaviour, and to study the effects of rate of deformation and initial deformation on the relaxation time. The results were as follows; 1. In the process of loading and unloading, there is any plastic deformation so called elasto-plastic hysterisis. 2. Loading and unloading of stem of rice for several cycles has also shown the reduction of plastic or residual deformation and work hardening. 3. The relaxation behaviour of stem of rice in compression may be described by a generalized Maxwell model consisting of three Maxwell units in parallel. The rheological equation of such a model is given as $$F(t)=C_1e^{{-t/{\tau}}_1}+C_2e^{{-t/{\tau}}_2}+C_3e^{{-t/{\tau}}_3}$$ 4. Force relaxation always increased with increasing rates of deformation and initial deformation.

• Journal of Korean Society on Water Environment
• /
• v.24 no.1
• /
• pp.123-128
• /
• 2008

The Dissolved Organic Carbon (DOC) existing in a water includes both hydrophobic and hydrophilic substances however, most of the discussion focuses on hydrophobic substances. The hydrophobic fraction was easily removed by absorption or coagulation more than hydrophilic fraction. Therefore, control of the hydrophilic fraction is very important in water treatment process. This study is to determine the variation of DOC, the removal efficiency of DOC, and Trihalomethane formation potential (THMFP) after each stage of water treatment process by fractionating Natural Organic Matters (NOM) into hydrophobic and hydrophilic substance. DOC from raw water was fractionated at acidic pH (pH<2) using XAD 8 resin column, into two fraction : hydrophobic substance (i.e. humic substance) adsorbed on XAD 8 and hydrophilic substance which represent the organics contained in the final effluent. THMFP was carried out according to the following set condition: Cl2/DOC=4 mg/mg, incubation at $25^{\circ}C$ in darkness, pH 7 adjust with HCl or NaOH as necessary, and 72hour-contact time. THMs analyzed in this study were chloroform, bromodichloromethane, dibromochloromethan, and bromoform. Sewage was almost evenly split between the hydrophobic (56%) and hydrophilic fraction (44%). But, Aldrich humic substance (AHS) was found to contain less hydrophilics (14%) than hydrophobics (86%). The formation of THMs may depend on the source which is characterized by the composition of organic matters such as AHS and sewage. The THMFP yield of sewage and AHS were assessed as follows. The value of the THMFP reaction yield, AHS $172.65{\mu}g/mg$, is much higher than that of sewage $41.68{\mu}g/mg$. This illustrates possible significant difference in THMFP according to the component type and the proportion of organic matter existing in water source. Apparently AHS react with chlorine to produce more THMFP than do the smaller molecules found in sewage. Water treatment process may reduce THMFP, nevertheless residual DOC (the more hydrophilic substance) has significant THMFP. Further reduction in organic halide precursors requires application of alternative treatment techniques.

• Korean Journal of Food Science and Technology
• /
• v.29 no.4
• /
• pp.716-721
• /
• 1997

In order to improve the quality of sikhe, Korean traditional sweat rice drink, wheat malt, covered barley malt and naked barley malt were used to prepare sikhe. The optimum temperature of amylase was $60^{\circ}C$ in malt extract. After heat treatment of amylase for 2 hr at $70^{\circ}C$, residual activity of amylase was less than 20% in malt extract. Amylase activity during sikhe preparation was decreased gradually. The sikhe saccharifyed for 6 hr had $6250{\sim}25029$ units of amylase acitivity. The contents of glucose, maltose and maltotriose were increased with increasing time. Maltose content was the highest, followed by glucose and maltotriose. The pH and titrable acidity were slightly changed. The sweetness of sikhe prepared with wheat was 11.3%, and others were 11.1% and 10.4%. The sikhe prepared with naked barley was evaluated the most palatable sikhe.

• Korean Journal of Materials Research
• /
• v.8 no.6
• /
• pp.538-544
• /
• 1998

The spallation of a thermal barrier coating layer depends on the formation of brittle spinels. thermal expansion mismatch between ceramic and metal. the phase transformation of a ceramic layer and residual stress of coating layer. In this work. the formation mechanism of oxide scale formed by oxidation treatment at 90$0^{\circ}C$ was investigated in order to verify oxidation behavior at the interface between E-beam coated $Zr0_2$-7wt.% $Y_20_3$ and plasma sprayed CoNiCrAIY. Some elements distributed in the bond coating layer were selectively oxidized after oxidation. At the initial time of oxidation. AI-depletion zone and $\alpha$-$Al_O_3$,O, were formed at the bond coating layer by the AI-outward diffusion. After layer grew until critical thickness. spinels. $Cr_20$, and $C0_2CrO_4$ by outward diffusion of Co. Cr, Ni were formed. It was found that the formation of spinels may be related to the spallation of $Zr0_2$-7wt.% $Y_20_3$ during isothermal oxidation.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
• /
• v.8 no.1
• /
• pp.65-70
• /
• 2010

The distillation rate on LiCl-KCl eutectic salt under different vacuums from 0.5-50 mmHg was first investigated by using both a non-isothermal and a isothermal thermogravimetric (TG) analysis. Based on the non-isothermal TG data, distillation rate equations as a function of the temperature could be derived. Calculated flux by these model flux equations was in agreement with the distillation rate obtained from isothermal TG analysis. A distillation rate of $10^{-4}-10^{-5}$ mole $cm^{-2}sec^{-1}$ is obtainable at temperatures less than 1300K and vacuums of 0.5-50 mmHg. About a 99% salt distillation efficiency was obtained after an hour at a temperature above 1150 K under 50 mmHg in a small scale distillation test system. An increase in the vaporizing surface area is relatively effective for removing residual salt in the remaining particles, when compared to that for the vaporizing time. Over 99.95% of total distillation efficiency was obtained for a 1-h distillation operation by increasing the inner surface area from $4.52cm^2$ to $12.56cm^2$.

• Applied Biological Chemistry
• /
• v.29 no.3
• /
• pp.266-272
• /
• 1986

The contents of water soluble ${\beta}-glucan$ were $1.4{\sim}4.0%$ in grains of 4 recommended varieties, and $0.3{\sim}0.6%$ in their malt. The ${\beta}-glucan$ content was subject to environmental factors such as cultivating region and nitrogen fertilizer level. The ${\beta}-glucan$ content of grains was positively correlated with the viscosity, but negatively with the protein and total gum contents. The ${\beta}-glucanase$ activity was $11.0{\sim}20.0$ sec as the reduced flow time in malt of 4 recommended varieties and was also subject to environmental factors. ${\beta}-Glucanase$ activity showed the highest level after the 6th day during malting. The ${\beta}-glucanase$ activity in malt was positively correlated with malt extract, but negatively with the residual ${\beta}-glucan$ content. The protein content in malt was negatively correlated with malt extract, but positively with the diastatic power.

• Journal of Korean Society of Environmental Engineers
• /
• v.28 no.3
• /
• pp.292-299
• /
• 2006

Batch experiments were performed to evaluate the effects of the electron donor dosage and the initial biomass on the reductive dechlorination of perchloroethene(PCE) with benzoate as an electron donor. When benzoate was added less than the theoretical requirement for dechlorination(electron donor/acceptor ratio=0.5 and 1), the dechlorination efficiency increased from 71% to 94.3% with the increase in benzoate dosage, but the fraction of electron equivalent utilized for dechlorination decreased from 92.7% to 79.6%. Methane production was observed when the hydrogen concentration was higher than the threshold value(10 nM) after PCE and trichloroethene (TCE) were reduced to cis-1,2-dichloroethene(cDCE). When benzoate was added more than the theoretical requirement, the residual hydrogen converted into methane after the completion of dechlorination. The increase in the seeding biomass shortened the lag time for dechlorination, but it did not affect the maximum dechlorination rate as it was mainly governed by the benzoate fermentation rate. When the seeding biomass concentration was high, active dechlorination during the early period increased dechlorination efficiency while decreasing methane production.

• Journal of the Society of Naval Architects of Korea
• /
• v.30 no.2
• /
• pp.141-154
• /
• 1993

In this paper, a method to calculate the ultimate compressive strength of welded one-sided stiffened plates simply supported along all edges is proposed. At first initial imperfections such as distortions and residual stresses due to welding are predicted by using simplified methods. Then, the collapse modes of the stiffened plate are assumed and collapse loads for each mode are calculated. Among these loads, the lowest value is selected as the ultimate strength of the plate. Collapse modes are assumed as follows ; (1) Overall buckling of the stiffened plate$\rightarrow$Overall collapse due to stiffener bending (2) Local buckling of the plate part$\rightarrow$Local collapse of the plate part$\rightarrow$Overall collapse due to stiffener yielding (3) Local buckling of the plate part$\rightarrow$Overall collapse due to stiffener berthing (4) Local buckling of the plate part$\rightarrow$Local collapse of the plate part$\rightarrow$Overall collapse due to stiffener tripping. The elastic large deflection analysis based on the Rayleigh-Ritz method is carried out, and plastic analysis assuming hinge lines is also carried out. Collapse load is defined as the cross point of the two analysis curves. This method enables the utimate strength to be calculated with small computing time and a good accuracy. Using the present method, characteristics of the stiffener including torsional rigidity, bending and tripping can also be clarified.

• The Journal of Korean Academy of Prosthodontics
• /
• v.39 no.5
• /
• pp.556-575
• /
• 2001

For the improvement of denture fitness of changed residual ridge, denture liner can be used. Denture liner should be very stable physically in various environments of the mouth as well as be bonded strongly with denture resin. In this study. the specimens bonded with four kinds of soft denture liner and three kinds of hard denture liner were used to test the physical properties of the liners. All experimental groups were stored in $37{\pm}1^{\circ}C$ distilled water for 24hours, followed by thermocycling between $15^{\circ}C$ and $45^{\circ}C$ with 15 second dwell time. 1000, 2000, 3000 cycles of thermocycling were excuted and physical properties were measured by Instron Universal Testing Machine. The obtained results were as follows : 1. In tensile bond test of sea liners, it was shown that both of $Molloplast-B^{(R)}$ specimens before and after thermocycling had the highest tensile strength, and in case of hard liners, Dura-Liner $II^{(R)}$ specimen had the highest tensile strength before and after thermocycling. Depending on thermocycling, $Soft-Relining^{(R)}$, $Denture-Relining^{(R)}$, $Molloplast-B^{(R)}$, $Coe-Soft^{(R)}$ and $Kooliner^{(R)}$ specimen showed significant difference(p<0.05). 2. In strain test of soft liners, it was shown that $Molloplast-B^{(R)}$ specimen before thermocycling and the $Coe-Soft^{(R)}$ after thermocycling showed highest results, and in case of hard liners, the Dura-Liner $II^{(R)}$ specimen before and after thermocycling had the highest result. Depending on thormocycling, $Denture-Relining^{(R)}$, $Molloplast-B^{(R)}$ and Dura-Liner $II^{(R)}$ specimen showed significant difference(p<0.05). 3. In maximum distance test of soft liners. the $Molloplast-B^{(R)}$ specimen before thermocycling and the $Coe-Soft^{(R)}$ after thermocycling showed highest results. and in case of hard liners, the Dura-Liner $II^{(R)}$ specimen before and after thermocycling showed highest result. Depending on thermocycling, $Denture-Relining^{(R)}$, $Molloplast-B^{(R)}$ specimens showed significant difference(p<0.05). 4. In elasticity test of soft liners, the $Molloplast-B^{(R)}$ specimen before and after thermocycling showed highest result. and in case of hard liners, the Dura-Liner $II^{(R)}$ specimen before thermocycling and the $Tokuso-Rebase^{(R)}$ after thermocycling showed highest results. Depending on thermocycling, $Soft-Relining^{(R)}$ $Molloplast-B^{(R)}$ specimens showed significant difference (p<0.05).