• Korean Journal of Environmental Agriculture
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• v.20 no.2
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• pp.86-92
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• 2001

The current study was conducted to elucidate the optimum density of free-ranging ducks in a rice-duck farming system in terms of effects on duck behavior, and growth and yield of rice plants. Four paddy fields were used for this experiment, with 6, 9, 12 and 15 birds per plot, respectively. Ducklings at eight days of age were free ranged in experimental paddy plots (4.0 a each) on the 9th day after the transplantation of rice plants. Ducks were kept in the plot for seventy days, at which point rice plants reached the earing stage. Foraging, moving, working, resting, diving and pecking behaviors of the ducks were observed two times during the experimental period. Also, rice plant growth and yield according to the density of ducks per plot were examined. The foraging and moving behavior of free-ranging ducks in paddy fields for 12 hours during the daytime tended to be longer in the 12-bird plot, and working behavior was significantly (P<0.01) longer in the 12-bird plot than in the other three plots. The resting behavior was significantly (P<0.01) higher in the 9- and 15-bird plots than in the 12-bird plot. The frequency of moving behavior for 6 hours during the daytime in the 15-bird plot tended to be lower than that in the other three plots, but this difference was not significant. The amount of diving and pecking behavior in the 9-bird plot was significantly (P<0.05) higher than that in the other three plots, and the number of hills pecked tended to be higher with increasing of duck density. From thirty days after ducks were introduced to the paddy fields, the length of rice plants tended to be significantly (P<0.05) shorter in high free-ranging density plots as compared to low free-ranging density plots. The number of tillers per hill was not affected by the free-ranging density. The culm length of rice plants was significantly (P<0.05) shorter in the 12- and 15-bird plots than in the other two plots, however, the duck free-ranging density did not affect panicle length. The dry weight of the root of rice plants was increased with high free-ranging density, but there was no such increase in the top parts of the rice plants. The percent of rice plants badly damaged by free-ranging density tended to be lower in the order of 12-, 9-, 6- and 15-bird plots. The number of ears, ripening grains and crop yield per hill of rice plants in the 12-bird plot were significantly (P<0.05) higher than those of the other three plots. Therefore, the yield of each rice plant per 10 a was significantly increased in the 12-bird plot.

• ETRI Journal
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• v.27 no.3
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• pp.319-325
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• 2005

In this paper the effect of temperature on the electrical properties of organic semiconductor disperse orange dye 25 (OD) have been examined. Thin films of OD have been deposited on $In_{2}O_{3}$ substrates using a centrifugal machine. DC current-voltage (I-V) characteristics of the fabricated devices $(Al/OD/In_{2}O_{3)$ have been evaluated at varying temperatures ranging from 40 to $60^{\circ}C$. A rectification behavior in these devices has been observed such that the rectifying ratio increases as a function of temperature. I-V characteristics observed in $Al/OD/In_{2}O_{3)$ devices have been classified as low temperature $({\leq} 50^{\circ}C)$ and high temperature characteristics (approximately $60^{\circ}C$). Low temperature characteristics have been explained on the basis of the charge transport mechanism associated with free carriers available in OD, whereas high temperature characteristics have been explained on the basis of the trapped space-charge-limited current. Different electrical parameters such as traps factor, free carrier density, trapped carrier density, trap density of states, and effective mobility have been determined from the observed temperature dependent I-V characteristics. It has been shown that the traps factor, effective mobility, and free carrier density increase with increasing values of temperature, whilst no significant change has been observed in the trap density of states.

• Journal of The Korean Astronomical Society
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• v.53 no.2
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• pp.49-57
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• 2020

We present numerical simulations of decaying hydrodynamic turbulence initially driven by solenoidal (divergence-free) and compressive (curl-free) drivings. Most previous numerical studies for decaying turbulence assume an isothermal equation of state (EOS). Here we use a polytropic EOS, P ∝ ρ^γ, with polytropic exponent γ ranging from 0.7 to 5/3. We mainly aim at determining the effects of γ and driving schemes on the decay law of turbulence energy, E ∝ t^-α. We additionally study probability density function (PDF) of gas density and skewness of the distribution in polytropic turbulence driven by compressive driving. Our findings are as follows. First of all, we find that even if γ does not strongly change the decay law, the driving schemes weakly change the relation; in our all simulations, turbulence decays with α ≈ 1, but compressive driving yields smaller α than solenoidal driving at the same sonic Mach number. Second, we calculate compressive and solenoidal velocity components separately and compare their decay rates in turbulence initially driven by compressive driving. We find that the former decays much faster so that it ends up having a smaller fraction than the latter. Third, the density PDF of compressively driven turbulence with γ > 1 deviates from log-normal distribution: it has a power-law tail at low density as in the case of solenoidally driven turbulence. However, as it decays, the density PDF becomes approximately log-normal. We discuss why decay rates of compressive and solenoidal velocity components are different in compressively driven turbulence and astrophysical implication of our findings.

• Journal of Biosystems Engineering
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• v.32 no.4
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• pp.237-246
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• 2007

In this study, the microwave free-space transmission technique was used to measure the dielectric property of powdered food at microwave frequencies. The sample holder was designed and fabricated to transmit the microwave signals ranging from 1 to 15GHz. From the microwave propagation theory the equation expressing the dielectric property of powdered food was derived and validated by standard dielectrics. The dielectric property of powdered food such as wheat flour, coffee powder and milk powder was measured and analyzed. In the uniform range of bulk density of material, the real parts of permittivity of the food samples increased with the increase of moisture content, bulk density and temperature of the samples. The propagation properties such as attenuation and phase shift increased linearly as the moisture density of the food samples increased. As a measuring frequency of the moisture content, the X-band was recommended.

• Korea-Australia Rheology Journal
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• v.20 no.2
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• pp.65-71
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• 2008

Pressure filtration technique was used to obtain defect-free microstructure of green cast ceramic bodies. Stable alumina suspensions of desired rheology (<5 Pa s at $1\;s^{-1}$) containing 60-80 mass. % solid loading were prepared in the alkaline region (at $pH{\approx}9$) with an optimum amount of 0.5 dmb % of Tiron added. Acidic region (at $pH{\approx}4$) enabled the preparation of 60 mass. % suspensions with addition of 1.5 dmb % of Tiron. The best quality slip was processed from an 80 mass.% suspension with 63% of theoretical density. The homogeneity of particle packing and the absence of defects in microstructure were proven by narrow pore size distribution (ranging from 32 to 64 nm, with up to 85% abundance), confirming advantages of the wet consolidation route.

• Journal of Welding and Joining
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• v.19 no.3
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• pp.267-273
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• 2001

In this study, welding phenomena involved in formation of penetrators during high frequency electric resistance welding were investigated. High speed cinematography of the process revealer that a molten bridge between neighboring skelp edges forms at apex point and travels along narrow gap toward to welding point at a speed ranging from 100 to 400 m/min. The bridge while moving along the narrow gap swept away oxide containing molten metal from the gap, providing oxide-free surface for a forge-welding at upsetting stand frequency of the budge formation, travel distance and speed of the bridge were affected by the heat input rate into strip. The travel distance and its standard deviation were found to have a strong relationship with the weld defect density. Based on the observation, a new mechanism of the penetrator formation during HF ERW process is proposed.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.05a
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• pp.20.2-20.2
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• 2011

III-nitrides have attracted much attention for optoelectronic device applications whose emission wavelengths ranging from green to ultraviolet due to their wide band gap. However, due to the strong polarization properties of conventional c-plane III-nitrides, the built-in polarization-induced electric field limits the performance of optical devices. Therefore, there has been a renewed interest in the growth of nonpolar III-nitride semiconductors for polarization free heterostructure optoelectronic and electronic devices. However, the crystal and the optical quality of nonpolar/semipolar GaN have been poorer than those of conventional c-plane GaN, resulting in the relative poor optical and electrical properties of light emitting diodes (LEDs). In this presentation, I will discuss the growth and characterization of high quality nonpolar a-plane and semipolar (11-22) GaN and InGaN multiple quantum wells (MQWs) grown on r- and m-plane sapphire substrates, respectively, by using metalorganic chemical vapor deposition (MOCVD) without a low temperature GaN buffer layer. Especially, the epitaxial lateral overgrowth (ELO) technique will be also discussed to reduce the dislocation density and enhance the performance of nonpolar and semipolar GaN-based LEDs.

• Journal of the Korean institute of surface engineering
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• v.47 no.5
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• pp.215-220
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• 2014

Electrodeposition behaviors of Pd-Ni alloys were investigated from the polarization curves in a solution containing ethylenediamine as complexing agent. The microstructure and hardness of electrodeposited Pd-Ni alloys were also characterized. Codeposition of Pd-Ni alloys was successfully performed in the wide current density ranging from 2 to $5000A{\cdot}m^{-2}$ because the deposition potential of Pd became close to that of Ni in the ethylenediamine-contained solution. It was also found from X-ray diffraction patterns that the solid solution between Pd and Ni was formed with variation of the composition of alloys. The measured hardness of Pd-Ni alloys increased with increasing the contents of Ni due to solid solution strengthening and grain refinement. The electrodeposited Pd-Ni alloys also exhibited a crack free smooth surface morphology from the SEM observation.

• Biotechnology and Bioprocess Engineering:BBE
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• v.7 no.3
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• pp.163-170
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• 2002

This report describes the use of a transtubular bioreactor to study the relative effects of diffusion versus perfusion of medium on antibody production by a hybridoma cell line. The study was performed with a high-density cell culture maintained in a serum-free, low-protein medium for 77 days. It was determined that the reactor possessed a macro-mixing pattern residence time distribution similar to a continuous stirred tank reactor (CSTR), However, due to the arrangement of the medium lines in the reactor, the flow patterns for nutrient distribution consist of largely independent medium path lengths ranging from short to long. When operated with cyclic, reversing, transtubular medium flow, some regions of the reactor (with short residence times) are more accessible to medium than others (with long residence times). From this standpoint, the reactor can be divided into three regions: a captive volume, which consists of medium primarily delivered via diffusion; a lapped volume, which provides nutrients through unilateral convection; and a swept volume, which operates through bilateral convection. The relative sizes of these three volumes were modified experimentally by changing the period over which the direction of medium flow was reversed from 15 min (larger captive volume) to 9 h (larger swept volume). The results suggest that antibody concentration increases as the size of the diffusion-limited (captive) volume is increased to a maximum at around 30 min with a sharp decrease thereafter. As reflected by changes in measured consumption of glucose and production of lactate, no significant difference in cellular metabolism occurred as the reactor was moved between these different states. These results indicate that the mode of operation of the transtubular bioreactor may influence antibody productivity under serum-free, low-protein conditions with minimal effects on cellular metabolism.

• Journal of Ecology and Environment
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• v.40 no.1
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• pp.12-19
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• 2016

Background: Direct impact of inorganic carbon (i.e., carbon dioxide ($CO_2$)) on the periphyton community is important to understand how and to what extent atmospheric conditions can affect the structure and dynamics of these communities in lotic systems. We investigated the influence of elevated $CO_2$ concentration on the periphyton community in the artificially constructed channels during the winter period. The channels made of acrylic paneling were continuously supplied with surface water discharged from a small reservoir, which was supported with ground water, at a flow rate of 5 L/min, and water temperature ranging $4-5^{\circ}C$. The effects of elevated $CO_2$ concentrations (790 ppm) were evaluated in comparison with the control (395 ppm $CO_2$) by analyzing pH, water carbon content and nutrients in water, periphyton composition and biomass, chlorophyll-a, ash-free dry-matter at 2-day intervals for 10 days. Results: After the addition of $CO_2$, significant decreases of pH, $NH_3-N$, and $PO_4-P$ (p < 0.05) and increases of chlorophyll-a, ash-free dry-matter, and the cell density of periphyton (p < 0.01) were observed, whereas the species composition of periphyton and water carbon content did not change. Conclusions: These results suggest that elevated $CO_2$ in flowing water system with low temperature could facilitate the growth of periphyton resulting in biomass increase, which could further influence water quality and the consumers throughout the food web.