• Journal of Wetlands Research
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• v.14 no.1
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• pp.75-87
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• 2012

Hyporheic zone is a region beneath and alongside a stream, river, or lake bed, where there is mixing of shallow groundwater and surfacewater. Hyporheic exchange controls a variety of physical, biogeochemical and thermal processes, and provides unique ecotones in a aquatic ecosystem. Field and experimental observations, and modeling studies indicate that hyporheic exchange is mainly in response to pressure gradients driven by the geomorphological features of stream beds. In the reach scale of a stream, pool-riffle structures dominate the exchange patterns. Flow over a pool-riffle sequence develops recirculation zones and stagnation points, and this flow structures make irregular pressure gradient which is driving force of the hyporheic exchange. In this study, 3 D hydro-dynamic model solves the Reynolds-averaged Navier-Stokes equations for the surface water and Darcy's Law and the continuity equation for ground water. The two sets of equations are coupled via the pressure distribution along the interface. Simulation results show that recirculation zones and stagnation points in the pool-riffle structures dominantly control the upwelling and downwelling patterns. With decrease of recirculation zones, length of donwelling zone formed in front of riffles is reduced and position of maximum downwelling point moves downward. The numerical simulation could successfully predict the behavior of hyporheic exchange and contribute the field study, river management and restoration.

• Journal of the Korean Society of Propulsion Engineers
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• v.2 no.2
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• pp.56-63
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• 1998

The present study investigated local heat transfer characteristics around a film cooling hole with variations of free stream turbulence intensity The film cooling jet is injected through a single hole inclined at $30^{\cire}$ to the surface and laterally at $45^{\cire}$ for the blowing rates of 0.5, 1.0 and 2.0. Turbulence generating grids are used at upstream of the film cooling hole to change the turbulence intensity of free stream. Free stream turbulence intensity without grids is 0.5%. Two different turbulence generating grid is installed at different at locations upstream of the film cooling hole so that turbulence intensity of free stream varies from 3% to 10%. The naphthalene sublimation technique has been employed to determine local heat/ mass transfer coefficients. With low free stream turbulence intensity, heat/mass transfer augmented area by coolant or free stream is distinguished evidently. However, when free stream turbulence intensity is high, heat transfer is enhanced in all region and heat transfer enhanced regions are not clearly divided due to vigorous mixing of coolant and free stream. The peak values of heat/mass coefficients are decreased and the distributions of heat/mass transfer coefficients are more uniform with high turbulence intensity. The effect of turbulence intensity on heat transfer characteristics is more evident as blowing rate is higher.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.24 no.12
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• pp.1167-1172
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• 2013

This paper presents a X-band doppler radar with high conversion gain using a self-oscillating-mixer(SOM) that oscillation and frequency mixing is realized at the same time. To improve phase noise of the SOM oscillator, a ${\lambda}/2$ slotted square patch resonator(SSPR) was proposed, which shows high Q-factor of 175.4 and the 50 % reduced circuit area compared to the conventional resonator. To implement the low power system, low biasing voltage of 1.7 V was supplied. To enhance the conversion gain of the SOM, bias circuit is configured near the pinch-off region of transistor, and the conversion gain was optimized. The output power of the proposed SOM was -3.16 dBm at 10.65 GHz. A high conversion gain of 9.48 dB was obtained whereas DC Power consumption is relatively low about 7.65 mW. The phase noise is -90.91 dBc/Hz at 100 kHz offset. The figure-of-merit(FOM) of the proposed SOM was measured as -181.8 dBc/Hz, which is supplier to other SOMs by more than about 7 dB.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.7 no.1
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• pp.11-22
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• 1987

A plane buoyant jet discharged vertically upward into a crossflow is analyzed by numerical solution of the governing equations of continuity, momentum and constituent transport. The turbulent transport is modelled by the Prandtl's mixing length theory. In the numerical solution procedure, the governing equations are transformed by stream function and vorticity transport, non-dimensionalyzed by discharge velocity, slot width, and parameters representing flow characteristics, and solved by Gauss-Seidel iteration method with successive underrelaxation. The numerical experiments were performed for the region of established flow of buoyant jet in the range of discharge densimetric Froude number of 4 to 32 and in the range of velocity ratio of 8 to 15, which is the ratio of discharge velocity to crossflow velocity. Variations of velocities and temperatures, flow patterns and vorticity patterns of receiving water due to buoyant jet were investigated. Also investigated are the effects of velocity ratio and discharge densimetric Froude number on the trajectories of buoyant jet. Computed are velocities, temperatures and local densimetric Froude numbers along the trajectory of the buoyant jet. Spreading rate and dispersion ratio were analyzed in terms of discharge densimetric Froude number, local densimetric Froude number and distance from the source along the jet trajectory. It was noted that the similarity law holds in both the profiles of velocity and temperatures across the jet trajectory and the integral type analysis of Gaussian distribution is applicable.

• Journal of Sensor Science and Technology
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• v.8 no.1
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• pp.10-15
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• 1999

White emission thin film electroluminescent device was fabricated using ZnS for phosphor layer and BST ferroelectric thin film for insulating layer. For fabrication conditions of BST thin film, stoichiometry of target was $Ba_{0.5}Sr_{0.5}TiO_3$, substrate temperature was $400^{\circ}C$, working pressure was 30 mTorr, and A:$O_2$ ratio was 9:1. At this time, dielectric constant was 209 at 1kHz frequency. For phosphor layer ZnS:Mn, ZnS:Tb, and ZnS:Ag were used. Mixing rates of activators were respectively 0.8, 0.8, and 1 wt%. Total thickness of phosphor tapers was 500 nm, thickness of lower insulating layer was 200 nm, and thickness of upper insulating layer was 400 nm. In this conditions, luminescence threshold voltage of thin film electroluminescent device was $95\;V_{rms}$, maximum brightness was $3,000\;cd/m^2$ at $150\;V_{rms}$. Luminescence spectrum peak was observed at region of blue(450 nm), green(550 nm), and red(600 nm).

• Proceedings of the Korea Water Resources Association Conference
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• 2005.05b
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• pp.543-547
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• 2005

해수소통을 전제한 경우 새만금호 내측의 염분변화가 만경강의 평수량 및 홍수량 유입에 따라 혼합확산되는 것을 평가하고 배수갑문 방류시 담수가 외해에 미치는 영향범위를 평가하기 위한 수치모형실험이 실시되었다. 이때 새만금호 내부의 관리수위는 DL=-1.5m, DL=-0.5m, DL=-0.0m, DL=+0.5m가 고려되었다. 외해역의 평가는 새만금을 포함한 전체해역에 대해 외해경계에서 4개의 주요분조($M_2,S_2,K_1,O_1$)의 진폭과 위상각을 대입하고 2차원 ADCIRC 및 3차원 TIDE3D 모형을 적용하였다. 내부는 여기에 3개 연직층을 고려한 3차원 ICM 모델이 추가 적용되었다. 내부의 혼합확산 평가 결과는 시간이 지남에 따라 외해에서 유입되는 염수가 상대적으로 저염인 담수호 내부로 유입 확산되는 것이 평면적으로나 연직방향으로 변화되는 것을 매우 뚜렷하게 나타남을 알 수 있고, 최소 1개월 이상 경과되어야 만경호측에 외해수가 혼합되는 것으로 분석된다. 수문을 개방하지 않은 상태에서 새만금 방조제 외해의 최강창낙조시 조류속도는 0.5-0.6m/s 정도에 해당되는 것으로 분석되었다. 신시갑문을 개방하는 경우 관리수위가 DL=-1.5m와 DL=+0.5m로 변함에 따라 갑문 전면 10Km-l3Km에 이르는 해역까지 수문개방에 따라 0.5m/s의 유속이 형성된다. 가력갑문을 개방하는 경우는 신시갑문의 개방에 따른 영향보다는 작지만 갑문 전면 14Km까지 0.5m/s의 강한 유동이 관리수위별로 나타나고 있다. 이러한 결과는 담수 방류로 인한 영향이 주기적으로 낙조시에 발생되어 새만금 방조제 전면의 해수순환과 유동에 적지 않은 영향을 미칠 개연성을 제시하는 것으로 해석된다.$\cdot$유출에 의한 수질변화양상을 단계적으로 구분하여 수질변화에 중요한 영향을 미치는 인자에 대한 이론적인 분석을 수행하고, 배수갑문 개방에 의한 수질개선효과를 최대화하기 위한 환경관리 방안 제시에 중점을 두어 수행하였다.ncy), 환경성(environmental feasibility) 등을 정성적으로(qualitatively) 파악하여 실현가능한 대안을 선정하였다. 이렇게 선정된 대안들은 중유역별로 검토하여 효과가 있을 것으로 판단되는 대안들을 제시하는 예비타당성(Prefeasibility) 계획을 수립하였다. 이렇게 제시된 계획은 향후 과학적인 분석(세부평가방법)을 통해 대안을 평가하고 구체적인 타당성(feasibility) 계획을 수립하는데 토대가 될 것이다.{0.11R(mm)}(r^2=0.69)$로 나타났다. 이는 토양의 투수특성에 따라 강우량 증가에 비례하여 점증하는 침투수와 구분되는 현상이었다. 경사와 토양이 같은 조건에서 나지의 경우 역시 $Ro_{B10}(mm)=20.3e^{0.08R(mm)(r^2=0.84)$로 지수적으로 증가하는 경향을 나타내었다. 유거수량은 토성별로 양토를 1.0으로 기준할 때 사양토가 0.86으로 가장 작았고, 식양토 1.09, 식토 1.15로 평가되어 침투수에 비해 토성별 차이가 크게 나타났다. 이는 토성이 세립질일 수록 유거수의 저항이 작기 때문으로 생각된다. 경사에 따라서는 경사도가 증가할수록 증가하였으며 $10\% 경사일 때를 기준으로 $Ro(mm)=Ro_{10}{\times}0.797{\times}e^{-0.021s(\%)}$로 나타났다.천성 승모판 폐쇄 부전등을 초래하는 심

• Journal of Conservation Science
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• v.26 no.3
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• pp.229-245
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• 2010

The pupose of this study was to identify the material characteristics, firing environments and making techniques for the jar coffins from the Oryangdong kiln site and the Ungokdong tomb site in Naju. All jar coffins had very similar physical, mineralogical and geochemical characteristics, although it was excavated from the different sites. The wall thickness of the jar coffins was about 2.3 to 5.3 cm. Under the microscopy, the jar coffins include a large quantity of various quartz with some microcrystalline and showed partly orthoclase and biotite. It is presumed that the mineral sherds added to maintain the thick wall and to control the percentage of contraction during drying and firing of jar coffins and it has contained about 11.4 to 19.8 %. Firing temperature of the jar coffins is estimated as 1,000 to $1,150^{\circ}C$. Also, all jar coffins and soils show similar geochemical behavior of elements and clay-mineralization degree within the site. This indicates making that the soil is probable to be a raw material of the jar coffins. But it shows different characteristics in major elements of soils which is collected at the kiln floor and the trench region of the Oryangdong kiln site because of the lack of quartz and feldspar in the soils. Therefore, it can use of the jar coffins making clay, if it goes through a simple special process such as mixing temper.

• Journal of the Korea Organic Resources Recycling Association
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• v.20 no.3
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• pp.71-82
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• 2012

Common bulking agents in composting system include woody materials such as sawdust and woodchips. These bulking agents are mainly used for the purpose of the proper control of C/N ratio and moisture content in the composting. The topic for the effect on air permeability of bulking agents has far received relatively little attention in the composting field. This study investigated the effect of bulk density, moisture content, air-filled porosity, particle size and air flow rate on air permeability of several mixture ratios of sawdust and woodchip bulking agent. Increasing the moisture contents, the air-filled porosity was decreased and the particle size was increased for all kinds of bulking agent mixtures. Especially, with the increasing of mixing ratio of woodchip, these effects were sharply magnified. The air permeability respond to air-filled porosity was very similar to that for moisture content which was anticipated the linear relationship between air-filled porosity and moisture content. Above the region of moisture content 0.25 or 0.43(d.b.)(20 or 30% w.b.), the pressure drop decreased even though air-filled pore spaces were filling with water. Especially, to the particle size of 5 mm the pressure drop was decreased exponentially, so the air permeability was dramatically improved. By the water had the role of binding of the small particles, the macropores less resistances to air flow were created in the matrix. The effect of particle size on air permeability was much stronger than that of air-filled porosity or moisture content. And it is needed the preparing of initial particle size above 5 mm for efficient composting.

• Analytical Science and Technology
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• v.7 no.3
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• pp.315-320
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• 1994

Li-GICs as a high performance energy storager were synthesized as a function of the Li content by the admixture and add-pressure method. The characteristics of these prepared compounds have been determined from the studies by X-ray diffraction, UV-VIS spectrometry and CHN analysis. It follows from the results of X-ray diffraction that the lower-stage intercalation compounds are formed as the Li contents increase, however the mixed stages in these compounds are also observed. In the case of the $Li_{40wt%}$, the compound with the structure of stage 1 has been predominently, but the structure of only stage 1 is not obtained. The $d_{001}$ value of stage 1 was determined to be ca. $3.70{\AA}$. An analysis of spectrometric data shows that each of the compounds gives distingushible energy state spectra. It is seen from the spectra that the positions of $R_{min}$ values, with increase in the Li contents, are shifted in the region of higher energy state. Such a result can be attributed to the formation of stable stages. The results of CHN analysis allow us to find the mixing state related to chemical compositions of the intercalated compounds and the superiority to admixture and add-pressure method. From the results determined, it reveals that $Li_{10wt%}$-GIC and $Li_{20wt%}$-GIC can be utilized for an anode of rechargable battery.

• The Journal of Engineering Research
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• v.6 no.1
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• pp.97-109
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• 2004

The synthesis and crystal structure of amorphous calcium carbonate obtained from gas-liquid reaction of CaO-$C_2 H_5 OH$-$CO_2$ system according to change of added amount of calcium oxide by blowing $CO_2$ gas and reaction time using ethanol and ethylene glycol were investigated by electric conductivity, X-ray diffraction, and scanning electron microscope. The powdery or gelatinous phases were prepared by passing $CO_2$ gas at a flow rate of 1$\ell$/min into the suspensions containing 10~40g of CaO in mixing solutions 900ml of $C_2 H_5 OH$- and 100ml of ethylene glycol. By rapid filtration and drying the both phases at $60^{\circ}C$ under reduced pressure, the phases converted to the spherical vaterite and amorphous phase. The stable phase of amorphous calcium carbonate(ACC) was formed in the region pH 7-9 but the formation regions of amorphous phase were remarkably affected by pH in the mother liquor. It seems that a part of ACC changed into chain calcite as an intermediate products. The initial reactants prior to the formation of precipitated calcium carbonate is ACC. And ACC is unstable in the aqueous solution and crystallizes finally to calcite by the through-solution reaction. Especially ACC was produced or gelatinous phase which precipitated from the reaction of CaO-$C_2 H_5 OH$-$CO_2$ system.