• Nuclear Engineering and Technology
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• v.50 no.5
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• pp.665-672
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• 2018

A venturi scrubber is an important element of Filtered Containment Venting System (FCVS) for the removal of aerosols in contaminated air. The present work involves computational fluid dynamics (CFD) study of dust particle removal efficiency of a venturi scrubber operating in self-priming mode using ANSYS CFX. Titanium oxide ($TiO_2$) particles having sizes of 1 micron have been taken as dust particles. CFD methodology to simulate the venturi scrubber has been first developed. The cascade atomization and breakup (CAB) model has been used to predict deformation of water droplets, whereas the Eulerian-Lagrangian approach has been used to handle multiphase flow involving air, dust, and water. The developed methodology has been applied to simulate venturi scrubber geometry taken from the literature. Dust particle removal efficiency has been calculated for forced feed operation of venturi scrubber and found to be in good agreement with the results available in the literature. In the second part, venturi scrubber along with a tank has been modeled in CFX, and transient simulations have been performed to study self-priming phenomenon. Self-priming has been observed by plotting the velocity vector fields of water. Suction of water in the venturi scrubber occurred due to the difference between static pressure in the venturi scrubber and the hydrostatic pressure of water inside the tank. Dust particle removal efficiency has been calculated for inlet air velocities of 1 m/s and 3 m/s. It has been observed that removal efficiency is higher in case of higher inlet air velocity.

• Korean Journal of Soil Science and Fertilizer
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• v.36 no.5
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• pp.280-289
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• 2003

The purpose of this study was to establish a model for recommendable application level of nitrogen fertilizer based on soil testing for summer chinese cabbage in highland. A field experiment was carried out with various nitrogen application levels in sand loamy soil with and without poultry manure compost. The application level of N in poultry manure compost plot was found to be $291kg\;ha^{-1}$ for maximum yield of chinese cabbage, and it was 87% of the required N application level, $335kg\;ha^{-1}$, for maximum yield of chinese cabbage in nonmanure plot. In the treatment of poultry manure, approximately $174kg\;ha^{-1}$ of N was required to obtain the same yield of chinese cabbage as the maximum yield obtained in the treatments without poultry manure application. Therefore, with poultry manure application, N application level can be reduced by 40%. Using these results, a new equation for N recommendation for chinese cabbage in highland soil was proposed. With the average organic matter content of $33g\;kg^{-1}$ in highland field, the application levels of N for chinese cabbage were in the range of $215-129kg\;ha^{-1}$, which means that 32.8-59.7% of current application amount of N fertilizer can be reduced.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.74-74
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• 2010

One-dimensional nanosturctures such as nanowires and nanotube have been mainly proposed as important components of nano-electronic devices and are expected to play an integral part in design and construction of these devices. Silicon carbide(SiC) is one of a promising wide bandgap semiconductor that exhibits extraordinary properties, such as higher thermal conductivity, mechanical and chemical stability than silicon. Therefore, the synthesis of SiC-based nanowires(NWs) open a possibility for developing a potential application in nano-electronic devices which have to work under harsh environment. In this study, one-dimensional nanowires(NWs) of cubic phase silicon carbide($\beta$-SiC) were efficiently produced by thermal chemical vapor deposition(T-CVD) synthesis of mixtures containing Si powders and hydrocarbon in a alumina boat about $T\;=\;1400^{\circ}C$ SEM images are shown that the temperature below $1300^{\circ}C$ is not enough to synthesis the SiC NWs due to insufficient thermal energy for melting of Si Powder and decomposition of methane gas. However, the SiC NWs are produced over $1300^{\circ}C$ and the most efficient temperature for growth of SiC NWs is about $1400^{\circ}C$ with an average diameter range between 50 ~ 150 nm. Raman spectra revealed the crystal form of the synthesized SiC NWs is a cubic phase. Two distinct peaks at 795 and $970\;cm^{-1}$ over $1400^{\circ}C$ represent the TO and LO mode of the bulk $\beta$-SiC, respectively. In XRD spectra, this result was also verified with the strongest (111) peaks at $2{\theta}=35.7^{\circ}$, which is very close to (111) plane peak position of 3C-SiC over $1400 ^{\circ}C$ TEM images are represented to two typical $\beta$-SiC NWs structures. One is shown the defect-free $\beta$-SiC nanowire with a (111) interplane distance with 0.25 nm, and the other is the stacking-faulted $\beta$-SiC nanowire. Two SiC nanowires are covered with $SiO_2$ layer with a thickness of less 2 nm. Moreover, by changing the flow rate of methane gas, the 300 sccm is the optimal condition for synthesis of a large amount of $\beta$-SiC NWs.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.160-160
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• 2010

테라헤르츠 소스로 저온 InGaAs를 대체하기 위해 저온에서 성장한 $In_{0.64}Al_{0.36}Sb$의 성장 온도에 따른 광학적 photoluminescence (PL)과 time-resolved PL (TRPL) 측정을 이용하여 분석하였다. 또한 Be 도핑 농도에 따른 p형 $In_{0.64}Al_{0.36}Sb$의 PL과 TRPL 특성을 undoped $In_{0.64}Al_{0.36}Sb$와 Si-doped $In_{0.64}Al_{0.36}Sb$ 결과와 비교 분석하였다. 본 연구에 사용한 시료는 분자선 엑피탁시 (molecular beam epitaxy)법으로 GaAs 기판 위에 $In_{0.64}Al_{0.36}Sb$을 다양한 성장온도에서 ${\sim}3.7\;{\mu}m$두께 성장하였다. $In_{0.64}Al_{0.36}Sb$의 성장온도는 $400^{\circ}C$ 에서 $460^{\circ}C$까지 변화시키며 성장하였으며, Si과 Be 도핑한 $In_{0.64}Al_{0.36}Sb$ 시료는 약 $420^{\circ}C$에서 성장하였다. 모든 시료의 PL 피크는 ~1450 nm 근처에서 나타나며 단파장 영역에 shoulder 피크가 나타났다. 그러나 가장 낮은 온도 $400^{\circ}C$에서 성장한 시료는 1400 nm에서 1600 nm에 걸쳐 매우 넓은 피크가 측정되었다. PL 세기는 $450^{\circ}C$ 에서 성장한 시료가 가장 강하게 나타났으며, $435^{\circ}C$에서 성장한 시료의 PL 세기가 가장 약하게 나타났다. 방출파장에 따른 PL 소멸곡선을 측정하였으며 double exponential function을 이용하여 운반자 수명시간을 계산하였다. 운반자 수명시간은 빠른 소멸성분 $\tau_1$과 느린 소멸성분 $\tau_2$가 존재하고 빠른 성분 $\tau_1$의 PL 진폭이 약 80%로 느린 성분 $\tau_2$보다 우세하게 나타났다. 각 PL 피크에서의 운반자 수명시간 $\tau_1$은 ~1 ns로 성장온도에 따른 변화는 관찰되지 않았다. 또한 방출파장이 1400 nm에서 1480 nm까지 PL 피크 근처에서 운반자 수명시간은 거의 일정하게 나타났다. Be-doped 시료의 PL 피크는 1236 nm에서 나타나며, Si-doped 시료는 1288 nm, undoped 시료는 1430 nm에서 PL 피크가 측정되었다. PL 피크에서 PL 소멸곡선은 Be-doped 시료가 가장 빨리 감소하였으며, Si-doped 시료가 가장 길게 나타났다. 이러한 결과로부터 $In_{0.64}Al_{0.36}Sb$의 광학적 특성은 성장 온도, dopant type, 도핑 농도에 따라 변화하는 것을 확인하였다.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.205-205
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• 2013

테라헤르쯔(terahertz: THz)파는 0.1~10 THz 의 범위로 적외선과 방송파 사이에 광대역 주파수 스펙트럼을 차지하고 있으며 직진성, 투과성, 그리고 낮은 에너지 (meV)를 가지고 있어 비 파괴적이고 무해한 장점을 지니고 있다. Ti:sapphire laser와 같은 femto-pulse source 등이 많은 발전이 되어 현재 많은 연구와 발전이 이루어지고 있다. femto-pulse source를 이용한 THz 응용에서는 높은 저항, 큰 전자 이동도, 그리고 아주 짧은 전하수명의 기판을 요구하는데 저온에서 성장한 (low-temperature grown : LT) GaAs는 격자 내에 Gallium 자리에 Arsenic이 치환 하면서 AsGa antisite가 발생하여 전하수명을 짧아지는 것을 응용하여 가장 많이 이용되고 있다. 현재 THz 응용분야에서 보다 작고 가격경쟁력이 있는 광통신을 이용한 THz photomixer등이 활발히 연구 하고 있다. 광섬유 내에서 손실과 분산이 최소값을 가지는 부분이 1.55 ${\mu}m$ 부근이고 In0.53Ga0.47As 기판을 이용하였을 때 여기에 완벽하게 만족하게 된다. 하지만 LT-InGaAs 의 경우 AsGa antisite로 인하여 carrier lifetime은 짧아지지만 높은 n-type 전하밀도를 가지게 된다. 이때 Be을 doping하여 전하밀도를 보상하여 높은 저항을 유지해야 하는데 Be의 활성화를 위해서는 열처리를 필요로 한다. 하지만 열처리를 하면 carrier lifetime이 길어지기 때문에 carrier lifetime과 저항을 적절히 조율해야 한다. 이는 물질자체의 특성이기 때문에 InGaAs는 GaAs보다 낮은 amplitude와 짧은 cut-off frequency를 가진다. 본 연구에서는 보다 높은 저항을 얻기 위하여 molecular beam epitaxy를 이용하여 semi-insulating InP:Fe 기판위에 격자 정합된 InGaAs:Be/InAlAs multi quantum well (MQW)를 온도별 ($250{\sim}400^{\circ}C$), 주기별 (50~150)로 성장을 하였고 이때 InGaAs layer의 Be doping level은 $2{\times}1018\;cm^{-3}$, Ex-situ annealing은 $550^{\circ}C$에서 10분으로 고정 하였다. THz 발생 실험에서는 InGaAs/InAlAs MQW은 4000 pA로 1,000 pA를 가지는 InGaAs epilayer보다 4배 높은 전류 신호를 얻을 수 있었고 모든 샘플이 2 THz에서 cut-off frequency를 가지고 있었다. THz 검출 실험에서는 LT-InGaAs:Be epilayer LT-InGaAs:Be/InAlAs, HT-InGaAs/InAlAs 샘플이 각각 180, 9000, 12000 pA의 전류신호를 가지고 있었고 모든 샘플이 2 THz에서 cut-off frequency를 가지고 있었다. HT-InGaAs/InAlAs MQW를 이용한 검출실험에서는 InGaAs layer가 defect free이지만 LT-InGaAs:Be/ InAlAs MQW 보다 높은 전류 신호를 얻을 수 있었다. 이는 InAlAs layer가 저항만 높이는 것뿐만 아니라 carrier trapping layer로써의 역할도 하는 것으로 사료된다.

• Korean Journal of Weed Science
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• v.7 no.2
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• pp.236-242
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• 1987

The study was conducted to interprete the fluctuation of weed vegetation in plant-sociological impacts as affected by the mixture use of oxyfluorfen and glyphosate with various dosages. Also, intended to know the real interaction between two herbicides in weeding efficacies. The better efficacy from the above mixture was recognized than from the oxyfluorfen + paraquat mixture on the perennial-sites. In lower rate mixture of oxyfluorfen, the dominance index was increased by the annual grass species (ie. Digitaria), and of glyphosate by the biennial Stellaria and perennial species (ie. Artemisia). Also, the positive maximum action of both oxyfluorfen and glyphosate in various mixture rates was categorized upto 0.55kg ai/ha for oxyfluorfen and 0.35kg ai/ha for glyphosate, respectively. However, the interaction between the above two herbicides recognized actually as negative. Consequently, the use of mixture compound of oxyfluorfen with glyphosate are expected rather to promote the control efficacy of specific weed species, to enlarge the weeding spectrum and to prolong the weeding periods than to reduce the application rate of both chemicals depending on any synergic interactions.

• Korean Journal of Weed Science
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• v.7 no.2
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• pp.220-235
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• 1987

The experiment was carried out to find the feasibility of using Oxyfluorfen in the paddy fields by investigating the difference of selective activity of Oxyfluorfen among rice cultivars and major paddy weed species. The dosage of Oxyfluorfen that show selective activity between rice cultivars and weed species ranged from 0.1 to 0.4kg ai/ha. The degree of growth inhibition was in order of whole-plant soaking application > root soaking application > stem bandage application, and in that case $10^{-5}$M Oxyfluorfen was treated after emergence. Especially the growth inhibition of rice cultivars and Cyperus serotinus was low, among others. Photosynthesis was severely inhibited at the Oxyfluorfen level above $10^{-4}$ M in all the tested weeds, but inhibition of respiration was not to be seen. Isolated single cells of two rice cultivars and Cyperus serotinus were tolerant to $10^{-5}$M Oxyfluorfen,but those of Echinochloa crus-galli and Sagittaria pygmaea were susceptible comparatively. The growth inhibition of suspension cultured rice cell induced by the increments of Oxyfluorfen concentration, and the degree of inhibition was higher in C.V. Mushakdanti than in C.V. Aichiasahi.

• Korean Journal of Weed Science
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• v.5 no.1
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• pp.24-34
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• 1985

To estimate the fundamental situation of weed emergence and it's competition to paddy rice (critical competition period and threshold level) in the southern paddy area in Korea, two rice cultivars (Pungsanbyo and Tongjinbyo) under two cropping periods (Mono- and After-barley-cropping) were experimented. As a result, the dominant weed species (Monochoria vaginalis and Scirpus juncoides Roxb.) and the better emerging conditions (rather at the monocropping and cv. Punsanbyo) were identified. Also, the main components of yield decrease (25-55% of the weed-free check) of both cultivars as affected by weed competition were the number of spikelets, panicle and ripening rate in monocropping, and the ripening rate and grain weight in after-barley-cropping, respectively. Under the situation of combinated dominance with Monochoria v. and Scirpus j. among others, the duration of critical competition periods was enlarged.

• Korean Journal of Weed Science
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• v.12 no.2
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• pp.166-172
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• 1992

The identification on blue-queen algae which were collected from paddy rice fields of the whole nation was carried out in 1991. The blue-green algae identified were 20 species in 5 families including 7 species in the Chroococcaceae. 1 species in the Chamaesiphonaceae. 1 species in the Pleurocapsaceae, 6 species in the Nostocaeae and 5 species in the Oscillatoriaceae. Among the blue-green algae, 6 species in 4 genera including Cylindrospernum, Anabaenopsis, Anabaena and Nostoc were characterized by heterocysts concerning with nitrogen fixation capacity. A concentrated population of Oscillatoria spp. induced soil flakes with blue tint in paddy rice fields. The genera. Spirulina and Oscillatoria, showed their specific motility.

• Korean Journal of Weed Science
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• v.15 no.2
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• pp.99-104
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• 1995

This experiment was conducted to evaluate effective weed control in direct-seeded rice under dry fields. The results obtained are as follows. Cyhalofop/bentazone EW and cyhalofop/pendimethalin EC were very effective for the weed control but cyhalofop/cinosulfuron WP and cyhalofop/azimsulfuron SC were tended to exhibit the lower weeding effect. The plant height and the tiller number of rice were not greatly affected by herbicides, but rice yield was greatly influenced by them. The control efficacy was observed the extend of 94% until 60days after seeding under the treatment of systematic herbicides such as foliar applied pendimethalin propanil EC at 15days after seeding mowed by pyrazosulfuron molinate GR at 5days after irrigation. Irrigation at 25days after seeding was able to control annual weeds by the extent of 25% and exhibited control effect of 94% on systematic treatment of herbicides compared with that of 35days after seeding.