• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집D
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• pp.782-789
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• 2001

Local heat/mass transfer and friction loss in a square duct roughened with various types of continuous and discrete rib turbulators are investigated. The combined effects of the gap flows of the discrete ribs and the secondary flows are examined for the purpose of the reduction of thermally weak regions and the promotion of the uniformity of heat/mass transfer distributions as well as the augmentation of average heat/mass transfer. The rib-to-rib pitch to the rib height ratio (p/e) of 8 and the rib angles of 90 and 60 deg are selected with $e/D_{h}=0.08$. The vortical structure of the secondary flows induced by the parallel angled arrays are quite distinct from that induced by the cross angled arrays. This distinction influences on heat/mass transfer and friction loss in all the tested cases. The gap flows of the discrete ribs reduce the strength of the secondary flows but promote local turbulence and flow mixing. As a result, the fairly uniform heat/mass transfer distributions are obtained with two row gaps.

• 한국광학회지
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• 제4권2호
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• pp.195-199
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• 1993

Rh-6G(Rhodamine 6G)를 주색소로 하고 C-545(Coumarin 545)를 첨가색소로 하는 펄스형 혼합 색소레이저의 출력을 조사하였다. 동축형의 섬광관을 펌핑 광원으로 이용하였으며 Rh-6G 단일 색소로 발진할 경우 전기 입력 에너지가 346 J 일 때 첨두 출력과 에너지는 각각 27kW, 59mJ이었다. Rh-6G의 흡수 스펙트럼과 일치하는 형광 스펙트럼을 갖는 C-545를 에서지 주개로 선택하였다. Rh-6G의 농도를 최적 농도인 $1{\times}10_-4mol/l$로 고정하고 C-545의 농도를 $1{\times}10_7mol/l$부터 변화시키면서 혼합 색소에 대한 레이저의 출력 특성을 조사하였다. C-545의 농도가 Rh-6G 농도의 0.4%일 때 출력 에너지는 약 70% 증가하였다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1999년도 학회창립 10주년 기념 1999년도 가을 학술발표회 논문집
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• pp.557-560
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• 1999

In civil engineering and construction field, recently the great enhancement of new material and building technique have been made by many studies and reports. These studies have attracted many countries, since 1980's those study on reinforcement with steel fiber have been done by America, Japan and the other countries. Designs and proposals on building method have been applied, several universities and laboratory centers in our country have been studied, but the study on field application is short. Also a part of study on the shear behavior of reinforced concrete beams with steel fiber has accomplished. but up to this time, reliable establishment is undone. Therefore, this study is performed the static loading test to analysis shear failure behavior in reinforced concrete beams with steel fiber. we have observed the limit load of shear force, primary bending crack load, primary diagonal crack load, evaluating relative of load and steel, crack increase and failure shape according to increase of load. Through the exam and the observation of output, we estimate the shear failure behavior of SFRC beams according to fiber mixing amount.

• KSBB Journal
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• 제4권1호
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• pp.11-14
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• 1989

Tower fermentor를 이용한 연속 알콜발효에서 cell re-cycle과 aeration에 대한 영향을 검토하였다. 균주는 floc-culationg 효모인 Saccharomyces cerecisiae TS4를 를 사용하였다. 15% glucose를 사용한 cell recycle system의 연속 알콜발효에서 cell 농도는 50%/1였고, ethanol productiv는 26.4g EtOH/l-hr로서 cell농도가 가장 높은 값을 나타내었으며, aeration rate는 3.8$\times$ $10^-^3$ VVM이상부터는 ethanol pro-ductivity가 감소하였다.

• Journal of Electrical Engineering and Technology
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• 제10권4호
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• pp.1712-1719
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• 2015

In recent days, there was a significant development on the electrical, thermal, mechanical, physical, chemical, magnetic and optical properties of the polyamide enamel, varnish and other insulating materials by the addition of nano fillers to it. Enamel was used in High Voltage Apparatuses used in Medical Electronics as insulation. Insulating materials determine the life time of the electrical apparatuses. The life time of the insulating materials was improved by the addition of nano fillers to it. Hence the life time of the electrical apparatuses was improved by the mixing of nano fillers to the enamel. In this research, the basic dielectric properties of the enamel and enamel mixed with nano composites of silica and alumina were analyzed and compared with each other. The addition of nano fillers has improved the quality factor and capacitance of the enamel. It was also observed that the addition of nano fillers has reduced the dissipation factor and dielectric losses of the enamel. Heat produced by the dielectric losses was also reduced by adding nano fillers to it.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2005년도 제31회 KOSCO SYMPOSIUM 논문집
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• pp.58-63
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• 2005

As fuel cells approach commercialization, hydrogen production becomes a critical step in the overall energy conversion pathway. Reforming is a process that produces a hydrogen-rich gas from hydrocarbon fuels. Hydrogen production via autothermal reforming (ATR) is particularly attractive for applications that demand a quick start-up and response time in a compact size. However, further research is required to optimize the performance of autothermal reformers and accurate models of reactor performance must be developed and validated. The design includes the requirement of accommodating a wide range of experimental set ups. Factors considered in the design of the reformer are capability to use multiple fuels, ability to vary stoichiometry, precise temperature and pressure control, implementation of enhancement methods, capability to implement variable catalyst positions and catalyst arrangement, ability to monitor and change reactant mixing, and proper implementation of data acquisition. A model of the system was first developed in order to calculate flowrates, heating, space velocity, and other important parameters needed to select the hardware that comprises the reformer. Predicted performance will be compared to actual data once the reformer construction is completed. This comparison will quantify the accuracy of the model and should point to areas where further model development is required. The end result will be a research tool that allows engineers to optimize hydrogen production via autothermal reformation.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2005년도 제31회 KOSCO SYMPOSIUM 논문집
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• pp.255-260
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• 2005

To achieve efficient combustion within a manageable length, a successful fuel injection scheme must provide rapid mixing between the fuel and airstreams. The aim of the present numerical research is to investigate the flame holding and combustion enhancement. Additional fuel into the cavity prevents shear flow impingement on the trailing edge of the cavity. The high temperature freestream flow mixes with the cold hydrogen fuel that is injected into the cavity and raises the fuel temperature remarkably and become to start combustion. The high pressure in the cavity due to the cavity structure and combustion leads the hydrogen fuel to upstream. The shock in the cavity to be generated by the fuel injection joins together and reflects off the ceiling wall. This makes high pressure and low mach number region and makes a small recirculation in this region. This high stagnation temperature is nearly recovered in the shear layer in front of the cavity and leads to start combustion. In the downstream of the cavity, the wall pressure drops significantly. This means that the combustion phenomenon is diminished. Because fuel lumps at the trailing edge of the cavity then it spreads after the cavity so, in this region there is a strong expansion.

• JSTS:Journal of Semiconductor Technology and Science
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• 제16권5호
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• pp.595-604
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• 2016

Utilizing a standard 130-nm CMOS process, a RF frontend is designed at 24 GHz for automotive collision avoidance radar application. Single IF direct conversion receiver (DCR) architecture is adopted to achieve high integration level and to alleviate the DCR problem. The proposed frontend is composed of a two-stage LNA and downconversion mixers. To save power consumption, and to enhance gain and linearity, stacked NMOS-PMOS $g_m$-boosting technique is employed in the design of LNA as the first stage. The switch transistors in the mixing stage are biased in subthreshold region to achieve low power consumption. The single balanced mixer is designed in PMOS transistors and is also realized based on the well-known folded architecture to increase voltage headroom. This frontend circuit features enhancement in gain, linearity, and power dissipation. The proposed circuit showed a maximum conversion gain of 19.6 dB and noise figure of 3 dB at the operation frequency. It also showed input and output return losses of less than -10 dB within bandwidth. Furthermore, the port-to-port isolation illustrated excellent characteristic between two ports. This frontend showed the third-order input intercept point (IIP3) of 3 dBm for the whole circuit with power dissipation of 6.5 mW from a 1.5 V supply.

• 한국조리학회지
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• 제7권3호
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• pp.145-161
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• 2001

In odor to develop fillet-type seasoner and mixed powder-type seasoner using smoked mackerel as primary material, processing conditions of the mackerel meat and flavoring extract from various materials were examined. The approximate composition of mackerel meat and mixed powde-type seasoner using mackerel as primary material were 10.9 and 11.7%, for moisture 79.1 and 57.2% for crude protein, 5.3 and 2.9% for crude lipid, and 4.3 and 24.6% for crude ash, respectively. It was suitable to simmer raw mackerel in 3% chitooligosaccaride solution at 8$0^{\circ}C$ for 10 min., for the enhancement of reaction their meat and chitooligosaccharide. Considering effect of type of woodsmoke on organoletic properties of mackerel after smoking, oak and mixture(oak wood ＋ citrus wood = 1 : 1) were superior to another woodsmoke, the smoking conditions favoring the most overall preference were 8$0^{\circ}C$, 25min. for smoking time, 20$0^{\circ}C$, 20min. for baking, and 10$0^{\circ}C$. 4hrs. for drying. The optimal material mixing ratio for mixed powder-type seasoner was powder of smoked mackerel 60%, dried anchovy 15%, dried sea tangle 10%. The most appropriate extraction condition of mixed powder seasoner with packing tea bag(10g/bag) was 98$^{\circ}C$ for 5min. in the boiling water.

• International Journal of Fluid Machinery and Systems
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• 제9권3호
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• pp.265-276
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• 2016

Energy systems working coherently in different conditions may not have a specific design which can provide optimal performance. A system working for a longer period at lower efficiency implies higher energy consumption. In this effort, a methodology demonstrated by a jet pump design and optimization via numerical modeling for fluid dynamics and implementation of an evolutionary algorithm for the optimization shows a reduction in computational costs. The jet pump inherently has a low efficiency because of improper mixing of primary and secondary fluids, and multiple momentum and energy transfer phenomena associated with it. The high fidelity solutions were obtained through a validated numerical model to construct an approximate function through surrogate analysis. Pareto-optimal solutions for two objective functions, i.e., secondary fluid pressure head and primary fluid pressure-drop, were generated through a multi-objective genetic algorithm. For the jet pump geometry, a design space of several design variables was discretized using the Latin hypercube sampling method for the optimization. The performance analysis of the surrogate models shows that the combined surrogates perform better than a single surrogate and the optimized jet pump shows a higher performance. The approach can be implemented in other energy systems to find a better design.