• Journal of the Korean institute of surface engineering
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• v.44 no.5
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• pp.185-189
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• 2011

$Cu_2ZnSnSe_4$ thin films for solar absorber application were prepared by pulsed laser deposition of a synthesized $Cu_2ZnSnSe_4$ compound target. The film's composition revealed that the deposited films possess an identical composition with the target material. Further film compositional control toward a stoichiometric composition was performed by optimizing substrate temperature, deposition time and target rotational speed. At the optimum condition, X-ray diffraction patterns of films showed that the films demonstrated polycrystalline stannite single phase with a high degree of (112) preferred orientation. The absorption coefficient of $Cu_2ZnSnSe_4$ thin films were above 104 cm.1 with a band gap of 1.45 eV. At an optimum condition, films were identified as a p type semiconductor characteristic with a resistivity as low as $10^{-1}{\Omega}cm$ and a carrier concentration in the order of $10^{17}cm^{-3}$.

• Journal of the Korean Wood Science and Technology
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• v.36 no.5
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• pp.56-65
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• 2008

In this paper experimental results are presented for the rheological behavior of high-solids saccharification of mixed northeast hardwood as a model feedstock. The experimental determination of the viscosity, shear stress, and shear rate relationships of the 10 to 20 percent slurry concentrations with constant enzyme concentrations were performed under variable rotational speed of a viscometer (2.0 to 200 RPM) at combined temperatures (50 to $30^{\circ}C$) for the initial four hours. The viscosities of saccharification slurries observed were in the ranges of 0.024 to 0.028, 0.401 to 0.058, and 0.840 to 0.087 Pa s for shear rates up to 100 reciprocal seconds at 10, 15, and 20 percent initial solids (w/v) respectively. The fluid behavior of the suspensions was modeled using the power-law, the Herschel-Bulkley, the Casson, and the Bingham model. The results showed that broth slurries were pseudoplastic with a yield stress. The model slope increased and the model intercept decreased with increasing fermentation time at shear rates normal for the fermentor. The broth slurries exhibited Newtonian behavior at high and low shear rates during initial saccharification process. The solid particle size ranged from 57.8 to $70.0{\mu}m$ for $40^{\circ}C$ and from 44.0 to 57.5 11m for combined temperatures at 10, 15, and 20 percent initial solids (w/v) respectively.

• International Journal of Fluid Machinery and Systems
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• v.4 no.1
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• pp.209-216
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• 2011

The flow upstream of a centrifugal pump impeller has been investigated by both experimental test and numerical simulation. For experimental study, the flow field at four sections in the pump suction is measured by using PIV method. For calculation, the three dimensional turbulent flow for the full flow passage of the pump is simulated based on RANS equations combined with RNG k-$\varepsilon$ turbulence model. From those results, it is noted that at both design lo ad and quarter load condition, the pre-swirl flow whose direction is the same as the impeller rotation exists at all four sections in suction pipe of the pump, and at each section, the pre-swirl velocity becomes obviously larger at higher rotational speed. It is also indicated that at quarter load condition, the low pressure region at suction surface of the vane is large because of the unfavorable flow upstream of the pump impeller.

• Journal of the Korean Ceramic Society
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• v.50 no.6
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• pp.533-538
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• 2013

Silicon carbide (SiC) materials are typical ceramic materials with a wide range of uses due to their high hardness and strength and oxidation resistance. In particular, due to the corrosion resistance of the material against acids and bases including the chemical resistance against ionic gases such as plasma, the application of SiC has been expanded to extreme environments. In the SiC deposition process, where chemical vapor deposition (CVD) technology is used, the reactions between the raw gases containing Si and C sources occur from gas phase to solid phases; thus, the merit of the CVD technology is that it can provide high purity SiC in relatively low temperatures in comparison with other fabrication methods. However, the product yield rarely reaches 50% due to the difficulty in performing uniform and dense deposition. In this study, using a computational fluid dynamics (CFD) simulation, the gas velocity inside the reactor and the concentration change in the gas phase during the SiC CVD manufacturing process are calculated with respect to the gas velocity and rotational speed of the stage where the deposition articles are located.

• IE interfaces
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• v.12 no.1
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• pp.68-78
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• 1999

A noncircular cutting such as a piston cutting has depended on the copy-machining because of its complex shape. But the copy-machining needs a master model and brings about a low quality of the piston caused by being worn out of the master model. And the lower cutting speed reduces the productivity. In this paper, for solving these problems, a specialized software system and its subsequent procedure are presented. The shape of a piston consists of an oval, an offset, recesses, and eccentricities. The paper describes these shapes as a consistent equation that is a function of the rotational angle and the position of longitudinal direction(Z-axis). It is simple to define the characteristic geometry of a piston and to generate a tool path for CNC machining. This paper proposes the a proper structure of a 4-axes CNC(Computerized Numerical Control) lathe for machining the piston. As well as X-axis and Z-axis, are attached to the machine a C-axis for rotation and a Y-axis for higher speedy prismatic motion parallel to X-axis.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.25 no.4
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• pp.245-252
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• 2016

Girth gears are applied in the mining, cement, and mineral processing industries and used in various types of horizontal mills, rotary dryers and kilns, and other heavy-gear ring applications. The large ring gears are normally fitted outside mills or kilns to provide the primary rotational drive. Recently, an external pinwheel gear set (e-PGS) was introduced to overcome manufacturing problems associated with girth gears. e-PGS is also suitable for low-speed, heavy-duty mechanical transmission and dusty and poor-lubrication conditions. This paper first presents a new profile modification of root relief for the e-PGS cam pinion. We then investigate load-stress factors to estimate the surface fatigue life by varying the shape design parameters. The results show that the contact fatigue life of an e-PGS can be extended significantly by increasing the profile shift coefficient. However, support bearing life of the pinwheel depends more on the contact force distribution than the profile shift coefficient.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.46 no.6
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• pp.9-13
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• 2009

In the three axis control of Low Earth Orbit (LEO) satellite by using reaction wheel and gyro, a reaction wheel produces the control torque by the wheel speed or momentum, and a gyro carries out measuring of the attitude angle and the attitude angular velocity. In this paper, the dynamic modelling of LEO is consisted of the one from the rotational motion of the satellite with basic rigid body model and a flexible model, in addition to the reaction wheel model. A robust controller $(H_\infty)$ is designed to stabilize the rigid body and the flexible body of satellite, which can be perturbed due to disturbance, etc. The result obtained by $H_\infty$ controller is compared with that of the PI (Proportional and Integration) controller, which has been traditionally using for the stabilizing LEO satellite.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.820-823
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• 2017

This study experimentally investigate how the Reynolds number affect cavitation performance in a turbopump inducer using water. Cavitation performance has been determined by the static pressure measured at the inlet of the inducer. Reynolds number has been varied by varying water temperature and inducer rotational speed to maintain constant non-dimensional thermal parameter. At low non-dimensional thermal parameter, the critical cavitation number is insensitive to Reynolds number. However, at high non-dimensional thermal parameter, the critical cavitation number increased as Reynolds number increases. Thus, cavitation performance is deteriorated as Reynolds number increases when thermal effect exists.

• International Journal of Fluid Machinery and Systems
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• v.3 no.1
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• pp.1-10
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• 2010

The present study is a fundamental approach to develop the measuring technology for minute fluctuating pressures on the three-dimensional blade surfaces of the fan which rotates with an arbitrary rotation-axis direction. In this situation, we are required to correct the centrifugal-force effect, the gravitational-force effect and the other leading-error effects for accurate measurements of the minute pressures. The working fluid is air. A pressure transducer rotating with an arbitrary attitude is closely sealed by a twofold shroud system. The rotational motion with an arbitrary attitude is produced by fixing the pressure transducer to the cantilever which is connected to a motor-driven disc of 500mm in diameter and 5mm in thickness. As a result, we have quantitatively determined main governing effects upon the non-effective component of the pressure-transducer signal.

• Journal of the Korean Graphic Arts Communication Society
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• v.29 no.1
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• pp.45-59
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• 2011

According as gradually increasing the demand for Eco-friendly products it has been progressed fairly development at a field of printing and printing inks. The Inks are used by soy oil beginning of ink industry for preventing environment. Now it is possible to make Eco-friendly inks with vegetable ester. So it is not necessary to use petroleum-based solvents for preventing environment. But There is some problems if using vegetable ester to inks. Vegetable ester has high solubility, it causes misting and low viscosity of the Inks. So resin is required high performance. Thus, in this paper, I studied about the properties variation of the Varnish and inks According to using the phenolic modified rosin ester and Soy oil Methyl esters. The compared in order of average molecular weight by the GPC method, rheological properties were found by rotational rheometer, and emulsion behavior were compared by high speed emulsification tester.