• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.5
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• pp.699-708
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• 2000

To make compact evaporator, experiments that show characteristics of evaporating heat transfer and pressure drop in the helically coiled small diameter tube were taken in this research. The experiments were performed with HCFC-22 in the helically coiled small diameter tube; inner diameter=1.0(mm), tube length=2.0(m), and curvature diameter=31, 34, 46.2(mm). The experiments were also carried out with the following test conditions; saturation pressure=0.588(MPa), mass velocity=$150{\sim}500(kg/m^2s)$, and heat flux=$1{\sim}5(kW/m^2)$. The experiment results are that the empirical correlation to predict heat transfer coefficient for single phase flow in helically coiled small diameter tube was obtained. It was found that dry-out is occurred at low-quality region for evaporation heat transfer because of breaking of annular liquid film. The friction factor of single phase flow of helically coiled tube was agreed with Prandtl's correlation. Finally, It was proposed for correlation that can precisely predict the friction factor of two phase flow of helically coiled tube.

• Journal of the Korean Vacuum Society
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• v.7 no.4
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• pp.306-313
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• 1998

The electrochromic $WO_3$thin films were prepared by using the electron-beam evaporatin technique. Flms prepared at a vacuum pressure of $10^{-4}$ mbar were found to be most stable during repeated potential cycles. The chemical stability of the film in aqueous solutions was also affected by the vacuum pressure during evaporation. The redox current and the optical properties of the degraded films were affected by the thickness of the film. The 5,000$\AA$-thick films were found to be most stable, undergoing the least degradation during the repeated coloring and bleaching cycles. The origin of the mechanism dominating the degradation during the repeated coloring and bleaching cycles was the accumulation of lithium in the film, which results in decreasing redox current. Tungsten oxide films with titanium content of about 10-15 mol% was found to be most stable, undergoing the least degradation during the repeated cycles. The origin of the mechanism dominating the least degradation during the repeated cycles was the reduction of lithium ion trapping sites in the films, which results in a increased durability.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.10a
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• pp.506-508
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• 2005

In general, organic TFTs are comprised of four components: gate electrode, gate dielectric, organic active semiconductor layer, and source and drain contacts. The TFT current, in turn, is typically determined by channel length and width, carrier field effect mobility, gate dielectric thickness and permittivity, contact resistance, and biasing conditions. More recently, a number of techniques and processes have been introduced to the fabrication of OTFT circuits and displays that aim specifically at reduced fabrication cost. These include microcontact printing for the patterning of metals and dielectrics, the use of photochemically patterned insulating and conducting films, and inkjet printing for the selective deposition of contacts and interconnect pattern. In the fabrication of organic TFTs, microcontact printing has been used to pattern gate electrodes, gate dielectrics, and source and drain contacts with sufficient yield to allow the fabrication of transistors. We were fabricated a pentacene OTFTs on flexible PEN film. Au/Cr was used for the gate electrode, parylene-c was deposited as the gate dielectric, and Au/Cr was chosen for the source and drain contacts; were all deposited by ion-beam sputtering and patterned by microcontact printing and lift-off process. Prior to the deposition of the organic active layer, the gate dielectric surface was treated with octadecyltrichlorosilane(OTS) from the vapor phase. To complete the device, pentacene was deposited by thermal evaporation and patterned using a parylene-c layer. The device was shown that the carrier field effect mobility, the threshold voltage, the subthreshold slope, and the on/off current ratio were improved.

• Korean Chemical Engineering Research
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• v.55 no.2
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• pp.214-219
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• 2017

In this work, we fabricated PS-b-P4VP block copolymer membranes from self-assembly and non-solvent induced phase separation (SNIPS), which combines the block copolymer self-assembly and conventional NIPS process. While previous studies mostly focused on the fabrication of well-defined structures, we systematically examined various processing parameters such as polymer concentration, solvent evaporation duration, solvent composition, and humidity, to optimized the membrane structures. As a result, the morphology of PS-b-P4VP membranes was optimized at a certain polymer concentration in solution and composition of volatile solvent at low humidity conditions, resulting in SNIPS separation membranes with well-defined nanopores on the surface, 75% of membrane porosity, and 18% of surface porosity.

• Journal of the Korean Vacuum Society
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• v.18 no.4
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• pp.259-265
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• 2009

We fabricated the field effect transistor using single crystalline ZnO nanowires synthesized by a conventional thermal evaporation method and investigated their basic properties under the various conditions such as ultraviolet irradiation, reducing gas and electrolyte. The typical carrier concentration and mobility of the single crystalline ZnO nanowire with a diameter of 100 nm and length of 5 um were $1.30{\times}10^{18}cm^{-3}$ and $15.6cm^2V^{-1}s^{-1}$, respectively. The current of ZnO nanowire under ultraviolet irradiation significantly increased about 400 times higher as compared to in the darkness. In addition, the ZnO nanowire showed typical sensing characteristics for $H_2$ and CO due to well-known surface reactions and typical current-voltage characteristics under the 0.1 M NaCl electrolyte.

• Atmosphere
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• v.26 no.3
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• pp.435-444
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• 2016

In spite of considerable progress in the recent decades, there still remain large uncertainties in numerical cloud models. In this study, effects of uncertainty in terminal velocity of graupel on cloud simulation are investigated. For this, a two-dimensional bin microphysics cloud model is employed, and deep convective clouds are simulated under idealized environmental conditions. In the sensitivity experiments, the terminal velocity of graupel is changed to twice and half the velocity in the control experiment. In the experiment with fast graupel terminal velocity, a large amount of graupel mass is present in the lower layer. On the other hand, in the experiment with slow graupel terminal velocity, almost all graupel mass remains in the upper layer. The graupel size distribution exhibits that as graupel terminal velocity increases, in the lower layer, the number of graupel particles increases and the peak radius in the graupel mass size distribution decreases. In the experiment with fast graupel terminal velocity, the vertical velocity is decreased mainly due to a decrease in riming that leads to a decrease in latent heat release and an increase in evaporative cooling via evaporation, sublimation, and melting that leads to more stable atmosphere. This decrease in vertical velocity causes graupel particles to fall toward the ground easier. By the changes in graupel terminal velocity, the accumulated surface precipitation amount differs up to about two times. This study reveals that the terminal velocity of graupel should be estimated more accurately than it is now.

• Korean Journal of Optics and Photonics
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• v.11 no.3
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• pp.147-151
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• 2000

We deposited the ion assisted ${Ta_2}{O_5}$ films and conventional thermal evaporated ${Ta_2}{O_5}$ films by using electron beam gun, and measured the optical properties and mechanical properties of the fabricated films according to the evaporation conditions. In the case of the TazOs films by oxygen ion assisted deposition with the anode voltage of 120 V, and current density of $50~500\muA/cm^2$, the refractive index exhibited 2.15 which was higher than the conventionally deposited film index 1.94 and the tensile stress exhibited $5.0\times10^8 dyne/cm^2$ which was lower than $7.0\times10^8 dyne/cm^2$. This properties coincided with the optical and mechanical properties of the films deposited at the elevated substrate temperature of $230^{\circ}C$. In the case of the argon ion assisted films the tensile stress was decreased but the absorption existed at the short wavelength in the visible spectral region. And all the fabricated films were found to be amorphous by the X-ray diffraction analysis. lysis.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.11a
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• pp.245-253
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• 2010

The present study shows some results of developing evaporative heat exchangers with mini-channels. Heat exchangers with three different water paths were manufactured and tested to compare performances of cooling and pressure drop. Among the three types of heat exchangers, Type 2 with full-etching was proved to be the best in the cooling performances for considered operating conditions, and thus it is recommended to adopt Type 2 for its simplicity of production and outstanding performance. However, Type 1 was shown to be better when it is operated at a high air inlet temperature condition. The developed evaporative heat exchanger will be installed in Environmental Control Systems(ECSs) for aerial vehicles, and it can be used effectively in case an ECS is not only limited in its weight and volume but also required to absorb heats without supplying water (or a coolant) for a certain period of time.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.250-250
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• 2012

Organic light-emitting diodes (OLED) and polymer light emitting diodes (PLED) have been regarded as the candidate for the next generation light source and flat panel display. Currently, the most common OLED industrial fabrication technology used in producing real products utilizes a fine shadow mask during the thermal evaporation of small molecule materials. However, due to high potential including low cost, easy process and scalability, various researches about solution process are progressed. Since polymer has some disadvantages such as short lifetime and difficulty of purifying, small molecule OLED (SMOLED) can be a good alternative. In this work, we have demonstrated high efficient solution-processed OLED with small molecule. We use CBP (4,4'-N,N'-dicarbazolebiphenyl) as a host doped with green dye (Ir(ppy)3 (fac-tris(2-phenyl pyridine) iridium)). PBD (2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole) and TPD (N,N'diphenyl-N,N'-Bis (3-methylphenyl)-[1,1-biphenyl]-4,4'-diamine) are employed as an electron transport material and a hole transport material. And TPBi (2,2',2''-(1,3,5-phenylene) tris (1-phenyl-1H-benzimidazole)) is used as an hole blocking layer for proper hole and electron balance. With adding evaporated TPBi layer, the current efficiency was very improved. Among various parameters, we observed the property of OLED device by changing the thickness of hole transporting layer and solvent which can dissolve organic material. We could make small molecule OLED device with finding proper conditions.

• Journal of Sensor Science and Technology
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• v.6 no.5
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• pp.414-422
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• 1997

CdS thin films with low resistivity and adequate transmittance in the visible region for the window of CdS/CdTe hetero junction solar cel1 were prepared by close spaced vapor transport(CSVT) method. The electrical and optical properties of the CdS thin films were investigated in terms of the deposition conditions, such as the substrate temperature, the working pressure, and the source temperature. The substrate temperature, the working pressure, and the source temperature for the optimum deposition of the CdS thin films were $300^{\circ}C$, 100mTorr, and $730^{\circ}C$, respectively. The resistivity and the transmittance of the CdS thin films deposited under this condition were about $7.21{\times}10^{3}{\Omega}cm$ and over 65%, respectively. The crystallinity, the resistivity, and optical band gap were improved greatly compared to the CdS thin films deposited by general high vacuum evaporation.