• Journal of ILASS-Korea
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• v.12 no.1
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• pp.38-44
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• 2007

Since the Liquid Phase LPG injection (LPLI) system has Advantages in power generation and emission characteristics compared to the mixer-type fuel-supply system, a variety of studies regarding LPLi system has been conducted and its applications are made in automobile industry. However, the heat extraction due to the evaporation of liquid fuel, causes not only a post-accumulation of fuel but also an icing phenomenon which is a frost of moisture in the air around the nozzle tip. Since there exists a difficulty in the accurate control of air fuel ratio in both fuel supply systems, it can result in poor engine performance and a large amount of harmful emissions. This research examines the characteristics of icing phenomenon and develops anti-icing bushing to prevent an icing on the surface of the injection tip. It was found that n-butane, which has a relatively high boiling point ($-0.5^{\circ}C$), was a main species of post-accumulation. Also the results show that the post-accumulation problem was allevaited the utilization of a large inner to outer bore ratio and smooth surface roughness. In addition, an icing phenomenon and its formation process were found to be mainly affected by the humidity and the temperature of inlet air in an inlet duct. Also, it was observed that an icing phenomenon is lessened using aluminum bushing whose end coincides with the end of fuel injection tip in length.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.6 no.3
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• pp.318-326
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• 1996

This study is to investigate a chemical vapor deposition technique of copper film which is expected to be more useful as metallizations of microcircuit fabrication. An experimental equipment was designed and set-up for this study, and a Cu-precursor used that is a metal-organic compound, named (hfac)Cu(I)VTMS ; (hevaflouoroacetylacetonate trimethyvinylsilane copper). Base pressure of the experimental system is in $10^{-6}$ Torr, and the chamber pressure and the substrate temperature can be controlled in the system. Before the deposition of copper thin film, tungsten or titanium nitride film was deposited onto the silicon wafer. Helium has been used as carrier gas to control the deposition rate. As a result, deposition rate was measured as $1,800\;{\AA}/min$ at $220^{\circ}C$ which is higher than the results of previous studies, and the average surface roughness was measured as about $200\;{\AA}$. A deposition selectivity was observed between W or TiN and $SiO_{2}$ substrates below $250^{\circ}C$, and optimum results are observed at $180^{\circ}C$ of substrate temperature and 0.8 Torr of chamber pressure.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.11 no.3
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• pp.195-202
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• 1998

The LPCVD system of batch type for the massproduction of semiconductor fabrication has a problem of phosphorous concentration uniformity in the boat. In this paper we study an improvement of the uniformity for phosphorous concentration and sheet resistance. These property was improved by using the nitrogen process and modified long nozzle for gas injection tube in the doped polysilicon deposition system. The phosphorous concentration and its uniformity for polysilicon film are measured by XRF(X-ray Fluorescence) for the conventional process condition and nitrogen process. In conventional process condition, the phosphorous concentration, it uniformity and sheet resistance for polysilicon film are in the range of 3.8~5.4$\times$10\ulcorner atoms/㎤, 17.3% and 59~$\Omega$/ , respectively. For the case of nitrogen process the corresponding measurements exhibited between 4.3~5.3$\times$10\ulcorner atoms/㎤, 10.6% and 58~81$\Omega$/ . We find that in the nitrogen process the uniformity of phosphorous concentration improved compared with conventional process condition, however, the sheet resistance in the up zone of the boat increased about 12 $\Omega$/ . In modified long nozzle, the phosphorous concentration, its uniformity and sheet resistance for polysilicon films are in the range of 4.5~5.1$\times$10\ulcorner atoms/㎤, 5.3% and 60~65$\Omega$/ respectively. Annealing after $N_2$process gives the increment of grain size and the decrement of roughness. Modification of nozzle gives the increment of injection amount of PH$_3$. Both of these suggestion result in the stable phosphorous concentration and sheet resistance. The results obtained in this study are also applicable to process control of batch type system for memory device fabrication.

• The Journal of Advanced Prosthodontics
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• v.10 no.2
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• pp.93-100
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• 2018

PURPOSE. The purpose of this study was to determine the changing frequency of a diamond bur after multiple usages on 3 different surfaces. MATERIALS AND METHODS. Human premolar teeth (N = 26), disc shaped direct metal laser sintered CoCr (N = 3) and zirconia specimens (N = 3) were used in this study. Groups named basically as Group T for teeth, Group M for CoCr, and Group Z for zirconia. Round tapered black-band diamond bur was used. The specimens were randomly divided into three groups and placed with a special assembly onto the surveyor. 1, 5, and 10 preparation protocols were performed to the first, second, and third sub-groups, respectively. The subgroups were named according to preparation numbers (1, 5, 10). The mentioned bur of each group was then used at another horizontal preparation on a new tooth sample. The same procedure was used for CoCr and zirconia disc specimens. All of the bur surfaces were evaluated using roughness analysis. Then, horizontal tooth preparation surfaces were examined under both stereomicroscope and SEM. The depth maps of tooth surfaces were also obtained from digital stereomicroscopic images. The results were statistically analyzed using One-Way ANOVA, and the Tukey HSD post-hoc tests (${\alpha}=.05$). RESULTS. All of the groups were significantly different from the control group (P<.001). There was no significant difference between groups Z5 and Z10 (P=.928). Significant differences were found among groups T5, M5, and Z5 (P<.001). CONCLUSION. Diamond burs wear after multiple use and they should be changed after 5 teeth preparations at most. A diamond bur should not be used for teeth preparation after try-in procedures of metal or zirconia substructures.

• Journal of the Korean Society of Laryngology, Phoniatrics and Logopedics
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• v.11 no.1
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• pp.39-45
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• 2000

Background and Objectives : Accent method is one of holistic approaches for behavior readjustment of voice therapy The aim of this study is to evaluate the efficacy of the accent method of voice therapy for the patients who have no improvement after LMS. Materials and Methods : Of the patients who had been undergone LMS during the period from Jan. 1999 to Dec. 1999, medical records of 38 patients who had not been improved were studied retrospectively. 19 patients(treatment group) were applied accent method and the other 19 patients(control group) refused voice therapy. The voice of all the patients of both group were analysed with CSL and Aerophone II programs in pre- and post operative period. The voice of treatment group were analysed with Visi-Pitch II program before the application of accent method and after the completion of accent method. Then, the results were compared using paired t-test. Results : The results of voice analysis were not different statistically between pre- and postoperative examination in both group. After application of accent method in the treatment group, fundamental frequency(F$_{0}$) of male, relative average pertubation, and shimmer were revealed significant differences(p＜0.01), and decrease in grade(G) scale and roughness(R) scale were statistically Important in perceptual analysis using GRBAS criteria(p＜0.01). But $F_0$ of female, maximal phonation time and S to Z ratio were not revealed significant differences. Conclusions : Accent method of voice therapy may be as a supplement- ary therapy in the patients who were not improved after surgery.

• Membrane and Water Treatment
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• v.6 no.5
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• pp.423-437
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• 2015

Polyvinylidene fluoride/fullerene nanoparticle (PVDF/$C_{60}$) composite microfiltration (MF) membranes were fabricated by a non-solvent induced phase separation (NIPS) using N, N-dimethylacetamide (DMAc) as solvent and deionized water (DI) as coagulation solution. Polyvinylpyrrolidone (PVP) was added to the casting solution to form membrane pores. $C_{60}$ was added in increments of 0.2% from 0.0% to 1.0% to produce six different membrane types: one pristine PVDF membrane type with no $C_{60}$ added as control, and five composite membrane types with varying $C_{60}$ concentrations of 0.2, 0.4, 0.6, 0.8 and 1.0%, respectively. The mechanical strength, morphology, pore size and distribution, hydrophilicity, surface property, permeation performance, and fouling resistance of the six membranes types were characterized using respective analytical methods. The results indicate that membranes containing $C_{60}$ have higher surface porosity and pore density than the pristine membrane. The presence of numerous pores on the membrane caused weaker mechanical strength, but the water flux of the composite membranes increased in spite of their smaller size. Initial flux and surface roughness reached the maximum point among the composite membranes when the $C_{60}$ concentration was 0.6 wt.%.

• Journal of the Korean Society for Precision Engineering
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• v.19 no.4
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• pp.93-100
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• 2002

The current from the feed motor of a machine tool contains substantial information about the machining state. There have been many researches that investigated the current as a measure for the cutting farces. However it has been reported that this indirect measurement of the cutting farces from the feed motor current is only feasible in low frequency. In this research, it was presented that the bandwidth of the current monitoring can be expanded to 130 Hz. And the unusual behavior of the current was examined in this bandwidth. The cross-feed directional cutting force influences the machined surface of the workpiece, which makes it necessary to estimate this force to control the roughness of the machined sulfate. The current exists in the stationary feed motor, and it can give the useful information on the quality of the machined surface. But the unpredictable behavior of the current prevents applying the current to prediction of the cutting state. Empirical approach was conducted to resolve the problem. As a result, the current was shown to be related to the accumulation of the accumulation of the infinitesimal rotation of the motor. rotation of the motor. Subsequently the relationship between the current and the cutting force was identified.

• Biomaterials and Biomechanics in Bioengineering
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• v.1 no.2
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• pp.81-93
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• 2014

An in vitro cell study evaluating cell adhesion to hydroxyapatite (HA) coated prosthetic Ti-6Al-4V alloy via laser treatment is presented in comparison with uncoated alloy. Based on our previous in vitro biocompatibility study, which demonstrated higher cell attachment and proliferation with MC3T3-E1 preosteoblast cells, the present investigation aims to reveal the effect of laser coating Ti alloy with HA on the adhesion strength of bone-forming cells against centrifugal forces. Remaining cells on different substrates after centrifugation were visualized using fluorescent staining. Semi-quantifications on the numbers of cells were conducted based on fluorescent images, which demonstrated higher numbers of cells retained on HA laser treated substrates post centrifugation. The results indicate potential increase in the normalized maximum force required to displace cells from HA coated surfaces versus uncoated control surface. The possible mechanisms that govern the enhancing effect were discussed, including surface roughness, chemistry, wettability, and protein adsorption. The improvement in cell adhesion through laser treatment with a biomimetic coating could be useful in reducing tissue damage at the prosthetic to bone junction and minimizing the loosening of prosthetics over time.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.8
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• pp.737-742
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• 2016

An elastomer (especially PDMS) sponge is considered to be a promising selective absorber in cleaning up oil spills. The performance of a PDMS sponge in capturing and separating oil from (sea) water depends on several parameters such as surface roughness, physicochemical treatments, and hydrostatic stability. Here, we first present a method of fabricating the PDMS sponges having numerous micro-sized pores that act as absorption and storage spaces for the target material, and then we report an experimental effort undertaken to control the surface physicochemistry (i.e., hydrophobicity or hydrophilicity) of the PDMS sponges by adjusting the size of the pores and the concentration of the surfactant (i.e., silwet L-77). From the experimental results, we develop an in-depth understanding of the mechanism for controlling the surface physicochemistry of PDMS using water-soluble micro-sized particles and a surfactant. The surface energy and absorbing behavior of the PDMS sponges are also extensively discussed.

• The Journal of Korean Academy of Prosthodontics
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• v.33 no.4
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• pp.693-704
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• 1995

This study was performed to evaluate effective surface conditioning method of In-Ceram core to improve bonding with resin cement. The surface of each sample was avraded with glass bead for 20 seconds and then subjected to one of the following conditions : no modification, sandblasting with $50{\mu}m$ slumimum oxide powders for 20 seconds, etching with 20% hydrofluoric acid for 5, 10, and 15 minutes(half of the etched samples were coated with silane), and sandblasting with $250{\mu}m$ aluminum oxide powders and silica coating whith Silicoater MD system(Kulzer, Germany). The surface morphology changes were examined with scanning electronic microscope(SEM. and the shear bond strength of In-Ceram core samples to resin cement(Panavis 21, Kurayay, Japan) were measured. It was concluded that : 1. By SEM observation, 20% HF acid etching did not create clear microretentive structure and surface roughness diminished with increace in etching time. Sandblasting was more effective than 20% hydrofluoric acid etching in producing microretentive structure. 2. The bond strengths of all In-Ceram core samples surface conditioned were increased that that of control group. 3. Silica coating showed higher bond strength than etching with 20% hydrofluoric acid. 4. The use of silane coating was more effective in improving bond strength than lengthening etching time.