• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.2
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• pp.175-180
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• 2009

In this article, we fabricated polytetrafluoroethylene(PTFE) nozzle treated by ion beam, in order to fabricate polymer based electrospray micro thruster with super hydrophobic nozzle. To obtain the super hydrophobic surface, PTFE surface is treated by argon and oxygen plasma treatment process. The optimal condition is investigated argon and oxygen flow rate as well as the paalied energy level for the treatment process. Fabricated nozzle was evaluated by measuring contact angle, and the surface morphology was examined by using scanning electron microscope(SEM) and atomic force microscope(AFM). We observe that jetting becomes more stable and repeatable on the treated nozzle. And to evaluate performance of fabricated nozzle, we measure micro scale thrust using a cantilever and a nozzle treated by ion beam laser displacement sensor.

• Journal of the korean academy of Pediatric Dentistry
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• v.31 no.4
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• pp.671-679
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• 2004

The purpose of this study was to develop a practical caries activity test by fluorescence using laser, plasma light and halogen light. The subjects of study were 45 children of 7-8 years old Argon laser, plasma light and halogen light were irradiated to buccal or labial surface of all teeth. Fluorescence of initial carious lesion from teeth was observed through barrier filter and the number of teeth showing lesion was counted. Visual examination for the dDfFtT, mutans streptococci screening test and Lactobacilli colony counting were also done. Data analysis was accomplished by Axelsson's method. The result from the present study can be summarized as follows. 1. Laser, plasma light and halogen light could detect the initial carious lesions better than visual examination(p<0.05). 2. There was positive correlation between laser(r=0.42), plasma light(r=0.41), halogen light(r=0.39) and dBfFtT rate(p<0.01). 3. The specificity sensitivity and predictive value was showed highest value in laser, but was showed favorable value in plasma light and halogen light. In regard to above results, laser, plasma light and halogen light all considered to be reliable method for determining individual caries activity. And they were also considered to be practical method because it would be simple, inexpensive, and time saving method.

• The Journal of Advanced Prosthodontics
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• v.5 no.4
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• pp.471-478
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• 2013

PURPOSE. The aim of the study was to evaluate the effect of annealing on the nanostructure and hardness of Co-Cr metal ceramic samples that were fabricated with a direct metal laser sintering (DMLS) technique. MATERIALS AND METHODS. Five groups of Co-Cr dental alloy samples were manufactured in a rectangular form measuring $4{\times}2{\times}2$ mm. Samples fabricated by a conventional casting technique (Group I) and prefabricated milling blanks (Group II) were examined as conventional technique groups. The DMLS samples were randomly divided into three groups as not annealed (Group III), annealed in argon atmosphere (Group IV), or annealed in oxygen atmosphere (Group V). The nanostructure was examined with the small-angle X-ray scattering method. The Rockwell hardness test was used to measure the hardness changes in each group, and the means and standard deviations were statistically analyzed by one-way ANOVA for comparison of continuous variables and Tukey's HSD test was used for post hoc analysis. P values of <.05 were accepted as statistically significant. RESULTS. The general nanostructures of the samples were composed of small spherical entities stacked atop one another in dendritic form. All groups also displayed different hardness values depending on the manufacturing technique. The annealing procedure and environment directly affected both the nanostructure and hardness of the Co-Cr alloy. Group III exhibited a non-homogeneous structure and increased hardness ($48.16{\pm}3.02$ HRC) because the annealing process was incomplete and the inner stress was not relieved. Annealing in argon atmosphere of Group IV not only relieved the inner stresses but also decreased the hardness ($27.40{\pm}3.98$ HRC). The results of fitting function presented that Group IV was the most homogeneous product as the minimum bilayer thickness was measured (7.11 ${\AA}$). CONCLUSION. After the manufacturing with DMLS technique, annealing in argon atmosphere is an essential process for Co-Cr metal ceramic substructures. The dentists should be familiar with the materials that are used in clinic for prosthodontics treatments.

• Journal of the korean academy of Pediatric Dentistry
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• v.32 no.4
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• pp.611-619
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• 2005

The aim of this study was to apply the quantitative light-induced fluorescence(QLF) and use of fluorescein-enhanced QLF method for quantitative assessment of early enamel demineralization in vitro, comparing effectiveness of light sources : argon laser, halogen lamp, light emitting diode (LED) and plasma arc lamp. Sixty extracted teeth were used, prepared by gentle pumicing and coating in an acid-resistant nail-varnish, except for an exposure to a demineralizing solution. Teeth were removed at regular intervals (24, 48 and 72hrs), air-dried and QLF image were taken. Mineral loss, as measured by difference of optical density, was recorded. For dyeenhanced QLF a 0.075% sodium fluorescein dye was applied after QLF examination and mineral loss was recorded. The following result were obtained : 1. Comparing with mean difference of optical density, plasma arc lamp was higher than other light sources in all group (p<0.05). 2. Comparing each group with mean difference of optical density, there was significant different using plasma are lamp and halogen lamp. 3. For use of dye-enhanced QLF, comparing with mean difference of optical density, plasma arc lamp were higher than other light sources in all group(p<0.05). 4. With this model dye-enhanced QLF compared with QLF in optical density, dye-enhanced QLF was higher than QLF in optical density. From the results presented in this paper, it was concluded that plasma light source was more effective compared with other light source for the detection and the quantification of early enamel caries.

• Bulletin of the Korean Chemical Society
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• v.24 no.3
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• pp.318-324
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• 2003

A time-resolved probe beam deflection (PBD) technique was employed to study the energy relaxation dynamics of photofragments produced by photodissociation of $CH_3I$ at 266 nm. Under 500 torr argon environment, experimental PBD transients revealed two energy relaxation processes; a fast relaxation process occurring within an acoustic transit time (less than 0.2 ㎲ in this study) and a slow relaxation process with the relaxation time in several tens of ㎲. The fast energy relaxation of which signal intensity depended linearly on the excitation laser power was assigned to translational-to-translational energy transfer from the photofragments to the medium. As for the slow process, the signal intensity depended on square of the excitation laser power, and the relaxation time decreased as the photofragment concentration increased. Based on experimental findings and reaction rate constants reported previously, the slow process was assigned to methyl radical recombination reaction. In order to determine the rate constant for methyl radical recombination reaction, a theoretical equation of the PBD transient for a radical recombination reaction was derived and used to fit the experimental results. By comparing the experimental PBD curves with the calculated ones, the rate constant for methyl recombination is determined to be $3.3({\pm}1.0)\;{\times}\;10^6\;s^{-1}torr^{-1}$ at 295 ± 2 K in 500 torr Ar.

• The Journal of Korean Academy of Prosthodontics
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• v.38 no.2
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• pp.200-213
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• 2000

Lasers have given dentistry a new rapid, economic, and accurate technique for metal joining. Although laser welding has been recommended as an accurate technique, there are some limitations with this technique. For example, the two joining surfaces must have a tight-fitting contact, which may be difficult to achieve in some situations. The tensile samples used for this study were made from a custom-made pure titanium and type III gold alloy plates. 27 of 33 specimens were sectioned perpendicular to their long axis with a carborundum disk and water coolant. Six specimens remained and served as the control group. A group of 6 specimens was posed as butt joints in custom parallel positioning device with a feeler gauge at each of three gaps : 0.00, 0.25. and 0.50mm. All specimens were then machined to produce a uniform cross-sectional dimension, none of the specimens was subjected to any subsequent form of heat treatment. Scanning electron microscopy was performed on representative tested specimens at fractured surfaces in both the parent metal and the weld. Vickers hardness was measured at the center of the welds with a micropenetrometer using a force of 300gm for 15 seconds. Measurement was made at approximately $200{\mu}m\;and\;500{\mu}m$ deep from each surface. One-way analysis of variance (ANOVA) and Scheffe's test was calculated to detect differences between groups. The purpose of this study is to compare the strength and properties of the joint achieved at various butt Joint gaps by the laser welding of type III gold alloy and pure titanium tensile specimens in an argon atmosphere. The results of this study were as follows : 1. When indexing and welding pure titanium, there was no decrease in ultimate tensile strength as compared with the unsectioned alloys for indexing gaps of 0.00 to 0.50mm, although with increasing gap size may come increased distortion (p>0.05). 2. When indexing and welding type III gold alloy, there were significant differences in ultimate tensile strength among groups with weld gaps of 0.00mm, 0.25 and 0.50mm, and the control group. Group with butt contact without weld gap demonstrated a significant higher ultimate tensile strength than groups with weld gaps of 0.25 and 0.50mm (p<0.05). 3. When indexing and welding the different metal combination of type III gold alloy and pure titanium, there were significant differences in ultimate tensile strength between groups with weld gaps of 0.00, 0.25, and 0.50mm. However, the mechanical properties of the welded joint would become too brittle to be acceptable clinically (p<0.05). 4. The presence of large pores in the laser welded joint appears to be the most important factor in controlling the tensile strength of the weld in both pure titanium and type III gold alloy.

• Journal of the korean academy of Pediatric Dentistry
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• v.28 no.1
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• pp.16-24
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• 2001

The purpose of this study was to evaluate the specificity, sensitivity, and diagnostic power of caries activity test using laser fluorescence. The subjects of this study were 50 children of $7\sim9$ years old. Fluorescence from initial carious lesion of teeth illuminated by an argon laser(480nm) was observed and photographed with barrier filter. Visual examination for the dDfFtT rate and Streptococcus mutans colony counting was done to evaluate correlation with caries activity test using laser fluorescence. Data analysis was accomplished by Axelsson's method. The results from the present study can be summarized as follows: 1. There was positive correlation $(\gamma=0.48)$ between laser fluorescence test and Streptococcus mutans count. And also positive correlation $(\gamma=0.39)$ exists between laser fluorescence test and dDfFtT rate (P<0.01). 2. Positive correlation $(\gamma=0.27)$ between Streptococcus mutans colony count and dDfFtT rate was found(P<0.05). 3. When dDfFtT rate was defined to standard testing method, the specificity, senstivity, and diagnostic power of laser fluorescence test were 44.4%, 85.7%, and 87.8%. 4. When dDfFtT rate was defined to standard testing method, the specificity, senstivity, and diagnostic power of S. mutans colony counting were 77.8%, 92.9%, 84.8%. 5. When S. mutans colony counting was defined to standard testing method, sensitivity, specificity and diagnostic power of laser fluorescence test were 40.0%, 84.8%, 95.1%. In regard to above results, laser fluorescence test considered to be accurate and reliable method for determining caries activity because of it's close relationship with caries susceptibility test and caries experience measurements. And it was also considered to be practical because it would be simple, inexpensive, and time saving method.

• Journal of the Korean Society of Visualization
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• v.3 no.1
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• pp.3-19
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• 2005

Novel optical techniques are presented for three-dimensional tracking of nanoparticles; Optical Serial Sectioning Microscopy (OSSM) and Ratiometric Total Internal Reflection Fluorescent Microscopy (R-TIRFM). OSSM measures optically diffracted particle images, the so-called Point Spread Function (PSF), and dotermines the defocusing or line-of-sight location of the imaged particle measured from the focal plane. The line-of-sight Brownian motion detection using the OSSM technique is proposed in lieu of the more cumbersome two-dimensional Brownian motion tracking on the imaging plane as a potentially more effective tool to nonintrusively map the temperature fields for nanoparticle suspension fluids. On the other hand, R-TIRFM is presented to experimentally examine the classic theory on the near-wall hindered Brownian diffusive motion. An evanescent wave field from the total internal reflection of a 488-nm bandwidth of an argon-ion laser is used to provide a thin illumination field of an order of a few hundred nanometers from the wall. The experimental results show good agreement with the lateral hindrance theory, but show discrepancies from the normal hindrance theory. It is conjectured that the discrepancies can be attributed to the additional hindering effects, including electrostatic and electro-osmotic interactions between the negatively charged tracer particles and the glass surface.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.6
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• pp.819-828
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• 2001

The operating point of a small-sized axial fan is strongly dependent upon the system resistance. Therefore, the turbulent flow characteristics around a small-sized axial fan may change significantly according to the operating point. This study represents three-dimensional turbulent flow characteristics around a small-sized axial fan measured at the ideal design point $\phi$=0.25, which is equivalent to the maximum total efficiency point, by using three dimensional fiber-optic type LDA system. This LDA system is composed of a 5 W Argon-ion laser, two optics in back-scatter mode, three BSAs, a PC, and a three-dimensional automatic traversing system. A kind of paraffin fluid is used to supply particles by means of fog generator. Mean velocity profiles downstream of a small-sized axial fan along the radial distance show that the streamwise and the tangential components exist in a predominant manner, while the radial component has a small scale distribution and shows the inflection which its flow direction is inward or outward. Moreover, the turbulent intensity profiles show that the radial component exists the most greatly among turbulent energies.

• Proceedings of the KSME Conference
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• 2001.11b
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• pp.371-376
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• 2001

The operating point of a small-sized axial fan for refrigerator is strongly dependent upon the system resistance. Therefore, the turbulent flow characteristics around a small-sized axial fan may change significantly according to the operating point. This study represents three-dimensional turbulent flow characteristics around a small-sized axial fan measured at the four operating points such as $\varphi=0.1$, 0.18, 0.25 and 0.32 by using fiber-optic type LDA system. This LDA system is composed of a 5 W Argon-ion laser, two optics in back-scatter mode, three BSA's, a PC, and a three-dimensional automatic traversing system. A kind of paraffin fluid is utilized for supplying particles by means of fog generator. Mean velocity profiles downstream of a small-sized axial fan along the radial distance show that both the streamwise and the tangential components exist predominantly in downstream except $\varphi=0.1$ and have a maximum value at the radial distance ratio of about 0.8, but the radial component, which its velocity is relatively small, is acting role that only turns flow direction to the outside or the central part of axial fan. Moreover, all of the velocity components downstream at $\varphi=0.1$ show much smaller than those upstream due to the static pressure rise at the low-flowrate region.