• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2012.05a
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• pp.367-376
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• 2012

To eliminate the onset of combustion instabilities and develop effective approaches for control, flame structure is very important. In this study, we conducted experiments under various operating conditions with a model gas turbine combustor to examine the relation of combustion instability and flame structure by OH chemiluminescence and laser diagnostics of He-Ne laser absorbtion system. The swirling LNG(CH4)/air flame was investigated with overall equivalence ratio of 1.2 and dump plane fuel-air mixture velocity 25 ~ 70 m/s. We founded that the combustion instability phenomenon occurs at lower mixing velocity and higher mixing velocity conditions. We also concluded that fluid dynamical vortex frequency has major effects on the combustion instability characteristics at lower mixing velocity condition.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.2
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• pp.355-365
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• 1994

An analytical model of return flow is presented outside the surf zone. The governing equation is derived from the Navier-Stokes equation and the continuity. Each term of the governing equation is evaluated by the ordering analysis. Then the infinitesimal terms, i.e. the turbulent normal stress, the squared vertical velocity of water particle and the streaming velocity, are neglected. The driving forces of return flow are calculated using the linear wave theory for the shallow water approximation. Especially, the space derivative of local wave heights is described considering a shoaling coefficient. The vertical distribution of eddy viscosity is discussed to the customary types which are the constant, the linear function and the exponential function. Each coefficient of the eddy viscosities which sensitively affect the precision of solutions is uniquely decided from the additional boundary condition which the velocity becomes zero at the wave trough level. Also the boundary conditions at the bottom and the continuity relation are used in the integration of the governing equation. The theoretical solutions of present model are compared with the various experimental results. The solutions show a good agreement with the experimental results in the case of constant or exponential function type eddy viscosity.

• Journal of the korean academy of Pediatric Dentistry
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• v.35 no.1
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• pp.11-17
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• 2008

The purpose of this study was to investigate early histological changes and calcitonin gene-related peptide (CGRP) expression in the dental pulp of the rat after Er:YAG laser preparation. Occlusal cavities were prepared in the upper first molars using either Er:YAG laser and conventional bur. At 48 hours after cavity preparation, the teeth were processed for hematoxylin-eosin stain and CGRP immunohistochemistry. The results were as follows : 1. The cavity floor by Er:YAG laser preparation was more irregular shape compared with those by bur preparation and there are some cracks in the directions of dentinal tubules. 2. There were more inflammatory cell infiltration and disruption of odontoblast in the dental pulp by Er:YAG laser preparation in comparison with the dental pulp by bur preparation. 3. CGRP expression in the pulp tissue by both Er:YAG laser and bur preparations were increased and higher than in the normal pulp. The expression pattern of CGRP was more strong in the pulp by Er:YAG laser preparation. These results indicate that Er:YAG laser is useful in the operative dentistry such as caries removal and cavity preparation if properly applied.

• Journal of the korean academy of Pediatric Dentistry
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• v.28 no.4
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• pp.683-693
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• 2001

The purpose of this study was to evaluate the effects of Er:YAG laser on cutting efficacy and its histologic findings. Dentin specimens of human premolars and molars were used and irradiated by Er:YAG laser with noncontact handpiece type delivery system under different treatment condition of irradiation time. Cavity pattern and volume were evaluated to determine the cutting efficacy and following results were obtained. 1. Cutting volume of sound dentin was getting larger with time immersed in water increase 2. With the condition of irradiation (150mJ, 10Hz, 30sec), surface irregularity was more increased in sound dentin comparing to carious dentin. For the light microscopic examination, dentinal tubules were opened and ash flecks and cracks were noted with inconsistence of dentinal tubules. 3. In case of 30 sec. irradiation in carious dentin, dark zone was limited to small focus whereas 1 min. irradiation, more wider, and cracks were noted in the perpendicular to direction of dentinal tubules. For the 2 min. irradiation, cavity was the widest and more cracks were found.

• The Journal of the Korean dental association
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• v.36 no.2 s.345
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• pp.144-150
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• 1998

The dental insurance had been enforced in Korea past 20 years. The major part of the insurance was filling, and the filling was divided into two parts-the cavity preparation and cavity filling, The Cavity filling was estimated into 6 levels according to the cavity types. But the tooth cavity preparations was not evaluated by the cavity types but merely only one-the one visit filling or cavity preparation. Korean dentists tend to turn away from the amalgam to the non-insurance treatments. The purpose of this study was to relate the cavity preparations and cavity fillings to the cavity types. So I measured the real time and surveyed the relative difficulties of cavity preparations from the 31 dentists according to the cavity types, who had been trained in conservative dentistry. The conclusion of this study was below. 1. The estimations of tooth cavity preparation was divided same as the cavity filling. 2. There must be reasonable considerations about the times and difficulties in cavity preparation. 3. There was differences between the premolars and molars, upper jaw and lower one. 4. Two or more cavities in one tooth must be evaluated according to the number of cavities, not in one cavity.

• Restorative Dentistry and Endodontics
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• v.15 no.1
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• pp.97-105
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• 1990

When conventional root canal treatment is failed or contraindicated, retrograde root canal filling following apicoectomy is a valuable procedure, aimed at hermetically sealing the root canal against leakage of irritants from the canal into the periapical tissue. In this in vitro investigation, to analyze apical microleakage electrochemically in teeth with different retrograde filling materials and preparation types, single - rooted tooth was cut 2mm from the apex and each Class I and Slot preparation was prepared. Experimental groups : Group 1. Amalgam filling with cavity varnish in Class I preparation Group 2. Scotchbond 2+Silux filling in Class I preparation Group 3. Gutta percha filling with ZOE cement in Class I preparation Group 4. Amalgam filling with cavity varnish in Slot preparation Group 5. Scotchbond 2+Silux filling in Slot preparation Each specimens was immersed in 1% solution of KCl, and applied a potential of 9V external power supply. Measurements of the current flow were obtained at 1, 2, 3, 7, 9, 12, 14, 18, 21, 25 and 28 day after immerson. Marginal microleakage were compared and evaluated. The results were as follows ; 1. The group filled with composite resin with dentin bonding agent shows lower apical microleakage value than the group filled with amalgam following varnish application (P<0.01). 2. In the group filled with gutta percha, apical microleakage value was the hightest 3. There was no significant difference between Class I cavity and Slot type cavity regardless of the used materials.

• Restorative Dentistry and Endodontics
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• v.23 no.1
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• pp.296-303
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• 1998

The purpose of this study was to assess the effects of cavity designs on the marginal leakage of class 5 glass ionomer restorations. The five cavity designs were as follows ; notch shape(A group), notch shape with groove(B group), combined lesion(C group), combined lesion with groove and deep chamfer margin(D group) and combined lesion with groove and shoulder(E group), and each design had 10 cavities. After the cavities were restored with GIC, they were immersed in 0.5% basic fuchsin solution for 6 hours. The specimens were washed thoroughly and sectioned longitudinally in a buccolingual direction through the center of the restorations. The degree of marginal leakage was measured as the extent of dye penetration under the stereoscope. The results of this study were as follows 1. The enamel margins of all groups showed lesser leakage than dentin/cementum margins(p<0.05). 2. The combined lesion(C group) showed more leakage than notch shape(A group), but there was no siginificant difference(p>0.05). 3. In the notch shape, there was no influence on the marginal leakage by the groove preparation. 4. In the combined lesion, marginal leakage was decreased by the groove preparation and marginal modification.

• Restorative Dentistry and Endodontics
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• v.36 no.6
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• pp.465-476
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• 2011

In current endodontic practice, introduction of operating microscope, ultrasonic instruments, and microinstruments has induced a big change in the field of surgical retreatment. In this study, we aimed to offer key steps of endodontic microsurgery procedure compared with traditional root-end surgery, and to evaluate factors influencing success and failure based on published articles. Endodontic microsurgery is a surgical procedure performed with the aid of a microscope, ultrasonic instruments and modern microsurgical instruments. The microscope provides magnification and illumination - essential for identifying minute details of the apical anatomy. Ultrasonic instruments facilitate the precise root-end preparation that is within the anatomical space of the canal. Modern endodontics can therefore be performed with precision and predictability, thus eliminating the disadvantages inherent in traditional periapical surgery such as large osteotomy, beveled apicoectomy, inaccurate root-end preparation and the inability to observe isthmus. Factors influencing the outcomes of endodontic microsurgery may be diverse, but standardization of procedures can minimize its range. Among patient and tooth-related factors, periodontal status and tooth position are known to be prognostic, but there are only few articles concerning this matter. High-evidence randomized clinical trials or prospective cohort studies are needed to confirm these findings.

• Restorative Dentistry and Endodontics
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• v.33 no.2
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• pp.115-124
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• 2008

The purpose of this study was to measure the polymerization shrinkage and hygroscopic expansion of resin-based temporary filling materials and to evaluate microleakage at the interface between the materials and cavity wall. Five resin-based temporary filing materials were investigated: Fermit (Vivadent), Quicks (Dentkist), Provifil (Promedica), Spacer (Vericom), Clip (Voco). Caviton (GC) was also included for comparison. Polymerization shrinkage of five resin-based temporary filling materials was measured using the bonded disc method. For the measurement of hygroscopic expansion, the discs of six cured temporary filling materials were immersed in saline and a LVDT displacement sensor was used to measure the expansion for 7 days. For estimating of microleakage, Class I cavities were prepared on 120 extracted human molars and randomly assigned to 6 groups of 20 each. The cavities in each group were filled with six temporary filling materials. All specimens were submitted to 1000 thermocycles, with temperature varying from $5^{\circ}C/55^{\circ}C$. Microleakage was determined using a dye penetration test. The results were as follows: 1. Fermit had significantly less polymerization shrinkage than the other resin-based temporary fill ing materials. Fermit (0.22%) < Spacer (0.38%) < Quicks (0.64%), Provifil (0.67%), Clip (0.67%) 2. Resin-based temporary filling materials showed 0.43-1.1% expansion in 7 days. 3. Fermit showed the greatest leakage, while Quicks exhibited the least leakage. 4. There are no correlation between polymerization shrinkage or hygroscopic expansion and microleakage of resin-based temporary filling materials.

• 한국해양학회지
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• v.30 no.3
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• pp.170-183
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• 1995

Eddies and surface current field in the southwestern part of the East Sea were investigated using satellite-tracked drifters, CTD, and ADCP from November 1992 to September 1993. Trajectories of surface drifters provided information for the first time on the meandering motion of the East Korean Warm Current in the Ullung Basin (referred as UB) and clearly indicated the existence of cyclonic and anticyclonic eddies of various scales. Anticyclonic eddies persisting for a relatively long period were observed in UB and the southwestern corner of the Northern (Japan) Basin (SNB), while a cyclonic eddy was found in the coastal area between Sokcho and Donghae during the summer. Analysis shows that the eddy in UB behaved as a stationary eddy at least during the observation period and the cyclonic eddy was closely related to the existence of a cold water mass. The anticyclonic eddy in SNB was larger than that in UB, but much elongated in shape. The eddy in UB is characteristic of major and minor axes of about 120 and 70 km, revolution period of 13.6 days, mean swirl velocity of about 24 cm/s, and mean eddy kinetic energy of 392 cm$\^$2//s$\^$2/. The eddy in SNB is described as follows; major and minor axes of 168 and 86 km, period of 14.9 days, mean swirl velocity of 29 cm/s and mean eddy kinetic energy of 629 cm$\^$2//s$\^$2/. The mean translational speed is about 3 cm/s for both eddies. The agreement of the surface current pattern in UB observed by ADCP with the geostrophic flow pattern may suggest that the eddy in UB was nearly in geostrophic balance. The eddy was found to be strongly bottom-controlled.