Ohyoung Kim

Synthesis and properties of violet light-emitting polymeric fluorophore

Abstract Chemiluminescent violet light-emitting polymeric fluorophores were synthesized by copolycondensation of N,N ′-dihydroxypropyl-1,6,7,12-tetrakis( p - tert -butylphenoxy)-3,4,910-perylene tetracarboxydiimide and 2-chloro-9,10-di( p -hydroxyphenyl)anthracene with sebacoyl chloride and hexamethylene diisocyanate. The properties of fluorophore polymers were studied by absorption and photoluminescent spectroscopies. The intensities of UV–vis absorbance and photoluminescence spectra appeared at the blue side and the red side of the spectral region. Peroxyoxalate chemiluminescence of polymers provided a strong chemiluminescent violet light emission according to the content of two chromophore units; these were similar to the photoluminescent spectra.

The rheological properties optimization of fumed silica dispersions using statistical experimental design and taguchi method

Abstract The rheological properties of fumed silica filled Bis-GMA dispersions were analyzed using statistical experimental design and Taguchi method. Viscosity and shear thinning property were considered as the rheological properties. Silica content, silane concentration, diluent concentration, shear rate, and temperature were chosen as significant factors. Statistical experimental design using analysis of variance and orthogonal array was applied to optimize the viscosity of the dispersions, and Taguchis parameter design was simultaneously performed to analyze the shear thinning property of the dispersions. Shear rate, silica content, and γ-MPS concentration showed major effects on the viscosity, and silica contents and γ-MPS concentration also had principal effects on shear thinning property of the fumed silica dispersions. Diluent concentration was determined as the only insignificant factor concerning the viscosity, while the temperature was the sole factor not to influence the shear thinning property of the dispersion. Optimum viscosity condition and less shear thinning condition were also determined using statistical experimental design and Taguchi method.

Microleakage of microfill and flowable composite resins in class V cavity after load cycling

Low-viscosity composite resins may produce better sealed margins than stiffer compositions (KempScholte and Davidson, 1988: Crim, 1989). Plowable composites have been recommended for use in Class V cavities but it is also controversial because of its high rates of shrinkage. On the other hand, in the study comparing elastic moduli and leakage, the microfill had the least leakage (Rundle et at. 1997) Furthermore, in the 1996 survey of the Reality Editorial Team, microfills were the clear choice for abfraction lesions. The purpose of this study was to evaluate the microleakage of 6 compostite resins (2 hybrids, 2 microfills, and 2 flowable composites) with and without load cycling. Notch-shaped Class V cavities were prepared on buccal surface of 180 extracted human upper premolars on cementum margin. The teeth were randomly divided into non-load cycling group (group 1) and load cycling group (group 2) of 90 teeth each. The experimental teeth of each group were randomly divided into 6 subgroups of 15 samples. All preparations were etched, and Single bond was applied. Preparations were restored with the following materials (n=15) : hybrid composite resin [Z250(3M Dental Products Inc. St. Paul, USA), Denfil(Vericom, Ahnyang, Korea)], microfill [Heliomolar RO(Vivadent, Schaan, Liechtenstein), Micronew(Bisco Inc. Schaumburg, IL, USA)], and flowable composite［AeliteFlo(Bisco Inc. Schaumburg, IL, USA), Revolution(Kerr Corp. Orange, CA, USA)]. Teeth of group 2 were subjected to occlusal load (100N for 50,000 cycles) using chewing simulator(MTS 858 Mini Bionix II system, MTS Systems Corp. Minn. USA). All samples were coated with nail polish 1mm short of the restoration, placed in 2％ methylene blue for 24 hours, and sectioned with a diamond wheel. Enamel and dentin/cementum margins were analyzed for microleakage on a sclale of 0 (no leakage) to 3 (3/3 of wall). Results were statistically analyzed by Kruscal-Wallis One way analysis, Mann-Whitney U-test, and Student-Newmann-Keuls method. (p = 0.05) Results : 1. There was significantly less microleage in enamel margins than dentinal margins of all groups (p＜0.05) 2. There was no significant between six composite resin in enamel margin of group 1. 3. In dentin margin of group 1, flowable composite had more microleakage than others but not of significant differences. 4. there was no significant difference between six composite resin in enamel margin of group 2. 5. In dentin margin of group 2, the microleakage were R＞A =H=M＞D＞Z. But there was no significant differences. 6. In enamel margins, load cycling did not affect the marginal microleakage in significant degree. 7. In enamel margins, load cycling did affect the marginal microleakage only in Revolution. (p＜0.05).

Analysis for a Generalized CHF Correlation in Uniformly Heated Vertical Round Tubes

For empirical models based on the local condition hypothesis, few important parameters give significant correlations on the prediction of CHF (Critical Heat Flux). This work is a preliminary study to develop a generalized CHF correlation in uniformly heated vertical round tubes for water. For this analysis, a total of 8,912 CHF data points from 12 different published sources were used. This database consisted of following parameter ranges: 0.101 ≤ P (pressure) ≤ 20.679 MPa, 9.92 ≤ G (mass flux) ≤ 18,619.39 kg/m2 s, 0.00102 ≤ D (diameter) ≤ 0.04468 m, 0.03 ≤ L (length) ≤ 4.97 m, 8.5 ≤ L/D ≤ 792.26, −609.33 ≤ Inlet subcooling ≤ 1,655.34 kJ/kg, 0.11 ≤ qc (CHF) ≤ 21.41 MW/m2 , and −0.85 ≤ Xe (exit qualities) ≤ 1.58. Five representative CHF data sets at pressure conditions of 0.101, 5.001, 10, 16 and 20 MPa were selected, analyzed, and compared to evaluate the effects of parameters on the CHF. It has revealed that the major variables which influenced the CHF, other than the system pressure (P), were tube diameter (D), mass flux of water (G), and local true mass fraction of vapor (Xt ). Square root of GXt and square root of D were the significant parameters that showed strong parametric trends of the data sets. The results of this study have reaffirmed the feasibility that an advanced generalized CHF correlation for uniformly heated vertical round tubes can be found.Copyright