• The korean journal of orthodontics
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• v.30 no.5 s.82
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• pp.625-642
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• 2000

The purpose of this study is to evaluate the effects of mechanical and thermal fatigue stress on the shear, tensile and shear-tensile combined bond strengths(SBS, TBS, CBS) in various orthodontic brackets bonded to human premolars with chemically cured adhesive(Ortho-one, Bisco, USA). Five types of commercially available metal brackets with various bracket base configurations of Photoetched base(Tomy, Japan), Non-Etched Foil Mesh base(Dentaurum, Germany), Micro-Etched Foil Mesh base(Ortho Organizers, USA), Chessboard base(Daesung, Korea), and Integral base(3M Unitek, USA) were used. Samples were divided into 3 groups, the first group was acted with shear-tensile combined loads($45^{\circ}$) of 200g for 4 weeks(mechanical fatigue stress), the second group was subjected to the 5,000 thermocycles of 15 second dwell time each in $5^{\circ}C\;and\;55^{\circ}C$ baths(thermal fatigue stress), and the third group was the control. Bond strengths were measured at the crosshead speed of 0.5mm/min. The cross-section of bracket base/adhesive interface and the fracture surface were examined with the stereoscope and the scanning electron microscope. The resin remnant on bracket base surface was assessed by ART(Adhesive Remnant Index). The obtained results were summarized as follows, 1. In static bond strength, Photoetched base bracket showed the maximum bond strength and Integral base bracket showed the minimum bond strength(p<0.05). In all brackets, shear bond strength(SBS) was in the greatest value and shear-tensile combined strength(CBS) was in the least value(p<0.05). 2. After mechanical fatigue test, Photoetched base bracket showed the maximum bond strength and Integral base bracket showed the minimum bond strength(p<0.05). In Photoetched base bracket and Micro-Etched Foil Mesh base bracket, shear bond strength(SBS), tensile bond strength(TBS) and shear-tensile combined strength(CBS) were decreased after mechanical fatigue test(p

• Journal of Conservation Science
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• v.28 no.3
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• pp.247-256
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• 2012

Amber has been used as gemstones and artifacts from the period of the Three Kingdoms or earlier, which are discovered in the process of excavation now. It is, however, very difficult to discuss the importing route and circulation of amber because there are no informations available on the provenance. In this study, we acquired the IR spectra of ambers originating from 5 different locations. We also monitored the change of characteristic IR peaks by artificially aging the ambers under heat, light and heat with oxygen, respectively. As the aging proceeded, the intensity of C=O band and O-H band increased, however, the bands related with C=C bond decreased. There needed some modifications in the discerning scheme because some peak disappeared with aging; yet, it was still possible to discern different ambers largely. Therefore, it is expected that the scheme can be used practically by appraising its applicability to the real amber relics excavated.

• Journal of the Korean Chemical Society
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• v.21 no.1
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• pp.3-15
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• 1977

Crystals of salicylaldehyde-4-morpholinothiosemicarbazone, $C_{12}H_{15}O_2N_3S$, are orthorhombic with space group Pna21. Unit-cell dimensions are a = 11.85(5), b = 15.45(5) c = 7.18(3)${\AA}$ with z = 4. Three-dimensional intensity data were collected from the multiple-film equi-inclination Weissenberg photographs taken with $CuK{\alpha}$ radiation. The intensities were estimated visually. The structure was solved by Patterson and Fourier methods and refined by the block-diagonal least-squares methods until the final R value becomes 0.11 for the 1064 observed independent reflections. The morpholine ring has a chair form. The rest atoms of salicylaldehyde-4-morpholinothiosemicarbazone molecule excluding morpholine ring and sulfur atom approximately lie on a plane. The hydroxyl group of the salicylaldehyde and the nitrogen atom of the thiosemicarbazone form an intramolecular hydrogen bond, $O-H{\cdot}{\cdot}{\cdot}N$, of 2.67${\AA}$. The short intermolecular distances all appear to be normal van der Waals contacts.

• Korean Journal of Materials Research
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• v.23 no.2
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• pp.104-111
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• 2013

In this study, GaN powders were synthesized from gallium oxide-hydroxide (GaOOH) through an ammonification process in an $NH_3$ flow with the variation of $B_2O_3$ additives within a temperature range of $300-1050^{\circ}C$. The additive effect of $B_2O_3$ on the hexagonal phase GaN powder synthesis route was examined by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Fourier transformation infrared transmission (FTIR) spectroscopy. With increasing the mol% of $B_2O_3$ additive in the GaOOH precursor powder, the transition temperature and the activation energy for GaN powder formation increased while the GaN synthesis limit-time ($t_c$) shortened. The XPS results showed that Boron compounds of $B_2O_3$ and BN coexisted in the synthesized GaN powders. From the FTIR spectra, we were able to confirm that the GaN powder consisted of an amorphous or cubic phase $B_2O_3$ due to bond formation between B and O and the amorphous phase BN due to B-N bonds. The GaN powder synthesized from GaOOH and $B_2O_3$ mixed powder by an ammonification route through ${\beta}-Ga_2O_3$ intermediate state. During the ammonification process, boron compounds of $B_2O_3$ and BN coated ${\beta}-Ga_2O_3$ and GaN particles limited further nitridation processes.

• Korean Journal of Metals and Materials
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• v.48 no.5
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• pp.401-409
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• 2010

This study was performed to develop an antibacterial film that can be dried at room temperature. A nanosized TiO$_2$ particle-dispersed solution was prepared by the hydrothermal treatment of peroxo-titanic acid at 160${^{\circ}C}$ for 4h. The binder was synthesized through the hydrolysis and condensation reactions of TEOS (10cc) and GPTS (3.5cc) in the mixture of H$_2$O (30cc) and EtOH (30cc). The synthesized binder was mixed with 0.1 M of TiO$_2$ solution in a volume ratio of binder/TiO$_2$ solution=0.25~0.5. The glass substrate was coated after using the dip coating method, which was then followed by drying for over 2h at room temperature. Although the TiO$_2$ particles did not chemically-bond to the binder, the coating layer strongly adhered to the substrate and displayed good antibacterial properties.

• Electrical & Electronic Materials
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• v.16 no.9
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• pp.63.2-64
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• 2003

Epitaxial yttrium-stabilized HfO$_2$ thin films were deposited on p-type (100) Si substrates by pulsed laser deposition at a relatively lower substrate temperature of 550. Transmission electron microscopy observation revealed a fixed orientation relationship between the epitaxial film and Si; that is, (100)Si.(100)HfO$_2$ and [001]Si/[001]HfO$_2$. The film/Si interface is not atomically flat, suggesting possible interfacial reaction and diffusion, X-ray photoelectron spectrum analysis also revealed the interfacial reaction and diffusion evidenced by Hf silicate and Hf-Si bond formation at the interface. The epitaxial growth of the yttrium stabilized HfO$_2$ thin film on bare Si is via a direct growth mechanism without involoving the reaction between Hf atoms and SiO$_2$ layer. High-frequency capacitance-voltage measurement on an as-grown 40-A yttrium-stabilized HfO$_2$ epitaxial film yielded an dielectric constant of about 14 and equivalent oxide thickness to SiO$_2$ of 12 A. The leakage current density is 7.0${\times}$ 10e-2 A/$\textrm{cm}^2$ at 1V gate bias voltage.

• Bulletin of the Korean Chemical Society
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• v.14 no.4
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• pp.439-444
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• 1993

The aerobic oxidation of the Fe(II) complex of 1,4,8,11-tetraazacyclotetradecane, [Fe(cyclam)$(CH_3CN)_2](ClO_4)_2$, in MeCN in the presence of a few drops of $HClO_4$ leads to low spin Fe(III) species [Fe(cyclam)$(CH_3CN)_2](ClO_4)_3$. The Fe(III) cyclam complex is further oxidized in the air in the presence of a trace of water to produce the deep green binuclear bismacrocyclic Fe(II) complex $[Fe_2(C_{20}H_{36}N_8)(CH_3CN)_4](ClO_4)_4{\cdot}2CH_3CN$. The Fe(II) ions of the complex are six-coordinated and the bismacrocyclic ligand is extensively unsaturated. $[Fe_2(C_{20}H_{36}N_8)(CH_3CN)_4](ClO_4)_4{\cdot}2CH_3CN$ crystallizes in the monoclinic space group $P2_1/n$ with a= 13.099 (1) ${\AA}$, b= 10.930 (1) ${\AA}$, c= 17.859 (1) ${\AA}$, ${\beta}$= 95.315 $(7)^{\circ}$, and Z= 2. The structure was solved by heavy atom methods and refined anisotropically to R values of R= 0.0633 and $R_w$= 0.0702 for 1819 observed reflections with F > $4{\sigma}$ (F) measured with Mo K${\alpha}$ radiation on a CAD-4 diffractometer. The two macrocyclic units are coupled through the bridgehead carbons of ${\beta}$-diimitie moieties by a double bond. The double bonds in each macrocycle unit are localized. The average bond distances of $Fe(II)-N_{imine}$, $Fe(II)-N_{amine}$, and $Fe(II)-N_{MeCN}$ are 1.890 (5), 2.001 (5), and 1.925 (6) ${\AA}$, respectively. The complex is diamagnetic, containing two low spin Fe(II) ions in the molecule. The complex shows extremely intense charge transfer band in the near infrared at 868 nm with ${\varepsilon}$= 25,000 $M^{-1}cm^{-1}$. The complex shows a one-electron oxidation wave at +0.83 volts and two one-electron reduction waves at -0.43 and-0.72 volts vs. Ag/AgCl reference electrode. The complex reacts with carbon monoxide in $MeNO_2$ to form carbonyl adducts, whose $v_{CO}$ value (2010 $cm^{-1}$) indicates the ${\pi}$-accepting property of the present bismacrocyclic ligand.

• Journal of Integrative Natural Science
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• v.8 no.1
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• pp.19-29
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• 2015

In view of the growing medicinal importance of chromene and its derivatives, the single crystal X-ray diffraction study was carried out for the potential active 4,6-dimethyl-9-phenyl-8,12-dioxa-4,6-diazatetracyclo [8.8.0.02,7.013,18]octadeca-2(7),13,15,17-tetraene-3,5,11-trione-2-ethoxyphenyl (2E)-but-2-enoate ($C_{18}H_{20}N_2O_5$). In the title compound are two molecules exist in the asymmetric unit. It crystallizes in the monoclinic space group $P2_1/c$ with unit cell dimension a=14.608(3) ${\AA}$, b=12.845(3) and c= 17.781(4) [alpha & gamma=$90^{\circ}$ beta=$91.233(5)^{\circ}$]. Both pyran and pyran ring of the chromene moiety adopts sofa conformation in the molecule A & B. The crystal structure is stabilized by intramolecular C-H...O hydrogen bond interaction.

• Journal of the Korean institute of surface engineering
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• v.45 no.6
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• pp.242-247
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• 2012

Yb-doped ITO (ITO:Yb) films were deposited on unheated non-alkali glass substrates by magnetron cosputtering using two cathodes (DC, RF) equipped with the ITO and $Yb_2O_3$ target, respectively. The composition of the ITO:Yb films was controlled by adjusting the RF powers from 0 W to 480 W in 120 W steps with the DC power fixed at 70 W. The ITO:Yb films had a higher crystallization temperature ($200^{\circ}C$) than that of the ITO films ($170^{\circ}C$), which was attributed to both larger ionic radius of $Yb^{3+}$ and higher bond enthalpy of $Yb_2O_3$, compared to ITO. This amorphous ITO:Yb film post-annealed at $170^{\circ}C$ showed a resistivity of $5.52{\times}10^{-4}{\Omega}cm$, indicating that a introduction of Yb increased resistivity of the ITO film. However, these amorphous ITO:Yb films showed a high etching rate, fine pattering property, and a very smooth surface morphology above the crystallization temperature of the amorphous ITO films (about $170^{\circ}C$). The transmittance of all films was >80% in the visible region.

• Journal of the Korean Chemical Society
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• v.30 no.6
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• pp.495-499
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• 1986

Structures of 4H-pyran-4-one(I), 4H-pyran-4-thione(II), 4H-thiapyran-4-one (III), 4H-thiapyran-4-thione(IV) have been determined by MNDO and MINDO/3 methods. Geometries and physicochemical properties, especially the aromaticity, were found to agree well with the results of microwave experiments. The order of aromaticity was found to be (IV) > (III) > (II) > (I), which demonstrated inhibitory effect of strongly electronegative oxygen atom on the electron delocaligation, and the order of dipole moment, (II) > (IV) > (I) > (III), indicated the dominant contribution of the bond length of carbonyl group (C=O or C=S)