• Korean Journal of Materials Research
• /
• v.8 no.7
• /
• pp.659-663
• /
• 1998

The effect of Bi-substitution in $BaO.(Nd_{1-x}Bi_x)_2O_3.4TiO_2$ ceramic was studied on the formation of crystal phases, microstructure, and microwave dielectric properties. $BaO.(Nd_{1-x}Bi_x)_2O_3.4TiO_2$, solid solution (0$\leq$x$\leq$0.2) were formed by Bi-substitution into the Nd site of $BaO.(Nd_{1-x}Bi_x)_2O_3.4TiO_2$ ceramics. Average grain size increased with Bi-substitution. Dielectric constant(${\varepsilon}_r$) increased from 84 to U8, and the temperature coefficient of resonant frequency(${\tau}_f$) decreased from 44 ppm/$^{\circ}C$ to -30 ppm/$^{\circ}C$ when Bi contents increased up to x=0.2 in $BaO.(Nd_{1-x}Bi_x)_2O_3.4TiO_2$ solid solutions. $BaO.(Nd_{1-x}Bi_x)_2O_3.4TiO_2$ solid solutions with x=0.04~0.08 showed the most superior microwave dielectric properties, those are ${\varepsilon}_r$= 89-92, Q . f = 5855~6091 GHz, and (${\tau}_f$)= -7.5-7.5 ppm/$^{\circ}C$.

• Archives of Pharmacal Research
• /
• v.27 no.4
• /
• pp.386-389
• /
• 2004

Repeated column chromatography of the CHCI_3-soluble fraction of Zingiber zerumbet led to the isolation and identification of two aromatic compounds, p-hydroxybenzaldehyde (1) and vanillin (2), and six kaempferol derivatives, kaempferol-3,4',7-O-trimethylether (3), kaempferol-3-O-methylether (4), kaempferol-3,4'-O-dimethylether (5), 4'-O-acetylafzel in (6), kaempferol-3-O-(4-O-acetyl-$\alpha$-L-rhamnopyranoside)], 2',4'-O-diacetylafzelin (7), kaempferol-3-O-(2,4-O-diacetyl-$\alpha$-L-rhamnopyranoside)], and 3',4'-O-diacetylafzelin (8), kaempferol-3-O-(3,4-O-diacetyl-$\alpha$-L-rhamnopyranoside)]. The structures of 1-8 were identifed by analysis of spectroscopic data as well as by comparison with published values. This is the first report on the isolation of compounds 1-3 from this plant.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.11 no.3
• /
• pp.242-247
• /
• 1998

In this study, we have synthesized $ZnGa_2O_4$:Mn,X powder doped with Mn, MnO, $MnF_2$ and $MnCl_2$, low voltage green emitting phosphor, in vacuum atmosphere. From PL spectra, the intensity of the emission peak, the brightness with coactivator show that $ZnGa_2O_4$:Mn,Cl > $ZnGa_2O_4$:Mn,F > $ZnGa_2O_4$:Mn,O > $ZnGa_2O_4$:Mn. These improvement of the brightness are caused by the increase of the concentration of $Mn^{2+}$ ion. In case of $ZnGa_2O_4$:Mn,Cl and ZnGa$_2$O$_4$:Mn,F, the brightness is enhanced much more, which is owed to the decrease of defect of host material. For $ZnGa_2O_4$:Mn,Cl phosphor fabricated with optimized condition, the decay time becomes short from 30 ms of the $ZnGa_2O_4$:Mn and $ZnGa_2O_4$:Mn,O to 6 ms and the brightness of CL at 1 kV, 1 mA is 60 cd/$m^2$.

• Bulletin of the Korean Chemical Society
• /
• v.14 no.2
• /
• pp.188-191
• /
• 1993

The reaction between methyl 2,3-di-O-benzyl-4,6-di-O-mesyl-${\alpha}$-D-glucopyranoside (1b) and potassium superoxide resulted in hydrolysis, and gave methyl 2,3-di-O-benzyl-${\alpha}$-D-glucopyranoside (1) as a sole product. When the reaction was performed with a vicinal dimesylate, methyl 4,6-O-benzylidene-2,3-di-O-mesyl-${\alpha}$-D-altropyranoside (4b), again the hydrolysis product, methyl 4,6-O-benzylidene-${\alpha}$-D-altropyranoside (4) was obtained. However, the reaction of potassium superoxide with another vicinal dimesylate, methyl 4,6-O-benzylidene-2,3-di-O-mesyl-${\alpha}$-D-glucopyranoside (3b), nucleophilic displacement took place to afford methyl 4,6-O-benzylidene-${\alpha}$-D-altropyranoside (4). Apparently different results from two trans vicinal dimesylates, 3b and 4b are explained by the transient formation of epoxides, methyl 2,3-anhydro-4,6-O-benzylidene-${\alpha}$-D-allopyranoside (8) and methyl 2,3-anhydro-4,6-O-benzylidene-${\alpha}$-D-mannopyranoside (9) by $KO_2$. The reaction between the allo epoxide 8 and $KO_2$ gave altro 4. The manno epoxide 9 also afforded altro 4 as the major product. Facile epoxide formation by the reaction of a vicinal dimesylate and superoxide was also observed with 3-O-benzyl-1,2-O-isopropylidene-5,6-di-O-mesyl-${\alpha}$-D-glucofuranose: 5,6-anhydro-3-O-benzyl-1,2-O-isopropylidene-${\beta}$-L-idofuranose was obtained.

• Transactions on Electrical and Electronic Materials
• /
• v.13 no.5
• /
• pp.262-265
• /
• 2012

The Microstructure and nonlinear electrical properties of the ZPCCYT (ZnO-$Pr_6O_{11}$-CoO-$Cr_2O_3$-$Y_2O_3$-$Tb_4O_7$) varistors were investigated for different amounts of $Tb_4O_7$. The addition of $Tb_4O_7$ has a significant effect on microstructure and electrical properties. Analysis of the microstructure indicated that the ceramics consisted of ZnO grain as a main phase and a few secondary phases as a mix of $Pr_6O_{11}$, $Y_2O_3$, and $Tb_4O_7$. As the amount of $Tb_4O_7$ increased, the sintered densities of pellets increased from $\rho$ = 5.70 to $5.78g/cm^3$ and the average grain size decreased from d = 4.8 to $3.6{\mu}m$. The increase in the amount of $Tb_4O_7$ increased from $E_B$ = 7,473 to 10,035 V/cm and from ${\alpha}$ = 39.7 to 52.2. In particular, it was found that the ceramics modified with 1.0 mol% in the amount of $Tb_4O_7$ are suited for the varistors for high voltage in the light of a high sintered density and a high voltage gradient.

• The Transactions of the Korean Institute of Electrical Engineers C
• /
• v.55 no.7
• /
• pp.344-348
• /
• 2006

The effect of x on microwave dielectric properties of the $(1-x)Mg_4Ta_2O_9-x(TiO_2,\;CaTiO_3,\;SrTiO_3)$ ceramics for microwave components were investigated. All spcecimens prepared by the conventional mixed oxied method and sintered at $1450^{\circ}C$. Microwave dielectric properties of the $(1-x)Mg_4Ta_2O_9-xTiO_2$ ceramics were influenced by $MgTi_2O_5$ phase. Also the microwave dielectric properties of the $(1-x)Mg_4Ta_2O_9-x(TiO_2,\;CaTiO_3,\;SrTiO_3)$ ceramics were dominated with an addition of $CaTiO_3\;and\;SrTiO_3$. The dielectric constant $(\varepsilon_r)$, quality factor $(Q{\times}f_r)$ and temperature coefficient of the resonant frequency $(TCRF,\;\tau_f)$ of the $(1-x)Mg_4Ta_2O_9-x(TiO_2,\;CaTiO_3,\;SrTiO_3)$ ceramics were $12.96\sim70.98,\;5,132\sim186,410GHZ$ and $-35.82\sim+75.96ppm/^{\circ}C$, respectively, and depend on x and addition materials.

• Journal of Electrochemical Science and Technology
• /
• v.2 no.3
• /
• pp.146-151
• /
• 2011

The formation of Li-Si-O phases, $Li_4SiO_4$ and $Li_2SiO_3$ from the starting materials SiO and $Li_2O$ are analyzed using Vienna Ab-initio Simulation (VASP) package and the total energies of Li-Si-O compounds are evaluated using Projector Augmented Wave (PAW) method and correlated the structural characteristics of the binary system SiO-$Li_2O$ with experimental data from electrochemical method. Despite $Li_2SiO_3$ becomes stable phase by virtue of lowest formation energy calculated through VASP, the experimental method shows presence of $Li_4SiO_4$ as the only product formed when SiO and $Li_2O$ reacts during slow heating to reach $550^{\circ}C$ and found no evidence for the formation of $Li_2SiO_3$. Also, higher density of $Li_4SiO_4$(2.42 g $ml^{-1}$) compared to the compositional mixture $1SiO_2-2Li_2O$ (2.226 g $ml^{-1}$) and better cycle capacity observed through experiment proves that $Li_4SiO_4$ as the most stable anode supported by better cycleabilityfor lithium ion battery remains as paradox from the point of view of VASP calculations.

• Journal of the Korean Ceramic Society
• /
• v.32 no.12
• /
• pp.1331-1336
• /
• 1995

The glass-ceramics for ferro-electric were made from compositions of 70PbO.16TiO2.8SiO2.4B2O3.2AlPO4 (wt%) and 67.5PbO.20TiO2.8.5SiO2.2B2O3.2AlPO4 (wt%). The crystallization kinetics for PbTiO3 crystalline phase formation from glass was studied using non-isothermal DSC techniques. The values of activation energy, ΔE using variables of heating rate and temperature were calculated at various reaction fractions obtained from peak area over DSC. The results indicated that activation energy was lowest at 60% reaction fractions and the activation energy of glass containing 20.0 wt% TiO2 is higher than that of glass containing 16.0 wt% TiO2. The crystallization mechanism was three dimensional growth (n=4).

• Journal of Korean Society of Environmental Engineers
• /
• v.36 no.6
• /
• pp.396-401
• /
• 2014

Nanomaterials have been widely used in many fields. This study investigates the effects of metal oxide nanoparticles (CuO, NiO, $TiO_2$, $Fe_2O_3$, $Co_3O_4$, ZnO) on germination and germination index (G.I.) of seeds, Lactuca and Raphanus. Under aqueous exposure, CuO on Lactuca shows the most significant impacts on activities compared to others, showing $EC_{50s}$ for germination and G.I. as 0.46 mg/L and 0.37%, respectively. The effects of nanoparticle phytotoxicity on seed Lactuca was much higher than that of Raphanus. In general, the toxicities on seed germination and germination index were as following orders : CuO > ZnO > NiO ${\gg}$ $TiO_2$, $Fe_2O_3$, $Co_3O_4$. No measurable inhibition was observed at 1,000 mg/L (maximum exposure concentration) of $TiO_2$, $Fe_2O_3$, $Co_3O_4$.

• Knowledge Management Research
• /
• v.21 no.3
• /
• pp.249-269
• /
• 2020

Recently, as the online market has matured, it is facing many problems to prevent the growth. The most common problem is the homogenization of online products, which fails to increase the number of customers any more. Moreover, although the portion of the online market has increased significantly, it now becomes essential to expand offline for further development. In response, many online firms have recently sought to expand their businesses and marketing channels by securing offline spaces that can complement the limitations of online platforms, on top of their existing advantages of online channels. Based on their competitive advantage in terms of analyzing large volumes of customer data utilizing information technologies (e.g., big data and artificial intelligence), they are reinforcing their offline influence as well through this online for offline (O4O) business model. On the other hand, most of the existing research has primarily focused on online to offline (O2O) business model, and there is still a lack of research on O4O business models, which have been actively attempted in various industrial fields in recent years. Since a few of O4O-related studies have been conducted only in an experience marketing setting following a case study method, it is critical to conduct an empirical study on O4O selection attributes and their impact on customer satisfaction and loyalty. Therefore, focusing on China's representative O4O business model, 'Fresh Hema,' this study attempts to identify some key selection attributes specialized for O4O services from the customers' viewpoint and examine the impact of these attributes on customer satisfaction and loyalty. The results of the structural equation modeling (SEM) with 300 O4O (Fresh Hema) experienced customers, reveal that, out of seven O4O selection attributes, four (mobile app quality, mobile payment, product quality, and store facilities) have an impact on customer satisfaction, which also leads to customer loyalty (reuse intention, recommendation intention, and brand attachment). This study would help managers in an O4O area well adapt to rapidly changing customer needs and provide them with some guidelines for enhancing both customer satisfaction and loyalty by allocating more resources to more significant selection attributes, rather than less significant ones.