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신동욱,Viswanathan S. Saji,Ravindra K. Gupta,조용수 한국세라믹학회 2007 한국세라믹학회지 Vol.44 No.11
The variations of physical and dielectric properties of low temperature dielectrics based on typical aluminoborosilicate glasses modified with several divalent oxides were investigated. The divalent oxides studied here included CaO, MgO, BaO, SrO and ZnO. All samples containing either 35 wt% or 45 wt% alumina filler were prepared at the same processing condition and then fired at 850oC for 30 min. The resultant characteristics of fired samples depended on the choice of the divalent ion and the content of the alumina filler. Except for the ZnO modification, all other samples containing 35 wt% filler demonstrated promising densification as they exhibited reasonably high densities of 3.07-3.31 g/cm3 and high shrinkages of 14.0-16.4%. Particularly, the sample containing ZnO was distinguished with large variations compared to the base sample, which can be highlighted with earlier densification and crystallization at unexpectedly low temperatures. The negative effects of the ZnO modification on densification and dielectric properties were thought to be associated with earlier crystallization potentially by influencing effective densification via viscous flow. As an optimum composition, the sample containing only CaO showed the most promising characteristics such as k~8.05 and tanδ~0.0018 when 35 wt% alumina filler was used.
Gupta, Ravindra K,Whang, Chin Myung IOP Pub 2007 Journal of physics, an Institute of Physics journa Vol.19 No.19
<P>The effect of composition on the structure of the new solid oxide fuel cell (SOFC) perovskite (La<SUB>1−<I>x</I></SUB>Sr<SUB><I>x</I></SUB>)(Cr<SUB>0.85</SUB>Fe<SUB>0.05</SUB>Co<SUB>0.05</SUB>Ni<SUB>0.05</SUB>)O<SUB>3−δ</SUB> is studied using x-ray diffractometry, pycnometry, and Fourier-transform infrared and Raman spectroscopy. Samples were synthesized using the Pechini method via doping the La site with Sr<SUP>2+</SUP>, to a composition with <I>x</I> = 0–0.4 mole fraction, and at the Cr site with 0.05 mol of Co<SUP>2+</SUP>,Fe<SUP>2+</SUP> and Ni<SUP>2+</SUP>, and the structural results were compared with those for orthorhombic LaCrO<SUB>3</SUB>. The samples were orthorhombic perovskite of the <I>Pnma</I> space group. A second phase, monoclinic SrCrO<SUB>4</SUB>, was also observed, whose content increased linearly with increasing <I>x</I>. A large decrease in the lattice and hence volume was observed for the sample with <I>x</I> = 0.1, which was accompanied by a sharp decrease in the Cr−O bond length, tilt angle and crystallite size. The structural parameters were almost invariant for <I>x</I> = 0.1–0.4, probably due to an increase in content of the high valence cations of smaller ionic radii, as suggested by an increase in the intensity of the defect band (∼515?cm<SUP>−1</SUP>, IR). The octahedral CrO<SUB>6</SUB> stretching, bending and tilting modes were found shifted accordingly. A mechanism employing a partial-charge model was proposed to explain the results. </P>
Gupta, P.S.P.,Ravindra, J.P.,Nandi, S.,Raghu, H.M.,Ramesha, K.P. Asian Australasian Association of Animal Productio 2005 Animal Bioscience Vol.18 No.11
Ovarian follicular fluid contains both stimulatory and inhibitory agents that influence the growth and maturation of oocyte. In the present study, an attempt was made to isolate and study the biological properties of ovarian follicular fluid peptide(s) in buffaloes. Bubaline ovarian follicular was made steroid- and cell-free. A protein fraction was obtained by saturation (30-35% level) of the follicular fluid with ammonium sulfate. The protein fraction was purified with Sephadex-G 50 gel filtration chromatography and a single peak was obtained in the eluant volume, which was lyophilized. SDS-PAGE of the lyophilized fraction revealed a single band and the molecular weight of the peptide was 26.6 kDa. The peptide stimulated the cumulus cell expansion and in vitro maturation rate of oocytes in buffaloes in a dose dependent manner when it was incorporated at different dose levels (0, 10, 25, 50, 100 and 1,000 ng $ml^{-1}$ of maturation medium). The basic culture medium consisted of TCM 199 with Bovine serum albumin (0.3%). The in vitro maturation rates were comparable to those obtained with a positive control medium (TCM 199+20 ng EGF $ml^{-1}$+steer serum (20%)). Further purification and biological assays may throw more light on the nature and functions of this peptide.
Effects of Ultrasonic Irradiation on Physical Properties of Silica/PEG Hybrids
Jung, Hwa-Young,Gupta, Ravindra K.,Lee, Sang-Ki,Whang, Chin-Myung The Korean Ceramic Society 2002 한국세라믹학회지 Vol.39 No.2
The effect of ultrasonic radiation is reported for silica-poly(ethylene glycol) system prepared without the solvent using sol-gel processing by varying various parameters such as ultrasonic irradiation time, PEG content and HCl/TEOS molar ratio. The property of sonogel is compared with classic gel which has been prepared with ethanol as a solvent by traditional sol-gel processing. SEM, BET, DTA-TGA, density and Vickers hardness measurements are carried out for analyzing the samples. The gelation time is found strongly dependent on radiation time, PEG content and pH value, and has been discussed on the basis of existing theories. The $SiO_2-10$ & 20 wt% PEG sonogel exhibited superior optical, physical and gel properties as compared to the classic gel, hence, found suitable for device applications. The ultrasonic radiation increased the density and surface area, and also reduced the pore size which is well supported by the shift in the peak of DTA curve. The DTA thermogram was found similar to that of pure silica gel.
Preparation and Characterization of Hybrid Silica-Poly(ethylene glycol) Sonogel
Jung, Hwa-Young,Gupta, Ravindra K.,Seo, Dong-Won,Kim, Yoo-Hang,Whang, Chin-Myung Korean Chemical Society 2002 Bulletin of the Korean Chemical Society Vol.23 No.6
An inorganic-organic hybrid system, silica-poly(ethylene glycol) songel is reported. This system was prepared via sol-gel method by varying varous processing variables. e.g. ultrasonic radiation time, gelling temperanture, PEG content and its molecular weight. Various experimental techniques wee employed to analyze the morphological, mechanical and optical properties of the system. The results were discussed in the light of existing theories. The sonogel system exhibited the common features of inorganic-organic hybrids. $SiO_2-10$ wt% PEG sonogel exhibited the morphological and optical properties superior to those reported earlier for the classic gels and found suitable for device applications.
Shin, Dong-Wook,Saji, Viswanathan S.,Gupta, Ravindra K.,Cho, Yong-Soo The Korean Ceramic Society 2007 한국세라믹학회지 Vol.44 No.11
The variations of physical and dielectric properties of low temperature dielectrics based on typical aluminoborosilicate glasses modified with several divalent oxides were investigated. The divalent oxides studied here included CaO, MgO, BaO, SrO and ZnO. All samples containing either 35 wt% or 45 wt% alumina filler were prepared at the same processing condition and then fired at $850^{\circ}C$ for 30 min. The resultant characteristics of fired samples depended on the choice of the divalent ion and the content of the alumina filler. Except for the ZnO modification, all other samples containing 35 wt% filler demonstrated promising densification as they exhibited reasonably high densities of 3.07-3.31 $g/cm^3$ and high shrinkages of 14.0-16.4%. Particularly, the sample containing ZnO was distinguished with large variations compared to the base sample, which can be highlighted with earlier densification and crystallization at unexpectedly low temperatures. The negative effects of the ZnO modification on densification and dielectric properties were thought to be associated with earlier crystallization potentially by influencing effective densification via viscous flow. As an optimum composition, the sample containing only CaO showed the most promising characteristics such as $k{\sim}8.05$ and $tan{\delta}{\sim}0.0018$ when 35 wt% alumina filler was used.