• Korean Journal of Materials Research
• /
• v.2 no.5
• /
• pp.330-336
• /
• 1992

Four distinctive hot pressed and heat treated S${i_3}{N_4}$ceramics, S${i_3}{N_4}$-8%${Y_2}{O_3}$, S${i_3}{N_4}$-6% ${Y_2}{O_3}$-2% $A{l_2}{O_3}$, S${i_3}{N_4}$-4% ${Y_2}{O_3}$-3% $A{l_2}{O_3}$, 그리고 S${i_3}{N_4}$-1% MgO-1% Si$O_2$(in wt%), were prepared and characterized by X-ray diffraction, scanning electron microscopy, image analysis and mechanical tests. The fracture toughness of S${i_3}{N_4}$-8% ${Y_2}{O_3}$specimens containing large elongated grains showed the highest value of about 9.8MPa$m^{1/2}$. Two out of four S${i_3}{N_4}$, ceramics(S${i_3}{N_4}$-6% ${Y_2}{O_3}$-2% $A{l_2}{O_3}$and S${i_3}{N_4}$-4% ${Y_2}{O_3}$-3% $A{l_2}{O_3}$) heat treated at 200 $0^{\circ}C$retained the fracture strength of over 900MPa and fracture toughness of over 8.0MPa$m^{1/2}$. Large ${\beta}$-S${i_3}{N_4}$grains having a diameter larger than 1${\mu}$m appeared to contribute to increase in fracture toughness.

• Journal of the Korean Ceramic Society
• /
• v.31 no.8
• /
• pp.861-868
• /
• 1994

CaO-Al2O3 glass is a good candidate as optical fiber amplifier and laser. In this study, optical properties for 4I13/2longrightarrow4I15/2 transition of Er3+ ions doped in CaO-Al2O3 glasses were investigated. Optical absorptions, radiative transition probabilities and lifetimes for 4I13/2 level were evaluated by using Judd-Ofelt theory. Also, induced- emmision cross-sections of 4I13/2longrightarrow4I15/2 transition were calculated. Radiative transition probability and lifetime of 4I13/2 level were 144.6s-1, 690$mutextrm{s}$ respectively for 60CaO.40Al2O3 glass(FS0) and 152.6s-1, 660 $mutextrm{s}$ for 54 CaO.36Al2O3.10SiO2 glass (FS10). Each induced-emission cross sections for FS0 and FS10 was 0.749$\times$10-20 $\textrm{cm}^2$, 0.892$\times$10-20 $\textrm{cm}^2$. Obtained values were comparable with those of ZBLA glass studied as optical fiber amplifier and laser material.

• Journal of the Korean Chemical Society
• /
• v.42 no.6
• /
• pp.679-695
• /
• 1998

A series of ${\alpha}{\omega}-bis[4-(4'-(S)-(+)-2-methylbutylbiphenyl-4-carboxy)phenoxy]alkanes$, were synthesized, and their thermal and liquid crystalline properties were studied. The chain length of the central polymethylene spacers, x, of the chiral twin compounds was varied from 3 to 12. These compounds were characterized by elemental analysis, IR and NMR spectroscopy, differential thermal analysis (DSC), and crosspolarized microscopy. All compounds were found to be enantiotropic liquid crystalline, and the values of melting $(T_m)$ and isotropization temperature $(T_i)$ as well as ${\delta}H_I$ and ${\delta}S_I$ decreased in a zig-zag fashion, revealing the so called odd-even effect as x increased. Their mesomorphic properties fell into four categories depending upon x; (a) compounds with x=3, 4 and 5 formed only a cholesteric phase on heating, while on cooling they went through two transitions of isotropic (I)-to-cholesteric (Ch) and Ch-to-smectic $A\;(S_A)$ phases before crystallization. (b) compounds with x=6, 8 and 10 exhibited only a cholesteric phase both on heating and on cooling. (c) compounds with x=7 and 9 went through three transitions of crystal $(C)-to-S_A,\;S_A-to-Ch,$ and Ch-to-I phases on heating while on cooling they went through four transitions of I-to-Ch, $Ch-to-S_A,\;S_A-to-Smectic\;C\;(S_C),\;and\;S_c-to-C$ phases in that order, and (d) compounds with x=11 and 12 went reversibly through four transitions of $C-to-S_C,\;S_C-to-S_A,\;S_A-to-Ch,$ and Ch-to-I phases.

• 한국신재생에너지학회:학술대회논문집
• /
• 2006.06a
• /
• pp.387-390
• /
• 2006

We report here that under strong attacksof external $CH_4$ guest molecules the sII and sH methane hydrates are structurally transformed to the crystalline me framework of sI, leading to favorable change of the lattice dimension of the host-guest networks. The High Power Decoupling $^{13}C$ NMR and Raman spectroscopies were used to identify structure transitions of the mixed $CH_4+C_2H_6$ hydrates (sIIl) and hydrocarbons (methylcyclohexane, isopentane) + $CH_4$ hydrates (sH). The resulting spectra indicate that most of the synthesized sII and sH hydrates were transformed to methane hydrate of sl under 110 bar and particularly the coexistence of sl with sII or sH appear according to the surrounding methane-rich gas conditions. The present findings might be expected to Provide rational evidences regarding the preponderant occurrence of naturally-occurring sI methane hydrates in marine sediments.

• Journal of KSNVE
• /
• v.4 no.2
• /
• pp.231-238
• /
• 1994

This paper presents an experimental method to find the vibrational transmission characteristics of structures by using the structural intensity method which is used as the important techniques of active vibration control method. Experimental results are obtained from measurements performed on a structure beam by 2, 3 and 4 position linear accelerometr array (2, 3 and 4 structural intensity : 2, 3 and 4 S.I.) methods at near and farfield conditions. These results are compared with the measurement values of conventional power flow measurement method called input power measurement in order to verify the accuracy of structural intensity methods. To minimize the errors associated with 2, 3 and 4 S.I. methods, the measurement locations were selected by the result of modal analysis and the averaged data by the inter-change of accelerometer array was utilized. In 3 and 4 S.I. methods measured wavenumber instead of theoretical wavenumber was used. This paper shows that measurements of bending wave power flow by using 2, 3 and 4 S.I. methods can give accurate values under general field conditions in structural beam and the accuracy of 2, 3 S.I. methods is higher than 4 S.I. methods. Finally, 2 position linear accelerometer array method is suggested as the practical structural intensity technique.

• Journal of the Korean Chemical Society
• /
• v.30 no.6
• /
• pp.500-509
• /
• 1986

For the development of new type cell, a study on new electrolyte, $AgI-Ag_8S_3SO_4$ system has been carried out by using electrical conductivity measurement, DTA and X-ray powder diffraction method. From both X-ray powder diffraction and DTA method, it is clearly known that 20mole% $ Ag_8S_3SO_4$-AgI system forms single phase, having monoclinic structure. It is also found that 20mole% $Ag_8S_3SO_4$-AgI system is purely $ Ag^+ $cation conduction from results of conductivity measurement by applying 4-probe method.

• Honam Mathematical Journal
• /
• v.36 no.4
• /
• pp.913-919
• /
• 2014

We investigate the relationships between the space X and the hyperspaces concerning admissibility and connectedness im kleinen. The following results are obtained: Let X be a Hausdorff continuum, and let A, $B{\in}C(X)$ with $A{\subset}B$. (1) If X is c.i.k. at A, then X is c.i.k. at B if and only if B is admissible. (2) If A is admissible and C(X) is c.i.k. at A, then for each open set U containing A there is a continuum K and a neighborhood V of A such that $V{\subset}IntK{\subset}K{\subset}U$. (3) If for each open subset U of X containing A, there is a continuum B in C(X) such that $A{\subset}B{\subset}U$ and X is c.i.k. at B, then X is c.i.k. at A. (4) If X is not c.i.k. at a point x of X, then there is an open set U containing x and there is a sequence $\{S_i\}^{\infty}_{i=1}$ of components of $\bar{U}$ such that $S_i{\longrightarrow}S$ where S is a nondegenerate continuum containing the point x and $S_i{\cap}S={\emptyset}$ for each i = 1, 2, ${\cdots}$.

• ETRI Journal
• /
• v.23 no.4
• /
• pp.151-157
• /
• 2001

Spectroscopic and thermal analysis indicates that tellurite glasses doped with $B_2O_3$ and $GeO_2$ are promising candidate host materials for wide-band erbium doped fiber amplifier (EDFA) with a high 980 nm pump efficiency. In this study, we measured the thermal stabilities and the emission cross-sections for $Er^{3+}:^{4}I_{13/2}\;{\to}\;^{4}I_{15/2}$ transition in this tellurite glass system. We also determined the Judd-Ofelt parameters and calculated the radiative transition rates and the multiphonon relaxation rates in this glass system. The 15 mol% substitution of $B_2O_3$ for $TeO_2$ in the $Er^{3+}-doped\;75TeO_2-20ZnO-5K_2O$ glass raised the multiphonon relaxation rate for $^4I_{11/2}\;{\to}\;^4I_{13/2}$ transition from 4960 $s^{-1}$ to 24700 $s^{-1}$, but shortened the lifetime of the $^4I_{13/2}$ level by 14 % and reduced the emission cross-section for the $^4I_{13/2}\;{\to}\;^4I_{15/2}$ transition by 11%. The 15 mol% $GeO_2$ substitution in the same glass system also reduced the emission cross-section but increased the lifetime by 7%. However, the multiphonon relaxation rate for $^4I_{11/2}{\to}^4I_{13/2}$ transition was raised merely by 1000 $s^{-1}$. Therefore, a mixed substitution of $B_2O_3$ and $GeO_2$ for $TeO_2$ was concluded to be suitable for the 980 nm pump efficiency and the fluorescence efficiency of $^4I_{13/2}{\to}^4I_{15/2}$ transition in $Er^{3+}-doped$ tellurite glasses.

• Journal of the Korea Institute of Military Science and Technology
• /
• v.13 no.6
• /
• pp.1080-1090
• /
• 2010

A study for improvement of credibility on test & evaluation result of interoperability in battle management information system which focused in C4I systems is very essential in rapid change of battle field environment. Realization of effective operation process with integration of developed IT also core factor for reducing of operational response time such as information gathering from sensor to shooter, time for commander's decision making. Therefore, by required to meet of high technical T&E, meet of complex software's user requirement, long-term system development period, system integration ability's request by various linkage of systems, it is high a M&S dependency to optimal performance, interpoerability's guarantee. Especially credibility on test & evaluation using M&S is very important. This paper will propse a VV&A applied methods using other VV&A case to improve credibility of M&S on test & evaluation.

• Nuclear Engineering and Technology
• /
• v.14 no.1
• /
• pp.22-40
• /
• 1982

The nuclear LS-energy matrix elements have been calculated with the harmonic oscillator shell model wave functions for the configurations ( $l_{i}$ $l_{i+1}$｜ $l_{i}$ $l_{i+1}$) where 1$_1$= $l_{s}$ , $l_2$=lp, $l_3$=ld, 2s, $l_4$=1f, 2p, $l_{5}$ =1g, 2d, 3s. The resulting matrix elements are expressed in terms of both Talmi integrals $I_1$ and Slater integrals $F^{k}$ . In addition to this various sum rules are derived and applied to check the results of the calculations.ons.