• Journal of the Korean Mathematical Society
• /
• v.51 no.6
• /
• pp.1251-1267
• /
• 2014

The semicommutative property of rings was introduced initially by Bell, and has done important roles in noncommutative ring theory. This concept was generalized to one of nil-semicommutative by Chen. We first study some basic properties of nil-semicommutative rings. We next investigate the structure of Ore extensions when upper nilradicals are ${\sigma}$-rigid ${\delta}$-ideals, examining the nil-semicommutative ring property of Ore extensions and skew power series rings, where ${\sigma}$ is a ring endomorphism and ${\delta}$ is a ${\sigma}$-derivation.

• 한국신재생에너지학회:학술대회논문집
• /
• 2007.06a
• /
• pp.133-136
• /
• 2007

Perovskite-structured samarium strontium cobaltite (SSC), which is mixed ionic electronic conductor (MIEC), is considered as a promising cathode material for intermediate temperature-operating solid oxide fuel cell (SOFC) due to its high electrocatalytic property. Cathode material containing cobalt (Co) is unstable at high temperature and has a relatively high thermal expansion property. In this paper, Sm-Sr-(Co,Fe,Ni)-O system with perovskite and spinel structures was investigated in terms of electrochemical property and thermal expansion property, respectively. Area specific resistance (ASR) was measured by ac impedance spectroscopy to investigate the electrochemical property of cathode, and thermal expansion coefficient (TEC) was measured by using dilatometer. Micro structure of cathode was observed by scanning electron microscopy. Perovskite-structured $Sm_{0.5}Sr_{0.5}CoO_{3-\delta}$ showed the ASR of $0.87{\Omega}/cm^{2}$, and $Sm_{0.5}Sr_{0.5}NiO_{3-\delta}$, which actually has a spinel structure, showed the lowest TEC value of $13.3{\times}10^{-6}/K$.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2004.11a
• /
• pp.297-300
• /
• 2004

In this paper, we investigated insulation property of epoxy resin which includes elastomers to improve mechanical property, as varied to additive elastomer contents and to moisture absorption. There are four samples with 5[phr], 10[phr], 15[phr] and 20[phr]. we experimented to acquire insulation property(absorption rate, dissolution rate, apparent rate) and electrical property(perittivity, $tan\delta$, BDV) during respectively the time such as 6[h], 12[h], 18[h], 24[h] for moisture absorption. According to the experimental results, it is appeared that when the additive elastomer contents are increasing or when specimens remain more moisture, absorption rate, dissolution rate, permittivity and $tan\delta$ are slightly increasing but apparent rate and BDV(break-Down Voltage) strength are decreasing in particular, elastomer content [20]phr appeared remarkedly the more increase or decrease than others.

• Journal of the Korean Ceramic Society
• /
• v.34 no.5
• /
• pp.449-452
• /
• 1997

Quick hardened property and compressive strength experimented to the C4A3 quantities. Workability experimented to the hydration behavior as retarder added to the C4A3. Compressive strength reached {{{{ delta }}3h=300~350 kgf/$\textrm{cm}^2$, {{{{ delta }}6h=400~450 kgf/$\textrm{cm}^2$, {{{{ delta }}24h=500~550 kgf/$\textrm{cm}^2$. Flow loss rate reached 70.1% to retarder addition 0.12% after 15 min. Test items were SEM, XRD, TG-DTA, MCC, porosity and zeta potential.

• Journal of Institute of Control, Robotics and Systems
• /
• v.6 no.2
• /
• pp.121-126
• /
• 2000

In the fast sampling limit the delta operator model tends to the analog system model. This fundamental property of the delta operator model unifies continuous and discrete time control system. In this paper we study robust linear optimal model following servo system in the presence of disturbances and parameter perturbations. A technique to directly design the generalized differential operator based unified control system that covers both differential operator based continuous time and delta operator based discrete time case is presented. The quadratic criterion function for a linear system is used to design the robust unified servo control system The characteristics of the proposed servo system are analysed and simulated to verify the robustness.

• The Transactions of the Korean Institute of Electrical Engineers A
• /
• v.48 no.6
• /
• pp.747-752
• /
• 1999

In the fast sampling limit, the delta operator model tends to the analog system model. This fundamental property of the delta operator model unifies continuous and discrete time control system. In this paper, we study robust linear optimal model following servo system in the presence of disturbances and parameter perturbations. A technique to directly design the generalized differential operator based unified control system that convers both differential operator based continuous time and delta operator based discrete time case is presented. The quadratic criterion function for a linear system is used to design the robust unified servo control. The characteristics of the proposed servo system are analysed and simulated to verify the robustness.

• Bulletin of the Korean Mathematical Society
• /
• v.45 no.4
• /
• pp.645-650
• /
• 2008

Let M be a generalized homogeneous compact space, and let Z(M) denotes the space of homeomorphisms of M with the $C^0$ topology. In this paper, we show that if the interior of the set of weak stable homeomorphisms on M is not empty then for any open subset W of Z(M) containing only weak stable homeomorphisms the orbital shadowing property is generic in W.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
• /
• v.5 no.4
• /
• pp.357-362
• /
• 2000

Stable isotope ratios of oxygen and hydrogen were investigated in southern Yellow Sea in August 1997. Salinity showed good positive correlation with ${\delta}^{18}$O and ${\delta}$. The correlation between ${\delta}^{18}$O and ${\delta}$D is good. From the relationship between these parameters, we obtained two lines of conclusion: 1) seawater of study area I in summer is a mixture of Changjiang Water and modified Kuroshio Water; 2) stable isotopes are very useful tracers in studying property and behavior of water masses in the study area. In case when water masses can not be easily distinguished by T-S analysis, the stable isotopes seem to be powerful tools for this purpose.

• Journal of the Chungcheong Mathematical Society
• /
• v.13 no.1
• /
• pp.53-63
• /
• 2000

The inverse shadowing property of a dynamical system is an "inverse" form of the shadowing property of the system. Recently, Kloeden and Ombach proved that if an expansive system on a compact manifold has the shadowing property then it has the inverse shadowing property. In this paper, we study topological stability of the inverse shadowing dynamical systems. In particular, we show that if an expansive system on a compact manifold has the inverse shadowing property then it is topologically stable, and so it has the shadowing property.

• Journal of the Korean Mathematical Society
• /
• v.42 no.2
• /
• pp.353-363
• /
• 2005

For a ring endomorphism $\alpha$ and an $\alpha$-derivation $\delta$, we introduce ($\alpha$, $\delta$)-skew Armendariz rings which are a generalization of $\alpha$-rigid rings and Armendariz rings, and investigate their properties. A semi prime left Goldie ring is $\alpha$-weak Armendariz if and only if it is $\alpha$-rigid. Moreover, we study on the relationship between the Baerness and p.p. property of a ring R and these of the skew polynomial ring R[x; $\alpha$, $\delta$] in case R is ($\alpha$, $\delta$)-skew Armendariz. As a consequence we obtain a generalization of [11], [14] and [16].