• 대한수학회보
• /
• 제53권5호
• /
• pp.1385-1394
• /
• 2016

Let (R, m) be a Noetherian local ring, I, J two ideals of R, and A an Artinian R-module. Let $k{\geq}0$ be an integer and $r=Width_{>k}(I,A)$ the supremum of lengths of A-cosequences in dimension > k in I defined by Nhan-Hoang [9]. It is first shown that for each $t{\leq}r$ and each sequence $x_1,{\cdots},x_t$ which is an A-cosequence in dimension > k, the set $$\Large(\bigcup^{t}_{i=0}Att_R(0:_A(x_1^{n_1},{\ldots},x_i^{n_i})))_{{\geq}k}$$ is independent of the choice of $n_1,{\ldots},n_t$. Let r be the eventual value of $Width_{>k}(0:_AJ^n)$. Then our second result says that for each $t{\leq}r$ the set $\large(\bigcup\limits_{i=0}^{t}Att_R(Tor_i^R(R/I,\;(0:_AJ^n))))_{{\geq}k}$ is stable for large n.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 1997년도 춘계학술대회논문집; 경주코오롱호텔; 22-23 May 1997
• /
• pp.272-277
• /
• 1997

The axial bearing using two ring type permanent magnets to support the weight of a flywheel is proposed to reduce the bearing loss in a flywheel energy storage , system. Two permanent magnet makes stable force in axial direction but unstable force in lateral direction. The lateral unstable stiffness is identified quantitatively using flux analysis, and then through the rotor dynamic analysis on a rigid flywheel system the unstable effects on the system by the stiffness is investigated.

• 대한화학회지
• /
• 제20권4호
• /
• pp.295-298
• /
• 1976

Organothioenamine phosphonate와 styrene oxide 와의 반응에서 얻어진 생성물의 구조를 규명한 결과 그것이 cyclopropane 유도체임을 알았다. 이것은 반응이 styrene oxide에 대한 thioenamine phosphonate의 친핵공격에 의해서 생긴 산소 음이온이 다시 인 원자를 공격함으로서 중간체로 betain이 형성 된다음 이어서 약한 P-C 결합이 끊어지면서 생성물로 이끌어져 감을 가리켜 주고있다. 또한 생성물의 광학활성을 조사한 결과는 우회전성 이어서 이 반응은 중간체에서 생긴 benzyl carbon의 입체적 효과를 받으며 어디까지나 안정한 경로를 거쳐서 이끌어져 감을 알 수 있었다.

• Bulletin of the Korean Chemical Society
• /
• 제25권8호
• /
• pp.1225-1230
• /
• 2004

The stability of fluoroalkyl groups as a pendent on the phenyl ring was measured in vitro using rat hepatic microsomes and human serum to predict their in vivo stabilities. We have prepared three [$^{18}F$]fluoroalkyl-biphenyls as the model compounds of fluoroalkyl aromatic compounds to compare the in vitro stabilities. In addition, in vitro stabilities were measured separately using rat hepatic microsomes and human serum at $37^{\circ}C$. Fluoroethylbiphenyl had similar or slightly superior stability to fluoropropylbiphenyl and these two compounds were much more stable than fluoromethylbiphenyl in vitro.

• Bulletin of the Korean Chemical Society
• /
• 제31권4호
• /
• pp.840-844
• /
• 2010

The new MPV type reagent, Al-methanesulfonyldiisobutylalane ($DIBAO_3SCH_3$), has been prepared and its reducing characteristics in the reduction of selected organic compounds containing representative functional groups have been examined in order to find out a new reducing system with high selectivity in organic synthesis. In general, the reagent is extremely mild, showing only reactivity toward aldehydes, ketones and epoxides. The reagent exhibits a unique reducing applicability in organic synthesis. Thus, the reagent can achieve a clean 1,2-reduction of $\alpha,\beta$-unsaturated aldehydes and ketones to produce the corresponding allylic alcohols in 100% purity. In addition, the reagent shows an excellent regioselectivity in the ring-opening reaction of epoxides. Finally, $DIBAO_3SCH_3$ shows a high stereoselectivity in the reduction of cyclic ketones to produce the thermodynamically more stable epimers exclusively.

• Nuclear Engineering and Technology
• /
• 제34권3호
• /
• pp.211-217
• /
• 2002

A 1-MW vacuum feedthrough for the KSTAR ICRF antenna is fabricated and high power RF test is performed. It is designed to have two alumina $(Al_2O_3)$ ceramic cylinders and O-ring seal instead of a brazed seal for good mechanical and thermal strength, which is important in long pulse or steady state operation. For cooling of the ceramics, dry air is circulated in a space between the two cylinders and the outer conductor. Independent cooling water channels are installed to cool the inner conductor of the feedthrough. RF high voltage test is performed using two kinds of ceramics with the purities of 99.7% and 97%. Stable operation is possible with the RF voltage of 30 kVp at long pulse of 300 sec without any severe damage.

• 한국염색가공학회지
• /
• 제16권5호
• /
• pp.35-41
• /
• 2004

Poly(ethylene terephthalate), polyimide(Kapton), and polypropylene surfaces were modified with argon low temperature plasma by RF glow discharge at 240m Torr, 40W to investigate the surface morphological changes due to the plasma treatment using atomic force microscopy(AFM). Analysis of the AFM images and Ra(average roughness) revealed that the plasma treatment resulted in significant ablation on the surfaces. The morphological changes and surface roughness, however, were different depending on material characteristics such as heat stability, presence of amorphous region, swelling phenomenon, and molecular structure of repeating unit. It was assumed that polypropylene due to its tertiary hydrogen was ablated easily compared to poly(ethylene terephthalate), and that polyimide was more resistant to the ablation than PET due to rigid skeleton of imide and stable phenyl ring structure.

• 한국전기전자재료학회논문지
• /
• 제14권11호
• /
• pp.885-891
• /
• 2001

Ring/dot-type step-down piezoelectric transformer was manufactured by using Pb[(Mn$\sub$1/3/Sb$\sub$2/3)$\sub$0.05/Zr$\sub$0.475/Ti$\sub$0.475/]O$_3$ ceramics, which have excellent high-power piezoelectric properties. The characteristics of step-down piezoelectric transformer as a function of load resistance at output terminal was examined. Voltage gain was greatly dependent on drive frequency and load resistance, and showed maximum voltage gain at the resonance frequency. The output voltage was linearly increased as the input voltage increased. Voltage gain of the step-down piezoelectric transformer with respect to input voltage was very stable when the load resistance was in the range of 50-500 $\Omega$ .

• 한국윤활학회:학술대회논문집
• /
• 한국윤활학회 2000년도 제32회 추계학술대회 정기총회
• /
• pp.298-303
• /
• 2000

The 3 mol% yttria stabilized zirconia (3-Y PSZ) powder was heat treated at 50 0$^{\circ}C$ to evaporate the polymer binder and stabilize the tetragonal phase. The wear experiments were carried out on a ring-on-plate type reciprocating wear tester at selected temperatures with in the range room temperature to 600$^{\circ}C$ The results show that the heat treatment of powder decreases the wear rate due to the reduction of microcracks and pores in coatings and the stabilization of the tetragonal phase. Powder heat treatment enhanced the quality of the coating layer by removing remnant gases during coating process and the powder heat treatment at which tetragonal phase is stable diminished phase ratio of monoclinic. These two effects improved wear resistance characters.

• Bulletin of the Korean Chemical Society
• /
• 제20권11호
• /
• pp.1303-1308
• /
• 1999

Conducting poly(3,4-ethylenedioxythiophene) (PEDT) films with metalloporphyrins incorporated as the counter ions were prepared by electropolymerization of the monomer in the presence of metal-tetra(sulfonatophenyl) porphyrin anions. Cathodic reduction of oxygen on the resulting conducting polymer films was studied. The overpotential for O2 reduction on electrodes with cobalt-porphyrin complex was significantly smaller in acidic solutions than on gold. In basic solutions, the overpotential at low current densities was close to those on platinum and gold. Polymer electrode with Co-complex yielded higher limiting currents than with Fe-complex, although the Co-complex polymer electrode was a poorer electrocatalyst for O2 reduction in the activation range of potential than the Fe counterpart. From the rotating ring-disk electrode experiments, oxygen reduction was shown to proceed through either a 4-electron pathway or a 2-electron pathway. In contrast to the polypyr-role-based electrodes, the PEDT-based metalloporphyrin electrodes were stable with wider potential windows, including the oxygen reduction potential. Their electrocatalytic properties were maintained at temperatures up to 80℃ in KOH solutions.