• 한국전기전자재료학회논문지
• /
• 제14권8호
• /
• pp.640-646
• /
• 2001

The electrical stability for DC stress of Pr$_{6}$O$_{11}$-based ZnO varistos consisting of ZnO-Pr$_{6}$O$_{11}$-CoO-Cr$_2$O$_3$-Er$_2$O$_3$-based ceramics were investigated with sintering temperature in the range of 1325~1345$^{\circ}C$. A the sintering temperature is raised, the nonlinear exponent of varistors was decreased, whereas the stability was markedly improved. The density of ceramics was found to greatly affect the electrical stability for DC stress. The varistors sintered at 13$25^{\circ}C$ were completely degraded because of thermal runaway attributing to low density. The varistors sintered at 1335$^{\circ}C$ exhibited the highest nonlinearity, with a nonlinear exponent of 70.53 and a leakage current of 1.92$\mu$A, whereas they did not exhibit relatively high stability. On the contrary, the varistors sintered at >134$0^{\circ}C$ exhibited not only a high nonlinearity marking the nonlinear exponent above 50 and the leakage current below 3$\mu$A, but also a high stability marking the variation rate of the varistor voltage below 2%, even under DC stress such as (0.80V$_{1mA}$/9$0^{\circ}C$/12h)+(0.85V$_{1mA}$/115$^{\circ}C$/12h)+(0.90V$_{1mA}$/12$0^{\circ}C$/12h)+(0.95V$_{1mA}$/1$25^{\circ}C$/12h)+(0.95V$_{1mA}$/15$0^{\circ}C$/12h). In particular, ti was found that the varistors sintered at 134$0^{\circ}C$ were more nonlinear and more stable, compared with that of 1345$^{\circ}C$.EX>.}C$.EX>.

• 한국정밀공학회지
• /
• 제22권7호
• /
• pp.155-163
• /
• 2005

Pressure heating rollers with temperature control were mounted to a flat cable laminating machine (FCLM). Pressure heating rollers should be heated up to the setting temperature $(175^{\circ}C)$ and kept on to producing good quality flexible flat cables (FFC). Existing Pressure heating rollers took more than 70minutes to the setting temperature and did not keep on the setting temperature in production. Temperature controller, electric power controller, material and diameter of rollers and heat capacities were changed to improve the temperature control of the pressure heat rollers for better production of the FFC. Thus, the reaching time to the setting temperature (RT), temperature stability time (TST) and temperature hunting (TH) were measured and compared with the existing pressure rollers case. The RT of A roller was shortened by 50minutes, and B roller was shortened by 15minutes. The TST of A roller was shortened by 13minutes, and B roller was shortened by 15minutes. The THs of both A and B rollers were settled up to ${\pm}5^{\circ}C$. Finally, the productivity of the FCLM and the quality of the FFC were increased.

• 우주기술과 응용
• /
• 제2권3호
• /
• pp.221-229
• /
• 2022

본 논문에서는 온도에 민감한 플럭스게이트 자력계 센서 온도를 일정하게 유지하기 위한 온도 조절 장치의 설계 및 설치, 그리고 설치 이후 데이터 안정성 평가에 대하여 기술하였다. 온도 조절 장치는 국립전파연구원 우주전파센터에서 운영 중인 이천 지자기 관측소에 설치되었다. 온도 조절 장치는 사고 안정성, 자기장 측정에 미치는 영향, 온도 조절 효율을 고려하여 설계하였다. 온도 조절 장치 설치 이후, 온도가 20℃ 수준에서 일정하게 유지되는 것을 확인하였다. 지자기 데이터 안정성 평가를 위하여 델타 F(delta-F)와 베이스라인(baseline) 값을 이용하였으며, 장치 설치 이후 델타 F와 베이스라인의 변동이 줄어든 것을 확인하였다.

• Progress in Superconductivity
• /
• 제10권2호
• /
• pp.133-138
• /
• 2009

The $Nd_{1+x}Ba_{2-x}Cu_3O_{7-{\delta}}$(Nd123) superconductor exhibits high performance in high magnetic field and high temperature. We have studied phase stability for Nd123 under reduced oxygen partial pressure and various heat-treatment conditions. The main phase is Nd123 and some samples contain small amounts of Nd422 depending on the temperature and oxygen partial pressure. The decomposition temperature decreases with decreasing oxygen partial pressure from $1052^{\circ}C(P(O_2)$=150 Torr) to about $845^{\circ}C(P(O_2)$=0.1 Torr). The liquidus line was steeper temperature with decreasing oxygen partial pressure. In same condition of oxygen partial pressure, the region of stable Nd123 phase was formed at slightly higher temperature than the region of stable YBCO phase.

• 대한설비공학회:학술대회논문집
• /
• 대한설비공학회 2005년도 동계학술발표대회 논문집
• /
• pp.386-391
• /
• 2005

An experimental study was conducted to analyze the thermal stability and to estimate the lifetime of refrigerating lubricants. PAG and POE oil are considered as a test fluids in this study. The viscosity of PAG and POE oil was measured by the vibration type viscometer while temperature is varied periodically in the range of $0^{\circ}C{\sim}100^{\circ}C$. The results indicate that the reduction rates of viscosity of PAG and POE oil were less than 5% after 510 cycles. In order to estimate lifetime of PAG and POE oil with temperature, the viscosity was measured while the temperature of oils was maintained at 180, 200 and $220^{\circ}C$. It is found that the lifetimes of PAG oil were shown to be 244, 177 and 89 hours at the temperature of 180, 200 and $220^{\circ}C$, respectively. Also the lifetimes of POE oil were estimated to be 1,744, 1,007 and 334 hours at the temperature of 180, 200 and $220^{\circ}C$, respectively. The lifetime correlations of PAG and POE oil are suggested in this paper.

• Advances in nano research
• /
• 제14권6호
• /
• pp.575-590
• /
• 2023

Many of small-scale devices should be designed to tolerate high temperature changes. In the present study, the states of buckling and stability of nano-scale cylindrical shell structure integrated with piezoelectric layer under various thermal and electrical external loadings are scrutinized. In this regard, a multi-layer composite shell reinforced with graphene nano-platelets (GNP) having different patterns of layer configurations is modeled. An outer layer of piezoelectric material receiving external voltage is also attached to the cylindrical shell for the aim of observing the effects of voltage on the thermal buckling condition. The cylindrical shell is mathematically modeled with first-order shear deformation theory (FSDT). Linear elasticity relationship with constant thermal expansion coefficient is used to extract the relationship between stress and strain components. Moreover, minimum virtual work, including the work of the piezoelectric layer, is engaged to derive equations of motion. The derived equations are solved using numerical method to find out the effects of temperature and external voltage on the buckling stability of the shell structure. It is revealed that the boundary condition, external voltage and geometrical parameter of the shell structure have notable effects on the temperature rise required for initiating instability in the cylindrical shell structure.

• 대한환경공학회지
• /
• 제29권6호
• /
• pp.670-677
• /
• 2007

비이온성 및 이온성 계면활성제를 이용하여 제조한 CGA(cllodial gas aphron)의 안정성을 고찰하였다. 실험에서 이용한 계면활성제는 SDS(Sigma-Aldrich, Co.), Triton X-100, Tween 80, Quillaja Saponin이다. CGA발생장치를 이용하여 단일 성분의 계면활성제 및 혼합 계면활성제에 의한 CGA를 제조하였고, 농도, 온도, 시간에 따른 CGA의 안정성을 조사하였다. 단일 성분 CGA의 경우, Saponin이 143분의 지속시간을 보여 가장 높은 안정성을 나타내었고 Triton X-100, SDS, Tween 80순으로 안정성이 높았다(상온). CGA제조시 계면활성제 용액을 $70^{\circ}C$로 가열한 경우, SDS가 가장 높은 안정성을 보였으며(116분) Saponin은 상온에 비해 안정성이 낮아졌다. (105분). 혼합 계면활성제일 경우, 두 계면활성제의 중간 수준의 안정성을 보였으며, SDS+Saponin 조합이 139분으로 가장 안정성이 컸다. 가열한 혼합 계면활성제에서는 Saponin+Triton X-100 조합이 가장 안정성이 낮아 53분에 불과했다. CGA는 초기 평균 입경이 약 140 ${\mu}m$ 였다가 융합이 일어나면 그 크기가 약 190 ${\mu}m$로 상승하고 이후 붕괴하는 양상을 띠었다. 가열하여 제조한 CGA에서는, Saponin이 포함된 경우 상온에 비해 그 크기가 감소하였으며, 타 계면활성제에서는 일반적으로 그 크기가 증가하였다. 요약하면 CGA는 가열 했을 때 보다는 상온일때, 분자간 상호작용이 크게 작용하는 혼합 계면활성제보다 단일 계면활성제일 경우, CGA 지속시간이 길어져 안정성이 높아졌다.

• 한국철도학회:학술대회논문집
• /
• 한국철도학회 2011년도 정기총회 및 추계학술대회 논문집
• /
• pp.2487-2492
• /
• 2011

At high rail temperature above the neutral temperature, high compressive axial stresses will occur in the rails. High thermal axial force and vehicle loads cause the track to shift in a lateral direction and the formation of track geometry imperfections (track irregularity). When the thermal stress level and track irregularity with vehicle load reach a critical value, the track loses stability. In many studies, the stability of CWR tracks is analyzed. However these studies are only considered in temperature load. The main objective of this investigation was to estimate a new, comprehensive, realistic, the stability of CWR tracks considering wheel load. The ballast resistance is changed by wheel load. When the wheel load is applied, rails and ties are moved upward or downward. In this case the friction between ties and ballasts is decreased or increased. In this study the change of the ballast resistance of each tie was applied to the nonlinear analysis of CWR tracks.

• 한국환경과학회지
• /
• 제3권4호
• /
• pp.305-315
• /
• 1994

The field observation was carried out to investigate the characteristics of surface inversion layer at Kimhae using the feild observed date and upper layer meteorological data during 4-5 February 1993. The results of the study can be summarized as follows : The maximum height of surface inversion layer observed at Kimhae is 193m and the height of upper level inversion layer ranges from 2nm to 300m. The surface weather elements was influenced the formation of surface inversion layer. According to the pasquill stability and time variation of temperature with height, both the surface heating from insolation and the disturbance of upper level of inversion layer was influenced the disappearance of inversion layer. And the stability of surface temperature inversion layer generally belongs to the class of F, that of upper level temperature inversion layer commonly to the class of E.

• Journal of Nutrition and Health
• /
• 제18권1호
• /
• pp.55-62
• /
• 1985

The storage stability of the developed Formula of infant foods was investigated. The results are summarized as follows : When formula A and B were stored at room temperature and refrigeration temperature, there was no remarkable changes in consistency. In frozen state, formula A showed more stability in consistency than formula B and formula A could be stored for 6 months without problems due to retrogradation of starch. The heat treatment of both A and B resulted in the increase of a-value, while L-and b-value showed no such change. But from the 4th month at room temperature, and 5th to 6th month at refrigeration appeared an increase in a -value, hence the browning reaction, while frozen samples did not show noticeable changes in surface color. The heat treatment also caused an increase in POV on both formula. The extent of changes in POV during storage varied with storage temperatures and samples.