• Progress in Superconductivity
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• 제14권1호
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• pp.1-10
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• 2012

We fabricated a closed coils by using resistive-joint method and the joint resistance of the coils were estimated by field decay technique in liquid nitrogen. We used the Runge-kutta method for the numerical analysis to calculate the decay properties. The closed coil was wound by $(Bi,Pb)_2Sr_2Ca_2Cu_3O_x$/Ag tape. Both ends the tape were overlapped and soldered to each other. The current was induced in a closed coils by external magnetic flux density. Its decay characteristic was observed by means of measuring the magnetic flux density generated by induced current at the center of the closed coil with hall sensor. The joint resistance was calculated as the ratio of the inductance of the loop to the time constants. The joint resistances were evaluated as a function of critical current of loop, contact length, sweep time, and external magnetic flux density in a contact length of 7 cm. It was observed that joint resistance was dependent on contact length of a closed coil, but independent of critical current, sweep time, and external magnetic flux density. The joint resistance was measured to be higher for a standard four-probe method, compared with that for the field decay technique. This implies that noise of measurement in a standard four-probe method is larger than that of field decay technique. It was estimated that joint resistance was $8.0{\times}10^{-9}{\Omega}$ to $11.4{\times}10^{-9}{\Omega}$ for coils of contact length for 7 cm. It was found that 40Pb/60Sn solder are unsuitable for persistent mode.

• Structural Engineering and Mechanics
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• 제53권1호
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• pp.89-104
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• 2015

In current bridge management systems (BMSs), load and speed restrictions are applied on unhealthy bridges to keep the structure safe and serviceable for as long as possible. But the question is, whether applying these restrictions will always decrease the internal forces in critical components of the bridge and enhance the safety of the unhealthy bridges. To find the answer, this paper for the first time in literature, looks into the design aspects through studying the changes in demand by capacity ratios of the critical components of a bridge under the train loads. For this purpose, a structural model of a simply supported bridge, whose dynamic behaviour is similar to a group of real railway bridges, is developed. Demand by capacity ratios of the critical components of the bridge are calculated, to identify their sensitivity to increase of speed and magnitude of live load. The outcomes of this study are very significant as they show that, on the contrary to what is expected, by applying restriction on speed, the demand by capacity ratio of components may increase and make the bridge unsafe for carrying live load. Suggestions are made to solve the problem.

• Smart Structures and Systems
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• 제26권5호
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• pp.641-656
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• 2020

The finite element solutions of thermal buckling load values of the graded sandwich curved shell structure are reported in this research using a higher-order kinematic model including the shear deformation effect. The numerical buckling temperature has been computed using an in-house specialized code (MATLAB environment) prepared in the framework of the current mathematical formulation. In addition, the mathematical model includes the excess structural distortion under the influence of elevated environment via Green-Lagrange nonlinear strain. The corresponding eigenvalue equation has been solved to predict the critical buckling temperature of the graded sandwich structure. The numerical stability and the accuracy of the current solution have been confirmed by comparing with the available published results. Thereafter, the model is extended to bring out the influences of structural parameters i.e. the curvature ratio, core-face thickness ratio, support conditions, power-law indices and sandwich types on the thermal buckling behavior of graded sandwich curved shell panels.

• 한국해양환경ㆍ에너지학회지
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• 제11권2호
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• pp.92-97
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• 2008

일반적으로 해수가 강으로 침입하거나 담수가 해양으로 유입을 하면 두 유체간의 밀도차에 의한 밀도류의 성질을 가진다. 하지만, 염분과 온도가 동시에 밀도의 차를 결정하는 경우, 특히 이 중 하나가 중력과 불안정한 수직 분포를 갖게되면 이중확산이 혼합을 결정하는 중요한 요인이 된다. 본 연구에서는 고온, 고염의 수괴가 저온, 저염의 수괴로 진입할 때 기계적 혼합과 이중확산에 의한 대류가 혼합에 미치는 상대적 영향을 비교 연구하였다. 실험실에서 차갑고 염도가 없는 주 흐름에 온도가 높고 염분이 높은 밀도류를 조심스럽게 방류시켜 정상상태의 염수침입 형태를 유지하였다. 수평방향으로 따라 밀도율(Turner 1979)이 15정도 되면 온도와 염분의 유출입량비율이 가파르게 변화하였고, 전체적으로 방출구 부분에서 이중확산의 영향이 강하게 나타나게 되며 이 경우에는 총 방출량도 함께 증가하였다. 아울러 밀도율이 낮은 경우 밀도율이 높은 경우에 비해서 약 $6{\times}10$배의 높은 혼합율을 보였다.

• 한국정보처리학회논문지
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• 제6권10호
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• pp.2790-2796
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• 1999

In video-on-demand systems, the I.O bandwidth of video servers is the critical resource which contributes to increase in latency. Several approaches: bridging, piggybacking are used to reduce the I/O demand on the video server through sharing. Batching delays the requests for the different videos for a batching window so that more requests for the same video arriving during the current batching window may be served using the same stream. In this paper, we propose an adaptive reservation-based batching policy which dynamically reserves video server capacity for popoular videos according to video server loads. The performance of the proposed policy is evaluated through a simulation, and is compared with simple batching and static reservation-based batching policies. As the result, we know that the adaptive reservation-based batching policy more improves service ratio and average waiting time than simple batching and simple reservation-based batching policy more improves service ratio and average waiting time than simple batching and simple reservation-based batching polices.

• 한국전기전자재료학회논문지
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• 제13권9호
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• pp.801-804
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• 2000

High-temperature superconductor of Bi-2212 system was fabricated by CFP(Centrifugal Forming Process). To make a uniform specimen slurry was prepared in the ratio of 7:3(powder : binder) and ball milled for 24 hours. Milled slurry was charged into a rotating mold with 450 rpm and dried at room temperature. Then the specimen was performed binder burn-out at 35$0^{\circ}C$ and heated for partial melting to 86$0^{\circ}C$. XRD analysis of most specimens were shown 2212 phase and observed a local plate shped microstructure with a well aligned c-axis direction from SEM images. Measured T$_{c}$(Critical temperature) was about 64 K.K.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2000년도 하계학술대회 논문집
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• pp.189-192
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• 2000

High-temperature superconductor of Bi-2212 system was fabricated by CFP(centrifugal forming process). To make a uniform specimen slurry was prepared in the ratio of 7:3(powder:binder) and ball milled for 24 hours. Milled slurry was charged into a rotating mold with 450 rpm and dried at room temperature. Then the specimen was performed binder burn-out at 35$0^{\circ}C$ and heated for partial melting to 86$0^{\circ}C$. XRD analysis of most specimens were shown 2212 phase and observed a local plate shaped microstructure with a well aligned c-axis direction from SEM images. T$_{c}$(Critical temperature) of Bi-2212 was 64K.K.

• 한국초전도ㆍ저온공학회논문지
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• 제24권4호
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• pp.11-15
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• 2022

We conducted numerical calculations to obtain the critical current as a function of the magnetic flux through the topologically trivial and non-trivial superconducting quantum interference devices (SQUIDs), with varying the capacitive and inductive couplings of Josephson junctions (JJs). Our calculation results indicate that a nontrivial SQUID is almost indistinguishable from trivial SQUID, considering the effective capacitance coupling. When the SQUID contains 2π- and 4π-periodic supercurrents, the periodicity of the current-flux relation can be distinguished from the purely trivial or nontrivial SQUID cases, and its difference is sensitive to the relative ratio between the topologically trivial and nontrivial supercurrents. We believe that our calculation results would provide a practical guide to quantitatively measure the portion of the topologically nontrivial supercurrents in experiments.

• 한국지반공학회지:지반
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• 제9권4호
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• pp.37-44
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• 1993

실내 모형실험을 통하여 모형말뚝 한계깊이의 확인과 기존 선단지지력의 이론식들을 실내모형실험의 선단지지력 실측치와 비교하여 그 차이를 분석하였으며, 말뚝의 직경차이에서 유발되는 지지력의 차이를 비교하고자 실내 모형실험을 실시하였다. 모형지반을 균질한 모래로 조성한 경우와 국내의 현장조건에 가깝게 모형지반을 조성한 모래/풍화토층 경우로 나누어 모형실험을 실시하여 치수효과를 비교하였다. 실험결과, 모형말뚝의 선단지지력은 모래지반의 경우 응력수 준이 높을 때 한계관입깊이 효과를 나타냈으며, 모래1풍화토층의 경우 한계관입깊이를 확연히 확인할 수는 없었으나 그 경향을 보임을 알 수 있었다. 정적지지력 공식으로부터 얻어진 계산치 들은 모형실험에 의한 실측치부다 훨씬 큰 값으로 과대평가 하는 경향이 있었다. 직경크기에 따른 지지력의 차이인 치수효과는 모래지반의 경우 확인할 수 있었으나. 모래/풍화토층 지반의 경 추에는 오히려 큰 직경의 말뚝이 작은 직경의 말뚝보다 크게 나타나는 경향을 얻었다.

• 전기학회논문지P
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• 제58권1호
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• pp.79-84
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• 2009

In order to increase the capacity of the superconducting fault current limiter(SFCL), the current and voltage grades of the SFCL must be increased. As a method for the increase of the current and voltage grades of the SFCL, we compared the various characteristics between the flux-lock type SFCL "With three superconducting units connected in series and the transformer type SFCL using the transformer with three secondary circuits. One of three superconducting units had not quenched in the flux-lock type SFCL. Therefore, the unbalanced power burden happened because of the voltage difference generated by unbalanced quenching between the superconducting units. In the meantime, the three superconducting units were all quenched in the transformer type SFCL using the transformer, and the voltage difference generated between the superconducting units was decreased. Therefore, the difference of critical characteristics was complemented by distribution of fault current in accordance with the turn's ratio between primary and secondary windings. The unbalanced power burden of the superconducting units was reduced due to flux-share between the superconducting units in the transformer. In conclusion, the capacity increment of the SFCL using a transformer was easier due to equal distribution of voltages generated by simultaneous quench of the superconducting units. We think that the characteristics is improved more because of the decrease of saturation in the iron core if the secondary winding is increased in the SFCL using the transformer.