1,722,501 research outputs found
Lee Yun Hyun
No full text학위논문(석사)--아주대학교 일반대학원 :공학계열,2019. 2화석연료를 대체하기 위한 신재생에너지에 관한 연구가 활발히 진행되고 있는 가운데 염도차 발전에 대한 관심이 커지고 있다. 그 중 역전기투석식 발전은 막의 성능이 중요한데 현재까지 고체상태의 나노포어 막에 대한 연구보다 폴리머 멤브레인에 대한 연구가 많이 진행되었다. 고체상태의 나노포어 중 하나인 알루미나 나노포어는 높은 포어 밀도와 제작이 용이하다는 장점이 있다. 따라서 본 논문의 목적은 다양한 포어의 직경을 가질 수 있는 비대칭형 AAO막을 이용하여 역전기투석식 발전시스템의 발전 성능 향상을 실험적으로 연구하는 것이다.
역전기투석식 발전시스템에서 막의 역할은 이온을 선택적으로 통과시키는 것이다. 이러한 현상을 수치적으로 나타낸 것이 이온선택성인데, 포어의 직경이 작을수록 이온선택성이 커지게 된다. 하지만 저항도 함께 커지기 때문에 발전 성능이 향상됨을 보장할 수 없다. 그래서 포어의 직경이 큰 층(support layer)위에 포어의 직경이 작은 층(active layer)을 얇게 증착시켜 이온선택성은 증가시키고 저항의 증가량은 최소로 할 수 있을 것이라 기대하고 비대칭형 AAO막을 제작하여 발전 성능을 연구하였다. 실험에 사용된 비대칭형 AAO는 InRedox사에서 제작했고 다양한 농도와 Active layer의 두께, Active layer의 포어 직경에 대해 실험하였다.
기존 일정한 포어의 직경을 가지고 있는 AAO막 대신 비대칭형 AAO막을 이용함으로써 역전기투석식 발전시스템의 발전 성능을 향상시킬 수 있을 것으로 기대된다. 또한 역전기투석식 발전 성능을 농도, 두께, 직경 별로 평가하여 최대 발전 밀도의 경향을 제시하고자 한다. 이와 더불어 비대칭형 AAO의 농도에 따른 이온선택성, 저항의 상관식을 제시하고 해당 상관식을 통해 OCV(Open Circuit Voltage), 발전밀도를 계산하여 실험값과 비교하였다.제 1 장 서론 1
제 1 절 연구 배경 1
제 2 절 역전기투석식 발전 3
제 3 절 연구 동향 5
제 4 절 연구 목적 및 범위 7
제 2 장 실험 장치 및 방법 9
제 1 절 염화나트륨(NaCl) 수용액 제조 9
제 2 절 은/염화은(Ag/AgCl) 전극 제작 9
제 3 절 비대칭형 AAO (Asymmetric AAO) 11
제 4 절 실험 장치 13
1. 아크릴 reservoir 13
2. Stirrers 15
3. Source meter 16
4. 오븐 18
5. Hot plate stirrer 19
6. 증류수 제조기 20
제 5 절 실험 방법 21
제 6 절 실험 조건 24
제 3 장 실험 결과 및 토의 26
제 1 절 실험 결과 26
1. 대칭형 AAO 26
2. 비대칭형 AAO (Pore diameter : 2nm, Activer layer thickness : 1μm) 36
3. 비대칭형 AAO (Pore diameter : 2nm, Activer layer thickness : 2μm) 49
4. 비대칭형 AAO (Pore diameter : 5nm, Activer layer thickness : 1μm) 60
5. 비대칭형 AAO (Pore diameter : 10nm, Activer layer thickness : 1μm) 71
제 2 절 실험 결과 비교 82
1. 대칭형 AAO와 비대칭형 AAO 결과 비교 82
2. 비대칭형 AAO - Thickness of active layer 결과 비교 89
3. 비대칭형 AAO - Pore diameter of active layer 결과 비교 91
제 4 장 결론 93
참고 문헌 95MasterResearch on renewable energy to replace fossil fuels is actively being carried out, and interest in salinity gradient power generation is increasing. Among them, reverse electrodialysis power generation is important for the performance of membranes. Up to now, research on polymer membranes has been carried out more than research on nanopore membranes. One of the nanopores, alumina nanopores, has the advantages of high pore density and easy fabrication. Therefore, the purpose of this paper is to experimentally investigate the improvement of power generation performance of reverse electrodialysis power generation system using asymmetric AAO membrane which can have various pore diameters.
The role of the membrane in a reverse electrodialysis power generation system is to selectively pass ions. This phenomenon is numerically represented by transference number. The smaller pore diameter, the greater transference number.
However, since the resistance also increases, the power generation performance can’t be guaranteed to be improved. Therefore, it is expected that the active layer which is smaller in pore size is thinly deposited on the support layer with a large diameter of the pore, thereby increasing the transference number and minimizing the increase of the resistance. Asymmetric AAO membrane was fabricated and power generation performance was studied. The asymmetric AAO used in this experiment was manufactured by InRedox, and various concentrations, active layer thicknesses, and pore diameters of active layers were tested.
It is expected that the generation performance of the reverse electrodialysis power generation system can be improved by using the asymmetric AAO membrane instead of the symmetric AAO membrane. Also, the tendency of maximum power generation density is suggested by evaluating reverse electrodialysis power generation performance by concentration, thickness, and diameter. In addition, correlation of transference number and resistance according to concentration is presented, and OCV (Open Circuit Voltage) and power density are calculated and compared with the experimental values
Lee, Yun Tso; Hongying, Wu. Chile y China: Cuarenta años de política exterior. Una trayectoria de continuidad y perseverancia. Santiago, Ril Editores, 2011 (244 p.). ISBN 978-956-284-824-4
No full textLee, Yun Tso; Hongying, Wu Chile y China: Cuarenta años de política exterior. Una trayectoria de continuidad y perseverancia. Santiago, Ril Editores, 2011 (244 p.). ISBN 978-956-284-824-
Lee, Yun Tso; Hongying, Wu. Chile y China: Cuarenta años de política exterior. Una trayectoria de continuidad y perseverancia. Santiago, Ril Editores, 2011 (244 p.). ISBN 978-956-284-824-4
Full text linkLee, Yun Tso; Hongying, Wu Chile y China: Cuarenta años de política exterior. Una trayectoria de continuidad y perseverancia. Santiago, Ril Editores, 2011 (244 p.). ISBN 978-956-284-824-
반사형 손목 용적맥파 측정기의 움직임에 의한 신호 왜곡 제거
No full text학위논문(석사) - 한국과학기술원 : 기계공학전공, 2009.2, [ vi, 43 p. ]One of the most important issues in the wearable healthcare sensors for continuous monitoring in daily life is motion artifact reduction. In this thesis, reflective-type photoplethysmographic (PPG) Sensor with motion artifact reduction algorithm on the wrist for measuring heart rates. The designed device is proposed which able to detect signals reliably and stably against motion artifact for monitoring on the wrist. Radial artery is the most optimal places for the integrated PPG sensor, because when light is emitting to the skin over radial artery, light pathway is the shorter than other area and intensity of reflected light is higher.
Active noise cancellation algorithm was applied to compensate the distorted signals by motions with Least Mean Square (LMS) adaptive filter ( order) algorithms, using accelerometer data. Since the wrist is generally more invulnerable to motion artifacts than finger, measurements were performed radial artery in the wrist because of strong intensity of reflected light. The Active noise cancellation algorithm validity testing is done through computing the cross-correlations and zero-crossing peak detection between the distorted signals and reference signal from ECG.
The experiments were performed on 5 humans, repeated 5 times with two different protocols of walking and running. Correlation coefficients are applied to evaluate the device and coefficients are very high over 0.8. As a result, designed device is effective enough to reduce the motion artifacts. The developed reflective-type sensor is suitable for integration of ubiquitous healthcare system, which provides a continuous health monitoring and diagnosis in daily life.한국과학기술원 : 기계공학전공
Task decomposition and newsvendor decision making
No full textWe conduct three behavioral laboratory experiments to compare newsvendor order decisions placed directly to order decisions submitted in a decomposed way by soliciting point forecasts, uncertainty estimates, and service-level decisions. Decomposing order decisions in such a way often follows from organizational structure and can lead to performance improvements compared with ordering directly. However, we also demonstrate that if the critical ratio is below 50%, or if the underlying demand uncertainty is too high, task decomposition may not be preferred to direct ordering. Under such conditions, decision makers are prone to set service levels too high or to suffer from excessive random judgment error, which reduces the efficacy of task decomposition. We further demonstrate that if accompanied by decision support in the form of suggested quantities, task decomposition becomes the better-performing approach to newsvendor decision making more generally. Decision support and task decomposition therefore appear as complementary methods to improve decision performance in the newsvendor context.
Empirical prediction intervals revisited
No full textEmpirical prediction intervals are constructed based on the distribution of previous out-of-sample forecast errors. Given historical data, a sample of such forecast errors is generated by successively applying a chosen point forecasting model to a sequence of fixed windows of past observations and recording the associated deviations of the model predictions from the actual observations out-of-sample. The suitable quantiles of the distribution of these forecast errors are then used along with the point forecast made by the selected model to construct an empirical prediction interval. This paper re-examines the properties of the empirical prediction interval. Specifically, we provide conditions for its asymptotic validity, evaluate its small sample performance and discuss its limitations. (C) 2013 International Institute of Forecasters. Published by Elsevier B.V. All rights reserved
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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