A Synthetic Condition Assessment Model for Power Transformers Using the Fuzzy Evidence Fusion Method

Condition-based maintenance decision-making of transformers is essential to electric enterprises for avoiding financial losses. However, precise transformer condition assessment was tough to accomplish because of the negligence of the influence of bushing and accessories, the difficulty of fuzzy grade division, and the lack of reasonable fuzzy evidence fusion method. To solve these problems, a transformer assessing model was proposed in the paper. At first, an index assessing system, considering the main body, the bushing and the accessories components, was established on the basis of components division of transformers. Then, a Cauchy membership function was employed for fuzzy grades division. Finally, a fuzzy evidence fusion method was represented to handle the fuzzy evidences fusion processes. Case studies and the comparison analysis with other methods were performed to prove the effectiveness of this model. The research results confirm that the proposed model could be recommendation for condition based maintenance of power transformers for electric enterprises

Effects of Tunnel and Its Ventilation Modes on the Aerodynamic Drag of a Subway Train

This paper reports an in situ measurement on the effects of a tunnel and its ventilation modes on the aerodynamic drag of a subway train with eight carriages during its routine operation. The train speed (V) varied continually from 0 to 22 m/s. Two modes of tunnel ventilation were examined, i.e., recirculation and free-cooling modes. The former mode is associated with pumping cooled air into the tunnel to provide extra cooling, while the latter is not. The friction coefficient Cf of the train surface was estimated using two hotwire probes mounted on the roof of the first and last carriages, respectively. The front- and rear-stagnation pressures (Pf and Pl) were measured using two pressure taps located at the center of the forward surface of the first carriage and the backward surface of the last carriage, respectively. It has been found that the presence of a tunnel significantly increases both Cf and Pf. For example, at V = 20.5 m/s, Cf and Pf were 30.2% and 24.5% higher, respectively, in the tunnel than their counterparts in open air. The tunnel ventilation mode also has remarkable effects on Cf. The recirculation mode resulted in 23.5% higher Cf than the free-cooling mode. On the other hand, the tunnel ventilation mode does not seem to have an appreciable effect on Pf. The physics behind these observations is also discussed

Effects of Tunnel and Its Ventilation Modes on the Aerodynamic Drag of a Subway Train

This paper reports an in situ measurement on the effects of a tunnel and its ventilation modes on the aerodynamic drag of a subway train with eight carriages during its routine operation. The train speed (V) varied continually from 0 to 22 m/s. Two modes of tunnel ventilation were examined, i.e., recirculation and free-cooling modes. The former mode is associated with pumping cooled air into the tunnel to provide extra cooling, while the latter is not. The friction coefficient Cf of the train surface was estimated using two hotwire probes mounted on the roof of the first and last carriages, respectively. The front- and rear-stagnation pressures (Pf and Pl) were measured using two pressure taps located at the center of the forward surface of the first carriage and the backward surface of the last carriage, respectively. It has been found that the presence of a tunnel significantly increases both Cf and Pf. For example, at V = 20.5 m/s, Cf and Pf were 30.2% and 24.5% higher, respectively, in the tunnel than their counterparts in open air. The tunnel ventilation mode also has remarkable effects on Cf. The recirculation mode resulted in 23.5% higher Cf than the free-cooling mode. On the other hand, the tunnel ventilation mode does not seem to have an appreciable effect on Pf. The physics behind these observations is also discussed

Characterization and propagation from meteorological to groundwater drought in different aquifers with multiple timescales

Study region: Zhanjiang City District, southwest of Guangdong Province, China, was selected as the case study area owing to its relatively frequent occurrence of droughts and groundwater overexploitation. Study focus: This study presents a useful framework to characterize the propagation from meteorological drought (MD) to groundwater drought (GD) in different aquifers from the perspective of multiple timescales. Two standardized drought indices, i.e., standardized groundwater index and standardized precipitation index with different timescales (1–48 months), were used to examine the propagation time from MD to GD in different aquifers. Three clusters, i.e., natural(P)-, natural+human(P + H)-, and human(H)-induced drought, were considered for revealing the potential driving mechanism of propagation. Four characteristic mechanisms of lag, pooling, lengthening, and attenuation were used to analyze the propagation process from MD to GD, among which the lag characteristic, showing the propagation time, was discussed corresponding to varied clusters. New hydrological insights for the region: Results indicate the following: (1) The propagation time in different aquifers varied; that is, in the shallow aquifer, the average propagation time showed 1 month for the P cluster and 3 months for the P + H cluster, while the propagation time in the middle and deep aquifers were found to be longer than that in the shallow layer though much uncertainty remained for the former. (2) The influences from MD obtained the decreasing order of P > P + H>H. The propagation time of the P + H cluster was longer than that of the P cluster, suggesting the negative influence of human activities. This study can provide additional information for policymakers involved in groundwater management during a drought

High-efficiency WPT system for CC/CV charging based on double-half-bridge inverter topology with variable inductors

Efficiency remains a key challenge in wireless charging in academia and industry. In this article, a new wireless power transfer (WPT) system based on a double-half-bridge (DHB) inverter with two variable inductors (VIs) is proposed. Compared with conventional full-bridge (FB) inverters, the DHB inverter can reduce the current through the mosfets under the same output power and thus, reduce the conduction loss. Next, by adjusting the inductances of the VIs instead of using phase shift (PS) method, the output voltage or current can be controlled, while the circulating current can be eliminated and wide-range zero voltage switching operation can be achieved. Consequently, the power loss can be further reduced. Circuit analysis, VI design, as well as hardware implementation, are provided in detail. A laboratory prototype is built to verify the feasibility of the proposed method. Close agreement is obtained between simulation and experimental results. The maximum efficiency can reach 92.4%, which is 3.65% higher than traditional PS control. © 1986-2012 IEEE

Immunotoxicity assessment of CdSe/ZnS quantum dots in macrophages, lymphocytes and BALB/c mice

Background: The toxicity of CdSe/ZnS quantum dots (QDs) in the environment and biological systems has become a major concern for the nanoparticle community. However, the potential toxicity of QDs on immune cells and its corresponding immune functions remains poorly understood. In this study, we investigated the immunotoxicity of CdSe/ZnS QDs using the in vitro in macrophages and lymphocytes and in vivo in BALB/c mice. Results: Our results indicated that macrophages treated with 1.25 or 2.5 nM QDs exhibited decreased cell viability, increased levels of reactive oxygen species (ROS), elevated apoptotic events, altered phagocytic ability, and decreased release of TNF-α and IL-6 by upon subsequent stimulation with Lipopolysaccharide (LPS). In contrast, lymphocytes exposed to QDs exhibited enhanced cell viability, increased release of TNF-α and IL-6 following exposure with CpG-ODN, and decreased transformation ability treatment in response to LPS. To study the in vivo effects in mice, we showed that QDs injection did not cause significant changes to body weight, hematology, organ histology, and phagocytic function of peritoneal macrophages in QDs-treated mice. In addition, the QDs formulation accumulated in major immune organs for more than 42 days. Lymphocytes from QDs-treated mice showed reduced cell viability, changed subtype proportions, increased TNF-α and IL-6 release, and reduced transformation ability in response to LPS. Conclusions: Taken together, these results suggested that exposures to CdSe/ZnS QDs could suppress immune-defense against foreign stimuli, which in turn could result in increased susceptibility of hosts to diseases.ASTAR (Agency for Sci., Tech. and Research, S’pore)Published versio

Fullerene Derivative with Flexible Alkyl Chain for Efficient Tin-Based Perovskite Solar Cells

Fullerene derivatives are considered excellent materials for the extraction and transportation of electrons in the production of efficient tin-based perovskite solar cells (TPSCs). However, it is not clear how the molecular structure of fullerene derivatives affects the efficiency and stability of TPSCs. In this study, the effects of fullerene derivatives, (6,6)-phenyl-C61-butyric acid hexyl ester (PCBH) and (6,6)-phenyl-C61-butyric acid methyl ester (PCBM), with different functional groups, on photovoltaic performance were investigated. The flexible alkyl chain of PCBH effectively improved the film morphology and stability, the electron extraction and transport capabilities, and the interface contact of fullerene and perovskite. As a result, the PCBH-based TPSC yielded a higher efficiency, of 9.21%, than the PCBM-based devices (7.54%). More importantly, the PCBH-based films exhibited higher stability and effectively suppressed the oxidation of Sn2+ by inhibiting oxygen permeation. Therefore, the PCBH-based devices exhibited significantly enhanced stability. This result indicates that optimizing the functional group of fullerene derivatives is crucial for improving the efficiency and stability of TPSCs

MOESM1 of Immunotoxicity assessment of CdSe/ZnS quantum dots in macrophages, lymphocytes and BALB/c mice

Additional file 1. Results from flow cytometry analysis of QDs uptake, ICP-MS analysis of Se element in major organs, the phagocytic assay of peritoneal macrophages, and MTT assay of macrophages treated with different types of QDs are presented