Search

Your search keyword '"Chang, Guofeng"' showing total 114 results
Start Over Author "Chang, Guofeng"
114 results on '"Chang, Guofeng"'

22. Online Monitoring of Fuel Cell Electrochemical Impedance Spectrum with Multi-stages Multi-sine Signals Based on DC–DC Converter

Author

Liu, Zhaoming, Wang, Xueyuan, Chang, Guofeng, Yuan, Hao, Tang, Wei, Wei, Xuezhe, and Dai, Haifeng

Abstract

Advanced sensors based on electrochemical impedance spectrum (EIS) are essential for fuel cell system state estimation, fault diagnosis, and health management. However, traditional EIS methods are unsuitable for real-time state management due to high costs, large sizes, and long acquisition times, limiting their online industrial application. To enhance onboard EIS application, this study proposes a novel multistage and multisine injection method to improve wideband frequency sweeping, balancing EIS quality, and measurement time using a four-phase floating-interleaving parallel dc–dc converter prototype with EIS injection functions. In addition, a fuel cell coupled with a four-phase floating-interleaving parallel dc–dc equivalent circuit model is established for comprehensive performance analysis in impedance calculation with different excitation methods. Experimental validation showed an impedance magnitude error within 3.2% from 1 kHz to 0.1 Hz, and the implementation reduces EIS measurement time from 900 s to approximately 150 s. Furthermore, a case study on fuel cell EIS sensitivity under dynamic conditions indicates that the proposed prototype can capture dynamic EIS variations using local multifrequency points.

Published
2024
Full Text
View/download PDF

35. Preparation and properties of graphite/polypropylene composite material reinforced by chopped carbon fibers for proton‐exchange membrane fuel cell bipolar plates.

Author

Wei, Huili, Chang, Guofeng, Shi, Rongqun, Xu, Sichuan, and Liu, Jinling

Subjects
PROTON exchange membrane fuel cells, SOLID state proton conductors, COMPOSITE materials, CARBON fibers, PROTON conductivity, BIPOLAR cells, FUEL cells, GRAPHITE
Abstract

In this work, chopped carbon fibers (CCFs) with different lengths were added to graphite/polypropylene (PP) composite materials to achieve high conductivity and flexural strength performances, which are required for use in proton exchange membrane fuel cells. The effects of CCF length (2–4 mm), CCF content (0–5 wt.%), graphite type‐natural flake graphite (NFG) and synthetic graphite (SG), and graphite particle size (18–106 µm) on the graphite/PP/CCFs composites are examined. The conductivities of the composites decrease significantly with increasing CCF length above 3 wt.%. CCFs improve the composite's strength, with a maximum strength of 45.8 MPa being achieved with 5 wt.% of 4 mm long CCFs. Composite with NFG exhibits superior conductivity to the one with SG but lacks flexural strength. The NFG particle size significantly affects the conductivity of the composite at high graphite contents, with a particle diameter of 75 µm resulting in maximum conductivity. An optimal composition with 38 µm/82 wt.% NFG and 2 mm/3 wt.% CCF, electrical conductivity, and flexural strength of 189.4 S/cm and 30.2 MPa, respectively, were achieved. Also, this composite exhibited interfacial contact resistance 2.52mΩ·cm2$2.52\;{\rm{m}}\Omega \cdot {\rm{c}}{{\rm{m}}^{\rm{2}}}$ and contact angles of 111°, which showed favorable interfacial conductivity and hydrophobicity performances. [ABSTRACT FROM AUTHOR]

Published
2023
Full Text
View/download PDF

45. Using Bayesian Networks to Measure Web Service QoS

Author

Chang Guofeng

Subjects
Measure (data warehouse), business.industry, Computer science, Quality of service, Key (cryptography), Bayesian network, Mobile QoS, Web service, computer.software_genre, business, WS-Policy, computer, Computer network
Abstract

Quality of Service (QoS) has been widely used to support Web Service selection and composition. Thus, QoS is very important for users to select the most suitable Web services. In this paper, we proposed a method to measure QoS of Web services. The key of the approach is to use Bayesian Network to measure each QoS value of Web services. The experimental results show that our proposed method can measure QoS of Web services effectively.

Published
2013
Full Text
View/download PDF

46. On How Stop the Loopholes in Windows 2003

Author

Zhao Xiaojie and Chang Guofeng

Subjects
Security bug, Cloud computing security, Security service, Computer science, Security through obscurity, Covert channel, Computer security model, Computer security, computer.software_genre, computer, Security testing, Security information and event management
Abstract

Though widely-known for its security and stability, window 2003 has some loopholes due to its default configuration. For the sake of security, it is necessary to change the default configuation so as to stop the loopholes and ensure the security of the system and information.

Published
2012
Full Text
View/download PDF

47. A Web Service Discovery Approach for QoS-Aware Service Composition

Author

Chang Guofeng

Subjects
medicine.medical_specialty, Database, Computer science, business.industry, Service design, Service discovery, Service level requirement, computer.software_genre, World Wide Web, Service catalog, medicine, Data as a service, Web service, WS-Policy, business, Web modeling, computer
Abstract

One key technology in web service composition systems is how to find a set of suitable web service candidates with regard to a user’s requirement. In this paper, we proposed a web service discovery approach. The approach adopts skyline computing to find the most suitable service for users with low cost. Experimental results show that our proposed approach is very effective for QoS-aware service composition system.

Published
2012
Full Text
View/download PDF

48. A reputation model of web services

Author

Chang Guofeng

Subjects
Service (business), Computer science, business.industry, media_common.quotation_subject, Internet privacy, computer.software_genre, Pearson product-moment correlation coefficient, World Wide Web, symbols.namesake, Trustworthiness, symbols, ComputingMilieux_COMPUTERSANDSOCIETY, Web service, business, computer, Reputation, media_common
Abstract

As trust is often built up over time by accumulating experience with others, reputation model is the most preferred mechanism to evaluate the trustworthiness of a service in many e-marketplaces. This paper proposes a reputation model of web services. The model adopts Pearson Correlation Coef­ficient to built a reputation model to adjust the reputation of web service. Experimental results show that our proposed model is very effective.

Published
2011
Full Text
View/download PDF

Catalog

Books, media, physical & digital resources
See catalog results