780 research outputs found
Effect of processing condition and composition on the microhardness of Cu-(2.5-10)vol.%AlâOâ nanocomposite powder particles produced by high energy mechanical milling
Nanostructured Cu-(2.5-10vol.%)AlâOâ nanocomposites were produced using high energy mechanical milling. For the as-milled Cu- AlâOâ composite powder particles having AlâOâ volume fractions of 2.5% and 5%, the increase in average microhardness is significant with the increase of milling time from 12 hours to 24 hours. With the increase of the content of AlâOâ nanoparticles the microhardness increases and in the range of 255HV-270HV. The milled nanocomposite powders were heat treated at 150, 300, 400 and 500°C for 1 hour, respectively, to determine the thermal stability of the powder particles as a function of annealing temperature. The average microhardness increased/decreased for the Cu- AlâOâ composites after annealing at 150°C due to the dislocation density, while increasing the annealing temperature to 300°C and 400°C the average microhardness almost remained mostly unchanged. Further increasing the annealing temperature to 500°C causes significant decrease in average microhardness due to reduction in dislocation density and coarsening of Cu grains of the Cu- AlâOâ composite powders produced after 24 hours of milling. This paper is to report and discuss the changes of the microhardness of the material, caused by the compositions and processing conditions, used to fabricate the Cu-(2.5-10)vol.% AlâOâ nanocomposite powders
Proper orthogonal decomposition and recurrence map for the identification of spatialâtemporal patterns in a low-Re wake downstream of two cylinders
Flow decomposition methods provide systematic ways to extract the flow modes, which can be regarded as the spatial distribution of a coherent structure. They have been successfully used in the study of wake, boundary layer, and mixing. However, real flow structures also possess complex temporal patterns that can hardly be captured using the spatial modes obtained in the decomposition. In order to analyze the temporal variation of coherent structures in a complex flow field, this paper studies the recurrence in phase space to identify the pattern and classify the evolution of the flow modes. The recurrence pattern depends on the time delay and initial condition. In some cases, the flow system will revisit a previous state regardless of the initial state, and in other cases, the systemâs recurrence will depend on the initial state. These patterns are determined by the arrangement and interactions of coherent structures in the flow. The temporal order of the repetition pattern reflects the possible ways of flow evolution
Proper Orthogonal Decomposition and Recurrence Map for the Identification of SpatialâTemporal Patterns in a Low-Re Wake Downstream of Two Cylinders
Flow decomposition methods provide systematic ways to extract the flow modes, which can be regarded as the spatial distribution of a coherent structure. They have been successfully used in the study of wake, boundary layer, and mixing. However, real flow structures also possess complex temporal patterns that can hardly be captured using the spatial modes obtained in the decomposition. In order to analyze the temporal variation of coherent structures in a complex flow field, this paper studies the recurrence in phase space to identify the pattern and classify the evolution of the flow modes. The recurrence pattern depends on the time delay and initial condition. In some cases, the flow system will revisit a previous state regardless of the initial state, and in other cases, the systemâs recurrence will depend on the initial state. These patterns are determined by the arrangement and interactions of coherent structures in the flow. The temporal order of the repetition pattern reflects the possible ways of flow evolution
Effect of Sport Media on Social Behaviour: The Attitude and Perception Change of Chinese College Students toward the International Media Reporting the Beijing Olympics
This study assessed the attitude and perceptions of college students in China before and immediately after the 2008 Beijing Olympics toward the international media's reporting of the Games and China. A total of 657 students from seven campuses eight months before the Olympics and 1,000 students from ten campuses immediately after the Olympics were randomly surveyed. The data analysis (independent t-Test) depicts that the students' attitudes and perceptions toward the international media had positively changed from the pre- to the post-Olympic surveys. One-way multivariate analysis of variance (MANOVA) and Scheffeâs post hoc test results revealed that the survey respondentsâ political preferences were the constant factors that influenced their attitude and perception change toward the international media. This study illustrates a media effect on changing the survey participantsâ and their represented populationâs attitude and perceptions toward the international mediaâs coverage of sport mega-events that is supported by the theories of mega-events and modernity, media communication and social behaviour, and social impact
Phase-Shift Cyclic-Delay Diversity for MIMO OFDM Systems
Phase-shift cyclic-delay diversity (PS CDD) scheme and space-frequency-block-code (SFBC) PS CDD are developed for multiple-input-multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems. The proposed PS CDD scheme preserves the diversity advantage of traditional CDD in uncorrelated multiantenna channels, and furthermore removes frequency-selective nulling problem of the traditional CDD in correlated multiantenna channels
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