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Shuyu Xiao Yaming Jin Xiaomei Lu Sang-Wook Cheong Jiangyu Li Yang Li Fengzhen Huang Jinsong Zhu 《国家科学评论(英文版)》2020,7(2):278
Ferroelectric domain walls differ from domains not only in their crystalline and discrete symmetry, but also in their electronic, magnetic, and mechanical properties. Although domain walls provide a degree of freedom to regulate the physical properties at the nanoscale, the relatively lower controllability prevents their practical applications in nano-devices. In this work, with the advantages of 3D domain configuration detection based on piezoresponse force microscopy, we find that the mobility of three types of domain walls (tail-to-tail, head-to-tail, head-to-head) in (001) BiFeO3 films varies with the applied electrical field. Under low voltages, head-to-tail domain walls are more mobile than other domain walls, while, under high voltages, tail-to-tail domain walls become rather active and possess relatively long average lengths. This is due to the high nucleation energy and relatively low growth energy for charged domain walls. Finally, we demonstrate the manipulation of domain walls through successive electric writings, resulting in well-aligned conduction paths as designed, paving the way for their application in advanced spintronic, memory and communication nano-devices. 相似文献
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Electroosmotic flow (EOF) with two or more fluids is commonly encountered in various microfluidics applications. However, no investigation has hitherto been conducted to investigate the hysteretic or flow direction-dependent behavior during the displacement flow of solutions with dissimilar ionic species. In this investigation, electroosmotic displacement flow involving dissimilar ionic solutions was studied experimentally through a current monitoring method and numerically through finite element simulations. The flow hysteresis can be characterized by the turning and displacement times; turning time refers to the abrupt gradient change of current-time curve while displacement time is the time for one solution to completely displace the other solution. Both experimental and simulation results illustrate that the turning and displacement times for a particular solution pair can be directional-dependent, indicating that the flow conditions in the microchannel are not the same in the two different flow directions. The mechanics of EOF hysteresis was elucidated through the theoretical model which includes the ionic mobility of each species, a major governing parameter. Two distinct mechanics have been identified as the causes for the EOF hysteresis involving dissimilar ionic solutions: the widening/sharpening effect of interfacial region between the two solutions and the difference in ion concentration distributions (and thus average zeta potentials) in different flow directions. The outcome of this investigation contributes to the fundamental understanding of flow behavior in microfluidic systems involving solution pair with dissimilar ionic species. 相似文献
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We present a new approach to enhance mixing in T-type micromixers by introducing a constriction in the microchannel under periodic electro-osmotic flow. Two sinusoidal ac electric fields with 180° phase difference and similar dc bias are applied at the two inlets. The out of phase ac electric field induces oscillation of fluid interface at the junction of the two inlet channels and the constriction. Due to the constriction introduced at the junction, fluids from these two inlets form alternative plugs at the constricted channel. These plugs of fluids radiate downstream from the constriction into the large channel and form alternate thin crescent-shaped layers of fluids. These crescent-shaped layers of fluids increase tremendously the contact surface area between the two streams of fluid and thus enhance significantly the mixing efficiency. Experimental results and mixing mechanism analysis show that amplitude and frequency of the ac electric field and the length of the constriction govern the mixing efficiency. 相似文献
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Ho Cheong Lam 《Scandinavian Journal of Educational Research》2014,58(3):337-360
The purpose of this paper is to elaborate the concepts of part and whole in Ference Marton's variation theory for dealing with how learners come to understand something of a whole as made up of its parts. Understanding of the parts and the whole is more difficult than expected; as the whole may have an influence on the parts, the nature of the parts of the whole may differ from that of the parts on their own. As such it is not enough for learners just to know the parts in isolation. They also have to recognize the whole to which the parts refer and how the whole influences the parts. To achieve this, teachers have to provide learners with the experience of variation of the parts and the whole. To demonstrate these concepts, I have applied them to the case of children's learning of Chinese characters in this paper. 相似文献
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This study examined the influence of the global reach of the product, multinational vs. domestic, on the degree of standardization of and the use of advertising values in 2008 Beijing Olympic commercials telecasted in China. This study is the first to examine systematically advertising standardization and values within one country in a mega-sporting event context. Overall, the study revealed that multinational product advertisements are more likely to be standardized, and more likely to portray Western-oriented values in their advertisements compared to domestic product advertisements. These findings indicate the importance of considering the global reach of the product in advertising to meet the expectations of the customers, especially during international sporting events such as Olympic Games. 相似文献
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Yin Cheong Cheng 《School Effectiveness & School Improvement》2013,24(1):35-61
The paper aims to report on an integration of my recent research and thinking on school effectiveness and school‐based management and to develop a school‐based management mechanism for continuous pursuit of school effectiveness and development. The matrix of school effectiveness in terms of four categories and seven different conceptions provides a framework for examining the basic issues of conceptualization, measurement and maximization of school effectiveness. Furthermore, a dynamic perspective can be used to reconceptualize school effectiveness and explore the relationship of school effectiveness to school‐based management and strategic management. The characteristics of school‐based management based on a strategic management system can reflect the emphases of different conceptions of school effectiveness and constitute a mechanism for pursuing long‐term school effectiveness, even in different categories. Based on the matrix of school process and the principle of congruence, the management concept should be shifted from the cell management to the layer management in establishing an effective school‐based management mechanism for school development. This article also reports the experience on training school administrators to establish such a school‐based management mechanism. 相似文献
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Yin Cheong Cheng 《School Effectiveness & School Improvement》2013,24(1):3-9
In the field of school effectiveness and school improvement, scholars as well as practitioners often complain about the absence of theory to guide their work. To fill this gap, Creemers (1994) developed a comprehensive model of educational effectiveness. In order to gain empirical evidence, we tested some of the main components of the model in lessons of mathematics in the 1st year of lower general education in The Netherlands. The results show that the main factors in the model – time spent, opportunity to learn, and the quality of instruction – are most important in predicting achievement. No evidence was found for the relationships between levels. 相似文献
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Yin Cheong Cheng 《School Effectiveness & School Improvement》2013,24(2):85-110
This study intends to investigate how school organizational culture is related to important organizational characteristics and observe how the profiles of strong culture‐effective schools are different from those of weak culture‐ineffective schools in terms of organizational variables (such as principal's leadership, organizational structure, and teachers’ social interactions), teachers’ job attitudes, and school effectiveness criteria. It is a cross‐sectional survey research involving 54 randomly sampled Hong Kong secondary schools and 588 teachers. The unit of analysis is the school. Organizational ideology index was found to be substantially correlated with schools’ perceived organizational effectiveness. Among the 10 measures of these organizational variables, teachers’ esprit and principal's charismatic leadership can contribute substantially to the prediction of school's strength of organizational culture. The organizational profile of perceived strong culture‐effective schools is contrastingly different from that of perceived weak culture‐ineffective schools. The findings suggest that difference in organizational culture can be reflected at least in three overt levels: 1. organizational level in terms of principal's leadership behaviors, organizational formalization and participation, and teachers’ social norms; 2. teachers’ attitudinal level in terms of organizational commitment, social job satisfaction, intrinsic job satisfaction, and influence job satisfaction; and 3. school effectiveness level in terms of perceived overall organizational effectiveness and academic achievements in public examinations. The findings reinforce the importance of organizational culture to the ongoing effort and discussion of school improvement and school effectiveness. 相似文献