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Droplet-based microfluidics has gained extensive research interest as it overcomes several challenges confronted by conventional single-phase microfluidics. The mixing performance inside droplets/slugs is critical in many applications such as advanced material syntheses and in situ kinetic measurements. In order to understand the effects of operating conditions on the mixing performance inside liquid slugs generated by a microfluidic T-junction, we have adopted the volume of fluid method coupled with the species transport model to study and quantify the mixing efficiencies inside slugs. Our simulation results demonstrate that an efficient mixing process is achieved by the intimate collaboration of the twirling effect and the recirculating flow. Only if the reagents are distributed transversely by the twirling effect, the recirculating flow can bring in convection mechanism thus facilitating mixing. By comparing the mixing performance inside slugs at various operating conditions, we find that slug size plays the key role in influencing the mixing performance as it determines the amount of fluid to be distributed by the twirling effect. For the cases where short slugs are generated, the mixing process is governed by the fast convection mechanism because the twirling effect can distribute the fluid to the flow path of the recirculating flow effectively. For cases with long slugs, the mixing process is dominated by the slow diffusion mechanism since the twirling effect is insufficient to distribute the large amount of fluid. In addition, our results show that increasing the operating velocity has limited effects on improving the mixing performance. This study provides the insight of the mixing process and may benefit the design and operations of droplet-based microfluidics. 相似文献
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Analyzing examinees’ responses using cognitive diagnostic models (CDMs) has the advantage of providing diagnostic information. To ensure the validity of the results from these models, differential item functioning (DIF) in CDMs needs to be investigated. In this article, the Wald test is proposed to examine DIF in the context of CDMs. This study explored the effectiveness of the Wald test in detecting both uniform and nonuniform DIF in the DINA model through a simulation study. Results of this study suggest that for relatively discriminating items, the Wald test had Type I error rates close to the nominal level. Moreover, its viability was underscored by the medium to high power rates for most investigated DIF types when DIF size was large. Furthermore, the performance of the Wald test in detecting uniform DIF was compared to that of the traditional Mantel‐Haenszel (MH) and SIBTEST procedures. The results of the comparison study showed that the Wald test was comparable to or outperformed the MH and SIBTEST procedures. Finally, the strengths and limitations of the proposed method and suggestions for future studies are discussed. 相似文献
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Ratna Nandakumar 《Journal of Educational Measurement》1991,28(2):99-117
This article addresses testing the hypothesis of one versus more than one dominant (essential) dimension in the possible presence of minor dimensions. The method used is Stout's statistical test of essential unidimensionality, which is based on the theory of essential unidimensionality. Differences between the traditional definition of dimensionality provided by item response theory, which counts all dimensions present, and essential dimensionality, which counts only dominant dimensions, are discussed. As Monte Carlo studies demonstrate, Stout's test of essential unidimensionality tends to indicate essential unidimensionality in the presence of one dominant dimension and one or more minor dimensions that have a relatively small influence on item scores. As the influence of the minor dimensions increases, Stout's test is more likely to reject the hypothesis of essential unidimensionality. To assist in interpreting these studies, a rough index of the deviation from essential unidimensionality is proposed. 相似文献
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The characteristic X-rays coming out from an unknown sample due to the irradiation of gamma rays or X-ray photons or due to
the bombardment of high velocity protons are used for elemental analysis in a sample. We describe here two techniques viz.,
Energy Dispersive X-Ray Fluorescence (EDXRF) and Proton Induced X-ray Emission (PIXE) which have the capability of nondestructive
and multi-elemental analysis of the sample.
N K Sharat Singh is a research scholar at the Department of Physics, Manipur University. His research interest lies in areas
of EDXRF and PIXE.
H Nandakumar Sarma is a professor of physics at Manipur University. His current research focuses on EDXRF, PIXE, ferroelectric,
ferrite, Mossbauer effect and solar energy. He occasionally writes popular science articles both in English and Manipuri.
An erratum to this article is available at . 相似文献
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Ghosh Ratna 《International Review of Education/Internationale Zeitschrift für Erziehungswissenschaft/Revue internationale l'éducation》2004,50(5-6):543-566
Education is a provincial responsibility in Canada, but there is a sharing of expenditure and strong support of public education, health and other welfare programs between the provinces and the federal government. Although the federal policy of multiculturalism has been aimed at making Canada a just society, the implementation of this policy in education in English-speaking Canada has been far from satisfactory, and there is great variation among the provinces in educational programs. In Quebec, the federal policy of multiculturalism is ideologically opposed to the vision of French-Québécois nationalism. While the federal policy of intercultural education has made some attempts to integrate immigrant populations, the focus remains on linguistic programs. In facing the dramatic changes driven by internationalization and a globalized economy, Canadians must respond – so the conclusion of the present study – to the urgent need to redefine the meaning of multiculturalism with radical educational programs. 相似文献
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Eulsun Seung Soonhye Park Ratna Narayan 《Journal of Science Education and Technology》2011,20(6):703-714
This study examined elementary preservice teachers’ beliefs about the role/image of a science teacher and science teaching
and how these beliefs change during an elementary science methods course; this examination was conducted through an analysis
of their metaphor writing. Data included personal metaphors and rationale papers for supporting them collected from 106 participants
at the start and end of the semester. Data were analyzed using the constant comparative method and also quantified for statistical
analysis. Results indicate that most participants came to the course with traditional views and developed more constructivist
views during the course. However, they tended to keep their traditional views and added new constructivist perspectives into
their original belief systems. This study suggests that metaphor writing can be used as both a reflection tool for preservice
teachers to clarify and refine their beliefs about science teaching and learning and a diagnostic assessment tool for teacher
educators to understand their students for tailoring a methods course accordingly. 相似文献
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Vibration and sound damping in polymers 总被引：2，自引：0，他引：2
Excessive vibrations or loud sounds cause deafness or reduced efficiency of people, wastage of energy and fatigue failure of machines/structures. Hence, unwanted vibrations need to be dampened. This article describes the transmission of vibrations/sound through different materials such as metals and polymers. Viscoelasticity and glass transition are two important factors which influence the vibration damping of polymers. Among polymers, rubbers exhibit greater damping capability compared to plastics. Rubbers reduce vibration and sound whereas metals radiate sound. The damping property of rubbers is utilized in products like vibration damper, shock absorber, bridge bearing, seismic absorber, etc. 相似文献
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