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Capillary wave phenomena are challenging to study, especially for microfluidics where the wavelengths are short, the frequencies are high, and the frequency distribution is rarely confined to a narrow range, let alone a single frequency. Those that have been studying Faraday capillary waves generated by vertical oscillation have chosen to work at larger scales and at low frequencies as a solution to this problem, trading simplicity in measurement for issues with gravity, boundary conditions, and the fidelity of the subharmonic capillary wave motion. Laser Doppler vibrometry using a Mach–Zehnder interferometer is an attractive alternative: The interface’s motion can be characterized at frequencies up to 40 MHz and displacements of as little as a few tens of picometers. 相似文献
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Jennifer Friend Loyce Caruthers 《Educational Studies A Journal of the American Educational Studies Association》2013,49(4):366-388
Through listening to the voices of students, educators and community members can begin to reconstruct the culture of urban schools that are often full of stories about student deficits, genetic explanations about achievement, and cultural mismatch theories that may be traced to historical and sociological ideologies. The purpose of this heuristic qualitative investigation was to explore the ways in which student voice can contribute to reculturing high schools in urban settings. Data sources for this study included videotaped interviews and observations in two Midwestern urban high schools to explore the stories of 28 culturally and linguistically diverse students in grades 10 through 12. Findings suggested that the teens in these urban high schools want caring teachers who listen attentively, provide engaging learning opportunities, and who demonstrate high expectations for achievement. They did not want teachers who, in essence, perpetuate hegemonic discourses via pedagogical practices, and school environments that resemble prisons. At the same time, students wanted more structure to “avoid chaos” and asked teachers to give attention to the paradigm of the personal within the school curriculum. We extend the meaning of the study to include student voice as a critical stance for reconstructing the cultural context of urban schools, which entails listening to students to identify complex and sensitive topics for dialogue and inquiry. 相似文献
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Alyssa Friend Wise Jennifer Speer Farshid Marbouti Ying-Ting Hsiao 《Instructional Science》2013,41(2):323-343
While a great deal of research has studied the messages students contribute to electronic discussion forums, productive participation in online learning conversations requires more than just making posts. One important pre-condition for productive interactivity and knowledge construction is engagement with the posts contributed by others. In this study, these actions (how learners interact with the existing discussion; which posts they attend to, when, and how) are conceptualized as “online listening behaviors” and are studied in the context of a large undergraduate business course taught in a blended format. Clickstream data was collected for 96 participants from 3 week-long online discussions to solve organizational behavior challenges in groups of 10–13. Listening behaviors accounted for almost three-quarters of the time learners spent in the discussions, and cluster analysis identified three distinct patterns of behavior: (1) Superficial Listeners, Intermittent Talkers; (2) Concentrated Listeners, Integrated Talkers; and (3) Broad Listeners, Reflective Talkers. The clusters differed in the depth, breadth, temporal contiguity, and reflectivity of their listening as well as in their patterns of speaking. An illustrative case study of how the listening behaviors were enacted by one student from each cluster over time was used to deepen the characterization and interpretation of each cluster. The results indicate that online listening is a complex phenomenon and a substantial component of students’ participation in online discussions. Findings are compared to the previous work on student learning approaches and implications for practice and future research are discussed. 相似文献
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Ultrafast microfluidics using surface acoustic waves 总被引：2，自引：0，他引：2
We demonstrate that surface acoustic waves (SAWs), nanometer amplitude Rayleigh waves driven at megahertz order frequencies propagating on the surface of a piezoelectric substrate, offer a powerful method for driving a host of extremely fast microfluidic actuation and micro∕bioparticle manipulation schemes. We show that sessile drops can be translated rapidly on planar substrates or fluid can be pumped through microchannels at 1–10 cm∕s velocities, which are typically one to two orders quicker than that afforded by current microfluidic technologies. Through symmetry-breaking, azimuthal recirculation can be induced within the drop to drive strong inertial microcentrifugation for micromixing and particle concentration or separation. Similar micromixing strategies can be induced in the same microchannel in which fluid is pumped with the SAW by merely changing the SAW frequency to rapidly switch the uniform through-flow into a chaotic oscillatory flow by exploiting superpositioning of the irradiated sound waves from the sidewalls of the microchannel. If the flow is sufficiently quiescent, the nodes of the transverse standing wave that arises across the microchannel also allow for particle aggregation, and hence, sorting on nodal lines. In addition, the SAW also facilitates other microfluidic capabilities. For example, capillary waves excited at the free surface of a sessile drop by the SAW underneath it can be exploited for micro∕nanoparticle collection and sorting at nodal points or lines at low powers. At higher powers, the large accelerations off the substrate surface as the SAW propagates across drives rapid destabilization of the drop free surface giving rise to inertial liquid jets that persist over 1–2 cm in length or atomization of the entire drop to produce 1–10 μm monodispersed aerosol droplets, which can be exploited for ink-jet printing, mass spectrometry interfacing, or pulmonary drug delivery. The atomization of polymer∕protein solutions can also be used for the rapid synthesis of 150–200 nm polymer∕protein particles or biodegradable polymeric shells in which proteins, peptides, and other therapeutic molecules are encapsulated within for controlled release drug delivery. The atomization of thin films behind a translating drop containing polymer solutions also gives rise to long-range spatial ordering of regular polymer spots whose size and spacing are dependent on the SAW frequency, thus offering a simple and powerful method for polymer patterning without requiring surface treatment or physical∕chemical templating. 相似文献
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We present a straightforward and rapid surface acoustic wave (SAW) atomization-based technique for encapsulating proteins into 10 μm order particles composed of a biodegradable polymeric excipient, using bovine serum albumin (BSA) as an exemplar. Scans obtained from confocal microscopy provide qualitative proof of encapsulation and show the fluorescent conjugated protein to be distributed in a relatively uniform manner within the polymer shell. An ELISA assay of the collected particles demonstrates that the BSA survives the atomization, particle formation, and collection process with a yield of approximately 55%. The SAW atomization universally gave particles with a textured morphology, and increasing the frequency and polymer concentration generally gave smaller particles (to 3 μm average) with reduced porosity. 相似文献
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Frederick J Friend 《图书情报工作》2006,50(1):24-27
New opportunities presented by technological developments are being realised but more can be achieved in opening access to scientific reports and data. Funding agencies and universities are beginning to realise the benefits from an open access model for the dissemination of research results. European funding agencies and universities are following two strategies towards open access, the deposit of research reports in repositories and the conversion of journals to an open access business model. Various public statements have been made in support of open access, and several organizations-such as JISC in the UK-are undertaking work to assist all stakeholders in scholarly communication in introducing beneficial changes. 相似文献
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Christina Cortez-Jugo Aisha Qi Anushi Rajapaksa James R. Friend Leslie Y. Yeo 《Biomicrofluidics》2015,9(5)
Nebulizers have considerable advantages over conventional inhalers for pulmonary drug administration, particularly because they do not require coordinated breath actuation to generate and deliver the aerosols. Nevertheless, besides being less amenable to miniaturization and hence portability, some nebulizers are prone to denature macromolecular drugs due to the large forces generated during aerosolization. Here, we demonstrate a novel portable acoustomicrofluidic device capable of nebulizing epidermal growth factor receptor (EGFR) monoclonal antibodies into a fine aerosol mist with a mass median aerodynamic diameter of approximately 1.1 μm, optimal for deep lung deposition via inhalation. The nebulized monoclonal antibodies were tested for their stability, immunoactivity, and pharmacological properties, which confirmed that nebulization did not cause significant degradation of the antibody. In particular, flow cytometry demonstrated that the antigen binding capability of the antibody is retained and able to reduce phosphorylation in cells overexpressing the EGFR, indicating that the aerosols generated by the device were loaded with stable and active monoclonal antibodies. The delivery of antibodies via inhalation, particularly for the treatment of lung cancer, is thus expected to enhance the efficacy of this protein therapeutic by increasing the local concentration where they are needed. 相似文献
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An effective mechanism for rapid and efficient microfluidic particle trapping and concentration is proposed without requiring any mechanically moving parts. When a voltage beyond the threshold atmospheric ionization value is applied on a sharp electrode tip mounted at an angle above a microfluidic liquid chamber, the bulk electrohydrodynamic air thrust that is generated results in interfacial shear and, hence, primary azimuthal liquid surface recirculation. This discharge driven vortex mechanism, in turn, causes a secondary bulk meridional liquid recirculation, which produces an inward radial force near the bottom of the chamber. Particles suspended in the liquid are then rapidly convected by the bulk recirculation toward the bottom, where the inward radial force causes them to spiral in a helical swirl-like fashion toward a stagnation point. In particular, we show that these flows, similar to Batchelor flows occurring in a cylindrical liquid column between a stationary and rotating disk, can be used for the separation of red blood cells from blood plasma in a miniaturized device. 相似文献
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