Solution pH change in non-uniform alternating current electric fields at frequencies above the electrode charging frequency

AC Faradaic reactions have been reported as a mechanism inducing non-ideal phenomena such as flow reversal and cell deformation in electrokinetic microfluidic systems. Prior published work described experiments in parallel electrode arrays below the electrode charging frequency (f_c), the frequency for electrical double layer charging at the electrode. However, 2D spatially non-uniform AC electric fields are required for applications such as in plane AC electroosmosis, AC electrothermal pumps, and dielectrophoresis. Many microscale experimental applications utilize AC frequencies around or above f_c. In this work, a pH sensitive fluorescein sodium salt dye was used to detect [H⁺] as an indicator of Faradaic reactions in aqueous solutions within non-uniform AC electric fields. Comparison experiments with (a) parallel (2D uniform fields) electrodes and (b) organic media were employed to deduce the electrode charging mechanism at 5 kHz (1.5f_c). Time dependency analysis illustrated that Faradaic reactions exist above the theoretically predicted electrode charging frequency. Spatial analysis showed [H⁺] varied spatially due to electric field non-uniformities and local pH changed at length scales greater than 50 μm away from the electrode surface. Thus, non-uniform AC fields yielded spatially varied pH gradients as a direct consequence of ion path length differences while uniform fields did not yield pH gradients; the latter is consistent with prior published data. Frequency dependence was examined from 5 kHz to 12 kHz at 5.5 V_pp potential, and voltage dependency was explored from 3.5 to 7.5 V_pp at 5 kHz. Results suggest that Faradaic reactions can still proceed within electrochemical systems in the absence of well-established electrical double layers. This work also illustrates that in microfluidic systems, spatial medium variations must be considered as a function of experiment time, initial medium conditions, electric signal potential, frequency, and spatial position.     

Movement Toward Interdisciplinary instruction: Teacher Educators Respond

Tracy completes her laboratory assignment and gathers her books as her second period science class draws to a close. As she leaves the room and heads to her next class, Tracy stops by her locker to drop off her science text and pick up an English literature book for third period. For her, the separation between science and English is both physical and mental. In the time it takes to move from one room to another, Tracy has also moved from one ‘mind set’ to another, exit science, enter English.     

Find the Message Puzzle

Instructions:Answer the clues (information which helps you find the answer) from 1-20.Put a line through each answer-the first one is done for you.In the boxes which you have not put a line through,you will find a message.What is the message?     

Reciprocal learning: One teacher’s narrative

This paper is a personal narrative from the perspective of one teacher in Toronto who participated in the Canada–China Reciprocal Learning in Teacher Education and School Education Partnership Grant Project. I took part in a Sister School partnership between 2013 and 2017. Over the four years, I came to understand relationships in an international professional learning community. Participating in the project gave me the benefit of seeing my practice through an international lens. For my students, it offered a global citizenship experience. Although there are numerous professional development opportunities in Toronto, this partnership extends beyond a lunch and learn, or a full day professional learning. The commitment to my partners has fueled my desire to incorporate new teaching ideas and has required ongoing reflection on my own teaching practice. In this article, I will explain some of the challenges, stages of development, reciprocal learning, and implications for future international professional learning communities.     

Graduate identity and employability

This paper develops the concept of graduate identity as a way of deepening the understanding of graduate employability. It does this through presenting research in which over 100 employers in East Anglia were asked to record their perceptions of graduates in respect of their employability. The findings suggest a composite and complex graduate identity, depending on employer size and sector. There is no one fixed identity for graduates. Nevertheless, certain themes emerged that seriously put into question the traditional model of graduate employability comprising skills, competencies and attributes. What emerges is a four‐stranded concept of identity that comprises value, intellect, social engagement and performance. Thus, when assessing the potential of graduates, performance is not the only criteria that employers take into account. Moreover, the four elements of identity are by no means independent of each other but are expected to interpenetrate producing a composite identity, with different employers emphasising different facets of this identity.

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‘The constant rejections hurt’: Skills and personal attributes needed to successfully complete a thesis by publication

The thesis by publication (TBP) is an increasingly popular approach to doctoral education that sees candidates publishing their research during their candidature, and including these outputs in their final thesis submission. Responsive to the realities of modern academia, a TBP provides doctoral candidates with opportunities to engage in the scholarly publication process, and to build their research portfolio. As the TBP gains further traction in many fields and countries, there is a need to better understand the skills and attributes needed to complete a TBP successfully. This paper draws on the views of 246 recent doctoral graduates of Australian universities to identify the skills and attributes they felt supported their success. Their responses have implications for the development and refinement of institutional policies and programs that are sensitive to the needs and experiences of doctoral candidates seeking to publish during candidature and create a TBP. As editors, peer‐reviewers, and publishers see a growing influx of papers sole‐ or co‐authored by doctoral candidates in response to the trend toward TBP, they may find themselves involved in supporting students to develop the skills and attributes needed to successfully publish during candidature.     

The force-time profile of elite front crawl swimmers

In this study, we used recently developed technology to determine the force-time profile of elite swimmers, which enabled coaches to make informed decisions on technique modifications. Eight elite male swimmers with a FINA (Federation Internationale de Natation) rank of 900+ completed five passive (streamline tow) and five net force (arms and leg swimming) trials. Three 50-Hz cameras were used to video each trial and were synchronized to the kinetic data output from a force-platform, upon which a motorized towing device was mounted. Passive and net force trials were completed at the participant's maximal front crawl swimming velocity. For the constant tow velocity, the net force profile was presented as a force-time graph, and the limitation of a constant velocity assumption was acknowledged. This allowed minimum and maximum net forces and arm symmetry to be identified. At a mean velocity of 1.92+0.06 m s?1, the mean passive drag for the swimmers was 80.3+4.0 N, and the mean net force was 262.4+33.4 N. The mean location in the stroke cycle for minimum and maximum net force production was at 45% (insweep phase) and 75% (upsweep phase) of the stroke, respectively. This force-time profile also identified any stroke asymmetry.     

Reading information about a scientific phenomenon on webpages varying for reliability: an eye-movement analysis

Students search the Web frequently for many purposes, one of which is to search information for academic assignments. Given the huge amount of easily accessible online information, they are required to develop new reading skills and become more able to effectively evaluate the reliability of web sources. This study investigates the distribution of their visual attention while reading webpages using eye-tracking methodology. The aim was to examine whether information received differential attention depending on the reliability of the source and whether the individual characteristics of topic-specific prior knowledge and epistemic beliefs moderated their visual behavior during reading. Factual knowledge after reading was also examined. Forty-nine university students read four webpages providing verbal and graphical information about the universal validity of the central dogma of molecular biology, which varied for reliability. Indices of first-pass and second-pass reading or inspection were used to trace the processing of information within each page. Findings revealed that readers made an implicit source evaluation as they spent a longer time inspecting the pictures about the more and less familiar information within the most reliable source during the immediate, more automatic, processing. In addition, topic-specific epistemic beliefs moderated this processing as readers with more availing convictions about knowledge attended more the information provided in pages that required more discernment. Moreover, readers increased their factual knowledge of the topic after reading. Educational implications are outlined.