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

Ran An  Katherine Massa  David O. Wipf  Adrienne R. Minerick 《Biomicrofluidics》2014,8(6)

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.  相似文献   

Cases,hypermedia and computer networks: three curricular innovations for teacher education     

Catherine A. Lacey  Katherine K. Merseth 《课程研究杂志》2013,45(6):543-551

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Counting Astronomers     

Hufbauer  Karl 《Minerva》2000,38(4):453-467

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Strategic ambiguity in the role development process     

Katherine Miller  Lori Joseph  Julie Apker 《Journal of Applied Communication Research》2013,41(3):193-214

Today's turbulent business and social environment often compels organizations to adopt internal programs that will help them cope with complexity. One organizational sector in which this is particularly true is the health care industry, as managed care programs and competitive forces have changed the way hospitals and clinics operate. This study looks at a specific organizational program designed to cope with these industry changes and considers the impact of the program on the nurses involved. Drawing on theory and research on role development and strategic ambiguity, this case analysis looks at a hospital system in which the nursing role of “care coordinator”; was defined in a strategically ambiguous way. After analyzing interviews with 19 care coordinators, conclusions are drawn regarding affective reactions to strategic role ambiguity, behavioral adaptation to strategic role ambiguity, and the importance of conceptualizing role ambiguity as a systemic process.  相似文献   

Philanthropy and the Maintenance of Democratic Elites     

Karl  Barry D. 《Minerva》1997,35(3):207-220

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运动对糖尿病大鼠ASP影响的研究   总被引：1，自引：0，他引：1  

王涌涛  景志强  张钧 《体育科学》2006,26(8):59-62

研究运动对链脲佐菌素所致糖尿病大鼠ASP的影响。选用雄性SD大鼠，随机分为4组（每组10只），即：正常对照组，正常运动组，糖尿病模型组，糖尿病模型＋运动组。运动组进行10周的游泳训练。结果表明：1）糖尿病模型组与正常对照组大鼠相比，血浆ASP浓度、血糖、TG、和LDL明显升高，血清FFA有升高趋势，血清胰岛素和ISI明显降低；2）糖尿病模型＋运动组较其非运动组血浆ASP浓度、血糖、TG、TC、FFA和LDL明显降低，血清胰岛素和HDL含量明显升高。提示：糖尿病机体血浆ASP浓度升高，伴随着其活性下降，使得FFA和富舍TG的脂蛋白消除障碍，长期中等负荷运动可以降低血浆中ASP浓度，增加其活性，进而降低FFA和TG水平，升高HDL，改善糖尿病机体的脂质代谢，预防其慢性并发症的发生。  相似文献   

How ethics was specialized away     

Karl D. Stephan 《Academic Questions》2003,16(4):31-40

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Christian Education,White Supremacy,and Humility in Formational Agendas     

Katherine Turpin 《Religious education (Chicago, Ill.)》2017,112(4):407-417

Christian education served as a tool of White supremacy that played a central role in the devastation of millions of human lives throughout the colonial era of Western expansion. An adequate account of how Christian education paired with colonial imperatives helps to identify where the legacy of White supremacy and imperial domination lives on in contemporary practices of Christian faith formation and religious education. While any educational venture requires authority and is an act of power, humility is an essential partnering virtue for Christian educators who do not wish to replicate this history of domination.  相似文献   

Designing a Bridging Discourse: Re-Mediation of a Mathematical Learning Disability     

Katherine E. Lewis 《学习科学杂志》2017,26(2):320-365

Students with disabilities present a unique instructional design challenge. These students often have qualitatively different ways of processing information, meaning that standard instructional approaches may not be effective. In this study I present a case study of a student with a mathematical learning disability for whom standard instruction on fractions had been ineffective. With regard to theory, I draw on Lev Vygotsky’s framing of disability and then use Anna Sfard’s conceptualization of mathematics as a discourse to design a fraction re-mediation that provided a bridge from the student’s discourse to the canonical mathematics discourse. This bridging discourse was used in 5 videotaped re-mediation sessions with the case study student. A fine-grained analysis of the re-mediation sessions traced the ways in which the student’s discourse shifted over time, which enabled her to solve problems she had previously been unable to solve. This study provides a proof of concept for reconceptualizing remediation and illustrates the potential utility of a bridging discourse to help students who have a history of failure gain access to the canonical mathematics discourse and content.  相似文献   

Leveraging critical literacies for social change: questioning the culture of compliance at an ‘F’ school     

Katherine Crawford-Garrett  Michelle Perez  Amanda Y. Short 《Teaching Education》2017,28(3):227-243

This article traces the experiences of two veteran elementary school teachers in the urban Southwest, who are positioned by district and state policy ‘texts’ as insubordinate and failing, and who employ critical literacy practices to reconstruct and redesign these texts as they seek to create more equitable and humane conditions in schools. Stemming from a larger phenomenological study, this article explores how teachers in a ‘failing’ elementary school in the Southwestern US understand and negotiate district, state, and federal policies and examines how these policies shape and inform their identities as professionals. This research has important implications concerning the potential of critical literacy as a mode of resistance, the promise inherent in school/university partnerships for promoting change, and the ways in which the practice of deconstructing/reconstructing dehumanizing texts can foster a re-professionalization of teaching.  相似文献