Preface to Special Topic: Dielectrophoresis

This Special Topic section is on dielectrophoresis, a growing area of widespread interest and relevance to the microfluidics and nanofluidics community.There was a time when the arrival of a telegram from the local post office would foreshadow a step-function change in one’s equilibrium. An internet service provider can now deliver the same effect, as illustrated by an unexpected e-mail from Leslie Yeo inquiring if I would “be interested in guest editing a special issue of Biomicrofluidics on recent advances in dielectrophoresis (DEP).” Flattery directed towards vanity can produce interesting results—which I hope this special issue of Biomicrofluidics demonstrates. The rationale for this special issue is the belief of the journal’s Editors (Dr. Chia Chang and Dr. Leslie Yeo) that dielectrophoresis is a growing area of widespread interest and relevance to the microfluidics and nanofluidics community. Papers, both fundamental and applied, were solicited from the leaders working across this broad interdisciplinary area of research. I was delighted by the positive responses of those whose invited contributions appear in this special issue—efforts certainly not motivated by vanity but through enthusiasm for the subject. Some of those invited to contribute were unable to do so because of other demands on their time. Ongoing advances being made in DEP, especially in its various applications, will surely merit another special issue in the future and hopefully include contributions from those unable to do so now.Two of the papers in this special issue address fundamental aspects of dielectrophoresis (DEP), namely the influences on DEP from electrical double-layers and from particle-particle interactions. Consideration of electrical double layers associated with charged particle surfaces is particularly important for nanoparticles because their effective polarizabilities, associated with field-induced dynamics of the counterions and co-ions in the double layer, can dominate over the intrinsic polarizability of the particle itself. This can influence, for example, to what extent the observation of changes in the DEP crossover frequency (marking the transition between positive and negative DEP) can be relied upon in new immunoassays based on the DEP behavior of functionalized nanoparticles. By considering the electrodynamics of double layers, Basuray et al.¹ propose a theory to predict how the DEP crossover frequency will vary as a function of particle size and the ionic strength of the suspending electrolyte. In their paper, Sancho et al.² derive a theoretical model to describe how particle-particle interactions (e.g., “pearl-chaining”) influence the DEP crossover frequency value. This model also describes well the changes in electrorotation and a newly observed precession effect as particles approach each other under the influence of a rotating field.DEP at the nanoscale is also addressed in contributions from the groups of Ralph Hölzel, Junya Suehiro, and Karan Kaler. Thus, Henning et al.³ describe a new method, based on the measurement of capacitance changes between planar microelectrodes, for the automatic acquisition of the DEP properties of nanoparticles without the need for labeling protocols or visual observations. Suehiro⁴ describes how DEP can be employed as a bottom-up approach for fabricating nanomaterial-based devices such as a carbon nanotube gas sensor and a ZnO nanowire photosensor. Kaler et al.⁵ describe how the DEP manipulation of miniscule amounts of polar aqueous samples, a method known as liquid-DEP, can be used for on-chip bioassays, such as nucleic acid analysis, and through parallel sample processing offer the potential for conducting automated multiplexed assays. The use of DEP to selectively trap and separate cells has been investigated over many years, and contributions from the groups of Hywel Morgan, Ana Valero, Masau Washizu, and Gerard Markx describe the latest advances and applications. Thomas et al.⁶ describe a new automated DEP cell trap design for the isolation, concentration, separation, and recovery of human osteoblast-like cells from a heterogeneous population. Recovery of small populations of human osteoblast-like cells with a purity of 100% is demonstrated. A cell-sorting device, based on the opposition of DEP forces that discriminates between cell types according to such properties as their membrane permittivity and cytoplasm conductivity, is described by Valeroet al.⁷ The versatility of the device is demonstrated by synchronizing a yeast cell culture at a particular phase of the cell cycle. Gel et al.⁸ describe a DEP-assisted cell trapping method for fusing pairs of cells in an array of micro-orifices. This method produces not only a high yield of viable cell fusants, but also allows for subsequent study of postfusion cell development. Zhu et al.⁹ describe a DEP-based microfluidic separation system in which dead and active cells can be collected from a given cell suspension, whilst at the same time eluting dormant cells. In the second paper from Gerard Markx’s group, Zhu et al.¹⁰ demonstrate that the rate-limiting resuscitation of a colony of dormant bacteria is determined by the diffusion of a resuscitation-promoting factor into the colony interior. This study involved the artificial engineering of different sizes and shapes of bacterial aggregates using DEP forces. Finally, in my own contribution,¹¹ I have attempted to summarize the growing output of DEP publications in terms of their contributions to the theory, technology, and applications of DEP.     

基于一般P-C矩阵的R族科学发展节律指标——科学发展节律指标研究(1)

一论文集的一般P-C矩阵由论文数据和引文数据两部分组成.基于一般P-C矩阵并引入"等时性"概念,我们创建了关键变量Ck.Ck表示的是不同年份发表的论文在各自发表后第k年的引文数量的平均值.借助Ck可以构建R族科学发展节律指标,定义为引文观察值和引文期望值的比值,用于反映科学发展的节律.R族指标包括4项指标①指标R--被引年视角加三角形引文窗口;②指标R′--被引年视角加平行四边形引文窗口;③指标r--引用年视角加三角形引文窗口;④指标r′--引用年视角加平行四边形引文窗口.以Journal of Documentation为例,本文具体说明了R族序列的计算和R族指标的应用.     

Mathematical properties of Q-measures

Q-measures are network indicators that gauge a node's brokerage role between different groups in the network. Previous studies have focused on their definition for different network types and their practical application. Little attention has, however, been paid to their theoretical and mathematical characterization. In this article we contribute to a better understanding of Q-measures by studying some of their mathematical properties in the context of unweighted, undirected networks. An external Q-measure complementing the previously defined local and global Q-measure is introduced. We prove a number of relations between the values of the global, the local and the external Q-measure and betweenness centrality, and show how the global Q-measure can be rewritten as a convex decomposition of the local and external Q-measures. Furthermore, we formally characterize when Q-measures obtain their maximal value. It turns out that this is only possible in a limited number of very specific circumstances.     

Is procedure acquisition as unstable as it seems?

Are students’ mathematical procedures as unstable as they seem? Students often produce different errors in response to the same kind of problems on different testing occasions. This finding is puzzling. Past research has shown that students induce overly general procedures from worked-out examples during learning, which lead to a host of predictable errors on new problems. Do students create rule-based errors only to then switch between them at random? In this paper, we show that seemingly diverse errors on two different testing episodes may result from the same underlying stable procedure and are part of the same error category. These findings suggest that students’ errors are more stable on a category vs. on an individual level. The current study consists of teaching students addition in a new number system, called NewRoman, and analyzing students’ solution strategies in detail. Implications for teaching are discussed.     

A teacher education program in elementary science that connects content,methods, practicum,and student teaching

Conclusion To educate teachers who have adequate content knowledge, possess the necessary skills to implement effective teaching strategies, and are confident and have positive attitudes toward science and the teaching of science, alternative teaching models are necessary. The University of Wyoming model provides such an alternative. Based on observations and interviews of students and the mentor teachers, it is apparent that it has created a very positive response in prospective teachers who have participated in it. The Wyoming model provided an effective process to train future elementary teachers. Even though it focused on science, the basis is general enough that it could be successfully extended to other disciplines with only minor modifications; however, all of the major components of the Wyoming model are vital to its success. Content courses designed specifically for prospective teachers have been successful in giving the students the content knowledge and providing opportunities for effective modeling. The seminars provide strong mechanisms to connect content to methodology and make the content relevant to teaching and to children. Because of their modeling, peer coaching, and sharing their time and students, the mentor teachers are essential partners in helping the university educate future teachers. Finally, the cooperation of all partners—district administrators, teachers, science content and science education university faculty, and students—is necessary to provide early and continuous experiences to prospective teachers. This material is based upon work supported in part by a grant from the National Science Foundation (Grant No. TTE-8851105). Any opinions, findings, conclusions, and/or recommendations expressed in this article are those of the authors and do not necessarily reflect those of the NSF.     

Formula-based research incentive plans at colleges and universities

Financial problems at colleges and universities have led many institutions to initiate extra efforts to obtain extramural funds. One such effort has been the establishment of formula-based research incentive plans. These plans generally utilize the recovery of indirect costs as the basis for allocating additional incentive funds to various areas as an encouragement to obtain additional extramural funds. Data from surveys conducted by the University of Missouri-Kansas City and Ohio University were combined with National Science Foundation reports to provide information about this relatively recent phenomena. The increasing popularity of these plans was shown in that a majority of institutions had such plans in effect during FY 1979. Analyses of the effectiveness of these plans showed no statistically significant differences between institutions with incentive plans and those without such plans, although mean federal research expenditures were approximately 20% greater at those institutions without these incentive plans. The evidence presented indicates that the receipt of federal research funds is not associated with the use of a formula-based research incentive plan.     

The Bleaching Syndrome: The Role of Educational Intervention

Per the Bleaching Syndrome, people of color, including African, Asian, and Latino Americans, are both victims and perpetrators of color discrimination. The Bleaching Syndrome encompasses perceptual, psychological, and behavioral sectors that affect students' schooling experiences. Education professionals, including teachers, administrators, and counselors, must address these factors to promote mental and emotional health among learners. In this article, I discuss how the Bleaching Syndrome and color bias affects dark-complexioned African American children in contemporary US schools.     

A Study of Academic and Nonacademic Predictors and Criteria of Success among Scholarship Recipients

This is an investigation of the relationships and differences among selected personality, demographic, and intellective variables in a sample of 267 Morehead Scholars, at the University of North Carolina at Chapel Hill, from the classes of 1965 through 1970 to determine the feasibility and practicality of their use as predictors and criteria of academic and nonacademic achievements. Analysis of variance was used to determine the differences among the various groups. Stepwise regression analysis was used to determine the association among the variables and to select the most efficient predictors of academic and nonacademic criteria.

There was a significant relationship between high school nonacademic achievements and (a) Opinion, Attitude, and Interest Survey (OAIS) scores, (b) high school rank in class and (c) Scholastic Aptitude Test (SAT) scores. High school nonacademic achievements and selected OAIS scales, when combined with SAT scores and high school rank in class, increase the efficiency of predicting subsequent college grade point average (GPA). The addition of high school nonacademic achievements to SAT scores increased the efficiency of predicting freshman and senior cumulative GPA for all groups. The OAIS scales, freshman GPA, and high school nonacademic achievements can be used to predict college nonacademic achievements.     

Event-Konzepte

In view of processes of individualization and pluralization, the requirements for living in modern societies result in significantly increased complexity of social constructions of reality. Especially for individualized juvenile people new forms of communities are a constitutive feature of social lifestyle progression and rearrangement. Within events a specific type of these juvenile communalities emerges. Based on two different cases, a music festival and an improvisational theater performance, this paper emphasizes a crucial similarity of events: the use of (physical) staging as a social mechanism for integration and distinction. The process of ‘eventization’ (i.e., spectacularization) provides a framework for action, in which emotional as well as mental affiliations constitute.     

Attitudes Towards and Limitations to ICT Use in Assisted and Independent Living Communities: Findings from a Specially-Designed Technological Intervention

Much literature has been devoted to theoretical explanations of the learning processes of older adults and to the methods of teaching best utilized in older populations. However, there has been less focus on the education of older adults who reside in assisted and independent living communities (AICs), especially with regards to information and communication technology (ICT) education. The purpose of this study is to determine whether participants' attitudes and views towards computers and the Internet are affected as a result of participating in an eight-week training program designed to enhance computer and Internet use among older adults in such communities. Specifically, we examine if ICT education specially designed for AIC residents results in more positive attitudes towards ICTs and a perceived decrease in factors that may limit or prevent computer and Internet use. We discuss the implications of these results for enhancing the quality of life for older adults in AICs and make recommendations for those seeking to decrease digital inequality among older adults in these communities through their own ICT classes.