From Manchester to Brighton: Conversations on higher education     

Boris Ford 《Higher Education Quarterly》1966,20(2):209-225

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Flow manipulation and cell immobilization for biochemical applications using thermally responsive fluids     

Anil Haraksingh Thilsted  Vahid Bazargan  Nina Piggott  Vivien Measday  Boris Stoeber 《Biomicrofluidics》2012,6(4)

A flow redirection and single cell immobilization method in a microfluidic chip is presented. Microheaters generated localized heating and induced poly(N-isopropylacrylamide) phase transition, creating a hydrogel that blocked a channel or immobilized a single cell. The heaters were activated in sets to redirect flow and exchange the fluid in which an immobilized cell was immersed. A yeast cell was immobilized in hydrogel and a 4′,6-diamidino-2-phenylindole (DAPI) fluorescent stain was introduced using flow redirection. DAPI diffused through the hydrogel and fluorescently labelled the yeast DNA, demonstrating in situ single cell biochemistry by means of immobilization and fluid exchange.The ability to control microfluidic flow is central to nearly all lab-on-a-chip processes. Recent developments in microfluidics either include microchannel based flow control in which microvalves are used to control the passage of fluid,¹ or are based on discrete droplet translocation in which electric fields or thermal gradients are used to determine the droplet path.^{2, 3} Reconfigurable microfluidic systems have certain advantages, including the ability to adapt downstream fluid processes such as sorting to upstream conditions and events. This is especially relevant for work with individual biomolecules and high throughput cell sorting.⁴ Additionally, reconfigurable microfluidic systems allow for rerouting flows around defective areas for high device yield or lifetime and for increasing the device versatility as a single chip design can have a variety of applications.Microvalves often form the basis of flow control systems and use magnetic, electric, piezoelectric, and pneumatic actuation methods.⁵ Many of these designs require complicated fabrication steps and can have large complex structures that limit the scalability or feasability of complex microfluidic systems. Recent work has shown how phase transition of stimuli-responsive hydrogels can be used to actuate a simple valve design.⁶ Beebe et al. demonstrated pH actuated hydrogel valves.⁷ Phase transition of thermosensitive poly(N-isopropylacrylamide) (PNIPAAm) using a heater element was demonstrated by Richter et al.⁸ Phase transition was also achieved by using light actuation by Chen et al.⁹ Electric heating has shown a microflow response time of less than 33 ms.¹¹ Previous work¹⁰ showed the use of microheaters to induce a significant shift in the viscosity of thermosensitive hydrogel to block microchannel flow and deflect a membrane, stopping flow in another microchannel. Additionally, Yu et al.¹² demonstrated thermally actuated valves based on porous polymer monoliths with PNIPAAm. Krishnan and Erickson¹³ showed how reconfigurable optically actuated hydrogel formation can be used to dynamically create highly viscous areas and thus redirect flow with a response time of  ～ 2?s. This process can be used to embed individual biomolecules in hydrogel and suppress diffusion as also demonstrated by others.^{15, 16} Fiddes et al.¹⁴ demonstrated the use of hydrogels to transport immobilized biomolecules in a digital microfluidic system. While the design of Krishnan and Erickson is highly flexible, it requires the use of an optical system and absorption layer to generate a geometric pattern to redirect flow.This paper describes the use of an array of gold microheaters positioned in a single layer polydimethylsiloxane (PDMS) microfluidic network to dynamically control microchannel flow of PNIPAAm solution. Heat generation and thus PNIPAAm phase transition were localized as the microheaters were actuated using pulse width modulation (PWM) of an applied electric potential. Additionally, hydrogel was used to embed and immobilise individual cells, exchange the fluid parts of the microfluidic system in order to expose the cells to particular reagents to carry out an in situ biochemical process. The PDMS microchannel network and the microheater array are shown in Figure ​Figure11.Open in a separate windowFigure 1A sketch of the electrical circuit and a microscope image of the gold microheaters and the PDMS microchannels. The power to the heaters was modulated with a PWM input through a H-bridge. For clarity, the electrical circuit for only the two heaters with gelled PNIPAAm is shown (H1 and V2). There are four heaters (V1-V4) in the “vertical channels” and three heaters (H1-H3) in the “horizontal” channel.The microchannels were fabricated using a patterned mould on a silicon wafer to define PDMS microchannels, as described by DeBusschere et al.¹⁷ and based on previous work.¹⁰ A 25 × 75 mm glass microscope slide served as the remaining wall of the microchannel system as well as the substrate for the microheater array. The gold layer had a thickness of 200 nm and was deposited and patterned using E-beam evaporation and photoresist lift-off.²¹ The gold was patterned to function as connecting electrical conductors as well as the microheaters.It was crucial that the microheater array was aligned with an accuracy of  ～ 20μm with the PDMS microchannel network for good heat localization. The PDMS and glass lid were treated with plasma to activate the surface and alignment was carried out by mounting the microscope slide onto the condenser lens of an inverted microscope (TE-2000 Nikon Instruments). While imaging with a 4× objective, the x, y motorized stage aligned the microchannels to the heaters and the condenser lens was lowered for the glass substrate to contact the PDMS and seal the microchannels.Local phase transition of 10% w/w PNIPAAm solution in the microchannels was achieved by applying a 7 V potential through a H-bridge that received a PWM input at 500 Hz which was modulated using a USB controller (Arduino Mega 2650) and a matlab (Mathworks) GUI. The duty cycle of the PWM input was calibrated for each microheater to account for differences in heater resistances (25?Ω to 52?Ω) due to varying lengths of on-chip connections and slight fabrication inconsistencies, as well as for different flow conditions during device operation. Additionally, thermal cross-talk between heaters required decreasing the PWM input significantly when multiple heaters were activated simultaneously. This allowed confining the areas of cross-linked PNIPAAm to the microheaters, allowing the fluid in other areas to flow freely.By activating the heaters in sets, it was possible to redirect the flow and exchange the fluid in the central area. Figure ​Figure22 demonstrates how the flow direction in the central microchannel area was changed from a stable horizontal flow to a stable vertical flow with a 3 s response time, using only PNIPAAm phase transition. Constant pressures were applied to the inlets to the horizontal channel and to the vertical channels. Activating heaters V1-4 (Figure ​(Figure2,2, left) resulted in flow in the horizontal channel only. Likewise, activating heaters H1 and H2 allowed for flow in the vertical channel only. In this sequence, the fluid in the central microchannel area from one inlet was exchanged with fluid from the other inlet. Additionally, by activating heater H3, a particle could be immobilised during the exchange of fluid as shown in Figure ​Figure33 (top).Open in a separate windowFigure 2Switching between fluid from the horizontal and the vertical channel using hydrogel activation and flow redirection with a response time of 3 s. A pressure of 25 mbar was applied to the inlet of the horizontal channel and a pressure of 20 mbar to the vertical channel. The flow field was determined using particle image velocimetry, in which the displacement of fluorescent seed particles was determined from image pairs generated by laser pulse exposure. Processing was carried out with davis software (LaVision).Open in a separate windowFigure 3A series of microscope images near heater H3 showing: (1a)-(1c) A single yeast cell captured by local PNIPAAm phase transition and immobilized for 5 min before being released. (2a) A single yeast cell was identified for capture by embedding in hydrogel. (2b) The cell as well as the hydrogel displayed fluorescence while embedded due to the introduction of DAPI in the surrounding region. (2c) The diffusion of DAPI towards the cell as the heating power of H3 is reduced after 15 min, showing a DAPI stained yeast cell immobilized.Particle immobilisation in hydrogel and fluid exchange in the central area of the microfluidic network were used to carry out an in situ biochemical process in which a yeast cell injected through one inlet was stained in situ with a 4′,6-diamidino-2-phenylindole (DAPI) solution (Invitrogen), which attached to the DNA of the yeast cell.¹⁸ A solution of yeast cells with a concentration of 5 × 10⁷cells/ml suspended in a 10% w/w PNIPAAm solution was injected through the horizontal channel. A solution of 2μg/l DAPI in a 10% w/w PNIPAAm solution was injected through the vertical channel. A single yeast cell was identified and captured near the central heater, and by deactivating the heaters in the vertical channel, DAPI solution was introduced in the microchannels around the hydrogel. After immobilising the cell for 15 min, the heater was deactivated, releasing the cell in the DAPI solution. This process is shown in Figure ​Figure33 (bottom). The sequence of the heater activation and deactivation in order to immobilize the cell and exchange the fluid is outlined in the supplementary material.²¹Eriksen et al.¹⁵ demonstrated the diffusion of protease K in the porous hydrogel matrix,¹⁹ and it was therefore expected that DAPI fluorescent stain (molecular weight of 350 kDa, Ref. ²⁰) would also diffuse. DAPI diffusion is shown in Figure 3(2b) in which the yeast cell shows fluorescence while embedded in the hydrogel. The yeast cell was released by deactivating the central heater and activating all the others to suppress unwanted flow in the microchannel. As a result, the single cell was fully immersed in the DAPI solution. Immobilization of a single cell allows for selection of a cell that exhibits a certain trait and introduction of a new fluid while maintaining the cell position in the field of view of the microscope such that a biochemical response can be imaged continuously.In summary, a microfluidic chip capable of local heating was used to induce phase transition of PNIPAAm to hydrogel, blocking microchannel flow, and thereby allowing for reconfigurable flow. Additionally, the hydrogel was used to embed and immobilise a single yeast cell. DAPI fluorescent stain was introduced using flow redirection, and it stained the immobilized cell, showing diffusion into the hydrogel. The versatile design of this microfluidic chip permits flow redirection, and is suitable to carry out in situ biochemical reactions on individual cells, demonstrating the potential of this technology for forming large-scale reconfigurable microfluidic networks for biochemical applications.  相似文献   

School-based Sex Education in Russia: The current reality and prospects     

Boris Yu. Shapiro 《Sex education》2013,13(1):87-96

The last decade has been characterised in Russia by a sharp increase in the number of cases of sexually transmitted diseases (STDs), especially in teenagers, as well as by a high level of unwanted pregnancies, sexual violence and other phenomena relevant to the issues of reproductive and sexual health and behaviour. Though the overwhelming majority of Russian teenagers, their parents and teachers favour the introduction of sex education in schools, there is no national programme of school-based sex education in Russia at the moment. Currently, some conservative forces and the Russian Orthodox Church are actively opposing school sex education and family planning. Opponents of sex education have mounted an aggressive campaign against the implementation of sex education in schools. The attempt of the Russian Ministry of Education, in cooperation with the United Nations Population Fund (UNFPA) and UNESCO, to implement in-school sex education has practically failed. At present, direct instruction of schoolchildren in these matters is in fact forbidden. So in the near future, it is only really feasible to promote direct educational work with youngsters on a local basis and in cooperation with some foreign experts within the framework of separate, fairly small-scale projects.  相似文献   

PSYCHOLOGY: ITS PRACTICE AND TEACHING IN A JEWISH COLLEGE     

Dr. Boris M. Levinson 《Journal of Jewish Education》2013,79(3):46-53

Abstract

Back to the Sources: Reading the Classic Jewish Texts. Edited by Barry W. Holtz. Summit Books, New York, 1984. pp. 448. $19.95.

The Chronicle of the Lodz Ghetto 1941-1944. Edited by Lucjan Dobroszycki. Yale University Press, New Haven, 1984. pp. 551. $35.00.

From Time Immemorial: The Origins of the Arab-Jewish Conflict Over Palestine by Joan Peters. Harper &; Row, New York 1984. pp. 601. $24.95.

The World Guide for the Jewish Traveler by Warren Freedman. E. P. Dutton, New York, 1984. pp. 360. $8.95 (paper).

Jews, Turks and Infidels by Morton Borden. University of North Carolina Press, Chapel Hill, 1984. pp. 163. $17.95.

The Land Question in Palestine, 1917-1939 by Kenneth W. Stein. University of North Carolina Press, Chapel Hill, 1984. pp. 314. $29.00.

The Jewish Family: Authority and Tradition in Modern Perspective by Norman Linzer. Human Sciences Press, New York, 1984. pp. 217. $I6.95 (paper).

Diaspora: Exile and the Jewish Condition Editied by Etan Levin. Jason Aronson, New York, 1983. pp. 337.

The Jerusalem Cathedra, Volume III Edited by Lee I. Levine. Wayne State University Press, Detroit, 1984. pp. 361. $25.00.

The Roots of Anti-Semitism by Heiko A. Oberman. Translated by James I. Porter, Fortress Press, Philadelphia, 1984. pp. 163.

Jewish Ethics and Halakhah for our Time: Sources and Commentary by Basil F. Herring. Ktav, Yeshiva Univesity Press, New York, 1984. pp. 243. $I5.00 cloth, $9.95 paper.

Jewish Life Under Islam: Jerusalem in the Sixteenth Century by Amnon Cohen. Harvard University Press, Cambridge 1984. pp. 267. $30.00.

Israel in the Mind of America by Peter Grose. Alfred A. Knopf, New York, 1984. pp. 361. $17.95.

Hitler, Germans and the “Jewish Question” by Sarah Gordon. Princeton Univerity Press, 1984, pp. 412. $40.00 cloth, $14.50 paper.

A Mediterranean Society, Volume IV: Daily Life by S. D. Goitein. University of California Press, Berkeley, 1984. pp. 492. $38.50.  相似文献   

THE CHANGE FROM TRANSFER TO CAREER EDUCATION AT COMMUNITY COLLEGES IN THE 1970s     

Boris Blai Jr. 《Community College Journal of Research & Practice》2013,37(1):71-76

For most of the twentieth century, up until the 1970s, the transfer curriculum, which prepared two‐year students for continuing their education at a four‐year school, was dominant in the community college; the ratio of enrollment in transfer programs to enrollment in occupational or career programs varied only between 2:1 and 3:1. In the 1970s, a dramatic shift occurred. Students began abandoning the transfer curriculum for the career curriculum in record numbers, and fewer decided to transfer to four‐year schools. This phenomenon has been widely quoted as fact, yet little has been done to document it, with actual figures from individual states. This paper first presents difficulties posed by this area for the researcher. Second, it examines the rise of career education and the decline of transfer education on a state‐by‐state basis. Finally, it concludes with a call for future researchers to study the repercussions of this change on the community college as a whole.  相似文献   

Investigation of Single-Case Multiple-Baseline Randomization Tests of Trend and Variability     

Levin  Joel R.  Ferron  John M.  Gafurov  Boris S. 《Educational Psychology Review》2021,33(2):713-737

Educational Psychology Review - Previous simulation studies of randomization tests applied in single-case educational intervention research contexts have typically focused on A-to-B phase changes...  相似文献   

Robust adaptive tracking with an additional plant identifier for a class of nonlinear systems     

Boris Mirkin  Per-Olof Gutman 《Journal of The Franklin Institute》2010,347(6):974-987

In this paper, we develop two new model reference adaptive control (MRAC) schemes for a class of nonlinear dynamic systems that is robust with respect to an uncertain state (output) dependent nonlinear perturbations and/or external disturbances with unknown bounds. The design is based on a controller parametrization with an adaptive integral action. Two types of adaptive controllers are considered—the state feedback controller with a plant parameter identifier, and the output feedback controller with a linear observer.  相似文献   

Zukunftsaussichten der Lehrveranstaltungsevaluation aus der Sicht von Studierenden, Lehrenden und Evaluationsanbietern     

Dr. Boris Schmidt 《Zeitschrift für Erziehungswissenschaft》2009,12(1):126-146

The current reforms of higher education are accompanied by new forms of evaluation-based quality development. In the area of higher education, the evaluation of specific lessons or seminars by students has become an important component of evaluative feedback along with accreditation and multi-level program evaluation. Using a sample of higher education teachers, students and providers of such evaluations (N?=?258), the prospects for development of this instrument (prognosis for 2015) were surveyed and analyzed. The majority of the surveyed stakeholders expect such evaluations to be widely used as compulsory instruments in the future. In contrast, the implementation of scenarios which are seen as empirically sound and sustainable for quality development is seen by the respondents to be less likely. Differences in the perspectives were most clear in respect of developments in the future. Providers of such evaluations were particularly optimistic about the prospects of particular future developments. Regarding the effectiveness of potential evaluation designs, there was little disagreement; they are seen by the majority of respondents as effective.  相似文献   

Paradigm development and leadership style of university department chairpersons     

Dr. Yoram Neumann  Steven Barnet Boris 《Research in higher education》1978,9(4):291-302

This article develops and tests the argument that leadership behavior in organizations can best be understood within a contingency technology-environment model. The major premise of this model is that one of the most influential intervening factors between organizational performance and leadership behavior is either the technology that the organization utilizes or the environment with which the organization interacts. Building upon this premise and the work of Kuhn (1970), four hypotheses are tested concerning the relationship between the effectiveness of natural science and social science departments in American universities using factor analysis. The data supports the conclusion that differential leadership styles are predictable in different scientific fields.  相似文献   

Ways of thinking associated with mathematics teachers’ problem posing in the context of division of fractions     

Boris Koichu  Guershon Harel  Alfred Manaster 《Instructional Science》2013,41(4):681-698

Twenty-four mathematics teachers were asked to think aloud when posing a word problem whose solution could be found by computing 4/5 divided by 2/3. The data consisted of verbal protocols along with the written notes made by the subjects. The qualitative analysis of the data was focused on identifying the structures of the problems produced and the associated ways of thinking involved in constructing the problems. The results suggest that success in doing the interview task was associated with perception the given fractions as operands for the division operation and, at the same time, the divisor 2/3 as an operator acting over 4/5. The lack of success was associated with perception of division of fractions as division of divisions of whole numbers and using the result of division of fractions as the only reference point. The study sheds new light on the teachers’ difficulties with conceptualization of fractions.  相似文献