排序方式： 共有35条查询结果，搜索用时 312 毫秒
11.
Walter Schrott Zdeněk Slouka Petr ?ervenka Ji?í Ston Marek Nebyla Michal P?ibyl Dalimil ?nita 《Biomicrofluidics》2009,3(4)
Electrokinetic properties and morphology of PDMS microfluidic chips intended for bioassays are studied. The chips are fabricated by a casting method followed by polymerization bonding. Microchannels are coated with 1% solution of bovine serum albumin (BSA) in Tris buffer. Albumin passively adsorbs on the PDMS surface. Electrokinetic characteristics (electro-osmotic velocity, electro-osmotic mobility, and zeta potential) of the coated PDMS channels are experimentally determined as functions of the electric field strength and the characteristic electrolyte concentration. Atomic force microscopy (AFM) analysis of the surface reveals a “peak and ridge” structure of the protein layer and an imperfect substrate coating. On the basis of the AFM observation, several topologies of the BSA-PDMS surface are proposed. A nonslip mathematical model of the electro-osmotic flow is then numerically analyzed. It is found that the electrokinetic characteristics computed for a channel with the homogeneous distribution of a fixed electric charge do not fit the experimental data. Heterogeneous distribution of the fixed electric charge and the surface roughness is thus taken into account. When a flat PDMS surface with electric charge heterogeneities is considered, the numerical results are in very good agreement with our experimental data. An optimization analysis finally allowed the determination of the surface concentration of the electric charge and the degree of the PDMS surface coating. The obtained findings can be important for correct prediction and possibly for robust control of behavior of electrically driven PDMS microfluidic chips. The proposed method of the electro-osmotic flow analysis at surfaces with a heterogeneous distribution of the surface electric charge can also be exploited in the interpretation of experimental studies dealing with protein-solid phase interactions or substrate coatings. 相似文献
12.
Eva Kotulanov Petr Bezdi
ka David Hradil Janka Hradilov Silvie &#x;varcov Tom&#x; Grygar 《Journal of Cultural Heritage》2009,10(3):367-378
Interactions of lead-based pigments with a number of inorganic salts, one of the most dangerous degradation agents of wall paintings, were studied under laboratory conditions. The results were used to interpret colour changes observed in 11th century frescoes from the church of Saint George in Kostoľany pod Tríbečom, the oldest preserved wall paintings in Slovakia. Interactions of selected pigments (lead white, massicot, red lead) with different salt solutions were performed within long-term laboratory experiments. We used a selection of naturally occurring salts (Na2SO4, MgSO4, CaSO4, NaCl, NaNO3, Ca(NO3)2, Na2CO3, K2CO3 and urea) and, additionally, a range of synthetic salts that are often applied to the wall paintings during their cleaning and conservation (NaHCO3, KHCO3, (NH4)2CO3, NH4HCO3). The reaction products were identified by X-ray powder diffraction. Red lead (Pb3O4) has a tendency to darken in all salt solutions containing dissolved atmospheric CO2 due to disproportionation to plattnerite (PbO2) and cerussite (PbCO3). Massicot (PbO) in a wet state reacts with atmospheric CO2 to form hydrocerussite and finally cerussite. Lead white (PbCO3 and Pb2CO3(OH)2) reacts with sulphates, carbonates and chlorides to form their respective salts in high yield and, sometimes, without any apparent colour change. Samples taken from the dark brown parts of the wall paintings in Saint George's church were analysed using laboratory X-ray powder microdiffraction. The presence of hydrocerussite, cerussite, plattnerite and lead magnesium carbonate was revealed. According to the results of laboratory experiments, the original lead-based pigment of the now darkened parts was red lead. 相似文献
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What is the history of educational assessment and research in Czechoslovakia? How have attitudes toward testing changed over the years? What are the prospects for the future? 相似文献
14.
Petr Johanes Candace Thille 《British journal of educational technology : journal of the Council for Educational Technology》2019,50(6):2959-2973
Education and education research are experiencing increased digitization and datafication, partly thanks to the rise in popularity of massively open online courses (MOOCs). The infrastructures that collect, store and analyse the resulting big data have received critical scrutiny from sociological, epistemological, ethical and analytical perspectives. These critiques tend to highlight concerns and/or warnings about the lack of the infrastructures' and builders' understanding of various nontechnical aspects of big data research (eg seeing data as neutral rather than as products of social processes). These critiques have primarily come from outside of the builder community, rendering the conversation largely one-sided and devoid of the voices of the builders themselves. The purpose of this paper is to re-balance the conversation by reporting the results of interviews with 11 data infrastructure builders in higher education institutions. The interviews reveal that builders engage deeply with the issues the critiques outline, not only thinking about them, but also developing practices to address them. The paper focuses the findings on three themes: designing a productive science, navigating ubiquitous ethics and achieving real human impact. Researchers, policymakers and infrastructure builders can use these accounts to better understand the building process and experience. 相似文献
15.
ABSTRACT This study was designated to investigate the kinematical differences between successful and faulty spikes, in order to identify the best strategies leading to better spike performance. Simulating a real-game condition, 13 elite youth attackers performed 6 spikes in the presence of 2 blocks. The kinematic variables of the spike performances were recorded using 6 optoelectronic cameras (Vicon Motion systems, Oxford, UK). The paired sample t-test was used to compare the kinematic variables recorded during the delivery of successful and faulty spikes. Among the successful trials, both the angular velocities of the knees (≈12.4%) and hips (≈13.3%), and the vertical velocity of the centre of mass at take-off (≈6.5%) and arm swing (≈8.2%) were considerably higher during the plant phase. Consequently, the jump (≈4.3%) and spike (≈1.5%) heights, as well as the wrist velocity (≈5.5%), were significantly higher during the jump phase of successful spikes. In successful spike performances, the attackers adopted higher hip and knee angular velocities, combined with efficient arm swings, to produce higher take-off velocities and reach higher jump heights. This approach provides them with the better position regarding the ball and the blockers to find the best path and hit the ball with higher arm velocities. 相似文献
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We concentrate on the linear spatially distributed time-invariant two-dimensional systems with multiple inputs and multiple outputs and with control action based on an array of sensors and actuators connected to the system. The system is described by the bivariate matrix polynomial fraction. Stabilisation of such systems is based on the relationship between stability of a bivariate polynomial and positiveness of a related polynomial matrix on the unit circle. Such matrices are not linear in the controller parameters, however, in simple cases, a linearising factorisation exists. It allows to describe the control design in the form of a linear matrix inequality. In more complicated cases, linear sufficient conditions are given. This concept is applied to a system with multiple outputs—a heat conduction in a long thin metal rod equipped with an array of temperature sensors and heaters, where heaters are placed in larger distances than sensors. 相似文献
18.
Tertiary Education and Management - This article provides a synthesizing overview of the roles of students in higher education governance in Europe. We first review the existing literature on... 相似文献
19.
Anna Paukova Milana Khachaturova Petr Safronov 《Mentoring & Tutoring: Partnership in Learning》2019,27(2):213-230
Unlike traditional teachers, tutors now are much less able to confine their practice to the classroom setting. Herein, we address the challenges of actual tutoring practice at one Master’s degree program comprising offline and online learning activities along with student work placements. Building on the autoethnography and narrative analysis we highlight core themes structuring tutoring experience. We examined the challenges we met. We offer suggestions for tutors supporting students in a blended learning environment, and we argue acknowledgment of different roles and strategies applied by tutors across learning contexts make them more productive and less vulnerable towards conflicting messages of other actors involved in instructional communication. 相似文献
20.
This article describes two heuristic strategies for problem solving: the use of false assumption strategy and the use of double false assumption strategy. Both of these strategies have their roots deep in history. In this article, we define these two strategies and illustrate their use in a problem developed by Frances Pellos. The article provides an overview of occurrences of these two strategies in various mathematical and educational texts. The texts show clearly that both of these strategies played a significant role in mathematics education in the past. We present some examples from concrete historical documents, which we use later for the preparation of a teaching experiment. We also present the conclusions of an experiment conducted on three lower secondary schools in the Czech Republic, the goal of which was to test the applicability of the use of false assumption strategy as a propaedeutic to solving word problems using equations. 相似文献