Reduction of water evaporation in polymerase chain reaction microfluidic devices based on oscillating-flow

Producing polymeric or hybrid microfluidic devices operating at high temperatures with reduced or no water evaporation is a challenge for many on-chip applications including polymerase chain reaction (PCR). We study sample evaporation in polymeric and hybrid devices, realized by glass microchannels for avoiding water diffusion toward the elastomer used for chip fabrication. The method dramatically reduces water evaporation in PCR devices that are found to exhibit optimal stability and effective operation under oscillating-flow. This approach maintains the flexibility, ease of fabrication, and low cost of disposable chips, and can be extended to other high-temperature microfluidic biochemical reactors.     

Structural and dynamic properties of linker histone H1 binding to DNA

Found in all eukaryotic cells, linker histones H1 are known to bind to and rearrange nucleosomal linker DNA. In vitro, the fundamental nature of H1∕DNA interactions has attracted wide interest among research communities-from biologists to physicists. Hence, H1∕DNA binding processes and structural and dynamical information about these self-assemblies are of broad importance. Targeting a quantitative understanding of H1 induced DNA compaction mechanisms, our strategy is based on using small-angle x-ray microdiffraction in combination with microfluidics. The usage of microfluidic hydrodynamic focusing devices facilitates a microscale control of these self-assembly processes, which cannot be achieved using conventional bulk setups. In addition, the method enables time-resolved access to structure formation in situ, in particular, to transient intermediate states. The observed time dependent structure evolution shows that the H1∕DNA interaction can be described as a two-step process: an initial unspecific binding of H1 to DNA is followed by a rearrangement of molecules within the formed assemblies. The second step is most likely induced by interactions between the DNA and the H1's charged side chains. This leads to an increase in lattice spacing within the DNA∕protein assembly and induces a decrease in the correlation length of the mesophases, probably due to a local bending of the DNA.     

Discrimination and Ethnic–Racial Identity: Understanding Direction of Effects Using Within- and Between-Person Analyses

Ethnic–racial identity (ERI) development and ethnic–racial discrimination are two salient experiences among adolescents in the United States. Despite growing awareness of the costs and benefits of these experiences individually, we know little about how they may influence one another. The current study examined competing hypotheses relating discrimination and components of ERI (i.e., exploration, resolution, affirmation) among a sample of Mexican-origin adolescent mothers (N = 181; M_age at Wave 1 = 16.83, SD = 1.01) across six waves of data. Findings revealed that within-person changes in discrimination predicted subsequent ERI resolution and affirmation; however, ERI did not predict subsequent discrimination. Between-person effects of discrimination on affirmation were significant. Our findings underscore the importance of discrimination experiences in shaping Mexican-origin adolescent mothers’ normative developmental competencies.     

The Use of Different Translation Devices to Analyze Knowledge-Building in a University Chemistry Classroom

Research in Science Education - This research draws on Legitimation Code Theory (LCT) to understand the epistemic dimension of the higher education classroom discourse of a professor who is well...     

The effects of various mastery criteria on student performance and attitude in a mastery-oriented course

The purpose of this study was to determine the effects of various mastery criteria on student performance and attitude in a course in which mastery learning strategies were employed. Undergraduates in an introductory course in educational psychology were randomly assigned to one of three treatments—one in which mastery criteria gradually increased from 70% to 90%, a second in which mastery criteria gradually decreased from 90% to 70%, or a third in which mastery criteria remained constant at 80%. Results indicated that although the high mastery criterion (90%) had a positive effect on some aspects of quiz performance, it did not have an effect on final examination performance. Results also indicated that students preferred that mastery criteria remain constant during a semester. These findings, when examined in light of previous research, call into question some prior notions regarding the levels at which mastery criteria should be set.     

The effects of ascending,descending, and fixed criteria on student performance and attitude in a mastery-oriented course

This study examined whether the criteria for mastering unit quizzes in a mastery-oriented course should increase, decrease, or remain fixed across units. Subjects were randomly assigned to one of three treatments, one in which mastery criteria on unit quizzes gradually increased, a second in which mastery criteria gradually decreased, and a third in which mastery criteria remained fixed. Results indicated that students in the fixed criterion condition proceeded through the course at the steadiest pace and performed better than the other students on the unit quizzes they mastered. In addition, the vast majority of subjects indicated that they preferred the fixed criterion condition. These results strengthen the notion that the level of performance expected of students in a mastery-oriented course should not vary across units.     

FísicActiva: applying active learning strategies to a large engineering lecture

This paper presents and analyses the results obtained by applying Active Learning techniques in overcrowded Physics lectures at the University of the Republic, Uruguay. The course referred to is Physics 1, the first Physics course that all students of the Faculty of Engineering take in their first semester for all the Engineering-related careers. Qualitative and quantitative data corresponding to three semesters are shown and discussed, indicating that the students that attended these lectures outperformed the students that followed the course in the traditional way: the pass rates increased, whereas the failure rates decreased. The students highly valued this methodology, in particular, the interactive and relaxed dynamics, highlighting the concern of professors to answer questions by means of new questions so as to promote reasoning. The results obtained point to a work path that deserves to be deepened and extended to other Engineering courses.     

Analysis of the Meanings of the Antiderivative Used by Students of the First Engineering Courses

In this article, we present the results of the administration of a questionnaire designed to evaluate the understanding that civil engineering students have of the antiderivative. The questionnaire was simultaneously administered to samples of Mexican and Colombian students. For the analysis of the answers, we used some theoretical and methodological notions provided by the theoretical model known as Onto-Semiotic Approach (OSA) to mathematical cognition and instruction. The results revealed the meanings of the antiderivative that are more predominantly used by civil engineering students. Also, the comparison between the mathematical activity of Mexican and Colombian students provides information that allows concluding that the meanings mobilized could be shared among their communities and are not particular of their classroom or university.