Advanced memory effects in the aging of a polymer glass

A new kind of memory effect on low frequency dielectric measurements on plexiglass (PMMA) is described. These measurements show that cooling and heating the sample at constant rate give an hysteretic dependence on temperature of the dielectric constant $\epsilon$. A temporary stop of cooling produces a downward relaxation of $\epsilon$. Two main features are observed i) when cooling is resumed $\epsilon$ goes back to the values obtained without the cooling stop (i.e. the low temperature state is independent of the cooling history) ii) upon reheating $\epsilon$ keeps the memory of all the cooling stops({\it Advanced memory}). The dependence of this effect on frequency and on the cooling rate is analyzed. The memory deletion is studied too. Finally the results are compared with those of similar experiments done in spin glasses and with the famous experiments of Kovacs.Comment: to be published in the European Physical Journa

Expanding Democracy in Classrooms: History Teacher Candidates\u27 Perceptions of Student Feedback as a Democratic Teaching Practice

This study examines the perceptions of middle and high school history teacher candidates about the use of student feedback as a democratic teaching practice. It explores preservice teachers\u27 responses when asking students to comment about the use of interactive, student-centered teaching. In a collaborative action research approach, qualitative research methodologies were used to document experiences of candidates as they designed and implemented student surveys in classes and responded to what students said. Participants included 14 history teacher license candidates at a public university in the Northeast United States who were completing their pre-practicum and student teaching field experiences in history and social studies classrooms in public middle and high schools during the 2013-2014 school year. Data was drawn from field notes, focus group discussions, papers, and online responses written by history teacher candidates as part of required teacher license courses. Based on themes generated from participant data, student feedback holds promise as a democratic teaching method in history classrooms. As candidates integrated democratic feedback in classes, their attitudes and behaviors changed from being reluctant inquirers to active solicitors. They became eager to learn what students had to say and prepared to make changes to curriculum content and instructional practices based on feedback. Some candidates acknowledged that asking students for feedback had transformed the culture of their classrooms and broadened their daily practice as a teacher. This study has implications for improving the preparation of new history teachers at every grade level, redefining the traditional supervision model in which student teachers receive feedback from university program supervisors but not from students. This study demonstrates ways to engage K-12 students as learning partners in history education. Student feedback reinforces and encourages future teachers\u27 engagement with continual reflective practice in their teaching. The implementation of the feedback as a part of reflective practice offers an alternative to the use of student surveys for teacher evaluation purposes

Scattering Mechanism in Modulation-Doped Shallow Two-Dimensional Electron Gases

We report on a systematic investigation of the dominant scattering mechanism in shallow two-dimensional electron gases (2DEGs) formed in modulation-doped GaAs/Al_{x}Ga_{1-x}As heterostructures. The power-law exponent of the electron mobility versus density, mu \propto n^{alpha}, is extracted as a function of the 2DEG's depth. When shallower than 130 nm from the surface, the power-law exponent of the 2DEG, as well as the mobility, drops from alpha \simeq 1.65 (130 nm deep) to alpha \simeq 1.3 (60 nm deep). Our results for shallow 2DEGs are consistent with theoretical expectations for scattering by remote dopants, in contrast to the mobility-limiting background charged impurities of deeper heterostructures.Comment: 4 pages, 3 figures, modified version as accepted in AP

From 19th Century Social Reform to 21st Century School Improvement: A Community Service-Learning Quilting Project for Middle School Students

From 19th Century Social Reform to 21st Century School Improvement: A Community Service-Learning Quilting Project for Middle School Students by Irene S. LaRoche, Leslie Kelly, and Cindy Tuttle is the fourth in a series of exemplary curriculum units on social studies and service learning developed by public school teachers and compiled by the Regional Information Center at the School of Education, University of Massachusetts Amherst

From 19th Century Social Reform to 21st Century School Improvement: A Community Service-Learning Quilting Project for Middle School Students

From 19th Century Social Reform to 21st Century School Improvement is an interdisciplinary teaching unit built around a community service learning quilting project. It is designed for use by middle schoolteachers who want to integrate lessons from United States history (19th Century social reform), English/ Language Arts (writing of school improvement plans), and mathematics (scale drawing and measurement in quilt design). The unit includes approximately two weeks of academic work; an additional period of time is needed in school or after school if students are going to sew their quilts

Soutiens perçus, engagements affectifs et succès de carrière subjectif : une approche en termes de profils

Perceived support, affective commitments and subjective career success: a person-centred approach (Soutiens perçus, engagements affectifs et succès de carrière subjectif : une approche en termes de profils)

Handling Temperature Bursts Reaching 464 C: Different Microbial Strategies in the Sisters Peak Hydrothermal Chimney

The active venting Sisters Peak (SP) chimney on the Mid-Atlantic Ridge holds the current temperature record for the hottest ever measured hydrothermal fluids (400 degrees C, accompanied by sudden temperature bursts reaching 464 degrees C). Given the unprecedented temperature regime, we investigated the biome of this chimney with a focus on special microbial adaptations for thermal tolerance. The SP metagenome reveals considerable differences in the taxonomic composition from those of other hydrothermal vent and subsurface samples; these could be better explained by temperature than by other available abiotic parameters. The most common species to which SP genes were assigned were thermophilic Aciduliprofundum sp. strain MAR08-339 (11.8%), Hippea maritima (3.8%), Caldisericum exile (1.5%), and Caminibacter mediatlanticus (1.4%) as well as to the mesophilic Niastella koreensis (2.8%). A statistical analysis of associations between taxonomic and functional gene assignments revealed specific overrepresented functional categories: for Aciduliprofundum, protein biosynthesis, nucleotide metabolism, and energy metabolism genes; for Hippea and Caminibacter, cell motility and/or DNA replication and repair system genes; and for Niastella, cell wall and membrane biogenesis genes. Cultured representatives of these organisms inhabit different thermal niches; i.e., Aciduliprofundum has an optimal growth temperature of 70 degrees C, Hippea and Caminibacter have optimal growth temperatures around 55 degrees C, and Niastella grows between 10 and 37 degrees C. Therefore, we posit that the different enrichment profiles of functional categories reflect distinct microbial strategies to deal with the different impacts of the local sudden temperature bursts in disparate regions of the chimney