Critical comparison of electrode models in density functional theory based quantum transport calculations

We study the performance of two different electrode models in quantum transport calculations based on density functional theory: Parametrized Bethe lattices and quasi-one dimensional wires or nanowires. A detailed account of implementation details in both cases is given. From the systematic study of nanocontacts made of representative metallic elements, we can conclude that parametrized electrode models represent an excellent compromise between computational cost and electronic structure definition as long as the aim is to compare with experiments where the precise atomic structure of the electrodes is not relevant or defined with precision. The results obtained using parametrized Bethe lattices are essentially similar to the ones obtained with quasi one dimensional electrodes for large enough sections of these, adding a natural smearing to the transmission curves that mimics the true nature of polycrystalline electrodes. The latter are more demanding from the computational point of view, but present the advantage of expanding the range of applicability of transport calculations to situations where the electrodes have a well-defined atomic structure, as is case for carbon nanotubes, graphene nanoribbons or semiconducting nanowires. All the analysis is done with the help of codes developed by the authors which can be found in the quantum transport toolbox Alacant and are publicly available.Comment: 17 pages, 12 figure

Lab notebooks as scientific communication: investigating development from undergraduate courses to graduate research

In experimental physics, lab notebooks play an essential role in the research process. For all of the ubiquity of lab notebooks, little formal attention has been paid to addressing what is considered `best practice' for scientific documentation and how researchers come to learn these practices in experimental physics. Using interviews with practicing researchers, namely physics graduate students, we explore the different experiences researchers had in learning how to effectively use a notebook for scientific documentation. We find that very few of those interviewed thought that their undergraduate lab classes successfully taught them the benefit of maintaining a lab notebook. Most described training in lab notebook use as either ineffective or outright missing from their undergraduate lab course experience. Furthermore, a large majority of those interviewed explained that they did not receive any formal training in maintaining a lab notebook during their graduate school experience and received little to no feedback from their advisors on these records. Many of the interviewees describe learning the purpose of, and how to maintain, these kinds of lab records only after having a period of trial and error, having already started doing research in their graduate program. Despite the central role of scientific documentation in the research enterprise, these physics graduate students did not gain skills in documentation through formal instruction, but rather through informal hands-on practice.Comment: 10 page

Instructor perspectives on iteration during upper-division optics lab activities

Although developing proficiency with modeling is a nationally endorsed learning outcome for upper-division undergraduate physics lab courses, no corresponding research-based assessments exist. Our longterm goal is to develop assessments of students' modeling ability that are relevant across multiple upper-division lab contexts. To this end, we interviewed 19 instructors from 16 institutions about optics lab activities that incorporate photodiodes. Interviews focused on how those activities were designed to engage students in some aspects of modeling. We find that, according to many interviewees, iteration is an important aspect of modeling. In addition, interviewees described four distinct types of iteration: revising apparatuses, revising models, revising data-taking procedures, and repeating data collection using existing apparatuses and procedures. We provide examples of each type of iteration, and discuss implications for the development of future modeling assessments.Comment: 4 pages, 1 figure; under revie

Student ownership of projects in an upper-division optics laboratory course: A multiple case study of successful experiences

We investigate students' sense of ownership of multiweek final projects in an upper-division optics lab course. Using a multiple case study approach, we describe three student projects in detail. Within-case analyses focused on identifying key issues in each project, and constructing chronological descriptions of those events. Cross-case analysis focused on identifying emergent themes with respect to five dimensions of project ownership: student agency, instructor mentorship, peer collaboration, interest and value, and affective responses. Our within- and cross-case analyses yielded three major findings. First, coupling division of labor with collective brainstorming can help balance student agency, instructor mentorship, and peer collaboration. Second, students' interest in the project and perceptions of its value can increase over time; initial student interest in the project topic is not a necessary condition for student ownership of the project. Third, student ownership is characterized by a wide range of emotions that fluctuate as students alternate between extended periods of struggle and moments of success while working on their projects. These findings not only extend the literature on student ownership into a new educational domain---namely, upper-division physics labs---they also have concrete implications for the design of experimental physics projects in courses for which student ownership is a desired learning outcome. We describe the course and projects in sufficient detail that others can adapt our results to their particular contexts.Comment: 22 pages, 3 tables, submitted to Phys. Rev. PE

Evaluating the impact of active labor programs : results of cross country studies in Europe and Central Asia

The objective of this cross country study was to determine if there was any significant difference those individuals who participated in active labor programs (ALP) and similar individuals who did not participate in the programs (the comparison group), with regard to agreed outcome measures of program success (e.g., employment, wage levels) in four countries: the Czech Republic, Poland, Hungary, and Turkey. The study evaluated five different ALPs across the four countries for several categories of program participants, grouped by demographic characteristics and geographic location. The active labor programs studies comprised: retraining, public works or temporary community employment, wage subsidy, self-employment initiatives, and general employment services. All five ALPs evaluated were found to have a significant positive net impact for some population subgroups, a general finding supported by the 1996 OECD review that concluded that there are ALPs that work for most groups of individuals. However, the study found the impact was not significant for some sub-groups, and for some ALPs the impact was negative. The final chapter summarizesthe general trends in findings on the various outcome measures across demographic and regional subgroups.Environmental Economics&Policies,Poverty Impact Evaluation,ICT Policy and Strategies,Health Monitoring&Evaluation,Poverty Monitoring&Analysis

The density of critical percolation clusters touching the boundaries of strips and squares

We consider the density of two-dimensional critical percolation clusters, constrained to touch one or both boundaries, in infinite strips, half-infinite strips, and squares, as well as several related quantities for the infinite strip. Our theoretical results follow from conformal field theory, and are compared with high-precision numerical simulation. For example, we show that the density of clusters touching both boundaries of an infinite strip of unit width (i.e. crossing clusters) is proportional to $(\sin \pi y)^{-5/48}\{[\cos(\pi y/2)]^{1/3} +[\sin (\pi y/2)]^{1/3}-1\}$. We also determine numerically contours for the density of clusters crossing squares and long rectangles with open boundaries on the sides, and compare with theory for the density along an edge.Comment: 11 pages, 6 figures. Minor revision