Silicon and III-V compound nanotubes: structural and electronic properties

Unusual physical properties of single-wall carbon nanotubes have started a search for similar tubular structures of other elements. In this paper, we present a theoretical analysis of single-wall nanotubes of silicon and group III-V compounds. Starting from precursor graphene-like structures we investigated the stability, energetics and electronic structure of zigzag and armchair tubes using first-principles pseudopotential plane wave method and finite temperature ab-initio molecular dynamics calculations. We showed that (n,0) zigzag and (n,n) armchair nanotubes of silicon having n > 6 are stable but those with n < 6 can be stabilized by internal or external adsorption of transition metal elements. Some of these tubes have magnetic ground state leading to spintronic properties. We also examined the stability of nanotubes under radial and axial deformation. Owing to the weakness of radial restoring force, stable Si nanotubes are radially soft. Undeformed zigzag nanotubes are found to be metallic for 6 < n < 11 due to curvature effect; but a gap starts to open for n > 12. Furthermore, we identified stable tubular structures formed by stacking of Si polygons. We found AlP, GaAs, and GaN (8,0) single-wall nanotubes stable and semiconducting. Our results are compared with those of single-wall carbon nanotubes.Comment: 11 pages, 10 figure

Magnetization profile for impurities in graphene nanoribbons

The magnetic properties of graphene-related materials and in particular the spin-polarised edge states predicted for pristine graphene nanoribbons (GNRs) with certain edge geometries have received much attention recently due to a range of possible technological applications. However, the magnetic properties of pristine GNRs are not predicted to be particularly robust in the presence of edge disorder. In this work, we examine the magnetic properties of GNRs doped with transition-metal atoms using a combination of mean-field Hubbard and Density Functional Theory techniques. The effect of impurity location on the magnetic moment of such dopants in GNRs is investigated for the two principal GNR edge geometries - armchair and zigzag. Moment profiles are calculated across the width of the ribbon for both substitutional and adsorbed impurities and regular features are observed for zigzag-edged GNRs in particular. Unlike the case of edge-state induced magnetisation, the moments of magnetic impurities embedded in GNRs are found to be particularly stable in the presence of edge disorder. Our results suggest that the magnetic properties of transition-metal doped GNRs are far more robust than those with moments arising intrinsically due to edge geometry.Comment: submitte

Teacher Knowledge as Context

Research has shown that teachers bring into the classroom multiple domains of knowledge, including disciplinary knowledge, pedagogical content knowledge (i.e., the process of relaying disciplinary knowledge to students), knowledge of how learning occurs, knowledge of students’ learning styles, knowledge of curricular and contextual demands, their own personal practical knowledge (e.g., experiences in the classroom as a student; cultural norms surrounding the role of a teacher), and knowledge of how to reflect on all of these domains in order to adapt one’s teaching accordingly. This piece will briefly explain and demonstrate the importance in examining teacher knowledge as context within classroom discourse analysis in order to enrich the understanding of what is happening in classroom interaction and explain why it is so

Knowing Your Reader: Text-External Influences on Textual Features in Résumé Construction

In the field of teaching English as a Second Language (ESL), great importance has often been placed on using language in authentic ways. As a result of the inability of many second language (L2) students to construct and adapt language for various academic and professional needs (St. John, 1996), genre analysis has gained attention as a framework for teaching ESL students to write texts they way they are constructed in authentic situations. However, the lack of empirically derived discipline-specific genre exemplars to practically utilize in the L2 writing classroom has prompted the need for (a) further analysis of various texts found outside of the classroom setting and (b) an investigation into how language is manipulated to meet the purposes of those texts. Following Bhatia’s (2008) and Cheng’s (2008) notions that students need to have practical genre exemplars to aid them in understanding how text-external influences (e.g., the purpose for writing and the reader’s expectations) affect linguistic choices, the focus of this paper is to demonstrate how one type of professional text, the résumé, is constructed using a genre-based framework. The analysis follows a genre perspective of analyzing texts both linguistically, based on the English for Specific Purposes school of genre, and contextually, from the New Rhetoric school. In constructing this specific text, the writer’s understanding of text-external influences, namely expectations the hiring company has for the desired applicant, was essential for the development of organizational patterns and lexical construction of their résumés. This study highlights the importance of having not only an understanding of the linguistic knowledge needed to construct various texts, but also of the text-external influences on those linguistic choices

New York state urban cultural park system

This study focused upon the New York State Urban Cultural Park System (UCP) . An urban cultural park is a designated historical area in a community which has been revitalized to interpret the community\u27s role in the cultural development of the region and state. Unlike typical green space parks , the UCP will include the areas where residents work, live and play- The roles of Cultural Tourism and Tourism Development in the UCP were investigated. Interviews of individuals involved in the planning, development and implementation of the UCP were conducted. Site visitations were conducted to several of the UCP communities. The UCP model does have applications to Tourism Development

Simmons v. Owens, 363 So. 2d 142 (Fla. 1st Dist. Ct. App. 1978)

Torts-CONTRACTOR LIABILITY-CONTRACTOR HELD LIABLE TO REMOTE PURCHASER FOR PROPERTY DAMAGE ATTRIBUTABLE TO LATENT DEFECTS IN CONSTRUCTIO

On Language Teachers’ Classroom Practices: Bridging Conversation Analysis with Language Teacher Education Research

Since the late 1980s, second language teacher education (SLTE) research has grown immensely as a field of inquiry within applied linguistics, particularly as teacher knowledge, expertise, and cognition have been found to influence students’ language learning processes in classroom contexts (Borg, 2011). Much empirical evidence illustrating this connection has been gathered using a variety of ethnographic data techniques such as individual interviews, focus groups, journal writing, questionnaires, field notes, and stimulated recall sessions. The strengths of these data sources are numerous in that, when triangulated, they provide insight into teachers’ thought processes and perceptions of their teaching practices. It has been asserted elsewhere (see Fagan, in press a), though, that while many studies within the SLTE field have attempted to draw implications from such findings for teachers’ classroom practices, the methods used do not allow for such assumptions. In fact, as Borg (2011) presents in his summary of SLTE research over the past two decades, there remains a lack of juxtaposition between findings on teachers’ perceptions and their actual classroom practices in situ. That is not to say that there have been no studies bridging such data sources. Tsui (2003), for example, utilizes varied ethnographic data sources, including the use of classroom discourse data, to get at language teachers’ development of expertise. This study, however, is representative of the few in the SLTE field that incorporates glosses of interactions into their analyses. In other words: (a) transcriptions tend to solely consist of the verbal non-suprasegmental components of the discourse rather than include other interactional resources (i.e., prosodic cues, pausing, nonverbal conduct) illustrating the intricate constructions of teachers’ communication; (b) the focus of the classroom data does not detail the specific sequential environments in which certain teacher practices appear

Impurity segregation in graphene nanoribbons

The electronic properties of low-dimensional materials can be engineered by doping, but in the case of graphene nanoribbons (GNR) the proximity of two symmetry-breaking edges introduces an additional dependence on the location of an impurity across the width of the ribbon. This introduces energetically favorable locations for impurities, leading to a degree of spatial segregation in the impurity concentration. We develop a simple model to calculate the change in energy of a GNR system with an arbitrary impurity as that impurity is moved across the ribbon and validate its findings by comparison with ab initio calculations. Although our results agree with previous works predicting the dominance of edge disorder in GNR, we argue that the distribution of adsorbed impurities across a ribbon may be controllable by external factors, namely an applied electric field. We propose that this control over impurity segregation may allow manipulation and fine-tuning of the magnetic and transport properties of GNRs.Comment: 5 pages, 4 figures, submitte

Do South African universities provide the required training platforms for otolaryngology specialist training?

Background. Concern exists about the quality of specialist training platforms at South African universities and teaching hospitals.Method. We conducted an audit of the quality of training at South African otolaryngology (ENT) training institutions from the perspective of the registrars.Results. Some institutions were deficient in terms of supervision, theatre time, access to teaching aids and research tools, and range of surgery, and do not provide the required training platforms for ENT specialist training. Five out of 8 institutions have produced &lt;2 publications in peer-reviewed journals over the past 5 years.Conclusions. The HPCSA fails to adequately police the quality of training in South Africa. Training programme shortcomings must urgently be addressed to ensure proper education and training of otolaryngologists