Crossover of the three-dimensional topological insulator Bi2 Se3 to the two-dimensional limit

A topological insulator1-9 is a new state of quantum matter that is characterized by a finite energy gap in the bulk and gapless modes flowing along the boundaries that are robust against disorder scattering. The topological protection of the surface state could be useful for both low-power electronics10 and error-tolerant quantum computing11,12. For a thin slab of three-dimensional topological insulator, the boundary modes from the opposite surfaces may be coupled by quantum tunnelling, so that a small, thickness-dependent gap is opened up13,15. Here we report such results from angle-resolved photoemission spectroscopy on Bi2 Se3 films of various thicknesses grown by molecular beam epitaxy. The energy gap opening is clearly seen when the thickness is below six quintuple layers. The gapped surface states also exhibit sizeable Rashba-type spin-orbit splitting because of the substrate-induced potential difference between the two surfaces. The tunable gap and the spin-orbit coupling make these topological thin films ideal for electronic and spintronic device applications. © 2010 Macmillan Publishers Limited. All rights reserved.link_to_subscribed_fulltex

Quasi-Elastic Scattering of C-16 from C-12 at 47.5 MeV/Nucleon

Differential cross sections for the quasi-elastic scattering of C-16 at 47.5 MeV/nucleon from C-12 target are measured. Coupled-channels calculations are carried out and the optical potential parameters are obtained by fitting the experimental angular distribution.National Basic Research Program of China 2007CB81500

COM TEXTO NO CONTEXTO DE 5ª SÉRIE − Inovações no ensino de Português e sua recepção por professores

Submitted by admin tede ([email protected]) on 2017-02-07T17:02:06Z No. of bitstreams: 1 Flomar Ambrosina Oliveira Chagas.pdf: 4090697 bytes, checksum: 2dbff1c21fc8027796f1d567801f46c0 (MD5)Made available in DSpace on 2017-02-07T17:02:06Z (GMT). No. of bitstreams: 1 Flomar Ambrosina Oliveira Chagas.pdf: 4090697 bytes, checksum: 2dbff1c21fc8027796f1d567801f46c0 (MD5) Previous issue date: 2001-09-14This study has as general theme the teaching of Portuguese Language in the elementary school, approaching, specifically, the forms which teachers of the mother-tongue receive and implant in the class, theoretical and methodological innovations related of the Portuguese teaching. The choice of the theme appeared of the verification of the occurrence of students of the 5th to 8th grades’s difficulties in developing the capacity to producing and to understanding texts in the most several communication situations, in a school where the teachers are licensed and they adopt the official orientations in relation to the Portuguese teaching. In function of the research, it was made a study of the main language conceptions and of teaching Portuguese presents in the Brazilian scientific production, with detach to the conception of the language as interaction form, for being this the most consensual among the researchers and, also, the adopted option in the official proposals. Being considered that this conception privileges as contents the practices of the reading, of the text production and of the linguistic analysis, the research constituted in verifying their reception, through teacher’s speech and teaching practices. The research, of qualitative type, was used of the case study and it consisted in the observation of classes of two Portuguese teachers, in the 5th grade, of two public schools. Also, were done interviews and questionnaires with these teachers and their students, and observation of informal situations in the school, collection of texts and students' productions, teacher’s teaching plan, etc. The final intention was to join the theoretical part of this study and the analysis of the collected data, considering to supplying contributions theoreticalpractices for the pedagogic practices of the current teaching of mother-tongue in the elementary school, in a perspective didactic-pedagogic of critical stamp and in a conception of interactive language.Este estudo tem como tema geral o ensino de Língua Portuguesa no ensino fundamental, abordando, especificamente, as formas pelas quais professores dessa área recebem e implantam na sala de aula inovações teóricas e metodológicas relacionadas com o ensino de Português. A escolha do tema de pesquisa decorreu da constatação de dificuldades de alunos da 5ª a 8ª séries em desenvolver a capacidade de produzir e compreender textos nas mais diversas situações de comunicação, numa escola em que os professores são licenciados e adotam as orientações oficiais em relação ao ensino da Língua Portuguesa. Em função da pesquisa, fez-se um estudo das principais concepções de linguagem e de ensino da Língua Portuguesa presentes na produção científica brasileira, com destaque à concepção da linguagem como forma de interação, por ser esta a mais consensual entre os pesquisadores e, também, a opção adotada nas propostas curriculares oficiais. Considerando-se que esta concepção privilegia como conteúdos as práticas da leitura, da produção de texto e da análise lingüística, a pesquisa constituiu em verificar sua recepção, através do discurso e das práticas de ensino de professores. A pesquisa, de tipo qualitativa, utilizou-se do estudo de caso e consistiu da observação de aulas de dois professores de Português, na 5ªsérie, de duas escolas públicas. Foram feitas, também, entrevistas e questionários com esses professores e seus alunos, bem como observação de situações informais na escola, coleta de textos e produções dos alunos, plano de ensino dos professores etc. A intenção final foi juntar o embasamento teórico deste estudo e a análise dos dados coletados, tendo em vista fornecer contribuições teórico - práticas ao aprimoramento das práticas pedagógicas do atual ensino de língua materna no ensino fundamental, lastreadas numa perspectiva didáticopedagógica de cunho crítico e numa concepção de linguagem interacionista