Confinamento de fónons ópticos em estruturas piezoelétricas periódicas e quasiperiódicas

We study the optical-phonon spectra in periodic and quasiperiodic (Fibonacci type) superlattices made up from III-V nitride materials (GaN and AlN) intercalated by a dielectric material (silica - SiO2). Due to the misalignments between the silica and the GaN, AlN layers that can lead to threading dislocation of densities as high as 1010 cm−1, and a significant lattice mismatch (_ 14%), the phonon dynamics is described by a coupled elastic and electromagnetic equations beyond the continuum dielectric model, stressing the importance of the piezoelectric polarization field in a strained condition. We use a transfer-matrix treatment to simplify the algebra, which would be otherwise quite complicated, allowing a neat analytical expressions for the phonon dispersion relation. Furthermore, a quantitative analysis of the localization and magnitude of the allowed band widths in the optical phonon s spectra, as well as their scale law are presented and discussed

Polaritons de exciton em super-redes semicondutoras

In this work we study the spectrum (bulk and surface modes) of exciton-polaritons in infinite and semi-infinite binary superlattices (such as, ···ABABA···), where the semiconductor medium (A), whose dielectric function depends on the frequency and the wavevector, alternating with a standard dielectric medium B. Here the medium A will be modeled by a nitride III-V semiconductor whose main characteristic is a wide-direct energy gap Eg. In particular, we consider the numerical values of gallium nitride (GaN) with a crystal structure wurtzite type. The transfer-matrix formalism is used to find the exciton-polariton dispersion relation. The results are obtained for both s (TE mode: transverse electric) and p (TM mode: transverse magnetic) polarizations, using three diferent kind of additional boundary conditions (ABC1, 2 e 3) besides the standard Maxwell's boundary conditions. Moreover, we investigate the behavior of the exciton-polariton modes for diferent ratios of the thickness of the two alternating materials forming the superlattice. The spectrums shows a confinement of the exciton-polariton modes due to the geometry of the superlattice. The method of Attenuated Total Reflection (ATR) and Raman scattering are the most adequate for probing this excitations

Sistemas Nanoestruturados: Heteroestruturas Quasi-Periódicas de Nitretos e Cálculos Ab initio em Polimorfos CaCO3

The physical properties and the excitations spectrum in oxides and semiconductors materials are presented in this work, whose the first part presents a study on the confinement of optical phonons in artificial systems based on III-V nitrides, grown in periodic and quasiperiodic forms. The second part of this work describes the Ab initio calculations which were carried out to obtain the optoeletronic properties of Calcium Oxide (CaO) and Calcium Carbonate (CaCO3) crystals. For periodic and quasi-periodic superlattices, we present some dynamical properties related to confined optical phonons (bulk and surface), obtained through simple theories, such as the dielectric continuous model, and using techniques such as the transfer-matrix method. The localization character of confined optical phonon modes, the magnitude of the bands in the spectrum and the power laws of these structures are presented as functions of the generation number of sequence. The ab initio calculations have been carried out using the CASTEP software (Cambridge Total Sequential Energy Package), and they were based on ultrasoft-like pseudopotentials and Density Functional Theory (DFT). Two di®erent geometry optimizations have been e®ectuated for CaO crystals and CaCO3 polymorphs, according to LDA (local density approximation) and GGA (generalized gradient approximation) approaches, determining several properties, e. g. lattice parameters, bond length, electrons density, energy band structures, electrons density of states, e®ective masses and optical properties, such as dielectric constant, absorption, re°ectivity, conductivity and refractive index. Those results were employed to investigate the confinement of excitons in spherical Si@CaCO3 and CaCO3@SiO2 quantum dots and in calcium carbonate nanoparticles, and were also employed in investigations of the photoluminescence spectra of CaCO3 crystal

Polaritons em materiais magnéticos nanoestruturados

In this work we present a theoretical study about the properties of magnetic polaritons in superlattices arranged in a periodic and quasiperiodic fashíons. In the periodic superlattice, in order to describe the behavior of the bulk and surface modes an effective medium approach, was used that simplify enormously the algebra involved. The quasi-periodic superlattice was described by a suitable theoretical model based on a transfer-matrix treatment, to derive the polariton's dispersion relation, using Maxwell's equations (including effect of retardation). Here, we find a fractal spectra characterized by a power law for the distribution of the energy bandwidths. The localization and scaling behavior of the quasiperiodic structure were studied for a geometry where the wave vector and the external applied magnetic field are in the same plane (Voigt geometry). Numerical results are presented for the ferromagnet Fe and for the metamagnets FeBr2 and FeCl2

Taxonomia de Papilionoideae (leguminosae) da Mata Atlântica do Rio Grande do Norte, Brasil

Leguminosae is the third largest family of angiosperms with about 19.325 species and 727 genera, and it is pantropically distributed. Papilionoideae is the most diverse of the three legume subfamilies, with around 13.800 species (71%), 478 genera, and 28 tribes. Papilionoid legumes include herbs, shrubs, lianas or trees with pinnate, trifoliolate, unifoliolate or simple leaves, flowers frequently papilionate with descending imbricate petal aestivation, the petals highly differentiated into standard, keel, and wings, androecium usually diplostemous, and seeds without pleurogram, with conspicuous hilum, and the embryo radicle usually curved. The current study aims to carry out a taxonomic account of the Papilionoideae from Atlantic Forest remnants in Rio Grande do Norte, Brazil, across the herbaria data surveys, collections of field samples and morphological analysis of the collected specimens and/or herbaria materials. Identification key, descriptions, diagnostic characters, illustrations, and geographic distribution of the 68 species and 32 genera within the following tribes Phaseoleae (11 genera/24 species), Dalbergieae (9/20), Swartzieae (3/3), Millettieae (2/4), Sophoreae (2/2), Abreae (1/1), Crotalarieae (1/3), Desmodieae (1/7), Indigofereae (1/3), and Sesbanieae (1/1). The most species-rich genera were Desmodium Desv. (7 species), Centrosema (DC.) Benth. (5), Stylosanthes Sw. (5), Aeschynomene L. (4) and Macroptilium (Benth.) Urb. (4). Concerning to the habit, the herbaceous and shrubby has predominated with 60% (41 spp.), following by the vine and lianas with 28% (19 spp.) and the woody with only 12% (8 spp.). Thirty two species and the following genera are newly recorded for the flora of Rio Grande do Norte: Chaetocalyx, Cochliasanthus, Crotalaria, Galactia, Geoffroea, Macroptilium, Rhynchosia, Swartzia, Trischidium, and Vigna

A intercompreensão em Línguas Românicas nas aulas de Espanhol: o que querem e o que podem essas línguas?

The official documents that guide the teaching and learning process of a Foreign Language in Brazil, Parâmetros Curriculares Nacionais de Língua Estrangeira, suggest a linguistic and intercultural communication as the main objective of teaching a foreign language inorderto contribute withareflexive formation of the students.Toachieve this goal, a Virtual Interchange was realized connecting distant places like Córdoba, in Argentina, and Natal in Brazil, between High School students through Moodle platform and Facebook. The Interchange is based in the Intercomprehension in Romance Languages(IC) guidelines, inthiscase between Portuguese and Spanish, according to which every student speaks their own language and makes an effort to comprehend the others througha collaborative process thatgo es beyond the limits of mere linguistic objectives and favors the students’ reality acceptance before the diversity. This qualitative study with thno graphic characteristic stries to know whe ther differentiate projects can increase students’ interest to learn the target language. It was also set as an aim of this study to develop the intercultural competence of our students and foster the respect for different cultures. In the case of Argentinian and Brazilian students, wetried to promote reflection about social representation trying to destroy stereotypes between both groups. As methodological resources, we used interviews, questionnaires and intercomprehension activities during the Project, as well as a participant observation of the interactions betweenthe students of both countries.Webe lieve tobe contributing towards the integral formation ofth student asacriticalcitizenthatthinksa bouttheir posture before the world, which is one of the formal education aims according to Parâmetros Curriculares Nacionais. Our theoretical foundation is based on Intercomprehension in Romance Languages (IC) as a plurilingualism didactics, (JAMET AND SPIŢĂ 2010; ARAÚJO AND SÁ et al., 2003; CAPUCHO, 2010; ANDRADE etal.,2003), some the oriesaboutinter culturalisman didentity(Vallespir, 1999;DUARTE&SANCHES,2004; REVUZ,1998;SILVA,2000;CHAUÍ2006; SERRANI-INFANTE 1998), motivation and second language learning (DECI & RYAN, 1985; DÖRNYEI AND OTTÓ, 1998; DÖRNYEI, 2000, 2001; 2011) and Significant Learning Theory (AUSUBEL, 1968). The results show an increase of students’ motivation when in contact with the target language through dynamic activities in an IC context. Moreover, we noticed that a deeper thinking aboutthe Argentinian culture helped to deconstruct previous cultural representation.

Intercompreensão de línguas românicas: uma proposta para a leitura literária plurilíngue no ensino fundamental

The developed research aimed to investigate how students behave on elementary school in a plurilingual context, based on Intercomprehension of Romanic Languages with literary texts in the classroom. The theoretical framework prioritizes authors who consider reading literary text as an essential tool to the formation of reading and writing skills for students, such as: Amarilha (1997; 2003; 2007), Resende (1993), Kleiman, (1999), Villardi (1997), Aguiar (1991), Perrone-Moisés (2000), Lajolo (1993), Zilberman (1991), Cosson (2006), Andrade, Melo-Pfeifer, Santos, (2009), Sá; De Carlo; Antoine (2011), Alas Martins (2014), Doyé (2005), Souza, (2013), and others, according to the intercomprehension approach and plurilingualism. We use questionnaires as a methodological resources for this research, and we applied some activities that was developed based on intercomprehension from literary texts which represent three types of Romanic languages (Spanish, French and Italian), in addition to the participant observation in classes with students of the 8th grade from an elementary public school in the city of Natal (RN). The students could read and (inter) understand some texts of classic literature in those Latin languages and also in Portuguese, whose titles include “D. Quixote de la mancha” by Miguel de Cervantes; “O pequeno príncipe” by Antoine de Saint-Exupéry; and “Pinóquio” by Carlo Collodi. The data analysis shows that students understood the lessons with plurilingual texts as something which goes beyond the structure of language teaching, awakening themselves to the knowledge of new languages and cultures, and linguistic diversity as motivation at the time of understanding and literature as transforming element to Citizen formation of students.

A produção oral de inglês como LE em uma escola pública de Natal: uma experiência com a abordagem baseada em tarefas

The aim of this action research of mixed-methods was investigating the role of the tasks proposed by the Task-Based Learning, TBL (WILLIS, 1996) in the process of development of speech production in English as a foreign language (EFL) at the public school. Twenty-three students from a grade of secondary school from a state school in Rio Grande do Norte were exposed systematically to the implementation of the learning tasks focused in the speech production in EFL during two months. The instruments used at the data collection – pre and post-questionnaire; field notes; focal group; and pre and post-tests - generated two kinds of data: a) qualitative (the perception of the students about their speech production and the teaching of this ability at the public school; and, the usage of strategies of communication for these learners facing TBL); and, b) quantitative (the development of pronunciation; of accuracy in the proficiency tests (test KET – Cambridge, adapted); and, of Global Oral Proficiency (POG) of these learners after the accomplishment of the learning tasks). The quantitative results of the study indicate that there was a statistically significant development of pronunciation and accuracy at the proficiency tests, after the tasks experience. The qualitative findings, in turn, represented by the learners‟ reports and from the research teacher, show that there has been greater focus on the use of communicative strategies during the learners‟ oral production throughout the intervention with the tasks.