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An?lise das avalia??es realizadas na disciplina de arquitetura at?mica e molecular no curso de qu?mica, modalidade a dist?ncia da UFRNClemente, Mayara Polyana Dantas Felipe 25 July 2013 (has links)
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Previous issue date: 2013-07-25 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / The field of education is very rich and allows us to research in various
aspects. The area of chemical education has been growing more and more, and
an important aspect that has been researching this area is about the learning
difficulties of students. The approach of the themes atomic structure and
chemical bonds are developed in high school and have many problems that are
often brought to higher education becoming an obstacle to the advancement of
learning. It is necessary for these initial themes - the atomic structure and
chemical bonds - are well understood by the student to the other contents of
Chemistry will be understood more easily. This paper aims to describe, analyze
errors and difficulties presented in the assessments of the discipline Atomic and
Molecular Architecture, the students of the degree course in Chemistry - EAD,
with respect to the contents of " Atomic Structure and Chemical Bonding ", by of
the assessments made by the students and the Virtual Learning Environment
(VLE), taking into account the activities , discussion forum and access to
materials . AVA allows obtaining reports which were used to analyze regarding
access / participation to assess their contribution to learning and its relation to the
final result (pass / fail). It was observed that the most frequent errors in the
assessments are related to the early part of the chemistry that is the
understanding of atomic structure and evolution models. Students who accessed
the extra material and participated in the activities and forums were students who
achieved success in the course. Ie, the difficulties were emerging and the use of
available teaching strategies, students could minimize such difficulties, making
their performance in activities and assessments were better. Was also observed
by attending the AVA, the discipline began with a large withdrawal from the page
access as well as the frequency of face- evidence from observation in Listing
presence of classroom assessments / O campo da educa??o ? muito rico e nos possibilita a investiga??o em
v?rios aspectos. A ?rea de ensino de qu?mica vem crescendo cada vez mais, e
um aspecto importante que essa ?rea vem pesquisando ? sobre as dificuldades
de aprendizagem dos alunos. A abordagem dos temas estrutura at?mica e
liga??es qu?micas s?o desenvolvidos no Ensino M?dio e apresentam muitos
problemas que, muitas vezes, s?o trazidos para o ensino superior se tornando
um obst?culo para o avan?o do aprendizado. ? necess?rio que esses temas
iniciais a estrutura at?mica e as liga??es qu?micas sejam bem
compreendidos pelo aluno para que os demais conte?dos de Qu?mica sejam
entendidos com mais facilidade. Neste trabalho tem-se como objetivo geral,
analisar os erros e as dificuldades apresentados nas avalia??es da disciplina
Arquitetura At?mica e Molecular, dos alunos do curso de gradua??o em Qu?mica
EAD, com rela??o ao conte?do de Estrutura At?mica e Liga??o Qu?mica ,
atrav?s das avalia??es realizadas pelos alunos e o Ambiente Virtual de
Aprendizagem (AVA), levando em considera??o as atividades realizadas,
discuss?o no f?rum e acesso aos materiais. O AVA permite a obten??o de
relat?rios os quais foram utilizados para analisar quanto ao acesso/participa??o
para avaliar sua contribui??o na aprendizagem e sua rela??o com o resultado
final (aprovado/reprovado). Foi poss?vel observar que os erros mais frequentes
nas avalia??es est?o relacionados ? parte inicial da qu?mica que ? a
compreens?o da estrutura at?mica e a evolu??o dos modelos. Os alunos que
acessaram o material extra e participaram das atividades e f?runs, foram os
alunos que obtiveram aprova??o na disciplina. Ou seja, as dificuldades iam
surgindo e ao utilizar as estrat?gias de ensino disponibilizadas, os alunos
conseguiam minimizar tais dificuldades, fazendo com que o seu desempenho
nas atividades e avalia??es fossem melhor. Tamb?m foi observado, atrav?s da
frequ?ncia ao AVA, que a disciplina come?ou com uma grande desist?ncia desde
o acesso ? p?gina como tamb?m ? frequ?ncia nas provas presenciais a partir da
observa??o na listagem de presen?a das avalia??es presenciais
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Modelos atômicos no início do século XX: da física clássica à introdução da teoria quânticaLopes, Cesar Valmor Machado 23 October 2009 (has links)
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Previous issue date: 2009-10-23 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The present research examines the history of atomic models in the early
twentieth century dealing with the contributions of Joseph John Thomson, Hantaro
Nagaoka, Ernest Rutherford, John William Nicholson and Niels Bohr and his
contemporaries. It emphasizes the explanations from the classical physics till the
introduction of the Quantum Theory.
This thesis presents an introduction and eight chapters. Chapter 1 presents
the investigations which took place before the proposition of the models pointed out in
the first paragraph. This chapter emphasizes the classical science, without diving into
the quantum explanations.
The next six chapters present a chronological sequence of biographies, ideas
and publications and discuss the atomic models proposed by the quoted scientists. The
publication of the papers on the quantized atom models had great impact and caused
many debates, which led us to produce a specific chapter dealing with such subject. .
In conclusion, the chapter eight presents some considerations about the
integration of the investigative trails that led to the publication of the atomic models
discussed, the work on investigative borders fields, the intricate dynamics of power
between fields, scientists and publications, and the assertion of new fields / Esta pesquisa analisa a história dos modelos atômicos no início do século XX
a partir das contribuições de Joseph John Thomson, Hantaro Nagaoka, Ernest
Rutherford, John William Nicholson e Niels Bohr e seus contemporâneos, enfatizando
as explicações desde a Física Clássica até a introdução da Teoria Quântica.
A tese apresenta uma introdução e oito capítulos. O primeiro capítulo procura
dar conta do estado da arte antes da proposição dos modelos discutidos. Neste
capítulo enfatizamos questões que se localizam no campo da ciência clássica, sem
mergulhar no campo da teoria quântica nascente.
Na continuidade, apresentamos seis capítulos, cronologicamente
organizados com uma breve biografia de cada um dos cientistas mencionados e o
detalhamento das idéias e dos episódios científicos que levaram às publicações que
apresentaram seus modelos pela primeira vez. A publicação dos modelos de átomo
quantizados teve grande impacto e suscitou muitos debates, o que nos levou a
produzir o capítulo sete tratando especificamente desses embates.
Para concluir no capítulo oito apresentamos algumas considerações sobre a
integração das diversas trilhas investigativas que levam à publicação dos modelos
atômicos discutidos; ao trabalho nas fronteiras de campos investigativos diversos; à
intrincada dinâmica de poder entre campos, cientistas e publicações; e à afirmação de
novos campos
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Estudo teórico das propriedades estruturais, eletrônicas e ópticas do tetraborato de lítio (Li2B4O7)Santos, Cledson dos 19 February 2014 (has links)
In present dissertation we studied theoretically the structural, electronic and optical properties of lithium tetraborate, Li2B4O7, an important material, frequently used as detector of radiation and neutrons. As a calculation tool we utilized first-principles Linear Augmented Plane Wave (LAPW) method, based on Density Functional Theory and implemented into WIEN2k computer code. Exchange and correlation effects within the electronic system were simulated by recently developed |Modified Becke Johnson| (mBJ) semi-local potential. The lattice parameters and atomic positions within the Li2B4O7 unit cell were computationally relaxed, and the resulting structure was found to agree well with the experimental one. Calculated electronic structure (band structure and density of states DOS) revealed the nature and magnitude of the band gap (indirect, 9,2 eV), as well as the orbital character of the bands around it. The valence band top consists predominantly of oxygen´s p-states, while the conduction band bottom is dominated by the p-states of boron which is trigonally coordinated with its neighboring oxygens (B(1)). The energies of principal peaks in the valence band DOS, as well as the calculated magnitude of the gap, are found to agree very well with experimental findings. Next, we calculated real and imaginary part of dielectric tensor of the Li2B4O7, as well as its refractive index. Analysis of imaginary part of dielectric tensor permitted us to interpret the optical absorption spectrum of the Li2B4O7 in terms of electronic transitions that occur between populated and empty electron states. The results revealed that absorption threshold starts at 9,2 eV approximately, and that the first absorption peak originates from electron transfer from the full O p-states to the empty B p-states within the trigonal, B(1)O3, structural motif. Refractive index is calculated for two directions of polarizations of incident light, parallel to the crystallographic axes a and c. It was concluded that the Li2B4O7 is optically anisotropic material. Calculated refractive indexes were compared to experimental ones, recorded in the wavelength range from 184 to 2325 nm, and it was found a good agreement between them. On the basis of present study we conclude that computationally efficient semi-local mBJ potential accurately describes the electronic and optical properties of the Li2B4O7. / No presente trabalho foram estudadas as propriedades estruturais, eletrônicas e ópticas do tetraborato de lítio, Li2B4O7, um material importante, frequentemente usado como detector de radiação e de nêutrons. Como ferramenta de cálculo foi utilizado o método ab-initio Linear Augmented Plane Wave (LAPW) baseado na Teoria do Funcional da Densidade (DFT) e implementado no código computacional Wien2k. Os efeitos de correlação e troca do sistema eletrônico foram simulados através de um potencial semi-local, Modified Becke Johnson mBJ, recentemente desenvolvido. Os parâmetros de rede e todas as posições atômicas na célula unitária cristalina do Li2B4O7 foram otimizados, a fim de atingir uma configuração de mínima energia para o sistema. Os resultados obtidos, referentes ao volume da célula unitária e das posições atômicas, mostraram boa concordância quando comparados com medidas experimentais. O cálculo da estrutura eletrônica (estrutura de bandas e densidade de estados - DOS) revelou a natureza e o tamanho do band gap fundamental do composto, bem como o caráter orbital das bandas por sua volta. De acordo com os resultados, o Li2B4O7 possui gap fundamental indireto de 9,2 eV. No topo da banda de valência predominam orbitais do tipo p dos átomos de oxigênio, enquanto que o fundo da banda de condução é formado, em sua maioria, por estados p referentes aos átomos de boro, B(1). As posições dos picos da DOS na banda de valência, assim como o valor calculado do gap, concordam muito bem com resultados experimentais. Neste trabalho também foram calculadas as partes real e imaginária do tensor dielétrico do Li2B4O7, bem como o seu índice de refração. A análise da parte imaginária do tensor dielétrico possibilitou a interpretação, em termos das transições eletrônicas, do espectro de absorção óptica do Li2B4O7. Os resultados revelaram que a borda de absorção se encontra perto da energia de 9,2 eV, e que o primeiro pico é devido às transições eletrônicas entre estados p dos átomos de oxigênio para estados P dos átomos de boro, as quais ocorrem dentro do grupo trigonal, B(1)O3. O índice de refração foi calculado para as duas direções de polarização da luz, paralelas aos eixos cristalinos a e c. De acordo com esses resultados, o Li2B4O7 é um material opticamente anisotrópico. O índice de refração calculado concorda bem com o experimental, medido em uma faixa de comprimentos de onda de 184 a 2325 nm. Na essência do presente estudo é possível concluir que o potencial mBJ, computacionalmente eficiente, descreve precisamente as propriedades eletrônicas e ópticas do Li2B4O7.
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La protéine M2-1 du virus respiratoire syncytial : structure et interactions avec des partenaires viraux et cellulaires / Respiratory Syncytial Virus M2-1 protein : structure and interactions with viral and/or cellular partnersRichard, Charles-Adrien 15 June 2017 (has links)
Le Virus Respiratoire Syncytial (VRS) est le principal agent responsable d’infections respiratoires sévères chez les nourrissons et les veaux. Le génome du VRS est constitué d’un ARN simple brin de polarité négative qui est répliqué et transcrit par le complexe ARN-polymérase viral (RdRp). Ce complexe est composé de la nucléoprotéine N, de la polymérase L, de la phosphoprotéine P et du facteur anti-terminateur de transcription M2-1. Le but de ce travail était de mieux caractériser la structure et le fonctionnement de deux protéines du complexe RdRp: P et M2-1.M2-1 est un tétramère constitué de 4 domaines : un « doigt de zinc », un domaine d’oligomérisation hélicoïdal, une région flexible, un domaine globulaire interagissant avec l'ARN et P, et une région C-terminale désordonnée. À partir de la structure cristalline de M2-1 pleine longueur, j'ai identifié des résidus critiques sur le doigt de zinc et la région flexible pour l'activité d'anti-terminaison de transcription de M2-1.Par la suite j'ai identifié une région de P critique pour l’interaction P - M2-1 et montre qu’elle est nécessaire au recrutement de M2-1 dans des corps d’inclusion cytoplasmiques. Je montre également que la déphosphorylation de M2-1, nécessaire à la transcription virale, est modulée par un complexe formé entre P et la phosphatase cellulaire PP1.Enfin, la cyclopamine, composé chimique naturel, inhibe la réplication du VRS. Je démontre qu'une seule mutation R151K sur M2-1 est suffisante pour conférer une résistance virale à la cyclopamine. Ces données ouvrent de nouvelles perspectives pour le développement de futures thérapies contre le VRS. / Respiratory syncytial virus (RSV) is the leading cause of lower respiratory tract illness in infants and calves. The RSV genome consists of a single strand, negative-sense RNA, which is replicated and transcribed by the viral RNA-dependent RNA polymerase complex (RdRp). This complex is composed of the nucleoprotein N, the large protein L, the phosphoprotein P and the transcription anti-terminator M2-1. The aim of this work was to better characterize the structure and function of P and M2-1.M2-1 is a tetramer with 4 domains: a zinc-finger, a helical oligomerization domain, a flexible region, a RNA and P binding core domain and a C-terminal disordered region. Based on the crystal structure of the full-length M2-1 protein, I identified residues in the zinc-finger and the flexible loop critical for M2-1 antitermination activity.Then I identified a region of P critical for P – M2-1 interaction and show that it is required for the recruitment of M2-1 to cytoplasmic inclusion bodies. I also show that M2-1 dephosphorylation, which is critical for viral transcription, is modulated by a complex formed by P and the cellular phosphatase protein-1 (PP1).Finally cyclopamine, a natural chemical compound, inhibits the RSV replication. I show that a single R151K mutation in M2-1 is sufficient to confer virus resistance to cyclopamine. These data open a new avenue for the development of future therapies against RSV infection.
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A Homologous Study of Lifetimes and Oscillator Strengths of Ultraviolet Transitions in Singly Ionized Lead, Tin, and GermaniumHeidarian, Negar January 2017 (has links)
No description available.
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Atomic scale simulations in zirconia : Effect of yttria doping and environment on stability of phases / Modélisation atomistique dans la zircone : Rôle du dopage par l'yttrium et de l'environnement sur la stabilité des différences phasesGebresilassie, Abel Gebreegziabher 29 April 2016 (has links)
Ce travail de thèse est une étude par des méthodes de simulation de structure électronique du phénomène de dégradation en milieu aqueux de la zircone yttriée. La zircone yttriée est notamment utilisée pour la fabrication de prothèses dont la durée de vie dépend du matériau et de son environnement. Pour ces applications, la zircone yttriée est de structure tétragone, mais en fonction du dopage en yttrium et de l'environnement, cette phase est en compétition avec des structures monoclinique et cubique. Cette compétition est cruciale dans ce travail car elle peut à la fois, augmenter la résistance, ou favoriser la détérioration de ce matériau. L'étude réalisée se concentre sur des taux de dopage inférieurs à 20% mol. en oxyde d'yttrium Y2O3.Dans un premier temps, les structures atomiques d'équilibre à basse température ont été déterminées dans les trois phases en utilisant une méthode de calcul basée sur la Théorie de la Fonctionnelle de la Densité, dans l'approximation de la densité locale. Les résultats incluent de nouvelles structures qui n'ont jusqu'alors pas été discutées dans la littérature et qui sont cohérentes avec le diagramme de phase de la zircone yttriée à basse température. Une analyse plus détaillée suggère que le mécanisme de stabilisation de la zircone yttriée tetragonale est un effet du dépistage ionocovalent particulièrement efficace dans cette phase et dont la signature dans la structure s'exprime par la présence d'ions zirconium en coordination 7. Ceci représente un point important permettant de lier stabilité et structure dans ces systèmes. Une deuxième partie de ce travail est consacrée à l’effet de l'eau dans la zircone yttriée en volume. Pour conclure, ce manuscrit représente une contribution originale à la compréhension de mécanismes à l'échelle atomique qui sont à l'origine des propriétés de la zircone yttriée et de ses applications.yttriée et de ses applications. / This PhD thesis is an electronic structure simulation work to study the stabilization mechanism of yttria stabilized zirconia (YSZ) and the phenomena of the degradation of YSZ due to the presence of an aqueous media. YSZ is used especially in dental and orthopedics application sbut its service depends on the environment. For these biomedical applications a crystallographic tetragonal YSZ (t-YSZ) structure is used, but depending on the concentration of yttria (Y2O3) and the environment, this tetragonal structure is thermodynamically in competition with a monoclinic and cubic phases. This competition is crucial in this work, because it has both effects : increase the resistance or promote the degradation of this material. The study is conducted for Y2O3 concentrations less than 20% mol. First, atomic structures of the three phases at low temperature were determined using density functional theory (DFT)with the local density approximations (LDA). The results include new structures that were not discussed in the literature and which are consistent with the phase diagram of YSZ at low temperature. A more detailed analysis suggests that the stabilization mechanism in YSZ is due to an effective ionocovalent screening : particularly in t-YSZ phase, its signature is expressed in Zr-ions with a coordination number of 7. This represents an important point for linking stability and structure in these systems. A second part of this work is devoted to the effect of water on YSZ bulk systems which leads to low temperature degradation (LTD) of YSZ based bioceramics materials. In conclusion, this PhD thesis represents an original contribution to the understanding of the mechanism and properties of YSZ and its applications at the atomic scale.
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Surfaces d'alliages métalliques complexes : structure, propriétés et nanostructuration / Complexe metallic alloys surfaces : structure, properties and nanostructurationAddou, Rafik 29 March 2010 (has links)
Ce travail a permis de déterminer les structures atomique et électronique de deux surfaces d'alliages métalliques complexes à l'aide d'une approche multi-techniques supportée par des calculs ab intio de structure électronique. Les surfaces de ces cristaux ont pu être corrélées à certains plans présents dans les modèles structuraux disponibles. La terminaison dominante de la surface (100) d'Al13Co4 est identifiée comme un plan corrugué incomplet du volume. La surface (010) de Al3(Mn, Pd) présente un nombre conséquent d'imperfections structurales. À l'exception de certains sites lacunaires, elle est identique au plan corrugué complet du massif. Dans une seconde étape, ces échantillons ont été utilisés comme substrat pour la croissance de films minces métalliques. Les atomes de Pb déposés sur ces deux surfaces suivent un mode de croissance pseudomorphique jusqu'à la formation de la monocouche. Dans le cas de l'Al13Co4, le coefficient de collage du Pb s'annule une fois cette monocouche formée. Sur la surface Al3(Mn, Pd), le croissance de couches additionnelles de Pb est observée. L'adsorption du Cu sur Al13Co4 mène de nouveau à un mode de croissance pseudomorphique jusqu'à la monocouche. Au-delà de ce dépôt, la phase ß-Al(Cu, Co) apparaît en surface. Pour des dépôts à des températures plus élevées, la phase- ß est suivie par la formation de la phase ?-Al4Cu9. Les phases ß et ? croissent suivant deux domaines (110) orientés l'un par rapport à l'autre avec un angle de 72° / We report the investigation of pseudo-ten-fold surfaces on two complex metallic alloys considered as approximants to the decagonal quasicristal. The atomic and electronic structure of the both samples is investigated by means of a multi-technique approach supported by ab initio electronic structure calculations. The main termination of the (100) surface of Al13Co4 is attributed to an incomplete puckered layer. The (010) surface of Al3(Mn, Pd) exhibits an important amount of structural imperfections. With the exception of several vacancies, this surface is identical to the complete puckered layer. In a second stage, both surfaces have been used as templates for the growth of metallic thin films. On both surfaces, Pb adatoms adopt a pseudomorphic growth mode up to one monolayer. For the Al13Co4 surface, the sticking coefficient of Pb vanishes upon the completion of the monolayer. However, it remains sufficient for the growth of additional layers on the Al3(Mn, Pd) (010) surface. The adsorption of Cu on the Al13Co4 surface follows also a pseudomorphic growth mode up to one monolayer. The ß-Al(Cu, Co) phase appears for coverages greater than one monolayer. For higher temperature deposition, the ß-phase is followed by the formation of the ?-Al4Cu9 phase. Both ß and ? phases grow as two (110) domains rotated by 72° from each other
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