An AM1 semiempirical study of the mechanism of sintering for ZnO in the presence of water and carbon dioxide

AM1 calculations were performed for the absorption of H2O and CO2 molecules on the surface of model ZnO crystals. The absorption of isolated molecules of each species and the co-absorption of both compounds simultaneously were considered. It was found that the absorption of H2O near a site where CO; is already absorbed favors the process of sintering, in agreement with the experimental findings. This is explained by the formation of Zn(OH)CO3H bound to the surface, a more mobile species than the ZnO unit itself. The roundening of the grains observed in atmospheres containing dry CO2 but suppressed when H2O is present, is also explained by these calculations. After absorption of CO2, the rupture of one bond - so that diffusion of the ZnCO3 species on the surface is allowed - requires much less energy than the breaking of two bonds, necessary for ZnO migration. These facts explain why the speed of surface transport does not decrease in CO2 atmospheres while sintering is indeed slowed down. © 1994.

Crystal, Molecular, and Electronic Structure of 1-Acetyl-indoline and Derivatives

The crystal and molecular structures of the following molecules have been determined: 1-acetyl-indoline, 1-acetyl-5-nitro-indoline, 1-acetyl-5-nitro-7-bromo-indoline, 1-acetyl-5-bromo-7-nitro-indoline, and 1-acetyl-5-bromo-7-nitro-indol. Molecular orbital calculations are performed for these compounds and two related species.

Comparative study on turning CI and CGI using silicon nitride cutting tools

There has been a great interest for improving the machining of cast iron materials in the automotive and other industries. Comparative studies for tool used to machine grey cast iron (CI) and compacted graphite iron (CGI) on dry machining were also performed in order to find out why in this case the tool lifetime is not significantly higher. However the machining these materials while considering turning with the traditional high-speed steel and carbide cutting tools present any disadvantages. One of these disadvantages is that all the traditional machining processes involve the cooling fluid to remove the heat generated on workpiece due to friction during cutting. This paper present a new generation of ceramic cutting tool exhibiting improved properties and important advances in machining CI and CGI. The tool performance was analyzed in function of flank wear, temperature and roughness, while can be observed that main effects were found for tool wear, were abrasion to CI and inter-diffusion of constituting elements between tool and CGI, causing crater. However the difference in tool lifetime can be explained by the formation of a MnS layer on the tool surface in the case of grey CI. This layer is missing in the case of CGI.

Propriedades estruturais e ópticas de filmes finos a-C:H:CI obtidos por deposição à vapor químico assistido por plasma e deposição e implantação iônica por imersão em plasma

Pós-graduação em Ciência e Tecnologia de Materiais - FC

Migração de K+, Cu2+ e CI- em solos do subgrupo Itararé no Estado de São Paulo: ensaios sorcivos, percolação em colunas e simulações geoquímicas

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Investigação da transição isolante-metal do CDM via algoritmos computacionais e estudo de nano-dispositivos orgânicos

Apresentamos neste trabalho um estudo teórico sobre polímeros orgânicos conjugados. É conhecido que estes sistemas, em geral semicondutores ou isolantes, sob dopagem química podem vir a adquirir propriedades elétricas de material condutor. E ainda, sob ação de campo elétrico, pequenos oligômeros podem apresentar comportamento equivalente ao de dispositivos usuais, mas com inúmeras vantagens como, por exemplo, tamanho extremamente reduzido (alguns nanômetros). Dessa forma no primeiro capítulo faremos uma breve introdução sobre polímeros orgânicos conjugados mostrando alguns resultados experimentais obtidos para o polímero 4-dicianometileno-4,4-ciclopenta [2,1-b: 3,4b’] ditiofeno – CDM, que é o objeto central de estudo desta dissertação. O capítulo 2 trata dos métodos quânticos utilizados. Citaremos a Teoria de Hartre-Fock (HF) e suas derivações semi-empíricas. A técnica de Interação de configuração (CI) e a Teoria do Funcional da Densidade (DFT) também serão tratadas neste capítulo. O capítulo 3 é dedicado a descrever as características de alguns dispositivos usuais como diodos e transistores. Aqui o fundamental é entender a composição, o funcionamento e principalmente, como se comportam suas curvas características corrente versus voltagem (IxV). Citaremos ainda alguns dispositivos eletrônicos extremamente pequenos. No capítulo 4 começa nossos resultados e discussões referentes a análise da transição isolante-metal em CDM sob ação de dopagem. Primeiramente a nível semiempírico, obtivemos a caracterização ótica de oligômeros de CDM neutro e na presença de defeitos conformacionais do tipo bipólarons negativo e positivo. Partindo de geometrias otimizadas via métodos AM1 e PM3 obtivemos o espectro de absorção para sistemas com e sem carga. A nível Hartree-Fock calculamos a Estrutura de Bandas e a Densidade de Estados (DOS) para o PCDM no estado neutro e dopado. O cálculo da DOS e da Dispersão foram realizados através de programas computacionais desenvolvidos aqui no Grupo de Física de Materiais da Amazônia (GFMA). Apresentamos ainda neste capítulo o espectro de absorção teórico para oligômeros de CDM com diversas configurações com geometrias totalmente otimizadas pelo DFT. No capítulo 5 temos os resultados relativos à análise de nanodispositivos baseados em tetrâmeros de CDM com e sem carga. As curvas do deslocamento de carga versus voltagem apresentam características de curvas de dispositivos usuais. Analisamos também o espectro de absorção teórico dos nanodispositivos para valores de tensão nula e em pontos de saturação de corrente nas regiões direta e reversa.

Habilidades informacionais abordadas em instrumentos de avaliação de CI

Internationally there are validated instruments that are used on a large scale to verify the information literacy of individuals in different contexts. Their results serve as a diagnostic for the planning and implementation of information literacy activities. In Brazil there is no validated assessment tools of information literacy. An analysis of contents of four international instruments attached to the upper level educational institutions duly recognized in the literature of the field and validated. The results will be presented related to information literacy addressed in these instruments. It was found that the instruments analyzed the skills focused on the identification of terms of the informational needs, the preparation and construction of search strategies available in parameter two of the Association of College and Research Libraries; differentiation of information sources (parameter one); evaluation and selection of informational sources and selection of the theme searched information (parameter three); and, finally, the abilities of the ethical issue related to use of the information (parameter five). The parameter four, which is facing the communication of information, was not addressed by the instruments. It was concluded that there is a concern of those responsible for preparing the instruments covered with more traditional technical aspects of training users and aspects of information literacy at the expense of ethical and aesthetic aspects.

AM1 and PM3 Calculations of the Potential Energy Surfaces for CH2OH Reactions with NO and NO2

The AM1 and PM3 molecular orbital methods have been utilized to investigate the reactions of CH20H with NO and NO2 PM3 and AM1 calculated heats of formation differ from experimental values by 8.6 and 18.8 kcal mol-', respectively. The dominant reaction of CH20H with NO is predicted to produce the adduct HOCH2N0, supporting the hypothesis of Pagsberg, Munk, Anastasi, and Simpson. Calculated activation energies for the NO2 system predict the formation of the adducts HOCH2N02 and HOCH20N0. In addition, the PM3 calculations predict that the abstraction reaction producing CH20 and HN02 is more likely than one producing CH20 and HONO from reactions of CH20H with NO2.

Wieczna kobiecość i emancypacja kobiet: obraz kobiecości w twórczości Karoliny Světlej

To nie przypadek, że wyrażenie „wieczna kobiecość" ukute przez Goethego zbiega się w czasie z pierwszymi zachodnimi próbami emancypacji kobiet. W chwili, kiedy model kobiety istniejącej tylko w zależności od mężczyzny zaczyna być kwestionowany, kategoria wiecznej kobiecości pozwala ponownie potwierdzić ten model, wypełniając go pozytywnymi wartościami. Naturą kobiety jest być uległą i oddaną, a te cechy sprawiają, że kobieta jest depozytariuszem wszelkiej potencjalnej zbawczej łaski. Tak w Fauście Goethego, przypada Małgorzacie, dziewczynie naiwniej, niewinnej, niewykształconej i bez własnej woli, wykupić Fausta siłą swojej miłości. Wszystko dzieje się tak, jakby pozytywna kodyfikacja właściwości kobiet dzięki kategorii wiecznej kobiecości służyła tylko lepszemu ukryciu rzeczywistości ich ucisku; feministki jednak nie dają się zwieść: ideały popierane przez kategorię wiecznej kobiecości są a priori niezgodne z emancypacją kobiet. Karolina Světlá, jedna z najważniejszych postaci w walce o zrównanie praw między mężczyznami i kobietami w Czechach w XIX wieku, wykorzystywała przecież intensywnie w swojej literackiej twórczości ten model kobiety, która poświęca się dla kochanego mężczyzny i tym samym udaje się jej go "podciągnąć do góry" ("hinan zu ziehen", Goethe) oraz dać mu dostęp do "nieskończoności", "nieśmiertelności" i "wieczności". Czy jej teoretyczne pisma i jej działalność na rzecz emancypacji kobiet zaprzeczałyby jej tekstom literackim, na pierwszy rzut oka tak konwencjonalnym? W tym wykładzie podejmuję próbę odpowiedzi na to pytanie uważną lekturą jednego z jej najbardziej faustowskich opowiadań, mianowice "Czarna dziewanna".