Abstract SrTiO3 is cubic at room temperature, and retains cubic until the phase transition to tetragonal at 105K (-168oC). It is a wide-band-gap semiconductor having an energy gap Eg ≈ 3.0 eV, when its semiconductivity is greatly improved by doping with donor oxides, e.g.Nb2O5 or heat treatment in low oxygen partial pressures (Po2). Donor oxides in solid solution with SrTiO3 forming substitutional defects create electron or cation vacancies as the principal charge compensation defect. In-gap levels are also modified by the oxygen partial pressure (Po2) adopted in sintering, which generates oxygen vacancies in order to maintain the overall charge neutrality in the ceramic. In this research, donor-doping and Po2 used in sintering are investigated for the in-gap-level modification using the cathodoluminescence (CL) spectrometry equipped with a scanning electron microscope (SEM). Other analytical techniques, e.g. transmission electron microscopy (TEM) will be used for characterizing the defect structure. Preliminary results suggest that the in-gap levels are registered at 3.10 eV and 2.69 eV, representing the intrinsic Eg and a donor-level created by oxygen vacancies, respectively.

A growing body of literature has provided evidence of the contribution of various metalinguistic skills to children's English literacy development; however, most of the studies focused on reading outcomes while spelling outcomes have been under-researched. Further, very few studies have been conducted to investigate if the results based on native English speakers can be generalized to speakers of other languages who are learning to read and spell in English. In this study, the simultaneous influence of phonological, morphological and orthographic knowledge that may impact English spelling acquisition, among Chinese students learning English as a foreign language in Grade 8 (n = 339) in mainland China and native English-speaking students in Grade 3 (n = 166) in the United States, was investigated. Measures in English tapping into the three aspects of metalinguistic skills—phonological awareness (PA), morphological awareness (MA) and orthographic awareness (OA)—were administered to both groups. Multi-group structural equation models were used to compare models between the Chinese and the American group. Results showed that 1) the overall model of metalinguistic skills predicting spelling outcome was highly similar between the American and the Chinese groups; 2) metalinguistic skills were correlated and worked in concert to compose the linguistic repertoire construct which concurrently predicted the spelling outcome; 3) MA was the major component, compared to PA and OA, of Linguistic Repertoire (LING) across the two groups. Linguistic repertoire explained 64.1 percent and 40.2 percent of the total variance in the spelling outcome for the American and the Chinese groups, respectively; and 4) the contribution of OA was greater in the Chinese group than it was in the American group, whereas the contribution of PA was greater in the American group than it was in the Chinese group. This study highlights the important contribution of MA to literacy development among both the American students and the Chinese students. It also sheds light on the influence of first language (L1) orthography on English literacy acquisition. That OA contributed more than PA to the LING construct may reflect that the English learners with L1-Chinese background have enhanced visual-orthographic processing skills. This study challenges phase models of literacy development that claim MA only contributes to literacy acquisition late in the process and offers some empirical evidence to support the emerging "linguistic repertoire" theory of literacy development.

1.Sn/Ag4.0/Cu0.5 solder with better performance by the improved reflow profile. 2.The Sn/Ag2.6/Cu0.6¡BSn/Ag4.0/Cu0.5 with similar reliability test performance.

Research concerning the formation and removal of black crusts on various historical objects is approached from many different angles. The so-called “yellowing effect”, observed after laser treatment for cleaning purposes, has also received a lot of attention. Evidence regarding this phenomenon differs considerably and the actual mechanisms are still speculated on by researchers. In an attempt to elucidate the processes involved in the yellowing effect associated with laser cleaning, a new analytical technique has been used to investigate the black crust, a region of the sample cleaned by laser irradiation at 1064 nm and another region of the same sample subjected to further laser irradiation at 355 nm, on a limestone sample from the cathedral of Seville in Spain. Micro-Raman spectrometry offers the advantage of spatial chemical characterization of the stone, based upon its molecular makeup and was performed on the bulk body of the stone. Raman and scanning electron microscopy/energy dispersive X-ray spectrometry (SEM/EDXS) results indicate that the surfaces cleaned by irradiation at 1064 nm and by double irradiation at 1064 and 355 nm differed in terms of their calcium sulphate, calcium oxalate and iron oxide content, and that this could contribute to the difference in colour observed.

WhisperGenTM heater head components are currently machined from the austenitic stainless steel Sandvik 253MA. The inner surface of the heater heads is subjected to the working gas of the engine, which is a high-pressure, high-temperature nitrogen-based environment with carbonaceous impurities. As a result of this exposure, a scale forms during operation and eventually spalls. This spalled scale causes abrasive damage to piston seals and guides, which leads to pressure loss and eventual failure of the engine. The aim of the present work was to compare the performance of the austenitic alloy 253MA with two alternative alloys, Incoloy 800H and AISI 310, thereby enabling a material recommendation. A literature review provided information about many general aspects of high temperature corrosion in similar alloys. However, little was found about the application of these alloys in environments similar to those experienced by a WhisperGenTM heater head. Therefore, laboratory experiments were conducted to indicate the relative performance characteristics of the three potential alloys (253MA, Incoloy 800H and AISI 310). To overcome the difficulties with testing at high temperatures and pressures, Thermo-Calc™ was used to calculate gas mixtures at 1 bar that approximated the chemical potentials of carbon and nitrogen in the working gas at 24 bar. Comparisons of the different materials were made via weight loss/gain measurements and metallographic analysis, which included optical microscopy, scanning electron microscopy, X-ray mapping and electron back scatter diffraction (EBSD). The laboratory test sample results were also compared with results from heater heads of the same materials that were run in an actual WhisperGenTM engine. The experimental results taken in total indicate that 253MA is the least suitable alloy for the heater head application because it exhibited poor spalling performance, internal oxidation and formation of a large amount of Cr23C6. AISI 310 was shown in all cases to develop the detrimental sigma phase, although this alloy was the least susceptible to internal oxidation. Incoloy 800H was the most resistant alloy to all forms of degradation and is thus recommended for the heater head application.

A new β and <I>N</I>-substituted pyrrole, <I>N</I>-trimethylsilylethoxymethyl-3-methyl-4-pyrrole carboxylate ethyl ester (MPCE-SEM) is synthesised and copolymerised electrochemically with unsubstituted pyrrole to gives free-standing films for conductivity measurements. The electrochemical polymerisation of MPCE-SEM gives only soluble dimers and oligomers rather than polymers because the steric constraints stabilise the oligomeric cation radical of MPCE-SEM. The thiophene monomers containing mesogenic group at the 3-position via an alkyl chain are synthesised and polymerised chemically to give insoluble, infusible polymers and do not exhibit liquid crystalline behaviour. The conductivities of pressed-pellets of the polymer powders are lower than 10<SUP>-5</SUP>S/cm. The electrochemical polymerisation of the thiophene monomers containing mesogenic group of 4-methoxyazbenzen-4'-yloxy or 4-butylazobenzen-4'-yloxy in dichloromethane solution gives a low yield of polymers, which is accompanied by the formation of soluble dimers and oligomers as well as degradation of the resulting polymer and the mesogenic group. Poly{<I>N </I>-11-[(4-cyanobiphenyl-4'-yloxy) undecyl] pyrrole} obtained from chemical polymerisation of the corresponding monomer shows high molecule weight, is soluble in common solvents and fusible showing smectic A liquid crystalline behaviour. This polymer in the melt (175<SUP>o</SUP>C) has a conductivity of 6.6 x 10<SUP>-15 </SUP>S/cm. X-ray photoelectron spectrometry analysis on the melt processed film gives an estimated doping level of an anion every 6-7 monomer units. Electrochemical oxidation of the <I>N</I>-substituted pyrrole monomers gives the electroactive conjugated free-standing polymer films. The conductivities of the free standing polymer films are lower than 10<SUP>-4</SUP> S/cm. A conducting copolymer containing a side chain liquid crystalline group, poly{<I>N</I>-8-[(4-cyanobiphenyl-4'-yloxy)octyl]-2,5-di(2-thienyl) pyrrole} can be obtained electrochemically from the corresponding monomer. The polymer is slightly soluble in chloroform giving a dark green solution but is not liquid crystalline.

O presente trabalho tem como objetivo a descrição e apresentação dos resultados obtidos através de simulações e implementação da técnica de modulação por espalhamento de espectro (Spread Spectrum). Maior ênfase será dada à técnica de espalhamento por seqüência direta (DSSS), dada a larga utilização nos sistemas de comunicação correntemente em uso, assim como serão apresentados os resultados de simulações e implementação de um sistema de comunicação Spread Spectrum utilizando o microcontrolador PIC 16F876 para a interligação de computadores padrão PC via interface serial RS232.

Submitted by Reginaldo Soares de Freitas (reginaldo.freitas@ufv.br) on 2017-04-17T13:19:58Z No. of bitstreams: 1 texto completo.pdf: 23689415 bytes, checksum: 20395ffc8aa03a902210747a173ddd59 (MD5) / Made available in DSpace on 2017-04-17T13:19:58Z (GMT). No. of bitstreams: 1 texto completo.pdf: 23689415 bytes, checksum: 20395ffc8aa03a902210747a173ddd59 (MD5) Previous issue date: 2005-07-01 / Conselho Nacional de Desenvolvimento Científico e Tecnológico / Poucos estudos enfatizam os sistemas reprodutores em insetos. Isto resulta em uma carência de informações que possibilitariam estabelecer padrões e relações entre os grupos. Os caracteres morfológicos do sistema reprodutor interno em machos se mostram promissores para estudos taxonômicos e filogenéticos. Além disso, apesar dos Meliponini serem bastante estudados, algumas questões, como as conseqüências da ausência das glândulas acessórias no trato reprodutivo masculino, precisam ser esclarecidas. Nesta tese, descrevemos aspectos estruturais e ultra-estruturais do epitélio dos ductos deferentes de Scaptotrigona xanthotricha a fim de identificarmos as principais modificações morfofisiológicas ocorridas nestes ductos durante o processo de maturação sexual dos machos. Para isto, utilizamos técnicas de microscopia de luz e microscopia de eletrônica de transmissão. Os resultados contribuíram para discussão de importantes questões sobre a biologia reprodutiva dos Meliponini, como a formação das espermátides atípicas e a compensação fisiológica da ausência das glândulas acessórias. / Few studies emphasize the reproductive systems in insects. This results in an carência of information that could make possible the establishment of patterns and relationships between groups. The morphological characters of the internal reproductive systems in males are promising to taxonomic and phylogenetic studies. Besides, although the Meliponini be a lot studied, some questions stay without answer as the absence of accessory glands in the male reproductive system. In this work we described the structural and ultrastructural features of the epithelium of the deferents ducts of Scaptotrigona xanthotricha in order to understand the main morphological modifications of the deferent ducts during the process of sexual maturation. For this we used techniques of light and electron transmission microscopy. The results contributed to the discussion of important questions about the reproductive biology of Meliponini, like the formation of atypical spermatides and the compensação fisiológica da ausência das glândulas acessórias.

This study is dedicated to the implementing of Electron-Beam-Induced Current (EBIC) microscopy to study the behavior of metal oxide semiconducting (MOS) nanowire (NW) gas sensor in situ under exposure to different environment. First, we reported the development of a single nanowire gas sensor compatible with an environmental cell. The major component of the device we use in this study is a single SnO2 nanowire attached to an electron transparent SiN membrane (50-100 nm thick), which was used for mounting nanowire working electrodes and surface imaging of NW. First the NW's conductivity is investigated in different temperatures. Higher temperature is proved to cause higher conductivity of NW. We also found that often the Schottky barrier is formed at the nanowire's contacts with Au and Au/Cr electrodes. Then NW's responses to gas and electron beam (from SEM) are analyzed quantitatively by current measurement. Electron-Beam-Induced Current technique was introduced for the first time to characterize the conductivity behavior of the nanowire during the gas sensing process. Resistive contrast was observed in the EBIC image.

FARIAS, E. J. P. Análise de sistemas OFDM cooperativos AF com amplificadores de potência não lineares. 2013. 95 f. Dissertação (Mestrado em Engenharia de Teleinformática) - Centro de Tecnologia, Universidade Federal do Ceará, Fortaleza, 2013. / Submitted by Marlene Sousa (mmarlene@ufc.br) on 2013-09-16T16:47:09Z No. of bitstreams: 1 2013_dis_ejpfarias.pdf: 1313258 bytes, checksum: f89c7413485adac95c363a188108be68 (MD5) / Approved for entry into archive by Marlene Sousa(mmarlene@ufc.br) on 2013-09-16T16:57:40Z (GMT) No. of bitstreams: 1 2013_dis_ejpfarias.pdf: 1313258 bytes, checksum: f89c7413485adac95c363a188108be68 (MD5) / Made available in DSpace on 2013-09-16T16:57:40Z (GMT). No. of bitstreams: 1 2013_dis_ejpfarias.pdf: 1313258 bytes, checksum: f89c7413485adac95c363a188108be68 (MD5) Previous issue date: 2013-07 / Cooperation diversity and orthogonal frequency division multiplexing (OFDM) are two key technologies for the modern wireless communication systems. The cooperative communication systems considered through this work use the OFDM technology and they are composed of: one transmitter with a nonlinear power amplifier (PA), one or more amplify-and-forward (AF) relays, also having a nonlinear PAs, and one destination node. In this dissertaion, it is initially proposed an optimal receiver, in the signal to noise ratio (SNR) sense, for a nonlinear cooperative AF system. The proposed receiver uses the maximum ratio combining (MRC) diversity technique to combine the received signas, assuming that both the source-destination and source-relay-destination links are available. In the sequel, closed-form expressions for the instantaneous SNR and outage probability of the considered system are developed. The outage analysis is then extended to the case of a multi-hop system, that is, with multiple serial relays. Finally, an outage analysis is also proposed for a nonlinear AF OFDM system using a Selection Combining receiver, considering two cases: one relay and multiple parallel relays. Numerical simulation results are presented through the work, evaluating the performance of the proposed receiver and theoretical expressions. / A diversidade cooperativa e a multiplexação por divisão de frequências ortogonais (Orthogonal Frequency Division Multiplexing - OFDM) são duas das principais tecnologias para os sistemas de comunicação sem fio modernos. Os sistemas de comunicação cooperativos considerados neste trabalho de dissertação utilizam a tecnologia OFDM e possuem: uma fonte com amplificador de potência não linear, um ou mais repetidores (relays) do tipo amplifica-e-encaminha (Amplify-and-Forward - AF), também com amplificadores de potência (Power Amplifier - PA) não lineares, e um nó destino. Propõe-se inicialmente um receptor ótimo, no sentido da razão sinal ruído (Signal-to-Noise Ratio - SNR) para um sistema OFDM cooperativo não linear. Usando a técnica de diversidade por combinação de razão máxima (Maximal Ratio Combining - MRC) para tratar os sinais recebidos, o receptor proposto considera tanto as informações oriundas do caminho direto (fonte-destino) como as provenientes do repetidor. Posteriormente, são apresentadas expressões para o cálculo da SNR instantânea e da probabilidade de outage do sistema proposto. Fez-se ainda, uma proposta de expressão para o cálculo da probabilidade de outage do sistema considerando múltiplos relays em série. Por fim, propõe-se expressões para o cálculo da probabilidade de outage do sistema utilizando receptor Selection Combining para um e para múltiplos relays dispostos paralelamente. Resultados de simulação são apresentados durante todo o trabalho, evidenciando o desempenho do receptor e das expressões propostas.