Er : YAB nanoparticles and vitreous thin films by the polymeric precursor method

The synthesis of Y(0.9)Er(0.1)Al(3)(BO(3))(4) crystalline powders and vitreous thin films were studied. Precursor solutions were obtained using a modified polymeric precursor method using D-sorbitol as complexant agent. The chemical reactions were described. Y(0.)9Er(0.1)Al(3)(BO(3))(4) composition presents good thermal stability with regard to crystallization. The Y(0.9)Er(0.1)Al(3)(BO(3))(4) crystallized phase can be obtained at 1,150 degrees C, in agreement with other authors. Crack- and porosity-free films were obtained with very small grain size and low RMS roughness. The films thickness revealed to be linearly dependent on precursor solution viscosity, being the value of 25 mPa s useful to prepare high-quality amorphous multi-layers (up to similar to 800 nm) at 740 degrees C during 2 h onto silica substrates by spin coating with a gyrset technology.

Energy transfer processes in Yb(3+)-Tm(3+) co-doped sodium alumino-phosphate glasses with improved 1.8 mu m emission

Sodium alumino-phosphate glasses co-doped with Yb(3+) and Tm(3+) ions have been prepared with notably low OH(-) content, and characterized from the viewpoint of their spectroscopic properties. In these glasses, Yb(3+) acts as an efficient sensitizer of excitation energy at 0.98 mu m - which can be provided by high power and low cost diode lasers, and subsequently undergoes non-resonant energy transfer to Tm(3+) ions ((2)F(5/2), (3)H(6) --> (2)F(7/2), (3)H(5)). Through this process, the emitting level (3)F(4) is rapidly populated, generating improved emission at 1.8 mu m ((3)F(4) --> (3)H(6)). In order to guarantee the efficiency of such favorable energy transfer, energy losses via multiphonon decay, Yb-Yb radiative trapping, and non- radiative transfer to OH(-) groups were evaluated, and minimized when possible. The dipole - dipole energy transfer microscopic parameters corresponding to Yb(3+) --> Tm(3+), Yb(3+) --> Yb(3+) and Tm(3+) --> Tm(3+) transfers, calculated by the Forster-Dexter model, are C(Yb-Tm) = 2.9 x 10(-40) cm(6) s(-1), C(Yb-Yb) = 42 x 10(-40) cm(6) s(-1) and C(Tm-Tm) = 43 x 10(-40) cm(6) s(-1), respectively.

Testing covariance stationarity

In this paper, we show that the widely used stationarity tests such as the KPSS test have power close to size in the presence of time-varying unconditional variance. We propose a new test as a complement of the existing tests. Monte Carlo experiments show that the proposed test possesses the following characteristics: (i) In the presence of unit root or a structural change in the mean, the proposed test is as powerful as the KPSS and other tests; (ii) In the presence a changing variance, the traditional tests perform badly whereas the proposed test has high power comparing to the existing tests; (iii) The proposed test has the same size as traditional stationarity tests under the null hypothesis of stationarity. An application to daily observations of return on US Dollar/Euro exchange rate reveals the existence of instability in the unconditional variance when the entire sample is considered, but stability is found in subsamples.

Ensaios em finanças públicas municipais

Esta tese busca discutir problemas relacionados às finanças públicas municipais no país. Um aprimoramento de nosso federalismo fiscal, com maior descentralização de recursos e implementação de regras de transferências federativas com maiores incentivos pró-eficiência – aumentando os incentivos pró-obtenção de melhores resultados sociais por parte das unidades subfederadas – pode se revelar instrumento importante na melhoria de nossas condições sociais. Para isto, dividiu-se esta tese em quatro partes distintas. No primeiro capítulo, discutem-se os impactos das receitas petrolíferas sobre as finanças públicas municipais. As mudanças legais ocorridas no país na década de noventa do último século - relativas ao setor petrolífero - levaram a crescente (e concentrada) transferência de recursos do setor para os estados e municípios brasileiros. A forte sensação que estes estariam sendo desperdiçados de alguma forma vem suscitando discussões sobre a necessidade de se reformular sua distribuição. As recentes descobertas de megacampos petrolíferos no pré-sal do litoral brasileiro somente intensificaram este processo. Buscou-se identificar os efeitos destas transferências sobre as variáveis fiscais municipais no país. Detectou-se que não ocorreu substituição tributária, ou seja, estes recursos não diminuíram o esforço arrecadatório dos municípios. Em compensação, tanto os recursos cuja distribuição é bem mais concentrada (referentes aos royalties excedentes) quanto aqueles mais bem-distribuídos (referentes aos royalties originais) levaram as prefeituras a aumentar seus gastos correntes (piorando sua composição do ponto de vista social) e diminuir seus investimentos. O contrário parece ocorrer com os recursos cuja distribuição se dá de forma intermediária (os royalties referentes às participações especiais). No segundo capítulo, discute-se o impacto das receitas petrolíferas sobre a proficiência dos alunos até a quarta série primária das escolas públicas municipais. As receitas petrolíferas – agregadas ou não – não se mostraram estatisticamente significativas na explicação do desempenho observado pelos alunos da quarta série primária das escolas municipais em português ou matemática. Este resultado, entretanto, deve ser olhado com cautela, uma vez que não é trivial identificar como (e o tempo necessário) estes efeitos seriam gerados. Entretanto, diferentes fontes de receitas municipais impactariam de forma diferenciada as proficiências observadas nos testes de português e matemática, explicitando a necessidade de se entender melhor estas diferenças para se desenhar mecanismo mais eficiente de repasse de recursos constitucionais aos municípios. No terceiro capítulo, estudam-se os impactos das emancipações municipais ocorridas na década de 90 sobre o bem-estar das populações locais. Devido à Constituição Federal de 1988, o número de municípios no Brasil multiplicou-se fortemente na década de 90 do último século. Mais de mil municípios foram criados em todo o país, fazendo seu número ultrapassar a casa dos 5.500. Este processo tem sido interpretado de forma bastante negativa. Baseado em evidências anedóticas, se pressupõe que os atores políticos locais o utilizaram para se apropriar de maior parcela dos recursos transferidos de outros níveis governamentais. Entretanto, nenhum esforço mais sistemático foi realizado buscando calcular, de maneira efetiva, os resultados sociais líquidos deste processo. É isto que se busca fazer aqui, utilizando dados sobre os municípios mineiros - cujo número passa de 723 em 1991 para 853 em 2000. Foram detectados impactos positivos relacionados a diversas variáveis educacionais e de saúde. Ao mesmo tempo, o contrário ocorreu com os indicadores de pobreza e indigência. Este resultado mostra que o movimento observado de emancipação municipal talvez tenha sido bastante benéfico, sinalizando para a existência de mercados políticos eficientes nestas localidades, o que indicaria a necessidade de se manter uma maior autonomia local relativa a processos de emancipação de distritos. Por fim, no quarto capítulo, analisam-se os impactos de lei (implementada em Minas Gerais) que buscou aumentar os incentivos pró-eficiência das prefeituras municipais a partir das transferências federativas. Buscando melhorar as condições de vida dos municípios mineiros, o governo estadual mineiro instituiu, em 1995, a lei 12.040, conhecida como Lei Robin Hood. Esta permitia que 25% dos recursos de ICMS a serem distribuídos aos municípios mineiros se dessem sobre resultados observáveis em diversas áreas tais como saúde, educação, conservação ecológica, entre outras. Ou seja, esta instituía, em relação a estas transferências, um contrato de alto poder com os municípios relacionados às políticas públicas implementadas. O estudo destas transferências (relativas à educação e saúde) mostrou resultados dúbios. Resultados positivos relativos à educação e à saúde parecem ocorrer em todo o estado, mas os incentivos dados poderiam ser bem maiores - faz-se necessário um refinamento das regras da partilha destas transferências. Dada a relativa escassez deste tipo de contrato em transferências federativas, seja no Brasil, seja no restante do mundo, este resultado aponta a necessidade de utilização de instrumentos de maior poder nas relações federativas, buscando incrementar as condições de vida locais.

Testing covariance stationarity

In this paper, we show that the widely used stationarity tests such as the KPSS test has power close to size in the presence of time-varying unconditional variance. We propose a new test as a complement of the existing tests. Monte Carlo experiments show that the proposed test possesses the following characteristics: (i) In the presence of unit root or a structural change in the mean, the proposed test is as powerful as the KPSS and other tests; (ii) In the presence a changing variance, the traditional tests perform badly whereas the proposed test has high power comparing to the existing tests; (iii) The proposed test has the same size as traditional stationarity tests under the null hypothesis of covariance stationarity. An application to daily observations of return on US Dollar/Euro exchange rate reveals the existence of instability in the unconditional variance when the entire sample is considered, but stability is found in sub-samples.

Desenvolvimento de antenas de microfita com aberturas nos patches condutores através do método da segmentação

Microstrip antennas are widely used in modern telecommunication systems. This is particularly due to the great variety of geometries and because they are easily built and integrated to other high frequency devices and circuits. This work presents a study of the properties of the microstrip antenna with an aperture impressed in the conducting patch. Besides, the analysis is performed for isotropic and anisotropic dielectric substrates. The Multiport Network Model MNM is used in combination with the Segmentation Method and the Greens function technique in the analysis of the considered microstrip antenna geometries. The numerical analysis is performed by using the boundary value problem solution, by considering separately the impedance matrix of the structure segments. The analysis for the complete structure is implemented by choosing properly the number and location of the neighboor element ports. The numerial analysis is performed for the following antenna geometries: resonant cavity, microstrip rectangular patch antenna, and microstrip rectangular patch antenna with aperture. The analysis is firstly developed for microstrip antennas on isotropic substrates, and then extended to the case of microstrip antennas on anisotropic substrates by using a Mapping Method. The experimental work is described and related to the development of several prototypes of rectangular microstrip patch antennas wtih and without rectangular apertures. A good agreement was observed between the simulated and measured results. Thereafter, a good agreement was also observed between the results of this work and those shown in literature for microstrip antennas on isotropic substrates. Furthermore, results are proposed for rectangular microstrip patch antennas wtih rectangular apertures in the conducting patch

Desenvolvimento de um protótipo para alimentação de pós para aspersão térmica em tocha de plasma

The nanometric powders have special features that usually result in new properties, originating applications or expanding them in various fields of knowledge. Because having a high area/volume ratio, phenomena such as superficial strength of adsorption becomes greater than the weight of the powder which makes more difficult its handling. The high power of agglomeration of these powders requires study and development of equipments to enable its management into the plasma torch. The objective of this work is to develop a powder feeder which can solve the mainly problems about insertion of powder into the thermal spray developed in the laboratory of plasmas, which are carried out with plasma torch arc not transferred (plasma spray). Therefore, it was made a aluminum s powder feeder and tests were performed to verify their operation and determine its rate of deposition by spraying powders of niobium pentoxide (Nb2O5) and titanium dioxide (TiO2) with particle sizes less than 250 mesh (<0.063 mm). We used masses of 0.5 g - 1.0 g and 1.5 g of each powder in tests lasting 15 seconds - 20 to 25 seconds for each mass. The tests were performed in two ways: at atmospheric pressure using argon gas with a flow of 9 l / min as carrier gas and through a Venturi pipe also using argon gas with a flow of 9 l / min as carrier gas and with a flow of 20 l/min as the feed gas passing through the Venturi pipe. The powder feeder developed in this paper is very easy to be handling and building, resulting in feeding rate of 0.25 cm3/min - 1.37 cm3/min. The TiO2 showed higher feeding rates than the Nb2O5 in all tests, and the best rates were obtained with tests using mass 1.5 g and time of 15 seconds, reaching feeding rate of 1.37 cm3/min. The flow of feed had low interference in feeding rate during the tests

Enhanced corrosion resistance of AISI H13 steel treated by nitrogen plasma immersion ion implantation

Electrochemical corrosion measurements of AISI H13 steel treated by Pill process in 3.5% (wt) NaCl solution were investigated. So far the corrosion behavior of AISI H 13 steel by Pill has not been studied. The electrochemical results are correlated with the surface morphology, nitrogen content and hardness of the nitride layer. Ion implantation of nitrogen into H 13 steel was carried out by Pill technique. SEM examination revealed a generalized corrosion and porosity over all analyzed sample surfaces. Penetration of nitrogen reaching more than 20 gm was achieved at 450 degrees C and hardness as high as 1340 HV (factor of 2.7 enhancement over standard tempered and annealed H 13) was reached by a high power, 9 h Pill treatment. The corrosion behavior of the samples was studied by potentiodynamic polarization method. The noblest corrosion behavior was observed for the samples treated by PIII at 450 degrees C, during 9 h. Anodic branches of polarization curves of PIII processed samples show a passive region associated with the formation of a protective film. The passive region current density of PIII treated H13 samples (3.5 x 10(-6) A/cm(2)) is about 270 times lower than the one of untreated specimens, which demonstrates the higher corrosion resistance for the Pill treated H 13 samples. (c) 2007 Elsevier B.V. All rights reserved.

The benefits of ethanol use for hydrogen production in urban transportation

The purpose of this paper is to describe the benefits of sugar cane ethanol in Brazil, appointing the productivity of this type of fuel based on hectares of plantation, its carbon dioxide cycle and the contribution to reduce the greenhouse effect. In the following step the uses of ethanol for hydrogen production by steam reforming is analyzed and some comparison with natural gas steam reforming is performed. The sugar cane industry in Brazil, in a near future, in the hydrogen era, could be modified according to our purpose, since besides the production of sugar, and ethylic and anhydric alcohol, Brazilian sugar cane industry will also be able to produce biohydrogen.Fuel cells appear like a promising technology for energy generation. Among several technologies in the present, the PEMFC (proton exchange membrane fuel cell) is the most appropriate for vehicles application, because it combines durability, high power density, high efficiency, good response and it works at relatively low temperatures. Besides that it is easy to turn it on and off and it is able to support present vibration in vehicles. A PEMFC's problem is the need of noble catalysts like platinum. Another problem is that CO needs to be in low concentration, requiring a more clean hydrogen to avoid fuel cell deterioration.One part of this paper was developed in Stockholm, where there are some buses within the CUTE (clean urban transport for Europe) project that has been in operation with FC since January 2004. Another part was developed in Guaratingueta, Brazil. Brazil intends to start up a program of FC buses. As conclusion, this paper shows the economical analysis comparing buses moved by fuel cells using hydrogen by different kinds of production. Electrolyze with wind turbine, natural gas steam reforming and ethanol steam reforming. (C) 2009 Elsevier Ltd. All rights reserved.

STUDY of THE TURNING NICKEL BASE ALLOY PYROMET (R) 31V (SAE HEV8)

Considering the constant technological developments in the aeronautical, space, automotive, shipbuilding, nuclear and petrochemical fields, among others, the use of materials with high strength mechanical capabilities at high temperatures has been increasingly used. Among the materials that meet the mechanical strength and corrosion properties at temperatures around 815 degrees C one can find the nickel base alloy Pyromet 31V (SAE HEV8). This alloy is commonly applied in the manufacturing of high power diesel engines exhaust valves where it is required high resistance to sulphide, corrosion and good resistance to creep. However, due to its high mechanical strength and low thermal conductivity its machinability is made difficult, creating major challenges in the analysis of the best combinations among machining parameters and cutting tools to be used. Its low thermal conductivity results in a concentration of heat at high temperatures in the interfaces of workpiece-tool and tool-chip, consequently accelerating the tools wearing and increasing production costs. This work aimed to study the machinability, using the carbide coated and uncoated tools, of the hot-rolled Pyromet 31V alloy with hardness between 41.5 and 42.5 HRC. The nickel base alloy used consists essentially of the following components: 56.5% Ni, 22.5% Cr, 2,2% Ti, 0,04% C, 1,2% Al, 0.85% Nb and the rest of iron. Through the turning of this alloy we able to analyze the working mechanisms of wear on tools and evaluate the roughness provided on the cutting parameters used. The tests were performed on a CNC lathe machine using the coated carbide tool TNMG 160408-23 Class 1005 (ISO S15) and uncoated tools TNMG 160408-23 Class H13A (ISO S15). Cutting fluid was used so abundantly and cutting speeds were fixed in 75 and 90 m/min. to feed rates that ranged from 0.12, 0.15, 0.18 and 0.21 mm/rev, and cutting depth of 0.8mm. The results of the comparison between uncoated tools and coated ones presented a machined length of just 30% to the first in relation to the performance of the second. The coated tools has obtained its best result for both 75 and 90 m/min. with feed rate of 0.15 mm/rev, unlike the uncoated tool which obtained its better results to 0.12 mm/rev.

A novel voltage step-down/up ZCS-PWM Zeta converter

This paper presents an analysis of a novel pulse-width-modulated (PWM) voltage step-down/up Zeta converter, featuring zero-current-switching (ZCS) at the active switches. The applications in de to de and ac to de (rectifier) operation modes are used as examples to illustrate the performance of this new ZCS-PWM Zeta converter. Regarding to the new ZCS-PWM Zeta rectifier proposed, it should be noticed that the average-current mode control is used in order to obtain a structure with high power-factor (HPF) and low total harmonic distortion (THD) at the input current.Two active switches (main and auxiliary transistors), two diodes, two small resonant inductors and one small resonant capacitor compose the novel ZCS-PWM soft-commutation cell, used in these new ZCS-PWM Zeta converters. In this cell, the turn-on of the active switches occurs in zero-current (ZC) and their turn-off in zero-current and zero-voltage (ZCZV). For the diodes, their turn-on process occurs in zero-voltage (ZV) and their reverse-recovery effects over the active switches are negligible. These characteristics make this cell suitable for Insulated-Gate Bipolar Transistors (IGBTs) applications.The main advantages of these new Zeta converters, generated from the new soft-commutation cell proposed, are possibility of obtaining isolation (through their accumulation inductors), and high efficiency, at wide load range. In addition, for the rectifier application, a high power factor and low THD in the input current ran be obtained, in agreement with LEC 1000-3-2 standards.The principle of operation, the theoretical analysis and a design example for the new de to de Zeta converter operating in voltage step-down mode are presented. Experimental results are obtained from a test unit with 500W output power, 110V(dc) output voltage, 220V(dc) input voltage, operating at 50kHz switching frequency. The efficiency measured at rated toad is equal to 97.3%for this new Zeta converter.Finally, the new Zeta rectifier is analyzed, and experimental results from a test unit rated at 500W output power, 110V(dc) output voltage, 220V(rms) input voltage, and operating at 50kHz switching frequency, are presented. The measured efficiency is equal to 96.95%, the power-factor is equal to 0.98, and the input current THD is equal to 19.07%, for this new rectifier operating at rated load.

Novel zero-current-switching PWM converters

This paper presents a new family of pulsewidth-modulated (PWM) converters, featuring soft commutation of the semiconductors at zero current (ZC) in the transistors and zero voltage (ZV) in the rectifiers, Besides operating at constant frequency and with reduced commutation losses, these new converters have output characteristics similar to the hard-switching-PWM counterpart, which means that there is no circulating reactive energy that would cause large conduction losses, the new family of zero-current-switching (ZCS)-PWM converters is suitable for high-power applications using insulated gate bipolar transistors (IGBT's). The advantages of the new ZCS-PWM boast converter employing IGBT's, rated at 1.6 kW and operating at 20 kHz, are presented, This new ZCS operation can reduce the average total power dissipation in the semiconductors practically by half, when compared with the hard-switching method, This new ZCS-PWM boost converter is suitable for high-power applications using Ie;BT's in power-factor correction, the principle of operation, theoretical analysis, and experimental results of the new ZCS-PWM boost converter are provided in this paper to verify the performance of this new family of converters.

Generalization of the Y-differential autotransformer for 12- and 18-pulse converters

This work proposes a methodology to generalize the Y-connections for 12- and 18-pulse autotransformers. A single mathematical expression, obtained through simple trigonometric operations, represents all the connections. The proposed methodology allows choosing any ratio between the input and the output voltages. The converters can operate either as step-up or as step-down voltage. To simplify the design of the windings, graphics are generated to calculate the turn-ratio and the polarity of each secondary winding, with respect to the primary winding. A design example, followed by digital simulations, illustrates the presented steps. Experimental results of two prototypes (12 and 18 pulses) are presented. The results also show that high power factor is an inherent characteristic of multi-pulse converters, without any active or passive power factor pre-regulators needs. (c) 2005 Elsevier B.V. All rights reserved.

DCM Boost interleaved converter for operation in AC and DC to trolleybus application

This paper is based on the development and experimental analysis of a DCM Boost interleaved converter suitable for application in traction systems of electrical vehicles pulled by electrical motors (Trolleybus), which are powered by urban DC or AC distribution networks. This front-end structure is capable of providing significant improvements in trolleybuses systems and in the urban distribution network costs, and efficiency. The architecture of proposed converter is composed by five boost power cells in interleaving connection, operating in discontinuous conduction mode. Furthermore, the converter can operate as AC-DC converter, or as DC-DC converter providing the proper DC output voltage range required by DC or AC adjustable speed drivers. Therefore, when supplied by single-phase AC distribution networks, and operating as AC-DC converter, it is capable to provide high power factor, reduced harmonic distortion in the input current, complying with the restrictions imposed by the IEC 61000-3-4 standards. The digital controller has been implemented using a low cost FPGA and developed totally using a hardware description language VHDL and fixed point arithmetic. Thus, two control strategies are evaluated considering the compliance with input current restrictions imposed by IEC 61000-3-4 standards, the regular PWM modulation and a current correction PWM modulation. In order to verify the feasibility and performance of the proposed system, experimental results from a 15 kW low power scale prototype are presented, operating in DC and AC conditions.

Análise das dificuldades de aprendizagem numa disciplina de química orgânica do curso de química na modalidade à distância da UFRN

In today`s society the use of so-called information technology and communication (ICT), is promoting a revolution in the forms of teaching and learning through the methods of distance learning courses, especially in higher education. Studies show that students in this way have great difficulties in the learning process, especially when dealing with experimental subjects that require high power of abstraction as chemistry. The goal of this work is to promote improvement in the teaching and learning in the discipline Chemistry of Life offered for the Bachelor`s Degree in Chemistry in distance UFRN. For this we analyzed evidence of the semester 2011.2, in order to identify what are the main difficulties of the students on the assessments. That`s why video lessons related to matters that create the majority of difficulties for students were developed, the final product this work. Being obtained the improvements by video classes in the learning process of the students, from a questionnaire answered by the students in the virtual learning environment, and from their success rate at the end of the course