X-ray spectroscopy applied to radiation shielding calculation in mammography

The protective shielding design of a mammography facility requires the knowledge of the scattered radiation by the patient and image receptor components. The shape and intensity of secondary x-ray beams depend on the kVp applied to the x-ray tube, target/filter combination, primary x-ray field size, and scattering angle. Currently, shielding calculations for mammography facilities are performed based on scatter fraction data for Mo/Mo target/filter, even though modern mammography equipment is designed with different anode/filter combinations. In this work we present scatter fraction data evaluated based on the x-ray spectra produced by a Mo/Mo, Mo/Rh and W/Rh target/filter, for 25, 30 and 35 kV tube voltages and scattering angles between 30 and 165 degrees. Three mammography phantoms were irradiated and the scattered radiation was measured with a CdZnTe detector. The primary x-ray spectra were computed with a semiempirical model based on the air kerma and HVL measured with an ionization chamber. The results point out that the scatter fraction values are higher for W/Rh than for Mo/Mo and Mo/Rh, although the primary and scattered air kerma are lower for W/Rh than for Mo/Mo and Mo/Rh target/filter combinations. The scatter fractions computed in this work were applied in a shielding design calculation in order to evaluate shielding requirements for each of these target/filter combinations. Besides, shielding requirements have been evaluated converting the scattered air kerma from mGy/week to mSv/week adopting initially a conversion coefficient from air kerma to effective dose as 1 Sv/Gy and then a mean conversion coefficient specific for the x-ray beam considered. Results show that the thickest barrier should be provided for Mo/Mo target/filter combination. They also point out that the use of the conversion coefficient from air kerma to effective dose as 1 Sv/Gy is conservatively high in the mammography energy range and overestimate the barrier thickness. (c) 2008 American Association of Physicists in Medicine.

Skew-normal linear calibration: a Bayesian perspective

In this paper, we present a Bayesian approach for estimation in the skew-normal calibration model, as well as the conditional posterior distributions which are useful for implementing the Gibbs sampler. Data transformation is thus avoided by using the methodology proposed. Model fitting is implemented by proposing the asymmetric deviance information criterion, ADIC, a modification of the ordinary DIC. We also report an application of the model studied by using a real data set, related to the relationship between the resistance and the elasticity of a sample of concrete beams. Copyright (C) 2008 John Wiley & Sons, Ltd.

Lithium Ion Electro-Insertion and Spectroelectrochemical Properties of Films from Hexaniobate

Layer-by-layer (LbL) films from K(2)Nb(6)O(17)(2-) and polyallylamine (PAH) and dip-coating films of H(2)K(2)Nb(6)O(17) were prepared on a fluorine-doped tin-oxide (FTO)-coated glass. The atomic force microscopy (AFM) images were carried out for morphological characterization of both materials. The real surface area and the roughness factor were determined on the basis of pseudocapacitive processes involved in the electroreduction/electrooxidation of gold layers deposited on these films. Next, lithium ion insertion into these materials was examined by means of electrochemical and spectroelectrochemical measurements. More specifically, cyclic voltammetry and current pulses under visible light beams were used to investigate mass transport and chromogenic properties. The lithium ion diffusion coefficient (D(Li)) within the LbL matrix is significantly higher than that within the dip-coating film, ensuring high storage capacity of lithium ions in the self-assembled electrode. Contrary to the LbL film, the potentiodynamic profile of absorbance change (Delta A) as a function of time is not similar to that obtained in the case of current density for the dip-coating film. Aiming at analyzing the rate of the coloration front associated with lithium ion diffusion, a spectroelectrochemical method based on the galvanostatic intermittent titration technique (GITT) was employed so as to determine the ""optical"" diffusion coefficient (D(op)). In the dip-coating film, the method employed here revealed that the lithium ion rate is higher in diffusion pathways formed from K(2)Nb(6)O(17)(2-) sites that contribute more significantly to Delta A. Meanwhile, the presence of PAH contributed to the increased ionic mobility in diffusion pathways in the LbL film, with low contribution to the electrochromic efficiency. These results aided a better understanding of the potentiodynamic profile of the temporal change of absorbance and current density during the insertion/deinsertion of lithium ions into the electrochromic materials.

Diagramas momento-curvatura para elementos estruturais de concreto armado submetidos a carregamento monotonico ou cíclico

Este trabalho tem por objetivo desenvolver e implementar, computacionalmente, procedimentos numéricos eficientes, aplicados à determinacão do diagrama momento-curvatura, correspondentes à: -uma seção tipica, em vigas de concreto armado, submetida à carga monotônica ou cíclica de curta duração; - um ponto genérico da superficie média em placas de concreto armado, submetidas à carga monotônica de curta duração. Ainda à luz dos resultados obtidos, visa também propôr um modelo simplificado em termos de resultantes de tensões e deformações generalizadas. Inicialmente, é descrito um modelo laminar para vigas, no qual a carga é aplicada de forma incremental sendo que para cada etapa, as equaçães de equilibrio não-lineares são resolvidas de maneira iterativa. Como consequência é proposta uma relação momento-curvatura em termos de resultantes. A fim de verificar a validade e aplicabilidade dos métodos e dos algorítmos estudados e comparar-se os resultados com dados experimentais e respostas obtidas por outros pesquisadores, é apresentada uma série de exemplos numéricos. A continuação, é aplicado o procedimento anterior para modelos de laje, livres de solicitações de membrana. Finalmente através de um estudo paramétrico dos diversos fatores que afetam o diagrama momento-curvatura, propõe-se uma relação simplificada.

Análise de treliças planas viscoelásticas com deformações finitas e pórticos planos viscoelásticos com vigas mistas

Este trabalho compõe-se de duas partes. A primeira parte propõe-se a apresentar um estudo e um programa computacional para a análise não linear geométrica de treliças planas com propriedades: viscoelásticas. Na segunda parte, tem-se o estudo e um programa sobre pórticos planos com propriedades viscoelásticas, usando o modelo reológico standard e o dado pelo CEB. Leva-se em consideração o efeito de temperatura e retração nesta análise. Estende-se o trabalho sobre pórtico para o estudo sobre vigas mistas, levando em consideração a mudança da linha neutra. A formulação está baseada no método dos elementos finitos para grandes deformações, particularizada para treliça e pórtico. É feita a descrição de ambos os programas e rodados diversos exemplos.

Analise de estruturas de edificios altos submetidos a carregamentos horizontais e verticais

O presente trabalho tem como objetivo analisar os esforços em estruturas tridimensionais de edificios altos, quando submetidos a carregamentos horizontais e verticais. A estrutura é idealizada como um conjunto de pilares, paredes e vigas podendo ser dispostos de uma maneira assimétrica no plano da laje e variarem suas propriedades geométricas ao longo da altura. A análise é feita pelo método dos deslocamentos. Admite-se que as lajes em cada nível dos pavimentos tenham o funcionamento de diafragma rígido. São utilizados elementos de barra para representação das vigas e pilares. Para a determinação dos esforços em paredes resistentes são apresentados vários elementos obtidos pela analogia de pórticos. Tais elementos são incorporados ao programa possuindo uma formulação bem simples.

Análise dinâmica de vigas assimétricas em curva com parede fina e aberta submetidas a ação de carga móveis

Fundamentalmente, o presente trabalho faz uma análise elástica linear de pontes ou vigas curvas assimétricas de seção transversal aberta e de parede fina, com propriedades físicas, geométricas e raio de curvatura constantes ao longo do eixo baricêntrico. Para tanto, utilizaram-se as equações diferenciais de VLASOV considerando o acoplamento entre as deformações nas direções vertical, transversal, axial de torcão nal. Na solução do sistema de quatro equações com derivadas parciais foi utilizado um apropriado método numérico de integração (Diferenças Finitas Centrais). A análise divide-se, basicamente, em dois tipos: análise DINÂMICA e ESTATICA. Ambas são utilizadas também na determinação do coeficiente de impacto (C.M.D.). A primeira refere-se tanto na determinação das características dinâmicas básicas (frequências naturais e respectivos modos de vibração), como também na determinação da resposta dinâmica da viga, em tensões e deformações, para cargas móveis arbitrárias. Vigas com qualquer combinação das condições de contorno, incluindo bordos rotulados e engastados nas três direções de flexão e na torção, são consideradas. 0s resultados da análise teórica, obtidos pela aplicação de programas computacionais implementados em microcomputador (análise estática) e no computador B-6700 (análise dinâmica), são comparados tanto com os da bibliografia técnica como também com resultados experimentais, apresentando boa correlação.

Filmes finos dielétricos para dispositivos microeletrônicos avançados

Apresentamos mecanismos de formação e de degradação térmica de filmes fi- nos (espessura da ordem de 10 nm) de diferentes dielétricos sobre substrato de silício monocristalino. Tendo em vista a aplicação dessas estruturas em MOSFETs (transistores de efeito de campo metal-óxido-semicondutor), estudamos o consagrado óxido de silício (SiO2), os atuais substitutos oxinitretos de silício (SiOxNy) e o possível substituto futuro óxido de alumínio (Al2O3). Nossos resultados experimentais baseiam-se em técnicas preparativas de substituição isotópica e de caracterização física com feixes de íons (análise com reações nucleares) ou raios- X (espectroscopia de fotoelétrons). Observamos que: (a) átomos de silício não apresentam difusão de longo alcance (além de ~ 2 nm) durante o crescimento de SiO2 por oxidação térmica do silício em O2; (b) nitretação hipertérmica é capaz de produzir filmes finos de oxinitreto de silício com até dez vezes mais nitrogênio que o resultante do processamento térmico usual, sendo que esse nitrogênio tende a se acumular na interface SiOxNy/Si; e (c) átomos de oxigênio, alumínio e silício migram e promovem reações químicas durante o recozimento térmico de estruturas Al2O3/SiO2/Si em presença de O2. Desenvolvemos um modelo de difusão-reação que poderá vir a permitir o estabelecimento de condições ótimas de processamento térmico para filmes finos de Al2O3 sobre silício a serem empregados na fabricação de MOSFETs.

Multilayer optimization in radio resource allocation for the packet transmission in wireless networks

In the last decade mobile wireless communications have witnessed an explosive growth in the user’s penetration rate and their widespread deployment around the globe. It is expected that this tendency will continue to increase with the convergence of fixed Internet wired networks with mobile ones and with the evolution to the full IP architecture paradigm. Therefore mobile wireless communications will be of paramount importance on the development of the information society of the near future. In particular a research topic of particular relevance in telecommunications nowadays is related to the design and implementation of mobile communication systems of 4th generation. 4G networks will be characterized by the support of multiple radio access technologies in a core network fully compliant with the Internet Protocol (all IP paradigm). Such networks will sustain the stringent quality of service (QoS) requirements and the expected high data rates from the type of multimedia applications to be available in the near future. The approach followed in the design and implementation of the mobile wireless networks of current generation (2G and 3G) has been the stratification of the architecture into a communication protocol model composed by a set of layers, in which each one encompasses some set of functionalities. In such protocol layered model, communications is only allowed between adjacent layers and through specific interface service points. This modular concept eases the implementation of new functionalities as the behaviour of each layer in the protocol stack is not affected by the others. However, the fact that lower layers in the protocol stack model do not utilize information available from upper layers, and vice versa, downgrades the performance achieved. This is particularly relevant if multiple antenna systems, in a MIMO (Multiple Input Multiple Output) configuration, are implemented. MIMO schemes introduce another degree of freedom for radio resource allocation: the space domain. Contrary to the time and frequency domains, radio resources mapped into the spatial domain cannot be assumed as completely orthogonal, due to the amount of interference resulting from users transmitting in the same frequency sub-channel and/or time slots but in different spatial beams. Therefore, the availability of information regarding the state of radio resources, from lower to upper layers, is of fundamental importance in the prosecution of the levels of QoS expected from those multimedia applications. In order to match applications requirements and the constraints of the mobile radio channel, in the last few years researches have proposed a new paradigm for the layered architecture for communications: the cross-layer design framework. In a general way, the cross-layer design paradigm refers to a protocol design in which the dependence between protocol layers is actively exploited, by breaking out the stringent rules which restrict the communication only between adjacent layers in the original reference model, and allowing direct interaction among different layers of the stack. An efficient management of the set of available radio resources demand for the implementation of efficient and low complexity packet schedulers which prioritize user’s transmissions according to inputs provided from lower as well as upper layers in the protocol stack, fully compliant with the cross-layer design paradigm. Specifically, efficiently designed packet schedulers for 4G networks should result in the maximization of the capacity available, through the consideration of the limitations imposed by the mobile radio channel and comply with the set of QoS requirements from the application layer. IEEE 802.16e standard, also named as Mobile WiMAX, seems to comply with the specifications of 4G mobile networks. The scalable architecture, low cost implementation and high data throughput, enable efficient data multiplexing and low data latency, which are attributes essential to enable broadband data services. Also, the connection oriented approach of Its medium access layer is fully compliant with the quality of service demands from such applications. Therefore, Mobile WiMAX seems to be a promising 4G mobile wireless networks candidate. In this thesis it is proposed the investigation, design and implementation of packet scheduling algorithms for the efficient management of the set of available radio resources, in time, frequency and spatial domains of the Mobile WiMAX networks. The proposed algorithms combine input metrics from physical layer and QoS requirements from upper layers, according to the crosslayer design paradigm. Proposed schedulers are evaluated by means of system level simulations, conducted in a system level simulation platform implementing the physical and medium access control layers of the IEEE802.16e standard.

The position effect of structural Eucalyptus round timber on the flexural modulus of elasticity

A madeira roliça possui grande emprego nas construções civis, desempenhando a função de vigas, colunas, fundações, postes para distribuição de energia elétrica, entre outras, apresentando a vantagem de não ser processada, como é o caso da madeira serrada. O projeto envolvendo elementos roliços requer, além de outras variáveis estruturais, o conhecimento do módulo de elasticidade. No Brasil, os documentos normativos que tratam da determinação das propriedades de rigidez e resistência para peças roliças de madeira estão em vigência há mais de vinte anos sem revisão técnica. A madeira roliça, por geralmente possuir eixo com curvatura não nula, pode apresentar, segundo a posição da peça no ensaio de flexão, valores diferentes do módulo de elasticidade. Este trabalho tem como objetivo analisara influência da posição de peças roliças de madeira de Eucalyptus grandis na determinação do módulo de elasticidade na flexão. O ensaio de flexão utilizado é o de três pontos, sendo cada peça avaliada em duas posições distintas, definidas mediante o giro da seção transversal em torno do eixo. Os resultados encontrados indicam a necessidade do ensaio de flexão em, pelo menos, duas posições distintas da peça.

Effects of caffeine on locomotor activity of horses: Determination of the no-effect threshold

Caffeine is the legal stimulant consumed most extensively by the human world population and may be found eventually in the urine and/or blood of race horses, the fact that caffeine is in foods led us to determine the highest no-effect dose (HNED) of caffeine on the spontaneous locomotor activity of horses and then to quantify this substance in urine until it disappeared. We built two behavioural stalls equipped with juxtaposed photoelectric sensors that emit infrared beams that divide the stall into nine sectors in a 'tic-tac-toe' fashion. Each time a beam was interrupted by a leg of the horse, a pulse was generated; the pulses were counted at 5-min intervals and stored by a microcomputer. Environmental effects were minimized by installing exhaust fans producing white noise that obscured outside sounds. One-way observation windows prevented the animals from seeing outside. The sensors were turned on 45 min before drug administration (saline control or caffeine), the animals were observed for up to 8 h after i.v. administration of 2.0, 2.5, 3.0 or 5.0 mg caffeine kg(-1). The HNED of caffeine for stimulation of the spontaneous locomotor activity of horses was 2.0 mg kg(-1). The quantification of caffeine in urine and plasma samples was done by gradient HPLC with UV detection. The no-effect threshold should not be greater than 2.0 mug caffeine ml(-1) plasma or 5.0 mug caffeine ml(-1) urine. Copyright (C) 2001 John Wiley & Sons, Ltd.

Propriedades físicas e mecânicas de painéis LVL de Eucalyptus grandis

This paper mainly aimed to evaluate the physical and mechanical properties of LVL panels made from Eucalyptus grandis, from reforestation at the region of Senges, in Parana state, Brazil. LVL panels were manufactured using 23 veneers (2,4mm thick each one) in commercial dimension of 2.500 mm long and 1,200 mm wide. The properties of static bending were analyzed (strength and rigidity) in beams of the LVL, in the flatwise and edgewise positions. The properties of compression parallel to grain and shear parallel in the plans L-X and L-Y and density in this LVL panels were also analyzed according to ASTM-D 5456/4761 and ASTM-D 198 codes. The mean values to flatwise bending MOE and MOR were 13114 MPa and 88.76 MPa, respectively, and for edgewise bending MOE and MOR were 15871 MPa and 88.63 MPa, respectively. The density (12%) of the LVL panels and of the veneers were 690 kg/m(3) and 649 kg/m(3). The mean values to parallel compression MOE and MOR were 16856 MPa and 58.05 MPa, respectively. The mean values of the maximum resistance to shear parallel in the plans L-X and L-Y were 5.96 MPa and 591 MPa, respectively. All these values reached partially or they passed the medium limits of reference (normative codes, researches and commercial catalogs) established for LVL panels and original solid wood, attesting overall the quality of those panels produced with this wood.

A special BEM for elastostatic analysis of building floor slabs on columns

This work presents a boundary element formulation for the analysis of building floor slabs, without beams, in which columns are coupled with the plate. An alternative formulation of boundary element method is presented, which considers three nodal displacements values (w, partial derivativew/partial derivativen and partial derivativew/partial derivatives) for the nodes at the boundary of the plate. In this formulation three boundary equations are written for all nodes at the boundary and in the domain of the plate. As the nodes of the column-plate connections are also represented by three nodal values, all these structural elements can be easily coupled. It is supposed that the cross-sections of the columns remain flat after the deflection and consequently the assumption of linear variation of the stress in the plate-column contact surface is also valid. (C) 2003 Elsevier B.V. Ltd. All rights reserved.

HIGH STRENGTH CONCRETE: THE REINFORCED CONCRETE OF THE CENTURY 21(ST)

This work is about the 21st century reinforced concrete analysis under the point of view of its constituent materials. First of all it is described the theoretical approach of the bending elements calculated based on the Norms BAEL 91 standarts. After that, numerical load-displacement are presented from reinforced concrete beams and plates validated by experimental data. The numerical modellings has been carried on in the program CASTEM 2000. In this program a elastoplastic model of Drucker-Prager defines the rupture surface of the concrete in non associative plasticity. The crack is smeared on the Gauss points of the finite elements with formation criterion starting from the definition of the rupture surface in the branch traction-traction of the Rankine model. The reinforcements were modeled in a discrete approach with perfect bond. Finally, a comparative analysis is made between the numerical results and calculated criteria showing the future of high performance reinforced concrete in this beginning of 21st century.

Analysis of the Coupled Stretching-Bending Problem of Stiffened Plates by a BEM Formulation Based on Reissner's Hypothesis

In this work, the plate bending formulation of the boundary element method - BEM, based on the Reissner's hypothesis, is extended to the analysis of plates reinforced by beams taking into account the membrane effects. The formulation is derived by assuming a zoned body where each sub-region defines a beam or a slab and all of them are represented by a chosen reference surface. Equilibrium and compatibility conditions are automatically imposed by the integral equations, which treat this composed structure as a single body. In order to reduce the number of degrees of freedom, the problem values defined on the interfaces are written in terms of their values on the beam axis. Initially are derived separated equations for the bending and stretching problems, but in the final system of equations the two problems are coupled and can not be treated separately. Finally are presented some numerical examples whose analytical results are known to show the accuracy of the proposed model.