Finite difference time domain (FDTD) method for modeling the effect of switched gradients on the human body in MRI

Numerical modeling of the eddy currents induced in the human body by the pulsed field gradients in MRI presents a difficult computational problem. It requires an efficient and accurate computational method for high spatial resolution analyses with a relatively low input frequency. In this article, a new technique is described which allows the finite difference time domain (FDTD) method to be efficiently applied over a very large frequency range, including low frequencies. This is not the case in conventional FDTD-based methods. A method of implementing streamline gradients in FDTD is presented, as well as comparative analyses which show that the correct source injection in the FDTD simulation plays a crucial rule in obtaining accurate solutions. In particular, making use of the derivative of the input source waveform is shown to provide distinct benefits in accuracy over direct source injection. In the method, no alterations to the properties of either the source or the transmission media are required. The method is essentially frequency independent and the source injection method has been verified against examples with analytical solutions. Results are presented showing the spatial distribution of gradient-induced electric fields and eddy currents in a complete body model.

Long-range automaton models of earthquakes: Power-law accelerations, correlation evolution, and mode-switching

We introduce a conceptual model for the in-plane physics of an earthquake fault. The model employs cellular automaton techniques to simulate tectonic loading, earthquake rupture, and strain redistribution. The impact of a hypothetical crustal elastodynamic Green's function is approximated by a long-range strain redistribution law with a r(-p) dependance. We investigate the influence of the effective elastodynamic interaction range upon the dynamical behaviour of the model by conducting experiments with different values of the exponent (p). The results indicate that this model has two distinct, stable modes of behaviour. The first mode produces a characteristic earthquake distribution with moderate to large events preceeded by an interval of time in which the rate of energy release accelerates. A correlation function analysis reveals that accelerating sequences are associated with a systematic, global evolution of strain energy correlations within the system. The second stable mode produces Gutenberg-Richter statistics, with near-linear energy release and no significant global correlation evolution. A model with effectively short-range interactions preferentially displays Gutenberg-Richter behaviour. However, models with long-range interactions appear to switch between the characteristic and GR modes. As the range of elastodynamic interactions is increased, characteristic behaviour begins to dominate GR behaviour. These models demonstrate that evolution of strain energy correlations may occur within systems with a fixed elastodynamic interaction range. Supposing that similar mode-switching dynamical behaviour occurs within earthquake faults then intermediate-term forecasting of large earthquakes may be feasible for some earthquakes but not for others, in alignment with certain empirical seismological observations. Further numerical investigation of dynamical models of this type may lead to advances in earthquake forecasting research and theoretical seismology.

A Poincare-Birkhoff-Witt commutator lemma for U-q[gl(m vertical bar n)]

We present and prove in detail a Poincare-Birkhoff-Witt commutator lemma for the quantum superalgebra U-q[gl(m\n)]. (C) 2003 American Institute of Physics.

The effect of heat transfer mode on heart rate responses and hysteresis during heating and cooling in the estuarine crocodile Crocodylus porosus

The effect of heating and cooling on heart rate in the estuarine crocodile Crocodylus porosus was studied in response to different heat transfer mechanisms and heat loads. Three heating treatments were investigated. C. porosus were: (1) exposed to a radiant heat source under dry conditions; (2) heated via radiant energy while half-submerged in flowing water at 23degreesC and (3) heated via convective transfer by increasing water temperature from 23degreesC to 35degreesC. Cooling was achieved in all treatments by removing the heat source and with C. porosus half-submerged in flowing water at 23degreesC. In all treatments, the heart rate of C. porosus increased markedly in response to heating and decreased rapidly with the removal of the heat source. Heart rate during heating was significantly faster than during cooling at any given body temperature, i.e. there was a significant heart rate hysteresis. There were two identifiable responses to heating and cooling. During the initial stages of applying or removing the heat source, there was a dramatic increase or decrease in heart rate ('rapid response'), respectively, indicating a possible cardiac reflex. This rapid change in heart rate with only a small change or no change in body temperature (

Modeling diffraction in free-space optical interconnects by the mode expansion method

Free-space optical interconnects (FSOIs), made up of dense arrays of vertical-cavity surface-emitting lasers, photodetectors and microlenses can be used for implementing high-speed and high-density communication links, and hence replace the inferior electrical interconnects. A major concern in the design of FSOIs is minimization of the optical channel cross talk arising from laser beam diffraction. In this article we introduce modifications to the mode expansion method of Tanaka et al. [IEEE Trans. Microwave Theory Tech. MTT-20, 749 (1972)] to make it an efficient tool for modelling and design of FSOIs in the presence of diffraction. We demonstrate that our modified mode expansion method has accuracy similar to the exact solution of the Huygens-Kirchhoff diffraction integral in cases of both weak and strong beam clipping, and that it is much more accurate than the existing approximations. The strength of the method is twofold: first, it is applicable in the region of pronounced diffraction (strong beam clipping) where all other approximations fail and, second, unlike the exact-solution method, it can be efficiently used for modelling diffraction on multiple apertures. These features make the mode expansion method useful for design and optimization of free-space architectures containing multiple optical elements inclusive of optical interconnects and optical clock distribution systems. (C) 2003 Optical Society of America.

Caenorhabditis elegans mutants resistant to phosphine toxicity show increased longevity and cross-resistance to the synergistic action of oxygen

Phosphine (hydrogen phosphide, PH3) is the fumigant most widely used to protect stored products from pest infestation. Despite the importance of this chemical, little is known about its mode of action. We have created three phosphine-resistant lines (pre-1, pre-7, pre-33) in the model organism C. elegans, with LC50 values 2, 5, and 9 times greater than the fully susceptible parental strain. Molecular oxygen was shown to be an extremely effective synergist with phosphine as, under hyperoxic conditions, 100% mortality was observed in wild-type nematodes exposed to 0.1 mg/l phosphine, a nonlethal concentration in air. All three mutants were resistant to the synergistic effects of oxygen in proportion to their resistance to phosphine with one mutant, pre-33, showing complete resistance to this synergism. We take the proportionality of cross-resistance between phosphine and the synergistic effect of oxygen to imply that all three mutants circumvent a mechanism of phosphine toxicity that is directly coupled to oxygen metabolism. Compared with the wild-type strain, all three mutants have an extended average life expectancy of from 12.5 to 25.3%. This is consistent with the proposed involvement of oxidative stress in both phosphine toxicity and ageing. Because the wild-type and mutant nematodes develop at the same rate, the longevity is unlikely to be caused by a clk-type reduction in oxidative metabolism, a potential alternative mechanism of phosphine resistance.

A class B switch-mode assisted linear amplifier

A switch-mode assisted linear amplifier (SMALA) combining a linear (Class B) and a switch-mode (Class D) amplifier is presented. The usual single hysteretic controlled half-bridge current dumping stage is replaced by two parallel buck converter stages, in a parallel voltage controlled topology. These operate independently: one buck converter sources current to assist the upper Class B output device, and a complementary converter sinks current to assist the lower device. This topology lends itself to a novel control approach of a dead-band at low power levels where neither class D amplifier assists, allowing the class B amplifier to supply the load without interference, ensuring high fidelity. A 20 W implementation demonstrates 85% efficiency, with distortion below 0.08% measured across the full audio bandwidth at 15 W. The class D amplifier begins assisting at 2 W, and below this value, the distortion was below 0.03%. Complete circuitry is given, showing the simplicity of the additional class D amplifier and its corresponding control circuitry.

O Fator Q no "MarQeting"

A sociedade e o mundo atual têm sido marcados pela inconstância dos mercados. A consciência de uma sociedade global, imprime nas organizações a necessidade de centrar a suas atenções na satisfação e fidelização do cliente, através de meios e recursos competentes, competitivos, assente numa cultura de gestão da qualidade transversal a toda a organização. A importância da questão “Qualidade” no contexto organizacional vai muito além da mera preocupação com a produção de produtos ou prestação de serviços com qualidade. Com a feroz concorrência, a inovação constante, a complexidade de realização do próprio produto ou serviço, a existência de clientes “bem informados”, as mudanças culturais, torna-se cada mais necessária alteração de comportamentos e adoção de uma nova filosofia de gestão, orientada para a gestão do relacionamento com o cliente. Neste projeto de investigação, o termo “cliente” será explorado para além do seu conceito lato. Consideraremos todos os stakeholders1, ou seja, todos os públicos que têm contacto com a organização. Enquadrar os clientes nos diversos segmentos de mercado, os canais de acesso ao cliente, a descoberta dos atributos requeridos num produto / serviço, a resposta a dúvidas, reclamações e sugestões, serão temáticas derivantes do Marketing que serão alvo de estudo neste trabalho. A presente investigação tem como objetivo perceber se existe relação entre o fator qualidade e o marketing, na satisfação do cliente e realização das suas expectativas face produto e serviço. Para alcançar os objetivos propostos, foi desenvolvido um modelo conceptual que estabelece relações entre o ciclo PDCA e os 4P´s de marketing. Com base neste modelo, foi aplicado um questionário de avaliação de satisfação dos clientes de uma empresa de eletrónica e automação, e a partir dos quais se basearam as conclusões apresentadas. Este estudo permitiu concluir que a integração destas ferramentas de gestão tem um efeito positivo na satisfação do cliente, na fidelização, e consequente recomendação do produto, serviço e da própria organização, resultado da combinação da qualidade percebida e do valor percebido pelo cliente. Verifica-se que a qualidade afeta diretamente a satisfação e consequente fidelização. A perceção do cliente sobre a qualidade do produto, do serviço e assistência pós venda, cria valor, confiança, compromisso e a recomendação da organização a outros. Os resultados apresentados realçam a necessidade das organizações adequarem-se aos seus clientes, levando em atenção as suas expressões e desejos.

A Técnica Q - como instrumento de medida na área da educação em saúde

Foi elaborado um instrumento de medida baseado na Técnica Q de W. Stephenson, cujas operações exigidas são semelhantes às primeiras etapas de construção de uma Escala Thurstone, pelo método de intervalos aparentemente iguais. Utilizando-se desse instrumento, foi realizado estudo sobre a "Percepção da Função do Educador de Saúde Pública, na Equipe de Saúde", desenvolvido em duas fases: a primeira, compreendendo a construção do Instrumento, propriamente dito, e a segunda, a execução de uma pesquisa exploratória fazendo uso do referido instrumento. São descritos todos os passos da primeira fase, que compreende: a coleta de informações sobre as atribuições da função do educador de saúde pública; listagem das mesmas, convertendo-as em afirmações transcritas em cartões: seleção de uma amostra de 70 cartões, por um corpo de juizes altamente especializado; tabulação dos dados obtidos e a definição do instrumento definitivo. Para preencher os requisitos de validade, a distribuição escalar deveria apresentar um certo equilíbrio entre as afirmações não pertinentes, intermediárias e pertinentes. Para a conveniência estatística e para garantir este equilíbrio, cada juiz foi instruído a colocar números variados de cartões em várias pilhas, fazendo de sua totalidade um continuum que se aproximasse de uma distribuição normal ou quase normal. Este equilíbrio foi alcançado e a distribuição de freqüência das afirmações amostradas pelos juizes demonstrou ótima concordância interna, o que permitiu considerar satisfatório este estudo. As 70 afirmações foram confirmadas como componentes definitivo do instrumento de medida PF-ESP-Percepção da Função do Educador de Saúde Pública, para a utilização na segunda fase desse estudo.

n-Hexane hydroisomerisation over bifunctional Pt/MCM-22 catalysts. Influence of the mode of Pt introduction

Three different methods were used to introduce 1.0 wt.% of Pt in bifunctional Pt/MCM-22 zeolite catalysts: ion exchange with Pt(NH3)(4)(2+), incipient wetness impregnation with PtCl6H2 and mechanical mixture with Pt/Al2O3. The Pt dispersion was estimated by transmission electron microscopy and the hydrogenating activity with toluene hydrogenation at 110 degrees C. From these experiments, it can be concluded that with the ion exchanged sample, platinum was located within the inner micropores and on the outer surface, whereas with the impregnated one, platinum was essentially on the outer surface under the form of large particles. With all the samples there is a fast initial decrease in the activity for n-hexane hydroisomerisation at 250 degrees C. With exchanged and impregnated samples, this decrease is followed by a plateau, the activity value being then higher with impregnated sample. For the sample prepared by mechanical mixture a continuous decrease in activity can be observed. All these differences can be related with the distinct locations of Pt.

Stability Condition Based Sliding Mode Modulators for Multilevel Power Converters

Sliding mode controllers for power converters usually employ hysteresis comparators to directly generate the power semiconductors switching states. This paper presents a new sliding mode modulator based on the direct implementation of the sliding mode stability condition, which for multilevel power converters shows advantages, as branch equalized switching frequencies and less distortion on the ac currents when operating near the rated converter power. The new sliding mode multilevel modulator is used to control a three-phase multilevel converter, operated as a reactive power compensator (STATCOM), implementing the stability condition in a digital signal processing system. The performance of this new sliding mode modulator is compared with a multilevel modulator based on hysteresis comparators. Simulation and experimental results are presented in order to highlight the system operation and control robustness.

Low Complexity Intra Mode Selection for Efficient Distributed Video Coding

Motion compensated frame interpolation (MCFI) is one of the most efficient solutions to generate side information (SI) in the context of distributed video coding. However, it creates SI with rather significant motion compensated errors for some frame regions while rather small for some other regions depending on the video content. In this paper, a low complexity Infra mode selection algorithm is proposed to select the most 'critical' blocks in the WZ frame and help the decoder with some reliable data for those blocks. For each block, the novel coding mode selection algorithm estimates the encoding rate for the Intra based and WZ coding modes and determines the best coding mode while maintaining a low encoder complexity. The proposed solution is evaluated in terms of rate-distortion performance with improvements up to 1.2 dB regarding a WZ coding mode only solution.

The role of European "ro-ro" port terminals in the automotive supply chain management

The aim of this paper is concerned with the design and development of a functional framework for maritime mode integration in European automotive supply chain management when considering outbound distribution. Furthermore, it provides a readjustment of traditional concepts and terminology with findings that the role of ro-ro port terminals should be considered as decoupling points, poles and postponement platforms. Case studies examine relevant Western European ro-ro port terminals for cars and respective links to assembly/factories of vehicles localized in the hinterland and concludes that ro-ro port terminals reduce logistical friction and impedance, as well as promote space/time compression.

Intelligent decision making in electricity markets: simulated annealing Q-Learning

Electricity markets are complex environments, involving a large number of different entities, playing in a dynamic scene to obtain the best advantages and profits. MASCEM is a multi-agent electricity market simulator to model market players and simulate their operation in the market. Market players are entities with specific characteristics and objectives, making their decisions and interacting with other players. MASCEM is integrated with ALBidS, a system that provides several dynamic strategies for agents’ behavior. This paper presents a method that aims at enhancing ALBidS competence in endowing market players with adequate strategic bidding capabilities, allowing them to obtain the higher possible gains out of the market. This method uses a reinforcement learning algorithm to learn from experience how to choose the best from a set of possible actions. These actions are defined accordingly to the most probable points of bidding success. With the purpose of accelerating the convergence process, a simulated annealing based algorithm is included.