The modeling of turbulent reactive flows based on multiple mapping conditioning

A new modeling approach-multiple mapping conditioning (MMC)-is introduced to treat mixing and reaction in turbulent flows. The model combines the advantages of the probability density function and the conditional moment closure methods and is based on a certain generalization of the mapping closure concept. An equivalent stochastic formulation of the MMC model is given. The validity of the closuring hypothesis of the model is demonstrated by a comparison with direct numerical simulation results for the three-stream mixing problem. (C) 2003 American Institute of Physics.

An electromagnetic-field method modeling of a radial line planar antenna with coupling probes

This communications describes an electromagnetic model of a radial line planar antenna consisting of a radial guide with one central probe and many peripheral probes arranged in concentric circles feeding an array of antenna elements such as patches or wire curls. The model takes into account interactions between the coupling probes while assuming isolation of radiating elements. Based on this model, computer programs are developed to determine equivalent circuit parameters of the feed network and the radiation pattern of the radial line planar antenna. Comparisons are made between the present model and the two-probe model developed earlier by other researchers.

Direction of Causation Modeling Between Cross-Sectional Measures of Parenting and Psychological Distress in Female Twins

Under certain conditions, cross-sectional analysis of cross-twin intertrait correlations can provide important information about the direction of causation (DOC) between two variables. A community-based sample of Australian female twins aged 18 to 45 years was mailed an extensive Health and Lifestyle Questionnaire (HLQ) that covered a wide range of personality and behavioral measures. Included were self-report measures of recent psychological distress and perceived childhood environment (PBI). Factor analysis of the PBI yielded three interpretable dimensions: Coldness, Overprotection, and Autonomy. Univariate analysis revealed that parental Overprotection and Autonomy were best explained by additive genetic, shared, and nonshared environmental effects (ACE), whereas the best-fitting model for PBI Coldness and the three measures of psychological distress (Depression, Phobic Anxiety, and Somatic Distress) included only additive genetic and nonshared environmental effects (AE). A common pathway model best explained the covariation between (1) the three PBI dimensions and (2) the three measures of psychological distress. DOC modeling between latent constructs of parenting and psychological distress revealed that a model which specified recollected parental behavior as the cause of psychological distress provided a better fit than a model which specified psychological distress as the cause of recollected parental behavior. Power analyses and limitations of the findings are discussed.

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.

Influence of magnetically-induced E-fields on cardiac electric activity during MRI: A modeling study

In modern magnetic resonance imaging (MRI), patients are exposed to strong, time-varying gradient magnetic fields that may be able to induce electric fields (E-fields)/currents in tissues approaching the level of physiological significance. In this work we present theoretical investigations into induced E-fields in the thorax, and evaluate their potential influence on cardiac electric activity under the assumption that the sites of maximum E-field correspond to the myocardial stimulation threshold (an abnormal circumstance). Whole-body cylindrical and planar gradient coils were included in the model. The calculations of the induced fields are based on an efficient, quasi-static, finite-difference scheme and an anatomically realistic, whole-body model. The potential for cardiac stimulation was evaluated using an electrical model of the heart. Twelve-lead electrocardiogram (ECG) signals were simulated and inspected for arrhythmias caused by the applied fields for both healthy and diseased hearts. The simulations show that the shape of the thorax and the conductive paths significantly influence induced E-fields. In healthy patients, these fields are not sufficient to elicit serious arrhythmias with the use of contemporary gradient sets. However, raising the strength and number of repeated switching episodes of gradients, as is certainly possible in local chest gradient sets, could expose patients to increased risk. For patients with cardiac disease, the risk factors are elevated. By the use of this model, the sensitivity of cardiac pathologies, such as abnormal conductive pathways, to the induced fields generated by an MRI sequence can be investigated. (C) 2003 Wiley-Liss, Inc.

Water table waves in an unconfined aquifer: Experiments and modeling

[1] Comprehensive measurements are presented of the piezometric head in an unconfined aquifer during steady, simple harmonic oscillations driven by a hydrostatic clear water reservoir through a vertical interface. The results are analyzed and used to test existing hydrostatic and nonhydrostatic, small-amplitude theories along with capillary fringe effects. As expected, the amplitude of the water table wave decays exponentially. However, the decay rates and phase lags indicate the influence of both vertical flow and capillary effects. The capillary effects are reconciled with observations of water table oscillations in a sand column with the same sand. The effects of vertical flows and the corresponding nonhydrostatic pressure are reasonably well described by small-amplitude theory for water table waves in finite depth aquifers. That includes the oscillation amplitudes being greater at the bottom than at the top and the phase lead of the bottom compared with the top. The main problems with respect to interpreting the measurements through existing theory relate to the complicated boundary condition at the interface between the driving head reservoir and the aquifer. That is, the small-amplitude, finite depth expansion solution, which matches a hydrostatic boundary condition between the bottom and the mean driving head level, is unrealistic with respect to the pressure variation above this level. Hence it cannot describe the finer details of the multiple mode behavior close to the driving head boundary. The mean water table height initially increases with distance from the forcing boundary but then decreases again, and its asymptotic value is considerably smaller than that previously predicted for finite depth aquifers without capillary effects. Just as the mean water table over-height is smaller than predicted by capillarity-free shallow aquifer models, so is the amplitude of the second harmonic. In fact, there is no indication of extra second harmonics ( in addition to that contained in the driving head) being generated at the interface or in the interior.

Surface stickiness of drops of carbohydrate and organic acid solutions during convective drying: Experiments and modeling

Drying kinetics of low molecular weight sugars such as fructose, glucose, sucrose and organic acid such as citric acid and high molecular weight carbohydrate such as maltodextrin (DE 6) were determined experimentally using single drop drying experiments as well as predicted numerically by solving the mass and heat transfer equations. The predicted moisture and temperature histories agreed with the experimental ones within 6% average relative (absolute) error and average difference of +/- 1degreesC, respectively. The stickiness histories of these drops were determined experimentally and predicted numerically based on the glass transition temperature (T-g) of surface layer. The model predicted the experimental observations with good accuracy. A nonsticky regime for these materials during spray drying is proposed by simulating a drop, initially 120 mum in diameter, in a spray drying environment.

Evaluating a model of parental influence on youth physical activity

Objective: To test a conceptual model linking parental physical activity orientations, parental support for physical activity, and children's self-efficacy perceptions with physical activity participation. Participants and Setting: The sample consisted of 380 students in grades 7 through 12 (mean age, 14.0 +/- 1.6 years) and their parents. Data collection took place during the fall of 1996. Main Outcome Measures: Parents completed a questionnaire assessing their physical activity habits, enjoyment of physical activity, beliefs regarding the importance of physical activity, and supportive behaviors for their child's physical activity. Students completed a 46-item inventory assessing physical activity during the previous 7 days and a 5-item physical activity self-efficacy scale. The model was tested via observed variable path analysis using structural equation modeling techniques (AMOS 4.0). Results: An initial model, in which parent physical activity orientations predicted child physical activity via parental support and child self-efficacy, did not provide an acceptable fit to the data. Inclusion of a direct path from parental support to child physical activity and deletion of a nonsignificant path from parental physical activity to child physical activity significantly improved model fit. Standardized path coefficients for the revised model ranged from 0.17 to 0.24, and all were significant at the p < 0.0001 level. Conclusions: Parental support was an important correlate of youth physical activity, acting directly or indirectly through its influence on self-efficacy. Physical activity interventions targeted at youth should include and evaluate the efficacy of individual-level and community-level strategies to increase parents' capacity to provide instrumental and motivational support for their children's physical activity.

Rates of electronic energy transfer in conformationally flexible bichromophoric macrocyclic complexes: a combined experimental and molecular modeling study

Electronic energy transfer (EET) rate constants between a naphthalene donor and anthracene acceptor in [ZnL4a](ClO4)(2) and [ZnL4b](ClO4)(2) were determined by time-resolved fluorescence where L-4a and L-4b are the trans and cis isomers of 6-((anthracen-9-yl-methyl)amino)-6,13-dimethyl-13-((naphthalen-1-yl-methyl)amino)-1,4,8,11-tetraazacyclotetradecane, respectively. These isomers differ in the relative disposition of the appended chromophores with respect to the macrocyclic plane. The trans isomer has an energy transfer rate constant (k(EET)) of 8.7 x 10(8) s(-1), whereas that of the cis isomer is significantly faster (2.3 x 10(9) s(-1)). Molecular modeling was used to determine the likely distribution of conformations in CH3CN solution for these complexes in an attempt to identify any distance or orientation dependency that may account for the differing rate constants observed. The calculated conformational distributions together with analysis by H-1 NMR for the [ZnL4a](2+) trans complex in the common trans-III N-based isomer gave a calculated Forster rate constant close to that observed experimentally. For the [ZnL4b](2+) cis complex, the experimentally determined rate constant may be attributed to a combination of trans-Ill and trans-I N-based isomeric forms of the complex in solution.

Representing organizational structures in enterprise architecture : an ontology-based approach

Arquitetura Corporativa promove o estabelecimento de uma visão holística da estrutura e forma de trabalho de uma organização. Um dos aspectos abordados em Arquitetura Corporativa está associada a "estrutura ativa" da organização, que diz respeito a “quem" realiza as atividades organizacionais. Várias abordagens têm sido propostas a fim de proporcionar um meio para a representação de Arquitetura Corporativa, entre as quais ARIS, RM-ODP, UPDM e ArchiMate. Apesar da aceitação por parte da comunidade, as abordagens existentes se concentram em propósitos diferentes, têm limitações de escopo e algumas não têm semântica de mundo real bem definida. Além das abordagens de modelagem, muitas abordagens de ontologias têm sido propostas, a fim de descrever o domínio de estrutura ativa, incluindo as ontologias de SUPER Project, TOVE, Enterprise Ontology e W3C Org Ontology. Embora especificadas para fundamentação semântica e negociação de significado, algumas das abordagens propostas têm fins específicos e cobertura limitada. Além disso, algumas das abordagens não são definidas usando linguagens formais e outras são especificadas usando linguagens sem semântica bem definida. Este trabalho apresenta uma ontologia de referência bem fundamentada para o domínio organizacional. A ontologia organizacional de referência apresentada abrange os aspectos básicos discutidos na literatura organizacional, tais como divisão do trabalho, relações sociais e classificação das unidades estruturais. Além disso, também abrange os aspectos organizacionais definidos em abordagens existentes, levando em consideração tanto abordagens de modelagem quanto abordagens ontológicas. A ontologia resultante é especificada em OntoUML e estende os conceitos sociais de UFO-C.

Modeling Carbon Nanotube Electrical Properties in CNT/Polymer Composites

In this work it is demonstrated that the capacitance between two cylinders increases with the rotation angle and it has a fundamental influence on the composite dielectric constant. The dielectric constant is lower for nematic materials than for isotropic ones and this can be attributed to the effect of the filler alignment in the capacitance. The effect of aspect ratio in the conductivity is also studied in this work. Finally, based on previous work and by comparing to results from the literature it is found that the electrical conductivity in this type of composites is due to hopping between nearest fillers resulting in a weak disorder regime that is similar to the single junction expression.

Multi-scale modeling of the mechanical behavior of polymer-based materials

Polymers have become the reference material for high reliability and performance applications. In this work, a multi-scale approach is proposed to investigate the mechanical properties of polymeric based material under strain. To achieve a better understanding of phenomena occurring at the smaller scales, a coupling of a Finite Element Method (FEM) and Molecular Dynamics (MD) modeling in an iterative procedure was employed, enabling the prediction of the macroscopic constitutive response. As the mechanical response can be related to the local microstructure, which in turn depends on the nano-scale structure, the previous described multi-scale method computes the stress-strain relationship at every analysis point of the macro-structure by detailed modeling of the underlying micro- and meso-scale deformation phenomena. The proposed multi-scale approach can enable prediction of properties at the macroscale while taking into consideration phenomena that occur at the mesoscale, thus offering an increased potential accuracy compared to traditional methods.

A problemática conceptual da contabilidade empresarial e pública – especial referência à valoração dos activos fixos tangíveis e das propriedades de investimento

A necessidade de comparabilidade da informação a nível internacional desencadeou os processos de harmonização da contabilidade, empresarial e pública, e a necessidade de criar uma base conceptual comum nos diferentes países. No âmbito empresarial, em Portugal, já se segue, com algumas adaptações, o descrito nas normas do IASB. Todavia, no âmbito público, neste mesmo país, os normativos nacionais ainda se afastam das normas internacionais do IPSASB. Dos vários elementos conceptuais da contabilidade, destaca-se a valoração dos activos, que constitui uma das preocupações das entidades públicas e privadas, na medida em que influi na fiabilidade e relevância da informação. No que tange à valoração dos activos fixos tangíveis e das propriedades de investimento, o custo histórico é um dos critérios mais indicados na sua valoração, se bem que o justo valor também seja indicado como critério aplicável, situação prevista nas normas internacionais e também em algumas normas portuguesas.

Estrutura conceptual para a Contabilidade Pública

Num contexto de globalização da economia mundial verifica-se uma constante e crescente preocupação pela normalização e harmonização contabilística. Tendo em mente essas preocupações e as mudanças ocorridas em Portugal na Contabilidade Pública, resultantes da Reforma da Administração Financeira do Estado, e mais recentemente da implementação do Plano Oficial de Contabilidade Pública, e de outros planos públicos sectoriais, a normalização da Contabilidade Pública sofreu alguns avanços com vista a uma maior coerência e convergência. Contudo, definir normas para a Contabilidade Pública implica ter subjacente um conjunto de conceitos capazes de orientar a interpretação dessa normativa. A definição de uma estrutura conceptual para a Contabilidade Pública pode partir das existentes para a Contabilidade Empresarial, em outros países ou no âmbito internacional, procedendo-se a uma adaptação destas em função das características e especificidades da Contabilidade Pública. Definir uma estrutura conceptual implica atender às características do meio ao qual o sistema de Contabilidade Pública se aplica, isto é, à Administração Pública, para a partir dessas, e das necessidades dos utilizadores da informação financeira pública, se definirem os objectivos que essa informação deve cumprir, bem como um conjunto de características qualitativas, ou também denominadas requisitos, aos quais ela deve obedecer. Partindo desses objectivos são enunciados os conceitos de cada um dos elementos das demonstrações financeiras públicas, para em conformidade com esses conceitos e com as características qualitativas, se enunciarem os critérios de reconhecimento e valorização de cada um desses elementos. O alcance da imagem fiel da situação económica e financeira da entidade implica a definição de um conjunto de princípios contabilísticos que, em conformidade com os objectivos e características da informação, contribua para o cumprimento destes e para tornar a Contabilidade Pública um sistema coerente e lógico. Todos estes elementos compõem a chamada estrutura conceptual para a Contabilidade Pública.

O controverso reconhecimento dos activos públicos face à actual situação conceptual da contabilidade pública em Portugal e Espanha

Con la reforma de la contabilidad pública, numeradamente en Portugal y España, la contabilidad patrimonial ha ganado importancia en este sistema contable, siendo necesario definir la composición y el valor del patrimonio de cada entidad pública. La clasificación de los diferentes elementos patrimoniales, numeradamente los activos, se convirtió en una de las preocupaciones de estas entidades, siendo necesario definir criterios exactos para su reconocimiento, lo que provocó una problemática conceptual en la Contabilidad Pública de los diversos países. En Portugal, la reforma de la Contabilidad Pública resultó en la implementación de planes públicos sectoriales, que poco se refieren à su encuadramiento conceptual, no haciendo mención, entre otros aspectos, al concepto y a los criterios de reconocimiento de los elementos de las demonstraciones financieras, por ejemplo de los activos. Por lo tanto, estos planes sectoriales de Contabilidad Pública muestran deficiencias conceptuales, que podrán superarse mediante la definición de un marco conceptual para la Contabilidad Pública en Portugal, partiendo de los existentes al nivel nacional e internacional de ámbito empresarial, y también de ámbito público, y haciendo los correspondientes ajustes, atendiendo a las particularidades de las entidades a las cuales este sistema contable se aplica. En España, el actual Plan General de Contabilidad Pública - PGCP, aprobado en 1994 y modificado posteriormente, tiene algunas deficiencias conceptuales. Sin embargo, en este país es evidente un avance conceptual en comparación con Portugal, ya que se ha publicado un borrador del nuevo PGCP en el año 2009, que incluye un marco conceptual para la Contabilidad Pública. Teniendo en cuenta el marco conceptual del PGCP (2009), así como otros marcos conceptuales existentes, la cuestión de lo que reconocer como un activo está más clara, mencionando dos requisitos de reconocimiento: el cumplimiento del concepto de activos y de sus dos criterios de reconocimiento, relacionados con la relevancia de un elemento para la entidad y la fiabilidad de su valoración. Por lo tanto, teniendo en cuenta estos dos requisitos, un elemento sólo puede ser reconocido como un activo cuando es económicamente controlado por la entidad, resulte de eventos pasados, se pueda utilizar en la prestación de servicios o en la obtención de beneficios para la entidad y, finalmente, cuando su valor puede ser valorado de forma fiable. Así, vemos que la definición del reconocimiento de los activos, y también los demás elementos de los estados financieros, es un elemento importante del marco conceptual de la contabilidad, que es esencial en la preparación y presentación de los estados financieros, que permite una aplicación más coherente de las normas contables, y por lo tanto una mayor comparabilidad de la información financiera.