A unified model of flames as gasdynamic discontinuities

Viewed on a hydrodynamic scale, flames in experiments are often thin so that they may be described as gasdynamic discontinuities separating the dense cold fresh mixture from the light hot burned products. The original model of a flame as a gasdynamic discontinuity was due to Darrieus and to Landau. In addition to the fluid dynamical equations, the model consists of a flame speed relation describing the evolution of the discontinuity surface, and jump conditions across the surface which relate the fluid variables on the two sides of the surface. The Darrieus-Landau model predicts, in contrast to observations, that a uniformly propagating planar flame is absolutely unstable and that the strength of the instability grows with increasing perturbation wavenumber so that there is no high-wavenumber cutoff of the instability. The model was modified by Markstein to exhibit a high-wavenumber cutoff if a phenomenological constant in the model has an appropriate sign. Both models are postulated, rather than derived from first principles, and both ignore the flame structure, which depends on chemical kinetics and transport processes within the flame. At present, there are two models which have been derived, rather than postulated, and which are valid in two non-overlapping regions of parameter space. Sivashinsky derived a generalization of the Darrieus-Landau model which is valid for Lewis numbers (ratio of thermal diffusivity to mass diffusivity of the deficient reaction component) bounded away from unity. Matalon & Matkowsky derived a model valid for Lewis numbers close to unity. Each model has its own advantages and disadvantages. Under appropriate conditions the Matalon-Matkowsky model exhibits a high-wavenumber cutoff of the Darrieus-Landau instability. However, since the Lewis numbers considered lie too close to unity, the Matalon-Matkowsky model does not capture the pulsating instability. The Sivashinsky model does capture the pulsating instability, but does not exhibit its high-wavenumber cutoff. In this paper, we derive a model consisting of a new flame speed relation and new jump conditions, which is valid for arbitrary Lewis numbers. It captures the pulsating instability and exhibits the high-wavenumber cutoff of all instabilities. The flame speed relation includes the effect of short wavelengths, not previously considered, which leads to stabilizing transverse surface diffusion terms.

Stability of planar flames as gasdynamic discontinuities

The stability of a steadily propagating planar premixed flame has been the subject of numerous studies since Darrieus and Landau showed that in their model flames are unstable to perturbations of any wavelength. Moreover, the instability was shown to persist even for very small wavelengths, i.e. there was no high-wavenumber cutoff of the instability. In addition to the Darrieus-Landau instability, which results from thermal expansion, analysis of the diffusional thermal model indicates that premixed flames may exhibit cellular and pulsating instabilities as a consequence of preferential diffusion. However, no previous theory captured all the instabilities including a high-wavenumber cutoff for each. In Class, Matkowsky & Klimenko (2003) a unified theory is proposed which, in appropriate limits and under appropriate assumptions, recovers all the relevant previous theories. It also includes additional new terms, not present in previous theories. In the present paper we consider the stability of a uniformly propagating planar flame as a solution of the unified model. The results are then compared to those based on the models of Darrieus-Landau, Sivashinsky and Matalon-Matkowsky. In particular, it is shown that the unified model is the only model to capture the Darrieus-Landau, cellular and pulsating instabilities including a high-wavenumber cutoff for each.

Numerical investigation of turbulent flow around a rotating stepped cylinder for corrosion study

Direct numerical simulation has been carried out for turbulent flow set up by a rotating cylinder with two backward-facing steps axisymmetrically mounted in the circumferential direction. This flow geometry creates a qualitatively similar flow pattern as observed near, a sudden, pipe expansion or a plane backward-facing step, characterized by flow separation and reattachment. A region of intense turbulence intensity and high wall-shear-stress fluctuations is formed in,the recirculating I region downstream of the step, where high mass-transfer capacity was also experimentally observed. Since, corrosion is frequently mass-transfer., controlled, our findings, put forward this apparatus as useful tool for future corrosion research.

Stratigraphy, facies architecture and tectonic implications of the Upper Devonian to Lower Carboniferous Campwyn Volcanics of the northern New England Fold Belt

Upper Devonian to Lower Carboniferous strata of the Campwyn Volcanics of east central Queensland preserve a substantial sequence of first-cycle volcaniclastic sedimentary and coeval volcanic rocks that record prolonged volcanic activity along the northern New England Fold Belt. The style and scale of volcanism varied with time, producing an Upper Devonian sequence of mafic volcano-sedimentary rocks overlain by a rhyolitic ignimbrite-dominated sequence that passes upward into a Lower Carboniferous limestone-bearing sedimentary sequence. We define two facies associations for the Campwyn Volcanics. A lower facies association is dominated by mafic volcanic-derived sedimentary breccias with subordinate primary mafic volcanic rocks comprising predominantly hyaloclastite and peperite. Sedimentary breccias record episodic and high energy, subaqueous depositional events with clastic material sourced from a mafic lava-dominated terrain. Some breccias contain a high proportion of attenuated dense, glassy mafic juvenile clasts, suggesting a syn-eruptive origin. The lower facies association coarsens upwards from a lithic sand-dominated sequence through a thick interval of pebble- to boulder-grade polymict volcaniclastic breccias, culminating in facies that demonstrate subaerial exposure. The silicic upper facies association marks a significant change in eruptive style, magma composition and the nature of eruptive sources, as well as the widespread development of subaerial depositional conditions. Crystal-rich, high-grade, low- to high-silica rhyolite ignimbrites dominate the base of this facies association. Biostratigraphic age controls indicate that the ignimbrite-bearing sequences are Famennian to lower-mid Tournaisian in age. The ignimbrites represent extra-caldera facies with individual units up to 40 m thick and mostly lacking coarse lithic breccias. Thick deposits of pyroclastic material interbedded with fine-grained siliceous sandstone and mudstone (locally radiolarian-bearing) were deposited from pyroclastic flows that crossed palaeoshorelines or represent syn-eruptive, resedimented pyroclastic material. Some block-bearing lithic-pumice-crystal breccias may also reflect more proximal subaqueous silicic explosive eruptions. Crystal-lithic sandstones interbedded with, and overlying the ignimbrites, contain abundant detrital volcanic quartz and feldspar derived from the pyroclastic deposits. Limestone is common in the upper part of the upper facies association, and several beds are oolitic (cf. Rockhampton Group of the Yarrol terrane). Overall, the upper facies association fines upward and is transgressive, recording a return to shallow-marine conditions. Palaeocurrent data from all stratigraphic levels in the Campwyn Volcanics indicate that the regional sediment-dispersal direction was to the northwest, and opposed to the generally accepted notion of easterly sediment dispersal from a volcanic arc source. The silicic upper facies association correlates in age and lithology to Early Carboniferous silicic volcanism in the Drummond (Cycle 1) and Burdekin Basins, Connors Arch, and in the Yarrol terranes of eastern Queensland. The widespread development of silicic volcanism in the Early Carboniferous indicates that silicic (rift-related) magmatism was not restricted to the Drummond Basin, but was part of a more substantial silicic igneous province.

Numerical simulations of wind and temperature structure within an Alpine lake basin, Lake Tekapo, New Zealand

High-resolution numerical model simulations have been used to study the local and mesoscale thermal circulations in an Alpine lake basin. The lake (87 km(2)) is situated in the Southern Alps, New Zealand and is located in a glacially excavated rock basin surrounded by mountain ranges that reach 3000 m in height. The mesoscale model used (RAMS) is a three-dimensional non-hydrostatic model with a level 2.5 turbulence closure scheme. The model demonstrates that thermal forcing at local (within the basin) and regional (coast-to-basin inflow) scales drive the observed boundary-layer airflow in the lake basin during clear anticyclonic summertime conditions. The results show that the lake can modify (perturb) both the local and regional wind systems. Following sunrise, local thermal circulations dominate, including a lake breeze component that becomes embedded within the background valley wind system. This results in a more divergent flow in the basin extending across the lake shoreline. However, a closed lake breeze circulation is neither observed nor modelled. Modelling results indicate that in the latter part of the day when the mesoscale (coast-to-basin) inflow occurs, the relatively cold pool of lake air in the basin can cause the intrusion to decouple from the surface. Measured data provide qualitative and quantitative support for the model results.

Integrated control of nitrate recirculation and external carbon addition in a predenitrification system

The integrated control of nitrate recirculation and external carbon addition in a predenitrification biological wastewater treatment system is studied. The proposed control structure consists of four feedback control loops, which manipulate the nitrate recirculation and the carbon dosage flows in a highly coordinated manner such that the consumption of external carbon is minimised while the nitrate discharge limits (based on both grab and composite samples) are met. The control system requires the measurement of the nitrate concentrations at the end of both the anoxic and the aerobic zones. Distinct from ordinary control systems, which typically minimise the variation in the controlled variables, the proposed control system essentially maximises the diurnal variation of the effluent nitrate concentration and through this maximises the use of influent COD for denitrification, thus minimising the requirement for external carbon source. Simulation studies using a commonly accepted simulation benchmark show that the controlled system consistently achieves the designated effluent quality with minimum costs.

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.

On the evaluation of some differential formulations for the pom-pom constitutive model

In recent years, progress has been made in modelling long chain branched polymers by the introduction of the so-called pompom model. Initially developed by McLeish and Larson (1998), the model has undergone several improvements or alterations, leading to the development of new formulations. Some of these formulations however suffer from certain mathematical defects. The purpose of the present paper is to review some of the formulations of the pom-pom constitutive model, and to investigate their possible mathematical defects. Next, an alternative formulation is proposed, which does not appear to exhibit mathematical defects, and we explore its modelling performance by comparing the predictions with experiments in non-trivial rheometric flows of an LDPE melt. The selected rheometric flows are the double step strain, as well as the large amplitude oscillatory shear experiments. For LAOS experiments, the comparison involves the use of Fourier-transform analysis.

Exclusi??n social y pol??ticas de inclusi??n. Algunos elementos sobre la realidad europea y espa??ola

La globalizaci??n econ??mica ha impactado fuertemente en el mercado laboral europeo, abriendo puertas para el trabajo precario. Mientras el capital se torna global, el trabajo permanece local y m??s sumiso a los flujos econ??micos mundiales. Adem??s, los patrones de la sociedad de consumo se han consolidado, promoviendo nuevas desigualdades sociales y aumentando los riesgos de exclusi??n y vulnerabilidad social. La ca??da progresiva del industrialismo tambi??n afecta las principales bases de la estructura social como los roles de g??nero o las relaciones familiares. Diferentes redes aparecen como clave para la inclusi??n, especialmente en el actual contexto de crisis del Estado de Bienestar Social en que se encuentra Europa. Es decir, el an??lisis de la exclusi??n social debe tener en cuenta la evoluci??n de las pol??ticas sociales en toda Europa y la tendencia actual de descentralizaci??n y focalizaci??n de los ser vicios sociales. El objetivo de este art??culo es, por lo tanto, no s??lo describir el fen??meno de la exclusi??n social, sino tambi??n lanzar ideas para construir nuevos criterios de redefinici??n de las pol??ticas sociales.

Articula????o federativa na presta????o de servi??os sociais no Brasil

O artigo analisa as mudan??as na presta????o de servi??os p??blicos a partir da Constitui????o de 1988, quando um novo pacto federativo acompanhou a redemocratiza????o pol??tica, resultando em ampla descentraliza????o para estados e munic??pios, acompanhada de nova estrutura de reparti????o dos recursos tribut??rios. Com esse objetivo, resgata-se o processo de forma????o de sistemas de presta????o de servi??os baseados na coopera????o entre as tr??s esferas de governo, focalizando as ??reas de educa????o, sa??de e assist??ncia social. Discutem-se as inova????es adotadas com a cria????o de formas organizacionais de negocia????o entre os entes federativos; a incorpora????o da participa????o social na formula????o e controle das pol??ticas p??blicas; a desburocratiza????o dos fluxos de recursos financeiros e de informa????es; e a ado????o de novos instrumentos jur??dicos de descentraliza????o de programas e a????es. O texto aponta ainda os impactos dessa descentraliza????o e das formas de articula????o federativa, indicando a necessidade de novas reformas nos sistemas administrativos e na pol??tica de recursos humanos.

Configurações territoriais múltiplas: reflexões a partir de O Anti-édipo : capitalismo e esquizofrenia de Gilles Deleuze e Félix Guattari

Este texto lança algumas reflexões sobre os axiomas do capitalismo que permitem descodificar todas as convenções das sociedades chamadas “selvagens”, e realizar as promessas de poder das sociedades déspotas, “bárbaras”. Simultaneamente, o capitalismo, provoca uma multiplicação das fraturas territoriais e de globalizações de toda ordem. Nessa descodificação de todos os valores, os fluxos (sociais, econômicos, políticos) liberados pelo capitalismo hesitam entre, de um lado, uma descodificação que levaria a uma desterritorialização radical dos processos e, de outro lado, um reaparecimento e re-atualização conservadora desses fluxos liberados pelo próprio processo de “criação destrutiva”.

Metodologia para obtenção do hidrograma de escoamento superficial em encostas e canais. Parte I: desenvolvimento e avaliação

Desenvolveu-se uma metodologia que permite obter o hidrograma de escoamento superficial e a vazão máxima para qualquer posição ao longo de uma encosta e para seções transversais de canais utilizando o modelo de ondas cinemáticas. A área da encosta é dividida num sistema matricial composto por 100 linhas e 100 colunas. Na encosta, considera-se que o escoamento ocorre na direção da declividade e que a vazão de cada pixel é a soma da vazão produzida nesse com a vazão advinda dos pixels que contribuem com o escoamento superficial para o pixel em análise. No canal, a vazão é calculada pela soma dos hidrogramas advindos das colunas do sistema reticulado. A comparação entre os valores de lâmina e vazão máxima de escoamento superficial obtidas experimentalmente e calculadas em duas condições (encosta e bacia) permitiu evidenciar que a metodologia, comparada aos métodos Racional e do Número da Curva, ofereceu boas estimativas tanto da lâmina quanto da vazão máxima de escoamento superficial.

Interfaces : educação especial & seguridade social

Com a Constituição da República Federativa do Brasil (1988), a intersetorialidade imprimiu nas políticas públicas de educação e seguridade social uma construção e uma operacionalidade mais articuladas e interdependentes. Entre as leis e portarias interministeriais, destaca-se o Programa Benefício de Prestação Continuada na Escola, que atende pessoas com deficiência de zero a dezoito anos de idade. Nesta pesquisa, questionam-se as interfaces entre as políticas públicas da educação especial e da seguridade social. São objetivos da pesquisa: analisar as interfaces das políticas públicas sociais – educação especial e seguridade social – no que se refere à garantia de direitos à educação de crianças com deficiência ou Transtornos Globais do Desenvolvimento, entre zero e cinco anos, no município de Vitória, Estado do Espírito Santo; identificar como se configuram as interdependências entre profissionais da educação especial e da seguridade social e os familiares (pais ou responsáveis) dessas crianças perante seus processos educacionais; compreender os diferentes movimentos entre as instituições de educação e da seguridade social e suas implicações para a inclusão escolar das crianças com deficiência ou Transtorno Global do Desenvolvimento; analisar como os profissionais da educação e da seguridade social lançam perspectivas para os processos de inclusão escolar e estabelecem diálogo com a família acerca da educação dessas crianças. Esta é uma pesquisa de natureza qualitativa, estudo de caso com coleta de dados empíricos e bibliográficos, na qual foram sujeitos: mães de três crianças de três Centros Municipais de Educação Infantil de Vitória; professoras da sala de atividades e de educação especial, pedagogas e diretoras; técnicos das Secretarias Municipais de Vitória: Educação, Saúde e Assistência Social e do Instituto Nacional do Seguro Social. As técnicas empregadas para coleta de dados foram a entrevista o grupo focal e o diário de itinerância. Foram procedimentos adotados para o registro dos dados a audiogravação de entrevistas e de grupos focais e anotações em diário de itinerância. Os dados foram organizados em cinco categorias de análise, produzidas por meio das narrativas dos familiares e dos profissionais participantes da pesquisa. Os conceitos de Norbert Elias, interdependência e configuração, relação de poder – estabelecidos e outsiders –, processos sociais e relação entre sociedade e Estado (balança do poder) contribuíram para compreender os dados, por serem observados nas categorias produzidas. Os resultados apontam para a fragilidade de Global do Desenvolvimento, no município de Vitória. Revelam, ainda, uma inconsistência de fluxos de referência e contrarreferência e lacunas na dimensão técnica e operativa para as interfaces das políticas públicas intersetoriais com práticas profissionais que cumpram o papel político conforme outorga a legislação federal e municipal. As considerações se ampliam para discussões entre o instituído e o instituinte – políticas públicas e práticas profissionais – que priorizem a efetivação da intersetorialidade diante das demandas do público investigado com vista à garantia dos direitos de acesso a uma educação de qualidade.

Currículo-fabulação : a curiosa metamorfose de Francis Tracart

Tem por proposta subversar a escrita linear acadêmica ao (re)fazê-la, vislumbrando as potências e transgressões da literatura menor em seus agenciamentos coletivos, políticos, em seus gaguejos e balbucios, em suas possibilidades de subversão. Fabular a escrita acadêmica e o currículo como ato político e coletivo, como reinvenção da própria língua. Trata da metamorfose de Francis Tracart em sua busca por traçar conceitos,conversações, percepções e afecções. A metodologia se dá por intermédio da pesquisa com os cotidianos e com a cartografia, buscando atentar-se a vozes, entrelinhas, efeitos, tensões, teórico-práticas e saberesfazeres dos sujeitos praticantes dos cotidianos da escola em que se realiza a pesquisa em pé de igualdade com os autores dos livros que permearam o processo de realização do trabalho de pesquisa. Os sujeitos cotidianos, tais como bibliotecária, professoras e alunos de 5º e 6º Ano, orientador, professores e alunos de Pós- Graduação, que participaram do processo de pesquisa, bem como os autores dos livros lidos, se fazem presentes nas vozes, nas falas, nos afectos e nas conversações com leituras, literaturas, currículos, cotidianos, redes de afecções, elementos éticos, estéticos e políticos, espaçostempos, com linhas de fuga, linhas molares e linhas moleculares, com os presentes politemporais,devires, conceitos, metamorfoses, com possíveis e improváveis leituras, fugas e reinvenções do leitor.