Accounting for convective effects in zero-Mach-number thermoacoustic models

This paper presents a methodology to account for some mean-flow effects on thermo-acoustic instabilities when using the zero-Mach-number assumption. It is shown that when a computational domain is represented under the M=0 assumption, a nonzero-Mach-number element can simply be taken into account by imposing a proper acoustic impedance at the boundaries so as to mimic the mean flow effects in the outer, not computed flow domain. A model that accounts for the coupling between acoustic and entropy waves is presented. It relies on a “delayed entropy coupled boundary condition” (DECBC) for the Helmholtz equation satisfied by the acoustic pressure. The model proves able to capture low-frequency entropic modes even without mean-flow terms in the fluctuating pressure equation

Modeling and Real-Time Simulation of a Vascularized Liver Tissue

International audienceIn Europe only, about 100,000 deaths per year are related to cirrhosis or liver cancer. While surgery remains the option that offers the foremost success rate against such pathologies, several limitations still hinder its widespread development. Among the limiting factors is the lack of accurate planning systems, which has been a motivation for several recent works, aiming at better resection planning and training systems, relying on pre-operative imaging, anatomical and biomechanical modelling. While the vascular network in the liver plays a key role in defining the operative strategy, its influence at a biomechanical level has not been taken into account. In the paper we propose a real-time model of vascularized organs such as the liver. The model takes into account separate constitutive laws for the parenchyma and vessels, and defines a coupling mechanism between these two entities. In the evaluation section, we present results of in vitro porcine liver experiments that indicate a significant influence of vascular structures on the mechanical behaviour of tissue. We confirm the val- ues obtained in the experiments by computer simulation using standard FEM. Finally, we show that the conventional modelling approach can be efficiently approximated with the proposed composite model capable of real-time calculations

Is Venice an ideal habitat for Legionella pneumophila?

Introduction. Legionella bacterium manifests itself in Legion- naire?s disease and Pontiac fever, it is mainly found and trans- mitted by aerosol produced in cooling towers, water distribution plants and medical equipment, and it affects mainly elder persons in poor health. Methods. The population of Venice Local Health Unit was divided in two areas of study and the incidence of legionellosis in residents of Venice historical centre (Distretto Sanitario 1) and in residents of the mainland and coastal areas (Distretti Sanitari 2, 3, 4) was calculated. The cases were those notified to the Public Health Unit by law, and the population of residents was that of the eligible for health care in the archives of the Local Health Unit. Only cases of legionellosis in residents who had not travelled in the 10 days previous of the onset of disease, and not related to nosocomial clusters were considered. The standardized incidence ratio was then calculated and confidence interval were defined by Poisson distribution. Results. Given the population of the two areas, 59801 in Distretto Sanitario 1 and 237555 in Distretti 2, 3, 4, the raw incidence of disease is respectively 87 per 100000 and 20 per 100000 in time 2002-2010. The standardized incidence ratio for the population of Distretto Sanitario 1 vs the remaining population is 4.3. Discussion. The difference in risk of getting the disease in this two residential areas geographically very close, is probably related to the different buildings? characteristics, old and difficult to main- tain in Venice historical centre

Índices de sítios para Hovenia dulcis Thunberg na região central do estado do Rio Grande do Sul, Brasil.

Este trabalho teve como objetivo construir curvas índice de sítios florestais, a partir da altura dominante e idade, de populações localizadas na região central do Estado do Rio Grande do Sul. Para tanto, foram utilizadas informações de três povoamentos (sítios) com idades de 25 anos, localizados na Fundação de Pesquisa Agropecuária (FEPAGRO). Para classificar os sítios florestais, coletaram-se informações de 18 árvores dominantes nos locais, observando a metodologia para análise de tronco. Na construção das curvas de índice de sítio, foi o selecionado o modelo de Backman, ficando constatada a necessidade da construção de dois conjuntos de curvas, com intervalo de 2 m, da idade de 5 a 25 anos, com idade índice de 25 anos. Para o Sítio I-A, foram geradas 3 curvas índices, de 22 a 24 m e, para os Sítios I-B+II+III, 6 curvas índices de 8 a 18 m

The multidimensional causal factors of ‘wet litter’ in chicken-meat production

The problem of ‘wet litter’, which occurs primarily in grow-out sheds for meat chickens (broilers), has been recognised for nearly a century. Nevertheless, it is an increasingly important problem in contemporary chicken-meat production as wet litter and associated conditions, especially footpad dermatitis, have developed into tangible welfare issues. This is only compounded by the market demand for chicken paws and compromised bird performance. This review considers the multidimensional causal factors of wet litter. While many causal factors can be listed it is evident that the critical ones could be described as micro-environmental factors and chief amongst them is proper management of drinking systems and adequate shed ventilation. Thus, this review focuses on these environmental factors and pays less attention to issues stemming from health and nutrition. Clearly, there are times when related avian health issues of coccidiosis and necrotic enteritis cannot be overlooked and the development of efficacious vaccines for the latter disease would be advantageous. Presently, the inclusion of phytate-degrading enzymes in meat chicken diets is routine and, therefore, the implication that exogenous phytases may contribute to wet litter is given consideration. Opinion is somewhat divided as how best to counter the problem of wet litter as some see education and extension as being more beneficial than furthering research efforts. However, it may prove instructive to assess the practice of whole grain feeding in relation to litter quality and the incidence of footpad dermatitis. Additional research could investigate the relationships between dietary concentrations of key minerals and the application of exogenous enzymes with litter quality

Taxa de corte sustentável para manejo das florestas tropicais.

Existe uma grande lacuna dos planos de manejo de florestas tropicais com relação à intensidade de extração e às taxas de corte, usualmente sendo definidas de forma arbitrária. Este trabalho visa definir intensidades de corte diferenciadas para grupos de espécies arbóreas comerciais, com diferentes ritmos de crescimento, por unidade de produção, no estado do Amazonas. Utilizou-se o incremento periódico anual percentual em volume, de 26 espécies arbóreas, obtido de parcelas permanentes. O incremento periódico anual, percentual em volume, para efeito diferenciador, considerou 1% como diferença limite. Foram identificadas três intensidades de corte, para as classes comerciais: 24,4% (grupo I), 35,4% (grupo II) e 42,4% (grupo III). Considerando a exploração total sustentável por hectare, para as 26 espécies, seria de 11,5 m³ha-1 com intensidade de corte de 37%. O procedimento de cálculo é simples e pode ser utilizado pelos órgãos fiscalizadores, certificadores ou legisladores como balizador do ciclo de corte e taxa de corte

Taxa de corte sustentável para manejo das florestas tropicais.

Existe uma grande lacuna dos planos de manejo de florestas tropicais com relação à intensidade de extração e às taxas de corte, usualmente sendo definidas de forma arbitrária. Este trabalho visa definir intensidades de corte diferenciadas para grupos de espécies arbóreas comerciais, com diferentes ritmos de crescimento, por unidade de produção, no estado do Amazonas. Utilizou-se o incremento periódico anual percentual em volume, de 26 espécies arbóreas, obtido de parcelas permanentes. O incremento periódico anual, percentual em volume, para efeito diferenciador, considerou 1% como diferença limite. Foram identificadas três intensidades de corte, para as classes comerciais: 24,4% (grupo I), 35,4% (grupo II) e 42,4% (grupo III). Considerando a exploração total sustentável por hectare, para as 26 espécies, seria de 11,5 m³ha-1 com intensidade de corte de 37%. O procedimento de cálculo é simples e pode ser utilizado pelos órgãos fiscalizadores, certificadores ou legisladores como balizador do ciclo de corte e taxa de corte

Using LES to Study Reacting Flows and Instabilities in Annular Combustion Chambers

Great prominence is put on the design of aeronautical gas turbines due to increasingly stringent regulations and the need to tackle rising fuel prices. This drive towards innovation has resulted sometimes in new concepts being prone to combustion instabilities. In the particular field of annular combustion chambers, these instabilities often take the form of azimuthal modes. To predict these modes, one must compute the full combustion chamber, which remained out of reach until very recently and the development of massively parallel computers. Since one of the most limiting factors in performing Large Eddy Simulation (LES) of real combustors is estimating the adequate grid, the effects of mesh resolution are investigated by computing full annular LES of a realistic helicopter combustion chamber on three grids, respectively made of 38, 93 and 336 million elements. Results are compared in terms of mean and fluctuating fields. LES captures self-established azimuthal modes. The presence and structure of the modes is discussed. This study therefore highlights the potential of LES for studying combustion instabilities in annular gas turbine combustors