A summary of new predictive high frequency thermo-vibrational models in porous media

In this chapter, we consider the effect of mechanical vibration on the onset of convection in porous media. The porous media is saturated either by a pure fluid or by a binary mixture. The importance of transport model on stability diagrams are presented and discussed. The stability threshold for the Darcy-Brinkman case in the RaTc-R and kc-R diagrams are presented (where RaTc, kc and R are the critical Rayleigh number, the critical wave number and the vibration parameters respectively). It is shown that there is a significant deviation from the Darcy model. In the thermo-solutal case with the Soret effect, the influence of vibration on the reduction of multi-cellular convection is emphasized. A new analytical relation for obtaining the threshold of mono-cellular convection is derived. This relation shows how the separation factor Ψ is related to controlling parameters of the problem, Ψ = f (R, ε*, Le) when the wave number k -> 0. The importance of vibrational parameter definition is highlighted and it is shown how, by using a proper definition for vibrational parameter, we may obtain compact relationship. It is also shown how this result may be used to increase components separation

Reação em campo à murcha bacteriana de cultivares de tomate em Roraima Bacterial wilt resistance in tomato cultivars in Roraima, Brazil

A murcha bacteriana causada por Ralstonia solanacearum (Smith) é a doença bacteriana mais importante do tomateiro na Região Norte do Brasil. Os objetivos deste trabalho foram avaliar o nível de resistência de cultivares de tomate, avaliar o progresso da murcha bacteriana nesses genótipos a fim de conhecer o comportamento da doença nos diferentes estádios de desenvolvimento da cultura, para auxiliar no manejo da epidemia, e determinar a época crítica para o desenvolvimento da doença nessas cultivares nas condições de Roraima. Os experimentos foram conduzidos em um campo naturalmente infestado com a biovar 1 de Rasltonia solanacearum, por dois anos. A área tinha um histórico de quatro anos de plantios sucessivos com plantas de tomate suscetíveis à murcha bacteriana, e as perdas alcançando até 100%. Para condução do experimento foram utilizadas mudas das cultivares Majestade, Nemonetta, Carmen, Liliane, Santa Clara, Sensação, San Vito, Gaúcho Melhorado, Hector e Laura. Foram feitas seis avaliações do número de tomateiros que apresentavam murcha irreversível e/ou morte durante o ciclo da cultura. Foram determinadas as variáveis área abaixo da curva de progresso da doença (AACPD) e a taxa de progresso da doença (r), incidência média (Y50), incidência máxima (Ymáx) e a incidência final da doença. Os valores de AACPD e da variável r para a cultivar Majestade foram menores que para as demais, demonstrando que houve menor incidência de plantas doentes nesta cultivar, indicando resistência. Embora o nível de resistência apresentado por esta cultivar não seja muito elevado, o cultivo da mesma é recomendável e viável para o plantio no Estado de Roraima, especialmente considerando-se os altos preços do tomate, que são adquiridos de outras regiões produtoras no país, embora somente esta resistência não garanta, sozinha, o controle adequado da doença, sendo necessárias outras medidas de controle associadas.<br>The bacterial wilt caused by Ralstonia solanacearum is the most important bacterial disease of tomato in the Brazilian North Region. The objectives of this study were to evaluate (1) the resistance level of ten tomato cultivars; (2) the progress of bacterial wilt in these genotypes in order to know the disease behavior in different stages of development of the crop, and (3) determine the critical time to disease development in these cultivars, in Roraima. The experiment was carried out in a field naturally infested with biovar 1 of R. solanacearum, during two years. The area was infested by cultivating susceptible tomato plants to bacterial wilt. The cvs. Majestade, Nemonetta, Carmen, Liliane, Santa Clara, Sensação, San Vito, Gaúcho Melhorado, Hector and Laura were cultivated in the infested field. Six disease incidence evaluations were done in seven plants with irreversible wilt and/or death during the crop cycle. The following variables were determined: area under the disease progress curve (AUPDC) and the progress rate (r), mean incidence (Y50), maximum incidence (Ymax) and the final incidence of the disease. The values of AUDPC and the variable r to 'Majestade' were the lowest, although the level of resistance shown by this cultivar was not very high. Therefore, 'Majestade' is recommended for planting in the State of Roraima, especially considering the high prices of tomatoes, which are purchased from other regions in the country. However, only the level of resistance of 'Majestade' is not sufficient for disease control, being necessary other control measures

Chaotic and Periodic Natural Convection for Moderate and High Prandtl Numbers in a Porous Layer subject to Vibrations

The analysis of natural convection for moderate and high Prandtl numbers in a fluid-saturated porous layer heated from below and subject to vibrations is presented with a twofold objective. First, it aims at investigating the significance of including a time derivative term in Darcy’s equation when wave phenomena are being considered. Second, it is dedicated to reporting results related to the route to chaos formoderate and high Prandtl number convection. The results present conclusive evidence indicating that the time derivative term in Darcy’s equation cannot be neglected when wave phenomena are being considered even when the coefficient to this term is extremely small. The results also show occasional chaotic “bursts” at specific values (or small range of values) of the scaled Rayleigh number, R, exceeding some threshold. This behavior is quite distinct from the case without forced vibrations, when the chaotic solution occupies a wide range of R values, interrupted only by periodic “bursts.” Periodic and chaotic solution alternate as the value of the scaled Rayleigh number varies.University of Pretoriahttp://link.springer.com/journal/11242hb201