Assessing aerodynamic flutter instability in prismatic structures with rectangular cross sections

Neste artigo estuda-se a ocorrência de instabilidade aerodinâmica por 'flutter' em estruturas prismáticas esbeltas de secção retangular. Considera-se um modelo com 2 graus de liberdade e obtém-se a sua formulação adimensional identificando-se um número mínimo de parâmetros adimensionais que regem a ocorrência de instabilidade por 'flutter' . Obtém-se uma muito boa concordância entre os resultados do modelo de 2 graus de liberdade e os resultados existentes na literatura. Este artigo tem 2 objetivos: (i) definir as condições para as quais estruturas esbeltas com secções retangulares podem instabilizar por 'flutter' sob a ação do vento e (ii) fornecer uma coleção alargada de resultados sob a forma de tabelas ou gráficos prontos a usar, cobrindo um largo número de casos, que proporciona aos projetistas de estruturas uma ferramenta que estes podem utilizar, a nível de pré-dimensionamento, para prever as velocidades críticas do vento que provocam a instabilidade por 'flutter' .This paper is dedicated to the study of the occurrence of 'flutter' instability in slender prismatic structures of rectangular cross section. A two degree of freedom model is considered and its non dimensional formulation is derived so that a minimum number of non dimensional parameters governing the occurrence of 'flutter' instability are put in evidence. A very good agreement has been obtained by comparing the results of the two degree of freedom model with the results available in the literature. The goal of this document is twofold: (i) to summarize the conditions for which slender structures with rectangular cross sections may get unstable by 'flutter' under the action of steady wind conditions and (ii) to supply a broad collection of data in the form of ready-to-use tables or graphics covering a wide range of cases, that provide a basis for designers to predict the critical wind velocities at the onset of 'flutter' instability.Peer Reviewe

A thermodynamically consistent growth law for collagen fiber reinforced tissues in a mixture context

International audienc

A thermodynamically consistent growth law for collagen fiber reinforced tissues in a mixture context

International audienc

Assessing aerodynamic flutter instability in prismatic structures with rectangular cross sections

This paper is dedicated to the study of the occurrence of flutter instability in slender prismatic structures of rectangular cross section. A two degree of freedom model is considered and its non dimensional formulation is derived so that a minimum number of non dimensional parameters governing the occurrence of flutter instability are put in evidence. A very good agreement has been obtained by comparing the results of the two degree of freedom model with the results available in the literature. The goal of this document is twofold: (i) to summarize the conditions for which slender structures with rectangular cross sections may get unstable by flutter under the action of steady wind conditions and (ii) to supply a broad collection of data in the form of ready-to-use tables or graphics covering a wide range of cases, that provide a basis for designers to predict the critical wind velocities at the onset of flutter instability

Complementarity eigenvalue problems for nonlinear matrix pencils

International audienc

microRNA transcriptome from activated ovaries of Apis mellifera workers

Póster presentado en el Sixth International symposium on Molecular Insect Science, celebrado en Amsterdam entre el 2 y 5 de octubre de 2011.When driven to extremes, continuous phenotypic variation can be broken giving rise to distinct dimorphic adaptive phenotypes, as is the case in the castes of highly social insects. In these, dimorphism is built around reproductive potential, such as in the honey bee, Apis mellifera, the best studied organism in this group. Queen ovaries are large and consist of 150-200 ovarioles, whereas those of workers are small, with only few ovarioles. Even though practically sterile while a queen is present in the colony, workers can activate their ovaries and lay male-producing eggs when queenless. The factors driving this change in the state of ovary activity in workers are still poorly understood. With microRNAs knowingly involved in fine tuning genomic responses in both developmental processes as well as systemic responses to environmental change we herein investigated the miRNA transcriptome in workers undergoing ovary activation. By means of Illumina deep-sequencing of size selected (<200 nt) transcripts we obtained 35 million reads. Read length ranged from 10 to 40 nt, the majority having 19 to 24 nt. About 90% of the reads could be mapped to the honey bee genome.Furthermore, 168 of the 331 miRNAs known for Apis mellifera were represented in our dataset, some highly expressed, as for instance the miRNAs 306, 317, 184, 1-2, 1-1, 276, 71, 14, 2-3 and 2-2. Independently of the expression rates and based on literature information, the identified miRNAs are described as linked to hormonal signaling cascades (miR-14, miR-34, let-7), germ cell or ovary development (miR-7, miR-278, miR-92b, miR-989, miR-318, miR-100, let-7), embryogenesis (miR-184, miR-989, miR-1-1), cell death suppression (miR-14, miR-263-b, miR-11, miR-2-2), cell growth (miR-318, miR-315, miR-8, miR-1-2), and caste differentiation (miR-9a, miR-9b). These biological processes are consistent with the molecular changes required to the ovary activation and miRNAs emerged as regulators of the reproductive status.Peer Reviewe

miR92b and miR-9a the novel candidates as regulators of the positive reproductive status in honeybees

Póster presentado en el Sixth International symposium on Molecular Insect Science, celebrado en Amsterdam entre el 2 y 5 de octubre de 2011.In a queenright colony of Apis mellifera the workers do not reproduce. However, the workers can activate their ovaries in response to the absence of the queen. However the genetic cascade behind this process is not fully understood. In view of miRNA multiple roles in gene regulation of a variety of developmental and reproductive processes, we investigated their occurrence by analyzing 35 million reads (Illumina) of a small RNA library from active ovaries of queenless A. mellifera workers. A set of 168 miRNA previously identified in honeybees were found. Using qPCR we compared the expression of let-7, miR-184, miR-92b and miR-9a (among the most differentially represented in the library and linked to reproductive and caste differentiation processes) in active and inactive worker ovaries. The miR-184 presented consistently highest expression levels in both samples. Despite its described function in Drosophila egg formation, our data suggest that miR-184 is also important in general ovary physiology.In addition, miR-184 showed the most stable expression rates in all analyzed samples and was used as internal control to normalize the expression of other miRNAs. The involvement of let-7 in reproduction, hormonal signaling and developmental timing is known for several metazoans. Since let-7 and miR-184 showed to be expressed at similar levels in both ovary types, we postulate they govern ovary basal metabolism independent of the activation status. The expression of miR-92b and miR-9a were significantly higher in active than inactive ovaries (p <0.05). These miRNAs are related to cell cycle control in embryonic stem cells and caste differentiation, respectively. Considering that egg laying workers behave as a queen as well as their active ovaries mimics the function of a queen ovary, our results add two novel candidates as regulators of the molecular cascade leading to maintaining the positive reproductive status in honeybee female castes.Peer Reviewe