Hybrid finite element method applied to the analysis of free vibration of a spherical shell filled with fluid

In present study, a hybrid finite element method is applied to investigate the free vibration of spherical shell filled with fluid. The structural model is based on a combination of thin shell theory and the classical finite element method. It is assumed that the fluid is incompressible and has no free-surface effect. Fluid is considered as a velocity potential variable at each node of the shell element where its motion is expressed in terms of nodal elastic displacement at the fluid-structure interface. Numerical simulation is done and vibration frequencies for different filling ratios are obtained and compared with existing experimental and theoretical results. The dynamic behavior for different shell geometries, filling ratios and boundary conditions with different radius to thickness ratios is summarized. This proposed hybrid finite element method can be used efficiently for analyzing the dynamic behavior of aerospace structures at less computational cost than other commercial FEM software

Hybrid finite element method applied to the analysis of free vibration of spherical shell

In this study, free vibration analysis of spherical shell is carried out. The structural model is based on a combination of thin shell theory and the classical finite element method. Free vibration equations using the hybrid finite element formulation are derived and solved numerically. The results are validated using numerical and theoretical data available in the literature. The analysis is accomplished for spherical shells of different boundary conditions and radius to thickness ratios. This proposed hybrid finite element method can be used efficiently for design and analysis of spherical shells employed in high speed aircraft structures

Vertebral cryptococcosis in an immunocompetent patient - a case report

We report an unusual case of 70 years old, immunocompetent woman who was diagnosed with vertebral cryptococcosis. The diagnosis was made on the basis of radiological and histological findings. The outcome was favorable under antifungal treatment

Méningite récurrente révélant une maladie de Behçet: à propos de deux cas

Les étiologies des méningites sont surtout infectieuses. Les causes non infectieuses, sont souvent de  diagnostic difficile et incertain, tel est le cas de la maladie de Behçet. Nous rapportons deux observations de patients ayant présenté des épisodes récurrents de méningite. Dans un premier temps, la suspicion d’une étiologie infectieuse a conduit à introduire un traitement anti-infectieux probabiliste. La découverte à posteriori d’une aphtose bipolaire a permis de poser le diagnostic de maladie de Behçet. Une corticothérapie s’est révélée efficace. La maladie de Behçet doit toujours faire partie des diagnostics différentiels des méningites récurrentes.Key words: Méningite récurrente, maladie de Behçet, neuro-Behçe

Supersonic flutter of a spherical shell partially filled with fluid

In the present study, a hybrid finite element method is applied to investigate the dynamic behavior of a spherical shell partially filled with fluid and subjected to external supersonic airflow. The structural formulation is a combination of linear spherical shell theory and the classic finite element method. In this hybrid method, the nodal displacements are derived from exact solution of spherical shell theory rather than approximated by polynomial functions. Therefore, the number of elements is a function of the complexity of the structure and it is not necessary to take a large number of elements to get rapid convergence. Linearized first-order potential (piston) theory with the curvature correction term is coupled with the structural model to account for aerodynamic loading. It is assumed that the fluid is incompressible and has no free surface effect. Fluid is considered as a velocity potential at each node of the shell element where its motion is expressed in terms of nodal elastic displacements at the fluid-structure interface. Numerical simulation is done and vibration frequencies are obtained. The results are validated using numerical and theoretical data available in literature. The investigation is carried out for spherical shells with different boundary conditions, geometries, filling ratios, flow parameters, and radius to thickness ratios. Results show that the spherical shell loses its stability through coupled-mode flutter. This proposed hybrid finite element method can be used efficiently for analyzing the flutter of spherical shells employed in aerospace structures at less computational cost than other commercial FEM software

Survey of cylindrical shell response and wall-pressure fluctuations

Cylindrical shell response -- Shells response to internal pressure -- Shells response to acoustic excitaiton -- Shells response to random excitation -- Shells response to turbulent boundary-layer excitation -- Shells response to turbulent two-phase flow excitation -- Fluacting wall-pressure field of a turbulent boundary-layer -- Wall-pressure fluctuations of panel -- Wall-pressure fluctuations of body of revolution -- Wall-pressure fluctuations of pipe flow -- Influence of pickups shape and orientation on wall-pressure fluctuations measurements -- Wall-pressure fluctuation structure

Zantedeschia aethiopica (Araceae) a new species naturalized in the Northwest of Tunisia

Zantedeschia aethiopica (L.) Spreng. (Araceae), originating from S Africa, was found naturalized in many sites of the Kroumiria region (Northwest of Tunisia). This report represents the first record for the Tunisian flora. Distribution and ecological notes are also given

Cytotoxic effect of nanoparticles synthesized from Salvia officinalis L. and Ricinus communis aqueous extracts against vero cell line and evaluation of their antioxidant activities

The development of safe carriers for the use of plant extracts in industrial and health fields constitute a matter of serious concern. The development of plant derived nanoparticles may help to overcome such barriers. However, the major concern is still the safety of these carriers. The present study describes the synthesis of nanoparticles derived from Salvia officinalis L. and Ricinus communis and the evaluation of their cytotoxic and antioxidant effects. It is shown in this study that the aqueous extracts of S. officinalis L. and R. communis have the potentials to reduce silver nitrate ions to silver nanoparticles. The biosynthesized nanoparticles were analyzed by spectrophotometer and granulometric tests. The biological activities of these extracts and nanoparticles were carried out. S. officinalis L. leaf extract had the strongest antioxidant activity, followed by R. communis leaf and fruit extracts. Altogether, the synthesized nanoparticles were safe and may serve as antioxidant products in many fields.Key words: Plant material, biosynthesis of nanoparticle, cytotoxicity, cell culture, free radicals

Cosavirus, Salivirus and Bufavirus in Diarrheal Tunisian Infants

International audienceThree newly discovered viruses have been recently described in diarrheal patients: Cosa-virus (CosV) and Salivirus (SalV), two picornaviruses, and Bufavirus (BuV), a parvovirus. The detection rate and the role of these viruses remain to be established in acute gastroen-teritis (AGE) in diarrheal Tunisian infants. From October 2010 through March 2012, stool samples were collected from 203 children <5 years-old suffering from AGE and attending the Children's Hospital in Monastir, Tunisia. All samples were screened for CosV, SalV and BuV as well as for norovirus (NoV) and group A rotavirus (RVA) by molecular biology. Positive samples for the three screened viruses were also tested for astrovirus, sapovirus, ade-novirus, and Aichi virus, then genotyped when technically feasible. During the study period, 11 (5.4%) samples were positive for one of the three investigated viruses: 2 (1.0%) CosV-A10, 7 (3.5%) SalV-A1 and 2 (1.0%) BuV-1, whereas 71 (35.0%) children were infected with NoV and 50 (24.6%) with RVA. No mixed infections involving the three viruses were found, but multiple infections with up to 4 classic enteric viruses were found in all cases. Although these viruses are suspected to be responsible for AGE in children, our data showed that this association was uncertain since all infected children also presented infections with several enteric viruses, suggesting here potential water-borne transmission. Therefore, further studies with large cohorts of healthy and diarrheal children will be needed to evaluate their clinical role in AGE