1,721,062 research outputs found
Rionero's critical perturbations method via weighted energy for global stability of penetrative convection in porous media
No full textOn the stability of the Bénard problem for fluid mixture with viscosity and solute diffusivity depending on temperature
No full textInfluenza della viscosità sulla convezione
No full textIn questa conferenza é analizzata l'influenza di viscosità variabili sull'insorgere della convezione naturale in fluidi chiari
On the dynamics of predator-prey models with the Beddington-DeAngelis functional response, under Robin boundary conditions
No full textThe paper concerns the Beddington-DeAngelis predator-prey model, under Robin boundary conditions. General properties - such as boundedness, uniqueness and existence of invariant regions - are obtained. Linear stability (instability) threshold of the positive equilibrium state S (biologically meaningful) and diffusion-driven instability (Turing effect) are studied. In the framework of the L^2-energy stability, conditions guaranteeing stability and local attractiveness are obtained
Inertia effect on the onset of convection in rotating porous layers via the Rionero approach
No full textVia the Rionero approach the onset of convection in rotating porous layers in the presence of inertia is investigated. The effects of rotation and inertia are respectively measured through the Taylor number T and adasz number V. For the tridimensional perturbations and the full nonlinear problem, it is shown that: i) exists a critical Taylor number (≈3.80) below which the inertia has no effect on the onset of convection; ii) for T
greater then the critical value exists an associate critical Vadasz below which the inertia has effect on the onset of convection, and only in this case the convection arises via an oscillatory motion (overstable convection); iii) do not exist subcritical instabilities; iv) the global nonlinear stability is guaranteed by the linear stability
Convection in magnetohydrodynamic porous media
No full textMagnetohydrodynamic convection (MHD convection) in a horizontal porous-layer filled by a plasma, imbedded in a transverse magnetic field and heated from below, is investigated. As it is well known, the aforesaid problem is named magnetic porous convection and is of relevant interest in geology (subterranean flows of electrically conducting fluids in the Hearth magnetic field) and in industrial processes (metallurgy, liquid metals as current medium in a variety of nuclear reactors in a presence of strong magnetic field). For this reason, the magnetic convection has attracted - in the past as nowadays - the attention of many writers. In the present conference, the critical Rayleigh number is found and, in simple algebraic closed forms, conditions necessary and sufficient for the onset of steady and oscillatory convection are obtained. It is shown that the stabilizing effect of the magnetic field grows with the Chandrasekhar number. Moreover the stabilizing effect of Brinkmann viscosity (B.V.) in MHD convection is analyzed. The coincidence betwee the global nonlinear stability and linear stability is obtained
Stability analysis for a spatial ecology model
No full textStability/instability analysis of biologically meningfull equilibria for a spatial ecology model based on Luckinbill's experiment is performe
Risultati di stabilità relativi al modello di Forchheimer nei mezzi porosi per fluidi con viscosità dipendente dalla temperatura
No full textSono esposti recenti risultati di stabilità/instabilità della soluzione di conduzione per il problema di Horton-Rogers Lapwood adoperando il modello di Forchheimer nel caso di un fluido con viscistà dipendente dalla temperatur
Convezione naturale con gradiente orizzontale di temperatura
No full textAnalisi dell'influenza di gradienti orizzontali di temperatura sull'insorgere della convezione naturale nei fluidi chiar
A nonlinear L^2 stability analysis for a spatial ecology model based on Luckinbill's experiment
No full textIn the last 30 years the use of appropriate reaction terms in (spatial) ecology models has attracted the attention of several researchers. In particular, for prey-predator type systems, the choice of reaction terms has been based on the results of several experimental studies made to test the effect of predator’s
density changes upon the feeding rate per unit predator.
Many experimental results indicate that the feeding rate per unit predator react strongly to changes in density of predators. Beddington (1975) and De Angelis et al (1975), contemporarely but independently, suggested to include negative effects of increased predator biomass on the feeding rate through a very simple term that can simulate many cases of trophic interaction
characterized by the predator interface. In the present communication the L^2 stability of the coexistence equilibrium state have been performed through a new methodology introduced by Prof. S. Rionero which consists in using some peculiar functionals which link stability - instability results directly to the eigenvalues of the linear operator of the problem at hand
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