1,359,152 research outputs found
Intervista a Pier Luigi Celli, Direttore generale Luiss
No full textIntervista a Pier Luigi Celli, Direttore generale Luiss realizzata realizzata al Congresso Nazionale AIDP, 2-3 maggio 2008 nell'ambito del progetto CEK-lab. Celli ha discusso di competenze manageriali, imperfezione manageriale, e leadership
Angelo Celli e le ferrovie
No full textGli studi sulla malaria nelle ferrovie, condotti da Angelo Celli, portarono ad adottare i primi rimedi a fini di profilassi. Allo stesso tempo, Celli, in qualità di parlamentare delle Marche si occupò della costruzione delle ferrovie secondarie nel proprio territorio. Il saggio ne ricostruisce l'attività e come medico e come parlamentare nel settore delle ferrovie
Marangoni convection of a viscous fluid over a vibrating plate
No full textThis research presents a new insight into Marangoni convection through investigating, both numerically and analytically, the surface tension driven instability activated by a coupled effect of a vibrating plate and viscous dissipation. A horizontal, thin fluid layer is bounded from below by an impermeable, adiabatic plate that vibrates in the horizontal direction. The upper boundary is modelled by a free surface subject to a thermal boundary condition of the third kind (Robin). The internal heat generation due to viscous dissipation yields a vertical, potentially unstable temperature gradient. The linear stability analysis of the stationary terms of the basic state is performed. The perturbed flow, in the form of plane waves, is superimposed onto the basic state. The obtained system of ordinary differential equations is solved numerically by means of the Runge-Kutta method coupled with the shooting method. For the two limiting cases, the isothermal upper boundary and adiabatic upper boundary, the analytical solutions of the eigenvalue problem are obtained. The values of the critical parameter, which identifies the threshold for the onset of Marangoni convection, are presented
The Horton–Rogers–Lapwood problem for an inclined porous layer with permeable boundaries
No full textA formulation of the Horton–Rogers–Lapwood problem for a porous layer inclined with respect to the horizontal and characterized by permeable (isobaric) boundary conditions is presented. This formulation allows one to recover the results reported in the literature for the limiting cases of horizontal and vertical layer. It is shown that a threshold inclination angle exists which yields an upper bound to a parametric domain where the critical wavenumber is zero. Within this domain, the critical Darcy–Rayleigh number can be determined analytically. The stability analysis is performed for linear perturbations. The solution is found numerically, for the inclination angles above the threshold, by employing a Runge–Kutta method coupled with the shooting method
Modal and absolute thermal instability in a vertical porous layer
No full textThe conduction regime in a vertical porous layer subject to a horizontal temperature gradient is studied. The boundaries are considered as isothermal, with different temperatures, and permeable to the external environment. The linear stability of this basic flow state is analysed by testing the dynamics of the normal modes of perturbation. The numerical solution of the stability eigenvalue problem leads to the determination of the neutral stability condition. Then, the evolution in time of localised wavepacket perturbations is investigated leading to the determination of the threshold to absolute instability
Anisotropy and the Onset of the Thermoconvective Instability in a Vertical Porous Layer
No full textThe thermoconvective instability of the parallel vertical flow in a fluid saturated porous layer bounded by parallel open boundaries is studied. The open boundaries are assumed to be kept at constant uniform pressure while their temperatures are uniform and different, thus forcing a horizontal temperature gradient across the layer. The anisotropic permeability of the porous layer is accounted for by assuming the principal axes to be oriented along the directions perpendicular and parallel to the layer boundaries. A linear stability analysis based on the Fourier normal modes of perturbation is carried out by testing the effect of the inclination of the normal mode wavevector to the vertical. The neutral stability curves and the critical Rayleigh number for the onset of the instability are evaluated by solving numerically the stability eigenvalue problem
[Federigo Celli (c.1899), funerary sculpture]
No full textFrom Berresford: Federigo Celli (c.1899), Raffaello Romanelli, Cimitero Urbano, Lucca.Angel lifting child from tomb.Title from Berresford
Effects of anisotropy on the transition to absolute instability in a porous medium heated from below
No full textThe emerging instability of a forced throughflow in a fluid saturated
horizontal porous duct of rectangular cross section is investigated. The duct
is heated from below by assuming the horizontal boundaries to be at different
temperatures. Both the horizontal and the vertical boundaries are impermeable
and the basic flow is parallel to such boundaries. The porous medium is
anisotropic with different permeabilities in the vertical and horizontal
directions. The effect of the anisotropy on the onset of the buoyancy driven
modal instability and absolute instability is analysed. The parametric
conditions leading to the instability of the basic flow are determined by
employing an analytical dispersion relation. The different permeabilities in
the vertical and horizontal directions come out to play opposite roles in the
onset of modal instability and in the transition to absolute instability. It is
shown that an increasing vertical permeability has a destabilising effect,
while an increasing horizontal permeability has a stabilising effect.Comment: 10 pages, 7 figure
Onset of convective instability within an inclined porous layer with a permeable boundary
No full textThe investigation of the thresholds that identify the onset of convective instability in a fluid saturated porous layer is performed. The layer is inclined with respect to the horizontal and the boundaries are held at different uniform temperatures. The layer is also semi-permeable: one boundary is impermeable and the other one is permeable. This configuration yields a basic state characterised by a single convective cell, with zero mass flow rate, that fades for small inclination becoming completely motionless for the horizontal case. Since the central part of this cell is considered, the basic flow is parallel and the basic temperature profile is dominated by conduction. This basic state is perturbed employing small-amplitude disturbances such that the linear stability analysis can be performed. A Squire-type transformation is applied to reduce the complexity of the problem. A numerical procedure is employed to obtain the critical values of the governing parameters
Instability of parallel buoyant flow in a vertical porous layer with an internal heat source
No full textBuoyant flow in a vertical porous layer whose open boundaries are kept at uniform and different temperatures is analysed. The presence of a uniform volumetric heat source alters the conduction profile of the temperature field for the stationary parallel flow. It is shown that this stationary flow becomes unstable when either the temperature difference between the boundaries or the intensity of the volumetric heat source are sufficiently large. The linear instability is investigated through a study of normal mode disturbances. The stability eigenvalue problem is solved numerically by employing the shooting method. The neutral stability curves are obtained and the critical parameters at onset of instability are determined
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