Different transport regimes in a spatially-extended recirculating background

Passive scalar transport in a spatially-extended background of roll convection is considered in the time-periodic regime. The latter arises due to the even oscillatory instability of the cell lateral boundary, here accounted for by sinusoidal oscillations of frequency $\omega$. By varying the latter parameter, the strength of anticorrelated regions of the velocity field can be controled and the conditions under which either an enhancement or a reduction of transport takes place can be created. Such two ubiquitous regimes are triggered by a small-scale(random) velocity field superimposed to the recirculating background. The crucial point is played by the dependence of Lagrangian trajectories on the statistical properties of the small-scale velocity field, e.g. its correlation time or its energy.Comment: 9 pages Latex; 5 figure

Large-Eddy Simulation closures of passive scalar turbulence: a systematic approach

The issue of the parameterization of small scale (``subgrid'') turbulence is addressed in the context of passive scalar transport. We focus on the Kraichnan advection model which lends itself to the analytical investigation of the closure problem. We derive systematically the dynamical equations which rule the evolution of the coarse-grained scalar field. At the lowest-order approximation in $l/r$, $l$ being the characteristic scale of the filter defining the coarse-grained scalar field and $r$ the inertial range separation, we recover the classical eddy-diffusivity parameterization of small scales. At the next-leading order a dynamical closure is obtained. The latter outperforms the classical model and is therefore a natural candidate for subgrid modelling of scalar transport in generic turbulent flows.Comment: 10 LaTex pages, 1 PS figure. Changes: comments added below previous (3.10); Previous (3.16) has been corrected; Minor changes in the conclusion

Flapping states of an el astically anchored wing in a uniform flow

Linear stability analysis of an elastically anchored wing in a uniform flow is investigated both analytically and numerically. The analytical formulation explicitly takes into account the effect of the wake on the wing by means of Theodorsen's theory. Three different parameters non-trivially rule the observed dynamics: mass density ratio between wing and fluid, spring elastic constant and distance between the wing center of mass and the spring anchor point on the wing. We found relationships between these parameters which rule the transition between stable equilibrium and fluttering. The shape of the resulting marginal curve has been successfully verified by high Reynolds number direct numerical simulations. Our findings are of interest in applications related to energy harvesting by fluid-structure interaction, a problem which has recently attracted a great deal of attention. The main aim in that context is to identify the optimal physical/geometrical system configuration leading to large sustained motion, which is the source of energy we aim to extract.Comment: 10 pages, 11 figures, submitted to J. Fluid. Mec

An approximation scheme for an Eikonal Equation with discontinuous coefficient

We consider the stationary Hamilton-Jacobi equation where the dynamics can vanish at some points, the cost function is strictly positive and is allowed to be discontinuous. More precisely, we consider special class of discontinuities for which the notion of viscosity solution is well-suited. We propose a semi-Lagrangian scheme for the numerical approximation of the viscosity solution in the sense of Ishii and we study its properties. We also prove an a-priori error estimate for the scheme in an integral norm. The last section contains some applications to control and image processing problems

Approaching deterministic and probabilistic truth: a unified account

The basic problem of a theory of truth approximation is defining when a theory is \u201cclose to the truth\u201d about some relevant domain. Existing accounts of truthlikeness or verisimilitude address this problem, but are usually limited to the problem of approaching a \u201cdeterministic\u201d truth by means of deterministic theories.Ageneral theory of truth approximation, however, should arguably cover also cases where either the relevant theories, or \u201cthe truth\u201d, or both, are \u201cprobabilistic\u201d in nature. As a step forward in this direction, we first present a general characterization of both deterministic and probabilistic truth approximation; then, we introduce a new account of verisimilitude which provides a simple formal framework to deal with such issue in a unified way. The connections of our account with some other proposals in the literature are also briefly discussed

Intellectual capital in nonprofit organizations: a focus on social capital as a marketing enabler

Design/methodology/approach: After a literature review about the intellectual capital (IC) and the social capital (SC) in the non-profit sector (NPS), at either national or international level, the study presents a bibliometric-systematic literature review (B-SLR) of the field in question. Purpose: The research has the aim of exploring whether and how relevant studies about nonprofit organizations (NPOs) have so far investigated the fruitful effects that can be generated by proactive governance, management and marketing of their IC – particularly when considering its extension to SC – with relation to the promotion of corporate reputation. Findings: According to a quantitative (more bibliometric) perspective, the scientific interest on this specific issue has not always been constant and methodical, while three themes (institutional scope, human resources and operational functioning) have so far mostly been analyzed according to a qualitative (and therefore more systematic) perspective. Originality/value: Despite some recent trends aimed at re-evaluating the effect of intangible assets in any organization, there is still some reticence within the NPS to consider the importance of these resources. This orientation also extends to IC, and more specifically to SC, which should now be considered as relevant factors in the creation of value for any socioeconomic organization, both nationally and internationally