We present a numerical study of two-dimensional turbulent flows in the enstropy cascade regime, with different large-scale energy sinks. In particular, we study the statistics of more-than-differentiable velocity fluctuations by means of two sets of statistical estimators, namely inverse statistics and second-order differences. In this way, we are able to probe statistical fluctuations that are not captured by the usual spectral analysis. We show that a new set of exponents associated to more-than-differentiable fluctuations of the velocity field exists. We also present a numerical investigation of the temporal properties of u measured in different spatial locations. (C) 2003 American Institute of Physics.

Front propagation in two-dimensional steady and unsteady cellular flows is investigated in the limit of very fast reaction and sharp front, i.e., in the geometrical optics limit. For the steady flow, a simplified model allows for an analytical prediction of the front speed v(f) dependence on the stirring intensity U, which is in good agreement with numerical estimates. In particular, at large U, the behavior v(f)similar toU/log(U) is predicted. By adding small scales to the velocity field we found that their main effect is to renormalize the flow intensity. In the unsteady (time-periodic) flow, we found that the front speed locks to the flow frequency and that, despite the chaotic nature of the Lagrangian dynamics, the front evolution is chaotic only for a transient. Asymptotically the front evolves periodically and chaos manifests only in its spatially wrinkled structure. (C) 2003 American Institute of Physics.

A pointwise stability result for the equation ut = ?F (u) in the exterior of a sphere is obtained, in the class of perturbations which a-priori are allowed to grow at least polinomially at large spatial distances.

This paper is devoted to the formulation of a model for the optimal asset-liability man- agement for insurance companies. We focus on a typical guaranteed investment con- tract, by which the holder has the right to receive after T years a return that cannot be lower than a minimum predened rate rg. We take account of the rules that usually are imposed to insurance companies in the management of this funds as reserves and solvency margin. We formulate the problem as a stochastic optimization problem in a discrete time setting comparing this approach with the so-called hedging approach. The utility function to maximize depends on various parameters including specific goals of the company management. Some preliminary numerical results are reported to ease the comparison between the two approaches.

L’articolo mette in evidenza come lo sviluppo culturale e civile di un paese sia strettamente collegato con il progresso della sua struttura socioeconomica e, contemporaneamente, con il livello generale di produzione e diffusione delle conoscenze scientifiche nei diversi strati sociali, dando risalto al ruolo che il bibliotecario degli istituti di ricerca, in qualità di operatore attivo nella produzione scientifica ed esperto dei sistemi informativi, può giocare. Nell'articolo inoltre si individua il contributo strategico del bibliotecario finalizzato alla divulgazione delle conoscenze e alla costruzione di un “senso comune” della scienza, rendendo più fluida la circolazione delle informazioni e accessibile a tutti il patrimonio bibliografico raccolto e conservato nelle biblioteche presso cui opera.

Elementary interpolation was used in nonlinear partial differential equations (PDE) to study higher integrability via Riesz transforms. The analysis was conducted in Dirichlet space of locally integrable functions in RN. The uniqueness statement for solutions of the nonlinear PDE was also proved.

A computational approach has been developed to assess the power of paramagnetism-based backbone constraints with respect to the determination of the tertiary structure, once the secondary structure elements are known. This is part of the general assessment of paramagnetism-based constraints which are known to be relevant when used in conjunction with all classical constraints. The paramagnetism-based constraints here investigated are the pseudo-contact shifts, the residual dipolar couplings due to self-orientation of the metalloprotein in high magnetic fields, and the cross correlation between dipolar relaxation and Curie relaxation. The relative constraints are generated by back-calculation from a known structure. The elements of secondary structure are supposed to be obtained from chemical shift index. The problem of the reciprocal orientation of the helices is addressed. It is shown that the correct fold can be obtained depending on the length of the α-helical stretches with respect to the length of the non helical segments connecting the α-helices. For example, the correct fold is straightforwardly obtained for the four-helix bundle protein cytochrome b562, while the double EF-hand motif of calbindin D9k is hardly obtained without ambiguity. In cases like calbindin D9k, the availability of datasets from different metal ions is helpful, whereas less important is the location of the metal ion with respect to the secondary structure elements.