1,145 research outputs found
Cosmological viability of a double field unified model from warm inflation
No full textIn this paper, we investigate the cosmological viability of a double scalar field model motivated by warm inflation. To this end, we first set up the theoretical framework in which dark energy, dark matter and inflation are accounted for in a triple unification scheme. We then compute the overall dynamics of the model, analyzing the physical role of coupling parameters. Focussing on the late-time evolution, we test the model against current data. Specifically, using the low-redshift Pantheon Supernovae Ia and Hubble cosmic chronometers measurements, we perform a Bayesian analysis through the Monte Carlo Markov Chains method of integration on the free parameters of the model. We find that the mean values of the free parameters constrained by observations lie within suitable theoretical ranges, and the evolution of the scalar fields provides a good resemblance to the features of the dark sector of the universe. Such behaviour is confirmed by the outcomes of widely adopted selection criteria, suggesting a statistical evidence comparable to that of the standard ΛCDM cosmology. We finally discuss the presence of large uncertainties over the free parameters of the model and we debate about fine-tuning issues related to the coupling constants
Nonlinear Warping and Torsional Elongation in the Response of channel section beam
No full textIn last years, many paper have been devoted to nonlinear dynamics of 3D beams. In a previous paper [1] the Authors studied a nonlinear one-dimensional model of inextensional, shear undeformable, thin-walled beam with an open cross-section. Nonlinear in-plane and out-of-plane warping and torsional elongation effects were included in the model. By using a generalization of the Vlasov kinematical hypotheses, the nonlinear warping was described in terms of the flexural and torsional curvatures. The displacement field depends on three components only, two transversal translations of the shear center and the torsional rotation. By taking into account the order of magnitude of the various terms, the equations were simplified and the effect of symmetry properties has been also outlined. A discrete form of the equations was derived to study dynamic coupling phenomena in conditions of internal resonance. The results showed that warping and torsional elongation produce notable modifications in the response of the beam to harmonic excitation [2]. Unfortunately this model is very complex and the interpretation of the mechanical behavior of the system is very difficult.
Aim of the present paper is to study more in detail the effects of nonlinear warping and torsional elongation that has been shown to play an important role in the nonlinear response.
A preliminary study is developed to determine the different order of the kinematical quantities in a realistic beam, that will be a prototype for an experimental investigation, loaded by a static force at the free end in the direction orthogonal to the symmetry axis. A beam is considered characterized by the following nondimensional parameters : t/h=0.02, b/h=0.5, h/l=0.05, where t is the thickness of the section, b and h are the dimensions of the C cross section, being h orthogonal to the symmetry axis, and l the length of the cantilever beam. For this beam the ratio between torsional and flexural curvatures is about forty; this circumstance makes it possible to introduce a great simplification in the model developed in [1].
Through Hamilton principle, under the hypothesis of large torsional curvature and small flexural curvatures, three equations of motion are derived describing dynamics of inextensional and shear undeformable nonlinear 3D beam. An harmonic load is considered acting in the direction orthogonal to the symmetry axis and applied to the free end of the cantilever beam. A Galerkin discretization is performed by introducing the first three eigenfunctions and, by using multiple scale method and amplitude-modulation equations are obtained. Frequency-response and amplitude-load curves are evaluated to characterize the behaviour of the beam and highlight the nonlinear warping and torsional elongation contributions. A numerical investigation using a finite element model including geometrical nonlinearities, is performed to validate the mechanical model and an experimental test is also expected in the next future.
1. A. Di Egidio, A. Luongo, F. Vestroni, A nonlinear model for open cross-section thin-walled beams, Part I: Formulation, Int. J. of Non-Linear Mechanics, 2003, 38(7), 1067-1081
2. A. Di Egidio, A. Luongo, F. Vestroni, A nonlinear model for open cross-section thin-walled beams, Part II: Forced motion, Int. Journal of Non-Linear Mechanics, 2003, 38(7), 1083-109
Divergence, Hopf and Double-Zero Bifurcations of a nonlinear Planar Beam
No full textReduction methods play a fundamental role in nonlinear dynamics. They allow the essential dynamics of the original system to be captured using models with a very low number of degrees of freedoms, thus avoidinng the use of brutal numerical modelling.
Reduction methods have been thoroughly discussed by Sheindl and Troger [1], who compared linear and nonlinear Galerkin methods, the center manifold and the approximate inertial manifold theories. Nayfeh [2] also developed a modified version of the Galerkin method, able to overcome the shortcomings of the classical procedure. Nayfeh and co-workers [3-4] have also widely applied the Multiple Scale Method in the so called direct form, i.e. by dealing with the partial differential equations and boundary conditions rather than with algebraic systems obtained by means of a priori discretization. Within the framework of bifurcation theory, the authors have systematically applied the Multiple Scale Method to finite dimensional systems to derive the relevant bifurcation equations [5-7]. The method make it possible to avoid both the search for the center manifold and the use of the normal form theory, since the algorithm furnishes bifurcation equations directly in normal form.
In this paper an attempt is made to extend the method to infinite-dimensional systems. A key point of the procedure lies in defining a scalar product and using the bilinear identity to get the linear adjoint problem. The solution of the relevant homogeneous problem supplies the tool to enforce the solvability conditions at any order of the perturbation procedure. After reconstitution [8], these equations furnish the desired bifurcation equations.
The method is directly applied, without discretization, to a one-dimensional continuous model of an inextensible and shear-undeformable planar beam, equipped with a lumped visco-elastic device and loaded by an axial follower force. The nonlinear equations of motion, expanded up-to cubic terms, are derived via the generalized Hamilton principle. After integration, the longitudinal displacement and the axial reactive force are condensed, and a single integro-differential equation in the transversal displacement component is finally drawn.
The spectral properties of the linear operator are then studied. First an adjoint operator is built-up, which differs from the original one for the presence of the non-conservative follower force in the boundary conditions. Then the linear stability of the trivial equilibrium is analyzed. It is found that the beam loses stability for (a) divergence, (b) Hopf and (c) double-zero bifurcations. The stability regions are plotted on the parameter plane, consisting of the load and of a stiffness ratio. Both right and left eigenvectors are evaluated at the critical conditions. At the double-zero bifurcation point the system is defective, i.e. it possess an incomplete set of eigenvectors; this entails the need to find an index-two generalized eigenvector.
The Multiple Scale Method is then applied as a reduction method to obtain the bifurcation equations capturing the asymptotic nonlinear dynamics of the infinite-dimensional system around the divergence, the Hopf and the double-zero bifurcations. A set of linear perturbation equation, with singular operator, is obtained, and solved in chain. From the solvability conditions, requiring the known terms are orthogonal to the left eigenvectors of the singular operator, amplitude-equations on the different time-scales are obtained. When these are recombined on the true time-scale, the bifurcation equations are drawn. They are found to be already in normal form. These equations are then numerically integrated to describe the whole scenario around the bifurcation points.
References
[1] A. Steindl and H. Troger, 2001. Methods for Dimension Reduction and their Application in Nonlinear Dynamics, Int. J. of Solids and Structures, 38, 3131-2147.
[2] A. H. Nayfeh, 1998. Reducted-Order Models of Weakly Nonlinear Spatially Continuous Systems, Nonlinear Dynamics, 16, 105-125.
[3] A. H. Nayfeh and W. Lacarbonara, 1998. On the Discretization of Spatially Continuous Systems with Quadratic and Cubic Nonlinearities, JSME International Journal, 41, 510-531.
[4] G. Rega, W. Lacarbonara, A. H. Nayfeh, and C. Chin, 1999. Multiple Resonances in Suspended Cables: Direct versus Reduced-Order Models, International Journal of Non-Linear Mechanics, 34, 901-924.
[5] A. Luongo, A. Paolone and A. Di Egidio, 2000. Sensitivity and Linear Stability Analysis Around a Double Zero Eigenvalues, AIAA Journal, 38/4, 702-710.
[6] A. Luongo, A. Di Egidio, and A. Paolone, 2003. Multiple Time Scale Analysis for Bifurcation from a Multiple-Zero Eigenvalue, AIAA Journal, 41/6, 1143-1150.
[7] A. Luongo, A. Di Egidio, and A. Paolone, 2002. Multiple Scale Bifurcation Analysis for Finite-Dimensional Autonomous Systems, Recent Research Developments in Sound & Vibration, Transworld Research Network, Kerala, India, 1, 161-201.
[8] Nayfeh, A. H., Introduction to Perturbation Techniques, Wiley-Interscience, New York, 1991
«In multitudine bonorum civium comunitati et reipublice fructuosa»: due casi di conferimento della cittadinanza fiorentina alla metà del Trecento
No full textRendiconto online della Soc.Geol.Ital.
No full textIn this study we provide a general structural picture of Ischia
island shallow crust to model the processes occurring at shallow
depth, by using geological, geophysical, historical seismicity data
and analytical structural models of the island (PENTA &
CONFORTO, 1951; CUBELLIS & LUONGO, 1998; CUBELLIS et alii,
2004; CARLINO et alii, 2006; PAOLETTI et alii, 2009; VEZZOLI et
alii., 2009; SBRANA et alii, 2009). These studies support the
hypothesis of the presence of a shallow laccolith, which is
responsible of the resurgence of Mt. Epomeo, following the
Green Tuff eruption, volcanic activity and seismicity...PublishedPisa3.5. Geologia e storia dei vulcani ed evoluzione dei magmi3.6. Fisica del vulcanismoope
Global well-posedness and interior regularity of 2D Navier–Stokes equations with stochastic boundary conditions
No full textThe paper is devoted to the analysis of the global well-posedness and the interior regularity of the 2D Navier–Stokes equations with inhomogeneous stochastic boundary conditions. The noise, white in time and coloured in space, can be interpreted as the physical law describing the driving mechanism on the atmosphere–ocean interface, i.e. as a balance of the shear stress of the ocean and the horizontal wind force.Analysi
SYNTHESIS AND BIOLOGICAL EVALUATION OF NOVEL A1 ADENOSINE RECEPTOR AGONISTS
No full textA1 adenosine receptor (A1AR) is the best characterized subtype of the four known adenosine receptors.1 Selective A1AR agonists show neuro- and cardio-protective effects, reduce intraocular pressure in glaucoma, and have anticonvulsivant activity. The majority of A1AR agonists are adenosine derivatives and even though many efforts have been carried out, only few drugs in advanced clinical studies are A1AR agonists. The main
problem is represented by the significant cardiovascular side effects (bradicardia and hypotension).1 In our previous studies we found that the replacement of the 5’-hydroxy-group by a chlorine atom in N6-substituted adenosine derivatives, improved both the A1AR affinity and selectivity. 5’-Chloro-5’-deoxy-N6-(±)-endo-
norbornyl-adenosine (5’Cl5’d-(±)-ENBA) resulted a potent and highly selective A1AR2 agonist showing
analgesic effects in a mice model of neuropathic pain.3 Interestingly, at analgesic doses it did not lower blood pressure and locomotor activity in mice.3 Moreover, it reduced dyskinesia evoked by L-DOPA in a mice model of Parkinson disease.4
Based on these interesting findings, a novel series of 5’-modified N6-substitued adenosine derivatives was synthesized and tested in human A1, A2A, A2B, and A3 adenosine receptors binding assay. The most potent and

selective compounds of the series were also assayed in a formalin test in mice. The results of this work will be discussed.
1Fredholm, B.B.; IJzerman, A.P.; Jacobson, K.A.; Linden, J.; Muller, C.E. Pharmacol. Rev. 2011, 63, 1-34.
2Franchetti, P.; Cappellacci, L.; Vita, P.; Petrelli, R.; Lavecchia, A.; Kachler, S.; Klotz, K.-N.; Marabese, I.; Luongo, L.; Maione, S.;
Grifantini, M. J. Med. Chem. 2009, 52, 2393−2406.
3(a) Luongo, L.; Petrelli, R.; Gatta, L.; Giordano, C.; Guida, F.; Vita, P.; Franchetti, P.; Grifantini, M.; De Novellis, V.; Cappellacci, L.; Maione, S. Molecules 2012, 17, 13712−13726. (b) Luongo, L.; Guida, F.; Imperatore, R.; Napolitano, F.; Gatta, L.; Cristino, L.; Giordano, C.; Siniscalco, D.; Di Marzo, V.; Bellini, G.; Petrelli, R.; Cappellacci, L.; Usiello, A.; de Novellis, V.; Rossi, F.; Maione, S. Glia 2014, 62, 122−132.
4Mango, D.; Bonito-Oliva, A.; Ledonne, A.; Cappellacci, L.; Petrelli, R.; Nisticò, R.; Berretta, N.; Fisone, G.; Mercuri, N.B. Exp. Neurol. 2014, 261, 733−743
Effetto antimicrobico dell’ozono su colture di pseudomonas aeuruginosa e Stafhilococcus aureus
No full textNovel N6/5’-Disubstituted Adenosine Derivatives As A1 Adenosine Receptor Agonists: Synthesis, Binding Assay And Antinociceptive Activity
No full textAdenosine is a regulatory nucleoside that can be generated in response to cellular stress and tissue damage as well as during episodes of tissue hypoxia or inflammation. It acts on specific G-protein coupled receptors that have been classified into four subtypes (A1, A2A, A2B and A3) on the basis of their structures and signal transduction systems.
Selective A1 adenosine receptor (A1AR) agonists have antinociceptive, antiarrhythmic and neuro- and cardioprotective effects. There is a large body of evidence to suggest that A1AR agonists produce antinociception at spinal cord level as well as at supraspinal level. Our previous work showed that replacement of the 5′ -hydroxy-group by a chlorine atom in N6-substituted adenosine derivatives increased selectivity for A1AR [1]. 5′-Chloro-5′-deoxy-N6-(±)-(endo-norborn-2-yl)-adenosine (5′Cl5′d-(±)- ENBA) displayed high A1AR affinity and selectivity. It was shown to reduce both mechanical allodynia and thermal hyperalgesia in a mice model of neuropathic pain without affecting motor and cardiovascular functions [2]. Moreover, it reduced dyskinesia evoked by L-DOPA in a mice model of Parkinson’s disease [3].
In this work, novel N6/5’-disubstituted adenosine derivatives were synthesized and evaluated for analgesic activity in a formalin test in mice. The most potent compound of the series was found to inhibit the second phase of the nocifensive response induced by intrapaw injection of formalin at a dose of 2 mg/kg i.p. [2] Franchetti, P.; Cappellacci, L.; Vita, P.; Petrelli, R.; Lavecchia, A.; Kachler, S.; Klotz, K.-N.; Marabese, I.; Luongo, L.; Maione, S.; Grifantini, M. J. Med. Chem. 2009, 52, 2393−2406.
[3] (a) Luongo, L.; Petrelli, R.; Gatta, L.; Giordano, C.; Guida, F.; Vita, P.; Franchetti, P.; Grifantini, M.; De Novellis, V.; Cappellacci, L.; Maione, S. Molecules 2012, 17, 13712−13726. (b) Luongo, L.; Guida, F.; Imperatore, R.; Napolitano, F.; Gatta, L.; Cristino, L.; Giordano, C.; Siniscalco, D.; Di Marzo, V.; Bellini, G.; Petrelli, R.; Cappellacci, L.; Usiello, A.; de Novellis, V.; Rossi, F.; Maione, S. Glia 2014, 62, 122−132.
[4] Mango, D.; Bonito-Oliva, A.; Ledonne, A.; Cappellacci, L.; Petrelli, R.; Nisticò, R.; Berretta, N.; Fisone, G.; Mercuri, N.B. Exp. Neurol. 2014, 261, 733−743
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