1,721,177 research outputs found
A Poincaré–Birkhoff theorem for multivalued successor maps with applications to periodic superlinear Hamiltonian systems
No full textWe provide a new version of the Poincaré–Birkhoff theorem for possibly multivalued successor maps associated with planar non-autonomous Hamiltonian systems. As an application, we prove the existence of periodic and subharmonic solutions of the scalar second order equation x ̈+λg(t,x)=0, for λ>0 sufficiently small, with g(t, x) having a superlinear growth at infinity, without requiring the existence of an equilibrium point
Periodic perturbations of central force problems and an application to a restricted 3-body problem
Full text linkWe consider a perturbation of a central force problem of the form x ̈=V′(|x|)[Formula presented]+ε∇xU(t,x),x∈R2∖{0}, where ε∈R is a small parameter, V:(0,+∞)→R and U:R×(R2∖{0})→R are smooth functions, and U is τ-periodic in the first variable. Based on the introduction of suitable time-maps (the radial period and the apsidal angle) for the unperturbed problem (ε=0) and of an associated non-degeneracy condition, we apply an higher-dimensional version of the Poincaré–Birkhoff fixed point theorem to prove the existence of non-circular τ-periodic solutions bifurcating from invariant tori at ε=0. We then prove that this non-degeneracy condition is satisfied for some concrete examples of physical interest (including the homogeneous potential V(r)=κ/rα for α∈(−∞,2)∖{−2,0,1}). Finally, an application is given to a restricted 3-body problem with a non-Newtonian interaction
Nearly-circular periodic solutions of perturbed relativistic Kepler problems: the fixed-period and the fixed-energy problems
Full text linkThe paper studies the existence of periodic solutions of a perturbed relativistic Kepler problem of the type (Formula presented.) with d=2 or d=3, bifurcating, for ε small enough, from the set of circular solutions of the unperturbed system. Both the case of the fixed-period problem (assuming that U is T-periodic in time) and the case of the fixed-energy problem (assuming that U is independent of time) are considered
Reliability-Targeted Behaviour Factor Evaluation for Code Compliant RC Italian Frames
No full textThe evaluation of structural safety, by means of the so-called reliability analysis, plays currently a key role in earthquake civil engineering. In particular, some recent studies focused on the quantification of seismic performance of code-conforming buildings. In fact, it is of interest to evaluate if the implicit performance approach adopted by current codes is capable of guaranteeing a uniform safety levels for new-designed buildings. In other terms, if it is necessary to redefine code formulation in order to directly state the desired performance levels at the beginning of the design workflow. For these reasons, the present study evaluates extensively the seismic behavior of code compliant Italian RC frames. To this aim, it has been developed a framework to parametrically design code-conforming buildings and then to estimate their vulnerability through nonlinear dynamic analyses. In this way, the quantification of seismic failure rates exhibits a strict link between them and seismic hazard of sites. To overcome this issue, the so-called risk-targeted design approach has been adopted, in order to reformulate the actual force-based approach. The new reduction factor, i.e. behavior factor, depends not only by inherent structural characteristic but also by the pre-defined desired safety level. This task has been achieved by means of a hands-on method applied to frames with different elevation configuration (3-, 6-, -9 floors) for both ductility class and considering both bare and infilled archetypes
Seismic Reliability and Cost Analysis of Code Compliant RC Italian Frames
No full textnowadays, many Codes develop a force-based design approach, which accounts for the inelastic capacity of structures by means of a reduction coefficient, i.e. behavior factor. At the same time, in earthquake engineering there is an ever-increasing interest on the evaluation of structural safety, through the so-called reliability analysis. Consequently, some studies analyzed failure probability of some code-conforming buildings and they pointed out that actual code’s provisions lead to a non-uniform structural safety level. For this reason, the first main objective of this study is to investigate extensively the failure rates of Italian code-conforming frame RC buildings, in order to establish how the rate of failure varies along the Italian territory. For this purpose, buildings with different number of floors, i.e. 3-6-9, with both levels of ductility (DCM-DCH) and in bare or infilled configuration have been studied, carrying on parametrically both the design and non-linear dynamic analyses in order to define frames vulnerability. Finally, a cost analysis has been carried out, in order to link structural safety with construction charge due to actual Codes provisions. In this way, it is possible to evaluate how different levels of ductility affects concrete and reinforcements steel quantity and if there is a clear trend between total cost and seismic hazard of design site
Una verifica della legge di Gibrat
No full textConfrontando due periodi distinti e caratterizzati da differenti condizioni macroeconomiche (1984-1991 e 1994-2001) viene analizzata, per il Veneto, la relazione tra caratteristiche individuali delle imprese (età e dimensione) e loro probabilità di sopravvivenza. L'analisi è incentrata su due tipici settori di specializzazione della regione, il "fashion" (tessile, abbigliamento, pelli cuoio e calzature) e la meccanica. Da un punto di vista metodologico, la relazione di interesse viene studiata utilizzando la procedura a due stadi di Heckman
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Piano di bonifica e di controllo dei pascoli dell'altopiano della Vezzena dall'infestazione di Deschampsia caespitosa
No full textHomoclinic and heteroclinic solutions for non-autonomous Minkowski-curvature equations
Full text linkWe deal with the non-autonomous parameter-dependent second-order differential equation [Formula presented] driven by a Minkowski-curvature operator. Here, δ>0, q∈L∞(R), f:[0,1]→R is a continuous function with f(0)=f(1)=0=f(α) for some α∈]0,1[, f(s)0 for all s∈]α,1[. Based on a careful phase-plane analysis, under suitable assumptions on q we prove the existence of strictly increasing heteroclinic solutions and of homoclinic solutions with a unique change of monotonicity. Then, we analyze the asymptotic behavior of such solutions both for δ→0+ and for δ→+∞. Some numerical examples illustrate the stated results
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