4,761 research outputs found
Symplectic and contact properties of the Ma\~n\'e critical value of the universal cover
We discuss several symplectic aspects related to the Ma\~n\'e critical value
c_u of the universal cover of a Tonelli Hamiltonian. In particular we show that
the critical energy level is never of virtual contact type for manifolds of
dimension greater than or equal to three. We also show the symplectic
invariance of the finiteness of the Peierls barrier and the Aubry set of the
universal cover. We also provide an example where c_u coincides with the
infimum of Mather's \alpha -function but the Aubry set of the universal cover
is empty and the Peierls barrier is finite. A second example exhibits all the
ergodic invariant minimizing measures with zero homotopy, showing that, quite
surprisingly, the union of their supports is not a graph, in contrast with
Mather's celebrated graph theorem.Comment: 25 pages, to appear on NoDE
Performance of a school hosted within a historical complex affected by the 2016 seismic sequence
Immediately after the August 24th, 2016, earthquake in Central Italy, universities have been asked to inspect
schools and assess their usability, under the coordination of ReLUIS (Rete Laboratori Universitari Ingegneria
Sismica = Earthquake Engineering University Laboratories Network). Later on, about one hundred schools deemed
as unfit to use have been evaluated in order to establish if it was possible to repair them before September 2017 or
if it was more appropriate to build a new school. Among investigated buildings there are not only those in the
epicentral area, but also some located even 30-45 km from the epicentres of the main events. One of those is the
music high school located in Teramo, Abruzzi region, housed within the former monastery of San Giovanni a
Scorzone established in 1384. The seismic vulnerability of the building was investigated in 2014 according to the
Italian Building Standard. Based on the documentation produced therein, observations made after the August event,
and a new inspection carried out in December 2016, the building has been assessed according to the procedure
proposed after the Emilia 2012 Earthquakes. Despite ground shaking not being very severe, due to high
vulnerability, the performance was that of a damage level 2 (damage between significant and severe), with
important distress to non-structural elements. Such performances call into question the suitability of housing
critical functions in historical buildings that, however, can suffer an accelerated decay if left unused and, thus,
unmaintained
clinical presentation and prevalence of spontaneous bacterial peritonitis in patients with cryptogenic cirrhosis and features of metabolic syndrome
BACKGROUND:Nonalcoholic steatohepatitis (NASH) may progress to cirrhosis. The prevalence and clinical relevance that spontaneous bacterial peritonitis may have in complicating ascites due to NASH-related cirrhosis have yet to be defined.METHODS:Among 611 cases of cirrhosis-associated ascites, 45 patients with cryptogenic cirrhosis were retrospectively identified. Of these, 36 patients and a control group of subjects with viral-associated ascites were followed up and compared in a case control study. Information on the onset of ascites, with or without spontaneous bacterial peritonitis, history of risk factors for multimetabolic syndrome, and serological and ascitic laboratory data were compared between groups.RESULTS:Spontaneous bacterial peritonitis occurred significantly more often in patients with cryptogenic cirrhosis than in equally symptomatic viral controls. The prevalence of obesity, diabetes and spontaneous bacterial peritonitis was significantly higher in patients with cryptogenic cirrhosis. Although liver function was similar in both groups, cryptogenic cirrhosis patients had lower aminotransferase levels. Multivariate analysis identified diabetes, juvenile obesity and spontaneous bacterial peritonitis as independent factors associated with ascites due to cryptogenic cirrhosis.CONCLUSIONS:Features suggestive of NASH are more frequently observed in patients with ascites and cryptogenic cirrhosis than in age- and sex-matched ascitic patients with well-defined viral etiology. Ascites may be a presenting symptom of NASH-related cirrhosis, and affected patients have a twofold greater risk of spontaneous bacterial peritonitis
The Efficacy of the Tabby Improved Prevention and Intervention Program in Reducing Cyberbullying and Cybervictimization among Students.
Background. This article presents results from the evaluation of the Tabby Improved Prevention and Intervention Program (TIPIP) for cyberbullying and cybervictimization. TIPIP is theoretically designed to address cyberbullying and cybervictimization. It is the first program in this field developed combining the Ecological System Theory and the Threat Assessment Approach. Method. The Tabby Improved program was evaluated using an experimental design with 759 Italian students (aged 10⁻17 years) randomly allocated via their classes to either the Experimental or Control Group. Results. Repeated measures ANOVAs showed a significant decrease both in cyberbullying and cybervictimization among students who received the intervention with a follow-up period of six months. The program was more effective for boys than for girls. Conclusions. Because cyberbullying is a cruel problem negatively affecting those involved, validated interventions that prove their efficacy in reducing the problem using experimental designs should be widely tested and promoted, paying particular attention to implementing a program fully to increase and guarantee its effectiveness
Network synchronization of groups
In this paper we study synchronized motions in complex networks in which
there are distinct groups of nodes where the dynamical systems on each node
within a group are the same but are different for nodes in different groups.
Both continuous time and discrete time systems are considered. We initially
focus on the case where two groups are present and the network has bipartite
topology (i.e., links exist between nodes in different groups but not between
nodes in the same group). We also show that group synchronous motions are
compatible with more general network topologies, where there are also
connections within the groups
Polynomial growth of volume of balls for zero-entropy geodesic systems
The aim of this paper is to state and prove polynomial analogues of the
classical Manning inequality relating the topological entropy of a geodesic
flow with the growth rate of the volume of balls in the universal covering. To
this aim we use two numerical conjugacy invariants, the {\em strong polynomial
entropy } and the {\em weak polynomial entropy }. Both are
infinite when the topological entropy is positive and they satisfy
. We first prove that the growth rate of the volume of
balls is bounded above by means of the strong polynomial entropy and we show
that for the flat torus this inequality becomes an equality. We then study the
explicit example of the torus of revolution for which we can give an exact
asymptotic equivalent of the growth rate of volume of balls, which we relate to
the weak polynomial entropy.Comment: 22 page
First assessment on suspension parameter optimization for a solar-powered vehicle
Optimization of suspension parameters with respect to comfort and road holding is a challenging issue for solar-powered cars, due to in-wheel electric engines on very light vehicles, carrying payloads which can exceed their total mass. The solar-powered car considered in this study was designed and manufactured for racing by the University of Bologna; with a mass of 300 kg and a payload of 320 kg due to four occupants, using 5 m2 of monocrystalline silicon photovoltaic panel on the roof, 64 kg of lithium-ion batteries and two electric engines coupled directly to the rear wheels, it can achieve either a range of 600 km at cruising speed, or velocity peaks of 120 km/h. In this contribution, equivalent vertical stiffness and equivalent damping coefficients are optimized for both axles, achieving results that in terms of comfort and road holding are comparable to those of standard passenger cars
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