Scientific Reports
The preprint collection of the Department of Mathematics.
Full-text generally not available for preprints prior to may 2006.
Found 868 products
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QDD105 - 07/20/2011
Frezzotti, A.; Ghiroldi, G.P.; Gibelli, L.
Solving Model Kinetic Equations on GPUs | Abstract | | We present an algorithm speci fically tailored for solving model kinetic equations
onto Graphics Processing Units (GPUs). The efficiency of the algorithm is demonstrated by solving the one-dimensional shock wave structure problem and the two-dimensional low Mach number driven cavity fl
ow. Computational results show that
it is possible to cut down the computing time of the sequential codes of two orders of
magnitude. The algorithm can be easily extended to more general collision models. |
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QDD104 - 07/13/2011
Elisabetta Maluta
A Class of P-convex Spaces Lacking Normal Structure | Abstract | | We consider a family of renormings of the infinite-dimensional separable Hilbert space introduced in literature by R.C. James in the sixties and prove that all its members are P-convex. It is known that these spaces lack normal structure when they are sufficiently far, in the sense of the Banach-Mazur distance, from being Hilbert, hence our result provides the first example of a P-convex space without normal structure. |
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QDD103 - 06/24/2011
Ieva, F.;Paganoni,A.M.;Pigoli,D.;Vitelli,V.
Multivariate Functional Clustering for the Morphological Analysis of ECG Curves | Abstract | | Cardiovascular ischemic diseases are one of the main causes of death all over the world. In this kind of pathologies, it is fundamental to be well-timed in order to obtain good prognosis in reperfusive treatment. In particular, an automatic classification procedure based on statistical analyses of tele-transmitted ECG traces would be very helpful for an early diagnosis. This work presents an analysis on
electrocardiographic (ECG) traces (both physiological and pathological ones) of patients whose 12-leads pre-hospital ECG has been sent by life supports to 118 Dispatch Center of Milan. The statistical analysis starts with a preprocessing step, in which functional data are reconstructed from noisy observations and biological variability is removed by a non linear registration procedure. Then, a multivariate
functional k-means clustering is carried out on reconstructed and registered ECG curves and their first derivatives. Hence, a new semi-automatic diagnostic procedure, based on the sole ECG’s morphology, is proposed to classify ECG traces
and the performance of this classification method is evaluated. |
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QDD102 - 06/23/2011
Maddalena, F.; Percivale, D.; Tomarelli, F.
Elastic structures in adhesion interaction | Abstract | | We study a variational model describing the interaction of two 1-dimensional elastic bodies through an adhesive layer, with the
aim of modeling a simplified CFRP structure: e.g. a concrete beam or a medical rehabilitation device glued to a reinforcing polymeric fiber. Different constitutive assumptions for the adhesive layer are investigated: quadratic law and two kinds of softening law. In all cases properties of the equilibrium states of the structural system are analytically deduced.
In the case of adhesion with softening, the minimum length of the elastic fiber avoiding debonding failure is estimated in terms of glue carrying capacity and the constitutive parameter of the fiber. |
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QDD101 - 06/09/2011
Gazzola, F.; Pavani, R.
Blow up oscillating solutions to some nonlinear fourth order differential equations | Abstract | | We give strong theoretical and numerical evidence that solutions to some nonlinear fourth order ordinary differential equations blow up in finite time with infinitely many wild oscillations. We exhibit an explicit example where this phenomenon occurs.
We discuss possible applications to biharmonic partial differential equations and to the suspension bridges model. In particular, we give a possible new explanation of the collapse of bridges. |
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QDD100 - 05/30/2011
Barutello, V.; Terracini, S.; Verzini, G.
Entire Parabolic Trajectories as Minimal Phase Transitions | Abstract | | For the class of anisotropic Kepler problems in any spatial dimension, with homogeneous potentials, we seek parabolic trajectories having prescribed asymptotic directions at infinity and which, in addition, are Morse minimizing geodesics for the Jacobi metric. Such trajectories correspond to saddle heteroclinics on the collision manifold, are structurally unstable and appear only for a codimension-one submanifold of such potentials. We give them a variational characterization in terms of the behavior of the parameter-free minimizers of an associated obstacle problem. We then give a full characterization of such a codimension-one manifold of potentials and we show how to parameterize it with respect to the degree of homogeneity. |
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QDD99 - 05/26/2011
Raimondi, M.; Causin, P.; Mara, A.; Nava, M.; Lagana , M.; Sacco, R.
Breakthroughs in Computational Modeling of Cartilage Regeneration in Perfused Bioreactors | Abstract | | We report about two specific breakthroughs, relevant to the mathematical modelling and numerical simulation of tissue growth in the context of cartilage tissue engineering in vitro. The proposed models are intended to form the building blocks of a bottom-up multiscale analysis of tissue growth, the idea being that a full Microscale analysis of the construct, a 3D PDE problem with internal moving boundaries, is computationally unaffordable. We propose to couple a PDE Microscale model of a single functional tissue sub-unit with the information computed at the Macroscale by 2D-0D models of reduced computational cost. Preliminary results demonstrate the effectiveness of the proposed models in describing the interplay among interstitial perfusion flow, nutrient delivery and consumption and tissue growth in realistic scaffold geometries. |
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QDD98 - 05/19/2011
Fragalà, I.; Gazzola, F.; Kawohl, B.
Overdetermined problems for the $ infty$-Laplacian and web functions | Abstract | | We give necessary and sufficient conditions for functions to be solutions to overdetermined problems for the equation $- Delta_ infty u=1$ in a bounded domain of $R^n$. To this end, we introduce a P-function for the study of the Dirichlet problem and we make use of its properties. |
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