Quaderni MOX
Pubblicazioni
del Laboratorio di Modellistica e Calcolo Scientifico MOX. I lavori riguardano prevalentemente il campo dell'analisi numerica, della statistica e della modellistica matematica applicata a problemi di interesse ingegneristico. Il sito del Laboratorio MOX è raggiungibile
all'indirizzo mox.polimi.it
Trovati 1238 prodotti
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23/2010 - 13/07/2010
Baeck, Joakim; Nobile, Fabio; Tamellini, Lorenzo; Tempone, Raul
Stochastic Spectral Galerkin and collocation methods for PDEs with random coefficients: a numerical comparison | Abstract | | Much attention has recently been devoted to the development of Stochastic Galerkin (SG) and Stochastic Collocation (SC) methods for uncertainty quanti fication. An open and relevant research topic is the comparison of these two methods. By introducing a suitable generalization of the classical sparse grid SC method, we are able to compare SG and SC on the same underlying multivariate polynomial space in terms of accuracy versus computational work.
The approximation spaces considered here include
isotropic and anisotropic versions of Tensor Product (TP), Total Degree(TD), Hyperbolic Cross (HC) and Smolyak (SM) polynomials.
Numerical results for linear elliptic SPDEs indicate a slight computational work advantage
of isotropic SC over SG, with SC-SM and SG-TD being the best choices of approximation spaces for each method. Finally, numerical results
corroborate the optimality of the theoretical estimate of anisotropy ratios introduced by the authors in a previous work for the construction of
anisotropic approximation spaces. |
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22/2010 - 12/07/2010
D'Angelo, Carlo; Zunino, Paolo
Numerical approximation with Nitsche s coupling of transient Stokes /Darcy s flow problems applied to hemodynamics | Abstract | | In this work, we consider a time dependent coupled Stokes-Darcy flow problem and study an approximation method based on a unifi ed finite element scheme complemented with implicit time stepping. Our fi nite element formulation relies on a weighing strategy in which the physical and discretization parameters are taken into account to robustly enforce interface and boundary conditions by means of the Nitsche s method. We prove unconditional absolute stability and optimal convergence of the scheme, and discuss the
algebraic properties of the associated discrete problem. Finally, we present numerical experiments con firming the predicted convergence behavior and algebraic properties, and report an application to the computational analysis of
blood flow and plasma filtration in arteries after the implantation of a vascular
graft. |
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21/2010 - 30/06/2010
Grieco, Niccolò; Ieva, Francesca; Paganoni, Anna Maria
Provider Profiling Using Mixed Effects Models on a Case Study concerning STEMI Patients | Abstract | | Provider profi ling is the evaluation process of the performance of hospitals, doctors, and other medical practitioners to enhance the quality of
medical care. In this work we describe statistical analyses conducted on MOMI2 (MOnth MOnitoring Myocardial Infarction in MIlan) survey, a collection of data concerning patients admitted with STEMI (ST-Elevation Myocardial Infarction) diagnosis in one of the hospitals belonging to the Milan urban area Network, with the aim of pointing out process indicators
to be used in health-care evaluation. An ff ective statistical support to decisional process for clinical and organizational governance is then obtained analyzing and modelling data coming from clinical registers and administrative data banks. Typically this kind of data are grouped at first level by structure where patients are admitted to, so multilevel models have been considered and tted to catch and explain overdispersion phenomena.
Moreover, we compare three di fferent techniques of hospitals classi cation based respectively on traditional survival rates comparison, on analysis of variance components in fitted generalized linear mixed e ects models and
non parametric random e ects estimation.
Key words:
Generalized Linear Mixed Models
In-hospital survival
ST-Elevation Myocardial Infarction
Provider Pro filing |
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20/2010 - 09/06/2010
Nobile, Fabio; Quarteroni, Alfio; Ruiz Baier, Ricardo
Numerical solution of an active strain formulation for the electromechanical activity in the heart | Abstract | | We propose a finite element method for solving a system of equations describing the coupling
between cardiac mechanics and electrical signalling. The model is based on a multiplicative
decomposition of the deformation tensor into a passive and active part, the latter carrying
the information of the electrical potential propagation and anisotropy of the cardiac tissue into the equations of incompressible or nearly incompressible nonlinear elasticity, governing the
mechanical response of the biological material. Moreover, by changing from an Eulerian to
a Lagrangian configuration, the underlying problem exhibits a nonlinear diffusion term in the
equations of the electrical propagation (namely, the bidomain and monodomain equations).
Piecewise quadratic finite elements are used to approximate the displacements field, while for
pressure, electrical potentials and ionic variables, we use piecewise linear elements. Various test cases show that the proposed method is able to capture some important features of the
studied phenomenon, and illustrate the behavior of the global model. |
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19/2010 - 08/06/2010
Gaudio, Loredana; Quarteroni, Alfio
hN-adaptive spectral element discretization of optimal control problems for environmental applications | Abstract | | In this work, we propose an hN adaptive algorithm for optimal control problems whose space discretization is based on the spectral element method.
We focus on a special class of problems described by quadratic cost functional and linear advection-di ffusion state equation. This model has been
employed to forecast and suitably reduce, by an optimization process, the pollutant concentration in air on a speci c area of interest. Moreover, a
local adaptive algorithm is employed to achieve a desired accuracy on the cost functional by reducing the computational cost of the problem. |
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18/2010 - 07/06/2010
Antonietti, P.F.; Fadel, N.A.; Verani, M.
Modelling and numerical simulation of the polymeric extrusion process in textile products | Abstract | | We present the mathematical modelling and the numerical simulation of the polymer extrusion process of hollow and non-hollow yarns. In particular, the polymeric material flow has been modelled as non-Newtonian, incompressible, isothermal and steady. We attempt to develop a possible strategy for effective die design in profile extrusion and we numerically asses the validity of the model on both academic and real industrial test cases. Keywords:Free boundary flow, Die-swell, Hollow yarn. 2000 Mathematics Subject Classification. 76D07, 35Q30. |
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17/2010 - 05/06/2010
Guglielmi, Alessandra; Ieva, Francesca; Paganoni, Anna Maria; Ruggeri, Fabrizio
A Bayesian random-effects model for survival probabilities after acute myocardial infarction | Abstract | | Studies of variations in health care utilization and outcome involve the analysis of multilevel clustered data, considering in particular the estimation of a cluster-specific adjusted response, covariates effect and components of variance. Besides reporting on the extent of observed variations, those studies quantify the role of contributing factors including patients
and providers characteristics. In addition, they may assess the relationship between health-care process and outcomes. In this article we present
a case-study, considering a Bayesian hierarchical generalized linear model, to analyze MOMI2 (MOnth MOnitoring Myocardial Infarction in MIlan)
data on patients admitted with ST-Elevation Myocardial Infarction diagnosis, in order to predict survival probabilities. We obtain posterior estimates of the regression parameters, as well as of the random-effects parameters
(the grouping factor is the hospital the patients were admitted to), through an MCMC algorithm. The choice of covariates is achieved in a Bayesian
fashion as a preliminary step. Some issues about model fitting are discussed through the use of predictive tail probabilities and Bayesian residuals.
Keywords:
Bayesian hierarchical models,
Multilevel data analysis,
Bayesian generalized linear mixed models, Logistic regression,
Health services research.
AMS Subject Classi¯cation: 62F15, 62P10, 62J12 |
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16/2010 - 04/06/2010
Formaggia, Luca; Scotti, Anna
Positivity and conservation properties of some integration schemes for mass action kinetics | Abstract | | The numerical schemes approximating chemical reactions according to the mass action law should reproduce at least two properties of the corresponding physical system: mass conservation and nonnegativity of the concentrations.
This paper analyzes the equations of mass action kinetics providing a proof of the existence, uniqueness, and positivity of the solution under
mild hypothesis on the reaction rate and the stoichiometric coefficients.
We then consider some classic integration schemes in terms of conservation, positivity and accuracy compared to schemes tailored for production-destruction systems, and propose an original scheme which guarantees conservation,
nonnegativity of the solution and has order of convergence between two and three. |
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