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 1239 prodotti
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12/2017 - 20/02/2017
Gasperoni, F.; Ieva, F.; Barbati, G.; Scagnetto, A.; Iorio, A.; Sinagra, G.; Di Lenarda, A.
Multi state modelling of heart failure care path: a population-based investigation from Italy | Abstract | | Background: How different risk profiles of Heart Failure (HF) patients can influence multiple readmission rate and outpatients management is widely unknown. To date, several models for predicting adverse outcomes have been developed, but they are mainly focused on a single outcome We propose the application of two different multi state models in real world setting to jointly evaluate the impact of different risk factors on multiple hospital admissions, on Integrated Home Care (IHC) activations, on Intermediate Care Unit (ICU) admissions and on death.
Methods and findings: We propose two multi state models. Each multi state model is characterized by a state space and an intensity transition matrix. A transition is defined as a possible passage from one state to another (in our case, we consider readmission, discharge and death as possible transitions).
The first model (Model 1) concerns only hospitalizations as possible events in patients’ clinical history. In the second one (Model 2), we consider both hospitalizations and ICU admission and IHC activation. Through Model 1, we want to detect the determinants of repeated hospitalizations, while, through Model 2, we want to evaluate which patients’ profiles are associated with transitions in intermediate care with respect to repeated hospitalizations or death. Both models are characterized by transition specific covariates, adjusting for patient’s risk factors.
We identified 4,904 patients (4,129 De Novo and 775 Worsening Heart Failure, WHF) hospitalized for HF from 2009 to 2014, corresponding to 23, 665 events. Among these events, 7, 634 (32%) were HF hospitalizations, 8, 329 (35%) were hospitalization for any cause, 2, 303
(10%) were admission in ICU and 5, 399 (23%) were activation of IHC. 2, 714 (55%) patients died, of these 407 deaths (8% out of the whole cohort) occurred during a HF hospitalization. 1, 316 De Novo HF patients had only one hospitalization and 520 (40% out of 1, 316 ) died after or during the first, and unique, hospitalization. Advanced age and higher morbidity load, measured by Charlson score, increased the rate of dying and of being rehospitalized
(Model 1). Increasing age was also correlated with a longer staying in the hospital (Model 1 and Model 2). Instead, age was inversely related to time spent in IHC (Model 2). The increasing comorbidity load was related to a longer hospital stay and a shorter time spent in IHC (Model 2). WHF condition did not increase the risk of being admitted in ICU/IHC significantly, whereas it was still an important risk factor associated with hospital readmission.
Conclusions: The application of multi state models enables a better identification of two patterns of HF patients. In fact, once adjusted for age and comorbidity load, the WHF condition identifies patients who are more likely to be readmitted several times to hospital, but does not represent an increasing risk factor for activating ICU/IHC. This highlights different ways to manage specific patients patterns of care. In so doing, the results of the paper provide useful healthcare support to patients management in real word context. Our study suggests that the epidemiology of the considered clinical characteristics are more nuanced than traditionally presented with single event by demonstrating their important and versatile role on different patterns of care.
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11/2017 - 20/02/2017
Ferro, N.; Micheletti, S.; Perotto, S.
Anisotropic Mesh Adaptation for Crack Propagation Induced by a Thermal Shock | Abstract | | In this paper we focus on the thermo-mechanical model which
describes crack genesis and propagation in brittle materials induced by a thermal shock.
Our goal is to provide an efficient numerical technique which employs a computational finite element mesh finely customized to the problem at hand to simulate such phenomena.
In particular, we generate automatically adapted anisotropic grids able to closely follow the narrow bands
of the damage, driven by a theoretically sound mathematical tool.
We carry out two numerical tests to assess the computational performance of the proposed method. |
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10/2017 - 20/02/2017
Pini, A.; Stamm, A.; Vantini, S.
Hotelling's $T^2$ in separable Hilbert spaces | Abstract | | We address the problem of finite-sample null hypothesis significance testing on the mean element of a random variable that takes value in a generic separable Hilbert space. For this purpose, we propose a (re)definition of Hotelling's $T^2$ statistic that naturally expands to any separable Hilbert space that we further embed within a permutation inferential approach. In detail, we present a unified framework for making inference on the mean element of Hilbert populations based on Hotelling's $T^2$ statistic, using a permutation-based testing procedure of which we prove finite-sample exactness and consistency; we showcase the explicit form of Hotelling's $T^2$ statistic in the case of some famous spaces used in functional data analysis (i.e., Sobolev and Bayes spaces); we propose simulations and a case study that demonstrate the importance of the space into which one decides to embed the data; we provide an implementation of the proposed tools in the R package fdahotelling |
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09/2017 - 20/02/2017
Antonietti, P.F.; Ferroni, A.; Mazzieri, I.; Paolucci, R.; Quarteroni, A.; Smerzini, C.; Stupazzini, M.
Numerical modeling of seismic waves by Discontinuous Spectral Element methods | Abstract | | We present a comprehensive review of Discontinuous Galerkin Spectral Element (DGSE) methods on hybrid hexahedral/tetrahedral grids for the numerical modeling of the ground motion induced by large earthquakes. DGSE methods combine the flexibility of discontinuous Galerkin methods to patch together, through a domain decomposition paradigm, Spectral Element blocks where high-order polynomials are used for the space discretization coupled with a leap-frog time marching schemes. This approach allows local adaptivity on discretization parameters, thus improving the quality of the solution without affecting the computational costs. The theoretical properties of the semidis- crete formulation are also revised, including well-posedness, stability and error estimates. A discussion on the dissipation, dispersion and stability properties of the fully-discrete (in space and time) formulation is also presented. The capabilities of the present approach are demonstrated through a set on computations of realistic earthquake scenarios obtained using the code SPEED (http://speed.mox.polimi.it), an open-source code specifically designed for the numerical modeling of large-scale seismic events jointly developed at Politecnico di Milano by The Laboratory for Modeling and Scientific Computing MOX and by the Department of Civil and Environmental Engineering. |
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08/2017 - 31/01/2017
Ambrosi, D.; Beloussov, L.V.; Ciarletta, P.
Mechanobiology and morphogenesis in living matter: a survey | Abstract | | Morphogenesis in living tissues is the paramount example of a time- and space-dependent orchestration of living matter where shape and order emerge
from undifferentiated initial conditions. The genes encode the protein expression that eventually drives the emergence of the phenotype, while energy supply and cell-to-cell communication mechanisms are necessary to such a process. The overall control of the system likely exploits the laws of chemistry and physics through robust and universal processes. Even if the identification of the communication mechanisms is a question of fundamental nature, a long-standing investigation settled in the realm of chemical factors only (also known as morphogens) faces a number of apparently unsolvable questions. In this paper, we investigate at what extent mechanical forces, alone or through their biological feedbacks, can direct some basic aspects of morphogenesis in development biology. In this branch of mechano-biology, we discuss the typical rheological regimes of
soft living matter and the related forces, providing a survey on how local mechanical feedbacks can control global size or even gene expression. We finally highlight the pivotal role of nonlinear mechanics to explain the
emergence of complex shapes in living matter.
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07/2017 - 27/01/2017
Cabassi A.; Pigoli D.; Secchi P.; Carter P.A.
Permutation tests for the equality of covariance operators of functional data with applications to evolutionary biology | Abstract | | In this paper, we generalize the metric-based permutation test for the equality of covariance operators proposed by Pigoli et al. (2014) to the case of multiple samples of functional data. To this end, the non-parametric combination methodology of Pesarin and Salmaso (2010) is used to combine all the pairwise comparisons between samples into a global test. Different combining functions and permutation strategies are reviewed and analyzed in detail. The resulting test allows to make inference on the equality of the covariance operators of multiple groups and, if there is evidence to reject the null hypothesis, to identify the pairs of groups having different covariances. It is shown that, for some combining functions, step-down adjusting procedures are available to control for the multiple testing problem in this setting. The empirical power of this new test is then explored via simulations and compared with those of existing alternative approaches in different scenarios. Finally, the pro- posed methodology is applied to data from wheel running activity experiments, that used selective breeding to study the evolution of locomotor behavior in mice. |
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06/2017 - 27/01/2017
Ekin, T.; Ieva, F.; Ruggeri, F.; Soyer, R.
On the Use of the Concentration Function in Medical Fraud Assessment | Abstract | | We propose a simple, but effective, tool to detect possible anomalies in the services prescribed by a health care provider (HP) compared to his/her colleagues in the same field and environment. Our method is based on the concentration function which is an extension of the Lorenz curve widely used in describing uneven distribution of wealth in a population. The proposed tool provides a graphical illustration of a possible anomalous behavior of the HPs and it can be used as a pre-screening device for further investigations of potential medical fraud. |
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05/2017 - 20/01/2017
Menafoglio, A.; Hron, K.; Filzmoser, P.
Logratio approach to distributional modeling | Abstract | | Symbolic data analysis (SDA) provides a unified approach to analyze distributional data, resulting from capturing intrinsic variability of groups of individuals as input observations. In parallel to the SDA approach, a concise methodology has been developed since the early 1980s to deal with compositional data — i.e., data carrying only relative information — through the logratios of their parts. Most methods in compositional data analysis aims to treat multivariate observations which can be identified with probability functions of discrete distributions. Nevertheless, a methodology to capture the specific features of continuous distributions (densities) has been recently introduced. The aim of this work is to describe a general setting that includes both the discrete and the continuous setting, and to provide specific details to both frameworks focusing on the implications on SDA. The theoretical developments are illustrated with real-world case studies. |
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