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 1153 prodotti
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1/2008 - 09/01/2008
Rosso, Riccardo: Verani, Marco
Stabilizing rôle of a curvature correction to line tension | Abstract | | We study the effects that a curvature correction to a bare value of the line tension has on the equilibrium and stability of droplets laid upon a rigid substrate. In the simple case of cylindric liquid bridges we prove that even a tiny curvature correction prevents the onset of wildly oscillating perturbations that would make the contact line unstable if a negative line tension were present alone. However, if the curvature correction is not large enough, unstable modes can persist that are not related to the classical Rayleigh instability.
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26/2007 - 12/12/2007
Colecchia, Maurizio; Nicolai, Nicola; Secchi, Piercesare; Bandieramonte, Gaetano; Paganoni, Anna M.; Sangalli , Laura M.; Piva, Luigi; Salvioni, Roberto
Penile Superficial Squamous cell Carcinoma (SCC) Submitted to CO2 Laser Excision only: Oncologic Outcome of T1 Disease in 25 Years-Long Experience | Abstract | | 1. Purpose. We retrospectively identified patients with ascertained T1 SCC pf the penis who were
submitted to laser excision only, in order to evaluate clinical and pathological characteristics
which can associate with outcomes.
2. Materials and Methods. Peniscopic magnification and 5% acetic acid application were
performed for diagnosis and prior to CO2 laser excision. Only naïve patients with no urethral (> 5
mm from the meatus) neither shaft lesions were considered. Specimens were all reviewed in
order to reassess
pathological characteristics: stage, grade, invasion depth, carcinoma in situ,
margins, tumor extension, lymphovascular invasion and HPV infection. Association between
local recurrence (LR) and prognostic factors was ascertained with Fisher exact test and ChiSquare
test for categorical variables and Wilcoxon rank sum test for continuous variables.
3. Results. A total of 56 pT1 stage patients were identified. After a median followup
of 66 months
(range: 12256),
53 patients are alive and disease free, whereas 3 died of unrelated and intercurrent
diseases. Thirteen (23.21%) had a LR, with 4 suffering multiple recurrences and 1
needing a partial amputation 30 months following primary excision. Only 2 (3.57%) patients had
inguinal nodal metastasis in one node. LR had a positive correlation with positive microsurgical
margins (onesided
Fisher p value .0019) and depth of invasion and a negative correlation with
tumor extension (onesided
Wilcoxon p value of .0028 and .0054, respectively). A logistic
regression model included margin status, depth of invasion, tumor extension and presence of CIS
as significant variables.
4. Conclusions. CO2 laser excision of selected pT1 SCC of the penis is a highly reliable procedure
which associates with excellent oncological and organsparing
long term results. Predictive
variables can be identified and a model that estimates the risk of this event could be adopted. |
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25/2007 - 10/12/2007
Micheletti, Stefano; Perotto, Simona
Space-Time Adaption for Advection-Diffusion-Reaction Problems on Anisotropic Meshes | Abstract | | We deal with the approximation of an unsteady advection-diffusion-
reaction problem by means of space-time finite elements, continuous affine
in space and piecewise constant in time. In particular, we are interested in
the advection-dominated framework. To face the trade-off between
computational cost and accuracy, we devise a space-time adaptive procedure
where both the time step and the spatial grid are adapted throughout the
simulation. Two are the key points involved: the derivation of an a
posteriori error estimator where the contributions of the spatial and of the
temporal discretization are split; a balance of these two contributions via a
proper adaptive scheme. The main novelty of the paper is the interest for
an anisotropic mesh adaption framework.
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24/2007 - 06/12/2007
Sangalli, Laura M.; Secchi, Piercesare; Vantini, Simone; Veneziani, Alessandro
A Case Study in Functional Data Analisys: Geometrical Features of the Internal Carotid Artery | Abstract | | This pilot study is a product of the AneuRisk Project, a
scientific program that aims at evaluating the role of vascular
geometry and hemodynamics in the pathogenesis of cerebral
aneurysms. By means of functional data analyses, we explore the
AneuRisk dataset to highlight the relations between the geometric
features of the internal carotid artery, expressed by its radius
profile and centerline curvature, and the aneurysm location. After
introducing a new similarity index for functional data, we
eliminate ancillary variability of vessel radius and curvature
profiles, through an iterative registration procedure. We then
reduce data dimension by means of functional principal components
analysis. Finally a quadratic discriminant analysis of functional
principal components scores allows to discriminate patients with
aneurysms in different districts. |
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23/2007 - 26/11/2007
Sangalli, Laura M.; Secchi, Piercesare; Vantini, Simone; Veneziani, Alessandro
Efficient estimation of 3-dimensional centerlines of inner carotid arteries and their curvature functions by free knot regression splines | Abstract | | This work stems from the need for accurate estimation of the
curvature function of an artery, that emerged within ANEURISK
Project, a research program that aims at investigating the role of
vascular morphology and hemodynamics on the pathogenesis of cerebral
aneurysms. We develop here a regression technique that exploits free
knot splines in a novel setting, to estimate 3-dimensional curves,
and their derivatives. We thoroughly compare this technique to a
classical regression method, local polynomial smoothing, showing
that 3-dimensional free knot regression splines yield more accurate
and efficient estimates.
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22/2007 - 20/11/2007
Roberts, Gareth O.; Sangalli, Laura M.
Latent diffusion models for event history analysis | Abstract | | We consider Bayesian hierarchical models for
event history analysis, where the event times are modeled through an underlying diffusion process, which determines the hazard rate. We show how these models can be efficiently treated by means of Markov
chain Monte Carlo techniques. |
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21/2007 - 06/11/2007
Massimi, Paolo; Quarteroni, Alfio; Saleri, Fausto; Scrofani, Giovanni
Modeling of Salt Tectonics | Abstract | | In this work a general framework for the simulation of sedimentary basins in presence of salt structures is addressed. Sediments and evaporites are modeled as non-Newtonian fluids and the thermal effects induced by the presence of salt are taken into account. The computational strategy is based on a Lagrangian methodology with intensive grid adaptivity, togheter with a kinematic modeling of faults and different kinds of boundary conditions representing sedimentation, erosion, basement evolution, lithospheric compression and extension. The proposed methodology is applied to simple test cases as well as to a geological reconstruction of industrial interest. |
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20/2007 - 05/11/2007
Burman, Erik; Quarteroni, Alfio; Stamm, Benjamin
Stabilization Strategies for High Order Methods for Transport Dominated Problems | Abstract | | Standard high order Galerkin methods, such as pure spectral or high order finite element methods, have
insufficient stability properties when applied to transport dominated problems. In this paper we review some stabilization
strategies for pure spectral methods and spectral multidomain approaches.
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