Sparse approximate inverse preconditioners on high performance GPU platforms

Simulation with models based on partial differential equations often requires the solution of (sequences of) large and sparse algebraic linear systems. In multidimensional domains, preconditioned Krylov iterative solvers are often appropriate for these duties. Therefore, the search for efficient preconditioners for Krylov subspace methods is a crucial theme. Recent developments, especially in computing hardware, have renewed the interest in approximate inverse preconditioners in factorized form, because their application during the solution process can be more efficient. We present here some experiences focused on the approximate inverse preconditioners proposed by Benzi and Tůma from 1996 and the sparsification and inversion proposed by van Duin in 1999. Computational costs, reorderings and implementation issues are considered both on conventional and innovative computing architectures like Graphics Programming Units (GPUs)

Modeling the short-term effect of traffic on air pollution in Torino with generalized additive models

Vehicular traffic typically plays an important role in atmospheric pollution. This is especially true in urban areas, where high pollutant concentrations are often observed. In this paper, we consider hourly measures of concentrations of nitrogen oxides (NO, NO2 and NOx), carbon oxide (CO) and particulate matter (PM), collected at the stations distributed throughout the city of Turin. To help explain the short-term behavior of the concentrations of these pollutants, we propose using generalized additive models (GAM), focusing in particular on traffic along with the meteorological predictors. All the data are collected during the period from December 2003 to April 2005.urban area, air quality, vehicular traffic, CO, NO2, NOx, NO, PM, generalized additive models

Efficient approximation of functions of some large matrices by partial fraction expansions

Some important applicative problems require the evaluation of functions $\Psi$ of large and sparse and/or \emph{localized} matrices $A$. Popular and interesting techniques for computing $\Psi(A)$ and $\Psi(A)\mathbf{v}$, where $\mathbf{v}$ is a vector, are based on partial fraction expansions. However, some of these techniques require solving several linear systems whose matrices differ from $A$ by a complex multiple of the identity matrix $I$ for computing $\Psi(A)\mathbf{v}$ or require inverting sequences of matrices with the same characteristics for computing $\Psi(A)$. Here we study the use and the convergence of a recent technique for generating sequences of incomplete factorizations of matrices in order to face with both these issues. The solution of the sequences of linear systems and approximate matrix inversions above can be computed efficiently provided that $A^{-1}$ shows certain decay properties. These strategies have good parallel potentialities. Our claims are confirmed by numerical tests

Spectral analysis of nonsymmetric quasi-toeplitz matrices with applications to preconditioned multistep formulas

The eigenvalue spectrum of a class of nonsymmetric preconditioned matrices arising in time-dependent partial differential equations is analyzed and discussed. The matrices generated by the underlying numerical integrators are small rank perturbations of block Toeplitz matrices; circulant-like preconditioners based on the former are considered. The eigenvalue distribution of the preconditioned matrix influences often crucially the convergence of Krylov iterative accelerators. Due to several reasons (lack of symmetry, band structure, and coefficients depending on the size) the classical approach based on smooth generating functions gives very little insight here. Therefore, to characterize the eigenvalues, a difference equation approach exploiting the band Toeplitz and circulant patterns generalizing the well-known results of Trench is proposed

L’approche variationniste à la pratique terminologique d’entreprise

Cet article présente un projet de recherche sur la terminologie des composants structurels de la motocyclette Aprilia, axé sur une enquête de « sociolinguistique en milieu de travail » et qui a pour but de décrire le rapport réel entre terminologie et variétés de la langue, tout en considérant les études de Rita Temmerman sur la « théorie de la terminologie sociocognitive ».La présence et l’utilisation de la variété vénète en milieu de travail a été vérifié à l’aide d’un questionnaire de sociolinguistique, distribué à 10% des actifs chez Aprilia S.p.A. L’examen des données, a finalement mené à une analyse contrastive entre la « stratification linguistique en milieu de travail » et l’architecture de la langue italienne standard proposée par Berruto.This paper attempts to shed new light on the possible relationships within terminology and language varieties, considering a more realistic approach to the linguistics facts and to the communication standards of a restricted “social network” from the viewpoint of Rita Temmerman’s theory on sociocognitive approach to terminological description. A questionnaire has been distributed to 10% of the working employees of Aprilia S.p.A, a motorcycle producer, axing on the prestige and visibility of the regional variety as main language of communication of the working place. The gathering and analysis of the data gave an interesting outline which led us to a comparison between the “linguistic stratification” of the firm and the architecture of the standard Italian language

cDNA-AFLP analysis of gene expression changes in apple trees induced by phytoplasma infection during compatible interaction

peer reviewedAbstract In order to gain insight into molecular and physiological changes in apple trees during compatible interaction with two ‘Candidatus Phytoplasma mali’ strains (AP and AT), cDNA-Amplified Fragment Length Polymorphism (cDNA-AFLP) technique was used. A rootstock of apple (MM106) susceptible to ‘Ca. P. mali’ was used to extend the range of the potential host responses by the maximum number of identified genes that will be deregulated by phytoplasma in apple. Gene expression comparisons were studied in three directions: healthy versus infected samples, symptomatic versus nonsymptomatic sample, and AP-infected versus ATinfected sample. Forty-five genes whose steady-state levels of expression significantly changed in response to phytoplasma infection were identified. Among their partial cDNA sequences, only 27 showed similarity to DNA or protein data bases; of these, 18 were related to known genes in plants, and the rest were related to unknown or hypothetical proteins. Eighteen out of 45 did not show any similarity with sequences in data bases (potential novel genes). Quantitative real-time RT-PCR (qRT-PCR) was used to confirm differential expression of AFLP identified genes, and showed the similar profile expression for 11 known genes among 18, and for 13 unknown, hypothetical or novel genes among 27. Changes in gene expression involved a wide spectrum of biological functions, including processes of metabolism, cell defence, senescence, photosynthesis, transport, transcription, signal transduction and protein synthesis. This is the first study of global gene profiling in plants in response to phytoplasma infections using cDNA-AFLP, and a model is proposed to explain the mode of action of the ‘Ca. P. mali’ in apple

Preliminary evaluation of antimicrobial activity of some chemicals on in vitro apple shoots infected by 'Candidatus Phytoplasma mali'.

peer reviewe

Early and late follow-up of untreated traumatic aortic lesion: a support to delayed surgery

Fuente Fuente, Carlos;Montes Gil, Antonio;Periel Piquer, Montserra