Even though the Hartley-entropy-based contrast function guarantees an unmixing local minimum, the reported nonsmooth optimization techniques that minimize this nondifferentiable function encounter computational bottlenecks. Toward this, Powell's derivative-free optimization method has been extended to a Riemannian manifold, namely, oblique manifold, for the recovery of quasi-correlated sources by minimizing this contrast function. The proposed scheme has been demonstrated to converge faster than the related algorithms in the literature, besides the impressive source separation results in simulations involving synthetic sources having finite-support distributions and correlated images.

A model is proposed to describe the spike-frequency adaptation observed in many neuronal systems. We assume that adaptation is mainly due to a calcium-activated potassium current, and we consider two coupled stochastic differential equations for which an analytical approach combined with simulation techniques and numerical methods allow to obtain both qualitative and quantitative results about asymptotic mean firing rate, mean calcium concentration and the firing probability density. A related algorithm, based on the Hazard Rate Method, is also devised and described.

The likelihood of a subglacial lake beneath Amundsenisen Plateau at Southern Spitzbergen, Svalbard, pointed out by the flat signal within the Ground Penetrating Radar (GPR) remote survey of the area, is justified, here, via numerical simulation.This investigation has been developed under the assumption that the icefield thickness does not change on average, as it is confirmed by recently published physical measurements taken over the past 40 years. As a consequence, we have considered admissible to assume the temperature and density in-depth profiles, snow and firn layers included, to be stationary. The upper icefield surface and the rocky bed surface are known in detail.The mathematical numerical model is based on an unsteady Stokes formulation of the ice flow and on a Large Eddy Simulation formulation of the lake water flow. Following the numerical sensitivity results that we presented on a recent issue of this journal, we have, here, upgraded the model by improving the description of critical aspects of icefield thermo-mechanics, such as the local water release within temperate ice as a strain heating effect and ice sliding on the bedrock. The first issue impacts on ice texture, i.e. its constitutive equation, while the second one drives icefield surging. Actually, we have obtained 13% enhancement of the numerical value of the ice top surface velocity versus measured one, and physically consistent numerical ice sliding velocity values at the rocky bottom.Adopting a new physically sound initial subglacial lake water temperature and velocity fields, we present the numerical simulation of the whole system, icefield and conjectured subglacial lake, within a time slot of 20,000. d (physical time), when its evolution trend was clearly captured. By then, although the maximum value of water temperature keeps rather low, metastability appears to be overcome on more than half of the conjectured basin, with a progressive trend in time in support to the subglacial lake existence. We stress that the numerical subglacial lake surface converges to the GPR flat signal spot with tolerance equal to the GPR measuring error.Finally, we observe that the numerical simulation results meet quantitatively and qualitatively the fundamental aspects of the conjecture, so that further on-site investigations on the subglacial lake (e.g. drilling operations) appear fully justified.

We derive and test a formal explicit approximated rule for the reconstruction of a damaged inaccessible portion of the boundary of a thin conductor from thermal data collected on the opposite accessible face.

In this paper, to complete the global dynamics of a multi-strains SIS epidemic model, we establish a precise result on coexistence for the cases of the partial and complete duplicated multiple largest reproduction ratios for this model.

MIPAS on ENVISAT performed almost continuous measurements of atmospheric composition for approximately 10 years, from June 2002 to April 2012. ESA processor, based on the algorithm ORM (Optimized Retrieval Model), originally designed for the Near Real Time analysis and developed by an European Consortium led by IFAC, is currently used for the reanalysis of the full MIPAS mission. The maintenance and the upgrade of the ESA processor are made in the frame of the Quality Working Group, where a fruitful collaboration among Level 1, Level 2 and validation teams can be exploited. This collaboration is essential to pursue improvements in the accuracy of the products and their characterization. This paper is meant to describe the most recent upgrades in the ESA processor performed to improve the quality of ESA products. In particular, the full mission was recently reprocessed with L1 V7 and L2 V7 processors, containing significant improvements with respect to previous version V6, and further improvements are in preparation, that will be collected in version 8 of the ESA processor. Improvements involve both L1 and L2 processors, as well as the auxiliary data. Improvements in the L1 processor consist in a correction of the instrumental drift, improved spike detection algorithm and new Instrument Line Shape, as well as the use of measured daily gain instead of weekly gain. Improvements in the L2 processor include a different approach for retrieving atmospheric continuum, the use of an a posteriori regularization with altitude dependent constraint, a better approach for handling interfering species, a reduced bias in CFC-11, the handling of horizontal inhomogeneities and the use of ECMWF altitude/pressure relation for determining more accurate altitudes. Improvements in the auxiliary data consist in the use of microwindows with larger information content, new spectroscopic database and diurnally varying climatological dataset. Furthermore, with each new version additional species are provided, leading to 20 the number of retrieved species by the L2 V8 processor. Improvements in the V7 products will be revised on the light of the results of the validation with correlative measurements, and, by comparing the first new L2 V8 products with the L2 V7 ones, a preliminary assessment of the performance of the new V8 processor will be performed.

We present the results of the algorithm modeling the horizontal gradients in the ESA retrieval of MIPAS data ORM v8.

Nell'ambito del workshop d'inaugurazione dell'anno accademico dell'Associazione Matematica & Realta', la presentazione intende offrire alla platea degli insegnanti di matematica delle scuole superiori di secondo grado un esempio realmente implementato di attivita' di studio e ricerca di matematica applicata. Vi si trovano ben delineati i passi fondamentali che conducono dal problema reale alla soluzione numerica proposta, manifestando la necessita' di conoscenze interdisciplinari per giungere all' uso critico ed efficace dello strumento matematico. Il problema specifico considerato e' la validazione dell'ipotesi dell'esistenza di un lago subglaciale a Spitzbergen, isola dell'arcipelago delle Svalbard.

The segmentation of speckled images, as the synthetic aperture radar (SAR) images, is usually recognized as a very complex problem, because of the speckle, multiplicative noise, which produces granular images. In segmentation problems, based on level set method, the evolution of the curve is determined by a speed function, which is fundamental to achieve a good segmentation. In this paper we propose a study of the new speed function obtained by the linear combination of image average intensity and image gradient speed functions. Thus the aim is tuning the combined speed in the segmentation process. We segmented synthetic images by tuning parameters of the new speed function and we evaluated the best computed results. Then we applied this experimental setup to real SAR images, which are PRecision Images, acquired during European Remote Sensing mission, and a Cosmo-SkyMed image. In particular, we are interested in monitoring complex areas with low light covered by clouds, as coastlines and polar regions may be. In Earth Observation, the acquisition of SAR data becomes fundamental, since the SAR sensor can work in the night/day and in all weather conditions.

The melting of glaciers coming with climate change threatens the heritage of the last glaciation of Europe likely contained in subglacial lakes in Greenland and Svalbard. This aspect urges specialists to focus their studies (theoretical, numerical, and on-field) on such fascinating objects. Along this line, we have approached the validation of the conjecture of the existence of a subglacial lake beneath the Amundsenisen Plateau at South-Spitzbergen, Svalbard, where ground penetrating radar measurements have revealed several flat signal spots, the sign of the presence of a body of water. The whole investigation aspects, mathematical modeling and numerical simulation procedure, and the numerical results are presented through a trilogy of papers of which the present one is the last. The time-dependent mathematical model in the background of the numerical algorithm includes the description of dynamics and thermodynamics of the icefield and of the subglacial lake, with heat exchange and liquid/solid phase-change mechanisms at the interface. Critical modeling choices and confidence in the algorithm are granted by the numerical results of the sensitivity analysis versus the contribution of ice water content, of firn and snow layers at top of the icefield and versus the approximation of ice sliding on bedrock. The two previous papers deal with these issues, show successful comparison with local measured quantities, and demonstrate numerically the likelihood of the subglacial lake. In this work, we aim at providing the studied case and the numerical algorithm with a possible paradigmatic value. At this aim, we introduce on-field measurement data related to the physical characteristics of the Amundsenisen Plateau that justify the adoption of significant modeling simplifications, here, focussed from physical viewpoint. Furthermore, we present the numerical algorithm and discuss several representative results from the numerical test to point out the type of results coming from the procedure. Such results might, eventually, provide a support to the decision to undertake drilling operations for tracing the subglacial water bio-chemicals generally present within the accreted ice above the presumed ice/water front.

L'articolo delinea un breve ritratto di Beppo Levi e narra di alcune vicende che lo videro protagonista prima, durante e dopo le leggi razziali fasciste quando venne costretto ad emigrare in Argentina. L'occasione è la donazione all'Archivio dell'Istituto per le Applicazioni del Calcolo "Mauro Picone" delle "carte italiane" di Beppo Levi provenienti dall'Argentina.

L'Istituto per le Applicazioni del Calcolo "Mauro Picone" (IAC) si appresta nel 2017 a celebrare nel 2017 i novantanni della sua fondazione. L'articolo fa una breve storia dell'IAC e ricorda i successi del passato.

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Neglecting the horizontal variability of the atmosphere in the forward model for the simulation of limb emission radiances causes a systematic error in MIPAS retrieved profiles. The horizontal gradient model will be introduced into the Optimized Retrieval Model (ORM) v8, which will be used for the final ESA reprocessing of the whole mission. Several optimizations exploiting the spherical symmetry of the atmosphere can no longer be used. Therefore, both the ray tracing and the radiative transfer integration algorithms have been completely rewritten. We illustrate the choices adopted for the implementation of the horizontal gradient model. We show its performances versus the previous algorithm that assumes the horizontal homogeneity of the atmosphere. Finally we compare our results to those of other retrieval models that take into account the horizontal variability of the atmosphere.

In this study non-negative matrix factorization (NMF) was hierarchically applied to simulated and in vivo three-dimensional 3 T MRSI data of the prostate to extract patterns for tumour and benign tissue and to visualize their spatial distribution. Our studies show that the hierarchical scheme provides more reliable tissue patterns than those obtained by performing only one NMF level. We compared the performance of three different NMF implementations in terms of pattern detection accuracy and efficiency when embedded into the same kind of hierarchical scheme. The simulation and in vivo results show that the three implementations perform similarly, although one of them is more robust and better pinpoints the most aggressive tumour voxel(s) in the dataset. Furthermore, they are able to detect tumour and benign tissue patterns even in spectra with lipid artefacts. Copyright (C) 2016 John Wiley & Sons, Ltd.

The proposed algorithm is based on the block anti-triangular form of the original matrix M, as introduced by the authors in [11]. Via successive orthogonal similarity transformations this form is then updated to a new form A = QMQ(T), whereby the first k rows and columns of M have elements bounded by a given threshold tau and the remaining bottom right part of M is maintained in block anti-triangular form. The updating transformations are all orthogonal, guaranteeing the backward stability of the algorithm, and the algorithm is very economical when the near rank deficiency is detected in some of the anti diagonal elements of the block anti-triangular form. Numerical results are also given showing the reliability of the proposed algorithm. 2015 Elsevier Inc. All rights reserved. We present an algorithm for computing a symmetric rank revealing decomposition of a symmetric n x n matrix A, as defined in the work of Hansen & Yalamov [9]: we factorize the original matrix into a product A = QMQ(T), with Q orthogonal and M symmetric and in block form, with one of the blocks containing the dominant information of A, such as its largest eigenvalues. Moreover, the matrix M is constructed in a form that is easy to update when adding to A a symmetric rank-one matrix or when appending a row and, symmetrically, a column to A: the cost of such an updating is O(n(2)) floating point operations.

We consider finite difference schemes which approximate one-dimensional dissipative hyperbolic systems. Using precise analytical time-decay estimates of the local truncation error, we show that it is possible to introduce some suitable modification in standard upwinding schemes to design schemes which are increasingly accurate for large times when approximating small perturbations of stable asymptotic states, respectively, around stationary solutions and in the diffusion (Chapman-Enskog) limit.

Numerical optimisation of a ship hull requires, like every shape design optimisation problem, the definition of a parametric expression of the object to be deformed. In this phase, some decisions are taken regarding the shape variability and the portion of the hull to be modified: the parameterisation of the hull is problem-dependent, with implications from the performances to be optimised (objective functions), and the right choice is not easy. In this paper, a parameterisation tool able to automatically select the optimal parameters selection and configuration, detecting together the most convenient portions of the hull to be modified and its optimal shape, is presented: the final solution is directly influenced by the characteristics of the specific optimisation problem. The total number of design parameters represents the only free choice about the parameterisation, while the areas on which the deformation is implemented, together with all the other parameters, are automatically selected without any further action by the designer.