132,719 research outputs found
Selection of negatives in Hopfield networks
No full textIn this work we propose a novel methodology for graph-based semi-supervised learning which is composed of two main steps: Step 1) a novel strategy for PU learning specific for Hopfield networks, which can be applied both to structured classes and to hierarchy-less contexts; Step 2) a semi-supervised classifier based on a family of parametric Hopfield networks, which embeds the negative selection
performed at Step 1) in the dynamics of network
Exploiting Negative Sample Selection for Prioritizing Candidate Disease Genes
No full textA major challenge in bio-medicine is finding the genetic causes of human diseases, and researchers are often faced with a large number of candidate genes. Gene prioritization methods provide a valuable support in guiding researchers to detect reliable candidate causative-genes for a disease under study. Indeed, such methods rank genes according to their association with a disease of interest. Actually, the majority of genetic disorders has few or none causative genes associated with them; this induces a high labeling unbalance in the corresponding ranking problems, thus linking the need of achieving reliable solutions to the adoption of imbalance-aware techniques. We propose the use of an expressly designed imbalance-aware methodology for prioritizing genes, which first rebalances the training set entries through a negative selection procedure, then applies a learning algorithm 'sensitive' to the misclassification of positive instances, to provide the gene ranking. The algorithm has a reduced time complexity, which makes feasible its application on large-sized datasets. The validation of this methodology proved its competitiveness with state-of-art techniques on a benchmark composed of 708 selected Medical Subject Headings diseases, and provided some putative novel gene-disease associations
Exponentially fitted methods with a local energy conservation law
No full textA new exponentially fitted version of the discrete variational derivative method for the efficient solution of oscillatory complex Hamiltonian partial differential equations is proposed. When applied to the nonlinear Schrodinger equation, this scheme has discrete conservation laws of charge and energy. The new method is compared with other conservative schemes from the literature on a benchmark problem whose solution is an oscillatory breather wave
On the Computational Solution of a Corrosion Model
No full textWe consider a phase field model for studying the corrosion of a 304 stainless steel metal immersed in a sodium chloride solution. Phase field models have been widely used to simulate moving interface problems in a variety of contexts. On one hand, these models have the benefit of treating implicitly the moving boundary by introducing an auxiliary variable. On the other hand, their nature is highly stiff and their computational cost is very high. In this talk we consider convenient numerical techniques for the efficient solution of the considered problem with a focus on their Matlab implementation
A MATLAB code for the computational solution of a phase field model for pitting corrosion
No full textPhase field models have been widely considered to simulate corrosion dynamics characterised by moving boundaries. The benefits of using these models rely on the fact that the moving interface is implicitly treated by means of the introduction of an auxiliary variable. However, the computational cost of these methods is typically very high. In this paper we consider a model for pitting corrosion of a metallic specimen immersed in an electrolytic solution. For its numerical solution we consider a method that relies on a suitable splitting of the governing equations and on the use of exponential integrators. The use of modern MATLAB functions to evaluate the effect of matrix exponentials on a vector is crucial for the efficient implementation of the method. The software used is presented and discussed in detail, and some numerical tests are introduced to show the performance of the proposed algorithms
La scimmia di Dio. L'emozione della guerra mediale
No full textAttraverso una serie di autori di riferimento, come Thomas Pynchon, J. D. Salinger e Philip K. Dick, la monografia indaga sulla modificazione della percezione dello spazio del tempo a seguito delle grandi innovazioni mediali del secondo dopoguerra
A conservative numerical method for a time fractional diffusion equation
No full textGeometric numerical integration, the branch of numerical analysis with the goal of finding approximate solutions of differential equations that preserve some structure of the continuous problem, is a well established field of research [5]. In particular, requiring that invariants or conservation laws are preserved, on one hand, applies on the approximations some constraints that are satisfied also by the exact solutions. On the other hand, it guarantees a better propagation of the error over long integration times [3].
In the last two decades, new techniques for finding conservation laws of fractional differential equations have been derived by suitably generalising methods for PDEs [4, 6]. However, the numerical preservation of conservation laws of time fractional differential
equations is a research topic still at an embryonic state. This talk deals with the numerical solution of diffusion equations in the form
D^α_t u = D^2_x K(u), α ∈ R,
where D_x is the partial derivative in space, K is an arbitrary regular function, and D^α_t
denotes the Riemann-Liouville fractional derivative of order α.
The proposed numerical method combines a finite difference scheme in space with a spectral time integrator and preserves discrete versions of the conservation laws of the original differential equation [1, 2].
The conservative and convergence properties of the proposed method are verified by the computational solution of some numerical experiments.
References
[1] K. Burrage, A. Cardone, R. D’Ambrosio, B. Paternoster. Numerical solution of time fractional diffusion systems. Appl. Numer. Math., 116 (2017), 82–94.
[2] A. Cardone, G. Frasca-Caccia. Numerical conservation laws of time fractional diffusion PDEs. arXiv.2203.01966, (2022).
[3] A. Dur ́an, J. M. Sanz-Serna. The numerical integration of relative equilibrium solutions. Geometric theory. Nonlinearity, 11, 1547–1567, (1998).
[4] G. S. F. Frederico, D. F. M. Torres. Fractional conservation laws in optimal control theory. Nonlinear Dyn., 53 (2008), 215–222.
[5] E. Hairer, C. Lubich, G. Wanner. Geometric Numerical Integration. Structure Preserving Algorithms for Ordinary Differential Equations, volume 31 of Springer Series in Computational Mathematics. Springer, Berlin, second edition, 2006.
[6] S. Y. Lukashchuk. Conservation laws for time-fractional subdiffusion and diffusionwave equations. Nonlinear Dyn., 80 (2015), 791–80
Illuminazione nell’architettura antica: ipotesi ricostruttive delle modalità di comunicazione visuale in alcuni contesti di edilizia religiosa tra V e VI secolo d.C.
No full textTema di questa ricerca è lo studio delle modalità di illuminazione artificiale e naturale dello spazio sacro in alcuni contesti di architettura religiosa di V e VI secolo. I contesti architettonici prescelti per questo studio sono la Basilica dell'Acheiropoietos di Salonicco e la Basilica dei Santi Sergio e Bacco, di Costantinopoli, dei quali sono stati realizzati dei modelli tridimensionali con il supporto della grafica computerizzata. Oltre allo studio dei due edifici e delle loro fasi edilizie (nonché delle loro compagini architettoniche e degli apparati di arredo liturgico), si è inteso cercare di ricostruire gli schemi di illuminazione artificiale al loro interno. A tal fine è stato condotto un lavoro preliminare di studio ad ampio raggio su questa classe di manufatti provenienti da scavi di edifici di culto di età tardo antica e protobizantina, con una particolare attenzione a quei siti che hanno restituito informazioni puntuali sul posizionamento dei lumi. Oltre a ciò sono stati considerati anche manufatti fuori contesto, contenuti in collezioni museali o private, nonchè le rappresentazioni iconografiche di questi oggetti nelle fonti documentali (anche più tarde). Un particolare approfondimento è stato dedicato alle fonti scritte che trattano, anche in maniera incidentale, di questi manufatti, soprattutto in relazione ad uno dei due casi scelti, ossia la Basilica dei Santi Sergio e Bacco. Sono stati quindi proposti schemi di distribuzione dei lumi fissi e, in parte, anche mobili per ricostruire l'assetto luminoso delle basiliche durante le celebrazioni liturgiche diurne festive. La seconda parte dello studio, invece, è consistita nel realizzare delle simulazioni virtuali, ottenute con l'ausilio della computer grafica, dell'illuminazione naturale di questi edifici in antico. Grazie ad un particolare applicativo, infatti, è stato possibile impostare la fonte luminosa naturale (sun) nel mondo virtuale calcolandone la posizione in un dato momento/giorno/anno georiferendo i modelli tridimensionali
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