DSpace collection:
http://ria.ua.pt:80/handle/10773/5868
Sun, 17 Jun 2018 19:22:56 GMT2018-06-17T19:22:56ZAnalysis of a fractional SEIR model with treatment
http://ria.ua.pt:80/handle/10773/23526
title: Analysis of a fractional SEIR model with treatment
authors: Almeida, RicardoMon, 01 Jan 2018 00:00:00 GMThttp://ria.ua.pt:80/handle/10773/235262018-01-01T00:00:00ZArea burned in Portugal over recent decades: an extreme value analysis
http://ria.ua.pt:80/handle/10773/23203
title: Area burned in Portugal over recent decades: an extreme value analysis
authors: Scotto, M. G.; Gouveia, S.; Carvalho, A.; Monteiro, A.; Martins, V.; Flannigan, M. D.; San-Miguel-Ayanz, J.; Miranda, A. I.; Borrego, C.
abstract: Forest fires are a major concern in Europe, particularly in Portugal where large forest fires are responsible for negative environmental, social and economic effects. In this work, a long time series of daily area burned in 18 Portuguese districts (north, coastal areas and inner-south) from 1980 to 2010 are analysed to characterise extreme area burned and regional variability. The analysis combines the peak-over-threshold method and classification techniques to cluster the time series on the basis either of their corresponding tail indices or their predictive distributions for 5- and 15-year return values, that is, the level that is exceeded on average once every 5 or 15 years. As previously reported in other wildfire studies, the results show that the distributions of area burned (1980-2010) are heavy tailed for all Portuguese districts, with considerable density in the tail, indicating a non-negligible probability of occurrence of days with very large area burned. Moreover, clustering based on tail indices identified three distinct groups with spatial pattern closely related to the percentage of shrub cover within each district. Finally, clustering based on return values shows that the largest return levels of area burned are expected to occur in districts located in the centre and south of Portugal.Wed, 01 Jan 2014 00:00:00 GMThttp://ria.ua.pt:80/handle/10773/232032014-01-01T00:00:00ZOn the multiplicity of α as an eigenvalue of Aα(G) of graphs with pendant vertices
http://ria.ua.pt:80/handle/10773/23003
title: On the multiplicity of α as an eigenvalue of Aα(G) of graphs with pendant vertices
authors: Cardoso, Domingos M.; Pastén, Germain; Rojo, Oscar
abstract: Let $G$ be a simple undirected graph. Let $0\leq \alpha \leq 1$. Let $$A_{\alpha}(G)= \alpha D(G) + (1-\alpha) A(G)$$ where $D(G)$ and $A(G)$ are the diagonal matrix of the vertex degrees of $G$ and the adjacency matrix of $G$, respectively. Let $p(G)>0$ and $q(G)$ be the number of pendant vertices and quasi-pendant vertices of $G$, respectively. Let $m_{G}(\alpha)$ be the multiplicity of $\alpha$ as eigenvalue of $A_{\alpha}(G)$.
It is proved that
\begin{equation*}
m_{G}(\alpha) \geq p(G) - q(G)
\end{equation*}
with equality if each internal vertex is a quasi-pendant vertex. If there is at least one internal vertex which is not a quasi-pendant vertex, the equality
\begin{equation*}
m_{G}(\alpha)= p(G)-q(G)+m_{N}(\alpha)
\end{equation*}
is determined in which $m_{N}(\alpha)$ is the multiplicity of $\alpha$ as eigenvalue of the matrix $N$. This matrix is obtained from
$A_{\alpha}(G)$ taking the entries corresponding to the internal vertices which are non quasi-pendant vertices. These results are
applied to search for the multiplicity of $\alpha$ as eigenvalue of $A_{\alpha}(G)$ when $G$ is a path, a caterpillar, a circular
caterpillar, a generalized Bethe tree or a Bethe tree. For the Bethe tree case, a simple formula for the nullity is given.Sun, 15 Apr 2018 23:00:00 GMThttp://ria.ua.pt:80/handle/10773/230032018-04-15T23:00:00ZRealizable lists on a class of nonnegative matrices
http://ria.ua.pt:80/handle/10773/23002
title: Realizable lists on a class of nonnegative matrices
authors: Andrade, Enide; Manzaneda, Cristina; Robbiano, María
abstract: A square matrix of order $n$ with $n\geq 2$ is called \textit{permutative matrix} when all its rows are permutations of the first row. In this paper recalling spectral results for partitioned into $2$-by-$2$ symmetric blocks matrices
sufficient conditions on a given complex list to be the list of the eigenvalues of a nonnegative permutative matrix are given. In particular, we study NIEP and PNIEP when some complex elements in the lists under consideration have non-zero imaginary part. Realizability regions for nonnegative permutative matrices are obtained. A Guo's realizability-preserving perturbations result is obtained.Tue, 14 Aug 2018 23:00:00 GMThttp://ria.ua.pt:80/handle/10773/230022018-08-14T23:00:00Z