Browsing by Author "Gomes, Teresa"
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- An effective algorithm for obtaining the minimal cost pair of disjoint paths with dual arc costsPublication . Gomes, Teresa; Craveirinha, José; Jorge, LuísaRouting optimisation in some types of networks requires the calculation of the minimal cost pair of disjoint paths such that the cost functions associated with the arcs in the two paths are different. An exact algorithm for solving this NP-complete problem is proposed, based on a condition which guarantees that the optimal path pair cost has been obtained. This optimality condition is based on the calculation of upper and lower bounds on the optimal cost. A formal proof of the correctness of the algorithm is described. Extensive experimentation is presented to show the effectiveness of the algorithm, including a comparison with an integer linear programming formulation.
- An effective algorithm for obtaining the set of all minimal cost pairs of disjoint paths with dual arc costsPublication . Gomes, Teresa; Craveirinha, José; Jorge, LuísaIn today’s telecommunications networks it is necessary, for reliability reasons, to use protection schemes involving the calculation of two (or more) disjoint paths for each node-to-node connection, especially when large amounts of traffic have to be routed in the network. This concern is particularly relevant in optical networks, namely WDM (Wavelength Division Multiplexing) networks due to the very high rates supported by lightpaths, and in the Internet using MPLS (Multiprotocol Label Switching). In this context the problem of obtaining optimal (arc or node) disjoint paths, for increasing network reliability while minimising bandwidth consumption, is extremely important. The problem of finding k disjoint paths from s to t (two distinct nodes), in a network with k different costs on every arc such that the total cost of the paths is minimised is NP-complete even for k = 2, when the relationship between the k arc costs (in the same arc) is arbitrary. When k = 2 these networks are usually designated as dual arc cost networks. In this paper we propose an exact algorithm for finding the whole set of arc-disjoint path pairs, with minimal cost in a network with dual arc costs. The addressed problem can be formalised as follows. Let G = (V,E) be a directed network with node set V = {v1, v2, . . . , vn} and and arc set E = {e1, e2, . . . , em} (were n and m designate the number of nodes and arcs in G, respectively), where two different non-negative cost functions (or metrics) in the arcs, are defined: η(j) : E → IN0 (j = 1, 2) (1) η(j)((va, vb)) = c(j) vavb (va, vb) ∈ E (2) The cost C(j) of a (loopless) path p in G with respect to metric η(j), is: C(j)(p) = X (va,vb)∈p c(j) vavb (j = 1, 2) (3) Let path p, p = hv1, e1, v2, . . . , vi−1, ei−1, vii, be given as an alternate sequence of nodes and arcs from G, such that the tail of ek is vk and the head of ek is vk+1, for k = 1, 2, . . . , i − 1 (all the vi in p are different). Let the set of nodes in p be V ∗(p) and the set of arcs in p be E∗(p). Two paths p = hv1, e1, v2, . . . , vi−1, ei−1, vii and q are arc-disjoint if E∗(p) ∩ E∗(q) = ∅. Two paths p and q are disjoint if V ∗(p) ∩ V ∗(q) = ∅, and are internally disjoint if {v2, . . . , vi−1} ∩ V ∗(q) = ∅. We will say that two paths are node disjoint if they are internally disjoint. The addressed problem is to find the whole set of pairs (p, q) of arc disjoint paths which minimise the total cost of the pair, defined by: C[(p, q)] = C(1)(p) + C(2)(q) (4) where p and q have the same source and sink node. An exact algorithm for solving this NP-complete problem will be proposed, based on a condition which guarantees that the optimal path pair cost has been obtained. This optimality condition is based on the calculation of increasingly tightened upper and lower bounds on the optimal cost. A formal proof of the correctness of the algorithm is described. Extensive experimentation is presented to show the effectiveness of the algorithm. It will also be explained how the proposed approach can also be used for obtaining the minimal cost disjoint path pair with constraints on the maximum number of arcs allowed per path, a problem of interest in various applications, namely in telecommunication networks.
- An effective algorithm for obtaining the whole set of minimal cost pairs of disjoint paths with dual arc costsPublication . Gomes, Teresa; Craveirinha, José; Jorge, LuísaIn telecommunication networks design the problem of obtaining optimal (arc or node) disjoint paths, for increasing network reliability, is extremely important. The problem of calculating kc disjoint paths from s to t (two distinct nodes), in a network with kc different (arbitrary) costs on every arc such that the total cost of the paths is minimised, is NP-complete even for kc = 2. When kc = 2 these networks are usually designated as dual arc cost networks. In this paper we propose an exact algorithm for finding the whole set of arc-disjoint path pairs, with minimal cost in a network with dual arc costs. The correctness of the algorithm is based on a condition which guarantees that the optimal path pair cost has been obtained and on a proposition which guarantees that at the end of the algorithm all the optimal pairs have been obtained. The optimality condition is based on the calculation of upper and lower bounds on the optimal cost. Extensive experimentation is presented to show the effectiveness of the algorithm.
- An on-line routing algorithm of locally protected paths with exact reservationsPublication . Jorge, Luísa; Gomes, TeresaRouting locally protected Label Switched Paths (LSPs) in MultiProtocol Label Switching (MPLS) networks, achieving efficient shared path protection under distributed control and partial information, is a difficult problem. An estimate of the additional protection bandwidth required in every link of the protection paths is deduced from an equivalent parameter defined in the context of global protection. A method for minimal allocation of protection bandwidth in the context of local shared protection will also be proposed. On-line routing algorithms solutions should be obtained in a very short time, therefore an improved version of the heuristic in [1] is presented, resulting in an new version of this on-line routing algorithm of locally protected paths. The performance of the algorithm in [1] and of the proposed algorithm were evaluated, using minimal allocation of protection bandwidth. Experimental results show that the new algorithm has significant advantages regarding the total bandwidth used, the average number of hops of the active path and the probability of the rejection of new requests.
- Análise sensorial de vários tipos de hidromelPublication . Gomes, Teresa; Dias, Teresa; Andrade, João Verdial; Cadavez, Vasco; Morais, Jorge Sá; Ramalhosa, Elsa; Estevinho, Leticia M.A região de Trás-os-Montes e uma das grandes produtoras de mel no pais. No entanto, existe dificuldade em escoar a produção surgindo o hidromel como uma alternativa possível para ultrapassar este problema. Com base em resultados obtidos pela nossa equipa, este trabalho teve como objective avaliar as características sensoriais do hidromel produzido a escala piloto. Resultados anteriores indicam que a levedura Saccharomyces cerevisiae Fermol® Reims Champagne (Pascal Biotech®) á a mais indicada para a fermentação do hidromel. As condições ideais para a produção de hidromel obtidas com base no desenho experimental foram: temperatura entre os 24°C e os 29°C e concentração de sais entre 85 e 100 g/hL.
- Antioxidant activity and bioactive compounds of lettuce improved by espresso coffee residuesPublication . Cruz, Rebeca; Gomes, Teresa; Ferreira, Anabela; Mendes, Eulália; Baptista, Paula; Cunha, Sara C.; Pereira, J.A.; Ramalhosa, Elsa; Casal, SusanaThe antioxidant activity and individual bioactive compounds of lettuce, cultivated with 2.5–30% (v/v) of fresh or composted espresso spent coffee grounds, were assessed. A progressive enhancement of lettuce’s antioxidant capacity, evaluated by radical scavenging effect and reducing power, was exhibited with the increment of fresh spent coffee amounts, while this pattern was not so clear with composted treatments. Total reducing capacity also improved, particularly for low spent coffee concentrations. Additionally, very significant positive correlations were observed for all carotenoids in plants from fresh spent coffee treatments, particularly for violaxanthin, evaluated by HPLC. Furthermore, chlorophyll a was a good discriminating factor between control group and all spent coffee treated samples, while vitamin E was not significantly affected. Espresso spent coffee grounds are a recognised and valuable source of bioactive compounds, proving herein, for the first time, to potentiate the antioxidant pool and quality of the vegetables produced.
- Application of response surface methodology for obtaining lettuce (Lactuca sativa L.) by-products extracts with high antioxidative propertiesPublication . Gomes, Teresa; Delgado, Teresa; Ferreira, Anabela; Pereira, J.A.; Baptista, Paula; Casal, Susana; Ramalhosa, ElsaThe main objective of the present work was to optimize the extraction conditions for simultaneous maximization of total reducing (TRC) and antioxidant (AC) capacities for lettuce (Lactuca sativa L.) by-products extracts, using response surface methodology. For this, a design of experiments (DOE) with different combinations of solvents (water, methanol and acetone) extraction temperatures (30–60 ◦C) and time (10–60 min) on the TRC and AC was applied. Higher and consistent fittings using second order polynomial models of the experimental data with regard to TRC (R2 = 0.529, p lack of fit > 0.05) and AC (R2 = 0.900, p lack of fit > 0.05) were obtained with methanol. The optimum extraction conditions based on combination responses for TRC and AC were: 30% methanol (v/v), 60 ◦C and 60 min. A close agreement between experimental and predicted values was found when applying these conditions. Furthermore, when aqueous extracts were prepared (e.g. 45 ◦ C, 10 min), these presented similar TRC and AC properties to those obtained by the above optimum extraction conditions, having the advantage of applying mild extraction conditions and avoiding the use of organic solvents in their preparation.
- Bacterial disease induced changes in fungal communities of olive tree twigs depend on host genotypePublication . Gomes, Teresa; Pereira, J.A.; Lino-Neto, Teresa; Bennett, Alison E.; Baptista, PaulaIn nature, pathogens live and interact with other microorganisms on plant tissues. Yet, the research area exploring interactions between bacteria-fungi and microbiota-plants, within the context of a pathobiome, is still scarce. In this study, the impact of olive knot (OK) disease caused by the bacteria Pseudomonas savastanoi pv. savastanoi (Psv) on the epiphytic and endophytic fungal communities of olive tree twigs from three different cultivars, was investigated in field conditions. The ITS-DNA sequencing of cultivable fungi, showed that OK disease disturbs the resident fungal communities, which may reflect changes in the habitat caused by Psv. In particular, a reduction on epiphyte abundance and diversity, and changes on their composition were observed. Compared to epiphytes, endophytes were less sensitive to OK, but their abundance, in particular of potential pathogens, was increased in plants with OK disease. Host genotype, at cultivar level, contributed to plant fungal assembly particularly upon disease establishment. Therefore, besides fungi - Psv interactions, the combination of cultivar - Psv also appeared to be critical for the composition of fungal communities in olive knots. Specific fungal OTUs were associated to the presence and absence of disease, and their role in the promotion or suppression of OK disease should be studied in the future.
- Calculating a maximally node and SRLG-disjoint path pair of min-sum cost in GMPLS networksPublication . Gomes, Teresa; Jorge, Luísa; Melo, Paulo; Girão-Silva, Rita; Mendes, SérgioIn end-to-end connections it is sometimes not possible to find a totally disjoint path pair. In this context it may be reasonable to accept a path pair which is as disjoint as possible, and thus provide the best (in a certain sense) level of the single fault protection that can be ensured. A Shared Risk Link Group (SRLG) is a group of links which have a common risk of failure (which may result from the sharing of common resources at a lower layer). The concept of SRLG allows an upper layer to be capable of implementing diverse routing, taking into account the existence of common risks of failure. Two heuristics for solving the min-sum maximally node and SRLG-disjoint path pair, formulated as a multi-objective optimization problem, are presented. The relative performance of the heuristics is evaluated using three different networks. The envisaged application scenario of these path calculation algorithms is Generalized Multiprotocol Label Switching (GMPLS) networks.
- Deciphering plant health status: the link between secondary metabolites, fungal community and disease incidence in olive treePublication . Gomes, Teresa; Pereira, J.A.; Moya-Larano, Jordi; Poveda, Jorge; Lino-Neto, Teresa; Baptista, PaulaPlant-associated microorganisms are increasingly recognized to play key roles in host health. Among several strategies, associated microorganisms can promote the production of specific metabolites by their hosts. However, there is still a huge gap in the understanding of such mechanisms in plant-microorganism interaction. Here, we want to determine whether different levels of olive leaf spot (OLS) disease incidence were related to differences in the composition of fungal and secondary metabolites (i.e. phenolic and volatile compounds) in leaves from olive tree cultivars with contrasting OLS susceptibilities (ranging from tolerant to highly susceptible). Accordingly, leaves with three levels of OLS incidence from both cultivars were used to assess epiphytic and endophytic fungal communities, by barcoding of cultivable isolates, as well as to evaluate leaf phenolic and volatile composition. Fungal and metabolite compositions variations were detected according to the level of disease incidence. Changes were particularly noticed for OLS-tolerant cultivars, opposing to OLS-susceptible cultivars, suggesting that disease development is linked, not only to leaf fungal and metabolite composition, but also to host genotype. A set of metabolites/fungi that can act as predictive biomarkers of plant tolerance/susceptibility to OLS disease were identified. The metabolites alpha-farnesene and p-cymene, and the fungi Fusarium sp. and Alternaria sp. were more related to disease incidence, while Pyronema domesticum was related to the absence of disease symptoms. Cultivar susceptibility to OLS disease is then suggested to be driven by fungi, volatile and phenolic host leaves composition, and above all to plant-fungus interaction. A deeper understanding of these complex interactions may unravel plant defensive responses.