Repositório Colecção:
http://hdl.handle.net/10198/2498
2016-12-07T08:41:30ZLaminar blood flow in stenotic microchannels
http://hdl.handle.net/10198/12199
Título: Laminar blood flow in stenotic microchannels
Autor: Calejo, Joana A. C.; Garcia, Valdemar; Fernandes, Carla S.
Resumo: In this work, Newtonian and non-Newtonian laminar blood flow in rectangular microchannels with symmetric and asymmetric atheroma were numerically studied. It was observed that the impact of symmetry of the atheroma is almost negligible and the non-Newtonian properties of blood leads to higher pressure drops and wall shear stresses than the ones obtained for Newtonian flows.2015-01-01T00:00:00ZDetermination of (0,2)-regular sets in graphs
http://hdl.handle.net/10198/10815
Título: Determination of (0,2)-regular sets in graphs
Autor: Pacheco, Maria F.; Cardoso, Domingos Moreira; Luz, Carlos J.
Resumo: An eigenvalue of a graph is main iff its associated eigenspace is not orthogonal to the all-one vector j. The main characteristic polynomial of a graph G with p main distinct eigenvalues is 𝑚_𝐺 (λ)=λ^𝑝−𝑐_0 λ^(𝑝−1)−𝑐_1 λ^(𝑝−2)-…-𝑐_(𝑝−2) λ−𝑐_(𝑝−1) and it has integer coefficients. If G has n vertices, the nxk walk matrix of G is 𝑾_𝒌=(j,𝑨_𝑮j,𝑨_𝑮^"2" "j",…,𝑨_𝑮^(𝒌−𝟏) j) and W, the walk matrix of G, is 𝑾_𝒌 for which rank(𝑾_𝒌)=k. The number k coincides with the number of distinct main eigenvalues of G. In [2] it was proved that the coefficients of the main characteristic polynomial of G are the solutions of 𝑾𝑿=𝑨_𝑮^𝒑j. A ( , )- regular set [3] is a subset of the vertices of a graph inducing a -regular subgraph such that every vertex not in the subset has neighbors in it. In [1], a strategy for the determination of (0,1)-regular sets is described and we generalize it in order to solve the problem of the determination of (0,2)-regular sets in arbitrary graphs. An algorithm for deciding whether or not a given graph has a (0,2)-regular set is described. Its complexity depends on the multiplicity of −2 as an eigenvalue of the adjacency matrix of the graph. When such multiplicity is low, the generalization of the results in [1] assure that the algorithm is polynomial. An example of application of the algorithm to a graph for which this multiplicity is low is also presented.2013-01-01T00:00:00ZDetermination of (0,2)-regular sets in graphs
http://hdl.handle.net/10198/10660
Título: Determination of (0,2)-regular sets in graphs
Autor: Pacheco, Maria F.; Cardoso, Domingos Moreira; Luz, Carlos J.
Resumo: An eigenvalue of a graph is main iff its associated eigenspace is not orthogonal to the all-one vector j. The main characteristic polynomial of a graph G with p main distinct eigenvalues is 𝑚_𝐺 (λ)=λ^𝑝−𝑐_0 λ^(𝑝−1)−𝑐_1 λ^(𝑝−2)-…-𝑐_(𝑝−2) λ−𝑐_(𝑝−1) and it has integer coefficients. If G has n vertices, the nxk walk matrix of G is 𝑾_𝒌=(j,𝑨_𝑮j,𝑨_𝑮^"2" "j",…,𝑨_𝑮^(𝒌−𝟏) j) and W, the walk matrix of G, is 𝑾_𝒌 for which rank(𝑾_𝒌)=k. The number k coincides with the number of distinct main eigenvalues of G. In [2] it was proved that the coefficients of the main characteristic polynomial of G are the solutions of 𝑾𝑿=𝑨_𝑮^𝒑j. A (,)- regular set [3] is a subset of the vertices of a graph inducing a -regular subgraph such that every vertex not in the subset has neighbors in it. In [1], a strategy for the determination of (0,1)-regular sets is described and we generalize it in order to solve the problem of the determination of (0,2)-regular sets in arbitrary graphs. An algorithm for deciding whether or not a given graph has a (0,2)-regular set is described. Its complexity depends on the multiplicity of −2 as an eigenvalue of the adjacency matrix of the graph. When such multiplicity is low, the generalization of the results in [1] assure that the algorithm is polynomial. An example of application of the algorithm to a graph for which this multiplicity is low is also presented.2013-01-01T00:00:00ZFlow of red blood cells in microchannel networks: in vitro studies
http://hdl.handle.net/10198/10039
Título: Flow of red blood cells in microchannel networks: in vitro studies
Autor: Cidre, Diana; Rodrigues, Raquel Oliveira; Faustino, V.; Pinto, Elmano; Pinho, Diana; Bento, David; Fernandes, Carla S.; Dias, Ricardo P.; Lima, R.
Resumo: Blood exhibits unique flow characteristics on micro-scale level, due to the complex biochemical structure of Red Blood Cells (RBCs) and their response to both shear and extensional flow, which influence the rheological properties and flow behavior of blood [1,2]. In the past years, several in
vitro studies where made and have revealed some physiologically significant phenomena, such as Fahraeus and Fahraeus-Lindqvist effect, that played a key role in recent developments of lab-onchip devices for blood sampling, analysis and cell culturing. However, the blood flow in microvascular networks phenomena it remains incompletely understood. Thus, it is important to
investigate in detail the behavior of RBCs flow occurring at a microchannel network, such as with divergent and convergent bifurcations. Previews in vitro studies in microchannels with a simple divergent and convergent bifurcation, have shown a pronounced cell depleted zone immediately
downstream of the apex of the convergent bifurcation. In the present work, by using a highspeed video microscopy system, we investigated the cell depleted zone in a microchannel network.
The working fluid used in this study was dextran 40 (Dx40) containing about 10% of haematocrit level (10 Hct) of ovine red blood cells. The high-speed video microscopy system used in our experiments consists of an inverted microscope (IX71, Olympus, Japan) combined with a highspeed
camera (i-SPEED LT, Olympus). A syringe pump Apparatus (PHD ULTRATM) with 1 ml
syringe (Terumo) was used to push the working fluids through the microchannel network.
Additionally, we investigated the effect of the flow rate on the formation of the cell free layer.2013-01-01T00:00:00Z