Repositório Comunidade: CMAT
http://hdl.handle.net/1822/1234
CMAT2019-03-24T14:10:02ZA note on global attractivity of the periodic solution for a model of hematopoiesis
http://hdl.handle.net/1822/59402
Título: A note on global attractivity of the periodic solution for a model of hematopoiesis
Autor: Faria, Teresa; Oliveira, José J.
Resumo: For a generalized periodic model of hematopoiesis, sufficient conditions for the global attractivity of its positive periodic solution are given, improving previous results in the literature. The effectiveness of the present criterion is illustrated by a numerical example.
<b>Tipo</b>: articleFailure rate of Birnbaum–Saunders distributions: shape, change-point, estimation and robustness
http://hdl.handle.net/1822/59401
Título: Failure rate of Birnbaum–Saunders distributions: shape, change-point, estimation and robustness
Autor: Athayde, Emilia; Azevedo, Assis; Barros, Michelli; Leiva, Víctor
Resumo: The Birnbaum–Saunders (BS) distribution has been largely studied and applied. A random variable with BS distribution is a transformation of another random variable with standard normal distribution. Generalized BS distributions are obtained when the normally distributed random variable is replaced by another symmetrically distributed random variable. This allows us to obtain a wide class of positively skewed models with lighter and heavier tails than the BS model. Its failure rate admits several shapes, including the unimodal case, with its change-point being able to be used for different purposes. For example, to establish the reduction in a dose, and then in the cost of the medical treatment. We analyze the failure rates of generalized BS distributions obtained by the logistic, normal and Student-t distributions, considering their shape and change-point, estimating them, evaluating their robustness, assessing their performance by simulations, and applying the results to real data from different areas.
<b>Tipo</b>: article2019-03-11T08:40:54ZOn the roots of coquaternions
http://hdl.handle.net/1822/59326
Título: On the roots of coquaternions
Autor: Falcão, M. I.; Miranda, Fernando; Severino, Ricardo; Soares, M. J.
Resumo: In this paper we give a complete characterization of the nth roots of a coquaternion q. In particular, we show that the number and type of roots-isolated and/or hyperboloidal-depend on the nature of q, on the parity of n and (eventually) on the sign of the real part of q. We also show how the coquaternionic formalism can be used to obtain, in a simple manner, explicit expressions for the real nth roots of any 2 x 2 real matrix.
<b>Tipo</b>: article2019-03-03T20:18:00ZFriction properties of polyoxymethylene (POM) materials in dry and lubricated conditions
http://hdl.handle.net/1822/59064
Título: Friction properties of polyoxymethylene (POM) materials in dry and lubricated conditions
Autor: Sabet, Seyyed M. M.; Dourado, Marco Daniel Malheiro; Pereira, António; Silva, Ana; Carvalho, Flávia; Brito, Irene; Machado, José; Meireles, José F.; Azevedo, José; Carvalho, Sergio; Gomes, J. R.; Abreu, Cristiano
Resumo: This work is based on dry and lubricated friction properties of Polyoxymethylene (POM) plastics widely used in multimedia and electronic sector of automotive industries. The results show that lubrication does not seem to influence the static coefficient of friction; however, significantly influences the dynamic one and increases it by two-fold.
<b>Tipo</b>: conferencePaperGravitational radiation and the evolution of gravitational collapse in cylindrical symmetry
http://hdl.handle.net/1822/59047
Título: Gravitational radiation and the evolution of gravitational collapse in cylindrical symmetry
Autor: García-Parrado Gómez-Lobo, Alfonso; Mena, Filipe C.
Resumo: Using the Sparling form and a geometric construction adapted to spacetimes
with a 2-dimensional isometry group, we analyse a quasi-local measure of
gravitational energy. We then study the gravitational radiation through
spacetime junctions in cylindrically symmetric models of gravitational collapse
to singularities. The models result from the matching of collapsing dust fluids
interiors with gravitational wave exteriors, given by the Einstein-Rosen type
solutions. For a given choice of a frame adapted to the symmetry of the
matching hypersurface, we are able to compute the total gravitational energy
radiated during the collapse and state whether the gravitational radiation is
incoming or outgoing, in each case. This also enables us to distinguish whether
a gravitational collapse is being enhanced by the gravitational radiation.
<b>Tipo</b>: article