Random-bond antiferromagnetic Ising model in a field.

Using combinatorial optimization techniques we study the critical properties of the two- and three-dimensional Ising models with uniformly distributed random antiferromagnetic couplings (1≤J_{i}≤2) in the presence of a homogeneous longitudinal field, h, at zero temperature. In finite systems of linear size, L, we measure the average correlation function, C_{L}(ℓ,h), when the sites are either on the same sublattice, or they belong to different sublattices. The phase transition, which is of first order in the pure system, turns to mixed order in two dimensions with critical exponents 1/ν≈0.

Scattering signatures of invasion percolation.

Motivated by recent experiments, we investigate the scattering properties of percolation clusters generated by numerical simulations on a three-dimensional cubic lattice. Individual clusters of given size are shown to present a fractal structure up to a scale of order of their extent, even far away from the percolation threshold p_{c}. The influence of intercluster correlations on the structure factor of assemblies of clusters selected by an invasion phenomenon is studied in detail.

Statistics of percolating clusters in a model of photosynthetic bacteria.

In photosynthetic organisms the energy of the illuminating light is absorbed by the antenna complexes and transmitted by the excitons to the reaction centers (RCs). The energy of light is either absorbed by the RCs, leading to their "closing" or is emitted through fluorescence. The dynamics of the light absorption is described by a simple model developed for exciton migration that involves the exciton hopping probability and the exciton lifetime.

Rounding of first-order phase transitions and optimal cooperation in scale-free networks.

We consider the ferromagnetic large- q state Potts model in complex evolving networks, which is equivalent to an optimal cooperation problem, in which the agents try to optimize the total sum of pair cooperation benefits and the supports of independent projects. The agents are found to be typically of two kinds: A fraction of m (being the magnetization of the Potts model) belongs to a large cooperating cluster, whereas the others are isolated one man's projects. It is shown rigorously that the homogeneous model has a strongly first-order phase transition, which turns to second-order for random interactions (benefits), the properties of which are studied numerically on the Barabási-Albert network.

[Results of a survey on post-transfusional malaria in France between 1960 and 1974].

This inquire demonstrated that transfusion malaria was not so rare as we thought. So 56 cases have been numbered between 1960 and 1974, and probably they do not reflect exactly the real situation. In our country, plasmodium falciparum, specifically responsible of the most serious accidents, is the form most frequently incriminated and its frequency increases among the years: 76,1% of the infects between 1970 and 1974.