Bose-Einstein condensation in diamond hierarchical lattices.

The Bose-Einstein condensation of noninteracting particles restricted to move on the sites of hierarchical diamond lattices is investigated. Using a tight-binding single-particle Hamiltonian with properly rescaled hopping amplitudes, we are able to employ an orthogonal basis transformation to exactly map it on a set of decoupled linear chains with sizes and degeneracies written in terms of the network branching parameter q and generation number n. The integrated density of states is shown to have a fractal structure of gaps and degeneracies with a power-law decay at the band bottom. The spectral dimension d(s) coincides with the network topological dimension d(f) = ln(2q)/ln(2). We perform a finite-size scaling analysis of the fraction of condensed particles and specific heat to characterize the critical behavior of the BEC transition that occurs for q > 2 (d(s) > 2). The critical exponents are shown to follow those for lattices with a pure power-law spectral density, with non-mean-field values for q < 8 (d(s) < 4). The transition temperature is shown to grow monotonically with the branching parameter, obeying the relation 1/T(c) = a + b/(q - 2).

Ising models on the regularized Apollonian network.

We investigate the critical properties of Ising models on a regularized Apollonian network (RAN), here defined as a kind of Apollonian network in which the connectivity asymmetry associated with its corners is removed. Different choices for the coupling constants between nearest neighbors are considered and two different order parameters are used to detect the critical behavior. While ordinary ferromagnetic and antiferromagnetic models on a RAN do not undergo a phase transition, some antiferrimagnetic models show an interesting infinite-order transition. All results are obtained by an exact analytical approach based on iterative partial tracing of the Boltzmann factor as an intermediate step for the calculation of the partition function and the order parameters.

Critical behavior of the ideal-gas Bose-Einstein condensation in the Apollonian network.

We show that the ideal Boson gas displays a finite-temperature Bose-Einstein condensation transition in the complex Apollonian network exhibiting scale-free, small-world, and hierarchical properties. The single-particle tight-binding Hamiltonian with properly rescaled hopping amplitudes has a fractal-like energy spectrum. The energy spectrum is analytically demonstrated to be generated by a nonlinear mapping transformation. A finite-size scaling analysis over several orders of magnitudes of network sizes is shown to provide precise estimates for the exponents characterizing the condensed fraction, correlation size, and specific heat. The critical exponents, as well as the power-law behavior of the density of states at the bottom of the band, are similar to those of the ideal Boson gas in lattices with spectral dimension d(s)=2ln(3)/ln(9/5)~/=3.74.

Critical properties of a superdiffusive epidemic process.

We introduce a superdiffusive one-dimensional epidemic process model on which infection spreads through a contact process. Healthy (A) and infected (B) individuals can jump with distinct probabilities D(A) and D(B) over a distance ℓ distributed according to a power-law probability P(ℓ)[proportionality]1/ℓ(µ). For µ≥3 the propagation is equivalent to diffusion, while µ<3 corresponds to Lévy flights. In the D(A)>D(B) diffusion regime, field-theoretical results have suggested a first-order transition, a prediction not supported by several numerical studies. An extensive numerical study of the critical behavior in both the diffusive (µ≥3) and superdiffusive (µ<3) D(A)>D(B) regimes is also reported. We employed a finite-size scaling analysis to obtain the critical point as well as the static and dynamic critical exponents for several values of µ. All data support a second-order phase transition with continuously varying critical exponents which do not belong to the directed percolation universality class.

[Chemical risk in health environment: contribution to the evaluation and management of the risk to health]. / Il rischio chimico in ambiente sanitario: contributo per la valutazione e la gestione del rischio per la salute.

Among the many workplaces where there is a chemical risk, hospitals are surely one of the most complex when it comes to risk assessment. Numerous highly toxic substances are routinely used; clinical decisions often mean health workers come into contact with latest-generation drugs whose secondary effects are not yet fully known; they may have to execute procedures using different chemicals at the same time, as often happens in therapy or surgery. We studied two provincial hospitals in order to make a preliminary risk assessment, using an algorithm model. The chemical risk in the environments analyzed was mainly moderate, though some specific settings call for closer attention. Certain at-risk conditions can be solved by simple procedural changes, but others need to be tackled with a view to residual risk management. Some critical points came to light, linked to the algorithm employed, which need further examination to fit the model better to this particular context.

Macroscopically frustrated Ising model.

A disordered spin-glass model in which both static and dynamical properties depend on macroscopic magnetizations is presented. These magnetizations interact via random couplings and, therefore, the typical quenched realization of the system exhibits a macroscopic frustration. The model is solved by using a revisited replica approach, and the broken symmetry solution turns out to coincide with the symmetric solution. Some dynamical aspects of the model are also discussed, showing how it could be a useful tool for describing some properties of real systems such as, for example, natural ecosystems or human social systems.

[Laboratory diagnosis: correlated health and environmental risks]. / La diagnostica di laboratorio: rischi sanitari e ambientali correlati.

Method description and initial results of a study to assess risks to health sector workers and environment due to chemical agents used and waste products generated in diagnostic clinical chemical laboratories, and image diagnostic testing. A survey was conducted of the methods and agents used and their toxicological classification, the number of workers exposed and an analytical profile of the waste produced. The assessment of risk to workers was based on cytogenetic tests (chromosome aberrations and micronuclei); the assessment of environmental risk from waste disposal was based on tests on plant systems.