Assessment of PTV margin adequacy for single isocenter multiple brain metastases using genetic algorithms.

. To study the impact on dose coverage and the dose to the healthy tissue applying optimized margins in single isocenter multiple brain metastases radiosurgery (SIMM-SRS) in linac machine based on setup rotations/translations induced errors calculated by a genetic algorithm (GA).The following quality indices of SIMM-SRS were analyzed for 32 plans (256 lesions): Paddick conformity index (PCI), gradient index (GI), maximum (D) and mean (D) doses, local and global Vfor the healthy brain.

Effects of different per translational kinetics on the dynamics of a core circadian clock model.

Living beings display self-sustained daily rhythms in multiple biological processes, which persist in the absence of external cues since they are generated by endogenous circadian clocks. The period (per) gene is a central player within the core molecular mechanism for keeping circadian time in most animals. Recently, the modulation PER translation has been reported, both in mammals and flies, suggesting that translational regulation of clock components is important for the proper clock gene expression and molecular clock performance.

Modeling spatial patterns in the visual cortex.

We propose a model for the formation of patterns in the visual cortex. The dynamical units of the model are Kuramoto phase oscillators that interact through a complex network structure embedded in two dimensions. In this way the strength of the interactions takes into account the geographical distance between units.

Emergent self-organized complex network topology out of stability constraints.

Although most networks in nature exhibit complex topologies, the origins of such complexity remain unclear. We propose a general evolutionary mechanism based on global stability. This mechanism is incorporated into a model of a growing network of interacting agents in which each new agent's membership in the network is determined by the agent's effect on the network's global stability.

Nonequilibrium structures and slow dynamics in a two-dimensional spin system with competing long-range and short-range interactions.

We present a lattice spin model that mimics a system of interacting particles through a short-range repulsive potential and a long-range attractive power-law decaying potential. We perform a detailed analysis of the general equilibrium phase diagram of the model at finite temperature, showing that the only possible equilibrium phases are the ferromagnetic and the antiferromagnetic ones. We then study the nonequilibrium behavior of the model after a quench to subcritical temperatures, in the antiferromagnetic region of the phase diagram region, where the pair interaction potential behaves in the same qualitative way as in a Lennard-Jones gas.

Interplay between coarsening and nucleation in an Ising model with dipolar interactions.

We study the dynamical behavior of a square lattice Ising model with exchange and dipolar interactions by means of Monte Carlo simulations. After a sudden quench to low temperatures, we find that the system may undergo a coarsening process where stripe phases with different orientations compete, or alternatively it can relax initially to a metastable nematic phase and then decay to the equilibrium stripe phase through nucleation. We measure the distribution of equilibration times for both processes and compute their relative probability of occurrence as a function of temperature and system size.

Quasistationary trajectories of the mean-field XY Hamiltonian model: a topological perspective.

We employ a topological approach to investigate the nature of quasistationary states of the mean-field XY Hamiltonian model. We focus on the quasistationary states reached when the system is initially prepared in a fully magnetized configuration. By means of numerical simulations and analytical considerations, we show that, along the quasistationary trajectories, the system evolves in a manifold of critical points of the potential energy function.

Aging in an infinite-range Hamiltonian system of coupled rotators.

We analyze numerically the out-of-equilibrium relaxation dynamics of a long-range Hamiltonian system of N fully coupled rotators. For a particular family of initial conditions, this system is known to enter a particular regime in which the dynamic behavior does not agree with thermodynamic predictions. Moreover, there is evidence that in the thermodynamic limit, when N--> infinity is taken prior to t--> infinity, the system will never attain true equilibrium.