C.O. Dorso

THE ROLE OF PANIC IN THE ROOM EVACUATION PROCESS

In the present work we studied the room evacuation problem using the social force model introduced by Helbing and coworkers. The faster is slower effect induced by panic was analyzed. It could be explained in terms of increasing mean clogging delays which shows a strong correlation with certain structures that we call blocking clusters. Also a steady state version of the problem was implemented. It shows that, from a macroscopic point of view, the optimal evacuation efficiency correspond to the state at which the difference between the system desire force minus the system granular force is maximum.

Evacuation under limited visibility

A multiplicity of situations can trigger off an evacuation of a room under panic conditions. For normal (with normal meaning absence of obstacles, perfect visibility, etc.) environmental conditions, the faster is slower effect dominates the dynamics of this process. It states that as the pedestrians desire to reach the exit increases, the clogging phenomena delays the time to get out of the room. But, environmental conditions are usually far from normal. In this work, we consider that pedestrians have to find their way out under low visibility conditions. Some of them might switch to a herding-like behavior if they do not remember where the exit was. Others will just trust on their memory. Our investigation handles the herding and memory effects on the evacuation of a single exit room with no obstacles. We also include a section on how signaling devices affect the evacuation process. Unexpectedly, some low visibility situations may enhance the evacuation performance. This can be resumed as a second paradoxical result, since we demonstrated in an earlier investigation that clever is not always better G. A. Frank and C. O. Dorso, Physica A 390, 2135 (2011).

Coherent state propagation in open systems

We introduce the generalized coherent states (G.C.S.) as eigenstates of the unitarily equivalent representations of the annihilation operator. The G.C.S. extension in phase space evolves with time and keeps the uncertainly product (with correlation) at its minimum. The conditions for the propagation of the G.C.S. in a time-dependent field are derived. In the presence of dissipation, an equation of motion is found that describes the G.C.S. decay towards the ground state; its results are compared with those of non-linear Schrodinger equations.

Room evacuation through two contiguous exits

Current regulations demand that at least two exits should be available for a safe evacuation during a panic situation. Although the “faster is slower” effect is expected to take place near the exits, the evacuation time will improve because of the additional exits. However, rooms having contiguous doors not always reduce the leaving time as expected. We investigated the relation between the doors separation and the evacuation performance. We found that there exists a separation distance range that does not really improve the evacuation time, or it can even worsen the process performance. To our knowledge, no attention has been given to this issue in the literature. This work reports how the pedestrians dynamics differ when the separation distance between two exit doors changes and how this affects the overall performance.

Effect of Coulomb screening length on nuclear “pasta” simulations

We study the role of the effective Coulomb interaction strength and length on the dynamics of nucleons in conditions according to those in a neutron stars crust. Calculations were made with a semi-classical molecular dynamics model, studying isospin symmetric matter at sub-saturation densities and low temperatures. The electrostatic interaction between protons interaction is included in the form of a screened Coulomb potential in the spirit of the Thomas-Fermi approximation, but the screening length is artificially varied to explore its effect on the formation of the non-homogeneous nuclear structures known as nuclear pasta. As the screening length increases, we can a transition from a one-per-cell pasta regime (due exclusively to finite size effects) to a more appealing multiple pasta per simulation box. This shows qualitative difference in the structure of neutron star matter at low temperatures, and therefore, special caution should be taken when the screening length is estimated for numerical simulations.

Dynamical aspects of phonon-phonon coupling in collective mode damping

We present an extension of the Quantal Brownian Motion (QBM) model of vibration damping that incorporates phonon-phonon or phonon-(two-particle-two-hole) interactions as sources of dissipative evolution of the excited mode. Starting from the Schrodinger-on Neumann equation of motion, a reduction procedure combined with the proper approximations leads to coupled, nonlinear master equations for the density vectors of the separate oscillators. The fermionic heat bath remains equilibrated at temperature T. The evolution of the phonon system is numerically analyzed under different initial conditions that simulate excitation of one or more collective vibrations, for several strengths of mode-mode coupling. It is found that in the majority of cases the system reaches statistical equilibrium with relaxation times that can be extracted from the numerical treatment.

Geometrical aspects of isoscaling

The property of isoscaling in nuclear fragmentation is studied using a simple bond percolation model with “isospin” added as an extra degree of freedom. It is shown, first, that with the assumption of fair sampling and with homogeneous probabilities it is possible to solve the problem analytically. Second, numerical percolations of hundreds of thousands of grids of different sizes and with different N to Z ratios confirm this prediction with remarkable agreement. It is thus concluded that isoscaling emerges even in the simple case of a classical non-interacting system such as two-species percolation under the assumption of fair sampling; if put in the nomenclature of the minimum information theory, isoscaling in percolation appears to require nothing more than the existence of equiprobable configurations in maximum entropy states.

Maximum Lyapunov exponent of highly excited finite systems

In this communication we analyze the behavior of the maximum global Lyapunov exponent (MGLE) and the maximum local Lyapunov exponent (MLLE) for highly excited two- and three-dimensional finite systems which undergo a fragmentation process. We relate the behavior of the MGLE with the caloric curve of the two-dimensional disks, and we relate the asymptotic fluctuations in the MLLE to the appearance of a power law spectra in the fragmentation of 3D drops.

High pressures in room evacuation processes and a first approach to the dynamics around unconscious pedestrians

Clogging raises as the principal phenomenon during many evacuation processes of pedestrians in an emergency situation. As people push to escape from danger, compression forces may increase to harming levels. Many individuals might fall down, while others will try to dodge the fallen people, or, simply pass through them. We studied the dynamics of the crowd for these situations, in the context of the “social force model”. We modeled the unconscious (fallen) pedestrians as inanimate bodies that can be dodged (or not) by the surrounding individuals. We found that new morphological structures appear along the evacuating crowd. Under specific conditions, these structures may enhance the evacuation performance. The pedestrian’s willings for either dodging or passing through the unconscious individuals play a relevant role in the overall evacuation performance.

Phase transitions and symmetry energy in nuclear pasta

Abstract Cold and isospin-symmetric nuclear matter at sub-saturation densities is known to form the so-called pasta structures, which, in turn, are known to undergo peculiar phase transitions. Here we investigate if such pastas and their phase changes survive in isospin asymmetric nuclear matter, and whether the symmetry energy of such pasta configurations is connected to the isospin content, the morphology of the pasta and to the phase transitions. We find that indeed pastas are formed in isospin asymmetric systems with proton to neutron ratios of x = 0.3 , 0.4 and 0.5, densities in the range of 0.05 xa0fm − 3 ρ 0.08 xa0fm − 3 , and temperatures T 2 xa0MeV . Using tools (such as the caloric curve, Lindemann coefficient, radial distribution function, Kolmogorov statistic, and Euler functional) on the composition of the pasta, determined the existence of homogeneous structures, tunnels, empty regions, cavities and transitions among these regions. The symmetry energy was observed to attain different values in the different phases showing its dependence on the morphology of the nuclear matter structure.