1,932 research outputs found
A Cellular Automaton Model for the Traffic Flow in Bogota
In this work we propose a car cellular automaton model that reproduces the
experimental behavior of traffic flows in Bogot\'a. Our model includes three
elements: hysteresis between the acceleration and brake gaps, a delay time in
the acceleration, and an instantaneous brake. The parameters of our model were
obtained from direct measurements inside a car on motorways in Bogot\'a. Next,
we simulated with this model the flux-density fundamental diagram for a
single-lane traffic road and compared it with experimental data. Our
simulations are in very good agreement with the experimental measurements, not
just in the shape of the fundamental diagram, but also in the numerical values
for both the road capacity and the density of maximal flux. Our model
reproduces, too, the qualitative behavior of shock waves. In addition, our work
identifies the periodic boundary conditions as the source of false peaks in the
fundamental diagram, when short roads are simulated, that have been also found
in previous works. The phase transition between free and congested traffic is
also investigated by computing both the relaxation time and the order
parameter. Our work shows how different the traffic behavior from one city to
another can be, and how important is to determine the model parameters for each
city.Comment: 14 pages and 13 figures (gzipped tar file). Submitted to
Int.J.Mod.Phys.C. Minor changes, specially at references and typoes, plus a
clearer summary of the CA rule
A Berger type normal holonomy theorem for complex submanifolds
We prove a kind of Berger-Simons' Theorem for the normal holonomy group of a complex submanifold of the projective spac
Long-range interacting many-body systems with alkaline-earth-metal atoms
Alkaline-earth-metal atoms exhibit long-range dipolar interactions, which are
generated via the coherent exchange of photons on the 3P_0-3D_1-transition of
the triplet manifold. In case of bosonic strontium, which we discuss here, this
transition has a wavelength of 2.7 \mu m and a dipole moment of 2.46 Debye, and
there exists a magic wavelength permitting the creation of optical lattices
that are identical for the states 3P_0 and 3D_1. This interaction enables the
realization and study of mixtures of hard-core lattice bosons featuring
long-range hopping, with tuneable disorder and anisotropy. We derive the
many-body Master equation, investigate the dynamics of excitation transport and
analyze spectroscopic signatures stemming from coherent long-range interactions
and collective dissipation. Our results show that lattice gases of
alkaline-earth-metal atoms permit the creation of long-lived collective atomic
states and constitute a simple and versatile platform for the exploration of
many-body systems with long-range interactions. As such, they represent an
alternative to current related efforts employing Rydberg gases, atoms with
large magnetic moment, or polar molecules
Stability of relative equilibria with singular momentum values in simple mechanical systems
A method for testing -stability of relative equilibria in Hamiltonian
systems of the form "kinetic + potential energy" is presented. This method
extends the Reduced Energy-Momentum Method of Simo et al. to the case of
non-free group actions and singular momentum values. A normal form for the
symplectic matrix at a relative equilibrium is also obtained.Comment: Partially rewritten. Some mistakes fixed. Exposition improve
Universal time-evolution of a Rydberg lattice gas with perfect blockade
We investigate the dynamics of a strongly interacting spin system that is
motivated by current experimental realizations of strongly interacting Rydberg
gases in lattices. In particular we are interested in the temporal evolution of
quantities such as the density of Rydberg atoms and density-density
correlations when the system is initialized in a fully polarized state without
Rydberg excitations. We show that in the thermodynamic limit the expectation
values of these observables converge at least logarithmically to universal
functions and outline a method to obtain these functions. We prove that a
finite one-dimensional system follows this universal behavior up to a given
time. The length of this universal time period depends on the actual system
size. This shows that already the study of small systems allows to make precise
predictions about the thermodynamic limit provided that the observation time is
sufficiently short. We discuss this for various observables and for systems
with different dimensions, interaction ranges and boundary conditions.Comment: 16 pages, 3 figure
Expected seismic performance of irregular isolated bridges
Bridge structures are usually built on irregular topographical surfaces which create substructures with pier heights of different lengths. Three height irregularity types of typical RC medium length
bridges are analyzed aimed at determining the best strength and stiffness parameters of an isolation system.
The models were located in a high seismicity zone of Mexico. The isolation system is composed by lead rubber bearings (LRB) located on each pile and abutment. The bridge and isolation parameters conducted to the nonlinear time history analysis (NLTHA) of 169 models. Ten seismic records representative of the subduction
zone in the Pacific Coast in Mexico were chosen to carry out the study. The maximum drift pier demands,
bending moments and shear forces were analyzed to identify the best isolation properties for improving the
bridges’ structural behavior, specially focused on looking for avoiding irregularity concentrations of shear forces on piers. Additionally, the seismic response of the bridges supported on traditional neoprene bearings was carried out
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