54 research outputs found
Modeling the desired direction in a force-based model for pedestrian dynamics
We introduce an enhanced model based on the generalized centrifugal force
model. Furthermore, the desired direction of pedestrians is investigated. A new
approach leaning on the well-known concept of static and dynamic floor-fields
in cellular automata is presented. Numerical results of the model are presented
and compared with empirical data.Comment: 14 pages 11 figures, submitted to TGF'1
The Effect of Integrating Travel Time
This contribution demonstrates the potential gain for the quality of results
in a simulation of pedestrians when estimated remaining travel time is
considered as a determining factor for the movement of simulated pedestrians.
This is done twice: once for a force-based model and once for a cellular
automata-based model. The results show that for the (degree of realism of)
simulation results it is more relevant if estimated remaining travel time is
considered or not than which modeling technique is chosen -- here force-based
vs. cellular automata -- which normally is considered to be the most basic
choice of modeling approach.Comment: preprint of Pedestrian and Evacuation 2012 conference (PED2012)
contributio
Analysis of Optical Pulse Propagation with ABCD Matrices
We review and extend the analogies between Gaussian pulse propagation and
Gaussian beam diffraction. In addition to the well-known parallels between
pulse dispersion in optical fiber and CW beam diffraction in free space, we
review temporal lenses as a way to describe nonlinearities in the propagation
equations, and then introduce further concepts that permit the description of
pulse evolution in more complicated systems. These include the temporal
equivalent of a spherical dielectric interface, which is used by way of example
to derive design parameters used in a recent dispersion-mapped soliton
transmission experiment. Our formalism offers a quick, concise and powerful
approach to analyzing a variety of linear and nonlinear pulse propagation
phenomena in optical fibers.Comment: 10 pages, 2 figures, submitted to PRE (01/01
Soliton formation from a pulse passing the zero-dispersion point in a nonlinear Schr\"odinger equation
We consider in detail the self-trapping of a soliton from a wave pulse that
passes from a defocussing region into a focussing one in a spatially
inhomogeneous nonlinear waveguide, described by a nonlinear Schrodinger
equation in which the dispersion coefficient changes its sign from normal to
anomalous. The model has direct applications to dispersion-decreasing nonlinear
optical fibers, and to natural waveguides for internal waves in the ocean. It
is found that, depending on the (conserved) energy and (nonconserved) mass of
the initial pulse, four qualitatively different outcomes of the pulse
transformation are possible: decay into radiation; self-trapping into a single
soliton; formation of a breather; and formation of a pair of counterpropagating
solitons. A corresponding chart is drawn on a parametric plane, which
demonstrates some unexpected features. In particular, it is found that any kind
of soliton(s) (including the breather and counterpropagating pair) eventually
decays into pure radiation with the increase of the energy, the initial mass
being kept constant. It is also noteworthy that a virtually direct transition
from a single soliton into a pair of symmetric counterpropagating ones seems
possible. An explanation for these features is proposed. In two cases when
analytical approximations apply, viz., a simple perturbation theory for broad
initial pulses, or the variational approximation for narrow ones, comparison
with the direct simulations shows reasonable agreement.Comment: 18 pages, 10 figures, 1 table. Phys. Rev. E, in pres
On the boundary of the dispersion-managed soliton existence
A breathing soliton-like structure in dispersion-managed (DM) optical fiber
system is studied. It is proven that for negative average dispersion the
breathing soliton is forbidden provided that a modulus of average dispersion
exceed a threshold which depends on the soliton amplitude.Comment: LaTeX, 8 pages, to appear in JETP Lett. 72, #3 (2000
Experimental feasibility of measuring the gravitational redshift of light using dispersion in optical fibers
This paper describes a new class of experiments that use dispersion in
optical fibers to convert the gravitational frequency shift of light into a
measurable phase shift or time delay. Two conceptual models are explored. In
the first model, long counter-propagating pulses are used in a vertical fiber
optic Sagnac interferometer. The second model uses optical solitons in
vertically separated fiber optic storage rings. We discuss the feasibility of
using such an instrument to make a high precision measurement of the
gravitational frequency shift of light.Comment: 11 pages, 12 figure
On non-local variational problems with lack of compactness related to non-linear optics
We give a simple proof of existence of solutions of the dispersion manage-
ment and diffraction management equations for zero average dispersion,
respectively diffraction. These solutions are found as maximizers of non-linear
and non-local vari- ational problems which are invariant under a large
non-compact group. Our proof of existence of maximizer is rather direct and
avoids the use of Lions' concentration compactness argument or Ekeland's
variational principle.Comment: 30 page
Hamiltonian form and solitary waves of the spatial Dysthe equations
The spatial Dysthe equations describe the envelope evolution of the
free-surface and potential of gravity waves in deep waters. Their Hamiltonian
structure and new invariants are unveiled by means of a gauge transformation to
a new canonical form of the evolution equations. An accurate Fourier-type
spectral scheme is used to solve for the wave dynamics and validate the new
conservation laws, which are satisfied up to machine precision. Traveling waves
are numerically constructed using the Petviashvili method. It is shown that
their collision appears inelastic, suggesting the non-integrability of the
Dysthe equations.Comment: 6 pages, 9 figures. Other author's papers can be downloaded at
http://www.lama.univ-savoie.fr/~dutykh
- …