329 research outputs found
Stereo image processing system for robot vision
More and more applications (path planning, collision avoidance
methods) require 3D description of the surround world. This paper
describes a stereo vision system that uses 2D (grayscale or color) images
to extract simple 2D geometric entities (points, lines) applying a
low-level feature detector. The features are matched across views with a
graph matching algorithm. During the projective reconstruction the 3D
description of the scene is recovered. The developed system uses uncalibrated
cameras, therefore only projective 3D structure can be detected
defined up to a collineation. Using the Euclidean information about a
known set of predefined objects stored in database and the results of the
recognition algorithm, the description can be updated to a metric one
Emission from dielectric cavities in terms of invariant sets of the chaotic ray dynamics
In this paper, the chaotic ray dynamics inside dielectric cavities is
described by the properties of an invariant chaotic saddle. I show that the
localization of the far field emission in specific directions is related to the
filamentary pattern of the saddle's unstable manifold, along which the energy
inside the cavity is distributed. For cavities with mixed phase space, the
chaotic saddle is divided in hyperbolic and non-hyperbolic components, related,
respectively, to the intermediate exponential (t<t_c) and the asymptotic
power-law (t>t_c) decay of the energy inside the cavity. The alignment of the
manifolds of the two components of the saddle explains why even if the energy
concentration inside the cavity dramatically changes from tt_c, the
far field emission changes only slightly. Simulations in the annular billiard
confirm and illustrate the predictions.Comment: Corrected version, as published. 9 pages, 6 figure
Chaotic Explosions
We investigate chaotic dynamical systems for which the intensity of
trajectories might grow unlimited in time. We show that (i) the intensity grows
exponentially in time and is distributed spatially according to a fractal
measure with an information dimension smaller than that of the phase space,(ii)
such exploding cases can be described by an operator formalism similar to the
one applied to chaotic systems with absorption (decaying intensities), but
(iii) the invariant quantities characterizing explosion and absorption are
typically not directly related to each other, e.g., the decay rate and fractal
dimensions of absorbing maps typically differ from the ones computed in the
corresponding inverse (exploding) maps. We illustrate our general results
through numerical simulation in the cardioid billiard mimicking a lasing
optical cavity, and through analytical calculations in the baker map.Comment: 7 pages, 5 figure
Thermodynamic interpretation of the uniformity of the phase space probability measure
Uniformity of the probability measure of phase space is considered in the
framework of classical equilibrium thermodynamics. For the canonical and the
grand canonical ensembles, relations are given between the phase space
uniformities and thermodynamic potentials, their fluctuations and correlations.
For the binary system in the vicinity of the critical point the uniformity is
interpreted in terms of temperature dependent rates of phases of well defined
uniformities. Examples of a liquid-gas system and the mass spectrum of nuclear
fragments are presented.Comment: 11 pages, 2 figure
Bevezetés a környezeti áramlások fizikájába
A környezettudomány és azon belül a környezetfizika egyik legnagyobb jelentőségű
területét a globális környezeti áramlások vizsgálata jelenti. A környezeti áramlások (akár
a légkörben vagy vizekben zajlanak, akár globális vagy lokális kiterjedésűek)
környezetünk alakulásának legfontosabb mozzanataihoz tartoznak. Ide sorolhatjuk még
a Földünk belsejében, elsősorban a folyékony köpenyben zajló áramlási jelenségeket is,
amelyek a Föld kialakulása óta eltelt évmilliárdok alatt markánsan alakították és
pillanatnyilag is alakítják a felszín viszonyait. Erről a közegről azonban a későbbiekben
nem lesz szó, mert tárgyunk a Nap energiája által hajtott légköri és óceáni áramlások,
amelyek nem geológiai, hanem „emberi” időskálán befolyásolják környezetünket.
Az áramlási jelenségeknek környezetünk szempontjából alapvetően meghatározó a
jelentősége. Gondoljunk csak a napi időjárás változásainak áramlási vonatkozásaira, a
Golf-áramlatra, amely lakhatóvá teszi Európa északi övezeteit, a világtengerek más,
jelentős áramlataira, vagy kisebb skálán azokra a jelenségekre, amelyek a bioszféra
egy-egy szegmensének benépesülését és létezését lehetővé tették és teszik. A modern
világ viszonyait kétség kívül alapvetően befolyásolják az emberi társadalmak gazdasági
tevékenységét kísérő nem kívánt mellékhatások, elsősorban a környezet szennyezése.
Ezek a szennyezések az áramlási folyamatok során mind a légkörben, mind a vizekben
távoli területekre is eljutnak. Nem kérdéses, hogy a káros hatások megelőzésének, és a
károk csökkentésének előfeltétele a kapcsolódó folyamatok megismerése, megértése, és
ezek után esetleges befolyásolása
Topological Entropy : A Lagrangian Measure of the State of the Free Atmosphere
Topological entropy is shown to be a useful characteristic of the state of the free atmosphere. It can be
determined as the stretching rate of a line segment of tracer particles in the atmosphere over a time span of
about 10 days. Besides case studies, the seasonal distribution of the average topological entropy is determined
in several geographical locations. The largest topological entropies appear in the mid- and high latitudes,
especially in winter, owing to the greater temperature gradient between the pole and the equator and the
more intense stirring and shearing effects of cyclones. The smallest values can be found in the trade wind belt.
The local value of the topological entropy is a measure of the chaoticity of the state of the atmosphere and of
how rapidly pollutants and contaminants spread from a given location
Poincare recurrences and transient chaos in systems with leaks
In order to simulate observational and experimental situations, we consider a
leak in the phase space of a chaotic dynamical system. We obtain an expression
for the escape rate of the survival probability applying the theory of
transient chaos. This expression improves previous estimates based on the
properties of the closed system and explains dependencies on the position and
size of the leak and on the initial ensemble. With a subtle choice of the
initial ensemble, we obtain an equivalence to the classical problem of Poincare
recurrences in closed systems, which is treated in the same framework. Finally,
we show how our results apply to weakly chaotic systems and justify a split of
the invariant saddle in hyperbolic and nonhyperbolic components, related,
respectively, to the intermediate exponential and asymptotic power-law decays
of the survival probability.Comment: Corrected version, as published. 12 pages, 9 figure
Reply to E.G.D. Cohen, L. Rondoni, Physica A 306 (2002) 117
In their paper Cohen and Rondoni severely question the physical relevance of
studies of transport by means of multibaker maps and other classes of dynamics
considering the motion of independen particles - like e.g. the Lorentz gas. We
argue that this is to a large extent due to inappropriate interpretation of the
models. In particular, the arguments concerning the lack of local thermodynamic
equilibrium are inconsistent for the models previously worked out by ourselves.Comment: 3 pages, revtex4 -- with a 4th item addresse
- …