2,836 research outputs found
Complex dynamics of elementary cellular automata emerging from chaotic rules
We show techniques of analyzing complex dynamics of cellular automata (CA)
with chaotic behaviour. CA are well known computational substrates for studying
emergent collective behaviour, complexity, randomness and interaction between
order and chaotic systems. A number of attempts have been made to classify CA
functions on their space-time dynamics and to predict behaviour of any given
function. Examples include mechanical computation, \lambda{} and Z-parameters,
mean field theory, differential equations and number conserving features. We
aim to classify CA based on their behaviour when they act in a historical mode,
i.e. as CA with memory. We demonstrate that cell-state transition rules
enriched with memory quickly transform a chaotic system converging to a complex
global behaviour from almost any initial condition. Thus just in few steps we
can select chaotic rules without exhaustive computational experiments or
recurring to additional parameters. We provide analysis of well-known chaotic
functions in one-dimensional CA, and decompose dynamics of the automata using
majority memory exploring glider dynamics and reactions
Cellular automaton supercolliders
Gliders in one-dimensional cellular automata are compact groups of
non-quiescent and non-ether patterns (ether represents a periodic background)
translating along automaton lattice. They are cellular-automaton analogous of
localizations or quasi-local collective excitations travelling in a spatially
extended non-linear medium. They can be considered as binary strings or symbols
travelling along a one-dimensional ring, interacting with each other and
changing their states, or symbolic values, as a result of interactions. We
analyse what types of interaction occur between gliders travelling on a
cellular automaton `cyclotron' and build a catalog of the most common
reactions. We demonstrate that collisions between gliders emulate the basic
types of interaction that occur between localizations in non-linear media:
fusion, elastic collision, and soliton-like collision. Computational outcomes
of a swarm of gliders circling on a one-dimensional torus are analysed via
implementation of cyclic tag systems
Note: "Lock-in accelerometry" to follow sink dynamics in shaken granular matter
Understanding the penetration dynamics of intruders in granular beds is
relevant not only for fundamental Physics, but also for geophysical processes
and construction on sediments or granular soils in areas potentially affected
by earthquakes. While the penetration of intruders in two dimensional (2D)
laboratory granular beds can be followed using video recording, it is useless
in three dimensional (3D) beds of non-transparent materials such as common
sand. Here we propose a method to quantify the sink dynamics of an intruder
into laterally shaken granular beds based on the temporal correlations between
the signals from a reference accelerometer fixed to the shaken granular bed,
and a probe accelerometer deployed inside the intruder. Due to its analogy with
the working principle of a lock in amplifier, we call this technique Lock in
accelerometry (LIA). During Earthquakes, some soils can lose their ability to
sustain shear and deform, causing subsidence and sometimes substantial building
damage due to deformation or tumblin
Spin-orbit induced mixed-spin ground state in NiO perovskites probed by XAS: new insight into the metal to insulator transition
We report on a Ni L edges x-ray absorption spectroscopy (XAS) study
in NiO perovskites. These compounds exhibit a metal to insulator ()
transition as temperature decreases. The L edge presents a clear
splitting in the insulating state, associated to a less hybridized ground
state. Using charge transfer multiplet calculations, we establish the
importance of the crystal field and 3d spin-orbit coupling to create a
mixed-spin ground state. We explain the transition in NiO
perovskites in terms of modifications in the Ni crystal field splitting
that induces a spin transition from an essentially low-spin (LS) to a
mixed-spin state.Comment: 4 pages, 4 figures, accepted as PRB - Rapid Comm. Dez. 200
First order transition and phase separation in pyrochlores with colossal-magnetoresistance
TlMnO pyrochlores present colossal magnetoresistance (CMR)
around the long range ferromagnetic ordering temperature (T). The
character of this magnetic phase transition has been determined to be first
order, by purely magnetic methods, in contrast to the second order character
previously reported by Zhao et al. (Phys. Rev. Lett. 83, 219 (1999)). The
highest CMR effect, as in TlCdMnO, corresponds to a
stronger first order character. This character implies a second type of
magnetic interaction, besides the direct superexchange between the Mn
ions, as well as a phase coexistence. A model is proposed, with a complete
Hamiltonian (including superexchange and an indirect interaction), which
reproduce the observed phenomenology.Comment: 6 pages. Figures include
Short-range charge-order in NiO perovskites (=Pr,Nd,Eu) probed by X-ray absorption spectroscopy
The short-range organization around Ni atoms in orthorhombic NiO
(=Pr,Nd,Eu) perovskites has been studied over a wide temperature range by Ni
K-edge x-ray absorption spectroscopy. Our results demonstrate that two
different Ni sites, with different average Ni-O bond lengths, coexist in those
orthorhombic compounds and that important modifications in the Ni nearest
neighbors environment take place across the metal-insulator transition. We
report evidences for the existence of short-range charge-order in the
insulating state, as found in the monoclinic compounds. Moreover, our results
suggest that the two different Ni sites coexists even in the metallic state.
The coexistence of two different Ni sites, independently on the ion,
provides a common ground to describe these compounds and shed new light in the
understanding of the phonon-assisted conduction mechanism and unusual
antiferromagnetism present in all NiO compounds.Comment: 4 pages, 3 figures, accepted PRB - Brief Report Dec.200
Aquifer vulnerability mapping and associated spatial uncertainty
Quantitative estimation of water resources is indispensable when it comes to getting the sustainability of aquifers through planning. This becomes an essential aspect in areas whose primary economic activity is agriculture, in which ensure the availability of water means ensuring the sustainability of the societal and economic systems. This is the example of the Cuellar Moor karstic aquifer, located in the international Duero watershed, in which more than 80% of its surface is aimed to agricultural use.
The main goal of this research is the introduction of a new vulnerability index, which gathers together the hydrogeological covariates and the spatial uncertainty associated with the estimation of groundwater level and nitrate concentration. An optimized monitoring network to piezometric level and nitrate concentration control is required, as well as, to determine the vulnerability associated with pumping wells.info:eu-repo/semantics/publishedVersio
A Classification of Integrable Quasiclassical Deformations of Algebraic Curves
A previously introduced scheme for describing integrable deformations of of
algebraic curves is completed. Lenard relations are used to characterize and
classify these deformations in terms of hydrodynamic type systems. A general
solution of the compatibility conditions for consistent deformations is given
and expressions for the solutions of the corresponding Lenard relations are
provided.Comment: 21 page
Electrical control of a laterally ordered InAs/InP quantum dash array
We have fabricated an array of closely spaced quantum dashes starting from a
planar array of self-assembled semiconductor quantum wires. The array is
embedded in a metallic nanogap which we investigate by micro-photoluminescence
as a function of a lateral electric field. We demonstrate that the net electric
charge and emission energy of individual quantum dashes can be modified
externally with performance limited by the size inhomogeneity of the
self-assembling process
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