1,716 research outputs found
The Complex Topology of Chemical Plants
We show that flowsheets of oil refineries can be associated to complex
network topologies that are scale-free, display small-world effect and possess
hierarchical organization. The emergence of these properties from such man-made
networks is explained as a consequence of the currently used principles for
process design, which include heuristics as well as algorithmic techniques. We
expect these results to be valid for chemical plants of different types and
capacities.Comment: 7 pages, 5 figures and 1 tabl
Extracting finite structure from infinite language
This paper presents a novel connectionist memory-rule based model capable of learning the finite-state properties of an input language from a set of positive examples. The model is based upon an unsupervised recurrent self-organizing map [T. McQueen, A. Hopgood, J. Tepper, T. Allen, A recurrent self-organizing map for temporal sequence processing, in: Proceedings of Fourth International Conference in Recent Advances in Soft Computing (RASC2002), Nottingham, 2002] with laterally interconnected neurons. A derivation of functionalequivalence theory [J. Hopcroft, J. Ullman, Introduction to Automata Theory, Languages and Computation, vol. 1, Addison-Wesley, Reading, MA, 1979] is used that allows the model to exploit similarities between the future context of previously memorized sequences and the future context of the current input sequence. This bottom-up learning algorithm binds functionally related neurons together to form states. Results show that the model is able to learn the Reber grammar [A. Cleeremans, D. Schreiber, J. McClelland, Finite state automata and simple recurrent networks, Neural Computation, 1 (1989) 372–381] perfectly from a randomly generated training set and to generalize to sequences beyond the length of those found in the training set
Short time decay of the Loschmidt echo
The Loschmidt echo measures the sensitivity to perturbations of quantum
evolutions. We study its short time decay in classically chaotic systems. Using
perturbation theory and throwing out all correlation imposed by the initial
state and the perturbation, we show that the characteristic time of this regime
is well described by the inverse of the width of the local density of states.
This result is illustrated and discussed in a numerical study in a
2-dimensional chaotic billiard system perturbed by various contour deformations
and using different types of initial conditions. Moreover, the influence to the
short time decay of sub-Planck structures developed by time evolution is also
investigated.Comment: 7 pages, 7 figures, published versio
Tractable Combinations of Global Constraints
We study the complexity of constraint satisfaction problems involving global
constraints, i.e., special-purpose constraints provided by a solver and
represented implicitly by a parametrised algorithm. Such constraints are widely
used; indeed, they are one of the key reasons for the success of constraint
programming in solving real-world problems.
Previous work has focused on the development of efficient propagators for
individual constraints. In this paper, we identify a new tractable class of
constraint problems involving global constraints of unbounded arity. To do so,
we combine structural restrictions with the observation that some important
types of global constraint do not distinguish between large classes of
equivalent solutions.Comment: To appear in proceedings of CP'13, LNCS 8124. arXiv admin note: text
overlap with arXiv:1307.179
On hyperovals of polar spaces
We derive lower and upper bounds for the size of a hyperoval of a finite polar space of rank 3. We give a computer-free proof for the uniqueness, up to isomorphism, of the hyperoval of size 126 of H(5, 4) and prove that the near hexagon E-3 has up to isomorphism a unique full embedding into the dual polar space DH(5, 4)
Spontaneous breaking of chiral symmetry, and eventually of parity, in a -model with two Mexican hats
A sigma-model with two linked Mexican hats is discussed. This scenario could
be realized in low-energy QCD when the ground state and the first excited
(pseudo)scalar mesons are included, and where not only in the subspace of the
ground states, but also in that of the first excited states, a Mexican hat
potential is present. This possibility can change some basic features of a
low-energy hadronic theory of QCD. It is also shown that spontaneous breaking
of parity can occur in the vacuum for some parameter choice of the model.Comment: 10 pages, 1 figur
Pseudofractal Scale-free Web
We find that scale-free random networks are excellently modeled by a
deterministic graph. This graph has a discrete degree distribution (degree is
the number of connections of a vertex) which is characterized by a power-law
with exponent . Properties of this simple structure are
surprisingly close to those of growing random scale-free networks with
in the most interesting region, between 2 and 3. We succeed to find exactly and
numerically with high precision all main characteristics of the graph. In
particular, we obtain the exact shortest-path-length distribution. For the
large network () the distribution tends to a Gaussian of width
centered at . We show that the
eigenvalue spectrum of the adjacency matrix of the graph has a power-law tail
with exponent .Comment: 5 pages, 3 figure
Stability of circular orbits of spinning particles in Schwarzschild-like space-times
Circular orbits of spinning test particles and their stability in
Schwarzschild-like backgrounds are investigated. For these space-times the
equations of motion admit solutions representing circular orbits with particles
spins being constant and normal to the plane of orbits. For the de Sitter
background the orbits are always stable with particle velocity and momentum
being co-linear along them. The world-line deviation equations for particles of
the same spin-to-mass ratios are solved and the resulting deviation vectors are
used to study the stability of orbits. It is shown that the orbits are stable
against radial perturbations. The general criterion for stability against
normal perturbations is obtained. Explicit calculations are performed in the
case of the Schwarzschild space-time leading to the conclusion that the orbits
are stable.Comment: eps figures, submitted to General Relativity and Gravitatio
Evolution of wave packets in quasi-1D and 1D random media: diffusion versus localization
We study numerically the evolution of wavepackets in quasi one-dimensional
random systems described by a tight-binding Hamiltonian with long-range random
interactions. Results are presented for the scaling properties of the width of
packets in three time regimes: ballistic, diffusive and localized. Particular
attention is given to the fluctuations of packet widths in both the diffusive
and localized regime. Scaling properties of the steady-state distribution are
also analyzed and compared with theoretical expression borrowed from
one-dimensional Anderson theory. Analogies and differences with the kicked
rotator model and the one-dimensional localization are discussed.Comment: 32 pages, LaTex, 11 PostScript figure
Density functional theory of spin-polarized disordered quantum dots
Using density functional theory, we investigate fluctuations of the ground
state energy of spin-polarized, disordered quantum dots in the metallic regime.
To compare to experiment, we evaluate the distribution of addition energies and
find a convolution of the Wigner-Dyson distribution, expected for noniteracting
electrons, with a narrower Gaussian distribution due to interactions. The tird
moment of the total distribution is independent of interactions, and so is
predicted to decrease by a factor of 0.405 upon application of a magnetic field
which transforms from the Gaussian orthogonal to the Gaussian unitary ensemble.Comment: 13 pages, 2 figure
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