14,823 research outputs found
Relationships between Models for Concurrency
Models for concurrency can be classified with respect to three relevant parameters: behaviour/system, interleaving/noninterleaving, linear/branching time. When modelling a process, a choice concerning such parameters corresponds to choosing the level of abstraction of the resulting semantics. The classifications are formalized through the medium of category theory
Synchronization is optimal in non-diagonalizable networks
We consider the problem of maximizing the synchronizability of oscillator
networks by assigning weights and directions to the links of a given
interaction topology. We first extend the well-known master stability formalism
to the case of non-diagonalizable networks. We then show that, unless some
oscillator is connected to all the others, networks of maximum
synchronizability are necessarily non-diagonalizable and can always be obtained
by imposing unidirectional information flow with normalized input strengths.
The extension makes the formalism applicable to all possible network
structures, while the maximization results provide insights into hierarchical
structures observed in complex networks in which synchronization plays a
significant role.Comment: 4 pages, 1 figure; minor revisio
Self-Organized Criticality and Synchronization in the Forest-Fire Model
Depending on the rule for tree growth, the forest-fire model shows either
self-organized criticality with rule-dependent exponents, or synchronization,
or an intermediate behavior. This is shown analytically for the one-dimensional
system, but holds evidently also in higher dimensions.Comment: Latex 4 pages, 4 figure
Distributed Decision Through Self-Synchronizing Sensor Networks in the Presence of Propagation Delays and Nonreciprocal Channels
In this paper we propose and analyze a distributed algorithm for achieving
globally optimal decisions, either estimation or detection, through a
self-synchronization mechanism among linearly coupled integrators initialized
with local measurements. We model the interaction among the nodes as a directed
graph with weights dependent on the radio interface and we pose special
attention to the effect of the propagation delays occurring in the exchange of
data among sensors, as a function of the network geometry. We derive necessary
and sufficient conditions for the proposed system to reach a consensus on
globally optimal decision statistics. One of the major results proved in this
work is that a consensus is achieved for any bounded delay condition if and
only if the directed graph is quasi-strongly connected. We also provide a
closed form expression for the global consensus, showing that the effect of
delays is, in general, to introduce a bias in the final decision. The closed
form expression is also useful to modify the consensus mechanism in order to
get rid of the bias with minimum extra complexity.Comment: Conference paper. Journal version submitted to IEEE Transactions on
Signal Processing, January 10, 2007. Paper accepted for the publication on
the VIII IEEE Workshop on Signal Processing Advances in Wireless
Communications, (SPAWC 2007), January 22, 200
On winning shifts of marked uniform substitutions
The second author introduced with I. T\"orm\"a a two-player word-building
game [Playing with Subshifts, Fund. Inform. 132 (2014), 131--152]. The game has
a predetermined (possibly finite) choice sequence , ,
of integers such that on round the player chooses a subset
of size of some fixed finite alphabet and the player picks
a letter from the set . The outcome is determined by whether the word
obtained by concatenating the letters picked lies in a prescribed target
set (a win for player ) or not (a win for player ). Typically, we
consider to be a subshift. The winning shift of a subshift is
defined as the set of choice sequences for which has a winning strategy
when the target set is the language of . The winning shift mirrors
some properties of . For instance, and have the same entropy.
Virtually nothing is known about the structure of the winning shifts of
subshifts common in combinatorics on words. In this paper, we study the winning
shifts of subshifts generated by marked uniform substitutions, and show that
these winning shifts, viewed as subshifts, also have a substitutive structure.
Particularly, we give an explicit description of the winning shift for the
generalized Thue-Morse substitutions. It is known that and have the
same factor complexity. As an example application, we exploit this connection
to give a simple derivation of the first difference and factor complexity
functions of subshifts generated by marked substitutions. We describe these
functions in particular detail for the generalized Thue-Morse substitutions.Comment: Extended version of a paper presented at RuFiDiM I
Maximum Performance at Minimum Cost in Network Synchronization
We consider two optimization problems on synchronization of oscillator
networks: maximization of synchronizability and minimization of synchronization
cost. We first develop an extension of the well-known master stability
framework to the case of non-diagonalizable Laplacian matrices. We then show
that the solution sets of the two optimization problems coincide and are
simultaneously characterized by a simple condition on the Laplacian
eigenvalues. Among the optimal networks, we identify a subclass of hierarchical
networks, characterized by the absence of feedback loops and the normalization
of inputs. We show that most optimal networks are directed and
non-diagonalizable, necessitating the extension of the framework. We also show
how oriented spanning trees can be used to explicitly and systematically
construct optimal networks under network topological constraints. Our results
may provide insights into the evolutionary origin of structures in complex
networks for which synchronization plays a significant role.Comment: 29 pages, 9 figures, accepted for publication in Physica D, minor
correction
Introduction to the ISO specification language LOTOS
LOTOS is a specification language that has been specifically developed for the formal description of the OSI (Open Systems Interconnection) architecture, although it is applicable to distributed, concurrent systems in general. In LOTOS a system is seen as a set of processes which interact and exchange data with each other and with their environment. LOTOS is expected to become an ISO international standard by 1988
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