84,981 research outputs found
On Safe Folding
In [3] a general fold operation has been introduced for definite programs wrt computed answer substitution semantics. It differs from the fold operation defined by Tamaki and Sato in [26,25] because its application does not depend on the transformation history. This paper extends the results in [3] by giving a more powerful sufficient condition for the preservation of computed answer substitutions. Such a condition is meant to deal with the critical case when the atom introduced by folding depends on the clause to which the fold applies. The condition compares the dependency degree between the fonding atom and the folded clause, with the semantic delay between the folding atom and the ones to be folded. The result is also extended to a more general replacement operation, by showing that it can be decomposed into a sequence of definition, general folding and unfolding operations
Generalisation of the Hammersley-Clifford Theorem on Bipartite Graphs
The Hammersley-Clifford theorem states that if the support of a Markov random
field has a safe symbol then it is a Gibbs state with some nearest neighbour
interaction. In this paper we generalise the theorem with an added condition
that the underlying graph is bipartite. Taking inspiration from "Gibbs Measures
and Dismantlable Graphs" by Brightwell and Winkler we introduce a notion of
folding for configuration spaces called strong config-folding proving that if
all Markov random fields supported on are Gibbs with some nearest neighbour
interaction so are Markov random fields supported on the 'strong config-folds'
and 'strong config-unfolds' of .Comment: 27 pages, 7 figures; Typos corrected and some notation has been
change
Nonlinear buckling and folding analysis of a storable tubular ultrathin boom for nanosatellites
In this work we investigated the stability behavior and the folding capability of an ultrathin tubular composite boom with C-cross section to be used in nanosatellites applications. A nonlinear buckling analysis was performed using the Riks method, adopting a perturbed finite element model to study the influence of the unavoidable geometrical variations of the boom thickness, arising from the composite manufacturing processes, on the stability behavior of the tubular structure. The effect of several levels of geometrical imperfection on the buckling behavior was analyzed. The minimum coil radius that can be used for a safe storage the boom was determined by quasi-static explicit analysis. The boom folding process was considered as formed by two sequential steps, the flattening and the coiling. The stress fields associated with both steps were investigated
Unfolding-Based Process Discovery
This paper presents a novel technique for process discovery. In contrast to
the current trend, which only considers an event log for discovering a process
model, we assume two additional inputs: an independence relation on the set of
logged activities, and a collection of negative traces. After deriving an
intermediate net unfolding from them, we perform a controlled folding giving
rise to a Petri net which contains both the input log and all
independence-equivalent traces arising from it. Remarkably, the derived Petri
net cannot execute any trace from the negative collection. The entire chain of
transformations is fully automated. A tool has been developed and experimental
results are provided that witness the significance of the contribution of this
paper.Comment: This is the unabridged version of a paper with the same title
appearead at the proceedings of ATVA 201
Transformations of Logic Programs with Goals as Arguments
We consider a simple extension of logic programming where variables may range
over goals and goals may be arguments of predicates. In this language we can
write logic programs which use goals as data. We give practical evidence that,
by exploiting this capability when transforming programs, we can improve
program efficiency.
We propose a set of program transformation rules which extend the familiar
unfolding and folding rules and allow us to manipulate clauses with goals which
occur as arguments of predicates. In order to prove the correctness of these
transformation rules, we formally define the operational semantics of our
extended logic programming language. This semantics is a simple variant of
LD-resolution. When suitable conditions are satisfied this semantics agrees
with LD-resolution and, thus, the programs written in our extended language can
be run by ordinary Prolog systems.
Our transformation rules are shown to preserve the operational semantics and
termination.Comment: 51 pages. Full version of a paper that will appear in Theory and
Practice of Logic Programming, Cambridge University Press, U
Transforming Normal Programs by Replacement
The replacement transformation operation, already defined in [28], is studied wrt normal programs. We give applicability conditions able to ensure the correctness of the operation wrt Fitting's and Kunen's semantics. We show how replacement can mimic other transformation operations such as thinning, fattening and folding, thus producing applicability conditions for them too. Furthermore we characterize a transformation sequence for which the preservation of Fitting's and Kunen's semantics is ensured
Simultaneous Replacement in Normal Programs
The simultaneous replacement transformation operation is here defined and studied w.r.t. normal programs. We give applicability conditions able to ensure the correctness of the operation w.r.t. the set of logical consequences of the completed database. We consider separately the cases in which the underlying language is infinite and finite; in this latter case we also distinguish according to the kind of domain closure axioms adopted. As corollaries we obtain results for Fitting's and Kunen's semantics. We also show how simultaneous replacement can mimic other transformation operations such as thinning, fattening and folding, thus producing applicability conditions for them too
Computers and Liquid State Statistical Mechanics
The advent of electronic computers has revolutionised the application of
statistical mechanics to the liquid state. Computers have permitted, for
example, the calculation of the phase diagram of water and ice and the folding
of proteins. The behaviour of alkanes adsorbed in zeolites, the formation of
liquid crystal phases and the process of nucleation. Computer simulations
provide, on one hand, new insights into the physical processes in action, and
on the other, quantitative results of greater and greater precision. Insights
into physical processes facilitate the reductionist agenda of physics, whilst
large scale simulations bring out emergent features that are inherent (although
far from obvious) in complex systems consisting of many bodies. It is safe to
say that computer simulations are now an indispensable tool for both the
theorist and the experimentalist, and in the future their usefulness will only
increase.
This chapter presents a selective review of some of the incredible advances
in condensed matter physics that could only have been achieved with the use of
computers.Comment: 22 pages, 2 figures. Chapter for a boo
- …