5,779 research outputs found
Noise Enhanced Stability
The noise can stabilize a fluctuating or a periodically driven metastable
state in such a way that the system remains in this state for a longer time
than in the absence of white noise. This is the noise enhanced stability
phenomenon, observed experimentally and numerically in different physical
systems. After shortly reviewing all the physical systems where the phenomenon
was observed, the theoretical approaches used to explain the effect are
presented. Specifically the conditions to observe the effect: (a) in systems
with periodical driving force, and (b) in random dichotomous driving force, are
discussed. In case (b) we review the analytical results concerning the mean
first passage time and the nonlinear relaxation time as a function of the white
noise intensity, the parameters of the potential barrier, and of the
dichotomous noise.Comment: 18 pages, 6 figures, in press Acta Physica Polonica (2004
The Influence of Space Exploration on Science Education
Scientific research and technological developments associated with space exploration have already had, and will continue to have, significant effects on course content and the learning process. Teachers and students in large numbers continually seek from NASA assistance to help them understand space science and exploration.
Therefore NASA strives to relate developments in space science and technology to classroom education. It prepares spacerelated instructional materials for teachers. These materials contain suggested classroom and laboratory activities and lists of selected references
Foundations of Declarative Data Analysis Using Limit Datalog Programs
Motivated by applications in declarative data analysis, we study
---an extension of positive Datalog with
arithmetic functions over integers. This language is known to be undecidable,
so we propose two fragments. In
predicates are axiomatised to keep minimal/maximal numeric values, allowing us
to show that fact entailment is coNExpTime-complete in combined, and
coNP-complete in data complexity. Moreover, an additional
requirement causes the complexity to drop to ExpTime and PTime, respectively.
Finally, we show that stable can express many
useful data analysis tasks, and so our results provide a sound foundation for
the development of advanced information systems.Comment: 23 pages; full version of a paper accepted at IJCAI-17; v2 fixes some
typos and improves the acknowledgment
Stratified Negation in Limit Datalog Programs
There has recently been an increasing interest in declarative data analysis,
where analytic tasks are specified using a logical language, and their
implementation and optimisation are delegated to a general-purpose query
engine. Existing declarative languages for data analysis can be formalised as
variants of logic programming equipped with arithmetic function symbols and/or
aggregation, and are typically undecidable. In prior work, the language of
was proposed, which is sufficiently powerful to
capture many analysis tasks and has decidable entailment problem. Rules in this
language, however, do not allow for negation. In this paper, we study an
extension of limit programs with stratified negation-as-failure. We show that
the additional expressive power makes reasoning computationally more demanding,
and provide tight data complexity bounds. We also identify a fragment with
tractable data complexity and sufficient expressivity to capture many relevant
tasks.Comment: 14 pages; full version of a paper accepted at IJCAI-1
The Bag Semantics of Ontology-Based Data Access
Ontology-based data access (OBDA) is a popular approach for integrating and
querying multiple data sources by means of a shared ontology. The ontology is
linked to the sources using mappings, which assign views over the data to
ontology predicates. Motivated by the need for OBDA systems supporting
database-style aggregate queries, we propose a bag semantics for OBDA, where
duplicate tuples in the views defined by the mappings are retained, as is the
case in standard databases. We show that bag semantics makes conjunctive query
answering in OBDA coNP-hard in data complexity. To regain tractability, we
consider a rather general class of queries and show its rewritability to a
generalisation of the relational calculus to bags
Bifurcations in the Lozi map
We study the presence in the Lozi map of a type of abrupt order-to-order and
order-to-chaos transitions which are mediated by an attractor made of a
continuum of neutrally stable limit cycles, all with the same period.Comment: 17 pages, 12 figure
epistemological inventiveness according to Diderot
UID/HIS/04666/2019
Copyright Year 2020In Thoughts on the Interpretation of Nature (1753), Denis Diderot discusses what may be the novelty of a science of becoming and morphogenesis, consequent with the autopoietic of nature. Far from arriving at a positivist conception, as is common among materialistic philosophies, the author projects a science of the probable, the contingent, the transitory, which requires the combined efforts of all capacities of the knowing subject to carry out the ceaseless dialectic between the two poles of observation and interpretation. Imagination, intuition, prospect, and conjecture are summoned to accompany experiential activity, introducing an inventive dimension in science, whose freedom contributes to subverting the epistemological canon, blurring the rigidity of disciplinary boundaries, intensifying scientific discovery, and giving meaning to the cluster of research. Consequently, science becomes a plurality of texts, intersecting facts and conjectures, data and metaphors, protocol rigour and rhetorical procedures. The unusual character of this exuberance has led the main commentators on the work to presume that it is the fruit of philosophy’s intervention, to which it would be fitting to add the step of creativity, unfeasible in scientific methodology. In contrast, we argue that, for the philosopher, those various processes are constitutive of the same scientific research, which finds in judgment the central faculty and in abduction the privileged process of discovery.authorsversionpublishe
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