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 $\mathit{Datalog}_{\mathbb{Z}}$---an extension of positive Datalog with arithmetic functions over integers. This language is known to be undecidable, so we propose two fragments. In $\mathit{limit}~\mathit{Datalog}_{\mathbb{Z}}$ 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 $\mathit{stability}$ requirement causes the complexity to drop to ExpTime and PTime, respectively. Finally, we show that stable $\mathit{Datalog}_{\mathbb{Z}}$ 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 $\mathit{limit\ programs}$ 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