arXiv subjects

Philippe A. Martin

Publications and source records attributed to Philippe A. Martin.

10 recordsLinked to original sources

arXiv2013

Collaborative ontology sharing and editing

This article first lists reasons why - in the long term or when creating a new knowledge base (KB) for general knowledge sharing purposes - collaboratively building a well-organized KB does/can provide more possibilities, with on the whole no more costs, than the mainstream approach where knowledge creation and re-use involves searching, merging and creating (semi-)independent (relatively small) ontologies or semi-formal documents. The article lists elements required to achieve this and describes the main one: a KB editing protocol that keeps the KB free of automatically/manually detected inconsistencies while not forcing them to discuss or agree on terminology and beliefs nor requiring a selection committee.

cs.AI↗

arXiv2013

For a Semantic Web based Peer-reviewing and Publication of Research Results

This article shows why the diffusion and peer-reviewing of research results would be more efficient, precise and relevant if all or at least some parts of the descriptions and peer-reviews of research results took the form of a fine-grained semantic network, within articles or knowledge bases, as part of the Semantic Web. This article also shows some ways this can be done and hence how research journal/proceeding publishers could allow this. So far, the World Wide Web Consortium (W3C) has not proposed simple notations and cooperation protocols - similar to those illustrated or referred to in this article - but it now seems likely that Wikipedia/Wikidata, Google or the W3C will propose them sooner or later. Then, research journal/proceeding publishers and researchers may or may not quickly use this approach.

cs.DL↗

arXiv2013

Organizing Linked Data Quality Related Methods

This article presents the top-level of an ontology categorizing and generalizing best practices and quality criteria or measures for Linked Data. It permits to compare these techniques and have a synthetic organized view of what can or should be done for knowledge sharing purposes. This ontology is part of a general knowledge base that can be accessed and complemented by any Web user. Thus, it can be seen as a cooperatively built library for the above cited elements. Since they permit to evaluate information objects and create better ones, these elements also permit knowledge-based tools and techniques - as well as knowledge providers - to be evaluated and categorized based on their input/output information objects. One top-level distinction permitting to organize this ontology is the one between content, medium and containers of descriptions. Various structural, ontological, syntactical and lexical distinctions are then used.

cs.DL↗

arXiv2013

Managing Knowledge to Enhance Learning

The article first summarizes reasons why current approaches supporting Open Learning and Distance Education need to be complemented by tools permitting lecturers, researchers and students to cooperatively organize the semantic content of Learning related materials (courses, discussions, etc.) into a fine-grained shared semantic network. This first part of the article also quickly describes the approach adopted to permit such a collaborative work. Then, examples of such semantic networks are presented. Finally, an evaluation of the approach by students is provided and analyzed.

cs.CY↗

arXiv2007

Thermal quantum electrodynamics of nonrelativistic charged fluids

The theory relevant to the study of matter in equilibrium with the radiation field is thermal quantum electrodynamics (TQED). We present a formulation of the theory, suitable for non relativistic fluids, based on a joint functional integral representation of matter and field variables. In this formalism cluster expansion techniques of classical statistical mechanics become operative. They provide an alternative to the usual Feynman diagrammatics in many-body problems which is not perturbative with respect to the coupling constant. As an application we show that the effective Coulomb interaction between quantum charges is partially screened by thermalized photons at large distances. More precisely one observes an exact cancellation of the dipolar electric part of the interaction, so that the asymptotic particle density correlation is now determined by relativistic effects. It has still the $r^{-6}$ decay typical for quantum charges, but with an amplitude strongly reduced by a relativistic factor.

quant-ph↗

arXiv2006

Equilibrium correlations in charged fluids coupled to the radiation field

We provide an exact microscopic statistical treatment of particle and field correlations in a system of quantum charges in equilibrium with a classical radiation field. Using the Feynman-Kac-Ito representation of the Gibbs weight, the system of particles is mapped onto a collection of random charged wires. The field degrees of freedom can be integrated out, providing an effective pairwise magnetic potential. We then calculate the contribution of the transverse field coupling to the large-distance particle correlations. The asymptotics of the field correlations in the plasma are also exactly determined.

cond-mat.stat-mech↗

arXiv2005

The Casimir effect for the Bose-Gas in Slabs

We study the Casimir effect for the perfect Bose-gase in the slab geometry for various boundary conditions. We show that the grand canonical potential per unit area at the bulk critical chemical potential $μ=0$ has the standard asymptotic form with universal Casimir terms.

cond-mat.stat-mech↗

arXiv2005

Long Cycles in a Perturbed Mean Field Model of a Boson Gas

In this paper we give a precise mathematical formulation of the relation between Bose condensation and long cycles and prove its validity for the perturbed mean field model of a Bose gas. We decompose the total density $ρ=ρ_{\rm short}+ρ_{\rm long}$ into the number density of particles belonging to cycles of finite length ($ρ_{\rm short}$) and to infinitely long cycles ($ρ_{\rm long}$) in the thermodynamic limit. For this model we prove that when there is Bose condensation, $ρ_{\rm long}$ is different from zero and identical to the condensate density. This is achieved through an application of the theory of large deviations. We discuss the possible equivalence of $ρ_{\rm long}\neq 0$ with off-diagonal long range order and winding paths that occur in the path integral representation of the Bose gas.

math-ph↗

arXiv2003

Self-consistent equation for an interacting Bose gas

We consider interacting Bose gas in thermal equilibrium assuming a positive and bounded pair potential $V(r)$ such that $0<\int d\br V(r) = a<\infty$. Expressing the partition function by the Feynman-Kac functional integral yields a classical-like polymer representation of the quantum gas. With Mayer graph summation techniques, we demonstrate the existence of a self-consistent relation $ρ(μ)=F(μ-aρ(μ))$ between the density $ρ$ and the chemical potential $μ$, valid in the range of convergence of Mayer series. The function $F$ is equal to the sum of all rooted multiply connected graphs. Using Kac's scaling $V_γ(\br)=γ^{3}V(γr)$ we prove that in the mean-field limit $γ\to 0$ only tree diagrams contribute and function $F$ reduces to the free gas density. We also investigate how to extend the validity of the self-consistent relation beyond the convergence radius of Mayer series (vicinity of Bose-Einstein condensation) and study dominant corrections to mean field. At lowest order, the form of function $F$ is shown to depend on single polymer partition function for which we derive lower and upper bounds and on the resummation of ring diagrams which can be analytically performed.

cond-mat.stat-mech↗

arXiv1998

Lifetimes of impurity states in crossed magnetic and electric fields

We study the quantum dynamics of localized impurity states created by a point interaction for an electron moving in two dimensions under the influence of a perpendicular magnetic field and an in-plane weak electric field. All impurity states are unstable in presence of the electric field. Their lifetimes are computed and shown to grow in a Gaussian way as the electric field tends to zero.

cond-mat↗