6,120 research outputs found
Towards an HLA Run-time Infrastructure with Hard Real-time Capabilities
Our work takes place in the context of the HLA standard and its application in real-time systems context. The HLA standard is inadequate for taking into consideration the different constraints involved in real-time computer systems. Many works have been invested in order to providing real-time capabilities to Run Time Infrastructures (RTI) to run real time simulation. Most of these initiatives focus on major issues including QoS guarantee, Worst Case Transit Time (WCTT) knowledge and scheduling services provided by the underlying operating systems. Even if our ultimate objective is to achieve real-time capabilities for distributed HLA federations executions, this paper describes a preliminary work focusing on achieving hard real-time properties for HLA federations running on a single computer under Linux operating systems. Our paper proposes a novel global bottom up approach for designing real-time Run time Infrastructures and a formal model for validation of uni processor to (then) distributed real-time simulation with CERTI
Parametric Modelling of Multivariate Count Data Using Probabilistic Graphical Models
Multivariate count data are defined as the number of items of different
categories issued from sampling within a population, which individuals are
grouped into categories. The analysis of multivariate count data is a recurrent
and crucial issue in numerous modelling problems, particularly in the fields of
biology and ecology (where the data can represent, for example, children counts
associated with multitype branching processes), sociology and econometrics. We
focus on I) Identifying categories that appear simultaneously, or on the
contrary that are mutually exclusive. This is achieved by identifying
conditional independence relationships between the variables; II)Building
parsimonious parametric models consistent with these relationships; III)
Characterising and testing the effects of covariates on the joint distribution
of the counts. To achieve these goals, we propose an approach based on
graphical probabilistic models, and more specifically partially directed
acyclic graphs
Effect of cerium concentration on corrosion resistance and polymerization of hybrid solâgel coating on martensitic stainless steel
Stainless steels are increasingly used in the aeronautics field for the manufacture of structural parts. One of them, the X13VD martensitic stainless steel (X12CrNiMoV12-3), known for its good mechanical properties, has a poor corrosion resistance in confined or severe environments. In the past years, Cr(VI) based pre-treatments have been currently used for corrosion protection of different metals, however, they are toxic and due to environmental regulations, they will be definitely banned in a near future. Alternatives to replace Cr(VI) show advantages and drawbacks considering key properties such as: corrosion resistance, adhesion of coatings, fatigue resistance, durability and reliability. However, some of their possible alternatives show high potential. In this paper, a process was developed to improve the corrosion resistance of the martensitic stainless steel. Organicâinorganic hybrid coatings with different cerium concentrations were deposited onto stainless steel by solâgel process. Corrosion resistance of the coatings was evaluated by electrochemical impedance measurements and it has been proved that cerium concentration of 0.01 M into hybrid coating was an optimal content. Adhesion tests were also carried out by "nanoscratchtest" to characterize the coatings mechanical properties as a function of cerium concentration but results do not clearly show the influence of cerium for the coating adhesion toward the substrate. To try to correlate with the electrochemical properties, liquid 29Si NMR spectroscopy was then performed to investigate hydrolysis and condensation reactions of solâgel process, and by this method, it was demonstrated that for higher cerium concentration (>0.01 M) there is a modification of the chemical structure of the solâgel network
Dressed diffusion and friction coefficients in inhomogeneous multicomponent self-gravitating systems
General self-consistent expressions for the coefficients of diffusion and
dynamical friction in a stable, bound, multicomponent self-gravitating and
inhomogeneous system are derived. They account for the detailed dynamics of the
colliding particles and their self-consistent dressing by collective
gravitational interactions. The associated Fokker-Planck equation is shown to
be fully consistent with the corresponding inhomogeneous Balescu-Lenard
equation and, in the weak self-gravitating limit, to the inhomogeneous Landau
equation. Hence it provides an alternative derivation to both and demonstrates
their equivalence. The corresponding stochastic Langevin equations are
presented: they can be a practical alternative to numerically solving the
inhomogeneous Fokker-Planck and Balescu-Lenard equations. The present formalism
allows for a self-consistent description of the secular evolution of different
populations covering a spectrum of masses, with a proper accounting of the
induced secular mass segregation, which should be of interest to various
astrophysical contexts, from galactic centers to protostellar discs.Comment: 27 pages, 1 figur
Benchmark of structured machine learning methods for microbial identification from mass-spectrometry data
Microbial identification is a central issue in microbiology, in particular in
the fields of infectious diseases diagnosis and industrial quality control. The
concept of species is tightly linked to the concept of biological and clinical
classification where the proximity between species is generally measured in
terms of evolutionary distances and/or clinical phenotypes. Surprisingly, the
information provided by this well-known hierarchical structure is rarely used
by machine learning-based automatic microbial identification systems.
Structured machine learning methods were recently proposed for taking into
account the structure embedded in a hierarchy and using it as additional a
priori information, and could therefore allow to improve microbial
identification systems. We test and compare several state-of-the-art machine
learning methods for microbial identification on a new Matrix-Assisted Laser
Desorption/Ionization Time-of-Flight mass spectrometry (MALDI-TOF MS) dataset.
We include in the benchmark standard and structured methods, that leverage the
knowledge of the underlying hierarchical structure in the learning process. Our
results show that although some methods perform better than others, structured
methods do not consistently perform better than their "flat" counterparts. We
postulate that this is partly due to the fact that standard methods already
reach a high level of accuracy in this context, and that they mainly confuse
species close to each other in the tree, a case where using the known hierarchy
is not helpful
Functional integral derivation of the kinetic equation of two-dimensional point vortices
We present a brief derivation of the kinetic equation describing the secular
evolution of point vortices in two-dimensional hydrodynamics, by relying on a
functional integral formalism. We start from Liouville's equation which
describes the exact dynamics of a two-dimensional system of point vortices. At
the order , the evolution of the system is characterised by the first
two equations of the BBGKY hierarchy involving the system's 1-body distribution
function and its 1-body correlation function. Thanks to the introduction of
auxiliary fields, these two evolution constraints may be rewritten as a
functional integral. When functionally integrated over the 2-body correlation
function, this rewriting leads to a new constraint coupling the 1-body
distribution function and the two auxiliary fields. Once inverted, this
constraint provides, through a new route, the closed non-linear kinetic
equation satisfied by the 1-body distribution function. Such a method sheds new
lights on the origin of these kinetic equations complementing the traditional
derivation methods.Comment: 7 pages, 1 figur
Secular diffusion in discrete self-gravitating tepid discs I : analytic solution in the tightly wound limit
The secular evolution of an infinitely thin tepid isolated galactic disc made
of a finite number of particles is described using the inhomogeneous
Balescu-Lenard equation. Assuming that only tightly wound transient spirals are
present in the disc, a WKB approximation provides a simple and tractable
quadrature for the corresponding drift and diffusion coefficients. It provides
insight into the physical processes at work during the secular diffusion of a
self-gravitating discrete disc and makes quantitative predictions on the
initial variations of the distribution function in action space.
When applied to the secular evolution of an isolated stationary
self-gravitating Mestel disc, this formalism predicts initially the importance
of the corotation resonance in the inner regions of the disc leading to a
regime involving radial migration and heating. It predicts in particular the
formation of a "ridge like" feature in action space, in agreement with
simulations, but over-estimates the timescale involved in its appearance. Swing
amplification is likely to resolve this discrepancy.
In astrophysics, the inhomogeneous Balescu-Lenard equation and its WKB limit
may also describe the secular diffusion of giant molecular clouds in galactic
discs, the secular migration and segregation of planetesimals in
proto-planetary discs, or even the long-term evolution of population of stars
within the Galactic center.Comment: 22 pages, 12 figure
HLA high performance and real-time simulation studies with CERTI
Our work takes place in the context of the HLA standard and its application in real-time systems context. Indeed, current HLA standard is inadequate for taking into consideration the different constraints involved in real-time computer systems. Many works have been invested in order to provide real-time capabilities to Run Time Infrastructures (RTI). This paper describes our approach focusing on achieving hard real-time properties for HLA federations through a complete state of the art on the related domain. Our paper also proposes a global bottom up approach from basic hardware and software basic requirements to experimental tests for validation of
distributed real-time simulation with CERTI
Addendum to "Local Controllability of the Two-Link Magneto-Elastic Micro-Swimmer"
In the above mentioned note (, , published in
IEEE Trans. Autom. Cont., 2017), the first and fourth authors proved a local
controllability result around the straight configuration for a class of
magneto-elastic micro-swimmers.That result is weaker than the usual small-time
local controllability (STLC), and the authors left the STLC question open. The
present addendum closes it by showing that these systems cannot be STLC
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