6,929 research outputs found
Expressing and enforcing user-defined constraints of AADL models
The Architecture Analysis and Design Language AADL allows one to model complete systems, but also to define specific extensions through property sets and library of models. Yet, it does not define an explicit mechanism to enforce some semantics or consistency checks to ensure property sets are correctly used. In this paper, we present REAL (Requirements and Enforcements Analysis Language) as an integrated solution to this issue. REAL is defined as an AADL annex language. It adds the possibility to express constraints as theorems based on set theory to enforce implicit semantics of property sets or AADL models. We illustrate the use of the language on case studies we developed with industrial partners
A MDE-based optimisation process for Real-Time systems
The design and implementation of Real-Time Embedded Systems is now heavily relying on Model-Driven Engineering (MDE) as a central place to define and then analyze or implement a system. MDE toolchains are taking a key role as to gather most of functional and not functional properties in a central framework, and then exploit this information. Such toolchain is based on both 1) a modeling notation, and 2) companion tools to transform or analyse models. In this paper, we present a MDE-based process for system optimisation based on an architectural description. We first define a generic evaluation pipeline, define a library of elementary transformations and then shows how to use it through Domain-Specific Language to evaluate and then transform models. We illustrate this process on an AADL case study modeling a Generic Avionics Platform
Variation of bulk Lorentz factor in AGN jets due to Compton rocket in a complex photon field
Radio-loud active galactic nuclei are among the most powerful objects in the
universe. In these objects, most of the emission comes from relativistic jets
getting their power from the accretion of matter onto supermassive black holes.
However, despite the number of studies, a jet's acceleration to relativistic
speeds is still poorly understood.
It is widely known that jets contain relativistic particles that emit
radiation through several physical processes, one of them being the inverse
Compton scattering of photons coming from external sources. In the case of a
plasma composed of electrons and positrons continuously heated by the
turbulence, inverse Compton scattering can lead to relativistic bulk motions
through the Compton rocket effect. We investigate this process and compute the
resulting bulk Lorentz factor in the complex photon field of an AGN composed of
several external photon sources.
We consider various sources here: the accretion disk, the dusty torus, and
the broad line region. We take their geometry and anisotropy carefully into
account in order to numerically compute the bulk Lorentz factor of the jet at
every altitude.
The study, made for a broad range of parameters, shows interesting and
unexpected behaviors of the bulk Lorentz factor, exhibiting acceleration and
deceleration zones in the jet. We investigate the patterns of the bulk Lorentz
factor along the jet depending on the source sizes and on the observation angle
and we finally show that these patterns can induce variability in the AGN
emission with timescales going from hours to months.Comment: 12 pages, 16 figures, accepted to A&
Time dependent modelisation of TeV blazars by a stratified jet model
We present a new time-dependent inhomogeneous jet model of non-thermal blazar
emission. Ultra-relativistic leptons are injected at the base of a jet and
propagate along it. We assume continuous reacceleration and cooling, producing
a relativistic quasi-maxwellian (or "pile-up") particle energy distribution.
The synchrotron and Synchrotron-Self Compton jet emissivity are computed at
each altitude. Klein-Nishina effects as well as intrinsic gamma-gamma
absorption are included in the computation. Due to the pair production optical
depth, considerable particle density enhancement can occur, particularly during
flaring states.Time-dependent jet emission can be computed by varying the
particle injection, but due to the sensitivity of pair production process, only
small variations of the injected density are required during the flares. The
stratification of the jet emission, together with a pile-up distribution,
allows significantly lower bulk Lorentz factors, compared to one-zone models.
Applying this model to the case of PKS 2155-304 and its big TeV flare observed
in 2006, we can reproduce simultaneously the average broad band spectrum of
this source from radio to TeV, as well as TeV light curve of the flare with
bulk Lorentz factor lower than 15
Applying WCET Analysis at Architectural Level
Real-Time embedded systems must enforce strict timing constraints. In this context, achieving precise Worst Case Execution Time is a prerequisite to apply scheduling analysis and verify system viability.
WCET analysis is usually a complex and time-consuming activity. It becomes increasingly complex when one also considers code generation strategies from high-level models. In this paper, we present an experiment made on the coupling of the WCET analysis tool Bound-T and our AADL to code generator OCARINA. We list the different steps to successfully apply WCET analysis directly from model, to limit user intervention
Job Turnover, Unemployment and Labor Market Institutions
This paper studies the role of labor market institutions on unemployment and on the cyclical properties of job flows. We construct an intertemporal general equilibrium model with search unemployment and endogenous job turnover, and examine the consequences of introducing an unemployment benefit, a firing cost and a downward wage rigidity. The simulations suggest that downward wage rigidities, rather than unemployment benefit or firing cost, may well play a dominant role in explaining both the high unemployment rate and the job flows dynamics of such an economy.Unemployment, Job flows dynamics, Institutions
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